JP7215123B2 - capacitance sensor - Google Patents

Description

The present invention relates to capacitive sensors.

2. Description of the Related Art Conventionally, as a capacitance sensor, for example, the one described in Patent Document 1 is known. This capacitance sensor includes a first capacitor, a second capacitor connected to the first capacitor and whose capacitance varies based on the presence or absence of an object, a first switch for initializing the first capacitor, first and first A second switch arranged between the two capacitors, a third switch for initializing the second capacitor, and a control circuit. After initializing the first capacitor by operating the first switch, the control circuit performs switch operations consisting of operating the second switch and operating the third switch a plurality of times, and adjusts the potential between the first and second capacitors. is acquired, and the number of times of detection corresponding to the number of switch operations when the intermediate potential exceeds the reference potential is derived. The number of times of detection correlates with the discharge capacity of the second capacitor per one operation, ie, the capacity of the second capacitor, and the capacity of the second capacitor is detected by deriving the number of times of detection.

In particular, the control circuit acquires intermediate potentials at multiple points in time for each switch operation, and derives the number of detections based on these multiple intermediate potentials. As a result, even if there is noise in the intermediate potential, the derivation accuracy of the number of detections, that is, the detection accuracy of the capacitance of the second capacitor is improved.

Note that the capacity of the second capacitor, that is, the number of times of detection varies based on the presence or absence of an object. Therefore, such a capacitive sensor is used to determine the existence or non-existence of an object to be detected based on, for example, the magnitude relationship between the amount of variation in the number of detections and a preset determination threshold value.

JP 2018-44917 A

By the way, the capacitance of the second capacitor changes under the influence of the parasitic capacitance contained therein even in the initial state where there is no object to be detected, for example. Therefore, in Patent Document 1, the discharge capacity that can be discharged by the second capacitor per one operation will change according to the parasitic capacitance, and the number of times of detection will vary, and the detection accuracy of the capacity of the second capacitor may decrease. have a nature. As a result, there is a possibility that the accuracy of determination of the presence or absence of a detection target (for example, the user's approach or operation) will be degraded.

First, in FIGS. 16A and 16B, the capacitance C11 of the first capacitor 91 is 100 [pF], the capacitance C12 including the parasitic capacitance of the second capacitor 92 in the initial state is 5 [pF], and the detection target Assuming that the variation ΔC12 of the capacitance C12 in the presence of an object is 5 [pF], the corresponding number of detections (hereinafter also referred to as “capacitance count value CN [LSB]”) and the like are simplified. to explain.

In the initial state shown in FIG. 16(a), the capacitance count value CN0 is represented by the following equation.
Capacitance count value CN0 = 100/5 = 20 [LSB]
On the other hand, in the state where the object to be detected exists as shown in FIG. 16(b), the capacitance count value CN1 is represented by the following equation.

Capacitance count value CN1=100/(5+5)=10 [LSB]
Then, the fluctuation amount ΔCN of the capacitance count value CN related to the existence determination of the detection target is represented by the following formula.

Variation amount ΔCN=|CN1-CN0|=|10-20|=10 [LSB]
That is, the capacitance sensor detects the amount of variation ΔC12 (5 [pF]) related to the existence determination of the detection target with the amount of variation ΔCN (10 [LSB]), and its resolution Res [pF/ LSB] is represented by the following equation.

Resolution Res=ΔC12/ΔCN=5/10=0.5 [pF/LSB]
On the other hand, in FIGS. 17A and 17B, assuming that only the capacitance C12 including the parasitic capacitance of the second capacitor 92 in the initial state is changed to 20 [pF], the corresponding number of detections ( The capacitance count value CN [LSB]) and the like will be simplified and explained.

In the initial state shown in FIG. 17(a), the capacitance count value CN0 is represented by the following equation.
Capacitance count value CN0=100/20=5 [LSB]
On the other hand, in the presence state of the detection target shown in FIG. 17B, the capacitance count value CN1 is represented by the following formula.

Capacitance count value CN1=100/(20+5)=4 [LSB]
Then, the fluctuation amount ΔCN of the capacitance count value CN related to the existence determination of the detection target is represented by the following formula.

Variation amount ΔCN=|CN1-CN0|=|4-5|=1 [LSB]
That is, the capacitance sensor detects the amount of variation ΔC12 (5 [pF]) related to the existence determination of the detection target with the amount of variation ΔCN (1 [LSB]), and its resolution Res [pF/ LSB] is given by the following equation.

Resolution Res=ΔC12/ΔCN=5/1=5 [pF/LSB]
As described above, the capacitance C12 including the parasitic capacitance of the second capacitor 92 is changed from 5 [pF] to 20 [pF], so that the resolution Res is changed from 0.5 [pF/LSB] to 5 [pF/LSB]. , resulting in a 10-fold difference.

