JPS61243598A - Vehicle sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Field of the Invention) The present invention can be used, for example, in a traffic control system that detects the number of vehicles traveling on a road and controls traffic lights to facilitate vehicle passage. The present invention relates to a vehicle sensor that detects a vehicle by detecting a change in a magnetic field as the vehicle passes by.

(Summary of the invention) The present invention improves the sensitivity of vehicle sensing, suppresses the occurrence of disconnection accidents, and simplifies the installation of vehicle sensing coils on 1ffl roads. This also makes maintenance easier.

(Prior art and its problems) One of the main types of conventional vehicle detectors is a loop coil type vehicle detector as shown in FIG.

In FIG. 10, 50 is in the passage (i!i path) 53.
.

The buried loop coil 51 is a high frequency oscillation circuit that outputs an excitation current to the loop coil 5°, and 52 is an output circuit that outputs a vehicle sensing signal S when a change in the current flowing through the loop coil 50 is a predetermined amount or more. .

The operation of this loop coil type vehicle sensor is as follows.

The excitation current from the high frequency oscillation circuit 51 is transmitted to the loop coil 50.
, a magnetic field H is created by the loop coil 50. When the vehicle passes through this magnetic field H, the magnetic flux concentrates on the metal parts of the vehicle, so the inductance of the loop coil 50 changes, and the input current to the output circuit 52 changes.

The output circuit 52 outputs a vehicle sensing signal S in response to this change in input current.

However, the conventional example having such a configuration has the following problems.

(a) In order to detect a vehicle, the loop coil 50 must be
must be buried in the passageway 53. loop coil 5
Normally, the loop coil 50 has a size of about 2 m x 2 m, and in order to bury such a large loop coil 50 in the passage (road) 53, the passage 53 must be cut in a large area. Such a cutting operation is extremely large-scale, and the construction cost is very high, and the construction requires a great deal of time and effort.

(b) The loop coil 50 buried in the passage 53 is frequently subjected to loads caused by passing vehicles, and is therefore prone to breakage accidents. If a disconnection accident occurs, vehicle detection becomes impossible.

One possible solution to this problem is to significantly reduce the size of the loop coil and use a ferrite coil in which the loop coil is wound around a ferrite core. However, since the vehicle sensing area is as narrow as the diameter of a single ferrite coil, there is a problem in that the sensitivity is low, and the reality is that it has not been put into practical use.

Another conventional example is an ultrasonic vehicle detector, but it is necessary to place an ultrasonic transducer that transmits and receives ultrasonic waves above the road surface. An L-shaped ball is installed upright, and an ultrasonic vibrator is attached to the tip of the ball.

In this case, to install the ball, a deep hole must be dug next to the path, and concrete must be poured to secure the ball that has been slightly loosened in the hole. As a result, construction costs are high and the construction period is long. Furthermore, there is also the problem that maintenance such as repair or replacement of the ultrasonic transducer becomes extensive.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and it is possible to suppress the occurrence of disconnection accidents while increasing the sensitivity of vehicle detection, and to improve the construction of vehicle detection coils in passageways. The purpose of this invention is to simplify the vehicle sensing coil and to facilitate maintenance of the vehicle sensing coil.

(Configuration and Effects of the Invention) In order to achieve the above object, the present invention has the following configuration.

That is, the vehicle sensor of the present invention includes: a transmitting coil whose core is a magnetic material installed on the road surface on one side in the width direction of the passage; a high-frequency oscillation circuit that outputs an excitation current to the transmitting coil; A receiving coil whose magnetic core is a magnetic material installed on the road surface on the other side in the width direction of the passage, and an output circuit that outputs a vehicle sensing signal in response to a change of a received signal of the receiving coil by a predetermined amount or more. It is equipped with the following.

In this configuration, the term "riill road" broadly refers to a place where vehicles pass, and refers not only to the road but also to the road surface, floor surface, etc. in the premises.

The effects of this configuration are as follows.

