Magnetic disk drive with feedback control
View Patent ↗A feedforward control system using a polynomial formula not affected by discretization error is realized in a magnetic disk drive. In one embodiment, the magnetic disk drive is intended to move a head for performing at least one of recording and playback to and from a magnetic recording medium to a target position. The feedforward input has a seek control system computed by a polynominal formula of a time function. The coefficients of the polynomial formula have been derived from boundary conditions including the characteristics of a zero-order hold.
1. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which a feedforward input is calculated with a polynomial formula of a time function, and
wherein coefficients of said polynomial formula have been derived from boundary conditions including characteristics of a zero-order hold.
2. A magnetic disk drive set forth in claim 1 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
3. A magnetic disk drive set forth in claim 2 , wherein said control portion has a reference model that outputs a model based on said feedforward input.
4. A magnetic disk drive set forth in claim 2 , wherein said control portion has an acceleration polynomial formula for outputting the feedforward input based on said target track signal, a reference model for outputting a model based on the feedforward input, and a position controller configured to decrease a deviation based on a tracking error that is the deviation between said outputted model and said head position signal and to output a position feedback input.
5. A magnetic disk drive set forth in claim 4 , wherein said reference model has characteristics containing a rigid-body model and modelization error existing between said magnetic head and said rigid-body model.
6. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which an instructed acceleration value given as a feedforward input is calculated with a polynomial formula u [n] of the number of samples n from the start of a seek, and
wherein the following holds for position p, velocity v, and input u:
u [N]=0,v [N]=0,and p [N]=Pt
regarding the following Eq. (3) and a defined v [n] and regarding the following Eq. (4) and a defined p [n]:
v
[
n
]
=
τ
∑
i
=
0
n
-
1
u
[
i
]
+
v
[
0
]
(
3
)
p
[
n
]
=
1
2
τ
2
∑
i
=
0
n
-
1
u
[
i
]
+
τ
∑
i
=
0
n
-
1
v
[
i
]
+
p
[
0
]
(
4
)
where N is the number of samples from the start of the seek to completion of the seek, P t (in meters) is a target movement distance, and τ (in seconds) is a sampling time.
7. A magnetic disk drive set forth in claim 6 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
8. A magnetic disk drive set forth in claim 7 , wherein said control portion has a reference model that outputs a model based on said feedforward input.
9. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which a feedforward input is calculated with a polynomial formula facc of the number of samples n from the start of a seek, and
wherein where the number of samples from the start of the seek to the completion of the seek is set to N, the target movement distance is set to P t (in meters), the sampling time is set to τ (in seconds), and boundary conditions for position p, velocity v, and input u are given by the following Eq. (6), said polynomial formula facc is the following Eq. (7):
p
[
0
]
=
0
,
v
[
0
]
=
0
,
u
[
0
]
=
0
,
(
6
)
p
[
N
]
=
P
t
,
v
[
N
]
=
0
,
u
[
N
]
=
0
,
u
′
[
N
]
=
0
facc
=
-
60
n
(
n
-
N
)
2
(
5
n
N
-
2
(
1
+
N
2
)
)
P
t
(
4
-
N
2
-
4
N
4
+
N
6
)
τ
2
.
(
7
)
10. A magnetic disk drive set forth in claim 9 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
11. A magnetic disk drive set forth in claim 10 , wherein said control portion has a reference model that outputs a model based on said feedforward input.
12. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which a feedforward input is calculated with a polynomial formula facc of the number of samples n from the start of a seek, and
wherein where the number of samples from the start of the seek to the completion of the seek is set to N, the target movement distance is set to P t (in meters), the sampling time is set to τ (in seconds), and boundary conditions for position p, velocity v, and input u are given by the following Eq. (8), said polynomial formula facc is the following Eq. (9):
p
[
0
]
=
0
,
v
[
0
]
=
0
,
u
[
0
]
=
0
,
u
′
[
0
]
=
0
,
(
8
)
p
[
N
]
=
P
t
,
v
[
N
]
=
0
,
u
[
N
]
=
0
,
u
′
[
N
]
=
0
facc
=
-
420
n
2
(
n
-
N
)
2
(
2
n
-
N
)
)
P
t
N
(
20
-
21
N
2
+
N
6
)
τ
2
.
(
9
)
13. A magnetic disk drive set forth in claim 12 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
14. A magnetic disk drive set forth in claim 13 , wherein said control portion has a reference model that outputs a model based on said feedforward input.
15. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which a feedforward input is calculated with a polynomial formula facc of the number of samples n from the start of a seek, and
wherein where the number of samples from the start of the seek to the completion of the seek is set to N, the target movement distance is set to P t (in meters), the sampling time is set to τ (in seconds), and boundary conditions for position p, velocity v, and input u are given by the following Eq. (10), said polynomial formula facc is the following Eq. (11):
p
[
0
]
=
0
,
v
[
0
]
=
0
,
u
[
0
]
=
0
,
u
′
[
0
]
=
0
,
(
10
)
p
[
N
]
=
P
t
,
v
[
N
]
=
0
,
u
[
N
]
=
0
,
u
′
[
N
]
=
0
,
u
″
[
N
]
=
0
facc
=
-
840
n
2
(
n
-
N
)
3
(
-
10
+
(
7
n
-
3
N
)
N
(
1
+
N
2
)
)
P
t
N
(
N
2
-
4
)
(
N
2
-
1
)
(
N
2
+
5
)
(
10
+
3
(
N
2
+
N
4
)
)
τ
2
.
(
11
)
16. A magnetic disk drive set forth in claim 15 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
17. A magnetic disk drive set forth in claim 16 , wherein said control portion has a reference model that outputs a model based on said feedforward input.
18. A magnetic disk drive for moving a magnetic head to a target position, the head performing at least one of recording and playback to and from a magnetic recording medium,
wherein said magnetic disk drive has a seek control system in which a feedforward input is calculated with a polynomial formula facc of the number of samples n from the start of a seek, and
wherein where the number of samples from the start of the seek to the completion of the seek is set to N, the target movement distance is set to P t (in meters), the sampling time is set to τ (in seconds), and boundary conditions for position p, velocity v, and input u are given by the following Eq. (12), said polynomial formula facc is the following Eq. (13):
p
[
0
]
=
0
,
v
[
0
]
=
0
,
u
[
0
]
=
0
,
u
′
[
0
]
=
0
,
u
″
[
N
]
=
0
(
12
)
p
[
N
]
=
P
t
,
v
[
N
]
=
0
,
u
[
N
]
=
0
,
u
′
[
N
]
=
0
,
u
″
[
N
]
=
0
facc
=
2520
n
3
(
n
-
N
)
3
(
2
n
-
N
)
P
t
N
(
168
-
190
N
2
+
21
N
4
+
N
8
)
τ
2
.
(
13
)
19. A magnetic disk drive set forth in claim 18 , wherein said seek control system has a control portion configured to calculate a control signal for positioning said magnetic head in position relative to a motor for driving said magnetic head based on a head position signal obtained by digitizing a present position of said magnetic head and based on a target track signal providing a target to which said magnetic head is to be moved and for outputting the control signal.
20. A magnetic disk drive set forth in claim 19 , wherein said control portion has a reference model that outputs a model based on said feedforward input.