JP2019203737A - Capacitance sensor - Google Patents

Abstract

To provide a capacitance sensor which can lower the detection accuracy of one electrode surface of a detection electrode without involving reduction in the detection accuracy of the other electrode surface.SOLUTION: A capacitance sensor 10 includes: a detection electrode 20 having a first electrode surface 21 as a front surface and a second electrode surface 22 as a back surface; a non-grounded electrode 30 facing the second electrode surface 22 across a space; a control circuit 40 for supplying pulse signals SG1, SG2 with the same phase to each of the detection electrode 20 and the non-grounded electrode 30; and a detection circuit 50 for outputting an output signal which changes according to changes in the capacitance formed between the first electrode surface 21 and a human body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a capacitance sensor.

  As a mechanism for locking and unlocking a door of a vehicle, a mechanism using a capacitance sensor that detects that a user has contacted the inside of a door handle through a change in capacitance between the user and a detection electrode is known. ing. In this type of capacitance sensor, since there is sensitivity on both sides of the detection electrode (for example, the electrode surface facing the inside of the door handle and the electrode surface facing the outside), a user who does not intend to lock and unlock the door can handle the door handle. Even when the outer side of the door is touched, a change in electrostatic capacitance between the user and the detection electrode may be detected, and the door may be erroneously locked and unlocked. In view of such circumstances, Japanese Patent No. 3614789 proposes a door handle including a ground electrode for lowering the detection sensitivity of the electrode surface facing the outside of the door handle out of both surfaces of the detection electrode of the capacitance sensor. .

Japanese Patent No. 3614789

  However, when such a ground electrode is provided, there is a problem that the detection sensitivity of the electrode surface facing the inside of the door handle out of both surfaces of the detection electrode of the capacitance sensor is also lowered.

  Accordingly, the present invention proposes a capacitance sensor that solves such a problem and can lower the detection sensitivity of the other electrode surface without lowering the detection sensitivity of one of the detection electrodes. The task is to do.

  In order to solve the above-described problem, a capacitance sensor according to the present invention includes a detection electrode having a first electrode surface and a second electrode surface that is the back surface of the first electrode surface, and a distance so as to face the second electrode surface. A non-grounded electrode disposed with a gap therebetween, a control circuit for supplying a pulse signal having the same phase to each of the detection electrode and the non-grounded electrode, and a capacitance formed between the first electrode surface and the human body And a detection circuit that outputs an output signal that changes in accordance with the change.

  According to the capacitance sensor according to the present invention, the detection sensitivity of the second electrode surface can be lowered without lowering the detection sensitivity of the first electrode surface of both surfaces of the detection electrode.

It is a schematic block diagram of the electrostatic capacitance sensor in connection with embodiment of this invention. It is a circuit diagram of a capacitance sensor according to an embodiment of the present invention. It is a graph which shows the relationship between the pulse signal in connection with embodiment of this invention, and the electric potential of a detection electrode. It is a graph of the output signal concerning embodiment of this invention. It is a graph which shows the relationship between the electric potential of the detection electrode in connection with embodiment of this invention, and an output signal. It is a graph which shows the relationship between the electric potential of the detection electrode in connection with embodiment of this invention, and an output signal. It is a graph which shows the result of the comparison experiment of the detection sensitivity of the electrostatic capacitance sensor in connection with this embodiment, and the detection sensitivity of the conventional electrostatic capacitance sensor. It is a graph which shows the comparison result of the detection sensitivity of the 1st electrode surface, and the detection sensitivity of the 2nd electrode surface in the capacitance sensor concerning this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the same code | symbol shall show the same component, and the overlapping description is abbreviate | omitted.
FIG. 1 is a schematic configuration diagram of a capacitance sensor 10 according to an embodiment of the present invention. The capacitance sensor 10 includes a detection electrode 20, a non-grounded electrode 30, a control circuit 40, and a detection circuit 50. The detection electrode 20 has a first electrode surface 21 and a second electrode surface 22 which is the back surface thereof. Here, the 1st electrode surface 21 is an electrode surface used for the detection of the change of the electrostatic capacitance formed between human bodies, and can also be called a detection surface. On the other hand, the second electrode surface 22 is an electrode surface that is not used for detecting a change in capacitance formed between the body and the human body, and can also be referred to as a non-detection surface. When using the capacitance sensor 10 as a mechanism for locking and unlocking the door of the vehicle, the first electrode surface 21 is positioned so as to face the inside of the door handle, for example, and the second electrode surface 22 is For example, you may position so that it may face the outer side of a door handle. The non-grounded electrode 30 is arranged in parallel with a gap between the non-ground electrode 30 and the second electrode surface 22 so as to face the second electrode surface 22. The control circuit 40 supplies the pulse signal SG1 to the detection electrode 20 and supplies the pulse signal SG2 to the non-grounded electrode 30. The detection circuit 50 outputs an output signal V1 that changes according to a change in capacitance formed between the first electrode surface 21 and the human body. The control circuit 40 detects the approach of the human body to the first electrode surface 21 based on the output signal V1.

