An Integrated, Force-Sensitive, Impedance Controlled, Tendon-Driven Wrist: Design, Modeling, and Control

Abstract

This paper presents a novel 2 degrees of freedom humanoid wrist with solely three tendons, based on an integrated 3S$\overline{P}$S-1U parallel kinematics (the $\overline{P}$ indicates the active degree of freedom) and driven by three electromechanical motors. Tendon-force measurement and control, combined with nonlinear kinematics mapping enable the implementation of a oint-level impedance controller, virtual walls, a momentum oberver and a virtual joint-torque sensor. The novel mechanical esign, especially the drive-train and the tendon force measurenent module, are discussed in the paper. Simulations show the easibility of the control methods. A static workspace analysis - eveals a configuration depending torque with a theoretical maximum torque of 6.1 Nm or 9.3 Nm (depending on the used gear ratio). All control modes as well as human interaction are validated experimentally. First experiments on a humanoid arm are shown. An experimental performance of a maximum speed of 400 deg/s, a maximum payload of 2.5 kg (lever arm 16 cm) and an accuracy of less than 0.1 deg (95% confidence interval) are achieved.