Sensors

Abstract

A sensor according to the present invention comprises: a piezoelectric film having a top main surface and a bottom main surface arranged in the vertical direction; an electrode member including a top electrode, and a bottom electrode provided to the bottom main surface of the piezoelectric film; and an adhesive member with which the electrode member is affixed to the top main surface of the piezoelectric film. The Young's modulus of the adhesive member is 0 MPa or more and 10 MPa or less.

Description

[Technical field]

[0001] The present invention relates to a sensor for detecting a pressing force. [Background technology]

[0002] As an example of an invention relating to a conventional electronic device, a pressure sensor described in Patent Document 1 is known. This pressure sensor includes an operation surface, a plate-shaped member, and a piezoelectric film. A user performs a pressing operation by touching the operation surface. The plate-shaped member is deflected by the pressing operation. The piezoelectric film is attached to the plate-shaped member and is deflected together with the plate-shaped member. As a result, the pressing force is detected by the output of the piezoelectric film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 083678 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the pressure sensor described in Patent Document 1, there is a demand for detecting with high accuracy the magnitude of the force with which the user presses the operation surface.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an electronic device that can accurately detect the amount of force with which a user presses an operation panel. [Means for solving the problem]

[0006] A sensor according to one aspect of the present invention includes: a piezoelectric film having upper and lower principal surfaces aligned in a vertical direction; a lower electrode provided on the lower main surface of the piezoelectric film; an electrode member including an upper electrode; an adhesive member that fixes the electrode member to the upper main surface of the piezoelectric film; Equipped with The adhesive member has a Young's modulus of 0 MPa or more and 10 MPa or less. Effect of the Invention

[0007] The sensor according to the present invention can accurately detect the magnitude of the force with which the user presses the operation panel. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an exploded perspective view of an electronic device 1. As shown in FIG. [Diagram 2] FIG. 2 is a cross-sectional view of the electronic device 1 taken along line AA. [Diagram 3] FIG. 3 is a bottom view and a cross-sectional view of the sensor 6. [Figure 4] FIG. 4 is a diagram showing the amount of extension in the left-right direction and the front-rear direction of piezoelectric film 14 of an electronic device according to a comparative example. [Diagram 5] FIG. 5 is a diagram showing the amount of extension in the left-right direction and the front-rear direction of piezoelectric film 14 of an electronic device according to a comparative example. [Figure 6] FIG. 6 is a graph showing the relationship between the position pressed by the user and the amount of charge generated by piezoelectric film 14 in an electronic device according to a comparative example. [Figure 7] FIG. 7 is a graph showing the relationship between Young's modulus and the difference. [Figure 8] FIG. 8 is a diagram showing the amount of stretch of piezoelectric film 14 in the left-right direction and the front-rear direction. [Figure 9] FIG. 9 is a diagram showing the amount of expansion of piezoelectric film 14 in the left-right direction and the front-rear direction. [Figure 10] FIG. 10 is a cross-sectional view of the sensor 6a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Embodiment) Hereinafter, a configuration of an electronic device 1 including a sensor 6 according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is an exploded perspective view of the electronic device 1. Fig. 2 is a cross-sectional view of the electronic device 1 taken along line AA. Fig. 3 is a bottom view and a cross-sectional view of the sensor 6.

[0010] In addition, in this specification, directions are defined as follows. In the electronic device 1, the direction in which the upper and lower main surfaces of the operation panel 2 are aligned is defined as the up-down direction. In addition, the direction in which the long side of the operation panel 2 of the electronic device 1 extends when viewed in the up-down direction is defined as the front-rear direction. In addition, the direction in which the short side of the operation panel 2 of the electronic device 1 extends when viewed in the up-down direction is defined as the left-right direction. The up-down direction, left-right direction, and front-rear direction are mutually perpendicular. Note that the definitions of directions in this specification are merely examples. Therefore, the directions in the actual use of the electronic device 1 do not need to match the directions in this specification. In addition, the up-down direction may be reversed in FIG. 1. The left-right direction may be reversed in FIG. 1. The front-rear direction may be reversed in FIG. 1.

[0011] The electronic device 1 is a portable electronic terminal such as a smartphone, a tablet computer, etc. The electronic device 1 includes an operation panel 2, a housing 3, a display panel 4, an adhesive member 5, a sensor 6, and a plate-shaped member 7, as shown in Fig. 1 and Fig. 2.

[0012] The operation panel 2 has upper and lower main surfaces aligned in the vertical direction. When viewed in the vertical direction, the operation panel 2 has a rectangular shape with two long sides extending in the front-to-back direction and two short sides extending in the left-to-right direction. A part of the user's body or an operation member comes into contact with the upper main surface of the operation panel 2. The operation panel 2 is a transparent plate. The operation panel 2 is, for example, a glass plate.

[0013] The display panel 4 has an upper main surface and a lower main surface aligned in the vertical direction. The display panel 4 has a rectangular shape with two long sides extending in the front-rear direction and two short sides extending in the left-right direction when viewed in the vertical direction. The display panel 4 is fixed to the lower main surface of the operation panel 2. The display panel 4 is fixed to the operation panel 2 with an adhesive, double-sided tape, or the like. The entire display panel 4 overlaps with the operation panel 2 when viewed in the vertical direction. Therefore, the display panel 4 does not protrude from the outer edge of the operation panel 2 when viewed in the vertical direction. The display panel 4 is, for example, an organic EL display or a liquid crystal display. The display panel 4 may also include a touch panel for detecting the position where the user touches the operation panel 2. However, the touch panel may be included in the operation panel 2.

[0014] The plate-shaped member 7 has an upper main surface and a lower main surface aligned in the vertical direction. The plate-shaped member 7 has a rectangular shape with two long sides extending in the front-rear direction and two short sides extending in the left-right direction when viewed in the vertical direction. The plate-shaped member 7 is fixed to the lower main surface of the display panel 4. The plate-shaped member 7 is fixed to the display panel 4 by adhesive, double-sided tape, or the like. The entire plate-shaped member 7 overlaps with the display panel 4 when viewed in the vertical direction. Therefore, the plate-shaped member 7 does not protrude from the outer edge of the display panel 4 when viewed in the vertical direction. The rigidity of the plate-shaped member 7 is higher than the rigidity of the sensor 6 described later. The material of such a plate-shaped member 7 is, for example, a metal such as SUS (Stainless Used Steel). However, the material of the plate-shaped member 7 may be a material other than a metal. The material other than a metal is, for example, a resin.

[0015] The housing 3 is located below the operation panel 2. The housing 3 is a box. The housing 3 has a rectangular shape when viewed in the vertical direction. The long sides of the housing 3 extend in the front-to-rear direction. The short sides of the housing 3 extend in the left-to-right direction. The outer edge of the housing 3 when viewed in the vertical direction coincides with the outer edge of the operation panel 2 when viewed in the vertical direction. However, the top surface of the housing 3 is open. The opening Op of the housing 3 has a rectangular shape when viewed in the vertical direction.

[0016] The adhesive member 5 fixes a portion of the lower main surface of the operation panel 2 to the housing 3. More specifically, the adhesive member 5 fixes the periphery of the opening Op of the housing 3 to the vicinity of the outer edge of the operation panel 2. Thus, the adhesive member 5 has a rectangular frame shape surrounding the display panel 4 when viewed in the vertical direction. Therefore, the adhesive member 5 does not overlap with the display panel 4 when viewed in the vertical direction. The adhesive member 5 as described above is waterproof.

[0017] The sensor 6 detects deformation of the operation panel 2. As shown in FIG. 1, the sensor 6 is fixed to the lower main surface of the plate-like member 7. More specifically, the sensor 6 has a rectangular shape when viewed in the up-down direction. The sensor 6 has a longitudinal direction extending in the left-right direction. The sensor 6 is located in the center of the plate-like member 7 in the front-rear direction when viewed in the up-down direction.

[0018] When the user presses the operation panel 2 and the operation panel 2 bends downward, the display panel 4 and the plate-like member 7 also bend downward. The sensor 6 then bends downward together with the plate-like member 7. This causes the sensor 6 to output a detection signal corresponding to the deformation of the operation panel 2 caused by the user pressing the operation panel 2. The sensor 6 will be described in detail below with reference to FIG. 3.

