JP2010272991A - Electrode structure of capacitance sensor and vehicle proximity sensor using the structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure of a capacitance sensor, which can reduce a high-frequency noise emitted to a surrounding area from an electrode portion which a human body approaches or contacts, and to provide a vehicle proximity sensor using the structure. <P>SOLUTION: An electrode structure of a capacitance sensor is a conductive body which a human body approaches or contacts, and has a detection electrode 3 to which a charging signal charging an unknown capacitance Cx is repeatedly supplied, an inversion electrode 4 which is a conductive body arranged adjacent to the detection electrode 3, and a phase inversion circuit 6 supplying to the inversion electrode 4 an inversion signal whose voltage changes in a direction opposite to the change of the voltage of the charging signal. The electrode structure reduces a high-frequency noise (N) emitted from the detection electrode by the inversion electrode. The detection electrode 3 of a long rail plate or stick and the inversion electrode 4 which is approximately the same length as that of the detection electrode can be arranged in parallel, and the phase inversion circuit 6 can be composed by an inverter circuit. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode structure of a capacitance sensor that detects proximity or contact of a human body, and a vehicle proximity sensor using the same.

Conventionally, a capacitance sensor that detects a proximity or contact of a human body by measuring a change in capacitance between the human body and a stray capacitance or ground (ground) is provided. It has been. In such a capacitance sensor, the change in capacitance is detected by charging or discharging the capacitance generated in the detection electrode to measure the voltage or charge amount, or by using the change in impedance of the detection circuit. Has been. However, the change in capacitance caused by the proximity or contact of the human body is a minute value, and it is difficult to accurately measure the capacitance with a single charge or discharge. It is common to improve.
For example, a method for measuring a minute capacitance is disclosed in which a predetermined voltage of a predetermined frequency is applied to a detection electrode in a predetermined cycle by a switched capacitor method, and a voltage value generated by a minute capacitance is integrated and measured. (See Patent Document 1). There is also known a charge transfer capacitance measuring circuit that includes a known capacitor and switch means, and repeatedly charges and discharges an unknown capacitor caused by a human body or the like, and accumulates charges in the known capacitor to accurately measure ( (See Patent Document 2).

The charge transfer capacitance measuring circuit is configured as shown in FIG. The circuit unit 82 includes a known capacitance C81, switch means SW81, SW82, and the like, and an unknown capacitance C8x generated at the detection electrode 83 is measured. Usually, the capacitance C8x is significantly smaller than the capacitance C81.
First, the capacitance C8x and the capacitance C81 are discharged (not shown). When SW81 is closed (ON) and SW82 is opened (OFF), the electrostatic capacity is charged, and charging voltages V8x and V81 are generated in electrostatic capacity C8x and C81 in inverse proportion to the respective capacitance values (step 1). . Next, when SW81 is turned off and SW82 is turned on, the charge of the capacitance C81 is held (step 2). Thereafter, when the state of step 1 is set again, the electrostatic capacity is charged, the electric charge moves between the electrostatic capacity C8x and the electrostatic capacity C81, and the charging voltage V81 of the electrostatic capacity C81 increases. Next, in the state of step 2, the charge of the capacitance C81 is held. Further, if Step 1 and Step 2 are repeated, the charge voltage V81 gradually increases as the charge is accumulated in the capacitance C81. FIGS. 13A and 13B show changes in the potentials of the detection electrodes 83 and 8A in FIG. Since the number of repetitions required until the potential at the point 8A in the state of Step 2 reaches a certain value depends on the magnitude of the capacitance C8x, the unknown capacitance C8x can be obtained from the number of repetitions.

  Further, in order to improve the detection accuracy of the capacitance, a device in which the configuration of the electrode of the sensor is devised is known. For example, there is disclosed a proximity detection device that eliminates the influence of noise by repeatedly charging and discharging a pair of differential electrodes with reversed phases and obtaining the sum of the apparent stray capacitances of the differential electrodes (Patent Document). 3).

