JP2014194691A - Pressing detection sensor and operation input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a small-sized pressing detection sensor capable of detecting a plurality of pressing positions and pressing forces.SOLUTION: A pressing detection sensor 1 includes: a piezoelectric sensor 10; conductors 21A-21N, 21P, 21Q for a switch; a switch connection conductor 24; an insulation base plate 40; and an operation reception base plate 50. The conductors 21A-21N, 21P, 21Q for the switch are provided on the surface of the insulation base plate 40. The operation reception base plate 50 is arranged on a front side of the insulation base plate 40, and is provided with the switch connection conductor 24 on the insulation base plate 40 side. A flat film-like piezoelectric sensor 10 is arranged on a rear side of the insulation base plate 40. The piezoelectric sensor 10 consists of a structure sandwiching a piezoelectric film 11 by a first pressing detection conductor 12 and a second pressing detection conductor 13. When the operation reception base plate 50 is pushed, the switch connection conductor 24 is brought into contact with the conductors 21A-21N, 21P, 21Q, further pushes the insulation base plate 40 and the piezoelectric film 11 of the piezoelectric sensor 10 is displaced.

Description

  The present invention relates to a pressure detection sensor for detecting pressure on an operation unit and an operation input device including the pressure detection sensor.

  Conventionally, various pressure detection sensors for detecting pressure have been devised, and Patent Document 1 discloses a pressure detection sensor using a piezoelectric thin film.

  The press detection sensor described in Patent Document 1 includes a plate-like piezoelectric thin film having electrodes formed on both main surfaces. Support pillars are disposed at each corner of the piezoelectric thin film, and the piezoelectric thin film is disposed by the support pillar in parallel and spaced from the flat support substrate. When a pressing force is applied to the main surface of the piezoelectric thin film, an electric charge corresponding to the pressing force is generated. The voltage generated between the electrodes on both main surfaces by this charge depends on the pressing force. Therefore, the detection force is detected by connecting a detection circuit downstream of the pressure detection sensor described in Patent Document 1 and detecting the voltage with the detection circuit.

JP 2000-275114 A

  The above-described press detection sensor described in Patent Document 1 can detect a pressing force, but cannot detect a pressing position in a plane. Therefore, in an electronic device including the press detection sensor, in order to detect a plurality of press positions, the press detection sensor must be arranged at each location where position detection is desired. That is, as many press detection sensors as the number of detection positions must be arranged in the electronic device. In this case, a detection circuit is required for each press detection sensor. Therefore, the structure for detecting the pressing force and the pressing position becomes complicated and large.

  In addition, by forming individual electrode patterns for each detection position on the main surface of the piezoelectric thin film, it is possible to realize a configuration in which a plurality of press detection sensors are not arranged, but only a detection circuit is required for the electrode pattern. However, simplification and downsizing of the structure cannot be easily realized. Further, in this configuration, the electrode pattern may be complicated, and it is difficult to easily form the electrode pattern on the piezoelectric thin film. In particular, when a resin-based piezoelectric thin film is used, it is difficult to pattern and form electrodes.

  Therefore, an object of the present invention is to realize a pressure detection sensor that can detect a plurality of pressure positions and can detect a pressure force, has a simple structure, and can downsize the entire operation input device including a subsequent circuit. There is.

  The press detection sensor of the present invention includes an insulating substrate, a plurality of sets of switch conductors, a switch connection conductor, an operation receiving substrate, a piezoelectric film, a first press detection conductor, and a second press detection conductor. The insulating substrate has a main surface parallel to the operation surface. The plurality of sets of switch conductors are arranged at different positions on the main surface on the operation surface side of the insulating substrate. The switch connection conductors are formed in regions facing the plurality of sets of switch conductors and overlapping each set of switch conductors when viewed in a direction orthogonal to the operation surface. The operation reception board includes a switch connection conductor, and a surface opposite to the arrangement surface of the switch connection conductor is an operation surface. The piezoelectric film is disposed on the surface opposite to the main surface on the operation surface side of the insulating substrate. The first press detection conductor is disposed between the insulating substrate and the piezoelectric film, and is connected to the plurality of switch conductors. The second press detection conductor has a flat film shape and sandwiches the piezoelectric film together with the insulating substrate.

  In this configuration, when one of the switch conductor regions on the operation reception board is pushed in, the operation reception board is bent, and the switch connection conductor in the pushed-in area conducts the switch conductor. By this conduction, a bias voltage for detecting the pressing force is applied between the first pressing detection conductor and the second pressing detection conductor that sandwich the piezoelectric film.

