Electronic devices, bed sensors, and shelf sensors

Abstract

An electronic apparatus (1) comprises a sensor (10), which is a piezoelectric element-type sensor that outputs a voltage corresponding to applied pressure, and a first detection circuit (20) that detects continuous pressure applied to the sensor (10) from the output voltage of the sensor (10). The first detection circuit (20) includes a capacitor (21) connected in parallel to the sensor (10), and a high input impedance circuit (22) connected in series to the sensor (10).

Description

Technical Field

[0001] The present invention relates to an electronic device, a bed sensor, and a shelf sensor. This application claims priority based on Japanese Patent Application No. 2022-044701 filed in Japan on March 18, 2022, and incorporates its content herein.

Background Art

[0002] There are various types of so-called pressure sensors that convert information related to pressure into an electrical signal, and various sensings have been studied using physical quantities such as light, magnetostriction, string vibration, capacitance, and inductance.

[0003] For example, in Patent Documents 1 to 3, technologies for detecting respiration, pulse, body movement, etc. using piezoelectric films such as PVDF films and porous polypropylene electret films have been proposed. Sensors using piezoelectric films such as PVDF films and porous polypropylene electret films are also called piezo element type sensors, and they detect the voltage generated by the pressure applied to the sensor. Since piezo element type sensors generally output a pulsed signal at the timing when a pressure change occurs, information regarding stimuli such as pressure and load changes (hereinafter also referred to as "dynamic information") can be obtained, but it has been considered difficult to obtain information regarding stimuli where a constant pressure or load continues to be applied (hereinafter also referred to as "static information").

[0004] On the other hand, in Patent Document 4, a technology for measuring body position using a static acceleration sensor has been proposed, and a piezoresistive type sensor is exemplified as the static acceleration sensor. A piezoresistive type sensor detects a change in the resistance inside the sensor due to pressure, and can acquire static information and quantify pressure and load, but it has been difficult to acquire dynamic information or accurately respond to an instantaneous pressure change or load change.

[0005] Furthermore, as a technique for quantifying pressure and load, Patent Document 5 proposes a technique for detecting changes in the load applied to the bed using a load cell. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-187030 [Patent Document 2] Japanese Patent Publication No. 2008-93395 [Patent Document 3] Japanese Patent Publication No. 2010-51588 [Patent Document 4] Japanese Patent Publication No. 2006-271501 [Patent Document 5] International Publication No. 2015 / 008677 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, sensors for the healthcare, robotics, and haptics fields sometimes require both dynamic and static information. For example, sensors for the healthcare field are required to acquire both dynamic information such as respiration, pulse, and body movement, and static information such as sleeping posture and sleeping position.

[0008] Traditionally, in order to acquire both dynamic and static information, it was necessary to arrange sensors according to the signal to be acquired, such as by combining a piezoelectric sensor that can obtain dynamic information with a piezoresistive sensor that can obtain static information, or by using a load cell. However, with the demand for lower costs and smaller space requirements for sensors in each field, hybrid systems using multiple sensors tend to be avoided. Therefore, there is a need for a technology that is cheaper than load cells and can acquire both dynamic and static information without using multiple types of sensors.

[0009] Therefore, the present invention aims to provide an electronic device that can acquire static information with a single piezoelectric element sensor, which is less expensive than a load cell, as well as a bed sensor and a shelf sensor equipped with the electronic device. [Means for solving the problem]

[0010] As a result of diligent research, the inventors have found that static information can be acquired using a piezoelectric sensor by devising a detection circuit for detecting the output voltage of the piezoelectric sensor. In other words, the gist of the present invention is as follows.

[0011] A first aspect of the present invention is an electronic device comprising a piezoelectric sensor that outputs a voltage corresponding to the applied pressure, and a first detection circuit that detects a continuous pressure applied to the piezoelectric sensor from the output voltage of the piezoelectric sensor, wherein the first detection circuit has a capacitor connected in parallel to the piezoelectric sensor and a high input impedance circuit connected in series to the piezoelectric sensor.

[0012] A second aspect of the present invention is that, in the first aspect, the input impedance of the high input impedance circuit is 0.1 TΩ or more and 10 TΩ or less.

[0013] A third aspect of the present invention further comprises, in the first or second aspect, a differential circuit connected in series with the first detection circuit, which detects a change in pressure applied to the piezoelectric sensor by differentiating the detection result of the first detection circuit.

[0014] A fourth aspect of the present invention further comprises a second detection circuit that detects a change in the pressure applied to the piezoelectric element sensor from the output voltage of the piezoelectric element sensor, in the first or second aspect of the present invention.

[0015] The fifth aspect of the present invention is that, in the fourth aspect, the input impedance of the high-input impedance circuit included in the first detection circuit is higher than the input impedance of the second detection circuit.

[0016] The sixth aspect of the present invention is that, in the fifth aspect, the input impedance of the high-input impedance circuit included in the first detection circuit is 10 4 times or more and 10 8 times or less of the input impedance of the second detection circuit.

[0017] The seventh aspect of the present invention is that, in any one of the fourth to sixth aspects, the input impedance of the second detection circuit is 0.1 MΩ or more and 10 MΩ or less.

[0018] The eighth aspect of the present invention is that, in any one of the fourth to seventh aspects, there is a switching circuit that switches whether to connect the first detection circuit or the second detection circuit to the piezoelectric element type sensor.

[0019] The ninth aspect of the present invention is that, in any one of the first to eighth aspects, the capacitance of the capacitor is 100 pF or more and 5000 pF or less.

