Distance measuring device and distance measuring method

Abstract

To accurately measure a distance to an object to be measured by removing the influence of unnecessary reflected waves.SOLUTION: A distance measuring device for measuring a distance to an object having a flat surface, has: an array antenna in which a transmission antenna element that transmits a microwave toward the flat surface of the object and a plurality of reception antenna elements that receive the reflected microwave as a reception wave are arranged along an arrangement direction parallel to the flat surface of the object; and an arithmetic processing unit that measures the distance to the object based on the reception wave. The arithmetic processing unit has: a map creation unit that creates a map of signal intensity according to the reception wave with a distance and an azimuth which is a direction along the arrangement direction, as axes; and a distance measurement unit that does not use the map for distance measurement when a peak at which the signal intensity is maximum exists in other than the vicinity of the azimuth of 0 degrees, and regards a distance to the peak as the distance to the object when the peak at which the signal intensity is maximum exists in the vicinity of the azimuth of 0 degrees.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a distance measurement device and a distance measurement method. [Background technology]

[0002] When determining the position of an object for distance measurement in an environment where steam, dust, etc. are generated, it may not be possible to measure the distance stably because infrared and visible light cannot pass through due to scattering materials such as steam that exist in the space between the sensor and the object.

[0003] On the other hand, if radio waves with long wavelengths are used for measurement, they can penetrate such scattering objects and enable stable distance measurement. For example, Patent Document 1 discloses a technology for measuring the distance to and thickness of an object using radio waves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-180869 Summary of the Invention [Problem to be solved by the invention]

[0005] Due to the high temperature of the object or restrictions on the facility structure, it may not be possible to install a sensor at a sufficiently close distance from the object. The technology disclosed in Patent Document 1 above uses a radar that uses microwaves or millimeter waves to measure the distance to an object located several meters away, since it is difficult to detect the geometric distance difference for an object located far away when measuring the geometric distance between the position where radio waves are transmitted and received and the position of a reflection point on the surface of the object, and there is a concern that accuracy will deteriorate. Furthermore, an example of such radar is FMCW (Frequency Modulated Continuous Wave radar).

[0006] Furthermore, since radio waves from the antenna element are, in principle, emitted in a cone-shaped spread, when the surface of the object occupies a large portion of the expanded radiation range as the distance to the object increases, it is possible that not only reflected waves from the front of the sensor to be measured but also unwanted reflected waves, which are waves reflected from the surface of the object in a direction other than the front, will be measured. Causes of unwanted reflected waves, which are points on the object that generate unwanted reflected waves, include adhesions, unevenness, cracks, peeling, etc., present on the surface of the object. If the intensity of the unwanted reflected waves from the unwanted reflection points is higher than the intensity of the reflected waves from the object in front of the sensor, the distance to the unwanted reflection points may be erroneously measured as the distance to the object in front of the sensor, rather than the distance to the object in front of the sensor to be measured.

[0007] The present disclosure has been made in consideration of the above circumstances, and provides a distance measurement device and a distance measurement method that can remove the influence of unnecessary reflected waves and accurately measure the distance to an object. [Means for solving the problem]

[0008] A distance measurement device according to a first aspect of the present disclosure is a distance measurement device that measures the distance to an object having a plane, and includes an array antenna in which a transmitting antenna element that transmits microwaves toward the plane of the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an array direction parallel to the plane of the object, and an arithmetic processing unit that measures the distance to the object based on the received waves, and the arithmetic processing unit includes a map creation unit that creates a map of signal strength corresponding to the received waves, with distance and an orientation that is along the array direction as axes, and a distance measurement unit that does not use the map for distance measurement if the peak in the map where the signal strength is greatest exists other than near an orientation of 0 degrees, and that considers the distance to the peak to be the distance to the object if the peak where the signal strength is greatest exists near an orientation of 0 degrees.

[0009] A distance measurement device according to a second aspect of the present disclosure is a distance measurement device that measures the distance to an object having a plane, and includes an array antenna in which a transmitting antenna element that transmits microwaves toward the plane of the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an array direction parallel to the plane of the object, and an arithmetic processing unit that measures the distance to the object based on the received waves, wherein the arithmetic processing unit includes a map creation unit that creates a map of signal strength corresponding to the received waves, with distance and orientation, which is a direction along the array direction, as axes, and a distance measurement unit that, if the map contains multiple peaks with signal strengths above a predetermined threshold at different distances near an orientation of 0 degrees, considers the distance to the peak corresponding to the closest distance to be the distance to the object.

