Capacitance sensor

Abstract

Provided is a capacitance sensor that is low-cost and highly convenient when performing failure determination. The capacitance sensor includes: a capacitor to which a first potential is applied to one terminal; a first switch provided across one terminal of the capacitor and the other terminal; a second switch in which one terminal is connected to the other terminal of the capacitor; a third switch in which one terminal is connected to the other terminal of the second switch and a first detection electrode and a second potential is applied to the other terminal; a fourth switch in which one terminal is connected to the other terminal of the capacitor; a fifth switch in which one terminal can be connected to a second detection electrode and is connected to the other terminal of the fourth switch and a second potential is applied to the other terminal; and a determination unit that determines a failure of the first detection electrode based on a potential difference between the potential of the other terminal of the capacitor and a reference potential set according to the first potential.

Description

Technical Field

[0001] The present invention relates to a capacitance sensor that detects the approach of a detection object based on a change in capacitance. Background Art

[0002] Conventionally, capacitance sensors for detecting the approach of a detection object have been used. In a capacitance sensor, there is a structure configured to have a detection electrode that capacitively couples with a detection object and detect the approach of the detection object based on a change in capacitance. In such a capacitance sensor, if the detection electrode or the wire connecting the detection electrode is in a short-circuit state or an open state, the approach of the detection object cannot be properly detected, and thus fault diagnosis techniques have been studied (for example, Patent Documents 1 and 2).

[0003] Patent Document 1 describes a grip sensor that detects an object held by hand. The grip sensor is configured to include a grip detection electrode, a disconnection determination electrode disposed near a first end, a disconnection determination electrode disposed near a second end, and a switch that switches the state of the disconnection determination electrode between grounded and non-grounded. The grip sensor determines whether there is a disconnection in the grip detection electrode based on a change in the capacitance of the grip detection electrode when the state of the disconnection determination electrode is switched from non-grounded to grounded.

[0004] Patent Document 2 describes an opening / closing body control device that determines whether an object is caught by an operating opening / closing body by comparing a detection signal output from a capacitance-type sensor electrode provided at an end of the opening / closing body with a catch determination threshold value, and reverses or stops the operating opening / closing body if a catch is detected. The opening / closing body control device includes an opening / closing position detection unit that detects the opening / closing position of the opening / closing body, a disconnection threshold value used when determining whether there is a disconnection in the sensor electrode, and a disconnection determination unit that determines whether the sensor electrode is disconnected based on the detection signal of the sensor electrode and the disconnection threshold value. The disconnection determination unit performs a determination of whether there is a disconnection using the disconnection threshold value when the opening / closing body is in a region where a catch determination is not performed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-67423

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-48640

[0009] Problems to be Solved by the Invention

[0010] In the technology described in Patent Document 1, a switch that is not used in the gripping detection is required for determining the disconnection of the electrode for gripping detection. Therefore, the components of the technology described in Patent Document 1 increase, resulting in an increase in manufacturing cost and mounting space, and there is room for improvement. In addition, in the technology described in Patent Document 2, when determining the presence or absence of disconnection, the opening / closing body needs to be located in an area where the clamping determination is not performed, and there is room for improving convenience. Summary of the Invention

[0011] Therefore, there is a need for a capacitance sensor that is low-cost and highly convenient when performing a failure determination.

[0012] Technical Means for Solving the Technical Problem

[0013] The capacitance sensor of the present invention can detect the approach of a detection object based on changes in the capacitance between the detection object and a first detection electrode and changes in the capacitance between the detection object and a second detection electrode. The characteristic structure thereof includes: a capacitor to which a preset first potential is applied to one terminal thereof; a first switch provided across one terminal of the capacitor and the other terminal of the capacitor; a second switch having one terminal thereof connected to the other terminal of the capacitor; a third switch having one terminal thereof connected to the other terminal of the second switch and the first detection electrode, and a second potential lower than the first potential is applied to the other terminal of the third switch; a fourth switch having one terminal thereof connected to the other terminal of the capacitor; a fifth switch having one terminal thereof capable of being connected to the second detection electrode and connected to the other terminal of the fourth switch, and the second potential is applied to the other terminal of the fifth switch; and a determination unit that determines at least a failure of the first detection electrode based on the potential difference between the potential of the other terminal of the capacitor and a reference potential set according to the first potential.

