JPS6293677A - Apparatus for detecting obstruction - Google Patents

Abstract

PURPOSE:To reduce power, by transmitting a continuous wave modulated by a signal having timewise correlation in place of a pulse wave. CONSTITUTION:High frequency having definite frequency, for example, about 10GHz is generated by a transmitting part 1 and two-phase modulation is performed on the basis of the output of a code generator PNG8 in a mixer 2. The signal modulated in the mixer 2 is amplified to a proper level by an amplifying part 3 to be emitted from an antenna 4 in the form of electromagnetic wave. When an obstruction 50 is present, a part of the electromagnetic wave is emitted to be received by an antenna 5 and amplified by an amplifying part 7 to be subjected to frequency conversion in a band which is easy to perform signal processing by means of a frequency converting part. Next, the receiving signal enters a correlation device 11 to take the correlation with the noise code delayed by a delay circuit 9 and, on the basis of the delay quantity when the correlation result from the correlation device became max., the distance up to the obstruction 50 is measured.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a radar that measures the distance to an obstacle;
The present invention particularly relates to an obstacle detection device suitable for use in automobiles.

[Background of the invention]

Conventionally, as an obstacle detection device that measures the distance to an obstacle using R-waves, the configuration shown in FIG. 52
-49790).

This supplies the high frequency generated by the high frequency oscillation unit 1 to the pulse modulation unit 22 which is driven by a single pulse generated by the pulse generation unit 23, and sends pulse-modulated radio waves into space from the transmitting antenna 4. radiate as.

If there is an obstacle 50, this radiation wave will be reflected there, and the reflected wave will be received by the receiving antenna 5.

Amplified and converted into two frequencies, demodulated by a comparator 25,
It is shaped into the original pulse waveform. Here, the pulse generated by the pulse generator 23 is used as a start signal, the pulse shaped by the comparator 25 is used as a stop signal, and the time measurement unit 26 uses the clock 24 to count the propagation time of radio waves between transmission and reception.

A common method is to calculate the distance from this.

However, in this method, as shown in FIG.

The propagation delay T of the received pulse with respect to the transmitted pulse is.

Since it is directly proportional to the distance to the obstacle, if the rise time t of the transmitted pulse is large, on the receiving side, the wave height value Vr of the received pulse will increase depending on the radio wave reflectance and distance of the obstacle, as shown in the figure.
changes greatly and when determining the occurrence of a pulse at a certain set voltage Vth, the peak value of the received pulse will be different from Vth 1Vr2 even if there is an obstacle at the same distance, resulting in a one-hour measurement error ΔT. , the rise time tr of the transmitted pulse is 2 m (the propagation path of the radio wave to the obstacle is twice the distance to the obstacle), considering the distance resolution of 1 m generally required for an obstacle detection device. ), that is, it needs to be approximately 6 nS or less.

Therefore, a wide occupied radio wave band is required. for example,
Even under the above conditions, a frequency band of approximately 200 MHz is required.

However, from a practical point of view, it is difficult to allow such a wide band to be occupied, and the radio noise resistance is weakened, resulting in decreased reliability and impractical use. In particular, the problem of reliability deterioration due to the weakening of radio noise resistance is significant (1) For example, as shown in FIG. Yes, if the bandwidth is wide at this time, the radio waves from now on will be directly received by the own troops 100, and as a result, the reflected waves from the obstacles 50 will be masked, making it impossible to measure the distance, making it difficult to put it into practical use. It becomes extremely difficult.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an obstacle detection device that eliminates the drawbacks of the prior art described above and can maintain sufficient accuracy while keeping the occupied bandwidth of radio waves sufficiently small.

[Summary of the invention]

To achieve this objective, the present invention transmits a continuous wave modulated by a temporally correlated signal instead of a pulse wave, thereby making it possible to measure the propagation time of radio waves from transmission to reception. It is characterized by the following points.

[Embodiments of the invention]

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

A signal for detecting the obstacle 50 is generated by the high frequency oscillator 1.
Noise volume generator (PNG)8. Frequency divider 10° clock circuit 14. Mixer 2. Amplifying section 3. The signal is emitted by a transmission system consisting of an antenna 4.

