Input-output linearizing and decoupling control of a nonholonomic power wheelchair

While nonholonomic-powered wheelchairs (NPWs) have made advances over the past three decades, the control algorithms remain virtually unchanged since 1980's. The simple proportional-integral (PI) controller is antiquated, and does not perform well in the presence of disturbances, sensors uncertainties, nonlinearities and load variations. The practical interest is driven by the fact that today's wheelchairs need to be operated under tighter performance specifications. At the same time more and more constraints, stemming for example from environmental and safety considerations, need to be satisfied. Often these demands can only be met when nonlinearities and constraints are explicitly considered in the controller. A new approach to trajectory tracking control for wheelchair systems containing uncertain, nonsmooth nonlinearities is proposed. The method is based on decoupling theory and system input-output feedback linearization technique by which the system stability and convergence of velocity tracking errors to zero are rigorously examined. The effectiveness and efficiency of the proposed controller is demonstrated through simulation studies. The study would result in better driving performance, smoother feel, and fewer accidents or inadvertent collisions.