Piezoelectric cable unit and detection system

Abstract

The present invention provides a piezoelectric cable unit and a detection system that can simplify the configuration of a detection system. [Solution] The piezoelectric cable unit 1 comprises a plurality of piezoelectric cables 10a to 10c having an internal conductor 11, a polymer piezoelectric layer 12 in contact with the internal conductor 11 and surrounding the outer surface of the internal conductor 11, and an external conductor 13 in contact with the polymer piezoelectric layer 12 and surrounding the outer surface of the polymer piezoelectric layer 12; resistors 20a, 20b provided between the internal conductors 11 of the plurality of piezoelectric cables 10a to 10c to form a first circuit 41 in which the internal conductors 11 are electrically connected in series; and connecting conductors 30a, 30b provided between the external conductors 13 to form a second circuit 42 in which the external conductors 13 are electrically connected in series.

Description

Technical Field

[0001] The present invention relates to a piezoelectric cable unit and a detection system.

Background Art

[0002] A piezoelectric cable in which a piezoelectric element is disposed between an inner conductor and an outer conductor surrounding the inner conductor is known. When a force is applied to the outer peripheral surface of the piezoelectric cable, the polarization of the piezoelectric element generated can be detected via the inner conductor and the outer conductor. A detection system that detects the position of a force applied to a measurement object using a plurality of such piezoelectric cables is known, and such a detection system is described in Patent Document 1 below.

[0003] The detection system of Patent Document 1 below includes a plurality of piezoelectric cables provided along the plate material of a bed, and a detection unit that is electrically connected to each piezoelectric cable and to which the voltage output output from each piezoelectric cable is input. The detection unit detects where a force is applied to the bed based on the voltage output from each piezoelectric cable. According to such a detection system, it is said that it is possible to detect where a person is located on the bed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the detection system described in Patent Document 1, each piezoelectric cable is individually electrically connected to the detection unit. As a result, there are many cables electrically connecting the piezoelectric cables to the detection unit, and many inputs to which the voltage output of the detection unit is input. Therefore, there is a need to simplify the configuration of the detection system.

[0006] Therefore, the present invention aims to provide a piezoelectric cable unit and a detection system that can simplify the configuration of a detection system. [Means for solving the problem]

[0007] One aspect of the present invention is a piezoelectric cable unit characterized by comprising: a plurality of piezoelectric cables having an internal conductor, a polymer piezoelectric layer in contact with the internal conductor and surrounding the outer surface of the internal conductor, and an external conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer; a resistor provided between one of the internal conductors and the external conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series; and a connecting conductor provided between the other of the internal conductor and the external conductor, forming a second circuit in which the other conductor is electrically connected in series.

[0008] Aspect 2 of the present invention is a detection system comprising: a plurality of piezoelectric cables having an internal conductor, a polymer piezoelectric layer in contact with the internal conductor and surrounding the outer surface of the internal conductor, and an external conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer; a piezoelectric cable unit including a resistor provided between one of the internal conductors and the external conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series; a connecting conductor provided between the other of the internal conductor and the external conductor, forming a second circuit in which the other conductor is electrically connected in series; a ground wire electrically connected to the second circuit; and a detection unit, wherein the detection unit includes a first input section electrically connected to one end of the first circuit and receiving an electrical output output from the first circuit; and a detection section that detects the pressed piezoelectric cable based on the electrical output received from the first input section.

[0009] In embodiments 1 and 2, the piezoelectric cable unit is configured with a first circuit in which one of the inner conductors and the outer conductor is electrically connected in series via a resistor, and a second circuit in which the other of the inner and outer conductors is electrically connected in series via a connecting conductor. When the piezoelectric cable is pressed, a voltage is generated between the first circuit and the second circuit. The number of resistors located from the piezoelectric cable to one end of the first circuit differs for each piezoelectric cable. Therefore, if different piezoelectric cables are pressed, a difference in voltage will occur at one end of the first circuit. The pressed piezoelectric cable can be detected by the electrical output from one end of the first circuit. One end of the first circuit is a specific piezoelectric cable that includes the conductor located furthest to one end in the first circuit. Therefore, the detection unit for detecting the pressed piezoelectric cable only needs to be connected to at least the specific piezoelectric cable among the multiple piezoelectric cables of the piezoelectric cable unit. In embodiment 2, the second circuit is connected to the ground line, and the first input section of the detection unit is electrically connected to one end of the first circuit and receives the electrical output from the first circuit as input. The electrical output input to this first input unit is the electrical output from the specific piezoelectric cable mentioned above. The detection unit detects the pressed piezoelectric cable based on the electrical output input from this first input unit. Therefore, according to Embodiment 2, compared to the case where the detection unit is electrically connected to each piezoelectric cable, the number of cables electrically connecting the piezoelectric cable and the detection unit can be reduced, and the number of input units to which the electrical output is input in the detection unit can be reduced. Accordingly, Embodiments 1 and 2 can simplify the configuration of the detection system.

[0010] A third aspect of the present invention is a detection system according to aspect 2, wherein the detection unit further includes a second input unit to which an electrical output output from the first circuit is electrically connected to the other end of the first circuit and to which an electrical output output from the first circuit is input, and the detection unit detects the pressed piezoelectric cable based on the electrical outputs input from the first input unit and the second input unit.

[0011] According to embodiment 3, the accuracy of detecting a pressed piezoelectric cable can be improved.

[0012] Aspect 4 of the present invention is a detection system comprising: a plurality of piezoelectric cables having an internal conductor, a polymer piezoelectric layer in contact with the internal conductor and surrounding the outer surface of the internal conductor, and an external conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer; a piezoelectric cable unit including a resistor provided between one of the internal conductors and the external conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series; and a connecting conductor provided between the other of the internal conductor and the external conductor, forming a second circuit in which the other conductor is electrically connected in series; and a detection unit, wherein the detection unit includes a first input unit individually electrically connected to one end of the first circuit and the second circuit and receiving the electrical outputs output from the first circuit and the second circuit; and a detection unit that detects the pressed piezoelectric cable based on the electrical output received from the first input unit.

[0013] In Embodiment 4, similar to Embodiments 1 and 2, the piezoelectric cable unit is configured with the above-described first circuit and second circuit. In Embodiment 4, the first input section of the detection unit is electrically connected individually to one end of the first circuit and the second circuit, and receives the electrical outputs from the first circuit and the second circuit. In other words, the first input section is the aforementioned specific piezoelectric cable, which is one end of the piezoelectric cable unit, and receives the electrical output from that specific piezoelectric cable. The detection section of the detection unit then detects the pressed piezoelectric cable based on the electrical output received from the first input section. Therefore, according to Embodiment 4, compared to the case where the detection unit is electrically connected to each of the multiple piezoelectric cables, similar to Embodiment 2, the number of cables electrically connecting the piezoelectric cable and the detection unit can be reduced, and the number of input sections in the detection unit to which the electrical output is received can be reduced. Accordingly, according to Embodiment 4, the configuration of the detection system can be simplified.

[0014] Aspect 5 of the present invention is a detection system according to aspect 4, wherein the detection unit further includes a second input unit which is individually electrically connected to the other ends of the first circuit and the second circuit and to which the electrical outputs output from the first circuit and the second circuit are input, and the detection unit detects the pressed piezoelectric cable based on the electrical outputs input from the first input unit and the second input unit.

[0015] According to embodiment 5, the accuracy of detecting a pressed piezoelectric cable can be improved.

[0016] Aspect 6 of the present invention is a detection system according to any one of aspects 2 to 5, characterized in that the detection unit detects the pressed piezoelectric cable based on the period from when the electrical output reaches a first reference value until it reaches a second reference value that is higher than the first reference value.

[0017] Aspect 7 of the present invention is a detection system according to any one of aspects 2 to 6, characterized in that the electrical output is a voltage.

[0018] Aspect 8 of the present invention is a detection system according to any one of aspects 2 to 6, characterized in that the electrical output is electric charge.

[0019] Aspect 9 of the present invention is a detection system according to any one of aspects 2 to 8, characterized in that the detection unit detects the pressed piezoelectric cable using a learning model constructed by machine learning the electrical output.

[0020] According to embodiment 9, the accuracy of detecting a pressed piezoelectric cable can be improved, and this becomes more useful as the number of piezoelectric cables increases.

[0021] Aspect 10 of the present invention is a detection system according to any one of aspects 2 to 9, characterized in that each of the piezoelectric cables is arranged along a plane in the object to be measured, and the longitudinal directions of two or more of the piezoelectric cables are non-parallel to each other.

[0022] According to Aspect 10, it may be possible to detect where a force is applied on the plane of the object to be measured.

[0023] Aspect 11 of the present invention is the detection system according to any one of Aspects 2 to 9, characterized in that each of the piezoelectric cables is arranged along the curved surface of the object to be measured.