[0014] According to such a characteristic structure, the determination unit determines whether the first detection electrode is faulty based on whether current flows through the first detection electrode itself, so that the failure determination of the first detection electrode can be performed with high accuracy. In addition, since the existing switches are used for the failure determination, there is no need to provide a new switch for the failure determination. Therefore, the failure determination can be performed at low cost and the mounting area of components can be suppressed from increasing. In addition, since the failure determination is performed based on the opening / closing operation of the switches during the detection of the detection object, the convenience is also high.

[0015] Further, preferably, after keeping the first switch in the closed state for a specified time, the first switch is turned on, and then, when the fifth switch is in the on state, the second switch is turned off. The determination unit determines whether the first detection electrode is in a short-circuited state based on the potential of the other terminal of the capacitor at this time.

[0016] According to such a configuration, it is possible to determine whether the first detection electrode is in a short-circuited state by using the second switch used when the first detection electrode detects the object to be detected, so there is no need to provide a new switch. Therefore, it is possible to implement failure determination at low cost.

[0017] Further, preferably, after keeping the first switch in the closed state for a specified time, the first switch is turned on, and then both the second switch and the fifth switch are turned off. The determination unit determines whether the first detection electrode is in an open state based on the potential of the other terminal of the capacitor at this time.

[0018] According to such a configuration, it is possible to determine whether the first detection electrode is in an open state by using the second switch used when the first detection electrode detects the object to be detected and the fifth switch used when the second detection electrode detects the object to be detected, so there is no need to provide a new switch. Therefore, it is possible to implement failure determination at low cost.

[0019] Further, preferably, when the second detection electrode is connected to one terminal of the fifth switch, after keeping the first switch in the closed state for a specified time, the first switch is turned on, and then, when the third switch is in the on state, the fourth switch is turned off. The determination unit determines whether the second detection electrode is in a short-circuited state based on the potential of the other terminal of the capacitor at this time.

[0020] According to such a configuration, it is possible to determine whether the second detection electrode is in a short-circuited state by using the fourth switch used when the second detection electrode detects the object to be detected, so there is no need to provide a new switch. Therefore, it is possible to implement failure determination at low cost.

[0021] Further, preferably, when the second detection electrode is connected to one terminal of the fifth switch, after keeping the first switch in the closed state for a specified time, the first switch is turned on, and then both the third switch and the fourth switch are turned off. The determination unit determines whether the second detection electrode is in an open state based on the potential of the other terminal of the capacitor at this time.

[0022] According to such a structure, it is possible to determine whether the second detection electrode is in an open state by using the third switch used for detecting the object to be detected by the first detection electrode and the fourth switch used for detecting the object to be detected by the second detection electrode. Therefore, there is no need to provide a new switch. Thus, it is possible to achieve failure determination at low cost.

[0023] In addition, preferably, after the failure determination of the first detection electrode, after performing a first operation, the second operation and the third operation are alternately repeated to detect the capacitance of the first detection electrode. The first operation is an operation of setting the first switch to a closed state for a predetermined time and then to an open state. The second operation is an operation of setting the second switch to an open state, then to a closed state, and then to an open state. The third operation is an operation of setting the third switch to an open state, then to a closed state, and then to an open state.

[0024] According to such a structure, it is possible to perform a detection operation of the object to be detected by the first detection electrode after the failure determination of the first detection electrode.

[0025] In addition, preferably, when one terminal of the second detection electrode is connected to the fifth switch, the determination unit determines the failure of the second detection electrode. After the failure determination of the second detection electrode, after performing a first operation of setting the first switch to a closed state for a predetermined time and then to an open state, the fourth operation and the fifth operation are alternately repeated to detect the capacitance of the second detection electrode. The fourth operation is an operation of setting the fourth switch to an open state, then to a closed state, and then to an open state. The fifth operation is an operation of setting the fifth switch to an open state, then to a closed state, and then to an open state.

[0026] According to such a structure, it is possible to perform a detection operation of the object to be detected by the second detection electrode after the failure determination of the second detection electrode.

[0027] In addition, preferably, the time of the closed state of the second switch during the failure determination of the first detection electrode is longer than the time of the closed state of the second operation.

