An optoelectronic measurement system for measuring 6-degree-of-freedom motion error of rotary parts

Abstract

This paper presents an optoelectronic measurement system for measuring 6 degree-of-freedom (DOF) motion error of rotary parts. It comprises a pyramid-polygon-mirror, three laser diodes and three 2-axis position sensing detectors (PSD). The laser/PSD pairs are arranged evenly around the pyramid-polygon-mirror, which is mounted rigidly on and aligned axially with the rotary part to be measured. Laser rays from the laser diodes are reflected off the respective mirrors to the respective PSDs. The incidence point of the laser ray on the PSD's surface varies with the pose of the pyramid-polygon-mirror, allowing the PSD to register variation in the mirror and, thereby, the rotary part. With appropriate orientation of the lasers and PSDs, this system can measure variation (error) during rotation of a rotary part. By use of skew-ray tracing and first order Taylor series expansion, the system achieves measurement of translational and rotational motion errors for each Cartesian axis. To validate the proposed methodology, a laboratory prototype system is built. System verification and stability tests are conducted to evaluate its performance. Stability test results show that measurement errors and maximum crosstalk are within +/-1 mum in translation and +/-1.5 arc sec in rotation.