JPH038487B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a device that uses ultrasonic waves to collect data regarding the height of a passing vehicle and determines the type of vehicle based on this vehicle height data.

Here, vehicle height refers not only to the height of the highest point of the vehicle, but also to the height of any arbitrary point on the upper edge of the longitudinal cross-sectional shape of the vehicle.

Conventional vehicle type identification devices using ultrasonic waves include an ultrasonic transducer installed at a predetermined height above the road surface, and the ultrasonic transducer emits pulsed ultrasonic waves intermittently at a fixed period. Ultrasonic waves are transmitted toward the road surface, reflected by the road surface or the vehicle, and returned to the ultrasonic waves. By measuring the time it takes for the ultrasonic waves to travel back and forth, it is possible to determine the presence or absence of a vehicle, measure the vehicle height, The vehicle type was determined based on vehicle height data. The reason why ultrasonic waves are transmitted intermittently is to avoid confusion between the transmitted ultrasonic waves and the ultrasonic waves that are reflected back. The next ultrasonic wave had to be transmitted after waiting for the next ultrasonic wave to be received. For this reason, the ultrasonic wave transmission period is a relatively long period of time, and there is a problem in that accurate vehicle detection cannot be expected when the vehicle speed is high. For example, if an ultrasonic transducer is installed at a height of 5 m from the road surface, and the speed of sound is 340 m/s, the time required for the ultrasonic waves to travel back and forth between the road surface and the road surface is approximately 30 ms. be. Assuming the vehicle speed is 100km/h and the vehicle length is 4~5m,
This vehicle passes the vehicle detection point in approximately 150ms. Therefore, even if the ultrasonic wave transmission cycle is set to 30 ms, sampling can only be performed at a maximum of 5 points for a vehicle traveling at 100 km/h. Not all sampling data is valid, so in reality there will be about three valid data points. With this number of sampling points, the vehicle height can only be measured partially, that is, vehicle data can only be obtained from the front and rear of the vehicle, or only from the roof of the vehicle, so there is a problem in that accurate vehicle type identification cannot be expected. .

Summary of the Invention An object of the present invention is to provide a vehicle type discriminating device capable of highly accurate vehicle type discrimination.

The vehicle type discrimination device according to the present invention includes means for generating an ultrasonic signal whose frequency is continuously changed;
An ultrasonic transmitter that is placed above the road surface and is continuously driven by this ultrasonic signal; an ultrasonic receiver that is placed above the road surface that receives reflected waves from the vehicle and the road surface; means for frequency demodulating the output signal of the wave generator and extracting a signal representing a change in frequency;
A means for generating a signal representing a vehicle height by comparing a signal representing a frequency change of a transmitted ultrasonic wave with a signal representing a frequency change of a received ultrasonic wave, a means for detecting vehicle speed, and a detected vehicle speed. means for sampling the signal representing the vehicle height at a sampling period determined by; and means for determining the vehicle type by comparing the sampled vehicle height data with preset vehicle height patterns for a plurality of vehicle types; It is characterized by having the following.

In this invention, ultrasonic waves are continuously transmitted to collect vehicle height data, and reflected ultrasonic waves from the road surface, the vehicle, etc. are continuously received. Continuous transmission and reception of ultrasonic waves is made possible by continuously changing the frequency of the ultrasonic waves, for example, at regular intervals. Since accurate information regarding the vehicle height can be obtained continuously, there is a wealth of information regarding the vehicle height, and therefore accurate vehicle type determination is possible. Further, in the present invention, the vehicle speed is measured, and the sampling period of the signal representing the vehicle height is determined based on the measured vehicle speed. Therefore, the sampled data includes information regarding the length of the vehicle, that is, the vehicle length, as the number of sampled data. In this invention, since the vehicle type is determined taking into consideration not only the vehicle height but also the vehicle length, extremely high precision vehicle type discrimination can be expected.

