JP7635887B2 - Deformation Detection Sensor - Google Patents

Description

The present invention relates to deformation detection, which detects deformation of an object.

The input device in Patent Document 1 includes an input pad whose periphery is held by a housing or the like. The input device accepts operations from a user when force is applied to the input pad. The input device detects and measures the position and magnitude of the force applied to the input pad using multiple sensors.

The input device of Patent Document 1 has multiple sensors arranged close to each corner of an input pad formed in the shape of a rectangular plate. The multiple sensors distort in response to the force applied to the input pad. The input device of Patent Document 1 measures the magnitude and position of the force applied to the input pad based on the output of the multiple sensors.

The vibration device in Patent Document 2 includes a vibration unit and a touch panel. When a user presses the touch panel, the vibration unit transmits vibrations to the user. The vibration unit includes a flat vibration section, a frame-shaped frame member, and a beam (support section) that connects the vibration section and the frame member. The frame member and vibration section are connected via a piezoelectric film. The vibration device in Patent Document 2 applies a voltage to the piezoelectric film to expand and contract the piezoelectric film, causing the vibration section to vibrate.

Special Publication No. 2008-546113 Re-table 2020/213477 publication

In the structure of Patent Document 1, at least two sensors are required to detect the position and magnitude of force applied to the input pad (touch panel) using multiple sensors.

On the other hand, if the voltage generated in the piezoelectric film of Patent Document 2 were detected, it would be possible to detect the deformation of the vibrating part and it would be possible to function as a deformation detection sensor that detects the deformation of the touch panel being pressed.

However, in the structure of Patent Document 2, a single sensor is connected to the vibration unit and the frame-shaped member, and so the deformation that occurs in the piezoelectric film differs depending on the position where force is applied in a plan view to the input pad. In other words, when a user presses a point close to the connection position between the piezoelectric film and the vibration unit, the vertical displacement of the vibration unit at the connection position becomes larger than when the user presses a point away from the connection position, resulting in greater bending of the piezoelectric film.

In this way, the deformation of the piezoelectric film caused by pressing vertically against the touch panel changes depending on the pressing position in a planar view. Therefore, even if the pressing amount is the same, the deformation detection sensor will output different output values depending on the pressing position.

The present invention aims to provide a deformation detection sensor that can output a uniform output value even when the pressing position is different.

The deformation detection sensor is connected to an operation panel that accepts a pressing operation by a user, and includes a holding section that holds the operation panel, and a piezoelectric film that is connected to the holding section and detects deformation of the holding section. The holding section has a first section that is connected to a housing, a second section that is connected to the operation panel, and an elastic beam section that connects the first section and the second section. The piezoelectric film is connected across the first section and the second section. The piezoelectric film includes a first piezoelectric film and a second piezoelectric film that are stacked on top of each other. The first piezoelectric film and the second piezoelectric film are polarized to the same potential with different polarities when bent in the stacking direction.

The deformation detection sensor is connected to an operation panel that accepts a user's pressing operation and includes a holding section that holds the operation panel, and a piezoelectric film that is connected to the holding section and detects deformation of the holding section. The holding section has a first section that is connected to a housing, a second section that is connected to the operation panel, and a plurality of elastic beam sections that connect the first section and the second section. The piezoelectric film is connected across the first section and the second section. The direction from a first connection position between the first section and the piezoelectric film toward a second connection position between the second section and the piezoelectric film is defined as a first direction. The plurality of beam sections include a first beam section that is provided at a position close to the second connection position along the first direction, and a second beam section that is provided at a position farther from the second connection position than the position of the first beam section. When the normal direction of the connection surface of the holding section that connects to the operation panel is defined as a thickness direction, the first beam section is less likely to deform in the thickness direction than the second beam section.

The deformation detection sensor of one embodiment of the present invention can output a uniform output value even if the pressing position is different.

1 is an exploded perspective view of an electronic device 100 including a deformation detection sensor 10 according to a first embodiment. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 2 is a bottom view of the deformation detection sensor 10 of the first embodiment. 3 is a side view of the piezoelectric film 4 of the first embodiment as viewed from the front-rear direction. FIG. FIG. 4 is a side view of a bent piezoelectric film 4. 4 is a cross-sectional view showing an example of a pressed position on the touch panel 1 as viewed from the front-rear direction Z1. FIG. 11 is a cross-sectional view showing an example of deformation of the deformation detection portion when point A is pressed; FIG. 11 is a cross-sectional view showing an example of deformation of the deformation detection portion when point B is pressed; FIG. 10 is a reference diagram showing an example of an output value of the piezoelectric film 4. FIG. 10 is a reference diagram showing an example of an output value of a piezoelectric film of a reference example. FIG. 11 is an exploded perspective view of an electronic device 100A including a deformation detection sensor 10A according to a second embodiment. FIG. 11 is a side view of a piezoelectric film 4A according to a second embodiment as viewed in the front-rear direction Z1. FIG. FIG. 10 is a bottom view of a deformation detection sensor 10A according to a second embodiment. 14 is a cross-sectional view taken along line BB in FIG. 13. 10 is a reference diagram showing the output values of the piezoelectric film 4A when point A is pressed and when point B is pressed. FIG. 11 is a side view of a member showing an example of deflection of the member. 17 is a cross-sectional view taken along line CC of FIG. 16.

[Embodiment 1]
[Structure of deformation detection sensor]
Hereinafter, a structure of a deformation detection sensor 10 according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is an exploded perspective view of an electronic device 100 including the deformation detection sensor 10 of the first embodiment. Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1. Fig. 3 is a bottom view of the deformation detection sensor 10 of the first embodiment.

The electronic device 100 includes a touch panel 1, a housing 2, a deformation detection sensor 10, and an actuator 5. The touch panel 1 in this example is an example of an operation panel of the present invention.

