Design and Application of a New Series Elastic Brake Used in Exoskeleton System of Gait Rehabilitation Robots

Rehabilitation robots have direct physical interaction with the human body. Ideally, the safety and control considerations, actuators for rehabilitation robots should be compliant, can be forcefully controlled, and can be driven in the reverse direction. However, current series elastic actuator (SEA) designs face common performance limitations because of compromised spring stiffness options. Physical interactions affect control variables and may even lead to system instability. Therefore, the human-computer interaction control design is very important in the research of the repair robot. In this paper, a new type of compact compliance control actuator designed for portable rehabilitation robots is proposed to overcome the current performance limitations of SEA and based on this, an interactive control strategy for gait rehabilitation robots is established. Our design consists of a servo motor, ball screw, a torsion spring between the motor and the ball screw, and a set of translator springs between the ball screw nut and the external load. The robot achieves compliance and reversibility of human-computer interaction using a novel compact series of elastic actuators. Due to direct physical interaction with humans, the controller design must meet stability requirements. In this paper, a theoretical proof is provided to show the guaranteed stability of the closed-loop system under the proposed controller.