WO2015093383A1

WO2015093383A1 - Piezoelectric sensor

Info

Publication number: WO2015093383A1
Application number: PCT/JP2014/082808
Authority: WO
Inventors: 河村秀樹
Original assignee: 株式会社村田製作所
Priority date: 2013-12-20
Filing date: 2014-12-11
Publication date: 2015-06-25
Also published as: JPWO2015093383A1; JP6052431B2

Abstract

A piezoelectric sensor (10) is provided with a glass plate (12), an SUS plate (15), a sensor unit (16), a pressing element (17), and a cushion (21). The glass plate (12) receives a pressing force. The SUS plate (15) is disposed so as to be parallel to the glass plate (12) and is strained by the pressing force. The sensor unit (16) has a piezoelectric film and is affixed to the main surface of the SUS plate (15). The pressing element (17) is disposed between the glass plate (12) and SUS plate (15) and transmits strain from the glass plate (12) to the SUS plate (15). The cushion (21) is disposed on the side of the SUS plate (15) opposite from the side facing the glass plate (12) and supports the SUS (15) plate. When viewed from a direction perpendicular to the main surface of the SUS plate (15), the cushion (21) overlaps with at least a portion of the pressing element (17) and does not overlap with the entirety of the sensor unit (16).

Description

Piezoelectric sensor

The present invention relates to a piezoelectric sensor that detects pressure.

The piezoelectric sensor is mounted on a multifunctional mobile terminal, for example, and is used to detect a press on the touch panel. There is an input device described in Patent Document 1 as a piezoelectric sensor for detecting pressure. This input device includes a rectangular flat touch panel and a striped piezoelectric element. The piezoelectric element is provided on the back surface of the touch panel along the short side of the touch panel.

When the operation surface of the touch panel is pressed, the touch panel bends. When the piezoelectric element bends according to the touch panel, a voltage corresponding to the pressure is generated in the piezoelectric element. Thereby, the press with respect to a touch panel is detectable.

JP 2012-203552 A

In the input device described in Patent Document 1, as described above, the piezoelectric element is provided on the back surface of the touch panel. However, the piezoelectric element may be arranged away from the touch panel due to design problems. In this case, since the bending of the touch panel due to the pressure is not transmitted well to the piezoelectric element, there is a possibility that the pressure on the touch panel cannot be accurately detected.

An object of the present invention is to provide a piezoelectric sensor capable of accurately detecting a press.

(1) The piezoelectric sensor of the present invention includes a receiving plate, a strain detection plate, a piezoelectric film, a strain transmission member, and an elastic member. The reception board accepts pushing. The strain detection plate is arranged so as to be parallel to the receiving plate, and is distorted by pressing. The piezoelectric film is attached to the main surface of the strain detection plate. The strain transmitting member is disposed between the receiving plate and the strain detecting plate, and transmits the strain from the receiving plate to the strain detecting plate. The elastic member is disposed on the side opposite to the receiving plate side with respect to the strain detection plate and supports the strain detection plate. When viewed from the direction perpendicular to the main surface of the strain detection plate, the elastic member overlaps at least a part of the strain transmission member and does not overlap the entire piezoelectric film.

When viewed from the direction perpendicular to the main surface of the strain detection plate, a region overlapping the strain transmission member is referred to as a first region, and a region overlapping the elastic member but not overlapping the strain transmission member is referred to as a second region. At the time of pushing, in the first region, the strain detection plate protrudes downward (in the direction opposite to the receiving plate side), and the upper surface of the strain detection plate shrinks. On the other hand, in the second region, since the strain detection plate is pushed back somewhat by the elastic member, the strain detection plate is deformed as follows. The strain detection plate is convex upward, and the upper surface of the strain detection plate extends. Alternatively, the strain detection plate protrudes downward, but the upper surface of the strain detection plate does not shrink much. At the time of pressing, the piezoelectric film attached to the strain detection plate is also deformed in the same manner as the upper surface of the strain detection plate.

