JPH0245122B2 - IDOBUTSUTAIKENCHISOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moving object detection device that detects the length of a moving object using a detection loop.

A well-known method is to detect the length of a moving object based on the fact that when a moving object such as a vehicle approaches the detection loop, the effective inductance of the detection loop decreases. .

Conventionally, when detecting a moving object such as a vehicle using this method, an output signal of a voltage proportional to the effective inductance is converted into a pulse signal at a certain threshold, and one continuous pulse is generated for each vehicle. I was trying to get a signal. The degree of reduction in effective inductance varies depending on the floor height of the vehicle. However, in the past, the same threshold was set even for vehicles with different vehicle heights.
The entry and passing of a vehicle is detected by the rise and fall of the pulse signal based on the threshold value, and the width of the pulse signal is defined as the passing time. However, if the same threshold value is used regardless of the height of the vehicle, the voltage will rise at a later time and fall at an earlier time for a vehicle with a high vehicle height. Therefore, even if vehicles of the same length are passing at the same speed, the passing time will vary slightly depending on the height of the vehicle.

The purpose of this invention is to
It is an object of the present invention to provide a device that can detect the averaged time during which a vehicle passes through a detection loop, thereby improving detection accuracy.

Hereinafter, the present invention will be explained in detail with reference to the illustrated embodiments. The detection loop 1 shown in FIG. 1 is buried in the road surface when detecting a vehicle. The oscillation circuit 2 uses this detection loop 1 as one oscillation element.

The output signal of the oscillation circuit 2 is applied to the resonance circuit 3. When the vehicle is not in the detection loop 1, the frequency of the output signal of the oscillation circuit 2 is set equal to the resonant frequency fo of the resonant circuit.

When a vehicle arrives at detection loop 1, detection loop 1
The effective inductance of oscillation circuit 2 decreases, and the frequency of the output signal of oscillation circuit 2 changes from fo to f. The resonant circuit 3 outputs a signal having a phase shift φ proportional to this frequency change (f/fo) between it and the output signal of the oscillation circuit 2. The output signal of the resonant circuit 3 is
The signal is guided to a phase discrimination circuit 4. The phase discrimination circuit 4 is
It also receives the output signal of the oscillation circuit 2 and generates an output signal with a voltage value proportional to the phase difference between the two signals. If the relationship between the frequency change (f/fo) and the phase displacement φ is made linear without increasing the Q of the resonant circuit, the output signal of the phase discrimination circuit 4 is shown as 41 in FIG. 2 for a small passenger car. For small trucks, I got one showing 42.

41 and 42 are shown with the horizontal axis representing the position of the vehicle relative to the detection loop 1 and the vertical axis representing the output of the phase discrimination circuit 4, that is, the inductance change rate. In this case, the length of the passenger car is longer than the length of the small truck.
Only short. A passenger car and a light truck also enter sensing loop 1 at time t ₁ shown in FIG. 2, and the passenger car exits sensing loop 1 at time t ₂ , while the light truck exits sensing loop 1 at time t ₃ .

That is, in the inductance change rate according to the position of the vehicle with respect to detection loop 1, 41 increases slightly before the passenger car enters detection loop 1, reaches the maximum value, then decreases, and becomes almost zero at time t ₂ , and 42 When the track enters detection loop 1, it rises and draws a waveform close to a trapezoid, and then
It becomes almost zero at t ₃ . And the maximum value of 42 is 41
The time difference T ₁ between time t ₂ and time t ₃ is less than 1/2 of the maximum value of , and is due to the difference L between the length of the small truck and the length of the passenger car.

When such output signals 41 and 42 are quantized using the threshold value 10 (S3) shown in FIG.
Pulse signals shown as 1 and 12 are obtained. The rise of these signals 11 and 12 does not coincide with _t1 . moreover,
The falling edge of signal 11 does not coincide with time _t2 , nor does the falling edge of signal 12 coincide with time _t3 .

In this embodiment, the output signal of the phase discrimination circuit 4 is guided to a peak hold circuit 5 and a comparator 6. A peak hold circuit 5 detects the peak value (maximum value) of the output signal of the phase discrimination circuit 4. The threshold value of the comparator 6 is set to a value corresponding to this peak value.

The signal waveforms 43 and 44 in FIG.
It is equal to 1,42. 43 is drawn in phase with 41, and 44 is drawn ahead of 42 by T ₁ .

The comparator 6 is composed of an operational amplifier, and the threshold value of the comparator 6 is determined when the peak value of the output signal of the phase discrimination circuit 4 detected by the peak hold circuit 5 is _M1 . It is set to S ₁ which is a saturated region, and when M ₂ is set to S ₂ which is also an unsaturated region. For example, these have the relationship shown in the following equation.

M ₁ /S ¹ =k·M ₂ /S ² (k: constant) On the other hand, another threshold value S ₃ is set in the comparator 6. This S ₃ is a fixed value.

The comparator 6 uses the threshold value S ₃ at the rising edge and the threshold value (S ₁ , S ₂ ) corresponding to the peak value (M ₁ , M ₂ ) at the falling edge.

Therefore, when the peak value M1 of the signal 43 and the peak value of the signal 44 are _M2 , a pulse signal shown as 61 is obtained for the signal 43, and a pulse signal shown as 62 is obtained for the signal 44, respectively. This pulse signal 61, 62 produces the output 7 of the comparator 6. When processed in this way, the fall of the pulse signal 61 is determined by the time T ₂ from the fall of the pulse signal 11, that is, the time when the pulse signal 61 falls due to the signal 43 when the threshold value S ₃ is set, and the threshold value is determined. This is earlier than the timing at which the pulse signal 61 falls due to the signal 43 in the case of _S1 by a time difference. The fall of the pulse signal 62 is a time T ₃ from the fall of the pulse signal 12, that is,
When the threshold value is _S3 , the timing of the fall of the pulse signal 62 due to the signal 44 and the threshold value are
It is delayed by the time difference from the timing at which the pulse signal 62 due to the signal 44 falls in the case of _S2 .

The time indicated as T ₄ in FIG.
This shows the time difference between the falling point of the signal 61 and the falling point of the signal 62 when the signal 61 is drawn delayed by the time T1. This T ₄ becomes approximately equal to T ₁ .

In other words, the signals 61 and 62 obtained at the output end of the comparator 7 can be made to fall when the distance between the vehicle and the detection loop reaches a constant value, regardless of the type of vehicle.

Therefore, it is necessary to provide two detection loops or one detection loop and other sensors along the vehicle travel path to know the width of the pulse signals 61, 62 or the interval between the pulse signals 61, 62. Therefore, regardless of the height of the vehicle, the time it takes the vehicle to pass through the detection loop can be averaged and detected, thereby improving detection accuracy.

In the above embodiment, the threshold value of the comparator 6 is set based on the maximum value of the output signal of the phase discrimination circuit 4, but it may be set based on the waveform of the output signal. Further, the present invention is not limited to detecting vehicles, but can be applied to other uses as long as it is a metal object.

The signal waveform in FIG. 2 is based on actually measured values, and the uneven shape of the signal waveform is due to the uneven shape of the bottom surface of the vehicle, but in reality, the peak value is taken as an averaged value.

FIG. 3 schematically shows the averaged values, and shows the case where the length of the vehicle is the same but the height of the vehicle is different. In this figure, the signal is a waveform diagram of a vehicle with a high vehicle height, and the signal is a waveform diagram of a vehicle with a low vehicle height.If a fixed threshold value _S3 is set for both waveforms, the pulse signal of the signal is A. The signal rises at time B, and the signal rises at time B, delayed from the signal. Similarly, looking at the falling point, the signal falls later than the signal. Therefore, when a fixed threshold value _S3 is used, even if the length of the vehicle is the same, the pulse signal width will differ and this will be detected as a difference in transit time.

Therefore, the peak hold circuit 5 detects the average value or peak value of the output signal of the phase discrimination circuit 4, and depending on the output signal, the comparator 6 sets the threshold value to S' ₁ for the signal and to S'1 for the signal. However, by setting S′ ₂ respectively, the falling point can be made constant regardless of the vehicle height, so the detection can be performed in an averaged state over the time when the vehicle passes through detection loop 1. , whereby detection accuracy can be improved.

According to this invention, in accordance with the signal waveform obtained in accordance with the height of a moving object passing on the loop, a threshold at the falling edge of the signal waveform is set for extracting an effective waveform portion of the signal waveform as a pulse signal. Since the value is changed, detection accuracy can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of this invention.
FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment shown in FIG. 1, and FIG. 3 is a signal waveform diagram for explaining the principle of the present invention. 1...Detection loop, 5...Peak hold circuit, 6...Comparator.

Claims (1)

[Claims] 1 a detection loop, a detection circuit that generates a signal of a level corresponding to an inductance change caused in the detection loop by a moving object moving on the detection loop, a waveform shaping circuit that shapes the output signal of the detection circuit, and a waveform shaping circuit that shapes the output signal of the detection circuit; A moving object detection device comprising: a conversion circuit in which a threshold value for determining a falling edge of a rectangular wave obtained from a shaping circuit is set to a different value depending on the height of the moving object.