[abstFig src='/00280006/08.jpg' width='300' text='Antagonistically twisted round belt actuator' ] In this study, a novel robotic joint mechanism is developed for enabling a robotic joint to rotate around the axis by twisting a small-diameter round belt. This twist drive actuator mechanism is composed of two small-diameter round belts with opposite configurations located near the joint. The two round belts are twisted by using individual DC motors; thus, the joint is activated because of the contraction forces generated by the twisting process. Experimental results, obtained using the proposed single-link robot, demonstrate that the joint can be controlled with a high position resolution by increasing and decreasing the amount of twisting. Using the experiments, we reveal that the antagonistic twist drive actuator system has a secondary role in speed reduction, which is capable of decreasing the velocity of the joint movement significantly. In addition, we indicate a linear relationship between the twist rotation and the joint angle of the robot. Furthermore, this paper formulates the Young’s modulus of the round belt used in the twist drive actuator. We demonstrate that the Young’s modulus decreases gradually with respect to the increase in the twisting of the round belt. Finally, we demonstrate a successful position control of the robotic joint, and the traditional PI controller is capable of suppressing the oscillatory motion by using a one-sided twin-twisted configuration.
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.
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