(i) When the excitation current from the high frequency oscillation circuit flows through the transmitting coil, a magnetic field is formed across the path between the transmitting coil and the receiving coil. When the vehicle passes through this magnetic field, the mutual inductance changes, and the level of the signal received by the receiving coil changes. This received signal is input to the output circuit, and when a change in the level of the received signal is equal to or greater than a predetermined amount (that is, when a vehicle is detected), a vehicle sensing signal is output from the output circuit.

(ii) Since the transmitting coil and receiving coil, which are sufficiently smaller than conventional loop coils, are simply installed on the road surface, it is of course less expensive than burying the loop coil or erecting a ball. Compared to the case where these transmitting coils and receiving coils are buried, construction of the transmitting coils and receiving coils can be greatly simplified.

(iii) As described in (ii) above, the possibility of disconnection accidents is significantly reduced compared to the conventional case where the entire large loop coil is buried in the passage.

(iv) Since the magnetic field formed between the transmitting coil and the receiving coil is formed across the upper path, the vehicle sensing area is sufficiently large compared to the case of a single ferrite coil. becomes highly sensitive.

(v) Since the transmitting coil and the receiving coil are installed on the road surface, maintenance such as repair or replacement can be easily performed on the side compared to an ultrasonic transducer attached to a ball.

As described above, according to the present invention, the occurrence of disconnection accidents can be suppressed while increasing the sensitivity of vehicle detection, and the The advantage is that construction can be simplified and maintenance such as repair and replacement of both coils can be easily performed.

(Description of Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

<First Embodiment> FIG. 1 is a schematic configuration diagram of a vehicle sensor according to a first embodiment of the present invention, FIG. 2 is a perspective view of a coil unit, and FIG. 3 is a block diagram of the vehicle sensor.

〔composition〕

In FIG. 1, 32 is a transmitting coil unit which incorporates a transmitting coil 2 having a magnetic core 2a made of a magnetic material such as ferrite as shown in FIG. 2, and has a fixing bolt insertion hole 35 formed in a heath 33. This transmitting coil unit 32 is installed in a fixed state on the road surface on one side in the width direction of the passage (road) 1. That is, Heath 3
3 is placed on the road surface, and by screwing a bolt (not shown) inserted into the bolt insertion hole 35 into the passage 1,
The transmitting coil unit 32 is fixed.

34 is a receiving coil unit configured similarly to the transmitting coil unit 32 as shown in FIG. 2, and this receiving coil unit 34 includes a receiving coil 4 having a magnetic core 4a made of a magnetic material such as ferrite. Built-in. The receiving coil unit 34 is fixedly installed on the road surface in the same manner as the transmitting coil unit 32 on the other side of the passageway 1 in the width direction.

36 is the passage 1 on the receiving coil unit 34 side.
The sensor main body 6 is attached to this pillar 36. Reference numeral 37 denotes a support post erected on the side of the passage 1 on the transmitting coil unit 32 side. This support 37 may be one using an existing telephone pole or the like.

A power transmission line 7a led out from the sensor main body 6 is passed from the upper end of the pillar 36 to the upper end of the pillar 37 while crossing above the passage 1, and is connected to the transmitting coil 2 of the transmitting coil unit 32. ing. Further, a power transmission line 7b led out from the sensor main body 6 is connected to the receiving coil 4 of the receiving coil unit 34.

The block diagram in FIG. 3 shows the circuit configuration of the sensor body 6. As shown in FIG. In FIG. 3, 3 is a high frequency oscillation circuit that outputs excitation current to the transmission coil 2, and a power amplification circuit 8 at the next stage of this high frequency oscillation circuit 3 is connected to the transmission coil 2 via a power transmission line 7a. Reference numeral 5 denotes an output circuit that outputs a vehicle sensing signal S to an external device (not shown) when a change of a predetermined amount or more in the received signal of the receiving coil 4 is detected, and this output circuit 5 is connected to the power transmission line 7b. It is connected to the receiving coil 4 via.

