A coupling constraint force problem with Coulomb friction between an end effector of a robot and a constraint surface and its solution

This paper points out that there is another singular point with Coulomb friction when an end effector of a robot contacts a surface of an object. The characteristics of Coulomb friction singular points are revealed by both of theoretical and numerical approaches. From the results, it is shown that contact forces dramatically increase as the robot closes Coulomb friction singular points. In this paper we also propose a new control method to overcome problems of Coulomb friction singular points. The effectiveness of the proposed method is demonstrated by some simulation results.