[0024] According to Aspect 11, it may be possible to detect where a force is applied on the curved surface of the object to be measured.

Advantages of the Invention

[0025] <000XX92>As described above, according to the present invention, there are provided a piezoelectric cable unit capable of realizing simplification of the configuration of the detection system, and a detection system.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram schematically showing the detection system according to the first embodiment. [Figure 2] It is a diagram showing the structure of the piezoelectric cable shown in FIG. 1. [Figure 3] It is a cross-sectional view of the piezoelectric cable. [Figure 4] It is a diagram showing an equivalent circuit of the piezoelectric cable unit. [Figure 5] It is a diagram for explaining the arrangement of the piezoelectric cable unit in the first embodiment. [Figure 6] It is a diagram showing an example of the voltage measured by the measurement unit when the piezoelectric cable located on the leftmost side in FIG. 4 is pressed from the outer peripheral surface. [Figure 7] It is a diagram showing, in the same manner as FIG. 6, an example of the voltage measured by the measurement unit when the piezoelectric cable located on the rightmost side in FIG. 4 is pressed from the outer peripheral surface. [Figure 8] It is a diagram showing, in the same manner as FIG. 6, an example of the voltage measured by the measurement unit when the piezoelectric cable located in the center in FIG. 4 is pressed from the outer peripheral surface. [Figure 9]Figure 4 shows an example of the electric charge measured at the measuring unit when the leftmost piezoelectric cable is pressed from its outer surface. [Figure 10] This figure, similar to Figure 9, shows an example of the electric charge measured at the measuring unit when the piezoelectric cable located on the far right in Figure 4 is pressed from its outer surface. [Figure 11] Figure 4 shows an example of the electric charge measured at the measuring unit when the piezoelectric cable located in the center is pressed from its outer surface, similar to Figure 9. [Figure 12] This figure shows the period including the rise of the charge input from the first input unit shown in Figure 9, and the period including the rise of the charge input from the first input unit shown in Figure 11. [Figure 13] This figure shows the detection system according to the fourth embodiment, similar to Figure 1. [Figure 14] This figure shows the equivalent circuit of the piezoelectric cable unit according to the fourth embodiment. [Figure 15] This diagram illustrates the arrangement of the piezoelectric cable unit in a modified example. [Figure 16] This diagram illustrates the arrangement of the piezoelectric cable unit in another modified example. [Modes for carrying out the invention]

[0027] Hereinafter, preferred embodiments of the piezoelectric cable unit and detection system according to the present invention will be described in detail with reference to the figures. The embodiments illustrated below are for the purpose of facilitating understanding of the present invention and are not intended to limit the interpretation of the present invention. The present invention can be modified and improved from the following embodiments within the scope of the claims without departing from the spirit thereof. Note that for ease of understanding, the scale of each figure may differ from the scale described in the following description.

[0028] (First Embodiment) Figure 1 is a schematic diagram showing the detection system according to this embodiment. As shown in Figure 1, the detection system 100 of this embodiment mainly comprises a piezoelectric cable unit 1, amplifiers 45 and 46, a detection unit 50, a memory 60, and a monitor 70. The piezoelectric cable unit 1 of this embodiment includes three piezoelectric cables 10a, 10b, and 10c, two resistors 20a and 20b, and two connecting conductors 30a and 30b.

[0029] First, the piezoelectric cables 10a to 10c will be described. In this embodiment, the piezoelectric cables 10a to 10c have generally similar configurations and are generally the same length. Therefore, only one piezoelectric cable 10a will be described. Figure 2 is a diagram showing the structure of the piezoelectric cable 10a shown in Figure 1, and Figure 3 is a cross-sectional view of the piezoelectric cable 10a. As shown in Figures 2 and 3, the piezoelectric cable 10a of this embodiment includes an inner conductor 11, a polymer piezoelectric layer 12, an outer conductor 13, and a protective layer 15. Note that the protective layer 15 is omitted in Figure 1.

[0030] The internal conductor 11 is a linear conductor. The internal conductor 11 is not particularly limited as long as it is a conductor, but examples include conductors made of copper, aluminum, tin-plated soft copper alloy, etc. In this embodiment, the internal conductor 11 is a stranded wire in which multiple conductors are twisted together. However, the internal conductor 11 may also be a conductor made of a single conductive wire.

[0031] The polymer piezoelectric layer 12 is a layer that is in contact with the internal conductor 11 and surrounds the outer surface of the internal conductor 11. The polymer piezoelectric layer 12 is made of a polymer that exhibits piezoelectric properties, and examples of such polymers include polyvinylidene fluoride (PVDF), polylactic acid, polyurea, etc. The polymer piezoelectric layer 12 in this embodiment is a cylindrical member formed by extrusion molding or the like, and the outer shape of the cross-section is approximately circular. The polymer piezoelectric layer 12 may also be configured by winding a tape-like film made of polymer piezoelectric material around the internal conductor 11, in which case the film may be wound in a spiral or longitudinal pattern.

[0032] The outer conductor 13 is a conductor that is in contact with the polymer piezoelectric layer 12 and surrounds the outer surface of the polymer piezoelectric layer 12. The outer conductor 13 is not particularly limited as long as it is a conductor, but for example, it could be a conductor similar to the inner conductor 11. In this embodiment, the outer conductor 13 is configured with multiple wires wound spirally in the same direction. The outer conductor 13 may also be a braided wire made of multiple wires.

[0033] The protective layer 15 of this embodiment includes an insulating layer 16, a shielding layer 17, and a jacket layer 18. The insulating layer 16 is an insulator that covers the outer surface of the outer conductor 13. The insulating layer 16 of this embodiment consists of an inner insulating layer 16a and an outer insulating layer 16b.

[0034] The inner insulating layer 16a consists of a tape-shaped film 16at made of an insulating resin, and the film 16at is spirally wound on the outer surface of the outer conductor 13. No adhesive layer is provided on any surface of the film 16at, and the inner insulating layer 16a is not adhered to the outer conductor 13. The material of the film 16at is not particularly limited, but examples include insulating resins such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyvinyl chloride, polypropylene, polyetheretherketone, polyetherimide, and polyphenylene sulfide. An adhesive layer may be provided on one surface of the film 16at.

[0035] The outer insulating layer 16b is the outermost layer of the insulating layer 16 and consists of a tape-shaped film 16bt made of an insulating resin and an adhesive layer 16ba provided on one surface of the film 16bt. The film 16bt is wound spirally on the outer surface of the inner insulating layer 16a with the adhesive layer 16ba facing the inner insulating layer 16a. Therefore, the adhesive layer 16ba is in contact with the inner insulating layer 16a, and the film 16bt is bonded to the inner insulating layer 16a by the adhesive layer 16ba. In this embodiment, the film 16bt of the outer insulating layer 16b is wound in the same direction as the film 16at of the inner insulating layer 16a, but it may be wound in the opposite direction to the film 16at. Also, at least one of the film 16at and the film 16bt may be wound longitudinally. The material of the film 16bt is not particularly limited, but for example, it can be the same material as the film 16at. The adhesive used in the adhesive layer 16ba is not particularly limited, but examples include acrylic adhesives, polyester adhesives, polyamide adhesives, and ethylene vinyl acetate copolymer (EVA) adhesives.

[0036] Furthermore, the adhesive layer 16ba may be omitted. Alternatively, one of the inner insulating layer 16a and the outer insulating layer 16b may be omitted, and the insulating layer 16 may consist of either the inner insulating layer 16a or the outer insulating layer 16b.

[0037] The shield layer 17 is a conductor that surrounds the outer surface of the insulator layer 16. The shield layer 17 is not particularly limited as long as it is made of a conductor, but for example, it is made of a conductor similar to the outer conductor 13. In this embodiment, the shield layer 17 is configured in which multiple conductors are wound spirally in the same direction. The shield layer 17 may also be a braided wire in which multiple conductors are woven together.

[0038] The jacket layer 18 is a layer that covers the outer surface of the shield layer 17. In this embodiment, the jacket layer 18 has an inner jacket layer 18a and an outer jacket layer 18b.

[0039] The inner jacket layer 18a consists of a tape-shaped film 18at made of resin, and the film 18at is wound spirally on the outer surface of the shield layer 17. No adhesive layer is provided on any surface of the film 18at, and the inner jacket layer 18a is not adhered to the shield layer 17. The material of the film 18at is not particularly limited, but for example, it can be the same material as the film 16at. An adhesive layer may be provided on one surface of the film 18at.

