JP2003202372A - Apparatus and method for measuring range - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring a range with a simple structure and a good measurement accuracy. <P>SOLUTION: A receiving antenna 21 is situated so as to receive both direct waves 24 directly traveling from a transmitting antenna and reflecting waves 23 from an object 10 that reflects radio waves 22, and a level of detected signals G5 of the direct waves 24 and the reflecting waves 23 is adjusted by using signals G7, G8. Therefore, the detected signals G5 of the direct waves 24 and the reflecting waves 23 having a large difference in the signal intensity are accurately detected using only one path, the range up to the object 10 is calculated, and so the number of parts can be reduced, and the structure is simplified. <P>COPYRIGHT: (C)2003,JPO

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 and a distance measuring method for performing highly accurate distance measurement by a short range radar.

[0002]

2. Description of the Related Art Conventionally, as a distance measuring device using such a radar, a technique using a horn antenna disclosed in Japanese Patent Laid-Open No. 2000-55715 has been disclosed.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The technology of 5715 describes a sampling pulse generation method using the beats of two crystal oscillators, but the reference signal and the measurement target radio wave are obtained by different paths, and circuits such as circuits for each path are used. There is a problem that parts are required and the number of parts is large.

Also, the horn antenna has a strong directivity,
There is a problem that the sensitivity changes depending on the inclination of the mounting. Since the directivity is strong, when it is applied to a liquid level meter, when the liquid level is wavy, an error becomes large or measurement becomes impossible. In addition, in a high-viscosity liquid or a pellet storage tank, the surface to be measured is inclined, which makes measurement impossible.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a distance measuring device and a distance measuring method with a simple structure and high measurement accuracy. .

[0006]

In order to achieve the above object, the distance measuring device of the present invention is a distance measuring device using a radar, wherein a transmission pulse is generated from a first frequency, A timing generation circuit that generates a sampling pulse from two frequencies and a beat signal from a difference frequency between a first frequency and a second frequency, a pulse transmitter that generates a pulsed electric wave by the transmission pulse, and the pulse transmitter. A transmitting antenna that radiates the radio wave generated in 1., a receiving wave that receives the direct wave in which the radio wave is directly transmitted from the transmitting antenna, and a reflected wave in which the radio wave is reflected by a target, and the direct wave and the reflected wave. A pulse receiver that outputs a detection signal by performing time expansion with the sampling pulse, and a detection signal of the direct wave or the reflected wave at a predetermined level. And level control means for adjusting the,
A measurement distance for calculating a distance to a target by using a first detection signal obtained by detecting the direct wave, a second detection signal obtained by detecting the reflected wave, and the beat signal included in the detection signal. And a calculating means.

It is preferable that the level control means controls the reception gains of the direct wave and the reflected wave in the pulse receiver.

It is preferable that the level control means controls the transmission output of the radio wave by the pulse transmitter.

The measuring distance calculating means calculates an equivalent time Te obtained from the beat signal, a reference time t0 obtained from the beat signal, a direct wave time Tx from t0 to the first detection signal, and t0 to the The reflected wave time Tr up to the second detection signal is derived, the second frequency is fs, the radio wave propagation velocity is Vc, and the distance R to the target is R = (Vc.
It is preferable to calculate by the formula of (Tr−Tx) / (2 · fs · Te).

The distance measuring method of the present invention is a distance measuring method using a radar, wherein a transmission pulse is generated from a first frequency, a sampling pulse is generated from a second frequency, and a first frequency and a second frequency are generated. A step of generating a beat signal from a difference frequency of two frequencies, a step of generating a pulsed electric wave by the transmission pulse, a step of radiating the generated electric wave with a transmitting antenna, and a step of receiving the electric wave with the receiving antenna. A step of receiving a direct wave directly transmitted from an antenna and a reflected wave of the radio wave reflected by a target; and a step of outputting a detection signal by expanding the time of the direct wave and the reflected wave by the sampling pulse. Adjusting the detection signal of the direct wave or the reflected wave to a predetermined level, and a first detection signal for detecting the direct wave included in the detection signal. When using a second detection signal obtained by detecting the reflected waves, the beat signal and a, characterized by comprising the step of calculating the distance to the target, the.

