Stiffness and Angle Control of Antagonistially driven joint

This paper presents an approach for developing an artificial skeleto-muscular 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. Authors have developed a new actuator that has non-linear elastic system, which is called ANLES. It fundamentally mimics the skeletal muscle. This paper describes the equations 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 followed. A method for controlling the joint angle is proposed, where two ANLESes drives one rotary joint with no angular feedback. A method for estimating the weight loaded at the end-point is also proposed. All of methods are evaluated and validated by the experiments