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Design and Simulation of a Robotic Knee Exoskeleton with a Variable Stiffness Actuator for Gait Rehabilitation*

Patients with knee impairments caused by neurological or orthopedic diseases such as a stroke, spinal cord injury, or physical injury are at a high risk of secondary complications, which include muscular dystrophy and hemiplegia. This seriously affect the quality of life of these patients. Therefore, it is necessary to assist these patients to regain the ability to perform activities of daily living. Robotic knee exoskeletons are wearable humane-machine cooperative systems, which can provide effective gait training by generating controllable torque at the wearer’s knee joint. This paper presents the design and simulation of a robotic knee exoskeleton with a variable stiffness actuator (VSA). First, a brief description of the human knee biomechanics during walking is introduced. Next, design of the robotic knee exoskeleton with the VSA is proposed. In the designed VSA, a disk-type torsion spring is employed as the compliant element in the actuator, which can absorb perturbations and guarantee a low system output impedance and stable torque control. Then, the dynamic model of the VSA is established and simulations are conducted. The simulation results indicate that the application of the VSA in the robotic knee exoskeleton has good torque tracking performance and stability.