Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-06-17
2004-06-08
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323020, C310S323120, C310S366000
Reexamination Certificate
active
06747397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stacked type electro-mechanical energy conversion element and a vibration wave driving apparatus of stacked structure consisting of a stack of a plurality of piezoelectric bodies and, more particularly, to a configuration for connecting electrodes between layers in the stacked type electro-mechanical energy conversion element.
2. Related Background Art
Piezoelectric elements having the electro-mechanical energy conversion function are used in various use applications. The piezoelectric elements are generally classified into the structure comprised of a single piezoelectric body of plate shape and the stacked structure comprised of multiple piezoelectric bodies of plate shape. The piezoelectric elements of the stacked structure can generate greater distortion with supply of a lower applied voltage than the piezoelectric elements of the structure comprised of only one piezoelectric body of plate shape.
A stacked type piezoelectric element is comprised of a plurality of piezoelectric layers of piezoelectric ceramics and electrode films (hereinafter referred to as internal electrodes) provided on surfaces of the respective piezoelectric layers. For connecting the internal electrodes on the respective piezoelectric layers to each other, it is common practice to provide electrode portions disposed on an outer peripheral surface or an inner peripheral surface of the stacked type piezoelectric element (hereinafter referred to as external electrodes), or to provide through holes along the stack direction in the piezoelectric layers and provide through electrodes (through holes) formed by burying an electrode material in the through holes.
FIGS. 5 and 6
show configurations of stacked type piezoelectric elements used in a vibration body of a rodlike vibration wave motor disclosed in U.S. Pat. No. 5,770,916.
The internal electrodes
103
indicated by hatching are formed on the surfaces of the second and lower piezoelectric layers
102
in the stacked type piezoelectric element
101
shown in FIG.
5
. The internal electrodes
103
are not formed on the outer peripheral edges of the piezoelectric layers
102
. In other words, the internal electrodes
103
are formed inside the outside diameter of the piezoelectric layers
102
. Further, the internal electrodes
103
are out of contact with each other. Connection electrodes
103
a
(black solid portions in the drawing) are formed on the outer peripheral edges of the piezoelectric layers
102
, and the connection electrodes
103
a
are in contact with the internal electrodes
103
.
The internal electrodes
103
on the respective piezoelectric layers
102
are stacked so as to be aligned in identical phases, and the connection electrodes
103
a
are formed at identical positions on every other layer. Then the external electrodes
104
are formed at positions to be superimposed on the connection electrodes
103
a
, on the outer peripheral surface of the stacked piezoelectric element
101
, so as to connect the connection electrodes
103
a
on every other layer. Namely, the internal electrodes
103
located in identical phases are arranged as electrically conductible on every other layer.
A plurality of surface electrodes
105
are provided along the circumferential direction and in the phases matched with those of the connection electrodes
103
a
, on the outer peripheral edge of the surface of the uppermost piezoelectric layer forming the stacked piezoelectric element
101
. The surface electrodes
105
are connected to the external electrodes
104
.
On the other hand,
FIG. 6
shows another stacked piezoelectric element
201
, in which the internal electrodes
203
are formed in structure similar to that shown in
FIG. 5
, on the surfaces of the piezoelectric layers
202
and in which the internal electrodes
203
are connected by the through electrodes (through holes)
204
. The through electrodes
204
are exposed at their ends in the surface of the uppermost piezoelectric layer of the stacked piezoelectric element
201
, thereby forming the surface electrodes
205
.
Further,
FIG. 7
shows an application example in which the aforementioned stacked piezoelectric element
101
of
FIG. 5
is applied to the vibration body of the rodlike vibration wave motor. A wiring board
111
is kept in contact with the surface electrodes
105
of the stacked piezoelectric element
101
, and the stacked piezoelectric element
101
and the wiring board
111
are placed between hollow metal members
21
and
22
of the vibration body. A bolt
23
penetrating a center hole of the stacked piezoelectric element
101
is inserted from the side of the metal member
22
to be screwed into the metal member
21
. By tightening this bolt
23
, the stacked piezoelectric element
101
and wiring board
111
are pinched and fixed between the two metal members
21
and
22
. The wiring board
111
is connected to an unrepresented drive circuit and the drive circuit applies alternating voltages for driving, to the stacked piezoelectric element
101
.
Likewise, in the case where the stacked piezoelectric element
201
shown in
FIG. 6
is applied, the stacked piezoelectric element
201
and the wiring board
211
in contact with the surface electrodes
205
are also pinched and fixed between the metal members
21
and
22
. The stacked piezoelectric element
201
, which uses all the through electrodes as means for connecting the internal electrodes to each other, is incorporated into the vibration wave motor of the structure shown in
FIG. 7
, which is now under practical use as a driving source for driving a camera lens to effect autofocus.
The principle of driving of the rodlike vibration wave motor is as follows: a plurality of different bending vibrations with a temporal phase difference are generated in the vibration body equipped with the stacked piezoelectric element to force the distal end of the metal member
21
forming the vibration body, to perform a motion like a swinging motion. This motion rotates a rotor
24
kept in press contact with the metal member
21
, through friction.
An example of the structure of the internal electrodes suitable for such driving is the quartered internal electrodes, as shown in
FIGS. 5 and 6
. Let us suppose that these internal electrodes are phase A, phase B, phase AG, and phase BG in the circumferential direction. Two internal electrodes located in the positional relation of 180° (phase A and phase AG; and phase B and phase BG) are polarized in directions different from each other. These phases A to BG are formed so as to be identical among the second and lower piezoelectric layers, and the internal electrodes of identical phases on the different layers are electrically connected to each other by the aforementioned external electrodes or through electrodes.
When with the phases AG and BG being ground a high-frequency voltage (alternating signal) having a frequency approximately equal to the natural frequency of the vibration body is applied to phase A and to phase B different 90° from the phase of phase A with a temporal phase difference between them, two bending vibrations perpendicular to each other are generated in the vibration body.
The method of interposing the stacked piezoelectric element
101
,
201
and the wiring board
111
,
211
between the metal members
21
and
22
as described above is high in reliability of electrical conduction between the stacked piezoelectric element
101
,
201
and the wiring board
111
,
211
, and easy to assemble.
However, since the wiring board
111
,
211
is interposed between the metal members forming the vibration body of the vibration wave motor, this wiring board
111
,
211
causes damping of the vibrations. For this reason, there is conceivably plenty of scope for improvement in drive efficiency.
In addition, in the case of the stacked piezoelectric element
101
shown in
FIG. 5
, where the surface electrodes
105
are formed, for example, by inexpensive screen printing, the heights o
Budd Mark
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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