JP-A-8-194025 Japanese translation of PCT publication No. 2002-530680 JP 2008-292446 A

  However, in the capacitance sensor such as the switched capacitor method, the detection electrode is repeatedly charged / discharged to the detection electrode that is close to or in contact with the human body, and the capacitance is measured by accumulating the charge / discharge characteristics. High-frequency noise due to charging / discharging is emitted from the surrounding environment. For example, when the repetition time for charging and discharging the detection electrode is about 7 μs, high-frequency noise is radiated not only in the frequency region centered at about 140 kHz but also in a wide frequency range. For this reason, electromagnetic interference (EMI, Electro Magnetic Interference) that the capacitance sensor affects the operation of surrounding electronic devices has been a problem. In general, in order to reduce high-frequency noise emitted from the device to the outside, there is a method in which the device is sealed with a case of metal or the like. However, in the case of a capacitance sensor, since the detection electrode that a human body approaches or approaches needs to be opened to the outside, it is impossible to take a countermeasure for electromagnetically shielding the electrode portion.

In addition, in the capacitance sensor, there is a problem that the detection accuracy is lowered due to the influence of external noise, and thus various electrode structures and configuration methods have been devised. For example, in the proximity detection device having the differential electrode described above, the influence of noise is removed by repeatedly charging and discharging the phase of the differential electrode to obtain a composite value of the floating capacitance of the differential electrode. High-precision detection is possible. However, in the conventional example, no consideration has been given to EMI in which the operation of the surrounding electronic device is hindered by high-frequency noise radiated from the electrode portion of the capacitance sensor.
In particular, in the case of a capacitance sensor used in an automobile, measures against EMI have become an important issue. When noise is radiated in a wide frequency range from the electrode portion of the capacitance sensor, there is a problem that, for example, the operation of an in-vehicle device such as a smart entry system or reception of radio broadcasts is hindered.

  The present invention has been made in view of the above-described situation, and an electrode structure of a capacitance sensor that can reduce high-frequency noise radiated from an electrode portion that is close to or in contact with a human body to the surroundings, and the same. An object of the present invention is to provide a vehicle proximity sensor.

The present invention is as follows.
1. An electrode structure of a capacitance sensor that detects proximity or contact of a human body by a change in capacitance, and is a conductor that is close to or in contact with a human body, and is repeatedly supplied with a charge signal for charging the capacitance. A detection electrode, an inversion electrode that is a conductor disposed in the vicinity of the detection electrode, and a phase inversion circuit that supplies an inversion signal whose voltage changes in the opposite direction to the change in the voltage of the charging signal to the inversion electrode And a high frequency noise radiated from the detection electrode is reduced by the inversion electrode.
2. The charging signal is a pulse signal, and the phase inversion circuit generates the inverted signal that falls when the pulse signal rises and rises when the pulse signal falls. The electrode structure of the described electrostatic capacitance sensor.
3. The phase inverting circuit is an inverter circuit to which the charging signal is input. The electrode structure of the described electrostatic capacitance sensor.
4). The detection electrode is a long plate-like or rod-shaped conductor, and the inversion electrode having a length substantially the same as the detection electrode is disposed in parallel with the detection electrode in the same plane. To 3. The electrode structure of the capacitance sensor according to any one of the above.
5). The detection electrode is a substantially rectangular flat conductor, and the inversion electrode is disposed substantially on the same plane as the detection electrode, surrounding the outer periphery of the detection electrode with a predetermined gap. To 3. The electrode structure of the capacitance sensor according to any one of the above.
6). A proximity sensor mounted on a vehicle, comprising: To 5. A proximity sensor for a vehicle, comprising the capacitance sensor electrode structure according to any one of the above.

