Abstract
In this paper, we analyze contact forces in robotic manipulation such as power grasps. In power grasps, the robot can keep grasping the object without changing its joint torques against external disturbances to some extent. However, the grasp forces in power grasps maybe indeterminate even if all the joint torques are given. A previous study by Omata et al. showed that there is a range of friction forces derived from a constraint on sliding. The range of contact forces can be calculated from the range of friction forces. Although the previous study only discuss power grasps, the method can be applied to other situations such as graspless manipulation. However, there are some cases where this method overlooks possible friction forces. We present a modified method to solve this problem.
