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JP2015231045

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DESCRIPTION JP2015231045
The present invention provides a piezoelectric film capable of suppressing deformation in the
width direction even if elongation or contraction occurs in the length direction. Kind Code: A1 A
piezoelectric film 1 in which an expansion or contraction stress occurs in a 45 ° direction and a
−45 ° direction in a clockwise direction with reference to a Y-axis direction when a voltage is
applied. The unit region 10 is arranged in the X-axis direction with the electrode forming portion
11 in which the electrodes are arranged on the front and back, and the electrode is on the front
and back with the opposite polarity to the electrode forming 11 An electrode forming portion 12
is provided, and an electrode non-forming portion 13 connected to a region adjacent to one edge
at one edge in the Y-axis direction. The other edge of the unit region 10 in the Y-axis direction A
notch 5 continuous to the electrode forming portion 12 is provided. [Selected figure] Figure 3
Piezoelectric film, vibration device, and strain detection device
[0001]
The present invention relates to a piezoelectric film, a vibrating device that utilizes the vibration
of the piezoelectric film, and a strain detection device that detects strain of the piezoelectric film.
[0002]
In a vibrating device or a strain detection device, a piezoelectric film mainly composed of a chiral
polymer may be used (see, for example, Patent Document 1).
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A piezoelectric film containing a chiral polymer as a main component develops shear
piezoelectricity by being subjected to a stretching process. Shear piezoelectricity is
piezoelectricity in which expansion and contraction simultaneously occur in the main surface by
application of an electric field, and when the polarity of the electric field applied to the
piezoelectric film is reversed, it has the property that expansion and contraction are reversed.
There is.
[0003]
Here, a planar speaker will be described as an example of a device utilizing a piezoelectric film
having shear piezoelectricity. 12A is a front view of the flat loudspeaker 101, and FIG. 12B is a
side view of the flat loudspeaker 101. As shown in FIG. The flat speaker 101 includes a
piezoelectric film 102, a diaphragm 103, and frame members 104 and 105. The piezoelectric
film 102 is cut out in a strip shape from a PLLA (L-type polylactic acid) film subjected to a
stretching process, with the 45 ° direction to the stretching direction as the length direction.
The piezoelectric film 102 is cut out in the direction of 45 ° with respect to the stretching
direction as a length direction, whereby the application of a voltage causes an extension or
contraction in the length direction. The frame members 104 and 105 are provided at both ends
of the piezoelectric film 102 in the longitudinal direction. The diaphragm 103 is connected to the
piezoelectric film 102 through the frame members 104 and 105 in a state of being curved so
that the distance to the piezoelectric film 102 is gradually separated from near both ends in the
length direction to near the center in a side view ing. For this reason, the piezoelectric film 102 is
pulled outward from the diaphragm 103 via the frame members 104 and 105. In such a flat
speaker 101, when an alternating electric field is applied to the piezoelectric film 102, expansion
and contraction in the longitudinal direction occur in the piezoelectric film 102, and along with
this, vibration is caused in the diaphragm 103.
[0004]
International Publication 2012/157691 brochure
[0005]
In the above-mentioned piezoelectric film, distortion in the width direction (transverse distortion)
occurs with the extension and contraction in the length direction.
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For this reason, stress load in the width direction is applied to the connection portion between
the piezoelectric film and the diaphragm, and this stress load in the width direction may cause a
failure in the vibration device or the strain detection device.
[0006]
Therefore, an object of the present invention is to provide a piezoelectric film capable of
suppressing the occurrence of shrinkage or elongation in the width direction even when the film
is stretched or shrunk in the length direction. Another object of the present invention is to
provide a vibration device and a strain detection device capable of suppressing stress load in the
width direction applied to the connection portion between the piezoelectric film and the other
member.
[0007]
In the piezoelectric film according to the present invention, when a voltage is applied, distortion
in the extension direction occurs in one of the two displacement directions in plan view, and
distortion in the contraction direction occurs in the other. The piezoelectric film is provided with
one or more unit areas having a length direction and a width direction that intersects the two
displacement directions in plan view. The unit regions are arranged in the width direction with a
first electrode forming portion in which electrodes are disposed on the front and back surfaces,
and a polarity reverse to the first electrode forming portion on the front and back surfaces. And
an electrode non-forming portion connected to a region adjacent in the longitudinal direction at
one edge of the unit region in the longitudinal direction. The other edge of the unit region in the
length direction is provided with a notch which is continuous from the first electrode forming
portion to the second electrode forming portion.
