JP2000171558A - Speed measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a speed measuring apparatus by which the speed of a moving body can be measured stably and precisely even under various conditons that the cause of a meauring error exists. SOLUTION: A central processing part 22 which constitutes this speed measuring apparatus 20 finds frequencies at upper second largest peaks on the basis of the distribution of a spectrum which is found when received data D(E1) based on a reflected echo Rw is FFT-computed. Out of them, the frequency whose value is larger is used as a target frequency corresponding the the speed (v) of a moving body, and the estimated speed (v0) of the moving body is found. Then, the found estimated speed (v0) is used as a new speed v (new), the new speed v (new) which is found in a previous processing operation is used as an old speed v (old). When the difference Δv between the new speed v (new) and the old speed v (old) is smaller than a prescribed value (vr), the new speed v (new) is adopted as the present speed (v) of the moving body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed measuring device for measuring the speed of a moving body, for example, a vehicle, or a Doppler sonar for measuring the ground speed of a moving body, for example, a ship. More specifically, a velocity measuring device measures the Doppler frequency component of an echo wave that is returned by reflection of ultrasonic waves transmitted from the vehicle or the ship or the like on a road surface or a water bottom (sea bottom), and this Doppler frequency component is measured. A speed measuring device for obtaining the speed of the vehicle or the like or the ship or the like based on the speed.

[0002]

2. Description of the Related Art Conventionally, a vehicle which is a moving body is provided with a navigation system, an ABS device,
A device for measuring the speed of the vehicle used in an external device such as a suspension control device (hereinafter, referred to as a first vehicle speed measuring device) is mounted. The first vehicle speed measurement device is generally configured to determine the speed of the vehicle based on the rotation speed of the wheel measured by a wheel speed sensor mounted on each wheel of the vehicle.

[0003] In the meantime, an error may occur in the speed of the vehicle obtained by the first vehicle speed measuring device due to the influence of changes in the air pressure of the wheels, changes in the amount of load on the vehicle, the size of the wheels, slip generated on the wheels, and the like. There is. Therefore, in the first vehicle speed measurement device, it has been difficult to obtain high measurement accuracy in some cases.

Therefore, recently, in order to further improve the measurement accuracy of a vehicle speed measuring device, a device for measuring the speed of a vehicle using an ultrasonic Doppler method (hereinafter referred to as a second vehicle speed measuring device) has been developed.・ Practical application is in progress.

FIG. 5 shows the configuration of the second vehicle speed measuring device 1. The second vehicle speed measuring device 1 has an ultrasonic transducer 5 mounted on a vehicle 3 traveling at a speed v. The ultrasonic transducer 5 transmits a tone burst wave Tw having a frequency (hereinafter referred to as a reference frequency) fa to the road surface A on which the vehicle 3 is traveling, based on a signal from the arithmetic circuit 7. The signal is transmitted to the front of the vehicle 3 at a predetermined depression angle θ.

[0006] The ultrasonic transmitter / receiver 5 generates a reflected echo R which is returned by the reflection of the tone burst wave Tw on the road surface A.
w. The receiving beam in the ultrasonic transducer 5 is set such that the main lobe ML coincides with the depression angle θ. Then, a received signal based on the reflected echo Rw obtained by the ultrasonic transducer 5 is supplied to the arithmetic circuit 7. The arithmetic circuit 7 calculates the frequency fb of the reflected echo Rw (hereinafter, referred to as target frequency) fb, and calculates the speed v of the vehicle 3 from the target frequency fb and the reference frequency fa.
Ask for. Note that the difference (fb−fa) between the target frequency fb and the reference frequency fa is also referred to as a Doppler frequency component Δf.

Here, the speed v of the vehicle 3 is calculated using the sound speed C and the reference frequency fa by using the target frequency fb (that is, the target frequency fb).
It is expressed as a function of the Doppler frequency component Δf). Therefore, by obtaining the target frequency fb, the speed v of the vehicle 3 can be obtained based on the function.

The Doppler sonar, which is a device for measuring the ground speed of a ship, can be configured similarly to the second vehicle speed measuring device 1. That is, Doppler sonar, for example, has an ultrasonic transducer mounted on the bottom of the ship,
Ultrasonic waves (tone burst waves) transmitted from the ultrasonic transducer toward the water floor (sea floor) are reflected on the sea floor and receive reflected echoes. Then, the ground speed of the ship is measured based on the Doppler frequency component of the reflected echo.

