JP2006084318A - Static capacitance type distance sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a static capacitance type distance sensor having sufficiently high detection precision even when the distance to a detected object is long. <P>SOLUTION: A sensor section 101 comprises a transmission electrode 101a, a shield electrode 101b for shielding electromagnetic wave from the rear side of the transmission electrode 101a, and an auxiliary electrode 101c for shielding current flowing between the transmission electrode 101a and the shield electrode 101b. Alternating voltage outputted by a buffer circuit 103 is supplied to the transmission electrode 101a via a resistance element 104, and supplied to the auxiliary electrode 101c without the resistance element 104. The resistance element 104 detects the value of the detected current flowing out of the transmission electrode 101a as voltage between terminals. The alternating voltage is supplied to the transmission electrode and auxiliary electrode from the buffer circuit via different wires, and only the current flowing through the transmission electrode is detected by a current detecting resistance element, so that the detection precision of the detected object can be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-contact capacitive distance sensor that detects a distance to an object to be detected based on the intensity of an electromagnetic field formed between the object and the object to be detected.

  2. Description of the Related Art Conventionally, a non-contact type sensor that measures the presence or absence of an object to be detected and the distance to the object to be detected using electromagnetic waves is known, and is called, for example, a capacitive distance sensor. In the capacitance type distance sensor, the distance to the detected object is detected from the capacitance formed between the sensor and the ground plane of the detected object.

  For example, the following Patent Document 1 is known as a document disclosing the capacitance type distance sensor. The capacitance type distance sensor 11 described in Patent Document 1 includes a detection electrode 12a, an in-phase shield pattern 12b, and a ground pattern 12c (see Paragraph 0008 of Patent Document 1 and FIG. 1). Since the detection electrode 12a and the in-phase shield pattern 12b are connected to each other, the voltage and phase of the detection electrode 12a and the in-phase shield pattern 12b are always the same. Thereby, since the influence of the electrostatic capacitance between the detection electrode 12a and the in-phase shield pattern 12b can be eliminated, the sensor unit 11 and the electronic circuit unit 14 can be separated (see Patent Document 1). (See paragraph 0012).

  In the technique of Patent Document 1, the value of the capacitance formed between the sensor unit 11 and the ground plane of the object to be detected is detected from the oscillation frequency of the oscillation circuit 17. For this reason, the technique of Patent Document 1 has a drawback that it is difficult to accurately detect the detection object when the distance to the detection object is a long distance.

Moreover, in patent document 1, since the sensor part 11 is comprised with the printed circuit board, there exists a fault that the said sensor part 11 does not have a softness | flexibility and the installation to a curved surface is difficult.
JP-A-7-29467

  An object of the present invention is to provide a capacitive distance sensor having sufficiently high detection accuracy even when the distance to an object to be detected is long.

  The present invention relates to a non-contact capacitive distance sensor that detects the presence and distance of a detection object based on the magnitude of a detection current flowing into the detection object.

  A transmission electrode that radiates electromagnetic waves for supplying a detection current to the object to be detected; a shield electrode that is disposed opposite to the transmission electrodes to shield electromagnetic waves radiated from the back side of the transmission electrode; and In order to supply an AC voltage generated by an oscillator to the transmission electrode and the auxiliary electrode, and a sensor unit having an auxiliary electrode arranged between these electrodes in order to cut off the current flowing between the electrode and the shield electrode A buffer circuit, a current detection resistor element for detecting the detection current as a voltage between terminals, a first wiring connecting the output terminal of the buffer circuit and the transmission electrode via the current detection resistor element, and a current detection resistor element And a second wiring for connecting the output end of the buffer circuit and the auxiliary electrode.

  According to the present invention, the AC voltage is supplied from the buffer circuit to the transmission electrode and the auxiliary electrode via different wirings, and only the current flowing through the transmission electrode is detected by the current detection resistance element, so that the detection accuracy of the detection object is improved. Can be made.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement relationship of each component are shown only schematically to the extent that the present invention can be understood, and the numerical conditions described below are merely examples. .

First Embodiment Hereinafter, a capacitance type distance sensor according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram showing the configuration of a capacitive distance sensor according to this embodiment.

  As shown in FIG. 1, the capacitive distance sensor 100 of this embodiment includes a sensor unit 101, an oscillation circuit 102, a buffer circuit 103, a current detection resistor element 104, a shield cable 105, a first cable, A differential amplifier 106, a band pass filter 107, a detection circuit 108, a low pass filter 109, a second differential amplifier 110, an analog / digital converter 111, a CPU (Central Processing Unit) 112, and a digital / analog And a converter 113.

  The sensor unit 101 includes a transmission electrode 101a, a shield electrode 101b, and an auxiliary electrode 101c. The transmission electrode 101a radiates an electromagnetic wave for forming an electromagnetic field with an object to be detected (not shown). The shield electrode 101b is an electrode for shielding electromagnetic waves radiated from the back surface side of the transmission electrode 101a. The auxiliary electrode 101c is an electrode for interrupting the current flowing between the transmission electrode 101a and the shield electrode 101b. In this embodiment, the auxiliary electrode 101c is provided between the transmission electrode 101a and the shield electrode 101b, and an AC voltage is supplied to the transmission electrode 101a and the auxiliary electrode 101c via different wirings. Detection accuracy can be improved (described later). As shown in FIG. 1, the shield electrode 101b is grounded.

  The oscillation circuit 102 generates and outputs an AC voltage for causing the transmission electrode 101a to emit an electromagnetic field. In the following description, the oscillation frequency of the oscillation circuit 102 is assumed to be f [Hz].

  The buffer circuit 103 is a buffer for supplying the AC voltage output from the oscillation circuit 102 to the sensor unit 101. As shown in FIG. 1, in this embodiment, the buffer circuit 103 is configured by one voltage follower circuit. That is, in this embodiment, AC voltage is supplied to the transmission electrode 101a and the auxiliary electrode 101c by the same voltage follower circuit. As a result, the influence of the fluctuation on the output side of the buffer circuit 103 on the output of the oscillation circuit 102 can be suppressed, and the detection accuracy of the detected object can be increased (described later).

  The current detection resistance element 104 is a resistance element for converting a current flowing through the sensor unit 101 into a voltage (described later). The current detection resistor element 104 is connected between the output terminal of the buffer circuit 103 and the shield cable 105.

  The shielded cable 105 supplies the AC voltage output from the buffer circuit 103 to the sensor unit 101. The shielded cable 105 has a core wire 105a and a covered wire 105b. One end of the core wire 105 a is connected to the output end of the buffer circuit 103 via the resistance element 104. The other end of the core wire 105a is connected to the transmission electrode 101a. One end of the covered wire 105 b is directly connected to the output end of the buffer circuit 103 without going through the resistance element 104. The other end of the covered wire 105b is connected to the auxiliary electrode 101c.

  The first differential amplifier 106 is an instrumentation amplifier, and both the non-inverting input terminal (+) and the inverting input terminal (−) have high input impedance, and a voltage corresponding to the potential difference between the non-inverting input terminal and the inverting input terminal. Is output. The non-inverting input terminal of the differential amplifier 106 is connected to one end of the resistance element 104 (that is, the end on the buffer circuit 103 side). The inverting input terminal of the differential amplifier 106 is connected to the other end of the resistance element 104 (that is, the end portion on the transmission electrode 101a side). Therefore, the differential amplifier 106 outputs an AC voltage signal having a value corresponding to the voltage across the resistance element 104. As will be described later, the current flowing through the resistance element 104 depends on the distance between the transmission electrode 101a and the object to be detected. Therefore, the voltage between the terminals of the resistance element 104 also varies depending on the distance.

  The band pass filter 107 passes only the signal component of the frequency f (that is, the component of the same frequency as that of the oscillation circuit 102) in the input AC voltage signal. This band pass filter 107 can remove noise components from the AC voltage signal output from the differential amplifier 106. For example, when a noise source such as a motor is disposed in the vicinity of the capacitive distance sensor 100, noise may be mixed into the AC voltage signal due to electromagnetic waves generated by the motor or the like, which may cause false detection. Therefore, such noise is removed by the band pass filter 107.

