Simulation of dc torque motor magnetic hysteresis and cogging effects

A mathematical model of the dc torque motor magnetic circuit is described. This model, considered suitable for any simulation of high-performance null-pointing servos, was developed to aid the design of a solar array drive for the Navstar Global Positioning System satellites. Estimates of the motor magnetic hysteresis were obtained by using the original Dahl solid friction model, which is explained. Disturbance torques and the effect of cogging angles are discussed. The pulse mode of operation, considered more reliable than a conventional linear servo, involves connecting one of the motors across the spacecraft power bus by turning on power transistors for a predetermined number of milliseconds, causing the array shaft to accelerate. After power is terminated, friction and drag decelerate the array and stop it.