Seagate Technology Incorporated

James N Krause

Raymond G Gauthier

Litko R Chan

Ramgopal Battu

David M Lancisi

William E Wevers

The present invention utilizes the output of a voltage regulator to control the drive voltage to the stepper motor driven transducer positioning system. This technique will significantly reduce the access time. More specifically, in this invention, the output of a digital-to-analog converter (DAC) is used to control the output voltage level of a voltage regulator circuit which supplies the voltage of the stepper motor drive transistors. In order to optimize the drive voltage output from the voltage regulator to the stepper motor for each disc drive, circuitry is provided to determine the minimum settling time for a specific actuator movement resulting from the application of a given drive voltage. A detector circuit monitors the settling time of the head over the center of the target track. The data identifying the voltage regulator output which results in minimum settling time is stored and used from then on for that stepper motor disc drive system as the optimum access tuned voltage. This data will be applied by the microprocessor to a DAC, and output from the voltage regulator to the stepper motor drivers during each stepping sequence. Typically, this tuning process is originally accomplished when the disc drive is first powered on and is part of the normal power-on recalibration routine.

Stepper motor torque variance compensation using varied applied voltage

The output of the ring detector is used to change or control the timing of specially generated torque damping pulses which are fed to the stepper motor at the end of a SEEK step sequence. These torque damping pulses are step pulses, the timing, amplitude and/or duration of which applies either a positive or negative torque to the stepper motor relative to the target track based on the 'energy' that has to be dissipated to settle the read/write head over the desired track. The energy is measured indirectly by monitoring the back emf voltage of an open winding or unenergized phase of the motor, and developing an indication of how fast the read/write head is going through the desired track center or target track point. By bringing an additional signal out of the ring detector, the direction in which the read/write head has crossed the track can also be defined. Based on how fast the read/write head is going and in which direction, the microprocessor accesses a look-up table for selecting the timing, amplitude and/or duration of the damping pulse.

Information storage disc transducer position control system using last

A motor is disclosed comprising a housing and a plurality of parallel stator laminations mounted on the interior wall of the housing surrounding the rotor. The stator comprises a plurality of coils wound around the stator poles. Each coil or group of coils connected in series with each other are further connected in series with a thermistor network. Preferably, the thermistor is supported on a printed circuit board mounted adjacent to the coils, with the thermistor being inserted in a space directly adjacent to or between adjacent stator coils in order for the thermistor to accurately respond to the actual operating temperature of the coils. With increases in temperature, the resistance of the negative temperature coefficient thermistor will decrease, lowering the resistance of the motor circuit and maintaining the L/R time constant of the system. The opposite effect will occur with decreasing tempreature. To adjust for the fact that thermistors that accurately reflect the changes in resistance of the wire used to wind the coils with changes in temperature are not available, a resistor is wired in parallel with the thermistor, the resistor having a value chosen to modify the total resistance represented by the thermistor network to the coils so that the compensation is accurate over a wide range of changes in temperature and motor design. The shunt resistor allows flexibility in motor design, as it can have any selected value from zero to infinity to compensate for variations in motor design.

Resistance compensation in a motor using a thermally variable resistive

A method and system using the magnetic hysteresis of a stepping motor to offset the position of a transducer relative to a disk target track during data recovery. The data recovery is accomplished by energizing selected phases of the stepping motor while moving to the target track and then de-energizing a selected phase during the final movement to the target track which results in the transducer being offset from the target track so that illegible information can be recovered.

Stepper motor data recovery method using a magnetic hysteresis based

The magnetic hysteresis or magnetic memory error in a stepper motor is erased by sequencing the motor phases in a particular manner. In positioning a transducer by energizing selected phases of the stepper motor, the sequence is selected to eliminate the memory of the previous stepper motor position, and reinforce only the new position. This cancellation is achieved by activating the stepper motor to move a transducer from a given track position to an adjacent track position, the sequence of energization of the phases including at least one reversal of the magnetic sense of each phase that was energized to position the transducer at the initial track, but that is not to be energized at the target track; further, the phases not energized at the initial track but that are energized at the target track are reinforced by the selective energization during more than one of the steps used for reaching the target track.

Stepper motor magnetic hysteresis correction using a stepping algorithm

A disc drive system is disclosed including a data storage disc having a plurality of data storage tracks. Each track has a centerline, the centerlines of adjacent tracks being spaced by a fixed track space distance. The disc surface also includes wedge servo sectors; servo data in each sector includes first servo information stored at a position on one side of said data track centerline and one-half said track space distance from said centerline, and second servo information stored at the other side of said data track centerline and one-half of said track space distance from said centerline. Positionable accessing is provided for reading the servo data and for generating servo signals representing the first and second servo burst information, to positioning said transducer accurately. The stepper motor has a plurality of stator coils subject to selective simultaneous energization at nominal current with currents of selected polarities of all or all but one of said coils for defining a plurality of motor detent positions. The servo information is located at positions defined by said motor detent positions. The data track is reached by the transducer by applying approximately one-half of said energization current to the one non-energized coil to reach said motor detent servo track position, the motor detent position on the other side of said track centerline being reached by energization of all the coils with currents of selected polarities.

Bipolar motor control

Electronic circuitry is provided to position the read/write heads in a designated landing zone when the electrical power is removed from the drive. When power is removed from the drive, the stored energy of the rotating spindle motor is used as a source of electrical power and timing pulses to the stepper motor which drives the actuator of the disc drive. The power generated by the spindle motor as it spins down is referred to as 'back EMF.' A sequencer circuit is provided to couple the power and clock pulses to selected windings of the stepper motor to cause the stepper motor to rotate in the direction necessary to move the transducer heads to a predetermined park position at the inner diameter of the disc whenever power is removed from the disc drive. Since the location of the heads at power down may not be known, the timing of the pulses is such that a sufficient number of steps will be taken to move the transducer heads to the parking zone within the time alloted even if the heads were at the outermost track. Step pulses will continue to be generated until the back EMF of the spindle motor is insufficient to generate such pulses. After the transducer heads are at the predetermined parking location, any additional steps will cause the actuator to contact a mechanical 'inner crash stop' designed to prevent damage to the transducer heads from contact with the clamp which retains the discs.

Method and means for parking read/write heads in a disc drive using the

A thermal test tract is provided outside the user-accessible area on the disc. A tack complete of a known frequency is then written on the either side of this thermal test track, preferably half the usual track separation distance away. To develop a thermal compensation constant, the transducer is moved to the thermal test track with no compensation applied. In this way, any thermally induced off-track error, which would affect seeks to user-accessible data tracks, will be reflected in the off-track from the nominal position of the thermal test track. The transducer is now moved in a series of defined increments smaller than normal track-to-track steps, or 'micro-steps,' away from the uncompensated position of the thermal track toward one of the tracks written with the known frequency. When the data on the written track to the side of the thermal test track is detected, a note is made of the number of micro-steps the transducer has been moved. The transducer is then micro-stepped incrementally in the opposite direction until the data written on the other side of the thermal test track is detected. A simple comparison of these two micro-step counts will yield the existing thermal shift, which can be converted into a thermal compensation constant for the transducer positioning mechanism by means of a simple look-up table.

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Santa Clara County, CA, United States of America

James N Krause