JP2021018693A - Capacitive sensor - Google Patents

Abstract

To provide a capacitive sensor capable of suppressing corrosion of sensor electrode by electrocorrosion protection.SOLUTION: A capacitive sensor 100 includes: a surface layer 111 that is touched by a hand; a sensor electrode 112 disposed on the rear surface of surface layer 111; a base material 113, which is arranged on the side opposite to the surface layer 111 side of the sensor electrode 112; a grounded electrode 114 located on the opposite side of the sensor electrode 112 on the base material 113; and a control circuit 121 that is electrically connected to the sensor electrode 112. The control circuit 121 alternately applies a measurement potential when measuring hand contact with sensor electrode 112 and a negative potential with respect to the ground electrode 114 to the sensor electrode 112.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a capacitance sensor.

Conventionally, a capacitance sensor 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 capacitance sensor is a control that receives a detection signal from a steering skin formed of leather or the like that comes into contact with the user's hand, a capacitance detection electrode arranged on the back surface side of the steering skin, and a capacitance detection electrode. It has a part. Such a capacitance detection electrode is used as a sensor electrode.

Japanese Patent No. 5947919

However, in the capacitance sensor in Patent Document 1, the steering skin is placed in a high temperature and high humidity state because the user's hand continues to be in contact with the steering skin. Steering skins, usually made of leather, have acidic residues generated during the tanning process. Therefore, the water given by the user's hand may reach the capacitance detection electrode or the like in a state containing this residue. In this case, there is a problem that the capacitance detection electrode or the like is corroded, or the capacitance sensor is defective due to the corrosion.

Therefore, an object of the present disclosure is to provide a capacitance sensor capable of suppressing corrosion of a sensor electrode by anticorrosion.

The capacitance sensor according to one aspect of the present disclosure includes a surface layer portion to be touched by a hand, a sensor electrode arranged on the back surface of the surface layer portion, and a group arranged on the side of the sensor electrode opposite to the surface layer portion side. A material, a ground electrode arranged on the opposite side of the base material from the sensor electrode, and a control circuit electrically connected to the sensor electrode are provided, and the control circuit is brought into contact with the hand by the sensor electrode. And the negative potential with respect to the ground electrode are alternately applied to the sensor electrode.

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 corrosion of the sensor electrode by anticorrosion.

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 block diagram illustrating in detail the configuration of the control device for the capacitance sensor according to the embodiment. FIG. 6 is a flowchart showing the operation of the capacitance sensor according to the embodiment. FIG. 7A is a schematic view showing a case where the current path is conducted along the warp or weft in the sensor electrode of the capacitance sensor according to the embodiment. FIG. 7B is a schematic view showing a case where the current path of the sensor electrode of the capacitance sensor according to the embodiment relies on the contact point between the warp and the weft to conduct the current. FIG. 8 is a block diagram showing a configuration of a capacitance sensor in a modified example.

The capacitance sensor according to one aspect of the present disclosure includes a surface layer portion to be touched by a hand, a sensor electrode arranged on the back surface of the surface layer portion, and a group arranged on the side of the sensor electrode opposite to the surface layer portion side. A material, a ground electrode arranged on the opposite side of the base material from the sensor electrode, and a control circuit electrically connected to the sensor electrode are provided, and the control circuit is brought into contact with the hand by the sensor electrode. And the negative potential with respect to the ground electrode are alternately applied to the sensor electrode.

For example, when the user's hand touches the surface layer, the moisture such as sweat generated by the user's hand (for example, water vapor) is mixed with the acidic residue contained in the material of the surface layer, and the acidic corrosive water. May become. Such corrosive water may permeate the inside of the capacitance sensor and reach the sensor electrodes. In this case, the corrosive water generates a local current on the surface of the sensor electrode, and the metal material constituting the sensor electrode is ionized. As a result, the metal material is oxidized and the sensor electrode is corroded.

However, according to the present disclosure, the control circuit alternately applies the measurement potential and the negative potential to the sensor electrode. That is, by applying a negative potential to the metal material based on the pH potential diagram of the metal material, it is more stable that the metal material remains as it is than that it is ionized, so that the ionization of the metal material is suppressed.

Therefore, in this capacitance sensor, corrosion of the sensor electrode can be suppressed by anticorrosion. As a result, the reliability of this capacitance sensor can be improved.

