JP2010203789A - Distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the accuracy of distance measurement with respect to a target existing at a short distance, and to prevent erroneous detection. <P>SOLUTION: When a reflected wave by the target 200 is received, signal processing of the reflected wave is performed in an amplitude-phase detection part 23, and outputs amplitude information Amp and phase information θ to a distance measurement/calculation part 24. The distance measurement/calculation part 24 acquires time information and phase information from a peak position of the amplitude signal of the reflected wave, and finds a time difference with respect to time information of a transmission wave being held as reference information. This time difference is then corrected with the phase information, and the distance R up to the target 200 is calculated from the corrected time difference. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a distance measuring device that measures a distance to a target based on time information of transmitted transmitted waves and received reflected waves.

As shown in FIG. 22, in general pulse radar, the basic principle is to calculate a distance using a round-trip propagation time from the completion of transmission of a transmitted pulse signal to reception by reflection at a target. It is said. The distance R to the object can be obtained by using the basic equation shown in the following equation (1), where ΔT is the time until a pulse wave is transmitted and received.
R = c · ΔT / 2 (1)
Where c: speed of light

  Therefore, in a general pulse radar device, the reflected pulse from the target returns before the pulse transmission is completed, or the target existing in the distance region, that is, the region where the round-trip propagation time ΔT is shorter than the pulse width T to be transmitted. In principle, it was impossible to detect existing targets. This is because a general pulse radar apparatus is premised on that the transmission pulse and the reflected pulse do not overlap.

  Therefore, a technique for detecting a target that exists in a region where the round-trip propagation time is shorter than the pulse width to be transmitted has been proposed. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-241535) discloses a technique for measuring a distance to a target based on a time difference between a rising time of a transmission signal and a rising time of a reception signal.

JP 2000-241535 A

  However, in the prior art disclosed in Patent Document 1, in the case of a pulse wave (basic frequency f, wavelength λ = c / f) having a gentle envelope as shown in FIG. It is difficult to accurately measure the distance.

  That is, in the case of a pulse wave as shown in FIG. 23, if a target existing in a region where the round-trip propagation time is shorter than the pulse width is detected, the first waveform of the reflected wave is affected by the influence of the magnitude of the reflected wave, background noise, and the like. The rising edge of the waveform cannot be detected, and the rising edge of the subsequent waveform may be detected. For this reason, in the detection of the rise time, a deviation of a half cycle (λ / 2) or more of the fundamental frequency occurs, so that a large error occurs in the distance measurement of the target, and the target may be detected later.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a distance measuring device capable of improving the distance measuring accuracy for a target existing in a region where the round-trip propagation time is shorter than the pulse width to be transmitted. It is said.

  In order to achieve the above object, a distance measuring device according to the present invention includes a transmitter that transmits a transmission wave in which a carrier wave having a predetermined fundamental frequency is amplitude-modulated, and a signal that receives a reflected wave reflected by the transmission wave being reflected by a target. An amplitude / phase detector that processes and detects amplitude information and phase information of the envelope, and corrects the time information of the transmitted wave and the reflected wave calculated from the amplitude information based on the phase information And a distance measurement calculation unit that calculates the distance from the time information to the target.

  According to the present invention, it is possible to improve the distance measurement accuracy with respect to a target existing in a region where the round-trip propagation time is shorter than the transmission pulse width, and prevent erroneous detection.

The block diagram which concerns on 1st Embodiment of this invention and shows the structure of a distance measuring device. Same as above, explanatory diagram showing an example of mounting as a back sonar on a car Same as above, explanatory diagram showing how the transmitted wave hits the object and returns as a reflected wave Same as above, explanatory diagram showing waveforms of transmitted wave and reflected wave Same as above, explanatory diagram showing envelope and phase of waveform of transmitted wave and reflected wave Same as above, explanatory diagram showing measurement results of reflected wave for each target distance Same as above, an explanatory diagram showing the data of FIG. 6 in absolute values As above, an explanatory diagram showing an envelope extracted from the data of FIG. Same as above, explanatory diagram showing phase information extracted from the data of FIG. As above, an explanatory diagram showing a basic model of a pulse radar device mounted on a moving object As above, an explanatory diagram showing the relationship between the position of the transmitting antenna and the receiving antenna and the target distance Same as above, graph showing the relationship between distance, time difference and phase Same as above, explanatory diagram showing the output waveform of the reflected wave measured by the receiving circuit Same as above, explanatory diagram showing amplitude information and phase information from reflected wave As above, an explanatory diagram showing an example in which the relationship between time difference, distance, and phase is tabulated As above, an explanatory diagram showing an example in which the relationship between phase difference and time correction is tabulated Same as above, explanatory diagram showing the processing result of the distance measurement algorithm The block diagram which concerns on 2nd Embodiment of this invention and shows the structure of a distance measuring device. Same as above, explanatory diagram showing an example of mounting as a back sonar on a car Explanatory drawing which shows the relationship between a transmission wave, a reference wave, and a reflected wave concerning 3rd Embodiment of this invention. Explanatory drawing which shows the restriction | limiting of the phase correction by distance range concerning 4th Embodiment of this invention. Explanatory drawing showing the basic principle of pulse radar Explanatory drawing showing a pulse waveform with a gentle envelope