[0040] The outer jacket layer 18b is the outermost layer of the jacket layer 18 and is located on the outermost periphery of the piezoelectric cable 10a. The outer jacket layer 18b consists of a tape-shaped film 18bt made of resin and an adhesive layer 18ba provided on one surface of the film 18bt. The film 18bt is wound spirally on the outer circumferential surface of the inner jacket layer 18a with the adhesive layer 18ba facing the inner jacket layer 18a. Therefore, the adhesive layer 18ba is in contact with the inner jacket layer 18a, and the film 18bt is adhered to the inner jacket layer 18a by the adhesive layer 18ba. In this embodiment, the film 18bt of the outer jacket layer 18b is wound in the same direction as the film 18at of the inner jacket layer 18a, but it may be wound in the opposite direction to the film 16at. Also, at least one of the film 18at and the film 18bt may be wound longitudinally. The material of film 18bt is not particularly limited, but for example, it can be a material similar to that of film 18at. The adhesive used in adhesive layer 18ba is not particularly limited, but for example, it can be an adhesive similar to that used in adhesive layer 18ba.

[0041] The inner jacket layer 18a may be omitted, and the jacket layer 18 may be composed of the outer jacket layer 18b.

[0042] In piezoelectric cables 10a to 10c with this configuration, the piezoelectric cables 10a to 10c are pressed from the outer surface, causing the polymer piezoelectric layer 12 to deform, which in turn causes polarization in the polymer piezoelectric layer 12 and generates a voltage between the inner conductor 11 and the outer conductor 13.

[0043] Returning to Figure 1, resistors 20a and 20b will be described. In this embodiment, resistor 20a is provided between the internal conductor 11 of piezoelectric cable 10a and the internal conductor 11 of piezoelectric cable 10b, and these internal conductors 11 are electrically connected in series via resistor 20a. Specifically, resistor 20a is electrically connected to the internal conductor 11 at one end of piezoelectric cable 10a and the internal conductor 11 at one end of piezoelectric cable 10b. Resistor 20b is provided between the internal conductor 11 of piezoelectric cable 10b and the internal conductor 11 of piezoelectric cable 10c, and these internal conductors 11 are electrically connected in series via resistor 20b. Specifically, resistor 20b is electrically connected to the internal conductor 11 at the other end of piezoelectric cable 10b and the internal conductor 11 at one end of piezoelectric cable 10c. With these resistors 20a and 20b, a first circuit 41 is formed in which the internal conductors 11 of the three piezoelectric cables 10a to 10c are electrically connected in series. Furthermore, as long as the first circuit 41 is formed, the connection positions between the resistors 20a and 20b and the internal conductor 11 are not restricted.

[0044] Examples of resistors 20a and 20b include leaded resistors, chip resistors, wound resistors, and conductors made of high-resistance materials. Examples of high-resistance materials include tyranno fiber, aramid fiber, carbon fiber, conductive silicone rubber, glass fiber, and nickel-chromium alloy. The resistance values ​​of resistors 20a and 20b are preferably between 1 kΩ and 10 GΩ, and more preferably between 1 MΩ and 1 GΩ. In this embodiment, the resistance values ​​of resistors 20a and 20b are approximately the same, 1 GΩ, but the resistance values ​​of resistors 20a and 20b may differ. For example, the resistance value of a resistor closer to one end of the first circuit 41 may be higher, and the resistance value of a resistor closer to one end of the first circuit 41 may be lower. The sum of the resistance values ​​of resistors 20a and 20b is preferably between 10 kΩ and 100 GΩ.

[0045] Next, the connecting conductors 30a and 30b will be described. In this embodiment, the connecting conductors 30a and 30b are electric wires. The connecting conductor 30a is provided between the outer conductor 13 of the piezoelectric cable 10a and the outer conductor 13 of the piezoelectric cable 10b, and these outer conductors 13 are electrically connected in series via the connecting conductor 30a. Specifically, the connecting conductor 30a is electrically connected to the outer conductor 13 at one end of the piezoelectric cable 10a and to the outer conductor 13 at one end of the piezoelectric cable 10b. The connecting conductor 30b is provided between the outer conductor 13 of the piezoelectric cable 10b and the outer conductor 13 of the piezoelectric cable 10c, and these inner conductors 11 are electrically connected in series via the connecting conductor 30b. Specifically, the connecting conductor 30b is electrically connected to the inner conductor 11 at the other end of the piezoelectric cable 10b and to the inner conductor 11 at one end of the piezoelectric cable 10c. These connecting conductors 30a and 30b form a second circuit 42 in which the internal conductors 11 of the three piezoelectric cables 10a to 10c are electrically connected in series. However, as long as the second circuit 42 is formed, the configuration of the connecting conductors 30a and 30b, and the connection positions between the connecting conductors 30a and 30b and the internal conductors 11, are not restricted. For example, the connecting conductors 30a and 30b may be plate-shaped or cylindrical conductors.

[0046] Although not shown in the diagrams, an insulating layer may be located between the resistor 20a and the connecting conductor 30a, with the outer circumference of the resistor 20a being surrounded by this insulating layer, and a protective layer may be located on the outer circumference side of the connecting conductor 30a, with the outer circumference of both the connecting conductor 30a and the insulating layer being surrounded by this protective layer. Alternatively, an insulating layer may be located between the resistor 20b and the connecting conductor 30b, with the outer circumference of the resistor 20b being surrounded by this insulating layer, and a protective layer may be located on the outer circumference side of the connecting conductor 30b, with the outer circumference of both the connecting conductor 30b and the insulating layer being surrounded by this protective layer. Examples of materials for such insulating and protective layers include insulating resins.

[0047] Here, the portion of the piezoelectric cable 10a to 10c consisting of the inner conductor 11, the polymer piezoelectric layer 12, and the outer conductor 13 can be considered as a capacitor in an electrical circuit, where one electrode of the capacitor is the inner conductor 11 and the other electrode is the outer conductor 13. Figure 4 is a diagram showing the equivalent circuit of the piezoelectric cable unit 1. As shown in Figure 4, the equivalent circuit 43 of the piezoelectric cable unit 1 is composed of piezoelectric cables 10a to 10c, resistors 20a and 20b, and connecting conductors 30a and 30b, and is a circuit in which three capacitors are connected in parallel. When piezoelectric cable 10a is pressed, it acts as a capacitor and becomes a power source; when piezoelectric cable 10b is pressed, it acts as a capacitor and becomes a power source; and when piezoelectric cable 10c is pressed, it acts as a capacitor and becomes a power source. Therefore, when at least one of the piezoelectric cables 10a to 10c is pressed, a voltage is generated between the first circuit 41 and the second circuit 42, the equivalent circuit 43 becomes a so-called RC circuit, and current flows through the equivalent circuit 43.

[0048] Figure 5 illustrates the arrangement of the piezoelectric cable unit 1 in this embodiment. As shown in Figure 5, the piezoelectric cable unit 1 in this embodiment is placed on the seat surface 111 of the bench 110, which is the object to be measured. The seat surface 111 is a long plane in the left-right direction, and the piezoelectric cables 10a to 10c are arranged along the seat surface 111 such that the longitudinal directions of the piezoelectric cables 10a to 10c are aligned with the longitudinal direction of the seat surface 111 and are aligned in that longitudinal direction. The piezoelectric cables 10a to 10c are generally located on the same straight line, but they do not have to be located on the same straight line. The piezoelectric cable unit 1 is also covered by a protective sheet 112 made of resin. As a result, the piezoelectric cables 10a to 10c, resistors 20a and 20b, and connecting conductors 30a and 30b are covered by the protective sheet 112. In the bench 110 in which the piezoelectric cable unit 1 is arranged in this way, the piezoelectric cable that is pressed changes according to the seating position of the person. In Figure 5, the protective sheet 112 is shown by a dotted line, and the resistors 20a and 20b, and the connecting conductors 30a and 30b are omitted from the description.

[0049] Returning to Figure 1, let's explain the detection unit 50.

[0050] The detection unit 50 consists of, for example, an integrated circuit such as a microcontroller, IC (Integrated Circuit), LSI (Large-scale Integrated Circuit), or ASIC (Application Specific Integrated Circuit), or an NC (Numerical Control) device. The detection unit 50 may or may not use a machine learning machine. The detection unit 50 is electrically connected to the piezoelectric cable unit 1, the memory 60, and the monitor 70.

[0051] The memory 60 is configured to store information and to be readable. The memory 60 is, for example, a non-transitory recording medium, and semiconductor recording media such as RAM (Random Access Memory) or ROM (Read Only Memory) are preferred, but any type of recording medium such as optical recording media or magnetic recording media may be included. Note that "non-transitory" recording media include all computer-readable recording media except transient propagation signals, and do not exclude volatile recording media. The memory 60 and the detection unit 50 may be provided in a single package. The memory 60 stores various programs for controlling some of the configurations of the detection unit 50 and generating information, as well as data necessary for generating information. The detection unit 50 reads the programs and information stored in the memory 60. The memory 60 also stores information, etc., based on instructions from the detection unit 50.

[0052] The detection unit 50 of this embodiment includes a first input unit 51, a second input unit 52, a measurement unit 53, a detection unit 54, and an output unit 55, each of which is electrically connected via a bus line.

