JP2011199206A - Piezoelectric element to be used for vibration device, vibration device, and dust removal device having vibration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element to be used for a vibration device for suppressing unwanted vibrations generated in a vibrator, causing bending deformation in a thickness direction by generating out-of-plane vibration in the vibrator, and attaining driving at a low voltage, and to provide a vibration device and a dust removal device.SOLUTION: The piezoelectric element to be used for a vibration device is configured of a plate-shaped piezoelectric element for causing a plate-shaped vibrator, configuring the vibration device to vibrate by applying an AC voltage, and the plate-shaped piezoelectric element is configured to be polarized to a direction which is orthogonal to the thickness direction of the plate-shaped vibrator, and generate out-of-plane vibration to cause bending deformation in the thickness direction of the vibrator.

Description

  The present invention relates to a piezoelectric element used in a vibration device, a vibration device, and a dust removing device having the vibration device, and in particular, foreign materials such as dust attached to the surface of an imaging device such as a digital camera and an optical component incorporated in the imaging device. The present invention relates to a piezoelectric element suitable for a dust removing device to be removed.

2. Description of the Related Art In an imaging apparatus such as a digital camera that captures an image signal by converting an image signal into an electrical signal, an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) receives light.
Then, the photoelectric conversion signal output from the image sensor is converted into image data and recorded on a recording medium such as a memory card.
In such an imaging apparatus, an optical low-pass filter and an infrared cut filter are arranged in front of the imaging element (subject side).
In this type of imaging apparatus, if foreign matter such as dust adheres to the cover glass of the image sensor or the surface of these filters, the foreign matter may become a black dot and appear in a captured image.
In particular, in a digital single lens reflex digital camera with interchangeable lenses, foreign matter such as dust may enter the digital camera body from the lens mount opening and adhere to the cover glass of the image sensor or the surface of the filter during lens replacement.

For this reason, conventionally, for example, as disclosed in Patent Document 1, a digital camera including a dust removing device that removes foreign matters such as dust attached to the surface using vibration of a piezoelectric element has been proposed. .
As shown in FIG. 6, in the dust removing device of Patent Document 1, the dust removing device 40 includes a piezoelectric element 41 and an infrared cut filter 42, which are main components, and a holding member (not shown).
In addition, as shown in FIG. 7, the A surface and the B surface on which the electrodes of the piezoelectric element 41 are disposed are opposed to each other in the thickness direction. The electrode on the A surface of the piezoelectric element 41 is divided into a + phase and a G phase. The electrode on the B surface of the piezoelectric element 41 is in the G phase, and is electrically connected to the G phase on the A surface by a conductive material (not shown).
The B surface of the piezoelectric element 41 is fixed to both ends of the plate-shaped rectangular infrared cut filter 42 by an adhesive, and the piezoelectric element 41 and the infrared cut filter 42 vibrate integrally.
A conductive connecting member such as a flexible printed board (not shown) is fixed to the A surface of the piezoelectric element 41 by adhesion or the like, and a predetermined voltage can be applied to the + phase and the G phase.
In addition, the vibration of the piezoelectric element 41 is used to generate two vibration modes, which are out-of-plane vibration modes that are bent and deformed in the thickness direction, of odd and even orders, thereby attaching to the surface of the infrared cut filter 42. The removed dust can be peeled off and removed.

Recently, in consideration of the environment, research on piezoelectric materials that do not use lead and development of products have been conducted.
Among these piezoelectric materials, for example, as disclosed in Patent Document 2, a multicomponent system mainly composed of bismuth sodium titanate ((Bi _0.5 Na _0.5 ) TiO ₃ ) that is relatively easy to manufacture. Piezoelectric ceramics that are solid solutions have been proposed.
Specifically, this is, for example, a solid solution ((Bi _0.5 Na _0.5 ) TiO ₃ − of bismuth sodium titanate ((Bi _0.5 Na _0.5 ) TiO ₃ ) and barium titanate (BaTiO ₃ ). BaTiO ₃ ). Furthermore, various elements and compounds are added as the third component, and the piezoelectric characteristics can be adjusted.
In addition to not using lead, this piezoelectric ceramic has a higher Curie temperature than barium titanate and is practical, and has the same firing temperature as lead zirconate titanate-based piezoelectric ceramics and can be used with conventional equipment. There is.

