JPH04221782A - Ultrasonic doppler type terrain speedometer - Google Patents

Abstract

PURPOSE:To perform high-accurate measurement of a speed by reducing a directional angle of a transmission ultrasonic wave to a value lower than a specified value. CONSTITUTION:After an ultrasonic signal 4 generated by an transmitter 1 is amplified, an echo sounder transmitter 2 is driven. The echo sounder transmitter 2 reduces directional characteristics to a half value half angle value of a transmission acoustic pressure to generate a signal in a range of 4-15 deg. and generates a signal in a range of 4-15 deg. to emit it toward a road surface 5. A signal 4 irregularly reflected by the road surface 5 is received by a receiver 6 to transmit the signal to a multiplier 8 through a preamplifier 7. The multiplier 8 determines a difference between a received frequency and the transmission frequency of the transmitter 1. After noise of the signal is removed, the waveform of a Doppler signal component is shaped by means of a zero cross comparator 10. A frequency is read by means of a pulse counter 11, and converted to a can speed by means of a car speed computing circuit 12. When the directional characteristics of a transmission ultrasonic wave are reduced to a half value half angle value and 10 deg. or less, especially 6 deg. or less, an S/N ratio of the Doppler signal is improved and steep Doppler signal characteristics are provided, and high- precise measurement of a terrain speed can be realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler ground speed meter used, for example, to detect the ground speed of a vehicle, and more particularly to optimal transmission directivity characteristics of the speed meter.

0002

2. Description of the Related Art A conventional ultrasonic Doppler type ground speed meter is described in, for example, Japanese Patent Laid-Open No. 60-76678. The above ground speed meter emits an ultrasonic signal toward the road surface, receives the reflected ultrasonic wave that is diffusely reflected from the road surface, and calculates the ground speed from the frequency change that occurs in the ultrasonic signal due to the Doppler effect. It is something to do.

0003

[Problems to be Solved by the Invention] However, in such conventional ultrasonic Doppler type ground speed meters,
There was no detailed analysis of the directional characteristics of the ultrasonic waves used, and appropriate directional characteristics were selected according to the characteristics of the transmitter and receiver, so the Doppler signal S/
There was a problem in that it was difficult to improve the N ratio, and therefore it was difficult to measure speed with high accuracy.

The present invention has been made to solve the problems of the prior art as described above, and the S/S of the signal is the most important among the Doppler signal characteristics for a ground speed meter.
The purpose of the present invention is to provide an ultrasonic Doppler ground speed meter that increases the N ratio and thereby enables highly accurate speed measurement.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention is constructed as described in the claims. That is, the present invention is characterized in that the directivity characteristic of the transmitted ultrasound signal is set to a value of at least 10 degrees or less, preferably 6 degrees or less, as the half angle of the transmitted sound pressure.

[0006]

[Operation] As detailed in FIGS. 2 to 8 below, according to the results of theoretical analysis and experiments conducted by the present inventors,
It has been found that the directivity characteristics of the transmitted ultrasonic waves have a large influence on the S/N ratio of the signal, which is the most important among the Doppler signal characteristics for a ground speed meter. Therefore, in the present invention, from the dependence of the ultrasonic propagation coefficient α on the directional characteristics of the transmitter shown in FIG. 2 and the dependence of the reflectivity β of the road surface on the directional characteristics of the transmitter shown in FIG. The dependence of the reception efficiency on the directional characteristics shown in FIG. 4 is determined, and the relationship between the fw value (bandwidth) and the ground speed as shown in FIGS. The optimum transmission ultrasonic directivity characteristics are set as follows. Furthermore, as shown in Fig. 5, the actual measurement results also support the theoretical values shown in Fig. 4, and if the directivity characteristics of the transmitted ultrasonic waves are set within the range of the present invention, a high S/N ratio and the resulting Highly accurate speed measurement can be achieved.

[0007]

Embodiment FIG. 1 is a diagram showing an embodiment of the present invention. First, to explain the configuration, an oscillator 1 generates a 120 kHz signal. The drive means 3 amplifies the above signal,
The output drives the transmitter 2. The wave transmitter 2 is a piezoelectric type wave transmitter, and its directional characteristic generates an ultrasonic signal 4 within a range of 4 degrees to 15 degrees as a half angle, and radiates it toward the road surface 5. . Further, the receiver 6 receives a reflected wave signal obtained by diffusely reflecting the ultrasonic signal 4 upon hitting the road surface 5 . Preamplifier 7 amplifies the received signal and sends it to multiplier 8. Multiplier 8 multiplies the oscillation frequency of oscillator 1 and the frequency of the received signal to find the difference between the two. Further, after the signal from the multiplier 8 is passed through a low-pass filter 9 to remove unnecessary noise, the waveform of the Doppler signal component is shaped by a zero-cross comparator 10, and the frequency thereof is read by a pulse counter 11. Then, the vehicle speed calculation circuit 12 converts the frequency of the Doppler signal into a vehicle speed.

