Design of a Nonlinear Backstepping Versus Sliding Mode Controller for a Human Musculoskeletal arm Model in Sagittal plane

A recent increase in stroke and diseases causing spinal cord injury has resulted in increased limitations to human mobility, particularly in the upper extremities. Because of these diseases, the brain cannot send correct signals to the muscles; therefore the use's movement system is disrupted, even if the user has healthy muscles. With a functional electrical stimulation, upper limb rehab can be assisted. As the main contribution of this paper, we propose a nonlinear backstepping controller that generates appropriated signals to replace the missed signals. For this aim, this study uses a planar musculoskeletal model that includes six muscles and two joints (shoulder and elbow). For the final step, numerical simulation is conducted for two different tasks to verify the accuracy and capability of the backstepping controller: 1- Set-point control for each joint; 2- Path tracking for the End-Effector and its results are compared with the results of the sliding mode controller.