  Further, when the switch connection conductor comes into contact with the switch conductor, the insulating substrate and the piezoelectric film are pushed and displaced. As a result, a charge corresponding to the pressing force is generated from the piezoelectric film, superimposed on the bias voltage, and can be detected as a detection voltage.

  Therefore, with the above-described configuration, the pressing force can be detected, and the pressing position can also be detected by detecting the conductive switch conductor. Thereby, a pressing force and a pressing position can be detected by one piezoelectric film. Further, the pressing force and the pressing position can be detected without forming a complicated electrode pattern on the piezoelectric film. Further, since the piezoelectric film is sandwiched between the first press detection conductor and the second press detection conductor, the piezoelectric film can be connected to the external circuit even when the first press detection conductor and the second press detection conductor are connected to an external circuit. No high heat is applied, and the piezoelectric film is not deformed or deteriorated. In addition, the detection voltage obtained from the electric charge due to the displacement of the piezoelectric film is output from the pair of the first press detection conductor and the second press detection conductor regardless of the pressing position, so that one detection circuit in the subsequent stage is provided. That's fine. Thereby, it is possible to simplify the detection circuit for detecting the pressing force and detecting the pressing position for a plurality of positions.

  Moreover, it is preferable that the 2nd press detection conductor of the press detection sensor of this invention is being fixed to the insulating board | substrate only by two opposing sides.

  In this configuration, cancellation of generated charges generated in the piezoelectric film due to the pressing position is suppressed. Thereby, the position nonuniformity of the charge amount generated from the piezoelectric film due to the pressing position can be suppressed.

  Further, the second press detection conductor of the press detection sensor of the present invention is curved so that the two opposing sides are separated from the piezoelectric film from both ends along the side toward the center when viewed from the direction orthogonal to the operation surface. It is preferable to consist of the shape.

  In this structure, the difference by the pressing position of the displacement amount with respect to pressing force is suppressed. Thereby, the position unevenness of the charge amount generated from the piezoelectric film due to the pressed position can be further suppressed.

  Moreover, in the press detection sensor of this invention, it is preferable that a piezoelectric film consists of polylactic acid.

  In this configuration, the charge generation amount with respect to the displacement amount can be improved. Thereby, the detection sensitivity of pressing force can be improved.

  Moreover, in the press detection sensor of this invention, it is preferable that an operation reception board | substrate is provided with a projection part higher than this switch connection conductor in the formation surface of a switch connection conductor.

  In this configuration, even if the pressing force is strong, the distance at which the operation receiving substrate approaches the insulating substrate can be regulated by the protrusion. Therefore, it can suppress that the several conductor for switches turns on simultaneously, and can improve the detection precision of a press position.

  In the press detection sensor of the present invention, the plurality of sets of switch conductors are arranged along the circumference as viewed in the direction orthogonal to the operation surface.

  In this configuration, it is possible to arrange the gaps between the sets of switch conductors so as to be easily widened. Thereby, it can suppress that the several conductor for a switch presses simultaneously, and can improve the detection accuracy of a press position.

  The operation input device of the present invention also detects a pressing force from the pressure detection sensor according to any one of the above, a voltage conversion circuit that converts voltage generated in the piezoelectric film into a voltage, and an output voltage of the voltage conversion circuit. And a detection circuit for detecting a set of switch conductors conducted from a plurality of sets of switch conductors.

  In this configuration, a plurality of pressing positions can be detected even if the number of detection circuits is one by providing the pressing detection sensor. Thereby, the operation input device can be configured in a small size with a simple configuration.

  According to this invention, it is possible to easily form a press detection sensor that can detect a plurality of pressing positions and can detect a pressing force with a simple structure. Moreover, according to this invention, the detection circuit of the back | latter stage of a press detection sensor can be simplified. Thereby, a miniaturized touch input device can be realized.

It is side surface sectional drawing which shows the structure of the press detection sensor which concerns on the 1st Embodiment of this invention. It is the top view which looked at the position detection surface of the press detection sensor which concerns on the 1st Embodiment of this invention. It is side surface sectional drawing which shows the pressing operation state of the press detection sensor which concerns on the 1st Embodiment of this invention. 1 is a circuit block diagram of an operation input device according to a first embodiment of the present invention. It is a circuit block diagram in the press operation state of the operation input device which concerns on the 1st Embodiment of this invention. It is the top view which looked at the position detection surface of the press detection sensor which concerns on the 2nd Embodiment of this invention. It is the top view which looked at the position detection surface of the press detection sensor which concerns on the 3rd Embodiment of this invention.

