On-line error compensation of coordinate measuring machines

Abstract

An on-line error compensation system for coordinate measuring machines (CMMs) is described, which is based on three laser optical Multi-Degree-of-Freedom Measurement Systems (MDFM systems), each for one axis of CMMs. Twelve of the twenty-one error components associated with a CMM are measured on-line by these MDFM systems. The remaining error components are measured by off-line methods which use commercially available measurement systems, such as a laser interferometer. Two mathematical error models have been developed to synthesize the error components and to predict the errors at the probe stylus tip. One model corresponds to the conventional off-line error compensation and the other to the on-line error compensation. The errors predicted by these models are then subtracted from the nominal coordinates of the CMM, thus improving its measurement accuracy. Diagonal tests using a laser interferometer system were designed to check the error compensation effect. Test results showed that the use of the on-line compensation system can further improve the compensation effect as compared with the conventional off-line compensation system.