Further, 9 is an amplifier circuit connected to the receiving coil 4, and 10
1 is a filter, 11 is a detection circuit, and 12 is an analog switch circuit. A first contact of the switch circuit 12 is grounded via a capacitor 13, and a second contact is grounded via a capacitor 14. Both capacitors 13
．． The capacitances of 14 are equal to each other. Both capacitors 13
．． The positive terminal of 14 is input connected to the differential amplifier circuit 15,
.

The output terminal of the differential amplifier circuit 15 is input connected to a comparator 16. 17 is a constant voltage power supply for determining the threshold voltage Vref of the comparator 16. Comparator 16 is connected to an external device (not shown). 18 outputs a pulse signal C to the switch circuit 12 when the output of the comparator 16 is at the "T" level, and when the output of the comparator 16 is at the "H" level,
This is a timing circuit that stops outputting the pulse signal C.

The switch circuit 12 connects the detection circuit 11 to the capacitor 13 when the pulse signal C from the timing circuit 18 is at the "H" level, and connects the detection circuit 11 to the capacitor 14 when the pulse signal C is at the "L" level. configured to connect.

〔motion〕

Next, the operation of this first embodiment will be explained based on the operation explanatory diagram of FIG. 4 and the time chart of FIG. 5.

■ The excitation current from the high frequency oscillation circuit 3 is transmitted to the power amplifier circuit 8.
The signal is amplified and excites the transmitting coil 2.

As a result, a magnetic field H is formed between the transmitting coil 2 and the receiving coil 4.

After the received current by the receiving coil 4 is amplified by the amplifier circuit 9, the noise component is removed by the filter 10 and the signal a is
becomes. This signal a is detected by a detection circuit 11 and becomes a signal S.

■ Time when vehicle M reaches magnetic field H1. Until time t2 when a minute time has elapsed, the pulse signal C is output from the timing circuit 18 to the switch circuit 12 (see ■ below).
The switching of the switch circuit 12 is repeated. The capacitor 13 is charged by the input signal d when the pulse signal C is at the "H" level, and the capacitor 14 is charged by the input signal e when the pulse signal C is at the "L" level. These input signals d and e are at the same level as the output signal of the detection circuit 11.

Since both the capacitor 13 and the capacitor 14 are repeatedly charged and discharged by switching, the charging voltage V I 3 of the capacitor 13 and the charging voltage v+4 of the capacitor I4 remain substantially equal. Therefore, the output signal f from the differential amplifier circuit 15 is at "L" level, and the comparator 1
Since the output signal g of No. 6 also maintains the "L" level, there is no output of the vehicle sensing signal S.

Since the output signal g is at the "L" level, the timing circuit 1B continues to output the pulse signal C, and the switching of the switch circuit 12 is repeated.

■ Suppose that vehicle M reaches magnetic field H at time t.

When the vehicle M is passing through the magnetic field H as shown in FIG. 4, magnetic flux concentrates on the metal parts of the vehicle M, so the mutual inductance between the transmitting coil 2 and the receiving coil 4 changes.

That is, the amplitude of the output signal a of the filter 10 begins to increase,
The level of the output signal of the detection circuit 11 begins to rise. At time t1, the pulse signal C rises, and the detection circuit 11 is connected to the capacitor 13. Therefore, the level of the input signal d to the capacitor 13 increases by the amount that the output signal d increases. Therefore, the level of the output signal f of the differential amplifier circuit 15 increases by a small amount. Since the rise in the output signal f is minute and lower than the threshold voltage V ref of the comparator 16, the comparator 1
The output signal g of No. 6 maintains the "L" level, and the vehicle sensing signal S is not output.

(2) At time t2, the pulse signal C falls, and the detection circuit 11 is connected to the capacitor 14. Time 1
．． Since the level of the output signal S of the detection circuit 11 has increased by -L between the time t2 and the time t2, the level of the input signal e to the capacitor I4 is sufficiently higher than the increase in the input signal d at the time ①. rise significantly. As a result, the level of the output signal f of the differential amplifier circuit 15 exceeds the threshold voltage V ref, and the output signal g of the comparator I6 becomes "H" level. As a result, the vehicle sensing signal S is output to the external device, the output signal g is input to the timing circuit 1, and the output of the pulse signal C from the timing circuit I8 is stopped. Therefore, switching of the switch circuit 12 is stopped at time t2, and the state in which the detection circuit 11 remains connected to the capacitor 14 is maintained.