In this configuration, since the strain detection plate is supported by the elastic member in the first region, the second region can be narrowed. In this case, since the distortion (shrinkage) of the piezoelectric film with respect to the pressing does not become small, the amount of charge that can be taken out from the piezoelectric film during the pressing does not decrease. As a result, pressing (pressing) can be detected with high accuracy.

(2) The elastic member is disposed in the strain transmission member as viewed from the direction perpendicular to the main surface of the strain detection plate.

In this configuration, since the second region does not occur, it is possible to prevent the distortion of the piezoelectric film with respect to pushing-in from being reduced.

(3) When viewed from the direction perpendicular to the main surface of the strain detection plate, the area of the elastic member that overlaps the strain transmission member is larger than the area of the portion that does not overlap the strain transmission member.

In this configuration, since the first region is larger than the second region, it is possible to suppress the distortion of the piezoelectric film with respect to pressing.

(4) When the piezoelectric sensor is viewed in cross section, the length of the elastic member is not more than 1.5 times the length of the strain transmitting member. Here, the “length” of the elastic member and the strain transmitting member is a length in a direction in which the piezoelectric film is contracted by pressing.

In this configuration, the influence on the generated charge amount due to the arrangement of the elastic member can be made almost zero.

(5) The piezoelectric film is formed from a chiral polymer.

(6) The chiral polymer is polylactic acid.

(7) Polylactic acid is L-type polylactic acid.

For example, when PVDF (polyvinylidene fluoride) is used for the piezoelectric film, a change in operating temperature may affect the piezoelectric characteristics of the piezoelectric film. However, in this configuration, since polylactic acid does not have pyroelectricity, it is possible to accurately detect pressing by the piezoelectric film.

According to the present invention, it is possible to detect the press with high accuracy.

It is a top view of the piezoelectric sensor which concerns on 1st Embodiment. 1 is a cross-sectional view of the piezoelectric sensor according to the first embodiment, taken along the line AA. FIG. 3 is a cross-sectional view of the sensor unit 16 along AA. It is sectional drawing explaining the press detection by the piezoelectric sensor which concerns on 1st Embodiment. It is AA sectional drawing of the piezoelectric sensor used as a comparative example. In the piezoelectric sensor of a comparative example, it is principal part sectional drawing which shows the state which the SUS board 15 bent by press. In the piezoelectric sensor which concerns on 1st Embodiment, it is principal part sectional drawing which shows the state which the SUS board 15 bent by press. It is a calculation result which shows the change of the generated electric charge amount with respect to cushion length. It is AA sectional drawing which shows the cushion which concerns on other embodiment.

<< First Embodiment >>
A piezoelectric sensor 10 according to an embodiment of the present invention will be described. The piezoelectric sensor 10 is used in, for example, a multifunctional portable terminal. FIG. 1 is a plan view of the piezoelectric sensor 10. FIG. 2 is a cross-sectional view of the piezoelectric sensor 10 taken along the line AA. The piezoelectric sensor 10 includes a box-shaped back housing 11, a rectangular flat glass plate 12,

spacers

14 a and 14 b, a striped SUS (stainless steel) plate 15, a striped sensor unit 16, a columnar presser 17, A columnar cushion 21 and a circuit part (not shown) are provided.

The glass plate 12 corresponds to the reception plate of the present invention. The SUS plate 15 corresponds to a strain detection plate of the present invention. The pusher 17 corresponds to a strain transmission member of the present invention. The cushion 21 corresponds to the elastic member of the present invention.

The back housing 11 is composed of a frame-shaped side surface and a rectangular bottom surface, and has a rectangular opening. When the glass plate 12 abuts on the back-side casing 11 so as to close the opening of the back-side casing 11, a rectangular parallelepiped casing 13 having a hollow portion is configured. Hereinafter, the longitudinal direction of the main surface of the housing 13 is referred to as the X direction, the short direction of the main surface of the housing 13 is referred to as the Y direction, and the direction perpendicular to the main surface of the housing 13 is referred to as the Z direction. There is.

