Stiffness control of multi-DOF joint

This paper deals with mechanical stiffness control of multi-DOF joint. It fundamentally mimics the skeleto-muscular system of human articulation, in which at least two muscles handle one rotary axis under their antagonistic (counteractive) action. In the first part of the paper one introduces basic formula for controlling the multi-DOF rotary joint that is assumed to be driven by a couple of novel actuators called ANLES (actuator with non-linear elastic system). It mimics a skeletal muscle in the sense of having a non-linear elasticity. Next the paper describes the structure of the ANLES that is designed and constructed for controlling the wrist joint of an anthropomorphic robot. The experimental results using three DOF joint controlled by four ANLES reveal that the joint angle and the joint stiffness can be independently controlled by the proposed formula.