That is, the level of the input signal d to the capacitor 13 is held constant, and the charging voltage V13 thereof is also kept constant, and the level of the human input signal e to the capacitor 14, that is, the charging voltage V14, is kept constant as the output signal of the detection circuit 11. Changes according to level changes. Further, the level of the output signal r of the differential amplifier circuit 15 changes similarly. This state continues until the vehicle M passes through the magnetic field 11.

■ The level of the output signal f of the detection circuit 11 decreases as the vehicle M passes through the magnetic field Htl-i11, and in response, the level of the output signal f of the differential amplifier circuit 15 becomes lower than the threshold voltage V ref at time L3. Then, the vehicle sensing signal S is no longer output, and the output signal g of the comparator 16 becomes "L" level. As a result, the pulse signal C is outputted from the timing circuit 18 to the switch circuit 12, and the switch soching is restarted. Then, the level of the input signal d to the capacitor 13 and the input signal e to the capacitor 14 becomes low corresponding to the level of the output signal S of the detection circuit 11, and the output signal f of the differential amplifier circuit 15 becomes low.
It is also stable at “L” level.

In the case of this embodiment, since the power transmission line 7a is passed over the passage 1, there is no need to cut it while crossing the passage 1.

Note that the power transmission line 7a may be buried in the passage 1.

Even in this case, the cutting of passage 1 is sufficient to cut the length of one power transmission line. Moreover, when the high frequency oscillation circuit 3, the power amplifier circuit 8, and the output circuit 5 are arranged on opposite sides of the passage 1, it is not necessary to wire the power transmission line 7a across the passage 1.

Further, by adjusting the interval between the transmitting coil 2 (transmitting coil unit 32) and the receiving coil 4 (receiving coil unit 34), the sensing area can be arbitrarily set. .

- Furthermore, since the transmitting coil 2 and the receiving coil 4 are placed separately, if the vehicle M is equipped with a transmitter/receiver,
It is also easy to develop the device so that it can communicate with the transceiver.

<Second example> Next, a second embodiment will be explained based on FIG. 6.

In FIG. 6, the same reference numerals as those shown in FIG. 3 according to the first embodiment refer to the same parts as the parts 9 indicated by the reference numerals in this embodiment as well.

〔composition〕

A series circuit including an attenuator 19 and a filter 20 is inserted between the high frequency oscillation circuit 3 and the power amplifier circuit 8.

The attenuator 19 is configured to receive an attenuator value control signal via a bus 23 from an output interface 22 of a microcomputer 21 (hereinafter referred to as microcomputer).

The circuit configuration from the receiving coil 4 to the detection circuit 11 is the first one.
This is similar to the example. An A/D conversion circuit 24 at the next stage of the detection circuit 11 is connected to an input interface 25 of the microcomputer 21.

In the microcomputer 21, 26 is a CPU, 27 is a ROM,
2B is a RAM, 29 is a timer, 30 is an output interface for communicating with an external device (not shown), and 31 is a bus.

〔motion〕

The basic operation of this embodiment will be explained.

The excitation current from the high-frequency oscillation circuit 3 is attenuated by an attenuator 19, and after unnecessary frequency components such as harmonics are removed by a filter 20, it is amplified by a power amplifier circuit 8 to excite the transmitting coil 2. By excitation of the transmitting coil 2,
A magnetic field H is formed between the transmitting coil 2 and the receiving coil 4. After the received current by the receiving coil 4 is amplified by the amplifier circuit 9, noise components are removed by the filter 10, and detected by the detection circuit 11.