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

[First embodiment of the present invention]
First, a first embodiment of the present invention shown in FIGS. 1 to 15 will be described. In FIG. 1, reference numeral 1 denotes a distance measuring device, which is used as a close-range radar that measures a distance from an object existing at a relatively short distance. The distance measuring device 1 is applied as, for example, a non-contact switch, a security sensor, an obstacle detection sensor, or the like. FIG. 2 shows an example of mounting as a back sonar on a moving body such as an automobile 100, and measures a distance R from an object (target) 200 present at a relatively short distance.

  In the present embodiment, the distance measuring device 1 is a transmission / reception antenna separation type pulse radar device. The distance measuring device 1 generates a pulse wave and receives the reflected wave reflected by the transmission unit 10 that transmits from the transmission antenna 2 and the target 200 by the reception antenna 3, performs signal processing, and performs the distance R with the target 200. Is provided.

  The transmission unit 10 includes a pulse generation circuit 11 that generates a pulse signal, a band pass filter (BPF) 12 that limits the pulse signal output from the pulse generation circuit 11 to a predetermined frequency band, and a pulse signal that has passed through the BPF 12. An amplifier 13 for amplifying to a predetermined output level and transmitting from the transmission antenna 2 is provided.

  As will be described below, the transmission wave transmitted from the transmission antenna 2 is a signal obtained by applying a mountain-shaped amplitude modulation to a carrier wave having a fundamental frequency f. This signal can be generated using a relatively simple pulse generation circuit 11 and BPF 12, and the circuit configuration can be simplified and the cost can be reduced.

  The receiving unit 20 includes an amplifier 21 that amplifies the reflected wave from the target 200 received by the receiving antenna 3 to a predetermined input level, a receiving circuit 22 that performs A / D conversion and quantization on the signal from the amplifier 21, and a receiving circuit 22 Amplitude / phase detection unit 23 that extracts the amplitude information and phase information by processing the signal quantized in step S3, and calculates the distance R from the target 200 based on the amplitude information and phase information, and outputs the result as a distance measurement result A distance measurement calculation unit 24 is provided. The amplitude / phase detection unit 23 and the distance measurement calculation unit 24 are functional units having a processing function by a microprocessor.

  The reflected wave received by the receiving antenna 3 includes a reflected wave that is a difference between the reflected wave from the target and the diffracted wave component when the diffracted wave from the transmitting antenna 2 overlaps with the reflected wave from the target. .

  The distance measurement algorithm in the amplitude / phase detection unit 23 and the distance measurement calculation unit 24 will be described below.

  This distance measurement algorithm pays attention to the fact that the output waveform of the pulse radar is a continuous waveform (carrier waveform) having a constant fundamental frequency accompanied by amplitude fluctuation along a mountain-shaped envelope. That is, the pulse wave of the pulse radar has a wave of a fundamental frequency f having a certain period rises gently along the mountain-shaped envelope, reaches a maximum at the peak point, and then gradually decreases (see FIG. 23).

Therefore, the pulse wave defined here (the transmission wave output from the transmission unit 10 via the transmission antenna 2) is assumed to have a signal of the fundamental frequency f as a carrier wave and a carrier wave having undergone mountain-shaped amplitude modulation. Such a pulse wave can be expressed by the following equation (2), where X (t) is the envelope (modulation signal) and θ is the phase shift from the carrier wave f.
X (t) · sin (2πft + θ) (2)

  Next, consider a case where a transmission wave (pulse wave) hits an object and returns as a reflected wave. As shown in FIG. 3, when the transmitted wave collides with the object S from free space, the phase of the reflected wave changes by π. This is because reflection (fixed-end reflection) occurs in a form where the density enters the boundary between sparse (free space) and dense (object S).