In this specification, directions are defined as follows. The normal direction of the touch panel 1 formed in a flat plate shape is defined as the up-down direction Y1. The touch panel 1 has a rectangular shape in a planar view. The longitudinal direction of the touch panel 1 in a planar view is defined as the left-right direction X1, and the short-side direction of the touch panel 1 when viewed from the up-down direction Y1 is defined as the front-rear direction Z1. The up-down direction Y1, the left-right direction X1, and the front-rear direction Z1 are perpendicular to each other. The vertical direction is the direction from top to bottom in the up-down direction Y1. The horizontal direction is the direction perpendicular to the vertical direction. Planar view refers to viewing from top to bottom. The left-right direction X1 in this example corresponds to the first direction of this invention. The up-down direction Y1 in this example corresponds to the second direction of this invention. In addition, in the drawings, "B" indicates the back. In the drawings, "F" indicates the front. In the drawings, "D" indicates the bottom. In the drawings, "U" indicates the top.

Note that the definitions of directions in this specification are merely examples. Therefore, the directions in this specification do not need to match the directions in actual use of the deformation detection sensor 10 and the electronic device 100 equipped with the deformation detection sensor 10. Also, in FIG. 1, the up-down direction Y1 may be inverted. Similarly, in FIG. 1, the left-right direction X1 may be inverted. Furthermore, in FIG. 1, the front-back direction Z1 may be inverted.

As shown in Fig. 1, the electronic device 100 includes a deformation detection sensor 10. The electronic device 100 is, for example, a smartphone or a laptop personal computer, and includes a touch panel 1. When a force is applied to the touch panel 1 by the user, the electronic device 100 provides tactile feedback to the user. In this example, the force applied to the touch panel 1 is a force pressing the touch panel 1.

The touch panel 1 includes, for example, a capacitive touch sensor. The capacitive touch sensor detects a user's contact with the touch panel 1. The touch panel 1 also accepts a pressing operation from the user. The deformation detection sensor 10 detects the pressing operation by the user.

The housing 2 is a rigid body and has a flat frame shape. The housing 2 is formed, for example, from SUS (Steel Use Stainless). The housing 2 is formed to be elongated in the left-right direction X1. In a plan view, the housing 2 has an opening Op1 formed therein that is elongated in the left-right direction X1. The opening Op1 is larger than the touch panel 1 in a plan view. The touch panel 1 is exposed from the housing 2 through the opening Op1.

The deformation detection sensor 10 comprises a holding portion 3 and a piezoelectric film 4.

The holding portion 3 has a flat plate shape. The holding portion 3 is formed, for example, from a single metal plate. The holding portion 3 is formed, for example, from SUS (Steel Use Stainless). The holding portion 3 is connected to the touch panel 1 and holds the touch panel 1. More specifically, the holding portion 3 includes, in plan view, a first portion 31 which is an outer frame portion, a second portion 32 which is an inner frame portion, and a plurality of beam portions 33 (four in FIG. 1) which connect the first portion 31 and the second portion 32. The first portion 31, the second portion 32, and the plurality of beam portions 33 are integrally formed, for example, by punching out a single SUS plate.

As shown in Figure 2, the first part 31 is connected to the underside of the housing 2 in the vertical direction Y1.

The second part 32 connects to the underside of the touch panel 1 in the vertical direction Y1.

The four beam portions 33 are elastic. When the holding portion 3 is viewed in a plane, each of the four beam portions 33 has a rectangular shape (see FIG. 1). The four beam portions 33 are provided near each corner of the second portion 32. When a force is applied to the touch panel 1, each of the four beam portions 33 elastically deforms, so that the second portion 32 deforms, for example, at least in the vertical direction Y1 relative to the first portion 31. The deformation of the beam portions 33 in the vertical direction Y1 and the horizontal direction X1 will be described later.

When force is applied to the touch panel 1, the four beam portions 33 may cause the second portion 32 to deform in the vertical direction Y1 and the horizontal direction X1 relative to the first portion 31.

As shown in FIG. 3, the piezoelectric film 4 is elongated in the left-right direction X1 in a plan view and has a film shape. The piezoelectric film 4 is disposed under the holding portion 3. The piezoelectric film 4 is connected across the right end of the first portion 31 and the right end of the second portion 32 of the holding portion 3. More specifically, as shown in FIG. 2 and FIG. 3, the first connection position 43, which is the right end of the piezoelectric film 4, is connected to the portion 31A of the first portion 31 of the holding portion 3. In addition, the second connection position 44, which is the left end of the piezoelectric film 4, is connected to the portion 32A of the second portion 32 of the holding portion 3. The piezoelectric film 4 deforms in response to the force applied to the touch panel 1 by the user. Details of the piezoelectric film 4 will be described below.

In this example, portion 31A is the right end side of first portion 31 in the left-right direction X1. Also, portion 32A is the right end side of second portion 32 in the left-right direction X1. Furthermore, portion 32B is the left end side of second portion 32 in the left-right direction X1.

As shown in Fig. 1, the actuator 5 is long in the left-right direction X1 in plan view and has a film shape. The actuator 5 is connected to the first part 31 and the second part 32 of the holding part 3. More specifically, as shown in Fig. 3, the actuator 5 is connected to the part 31A of the first part 31 at its right end in the left-right direction X1. The actuator 5 is connected to the part 32B of the second part 32 at its left end in the left-right direction X1.

The actuator 5 includes a piezoelectric body. More specifically, the actuator 5 has a piezoelectric film and a first electrode portion 51 and a second electrode portion 52 arranged on both main surfaces (upper and lower surfaces) of the piezoelectric film. Each of the first electrode portion 51 and the second electrode portion 52 is a metal coating of, for example, Cu, Al, Ni, or the like, formed by vapor deposition.

