Human–Robot Interaction Force Control of Series Elastic Actuator-Driven Upper Limb Exoskeleton Robot

To achieve ideal force control in robots interacting with humans, an accurate and stable actuating system is essential. In this article, a novel series elastic actuator (NSEA) with torsion spring and linear spring is designed to provide pliability and safety for physical human–robot interaction in the upper limb exoskeleton robot (ULER). The Hill-based muscle model predicted human joint torques are utilized to determine the linear spring stiffness of the NSEA that facilitates the ULER to provide the reasonable assistive torque. In addition, a human–robot interaction force control (HRIFC) scheme based on an actuator dynamics model is designed, which enables the NSEA-driven ULER to achieve stability of interactive torque in human-in-charge mode and accurate force tracking in robot-in-charge mode. Theoretical proofs demonstrate the stability of the closed-loop system under the proposed HRIFC scheme. The stability and accuracy of force trajectory tracking for the NSEA-driven ULER are verified through simulations and experiments. The muscle activation of the subjects is obtained, which infers the capability of the NSEA-driven ULER to provide effective assistive forces and maintain normal movement modes. Finally, the torsion spring performance test experiments verify that the NSEA-driven ULER can achieve real-time protection and avoid secondary injuries to the subjects.