Then, when the resolution Res changes in this way, the variation amount ΔCN of the capacitance count value CN does not become constant with respect to the equivalent variation amount ΔC12. In this case, the detection distance of the detection target related to the determination of the presence or absence of the detection target changes, and the determination accuracy decreases. From the above, it is confirmed that the accuracy of determining the presence or absence of the object to be detected decreases due to changes in the parasitic capacitance included in the capacitance of the second capacitor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitive sensor capable of suppressing deterioration in the accuracy of determining the presence or absence of an object to be detected due to changes in parasitic capacitance.

A capacitive sensor that solves the above problems includes first and second capacitors connected in series and connected to a power source, a first switch connected between both terminals of the first capacitor, and the first capacitor. and a second switch connected between the second capacitor, a third switch connected between both terminals of the second capacitor, and a first switching process of turning on the first switch. a switch control unit for repeatedly performing a second switching process of complementarily switching the second switch and the third switch to an off state and an on state after the first switch is off, and the first and second capacitors; a derivation unit for deriving, as a sensor output value, the number of repetitions of the second switching process when it is determined that the magnitude relationship between the intermediate potential and the preset reference potential is reversed, and the resolution of the sensor output value A calculation unit that calculates a correction threshold value obtained by correcting a preset determination threshold value so as to be proportional to the reciprocal of, and a sensor that is the difference between the current sensor output value and the reference sensor output value based on the past sensor output value a determination unit that determines presence/absence of the detection target based on the magnitude relationship between the output difference value and the correction threshold.

According to this configuration, the sensor output difference value basically has the same resolution as the resolution of the sensor output value together with the reference sensor output value. Therefore, the sensor output difference value changes in proportion to the reciprocal of the resolution if the fluctuation amount of the capacitance of the second capacitor is the same. On the other hand, the corrected threshold is obtained by correcting the determination threshold so as to be proportional to the reciprocal of the resolution of the sensor output value. Accordingly, even if the parasitic capacitance included in the capacitance of the second capacitor is different, the determination unit determines the presence or absence of the detection target based on the magnitude relationship between the sensor output difference value and the correction threshold. It can be judged at the same level. In this way, it is possible to suppress deterioration in the accuracy of determining the presence or absence of the object to be detected due to changes in the parasitic capacitance included in the capacitance of the second capacitor.

The “resolution” is the change in capacitance of the second capacitor per unit amount of the sensor output value.
For the capacitance sensor, a division determination unit that determines to which division the sensor output value belongs among a plurality of divisions into which the entire range of the sensor output value is divided, and for each of the plurality of divisions, It is preferable to include a division counting section that counts the number of times the sensor output value is determined to belong, and a storage section that stores the result of counting the number of times for each of the plurality of divisions.

According to this configuration, the number of times the sensor output value correlated to the capacitance (parasitic capacitance) of the second capacitor is determined to belong to each of the plurality of categories is counted, and the result of the counting is the Stored in the storage unit. Therefore, by reading the result of the counting from the storage section at the time of maintenance, for example, it is possible to grasp the characteristics such as the distribution of the parasitic capacitance of the second capacitor.

ADVANTAGE OF THE INVENTION This invention has the effect of being able to suppress the deterioration of the determination accuracy of the presence or absence of the detection target due to the change of the parasitic capacitance.

1 is a perspective view showing the rear part of a vehicle to which one embodiment of a capacitive sensor is applied; FIG. FIG. 4 is a schematic diagram showing the relationship between the electrodes and the object to be detected in the capacitance sensor of the same embodiment. FIG. 2 is a block diagram showing the electrical configuration of the capacitance sensor of the same embodiment; FIG. 2 is a circuit diagram showing the electrical configuration of the capacitance sensor of the same embodiment; 4 is a time chart showing switching processing and transition of the intermediate potential accompanying this; 4 is a graph showing the relationship between the sensor output value and the capacity of the second capacitor; 4 is a graph showing the relationship between sensor output value and resolution; Graph showing the relationship between resolution and correction factor. 7 is a graph showing the relationship between the sensor output value (fluctuation amount) and the correction threshold according to the resolution accompanying the capacitance fluctuation of the equivalent second capacitor; FIG. 10 is a list diagram briefly explaining that the correction threshold varies according to the sensor output value (fluctuation amount) according to the resolution accompanying the capacitance variation of the equivalent second capacitor; 4 is a flow chart showing how the capacitive sensor of the same embodiment determines whether or not an object to be detected exists. Schematic diagram showing the relationship between a sensor output value and a plurality of divisions dividing the entire range. 6 is a flow chart showing how the capacitance sensor of the same embodiment counts the number of times for each of a plurality of categories; FIG. 4 is a perspective view showing the rear portion of a vehicle to which a modified form of the capacitance sensor is applied; FIG. 4 is a perspective view showing a side portion of a vehicle to which another modification of the capacitive sensor is applied; 4A and 4B are diagrams for explaining the resolution when the parasitic capacitance of the second capacitor is relatively small; FIG. 4A and 4B are diagrams for explaining resolution when the parasitic capacitance of the second capacitor is relatively large; FIG.

