Position and Stiffness Control of Musculoskeletal-Inspired Robot Arm Based on Direct Sum Decomposition

This paper presents a method for controlling the position and stiffness of a 2-DOF robot arm driven by three pairs of antagonistic actuators, which mimics the musculoskeletal system of human limbs. In this study, we propose a new method of solving the distribution problem of the musculoskeletal-inspired robot arm based on a direct sum decomposition of the actuator force space. The proposed solution allows to control the stiffness separately from the position, thus simplifying controller design. We then design a position and stiffness controller. The control law consists of a PD feedback position controller and a feedforward stiffness controller in joint space that are designed independently from each other. The proposed controller can asymptotically stabilize the equilibrium point of the closed-loop system and does not require a force sensor for stiffness control. Simulation results prove the effectiveness of the proposed solution and controller.