Mechanical stiffness control of tendon-driven joints

We present a method for mechanical stiffness control of the tendon-driven joints of a manipulator. First we propose a formula for controlling the joint stiffness and the joint angles independently. Next, we propose an elastic mechanism (nonlinear elastic module, NLEM) of which nonlinear elastic characteristics are easily designed. It is situated between the actuator and the tendon and it plays a key role for mechanically controlling the stiffness. Two types of the NLEM are designed and produced. A computer simulation of and experiments on the stiffness and joint displacement control, which show validity of the proposed formula are described.