Adaptive control of stepper motors without current measurements

In this paper, a robust adaptive nonlinear dynamic controller is designed to achieve practical stabilization for position tracking error of a voltage-fed permanent-magnet stepper motor. The control design is an output-feedback design that utilizes only rotor position and velocity measurements. Currents are not available for feedback. Furthermore, adaptations are utilized so that no knowledge of motor parameters is required. The proposed controller is robust to load torques, friction, cogging forces, and other disturbances satisfying certain bounds. The controller also guarantees asymptotic stabilization and set-point regulation if the torque disturbances vanish at the setpoint. This represents the first output-feedback (i.e., no current measurements) results with all motor parameters assumed unknown. These results can also be extended to other classes of motors.