The relationship between the amplitude of the transmitted wave and the reflected wave at this time and time is shown in FIG. Using the above equation (2), the transmitted wave and the reflected wave can be expressed by the following equations (3) and (4).
Xb (t) · sin (2πft + θb) (3)
Xp (t) · sin (2πft + θp) (4)
Where Xb (t) is the envelope of the transmitted wave
Xp (t): envelope of reflected wave
θb: phase shift of transmission wave from carrier
θp: phase shift of reflected wave from carrier

  When the transmitted wave and the reflected wave are compared in FIG. 4, the waveform is inverted. This is because the phase has changed by π due to reflection. As shown in FIG. 5, since the envelope is positive / negative symmetrical, it is not affected by the phase change of π due to reflection.

Therefore, the time information Tb, Tp is extracted with the peak positions of the envelopes of the transmitted wave and the reflected wave (positions indicated by ▼ in FIG. 5) as characteristic points, and the time difference ΔT between Tp and Tb is taken as the basis for distance measurement By applying the equation (1), the distance R to the object can be obtained. Here, the calculation formula of the distance R by the time difference ΔT is described again.
R = c · ΔT / 2 (1)
Where c: speed of light

  In this embodiment, the transmission wave is used as a reference for distance measurement, and the time information Tb and Tp is the time to the peak position with the rising edge of the reference wave (transmission wave) as the origin.

  The above is the basic algorithm for distance measurement. In the distance measurement by this basic algorithm, compared to the conventional technique for detecting the rising edge of the waveform of the reflected wave and measuring the distance, there is no deviation due to erroneous detection of the rising edge, and the distance accuracy can be improved. . In the present embodiment, an algorithm for correcting the time difference ΔT using the phase information of the reflected wave is further added to further improve the distance resolution by the basic algorithm.

The phase shift amount θp of the reflected wave can be expressed by the following equation (5) using the radio wave path length L with respect to the phase shift θb of the transmission wave. The radio wave path length L is the distance of the path from when the radio wave is transmitted to the target and reflected and received. In the following, the phases other than those specifically mentioned are in the range of −π <θ <π.
θp = 2π · L / λ + θb + π (5)

Here, it is assumed that the radio wave path length L and the distance R to the target have a relationship of L = 2 · R (the relationship between the radio wave path length L and the distance R will be described later). The wavelength λ is λ = c / f. Therefore, the equation (5) can be transformed into an equation including the distance R as the following equation (6). From this equation (6), the distance R can be expressed by the following equation (7).
θp = 2π · 2 · R / λ + θb + π (6)
R = (λ / 2) · (θp−θb−π) / 2π (7)

  Equation (7) means that the position of the distance R from the object appears innumerably at intervals of the wavelength λ / 2 from the phase difference between the reflected wave and the transmitted wave. FIG. 6 shows the result of actually measuring the reflected wave while moving away from the target distance Ra by a distance d such as Ra, Ra + d, Ra + 2d. The distance d is about 1/10 of the wavelength λ. FIG. 7 shows the data of FIG. 6 in absolute values.

  6 and 7 that the envelope and phase of the pulse wave are regularly delayed in time series as the distance increases. Therefore, although the distance cannot be obtained directly from the phase, the distance resolution is obtained by using two information for the distance measurement, the time difference between the transmitted wave and the reflected wave and the phase difference of the carrier wave between the transmitted wave and the reflected wave. Can be improved. In the following description, unless otherwise specified, the phase indicates a phase shift.

  In order to extract an envelope (amplitude information) and a phase (phase information) from a signal wave having a carrier wave, various methods such as filtering of the absolute value of the waveform, detection by delay or counter, and quadrature detection can be used. Here, as a typical example, using an orthogonal detection method, an I component (In-Phase) and a Q component (Quadrature) are detected from a signal wave, and an amplitude component and a phase component are detected from the relationship between them. Ask.

  FIG. 8 shows the result of extracting the envelope from the data of FIG. 7 by the quadrature detection method. The time of the peak position of the amplitude for each target distance (peak position time; the time at the detection position indicated by ▼) should shift backward as the distance increases, but in reality the peak position is You can see that they are not in line.

