Development of computer integrated system for error diagnosis of a CMM using calibrated mechanical artefacts

Abstract Error calibration and frequent reverification of coordinate measuring machines (CMMs) and machine tools are currently acknowledged as essential processes in order to maintain high performance of the machines and high quality of products. This paper shows a micro-computer integrated error calibration system, which is a fast and efficient error calibration system: a micro-computer stores calibration data of mechanical artefacts, such as ring and step gauges that have been calibrated with respect to more precise equipment, then the machine probes the gauges. The gauge probing data are compared with the gauge calibration data. The micro-computer plans measurement paths thus generating CNC codes for measurement of the mechanical artefacts located in a working volume of a commercial CMM. Then measurement operations are performed according to the planned paths for practical measurement of the gauges. For ring gauge measurement, the lobing error of the probe stylus has been efficiently measured then used for the probe compensation. The circular errors are successfully calculated from the comparison between the ring gauge geometry and the ring gauge probing data after the probe stylus compensation in terms of software. Then from the error pattern of circular error, machine errors such as scale errors and orthogonality error are successfully calculated, showing good approximation to the evaluated circular error. In the case of the step gauge measurement, the gauge probing data are compared with those of calibration data; thus complete linear displacement error analysis is successfully evaluated along any direction in a working volume. The error evaluations are then processes in real time, and presented in computer graphic environments. Practical application to a commercial CMM of CNC-type shows the validity and efficiency of the developed system. Thus a rigorous computer integrated error calibration system is proposed with the full potential of practical application to most commercial CMMs and machine tools of a CNC-type.