JP2002039708A - Capacitance type proximity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sensor which detects surely approach of an object and a sensor constitution capable of coping with low cost and miniaturization. SOLUTION: In this capacitance type proximity sensor, approach of an object 9 to a sensor electrode 19 is detected on the basis of change of capacitance by using a resonance circuit 15. Electrode capacitance Cs of the sensor electrode 19 and capacitance Ci which a resonance circuit has are made resonance capacitance C. The resonance capacitance C and a resonance inductor L are connected in series, and the series resonance circuit 15 having resonance frequency fr is formed. When the series resonance circuit 15 is made to resonate at an exciting frequency f0, it is set higher than the resonance frequency fr, and the object 9 is detected on the basis of resonance voltage Vr of the series resonance circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a resonance circuit,
The present invention relates to a capacitance type proximity sensor that detects an approach of an object to a sensor electrode based on a change in capacitance between the object and the sensor electrode.

[0002]

2. Description of the Related Art Conventionally, this type of capacitance type sensor has
At least two sensor electrodes are provided, one sensor electrode is grounded, the other sensor electrode is connected to a resonance circuit, and the sensor electrodes are resonated in a constant oscillation state. In this state, when an object (a person or an obstacle, for example, a person is approached) approaches the sensor electrode that performs sensing, the capacitance Cfe between the person and the sensor electrode is increased. Formed and its capacitance Cfe is greater than the capacitance Ce when a person is not near the sensor electrode. As a result, a resonance voltage (also referred to as an oscillation level) of an oscillation circuit that resonates due to a change in capacitance changes. Therefore, the approach of a person can be detected by detecting a change in the resonance voltage. Such a proximity sensor,
For example, it is disclosed in JP-A-10-48345.

An oscillation circuit (resonant circuit) usually composed of LC
Because the LC resonance phenomenon is used, the characteristics (for example, Q value) of the oscillation circuit vary due to environmental changes (for example, temperature changes) and component tolerances. Voltage) to maintain the sensor performance by adding a temperature compensation circuit or internal adjustment circuit to the oscillation circuit, making corrections with such a temperature compensation circuit or internal adjustment circuit, stabilizing the oscillation state, and maintaining the sensor performance. are doing.

[0004]

However, when the oscillation level changes due to the temperature change or the like in the oscillation circuit as described above, the oscillation state is maintained at a predetermined oscillation state. Even if the oscillation state fluctuates, the object must be reliably detected and the sensor performance must be prevented from deteriorating.

Further, as described above, the method of maintaining the resonance voltage by using the temperature compensation circuit and the internal adjustment circuit complicates the circuit and increases the size of the sensor circuit, resulting in cost reduction and miniaturization. Can not respond.

Therefore, the present invention has been made in view of the above-mentioned problems, and it is intended to reliably detect the approach of an object,
Further, it is a technical object to provide a sensor configuration which can cope with cost reduction and miniaturization.

[0007]

The technical means taken to solve the above-mentioned problem is to use a resonance circuit to detect the approach of an object to a sensor electrode and to detect the static between the object and the sensor electrode. In a capacitance type proximity sensor that detects based on a change in capacitance, a capacitance of the resonance circuit including an electrode capacitance of a sensor electrode is defined as a resonance capacitance, and the resonance capacitance and a resonance inductor are connected in series to change a resonance frequency fr. Forming a series resonance circuit having a resonance frequency at the excitation frequency f0, the excitation frequency f0 is changed to the resonance frequency fr.
The object is detected at a higher setting based on the resonance voltage of the series resonance circuit.