[0053] The first input unit 51 of this embodiment has terminals 51a and 51b. Terminal 51a is electrically connected to the internal conductor 11 of the piezoelectric cable 10a, which is one end of the first circuit 41, via amplifier 45, and terminal 51b is electrically connected to the external conductor 13 of the piezoelectric cable 10a, which is one end of the second circuit 42, via amplifier 45. In other words, the first input unit 51 is electrically connected to one end of the first circuit 41 and one end of the second circuit 42 individually. These terminals 51a and 51b of the first input unit 51 are electrically connected to the measuring unit 53 individually.

[0054] The second input unit 52 of this embodiment has terminals 52a and 52b. Terminal 52a is electrically connected to the inner conductor 11 of the piezoelectric cable 10c, which is the other end of the first circuit 41, via amplifier 46, and terminal 52b is electrically connected to the outer conductor 13 of the piezoelectric cable 10c, which is the other end of the second circuit 42, via amplifier 46. In other words, the second input unit 52 is electrically connected to the other ends of the first circuit 41 and the second circuit 42 individually. These terminals 52a and 52b of the second input unit 52 are electrically connected to the measuring unit 53 individually.

[0055] In this embodiment, the measuring unit 53 is electrically connected to one end of the first circuit 41 and the second circuit 42 via the first input unit 51 and amplifier 45, and electrically connected to the other ends of the first circuit 41 and the second circuit 42 via the second input unit 52 and amplifier 46. When a force is applied to at least one of the piezoelectric cables 10a to 10c, the voltages output from one end of the first circuit 41 and the second circuit 42, and the voltages output from the other ends of the first circuit 41 and the second circuit 42 are amplified by amplifiers 45 and 46 and input to the measuring unit 53 as electrical outputs from the piezoelectric cable unit 1. In other words, the voltages as electrical outputs from one end of the first circuit 41 and the second circuit 42 are amplified and input to the first input unit 51, and the voltages as electrical outputs from the other ends of the first circuit 41 and the second circuit 42 are amplified and input to the second input unit 52. One end of the first circuit 41 and the second circuit 42 are the internal conductor 11 and the external conductor 13 of the piezoelectric cable 10a, and the other ends of the first circuit 41 and the second circuit 42 are the internal conductor 11 and the external conductor 13 of the piezoelectric cable 10c. The measuring unit 53 is a voltmeter that measures the voltages input from the first input unit 51 and the second input unit 52 in this manner. The measuring unit 53 outputs a signal related to the measured voltage, and this signal is input to the detection unit 54 via the bus line.

[0056] The detection unit 54 detects the pressed piezoelectric cable. As described above, in the equivalent circuit 43 shown in Figure 4, when force is applied to the piezoelectric cables 10a to 10c, they change from capacitors to power sources, and a voltage is generated between the first circuit 41 and the second circuit 42. One end of the first circuit 41 is the internal conductor 11 of the piezoelectric cable 10a. There is one resistor located from the internal conductor 11 of the piezoelectric cable 10b, which is part of the first circuit 41, to one end of the first circuit 41. There are two resistors located from the internal conductor 11 of the piezoelectric cable 10c, which is the other end of the first circuit 41, to one end of the first circuit 41. In other words, the number of resistors located from the piezoelectric cables 10b and 10c to one end of the first circuit 41 differs for each piezoelectric cable 10b and 10c. Also, the number of resistors located from the piezoelectric cables 10a and 10b to the other end of the first circuit 41 differs for each piezoelectric cable 10a and 10b. The first input unit 51 is electrically connected to the piezoelectric cable 10a, which is one end of the first circuit 41 and the second circuit 42, and the second input unit 52 is electrically connected to the piezoelectric cable 10c, which is the other end of the first circuit 41 and the second circuit 42. Therefore, when the piezoelectric cable being pressed changes, the voltage input to the first input unit 51 and the voltage input to the second input unit 52 change.

[0057] Figure 6 shows an example of the voltage measured by the measuring unit 53 when the piezoelectric cable 10a, located on the far left in Figure 4, is pressed from its outer surface. It is a diagram showing an example of the voltage when the piezoelectric cable 10a is pressed from its outer surface with a predetermined force for a predetermined period of time. In Figure 6, the voltage V1 input from the first input unit 51 and the voltage V2 input from the second input unit 52 are shown side by side. The polymer piezoelectric layer 12 of the piezoelectric cables 10a to 10c undergoes polarization due to the piezoelectric effect when deformed, and the polarization disappears after deformation. Therefore, a voltage is generated between the inner conductor 11 and the outer conductor 13 of the piezoelectric cable 10a at the moment force is applied to it. During the period when a constant force is applied to the piezoelectric cable 10a, there is no voltage between the inner conductor 11 and the outer conductor 13. A voltage is generated between the inner conductor 11 and the outer conductor 13 at the moment the force applied to the piezoelectric cable 10a is stopped, and thereafter, there is no voltage between the inner conductor 11 and the outer conductor 13.

[0058] The piezoelectric cable 10a is one end of the first circuit 41 and the second circuit 42, and there are zero resistors between the first input unit 51 and the piezoelectric cable 10a. Therefore, as shown in Figure 6, the waveform of the voltage V1 input from the first input unit 51 has a waveform with a positive peak and a negative peak. However, there are two resistors between the second input unit 52 and the piezoelectric cable 10a. Therefore, the voltage V2 input from the second input unit 52 is smaller than the voltage V1, and the waveform of the voltage V1 in this example is a waveform that is approximately zero and constant.

[0059] Figure 7 shows an example of the voltage measured by the measuring unit 53 when the piezoelectric cable 10c, located on the far right in Figure 4, is pressed from its outer surface, similar to Figure 6. The force and duration of pressing on the piezoelectric cable 10c are approximately the same as the force and duration of pressing on the piezoelectric cable 10a when the voltage shown in Figure 6 was measured. There are two resistors located between the first input unit 51 and the piezoelectric cable 10c, and zero resistors located between the second input unit 52 and the piezoelectric cable 10c. Therefore, the waveform of the voltage V1 input from the first input unit 51 is approximately zero and constant. The waveform of the voltage V2 input from the second input unit 52 has a positive peak and a negative peak, and is approximately the same as the waveform of voltage V1 shown in Figure 6.

[0060] Figure 8 shows an example of the voltage measured by the measuring unit 53 when the piezoelectric cable 10b, located in the center of Figure 4, is pressed from its outer surface, similar to Figure 6. The force and duration of pressing on the piezoelectric cable 10c are approximately the same as the force and duration of pressing on the piezoelectric cable 10a when the voltage shown in Figure 6 was measured. There is one resistor between the first input unit 51 and the piezoelectric cable 10b, and one resistor between the second input unit 52 and the piezoelectric cable 10b. Therefore, the waveform of the voltage V1 input from the first input unit 51 and the waveform of the voltage V2 input from the second input unit 52 are approximately the same, and are waveforms having a positive peak and a negative peak. The absolute value of the peak is smaller than the absolute value of the peak of voltage V1 shown in Figure 6 and the absolute value of the peak of voltage V2 shown in Figure 7.

[0061] Thus, when the piezoelectric cable being pressed changes, the voltage V1 input to the first input unit 51 and the voltage V2 input to the second input unit 52 change. In this embodiment, the detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 measured by the measurement unit 53, that is, the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. More specifically, the detection unit 54 detects the pressed piezoelectric cable based on the intensity of the voltages V1 and V2 input from the first input unit 51 and the second input unit 52.

[0062] For example, if the maximum value of voltage V1 is greater than or equal to the first threshold TL1, and the maximum value of voltage V2 is less than or equal to the second threshold TL2 (which is less than the first threshold TL1), the detection unit 54 detects that the piezoelectric cable 10a has been pressed. Also, if the maximum values ​​of both voltage V1 and voltage V2 are less than the first threshold TL1 and greater than or equal to the second threshold TL2, the detection unit 54 detects that the piezoelectric cable 10b has been pressed. If the maximum value of voltage V1 is less than the second threshold TL2, and the maximum value of voltage V2 is greater than or equal to the first threshold TL1, the detection unit 54 detects that the piezoelectric cable 10c has been pressed. Note that the method for detecting a pressed piezoelectric cable based on the intensity of voltages V1 and V2 is not limited to the above method. For example, the detection unit 54 may detect a pressed piezoelectric cable based on the ratio V1 / V2, which is the ratio of the maximum value of voltage V1 to the maximum value of voltage V2. When piezoelectric cable 10a is pressed, the ratio V1 / V2 is greater than when piezoelectric cable 10b is pressed, and when piezoelectric cable 10c is pressed, the ratio V1 / V2 is less than when piezoelectric cable 10b is pressed. For this reason, for example, a first threshold value is set that is less than the ratio V1 / V2 when piezoelectric cable 10a is pressed and greater than the ratio V1 / V2 when piezoelectric cable 10b is pressed, and a second threshold value is set that is less than the ratio V1 / V2 when piezoelectric cable 10b is pressed and greater than the ratio V1 / V2 when piezoelectric cable 10c is pressed. The detection unit 54 then detects that the piezoelectric cable 10a is pressed if the ratio V1 / V2 is greater than or equal to the first threshold, detects that the piezoelectric cable 10b is pressed if the ratio V1 / V2 is less than the first threshold and greater than or equal to the second threshold, and detects that the piezoelectric cable 10c is pressed if the ratio V1 / V2 is less than the second threshold. The detection unit 54 may also detect the pressed piezoelectric cable based on the ratio V1 / V2 and the ratio V2 / V1 of the maximum value of voltage V2 to the maximum value of voltage V1.

