Tension control for tendon mechanisms by compensation of nonlinear spring characteristic equation error

Safety and versatility are necessary for manipulators in human environment, which will be acquired by tendon mechanisms using nonlinear springs. The nonlinear spring used in this paper is stiffness adjustable tendon (SAT), which is light, cheap, and simple structure. Conventional tension controllers based on a spring characteristics equation, however, do not realize precise tension control due to hysteresis characteristics of SAT. In this paper, we propose a tension controller for tendon mechanisms using nonlinear springs with hysteresis characteristics, which is realized by using a disturbance observer and a reaction force observer. Experimental results show the usefulness of the proposed method.