An omnidirectional mobile robot equipped with four independent omnidirectional wheels can perform 3 DOF motion and has one redundant DOF. This redundancy can be used to drive the mechanism enabling the wheel arrangement to vary, which can function as a continuously-variable transmission (CVT). In this research, a special mechanism called a variable wheel arrangement mechanism is proposed to increase the range of velocity ratio for the CVT from the wheel velocities to robot velocity, which may improve performance of the mobile robot. A mobile robot with this mechanism was constructed and various tests have been conducted to demonstrate the validity and feasibility of the proposed mechanism.

Most omnidirectional wheels with passive rollers have a gap between rollers. This gap causes the wheel to make discontinuous contact with the ground, and leads to vertical and/or horizontal vibrations. In this paper a novel design of continuous alternate wheel is proposed to minimize a gap between rollers. In the continuous alternate wheel, inner and outer rollers are arranged continuously, thus resulting in no gap between the rollers. This paper details the design process including the systematic approaches to determine the optimum number of rollers, the radii of rollers and the inclination angle of the inside of an outer roller for given design specifications. Finally, an actual continuous alternate wheel is constructed to verify validity of the design guidelines.