Disk file with clearance and glide measurement and early head crash warning

• US 5,410,439 A
• Filed: 02/22/1994
• Issued: 04/25/1995
• Est. Priority Date: 05/19/1992
• Status: Expired due to Term

• Current Assignee: Hitachi Global Storage Technologies Netherlands BV (Western Digital Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Egbert, Gary T., Ottesen, Hal H., Smith, Gordon J.
• Primary Examiner(s): Psitos, Aristotelis
• Assistant Examiner(s): WILSON, JAMES
• Application Number:
  US08/200,838
• Time in Patent Office: 427 Days
• Field of Search: 360/75, 360/77.04, 360/77.05, 360/103, 360/73.03, 324/212
• US Class Current: 360/75
• CPC Class Codes: G06F 11/2205 using arrangements specific to the hardware being tested
• CPC Class Codes: G06F 11/2273 Test methods
• CPC Class Codes: G11B 19/04 Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions
• CPC Class Codes: G11B 19/20 Driving; Starting; Stopping; Control thereof
• CPC Class Codes: G11B 20/1816 Testing
• CPC Class Codes: G11B 33/10 Indicating arrangements; Warning arrangements G11B15/04, G11B19/04, G11B27/34, G11B27/36 take precedence

Abstract

The invention produces and maintains clearance and glide test results for a disk file, stores these results, and monitors head clearance and disk asperities over the useful life of the file using native disk file electronics. The disk file includes a predictive failure analysis component which utilizes clearance and glide test results to predict impending failure of a disk in the disk file.

Claims

1. In a disk file which includes a rigid disk, means for rotating the rigid disk, a read/write head, actuator means for moving the head across a surface of the disk, servo processor means controlling the actuator means and the means for rotating for radially positioning the head with respect to the surface and for setting a speed at which the disk is rotated, and data channel means connected to the head for reading signals from, and writing signals to, the disk, a combination for measuring flying height of the head with respect to the surface, the combination comprising:

digital signal processing means in the disk file and responsive to a clearance control signal which indicates speed of the disk for producing first signals corresponding to predetermined harmonics of a flying height measurement signal read from the surface by the head;

test condition means in the servo processor means for;

positioning the head with respect to a predetermined area of the surface where the flying height measurement signal is located;

setting an initial speed at which the disk is rotated;

selectively changing the speed at which the disk is rotated in a sequence of more than two discrete steps, the disk being rotated at a respective speed at each step of the sequence and being held constant at the respective speed at each step of the sequence; and

generating the clearance control signal at each respective speed;

test performance means in the disk file, connected to the digital signal processing means, and responsive to the first signals for producing at each respective speed spacing signals representing the flying height of the head with respect to the surface at each of a plurality of predetermined locations on a circumferential track on the surface; and

storage means in the disk file and connected to the test performance means for storing spacing signals for a plurality of circumferences on the surface.

2. The combination of claim 1, wherein:

the flying height measurement signal includes a periodic signal of a substantially constant period in a circumferential track on the surface.

3. The combination of claim 2, wherein:

the digital signal processing means includes means for sampling the flying height signal at a rate proportional to the speed at which the disk is rotated; and

the clearance control signal includes a portion which indicates the speed at which the disk is rotated.

4. The combination of claim 2, wherein:

the digital signal processing means includes digital filter means for obtaining the predetermined harmonics in response to filter coefficient values which are proportional to the speed at which the disk rotates; and

the control signal includes a portion indicating the filter coefficient values,

5. The combination of claim 1, wherein:

the digital signal processing means are responsive to the flying height measurement signal for producing a second signal proportional to the amplitude of the flying height measurement signal;

the combination further including;

glide test means in the disk file for providing a profile signal indicating defects on the surface in response to the second signal the profile signal being determined by the glide test means according to the difference between an average value of the second signal and an instantaneous value of the second signal.

6. The combination of claim 5, further including predictive failure analysis means connected to the storage means for providing a failure signal indicating disk file failure:

in response to spacing signals which indicate a change in the flying height of the head;

or

in response to the contact signal.

7. The combination of claim 1, wherein:

the digital signal processing means are further responsive to the flying height measurement signal for producing a second signal proportional to the amplitude of the flying height measurement signal;

the combination further including;

means in the disk file for producing third signals in response to the second signal, the third signals representing the difference between an average value of the second signal and an instantaneous value of the second signal and corresponding to a profile of a portion of the surface lying in a circumferential track containing the flying height measurement signal; and

glide test means in the disk file and responsive to the third signal for providing surface profile signals indicating contact between the head and the surface while the disk is rotating.

8. The combination of claim 1, further including predictive failure analysis means connected to the storage means for providing a failure signal indicating disk file failure:

in response to spacing signals which indicate a change in the flying height of the head;

or

in response to the third signals.

9. The combination of claim 1 further including predictive failure analysis means connected to the storage means for providing a failure signal indicating disk file failure:

in response to spacing signals which indicate a change in the flying height of the head.