The spacer 14 a is disposed in the vicinity of the first side surface parallel to the X direction among the side surfaces of the housing 13. The spacer 14 b is disposed in the vicinity of the second side surface (side surface facing the first side surface) of the housing 13. The

spacers

14 a and 14 b are disposed at a substantially central portion in the X direction of the housing 13.

The SUS plate 15 is disposed inside the housing 13 so that its main surface is parallel to the main surface of the glass plate 12. The SUS plate 15 is disposed at a substantially central portion of the housing 13 in the X direction. The longitudinal direction of the SUS plate 15 is parallel to the Y direction. Both ends of the SUS plate 15 in the longitudinal direction are supported by

spacers

14a and 14b, respectively. Spaces are formed between the SUS plate 15 and the glass plate 12 and between the SUS plate 15 and the bottom surface of the back side housing unit 11.

The sensor unit 16 is affixed to the main surface of the SUS plate 15 on the glass plate 12 side so that the longitudinal direction thereof is the Y direction. The sensor unit 16 is affixed to substantially the entire surface of the SUS plate 15. The circuit unit is disposed inside the housing 13 and is electrically connected to the sensor unit 16.

The pusher 17 is disposed between the glass plate 12 and the sensor unit 16 and is in contact with the glass plate 12 and the sensor unit 16. The pusher 17 is shorter than the sensor unit 16 in the Y direction. The pusher 17 is disposed at a substantially central portion of the SUS plate 15 in the Y direction. The pusher 17 transmits strain from the glass plate 12 to the SUS plate 15.

The cushion 21 is disposed between the bottom surface of the back-side housing unit 11 and the SUS plate 15 and is in contact with the bottom surface of the back-side housing unit 11 and the SUS plate 15. The cushion 21 is shorter than the sensor unit 16 in the Y direction. The cushion 21 is disposed at a substantially central portion of the SUS plate 15 in the Y direction. The cushion 21 is disposed at substantially the same position as the pusher 17 when viewed from the Z direction (in plan view), and has substantially the same shape and size as the pusher 17.

That is, the cushion 21 overlaps with a part of the pusher 17 when viewed from the Z direction (direction perpendicular to the main surface of the SUS plate 15) and does not overlap the entire piezoelectric film 31 described later. Also, as viewed from the Z direction, the area of the portion of the cushion 21 that overlaps the pusher 17 is larger than the area of the portion that does not overlap the pusher 17.

The cushion 21 presses the SUS plate 15 against the pusher 17 via the sensor unit 16 so that the sensor unit 16, the pusher 17 and the glass plate 12 are connected. That is, the cushion 21 supports the SUS plate 15. Thereby, the press applied to the glass plate 12 can be transmitted to the SUS plate 15. When the glass plate 12 is pressed, the SUS plate 15 bends. When the glass plate 12 is no longer pressed, the cushion 21 pushes the SUS plate 15 back. Thereby, when the glass plate 12 is no longer pressed, the SUS plate 15 can be returned to the original flat state.

FIG. 3 is a cross-sectional view of the sensor unit 16 taken along the line AA. The sensor unit 16 includes a piezoelectric film 31, adhesive layers 32 and 33,

flat plate electrodes

34 and 35, and base material layers 36 and 37. A plate electrode 34 is attached to one main surface of the piezoelectric film 31 with an adhesive layer 32. A flat plate electrode 35 is attached to the other main surface of the piezoelectric film 31 with an adhesive layer 33. The

plate electrodes

34 and 35 are electrically connected to a circuit unit (not shown). A base material layer 36 is disposed on the main surface of the plate electrode 34 opposite to the piezoelectric film 31 side. A base material layer 37 is disposed on the main surface of the plate electrode 35 opposite to the piezoelectric film 31 side. The sensor unit 16 is affixed to the main surface of the SUS plate 15 by the affixing layer 38 so that the base material layer 36 side faces the SUS plate 15.