  The control circuit 40 includes an output terminal OUT that outputs the pulse signals SG1 and SG2, an input terminal IN that receives the output signal V1, and a control terminal CTL. The function of the control terminal CTL will be described later.

  FIG. 2 is a circuit diagram of the capacitance sensor 10. The signal line S1 from the output terminal OUT is connected to the detection electrode 20 through the diode element D and the detection circuit 50. The signal line S2 branches from the signal line S1 and is connected to the non-ground electrode 30 on the anode side of the diode element D. The phase of the pulse signal SG1 supplied to the detection electrode 20 through the signal line S1 is the same as the phase of the pulse signal SG2 supplied to the non-grounded electrode 30 through the signal line S2. The detection circuit 50 includes a resistance element R and a capacitance element C. One end of the resistor element R is branched and connected to the signal line S1 on the cathode side of the diode element D, and the other end is connected to one end of the capacitor element C. The other end of the capacitive element C is connected to a frame ground (for example, a vehicle body). A signal line S3 from the input terminal IN and a signal line S4 from the control terminal CTL are connected to a connection point between the resistance element R and the capacitance element C.

  The capacitance formed between the detection electrode 20 and the non-ground electrode 30 is Cp, and the capacitance formed between the first electrode surface 21 of the detection electrode 20 and the signal ground is Cst1. The capacitance formed between the first electrode surface 21 of the detection electrode 20 and the human body is Cst2, the charge amount of the detection electrode 20 is Q, the potential of the detection electrode 20 is V0, and the pulse signal SG1, The voltage at the high level of SG2 is V, and the ON voltage of the diode element D is Vf. The output signal V1 indicates the potential at the connection point between the resistance element R and the capacitance element C.

Next, the operation of the capacitance sensor 10 will be described with reference to FIGS. 3 to 6.
FIG. 3 is a graph showing the relationship between the pulse signal SG1 and the potential V0. The horizontal axis of this graph represents time, and the vertical axis represents potential. When the pulse signal SG1 is at a high level (for example, 3V), the detection electrode 20 is charged with the charge Q, and the capacitive element C is charged through the resistance element R. At this time, the pulse signal SG2 supplied to the non-ground electrode 30 is also at a high level, and the voltage between the detection electrode 20 and the non-ground electrode 30 is equal to Vf, so that the electrostatic capacitance between these electrodes is charged. The amount of charge (Cp × Vf) is negligibly small compared to Q. For this reason, Q can be approximated as in equation (1).

Q = (V−Vf) × (Cst1 + Cst2) (1)

  When the pulse signal SG1 changes from a high level to a low level (for example, 0 V), a part of the charge Q moves to the capacitance between the detection electrode 20 and the non-grounded electrode 30, and the potential V0 decreases. The potential V0 at this time can be obtained from the equation (2).

V0 = Q / (Cst1 + Cst2 + Cp) (2)

  Since Cst1 and Cp may be considered to be constant, the potential V0 changes according to the change in the capacitance Cst2 formed between the first electrode surface 21 of the detection electrode 20 and the human body. For example, in FIG. 3, V0 (approach) indicates the potential V0 when the human body approaches the first electrode surface 21 of the detection electrode 20, and V0 (non-approach) indicates the first electric potential of the detection electrode 20 by the human body. The electric potential V0 when not approaching the electrode surface 21 is shown.

  FIG. 4 is a graph of the output signal V1. The horizontal axis of this graph represents time, and the vertical axis represents potential. Charging / discharging of the capacitive element C is performed according to the magnitude relationship between the potential at the connection point between the resistance element R and the capacitive element C and the potential V0. As a result, the output signal V1 changes according to the change in the capacitance Cst2 formed between the first electrode surface 21 of the detection electrode 20 and the human body. For example, in FIG. 4, V <b> 1 (approach) indicates an output signal V <b> 1 when the human body approaches the first electrode surface 21 of the detection electrode 20, and V <b> 1 (non-approach) indicates the first of the detection electrode 20. The output signal V1 when not approaching the electrode surface 21 is shown. If the difference between V1 (approach) and V1 (non-approach) is ΔV, the detection sensitivity is higher as ΔV is larger. For example, the control circuit 40 compares ΔV with a threshold value, and can detect whether or not a human body is approaching based on the magnitude relationship.

  5 and 6 are graphs showing the relationship between the potential V0 and the output signal V1. As shown in FIG. 5, when the potential V0 is higher than the output signal V1, a charging current flows from the detection electrode 20 to the capacitive element C. On the other hand, as shown in FIG. 6, when the potential V0 is lower than the output signal V1, a discharge current flows from the capacitive element C to the detection electrode 20. In this way, the output signal V1 converges to a value proportional to Cst2. Note that the charge of the capacitor C may be discharged through the control terminal CTL when the number of pulses of the pulse signal SG1 supplied to the detection electrode 20 reaches a predetermined number.

  FIG. 7 shows the result of a comparison experiment between ΔV that is an index of detection sensitivity of the capacitance sensor 10 according to the present embodiment and ΔV that is an index of detection sensitivity detection sensitivity of the conventional capacitance sensor. The conventional capacitance sensor is provided with a ground electrode instead of the non-ground electrode 30, and a pulse signal having the same phase is not supplied to the ground electrode. In this experiment, a 20 mm × 84 mm copper tape was used as the ungrounded electrode 30. In addition, as the ground electrode of the conventional capacitance sensor, the same size and the same material as the non-ground electrode 30 were used.

