JP2009174978A - Capacitive sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure a distance between an object to be sensed and a sensor by lowering a difference between variations of a sensor output, thereby to precisely detect the object to be sensed. <P>SOLUTION: Sensor electrodes 11-15 for the capacitive sensor, for example, each being made up in a rectangle strip form, are arranged in a juxtapositional fashion on a substrate. The capacitive sensor further has guard electrodes 11a, 11b, 15a and 15b, which are formed on at least a portion of the area surrounding at least sensor electrodes 11, 15 out of the sensor electrodes 11-15 disposed on the outer side of the juxtapositional direction, so as to be out of contact with the sensor electrodes 11, 15. Each of the sensor electrodes 11-15 is driven by applying a sensor potential thereto, and each of the guard electrodes 11a, 11b, 15a and 15b is driven by applying a guard potential thereto, which is equivalent to the sensor potential. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a capacitance type sensor that detects a capacitance between a detection target and a detection target existing in a detection region, and particularly to a capacitance type that can detect the position of a detection target in the detection region with high accuracy. It relates to sensors.

  Conventionally, the following is known as a detection object (such as an object) existing in a detection area. That is, the headrest driving device disclosed in the following Patent Document 1 is separated from the inside of the supporting means for movably supporting the headrest, the driving means for reciprocating the headrest, and the portion of the headrest outer cover that supports the head. A plurality of detection electrodes (sensing electrodes), a capacitance detecting means for detecting a capacitance formed by the plurality of detection electrodes with respect to the common potential line, and a headrest in a direction in which the capacitance balances And a position control means for controlling a drive means for driving the actuator to move.

  In this headrest driving device, the headrest is controlled by the position control means so that the head is positioned at the center of the plurality of detection electrodes, in other words, the headrest moves following the movement of the head. It is driven by the driving means and automatically adjusts the position of the headrest.

  Moreover, the apparatus for adjusting the headrest disclosed in the following Patent Document 2 is configured to have a sensor including two capacitor plates arranged in the headrest for detecting the head position of the occupant. These two capacitor plates are arranged one above the other in the headrest.

  As long as the increase in the sensor signal of one capacitor plate occurs simultaneously with the decrease in the sensor signal of the other capacitor plate, the height position of the headrest is adjusted to change starting from the fixed position where the headrest is retracted. To be.

  In addition, the headrest adjusting device disclosed in Patent Document 3 below includes a headrest disposed on an upper portion of a seat back (backrest portion) so that the headrest can be moved up and down by driving a motor, and a head position of a seated person (occupant) And a CPU that adjusts the height of the headrest according to the position of the head of the seated person based on a signal from the head detection sensor.

  In this headrest adjusting device, when the CPU detects the electrical continuity of the ignition switch, the seating sensor detects that there is a seating, and the seatbelt buckle switch detects that the seatbelt of the vehicle is mounted In addition, the headrest adjustment operation is started.

  Furthermore, in the object detection device disclosed in Patent Document 4 below, a plurality of sensor electrodes having a constant electrode interval are inserted into a resin, and a sensor electrode unit is formed by insert molding. This sensor electrode unit has a hollow rectangular cross section and is provided with a sensor electrode on at least one side thereof, thereby maintaining detection performance and improving the degree of freedom of attachment.

JP-A 64-11512 JP 2000-309242 A JP 11-180200 A JP-A-11-213296

  However, in the headrest driving device disclosed in Patent Document 1 described above, the position of the headrest is adjusted by the capacitance between the headrest and the ceiling of the vehicle. Moreover, in the apparatus for adjusting the headrest disclosed in Patent Document 2 described above, the capacitance between the head and the detection electrode is measured by two or three capacitor plates and used for position adjustment. It is said that.

  In the headrest position adjusting device disclosed in Patent Document 3 described above, the headrest position is adjusted based on the adjustment result of each part of the seat. Furthermore, in the object detection device disclosed in Patent Literature 4 described above, for example, when the centers of a plurality of sensor electrodes and the centers of detection objects are facing each other, each sensor electrode stably stabilizes the object. It is supposed to detect the electric capacity.

  As described above, in the conventional device, it is necessary to detect an object by comparing the output balance of the sensor and the output peak of each detection electrode. In such a detection method, for example, depending on the position where a plurality of detection electrodes are arranged. In some cases, the initial capacitance of the detection electrode (that is, the capacitance value in the state where the detection target does not exist) and the detection sensitivity differ greatly.