[0019] The sensor 6 includes an electrode member 13, a piezoelectric film 14, a lower electrode 15b, a substrate 16, an adhesive member 17, and adhesive layers 18 and 20. The piezoelectric film 14 has a sheet shape. Therefore, the piezoelectric film 14 has upper and lower main surfaces aligned in the vertical direction. The length of the piezoelectric film 14 in the left-right direction is longer than the length of the piezoelectric film 14 in the front-rear direction. In this embodiment, the piezoelectric film 14 has a rectangular shape with long sides extending in the left-right direction when viewed in the vertical direction. The piezoelectric film 14 generates a charge according to the deformation amount of the piezoelectric film 14. In this embodiment, the piezoelectric film 14 is a PLA film. The piezoelectric film 14 will be described in more detail below.

[0020] The piezoelectric film 14 has a characteristic that the polarity of the electric charge generated when the piezoelectric film 14 is stretched in the left-right direction is opposite to the polarity of the electric charge generated when the piezoelectric film 14 is stretched in the front-back direction. Specifically, the piezoelectric film 14 is a film formed from a chiral polymer. The chiral polymer is, for example, polylactic acid (PLA), particularly L-type polylactic acid (PLLA). PLLA made of a chiral polymer has a helical structure of the main chain. PLLA has a piezoelectricity in which the molecules are oriented by uniaxial stretching. The piezoelectric film 14 has a piezoelectric constant of d14. The uniaxial stretching direction (orientation direction) of the piezoelectric film 14 forms an angle of 45 degrees with respect to each of the front-back direction and the left-right direction. This 45 degrees includes, for example, an angle including about 45 degrees ±10 degrees. As a result, the piezoelectric film 14 generates an electric charge when the piezoelectric film 14 is stretched in the left-right direction or the front-back direction. The polarity of the charge generated by the piezoelectric film 14 when it is stretched in the left-right direction is different from the polarity of the charge generated by the piezoelectric film 14 when it is stretched in the front-back direction. For example, the piezoelectric film 14 generates a positive charge when it is stretched in the left-right direction. For example, the piezoelectric film 14 generates a negative charge when it is stretched in the front-back direction. The magnitude of the charge depends on the amount of deformation of the piezoelectric film 14 due to stretching or compression. More precisely, the magnitude of the charge is proportional to the derivative of the amount of deformation of the piezoelectric film 14 due to stretching or compression.

[0021] The piezoelectric film 14 generates electric charges mainly by expanding and contracting in the left-right direction. Therefore, for example, the length of the sensor 6 in the front-rear direction (short side direction) is 10 mm or less, and the ratio (aspect ratio) of the length of the sensor 6 in the left-right direction (longitudinal direction) to the length of the front-rear direction (short side direction) is 3 or more and 10 or less.

[0022] The lower electrode 15b is a ground electrode. The lower electrode 15b is connected to a ground potential. The lower electrode 15b is provided on the lower main surface of the piezoelectric film 14. The lower electrode 15b covers the entire lower main surface of the piezoelectric film 14. The lower electrode 15b includes an adhesive layer (not shown). The lower electrode 15b is fixed to the lower main surface of the piezoelectric film 14 by this adhesive layer.

[0023] The electrode member 13 is located on the piezoelectric film 14. The electrode member 13 includes an upper electrode 15a and a flexible printed circuit board 19. The flexible printed circuit board 19 is a flexible circuit board. The flexible printed circuit board 19 has an upper main surface and a lower main surface aligned in the vertical direction. The flexible printed circuit board 19 includes a signal line, a ground line, and a plurality of insulator layers. The plurality of insulator layers are stacked in the vertical direction. The signal line and the ground line are conductor layers provided on the insulator layers. The signal line is electrically connected to the upper electrode 15a. A detection signal of the upper electrode 15a is transmitted to the signal line. The ground line is electrically connected to the lower electrode 15b. The ground line is connected to a ground potential.

[0024] The upper electrode 15a is a signal electrode. A detection signal is output from the upper electrode 15a. In this embodiment, the upper electrode 15a is provided on the lower main surface of the flexible printed circuit board 19. That is, the upper electrode 15a is a conductor layer provided on the lower main surface of the insulating layer located at the bottom among the multiple insulating layers of the flexible printed circuit board 19.

