CONTACT DETECTING APPARATUS

A contact detecting apparatus comprises an electrostatic sensor, a first bridge capacitor, a charge/discharge switching element, a control device, and a measuring instrument. The electrostatic sensor is configured to have an electrostatic capacitance that changes in accordance with at least one of an area contacted by a conductor and a distance to the conductor, and is configured to have a time constant τ hat changes depending on an electrical resistance corresponding to a distance from a first measurement position; and in a charging process, the measuring instrument detects a position where the conductor is in contact with the electrostatic sensor based on a first potential first sampling value, which is a first potential acquired at a first sampling time point, and a first potential second sampling value, which is the first potential acquired at a second sampling time point after a predetermined time has elapsed from the first sampling time point.

TECHNICAL FIELD

The disclosure relates to a contact detecting apparatus.

RELATED ART

A contact detecting apparatus that detects contact of a human body based on a change in electrostatic capacitance has been proposed in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2015-55589).

This contact detecting apparatus of Patent Document 1 includes a flexible sensor body formed in a sheet shape. The sensor body includes a plurality of rows of first electrodes and a plurality of columns of second electrodes. The first electrodes in each of the plurality of rows of first electrodes are formed in a strip shape and arranged in parallel to each other (see FIG. 11 of Patent Document 1). The second electrodes in each of the plurality of columns of second electrodes are formed in a strip shape and are arranged in parallel to each other. The plurality of rows of first electrodes and the plurality of columns of second electrodes are arranged to cross each other.

The plurality of rows of first electrodes and the plurality of columns of second electrodes are arranged in a matrix. Thus, when a conductor such as a human hand or finger comes into contact with the sensor body, the position and area where the conductor comes into contact can be detected by the plurality of rows of first electrodes and the plurality of columns of second electrodes arranged in a matrix.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2019-196904) has proposed a pressure sensing device that can detect both a pressed position and a pressing force. This pressure sensing device includes a pressure sensing part2having a dielectric, a first electrode having a predetermined volume resistivity, and a second electrode. The pressure sensing device further includes a first measurement instrument30aconnected to a first left terminal21alocated at the left end of the first electrode and a second left terminal22alocated at the left end of the second electrode, and a second measurement instrument30bconnected to a first right terminal21blocated at the right end of the first electrode and a second right terminal22blocated at the right end of the second electrode.

The pressure sensing part2forms an RC circuit with an electrostatic capacitance C between the electrodes and an electrical resistance R mainly of the first electrode. The pressure sensing part is deformed by a pressing force applied from outside, which causes the electrostatic capacitance C to change. In addition, since the first electrode has a predetermined volume resistivity, the electrical resistance between the pressed position and the first left terminal21achanges according to the distance between the pressed position where external pressure is added to the pressure sensing part and the first left terminal21a,and similarly the electrical resistance between the pressed position and the first right terminal21bchanges. The pressing force and the pressed position can be obtained using an RC delay time in the measurement value of the first measurement instrument30aand an RC delay time in the measurement value of the second measurement instrument30b.

However, according to the technology described in Patent Document 1, the plurality of rows of first electrodes and the plurality of columns of second electrodes are arranged in a matrix, so it is necessary to increase the wirings and the terminals for connecting the wirings, which causes problems that the number of parts increases and the structure becomes complicated.

According to the technology described in Patent Document 2, in order to obtain the pressing force and the pressed position, it is necessary to use the measurement value of the first measurement instrument and the measurement value of the second measurement instrument, which are respectively connected to terminals at different positions. That is, two measurement instruments are required in order to obtain the pressing force and the pressed position. Thus, there are problems that the number of parts increases and the structure becomes complicated.

The disclosure provides a contact detecting apparatus that is capable of detecting at least one of a contact position and a contact area with a simple configuration.

SUMMARY

One aspect of the disclosure provides a contact detecting apparatus, including:an electrostatic sensor for detecting contact of a conductor, the electrostatic sensor including an application electrode to which an input voltage that is a constant voltage is applied from a power source, a measurement electrode which is disposed opposite to the application electrode and whose potential is measured, and a dielectric which is disposed between the application electrode and the measurement electrode;a first bridge capacitor connected in series between a first measurement position of the measurement electrode and a ground potential;a charge/discharge switching element connected in series between the measurement electrode and the ground potential and connected in parallel to the first bridge capacitor, and discharging the potential of the measurement electrode to the ground potential when in a closed state;a control device executing a process of discharging the potential of the measurement electrode to the ground potential by setting a state in which the input voltage is not applied to the application electrode and setting the charge/discharge switching element to the closed state, and a process of charging the electrostatic sensor by setting the charge/discharge switching element to an open state and setting a state in which the input voltage is applied to the application electrode after the process of discharging; anda measuring instrument acquiring a first potential between the first measurement position of the measurement electrode and the first bridge capacitor in the process of charging, in whichthe electrostatic sensor is configured so that an electrostatic capacitance changes in response to at least one of an area of contact with the conductor and a distance from the conductor, and is configured so that a time constant changes due to an electrical resistance according to a distance from the first measurement position, andthe measuring instrument detects a position where the conductor is in contact with the electrostatic sensor based on a first potential first sampling value and a first potential second sampling value in the process of charging, in which the first potential first sampling value is the first potential acquired at a first sampling time point after a predetermined time has elapsed since start of charging the electrostatic sensor, and the first potential second sampling value is the first potential acquired at a second sampling time point after a predetermined time has elapsed since the first sampling time point.

According to one aspect of the disclosure, at least one of the contact position and the contact area where a conductor comes into contact with the electrostatic sensor can be detected with a simple configuration using one measuring instrument.

It should be noted that the reference numerals in parentheses described in the claims indicate the corresponding relationship with the specific means described in the following embodiments, and are not intended to limit the technical scope of the disclosure.

DESCRIPTION OF EMBODIMENTS

First Embodiment

1. Configuration of the Steering Wheel1

The first embodiment in which a contact detecting apparatus10according to the disclosure is applied to a steering wheel1of a vehicle (not shown) will be described. First, the structure of the steering wheel1will be described with reference toFIG.1toFIG.2. As shown inFIG.1, the steering wheel1includes a ring portion2formed in a circular ring shape, a core portion3formed smaller than the ring portion2and disposed radially inside the ring portion2, and a plurality of (three in this embodiment) connection portions4that connect the core portion3and the ring portion2. However, the number of connection portions4is not particularly limited, and may be one or two, or four or more.

As shown inFIG.2, the ring portion2includes a core body5, a resin inner layer material6, an electrostatic sensor7, and a skin material8. The core body5constitutes the central portion of the ring portion2and is formed in a shape corresponding to the shape of the ring portion2. That is, the core body5is formed in a circular ring shape and has a circular cross section perpendicular to the axis. Here, the cross-sectional shape of the core body5perpendicular to the axis is not limited to a circular shape, but may be any shape such as an elliptical shape, an egg shape, a U-shape, a C-shape, or a polygonal shape. The core body5in this embodiment is made of metal such as aluminum or magnesium, and has electrical conductivity. The material of the core body5can be a material other than metal.

The resin inner layer material6covers the outer surface of the core body5over the entire circumference of the ring shape of the core body5and over the entire circumference of the circular cross-sectional shape of the core body5. In this embodiment, the cross section of the resin inner layer material6perpendicular to the axis is formed in a circular shape. If the core body5has a U-shaped cross section perpendicular to the axis, the resin inner layer material6is filled not only on the radial outside of the cross section of the core body5perpendicular to the axis, but also in the U-shaped recess of the core body5. The resin inner layer material6is molded on the outer surface side of the core body5by injection molding, and is directly bonded to the outer surface of the core body5. The cross-sectional shape of the resin inner layer material6perpendicular to the axis is not limited to a circular shape, but may be any shape such as an egg shape, an elliptical shape, or a polygonal shape. Foamed urethane resin, for example, is used as the resin inner layer material6. However, it is also possible to use non-foamed resin as the resin inner layer material6.