The detected analog signal is converted into a digital signal by the A/D conversion circuit 24, sent to the CPU 26 via the input interface 25 and the bus 31, and sent from the CPU 26 to the RAM 28.

The CPU 26 adjusts the attenuator value of the attenuator 19 according to the program written in the ROM 27, processes the received data from the receiving coil 4, and outputs the vehicle sensing signal S to the output interface 30 in the case of vehicle sensing. output to an external device via

Next, the detailed operation will be explained based on the flowchart of FIG. 7, the time chart of FIG. 8, and the memory map of FIG. 9. The memory map in FIG. 9 is for the RAM 28, and has an address ADI of the received data from the A/D conversion circuit 24 and an address ATT of the attenuator value.

(1) Turn on the power at time T, and set the attenuator value to the maximum value in step (see Figure 8 (A)).
, minimize the transmit level. This attenuator value is stored at address ATT. In step (2), the received data (see FIG. 8(B)), which is the output value of the A/D conversion circuit 24, is read. In step ■, the level of the received data is
A reference value Va corresponding to a predetermined voltage necessary to sense
Determine whether it has been reached. If no, step■
The attenuator value of the address ATT is decreased by 1, and the process returns to step (2). By repeating this process, the attenuator value decreases stepwise, and the level of the received data increases stepwise.

(At time T2 on the 21st, when the level of the received data reaches the reference value Va and the judgment in step ■ becomes YES, the process moves to step ■, reads the level of the received data from the A/D conversion circuit 24 again, and steps Then, in step ■, idling is performed for a certain period of time.In step ■, the received data, 1.11P, and □ level are read again, and in step ■, the previous received data stored in address AD1 is stored. The difference from the data level is calculated.In step [phase], it is determined whether the difference exceeds the sensing reference value vth.

If NO, the process moves to step (2), stores the received data level read in step (2) in address ADI, idles in step @, and then returns to step (2).

(3) The vehicle M reaches the magnetic field H, and at time T3, the difference between the current received data level and the previous received data level exceeds the sensing reference value vth, and the judgment at step [phase] is Y.
When it becomes ES, it moves to step 0 and outputs the vehicle sensing signal S to the external device via the output interface 30 (
(See Figure 8(C)).

(4) Next, in step (2), the received data level is read again, and in step [phase], it is determined whether the difference between the address ADI stored in step (2) and the received data level exceeds the sensing reference value vth.

If YES, return to step [phase].

(5) Vehicle M passes through magnetic field I (at time T4,
Assuming that the difference between the received data level of the address ADI stored in step ■ becomes smaller than the sensing reference value vth, it is determined No in step [phase], and the process moves to step [phase] to output the vehicle sensing signal S. stop.

[Brief explanation of the drawing]

1 to 5 relate to a vehicle sensor according to a first embodiment of the present invention, in which FIG. 1 is a schematic configuration diagram of the vehicle sensor, FIG. 2 is a perspective view of a coil unit, and FIG. 3 is a vehicle sensor. A block diagram of the sensor, FIG. 4 is an operation explanatory diagram, FIG. 5 is a time chart, FIGS. 6 to 9 relate to the second embodiment, FIG. 6 is a block diagram, FIG. 7 is a flowchart, and FIG. FIG. 8 is a time chart, FIG. 9 is a memory map, and FIG. 10 is a schematic diagram of a conventional example. In the figure, the symbol l is a passage, 2 is a transmitting coil, 2a is a magnetic core,
3 is a high frequency oscillation circuit, 4 is a receiving coil, 4a is a magnetic core,
5 is an output circuit.

Claims (1)

[Claims] (1) A transmitting coil whose magnetic core is a magnetic material installed on the road surface on one side in the width direction of the passage, a high frequency oscillation circuit that outputs an excitation current to this transmitting coil, and the other side in the width direction of the passage A vehicle sensor comprising: a receiving coil whose magnetic core is a magnetic material installed on a road surface; and an output circuit that outputs a vehicle sensing signal in response to a change of more than a predetermined amount in a signal received by the receiving coil.