Robust Tracking Control of Spherical Motion Platform for Virtual Reality

This article presents to develop a robust control system of spherical motion platform (SMP) capable of controlling six-degree-of-freedom motion, particularly unlimited rotational motion for better virtual reality. The SMP is the new design of a motion manipulator/simulator driven by the frictional force between a set of spherical wheels and cockpit sphere. However, it has intrinsic difficulties in control due to numerous uncertainties, including slipping motion between spherical wheels and cockpit sphere. Inaccurate motion control may degrade human perception as well as tracking performance. In this article, sliding mode control based on a disturbance observer is developed for the SMP to achieve precise motion tracking performance and provide a more realistic environment regardless of kinematic and dynamic uncertainties. Numerical simulation and experimental results with proportional-integral-differential and the robust controllers are compared for step and sinusoidal inputs to demonstrate the feasibility of motion control and tracking performance in spite of uncertainties. Finally, the SMP is operated using two representative flight maneuvers as a flight simulator. The results show that the SMP with the control system can be utilized to provide motion cue for a human on board for virtual reality.