The electrostatic sensor7is disposed on the outer surface of the resin inner layer material6. The electrostatic sensor7is configured so that when a conductor (not shown) such as a finger or a hand comes into contact with or approaches the electrostatic sensor7, an electrostatic capacitance equivalent value of the electrostatic sensor7changes. The electrostatic sensor7according to this embodiment is a steering wheel sensor that is applied to the steering wheel1of the vehicle. The electrostatic sensor7will be described in detail later.

The skin material8covers the outer surface of the electrostatic sensor7(the surface of the electrostatic sensor7on the side opposite to the resin inner layer material6) over the entire circumference of the electrostatic sensor7. That is, as will be described later, in a case where a measurement electrode22is exposed on a first surface24side of a dielectric23, the skin material8also functions as a covering material of the measurement electrode22. The skin material8is molded by injection molding, and is wrapped on the outer surface side of the electrostatic sensor7and bonded to the outer surface of the electrostatic sensor7. The skin material8is made of, for example, urethane resin. The outer surface of the skin material8constitutes a design surface. Thus, it is preferable to use non-foamed urethane resin or slightly foamed urethane resin as the skin material8.

2. Configuration of the Electrostatic Sensor

Next, the configuration of the electrostatic sensor7will be described with reference toFIG.3andFIG.4. The electrostatic sensor7includes an application electrode21, the measurement electrode22, and the dielectric23. The application electrode21receives an input voltage Vin, which is a constant voltage, from a power source41, which will be described later. The measurement electrode22is disposed opposite to the application electrode21and measures the potential. The dielectric23is disposed between the application electrode and the measurement electrode. The application electrode21and the measurement electrode22have electrical conductivity and are formed in a layered shape.

The application electrode21is disposed on a second surface25of the dielectric23. The application electrode21is formed slightly smaller than the dielectric23and has a similar shape. Thus, an edge portion of the second surface25of the dielectric23is exposed from an edge portion of the application electrode21.

The measurement electrode22is disposed on the first surface24of the dielectric23. The measurement electrode22is formed slightly smaller than the dielectric23and has a similar shape. Thus, an edge portion of the first surface24of the dielectric23is exposed from an edge portion of the measurement electrode22.

As shown inFIG.3andFIG.4, the measurement electrode22has a plurality of through holes26that penetrate the measurement electrode22in the thickness direction. The through holes26are disposed side by side in the longitudinal direction of the measurement electrode22. Further, the through holes26are disposed side by side in the width direction perpendicular to the longitudinal direction of the measurement electrode22. The inner shape of the through hole26is a circular shape. The plurality of through holes26are formed to have the same shape and size. However, the through holes26may not be disposed side by side in the longitudinal direction, and may not be disposed side by side in the width direction. Furthermore, the inner shape of the plurality of through holes26is not limited to a circular shape, but may be a polygonal shape such as a square shape, or an oval shape, and any shape can be selected. In addition, the plurality of through holes26are not limited to having the same shape and size, but may be formed in any shape or size as appropriate.

As shown inFIG.3, in this embodiment, the application electrode21is formed flush with the second surface25of the dielectric23. Moreover, the measurement electrode22is formed flush with the first surface24of the dielectric23. In this embodiment, the inside of the plurality of through holes26is filled with the dielectric23. However, the application electrode21may protrude from the second surface25of the dielectric23, and the measurement electrode22may protrude from the first surface24of the dielectric23.

The dielectric23is formed to contain, for example, an elastomer as a main component. Therefore, the dielectric23is flexible. In other words, the dielectric23has flexibility and is configured to be extensible in the planar direction. The dielectric23is formed to contain, for example, a thermoplastic material, particularly a thermoplastic elastomer, as a main component. The dielectric23may be made of a thermoplastic elastomer itself, or may be made mainly of an elastomer that is crosslinked by heating a thermoplastic elastomer as a material.

Further, the dielectric23may contain rubber, resin, or other materials other than a thermoplastic elastomer. For example, in the case where the dielectric23contains rubber such as ethylene-propylene rubber (EPM, EPDM), the flexibility of the dielectric23is improved. From the viewpoint of improving the flexibility of the dielectric23, the dielectric23may contain a flexibility-imparting component such as a plasticizer. Furthermore, the dielectric23may be made mainly of a reactive curing elastomer or a thermosetting elastomer.

Furthermore, the dielectric23is preferably a material with good thermal conductivity. Therefore, the dielectric23may use a thermoplastic elastomer having high thermal conductivity, or may contain a filler that can increase thermal conductivity.

The application electrode21is disposed on the second surface25side of the dielectric23, and the measurement electrode22is disposed on the first surface24side of the dielectric23. The application electrode21and the measurement electrode22have electrical conductivity. Furthermore, the application electrode21and the measurement electrode22are flexible. In other words, the application electrode21and the measurement electrode22have flexibility and are configured to be extensible in the planar direction.

The application electrode21and the measurement electrode22may be made of an electrically conductive elastomer. In the case where the application electrode21and the measurement electrode22are made of an electrically conductive elastomer, the application electrode21and the measurement electrode22are formed by using an elastomer as a base material and by containing an electrically conductive filler. The elastomer that is the base material of the application electrode21and the measurement electrode22may have the same main component as the dielectric23, or may use a different material. The application electrode21and the measurement electrode22are bonded to the dielectric23by fusion (thermal fusion) with each other.

The application electrode21and the measurement electrode22may be made of an electrically conductive cloth. The electrically conductive cloth is a woven or nonwoven fabric made of electrically conductive fibers. Here, the electrically conductive fibers are formed by coating the surface of flexible fibers with an electrically conductive material. The electrically conductive fibers are formed, for example, by plating the surface of resin fibers such as polyethylene with copper or nickel. In this case, the application electrode21and the measurement electrode22are bonded to the dielectric23by fusion (thermal fusion) of the dielectric23itself.

The application electrode21and the measurement electrode22may be made of a metal foil. The metal foil may be any conductive metal material such as a copper foil or an aluminum foil. Furthermore, the application electrode21and the measurement electrode22are bonded to a sensor sheet by fusion (thermal fusion) of the dielectric23itself, in the same manner as in the case of an electrically conductive cloth.

The application electrode21may or may not have a through hole penetrating the application electrode21in the thickness direction. In the case where the application electrode21does not have a through hole, the measurement electrode22has the plurality of through holes26, so that the electrical resistance value of the measurement electrode22can be made greater than the electrical resistance value of the application electrode21. In detail, the electrical resistance value per unit length of the measurement electrode22in the longitudinal direction is configured to be greater than the electrical resistance value per unit length of the application electrode21.

On the other hand, in the case where the application electrode21has a through hole, by forming the hole diameter of the through holes26of the measurement electrode22to be greater than the hole diameter of the through hole of the application electrode21, the electrical resistance value of the measurement electrode22can be made greater than the electrical resistance value of the application electrode21.

3. Overall Configuration of the Contact Detecting Apparatus10

As shown inFIG.5, the contact detecting apparatus10includes the electrostatic sensor7, a first input switching element11, a first bridge capacitor12, a charge/discharge switching element13, a control device14, and a measuring instrument15.

The first input switching element11is disposed between the power source41and the application electrode21and turns on or off the input voltage Vin applied from the power source41to the application electrode21. The power source41according to this embodiment is a power source line connected to a DC power source (not shown). The electrostatic sensor7is formed in a shape that is elongated in the longitudinal direction (seeFIG.3andFIG.4). The electrostatic sensor7has a first end portion27and a second end portion28at both ends in the longitudinal direction. The first end portion27in the longitudinal direction of the application electrode21is connected to the power source41.

The first bridge capacitor12is connected in series between the first end portion27in the longitudinal direction of the measurement electrode22and a ground potential42. The first end portion27in the longitudinal direction of the measurement electrode22is an example of a first measurement position29of the measurement electrode22.

The charge/discharge switching element13is connected in series between the first measurement position29of the measurement electrode22and the ground potential42, and is connected in parallel to the first bridge capacitor12. When the charge/discharge switching element13is in the closed state, the charge/discharge switching element13discharges the potential of the measurement electrode22to the ground potential42.