The actuator 5 is connected to, for example, a drive circuit (not shown). When the deformation detection sensor 10 detects a pressing operation on the touch panel 1, the drive circuit applies an AC voltage to the first electrode portion 51 and the second electrode portion 52 of the piezoelectric film of the actuator 5. The piezoelectric film of the actuator 5 expands and contracts in the left-right direction X1 when an AC voltage is applied to the first electrode portion 51 and the second electrode portion 52. The actuator 5 expands in the left-right direction X1 when a positive voltage is applied, for example. On the other hand, the actuator 5 contracts in the left-right direction X1 when a negative voltage is applied, for example. The actuator 5 is connected to the second portion 32, and therefore vibrates the second portion 32. The holding portion 3 transmits the vibration to the touch panel 1 when the second portion 32 vibrates. As a result, the electronic device 100 provides tactile feedback to the user.

[Detailed Description of Piezoelectric Film 4]
The piezoelectric film 4 will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a side view of the piezoelectric film 4 as viewed from the front-rear direction in the embodiment 1. Fig. 5 is a side view of the bent piezoelectric film 4.

As shown in FIG. 4, the piezoelectric film 4 includes a first piezoelectric film 41 and a second piezoelectric film 42 stacked together along the vertical direction Y1. The first piezoelectric film 41 and the second piezoelectric film 42 are configured to be polarized with different polarities and equal potentials when bent (flexed) in the stacking direction. In other words, the first piezoelectric film 41 and the second piezoelectric film 42 are configured to generate opposite charges and generate opposite potentials in the stacking direction. In addition, the first piezoelectric film 41 and the second piezoelectric film 42 generate opposite charges, and generate opposite potentials when the charge capacity of the first piezoelectric film 41 and the charge capacity of the second piezoelectric film 42 are the same or approximately the same. The stacking direction is the same as the vertical direction Y1 in this example.

The first piezoelectric film 41 and the second piezoelectric film 42 will be described in detail.

The first piezoelectric film 41 and the second piezoelectric film 42 are films of the same piezoelectric material. The first piezoelectric film 41 and the second piezoelectric film 42 are rectangular films made of, for example, polyvinylidene fluoride (PVDF). PVDF has piezoelectric properties. The first piezoelectric film 41 and the second piezoelectric film 42 have a piezoelectric constant of d31.

In this example, the thickness ts1 of the first piezoelectric film 41 and the thickness ts2 of the second piezoelectric film 42 are the same length. The thickness ts1 of the first piezoelectric film 41 and the thickness ts2 of the second piezoelectric film 42 are, for example, 30 μm. Furthermore, the first piezoelectric film 41 and the second piezoelectric film 42 have the same shape and size in a planar view. In this example, the first piezoelectric film 41 and the second piezoelectric film 42 are elongated rectangular shapes along the left-right direction X1 in a planar view.

Each of the first piezoelectric film 41 and the second piezoelectric film 42 has an electrode portion formed on the front and back (top and bottom surfaces in FIG. 4). The first piezoelectric film 41 has a first electrode portion P11 formed on the top surface. The first piezoelectric film 41 has a second electrode portion P12 formed on the bottom surface. The second piezoelectric film 42 has a first electrode portion P21 formed on the top surface. The second piezoelectric film 42 has a second electrode portion P22 formed on the bottom surface. Each of the first electrode portion P11, the second electrode portion P12, the first electrode portion P21 and the second electrode portion P22 is a metal coating such as Cu, Al, Ni, etc., formed by vapor deposition.

The dotted arrow in Figure 4 indicates the direction of stretching. In this example, stretching means being pulled in the longitudinal direction (in this example, the left-right direction X1).

When the first piezoelectric film 41 and the second piezoelectric film 42 are stretched in the left-right direction X1, the surface of the first piezoelectric film 41 and the second piezoelectric film 42 on which a positive potential is generated is the front surface, and the opposite surface is the back surface. The first piezoelectric film 41 and the second piezoelectric film 42 are connected at the front or back surfaces with, for example, a double-sided adhesive conductive tape. In this example, the second electrode portion P12 of the first piezoelectric film 41 and the first electrode portion P21 of the second piezoelectric film 42 are connected. In addition, the second electrode portion P12 and the second electrode 21 are connected to, for example, ground.

In this example, when the first piezoelectric film 41 is stretched in the left-right direction X1, a positive potential is generated in the first electrode portion P11 relative to the second electrode portion P12. Also, when the second piezoelectric film 42 is stretched in the left-right direction X1, a positive potential is generated in the second electrode portion P22 relative to the first electrode portion P21.

The potential difference between the first electrode portion P11 and the second electrode portion P12 is defined as a first potential difference V1. The potential difference between the first electrode portion P21 and the second electrode portion P22 is defined as a second potential difference V2.

When the first piezoelectric film 41 and the second piezoelectric film 42 are stretched in the left-right direction X1 with the same force, the first potential difference V1 and the second potential difference V2 become the same magnitude.

An arithmetic circuit (not shown) connected to the piezoelectric film 4 outputs an output value based on the sum of the first potential difference V1 and the second potential difference V2.

On the other hand, for example, the piezoelectric film 4 may bend in the up-down direction Y1 due to a vertical force, as shown in Figure 5.

When the first piezoelectric film 41 and the second piezoelectric film 42 are bent by a force in the vertical direction (up-down direction Y1), it is assumed that there is a neutral line of stress between the first piezoelectric film 41 and the second piezoelectric film 42. In this case, the first piezoelectric film 41 expands in the longitudinal direction (left-right direction X1). Meanwhile, the second piezoelectric film 42 contracts in the longitudinal direction (left-right direction X1). The dotted arrows in Figure 5 indicate the expansion direction of the first piezoelectric film 41. The dashed arrows in Figure 5 indicate the contraction direction of the second piezoelectric film 42.

In the first piezoelectric film 41, a positive potential (+V1) is generated at the first electrode portion P11 relative to the second electrode portion P12. In addition, since the first piezoelectric film 41 and the second piezoelectric film 42 are connected so that their back surfaces are facing each other when they are stretched in the left-right direction X1, when they are bent in the vertical direction, a negative potential (-V2) is generated at the second electrode portion P22 relative to the first electrode portion P21 of the second piezoelectric film 42.