The step of adjusting the level of the detection signal includes
It is preferable to control the reception gain of the direct wave and the reflected wave.

The step of adjusting the level of the detected signal includes
It is preferable to control the transmission output of the radio wave.

The step of calculating the distance to the target includes an equivalent time Te obtained from the beat signal, a reference time t0 obtained from the beat signal, and a direct wave time Tx from t0 to the first detection signal. And the reflected wave time Tr from t0 to the second detection signal, the second frequency is fs, the radio wave propagation speed is Vc, and the distance R to the target is
It is preferable to calculate by the formula of R = (Vc · (Tr−Tx)) / (2 · fs · Te).

In the present invention, the direct wave in which the radio wave is directly transmitted from the transmitting antenna and the reflected wave in which the radio wave is reflected by the target are obtained from the receiving antenna, and the levels of the detection signals of the direct wave and the reflected wave are adjusted. As a result, the detection signals of the direct wave and the reflected wave, which have a large signal strength difference, can be detected accurately with only one path,
Since the distance to the target is calculated, it is possible to reduce the number of parts such as a circuit required by having another path, and the configuration becomes simple, and for example, downsizing and cost reduction can be achieved.

Further, the transmitting antenna and the receiving antenna are separately provided, and the transmitting antenna having a wide directivity is used to radiate radio waves in a wide range to capture the surface to be measured. As described above, it is advantageous to widely radiate radio waves to reduce the electric field strength when using weak radio according to the Japanese Radio Law.

When the reception gain of the direct wave and the reflected wave is controlled by the pulse receiver, the reception level of the detection signal when the direct wave and the reflected wave are received is adjusted so that the direct wave and the reflected wave having a large signal strength difference. It is possible to accurately detect the detection signal of (1) with only one path.

When the transmission output of the radio wave is controlled by the pulse transmitter, the transmission level when the radio wave is generated is adjusted, and the detection signal of the direct wave and the reflected wave with a large signal strength difference is accurately detected by only one path. can do.

The distance R to the target is R = (Vc. (Tr
-Tx)) / (2 · fs · Te), the error factor due to the change in the circuit element delay time is (Tr−
Tx) and the accuracy error of the time expansion rate is (Tr
Since it is erased by the proportional calculation by −Tx) / Te, the accuracy of the measurement distance calculation is uniquely determined by the second frequency fs, and the measurement distance can be calculated with high accuracy. For example, the second frequency fs
By using a high-precision oscillator such as a crystal oscillator as the oscillator, the accuracy of the measurement distance calculation can be dramatically improved.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions of the components described in this embodiment,
Unless otherwise specified, the material, the shape, the relative arrangement, and the like are not intended to limit the scope of the present invention thereto.

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

The distance measuring device 1 mainly includes an antenna section 2, a timing generating circuit 3, a microwave band pulse transmitter 4, a microwave band pulse receiver 5, a pulse detecting circuit 6, and a microprocessor 7. , Is provided.

The antenna unit 2 has a transmitting antenna 20 for radiating radio waves (microwave impulses) and a receiving antenna 21 for receiving radio waves.

Radio waves are radiated from the transmitting antenna 20 toward the target 10. In the receiving antenna 21, the radio wave 22
Reflected wave 23 reflected by the target 10 and the transmitting antenna 20
And the direct waves 24, which arrive directly from.

The timing generation circuit 3 has a first crystal oscillator 30 and a second crystal oscillator 31 which generate different clocks. The first crystal oscillator 30 has an oscillation frequency ft and generates a transmission pulse G2. The second crystal oscillator 31 has an oscillation frequency fs and generates a sampling pulse G3.

Further, the timing generation circuit 3 has a difference frequency Δf = ft−f between the oscillation frequency ft and the oscillation frequency fs.
A beat signal of about s = 100 Hz is generated, and an interrupt signal G4 synchronized with a predetermined change point of the beat signal is generated by a pulse detection circuit (not shown).

The interrupt signal G4 is sent to the microprocessor 7
Input to the interrupt port of. Microprocessor 7
Can measure the cycle of the interrupt signal G4 to derive the equivalent time Te, which is the current cycle of the beat signal.

