Local and Global Calibration of Coordinate Measuring Machines

Abstract

In the last years, we assisted to the development of new high precision machine tools: the hexapod machines. We tried to use the hexapod machine as an artefact for CMM’s calibration. However, given their cost and their resolution, they are not the best solution for a transportable artefact. By modifying the hexapod structure, we develop two different artefacts: one for local CMM’s calibration and another one for global calibration. Local calibration allows us the determination of the transfer function characterizing the sensor displacement of the CMM. This local calibration is based on the measurement of a rigid artefact of a known geometry, derived from hexapod geometry, which allows us to determine the errors of displacement of the sensor of the CMM. The artefact for global calibration uses a self-calibrated method, based on measurements from three miniature laser interferometers, measuring the position of a sphere in the volume of the CMM. The paper describes the patented artefacts for local and global calibration, as well as the referring mathematical problems resulting from self-calibration of global artefact and the method of interpretation of the measurement results of the artefact used in the measure of local errors.