  A press detection sensor and a touch input device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing a configuration of a press detection sensor according to a first embodiment of the present invention. FIG. 2 is a plan view of the position detection surface of the pressure detection sensor according to the first embodiment of the present invention.

  The pressure detection sensor 1 includes a piezoelectric sensor 10, switch conductors 21A, 21B, 21C, 21D, 21E, 21F, 21G, 21H, 21I, 21J, 21K, 21L, 21M, and 21N (hereinafter simply representing a collection thereof) Are referred to as 21A to 21N), 21P, 21Q, a switch connection conductor 24, a housing 30, an insulating substrate 40, and an operation receiving substrate 50.

  The housing | casing 30 is provided with the internal space 31 which the surface side opens. A support column 32 is formed in the internal space 31 so as to stand from the bottom wall of the housing 30.

  The insulating substrate 40 is formed of a rectangular flat plate, and the outer peripheral edge thereof is supported by the support pillar 32 from the back surface side. That is, the insulating substrate 40 is disposed in the internal space 31 of the housing 30 so as not to contact the housing 30 except for the outer peripheral portion on the back surface side. The insulating substrate 40 is made of a material having relatively high elasticity, for example, glass epoxy resin.

  Switch conductors 21 </ b> A to 21 </ b> N, 21 </ b> P, and 21 </ b> Q are formed on a surface (front surface) on the operation surface side of the insulating substrate 40. The switch conductors 21A to 21N, 21P, and 21Q are composed of a plurality of conductor patterns. In FIG. 2, the description of specific symbols is omitted except for the switch conductors 21A and 21I, but it has the same structure as the switch conductors 21A and 21I. In the present embodiment, an example in which 16 switch conductors 21A to 21N, 21P, and 21Q are provided has been described. However, the number may be set as appropriate according to the required number and resolution of the press detection positions.

  The switch conductors 21 </ b> A to 21 </ b> N, 21 </ b> P, and 21 </ b> Q are arranged along the circumference of a circle having a predetermined radius with the predetermined position PO on the surface of the insulating substrate 40 as the center. The switch conductors 21A to 21N, 21P, and 21Q are arranged at predetermined angular intervals, for example, 22.5 ° intervals in the present embodiment. Here, a plurality of switch conductors are arranged at equiangular intervals, but the intervals may be non-uniform.

  The switch conductor 21A includes individual conductors 22A and 23A. The individual conductors 22A and 23A are separated. The individual conductors 22A and 23A are long conductors, and are arranged in parallel so that their long directions coincide with each other. The individual conductors 22A and 23A are arranged such that the longitudinal direction is perpendicular to the tangent of the circle and radiates outwardly opposite to the center PO side of the circle. The number of the individual conductors 23A is two, and the individual conductors 23A are arranged at a predetermined interval so as to sandwich the individual conductors 22A in the direction orthogonal to the longitudinal direction. The two individual conductors 23A are connected by a common conductor 230 formed on the center PO side of the end of the individual conductor 22A on the center PO side of the circle.

  Similarly to the switch conductor 21A, the switch conductors 21B, 21C, 21D, 21E, 21F, 21G, 21H, 21I, 21J, 21K, 21L, 21M, 21N, 21P, and 21Q are also formed radially. The individual conductors 23A to 23N, 23P, and 23Q of all the switch conductors 21A to 21N, 21P, and 21Q are connected by the common conductor 230. The common conductor 230 is connected to a first press detection conductor 12 of the piezoelectric sensor 10 described later by a conductor pattern (for example, a conductive via conductor) formed on the insulating substrate 40.

  On the front surface side (operation surface side) of the insulating substrate 40, an operation receiving substrate 50 is arranged at a predetermined distance from the insulating substrate 40. The operation reception board 50 is flat and is disposed on the opening surface of the housing 30. The operation receiving substrate 50 is supported by the side wall of the housing 30 at the outer peripheral edge. In other words, the opening of the housing 30 is closed by the operation reception board 50. The operation reception board 50 is made of a flexible material, for example, a PET film. The operation receiving board 50 is formed so as not to bend in a state where no external force is applied to the flat plate surface from the outside.

  A switch connection conductor 24 is formed on a surface (back surface) of the operation receiving substrate 50 on the insulating substrate 40 side. The switch connection conductor 24 is formed on a pedestal 51 having a shape that partially rises with respect to the back surface of the operation reception board 50.