[0008] The frequency component changed by the Doppler effect, that is, the Doppler shift frequency fd, is fd≒2f0, where f0 is the oscillation frequency, C is the speed of sound, V is the vehicle speed, and θ is the radiation angle of the ultrasonic wave with respect to the road surface.・It is expressed as Vcosθ/C. Therefore, the vehicle speed V can be determined by determining the Doppler shift frequency fd. As described above, the frequency of the transmitted ultrasonic wave and the frequency of the received reflected wave are compared, and the ground speed is calculated from the frequency change based on the Doppler effect.

Next, the operation will be explained. FIG. 2 is a diagram showing the experimental results of the dependence of the propagation rate α (corresponding to 1 - attenuation rate) on the directivity characteristics of the transmitter during air propagation of ultrasonic waves, where the vertical axis is the transmissibility α, The horizontal axis is the directivity angle (half angle)
shows. In this experiment, by changing the shape of the acoustic horn provided in the transmitter 2, the unique directivity characteristics of the transmitter were
Experiments were conducted by varying the directivity angle from 4 degrees to 15 degrees.

As can be seen from FIG. 2, the directional characteristics are broadened (
(the directivity angle is large), and the half-angle value of the transmitted sound pressure of the transmitter increases, the propagation rate decreases. This is because the wider the directional characteristic, the more the energy of the sound wave transmitted from the transmitter is absorbed in the air, the attenuation rate increases, and the propagation rate decreases as a result.

Another characteristic phenomenon shown by the measurement results shown in FIG. 2 is that in a region where the half-angle value is approximately 10 degrees or less, the propagation rate increases rapidly as the half-angle value decreases. It can be seen that in a range where the half-angle value is larger than 10 degrees, the change in the propagation rate becomes gradual and the value is low.

Next, FIG. 3 is a diagram showing the actual measurement results of the dependence of road surface reflectivity β on the directivity characteristics of the transmitter, where the vertical axis represents the reflectivity β and the horizontal axis represents the directivity angle (half-angle). show. As can be seen from FIG. 3, the reflectivity β, unlike the propagation coefficient α, does not have dependence on the directivity characteristics. Note that the actual measurement results shown in FIG. 3 are for an asphalt road as an example, but the absolute value of the reflectivity β increases on a gravel road where the road surface is rougher than an asphalt road. However, the dependence on the directional characteristics is similar to that of the Alphard path, where the reflexivity β
It has been confirmed by actual measurement results that there is no dependence on directional characteristics.

Next, FIG. 4 is a diagram showing the dependence of reception efficiency on directional characteristics. The reception efficiency is the calculated value of the coupling product α and β between the propagation coefficient α and the reflection power β. Here, the reception efficiency is the ratio of the reception sound pressure of the Doppler signal component to the transmission sound pressure, and is an index indicating the generation efficiency of the Doppler effect.

As can be seen from FIG. 4, the receiving efficiency α and β are:
In a region where the directivity characteristics are narrow, where the half-value half-angle value is up to about 10 degrees, when the half-value half-angle value decreases, it increases rapidly, and at about 6 degrees, it becomes much larger than when it is 10 degrees or more. However, in a range where the half-angle exceeds 10 degrees, the reception efficiency changes slowly and has a low value. The above-mentioned dependence of the receiving efficiency (therefore, the S/N ratio) on the directional characteristics of the ultrasonic Doppler signal is due to the superposition of two characteristics unique to ultrasonic waves: air propagation coefficient and road surface reflectivity characteristics. It is explained as.

As can be seen from the above FIG. 4 and its explanation,
In a range where the directivity of the transmitted ultrasonic wave is less than 10 degrees as a half-angle value, the reception efficiency rapidly improves as the directivity becomes narrower, and especially in the range of about 6 degrees or less, the reception efficiency shows a high value.

Next, FIG. 5 is a diagram showing actually measured values of the directional characteristic dependence of the S/N ratio of the Doppler signal.
The characteristics at 0 km/h are shown. The characteristics shown in FIG. 5 are very similar to the calculated values of reception efficiency shown in FIG. 4, which proves that the above analysis is correct.