  This is because when the envelope is extracted from the signal wave, an error occurs in the peak position of the envelope due to the influence of the surrounding waveform, noise, and the like. The position accuracy of the peak position time is approximately ± λ / (2 · c) or less, and is converted to distance accuracy from equation (1) and is ± λ / 4 or less.

  FIG. 9 shows the result of extracting the phase from the data of FIG. 7 by the quadrature detection method. It can be seen that the phases are arranged at almost equal intervals according to the time series, and almost constant and stable data is acquired in the time direction.

  This indicates that the phase has a smaller error than the peak position of the envelope, and the position accuracy is good. This is because the peak position detection by the envelope captures the phenomenon as a point, whereas the phase captures the phenomenon with the entire waveform, and is less susceptible to noise and the like.

  Next, a method for correcting the distance obtained by the time difference ΔT with the phase will be described. The correction of the distance based on the phase is performed by obtaining the phase of the same reflected wave based on the time information and the phase information, and using the difference between the two. The phase of the reflected wave obtained from the time information is θp ′, and the phase of the reflected wave obtained directly from the phase information is θp.

First, the phase θp ′ is calculated from the time difference ΔT. This phase θp ′ can be obtained from the following equation (8) based on the equation (6).
θp ′ = 2π · {c · ΔT / λ} + θb + π (8)

  Next, the phase θp is obtained directly from the phase information. This phase θp is obtained as θp the phase at the peak position time Tp of the amplitude information (time at the detection position indicated by ▼ in FIG. 9).

Subsequently, a phase difference Δθ between the two phases θp and θp ′ is obtained. This phase difference Δθ is a value for correcting the phase shift of the reflected wave, and a value for correcting the measurement distance can be obtained by obtaining a time correction value from the phase difference Δθ. In order to reflect the phase difference Δθ in the distance measurement value, when the equations (6) and (8) are replaced with the time correction value aT, the following equation (9) can be obtained.
aT = Δθ · λ / (2π · c) (9)

Using this time correction value aT, the time difference ΔT is corrected as shown in the following equation (10). Then, the corrected time difference ΔT ′ is applied to the equation (1) to calculate the distance R.
ΔT ′ = ΔT + aT = ΔT + λ · Δθ / (2π · c) (10)

  The distance accuracy can be further improved by adding the above algorithm to the basic algorithm and calculating the distance. However, in the transmission / reception antenna separation type apparatus in which the transmission antenna 2 and the reception antenna 3 are separated as in this embodiment, the influence of the distance between the transmission antenna 2 and the reception antenna 3 is also considered. There is a need to.

  For this reason, in the present embodiment, the distance between the transmission and reception antennas is added as one of the calculation parameters, and processing that takes into account the influence of the distance between the transmission and reception antennas is added. If the transmission antenna and the reception antenna are integrated, the following processing is not necessary.

As shown in FIG. 10, a basic model is assumed as a pulse radar device mounted on a moving body 100 ′. In this basic model, when the distance between the transmission antenna 2 and the reception antenna 3 is A, the relationship between the transmission / reception antenna distance A, the target distance R, and the radio path length L is expressed by the following equation (11). As shown, it can be determined geometrically.
L = 2 · (R ² + 0.5 · A ² ) ^0.5 (11)

  Here, for the sake of simplicity, it is assumed that the distance from the transmission antenna 2 to the target 200 is the same as the distance from the target 200 to the reception antenna 3. Further, it is assumed that the target distance R has the same radio wave path length L, that is, a distance on an elliptical trajectory having the transmitting antenna 2 and the receiving antenna 3 as two focal points as shown in FIG.

The relationship between the time ΔT when the radio wave emitted from the transmitting antenna 2 hits the target 200, is reflected by the target 200, and returns to the receiving antenna 3 and the radio path length L is expressed by the following equation (12).
L = c · ΔT (12)

Therefore, the distance R to the target can be expressed by the following equation (13) from the equations (11) and (12).
R = 0.5 · (L ² −A ² ) ^0.5
= 0.5 · {(c · ΔT) ² −A ² } ^0.5 (13)

At this time, the relationship between the phase θr of the reflected wave, the time difference ΔT, and the phase θb of the transmission wave is expressed by the following equation (14). Here, for convenience, the phase of the reflected wave is described as θr, but this is synonymous with the phase θp ′ calculated by the equation (8).
θr = 2π · L / λ + θb + π
= 2π · c · ΔT / λ + θb + π
= 2π · {2 · (R ² + 0.5 · A ² ) ^0.5 } / λ + θb + π (14)