JP 2008-228074 A JP 2006-306668 A

However, the above-described conventional dust removing apparatus such as Patent Document 1 has the following problems.
When an out-of-plane vibration mode is generated in which the longitudinal direction of the infrared cut filter 42 is bent and deformed in the thickness direction, the piezoelectric element 41 is also bent and deformed in the thickness direction in a direction orthogonal to the longitudinal direction of the infrared cut filter 42. Cause out-of-plane vibration mode.
The vibration in the direction orthogonal to the longitudinal direction of the infrared cut filter 42 is originally unnecessary vibration, and becomes an obstruction factor for two out-of-plane vibration modes that cause bending deformation in the thickness direction of the original infrared cut filter 42. .
If such an obstruction factor can be eliminated, the dust removing performance of the dust removing device can be further improved, but this is not taken into consideration in the above-mentioned Patent Document 1.
Further, in the piezoelectric ceramic mainly composed of bismuth sodium titanate ((Bi _0.5 Na _0.5 ) TiO ₃ ) as in the above-mentioned conventional patent document 2, a large voltage is required to obtain displacement. Become.

  In view of the above problems, the present invention can suppress unnecessary vibration generated in a vibrating body, cause the vibrating body to bend in the thickness direction by out-of-plane vibration, and can be driven at a low voltage. An object of the present invention is to provide a piezoelectric element, a vibration device, and a dust removing device used in the vibration device.

The piezoelectric element of the present invention is a piezoelectric element used in a vibration device,
The piezoelectric element is composed of a plate-like piezoelectric element that vibrates a plate-like vibrating body constituting the vibration device by application of an alternating voltage,
The plate-like piezoelectric element is polarized in a direction perpendicular to the thickness direction of the plate-like vibrating body, and generates an out-of-plane vibration that causes bending deformation in the thickness direction of the vibrating body. .
In addition, a vibration device of the present invention includes the above-described piezoelectric element and a plate-like vibration body.
In addition, a dust removing device of the present invention includes the above-described vibration device, and the dust is moved and removed in a predetermined direction by the vibration device.

  According to the present invention, an unnecessary vibration generated in a vibrating body can be suppressed, the vibrating body can be bent and deformed in the thickness direction by out-of-plane vibration, and the vibration device can be driven at a low voltage. The piezoelectric element, the vibration device, and the dust removing device used can be realized.

It is a figure which shows the dust removal apparatus which concerns on embodiment of this invention, and its surrounding components. It is a figure which shows the piezoelectric element used for the dust removal apparatus which concerns on embodiment of this invention. It is a figure which shows the vibration which generate | occur | produces in the plate-shaped vibrating body of the dust removal apparatus which concerns on embodiment of this invention. It is a figure which shows manufacture of the piezoelectric element used for the dust removal apparatus which concerns on embodiment of this invention. It is a figure which shows manufacture of the multilayer piezoelectric element used for the dust removal apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the dust removal apparatus which concerns on a prior art example. It is a figure which shows the piezoelectric element used for the dust removal apparatus which concerns on a prior art example.

Below, the dust removal apparatus in embodiment using the vibration apparatus of this invention is demonstrated using figures.
As shown in FIG. 1, a dust removing device 1 for a digital camera according to this embodiment has a configuration including a piezoelectric element 2 and an infrared cut filter 3 that is a plate-like vibrating body and also an optical component.
An optical low-pass filter 4 is provided on the front surface, and is disposed on the front surface of the image pickup device package 5 having the image pickup device portion therein, and holds the corners of the frame-shaped support member 6 and the infrared cut filter 3 (not shown). It is protected by a frame-shaped holding member that prevents displacement.
The support member 6 is fixed between the imaging element package 5 and the infrared cut filter 3 by an adhesive material.
The support member 6 supports the infrared cut filter 3 while positioning the imaging device package 5 and the infrared cut filter 3 relative to each other.
As shown in FIG. 1, the two piezoelectric elements 2 are fixed to both ends of the infrared cut filter 3 by adhesion, and the piezoelectric element 2 and the infrared cut filter 3 can vibrate integrally.