According to this, the resonance frequency fr of the resonance circuit is
As an object (for example, a person or an obstacle) approaches a sensor electrode, a change in capacitance between the object and the sensor electrode occurs. In this case, since the capacitance is formed between the object and the sensor electrode, the capacitance increases as compared to a case where the object does not exist near the sensor electrode. As a result, the resonance frequency fr (= 1 / (2π√LC)) of the resonance circuit shifts to a lower frequency (fr ′) as the capacitance increases. In this case, when f0 <fr '<fr, the resonance voltage Vr at the excitation frequency f0 increases, and when the frequency f' shifts to the lower frequency side, the resonance at the excitation frequency f0 when fr '<f0 <fr. The voltage will decrease. For this reason, if the range of the excitation frequency f0 is not determined, the oscillation voltage will increase or decrease depending on the approaching state of the object to the sensor electrode.
Is set to be higher than the resonance frequency fr,
fr '<fr <f0, and the resonance voltage only decreases when the object approaches the sensor electrode. Therefore, it is possible to reliably detect the approach of the object, thereby improving the sensor performance.

In this case, if the object is detected based on the change in the resonance voltage, it is possible to reliably detect the object from the state in which the resonance voltage changes as the object approaches the sensor electrode. .

Further, if the resonance voltage is detected, and the detected detection voltage is differentiated to detect an object based on a change in the detection voltage, the AC component can be converted into a DC component by detecting the resonance voltage. By performing the conversion and differentiating the detection voltage of the detected DC component, the movement of the object with respect to the sensor electrode can be detected, and the approaching state (change) of the object can be accurately detected. This enables the detection to be performed by a simple differentiating circuit, and a change accompanying the approach of an object can be found by differentiating the detection voltage. In addition, even if the Q value of the resonance circuit changes due to an environmental change or the like, the change due to the differentiation of the detection voltage is not affected, and only the change in the resonance circuit is detected, so that the correction by fine adjustment of the resonance voltage can be performed. Since the object can be detected even without the above, a temperature compensating circuit and an adjusting circuit are not required unlike the related art, and a sensor configuration that can be reduced in size, reduced in cost, and simplified can be provided. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system block diagram when the capacitance type proximity sensor of the present invention is applied to a keyless entry system (also referred to as a smart entry system) 1 of a vehicle. In this system 1, a user, for example, a driver carries a portable device 60 called a remote controller,
When approaching or leaving the vehicle, the vehicle door 3
The locking / unlocking of the door lock device (door lock unit 44) does not require an operation door opening / closing operation by a vehicle key, and the vehicle door 3 is based on communication between the vehicle side and the portable device 60 and on human intention. The operation such as locking / unlocking can be performed.

In this system 1, the vehicle has two external / internal antennas, a first transmitting antenna 10 and a second transmitting antenna 33 for communicating with the outside of the vehicle. The first transmitting antenna 10 is provided in a door handle 2 provided on the vehicle door 3, and the second transmitting antenna 33 is provided in an instrument panel in a vehicle compartment. First transmitting antenna 10
Is connected to the first transmitting unit 34, the second transmitting antenna 33 is connected to the second transmitting unit 36, and both the transmitting units 34 and 36 are connected to the controller 20 which controls the control. The controller 20 has a sensor electrode 1 for detecting the approach of an object (here, a person) to the vehicle door 3.
9 and a sensor detector 18 for detecting a person based on information from the sensor electrode 19 are connected. Sensor detector 1
8 and the first transmission unit 34 may be provided separately, but in the present embodiment, they are integrated and constitute an outside-vehicle transmitter 31 for transmitting a signal outside the vehicle.

The controller 20 includes a first transmitting unit 34 and a second transmitting unit 34.
The first request signal (out-of-vehicle request signal) and the second request signal (in-vehicle request signal) are transmitted to the transmission unit 36, respectively. This code is modulated, for example, 1
A request signal of 34 KHz transmits an outside request signal and an indoor request signal from the first transmitting antenna 10 and the second transmitting antenna 33 to a portable device 60 called a remote controller carried by the driver when the driver gets on the vehicle.

Further, the vehicle is provided with a receiving antenna 35, and the receiving antenna 35 receives the ID information signal output from the portable device 60. For example, a 300 MHz signal output from the portable device 60 is transmitted to the vehicle-side receiving unit 2.
4, demodulated and input to the controller 20. The controller 20 has a function of storing a code such as a first code for door lock, a second code for starting the engine, and an ID code of a transponder in the memory 26 even when the power is turned off.