The microwave band pulse transmitter 4 generates a radio wave (microwave impulse) of about 3 ns based on the transmission pulse G2 from the timing generation circuit 3. The generated radio wave is radiated from the transmitting antenna 20 into the air.

The microwave band pulse receiver 5 receives the sampling pulse G3 from the timing generation circuit 3
Reflected wave 23 and direct wave 24 received by the receiving antenna 21
Sampling amplification with high gain is performed on the detected signal G
5 is output.

In the detected signal G5, the phase of the sampling pulse G3 linearly deviates from the phase of the transmission pulse G2 at a cycle of 1 / Δf, so that an event of 1 / fs is equivalent to fs /. The signal is expanded by Δf times.

The pulse detection circuit 6 generates a pulse detection signal G6 from the detection signal G5 and a predetermined threshold value.

The pulse detection signal G6 is input to the interrupt port of the microprocessor 7. The microprocessor 7 triggers the pulse detection signal G6 to capture the detection signal G5 having a predetermined threshold value or higher, and the reflected wave 23
The peak level of the direct wave 24 can be detected.

Here, the microprocessor 7 is used.
In the above, the peak level of the reflected wave 23 or the direct wave 24 is detected, but a point that intersects with a predetermined threshold value may be detected instead of the peak.

The microprocessor 7 is an A / D converter 7
It has a third crystal oscillator 71 of 0 and oscillation frequency fc. A
The / D converter 70 A / D converts the input detection signal G5. The third crystal oscillator 71 is used to measure the cycle of the interrupt signal G4 of the timing generation circuit 3 with accuracy based on the oscillation frequency fc. The microprocessor 7 also outputs the output signal G1 to the timing generation circuit 3.

Here, as a feature of the present invention, the reception gain control signal G7 is output from the microprocessor 7 to the microwave band pulse receiver 5. Also, the microprocessor 7
To the microwave band pulse transmitter 4 from the transmission output control signal G
8 is output.

The reception gain control signal G7 and the transmission output control signal G8 have the signal strength of the direct wave 24 higher than that of the reflected wave 23, so that the reflected wave 23 cannot be measured at the same time. And to adjust the level of the detection signal G5 based on the direct wave 24.

In this embodiment, both the reception gain control signal G7 and the transmission output control signal G8 are used, but in addition to this, either the reception gain control signal G7 or the transmission output control signal G8 is used. It may be configured to use only one.

The distance measuring process of the distance measuring apparatus 1 of the embodiment will be described below with reference to the flowcharts of FIGS. 2 to 4 and the signal waveform diagram of FIG. FIG. 2 is a flowchart showing the distance measurement processing according to the embodiment. FIG. 3 is a flowchart showing a direct wave time measurement process according to the embodiment. FIG. 4 is a flowchart showing a reflected wave time measurement process according to the embodiment. FIG. 5 is a signal waveform diagram showing respective signals in which the direct wave and the reflected wave have different waveforms depending on the reception gain control signal G7 and the transmission output control signal G8.

In FIG. 2, when the distance measurement is started,
First, the microprocessor 7 measures the equivalent time Te (S1). The equivalent time Te is the microprocessor 7
Receives an interrupt signal G4 (interrupt signal G4 in FIG. 5B) synchronized with a predetermined change point of the beat signal generated by the timing generation circuit 3, and determines the cycle of the peak P1 of the interrupt signal G4 as the third crystal. By measuring the oscillation frequency fc of the oscillator 71 with accuracy as a reference, the equivalent time Te, which is the current cycle of the beat signal, is derived and stored. As a result, the equivalent time Te of the beat signal shown in FIG. 5A is obtained.

Next, the microprocessor 7 directs the direct wave 2
In order to control 4 to a level at which measurement is possible, the reception gain control signal G7 and the transmission output control signal G8 are output to control the level of the detection signal G5 (S2). With these control signals, the detection signal G5 obtained by the microprocessor 7 from the microwave band pulse receiver 5 is adjusted to the level of the detection signal G5 shown in FIG. 5C.