  Based on the equations (11), (12), and (14), the relationship between the distance R, the time difference ΔT, and the phase θr is shown in FIG. 12 (where θb = −π). From FIG. 12, it can be seen that the influence of the distance between the transmitting and receiving antennas is large at a close distance and is nonlinear. Therefore, in the short-range nonlinear region, the transmission / reception antenna is calculated by using the equation (13) instead of the equation (1) and calculating the distance by applying the corrected time difference ΔT ′ to the equation (13). The influence of the distance can be reduced and the distance accuracy can be improved.

  As described above, the distance measuring apparatus 1 according to the present embodiment uses the envelopes of the reference wave and the reflected wave based on the expressions (11) to (14) including the distance A between the transmitting and receiving antennas as a parameter. The time difference ΔT depending on the position is calculated, and the target distance within an error ± λ / 4 is grasped. Further, by using the phase information of the reflected wave, the time difference ΔT obtained from the peak position of the envelope is corrected, and the position of ± λ / 4 or less is specified, thereby improving the distance accuracy.

  When actually performing distance measurement, it is necessary to hold time Tb and phase θb of the peak position of the envelope of the transmission wave as reference information for measurement. The phase reference at this time is a sine wave of the fundamental frequency f (the distance measurement process is also the same).

  The time Tb and the phase θb, which are the reference information for this measurement, are directly input to the receiving circuit 22 and are calculated and held by the amplitude / phase detection unit 23 and the distance measurement calculation unit 24. Alternatively, the time Tb and the phase θb may be obtained in advance from the measurement results and theoretical values, and stored in the amplitude / phase detection unit 23 and the distance measurement calculation unit 24.

  Next, when the reflected wave is received and the reflected wave is input to the amplitude / phase detection unit 23 via the receiving circuit 22, the amplitude / phase detection unit 23 processes the reflected wave to obtain amplitude information Amp and phase information. θ is output to the distance measurement calculation unit 24. FIG. 13 shows the reflected wave measured by the receiving circuit 22. FIG. 14 shows the result of processing the reflected wave by the amplitude / phase detector 23 and outputting the amplitude information and the phase information.

The amplitude information Amp and the phase information θ of the reflected wave from the amplitude / phase detection unit 23 are processed by the distance measurement calculation unit 24. The distance measurement calculation unit 24 sequentially performs the following processes (1) to (6).
(1) The time Tp and the phase θp are obtained from the peak position of the amplitude signal of the reflected wave.
(2) The time difference ΔT is obtained from the time Tp of the reflected wave and the time Tb of the transmission wave held as reference information.
(3) Using the time difference ΔT, obtain the phase θp ′ from the equation (8).
(4) The phase difference Δθ is obtained from the phases θp and θr.
(5) The time correction value aT is calculated from the phase difference Δθ by the equation (9). Then, using this time correction value aT, the time difference ΔT is corrected by the equation (10) to obtain the time difference ΔT ′ reflecting the phase difference Δθ.
(6) The distance R is calculated by applying the corrected time difference ΔT ′ to the equation (13).

  The above processing does not require complicated signal processing such as FFT (Fast Fourie Transform), and can be constructed as a signal processing algorithm based on a simple calculation formula. Therefore, signal processing at the microprocessor level is possible, and the distance can be calculated by online calculation processing.

  In this case, the main arithmetic processing may be replaced with processing by table reference. For example, using the equations (13) and (14), the relationship between the time difference ΔT, the distance R, and the phase θr shown in FIG. 12 is calculated in advance, and a table as shown in FIG. 15 is created. Similarly, the relationship between the phase difference Δθ and the time correction value aT is calculated using equation (9), and a table as shown in FIG. 16 is created.

  These tables are created by off-line calculation or calculation for preparation before distance measurement by the distance measurement calculation unit 24 and stored in the distance measurement calculation unit 24. Thereby, at the time of distance measurement processing, complicated calculation processing including units, squares, square roots, and the like can be replaced with table reference, and the calculation load can be reduced.

  FIG. 17 shows a distance measurement result by the above processing. The distance measurement data of the alternate long and short dash line in FIG. 17 indicates the distance based on only the amplitude information (the distance calculated by the time difference ΔT). Moreover, the distance measurement data of the solid line in FIG. 17 indicates the distance obtained by adding phase correction to the amplitude information (distance calculated using the time correction value aT).