According to the electrode structure of the capacitance sensor of the present invention, the human body is a conductor that comes close to or contacts, and a detection electrode to which a charging signal for charging the capacitance is repeatedly supplied, and the detection electrode are arranged close to the detection electrode. An inversion electrode that is a conductor provided, and a phase inversion circuit that supplies an inversion signal whose voltage changes in a direction opposite to a change in the voltage of the charging signal to the inversion electrode. The high frequency noise radiated | emitted from the electrode part comprised by can be reduced, and the electromagnetic interference (EMI) given to a surrounding electronic device can be prevented. In addition, the structure and configuration of the electrode is simple, and the present invention can be widely applied to capacitance sensors that measure capacitance by repeatedly charging and discharging the detection electrode.
The charging signal is a pulse signal, and the phase inversion circuit generates the inverted signal that falls at the rising edge of the pulse signal and rises at the falling edge of the pulse signal. High frequency noise radiated at the time of falling can be effectively reduced.
Further, when the phase inverting circuit is an inverter circuit to which the charging signal is input, the high frequency noise radiated at the time of rising and falling of the charging signal exceeding a certain level can be effectively achieved by a small number of components and a simple circuit. Can be reduced.

When the detection electrode is a long plate-like or rod-like conductor, and the inversion electrode having the same length as the detection electrode is arranged in parallel to the detection electrode, The proximity or contact of the human body can be detected in a region corresponding to the length of the detection electrode, and high-frequency noise radiated from the long electrode as an antenna can be reduced.
In addition, the detection electrode is a substantially rectangular flat conductor, and the inversion electrode is disposed on the same plane as the detection electrode with a predetermined gap around the outer periphery of the detection electrode. The proximity or contact of the human body can be detected in a region corresponding to a wide area of the detection electrode, and high-frequency noise radiated from the detection electrode as an antenna can be reduced.

  According to the proximity sensor for a vehicle including the electrode structure of the capacitance sensor according to any one of the above, a proximity sensor having a low level of high-frequency noise radiated from the electrode portion may be used as a switch of various in-vehicle devices. It is possible to greatly reduce electromagnetic interference with respect to surrounding on-vehicle electronic devices.

The present invention will be further described in the following detailed description with reference to the drawings referred to, with reference to non-limiting examples of exemplary embodiments according to the present invention. Similar parts are shown throughout the several figures.
It is a block diagram which shows the structure of the electrode structure of the electrostatic capacitance sensor of this invention. It is a figure explaining the example of a connection of the detection electrode and reversal electrode of this electrostatic capacitance sensor. It is a schematic diagram explaining the shape and arrangement | positioning of a elongate detection electrode and an inversion electrode. It is a schematic diagram explaining the shape and arrangement | positioning of a rectangular flat detection electrode and the inversion electrode surrounding the outer periphery. It is a circuit diagram which shows the structural example of the charging / discharging means applied to the electrode structure of this electrostatic capacitance sensor, and a phase inversion circuit. It is a circuit diagram which shows another structural example of the charging / discharging means applied to the electrode structure of this electrostatic capacitance sensor, and a phase inversion circuit. 6 is a time chart for explaining an example of signals supplied to the detection electrode and the inversion electrode by the circuit shown in FIG. 5. 6 is a time chart for explaining another example of signals supplied to the detection electrode and the inversion electrode by the circuit shown in FIG. 5. It is a time chart for demonstrating the example of a signal supplied to a detection electrode and an inversion electrode by the circuit shown in FIG. It is a graph which shows the result of having measured the level of the high frequency noise radiated | emitted from the electrode structure of the electrostatic capacitance sensor of this invention compared with the prior art example. It is a figure which shows the structural example of the proximity sensor for vehicles using the electrode structure of the electrostatic capacitance sensor of this invention. It is a circuit diagram for demonstrating the structure of the electrostatic capacitance sensor of a prior art example. It is a figure for demonstrating the example of the charge signal supplied to a detection electrode in the electrostatic capacitance sensor of FIG.

  The items shown here are exemplary and illustrative of the embodiments of the present invention, and are the most effective and easy-to-understand explanations of the principles and conceptual features of the present invention. It is stated for the purpose of providing what seems to be. In this respect, it is not intended to illustrate the structural details of the present invention beyond what is necessary for a fundamental understanding of the present invention. It will be clear to those skilled in the art how it is actually implemented.