A reference time t0 as a reference is set (S
3). The reference time t0 is the interrupt signal G as shown in FIG.
The time of the peak P1 of 4 is used as a reference and stored.

Then, the direct wave time Tx of the direct wave 24 is measured (S4). The measurement of the direct wave time Tx will be described in detail with reference to the flowchart of FIG.

In FIG. 3, first, when the measurement is started, the pulse of FIG. 5 (d) generated when the peak P2 of the direct wave 24 of the detection signal G5 of FIG. 5 (c) exceeds a predetermined threshold value. The microprocessor 7 detects the peak P4 of the detection signal G6 (S40). Here, the peak P3 of the reflected wave 23 of the detection signal G5 in FIG. 5C exceeds the predetermined threshold value because the peak P3 of the reflected wave 23 hardly appears due to the level control (S2) of the previous detection signal G5. Therefore, the peak of the reflected wave 23 does not appear as a peak in the pulse detection signal G6 ((d) of FIG. 5) output from the pulse detection circuit 6.

When the peak P4 of the pulse detection signal G6 is detected, the detection signal G5 is taken in, and if the detection signal G5 of FIG. .

The peak P2 of the direct wave 24 is detected from the detected detection signal G5 (S42).

Then, the peak P2 of the detected direct wave 24
The direct wave time Tx is calculated from the peak time and the stored reference time t0 (S43). The direct wave time Tx is the time from the reference time t0 to the peak time of the peak P2.

Thus, the direct wave time Tx is measured (S
4) ends. The measurement of the direct wave time Tx is
It is not necessary to perform the same number of times as the reflected wave 23 each time, and in this embodiment, the direct wave 24 is measured once for every 255 measurements of the reflected wave 23. In addition to this, for example, the measurement cycle can be shortened by performing the operation at a predetermined interval when the power is turned on.

In the flow chart of the present embodiment, the flow chart in the case of measuring the direct wave 24 is described, but in the case of not measuring the direct wave 24, for example, S2
The measurement is performed by omitting steps S4 to S4.

Next, the microprocessor 7 causes the reflected wave 2
In order to control 3 to a measurable level, the reception gain control signal G7 and the transmission output control signal G8 are output, and the level of the detection signal G5 is controlled (S5). By these control signals, the detection signal G5 is the detection signal G5 of FIG.
Adjusted to the level of. The detection signal G of FIG.
5 shows a waveform in which both the peak P2 ′ of the direct wave 24 and the peak P3 ′ of the reflected wave 23 have peaks equal to or higher than a predetermined threshold.

The level control in S5 may be performed by setting the initial setting at the time of power-on, for example, in consideration of the fact that the reflected wave 23 is always measured. Then, only when the direct wave 24 is measured, S
The measurement cycle may be shortened by performing level control of 2.

Then, the reflected wave time Tr of the reflected wave 23 is measured (S6). The measurement of the reflected wave time Tr will be described in detail with reference to the flowchart of FIG.

In FIG. 4, first, when the measurement starts, the peak P2 'of the direct wave 24 and the peak P3' of the reflected wave 23 of the detection signal G5 in FIG. 5 (e) are generated when they exceed a predetermined threshold value. The pulse detection signal G of FIG.
The microprocessor 7 detects the peak P4 'and the peak P5' of 6 (S60).

Direct wave 2 is added to the detection signal G5 in FIG. 5 (e).
Since both the peak P2 ′ of 4 and the peak P3 ′ of the reflected wave 23 exceed the predetermined threshold value, the peak P4 ′ corresponding to the direct wave 24 is included in the pulse detection signal G6 output from the pulse detection circuit 6. And a peak P5 'corresponding to the reflected wave 23 appears.

When the pulse detection signal G6 is detected, it is determined whether the peak count from the reference time t0 is the second count (S61). When the peak count is not the second time (N), the process returns to S60.

When it is determined in S61 that the peak count is the second time (Y), the second time peak is the reference time t0.
From the direct wave time Tx or more (S6)
2). When the direct wave time Tx or more has not elapsed (N),
Return to S60.

If the direct wave time Tx or more has elapsed in the determination of S62 (Y), the peak of the pulse detection signal G6 is detected as the peak P5 'of the reflected wave 23.

