Design of a Variable-Stiffness Exoskeleton for Upper Limb Rehabilitation

Robot-assisted rehabilitation training has been demonstrated to be an effective approach for restoring motor function in post-stroke patients. This paper presents the design of a novel upper limb exoskeleton robot with the characteristic of variable stiffness. The upper limb exoskeleton system is a 7-degree-of-freedom system that includes shoulder, elbow, and forearm movements. The core focus of the system is to integrate variable stiffness mechanism into the exoskeleton, which can enhance the safety and comfort of the robot-assisted rehabilitation training. In addition, the exoskeleton robot is equipped with an adjustable wear-size mechanism and a locking device, allowing it to adapt to different user sizes in order to enhance human-machine adaptability. The exoskeleton robot structural system is composed of a backpack platform with a tandem kinematic chain, which is modularly designed to achieve coverage and flexibility of multi-joint motion. A variable stiffness actuator is integrated into the elbow joint of the exoskeleton, in which the cable tension is modulated by servo motors to facilitate dynamic stiffness adjustment. In addition, the kinematic model of the system was established by mathematical modelling and simulation verification using the improved Denavit-Hartenberg (D-H) parametric method. The accuracy of the model was verified by Matlab Robotics Toolbox. This design has been demonstrated to effectively simulate human upper limb movement and provide safe and reliable rehabilitation training.