[0008]
In this configuration, when an electric field of reverse polarity is applied to the first electrode
formation portion and the second electrode formation portion, the expansion and contraction
that occur in the two displacement directions are determined by the first electrode formation
portion and the second electrode formation portion. And vice versa. Then, the deformation in the
width direction is offset by the first electrode formation portion and the second electrode
formation portion, and the expansion and contraction in the displacement direction in the first
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electrode formation portion and the second electrode formation portion are in the length
direction of the entire piezoelectric film Is transformed into a variant of. Therefore, even if the
piezoelectric film is expanded and contracted in the length direction, the generation of the
contraction and the expansion in the width direction can be suppressed.
[0009]
A plurality of unit areas may be arranged in the width direction. In this way, the force applied to
the entire film can be dispersedly held in the width direction in the application requiring the
force.
[0010]
It is preferable that a plurality of unit areas are arranged in the longitudinal direction. Thereby,
the amount of deformation in the longitudinal direction of the piezoelectric film can be further
increased.
[0011]
It is preferable that the notches adjacent to each other in the longitudinal direction have the
same shape and are offset from each other in the width direction, and the unit areas adjacent to
each other in the longitudinal direction are mirror images of each other. As a result, a large
number of unit regions can be arranged in the longitudinal direction, and the amount of
deformation in the longitudinal direction of the piezoelectric film can be further increased.
[0012]
One of the electrodes disposed on the front and back of the first electrode forming portion and
one of the electrodes disposed on the front and back of the second electrode forming portion
may be provided as a common electrode. Thereby, the common electrode can be easily formed.
[0013]
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The electrodes disposed on the front and back of the first electrode forming portion and the
electrodes disposed on the front and back of the second electrode forming portion may be
provided as separate electrodes. Thereby, the electrode area of the front and back can be arrange
¦ equalized by a 1st electrode formation part or a 2nd electrode formation part, and the
curvature of a piezoelectric film can be relieve ¦ moderated.
[0014]
The above-mentioned piezoelectric film preferably contains a chiral polymer whose orientation
direction is the length direction or the width direction.
[0015]
The chiral polymer is preferably polylactic acid.
[0016]
According to a vibrating device of the present invention, a vibration unit connected to the
piezoelectric film, a driving unit that applies an electric field with reverse polarity to each of the
piezoelectric film, the first electrode forming unit and the second electrode forming unit, and And
a member.
Even if the piezoelectric film is stretched or shrunk in the lengthwise direction, the shrinkage or
elongation occurring in the width direction is suppressed. Therefore, even if the piezoelectric film
is vibrated in the lengthwise direction in the vibrating device, the vibrating member and the
piezoelectric film There is no stress in the width direction applied to the connecting part.
[0017]
The strain detection device according to the present invention is connected to the piezoelectric
film described above, a detection unit that detects an electric charge generated in at least one of
the first electrode forming unit and the second electrode forming unit, and the piezoelectric film
And a strain member.
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Even if the piezoelectric film is stretched or shrunk in the lengthwise direction, the shrinkage or
stretching occurring in the width direction is suppressed, so that the strain detection device
detects the stretching or the shrinkage caused by the strain in the lengthwise direction acting on
the piezoelectric film Even in this case, no stress load is applied in the width direction to the
connection portion between the strain member and the piezoelectric film.
[0018]
According to the present invention, in the piezoelectric film, even if stretching or shrinking
occurs in the length direction, it is possible to suppress the occurrence of shrinkage or stretching
in the width direction. Further, in the vibration device or the strain detection device, the stress
load in the width direction applied to the connection portion between the piezoelectric film and
the other member can be suppressed, and the failure of the device can be suppressed.
[0019]
It is a top view of the piezoelectric film concerning a 1st embodiment. It is a side sectional view
of a piezoelectric film concerning a 1st embodiment. It is a top view which shows the unit area ¦
region of the piezoelectric film which concerns on 1st Embodiment. It is a top view which shows
the deformation ¦ transformation aspect of the piezoelectric film which concerns on 1st
Embodiment. It is side surface sectional drawing of the piezoelectric film which concerns on 2nd
Embodiment. It is a top view of the piezoelectric film concerning a 3rd embodiment. It is a top
view of the piezoelectric film concerning a 4th embodiment. It is a top view which shows the
deformation ¦ transformation aspect of the unit area ¦ region in the piezoelectric film which
concerns on 4th Embodiment. It is a typical block diagram of a vibrating device concerning a 5th
embodiment. It is a side view in the case of comprising a tactile sense presentation device as an
oscillating device concerning a 5th embodiment. It is a typical block diagram of the distortion
detection device concerning a 6th embodiment. It is a schematic diagram of the conventional
device.
[0020]
Hereinafter, referring to the drawings, some specific examples will be given to show a plurality of
modes for carrying out the present invention. The same reference numerals are given to the
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same parts in each drawing. It goes without saying that each embodiment is an example, and
partial replacement or combination of the configurations shown in different embodiments is
possible.