An operation detecting section 28 connected to the controller 20 detects a switch operation such as an ignition, and a door opening / closing detecting section 30 typified by a courtesy SW or the like detects opening / closing of a door. The sensor group 32 detects the vehicle speed and the opening / closing of windows by various sensors.

The controller 20 also includes a steering lock unit 40 capable of mechanically locking and prohibiting the steering operation, and an immobilizer unit 42 for prohibiting fuel supply to the engine and prohibiting an ignition operation in case of unauthorized use. And a door lock unit 44 typified by a door lock device that locks or unlocks all doors. Further, the controller 20 includes an engine control unit 4 that performs engine control of the engine 50 of the vehicle.
8 are connected.

FIG. 2 shows a portable device 60 used in the present system 1.
FIG. The portable device 60 includes a transmitting antenna 62 for transmitting a signal at 300 MHz to the vehicle and a receiving antenna 64 for receiving an ID request signal of 134 KHz transmitted from the vehicle.
8 is connected to a transmission / reception circuit 66 connected to the transmission / reception circuit 8.

When a request signal (out-of-vehicle request signal) of 134 kHz from a vehicle-mounted device of the vehicle received by the receiving antenna is received, the signal is demodulated by a transmission / reception circuit 66 and input to a controller 68. The controller 68 includes a first code including ID information stored in the memory 70,
The second code is transmitted to the transmission / reception circuit 66, and the transmission / reception circuit 66
And transmitted as a 300 MHz signal from the transmitting antenna 62 to the vehicle-mounted device.

An ID request signal having a frequency of 134 KHz is transmitted from the first transmitting antenna 10 and the second transmitting antenna of the vehicle-mounted device, and the portable device 60 carried by the user (particularly, the driver) transmits these request signals. Upon receipt,
A signal having a frequency of 300 MHz obtained by modulating the first and second codes including the ID information according to the received signal is returned as an acknowledge signal. The receiving antenna 35 is attached to an inner mirror in the vehicle, and a 300 MHz signal from the portable device 60 received by the receiving antenna 35 is demodulated by the receiving circuit 24 and input to the controller. 2 codes can be received.

Next, the door handle 2 attached to the vehicle door 3 will be described with reference to FIGS.
The door handle 2 is attached to the vehicle door 3 so as to protrude outward from the metal door in the vehicle width direction. The door handle 2 can open and close the vehicle door 3 by grasping the central grip portion GP with a hand and operating the door handle 2 in the opening direction in the vehicle width direction. FIG. 3 shows an outline in which an antenna (first transmitting antenna) 10 called a two-axis loop antenna is provided in the door handle 2, and a specific configuration thereof is shown in FIG. In the present embodiment, the door handle 2 is described as a grip-type handle, but is not limited to this.

In the explanatory view of FIG. 3, a two-axis antenna 10 in two directions whose winding directions are orthogonal to each other and a resonance capacitance for giving resonance to the antenna 10 are set to 1 in the door handle 2.
It is arranged in an elongated resin case 5 having an opening on its surface. When the antenna 10 is disposed in the case as shown in FIG. 3, power is supplied to the antenna 10 through the hole 2 provided at the rear (right side in FIG. 3) of the grip GP of the door handle 2.
Via ba, it is connected to an external transmitter 31 arranged between the vehicle door 3 and the door panel, and functions as a two-axis antenna by supplying power to the antenna 10. In addition, as for a specific coil winding method and antenna configuration of the antenna 10 used in the present embodiment, a known technique disclosed in Japanese Patent Application Laid-Open No. H11-340734 proposed by the present applicant is adopted.

