Position Control of Robotic Systems via Linear Controllers with Application to a Lower Limb Rehabilitation Exoskeleton Robot: Design and Comparative Analysis

The control of robotic systems and more particularly exoskeletons for human lower- and upper-limb rehabilitation has received a great attention as a promising healthcare solution to address the problems related to limb impairment. These rehabilitation exoskeletons, which are characterized as Lagrangian robotic systems, are intended to help individuals restore lost motor function, improve muscle strength, and improve overall mobility. One of the common tasks for these robotic systems in the rehabilitation exercise is to move from their current position to a desired one. To achieve this objective, it is necessary to apply an appropriate controller with the right feedback gains. This work mainly focuses on the design of some linear control laws, namely the PD-based controller, the PID-based controller, and the LQR controller, for the position control problem. The key idea behind designing such controllers is to develop a linear dynamic model around the desired position. Additionally, some conditions are developed to help calculate the feedback gains of these controllers. Finally, as an illustrative example, a robot with two degrees of freedom is adopted, as a rehabilitation exoskeleton robotic system for either lower limbs, to demonstrate simulation results that compare between the proposed linear controllers.