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ACROBAT-S Omnidirectional Mobile Robot Prototype : And Study on Ball Drive Mechanism

This paper presents a holonomic omnidirectional mobile robot using an active-caster robotic drive with a singlelayer ball transmission (ACROBAT-S). This robot can move and turn independently in 3DOF and the number of motors is equal to the number of the robot DOF, therefore the control system can not be redundant. The proposed ball transmission contributes to simplify a control system since it needs no angle sensor and complicated calculations for cooperative motor control. We prototype the proposed mobile robot and test the performance in moving accuracy and drive efficiency.We also study about the change in wheel thrust according to the direction of robot movement. Since this performance is depends on the arrangement of the rollers, namely relative angle of two drive rollers that drive the ball transmission. We analyze the statics of the ACROBAT-S and the robot with two ACROBAT-Ss and derive the optimal arrangement of the drive rollers so that the wheel thrust is uniform in all directions of robot movement. Finally, we measure the actual thrust of the wheels using a prototype to confirm that the arrangement of the drive rollers is appropriate.