Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-01-06
2002-10-22
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06469861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a head positioning control apparatus and a method therefor and more particularly, is suitably applied to a disc apparatus for recording on and reproducing from a disc recording medium, such as a magnetic disc, a magneto-optical disc, and an optical disc.
2. Description of the Related Art
A magnetic disc apparatus out of this type of disc apparatus is adapted to control the positioning of a magnetic head by sequentially switching three kinds of operation modes: a seek mode for rapidly moving the magnetic head to the vicinity of target position, a settling mode for settling the magnetic head at the target position, and a tracking mode for forcing the magnetic head to track the target position, in accordance with a positioning state of the magnetic head.
Particularly in a magnetic disc apparatus having a fixed medium, such as a Winchester disc, servo information is often written (hereinafter, this operation is referred to as the “servo write” ) after the apparatus is assembled. A disturbance produced in synchronism with a rotation of a disc at that time (hereinafter, this is referred to as the disc rotation synchronized disturbance) is not so large, so that it can be suppressed by ensuring a sufficient control bandwidth through a closed loop system using a proportional, integration and differential (PID) compensator, an H ∞ controller or the like upon tracking.
However, in a magnetic disc apparatus of a medium exchangeable type, such as a disc pack, a first-order component of disc rotation synchronized disturbance (eccentricity) generally varies whenever a medium is replace with another. Also, second-order and more disturbance components may often become large as compared with a magnetic disc apparatus of the fixed medium type, depending upon the rotation accuracy of a spindle motor or the like during the servo write.
More specifically, an ith component (i is a natural number) of disc rotation synchronized disturbance may occur when the disc suffers from eccentricity (i=1); when a track on the disc is deformed into an oval or indefinite shape (i=2); when a stamper, from which the disc is manufactured, has been deformed (i≧3); and so on.
Further, from the fact that requirements to the head positioning accuracy has become more strict due to narrower track pitches, it is more and more difficult to ensure a sufficient suppression ratio for the disc rotation synchronized disturbance. For this reason, the introduction of a filter for suppressing the disc rotation synchronized disturbance has been proposed, wherein a sinusoidal wave generating model is inserted in a closed loop, in an application of an internal model principle, to increase the gain at its disturbance frequency to ensure the suppression ratio. As one of such filters for suppressing disc rotation synchronized disturbance, an adaptive feedforward canceller (AFC: Adaptive Feedforward Cancellation) has been proposed.
Here, a control system
1
using the AFC is illustrated in FIG.
1
. This control system
1
is operative when a synchronized disturbance d(t) at a predetermined frequency is inputted to a controlled object P(s) to suppress the disturbance frequency using a digital AFC filter
2
. First, when a periodic synchronized disturbance d(t) is inputted to the controlled object P(s) through an adder
3
, the controlled object P(s) is provided with a component of the periodic synchronized disturbance d(t), and sends an output y(t) in accordance with the component to the outside and to the AFC filter
2
.
Assuming that the frequency of this periodic synchronized disturbance d(t) is represented by &ohgr;
i
/2&pgr;, the periodic synchronized disturbance d(t) is expressed by the following equation:
d
(
t
)=
A
i
cos(&ohgr;
i
t
)+
B
i
sin (&ohgr;
i
t
) (1)
Subsequently, in the AFC filter
2
, the output y(t) of the controlled object P(s) is provided to corresponding multipliers
3
,
4
, where the output y(t) is multiplied by cos (&ohgr;
i
t+&PHgr;
i
) and sin (&ohgr;
i
t+&PHgr;
i
), respectively. Then, the multiplication results are supplied to integrators
6
,
7
, respectively. The integrators
6
,
7
integrate the multiplication results of the multipliers
4
,
5
, respectively, to produce AFC coefficients a
i
and b
i
, respectively. &PHgr;
i
represents the phase value of the frequency &ohgr;
i
/2&pgr; in the transfer function from an AFC addition point (u(t)) of the controlled object P(s) to an AFC draw-in point (y(t)).
The AFC coefficients a
i
and b
i
thus produced are multiplied by cos (&ohgr;
i
t) and sin (&ohgr;
i
t), respectively, in multipliers
8
,
9
corresponding thereto, and then the respective multiplication results are added in an adder
10
, with the addition result serving as an input u(t) to the controlled object P(s). This input u(t) is expressed by the following equation:
u
(
t
)=
a
i
cos(&ohgr;
i
t
)+
b
i
sin (&ohgr;
i
t
) (2)
The adder
3
adds this input u(t) to the periodic synchronized disturbance d(t) to suppress a predetermined frequency component within the periodic synchronized disturbance d(t). In this way, a feedforward control using the AFC filter
2
as mentioned is repeated so that the AFC coefficients a and b are both converged to the AFC coefficients A and B represented in the periodic synchronized disturbance d(t), and consequently, the periodic synchronized disturbance d(t) is canceled by the input u(t) in the adder
3
.
Actually, since the calculation processing performed by the AFC filter
2
(hereinafter, this is referred to as the “AFC calculation processing” ) is generally performed in a digital signal processor (DSP), the AFC coefficients a and b are updated in accordance with update rules expressed by the following equations, respectively:
a
i
(
kT
)=
a
i
((
k
−1)
T
)+
g
i
y
(
kT
)cos(&ohgr;
i
kt+&PHgr;
i
) (3)
b
i
(
kt
)=
b
i
((
k
−1)
T
)+
g
i
y
(
kT
)sin(&ohgr;
i
kt+&PHgr;
i
) (4)
where k is an integer indicative of a sampling time, and T is a sampling interval. In this event, the system function (transfer function) of the AFC filter
2
, C(t) (=u(t)/y(t)), is expressed by the following equation:
C
i
(
t
)
=
t
(
cos
(
Φ
i
)
t
-
cos
(
ω
i
T
+
Φ
i
)
)
t
2
-
2
cos
(
ω
i
T
)
t
+
1
(
5
)
Next,
FIG. 2
illustrates a conventional magnetic disc apparatus
10
. The magnetic disc apparatus
10
rotates a plurality of magnetic discs
11
A and
11
B at a high speed in accordance with the rotation of a spindle motor
12
for driving them, and simultaneously moves magnetic heads
14
A to
14
D mounted at respective tips of movable arms
13
in accordance with the driving of a voice coil motor (VCM)
15
to align them corresponding to one face
11
AX,
11
BX and the other face
11
AY,
11
BY of each magnetic disc
11
A,
11
B, so that data is recorded or reproduced by each of the magnetic heads
14
A to
14
D which follows respective tracks formed concentrically or spirally on the one face
11
AX,
11
BX and the other face
11
AY,
11
BY of each of the magnetic discs
11
A,
11
B.
Servo schemes for use in this magnetic disc apparatus
10
include a so-called embedded servo scheme, a servo face servo scheme, and so on. In the embedded servo scheme, a plurality of servo regions are formed such that they radially extend from the center of a disc to equi-angularly divide data regions, and servo information is embedded between the data regions. The servo face servo scheme, which is intended for a large capacity magnetic disc apparatus having a plurality of discs, specifies one face of one magnetic disc among them as a face dedicated to servo information, such that servo information is embedded entirely over the specified face.
With a servo scheme as mentioned, respective servo regions formed on the faces
11
AX,
11
BX and the other faces
11
AY,
11
BY of the magnetic discs
11
A
Ishioka Hideaki
Onuki Yoshikazu
Frommer William S.
Frommer & Lawrence & Haug LLP
Hudspeth David
Wong K.
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