Adaptive output-feedback control of planar hybrid step motors using position-only feedback

In this paper, the design of a nonlinear robust adaptive dynamic output-feedback controller for voltage-fed dual-axis linear stepper (Sawyer) motors is addressed using a detailed motor model with electrical dynamics and significant uncertainties and disturbances. The proposed controller utilizes only position measurements in each axis, and achieves practical stabilization of position tracking errors. Velocity and current measurements are not required for feedback. Furthermore, the only electromechanical motor parameter that is required to be known is the time constant of the electrical subsystem. Adaptations are utilized to remove requirement of knowledge of any other electromechanical system parameters. The controller is robust to load torques, friction, cogging forces, and other disturbances satisfying certain bounds. The controller also corrects for the yaw rotation to achieve synchrony of motor and rotor teeth.