  The horizontal axis in FIG. 7 indicates the distance between the detection electrode 20 and the finger, and the vertical axis indicates ΔV. Reference numerals 701 to 703 denote ΔV of the capacitance sensor 10 according to the present embodiment. In particular, reference numeral 701 indicates ΔV that changes according to the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 1 mm. Reference numeral 702 indicates ΔV that changes according to the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 2 mm. Reference numeral 703 indicates ΔV that changes according to the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 3 mm.

  On the other hand, reference numerals 704 to 706 denote ΔV of the conventional capacitance sensor. In particular, reference numeral 704 indicates ΔV that changes according to the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the ground electrode is set to 1 mm. Reference numeral 705 indicates ΔV that changes according to the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the ground electrode is set to 2 mm. Reference numeral 706 indicates ΔV that changes in accordance with the distance between the detection electrode 20 and the finger when the distance between the detection electrode 20 and the ground electrode is set to 3 mm. Reference numeral 707 denotes ΔV of a conventional capacitance sensor that does not include the non-ground electrode 30 and the ground electrode.

  From the experimental results shown in FIG. 7, it can be seen that the detection sensitivity of the capacitance sensor 10 according to the present embodiment is higher than the detection sensitivity of a conventional capacitance sensor including a ground electrode.

  FIG. 8 shows a comparison result between ΔV that is an index of detection sensitivity of the first electrode surface 21 and ΔV that is an index of detection sensitivity of the second electrode surface 22 in the capacitance sensor 10 according to this embodiment. Indicates.

  The horizontal axis in FIG. 8 indicates the distance between the detection electrode 20 and the finger, and the vertical axis indicates ΔV. Reference numerals 801 to 803 denote ΔV that is an index of detection sensitivity of the first electrode surface 21. In particular, reference numeral 801 denotes ΔV that changes according to the distance between one index finger and the first electrode surface 21 when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 1 mm. Show. Reference numeral 802 indicates ΔV that changes according to the distance between one index finger and the first electrode surface 21 when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 2 mm. Reference numeral 803 indicates ΔV that changes in accordance with the distance between one index finger and the first electrode surface 21 when the distance between the detection electrode 20 and the non-ground electrode 30 is set to 3 mm.

  On the other hand, reference numerals 804 to 806 denote ΔV that is an index of detection sensitivity of the second electrode surface 22. In particular, reference numeral 804 changes according to the distance between the four fingers excluding the thumb and the second electrode surface 22 when the distance between the detection electrode 20 and the non-grounded electrode 30 is set to 1 mm. ΔV to be shown. Reference numeral 805 denotes ΔV that changes according to the distance between the four fingers excluding the thumb and the second electrode surface 22 when the distance between the detection electrode 20 and the non-ground electrode 30 is set to 2 mm. Indicates. Reference numeral 806 denotes ΔV that changes according to the distance between the four fingers excluding the thumb and the second electrode surface 22 when the distance between the detection electrode 20 and the non-ground electrode 30 is set to 3 mm. Indicates.

  From the experimental results shown in FIG. 8, it can be seen that the detection sensitivity of the detection surface 21 for one index finger is sufficiently higher than the detection sensitivity of the non-detection surface 22 for four fingers excluding the thumb. Thus, it can be seen that the detection sensitivity of the second electrode surface 22 can be lowered to a practically sufficient level without reducing the detection sensitivity of the first electrode surface 21.

  According to the capacitance sensor 10 according to the embodiment of the present invention, in-phase pulse signals SG1 and SG2 are supplied to the detection electrode 20 and the non-grounded electrode 30, respectively, and between the first electrode surface 21 and the human body. By obtaining an output signal that changes in accordance with a change in the capacitance that is formed, the detection sensitivity of the second electrode surface 22 that faces the non-grounded electrode 30 is reduced without reducing the detection sensitivity of the first electrode surface 21. Can be lowered to a practically sufficient level.

  Note that this embodiment is intended to facilitate understanding of the present invention and is not intended to limit the present invention. The present invention can be changed / improved without departing from the spirit thereof, and the present invention includes equivalents thereof. For example, a single circuit having the function of the control circuit 40 and the function of the detection circuit 50 may be used in place of the control circuit 40 and the detection circuit 50.

DESCRIPTION OF SYMBOLS 10 ... Capacitance sensor 20 ... Detection electrode 21 ... 1st electrode surface 22 ... 2nd electrode surface 30 ... Ungrounded electrode 40 ... Control circuit 50 ... Detection circuit

Claims (1)

A detection electrode having a first electrode surface and a second electrode surface which is the back surface thereof;
A non-grounded electrode disposed at a distance so as to face the second electrode surface;
A control circuit for supplying in-phase pulse signals to each of the detection electrode and the non-grounded electrode;
A detection circuit that outputs an output signal that changes in accordance with a change in capacitance formed between the first electrode surface and the human body;
A capacitance sensor comprising: