Analysis, design and control of a novel spherical permanent-magnet actuator

The authors describe the analysis, design and control of a novel actuator with a spherical permanent-magnet rotor and a simple stator winding and position-sensing arrangement. It is capable of two degrees of freedom, and has a high specific torque. Expressions for the magnetic field distribution and the torque vector and back- EMF constants are derived analytically, and optimal design parameters, which result in maximum output torque or maximum acceleration for a given payload, are derived. The control of the actuator, whose dynamics are similar to those of robotic manipulators, is facilitated by the establishment of a complete actuation system model and the application of a robust control law. The validity of the analysis and design techniques, and the effectiveness of the control strategy, are confirmed by measurements.