JP2021018692A - Capacitive sensor - Google Patents

Abstract

To provide a capacitive sensor capable of suppressing a decrease of the detection accuracy of sensor electrodes even in hot and humid conditions.SOLUTION: A capacitive sensor 100 includes: a foam sheet 113 that has the front side and the back side; a capacitive sensor electrode 112 placed on the surface of the foam sheet 113; and a surface layer 111 arranged over the surface opposite to the side where the foam sheet 113 is disposed on the sensor electrode 112. In the foam sheet 113, multiple open pores 113b are formed from multiple closed pores 113a which are formed along one side at least of the front side and the back side.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a capacitance sensor.

Conventionally, a capacitive touch panel that detects whether or not a human hand is touching the steering wheel of a vehicle has been proposed (see, for example, Patent Document 1).

This capacitive touch panel includes a protective substrate whose main surface constitutes a touch surface, and a capacitive touch panel sensor which is arranged on the side opposite to the main surface of the protective substrate and can detect contact with an object.

Japanese Patent No. 5689931

However, in the capacitive touch panel in Patent Document 1, the protective substrate is placed in a high temperature and high humidity state because the user's hand continues to be in contact with the protective substrate. Therefore, the capacitance of the protective substrate may change. As a result, the capacitive touch panel has a problem that it cannot accurately detect the contact of an object with the protective substrate.

Therefore, an object of the present disclosure is to provide a capacitance sensor capable of suppressing a decrease in detection accuracy of a sensor electrode even in a high temperature and high humidity state.

The capacitance sensor according to one aspect of the present disclosure includes a foamable foam sheet having a front surface and a back surface, a capacitance type sensor electrode arranged on the surface of the foam sheet, and the sensor electrode. A plurality of surface layer portions arranged on a surface opposite to the side on which the foam sheet is arranged are provided, and the foam sheet is formed along at least one surface of the front surface and the back surface. Multiple open pores are formed from the closed pores of.

It should be noted that this comprehensive or specific embodiment may be realized by any combination of systems, methods, integrated circuits, and the like.

The capacitance sensor of the present disclosure can suppress a decrease in detection accuracy of the sensor electrode even in a high temperature and high humidity state.

FIG. 1 is a diagram showing an example of a passenger compartment of a vehicle in which a capacitance sensor is arranged according to the embodiment. FIG. 2 is a cross-sectional view showing a rim around which the steering cover is wound and a steering cover in the line AA of FIG. FIG. 3 is a diagram showing an example of how to wind the steering cover having the capacitance sensor in the embodiment around the rim. FIG. 4 is a block diagram showing the configuration of the capacitance sensor according to the embodiment. FIG. 5 is a cross-sectional view showing a foam sheet of the capacitance sensor according to the embodiment. FIG. 6 is a partially enlarged cross-sectional view showing an open pore of the foam sheet of the capacitance sensor according to the embodiment. FIG. 7 is a flowchart showing a method of manufacturing a capacitance sensor.

The capacitance sensor according to one aspect of the present disclosure includes a foamable foam sheet having a front surface and a back surface, a capacitance type sensor electrode arranged on the surface of the foam sheet, and the sensor electrode. A plurality of surface layer portions arranged on a surface opposite to the side on which the foam sheet is arranged are provided, and the foam sheet is formed along at least one surface of the front surface and the back surface. Multiple open pores are formed from the closed pores of.

For example, when the user's hand touches the surface layer portion, moisture such as sweat generated in the user's hand (for example, water vapor) may pass through the surface layer portion and the sensor electrode and reach the foam sheet. In this case, since the foamed sheet has a structure containing a large amount of closed pores (voids), the moisture remains in the closed pores. As a result, the dielectric constant of the foamed sheet increases, and the capacitance of the foamed sheet changes. In this case, the capacitance sensor cannot accurately detect the contact of the object with the protective substrate.

