High-backdrivable parallel-link manipulator with Continuously Variable Transmission

This paper proposes a novel high-backdrivable parallel-link manipulator with Continuously Variable Transmission (CVT) mechanism using several shaft actuators. The backdrivability is important and necessary for robots that operate around our life space to guarantee the safety of us, themselves and environments. A rotational actuator with a high reduction ratio reducer has been commonly used in traditional robotics field, but it cannot realize the high-backdrivability without any sensory feedback. In this study, several high-backdrivable shaft actuators are used instead of it. Moreover, the CVT mechanism which is brought by a novel configuration of the parallel mechanism is employed effectively. To utilize multiple shaft actuators with the CVT mechanism is able to surmount a drawback of the shaft actuator whose output force is relatively weak. A simple 1 DOF manipulator is proposed as the first step of this study. Firstly, its kinematic and dynamic models are given. Next, a PD type feedback control signal to regulate the arm´s angle and the CVT simultaneously is designed. A static relation between an output end-point force and the CVT mechanism is analyzed. Finally, several fundamental experiments are conducted to show the effectiveness of proposed mechanism.