Method for iteratively determining repeatable runout cancellation values in a magnetic disk drive
View Patent ↗The present invention may be embodied in a method of determining a repeatable runout (RRO) compensation value set for a data track on a magnetic disk in a disk drive. The track comprises a plurality of embedded sectors that define a circumferential path having RRO requiring compensation during data read and write operation. In the method, track following is performed along the track and a position error signal (PES) is determined for each servo sector. An RRO compensation value is iteratively learned for each servo sector using the previously learned value for the servo sector and using the PES for the servo sector and for adjacent servo sectors.
1. A method of determining a repeatable runout (RRO) compensation value set for a data track on a magnetic disk in a disk drive, wherein the track comprises a plurality of embedded sectors that define a circumferential path having RRO requiring compensation during data read and write operation, the method comprising:
track following along the track and determining a position error signal e for each servo sector t,
iteratively learning a RRO compensation value u for each servo sector t of the track based on the equation:
u
k
(
t
-
M
)
=
u
k
-
1
(
t
-
M
)
+
∑
i
=
0
M
α
i
e
k
-
1
(
t
-
(
M
-
i
)
)
where
k is a disk revolution number during track following,
α i are learning gain coefficients, and
M is greater than or equal to 2 and less than a total number N of servo sectors for the track.
2. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 1 , wherein the iterative learning is completed using 5 disk revolutions.
3. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 1 , wherein M is equal to 3.
4. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 3 , wherein α 0 is equal to about 1/32, α 1 is equal to about 1/16, α 2 is equal to about 1/16, and α 3 is equal to about −⅛.
5. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 1 , wherein M is equal to 7.
6. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 1 , wherein M is less than 9.
7. A method of determining a repeatable runout (RRO) compensation value set for a data track on a magnetic disk in a disk drive, wherein the track comprises a plurality of embedded sectors that define a circumferential path having RRO requiring compensation during data read and write operation, the method comprising:
track following along the track and determining a position error signal e for each servo sector t,
iteratively learning the RRO compensation value u for each servo sector t of the track based on the equation:
u k ( t− 3)= u k−1 ( t− 3)+α 0 e k−1 ( t− 3)+α 1 e k−1 ( t− 2)+α 2 e k−1 ( t− 1)+α 3 e k−1 ( t )
where
k is the disk revolution number during track following, and
α 0 , α 1 , α 2 , and α 3 are learning gain coefficients.
8. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 7 , wherein α 0 is equal to about 1/32, α 1 is equal to about 1/16, α 2 is equal to about 1/16, and α 3 is equal to about −⅛.
9. A method of determining a repeatable runout (RRO) compensation value set as defined in claim 7 , wherein the iterative learning is completed using 5 disk revolutions.