Calibration of Articulated Arm Coordinate Measuring Machine Considering Measuring Posture

A three-dimensional coordinate measuring machine (CMM) is widely used for measurement accuracy and wide measurement range. It is necessary to calibrate the parameters which describe the mechanism to use it as CMM. The geometric calibration is to find the parameters related with the straightness, rotational and scale errors and so on. Non-geometric calibration is to find the parameters except geometric parameters. The method to calibrate CMM is that the artifact is measured by the target CMM. However the most studies of the calibration of CMM are focused on the orthogonal CMM. The only some studies are focused on nonorthogonal CMM. This paper describes the calibration method and the result of the articulated arm CMM (ACMM) which is one of nonorthogonal CMM. It has more measuring freedom than orthogonal CMM. However, the measuring error of ACMM is larger than that of the orthogonal CMM. The kinematic parameters of ACMM are calibrated using the center coordinates of the spheres as the artifact. As in this method, a part of measuring volume is calibrated, ACMM is not sufficiently calibrated. Moreover, as it has more freedom of mechanism, the identical coordinates can be measured in a various posture of it. Therefore the deformations of the arms are different in each measurement. In this paper, to calibrate the deformations of the arms in different measuring posture in addition to the kinematic parameters, a new artifact is produced, a calibration method is proposed and the experiment is reported.