Entwicklung von Strategien zum optimierten und objektivierten Einsatz von Koordinatenmeßgeräten für die Formprüfung
Final Report Abstract
The project objective was the development of strategies for the optimization of the form measurement process on coordinate measuring machines (CMMs) regarding measuring time and measurement uncertainty. Therefore, the influencing variables and interactions of variables as well as methods for the estimation of the task-specific measurement uncertainty were analyzed. The scanning speed was identified as the main variable due to its influence to both goals measuring time and uncertainty. Based on the realized experiments a strong coherence between increasing speed and error in form measurement became obvious. The resulting effects showed a strong dependence from the used CMM and the applied sensor. Furthermore, the results are strongly dependent on the surface of the measured workpieces and variations on their production processes. By use of special developed multi wave standards the analyzed CMMs are evaluated regarding the influences of increasing scanning speed. By adding the multi wave standards with structured areas for straightness and flatness and using higher amplitudes for the superposed waves they satisfy the requirements of measurement fonn deviations on CMMs. During the project algorithm for interpolation, outlier recognition and elimination, filtering, Fourier transformation (FFT) and form parameter evaluation as welt as measurement uncertainty evaluation were implemented in a tool with graphical output to support the error analysis. The analysis tool uses all results of the studies of data processing techniques to minimize potential errors and to assure high accuracy data processing. Considered aspects are the uneven spacing of profiles and the influence of outliers. The acquired points are uneven distributed regarding the distribution parameter space or angle. This causes errors in filtering and by using the FFT for data analysis. To improve the data sets the cubic Spline interpolation showed the best results. To perform the subsequent outlier elimination different methods are analyzed. Profiles with high waviness and outliers with a small profile deviation require band separation methods to perform outlier detection and elimination. To evaluate the impact of increasing scanning speed on the measurement result a method was developed by using the multi wave standards. By separating the calibrated profile from the measured one in frequency space domain, it is possible to analyze errors like ovalization and noise at the profile. Therefore, the multi wave standards proved to be well suitable because the real profile is produced and calibrated with high accuracy. Hence, they are a good basis for error analyses. Besides, this method enables the evaluation of the long term stability of CMMs. To ensure the transferability of the results gained by the multi wave standards, requirements on dimension and surface of the workpieces have to be considered. To estimate the task-specific uncertainty the method based on calibrated workpieces proved to be the most practical. The results cannot be considered without connection to the measurement feature and the strategy. Therefore, criteria on similarity of workpiece dimension and surface as well as the values of measurement variables like scanning speed have to be fulfilled. Detected influences caused by varying production processes must be considered if the variation of the features is bigger than the variation of the measurement process. Bias variation is expected to occur when limited sampling strategies are used to measure surfaces with significant form deviations. Thus, this effect was not expected to be found on scanning measurements. However, bias variation was observed in all performed measurements using calibrated workpieces. By analyzing the harmonic content of the measured workpieces, it was possible to observe an interaction between the residual errors of the CMM with the variations of the harmonic content ofthe surfaces between produced parts, which was responsible for the resulting bias variation. This Interaction between measurement and production processes will not only affect evaluation of form specifications, but every kind of geometrical specification. The transfer of the resulting measurement uncertainty to other workpieces with similar measurement strategy requires a high level on comparability of the workpieces and the boundary conditions of the production and the measurement process. Hence, a knowledge-based approach was developed to support the stepwise optimization by considering the process conditions. Applying knowledge obtained from a simple set of experiments and already validated measurement strategies, the known sensitivity and direction of influencing variables on the measurement result is used to define the measurement strategy of a new feature. By using optimization strategies for comparable measurement processes of Industries the measurement time could be increased up to 60% and the task specific uncertainty is reducible up to 10 %.
Publications
- Effizientere Abläufe erreichen - Formen mit Koordinatenmessgeräten erfassen. In: Qualität und Zuverlässigkeit 50. Jg., 2005, Nr. 5, Carl Hanser Verlag, München 2005, p. 45-49
Pfeifer, T.; Schmitt, R.; Napierala, A.
- Avaliagäo em mäquinas de medir por coordenadas usando tecnologia de scanning. In: Proceedings of Metrologia & Instrumentagäo, Säo Paulo, September 2006
Schmidt, Ä.; Donatelli, G. D.; Napierala, A.; Schneider, C. A.; Schmitt, R.
- A Universal Method to Optimize Measurement Uncertainty, Time and Cost for CMM Scanning Technology. In: Proceedings of ISMTII-2009 - The 9th International Symposium on Measurement Technology and Intelligent Instruments. Saint-Petersburg, 29.06.-02.07. 2009. Saint-Petersburg: D. S. Rozhdestvensky Optical Society, 2009, P. 1-051 - 1-055
Schmitt, R.; Nisch, S.
- Evaluation of the Metrological Performance of Form Measurement Processes by Scanning Based on Measurement Uncertainty. 20th International Congress of Mechanical Engineering (COBEM), Gramado, Brazil, November 2009
Arenhart, F. A.
- Knowledge-based Optimization of the tactile Scanning Process on CMM. In: Proceedings of XIX IMEKO World Congress. Lisbon, 06.-11. September 2009. Oxford: Elsevier Science Ltd, 2009, p. 1981-1986
Schmitt, R.; Nisch, S.
- Measurement Uncertainty on Coordinate Measuring Machines - Relevant Issues on Evaluation by the Experimental Method. In: V Brazilian Congress of Metrology, Salvador, Brazil, November 2009
Arenhart, F. A.; Donatelli, G. D.
- Minimization of the Uneven Sampling Effects on Evaluating Roundness with Coordinate Measuring Machines. In: Proceedings of XIX IMEKO World Congress. Lisbon, 06.-11. September 2009. Oxford: Elsevier Science Ltd, 2009, p. 1796-1800
Arenhart, F. A.; Donatelli, G. D.; Porath, M. C.
- Wissensbasierte Optimierungsstrategien für komplexe Messprozesse am Beispiel der taktilen Formprüfung auf Koordinatenmessgeräten. In: Proceedings of Sensoren und Messsysteme 2010, 15. ITG/GMA-Fachtagung
Schmitt, R.; Mallmann, G. F.; Nisch, S.; Arenhart, F. A.