[0021]
FIG. 1 is a plan view of a piezoelectric film according to a first embodiment of the present
invention. FIG. 2 is a side cross-sectional view passing through the position shown by a dashed
dotted line A-A 'in FIG. In the drawings described below, the Z axis along the thickness direction
of the piezoelectric film, the Y axis along the length direction, and the X axis along the width
direction are attached.
[0022]
The piezoelectric film 1 includes a film substrate 2, a front electrode 3, and a back electrode 4.
[0023]
The film substrate 2 is subjected to a stretching treatment in which uniaxially or biaxially
stretching is performed on a film mainly composed of L-type polylactic acid (PLLA) which is a
chiral polymer, and the main stretching direction having a larger stretching ratio is As a length
direction (Y-axis direction), it cut out in strip shape.
In FIG. 1, the main stretching direction of the film is indicated by a black arrow. The chiral
polymer such as PLLA has a main chain having a helical structure, and the main chain of the
chiral polymer can be oriented in the main stretching direction by the stretching process. Thus,
the film substrate 2 has piezoelectricity. The film substrate 2 is stretched and contracted in each
displacement direction by the application of an electric field, with the 45 ° direction and the
−45 ° direction clockwise as two displacement directions with reference to the length direction
(Y axis direction) It happens at the same time. The film substrate 2 has such a property that when
the polarity of the applied electric field is reversed, the elongation and the contraction in the 45
° direction and the −45 ° direction are reversed.
[0024]
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The stretching ratio in the stretching process is preferably about 3 to 8 times, and by applying
heat treatment after stretching, crystallization of extended chain crystals of polylactic acid can be
promoted to improve the piezoelectric constant. In the case of biaxial stretching, the same effect
as uniaxial stretching can be obtained by making the stretching ratio of each axis different. For
example, when stretching is performed eight times in the Y-axis direction and twice in the X-axis
direction, substantially the same effect as in the case where uniaxial stretching is performed
about four times in the Y-axis direction can be obtained. Since a film uniaxially stretched simply
tears along the stretching axis direction, the strength can be somewhat increased by performing
biaxial stretching as described above.
[0025]
In addition, PLLA produces piezoelectricity by drawing processing, and it is not necessary to
perform poling processing as in other polymers such as polyvinylidene fluoride (PVDF) and
piezoelectric ceramics. That is, the piezoelectricity of PLLA, which does not belong to the
ferroelectric substance, is not expressed by the polarization of ions as in the case of a
ferroelectric substance such as PVDF or lead zirconate titanate (PZT), but is a characteristic
structure of the molecule. It is derived from a helical structure. For this reason, PLLA does not
have pyroelectricity that occurs with other ferroelectric piezoelectric materials. Furthermore,
although PVDF and the like show variations in the piezoelectric constant over time, and in some
cases the piezoelectric constant may significantly decrease, the piezoelectric constant of PLLA is
extremely stable over time. Therefore, the piezoelectric constant of PLLA is unlikely to be
affected by the surrounding environment.
[0026]
The film base 2 is provided with a plurality of notches 5. Each notch 5 penetrates the film
substrate 2 in the thickness direction (Z-axis direction), and extends along the width direction (Xaxis direction). The plurality of notches 5 are arranged in a staggered manner while shifting the
position in the width direction (X-axis direction). That is, some of the plurality of notches 5 are
arranged on a straight line extending in the width direction (X-axis direction), and each set of
notches 5 aligned in the width direction (X-axis direction) is They are arranged side by side in the
length direction (Y-axis direction) while shifting the position (X-axis direction). Then, in two
notches 5 adjacent in the length direction (Y-axis direction), one end in the width direction (Xaxis direction) of one notch 5 and the width direction (X-axis direction) of the other notch 5 It is
made to oppose the other end by a predetermined length in the length direction (Y-axis
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direction).
[0027]
A plurality of surface electrodes 3 are provided side by side in the width direction (X-axis
direction), and provided in plurality in the length direction (Y-axis direction). Each surface
electrode 3 is disposed at a predetermined interval in the width direction (X-axis direction) so as
to be sandwiched by the regions where the two notches 5 are opposed in the length direction (Yaxis direction). The cutouts 5 are provided to have substantially the same width as the opposing
length. As shown in FIG. 2, these surface electrodes 3 are alternately connected to a positive
potential (100 V) or a negative potential (−100 V) in order of alignment in the width direction
(X-axis direction). In addition, these surface electrodes 3 are alternately connected to a positive
potential (100 V) or a negative potential (−100 V) in order of alignment in the length direction
(Y-axis direction).
