Modeling and Mechanical Design of an Active-Caster Omnidirectional Mechanism with a Ball Transmission

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This paper presents kinematic and static analyses of an active-caster robotic drive with a single-layer ball transmission (ACROBAT-S). On the basis of the analyses, a single-wheel prototype is designed, and fundamental experiments using the prototype are conducted. The proposed ACROBAT-S includes a ball transmission that transmits power to a wheel axis and steering axis of an active-caster wheel in an appropriate ratio to produce so-called “caster motion.” The power distribution is realized mechanically rather than by complicated computer control algorithms. Therefore, the angle sensor for detecting the wheel orientation, and the control calculations for coordinated control of the wheel and steering motors of a conventional system are eliminated. Thus, the proposed mechanical design, which transfers a part of the control function to the mechanism, contributes to simplifying the overall control system. The results of the analyses and experiments with a prototype confirm that the proposed active-caster mechanism, ACROBAT-S, can realize the expected omnidirectional motion with simple motor control, such as Point-To-Point control.