[0010] A distance measurement method according to a third aspect of the present disclosure is a distance measurement method for measuring the distance to an object having a plane, using a distance measurement device having an array antenna in which a transmitting antenna element that transmits microwaves toward the plane of the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane of the object, and an arithmetic processing unit that measures the distance to the object based on the received waves, and includes a map creation step using the arithmetic processing unit to create a map of signal strength corresponding to the received waves, with distance and orientation along the arrangement direction as axes, and a distance measurement step in which, if the peak in the map where the signal strength is greatest exists other than near an orientation of 0 degrees, the map is not used for distance measurement, and if the peak where the signal strength is greatest exists near an orientation of 0 degrees, the distance to the peak is considered to be the distance to the object.

[0011] A distance measurement method according to a fourth aspect of the present disclosure is a distance measurement method for measuring the distance to an object having a plane, using a distance measurement device having an array antenna in which a transmitting antenna element that transmits microwaves toward the plane of the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane of the object, and an arithmetic processing unit that measures the distance to the object based on the received waves, and the distance measurement method includes a map creation step using the arithmetic processing unit to create a map of signal strength corresponding to the received waves, with distance and orientation, which is a direction along the arrangement direction, as axes, and a distance measurement step in which, if there are multiple peaks in the map at different distances near an orientation of 0 degrees and having signal strengths above a predetermined threshold, the distance to the peak corresponding to the closest distance is considered to be the distance to the object. [Effects of the Invention]

[0012] According to the present disclosure, the influence of unwanted reflected waves can be removed and the distance to the object to be measured can be measured with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of a distance measurement device according to the present disclosure. [Figure 2] FIG. 2 is a perspective view for explaining a transmission wave transmitted to an object and a reception wave received from the object. [Figure 3] 3A and 3B are waveform diagrams showing waveforms of a transmission wave and a reception wave transmitted to an object. [Figure 4] FIG. 10 is a diagram illustrating an example of a distance spectrum. [Figure 5] 10A and 10B are diagrams for explaining differences in propagation paths of microwaves received by receiving antenna elements. [Figure 6] FIG. 10 is a diagram illustrating an example of an azimuth spectrum. [Figure 7] FIG. 2 is a functional block diagram of a calculation processing unit. [Figure 8] FIG. 10 is a diagram for explaining the creation of a map. [Figure 9]FIG. 10 is a diagram for explaining a case where a distance is calculated from a map. [Figure 10] FIG. 10 is a diagram for explaining a case where a distance is calculated from a map. [Figure 11] 10 is a flowchart of a calculation process according to the present disclosure. [Figure 12] 10 is a flowchart of a distance measurement process according to the present disclosure. [Figure 13] FIG. 2 is a block diagram showing a hardware configuration of a processing unit according to the present disclosure. [Figure 14] FIG. 10 is a diagram illustrating an example of a signal intensity distribution. [Figure 15] FIG. 10 is a diagram illustrating an example of an azimuth spectrum. [Figure 16] 1 is a trend graph of distance measurements. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that, hereinafter, the conveying direction in which the object S is conveyed is referred to as the Y direction, the width direction of the object S, which is the horizontal direction perpendicular to the conveying direction, is referred to as the X direction, and the vertical direction is referred to as the Z direction.

[0015] FIG. 1 shows a schematic configuration of a distance measurement device 10 according to the present disclosure.

[0016] The distance measurement device 10 is a device that measures the distance (shortest distance) to an object S having a flat surface, and an example thereof is an FMCW radar. The object S may be, for example, a slab (steel billet) produced by a continuous casting facility, but is not limited to this. Various objects can be used as appropriate as long as they have a flat shape and are made of a material that can reflect microwaves. The distance measurement device 10 is positioned opposite the flat surface of the object S. As will be described later, the distance measurement device 10 uses microwaves to measure the distance to the plane formed by the object S, which is positioned opposite the distance measurement device 10, for the transported object S.

[0017] 1, the distance measurement device 10 includes a microwave oscillator 12, a circulator 14, a power amplifier 16, a transmitting antenna element 18, multiple receiving antenna elements 20, multiple mixers 26, multiple IF amplifiers 28, multiple AD converters 30, and an arithmetic processing unit 32. Note that the distance measurement device 10 may include multiple circulators 14, power amplifiers 16, and transmitting antenna elements 18.