  As an example, FIG. 11 shows a sample configuration for an experiment conducted by the present applicant, and FIG. 12 shows a result of the experiment. In this experiment, as shown in FIG. 11, for example, a sensor unit 102 having a plurality of sensor electrodes 102 a to 102 e formed on a substrate 102 f is disposed on a pedestal 101 made of foamed polystyrene. A flat plate 104 to which a ground (GND) potential was applied in the direction of a white arrow in FIG. 11 was placed on the sensor unit 102 with a plate material 103 made of foamed polystyrene having a predetermined thickness L interposed therebetween.

  As described above, in a state where the distance between the sensor electrodes 102a to 102e of the sensor unit 102 and the flat plate 104 (thickness L of the plate member 103) is constant, each of the distances L relative to the distance L between the sensor unit 102 and the flat plate 104 is determined. The output (V) of the sensor electrodes 102a to 102e (see FIG. 12A) and the output change amount (V) with respect to the change of the distance L (see FIG. 12B) were measured.

  The vertical axis of the graph in FIG. 12A represents the sensor output (V), and the horizontal axis represents the electrode numbers assigned to the sensor electrodes 102a to 102e (for example, electrode numbers 1 to 1 in order from the sensor electrodes 102a to 102e). 5 is attached). In addition, the vertical axis of the graph in FIG. 12B represents the sensor output (V), and the horizontal axis represents the movement distance (mm).

  If the distance L between the sensor unit 102 and the flat plate 104 is changed to 20 mm, 40 mm, 60 mm, and 75 mm as shown in FIG. 12A, for example, as shown in FIG. 12A, the sensor electrode 102a (electrode number 1) The sensor output (V) of the sensor electrode 102e (electrode number 5) was the largest. In other words, the output of the electrodes arranged on the outermost side in the arrangement direction (parallel direction) of the sensor electrodes 102a to 102e was the largest.

  Further, for example, as shown in FIG. 12B, the difference (= ΔC) between the respective capacitance values when the change amount ΔL of the distance L is 20 mm-40 mm, 40 mm-60 mm, 60 mm-75 mm is as follows. A different locus was drawn for each of the sensor electrodes 102a to 102e. In particular, the difference between the loci is a difference in the amount of change in output. For example, the point group of each sensor output in a place where the amount of change ΔL is 20 mm to 40 mm is within a range having a variation of about 100 mV. I understood that.

  Therefore, when the difference in the output change amount of the sensor output for each of the sensor electrodes 102a to 102e becomes significant, the distance between the detection target and the sensor unit 102 is accurate depending on the various detection methods as described above. May be difficult to measure.

  The present invention has been made in view of the above points, and can accurately measure the distance between the detection target and the sensor by reducing the difference in the amount of change in output of the sensor. It is an object of the present invention to provide a capacitive sensor that can detect with high accuracy.

  A capacitance type sensor according to the present invention is a capacitance type sensor that detects a capacitance between a detection object existing in a detection region and a plurality of sensor electrodes arranged in parallel on a substrate, And a guard electrode formed on at least a part of the periphery of the sensor electrode disposed at least on the outer side in the juxtaposition direction among the plurality of sensor electrodes.

  By configuring the capacitance type sensor of the present invention as described above, the difference between the sensor output change amount due to the difference in the arrangement position of the plurality of sensor electrodes is reduced, and the distance between the detection target and the sensor is reduced. Can be measured accurately, and the detection object can be detected with high accuracy.

  A guard electrode is further formed in at least a part of the periphery of the inner sensor electrode adjacent to the sensor electrode in which the guard electrode is formed in at least a part of the periphery. For example, the area of the guard electrode is larger than that in the juxtaposed direction. The outer side is formed so as to be larger.

  In addition, a guard electrode is further formed on at least a part of the periphery of the sensor electrode on the inner side in the juxtaposition direction of the sensor electrode on which the guard electrode is formed on at least a part of the periphery. The sensor electrode may be formed so as to be larger on the outer side and the inner side in the side-by-side direction than on the sensor electrode on the inner side in the installation direction.

  Further, for example, the area of the guard electrode is equal to the area of the sensor electrode other than the sensor electrode in which the guard electrode is formed on at least a part of the periphery, and the area of the sensor electrode in which the guard electrode is formed on at least a part of the periphery. It is arranged and formed so that the added area is equivalent.