When the piezoelectric film 4 is bent by a vertical force, if the absolute value of the first potential difference V1 and the absolute value of the second potential difference V2 are the same, the output value output from the deformation detection circuit becomes zero or a value close to zero.

Therefore, the deformation detection sensor 10 outputs a high output value for expansion and contraction deformation in the horizontal direction (including the longitudinal direction), and outputs an output value of zero or close to zero for bending deformation in the vertical direction.

[Operation of deformation detection sensor]
The deformation of the piezoelectric film 4 caused by pressing the touch panel 1 will be described with reference to Fig. 6, Fig. 7, and Fig. 8. Fig. 6 is a cross-sectional view showing an example of a pressed position on the touch panel 1 as viewed from the front-rear direction Z1. Fig. 7 is a cross-sectional view showing an example of deformation of the deformation detection section when point A is pressed. Fig. 8 is a cross-sectional view showing an example of deformation of the deformation detection section when point B is pressed.

When the touch panel 1 is pressed by a user (at this time, the force acting in the horizontal direction is Pd1, and the force acting in the vertical direction is Pd2 (see Figure 6)), a vertical force Pd1 and a horizontal force Pd2 act on the beam portion 33. In this example, the deformation of the beam portion 33 due to the vertical force Pd1 will be described in detail. When the touch panel 1 is pressed by a user, the beam portion 33 is elastically deformed by the vertical force. Furthermore, as shown in Figures 7 and 8, the second part 32 of the holding portion 3 is displaced diagonally (horizontally and vertically). In this case, the piezoelectric film 4 is deformed so as to be pulled in the horizontal direction (left-right direction X1) by the horizontal force Pd1. In other words, the piezoelectric film 4 is stretched in the left-right direction X1 by the horizontal force Pd1. Furthermore, the piezoelectric film 4 is bent in the vertical direction by the vertical force Pd2. In this case, the piezoelectric film 4 is connected to the portion 31A of the first portion 31 at the first connection position 43 and is connected to the second portion 32 at the second connection position 44, and therefore bends with the first connection position 43 as a fulcrum.

We will explain what happens when the user presses the touch panel 1 at points A and B.

Point A is on the left end side of the touch panel 1 in the left-right direction X1, as shown in Figure 6. Point B is on the right end side of the touch panel 1 in the left-right direction X1. In other words, point A is farther from the second connection position 44 between the piezoelectric film 4 and the holding portion 3 than point B. Note that the force applied when the user presses point A and point B on the touch panel 1 is assumed to be the same.

If the force applied by the user when pressing is the same, the amount of horizontal expansion deformation is the same whether the user presses at point A or point B. However, even if the force applied by the user when pressing at point A and point B is the same, the amount of vertical bending deformation of the piezoelectric film 4 differs between when the film is pressed at point A and when it is pressed at point B, as shown in Figures 7 and 8.

When pressed at point B, the vertical force Pd2 has a greater effect on the bending deformation of the piezoelectric film 4 than when pressed at point A. If the force with which a user presses point A and point B on the touch panel 1 is the same, the amount of vertical bending deformation of the piezoelectric film 4 will be greater when pressed at point B.

When the touch panel 1 is viewed in a plan view, the closer the pressed position is to the fulcrum, which is the first connection position 43, the greater the amount of vertical bending deformation of the piezoelectric film 4. In this way, the amount of bending deformation of the piezoelectric film 4 caused by pressing the touch panel 1 changes depending on the pressing position when the touch panel 1 is viewed in a plan view.

[Action and Effects]
The amount of depression of the touch panel 1 corresponds to the amount of deformation due to expansion and bending of the piezoelectric film 4, and is detected by the output value (first potential difference V1+second potential difference V2). In this embodiment, the first potential difference V1 and the second potential difference V2 with respect to a change in the vertical direction have opposite polarities and cancel each other out, so the deformation detection sensor 10 does not output, or hardly outputs, an output value due to bending in the vertical direction.

A comparison between the output value of the piezoelectric film 4 of this embodiment and the output value of the piezoelectric film of the reference example will be described with reference to Figures 9 and 10. The reference example here is a piezoelectric film that does not have the features of the present invention. Specifically, the piezoelectric film of the reference example does not have two piezoelectric films that generate different charges when bent in the stacking direction, and as a result, generate reverse potentials. Figure 9 is a reference diagram showing an example of the output value of the piezoelectric film 4. The horizontal axis shown in Figure 9 indicates time. The vertical axis shown in Figure 9 is the output value of the piezoelectric film 4. Figure 10 is a reference diagram showing an example of the output value of the piezoelectric film of the reference example. The horizontal axis shown in Figure 10 indicates time. The vertical axis shown in Figure 10 is the output value of the piezoelectric film. Note that the dotted lines Oa1 and Oa2 shown in Figures 9 and 10 indicate the output value at point A, and the solid lines Ob1 and Ob2 indicate the output value at point B.

As shown in FIG. 9, the output value from the piezoelectric film 4 is approximately the same at points A and B. That is, the output value of the piezoelectric film 4 in this embodiment is hardly affected by bending in the vertical direction. On the other hand, in the piezoelectric film of the reference example, the output value is significantly different at points A and B, as shown in FIG. 10. When pressed at point B, the output value of the piezoelectric film of the reference example detects not only the amount of extension deformation due to a horizontal force, but also the amount of bending deformation due to a vertical force. That is, the piezoelectric film of the reference example outputs an output value influenced by bending due to a vertical force depending on the position at which the touch panel 1 is pressed.

