Robotic joint design by agonist and antagonist arrangement with twisting small-diameter round-belts

This paper develops a novel robotic joint mechanism by means of twisting a small-diameter round-belt, which enables slow movements of joint rotation unlike direct-drive actuator mechanisms. The actuator mechanism proposed in this manuscript is composed of two small-diameter round-belts located near the joint with opposite configurations. The two round-belts are twisted by DC motors placed on a motor stage, which can be activated by a step motor. This novel mechanism realizes movement of the robotic joint around its axis due to contraction forces generated by twisting both round-belts. That is, these round-belts act as agonist and antagonist actuators for the robotic joint, which give a human-like compliance to the rotational motion of the joint. Experimental results using the proposed one-link robot show that a high position resolution of the joint control can be achieved by increases and decreases in the amount of twisting. In addition, we clearly indicate a linear relationship between twisting and the joint angle of the robot. Finally, this paper reveals that the antagonistic twist-actuator system has a secondary role as a gear reducer that is capable of largely decreasing the velocity of joint movement.