Mechanism and control of a 4WD robotic platform for omnidirectional wheelchairs

This paper presents mechanism and control of a four-wheel-drive (4WD) robotic platform for wheelchairs. The 4WD mechanism equips four wheels, two omni-wheels in front and two normal tires in rear. The normal wheel and the omni-wheel, mounted on the same side of the base, are interconnected by a synchro-drive transmission to rotate in unison with a drive motor. To control chair orientation on the 4WD platform, the third motor is installed on the platform. The chair with the proposed omnidirectional 4WD system is capable of moving in any direction which is so-called holonomic and omnidirectional mobility. The holonomic omnidirectional mobile capability enables a person to drive a mobile system with no knowledge about the drive mechanism or its configuration since it can move in any direction and rotate from any configuration of the mechanism. This paper presents the mechanism and control of 4WD platform to which powered-caster omnidirectional control is applied. The rotations of two pairs of wheel and vertical axis of a chair are controlled in such a way that it performs as a powered twin-caster to realize holonomic motions. The prototype wheelchair is designed and built to verify the mechanism design and control method. The smooth and flexible onidirectional motions are presented by the experiments.