The control device14is a microcomputer including a CPU (not shown), a RAM (not shown), a ROM (not shown), etc. The control device14controls the first input switching element11to the open state or the closed state. In addition, the control device14controls the charge/discharge switching element13to the open state or the closed state.

The control device14sets the first input switching element11to the open state and sets the charge/discharge switching element13to the closed state. Thus, the control device14executes a process of discharging the potential of the measurement electrode22to the ground potential42. After the process of discharging the potential of the measurement electrode22to the ground potential42, the control device14sets the charge/discharge switching element13to the open state and sets the first input switching element11to the closed state. Thus, the control device14executes a process of charging the electrostatic sensor7.

In the process of charging the electrostatic sensor7, the measuring instrument15acquires a first potential V1between the first measurement position29of the measurement electrode22and the first bridge capacitor12.

The storage device16stores a saturation first potential SV1. The saturation first potential SV1is the first potential V1when the potential of the measurement electrode22is saturated in a state where a conductor is in contact with the entire surface of the electrostatic sensor7on the measurement electrode22side in the process of charging the electrostatic sensor7.

(1) Electrostatic Capacitance Measuring Method of the Electrostatic Sensor7

Next, the relationship between the timing of opening and closing the charge/discharge switching element13executed by the control device14, and the potential Vin on one end side of the electrostatic sensor7and the output voltage Vout will be described with reference toFIG.6. In t1to t2, the charge/discharge switching element13is turned ON (closed state). Further, the first input switching element11is connected to the ground potential42side. Therefore, the potential Vin on one end side of the electrostatic sensor7becomes the ground potential42.

By the above operation, the electric charge of the electrostatic sensor7is discharged via the charge/discharge switching element13. As a result, the potential (output voltage) Vout between the electrostatic sensor7and the first bridge capacitor12becomes the ground potential42as the reference state. That is, before the above operation, the output voltage Vout is indefinite, but the above operation sets the output voltage Vout to the ground potential42.

Subsequently, in t2to t4, the charge/discharge switching element13is turned OFF (open state), and the first input switching element11is connected to the power source41side. Therefore, the potential Vin on one end side of the electrostatic sensor7becomes the input voltage Vin. By the above operation, the electrostatic sensor7is charged with electric charge. After charging is started, the measuring instrument15measures the output voltage Vout at times (ST1, ST2) after a predetermined time has elapsed.

Subsequently, in t4to t5, the charge/discharge switching element13is turned ON (closed state), and the first input switching element11is connected to the ground potential42side. By this operation, the potential Vin on one end side of the electrostatic sensor7becomes the ground potential42, and the electric charge of the electrostatic sensor7is discharged. That is, the output voltage Vout becomes the ground potential42. Subsequently, in t5to t9, the same operation as in t1to t5described above is repeated.

As described above, the first bridge capacitor12is connected in series to the electrostatic sensor7, and the measuring instrument15acquires an electrostatic capacitance equivalent value based on the potential on the other end side of the electrostatic sensor7, that is, the potential (output voltage) Vout between the electrostatic sensor7and the first bridge capacitor12. Here, since the intermediate potential between mere two capacitors is indefinite, the electrostatic capacitance measured using the intermediate potential is not highly accurate.

However, by setting the charge/discharge switching element13to the closed state, as described above, the electric charge of the electrostatic sensor7is discharged. That is, the output voltage (intermediate potential) Vout becomes the ground potential42as the reference state. In other words, by setting the charge/discharge switching element13to the closed state, the output voltage Vout can be calibrated.

Then, after discharging, the measuring instrument15measures the potential on the other end side of the electrostatic sensor7when the charge/discharge switching element13is set to the open state and the input voltage Vin is applied to one end side of the electrostatic sensor7. In other words, the potential measured by the measuring instrument15becomes a potential corresponding to the electrostatic sensor7. Therefore, the contact detecting apparatus10is capable of measuring the electrostatic sensor7with high accuracy.

(2) Time Constant τ of the Electrostatic Sensor7

FIG.7shows a change in the output voltage Vout of the electrostatic sensor7over time in t2to t3described above. As the electrostatic sensor7is charged, the output voltage Vout increases, and converges to a saturation voltage when a sufficient time has elapsed.

FIG.7shows the percentage of the output voltage Vout of the electrostatic sensor7with respect to the saturation voltage when τ, 2τ (twice τ), 3τ (three times τ), 4τ (four times τ), and 5τ (five times τ) have elapsed since the start of charging the electrostatic sensor7, in regard to a time constant τ in the case where the electrostatic sensor7is defined as an RC equivalent circuit. The percentage of the output voltage Vout of the electrostatic sensor7with respect to the saturation voltage is 63.2% after τ has elapsed since the start of charging the electrostatic sensor7, 86.5% after 2τ has elapsed, 95.0% after 3τ has elapsed, 98.2% after 4τ has elapsed, and 99.3% after 5τ has elapsed.

When measuring the output voltage Vout of the electrostatic sensor7, if the measurement is performed after waiting for the output voltage Vout to converge to a saturation voltage, the measurement requires time, so the efficiency is low. Therefore, the time point at which the output voltage Vout of the electrostatic sensor7is measured is set to be five times or more the time constant τ. This makes it possible to improve the efficiency of measuring the output voltage Vout of the electrostatic sensor7.

(3) Change in Electrostatic Capacitance of the Electrostatic Sensor7Due to Contact or Non-Contact of a Conductor

Next, how the electrostatic capacitance of the electrostatic sensor7changes depending on whether or not a conductor such as a finger51comes into contact with the electrostatic sensor7of this embodiment will be illustrated with reference toFIG.8. For ease of illustration, the size of the finger51is exaggerated. However, the state where the conductor is in contact with the electrostatic sensor7includes a state where the conductor is in direct contact with the electrostatic sensor7, and also a state where the conductor is in indirect contact with the electrostatic sensor7via the skin material8.

In the upper part ofFIG.8, the state of the electrostatic sensor7and the finger51which is a conductor is illustrated. In the middle part ofFIG.8, the state of the electric force lines30of the electrostatic sensor7in each state is illustrated using partially enlarged cross-sectional views of the electrostatic sensor7. In the lower part ofFIG.8, the electrostatic capacitance of the electrostatic sensor7in each state is illustrated.

The upper left part ofFIG.8illustrates a “non-contact state.” That is, a state is illustrated in which the finger51, which is an example of the conductor, is not in contact with the electrostatic sensor7. The middle left part ofFIG.8illustrates a state of the electric force lines30in a state where the finger51is not in contact with the electrostatic sensor7. In the region where the application electrode21and the measurement electrode22face each other, the electric force lines30are illustrated from the application electrode21to the measurement electrode22. The electric force lines30leak out from the through hole26of the measurement electrode22to a region of the measurement electrode22on the opposite side to the application electrode21. Among the electric force lines30leaking out from the through hole26, the electric force lines30located near the hole edge portion of the through hole26flow around the hole edge portion of the through hole26of the measurement electrode22from the region on the opposite side to the application electrode21toward the measurement electrode22.

The electrostatic capacitance of the electrostatic sensor7in the non-contact state is illustrated in the lower left part ofFIG.8. In the non-contact state, the electric force lines30leak out from the through hole26of the measurement electrode22, so the electrostatic capacitance of the electrostatic sensor7is smaller than the electrostatic capacitance in the case where the through hole26is not formed in the measurement electrode22. On the other hand, the electric force lines30located near the hole edge portion of the through hole26leak out from the through hole26to the outside, and then return to the measurement electrode22. Therefore, the electrostatic capacitance of the electrostatic sensor7is slightly greater than the electrostatic capacitance in the case where the electric force lines30leaking out from the through hole26do not return to the measurement electrode22.

