| In practical industrial application of Portable Articulated Coordinate Measuring Machines(PACMMs),the angle measurement error calibration of the circular gratings installed on the rotating joints of the shaft system is an important research part to improve the measurement accuracy of machines.This paper for the purpose of improving the accuracy of the angle encoders proposes a new self-calibration method for angle measurement error of the circular gratings with optimal arrangement of scanning heads,and designs a set of data acquisition and processing system for angle measurement error compensation.The details are as follows:1.Classified and analyzed sources of the angle error of circular gratings installed on the rotating joints of the shaft system.Listed and compared different error compensation function models.An angle error compensation model based on optimal arrangement of scanning heads was proposed.2.Analyzed the principle of the self-calibration model based on optimal arrangement of multiple scanning heads and the suppression effect of the error harmonic components of each calibration scheme,and verified the compensation effect through simulation comparison experiments.3.Analyzed the functional requirements of the data acquisition system of PACMMs,determined the data acquisition and processing system scheme based on FPGA,SCM,computer software development and other technologies,which can achieve simultaneous data acquisition and correction of angle measurement error.4.Designed comparative experiments according to the simulation results and verified the reliability and feasibility of the self-calibration method.The results of the experiment indicate that the self-calibration model based on multi-reading heads proposed in this paper have improved the angular accuracy of the circular grating by 5times.It can effectively compensate the angle error of circular gratings installed on the rotating joints. |
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