International Business Machines Corporation

Western Digital Corporation

Western Digital Technologies, Inc.

Michael Charles Stich

John Jeffrey Stephenson

Todd Barry Anderson

Martin R Green

Hal Hjalmar Ottesen

Arun Sharma

Eric Gregory Oettinger

Mark David Hagen

Muthuthamby Sri-Jayantha

David W Collins

Koichi Arai

Hakam D Hussein

Jeffrey E Mason

Hjalmar H Ottesen

John J Neesz

Lawrence P Segar

John B Resman

Mark E Bofferding

Joseph M Humel

William J Hunt

In a disk drive having a dual stage actuator, a method to improve head switching time by aligning a target head with a target track before a head switch occurs by using a second stage actuator attached to the target head to align the target head with the new track. The radial offset required to align the target head with the target track is either calibrated at startup or is measured dynamically during normal disk operations. A dual stage actuator with either a milli-actuator second stage or a micro-actuator second stage, positions a read/write head over a disk surface. The disk drive has a radial offset table for storage of radial offsets for head switches.

Disk drive with dual stage actuator radial offset calibration

A disk drive includes a voice coil motor (VCM) and a VCM power source circuit which is coupled to a standard power supply having a fixed voltage. During seek operations the VCM power source circuit provides a boosted voltage, greater than the fixed supply voltage, for the VCM. The VCM power source circuit provides the boosted voltage independently from the back EMF generated in the voice coil motor. The increased VCM voltage allows faster access times and more efficient VCM operation.

Faster access time in a disk drive by utilizing increased VCM potential voltage

A method to adaptively reduce error introduced by the coil current rise time. A disk drive with a moving arm actuator driven by a voice coil motor is controlled by periodically modeling the coil current rise time. An adjustment to a commanded current value is based on the model of the coil current rise time and a magnitude change in commanded value. The model of the coil current is based on a linear approximation to the exponential rise time of the coil current. The commanded value is adjusted to compensate for the error in the control effort. For small commanded value differences no compensation is made for the coil current rise time. For medium command value differences a slope intercept equation is used to compute the compensated commanded value. For large commanded value differences half of an estimate of the maximum largest physical current change is used. The adjustment is made by the estimator in a position error signal feedback control system. The voice coil rise time adjustment is made to a voice coil motor control signal. The actuator velocity estimate is also improved with the model of the coil current rise time.

Disk drive with voice coil motor rise time manager

An initialization for runout cancellation for a hard disk drive such as a Small Computer System Interface (SCSI) hard disk drive. The hard disk drive at a servo sample rate updates a set of state variables. At an index wedge the state variables are stored to a memory. Upon a command to perform a head switch the hard disk reads the previously stored state variables from the memory. The previously stored state variables are used to adjust the repeatable runout based on the location of a head relative to an index wedge.

initialization method and apparatus for a runout cancellation method

A direct access storage device and a method of operation thereof where the output of the circuit which controls energy to the position actuator for the head may be changed at times between receipt of sequential position error signals from the medium. Instead of waiting for the next position error signal, a computation is done based on at least the current position and the desired position of the head as to when the head velocity will be equal to a desired velocity. The optimum time to switch is estimated, the energy required to achieve a predetermined velocity and a predetermined offset with respect to the desired position are computed, and operation is conducted accordingly. The amount of energy may again be changed at a time subsequent to the estimated time. The predetermined velocity and the predetermined offset may be zero or may have values other than zero in accordance with the requirements of the track following controller.

Inter-sample switching of servo control in direct access storage devices

In a disk storage device dedicated servo system, a reference track is written in the outer guardband of the servo surface and each of the data surfaces. Supplemental position error signal (PES) values are obtained from the difference of servo and data surface samples at a plurality of locations around the disk and stored for access during read/write operations. The supplemental PES values are combined with the dedicated surface PES values to yield a composite PES that more accurately follows the data track centerline of the disk surface being addressed. The supplemental PES values are also periodically updated. To provide a more accurate correction of the composite PES, two consecutive supplemental values are used and an interpolation is calculated to provide a continuously changing supplemental PES value for modification of each sector actuator drive pulse between the two current supplemental PES values. Provision is also made in the apparatus to make the correction technique tolerant of tangential skew that may make tracks unreadable because of early or late timing through the provision of sequences of alternative early and later sample sector sequences.

Disk drive servo control

Disclosed is a method for performing a seek operation in a disk drive using current in the saturation mode to accelerate and decelerate the actuator arm. In a first embodiment, several measurements are made during the acceleration portion of the seek to estimate the deceleration available in saturation mode. In a second embodiment, the point at which the current is switched from acceleration current to deceleration current is adjusted based upon the position where the actuator arm comes within a desired amount of the velocity of a velocity profile assuming worst case conditions.

Method and apparatus for performing a seek

A controller for a voice coil motor driven disk file actuator is described. The device has an online adjustable gain characteristic for controlling movement of the actuator assembly and an estimator that estimates actuator velocity and bias. Forward gain is estimated from position and coil current measurements and compared with a nominal value to create an error signal used to adjust the controller and estimator gain characteristics. The control technique allows changes in the open loop system without changing the closed loop performance. By monitoring loop gain it is possible to alter compensator gains to maintain a constant closed loop performance.

Adaptive control technique for a dynamic system

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

Michael Charles Stich