Omnidirectional Control of 4WD Robotic Base

Abstract

In this paper, a new type of omnidirectional mobile base with four-wheel drive (4WD) mechanism is proposed for improving traction forces and enhancing mobility of holonomic and omnidirectional robots. The mobile base includes a pair of normal wheels on the rear side of the base and a pair of omni-wheels on the front side. The normal wheel in rear and the omni-wheel in front, mounted on the same side of the base, are interconnected by a chain or a belt transmission to rotate in unison with a common motor. The front omni-wheels allow the front end of the mobile base to slide freely from side to side. Additionally, the third motor is installed on the base to turn a robot body about a vertical axis at the center of the mobile base. For omnidirectional control of the 4WD mobile base, two wheel motors are coordinated to translate the center of the robot body in an arbitrary direction while its orientation is controlled by the third motor separately. Thus a robot with proposed mobile base can move in any direction without changing the orientation and turn in a place. The 4WD mechanism guarantees the traction force even on the irregular surface and the step climbing ability is enhanced since all wheels are large in diameter and no passive caster is used. Moreover three motors provide 3DOF motion with no redundancy. The configuration with the minimum number of motor contributes not only to a cost saving but also the high reliability of the mechanism. In the paper, motion analysis of the 4WD mechanism and the omnidirectional control method are presented followed by simulations and experiments for verification of the proposed omnidirectional drive system