Other features and detailed configurations of the invention will become apparent in the following description of embodiments with reference to the drawings.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows the arrangement of an ultrasonic transmitter and a receiver for measuring vehicle height and an optical sensor for measuring vehicle speed. An ultrasonic wave transmitter 1 and an ultrasonic wave receiver 2 are provided at a predetermined height H above the road surface L, and are fixed to a suitable support member. The transmitter 1 transmits ultrasonic waves toward the road surface L, and the receiver 2 receives the ultrasonic waves that are reflected back from the road surface L or the vehicle CA. The frequency of the transmitted ultrasound is the second
As shown by the solid line in the figure, it changes continuously at a constant period T. In this example, the change in frequency is triangular in time, but any other waveform can be employed. For example, if we create a sawtooth waveform in which the frequency monotonically increases from the lower limit frequency, reaches the upper limit frequency, suddenly reaches the lower limit frequency, and then monotonically increases again at a constant cycle, the frequency increases monotonically. Since it is only necessary to consider changes in , signal processing is simplified. The frequency change period T is the time required for the ultrasonic waves to travel back and forth between the transmitter, the receivers 1 and 2, and the road surface L, for example.
It is preferable that it is 30ms or more. It is desirable that the width between the upper and lower limits of the ultrasonic frequency be wide.
Currently, there are ultrasonic transducers that generate (detect) ultrasonic waves with a substantially constant amplitude (sensitivity) over a bandwidth of about 22 to 30 KHz.

In FIG. 2, the waveform indicated by a broken line indicates a change in the frequency of the ultrasonic signal received by the receiver 2. In FIG. The reflected wave from the road surface L is received when time td has elapsed after the ultrasonic wave was transmitted. On the other hand, the reflected wave from vehicle CA is received after time tv (<td). When the sound speed is Vs and the distance between the transmitter and receiver 1, 2 and the vehicle CA is h, the following equation holds true.

td=2H/Vs...(1) tv=2h/Vs...(2) By comparing the transmitted and received waveforms shown in Figure 2, the presence or absence of vehicle CA and the longitudinal cross-sectional shape of vehicle CA can be determined. Understand that it is possible to judge.

The vehicle height Hc is the height of the point on the upper edge of the longitudinal cross-sectional shape of the vehicle CA, so from Hc = H - h, it is expressed by the following equation using equations (1) and (2). .

Hc=H-(tv×Vs)/2=(td-tv)×Vs/2 (3) The optical sensor is also installed at a height H above the road surface. The optical sensor includes an optical system including a lens 4 that captures the vehicle CA within its field of view;
A detection array 3, which is arranged on the imaging plane of the sensor and constitutes a spatial filter, and a differential amplifier circuit 5 are built in. The vehicle sensing area of this optical sensor is set at the same location as the vehicle sensing area of the sensor consisting of transmitter and receiver 1 and 2 using ultrasonic waves. The detector array 3 consists of a large number of elongated photoelectric conversion elements 3a and 3b arranged alternately in parallel and in a line, and every other photoelectric conversion element is connected to each other. Two outputs are taken. These two outputs are sent to a differential amplifier circuit 5, which outputs a difference signal g between the two output signals.

When a vehicle CA passes within the field of view of the optical system, its emitted light (e.g. from headlights) or reflected light is detected by the detection array 3 and has a frequency dependent on the height of the detection point of the vehicle and the speed V of the vehicle. An output signal g of o is obtained from the differential amplifier circuit 5. This output signal g, vehicle speed V, and distance h to the vehicle
The relationship with is given by the following equation.

o=K ₁ V/ph (4) where K ₁ is a proportionality constant, p is the pitch of the spatial filter, and is the gap between one photoelectric conversion element 3a or 3b.

It will be easily understood that by dividing equation (4) by equation (2), the component related to distance h is eliminated, and the frequency of signal g is converted into a function of only vehicle speed V.

The time required for the vehicle to pass the detection point, that is, the time Tp during which the vehicle is detected (Fig. 4, signal i
), the vehicle length Lc of the vehicle CA is calculated using the measured vehicle speed V using the following equation.

Lc=Tp×V...(5) Figure 3 shows the electrical configuration of the vehicle type discrimination device, and
The figure shows the output signal waveforms of each block of this electric circuit.

