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Prof. Dr.-Ing. Rolf Rascher

Retired professors

Faculty of Applied Natural Sciences and Industrial Engineering

Retired Professor

consulting time

On request

publications

Sortierung:

Journal article

Rolf Rascher

Schleifmaschinen auf der 6. EMO in Hannover.

In: maschine + werkzeug - Fertigungstechnik pg. 48-54

(1985)

Contribution

Rolf Rascher

Technologie metallischer und keramischer Verbundwerkstoffe.

In: Sonderschau „Neue Werkstoffe“ auf der METAV 86. pg. 34-44

(1986)

Journal article

Rolf Rascher

Integration im Verborgenen – Die 7. EMO in Mailand.

In: Moderne Fertigung pg. 90-98

(1987)

Book

Rolf Rascher

Practical analysis of the process of producing balls for ball bearings.

Springer Verlag

(1988)

Journal article

Rolf Rascher

IMTS ‘88 in Chicago.

In: maschine + werkzeug - Fertigungstechnik pg. 88-97

(1988)

Book

Rolf Rascher

Experimentelle Untersuchungen zur Technologie der Kugelherstellung.

In: iwb Forschungsberichte

Springer Berlin Heidelberg Berlin, Heidelberg

(1989)

Journal article

Rolf Rascher

Entwicklungstendenzen beim Schleifen von Kugeln.

In: MM Industriemagazin-Maschinenmarkt vol. 97 pg. 34-38

(1991)

Journal article

Rolf Rascher

Experimentelle Untersuchungen zur Technologie der Kugelherstellung.

In: wt (Werkstattstechnik) Produktion und Management vol. 81 pg. 663-664

(1991)

Contribution

Rolf Rascher
Peter Sperber

IFHEM – Innovatives Fertigungskonzept für High Tech-Flächen durch Einsatz von MRF-Technologie.

In: Bericht über angewandte Forschung und Entwicklung sowie wissenschaftlichen Technologietransfer der Fachhochschule Deggendorf, 2000-2002.

(2002)

Journal article

Florian Schneider
Roland Maurer
A. Bickert
R. Stamp
G. Smith
Rolf Rascher

SG-Sensor – an affordable tactile alternative.

(2002)

Journal article

Elmar Pitschke
Peter Sperber
R. Stamp
Rolf Rascher
L. Smith
M. Smith
Markus Schinhärl

Prediction of MRF polishing by classification of the initial error with Zernike polynomials.

In: Optical Manufacturing and Testing V vol. 5180 pg. 115-122

(2003)

DOI: 10.1117/12.507652

show abstract

The magnetorheological finishing (MRF) process makes use of a magnetically stiffened magnetorheological abrasive fluid to polish the surface of a workpiece in a precise fashion. The process may be used to finish the surface of high quality optical lenses. Investigations have been undertaken to quantify the operation of MRF and to identify those parameters key to an optimal operation of this lens production process. A correlation has been developed to relate the parameters important to the removal characteristics and to the precision of the polishing result and to the duration of polishing. A relationship to indicate the most appropriate MRF processing parameters for a lens is presented. In the examples discussed Fringe-Zernike polynomials are used to quantify the error on a lens.

Lecture

Elmar Pitschke
Peter Sperber
R. Stamp
Rolf Rascher
L. Smith
M. Smith
Markus Schinhärl

Prediction of MRF polishing by classification of the initial error with Zernike polynomials.

In: Optical Manufacturing and Testing V

San Diego, CA, USA

03.08.2003 (2003)

Lecture

Elmar Pitschke
Peter Sperber
Rolf Rascher
R. Stamp
M. Smith
L. Smith
Markus Schinhärl

Lens production enhancement by adoption of artificial influence functions and a knowledge-based system in a magnetorheological finishing process.

In: Optical Manufacturing and Testing VII

San Diego, CA, USA

03.08.2003 (2003)

Lecture

Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

Temporal stability and performance of MR polishing fluid.

In: Current Developments in Lens Design and Optical Engineering V

SPIE, The International Society for Optics and Photonics San Diego, CA, USA

2004 (2004)

Journal article

Elmar Pitschke
Markus Schinhärl
Peter Sperber
Rolf Rascher
R. Stamp
L. Smith
M. Smith
A. Hammer

Comparison of a new contact topographical measurement system for spherical and aspherical surfaces with interferometry.

In: Current Developments in Lens Design and Optical Engineering V vol. 5523 pg. 225-234

(2004)

DOI: 10.1117/12.558899

show abstract

Since end of 2003 the TII-3D - the new contact topography measuring device for measuring aspherical and spherical surfaces - is available on market. Due to its novel technology, the system is specified to measure a large range with λ/10 accuracy, therefore being a very flexible tool for pre- and post-measurements in high quality zonal polishing processes like MRF. At the University of Applied Sciences Deggendorf a testing series has been carries out to compare the results of the TII-3D with CGH-interferometric measurements on aspherical surfaces. An analysis of the measurement errors is shown and ranking of the different metrology systems for production processes of high quality aspherical lenses is given.

Journal article

Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

Temporal stability and performance of MR polishing fluid.

In: Current Developments in Lens Design and Optical Engineering V vol. 5523 pg. 273-280

(2004)

DOI: 10.1117/12.558897

show abstract

The lifetime of standard magnetorheological (MR) polishing fluids, used for example in polishing machines for optical applications, is limited. Scanning electron microscope examinations as well as chemical analyses of the fluid had been undertaken in order to investigate reasons for limited lifetime. We found out that the removal rate decreases during the course of time. However, the usable fluid life is most limited by the point of time when the critical minimum amount of fluid, necessary to ensure circulation, is reached. The results in association with a new fluid conditioner show, that a standard MR polishing fluid may be used for longer periods than common periods of about 2 weeks.

Contribution

Elmar Pitschke
Markus Schinhärl
Rolf Rascher
Peter Sperber

Erzeugung hochpräziser Oberflächen auf optischen Bauelementen für die Präzisionsoptik mit magnetorheologischem Finishing (MRF).

In: Fünftes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt, page 8998. OTTI. pg. 89-98

(2004)

Lecture

Elmar Pitschke
Markus Schinhärl
Rolf Rascher
Peter Sperber

Erzeugung hochpräziser Oberflächen auf optischen Bauelementen für die Präzisionsoptik mit magnetorheologischem Finishing (MRF).

In: Fünftes Symposium - Zukunft Glas - Von der Tradition zum High-Tech-Produkt

Zwiesel

17.06.2004 (2004)

Lecture

Elmar Pitschke
Markus Schinhärl
Peter Sperber
Rolf Rascher
R. Stamp
L. Smith
M. Smith
A. Hammer

Comparison of a new contact topographical measurement system for spherical and aspherical surfaces with interferometry.

In: Current Developments in Lens Design and Optical Engineering V

Denver, CO, USA

02.08.2004 (2004)

Lecture

Rolf Rascher

Labor Optical Engineering – Moderne Fertigungstechnik im Fokus.

In: BayTech Optik Seminar

Deggendorf

2005 (2005)

Journal article

Markus Schinhärl
Elmar Pitschke
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

Comparison of different magnetorheological polishing fluids.

In: Optical Fabrication, Testing, and Metrology II vol. 5965 pg. 659-670

(2005)

DOI: 10.1117/12.656430

show abstract

Magnetorheological Finishing (MRF) is commonly used to finish high quality optical surfaces. The process is based on a magnetorheological fluid, which stiffens in a magnetic field and thus may be used as a polishing tool. The fluid removal characteristic depends on several parameters, for example the magnetic field strength or the relative velocity between workpiece and polishing tool. Another parameter is the fluid itself. Different compositions of polishing abrasives result in different removal characteristics. At the University of Applied Sciences Deggendorf, five different magnetorheological polishing fluids have been analysed. The results of the research are scanning electron microscope analyses as well as spectra analyses. The removal characteristic for each fluid has been determined for different glass materials. Finally, the fluid conditions during polishing have been analysed. For this purpose, the fluid flow rate, the fluid pressure and the fluid viscosity have been investigated.

Journal article

Elmar Pitschke
Markus Schinhärl
Peter Sperber
Rolf Rascher

Utilizing a TII aspherical measurement machine in a computer-controlled polishing process.

In: Optical Measurement Systems for Industrial Inspection IV vol. 5856 pg. 987-993

(2005)

DOI: 10.1117/12.612597

show abstract

The demand on quality of optical surfaces is increasing from year to year. Computer controlled polishing is one way to fulfill these demands. The process depends on the error-profile of the optical surface. In this paper the usage of the TII measurement machine is discussed to manufacture optical surfaces.

Journal article

Elmar Pitschke
Markus Schinhärl
Andreas Geiss
Peter Sperber
Rolf Rascher
R. Stamp
L. Smith
M. Smith

A new approach to predict computer-controlled polishing results.

In: Optical Manufacturing and Testing VI vol. 5869 pg. 94-102

(2005)

DOI: 10.1117/12.616780

show abstract

A novel approach to handle and quantify a computer controlled polishing process will be introduced. This approach will be compared to real data. This comparison indicates the correctness of this approach. Based on it a formula has been developed to predict the results of a computer controlled polishing process. The formula will be used to predict real polishing processes and the results will be compared to the real results. The limits when using this formula will be shown along with suggestions when the formula would be useful. This rough prediction of the computer controlled polishing results may be used to enhance the automation of a computer controlled polishing process. Also a way to improve the formula itself will be introduced. It is the opinion of the author that by further stabilizing of the whole computer controlled polishing process the whole system becomes more robust, the prediction more accurate and the whole system improves in reliability and the results become better.

Journal article

Markus Schinhärl
Elmar Pitschke
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

New viscosity measurement for magnetorheological polishing fluid.

In: Optical Manufacturing and Testing VI vol. 5869 pg. 133-141

(2005)

DOI: 10.1117/12.616690

show abstract

In Magnetorheological Finishing (MRF) a magnetic field is applied to a stream of abrasive magnetorheological fluid, in order that the fluid behaves as the polishing tool. The process may be used to finish the surface of high quality optical lenses. The fluid viscosity is one important parameter the polishing tool characteristic depends on. At the University of Applied Sciences Deggendorf a new viscosity measurement, which uses the inductance of the fluid had been tested. The result of the research is a close relationship between viscosity and inductance. The new viscosity measurement is not an absolute, but a comparative system, based on inductance of the flowing fluid and the fluid age.

Journal article

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber

Analysis of thermal sources in a magnetorheological finishing (MRF) process.

In: Optical Manufacturing and Testing VI vol. 5869 pg. 111-120

(2005)

DOI: 10.1117/12.616751

show abstract

Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high quality surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the polishing tool. At the University of Applied Sciences Deggendorf thermal sources in a MRF polishing unit have been analysed using an infrared camera. The result of the research is a warming of the fluid in the fluid conditioner caused by the mixer motor. The existing cooling is therefore essential, in order to ensure a constant polishing tool characteristic during polishing runs. A new fluid conditioner, which was developed at the University of Applied Sciences Deggendorf, with the aim of an extended fluid lifetime may be used without cooling, because an increase of the fluid temperature in the conditioner could not been detected. Furthermore, a warming of the workpiece during the polishing process was not ascertainable.

Lecture

Peter Sperber
Elmar Pitschke
Markus Schinhärl
Rolf Rascher

MRF in der Praxis – Optimierung der Wirtschaftlichkeit.

In: BayTech Optik Seminar

Deggendorf

19.04.2005 (2005)

Lecture

Elmar Pitschke
Markus Schinhärl
Peter Sperber
Rolf Rascher

Utilizing a TII aspherical measurement machine in a computer-controlled polishing process.

In: Optical Measurement Systems for Industrial Inspection IV

München

13.06.2005 (2005)

Lecture

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber

Analysis of thermal sources in a magnetorheological finishing (MRF) process.

In: Optical Manufacturing and Testing VI

San Diego, CA, USA

31.07.2005 (2005)

Lecture

Markus Schinhärl
Elmar Pitschke
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

New viscosity measurement for magnetorheological polishing fluid.

In: Optical Manufacturing and Testing VI

SPIE, The International Society for Optics and Photonics San Diego, CA, USA

31.07.2005 (2005)

Lecture

Elmar Pitschke
Markus Schinhärl
Andreas Geiss
Peter Sperber
Rolf Rascher
R. Stamp
L. Smith
M. Smith

A new approach to predict computer-controlled polishing results.

In: Optical Manufacturing and Testing VI

San Diego, CA, USA

31.07.2005 (2005)

show abstract

Lecture

Markus Schinhärl
Elmar Pitschke
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith

Comparison of different magnetorheological polishing fluids.

Jena

12.09.2005 (2005)

Journal article

Elmar Pitschke
Markus Schinhärl
Peter Sperber
Rolf Rascher
R. Stamp
M. Smith
L. Smith

Correlation between influence- function quality and predictability of a computer-controlled polishing process.

In: Optical Engineering vol. 45 pg. 063401 ff.

(2006)

DOI: 10.1117/1.2213630

show abstract

A mathematical method has been developed to analyze influence functions that are used in a computer-controlled polishing process. The influence function itself is usually generated by some kind of calibration where the exact procedure is dependent on the process used. The method is able to determine asymmetries in an influence function. Application of this method yields a value that may be used to judge the quality of an influence function. That quality is also an indicator of the variance of the evolving surface error profile, since a close relationship between it and the polishing process exists. On the basis of an ideal, theoretical process, a model to handle and quantify the result of a real polishing process is described. Practical application of this model demonstrates the effect of influence-function quality on the polishing result. Based on this model, the predictability of the polishing result is evaluated. This initiative to judge influence functions by their quality is an important contribution to the development of computer-controlled polishing. Due to improved process reliability, the reject rate will decrease, and the result will be more economic manufacture.

Journal article

Markus Schinhärl
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith
Elmar Pitschke

Coherences between influence function size, polishing quality and process time in the magnetorheological finishing.

In: Current Developments in Lens Design and Optical Engineering VII vol. 6288 pg. 62880Q ff.

(2006)

DOI: 10.1117/12.678720

show abstract

Magnetorheological finishing (MRF) is a computer controlled polishing process (CCP), which is commonly used in the field of high quality optical lens production. The process uses the material removal characteristic of the polishing tool (influence function) and the surface error-profile to calculate individual, surface error-profile dependent polishing sequences. At the University of Applied Sciences Deggendorf a testing series with a magnetorheological finishing machine has been performed, and effects of the influence function size and its removal capacity on the polishing quality and the process time have been investigated. The result of the research shows that the influence function size has a major effect on the process time, whereas the polishing quality is nearly independent of the influence function size. During the testing series the process time was significantly reduced using an appropriate influence function size. The process time decreased about 9% relating to the original influence function.

Contribution

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
J. Slabeycius

Deposits and damages on high precision surfaces of advanced materials.

In: Proceedings of the 5th Youth Symposium on Experimental Solid Mechanics, Puchov, Slowakei.

(2006)

Journal article

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
J. Slabeycius

Sedimentations on high-precision surfaces of advanced materials by magnetorheological finishing.

In: Current Developments in Lens Design and Optical Engineering VII vol. 6288 pg. 62880R ff.

(2006)

show abstract

Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high precision surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the polishing tool. A standard MR fluid consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives and liquid. To delaying oxidation of the iron particles and avoiding agglomeration the liquid consists of water completed with stabilizers. For the material removal and smoothing of the surface mostly cerium oxide or diamond is used. The materials to be polished may tend toward to different sedimentations of the MR fluid on the machined surface. These sedimentations result from the machining and may develop a polishing layer with MR fluid components. At the University of Applied Sciences Deggendorf analysis of the machined surface are made by the scanning electronic microscope (SEM) to determine the sedimentations of the finishing. The results of the research display the influence for the surface properties due to developing polishing layer by magnetorheological finishing.

