Mechanical stiffness control of a three DOF wrist joint that mimics musculo-skeletal system

Abstract

This paper shows a prosthetic wrist joint that has 3 rotary axes controlled in antagonistic actuation similar to a human musculo-skeletal system. Some dexterous actions of human arm toward external entities are much attributed to adjustability of its joint stiffness. The joint stiffness of human articulations or of those of any other vertebrate animals is adjustable due to an antagonistic structure of their musculoskeletal system and non-linear elasticity of individual muscle. In our previous studies we have developed a mechanical system that mimics the human musculoskeletal system, in which muscle-like actuators: ANLES (actuator with non-elasticity system) was developed and deployed in antagonistic configuration to control rotation angles and rotary stiffness of a multi-DOF robotic joint. This paper shows a subsequent development of the 3 DOF wrist joint. Main points of refinement are as follows. First is a downsizing to serve it as a forearm prosthesis having an active wrist joint, second is an extension of stiffness adjustable range especially that of inner/outer rotation.