Robust control of a spherical motor in moving frame

Abstract

In order to facilitate a ball-joint-like spherical motor to operate with positioning systems to offer cascaded 6-DOF motion, a control method for precisely manipulating the spherical motor orientation in moving frame is proposed. By characterizing the cascaded motion with a pendulum-cart model, the rotor dynamics operated in moving frame is formulated. The properties of the dynamic model and the system uncertainties due to parameter inaccuracies of the cascaded system are analyzed. A terminal-sliding-mode control system is developed which incorporates a feedforward term to compensate for the effects of external motion inputs on the rotor orientation. The effectiveness of the proposed control method is experimentally validated on a cascaded platform consisting of a spherical motor and a XY-stage. The capabilities of chatter suppression and error convergence of the proposed control law are investigated, leading to a fine-tuning algorithm to find optimal control parameters based on a histogram analysis of tracking errors. The cascaded system with proposed control system is demonstrated in the context of a conformal printing task for curved electronics.