JPH07149192A - Obstacle detecting device - Google Patents

Abstract

PURPOSE:To correctly discriminate a vehicle and a stopped object by estimating relative speed and distance at the next time from measured relative speed and distance and memorizing them, and judging it to be a guide rail or a soundproof wall when the error of the measured distance and the estimated distance is over a prescribed value and a plurality of distances measured in the past are fixed. CONSTITUTION:A received wave with a receiving antenna 4 is converted to an electric signal by a receiving circuit 5, an emission wave and the received wave are synthesized by a mixer 6, and it is converted to a beat signal (c) by a demodulation circuit. A demodulated signal is separated by a demodulated signal separation circuit 12, and the relative speed and the distance of an electric wave reflecting body are obtained by a frequency analysis/signal processing part 13. A CPU 10 stores the measured data of relative speed and distance in the memory part 14. When the measured relative speed is not equal to actual vehicle speed in the approaching direction, the reflecting body is judged to be a vehicle, and in the other case when the error of the measured distance and the estimated distance is over a prescribed value and a plurality of measured distances are actually fixed, the reflecting body is judged to be a guard rail or a soundproof wall.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an obstacle detection device,
In particular, the present invention relates to an apparatus that measures an inter-vehicle distance and a speed with a vehicle in front using FM-CW waves and detects whether or not a reflecting object is an obstacle.

[0002]

2. Description of the Related Art FIG. 10 schematically shows a conventionally well-known obstacle detecting device using FM-CW waves. FIG. 11 shows a vehicle equipped with this obstacle detecting device and a forward vehicle. 20 is a plan view showing the relationship with 20. FIG.

FM-C transmitted from the radio wave transmitter 21
The W wave is reflected by the front vehicle 20 when the front vehicle 20 is present, and is received by the radio wave reception device 22.

Then, by mixing with a mixer (not shown), the beat frequencies of the waveform emission wave and the reception wave are obtained, and a signal measuring the inter-vehicle distance (and relative speed) to the preceding vehicle 20 is output. .

FIG. 12 shows the change over time of the mixing waveform. The solid line in FIG. 12 (a) shows the emission wave (electromagnetic wave frequency-modulated in a triangular shape), which is reflected by a radio wave reflecting object such as a vehicle. If the object is a moving object, the received wave will have a frequency transition as shown by the dotted line due to the Doppler effect.

When these waves are mixed, the same figure (b)
A beat frequency waveform is obtained as shown in FIG. The beat signal frequency f _b is represented by the sum or difference of the distance frequency f _r and the velocity frequency f _d corresponding to the distance and velocity of the radio wave reflecting object, respectively, according to the following principle equation (1).

[0007]

[Number 1] _{f b = (4 △ f ·} f m / C) R ± (2f o / C) V (1) where, V: relative speed of the reflective object relative to the radar sensor [m / sec] R: Radar sensor the distance to the reflecting object from the [m] C: velocity of light [m / sec] △ f: frequency modulation width [Hz] f _m: modulation frequency [Hz] f _o: radar carrier frequency [Hz]

Here, when the beat frequency on the rising side of the modulated wave frequency is f _up and the beat frequency on the falling side is f _dn ,

[0009]

## EQU00002 ## f _r = 0.5 (f _up + f _dn ) and f _d = 0.5 (f _up −f _dn ) (2) Then, from equations (1) and (2),

[0010]

Equation 3] _{V = (C / 2f o)} f d, is R = (C / 4 △ f · f m) f r (3), the distance R and the relative radio wave reflecting object by the equation (3) The speed V is required.

In such an FM-CW obstacle detection device, frequency analysis is performed on the beat signals of the emitted wave and the received wave. This frequency analysis is, as shown in FIG.
It shows that the frequency is analyzed using FFT (Fast Fourier Transform) etc. in the part where the frequency rises and the part where the frequency falls in the frequency modulation pattern, which corresponds to the speed and distance of the radio wave reflecting object such as a vehicle. The location of the frequency peak to be analyzed is analyzed. Then, a combination of peaks was found on both the rising and falling sides of the modulated wave, and the above-mentioned principle equation (1)
The distance and relative velocity of the radio wave reflecting object are calculated from (3).

However, due to the nature of electromagnetic waves, when there is a radio wave reflecting object other than the vehicle, the reflected wave from the object cannot be distinguished from the reflected wave from the vehicle, it is judged as a vehicle, and false information is issued. As a result, the warning to the driver must be false alarm output.