[0028]
The back surface electrode 4 is provided so as to cover the entire back surface of the film
substrate 2 as shown in FIG. The back electrode 4 covers the entire back surface of the film
substrate 2 and is common to the plurality of front electrodes 3 as opposed electrodes, so the
back electrode 4 is easy to form.
[0029]
As shown in FIG. 1, since the notch 5 and the surface electrode 3 are regularly provided on the
piezoelectric film 1 in plan view, the piezoelectric film 1 has a plurality of units having the same
shape in plan view. Area 10 can be divided.
[0030]
FIG. 3 is a plan view showing a unit area 10 of the film substrate 2 in an enlarged manner.
The film substrate 2 includes, for each unit region 10, a first electrode forming portion 11, a
second electrode forming portion 12, and an electrode non-forming portion 13. The first
04-05-2019
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electrode forming portion 11 and the second electrode forming portion 12 are regions of the film
substrate 2 in which the surface electrode 3 and the back electrode 4 are disposed on the front
and back, respectively. The electrode non-formed portion 13 is a region in which the front
electrode 3 and the back electrode 4 are not formed on at least one of the front and back
surfaces.
[0031]
The first electrode forming portion 11 and the second electrode forming portion 12 are arranged
in the width direction (X-axis direction). The electrode non-forming portion 13 is located between
the first electrode forming portion 11 and the second electrode forming portion 12 in the width
direction (X-axis direction). The non-electrode-formed portion 13 of each unit region 10 extends
on one side (upper side in FIG. 3) in the longitudinal direction (Y-axis direction) and is connected
to another adjacent region. Notches 5 are provided on both sides of the non-electrode forming
portion 13 at an edge (upper side in FIG. 3) of one unit direction 10 in the longitudinal direction
(Y-axis direction). In addition, a notch 5 is formed on the other end (lower side in FIG. 3) of the
length direction (Y axis direction) of each unit region 10 so as to be continuous from the first
electrode forming portion 11 to the second electrode forming portion 12. Is provided.
[0032]
The surface electrodes 3 adjacent to each other in the width direction (X-axis direction) of the
piezoelectric film 1 are connected to different potentials, so that the first electrode forming
portion 11 and the second electrode forming portion 12 have opposite polarities to each other.
An electric field is applied. And since each of the 1st electrode formation part 11 and the 2nd
electrode formation part 12 has shear piezoelectricity, if the polarity of the applied electric field
is reverse, along 45 degrees direction and -45 degrees direction Elongation and contraction
occur in reverse.
[0033]
For example, as shown in FIG. 3A, when the first electrode forming portion 11 is deformed so as
to extend along the 45 ° direction and extend along the −45 ° direction, the second electrode
forming portion 12 Elongate along the 45 ° direction and deform to shrink along the −45 °
direction. Thereby, the edge of the upper side (the side where the non-electrode forming portion
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10
13 is connected to the other area) in FIG. 3A of the unit area 10 is deformed into a concave
shape, and the edge in FIG. The edge of the lower side (the side where the notch 5 continues in
the width direction) is deformed in a convex shape.
[0034]
Conversely, as shown in FIG. 3B, when the first electrode forming portion 11 extends along the
45 ° direction and deforms so as to contract along the −45 ° direction, the second electrode
forming portion 12 Shrink along the 45 ° direction and deform to extend along the −45 °
direction. Thus, the edge of the upper side (the side where the electrode non-formed portion 13
is connected to the other area) in FIG. 3B of the unit area 10 is convex, and the lower side in FIG.
The edge of the side (the side where the notch 5 is continuous in the width direction (X-axis
direction)) is deformed in a concave shape.
[0035]
As described above, in the entire unit region 10, the expansion and contraction in the first
electrode formation portion 11 and the second electrode formation portion 12 are offset in the
width direction (X-axis direction), and convex in the length direction (Y-axis direction) Or it is
transformed into a deformation that bends concavely.
[0036]
FIG. 4 is a plan view showing the entire deformation mode (at the time of shortening) of the
piezoelectric film 1.
In FIG. 4, the gray level display is made thinner as the deformation amount in the length
direction (Y-axis direction) from the time of non-deformation of the piezoelectric film 1 is larger.
[0037]
The piezoelectric film 1 can partition the unit area 10 for each combination of two surface
electrodes 3 adjacent in the width direction (X-axis direction). Therefore, in this piezoelectric film
1, three unit regions 10 are arranged so that parts overlap each other in the width direction (X-
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11
axis direction), and the notches 5 are separated in the length direction (Y-axis direction) A
plurality of unit areas 10 can be divided such that eight unit areas 10 are aligned. Hereinafter,
the unit areas 10 aligned in the length direction (Y-axis direction) will be referred to as unit areas
C1 to C8 in order from the upper side in FIG. 4. Unit regions C <b> 1 to C <b> 8 are mirror
images of adjacent ones in the length direction (Y-axis direction).