The upper center ofFIG.8illustrates an approaching state. That is, a state is illustrated in which the finger51and the electrostatic sensor7are in the non-contact state and the finger51is approaching the vicinity of the electrostatic sensor7. The middle center ofFIG.8illustrates a state of the electric force lines30in the approaching state. The finger51is located on the measurement electrode22side with respect to the electrostatic sensor7. The electric force lines30leaking out from the through hole26of the measurement electrode22are attracted by the finger51. Thus, some of the electric force lines30located near the hole edge portion of the through hole26are also attracted by the finger51. Then, the electric force lines30that leak out from the through hole26to the outside and then return to the measurement electrode22are reduced. As a result, as shown in the lower center ofFIG.8, the electrostatic capacitance of the electrostatic sensor7in the approaching state is reduced compared to the electrostatic capacitance of the electrostatic sensor7in the non-contact state.

The upper right part ofFIG.8illustrates a “contact state.” That is, a state in which the finger51and the electrostatic sensor7are in contact with each other is illustrated. The right center ofFIG.8illustrates a state of the electric force lines30in the contact state. The finger51is in contact with the surface of the skin material of the electrostatic sensor7. In other words, the finger51is in contact with the measurement electrode22side of the electrostatic sensor7. The finger51is located above the through hole26of the measurement electrode22. In other words, the finger51indirectly blocks the through hole26of the measurement electrode22via the skin material. All the electric force lines30leaking out from the through hole26are attracted by the finger51. Thus, there are no electric force lines30that leak out from the through hole26and then return to the measurement electrode22.

On the other hand, the electric force lines30extend from the hole edge portion of the through hole26of the measurement electrode22toward the finger51that is in contact with the surface of the skin material8. Thus, as shown in the lower right part ofFIG.8, the finger51, which is a conductor, becomes a pseudo part of the measurement electrode22. Since the electric force lines30extending from the application electrode21toward the measurement electrode22do not leak out from the through hole26, the electrostatic capacitance of the electrostatic sensor7increases. As a result, the electrostatic capacitance of the electrostatic sensor7in the contact state is greater than the electrostatic capacitance of the electrostatic sensor7in the non-contact state and the approaching state where the electric force lines30leak out from the through hole26.

In the electrostatic sensor7of this embodiment, the electrostatic capacitance of the electrostatic sensor7increases as the number of through holes26that are indirectly blocked by the conductor such as the finger51increases. In addition, the electrostatic sensor7of this embodiment is configured so that the electrostatic capacitance per unit area corresponding to a position where the conductor such as the finger51contacts and the electrostatic capacitance per unit area corresponding to a position where the conductor such as the finger51does not contact have different values.

Next, the relationship between the contact area of the conductor with the electrostatic sensor7and the electrostatic capacitance of the electrostatic sensor7will be described with reference toFIG.9toFIG.11. For ease of illustration, the size of the finger51or the hand52is exaggerated.

FIG.9shows the electrostatic sensor7in a state where a plurality of through holes26are indirectly blocked by the finger51. InFIG.9, five electric force lines30leaking out from five through holes26are attracted by the finger51. However, the number of electric force lines30attracted by the finger51is not limited. As for the electric force lines30leaking out from the other through holes26, although not shown in detail, the electric force lines30located near the center of each through hole26leak out to the outside of the electrostatic sensor7, and the electric force lines30near the hole edge portion of each through hole26return to the measurement electrode22.

FIG.10shows the electrostatic sensor7in a state where a plurality of through holes26are indirectly blocked by the entire hand52. InFIG.10, twenty electric force lines30are attracted by the entire hand52. However, the number of electric force lines30attracted by the entire hand52is not limited to twenty. The electric force lines30leaking out from the other through holes26are similar to the electric force lines30in the case of the finger51.

FIG.11shows an output voltage VHout when the hand52is in contact with the electrostatic sensor7, an output voltage VFout when the finger51is in contact with the electrostatic sensor7, and an output voltage VNout when the conductor such as the finger51or the hand52is not in contact with the electrostatic sensor7. InFIG.11, the output voltages VHout, VFout, and VNout of the electrostatic sensor7are compared using the output voltages VHout, VFout, and VNout at a saturation time Ts when the electrostatic capacitance of the electrostatic sensor7is saturated. Since the electric force lines30leak out from a plurality of through holes26to the outside when the conductor such as the finger51or the hand52is not in contact with the electrostatic sensor7, the electrostatic capacitance of the electrostatic sensor7becomes the lowest, and the output voltage VNout of the electrostatic sensor7becomes the lowest.

When the finger51comes into contact with the electrostatic sensor7, as the electric force lines30in the portion of the plurality of through holes26indirectly covered by the finger51are attracted by the finger51, the electrostatic capacitance of the electrostatic sensor7increases, and the output voltage VFout of the electrostatic sensor7rises.

When the entire hand52comes into contact with the electrostatic sensor7, since the hand52can indirectly cover more through holes26than the finger51, the electrostatic capacitance of the electrostatic sensor7further increases, and the output voltage VHout of the electrostatic sensor7further rises.

The above-described saturation first potential SV1is, for example, the first potential V1when the potential of the measurement electrode22is saturated in a state where the conductor is in contact with the entire surface of the electrostatic sensor7on the measurement electrode22side. Therefore, although not shown in detail inFIG.11, the saturation first potential SV1is even greater than the output voltage Vout when the hand52is in contact with the electrostatic sensor7.

The measuring instrument15can detect the area where the conductor such as the finger51is in contact with the electrostatic sensor7based on the ratio of the first potential V1when the conductor is in contact with the electrostatic sensor7to the saturation first potential SV1.

(4) Method of Detecting the Contact Position of the Conductor

Next, a method of detecting the position where the conductor exemplified by the finger51comes into contact with the electrostatic sensor7will be described with reference toFIG.12toFIG.15.FIG.12shows a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow A, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow B.

As described above, the electrical resistance value per unit length in the longitudinal direction of the measurement electrode22is configured to be greater than the electrical resistance value per unit length in the longitudinal direction of the application electrode21. Thus, when the distance between the first measurement position29of the measurement electrode22and the position where the finger51comes into contact with the electrostatic sensor7changes, the electrical resistance value R1between the first measurement position29and the position corresponding to the finger51in the measurement electrode22changes more significantly than in the application electrode21. Therefore, the time constant τ of the electrostatic sensor7changes depending on the distance between the first measurement position29of the measurement electrode22and the position where the finger51comes into contact with the electrostatic sensor7.

FIG.13shows a change over time in the output voltage Vout of the electrostatic sensor7in the process of charging the electrostatic sensor7in a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. The output voltage Vout of the electrostatic sensor7increases over time and saturates. The output potential at a first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7is set to a first potential first sampling value V11. Further, the output potential at a second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1is set to a first potential second sampling value V12.

The second sampling time point ST2is a time point at which the potential of the measurement electrode22is saturated. The time point at which the potential of the measurement electrode22is saturated refers to a state where the change in the potential of the measurement electrode22becomes smaller than a predetermined value after charging of the electrostatic sensor7is started. In this embodiment, the second sampling time point ST2is a time point at which the time is 5 times or more the time constant τ.

The first sampling time point ST1is a time point in a transitional state before the electrostatic sensor7reaches a saturated state. In this embodiment, the first sampling time point ST1is a time point at which the time is 1 to 4 times the time constant τ.

In this embodiment, the position where the conductor such as the finger51comes into contact with the electrostatic sensor7is detected based on the ratio of the first potential first sampling value V11to the first potential second sampling value V12. This will be described in detail below. As described above, the electrostatic sensor7of this embodiment is configured so that the time constant τ of the electrostatic sensor7changes depending on the distance between the first measurement position29of the measurement electrode22and the position where the finger51comes into contact with the electrostatic sensor7. Therefore, the first potential first sampling value V11at the first sampling time point ST1differs depending on the distance between the first measurement position29of the measurement electrode22and the position where the finger51comes into contact with the electrostatic sensor7. Thus, by calculating the ratio (V11/V12) of the first potential first sampling value V11to the first potential second sampling value V12, it is possible to detect how far away from the first measurement point the position is, at which the conductor such as the finger51is in contact with the electrostatic sensor7.

FIG.14shows a state where the finger51is in contact with the electrostatic sensor7at a position away from the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow C, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow D.

