ERROSphere: an Equilibrator Robot

Abstract

This paper explores a specialized topic in mechanical stabilization control which has not previously attracted much attention, namely the active equilibration of a body balancing on top of a sphere. This task is, in principle, similar to other equilibration problems where the control system has to balance the controlled body about a position of unstable equilibrium. Our robot, called ERROSphere (equilibrating robot rolling on sphere), uses a mechanically simple drive-assembly and a special control architecture to achieve the closed-loop stabilization. This paper introduces the structure of the robot, and summarizes the first stage of our experiment. Our present goal has been only to stabilize the robot locally about the static unstable-equilibrium position. However, a successful device of this nature opens prospects for a versatile new type of drive-mechanism for locomotion applications. The control strategy employs two non-coupled linear models, which mimic the movements of the robot in two orthogonal projection planes. The balancing controller uses optimal control theory employing a linear quadratic regulator (LQR) model based on a linear approximation of the system equations.