Western Digital Technologies, Inc.

Other

Vinay Kumar Agarwal

Robert L Cloke

Hemant Melkote

Raffi Codilian

Jack M Chue

Edgar D Sheh

A method and system for determining whether a consensus has been achieved for adding a block to a distributed ledger. The system receives a candidate block to add to the distributed ledger and receives block approvals of approving participants for the candidate block. The system calculates a total block approval stake that the approving participants have in the distributed ledger. The system identifies a total stake that participants have in the distributed ledger. When the total block approval stake is at least a threshold fraction of the total skate, the system indicates that the consensus has been achieved for adding the candidate block to the distributed ledger.

Proof-of-approval distributed ledger

A method is disclosed for writing servo patterns for tracks on a rotating magnetic disk medium of a magnetic disk drive. In the method, track following is performed along a reference track, defined by previously written servo burst patterns, using a servo loop having a closed-loop response. A position error signal is generated for the reference track based on the track following. A correction signal is generated based on the track following using an observer of a one-dimensional state model that is equivalent to the two-dimensional state model of the servo loop. Servo patterns are written at a target radial location on the magnetic disk medium during track following of the reference track. The position error signal of the servo loop is adjusted based on the correction signal to reduce radial error propagation from the reference track to the servo burst patterns at the target radial location.

Method and apparatus for self servowriting of tracks of a disk drive using an observer based on an equivalent one-dimensional state model

A method of writing product servo sectors to a disk of a disk drive is disclosed. An external spiral servo writer writes a plurality of spiral tracks to the disk by actuating in a closed loop system a head positioning pin inserted into the disk drive. Each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark. The high frequency signal and sync marks in the spiral tracks are demodulated to maintain synchronization of a servo write clock as well as maintain the head along a circular target path while writing product servo sectors to the disk.

Using an external spiral servo writer to write spiral tracks to a disk to facilitate writing product servo sectors to the disk

A method is disclosed for defining tracks on a rotating magnetic disk medium of a disk drive. Reference tracks are followed using a servo control loop while writing servo burst patterns defining a first target servo track. The servo control loop includes a two-dimensional digital state compensator having a first input that receives position error signals, a first output that generates control signals for positioning a transducer head, a second output that generates track-following state variables, and a second input that receives processed and stored track-following state variables. The first target track is followed using the servo control loop while servo burst patterns are written, and while the processed and stored track-following state variables corresponding to the servo burst patterns defining the first target track are applied to the second input.

Method and apparatus for self servowriting of tracks of a disk drive using a servo control loop having a two-dimensional weighted digital state compensator

A method of writing product servo bursts to a disk in a disk drive is disclosed. An external spiral servo writer comprising a head positioning pin and head positioning mechanics periodically writes a plurality of reference servo bursts in a plurality of spiral reference patterns to the disk. The reference servo bursts in the spiral reference patterns are processed to write product servo bursts to the disk. In one embodiment control circuitry within the disk drive processes the reference servo bursts to self-servo write the disk drive, and in another embodiment an external product servo writer processes the reference servo bursts to write the product servo bursts to the disk. In one embodiment, a slope of each spiral reference pattern is selected so that each spiral reference pattern is written over at least twenty revolutions of the disk to increase the accuracy of the head position error generated from the reference servo bursts.

Using an external spiral servo writer to write spiral reference patterns to a disk to facilitate writing product servo bursts to the disk

A method is disclosed for determining repeatable runout (RRO) cancellation values in a disk drive having a head disk assembly (HDA) and a sampled servo controller. The HDA includes a disk having distributed position information in servo wedges, a rotary actuator carrying a head that periodically reads the position information, and a voice coil motor circuit that responds to a control effort signal. The servo controller periodically adjusts the control effort signal during a track-following operation. In the method, the position information related to a predetermined track is read during track following for more than one disk rotation. The position information is averaged for each servo wedge obtained during the disk rotations. The averaged servo position values are filtered with a filter for compensating effects of the sampled servo controller, which tend to distort the averaged servo position values, to generate the RRO cancellation values for the predetermined track.

Method for determining repeatable runout cancellation values in a magnetic disk drive using filtering

A method is disclosed for writing servo patterns for tracks on a rotating magnetic disk medium of a disk drive. Servo patterns are written on a reference track of the disk medium. Track following of the written servo patterns on the reference track is performed using a servo loop having a closed-loop response. A position error signal is generated for the reference track based on the track following. A correction signal is generated based on the track following using an observer of a one-dimensional state model that is equivalent to a two-dimensional state model of the servo loop. Servo patterns are written on a target track during track following of the reference track. The position error signal of the servo loop is adjusted based on the correction signal to reduce radial error propagation from the reference track to the target track.

A method is disclosed for defining tracks on a rotating magnetic disk medium of a disk drive. Reference tracks are followed using a servo control loop while writing servo burst patterns defining a first target servo track. The servo control loop includes a two-dimensional digital state compensator having a first input that receives position error signals, a first output that generates control signals for positioning a transducer head, a second output that generates track-following state variables, and a second input that receives stored track-following state variables. The first target track is followed using the servo control loop while servo burst patterns are written, and while the stored track-following state variables corresponding to the servo burst patterns defining the first target track are applied to the second input.

Method and apparatus for self servowriting of tracks of a disk drive using a servo control loop having a two-dimensional digital state compensator

The present invention may be embodied in a method and a disk drive for improving head position accuracy during track following through real-time identification of external vibration. A selected track is followed using a servo control loop having a nominal gain and being responsive to position error signal samples generated based on a difference between head position samples and a reference head position value. A spectral power value within a predetermined frequency band is determined from a sequence of the position error signal samples. If a property of the spectral power value exceeds a threshold, the gain of the servo control loop is increased within the predetermined frequency band to attenuate the effect of external vibration on the position of the head over the selected track during track following.

Growing community of inventors

Cupertino, CA, United States of America

Vinay Kumar Agarwal