Sliding Mode Posture Control of a Parallel Biwheel Vehicle Driven with a Stepping Motor.

Abstract

A sliding mode control scheme with a discrete time control model is applied to posture control of a parallel biwheel vehicle (PBV) which is driven with a stepping motor operated in an open-loop mode. Both equivalent and discontinuous control inputs are applied to the PBV. The former brings states on a sliding surface to the origin of state space along the surface. The latter causes states off the sliding surface to move toward the surface and be bound on it. Posture of the PBV can be controlled within ±0.005 rad around an unstable equilibrium position when the PBV starts from an initial inclination of 0.1 rad off the perpendicular. Trajectories of the initial response in state space reveal that the state of the PBV is closely bound on a sliding surface, hence the sliding mode is established. The stable initial responses are also maintained under additional weighting of up to 1.5kg, which is almost equal to the weight of the PBV, near the center of mass or on the bottom of the PBV. The vehicle can easily recover stable posture when the body is pushed from the stable position. Consequently, the occurrence of the sliding mode is confirmed using the PBV with the step rate as the control input. The sliding mode can result in quick response, stable posture and robustness of the vehicle motion.