Development of strategies for the optimized and objectivated use of coordinate measuring machines for form measurement. Final report. Period: 01.01.2004 - 30.04.2010
(English)
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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 form deviations on CMMs. During the project algorithm for interpolation, outlier recognition and elimination, filtering, Fourier transformation (FFT) and form parameter evaluation as well 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.
Development of strategies for the optimized and objectivated use of coordinate measuring machines for form measurement. Final report. Period: 01.01.2004 - 30.04.2010
Additional title:
Entwicklung von Strategien zum optimierten und objektivierten Einsatz von Koordinatenmessgeräten für die Formprüfung