The door handle 2 includes a door handle 2.
Sensor electrode 1 having a substantially U-shape for detecting the approach of a person to a vehicle
9 are provided. The sensor electrode 19 has a generally U-shaped tuning fork shape elongated in the horizontal direction. The sensor electrode 19 is made of a non-magnetic material such as copper or brass and has good conductivity. The size of the electrode on the open end side of the sensor electrode 19 in the width direction is the width of the electrode on the way to the open end. It is larger than the size. By forming a space in the middle part of the sensor electrode 19 in this manner, 1
When the antenna 10 and the sensor electrode 19 are disposed facing each other in the two door handles 2, the outward radiation characteristics of the antenna 10 can be hardly hindered by the shape of the sensor electrode 19. Therefore, it is possible to fly a signal (for example, an ID request signal or the like) from the antenna 10 to the portable device 60 outside the vehicle far away.

An end 19a opposite to the open end of the sensor electrode 19 has a terminal shape with a hole in the center so that the end of the harness 7 connected to the sensor detector 18 is connected. I have. The sensor electrode 19 has a substantially U-shaped portion (sensor portion) SEN and a root portion of an end portion 19a extending from the center of the U-shaped portion, where the sensor electrode 19 is affected by raindrops or the like, and corrosion or the like occurs. However, it is covered with a film (not shown) so that the detection sensitivity as a human sensor does not deteriorate.

The harness 7 is connected to the sensor electrode 19 by fixing means such as caulking or soldering. The harness 7 extending from the sensor electrode 19 is also connected to the rear part of the grip portion GP of the door handle 2 (FIG. (Right side shown in FIG. 2) is connected to the sensor detection unit 18 of the external transmitter 31 via a hole 2ba provided on the right side.

The door handle 2 is provided behind the vehicle door 3 which is opened and closed when getting on and off.
a to open and close the grip portion GP with the arm 2b extending continuously from the inner side of the vehicle door 3 as an axis.
The vehicle door 3 can be opened and closed.

The door handle 2 has a base portion 2a, and has a shape that is gradually curved toward the front portion for the purpose of improving the design surface. The door handle 2 is made of metal (for example, zinc or the like) in order to have strength.
The outer surface is plated with chrome or the like. The metal door handle 2 has an opening 32 on the outside (in the direction of being outside during mounting), and the antenna 10 is disposed therein. The antenna 10 disposed in the door handle is entirely covered with the resin door handle cover 2c so that the antenna function is not affected even if the opening 32 is exposed to wind and rain.

Next, the configuration of the sensor electrode 19 attached to the grip portion GP of the door handle 2 and the configuration of the sensor detecting section 18 of the outside transmitter will be described with reference to FIG.
Here, assuming that the capacitance of the sensor electrode 19 is the electrode capacitance Cs, a circuit formed by LC shown in FIG. 5 (the inductance L of the resonance inductor 16, the capacitance Cs of the sensor electrode 19, and the sensor detection in the transmitter outside the vehicle) When the total capacitance of the capacitance (adjustment capacitance) Ci of the section 18 is defined as the resonance capacitance C, the resonance capacitance C (= Cs + Ci) and the resonance inductor 16
Are connected in series, so that a series resonance circuit (simply called a resonance circuit) 15 having a resonance frequency fr is formed. The resonance circuit 15 can obtain a desired resonance frequency fr by arbitrarily adjusting the adjustment capacitance Ci of the sensor detector 18.

In the present embodiment, the resonance circuit 15
Is grounded, and the other resonance inductor 1 is grounded.
The oscillator OSC is connected to the coil end of the excitation frequency f
A method of resonating at 0 (for example, 134 KHz) is adopted.

A resonance voltage V having an AC component due to resonance is provided between the resonance inductor L and the resonance capacitor C of the resonance circuit 15.
Although r is generated, a detection circuit 14 for detecting and converting this resonance voltage into a DC component is connected, and a differentiator 13 for detecting a change state of the detection voltage Va is connected to an output of the detection circuit 14. One terminal (non-inverting input terminal) of the comparator 21 is connected to the output of the differentiator 13, and the other terminal (inverting input terminal) of the comparator 21 is connected to the reference voltage 22. Therefore, when the output voltage Vb of the differentiator 13 is higher than the reference voltage Vc, the output is switched from a low level to a high level, and the output voltage Vb of the differentiator 13 is changed to the reference voltage Vc.
If it is lower than the threshold, the level is switched from the high level to the low level, and the output signal from the comparator 21 becomes a sensor signal.

