Data storage device configuring a gain of a servo control system for actuating a head over a disk
View Patent ↗A data storage device is disclosed comprising a first disk surface comprising servo data defining servo tracks at a first radial density, a first head, and a voice coil motor (VCM) configured to actuate the first head over the first disk surface using a servo control system. A load operation is executed to load the first head over the first disk surface, and a back electromotive force (BEMF) voltage generated by the VCM during the load operation is evaluated to generate an estimated distance traveled. The servo data on the first disk surface is detected, and an initial servo track during the load operation based on the detected servo data to generate a measured distance traveled. A gain of the servo control system is configured based on the estimated distance traveled and the measured distance traveled.
1. A data storage device comprising:
a first disk surface comprising servo data defining servo tracks at a first radial density;
a first head;
a voice coil motor (VCM) configured to actuate the first head over the first disk surface; and
control circuitry comprising a servo control system configured to control the VCM, the control circuitry configured to:
execute a load operation to load the first head over the first disk surface;
evaluate a back electromotive force (BEMF) voltage generated by the VCM during the load operation to generate an estimated distance traveled;
detect the servo data on the first disk surface;
detect an initial servo track during the load operation based on the detected servo data to generate a measured distance traveled; and
configure a gain of the servo control system based on the estimated distance traveled and the measured distance traveled.
2. The data storage device as recited in claim 1 , wherein the control circuitry is further configured to:
generate a first measured radial density of the servo tracks on the first disk surface based on a ratio of the estimated distance traveled and the measured distance traveled; and
configure the gain of the servo control system based on the first measured radial density.
3. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to configure the gain of the servo control system based on:
Gain
0
·
TPI
m
TPI
0
where Gain 0 represents a nominal gain, TPI m represents the first measured radial density, and TPI 0 represents a nominal radial density.
4. The data storage device as recited in claim 3 , wherein the radial density of the servo tracks is different than TPI 0 .
5. The data storage device as recited in claim 3 , wherein the control circuitry is further configured to:
seek the head a seek distance from a first track to a second track on the first disk surface; and
update the gain of the servo control system based on:
S
∑
1
N
∑
1
N
u
(
k
)
-
N
2
∑
1
N
u
(
k
)
where S represents the seek distance and u(k) represents a control signal applied to the VCM during the seek over N samples.
6. The data storage device as recited in claim 2 , wherein the control circuitry is further configured to configure the gain of the servo control system based on:
Gain
0
·
TPI
0
TPI
m
where Gain 0 represents a nominal gain, TPI m represents the first measured radial density, and TPI 0 represents a nominal radial density.
7. The data storage device as recited in claim 6 , wherein the radial density of the servo tracks substantially equals TPI 0 .
8. The data storage device as recited in claim 2 , further comprising a second head actuated over a second disk surface comprising servo data defining servo tracks at a second radial density, wherein the control circuitry is further configured to:
execute a head switch operation to switch from the first head to the second head;
detect the servo data on the second disk surface; and
generate a second measured radial density of the servo tracks on the second disk surface based on the servo data detected on the first disk surface, the servo data detected on the second disk surface, and the first measured radial density of the servo tracks on the first disk surface.
9. The data storage device as recited in claim 8 , wherein the first radial density of the servo tracks on the first disk surface is substantially different from the second radial density of the servo tracks on the second disk surface.
10. The data storage device as recited in claim 8 , wherein the control circuitry is further configured to update the gain of the servo control system after executing the head switch operation based on the second measured radial density of the servo tracks on the second disk surface.
11. A data storage device comprising:
a disk surface comprising servo data defining servo tracks at a first radial density;
a head;
an actuator configured to actuate the head over the disk surface; and
control circuitry comprising a servo control system configured to control the actuator, the control circuitry configured to:
seek the head a seek distance from a first track to a second track on the disk surface; and
configure a gain of the servo control system based on:
S
∑
1
N
∑
1
N
u
(
k
)
-
N
2
∑
1
N
u
(
k
)
where S represents the seek distance and u(k) represents a control signal applied to the actuator during the seek over N samples.
12. A method of operating a data storage device, the method comprising:
executing a load operation to load a first head over a first disk surface using a voice coil motor (VCM);
evaluating a back electromotive force (BEMF) voltage generated by the VCM during the load operation to generate an estimated distance traveled;
detecting servo data on the first disk surface;
detecting an initial servo track during the load operation based on the detected servo data to generate a measured distance traveled; and
configuring a gain of a servo control system based on the estimated distance traveled and the measured distance traveled, wherein the servo control system is configured to control the VCM.
13. The method as recited in claim 12 , further comprising:
generating a first measured radial density of the servo tracks on the first disk surface based on a ratio of the estimated distance traveled and the measured distance traveled; and
configuring the gain of the servo control system based on the first measured radial density.
14. The method as recited in claim 13 , further comprising configuring the gain of the servo control system based on:
Gain
0
·
TPI
m
TPI
0
where Gain 0 represents a nominal gain, TPI m represents the first measured radial density, and TPI 0 represents a nominal radial density.
15. The method as recited in claim 14 , wherein the radial density of the servo tracks is different than TPI 0 .
16. The method as recited in claim 14 , further comprising:
seeking the head a seek distance from a first track to a second track on the first disk surface; and
updating the gain of the servo control system based on:
S
∑
1
N
∑
1
N
u
(
k
)
-
N
2
∑
1
N
u
(
k
)
where S represents the seek distance and u(k) represents a control signal applied to the VCM during the seek over N samples.
17. The method as recited in claim 13 , further comprising configuring the gain of the servo control system based on:
Gain
0
·
TPI
0
TPI
m
where Gain 0 represents a nominal gain, TPI m represents the first measured radial density, and TPI 0 represents a nominal radial density.
18. The method as recited in claim 17 , wherein the radial density of the servo tracks substantially equals TPI 0 .
19. The method as recited in claim 13 , further comprising:
executing a head switch operation to switch from the first head to a second head actuated over a second disk surface;
detecting servo data on the second disk surface; and
generating a second measured radial density of the servo tracks on the second disk surface based on the servo data detected on the first disk surface, the servo data detected on the second disk surface, and the first measured radial density of the servo tracks on the first disk surface.
20. The method as recited in claim 19 , wherein the first radial density of the servo tracks on the first disk surface is substantially different from the second radial density of the servo tracks on the second disk surface.
21. The method as recited in claim 19 , further comprising updating the gain of the servo control system after executing the head switch operation based on the second measured radial density of the servo tracks on the second disk surface.
22. A method of operating a data storage device, the method comprising:
using a servo control system to seek a head a seek distance from a first track to a second track on a disk surface; and
configuring a gain of the servo control system based on:
S
∑
1
N
∑
1
N
u
(
k
)
-
N
2
∑
1
N
u
(
k
)
where S represents the seek distance and u(k) represents a control signal applied to an actuator during the seek over N samples.