Contribution

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber

Rauhigkeitsentwicklung bei der Bearbeitung von Komponenten für die Präzisionsoptik mit Diamantwerkzeugen.

In: Sechstes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt, OTTI, Zwiesel.

(2006)

Lecture

Rolf Rascher
Peter Sperber

Aktuelle Ergebnisse aus dem Labor Optical Engineering der FH Deggendorf zu den Arbeiten auf den Gebieten Ultraschallunterstütztes Schleifen und ELID-Schleifen.

In: BayTech Optik Seminar

Deggendorf

2006 (2006)

Lecture

Markus Schinhärl
Andreas Geiss
Rolf Rascher
Peter Sperber
R. Stamp
L. Smith
G. Smith
Elmar Pitschke

Coherences between influence function size, polishing quality and process time in the magnetorheological finishing.

In: Current Developments in Lens Design and Optical Engineering VII

San Diego, CA, USA

2006 (2006)

Contribution

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber

Rauhigkeitsentwicklung bei der Bearbeitung von Komponenten für die Präzisionsoptik mit Diamantwerkzeugen.

In: Sechstes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt, OTTI, Zwiesel. pg. 143-153

(2006)

Journal article

Elmar Pitschke
Markus Schinhärl
Rolf Rascher
Peter Sperber
L. Smith
R. Stamp
M. Smith

Simulation of a complex optical polishing process using a neural network.

In: Robotics and Computer-Integrated Manufacturing vol. 24 pg. 32-37

(2006)

DOI: 10.1016/j.rcim.2006.07.003

show abstract

Most modern manufacturing processes change their set of parameters during machining in order to work at the optimum state. But in some cases, like computer-controlled polishing, it is not possible to change these parameters during the machining. Then usually a standard set of parameters is chosen which is not adjusted to the specific conditions. To gather the optimum set of parameters anyway simulation of the process prior to manufacturing is a possibility. This research illustrates the successful implementation of a neural network to accomplish such a simulation. The characteristic of this neural network is described along with the decision of the used inputs and outputs. Results are shown and the further usage of the neural network within an automation framework is discussed. The ability to simulate these advanced manufacturing processes is an important contribution to extend automation further and thus increase cost effectiveness.

Lecture

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
J. Slabeycius

Deposits and damages on high precision surfaces of advanced materials.

In: 5th Youth Symposium on Experimental Solid Mechanics

Puchov, Slowakei

10.-13.05.2006 (2006)

Lecture

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
J. Slabeycius

Sedimentations on high-precision surfaces of advanced materials by magnetorheological finishing.

In: Current Developments in Lens Design and Optical Engineering VII

San Diego, CA, USA

13.08.2006 (2006)

Journal article

Markus Schinhärl
G. Smith
Andreas Geiss
L. Smith
Rolf Rascher
Peter Sperber
Elmar Pitschke
R. Stamp

Calculation of MRF influence functions.

In: Optical Manufacturing and Testing VII vol. 6671 pg. 66710Y ff.

(2007)

show abstract

Magnetorheological finishing (MRF) is a commonly used computer-controlled polishing (CCP) technique for high precision optical surfaces. The process is based on a magnetorheological abrasive fluid, which stiffens in a magnetic field and may be employed as a sub-aperture polishing tool. Dependent upon the surface error-profile of the workpiece and the polishing tool characteristic (influence function) an individual polishing procedure is calculated prior to processing. However, determination of the influence function remains a time consuming and laborious task. A user friendly and easy to use software tool has been developed, which enables rapid computation of MRF influence functions dependent on the MRF specific parameters, such as, magnetic field strength or fluid viscosity. The software supersedes the current cumbersome and time consuming determination procedure and thus results in considerably improved and more economical manufacture. In comparison with the conventional time period of typically 20 minutes to ascertain an influence function, it may now be calculated in a few seconds. An average quality improvement of 57% relating to the peak-valley (PV) value, and approximately 66% relating to the root-mean-square (RMS) of the surface error-profiles was observed during employment of the artificial computed influence functions for polishing.

Lecture

Rolf Rascher

Ultraschallbearbeitung von Glas.

In: 5. Technologietreff

Österreichische Arbeitsgruppe für Zerspanungstechnik AFA e.V.

2007 (2007)

Journal article

Elmar Pitschke
Peter Sperber
Rolf Rascher
R. Stamp
M. Smith
L. Smith
Markus Schinhärl

Lens production enhancement by adoption of artificial influence functions and a knowledge-based system in a magnetorheological finishing process.

In: Optical Manufacturing and Testing VII vol. 6671 pg. 66711J ff.

(2007)

DOI: 10.1117/12.761356

show abstract

High quality optical lenses are usually finished by magnetorheological finishing (MRF). In this process an abrasive fluid, with the ability to stiffen in a magnetic field, is used as the polishing tool in a computer-controlled machine tool. Although the machine is automated it is necessary for a skilled operator to set the machine and make judgments with regard to its operation. An investigation has been under way to examine the detailed operation of the MRF process, and the information that is necessary to establish best practice. This has resulted in the incorporation of a knowledge based system (KBS) into the machine control regime, and a methodology for the creation of artificial polishing tool characteristics, the machine influence function. The incorporation of the these elements has been instrumental in the operation of an enhanced MRF machine. This has been subject to extensive test procedures, and it has been demonstrated that the production process may be enhanced significantly and consistently. Batch production time may be significantly reduced, a figure in excess of a 50% reduction was met consistently during prolonged operation. Furthermore the incorporation of the KBS is instrumental in increasing the automation of the MRF process, reducing the levels of manual input necessary to manage machine operation.

Contribution

K. Fathima
Andreas Geiss
Rolf Rascher
Peter Sperber
Markus Schinhärl
Elmar Pitschke

Design and development of a novel computer-controlled power device for electrical-assisted optical grinding.

In: Optifab 2007: Technical Digest, volume TD04. pg. TD0406-1 ff.

(2007)

Journal article

Markus Schinhärl
Rolf Rascher
R. Stamp
G. Smith
L. Smith
Elmar Pitschke
Peter Sperber

Filter algorithm for influence functions in the computer-controlled polishing of high-quality optical lenses.

In: International Journal of Machine Tools and Manufacture vol. 47 pg. 107-111

(2007)

show abstract

Computer controlled polishing (CCP) is widely used in the production of high-quality optical lenses. CCP enables surface error-profile-dependent calculation of polishing sequences prior to processing, and facilitates the cost-effective manufacture of high-quality optical surfaces. Calculation of an individual polishing sequence requires knowledge of the surface error-profile in addition to knowledge of the material removal characteristic (influence function) of the polishing tool. Measurement errors during both determination of the surface error-profile, and the influence function, may lead to an incorrect polishing sequence calculation, which in turn may result in an inadequate product quality. A new method has been developed which minimises the effects of measurement errors on the influence function. The resulting algorithm renders an influence function symmetrical and filters noisy data. Practical polishing tests with magnetorheological finishing have been performed to verify this new technique. The improvement of the peak-valley (PV) value of the surfaces polished with the symmetrical rendered influence function was observed to average 14% greater than that which related to the PV value improvement of those surfaces which were polished with the unmodified influence function. The algorithm developed is based on software and is easily implemented. Thus, artificial enhancement of an influence function is a straightforward technique to improve the result of the polishing process.

Contribution

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
K. Fathima
Rolf Rascher
Peter Sperber
J. Slabeycius

Correcting silicon carbide and silicon nitride moulds by Magnetorheological Finishing.

In: Proceedings of the 7th euspen International Conference, Bremen, Vol. 2. pg. 360-363

(2007)

Lecture

Markus Schinhärl
G. Smith
Andreas Geiss
L. Smith
Rolf Rascher
Peter Sperber
Elmar Pitschke
R. Stamp

Calculation of MRF influence functions.

In: Optical Manufacturing and Testing VII, SPIE

San Diego, CA, USA

2007 (2007)

Contribution

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
K. Fathima
J. Slabeycius

Subsurface damages detecting on standard optical glass by dimple method.

In: Proceedings of the 12th International Conference on Problems of Material Engineering, Mechanics and Design, Jasna, Slowakei. pg. 13 ff.

(2007)

Lecture

Andreas Geiss
Markus Schinhärl
Elmar Pitschke
Rolf Rascher
Peter Sperber
K. Fathima
J. Slabeycius

Subsurface damages detecting on standard optical glass by dimple method.

In: The 12th International Conference on Problems of Material Engineering, Mechanics and Design

Jasna, Slowakei

29.-31.08.2007 (2007)

Journal article

Markus Schinhärl
Rolf Rascher
R. Stamp
L. Smith
G. Smith
Peter Sperber
Elmar Pitschke

Utilisation of time-variant influence functions in the computer-controlled polishing.

In: Precision Engineering vol. 32 pg. 47-54

(2008)

DOI: 10.1016/j.precisioneng.2007.04.005

show abstract

In the computer controlled polishing, a polishing tool moves in a well-defined manner across the workpiece surface in order to individually remove the surface error-profile. The commonly used technique to calculate the moving of the polishing tool is the dwell time method. Based on a constant (time-invariant) removal characteristic of the polishing tool (influence function) the amount of material to be removed is controlled via the dwell time. The longer the polishing tool is in contact with a particular area of the workpiece, the more material is removed at this position. Mathematical basics to calculate dwell time-profiles are shown, and a new approach considering time-variant influence functions for the computer controlled polishing is introduced. The results point out that time-variant influence functions may contribute to further decrease the process time, and thus to make a computer controlled polishing process more efficient. The reduction of the process time was observed to approximately 35% using a combination of the dwell time method with time-variant influence functions.

Journal article

Markus Schinhärl
G. Smith
R. Stamp
Rolf Rascher
L. Smith
Elmar Pitschke
Peter Sperber
Andreas Geiss

Mathematical modelling of influence functions in computer-controlled polishing. Part I.

In: Applied Mathematical Modelling vol. 32 pg. 2888-2906

(2008)

show abstract

Computer-controlled polishing (CCP) is commonly used to finish high-quality surfaces, such as optical lenses. Based on magnetorheological finishing (MRF), a mathematical model to calculate the polishing tool characteristic (influence function) was developed and verified experimentally. The first part of this paper introduces the model to predict the size and shape of an influence function. The second part of this paper describes the calculation of the distribution of material removal within the size of an influence function. The model supersedes the current cumbersome procedure for determining an influence function and thus results in considerably improved and more economical manufacture. Furthermore, the model enables the quality of the final surface to be enhanced when polishing complex, for example aspherical or free-form, workpiece geometries and provides the first step in the application of time-variant influence functions.

Contribution

Christian Schopf
K. Fathima
Andreas Geiss
Markus Schinhärl
Christian Vogt
Rolf Rascher
Peter Sperber

Ultraschallunterstütztes Schleifen von Linsen.

In: Siebtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt. pg. 191-203

(2008)

Journal article

Markus Schinhärl
G. Smith
R. Stamp
Rolf Rascher
L. Smith
Elmar Pitschke
Peter Sperber
Andreas Geiss

Mathematical modelling of influence functions in computer-controlled polishing. Part II.

In: Applied Mathematical Modelling vol. 32 pg. 2907-2924

(2008)

show abstract

Computer-controlled polishing (CCP) is commonly used to finish high-quality surfaces, such as optical lenses. Based on magnetorheological finishing (MRF), a mathematical model to calculate the polishing tool characteristic (influence function) was developed and verified experimentally. The second part of this paper describes the calculation of the distribution of material removal within the size of an influence function and is based on Preston’s fundamental polishing equation. The complete influence function model was implemented using MATLAB. The result is a user-friendly and easy-to-use software tool that enables fast computation of MRF influence functions without the current cumbersome determination procedure, and thus gives improved and more economical production of high-quality surfaces.

Lecture

Rolf Rascher
Peter Sperber

Blick in die Zukunft - Eine Agenda zur Optikfertigung 2015?.

In: BayTech Optik Seminar

Deggendorf

2008 (2008)

Journal article

Elmar Pitschke
Markus Schinhärl
Rolf Rascher
Peter Sperber
L. Smith
R. Stamp
M. Smith

Simulation of a complex optical polishing process using a neural network.

In: Robotics and Computer-Integrated Manufacturing vol. 24 pg. 32-37

(2008)

DOI: 10.1016/j.rcim.2006.07.003

show abstract

Contribution

Andreas Geiss
K. Fathima
J. Slabeycius
L. Hajduchova
Rolf Rascher
Peter Sperber
Markus Schinhärl

Examination of surface and subsurface damages on silicon wafers using dimple polishing.

In: Proceedings of the 13th International Conference on Problems of Material Engineering, Mechanics and Design, Rajeke, Slowakei, 26.-29.08.2008.

(2008)

Journal article

Andreas Geiss
Rolf Rascher
J. Slabeycius
Markus Schinhärl
Peter Sperber
K. Fathima

Material removal study at silicon nitride molds for the precision glass molding using MRF process.

In: Current Developments in Lens Design and Optical Engineering IX vol. 7060 pg. 706007 ff.

(2008)

DOI: 10.1117/12.794583

show abstract

High-technology applications which are using high precision optic components in high and medium quantities have increased during recent years. One possibility to mass-produce e.g. such lenses is the precision glass molding (PGM) process. Especially for aspheric and free-form elements the PGM process has certain advantages. Premise is to manufacture accurate press molds, which have to feature smaller figure errors as the required lenses and may be made of materials, which are difficult to machine, like silicon nitride ceramics. These work pieces have to be machined in economical and steady process chains. However, due to the complex shapes and the corresponding accuracy an error dependent polishing is required. The Magnetorheological Finishing (MRF) as a high precision computer controlled polishing (CCP) technique is used and will further be presented in this work. To achieve the postulated demands a previous study of the material removal at selected machining parameters is needed. Changing machining parameters modify the removal, which is presented through values like the peak and volume removal rate. The value changes during the controlled variation of process parameters are described and discussed. Magnetorheological Finishing (MRF) provides one of the best methods to finish PGM molds that are relatively inaccurate to high precision in an economical, steady and efficient way. This work indicates the MRF removal selection and removal interference for the correction and finishing of precise silicon nitride molds for the precision glass molding.

Contribution

K. Fathima
Christian Schopf
Andreas Geiss
Markus Schinhärl
Christian Vogt
Rolf Rascher
Peter Sperber

Precision finishing of aspherical optical components using ELID grinding.

In: Siebtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt. pg. 191-203

(2008)

Contribution

Andreas Geiss
J. Slabeycius
Rolf Rascher
Markus Schinhärl
Peter Sperber
K. Fathima

Material influence of silicon nitride at Magnetorheological Finishing (MRF).

In: Proceedings of the 12th International Research/Expert Conference ”Trends in the Development of Machinery and Associated Technology” TMT 2008, Istanbul, Türkei, 26.-30.08.2008.

(2008)

Lecture

Rolf Rascher

Advanced technologies in precision optics manufacturing - a view to 2015?.

Meopta-Optika Prerov, Tschechische Republik

2008 (2008)

Contribution

Markus Schinhärl
Christian Vogt
Andreas Geiss
R. Stamp
Peter Sperber
L. Smith
G. Smith
Rolf Rascher

Forces acting between polishing tool and workpiece surface in magnetorheological finishing.

In: Proceedings of SPIE, Volume 7060, Current Developments in Lens Design and Optical Engineering IX (Optical Engineering + Applications, San Diego, CA, USA; August 10-14, 2008). vol. 7060 pg. 706006 ff.

