Development of a 4WD omnidirectional wheelchair

In this paper, a development of a four-wheel-drive (4WD) omnidirectional wheelchair is presented. For enhancing the mobility of conventional wheelchairs, a new type of omnidirectional mobile mechanism with 4WD system is introduced. The mobile mechanism equips four wheels, two omni-wheels in front side and two normal tires in rear side. The normal wheel and the omni-wheel, mounted on the same side of the base, are interconnected by belt transmissions to rotate in unison with a drive motor, i.e. a synchro-drive transmission. To rotate a chair at the center of the mobile base about vertical axis, the third motor is installed on the platform. The prototype wheelchair with the proposed 4WD system is capable of climbing over a high single step and translating a chair in any direction with/without rotation. The developed 4WD system provides enhanced step climb capability compared with conventional wheelchairs, the maximum step height is restricted by the rear wheels. Namely, front wheels can climb up higher step than the rear. To enhance the step climb capability of the rear wheels, a chair tilting system is developed. The chair tilting system is effective not only for maintaining the static stability of the wheelchair but also recovering the load distribution ratio between rear and front which is required to climb up the high step. To verify the effectiveness of the developed system, step climb capability of a 4WD wheelchair prototype is tested in experiments. For varying a vehicle weight distribution ratio between front and rear wheel axes, we develop a chair tilting mechanism for the 4WD wheelchair with a linear drive mechanism controlled by a stability algorithm using an inclination sensor. In the experiments, both front and rear wheels of the prototype wheelchair can successfully climb a 9 cm step while the rear wheels fail when the chair tilting system is disabled.