[0063] The detection unit 54 outputs a signal related to the detection result, and this signal is output to the monitor 70 from the output unit 55 via the bus line.

[0064] The monitor 70 displays information corresponding to the detection result signal input from the output unit 55, for example. Note that the monitor 70 is not an essential component of the detection system 100.

[0065] As described above, the piezoelectric cable unit 1 of this embodiment is placed on the seat surface 111 of the bench 110, which is the object to be measured. Therefore, the detection system 100 of this embodiment can detect, for example, where on the bench 110 a person is seated by detecting the piezoelectric cable pressed by the detection unit 54.

[0066] As described above, the piezoelectric cable unit 1 of this embodiment comprises three piezoelectric cables 10a to 10c, two resistors 20a and 20b, and two connecting conductors 30a and 30b. Each piezoelectric cable 10a to 10c has an internal conductor 11, a polymer piezoelectric layer 12 that is in contact with the internal conductor 11 and surrounds the outer surface of the internal conductor 11, and an external conductor 13 that is in contact with the polymer piezoelectric layer 12 and surrounds the outer surface of the polymer piezoelectric layer 12. The resistors 20a and 20b are provided between the internal conductors 11 in the piezoelectric cables 10a to 10c, forming a first circuit 41 in which the internal conductors 11 are electrically connected in series. The connecting conductors 30a and 30b are provided between the external conductors 13 in the piezoelectric cables 10a to 10c, forming a second circuit 42 in which the external conductors 13 are electrically connected in series.

[0067] In the piezoelectric cable unit 1 of this embodiment, a first circuit 41 is configured in which the internal conductor 11 is electrically connected in series, and a second circuit 42 is configured in which the external conductor 13 is electrically connected in series. When the piezoelectric cable is pressed, a voltage is generated between the first circuit 41 and the second circuit 42. The number of resistors located from the piezoelectric cable to one end of the first circuit 41 differs for each piezoelectric cable. Therefore, if different piezoelectric cables are pressed, a difference in voltage will occur at one end of the first circuit 41. The pressed piezoelectric cable can be detected by the electrical output from one end of the first circuit 41. One end of the first circuit 41 is the piezoelectric cable 10a, which includes the internal conductor 11 located closest to one end in the first circuit 41. Therefore, the detection unit 50 that detects the pressed piezoelectric cable only needs to be connected to at least one of the multiple piezoelectric cables 10a to 10c of the piezoelectric cable unit 1. Thus, the piezoelectric cable unit 1 of this embodiment can simplify the configuration of the detection system.

[0068] The detection system 100 of this embodiment comprises the piezoelectric cable unit 1 described above, and a detection unit 50 including a first input unit 51, a second input unit 52, and a detection unit 54. The first input unit 51 is electrically connected individually to one end of the first circuit 41 and the second circuit 42, and receives the voltage V1 output from the first circuit 41 and the second circuit 42. The voltage V1 input to the first input unit 51 is the voltage output from the piezoelectric cable 10a, which is one end of the first circuit 41 and the second circuit 42. The second input unit 52 is electrically connected individually to the other end of the first circuit 41 and the second circuit 42, and receives the voltage V2 output from the first circuit 41 and the second circuit 42. The voltage V2 input to the second input unit 52 is the voltage output from the piezoelectric cable 10c, which is the other end of the first circuit 41 and the second circuit 42. The detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. Therefore, according to the detection system 100 of this embodiment, compared to the case where the detection unit 50 is electrically connected to each of the piezoelectric cables 10a to 10c, the number of cables electrically connecting the piezoelectric cables 10a to 10c and the detection unit 50 can be reduced, and the number of input units to which the electrical output of the detection unit 50 is input can be reduced. Accordingly, according to the detection system 100 of this embodiment, the configuration of the detection system 100 can be simplified.

[0069] In this embodiment, the detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. However, the detection unit 54 may also detect the pressed piezoelectric cable based on the voltage V1 input from the first input unit 51. In this case, for example, the resistance values ​​of resistors 20a and 20b are adjusted so that the voltage V1 when piezoelectric cable 10a is pressed, the voltage V1 when piezoelectric cable 10b is pressed, and the voltage V1 when piezoelectric cable 10c is pressed are greater than zero, and these voltages V1 decrease in that order. Such a configuration can further simplify the configuration of the detection system 100. Furthermore, when the detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52, as in this embodiment, the accuracy of detecting the pressed piezoelectric cable can be improved.

[0070] Here, if the sum of the resistance values ​​of resistors 20a and 20b in the first circuit 41 is greater than 100 GΩ, the output due to the piezoelectric effect is excessively attenuated by resistors 20a and 20b, causing the voltages V1 and V2 input from the first input section 51 and the second input section 52 to become small, making detection difficult. Also, if the sum of the resistance values ​​of resistors 20a and 20b is less than 10 kΩ, the changes in voltages V1 and V2 due to changes in the pressed piezoelectric cable become small, making it difficult to detect the pressed piezoelectric cable using voltages V1 and V2. In this embodiment, the sum of the resistance values ​​of resistors 20a and 20b is 2 GΩ, which is between 10 kΩ and 100 GΩ. Therefore, the detection system 100 of this embodiment can suppress the difficulty in detecting the pressed piezoelectric cable. From the viewpoint of making it easier to detect the pressed piezoelectric cable, it is preferable that the sum of the resistance values ​​of resistors 20a and 20b is between 1 MΩ and 1 GΩ.

[0071] (Second Embodiment) Next, a second embodiment of the present invention will be described in detail. Note that components identical or equivalent to those in the first embodiment are denoted by the same reference numerals unless otherwise specified, and redundant descriptions will be omitted.

[0072] The detection system 100 of this embodiment differs from the detection system 100 of the first embodiment in that the detection unit 54 detects a pressed piezoelectric cable based on the electric charge as an electrical output input from the first input unit 51 and the second input unit 52.

[0073] Here, the integral of the voltage is approximately equal to the charge. Therefore, the measuring unit 53 in this embodiment measures the charge by integrating the voltages input from the first input unit 51 and the second input unit 52.

[0074] Figure 9 shows an example of the charge measured by the measuring unit 53 when the piezoelectric cable 10a, located on the far left in Figure 4, is pressed from its outer surface. It also shows an example of charges Q1 and Q2 obtained by integrating the voltages V1 and V2 shown in Figure 6. In Figure 9, the charge Q1 obtained by integrating the voltage V1 input from the first input unit 51 and the charge Q2 obtained by integrating the voltage V2 input from the second input unit 52 are shown side by side. As shown in Figure 9, the charge Q1 input from the first input unit 51 is approximately constant during the period when the piezoelectric cable 10a is pressed, and close to zero during the period when the piezoelectric cable 10a is not pressed. The charge Q2 input from the second input unit 52 is close to zero during both the period when the piezoelectric cable 10a is pressed and the period when it is not pressed. For most of the period when the piezoelectric cable 10a is pressed, the charge Q1 is greater than the charge Q2, and the maximum value of the charge Q1 is greater than the maximum value of the charge Q2.

[0075] Figure 10 is a diagram similar to Figure 9, showing an example of the charge measured by the measuring unit 53 when the piezoelectric cable 10c, located on the far right in Figure 4, is pressed from its outer surface. It also shows an example of charges Q1 and Q2 obtained by integrating the voltages V1 and V2 shown in Figure 7. As shown in Figure 10, the charge Q1 input from the first input unit 51 is close to zero during the period when the piezoelectric cable 10c is pressed and the period when it is not pressed. The waveform of the charge Q2 input from the second input unit 52 is roughly the same as the waveform of charge Q1 shown in Figure 9. This charge Q2 is roughly constant during the period when the piezoelectric cable 10c is pressed, and close to zero during the period when the piezoelectric cable 10c is not pressed. Furthermore, for most of the period when the piezoelectric cable 10c is pressed, the charge Q2 is greater than the charge Q1, and the maximum value of charge Q2 is greater than the maximum value of charge Q1.