Eds.:
P. Mouroulis
W. Smith
R. Johnson

(2008)

DOI: 10.1117/12.794196

show abstract

Magnetorheological finishing is a computer-controlled polishing technique that is used mainly in the field of high-quality optical lens production. The process is based on the use of a magnetorheological polishing fluid that is able, in a reversible manner, to change its viscosity from a liquid state to a solid state under the control of a magnetic field. This outstanding characteristic facilitates rapid control (in milliseconds) of the yield stress, and thus the pressure applied to the workpiece surface to be polished. A three-axis dynamometer was used to measure the forces acting between the magnetorheological fluid and the workpiece surface during determination of the material removal characteristic of the polishing tool (influence function). The results of a testing series using a QED Q22-X MRF polishing machine with a 50 mm wheel assembly show that the normal forces range from about 2 to 20 N. Knowledge of the forces is essential, especially when thin workpieces are to be polished and distortion becomes significant. This paper discusses, and gives examples of, the variation in the parameters experienced during a programme of experiments, and provides examples of the value of this work.

Journal article

Markus Schinhärl
R. Stamp
Elmar Pitschke
Rolf Rascher
L. Smith
G. Smith
Andreas Geiss
Peter Sperber

Advanced techniques for computer-controlled polishing.

In: Current Developments in Lens Design and Optical Engineering IX vol. 7060

(2008)

DOI: 10.1117/12.808036

show abstract

Computer-controlled polishing has introduced determinism into the finishing of high-quality surfaces, for example those used as optical interfaces. Computer-controlled polishing may overcome many of the disadvantages of traditional polishing techniques. The polishing procedure is computed in terms of the surface error-profile and the material removal characteristic of the polishing tool, the influence function. Determinism and predictability not only enable more economical manufacture but also facilitate considerably increased processing accuracy. However, there are several disadvantages that serve to limit the capabilities of computer-controlled polishing, many of these are considered to be issues associated with determination of the influence function. Magnetorheological finishing has been investigated and various new techniques and approaches that dramatically enhance the potential as well as the economics of computer-controlled polishing have been developed and verified experimentally. Recent developments and advancements in computer-controlled polishing are discussed. The generic results of this research may be used in a wide variety of alternative applications in which controlled material removal is employed to achieve a desired surface specification, ranging from surface treatment processes in technical disciplines, to manipulation of biological surface textures in medical technologies.

Contribution

Andreas Geiss
Markus Schinhärl
Rolf Rascher
Peter Sperber
J. Slabeycius
K. Fathima
Christian Vogt

Magnetorheological Finishing of silicon nitride moulds.

In: Proceedings of the 10th Anniversary International Conference of the European Society of Precision Engineering and Nanotechnology, Zürich, Schweiz, Volume 2.

(2008)

Lecture

K. Fathima
Christian Schopf
Andreas Geiss
Markus Schinhärl
Christian Vogt
Rolf Rascher
Peter Sperber

Precision finishing of aspherical optical components using ELID grinding.

In: Siebtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt

OTTI e.V., Zwiesel Zwiesel

04.-05.06.2008 (2008)

Lecture

Christian Schopf
K. Fathima
Andreas Geiss
Markus Schinhärl
Christian Vogt
Rolf Rascher
Peter Sperber

Ultraschallunterstütztes Schleifen von Linsen.

In: Siebtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt

OTTI e.V., Zwiesel Zwiesel

04.-05.06.2008 (2008)

Contribution

Christian Schopf
Rolf Rascher

Ultrasonic assisted drilling of brittle hard materials.

In: Proceedings of the 9th euspen International Conference, Volume 1, San Sebastian, Spanien, 02.-05.06.2009. pg. 455-458

(2009)

Journal article

H. Sporer
Rolf Rascher

Second Design ‐ Der große Wurf.

In: AUTOMOBIL PRODUKTION pg. 24

(2009)

Lecture

Rolf Rascher
et al.

2^nd Design ‐ Kosten senken in der 2. Runde.

In: Fachsymposium Faszination Kleben

3M Neuss

2009 (2009)

Lecture

Rolf Rascher
Christian Vogt

Strategies for grinding optical free forms using ball shaped grinding wheels.

In: Optifab 2009: Conference TD06

SPIE, The International Society for Optics and Photonics Rochester, NY, USA

11.-14.05.2009 (2009)

Lecture

Christian Vogt
R. Stamp
G. Smith
Rolf Rascher
Peter Sperber
Florian Schneider
Roland Maurer
Markus Schinhärl

Strategies for grinding optical free-forms using ball-shaped grinding wheels.

In: SPIE Optifab

SPIE - The International Society for Optical Engineering Rochester, NY, USA

11.05.2009 (2009)

show abstract

The demand for non-spherical surfaces and free-forms is steadily growing. Aspherical lenses can reduce the number of necessary lenses in optical systems e.g. used for lithographic devices for production of microprocessors. Parabolic mirrors can be used to focus light beams highly efficiently because of low absorption rates without colour distortion. Combined optical devices with included mechanical functions for assembly reduce necessary production steps. The most common pre-machining method for small numbers of high-precision lenses and mirrors is grinding. Depending on the required shape there are different options for generating surfaces e. g. spheres, parabolic mirrors or combined forms. The most flexible ones are grinding with (i) workpiece and ball-shaped tool rotating and (ii) fixed workpiece with ball-shaped tool rotating. In this manuscript grinding strategies dealing with meander and spiral tool paths are investigated in order to define which strategy works best for machining off-axis parabolic mirrors.

Lecture

Rolf Rascher
et al.

Vortrag ELSA Grind ‐ ELID supported grinding of thin micro-structured sapphire wafers.

In: 2. Internationale Konferenz zum Ultrapräzisions- und

Fraunhofer IPT Aachen

17.-18.11.2009 (2009)

Contribution

Markus Schinhärl
Florian Schneider
Rolf Rascher
Christian Vogt
Peter Sperber

Relationship between influence function accuracy and polishing quality in magnetorheological finishing.

In: Proceedings of the 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies (Dalian, China; April 26-29, 1010). pg. 76550Y ff.

Eds.:
L. Xiang
L. Zhang
J. Sasian
S. To

(2010)

DOI: 10.1117/12.865508

show abstract

Magnetorheological finishing is a typical commercial application of a computer-controlled polishing process in the manufacturing of precision optical surfaces. Precise knowledge of the material removal characteristic of the polishing tool (influence function) is essential for controlling the material removal on the workpiece surface by the dwell time method. Results from the testing series with magnetorheological finishing have shown that a deviation of only 5% between the actual material removal characteristic of the polishing tool and that represented by the influence function caused a considerable reduction in the polishing quality. The paper discusses reasons for inaccuracies in the influence function and the effects on the polishing quality. The generic results of this research serve for the development of improved polishing strategies, and may be used in alternative applications of computer-controlled polishing processes that quantify the material removal characteristic by influence functions.

Contribution

Florian Schneider
Markus Schinhärl
Christian Vogt
Roland Maurer
Peter Sperber
Rolf Rascher
R. Stamp
G. Smith

Effects of mechanical inaccuracies on the measurement result in metrology systems.

In: Proceedings of the 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment. vol. 7656 pg. 765611 ff.

(2010)

Contribution

Markus Schinhärl
Christian Vogt
Florian Schneider
Peter Sperber
Rolf Rascher

Investigations on Magnetorheological Finishing of High-Quality Optical Surfaces with Varying Influence Function (Proceedings of Optical Fabrication and Testing 2010; Jackson Hole, WY, USA; June 13-17, 2010).

In: Optical Fabrication and Testing on CD-ROM. pg. OWD3 ff.

Washington, DC, USA

(2010)

DOI: 10.1364/OFT.2010.OWD3

Contribution

Christian Vogt
Markus Schinhärl
Florian Schneider
Peter Sperber
Rolf Rascher

Investigations on Grinding Tools for Silicon Carbide Based Advanced Materials.

In: International Optical Design Conference 2010 (13-17 June 2010, Jackson Hole, WY, USA). (Proceedings of SPIE. 2004-) pg. OWD2 ff.

Eds.:
G. Anurag
J. Bentley
R. Youngworth

SPIE Bellingham

(2010)

Lecture

Florian Schneider
Christian Vogt
Roland Maurer
Rolf Rascher
Peter Sperber

Effects of mechanical inaccuracies on the measurement result in metrology systems.

In: SPIE Conference

Dalian, China

2010 (2010)

Contribution

Christian Schopf
Rolf Rascher
Peter Sperber

Vor- und Nachteile der Ultraschalltechnologie beim Schleifen von optischen Flächen.

In: Achtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt. pg. 59-72

OTTI

(2010)

Contribution

Igor Makarenko
Christian Vogt
Rolf Rascher
Peter Sperber
Thomas Stirner

ELID supported grinding of thin sapphire wafers.

In: Proceedings of SPIE: 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies, Volume 7655. pg. 76550S ff.

(2010)

Lecture

Christian Schopf
Peter Sperber
Rolf Rascher

Forschung für die Industrie im Technologiecampus Teisnach, Hochschule für Angewandte Wissenschaften – FH Deggendorf.

In: Achtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt

OTTI e.V., Zwiesel Zwiesel

2010 (2010)

Lecture

Christian Schopf
Rolf Rascher
Peter Sperber

Vor- und Nachteile der Ultraschalltechnologie beim Schleifen von optischen Flächen.

In: Achtes Symposium - Zukunft Glas - von der Tradition zum High-Tech-Produkt

OTTI e.V., Zwiesel Zwiesel

2010 (2010)

Lecture

Rolf Rascher

Erfahrungen zum ELID-Schleifen hochfester, spröder Werkstoffe.

In: 8. Seminar Moderne Schleiftechnologie und Feinstbearbeitung

Hochschule Furtwangen Furtwangen

11.03.2010 (2010)

Lecture

Christian Schopf
Rolf Rascher

Ultraschalluntersütztes Bearbeiten optischer Materialien.

In: 4. Optikseminar

Technologie Campus Teisnach Teisnach

20.-21.04.2010 (2010)

Lecture

Markus Schinhärl
Rolf Rascher

Relationship between influence function accuracy and polishing quality in magnetorheological finishing.

In: 5th SPIE International Symposium on Advanced Optical Manufacturing and Testing Technologies

Dalian, China

26.-29.04.2010 (2010)

Lecture

Igor Makarenko
Rolf Rascher

ELID supported grinding of thin Sapphire wafers.

In: 5th SPIE International Symposium on Advanced Optical Manufacturing and Testing Technologies

Dalian, China

26.-29.04.2010 (2010)

Lecture

Florian Schneider
Rolf Rascher

Effects of mechanical inaccuracies on the Measurement result in metrology systems.

In: 5th SPIE International Symposium on Advanced Optical Manufacturing and Testing Technologies

Dalian, China

26.-29.04.2010 (2010)

Journal article

Christian Vogt
S. Sinzinger
H. Adelsberger
Roland Maurer
Florian Schneider
R. Mandler
L. Kuepper
Rolf Rascher
Peter Sperber

An Experimental Study on a Flexible Grinding Tool.

In: Advanced Materials Research vol. 325 pg. 91-96

(2011)

DOI: 10.4028/www.scientific.net/AMR.325.91

Contribution

Roland Maurer
Florian Schneider
Christian Vogt
Markus Schinhärl
Peter Sperber
Rolf Rascher

Physical marker based stitching process of circular and non-circular interferograms.

In: Proc. SPIE 8083, Modeling Aspects in Optical Metrology III (SPIE Optical Metrology; May 20122; Munich, Germany).

Eds.:
B. Bodermann

(2011)

DOI: 10.1117/12.889491

Journal article

Rolf Rascher
Igor Makarenko

Use of ELID-grinding on brittle-hard materials.

In: International Journal of Mechatronics and Manufacturing Systems vol. 4 pg. 553-568

(2011)

DOI: 10.1504/IJMMS.2011.044105

show abstract

Abstract: Electrolytic in-process dressing (ELID) is a grinding technology which enables to manufacture surfaces in a quality that is close to polished on advanced, brittle-hard materials such as used in optics. ELID grinding requires exactly aligned machining pa rameters of the grinding process. Sapphire is, due to its crystal structure, difficult to m achine. There is a request for thin, i.e., below 0.2 mm thickness, sub-surface dama ge free wafers. To grind sapphire, the material’s behaviour is to be c onsidered. Studies on the necessary oxide layer on the ELID grinding wheel and influe nces on its build-up process will be presented. In-feed and grinding velocity are varied and the results on wear, removal rate and surface quality are shown. The influence of the coolant and the stiffness of the machine, the grinding forces and pressure are evaluated. The ELID grinding is compared to conventio nal grinding. The achieved excellent surface roughness on sapphire is discussed

Lecture

Heiko Biskup
Rolf Rascher
Christine Wünsche

Poliermittelerprobung I.

In: Spectaris - 4. Treffen des Industriekonsortiums Seltene Erden

Technische Hochschule Deggendorf/Technologie Campus Teisnach Teisnach

13.07.2011 (2011)

Contribution

M. Fuchs
Rolf Rascher
Alois Kasberger
Christian Wistl

Precision Glass Molding of lenses by using the nanotech molding process - a practical summary. Joint Poster Session (JTu5A).

In: Proceedings of Applied Industrial Optics: Spectroscopy, Imaging and Metrology; Monterey, CA, USA; 24.-28.06.2012.

(2012)

Lecture

Heiko Biskup
Rolf Rascher
Christine Wünsche

Poliermittelerprobung II.

In: Spectaris - 6. Treffen des Industriekonsortiums Seltene Erden

Mainz

23.02.2012 (2012)

Lecture

Heiko Biskup
Rolf Rascher
Christine Wünsche

Laserdiffraktometrie zur Charakterisierung von Korngrößen und deren Verteilung in Poliermitteln.

In: 5. Optikseminar

Technische Hochschule Deggendorf/Technologie Campus Teisnach Teisnach

30.07.2012 (2012)

Lecture

Heiko Biskup
Rolf Rascher
Christine Wünsche

Laserdiffraktometrie - Korngrößenverteilung in Poliermitteln. Posterbeitrag.

In: 5. Optikseminar

Technische Hochschule Deggendorf/Technologie Campus Teisnach Teisnach

30.07.2012 (2012)

Lecture

Paul Schötz
Johannes Liebl
Rolf Rascher
Christine Wünsche
Engelbert Hofbauer
Karlheinz Penzkofer

Metrology at Technologie Campus Teisnach.

In: 8th Workshop Asphere Metrology

Physikalisch-Technische Bundesanstalt (PTB)/Kompetenzzentrum Ultrapräzise Oberflächenbearbeitung e.V. Braunschweig

12.-13.11.2012 (2012)

Lecture

Rolf Rascher
Johannes Liebl
et al.

Hochgenaue Optische Abstandssensoren in Messtechnik und Qualitätssicherung.

In: 1. Optence Messtechnik Symposium

Darmstadt

15.11.2012 (2012)

Lecture

Johannes Liebl
Rolf Rascher
Katharina Dieser

GF-Projekt Optasens - Combination and evaluation of different optical and tactile sensor and measuring methods for analysis and global form-measurement on optical surfaces. Posterpräsentation.

In: F.O.M.-Marktplatz der Forschungsprojekte

Berlin

29.11.2012 (2012)

Contribution

Engelbert Hofbauer
Rolf Rascher
Thomas Stubenrauch
Johannes Liebl
Roland Maurer
et al.

Approach to the measurement of astronomical mirrors with new procedures.

In: Optical Metrology 2013, Optical Measurement Systems for Industrial Inspection VIII, volume 8788.

Eds.:
Z. Bokor
A. Adrienn
R. Markovits-Somogyi

(2013)

Contribution

Roland Maurer
Florian Schneider
Christine Wünsche
Rolf Rascher

Calculation of the reference surface error by analyzing a multiple set of sub-measurements.

In: SPIE Optics + Photonics 2013, Optical Manufacturing and Testing X, volume 8838.