  The plurality of sensor electrodes are driven, for example, given a sensor potential or a guard potential equivalent to the sensor potential.

  The detection circuit further includes a detection circuit that detects a capacitance value of the detection object based on outputs from the plurality of sensor electrodes, and the detection circuit switches, for example, the sensor potential or the guard potential applied to the plurality of sensor electrodes. A switching unit; and a detection unit that applies the sensor potential or the guard potential to the plurality of sensor electrodes via the switching unit and detects a capacitance value detected by each sensor electrode.

  For example, when the sensor potential is applied to one of the plurality of sensor electrodes, the switching unit performs switching so that the guard potential is applied to the other sensor electrode.

  For example, at least five of the plurality of sensor electrodes are provided.

  The plurality of sensor electrodes are formed, for example, in a rectangular strip shape, and are arranged side by side on the substrate along the short direction.

  The detection means detects, for example, electrostatic capacitance values from the plurality of sensor electrodes in order from one side to the other side in the juxtaposed direction.

  Further, the detecting means detects, for example, the capacitance values from the plurality of sensor electrodes from one side of the parallel arrangement direction to the other side in the order of odd numbered arrangement or even numbered arrangement, and then further detects the order of even numbered arrangement or odd numbered arrangement. To do.

  The switching means includes, for example, a plurality of FETs, a plurality of analog switches, or a plurality of multiplexers.

  According to the present invention, it is possible to accurately measure the distance between the detection target object and the sensor by reducing the difference in the output change amount of the sensor, and to detect the detection target object with high accuracy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of a capacitive sensor according to the invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an explanatory diagram for explaining an example of an electrode structure of a capacitive sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the overall configuration of the capacitive sensor. FIG. 3 is a block diagram showing a configuration example of a sensor IC of the capacitance type sensor, and FIG. 4 is an operation waveform diagram showing an example of an operation waveform of the sensor IC of the capacitance type sensor.

  As shown in FIG. 1, a capacitive sensor according to an embodiment of the present invention is formed, for example, in a rectangular strip shape on a substrate (not shown) along its short direction (direction intersecting the longitudinal direction). A plurality of sensor electrodes 11 to 15 arranged in parallel to each other, and at least a part of the periphery of sensor electrodes (for example, sensor electrodes 11 and 15) arranged at least outside of the sensor electrodes 11 to 15 in the parallel arrangement direction. For example, guard electrodes 11a, 11b, 15a, and 15b formed in a non-contact state with the sensor electrodes 11 and 15, respectively, are provided (for example, both ends along the longitudinal direction).

  This electrostatic capacitance type sensor detects the electrostatic capacitance between the detection objects existing in the detection region by the sensor electrodes 11 to 15 configured as described above. The sensor electrode and the guard electrode include the area A of the sensor electrodes 12 to 14 other than the sensor electrodes 11 and 15 on which the guard electrodes 11a, 11b, 15a and 15b are formed, and the guard electrodes 11a, 11b, 15a and 15b. An area A ′ obtained by adding the areas of the guard electrodes 11a, 11b, 15a, and 15b to the area of the sensor electrodes 11 and 15 on which the electrode is formed is arranged and formed so as to be equivalent, for example.

  Each of the sensor electrodes 11 to 15 is driven by being given a predetermined sensor potential or a guard potential equivalent to the sensor potential, and a guard potential is given to each of the guard electrodes 11a, 11b, 15a and 15b.

  The sensor electrodes 11 to 15 and the guard electrodes 11a, 11b, 15a, and 15b are formed on a substrate made of, for example, a flexible printed board, a rigid board, or a rigid flexible board. The sensor electrodes 11 to 15 and the guard electrodes 11a, 11b, 15a, and 15b are made of an insulator such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyamide (PA), or epoxy resin. It consists of copper, copper alloy or aluminum patterned on the substrate.

  In addition, for example, electrode numbers 1 to 5 are assigned to the sensor electrodes 11 to 15, respectively. Although five sensor electrodes 11 to 15 are provided in this example, five or more sensor electrodes may be provided, for example.

  And as shown in FIG. 2, each sensor electrode 11-15 is connected to the detection circuit which detects the electrostatic capacitance value of a detection target based on the output from these electrodes 11-15. The detection circuit switches the sensor potential or guard potential to be applied to the sensor electrodes 11 to 15, and applies the sensor potential or guard potential to the sensor electrodes 11 to 15 via the switch 20, thereby Sensor IC21 which detects the electrostatic capacitance value detected by -15.

  Further, the detection circuit includes an ECU (electronic control unit) 22 that controls the switcher 20 based on the output from the sensor IC 21 and performs various processes based on the output. The switcher 20 is configured by, for example, a plurality of FETs, a plurality of analog switches, or a plurality of multiplexers configured to be able to switch the sensor potential or guard potential from the sensor IC 21 and supply the sensor potential to each sensor electrode 11-15.

  The switcher 20 switches, for example, a guard potential to the guard electrodes 11a, 11b, 15a, and 15b while giving a sensor potential to the sensor electrodes 11 to 15, or one sensor among the sensor electrodes 11 to 15. When a sensor potential is applied to an electrode (for example, the sensor electrode 11), switching is performed so that a guard potential is applied to the other sensor electrodes (for example, the sensor electrodes 12 to 15). Note that a guard potential may be constantly applied to the guard electrodes 11a, 11b, 15a, and 15b by, for example, the sensor IC 21.

  The sensor IC 21 detects the capacitance values from the sensor electrodes 11 to 15 at the same time, that is, without scanning each sensor electrode 11 to 15 at a different time, or from one side of the juxtaposed direction to the other side. Detected in order (for example, an order different from electrode number 1 → 5), or an odd numbered arrangement order (for example, electrode number 1 → 3 → 5) Or even numbered order (for example, scanning with electrode number 2 → 4 at a different time) and then further detected in even numbered order or odd numbered order.

  The sensor IC 21 generates a pulse signal whose duty ratio changes according to the capacitance between the sensor electrodes 11 to 15 and a detection target (not shown), for example, and outputs the pulse signal after smoothing. The ECU 22 includes, for example, a CPU, a RAM, a ROM, and the like, and performs various processes using the capacitance value detected by the sensor IC 21.

  As shown in FIG. 3, the sensor IC 21 has a duty ratio that changes in accordance with the capacitance C. For example, the sensor IC 21 is connected to a trigger signal generation circuit 101 that outputs a trigger signal TG having a constant period and an input terminal. The timer circuit 102 outputs a pulse signal Po whose duty ratio changes depending on the capacitance C, and a low-pass filter (LPF) 103 that smoothes the pulse signal Po.

  The timer circuit 102 is, for example, two comparators 201 and 202, and an RS flip-flop (hereinafter referred to as “RS-FF”) in which outputs of the comparators 201 and 202 are input to a reset terminal R and a set terminal S, respectively. ) 203, a buffer 204 that outputs the output DIS of the RS-FF 203 to the LPF 103, and a transistor 205 that is turned on / off by the output DIS of the RS-FF 203.

  The comparator 202 compares the trigger signal TG as shown in FIG. 4 output from the trigger signal generation circuit 101 with a predetermined threshold value Vth2 divided by the resistors R1, R2, and R3, and generates a trigger signal TG. Output synchronized set pulse. This set pulse sets the Q output of the RS-FF 203.

  The Q output turns off the transistor 205 as a discharge signal DIS, and between the sensor electrode 11 (12 to 15) and the ground, the capacitance C to the ground of the sensor electrode 11 (12 to 15), the input terminal, and the power supply The battery is charged at a speed determined by a time constant by a resistor R4 connected to the line. As a result, the potential of the input signal Vin increases at a speed determined by the capacitance C.

  When the input signal Vin exceeds the threshold value Vth1 determined by the resistors R1, R2, and R3, the output of the comparator 201 is inverted and the output of the RS-FF 203 is inverted. As a result, the transistor 205 is turned on, and the charge accumulated in the sensor electrode 11 (12 to 15) is discharged through the transistor 205.

  Therefore, as shown in FIG. 4, the timer circuit 102 oscillates at a duty ratio based on the capacitance C between the sensor electrode 11 (12 to 15) and a detection target (not shown) existing in the detection region. The pulse signal Po to be output is output. The LPF 103 smoothes the output to output a DC signal Vout as shown in FIG. In FIG. 4, a waveform indicated by a solid line and a waveform indicated by a dotted line indicate that the former has a smaller capacitance than the latter, and for example, the latter indicates an object approaching state.