An embodiment of the capacitive sensor will be described below.
As shown in FIG. 1, an opening 2a is formed in the rear portion of a body 2 of a vehicle 1 such as an automobile. A back door 3 is attached to the rear portion of the body 2 so as to be openable and closable via a door hinge (not shown) provided above the opening 2a. The back door 3 is opened by being pushed upward around the door hinge. Furthermore, a door lock 5 for locking and unlocking the back door 3 in the closed state is installed at the front end of the back door 3 on the inside of the passenger compartment.

A rear portion of the body 2 is provided with a bumper 6 extending in the width direction of the vehicle below the opening 2a. The bumper 6 is provided with a pair of substantially linear electrodes 21 extending in the width direction of the vehicle along the bumper 6 . As shown in FIG. 2, each electrode 21 forms a second capacitor 12 whose capacitance varies, for example, as the user's foot F approaches. Both of the second capacitors 12 are used to determine whether or not there is an operation of putting the foot F in and out between the lower portion of the bumper 6 and the road surface (hereinafter also referred to as a "kick operation") (existence or absence of an object to be detected).

Next, the electrical configuration of this embodiment will be described.
As shown in FIG. 3, the electrostatic capacitance sensor 10 including both electrodes 21 is electrically connected to a door ECU 30, which is, for example, an MCU (microcomputer). A door lock drive unit 32 is electrically connected. The door drive unit 31 is mainly composed of an electric drive source such as an electric motor, and is mechanically linked to the back door 3 via an appropriate door drive mechanism to drive the back door 3 to open and close. do. The door lock drive unit 32 mainly includes an electric drive source such as an electric motor, and unlocks the door lock 5 by mechanically linking it with the door lock 5 via an appropriate lock drive mechanism. lock drive.

The capacitance sensor 10 outputs to the door ECU 30 a detection signal Sx representing the result of determination as to whether or not the kick operation has been performed. The door ECU 30 individually drives and controls the door drive unit 31 and the door lock drive unit 32 based on the detection signal Sx from the capacitance sensor 10 .

Specifically, when the detection signal Sx indicates that there is a "kick operation", the door ECU 30 detects an opening operation input (an operation input to the operation target) of the back door 3 in the closed state, and locks the back door 3. An unlocking operation input for a certain door lock 5 (an operation input for an operation target) is detected. The door ECU 30 drives and controls the door drive unit 31 to open the back door 3 and controls the door lock drive unit 32 to unlock the door lock 5 .

Alternatively, when the detection signal Sx indicates that there is a "kick operation", the door ECU 30 detects a closing operation input (an operation input to the operation target) of the back door 3 in the open state, and also detects the door in the unlocked state. Locking operation input of the lock 5 (operation input for the operation target) is detected. The door ECU 30 drives and controls the door drive unit 31 to close the back door 3 and controls the door lock drive unit 32 to lock the door lock 5 .

Next, the electrical configuration of the capacitance sensor 10 will be described. Since the electrical connections of both the second capacitors 12 (electrodes 21) are the same, one of them will be described below as a representative.

As shown in FIG. 4, the capacitance sensor 10 includes a first capacitor 11, a second capacitor 12, a first switch 13, a second switch 14, a third switch 15, and a control circuit 16. Prepare.

The first capacitor 11 has a predetermined capacitance C11. The first capacitor 11 is configured and arranged so that the capacitance C11 does not fluctuate, for example, even if the surrounding environment of the vehicle 1 changes or the user's foot F approaches.

The second capacitor 12 has a generally stable capacitance C12 determined, for example, by the surrounding environment of the vehicle 1, unless the user's foot F is in close proximity. However, the capacitance C12 changes along with the stray capacitance included therein due to a change in the surrounding environment of the vehicle 1 such as a foreign matter adhering to the bumper 6 (or the electrode 21). Also, as described above, the capacitance C12 varies as the user's foot F approaches.

The first capacitor 11 and the second capacitor 12 are connected in series to the power supply. That is, one end of the first capacitor 11 is electrically connected to the high-side potential V1 as a power supply, and the other end is electrically connected to one end of the second capacitor 12 via the second switch 14. . The other end of the second capacitor 12 is electrically connected to a low-side potential V2 (<V1) as a power supply. The low-side potential V2 is set, for example, to the same potential as the ground.

The first switch 13 initializes the first capacitor 11 . Specifically, the first switch 13 is connected (connected in parallel) between both terminals of the first capacitor 11, and switches between both terminals of the first capacitor 11 as it is switched to the ON state and the OFF state. Connect (short) and disconnect. The second switch 14 is electrically connected between the first capacitor 11 and the second capacitor 12, and connects and disconnects the first capacitor 11 and the second capacitor 12, respectively, according to switching to the ON state and the OFF state. do. A third switch 15 initializes the second capacitor 12 . Specifically, the third switch 15 is connected (connected in parallel) between both terminals of the second capacitor 12, and switches between both terminals of the second capacitor 12 as it is switched to the ON state and the OFF state. Connect (short) and disconnect.

