Magnetic disk drive with head retraction control

• US 20090034114A1
• Filed: 09/19/2008
• Published: 02/05/2009
• Est. Priority Date: 10/19/2005
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Hitachi Global Storage Technologies Netherlands BV (Western Digital Corporation)
• Inventors: Kuroki, Kenji, Kuramoto, Kenichi, Aida, Toru, Kotani, Yasuhiro
• Granted Patent: US 7,706,097 B2
• Time in Patent Office: Days
• US Class Current: 360/75
• CPC Class Codes: G11B 19/043 by detecting a free-fall condition
• CPC Class Codes: G11B 21/12 Raising and lowering; Back-spacing or forward-spacing along track; Returning to starting position otherwise than during transducing operation
• CPC Class Codes: G11B 5/54 with provision for moving the head into or out of its operative position or across tracks
• CPC Class Codes: G11B 5/5526 Control therefor; circuits, track configurations or relative disposition of servo-information transducers and servo-information tracks for control thereof G11B5/556 takes precedence

Abstract

Embodiments of the invention improve utility of a magnetic disk drive in which a head is retracted if the magnetic disk drive is in a dropping state. In one embodiment, an HDC/MPU provided in a magnetic disk drive judges whether the magnetic disk drive is in a dropping state based on an output from an acceleration sensor which may detect an acceleration and performs a retraction operation of a head. After the HDC/MPU judges that a drop is occurring, the HDC/MPU detects whether the drop judgment is incorrect according to whether a shock sensor detects a shock occurrence and changes the drop judgment condition based on a detection history of detected incorrect judgments.

Claims

1. A magnetic disk drive comprising:

a magnetic disk;

a head which accesses the magnetic disk;

a sensor section configured to detect an acceleration;

a first judgment section which judges whether a drop is occurring based on an output of the sensor section;

a processing section which executes a retraction of the head if the first judgment section judges that a drop is occurring; and

a second judgment section which detects the occurrence of a shock based on the output of the sensor section;

wherein, after the first judgment section judges that a drop is occurring, the processing section detects whether the drop judgment is incorrect according to whether the occurrence of a shock is detected by the second judgment section and changes the drop judgment condition of the first judgment section based on a history of detected incorrect drop judgments.

2. A magnetic disk drive according to claim 1, wherein:

the sensor section includes a gravity sensor which generates a detection signal by detecting a zero gravity state, and a shock sensor which detects a change in acceleration due to a landing shock;

the first judgment section judges whether a drop is occurring based on the detection signal of the gravity sensor; and

the second judgment section judges whether a shock is occurring based on the detection signal of the shock sensor.

3. A magnetic disk drive according to claim 1, wherein if the number of incorrect drop judgments exceeds a predetermined number, the processing section changes the judgment condition of the first judgment section so as to more stringently make a drop judgment.

4. A magnetic disk drive according to claim 1, wherein the judgment condition is changed by shifting the timing at which a drop judgment is made after a change in the output signal of the sensor section is detected by the first judgment section.

5. A magnetic disk drive according to claim 1, wherein:

the first judgment section makes a drop judgment by comparing a threshold with the acceleration detected by the sensor section; and

the judgment condition is changed by modifying the threshold.

6. A magnetic disk drive according to claim 1, further comprising a low-pass filter between the sensor section and the first judgment section;

wherein if the number of incorrect drop judgments exceeds a predetermined number, the low-pass filter is disabled or a passband of the low-pass filter is increased for higher frequencies.

7. A magnetic disk drive comprising:

a magnetic disk;

a head which accesses the magnetic disk;

a sensor section configured to detect an acceleration;

a first judgment section which judges whether a drop is occurring based on the output of the sensor section;

a processing section which executes a retraction of the head if the first judgment section judges that a drop is occurring; and

a second judgment section which detects the occurrence of a shock based on the output of the sensor section;

wherein the processing section performs re-loading of the head if the affirmative drop judgment made by the first judgment section is cancelled after the head begins to be retracted, and if no shock is detected by the second judgment section after the affirmative drop judgment is cancelled.

8. A magnetic disk drive according to claim 7, wherein the processing section performs re-loading of the head when a first predetermined amount of time has passed with no shock detected by the second judgment after the affirmative drop judgment is cancelled by the first judgment section.

9. A magnetic disk drive according to claim 8, wherein if a shock is detected by the second judgment section after the head begins to be retracted, the processing section performs re-loading of the head when a second predetermined amount of time has passed.

10. A magnetic disk drive according to claim 9, wherein the first predetermined amount of time is shorter than the second predetermined amount of time.

11. A magnetic disk drive according to claim 7, wherein if the affirmative drop judgment made by the first judgment section is cancelled after the head begins to be retracted, the processing section performs re-loading of the head if no shock is detected by the second judgment section within a predetermined period of time including the point of time when the affirmative drop judgment is cancelled.

12. A magnetic disk drive according to claim 7, wherein if a shock is detected by the second judgment section after the head begins to be retracted, the processing section performs re-loading of the head when a second predetermined amount of time has passed after the shock detection detected by the second judgment section is cancelled.

13. A magnetic disk drive according to claim 12, wherein if a new shock is detected by the second judgment section before the second predetermined amount of time elapses, the processing section performs re-loading of the head when the second predetermined amount time has passed after the new shock detection detected by the second judgment section is cancelled.

14. A magnetic disk drive according to claim 7, wherein in the case where a shock is detected by the second judgment section and the shock detection is cancelled, and the case where the affirmative drop judgment is cancelled without a shock detected by the second judgment section, the time from the cancellation to the re-loading of the head is capable of being varied depending on the cases.

15. A magnetic disk drive comprising:

a magnetic disk;

a head which accesses the magnetic disk;

a sensor section configured to detect an acceleration; and

a processing section which judges whether a drop is occurring based on the output of the sensor section and executes a retraction of the head if the processing section judges that the drop is occurring;

wherein, the processing section executes the retraction of the head in such a manner that at least until the head reaches the periphery of the magnetic disk, the head position continues to be detected based on servo data recorded on the magnetic disk and a head seek speed continues to be controlled by using the detected head position.

16. A magnetic disk drive according to claim 15, wherein the processing section continues to control the head seek speed based on the servo data during the retraction of the head until the head reaches a non-data area on the magnetic disk.

17. A magnetic disk drive according to claim 15, wherein:

an actuator for moving the head is provided; and

the processing section drives the actuator so that the head is retracted at a constant speed when the head is retracted from the periphery of the magnetic disk to a head retraction place.

18. A magnetic disk drive according to claim 17, wherein:

the actuator is provided with a voice coil motor which generates a driving force to move the head; and

the processing section drives the actuator so that the back electromotive force of the voice coil motor falls within a predetermined range when the head is retracted from the periphery of the magnetic disk to the head retraction place.

19. A magnetic disk drive according to claim 15, wherein:

an actuator for moving the head is provided; and

the processing section retracts the head from the periphery of the magnetic disk to the head retraction place by supplying a predetermined level of a drive voltage or a drive current to the actuator.