[0009]

However, in the second vehicle speed measuring device 1 described above, when used in rainy weather or the like, an error may occur in the measured speed v. This is because, when the road surface A is wet, such as when it is raining, the road surface A is close to a mirror surface for ultrasonic waves. In this case, most of the tone burst wave Tw transmitted from the ultrasonic transducer 5 at the predetermined depression angle θ is specularly reflected on the road surface A, and the main lobe M of the received beam is
L causes the level of the reflected echo Rw received by the ultrasonic transducer 5 to be low. Therefore, it is difficult to reliably receive the reflected echo Rw in the ultrasonic transducer 5.

In order to avoid such a problem that occurs in rainy weather or the like, the gain of a receiving circuit (not shown) constituting the arithmetic circuit 7 is used to reliably receive the low-level reflected echo Rw. Can be considered.

By the way, in the ultrasonic transducer 5,
The reflected echo Rw of the tone burst wave Tw transmitted from the ultrasonic transducer 5 substantially downward is also received by the side lobe SL of the received beam. Therefore, when the gain of the receiving circuit is increased, the influence of the reflected echo Rw received by the side lobe SL becomes dominant in the received signal. When the speed v of the vehicle 3 is obtained based on such a reception signal, there is a disadvantage that the measurement accuracy of the speed v is reduced.

A cause of an error in the speed v measured in rainy weather or the like is an effect of water splashing up by another vehicle running ahead of the vehicle 3. When a vehicle travels at a speed of, for example, several tens of km / h or more, a large amount of water droplets will be wound behind the vehicle. As described above, when the speed v is measured in a situation where a large amount of water droplets exist in front of the vehicle 3,
The cause of the measurement error caused by the wet road surface A described above (in the ultrasonic transducer 5, the level of the reflected echo Rw received by the main lobe ML decreases, and the reception signal of the reflected echo Rw received by the side lobe SL) In addition to the above, the error factor due to the reflected echo Rw that is reflected and returned from the water droplets is superimposed.

The frequency of the reflected echo Rw from the water droplet is
It has been experimentally found that the tone burst wave Tw is distributed almost uniformly over a wide band with respect to the reference frequency fa.
As a method for obtaining a target frequency fb of the reflected echo Rw reflected from the frequency A having such a distribution and returned to the road surface A and received by the main lobe ML in the ultrasonic transducer 5, the ultrasonic transceiver The Xerox method of calculating the average value of the frequency of the reflected echo Rw received by the wave device 5 as the target frequency fb, the complex autocorrelation method, or the like can be adopted, but the velocity v is obtained by using such a method. In such a case, there is a possibility that the measurement accuracy is reduced.

When the above-mentioned Doppler sonar is used in a sea area where there are a lot of floating substances in the sea, such as plankton, the Doppler sonar is reflected on the plankton and returned as in the case of the influence of water droplets in the second vehicle speed measuring device 1. Due to the influence of the reflected echo, there is a possibility that an error may occur in the measured ground speed of the ship.

The present invention has been made in view of such a problem, and has a speed measurement capable of stably and accurately measuring the speed of a moving body even under various conditions in which a measurement error factor exists. It is intended to provide a device.

[0016]

A velocity measuring device according to the present invention is a device for measuring the speed of a moving body using ultrasonic waves, and transmits ultrasonic waves from the moving body in a predetermined direction. Transmitting means, receiving means for receiving received ultrasonic echoes of the ultrasonic waves reflected back to the target to obtain received information, timing detecting means for detecting the timing of sampling the received information from the receiving means, First calculating means for sampling the received information based on a timing and performing an FFT operation on the received information to obtain a spectrum distribution; and extracting a Doppler frequency component corresponding to the speed of the moving object from the spectrum distribution. 2 calculation means, and based on the Doppler frequency component,
A third step of determining a speed of the moving object with respect to the target;
And an arithmetic means (the invention according to claim 1).

In this case, in the second arithmetic means,
From the spectrum distribution, the frequency at the second highest peak is selected, and the Doppler frequency component is extracted based on this frequency. Then, in the third calculation means, a new speed is obtained based on the Doppler frequency component, and when a difference between this new speed and an old speed obtained last time in the same processing is smaller than a predetermined value, The new speed is adopted as the current speed of the moving object (the invention according to claim 2).