[0018] The microwave oscillator 12 generates microwaves whose frequency changes linearly by a predetermined sweep frequency F during a predetermined sweep time T. The microwaves generated by the microwave oscillator 12 are output to a circulator 14.

[0019] The circulator 14 splits the microwave input from the microwave oscillator 12 into two waves: a transmission wave and a reference wave. The transmission wave is output to a power amplifier 16, and the reference wave is output to a plurality of mixers 26.

[0020] The power amplifier 16 amplifies the power of the transmission wave and outputs it to the transmission antenna element 18 .

[0021] As shown in Fig. 1, the array antenna 24 is configured by arranging a transmitting antenna element 18 that transmits microwaves toward a plane formed by the object S and a plurality of receiving antenna elements 20 that receive the reflected microwaves as received waves along an arrangement direction parallel to the plane formed by the object S. As an example, the transmitting antenna element 18 and the plurality of receiving antenna elements 20 are arranged in a line in the Y direction at equal intervals, but they may also be arranged at uneven intervals. Furthermore, in the example of Fig. 1, the array antenna 24 is configured with one transmitting antenna element 18 and four receiving antenna elements 20, but it may also be configured as a MIMO (multiple-input and multiple-output) system that combines two or more transmitting antenna elements 18 and two or more receiving antenna elements 20.

[0022] FIG. 2 is a perspective view for explaining a transmission wave transmitted to the target S and a reception wave received from the target S. In FIG.

[0023] The transmitting antenna element 18 is an element that transmits microwaves toward the plane of the object S, and as shown in FIG. 2, transmits microwaves as transmission waves SW toward the object S (the plane facing the array antenna 24) along the X direction, which is perpendicular to the Y direction, which is the transport direction of the object S. The directivity of the transmitting antenna element 18 is limited, and the transmission waves SW propagate through the air, spreading in the direction of travel. For this reason, the transmission waves SW are irradiated not only to the measurement point D1 to be measured in front of the transmitting antenna element 18, but also to other areas.

[0024] The receiving antenna element 20 is an element that receives microwaves that are the result of the transmission wave SW being reflected by the target object S or structures around the target object S as received waves. The receiving antenna element 20 receives, as received waves, reflected waves that are generated when the transmission wave SW is irradiated on the target object S and reflected therefrom. Therefore, as shown in Fig. 2, the multiple receiving antenna elements 20 receive not only a received wave RW1 reflected from a measurement target point D1 on the target object S, which is the point to be measured for distance, but also a received wave RW2 reflected from an unwanted reflection point D2 different from the measurement target point D1. Note that, hereinafter, when there is no need to distinguish between the received wave RW1 reflected from the measurement target point D1 and the received wave RW2 reflected from the unwanted reflection point D2, the received wave RW1 and the received wave RW2 will be collectively referred to as the received wave RW.

[0025] The received waves RW received by the plurality of receiving antenna elements 20 are input to the plurality of mixers 26, respectively, as shown in FIG.

[0026] The mixer 26 combines the reference wave input from the circulator 14 with the received received wave RW. The combined wave obtained by combining has a waveform corresponding to the beat of the reference wave and the reflected wave, i.e., a waveform having a frequency corresponding to the frequency difference between the frequency of the reference wave and the frequency of the received wave RW. This waveform is called a beat wave. The beat wave includes a component due to the received wave RW1 from the object S and a component due to the received wave RW2, which is an unwanted reflected wave, but these cannot be distinguished at this point.

[0027] The IF amplifier 28 amplifies the beat wave generated by the mixer 26 and outputs the amplified wave to the AD converter 30 .

[0028] The AD converter 30 converts the amplified beat wave, which is an analog signal, into a digital signal and outputs it to the arithmetic processing unit 32 .

[0029] The arithmetic processing unit 32 is a functional unit that measures the distance to the object S based on the received wave RW. That is, the arithmetic processing unit 32 measures the distance to the object S based on the received wave RW converted into a beat wave. That is, the arithmetic processing unit 32 performs arithmetic processing on the digital signal output from the AD converter 30, thereby calculating the distance in the Y direction from the array antenna 24 to the measurement point D1 on the object S.

[0030] 3 is a waveform diagram showing an example of a transmission wave SW transmitted to the target S and a received wave RW as a reflected wave. The horizontal axis of FIG. 3 represents time, and the vertical axis represents frequency.