1. Electrode Structure of Capacitance Sensor Generally, a capacitance sensor includes a detection electrode for detecting a change in capacitance caused by a human body or the like, and a proximity detection unit that measures the change in capacitance. The proximity detection unit includes charge / discharge means, capacity detection means, proximity determination means, and the like.
As shown in FIG. 1, the present invention is an electrode structure of a capacitance sensor that detects proximity or contact of a human body by a change in capacitance Cx, and a charging signal for charging the capacitance is repeatedly supplied. Detection electrode 3, an inversion electrode 4 that is a conductor disposed in the vicinity of the detection electrode 3, and an inversion signal whose voltage changes in the opposite direction to the change in the voltage of the charging signal is supplied to the inversion electrode. And a phase inversion circuit 6. The charging / discharging unit 5, the capacity detecting unit 22, and the proximity determining unit 24 constituting the proximity detecting unit 2 can be configured using a known technique.

  The detection electrode 3 is a conductor disposed so that a human body is close to or in contact with the surface thereof, and its shape, size, structure, etc. are not particularly limited. The material of the conductor is not particularly limited, and a conductive cloth or the like may be used in addition to the metal. The “proximity” of the human body to the detection electrode 3 includes not only a form in which a palm or a finger is brought close to the surface of the detection electrode but also a form in which the human body is in contact via an insulator covering the surface of the detection electrode. “Contact” refers to a form in which the human body directly contacts the surface of the detection electrode.

The inversion electrode 4 acts to cancel the high-frequency electric field generated by the detection electrode 3 and is provided for the purpose of reducing high-frequency noise radiated from the electrode portion 32 having the detection electrode 3 and the inversion electrode 4 to the surroundings. The inversion electrode 4 is a conductor disposed in the vicinity of the detection electrode 3, and its shape, size, structure and material correspond to or approximate the shape, size, structure and material of the detection electrode 3. It is preferable.
When a plurality of detection electrodes 3 are provided, a plurality of inversion electrodes 4 may be provided corresponding to each detection electrode 3.

  The charging / discharging unit 5 is electrically connected to the detection electrode 3 and configured to apply a charging voltage (charging signal) for repeatedly charging / discharging the electrostatic capacitance Cx to the detection electrode 3. The structure of the charging / discharging means 5 is not specifically limited, A well-known technique can be used. Further, the amplitude and frequency of the charging signal are not particularly limited. For example, a pulse-like signal that changes within the range of the reference potential (0 V) and the power supply voltage (Vcc) and has a frequency of several kHz to several hundred kHz can be mentioned.

The phase inversion circuit 6 is electrically connected to the inversion electrode 4 and is configured to apply an inversion signal having a phase opposite to that of the charge signal applied to the detection electrode 3 by the charge / discharge means 5 to the inversion electrode 4. . Here, the reverse phase means that the voltage changes in the opposite direction to the change in the voltage of the charging signal. That is, the inverted signal can be a signal whose voltage value decreases (−ΔV ′) when the voltage value of the charging signal increases (+ ΔV). For example, when the charge signal changes from 0V to + ΔV, the inverted signal may be a signal that changes from + ΔV ′ to 0V, may be a signal that changes from 5V to 5V−ΔV ′, or may be 0V. The signal may change from −ΔV ′. At this time, the change width ΔV ′ of the voltage of the inverted signal does not need to be the same as the change width ΔV of the voltage of the charging signal, and is appropriately designed according to the effect of reducing the high frequency noise (A) radiated from the electrode portion 32. be able to.
When the charging signal is a pulse signal, the phase inverting circuit 6 can be configured to generate an inverted signal that falls at the rising edge of the pulse signal and rises at the falling edge of the pulse signal.

  In addition, the proximity detection unit 2 can be configured to include a capacitance detection unit 22 and a proximity determination unit 24. The configuration of the capacitance detection means 22 is not particularly limited. For example, the capacitance of the detection electrode 3 is measured using a capacitance measuring circuit for measuring the voltage between terminals, a circuit for converting a change in capacitance into a frequency change, or the like. Changes can be detected. The configuration of the proximity determination unit 24 is not particularly limited, and may be configured to determine the proximity or contact of the human body by performing processing such as calculation and comparison based on the measurement value obtained by the capacitance detection unit 22. Can do.