The piezoelectric film 31 is made of PLLA (L-type polylactic acid). PLLA is a chiral polymer, and the main chain has a helical structure. PLLA is uniaxially stretched and has piezoelectricity when the molecules are oriented. The piezoelectric constant of uniaxially stretched PLLA belongs to a very high class among polymers.

In addition, PLLA generates piezoelectricity by molecular orientation processing such as stretching, and there is no need to perform poling processing like other polymers such as PVDF and piezoelectric ceramics. That is, the piezoelectricity of PLLA that does not belong to ferroelectrics is not expressed by the polarization of ions like ferroelectrics such as PVDF and PZT, but is derived from a helical structure that is a characteristic structure of molecules. is there. For this reason, the pyroelectricity generated in other ferroelectric piezoelectric materials does not occur in PLLA. Further, PVDF or the like shows a change in piezoelectric constant over time, and in some cases, the piezoelectric constant may be significantly reduced, but the piezoelectric constant of PLLA is extremely stable over time.

Stretching direction of PLLA to take three axes, taking uniaxially and biaxially in a direction perpendicular to the three axial directions, the PLLA there is the piezoelectric constant of d ₁₄ (piezoelectric constant shear). The striped piezoelectric film 31 is cut so that the uniaxial direction is the thickness direction and the direction that forms an angle of 45 ° with respect to the triaxial direction (stretching direction) is the longitudinal direction. Thereby, when the piezoelectric film 31 expands and contracts in the longitudinal direction, the piezoelectric film 31 is polarized in the thickness direction.

The material of the adhesive layers 32, 33, 38 is an adhesive. The characteristic of the pressure-sensitive adhesive is that, while the adhesive is changed from a liquid to a solid at the time of bonding, the wet state is always kept stable. By using a pressure-sensitive adhesive as the material of the adhesive layers 32, 33, and 38, the thickness of the pressure-sensitive adhesive can be easily controlled as compared with the adhesive. The

plate electrodes

34 and 35 are made of a metal film such as a copper foil. The material of the base material layers 36 and 37 is a resin such as polyimide.

FIG. 4 is a cross-sectional view for explaining detection of pressing (pushing) by the piezoelectric sensor 10. When the glass plate 12 is pushed in, the SUS plate 15 is pushed in via the pusher 17. Since the end portion of the SUS plate 15 is fixed by the

spacers

14a and 14b, the SUS plate 15 bends so as to be convex in the pushed-in direction. Since the main surface of the SUS plate 15 on the glass plate 12 side contracts (distorts) in the longitudinal direction (Y direction), the sensor unit 16 attached to the main surface also contracts in the longitudinal direction. Since the piezoelectric film 31 (see FIG. 3) constituting the sensor unit 16 contracts in the longitudinal direction, as described above, the piezoelectric film 31 is polarized in the thickness direction by the piezoelectric effect. Electric charges are induced in the

plate electrodes

34 and 35 by the electric charges generated on both main surfaces of the piezoelectric film 31. The charges induced in the

plate electrodes

34 and 35 are absorbed by a circuit unit (not shown). The circuit unit converts this flow of electric current (current) into a voltage. In this way, the pressure applied to the glass plate 12 can be detected as a voltage.

A piezoelectric sensor 40 as a comparative example will be described. The configuration of the piezoelectric sensor 40 is the same as that of the first embodiment except for the cushion. FIG. 5 is a cross-sectional view taken along the line AA of the piezoelectric sensor 40 as a comparative example. The cushion 22 is provided so as to fill almost all the space between the bottom surface of the back-side housing unit 11 and the SUS plate 15. The cushion 22 is in contact with the bottom surface of the back housing 11 and the SUS plate 15. The cushion 22 includes the sensor unit 16 and the pusher 17 when viewed from the Z direction.