[0031] As shown in Fig. 3, microwave oscillator 12 generates microwaves with a sawtooth waveform by repeatedly emitting a waveform whose frequency changes linearly by a frequency F during a time T. Here, time T is referred to as the sweep time, and frequency F is referred to as the sweep frequency. Furthermore, such a waveform that changes linearly by the sweep frequency F during sweep time T is referred to as a chirp waveform, since it is a waveform whose frequency changes over time.

[0032] For example, the transmission wave SW transmitted from the transmitting antenna element 18 has a frequency f(t1) at time t1 and a frequency f(t2) at time t2. Furthermore, a reference wave, which is a waveform having the same frequency and phase as the transmission wave SW, is generated by branching off from the transmission wave SW or by synthesizing the same waveform as the transmission wave SW. In this case, the reception wave RW received by the receiving antenna element 20 has a waveform defined by the same sweep time T and sweep frequency F as the transmission wave (or reference wave), but is received with a time delay from the transmission wave SW by the time (t2-t1) it takes for the microwave to travel to and from the target S. In the example of FIG. 3, the microwave transmitted at time t1 becomes the reception wave RW and is received at time t2.

[0033] In this case, the distance r0 (the shortest distance) from the distance measurement device 10 to the object S is expressed by the following equation (1), where c is the propagation speed of microwaves in the air.

[0034] JPEG2025119996000002.jpg2350...(1)

[0035] Here, Δt = t2 - t1.

[0036] The mixer 26 generates a beat wave, which is a signal (beat signal) that is the difference in frequency between the reference wave (frequency f(t2)) corresponding to the transmitted wave SW at time t2 and the received wave RW (frequency f(t1)). The frequency Δf of the beat wave generated by the mixer 26 is expressed as |f(t2)-f(t1)|.

[0037] The frequency of the microwaves oscillated by microwave oscillator 12 changes linearly with time, so the relationship Δf / Δt=F / T holds, and by substituting this into equation (1), the following equation (2) is obtained.

[0038] JPEG2025119996000003.jpg2253...(2)

[0039] From the above equation (2), it can be seen that if the frequency of the beat wave can be determined, the distance r0 can be measured.

[0040] From the above, when the object S is at a distance r0, the received wave RW received by the same receiving antenna element 20 is a sine wave with a frequency of Δf. Therefore, if the amplitude of the received wave RW is 1, the initial phase is 0, and it does not contain noise, the signal x(n) of the received wave RW is expressed by the following equation (3).

[0041] x(n)=cos(φ Δf (n)) ···(3)

[0042] where φ Δf (n) is the phase of the signal that changes over time according to the frequency Δf of the beat wave that corresponds to the distance to the object S, and is expressed by the following equation (4).

[0043] φΔf(n)=2π×Δf×n×T S ···(4)

[0044] where n (n=0, 1, 2, . . . , N-1) is the index of the time when all N points of the digital signal are sampled, and T S is the sampling interval of the AD converter 30.

[0045] To find the frequency Δf of the signal x(n), FFT (Fast Fourier Transform) is used as a means of analyzing the frequency.

[0046] Assuming that the target object S is located at a distance r0 and that there are no unwanted reflected waves, the signal x(n) is a sine wave with a single frequency component consisting of a finite data length of N points, so the FFT calculation result can be expressed as a sinc function as shown in equation (5) below.

[0047] JPEG2025119996000004.jpg3371...(5)

[0048] However, in this embodiment, the absolute value of the FFT calculation result is used so that the FFT output value is a real number greater than or equal to 0. Furthermore, when the frequency notation is converted to distance using the above equation (2), the above equation (5) can be expressed as the following equation (6).

[0049] JPEG2025119996000005.jpg2467...(6)

[0050] Fig. 4 shows the distance spectrum of the above equation (6). The horizontal axis of Fig. 4 is the distance r [mm] from the array antenna 24, and the vertical axis is the signal strength corresponding to the strength of the beat signal. Note that the calculated value of the above equation (6), i.e., the output value of the FFT, is referred to as the signal strength in this embodiment.

[0051] In FIG. 4, the signal strength reaches its maximum when the value on the horizontal axis (distance axis) corresponds to the distance r0 from the array antenna 24 to the measurement target point D1. This maximum peak, such as the peak with maximum strength, is called the main lobe ML. On the distance axis, the signal strength attenuates as the distance increases from the distance r0, but the peaks are repeated. The periodic peaks that appear on both sides of the main lobe ML are individually or collectively called side lobes SL. In such cases, regardless of the presence of side lobes SL, the distance to the target S can be determined by reading the distance at which the signal strength reaches its maximum (in the case of FIG. 4, this is the distance r0 corresponding to the main lobe ML).

