Hewlett-packard Company

Boyd N Shelton

Charles E Hessing

Robert K Barnes

Jeffrey S McAllister

Richard Lee Hilton

Henricus C Buthker

Samuel H Gailbreath

Henricus M Van Hout

A PWM controlled multiphase DC motor apparatus has a multiphase DC motor, a current sensor, and a PWM controller. The DC motor has multiple windings which turn on and off during commutation at a commutation frequency. The current sensor is coupled to sense power supply current flowing in all windings of the DC motor. The PWM controller is coupled to control the DC motor using a PWM signal at selected PWM frequency with variable duty cycle. Using the feedback from the current sensor, the PWM controller maintains approximately constant torque in the DC motor by adjusting the duty cycle of the PWM signal. The PWM controller includes a soft switching circuit which manipulates a voltage used to generate the controlling PWM signal in a manner which causes linear stewing of currents in the windings during commutation. The linear current stewing occurs at a slew rate that is slow relative to the PWM frequency to thereby reduce torque ripple during commutation. The combined features of continuous PWM duty cycle control and linear current slewing during commutation significantly reduces torque ripple at the fundamental commutation frequency, as well as at the first few harmonics. A method for PWM control of a multiphase DC motor is also described.

Soft switching, PWM controller and method for reducing torque ripple in

A multiple pole, multiple phase, sensorless DC disk spindle motor in a disk drive is powered by direct current which is commutated among the motor phases from a DC power supply to start the motor and to rotate the disks at constant speed in a predetermined direction whenever the disk drive is in use. When the motor is prevented from rotating by the stiction bond of one or more transducers which have adhered to the disks, the direct current is reversibly commutated among the motor phases near the resonant frequency, a predetermined number of times, to produce substantially sinusoidal, bi-polar motor torques to achieve torque amplification to break the stiction bonds. Following the last of the predetermined number of reversible commutations of direct current, direct current commutation is initiated among the motor phases to rotate the motor and the disks in the desired direction at constant speed.

Bi-polar disk torquing system for a disk drive to free stuck transducers

A disk drive has a disk format that includes servo fields and interspersed data fields. The disk drive includes a timing generator for generating timing signals to synchronize and control operation of read/write and servo positioning circuits. The disk drive also includes a writable program store that stores a plurality of timing signal commands for generating timing signals in conformance with the format of a disk. A processor loads the writable program store with the timing signal commands and the processor further enables readout of those commands from the writable program store. An execution register receives the timing signal commands and generates timing signals in response, the timing signals controlling synchronization and operation of the read/write circuits. As the writable program store is reprogrammable, at will, substantial flexibility is achieved in the creation of such timing signals.

Programmable servo timing generator

A disk drive system employs uniform size data blocks, with each disk having a sectorized track format and each sector of a track including at least one servo burst. Data blocks exhibit a constant data density across a plurality of disk tracks of differing radii. The system comprises read/write apparatus for accessing both servo signals and data signals in each disk sector. A servo system is responsive to servo signals fed from the read/write apparatus to generate a synchronizing signal. A data sector pulse generation circuit is responsive to the synchronizing signal to generate and pass to the read/write apparatus, a data sector pulse for each block of data commencing in a sector. That data sector pulse enables operation of the read/write apparatus upon the data block. A control circuit enables the delay of generation of a next data sector pulse when any block of data is split by a servo burst. The delay period is the duration of the servo burst and the portion of the data block that follows the servo burst.

Programmable start-of-sector pulse generator for a disk drive using

A method and apparatus for operating a magnetic disk drive having a pole piece spaced apart from a magnetic disk surface by a predetermined distance to effectively form two plates of a parasitic capacitance capable of sustaining an undesirable electrical discharge capable of destroying data on the disk either by random discharge between the pole piece and magnetic disk or by discharge into imperfections on the disk. The invention comprises a circuit and method for applying a DC voltage to the pole piece and for simultaneously applying a DC voltage to the magnetic disk surface which is approximately equal to the DC voltage applied to the pole piece and thereby preventing the above parasitic capacitance between the pole piece and the magnetic disk surface from charging to a level sufficient to sustain any electrical discharge.

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Boise, ID, United States of America

Boyd N Shelton