FIG. 6 is a cross-sectional view of the main part showing a state in which the SUS plate 15 is bent by pressing in the piezoelectric sensor 40 of the comparative example. As described above, when viewed from the Z direction, a region that overlaps the pusher 17 is referred to as a first region, and a region that overlaps the cushion 22 (or the cushion 21) but does not overlap the pusher 17 is referred to as a second region.

When the glass plate 12 (see FIG. 2) is pushed in, the upper surface of the SUS plate 15 (main surface on the glass plate 12 side) is pressed by the pusher 17, while the lower surface (opposite side of the upper surface) of the SUS plate 15 by the cushion 22. The main surface) is pressed. The pressing by the pusher 17 is applied only to the first region. The pressure applied by the cushion 22 is applied to the first region and the second region.

In the first region, the SUS plate 15 is convex downward (the direction opposite to the glass plate 12 side), and the upper surface of the SUS plate 15 is contracted in the longitudinal direction (Y direction). On the other hand, in the second region, since the SUS plate 15 is pushed back somewhat by the cushion 22, the SUS plate 15 is deformed as follows. The SUS plate 15 is convex upward, and the upper surface of the SUS plate 15 extends in the longitudinal direction. Or although the SUS board 15 becomes convex below, the upper surface of the SUS board 15 does not shrink so much in a longitudinal direction compared with the case where the cushion 22 is not provided.

The piezoelectric film 31 (see FIG. 3) affixed to the strain detection plate is also deformed in the same manner as the upper surface of the strain detection plate. For this reason, the piezoelectric film 31 is polarized as follows. The polarization in the second region is opposite to the polarization in the first region. Alternatively, the polarization in the second region is in the same direction as the polarization in the first region, but is smaller than that without the cushion 22.

As described above, the cushion 22 includes the sensor unit 16 when viewed from the Z direction. For this reason, since most of the piezoelectric film 31 is included in the second region, the polarization of the piezoelectric film 31 becomes small. As a result, the amount of charge that can be taken out by the circuit unit is reduced, so that the pressure cannot be accurately detected by the piezoelectric sensor 40 of the comparative example.

FIG. 7 is a cross-sectional view of the main part showing a state in which the SUS plate 15 is bent by pressing in the piezoelectric sensor 10 according to the first embodiment. As described above, the cushion 21 is disposed at substantially the same position as the pusher 17 as viewed from the Z direction, and has substantially the same shape and size as the pusher 17. That is, the second region hardly occurs in the piezoelectric sensor 10. Therefore, the piezoelectric film 31 (see FIG. 3) contracts in the longitudinal direction at all portions and is polarized in the same direction at all portions. Further, the polarization of the piezoelectric film 31 is not hindered by the cushion 21. As a result, the polarization of the piezoelectric film 31 does not become small. Therefore, since the amount of charge that can be taken out by the circuit unit does not decrease, the piezoelectric sensor 10 according to the first embodiment can accurately detect the pressing.

FIG. 8 is a calculation result showing a change in the generated charge amount with respect to the cushion length. The calculation result is obtained by changing the length of the cushion in the Y direction in the same configuration as in the first embodiment. Regarding the dimensions of each member, SUS plate: 64.30 × 7.55, piezoelectric film (PLLA): 45.00 × 5.75, cushion: <cushion length> × 6.25, pusher: 6.00 X6.25. The dimension of each member is represented by <length in the Y direction> × <length in the X direction>, and the unit is mm. Each member is laminated so that the centers of the members overlap in plan view.

The cushion length is the length of the cushion in the Y direction. That is, the cushion length is the length of the cushion in the direction in which the piezoelectric film is contracted by pressing. The amount of generated charge is the amount of charge generated in the piezoelectric film upon pressing. When the cushion length is 9 mm or less, that is, when the cushion length is 1.5 times or less the length of the pusher in the Y direction, the generated charge amount is almost equal to the generated charge amount when there is no cushion. As the cushion length becomes longer than 9 mm, the generated charge amount tends to decrease. As can be seen from this result, by setting the cushion length to 1.5 times or less of the length of the pusher in the Y direction, the influence on the amount of generated charges by arranging the cushion can be made almost zero. .