  The switch connection conductor 24 and the pedestal 51 are formed in an annular shape when viewed from the direction orthogonal to the operation surface. The switch connection conductor 24 is disposed so as to overlap the switch conductors 21A to 21N, 21P, and 21Q when viewed from a direction orthogonal to the switch connection conductor 24.

  With such a configuration, when a pressing force is applied from the outside to a predetermined position on the operation surface of the operation reception board 50, the operation reception board 50 is bent inward of the housing 30 around the pressed position. As a result, the individual conductors 22 and 23 constituting the switch conductor 21 having the closest pressing position among the switch conductors 21A to 21N, 21P and 21Q come into contact with the switch connection conductor 24. For this reason, the individual conductors 22 and 23 become conductive, and the switch becomes conductive. For example, when a pressing force is applied to a region near the switch conductor 21 </ b> A on the operation surface, the individual conductors 22 </ b> A and 23 </ b> A come into contact with the switch connection conductor 24 and become conductive. In addition, when a pressing force is applied to a region near the switch conductor 21I on the operation surface, the individual conductors 22I and 23I come into contact with the switch connection conductor 24 and become conductive. Therefore, the pressed position can be detected by detecting the conductive switch.

  A key top 500 is arranged on the surface (front surface) of the operation receiving substrate 50 opposite to the insulating substrate 40. The key top 50 is made of a flat plate having a predetermined hardness. The surface of the operation reception board 50 on which the key top 50 is formed becomes the operation surface of the press detection sensor 1. Although such a key top 50 can be omitted, the operability when the operator presses the operation surface can be improved by providing the key top 50 having a predetermined hardness.

  In addition, a protrusion 52 that protrudes from the back surface is formed on the back surface of the operation receiving substrate 50. The protrusion 52 is disposed on the outer peripheral side with respect to the switch connection conductor 24. At this time, the protrusion 52 may be formed over the entire circumference so as to include the formation region of the switch connection conductor 24 when viewed in the direction orthogonal to the operation surface.

  The height of the protrusion 52 is higher than the height (thickness) of the base 51 and the switch connection conductor 24. Even if the height of the operation receiving board 50 is curved so as to approach the insulating board 40 by pressing the operation surface of the operation receiving board 50, one switch conductor 21 and the switch connecting conductor 24 are not connected. The height is set so as to abut and the other switch conductor and the switch connection conductor 24 are not connected. That is, the height of the projection 52 may be set as appropriate based on the specifications, the detection resolution of the pressed position, the flexibility of the operation receiving board 50, and the like. By setting it as such height, it can suppress that the detection resolution of a press position falls by pressing force. In other words, even if the operation surface is pressed more strongly than necessary, the detection resolution does not decrease and the pressed position can be detected with high accuracy.

  Further, the protrusion 52 is preferably overlapped with the support pillar 32 when viewed in a direction orthogonal to the operation surface. As a result, even if the protrusion 52 comes into contact with the insulating substrate 40, the insulating substrate 40 is not curved. Therefore, even if the protrusion 52 comes into contact with the insulating substrate 40, no external stress is applied to the piezoelectric sensor 10. Therefore, even if the protrusion 52 contacts the insulating substrate 40, the electric charge generated in the piezoelectric sensor 10 is not affected.

  On the back surface of the insulating substrate 40, a flat film-shaped piezoelectric sensor 10 is disposed. At this time, the back surface of the insulating substrate 40 and the flat film surface of the piezoelectric sensor 10 are arranged in parallel.

  The piezoelectric sensor 10 includes a piezoelectric film 11, a first press detection conductor 12, and a second press detection conductor 13. The piezoelectric film 11 is a rectangular flat film. As shown in FIG. 2, the piezoelectric film 11 is disposed so as to include the formation regions of the switch conductors 21 </ b> A to 21 </ b> N, 21 </ b> P, and 21 </ b> Q when viewed in a direction orthogonal to the operation surface.

  The first press detection conductor 12 is disposed on the surface (surface) of the piezoelectric film 11 on the insulating substrate 40 side. The second press detection conductor 13 is disposed on the surface (back surface) opposite to the insulating substrate 40 in the piezoelectric film 11. The second press detection conductor 13 has a larger area than the piezoelectric film 11 and has a region that does not overlap the piezoelectric film 11 when viewed in the direction orthogonal to the operation surface. The four sides of the second press detection conductor 13 that do not overlap the piezoelectric film 11 are fixed to the conductor pattern on the back surface of the insulating substrate 40 with a predetermined width by a conductive connecting member 14 such as a conductive adhesive. Yes. Thereby, the structure which clamps the laminated film of the 1st press detection conductor 12 and the piezoelectric film 11 by the insulating board | substrate 40 and the 2nd press detection conductor 13 is implement | achieved. With such a structure, it is possible to realize a configuration in which the flat film-like piezoelectric sensor 10 is mounted on the back surface of the insulating substrate 40.