[0020] The tenth aspect of the present invention is that, in any one of the first to ninth aspects, the piezoelectric element type sensor includes an electret film.

[0021] The eleventh aspect of the present invention is that, in the tenth aspect, the electret film contains a polyolefin-based resin.

[0022] The twelfth aspect of the present invention is a bed sensor including the electronic device according to any one of the first to eleventh aspects.

[0023] The thirteenth aspect of the present invention is a shelf sensor including the electronic device according to any one of the first to eleventh aspects.

Advantages of the Invention

[0024] According to the present invention, static information can be acquired using a single piezoelectric element sensor, which is less expensive than a load cell, thus enabling lower sensor costs and space savings. [Brief explanation of the drawing]

[0025] [Figure 1] This is a block diagram showing the main components of an electronic device according to a first embodiment of the present invention. [Figure 2] This is an exploded perspective view showing the basic configuration of the sensor used in the first embodiment of the present invention. [Figure 3] This is a block diagram showing the main components of an electronic device according to a second embodiment of the present invention. [Figure 4] This is a block diagram showing the main components of an electronic device according to a third embodiment of the present invention. [Figure 5] This is a block diagram showing the main components of an electronic device according to a fourth embodiment of the present invention. [Figure 6] This figure shows the waveform of the output voltage acquired by the second detection circuit when using the sensor of Example 1. [Figure 7] This figure shows the waveform of the output voltage acquired by the first detection circuit when using the sensor of Example 1. [Figure 8] This figure shows the relationship between the magnitude of the load applied to the sensor in Example 1 and the magnitude of the output voltage of the first detection circuit. [Figure 9] This figure shows the waveform of the output voltage acquired by the first detection circuit when using the sensor of Example 2. [Modes for carrying out the invention]

[0026] The embodiments of the present invention will be described in detail below. The configurations of the following embodiments are illustrative, and the present invention is not limited to the configurations of these embodiments.

[0027] [First Embodiment] <Electronic equipment> Figure 1 is a block diagram showing the main components of an electronic device according to a first embodiment of the present invention. As shown in Figure 1, the electronic device 1 of this embodiment includes a sensor 10 and a first detection circuit 20, and detects static information applied to the sensor 10. Here, static information is information about a stimulus that is continuously subjected to a constant pressure or load. This static information can also be described as the continuous pressure applied to the sensor 10. Here, continuous pressure can also be described as pressure or load that does not change with respect to time, or pressure or load that changes only slightly with respect to time. In other words, it can also be described as pressure or load whose rate of change with respect to time is zero, or can be considered to be zero.

[0028] Sensor 10 is a sensor that outputs a voltage corresponding to the applied pressure. This sensor 10 is a piezoelectric sensor and outputs a pulsed signal at the timing when a pressure change occurs. Sensor 10 has two output terminals T11 and T12. Output terminal T11 is connected to the first detection circuit 20, and output terminal T12 is grounded. When pressure is applied, sensor 10 outputs the pulsed signal from output terminal T11. Further details of sensor 10 will be described later.

[0029] The first detection circuit 20 comprises a capacitor 21 and a high input impedance circuit 22, and detects static information applied to the sensor 10 from the output voltage of the sensor 10. The first detection circuit 20 may be an analog circuit or a digital circuit. The capacitor 21 is connected in parallel to the sensor 10. Specifically, one electrode of the capacitor 21 is connected to the output terminal T11 of the sensor 10, and the other electrode is grounded. The capacitor 21 is provided to control the waveform of the pulsed signal output from the output terminal T11 of the sensor 10 by charging and discharging the charge generated in the sensor 10. The capacitance of the capacitor 21 is, for example, 100pF or more and 5000pF or less, preferably 200pF or more and 3000pF or less, and more preferably 500pF or more and 2000pF or less.

[0030] The high input impedance circuit 22 includes an operational amplifier 22a and is connected in series with the sensor 10. This high input impedance circuit 22 is a circuit in which the inverting input terminal and output terminal of the operational amplifier 22a are connected (a so-called voltage follower circuit (buffer circuit)), and the non-inverting input terminal of the operational amplifier 22a is connected to the output terminal T11 of the sensor 10. The high input impedance circuit 22 is provided to prevent the outflow of charge generated in the sensor 10. The input impedance of the high input impedance circuit 22 is, for example, 0.1 TΩ or more and 10 TΩ or less, preferably 0.2 TΩ or more and 8 TΩ or less, and more preferably 0.5 TΩ or more and 5 TΩ or less.

[0031] The output terminal of the high input impedance circuit 22 (the output terminal of the operational amplifier 22a) is connected to the output terminal T20 of the first detection circuit 20. The output terminal T20 of the first detection circuit 20 outputs a signal indicating static information applied to the sensor 10. A circuit such as an amplification circuit for amplifying the signal output from the high input impedance circuit 22 may be provided between the high input impedance circuit 22 and the output terminal T20 of the first detection circuit 20.

[0032] <sensor> As mentioned above, sensor 10 is a piezoelectric sensor. This piezoelectric sensor is not particularly limited as long as it is a sensor that can detect a voltage generated by the pressure applied to the sensor, but examples include sensors that include ceramic or organic polymer piezoelectric materials. Examples of ceramic piezoelectric materials include lead zirconate titanate (PZT) and barium strontium titanate (BST). Examples of organic polymer-based piezoelectric materials include permanent dipole materials such as PVDF (polyvinylidene fluoride), vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)), vinylidene fluoride-tetrafluoroethylene copolymer (P(VDF-TFE)), and polylactic acid (PLA), as well as electret films made by charging films made of polyolefin resins. In particular, from the viewpoint of piezoelectric properties and sensor flexibility, organic polymer-based piezoelectric materials are preferred, and electret films are more preferred.

