JPS6058520B2 - vehicle sensing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle sensing method that enables highly accurate vehicle detection.

Currently, there are ultrasonic type, loop type, etc. used as vehicle detectors, but these are all called presence detection types, which emit pulses proportional to the time the vehicle is present in the vehicle sensing area. This is what is output.

On the other hand, recently, as speed detection type vehicle sensors that can detect the speed of a vehicle in a non-contact manner, a radar type vehicle sensor, an ultrasonic Doppler type vehicle sensor, and an optical type vehicle sensor have been put into practical use.

In the case of speed detection type detectors, the signal output form of the detected speed is generally a binary code or a binary w-adic code (BCD code), so it is necessary to output a signal of several bits. .

A transmission device used when information expressed by this code is to be collected, for example, by a processing device at a center, converts it into a certain serial code, modulates it, and transmits it over a communication line. At the center, operations such as demodulating and decoding are required. In other words, in order to transmit the speed signal expressed as a code of several bits to the processing unit at the center, a relatively complex device such as an encoder is required for each vehicle sensor. There is a need for a means to accurately transmit speed signals using an economical transmission device.On the other hand, there has been no effective transmission method for transmitting the output signal of a presence detection type vehicle sensor with a significant pulse width. As an example, there is a method of performing FS modulation on a pulse width signal and transmitting the signal.In this case, a general low speed modem of about 50 b/s is effective and is effective in accurately transmitting the pulse width.

There is also a method of performing operations such as FS modulation and direct current transmission, which is effective when the transmission distance is short. Here, there is a method of converting speed information into a pulse width that can be transmitted only by s modulation or suitable for direct transmission.One of the conversion methods is a method of converting it into a pulse width that is directly proportional to the traveling speed. is possible.

This conversion method requires a relatively long time for fast speeds.
For slow speeds, this translates into relatively short pulse widths. Now, radar type vehicle detectors, ultrasonic Doppler type vehicle detectors, etc. have a vehicle detection area 9 of several meters in the direction of vehicle travel, as shown in Figure 4, and two or more devices are installed in this sensing area 9. If vehicles 7 and 8 exist, and if vehicle 8, which first entered detection area 9, still exists, the speed of vehicle 7, which entered detection area 9 later, should be measured. Furthermore, while the pulse width signal is being output to the outside, the speed of a vehicle 7 newly entering the sensing area 9 cannot be measured. Therefore, if a relatively long pulse width is output at a high speed, the vehicle will pass through the deceptive area in a short time.
Even after the vehicle in front has moved out of the detection area, a pulse-width signal will continue to be output while the vehicle is moving, and the speed of the vehicle will not be measured again, making the resolution of the vehicle detection system worse than necessary. There are drawbacks to doing so. The present invention has improved these drawbacks, and since the signal is a 1-bit signal, the configuration of the transmission device is simple. For example, it can be transmitted using one channel of a low-speed transmission device of 50 b/s, and moreover, the processing device can accurately transmit information. can be obtained. FIG. 3 is a block diagram of a vehicle detection device according to an embodiment of the present invention, and FIG. 1 is a diagram showing the relationship between vehicle running speed and pulse width of the same embodiment.

In FIG. 3, reference numeral 1 denotes a radar head of a radar type vehicle detector, which serves both as a transmitter and a receiver. 2 is a Doppler waveform shaping circuit that converts the sine wave signal of the radar head 1 into a rectangular wave signal, and 3 is the speed V of the vehicle from the Doppler waveform shaping circuit 2.
A speed calculation circuit 4 detects the speed .function. from this speed .function..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times..times...times..times..times..times..times..times..times..times.2.. This is a speed/pulse width conversion circuit.

5 is a modulation/demodulation circuit for sending this pulse width P7 to the transmission line 6.

It shows the relationship between the vehicle speed measured by the vehicle detector and the pulse width signal output, which is converted into a pulse width that is inversely proportional to the speed. Expressing this relationship j using a mathematical formula, the pulse width Pw is a function P(v) of the measured running speed V of the vehicle.
It is expressed as Equation (1). - However, in equation (1), Vmax is the maximum perceivable speed/degree, Pmin is the minimum pulse width, and A is a proportionality constant, where Vmax = 200CKm/h) Pmir! =100
[m? Ec) A=10Cmsec/Km/h]7. -i-Tjf>chi-40rKm/h] If you test the speed limit of 1700 [Msec], 80 [K
m/h] is 1300 [Msec] 120 [Km/h]
Then, it is converted into a pulse width of 900 [Msec] and output. By the way, when transmitting the pulse width signal output from the vehicle detector to, for example, a central processing device and processing it,
This produces errors at some points. The first
The second point is a sampling error in the processing device, and the second point is a sampling error in the transmission device or an error due to modulation/demodulation distortion.