However, in the capacitive sensors of the present disclosure, the open pores are formed by tearing the epidermis of the closed pores formed along that surface of the foam sheet. Compared to the case where water is accumulated in the closed pore, the water is more likely to escape in the open pore. That is, in the foamed sheet of the present disclosure, the moisture easily escapes from the foamed sheet as compared with the foamed sheet before forming the plurality of open pores from the plurality of closed pores, so that the state before the moisture reaches the foamed sheet. The time to return is shortened. As a result, the dielectric constant of the foamed sheet is less likely to increase, and thus the capacitance of the foamed sheet is less likely to change.

Therefore, in this capacitance sensor, it is possible to suppress a decrease in the detection accuracy of the sensor electrode even in a high temperature and high humidity state. In particular, when a plurality of open pores are formed from a plurality of closed pores on the front surface of the foamed sheet, moisture can easily escape from the foamed sheet as compared with the case where such a plurality of open pores are formed on the back surface of the foamed sheet. Therefore, the dielectric constant of the foamed sheet is less likely to increase, so that the capacitance of the foamed sheet is less likely to change.

Further, it is easier for moisture to escape from the foamed sheet by forming a plurality of such open pores on the front surface and the back surface of the foamed sheet. Therefore, the dielectric constant of the foamed sheet is less likely to increase, so that the capacitance of the foamed sheet is less likely to change more reliably.

Further, in the capacitance sensor according to another aspect of the present disclosure, openings are formed in the plurality of open pores, and the average diameter of the openings of the plurality of open pores is the plurality of open pores and the plurality of open pores. Smaller than the average pore diameter of the closed pores.

According to this, when a plurality of closed pores formed along at least one surface of the front surface and the back surface are made into open pores, for example, the open pores are formed by processing at least one surface of the foam sheet. There is. In this case, when the average diameter of the openings of the plurality of open pores is larger than the average pore diameter, it is necessary to scrape a lot of surfaces to be processed, and the manufacturing cost of the foam sheet is high in forming the plurality of open pores. It may be soaring.

However, in the capacitance sensor of the present disclosure, since the average diameter of the openings of the plurality of open pores is smaller than the average diameter of the pores of the plurality of closed pores, it is not necessary to scrape a lot of foam sheets. Therefore, in this capacitance sensor, the manufacturing cost of the foamed sheet is unlikely to rise.

Further, in the capacitance sensor according to another aspect of the present disclosure, a ground electrode is arranged on the back surface of the foam sheet.

For example, when the capacitance sensor is wound around the steering rim, in the present disclosure, the distance between the ground electrode and the sensor electrode is compared with the distance between the conductive core metal included in the rim and the sensor electrode. Can be made smaller. Therefore, the first capacitance between the ground electrode and the sensor electrode is larger than the second capacitance between the core metal and the sensor electrode. That is, the contact of the hand with the surface layer portion is detected by the sum of the capacitance from the hand to the sensor electrode and the capacitance from the sensor electrode to the ground electrode. Here, the foamed sheet of the present disclosure can stabilize the fluctuation of the first capacitance due to moisture. As a result, the decrease in the detection accuracy of the capacitance sensor can be further suppressed.

Further, in the capacitance sensor according to another aspect of the present disclosure, the foamed sheet is formed from the plurality of closed pores to the plurality of open pores by roughening at least one surface of the front surface and the back surface. Is formed.

According to this, a plurality of open pores can be formed from a plurality of closed pores formed along at least one surface of the front surface and the back surface. That is, since the surface after processing is rougher than the surface before rough surface processing, when an adhesive layer is formed on the surface that has been roughened, the adhesive layer is peeled off from the foam sheet due to the anchor effect. Strength is improved. As a result, the reliability of the adhesive layer with respect to the foamed sheet is improved.

Hereinafter, embodiments will be specifically described with reference to the drawings.

It should be noted that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, etc. shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components.