  In this configuration, the piezoelectric sensor 10 is connected to the subsequent circuit and the power supply unit by the conductor pattern disposed on the insulating substrate 40. Thereby, the piezoelectric sensor 10 can be connected to a post-stage circuit or a power supply unit without adding a high heat history to the piezoelectric film 11 as in the prior art. Therefore, deformation and characteristic deterioration of the piezoelectric film 11 can be prevented, and characteristic deterioration of the piezoelectric sensor 10 can be prevented.

  In this configuration, between the piezoelectric film 11 and the first press detection conductor 12, between the first press detection conductor 12 and the insulating substrate 40, and between the piezoelectric film 11 and the second press detection conductor 13. In addition, a conductive adhesive or the like may be used. However, since the piezoelectric film 11 and the first press detection conductor 12 are sandwiched between the insulating substrate 40 and the second press detection conductor 13, these members can be fixed without using a conductive adhesive or the like. can do. By not using conductive adhesion, the components of the pressure detection sensor 1 can be reduced, the manufacturing is easy, and the pressure detection sensor 1 can be realized at low cost.

  Note that the piezoelectric film 11 of the piezoelectric sensor 10 preferably has the following configuration.

  The piezoelectric film 11 is a film formed from a chiral polymer. In this embodiment, polylactic acid (PLA), particularly L-type polylactic acid (PLLA) is used as the chiral polymer. PLLA is uniaxially stretched.

  The uniaxial stretching direction of the piezoelectric film 11 is, for example, substantially parallel to one of the two orthogonal axes that form a rectangle. This angle is an example and is a design matter determined according to the design, but it is preferable that the angle be 45 ° with respect to the direction of the main stress generated when the flat plate surface is pressed.

  PLLA made of such a chiral polymer has a helical structure in the main chain. PLLA has piezoelectricity when uniaxially stretched and molecules are oriented. The uniaxially stretched PLLA generates an electric charge when the flat plate surface of the piezoelectric film is pressed. At this time, the amount of generated charge is uniquely determined by the amount of displacement by which the flat plate surface is displaced in the direction orthogonal to the flat plate surface by pressing. The piezoelectric constant of uniaxially stretched PLLA belongs to a very high class among polymers. Therefore, displacement due to pressing can be detected with high sensitivity.

  The draw ratio is preferably about 3 to 8 times. By performing a heat treatment after stretching, crystallization of the extended chain crystal of polylactic acid is promoted and the piezoelectric constant is improved. In the case of biaxial stretching, the same effect as that of uniaxial stretching can be obtained by varying the stretching ratio of each axis. For example, when a certain direction is taken as an X-axis, 8 times in that direction, and 2 times in the Y-axis direction perpendicular to that axis, the piezoelectric constant is about 4 times in the X-axis direction, Almost the same effect can be obtained. A film that is simply uniaxially stretched easily tears along the direction of the stretch axis, and thus the strength can be increased somewhat by performing biaxial stretching as described above.

  In addition, PLLA generates piezoelectricity by molecular orientation treatment such as stretching, and does not need to be polled like other polymers such as PVDF or 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. Therefore, it is possible to detect displacement due to pressing with high sensitivity without being affected by the surrounding environment.

Since PLLA has a very low relative dielectric constant of about 2.5, the piezoelectric output constant (= piezoelectric g constant, g = d / ε ^T ) is large when d is a piezoelectric constant and ε ^T is a dielectric constant. Value. Here, the piezoelectric g constant of PVDF having a dielectric constant ε ₃₃ ^T = 13 × ε ₀ and a piezoelectric constant d ₃₁ = 25 pC / N is g ₃₁ = 0.2172 Vm / N from the above formula. On the other hand, when the piezoelectric g constant of PLLA having a piezoelectric constant d ₁₄ = 10 pC / N is converted to g ₃₁ , d ₁₄ = 2 × d ₃₁ , so d ₃₁ = 5 pC / N, and the piezoelectric g constant , G ₃₁ = 0.2258 Vm / N. Therefore, the detection sensitivity of the pressing force similar to that of PVDF can be sufficiently obtained with PLLA having a piezoelectric constant d ₁₄ = 10 pC / N. The inventors of the present invention have experimentally obtained PLLA with d ₁₄ = 15 to 20 pC / N, and by using the PLLA, it is possible to detect the pressing force with extremely high sensitivity. Become.

