CONTROL OF GRASP STIFFNESS USING A MULTIFINGERED ROBOT HAND WITH REDUNDANT JOINTS

This paper addresses a method of satisfactorily controlling the grasp of objects. Emphasis is placed on achieving the desired stiffness of a grasped object as accurately as possible, especially when the fingers have redundant joints. A model describing the relation between stiffn ess and force is derived. Based upon this model, a hierarchical contro l scheme of the grasp stiffness, called decentralized object stiffness control (DOSC) is proposed. DOSC is composed of a fingertip stiffness synthesis (FSS) algorithm and orthogonal stiffness decomposition cont rol (OSDC). Employing the proposed FSS always achieves the desired gra sp stiffness by solving the constrained least square problem. The comp uted fingertip stiffness is achieved by OSDC. It offers a feasible way of controlling the fingertip stiffness as well as maintaining the sta bility of the finger configuration by modulating the joint stiffness. The developed control method is implemented on a two-fingered planar r obot hand one finger of which has a redundant joint. The effectiveness of the control method is confirmed experimentally.