As shown in FIG. 2, the piezoelectric element 2 is formed with an electrode + phase and a G phase that face each other in a direction orthogonal to the thickness direction of the piezoelectric element 2.
It is polarized by applying a voltage between the electrode + phase and the G phase, and the polarization direction is the direction indicated by the arrow P. That is, the piezoelectric element 2 is polarized in a direction orthogonal to the thickness direction of the plate-shaped infrared cut filter 3. In the present invention, the term “orthogonal” may include a certain error within a range that does not adversely affect the function as well as a case where the angles intersect with each other while maintaining a strictly 90 ° angle.
A conductive connecting member such as a flexible printed circuit board (not shown) is fixed to the opposing electrode + phase and G phase of the piezoelectric element 2 by adhesion or the like, and two piezoelectric elements 2 are connected from a driving power supply (not shown). A predetermined high frequency voltage can be applied to the + phase and the G phase.

Next, the difference between the piezoelectric element 2 of the present embodiment and the piezoelectric element 41 of the conventional example will be described.
As shown in FIG. 7, the piezoelectric element 41 of the conventional example is polarized and can vibrate by applying a voltage between the + phase on the A surface of the two opposing electrodes and the G phase on the B surface. The polarization direction is the direction indicated by the arrow P.
For this reason, the piezoelectric constant in the X direction that causes expansion and contraction in the X direction is d31, and the piezoelectric constant in the Y direction related to expansion and contraction in the Y direction is also d31.
On the other hand, in the piezoelectric element 2 according to the present invention, as shown in FIG. 2, two opposing electrodes are polarized by applying a voltage between the + phase and the G phase, and can vibrate. The polarization direction is the direction indicated by the arrow P.
For this reason, the piezoelectric constant in the X direction related to expansion and contraction in the X direction (direction perpendicular to the thickness direction of the vibrating body) is d33, whereas the Y direction (in-plane direction of the vibrating body perpendicular to the X direction). The piezoelectric constant in the Y direction related to the expansion and contraction of d is d31, which has different characteristics in the X direction and the Y direction.

Here, the piezoelectric constant d represents the strain with respect to the voltage per unit length.
D31 is an applied voltage in the same direction as the polarization direction 3 (Z direction), and in a direction 1 orthogonal to the direction 1 (X direction and Y direction, in the case of piezoelectric ceramics, the X direction and Y direction are equivalent characteristics). It means the piezoelectric constant d.
D33 means the piezoelectric constant d in the same direction 3 (Z direction) with respect to the applied voltage in the same direction 3 (Z direction) as the polarization direction 3 (Z direction). Normally, d31 is expressed with a negative sign, but here it is expressed as an absolute value.
In general, a piezoelectric material mainly composed of lead zirconate titanate or a piezoelectric material mainly composed of barium titanate, which is a general piezoelectric ceramic, generally has a ratio d33 / d31 between the piezoelectric constant d33 and the piezoelectric constant d31 of about 2. 0.0-2.5.
If the piezoelectric constant d33 is large, the same size and the same applied voltage, a large displacement of about 2.0 to 2.5 times is obtained when the displacement occurs along the polarization direction 3.
That is, as shown in FIG. 2, the displacement in the Y direction with respect to the displacement in the X direction of the piezoelectric element 2 is smaller than the piezoelectric element 41 of the conventional example by an inverse number (0.4 to 0.5) of this ratio d33 / d31. Become.

