JP3481373B2 - Loop coil type vehicle detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop coil type vehicle detector used for detecting a vehicle in a parking lot or the like.

[0002]

2. Description of the Related Art Generally, in a loop coil type vehicle detector, the inductance of the loop coil is different depending on the place of installation, so that the work of adjusting the sensing sensitivity is complicated.

Further, since the output of the sensor is only the sensing state and the failure signal, complicated adjustment and dedicated measuring instruments are required also in the maintenance work.

[0004]

A loop coil, which is a sensor portion of a loop coil type vehicle detector generally used in a parking lot, has different loop coil inductances because the burying environment and the coil size are different for each parking lot. there were. In addition, if metal such as rebar is near the coil, Q may be abnormally reduced, and the sensitivity for detecting a vehicle may be extremely reduced. Therefore, large-scale facilities and equipment are required for sensitivity adjustment. there were.

An object of the present invention is to provide a loop coil type vehicle detector that automatically sets an appropriate vehicle detection sensitivity even in the above situation.

Another object of the present invention is to provide a loop coil type vehicle detector which senses at high speed or has little influence of noise.

Another object of the present invention is to provide a loop coil type vehicle detector which senses with a sensitivity suitable for a vehicle.

Another object of the present invention is to provide a loop coil type vehicle sensor which facilitates maintenance by outputting a sensing condition and loop coil performance information.

[0009]

In order to solve the above problems, a loop coil type vehicle sensor according to the present invention is constructed as follows.

According to a first aspect of the present invention, a self-excited oscillation circuit that uses a loop coil as an inductance of a parallel resonant circuit, an AD converter that digitally converts an output voltage of the self-excited oscillation circuit, and a self-excited oscillation circuit. A programmable counter circuit that creates a gate signal by dividing an oscillation frequency signal that is determined by the inductance into a frequency that is determined by a preset value that is changed at a fixed cycle, and starts counting a reference clock at the fixed cycle, and counts at the gate signal. A reference clock counter that stops the detection, a determination table that stores detection determination information including failure information, a count value of the reference clock counter that is read at the input of the gate signal, and a count value of the reference clock counter at the constant cycle. Clear and calculate the preset value from the read count value of the reference clock counter Is written in the programmable counter circuit according to the output peak value of the A-D converter, and the sensing determination information is read from the determination table according to the output peak value of the AD converter. And a control unit for making a determination.

A second invention is the same as the first invention,
The control unit reads the count value of the reference clock counter by inputting the gate signal, clears the count value of the reference clock counter at the constant period, and calculates the preset value by the read count value of the reference clock counter. Then, the sensing determination information is read from the determination table in accordance with the output peak value of the A / D converter at every constant period, and the sensing determination information is compared with the count value of the reference clock counter. Then, the sensing judgment of the loop coil is performed, and the sensing output is issued when the sensing judgment is continued a predetermined number of times or more.

In a third aspect based on the first or second aspect, the determination table groups the detection determination information including the failure information by vehicles having different degrees of changing the inductance of the self-excited oscillator. The control unit reads out the count value of the reference clock counter at the input of the gate signal, clears the count value of the reference clock counter at the constant period, and stores the count value of the reference clock counter according to the read value. A preset value is calculated and written in the programmable counter circuit, and the A-
The detection determination information is read from the determination table according to the output peak value of the D converter and the group previously selected by the sensitivity changeover switch, and the detection determination information is compared with the count value of the reference clock counter to detect the detection of the loop coil. Is what you do.

A fourth invention is the above-mentioned first, second or third invention.
In the above invention, a communication circuit is provided which receives and outputs the detection determination information including the vehicle detection state, the count value of the reference clock counter, and the failure information from the determination table from the control unit.