Each unit constituting the proximity detection unit 2 and overall control processing may be realized by either hardware or software, and preferably includes a CPU, a memory (ROM, RAM, etc.), an input / output circuit, etc. (not shown). It can be configured by providing peripheral circuits around a microcontroller (microcomputer). A digital signal processor, a programmable logic circuit, a gate array, or other logic circuits may be used.
In addition, the proximity detector 2 is connected to various devices / devices (for example, a light emitter, a display panel, an air conditioner, etc.), and when it is determined that the human body is close or in contact, the determination or the operation based on the determination is performed. The proximity detection signal can be output.

  FIG. 2 shows a connection example of the detection electrode 3, the inversion electrode 4, the phase inversion circuit 6, and the charge / discharge circuit 51 constituting the charge / discharge means. The phase inversion circuit 6 generates an inversion signal having an opposite phase based on a signal in the charge / discharge circuit 51 or a charge signal applied to the detection electrode 3 and supplies the inverted signal to the inversion electrode 4. As illustrated, in addition to the detection electrode 3 and the inversion electrode 4, a ground electrode 31 having a ground potential may be provided in order to reduce the influence of noise or the like.

The electrode structure 1 of the present capacitive sensor can be suitably used when the detection electrode 3 is a long conductor. For example, as shown in FIG. 3, an electrode structure including a long flat plate-like detection electrode 3a and an inversion electrode 4a of substantially the same size and the same material can be used. The length L _4a and the width W _4a of the inversion electrode 4a are substantially the same as the length L _3a and the width W _3a of the detection electrode 3a, and both electrodes are arranged in parallel with _a gap ga in substantially the same plane. . The size of each electrode may be determined depending on the application. For example, the length (L _4a , L _3a ) of each electrode is about 20 to 500 mm, and the width (W _4a , W _3a ) is about 2 to 50 mm. The gap (g _a ) between both electrodes is preferably about 10 to 100 mm.
By disposing the inversion electrode 4a, it is possible to reduce high-frequency noise radiated from the electrode section with the Z direction shown in the figure as the center.

When the area of the detection electrode 3 is large, the inversion electrode 4 can be disposed so as to be substantially flush with the detection electrode 3 and surround the outer periphery of the detection electrode 3 with a predetermined gap. For example, as shown in FIG. 4, an electrode structure in which the outer periphery of a rectangular and flat detection electrode 3b is disposed so as to be surrounded by an inversion electrode 4b made of the same material as that of the detection electrode 3b. Inversion electrode 4b is disposed at a gap g _b on the outer periphery of the detection electrode 3b. The size of each electrode may be determined depending on the use and effect. For example, the length and width (L _3b , W _3b ) of the detection electrode 3b are about 20 to 500 mm, and the width (W _4b ) of the inversion electrode 4b is 5 The gap (g _b ) between both electrodes is preferably about 5 to 20 mm.

Next, the operation will be described with reference to a specific circuit configuration example of the electrode structure 1 of the capacitance sensor.
FIG. 5 shows a configuration example of the charging / discharging means 5 and the phase inversion circuit 6. Since the present invention is characterized in that it includes the detection electrode 3, the inverting electrode 4, and the phase inverting circuit 6, the configuration of charging / discharging means, capacity detecting means, etc. is arbitrary. The charging / discharging means 5a in this figure merely exemplifies a general switched capacitor type configuration.
The detection electrode 3 is connected to the charging / discharging means 5a, and the inversion electrode 4 is connected to the output of the phase inversion circuit 6a. In FIG. 5, the signal at the connection point between the charging / discharging means 5a and the detection electrode 3 is input to the phase inversion circuit 6a, but the signal input to the phase inversion circuit 6a is as long as the inversion signal can be generated. An appropriate signal in the charging / discharging unit 5a can be used (for example, a control signal for a switch unit provided in the charging / discharging unit).

