JPH06138218A - Distance measuring device - Google Patents

Abstract

PURPOSE:To provide a distance measuring device capable of simultaneous measurement of a plurality of distances to only reflecting objects such as preceding vehicles where changes in the distance are relatively small. CONSTITUTION:The frequency sweep signal to be outputted from a sweep voltage generator 2 and a voltage control oscillator 3 through a mixer 5 is transmitted through a transmitting antenna 7, the reflected wave from the reflecting object of the signal is received by a receiving antenna 8, and the differential frequency between the reflected wave and the frequency sweep signal is obtained by a mixer 11. The signal of the differential frequency is quantized by an A-D converter 21, and in addition, Fourier conversion is executed by a high speed Fourier converter 22, and the signal level of the frequency component for each specified band is obtained. The obtained signal level for each band is summed for the specified time period by a computer 13, the frequency components of the signal level where this summed signal level exceeds a specified threshold are extracted, and the distance to the reflecting object is computed from the frequency components by the computer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device for measuring a distance by a frequency sweep method.

[0002]

2. Description of the Related Art In a conventional distance measuring device of this type, as shown in FIG. 5, for example, a sweep voltage signal is generated from a sweep voltage generator 2 in response to a signal from a sync signal generator 1, and the sweep voltage signal is generated. The voltage signal is supplied to the voltage controlled oscillator 3, and the frequency swept signal output from the voltage controlled oscillator 3 according to the swept voltage signal is mixed with the stable frequency output signal from the stable oscillator 4 in the mixer 5. The mixer 5 outputs a signal having a frequency that is the sum of the frequency of the stable frequency output signal and the frequency of the frequency sweep signal, and transmits this signal as a transmission signal via the amplifier 6 and the transmission antenna 7, and at the same time, the amplifier 10 Is supplied to the mixer 11 via.
Then, the reflected wave of the reflection signal of the transmission signal transmitted from the transmission antenna 7 is received via the reception antenna 8, the received signal is amplified by the amplifier 9 and supplied to the mixer 11, and in the mixer 11. Mixed with the transmitted signal,
As a result, a signal having a difference frequency between the transmission signal and the reception signal is obtained.

This differential frequency corresponds to the amount of change in the frequency of the frequency sweep signal during the time until the radio wave is transmitted from the transmitting antenna 7, reflected by a reflector, and received by the receiving antenna 8. Therefore, the distance to the reflector can be calculated by counting the difference frequency with the frequency counter 12 and supplying the count result to the calculator 13 including a CPU to calculate the time required for transmission and reception.

[0004]

In the above-described conventional distance measuring device, the difference frequency between the transmitted and received signals is simply counted by the frequency counter 12 to calculate the distance to the reflecting object. When the device is applied to an inter-vehicle distance measuring device, it is difficult to measure the distance to a plurality of reflecting objects at the same time as measuring unnecessary reflecting objects such as road stop objects due to multipath etc. There is a problem.

The present invention has been made in view of the above,
It is an object of the present invention to provide a distance measuring device capable of simultaneously measuring a plurality of distances to only a reflecting object such as a preceding vehicle whose distance change is relatively small.

[0006]

In order to achieve the above object, the distance measuring device of the present invention transmits a frequency sweep signal and receives a reflected wave of a reflected object of the frequency sweep signal,
A distance measuring device that measures the distance to the reflector from the difference frequency between the received reflected wave and the transmitted frequency sweep signal, for each frequency band of the difference frequency between the reflected wave and the frequency sweep signal. Signal level measuring means for each band for obtaining a signal level, accumulating means for accumulating the signal level for each frequency band obtained by the signal level measuring means for each band for a predetermined time, and signal level accumulated by the accumulating means Has a distance calculating means for extracting a frequency component of a signal level exceeding a predetermined threshold value and calculating a distance from the frequency component to a reflecting object.

[0007]

In the distance measuring device of the present invention, the frequency sweep signal is transmitted, the signal level for each frequency band of the differential frequency between the reflected wave of the signal and the frequency sweep signal is obtained, and the obtained frequency band is obtained for each frequency band. Of the signal level is accumulated for a predetermined time, the frequency component of the signal level at which the accumulated signal level exceeds a predetermined threshold value is extracted, and the distance from the frequency component to the reflector is calculated.

[0008]

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

FIG. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention. The distance measuring device shown in the figure is different only in that an A-D converter 21 and a fast Fourier transformer 22 are provided in place of the frequency counter 12 in the conventional distance measuring device described above, and the other configurations are the same. Therefore, the same components are designated by the same reference numerals. With this configuration, the mixer 1
The output signal corresponding to the difference frequency signal from 1 is A-
Quantization is performed by the D converter 21, a signal level in each band is obtained by the fast Fourier transformer 22, this signal level is accumulated for a predetermined time by the calculator 13, and the accumulated signal level exceeds a predetermined threshold value. The frequency component is extracted and the distance from this frequency to the reflector is calculated.

The operation of the distance measuring device of this embodiment described above will be described below.

