JPH0450543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a distance measuring method using an electromagnetic wave radar for measuring distance in a non-contact manner in a highly dusty environment.

[Prior Art] Radar that uses electromagnetic waves such as microwaves has high transparency even in environments with high dust content, so it is effective as a measurement means in the steel industry, etc., and is used, for example, to measure the shape of charge distribution in blast furnaces. It is applied to molten steel level measurement and slag level measurement in converters.

Figure 3 is an example of a conventionally used frequency modulation type microwave radar, and is a block diagram of a device based on the method proposed as a "distance measurement method using electromagnetic waves" in Japanese Patent Application Laid-Open No. 55-59359. is a constant current DC power supply, 22 is a Gunn diode, 23 is a microwave, 24 is a resonator, 25 is a bias circuit, 26 is a varactor diode, 27
is a frequency modulated microwave, 28 is a directional coupler, 29 is a circulator, 30 is a mixer, 3
1 is an antenna, 32 is a transmitted wave, 33 is a distance measurement target,
34 is a motor, 35 is a ball screw, 36 is a reflected wave, 37 is a beat wave, 38 is a filter, 39 is an amplifier, 40 is a waveform shaping circuit, 41 is a counter, 4
2 is an arithmetic circuit, and d is a measurement distance.

In addition to the usual frequency modulation method, this conventional method uses an appropriate moving device such as a ball screw 35 rotated by a motor 34 to move the antenna 31 in the same direction as the beam of the transmitted wave 32;
λ/4(λ
is the microwave wavelength) or its integer multiple (k
Beat wave 37
Phase modulation with an initial phase ranging from 0 to kπ is applied to obtain highly accurate distance data.

[Problems to be solved] However, in the above-mentioned conventional technology, the time to apply phase modulation to the beat wave, that is, the antenna is
It only takes time to move mechanically. As a result, the measurement time required is approximately 1 second, which results in a lack of responsiveness when the object to be measured moves very quickly, and a driving mechanism is required, resulting in an increase in the size of the device.

An object of the present invention is to solve the above-mentioned problems and to obtain an electromagnetic wave radar ranging method that achieves quick measurement time and high accuracy without requiring a mechanical drive mechanism.

[Means for Solving the Problems] The electromagnetic wave radar ranging method of the present invention involves squaring the instantaneous value of the beat signal, then removing the DC component and amplifying it to produce a new beat signal one or more times. , the number of waves of the beat signal obtained by the same processing is counted, and the distance to the measurement target is calculated from the result of counting the number of the same waves.

[Function] In frequency modulation type electromagnetic wave radar, distance information to be measured is obtained as a beat signal of the transmitted wave and received wave, but conventionally information is extracted from the beat signal at the zero crossing point (AC voltage, current This is done by counting the moment when the value changes from positive to negative or from negative to positive.

Since the zero crossing point is one per half wavelength of the alternating current signal, information below the half wavelength of the beat signal is truncated. Therefore, detection sensitivity can be improved by picking up this truncated information.

The present invention has been made from the above-mentioned viewpoint, and aims to detect a beat signal phase of half a wavelength or less while making use of a zero-crossing point detection method that is easy to detect and has few malfunctions.

To do this, the beat signal voltage, which is a sine wave alternating current, is squared to create a pulsating flow with ripples (double the frequency), and the DC component of the pulsating current is removed to create an alternating current with a frequency twice that of the original beat signal. Get voltage. If this alternating current voltage is subjected to zero-crossing point detection processing, the number of zero-crossing points will be twice, so the detection sensitivity will be twice that of the conventional method.

If this process of squaring and direct current removal is repeated many times, the number of zero crossing points will also increase by a factor of two, and the distance detection sensitivity will improve accordingly.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an electromagnetic wave radar distance measuring device using an electromagnetic wave radar distance measuring method as an example, in which 1 is a radar section, which is composed of the following parts 2 to 6, and 2 is a high frequency wave generator that generates microwaves. 3 is a duplexer, 4 is a tuner, 5 is a transmitting/receiving antenna, and 6 is a detector.

7a and 7b are first and second beat signal square amplification circuits; first and second squarers 8a and 8b square the instantaneous value of the input beat signal and output it; and remove the DC component of the beat signal. First and second offset removal circuits 9a and 9b, first and second amplifiers 10a and 10b that amplify the beat signal and recover the attenuation.
It's getting more familiar.

11 is a frequency modulation oscillator that generates a modulation signal that changes the oscillation frequency of the high frequency oscillator 2; 12;
13 is a counter for counting the number of zero crossing points in response to the beat signal squared amplifying circuit 7 and the output beat signal;
1 is a distance calculating circuit that calculates the distance to the target 14 from the count value of the counter 12, 14 is the target whose distance is to be measured, 15 is a transmitted wave, and 16 is a reflected wave.

Here, the square processing of the beat signal will be explained. When an electromagnetic wave such as a microwave is frequency-modulated with a sine wave and a transmitted wave and a received wave are superimposed, the beat signal Wb is expressed by equation (1).