  FIG. 5 shows the results of measurement performed under the same conditions as described above with reference to FIGS. 11 and 12, as described above, using the capacitive sensor configured as described above. In addition, the vertical axis | shaft of the graph in FIG. 5 represents sensor output (V), and the horizontal axis represents the movement distance (mm). As shown in FIG. 5, according to the capacitive sensor including the sensor electrodes 11 to 15 and the guard electrodes 11a, 11b, 15a, and 15b of this example, compared to the case shown in FIG. As a result, the difference in the change amount ΔL of the distance L was reduced.

  That is, according to the capacitance type sensor of this example, the point group of the sensor outputs of the electrode numbers 1 to 5 where the change ΔL is 20 mm to 40 mm is about 100 mV as shown in FIG. However, it was possible to keep within a range with a variation of about 60 mV. Moreover, the point group of each sensor output in the place where the change amount ΔL is 60 mm-75 mm is almost the same value.

  Thereby, the difference in the amount of change between the sensor electrodes 11 to 15 is reduced, and the detection object and the sensor electrodes 11 to 15 are also detected when detecting the head of an uneven human body, for example, as the detection object. It has been found that the distance between the detection object and the sensor electrodes 11 to 15 can be measured accurately and accurately even if the distance between the sensor electrode and the sensor electrode is long.

  Thus, according to the capacitance type sensor described above, the difference between the sensor output change amounts due to the difference in the arrangement position of the plurality of sensor electrodes 11 to 15 is reduced, and the distance between the detection target and the sensor is reduced. Therefore, it is possible to detect the detection object with high accuracy.

  FIG. 6 is an explanatory diagram illustrating an example of a headrest when the capacitive sensor according to the embodiment of the present invention is applied to a headrest position adjusting device for a seat. In the following description, the same reference numerals are assigned to portions that overlap the already described portions, and the description thereof is omitted. Description is omitted except for portions that are particularly related to the capacitance type sensor.

  The headrest position adjusting device is provided in a seat of a vehicle or the like, for example, and the sensor unit 10 including the sensor electrodes 11 to 15 and the guard electrodes 11a, 11b, 15a, and 15b disposed on the headrest 43 of the seat, and the seat, for example, And a drive motor portion disposed on the backrest portion. The sensor unit 10 and the drive motor unit are electrically connected by wire or wirelessly.

  The sensor unit 10 includes the sensor units 11 to 15 and guard electrodes 11a, 11b, 15a, and 15b (not shown in the figure) formed on one surface side of the substrate and, for example, the other surface side of the substrate. The sensor IC 21 is provided. And the electrostatic capacitance between the head (detection target object) of the human body seated on the seating part of the seat and the headrest 43 (specifically, the sensor electrodes 11 to 15) is detected.

  The sensor IC 21 detects a capacitance value based on the signals from the sensor electrodes 11 to 15, and the ECU 22 detects, for example, the output value of the signal among the sensor electrodes 11 to 15 based on the output from the sensor IC 21. The highest sensor electrode is detected, and headrest drive information corresponding to the detection result is output to the drive motor unit.

  The drive motor unit adjusts the position of the headrest to an appropriate position with respect to the head in accordance with the output from the ECU 22. Specifically, the position of the detected sensor electrode is adjusted so as to be directly opposite to the center position of the headrest in the height direction, or the position of the sensor electrode is positioned above the center position of the headrest. Or the headrest is adjusted to an appropriate position based on preset profile information of the head shape.

  The electrode structure such as the sensor electrode and the guard electrode of the capacitance type sensor according to the above-described embodiment may be as follows. FIG. 7 is an explanatory view showing another example of the electrode structure of the capacitive sensor according to one embodiment of the present invention, and FIG. 8 is an output corresponding to a change in the distance between the sensor electrode and the flat plate in the electrode structure. It is a figure which shows the variation | change_quantity.

  As shown in FIG. 7, the sensor electrodes 11 to 15 of this example are formed in a rectangular strip shape like the sensor electrodes 11 to 15 of the previous example, and are arranged in parallel on a substrate (not shown) along the short direction. Has been. And at least a part (for example, both ends along the longitudinal direction) around the sensor electrode (for example, the sensor electrodes 11 and 15) arranged outside the parallel arrangement direction among these sensor electrodes 11 to 15, For example, guard electrodes 11a, 11b, 15a, 15b formed in a non-contact state with the sensor electrodes 11, 15 are provided.

