Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-02-02
2003-04-08
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S364000, C310S365000
Reexamination Certificate
active
06545395
ABSTRACT:
This disclosure is based on application No. 00-0038993 filed in Japan on Feb. 17, 2000, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to piezoelectric devices and, more particularly, to a roll-type piezoelectric conversion element formed as a tube by rolling up at least one piezoelectric sheet element and to methods of making the same. The roll-type piezoelectric conversion element may be used, for example, as an actuator.
2) Brief Description of Related Art
Actuators using piezoelectric conversion elements are used to drive and position driven parts in cameras, measuring devices, and other precision machinery because they have high conversion efficiency for converting an applied electrical energy to a drive force, are compact and light weight, and are capable of generating large drive forces. Further, the drive force is readily controllable.
A drive source piezoelectric conversion element used as an actuator may be constructed by laminating a plurality of single piezoelectric elements. This arrangement increases as much as possible the displacement generated in the thickness direction of a single piezoelectric element.
However, piezoelectric conversion elements (also referred to as piezoelectric conversion devices) constructed by laminating a plurality of individual piezoelectric elements are expensive because they are typically manufactured through complex operations including a process to apply an electrode to the surface of the individual piezoelectric elements, a process for lamination and adhesion of the piezoelectric elements, and a process for connecting the wiring of the electrodes of the various layers.
For this reason, other piezoelectric conversion elements have been proposed. One type is a conventional roll-type piezoelectric conversion element formed by laminating two thin piezoelectric sheet elements having electrodes formed on their surfaces so as to form a laminate member which is then rolled in a hollow tube shape (hereinafter referred to as “two-layer type”). Another type is a conventional roll-type piezoelectric conversion element formed by folding a single thin piezoelectric sheet element having electrodes formed on the front surface and back surface so as to form a lamination which is then rolled into a hollow tube shape (hereinafter referred to as “single-layer type”).
The conventional two-layer type piezoelectric conversion element is provided with an electrode on the entire front surface of each of the two layers of individual piezoelectric sheet elements. The two layers are laminated and rolled into a hollow tube shape. In order to apply a voltage to the electrodes, the two electrodes are exposed on the side surface of the piezoelectric sheet elements when forming the hollow tube shape by staggering the position of the rolled ends of the two individual piezoelectric sheet elements. Such a configuration is illustrated in
FIG. 10
, which shows a perspective view of an example of a conventional two-layer piezoelectric conversion element
100
. FIGS.
11
(
a
) and
11
(
b
) illustrate the electrode surfaces and the lamination state of this element.
A conventional single-layer type piezoelectric conversion element, such as illustrated in
FIGS. 12 and 13
, is formed by folding approximately in half a single thin piezoelectric sheet element having electrodes formed on the front surface and the back surface, thereby creating a lamination. The folded part is shifted slightly to the right or left from the center part of the single layer element, such that both ends of the folded unit piezoelectric sheet element are shifted to expose the two electrodes on the side surface of the piezoelectric conversion element when formed in a hollow tube shape, thereby allowing leads to be readily connected to the electrodes.
The process for manufacturing the conventional two-layer type piezoelectric conversion element
100
is described below. First, a thin sheet-like material called a “green sheet” formed of piezoelectric ceramic material is cut to suitable dimensions to provide a first piezoelectric sheet element
101
and a second piezoelectric sheet element
102
, as shown in FIG.
11
(
a
). The length of the second piezoelectric sheet element
102
in the rolling direction is longer by a measure d than the first piezoelectric sheet element
101
.
A first electrode
103
is formed on the surface of the first piezoelectric sheet element
101
, and the back surface is designated a non-electrode surface. A second electrode
104
is formed on the surface of the second piezoelectric sheet element
102
, and the back surface is designated a non-electrode surface (refer to
FIG. 11
a
).
Then, the first piezoelectric sheet element
101
is arranged adjacent to the second piezoelectric sheet element
102
such that the non-electrode surface of the first piezoelectric sheet element
101
confronts the electrode surface of the second piezoelectric sheet element
102
, forming a laminate body as shown in FIG.
11
(
b
). This laminate body is rolled using a rolling shaft formed of cellulose or the like so as to form the tube-like shape shown in FIG.
10
. Thereafter, the tube is calcined at a specific temperature, and subjected to a polarization process to complete the piezoelectric conversion element. Selecting the appropriate calcination temperature and polarizing conditions depends upon the particular piezoelectric material utilized and is within the purview of one of ordinary skill in the art. The rolling shaft is incinerated by the calcination process, leaving the interior of the tube hollow.
As shown in FIGS.
10
and
11
(
b
), when the length of the first piezoelectric sheet element
101
is shorter than the length of the second piezoelectric sheet element
102
in the rolling direction, the ends of the first electrode
103
and the second electrode
104
can be staggered, and a lead
103
a
and a lead
104
a
can be easily connected to the respective electrode.
A conventional single-layer type piezoelectric conversion element is similar to the conventional two-layer type piezoelectric conversion element
100
described above.
FIGS. 12 and 13
illustrate a conventional single-layer, roll-type piezoelectric conversion element
200
formed by folding in half a single-layer piezoelectric sheet element
201
, which is then rolled up to form a hollow tube shape.
FIG. 12
is a cross section view, and
FIG. 13
is a perspective view. The construction of the conventional single-layer type piezoelectric conversion element
200
will now be described in more detail.
A piezoelectric sheet element
201
formed of a material called a “green sheet” having a thin sheet shape and formed of a piezoelectric ceramic material is cut to a suitable dimension. A first electrode
203
is formed on the front surface of the piezoelectric sheet element
201
, and a second electrode
204
is formed on the back surface thereof. Then, the piezoelectric sheet element
201
is folded in half from a position
205
at the approximate center, forming a lamination as shown in
FIGS. 12 and 13
. This laminate body is rolled up in a tube shape in the same way as the previously described two-layer piezoelectric conversion element, calcinated at a specified temperature, and subjected to a polarization process to complete the piezoelectric conversion element.
A conventional tube-shaped two-layer type or single-layer type piezoelectric conversion element (
100
or
200
) of the aforesaid construction may suffer from short circuiting problems. As described above, a conventional piezoelectric conversion element (
100
or
200
) is formed by rolling up a laminate body into a tube shape, such that the piezoelectric conversion element (
100
or
200
) has many overlapping layers. This tube-shaped conversion element (
100
or
200
) is then calcinated at a specified temperature. During the calcination process, a difference in contraction occurs between the electrode and green sheet layers of the piezoelectric lamina
Katsuragi Hiroji
Matsui Naoki
Burns Doane , Swecker, Mathis LLP
Gonzalez Julio C.
Minolta Co. , Ltd.
Ramirez Nestor
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