Next, FIG. 6 is a diagram showing experimental results of the dependence of the directivity angle on the fw characteristic representing the steepness of the Doppler signal. As shown in FIG. 7, the above-mentioned fw characteristic is defined as the bandwidth of the Doppler signal when it is 12 dB lower than the peak value of the Doppler signal. That is, the bandwidth fw is expressed by the following (Equation 1).

[0018]

[Math 1]

The above fw characteristic is steep, that is, the fw value (
The smaller the bandwidth (bandwidth), the more accurate the Doppler signal can be detected. From the experimental results shown in Figure 6, ■ the narrower the beam direction angle, the more f
It can be seen that as the w value becomes smaller and the ground speed increases, the fw value also increases, but the narrower the pointing angle, the smaller the tendency for the fw value to increase with respect to the increase in ground speed.

FIG. 8 is a diagram showing the relationship between the fw value (bandwidth) and the ground speed using the directivity angle as a parameter in order to display the above results in an easy-to-understand manner. As can be seen from FIG. 8, when the pointing angle is 15 degrees, the curve is convex downward, and the bandwidth increases rapidly as the ground speed increases. Furthermore, in the case of a pointing angle of 10 degrees, the bandwidth increases almost linearly as the ground speed increases. On the other hand, when the directivity angle is 6 degrees, the curve is upwardly convex.
Bandwidth does not increase significantly as ground speed increases. In other words, in the case of a directivity angle of 6 degrees, the fw value (bandwidth)
is small and does not increase significantly even when the vehicle speed increases, so the Doppler signal can always be detected with high accuracy regardless of the vehicle speed. On the other hand, in the case of a directivity angle of 15 degrees, the fw value (bandwidth) is large and increases rapidly as the vehicle speed increases, so it can be seen that the accuracy rapidly decreases. In the case of a directivity angle of 10 degrees, the characteristics are intermediate between the two, and are located at the boundary where a downwardly convex curve changes to an upwardly convex curve. That is, it can be seen that when the pointing angle is 10 degrees or less, the fw value increases to a small degree with respect to an increase in vehicle speed, and relatively good accuracy can be obtained even at a high vehicle speed. Considering the above results and the results shown in FIGS. 4 and 5, it can be seen that in order to obtain good accuracy, the directivity angle should be at least 10 degrees or less, preferably 6 degrees or less.

[0021]

As explained above, according to the present invention, the directional characteristic of the transmitted ultrasonic wave is set to a value of 10 degrees or less, preferably 6 degrees or less as a half-width value. The S/N ratio of the Doppler signal can be improved, steep Doppler signal characteristics can be obtained, and highly accurate ground speed measurement can be achieved from low speeds to high speeds.

[Brief explanation of the drawing]

[Fig. 1] Block diagram of one embodiment of the present invention

FIG. 2 is a diagram showing the dependence of the air propagation coefficient of ultrasonic waves on the directional characteristics.

FIG. 3 is a diagram showing the dependence of ultrasonic road reflectivity on directional characteristics.

FIG. 4 is a dependence characteristic diagram of reception efficiency on directional characteristics.

FIG. 5 is a diagram showing actually measured values of the dependence of the S/N ratio of a Doppler signal on the directional characteristics.

FIG. 6 is a characteristic diagram of directivity angle dependence on fw characteristics.

FIG. 7 is a frequency characteristic diagram of Doppler signal level.

FIG. 8 is a characteristic diagram showing the relationship between fw value and ground speed using directivity angle as a parameter.

[Explanation of symbols]

1...Oscillator 2... Transmitter 3...Drive circuit 4...Ultrasound 5...Road surface 6...Receiver 7...Preamplifier 8... Multiplier 9...Low pass filter 10...Zero cross comparator 11...Pulse counter 12...Vehicle speed calculation circuit

Claims (1)

[Claims] 1. Ultrasonic transmitting means for transmitting ultrasonic signals diagonally at a predetermined angle with respect to the road surface; ultrasonic receiving means for receiving the ultrasonic signals reflected from the road surface; In an ultrasonic Doppler ground speed meter equipped with a calculating means for calculating ground speed from a frequency change occurring in the signal, the directivity of the transmitted ultrasonic signal is preferably at least 10 degrees or less as a half angle of the transmitted sound pressure. An ultrasonic Doppler ground speed meter characterized by being set at a value of 6 degrees or less.