  The detection circuit 108 converts the input AC voltage signal into a DC voltage signal. In this embodiment, a full-wave rectifier circuit having a time constant τ set to about 1 / f is used as the detection circuit 108 (f is the output frequency of the oscillation circuit 102). FIG. 4 is a waveform diagram conceptually showing the relationship between the time constant of the detection circuit 108 and the output signal, where A is the input signal waveform, B is the output signal waveform when the time constant τ is 1 / f, and C is It is an output signal waveform when the time constant τ is very large. Here, the input signal waveform A shows a case where the noise component An is mixed in the original signal waveform. As can be seen from FIG. 4, when the time constant τ is very large, a flat output signal waveform (that is, an output signal waveform with a small ripple component) C with small fluctuation can be obtained when the original input signal waveform is input. However, when the noise component An is input, the output signal level is maintained at the noise level. On the other hand, when the time constant τ is about 1 / f, an output signal waveform (that is, an output signal waveform having a large ripple component) B having a large fluctuation when the original input signal waveform is input becomes a noise component. When An is input, the influence of the noise is small. Here, the ripple component can be removed by providing a low-pass filter after the detection circuit 108. For this reason, in this embodiment, the time constant τ is set to about 1 / f and the low-pass filter 109 is provided in the subsequent stage.

  The low pass filter 109 removes high frequency components from the input signal. This low-pass filter 109 can remove a ripple component from the DC voltage signal output from the detection circuit 108.

  The second differential amplifier 110 outputs a voltage corresponding to the potential difference between the non-inverting input terminal (+) and the inverting input terminal (−). The non-inverting input terminal of the differential amplifier 110 is connected to the output terminal of the low-pass filter 109. The inverting input terminal of the differential amplifier 110 is connected to the output terminal of the digital / analog converter 113. As will be described later, the differential amplifier 110 corrects the output signal of the detection circuit 108 so that the value when the detected object is not detected becomes zero. The DC voltage signal output from the differential amplifier 110 is output to the outside as the detection signal Sd.

  The analog / digital converter 111 converts the DC voltage signal (that is, the detection signal Sd) output from the differential amplifier 110 from an analog signal to a digital signal.

  The CPU 112 generates a correction signal Sa by performing arithmetic processing using a predetermined algorithm on the digital signal input from the analog / digital converter 111, stores the correction signal Sa inside, and outputs the correction signal Sa to the digital / analog converter 113. As will be described later, the detection signal Sd is corrected by the correction signal Sa.

  The digital / analog converter 113 converts the output signal of the CPU 112 from a digital signal to an analog signal.

  2 and 3 are conceptual diagrams showing the configuration of the sensor unit 101, FIG. 2 is a side view, and FIG. 3 is an exploded perspective view.

  As shown in FIGS. 2 and 3, the sensor unit 101 has a printed circuit board 201. A metal thin film as the transmission electrode 101a is printed on the front surface of the printed board 201, and a metal thin film as the auxiliary electrode 101c is printed on the back surface. For this reason, the base material 202 of the printed circuit board 201 becomes a dielectric of a capacitor formed by the transmission electrode 101a and the auxiliary electrode 101c. As the substrate 202, a sufficiently flexible insulating plate is used. For example, a Teflon (registered trademark) plate having a thickness of 0.2 to 0.4 mm can be used as the substrate 202.

  The shield electrode 101b is formed of a conductive material having sufficient flexibility and stretchability. For example, conductive rubber, conductive cloth, or the like can be used as the shield electrode 101b.

  The auxiliary electrode 101c and the shield electrode 101b are fixed via a spacer 203. The spacer 203 is used to fix the auxiliary electrode 101c and the shield electrode 101b at a predetermined uniform interval. For this reason, the spacer 203 is bonded to the auxiliary electrode 101c and the shield electrode 101b using a conductive adhesive or the like (not shown). The spacer 203 is formed of a flexible insulating material (for example, resin). As shown in FIG. 3, the spacer 203 is formed in a lattice shape, and the hollow portion 203a passes therethrough. This hollow portion 203a becomes an insulating layer of a capacitor formed by the auxiliary electrode 101c and the shield electrode 101b. If the height d1 of the spacer 203 is too large, sufficient flexibility as the entire sensor unit 101 cannot be secured, and if it is too small, the capacitance of the capacitor becomes too large. Accordingly, the height d1 (see FIG. 3) of the spacer 203 is, for example, about 1 mm. Further, the thickness d2 (see FIG. 3) of the lattice portion is determined so as to obtain an area necessary for bonding the spacer 203 and the electrodes 101b and 101c with sufficient strength.

  Next, the operation of the capacitive distance sensor 100 according to this embodiment will be described with reference to FIGS. 5A is a conceptual diagram illustrating a case where an object to be detected does not exist within the detectable range of the sensor unit 101, and FIG. 5B illustrates a case where an object to be detected exists within the detectable range. It is a conceptual diagram.

  First, the initial adjustment operation of the capacitive distance sensor 100 will be described with reference to FIGS. 1 and 5A. This adjustment is performed when there is no object to be detected within the detectable range.

  When the buffer circuit 103 starts outputting an alternating voltage, the alternating voltage is applied to the transmission electrode 101a via the resistance element 104. Here, since there is no object to be detected, no current flows from the transmission electrode 101a to the capacitor formed by the object to be detected. Therefore, the voltage drop of the resistance element 104 does not occur due to the presence of the object to be detected.

  The AC voltage output from the buffer circuit 103 is also applied to the auxiliary electrode 101c. On the other hand, the shield electrode 101b is grounded. Therefore, an inter-terminal voltage is generated in the capacitor formed by the auxiliary electrode 101c and the shield electrode 101b, whereby a current I1 flows from the auxiliary electrode 101c to the shield electrode 101b. When the current I1 flows through the auxiliary electrode 101c, the voltage of the auxiliary electrode 101c slightly decreases due to the wiring resistance of the covered wire 105b of the shield cable 105. For this reason, a very small potential difference is generated between the transmission electrode 101a and the auxiliary electrode 101c. Therefore, a minute current I0 flows from the transmitting electrode 101a to the auxiliary electrode 101c, and a minute voltage drop occurs in the resistance element 104. Therefore, a slight potential difference is generated between the inverting input terminal (−) and the non-inverting input terminal (+) of the differential amplifier 106.

  The differential amplifier 106 outputs an AC voltage signal corresponding to this potential difference. This voltage signal has its noise component removed by the band-pass filter 107, converted from an AC signal to a DC signal by the detection circuit 108, and after the ripple component has been removed by the low-pass filter 109, the non-inverting input terminal of the differential amplifier 110 Input to (+). At this time, the CPU 112 outputs zero as the correction signal Sa. Accordingly, zero volt is output from the digital / analog converter 113 to the inverting input terminal of the differential amplifier 110. Therefore, the differential amplifier 110 outputs the DC voltage signal output from the low-pass filter 109 as it is as the detection signal Sd.

  Here, in order to obtain sufficient detection accuracy when the sensor unit 101 detects an object to be detected, detection is performed so that the signal value when there is no object to be detected becomes a predetermined value (here, zero volts). It is desirable to correct the signal Sd. This correction is performed by the CPU 112 or the like as follows.

  The detection signal Sd is digitized by the analog / digital converter 111 and sent to the CPU 112. The CPU 112 calculates the difference between the actual signal value of the digital detection signal Sd and the target value (here, zero volts) by a predetermined algorithm, stores the calculation result inside, and also outputs the digital / value as the value of the correction signal Sa. Send to analog converter 113. The digital / analog converter 113 changes the output voltage to a value corresponding to the correction signal Sa. As a result, the value of the signal supplied to the inverting input terminal of the differential amplifier 110 is changed. In this way, the input voltage of the inverting input terminal becomes the same as the input voltage of the non-inverting input terminal (that is, the output signal value of the low-pass filter), and the output of the differential amplifier 110 becomes zero volts.

  Next, an operation when an object to be detected exists within the detectable range of the sensor unit 101 will be described with reference to FIGS. 1 and 5B.

  The detected object 501 such as a human being or an animal can be regarded as a dielectric. Furthermore, when the detected object 501 is in contact with the floor or the ground, it can be considered that one end of the dielectric is grounded. For this reason, when the detected object 501 is sufficiently close to the transmission electrode 101a, it can be considered that a capacitor (capacitance is Cs) exists between the transmission electrode 101a and the ground or the like. For this reason, when an AC voltage is applied from the buffer circuit 103 to the transmission electrode 101a, the current Is flows between the transmission electrode 101a and the ground or the like via the detected object 501. As the detected object 501 approaches the sensor unit 101, the distance between the transmission electrode 101a and the detected object 501 becomes shorter, so that the capacitance Cs increases, and thus the current Is also increases. Conversely, when the object to be detected 501 moves away from the sensor unit 101, the distance between the transmission electrode 101a and the object to be detected 501 increases, so that the capacitance Cs decreases, and therefore the current Is also decreases.

  The current Is is supplied from the buffer circuit 103 to the transmission electrode 101a via the resistance element 104. That is, the current flowing through the resistance element 104 is the sum of the current I0 flowing from the transmission electrode 101a to the auxiliary electrode 101c and the current Is flowing from the transmission electrode 101a to the detected object 501. Thereby, the input potential difference (potential difference between the inverting input terminal and the non-inverting input terminal) of the differential amplifier 106 is increased due to the generation of the current Is.

  As described above, the differential amplifier 106 outputs an AC voltage signal corresponding to this potential difference. This voltage signal has its noise component removed by the band-pass filter 107, converted from an AC signal to a DC signal by the detection circuit 108, and after the ripple component has been removed by the low-pass filter 109, the non-inverting input terminal of the differential amplifier 110 Is input. The differential amplifier 110 outputs a voltage corresponding to the difference between the DC signal and the correction signal Sa as a detection signal Sd. As described above, the correction signal Sa is set so that the detection signal Sd when the detected object 501 does not exist is zero volts. Therefore, the detection signal Sd has a value corresponding to the current Is flowing through the detected object 501.

  For this reason, the capacitive distance sensor according to this embodiment can detect the presence / absence and the distance of the detection object 501 in a non-contact manner.

  As described above, in this embodiment, the auxiliary electrode 101c is provided between the transmission electrode 101a and the shield electrode 101b, and an alternating current is transmitted from one buffer circuit 103 to the transmission electrode 101a and the auxiliary electrode 101c via different wires. It was decided to supply voltage. Therefore, the detection accuracy for the detection object can be increased for the following reasons.

  First, the reason why one buffer circuit 103 is used will be described.

As shown in FIG. 1, in the capacitive distance sensor 100 of this embodiment, the sensor unit 101 and the electronic circuit portion (circuits 102 to 104 and 106 to 112) are connected by a shielded cable 105. . For this reason, when the sensor unit 101 and the electronic circuit part are installed apart from each other, the shielded cable 105 may be close to another device or the like. Here, if a grounded metal shield cable 105 are in close proximity, the electrostatic capacitance between the metal and the covered wire 105b (the C _L in this case) is generated. Therefore, when an AC voltage is supplied from the buffer circuit 103 to the covered wire 105b, a current (here, I _L ) flows from the covered wire 105b to the metal. For this reason, the electrostatic capacitance C _L becomes a load of the buffer circuit 103. In general, when a capacitive load increases in an operational amplifier, an output phase delay with respect to an input increases. For this reason, when an alternating voltage is supplied to the transmission electrode 101a and the auxiliary electrode 101c from separate voltage follower circuits, a phase difference occurs between the alternating voltages supplied to these electrodes 101a and 101c. A potential difference is generated between the electrodes 101a and 101c. Therefore, so that the current flowing through the resistor 104 due to the electrostatic capacitance C _L is increased. Here, if the value of the capacitance C _L is constant, the influence of this current is eliminated by the correction signal Sa (see FIG. 1). However, when the value of the capacitance C _L is not constant (that is, when the distance between the grounded metal and the shield cable 105 varies), the variation in the capacitance C _L causes a detection error. become. In contrast, when an AC voltage is supplied from the same buffer circuit 103 to the transmission electrode 101a and the auxiliary electrode 101c, the transmission electrode 101a and the auxiliary electrode 101c are generated even if a phase delay due to the capacitance C _L occurs. There is no phase difference between the two. Therefore, the detection accuracy of the detection object can be improved by using one buffer circuit 103.

  Next, the reason why the auxiliary electrode 101c is provided and the reason why an AC voltage is supplied to the transmission electrode 101a and the auxiliary electrode 101c via different wirings will be described.

  Originally, the sensor unit 101 detects an object to be detected only in the surface direction of the transmission electrode 101a. However, actually, electromagnetic waves are also emitted in the direction of the back surface of the transmission electrode 101a. Therefore, even when an object is present in the back surface direction of the transmission electrode 101a, it is necessary to prevent an electric field from being formed between the object and the transmission electrode 101a. When an electric field is formed between the object in the back surface direction and the transmission electrode 101a, the current flowing through the resistance element 104 fluctuates due to a change in position of the object, which causes false detection and deterioration of detection accuracy. Because. Therefore, a grounded shield electrode 101b is provided on the back side of the transmission electrode 101a. However, when only the shield electrode 101b is provided (that is, when the auxiliary electrode 101c is not provided), a current flows between the transmission electrode 101a and the shield electrode 101b. Normally, the capacitance between the transmission electrode 101a and the shield electrode 101b is very large compared to the capacitance between the transmission electrode 101a and the object to be detected, and therefore the transmission electrode 101a and the shield electrode 101b. The current flowing between the transmission electrode 101a and the object to be detected is also very large. For this reason, when a current flows between the transmission electrode 101a and the shield electrode 101b, it becomes very difficult to accurately detect the current between the transmission electrode 101a and the object to be detected. On the other hand, when the auxiliary electrode 101c is provided between the transmission electrode 101a and the shield electrode 101b and the potentials of these electrodes 101a and 101c are set to substantially the same potential, the influence of an object existing on the back surface side of the transmission electrode 101a. The current flowing on the back surface side can be kept very small while eliminating the above.

  In addition, in this embodiment, an alternating voltage is supplied to the transmission electrode 101a and the auxiliary electrode 101c via different wirings, and the resistance element 104 is provided on the wiring that connects the buffer circuit 103 and the transmission electrode 101a. . That is, the transmission electrode 101 a is connected to the buffer circuit 103 via the core wire 105 a of the shielded cable 105 and the resistance element 104, and the auxiliary electrode 101 c is connected to the buffer circuit 103 via the covered wire 105 b of the shielded cable 105. That is, the current flowing through the transmission electrode 101a and the current flowing through the auxiliary electrode 101c are separated, and the current flowing through the auxiliary electrode 101c does not flow through the resistance element 104. For this reason, the electric current which flows through the resistive element 104 can be made small, Therefore The detection accuracy of the electric current which flows into the to-be-detected object from the transmission electrode 101a improves.

  As described above, according to the capacitive distance sensor 100 according to this embodiment, an AC voltage is supplied from one buffer circuit 103 to the transmission electrode 101a and the auxiliary electrode 101c via different wires. The current flowing out from the electrode 101a to the detected object can be detected with high accuracy, and therefore the detection accuracy of the detected object can be improved.

  Further, since the detection signal Sd when the detected object is detected is corrected using the detection signal value when the detected object is not detected, the detection accuracy of the detected object can be further improved.

  In addition, since the printed circuit board 201 and the spacer 203 are formed of a flexible material and the shield electrode 101b is formed of a flexible and stretchable material, the sensor unit 101 can be easily attached to a curved surface or the like.

Second Embodiment Hereinafter, a capacitive distance sensor according to a second embodiment of the present invention will be described with reference to FIG. This embodiment is an example of a capacitive distance sensor capable of performing temperature correction.

  FIG. 6 is a schematic diagram showing the configuration of the capacitive distance sensor according to this embodiment. In FIG. 6, components denoted by the same reference numerals as those in FIG. 1 are the same as those in FIG. 1.

  The capacitive distance sensor 600 according to this embodiment includes a temperature correction circuit 610. The temperature correction circuit 610 forms an equivalent circuit of the original sensors (101 to 110, 113). In order to perform accurate temperature correction, it is desirable that the temperature correction circuit 610 has the same temperature as the detection circuit portions (102 to 104, 106 to 110, 113) of the original sensor. It is desirable to be formed on the same substrate as the part.

  As shown in FIG. 6, the temperature correction circuit 610 includes a temperature correction pseudo sensor unit 611, a temperature correction buffer circuit 612, a temperature correction current detection resistor element 613, and a temperature correction first differential amplifier 614. A temperature correction band-pass filter 615, a temperature correction detection circuit 616, a temperature correction low-pass filter 617, a temperature correction second differential amplifier 618, and a temperature correction digital / analog converter 619. ing. The capacitive distance sensor 600 of this embodiment includes a CPU (Central Processing Unit) 630 and an analog / digital converter 620. In the temperature correction circuit 610 of this embodiment, it is not necessary to dispose the temperature correction pseudo sensor unit 611 away from other circuit parts (611, 612, etc.), and therefore a shielded cable is not used.

  The temperature correction pseudo sensor unit 611 includes a first capacitor 611a and a second capacitor 611b. The first capacitor 611a has the same capacitance as the capacitance between the transmission electrode 101a and the auxiliary electrode 101c. The second capacitor 611b has the same capacitance as the capacitance between the auxiliary electrode 101c and the shield electrode 101b. The second capacitor 611b is grounded at one end. In this application, “the same” (or “same”) means that the configuration or characteristics (particularly temperature dependency) of the circuit or element are the same in design.

  The temperature correction buffer circuit 612 is a buffer for supplying the pseudo-sensor unit 611 with the AC voltage output from the oscillation circuit 102. As the temperature correction buffer circuit 612, the same one as the buffer circuit 103 is used. As shown in FIG. 6, the temperature correction buffer circuit 612 is configured by one voltage follower circuit, like the buffer circuit 103.

  The temperature correction current detection resistance element 613 is a resistance element for converting a current flowing through the first capacitor 611a into a voltage (described later). As the temperature correction current detection resistor element 613, the same one as the current detection resistor element 104 is used. The temperature correction current detection resistor element 613 has one end connected to the output end of the buffer circuit 612 and the other end connected to one end of the first capacitor 611a.

  The temperature correction first differential amplifier 614 outputs a voltage corresponding to the potential difference between the non-inverting input terminal (+) and the inverting input terminal (−). The same temperature differential first differential amplifier 614 as the first differential amplifier 106 is used. The non-inverting input terminal of the temperature correction differential amplifier 614 is connected to one end of the temperature correction resistance element 613 (that is, the end on the temperature correction buffer circuit 612 side). The inverting input terminal of the temperature correcting differential amplifier 614 is connected to the other end of the temperature correcting resistor 613 (that is, the end on the first capacitor 611a side). Accordingly, the differential amplifier 614 outputs an AC voltage signal having a value corresponding to the voltage across the resistance element 613.

  As the temperature correction band-pass filter 615, the same one as the band-pass filter 107 is used. That is, the temperature correction band-pass filter 615 removes a noise component from the AC voltage signal by passing only a signal component having a frequency f (that is, a component having the same frequency as that of the oscillation circuit 102).

  As the temperature correction detection circuit 616, the same one as the detection circuit 108 (time constant τ≈1 / f) is used. The temperature correction detection circuit 616 converts the AC voltage signal input from the temperature correction bandpass filter 615 into a DC voltage signal.

  As the temperature correcting low-pass filter 617, the same one as the low-pass filter 109 is used. The temperature correction low-pass filter 617 receives a DC voltage signal from the temperature correction detection circuit 616 and removes a high-frequency component. Thereby, the ripple component can be removed from the DC voltage signal.

  As the second differential amplifier 618 for temperature correction, the same one as the second differential amplifier 110 is used. The temperature correction second differential amplifier 618 outputs a voltage corresponding to the potential difference between the non-inverting input terminal (+) and the inverting input terminal (−). The non-inverting input terminal of the temperature correction second differential amplifier 618 is connected to the output terminal of the low-pass filter 617. Further, the inverting input terminal of the temperature correction second differential amplifier 618 is connected to the output terminal of the digital / analog converter 619. The DC voltage signal output from the temperature correction second differential amplifier 618 is sent to the analog / digital converter 620.

  The temperature correction digital / analog converter 619 converts the output signal of the CPU 630 from a digital signal to an analog signal. As the temperature correcting digital / analog converter 619, the same one as the digital / analog converter 113 is used.

  The analog / digital converter 620 converts the DC voltage signals output from the differential amplifiers 110 and 618 (that is, the detection signals Sd1 and Sd2) from analog signals to digital signals, respectively.

  The CPU 630 generates correction signals Sa1 and Sa0 using the digital signal input from the analog / digital converter 620, stores the correction signals Sa1 and Sa0 therein, and outputs them to the digital / analog converters 113 and 619. Thereby, temperature correction as described later can be performed.

  Next, the operation of the capacitive distance sensor 600 according to this embodiment will be described.

  First, the initial adjustment operation of the capacitive distance sensor 600 will be described. This adjustment is performed when there is no object to be detected within the detectable range.

  When the buffer circuit 103 starts outputting an alternating voltage, a very small potential difference is generated between the transmission electrode 101a and the auxiliary electrode 101c, as in the first embodiment. This potential difference is converted into a DC voltage signal Sd1 as in the first embodiment, converted into a digital signal by the analog / digital converter 620, and input to the CPU 630. The CPU 630 generates and outputs the correction signal Sa1 in the same manner as the CPU 112 of the first embodiment. The correction signal Sa1 is converted into an analog signal by the digital / analog converter 113 and supplied to the inverting input terminal of the differential amplifier 110. As a result, the value of the detection signal Sd1 is corrected to zero.

  Simultaneously with the start of the operation of the buffer circuit 103, the temperature correction buffer circuit 612 also starts to output an AC voltage. This AC voltage is applied to one end of the first capacitor 611a via the correcting resistor 613. Further, the output of the temperature correction buffer circuit 612 is directly applied to the other ends of the first and second capacitors 611a and 611b without passing through the resistance element 613. As a result, an inter-terminal voltage is generated in the second capacitor 611b, and a current I2 (not shown) flows. When the current I2 flows, the voltage at the other end of the second capacitor 611b slightly decreases due to the wiring resistance between the correction buffer circuit 612 and the second capacitor 611b. For this reason, a very small potential difference is generated between the terminals of the first capacitor 611a. Therefore, a minute current I3 (not shown) flows through the first capacitor 611a, and a slight voltage drop occurs in the temperature correcting resistance element 613. As a result, a slight potential difference occurs between the inverting input terminal (−) and the non-inverting input terminal (+) of the temperature correction first differential amplifier 614. The output signal of the differential amplifier 614 is subjected to the same processing as in the case of the circuit elements 107 to 109 by the circuit elements 615 to 617 in the subsequent stage, and is supplied to the second differential amplifier 618 for temperature correction. Then, the DC voltage signal Sd0 is output from the temperature correction second differential amplifier 618. The DC voltage signal Sd0 is converted into a digital signal by the analog / digital converter 620 and input to the CPU 630. The CPU 630 generates and outputs a correction signal Sa0 in the same manner as the signal Sd1 described above. The correction signal Sa0 is converted into an analog signal by the digital / analog converter 619 and supplied to the inverting input terminal of the differential amplifier 618. As a result, the value of the signal Sd0 is corrected to zero.