In order to solve this problem, as shown in FIG. 14 (a), the frequency peak shape for a radio wave reflecting object such as a guardrail or a soundproof wall other than the vehicle is detected during frequency analysis, and particularly the frequency of the frequency peak is detected. An invention has already been proposed which attempts to solve the problem by detecting that the bandwidth is wider than that of the vehicle.

[0014]

However, in such a conventional example, when the frequency peak of the system noise and the frequency peak of the vehicle overlap in frequency due to the influence of the system noise in the electromagnetic wave measuring section, for example. Since the vehicle has a shape in which the bandwidth of the frequency peak of the vehicle is widened, the vehicle cannot be determined and detected as a non-vehicle.

This will be described with reference to FIG.
As shown in (a), when the frequency peak for a reflective object that is a vehicle, the frequency peak for a stationary object such as a guardrail, and the system noise peak are separated in terms of frequency, the peak frequency bandwidth of each It is possible to discriminate between the stationary object and the stationary object.

However, as shown in FIG. 2B, the system noise level is increased due to the thermal characteristics of the system, the frequency band is widened at the same time, and the peak frequency is moved according to the movement of the vehicle. When the noise peak and the vehicle peak overlap in frequency, the bandwidth of the overlapped peak is widened, and there is a drawback that the vehicle and the guardrail cannot be distinguished.

Therefore, according to the present invention, the FM-CW wave is transmitted as the emission wave, the reception wave reflected by the reflecting object is mixed with the emission wave to generate a beat signal, and the beat signal is subjected to frequency analysis to perform the reflection. In an apparatus that detects obstacles by measuring the relative speed and distance to an object, it is possible to accurately distinguish between a vehicle and a stopped object such as a guardrail or a sound barrier without being affected by system noise. To aim.

[0018]

[Means and Actions for Solving the Problems] (1) Description of Points of Interest of the Present Invention: FIGS. 3 to 6 First, as shown in FIG. 3, a vehicle that transmits an FM-CW wave as a launch wave (hereinafter, The guardrail GR (or soundproof wall) is a "stopped object" for A). Therefore,
In each measurement (distance / relative speed) at regular intervals while the vehicle is traveling, the relative speed is the same as that of the vehicle A and in the approaching direction.

Therefore, when it is found that the measured relative speed of the vehicle and the stationary object are substantially the same as the actual speed of the host vehicle A, the radio wave reflecting object is not the vehicle but the approaching direction. It can be determined as a stationary object, and if not, it can be determined as a vehicle.

However, in addition to the guardrail GR as the stopped object, there is a stopped object C as shown in FIG. 4, and it is necessary to identify these.

Here, the traveling direction of the vehicle A is always tangential to the curve of the corner in the corner of the guardrail GR.

Therefore, from the geometrical relationship, the distance from the vehicle A to the guardrail GR is the same distance between the measured value L1 at the current vehicle position P1 and the measured value L2 at the next vehicle position P2. (L1 = L2).

In this case, however, the guardrail GR (or soundproof wall) shown in FIG. 3 draws an ideal arc macroscopically, but microscopically, it is a continuous short straight line as shown in FIG. And each straight line portion is an ideal arc A of the guardrail GR (or soundproof wall) as shown in FIG.
RC and the guardrail GR itself are shortened by a length Δd.

Therefore, as shown in FIG. 6, the locus T1 of the distance between the vehicle A and the guardrail GR for each measurement slightly fluctuates within a fixed range. This is because the distance component in the radar principle formula is not constant for each measurement.

Although the guardrail GR is a kind of the stopped object as described above, it must be distinguished from the stopped object C as shown in FIG. In this case, the stopped object C is the trajectory T
As shown in Fig. 2, there is a characteristic that the measurement distance gradually becomes shorter, and it is different from the fact that even if the past measurement results fluctuate, the average value is almost the same as in the case of the guardrail GR. . If the vehicle is traveling at the same speed as the own vehicle, the locus becomes as shown by the trajectory T3.

(2) Means By this property, the measurement information of each time is observed, and the correlation between the information predicted from this measurement information and the measurement information allows the vehicle, the guardrail (or sound barrier), and the stopped object to be identified. It will be possible.

