Error modeling and sensitivity analysis of a parallel robot with R-(SS)2 branches

Abstract

Parallel robots with R-(SS)2 (R, actuated revolute joint; S, spherical joint) branches are widely used in high-speed sorting. This kind of robot has been developed into a variety of robots with different moving platforms, but the error model is usually only applicable to the specific features of the moving platform. Thus, an adaptable error modeling method is in need. To solve this problem, this paper improves the existing error modeling method by considering the error transmission mode of the dual-moving platform as a common straight line. On this basis, the general form of the error model containing all possible geometric errors is established. Based on the error model and contribution concept, sensitivity indices are defined and the sensitivity is analyzed. Then some atlases are obtained to describe each geometric error’s influence on the moving platform’s pose errors. Accordingly, the linear errors and angular errors that have greater impact on the moving platform’s pose accuracy are identified. Compared with the existing error modeling methods, this improved error modeling method takes the adaptability of the error modeling into account, and can be extended to the specific error modeling of the corresponding robot.