Upon comparison betweenFIG.12andFIG.14, the distance between the first measurement point and the portion of the electrostatic sensor7where the finger51contacts is greater inFIG.14than inFIG.12. Therefore, the electrical resistance value R2of the measurement electrode22shown inFIG.14in the portion where the finger51contacts from the first measurement position29is greater than the electrical resistance value R1of the measurement electrode22shown inFIG.12in the portion where the finger51contacts from the first measurement position29(R2>R1). As a result, the time constant τ of the electrostatic sensor7shown inFIG.15changes compared to the time constant τ of the electrostatic sensor7shown inFIG.13.

FIG.15shows a change over time in the output voltage Vout of the electrostatic sensor7in the process of charging the electrostatic sensor7in a state where the finger51is in contact with the electrostatic sensor7at a position away from the first measurement position29. The output voltage Vout of the electrostatic sensor7increases over time and saturates. The output potential at the first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7is set to the first potential first sampling value V11. Further, the output potential at the second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1is set to the first potential second sampling value V12.

In the case where the finger51is in contact with the electrostatic sensor7at a position away from the first measurement position29(FIG.14), compared to the case where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29(FIG.12), the electrical resistance value R2of the measurement electrode22from the first measurement position29to the finger51increases, and the time constant τ changes so that the first potential first sampling value V11decreases. Thus, according to this embodiment, in the electrostatic sensor7, the first potential first sampling value V11can be made different depending on the distance where the finger51contacts from the first measurement position29. As a result, by calculating the ratio (V11/V12) of the first potential first sampling value V11to the first potential second sampling value V12, it is possible to detect how far away from the first measurement point the position is, at which the conductor such as the finger51is in contact with the electrostatic sensor7.

5. Operation of the Contact Detecting Apparatus

FIG.16is a flowchart showing the operation of the contact detecting apparatus of this embodiment. When the contact detecting apparatus is activated, a process (S1) of discharging the potential of the measurement electrode22to the ground potential42is executed. In S1, the control device14sets the first input switching element11to the open state and sets the charge/discharge switching element13to the closed state. Thus, the potential of the measurement electrode22is discharged to the ground potential42in a state where the input voltage Vin is not applied to the application electrode21.

After a predetermined time has elapsed and the potential of the measurement electrode22has been discharged to the ground potential42, a process (S2) of charging the electrostatic sensor7is executed. In S2, the control device14sets the charge/discharge switching element13to the open state and sets the first input switching element11to the closed state. Thus, the electrostatic sensor7is charged.

The process (S2) of charging the electrostatic sensor7is executed, and until the electrostatic sensor7is completely charged, the measuring instrument15measures the first potential sampling value at the first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7(S3), and measures the first potential second sampling value at the second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1(S4).

The measuring instrument15detects the position where the conductor is in contact with the electrostatic sensor7based on the ratio of the first potential first sampling value V11to the first potential second sampling value V12(S5).

The measuring instrument15detects the area where the conductor is in contact with the electrostatic sensor7based on the first potential second sampling value V12(S6).

Through the above, the operation of the contact detecting apparatus10is completed.

6. Effects of this Embodiment

Next, the effects of this embodiment will be described. The contact detecting apparatus10of this embodiment includes the electrostatic sensor7, the first bridge capacitor12, the charge/discharge switching element13, the control device14, and the measuring instrument15.

The electrostatic sensor7includes the application electrode21to which the input voltage Vin which is a constant voltage is applied from the power source41, the measurement electrode22which is disposed opposite to the application electrode21and whose potential is measured, and the dielectric23which is disposed between the application electrode21and the measurement electrode22, and detects contact of the conductor.

The first bridge capacitor12is connected in series between the first measurement position29of the measurement electrode22and the ground potential42. The charge/discharge switching element13is connected in series between the measurement electrode22and the ground potential42and is connected in parallel to the first bridge capacitor12, and discharges the potential of the measurement electrode22to the ground potential42when in the closed state.

The control device14executes a process of discharging the potential of the measurement electrode22to the ground potential42by setting a state where the input voltage Vin is not applied to the application electrode21and setting the charge/discharge switching element13to the closed state. After the discharging process, the control device14executes a process of charging the electrostatic sensor7by setting the charge/discharge switching element13to the open state and setting a state where the input voltage Vin is applied to the application electrode21.

In the process of charging the electrostatic sensor7, the measuring instrument15acquires the first potential V1between the first measurement position29of the measurement electrode22and the first bridge capacitor12.

The electrostatic sensor7is configured so that the electrostatic capacitance changes in response to at least one of the area of contact with the conductor and the distance from the conductor, and is configured so that the time constant changes due to the electrical resistance according to the distance from the first measurement position29.

The measuring instrument15detects the position where the conductor is in contact with the electrostatic sensor7based on the first potential first sampling value V11and the first potential second sampling value V12. The first potential first sampling value V11is the first potential V1acquired at the first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7in the process of charging the electrostatic sensor7. The first potential second sampling value V12is the first potential V1acquired at the second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1.

According to this embodiment, the position where the conductor comes into contact with the electrostatic sensor7can be detected with a simple configuration of one measuring instrument15.

Further, according to this embodiment, the first sampling time point ST1is a time point in the transitional state after a predetermined first time has elapsed since the start of charging the electrostatic sensor7and before the change in the potential of the measurement electrode22reaches the saturated state. Further, the second sampling time point ST2is a time point later than the first sampling time point ST1and after a predetermined second time has elapsed since the start of charging the electrostatic sensor7. The position where the conductor comes into contact with the electrostatic sensor7can be detected with high accuracy based on the first potential first sampling value V11acquired at the first sampling time point ST1in the transitional state, and the first potential second sampling value V12acquired at the second sampling time point ST2after the first sampling time point ST1.

According to this embodiment, the measuring instrument15detects the position where the conductor comes into contact with the electrostatic sensor7based on the ratio of the first potential first sampling value V11to the first potential second sampling value V12.

According to this embodiment, the electrostatic sensor7is formed in a shape that is elongated in the longitudinal direction, and has the first end portion27and the second end portion28at both ends in the longitudinal direction. The first bridge capacitor12is connected between the first end portion27in the longitudinal direction, which is the first measurement position29of the measurement electrode22, and the ground potential42. The first end portion27in the longitudinal direction of the application electrode21is connected to the power source41. Since the first bridge capacitor12and the power source41are connected to the first end portion27of the electrostatic sensor7, the lead wires (not shown) connected to the first bridge capacitor12and the power source41are led out from the first end portion27of the electrostatic sensor7. This makes it possible to easily arrange the lead wires when attaching the electrostatic sensor7to the steering wheel1.

According to this embodiment, the measurement electrode22and the application electrode21are made of an electrically conductive elastomer. Since the electrostatic sensor7has flexibility, it is easy to attach the electrostatic sensor7along the shape of the steering wheel1.

The measurement electrode22of this embodiment has a plurality of through holes26. Thus, the electric force lines30can leak out from the through holes26to the outside of the electrostatic sensor7. As a result, the conductor comes into contact with the electrostatic sensor7at a position that blocks the through holes26, so that leakage of the electric force lines30from the through holes26can be suppressed. Since the electrostatic capacitance of the electrostatic sensor7is increased when the conductor comes into contact with the electrostatic sensor7, contact of the conductor with the electrostatic sensor7can be easily detected.

The contact detecting apparatus10of this embodiment includes the electrostatic sensor7, the first bridge capacitor12, the charge/discharge switching element13, the control device14, and the measuring instrument15.

The electrostatic sensor7includes the application electrode21to which the input voltage Vin which is a constant voltage is applied from the power source41, the measurement electrode22which is disposed opposite to the application electrode21and whose potential is measured, and the dielectric which is disposed between the application electrode21and the measurement electrode22, and detects contact of the conductor with the measurement electrode22side.

The first bridge capacitor12is connected in series between the first measurement position29of the measurement electrode22and the ground potential42. The charge/discharge switching element13is connected in series between the measurement electrode22and the ground potential42and is connected in parallel to the first bridge capacitor12, and discharges the potential of the measurement electrode22to the ground potential42when in the closed state.