That is, when a TDM transmission method is used as a transmission device, there is a sampling error with respect to a pulse signal input to the transmitter, and when a low-speed FS modulator is used, there is an error due to modulation/demodulation distortion. The maximum value of the pulse width error at each point mentioned above is considered to be constant regardless of the true pulse width signal (i.e., the pulse width signal output from the vehicle sensor), and therefore these The maximum value of the total error, that is, the maximum value of the difference between the true pulse width and the pulse width obtained after processing by the processing device via the transmission system, is also considered to be unrelated to the true pulse width. be able to.

Now, when the pulse width is converted into speed, consider the relative error of the speed error with respect to the true speed (that is, the speed measured by the vehicle detector).

Now, suppose that when the true pulse width is PWl, the error between the true pulse width and the pulse width obtained by the processing device takes the maximum value D, and as a result of converting it into speed at this time, the speed error is Vmis.
Suppose it becomes. When the conversion shown in equation (1) is performed, the speed error (S) is expressed as equation (2) by inversely transforming equation (1). Now, if the relative error of this Vmjs with respect to the true speed V is Q, it is expressed as in equation (3). Since both D and A are constants, the relative error Q in this case changes depending on the true speed (2). That is, when the speed is relatively high, the reproduced relative error is small, and when the speed is relatively low, the relative error is large. Figure 2 shows another embodiment, and shows the relationship between the vehicle running speed measured by the vehicle detector and the pulse width signal output, where the running speed is a logarithmically proportional pulse with a negative coefficient. I am trying to convert it to width.

When this relationship is expressed mathematically, the pulse width Pw is expressed as a function P(v) of the vehicle running speed, as shown in Equation (4). In formula (4), ■Max is the maximum detectable speed, Pmjn is the minimum pulse width, A is a proportionality constant,
Vmax=200 [Km/h], Pmin=100Cm
sec], A=400.

Suppose now that when the true speed, that is, the measured running speed of the vehicle is V1, and the pulse width output is PWl, the error with the pulse width PW2 obtained by the processing device reaches its maximum value.

When the speed reproduced by the processing device is V2, the speed error Vmis at this time is expressed as shown in Equation (5) by inversely transforming Equation (4). (However, E is a constant, E=AlOgeVmax+Pmin) Therefore, the relative error Q of the speed error at this time with respect to the true speed
Since D and -A are constants, the relative error between the maximum speed error and the true speed always takes a constant value.

As is clear from the above embodiments, the present invention uses a speed detection device such as a Doppler radar.
It only needs to be installed in one location, which reduces equipment costs such as installing signal cables, and since the speed signal is output by converting it into a pulse width that is inversely proportional to the running speed of the vehicle, two cars can be driven at high speeds. This has the advantage that even if two vehicles enter the sensing area one after another, both vehicles can accurately send pulse width signals.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing vehicle running speed versus pulse width of a vehicle sensing device according to an embodiment of the present invention, FIG. 2 is a diagram showing vehicle running speed versus pulse width according to a second embodiment, and FIG. 3 is the same diagram. The block diagram of the embodiment, FIG. 4, is a diagram showing a general misunderstanding area. 1... Rouder head, 2... Doppler waveform shaping circuit, 3... Velocity calculation circuit, 4...
... Speed P pulse width conversion circuit, 5... Modulation/demodulation circuit.

Claims (1)

[Claims] 1 A radar head that transmits toward a traveling vehicle and receives the reflected wave, a Doppler waveform shaping circuit that converts the received signal of this radar head into a rectangular wave signal, and the speed of the vehicle from the signal of this Doppler waveform shaping circuit. A speed calculation circuit that detects V, and a pulse width P_w from this speed V, P_w
= A (V_m_a_x - V) + P_m_i_n (where, A: proportionality constant, V_m_a_x: maximum detectable speed,
P_m_i_n: maximum pulse width)