A clock signal generating circuit 11 outputs a square wave signal a with a constant period T, and this signal a is converted into a triangular wave signal b by an integrating circuit 12. This signal b is input to the voltage controlled oscillation circuit 13. Voltage controlled oscillation circuit 1
3 has a voltage/frequency conversion function that outputs a signal with a frequency proportional to the input voltage. The output signal of the oscillation circuit 13 is sent to a power amplification circuit 14, and the ultrasonic transmitter 1 is driven by this amplification circuit 14.
In this way, ultrasonic waves whose frequency changes continuously at a constant period T, that is, frequency-modulated ultrasonic waves are transmitted from the transmitter 1 toward the road surface L.

The ultrasonic signal reflected by the road surface L or the vehicle CA and received by the receiver 2 is amplified by the voltage amplification circuit 21 and then input to the phase comparison circuit 22 .
This phase comparison circuit 22 includes a voltage controlled oscillation circuit 24
Compare the phase of the output signal and the phase of the received signal,
A voltage signal corresponding to these phase differences is output. This phase difference component is sent to a low-pass filter 23, and its high frequency component is removed. The output c of the filter 23 controls the oscillation frequency of the voltage controlled oscillation circuit 24. The voltage controlled oscillation circuit 24, the phase comparator circuit 22 and the low pass filter 23 constitute a phase locked loop (PLL), which is used here as an FM demodulation circuit. In this way, a voltage signal c proportional to the frequency of the received signal is obtained.

The output signal b of the integrating circuit 12 is delayed by the above-mentioned time td in the delay circuit 15. The delayed signal d and the demodulated signal c are input to the differential amplifier circuit 25, and a difference signal e between them is obtained. The differential amplifier circuit 25 outputs a signal at the maximum level when the difference between both input signals is zero, and outputs a signal at a level lower than the maximum level by the difference when the difference between the two signals is not zero. It is configured.
Therefore, the output signal e is determined by the time td or tv from ultrasonic transmission to reception (therefore, equations (1) and (2)
From the formula, it represents H or h). delay time td
is the time required for the ultrasonic waves to travel back and forth over the distance H between the transmitter and receiver 1, 2 and the road surface L, so if there is no vehicle, both signals c and d have the same shape, The difference signal e reaches the maximum level. However, when the vehicle CA is present, the waveform of the signal e shows a shape similar to the vertical cross-sectional shape of the vehicle CA toward the negative side.
By discriminating the signal e at a suitable threshold level Sh in the comparison circuit 26, a detection signal i representing the presence of a vehicle is obtained. This detection signal i is used as a gate control signal for AND gates 28 and 29, and is also sent to a microprocessor (MPU) 40 via an interface 43.
Enter.

The speed of sound Vs changes with temperature, and the time td changes accordingly. In order to prevent malfunctions due to changes in ambient temperature, it is preferable to perform temperature compensation on the delay time td of the delay circuit 15. However, if the threshold level Sh is selected in consideration of level fluctuations in the signal e due to temperature changes, the temperature compensation circuit is not necessarily necessary.

The output signal e of the differential amplifier circuit 25 is also sent to an inverting circuit 27 and becomes an inverted signal r. This signal r is similar to the longitudinal cross-sectional shape of the vehicle, and the vehicle height Hc
It represents. A signal representing the vehicle height Hc is sent to an AND gate 28. Since the gate of this gate circuit 28 is opened by the vehicle detection signal i, the signal r is input to the sample-and-hold circuit 30 when a vehicle is detected. The sample and hold circuit 30 samples the input signal r at a sampling period t and holds it until the next sampling. The sampling period t is determined by the MPU based on the measured vehicle speed V, as described later.
40 and provided to the sample and hold circuit 30 for each vehicle detection. The sampled signal is analog/digital (A/D) converted by the interface 43 and then read by the MPU 40 as vehicle height data.

The output signal e of the differential amplifier circuit 25 is further A/D
The signal is also sent to a conversion circuit 31 and converted into a digital signal. This digital signal becomes the setting input for the programmable counter 32. The programmable counter 32 receives an input signal (voltage controlled oscillation circuit 35
The frequency of the output signal) is divided by 1/N, with N being the setting input. If the frequency of the input signal is the frequency of the output signal of the counter 32, the frequency of the output signal of the counter 32 is /N. The setting input N is given by the output of the A/D conversion circuit 31, and since this output is proportional to the distance h from the sensor to the vehicle (or the distance H to the road surface), K ₂ is used as a proportionality constant. It can be set as N=K ₂ h ……(6).

