Physical Control of the Rotation of a Flexible Object — Rope Turning with a Humanoid Robot

Rope turning tasks are useful to explore rhythmic physical human–robot interaction. However, in traditional studies, a robot was not able to turn a rope by itself, because simultaneous control of three factors, i. e., energy transmission, rotational axis and centrifugal force, is difficult when a robot rotates a flexible object such as a rope. In this paper, we propose a method to control these three factors simultaneously. We developed the method by adding a compensator to an attractor that attracts the end-effector of a robot to a uniform circular motion within a fixed radius. In a rope turning simulation, the end-effector of a robot and the center of mass of a simplified rope converged to uniform circular motions. In addition, we applied the proposed method to a rope turning task performed by a humanoid robot. The robot was able to turn a rope with one fixed end or in cooperation with a human.