[0033] (1-1) Electret film The type of electret film is not particularly limited as long as it has piezoelectric properties, but a porous electret film is preferred in order to further enhance the piezoelectric properties. Furthermore, it is even more preferable to use a porous film that has been charged. When using a porous electret film, the method of making the film porous is not particularly limited, but examples include chemical or physical foaming and stretching. Among these, stretching is preferred because it yields a dense porous structure and allows for easy control of the pore shape.

[0034] Materials for electret films include polyolefin resins, fluororesins, vinyl chloride resins, polystyrene resins, butadiene resins, polyester resins, and acrylic resins. However, polyolefin resins are preferred because they have a low environmental impact and are easy to electrostatically treat.

[0035] (1-1-1) Polyolefin resin In this embodiment, the electret film is preferably composed mainly of a polyolefin resin, and more preferably of a polypropylene resin. In this invention, "main component" refers to a component whose content in the electret film is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit of the content is not particularly limited, and it may be 100% by mass or less.

[0036] Examples of polypropylene resins include homopolypropylene (propylene homopolymer), or random copolymers or block copolymers of propylene with α-olefins such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, or 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

[0037] Furthermore, the polypropylene resin preferably has an isotactic pentad fraction exhibiting stereoregularity of 80% or more, more preferably 83% or more, even more preferably 85% or more, and also preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. If the isotactic pentad fraction is 80% or higher, the mechanical strength is good. On the other hand, the upper limit of the isotactic pentad fraction is currently defined as the upper limit achievable industrially, but this may change in the future if resins with even higher orderliness are developed at an industrial level. The isotactic pentad fraction refers to the stereostructure or ratio in which the five methyl groups of the side chain are all located in the same direction relative to the carbon-carbon bonded main chain composed of any five consecutive propylene units. The assignment of signals in the methyl group region follows A. Zambelli et al. (Macromol. 8, 687 (1975)).

[0038] Furthermore, the polypropylene resin has a molecular weight distribution parameter Mw / Mn of preferably 1.5 or higher, more preferably 2.0 or higher, preferably 10.0 or lower, more preferably 8.0 or lower, and even more preferably 6.0 or lower. A smaller Mw / Mn ratio indicates a narrower molecular weight distribution. However, by setting the Mw / Mn ratio to 1.5 or higher, sufficient extrusion moldability can be obtained, making industrial mass production possible. On the other hand, by setting the Mw / Mn ratio to 10.0 or lower, sufficient mechanical strength can be ensured. Mw / Mn is measured as a polystyrene equivalent value by GPC (Gel Per Emission Chromatography).

[0039] Furthermore, the melt flow rate (MFR) of the polypropylene resin is not particularly limited, but is preferably 0.5 g / 10 min or more, more preferably 1.0 g / 10 min or more, and preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less. By setting the MFR to 0.5g / 10min or higher, sufficient melt viscosity can be achieved during molding, ensuring high productivity. On the other hand, by setting the MFR to 15g / 10min or lower, sufficient strength can be ensured. The MFR is measured in accordance with JIS K7210-1 (2014) under conditions of 230°C temperature and 2.16 kg load.

[0040] Furthermore, the method for producing polypropylene resins is not particularly limited, and examples include known polymerization methods using known polymerization catalysts, such as multi-site catalysts represented by Ziegler-Natta type catalysts and single-site catalysts represented by metallocene catalysts.

[0041] Examples of commercially available polypropylene resins that can be suitably used in this embodiment include products such as "Novatec PP," "WINTEC," and "WAYMAX" (manufactured by Nippon Polypropylene Co., Ltd.), "Versify," "Notio," and "Toughmer XR" (manufactured by Mitsui Chemicals, Inc.), "Zelus" and "Thermoran" (manufactured by Mitsubishi Chemical Corporation), "Sumitomo Noblen" and "Toughselenium" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime Polypropylene" and "Prime TPO" (manufactured by Prime Polymer Co., Ltd.), "Adflex," "Adsyl," and "HMS-PP (PF814)" (manufactured by Sun Allomer Co., Ltd.), and "Inspire" (Dow Chemical Co., Ltd.).

[0042] [β crystal activity] In this embodiment, when the electret film contains a polypropylene resin as its main component, it is preferable that the electret film is made of a resin composition mainly composed of a polypropylene resin that contains a large amount of β-crystals, which are one of the crystalline forms. A non-porous film made of a resin composition mainly composed of a polypropylene resin that contains a large amount of β-crystals exhibits excellent piezoelectricity even in itself after electrostatic treatment, but even better piezoelectricity can be obtained by stretching it to create a porous structure. Forming a porous structure using β-crystals is advantageous because the porous structure is dense, as porosity occurs during the process in which β-crystals in the polypropylene resin are transformed into α-crystals during the stretching process, and it does not depend on particle size or dispersion diameter compared to conventionally known methods of porosity formation by adding inorganic fillers or incompatible organic substances, thus making it advantageous for preparing a porous structure.

[0043] Porous films using β-crystals have a dense porous structure, and the surface area of ​​the pores is large, making it easier to trap more charge during charging treatment. Since porous electret films exhibit piezoelectricity due to the charge trapped at the interface between the pores and the matrix, a dense porous structure in the film tends to result in good piezoelectric properties. Furthermore, a dense porous structure results in very short distances between pores, making it easier for trapped charges to be fixed by mutual Coulomb forces. This makes it difficult for trapped charges to discharge, and thus prevents a decrease in the properties of the electret film.

