Stiffness and Angle Control of Antagonistially Driven Joint using the Actuator with Non-Linear Elastic System (ANLES)

This paper presents an approach for developing a mechanical system that is similar to a musclo-skeletal system. Antagonistic driving of articulation is a key mechanism, in which at least two muscles control a single rotary axis in the antagonistic manner. It provides not only to control the joint angle but also to control the joint stiffness. The stiffness control requires for individual muscle to have a non-linear elasticity. Hence we have developed an actuator system having non-linear elasticity, which is called ANLES. It fundamentally mimics the skeletal muscle in the sense of having non-linear elasticity. This paper describes a method for designing the elastic characteristics of ANLES and shows the developed ANLES followed by the theoretical and experimental result of its non-linear elasticity. Next one rotary joint controlled by two ANLESes is introduced. The experimental result of measuring stiffness of the joint is shown. A method for controlling the joint angle is proposed, in which two ANLESes drives one rotary joint with no angular feedback. An on-line method for estimating the weight loaded at the end-point is also proposed. All of methods are evaluated and validated by the experiments.