10. In a disk file which includes one or more disks, means for rotating the one or more disks, one or more transducers, actuator means for moving the one or more disks, servo processor means controlling the actuator means and the means for rotating for radially positioning one or more transducers with respect to one or more disk surfaces and for setting a speed at which the disks are rotated, and data channel means for each transducer for reading signals from, or writing signals to, a disk, a method for in-situ measurement of the clearance between at least one transducer and a surface of a respective disk, the method including the steps of:

(1) in the disk file, at a first time initially measuring flying height of a transducer and the contour of the respective surface at each speed of a plurality of respective speeds, the plurality of respective speeds forming a sequence of more than two speeds in which the respective disk is held at each respective speed during the measuring;

(2) storing measurement results of step (1) in the disk file;

(3) operating the disk file;

(4) in the disk file, at a second time following the first time measuring the flying height of the head and the contour of the respective surface;

(5) providing from the disk file an indication of disk file failure if comparison of the stored results of step (2) and the measured results of step (4) indicate a change in the flying height or a change in the surface profile;

otherwise,

(6) storing the measurement results of step (4) in the disk file and performing steps (3)-(5).

11. The method of claim 10, wherein the measuring steps (1) and (4) include measuring the flying height of the head with respect to predetermined locations on each of a plurality of circumferential tracks on the respective surface.

12. In a disk file which includes one or more rigid disks, means for rotating the one or more rigid disks, one or more transducers, actuator means for moving the one or more transducers across corresponding surfaces of the one or more disks, servo processor means controlling the actuator means and the means for rotating for radially positioning one or more transducers with respect to one or more disk surfaces and for setting a speed at which the disks are rotated, and data channel means for each transducer for reading signals from, or writing signals to, a disk, a combination for evaluating disk file operation, the combination comprising, for at least one transducer:

digital signal processing means in a data channel means connected to the transducer, the digital signal processing means responsive to a clearance control signal indicative of the speed of the disks for producing a readback signal in response to a measurement signal read from a disk surface by the transducer;

test condition means in the servo processor means for;

positioning the transducer with respect to a predetermined area of the surface where the measurement signal is located;

setting an initial speed at which the disk is rotated;

selectively changing the speed at which the disk is rotated in a sequence of more than two discrete steps, the disk being rotated at a respective speed at each step of the sequence and being held constant for a period of time at each respective speed; and

generating the clearance control signal;

clearance test means in the disk file means, connected to the digital signal processing means, and responsive to the readback signal for producing spacing signals at each respective speed representing the flying height of the transducer with respect to the surface at each of a plurality of predetermined locations on a circumferential track on the surface;

glide test means in the disk file means, connected to the digital signal processing means, and responsive to the readback signal for producing profile signals representing a relative height of the surface at each of a plurality of predetermined locations on the circumferential track;

storage means in the disk file and connected to the clearance test means and to the glide test means for storing spacing signals and profile signals for a plurality of circumferences on the surface; and

predictive failure analysis means connected to the clearance test means, the glide test means, and the storage means, for providing a failure signal indicating disk file failure;

in response to spacing signals which indicate a change in the flying height of the transducer;

or

in response to profile signals which indicate an asperity on the surface.

13. The combination of claim 12, wherein the measurement signal includes a periodic signal of a substantially constant period positioned radially on the disk surface.

14. The combination of claim 13, wherein:

the digital signal processing means includes means for sampling the measurement signal at a rate proportional to the speed of the disks.

15. The combination of claim 13, wherein:

the readback signal includes predetermined harmonics of the measurement signal;

the digital signal processing means includes digital filter means for obtaining the predetermined harmonics in response to filter coefficient values which are proportional to the speed of the disks; and

the clearance control signal includes a portion indicating the filter coefficient values.

16. In a disk file which includes one or more rigid disks, means for rotating the one or more rigid disks, and processor means controlling the means for rotating for setting a speed at which the rigid disks are rotated, a combination comprising:

a circumferential portion of a surface on a rigid disk in which a measurement signal with substantially constant periodicity is written once and stored;

a head assembly including a transducer positioned adjacent the surface which is supported over the surface by rotation of the rigid disk;

signal processing means connected to the transducer and responsive to rotation of the rigid disk for producing a readback signal in response to the measurement signal;

clearance measurement means in the disk file and responsive to the readback signal for producing a set of first signals indicating clearance between the transducer and the surface at each of a plurality of locations on the circumferential portion at each speed of a plurality of speeds at which the rigid disk is rotated, each speed being held constant while the set of first signals is produced;

glide measurement means in the disk file and responsive to the readback signals for producing a set of second signals corresponding to surface contour measurements at a plurality of locations on the circumferential portion;

storage means in the disk file connected to the clearance and glide measurement means for storing sets of first and second signals for a plurality of circumferential portions of the disk; and

failure analysis means in the disk file, responsive to sets of first and second signals produced by said clearance and glide measurement means and to sets of first and second signals stored in said storage means for producing a third signal indicating impending failure of the disk file.