NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenZeitschriftenartikel
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)
Bavarian Journal of Applied Sciences, no. 2, pp. 146-161
2016
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Christian Schopf, Rolf Rascher
Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant
Proceedings of SPIE 10151
2016
DOI: 10.1117/12.2257106
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Christian J. Trum, Rolf Rascher
Improving efficiency of chemo-mechanical polishing processes by systematic selection and conditioning of the polishing suspension
Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach])
2016
DOI: 10.1117/12.2236000
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Johannes Liebl, Horst Linthe, Sebastian Sitzberger, Rolf Rascher
Interferometric measurement of highly accurate flat surfaces
Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach])
2016
DOI: 10.1117/12.2235525
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Sebastian Sitzberger, Rolf Rascher
An investigation on the efficiency of the manufacturing of components in precision optics
Proceedings of SPIE 10009 (Third European Seminar on Precision Optics Manufacturing, 100090Y [April 12th 2016, Teisnach])
2016
DOI: 10.1117/12.2236137
Abstract anzeigen
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.
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenBeitrag (Sammelband oder Tagungsband)
Heiko Biskup, Alexander Haberl, Rolf Rascher
Surface errors in the course of machining precision optics
Proceedings of SPIE Volume 9575, Optical Manufacturing and Testing XI (Aug 27th 2016, San Diego, CA)
2015
DOI: 10.1117/12.2189991
Abstract anzeigen
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.
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