Hochschulleitung und -einrichtungenZeitschriftenartikel
K. Hamal, I. Prochazka, G. Kirchner, U. Schreiber, R. Riepl, Peter Sperber, W. Gurtner, G. Appleby, P. Gibbis, Y. FuMin, R. Neubert, L. Grunwaldt
Satellite Laser Ranging Portable Calibration Standard Missions 1997-2002
Geophysical Research Abstracts, vol. 5
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The recent requirement of the Satellite Laser Ranging SLR technique is to reach the accuracy of a millimeter. This requires keeping all the system biases on the sub millimeter level. The Portable Calibration Standard is a global reference for Satellite Laser Ranging systems biases identification and evaluation. It consists of the Pico Event Timer P-PET, meteorological station, epoch and frequency time base, set of reference retroreflectors and the control / data processing software package. The P-PET is compact, stable and easy to re-allocate within days. Its properties are appropriate for calibration standard purposes: the timing resolution is 1.2 psec, 2.5 psec per channel timing jitter, the temporal stability is less than 0.5 psec per hour and below 0.5 psec per Kelvin. The key feature of the timing system is its long term stability: no adjustments and settings are needed. Before we could start the global SLR network calibration, we had to succeed with the calibration missions at several SLR stations in Austria, Germany, Switzerland, United Kingdom, China and Chile. This enabled us to understand the feasibility of using the Pico Event Timer P-PET. Summarizing the results: the ranging precision to ground target is 1-3 millimeters, to satellites is 3-7 millimeters rms, the Calibration Standard demonstrated its capability to identify the SLR system range and time biases at the one-millimeter level. These results might serve as a background to the proposed 6th Framework programme EU Integrated Project EUROLAS CALNet.
Elektrotechnik und MedientechnikHochschulleitung und -einrichtungenZeitschriftenartikel
Peter Sperber, W. Spangler, B. Meier, A. Penzkofer
Experimental and theoretical investigation of tunable picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers
Optical and Quantum Electronics, vol. 20, pp. 395-431
DOI: 10.1007/BF00632467
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Picosecond pulse generation in longitudinally pumped dye laser generators and amplifiers is studied experimentally and theoretically. Frequency-tunable pulses between 720 and 940 nm are generated with a picosecond ruby laser pump source. The amplification of spontaneous emission and of seeding pulses in the generator and amplifier cells is investigated. Stimulated emission cross-sections and excited-state absorption cross-sections are determined by computer simulations. The coherence properties of the generated radiation are analysed. Resonance Raman contributions are resolved.
Elektrotechnik und MedientechnikHochschulleitung und -einrichtungenZeitschriftenartikel
Peter Sperber, A. Penzkofer
S0-S1 two-photon absorption dynamics of rhodamine dyes
Optical and Quantum Electronics, vol. 18, pp. 381-401
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The intensity-dependent transmission of picosecond ruby laser pulses of different duration through methanolic and ethanolic solutions of rhodamine B and rhodamine 6G is analysed. The transmission is affected by S0-S n two-photon absorption, by stimulated emission at the pump-laser frequency, by amplified spontaneous emission and by excited-state absorption. Various parameters involving the two-photon absorption dynamics are determined by comparing experiments with numerical simulations.
Angewandte Naturwissenschaften und WirtschaftsingenieurwesenElektrotechnik und MedientechnikHochschulleitung und -einrichtungenMaschinenbau und MechatronikZeitschriftenartikel
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
Optical Engineering, vol. 45, no. 6
DOI: 10.1117/1.2213630
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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.
Angewandte Naturwissenschaften und WirtschaftsingenieurwesenElektrotechnik und MedientechnikHochschulleitung und -einrichtungenMaschinenbau und MechatronikZeitschriftenartikel
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
Robotics and Computer-Integrated Manufacturing, vol. 24, no. 1, pp. 32-37
DOI: 10.1016/j.rcim.2006.07.003
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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.
Angewandte Naturwissenschaften und WirtschaftsingenieurwesenElektrotechnik und MedientechnikHochschulleitung und -einrichtungenMaschinenbau und MechatronikZeitschriftenartikel
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
International Journal of Machine Tools and Manufacture, vol. 47, no. 1, pp. 107-111
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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.
Angewandte Naturwissenschaften und WirtschaftsingenieurwesenElektrotechnik und MedientechnikHochschulleitung und -einrichtungenMaschinenbau und MechatronikZeitschriftenartikel
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
Applied Mathematical Modelling, vol. 32, no. 12, pp. 2907-2924
Abstract anzeigen
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.
Angewandte Naturwissenschaften und WirtschaftsingenieurwesenElektrotechnik und MedientechnikHochschulleitung und -einrichtungenMaschinenbau und MechatronikZeitschriftenartikel
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
Applied Mathematical Modelling, vol. 32, no. 12, pp. 2888-2906
Abstract anzeigen
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.
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