Further, each figure is a schematic view and is not necessarily exactly illustrated. Further, in each figure, the same components are designated by the same reference numerals. Further, in the following embodiments, expressions such as an approximately T-shape are used. For example, a substantially T-shape not only means that it is completely T-shaped, but also means that it is substantially T-shaped, that is, it includes an error of, for example, about several percent. Further, the substantially T-shape means a T-shape within the range in which the effects of the present disclosure can be achieved. The same applies to expressions using other "abbreviations".

(Embodiment)
[Configuration: Capacitance sensor 100]
FIG. 1 is a diagram showing an example of a passenger compartment of a vehicle 1 in which the capacitance sensor 100 according to the embodiment is arranged.

As shown in FIG. 1, the vehicle 1 includes a steering wheel 200, a speaker, and a display device such as a liquid crystal display. The speaker and the display device are configured as, for example, a warning device.

The steering wheel 200 provides a steering angle to the steering wheel of the vehicle 1. The steering wheel 200 includes a rim 210, a substantially T-shaped spoke 202 integrally formed on the inner peripheral surface of the rim 210, and a horn that covers a horn switch (not shown) arranged in the central portion of the spoke 202. It has a switch cover.

FIG. 2 is a cross-sectional view showing the rim 210 around which the steering cover 110 is wound and the steering cover 110 in the line AA of FIG. FIG. 3 is a diagram showing an example of how to wind the steering cover 110 having the capacitance sensor 100 in the embodiment around the rim 210.

As shown in FIGS. 2 and 3, the rim 210 is a grip portion for being gripped by a user (person) and has a ring shape. The rim 210 has a core metal 201b, which is a metal annular core, and a resin layer 201a that covers the core metal 201b. A steering cover 110 is wound around the rim 210.

The capacitance sensor 100 is a device that detects the contact of the steering cover 110 by the user's hand, and is provided on the rim 210 of the vehicle 1. The contact means not only that the user's hand comes into direct contact with the steering cover 110, but also includes a state in which the capacitance sensor 100 is separated from the steering cover 110 if the human hand can be detected. Is.

The capacitance sensor 100 is, for example, a capacitance type proximity sensor, and is a grip sensor that detects the grip of a user (person) in a vehicle 1 having a steering wheel 200. Specifically, the capacitance sensor 100 detects a change in capacitance between the user's hand and the sensor electrode 112 in the capacitance sensor 100, so that the user's hand touches the steering wheel 200. Detects whether or not it is. When the user's hand is away from the steering wheel 200, the capacitance sensor 100 detects the capacitance between the vehicle 1 and the sensor electrode 112. Further, when the user's hand approaches or comes into contact with the steering cover 110, the capacitance changes because the user's hand intervenes between the capacitance sensor 100 and the vehicle body. If the detected capacitance is equal to or greater than the specified value, it can be determined that the user's hand is touching or holding the steering wheel 200.

FIG. 4 is a block diagram showing the configuration of the capacitance sensor 100 according to the embodiment.

As shown in FIGS. 2 and 4, the capacitance sensor 100 includes a surface layer portion 111, a sensor electrode 112, a foam sheet 113, a ground electrode 114, and a control device 120.

The surface layer portion 111 is a portion touched by a hand and constitutes the outer circumference of the capacitance sensor 100. That is, the surface layer portion 111 is a portion that comes into direct contact with the user's hand when the user grips the rim 210. Further, the surface layer portion 111 is made of leather, wood, resin or the like, and is leather in the present embodiment. A single sensor electrode 112 may be provided on the foam sheet 113, or a plurality of sensor electrodes 112 may be provided. Further, the numbers of the sensor electrodes 112 and the ground electrodes 114 do not necessarily have to match. FIG. 4 illustrates a case where the pair of sensor electrodes 112 and the pair of ground electrodes 114 are provided, and the description will be described below with reference to this figure.