[0044] In this embodiment, the β-crystal activity of the electret film can be considered an indicator that the polypropylene resin generated β-crystals in the non-porous film before stretching. If the polypropylene resin in the non-porous film before stretching generates β-crystals, then stretching will create many fine and uniform pores, resulting in excellent mechanical properties and superior dielectric strength due to the formation of fine and uniform pores.

[0045] In this embodiment, the presence or absence of β-crystal activity in the electret film is determined by performing differential thermal analysis of the electret film using a differential scanning calorimeter (DSC) and checking whether or not a crystal melting peak temperature originating from the β-crystal of the polypropylene resin is detected. Specifically, when a laminated porous film is heated from 40°C to 200°C at a rate of 10°C / min using a differential scanning calorimeter, held for 1 minute, then cooled from 200°C to 40°C at a rate of 10°C / min, held for 1 minute, and then reheated from 40°C to 200°C at a rate of 10°C / min, if the crystal melting peak temperature (Tmβ) originating from the β crystal of the polypropylene resin is detected during the reheating, it is determined that the film has β crystal activity.

[0046] The presence or absence of β-crystal activity can also be determined from the diffraction profile obtained by X-ray diffraction measurement of an electret film subjected to a specific heat treatment. Specifically, an electret film is subjected to heat treatment at a temperature of 170-190°C, which is above the crystal melting peak temperature of the polypropylene resin, and then slowly cooled to generate and grow β-crystals. X-ray diffraction measurement is performed on the electret film, and if a diffraction peak originating from the (300) plane of the β-crystal of the polypropylene resin is detected in the range of 2θ = 16.0° to 16.5°, then β-crystal activity is determined to be present. For further details on the β-crystal structure and X-ray diffraction measurements of polypropylene resins, please refer to Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and the references cited in these publications.

[0047] Methods for obtaining the β-crystal activity of the polypropylene resin mentioned above include methods that do not add substances that promote the formation of α-crystals in the polypropylene resin, methods that add a polypropylene resin that has been treated to generate peroxide radicals as described in Japanese Patent Publication No. 3739481, and methods that add a β-crystal nucleating agent. In this embodiment, however, it is particularly preferable to obtain β-crystal activity by adding a β-crystal nucleating agent. By adding a β-crystal nucleating agent, the formation of β-crystals in the polypropylene resin can be promoted more homogeneously and efficiently, and an electret film having β-crystal activity can be obtained.

[0048] The degree of β-crystal activity can be quantified by measuring the β-crystal formation ability. The β-crystal formation ability of the polypropylene resin contained in the electret film is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The polypropylene resin exhibits suitable piezoelectric properties when its β-crystal formation ability is above the lower limit mentioned above. There is no particular upper limit, but it is usually 100% or less. The β-crystal formation ability is calculated using the method described later.

[0049] (1-1-2) β-crystal nucleating agent In this embodiment, when the electret film contains a polypropylene resin as its main component, it is preferable that the electret film contains a β-nucleating agent in order to obtain excellent piezoelectric properties. By including a β-nucleating agent in the electret film, β-crystal activity can be obtained. Examples of β-nucleating agents used in this embodiment are listed below. The β-nucleating agent may be used alone, or two or more may be used in any combination and ratio.

[0050] Examples of β-crystal nucleating agents include amide compounds; tetraoxaspiro compounds; quinacridones; nanoscale iron oxides; alkali metal salts or alkaline earth metal salts of carboxylic acids, such as potassium 1,2-hydroxystearate, magnesium benzoate, magnesium succinate, and magnesium phthalate; aromatic sulfonic acid compounds, such as sodium benzenesulfonate and sodium naphthalenesulfonate; diesters or triesters of dibasic or tribasic carboxylic acids; phthalocyanine pigments, such as phthalocyanine blue; two-component compounds consisting of component A, which is an organic dibasic acid, and component B, which is an oxide, hydroxide, or salt of a Group 2 metal in the periodic table; and compositions consisting of cyclic phosphorus compounds and magnesium compounds.

[0051] Among these β-nucleating agents, amide compounds are preferred. Using amide compounds in electret films can enhance piezoelectric properties. Examples of amide compounds include N,N'-dicyclohexyl-2,6-naphthalenedicarboxyamide, N,N'-dicyclohexyl terephthalamide, and N,N'-diphenylhexanediamide, with N,N'-dicyclohexyl-2,6-naphthalenedicarboxyamide being particularly preferred. Because amide compounds have highly polar amide groups, they can localize charges within the crystal structure, and are thought to possess high piezoelectric properties. On the other hand, highly polar compounds such as amide compounds have a problem of poor dispersibility and tendency to aggregate due to electrostatic interactions with low-polarity polypropylene resins. However, general β-nucleating agents have the property of dissolving in polypropylene resins within a certain temperature range. Due to this property, the β-nucleating agent is uniformly dispersed in the polypropylene resin, and crystals derived from the β-nucleating agent are more easily precipitated uniformly. Therefore, it is thought that crystals of highly polar amide compounds can be uniformly dispersed in low-polarity polypropylene resins, resulting in high piezoelectric properties.

[0052] Specific examples of commercially available β-nucleating agents include "NJester NU-100" manufactured by Shin Nippon Rika Co., Ltd., and specific examples of propylene resins with added β-nucleating agents include "Bepol B-022SP" polypropylene from Aristech, "Beta(β)-PP BE60-7032" polypropylene from Borealis, and "BNX BETAPP-LN" polypropylene from Mayzo.