  Next, the operation of the capacitive distance sensor 600 after the initial adjustment will be described.

  When the object to be detected falls within the detectable range of the sensor unit 101, the current I0 flowing through the resistance element 104 varies and becomes I0 + Is (see FIG. 5B), as in the first embodiment described above. As a result, similarly to the first embodiment, the detection signal Sd1 changes from zero volts to a value corresponding to the current Is flowing through the detected object.

  On the other hand, the current flowing through the temperature correction pseudo sensor unit 611 does not change according to the presence or absence of the object to be detected and the distance. Therefore, if the environmental temperature does not change, the value of the signal Sd0 is maintained as in the initial adjustment described above.

  Here, when the environmental temperature of the circuit portion of the capacitive distance sensor 600 (that is, the portion other than the sensor unit 101 and the shielded cable 105) changes, the circuits 103 and 106 to 110 are caused by this temperature change. The offset voltage etc. of each operational amplifier etc. to change fluctuate. As described above, in this embodiment, initial adjustment is performed so that the output of the differential amplifier 110 becomes zero volts. Therefore, if the environmental temperature remains at the time of initial adjustment, the detection signal Sd1 caused by the offset voltage or the like Errors do not matter. However, when the offset voltage or the like due to a change in environmental temperature varies greatly, the error of the detection signal Sd1 due to the offset voltage or the like cannot be ignored.

  The capacitive distance sensor 600 according to this embodiment includes a temperature correction circuit 610 equivalent to the original sensor. When the offset voltage or the like fluctuates in the original sensor portion, the same fluctuation occurs in the temperature correction circuit 610. Therefore, if the detection signal Sd1 is corrected using the fluctuation amount of the output voltage Sd0 of the temperature correction circuit 610, the error of the detection signal Sd1 can be canceled.

  Therefore, in the capacitive distance sensor 600 according to this embodiment, the CPU 630 checks the value of the signal Sd0 every predetermined time. When the value of the signal Sd0 changes from ΔV by ΔSd, the CPU 630 performs an operation based on a predetermined algorithm and adjusts the value of the correction signal Sa0 so that the signal Sd0 becomes zero volts. As a result, the signal Sd0 returns to zero volts. Since the original sensor and the temperature correction circuit 610 are equivalent as described above, when the error ΔSd occurs in the signal Sd0, the error ΔSd should also occur in the detection signal Sd1. For this reason, the CPU controls the value of the correction signal Sa1 so as to be the same value as the correction signal Sa0 when the error of the signal Sd0 is canceled. As a result, the error ΔSd is corrected in the detection signal Sd1, and the error due to the change in the environmental temperature is cancelled. Such correction processing can be performed not only when the detected object does not exist within the detectable range of the sensor unit 101 but also during detection of the detected object.

  In this embodiment, the value of the detection signal Sd1 when there is no object to be detected is set to zero volts, but it goes without saying that the value may be set to other values.

  As described above, according to the capacitive distance sensor 600 according to this embodiment, an error in the detection signal due to a change in the environmental temperature can be corrected. Therefore, the capacitive type sensor according to the first embodiment described above. Compared with the distance sensor 100, the detection accuracy can be further increased.

  In addition, since the AC voltage is supplied from one buffer circuit 103 to the transmission electrode 101a and the auxiliary electrode 101c via different wires, the detection accuracy is improved, and the detection signal value when the detected object is not detected is used. The detection signal is corrected when the object to be detected is corrected, and the detection accuracy is improved. The printed circuit board 201 and the spacer 203 are made of a flexible material, and the shield electrode 101b is flexible and stretchable. It is the same as in the first embodiment in that the sensor unit 101 can be easily attached to a curved surface or the like by forming with a certain material.

Third Embodiment Hereinafter, a capacitance type distance sensor according to a third embodiment of the present invention will be described with reference to FIG. This embodiment is an example of a capacitance type distance sensor that has a plurality of detection systems and can perform temperature correction of each detection system.

  FIG. 7 is a schematic diagram showing the configuration of the capacitive distance sensor according to this embodiment. In FIG. 7, components denoted by the same reference numerals as those in FIG. 1 are the same as those in FIG. 1.

  As shown in FIG. 7, the capacitance type distance sensor 700 of this embodiment includes two detection systems 710 and 720, one temperature correction circuit 730, and switches 741 and 742 with three inputs and one output. CPU750.

  The detection system 710 includes a sensor unit 711, a buffer circuit 712, a current detection resistor element 713, and a shield cable 714. Similarly, the detection system 720 includes a sensor unit 721, a buffer circuit 722, a current detection resistance element 723, and a shield cable 724. Further, the temperature correction circuit 730 includes a temperature correction pseudo sensor unit 731, a temperature correction buffer circuit 732, and a temperature correction current detection resistor element 733.

  The sensor units 711 and 721 have the same configuration as the sensor unit 101 of the first embodiment. That is, the sensor unit 711 includes a transmission electrode 711a, a shield electrode 711b, and an auxiliary electrode 711c, and the sensor unit 721 includes a transmission electrode 721a, a shield electrode 721b, and an auxiliary electrode 721c.

  The pseudo sensor unit for temperature correction 731 has the same configuration as the pseudo sensor unit 611 of the second embodiment. That is, the temperature correction pseudo sensor unit 731 includes first and second capacitors 731a and 731b. The capacitance of the first capacitor 731a is the same as the capacitance between the electrodes 711a and 711c and between the electrodes 721a and 721c. The capacitance of the second capacitor 731b is the same as the capacitance between the electrodes 711b and 711c and between the electrodes 721b and 721c.

  The buffer circuits 712, 722, and 732 have the same configuration as the buffer circuit 103 of the first embodiment. These buffer circuits 712, 722, and 732 have the same configuration and characteristics.

  The current detection resistance elements 713 and 723 are resistance elements for converting the current flowing through the corresponding transmission electrodes 711a and 721a into a voltage, like the current detection resistance element 104 of the first embodiment. The temperature correction current detection resistor element 733 is a resistor element for converting the current flowing through the first capacitor 731 into a voltage, like the temperature correction current detection resistor element 613 of the second embodiment. These resistance elements 713, 723, and 733 have the same resistance value.

  The same shielded cables 714 and 724 as the shielded cable 105 of the first embodiment are used. In the shielded cable 714, the core wire 714a connects the resistance element 713 and the transmission electrode 711a, and the covered wire 714b connects the output end of the buffer circuit 712 and the auxiliary electrode 711c. Similarly, in the shielded cable 724, the core wire 724a connects the resistance element 723 and the transmission electrode 721a, and the covered wire 724b connects the output end of the buffer circuit 722 and the auxiliary electrode 721c.

  The switch 741 is connected to one end of the resistance element 713 (the end on the buffer circuit 712 side) at the input terminal S11, connected to one end of the resistance element 723 (the end on the buffer circuit 722 side) at the input terminal S12, and The input terminal S13 is connected to one end of the resistance element 733 (the end on the buffer circuit 732 side). The output terminal of the switch 741 is connected to the non-inverting input terminal of the differential amplifier 106.

  The switch 742 is connected to the other end of the resistance element 713 (end on the transmission electrode 711a side) at the input terminal S21, and connected to the other end of the resistance element 723 (end on the transmission electrode 721a side) at the input terminal S22. In addition, the input terminal S23 is connected to the other end of the resistance element 733 (the end portion on the first capacitor 731a side). The output terminal of the switch 742 is connected to the inverting input terminal of the differential amplifier 106.

  The CPU 750 generates correction signals Sa1, Sa2, and Sa0 using the digital signals input from the analog / digital converter 111, stores them inside, and outputs them to the digital / analog converter 113. Thereby, temperature correction as described later can be performed. In addition, the CPU 750 performs control such as input switching of the switches 741 and 742.

  Next, the operation of the capacitive distance sensor 700 according to this embodiment will be described with reference to FIG.