  As described above, by using PLLA for the piezoelectric film 11, the piezoelectric sensor 10 having high sensitivity to the pressing force and high reliability can be realized.

  For the pressure detection sensor 1 having such a configuration, the operation input device 100 can be realized with a circuit configuration as shown in the circuit block diagram of FIG. FIG. 3 is a circuit block diagram of the operation input device according to the first embodiment of the present invention.

  The operation input device 100 includes a piezoelectric sensor 10, a switch unit 20, a voltage conversion unit 101, and a detection unit 102. The switch unit 20 is formed by connecting a plurality of switches composed of the switch conductors 21A to 21N, 21P, 21Q and the switch connection conductor 24 in parallel. The voltage conversion unit 101 includes a capacitor C1 and an operational amplifier U1.

  One end (first press detection conductor 12) of the piezoelectric sensor 10 is connected to a connection point between the resistor R1 and the resistor R2 via the switch unit 20. The resistors R1 and R2 are connected in series between the drive voltage application terminal Vdd and the ground. A capacitor C1 is connected to the piezoelectric sensor 10 in parallel. The other end (second pressing detection conductor 13) of the piezoelectric sensor 10 is connected to the non-inverting input terminal of the operational amplifier U1.

  The output terminal of the operational amplifier U1 is connected to the inverting input terminal of the operational amplifier U1. With this configuration, a buffer circuit is realized. A driving voltage is supplied from the driving voltage application terminal Vdd to the operational amplifier U1. The output terminal of the operational amplifier U1 is connected to the detection unit 102.

  In such a configuration, a bias voltage is applied to the piezoelectric sensor 10 through the conductive switch in the switch unit 20. The piezoelectric film 11 of the piezoelectric sensor 10 generates a charge corresponding to the amount of displacement. Therefore, when displacement occurs in the piezoelectric film 11, the input potential of the operational amplifier U1 changes according to the amount of displacement. At this time, by connecting the capacitor C1 to the piezoelectric sensor 10 in parallel, the extinction time of the charges generated by the displacement can be extended. The operational amplifier U1 buffers and outputs a voltage signal formed by the difference between the output potential from the piezoelectric sensor 10 (input potential of the operational amplifier U1) and a reference potential.

  The detector 102 samples the output signal of the operational amplifier U1 at a predetermined sampling period, converts it into digital output data, and integrates it for a predetermined time. The detection unit 102 detects the pressing force from the accumulated output data.

  The detection unit 102 is connected to the switch unit 20. The detection unit 102 detects a conductive switch in the switch circuit 20. The conductive switch can be detected from, for example, the difference in electrical characteristics between the conductive switch and the non-conductive switch.

  With such a configuration, it is possible to detect the pressing force and the pressing position.

  Next, a method for detecting the pressing position and the pressing force will be described using a more specific operation example. FIG. 4 is a side sectional view showing a pressing operation state of the pressing detection sensor according to the first embodiment of the present invention. FIG. 5 is a circuit block diagram in the pressing operation state of the operation input device according to the first embodiment of the present invention. 4 and 5 show the case where the region of the switch conductor 21A is pressed, the pressing position and the pressing force can be detected by the same behavior in the regions of the other switch conductors.

  As shown in FIG. 4, the operator presses the region of the switch conductor 21 </ b> A on the surface of the operation reception board 50. Since the outer peripheral edge of the operation receiving board 50 is fixed to the housing 30, the pressing operation causes the operation receiving board 50 to be pushed into the back side in a planar manner with the pressing position as the center as shown in FIG. Dent. In other words, the back surface of the operation receiving substrate 50 is deformed so that the pressing position is closest to the insulating substrate 40. Thereby, the area | region which opposes the switch conductor 21A in the switch connection conductor 24 approaches the individual conductors 22A and 23A of the switch conductor 21A. And when it becomes more than predetermined pressing force, the switch connection conductor 24 will contact | abut on the surface of individual conductor 22A, 23A. As a result, the individual conductors 22A and 23A become conductive, and the switch becomes conductive. When the switch becomes conductive, as shown in FIG. 5, the drive voltage application terminal Vdd for applying the bias voltage and the piezoelectric sensor 10 are connected via the switch 21A, and the bias voltage is applied to the piezoelectric sensor 10. .