[0076] Figure 11 is a diagram similar to Figure 9, showing an example of the charge measured by the measuring unit 53 when the piezoelectric cable 10b, located in the center in Figure 4, is pressed from its outer surface. It also shows an example of charges Q1 and Q2 obtained by integrating the voltages V1 and V2 shown in Figure 8. As shown in Figure 11, the waveform of charge Q1 input from the first input unit 51 is approximately the same as the waveform of charge Q2 input from the second input unit 52. Charges Q1 and Q2 are approximately constant during the period when the piezoelectric cable 10b is pressed, and close to zero during the period when the piezoelectric cable 10b is not pressed. The maximum values ​​of charges Q1 and Q2 are smaller than the maximum value of charge Q1 shown in Figure 9 and the maximum value of charge Q2 shown in Figure 10.

[0077] Thus, when the piezoelectric cable being pressed changes, the charge Q1 input to the first input unit 51 and the charge Q2 input to the second input unit 52 change. The detection unit 54 in this embodiment detects the pressed piezoelectric cable based on the charges Q1 and Q2 measured by the measurement unit 53, that is, the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52. More specifically, the detection unit 54 detects the pressed piezoelectric cable based on the intensity of the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52.

[0078] For example, if the maximum value of charge Q1 is greater than or equal to the first threshold TL11, and the maximum value of charge Q2 is less than or equal to the second threshold TL12 (which is less than the first threshold TL11), the detection unit 54 detects that the piezoelectric cable 10a has been pressed. Also, if the maximum values ​​of both charge Q1 and charge Q2 are less than the first threshold TL11 and greater than or equal to the second threshold TL12, the detection unit 54 detects that the piezoelectric cable 10b has been pressed. If the maximum value of charge Q1 is less than the second threshold TL12, and the maximum value of charge Q2 is greater than or equal to the first threshold TL11, the detection unit 54 detects that the piezoelectric cable 10c has been pressed. Note that the method for detecting a pressed piezoelectric cable based on the intensity of charges Q1 and Q2 is not limited to the above method. For example, the detection unit 54 may detect a pressed piezoelectric cable based on the ratio Q1 / Q2, which is the ratio of the maximum value of charge Q1 to the maximum value of charge Q2. When piezoelectric cable 10a is pressed, the ratio Q1 / Q2 is greater than when piezoelectric cable 10b is pressed, and when piezoelectric cable 10c is pressed, the ratio Q1 / Q2 is smaller than when piezoelectric cable 10b is pressed. For this reason, for example, a first threshold is set that is smaller than the ratio Q1 / Q2 when piezoelectric cable 10a is pressed and greater than the ratio Q1 / Q2 when piezoelectric cable 10b is pressed, and a second threshold is set that is smaller than the ratio Q1 / Q2 when piezoelectric cable 10b is pressed and greater than the ratio Q1 / Q2 when piezoelectric cable 10c is pressed. The detection unit 54 then detects that the piezoelectric cable 10a is pressed if the ratio Q1 / Q2 is greater than or equal to the first threshold, detects that the piezoelectric cable 10b is pressed if the ratio Q1 / Q2 is less than the first threshold but greater than or equal to the second threshold, and detects that the piezoelectric cable 10c is pressed if the ratio Q1 / Q2 is less than the second threshold. The detection unit 54 may also detect the pressed piezoelectric cable based on the ratio Q1 / Q2 and the ratio Q2 / Q1 of the maximum value of charge Q1 to the maximum value of charge Q2.

[0079] According to the detection system 100 of this embodiment, the configuration of the detection system 100 can be simplified in the same way as the detection system 100 of the first embodiment.

[0080] In this embodiment, the measurement unit 53 measured charges Q1 and Q2 by integrating voltages V1 and V2. However, the method for measuring charges Q1 and Q2 is not limited; for example, the measurement unit 53 may be a coulomb meter.

[0081] The detection unit 54 may also detect the pressed piezoelectric cable based on the charge Q1 input from the first input unit 51. In this case, as described in the first embodiment, for example, the resistance values ​​of resistors 20a and 20b are adjusted so that the voltage V1 when piezoelectric cable 10a is pressed, the voltage V1 when piezoelectric cable 10b is pressed, and the voltage V1 when piezoelectric cable 10c is pressed become greater than zero, and these voltages V1 decrease in that order. With such a configuration, the configuration of the detection system 100 can be further simplified. Furthermore, when the detection unit 54 detects the pressed piezoelectric cable based on the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52, as in this embodiment, the accuracy of detecting the pressed piezoelectric cable can be improved.

[0082] (Third embodiment) Next, a third embodiment of the present invention will be described in detail. Note that components identical or equivalent to those in the first embodiment are denoted by the same reference numerals unless otherwise specified, and redundant descriptions will be omitted.

[0083] The detection system 100 of this embodiment differs from the detection system 100 of the first embodiment in that the detection unit 54 detects the pressed piezoelectric cable based on the rising edges of charges Q1 and Q2 input from the first input unit 51 and the second input unit 52.

[0084] It is known that the time constant of an RC circuit can be determined by the product of the capacitance of the capacitor and the resistance of the resistor. As mentioned above, in the equivalent circuit 43 of the piezoelectric cable unit 1 shown in Figure 4, the piezoelectric cable that is pressed changes from a capacitor to a power source, and the equivalent circuit 43 becomes a so-called RC circuit. For example, when piezoelectric cable 10a is the power source, there is one resistor between piezoelectric cable 10b and the power source, and there are two resistors between piezoelectric cable 10c and the power source. Also, when piezoelectric cable 10b is the power source, there is one resistor between piezoelectric cable 10a and the power source, and there is one resistor between piezoelectric cable 10c and the power source. Also, when piezoelectric cable 10c is the power source, there is one resistor between piezoelectric cable 10b and the power source, and there are two resistors between piezoelectric cable 10a and the power source. Therefore, if the piezoelectric cable that is pressed and changes from a capacitor to a power source is different, there will be a difference in the time required for the voltage to rise in piezoelectric cable 10a and piezoelectric cable 10c. In other words, there is a difference in the time required for the rise of the voltages V1 and V2 input from the first input unit 51 and the second input unit 52, and there is also a difference in the time required for the rise of the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52.

[0085] Figure 12 shows the period including the rise of the charge Q1 input from the first input unit 51 shown in Figure 9, and the period including the rise of the charge Q1 input from the first input unit 51 shown in Figure 11. In Figure 12, the charge Q1 when the piezoelectric cable 10a is pressed is shown by a solid line, and the charge Q1 when the piezoelectric cable 10b is pressed is shown by a dashed line. As shown in Figure 12, the period TQa from when the charge Q1 when the piezoelectric cable 10a is pressed reaches the first reference value BL1 to the second reference value BL2, which is higher than the first reference value BL1, is shorter than the period TQb from when the charge Q1 when the piezoelectric cable 10b is pressed reaches the second reference value BL2. Note that the first reference value BL1 and the second reference value BL2 are smaller than the maximum value of the charge Q1 when the piezoelectric cable 10b is pressed. Although a diagrammatic explanation is omitted, the period from when the piezoelectric cable 10c is pressed to when the charge Q2 reaches the first reference value BL1 and then to when it reaches the second reference value BL2 is shorter than the period from when the piezoelectric cable 10b is pressed to when the charge Q2 reaches the first reference value BL1 and then to when it reaches the second reference value BL2.

[0086] In this embodiment, the measurement unit 53 measures the period from when the charge Q1 input from the first input unit 51 reaches the first reference value BL1 until it reaches the second reference value BL2. The measurement unit 53 also measures the period from when the charge Q2 input from the second input unit 52 reaches the first reference value BL1 until it reaches the second reference value BL2. The measurement unit 53 then outputs signals related to these measured periods, and these signals are input to the detection unit 54 via a bus line.

[0087] In this embodiment, the detection unit 54 detects a pressed piezoelectric cable based on the period from when the charge Q1 input from the first input unit 51 reaches a first reference value BL1 until it reaches a second reference value BL2, and the period from when the charge Q2 input from the second input unit 52 reaches a first reference value BL1 until it reaches a second reference value BL2.

[0088] For example, if the period from when the charge Q1 reaches the first reference value BL1 to when it reaches the second reference value BL2 is less than or equal to a predetermined threshold, the detection unit 54 detects that the piezoelectric cable 10a has been pressed. The predetermined threshold is longer than the period TQa and shorter than the period TQb. Also, if the period from when the charge Q1 reaches the first reference value BL1 to when it reaches the second reference value BL2 exceeds a predetermined threshold, the detection unit 54 detects that the piezoelectric cable 10b has been pressed. Also, if the period from when the charge Q2 reaches the first reference value BL1 to when it reaches the second reference value BL2 is less than or equal to a predetermined threshold, the detection unit 54 detects that the piezoelectric cable 10c has been pressed.

