Stepper motor control for data disk system

Abstract

A data disk storage system utilizing a bipolar stepper motor for use in conjunction with the controlling of the operation of the storage system. The stepper motor imparts a drive force for moving a control arm to which a read/write head is coupled. The operation of the stepper motor through driving of the control arm causes the read/write head to move across the various tracks of the data disk within the data storage system during operation of such system. The stepper motor includes a stator and a rotor coupled to an output shaft of the motor which output shaft in turn is coupled to the read/write head through the control arm. A first drive mechanism within the stepper motor generates a first phase signal within the stator for creating a first drive force for rotating a rotor. A second drive mechanism of the stepper motor generates a second phase signal within the stator for creating a second drive force for rotating the rotor. These first and second drive forces are out of phase with each other, normally by 90.degree. when both signals are positive or both are negative or by multiples of 90.degree. when one of the signals is positive and the other is negative. A control mechanism selectively provides positive and negative phase current signals to the first and second drive mechanisms for generating 8 stable step positions for the rotor during each motor cycle. This control mechanism controls the current supplied to the first and second drive mechanism so that the resulting holding torque on the rotor generated by the first and second drive mechanisms is substantially the same at each step position.