[0038]
In FIG. 4, in each of the unit regions C1 to C8, the same deformation as the deformation shown in
FIG. 3A occurs. That is, in each unit region C1 to C8, the edge on the side where notch 5 breaks
in the width direction (X-axis direction) is deformed into a concave shape, and notch 5 is
continuous in the width direction (X-axis direction) The side edge deforms into a convex shape.
Since the odd-numbered unit areas C1, C3, C5, and C7 and the even-numbered unit areas C2, C4,
C6, and C8 are mirror images of each other, in the length direction (Y-axis direction) An opposite
deformation occurs. As a result, the piezoelectric film 1 is deformed so as to narrow the line
width of each notch 5, and the entire length of the piezoelectric film 1 in the length direction (Yaxis direction) is shortened.
[0039]
When the polarity of the potential connected to each surface electrode 3 is reverse, deformation
similar to the deformation shown in FIG. 3B occurs in each unit region C1 to C8 of the
piezoelectric film 1. That is, in each of the unit regions C1 to C8, the edge on the side where the
notch 5 is interrupted in the width direction (X-axis direction) is deformed into a convex shape,
and the notch 5 is continuous in the width direction (X-axis direction) The edge on the side to be
deformed will be concave. In this case, the piezoelectric film 1 is deformed so that the line width
of each notch 5 is expanded, and the entire length in the length direction (Y-axis direction) of the
piezoelectric film 1 is extended.
[0040]
As described above, when the unit regions C1 to C8 are deformed, while the deformation in the
width direction (X-axis direction) of the piezoelectric film 1 as a whole is suppressed, the
elongation or contraction in the 45 ° direction or −45 ° direction is long. It can be converted
into deformation in the longitudinal direction (Y-axis direction). Therefore, even if the
04-05-2019
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piezoelectric film 1 stretches or contracts in the length direction, displacement in the width
direction does not occur. Thereby, when utilizing the piezoelectric film 1, generation ¦ occurrence
¦ production of interference with the piezoelectric film 1 and the other member adjacent to the
width direction can be prevented. Moreover, the arrangement ¦ positioning space of the
piezoelectric film 1 and another member can be narrowed.
[0041]
In the present embodiment, since a plurality of unit regions 10 are arranged in the width
direction (X-axis direction), the force applied to the entire piezoelectric film 1 is used in the width
direction when used for applications requiring a force. Can be dispersed. Further, since a large
number of unit regions 10 are arranged in the longitudinal direction (Y-axis direction) of the
piezoelectric film 1, the deformation amount in the longitudinal direction (Y-axis direction) of the
piezoelectric film 1 can be increased. In addition, since the unit areas 10 adjacent to each other
in the length direction (Y-axis direction) are mirror images, the arrangement interval between the
unit areas 10 adjacent to each other in the length direction (Y-axis direction) is narrowed. A large
number of unit areas 10 can be arranged in the Y axis direction). Moreover, since a large number
of unit regions 10 are provided in a miniaturized manner, the total displacement of the
piezoelectric film 1 can be controlled and increased. Further, since the notch 5 is formed in a
strip shape which is thin in the length direction (Y-axis direction) and long in the width direction
(X-axis direction), the area utilization efficiency of the piezoelectric film 1 can be maximized. Due
to these, the configuration of the present embodiment is more effective when used in an
application where importance is given to maximizing the displacement amount.
[0042]
In the present embodiment, a configuration example in which the front surface electrode 3 and
the back surface electrode 4 are directly bonded to the film base 2 has been described, but the
front surface electrode 3 and the back surface electrode 4 may be made of a film different from
the film base 2 The front electrode 3 and the back electrode 4 may be disposed on the front and
back of the film substrate 2 by bonding them and arranging the film so as to sandwich the film
substrate 2.
[0043]
In addition, regardless of the angle direction in which the length direction and the width direction
of the film substrate 2 are, if it is an angle direction that intersects with two displacement
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directions in plan view, the width direction of the film substrate 2 Can be suppressed to some
extent.
And, if the length direction and the width direction of the film substrate 2 are substantially equal
to the angular direction that equally divides the two displacement directions, the displacement in
the width direction of the film substrate 2 can be almost eliminated. In the present invention, two
angular directions being substantially equal means that the difference between the two angular
directions falls within the range of -5 ° to + 5 °.
[0044]
Next, a piezoelectric film according to a second embodiment of the present invention will be
described. FIG. 5 is a side cross-sectional view of the piezoelectric film according to the second
embodiment.