In particular, the control circuit does not apply a negative potential to the sensor electrodes when measuring hand contact with the sensor electrodes. Therefore, the capacitance sensor can reliably measure the hand in contact with the surface layer portion.

Further, in the capacitance sensor according to another aspect of the present disclosure, in the control circuit, the first period in which the measurement potential is applied to the sensor electrode is longer than the second period in which the negative potential is applied to the sensor electrode. shorten.

According to this, the control circuit can sufficiently secure the period for applying the negative potential to the sensor electrode by making the first period shorter than the second period. On the other hand, it is possible to secure a period for measuring the contact of the hand by the sensor electrode. Therefore, it is possible to detect the contact of the hand with the surface layer portion and more reliably suppress the corrosion of the sensor electrode.

Further, in the capacitance sensor according to another aspect of the present disclosure, the control circuit estimates the humidity of the base material by applying the measurement potential to the sensor electrode, and the higher the estimated humidity, the higher the humidity. The first period is shortened and the second period is lengthened.

According to this, since the capacitance of the base material changes according to the change in the humidity of the base material (the amount of water contained in the base material), the humidity of the base material can be estimated based on the change amount. Therefore, since the first period and the second period are changed according to the humidity of the base material, the second period in which the negative potential is applied to the sensor electrode can be optimized. That is, if the humidity of the base material is low, the amount of corrosive water in the base material is reduced. Therefore, by positively measuring the contact of the hand with the sensor electrode, the contact of the hand in contact with the surface layer portion can be reliably measured. , Corrosion of sensor electrodes can be suppressed. Further, if the humidity of the base material is high, the amount of corrosive water in the base material increases, so that the time for applying the negative potential to the sensor electrode (second period) is relatively longer than the first period for measurement. As a result, it is possible to strengthen the corrosion suppression of the sensor electrode while performing the contact measurement of the hand.

Further, in the capacitance sensor according to another aspect of the present disclosure, the control circuit acquires humidity information from the outside, and the higher the humidity shown in the acquired humidity information, the shorter the first period. , The second period is lengthened.

According to this, for example, a negative potential can be applied to the sensor electrode based on the ambient humidity indicated by the humidity information acquired from peripheral devices and the like. Therefore, corrosion of the sensor electrode can be suppressed even when the hand is not touching the surface layer portion.

Further, in the capacitance sensor according to another aspect of the present disclosure, the sensor electrode is a conductive cloth.

For example, when the conductive cloth is composed of warp and weft, if the sensor electrode is arranged in a state of being cut along the warp or weft, the current path is conducted along the warp or weft, so that the sensor electrode is , The contact of the hand with the surface layer can be detected. However, for example, when the conductive cloth is not cut along the warp and the weft, that is, when the sensor electrode is arranged in a state of being cut in the direction intersecting the warp and the weft, the contact point between the warp and the weft Since the reliant conduction is performed, if the warp and the weft are corroded and it becomes difficult to conduct the conduction at the contact point between the warp and the weft, it becomes difficult for the sensor electrode to detect the contact of the hand with the surface layer portion.

However, according to the present disclosure, since corrosion of the sensor electrode can be suppressed by anticorrosion, the sensor electrode can be placed on the surface layer regardless of the direction in which the conductive cloth is cut and the arrangement. Contact can be detected. Therefore, the capacitance sensor makes it easy to assemble the steering wheel using the sensor electrodes.

In particular, in the case of a conductive cloth made of a resin as a base material, the sensor electrode has elasticity. Therefore, for example, when the capacitance sensor is wound around the steering wheel of the vehicle, the conductive cloth can be stretched, so that the capacitance sensor can be easily wound around the steering wheel, and the sensor electrode is less likely to be broken even if the capacitance sensor is stretched. Become. As a result, the capacitance sensor can be wound around the steering wheel without worrying about whether or not the sensor electrode is broken, which facilitates winding.

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 base material 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 surface of the base material 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 base material 113. That is, the pair of sensor electrodes 112 are sandwiched between the surface layer portion 111 and the base material 113. The sensor electrode 112 is adhered to the back surface of the surface layer portion 111 with an adhesive (not shown) and to the surface of the base material 113 with an adhesive (not shown). The surface of the base material 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 base material 113 is a non-woven fabric formed in the form of a long sheet by a material having elasticity, flexibility and ductility. For example, the base material 113 is made of a synthetic resin such as polyethylene (PE) and polyethylene terephthalate (PET). The base material 113 is formed according to the shape and size of the rim 210.