Therefore, in the present system 1, the approach of the person 9 having the portable device 60 to the vehicle door 3 can be detected by the sensor electrode 19 provided on the door handle 2. For example, when the person 9 opens the vehicle door 3 in the open state, the approach of the person can be detected by changing the capacitance by the operation of gripping the grip portion GP of the door handle 2 (hand approach). . Normally, when the vehicle door 3 is to be opened, the person 9 approaches the grip portion GP, grasps the grip portion GP of the door handle 2, pulls the grip portion GP outward, and operates in the opening direction. In this case, the operation of opening the vehicle door 3 is performed. In this case, the total sum between the metal door handle 2 and the sensor electrode 19 and between the sensor electrode 19 and an infinite extension line of the sensor electrode 19 are calculated. Increases due to the approach of the person 9. That is, when a person (usually a finger or a palm) 9 approaches the sensor electrode 19, the capacitance is newly added to the person 9 and the sensor electrode 19 as compared with the case where the person 9 is not near the sensor electrode 19. Is added. Thus, the distance between the person 9 and the sensor electrode 19 gradually decreases with the approaching operation of the sensor electrode 19,
The capacitance between the person 9 and the sensor electrode 19 gradually increases, and a capacitance change occurs.

On the other hand, the resonance circuit 15 composed of LC maintains a constant oscillation at the resonance frequency fr (= 1 / (2π√LC)) and at a predetermined resonance voltage Vr when the person 9 is not nearby. ing. However, when the person 9 approaches, the capacitance C increases as described above. As a result, the resonance frequency fr shifts to fr 'to a frequency lower than fr. In this case, if the state of approach to the sensor electrode 19 is sudden, the resonance frequency f
The transition change of r is large and instantaneously transitions to fr '.

In this case, the resonance frequency fr becomes fr ', but as shown in FIG. 6A, when f0 <fr'<fr, the resonance voltage Vr at the excitation frequency f0 increases.
On the other hand, as shown in FIG. 6B, fr '<f0 <fr
In this case, the resonance voltage at the excitation frequency f0 decreases. Therefore, when the relationship between the resonance frequency fr of the resonance circuit 15 and the excitation frequency f0 is not defined, the approach of the person 9 to the sensor electrode 19 as shown in FIGS. Accordingly, the oscillation voltage Vr increases or decreases, but in the present embodiment, the excitation frequency f0 is set to be higher than the resonance frequency fr, as shown in FIG. 6C.

That is, if the condition of fr '<fr <f0 is set, the oscillation voltage Vr will be
Only decreases when approaching.

Therefore, when the person 9 approaches the sensor electrode 19, the resonance voltage Vr of the AC component changes (decreases). When the change in the resonance voltage Vr is detected by the detection circuit 14 and converted into a DC component, the person 9 The change accompanying the operation appears as a change in the DC component. If the DC change is differentiated by the differentiating circuit 13, the signal change can be amplified at the timing when the motion of the person 9 changes, and the change state can be detected reliably. Further, by passing the amplified change through the comparator 21, a reference level is set, and the approach level of the person 9 can be detected using the level as a criterion for detecting a person (see FIG. 7). .

Thus, the approach of the person 9 (here,
When detecting the door opening operation based on human intention), the controller 20 provides a door lock release signal to the door lock unit 44 when the vehicle is in the door locked state, and operates the unlocking operation by the vehicle key. Instead, the vehicle door 3 can be automatically unlocked and the open state can be permitted.

As described above, in the present embodiment, in order to detect a simple change in the resonance level, the detection circuit 14, the differentiation circuit 13, and the comparator 21 are inexpensive and have a simple configuration.
, The person 9 can be detected. This means that even if the Q value of the resonance circuit changes due to an environmental change or the like, it is not affected by the change due to the differentiation of the detection voltage, and only the change in the resonance circuit can be detected. The state in which the person 9 approaches is described with respect to 19; however, the state is not limited to the person 9, but may be an animal, an obstacle, an object, or the like other than the person.