The control circuit 16 includes a control section 17 such as an MCU (microcomputer) and a comparison section 18 such as a comparator.
The comparison unit 18 compares the intermediate potential VM, which is the potential of the connection point N between the first capacitor 11 and the second switch 14 , with the reference potential Vref, and outputs a signal representing the comparison result to the control unit 17 . The reference potential Vref is set to an intermediate potential (V2<Vref<V1) between the high-side potential V1 and the low-side potential V2.

The control unit 17 performs on/off control (switching control) of the first switch 13 , the second switch 14 and the third switch 15 . Further, the control unit 17 derives the sensor output value Craw based on the output signal (that is, comparison result) of the comparison unit 18 .

Here, with reference to FIG. 5, the switching control executed by the control unit 17 and the derivation process of the sensor output value Craw will be described.
The control unit 17 as the switch control unit 17a operates the first switch 13, the second switch 14, and the third switch 15 at predetermined intervals. That is, at the beginning of the cycle, the control unit 17 performs the first switching process of turning on the first switch 13 while the second switch 14 and the third switch 15 are in the off state. As a result, the first capacitor 11 is initialized and the intermediate potential VM becomes equal to the high side potential V1.

After that, the control unit 17 turns on the second switch 14 and turns on the third switch 15 while the first switch 13 is turned off (hereinafter, this switch operation is referred to as the "second switch operation”). At this time, a current flows through the first capacitor 11 and the second capacitor 12, and the intermediate potential VM drops.

Next, the control unit 17 turns off the second switch 14 and turns on the third switch 15 while maintaining the off state of the first switch 13 (hereinafter, this switch operation is referred to as "third switch operation”). At this time, the second capacitor 12 is initialized.

Subsequently, the control unit 17 alternately performs the second switch operation and the third switch operation while maintaining the first switch 13 in the OFF state. That is, the control unit 17 repeats the second switching process of complementarily switching the second switch 14 and the third switch 15 between the off state and the on state while the first switch 13 is in the off state. Along with this, intermediate potential VM gradually decreases.

The control unit 17 repeats the second switching process until the number of repetitions of the second switching process while maintaining the off state of the first switch 13 reaches a predetermined number of times Nth. The predetermined number of times Nth is set larger than the number of repetitions of the second switching process required until the magnitude relationship between the intermediate potential VM and the reference potential Vref is reversed when the capacitance C12 of the second capacitor 12 is the minimum value. This is because regardless of the capacitance C12 of the second capacitor 12, the magnitude relationship between the intermediate potential VM and the reference potential Vref is always inverted until the number of repetitions of the second switching process reaches the predetermined number of times Nth. be.

When the number of repetitions of the second switching process while maintaining the off state of the first switch 13 reaches a predetermined number of times Nth, the control unit 17 restarts the first switching process and repeats the same process.

The control unit 17 as the deriving unit 17b counts the number of repetitions of the second switching process until the magnitude relationship between the intermediate potential VM and the reference potential Vref is reversed. That is, based on the output signal of the comparison unit 18, the control unit 17 counts the number of repetitions of the second switching process until it is determined that the intermediate potential VM is lower than the reference potential Vref (VM<Vref). Then, the control unit 17 derives the number of repetitions when it is determined that the intermediate potential VM is lower than the reference potential Vref as the sensor output value Craw [LSB]. This sensor output value Craw [LSB] correlates with the discharge capacity that the second capacitor 12 can discharge per operation of the second switching process, that is, the capacity C12 [pF] of the second capacitor 12 . That is, the sensor output value Craw [LSB] serves as an index of the capacitance C12 [pF].

Specifically, the capacitance C12 [pF] is a known exponential function of the sensor output value Craw [LSB]. As shown in FIG. 6, this exponential function basically exhibits a feature that the capacitance C12 [pF] increases as the sensor output value Craw [LSB] decreases. This is because the larger the capacitance C12 [pF], the larger the discharge capacity per operation of the second switching process, and the smaller the number of repetitions of the second switching process, that is, the sensor output value Craw [LSB]. be.

The control unit 17 as the calculation unit 17c corrects the preset predetermined determination threshold value Cth [LSB] so as to be proportional to the reciprocal of the resolution Res [pF/LSB] of the sensor output value Craw [LSB]. A threshold CthR [LSB] is calculated. The determination threshold value Cth [LSB] is set to a suitable value representing the variation amount of the sensor output value Craw accompanying the kick operation when there is no influence of the resolution Res [pF/LSB]. The correction threshold CthR [LSB] is obtained by correcting the determination threshold Cth [LSB] according to the amount of change in the sensor output value Craw accompanying the kick operation according to the resolution Res [pF/LSB].

