Design and Control of a Sleeve Muscle-Actuated Robotic Elbow

This paper describes the design and control of a robotic elbow system, which is actuated with a novel sleeve muscle actuator. The sleeve muscle is a significant step forward from the traditional pneumatic muscle, and provides a substantially improved performance through a fundamental structural change. Specifically, the sleeve muscle incorporates a cylindrical insert to the center of the pneumatic muscle, which eliminates the central portion of the internal volume. As a result of this change, the sleeve muscle provides multiple advantages over the traditional pneumatic muscle, including the increased force capacity over the entire range of motion, reduced energy consumption, and expedited dynamic response. Furthermore, utilizing the load-bearing tube as the insert, the sleeve muscle enables an innovative “actuation-load bearing” structure, which generates a highly compact robotic system to mimic the structure and functionality of biological limbs. The robotic elbow design in this paper serves an example that shows the design and control process of a robotic joint in this integrated structure. This robotic elbow provides a range of motion of 110 deg, approximately 80% of that for a human elbow, and an average torque capacity that exceeds the peak torque of the human elbow. The servo control capability is provided with a model-based sliding-mode control approach, which is able to provide good control performance in the presence of disturbances and model uncertainties. This controller is implemented on the robotic elbow prototype, and the effectiveness was demonstrated with step response and sinusoidal tracking experiments.