Modeling and Control of a Pair of Robot Fingers with Soft Tips and Orderless Saddle-joint Actuations

Abstract

A new robot hand dynamics model is proposed, in which rolling constraints are incorporated and orderless relation between two actuations of a saddle joint is taken into account. For realizing a dexterous robot hand, it is necessary to imitate the orderless actuations because a saddle joint of human being plays a vital role to perform thumb opposability. Arising around the opposition axis connecting the two contact points of each finger-tip with an object, spinning motion is treated in a faithful manner by introducing a physical model of viscous force around the spinning axis of the object. A class of control signals without object kinematics or external sensing is used. It is shown that the two trajectories of the models with ordered joint actuations and the proposed model with the orderless ones are different through numerical simulations. The difference demands to consider the orderless joint model as a saddle joint model. Any solution of the colosed-loop dynamics converges to an equilibrium state establishing force/torque balance through numerical simulations based on the derived model.