The pair of sensor electrodes 112 is, for example, a conductive cloth formed by plating a non-metal fiber. Specifically, the pair of sensor electrodes 112 form a first metal (first metal plating) on the surface of a cloth woven with non-metal fibers such as polyethylene terephthalate (PET), and further, the surface of the first metal. A second metal (second metal plating) is formed on the surface. Alternatively, the pair of sensor electrodes 112 form a first metal (first metal plating) on the surface of a non-metal fiber such as polyethylene terephthalate (PET), and further form a second metal (second metal) on the surface of the first metal. It is formed by weaving conductive fibers that have formed (plating). For example, the first metal is copper or the like, and the second metal is nickel or the like.

The pair of sensor electrodes 112 are arranged on the back surface of the surface layer portion 111 and on the front surface of the foam sheet 113. That is, the pair of sensor electrodes 112 are sandwiched between the surface layer portion 111 and the foam sheet 113. The sensor electrode 112 is adhered to the back surface of the surface layer portion 111 with an adhesive (not shown), and is adhered to the front surface of the foam sheet 113 with an adhesive (not shown). The surface of the foam sheet 113 is a surface arranged toward the surface layer portion 111 side.

Of the pair of sensor electrodes 112, one sensor electrode 112 is arranged on one side when the capacitance sensor 100 is wound around the rim 210 (for example, the right side when viewed in a state facing the rim 210). The other sensor electrode 112 is arranged on the other side when the capacitance sensor 100 is wound around the rim 210 (for example, the left side when viewed in a state facing the rim 210).

The foam sheet 113 is a foam formed in the form of a long sheet made of a material having elasticity, flexibility and ductility. For example, the foamed sheet 113 is made of a synthetic resin such as polyethylene (PE) and polyethylene terephthalate (PET). The foam sheet 113 is formed according to the shape and size of the rim 210.

Further, the foam sheet 113 is arranged on the side opposite to the surface layer portion 111 side of the sensor electrode 112, and is arranged on the surface of the ground electrode 114 on the sensor electrode 112 side. That is, the foam sheet 113 is sandwiched between the sensor electrode 112 and the ground electrode 114.

The foamed sheet 113 is a foamable sheet having a front surface and a back surface. The surface is a surface facing the sensor electrode 112. The back surface is a surface facing the ground electrode 114. The foamed sheet 113 may be a porous porous sheet.

FIG. 5 is a cross-sectional view showing a foam sheet 113 of the capacitance sensor 100 according to the embodiment. In FIG. 5, only the cross section of the foam sheet 113 is displayed.

As shown in FIG. 5, the foamed sheet 113 includes a plurality of closed pores 113a and a plurality of open pores 113b changed from the plurality of closed pores 113a formed along at least one of the front surface and the back surface. It is formed.

The closed pore 113a is a substantially spherical bubble containing air. The closed pore 113a is a void that allows moisture or the like to penetrate into the inside through the film forming the foamed sheet 113. That is, the closed pore 113a has a much narrower opening path to the outside of the foam sheet 113 than the open pore 113b. The plurality of closed pores 113a are formed everywhere in the foam sheet 113.

The open pore 113b is an open path to the outside of the foam sheet 113, that is, a substantially spherical void (vacancy) having an opening 113c. The plurality of open pores 113b are formed on at least one of the front surface and the back surface of the foam sheet 113. The plurality of open pores 113b are formed by roughening at least one of the front surface and the back surface of the foam sheet 113.

Specifically, by applying the rough surface processing treatment to the foam sheet 113, the skins of the plurality of closed pores 113a formed along at least one surface of the front surface and the back surface are torn to form the opening 113c. Then, a plurality of open pores 113b are formed. That is, the plurality of closed pores 113a formed in the vicinity of the front surface and the vicinity of the back surface of the foamed sheet 113 become a plurality of open pores 113b by the rough surface processing treatment. In the present embodiment, by performing the rough surface processing treatment, several tens of percent or more of the plurality of closed pores 113a formed along at least one surface of the front surface and the back surface become open pores 113b. .. Preferably, 90% or more may be open pore 113b.

The density of the open pores 113b per unit area on the surface of the foam sheet 113 after rough surface processing is higher than the density of the open pores 113b per unit area on the surface of the foam sheet 113 before rough surface processing.