[0052] 5 shows a diagram for explaining the propagation path difference of microwaves received by each receiving antenna element 20 of the array antenna 24. Here, k (k=0, 1, 2, . . . , K-1) is an index for identifying each of the K receiving antenna elements 20, and the distance between each receiving antenna element 20 is d. When the reflection point is in the direction θ0 as seen from the array antenna 24, the difference (path difference) between the propagation path length of the received wave RW received by the receiving antenna element 20 with k=0 and the propagation path length of the received wave RW received by the k-th receiving antenna element 20 is kd sinθ0.

[0053] Therefore, when the object S is in the direction θ0, the signal x(k) of the received wave received at the same time by each receiving antenna element 20 is expressed by the following equation (7), assuming that its amplitude is 1, its initial phase is 0, and it does not contain noise.

[0054] x(k)=cos(φ θ0 (k)) ···(7)

[0055] The phase φ of the signal generated between the receiving antenna elements 20 varies depending on the direction θ of the target S. θ0 (k) is expressed by the following equation (8).

[0056] JPEG2025119996000006.jpg2074...(8)

[0057] As with distance measurement, signal x(k) is a sine wave, so the frequency of signal x(k) is found using FFT to determine the direction θ0. If there are no unwanted reflected waves and the object S that generates signal x(k) exists only at direction θ0, signal x(k) will be a sine wave with a single frequency component consisting of a finite data length of K points. For this reason, the results of performing FFT are expressed as a sinc function, similar to equations (5) and (6) above, and are given by equation (9) below.

[0058] JPEG2025119996000007.jpg2379...(9)

[0059] FIG. 6 shows the above equation (9) expressed as an azimuth spectrum. The horizontal axis (azimuth axis) of FIG. 6 represents the azimuth θ [°] of the measurement target points (D1, D2) as seen from the array antenna 24 when the normal direction of the array antenna 24 is set to 0 degrees, and the vertical axis represents the signal strength of the received beat wave. In FIG. 6, as in FIG. 4, the maximum peak is referred to as the main lobe ML, and the peaks that repeatedly appear on both sides of it are individually or collectively referred to as side lobes SL. As shown in FIG. 6, the main lobe ML appears in the azimuth direction of the measurement target points (D1, D2) when the normal direction of the array antenna 24 is set to 0 degrees. In addition, side lobes SL, where the signal strength is attenuated, appear on the azimuth axis. The azimuth θ0 of the target S can be determined by reading the azimuth when the signal strength reaches its maximum in FIG. 6.

[0060] From the above, when the distance measurement device 10 as an FMCW radar using the array antenna 24 receives the reflected wave from an object at a distance r0 and an orientation θ0, the signal x(n, k) is expressed by the following equation (10) assuming that the amplitude is 1, the initial phase is 0, and no noise is included.

[0061] x(n, k)=cos(φ Δf (n)+φ θ0 (k)) ···(10)

[0062] In a signal obtained by arranging received waves RW received by a certain receiving antenna element 20 in time, φ θ0 (k) is a constant value. Therefore, the above equation (10) becomes a sine wave indicating the frequency of the beat wave according to the distance to the object S. Also, in a signal in which the received waves RW received at a certain time are arranged in the order of the receiving antenna elements 20, φ Δf (n) is a constant value. Therefore, the above equation (10) becomes a sine wave that indicates a frequency according to the direction of the target S.

[0063] Here, a description will be given of the functional configuration of the arithmetic processing unit 32. Fig. 7 shows a functional block diagram of the arithmetic processing unit 32. As shown in Fig. 7, the arithmetic processing unit 32 includes a map creating unit 34 and a distance measuring unit 36.

[0064] The map creation unit 34 creates a map of signal strength corresponding to the received wave RW, with the distance and the azimuth along the array direction of the transmitting antenna elements 18 and the receiving antenna elements 20 as axes. That is, the map creation unit 34 draws a map showing the signal strength of the beat wave, for example in the form of a heat map, with the distance to the distance measurement points (D1, D2) obtained from the beat wave generated based on the received wave RW and the azimuth (i.e., the azimuth along the array direction) as axes, with the normal direction of the array antenna 23 set to 0 degrees. The map drawn by the map creation unit 34 will be referred to below as a signal strength map (corresponding to the received wave RW) or simply as a map.