[0053] The content of the β-nucleating agent in the electret film in this embodiment can be appropriately adjusted depending on the type of β-nucleating agent or the composition of the polypropylene resin, but is preferably 0.0001 parts by mass or more, more preferably 0.001 parts by mass or more, even more preferably 0.01 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 1.0 part by mass or less, per 100 parts by mass of the polypropylene resin. If the content of the β-nucleating agent is 0.0001 parts by mass or more per 100 parts by mass of the polypropylene resin, sufficient β-crystals of the polypropylene resin can be generated and grown during manufacturing, ensuring sufficient β-crystal activity, and sufficient β-crystal activity can also be ensured when a porous film is made. Therefore, a porous electret film with the desired piezoelectric properties can be obtained by electrostatic treatment of the porous film. On the other hand, if the content of the β-nucleating agent is 5.0 parts by mass or less per 100 parts by mass of the polypropylene resin, it is economically advantageous and preferable because there is no bleeding of the β-nucleating agent to the film surface.

[0054] (1-1-3) Other ingredients If the electret film of the present invention is a porous film, it may contain a foaming agent or a filler, etc., instead of, or in addition to, the above-mentioned β-nucleating agent. For example, when using a porous film made by chemical or physical foaming as the electret film of the present invention, it is preferable to add a chemical foaming agent, a physical foaming agent, a supercritical fluid, a thermally expandable microcapsule, etc., to the main component resin. These may be used individually or in combination of two or more. Furthermore, when using a film that has been made porous by stretching as the electret film of the present invention, it is also preferable to add a resin that is immiscible with the main component resin, or an inorganic filler. Examples of inorganic fillers include calcium carbonate, calcium sulfate, barium carbonate, barium sulfate, titanium dioxide, talc, clay, kaolinite, montmorillonite, and the like.

[0055] The electret film in this embodiment may contain various additives, such as heat stabilizers, antioxidants, ultraviolet absorbers, light stabilizers, crystal nucleating agents, colorants, antistatic agents, hydrolysis inhibitors, lubricants, flame retardants, conductive agents, and elastomers, to an extent that does not impair its properties.

[0056] The porosity of the electret film in this embodiment is typically 0% or more, preferably 5% or more, more preferably 10% or more, preferably 70% or less, more preferably 50% or less, even more preferably 40% or less, and even more preferably 30% or less. When the porosity of the electret film is below the upper limit mentioned above, the pores are less likely to collapse, resulting in good pressure resistance. Furthermore, when the porosity of the electret film is above the lower limit mentioned above, the piezoelectric properties can be further enhanced. The porosity of the electret film is calculated using the method described later.

[0057] The thickness of the electret film in this embodiment is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and also preferably 1000 μm or less, more preferably 750 μm or less, and even more preferably 500 μm or less. By keeping the electret film thickness within the above range, good piezoelectric properties can be achieved without making the piezoelectric sensor unnecessarily thick. The thickness of the electret film is measured by the method described later.

[0058] (1-2) Electrode Figure 2 is an exploded perspective view showing the basic configuration of a sensor 10 used in the first embodiment of the present invention. As shown in Figure 2, the sensor 10 preferably comprises an electret film 11 and at least one pair of electrodes 12a and 12b. As shown in Figure 2, the pair of electrodes 12a and 12b are preferably arranged so as to sandwich the electret film 11. The pair of electrodes 12a and 12b are each provided with signal extraction lines 13a and 13b that output signals (voltages) from the electrodes 12a and 12b, respectively. These signal extraction lines 13a and 13b function as output terminals T11 and T12, respectively, as shown in Figure 1.

[0059] Electrodes 12a and 12b only need to be conductive, and aluminum foil, copper foil, silver foil, gold foil, nickel foil, tin foil, carbon sheets, etc., are preferably used. The signal extraction wires 13a and 13b are not particularly limited, but a structure in which a conductive wire is covered with an insulating material is preferred. The conductive wire is preferably made of a conductor such as copper or aluminum. Examples of insulating materials include tetrafluoroethylene-ethylene copolymer (ETFE), polyvinyl chloride, and cross-linked polyethylene. The diameter and length of the signal extraction wires 13a and 13b are also not particularly limited and can be appropriately selected according to the size of the sensor 10, the type of electrodes 12a and 12b, etc.

[0060] The thickness of electrodes 12a and 12b is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, and also preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. By having electrodes 12a and 12b with a thickness of 2 μm or more, conductive stability can be achieved for electrodes 12a and 12b. On the other hand, by having electrodes 12a and 12b with a thickness of 100 μm or less, the flexibility of the sensor 10 can be increased.

[0061] As described above, this embodiment includes a sensor 10, which is a piezoelectric element type sensor, and a first detection circuit 20 that detects the continuous pressure applied to the sensor 10 from the output voltage of the sensor 10. Here, the first detection circuit 20 has a capacitor 21 connected in parallel with the sensor 10 and a high input impedance circuit 22 connected in series with the sensor 10. As a result, the first detection circuit 20 can obtain a signal that is, so to speak, an integrated signal of the pulsed signal output from the sensor 10. This makes it possible to acquire static information with a single piezoelectric element type sensor, which is less expensive than a load cell.

[0062] [Second Embodiment] Figure 3 is a block diagram showing the main components of an electronic device according to a second embodiment of the present invention. In Figure 3, components similar to those shown in Figure 1 are denoted by the same reference numerals. As shown in Figure 3, the electronic device 2 of this embodiment has a configuration in which a differential circuit 30 is added to the electronic device 1 shown in Figure 1. Such an electronic device 2 is configured to acquire dynamic information in addition to static information using a single piezoelectric sensor.