The rough surface processing is, for example, a scratch processing, a blast processing, or the like. The rough surface processing may be performed by etching with a chemical that dissolves the material of the foam sheet 113.

In the foam sheet 113, the surface area per unit area after the rough surface processing treatment (including the area of the inner surface of the plurality of open pores 113b) is the surface area per unit area before the rough surface processing treatment is performed. Larger than (including the inner surface area of the plurality of open pores 113b).

FIG. 6 is a partially enlarged cross-sectional view showing the open pore 113b of the foam sheet 113 of the capacitance sensor 100 according to the embodiment. In FIG. 6, only the cross section of the foam sheet 113 is displayed.

As shown in FIG. 6, the average diameter A1 of the openings 113c of the plurality of open pores 113b is smaller than the average pore diameter A2 (diameter) of the plurality of open pores 113b and the plurality of closed pores 113a. The average diameter A1 of the openings 113c of the plurality of open pores 113b is about several tens of percent of the average pore diameter A2 of the plurality of closed pores 113a. In the present embodiment, the average diameter A1 of the opening 113c is about 30% of the average pore diameter A2.

In the present embodiment, a plurality of open pores 113b are formed from the plurality of closed pores 113a on the surface of the foamed sheet 113. In this case, since the surface of the foamed sheet 113 is the surface on the surface layer portion 111 side, the surface layer portion 111 side is compared with the case where a plurality of open pores 113b are formed from the plurality of closed pores 113a on the back surface of the foamed sheet 113. The reached moisture easily escapes from the foam sheet 113.

Further, a plurality of open pores 113b may be formed from the plurality of closed pores 113a on the front surface and the back surface of the foam sheet 113. In this case, further, the water arriving from the surface layer portion 111 side can easily escape from the foamed sheet 113.

The ground electrode 114 is a metal wire (conductive wire) such as a copper wire. The ground electrode 114 is electrically connected to the control device 120 via the wirings 119b and 119c and is grounded.

The ground electrode 114 may be a solid electrode having a planar structure made of a conductor or a resistor. That is, the ground electrode 114 may be linear or plate-shaped. The ground electrode 114 is made of a conductive wire, but may have any form as long as it is a conductive member.

The ground electrode 114 is arranged on the opposite side of the foam sheet 113 from the sensor electrode 112, that is, on the back surface of the foam sheet 113 and on the front surface of the rim 210. In other words, the ground electrode 114 is sandwiched between the rim 210 and the foam sheet 113. For example, the ground electrode 114 is sewn on the foam sheet 113 by sewing thread. The back surface of the foam sheet 113 is a surface arranged toward the rim 210 side of the steering wheel 200.

One of the ground electrodes 114 of the pair of ground electrodes 114 corresponds to the one sensor electrode 112, and is arranged on one side (for example, the right side) when the capacitance sensor 100 is wound around the rim 210. Further, the other ground electrode 114 of the pair of ground electrodes 114 corresponds to the other sensor electrode 112, and is arranged on the other side (for example, the left side) when the capacitance sensor 100 is wound around the rim 210. ..

The control device 120 is embedded in the spokes 202, for example. The control device 120 is electrically connected to the ground electrode 114 and the sensor electrode 112, and detects the contact of the steering wheel 200 by the user's hand based on the signal transmitted from the sensor electrode 112. That is, the control device 120 measures that the user's hand comes into contact with the surface layer portion 111. That is, the control device 120 detects whether or not the user's hand is in contact with the rim 210, that is, detects the contact of the hand, the contact position of the hand, and the like.

The control device 120 includes a control circuit 121 and a power supply circuit 124.

