NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenS: IPH TeisnachBeitrag (Sammelband oder Tagungsband)
Johannes Liebl, Christian Schopf, Rolf Rascher
DefGO
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2318704
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenS: IPH TeisnachBeitrag (Sammelband oder Tagungsband)
Olga Kukso, Rolf Rascher, R. Börret, M. Pohl
On the metrology of the MSF errors
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2318675
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenS: IPH TeisnachBeitrag (Sammelband oder Tagungsband)
Sebastian Sitzberger, Christian J. Trum, Rolf Rascher, M. Zaeh
Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2318577
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenS: IPH TeisnachBeitrag (Sammelband oder Tagungsband)
Alexander Haberl, Johannes Liebl, Rolf Rascher
ABC-polishing
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2318549
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenS: IPH TeisnachBeitrag (Sammelband oder Tagungsband)
M. Pohl, R. Börret, Rolf Rascher, Olga Kukso
Simulation of MSF errors using Fourier transform
Proceedings of SPIE 10829 (Fifth European Seminar on Precision Optics Manufacturing [April 10-11, 2018; Teisnach])
2018
ISBN: 978-1-5106-2270-8
DOI: 10.1117/12.2317484
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenZeitschriftenartikel
O. Fähnle, Rolf Rascher, Christian Vogt, D.W. Kim
Closed-loop laser polishing using in-process surface finish metrology
Applied Optics, vol. 57, no. 4, pp. 834-838
2018
DOI: 10.1364/AO.57.000834
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Christian Vogt, O. Fähnle, Rolf Rascher
Setting-up high-end cnc grinding processes: a Preston-based approach
Proceedings of EOS Optical Technologies Conferences at the World of Photonics Congress (WPC 2017) [Munich, Germany; June 26-29, 2017]
2017
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Rolf Rascher, Christian Vogt, C. Faehnle
In situ laser polishing optimization method: Control of LASer Surface Optimisation (C-Lasso)
Proceedings of EOS Optical Technologies Conferences at the World of Photonics Congress (WPC 2017) [Munich, Germany; June 26-29, 2017]
2017
Abstract anzeigen
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.
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