Wb=cos [Wc・τ＋γ・cos(2πt/Tf)] …(1) γ=2π・ΔF・τ=2π・ΔF・(2d/c) ……(2) Here, Wc: carrier wave center angular frequency τ: Electromagnetic wave propagation time (=2d/c) d: Measurement distance c: speed of light Tf: Frequency modulation period ΔF: Maximum frequency deviation.

Therefore, the phase change amount γ includes information on the measurement distance d.

Now, the signal Wb ₁ obtained by squaring the beat signal Wb is Wb ₁ = 1/2 {1 + cos [2Wc・τ+2γ・cos (2πt/Tf
)}...(3), and the signal Wb ₂ after DC component (offset) removal and amplification is expressed as equation (4).

Wb ₂ = cos [2Wc・τ+2γ・cos (2πt/Tf)]
...(4) Therefore, the phase change amount of signal Wb ₂ is 2γ, which is twice that of Wb. As a result, the number of zero crossing points of the beat signal also doubles.

The device of this embodiment is configured as described above,
It operates as described below.

The beat signal Wb obtained by the radar section 1 is processed by a beat signal square amplification circuit 7a including a squarer 8a, an offset removal circuit 9a, and an amplifier 10a.
When the above equations (3) and (4) are processed, the number of zero crossing points where the beat signal instantaneously becomes zero during one period of frequency modulation is doubled, and the result is calculated using the same number of zero crossing points. , the quantization error will be 1/2.

Furthermore, if a large number of beat signal square amplification circuits 7b are connected in N stages in series, the amount of phase change will be _2N ·γ.

The beat signal processed by the beat signal square amplification circuits 7a, b, . The count result is converted into a measured distance d by the distance calculation circuit 13. As a result, the inherent error (quantization error) of frequency modulation electromagnetic wave radar can be reduced to 1/2 _N.

FIG. 2 shows the results of a distance measurement test of the frequency modulation electromagnetic wave radar based on the present invention. In this test, the number N of the beat signal square amplification circuits connected in series was set to 2. The horizontal axis represents the distance to the target 14, and the vertical axis represents the number of detected beat signal zero crossing points. ○ mark and solid line 18 are measurement results according to this example, × mark and dotted line 19
These are the measurement results obtained in the prior art when the measurement time was set to the frequency modulation period of 1 ms, which is the same as in the present invention (the antenna was not mechanically driven).

From Figure 2, the inherent error due to the conventional technology is 1m.
On the other hand, it can be seen that the inherent error in this test was 25 cm, which is reduced to 1/4.

In this way, the following effects could be obtained by the apparatus using the electromagnetic wave radar ranging method of this embodiment.

(1) The measurement time is one cycle of frequency modulation, so
For example, it is 1/1000 of the conventional technology.

(2) Multi-stage beat signal square amplification processing enables highly accurate measurement even in a narrow frequency modulation band of about 100MHz.

(3) No mechanical drive mechanism is required, and the device can be made smaller.

[Effects of the Invention] The electromagnetic radar ranging method of the present invention squares the instantaneous value of the beat signal, then removes the DC component and amplifies it to produce a new beat signal one or more times. The electromagnetic wave radar ranging device of the present invention counts the number of waves of the beat signal and calculates the distance to the measurement target from the result of counting the number of waves. (1) No phase modulation is required, saving phase modulation time;
It has excellent responsiveness and can shorten measurement time.

(2) Highly accurate measurements are possible because the errors inherent in frequency modulation electromagnetic wave radar can be reduced by square amplification processing of multiple beat signals.

(3) Since the frequency modulation band can be narrowed by the improvement in beat signal detection accuracy, the microwave radar section can be made smaller and lighter. In addition, the configuration of the signal processing circuit is simple,
It becomes possible to downsize the signal processing circuit.

It has excellent effects as mentioned above.

[Brief explanation of drawings]

Figure 1 is a block diagram of an electromagnetic radar ranging device using an electromagnetic radar ranging method as an example, Figure 2 is a ranging test result, and Figure 3 is a block diagram of a device using a conventional electromagnetic radar ranging method. be. 1... Radar section, 2... High frequency oscillator, 3...
Duplexer, 4... Tuner, 5... Transmitting/receiving antenna, 6... Detector, 7a, 7b... First and second beat signal square amplification circuits, 8a, 8b... First,
Second squarer, 9a, 9b...first, second offset removal circuit, 10a, 10b...first, second
amplifier, 11... frequency modulation oscillator, 12...
...Counter, 13...Distance calculation circuit, 14...Target, 15...Transmitted wave, 16...Reflected wave, 1
8... Distance measurement results according to this embodiment, 19... Distance measurement results according to the conventional technology.

Claims (1)

[Claims] 1. Sending a frequency-modulated electromagnetic wave to a measurement target, receiving a reflected wave from the ranging target, and performing mixed detection of the received reflected wave and the frequency-modulated electromagnetic wave to obtain a beat signal, In an electromagnetic wave radar ranging method that measures the distance to a distance measurement target from the obtained beat signal, steps 1 to 1 include squaring the instantaneous value of the beat signal, removing the DC component, and amplifying it to create a new beat signal. An electromagnetic wave radar ranging method characterized in that the process is performed multiple times, the number of waves of a beat signal obtained by the same process is counted, and the distance to the measurement target is calculated from the result of counting the number of the same waves.