[0018] Therefore, even in a situation where a measurement error occurs, it is possible to accurately obtain the speed of the moving body based on the ultrasonic echo from the target. Therefore, the measurement accuracy and stability are greatly improved.

The moving body may be a vehicle, and the target may be a road surface on which the vehicle travels to constitute a speed measuring device (the invention according to claim 3), and the moving body is a ship. The target may be used as a water bottom to constitute a velocity measuring device.
Described invention).

[0020]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a speed measuring device 20 to which an embodiment of the present invention is applied. In this embodiment, a case will be mainly described in which the speed measuring device 20 is mounted on a vehicle.

The speed measuring device 20 is
A central processing unit (arithmetic unit) 22 that controls the entire system and performs a process of calculating a velocity v, which will be described later, and an RO that is a storage unit (memory) that stores a control program.
M24. The central processing unit 22 includes, for example, D
It is composed of an SP (Digital Signal Processor) or the like. Further, the speed measuring device 20 includes a transducer TD1 for transmitting and receiving an ultrasonic wave, which is configured using a vibrator or the like.
A transmission system 26 for transmitting a tone burst wave Tw, which is a single frequency ultrasonic wave, via the transducer TD1, and the tone burst wave Tw as a target through the transducer TD1. {For example, a receiving system 28 that performs processing for receiving a reflected echo (ultrasonic echo) Rw that is reflected back on the road surface A on which the vehicle runs (see FIG. 5). Switching between transmission and reception in the transceiver TD1 is performed by the transceiver 30.

In this case, the transmission system 26 and the transmitter / receiver TD1 constitute transmission means of the tone burst wave Tw, and the reception system 28 and the transmitter / receiver TD1 constitute the reception means of the reflected echo Rw. I have.

The transmitter / receiver TD1, like the second vehicle speed measuring device 1 (see FIG. 5), transmits a tone burst wave Tw in a transmitting direction and a receiving beam to a moving body such as a vehicle. The main lobe ML has a predetermined depression angle θ (0 <
θ <π / 2) so as to be directed forward of the vehicle or the like. Also, the height of the transducer TD1 from the road surface A is H.

The transmission system 26 includes a drive signal generation circuit 32 and a power amplification circuit 34.

The drive signal generation circuit 32 has a built-in counter (not shown), and divides a 10 MHz reference signal Sr supplied from the central processing unit 22 at a predetermined frequency division ratio. As a result, the transmission drive signal P1 is generated (see FIG. 2A). Specifically, the drive signal generation circuit 32
Is a frequency (reference frequency) based on the frequency division ratio supplied as the control signal Sc1 from the central processing unit 22.
generating a signal of fa (for example, fa = 200 kHz);
By pulse-modulating this signal in synchronization with the reference signal Sr, a transmission drive signal P1 having a pulse width Ta (for example, Ta = 1 ms) and a repetition period T0 (for example, T0 = 10 ms) is generated. The repetition period T0 is determined based on the timing at which the control signal Sc1 is output from the central processing unit 22.

The power amplifying circuit 34 includes a drive signal generating circuit 3
Of the transmission drive signal P1 from the power signal
x is generated and supplied to the transducer TD1 via the transceiving switch 30. The transducer TD1 is driven by the electric signal Tx, and transmits the tone burst wave Tw to the road surface A (see FIG. 5).

On the other hand, as shown in FIG.
A band filter 40, an amplification circuit 42, a detection circuit 44, a level comparison circuit 46, and an A / D converter 48 are provided.

When the transceiver TD1 receives the reflected echo Rw reflected and returned on the road surface A (see FIG. 5), the transceiver TD1 generates an electric signal Rx corresponding to the reflected echo Rw. Is output. Bandpass filter 40
Extracts (filters) a component belonging to a predetermined frequency band from the electric signal Rx and outputs it as a received signal E1 (for example, see FIG. 2B showing the received signal E1 in fine weather). Note that the received signal E1 is reflected by the road surface A (see FIG. 5), and the component a of the reflected echo Rw received by the transmitter / receiver TD1 by the main lobe ML of the received beam, together with the leakage of the electric signal Tx. Component b is included.
After being amplified by the amplifier circuit 42, the received signal E1 is supplied to the detection circuit 44 and the A / D converter 48, respectively (see FIG. 1).