On the other hand, the receiving system includes antenna 5. Amplification section 62 Frequency conversion section 7
．． ! ! Extension circuit 9. Correlator 11. It consists of a detector 12° and a comparator 13.

The transmitter 1 generates a high frequency of a certain frequency 1, for example, about 10 GHz, and the mixer 2 performs two-phase phase modulation using the output of the PNG 8. PNG8 generates a pseudorandom noise code such as a so-called maximum periodic code sequence (m sequence), and this code is suitable because it has sharp autocorrelation characteristics. Note that for m-series autocorrelation, the bit width of the code is T
Then, it has a width of ±T. And this correlation property.

Affects the resolution of obstacle detection. Therefore, the higher the bit rate of the code, the better the resolution.

In this example, the frequency is 100MHz, so ±10n
There is a range of correlation of S, which is ±3m when converted to distance, but when considering that it corresponds to round trip time, it is ±1.
Equivalent to 5m. PNG8 clock is clock circuit 1
It is obtained by dividing the output of 4 into 2. Of course, it goes without saying that if the peak of correlation can be detected accurately, the distance accuracy will be even better.

The signal modulated by the mixer 2 is amplified to an appropriate level by the amplifier 3 and radiated from the antenna 4 in the form of electromagnetic waves.

When the obstacle 50 exists, part of the electromagnetic waves is reflected,
It is received by the antenna 5 and amplified by the amplification section 6.
Frequency converter 7 allows for easy signal processing up to 1 band.
Perform frequency conversion.

Next, the received signal is correlated with the noise code delayed by the delay circuit 9 in the correlator 11 .

Therefore, when there is no one reflected wave, the output of the correlator 11 is just noise, and even if there is one reflected wave, when the delay amount of the delay circuit 9 is not appropriate, that is, the output of the radio wave going back and forth to the obstacle 50 is If the delay amount is not equal to the propagation time, it is still only noise. Then, when the mutual time difference comes within ±T as shown in Figure 5, a signal with an amplitude greater than the noise begins to appear in the correlator output for the first time, and when they match perfectly, The output of the correlator 11 that takes the peak value is usually in the form of alternating current, in which case it is detected by a diode or the like.

The comparator 13 is designed to detect a level higher than a certain value.

In order to cover the detection range (1.5 m to 150 m in this embodiment), the delay amount is swept at a constant cycle. Therefore, the output of the PNG 8 is variably delayed in the delay circuit 9, and the amount of delay is output as distance information. A specific example of the delay circuit will be described later.

Since it is difficult to realize the delay circuit 9 in a continuously variable form, this embodiment uses a discrete delay characteristic. The amount of delay is 10 nS to 1 μs'. Here, the step width of the delay becomes an issue. In other words, as is clear from Fig. 5, the step width must be at least equal to or greater than the period of the code.For example, if T is selected as the period of the code, the correlation characteristic shown in Fig. 5 becomes as shown in Fig. 6. deteriorates to. That is, the peak level also decreases, and furthermore, the disadvantage that the peak position shifts becomes more noticeable. Therefore, in this embodiment, half the chip period/2 is selected as the step width. Of course, the step width may be even shorter.

The delay circuit 9 as described above can be realized by a circuit as shown in FIG. The input code is first input to a 10-stage shift register 90.
Shifted by group 0-908.

One system of each output (9 outputs in total) is selected by a switch 91 and input to a primary 9-stage shift register 92 . The output of each stage of the shift register 92 is further connected to a switch 9.
3, one system is selected and inputted to a flip-flop 94, which is a one-stage shift register, and one system is selected by a switch 95. Flip-flop 94 is clocked by the input clock (2f) and shift registers 900-908 and 92 are clocked at half the clock frequency. Therefore, it is possible to shift the delay amount from 0 to 199 steps using the 2j clock as a reference.

FIG. 8 shows an embodiment of another delay circuit.

This circuit uses PN09, which has exactly the same configuration as PH10 on the transmitting side.
C is provided, and a delayed output is obtained by thinning out the clock pulses of PNG9C.

First, a signal of an appropriate frequency is obtained by the oscillator 9F, and the frequency is divided by the counter 9D to periodically generate thinning pulses. In response to the thinning pulse, the pulse removal circuit 9A removes the pulse from the clock input. By dividing the frequency using flip-flop 9B, the phase of the output of PNG 9C is delayed by 180'. Repeat this action,
When a delay corresponding to 199 clocks is achieved, the decoder 9E generates a control pulse by decoding the output of the counter 9D and transfers the data of PH10 to PN09.
By loading the data into C in parallel, both PNGs are synchronized.