That is, the control unit 17 calculates the capacitance C12 [pF] by substituting the sensor output value Craw [LSB] at this time into the aforementioned exponential function (see FIG. 6).
Further, the control unit 17 differentiates the capacitance C12 [pF] to calculate the resolution Res [pF/LSB]. Specifically, the control unit 17 assigns a value obtained by subtracting 1 [LSB] from the sensor output value Craw [LSB] to the exponential function described above, and the capacitance C12 [pF] and the value [pF] obtained by Then, the resolution Res [pF/LSB] is calculated based on the difference between . As shown in FIG. 7, the resolution Res [pF/LSB] changes according to the sensor output value Craw [LSB].

Furthermore, the control unit 17 calculates the magnitude (absolute value) of the reciprocal of the resolution Res [pF/LSB] as a correction coefficient K. FIG. As shown in FIG. 8, the correction coefficient K is inversely proportional to the resolution Res [pF/LSB].

Then, the control unit 17 multiplies the determination threshold Cth[LSB] by the correction coefficient K to calculate the correction threshold CthR[LSB].
As described above, the control unit 17 calculates the corrected threshold value CthR[LSB] by correcting the determination threshold value Cth[LSB] so as to be proportional to the reciprocal of the resolution Res[pF/LSB] of the sensor output value Craw[LSB]. This is because when the sensor output value Craw [LSB] changes more than the fluctuation due to the presence or absence of the kick operation, the resolution Res [pF/LSB] changes and remains constant with respect to the amount of change in the equivalent capacitance C12 [pF]. This is because the sensor output value Craw [LSB] does not change. That is, since the amount of change in the sensor output value Craw [LSB] with respect to the amount of change in the equivalent capacitance C12 [pF] is proportional to the reciprocal of the resolution Res [pF/LSB], the presence or absence of the kick operation is determined accordingly. The determination threshold Cth[LSB] is corrected to the correction threshold CthR[LSB].

FIG. 9 is a graph showing the relationship between the amount of change in the sensor output value Craw [LSB] and the calculated determination threshold value Cth [LSB] when the amount of change in the capacitance C12 [pF] due to the kick operation is assumed to be equivalent. is. The determination threshold value Cth [LSB] calculated in this way is proportional to the variation amount of the sensor output value Craw [LSB] that varies according to the resolution Res [pF/LSB]. In this case, the detection distance of the foot F related to the determination of the presence or absence of the kick operation remains unchanged, and the possibility of lowering the determination accuracy is reduced.

Here, the relationship between the amount of change according to the resolution Res [pF/LSB] of the sensor output value Craw [LSB] with respect to the amount of change in the capacitance C12 [pF] accompanying the kick operation and the correction threshold CthR [LSB] will be simplified. explain. In the following description, the resolution Res [pF/LSB] is set to a positive number in accordance with the correction coefficient K for convenience. Also, the sensor output value Craw [LSB] represents the magnitude (absolute value) of the amount of variation.

As shown in FIG. 10, the variation amount of the capacitance C12 [pF] due to the kick operation is 10 [pF], and the sensor output value Craw [LSB] with respect to the variation amount differs due to the difference in the resolution Res [pF/LSB]. and It is also assumed that the determination threshold value Cth [LSB] before correction is 10 [LSB].

Assume that the resolution Res is 0.5 [pF/LSB] and the sensor output value Craw is 20 [LSB]. In this case, if the determination threshold Cth [LSB] is multiplied by the reciprocal of 0.5 (=2) as the correction coefficient K, the determination threshold Cth after correction (that is, the correction threshold CthR) becomes 20 (=10×2) [LSB ] becomes.

It is also assumed that the sensor output value Craw is 10 [LSB] because the resolution Res is 1 [pF/LSB]. In this case, if the determination threshold Cth [LSB] is multiplied by the reciprocal of 1 (=1) as the correction coefficient K, the determination threshold Cth after correction (that is, the correction threshold CthR) is 10 (=10×1) [LSB]. Become.

Furthermore, it is assumed that the sensor output value Craw is 2 [LSB] because the resolution Res is 5 [pF/LSB]. In this case, if the determination threshold Cth [LSB] is multiplied by the reciprocal of 5 (=0.2) as the correction coefficient K, the determination threshold Cth after correction (that is, the correction threshold CthR) becomes 2 (=10×1) [LSB ] becomes.

As described above, the correction threshold value CthR [LSB] is corrected in accordance with the amount of change according to the resolution Res [pF/LSB] of the sensor output value Craw [LSB] with respect to the amount of change in the capacitance C12 [pF] due to the kick operation. It is confirmed that

Next, a manner of determining whether or not there is a kick operation according to the present embodiment will be described. This process is repeatedly executed by regular interrupts at predetermined time intervals (for example, the repetition cycle of the first switching process).

As shown in FIG. 11, when the process shifts to this routine, the control unit 17 calculates (derives) the sensor output value Craw in the manner described above (step S1), and based on the sensor output value Craw, the capacitance C12 is calculated (step S2), and the resolution Res is calculated based on the capacitance C12 (step S3). Subsequently, the control unit 17 calculates the correction coefficient K based on the reciprocal of the resolution Res (step S4), and multiplies the determination threshold Cth by the correction coefficient K to calculate the correction threshold CthR (step S5).