Next, vibration generated in the infrared cut filter 3 which is a plate-like vibrating body that vibrates integrally with the piezoelectric element 2 and is also an optical component will be described with reference to FIG.
Similarly to Patent Document 1, when the voltage applied to the piezoelectric element 2 is periodically switched between positive and negative, the Z direction (thickness direction of the infrared cut filter 3) has a displacement distribution in the longitudinal direction that is the X direction of the infrared cut filter 3. ) Bending vibration occurs.
That is, when an alternating voltage having a frequency close to the natural frequency of the vibration mode to be generated is applied to the + phase of the two piezoelectric elements 2 in the same phase, an odd-order out-of-plane mode vibration that causes bending deformation in the thickness direction is generated. .
Further, when this AC voltage is applied in the opposite phase to the + phase of the two piezoelectric elements 2, even-order out-of-plane mode vibrations that cause bending deformation in the thickness direction are generated.
For example, the two vibration modes are out-of-plane vibration modes that are bent and deformed in the thickness direction. The first vibration mode 10 has an odd order (eg, 19th mode) and the even order (eg, 20th order). A second vibration mode 11 occurs.
The first vibration mode 10 and the second vibration mode 11 are bending vibrations of standing waves that occur in the X direction of the infrared cut filter and have different wavelengths (the vibration mode 11 has a shorter wavelength than the vibration mode 10).
Both of the two piezoelectric elements 2 have nodes at two locations in contact with the inner support members.

FIG. 3 shows a first vibration mode 10 and a second vibration mode 11 that are generated in the X direction, which is the longitudinal direction of the infrared cut filter 3. One of the nodes N inside the piezoelectric element and the vibration are shown in FIG. A part of the waveform is represented.
At the same time, not only the first vibration mode 10 in the X direction and the vibration mode 11 of the younger brother 2 but also a bending vibration having a displacement distribution in the Y direction is generated.
That is, the vibration mode 12 that is an out-of-plane vibration mode that is bent and deformed in the thickness direction in a direction orthogonal to the longitudinal direction of the infrared cut filter 3 is likely to occur. For example, the vibration mode 12 is likely to be a bending primary vibration mode having two nodes.
However, this vibration mode 12 is originally unnecessary vibration, and the position of the vibration node is changed to the original first vibration mode 10 and the second vibration mode 11 in the X direction which is the longitudinal direction of the infrared cut filter 3. Causing effects such as causing non-uniform vibrations. As a result, the ability to remove dust as a dust removing device has been reduced.
It has been found that the smaller the influence of this unnecessary vibration mode 12, the greater the effect of removing foreign matter by vibration.

Here, as described above, the piezoelectric element 2 has the same dimensions as the piezoelectric element 41 of the conventional example, but the polarization direction and the location of the electrodes are different.
That is, in the piezoelectric element 2 shown in FIG. 2, in the piezoelectric material mainly composed of lead zirconate titanate, as described above, the reciprocal (0.4 to 0.5) of the ratio d33 / d31 corresponds to the X direction. Can be made smaller than the displacement in the Y direction.
As a result, the first vibration mode 10 is generated on the entire surface of the infrared cut filter 3, so that dust attached to the antinode position of the vibration of the first vibration mode 10 is more effectively separated and scattered.
Further, by causing the vibration of the second vibration mode 11 to occur, the dust adhering to the vibration node of the first vibration mode 10 is more effectively separated and scattered.
As described above, the dust removing device 10 can remove foreign matters such as dust adhering to the surface by using the vibration of the piezoelectric element 2, and can realize a high-performance dust removing device. .