Therefore, in the present invention, the storage unit for predicting the next relative speed and distance from the measured relative speed and distance and storing the result, the vehicle speed sensor, and the measured relative speed are the actual vehicle speed by the sensor. It is determined that the reflecting object is a vehicle when the approaching direction is the same, and otherwise the error between the measured distance and the predicted distance is equal to or greater than a certain value and the plurality of distances measured in the past are substantially constant. And a determination unit that determines that the reflective object is a guardrail or a soundproof wall and that otherwise determines that the reflective object is a stationary object other than the guardrail.

(3) Operation In the present invention, first, the relative velocity and distance of the reflecting object, which is the previous measurement information, is stored in the storage unit. Then, the next relative speed and distance are predicted from the measured values of the relative speed and distance measured last time.

It is determined whether or not the predicted relative speed for each time stored in the storage unit is substantially the same as the actual vehicle speed of the host vehicle in the approaching direction. If they are not the same, as shown by the locus T3 in FIG. It is determined that the reflecting object is a vehicle ahead.

When it is determined that the predicted relative speed at each time is substantially the same as the actual vehicle speed, it is further determined whether or not the distance predicted value at each time is different from the distance predicted value at each time by a certain value or more, and the constant value is determined. If it is less than the value, it is determined that the reflecting object is a stopped object other than the guardrail, as shown by the trajectory T2 in FIG.

Further, when it is determined that the distance measurement value is different from the distance prediction value of each time by a predetermined value or more, it is determined whether or not it is fluctuating as shown by the trajectory T1 in FIG. It is determined whether or not the distance measurement values are substantially the same, and when they are the same, it is determined that the reflective object is the guardrail in the stationary object.

As described above, in the present invention, the measured value for each time is stored, the vehicle and the stopped object are identified from the relationship between the measured relative speed and the actual vehicle speed, and the distance measured values for a plurality of times are correlated. It is possible to distinguish between the guardrail (or soundproof wall) and other stationary objects.

[0033]

1 is a block diagram showing an embodiment of an obstacle detecting apparatus according to the present invention, in which 1 is a transmitting antenna, 2 is a transmitting circuit, and 3 is a VCO (voltage controlled oscillator).
5 is a receiving antenna, 5 is a receiving circuit, and 6 is a mixer. The transmitting circuit 2 and the modulating circuit 3 correspond to the radio wave transmitting device 21 shown in FIG. The circuit 5 also corresponds to the radio wave receiving device 22.

Further, the signal given to the modulation circuit 3 is generated by the signal generation circuit 8, which constantly receives the clock signal from the synchronization signal generation circuit 9, and further stores the modulation pattern composed of ROM or RAM. The modulated wave composed of the triangular shape and the linear part stored in the section 11 is received to generate a modulated wave as shown in FIG.

The output signal of the mixer 6 is supplied to the demodulation circuit 7. The output signal of the demodulation circuit 7 is supplied to the demodulation signal separation circuit 12 to be signal-separated and further frequency analyzed as a digital signal.・ Signal processing unit 13
Is sent to the CPU 10 and the analysis result is given to the CPU 10 as a determination unit to output a determination signal.

The demodulation signal separation circuit 12 is also configured to receive the synchronization signal from the synchronization signal generation circuit 9.

Further, 14 is the measured data and the CPU 1.
Reference numeral 15 is a storage unit that stores data that is predicted and calculated (described later) by 0, and 15 is a vehicle speed sensor that detects the actual vehicle speed.

The operation of the above embodiment will be described below with reference to the flow chart shown in FIG.

Step S1: First, in this measuring device,
When the CPU 10 instructs the modulation pattern storage unit 11 to output the modulation pattern, the storage unit 11 outputs the data of the modulation signal as shown in FIG. 12 to the signal generation circuit 8.

In response to this, the signal generation circuit 8 converts the modulation signal data into the analog signal a, and the modulation circuit (VCO)
3 and the signal b subjected to the triangular frequency modulation is transmitted via the transmission circuit 2 and the transmission antenna 1.
Incidentally, these modulation patterns may be program type variable data by a CPU or the like.

The reception wave received by the reception antenna 4 is converted into an electric signal by the reception circuit 5 and converted into an electric signal by the mixer 6.
Then, the emitted wave and its received wave are combined. This combined signal is sent to the demodulation circuit 7, where it is converted into a beat signal c.

This beat signal c is a demodulation signal separation circuit 12
In, the demodulation signal is separated based on the synchronization signal from the synchronization signal generation circuit 9, and the information is sent to the frequency analysis / signal processing unit 13.