The control circuit 121 has a sensor circuit that detects a hand contact with the steering wheel 200. The control circuit 121 is electrically connected to one of the sensor electrodes 112 by wiring 119a. Further, the control circuit 121 is electrically connected to the other sensor electrode 112 by the wiring 119a. That is, the control circuit 121 applies an alternating current to the sensor electrode 112 on one side via the wiring 119a, that is, applies a measurement potential to the sensor electrode 112 on the one side. Further, the control circuit 121 applies an alternating current to the sensor electrode 112 on the other side via the wiring 119a, that is, applies a measurement potential to the sensor electrode 112 on the other side. The control circuit 121 is electrically connected to the sensor electrode 112 by wiring 119a. That is, the control circuit 121 applies an alternating current to the sensor electrode 112 via the wiring 119a, that is, applies a measurement potential to the sensor electrode 112. When a hand comes into contact with the surface layer portion 111 of the rim 210, the capacitance of the sensor electrode 112 corresponding to the contact portion changes, so that the control circuit 121 is based on the current value (measurement potential) of the current flowing through the sensor electrode 112. , The change in capacitance at the sensor electrode 112 is measured. In this way, the control circuit 121 can detect whether or not the hand has come into contact with the steering wheel 200 from the signal indicating the change in capacitance output from the sensor electrode 112.

Further, the control circuit 121 is electrically connected to the power supply circuit 124 via wiring. The control circuit 121 supplies electric power to the ground electrode 114 by controlling the power supply circuit 124.

The control circuit 121 may cause the alerting device to alert the driver when the vehicle 1 is being driven but the contact is not detected. For example, a warning device such as a speaker may call attention to the driver by a warning sound or voice. The display device may also display a warning message urging the driver to firmly grasp the steering wheel 200.

The power supply circuit 124 is electrically connected to the control circuit 121 via wiring and is controlled by the control circuit 121. Further, the power supply circuit 124 is electrically connected to the ground electrode 114 via the wiring 119b. The power supply circuit 124 is controlled by the control circuit 121 so that a direct current flows through the ground electrode 114. Therefore, the ground electrode 114 also has a function as a heater by flowing a direct current. In this case, since only a direct current flows through the ground electrode 114, it is grounded when viewed from the alternating current flowing through the sensor electrode 112. The ground electrode 114 is not limited to a configuration having a heater function, and may be simply grounded without passing a direct current.

[Manufacturing method of capacitance sensor 100]
FIG. 7 is a flowchart showing a manufacturing method of the capacitance sensor 100.

As shown in FIG. 7, first, a surface layer portion 111, a sensor electrode 112, a foam sheet 113, a ground electrode 114, and an adhesive layer (not shown) such as double-sided tape and an adhesive are prepared (S11: preparation step).

Next, at least one of the front surface and the back surface of the foamed sheet 113 is subjected to rough surface processing (S12: base material processing step). As a result, a plurality of open pores 113b are formed from the plurality of closed pores 113a on the surface subjected to the rough surface processing treatment. That is, a large number of open pores 113b are formed on the foam sheet 113.

Next, the foam sheet 113 obtained in step S12 and the ground electrode 114 are assembled (S13: ground electrode assembly step). At this time, the foam sheet 113 and the ground electrode 114 are assembled so that the back surface of the foam sheet 113 and the front surface of the ground electrode 114 overlap. As a specific assembly method, for example, the foam sheet 113 and the ground electrode 114 may be sewn with a sewing thread, or the foam sheet 113 and the ground electrode 114 may be bonded with an adhesive layer.

Next, the laminate of the foam sheet 113 and the ground electrode 114 obtained in step S13 and the sensor electrode 112 are adhered by an adhesive layer (S14: sensor electrode assembly step). At this time, the foam sheet 113 and the sensor electrode 112 are adhered so that the front surface of the foam sheet 113 and the back surface of the sensor electrode 112 overlap.

Next, the laminated body of the foam sheet 113, the ground electrode 114, and the sensor electrode 112 obtained in step S14 and the surface layer portion 111 are adhered by an adhesive layer (S15: surface layer portion assembling step). At this time, the surface layer portion 111 and the sensor electrode 112 are adhered so that the back surface of the surface layer portion 111 and the front surface of the sensor electrode 112 overlap.

