Chattering Free Motion Control of an Assistive Robotic Device for Paraplegics

One of the major concerns for paraplegic patients is their ability to sit and stand independently. Various studies are available in literature which discuss the design, modeling, and control of specially designed assistive devices for this purpose. In this paper, chattering free sliding mode control for an Assistive Robotic Device for Paraplegic patients is proposed. Mathematical modeling of the device reveals the nonlinear nature of the system. A sliding mode controller is thus designed to control the system. The controller is designed based on a first order sliding surface. The oscillation in the response, also known as "chattering effect," is minimized by selecting a suitable time-varying boundary layer. Simulation results show that the oscillations in the response are eliminated after the implementation of the boundary layer. The torque requirement in chattering free results are also significantly decreased as compared to the torque required in the oscillatory response, which demonstrates the reduction in control effort. The chattering-free response also ensures the comfort of the patient while using the device.