  When the pressing force is further applied in a state where the switch connection conductor 24 of the operation receiving substrate 50 and the switch conductor 21A of the insulating substrate 40 are in contact with each other, the insulating substrate 40 is pushed to the back side and is bent. As the insulating substrate 40 is curved, the piezoelectric sensor 10 that contacts the back surface of the insulating substrate 40 is also curved. That is, the piezoelectric film 11 is bent and displaced. Due to this displacement, the piezoelectric film 11 generates an electric charge. The amount of charge generated by the piezoelectric film 11 depends on the amount of displacement. The electric charge generated in the piezoelectric film 11 is acquired by the first press detection conductor 12 and the second press detection conductor 13, and the potential of the output end of the piezoelectric sensor 10 (terminal connected to the operational amplifier U1) changes. Due to this change in potential, the voltage of the output signal of the operational amplifier U1 changes, and the detection unit 102 can detect the pressing force from the change amount.

  As described above, by using the configuration of the present embodiment, it is possible to realize a press detection sensor that can detect a plurality of pressing positions and detect a pressing force by using only one piezoelectric film. Thereby, a press detection sensor can be easily formed with a simple structure. In addition, since only one piezoelectric film is used to detect a plurality of pressing positions, crosstalk between sensors that occurs when a piezoelectric sensor including a piezoelectric film is disposed at each of the plurality of positions can be prevented. it can. Thereby, detection accuracy can be improved.

  In addition, by using the configuration of the present embodiment, since the switch for detecting the pressed position is turned on, voltage is supplied to the piezoelectric sensor 10, so that power consumption can be reduced. Since the time for energizing the piezoelectric sensor 10 can be shortened, deterioration of the characteristics of the piezoelectric sensor 10 due to energization with time can be suppressed.

  Furthermore, by using the configuration of the present embodiment, even if it is an aspect of detecting a plurality of pressing positions, only one output terminal of the pressing detection sensor is required, so only one detection circuit subsequent to the pressing detection sensor is required. The detection circuit can be simplified. Thereby, an operation input device can be formed small.

  Furthermore, by using the configuration of the present embodiment, the piezoelectric film 11 is attached to the rigid insulating substrate 40, so that the life of the piezoelectric film can be extended. In addition, the above-described operational amplifier U1, capacitor C1, and detection circuit 102 can be mounted by forming a conductor pattern on the insulating substrate 40, and the operation input device 100 can be formed in a small size.

  Furthermore, by using the configuration of the present embodiment, the switch conductors 21A to 21N, 21P, and 21Q are arranged on the circumference, and the interval between adjacent switch conductors can be widened in a limited region. Thereby, the detection resolution of a press position can be improved.

  In the above configuration, the switch circuit 20 is connected to the drive voltage application terminal Vdd side of the piezoelectric sensor 10, but the switch circuit 20 may be connected between the piezoelectric sensor 10 and the operational amplifier U1. However, considering the loss of the switch circuit 20, it is preferable to connect the switch circuit 20 to the drive voltage application terminal Vdd side of the piezoelectric sensor 10. Further, the switch circuit 20 may be arranged at a connection point between the drive voltage application terminal Vdd, the resistor R1, and the operational amplifier U1. In this case, power consumption in the operational amplifier U1 can also be reduced.

  Next, a press detection sensor according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a plan view of the position detection surface of the press detection sensor according to the second embodiment of the present invention. The hatched portion in FIG. 6 is a region where the second press detection conductor 13A is fixed in contact with the insulating substrate 40.

  The pressing detection sensor 10A according to the present embodiment is different from the pressing detection sensor 10 according to the first embodiment in the fixing structure of the second pressing detection conductor 13A with respect to the insulating substrate 40. Moreover, the uniaxial stretching direction of the piezoelectric film 11 differs depending on this configuration. About another structure, it is the same as the press detection sensor 10 which concerns on 1st Embodiment, and description is abbreviate | omitted.

  Only the opposite two sides of the second press detection conductor 13 are fixed to the insulating substrate 40. In such a configuration, the two unfixed sides are free ends with respect to extension and displacement. Therefore, when the operation surface is pressed, the piezoelectric film 11 mainly extends in the direction connecting the two fixed sides. This is the same without depending on the pressing position.

  By setting it as such a structure, the electric charge which the piezoelectric film 11 generate | occur | produces becomes the same code | symbol irrespective of a press position. Thereby, the electric charges generated in the piezoelectric film 11 are not canceled out in the piezoelectric film 11. Therefore, the detection sensitivity with respect to the pressing force can be improved.

