Rigid body analysis of the indeterminate grasp force in power grasps

This paper analyzes the indeterminate grasp force in power grasps with a ri gid body model. A power grasp overconstrains an object with multiple contac t points using the surfaces of finger links and palm. It is known that the overconstrained grasp results in the static indeterminacy of the grasp forc e. This paper shows that it also results in an infeasible combination of th e sliding directions at the contact points. A static friction force acts on ly in the opposite direction of the trend of sliding. This characteristic o f friction restricts the grasp force in power grasps although it is indeter minate. First, we show an example to illustrate the restriction on the gras p force. Then, we formulate it formally, This analysis leads to a special c ase where the grasp force is unique.