The detection circuit 44 performs full-wave rectification on the reception signal E1 from the amplification circuit 42, thereby obtaining a DC detection signal Sd.
Convert to The level comparison circuit 46 compares the voltage value V (Sd) of the DC detection signal Sd from the detection circuit 44 with a predetermined reference voltage Vref, and only when the voltage value V (Sd) exceeds the reference voltage Vref. The reception detection gate signal G1 (see FIG. 2C) at a high level is output to the central processing unit 22. The central processing unit 22 measures the time from the time when the control signal Sc1 is output to the time when the reception detection gate signal G1 rises, so that the reflected echo Rw is transmitted after the tone burst wave Tw is transmitted from the transmitter / receiver TD1. A time T1 until is received. Note that the reception wave detection gate signal G1 is equal to the reception signal E
When the signal b includes the component b due to the leakage of the electric signal Tx, the signal level also becomes high. However, the central processing unit 22 generates the reception detection gate signal G1 based on the leakage of the electric signal Tx.
Is estimated based on the output time point of the control signal Sc1, and is not considered in the processing for obtaining the time T1.

The A / D converter 48 operates according to the control signal Sc2 supplied from the central processing unit 22.
The reception signal E1 from the amplification circuit 42 is converted into reception data (reception information) D (E1), which is digital data, and supplied to the central processing unit 22. This control signal Sc
In the central processing unit 22, the received data D
A timing T2 to start the sampling of (E1) is specified (see FIG. 2D). That is, the central processing unit 2
Reference numeral 2 functions as timing detection means for detecting the timing T2.

In this case, the timing T2 is set to
At a time obtained based on the height H of the road D1 from the road surface A and the depression angle θ for transmitting the tone burst wave Tw, the transmitter / receiver TD1 is mounted, for example, due to the effect of vertical movement of a vehicle or the like. It is obtained by adding values taking into account the fluctuation of time (see FIG. 5).

More specifically, the timing T2 is obtained based on the following equation (1).

T 2 = 2 × H / (C × sin θ) −0.25 × 10 ⁻³ [sec] (1) where C is a sound speed and the ambient temperature t of the transducer TD 1
And is calculated based on the following equation (2).

C = 331.6 + 0.61 × t [m / s] (2) The ambient temperature t is measured by the thermistor 50 provided near the transducer TD1 (see FIG. 1). Specifically, a temperature signal (voltage) St based on the ambient temperature t obtained by the thermistor 50 is supplied to the central processing unit 22 as temperature data D (t) via the A / D converter 52. Note that one terminal of the thermistor 50 is connected to a power supply via a resistor R for applying a bias to the thermistor 50, and the other terminal is grounded.

The central processing unit 22 stores the temperature data D
The ambient temperature t is obtained based on (t). In this case, the timing at which the temperature data D (t) is taken into the central processing unit 22 is determined by the A / D converter 5 from the central processing unit 22.
2 is indicated by the control signal Sc3 supplied to the control signal No. 2.

The control data Sc2 supplied from the central processing unit 22 to the A / D converter 48 causes the received data D (E
1) The sampling interval ΔT (ΔT = 1.5 μs in this embodiment) and the number of sampling points N
(Eg, N = 1024 points) (FIG. 2)
D). The number N of sampling points is set based on the sampling interval ΔT.

The central processing unit 22 samples the reception data D (E1) based on the timing T2, the sampling interval ΔT, and the number N of sampling points. By setting the timing T2, the sampling interval ΔT, and the number N of sampling points in this manner, the main lobe M of the received beam is transmitted to the transmitter / receiver TD1.
The reflected echo Rw from the road surface A received by L
Sampling can be reliably performed as the reception data D (E1) (see FIGS. 2B and 2D).

The central processing unit 22 performs an FFT (Fast Fourier Transform) process (also referred to as an FFT operation) on the sampled received data D (E1), thereby obtaining the data shown in FIG. 3A.
Find the spectrum distribution shown in This spectrum distribution is 0.651 kHz ｛= 1 / (1024 × 1.5 ×
10 ⁻⁶ ) kHz｝, and 0 to 333 kHz (= 51
It is set to be distributed over a frequency band of 2 × 0.651 kHz).