  The charging / discharging unit 5a includes a known capacitance C1a and switch units SW1a and SW2a, and repeatedly charges and discharges the unknown capacitance Cx via the detection electrode 3. The switches SW1a and SW2a are not turned on at the same time. First, the electrostatic capacitance Cx and the electrostatic capacitance C1a are discharged (not shown). When SW1a is turned on (closed) and SW2a is turned off (open), the capacitance Cx is charged by the power supply Vcc (step 1a). Next, when SW1a is turned off and SW2a is turned on, a part of the charge of the capacitance Cx moves to the capacitance C1a according to the value of the capacitance (step 2a). In the state of step 1a again, the electrostatic capacitance Cx is charged by the power source Vcc and the electric charge of the electrostatic capacitance C1a is held. That is, if Step 1a and Step 2a are repeatedly executed, charging / discharging of the capacitance Cx is repeated, and charges are accumulated in the capacitance C1a. By repeating Step 1a and Step 2a, the charging signal applied to the detection electrode 3 changes as shown in FIGS. 7 (a) and 8 (a).

The phase inverting circuit 6a in FIG. 5 is a general inverting amplifier circuit using an operational amplifier 62, and the charging signal is connected to the inverting input terminal of the operational amplifier 62 through a resistor, and the reference voltage is applied to the non-inverting input terminal. Vref is connected. The output of the operational amplifier 62 is connected to the inverting electrode 4.
Here, when the reference voltage Vref is applied so as to be the same voltage as the Vcc, the output of the operational amplifier 62 becomes Vcc− (the voltage value of the charging signal), and charging as shown in FIG. The signal is in the opposite phase to the signal. That is, for example, when the charge signal is 0V, the inverted signal is Vcc, and when the charge signal is Vcc, the inverted signal is 0V. Then, when the charge signal applied to the detection electrode 3 changes, an inverted signal that changes in the opposite direction is supplied to the inverted electrode 4. As a result, the high-frequency electric field generated by the detection electrode 3 and the inversion electrode 4 cancels out, and high-frequency noise radiated from the electrode portion can be reduced.

  Further, in the phase inverting circuit 6a, when the reference voltage Vref applied to the operational amplifier 62 is set to 0V, the output of the operational amplifier 62 becomes 0V− (voltage value of the charging signal), as shown in FIG. An inverted signal having a phase opposite to that of the charging signal is applied. That is, for example, when the charge signal is 0V, the inverted signal is 0V, and when the charge signal is Vcc, the inverted signal is −Vcc. Then, when the charge signal applied to the detection electrode 3 changes, an inverted signal that changes in the opposite direction is supplied to the inverted electrode 4. As a result, the high-frequency electric field generated by the detection electrode 3 and the inversion electrode 4 cancels out, and high-frequency noise radiated from the electrode portion can be reduced.

  When the charge signal applied to the detection electrode 3 is a pulse signal, the phase inversion circuit 6 may be configured using an inverter circuit. For example, as shown in FIG. 6, the phase inversion circuit 6 b can be configured using the inverter element 64. 6 illustrates the charge / discharge means 5b having a circuit configuration different from that of the charge / discharge means 5a, the configuration of the charge / discharge means is not limited to this as described above.

  The charging / discharging unit 5b of FIG. 6 includes a known capacitance C1b and switch units SW1b and SW2b, and repeatedly charges and discharges an unknown capacitance Cx via the detection electrode 3. The switches SW1b and SW2b are not turned on at the same time. First, the electrostatic capacitance Cx and the electrostatic capacitance C1b are discharged (not shown). When SW1b is turned on (closed) and SW2b is turned off (opened), the capacitance is charged by the power source Vcc, and the voltage Vxb and the capacitance Vxb, which are inversely proportional to the capacitance, are respectively connected between the capacitance Cx and the capacitance C1b. V1b is generated (step 1b). Next, when SW1b is turned off and SW2b is turned on, the inter-terminal voltage V1b of the capacitance C1b is held (step 2b). In the state of step 1b again, the electrostatic capacity is charged by the power source Vcc, the electric charge moves between the electrostatic capacity Cx and the electrostatic capacity C1b, and the inter-terminal voltage V1b of the electrostatic capacity C1b increases. . That is, if Step 1b and Step 2b are repeatedly executed, charging / discharging of the capacitance Cx is repeated, and the voltage V1b of the capacitance C1b gradually increases. By repeating Step 1b and Step 2b, the charge signal applied to the detection electrode 3 changes as shown in FIG.