Finally, the steering cover 110 made of a laminate of the foam sheet 113, the ground electrode 114, the sensor electrode 112, and the surface layer portion 111 obtained in step S15 is bonded to the steering wheel 200 by an adhesive layer. At this time, the steering wheel 200 and the ground electrode 114 (foam sheet 113) are adhered so that the front surface of the steering wheel 200 and the back surface of the ground electrode 114 (foam sheet 113) overlap. Further, the ground electrode 114 and the sensor electrode 112 are electrically connected to the control device 120 by wirings 119a, 119b, and 119c (S16: assembly step to the steering wheel). As a result, the capacitance sensor 100 can be obtained.

The surface layer portion 111 is assembled in S15, but this may be assembled in S16. When assembling in S16, the process of S15 is not performed, and instead, the process is as follows.

First, the laminated body of the foam sheet 113, the ground electrode 114 and the sensor electrode 112 obtained in S14 and the steering wheel 200 are adhered by an adhesive layer. At this time, the steering wheel 200 and the ground electrode 114 (foam sheet 113) are adhered so that the front surface of the steering wheel 200 and the back surface of the ground electrode 114 (foam sheet 113) overlap.

Next, the surface layer portion 111 is adhered to the structure including the laminated body of the foam sheet 113, the ground electrode 114 and the sensor electrode 112, and the steering wheel 200 by an adhesive layer. At this time, in the adhesive layer, the sensor electrode 112 and the back surface of the surface layer portion 111 are adhered so that the front surface of the sensor electrode 112 and the back surface of the surface layer portion 111 overlap. Further, the ground electrode 114 and the sensor electrode 112 are electrically connected to the control device 120 by wirings 119a, 119b, and 119c. As a result, the capacitance sensor 100 can be obtained.

[Action effect]
As described above, in the capacitance sensor 100 according to the present embodiment, the foam sheet 113 has a plurality of closed pores 113a to a plurality of open pores 113b formed along at least one of the front surface and the back surface. It is formed.

That is, in the capacitance sensor 100 of the present embodiment, the open pore 113b is formed by tearing the skin of the closed pore 113a formed along the surface of the foam sheet 113. Compared with the case where water is accumulated in the closed pore 113a, the water is more likely to escape in the open pore 113b. That is, as compared with the foamed sheet before forming the plurality of open pores 113b from the plurality of closed pores 113a, in the foamed sheet 113 of the present embodiment, moisture easily escapes, so that before the moisture reaches the foamed sheet 113. The time to return to the state of is shortened. As a result, the dielectric constant of the foamed sheet 113 is less likely to increase, so that the capacitance of the foamed sheet 113 is less likely to change.

Therefore, in this capacitance sensor 100, it is possible to suppress a decrease in the detection accuracy of the sensor electrode 112 even in a high temperature and high humidity state. In particular, when a plurality of open pores 113b are formed from a plurality of closed pores 113a on the surface of the foamed sheet 113, the moisture content of the foamed sheet is higher than when the plurality of open pores 113b are formed on the back surface of the foamed sheet 113. It becomes easier to escape from 113. Therefore, the dielectric constant of the foamed sheet 113 is less likely to increase, so that the capacitance of the foamed sheet 113 is less likely to change.

Further, when a plurality of such open pores 113b are formed on the front surface and the back surface of the foamed sheet 113, it becomes easier for moisture to escape from the foamed sheet 113. Therefore, the dielectric constant of the foamed sheet 113 is less likely to increase, so that the capacitance of the foamed sheet 113 is less likely to change more reliably. As a result, in this capacitance sensor 100, it is possible to further suppress a decrease in the detection accuracy of the sensor electrode 112 even in a high temperature and high humidity state.

In this embodiment, since the ground electrode 114 is also used as a heater, the foam sheet 113 can be heated. Thereby, it is possible to further facilitate the escape of water from the foamed sheet 113.