The deformation detection sensor 10 of embodiment 1 is provided with a first piezoelectric film 41 and a second piezoelectric film 42 that generate different charges when bent in the stacking direction, resulting in an opposite potential, thereby reducing the effect of forces acting vertically on the piezoelectric film 4. In other words, the deformation detection sensor 10 detects only horizontal deformation across the entire surface of the touch panel 1, regardless of the position of the press, and the output value of the deformation detection sensor 10 does not change regardless of where the touch panel 1 is pressed. Therefore, the deformation detection sensor 10 of one embodiment of the present invention can output a uniform output value as long as the amount of pressing is uniform, even if the pressing position of the touch panel 1 is different.

[Modification of the first embodiment]
The following describes configurations of the piezoelectric film 4 other than those of the above-described embodiment 1. In a modification of embodiment 1, the film length of the first piezoelectric film 41 and the film length of the second piezoelectric film 42 in the left-right direction X1 are the same, and the film width of the first piezoelectric film 41 and the film width of the second piezoelectric film 42 in the front-rear direction Z1 are the same.

When the first piezoelectric film 41 expands in the left-right direction X1 and the second piezoelectric film 42 contracts in the left-right direction X1, the conditions for the first potential difference V1 and the second potential difference V2 to be the same are explained using the following formulas [Formula 1] to [Formula 3].

The stress generated in the piezoelectric film is σ, the strain generated in the piezoelectric film is s, the Young's modulus of the piezoelectric film is Y, the electric field generated in the piezoelectric film is E, the potential difference (voltage) between the first main surface and the second main surface of the piezoelectric film is V, the piezoelectric constant of the piezoelectric film is d31, the amount of bending deformation of the piezoelectric film in the left-right direction X1 is Δ, the film length of the piezoelectric film in the left-right direction X1 is L, the dielectric constant of the piezoelectric film is ε, and the thickness of the piezoelectric film is ts.

Stress σ can be calculated using the following equation (1).

[Formula 1]
σ=Y×s=Y×Δ/L
The electric field E is calculated by the following formula 2.

[Formula 2]
E=d31/ε×σ=d31/ε×Y×Δ/L
The potential difference (voltage) V is calculated by the following [Equation 3].

[Formula 3]
V=t×E=t/ε×Δ/L×d31×Y
Assuming that the thickness of the first piezoelectric film 41 is ts1, the thickness of the second piezoelectric film 42 is ts2, the dielectric constant of the first piezoelectric film is ε1, and the dielectric constant of the second piezoelectric film is ε2, then if a first ratio ts1/ε1 which is the ratio between the thickness ts1 of the first piezoelectric film 41 and the dielectric constant ε1 of the first piezoelectric film 41 is the same as a second ratio ts2/ε2 which is the ratio between the thickness ts2 of the second piezoelectric film 42 and the dielectric constant ε2 of the second piezoelectric film 42 (ts1/ε1=ts2/ε2) and the piezoelectric constant of the first piezoelectric film 41 and the piezoelectric constant of the second piezoelectric film 42 are the same d31, then the first potential difference V1 and the second potential difference V2 generated by the first piezoelectric film 41 and the second piezoelectric film 42, respectively, will be equal.

Furthermore, apart from the above, from Equation 3, if the product ( _{d311) × ts1 of the piezoelectric constant (d311 )} of the first piezoelectric film and the thickness ts1 of the first piezoelectric film 41 is the same as the product ( _d312 ) × ts2 of the piezoelectric constant ( _d312 ) of the second piezoelectric film 42 and the thickness ts2 of the second piezoelectric film 42 ( _d311 × ts1 = _d312 × ts2) and the dielectric constant ε1 of the first piezoelectric film 41 and the dielectric constant ε2 of the second piezoelectric film 42 are the same, then the first potential difference V1 and the second potential difference V2 generated by the first piezoelectric film 41 and the second piezoelectric film 42, respectively, will be equal.

[Embodiment 2]
The deformation detection sensor 10A of the second embodiment will be described with reference to Figs. 11, 12, 13, 14, and 15. Fig. 11 is an exploded perspective view of an electronic device 100A including the deformation detection sensor 10A of the second embodiment. Fig. 12 is a side view of the piezoelectric film 4A of the second embodiment as viewed from the front-rear direction Z1. Fig. 13 is a bottom view of the deformation detection sensor 10A of the second embodiment. Fig. 14 is a cross-sectional view taken along line B-B in Fig. 13. Fig. 15 is a reference diagram showing the output values of the piezoelectric film 4A when point A is pressed and when point B is pressed. The horizontal axis of Fig. 15 indicates the distance from the second connection position 44. The vertical axis of Fig. 15 indicates the output value of the deformation detection sensor 10A. The same components as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this example, the amount of displacement of the second part 32 of the holding portion 3A due to pressing against the touch panel 1 is controlled.

In this example, the deformation detection sensor 10A includes a piezoelectric film 4A as shown in FIG. 11. The piezoelectric film 4A has a long film shape in the left-right direction X1 as shown in FIG. 11 and FIG. 12. The piezoelectric film 4A has a first electrode portion P31 on the upper surface and a second electrode portion P32 on the lower surface as shown in FIG. 12. Furthermore, the piezoelectric film 4A has a piezoelectric body between the electrode portions. The piezoelectric film 4A is connected to an arithmetic circuit (not shown). In this example, an example in which the piezoelectric film 4A is composed of a single film will be described. The piezoelectric film 4A may be a single sheet, or may be composed of multiple filters stacked together.

When the touch panel 1 is pressed, the piezoelectric film 4A expands in the horizontal direction (for example, the left-right direction X1). When the touch panel 1 is pressed, the piezoelectric film 4A bends in the vertical direction (the up-down direction Y1). An arithmetic circuit (not shown) calculates the potential difference based on the output value output from the piezoelectric film 4A.

As shown in FIG. 13, the holding portion 3A has a plurality (two in FIG. 13) of first beam portions 33A and a plurality (two in FIG. 13) of second beam portions 33B.

[Structure of holding part]
The multiple first beam portions 33A are provided at positions close to the second connection position 44 along the left-right direction X1. The multiple second beam portions 33B are provided at positions farther from the second connection position 44 than the positions of the first beam portions 33A. The number of first beam portions 33A may be one. The number of second beam portions 33B may be one.