Piezoelectric materials that do not use lead are currently being studied. Among them, piezoelectric ceramics mainly composed of bismuth sodium titanate ((Bi _0.5 Na _0.5 ) TiO ₃ ) have anisotropy after polarization. Arise.
That is, it is the ratio between the piezoelectric constant d33 that causes displacement in the direction orthogonal to the thickness direction of the vibrator and the piezoelectric constant d31 that causes displacement in the in-plane direction of the vibrator perpendicular to the direction of displacement of the piezoelectric constant d33. d33 / d31 is 3 or more.
This characteristic can be said to be a material more suitable for suppressing unnecessary vibration than the lead zirconate titanate system as the piezoelectric material of the piezoelectric element of the present invention.
However, in a general lead zirconate titanate system, d33 is at least 200 to 300 × 10 ⁻¹² m / V or more.
On the other hand, in bismuth sodium titanate-based piezoelectric ceramics, d33 is currently a small value of about 80 to 160 × 10 ⁻¹² m / V, and a large voltage is required to obtain the same displacement. .
Therefore, in this embodiment, as will be described later, by stacking, the displacement is increased by the number of layers in the stacking direction, and low voltage driving is possible.

The piezoelectric element 2 can be manufactured as follows.
First, as shown in FIG. 4A, a piezoelectric ceramic powder is press-molded and fired to produce a block-shaped piezoelectric ceramic, and then ground to a predetermined size to produce a block-shaped piezoelectric ceramic 20.
Thereafter, the opposing electrodes 21 and 22 are formed by baking on a silver paste.
And a voltage is applied between the electrodes 21 and 22, and a polarization process (polarization direction P) is performed. After that, as shown in FIG. 4B, the block-shaped piezoelectric ceramic 20 is cut into a predetermined thickness by a cutting machine, and the piezoelectric element 2 is manufactured.
In such a block-shaped piezoelectric ceramic 20, it is possible to produce a large number of piezoelectric elements 2 by providing an electrode by one printing and performing a polarization process once.
Therefore, like the conventional piezoelectric element 41, it is easier to work and can produce a large number of pieces in a short time compared to the method of making each plate-like piezoelectric ceramic by printing and providing electrodes and individually performing polarization treatment. It becomes possible.

The laminated piezoelectric element 2 ′ can be manufactured as shown in FIG.
First, a sheet is formed from a piezoelectric ceramic powder, and an electrode paste for forming an internal electrode layer 34 is printed on the surface, and at the same time, holes 35-1 and 35- 2 is provided, and a conductive paste is filled in the hole to form a conductive portion.
Next, a plurality of these sheets are stacked and pressed to form a laminate. And this laminated body is baked simultaneously with an electrode paste, and the laminated piezoelectric ceramic 30 is made.
A voltage is applied to the electrodes 31 and 32 formed on the surface of the laminated piezoelectric ceramic 30 to perform polarization processing of the piezoelectric layer 33 between the electrode layers.
FIG. 5B shows a cross section of the multilayer piezoelectric ceramic 30 of FIG.
Inside, there are holes 35-1 and 35-2 that are electrically connected to the electrode layer 34 and the electrode layer 34, and the holes 35-1 and 35-2 are exposed on the surface.
By the polarization process, the polarization direction of the piezoelectric layer 33 becomes as indicated by an arrow P, and vibration can be caused by applying a voltage from an external power source (not shown).
After the polarization treatment, as shown in FIG. 5C, the electrodes 31 and 32 formed on the surface after being ground to a predetermined dimension are deleted to obtain a block-shaped laminated piezoelectric ceramic 36.
Then, it cuts out to predetermined thickness with a cutting machine, and can produce laminated piezoelectric element 2 'like FIG.5 (d).

A conductive connecting member such as a flexible printed circuit board is fixed to the opposing holes 35-1 and 35-2 of the piezoelectric element 2 ′ by bonding or the like, and the holes 35-1 and 35-2 of the piezoelectric element 2 ′ are connected from the driving power source. A voltage having a predetermined high frequency can be applied.
Both the piezoelectric element 2 and the laminated piezoelectric element 2 ′ are made of a piezoelectric material mainly composed of lead zirconate titanate, a piezoelectric material mainly composed of barium titanate, and a piezoelectric material mainly composed of bismuth sodium titanate. Can do.
When stacked, the vibration displacement can be increased by the same applied voltage as the number of layers in the stacking direction. In this example, since the two piezoelectric layers 33 are provided inside, in order to obtain the same displacement, the applied voltage can be halved.
In piezoelectric ceramics based on sodium bismuth titanate, d33 is a small value of about 80 to 160 × 10 ⁻¹² m / V at most, and a large voltage is required to obtain the same displacement. However, if the layers are stacked, the displacement can be increased by the number of layers in the stacking direction, and driving at a low voltage is possible.