[0045]
The piezoelectric film 21 shown in FIG. 5 has the same configuration as that of the first
embodiment, but includes the surface electrode 23 and the back electrode 24 having a
configuration different from that of the first embodiment. A plurality of back electrodes 24 are
provided in the same electrode area as the facing surface electrodes 23 so as to individually face
the surface electrodes 23. The surface electrodes 23 are alternately connected to a positive
potential (100 V) or a ground potential in order of being arranged in the width direction (X-axis
direction) and the length direction (Y-axis direction). The back electrode 24 is used if it is
connected to the ground potential if it is opposed to the surface electrode 23 connected to the
positive potential (100 V), and if it is opposed to the surface electrode 23 connected to the
ground potential, It is connected to a positive potential (100 V) and used.
[0046]
Even with this configuration, as in the first embodiment, deformation in the length direction (Yaxis direction) can be generated while suppressing deformation in the width direction (X-axis
direction) in each unit region. Moreover, as in the present embodiment, by making the electrode
areas of the front surface electrode 23 and the back surface electrode 24 uniform, the stress
04-05-2019
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acting on the film substrate 2 from the front surface electrode 23 and the back surface electrode
24 can be made uniform on the front and back surfaces. As a result, the warp of the piezoelectric
film 21 can be alleviated.
[0047]
Next, a piezoelectric film according to a third embodiment of the present invention will be
described. FIG. 6 is a plan view of a piezoelectric film according to a third embodiment.
[0048]
The piezoelectric film 31 shown in FIG. 6 has the same configuration as that of the first
embodiment, but includes a film substrate 32 having a configuration different from that of the
first embodiment. The film substrate 32 is a strip of the PLLA film subjected to the stretching
process, with the main stretching direction being the width direction (X-axis direction). In FIG. 6,
the main stretching direction of the film is indicated by black arrows.
[0049]
Even in such a configuration, application of an electric field is applied to the film substrate 32
with the 45 ° direction in the clockwise direction and the −45 ° direction as two displacement
directions with reference to the length direction (Y-axis direction). Causes stretching and
contraction. Therefore, the same deformation (as shown in FIG. 3) as in the first embodiment
occurs in the unit area. Therefore, also in the piezoelectric film 31 of the present embodiment,
deformation in the length direction (Y-axis direction) can be generated while suppressing
deformation in the width direction (X-axis direction) in each unit region.
[0050]
Next, a piezoelectric film according to a fourth embodiment of the present invention will be
described. FIG. 7 is a plan view of a piezoelectric film according to a fourth embodiment.
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[0051]
The piezoelectric film 41 includes a film base 42, a front electrode 43, and a back electrode 44
(not shown).
[0052]
The film substrate 42 is almost the same as that of the first embodiment, but is provided with a
notch 45 having a shape different from that of the first embodiment.
The notch 45 is a substantially rhombic shape having a diagonal along the length direction (Yaxis direction) and the width direction (X-axis direction) of the piezoelectric film 41 in plan view,
and one diagonal line (length) of the rhombus Direction) The upper corner part is cut out to
make it hexagonal. The plurality of notches 45 are arranged in a staggered manner while shifting
the position in the width direction (X-axis direction). That is, the plurality of notches 45 are
arranged in the 45 ° direction and the −45 ° direction with respect to the length direction.
[0053]
The surface electrode 43 is a rhombic shape having a diagonal along the length direction (Y-axis
direction) and the width direction (X-axis direction) of the piezoelectric film 41 in plan view. A
plurality of surface electrodes 43 are arranged in the length direction and the width direction.
Each surface electrode 43 is disposed in a region sandwiched by opposing sides of two notches 5
adjacent in the 45 ° direction and the −45 ° direction with respect to the length direction.
[0054]
The back electrode 44 (not shown) is provided on the entire back surface of the piezoelectric film
41 or on the back surface of the piezoelectric film 41 so as to overlap with the surface electrode
43 so as to substantially match.
[0055]
Also in the piezoelectric film 41 having such a configuration, since the notches 45 and the
surface electrodes 43 are regularly provided in plan view, the piezoelectric film 41 has a plurality
of unit areas having the same shape in plan view. It can be divided into 40.
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[0056]
FIG. 8 is a plan view showing a unit region 40 of the piezoelectric film 41 in an enlarged manner.
[0057]
The film base 42 includes, for each unit region 40, a first electrode forming portion 46, a second
electrode forming portion 47, and an electrode non-forming portion 48.
The first electrode forming portion 46 and the second electrode forming portion 47 are arranged
in the width direction (X-axis direction).
The electrode non-forming portion 48 forms a first electrode between the first electrode forming
portion 46 and the second electrode forming portion 47 in the width direction (X-axis direction)
and on one side in the length direction (Y-axis direction) It arranges from the part 46 and the
2nd electrode formation part 47 as it is shifted.
