Accuracy analysis of a spherical 3-DOF parallel underactuated robot wrist

As an underactuated mechanism, the accuracy analysis of the spherical 3 degrees of freedom (3-DOF) parallel underactuated robot wrist becomes an important issue. However, current researches in the accuracy analysis always focus on the full-actuated mechanism. In this paper, the loop incremental method is applied to the accuracy analysis of the spherical 3-DOF parallel underactuated robot wrist. After the novel underactuated robot wrist is introduced, this paper presents the loop selection rules. According to the above rules, four loops are selected from the underactuated robot wrist. After error model of each loop is proposed, the error model of the underactuated robot wrist, including both position error and orientation error, is then established by the loop incremental method. After the accuracy analysis of the underactuated robot wrist is verified with the experiments on coordinate measuring machine, the robot wrist is then guided to be assembled with the minimum global error. The result is testified to demonstrate that the methodology is helpful for robot design.