Mechanical Design and Control Method for SEA and VSA-based Exoskeleton Devices for Elbow Joint Rehabilitation

Robot-aided rehabilitation training allows patients to receive a more effective and stable rehabilitation process. Exoskeleton devices are superior to the endpoint manipulators and cable suspension devices on the aspect that they can train and measure the angle and torque on each joint of impaired limbs. For robotic devices, physical safety should be guaranteed since the robot-assisted training relies on high human-robot interaction especially for exoskeletons. Traditional robotic devices mainly introduce the stiffness actuator, while the high levels of kinetic energy of robots will induce unsafe. For guaranteeing the safety of patients, compliant actuator such as the series elastic actuator (SEA) and variable stiffness actuator (VSA) design has been involved into these devices. The added compliance can make robots intrinsically safe and realize the energy-efficient actuation. The VSA used a variable stiffness elastic component instead of a constant stiffness elastic component, and VSAs is deemed to a kind of SEAs. A closed-loop interaction control method was used for SEAs to generate low impedance. By comparison, the VSA realizes adaptable compliance properties with inherent mechanical design. Thus, for SEAs, an additional mechanism is needed to adjust the output stiffness. In this paper, two kinds of compliant exoskeleton devices designed with the SEA and VSA respectively are introduced. The mechanical design and control method for each device are introduced; especially the design for guaranteeing patients’ safety.