  Furthermore, the piezoelectric film 11 is disposed so that the direction forming 45 ° with respect to the fixed two sides is the uniaxial stretching direction. Thereby, the detection sensitivity with respect to pressing force can further be improved.

  Next, a press detection sensor according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a plan view of the position detection surface of the press detection sensor according to the third embodiment of the present invention. The hatched portion in FIG. 7 is a region where the second press detection conductor 13B is fixed in contact with the insulating substrate 40.

  The press detection sensor 10B according to the present embodiment is different from the press detection sensor 10A according to the second embodiment in the shape of the second press detection conductor 13B. About another structure, it is the same as the press detection sensor 10A which concerns on 2nd Embodiment, and description is abbreviate | omitted.

  Only the two opposite sides of the second press detection conductor 13B are fixed to the insulating substrate 40. The second pressing detection conductor 13B is formed in a shape in which the two fixed sides are curved when viewed from a direction orthogonal to the operation surface. More specifically, the distance Lc between the two sides at the center of the two sides to be fixed is longer than the distance Le between the two sides at both ends of the two sides (Lc> Le). The second press detection conductor 13B is formed and fixed to the insulating substrate 40.

  In such a configuration, the two unfixed sides are free ends with respect to extension and displacement. Furthermore, the difference in the displacement amount due to the pressing position in the piezoelectric film 11 fixed to the second pressing detection conductor 13B becomes small. Therefore, the difference in detection sensitivity with respect to the pressing force due to the difference in pressing position can be reduced. Thereby, it is possible to detect the pressing force with the same detection sensitivity without depending on the pressing position.

  Furthermore, the piezoelectric film 11 is disposed so that the direction forming 45 ° with respect to the fixed two sides is the uniaxial stretching direction. Thereby, the detection sensitivity with respect to pressing force can further be improved.

1: Press detection sensor,
10, 10A, 10B: Piezoelectric sensor,
11: Piezoelectric film,
12: 1st press detection conductor,
13, 13B: second press detection conductor,
20: Switch part,
21A, 21B, 21C, 21D, 21E, 21F, 21G, 21H, 21I, 21J, 21K, 21L, 21M, 21N, 21P, 21Q: switch conductors,
22A, 23A, 22I, 23I: individual conductors,
24: Switch connection conductor,
30: housing,
31: Internal space,
32: Support pillar,
40: Insulating substrate,
50: Operation reception board,
51: Pedestal,
52: protrusion,
100: operation input device,
101: Voltage converter
102: detection unit,
500: Key top,
C1: capacitor,
U1: Operational amplifier

Claims (7)

An insulating substrate having a main surface parallel to the operation surface;
A plurality of sets of switch conductors arranged at different positions on the main surface on the operation surface side of the insulating substrate;
A switch connection conductor formed in a region facing the plurality of sets of switch conductors and overlapping each set of switch conductors when viewed in a direction perpendicular to the operation surface;
An operation receiving board comprising the switch connection conductor, wherein the surface opposite to the arrangement surface of the switch connection conductor is the operation surface;
A piezoelectric film disposed on a surface opposite to the main surface on the operation surface side of the insulating product substrate;
A first press detection conductor disposed between the insulating substrate and the piezoelectric film and connected to the plurality of switch conductors;
A flat film-like second press detection conductor that sandwiches the piezoelectric film together with the insulating substrate;
A pressure detection sensor. The second press detection conductor is fixed to the insulating substrate only at two opposite sides.
The pressure detection sensor according to claim 1. The second pressing detection conductor has a curved shape so that the two opposite sides are separated from the piezoelectric film from both ends along the side toward the center when viewed from a direction orthogonal to the operation surface.
The pressure detection sensor according to claim 2.   The pressure detection sensor according to any one of claims 1 to 3, wherein the piezoelectric film is made of polylactic acid.   The pressure detection sensor according to any one of claims 1 to 4, wherein the operation reception board includes a protrusion higher than the switch connection conductor on a surface where the switch connection conductor is formed.   The pressure detection sensor according to any one of claims 1 to 5, wherein the plurality of sets of switch conductors are arranged along a circumference when viewed in a direction orthogonal to the operation surface. . A pressure detection sensor according to any one of claims 1 to 6,
A voltage conversion circuit that converts voltage generated in the piezoelectric film into a voltage;
An operation input device comprising: a detection circuit that detects a pressing force from an output voltage of the voltage conversion circuit and detects a set of switch conductors that are conducted from the plurality of sets of switch conductors.

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