Regardless of the configuration of the charging / discharging means used, when the charging signal is a pulse signal, a signal obtained by inverting the charging signal by the inverter element can be applied to the inverting electrode 4. In FIG. 6, the signal at the connection point (point B) between the charging / discharging means 5b and the detection electrode 3 is input to the logic inverter element 64, but the signal input to the inverter element 64 may generate the inverted signal. An appropriate signal can be used as much as possible (for example, a control signal for a switch unit provided in the charge / discharge unit).
When a CMOS inverter element is used as the inverter element 64, if the charge signal applied to the detection electrode 3 is a pulse signal of the maximum voltage Vcc as shown in FIG. 9A, the inversion as shown in FIG. A signal can be applied to the inverting electrode 4. In the case of a CMOS inverter element, when the charge signal is smaller than (1/2) Vcc, an inverted signal is generated that becomes voltage Vcc, and when the charge signal exceeds (1/2) Vcc, it becomes 0V. Then, when the charge signal applied to the detection electrode 3 changes greatly and steeply, an inversion signal that changes in the opposite direction is supplied to the inversion electrode 4. As a result, the high-frequency electric field generated by the detection electrode 3 and the inversion electrode 4 cancels out, and high-frequency noise radiated from the electrode portion can be reduced.

Next, in order to confirm the effect of the electrode structure of the capacitance sensor of the present invention, the capacitance sensor having the same charging / discharging means is used and the phase inverting circuit and the inverting electrode are provided (this configuration). The results of a comparative test on radiation noise with and without the phase inversion circuit and inversion electrode (conventional configuration) will be described.
The detection electrode 3 and the reversal electrode 4 used for the measurement are metal having the shape shown in FIG. 3, the length (L _3a , L _4a ) is about 300 mm, the width (W _3a , W _4a ) is about 7 mm, both The gap (g _a ) between the electrodes is about 10 mm. Further, the charging / discharging means and the phase inversion circuit have the configuration shown in FIG. 6, and the cycle of the charging pulse signal of the detection electrode 3 is about 7 μs (frequency: about 140 kHz).
With the above configuration, the level of the high-frequency signal at a point 1 m away from the electrode surface in the vertical direction (Z direction in the same), that is, the reception level of radiation noise radiated from the electrode portion was measured.

FIG. 10 shows the measured reception level (peak value) of radiation noise. The horizontal axis indicates the frequency, and the vertical axis indicates the signal level. The measurement was performed in the frequency ranges of 100 to 160 kHz and 500 kHz to 1.7 MHz. The band of 100 to 160 kHz is used for smart entry systems and the like in the case of automobiles. The band of 500 kHz to 1.7 MHz corresponds to the frequency of medium wave broadcasting.
In FIG. 10, the measurement value according to the present configuration is indicated by a solid line, and the measurement value according to the conventional configuration is indicated by a broken line. From the figure, it can be seen that the radiation noise according to the present configuration is suppressed by about 10 dB lower in the frequency range of 100 to 160 kHz and lower by about 15 dB in the frequency range of 500 kHz to 1.7 MHz than the conventional configuration. Thus, it is clear that the electrode structure of the capacitance sensor of the present invention is effective in reducing radiation of high frequency noise from the electrode portion.

  In the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, in the above embodiment, a rectangular wave-shaped charging signal is illustrated, but the waveform is not limited to this. Moreover, in the said Example, although the pulse signal which changes in the range of 0V to predetermined voltage value was illustrated, not only this but a charge signal may be an alternating current signal etc.

2. Proximity sensor for vehicle This proximity sensor for vehicle is a proximity sensor that is mounted on a vehicle and detects the proximity or contact of a human body, and is radiated from the electrode portion to the surroundings by including the electrode structure of the capacitance sensor. This is a proximity sensor that can reduce high-frequency noise.
As shown in FIG. 11, the vehicle proximity sensor 7 includes an electrode unit 32 including the detection electrode 3 and the reverse electrode 4, and the proximity detection unit 2. The structure and material of each electrode are not particularly limited. Further, the shape, dimensions, etc. of the electrode part 32 may be appropriately determined depending on the application, and are not limited to the elongated electrodes. For example, the detection electrode 3 has a substantially rectangular shape as described above. Various modifications, such as disposing the inversion electrode 4 so as to surround the outer periphery (see FIG. 4), are possible.
The proximity detection unit 2 includes a charging / discharging unit 5, a phase inversion circuit 6, a capacitance detection unit 22, and a proximity determination unit 24. Each configuration and operation are as described above.