For example, a peak Pa corresponding to the component a of the received signal E1 (see FIG. 2B) exists in the spectrum distribution in fine weather. Therefore, by calculating the frequency f1 at the peak Pa, the frequency (target frequency) of the reflected echo Rw reflected from the road surface A (see FIG. 5) and received by the transmitter / receiver TD1 by the main lobe ML of the received beam. fb is obtained as fb = f1.

By the way, when the road surface A is wet, such as when it is raining, most of the tone burst wave Tw is generated on the road surface A.
(See FIG. 5). Therefore, as shown in FIG. 2E, the reflection reflected from the road surface A (see FIG. 5) included in the reception signal E1 and received by the transmitter / receiver TD1 by the main lobe ML (see FIG. 5) of the reception beam. The level of the component a of the echo Rw decreases. Also, in comparison with this, the reflected echo Rw received by the transmitter / receiver TD1 by the side lobe SL (see FIG. 5) of the received beam.
The level of the component c increases.

In this case, the spectrum distribution of the reflected echo Rw includes a component a (see FIG. 2E) as shown in FIG. 3B.
In addition to the peak Pa corresponding to the component c (see FIG. 2E)
There is a peak Pc corresponding to. The frequency f0 at the peak Pc is equal to the reference frequency fa of the tone burst wave Tw.
Is almost the same value (f0 = fa). Thus, when a plurality of peaks Pa and Pc exist in the spectrum distribution, it is difficult to obtain the target frequency fb based on the peak Pa or Pc having the largest magnitude.

Further, in a situation where water droplets are wound by a vehicle traveling ahead of the transducer TD1, the tone burst wave Tw is reflected by the water droplets. For this reason, the received signal E1 includes the component d of the reflected echo Rw that is reflected and returned to the water droplets (FIG. 2).
F). Since the frequency of the reflected echo Rw returning from the water droplets is distributed over a wide band, the spectrum distribution of the reflected echo Rw shown in FIG. 3C includes a plurality of peaks Pd1 and Pd2 corresponding to the component d (see FIG. 2F). Etc. exist. Also in this case, it is difficult to obtain the target frequency fb based on the peaks Pa, Pc or Pd1, Pd2 having the largest magnitude.

Hereinafter, in the central processing unit 22, FIG.
A (at the time of fine weather) and the peak P as the target frequency fb from the spectrum distribution shown in FIG. 3B or FIG. 3C (at the time of rainy weather).
A processing method for extracting the frequency f1 at a and calculating the speed v of the moving object (vehicle) based on the target frequency fb will be described with reference to the flowchart in FIG.

First, in step S1, based on the timing T2 set by the control signal Sc2, the sampling interval ΔT, and the number N of sampling points,
The sampling of the reception data D (E1) is performed. Subsequently, in step S2, a spectrum distribution of the reflected echo Rw (see FIGS. 3A to 3C) is obtained by performing an FFT operation on the sampled reception data D (E1).

Then, in step S3, the peak Pa having the second largest magnitude from the spectrum distribution is obtained.
Pc and the like are extracted, and the frequencies f1 and f0 at the peaks Pa and Pc are obtained. Then, step S4
In the above, the frequency having the larger (higher) value (in this case, f1) is determined as the first candidate of the target frequency fb (fb = f1), and the speed measuring device is determined based on the following equation (3). An estimated speed v0 of the vehicle or the like on which the vehicle 20 is mounted is calculated.

V0 = Δf × C / {(2 × fa + Δf) × cos θ} (3) where Δf represents a Doppler frequency component, and Δf = fa
-Fb. C is a sound speed, which is obtained based on the above equation (2).

The estimated speed v obtained in step S4
0 is the new speed v (new) in step S5.
For example, {v (new) ← v0} stored in a memory (not shown) of the central processing unit 22. Prior to this, the new speed v determined in the previous process
(New) is stored in the memory as the old speed v (old) {v (old) ← v (new)}.