The electrode non-forming portion 48 is connected to another region adjacent in the longitudinal
direction (Y-axis direction) at one edge in the longitudinal direction (Y-axis direction) of each unit
region 40. An electrode non-formed from the first electrode-formed portion 11 on the opposite
side in the length direction (Y-axis direction) of the electrode non-formed portion 48, that is, the
other edge in the length direction (Y-axis direction) of each unit region 40 A notch 45 is provided
so as to be continuous to the portion 48.
[0058]
Also in such a unit region 40, when different positive and negative potentials are connected to
the surface electrode 3 adjacent in the width direction (X-axis direction), for example, as shown
by a white arrow in FIG. In the portion 46, a stress in the direction of contraction occurs along
the 45 ° direction, and a stress in the direction of elongation occurs along the −45 ° direction.
In addition, in the second electrode forming portion 12, a stress in the extension direction is
generated along the 45 ° direction, and a stress in the contraction direction is generated along
the −45 ° direction. Therefore, stress acts isotropically on the electrode non-formed portion 48
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from unit areas adjacent in the length direction (Y-axis direction) (four electrode formed
portions).
[0059]
Thus, in each unit region 40, the electrode non-forming portion 48 is restrained in shape and
hardly deformed, and the first electrode forming portion 46 and the second electrode forming
portion 47 are at the boundary with the electrode non-forming portion 48. It will deform so that
the located side moves approximately parallel. Thereby, in each unit area 10, as shown in FIG. 8B,
the notch 45 is deformed so as to be crushed in the length direction (Y-axis direction), and the
first electrode forming portion 46 and the second electrode forming portion The expansion and
contraction of 47 are offset in the width direction (X-axis direction). Therefore, as a whole of the
piezoelectric film 41, deformation in the width direction (X-axis direction) hardly occurs, and
only the entire length in the length direction (Y-axis direction) is shortened.
[0060]
When the polarity of the voltage applied to the first electrode forming portion 46 and the second
electrode forming portion 47 is reversed, a stress in the direction of elongation is generated in
the first electrode forming portion 46 along the 45 ° direction, Stress in the direction of
shrinkage occurs along the 45 ° direction. In addition, stress in the direction of contraction is
generated along the 45 ° direction in the second electrode forming portion 12, and stress in the
direction of elongation is generated along the −45 ° direction. Then, in each unit region 40, the
notch 45 is deformed so as to extend in the length direction (Y-axis direction), and as a whole of
the piezoelectric film 41, deformation in the width direction (X-axis direction) hardly occurs. Only
the entire length in the longitudinal direction (Y-axis direction) extends.
[0061]
As shown in the above embodiments, the shape of the notch in the piezoelectric film and the
shape of the surface electrode can be appropriately modified. In any case, the stress generated in
the first electrode forming portion and the second forming portion in each unit region is offset in
the width direction, thereby causing displacement in the width direction as the entire
piezoelectric film. Without, it is possible to cause expansion and contraction in the longitudinal
direction.
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[0062]
And in this embodiment, since each notch 45 is made into the hexagon shape which cut off the
corner part on one diagonal (longitudinal direction) of a rhombus, it is possible to relieve the
stress concentration in a corner part. As a result, the piezoelectric film 41 can be prevented from
being torn. For this reason, the configuration of the present embodiment is more effective when
used for applications in which reliability is more important than displacement.
[0063]
Next, a vibrating device according to a fifth embodiment of the present invention will be
described. FIG. 9 is a block diagram of a vibration device according to a fifth embodiment.
[0064]
The vibration device 51 shown in FIG. 9 includes the piezoelectric film 1 similar to that of the
first embodiment, a drive unit 52, and a vibration member 53. The drive unit 52 outputs a drive
signal (AC signal) to the piezoelectric film 1, and always applies an electric field of reverse
polarity to the first electrode formation portion and the second electrode formation portion of
the piezoelectric film 1. Thereby, the piezoelectric film 1 vibrates in the length direction in a state
in which the deformation in the width direction is suppressed. The vibration member 53 is
connected to the piezoelectric film 1 so that a stress is transmitted from the piezoelectric film 1
in accordance with the vibration in the longitudinal direction of the piezoelectric film 1 and the
vibration is caused by the stress.
[0065]
The specific structure of the vibration device 51 described above can be an appropriate
configuration, but may be, for example, a planar speaker having a structure as shown in FIG. 12
or a haptic (tactile presentation) device.
[0066]
Here, an embodiment of the vibrating device 51 will be described.
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[0067]
FIG. 10 is a side view of the vibration device 51. As shown in FIG.