  First, the initial adjustment operation of the capacitive distance sensor 700 will be described. This adjustment is performed when there is no object to be detected within the detectable range.

  When the buffer circuits 712, 722, and 732 start outputting an alternating voltage, a very small potential difference is generated between the electrodes 711a and 711c and between the electrodes 721a and 721c, as in the first embodiment. A minute current also flows through the second capacitor 731b.

  When the CPU 750 causes the switches 741 and 742 to select the input terminals S11 and S21, the voltage between the terminals of the resistance element 713 is input to the differential amplifier 106. Then, the AC voltage signal output from the differential amplifier 106 is free from noise and the like, converted into a DC voltage signal Sd1, converted into a digital signal, and sent to the CPU 750 in the same manner as in the first embodiment. The CPU 750 calculates a correction value and stores the calculation result in the same manner as the CPU 112 of the first embodiment, and outputs it as a correction signal Sa1. As a result, the detection signal output from the differential amplifier 110 becomes zero volts.

  Next, when the CPU 750 causes the switches 741 and 742 to select the input terminals S12 and S22, the voltage across the resistance element 723 is input to the differential amplifier 106. Then, the AC voltage signal output from the differential amplifier 106 is output from the differential amplifier 110 as a DC voltage signal Sd2, converted into a digital signal, and sent to the CPU 750 in the same manner as described above. In the same manner as described above, the CPU 750 calculates a correction value, stores the calculation result therein, and outputs it as a correction signal Sa2. As a result, the detection signal output from the differential amplifier 110 becomes zero volts.

  Further, when the CPU 750 causes the switches 741 and 742 to select the input terminals S13 and S23, the voltage across the resistance element 733 is input to the differential amplifier 106. In the same manner as described above, the AC voltage signal output from the differential amplifier 106 is output from the differential amplifier 110 as a DC voltage signal Sd0, converted into a digital signal, and sent to the CPU 750. The CPU 750 calculates the correction value in the same manner as described above, stores the calculation result therein, and outputs it as the correction signal Sa0. As a result, the detection signal output from the differential amplifier 110 becomes zero volts.

  After completion of the initial adjustment, the CPU 750 activates an internal timer and generates interrupts at regular time intervals.

  At this interrupt timing t1 (see FIG. 8), the CPU 750 first causes the switches 741 and 742 to select the input terminals S11 and S21 (see P1 in FIG. 8) and outputs the correction signal Sa1 to the digital / analog converter 113. To do. Thus, the corrected detection signal Sd1 is output from the differential amplifier 110.

  When this processing is completed, the CPU 750 then causes the switches 741 and 742 to select the input terminals S12 and S22 (see P2 in FIG. 8) and outputs the correction signal Sa2 to the digital / analog converter 113. Thus, the corrected detection signal Sd2 is output from the differential amplifier 110.

  Subsequently, the CPU 750 causes the switches 741 and 742 to select the input terminals S13 and S23 (see P3 in FIG. 8) and outputs the correction signal Sa0 to the digital / analog converter 113. Accordingly, the corrected voltage signal Sd0 is input to the CPU 750 via the analog / digital converter 111. As in the second embodiment, the CPU 750 performs an operation based on a predetermined algorithm, and calculates an adjustment value ΔSa so that the signal Sd0 becomes zero volts. When the CPU 750 changes the value of the correction signal to Sa0 + ΔSa, the signal Sd0 returns to zero volts.

  Further, the CPU 750 rewrites the correction signal values Sa1 and Sa2 stored therein to Sa1 + ΔSa and Sa2 + ΔSa. As a result, the temperature of the detection signals Sd1 and Sd2 can be corrected by using this ΔSa in the detection when the next interruption occurs.

  Similar processing P1, P2, and P3 are repeated after the interrupt timing t2 (see FIG. 8).

  As described above, according to this embodiment, in the capacitive distance sensor 700 having two detection systems, an error in the detection signal due to a change in the environmental temperature can be corrected, and the detection accuracy is improved. be able to.

  Also, AC voltage is supplied from one buffer circuit to the transmission electrode and auxiliary electrode via different wires, so that detection accuracy is improved, and detection is performed using the detection signal value when no detection object is detected. Correction of detection signal Sd when an object is detected improves detection accuracy, and printed board 201 and spacer 203 are formed of a flexible material, and a shield electrode is formed of a flexible and stretchable material This is the same as the first embodiment in that the sensor part can be easily attached to a curved surface or the like.

  In this embodiment, the case where the two detection systems 710 and 720 are provided has been described. However, three or more detection systems may be provided. Furthermore, this embodiment can also be applied when only one detection system is provided. Even when there is only one detection system, the circuit after the first differential amplifier 106 can be shared by applying this embodiment, so that the scale and cost of the circuit can be reduced.

Fourth Embodiment Hereinafter, a capacitance type distance sensor according to a fourth embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG. This embodiment is another example of a capacitive distance sensor that can correct an error caused by a temperature change of the sensor unit.

  FIG. 9 is a schematic diagram showing the configuration of a capacitive distance sensor 900 according to this embodiment. 9, components having the same reference numerals as those in FIG. 1 are the same as those in FIG.

  The capacitive distance sensor 900 of this embodiment includes a temperature correction circuit 910. The temperature correction circuit 910 includes temperature correction resistance elements 911, 912, and 913.

  The temperature correcting resistance element 911 includes one end (an end on the buffer circuit 103 side) of the current detection resistance element 104 (resistance value Rs1) and a non-inverting input terminal (+) of the first differential amplifier 106. Between. The resistance value of the resistance element 911 is Rs2.

  The temperature correcting resistive element 912 is connected at one end to the other end (the end on the transmission electrode 101a side) of the current detecting resistive element 104 and grounded at the other end. The resistance value of the resistance element 912 is Rf1.

  The temperature correcting resistance element 913 is connected to the non-inverting input terminal of the first differential amplifier 106 at one end and grounded at the other end. The resistance value of the resistance element 912 is Rf2.

Here, the resistance values Rs1, Rs2, Rf1, and Rf2 of the resistance elements 104 and 911 to 913 are determined so as to satisfy the following expressions (1) and (2).
Rs1 / Rf1 = Rs2 / Rf2 (1)
Rs1 = Rf1, Rs2 = Rf2 (2)

  By setting each resistance value so as to satisfy the expressions (1) and (2), it becomes possible to suppress errors due to fluctuations in the environmental temperature. Hereinafter, the reason will be described.

  When the environmental temperature of the sensor unit 101 changes, the relative dielectric constant of the dielectric constituting the sensor unit 101 changes. Therefore, the capacitance between the transmission electrode 101a and the auxiliary electrode 101c and between the auxiliary electrode 101c and the shield electrode 101b changes. In particular, since a current flows from the buffer circuit 103 without passing through a resistor between the auxiliary electrode 101c and the shield electrode 101b, the load on the buffer circuit 103 increases. As shown in FIG. 9, the buffer circuit 103 is a voltage follower circuit of an operational amplifier. Here, when the output current of the operational amplifier fluctuates, the temperature of the operational amplifier fluctuates, and as a result, the gain of the voltage follower circuit changes. For this reason, the output amplitude of the buffer circuit 103 varies according to the variation of the environmental temperature of the sensor unit 101. Therefore, the amplitude of the AC voltage input to the non-inverting input terminal and the inverting input terminal of the first differential amplifier 106 also varies depending on the environmental temperature of the sensor unit 101.

  The first differential amplifier 106 is an instrumentation amplifier, and both the non-inverting input terminal and the inverting input terminal have high input impedance, but a minute current flows into the non-inverting input terminal and the inverting input terminal. This inflow current changes depending on the amplitude change of the input voltage. For example, when the amplitude increases due to a change in the environmental temperature, this inflow current also increases.