As shown in FIG. 2, the transmission signal of the frequency f _o transmitted at the time T _o via the transmission antenna 7 is reflected by the reflector and received by the reception antenna 8 at the time T _o + ΔT. At the time of this reception, the frequency of the transmission wave transmitted from the distance measuring apparatus is f as shown in FIG.
Since it has changed to _o + Δf, the mixer 11 outputs a signal corresponding to the frequency change Δf. Then, in this case, when there are a plurality of reflectors, the output signal from the mixer 11 is a signal in which frequency components corresponding to the distances of the reflectors are superimposed. FIG. 2 shows the relationship between the transmitted wave and the reflected wave that is the received wave described above.

The differential frequency signal output from the mixer 11 is supplied to the AD converter 21, quantized, and then Fourier-transformed by the fast Fourier transformer 22, whereby the signal of the frequency component for each constant band is obtained. You get a level. This frequency band determines the resolution of distance. In addition,
If the band is not fixed and is arbitrarily set, it is possible to provide an arbitrary distance measurement characteristic. For example, if the band is narrowed at a low frequency and widened at a high frequency, it is possible to provide a characteristic with higher resolution as the distance becomes shorter.

Then, as described above, the output signal from the fast Fourier transformer 22 is supplied to the arithmetic unit 13, and the arithmetic unit 13 accumulates the signal level of each band for a certain period of time. FIG. 3 shows the relationship between the frequency and the signal level when the signal level of each band is accumulated for a certain period of time. As can be seen from the figure, the reflected waves from the reflecting objects A and C having almost no change in distance, that is, almost no change in the frequency change Δf, are emphasized by being accumulated, and exceed the threshold value. Is changing. That is, the reflected wave from the object B in which the frequency change Δf changes is spread over a wide band, but the level is not emphasized and does not exceed the threshold value.

Therefore, if all the frequency components whose signal level has reached the threshold value are selected, the transmission / reception time can be obtained from this frequency in the same manner as in the conventional case, and the distance to the reflector can be calculated.

For example, when the present distance measuring device is used as a distance measuring device for automatic tracking of a preceding vehicle, it is sufficient to extract only the preceding vehicle having a small distance change from the subject vehicle and measure the distance. The reflection from a stationary object or the like can be eliminated.

That is, in the present distance measuring device, it is possible to simultaneously measure a plurality of distances only for a reflecting object, such as a preceding vehicle, whose distance change with the present device is small. In addition,
In the distance measuring device shown in FIG. 1, the fast Fourier transformer 22
Can analyze the frequency components with high accuracy,
It is possible to obtain high distance measurement accuracy.

FIG. 4 is a block diagram showing the structure of a distance measuring device according to another embodiment of the present invention. The distance measuring device shown in the figure is the same as the mixer 11 in the embodiment shown in FIG.
A plurality of bandpass filters 31 and signal selectors 32 having different bands are provided between the AD converter 21 and the A-D converter 21, and the fast Fourier transformer 22 is removed, whereby the output signal of the mixer 11 is converted into a plurality of bandpass filters. Each frequency component is separated by 31 and the output signal from the bandpass filter 31 separated for each frequency component is switched by the signal selector 32 to extract the signal level of each frequency component. Quantization is performed by the A / D converter 21, and this operation is performed for a certain period of time.
In Fig. 3, the distance to the reflecting object is calculated by accumulating each frequency component. In the embodiment shown in FIG. 4, the bands are separated by a plurality of band pass filters, and therefore high speed processing is possible.

[0018]

As described above, according to the present invention,
A frequency sweep signal is transmitted, a signal level for each frequency band of a differential frequency between the reflected wave of the signal and the frequency sweep signal is obtained, and the signal level for each frequency band thus obtained is accumulated for a predetermined period of time. Since the frequency component of the signal level at which the accumulated signal level exceeds a predetermined threshold value is extracted and the distance from the frequency component to the reflecting object is calculated, there is almost no change in distance, such as in a preceding vehicle. It is possible to extract a plurality of reflected waves from only the reflector and measure a plurality of distances to the preceding vehicle that is the reflector at the same time.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a distance measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a transmitted wave and a received wave.

FIG. 3 is a diagram showing a relationship between a frequency and a signal level when the signal levels of respective bands are accumulated for a certain period of time.

FIG. 4 is a block diagram showing a configuration of a distance measuring device according to another embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional distance measuring device.

[Explanation of symbols]

 1 Synchronous Signal Generator 2 Sweep Voltage Generator 3 Voltage Controlled Oscillator 4 Stable Oscillator 5,11 Mixer 7 Transmit Antenna 8 Receive Antenna 13 Calculator 21 A-D Converter 22 Fast Fourier Transform 31 Bandpass Filter

Claims (1)

[Claims] 1. A frequency sweep signal is transmitted, a reflected wave of the frequency sweep signal by a reflector is received, and a distance from the difference frequency between the received reflected wave and the transmitted frequency sweep signal to the reflector is determined. A distance measuring device for measuring,
A signal level measuring means for each band for obtaining a signal level for each frequency band of the differential frequency between the reflected wave and the frequency sweep signal, and a signal level for each frequency band obtained by the signal level measuring means for each band is accumulated for a predetermined time. Accumulating means for calculating, and a distance calculating means for extracting a frequency component of a signal level in which the signal level accumulated by the accumulating means exceeds a predetermined threshold value, and calculating a distance from the frequency component to a reflector. A distance measuring device comprising: