Data storage device attenuating thermal decay effect on fly height measurement
View Patent ↗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: (Δ FHM 2− B·ΔFHM 1)/( 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.
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 FHM 2− B·ΔFHM 1)/( 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.
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:
FHM 2= A·FHM 1+ 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 T 1 , generating a first fly height measurement (FHM1_T 1 ) by reading the first spacing pattern and generate a first fly height measurement (FHM2_T 1 ) by reading the second spacing pattern;
after generating FHM1_T 1 and FHM2_T 1 , increase the operating temperature of the data storage device to T 2 ;
after an interval at the second temperature T 2 , generating a second fly height measurement (FHM1_T 2 ) by reading the first spacing pattern and generate a second fly height measurement (FHM2_T 2 ) by reading the second spacing pattern; and
generating the B constant according to:
B =( FHM 2 — T 2− FHM 2 — T 1)/( FHM 1 — T 2− FHM 1 — T 1).
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 FHM 2− B·ΔFHM 1)/( 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.
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:
FHM 2= A·FHM 1+ 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 T 1 , generating a first fly height measurement (FHM1_T 1 ) by reading the first spacing pattern and generate a first fly height measurement (FHM2_T 1 ) by reading the second spacing pattern;
after generating FHM1_T 1 and FHM2_T 1 , increase the operating temperature of the data storage device to T 2 ;
after an interval at the second temperature T 2 , generating a second fly height measurement (FHM1_T 2 ) by reading the first spacing pattern and generate a second fly height measurement (FHM2_T 2 ) by reading the second spacing pattern; and
generating the B constant according to:
B =( FHM 2 — T 2 −FHM 2 — T 1)/( FHM 1 — T 2 −FHM 1 — T 1).