[0025] The adhesive member 17 is located between the upper electrode 15a and the piezoelectric film 14. The adhesive member 17 fixes the upper electrode 15a to the upper main surface of the piezoelectric film 14. The adhesive member 17 is made of a thermoplastic resin. The adhesive member 17 is made of a material such as polyester, polyurethane, or polyolefin.

[0026] The substrate 16 is provided on the electrode member 13. The substrate 16 holds the piezoelectric film 14, the upper electrode 15a, and the lower electrode 15b, and is deformed together with the piezoelectric film 14. The substrate 16 has a sheet shape. The substrate 16 has an upper main surface and a lower main surface. The length of the substrate 16 in the left-right direction is longer than the length of the substrate 16 in the front-rear direction. In this embodiment, the substrate 16 has a rectangular shape having long sides extending in the left-right direction when viewed in the up-down direction. The long sides of the substrate 16 are longer than the long sides of the piezoelectric film 14, the long sides of the upper electrode 15a, and the long sides of the lower electrode 15b. The short sides of the substrate 16 are longer than the short sides of the piezoelectric film 14, the short sides of the upper electrode 15a, and the short sides of the lower electrode 15b. The piezoelectric film 14, the upper electrode 15a, and the lower electrode 15b are arranged in a region surrounded by the outer edge of the substrate 16 when viewed in the up-down direction. The material of the substrate 16 is, for example, polyurethane or PET.

[0027] The adhesive layer 18 fixes the piezoelectric film 14, the upper electrode 15a, the lower electrode 15b, and the flexible printed circuit board 19 to the substrate 16. More specifically, the adhesive layer 18 is provided on the lower main surface of the substrate 16. The adhesive layer 18 covers a part of the lower main surface of the substrate 16. The adhesive layer 18 also covers the entire upper main surface of the flexible printed circuit board 19. The outer edge of the adhesive layer 18 is surrounded by the outer edge of the substrate 16 when viewed in the up-down direction. The adhesive layer 18 bonds the flexible printed circuit board 19 and the substrate 16. As a result, the deformation of the substrate 16 is transmitted to the piezoelectric film 14 via the adhesive layer 18 and the electrode member 13. The material of the adhesive layer 18 is, for example, a double-sided tape, a thermosetting adhesive, or a thermoplastic adhesive.

[0028] The adhesive layer 20 is provided on the upper main surface of the base material 16. The adhesive layer 20 fixes the base material 16 to the lower main surface of the plate-like member 7. The material of the adhesive layer 20 is, for example, a double-sided tape, a thermosetting adhesive, or a thermoplastic adhesive.

[0029] Incidentally, the electronic device 1 has a structure that can accurately detect the magnitude of the force with which the user presses the operation panel 2. This structure will be described below. Figs. 4 and 5 are diagrams showing the left-right and front-rear extension amounts of the sensor 6 of the electronic device according to the comparative example. In Fig. 4, the user presses down at position P0 in Fig. 1. In Fig. 5, the user presses down at position P1 or position P2 in Fig. 1. Fig. 6 is a graph showing the relationship between the user's pressing position and the amount of charge generated by the piezoelectric film 14 in the electronic device according to the comparative example. The vertical axis indicates the amount of charge. The horizontal axis indicates the position. At the position, the forward direction as viewed from position P0 is the positive direction, and the backward direction as viewed from position P0 is the negative direction. Figs. 4 to 6 are the results of computer simulation.

[0030] First, an electronic device according to a comparative example and the electronic device 1 will be described. In the electronic device according to the comparative example, the Young's modulus of the adhesive member 17 is greater than 10 MPa. The Young's modulus of the adhesive member 17 of the electronic device according to the comparative example is 100 MPa. On the other hand, in the electronic device 1, the Young's modulus of the adhesive member 17 is equal to or greater than 0 MPa and equal to or less than 10 MPa. The Young's modulus of the adhesive member 17 of the electronic device 1 is 10 MPa.