On the other hand, the output g of the differential amplifier circuit 5 of the optical sensor is input to the phase comparator circuit 33. This phase comparison circuit 33 compares the phases of the signal g and the output signal of the counter 32, and outputs a voltage according to the phase difference.
After this phase difference voltage has its high frequency component removed by a low-pass filter 34, the voltage controlled oscillation circuit 3
5 to control its oscillation frequency. The voltage controlled oscillation circuit 35 includes a programmable counter 3
2. Phase comparison circuit 33 and low-pass filter 3
The oscillation frequency is controlled by the closed loop consisting of 4 so that it matches =No.

When equations (4) and (6) are substituted into the above equation = No, and the new proportionality constant is _K3 , the frequency is expressed by the following equation.

=K ₃ V...(7) That is, the output signal j of the voltage controlled oscillation circuit 35
The frequency is proportional only to the vehicle speed V. This signal j is determined by the vehicle detection signal i.
When the AND gate 29 is opened, the speed signal m is taken out. The speed signal m is converted into data directly representing the vehicle speed V at the interface 43 by a known processing circuit, such as a counter that counts the number of pulses (frequency) of the signal m, and is input to the MPU 40 .

The MPU 40 performs vehicle discrimination processing, and includes a ROM 41 that stores its execution program and standard vehicle height patterns for a plurality of vehicle types, and a RAM 42 that stores various data.

An example of the vehicle height standard pattern stored in the pattern area in the ROM 41 is shown in FIG. A is a standard vehicle height pattern for ordinary passenger cars, and B is a standard vehicle height pattern for large trucks. Each vehicle height data of these standard patterns is taken at regular intervals l for all vehicle types. Therefore, the longer the vehicle length, the more vehicle height data there is. The fixed interval l is a value obtained by dividing the maximum vehicle length Lcmax (for example, 10 m) of all vehicles by a predetermined number M. The number of vehicle height data of the vehicle type with this maximum vehicle length Lcmax is M. The addresses where each vehicle height data that constitutes the vehicle height standard pattern for ordinary passenger cars are stored are A ₁ , A ₂ , ...,
A _n , those for heavy trucks B ₁ , B ₂ ,
..., B _n .

FIG. 6 shows sampling data of passing vehicles loaded into RAM 42. The sampling data is sequentially stored in the data area in the RAM 42 in the order of sampling (order of reading). Addresses of storage locations where each piece of data is stored are represented by a ₁ , a ₂ , . . . , a _j . The sampling period t is given by t=l/V (8) using the above-mentioned interval l and the measured vehicle speed V. This time t is the time required for the vehicle to move the distance l. This data area has a capacity to store up to M pieces of data.

Also in the RAM 42, as shown in FIG.
There is an area that is used as a matching counter for vehicle type identification. In this embodiment, the vehicles include a regular passenger car, a small passenger car, a large truck, a small truck,
The vehicles are classified into six types: large buses and small buses, and a matching counter is provided for each type of vehicle.

FIG. 8 shows the operation of the MPU 40. When the vehicle detection signal i is input (step (51)), a timer (not shown) provided in the MPU 30 for timing the sampling period t is reset to start a timing operation (step (52)), and the RAM 4
The first address _a1 of the data area within 2 is set in an address counter (not shown) (step (53)). Then, the speed data is read (step (54)), and the sampling period t is determined using equation (8) using this speed V (step (55)).
The determined period t is determined by the sample and hold circuit 30.
given to. Also, the data area in RAM 42 is cleared.

When the sampling period t has elapsed (step (56)), the above-mentioned timer is reset again (step (57)). After this, the timer starts timing operation again. The sampled vehicle height data is then passed through the interface 43 and stored in the memory location addressed by the address counter in the data area (step (58)). Next, the count value of the address counter is incremented by 1 to store the sampling data (step (59)). Steps (56) to (59) above
The processing is repeated every time t, and the sampling data is stored in the RAM 32 in sequence. When the vehicle detection signal i stops, it means that a vehicle has passed (step (60)), so the data collection operation ends and the process proceeds to the vehicle type discrimination operation.