[0063] The differentiating circuit 30 is connected to the output terminal T20 of the first detection circuit 20. In other words, the differentiating circuit 30 is connected in series with the first detection circuit 20. The differentiating circuit 30 is a circuit that detects changes in pressure applied to the sensor 10 by differentiating the signal output from the output terminal T20 of the first detection circuit 20 with respect to time. In other words, the differentiating circuit 30 obtains dynamic information from the detection result (static information) of the first detection circuit 20. The differentiating circuit 30 outputs its detection result from the output terminal T30. Any well-known differentiating circuit can be used for the differentiating circuit 30. The differentiating circuit 30 may be an analog circuit or a digital circuit.

[0064] Here, the signal output from the output terminal T20 of the first detection circuit 20 is, so to speak, the integrated signal (static signal) of the pulsed signal output from the sensor 10. In contrast, the signal output from the output terminal T30 of the differentiating circuit 30 is the differentiated signal (dynamic signal) of the signal output from the output terminal T20 of the first detection circuit 20. Therefore, in this embodiment, both static and dynamic information can be acquired with a single piezoelectric sensor.

[0065] As described above, in this embodiment, in addition to the sensor 10 and the first detection circuit 20, a differential circuit 30 is provided, which is connected in series with the first detection circuit 20 and detects changes in the pressure applied to the sensor 10 by differentiating the detection result of the first detection circuit 20. Therefore, static and dynamic information can be acquired with a single piezoelectric element sensor.

[0066] [Third Embodiment] Figure 4 is a block diagram showing the main components of an electronic device according to a third embodiment of the present invention. In Figure 4, components similar to those shown in Figure 1 are denoted by the same reference numerals. As shown in Figure 4, the electronic device 3 of this embodiment has a configuration in which a second detection circuit 40 is added to the electronic device 1 shown in Figure 1. Similar to the electronic device 2 shown in Figure 3, this electronic device 3 is configured to acquire dynamic information in addition to static information using a single piezoelectric sensor.

[0067] The second detection circuit 40 is a circuit equipped with a resistor 41, and detects changes in the pressure applied to the sensor 10 from the output voltage of the sensor 10. In other words, the second detection circuit 40 detects dynamic information from the output voltage of the sensor 10. The second detection circuit 40 is connected to the output terminal T11 of the sensor 10, just like the first detection circuit 20. In other words, the first detection circuit 20 and the second detection circuit 40 are connected in parallel.

[0068] The resistor 41 of the second detection circuit 40 is connected in parallel with the sensor 10. Specifically, one end of the resistor 41 is connected to the output terminal T11 of the sensor 10, and the other end is grounded. One end of the resistor 41 (the end connected to the output terminal T11 of the sensor 10) is connected to the output terminal T40 of the second detection circuit 40. The second detection circuit 40 outputs its detection result from the output terminal T40. The input impedance of the second detection circuit 40 is, for example, 0.1 MΩ or more and 10 MΩ or less.

[0069] The input impedance of the high input impedance circuit 22 of the first detection circuit 20 is set higher than the input impedance of the second detection circuit 40. Specifically, the input impedance of the high input impedance circuit 22 is 10 times higher than the input impedance of the second detection circuit 40. 4 more than 10 times 8 It is less than double. For example, if the input impedance of the second detection circuit 40 is 0.1 MΩ, the input impedance of the high input impedance circuit 22 is set to be between 1 GΩ and 10 TΩ. Also, for example, if the input impedance of the second detection circuit 40 is 10 MΩ, the input impedance of the high input impedance circuit 22 is set to be between 0.1 TΩ and 1 PTΩ.

[0070] Here, the signal output from the output terminal T20 of the first detection circuit 20 is, so to speak, an integrated signal (static signal) of the pulsed signal output from the sensor 10. In contrast, the signal output from the second detection circuit 40 is a signal (dynamic signal) similar to the pulsed signal output from the sensor 10. Therefore, in this embodiment, both static and dynamic information can be acquired with a single piezoelectric sensor.

[0071] As described above, in this embodiment, in addition to the sensor 10 and the first detection circuit 20, a second detection circuit 40 is provided that detects changes in the pressure applied to the sensor 10 from the output voltage of the sensor 10. Therefore, static and dynamic information can be acquired with a single piezoelectric element sensor.

[0072] [Fourth Embodiment] Figure 5 is a block diagram showing the main components of an electronic device according to a fourth embodiment of the present invention. In Figure 5, components similar to those shown in Figure 4 are denoted by the same reference numerals. As shown in Figure 5, the electronic device 4 of this embodiment has a configuration in which a switching circuit 50 is added to the electronic device 3 shown in Figure 4. Similar to the electronic device 3 shown in Figure 4, this electronic device 4 is configured to acquire both static and dynamic information using a single piezoelectric sensor, but it is configured to selectively acquire static and dynamic information.

[0073] The switching circuit 50 has one input terminal T50 and two output terminals T51 and T52, and is a circuit that connects input terminal T50 to output terminal T51 or output terminal T52. Input terminal T50 of the switching circuit 50 is connected to output terminal T11 of the sensor 10, output terminal T51 is connected to the first detection circuit 20, and output terminal T52 is connected to the second detection circuit 40. The switching circuit 50 allows the sensor 10 to be connected to the first detection circuit 20 to acquire static information, or to be connected to the sensor 10 to acquire dynamic information.