The vehicle proximity sensor 7 can be configured to be connected to an external device / device 71 and to output a proximity detection signal indicating proximity or contact of a human body to them. Accordingly, when it is determined that the human body is in the proximity or contact state, the user can be notified of the determination or the operation based on the determination, or the corresponding device / device 71 can be controlled.
Examples of the device / device 71 include various in-vehicle electronic devices / devices such as lighting in a car, a decorative panel, a display panel, an air conditioner, and a seating determination device. For example, by arranging the long detection electrode 3 in a console box or glove box, the inside of the box can be illuminated when the palm or finger of the occupant approaches the detection electrode 3. In addition, for example, by arranging the detection electrode 3 having a large area on the ceiling, the room lamp can be turned on when a palm or a finger approaches the detection electrode 3.
According to the vehicle proximity sensor 7, high-frequency noise (A) radiated by the electrode structure including the inversion electrode 4 and the phase inversion circuit 6 is reduced even when the detection electrode 3 having a long or large area is used. It is possible to prevent electromagnetic interference that affects the operation of electronic circuits in the automobile.

In addition, it is not restricted to the said Example, It can be set as the Example variously changed within the range of this invention according to the objective and the use.
For example, in the above-described embodiment, the vehicle proximity sensor 7 including one detection electrode 3 is shown. However, the present invention is not limited to this, and a vehicle proximity sensor including a plurality of detection electrodes and inversion electrodes may be configured. Good.
In addition, the proximity sensor for a vehicle is a proximity sensor mounted on a vehicle, but the application is not limited to this, and the proximity sensor may be applied to, for example, a proximity sensor used for industrial machines, household electrical appliances, and the like. .

  DESCRIPTION OF SYMBOLS 1; Electrode structure of an electrostatic capacitance sensor, 2; Proximity detection part, 22 capacity | capacitance detection means, 24; Proximity determination means 3, 3a, 3b, 83; Detection electrode, 32; Electrode part 4, 4a, 4b; Electrodes 5, 5a, 5b; charge / discharge means, 6, 6a, 6b; phase inversion circuit, 7: vehicle proximity sensor, C1a, C1b, C81; known capacitance, Cx; unknown capacitance, a High frequency noise.

Claims (6)

An electrode structure of a capacitance sensor that detects proximity or contact of a human body by a change in capacitance,
A detection electrode to which a human body is a conductor that is in close proximity or in contact, and is repeatedly supplied with a charging signal for charging the capacitance;
An inversion electrode that is a conductor disposed in proximity to the detection electrode;
A phase inverting circuit for supplying an inverting signal whose voltage changes in the opposite direction to the voltage change of the charging signal to the inverting electrode;
With
An electrode structure of a capacitance sensor, wherein high frequency noise radiated from the detection electrode is reduced by the inversion electrode. The charging signal is a pulse signal;
The capacitive sensor electrode structure according to claim 1, wherein the phase inversion circuit generates the inverted signal that falls when the pulse signal rises and rises when the pulse signal falls.   3. The capacitance sensor electrode structure according to claim 2, wherein the phase inversion circuit is an inverter circuit to which the charging signal is input. The detection electrode is a long plate-like or rod-like conductor,
The capacitive sensor electrode structure according to claim 1, wherein the inversion electrode having substantially the same length as the detection electrode is disposed in parallel with the detection electrode in substantially the same plane. The detection electrode is a substantially rectangular flat conductor,
4. The capacitance sensor electrode structure according to claim 1, wherein the inversion electrode is disposed in substantially the same plane as the detection electrode so as to surround an outer periphery of the detection electrode with a predetermined gap. 5.   A proximity sensor mounted on a vehicle, comprising the electrode structure of the capacitance sensor according to any one of claims 1 to 5.

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