A new active-caster drive system with a dual-ball transmission for omnidirectional mobile robots

This paper presents a new active-caster drive system for omnidirectional mobile robots. The active-caster presents omnidirectional motion on the ground with providing an active traction force in an arbitrary direction by controlling a 2DOF planar velocity vector created by independent two motors. The proposed mechanism includes a dual-ball transmission to transmit traction power to rotate and orient a drive wheel with distributing velocity components to wheel and steering axes in an appropriate ratio. One of the significant features of the proposed mechanism is that a velocity ratio between wheel rotation and steering rotation is determined mechanically by the dual-ball transmission, where the ratio is a function of an orientation of a wheel, therefore a sensor for measuring a wheel orientation and calculations for velocity decomposition are totally removed from a conventional control system.