[0031] Next, problems with the electronic device of the comparative example will be described. In the electronic device of the comparative example, it is difficult to accurately detect the magnitude of the force with which the user presses the operation panel 2. When the user presses directly above the sensor 6 (position P0 in FIG. 1) downward, position P0 of the operation panel 2 deforms downward. At this time, position P0 of the operation panel 2 extends in the front-rear and left-right directions. And, as shown in FIG. 4, the piezoelectric film 14 extends in the front-rear and left-right directions.

[0032] Here, the piezoelectric film 14 generates a positive charge when it is stretched in the left-right direction, for example. The piezoelectric film 14 generates a negative charge when it is stretched in the front-back direction, for example. Therefore, when the position P0 of the operation panel 2 is pressed downward, the charge generated by the piezoelectric film 14 stretching in the left-right direction and the charge generated by the piezoelectric film 14 stretching in the front-back direction cancel each other out. Therefore, the piezoelectric film 14 is unlikely to generate a large charge.

[0033] On the other hand, when the user presses downward at a position shifted forward or backward from directly above the sensor 6 (positions P1 and P2 in FIG. 1), position P1 or position P2 of the operation panel 2 deforms downward. At this time, position P0 of the operation panel 2 extends significantly in the left-right direction, but does not extend significantly in the front-back direction. Therefore, as shown in FIG. 5, the piezoelectric film 14 extends significantly in the left-right direction, but does not extend significantly in the front-back direction. In this case, the charge generated by the piezoelectric film 14 expanding in the left-right direction and the charge generated by the piezoelectric film 14 expanding in the front-back direction are unlikely to cancel each other out. Therefore, the piezoelectric film 14 is likely to generate a large charge.

[0034] 6, the amount of charge generated by piezoelectric film 14 when position P0 is pressed is smaller than the amount of charge generated by the piezoelectric film when positions P1 and P2 are pressed. Therefore, in the electronic device of the comparative example, it is difficult to accurately detect the magnitude of the force with which the user presses operation panel 2.

[0035] Therefore, after much study, the inventors of the present application have concluded that it would be sufficient to soften the adhesive member 17. In order to confirm the results of this study, the inventors of the present application have carried out the following computer simulation.

[0036] The inventors of the present application calculated the difference (%) when the Young's modulus of the adhesive member 17 was changed. The difference is a value obtained by dividing the difference between the amount of charge when the position P1 in FIG. 6 is pressed and the amount of charge when the position P0 is pressed by the amount of charge when the position P0 is pressed, and multiplying the result by 100. FIG. 7 is a graph showing the relationship between Young's modulus and the difference. The vertical axis shows the difference. The horizontal axis shows Young's modulus. FIG. 8 and FIG. 9 are diagrams showing the amount of extension of the piezoelectric film 14 in the left-right direction and the front-back direction. In FIG. 8, the user presses the position P0 in FIG. 1 downward. In FIG. 9, the user presses the position P1 or the position P2 in FIG. 1 downward.

[0037] The difference should be 10% or less. Therefore, according to FIG. 7, it is understood that the Young's modulus of the adhesive member 17 should be 0 MPa or more and 10 MPa or less. Also, if the Young's modulus is 0 MPa or more and 2 MPa or less, the difference is 0%. And, as shown in FIG. 8, if the Young's modulus of the adhesive member 17 is 10 MPa, it is understood that the amount of extension in the front-rear direction of the piezoelectric film 14 is reduced. On the other hand, as shown in FIG. 9, even if the Young's modulus of the adhesive member 17 is 10 MPa, it is understood that the amount of extension in the left-right direction of the piezoelectric film 14 is sufficiently large. In this way, if the adhesive member 17 is made soft, the piezoelectric film 14 can generate a sufficient charge even if the position P0 is pressed. As a result, the sensor 6 can accurately detect the magnitude of the force with which the user presses the operation panel 2.

[0038] Here, the inventors of the present application considered the following reason why sensor 6 can accurately detect the magnitude of the force with which the user presses operation panel 2. In the electronic device of the comparative example, when piezoelectric film 14 is pulled in the left-right direction, piezoelectric film 14 tries to shrink in the up-down direction. However, if adhesive member 17 has a high Young's modulus, deformation of piezoelectric film 14 is hindered by plate-like member 7. As a result, piezoelectric film 14 cannot shrink in the up-down direction, and is stretched in the up-down direction together with plate-like member 7. As a result, the amount of charge generated by piezoelectric film 14 was reduced in the electronic device of the comparative example.