The control device14executes a process of discharging the potential of the measurement electrode22to the ground potential42by setting a state where the input voltage Vin is not applied to the application electrode21and setting the charge/discharge switching element13to the closed state. After the discharging process, the control device14executes a process of charging the electrostatic sensor7by setting the charge/discharge switching element13to the open state and setting a state where the input voltage Vin is applied to the application electrode21.

In the process of charging the electrostatic sensor7, the measuring instrument15acquires the first potential V1between the first measurement position29of the measurement electrode22and the first bridge capacitor12.

The electrostatic sensor7is configured so that the electrostatic capacitance changes in response to at least one of the area and the distance from the conductor, and is configured so that the time constant changes due to the electrical resistance according to the distance from the first measurement position29.

The measuring instrument15detects the area where the conductor is in contact with the electrostatic sensor7based on the first potential second sampling value V12. The first potential second sampling value V12is the first potential V1acquired at the second time point that is later than the first time point after a predetermined first time has elapsed since the start of charging the electrostatic sensor7and when the change in the potential of the measurement electrode22is in the transitional state before reaching the saturated state, and after a predetermined second time has elapsed since the start of charging the electrostatic sensor7in the process of charging the electrostatic sensor7.

According to this embodiment, the area where the conductor comes into contact with the electrostatic sensor7can be detected with a simple configuration of one measuring instrument15.

Second Embodiment

Next, a contact detecting apparatus60of the second embodiment will be described with reference toFIG.17. As shown inFIG.17, in the contact detecting apparatus60of this embodiment, the second end portion28in the longitudinal direction of the application electrode21is connected to the power source41. The configuration other than that described above is substantially the same as in the first embodiment, so the same components are given the same reference numerals and repeated description will be omitted.

FIG.18shows a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow E, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow F.

The output potential of the measurement electrode22in a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29is the same as the graph shown inFIG.13of the first embodiment, so repeated description will be omitted.

FIG.19shows a state where the finger51is in contact with the electrostatic sensor7at a position away from the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow G, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow H.

The output potential of the measurement electrode22in a state where the finger51is in contact with the electrostatic sensor7at a position away from the first measurement position29is the same as the graph shown inFIG.15of the first embodiment, so repeated description will be omitted.

According to this embodiment, the electrostatic sensor7is formed in a shape that is elongated in the longitudinal direction, and has the first end portion27and the second end portion28at both ends in the longitudinal direction. The first bridge capacitor12is connected between the first end portion27in the longitudinal direction, which is the first measurement position29of the measurement electrode22, and the ground potential42. The second end portion28in the longitudinal direction of the application electrode21is connected to the power source41.

According to this embodiment, the power source41and the first bridge capacitor12can be connected to different end portions of the electrostatic sensor7. Thus, it is possible to apply the disclosure even in the case where it is difficult to lead out lead wires from the same end portion of the electrostatic sensor7.

Third Embodiment

Next, a contact detecting apparatus70of the third embodiment will be described with reference toFIG.20. As shown inFIG.20, a second bridge capacitor17is connected in series between the second end portion28of the electrostatic sensor7of the contact detecting apparatus70of this embodiment and the ground potential42. The measuring instrument15is configured to acquire a second potential Vout2between the second end portion28of the measurement electrode22and the second bridge capacitor17in the process of charging the electrostatic sensor7. In this embodiment, the second end portion28of the measurement electrode22is set as a second measurement position31. The measurement electrode22is configured so that the electrical resistance changes depending on the distance from the second measurement position31.

In the process of charging the electrostatic sensor7, the measuring instrument15detects the position where the conductor is in contact with the electrostatic sensor7based on a first potential first sampling value V11, a second potential first sampling value V21, a first potential second sampling value V12, and a second potential second sampling value V22. The second potential first sampling value V21is the second potential Vout2acquired at the first sampling time point ST1. The second potential second sampling value V22is the second potential V2acquired at the second sampling time point ST2.

FIG.21shows a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow I, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow J. Further, the current for charging the electrostatic sensor7flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the second measurement position31as shown by the arrow K.

As shown inFIG.21, the distance between the first measurement position29and the position where the finger51is in contact with the electrostatic sensor7is shorter than the distance between the second measurement position31and the position where the finger51is in contact with the electrostatic sensor7. Therefore, the electrical resistance value R3of the measurement electrode22between the first measurement position29and the finger51is smaller than the electrical resistance value R4of the measurement electrode22between the second measurement position31and the finger51(R3<R4). Therefore, in the electrostatic sensor7, the time constant t associated with the first potential V1is different from the time constant τ associated with the second potential V2.

FIG.22shows changes over time in the first potential Vout1and the second potential Vout2. The first potential Vout1is indicated by a solid line, and the second potential Vout2is indicated by a dashed line. Since the time constant τ associated with the first potential Vout1and the time constant τ associated with the second potential Vout2are different, the change over time in the second potential Vout2is more gradual than the change over time in the first potential Vout1.

The measuring instrument15acquires the first potential first sampling value V11and the first potential second sampling value V12, and calculates the ratio (V11/V12) of the first potential first sampling value V11to the first potential second sampling value V12. Based on this ratio, the measuring instrument15calculates the distance between the first measurement position29and the position where the finger51is in contact with the electrostatic sensor7.

The measuring instrument15acquires the second potential first sampling value V21and the second potential second sampling value V22, and calculates the ratio (V21/V22) of the second potential first sampling value V21to the second potential second sampling value V22. Based on this ratio, the measuring instrument15calculates the distance between the second measurement position31and the position where the finger51is in contact with the electrostatic sensor7.

The measuring instrument15detects the position where the finger51is in contact with the electrostatic sensor7based on the distance between the first measurement position29and the position where the finger51is in contact with the electrostatic sensor7, and the distance between the second measurement position31and the position where the finger51is in contact with the electrostatic sensor7. According to this embodiment, the measuring instrument15can detect the position where the finger51is in contact with the electrostatic sensor7based on the first potential first sampling value V11and the first potential second sampling value V12associated with the first potential Vout1, and the second potential first sampling value V21and the second potential second sampling value V22associated with the second potential Vout2, so the accuracy of the contact detecting apparatus70can be improved.

FIG.23shows a state where the finger51is in contact with the electrostatic sensor7at a position far from the first measurement position29. In this state, when the electrostatic sensor7is charged by the above-described method, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow L, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow M. Further, the current for charging the electrostatic sensor7flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the second measurement position31as shown by the arrow N.

As shown inFIG.23, the distance between the first measurement position29and the position where the finger51is in contact with the electrostatic sensor7is longer than the distance between the second measurement position31and the position where the finger51is in contact with the electrostatic sensor7. Therefore, the electrical resistance value R2of the measurement electrode22between the first measurement position29and the finger51is greater than the electrical resistance value R4of the measurement electrode22between the second measurement position31and the finger51(R2>R4). Therefore, in the electrostatic sensor7, the time constant τ associated with the first potential V1is different from the time constant τ associated with the second potential V2.

FIG.24shows changes over time in the first potential V1and the second potential V2. The first potential V1is indicated by a solid line, and the second potential V2is indicated by a dashed line. Since the time constant τ associated with the first potential V1and the time constant t associated with the second potential V2are different, the change over time in the first potential V1is more gradual than the change over time in the second potential V2.

Similarly to the case where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29, the measuring instrument15can detect the position where the finger51is in contact with the electrostatic sensor7based on the first potential first sampling value V11and the first potential second sampling value V12associated with the first potential V1, and the second potential first sampling value V21and the second potential second sampling value V22associated with the second potential V2. Thus, the accuracy of the contact detecting apparatus70can be improved.

The configuration other than that described above is substantially the same as in the first embodiment, so the same components are given the same reference numerals and repeated description will be omitted.

