Joint mechanism with a multi-directional stiffness adjuster

This paper describes a novel joint mechanism with variable stiffness for a human-friendly robot. In the proposed mechanism, a set of two different hollow-shaped silicone rubber cushions (SRC_trans and SRC_stiff : Silicone Rubber Cushion for transmission and for adjusting stiffness, respectively) are sandwiched between an output link and a motor-driven disk. SRC_trans, which is pressed against the motor-driven disk, plays the following three important roles: (1) it transmits rotational motion from the motor to the output link; (2) it absorbs excessive external forces by its elastic deformation and the slippage on the surface of the motor-driven disk; and (3) it allows the estimation of external forces using the information regarding the degree of deformation. On the other hand, SRC_stiff, which is placed below SRC_trans, controls the characteristics of joint compliance. SRC_trans is pressed strongly against the motor-driven disk by the expansion of SRC_stiff. As a result, the output link can endure the external force without slippage. This paper describes the detail of joint structure and its fundamental performance.