Further, the base material 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 base material 113 is sandwiched between the sensor electrode 112 and the ground electrode 114.

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 wirings 119b, 119c, etc., 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 side of the base material 113 opposite to the sensor electrode 112, that is, on the back surface of the base material 113 and on the front surface of the rim 210. That is, the ground electrode 114 is sandwiched between the rim 210 and the base material 113. For example, the ground electrode 114 is sewn to the base material 113 by sewing thread. The back surface of the base material 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.

FIG. 5 is a block diagram illustrating in detail the configuration of the control device 120 of the capacitance sensor 100 in the embodiment. In FIG. 5, for convenience, one sensor electrode ground 112 and one ground electrode 114 are shown, and the other sensor electrode ground 112 and the other ground electrode 114 are not shown. For this reason, the switch unit 125 and the power conversion unit 123 that connect the other sensor electrode ground 112 to the control circuit 121 and the like are also omitted.

As shown in FIGS. 4 and 5, the control device 120 includes a control circuit 121, a switch unit 125, a power conversion unit 123, 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. Further, the control circuit 121 is electrically connected to the other sensor electrode 112. That is, the control circuit 121 applies an alternating current to the sensor electrode 112 on one side via the wirings 119a and 119d, that is, applies a measurement potential to the sensor electrode 112 on one side. Further, the control circuit 121 applies an alternating current to the sensor electrode 112 on the other side via the wirings 119a and 119d, 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 wirings 119a and 119d. That is, the control circuit 121 applies an alternating current to the sensor electrode 112 on the other side via the wirings 119a and 119d, that is, applies a measurement potential to the sensor electrode 112 on the other side. 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 alternately applies the measured potential when measuring the contact of the hand to the steering wheel 200 and the negative potential with respect to the ground electrode 114 to the sensor electrode 112. Details of the power conversion unit 123 that generates a negative potential will be described later. At this time, the control circuit 121 makes the first period in which the measurement potential is applied to the sensor electrode 112 shorter than the second period in which the negative potential is applied to the sensor electrode 112. The control circuit 121 changes the potential applied to the sensor electrode 112 by switching the switch unit 125 so as to alternately repeat the first period and the second period.

Here, for example, the first period is 100 (ms) and the second period is 900 (ms). As a result, the second period is about ten times as large as the first period. The first period and the second period are examples, and the first period may be several (ms), several tens (ms), etc. In this case, the second period is also about ten times as large as the first period. ..

Further, when the measurement potential is applied to the sensor electrode 112, the control circuit 121 transmits a first switch control signal for electrically connecting the control circuit 121 and the sensor electrode 112 to the switch unit 125. As a result, the control circuit 121 switches the switch unit 125 so that the control circuit 121 and the sensor electrode 112 are electrically connected via the wirings 119a and 119d. Further, the control circuit 121 controls a second switch for electrically connecting the power supply circuit 124 to the sensor electrode 112 via the power conversion unit 123 or the like when a negative potential with respect to the ground electrode 114 is applied to the sensor electrode 112. The signal is transmitted to the switch unit 125. As a result, the control circuit 121 switches the switch unit 125 so that the power supply circuit 124 is electrically connected to the sensor electrode 112 via the power conversion unit 123 or the like.

Further, the control circuit 121 estimates the humidity of the base material 113 by applying the measurement potential to the sensor electrode 112. Specifically, when the measurement potential is applied to the sensor electrode 112, if the amount of change in capacitance does not exceed the specified value for determining hand contact, if the humidity of the base material 113 is high, it will be static. The electric capacity changes. The control circuit 121 estimates the humidity of the base material 113 according to this change.

Further, the control circuit 121 controls the period of the potential applied to the sensor electrode 112 so that the higher the estimated humidity, the shorter the first period and the longer the second period. That is, the control circuit 121 minimizes the first period of the measurement potential applied to the sensor electrode 112 so that the contact of the hand with the steering wheel 200 can be detected if the humidity of the base material 113 is high. Maximize the second period of negative potential applied to the sensor electrode 112. If the humidity of the base material 113 is low, corrosion of the sensor electrode 112 is unlikely to proceed. Therefore, the control circuit 121 sets a period for applying the potential to the sensor electrode 112 so that the difference between the first period and the second period becomes small. Control.