[0028] According to such a structure, it is possible to completely discharge the charge of the capacitor during the failure determination of the first detection electrode. Therefore, it is possible to perform failure determination with good accuracy.

[0029] In addition, preferably, the time of the closed state of the fourth switch during the failure determination of the second detection electrode is longer than the time of the closed state of the fourth operation.

[0030] According to such a configuration, when determining a failure of the second detection electrode, the charge of the capacitor can be completely discharged, so that the failure determination can be performed with good accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 FIG. is a diagram showing the configuration of the capacitance sensor.

[0032] Figure 2 FIG. is a timing chart showing the operation of the capacitance sensor.

[0033] Figure 3 FIG. is a diagram showing the process and determination criteria for failure determination.

[0034] REFERENCE SIGNS LIST

[0035] 1: Capacitance sensor

[0036] 11: First switch

[0037] 12: Second switch

[0038] 13: Third switch

[0039] 14: Fourth switch

[0040] 15: Fifth switch

[0041] 21: First detection electrode

[0042] 22: Second detection electrode

[0043] 31: Determination unit

[0044] Vcc: First potential

[0045] Vr: Reference potential

[0046] Vss: Second potential DETAILED DESCRIPTION OF THE INVENTION

[0047] The capacitance sensor of the present invention can detect the approach of a detection object based on changes in the capacitance between the detection object and the first detection electrode and changes in the capacitance between the detection object and the second detection electrode, and is configured to perform failure determination without new components. Hereinafter, the capacitance sensor 1 of the present embodiment will be described.

[0048] Figure 1 FIG. is a diagram showing the configuration of the capacitance sensor 1. The capacitance sensor 1 of the present embodiment includes a capacitor Cs, a first switch 11, a second switch 12, a third switch 13, a fourth switch 14, a fifth switch 15, a first detection electrode 21, a second detection electrode 22, a comparison unit 30, and a determination unit 31.

[0049] A capacitor Cs has a first potential set in advance applied to one of its terminals. This capacitor Cs is used both for detecting an object and for fault determination. The capacitor Cs has a pair of terminals, and a first potential, which is a fixed voltage, is applied to one of the terminals. In the present embodiment, this first potential is denoted as Vcc. Additionally, in order to reduce the variation (ripple voltage) of this first potential, a filter capacitor C1 is provided between the pair of terminals of the capacitor Cs and the ground potential.

[0050] A first switch 11 is provided across one terminal and the other terminal of the capacitor Cs. One terminal and the other terminal of the capacitor Cs are the pair of terminals that the capacitor Cs has. Providing across one terminal and the other terminal means that one terminal of the first switch 11 is electrically connected to one terminal of the capacitor Cs, and the other terminal of the first switch 11 is electrically connected to the other terminal of the capacitor Cs. Thus, when the first switch 11 is in the open state, the capacitor Cs is charged with the first potential Vcc, and when the first switch 11 is in the closed state, the charge stored in the capacitor Cs is discharged.

[0051] A second switch 12 has a pair of terminals. One terminal of the second switch 12 is connected to the other terminal of the capacitor Cs. The other terminal of the capacitor Cs is the side of the pair of terminals of the capacitor Cs that is not applied with the first potential Vcc. Thus, one terminal of the pair of terminals of the second switch 12 is electrically connected to the side of the pair of terminals of the capacitor Cs that is not applied with the first potential Vcc.

[0052] A third switch 13 has a pair of terminals. One terminal of the third switch 13 is connected to the other terminal of the second switch 12 and a first detection electrode 21, and a second potential Vss lower than the potential of the first potential Vcc is applied to the other terminal. The other terminal of the second switch 12 is the side of the pair of terminals of the second switch 12 that is not connected to the capacitor Cs. The first detection electrode 21 is an electrode that performs capacitive coupling with the object to be detected. Additionally, in the present embodiment, the second potential Vss lower than the potential of the first potential Vcc is the ground potential. Thus, one terminal of the pair of terminals of the third switch 13 is electrically connected to the side of the pair of terminals of the second switch 12 that is not connected to the capacitor Cs and the electrode that performs capacitive coupling with the object to be detected, and the other terminal of the pair of terminals of the third switch 13 is applied with the ground potential. Additionally, in the present embodiment, a filter unit 51 composed of a resistor R, a capacitor C, a coil L, and a varistor Vs is provided between one terminal of the third switch 13 and the first detection electrode 21.

