Open loop acceleration/deceleration control for disk drive stepper motors

DETAILED DESCRIPTION In accordance with the present invention, there is a relatively inexpensive, but efficient open loop, pulse width modulation technique for controlling the acceleration and deceleration profile of a stepper motor driven actuator for a disk drive.
Pulse width modulation routines are invoked under program control for single track seeks and for the first two and the last two steps of multi-track seeks, so that the settling time, positional hysterysis, and mid-frequency resonance of the actuator assembly are optimized.
Different routines are provided for single and multi-track seeks because (1) mid-frequency resonance is not at issue on single track seeks, (2) the maximum allowable step rate or speed of the stepper motor is different for single track and multi-track seeks, and (3) the optimal acceleration/deceleration characteristics are different for single track and multi-track seeks.
Typically, the pulse width modulation routines are microcoded into a look up table within a microprocessor and are invoked under the control of a counter which is incremented to count the number of steps commanded for each seek.