Cooperative control of multiple modular mobile systems with active-caster omnidirectional drive mechanisms

Abstract

In this paper, an "active-caster" omnidirectional wheel mechanism is introduced. The original type of the active caster was invented more than twenty-five years ago, and various types of active casters were developed by the author's group, some of which are described in this paper as well. Unlike other omnidirectional wheels such as Mecanum Wheel or Universal Wheel, active casters do not need freely rotating parts. An active caster is an orientable wheel with a normal tire, the steering and wheel shafts of which do not intersect like a normal passive caster. The wheel and steering shafts are driven by the respective motors to perform the omnidirectional movement of the robot.To apply this technology to various fields, many types of active casters have been developed. For example, a two-wheeled active caster was developed to avoid redundant actuation, dual-wheeled active caster-to reduce turning friction, and differential-drivetype active caster-to improve the operating rate of the actuators.A cooperative transporting system with multiple two-wheeled mobile robots is presented as a future work that realizes the omnidirectional transportation of large objects with multiple mobile robots. Each mobile robot is controlled to perform the active-caster motion during the transporting task, and it can move independently in the same manner as a two-wheeled robot. This configuration increases flexibility in object transport applications.