[0089] The detection unit 54 may also detect a pressed piezoelectric cable based on the period from when the charge Q1 input from the first input unit 51 reaches a first reference value BL1 until it reaches a second reference value BL2. In this case, as described in the first embodiment, for example, the resistance values ​​of resistors 20a and 20b are adjusted so that the voltage V1 when piezoelectric cable 10a is pressed, the voltage V1 when piezoelectric cable 10b is pressed, and the voltage V1 when piezoelectric cable 10c is pressed are greater than zero, and these voltages V1 decrease in that order. In addition, the first reference value BL1 and the second reference value BL2 are made smaller than the maximum value of charge Q1 when piezoelectric cable 10c is pressed. In this case, for example, if the period from when the charge Q1 reaches the first reference value BL1 until it reaches the second reference value BL2 is less than or equal to a predetermined threshold, the detection unit 54 detects that piezoelectric cable 10a has been pressed. Furthermore, if the period from when the charge Q1 reaches the first reference value BL1 to when it reaches the second reference value BL2 exceeds a predetermined threshold but is less than or equal to another predetermined threshold that is longer than the first predetermined threshold, it is detected that the piezoelectric cable 10b has been pressed. The other predetermined threshold is longer than the period TQb and shorter than the period from when the charge Q1 reaches the first reference value BL1 to when it reaches the second reference value BL2 when the piezoelectric cable 10c is pressed. Furthermore, if the period from when the charge Q1 reaches the first reference value BL1 to when it reaches the second reference value BL2 exceeds another predetermined threshold, it is detected that the piezoelectric cable 10c has been pressed. With such a configuration, the configuration of the detection system 100 can be further simplified. Furthermore, in this embodiment, when the detection unit 54 detects a pressed piezoelectric cable based on the period from when the charge Q1 input from the first input unit 51 reaches the first reference value BL1 to when it reaches the second reference value BL2, and the period from when the charge Q2 input from the second input unit 52 reaches the first reference value BL1 to when it reaches the second reference value BL2, the accuracy of detecting the pressed piezoelectric cable can be improved.

[0090] Furthermore, as mentioned above, if the piezoelectric cable that is pressed and changes from a capacitor to a power source is different, there will be a difference in the time required for the voltages V1 and V2 input from the first input unit 51 and the second input unit 52 to rise. For this reason, the pressed piezoelectric cable can be detected based on the time required for the voltages V1 and V2 to rise, similar to the charges Q1 and Q2. For this reason, the detection unit 54 may detect the pressed piezoelectric cable based on the rise of the voltage V1 input from the first input unit 51, or it may detect the pressed piezoelectric cable based on the rise of the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. The voltages V1 and V2 and the charges Q1 and Q2 are electrical outputs from the circuit consisting of the first circuit 41 and the second circuit 42. For this reason, the detection unit 54 may detect the pressed piezoelectric cable based on the period from when the electrical output reaches a first reference value until it reaches a second reference value which is higher than the first reference value.

[0091] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described in detail. Note that components identical or equivalent to those in the first embodiment are denoted by the same reference numerals unless otherwise specified, and redundant descriptions will be omitted.

[0092] Figure 13 is a diagram showing the detection system 100 according to this embodiment, similar to Figure 1. As shown in Figure 13, the detection system 100 of this embodiment differs from the detection system 100 of the first embodiment in that it includes a ground line 48.

[0093] In this embodiment, the ground wire 48 is electrically connected to the connecting conductor 30b. The ground wire 48 only needs to be electrically connected to the second circuit 42, and may be electrically connected to the connecting conductor 30b, or to any of the outer conductors 13 of the piezoelectric cables 10a to 10c.

[0094] Figure 14 shows the equivalent circuit of the piezoelectric cable unit 1 of this embodiment. As shown in Figure 14, the equivalent circuit 43 is a circuit in which three capacitors are connected in parallel, similar to the first embodiment. When at least one of the piezoelectric cables 10a to 10c is pressed, a voltage is generated between the first circuit 41 and the second circuit 42, and the equivalent circuit 43 becomes a so-called RC circuit, and current flows through the equivalent circuit 43.

[0095] In the first input unit 51 of this embodiment, terminal 51a is electrically connected to the internal conductor 11 of the piezoelectric cable 10a via the amplifier 45, but terminal 51b is not electrically connected to the piezoelectric cable unit 1. In other words, the first input unit 51 is electrically connected to one end of the first circuit 41.

[0096] In the second input section 52 of this embodiment, terminal 52a is electrically connected to the internal conductor 11 of the piezoelectric cable 10c via the amplifier 46, but terminal 52b is not electrically connected to the piezoelectric cable unit 1. In other words, the second input section 52 is electrically connected to the other end of the first circuit 41.

[0097] In this embodiment, the measuring unit 53 is electrically connected to one end of the first circuit 41 via the first input unit 51 and amplifier 45, and electrically connected to the other end of the first circuit 41 via the second input unit 52 and amplifier 46. The measuring unit 53 is a voltmeter that measures the voltages to ground input from the first input unit 51 and the second input unit 52.

[0098] In this embodiment, as in the first embodiment, when the piezoelectric cable being pressed changes, the voltage V1 to ground input to the first input unit 51 and the voltage V2 to ground input to the second input unit 52 change. Then, as in the first embodiment, the detection unit 54 detects the pressed piezoelectric cable based on the strength of the voltages V1 and V2 input from the first input unit 51 and the second input unit 52.

[0099] As described above, the detection system 100 of this embodiment comprises a piezoelectric cable unit 1, a ground line 48 electrically connected to the second circuit 42, and a detection unit 50 including a first input unit 51, a second input unit 52, and a detection unit 54. The first input unit is electrically connected to one end of the first circuit 41 and receives the voltage V1 output from the first circuit 41. The second input unit 52 is electrically connected to the other end of the first circuit 41 and receives the voltage V2 output from the first circuit 41. The detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. According to the detection system 100 of this embodiment, the configuration of the detection system 100 can be simplified in the same way as the detection system 100 of the first embodiment.

[0100] In this embodiment, the detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52. However, the detection unit 54 may also detect the pressed piezoelectric cable based on the voltage V1 input from the first input unit 51. In this case, as described in the first embodiment, for example, the resistance values ​​of resistors 20a and 20b are adjusted so that the voltage V1 when piezoelectric cable 10a is pressed, the voltage V1 when piezoelectric cable 10b is pressed, and the voltage V1 when piezoelectric cable 10c is pressed are greater than zero, and these voltages V1 decrease in that order. With such a configuration, the configuration of the detection system 100 can be further simplified. In this embodiment, if the detection unit 54 detects the pressed piezoelectric cable based on the voltages V1 and V2 input from the first input unit 51 and the second input unit 52, the accuracy of detecting the pressed piezoelectric cable can be improved.

[0101] Furthermore, similar to the second embodiment, the measuring unit 53 may measure the charge Q1 input from the first input unit 51 and the charge Q2 input from the second input unit 52, and the detection unit 54 may detect the pressed piezoelectric cable based on the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52.

[0102] Furthermore, similar to the third embodiment, the detection unit 54 may detect a pressed piezoelectric cable based on the period from when the electrical output input from the first input unit 51 and the second input unit reaches a first reference value until it reaches a second reference value that is higher than the first reference value.

[0103] Although the present invention has been described above with reference to the above embodiments, the present invention is not limited to these.

[0104] For example, in the above embodiment, resistors 20a and 20b were provided between the internal conductors 11 of the piezoelectric cables 10a to 10c to form a first circuit 41 in which the internal conductors 11 are electrically connected in series, and connecting conductors 30a and 30b were provided between the external conductors 13 of the piezoelectric cables 10a to 10c to form a second circuit 42 in which the external conductors 13 are electrically connected in series. However, resistors 20a and 20b may also be provided between the external conductors 13 of the piezoelectric cables 10a to 10c to form a first circuit in which the external conductors 13 are electrically connected in series, and connecting conductors 30a and 30b may be provided between the internal conductors 11 of the piezoelectric cables 10a to 10c to form a second circuit in which the internal conductors 11 are electrically connected in series. Furthermore, in the above embodiment, a piezoelectric cable unit 1 comprising three piezoelectric cables 10a to 10c was described as an example, but there may be multiple piezoelectric cables.

[0105] In other words, the piezoelectric cable unit 1 may include a plurality of piezoelectric cables having an inner conductor 11, a polymer piezoelectric layer 12 in contact with the inner conductor 11 and surrounding the outer surface of the inner conductor 11, and an outer conductor 13 in contact with the polymer piezoelectric layer 12 and surrounding the outer surface of the polymer piezoelectric layer 12; a resistor provided between one of the inner conductors 11 and the outer conductor 13 in the plurality of piezoelectric cables, forming a first circuit 41 in which one of the conductors is electrically connected in series; and a connecting conductor provided between the other of the inner conductor 11 and the outer conductor 13, forming a second circuit 42 in which the other conductor is electrically connected in series.