According to this embodiment, the application electrode21and the measurement electrode22have different electrical resistances per unit length. Furthermore, the electrical resistance per unit length of the measurement electrode22is greater than the electrical resistance per unit length of the application electrode21. Since the first potential V1acquired from the first end portion27of the measurement electrode22can be made different from the second potential V2acquired from the second end portion28, the accuracy of detecting the contact position of the conductor can be improved.

Fourth Embodiment

Next, the fourth embodiment will be described with reference toFIG.25. As shown inFIG.25, in a contact detecting apparatus80of this embodiment, a second input switching element18is connected between the second end portion28of the application electrode21and the power source41. The second input switching element18turns on or off the input voltage Vin applied from the power source41to the second end portion28of the application electrode21. The second input switching element18is connected in parallel to the first input switching element11.

The control device14controls the second input switching element18to the closed state or the open state. The control device14sets the first input switching element11and the second input switching element18to the open state and sets the charge/discharge switching element13to the closed state, thereby executing a process of discharging the potential of the measurement electrode22to the ground potential42. After the process of discharging the potential of the measurement electrode22to the ground potential42, the control device14sets the charge/discharge switching element13to the open state, sets the first input switching element11to the closed state, and sets the second input switching element18to the open state, thereby executing a process of charging the electrostatic sensor7from the first end portion27of the electrostatic sensor7. In addition, after the process of discharging the potential of the measurement electrode22to the ground potential42, the control device14sets the charge/discharge switching element13to the open state, sets the first input switching element11to the open state, and sets the second input switching element18to the closed state, thereby executing a process of charging the electrostatic sensor7from the second end portion28of the electrostatic sensor7.

FIG.26shows a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. In this state, when the electrostatic sensor7is charged from the first end portion27, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow O, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow P. Further, the current for charging the electrostatic sensor7flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the second measurement position31as shown by the arrow Q.

FIG.27shows a state where the finger51is in contact with the electrostatic sensor7at a position close to the first measurement position29. In this state, when the electrostatic sensor7is charged from the second end portion28, the current for charging the electrostatic sensor7flows through the application electrode21as shown by the arrow R, the application electrode21and the measurement electrode22are charged with electric charge, and the current flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the first measurement position29as shown by the arrow S. Further, the current for charging the electrostatic sensor7flows from a portion of the measurement electrode22that overlaps with the finger51in the thickness direction to the second measurement position31as shown by the arrow T.

Next, the operation of the contact detecting apparatus80of this embodiment will be described with reference toFIG.28.FIG.28shows a flowchart of the main flow of the contact detecting apparatus80of this embodiment. When the contact detecting apparatus80is activated, a first cycle is executed (S10). Next, a second cycle is executed (S20). Next, based on the result obtained in the first cycle and the result obtained in the second cycle, the position where the conductor such as the finger51is in contact with the electrostatic sensor7and the area where the conductor such as the finger51is in contact with the electrostatic sensor7are detected (S30). Through the above, the operation of the contact detecting apparatus80is completed.

FIG.29shows a flowchart of the first cycle. When the first cycle is executed (S10), the control device14sets the second input switching element18to the open state. The control device14sets the first input switching element11to the open state and sets the charge/discharge switching element13to the closed state. Thus, the potential of the measurement electrode22is discharged to the ground potential42in a state where the input voltage Vin is not applied to the application electrode21(S11).

After a predetermined time has elapsed and the potential of the measurement electrode22has been discharged to the ground potential42, a process (S12) of charging the electrostatic sensor7is executed. In S12, the control device14sets the charge/discharge switching element13to the open state and sets the first input switching element11to the closed state. Thus, the electrostatic sensor7is charged from the first end portion27of the electrostatic sensor7.

The process (S12) of charging the electrostatic sensor7is executed, and until the electrostatic sensor7is completely charged, the measuring instrument15measures and acquires the first potential first sampling value V11at the first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7, and measures and acquires the first potential second sampling value V12at the second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1(S13).

The measuring instrument15detects the position where the conductor is in contact with the electrostatic sensor7based on the ratio of the first potential first sampling value V11to the first potential second sampling value V12(S14). However, the measuring instrument15may detect the position where the conductor is in contact with the electrostatic sensor7based on the ratio of the second potential first sampling value V21to the second potential second sampling value V22.

The measuring instrument15detects the area where the conductor is in contact with the electrostatic sensor7based on the first potential second sampling value V12(S15). However, the measuring instrument15may detect the area where the conductor is in contact with the electrostatic sensor7based on the second potential second sampling value V22.

Through the above, the first cycle (S10) is completed.

Next,FIG.30shows a flowchart of the second cycle. When the second cycle is executed (S20), the control device14sets the first input switching element11to the open state. The control device14sets the second input switching element18to the open state and sets the charge/discharge switching element13to the closed state. Thus, the potential of the measurement electrode22is discharged to the ground potential42in a state where the input voltage Vin is not applied to the application electrode21(S21).

After a predetermined time has elapsed and the potential of the measurement electrode22has been discharged to the ground potential42, a process (S21) of charging the electrostatic sensor7is executed. In S21, the control device14sets the charge/discharge switching element13to the open state and sets the second input switching element18to the closed state. Thus, the electrostatic sensor7is charged from the second end portion28of the electrostatic sensor7.

The process (S21) of charging the electrostatic sensor7is executed, and until the electrostatic sensor7is completely charged, the measuring instrument15measures and acquires the second potential first sampling value V21at the first sampling time point ST1after a predetermined time has elapsed since the start of charging the electrostatic sensor7, and measures and acquires the second potential second sampling value V22at the second sampling time point ST2after a predetermined time has elapsed since the first sampling time point ST1(S23).

The measuring instrument15detects the position where the conductor is in contact with the electrostatic sensor7based on the ratio of the second potential first sampling value V21to the second potential second sampling value V22(S24). However, the measuring instrument15may detect the position where the conductor is in contact with the electrostatic sensor7based on the ratio of the first potential first sampling value V11to the first potential second sampling value V12.

The measuring instrument15detects the area where the conductor is in contact with the electrostatic sensor7based on the second potential second sampling value V22(S25). However, the measuring instrument15may detect the area where the conductor is in contact with the electrostatic sensor7based on the first potential second sampling value V12.

Through the above, the second cycle (S20) is completed.

The configuration other than that described above is substantially the same as in the third embodiment, so the same components are given the same reference numerals and repeated description will be omitted.

According to this embodiment, the control device14executes the first cycle (S10) that includes the discharging process and the charging process following the discharging process in order for the measuring instrument15to acquire the first potential V1, and after the first cycle, executes the second cycle (S20) that includes the discharging process and the charging process following the discharging process in order for the measuring instrument15to acquire the second potential V2.

Based on the result obtained in the first cycle (S10) and the result obtained in the second cycle (S20), the position where the conductor is in contact with the electrostatic sensor7can be detected, so the accuracy of the contact detecting apparatus80can be improved. Further, based on the result obtained in the first cycle (S10) and the result obtained in the second cycle (S20), the area where the conductor is in contact with the electrostatic sensor7can be detected, so the accuracy of the contact detecting apparatus80can be improved.

Fifth Embodiment

Next, the fifth embodiment will be described with reference toFIG.31. The measurement electrode22A of the electrostatic sensor7A according to the fifth embodiment has the same shape and size as the application electrode21. The measurement electrode22A of this embodiment differs from the first embodiment in that the measurement electrode22A does not have the through holes26. The configuration other than that described above is substantially the same as in the first embodiment, so the same components are given the same reference numerals and repeated description will be omitted.

When a conductor such as the finger51comes into contact with the measurement electrode22A side of the electrostatic sensor7A, a kind of capacitor is formed between the measurement electrode22A and the conductor such as the finger51with the skin material8interposed therebetween. Thus, the electrostatic capacitance of the electrostatic sensor7A changes. Due to this change in electrostatic capacitance, the electrostatic sensor7A is charged, so similar to the first embodiment described above, the position where the finger51is in contact with the electrostatic sensor7A and the area where the finger51is in contact with the electrostatic sensor7A can be detected.

