Active omni wheel capable of active motion in arbitrary direction and omnidirectional vehicle

Abstract

A transportation vehicle or mobile robot that can move to a target location in an arbitrary direction on the floor is important to ensure that work can proceed quickly and effectively in a limited space. To move in an arbitrary direction, conventional methods such as omni wheels have free rollers along the outer circumference of the wheel that can rotate passively. However, the conventional methods are difficult to control precisely because of the rotational resistance of the free rollers. In addition, the direction that the conventional methods can move actively by themselves is limited. This paper proposes a novel mechanism called the active omni wheel, which is able to actively move in an arbitrary direction by using only one wheel unit. The active omni wheel is composed of a main body and outer rollers arranged around the outer circumference of the wheel. By using a differential gear mechanism, the active omni wheel enables active rotation of not only the main body of the wheel but also the outer rollers. The theoretical equation of motion of the active omni wheel is clarified to control the wheel. An omnidirectional vehicle using the active omni wheel is discussed. The appropriate arrangement of wheels that enables the omnidirectional vehicle to move actively in arbitrary directions by using the active omni wheel is shown and the motion theory is constructed. This paper also discusses the structure appropriate for the vehicle using the active omni wheel, including the arrangement of input shafts, the structure supporting the wheels, the main body of the vehicle, and its suspension. The active omni wheel and omnidirectional vehicle were designed and manufactured. Experiments conducted on the manufactured vehicle verify the effectiveness of the active omni wheel and the omnidirectional vehicle.