  Further, between the guard electrodes 11a, 11b, 15a, 15b and the sensor electrodes 11, 15, the guard electrodes 11aa, 11bb, 15aa, which are shorter in the width direction than the guard electrodes 11a, 11b, 15a, 15b, 15bb is provided.

  Furthermore, another guard electrode 12a is provided on at least a part of the periphery of the sensor electrodes 12 and 14 on the inner side (adjacent) of the sensor electrodes 11 and 15 in which these guard electrodes are formed on at least a part of the periphery. , 12b, 14a, 14b are formed. The area of these guard electrodes is larger than the guard electrodes 12a, 12b, 14a, 14b arranged around the sensor electrodes 12, 14, and the guard electrodes 11a, 11aa, 11b arranged around the sensor electrodes 11, 15. , 11bb, 15a, 15aa, 15b, 15bb are formed to be larger overall.

  The sensor electrode and the guard electrode include an area A of the sensor electrode 13 other than the sensor electrodes 11, 12, 14, 15 on which the guard electrode is formed, and a sensor on which the guard electrodes 12a, 12b, 14a, 14b are formed. An area A ′ obtained by adding the area of the guard electrodes to the area of the electrodes 12 and 14 and the area of the sensor electrodes 11 and 15 where the guard electrodes 11a, 11aa, 11b, 11bb, 15a, 15aa, 15b, and 15bb are formed. The area A ″ obtained by adding the areas of the guard electrodes is arranged and formed to be equal to each other as described above.

  FIG. 8 shows the result of the measurement performed under the same conditions as described above with reference to FIGS. 11 and 12 by the capacitance sensor in which the sensor electrode and the guard electrode are formed as described above. Thus, compared to the case shown in FIG. 12B, the difference in the change amount ΔL of the distance L is reduced as in the case shown in FIG.

  Specifically, according to this capacitance type sensor, for example, the point groups of the sensor outputs of the electrode numbers 1 to 5 at a place where the change ΔL is 60 mm to 75 mm have almost the same value. Therefore, similarly to the case shown in FIG. 5, even with the sensor electrode and guard electrode having this structure, even if the distance between the detection object and the sensor electrodes 11 to 15 is long, the detection object is accurate and highly accurate. And it becomes possible to measure the distance between the sensor electrodes 11-15, and to detect a detection target object with high precision.

  The electrode structure such as a sensor electrode and a guard electrode of this capacitive sensor may be as follows. FIG. 9 is an explanatory view showing still another example of the electrode structure of the capacitive sensor according to one embodiment of the present invention, and FIG. 10 is for the change in the distance between the sensor electrode and the flat plate in the electrode structure. It is a figure which shows output variation | change_quantity.

  As shown in FIG. 9, the sensor electrodes 11 to 15 of the present example have sensor electrodes 11, 12, 14, 15 and guard electrodes around them having the same structure as the example shown in FIG. 13 differs from the previous example in that it further includes a guard electrode.

  That is, at least around the sensor electrode 13 on the inner side in the juxtaposition direction than the sensor electrodes 12 and 14 on the inner side in the juxtaposition direction of the sensor electrodes 11 and 15 arranged outside the sensor electrode 11 to 15 in the juxtaposition direction. Guard electrodes 13a, 13aa, 13b, and 13bb are further formed in part. The guard electrodes 13aa and 13bb are provided such that the width in the short direction is shorter than the guard electrodes 13a and 13b.

  FIG. 10 shows the result of the measurement performed under the same conditions as described above with reference to FIGS. 11 and 12 by the capacitance sensor having the sensor electrode and the guard electrode formed as described above. Thus, compared with the case shown in FIG. 12B, the difference in the change amount ΔL of the distance L is reduced as in the case shown in FIGS.

  Therefore, similarly to the case shown in FIGS. 5 and 7, even with the sensor electrode and the guard electrode having this structure, even if the distance between the detection target and the sensor electrodes 11 to 15 is long, the accuracy and accuracy are high. It becomes possible to measure the distance between the detection object and the sensor electrodes 11 to 15 and detect the detection object with high accuracy.

  As described above, according to the capacitive sensor according to the above-described embodiment, the difference in the sensor output change amount due to the difference in the arrangement positions of the plurality of sensor electrodes 11 to 15 can be reduced. Thereby, the distance between a detection target object and a sensor can be measured correctly, and a detection target object can be detected with high accuracy.