  As described above, in distance measurement using only amplitude information, a distance accuracy of ± λ / 4 or less can be obtained. However, the closer the distance is, the more conspicuous the measured value is from the zero error line indicated by the broken line. On the other hand, it can be seen that the distance measurement result obtained by adding the phase correction to the amplitude information is close to the error zero line in almost the entire region, and the error is greatly reduced.

  As described above, in the present embodiment, time information is extracted using the peak positions of the envelopes of the transmitted wave and the reflected wave as feature points. Thereby, the influence on the measurement value by the magnitude of the amplitude of the reflected wave due to the effective reflection area of the object can be reduced, and the distance measurement accuracy for the target existing at a close distance can be improved. Furthermore, the distance measurement accuracy can be greatly improved by adding the correction based on the phase information to the time information.

  In addition, since the distance between the transmitting and receiving antennas is previously taken as a parameter in the calculation formula for the distance measurement calculation, the distance to the target can be accurately obtained regardless of the distance between the antennas.

[Second Embodiment of the Present Invention]
Next, a second embodiment of the present invention will be described. The second form is an example in which the transmitting antenna and the receiving antenna are integrated with respect to the first form.

  As shown in FIG. 18, the distance measuring device 1A of the second embodiment includes a transmission / reception antenna 2A that transmits a pulse wave to the target and receives a reflected wave from the target. The transmission / reception antenna 2A is connected to the output terminal of the amplifier 13 of the transmission unit 10 and the input terminal of the amplifier 21 of the reception unit 20 via the antenna duplexer 30. Other configurations are the same as those of the first embodiment.

  FIG. 19 shows an example in which the distance measuring device 1A is mounted as a back sonar on a moving body such as an automobile 100A. The distance measuring device 1A as the back sonar transmits a pulse wave from the transmission / reception antenna 2A to the target 200 existing at a short distance, and the reflected wave returned by the target 200 is returned to the same transmission / reception antenna 2A. And the distance R is measured.

  The distance measurement in the distance measuring apparatus 1A is performed by setting the distance A between the transmission and reception antennas as A = 0 in the expressions (11) and (13) of the first embodiment because the transmission antenna and the reception antenna are integrated. I do. That is, in the second embodiment, the distance R is calculated by an algorithm obtained by adding a correction based on the phase of the reflected wave to the basic algorithm for calculating the distance from the time information of the peak position of the envelope.

  In the second embodiment, since the transmission antenna and the reception antenna are integrated, there is no need for calculation for correcting the influence of the distance between the transmission and reception antennas. For this reason, in the second form, it is possible to accurately measure the distance to the target existing at a close distance while reducing the calculation load with respect to the first form.

[Third embodiment of the present invention]
Next, a third embodiment of the present invention will be described. The third mode is an example in which the reference wave that is the measurement reference is based on the transmission wave as compared to the first mode. Specifically, the processing in the amplitude / phase detection unit 23 and the distance measurement calculation unit 24 of the distance measurement device 1 shown in FIG. 1 is slightly changed, and instead of using the transmission wave as a reference wave, as shown in FIG. A reflected wave having a target distance of 0 is used as a reference wave.

When the target distance is 0, from the equation (13) described in the first embodiment, it can be regarded that the radio wave path length L has been advanced by the distance A (the distance between the transmitting and receiving antennas) after the reflected wave is transmitted. Therefore, the expression (12) can be expressed as the following expression (15).
L = c · ΔT + A (15)

Therefore, π corresponding to the phase change is not necessary, and the expressions (13) and (14) become as the following expressions (16) and (17).
R = 0.5 · (L ² −A ² ) ^0.5
= 0.5 · {(c · ΔT + A) ² −A ² } ^0.5 (16)
θp ′ = 2π · (c · ΔT) / λ + θb
= 2π · (LA) / λ + θb (17)

  Thus, when a signal conforming to the transmission wave is used as a reference wave, the time or path length of transmission of the reference wave is reflected in the radio wave path length L, thereby applying the algorithm of the first form to the target. The distance R can be calculated.

In the third embodiment, when the distance measurement is performed, the following processes (1) to (3) are performed as preparation before measurement.
(1) A received signal without a target is recorded and held as a reference wave.
(2) Processing the reference wave to extract amplitude / phase information.
(3) The time Tb and the phase θb at which the transmission signal reaches its peak are calculated and held as reference information for subsequent measurements. The phase reference at this time is a sine wave of the fundamental frequency f (the same applies to the distance measurement process). The reference information is acquired by performing signal processing on the received reference wave to calculate and hold peak phase information. Alternatively, the time Tb and the phase θb may be obtained in advance from measurement results and theoretical values, and these may be stored as reference information.

Next, as the distance measurement process, the following processes (4) to (9) are sequentially performed.
(4) The reflected wave is signal-processed by the amplitude / phase detector 23, and amplitude information Amp and phase information θ are output.
(5) The distance measurement calculation unit 24 obtains the peak position time Tp and the phase θp from the peak value of the amplitude signal of the reflected wave.
(5) The time difference ΔT is obtained from the difference between the peak position time Tp of the reflected wave and the peak position time Tb of the reference wave.
(6) The phase θp ′ is obtained from the equation (17) using the time difference ΔT.
(7) The phase difference Δθ is obtained from the phases θp and θp ′.
(8) The time correction value aT is calculated from the phase difference Δθ by the equation (9), and the time difference ΔT is corrected by the equation (10) using the time correction value aT.
(9) Using the corrected time difference ΔT ′, the distance R is calculated by equation (16).

  Similar to the first embodiment, the above process may be an online calculation process or a process using table reference.

  In the third embodiment, even when the reference for distance measurement is a reference wave synchronized with the transmission wave, the distance or the path length for transmitting the reference wave is taken into consideration, as in the first embodiment. The distance to the existing target can be accurately measured.

[Fourth Embodiment of the Invention]
Next, a fourth embodiment of the present invention will be described. The fourth form is an example in which the correction by the phase is limited in the distance measurement process.

  That is, in the first embodiment, in order to further improve the distance measurement accuracy, phase correction is performed to correct the time difference ΔT with the phase difference θ. On the other hand, in the fourth embodiment, when the absolute value of the phase difference Δθ is greater than or equal to the correction limit value Δθm, a condition for not performing phase correction is added. This can prevent overcorrection due to phase correction.

  In addition, as shown in FIG. 21, when the distance calculated from the time difference ΔT is not within the distance range between the lower limit value Rd and the upper limit value Ru, it may be added on condition that phase correction is not performed. . In FIG. 21, in the distance range between the lower limit value Rd and the upper limit value Ru, data calculated from the time difference ΔT ′ obtained by adding phase correction to the amplitude information (data indicated by Δ in FIG. 21) is the distance R. It is determined. In the distance range exceeding the upper limit Ru, data (data indicated by □ in FIG. 21) calculated from the time difference ΔT based only on the amplitude information is determined as the distance R.

  Thereby, at the time of measurement in a distance range where an error is large only by amplitude information, phase correction can be performed to improve distance accuracy. On the other hand, over-correction due to a phase shift can be prevented by limiting the phase correction at the time of measurement in a distance range with sufficient accuracy only by amplitude information.

DESCRIPTION OF SYMBOLS 1 Distance measuring device 2 Transmitting antenna 3 Receiving antenna 10 Transmitting part 20 Receiving part 23 Amplitude / phase detection part 24 Distance measurement calculating part

Claims (6)

A transmission unit for transmitting a transmission wave obtained by amplitude-modulating a carrier wave of a predetermined fundamental frequency;
An amplitude / phase detection unit that receives and processes the reflected wave reflected by the transmission wave hitting the target, detects amplitude information and phase information of the envelope, and
A distance measurement calculation unit that corrects time information of the transmission wave and the reflected wave calculated from the amplitude information based on the phase information, and calculates a distance from the corrected time information to the target. Characteristic distance measuring device.   2. The distance measuring apparatus according to claim 1, wherein the distance measurement calculation unit extracts time information and phase information of an envelope peak position from amplitude information of the reflected wave.   The distance measuring apparatus according to claim 1, wherein a distance between the transmitting antenna and the receiving antenna is introduced as a parameter in the distance calculation based on the time information.   The distance calculation device according to claim 1, wherein the amplitude information and the phase information are detected with reference to the transmission wave or a reception wave according to the transmission wave.   The distance measuring device according to claim 1, wherein the correction of the time information is not performed when the phase information is equal to or greater than a set value.   2. The distance measuring device according to claim 1, wherein the time information is not corrected outside a set distance range.

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