  Here, in the case of a capacitive distance sensor (see FIG. 1) that does not have the temperature correction circuit 910, the non-inverting input terminal (+) of the differential amplifier 106 is connected to the buffer circuit 103 without passing through a resistance element. Connected to the output terminal. Therefore, since the electric resistance in the path from the buffer circuit 103 to the non-inverting input terminal can be regarded as zero, the voltage drop is zero volts. On the other hand, the inverting input terminal (−) of the differential amplifier 106 is connected to the output terminal of the buffer circuit 103 via the resistance element 104. For this reason, a voltage drop occurs due to the current flowing through the resistance element 104, and the potential of the inverting input terminal is lowered. For this reason, the differential amplifier 106 generates a potential difference between the non-inverting input terminal and the inverting input terminal. The detection error due to this potential difference is canceled by the initial adjustment using the correction signal Sa. For this reason, if the environmental temperature does not change (that is, if the output amplitude of the buffer circuit 103 does not change), it does not cause an error in the detection signal Sd. However, when the environmental temperature fluctuates, the output amplitude of the buffer circuit 103 also fluctuates, and thereby the voltage drop amount due to the resistance element 104 also fluctuates. Therefore, the potential difference between the non-inverting input terminal and the inverting input terminal is also deviated from the initial adjustment value. This “deviation” appears as an error in the detection signal Sd.

On the other hand, in this embodiment, the temperature correction circuit 910 is provided to prevent a potential difference between the non-inverting input terminal and the inverting input terminal. In this embodiment, when the output potential of the buffer circuit 103 is V0, the potential V (−) of the inverting input terminal and the potential V (+) of the non-inverting input terminal of the differential amplifier 106 are expressed by the following equations (3), ( 4). Therefore, when the above expressions (1) and (2) are satisfied, V (−) = V (+). In the case of V (−) = V (+), a potential difference between the input terminals of the differential amplifier 106 does not occur regardless of the environmental temperature. Therefore, an error of the detection signal Sd occurs due to the fluctuation of the environmental temperature. There is nothing.
V (−) = (Rf1 / (Rs1 + Rf1)) · V0 (3)
V (+) = (Rf2 / (Rs2 + Rf2)) · V0 (4)

  FIG. 10 is a graph showing a measurement result of the relationship between the environmental temperature and the detection signal Sd. In FIG. 10, the vertical axis represents the voltage value [V] and the environmental temperature [° C.] of the detection signal Sd, and the horizontal axis represents the elapsed time [hour]. In FIG. 10, a curve T is an environmental temperature, a curve A is a detection signal Sd of the capacitive distance sensor 900 according to this embodiment, and a curve B is a capacitive distance sensor (without a temperature correction circuit 910). FIG. 1 shows a detection signal Sd. Note that both A and B are values when there is no object to be detected within the detectable range of the sensor unit 101.

  As can be seen from FIG. 10, in the capacitive distance sensor that does not have the temperature correction circuit 910, when the environmental temperature T is changed from 10 ° C. to 70 ° C., the value of the detection signal Sd almost follows this. Change (see curve B). On the other hand, in the capacitive distance sensor 900 of this embodiment, even when the environmental temperature T changes, the detection signal Sd hardly fluctuates.

  As described above, according to the capacitive distance sensor 900 according to this embodiment, the error of the detection signal due to the environmental temperature change can be eliminated, so the capacitive distance sensor according to the first embodiment described above. Compared with 100, the detection accuracy can be further increased.

  In addition, since the AC voltage is supplied from one buffer circuit 103 to the transmission electrode 101a and the auxiliary electrode 101c via different wires, the detection accuracy is improved, and the detection signal value when the detected object is not detected is used. The detection signal Sd when the detected object is detected is corrected to improve the detection accuracy, and the printed board 201 and the spacer 203 are made of a flexible material, and the shield electrode 101b is flexible and stretchable. It is the same as in the first embodiment that the sensor unit 101 can be easily attached to a curved surface or the like by forming the material with a characteristic material.

Fifth Embodiment Next, a capacitive distance sensor according to a fifth embodiment of the present invention will be described with reference to FIGS. In this embodiment, another example of the sensor unit will be described.

  FIG. 11 is a diagram conceptually showing the sensor unit 1100 according to this embodiment, in which (A) is a side view and (B) is a front view.

  As shown in FIG. 11, the printed circuit board 1110 has an insulating base material 1111. A transmission electrode 1112 is printed on the surface of the insulating base material 1111, and an auxiliary electrode 1113 is printed on the back surface.

  A carbon fiber plate 1141 is bonded to the surface of the transmission electrode 1112 with an adhesive 1151. The area of the carbon fiber plate 1141 is, for example, several times to several tens of times the area of the transmission electrode 1112.

  A carbon fiber plate 1142 is bonded to the back surface of the auxiliary electrode 1113 with an adhesive 1152. The area of the carbon fiber plate 1142 may be the same as that of the carbon fiber plate 1141.

  A spacer 1120 is bonded to the back surface of the carbon fiber plate 1142 with an adhesive 1153. As the spacer 1120, for example, the same spacer as the spacer 203 (see FIG. 3) of the first embodiment can be used.

  A carbon fiber plate 1143 is bonded to the back surface of the spacer 1120 with an adhesive 1154. The area of the carbon fiber plate 1143 may be the same as that of the carbon fiber plates 1141 and 1142.

  A shield electrode 1130 is bonded to the back surface of the carbon fiber plate 1143 by an adhesive 1155. The shield electrode 1130 can be formed of, for example, conductive rubber or conductive cloth.

  Next, the operation principle of the sensor unit 1100 will be described with reference to FIG. FIG. 12 shows a main configuration of the capacitive distance sensor 1200 according to this embodiment. In FIG. 12, since the configuration other than the sensor unit 1100 is the same as that of the capacitive distance sensor 100 according to the first embodiment (see FIG. 1), a part thereof is omitted.

  The carbon fiber plates 1141 to 1143 are electrically conductive inside, but the surface is insulative, and are connected to the electrodes 1112, 1113 and 1130 via very thin adhesive layers 1151, 1152 and 1155. Therefore, it becomes a capacitive coupling. In this embodiment, the case where an insulating material is used as the adhesives 1151 to 1155 will be described. Here, since the adhesive layers 1151, 1152, and 1155 are very thin, the coupling capacity becomes very large.

  When the detection object 1201 exists in front of the carbon fiber plate 1141, it can be considered that a capacitor exists between the transmission electrode 1112 and the ground. At this time, the adhesive layer 1151, the carbon fiber plate 1141, the detected object 1201, and the space between the carbon fiber plate 1141 and the detected object 1201 constitute a dielectric of the capacitor. Here, the electrostatic capacity of the adhesive layer 1151 is Cc, and the electrostatic capacity of the portion composed of the carbon fiber plate 1141, the detected object 1201, and the space is Cs. Since the capacitances Cc and Cs are connected in series, the combined capacitance C is given by the following equation (4).

C = Cs · Cc / (Cs + Cc) (4)
As described above, the adhesive layer 1151 is very thin, and thus the capacitance Cc is very large. Compared with this, the electrostatic capacity Cs of the part which consists of the carbon fiber board 1141, the to-be-detected object 1201, and space is very small. That is, Cc >> Cs. Here, in the case of Cc >> Cs, Cc / (Cs + Cc) ≈1, so C≈Cs from the above equation (4). Therefore, it is possible to detect the presence / absence and distance of the detection object using the carbon fiber plate 1141.

  In the capacitive distance sensor 1200 according to this embodiment, the value of the detection signal Sd (see FIG. 1) does not change even if the position of the detection object 1201 is shifted in parallel with the carbon fiber plate 1141. That is, in FIG. 12, the value of the detection signal Sd is the same when the detected object 1201 exists and when the detected object 1202 exists. The value of the current flowing between the transmission electrode 1112 and the ground depends on the distance between the carbon fiber plate 1141 and the detected object 1201 and the projection area of the detected object 1201 on the carbon fiber plate 1141, but the detected object 1201. This is because the position does not change even if the position of is shifted in parallel with the carbon fiber plate 1141.

  The reason why the carbon fiber plates 1142 and 1143 are provided in the back surface direction of the carbon fiber plate 1141 is to prevent an object in the back surface direction of the carbon fiber plate 1141 from affecting the detection signal Sd.