[0053] The fourth switch 14 has a pair of terminals. One terminal of the fourth switch 14 is connected to the other terminal of the capacitor Cs. The other terminal of the capacitor Cs is the terminal on the side of the pair of terminals of the capacitor Cs that is not applied with the first potential Vcc. Therefore, one terminal of the pair of terminals of the fourth switch 14 is electrically connected to the terminal on the side of the pair of terminals of the capacitor Cs that is not applied with the first potential Vcc.

[0054] The fifth switch 15 has a pair of terminals. One terminal of the fifth switch 15 can be connected to the second detection electrode 22 and is connected to the other terminal of the fourth switch 14, and the second potential Vss is applied to the other terminal of the fifth switch 15. The second detection electrode 22 is an electrode that performs capacitive coupling with the object to be detected. "Can be connected" means that when the capacitance sensor 1 detects the object to be detected, the detection of the object to be detected can be performed only by the first detection electrode 21, or the detection of the object to be detected can be performed by both the first detection electrode 21 and the second detection electrode 22. Therefore, the second detection electrode 22 may not be provided. In the present embodiment, an example of the case where the second detection electrode 22 is provided is cited. The other terminal of the fourth switch 14 is the terminal on the side of the pair of terminals of the fourth switch 14 that is not connected to the capacitor Cs. In addition, in the present embodiment, the second potential Vss is a ground potential. Therefore, one terminal of the pair of terminals of the fifth switch 15 is electrically connected to the terminal on the side of the pair of terminals of the fourth switch 14 that is not connected to the capacitor Cs and the electrode that performs capacitive coupling with the object to be detected and is different from the first detection electrode 21, and the other terminal of the pair of terminals of the fifth switch 15 is applied with the ground potential. In addition, in the present embodiment, a filter unit 52 composed of a resistor R, a capacitor C, a coil L, and a varistor Vs is provided between one terminal of the fifth switch 15 and the second detection electrode 22.

[0055] Here, in the present embodiment, the first detection electrode 21 is electrically connected to the filter unit 52 via the resistor R1 and the diode D1. Therefore, the first detection electrode 21 is configured to be able to be grounded via the resistor R1, the diode D1, the coil L of the filter unit 52, the resistor R, and the fifth switch 15. In addition, the second detection electrode 22 is electrically connected to the filter unit 51 via the resistor R2 and the diode D2. Therefore, the second detection electrode 22 is configured to be able to be grounded via the resistor R2, the diode D2, the coil L of the filter unit 51, the resistor R, and the third switch 13.

[0056] The comparison unit 30 compares the potential of the other terminal of the capacitor Cs with the magnitude relationship of the reference potential Vr set according to the first potential Vcc. Then, one terminal of a pair of input terminals of the comparison unit 30 is electrically connected to the terminal on the side where the first potential Vcc is not applied among the pair of terminals of the capacitor Cs (the potential of the connection node is set as Vcs), and the other terminal of the pair of input terminals of the comparison unit 30 is applied with the following potential: the potential after the first potential Vcc is divided by two resistors R3 and R4 having a specified resistance value (the applied potential is set as Vr). In the present embodiment, it is configured such that the potential of 1 / 2 of the first potential Vcc is applied to the other terminal of the pair of input terminals of the comparison unit 30.

[0057] The determination unit 31 determines the failure of at least the first detection electrode 21 based on the potential difference between the potential of the other terminal of the capacitor Cs and the reference potential Vr set according to the first potential Vcc. In the present embodiment, the potential difference between the potential of the other terminal of the capacitor Cs and the reference potential set according to the first potential Vcc is the magnitude relationship between the potential of the other terminal of the capacitor Cs and the reference potential set according to the first potential Vcc, and is compared by the comparison unit 30. Therefore, the determination unit 31 determines whether the first detection electrode 21 has failed based on the comparison result of the comparison unit 30. Here, in the present embodiment, a second detection electrode 22 is also provided. Therefore, the determination unit 31 determines whether the first detection electrode 21 and the second detection electrode 22 have failed.

