Development of human-friendly robot arm with adjustable joint compliance

Safety is primary considered in designing a robot that operates in human environment. This paper presents a human-friendly robot arm designed so as to realize a physical interaction with human safely. This arm has a 3-D.O.F (shoulder joint : 2-D.O.F, elbow joint : 1-D.O.F). To guarantee the safety of robot motion, elbow joint has a multi-directional passive compliance. In this joint, two kinds of air cushions (Cushion A and Cushion B) are placed between a motor-driven disk and an output link. The rotational motion of the motor is transmitted to the output link with the friction force between the surface of Cushion A and the motor-driven disk. In addition, Cushion A plays following two important roles: (1) Absorption of external forces by its elastic deformation and slippage on the motor-driven disk and (2) Sensing the directions and amplitude of external forces with the pressure change in it. On the other hand, Cushion B controls the degree of pressing Cushion A against the motor-driven disk by its expansion. The increment of pressing force of Cushion A results in the increment of joint stiffness, because the elastic deformation and slippage of Cushion A are prevented. This paper describes the structure of the robot arm and the detail mechanism and performance of the proposed joint module.