A new reconfigurable mechanism for varying the footprint of a four-wheeled omnidirectional vehicle is presented. A chair is mounted on a moving platform with four ball-wheels allowing holonomic, omnidirectional motion. Two pairs of ball-wheels at the diagonal positions of the chassis are mounted, respectively, on two beams that intersect at a pivotal point in the middle. The angle between the two beams crossing at the pivotal point is varied actively so that the ratio of the wheel base to the tread may change. Four independent servomotors driving the four ball-wheels allow the vehicle to exhibit holonomic motion. The beam angle is controlled based on the measurement of the mass centroid position in such a way that the mass centroid can be kept within the footprint at all times. The concept of the reconfigurable footprint mechanism is described, and its kinematics is analyzed followed by the control design for augmenting vehicle stability. A prototype vehicle for wheelchair platform application is designed.
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