[0014]

The first invention operates as follows. The self-excited oscillating circuit oscillates at a frequency determined by the inductance of the loop coil, and the loop coil changes the inductance due to the approach of the magnetic body, and thereby changes the oscillating frequency of the self-excited oscillating circuit. The A-D converter digitally converts the output voltage of the self-oscillation circuit. This digital signal is read by the control unit to determine the peak value. The programmable counter receives a preset value from the control unit at regular intervals, counts the oscillation frequency signal of the self-excited oscillation circuit according to the preset value, and divides the frequency. The output signal of the programmable counter is output to the reference clock counter and the control unit as a gate signal. The reference clock counter starts counting the reference clock at each fixed cycle period and stops counting at the gate signal. At this time, the gate signal is also input to the control unit, and the control unit reads and clears the count value of the reference clock counter,
A preset value is calculated from this count value. This preset value is rewritten in the programmable counter circuit at regular intervals. Further, the control unit reads the sensing determination information of the determination table according to the A / D converter output peak value at a constant cycle, and compares the read sensing determination information with the count value of the reference clock counter. The count value of the reference clock counter is based on the count of the reference clock from the start of a fixed cycle to the gate signal, and
The generation of the gate signal is determined by the frequency signal due to the inductance of the loop coil, the count value of the reference clock counter is determined by the inductance of the loop coil, and it is possible to determine the inductance change, that is, the vehicle detection. Note that, for example, when the self-excited oscillation circuit does not operate, there is no output from the AD converter and the programmable counter does not change, so the control unit reads the failure information from the determination table.

The second invention has the above-mentioned function of the first invention and further functions as follows. The control unit
When the sensing judgment of the loop coil for every constant period is continuous for a predetermined number of times or more, a sensing output is issued.

The third invention has the above-described function of the first invention or the second invention, and further functions as follows. The determination unit reads the determination table according to not only the output peak value of the A-D converter but also the group information selected and set in advance by the sensitivity changeover switch, and reads the detection determination information. Thus, it is possible to make a judgment by entering vehicles having different degrees of inductance change into the vehicle detectors having the detection judgment information set according to the respective vehicle groups.

The fourth invention has the above-described function of the first, second, or third invention, and further functions as follows. The communication circuit receives the detection determination information including the vehicle detection state, the count value of the reference clock counter, and the failure information from the determination table from the control unit, and outputs it in a signal format suitable for transmission to the communication line. This output signal can be useful information for maintenance.

[0018]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a functional block diagram of the embodiment, FIG. 2 is a timing chart, FIG. 3 is a determination table, and FIG. 4 is a diagram showing serial communication data.

In FIG. 1, 101 is a loop coil and 1
Reference numeral 02 designates the loop coil 101 as L of an LC parallel resonance circuit.
A self-excited oscillation circuit, 103 is an A / D converter circuit that digitally converts the output voltage of the self-excited oscillation circuit 102, and 104 is a comparator circuit that waveform-shapes the oscillation frequency of the self-excited oscillation circuit 102 into a digital periodic signal. ,
Reference numeral 105 denotes a programmable counter that counts the digital periodic signal of the comparator circuit 104 for a predetermined period.
6 is a reference clock oscillation circuit using a crystal oscillator, 10
Reference numeral 7 is a reference clock counter circuit for creating an accurate clock, 108 is a sensitivity changeover switch, 109 is a sense speed changeover switch for changing the sensed output speed, 110 is a control unit composed of a one-chip microcomputer element, 111 is a ROM memory Is a determination table configured by the above, and stores the detection determination information (threshold amount and failure information) which is built in the control unit 110 and is the basis of detection and determination. Reference numeral 112 is a serial communication circuit that serially outputs the vehicle detection state and other various data, and 113 is a power supply circuit.

The loop coil 101 is embedded in the road, has an inductance L, and has the self-excited oscillation circuit 1
02 is connected. The self-excited oscillation circuit 102 is composed of a Colpitts type oscillation circuit and performs self-excited oscillation at the following oscillation frequency together with the _two capacitors C ₁ and C ₂ connected inside.

[0022]

F = 1 / ( 2π (LC ₁ C ₂ / (C ₁ + C ₂ )) ^1/2 ) (1)

The voltage amplitude of the self-excited oscillation circuit 102 is input to the A / D converter 103, and this voltage is converted into a digital amount and output to the control unit 110. Since the power supply voltage of 15 V is used in this embodiment, the AD converter 103
Converts 0FFH at 15V _PP and 00H at 0V to a signal obtained by dividing this interval into 255, and outputs the signal to the control unit 110. Control unit 110
Determines the peak value of the output of the AD converter 103 by a program. This peak value is "maximum, 9, 8, 7, 6, 5, 5" in each row of "AD converter reading" in FIG.
4, 3, 2, lowest ”. The control unit 110 determines the output of the A-D converter 103 when the initialization is performed (when the power is turned on).
When the output of the D converter 103 is read to determine which row of the determination table 111 shown in FIG. 3 is to be selected, it is periodically read so that the output of the AD converter 103 is the failure of the bottom row in FIG. It is time to determine whether or not there is a loop coil disconnection). When the loop coil is disconnected, the output voltage amplitude of the self-excited oscillation circuit 102 becomes 0 V. In this case, it is determined that the loop coil 101 is disconnected, and the failure information in the determination table 111 is read.

The comparator 104 is the self-excited oscillation circuit 102.
Convert the analog waveform of to a digital signal. The output signal of the comparator 104 is the programmable counter circuit 1
5 and functions as a clock for the programmable counter circuit 105.

The programmable counter circuit 105 preliminarily sets the preset value 21 and the preset load signal 22 from the control unit 110 before starting counting, as shown in FIG.
Are written at the timings t11, t12 ... (Constant period). Comparator circuit 1 that inputs when counting starts
The rising edge of the clock signal, which is the output of 04, obtains a count value obtained by sequentially incrementing the internal counter preset to the preset value by +1. When the count value reaches hexadecimal FFFFH, the gate signal 23 becomes active (see FIG. 2). Of ta
Timing). In the embodiment, four hexadecimal digits are used for the internal counter. The gate signal 23 is connected to the reference clock counter 107 to function as a clock counting gate signal, and is also connected to the control unit 110 to function as a counting end signal. The control unit 110 controls the gate signal 2
When the signal 3 is active, the reference clock counter data 24 is read from the reference clock counter 107, and the process of determining the sensing state is performed as described later.

The reference clock counter 107 counts the reference clock input as a clock from the reference clock oscillation circuit 106 during the period (sampling time) in which the gate signal 23 is inactive. The count value can be read from the control unit 110. In the embodiment, the reference clock counter 107 is composed of an internal hexadecimal 6-digit counter.

The reference clock oscillation circuit 16 uses a crystal oscillator because it is used as a reference signal for counting. The reference clock signal is used as a clock for the reference clock counter 107. In this embodiment, 20 MHz is used as the oscillation frequency Fr of the reference clock.

Here, the preset value written in the programmable counter 105 by the control unit 110 will be described. First, in the initialization operation that is performed immediately after the power of this device is turned on, a temporary 4096 counts are made and ended, so counting is started from the preset value and 0FFFF
In order to end at H, 0EFFFH is written in the programmable counter 105, the end of the count is awaited, and the numerical value No of the reference clock counter 107 is read. The self-oscillation period To at this time can be calculated by the following equation. This number To
Indicates the reciprocal of the frequency in equation (1).

[0029]

[Equation 2]   To = No / (4096 · Fr) (sec) (2)

When the sampling time Ts at the time of initialization is set to 40 ms and the L of the loop coil 101 is not changed, the preset value Po loaded to the programmable counter 105 before the start of each subsequent sampling is the above formula (2) and It can be obtained from the following equation as follows.

[0031]

(3) Po = Ts ÷ To = 40 × 10 ⁻³ × 20 × 10 ⁶ × 4096 / No (3)

Expression (3) shows how many times the self-excited oscillation period is sampled in the initialization process to obtain the specified sampling time. In addition, the reference clock counter 107 that is counted during this sampling time
The count number No of can be calculated as follows.

[0033]

[Equation 4]   No = Fr × (Po × To) (4)

Considering the initialization process, the preset value Po does not change and Po * To is constant, which is equal to Ts in the equation (3).

When the vehicle approaches the loop coil 101 and the loop coil inductance L changes by the ratio d during operation, the self-excited oscillation period is d when approximated by the equation (1).
It changes by / 2. That is, for simplicity in equation (1)

[0036]

## EQU5 ## K = 1 / 2π (C ₁ C ₂ / (C ₁ + C ₂ )) ^1/2 (5)

[0037]

[0038]

[ ^Equation 6] f = K × L ^−1/2 (6)

When L changes by a small amount to become (1-d) L and becomes f ₁ ,

[0040]

F ₁ = K × L ^−1/2 × (1-d) ^{−1/2 ≈K} × L ^−1/2 × (1 + d / 2) (7)

In the equation (7), (1-d) ^-1/2 is Ty
Lor expansion gave (1 + d / 2). Therefore,
The frequency change amount is d / 2 as follows.

[0042]

F ₁ −f = f × d / 2 (8)

When the count number of the reference clock counter 107 at this time is Nm, the difference D between the count numbers is expressed by the following equation.

[0044]

[Equation 9]   D = No-Nm     = No- (1-d / 2) * No     = D × No / 2 (9)

Here, No means that the vehicle is the loop coil 101.
Since the value is a fixed value in the state where it is not close to, it indicates that the difference D in the number of counts due to the inductance change ratio d does not depend on the individual loop coil inductance.

Focusing on the fact that the amount of change in the loop coil inductance is extremely small in a bicycle or a minibike, for example, as compared with a passenger car, the determination table 1
The number of sensing judgments, that is, the threshold amount, stored in 11 is classified into a vehicle group such as a passenger vehicle that changes the inductance relatively large and a vehicle group such as a bicycle and a minibike that change the inductance relatively small. For each loop coil,
The sensitivity changeover switch 108 is set in advance depending on whether or not a bicycle or a mini-bike is to be detected so that the threshold amount can be read.

The determination table 111 shown in FIG. 3 is divided into 10 rows to which the output of the AD converter 103 is assigned,
It is configured as a matrix with columns divided into two according to the setting of the sensitivity changeover switch 108. The control unit 110 is AD
The numerical values in the columns corresponding to the two parameters depending on the output of the converter 103 and the switching setting of the sensitivity changeover switch 108 are read, and the numerical threshold for performing the sensing judgment is determined. In the determination table 111, the reference clock counter 1
As a criterion for determining the count value of 07, corresponding to when the sensed state of the loop coil is the best (“maximum” row in FIG. 3),
When the threshold value “400” corresponding to the inductance change of 0.1% is set and the loop coil state is “2”, the value “2” corresponding to the inductance change of 0.06% is set.
40 "is set. In the following, change the inductance from the state of the loop coil "maximum" to "2" by 0.0
Allotted to each 05%. By the way, assuming that “400” in “maximum” is d = 0.001 and “240” in “2” is d = 0.0006, it is obtained from the equation (9) as follows.

[0048]

[Number 10] "maximum", d = 0.001 0.001 × 800 × 10 3/2 = 400 (10)

[0049]

[Number 11] "2", d = 0.0006 0.006 × 800 × 10 3/2 = 240 (11)

Generally, even if the loop coil 101 has the same specifications, its performance is inferior to that of the loop coil 101 constructed in the free space due to the embedded condition. This is because metal objects such as rebars buried in close proximity are affected, and the magnetic field lines emitted from the loop coil 101 are affected by eddy current loss and the like by the metal parts around them, and these metal objects are If it is in the vicinity, the detection sensitivity of the intended metal object of the vehicle will be reduced. When this influence is exerted, the self-excited oscillation circuit 102 is affected by a decrease in the oscillation amplitude voltage. According to the present invention, this effect is calculated in advance from the self-excited oscillation amplitude voltage, a determination numerical value is assigned according to the amplitude voltage, and correction is performed to increase the sensitivity.

That is, at the time of initialization, the peak value of the output of the A / D converter 103 is determined, and it is assigned to each row as shown in FIG. 3 according to the peak value. In the embodiment, the sampling time is 40 m when the vehicle is not detected.
Since it is set to sec, the reference clock counter 1 when not sensing
Since the count value of 07 is 800 × 10 ³ , 400 counts corresponding to an inductance change amount of 0.1% is used as the threshold best value.

Although the judgment table 111 is used in the embodiment, the calculation of the threshold amount may be carried out every time by using a calculation formula.

In the sensor in the operating state, the oscillation frequency gradually changes even when there is no vehicle due to changes in the natural world (temperature, changes over time, etc.), so it is necessary to follow this change. The moving average value is used as a reference value when there is no vehicle. Therefore, the control unit 1
10 stores a moving average value of, for example, 50 times the count value of the reference clock counter 107 read after the elapse of each sampling time in an internal memory (for example, RAM),
The difference between the count value read from the reference clock counter 107 and the moving average is calculated every time. In equation (9), the count value is Nm, the moving average value is No, and the difference between them corresponds to D. Here, the moving average value is obtained by averaging the nearest numerical values of data sampled in time series by a designated number. For example, suppose that the data dn is a newer sample to the right in the following equations (12) and (13), and the moving average value when the number of data is K is Ns.

[0054]

[Equation 12]   Ns1 = (dn + 1 + dn + 2 + ... + dn + K) ÷ K (12)

In the next sample,

[0056]

[Equation 13]   Ns2 = (dn + 2 + dn + 3 + ... + dn + K + 1) ÷ K (13)

If the difference D between the count value and the moving average exceeds the threshold value of the number of sensing judgments in the judgment table 111, it is judged that there is a change. The sensing signal is output only when the changed state continues for a predetermined number of times. This number of times is determined by the sensing speed changeover switch 109. In the present embodiment, it is set to 2 times when the high speed is selected and 10 times when the low speed is detected. The smaller the number of times, the more suitable it is to detect a high-speed vehicle, but the resistance to external electric noise is weak, and the opposite is true in low-speed selection. It should be noted that similar processing is performed when a change from the sensed state to the non-sensed state occurs.

The serial communication circuit 112 includes a control unit 110.
To the detection state depending on the presence or absence of vehicle detection, the operating state based on the detection determination numerical value read from the determination table, the presence or absence of disconnection of the loop coil and the loop coil state based on the A / D converter output, the moving average value, the reference clock counter count value, the detection The data of the number of times is received, and the data is sequentially output as shown in FIG. The host device (not shown) that receives this data can be used not only for the sensing state output but also for the vehicle type discrimination software or the like by utilizing the output of the reference counter 107 which is the sequential sampling data itself. Moreover, since the voltage amplitude of the oscillation waveform can be read from the loop coil state information, it is possible to provide information as to whether or not the loop coil can easily sense the vehicle.

Further, although the vehicle sensing signal and the failure signal are output using the serial communication circuit 112 in the above, it is also possible to output them as parallel information of a relay or a photocoupler.

[0060]

As described above in detail, according to the present invention, the appropriate sensing judgment information of the judgment table is automatically obtained by the output of the AD converter regardless of the inductance value of the loop coil and the sensitivity of the loop coil. Since it is set to, accurate vehicle detection is possible.

Further, since the sensing output is issued when the sensing judgment is continued for a predetermined number of times or more, it is possible to sense at a high speed by setting a predetermined number of times or to reduce the speed to reduce the influence of noise.

