Stiffness control of antagonistically driven redundant D.O.F. manipulator

Abstract

This paper presents a method for control stiffness of the end-point of manipulator that has redundant DOFs. It is assumed that all of the joints of the manipulator are capable of regulating their joint stiffness mechanically, not by the software feedback using force/torque information. The particular mechanism for regulating the joint stiffness, called the NonLinear Elastic Module (NLEM) is introduced on the antagonistically driven joint system. A new formula for controlling the stiffness ellipsoid of the end-point is derived Although the shape of the stiffness ellipsoid is essentially determined by the configuration of the joints and the posture of the manipulator, the computer simulation demonstrates the volume and the shape of the stiffness ellipsoid can be substantially regulated by using the proposed formula. Next, the optimal posture of the redundant manipulator suited for an associated task is investigated from the viewpoint of the stiffness ellipsoid An anthropomorphic type seven DOF manipulator is taken as a simulation model.