Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-12-27
2002-07-16
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077040
Reexamination Certificate
active
06421200
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a control method and control device for controlling an actuator to move a head to a target position in a disk storage device, that reads or reads/writes information from a disk storage medium by the head.
BACKGROUND OF THE INVENTION
Disk storage devices such as magnetic disk drives or optical disk drives are widely used as storage devices for computers and the like. In these kinds of disk storage devices, eccentricity of the disk medium occurs. This eccentricity occurs when the center of rotation of the disk medium that was recorded the position information shifts when that of writing the position information.
In the sector servo method, the position information (servo information) for detecting the actuator position is recorded on each disk surface. This position information is formed on concentric circles. When the center of rotation of the disk matches with the center of rotation of the disk when the position information was written, then ideally no eccentricity will occur.
However, in actuality, the centers of rotation do not match and eccentricity occurs. The reason for this is probably due to thermal deformation of the disk medium and a spindle shaft, or shifting of the disk due to external impact. When there is eccentricity, it can be seen from the actuator's point of view that sinusoidal disturbance on the order of integral multiples of the rotation frequency is applied. Therefore, a technique for correcting this eccentricity is necessary.
Control using an eccentricity estimation observer (estimator) has been known as a technique for correcting this eccentricity. In the control by this eccentricity estimation observer, steady position control by the estimated values is required.
FIG. 12
is a configuration drawing of this prior art, and
FIG. 13
is a drawing for explaining this prior art.
Position control of a magnetic head by the use of an eccentricity estimation observer is described in detail in Japanese Unexamined Published patent No. 7-50075 (U.S. Pat. No. 5,404,235). Therefore, the eccentricity estimation observer will only be simply explained here.
First, an ideal actuator model that does not include resonance will be considered. Here, when ‘x1’ is taken to be the position, ‘x2’ the velocity, ‘y’ the observed position (detected position), ‘u’ the control current and ‘s’ the Laplace operator, then the state equations are given by equations (1) and (2) below.
S
(
X
1
X
2
)
=
(
0
1
0
0
)
(
X
1
X
2
)
+
Kp
(
0
1
)
u
(
1
)
y
=
(
1
0
)
(
X
1
X
2
)
(
2
)
Here, ‘Kp’ is the acceleration constant when rotating type actuator of the model is considered to be an equivalent linear type actuator.
When considering the current feedback, the steady-state current (bias current) state ‘x3’ is added to the state equations, and thus the state equations are given by equations (3) and (4) below.
S
(
X
1
X
2
X
3
)
=
(
0
1
0
0
0
K
p
0
0
0
)
(
X
1
X
2
X
3
)
+
Kp
(
0
1
0
)
u
(
3
)
y
=
(
1
0
0
)
(
X
1
X
2
X
3
)
(
4
)
Furthermore, the eccentricity disturbance state is added to these state equations. When ‘x4’ and ‘x5’ are taken to be the state variable of the eccentricity, and ‘&ohgr;0’ is taken to be the eccentric angular velocity, then the state equations are given by equations (5) and (6) below.
S
(
X
1
X
2
X
3
X
4
X
5
)
=
(
0
1
0
0
0
0
0
Kp
Kp
0
0
0
0
0
0
0
0
0
0
1
0
0
0
-
ω
0
2
0
)
(
X
1
X
2
X
3
X
4
X
5
)
+
Kp
(
0
1
0
0
0
)
u
(
5
)
y
=
(
1
0
0
0
0
)
(
X
1
X
2
X
3
X
4
X
5
)
(
6
)
Here, when x4=cos(&ohgr;0·t) and x5=sin(&ohgr;0·t), then sx4 =−&ohgr;0·sin(w0·t) and sx
5=&ohgr;0 ·cos(&ohgr;
0·t), so sx4=−&ohgr;0·x5and sx5=&ohgr;0·x4. Therefore, the state equations (5) and (6) are given by equations (7) and (8) below.
S
(
X
1
X
2
X
3
X
4
X
5
)
=
(
0
1
0
0
0
0
0
Kp
Kp
0
0
0
0
0
0
0
0
0
0
-
ω
0
0
0
0
ω
0
0
)
(
X
1
X
2
X
3
X
4
X
5
)
+
Kp
(
0
1
0
0
0
)
u
(
7
)
y
=
(
1
0
0
0
0
)
(
X
1
X
2
X
3
X
4
X
5
)
(
8
)
In equation (5) the eccentricity is estimated by the sinusoidal transfer function (1/(S
2
+&ohgr;0
2
)). As shown in
FIG. 13
, equation (7) shows the movement in rectangular coordinates (x4,x5) of a point on the circle with radius (x4{circumflex over ( )}2+x5{circumflex over ( )}2) that is rotating at constant velocity.
The observer is designed to transfer the state equations (7) and (8) to a discrete form. The equations are transferred into a discrete form by estimating the zero-dimension hold. In other words, it performs Z conversion. By considering the time lag from when the position is detected until current is output to the actuator, state equations become 6 dimensional. Even when not considered, the state equations are given by equations (9) and (10) below.
(
X
1
[
K
+
1
]
X
2
[
K
+
1
]
X
3
[
K
+
1
]
X
4
[
K
+
1
]
X
5
[
K
+
1
]
)
=
(
1
T
KpT
2
2
Kp
ω
0
2
(
1
-
cos
(
ω
0
T
)
)
Kp
ω
0
2
(
ω
0
T
-
sin
(
ω
0
T
)
)
0
1
KpT
Kp
-
sin
(
ω
0
T
)
)
ω
0
Kp
ω
0
(
1
-
cos
(
ω
0
T
)
)
0
0
1
0
0
0
0
0
cos
(
ω
0
T
)
-
sin
(
ω
0
T
)
0
0
0
sin
(
ω
0
T
)
cos
(
ω
0
T
)
)
(
X
1
[
K
]
X
2
[
K
]
X
3
[
K
]
X
4
[
K
]
X
5
[
K
]
)
+
Kp
(
T
2
/
2
T
0
0
0
)
u
[
k
]
(
9
)
y
[
k
]
=
(
1
0
0
0
0
)
(
X
1
[
K
]
X
2
[
K
]
X
3
[
K
]
X
4
[
K
]
X
5
[
K
]
)
(
10
)
Here, T is the sample period. As shown in equation (11), the coefficients in equations (9) and (10) are A, B and C.
A
=
(
1
T
KpT
2
2
Kp
ω
0
2
(
1
-
cos
(
ω
0
T
)
)
Kp
ω
0
2
(
ω
0
T
-
sin
(
ω
0
T
)
)
0
1
KpT
Kp
-
sin
(
ω
0
T
)
)
ω
0
Kp
ω
0
(
1
-
cos
(
ω
0
T
)
)
0
0
1
0
0
0
0
0
cos
(
ω
0
T
)
-
sin
(
ω
0
T
)
0
0
0
sin
(
ω
0
T
)
cos
(
ω
0
T
)
)
,
B
=
Kp
(
T
2
/
2
T
0
0
0
)
C
=
(
1
0
0
0
0
)
(
11
)
Here, the observer is expressed by the equations (12), (13) and (14) below.
(
PX
1
[
K
+
1
]
PX
2
[
K
+
1
]
PX
3
[
K
+
1
]
PX
4
[
K
+
1
]
PX
5
[
K
+
1
]
)
=
A
(
PX
1
[
K
]
PX
2
[
K
]
PX
3
[
K
]
PX
4
[
K
]
PX
5
[
K
]
)
+
B
·
u
[
k
]
+
(
L
1
L
2
L
3
L
4
L
5
)
(
y
[
k
]
-
PX
1
[
k
]
)
(
12
)
py
[
k
]
=
C
(
PX
1
[
K
]
PX
2
[
K
]
PX
3
[
K
]
PX
4
[
K
]
PX
5
[
K
]
)
(
13
)
u
[
k
]
=
-
(
F
1
F
2
1
1
0
)
(
PX
1
[
K
]
PX
2
[
K
]
PX
3
[
K
]
PX
4
[
K
]
PX
5
[
K
]
)
(
14
)
Here, px1 is the state variable for position (estimated position), px2 is the state variable for velocity (estim
Greer Burns & Crain Ltd
Hudspeth David
Wong K.
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