Step S2: In the frequency analysis / signal processing unit 13, the FFT calculation is performed on the rising side and the falling side of the demodulated signal, so that the distance and the relative speed with respect to the front obstacle are determined as described above. There are spectrum peaks at different frequencies (see FIG. 13).

Step S3: Combine the rising beat frequency f _up and falling beat frequency f _dn of the FFT-analyzed modulator in this case and substitute them in the above equation (2) to obtain the distance frequency f _r and the relative speed. The frequency f _d is calculated, and then the relative velocity V and the distance R of the radio wave reflecting object are obtained by the equations (1) and (2).

An example of the data of the relative velocity V and the distance R thus obtained "5 times" is shown in FIG. 7 (a) (left side).
Is shown in. The measurement targets are “vehicle”, “guardrail (or soundproof wall)”, and “stopped object” as shown in FIG. 4, but the measured value data in FIG. 7 are “near”, “medium”,
"Far" is parted because the FM-CW method can obtain the relative speed and distance of a plurality of obstacles at the same time by one measurement, and therefore it is impossible to identify what the reflecting object is as it is. .

Step S4: The CPU 10 stores the relative speed and distance measurement data obtained in step 3 in the storage unit 14 as described above.

Step S5: Further, the CPU 10 fetches the own vehicle speed signal from the vehicle speed sensor 15.

Step S6: The distance and relative speed for the next measurement are predicted from the relative speed and distance measurement data stored in the storage unit 14 in step S4.

Here, the calculation formula of the predicted value obtained from the measured value is shown in FIG. 8, and like the general calculation formula shown,
The predicted distance can be calculated from the previous distance measurement value, the relative speed measurement value, and the sampling time Δt (the cycle in which the flowchart of FIG. 2 is periodically executed), and the relative speed is the previous relative speed and the last two times. It can be obtained from the measured speed value and the sampling time Δt.

Data predicted in this way from the measurement data shown in FIG. 7A is shown in FIG. 7B (right side), and the predicted value for "near" data is the predicted value.
The predicted value for the "medium" data is the predicted value, and the predicted value for the "far" data is the predicted value.
In addition, in the same figure, the mark x indicates that it is in the unpredictable state.

Step S7: The predicted distance and predicted relative speed obtained in step S6 are stored in the storage unit 14.

Step S8: The measurement data and prediction data (FIG. 7) stored in the storage unit 14 as described above are again retrieved from the storage unit 14 and the following judgment is made.

Step S9: Here, it is determined whether or not the measured value of the relative speed (FIG. 7A) extracted from the storage unit 14 is substantially equal to the own vehicle speed acquired in step S5 in the approach direction (negative). To determine.

As a result, if the vehicle speed is 72 Km / h, the "near" data and the "medium" data in which the relative speed is "-72" are given.
The data indicates that it is a stationary object or a guardrail, and the relative speed of the "far" data other than these is "0", so this "far" data is determined to be a vehicle (step S10). This can be seen from the vehicle trajectory T3 in FIG.

Step S11: Although the vehicle and the stopped object other than the vehicle were distinguished in the above step S9, since the stopped object and the guardrail are further distinguished, an error between the predicted value and the measured value in the measurement at that time is generated. It is determined whether it is large or not.

That is, for example, in the example of FIG. 7, the predicted value data "38" out of the second predicted value does not have data corresponding to the second measured value, and the measured value is "2".
No predicted value is found in the second predicted value corresponding to the “near” data for the second time.

On the other hand, the second predicted value data "40"
Coincides with the "medium" data "40" of the second measurement value, and the predicted value of this time and the previous measurement value are not significantly different as shown by the trajectory T2 in FIG. 6, so the radio wave reflection in this case The object is determined to be a "stopped object" other than the guardrail (step S12).

In this way, if the measured distance deviates from the predicted value, it can be judged that it is not at least a "stopped object", which is the "medium" data "of the fourth measured value". 38 ”corresponds, and the fifth“ middle ”
Similarly, it can be determined that the data “40” is not a stopped object.

Step S13: As described above, the same data as that of a stopped object may be temporarily displayed depending on the situation of measurement on the guardrail, so here, the change is referred to from the past data of the measured distance. Distinguish between stops and guardrails.