Next, the control unit 17 calculates a reference sensor output value Cbase based on the past sensor output value Craw (step S6). Specifically, the average value of the sensor output values Craw within a predetermined time period sufficiently longer than the calculation cycle is calculated as the reference sensor output value Cbase (step S6).

This reference sensor output value Cbase is a stable value that serves as a reference for comparison with the sensor output value Craw, which fluctuates during a kick operation, for example. In other words, the past sensor output value Craw is reflected so that the reference sensor output value Cbase does not fluctuate as it is due to the kick operation. Needless to say, the resolution Res of the reference sensor output value Cbase is equivalent to the sensor output value Craw. The current sensor output value Craw may be included in the calculation of the reference sensor output value Cbase. Alternatively, the sensor output value Craw a predetermined time ago may be used as it is as the reference sensor output value Cbase.

Next, the control unit 17 calculates a sensor output difference value Cdiff, which is the magnitude (absolute value) of the difference between the current sensor output value Craw and the reference sensor output value Cbase (step S7). This sensor output difference value Cdiff serves as an index of the amount of change in the capacitance C12, and its resolution Res is equivalent to the sensor output value Craw and the like.

Subsequently, the control unit 17 as the determination unit 17d determines whether or not the sensor output difference value Cdiff exceeds the correction threshold value CthR (step S8). Then, when it is determined that the sensor output difference value Cdiff has exceeded the correction threshold value CthR, the control unit 17 determines that there is a kick operation because the variation amount of the sensor output value Craw is large (step S9), and the subsequent processing is performed. exit. On the other hand, when it is determined that the sensor output difference value Cdiff is equal to or less than the determination threshold value Cth, the control unit 17 determines that there is no kick operation because the amount of variation in the sensor output value Craw is small (step S10). End the process.

As described above, it is possible to suppress deterioration in accuracy in determining the presence or absence of a kick operation due to changes in the resolution Res, that is, the parasitic capacitance included in the capacitance C12.
As schematically shown in FIG. 12, the entire range of the sensor output value Craw is preliminarily divided into a plurality of continuous segments n (n=1, 2, . . . ) without intersecting each other. Then, the control unit 17 as the division determination unit 17e determines to which division n of the plurality of divisions n the current sensor output value Craw belongs. In addition, the control unit 17 as the division counting unit 17f counts the number of times (frequency) CNTn (n=1, 2, . , the control unit 17 stores the counting result of the number of times CNTn for each of the plurality of divisions n in the storage unit 17g composed of the built-in non-volatile memory. This is because the distribution of the parasitic capacitance (capacitance C12) of the second capacitor 12 and the like can be captured by reading the result of the counting (number of times CNTn) from the storage unit 17g during maintenance, for example.

Next, the manner of counting the number of times CNTn for each of a plurality of sections n according to this embodiment will be described. This process is activated, for example, when the determination result of the category n to which the sensor output value Craw belongs is switched from the previous time.

As shown in FIG. 13, when the process shifts to this routine, the control unit 17 increments by "1" the number of times CNTn of the current segment n in which the determination result has been switched, and updates this (step S11). Subsequently, the control unit 17 stores the updated number of hits CNTn in the storage unit 17g (step S12), and terminates subsequent processing.

From the above, the characteristics such as the distribution of the parasitic capacitance (capacitance C12) of the second capacitor 12 can be grasped.
The action and effect of this embodiment will be described.

(1) In the present embodiment, the sensor output difference value Cdiff basically has the same resolution as the resolution Res of the sensor output value Craw together with the reference sensor output value Cbase. Therefore, the sensor output difference value Cdiff changes in proportion to the reciprocal of the resolution Res if the variation amount of the capacitance C12 of the second capacitor 12 is the same. On the other hand, the corrected threshold CthR is obtained by correcting the determination threshold Cth so as to be proportional to the reciprocal of the resolution Res of the sensor output value Craw. As a result, even if the parasitic capacitance included in the capacitance C12 of the second capacitor 12 is different, the control unit 17 (determining unit 17d) can determine the kick based on the magnitude relationship between the sensor output difference value Cdiff and the correction threshold value CthR. The presence or absence of an operation (the presence or absence of a detection target) can be determined at the same level. In this way, it is possible to suppress deterioration in accuracy in determining whether or not there is a kick operation due to changes in the parasitic capacitance included in the capacitance C12 of the second capacitor 12 .

(2) In the present embodiment, the number of times CNTn that it is determined that the sensor output value Craw correlated with the capacitance C12 (parasitic capacitance) of the second capacitor 12 belongs to each of a plurality of sections n is counted. The result is stored in the storage section 17g. Therefore, by reading the result of the counting from the storage unit 17g at the time of maintenance, for example, characteristics such as the distribution of the capacitance C12 (parasitic capacitance) of the second capacitor 12 can be grasped. In addition, depending on the distribution of the capacitance C12 (parasitic capacitance) of the second capacitor 12, it is possible to assume the operating environment of the electrostatic capacitance sensor 10 that has been recovered, for example, during maintenance, which can contribute to the analysis of failure factors.

