Robust Position Control of Assistive Robot for Paraplegics

Paraplegia refers to the paralysis of the lower limbs resulting from the damage to the spinal cord. Thus far, considerable efforts have been devoted to the rehabilitation of paraplegics and the improvement of their quality of life. This study focuses on the position control of the sit-stand mechanism of an assistive robot developed to aid paraplegics in shifting from a sitting to a standing position and vice versa. Two control techniques for the model were proposed: sliding mode control (SMC) and SMC integrated with a sliding perturbation observer (SMCSPO). The control algorithm was designed and implemented in MATLAB/Simulink. The simulation results indicate that the SMC is a nonlinear control; however, because the robot is a highly nonlinear model, which requires a high switching gain, the controller introduces chattering into the system. The SMC has been observed to exhibit inadequate performance when controlling a system with uncertainties. In contrast, the SMCSPO is a robust nonlinear control integrated with a nonlinear compensator, which performs better than the SMC even in the presence of external disturbances.