[0106] Alternatively, the detection system 100 may include the piezoelectric cable unit 1 described above, a ground wire 48 electrically connected to the second circuit 42, and a detection unit 50, wherein the detection unit 50 may include a first input section 51 electrically connected to one end of the first circuit 41 and receiving the electrical output from the first circuit 41 as input, and a detection section 54 that detects a pressed piezoelectric cable based on the electrical output received from the first input section 51.

[0107] Furthermore, in the above embodiment, a detection unit 54 was described as detecting a pressed piezoelectric cable when one of the multiple piezoelectric cables 10a to 10c is pressed. However, even when two or more of the multiple piezoelectric cables 10a to 10c are pressed, the electrical output input from the first input unit 51 and the electrical output input from the second input unit 52 change. Therefore, even when two or more of the multiple piezoelectric cables 10a to 10c are pressed, the pressed piezoelectric cable can be detected from the electrical output input from the first input unit 51 and the electrical output input from the second input unit 52. For this reason, the detection unit 54 may also detect the pressed piezoelectric cable in such cases.

[0108] Furthermore, in the above embodiment, a piezoelectric cable comprising a protective layer 15 including an insulating layer 16, a shielding layer 17, and a jacket layer 18 was described as an example. However, the protective layer 15 is not limited and may consist of, for example, only the jacket layer 18. Also, the piezoelectric cable may not have a protective layer 15.

[0109] Furthermore, the detection unit 54 may detect a pressed piezoelectric cable using a learning model constructed by machine learning the electrical output from the piezoelectric cable unit 1. For example, the learning model is constructed using the voltages V1 and V2 input from the first input unit 51 and the second input unit 52 and measured by the measurement unit 53, and the machine learning used to construct this learning model is supervised learning. Specifically, for example, in the first embodiment, the learning model is constructed by machine learning assuming that the voltages V1 and V2 shown in Figure 6 are those of piezoelectric cable 10a being pressed, the voltages V1 and V2 shown in Figure 7 are those of piezoelectric cable 10c being pressed, and the voltages V1 and V2 shown in Figure 8 are those of piezoelectric cable 10b being pressed. The detection unit 54 then uses the learning model constructed in this way to detect the pressed piezoelectric cable. With this configuration, the accuracy of detecting the pressed piezoelectric cable can be improved, and it becomes more useful as the number of piezoelectric cables increases. The electrical output from the piezoelectric cable unit 1 may be the charges Q1 and Q2 input from the first input unit 51 and the second input unit 52 and measured by the measurement unit 53, or it may be the voltage V1 or charge Q1 input from the first input unit 51 and measured by the measurement unit 53. Alternatively, a learning model may be constructed by machine learning the electrical output from the piezoelectric cable unit 1 when multiple piezoelectric cables among the piezoelectric cables 10a to 10c are pressed.

[0110] Furthermore, in the above embodiment, a piezoelectric cable unit 1 was described as being arranged along a seating surface 111 such that the piezoelectric cables 10a to 10c are aligned along the longitudinal direction of the seating surface 111, which is a flat surface, with the longitudinal direction of the piezoelectric cables 10a to 10c aligned along that longitudinal direction. However, the arrangement of the piezoelectric cable unit 1 is not limited.

[0111] Figure 15 illustrates the arrangement of the piezoelectric cable unit 1 in a modified example. In Figure 15, the resistor 20 is shown by a solid line and the connecting conductor 30 is shown by a dotted line. As shown in Figure 15, in this modified example, each piezoelectric cable 10 is arranged along the plane 121 of the object to be measured so that the piezoelectric cable unit 1 meanders. Therefore, the longitudinal directions of two or more piezoelectric cables 10 are not parallel to each other. With this configuration, it is possible to detect where a force is applied on the plane 121 of the object to be measured. An example of an object to be measured is the floor of a room, and for example, it is possible to detect where a person is in the room. Note that the piezoelectric cable unit 1 does not have to meander; for example, each piezoelectric cable 10 may be arranged in a spiral shape.

[0112] Figure 16 illustrates the arrangement of the piezoelectric cable unit 1 in another modified example. In Figure 16, the resistor 20 is shown by a solid line and the connecting conductor 30 is shown by a dotted line. As shown in Figure 16, in this modified example, each piezoelectric cable 10 is arranged along the curved surface 122 of the object to be measured so that the piezoelectric cable unit 1 meanders. With this configuration, it is possible to detect where a force is applied on the curved surface 122 of the object to be measured. Note that the piezoelectric cable unit 1 does not have to meander; for example, each piezoelectric cable 10 may be arranged in a spiral shape. Also, the object to be measured may be a sphere, and the curved surface 122 may be a sphere.

[0113] Furthermore, although the detection system 100 had only one piezoelectric cable unit 1 in the above embodiment, there may be multiple piezoelectric cable units 1. [Industrial applicability]

[0114] As described above, the present invention provides a piezoelectric cable unit and a detection system that can simplify the configuration of a detection system, and can be used in fields such as object position detection systems. [Explanation of symbols]

[0115] 1. Piezoelectric Cable Unit 10, 10a, 10b, 10c... Piezoelectric cable 11. Internal Conductor 12. Polymer piezoelectric layer 13. Outer conductor 20,20a,20b...Resistor 30, 30a, 30b... Connecting conductors 41...1st circuit 42...2nd circuit 50...Detection Unit 51...First Input Section 52...Second Input Section 53...Measurement part 54...Detection unit 100 detection system

Claims

1. A plurality of piezoelectric cables having an inner conductor, a polymer piezoelectric layer in contact with the inner conductor and surrounding the outer surface of the inner conductor, and an outer conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer, A resistor provided between one of the inner conductors and outer conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series, A connecting conductor is provided between the inner conductor and the other of the outer conductors, forming a second circuit in which the other conductor is electrically connected in series, Equipped with A piezoelectric cable unit characterized by the following features.

2. A piezoelectric cable unit comprising: a plurality of piezoelectric cables having an internal conductor, a polymer piezoelectric layer in contact with the internal conductor and surrounding the outer surface of the internal conductor, and an external conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer; a resistor provided between one of the internal conductors and the external conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series; and a connecting conductor provided between the other of the internal conductor and the external conductor, forming a second circuit in which the other conductor is electrically connected in series; A ground wire electrically connected to the second circuit, Detection unit and Equipped with, The detection unit includes a first input unit which is electrically connected to one end of the first circuit and receives the electrical output output from the first circuit, and a detection unit which detects the pressed piezoelectric cable based on the electrical output received from the first input unit. A detection system characterized by the following features.

3. The detection unit further includes a second input section which is electrically connected to the other end of the first circuit and to which the electrical output output from the first circuit is input. The detection unit detects the pressed piezoelectric cable based on the electrical outputs input from the first input unit and the second input unit. The detection system according to feature 2.

4. A piezoelectric cable unit comprising: a plurality of piezoelectric cables having an internal conductor, a polymer piezoelectric layer in contact with the internal conductor and surrounding the outer surface of the internal conductor, and an external conductor in contact with the polymer piezoelectric layer and surrounding the outer surface of the polymer piezoelectric layer; a resistor provided between one of the internal conductors and the external conductors in the plurality of piezoelectric cables, forming a first circuit in which the one conductor is electrically connected in series; and a connecting conductor provided between the other of the internal conductor and the external conductor, forming a second circuit in which the other conductor is electrically connected in series; Detection unit and Equipped with, The detection unit includes a first input unit that is individually electrically connected to one end of the first circuit and the second circuit and receives the electrical outputs from the first circuit and the second circuit, and a detection unit that detects the pressed piezoelectric cable based on the electrical output received from the first input unit. A detection system characterized by the following features.

5. The detection unit further includes a second input section which is electrically connected individually to the other ends of the first circuit and the second circuit and to which the electrical outputs output from the first circuit and the second circuit are input. The detection unit detects the pressed piezoelectric cable based on the electrical outputs input from the first input unit and the second input unit. The detection system according to feature 4.

6. The detection unit detects the pressed piezoelectric cable based on the period from when the electrical output reaches a first reference value until it reaches a second reference value that is higher than the first reference value. The detection system according to any one of claims 2 to 5.

7. The aforementioned electrical output is voltage. The detection system according to any one of claims 2 to 5.

8. The aforementioned electrical output is electric charge. The detection system according to any one of claims 2 to 5.

9. The detection unit detects the pressed piezoelectric cable using a learning model constructed by machine learning the electrical output. The detection system according to any one of claims 2 to 5.

10. Each of the piezoelectric cables is arranged along a plane in the object being measured. The longitudinal directions of the two or more piezoelectric cables are non-parallel to each other. The detection system according to any one of claims 2 to 5.

11. Each of the piezoelectric cables is positioned along the curved surface of the object being measured. The detection system according to any one of claims 2 to 5.

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