Development of robot hand with multi-directional variable stiffness for human-care services

This paper describes a novel human-sized robot hand that has the ability to adjust its joint stiffness and sense external forces. This robot hand consists of four fingers, each with three joints. To downsize the finger modules, the DIP and PIP joints are coupled with a linkage mechanism and actuated by a single motor. In addition, for the MP joint, two kinds of silicone rubber cushion, SRC_trans and SRC_stiff , are inserted between the motor and the output link. The elasticity of the SRC_trans provides softness to the joint. On the other hand, the SRC_stiff compresses the SRC_trans by its expansion and as a result controls the stiffness of the joint. Furthermore, the MP joint can estimate the direction and magnitude of the forces exerted from multiple directions by measuring the pressure inside the SRC_trans. In this paper, we present the detailed mechanism of the robot fingers and examine their basic performance for an adjustable range of joint stiffness, controllability, output, and sensing of external forces. We then demonstrate the effectiveness of this hand for human-care by applying it to a human massage.