It is explanatory drawing for demonstrating the example of the electrode structure of the capacitive sensor which concerns on one embodiment of this invention. It is a block diagram which shows the example of the whole structure of the electrostatic capacitance type sensor. It is a block diagram which shows the structural example of sensor IC of the electrostatic capacitance type sensor. It is an operation waveform diagram showing an example of an operation waveform of a sensor IC of the same capacitive sensor. It is a figure which shows the output variation | change_quantity with respect to the change of the distance between the sensor electrode and flat plate of the same capacitive sensor. It is explanatory drawing which shows the example of a headrest at the time of applying the electrostatic capacitance type sensor to the headrest position adjustment apparatus of a seat. It is explanatory drawing which shows the other example of the electrode structure of the electrostatic capacitance type sensor which concerns on one embodiment of this invention. It is a figure which shows the output variation | change_quantity with respect to the change of the distance between the sensor electrode and flat plate in the same electrode structure. It is explanatory drawing which shows the further another example of the electrode structure of the capacitive sensor which concerns on one embodiment of this invention. It is a figure which shows the output variation | change_quantity with respect to the change of the distance between the sensor electrode and flat plate in the same electrode structure. It is a figure which shows the sample structure about the experiment which the present applicant conducted. It is a figure which shows the experimental result about the experiment which the present applicant conducted.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Sensor part, 11-15 ... Sensor electrode, 11a, 11aa, 11b, 11bb, 12a, 12b, 13a, 13aa, 13b, 13bb, 14a, 14b, 15a, 15aa, 15b, 15bb ... Guard electrode, 20 ... Switching 21 ... sensor IC, 22 ... ECU, 43 ... headrest.

Claims (11)

A capacitance type sensor that detects a capacitance between a detection object and a detection object in a detection region,
A plurality of sensor electrodes arranged side by side on the substrate;
And a guard electrode formed on at least a part of the periphery of the sensor electrode disposed at least on the outer side in the juxtaposition direction among the plurality of sensor electrodes.   A guard electrode is further formed on at least a part of the periphery of the inner sensor electrode adjacent to the sensor electrode on which the guard electrode is formed on at least a part of the periphery, and the area of the guard electrode is outside of the juxtaposed direction. 2. The capacitive sensor according to claim 1, wherein the capacitance sensor is formed so as to be larger.   The area of the sensor electrode other than the sensor electrode in which the guard electrode is formed on at least a part of the periphery, and the area obtained by adding the area of the guard electrode to the area of the sensor electrode in which the guard electrode is formed on at least a part of the periphery The capacitance type sensor according to claim 1, wherein the capacitance type sensors are arranged so as to be equivalent to each other.   The capacitive sensor according to claim 1, wherein each of the plurality of sensor electrodes is driven by being given a sensor potential or a guard potential equivalent to the sensor potential. A detection circuit for detecting a capacitance value of the detection object based on outputs from the plurality of sensor electrodes;
The detection circuit is configured to switch the sensor potential or the guard potential applied to the plurality of sensor electrodes, and to apply the sensor potential or the guard potential to the plurality of sensor electrodes via the switching unit. 5. The capacitance type sensor according to claim 4, further comprising detection means for detecting the capacitance value detected by the step.   The switching means, when the sensor potential is applied to one sensor electrode of the plurality of sensor electrodes, switches so that the guard potential is applied to another sensor electrode. 5. The capacitive sensor according to 5.   The capacitive sensor according to claim 1, wherein at least five of the plurality of sensor electrodes are provided.   The electrostatic capacitance according to any one of claims 1 to 7, wherein the plurality of sensor electrodes are formed in a rectangular strip shape and are arranged in parallel on the substrate along a short direction thereof. Type sensor.   9. The static according to claim 5, wherein the detection unit detects the capacitance values from the plurality of sensor electrodes in order from one side to the other side in the juxtaposed direction. Capacitive sensor.   The detecting means detects the capacitance values from the plurality of sensor electrodes from one side of the parallel arrangement direction to the other in the odd numbered order or even numbered order, and further detects the electrostatic capacity value in the even numbered order or odd numbered order. 8. The capacitive sensor according to claim 7, wherein:   The capacitance type sensor according to claim 5, wherein the switching unit includes a plurality of FETs, a plurality of analog switches, or a plurality of multiplexers.

Images