Such a block-shaped laminated piezoelectric ceramic 30 can produce a large number of laminated piezoelectric elements 2 ′ by performing the polarization treatment only once, and can produce a large number in a short time.
In the present embodiment, the two vibration modes of the first vibration mode and the second vibration mode are used as the vibration mode for removing dust. However, the present invention is not limited to this. In addition, a plurality of other vibration modes may be added. In addition, although two piezoelectric elements 2 are used, a large vibration can be obtained if the diaphragm is a component made of a material with less vibration attenuation.

As described above, according to the present invention, when removing foreign matter such as dust attached to the surface of an optical component or the like by vibration, the plate-like piezoelectric element is orthogonal to the thickness direction of the plate-like vibrating body. It becomes possible to further improve the effect of removing the foreign matter by polarizing to.
In addition, since such a piezoelectric element can be produced in a single electrode formation and a single polarization process, the cost of the piezoelectric element can be reduced.
As a result, in the dust removing device, the dust attached to the vibrating body can be moved and removed more effectively than before by vibration, and the quality of the photographed image by the digital camera can be improved.
In addition, an equivalent effect can be made possible with a lower applied voltage. Accordingly, it is possible to reduce the voltage of the power supply circuit, that is, to use a circuit element having a low withstand voltage, and to reduce the cost.
Moreover, although the case where the dust removal apparatus was applied to the digital digital camera was mentioned as an example in the above description, the present invention is not limited to this.
The dust removing apparatus of the present invention can be applied to various image apparatuses such as a video digital camera, a copying machine, a facsimile machine, and a scanner.

1: Dust removing device 2: Piezoelectric element 2 ′: Multilayer piezoelectric element 3: Vibrating body 10: First vibration mode 11: Second vibration mode 12: Unnecessary vibration mode

Claims (9)

A piezoelectric element used in a vibration device,
The piezoelectric element is composed of a plate-like piezoelectric element that vibrates a plate-like vibrating body constituting the vibration device by application of an alternating voltage,
The plate-like piezoelectric element is polarized in a direction perpendicular to the thickness direction of the plate-like vibrating body, and generates an out-of-plane vibration that causes bending deformation in the thickness direction of the vibrating body. Piezoelectric element.   The piezoelectric element according to claim 1, wherein the piezoelectric element is made of piezoelectric ceramics. In the piezoelectric element, a piezoelectric constant that causes displacement in a direction perpendicular to the thickness direction of the vibrating body is d33, and a piezoelectric constant that causes displacement in an in-plane direction of the vibrating body perpendicular to the displacement direction of the piezoelectric constant d33. When d31
The piezoelectric element according to claim 2, wherein a ratio d33 / d31 thereof is 3 or more.   4. The piezoelectric element according to claim 3, wherein the piezoelectric element is made of the piezoelectric ceramic mainly composed of bismuth sodium titanate.   5. The piezoelectric element according to claim 2, wherein the plate-like piezoelectric element is configured by polarizing the piezoelectric ceramic formed in a block shape. 6.   6. The piezoelectric element according to claim 2, wherein the piezoelectric element is configured by polarizing a laminated piezoelectric ceramic formed by the piezoelectric ceramic and an electrode.   A vibration device comprising the piezoelectric element according to claim 1 and a plate-like vibration body.   The plate-like vibration device according to claim 7, wherein the plate-like vibrating body is configured by an optical component.   9. A dust removing device comprising the vibrating device according to claim 8, wherein the dust is moved and removed in a predetermined direction by the vibrating device.

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