(2013)

DOI: 10.1117/12.2024003

show abstract

In the field of precision optics the interferometry is the most applied measurement method to test spherical and flat objects. In principle, a standard interferometer setup is limited to these surface geometries, but interferometric systems may be modified with the aid of CGH’s or the stitching technology. As a consequence aspherical shapes and even freeform optics are measurable up to a certain extent. In an interferometric measurement the measured variable is the optical path difference (OPD) between the reference wave and the test wave. Based on the detected OPD the surface error of the test object is calculated by phase shifting methods for instance. It is evident, that the error from the reference surface affects the determination of the test object surface error. One option to face this problem is the calibration of the system prior to the measurement. For this the determination of the reference surface error may be realized with the aid of a two sphere test or a random ball test e.g. [1]. In the well-known SSI-technology from QED technologies the reference surface error is calculated on the basis of the sub-measurements. Due to the self-calibrating nature of the QED stitching principle [2-4] a calibration of the system prior to the measurement is not necessary. The University of Applied Sciences Deggendorf has implemented a similar algorithm to estimate the reference wave front error, or to be exact the error of the whole optical system, based on a multiple set of sub-measurements. This paper describes the applied algorithm in detail and discusses the results. To verify the implemented tool the results are compared to the outcomes of the QED stitching software. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Contribution

Christian Vogt
Florian Schneider
Rolf Rascher

Grinding Processes for Silicon Carbide (CSiC) Materials.

In: Proceedings of the 13th International Conference of the European Society for Precision Engineering & Nanotechnology . vol. 2 pg. 285-288

Sieca Repro Berlin

(2013)

Journal article

Christian Schopf
Rolf Rascher
Christine Wünsche

Rauhigkeitsmessungen an großen und schwer zugänglichen Bauteilen.

In: MM Industriemagazin-Maschinenmarkt pg. 40-41

(2013)

Lecture

Rolf Rascher

Moderne Optikfertigung.

In: 6. Optikseminar - Agenda zur modernen Optikfertigung

Technische Hochschule Deggendorf/Technologie Campus Teisnach Teisnach

12.03.2013 (2013)

Lecture

M. Willert-Porada
Thorsten Gerdes
A. Rosin
A. Saberi
A. Füller
Rolf Rascher
Christine Wünsche

Flexiplant: schmelzebasierte kontinuierliche Herstellung von low TG-Glas-Preformen (mittels Minimeltertechnologie).

In: 87. Glastechnische Tagung

HVG-DGG: Service und Forschung für die Glasherstellung Bremen

27.-29.05.2013 (2013)

Lecture

Rolf Rascher

Fertigung präziser Optikflächen – schleifen und polieren oder pressen?.

In: DGG-Glasforum

Wertheim-Bronnbach

26.09.2013 (2013)

Contribution

Roland Maurer
Heiko Biskup
Christian J. Trum
Rolf Rascher
Christine Wünsche

Determination of a suitable parameter field for the active fluid jet polishing process.

In: Optifab 2013. (Proceedings of SPIE)

Eds.:
J. Bentley
M. Pfaff

(2013)

DOI: 10.1117/12.2028752

show abstract

In 2012 a well-known company in the field of high precision optics assigned the University of Applied Sciences Deggendorf to determine a suitable parameter field for the active fluid jet polishing (AFJP) process in order to reach a surface accuracy of at least lambda / 5. The active fluid jet polishing is a relatively new and an affordable sub-aperture polishing process. For a fast and precise identification of the parameter field a considered design of experiment is necessary. The available control variables were the rotational speed of the nozzle, the distance between the test object and the jet, the feed rate, the material of the pin inside the nozzle and the material of the test object itself. In order to reach a significant data density on the one hand and to minimize the number of test runs on the other hand a meander shaped tool path was chosen. At each blank nine paths had been driven whereby at each path another parameter combination was picked. Thus with only one test object nine parameter settings may be evaluated. For the automatized analysis of the tracks a software tool was developed. The software evaluates ten sections which orthogonally intersect the nine tracks on the test-lens. The significant measurement parameters per section are the width and the height of each path as well as the surface roughness within the polished tracks. With the aid of these parameters and further statistical evaluations a suitable parameter field for the goal to find a constant and predictable removal spot was determined. Furthermore up to now over 60 test runs have been successfully finished with nine parameter combinations in each case. As a consequence a test evaluation by hand would be very time-consuming and the software facilitates it dramatically.

Lecture

S. Draxinger
Christine Wünsche
Rolf Rascher

Subaperture-polishing with variable spots.

In: Renewable Energy and the Environment, Freeform Optics (Freeform)

The Optical Society of America (OSA) Tucson, AZ, USA

03.-06.11.2013 (2013)

Journal article

Johannes Liebl
Heiko Biskup
S. Draxinger
Rolf Rascher
Christine Wünsche

Process developement fort the reproducible roughness measurement of optical surfaces using white light interferometry.

In: International Journal of Metrology and Quality Engineering (EDP Sciences) vol. 5 pg. 29-35

(2014)

Contribution

Christian Vogt
S. Sinzinger
Rolf Rascher

A Study on Elastic Grinding Tools.

In: Proceedings of the International Optical Design Conference. Part of Classical Optics 2014 ; 22-26 June 2014, Kohala Coast, Hawaii, United States (OSA Technical Digest (online)) pg. OTu3B.3

OSA, The Optical Society Washington, DC

(2014)

DOI: 10.1364/OFT.2014.OTu3B.3

show abstract

This paper reports on results of testruns with experimental grinding tools. The ball shaped tools comprise of abrasive layers with diamond grits, on top of an elastic layer. The tool’s design allows dwell time based corrections on simple and complex shapes, such as spheres and parabolic shapes.

Contribution

Engelbert Hofbauer
Rolf Rascher
K. Wühr
Felix Friedke
Thomas Stubenrauch
B. Pastötter
S. Schleich
C. Zöcke

3D-optical measurement system using vignetting aperture procedure.

In: Proceedings of SPIE Vol. 9132. Optical Micro- and Nanometrology V (April 15th-17th 2014; Brussels, Belgium) pg. 913206

Eds.:
A. Asundi
C. Gorecki
W. Osten

(2014)

DOI: 10.1117/12.2052631

Contribution

O. Fähnle
E. Langenbach
F. Frost
A. Schindler
Heiko Biskup
Johannes Liebl
Christine Wünsche
Rolf Rascher

Generation and field testing of roughness reference samples for industrial testing of surface roughness levels below 0.5nm Sq.

In: Proceedings of EOSAM 2014 (European Optical Society Annual Meeting) [Sep 15-19 2014, Berlin, Germany]. pg. 216-218

(2014)

Lecture

Thorsten Gerdes
K. Kyrgyzbayev
A. Rosin
A. Saberi
A. Füller
Rolf Rascher
Christine Wünsche

Aims for the development of new optical glass materials.

In: 1st European Seminar on Precision Optics Manufacturing

Technische Hochschule Deggendorf/Technologie Campus Teisnach Teisnach

01.-02.04.2014 (2014)

Lecture

Rolf Rascher

Technologies and results for the mirror production in Teisnach.

In: 1st European Seminar on Precision Optics Manufacturing

Technische Hochschule Deggendorf Teisnach

01.04.2014 (2014)

Lecture

Christian Vogt
S. Sinzinger
Rolf Rascher

A study on elastic grinding tools.

In: Optical Fabrication and Testing (OF&T)

The Optical Society of America (OSA) Kohala Coast, HI, USA

Juni 2014 (2014)

Lecture

Rolf Rascher
Johannes Liebl
Paul Schötz
P. Frieder

Automatische Kratzererkennung an hochpräzisen Drehteilen. „Projekt KonoScan“.

In: SENSOR + TEST

Nürnberg

04.06.2014 (2014)

Lecture

S. Draxinger
Christian J. Trum
Heiko Biskup
Christine Wünsche
Rolf Rascher

Active Fluid Jet Polishing - Behaviour on Different Materials.

In: Optical Fabrication and Testing (OF&T)

The Optical Society of America (OSA) Kohala Coast, HI, USA

22.-26.06.2014 (2014)

Lecture

Patrick Schäfer
Christine Wünsche
Rolf Rascher

Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument.

In: Optics and Measurement International Conference 2014

Liberec, Tschechische Republik

07.-10.10.2014 (2014)

Journal article

Heiko Biskup
Christian J. Trum
Rolf Rascher

Stabilität im Polierprozess.

In: Newsletter Bayern Photonics (Innovationsnetzwerk Optische Technologien)

(2015)

Contribution

Engelbert Hofbauer
Rolf Rascher
Felix Friedke
Thomas Stubenrauch
Johannes Liebl
J.-P. Richters

The vignetting field stop procedure: A new physical measurement principle for the Deflectometric acquisition of big Optical Surfaces - DaOS.

In: DGaO Proceedings (116. Jahrestagung in Brno, Tschechische Republik, 25.-29.05.2015).

(2015)

Contribution

Patrick Schäfer
Christine Wünsche
Rolf Rascher

Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument.

In: Proceedings of SPIE 9442. Optics and Measurement International Conference 2014 (07.-10.10.2014, Liberec, Tschechische Republik) pg. 944219

(2015)

Contribution

Christian Vogt
Martin Rohrbacher
Rolf Rascher
S. Sinzinger

Dependency between removal characteristics and defined measurement categories of pellets.

In: Proceedings of SPIE 9573. Optomechanical Engineering 2015 (10-12 August 2015, San Diego, CA, USA) pg. 95730N

Eds.:
A. Hatheway

(2015)

DOI: 10.1117/12.2189987

Contribution

Heiko Biskup
Alexander Haberl
Rolf Rascher

Surface errors in the course of machining precision optics.

In: Proceedings of SPIE Volume 9575, Optical Manufacturing and Testing XI (Aug 27th 2016, San Diego, CA). pg. 95750O

(2015)

DOI: 10.1117/12.2189991

show abstract

Precision optical components are usually machined by grinding and polishing in several steps with increasing accuracy. Spherical surfaces will be finished in a last step with large tools to smooth the surface. The requested surface accuracy of non-spherical surfaces only can be achieved with tools in point contact to the surface. So called mid-frequency errors (MSFE) can accumulate with zonal processes. This work is on the formation of surface errors from grinding to polishing by conducting an analysis of the surfaces in their machining steps by non-contact interferometric methods. The errors on the surface can be distinguished as described in DIN 4760 whereby 2nd to 3rd order errors are the so-called MSFE. By appropriate filtering of the measured data frequencies of errors can be suppressed in a manner that only defined spatial frequencies will be shown in the surface plot. It can be observed that some frequencies already may be formed in the early machining steps like grinding and main-polishing. Additionally it is known that MSFE can be produced by the process itself and other side effects. Beside a description of surface errors based on the limits of measurement technologies, different formation mechanisms for selected spatial frequencies are presented. A correction may be only possible by tools that have a lateral size below the wavelength of the error structure. The presented considerations may be used to develop proposals to handle surface errors. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Lecture

Heiko Biskup
Christian Schopf
Rolf Rascher

Surface roughness testing below 0.5 nm Sq. Measuring of Sub-Nanometer Surface Texture by White-Light Interferometry.

In: 6. Fachtagung Produktionsmesstechnik für die Praxis

NTB - Interstaatliche Hochschule für Technik Buchs, Schweiz

03.09.2015 (2015)

Contribution

Robert Schneider
Christian J. Trum

Hexapod as primary kinematic system for applications in the optic industry.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2235400

Contribution

Manon Schilke
Johannes Liebl
Christine Wünsche

Surface reconstruction by using Zernike polynomials.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2236305

show abstract

The development of high precision methods for the measurement of plano surfaces became of increasing importance over the last years. Recently accuracies in sub-nanometer range have been achieved on samples up to one meter in diameter. The used measurement method was based on direct deflectometry. The main part of the system was an electronic autocollimator measuring local angular displacements on defined traces along the surface of the plano lens. To stabilize the optical path a pentaprism was used. The measurement accuracy of a similar system was evaluated at the Technologie Campus Teisnach. The used system delivered twenty measurement spots along the profile on one diameter. Four diameters were measured at every 45 degrees. An evaluation algorithm was developed to model the complete threedimensional surface out of a small amount of measurement points. Within this modelling Zernike polynomials were used to reconstruct the surface topography. Two different approaches in using the hierarchy of the polynomials were compared. At first a reference surface was created by rotating a symmetrical averaged curve of all measured profiles. On the residuals of the original measurements to the symmetrical averaged curve a serial development of the error surface was applied with the help of Zernike polynomials. Different order of Zernike terms were tested because we saw a big influence on the result. This surface was added to the reference surface. The results of the two different approaches were compared. To enable us to compare the results of this measurement method to interferometric and optical 3Dprofilometric measurements the data was converted to xyz-format. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Contribution

Christian Vogt
S. Sinzinger
Martin Rohrbacher
Rolf Rascher

Prediction of grinding tool wear and lifetime by using a test bench.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

Contribution

Engelbert Hofbauer
Rolf Rascher
Manon Schilke
Johannes Liebl
J.-P. Richters

Deflectometric acquisition of large optical surfaces (DaOS) using a new physical measurement principle: vignetting field stop procedure.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2236134

Contribution

Christian Schopf
Rolf Rascher

Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant.

In: Proceedings of SPIE 10151. Optics and Measurement International Conference 2016 (Okt 11th 2016, Liberec, Czech Republic) pg. 1015107

(2016)

DOI: 10.1117/12.2257106

show abstract

The process of ultrasonic machining is especially used for brittle hard materials as the additional ultrasonic vibration of the tool at high frequencies and low amplitudes acts like a hammer on the surface. With this technology it is possible to drill holes with lower forces, therefor the machining can be done faster and the worktime is much less than conventionally. A three-axis dynamometer was used to measure the forces, which act between the tool and the sample part. A focus is set on the sharpness of the tool. The results of a test series are based on the Sauer Ultrasonic Grinding Centre. On the same machine it is possible to drill holes in the conventional way. Additional to the ultasonic Input the type an concentration of coolant is important for the Drilling-force. In the test there were three different coolant and three different concentrations tested. The combination of ultrasonic vibration and the right coolant and concentration is the best way to reduce the Forces. Another positive effect is, that lower drilling-forces produce smaller chipping on the edge of the hole. The way to reduce the forces and chipping is the main issue of this paper.

Journal article

Engelbert Hofbauer
Rolf Rascher
Manon Schilke
Johannes Liebl
J.-P. Richters

Deflectometric Acquisition of Large Optical Surfaces “DaOS” Using a New Physical Measurement Principle: Vignetting Field Stop. (Reprinted from Proceedings of SPIE Volume 10009: Third European Seminar on Precision Optics Manufacturing, 100090Y [Teisnach, April 12th 2016] doi:10.1117/12.2236134).

In: Bavarian Journal of Applied Sciences pg. 146-161

(2016)

show abstract

The vignetting field stop procedure uses a deflectometric approach to acquire big Optical Surfaces – DaOS – and it offers the possibility to measure nearly any shape or form using a scanning routine. The basic physical measurement principle in DaOS is the vignettation of a quasi-parallel light beam emitted by an expanded light source in auto collimation arrangement with a reflecting element. Thereby nearly any curvature of the specimen, is measurable. Due to the fact, that even sign changes in the curvature can be detected, also aspheres and freeform surfaces of any size can be evaluated. In this publication the vignetting field stop procedure is discussed. Additionally the deflectometric setup is described. Because of some typical influences of beam deflection to the accuracy of angle measurement by using the vignetting principle, suitable methods of calibration for the sensor are examined and the results of these methods are presented. Furthermore, the technical principle of deflectometric measurements using an angle detecting device is explained inclusive of all random and systematic errors generated by the setup. The last part of this publication shows the actual result of test measurements with calculated absolute deviation of errors with a large lateral dimension as well as the determination of the maximal achievable lateral resolution by detecting mid frequent structures on flat and spherical test parts with a diameter of 300 mm. These measurements are compared critically to reference results which are recorded by interferometry and further scanning methods.

