Analysis of indeterminate contact forces in robotic grasping and contact tasks

In this paper, we analyze indeterminate contact forces in robotic grasping and contact tasks. Previous studies by Omata and Nagata showed that there is a constraint on static friction forces, which is derived from contact kinematics, in rigid-body power grasps. The set of possible contact forces can be calculated using the constraint. This approach can be applied to not only mechanical analysis of power grasps but also that of other robotic contact tasks. However, there are some cases where Omata and Nagata´s formulation generates paradoxical results on contact forces. In this paper, we investigate this problem and propose a modified method to calculate the set of possible indeterminate contact forces. We also study how to reduce the computation.