Further, the judgment table stores the detection judgment information including the failure information in groups according to vehicles having different degrees of change in the inductance of the self-excited oscillator, and stores the detection judgment information in the A / D converter. It can be read by output and can be sensed by sensing determination information suitable for the vehicle.

Further, since the communication circuit outputs the detection determination information including the vehicle detection state, the count value of the reference clock counter, and the failure information from the determination table, maintenance can be facilitated.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an embodiment of the present invention.

FIG. 2 is a timing chart illustrating the present invention.

FIG. 3 is a diagram illustrating a determination table that constitutes the present invention.

FIG. 4 is a diagram illustrating serial communication data of a communication circuit that constitutes the present invention.

[Explanation of symbols]

101 ... Loop coil, 102 ... Self-oscillation circuit, 103
... A-D converter circuit, 104 ... Comparator circuit,
105 ... Programmable counter, 106 ... Reference clock oscillator circuit, 107 ... Reference clock counter circuit, 10
8 ... Sensitivity changeover switch, 109 ... Sensing speed changeover switch, 110 ... Control part, 111 ... Judgment table (ROM memory), 112 ... Serial communication circuit, 113 ... Power supply circuit.

Continuation of the front page (56) Reference JP-A-5-188156 (JP, A) JP-A-7-105476 (JP, A) JP-A-59-193381 (JP, A) JP-A-7-105475 (JP , A) JP 5-225492 (JP, A) JP 5-189695 (JP, A) JP 5-188155 (JP, A) JP 5-85958 (JP, B2) JP 5-3040 (JP, B2) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01V 3/00-3/40 G08G 1/00-1/16 JISST file (JOIS)

Claims (4)

(57) [Claims] 1. A self-excited oscillation circuit using a loop coil as an inductance of a parallel resonance circuit, and an AD for digitally converting an output voltage of the self-excited oscillation circuit.
A converter, a programmable counter circuit that creates a gate signal by dividing an oscillation frequency signal determined by the inductance of the self-excited oscillation circuit into a frequency determined by a preset value that is changed in a constant cycle, and a reference clock in the constant cycle. A reference clock counter that starts counting and stops counting by the gate signal, a determination table that stores sensing determination information including failure information, a count value of the reference clock counter that is read by inputting the gate signal, and the fixed period And clears the count value of the reference clock counter, calculates the preset value from the read count value of the reference clock counter, and writes the preset value in the programmable counter circuit.
And a control unit for reading the detection determination information from the determination table according to the output peak value of the D converter and comparing the detection determination information with the count value of the reference clock counter to determine the detection of the loop coil. Loop coil type vehicle detector. 2. The control unit reads the count value of the reference clock counter at the input of the gate signal, clears the count value of the reference clock counter at the constant period, and uses the read count value of the reference clock counter. The preset determination value is calculated and written in the programmable counter circuit, and the sensing determination information is read from the determination table according to the output peak value of the A / D converter at the constant cycle, and the sensing determination information and the reference clock counter are read. 2. The loop coil type vehicle sensor according to claim 1, wherein the loop coil sensing judgment is performed by comparing the count value with the count value, and the sensing output is issued when the sensing judgment is continued a predetermined number of times or more. 3. The judgment table stores the detection judgment information including the failure information in groups according to vehicles having different degrees of changing the inductance of the self-excited oscillator, and the control unit receives the gate signal as input. The count value of the reference clock counter is read, the count value of the reference clock counter is cleared at the fixed cycle, the preset value is calculated by the read count value of the reference clock counter, and the preset value is written in the programmable counter circuit, According to the output peak value of the A / D converter and the group selected in advance by the sensitivity changeover switch, the detection determination information is read from the determination table and the detection determination information is compared with the count value of the reference clock counter to form a loop coil. 3. The loop coil type according to claim 1 or 2, characterized in that Both sensor. 4. A communication circuit according to claim 1, 2 or 3, wherein the control unit receives and outputs detection determination information including a vehicle detection state, a reference clock counter count value, and failure information from a determination table. A loop coil type vehicle detector having.