Contribution

Sebastian Sitzberger
Rolf Rascher

An investigation on the efficiency of the manufacturing of components in precision optics.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2236137

show abstract

By adaption and coordination of successive process steps the efficiency of producing optics can be improved. In the beginning of this investigation, the focus is on two crucial process steps of the optical manufacturing process. First, there is the optical and mechanical design of the optical part and system. In this context, it is important to consider what modifications compared to the current standard design are possible respectively useful. Thus, the modifications will only concentrate on parts of the optic that do not interfere with the optical functionality. Furthermore in this part of the study the main aspect is the clamping situation of the optical part in a holder or an optical system. It will be discussed, whether it is useful to add special clamping surfaces respectively a clamping flange in contrast to the standard design. The faultless functioning of the optics has always first priority. Second, the manufacturing process itself has a great number of single steps. Therefore, a main part of the research is the investigation of current clamping situations in optics manufacturing, with prospect to improve them in order to work perfectly with the design modifications, as mentioned above. This part of the investigation focuses on the clamping system for the lens on each machine necessary for manufacturing. In the scope of this paper the authors want to summarize characteristics and deficits of current clamping systems and workpiece mounts and give a prospect of the following course of action. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Journal article

Engelbert Hofbauer
Rolf Rascher

Deflectometric Acquisition of Large Optical Surfaces DaOS. Using a new physical measurement principle: vignetting field stop procedure.

In: Optik&Photonik vol. 11 pg. 40-44

(2016)

DOI: 10.1002/opph.201600036

Contribution

Johannes Liebl
Horst Linthe
Sebastian Sitzberger
Rolf Rascher

Interferometric measurement of highly accurate flat surfaces.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2235525

show abstract

The most important part in manufacturing precision optics is a reliable measurement procedure which provides results a few times more accurate than the quality to be produced. In general two specific values are important, the repeatability of several measurements which are done in a row and the absolute accuracy which is mostly defined by the systematical error of the measurement device. The repeatability can be improved relatively simple, by increasing the number of measurements and a following averaging step. To increase the absolute accuracy of a measurement device in the field of precision optics is far more challenging. In this paper several interferometer absolute testing methods to measure flat surfaces are compared. The main objective was to name a value for the achievable accuracy. Therefor four different methods were analyzed: 1. The three flat test, a method which is already used several decades to determine the quality of a flat surface. As a result, two absolute measured profiles, horizontal and vertical, can be calculated. 2. The multi rotation test, an extension of the classical three flat test. The big advantage of this method is a fully three dimensional map of the systematical error. 3. The systematical error calculated by the SSI-A. Hereby several subapertures are measured over the whole surface. The redundant information’s of the overlapping regions can be used to calculate the systematical error of the system. 4. The rotation of the transmission flat relatively to the interferometer. Thereby the rotation unsymmetrical errors can be calculated and subtracted. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Contribution

Gerald Fütterer

From Holographic displays to Volume Gratings and Off-Axis Parabolic Mirrors.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]). pg. 1000912

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2245183

show abstract

An important chain link in modeling of three dimensional data (3D data), 3D prototyping, CAD-CAM, computerintegrated manufacturing (CIM), PC gaming, global 3D teleconferencing, future e-commerce, product advertisement and mobile infotainment is the visualization of 3D data and 3D objects. On the one hand, there is an increasing demand for 3D displays providing natural three dimensional viewing experience, but on the other hand there is a lack of available 3D displays capable of generating all depth cues. Available state of the art 3D displays can provide only a few depth cues and a very limited 3D experience. This is due to the inherent physical limits of the different approaches used. Holographic displays, for instance based on space bandwidth limited wave segment reconstruction, can provide all depth cues and a large viewing volume. They can provide satisfying 3D visualization. But still they are not available. Thick hologram gratings 1, which also can be referred to as Bragg diffraction based volume gratings, are key components, which enable small form factor holographic 3D displays. Manufacturing large, display size Bragg diffraction based volume gratings is challenging. Collimators are key components within interference lithographic exposure setups. Using off-axis parabolic mirrors (OAPM) as collimating optical elements enables the generation of exact plane waves by using a single reflective surface. Thus, off-axis parabolic mirrors are preferred in order to realize the collimation of large wave fronts. The surface roughness has to be very low. The relationship between holographic 3D displays and specific requirements, which have to be taken into account when manufacturing off-axis parabolic mirrors, will be presented. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Contribution

Christian J. Trum
Rolf Rascher

Improving efficiency of chemo-mechanical polishing processes by systematic selection and conditioning of the polishing suspension.

In: Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach]).

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2016)

DOI: 10.1117/12.2236000

show abstract

During design of optical systems or individual components, customers and designers already predetermine the way through production and the necessary resources. They define the tolerances that are required for their application like shape, micro-roughness and cleanliness, as well as the glass material that is necessary for the targeted optical effect. By the tolerances, they have also an influence on the manufacturer and his decisions on the production environment, measurement technology and the process chain that in his opinion is necessary to meet the specification. In most cases the type of polishing suspension and its parameters are also predetermined by the use of central polishing supply systems. With this paper, the authors want to give a prospect of a currently running research with the aim of increasing the efficiency of chemo-mechanical polishing processes by a systematic selection and conditioning of the polishing suspension. They want to show that small amounts of well-conditioned and stabilized polishing suspension could be a tool to improve the efficiency in CMP processes under the influence of the global trend to products that are more individual and down to one piece flow production. Main parts of this research are the identification of influences of polishing suspensions on the quality criteria of optical components and the creation of a method to find well-working suspension parameters in a deterministic and reproducible way. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Lecture

Rolf Rascher
Christine Wünsche
Christian Schopf

Aspects in laser polishing of precision optical components.

In: LaP 2016 - 2nd Conference on Laser Polishing

Aachen

26.-27.04.2016 (2016)

Lecture

Rolf Rascher

Innovationsentwicklung mit der Technischen Hochschule Deggendorf.

In: Innovationsworkshop "Innovation in der Photonik" im Rahmen der 13. Optatec 2016 - Internationale Fachmesse für optische Technologien, Komponenten und Systeme

Frankfurt am Main

07.06.2016 (2016)

Lecture

Christian Schopf
Rolf Rascher

Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant.

In: Optics and Measurement International Conference 2016

SPIE, The International Society for Optics and Photonics Liberec, Tschechische Republik

11.10.2016 (2016)

Lecture

Rolf Rascher
C. Weingarten

Hybridfertigung optischer Oberflächen.

In: F.O.M.-Konferenz 2016 - Innovative Industrien unterstützen

Forschungsvereinigung Feinmechanik, Optik und Medizintechnik e.V. Berlin

02.11.2016 (2016)

Contribution

Rolf Rascher
Christian Vogt
C. Faehnle

In situ laser polishing optimization method: Control of LASer Surface Optimisation (C-Lasso).

In: Proceedings of EOS Optical Technologies Conferences at the World of Photonics Congress (WPC 2017) [Munich, Germany; June 26-29, 2017].

(2017)

show abstract

Laser polishing is achieved by local absorption of laser power within the polishing spot causing the surface and its sub-surface region to melt and flow reducing surface roughness and removing sub-surface damage. In this paper we present a novel fabrication controlling method for laser polishing processes called C-Lasso (Control of LASer Surface Optimization, Patent Pending), monitoring in situ the surface smoothening process. It is possible to determine and control the minimum dwell time a footprint needs to stay at a certain point before moving further. C-Lasso enables to avoid unnecessarily long local dwell times. Besides the functioning principle, a proof of concept will be presented as well as experimental data demonstrating the in situ monitoring.

Contribution

Christian Schopf
Rolf Rascher
Johannes Liebl

Cheap and fast measuring roughness on big surfaces with an imprint method.

In: Proceedings of SPIE 10448 (SPIE Optifab [October 16-19, 2017; Rochester, NY, USA]). pg. 1044822

Eds.:
S. Stoebenau
J. Bentley

(2017)

Journal article

Christian Vogt
C. Faehnle
Rolf Rascher

Grinding Process Validation Approach (gPVA).

In: Journal of Physical Science and Application vol. 7

(2017)

DOI: 10.17265/2159-5348/2017.05.004

Contribution

Christian Vogt
O. Fähnle
Rolf Rascher

Three wagons Approach Applied to Optimization of Industrial Grinding Processes.

In: Optical Fabrication and Testing part of Optical Design and Fabrication: 9-13 July 2017, Denver, Colorado, United States. pg. OTu2B.2

Eds.:
Optical Fabrication
OSA Optical Design
Optical Design
Testing
OFT
Fabrication Congress
OF&T
Fabrication
Optical Society of America

OSA - The Optical Society Washington, D.C., USA

(2017)

DOI: 10.1364/OFT.2017.OTu2B.2

Contribution

Alexander Haberl
Rolf Rascher

Yet one more dwell time algorithm.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 1032606

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2270540

Contribution

P. Rinck
Sebastian Sitzberger
M. Zaeh

Actuator design for vibration assisted machining of high performance materials with ultrasonically modulated cutting speed.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260C

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2272133

Contribution

Josef Stettmer

Process optimization at small and medium-sized enterprises: production of small and medium-sized batches.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260P

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2275028

Contribution

Gerald Fütterer

Polarization-Fizeau interferometer enabling phase measurement with reduced uncertainty.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260B

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2272001

Contribution

Christian Vogt
O. Fähnle
Rolf Rascher

Setting-up high-end cnc grinding processes: a Preston-based approach.

In: Proceedings of EOS Optical Technologies Conferences at the World of Photonics Congress (WPC 2017) [Munich, Germany; June 26-29, 2017].

(2017)

show abstract

The design of grinding processes is commonly based on the principle of trial and error. In most cases this will end up with a usable setup that delivers acceptable results. On the other hand this method is unlikely to reveal the process’s total potential. Allthough the principles of grinding and polishing are entirly different, the preston approach can be used to design grinding processes more intelligent and highly efficient. Carrying out a testing procedure for grinding tools reveals the tool’s removal properties on different materials. This allows to choose ideal sequences of pre and fine-grinding. Furthermore it is possible to choose the optimum machining parameters to optain a maximum output.

Contribution

Christian J. Trum
Sebastian Sitzberger
Rolf Rascher

Advanced method for the characterization of polishing suspensions.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260I

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2272431

Contribution

Robert Schneider
Alexander Haberl
Rolf Rascher

Parametrization of a Subaperture Polishing Tool - Analysis of the Path Tests.

In: Optical Fabrication and Testing part of Optical Design and Fabrication: 9-13 July 2017, Denver, Colorado, United States. vol. Paper OM3B.2

Eds.:
Optical Fabrication
OSA Optical Design
Optical Design
Testing
OFT
Fabrication Congress
OF&T
Fabrication
Optical Society of America

OSA - The Optical Society Washington, D.C., USA

(2017)

Contribution

Christian Vogt
O. Fähnle
Rolf Rascher

Force-controlled analysis tool for optimization of precision CNC grinding processes.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260M

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2272713

Contribution

Engelbert Hofbauer
Rolf Rascher
Felix Friedke
R. Kometer

Resolution, measurement errors and uncertainties on deflectometric acquisition of large optical surfaces "DaOS".

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 1032603

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2267513

Contribution

Sebastian Sitzberger
Christian J. Trum
Rolf Rascher

Analysis of the influence of the workpiece self-weight in precision optics manufacturing using FEM simulation.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 103260O

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2273023

Contribution

Bin Dong
Christian Vogt
Rolf Rascher

Wear detection of brass bond diamond grinding wheel by spectral coherence of grinding forces.

In: Proceedings of the 17th International Conference of the European Society for Precision Engineering and Nanotechnology [euspen] (May 29 - June 2, 2017; Hanover, Germany). pg. 221-222

(2017)

Contribution

Robert Schneider
Alexander Haberl
Rolf Rascher

Polishing tool and the resulting TIF for three variable machine parameters as input for the removal simulation.

In: Proceedings of SPIE 10326 (Fourth European Seminar on Precision Optics Manufacturing, 1032601 [April 4th-5th 2017, Teisnach]). pg. 1032602

Eds.:
Rolf Rascher
Christian Schopf
O. Fähnle
Christine Wünsche

(2017)

DOI: 10.1117/12.2267415

Contribution

Olga Kukso
Rolf Rascher
R. Börret
M. Pohl

On the metrology of the MSF errors.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 108290F

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318675

show abstract

The aim of our research is to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after all manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. In this paper we describe some middle spatial frequency errors, which occur during grinding. As there are limited possibilities to measure ground surfaces, their analysis from the point of measurement is most difficult. Therefore, it is of utmost importance to optimally organize the measurement guaranteeing sufficient data for the reconstruction of the toolpath and avoidance of aliasing effects. In the paper discuss possible classifications and some difficulties during measuring of grinded surfaces.

Contribution

M. Doetz
O. Fähnle
Christian Vogt

SPDT and standard CNC-grinding of tungsten carbide molds for precision glass molding: an experimental process analysis.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 31

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318710

Contribution

Christian Vogt
O. Fähnle
Rolf Rascher

gPVA: a system for the classification of grinding tools.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 26

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318695

Contribution

Sebastian Sitzberger
Christian J. Trum
Rolf Rascher
M. Zaeh

Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 108290A

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318577

show abstract

The effects, the extent and the importance of workpiece deformations, particularly lenses, caused by the weight of the workpiece itself, were examined in a previous paper1 . The considered deformations are in the single-digit to two-digit nanometer range. The investigation was carried out by FEM calculations. The conclusion of the previous aper was that a full-surface support of a workpiece in the processing of one surface presumably produces the best results. Furthermore, it was found that if the second functional surface is not to be touched in the process, a full contact lens mounting on its circumference is advisable. An alternative method for fixing precision lenses is therefore desirable. This can be accomplished in two steps. As a first step, the lens must be gripped at its periphery so that none of the optically functional surfaces of the lens is compromised. However, the complete circumference has to be fixated gaplessly because a punctual fixation has the disadvantage of deforming the lens surface asymmetrically. As a second step, the freely hanging lens surface should be supported to minimize deformation. An approach had to be found that supports the surface like a solid bearing but at the same time does not touch it. Therefore, the usage of an incompressible fluid as a hydrostatic bearing for full-surface support is pursued. For this purpose, the bottom side of the lens has to be stored on water. The results of the FEM simulation showed that with a fluid bearing the resulting deformations can be drastically reduced in comparison to a freely hanging surface. Furthermore, under the right conditions, a resulting deformation comparable to a full surface solid support can be achieved. The content of this paper is a test series under laboratory conditions for a first validation of the theoretical results. Therefore, a prototype model to test a lens fixation with a fluid bearing was developed and manufactured. The resulting deformations were measured with an interferometer and the effects are discussed.

Journal article

O. Fähnle
Rolf Rascher
Christian Vogt
D.W. Kim

Closed-loop laser polishing using in-process surface finish metrology.

In: Applied Optics vol. 57 pg. 834-838

(2018)

DOI: 10.1364/AO.57.000834

show abstract

This paper lays out the trail onto a closed-loop polishing process of optical elements enabling the application of the optimum polishing time needed. To that aim, an in-process testing method for monitoring an inclusive micro surface quality (e.g., comprising surface roughness and scratch-and-dig) within the polishing spot is analyzed and its applicability to closed-loop polishing for classical loose-abrasive full-aperture polishing as well as for computer controlled laser polishing is experimentally tested and verified. This enables the determination of the optimum local dwell time resulting in a stable and cost optimized polishing.

Contribution

Christian J. Trum
Sebastian Sitzberger
Rolf Rascher

Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad.

