JPS61294383A - Speed measuring method - Google Patents

Abstract

PURPOSE:To measure a vehicle speed with a high precision even if a Doppler wave is unstable, by abandoning or compensating measured data in accordance with the level strength of the Dopper wave and the measured time. CONSTITUTION:A difference device 14 operates the difference between a trans mission frequency f0 from a transmitting circuit 11 and a reception frequency f0+ or -DELTAf from a receiver 13 to generate a Doppler wave + or -DELTAf. A period measuring part 15 measures successively the period of DELTAf. A vehicle detecting part 16 detects a vehicle by reception of a certain quantity of the Doppler wave and outputs a start signal to an elapsed time measuring part 17, and the measuring part 17 measures the time after vehicle detection. A speed operating part 18 calculates successively the vehicle speed and the vehicle covered distance in accordance with the period measured value of the Doppler wave and the elapsed time measured value; and if the vehicle covered distance exceeds a certain value, measured values after this excess are not adopted, and the vehicle speed is operated in accordance with the period measured value of the Doppler wave obtained before this excess.

Description

[Detailed Description of the Invention] [l] Industrial Application Field This invention relates to an ultrasonic Doppler type vehicle speed measuring device, which calculates the approximate traveling distance of a vehicle from the point where Doppler waves are first obtained. , a period measurement point is determined, and if the value deviates significantly from a predetermined point, the measured value is not adopted.

In this way, the instability of Doppler measurement due to the shape of the moving vehicle can be eliminated, and accurate speed measurement can be performed. .

[2] Prior Art An ultrasonic Doppler vehicle sensor is well known as a means for measuring the speed of a moving vehicle.

In other words, as shown in Figure 3, approximately 5.5 mm of pole land on the road side.
An ultrasonic transmitter/receiver (total) is installed at a height of 5 m and emits ultrasonic waves of frequency fp (Hz). When there is a moving object such as a vehicle (3υ), its reflected wave causes a frequency shift of Δf (Hz) that is proportional to the speed (V) of the vehicle Oυ.The Doppler vehicle sensor measures this frequency shift, The vehicle speed is calculated from this value.In reality, this frequency-shifted wave (hereinafter referred to as Doppler wave) is usually caused by unevenness of the moving object's reflective surface and reflections from outside the moving object. are various reflected waves with different widths, frequencies and phases,
In order to improve the accuracy of measuring the period of Doppler waves, N Doppler waves are determined and the vehicle speed is calculated from the average value.

From the viewpoint of measurement accuracy, it is generally advantageous to have a larger period measurement wave number N.

[3] Problems with the conventional technology In the conventional technology, the Doppler waves are relatively stable, which is good for ordinary passenger cars, but in the case of motorcycles, etc., the Doppler waves are unstable or may not even be obtained. . In such a case, the time required to measure n waves N times increases, and the distance the vehicle travels during that time increases, causing a problem in that the Doppler wave period measurement deviates and the speed measurement accuracy deteriorates. be.

In other words, in Figs. 3 and 4, the Doppler waves of a regular passenger car are shown in Fig. 4 (A), and the Doppler waves of a two-wheeled vehicle are shown in Fig. 4 (A).
F]) and the Doppler frequency Δf are shown in FIG. 4(C). The ultrasonic transceiver has an installation angle θ (usually 40 to 45 degrees),
The speed of the vehicle to be measured C(1) is measured at a directivity angle of 2ψ. As is clear from both figures, the reception level is as shown in Figure 4 (3).
However, in (6) of the figure, which targets a motorcycle, the overall level is lower than in (g), and there are cases where no Doppler waves are obtained at all.

The Doppler frequency Δf is expressed by the following equation.

Here, C is the speed of sound, ■ is the vehicle speed, and ψ is the angle between the handset and the direction of travel of the vehicle.

In the case of a two-wheeled vehicle, if the Doppler wave is missing (Fig. 4 @), the number of period measurement points decreases, so even if the vehicle speed V is the same, ψ increases and Δf decreases. On the other hand, since the Doppler sensor calculates V at a predetermined angle, if ψ becomes larger than a predetermined value, V will be calculated to be lower.

[4] Means to solve problems The configuration of the present invention will be explained using FIG. 1.