[0037]

According to the present invention, since the excitation frequency f0 is set to be higher than the resonance frequency fr, the resonance voltage only decreases when the object approaches the sensor electrode. Detection can be performed reliably, and sensor performance is improved.

In this case, if the object is detected based on the change in the resonance voltage, the object can be reliably detected from the state in which the resonance voltage changes as the object approaches the sensor electrode.

Further, by detecting the resonance voltage and differentiating the detected detection voltage to detect an object based on a change in the detection voltage, the AC component can be converted into a DC component by detecting the resonance voltage. By converting and differentiating the detected detection voltage of the DC component, the movement of the object with respect to the sensor electrode can be detected, and the approaching state (change) of the object can be accurately detected. This can be detected by a simple differentiating circuit, and the change due to the approach of the object can be found by differentiating the detection voltage. In addition, even if the Q value of the resonance circuit changes due to an environmental change or the like, the change due to the differentiation of the detection voltage is not affected, and only the change in the resonance circuit is detected, so that the correction by fine adjustment of the resonance voltage can be performed. Since an object can be detected even without such a configuration, unlike the related art, a temperature compensating circuit and an adjusting circuit are not required, and a sensor configuration that can be reduced in size, reduced in cost, and simplified can be provided.

[Brief description of the drawings]

FIG. 1 is a system block diagram of a vehicle when a capacitive proximity sensor according to an embodiment of the present invention is applied to a keyless entry system (smart entry system) of a vehicle.

2 is a block diagram of a portable device carried by a user who transmits an ID information signal to a vehicle when a request signal is received by the system shown in FIG.

FIG. 3 is an explanatory diagram showing an outline of a case where a first transmitting antenna and a sensor electrode according to an embodiment of the present invention are provided on a door handle of a vehicle.

FIG. 4 is a diagram illustrating a relationship between a door handle attached to a vehicle door and an object according to an embodiment of the present invention.

FIG. 5 is a circuit block diagram illustrating a configuration of a sensor electrode and a sensor detection unit illustrated in FIG. 1;

6 is a graph showing a change in resonance voltage at an excitation frequency f0 when the resonance frequency fr changes to fr 'when an object approaches the sensor electrode shown in FIG.

FIG. 7 is a graph showing an output waveform (voltage waveform) at each point shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Keyless entry system (including a capacitive proximity sensor) 2 Door handle 3 Vehicle door (door) 9 Object (people, obstacle) 13 Differentiator 14 Detection circuit 15 Resonance circuit (series resonance circuit) 18 Sensor detection unit 19 Sensor electrode 20 Controller 21 Comparator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Eiji Mushiaki 2-1-1 Asahi-cho, Kariya-shi, Aichi F-term in Aisin Seiki Co., Ltd. 2F063 AA02 AA49 BA29 BA30 BB08 CA34 DA01 DD02 HA01 KA01 KA04 LA04 LA05 LA12 LA30 ZA01 ZA10 5J050 AA24 AA49 BB22 EE34 EE35 FF29

Claims (3)

[Claims] 1. A capacitive proximity sensor for detecting the approach of an object to a sensor electrode based on a change in capacitance between the object and the sensor electrode using a resonance circuit. The capacitance of the resonance circuit including the electrode capacitance is a resonance capacitance, the resonance capacitance and a resonance inductor are connected in series to form a series resonance circuit having a resonance frequency fr, and the series resonance circuit is caused to resonate at an excitation frequency f0. In this case, an excitation frequency f0 is set higher than the resonance frequency fr, and the object is detected based on a resonance voltage of the series resonance circuit. 2. The capacitive proximity sensor according to claim 1, wherein the detection of the object is performed based on a change in the resonance voltage. 3. The capacitance proximity sensor according to claim 2, wherein the resonance voltage is detected, the detected detection voltage is differentiated, and the object is detected based on a change in the detection voltage. .