Stiffness ellipse control of tendon mechanisms with nonlinear springs

Versatility and safety are required for manipulators used in human environments. Tendon mechanisms with nonlinear springs that can mechanically adjust joint stiffness is one candidate for the requirement. This paper proposes a stiffness ellipse control method of both mechanical and control stiffness at tip of the manipulator called hybrid stiffness control. A conventional controller for the manipulator can adjust mechanical joint stiffness. This paper shows a transformation from stiffness ellipse at the tip to joint stiffness. The transformation is applied to both mechanical joint stiffness and controller gain of joint angle controller. Simulation results shown validity of the proposed method.