Further, the control circuit 121 is electrically connected to the power supply circuit 124 via the wiring 119h, electrically connected to the power conversion unit 123 via the wiring 119g, and grounded via the wiring 119i. There is. The control circuit 121 supplies electric power to the power conversion unit 123 by controlling the power supply circuit 124. Further, the control circuit 121 adjusts the voltage of the power to be converted by controlling the power conversion unit 123.

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 switch unit 125 is, for example, a relay switch, a semiconductor switch, or the like. The switch unit 125 is connected to the sensor electrode 112 via the wiring 119a, is connected to the power conversion unit 123 via the wiring 119e, and is connected to the control circuit 121 via the wiring 119d. When the switch unit 125 acquires the first switch control signal from the control circuit 121, the switch unit 125 switches from the electrical connection between the wiring 119e and the wiring 119a to the electrical connection between the wiring 119a and the wiring 119d, thereby switching the control circuit 121. And the sensor electrode 112 are electrically connected. Further, when the switch unit 125 acquires the second switch control signal from the control circuit 121, the switch unit 125 switches from the electrical connection between the wiring 119d and the wiring 119a to the electrical connection between the wiring 119a and the wiring 119e to generate power. The conversion unit 123 and the sensor electrode 112 are electrically connected.

The power conversion unit 123 is a DC-DC converter that converts the voltage of the DC power supplied from the power supply circuit 124 when the switch unit 125 electrically connects the wiring 119e and the wiring 119a. The power conversion unit 123 converts the voltage of the DC power supplied from the power supply circuit 124 into a negative potential lower than the ground potential only during the second period in which the wiring 119e and the wiring 119a are electrically connected by switching the switch unit 125. Then, it is supplied to the sensor electrode 112. In the present embodiment, the power conversion unit 123 converts the voltage of 12V or 5V supplied from the power supply circuit 124 into, for example, −1.5V and supplies it to the sensor electrode 112. The negative potential value may be set so as to be a negative potential in which corrosion is suppressed, depending on the metal material of the conductive cloth constituting the sensor electrode 112.

The power supply circuit 124 is electrically connected to the control circuit 121 via the wiring 119h and to the power conversion unit 123 via the wiring 119f. The power supply circuit 124 applies a measurement potential to the sensor electrode 112 via the control circuit 121 or the like. Further, the power supply circuit 124 is controlled by the control circuit 121 to supply electric power to the power conversion unit 123.

[motion]
FIG. 6 is a flowchart showing the operation of the capacitance sensor 100 according to the embodiment.

First, as shown in FIG. 6, the control circuit 121 of the control device 120 transmits the second switch control signal to the switch unit 125. When the switch unit 125 acquires the second switch control signal, the switch unit 125 switches from the electrical connection between the wiring 119a and the wiring 119d to the electrical connection between the wiring 119a and the wiring 119e. That is, the control circuit 121 controls the switch unit 125 so that the power supply circuit 124 is electrically connected to the sensor electrode 112 via the power conversion unit 123 and the like. As a result, the control circuit 121 applies a negative potential with respect to the ground electrode 114 to the sensor electrode 112 (S11). As a result, even in the presence of acidic corroded water, the sensor electrode 112 is suppressed from being ionized and corroded by applying a negative potential.

Next, the control circuit 121 determines whether or not the second period has elapsed (S12).

When the second period has not elapsed (NO in S12), the control circuit 121 returns the process to step S12 and repeats the determination in step S12.

When the second period has elapsed (YES in S12), the control circuit 121 transmits the first switch control signal to the switch unit 125. When the switch unit 125 acquires the first switch control signal, the switch unit 125 switches from the electrical connection between the wiring 119a and the wiring 119e to the electrical connection between the wiring 119a and the wiring 119d. That is, the control circuit 121 is electrically connected to the sensor electrode 112 by controlling the switch unit 125. As a result, the control circuit 121 stops the application of the negative potential to the sensor electrode 112 (S13) and applies the measurement potential to the sensor electrode 112 (S14).

Next, the control circuit 121 determines whether or not the first period has elapsed (S15).

