Abstract: One new kind of robot wrist which is composed of ring involute spherical gear and driven by eight-bar linkages is introd-uced. The new robot wrist is composed of six spherical gears, all these spherical gears are linked one to another in series. The robot wrist is one of multi-bracket gear train with spatial motion. The new wrist has three degree of freedom and can oscillate towards any orientation. The maximal oscillating angle equate to 126°. The motional performance is far better than that of famous Tral- lffa robot wrist. The construction type of series-mounting with more than two spherical gears is introduced. The characteristics of wrist’s structure and its action theory are analyzed. The mov- ability of driving linkages is also analyzed, and its kinematics mo- del is built up. Then the analysis of the oscillating motion and cir- cumgyrating motion of robot wrist is accomplished. The position and orientation matrix of six spherical gears in wrist is determined by Denavit-Hartenberg method. After deducing the relationship of tow oscillating angle between output axis and first bracket, the position of end point of output axis is determined. The kinematics and inverse kinematics model of circumgyrating motion of robot wrist are founded. The kinematics model of diving linkage and robot wrist is the gist for designing control system.

Key words: Flexible wrist, Mechanisms, Planetary, Robot, tranmission