Data storage device attenuating thermal decay effect on fly height measurement

• US 9,076,474 B1
• Filed: 12/23/2014
• Issued: 07/07/2015
• Est. Priority Date: 12/23/2014
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Tang, Kathy X., Le, Jerry G.
• Primary Examiner(s): Agustin, Peter Vincent
• Application Number:
  US14/582,004
• Time in Patent Office: 196 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G11B 5/6029 Measurement using values derived from the data signal read from the disk

Abstract

A data storage device is disclosed comprising a head actuated over a disk. A first spacing pattern is written to the disk and a second spacing pattern is written to the disk different from the first spacing pattern. A first fly height measurement (FHM1_1) is generated by reading the first spacing pattern and a first fly height measurement (FHM2_1) is generated by reading the second spacing pattern. After an interval, a second fly height measurement (FHM1_2) is generated by reading the first spacing pattern and a second fly height measurement (FHM2_2) is generated by reading the second spacing pattern. A change in the fly height of the head is estimated based on:
(ΔFHM2−B·ΔFHM1)/(A−B)
where ΔFHM1 represents a difference between FHM1_1 and FHM1_2, ΔFHM2 represents a difference between FHM2_1 and FHM2_2, and A and B are constants.

Claims

1. A data storage device comprising:

a disk;

a head; and

control circuitry configured to;

write a first spacing pattern to the disk;

write a second spacing pattern to the disk different from the first spacing pattern;

generate a first fly height measurement (FHM1_—

1) by reading the first spacing pattern and generate a first fly height measurement (FHM2_—

1) by reading the second spacing pattern;

after an interval, generate a second fly height measurement (FHM1_—

2) by reading the first spacing pattern and generate a second fly height measurement (FHM2_—

2) by reading the second spacing pattern; and

estimate a change in the fly height of the head based on;

(Δ

FHM2−

B·

Δ

FHM1)/(A−

B)

where;

Δ

FHM1 represents a difference between FHM1_—

1 and FHM1_—

2;

Δ

FHM2 represents a difference between FHM2_—

1 and FHM2_—

2; and

A and B are constants.

2. The data storage device as recited in claim 1, further comprising a fly height actuator (FHA) configured to adjust a fly height of the head over the disk based on an FHA setting, wherein the control circuitry is further configured to generate the A constant by:

generating a first actuation curve for the first spacing pattern by generating fly height measurements over a range of FHA settings;

generating a second actuation curve for the second spacing pattern by generating fly height measurements over a range of FHA settings; and

evaluating a relationship between the first actuation curve and the second actuation curve.

3. The data storage device as recited in claim 2, wherein the control circuitry is further configured to generate the relationship by curve fitting data points of the first and second actuation curves to generate:

FHM2=A·

FHM1+C

where FHM2 represents a fly height measurement corresponding to the second spacing pattern computed as a function of the fly height measurement FHM1 corresponding to the first fly height pattern, and C is a constant.

4. The data storage device as recited in claim 1, wherein the control circuitry is further configured to generate the B constant by:

at a first operating temperature T1, generating a first fly height measurement (FHM1_T1) by reading the first spacing pattern and generate a first fly height measurement (FHM2_T1) by reading the second spacing pattern;

after generating FHM1_T1 and FHM2_T1, increase the operating temperature of the data storage device to T2;

after an interval at the second temperature T2, generating a second fly height measurement (FHM1_T2) by reading the first spacing pattern and generate a second fly height measurement (FHM2_T2) by reading the second spacing pattern; and

generating the B constant according to;

B=(FHM2_—

T2−

FHM2_—

T1)/(FHM1_—

T2−

FHM1_—

T1).

5. A method of operating a data storage device, the method comprising:

writing a first spacing pattern to a disk;

writing a second spacing pattern to the disk different from the first spacing pattern;

generating a first fly height measurement (FHM1_—

1) by reading the first spacing pattern and generating a first fly height measurement (FHM2_—

1) by reading the second spacing pattern;

after an interval, generating a second fly height measurement (FHM1_—

2) by reading the first spacing pattern and generating a second fly height measurement (FHM2_—

2) by reading the second spacing pattern; and

estimating a change in the fly height of a head over the disk based on;

(Δ

FHM2−

B·

Δ

FHM1)/(A−

B)

where;

Δ

FHM1 represents a difference between FHM1_—

1 and FHM1_—

2;

Δ

FHM2 represents a difference between FHM2_—

1 and FHM2_—

2; and

A and B are constants.

6. The method as recited in claim 5, further comprising generating the A constant by:

generating a first actuation curve for the first spacing pattern by generating fly height measurements over a range of FHA settings;

generating a second actuation curve for the second spacing pattern by generating fly height measurements over a range of FHA settings; and

evaluating a relationship between the first actuation curve and the second actuation curve.

7. The method as recited in claim 6, further comprising generating the relationship by curve fitting data points of the first and second actuation curves to generate:

FHM2=A·

FHM1+C

where FHM2 represents a fly height measurement corresponding to the second spacing pattern computed as a function of the fly height measurement FHM1 corresponding to the first fly height pattern, and C is a constant.

8. The method as recited in claim 5, further comprising generating the B constant by:

at a first operating temperature T1, generating a first fly height measurement (FHM1_T1) by reading the first spacing pattern and generate a first fly height measurement (FHM2_T1) by reading the second spacing pattern;

after generating FHM1_T1 and FHM2_T1, increase the operating temperature of the data storage device to T2;

after an interval at the second temperature T2, generating a second fly height measurement (FHM1_T2) by reading the first spacing pattern and generate a second fly height measurement (FHM2_T2) by reading the second spacing pattern; and

generating the B constant according to;

B=(FHM2_—

T2−

FHM2_—

T1)/(FHM1_—

T2−

FHM1_—

T1).