The pulse detection signal G is passed through S61 and S62.
When the peak P5 'of the reflected wave 23 of No. 6 is detected, the detection signal G5 is taken in, and if the detection signal G5 of FIG.

At this time, for example, after setting the reception gain control signal G7 and the transmission output control signal G8 according to the signal strength, etc., the peak P of the reflected wave 23 from the captured detection signal G5.
3'is detected (S64).

Then, the peak P of the detected reflected wave 23
The reflected wave time Tr is calculated from the peak time of 3 ′ and the stored reference time t0 (S65). The reflected wave time Tr is
It is the time from the reference time t0 to the peak time of the peak P3 ′.

Thus, the reflected wave time Tr is measured (S
6) ends.

Next, the microprocessor 7 uses the equivalent time Te, the direct wave time Tx, the reflected wave time Tr, and the target distance R based on the oscillation frequency fs and the radio wave propagation velocity Vc, which are obtained by the above processing. Is calculated (S7).

The target distance R to the target is R = (Vc ·
It is calculated by the formula of (Tr−Tx) / (2 · fs · Te).

This target distance R is a constant (Vc / 2 · f
s), the equivalent time Te of each measured value, the direct wave time Tx, and the reflected wave time Tr. Therefore, the error factor due to the change in the circuit element delay time that occurs when transmitting the element in the circuit is canceled by (Tr-Tx) and does not become the error factor. And the accuracy error of the time expansion rate is (Tr
It is erased by the proportional calculation by −Tx) / Te and no precision error occurs. Then, the accuracy of calculation of the measured distance is uniquely determined by the oscillation frequency fs of the second crystal oscillator 31.

The target distance R was measured according to the flowcharts of FIGS.

The measurement result R1 of the present embodiment of the target distance,
Distance measurement value R from the interrupt signal G4 to the peak of the reflected wave
2 was compared with FIG. Further, in FIG. 6, the temperature change D
As shown in, the temperature is changed from −10 ° C. to + 55 ° C.

As shown in FIG. 6, a change in signal propagation time caused in the internal circuit element due to a change in temperature appears in the direct wave time Tx. Therefore, in R2, which is calculated as it is without including Tx, the distance measurement value largely changes due to temperature change. However, in R1 in which the fluctuation of Tx at each temperature is calculated and removed as in this embodiment, the error of the distance measurement value is 1c.
The change is less than m.

As described above, according to this embodiment, the distance measuring device 1 functioning as a short-range radar can be constructed with a simple structure and at low cost. The accuracy of the measurement distance is determined by the accuracy of the second crystal oscillator 31, and the adjustment and calibration related to the time accuracy, which is required in the conventional technique, is not necessary, and the number of steps can be significantly reduced.

Since the microprocessor 7 calculates the target distance R using Tx and Tr, it is stable against variations in circuit elements, changes over time, and changes in temperature. Further, it is possible to configure a short-range radar that suppresses the transmitted radiated power to a necessary minimum and complies with the weak radio standard.

The above effects eliminate the drawbacks of the conventional radio distance sensor and contribute to the spread of the radio distance sensor.

[0069]

As described above, according to the present invention, it is possible to provide a distance measuring device and a distance measuring method for performing highly accurate distance measurement with a small number of parts.

Further, according to the present invention, the adjustment and calibration relating to the time accuracy, which have been conventionally required, are not required, and the number of steps can be greatly reduced.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing processing of distance measurement according to the embodiment.

FIG. 3 is a flowchart showing processing of distance measurement according to the embodiment.

FIG. 4 is a flowchart showing a distance measurement process according to the embodiment.

FIG. 5 is a signal waveform diagram showing each signal according to the embodiment.

FIG. 6 is a graph comparing the measurement results according to the embodiment with the temperature change.

