Design and experiment of a compact wrist mechanism with high torque density

This paper proposes a new wrist mechanism for robot manipulation. To develop multi-DOF wrist mechanisms that can emulate human wrists, compactness and high torque density are the major challenges. Traditional approaches use a series of rotary motors that require gearing to amplify the output torque. This often results in an oversized wrist. Alternatively, large linear force can be easily attained in a compact space by using leadscrew motors. Inspired by the muscle-tendon actuation pattern, the proposed mechanism consists of two parallel placed linear motors. Their translational motions are transmitted to two perpendicular axes of rotation through a spherical mechanism and two slider crank mechanisms. A high torque density can be achieved. Static and dynamic models are developed to design and analyze the wrist mechanism. Experiments of a wrist prototype are presented and the results are discussed. The novel mechanism is lightweight and has a humanlike appearance. It is expected to serve as a basis to develop humanoid manipulators for human-friendly interactions.