In: Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA). pg. 20

Eds.:
R. Williamson
Rolf Rascher
Dae Kim

SPIE San Diego, United States

(2018)

DOI: 10.1117/12.2321031

show abstract

Chemical-mechanical polishing (CMP) of optical glasses is widespread and forms the basis for many high-precision polishing processes. The pads, slurries and glass materials used in polishing have many different properties. The effects of these properties on the process results are often unknown. The right choice and combination is therefore often a challenge. By means of a plan processing of N-BK7 and SF56 samples by a plan-polishing process, the influence on the process results, material removal rate (MRR), micro roughness and cleanliness caused by slurry and polishing pad is shown. It turns out that the type of polish pad has the biggest impact on the results. The easy-to-process material N-BK7 shows only little influence by the type of slurry used. The more challenging SF56, however, shows significant effects, especially in the area of the resulting micro roughness and the appearance of surface damages like orange peel. Especially the use of Auerpol® PZ500 shows clear advantages here. For a selection of three out of nine polishing pads, the effect of density variation of the slurry was also investigated. Lower particle concentrations lead to lower material removal rates. This applies to both materials. The more sensitive SF56 shows a reduction in micro roughness by the use of a less dense slurry. The correct selection of the polishing pad has a positive effect on the material removal rate and/or the micro roughness in all tested materials. An adaptation of the type and concentration of the slurry is especially important for more sensitive materials and in combination with the right polishing pad. In view of the development towards special materials and small lot sizes, the targeted and correct selection of polishing slurries and pads becomes more and more important. The information required for this purpose on the behavior of the pads and slurries available on the market must therefore first be determined in a targeted manner and clearly presented.

Contribution

O. Fähnle
Christian Vogt
Rolf Rascher
M. Doetz
O. Dambon
F. Klocke

Ductile grinding of tungsten carbide molds applying standard CNC machines.

In: Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA). pg. 24

Eds.:
R. Williamson
Rolf Rascher
Dae Kim

SPIE San Diego, United States

(2018)

DOI: 10.1117/12.2323245

Contribution

O. Fähnle
Christian Vogt
Rolf Rascher
M. Doetz
O. Dambon
F. Klocke

From turning to grinding: ductile machining with gPVA.

In: Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA). pg. 30

Eds.:
R. Williamson
Rolf Rascher
Dae Kim

SPIE San Diego, United States

(2018)

DOI: 10.1117/12.2323246

Contribution

Alexander Haberl
Johannes Liebl
Rolf Rascher

ABC-polishing.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 1082906

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318549

show abstract

In the past, steadily increasing demands on the imaging properties of optics have led more and more precise spherical apertures. For a long time, these optical components have been produced in a satisfying quality using classic polishing methods such as pitch polishing. The advance of computer-controlled subaperture (SA) polishing techniques improved the accuracy of spheres. However, this new machine technology also made it possible to produce new lens geometries, such as aspheres. In contrast to classic polishing methods, the high determinism of SA polishing allows a very specific correction of the surface defect. The methods of magneto-rheological finishing (MRF) [1], [2] and ion beam figuring (IBF) [3], [4] stand out in particular because of the achievable shape accuracy. However, this leads to the fact that a principle of manufacturing "As exact as possible, as precise as necessary" [5] is often ignored. The optical surfaces often produced with unnecessary precision, result at least in increased processing times. The increasing interconnection of the production machines and the linking with databases already enables a consistent database to be established. It is possible to store measurements, process characteristics or tolerances for the individual production steps in a structured way. The difficulty, however, lies in the reasonable evaluation of the measurement data. This is where this publication comes in. The smart evaluation of the measurement data with the widespread Zernike polynomials should result in a classification, depending on the required manufacturing tolerance. In combination with the so-called ABC analysis, all surface defects can be categorized. In this way, an analytic breakdown of a - initially confusing - overall problem is made. With the aid of cost functions [6] an evaluation and consequently a deduction of actions is made possible. Thus, for example, the isolated processing of rotationally symmetrical errors in spiral mode, setup times and machining times can be reduced while avoiding mid spatial frequency errors (MSFE) at the same time.

Contribution

Christian J. Trum
Christian Vogt
Sebastian Sitzberger
Rolf Rascher
O. Fähnle

Filled-Up-Microscopy (FUM): a non-destructive method for approximating the depth of sub-surface damage on ground surfaces.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 11

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318576

Contribution

Christian Vogt
O. Fähnle
E. Langenbach
Rolf Rascher

In situ monitoring of laser polishing.

In: DGaO-Proceedings 2018. 119. DGaO-Jahrestagung 2018

Eds.:
Deutsche Gesellschaft für angewandte Optik e.V.

(2018)

Contribution

Alexander Haberl
H. Harsch
Gerald Fütterer
Johannes Liebl
C. Pruß
Rolf Rascher
W. Osten

Model based error separation of power spectral density artefacts in wavefront measurement.

In: Proceedings of SPIE 10749 (SPIE Optical Engineering + Applications Conference on Interferometry XIX [August 19-23, 2018; San Diego, CA, USA]). pg. 107490T

(2018)

DOI: 10.1117/12.2321106

Contribution

O. Fähnle
M. Doetz
O. Dambon
F. Klocke
Christian Vogt
Rolf Rascher

Ductile mode single point diamond turning (SPDT) of binderless tungsten carbide molds.

In: Proceedings of SPIE Optical Engineering + Applications (19-23 August, 2018; Optical Manufacturing and Testing XII; San Diego, CA, USA). pg. 15

Eds.:
R. Williamson
Rolf Rascher
Dae Kim

SPIE San Diego, United States

(2018)

DOI: 10.1117/12.2323244

Contribution

Christian Vogt
M. Doetz
Rolf Rascher
O. Fähnle

Standardized evaluation of grinding tools for brittle and ductile mode grinding. Invited Paper.

In: Proceedings of EOSAM 2018 (European Optical Society Biennial Meeting; October 2018; Delft, The Netherlands): Optical System Design, Tolerancing, and Fabrication.

Eds.:
The European Optical Society

(2018)

Lecture

Christian J. Trum
Sebastian Sitzberger
Rolf Rascher

Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad.

In: SPIE Optical Engineering + Applications 2018

San Diego, CA, USA

2018 (2018)

Contribution

A. Harsch
C. Pruss
Alexander Haberl
W. Osten

Tilted wave interferometry for testing large surfaces.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 1082908

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318573

show abstract

Measuring large surfaces interferometrically is a straight forward established technology, as long as they are concave and spherical. The situation chnages completely if aspheres and freeforms have to be measured. The application of a Tilted Wave Interferometer opens up possibilities to measure large concave surfaces of any shape without compensation optics. For the investigation of large convex aspheres, it is necessary to make use of stitching methods. Due to the freeform capability of the Tilted Wave Interefrometer, it is possible to acquire larger subapertures compared to null interferometers. Therefore measurement and computation time are reduced.

Contribution

O. Fähnle
O. Dambon
M. Doetz
F. Klocke
Christian Vogt
Rolf Rascher

Ductile grinding of tungsten carbide applying standard CNC machines: a process analysis.

In: Proceedings of SPIE 10692: SPIE Optical Systems Design/Optical Fabrication, Testing, and Metrology VI (14.-17.05.2018; Frankfurt/Main). pg. 34

Eds.:
SPIE - The International Society for Optical Engineering

(2018)

DOI: 10.1117/12.2315338

Contribution

M. Doetz
O. Dambon
Christian Vogt
Rolf Rascher
E. Langenbach
O. Fähnle

Enlarging process window of ductile mode machining of WC molds.

In: Proceedings of EOSAM 2018 (European Optical Society Biennial Meeting; October 2018; Delft, The Netherlands): Optical System Design, Tolerancing, and Fabrication.

Eds.:
The European Optical Society

(2018)

Contribution

O. Fähnle
Christian Vogt
Rolf Rascher

Load controlled process window analysis of feed controlled CNC grinding.

In: PROCEEDINGS VOLUME 10692 SPIE OPTICAL SYSTEMS DESIGN, 14-17 MAY 2018 Optical Fabrication, Testing, and Metrology VI. pg. 32

Eds.:
S. Schröder
R. Geyl

SPIE Frankfurt, Germany

(2018)

DOI: 10.1117/12.2315336

Contribution

M. Pohl
R. Börret
Rolf Rascher
Olga Kukso

Simulation of MSF errors using Fourier transform.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 1082903

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2317484

show abstract

This research is focused on the link between manufacturing parameters and the resulting mid spatial frequency error in the manufacturing process of precision optics. This first publication focuses on the parameters of the grinding step. The Goal is to understand and avoid the appearance of the mid spatial frequency error and develop a simulation which is able to predict the resulting mid spatial frequency error for/of a manufacturing process.

Contribution

Johannes Liebl
Christian Schopf
Rolf Rascher

DefGO.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 108290I

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318704

show abstract

The manufacturing of optical lenses has various steps. Generally, the manufacturing can be split up into the following steps: the workpiece is pre-ground with a coarse tool; it is then fine-ground with a finer tool. As the final polishing is a demanding and time-consuming process that cannot manage large removal rations not can it equalise rough shape errors, the starting quality and surface quality needs to be as high as possible. According to the current state of technology, ground lenses must be measured with tactile measuring techniques in order to detect shape errors. This is timeconsuming and expensive, and only two dimensional profiles can be measured. DefGO’s project objective is to introduce deflectometry as a new, three dimensional lens measuring standard. A problem with the application of deflectometry is that the object to be measured has to reflect enough light, which is not the case for ground glass with rough surfaces. DefGO’s solution is to wet the lens with a fluid to create a closed reflecting surface.

Contribution

Gerald Fütterer
Johannes Liebl
Alexander Haberl

Contribution of the phase transfer function of extended measurement cavities to mid spatial frequencies and the overall error budget.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 108290L

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318711

show abstract

A challenge of coaxial - measurement cavity based - interferometer is to realize an interference contrast in the vicinity of one and to realize a complete elimination of the parasitic reflections. Another challenge, which also exists in non-coaxial setups, is the phase transfer function of extended measurement cavities. Ideally, the surface under test (SUT) and the reference surface (REF) are both exactly imaged onto the detector plane. In practice, SUT and REF have to be placed within the depth of field (DOF), which refers to the object space. The term depth of focus refers to the image space. To avoid confusion, the depth of field might be referred to as DOOF (depth of object field) and the depth of focus might be referred to as DOIF (depth of image field). However, in many measurement situations, the REF is not placed within the DOOF, which is the small z-range, which is imaged onto the detector plane. Furthermore, the phase transfer function (PTF) of the REF and the image distortion of the REF are both dependent on the focal plane used to image the SUT onto the detector plane. Effects as phase deformation, image distortion and image blurring have to be taken into account when using extended measurement cavities. This can be done by using a look up table (LUT), which contains simulated and/or calibrated data. Thus, the related system error can be subtracted. A remaining challenge is an unknown object under test (OUT), which is measured by using a double path arrangement. The measured wave front depends on the two surfaces of the OUT and the position of the return mirror. For simplicity, a homogeneous substrate and a perfect return mirror might be presumed. The simulation of waves propagating within extended measurement cavities, as well as measurement results, will be discussed. In addition, the influence on the power spectral density (PSD) will be described. This is important for high end correction techniques as e.g. magneto rheological figuring (MRF) and ion beam figuring (IBF).

Contribution

Christian J. Trum
Christian Vogt
O. Fähnle
Sebastian Sitzberger
Rolf Rascher

First experiences with Filled-Up-Microscopy (FUM) to evaluate the depth of sub-surface damages on ground surfaces.

In: Proceedings of EOSAM 2018 (European Optical Society Biennial Meeting; October 2018; Delft, The Netherlands): Optical System Design, Tolerancing, and Fabrication.

Eds.:
The European Optical Society

(2018)

Contribution

Christian Vogt
Rolf Rascher
O. Fähnle
Dae Kim

Closed-loop next generation laser polishing.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 34

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318749

Journal article

Christian J. Trum
Rolf Rascher
M. Zäh

Effizientes chemisch-mechanisches Polieren (CMP).

In: Werkstattstechnik online-wt-online pg. 174-179

(2018)

Contribution

R. Kometer
Engelbert Hofbauer

Fast and reliable in-situ measurements of large and complex surfaces using a novel deflectometric device.

In: Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach]). pg. 108290B

Eds.:
Rolf Rascher
Christian Schopf

(2018)

DOI: 10.1117/12.2318583

show abstract

In-situ measurements of complex surfaces during the polishing process is a challenge for the production of aspheric surfaces or freeforms. We are providing a new attempt by using a scanning deflectometric device based on our recently published DaOS [1] principle, which allows in-situ measurements of large optical surfaces in realistic production environments and offers the conditions for direct intervention and correction in the polishing process. The results of insitu surface measurements after three polishing steps of a large glass substrate (320 mm in diameter) in a lever-polishing machine (NLP500 from Stock Konstruktion GmbH) are shown and critically compared with interferometric measurements on a SSI-A Interferometer. In this paper, the technical setup consisting of a highly precise scanning penta prism device and a Vignetting Field Stop (VFS) Sensor is explained. Secondly, we are discussing the mathematical algorithm to reconstruct the complete surface from angle measurements from a given number of cross-sectional cuts. The data of the surface reconstruction are transformed into a XYZ-file format to be analyzed with MetroPro®. The results are shown and discussed in terms of accuracy and reproducibility. Finally, a comparison with interferometric measurements on an SSI-A (QED) at TH Deggendorf (THD), Technology Campus Teisnach is shown to proof the degree of accuracy and applicability of our new, fast and reliable device for in-situ measurements of complex surfaces.

Lecture

Christian Schopf
Florian Schneider
Rolf Rascher

ArenA – Foi: Erprobung des ADAPT-Polierwerkzeugs. Posterpräsentation.

In: 5. Tag der Forschung der THD 2018

Technische Hochschule Deggendorf Deggendorf

08.03.2018 (2018)

Lecture

Christian Vogt
Rolf Rascher

grinding Process Validation Approach (gPVA). Posterpräsentation.

In: 5. Tag der Forschung der THD 2018

Technische Hochschule Deggendorf Deggendorf

08.03.2018 (2018)

Lecture

Olga Kukso
Rolf Rascher
M. Pohl
R. Börret

EmmaV - Entstehungsmechanismen mittelfrequenter Fehler und deren aktive Vermeidung. Posterpräsentation.

In: 5. Tag der Forschung der THD 2018

Technische Hochschule Deggendorf Deggendorf

08.03.2018 (2018)

Lecture

Sebastian Sitzberger
Christian J. Trum
Rolf Rascher
M. Zaeh

Workpiece self-weight induced deformation in precision optics manufacturing. Posterpräsentation.

In: 5. Tag der Forschung der THD 2018

Technische Hochschule Deggendorf Deggendorf

08.03.2018 (2018)

Lecture

Christian Vogt
O. Fähnle
E. Langenbach
Rolf Rascher

In situ laser monitoring of laser polishing.

In: 119. Jahrestagung der Deutschen Gesellschaft für angewandte Optik (DGaO)

Technische Hochschule Aalen

23.05.2018 (2018)

show abstract

A novel fabrication parameter controlling method for laser polishing is presented, measuring within the footprint the smoothening process in real time. Recently, a new method for in situ measuring level of surface roughness has been developed [1] where a HeNe laser beam is being reflected from within the sample at the surface under test and the intensity of its reflected beam is being monitored.In this paper we report on an experimental study where this method has been applied to laser polishing. The internal local surface area under test is chosen to be located at the very spot where the laser polishing footprint is located from the outside of the sample melting its surface locally. Because fused silica is not transparent at the operating CO2 laser wavelength, the intensity of the reflected beam can be monitored enabling an in situ control of the laser polishing process. Consequently, the optimum dwell time can be determined, a footprint needs to stay at a certain point before moving further enabling a more stable and cost optimized polishing. [1] O.Fähnle,“In process monitoring of optics fabrication”, SPIEconference “PrecisionOptics Manufacturing”2017

Lecture

Rolf Rascher

Grinding and polishing of glass - Basis for a perfect coating.

In: 12th International Conference on Coatings on Glass and Plastics (Joint session of DGG-Glasforum and the ICCG): The Glass Surface - The Basis for Innovative Coatings

Würzburg

11.06.2018 (2018)

Lecture

Alexander Haberl
H. Harsch
Gerald Fütterer
Johannes Liebl
C. Pruß
Rolf Rascher
W. Osten

Model based error separation of power spectral density artefacts in wavefront measurement.