  As described above, according to this embodiment, the detectable area of the sensor unit 1100 can be expanded without increasing the areas of the electrodes 1112, 1113, 1130, and the like. Therefore, according to this embodiment, the capacitive distance sensor 1200 having a wide detectable area can be provided at a low cost.

  In addition, since the AC voltage is supplied from one buffer circuit 103 to the transmission electrode 1112 and the auxiliary electrode 1113 via different wires, the detection accuracy is improved, and the detection signal value when the detection target is not detected is used. The detection signal Sd when the detected object is detected is corrected to improve the detection accuracy, and the printed board 1110 and the spacer 1120 are made of a flexible material, and the shield electrode 1130 is flexible and stretchable. It is the same as in the first embodiment that the sensor unit 1100 can be easily attached to a curved surface or the like by forming the material with a characteristic material.

1 is a circuit diagram schematically showing a configuration of a capacitive distance sensor according to a first embodiment. FIG. It is a side view which shows roughly the structure of the sensor part which concerns on 1st Embodiment. It is a disassembled perspective view which shows schematically the structure of the sensor part which concerns on 1st Embodiment. It is a voltage waveform diagram for demonstrating operation | movement of the electrostatic capacitance type distance sensor which concerns on 1st Embodiment. It is a conceptual diagram for demonstrating operation | movement of the electrostatic capacitance type distance sensor which concerns on 1st Embodiment. It is a circuit diagram which shows roughly the structure of the electrostatic capacitance type distance sensor which concerns on 2nd Embodiment. It is a circuit diagram which shows roughly the structure of the electrostatic capacitance type distance sensor which concerns on 3rd Embodiment. It is a timing chart for demonstrating operation | movement of the electrostatic capacitance type distance sensor which concerns on 3rd Embodiment. It is a circuit diagram which shows roughly the structure of the electrostatic capacitance type distance sensor which concerns on 4th Embodiment. It is a graph which shows the characteristic measurement result of the capacitance type distance sensor concerning a 4th embodiment. It is a circuit diagram which shows roughly the structure of the sensor part which concerns on 5th Embodiment. It is a conceptual diagram for demonstrating operation | movement of the electrostatic capacitance type distance sensor which concerns on 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Capacitance type distance sensor 101 Sensor part 102 Oscillation circuit 103 Buffer circuit 104 Current detection resistive element 105 Shield cable 106 1st differential amplifier 107 Band pass filter 108 Detection circuit 109 Low pass filter 110 2nd differential amplifier 111 Analog / digital Converter 112 CPU
113 Digital / analog converter

Claims (10)

A non-contact capacitive distance sensor that detects the presence and distance of the detected object based on the magnitude of the detected current flowing into the detected object,
A transmission electrode that radiates an electromagnetic wave for supplying the detection current to the object to be detected; and a shield electrode that is disposed opposite the transmission electrode to shield the electromagnetic wave radiated from the back side of the transmission electrode; A sensor unit having an auxiliary electrode disposed between the transmitting electrode and the shield electrode to interrupt a current flowing between the transmitting electrode and the shield electrode;
A buffer circuit for supplying an alternating voltage generated by an oscillator to the transmission electrode and the auxiliary electrode;
A current detection resistance element for detecting the detection current as a voltage between terminals;
A first wiring that connects the output terminal of the buffer circuit and the transmission electrode via the current detection resistor element;
A second wiring that connects the output terminal of the buffer circuit and the auxiliary electrode without passing through the current detection resistor element;
A capacitance type distance sensor comprising: A first differential amplifier that outputs a voltage corresponding to the voltage between the terminals of the current detection resistor element;
A detection circuit for converting an output signal of the first differential amplifier into a DC signal;
A second differential amplifier that inputs an output signal of the detection circuit from one input terminal and outputs a detection signal from the output terminal;
An arithmetic processor for supplying a correction signal generated based on the value of the detection signal when the detection object is not detected to the other input terminal of the second differential amplifier;
The capacitive distance sensor according to claim 1, further comprising: A temperature correction circuit that generates a voltage signal that matches the detection signal when the object to be detected does not exist and has the same temperature dependency as the detection signal, and outputs the voltage signal as a temperature correction detection signal;
The capacitance type distance sensor according to claim 2, wherein the arithmetic processor further corrects the correction signal according to a change in the temperature correction detection signal. The temperature correction circuit is
A first capacitor having the same capacitance as the capacitance between the transmission electrode and the auxiliary electrode, a capacitance equal to the capacitance between the auxiliary electrode and the shield electrode, and A pseudo sensor unit for temperature correction having a second capacitor having one end grounded;
A buffer circuit for temperature correction having the same configuration as the buffer circuit, which supplies the AC voltage generated by the oscillator to one end of the first and second capacitors;
A current correction element for temperature correction having the same temperature dependency as the current detection resistor element, which detects a current supplied from the temperature correction buffer circuit to the other end of the first capacitor as a voltage between terminals;
A first differential amplifier for temperature correction having the same configuration as that of the first differential amplifier, which outputs a voltage corresponding to the voltage between the terminals of the current detection resistor element for temperature correction;
A temperature correction detection circuit configured to convert the output signal of the temperature correction first differential amplifier into a DC signal and having the same configuration as the detection circuit;
A second differential amplifier for temperature correction having the same configuration as the second differential amplifier, wherein the output signal of the temperature correction detection circuit is input from one input terminal and the temperature correction detection signal is output from the output terminal; ,
The capacitance type distance sensor according to claim 3, further comprising: One or a plurality of detection systems including the sensor unit, the buffer circuit, the current detection resistor element, and the first and second wirings;
A temperature correction circuit that generates the same inter-terminal voltage as the inter-terminal voltage generated in the current detection resistor element when the object to be detected does not exist and has the same temperature dependency as the current detection resistor element;
A switch that selectively supplies one of the inter-terminal voltage generated by the current detection resistor element of the detection system and the inter-terminal voltage generated by the temperature correction circuit to the first differential amplifier;
The capacitive distance sensor according to claim 2, further comprising: The temperature correction circuit is
A first capacitor having the same capacitance as the capacitance between the transmission electrode and the auxiliary electrode, a capacitance equal to the capacitance between the auxiliary electrode and the shield electrode, and A pseudo sensor unit for temperature correction having a second capacitor having one end grounded;
A buffer circuit for temperature correction having the same configuration as the buffer circuit, which supplies the AC voltage generated by the oscillator to one end of the first and second capacitors;
A current correction element for temperature correction having the same temperature dependency as the current detection resistor element, which detects a current supplied from the temperature correction buffer circuit to the other end of the first capacitor as a voltage between terminals;
The capacitive distance sensor according to claim 5, comprising: A first temperature correction resistor element provided on a wiring for supplying the buffer circuit side potential of the current detection resistor element to one input terminal of the first differential amplifier;
A second temperature correction resistor element provided between the one input terminal of the first differential amplifier and the ground;
A third temperature correction resistor element provided between the other input terminal of the first differential amplifier and the ground;
The capacitance type distance sensor according to claim 1, further comprising a temperature correction circuit including The transmission electrode is a conductive thin film printed on the surface of a printed circuit board,
The auxiliary electrode is a conductive thin film printed on the back surface of the printed circuit board,
The capacitive distance sensor according to claim 1, wherein the shield electrode is a conductive plate bonded on the auxiliary electrode through a spacer.   9. The capacitive distance sensor according to claim 8, wherein the shield electrode is made of a conductive flexible material, and the spacer is made of an insulating flexible elastic material. A first conductive plate capacitively coupled to the transmission electrode by being bonded onto the transmission electrode;
A second conductive plate capacitively coupled to the auxiliary electrode by being bonded between the auxiliary electrode and the spacer;
A third conductive plate capacitively coupled to the shield electrode by being bonded between the spacer and the shield electrode;
The capacitive distance sensor according to claim 8 or 9, further comprising:

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