A servo control system provides adaptive compensation for a variety of tracking and seek problems found in disk drives. The servo control system is ideally implemented in digital form for accuracy, speed and compactness. A first embodiment includes two modes, a tracking (or position) mode and a seek (or velocity) mode, each mode employing a variety of compensation functions. A second embodiment includes a single comprehensive control system which functions during both tracking and seek operations.

Digital servo control system for use in disk drives

A positioning control system for a controlled device, such as a disk drive head, estimates a moving time for moving the controlled device from a current position of the controlled device to a newly designated position. The system sets the estimated moving time as a target moving time. Positioning elements then move the controlled device to the designated position in response to the target moving time. Positioning elements may include an actuator for moving the controlled device, a position detector for tracking movement of the controlled device, and a control element for controlling the actuator. The control element calculates a trajectory for the controlled device to follow based on the target moving time, and controls the actuator based on the calculated trajectory and controlled device position as determined by the position detector. The control system may also have a position correcting element included in the control element. The correcting element compares the actual position of the controlled device with a calculated position of the controlled device and makes necessary adjustments.

Positioning control system

A disk drive comprising an actuator including a head, a disk, and a processor connected to the actuator by a flex circuit cable. The processor under the control of a program to: apply a control signal for a seek operation and to apply a bias signal to the control signal to approximate the bias imparted by the flex circuit cable. The bias is determined from a data structure that stores: bias values for track zones representative of a first and second bias curves that approximate a bias imparted by the flex circuit cable upon the actuator as the actuator moves the head from the OD to the ID of the disk and from the ID to the OD of the disk, respectively. The bias values representative of the first and second bias curves are determined based upon a non-linear apportionment of track zones.

Disk drive compensation of bias imparted by a flex circuit cable utilizing a dual bias curve estimation scheme

A disk drive is disclosed comprising a disk, a head coupled to a distal end of an actuator arm, a voice coil motor (VCM) operable to rotate the actuator arm about a pivot in order to actuate the head radially over the disk, and a ramp located near an outer edge of the disk for parking the head. A first back electromotive force (BEMF) voltage of the VCM is measured, and a current is applied to the VCM for a first interval in order to move the actuator arm in a first radial direction. After the first interval, a second BEMF voltage of the VCM is measured, and whether the head is parked is detected in response to the first and second BEMF voltages.

Disk drive detecting when head is parked on ramp

An embodiment of the present invention is a disk drive comprising a rotating disk with a recording surface, a transducer in communication with the surface and swept radially over the surface by a servo-actuator, a variable gain read amplifier connected to the transducer, an analog-to-digital converter (ADC) attached to the variable gain amplifier, an erase frequency oscillator coupled to the transducer for erasing of the disk surface, a memory for storing digital outputs appearing at the ADC, and a controller for signaling the servo-actuator to move to such radial positions that result in transducer read amplitudes that are a percentage of previous read amplitudes represented in the digital memory. Bit-synchronism between tracks is maintained by writing an initial clock track with closure and then writing a next clock track including a regular sequence of clock bursts a half-track space offset such that the initial clock track can be read in between writing clock bursts and the read signal is used to frequency-lock an oscillator which is used as a reference for the writing of clock bursts of the next track. A checkerboard pattern of clock bursts is thus created. All subsequent tracks are built incrementally by stepping off a half of a track from the last track written, which comprises clock bursts, and writing a next new sequence of clock bursts that interlace with the previous track's clock bursts.

Self-servowriting disk drive and method

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

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

A method and an apparatus for optimizing movement of a disk drive's head actuator arm away from a magnetic latch that holds the arm in a parked position at the Inner Diameter (ID) of a disk. Current energizing of the arm's actuator motor moves the arm away from the magnetic latch and is controlled to compensate for any change in magnetic holding force. When the disk drive is powered up, a current pulse of one polarity is applied to the actuator motor. This initial current pulse normally moves the arm away from the magnetic latch and is followed by a current pulse of the opposite polarity to decelerate movement of the arm. If this initial sequence fails to move the arm away from the magnetic latch, the magnitude of the two current pulses is increased, and the opposite polarity pulse is followed by a small magnitude current of the one polarity. The read signal from the head is monitored to indicate that the arm has moved into the disk's central databand area, and then into the disk's Outer Diameter (OD) area. At this point, the magnitude of current of the one polarity is increased in small steps to gently bring the arm into contact with the disk drive's OD crash stop. The current of the one polarity is then decreased in small steps, and the arm gently moves away from the OD crash stop. The head signal is monitored until the head is positioned at a selected track.

Method and apparatus for moving a disk drive actuator away from a magnetic latch

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 controller for a voice coil motor driven disk file actuator (10) is described. The device has an online adjustable gain characteristic for controlling movement of the actuator assembly and an estimator (56) 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.

Todd Barry Anderson

Papers

Adaptive control technique for a dynamic system

Disk drive servo control

Method and apparatus for moving a disk drive actuator away from a magnetic latch

Sector servo seek control

Adaptative control technique for a dynamic system