Western Digital Technologies, Inc.

Kabushiki Kaisha Toshiba

Toshiba Electronic Devices & Storage Corporation

Jiangang Liang

Gabor Szita

Siri S Weerasooriya

Gary W Calfee

Yilin Cai

Hongchao Tim Zhao

Wei Guo

Charles A Park

Anton Gerasimov

Ting-Chun Janet Liu

Zhi Wang

Li Zhang

Don Brunnett

Brian P Rigney

Duc H Banh

Yun Hong

Tony Huang

Jeng-Yu Wang

A method of determining radial position of a magnetic head that includes a first read sensor and a second read sensor includes: with the first read sensor, detecting a servo spiral formed on a disk; with the second read sensor, detecting the servo spiral; measuring a time interval between when the servo spiral is detected by the first read sensor and when the servo spiral is detected by the second read sensor; and based on the time interval, determining a radial position of the magnetic head relative to the disk.

Determining absolute position on HDD spiral patterns using dual TDMR readers

A method for writing servo information in a disk drive that includes a write head and one or more recording surfaces includes: writing a first portion of a first spiral with the write head on a first recording surface of the one or more recording surfaces while controlling a radial position of the write head with a controller that is configured with a first set of controller parameter values; after the read head crosses a second spiral formed on a second recording surface of the one or more recording surfaces, determining a radial position error for the write head based on information associated with the second spiral; and in response to the radial position error exceeding a disturbance threshold value, writing a second portion of the first spiral with the write head while controlling the radial position of the write head with the controller while the controller is configured with a second set of controller parameter values.

Gain scheduled controller to handle unpredictable disturbances during spiral write

Motion of a first actuator in a multi-actuator drive is prevented from affecting a second actuator in the drive or from being affected by the second actuator. A coupling coordinator generates a hold command for the second actuator based on an operation to be carried out using the first actuator, where the hold command is generated before commands to carry out the operation are issued. The hold command may cause an aggressor actuator in the drive to halt a disturbance-generating operation being performed by the aggressor actuator or delay initiation of such an operation that is to be performed by the aggressor actuator. The hold command may cause a victim actuator in the drive to pause the execution of a sensitive operation being performed by the victim actuator or delay initiation of such an operation that is to be performed by the victim actuator.

Reducing the effect of actuator cross-coupling in split actuator drives

A hard disk drive (HDD) is configured to move a read head over a region of a storage surface that includes unreadable segments of reference spirals that have been overwritten by a reference spiral in a set of spirals that is currently being written on the storage surface. By moving the read head across the region of the storage surface at a return radial velocity that is selected such that the write head crosses no consecutive reference spirals at an unreadable segment, the servo system of the HDD does not experience an error due to crossing multiple consecutive reference spirals at unreadable segments. Thus, a set of spirals that includes partially damaged reference spirals can be employed to control the position of a read head. Consequently, a second surface is not required for the set of spirals employed in controlling the writing process.

Spiral-based self-servo-write on single disk surface

A repeatable runout (RRO) is accurately compensated for while moving a magnetic head radially across a disk surface. An iterative learning control algorithm is employed to determine appropriate feed-forward coefficients for an RRO compensation signal for each of a plurality of radial locations across the disk surface. The feed-forward coefficients are determined by performing multiple iterations of continuously moving the magnetic head across the disk surface along a target path while measuring a position error signal that indicates the radial error between the magnetic head and the target path. With each iteration, the iterative learning control algorithm computes new feed-forward coefficients for each of the plurality of radial locations, where the new feed-forward coefficients are selected to reduce the measured position error signal when employed to move the magnetic head along the target path.

Accurate repeatable runout compensation in disk drives during seeks

In an in-drive erase process in a single-surface HDD, erase spirals on the surface being erased can be employed to control writer position. A reader-to-writer timing offset value is determined for a plurality of radial locations on the surface to be erased, and an erase window is determined for a radial location disposed between two erase spirals. The erase window includes an erase start time, which is based on a spiral exit time of a reader and the reader-to-writer timing offset value for the radial location, and an erase stop time, which is based on a spiral encounter time of the reader and the reader-to-writer timing offset value. The erase window prevents complete erasure of erase spirals, so that the servo system of the HDD can continue to servo off of the erase spirals. The erase spirals may be written with a lower slope than conventional spiral tracks.

Single surface in-drive erase

A reference spiral is written on a recording surface of a hard disk drive. By launching writing of fine guide spirals from a launch point that is disposed on a pre-existing coarse guide spiral, writing of the fine guide spiral can be launched in response to a write head crossing the pre-existing coarse guide spiral, rather than in response to a precisely timed event. To enable launch points being disposed on pre-existing coarse guide spirals, launch points are not all located at the same radial position on the recording surface.