Next, in step S6, the difference Δv ｛Δv between the new speed v (new) and the old speed v (old)
= V (new) -v (old)}. Subsequently, in step S7, the difference Δv obtained in step S6 is compared with a predetermined value vr (for example, vr = 5 km / h). If Δv <vr, step S8 is performed.
, The new speed v (new) is adopted as the current speed v of the moving object (vehicle) {v ← v (new)}.
If it is determined in step S7 that Δv ≧ vr, the process returns to step S1 without adopting the new speed v (new) as the current speed v.

The speed v obtained in the above steps S1 to S8 is output from the central processing unit 22 as speed data D (v) as shown in FIG. , A suspension control device and the like.

As described above, in this embodiment, the processing of steps S1 to S8 for obtaining the speed v is as follows.
It functions as a kind of frequency filter for extracting a target frequency fb (ie, a Doppler frequency component Δf) corresponding to the vehicle speed v from the spectrum distribution. Therefore, the speed v of the vehicle can be accurately obtained based on the Doppler frequency component Δf.

In particular, the velocity v can be accurately obtained even in a situation where a measurement error occurs, such as in rainy weather. Therefore, measurement methods such as the Xerox method and the complex autocorrelation method are used. The measurement accuracy and stability are greatly improved as compared with the case where the measurement is performed.

It should be noted that the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

For example, in addition to the transducer TD1 for transmitting and receiving ultrasonic waves (tone burst wave Tw, reflected echo Rw) to and from the front of the vehicle, another transducer for transmitting and receiving ultrasonic waves to and from the rear of the vehicle. So-called 2
A beam method may be adopted. The other transducer transmits a tone burst wave to the rear of the vehicle at a predetermined depression angle (for example, θ) and receives a reflected echo that is returned when the tone burst wave is reflected on a road surface.

Then, the velocities v1 and v2 are obtained based on the reflected echoes Rw received by the transducer TD1 and the other transducers, respectively, and the average value of the velocities v1 and v2 is calculated to obtain the vehicle speed. The speed v is obtained.
In this case, the factor of the measurement error generated by the inclination or the vertical movement of the vehicle can be significantly reduced. Such an effect can be obtained similarly when the speed measuring device 20 is mounted on a ship or the like, as described later.

If the height H of the transmitter / receiver TD1 from the road surface A (see FIG. 5) is not known, the central processing unit 22 calculates the time T1 obtained based on the reception detection gate signal G1. The height H may be obtained by performing a learning process using In performing the learning process, it is preferable to use the time T1 obtained when the road surface A is dry asphalt.

Further, in steps S7 and S8, the new value {new speed v (new)} and the old value {old speed v (ol) of the estimated speed v0 obtained by equation (3).
d) Instead of the process of obtaining the current speed v based on the difference Δv from｝, the vehicle speed v ′ measured by the wheel speed sensor provided on the vehicle wheel and the vehicle speed v ′ obtained by the above equation (3) are obtained. Processing for determining the estimated speed v0 as the current speed v when the difference Δv 'from the estimated speed v0 is within 15% of the speed v' or the estimated speed v0. May be performed. In this case, the speed measuring device 20 is provided with a unit for inputting a signal from the wheel speed sensor.

It should be noted that, in addition to the processing in steps S7 and S8, a processing for selecting whether the current speed v is determined or not based on the speed v 'may be performed.

Further, the processing in step S3,
That is, instead of extracting the peaks having the second highest magnitude from the spectrum distribution and obtaining the frequencies at these peaks, the n-th highest magnitudes (n ≧ 3,
The processing of extracting peaks up to (n: integer) and calculating the frequencies at these peaks may be performed. In this case, in step S4, among the frequencies at each peak, the frequency with the larger (higher) value is determined as the first candidate of the target frequency fb, and the process of calculating the estimated speed v0 is performed instead of the process of calculating the estimated speed v0. Among the estimated speeds v0 as the candidates calculated as the first to n-th candidates of the target frequency fb, for example, the estimated speed v0 closest to the speed v ′ measured by the wheel speed sensor should be obtained in step S4. A process for selecting the estimated speed v0 is performed.

In this embodiment, the case where the speed measuring device 20 is mounted on a vehicle is mainly described, but the vehicle includes a railway vehicle in addition to an automobile. The speed measuring device 20 can be mounted on a ship or the like.