In this example, when the normal direction (vertical direction Y1) of the upper surface (connection surface) of the holding portion 3 is defined as the thickness direction, the first beam portion 33A is formed to be less susceptible to deformation in the thickness direction than the second beam portion 33B.

The structure of the first beam portion 33A and the second beam portion 33B is described in more detail below.

As shown in FIG. 14, the first beam portions 33A have a rectangular shape when viewed in a plane. Similarly, the second beam portions 33B have a rectangular shape when viewed in a plane. In this example, the first thickness tf1, which is the length of the first beam portion 33A in the vertical direction Y1, and the second thickness tf2, which is the length of the second beam portion 33B in the vertical direction Y1, are the same. It is preferable that the first thickness tf1 and the second thickness tf2 are 0.3 mm to 10 mm.

13, the first length L1, which is the length of the first beam portion 33A in the front-rear direction Z1, and the second length L2, which is the length of the second beam portion 33B in the front-rear direction Z1, are the same. It is preferable that the first length L1 and the second length L2 are 5 mm to 30 mm.

The first beam portion 33A has a first width W1, which is the length in the left-right direction X1, that is longer than the second width W2, which is the length in the left-right direction X1, of the second beam portion 33B. The first width W1 of the first beam portion 33A and the second width W2 of the second beam portion 33B are preferably 0.5 mm to 2 mm.

Because the first width W1 is longer than the second width W2, the first beam portion 33A is less likely to bend in the vertical direction Y1 than the second beam portion 33B. In addition, the second beam portion 33B, which has a second width W2 shorter than the first width W1, is more likely to bend in the vertical direction Y1 than the first beam portion 33A.

Here, the output value of the piezoelectric film 4A when point B is pressed is set to "1", and the output value of the piezoelectric film 4A when point A is pressed will be described. The straight line Cp1 shown in FIG. 15 indicates the inclination when the ratio of the first width W1 of the first beam portion 33A to the second width W2 of the second beam portion 33B is "1" to "1". The straight line Cp2 shown in FIG. 15 indicates the inclination when the ratio of the first width W1 of the first beam portion 33A to the second width W2 of the second beam portion 33B is "2" to "1". The straight line Cp3 shown in FIG. 15 indicates the inclination when the ratio of the first width W1 of the first beam portion 33A to the second width W2 of the second beam portion 33B is "3" to "1". In FIG. 15, the force applied to the touch panel 1 is the same at points A and B.

Furthermore, comparing the slopes of the lines Cp1, Cp2, and Cp3, the slope of the line Cp1 is the greatest. Meanwhile, the slope of the line Cp3 is the smallest. In other words, when the ratio of the first width W1 to the second width W2 is "1" to "1", the deformation amount and difference of the piezoelectric film 4A when point B is pressed increases as the pressed position moves away from the second connection position 44.

Furthermore, in line Cp1, as shown in Figure 15, the output value as a relative value of the piezoelectric film 4A when point A is pressed is the smallest compared to lines Cp2 and Cp3.

On the other hand, compared to lines Cp1 and Cp2, line Cp3 is the closest to "1" in the output value of piezoelectric film 4A when point A is pressed. In this way, if the ratio of first width W1 to second width W2 is "3" to "1", it can be considered that there is no practical difference in the amount of deformation of piezoelectric film 4A when point A is pressed and when point B is pressed.

[Action and Effects]
When the touch panel 1 is pressed at point B, the piezoelectric film 4A is less likely to deform in the vertical direction Y1 than when the touch panel 1 is pressed at point A. Moreover, when the piezoelectric film 4A is pressed at point A, it is more likely to deform in the vertical direction Y1 than when the touch panel 1 is pressed at point B.

For example, if the first width W1 of the first beam portion 33A is about three times the second width W2 of the second beam portion 33B, the amount of deformation of the piezoelectric film in the vertical direction Y1 when point A is pressed will be the same. In other words, if the first width W1 of the first beam portion 33A is about three times the second width W2 of the second beam portion 33B, the output value of the piezoelectric film 4A will be the same as the output value of the piezoelectric film 4A when point B is pressed.

In this way, by making the first width W1 larger than the second width W2, the effect of the force acting in the vertical direction on the piezoelectric film 4A can be reduced. Therefore, the deformation detection sensor 10A of the second embodiment can output a uniform output value if the amount of pressing is uniform, even if the pressing position on the touch panel 1 is different.

[Definition of bendability based on the second moment of area]
The ease of bending based on the second moment of area will be described with reference to FIG. 16 and FIG. 17. The ease of bending based on the second moment of area will be described with reference to the member 6 shown in FIG. 16 and FIG. 17. FIG. 16 is a side view of a member showing an example of the deflection of the member used in the following description. FIG. 16 is a side view of the member 6. L shown in FIG. 16 indicates the length of the member 6 in the longitudinal direction of the member 6. P shown in FIG. 16 indicates the force applied perpendicularly to the member 6. The direction of the force P shown in FIG. 17 is indicated by an arrow. δ shown in FIG. 16 indicates the magnitude of the deflection of the member 6. FIG. 17 is a cross-sectional view taken along the line CC in FIG. 16. h shown in FIG. 17 indicates the length (thickness) of the member 6 in the direction in which the member 6 is bent by the force P. Also, b shown in FIG. 17 indicates the length (width) of the member 6 in the direction perpendicular to the direction in which the force P is applied.

As shown in Fig. 16, member 6 is a long member with one end (the left end in Fig. 16) fixed. Also, member 6 has a rectangular cross section, for example, as shown in Fig. 17.

When a vertical force P is applied to the other end (free end) of member 6 (the right end in Figure 16), it bends downward. The cross section of member 6 is rectangular with width b and thickness h. The second moment of area l of member 6 is calculated using the following [Equation 4].