[Explanation of symbols]

1 Distance measuring device 2 antenna 3 Timing generation circuit 4 microwave band pulse transmitter 5 microwave band pulse receiver 6 pulse detection circuit 7 microprocessors 10 Target 20 transmitting antenna 21 receiving antenna 22 radio waves 23 Reflected wave 24 direct waves 30 first crystal oscillator 31 second crystal oscillator 70 A / D converter 71 Third crystal oscillator fs oscillation frequency ft oscillation frequency G1 output signal G2 transmission pulse G3 sampling pulse G4 interrupt signal G5 detection signal G6 pulse detection signal G7 Received gain control signal G8 transmission output control signal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Minoru Tanaka             Kyoto Prefecture Otokuni-gun Oyamazaki-cho Enmyoji Wakiyama 1             312 Microwave Lab Co., Ltd. (72) Inventor Tetsuo Nishidai             Shiokyo-ku, Kyoto-shi, Kyoto Prefecture             801 Kudo-cho Omron Co., Ltd. F term (reference) 5J070 AB01 AC02 AD02 AH14 AH26                       AK22

Claims (8)

[Claims] 1. A distance measuring device using a radar, wherein a transmission pulse is generated from a first frequency, a sampling pulse is generated from a second frequency, and a beat signal is generated from a difference frequency between the first frequency and the second frequency. A timing generation circuit to generate, a pulse transmitter that generates a pulsed radio wave by the transmission pulse, a transmission antenna that radiates the radio wave generated by the pulse transmitter, and a direct wave that the radio wave directly propagates from the transmission antenna. ,
A receiving antenna that receives a reflected wave in which the radio wave is reflected by a target, a pulse receiver that outputs a detection signal by performing time expansion of the direct wave and the reflected wave by the sampling pulse, and the direct wave or Level control means for adjusting the detection signal of the reflected wave to a predetermined level; a first detection signal for detecting the direct wave included in the detection signal; a second detection signal for detecting the reflected wave; A distance measuring device comprising: a beat signal; and a measuring distance calculating unit that calculates a distance to a target using the beat signal. 2. The distance measuring device according to claim 1, wherein the level control means controls the reception gain of the direct wave and the reflected wave in the pulse receiver. 3. The distance measuring device according to claim 1, wherein the level control means controls the transmission output of the radio wave by the pulse transmitter. 4. The equivalent distance Te obtained from the beat signal, a reference time t0 obtained from the beat signal, a direct wave time Tx from t0 to the first detection signal, and t0. From the above to the second detected signal, the reflected wave time Tr is derived, the second frequency is fs, the radio wave propagation velocity is Vc, and the distance R to the target is R = (Vc · (Tr-Tx)). /
The distance measuring device according to claim 1, 2 or 3, wherein the distance is calculated by the formula (2 · fs · Te). 5. A distance measuring method using a radar, wherein a transmission pulse is generated from a first frequency, a sampling pulse is generated from a second frequency, and a beat signal is generated from a difference frequency between the first frequency and the second frequency. A step of generating, a step of generating a pulsed electric wave by the transmission pulse, a step of radiating the generated electric wave with a transmitting antenna, a direct wave in which the electric wave is directly transmitted from the transmitting antenna with a receiving antenna, The reflected wave of the radio wave reflected by the target,
A step of receiving a detection signal by performing time expansion with the sampling pulse for the direct wave and the reflected wave, and a step of adjusting the detection signal of the direct wave or the reflected wave to a predetermined level, Calculating a distance to a target using a first detection signal that detects the direct wave, a second detection signal that detects the reflected wave, and the beat signal that are included in the detection signal And a distance measuring method. 6. The step of adjusting the level of the detected signal comprises:
The distance measuring method according to claim 5, wherein the reception gains of the direct wave and the reflected wave are controlled. 7. The step of adjusting the level of the detection signal comprises:
7. The distance measuring method according to claim 5, wherein the transmission output of the radio wave is controlled. 8. The step of calculating the distance to the target includes an equivalent time Te obtained from the beat signal, a reference time t0 obtained from the beat signal, and a direct wave from t0 to the first detection signal. The time Tx and the reflected wave time Tr from t0 to the second detection signal are derived, the second frequency is fs, the radio wave propagation speed is Vc, and the distance R to the target is R = (Vc. ( Tr-Tx)) /
The distance measuring method according to claim 5, wherein the distance is calculated by the formula (2 · fs · Te).