In this case, the tone burst wave Tw transmitted from the transmitter / receiver TD1 is reflected on the bottom of the water (sea bottom), returns as a reflected echo Rw, and is received by the transmitter / receiver TD1. That is, in the speed measuring device 20, the speed v
As a result, a ground speed of a ship or the like on which the speed measuring device 20 is mounted is obtained.

When the ground speed is measured in a sea area where there are many floating substances such as plankton in the sea, the waveform of the reception signal E1 from the bandpass filter 40 is similar to the waveform shown in FIG. 2E. Furthermore, the spectrum distribution is shown in FIG.
Similar to the distribution shown in C. That is, the speed measuring device 2
In the case of No. 0, floating seawater such as plankton is
It is possible to accurately measure the ground speed of a ship or the like by processing it as a factor of the measurement error as in the case of the water droplets above.

[0063]

According to the velocity measuring apparatus of the present invention, the peak corresponding to the velocity of the moving object is obtained from the spectrum distribution obtained by performing the FFT operation on the reception information obtained by receiving the ultrasonic echo. Is extracted, and the speed is obtained based on this frequency.
Therefore, it is possible to obtain a speed measuring device capable of stably and accurately measuring the speed of the moving body even under various conditions in which a factor of the measurement error exists.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a speed measuring device to which an embodiment of the present invention is applied.

2A is a waveform diagram showing a transmission drive signal corresponding to a tone burst wave transmitted from a transmitter / receiver constituting the speed measuring device shown in FIG. 1, and FIG. 2B is a waveform diagram showing the transmission / reception wave. FIG. 2C is a waveform diagram showing a received signal corresponding to the reflected echo received by the transmitter, and FIG. 2C is a waveform diagram showing a received wave detection gate signal indicating that the reflected echo has been received by the transducer. 2D is a waveform diagram showing a timing of sampling the reception data in the central processing unit constituting the speed measurement device, and FIG. 2E is a waveform diagram showing the reception signal in a situation where the road surface is wet. FIG. 2F is a waveform diagram showing the received signal in a situation where water droplets exist in the transmission direction of the tone burst wave.

3A is a diagram showing a spectrum distribution corresponding to the received signal shown in FIG. 2B; FIG. 3B is a diagram showing a spectrum distribution corresponding to the received signal shown in FIG. 2E; FIG. 2B is a diagram showing a spectrum distribution corresponding to the received signal shown in FIG. 2F.

FIG. 4 is a flowchart illustrating a process for obtaining a speed of a moving object based on reception data of a reflected echo received by a transducer in a central processing unit included in the speed measuring device illustrated in FIG. 1; .

FIG. 5 is a diagram showing a configuration of a second vehicle speed measuring device according to a conventional technique.

[Explanation of symbols]

Reference Signs List 20 speed measuring device 22 central processing unit (computing means) 30 transmission / reception switch 32 drive signal generating circuit 34 power amplifier circuit 40 bandpass filter 42 amplifier circuit 44 detection circuit 46 level comparator circuit 48 52: A / D converter TD1: Transducer Tw: Tone burst wave Rw: Reflected echo P1: Driving drive signal E1: Received signal

Claims (4)

[Claims] 1. A speed measuring device for measuring the speed of a moving object using ultrasonic waves, comprising: transmitting means for transmitting ultrasonic waves from the moving object in a predetermined direction; and reflecting the ultrasonic waves on a target. Receiving means for receiving received ultrasonic echoes to obtain received information, timing detecting means for detecting timing for sampling the received information from the receiving means, and sampling the received information based on the timing, A first calculating unit that obtains a spectrum distribution by performing an FFT operation on the received information; a second calculating unit that extracts a Doppler frequency component corresponding to the speed of the moving object from the spectrum distribution; And a third calculating means for calculating a speed of the moving body with respect to the target. 2. The apparatus according to claim 1, wherein said second calculating means selects a frequency at a peak having the second highest magnitude from said spectrum distribution,
The Doppler frequency component is extracted based on this frequency, and the third calculating means obtains a new speed based on the Doppler frequency component, and calculates the new speed and the old speed previously obtained in the same process. When the difference is smaller than a predetermined value, the new speed is adopted as the current speed of the moving object. 3. The speed measuring device according to claim 1, wherein the moving body is a vehicle, and the target is a road surface on which the vehicle runs. 4. An apparatus according to claim 1, wherein said moving body is a ship, and said target is a water bottom.