When the first period has not elapsed (NO in S15), the control circuit 121 returns the process to step S14 and repeats the determination in step S12.

When the first period has elapsed (YES in S15), the control circuit 121 transmits a second switch control signal to the switch unit 125. When the switch unit 125 acquires the second switch control signal, the switch unit 125 switches from the electrical connection between the wiring 119e and the wiring 119a to the electrical connection between the wiring 119d and the wiring 119a. That is, the control circuit 121 is electrically connected to the sensor electrode 112 by controlling the switch unit 125. As a result, the control circuit 121 stops applying the measurement potential to the sensor electrode 112 (S16), returns the process to step S11, and applies a negative potential to the sensor electrode 112.

In this way, the control device 120 alternately repeats the control of applying the negative potential during the second period and then applying the measurement potential during the first period. In the description of FIG. 6, the measurement potential is applied after the negative potential is applied, but the opposite may be true. That is, steps S11 to S13 may be performed after steps S14 to S16, and the process is not limited to the process shown in FIG.

[Action effect]
As described above, in the capacitance sensor 100 according to the present embodiment, the control circuit 121 sets the measurement potential when measuring the contact of the hand by the sensor electrode 112 and the negative potential with respect to the ground electrode 114 to the sensor electrode 112. Alternately applied to. Therefore, when a negative potential is applied to the sensor electrode 112, ionization is suppressed even in the presence of acidic corrosive water.

Therefore, in the capacitance sensor 100, corrosion of the sensor electrode 112 can be suppressed by anticorrosion. As a result, the reliability of the capacitance sensor 100 can be improved.

In particular, the control circuit 121 does not apply a negative potential to the sensor electrode 112 when measuring hand contact with the sensor electrode 112. Therefore, the capacitance sensor 100 can reliably measure the hand in contact with the surface layer portion 111.

Further, in the capacitance sensor 100 of the present embodiment, the control circuit 121 makes the first period shorter than the second period, so that a sufficient period of applying the negative potential to the sensor electrode 112 can be sufficiently secured. On the other hand, it is possible to secure a period for measuring the contact of the hand by the sensor electrode 112. Therefore, it is possible to detect the contact of the hand with the surface layer portion 111 and more reliably suppress the corrosion of the sensor electrode 112.

Further, in the capacitance sensor 100 according to the present embodiment, since the capacitance of the base material 113 changes due to a change in the humidity of the base material 113 (the amount of water contained in the base material 113), the capacitance of the base material 113 changes based on the change amount. , The humidity of the base material 113 can be estimated. Further, in the control circuit 121, the higher the estimated humidity, the shorter the first period and the longer the second period. That is, since the first period and the second period are changed according to the humidity of the base material 113, the second period in which the negative potential is applied to the sensor electrode 112 can be optimized. That is, if the humidity of the base material 113 is low, the amount of corrosive water in the base material 113 is reduced. Therefore, by positively measuring the contact of the hands with the sensor electrode 112, the hands in contact with the surface layer portion 111 can be reliably measured. At the same time, corrosion of the sensor electrode 112 can be suppressed. Further, if the humidity of the base material 113 is high, the amount of corroded water in the base material 113 increases, so that the application time of the negative potential to the sensor electrode 112 (second period) is relative to the first period for measurement. By making it longer, it is possible to strengthen the corrosion suppression of the sensor electrode 112 while performing the contact measurement of the hand.

FIG. 7A is a schematic view showing a case where the current path is conducted along the warp or weft in the sensor electrode 112 of the capacitance sensor 100 according to the embodiment. FIG. 7B is a schematic view showing a case where the current path of the sensor electrode 112 of the capacitance sensor 100 in the embodiment relies on the contact point between the warp and the weft to conduct the current.

Further, for example, when the conductive cloth is composed of warp threads and weft threads, if the sensor electrodes are arranged in a state of being cut along the warp threads or weft threads as shown in FIG. 7A, the current path is along the warp threads or weft threads. Therefore, the sensor electrode can detect the contact of the hand with the surface layer portion. However, for example, when the conductive cloth is not cut along the warp and weft as shown in FIG. 7B, that is, when the sensor electrode is arranged in a state of being cut in the direction intersecting the warp and weft, the warp Since conduction is performed depending on the contact point between the warp and the weft, if the warp and the weft become difficult to conduct at the contact point between the warp and the weft due to corrosion, the sensor electrode can detect the contact of the hand with the surface layer. It becomes difficult.