[0074] As described above, in this embodiment, in addition to the sensor 10, the first detection circuit 20, and the second detection circuit 40, a switching circuit 50 is provided to switch whether to connect the first detection circuit 20 or the second detection circuit 40 to the sensor 10. Therefore, static and dynamic information can be selectively acquired with a single piezoelectric sensor.

[0075] The electronic devices described above can be used as bed sensors or shelf sensors. When used as a bed sensor, for example, by placing the film-like sensor 10 under the mattress of a bed, it becomes possible to measure static information such as constant pressure and dynamic information such as the subject's vital data (respiration, pulse, body movement, etc.). When used as a shelf sensor, for example, by placing the film-like sensor 10 on a shelf, it becomes possible to measure the weight of items placed on the shelf (static information) and the change in the weight of the items (dynamic information). [Examples]

[0076] Examples 1 and 2 are shown below to further describe the electronic device of the present invention, but the present invention is not limited in any way by the following examples as long as it does not exceed its gist. In Examples 1 and 2, two different types of organic polymer piezoelectric materials are compared when applied to the electronic device shown in the third or fourth embodiment.

[0077] <Example 1: Porous Electret Film> A resin composition for electret film was obtained by mixing 100 parts by mass of homopolypropylene ("Novatec PP FY6HA", MFR: 2.4 g / 10 min [230°C, 2.16 kg load], Mw / Mn=3.2, manufactured by Nippon Polypropylene Co., Ltd.) as a polyolefin resin material for porous electret film, which is an organic polymer-based piezoelectric material; 0.2 parts by mass of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide ("NU-100", manufactured by Shin Nippon Rika Co., Ltd.) as a β-crystal nucleating agent; and 0.1 parts by mass of a 1:1 mixture of tris(2,4-di-t-butylphenyl) phosphite and tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid]pentaerythritol ("IRGANOX-B225", manufactured by BASF) as an antioxidant, and melt-extruding the mixture at 280°C using a twin-screw extruder. The resin composition for electret film was fed into an extruder connected to a T-die with a lip opening of 1 mm and molded, and guided to a cast roll to obtain a non-porous film with a thickness of 300 μm. Subsequently, it was stretched seven times laterally at a stretching temperature of 100°C in a film tenter (manufactured by Kyoto Machinery Co., Ltd.) to obtain a porous film. The resulting porous film was placed on a ground plate, and a voltage of -11kV was applied using wire electrodes with a distance of 20mm between the electrodes to perform a charging treatment, thereby obtaining a porous electret film.

[0078] The resulting porous electret film had a thickness of 55 μm, a porosity of 20%, and a β-crystal formation ability of 92%. The thickness was measured at 10 random points using a 1 / 1000 mm dial gauge, and the average value was calculated. Furthermore, the porosity was calculated using the following formula, based on the actual mass W1 of a sample cut from a porous electret film to a width of 100 mm x length of 100 mm, and the mass W0 when the porosity is 0%, which was calculated based on the density of the resin composition for the electret film. Porosity (%)={(W0-W1) / W0}×100 The β-crystal formation ability was determined by differential scanning calorimetry (DSC) of a porous electret film performed using the method described below. A NETZSCH "DSC 204F1" was used as the test apparatus. First, the temperature was increased from 40°C to 200°C at a rate of 10°C / min under a nitrogen atmosphere, held for 1 minute, and then cooled to 40°C at a rate of 10°C / min. After holding for 1 minute, the temperature was increased again at a rate of 10°C / min. Melting peaks observed were identified as β-crystal melting peaks if the peak was in the temperature range of 145-157°C, and α-crystal melting peaks if the peak was observed above 158°C. The heat of fusion for each was determined from the area of ​​the region enclosed by the baseline drawn based on the flat area on the high-temperature side and the peak. The heat of fusion for α-crystal was denoted as ΔHα and the heat of fusion for β-crystal was denoted as ΔHβ, and the calculation was performed using the following formula. β crystal formation ability (%) = [ΔHβ / (ΔHα+ΔHβ)]×100

[0079] A piezoelectric sensor was fabricated using the porous electret film obtained above by the following method. A conductive copper foil adhesive tape "E20CU" (manufactured by DIC Corporation, electrode thickness 19 μm, adhesive layer thickness 21 μm) having an adhesive layer on one side was cut into 5 mm squares, and the copper foil was attached to the center of a 10 mm square protective film (Kapton tape, thickness 50 μm) via the adhesive layer to obtain an electrode-attached protective film. Two of these electrode-attached protective films were arranged so that the two electrodes faced each other, and a porous electret film cut into a 6 mm square was placed between the two electrodes. At this time, care was taken to ensure that the porous electret film did not protrude from the protective film. In addition, one signal extraction wire (Junflon wrapping wire, manufactured by Junko Co., Ltd.) with a wire width of 0.56 mm was sandwiched between the adhesive layer of the protective film and the conductive copper foil adhesive tape. Subsequently, the edges of the protective films were heat-sealed together using a heat sealer to obtain the sensor of Example 1.

[0080] [Test 1: Dynamic and Static Stimuli] The sensor 10 of Example 1 was placed on top of a load cell, and the waveforms of the output voltages of the first detection circuit 20 and the second detection circuit 40 were obtained when pressure was applied to the sensor from above by a robot. The capacitance of the capacitor 21 of the first detection circuit 20 was set to 1000pF, and the input impedance of the high input impedance circuit 22 was set to 1TΩ. The input impedance of the second detection circuit 40 was set to 1MΩ.

