Machining, Measurement, and Control Laboratory

Compensation of Gravity-induced Errors on Hexapod-type Parallel Mechanism Machine Tools
Masao Nakagawa (Okuma Corp.)
Tetsuya Matsushita (Okuma Corp.)
Tomoharu Ando (Okuma Corp.)
Yoshiaki Kakino (Kyoto University)
Soichi Ibaraki (Kyoto University)
Hiroya Takaoka (Kyoto University)

This paper proposes a motion error compensation methodology for a Hexapod-type parallel mechanism machine tool. First, the contouring error attributable to the elastic deformation of struts caused by the gravity is predicted for an arbitrary position and orientation of spindle head. By compensating the predicted error on a reference trajectory, the machine's motion accuracy can be improved. It is experimentally verified that predicted and measured motion trajectories coincide well, even when the spindle is tilted by more than 23 degrees, where the gravity significantly deteriorates the machine's motion accuracy. By applying the pro-posed compensation method, the motion accuracy is significantly improved particularly near an edge of the machine's workspace.

Key words: Hexapod machine tool, Accuracy calibration, Motion accuracy, Double Ball Bar, Gravity error.