Specifically, PNG8 and 9C are composed of multi-stage shift registers, and the shift register contents of PNG8 are transferred to PN09G.

FIG. 9 shows an example of a signal when an obstacle is present. If an obstacle exists in the arrangement shown in A of the same figure, when the delay amount is changed as shown in the figure, the detection will be as shown in C of the same figure, corresponding to the distance Ll and L2 to the obstacle. I get the output. The level of the detection output corresponding to a distant obstacle becomes small, and if a certain threshold is provided, there is a high possibility that distant objects will be difficult to detect. In order to eliminate this problem, in this embodiment, the gain of the amplifier 6 in the receiving system is increased in proportion to the amount of delay. The result of such correction is shown in Figure 9, and almost the same detection output can be obtained regardless of distance.

Next, the correlator 11 in this embodiment can be of various types, such as a surface acoustic wave (SAW) device, a charge-coupled device (COD), or a digital matched filter.
A format that takes correlation in parallel, such as (DMF), is used to reduce processing time.

By the way, in the example of the delay circuit shown in FIGS. 7 and 8,
The delay is done in steps. In other words, the detection distance is reduced and switched one after another, but after switching, the parallel processing type described above can obtain one output from each phase in a short time, so one cycle of the sweep can be shortened. It has the advantage of being possible. on the other hand.

In the case of a correlator that combines a mixer and a filter.

The disadvantage is that the rise time of the correlation output is limited by the filter band, making one period of sweep longer, but if a very fast sweep is not required,
Practicality increases.

〔Effect of the invention〕

As explained above, according to one aspect of the present invention, since modulation is performed so as to provide a continuous wave, power can be reduced. for example,
Conventionally, a pulse wave of 10 n S' is emitted with a period of 1 mS', and under the condition that the average power is the same, 1
The peak power is 1/00,000 times lower, which can be significantly reduced. Furthermore, by sweeping the code delay time, it is possible to detect obstacles within a certain detection range.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional example, Fig. 3 is an explanatory diagram showing the operating principle of the conventional example, and Fig. 4 explains the problems of the conventional example. FIG. 5 is an explanatory diagram showing the correlation characteristics of m-sequence codes, FIG. 6 is an explanatory diagram of sampled correlation characteristics, FIG. 7 is a block diagram showing one embodiment of the delay circuit, and FIG. 9 is a block diagram showing another embodiment of the delay circuit, and FIG. 9 is an explanatory diagram of the operation of FIG. 1. 1...High frequency oscillation section, 2...Mixer, 3, 6...
Amplification section, 4.5... Antenna, 7... Frequency conversion section, 8... Code generator (PNG), 9... Delay circuit, 1
0... Frequency divider, 11... Correlator, 12... Detector, 13... Comparator, 14... Clock.

Claims (1)

[Scope of Claims] 1. Means for transmitting radio waves to a detection target and means for receiving reflected radio waves from the detection target, and distance to the detection target can be determined by the propagation time from transmission to reception of the radio waves. In the obstacle detection device of the detection method, a transmitting means modulates a radio wave to be transmitted with a predetermined time series signal and emits it as a continuous wave, a receiving means extracting the time series signal from a signal of the received reflected radio wave, A variable delay means that receives as input the time series signal supplied to the transmitting means, and a correlation means that receives as input the time series signal extracted by the receiving means and the time series signal obtained as the output of the variable delay means. and
An obstacle detection device characterized in that the distance to the obstacle is measured based on the amount of delay by the variable delay means when the correlation result by the correlation means reaches a maximum. 2. An obstacle detection device according to claim 1, characterized in that the correlation detection processing by the correlation means is configured to be a parallel processing method. 3. Claim 1 is characterized in that the gain given to the time-series signal by the receiving means is configured to be proportionally controlled according to the amount of delay of the variable delay means. Obstacle detection device. 4. Claim 1 is characterized in that the detection threshold of the time-series signal in the receiving means is controlled in inverse proportion to the amount of delay of the variable delay means. Obstacle detection device.