[0081] Figure 6 shows the waveform of the output voltage acquired by the second detection circuit 40 when using the sensor 10 of Example 1. In addition to the output voltage waveform WF2 acquired by the second detection circuit 40, Figure 6 also shows the output waveform WF0 of the load cell, which indicates the state of pressurization by the robot. As shown in Figure 6, the waveform WF2 of the output signal acquired by the second detection circuit 40 is pulsed, and information regarding the change in pressure (dynamic stimulation) applied to the sensor 10 can be confirmed.

[0082] Figure 7 shows the waveform of the output voltage acquired by the first detection circuit 20 when the sensor 10 of Example 1 is used. In addition to the output voltage waveform WF1 acquired by the first detection circuit 20, Figure 7 also shows the output waveform WF0 of the load cell, which indicates the state of pressure applied by the robot. As shown in Figure 7, the waveform WF1 of the output signal acquired by the first detection circuit 20 (a circuit with a higher input impedance than the second detection circuit 40 and containing a capacitor 21) is similar to the output waveform WF0 of the load cell, and it is possible to confirm how long pressure has been applied to the sensor 10 (static stimulus).

[0083] [Test 2: Correlation between load and signal intensity] For the first detection circuit 20, the load applied to the sensor 10 was varied and the signal waveform was acquired to confirm the correlation between the load and the signal strength. Figure 8 shows the relationship between the magnitude of the load applied to the sensor 10 in Example 1 and the magnitude of the output voltage of the first detection circuit 20. As shown in Figure 8, it was confirmed that the signal strength tends to increase as the load increases.

[0084] <Example 2: Polyvinylidene fluoride film> A piezoelectric element sensor was fabricated using the same method as in Example 1, with a polyvinylidene fluoride film with a thickness of 80 μm (Kureha KF Piezo Film, manufactured by Kureha Corporation) as the organic polymer piezoelectric material.

[0085] [Test 3: Static Stimulation] In the case of polyvinylidene fluoride film, the signal waveform output by a normal circuit such as an oscilloscope (second detection circuit 40) is a pulse wave similar to that in Figure 6. Therefore, we confirmed whether information regarding static stimuli could be obtained when the first detection circuit 20 was formed. Figure 9 shows the waveform of the output voltage acquired by the first detection circuit 20 when using the sensor 10 of Example 2. In addition to the output voltage waveform WF1 acquired by the first detection circuit 20, Figure 9 also shows the output waveform WF0 of the load cell, which indicates the state of pressure applied by the robot, as in Figure 7. As shown in Figure 9, the output voltage waveform WF1 acquired by the first detection circuit 20 is similar to the output waveform WF0 of the load cell, and it was possible to confirm how long pressure was being applied to the sensor 10 (static stimulus).

[0086] From the above tests 1 to 3, it was confirmed that by combining the second detection circuit 40 with the first detection circuit 20, which has a higher input impedance than the second detection circuit 40 and includes a capacitor 21, both dynamic and static information can be acquired with a single piezoelectric sensor. Furthermore, the signal waveform obtained by the sensor 10 of Example 1 showed a higher similarity to the signal waveform of the load cell than the signal waveform obtained by the sensor 10 of Example 2. Therefore, it was confirmed that by using a piezoelectric sensor, particularly one equipped with a porous electret film, the load applied to the sensor can be acquired with the same accuracy as that of a load cell. [Industrial applicability]

[0087] We can provide an electronic device that can acquire static information using a single piezoelectric element sensor, which is less expensive than a load cell, as well as a bed sensor and a shelf sensor equipped with this electronic device. [Explanation of symbols]

[0088] 1~4 Electronic equipment 10 sensors 11 Electret film 20 First detection circuit 21 Capacitors 22 High Input Impedance Circuits 30 Differential circuit 40 Second detection circuit 50 Switching Circuit

Claims

1. A piezoelectric sensor that outputs a voltage corresponding to the applied pressure, A first detection circuit that detects the continuous pressure applied to the piezoelectric sensor from the output voltage of the piezoelectric sensor, A differential circuit connected in series with the first detection circuit detects the change in pressure applied to the piezoelectric sensor by differentiating the detection result of the first detection circuit, Equipped with, The first detection circuit is, A capacitor connected in parallel to the aforementioned piezoelectric sensor, A high input impedance circuit connected in series with the piezoelectric element type sensor, Electronic devices having

2. The electronic device according to claim 1, wherein the input impedance of the high input impedance circuit is 0.1 TΩ or more and 10 TΩ or less.

3. The electronic device according to claim 1, further comprising a second detection circuit that detects a change in pressure applied to the piezoelectric element sensor from the output voltage of the piezoelectric element sensor.

4. The electronic device according to claim 3, wherein the input impedance of the high input impedance circuit provided in the first detection circuit is higher than the input impedance of the second detection circuit.

5. The input impedance of the high input impedance circuit of the first detection circuit is 10 times the input impedance of the second detection circuit. 4 more than 10 times 8 The electronic device according to claim 4, which is less than or equal to twice the original value.

6. The electronic device according to claim 3, wherein the input impedance of the second detection circuit is 0.1 MΩ or more and 10 MΩ or less.

7. The electronic device according to claim 3, further comprising a switching circuit that switches whether to connect the first detection circuit or the second detection circuit to the piezoelectric element type sensor.

8. The electronic device according to claim 1, wherein the capacitance of the capacitor is 100 pF or more and 5000 pF or less.

9. The electronic device according to claim 1, wherein the piezoelectric sensor comprises an electret film.

10. The electronic device according to claim 9, wherein the electret film contains a polyolefin resin.

11. A bed sensor comprising the electronic device described in any one of claims 1 to 10.

12. A shelf sensor comprising the electronic device described in any one of claims 1 to 10.

Images