(3) In the present embodiment, even if the parasitic capacitance included in the capacitance C12 of the second capacitor 12 is different, the presence or absence of the kick operation is determined at the same level. target) can be suppressed from deteriorating in detection accuracy of operation input. That is, for example, even if a foreign object adheres to the bumper 6 (or the electrode 21) and the parasitic capacitance included in the capacitance C12 of the second capacitor 12 changes, the detection accuracy of the operation input to the back door 3 and the door lock 5 decreases. can be suppressed. Further, erroneous detection of operation input to the back door 3 and the door lock 5 can be suppressed.

(4) In the present embodiment, the section counting section 17f updates the number of times CNTn of the corresponding section n when the section n determination result by the section determining section 17e is switched. Therefore, for example, when the determination result of the section n by the section determining section 17e remains unchanged for a long time, the section counting section 17f can be prevented from continuously updating the number of times CNTn of the section n. In addition, since the division counting unit 17f only needs to monitor the switching of the judgment result of the division n by the division judging unit 17e, the calculation load (processing load) can be reduced. In addition, since the calculation load of the division counting section 17f (the control section 17) is reduced, the processing time of the control section 17 can be shortened, and the sampling cycle can be shortened.

This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
・As shown in FIG. 14, when a mark 7 such as a company name is installed in the center of the outer surface of the back door 3, the electrode 26 is formed on the back of the mark 7. It may be the second capacitor 25 . The second capacitor 25 is used to determine whether or not the user has operated his or her finger to approach the mark 7 (whether or not a detection target exists). In this case, for example, even if a foreign object adheres to the mark 7 (or the electrode 26) and the parasitic capacitance included in the capacitance of the second capacitor 25 changes, it is possible to suppress a decrease in accuracy in determining whether or not the operation has been performed.

・As shown in FIG. 15, when a slide door 43 is provided for opening and closing an opening 42a formed on the side of a body 42 of a vehicle 41, an electrode 46 installed on a window glass 44 of the slide door 43 It may be the second capacitor 45 configured. The second capacitor 45 is used to determine whether or not the user has operated the finger H to approach the window glass 44 (whether or not there is an object to be detected). In this case, for example, even if a foreign object adheres to the window glass 44 (or the electrode 46) and the parasitic capacitance included in the capacitance of the second capacitor 45 changes, it is possible to suppress the deterioration of the determination accuracy of the presence or absence of the operation.

- In the said embodiment, the 2nd capacitor|condenser comprised by the electrode installed in the side locker of the vehicle 1 may be sufficient. The second capacitor is used to determine whether there is a kick operation (presence or absence of an object to be detected). In this case, for example, even if a foreign object adheres to the side rocker (or the electrode) and the parasitic capacitance included in the capacitance of the second capacitor changes, it is possible to suppress a decrease in accuracy in determining the presence or absence of the kick operation.

- In the above-described embodiment, the control unit 17 may store in advance a map or table representing the relationship between the sensor output value Craw and the capacitance C12 in the storage unit 17g. Then, the control unit 17 may calculate the capacitance C12 based on the map or table read from the storage unit 17g. In this case, the control unit 17 does not need to calculate the capacitance C12 by substituting the sensor output value Craw into the above-described exponential function, thereby reducing the calculation load (processing load).

- In the above-described embodiment, the control unit 17 may store a map or table representing the relationship between the sensor output value Craw and the resolution Res in advance in the storage unit 17g. Then, the control unit 17 may calculate the resolution Res based on the map or table read from the storage unit 17g. In this case, the control unit 17 does not need to calculate the resolution Res based on, for example, a theoretical arithmetic expression (exponential function, etc.), thereby reducing the arithmetic load.

- In the above embodiment, the control unit 17 may store a map or table representing the relationship between the sensor output value Craw and the correction coefficient K in the storage unit 17g in advance. Then, the control unit 17 may calculate the correction coefficient K based on the map or table read from the storage unit 17g. In this case, the control unit 17 does not need to calculate the correction coefficient K based on, for example, a theoretical calculation formula (exponential function, etc.), so that the calculation load can be reduced. In addition, since the calculation load of the control unit 17 is reduced, the processing time of the control unit 17 can be shortened, and the sampling period can be shortened. Alternatively, the computing power of the control unit 17 can be made lower, and the cost can be reduced.

A table in which the correction coefficient K changes stepwise according to the sensor output value Craw may be used. As a result, the data representing the relationship between the sensor output value Craw and the correction coefficient K can be thinned out, and the required storage capacity of the storage unit 17g (or the storage amount used by the storage unit 17g) can be reduced. Further, in this case, the correction coefficient K may be corrected by, for example, linear interpolation. As a result, the correction coefficient K obtained by thinning the data can be calculated more accurately.

- In the above-described embodiment, the control unit 17 may store a map or table representing the relationship between the sensor output value Craw and the correction threshold value CthR in the storage unit 17g in advance. Then, the control unit 17 may calculate the sensor output correction value CrawR based on the map or table read from the storage unit 17g. In this case, the control unit 17 does not need to calculate the correction threshold value CthR based on, for example, a theoretical calculation formula (exponential function, etc.), thereby reducing the calculation load. In addition, since the calculation load of the control unit 17 is reduced, the processing time of the control unit 17 can be shortened, and the sampling period can be shortened. Alternatively, the computing power of the control unit 17 can be made lower, and the cost can be reduced.

A table in which the correction threshold value CthR changes stepwise according to the sensor output value Craw may be used. As a result, the data representing the relationship between the sensor output value Craw and the correction threshold CthR can be thinned out, and the required storage capacity of the storage unit 17g (or the storage amount used by the storage unit 17g) can be reduced. Further, in this case, the correction threshold CthR may be corrected by, for example, linear interpolation. As a result, the corrected threshold value CthR obtained by thinning the data can be calculated more accurately.

- In the above embodiment, the plurality of divisions (n) may divide the entire range of any one of the correction threshold value CthR, the correction coefficient K, the resolution Res, and the capacitance C12 that are correlated with the sensor output value Craw. . Alternatively, the plurality of divisions (n) may divide the entire range of the reference sensor output value Cbase based on the past sensor output value Craw. Then, the control unit 17 counts the number of times that the corresponding correction threshold value CthR, correction coefficient K, resolution Res, capacitance C12, or reference sensor output value Cbase belongs to each of the plurality of categories (n). , the counting result of the number of times may be stored in the storage unit 17g.

- In the above-described embodiment, the processing of counting the number of times CNTn for each of a plurality of divisions n and storing the same may be omitted.
- In the above-described embodiment, the operation of the opening/closing body of the vehicle such as the back door 3 and the slide door 43 is not limited to the opening/closing operation or the locking/unlocking operation, and may be, for example, a halfway stop operation or a reservation operation. .

- In the above-described embodiment, the operation target related to the detection of the operation input is a movable part of the vehicle other than the back door 3 and the sliding door 43 (for example, swing door, trunk lid, sunroof, window regulator, fuel lid, bonnet, seat, etc.). There may be.

Technical ideas that can be grasped from the above embodiment and modifications will be described.
(B) In the above capacitance sensor,
The segment counting unit updates the number of times of the corresponding segment when the determination result of the segment by the segment determining unit is switched.

According to this configuration, for example, when the determination result of the segment by the segment determination unit remains unchanged for a long time, it is possible to prevent the segment counter from continuously updating the number of times of the segment. In addition, since the division counting unit only needs to monitor the switching of the judgment result of the division by the division judging unit, the calculation load can be reduced.

(B) In the above capacitance sensor,
The capacitance sensor, wherein the calculation unit calculates the correction threshold from the sensor output value based on a preset table.

According to this configuration, the calculation unit can calculate the correction threshold value based on the table, so that the calculation load can be reduced compared to the calculation based on, for example, a theoretical calculation formula.

n: division, VM: intermediate potential, C12: capacity, Cth: determination threshold, CthR: correction threshold, Res: resolution, Craw: sensor output value, Vref: reference potential, Cbase: reference sensor output value, Cdiff: sensor output difference Value, CrawR... sensor output correction value, 11... first capacitor, 12, 25, 45... second capacitor, 13... first switch, 14... second switch, 15... third switch, 17... control unit. 17a switch control section, 17b derivation section 17c calculation section 17d determination section 17e division determination section 17f division counting section 17g storage section.

Claims (2)

a series-connected first capacitor and a second capacitor connected to a power supply;
a first switch connected between both terminals of the first capacitor;
a second switch connected between the first capacitor and the second capacitor;
a third switch connected between both terminals of the second capacitor;
After performing a first switching process for turning on the first switch, a second switching process for complementarily switching the second switch and the third switch to an off state and an on state while the first switch is off. a switch control unit that repeatedly performs
a deriving unit that derives, as a sensor output value, the number of repetitions of the second switching process when it is determined that the magnitude relationship between the intermediate potential between the first and second capacitors and a preset reference potential is reversed; ,
a calculation unit that calculates a correction threshold obtained by correcting a preset determination threshold so as to be proportional to the reciprocal of the resolution of the sensor output value;
a determination unit that determines the presence or absence of a detection target based on a sensor output difference value that is a difference between a reference sensor output value based on the current sensor output value and the past sensor output value, and the magnitude relationship of the correction threshold; Capacitive sensor with The capacitance sensor according to claim 1,
a division determination unit that determines to which division the sensor output value belongs among a plurality of divisions obtained by dividing the entire range of the sensor output value;
a division counting unit that counts the number of times the sensor output value is determined to belong to each of the plurality of divisions;
and a storage unit that stores the result of counting the number of times for each of the plurality of categories.

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