Method of controlling rotary position of a torque motor

Abstract

A control system is provided for a limited angle torque motor used as a rotary position control device. A motor for which the system is intended would consist of a rotor and a stator. The system uses an analog Hall-effect sensor to sense the position of the rotor. Rather than attempting to shield the Hall-effect sensor from the influences of magnetic fields generated by the field windings in the stator during motor operation, the system allows the output signal from the Hall effect sensor to contain elements of both the angular position and the extraneous magnetic field generated by the field windings of the motor. Current feedback from a circuit which independently senses the motor current is then combined with this signal to eliminate the influence of the motor coil magnetic field. The system is applicable to a number of limited angle torque motor designs. A preferred embodiment is shown wherein a unique sandwich construction of the rotor magnets on a soft iron rotor core provides a highly linear angular position signal for the system to process. Furthermore, a means of fixturing the Hall-effect sensor within the motor end windings to facilitate the position sensing for the preferred embodiment is described. Finally, a detailed description of the electronic circuit used to implement the system in the preferred embodiment is provided, and a number of alternate analog and digital implementations of the circuit are discussed.