11 is a transmitting circuit that drives 12 transmitters. 13 is a delivery device that receives reflected waves from the vehicle. 14 is the transmission frequency f
The difference between o and the reception frequency fo±Δf is taken to generate Doppler input f. Reference numeral 15 denotes a cycle measuring unit that sequentially measures the cycle of Δf. Reference numeral 16 indicates a vehicle detection unit which receives a constant Doppler wave to detect a vehicle, outputs a start signal to an elapsed time measurement unit 17, and measures the time after vehicle detection. The speed calculation unit 18 sequentially calculates the vehicle speed and the vehicle traveling distance from the period measurement value of the Dotsupura wave and the elapsed time measurement value,
If the distance traveled by the vehicle exceeds a certain value, the vehicle speed is calculated from the periodic measurements of the Doppler waves before that point, without using the measured values after this point.

[5] Effect According to the invention of the present application, it is noted that the point obtained at the beginning of the Doppler wave does not change greatly even if the type of moving object changes, and the distance traveled by the vehicle from that point is calculated, and each We decided to find the period measurement point.

If this periodic measurement point deviates significantly from a predetermined point, the measured value is discarded. In this way, the vehicle speed can be measured accurately even when the Doppler waves are unstable.

[6] Embodiment In the speed measuring method of the present invention, the approximate traveling distance of the vehicle is determined by measuring the elapsed time after vehicle detection in addition to Doppler frequency measurement.

When this traveling distance is a certain distance or more, by discarding the Doppler cycle measurement values after that, the speed can be measured accurately even when the Doppler wave is unstable, such as in the case of the two-wheeled vehicle. In the example of FIG. 2, if the Doppler wave can be stably received, the cycle measurement is completed between the points ArVA2. As is clear from FIG. 2, the change in Δf during this period is small, so the speed measurement accuracy is high. Next, Dotsupura waves occur intermittently,
In other words, when reception is possible only in an unstable state, measurements are made intermittently at points BI NBg , Bs to B4, and B5 to B6, and the change in Δf is extremely large. In such a case, if the measured values at point BINB6 are averaged and the speed is calculated based on that, a lower value than the actual value will be obtained.

In this case, in this case, the distance traveled by the vehicle is calculated along with the period measurement, and if the distance traveled exceeds the upper limit + max, the subsequent Dotsupura period measurements are discarded and Bl"-
The vehicle speed is calculated using the cycle measurement value of 82.

[7] Effect In the present invention, when measuring vehicle speed using the ultrasonic Doppler effect, the directivity angle (ψ) of the ultrasonic transceiver is measured from the first Doppler wave reception point, and the measurement time ( 1) is also measured, and the measurement data is discarded or corrected based on the level intensity of the Doppler wave (Δf) and the measurement time (1). Therefore, even if the type of moving object changes and Doppler waves are obtained intermittently, accurate Doppler measurement can be performed by selecting appropriate data.

Brief explanation of the table screen FIG. 1 is a diagram showing the configuration of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram for explaining the measurement principle of the ultrasonic Doppler velocity sensor.

Figure 4 is the kth diagram explaining the problems of the prior art, and Figure 4 (a) is the waveform of the Doppler wave of a passenger car.
]) is the waveform of the Doppler wave of a motorcycle. Figure 4 (C) is the waveform of the Doppler frequency Δf. 11: Transmission circuit 31
: Vehicle to be measured 12: Transmitter 32: Travel path 1
3: Receiver 38: Ball 14: Differentiator
34: Ultrasonic transceiver 15: Period measurement section 16: Vehicle detection section 17 Two elapsed time measurement section 18: Speed calculation section Ale As: Dotsupura period measurement point Bl"B
4: Doppler period measurement point C: Sound speed fo: Ultrasonic source frequency Δf: Doppler frequency 2ψ: Ultrasonic transceiver directivity angle θ: Ultrasonic transceiver mounting angle V Two vehicle speed η: Constant tx Nta: Measurement time ψ :Angle between the ultrasonic transmitter and receiver at the period measurement point and the direction of vehicle travel Figure 1 Figure 2

Claims (1)

[Claims] (1) In a speed measurement method that uses the Doppler effect of ultrasound or microwaves to measure the speed of a moving object such as a vehicle running on a road, the period of the Doppler wave is repeatedly measured for multiple waves, and the period of the Doppler wave is measured repeatedly. a means for measuring the elapsed time after the detection of the moving object when the period of the moving object is measured; a means for calculating the traveling distance of the moving object from the period of the obtained Doppler wave and the elapsed time; A speed measurement method characterized by determining which cycle measurement value to adopt based on the following.