Kinematics and Friction in Grasping by Robotic Hands

Using the extended screw theory, grasping is analyzed in terms of the complete and partial constraint of a rigid body. The underlying kinematic theory is first reviewed and illustrated. The extended screw theory is then used to determine the disturbing and nondisturbing external wrenches, and resulting disturbances for a grasped object. This is a new application of the concept of total freedom based on the idea of component motions and the wrenches that can cause them. Determining the disturbing and nondisturbing wrenches is tantamount to determining the stability of the grasp in regard to total freedom. Finally, a novel method of incorporating friction in the kinematic analysis of grasping using screw theory is also developed using the concepts of apparent normals and apparent motions.