[0039] On the other hand, when the Young's modulus of adhesive member 17 is reduced as in sensor 6, the deformation of piezoelectric film 14 is less likely to be hindered by plate-like member 7. This allows piezoelectric film 14 to shrink in the vertical direction. As a result, the amount of charge generated by piezoelectric film 14 increases. This reduces the difference in FIG. 6. As a result, sensor 6 can accurately detect the magnitude of the force with which the user presses operation panel 2.

[0040] (Modification) A sensor 6a according to a modified example will be described below. Fig. 10 is a cross-sectional view of the sensor 6a.

[0041] Sensor 6a differs from sensor 6 in the position of upper electrode 15a. More specifically, upper electrode 15a is provided between the upper and lower main surfaces of flexible printed circuit board 19. That is, upper electrode 15a is located inside flexible printed circuit board 19. Adhesive member 17 fixes flexible printed circuit board 19 to the upper main surface of piezoelectric film 14. Other structures of sensor 6a are the same as those of sensor 6, and therefore description thereof will be omitted. Sensor 6a can achieve the same effects as sensor 6.

[0042] (Other embodiments) The sensor according to the present invention is not limited to the sensors 6 and 6a, and can be modified within the scope of the gist of the present invention.

[0043] In the electronic device 1, the piezoelectric film 14 may be a PVDF (polyvinylidene fluoride) film. The piezoelectric film 14 may be a piezoelectric ceramic. The piezoelectric film 14 may be a strain sensor.

[0044] In the sensors 6 and 6a, the flexible printed circuit board 19 is not an essential component.

[0045] The adhesive member 5 does not necessarily have to be waterproof.

[0046] In addition, the two sides extending in the front-rear direction may be short sides, and the two sides extending in the left-right direction may be long sides.

[0047] The sensor 6 may be provided at a position other than the center of the plate member 7 in the front-rear direction when viewed in the up-down direction.

[0048] The operation panel 2 may be a resin plate.

[0049] The sensor 6 does not necessarily have a longitudinal direction extending in the left-right direction, but may have a longitudinal direction extending in the front-rear direction.

[0050] Although the electronic device 1 is described as having a touch panel, it may be a touch pad. In this case, the display panel 4 is not necessary. Moreover, the operation panel 2 does not have to be made of a transparent material. [Explanation of symbols]

[0051] 1:Electronic equipment 2: Operation panel 3: Housing 4: Display panel 5: Adhesive material 6, 6a: Sensor 7: Plate-shaped member 13: Electrode material 14: Piezoelectric film 15a: Upper electrode 15b: Lower electrode 16: Base material 17: Adhesive material 18,20: Adhesive layer 19: Flexible printed circuit board

Claims

1. a piezoelectric film having upper and lower principal surfaces aligned in a vertical direction; a lower electrode provided on the lower main surface of the piezoelectric film; an electrode member including an upper electrode; an adhesive member that fixes the electrode member to the upper main surface of the piezoelectric film; Equipped with The piezoelectric film is a film that generates electric charges when stretched in both the front-back direction and the left-right direction, The Young's modulus of the adhesive member is 0 MPa or more and 10 MPa or less, a polarity of an electric charge generated by the piezoelectric film when the piezoelectric film is stretched in a left-right direction is different from a polarity of an electric charge generated by the piezoelectric film when the piezoelectric film is stretched in a front-back direction; Sensor.

2. The electrode member is a member including a flexible printed circuit board. The sensor of claim 1 .

3. The flexible printed circuit board has an upper main surface and a lower main surface aligned in a vertical direction, the upper electrode is provided on the lower main surface of the flexible printed circuit board, the adhesive member fixes the upper electrode to the upper main surface of the piezoelectric film; The sensor of claim 2.

4. The flexible printed circuit board has an upper main surface and a lower main surface aligned in a vertical direction, the upper electrode is provided between the upper main surface of the flexible printed circuit board and the lower main surface of the flexible printed circuit board, the adhesive member fixes the flexible printed circuit board to the upper main surface of the piezoelectric film; The sensor of claim 2.

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