Direct field-feedback control for multi-DOF spherical actuators

This paper presents an alternative control strategy for permanent magnet (PM) based spherical actuators capable of multi-DOF precision manipulation. Unlike existing control methods which rely on separate sensing systems, this direct approach utilizes magnetic field measurements for feedback and eliminates the complicated multi-DOF orientation detection in closed-loop control which may cause time-delay and affect system sampling rate. By capitalizing on the rotor magnetic field implicit dependence on orientation, the control law derivation and torque coefficient estimation can be obtained simultaneously and directly from field measurements without explicit determination of the rotor orientation, thereby improving computational efficiency and eliminating error accumulation. The control method is simulated in 2-DOF motion with a CAD model of a spherical actuator.