[0058] Hereinafter, the failure determination of the determination unit 31 will be described. Figure 2 is a timing chart showing the operation of the capacitance sensor 1. As Figure 2 shown, the failure determination is performed before the proximity detection in which the capacitance sensor 1 detects the proximity of the detection object. For example, it is preferable to perform the failure determination when the capacitance sensor 1 starts to be powered on. In addition, as Figure 2 shown, the failure determination and the proximity detection are performed based on the CLK signal that counts a specified time.

[0059] At the moment (before t1) when the power supply to the capacitance sensor 1 is started, the first switch 11, the second switch 12, the third switch 13, the fourth switch 14, and the fifth switch 15 are set to the open state. At this time, the capacitor Cs stores electric charge. When the determination unit 31 performs the failure determination, first, the first switch 11 is set to the closed state for a specified time. The time (the above-mentioned "specified time") for setting the first switch 11 to the closed state may be set to be longer than the time until the electric charge stored in the capacitor Cs is discharged. In Figure 2In the example, during the time from t1 to t2 (T1 [milliseconds]), the first switch 11 is set to the closed state, whereby the potential of the other terminal of the capacitor Cs becomes below a specified value (close to zero). Here, for the sake of easy understanding, the potential of the other terminal of the capacitor Cs is designated as Vcs.

[0060] After the determination unit 31 sets the first switch 11 to the closed state and Vcs becomes below the specified value, it sets the first switch 11 to the open state, and then, when the fifth switch 15 is in the open state, sets the second switch 12 to the closed state. In Figure 2 the example, during the time from t2 to t3 (T2 [milliseconds]), the fifth switch 15 is set to the open state and the second switch 12 is set to the closed state. The determination unit 31 determines whether the first detection electrode 21 is in a short-circuit state based on the potential Vcs of the other terminal of the capacitor Cs at this time. That is, if the first detection electrode 21 is in a short-circuit state, Vcs rises when the second switch 12 is in the closed state. At this time, if Vcs rises to the reference potential Vr set as the determination threshold, the determination unit 31 determines that the first detection electrode 21 is in a short-circuit state. On the other hand, as Figure 2 shown, if the first detection electrode 21 is not in a short-circuit state, Vcs does not rise significantly even when the second switch 12 is in the closed state. Therefore, when Vcs does not rise to the reference potential Vr as the determination threshold, the determination unit 31 determines that the first detection electrode 21 is not in a short-circuit state.

[0061] Next, the determination unit 31 sets both the second switch 12 and the fifth switch 15 to the closed state. In Figure 2 the example, during the time from t3 to t4 (T3 [milliseconds]), both the second switch 12 and the fifth switch 15 are set to the closed state. The determination unit 31 determines whether the first detection electrode 21 is in an open state based on the potential Vcs of the other terminal of the capacitor Cs at this time. That is, if the first detection electrode 21 is in an open state, Vcs does not rise even when the second switch 12 and the fifth switch 15 are in the closed state. Therefore, at this time, if Vcs does not rise to the reference potential Vr set as the determination threshold, the determination unit 31 determines that the first detection electrode 21 is in an open state. On the other hand, if the first detection electrode 21 is not in an open state, Vcs rises significantly when the second switch 12 and the fifth switch 15 are in the closed state. Therefore, as Figure 2 shown, when Vcs rises to the reference potential Vr as the determination threshold, the determination unit 31 determines that the first detection electrode 21 is not in an open state.

[0062] In addition, when one terminal of the fifth switch 15 in this embodiment is connected to the second detection electrode 22, it is also possible to perform a failure determination of the second detection electrode 22. When performing the failure determination of the second detection electrode 22, the determination unit 31 keeps the first switch 11 in the closed state for a specified time. In Figure 2 the example of, the first switch 11 is set to the closed state from time t5 to t6 (T1 [milliseconds]), and thus Vcs becomes zero.

[0063] After the determination unit 31 keeps the first switch 11 in the closed state and Vcs becomes equal to or lower than a specified value, the determination unit 31 sets the first switch 11 to the open state, and then, when the third switch 13 is in the open state, sets the fourth switch 14 to the closed state. In Figure 2 the example of, the third switch 13 is set to the open state and the fourth switch 14 is set to the closed state from time t6 to t7 (T2 [milliseconds]). The determination unit 31 determines whether the second detection electrode 22 is in a short-circuit state based on the potential Vcs of the other terminal of the capacitor Cs at this time. That is, if the second detection electrode 22 is in a short-circuit state, Vcs rises when the fourth switch 14 is in the closed state. At this time, if Vcs rises to the reference potential Vr set as the determination threshold, the determination unit 31 determines that the second detection electrode 22 is in a short-circuit state. On the other hand, as Figure 2 shown, if the second detection electrode 22 is not in a short-circuit state, Vcs does not rise significantly even when the fourth switch 14 is in the closed state. Therefore, when Vcs does not rise to the reference potential Vr as the determination threshold, the determination unit 31 determines that the second detection electrode 22 is not in a short-circuit state.

[0064] Next, the determination unit 31 sets both the third switch 13 and the fourth switch 14 to the closed state. In Figure 2 the example of, both the third switch 13 and the fourth switch 14 are set to the closed state from time t7 to t8 (T3 [milliseconds]). The determination unit 31 determines whether the second detection electrode 22 is in an open state based on the potential Vcs of the other terminal of the capacitor Cs at this time. That is, if the second detection electrode 22 is in an open state, Vcs does not rise even when the third switch 13 and the fourth switch 14 are in the closed state. Therefore, at this time, if Vcs does not rise to the reference potential Vr set as the determination threshold, the determination unit 31 determines that the second detection electrode 22 is in an open state. On the other hand, if the second detection electrode 22 is not in an open state, Vcs rises significantly when the third switch 13 and the fourth switch 14 are in the closed state. Therefore, as Figure 2 shown, when Vcs rises to the reference potential Vr as the determination threshold, the determination unit 31 determines that the second detection electrode 22 is not in an open state. In addition, in Figure 2Also shown is the output (comparison result) of the comparison unit 30 output when the determination unit 31 is used for failure determination, that is, when Vcs exceeds the reference potential Vr.

[0065] In Figure 3 represents the processing and determination criteria for the failure determination of the present embodiment described above. Further, in Figure 3 the switch not shown is in the open state. When determining the failure of the first detection electrode 21, the first switch 11 is set to the closed state for a specified time, and the capacitor Cs discharges (step #1). When the first switch 11 is set to the open state, the second switch 12 is set to the closed state and the fifth switch 15 is set to the open state (step #2). At this time, when Vcs is less than the reference potential Vr, the first detection electrode 21 is determined not to be in the short-circuit state, and when Vcs is greater than the reference potential Vr, the first detection electrode 21 is determined to be in the short-circuit state. Then, the second switch 12 and the fifth switch 15 are set to the closed state (step #3). At this time, when Vcs is greater than the reference potential Vr, the first detection electrode 21 is determined not to be in the open state, and when Vcs is less than the reference potential Vr, the first detection electrode 21 is determined to be in the open state.

[0066] Regarding the second detection electrode 22, the first switch 11 is set to the closed state for a specified time, and the capacitor Cs discharges (step #1). When the first switch 11 is set to the open state, the third switch 13 is set to the open state and the fourth switch 14 is set to the closed state (step #2). At this time, when Vcs is less than the reference potential Vr, the second detection electrode 22 is determined not to be in the short-circuit state, and when Vcs is greater than the reference potential Vr, the second detection electrode 22 is determined to be in the short-circuit state. Then, the third switch 13 and the fourth switch 14 are set to the closed state (step #3). At this time, when Vcs is greater than the reference potential Vr, the second detection electrode 22 is determined not to be in the open state, and when Vcs is less than the reference potential Vr, the second detection electrode 22 is determined to be in the open state.

[0067] As described above, the capacitance sensor 1 performs a failure determination. This failure determination does not involve setting a switch for the purpose of making the failure determination, but rather uses the switches that are originally provided to perform the failure determination. That is, in the failure determination of the first detection electrode 21, the second switch 12 and the fifth switch 15 are used for the failure determination. The second switch is used in the detection of the detection object by the first detection electrode 21, and the fifth switch 15 is used in the detection of the detection object by the second detection electrode 22. In addition, in the failure determination of the second detection electrode 22, the fourth switch 14 and the third switch 13 are used for the failure determination. The fourth switch 14 is used in the detection of the detection object by the second detection electrode 22, and the third switch 13 is used in the detection of the detection object by the first detection electrode 21. Therefore, the cost of the failure determination is not increased, and it is easy to control the failure determination and the convenience is improved.

[0068] After the failure determination of the first detection electrode 21 and the second detection electrode 22, that is, when the first detection electrode 21 and the second detection electrode 22 are determined to have no failure, the capacitance sensor 1 starts the detection of the detection object. The detection of the detection object by the capacitance sensor 1 is well-known, so the detailed description is omitted, but after Figure 2 t9 of Figure 2 it is represented as "detection operation". For example, regarding the first detection electrode 21, after performing the first operation (the operation of the first switch 11 equivalent to before each "detection operation" in Figure 2 ), the second operation and the third operation are alternately repeated to detect the capacitance of the first detection electrode 21 (the first operation is not repeated, and the second operation and the third operation are alternately repeated). That is, the value of Vcs at this time is used to determine whether the detection object is approaching. The first operation is the operation of setting the first switch 11 to the closed state for a specified time and then to the open state. The second operation is the operation of setting the second switch 12 to the open state, then to the closed state, and then to the open state. The third operation is the operation of setting the third switch 13 to the open state, then to the closed state, and then to the open state. Similarly, for the second detection electrode 22, after performing the first operation (the operation of the first switch 11 equivalent to before each "detection operation" in Figure 2 , but when continuing after the detection operation of the first detection electrode 21, this first operation may not be performed), the fourth operation and the fifth operation are alternately repeated to detect the capacitance of the second detection electrode 22 (the first operation is not repeated, and the fourth operation and the fifth operation are alternately repeated). That is, the value of Vcs at this time is used to determine whether the detection object is approaching. The first operation is the operation of setting the first switch 11 to the closed state for a specified time and then to the open state. The fourth operation is the operation of setting the fourth switch 14 to the open state, then to the closed state, and then to the open state. The fifth operation is the operation of setting the fifth switch 15 to the open state, then to the closed state, and then to the open state.

[0069] That is, the detection of the object to be detected is performed according to the switching of the first switch 11 from the open state to the closed state. Further, as described above, in the case of performing the failure determination of the first detection electrode 21 and the second detection electrode 22, the first operation of setting the first switch 11 to the open state after being in the closed state for a predetermined time is also performed, but the time of the closed state of the second switch 12 during the failure determination of the first detection electrode 21 is set to be longer than the time of the closed state of the second operation. That is, Figure 2 the times of t2 - t3 and t3 - t4 required for the failure determination of the first detection electrode 21 in Figure 2 are set to be longer than the closed state of the second switch 12 during the "detection operation". Further, the time of the closed state of the fifth switch 15 during the failure determination of the first detection electrode 21 is set to be longer than the time of the closed state of the fifth operation. That is, Figure 2 the time of t3 - t4 required for the failure determination of the first detection electrode 21 in Figure 2 is set to be longer than the closed state of the fifth switch 15 during the "detection operation". Further, the time of the closed state of the fourth switch 14 during the failure determination of the second detection electrode 22 is set to be longer than the time of the closed state of the fourth operation. That is, Figure 2 the times of t6 - t7 and t7 - t8 required for the failure determination of the second detection electrode 22 in Figure 2 are set to be longer than the closed state of the fourth switch 14 during the "detection operation". Further, the time of the closed state of the third switch 13 during the failure determination of the second detection electrode 22 is set to be longer than the time of the closed state of the third operation. That is, Figure 2 the time of t7 - t8 required for the failure determination of the second detection electrode 22 in Figure 2 is set to be longer than the closed state of the third switch 13 during the "detection operation". Thereby, the charge of the capacitor Cs can be completely discharged during the failure determination, and thus the failure determination can be performed with good accuracy.

[0070] <Other Embodiments>

[0071] In the above embodiment, the case where one terminal of the second detection electrode 22 is connected to the fifth switch 15 is illustrated, but the second detection electrode 22 may not be connected to one terminal of the fifth switch 15. This configuration can also perform the failure determination of the first detection electrode 21 and the detection of the object to be detected by the first detection electrode 21.