However, in the capacitance sensor 100 of the present embodiment, since corrosion of the sensor electrode 112 can be suppressed by electrolytic corrosion protection, the sensor electrode can be suppressed regardless of the direction in which the conductive cloth is cut and the arrangement. The 112 can detect the contact of the hand with the surface layer portion 111. Therefore, in the capacitance sensor 100, the steering wheel 200 can be easily assembled by using the sensor electrode 112.

In particular, in the case of a conductive cloth based on a resin, the sensor electrode 112 has elasticity. Therefore, for example, when the capacitance sensor 100 is wound around the steering wheel 200 of the vehicle 1, the conductive cloth can be stretched, so that the capacitance sensor 100 can be easily wound around the steering wheel 200, and even if the capacitance sensor 100 is stretched, the electrodes can be stretched. Is hard to break. As a result, the capacitance sensor 100 can be wound around the steering wheel 200 without worrying about whether or not the sensor electrode 112 is broken, so that the winding is easy.

(Modification example)
In the above embodiment, the humidity of the base material 113 is estimated by applying the measurement potential to the sensor electrode 112, but this modification differs in that the humidity information indicating the humidity is acquired from the external device 150.

Unless otherwise specified, the configuration of the capacitance sensor 100 of this modification is the same as that of the embodiment, and the same configuration is designated by the same reference numerals and detailed description of the configuration will be omitted.

FIG. 8 is a block diagram showing the configuration of the capacitance sensor 100 in the modified example.

As shown in FIG. 8, the control circuit 121 acquires humidity information from the outside. Here, the outside includes an external device 150 such as an air conditioner equipped with a hygrometer or the like, a humidity input by a user, and the like.

In the present embodiment, the outside is an external device 150, and the control circuit 121 acquires humidity information indicating the humidity inside the vehicle 1 from the external device 150 via the communication unit 126. In the control circuit 121, the higher the humidity shown in the acquired humidity information, the shorter the first period and the longer the second period.

The communication unit 126 is a communication module capable of wired or wireless communication with the external device 150. The communication unit 126 receives humidity information from the external device 150.

Further, in the capacitance sensor 100 according to the present embodiment, the control circuit 121 acquires humidity information from the outside. For example, a negative potential can be applied to the sensor electrode 112 based on the ambient humidity indicated by the humidity information acquired from peripheral devices and the like. Therefore, corrosion of the sensor electrode 112 can be suppressed even when the hand is not touching the surface layer portion 111. Further, since the control circuit 121 acquires the humidity information, it does not perform arithmetic processing as compared with the case of estimating the humidity. Therefore, in the capacitance sensor 100, the processing load can be reduced.

(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 in each of the above embodiments, the steering cover has two sensor electrodes and two ground electrodes, but has one or three or more sensor electrodes and one or three or more. It may have a ground electrode of. 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 Base material 114 Ground electrode 121 Control circuit 150 External device (external)

Claims (5)

The surface layer that you can touch and
The sensor electrodes arranged on the back surface of the surface layer portion and
A base material arranged on the side of the sensor electrode opposite to the surface layer side,
A ground electrode arranged on the side of the base material opposite to the sensor electrode,
A control circuit that is electrically connected to the sensor electrode is provided.
The control circuit is a capacitance sensor that alternately applies a measurement potential when measuring hand contact by the sensor electrode and a negative potential with respect to the ground electrode to the sensor electrode. The capacitance sensor according to claim 1, wherein the control circuit makes the first period in which the measurement potential is applied to the sensor electrode shorter than the second period in which the negative potential is applied to the sensor electrode. The control circuit
The humidity of the base material is estimated by applying the measurement potential to the sensor electrode, and the humidity is estimated.
The capacitance sensor according to claim 2, wherein the higher the estimated humidity, the shorter the first period and the longer the second period. The control circuit
Obtain humidity information from the outside and
The capacitance sensor according to claim 2, wherein the higher the humidity shown in the acquired humidity information, the shorter the first period and the longer the second period. The capacitance sensor according to any one of claims 1 to 4, wherein the sensor electrode is a conductive cloth.

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