As can be seen from the above, the effect of the present invention becomes more remarkable as the area of the portion of the cushion that does not overlap the pusher is smaller in plan view.

<< Other embodiments >>
A piezoelectric sensor according to another embodiment of the present invention will be described. The configuration of the piezoelectric sensor according to another embodiment is the same as that of the first embodiment except for the cushion. FIG. 9 is a cross-sectional view taken along line AA showing a cushion according to another embodiment. As shown in FIG. 9A, the cushion 23 is smaller than the pusher 17 when viewed from the Z direction. The cushion 23 is disposed in the pusher 17 when viewed from the Z direction. As shown in FIG. 9B, the cushion 24 is somewhat larger than the pusher 17 when viewed from the Z direction. The cushion 24 includes a pusher 17 when viewed from the Z direction. As shown in FIG. 9C, the position of the cushion 25 is somewhat shifted from the position of the pusher 17 when viewed from the Z direction. Most portions of the cushion 25 overlap with the pusher 17 when viewed from the Z direction.

In other embodiments, the cushions 23 to 25 have no or almost no portion that does not overlap the pusher 17 when viewed from the Z direction. Therefore, the piezoelectric film 31 (see FIG. 3) contracts in the longitudinal direction at all portions and is polarized in the same direction at all portions. Further, the polarization of the piezoelectric film 31 is not hindered by the cushions 23-25. As a result, in the piezoelectric sensors according to other embodiments, as in the piezoelectric sensor 10, the amount of charge that can be extracted to the circuit unit does not decrease.

In addition, although the glass plate was pushed in in the above-mentioned embodiment, the piezoelectric sensor of this invention is not limited to this. Instead of the glass plate, a panel in which a glass plate, a touch panel and a liquid crystal panel are stacked in layers may be used.

10, 40 ... Piezoelectric sensor 11 ... Back side housing 12 ... Glass plate (reception plate)
13 ...

Cases

14a, 14b ... Spacer 15 ... SUS plate (strain detection plate)
16 ... sensor 17 ... presser (strain transmitting member)
21-25 ... Cushion (elastic member)
31 ... Piezoelectric films 32, 33, 38 ... Adhesive layers 34, 35 ...

Flat plate electrodes

36, 37 ... Base material layers

Claims

A reception board that accepts push-in,
A strain detection plate disposed parallel to the receiving plate and distorted by the pushing,
A piezoelectric film attached to the main surface of the strain detection plate;
A strain transmitting member disposed between the receiving plate and the strain detecting plate, and transmitting strain from the receiving plate to the strain detecting plate;
An elastic member disposed on the opposite side of the receiving plate side with respect to the strain detecting plate, and supporting the strain detecting plate;
The piezoelectric sensor, wherein the elastic member overlaps at least a part of the strain transmission member and does not overlap the entire piezoelectric film when viewed from a direction perpendicular to the main surface of the strain detection plate.
The piezoelectric sensor according to claim 1, wherein the elastic member is disposed in the strain transmitting member when viewed from a direction perpendicular to a main surface of the strain detecting plate.
The area of the portion of the elastic member that overlaps with the strain transmission member is larger than the area of the portion that does not overlap with the strain transmission member, as viewed from a direction perpendicular to the main surface of the strain detection plate. 3. The piezoelectric sensor according to 1 or 2.
The piezoelectric sensor according to any one of claims 1 to 3, wherein when the piezoelectric sensor is viewed in cross section, the length of the elastic member is 1.5 times or less the length of the strain transmitting member.
The piezoelectric sensor according to any one of claims 1 to 4, wherein the piezoelectric film is formed of a chiral polymer.
The piezoelectric sensor according to claim 5, wherein the chiral polymer is polylactic acid.
The piezoelectric sensor according to claim 6, wherein the polylactic acid is L-type polylactic acid.