Further, in the capacitance sensor 100 according to the present embodiment, since the average diameter A1 of the openings 113c of the plurality of open pores 113b is smaller than the average pore diameter A2 of the plurality of closed pores 113a, it is not necessary to scrape a lot of the foam sheet 113. .. Therefore, in the capacitance sensor 100, the manufacturing cost of the foam sheet 113 is unlikely to rise.

Further, in the capacitance sensor 100 according to the present embodiment, for example, when the capacitance sensor 100 is wound around the steering rim 210, the distance between the conductive core metal 201b included in the rim 210 and the sensor electrode 112 is set. In comparison, the distance between the ground electrode 114 and the sensor electrode 112 can be reduced. Therefore, the first capacitance between the ground electrode 114 and the sensor electrode 112 is larger than the second capacitance between the core metal and the sensor electrode 112. That is, the contact of the hand with the surface layer portion is detected by the sum of the capacitance from the hand to the sensor electrode and the capacitance from the sensor electrode to the ground electrode. Here, the foamed sheet 113 of the present disclosure can stabilize the fluctuation of the first capacitance due to moisture. As a result, the capacitance sensor 100 can further suppress a decrease in the detection accuracy of the capacitance sensor 100 even in a high temperature and high humidity state.

Further, in the capacitance sensor 100 according to the present embodiment, a plurality of open pores 113b can be formed from a plurality of closed pores 113a formed along at least one surface of the front surface and the back surface of the foam sheet 113. .. That is, since the surface after processing is rougher than the surface before rough surface processing, when an adhesive layer is formed on the surface that has been roughened, the adhesive layer to the foamed sheet 113 is affected by the anchor effect. Peeling strength is improved. As a result, the reliability of the adhesive layer with respect to the foamed sheet 113 is improved.

(Other variants)
The capacitance sensor according to the present disclosure has been described above based on each of the above embodiments, but the present disclosure is not limited to these embodiments. As long as it does not deviate from the gist of the present disclosure, various modifications that can be conceived by those skilled in the art may be included in the scope of the present disclosure.

For example, in the capacitance sensor according to each of the above embodiments, the steering cover has two sensor electrodes and two ground electrodes, but has three or more sensor electrodes and three or more ground electrodes. You may be. In this case, the control device may have a switch unit according to the number of sensor electrodes. Specifically, for example, one base material has three or four sensor electrodes to increase the gripping position detection resolution of the steering wheel, while only two ground electrodes are provided on the same base material. It may be provided to simplify the configuration of the ground electrode.

Further, in the capacitance sensor in each of the above embodiments, the ground electrode is fixed to the foam sheet by being sewn on the foam sheet by sewing, but is fixed to the foam sheet by another method. May be good.

In addition, it is realized by arbitrarily combining the components and functions in each embodiment within the range obtained by applying various modifications that can be conceived by those skilled in the art to each of the above embodiments and the purpose of the present disclosure. The form to be used is also included in the present disclosure.

The capacitance sensor of the present disclosure can be applied to, for example, a steering wheel of a vehicle, a grip of a motorcycle, or the like.

100 Capacitance sensor 111 Surface layer 112 Sensor electrode 113 Foam sheet 113a Closed pore 113b Open pore 113c Opening 114 Ground electrode

Claims (4)

An effervescent foam sheet with a front surface and a back surface,
Capacitive sensor electrodes arranged on the surface of the foam sheet and
The sensor electrode includes a surface layer portion arranged on a surface opposite to the side on which the foam sheet is arranged.
A capacitance sensor in which a plurality of open pores are formed from a plurality of closed pores formed along at least one surface of the front surface and the back surface of the foam sheet. An opening is formed in the plurality of open pores.
The capacitance sensor according to claim 1, wherein the average diameter of the openings of the plurality of open pores is smaller than the average diameter of the plurality of open pores and the plurality of closed pores. The capacitance sensor according to claim 1 or 2, wherein a ground electrode is arranged on the back surface of the foam sheet. The foamed sheet according to any one of claims 1 to 3, wherein the plurality of open pores are formed from the plurality of closed pores by roughening at least one of the front surface and the back surface. Capacitance sensor.

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