Machining, Measurement, and Control Laboratory

2 0 0 1    J o u r n a l    P a p e r

A Study on the Improvement of Motion Accuracy of Hexapod type Parallel Mechanism Machine Tool (1st Report)
-- The method of Kinematic Calibration without Gravitation Deformation --
Masao NAKAGAWA (Ohkuma Co., Ltd.)
Tetsuya MATSUSHITA (Ohkuma Co., Ltd.)
Masayuki NASHIKI (Ohkuma Co., Ltd.)
Yoshiaki KAKINO (Kyoto University)
Yukitoshi IHARA (Kyoto University)

This paper describes a method to obtain the kinematic parameter for the hexapod machine tools by using telescoping ball bar device. This method deals with length error of struts, positional errors of base and platform joints as kinematic parameters. For finding a better set of ball bar measurement conditions, Fourier transformation is applied to explain error trace patterns of the circular test. Although it is difficult to identify all kinematic parameter errors with about fifteen circles of ball bar measurement, the machine's motion error can be decreased to one sixth when this method is applied. However, in this report, the deformations of struts are not taken into consideration.

Key words: Hexapod machine tool, kinematic parameter, calibration, ball bar test, Double Ball Bar

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