International Business Machines Corporation

John J Neesz

Michael Charles Stich

Thomas W Glaser

Todd Barry Anderson

David W Collins

The circuit provides damping for digitally controlled devices where the provision of power pulses in response to sensing a given device parameter may result in a regularity of pulses that causes a resonant condition with a frequency that interferes with other device functions or induces error conditions. The circuit shown randomizes to a motor by random gating of a sequence of commands retained in a shift register. Random gating from the shift register positions occurs through the use of a counter driven by an oscillator, independent of other device functions and clocking circuits, in conjunction with an enabling circuit from a random digitized data source that enables or disables counter advance by the oscillator. In the disk drive environment shown, randomizing has no significant effect on the closely regulated speed since the corrective commands occur during each sector of revolution or about thirty-six hundred times per second and motor rotational inertia precludes any meaningful change during a sector rotation.

Randomized motor drive

A sector servo seek control samples each sector to obtain sector time, the track identification within a sequence of track types and a position error signal for a track location to track location seek. The device during each sector determines the actual transducer track location and the next sector projected track location with respect to the sequence of track types. The projected track location is corrected using the error signal to find the actual location, but if a sector signal is missing or erroneous, the projected location is used as the actual location, permitting a composite correction to be made when a correct sector signal is obtained. The seek time is minimized by using maximum acceleration followed by maximum deceleration while not exceeding a velocity value that would cause the device to overshoot the target track using full deceleration.

Sector servo seek control

A three level motor speed control for a device such as a magnetic disk drive requiring a closely regulated running speed provides for acceleration, deceleration, obtaining close speed regulation and maintaining speed regulation of a rotating device during operation. The first level control provides acceleration or deceleration while checking velocity each eighth revolution and the second level control uses single revolutions to measure speed over an accurate rotational distance to obtain close speed regulation. Both level one and level two are controlled by the device controller. During run conditions with no error signal, a third level of control of the closely regulated velocity is maintained by separate hardware circuits which frees the processor for other uses. An error condition forces control to level one for re-establishment of the regulated running speed and a command to stop the drive forces control to level one for deceleration and stop procedures.

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Rochester, MN, United States of America

John J Neesz