The disclosure is not limited to the above-described embodiments, and includes the following aspects without departing from the gist of the disclosure.(1) A contact detecting apparatus, including:an electrostatic sensor for detecting contact of a conductor with a measurement electrode side, the electrostatic sensor including an application electrode to which an input voltage that is a constant voltage is applied from a power source, a measurement electrode which is disposed opposite to the application electrode and whose potential is measured, and a dielectric which is disposed between the application electrode and the measurement electrode;a first bridge capacitor connected in series between a first measurement position of the measurement electrode and a ground potential;a charge/discharge switching element connected in series between the measurement electrode and the ground potential and connected in parallel to the first bridge capacitor, and discharging the potential of the measurement electrode to the ground potential when in a closed state;a control device executing a process of discharging the potential of the measurement electrode to the ground potential by setting a state in which the input voltage is not applied to the application electrode and setting the charge/discharge switching element to the closed state, and a process of charging the electrostatic sensor by setting the charge/discharge switching element to an open state and setting a state in which the input voltage is applied to the application electrode after the process of discharging; anda measuring instrument acquiring a first potential between the first measurement position of the measurement electrode and the first bridge capacitor in the process of charging, in whichthe electrostatic sensor is configured so that an electrostatic capacitance per unit area corresponding to a position where the conductor is in contact and an electrostatic capacitance per unit area corresponding to a position where the conductor is not in contact have different values,the measurement electrode is configured so that an electrical resistance changes depending on a distance from the first measurement position, andthe measuring instrument detects a position where the conductor is in contact with the electrostatic sensor based on a first potential first sampling value and a first potential second sampling value in the process of charging, in which the first potential first sampling value is the first potential acquired at a first sampling time point after a predetermined time has elapsed since start of charging the electrostatic sensor, and the first potential second sampling value is the first potential acquired at a second sampling time point after a predetermined time has elapsed since the first sampling time point.(2) The contact detecting apparatus according to (1) above, in which the first sampling time point is a time point in a transitional state from when charging of the electrostatic sensor is started until when a change in the potential of the measurement electrode reaches a saturated state smaller than a predetermined value, andthe second sampling time point is a time point which is later than the first sampling time point and when the potential of the measurement electrode is saturated.(3) The contact detecting apparatus according to (2) above, in which the measuring instrument detects the position where the conductor is in contact with the electrostatic sensor based on a ratio of the first potential first sampling value to the first potential second sampling value.(4) The contact detecting apparatus according to (2) above, in which the first sampling time point is a time point when the time is 1 to 4 times the time constant τ in the case where the electrostatic sensor is defined as an RC equivalent circuit, and the second sampling time point is a time point when the time is 5 times or more the time constant τ.(5) The contact detecting apparatus according to (2) above, in which the measuring instrument further detects an area where the conductor is in contact with the electrostatic sensor based on the first potential second sampling value in the process of charging.(6) The contact detecting apparatus according to (5) above, further including a storage device that stores a saturation first potential, which is the first potential when the potential of the measurement electrode is saturated, in a state where the conductor is in contact with the entire surface of the electrostatic sensor on the measurement electrode side in the process of charging, andthe measuring instrument detects the area where the conductor is in contact with the electrostatic sensor based on the first potential second sampling value in the process of charging and the saturation first potential.(7) The contact detecting apparatus according to any one of (1) to (6) above, in which the electrostatic sensor is formed in a shape that is elongated in a longitudinal direction, and has a first end portion and a second end portion at both ends in the longitudinal direction,the first bridge capacitor is connected between the first end portion in the longitudinal direction, which is the first measurement position of the measurement electrode, and the ground potential, andthe first end portion in the longitudinal direction of the application electrode is connected to the power source.(8) The contact detecting apparatus according to any one of (1) to (6) above, in which the electrostatic sensor is formed in a shape that is elongated in a longitudinal direction, and has a first end portion and a second end portion at both ends in the longitudinal direction,the first bridge capacitor is connected between the first end portion in the longitudinal direction, which is the first measurement position of the measurement electrode, and the ground potential, andthe second end portion in the longitudinal direction of the application electrode is connected to the power source.(9) The contact detecting apparatus according to any one of (1) to (6) above, in which the electrostatic sensor is formed in a shape that is elongated in a longitudinal direction, and has a first end portion and a second end portion at both ends in the longitudinal direction,the first bridge capacitor is connected between the first end portion in the longitudinal direction, which is the first measurement position of the measurement electrode, and the ground potential,the contact detecting apparatus further includes a second bridge capacitor connected in series between the second end portion in the longitudinal direction, which is a second measurement position of the measurement electrode, and the ground potential,the measurement electrode is configured so that an electrical resistance changes depending on a distance from the first measurement position, and is configured so that an electrical resistance changes depending on a distance from the second measurement position, andthe measuring instrument acquires a second potential between the second measurement position of the measurement electrode and the second bridge capacitor in the process of charging; anddetects the position where the conductor is in contact with the electrostatic sensor based on the first potential first sampling value, a second potential first sampling value, the first potential second sampling value, and a second potential second sampling value in the process of charging, in which the second potential first sampling value is the second potential acquired at the first sampling time point, and the second potential second sampling value is the second potential acquired at the second sampling time point.(10) The contact detecting apparatus according to (9) above, in which the first sampling time point is a time point in a transitional state from when charging of the electrostatic sensor is started until when a change in the potential of the measurement electrode reaches a saturated state smaller than a predetermined value,the second sampling time point is a time point which is later than the first sampling time point and when the potential of the measurement electrode is saturated, andthe measuring instrument further detects the area where the conductor is in contact with the electrostatic sensor based on the first potential second sampling value and the second potential second sampling value in the process of charging.(11) The contact detecting apparatus according to (9) above, in which the control device executes a first cycle which includes the process of discharging and the process of charging following the process of discharging in order for the measuring instrument to acquire the first potential, andafter the first cycle, executes a second cycle which includes the process of discharging and the process of charging following the process of discharging in order for the measuring instrument to acquire the second potential.(12) The contact detecting apparatus according to any one of (1) to (6) above, in which the measurement electrode and the application electrode are made of an electrically conductive elastomer.(13) The contact detecting apparatus according to (12) above, in which the application electrode and the measurement electrode have different electrical resistances per unit length.(14) The contact detecting apparatus according to (13) above, in which the electrical resistance per unit length of the measurement electrode is greater than the electrical resistance per unit length of the application electrode.(15) The contact detecting apparatus according to (14) above, in which the measurement electrode has a plurality of through holes.(16) A contact detecting apparatus, including:an electrostatic sensor for detecting contact of a conductor with a measurement electrode side, the electrostatic sensor including an application electrode to which an input voltage that is a constant voltage is applied from a power source, a measurement electrode which is disposed opposite to the application electrode and whose potential is measured, and a dielectric which is disposed between the application electrode and the measurement electrode;a first bridge capacitor connected in series between a first measurement position of the measurement electrode and a ground potential;a charge/discharge switching element connected in series between the measurement electrode and the ground potential and connected in parallel to the first bridge capacitor, and discharging the potential of the measurement electrode to the ground potential when in a closed state;a control device executing a process of discharging the potential of the measurement electrode to the ground potential by setting a state in which the input voltage is not applied to the application electrode and setting the charge/discharge switching element to the closed state, and a process of charging the electrostatic sensor by setting the charge/discharge switching element to an open state and setting a state in which the input voltage is applied to the application electrode after the process of discharging; anda measuring instrument acquiring a first potential between the first measurement position of the measurement electrode and the first bridge capacitor in the process of charging, in whichthe electrostatic sensor is configured so that an electrostatic capacitance per unit area corresponding to a position where the conductor is in contact and an electrostatic capacitance per unit area corresponding to a position where the conductor is not in contact have different values,the measurement electrode is configured so that an electrical resistance changes depending on a distance from the first measurement position, andthe measuring instrument detects an area where the conductor is in contact with the electrostatic sensor based on a first potential saturation sampling value which is the first potential acquired at a time point when the potential of the measurement electrode is saturated and smaller than a predetermined value in a process of charging.