Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-06-28
2003-09-09
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S077020, C360S294400, C360S294100
Reexamination Certificate
active
06618220
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a head actuator, used in an information recording and reproduction apparatus, for positioning a head on a desired track of an information medium, and a hard disc drive including the same.
2. Description of the Related Art
Recently, recording and reproduction apparatuses using a circular information medium, such as, for example, a magnetic disc apparatus and an optical disc apparatus have been widely used. Among these apparatuses, a magnetic disc apparatus is especially widely used as an external memory apparatus for a personal computer with its characteristic of transferring data at a high speed being utilized.
One small-size magnetic disc apparatus commonly used in recent years uses a magnetic disc having concentric recording tracks and performs information recording and reproduction by positioning a magnetic head on a desired recording track position of the magnetic disc by a swingable head actuator. In order to further improve the recording density, a system for improving the head positioning precision by providing a secondary small head actuator at a tip of the swingable head actuator has been proposed. Several types of small head actuators used for this system have also been proposed.
One exemplary small head actuator is disclosed in Japanese Laid-Open Publication No. 5-47126, which has the following structure. A head supporting spring is formed of two beams. The two beams are connected together at tips thereof, and a head is supported in the vicinity of the connection point. At least one of the beams integrally has a thin film-like displacement element bonded on at least one surface thereof. The displacement element is expandable in accordance with the level of a voltage externally applied. (This type of small head actuator will be referred to as “conventional example 1”).
Another exemplary small head actuator is disclosed in Japanese Laid-Open Publication No. 7-224838. In the actuator disclosed in this publication, a piezoelectric element is provided on a surface of a load beam on which a head is to be mounted. (This type of small head actuator will be referred to as “conventional example 2”).
Conventional examples 1 and 2 are common in the basic structure. These examples will be described below.
FIG. 15
schematically shows a structure of a conventional head actuator
1200
(corresponding to conventional example 1). As shown in
FIG. 15
, a head supporting member
50
has a head slider
52
bonded at one end thereof. The head supporting member
50
also has a late-like displacement element
51
bonded to a surface near the center thereof.
As shown in
FIG. 15
, an area of the head supporting member
50
provided with the displacement element
51
is defined as an area
1201
, and areas of the head supporting member
50
where the displacement element
51
is not provided is defined as areas
1202
.
In this specification, the term “neutral face” is defined to indicate a face which is not expanded or contracted when a beat is bent.
Referring to
FIG. 15
, a neutral face NB
1
of the areas
1202
matches a geometrically central face of the head supporting member
50
. In the area
1201
, the displacement element
51
is integrally bonded to the head supporting member
50
. Therefore, a neutral face NA
1
of the area
1201
is inevitably closer to the displacement element
51
than the neutral face NB
1
. (Hereinafter, a distance D
1
between the neutral faces NA
1
and NB
1
will be referred to as a “neutral face step”. Corresponding distances in the following examples each will also be referred to as the “neutral face step”.) A geometrically central face L
1
(also referred to simply as the “central face L
1
”) of the displacement element
51
is on the opposite side to the neutral face NB
1
with respect to the neutral face NA
1
. A distance between the central face L
1
and the neutral face NA
1
is defined as H
1
.
When a voltage is applied to the displacement element
51
, the head supporting member
50
expands or contracts in longitudinal directions relative to the head supporting member
50
, and thus the head slider
52
is slightly displaced in a radial direction of a magnetic disc.
In general, two basic performance requirements of a small head actuator are (i) a sufficiently large displacement amount at a lower voltage and (ii) a sufficiently high mechanical resonance frequency so as to realize positioning control in a wide range of band.
The conventional head actuator
1200
has the following two problems. The displacement generated by the expansion and contraction in the longitudinal directions of the head supporting member
50
caused by the voltage application to the displacement element
51
is lost by a flexure of the head supporting member
50
, and thus an effective displacement is not obtained. The mechanical resonance frequency mainly relies on the rigidity in flexure directions of the head supporting member
50
, and thus it is difficult to obtain a resonance frequency in a wider band range.
First, the problem regarding the displacement will be described.
FIG. 16
shows a static model of the conventional head actuator
1200
(FIG.
15
). From the viewpoint of statics, the head actuator
1200
can be represented as a model shown in part (a) of FIG.
16
. In part (a) of
FIG. 16
, the head supporting member
50
is represented by the neutral faces NA
1
and NB
1
. A force provided by the displacement element
51
acts on the head supporting member
50
as an external force.
Now, it is assumed that a voltage is applied to the displacement element
51
in such a direction as to expand the displacement element
51
. An expanding force F
1
acts outward as shown in part (a) of FIG.
16
. Since the central face L
1
of the displacement element
51
is on the opposite side to the neutral face NB
1
with respect to the neutral face NA
1
as described above, a bending moment M
1
is generated by the expanding force F
1
. The bending moment M
1
has a magnitude obtained by multiplying the expandable force F
1
by the distance H
1
. On the sheet of
FIG. 15
, the central face L
1
is above the neutral face NA
1
by the distance H
1
. Thus, the bending moment M
1
acts in such a direction to cause the neutral face NA
1
to project upward on the sheet of FIG.
15
. This state is considered to be obtained by the combination of (i) a state of only the expanding force F
1
being applied (part (b) of
FIG. 16
) and (ii) a state of only the bending moment M
1
being applied (part (C) of FIG.
16
). Considering a length of the area
1201
, i.e., the distance between point A and point B, as shown in part (b) of
FIG. 16
, point A is displaced in such a longitudinal direction as to expand the displacement element
51
by a displacement amount X
1
. When, as shown in part (c) of
FIG. 16
, the bending moment M
1
is applied in such a direction to cause the neutral face NA
1
to project upward, the bending moment M
1
generates flexure angles &thgr;A and &thgr;B at two ends of the displacement element
51
. At each of the flexure angles &thgr;A and &thgr;B, a displacement amount in a longitudinal direction which is obtained by multiplying each of the flexure angles &thgr;A and &thgr;B by the neutral face step D
1
is generated. Thus, points A is displaced in such a longitudinal direction as to contract the displacement element
51
by a displacement amount X
2
. As is clear from parts (a) and (b) of
FIG. 16
, the displacement amounts X
1
and X
2
are in opposite directions. A difference therebetween is a total displacement amount.
When a voltage is applied in such a direction as to contract the displacement element
51
, the displacement amounts X
1
and X
2
are in opposite directions, and a difference therebetween is a total displacement amount. Accordingly, with the structure of the conventional head actuator
1200
, the displacement amount X
1
generated by the expanding force in one longitudinal direction is lost by the displacement amount X
2
generated in the opposite longitudin
Inagaki Tatsuhiko
Kuwajima Hideki
Renner Otto Boisselle & Sklar
Sniezek Andrew L.
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