[Formula 4]
l = b h ³ / 12
The deflection δ of the member 6 when a force P in the vertical direction is applied is calculated by the following [Equation 5]. Note that the longitudinal elastic modulus (Young's modulus) of the member 6 is represented as Y.

[Formula 5]
δ=(PL ³ )/3Yl
If we assume that the member 6 is an elastic body and the spring constant of the member 6 as an elastic body is K, the force P applied to the member 6 can be calculated as shown in the following [Equation 6].

[Formula 6]
P = K × δ
When [Formula 5] is substituted for δ in [Formula 6] and [Formula 4] is substituted for the second moment of area l, the spring constant can be expressed as the following [Formula 7].

[Formula 7]
K=3Yl/L ³ ∝(3Y×bh ³ )/(12L ³ )∝bh ³ /L ³
In this embodiment, the spring constant K shown in [Equation 7] is defined as the ease with which the member 6 bends.

The bending ease K1 of the first beam portion 33A in the vertical direction (up-down direction Y1) is calculated using the above [Equation 7]. In this case, when the vertical force is force P, the thickness h shown in FIG. 17 corresponds to the first thickness tf1 of the first beam portion 33A. The width b shown in FIG. 17 corresponds to the first width W1 of the first beam portion 33A. The L shown in FIG. 16 corresponds to the first length L1 of the first beam portion 33A.

Therefore, the vertical bending ease K1 of the first beam portion 33A is expressed by the following [Equation 8].

[Formula 8]
K1=(W1×(tf1) ³ )/(L1) ³ =(tf1) ³ (W1)/(L1) ³
The bending ease K2 of the second beam portion 33B in the vertical direction (up-down direction Y1) is expressed by the following [Equation 9].

[Formula 9]
K2=(W2×(tf2) ³ )/(L2) ³ =(tf2) ³ (W2)/(L2) ³
It is assumed that the first length L1 and the second length L2 are the same, and the first thickness tf1 and the second thickness tf2 are the same. In this case, the ratio (K1:K2) of the bending ease K1 of the first beam portion 33A and the bending ease K2 of the second beam portion 33B due to the vertical force P is the ratio (W1:W2) of the first width W1 and the second width W2 from the above formula. Therefore, the ratio of the bending ease K1 of the first beam portion 33A and the bending ease K2 of the second beam portion 33B due to the perpendicular force P can be controlled by the first width W1 and the second width W2.

[Modification of the second embodiment]
A description will be given of a configuration according to a modification of the above-mentioned embodiment 2. In this example, the first width W1, the second width W2, the first length L1, and the second length L2 are calculated when the first length L1 and the second length L2 are different.

In this example, the following conditions are assumed. The first beam portion 33A and the second beam portion 33B are formed of the same material. A first thickness tf1, which is the length of the first beam portion 33A in the vertical direction Y1 (thickness direction), is the same as a second thickness tf2, which is the length of the second beam portion 33B in the vertical direction Y1 (see Figure 14). The bending ease K of the first beam portion 33A in the horizontal direction (left-right direction X1) and the bending ease K of the second beam portion 33B in the horizontal direction (left-right direction X1) are the same.

By using the above-mentioned [Equation 7], the bending ease K1 of the first beam portion 33A and the bending ease K2 of the second beam portion 33B due to the vertical force Pd2 (see Figure 6) are calculated.

For the first beam portion 33A, if the force Pd1 in the left-right direction X1 is the force P shown in Figure 17, the thickness h shown in Figure 17 corresponds to the first width W1 of the first beam portion 33A. Also, the width b shown in Figure 17 corresponds to the first thickness tf1 of the first beam portion 33A. Furthermore, for the second beam portion 33B, if the force Pd1 in the left-right direction X1 is the force P shown in Figure 17, the thickness h shown in Figure 17 corresponds to the second width W2 of the second beam portion 33B. Also, the width b shown in Figure 17 corresponds to the second thickness tf2 of the second beam portion 33B.

From Equation 7, the bending ease K of the first beam portion 33A and the second beam portion 33B in the left-right direction X1 is obtained as follows: [Equation 10]

[Formula 10]
((W1) ³ ×tf1)/(L1) ³ = ((W2) ³ ×tf2)/(L2) ³ =K
When [Equation 10] is used as a constraint, the bending ease K1 of the first beam portion 33A in the vertical direction is calculated as follows.

K1=(W1×(tf1) ³ )/(L1) ³ =K(tf1) ² /(W1) ²
Furthermore, when [Equation 10] is used as a constraint, the bending ease K2 of the second beam portion 33B in the vertical direction is calculated as follows.

K2=(W2×(tf2) ³ )/(L2) ³ =K(tf2) ² /(W2) ²
The ratio of the bending ease K1 of the first beam portion 33A in the vertical direction to the bending ease K2 of the second beam portion 33B in the vertical direction is defined as U. In this case, the bending ease ratio U is controlled by (W2/W1) ^2. Furthermore, the first length L1 and the second length L2 are selected so as to satisfy [Equation 10] for the determined (W2/W1) ² .

For example, the first beam portion 33A and the second beam portion 33B may be formed so that the first length L1 is longer than the second length L2.

As a result, the amount of vertical deformation of the piezoelectric film 4A can be considered practically unchanged regardless of the pressing position on the touch panel 1. Therefore, the deformation detection sensor 10A can reduce the effect of forces acting in the vertical direction on the piezoelectric film 4A, regardless of the pressing position on the touch panel 1 when viewed in a plan view.

Finally, the description of each of the above embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, not by the above-described embodiments. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope of the claims.

The metal plate forming the housing 2 may be coated with a resin such as polyimide. Furthermore, the housing 2 may be formed from a material other than a metal plate (e.g., acrylic resin, PET, polycarbonate, glass epoxy, FRP, metal, glass, etc.).