Spiral write launch while servoing on reference guide spirals

A reference spiral is written on a recording surface of a magnetic storage disk that is free of position or timing information. The reference spirals are written on the recording surface with a substantially uniform slope by using open loop control of the position of a read/write head in conjunction with an iterative learning control scheme. A voltage profile applied to a voice coil motor is adapted over multiple iterations of moving the read/write head across the recording surface to closely approximate a target voltage profile, and the reference spiral is written using the adapted voltage profile. In addition, ramp contact detection based on actuator current profile may be employed to achieve full utilization of available actuator stroke.

Writing spirals with accurate slope on a disk drive media

A write head is positioned over a disk surface of a hard disk drive during a self-servo write process. A virtual window mode is employed for positioning the write head, in which the read channel of the hard disk drive continuously searches for servo spirals, but spiral detection is disabled except during specific time intervals, or 'virtual windows.' Each virtual window is associated with one specific servo spiral on the disk surface, and has a predetermined duration. The duration and timing of these virtual windows may be selected to ensure that spiral detection is enabled while a read head of the hard disk drive passes over the associated servo spiral, even when servo spiral placement is not ideal.

Virtual window mode for guide spiral servo demodulation

A magnetic write head is positioned based on position signals generated by a read head as the read head crosses a plurality of reference spirals. The spiral gate for monitoring a particular reference spiral is timed to begin at a time based on the radial position of the magnetic head when crossing the preceding reference spiral. In this way, the spiral crossing time for the particular reference spiral can be estimated with sufficient accuracy that the spiral gate coincides with the magnetic head crossing the particular reference spiral. Consequently, spiral detection is assured, even in the presence of large non-repeatable runout.

Accurate spiral gate positioning in the presence of large non-repeatable runout

During a self-servo write process, servo sectors that have uniform radial spacing are written on a disk surface. As part of the in-drive writing of the servo sectors, a radial offset between a reader element and a writer element of a magnetic head is measured. The measured radial offset, or micro-jog, is compared to a known nominal micro-jog value for the current radial position of the magnetic head. When the measured micro-jog value does not match the nominal micro-jog value, an appropriate correction to the self-servo write step size is applied to the radial spacing between the servo sectors being written. Variations from ideal servo spiral slope that are inherent in some servo spirals can be compensated for, thereby improving the uniformity of radial spacing of data tracks associated with the servo sectors.

Spiral pitch correction based on micro-jog variation

In an in-drive erase process for erasing disk surfaces of a hard disk drive, erase spirals are written on multiple disk surfaces and at a different write frequency than that of other data patterns on the disk surfaces. The erase spirals written on a first disk surface can be used to control an erase process on a portion of the remaining disk surfaces. Erase spirals are then written on a different disk surface and can then be used to erase all data on the first disk surface. Consequently, even when every disk surface includes previously written data patterns that can potentially interfere with control of the erase process, the erase spirals so written can control the erase process with sufficient precision to thoroughly erase each disk surface.

Erase coarse guide spiral-based in-drive erase process

A disk drive is disclosed comprising a disk comprising servo data, and a head actuated over the disk. An offset rrepresenting a difference between an axial rotation of the disk and an axial rotation of the servo data is estimated, and radial dependent timing compensation values are generated in response to the estimated r. A phase error is generated in response to the servo data, and a control signal is generated in response to the phase error and the radial dependent timing compensation values. A frequency of an oscillator is adjusted in response to the control signal.

Disk drive generating a disk locked clock using radial dependent timing feed-forward compensation

A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of spiral tracks, wherein each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark. An offset rrepresenting a difference between an axial rotation of the disk and an axial rotation of the spiral tracks is estimated. Radial dependent timing compensation values are generated in response to the estimated r. A phase error is generated in response to the sync marks in the spiral track crossings. A control signal is generated in response to the phase error and the radial dependent timing compensation values, and a frequency of an oscillator is adjusted in response to the control signal.

Disk drive servo writing from spiral tracks using radial dependent timing feed-forward compensation

A method is disclosed for selecting a global digital-to-analog setting for a plurality of heads in a disk drive, the disk drive comprising a plurality of disk surfaces and a plurality of respective heads. The method comprises: adjusting a first digital-to-analog setting for a first head to generate a first signal, adjusting a second digital-to-analog setting for a second head to generate a second signal, selecting a first scalar setting for scaling the first signal, selecting a second scalar setting for scaling the second signal, and selecting the global digital-to-analog setting in response to the adjusted first digital-to-analog setting, the adjusted second digital-to-analog setting, the first scalar setting, and the second scalar setting.

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San Jose, CA, United States of America

Jiangang Liang