[0068]
The vibrating device 51 is configured as a touch keyboard, and provides tactile presentation to a
finger or the like operated as a key.
The vibration device 51 includes the piezoelectric film 1, a drive unit 52, a vibration member 53,
an adhesive layer 54, a control unit 55, and a touch sensor 56.
The piezoelectric film 1 has the same configuration as that of the piezoelectric film shown in the
previous embodiment, and can expand and contract in the length direction (Y-axis direction)
without displacement in the width direction (X-axis direction).
The vibrating member 53 is a flat-plate-like member, and both ends in the longitudinal direction
are curved in a bow shape so that the distance to the piezoelectric film 1 gradually increases
from near both ends in the longitudinal direction to near the center, It is connected to both ends
in the longitudinal direction of the piezoelectric film 1 through the adhesive layer 54. For this
reason, the piezoelectric film 1 is pulled outward from the vibrating member 53 via the adhesive
layer 54. The touch sensor 56 is attached to the upper surface of the vibrating member 53.
When the touch sensor 56 detects the contact or proximity of a finger or the like on the upper
surface of the vibrating member 53, the control unit 55 controls the drive unit 52 to apply an
alternating electric field to the piezoelectric film 1. Thereby, with the application of the
alternating electric field from the drive unit 52, expansion and contraction in the length direction
(Y-axis direction) occurs in the piezoelectric film 1. Thereby, the vibration in the thickness
direction (Z-axis direction) is caused in the vibrating member 53, and the vibration is transmitted
to a finger or the like in contact with the touch sensor 56. From this, the user operating the
vibrating device 51, which is a touch keyboard, can perceive the vibration of the vibrating
member 53 along with the key touch, and can obtain an operation feeling of the touch keyboard.
[0069]
In the vibration device 51 having such a configuration, even if the piezoelectric film 1 is vibrated
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so as to expand and contract in the length direction, stress load in the width direction is applied
to the adhesive layer 54 of the connection portion between the vibration member 53 and the
piezoelectric film 1 Therefore, it is possible to suppress the occurrence of a failure in the
connection portion between the vibration member 53 and the piezoelectric film 1.
[0070]
Next, a strain detection device according to a sixth embodiment of the present invention will be
described.
FIG. 11 is a block diagram of a distortion detection device according to the sixth embodiment.
[0071]
A strain detection device 61 shown in FIG. 11 includes the piezoelectric film 1 similar to that of
the first embodiment, a detection unit 62, and a strain member 63. The detection unit 62 is
configured to detect the charge generated in at least one of the first electrode formation portion
and the second electrode formation portion of the piezoelectric film 1. The strain member 63 is
connected to the piezoelectric film 1 so as to transmit strain to the piezoelectric film 1 and cause
the piezoelectric film 1 to deform in the length direction (Y-axis direction). The specific structure
of the piezoelectric film 1 and the strain member 63 can be an appropriate configuration, and
may be, for example, a pressure sensor or a touch panel.
[0072]
In the strain detection device 61 having such a configuration, even if the strain member 63 is
strained such that the piezoelectric film 1 expands and contracts in the length direction, a stress
load in the width direction is applied to the connection portion between the strain member 63
and the piezoelectric film 1 And the failure of the distortion detection device 61 can be
suppressed.
[0073]
The invention can be implemented as described above.
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The present invention can be implemented with any configuration as long as the configuration
falls within the scope of the claims. For example, the present invention can be realized by using a
piezoelectric film which does not have shear piezoelectricity as the piezoelectric film. For
example, PVDF has piezoelectricity in which expansion and contraction occur in the film
stretching direction (roll winding direction). In the case of PVDF, shrinkage and elongation occur
in the direction intersecting the stretching direction of the film by Poisson's ratio. Therefore, in
the case of using PVDF, the present invention can be realized by cutting out the piezoelectric film
with the direction of 45 degrees as the longitudinal direction and the width direction with
respect to the stretching direction of PVDF. Thus, the present invention is realizable if it is a
piezoelectric film in which expansion or contraction occurs in one direction in the in-plane
direction of the film and the opposite contraction or expansion occurs in the in-plane direction
crossing it.
[0074]
1, 21, 31, 41 Piezoelectric films 2, 3, 42: Film base 3, 23, 43: Surface electrode 4, 24, 44: Back
electrode 5, 45: Notch 10, 40: Unit area 11, 46 ... 1st electrode formation part 12, 47 ... 2nd
electrode formation part 13, 48 ... electrode non-formation part 51 ... vibration device 52 ... drive
part 53 ... vibration member 54 ... adhesion layer 55 ... control part 56 ... touch sensor 61 ...
distortion Detection device 62 ... detection unit 63 ... distortion member
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