Design and development of a 3-DoF robotic wrist joint with tension amplification mechanism

The robotic wrist is an essential component of a robot manipulator, consisting of modules that rotate around the axes and feature joints that allow the end-effector to move in several directions. Designing an efficient actuation system for a robotic wrist has always been challenging because of its critical positioning, restricted space, weight, and critical shape. A general way to give rotational mobility to the end-effector around several axes is to mount multiple high torque actuators at the adjacent link of the wrist. However, this increases the mass which causes a reduction of stability and creates vibration. This paper discusses the design and development of a tendon-driven wrist joint with a tension amplification method, which can establish three rotational degrees of freedom (pitching, rolling, and yawing) in just one joint, hence solving the issue of positioning heavy actuators at a crucial position. Furthermore, unidirectional pose accuracy and repeatability of the wrist are measured to evaluate the unidirectional precision of the wrist by using feedback data. After 30 distinct tests, the attained result of pose accuracy and pose repeatability are obtained as 0.050002222 mm and 0.050211199 mm respectively.