That is, in the second data, the predicted value data "38" is significantly different from the measured value "near" data "40", but the third predicted value is compared with the measured value. It is "38", which means that the "near" data and the "medium" data match not only the predicted value but also the predicted value as the data "38". When comparing the second time and the third time in the vertical direction, it can be seen that the “near” data is more constant than the “medium” data.
It is possible to determine that the value of the third time "38" is a guardrail (step S14).

FIG. 9 shows the result obtained by the judgment as described above. In order to make the data of FIG. 9 correspond to the data of FIG. 7, the guard rail is marked with a triangle and stopped. Items are identified with a circle.

Since the measurement data is correlated in the present invention, the time required for each measurement → frequency analysis must be extremely short. However, with the advent of high-speed CPU,
Since the required number of measurements is about 3 to 4 times, it can be realized in about several tens of milliseconds. Temporarily, 100 [msec]
Even if it is required, a vehicle traveling at a speed of 150 [Km / h] is equivalent to a traveling distance of 4.2 [m], which is sufficiently practical.

[0063]

As described above, according to the obstacle detecting device of the present invention, the next relative speed and distance are predicted and stored from the measured relative speed and distance, and the measured relative speed is calculated. When the actual vehicle speed and the approaching direction are not substantially the same, it is determined that the reflecting object is a vehicle, and in other cases, the error between the measured distance and the predicted distance is a certain value or more and a plurality of distances measured in the past. Is determined to be a guardrail or a sound barrier while it is substantially constant, and is determined to be a stopped object other than the guardrail in other cases, so that the predicted value of this time and a plurality of past measured values Since the correlation is obtained, it is possible to determine the vehicle, the guardrail, and the stopped object other than the guardrail without being affected by noise.

Further, when the alarm operation is performed using such a determination result, false alarms can be reduced, and the alarm operation becomes more accurate.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an obstacle detection device according to the present invention.

FIG. 2 is a flow chart diagram of an obstacle detection process which is stored and executed in a CPU used in the obstacle detection device according to the present invention.

FIG. 3 is a diagram showing the orientation of the vehicle in the corner of the guardrail and how the measurement is performed in the operation of the obstacle detection device according to the present invention.

FIG. 4 is a diagram showing a measurement example of an obstacle detection device according to the present invention.

FIG. 5 is a view showing an actual guardrail portion for explaining the principle of the obstacle detection device according to the present invention.

FIG. 6 is a graph showing an example of a locus of measured distance in the obstacle detection device according to the present invention.

FIG. 7 is a diagram showing data of measured values and predicted values of the obstacle detection device according to the present invention.

FIG. 8 is a diagram showing a relationship between measured values and predicted values in the obstacle detection device according to the present invention.

FIG. 9 is a diagram showing a result determined by the obstacle detection device according to the present invention.

FIG. 10 is a block diagram schematically showing an obstacle detection device using an FM-CW wave, which is generally known in the past.

11 is a block diagram showing the obstacle detection device shown in FIG. 10 in a plan view.

FIG. 12 is a transmission / reception waveform diagram of a conventional example.

FIG. 13 is a waveform diagram showing a spectrum of a modulation frequency.

FIG. 14 is a diagram for explaining a drawback of the conventional example.

[Explanation of symbols]

 1 Transmission Antenna 2 Transmission Circuit 3 Modulation Circuit 4 Reception Antenna 5 Reception Circuit 6 Mixer 7 Demodulation Circuit 8 Signal Generation Circuit 9 Synchronous Signal Generation Circuit 10 CPU 11 Modulation Pattern Storage Unit 12 Demodulation Signal Separation Circuit 13 Frequency Analysis / Signal Processing Unit 14 Data Storage unit 15 vehicle speed sensor In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An FM-CW wave is transmitted as a launch wave, a reception wave reflected by a reflecting object is mixed with the launch wave to generate a beat signal, and the beat signal is subjected to frequency analysis to obtain a beat signal from the reflecting object. In an apparatus for detecting an obstacle by measuring a relative speed and a distance, a storage unit that predicts the next relative speed and distance from the measured relative speed and distance and stores the result, a vehicle speed sensor, and a measured relative speed When the speed is not substantially the same as the actual vehicle speed by the sensor in the approach direction, it is determined that the reflective object is a vehicle, and in other cases, the error between the measured distance and the predicted distance is equal to or greater than a certain value and the past When the plurality of measured distances are substantially constant, it is determined that the reflective object is a guardrail or a sound barrier, and otherwise the reflective object is a stationary object other than the guardrail. That the determination unit, the obstacle detecting device characterized by comprising a.