First, the start address _a1 is set in the address counter (first counter) for the data area of the RAM 42 (step (61)), and the address counter (second counter) for the pattern area of the ROM is set. This counter is for each car type)
The first address (for example, A ₁ ) is set at (step (62)). The sampling data and standard pattern vehicle height data addressed by these counters are read and compared (step (63)). This comparison is based on the sampling
This is done between the vehicle height data and the standard pattern vehicle height data for all vehicle types. And sampling
The match counter (FIG. 7) for the vehicle type with the smallest difference between the data and the vehicle height data is incremented by 1 (step (64)). The first counter is incremented by 1 to read the next sampling data, and the second counter is incremented by 1 to read the next standard vehicle height data (step (65)). Then, the counter CN for counting the number of data for which comparison has been completed is incremented by 1 (step (66)). Steps mentioned above (63) ~
The process in (66) is continued until the comparison is completed for the maximum number M of vehicle height data of the standard pattern, and for each comparison, the vehicle model whose standard vehicle height data is closest to the sampled data that has been read out is selected. The match counter is incremented by 1. And counter CN
When the value of M reaches M (step (67)), the counted values of the matching counters are compared with each other, and it is determined that the vehicle type whose matching counter has the largest counted value is the vehicle type of the vehicle that passed (step (68)). )).

In Figure 8, the sampling period t is
The MPU 40 also measures time, but after giving the determined period t to the sample and hold circuit 30, the period t is managed by this circuit 30, and the circuit 30 sends a signal to the MPU every time t elapses. An interrupt signal is input, and when this interrupt occurs, the A/D converted sampling data is sent to the MPU.
40 may be read. Further, in the above-described vehicle type determination process, the vehicle type is determined based on the number of standard vehicle height data closest to the sampling data, but it goes without saying that other known pattern determination methods may also be used. For example, the 9th
As shown in the figure, an allowable range of vehicle height data is determined in advance as a standard vehicle height pattern, and it is determined whether each sampled data falls within this range. The type of vehicle can also be determined based on the number of sampling data that falls within a permissible range, or based on whether the number is greater than a predetermined number.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the arrangement of ultrasonic transmitters, receivers and optical sensors, Figure 2 is a time chart showing changes in the frequencies of transmitting and receiving waves, and Figure 3 is an electrical diagram of the vehicle type discrimination device. Block diagram showing the physical structure, No. 4
Figure 5 is a time chart showing the output signals of this block diagram, Figure 5 is a diagram showing an example of a vehicle height standard pattern, Figure 6 is a diagram showing a sampling data pattern, and Figure 7 is a diagram showing a coincidence counter. , FIG. 8 is a flow chart showing the processing of the MPU, and FIG. 9 is a diagram showing another example of the vehicle height standard pattern. 1... Ultrasonic transmitter, 2... Ultrasonic receiver, 3
...Detector array, 5,25...Differential amplifier circuit,
11... Clock signal generation circuit, 12... Integrating circuit, 13, 24, 35... Voltage controlled oscillation circuit, 1
5... Delay circuit, 22, 33... Phase comparison circuit,
23, 34...Low pass filter, 26...Comparison circuit, 27...Inverting circuit, 30...Sample and hold circuit, 32...Programmable counter, 40...Microprocessor (MPU), 41
...ROM, 42...RAM, 43...Interface.

Claims (1)

[Claims] 1. A means for generating an ultrasonic signal whose frequency is continuously changed; An ultrasonic transmitter placed above the road surface and continuously driven by the ultrasonic signal; A road surface. An ultrasonic receiver placed above to receive reflected waves from vehicles and road surfaces; means for frequency demodulating the output signal of the ultrasonic receiver and extracting a signal representing a change in frequency; means for generating a signal representing a vehicle height by comparing a signal representing a frequency change of the received ultrasonic wave with a signal representing a frequency change of the received ultrasonic wave, a means for detecting vehicle speed, and a sampling period determined by the detected vehicle speed. means for sampling the signal representing the vehicle height, and means for determining the vehicle type by comparing the sampled vehicle height data with preset vehicle height patterns for a plurality of vehicle types. Vehicle type identification device.