Tension Control for Tendon Mechanisms by Compensation of Nonlinear Spring Characteristic Equation Error

Abstract

Versatility and adherence to safety norms that are required of manipulators used in a human environment can be achieved by using tendon mechanisms that employ nonlinear springs. The nonlinear spring used in this paper is stiffness adjustable tendon (SAT), which has advantages such as it is light weight, low cost, and has a simple structure. However, precise tension control of SAT cannot be achieved by conventional methods based on a spring characteristic equation because of the SAT's hysteresis characteristics. Therefore, we propose a tension control method for nonlinear springs whose precise equation is difficult to obtain, such as SAT; this method is realized by using a disturbance observer and a reaction force observer. Experimental results validate the proposed method.