Patent Grant
8913338
Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
In the embodiment of
Each servo sector also comprises a compensation value, such as a repeatable runout (RRO) compensation value that compensates for a repeatable runout of the servo tracks due, for example, to written-in errors of the servo sectors 200-20N. In the embodiment shown in
The control circuitry 24 may abort a normal write operation when the PES (or a predicted PES) exceeds a write unsafe threshold in order to prevent the head from overwriting data in an adjacent data track. The PES may exceed the write unsafe threshold when, for example, the disk drive is subjected to a vibration that disturbs the servo system. The PES is compared to the write unsafe threshold after being adjusted by the compensation value of each servo sector. However, if the compensation value of a servo sector is unrecoverable due, for example, to a defect on the disk, the non-adjusted PES cannot be reliably compared to the write unsafe threshold. For example, the compensation value may increase the PES so that it exceeds the write unsafe threshold, but this cannot be detected when the compensation value is unrecoverable. When a compensation value of a servo sector is unrecoverable, the write operation may be aborted to ensure an off-track write condition does not occur. However, aborting the write operation each time a compensation value is unrecoverable may increase the latency of the disk drive and/or result in a relocation of data wedges away from a defective servo sector which is undesirable.
To overcome these problems, in one embodiment the write unsafe threshold is reduced from a first write unsafe threshold to a lower, second write unsafe threshold when a compensation value of a servo sector is unrecoverable. An example of this embodiment is illustrated in
The second, lower write unsafe threshold (WUS2) may be selected based on any suitable criterion (or criteria). In one embodiment, the WUS2 may be selected based on a predetermined worst case magnitude for the compensation value. This is equivalent to adding the worst case compensation value to the PES, and then comparing the adjusted PES to the normal WUS1 threshold. Accordingly, even under the worst case condition for the compensation value, the write operation need not be aborted since the adjusted PES will not exceed the WUS1 threshold. In one embodiment, the worst case magnitude for the compensation value may be determined based on the compensation values generated for the entire disk surface. In another embodiment, the worst case magnitude for the compensation value may be determined based on at least two recoverable compensation values of the same servo track.
This embodiment is understood with reference to
In another embodiment, the compensation value (e.g., RRO) for at least one servo sector of the target data track shown in
In another embodiment, a Δ may be generated for each data track that comprises at least one unrecoverable compensation value. For example, the Δ may be generated during a manufacturing operation such as when executing a defect scan of the disk in order to identify the data tracks comprising an unrecoverable compensation value. In another embodiment, the Δ may be generated while accessing a data track during a normal write/read operation while the disk drive is deployed in the field. For each data track comprising an unrecoverable compensation value, the corresponding Δ may be stored in a lookup table. Referring to the example of
In one embodiment, the control circuitry 24 may generate a predicted PES (pPES) at each servo sector during a write operation that predicts the value of the PES at a following servo sector. For example, in one embodiment the control circuitry may generate a predicted PES for a next servo sector based on:
pPES[k+1]=2·PES[k]−PES[k−1]
The control circuitry 24 may abort a write operation if the pPES exceeds a corresponding write unsafe threshold (pWUS1). In one embodiment, the pWUS1 threshold is less than the normal WUS1 threshold to compensate for the error in generating the pPES. In one embodiment, when the compensation value of servo sector k is unrecoverable, the PES[k] in the above equation may be generated with a zero compensation value, and the pPES[k+1] may be compared to a pWUS2 threshold that is less than the pWUS1 threshold. For example, the pWUS2 threshold may be generated by subtracting the Δ described above from the pWUS1 threshold. In this manner when an unrecoverable compensation value is encountered during a write operation, the servo system may continue the write operation if the pPES[k+1] is less than the lower pWUS2 threshold.
Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions disclosed herein.
This application claims priority to provisional U.S. Patent Application Ser. No. 61/829,089, filed on May 30, 2013, which is hereby incorporated by reference in its entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6671119 | Baumann et al. | Dec 2003 | B2 |
| 6735033 | Codilian et al. | May 2004 | B1 |
| 6853511 | Seng et al. | Feb 2005 | B2 |
| 6882489 | Brunnett et al. | Apr 2005 | B1 |
| 6975468 | Melrose et al. | Dec 2005 | B1 |
| 6995942 | Schmidt | Feb 2006 | B2 |
| 6999266 | Schmidt | Feb 2006 | B1 |
| 7002770 | Schmidt | Feb 2006 | B2 |
| 7023649 | Schmidt | Apr 2006 | B2 |
| 7027255 | Schmidt | Apr 2006 | B2 |
| 7130142 | Hara | Oct 2006 | B2 |
| 7136245 | Mori et al. | Nov 2006 | B2 |
| 7154690 | Brunnett et al. | Dec 2006 | B1 |
| 7193798 | Byrd et al. | Mar 2007 | B2 |
| 7253982 | Brunnett et al. | Aug 2007 | B1 |
| 7423828 | Emo et al. | Sep 2008 | B2 |
| 7474491 | Liikanen et al. | Jan 2009 | B2 |
| 7502283 | Schmidt et al. | Mar 2009 | B2 |
| 7545593 | Sun et al. | Jun 2009 | B1 |
| 7570445 | Alfred et al. | Aug 2009 | B2 |
| 7580212 | Li et al. | Aug 2009 | B1 |
| 7633698 | Finamore et al. | Dec 2009 | B2 |
| 7855851 | Shirai | Dec 2010 | B2 |
| 8315006 | Chahwan et al. | Nov 2012 | B1 |
| 20040125496 | Schmidt | Jul 2004 | A1 |
| 20050128634 | Schmidt | Jun 2005 | A1 |
| 20050141129 | Schmidt et al. | Jun 2005 | A1 |
| 20050152057 | Schmidt | Jul 2005 | A1 |
| 20050152058 | Schmidt | Jul 2005 | A1 |
| 20050190480 | Mori et al. | Sep 2005 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 61829089 | May 2013 | US |
