Machining, Measurement, and Control Laboratory

The Improvement of Motion Accuracy of Hexapod-type Parallel Mechanism Machine Tool

Masao Nakagawa (Okuma Corporation)
Tetsuya Matsushita (Okuma Corporation)
Soichi Ibaraki (Kyoto University)
Yoishiaki Kakino (Kakino Research Institute)

This paper presents a methodology to calibrate kinematic parameter in a Hexapod-type parallel mechanism machine tool. In a conventional procedure of the DBB (Double Ball Bar) test to measure a machine's contouring accuracy in a circular operation, the center deviation in an error profile is ignored to cancel setup errors. We propose to use a specialized jig plate to fix a ball of a DBB device in order to evaluate the machine's positioning error in the global coordinate system. Experimental comparison shows the machine's positioning error is significantly improved by using the proposed calibration method. The improvement of the machine's motion accuracy is verified by both motion accuracy tests and machining tests.