The metal plate forming the holding portion 3, 3A may be coated with a resin such as polyimide. Furthermore, the holding portion 3, 3A may be formed of a material other than a metal plate (e.g., acrylic resin, PET, polycarbonate, glass epoxy, FRP, metal, glass, etc.).

The first portion 31, the second portion 32, and the plurality of beam portions 33 do not have to be formed of a single member. The first portion 31, the second portion 32, the first beam portion 33A, and the second beam portion 33B do not have to be formed of a single member.

The electrode on the lower surface of the first piezoelectric film 41 and the electrode on the upper surface of the second piezoelectric film 42 do not have to be at ground potential (reference potential). In this case, the electrode on the upper surface of the first piezoelectric film 41 and the electrode on the lower surface of the second piezoelectric film 42 may be at ground potential.

The thickness ts1 of the first piezoelectric film 41 and the thickness ts2 of the second piezoelectric film 42 do not have to be the same. For example, the dielectric constant of the first piezoelectric film 41 is ε1, the piezoelectric constant of the first piezoelectric film 41 is _{d31_1} , and the thickness of the first piezoelectric film 41 is ts1. Furthermore, for example, the dielectric constant of the second piezoelectric film 42 is ε2, the piezoelectric constant of the second piezoelectric film 42 is _{d31_2} , and the thickness of the second piezoelectric film 42 is ts2. In this case, the following [Formula 11] and [Formula 12] hold true.

[Formula 11]
ts1×ε2=ts2×ε1
[Formula 12]
ts1×d31 ₁ = ts2×d31 ₂
Select ts1 and ts2 that satisfy [Equation 11] and [Equation 12]. In this case, ts1 and ts2 may be selected to be different values.

1...Touch panel (operation panel)
2...Housing 3, 3A...Holding portion 4, 4A...Piezoelectric film 5...Actuator 10, 10A...Deformation detection sensor 31...First portion 32...Second portion 33...Beam portion 33A...First beam portion 33B...Second beam portion 41...First piezoelectric film 42...Second piezoelectric film 43...First connection position 44...Second connection position d31...Piezoelectric constant L1...First length L2...Second length tf1...First thickness tf2...Second thickness ts1...Thickness of first piezoelectric film ts2...Thickness of second piezoelectric film W1...First width W2...Second width X1...Left-right direction (first direction)
Y1: Up-down direction (second direction)
ε…Dielectric constant

Claims (8)

a holding section connected to an operation panel that accepts a pressing operation by a user and holds the operation panel;
a piezoelectric film connected to the holding portion and detecting deformation of the holding portion;
Equipped with
The holding portion is
A first portion connected to a housing;
A second portion connected to the operation panel;
a beam portion connecting the first portion and the second portion and having elasticity;
the piezoelectric film is connected across the first portion and the second portion;
The piezoelectric film includes a first piezoelectric film and a second piezoelectric film laminated together,
The first piezoelectric film and the second piezoelectric film are polarized to the same potential with different polarities when bent in the lamination direction.
Deformation detection sensor. The first piezoelectric film and the second piezoelectric film have the same shape and size in a plan view.
The deformation detection sensor according to claim 1 . The length of the first piezoelectric film in the stacking direction is defined as a thickness of the first piezoelectric film,
The length of the second piezoelectric film in the stacking direction is defined as a thickness of the second piezoelectric film,
a first ratio, which is a ratio between a thickness of the first piezoelectric film and a dielectric constant of the first piezoelectric film, is equal to a second ratio, which is a ratio between a thickness of the second piezoelectric film and a dielectric constant of the second piezoelectric film;
The deformation detection sensor according to claim 2 . The piezoelectric constant of the first piezoelectric film is the same as the piezoelectric constant of the second piezoelectric film.
4. The deformation detection sensor according to claim 1. a product of a piezoelectric constant of the first piezoelectric film and a thickness of the first piezoelectric film is equal to a product of a piezoelectric constant of the second piezoelectric film and a thickness of the second piezoelectric film;
4. The deformation detection sensor according to claim 1. a holding section connected to an operation panel that accepts a pressing operation by a user and holds the operation panel;
a piezoelectric film connected to the holding portion and detecting deformation of the holding portion;
Equipped with
The holding portion is
A first portion connected to a housing;
A second portion connected to the operation panel;
a plurality of elastic beam portions connecting the first portion and the second portion,
the piezoelectric film is connected across the first portion and the second portion;
a first direction is a direction from a first connection position between the first portion and the piezoelectric film toward a second connection position between the second portion and the piezoelectric film;
the plurality of beam portions include a first beam portion provided at a position close to the second connection position along the first direction, and a second beam portion provided at a position farther from the second connection position than a position of the first beam portion;
When a normal direction of a connection surface of the holding portion connected to the operation panel is defined as a thickness direction, the first beam portion is less likely to deform in the thickness direction than the second beam portion.
Deformation detection sensor. A first thickness that is a length of the first beam portion in the thickness direction is equal to a second thickness that is a length of the second beam portion in the thickness direction,
a second direction is parallel to the connection surface and perpendicular to the first direction;
A length of the first beam portion in the second direction is equal to a length of the second beam portion in the second direction,
a length of the first beam portion in the first direction is defined as a first width of the first beam portion;
When the length of the second beam portion in the first direction is defined as a second width of the second beam portion,
The first width is greater than the second width.
The deformation detection sensor according to claim 6 . A first thickness that is a length of the first beam portion in the thickness direction is equal to a second thickness that is a length of the second beam portion in the thickness direction,
a second direction is parallel to the connection surface and perpendicular to the first direction;
a length of the first beam portion in the second direction is different from a length of the second beam portion in the second direction,
a length of the first beam portion in the first direction is defined as a first width of the first beam portion;
When the length of the second beam portion in the first direction is defined as a second width of the second beam portion,
Satisfying the following formula 1:
The deformation detection sensor according to claim 6 .
Equation 1
(W ₁ ³ × t) / L ₁ ³ = (W ₂ ³ × t) / L ₂ ³

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