In: SPIE Optical Engineering + Applications Conference on Interferometry XIX

San Diego, CA, USA

19.-23.08.2018 (2018)

Lecture

Rolf Rascher
Christian Vogt
O. Fähnle
E. Langenbach

Closed-loop laser polishing of glass.

In: LaP 2018 - 3rd Conference on Laser Polishing

Fraunhofer-Institut für Lasertechnik (ILT) Aachen

12.09.2018 (2018)

Lecture

Christian J. Trum
Rolf Rascher
M. Zäh

Steigerung der Effizienz chemisch-mechanischer Polierprozesse durch Anpassung der Poliersuspension.

In: 1. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

29.11.2018 (2018)

Lecture

Sebastian Sitzberger
Rolf Rascher
M. Zäh

Vorrichtungssystem für eine beidseitige hochgenaue Bearbeitung von Linsen.

In: 1. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

29.11.2018 (2018)

Contribution

Gerald Fütterer

Wave front sensing for metrology by using optical filter.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710K1-111710K11

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2530013

show abstract

An interferometric problem is the limited fringe density, which is due to the limited allowed slope difference of superimposed wave fronts. Thus, the angular dynamic range of measurable surfaces and objects under test is limited. In other words, all shapes that deviate from a plane surface or a sphere represent a measuring problem in interferometers, or require an individually adapted null optics, which might cost e.g. 10 k∈ or more. In addition, ground surfaces cannot be measured in standard interferometers, except by using Speckle interferometry, which is limited in resolution. Freeform optics are very problematic. Even when polished, only tactile or confocal coordinate measurement might work. Several interferometers address the problem of the angular deviation to a sphere. For instance, lateral stitching on a curved surface, which is equivalent to the best-fit sphere, or longitudinal stitching is used. To use a tilted wave interferometer for asphere metrology is another option, which provides versatile measurement configurations. The approach discussed here is to use optical filters. The development of this technique is part of a project most recently started at the Technology Campus in Teisnach. The surface under test (SUT) is imaged onto an optical filter, which has a calibrated angular selectivity. Thus, the angles of the local wave front normal vectors are transferred into an intensity distribution. A set of angular measurements enables reduced uncertainty of the wave front measurement. Aspects as e.g. the working principle, boundary conditions and the identification of practical filters are discussed in the paper.

Contribution

Jessica Stelzl
Christine Wünsche
S. Höfer

Processing of a new nonlinear optical crystal for continuous wave UV-laser applications.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710H1-111710H4

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2528140

show abstract

Lasers have been known for a long time and are used in a wide variety of fields such as industrial and material processing or measuring and control technology. A new application is being tested which aims to use continuous wave UV-lasers in metrology. For this application a nonlinear optical crystal is needed. Its processing is developed in a two-year project at the Institute for Precision Manufacturing and High-Frequency Technology of Deggendorf Institute of Technology. The crucial factor for the full optical performance in the UV range is the low roughness of the crystal surface, as it is installed between two prisms and the contactability between them should be ensured. In China, a nonlinear crystal that meets the requirements has already been designed and a production process for the raw crystal has been established. However, since the production of optically homogenous crystals has proven to be difficult, the availability of such is very limited. For this reason, a reference material with similar hardness and material behaviour is used in the process development in order not to be limited in the number of trials. It is important to be able to transfer the results from the reference material in an analogous way to the original crystal. One challenge of the project lies in the crystal thickness, since only a maximum thickness of three millimetres can be achieved for the purest form of the crystal required in the application. Therefore, it is important to handle the material sparingly during the process. In addition, the small dimensions of about ten to five millimetres and the brittleness of the material pose a problem. The goal of the project will be to develop a process that can circumvent all these problems so that small roughness of the crystal can be achieved by precision polishing.

Contribution

Gerald Fütterer
Michael Wagner
Lucas Bauer
Simon Wittl

Alignment and thermal drift aspects of a four-tilted-mirror student project telescope.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710L1-111710L9

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2530076

show abstract

The Deggendorf Institute of Technology (DIT) and its Faculty of Applied Natural Sciences and Industrial engineering transfer a broad spectrum of knowledge to the students. The clarification of the interrelations that exist between seemingly isolated fields of knowledge is a permanent process. In order to put this into practice, a telescope construction project was started. The base of the in-house student project is the Technology Campus in Teisnach, which bundles capacities for process development, production and measurement of high-precision optics, including telescope optics. A first optical design, which is based on a subset of the parameter space published in 1989 by M. Brunn1, 2 (later built by D. Stevick as f/12-system3 ), made use of a primary mirror M1 with a diameter of 400 mm. An f/8-system provide a Strehl ratio SR ≥ 0.8 over an entire field of view of 0.7° deg. Even if this seems to be sufficient, manufacturing tolerances, adjustment tolerances, thermal drift and positional changes considerably reduce the Strehl ratio. In order to obtain reliable values of acceptable tolerances, statistical Monte Carlo analyses had been carried out. As consequences, the tube design was changed and the design of new mirror mounts started. This was done to achieve the required stiffness. The new tube designs, one based on carbon-fiber-reinforced polymer (CFRP) and one based on FeNi36, had been tested by using FEM analysis. In addition, the practicability of deep learning based aberration detection was tested. Zernike polynomials obtained by analyzing the star images with a Convolutional Neuronal Network (CNN). The current state of the development is described.

Contribution

M. Pohl
U. Bielke
R. Börret
Rolf Rascher
Olga Kukso

MSF-error prevention strategies for the grinding process.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 11171061-11171067

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2526581

show abstract

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. This third publication focuses on strategies of avoidance and generation mechanisms of the mid-spatial frequency errors from the grinding process. The Goal is to understand the generation mechanisms of the mid-spatial frequency errors and avoid their appearance in the manufacturing process.

Contribution

Robert Wildenauer
Karl Leidl
Martin Schramm

Hacking an optics manufacturing machine: You don't see it coming?!.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 11171071-11171076

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2526691

show abstract

With more and more industrial devices getting inter-connected the attack surface for cyber attacks is increasing steadily. In this paper the possible approach of an attacker who got access to the office network at the Institute for Precision Manufacturing and High-Frequency Technology (IPH) to attack one of the optic machines that reside in another network segment is presented. Based on known vulnerabilities from the Common Vulnerabilities and Exposures (CVE), like the shellshock exploit or remote code execution with PsExec, for devices identified in the network, an attacker can bypass the firewall between the office network and the laboratory network and get full access to the HMI of the target machine.

Contribution

Simon Killinger
Johannes Liebl
Rolf Rascher

Mid-spatial frequency errors in feed direction occurring in ADAPT polishing.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710G1-111710G8

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2528114

show abstract

Previous work shows the effectiveness of computer controlled polishing (CCP) with the ADAPT tool by Satisloh for correcting form errors in optics manufacturing. This method however has a risk of producing residual errors in the range of mid spatial frequency errors (MSFE). In order to prevent these errors the residual in feed direction is investigated as well as the behavior at different parameters.

Contribution

Michael Benisch
Werner Bogner
Rolf Rascher

Using A Digital Temperature Sensor To Measure The Temperature Development During A Polishing Process.

In: Proceedings of the 2019 EOS Optical Technologies Conference. Manufacturing, Tolerancing and Testing of Optical Systems (MOS) – Session 1

(2019)

Contribution

Emilio Zambrano
Christine Wünsche
S. Mechold
S. Herr

Cleaning effects in optical layers: error characteristics and analysis methods.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710F1-111710F9

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2527974

show abstract

In the course of the ever-increasing demand of high-performance optical components, dielectric coating processes are the key technology for the refinement of optics, ensuring their functionality. These optics are based on optical interference coatings, which are formed by a layer stack of alternating transparent single layers of high and low refractive index material. Assuming that turbidity as well as defects embedded in coatings are considered as a primary factor limiting the quality of optical coatings, the level of cleaning the substrates before coating has to be extremely high. Particular importance is attached to the interface between the layer stack and the substrate, especially to the interaction during the transition from the glass surface to the coating during the manufacturing process. This interaction is assumed to be caused by polishing, by corrosion during storage time or by effects during cleaning of the substrate before coating. Thus, it is necessary to characterize each type of defect and to define which technique is adequate to analyze each one of them efficiently. The project aims to raise the awareness and knowledge in terms of what happens during the coating process and, in particular, to understand the physical processes at the substrate during the manufacturing process. After analyzing the material flow, first focus was set on the cleaning procedure. It is assumed that one of the main influences on defects in the interface is the chemical cleaning. Chemical reactions on the surface of the glass substrate may occur due to additional effects of external components and elevated temperature in the washing basins.

Contribution

Sebastian Sitzberger
Johannes Liebl
J. Reitberger
Rolf Rascher

Zero-point clamping systems in optical production.

In: Proceedings of SPIE 11171 (Sixth European Seminar on Precision Optics Manufacturing, 1117101 [9-10 April 2019, Teisnach]). pg. 111710J1-111710J10

Eds.:
Rolf Rascher
Christian Schopf

Bellingham, WA, USA

(2019)

DOI: 10.1117/12.2528774

show abstract

Zero point clamping systems are an integral part of the manufacturing industry. They have only yet to find their way into the optical industry. This article compares the hydraulic expansion holder, a clamping system currently used in the optical industry with a zero-point clamping system. The achievable accuracies of both systems are compared over several measurement series. In addition, the process capability evaluation is used for the comparison. Finally, the results are summarized to provide every researcher and practitioner with a foundation for assessing whether zero point clamping systems meet the requirements for the use in optical manufacturing.

Lecture

Sebastian Sitzberger
J. Reitberger
Rolf Rascher

Clamping system for optical components for adaptation in optical production.

In: 10th HLEM 2019 - High Level Expert Meeting Asphere Metrology on Joint Investigations

Physikalisch-Technische Bundesanstalt Braunschweig

19.-20.03.2019 (2019)

Lecture

Sebastian Sitzberger
P. Rinck
A. Gueray
Rolf Rascher

Ultraschallunterstützte Zerspanung von Advanced Materials.

In: 3. Wissenschaftliches Forum zur ULTRASONIC-Bearbeitung

Jena

23.05.2019 (2019)

Lecture

Simon Killinger
Alexander Haberl
Rolf Rascher

Analysis of residual errors during computer controlled polishing.

In: EOS Optical Technologies: Conference on Manufacturing, Tolerancing and Testing of Optical Systems (MOS) – Session 7: Plenary Session

World of Photonics Congress München

24.-26.06.2019 (2019)

show abstract

In computer controlled subapertur polishing the formation of mid spatial frequency errors (MSFE) needs special attention. In this work the formation of MSFE in feed direction is investigated using the ADAPT tool from Satisloh.

Lecture

Christian J. Trum
Rolf Rascher
M. Zäh

Steigerung der Effizienz chemisch-mechanischer Polierprozesse durch eine systematische Auswahl und Anpassung von Poliersuspension und Poliermittelträger.

In: 2. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

28.11.2019 (2019)

Lecture

Sebastian Sitzberger
Rolf Rascher
M. Zäh

Steigerung von Fertigungsgenauigkeit und -geschwindigkeit bei der Herstellung von Präzisionslinsen.

In: 2. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

28.11.2019 (2019)

Contribution

Armin Reif
Sebastian Sitzberger
Rolf Rascher

Cutting high-performance materials with ultrasonically modulated cutting speed.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]).

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2565757

show abstract

The continuing trend towards lightweight construction and the associated machining rates of up to 95 % lead to an increased use of high-performance materials. The ever growing demands on the strength and quality of components and the associated use of materials which are hard to machine require the further development of new, economical machining techniques. In ultrasonic-assisted machining, an additional high-frequency vibration is superimposed on the conventional machining process. The vibration of the tool is usually excited axially or longitudinally to the workpiece, i.e. vertical to the cutting direction. An additional vibration overlay around the rotation axis (torsional) of the tool is also possible. This generates a vibration overlay in the cutting direction. The vibration initiation causes vibration amplitudes in the range of a few micrometers at the tool cutting edge. This leads in turn to a high-frequency change in the cutting speed or feed rate. Overall, an additional torsional vibration overlap can further reduce cutting forces, increase tool life and improve workpiece quality. In order for a grinding tool to generate a torsional vibration, a special tool was required that had to be designed by simulation. The formation of a torsional vibration was achieved by helical slots in the sonotrode. Depending on the angle of rotation and the length of the slots, a part of the axial vibration is converted into a torsional vibration by an axial excitation of the sonotrode. The aim in designing the slots was to achieve the highest possible vibration amplitude. Following the simulation, the slots were inserted into the tool in the corresponding optimum geometric position. Afterwards, the specially designed grinding tool was validated by machining the brittle-hard glass-ceramic material Zerodur. The first test results with the torsionally vibrating tool are presented in the following.

Journal article

Armin Reif
P. Rinck
Sebastian Sitzberger
Rolf Rascher
M. Zäh

Zerspanung von Hochleistungswerkstoffen mit ultrasonisch modulierter Schnittgeschwindigkeit.

In: ZWF - Zeitschrift für wirtschaftlichen Fabrikbetrieb vol. 115 pg. 2-5

(2020)

DOI: 10.3139/104.112255

show abstract

Die steigenden Anforderungen an die Festigkeit und die Qualität von Bauteilen und die damit verbundene Verwendung hochfester Materialien erfordert die Weiterentwicklung neuer wirtschaftlicher Zerspanungstechniken. Durch eine werkzeugseitige Schwingungsüberlagerung können bei der Bearbeitung von schwer zerspanbaren Werkstoffen die Zerspankräfte und der Werkzeugverschleiß reduziert sowie die Oberflächenqualität verbessert werden.

Contribution

Olga Kukso
Rolf Rascher
M. Pohl
R. Börret

On the metrology and analysis of MSF error.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 1147809

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2566251

show abstract

The aim of our research was to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. To find an appropriate parameter window we have to be able not only to define the factors, which lead to MSFE, but also to analyze the change of the error after next following production steps.

Contribution

Jessica Stelzl
Christine Wünsche
S. Höfer

Influencing factors for a continuous wave UV-laser component.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780C

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2564916

show abstract

During the development of an optical system, one comes to the point where you have to build the optically active element into a mechanical device that becomes part of the system. At this point you come across the well-known question that it is not only necessary to consider and ensure the quality of the individual element. It is also important to look at the entire component in order to identify potential influencing factors on the performance of the optical system. At the beginning of a two-year project at Technologiecampus Teisnach the polishing process of a nonlinear crystal as the crucial component of the optical system was being explored. This system is designed to create continuous wave laser beams in the deep UV range. The crystal has to be embedded between two prisms. Roughness and shape of the crystal is ensured via the polishing process which alone has many influencing factors and was examined at the beginning of the project. The quality of the crystal can be as good as it can be, but if the contacting prisms do not fit, the whole prism-coupled device will become unusable in the overall optical laser system. The performance of the laser can only be achieved by harmonizing all elements of the PCD and the PCD itself into the laser set-up. In the current phase of the project this question will be dealt with. The prism-coupled device is split up into its individual parts, which are the nonlinear crystal, the prisms as optical auxiliary components, micro screws and mechanical support. Going through the requirements to the properties of the crystal and their limitations, the influence of the PCD on the optical performance of the crystal is presented. Here, the main focus is placed on the mode of fixing the crystal between the prisms and on putting the stack of crystal and prisms in the laser beam. The influencing factors between the crystal, the prisms and the method of fixing the PCD are described.

Journal article

M. Pohl
Olga Kukso
R. Boerret
Rolf Rascher

Mid-spatial frequency error generation mechanisms and prevention strategies for the grinding process.

