Formulation of the influence of rotary axis geometric errors on five-axis on-machine optical scanning measurement-application to geometric error calibration by "chase-the-ball" test

The efficiency of on-machine scanning measurement using an optical displacement sensor may be significantly enhanced when the orientation of the workpiece or the sensor is regulated by rotary axes on five-axis machine tools. This paper formulates the influence of rotary axis location errors on its measurement uncertainty. The well-known five-axis kinematic model describes the position and the orientation of the sensor in the workpiece coordinate system under rotary axis location errors, but it does not complete the formulation. Unlike contact-type probes, the laser displacement sensor's orientation and position must be pre-calibrated in reference to the machine's motion, and rotary axis location errors influence this pre-calibration as well. Based on the present formulation, the calibration of rotary axis location errors by the "chase-the-ball" test using the on-machine laser measurement is formulated. Experimental demonstration is presented. Experimental uncertainty assessment of the sphere center position measurement by the optical profile scanning is also presented. With a commercial triangulation-based laser displacement sensor was used, the standard uncertainty (k = 1) in the measurement of sphere center position was about 0.5 mu m (in distance).