Development of a Robot Balanced on a Ball - First Report, Implementation of the Robot and Basic Control -

This paper proposes the implementation and control scheme of a robot balanced on a ball. Unlike a twowheeled inverted pendulum, such as the Segway Human Transporter, an inverted pendulum using a ball moves in any direction without changing orientation, enabling isotropic movement and stabilization. The robot on the ball can be used in place of the twowheeled robots. Our robot has three omnidirectional wheels with stepping motors that drive the ball and two sets of rate gyroscopes and accelerometers as attitude sensors. It can keep station, traverse in any direction, and turn around its vertical axis. Inverted pendulum control is applied to two axes to maintain attitude. Ball acceleration is used as control input of the system, unlike most of inverted pendulums which use torque or force as input. This acceleration input makes the robot robust against change of inertia parameters, as confirmed by Nyquist diagrams. The mechanism of the robot, the control method, and the experimental results are described in this paper.