In: Journal of the European Optical Society, Rapid Publications vol. 16

(2020)

DOI: 10.1186/s41476-020-00140-9

show abstract

The research presented in this paper is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. The goal is to understand the generation mechanisms of mid-spatial frequency errors and avoid their appearance in the manufacturing process. Also, a simulation which is able to predict the resulting mid-spatial frequency error from a manufacturing process is developed and verified.

Contribution

Simon Killinger
Johannes Liebl
Rolf Rascher

Interferometric measurement with robot kinematics.

In: Proceedings of SPIE Optical Engineering + Applications (24 August - 04 September, 2020); Optical Manufacturing and Testing XIII; online conference). pg. 114870I

Eds.:
K. Dae Wook
Rolf Rascher

SPIE San Diego, United States

(2020)

DOI: 10.1117/12.2568348

show abstract

Polishing precision optics is highly depending on the operator. Hence, a good result relies on a skilled optician who controls the process chain. This process chain consists of different manual steps such as loading, cleaning and calibrating different machines. To get more control over the process and to speed up the production we currently build an operator independent polishing cell using a single robot. Therefore, we positioned the robot in the middle of the production cell, which enables the robot to reach and manipulate different tools located around the kinematic. One major issues is the lower positioning accuracy and stiffness of an industrial robot in comparison to standard optic machines. Probably the most challenging step concerning accuracy in precision optics manufacturing is the interferometric measurement. In this paper, we present a method using an ESDI Intellium H2000 interferometer, designed for use in unsteady conditions. The robot positions the surface under test without the use of any additional mechanics to enhance the accuracy. The measurement position was manually teached in and approached several times for a statistically significant evaluation. The results show that the robot is sufficiently accurate and stable to perform interferometric measurements. This is a key element towards a completely operator-independent manufacturing cell for precision optics.

Contribution

M. Pohl
R. Börret
Olga Kukso
Rolf Rascher

Mid spatial frequency error prevention strategies for the grinding process.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780E

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2565261

show abstract

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. The goal is to understand the generation mechanisms of mid-spatial frequency errors and avoid their appearance in the manufacturing process. Also, a simulation which is able to predict the resulting mid spatial frequency error from a manufacturing process is desired.

Contribution

Christian J. Trum
M. Jung
Beate Schmidbauer
Sebastian Sitzberger
E. Willenborg
Rolf Rascher

Hybrid-process-chain for polishing optical glass lenses – HyoptO.

In: Proceedings of SPIE Optical Engineering + Applications (24 August - 04 September, 2020); Optical Manufacturing and Testing XIII; online conference). pg. 114871L

Eds.:
K. Dae Wook
Rolf Rascher

SPIE San Diego, United States

(2020)

DOI: 10.1117/12.2568400

show abstract

A number of process steps that build on one another are required to manufacture optical components from glass. The polishing steps are the most time-consuming and therefore cost-intensive parts of the process chain. Low removal rates and the depth of the Sub Surface Damage (SSD) to be removed contribute to this. An alternative for the complete removal of the SSD-penetrated material using contactless polishing methods such as Ion Beam Figuring (IBF) is the healing of the SSD. Due to the induced energy during laser-polishing, the material is remelted at the defects and the SSD are closed. However, laser-polishing is also associated with disadvantages in terms of shape accuracy and surface quality. The project HyoptO is therefore devoted to the development of a hybrid-process-chain consisting of laser processing and conventional polishing. It is expected that the healing times of the SSD can significantly reduce the process times in the subsequent polishing steps. However, there are a few questions to be answered regarding the economic use of the hybrid-process-chain. These include:

Contribution

M. Jung
Christian J. Trum
Beate Schmidbauer
E. Willenborg
Rolf Rascher

Non-ablative removal of sub surface damages in ground optical glass substrates by controlled melting of thin surface layers using CO2-laser radiation.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 1147804

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2564801

show abstract

The form generation of optical surfaces by grinding and mechanical polishing results in small sub surface damages in the form of micro cracks that conventionally have to be removed by further removal of the damaged surface layers. In order to reduce process time and material cost non-ablative methods for removal of micro cracks are desired. Utilising the low optical penetration depths of less than 10 μm for CO2-laser radiation in glass, the laser energy can be used to heat up and melt thin surface layers. Using a 1.5 kW CO2-laser, a quasi-line focus formed by a scanner unit and a constant feed speed, it is possible to close all micro cracks present in the rough grinded test surfaces (max. SSD-depth ~ 63 μm), while achieving a process time of less than 2 seconds for a Ø 30 mm N-BK7 lens, respectively 7.5 seconds for fused silica. With a Sa as low as 50 nm and low distortion from the original shape the surfaces can directly be conventionally polished, further reducing the process chain complexity.

Contribution

Simon Killinger
Johannes Liebl
Rolf Rascher

First steps towards an automated polishing process chain using one robot.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780I

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2564840

show abstract

Manufacturing precision optics is a complex process chain, which requires many operations on different machines. This is combined with operator-dependent steps such as manual cleaning, loading and measuring. In order to realize this process chain on a smaller shop area and to achieve a higher level of automation we build an operator-independent polishing cell. In this cell, an ABB robot serves as the actuator handling the workpiece. We positioned the robot in the center of the polishing cell to operate several workstations, so the whole process chain works with one single actuator. This arrangement allows a smaller and cheaper system, since no additional handling is required.

Contribution

Michael Benisch
O. Fähnle
Rolf Rascher

Application of a pressure measuring film for pressure observation in overarm polishing.

In: Proceedings of EOSAM 2020 (European Optical Society Biennial Meeting; 7-11 September 2020; online). Topical Meeting (TOM) 3- Optical System Design, Tolerancing and Manufacturing

Eds.:
The European Optical Society

(2020)

DOI: 10.1051/epjconf/202023803003

show abstract

In previous publications the inhomogeneous pressure transfer through the polishing tool onto a glass surface could be shown. This experiment shows polishing trials with different polishing materials and the differences in the homogeneity of the pressure transfer through them. Only the properties of the material will be discussed explicitly, the change of the tool constitution through the process will be part of further publications.

Contribution

Michael Wagner
Gerald Fütterer

Computer-aided beam path generation and assessment for Stevick-Paul telescopes.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780B

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2564852

show abstract

At Deggendorf Institute of Technology a student project is currently under way to build a Stevick-Paul telescope for astrophotography. An important step in the overall development procedure of each telescope is the design of a beam-path and ensuring its suitability under optical and engineering aspects. The students performed this process in a sequential manner by using several different computer programs (e.g. MATLAB, Zemax, Creo Parametric). To accelerate the beam path design process, a Python program to automate the major part of the design process with minimum human supervision was created. The input data of the python program consists of ranges of the desired characteristics of the Stevick-Paul telescope, such as focal lengths, primary mirror diameters and tilts etc., mirror thickness and mount geometries, as well as the specific type of camera. After setting the input, the program creates 2D cross-sections of beam paths according to the formulas of D. Stevick and may introduce a flat fold mirror to reduce the overall system size as well as improve the accessibility of the focus plane. The subsequent assessment routine checks against the susceptibility for stray light and performs a complex analysis of the available installation space to ensure sufficient mechanical tolerances. In this way, collisions between mirrors, mounts and cameras are avoided and obstructions of the beam path are prevented. At any stage, the program can produce graphical representations of the beam paths. In this paper the computer-aided design of a telescope beam path with a focal length of 2400 mm is demonstrated. During development of the software, a subset of folded Stevick-Paul telescopes, in which certain components are parallel, was found. This subset may be useful to simplify the alignment procedure. In conclusion, further refinement of the software is necessary, although the program is already a useful aid for certain aspects when creating a beam path design.

Contribution

Michael Benisch
Christian Vogt
Rolf Rascher
O. Fähnle

Octopus: A simple and effective tool for polishing slurry monitoring.

In: Proceedings of SPIE Optical Engineering + Applications (24 August - 04 September, 2020); Optical Manufacturing and Testing XIII; online conference).

Eds.:
K. Dae Wook
Rolf Rascher

SPIE San Diego, United States

(2020)

DOI: 10.1117/12.2567952

show abstract

The present paper shows a way for a cost-effective, integrated measurement of the density p of polishing suspensions. It is based on the principle of measuring the turbidity of a solution on the basis of the light transmitted through it, and of calculating back to the density on the basis of the turbidity. The tool is suitable for monitoring polishing agents and for detecting when the density of the polishing slurry leaves the permissible parameter space and can perspectively enable the automated monitoring and adjustment of polishing suspensions. The tool is named after an Octopus. These animals have amazing abilities, for example they can copy the behaviour of other sea animals or act with a plan. Their tentacles each have their own brain and can perform biochemical analyses.

Contribution

Michael Benisch
O. Fähnle
Rolf Rascher

Observation of pressure distribution between tool and surface in different polishing situations.

In: Proceedings of SPIE Optical Engineering + Applications (24 August - 04 September, 2020); Optical Manufacturing and Testing XIII; online conference). pg. 1148704

Eds.:
K. Dae Wook
Rolf Rascher

SPIE San Diego, United States

(2020)

DOI: 10.1117/12.2567885

show abstract

Pressure is a relevant parameter in the polishing of components according to the Preston equation.1, 2 Preliminary investigations have shown that the pressure can vary with inclined position and different polishing pads. It is not constant with regard to its distribution in the contact area between polishing pad and glass surface. In this publication, the pressure distribution during the polishing of glass components is analyzed. For the measurement of the pressure distribution a pressure sensitive foil is used.

Contribution

Sebastian Sitzberger
Johannes Liebl
Christian J. Trum
Rolf Rascher

Concept of a two-part clamping system for lenses in optical metrology.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780G

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2566547

show abstract

The developed concept represents a universally applicable clamping system designed to fit in any measuring machine with any measuring principle. The design ensures that, as long as the lens remains clamped, the measurement results are reproducible. Form errors due to tension remain constant across all measuring and processing steps. The version presented in this paper was developed especially for small lenses in the diameter range up to 40 mm. On the one hand, the design allows for fast measurement of loose lenses. On the other hand, the device can also be used for measurement comparisons, since lenses can also be mounted permanently. In the following, the concept and first results of measurement tests are presented.

Contribution

Michael Benisch
O. Fähnle
Rolf Rascher
Werner Bogner

Force and pressure analysis during overarm polishing.

In: Proceedings of SPIE 11478 (Seventh European Seminar on Precision Optics Manufacturing [8 July 2020; Teisnach]). pg. 114780H

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

Bellingham, WA, USA

(2020)

DOI: 10.1117/12.2564903

show abstract

The Preston-equation implies, that, besides the relative speed υrel and a specific constant KP, the pressure p plays a significant role for the removal rate when polishing an optical component. This paper demonstrates a possibility for a qualitative evaluation of the pressure distribution before the polishing process. A pressure-sensitive foil is used as a gauge for pressure measurement. The effectiveness of this measuring method is explained. Specific weaknesses and limitations in the use of these foils are discussed. A method for an integrated evaluation of the pressure on different spots of the polishing pad is proposed at the end of the paper.

Lecture

M. Jung
Christian J. Trum
Rolf Rascher

Hybrid Process Chain for Polishing of Optics Made from Glass.

In: LaP 2020 - 4th Conference on Laser Polishing

Fraunhofer-Institut für Lasertechnik (ILT) Aachen (video conference)

16.09.2020 (2020)

Lecture

Rolf Rascher

Produktion aus dem Home Office – Fiktion oder Zukunftsmodell.

In: Hausmesse online

Firma Stock Konstruktion Online

23.11.2020 (2020)

Lecture

Sebastian Sitzberger
M. Zäh
Rolf Rascher

Untersuchungen zu einer durchgängigen Werkstückaufnahme für die Herstellung von Hochpräzisionsoptiken.

In: 3. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

26.11.2020 (2020)

Lecture

Christian J. Trum
M. Zäh
Rolf Rascher

Steigerung der Effizienz chemisch-mechanischer Polierprozesse durch eine systematische Auswahl und Anpassung von Poliersuspension und Poliermittelträger.

In: 3. Ko-op Symposium

Graduate Center der Munich School of Engineering Garching

26.11.2020 (2020)

ConferenceProceedings

Proceedings of SPIE 11853 (Eighth European Seminar on Precision Optics Manufacturing, 100090Y [April 13th-14th, 2021, Teisnach]).

vol. Volume 11853

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

SPIE, Society of Photo-Optical Instrumentation Engineers Teisnach, Germany

(2021)

DOI: 10.1117/12.2602818

Contribution

Stefan Anthuber
Michael Benisch
Rolf Rascher

Industry 4.0 in the fabrication of optical components: development, presence, and requirements.

In: Proceedings of SPIE 11853 (Eighth European Seminar on Precision Optics Manufacturing, 100090Y [April 13th-14th, 2021, Teisnach]). pg. 118530D

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

SPIE, Society of Photo-Optical Instrumentation Engineers

(2021)

DOI: 10.1117/12.2595037

show abstract

Optics and photonics are considered as an enabling technology for innovations in other technological fields (e. g. astronomy, medicine, military, …). Their first applications date back to jewellery processing in ancient times. In the medieval age Vikings on Gotland (1050) buried the Visby lenses. They have a quality of workmanship and imaging comparable to a high quality lens made in the mid-20th century. The specific use of spectacles to correct long-sightedness or presbyopia is known from the 13th century. Around the transition from the 16th to the 17th century, the microscope and the telescope were invented, combining several lenses for the first time. This shows that the exploitation of the optical properties of materials can be dated back very early in human history. In particularly, today`s optics industry is still based on personal knowledge which results in a relatively workmanship production environment. The challenges of globalisation and the current pandemic situation demonstrate that increasing the degree of automation is a possible way to keep a leading position in the market. This is not only important due to the high quality of optical components but also by enabling competitive prices for production through reducing the labour costs. The third industrial revolution established the digitalisation of production and the usage of CNC-machinery. In most industries including optics industries this is the status quo of production. The target of industry 4.0 and internet of things is to lead into a new industrial revolution. The German government developed the buzzword “Industrie 4.0” (eng. Industry 4.01 ). This concept includes the contradiction of mass production and production according to individual customer requests. This should be carried out by connecting all production units with the goal of an intelligent factory. Among other things this includes seamless monitoring of the manufacturing processes along all steps and remote access to involved machines. A further target is manufacturing under the constraint of a small batch size down to one piece. This publication aims to present the current situation in the manufacturing of optical components and compare this with manufacturing of metallic components. It will outline, which measures are necessary to ensure a comprehensive transformation of the optical industry in accordance with the Industry 4.0 idea and which benefits can be expected.

Contribution

Olga Kukso
Michael Benisch
Rolf Rascher
S. Sundar
M. Hacker
M. Duschl
M. Nussbaum

Acoustic measurements for optics.

In: Proceedings of SPIE 11853 (Eighth European Seminar on Precision Optics Manufacturing, 100090Y [April 13th-14th, 2021, Teisnach]). pg. 118530K

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

SPIE, Society of Photo-Optical Instrumentation Engineers

(2021)

show abstract

The aim of the research was the development of a measurement and analysis method that enables the detection of errors and malfunctions within a machine tools and in the manufacturing process using acoustic sensors (microphones).

Contribution

David Moszko
O. Fähnle
Christian Vogt
D.W. Kim

In-process surface roughness measuring device for information-based real-time polishing process adjustment and optimization.

In: Proceedings of SPIE 11853 (Eighth European Seminar on Precision Optics Manufacturing, 100090Y [April 13th-14th, 2021, Teisnach]). pg. 118530E

Eds.:
Alexander Haberl
Rolf Rascher
Gerald Fütterer
O. Fähnle

SPIE, Society of Photo-Optical Instrumentation Engineers

(2021)

DOI: 10.1117/12.2596034

show abstract

In this paper we present a feasible variant of a device for in-process roughness measurement during an optical polishing process. The system, already presented as Tirm respectively I-Tirm, has been technically varied and can now be integrated into almost any lever polishing process with little effort. This enables new possibilities regarding real-time optical manufacturing process monitoring and optimization.