[0072] In the above-described embodiment, the case where the time of the closed state of the second switch 12 at the time of failure determination of the first detection electrode 21 is set to be longer than the time of the closed state of the second operation, and the time of the closed state of the fourth switch 14 at the time of failure determination of the second detection electrode 22 is set to be longer than the time of the closed state of the fourth operation has been described. However, the time of the closed state of the second switch 12 at the time of failure determination of the first detection electrode 21 and the time of the closed state of the fourth switch 14 at the time of failure determination of the second detection electrode 22 may be the same as the time of the closed state of the second operation and the time of the closed state of the fourth operation, respectively, or may be shorter than the time of the closed state of the second operation and the time of the closed state of the fourth operation, respectively.

[0073] The present invention can be used for a capacitance sensor that detects the approach of a detection object based on a change in capacitance.

Claims

1. An electrostatic capacitance sensor that can detect the approach of a detection object based on changes in the electrostatic capacitance between the detection object and a first detection electrode and changes in the electrostatic capacitance between the detection object and a second detection electrode, comprising: A capacitor to which a preset first potential is applied to one terminal of the capacitor; A first switch provided across one terminal of the capacitor and the other terminal of the capacitor; A second switch, one terminal of which is connected to the other terminal of the capacitor; A third switch, one terminal of which is connected to the other terminal of the second switch and the first detection electrode, and a second potential lower than the first potential is applied to the other terminal of the third switch; A fourth switch, one terminal of which is connected to the other terminal of the capacitor; A fifth switch, one terminal of which can be connected to the second detection electrode and is connected to the other terminal of the fourth switch, and the second potential is applied to the other terminal of the fifth switch; And A determination unit that determines at least a failure of the first detection electrode based on the potential difference between the potential of the other terminal of the capacitor and a reference potential set according to the first potential.

2. The electrostatic capacitance sensor according to claim 1, wherein After the first switch is closed for a specified time and then opened, and then the second switch is closed when the fifth switch is open, the determination unit determines whether the first detection electrode is in a short-circuit state based on the potential of the other terminal of the capacitor at this time.

3. The electrostatic capacitance sensor according to claim 1 or 2, wherein After the first switch is closed for a specified time and then opened, and then both the second switch and the fifth switch are closed, the determination unit determines whether the first detection electrode is in an open state based on the potential of the other terminal of the capacitor at this time.

4. The electrostatic capacitance sensor according to claim 1, wherein When the second detection electrode is connected to one terminal of the fifth switch, after the first switch is closed for a specified time and then opened, and then the fourth switch is closed when the third switch is open, the determination unit determines whether the second detection electrode is in a short-circuit state based on the potential of the other terminal of the capacitor at this time.

5. The electrostatic capacitance sensor according to claim 1, wherein When the second detection electrode is connected to one terminal of the fifth switch, after the first switch is closed for a specified time and then opened, and then both the third switch and the fourth switch are closed, the determination unit determines whether the second detection electrode is in an open state based on the potential of the other terminal of the capacitor at this time.

6. The capacitance sensor according to claim 1, wherein after the failure determination of the first detection electrode, after performing a first operation, the second operation and the third operation are alternately repeated to detect the capacitance of the first detection electrode. The first operation is an operation of setting the first switch to the closed state for a predetermined time and then to the open state. The second operation is an operation of setting the second switch to the open state, then to the closed state, and then to the open state. The third operation is an operation of setting the third switch to the open state, then to the closed state, and then to the open state.

7. The capacitance sensor according to claim 6, wherein the determination unit determines the failure of the second detection electrode when one terminal of the second detection electrode is connected to the fifth switch, after the failure determination of the second detection electrode, after performing a first operation of setting the first switch to the closed state for a predetermined time and then to the open state, the fourth operation and the fifth operation are alternately repeated to detect the capacitance of the second detection electrode. The fourth operation is an operation of setting the fourth switch to the open state, then to the closed state, and then to the open state. The fifth operation is an operation of setting the fifth switch to the open state, then to the closed state, and then to the open state.

8. The capacitance sensor according to claim 6 or 7, wherein the time of the closed state of the second switch during the failure determination of the first detection electrode is longer than the time of the closed state of the second operation.

9. The capacitance sensor according to claim 7, wherein the time of the closed state of the fourth switch during the failure determination of the second detection electrode is longer than the time of the closed state of the fourth operation.

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