Static and dynamic performances of a round-belt Twist Actuator mechanism

This paper introduces a novel joint mechanism composed of an Antagonistically-twisted Round-belt Actuator (ARA), which is able to make rotating motion by means of contraction forces induced by twisting small-diameter elastic round-belts. First, we formulate Young's modulus model of a round-belt on a constant-volume basis suitable for largely-deformable elastic materials. As a result, we show by experimental results that the Young's modulus varies with respect to the number of twist rotations of the belt. This means that the Young's modulus linearly decreases as the twist rotation increases. Next, this paper reveals a linear transmission ratio between the joint angle and the twist rotation of an ARA robot, which corresponds to so-called speed reduction capability. In addition, we introduce a twist-drive mechanism in which twint-wisted round-belts are located at the agonist side of the robot. Finally, we demonstrate the position control of the robotic link, and verify that a simple traditional PI controller enables suppression of the oscillating motion of the joint.