[0065] The distance measurement unit 36 is a functional unit that does not use a map of signal strength according to the received wave RW created by the map creation unit 34 for distance measurement if the peak at which the signal strength is maximum exists other than near the 0 degree azimuth, and considers the distance to the peak to be the distance to the object S if the peak at which the signal strength is maximum exists near the 0 degree azimuth. In other words, if the map created by the map creation unit 34 has a peak at which the signal strength is maximum other than near the 0 degree azimuth, the distance measurement unit 36 does not use the map for distance measurement, for example, discards it, and only uses the map if the peak at which the signal strength is maximum exists near the 0 degree azimuth, and considers the distance to the peak in the map to be the distance to the object S, thereby determining the accurate distance to the object S.

[0066] A diagram for explaining the creation of the map is shown in Fig. 8. As the map to be created, the map creation unit 34 creates a map of signal strength with axes of distance r and azimuth θ using beat waveform signals x(n, k) measured by each receiving antenna element 20 of the array antenna 24, for example, as shown in Fig. 8(C).

[0067] More specifically, when creating a map such as that shown in Fig. 8(C), the map creation unit 34 first creates a map such as that shown in Fig. 8(A). Fig. 8(A) is a map showing the signal strength of the beat waveform signal x(n, k) received by each receiving antenna element 20, with the horizontal axis representing antenna number k and the vertical axis representing time n. The hatched area H1 in Fig. 8(a) indicates the beat waveform received by the receiving antenna element 20 where k=0.

[0068] Next, the map creation unit 34 converts the time axis of the map shown in FIG. 8A into distance (distance analysis) to create a map such as that shown in FIG. 8B. FIG. 8B shows distance spectra y(0, k) to y(R-1, k) calculated by performing an FFT on beat waveform signals x(0, k) to x(N-1, k) received by each receiving antenna element 20, with the horizontal axis representing antenna number k and the vertical axis representing distance r. This FFT is referred to as a distance FFT. y(0, k) to y(R-1, k) are distance spectra for a signal synthesized from reflected signals from all directions. The hatched area H2 in FIG. 8B indicates the distance spectrum y(0, 0) to y(R-1, 0) of the beat waveform received by the receiving antenna element 20 where k=0.

[0069] Here, r (r=0, 1, 2, . . . , R-1) is a distance index of the distance spectrum, and is called a distance bin. R is the total number of distance bins. Note that the resolution of the distance FFT can be improved by increasing the signal length to R by performing zero-padding, which adds RN signals with a value of 0 after the signal length N before performing the distance FFT. In this case, due to the constraints imposed when calculating the distance FFT, R is a power of 2. Furthermore, when calculating the distance FFT without performing zero-padding, N matches R, so N must be a power of 2. Then, for each distance bin r of the distance spectrum shown in FIG. 8(B), K values resulting from the calculation of the distance FFT are arranged in the order of the antenna numbers of the receiving antenna elements 20. The hatched area H3 in FIG. 8(B) indicates the waveforms y(0, 0) to y(0, K-1) of the receiving antenna elements 20 (k=0 to K-1) corresponding to the distance bin r=0 among the calculation results of the distance FFT.

[0070] Furthermore, the map creation unit 34 converts the antenna number axis of the map shown in FIG. 8(B) into the azimuth axis (azimuth analysis) to create a map such as that shown in FIG. 8(C). FIG. 8(C) shows the azimuth spectrum z(r, Θ) calculated by performing an FFT on K waveforms y(r, 0) to y(r, K-1) obtained from the calculation results of the distance FFT. Note that the hatched area H4 in FIG. 8(C) indicates the azimuth spectrum z(0, 0) to z(0, Θ-1) in the distance bin where r=0. Note that this FFT is referred to as the azimuth FFT. Note that θ (θ=0, 1, 2, . . . , Θ-1) is the azimuth index of the azimuth spectrum and is referred to as the azimuth bin. For the same reason as the distance FFT, the number Θ of all azimuth bins must also be a power of two. If zero-padding is not performed, the number K of all receiving antenna elements 20 must also be a power of two. Furthermore, when calculating the azimuth spectrum by FFT calculation as described above, the radio waves are limited to propagating as plane waves due to the relationship between the aperture length of the array antenna 24 with all K elements, the wavelength of the radio waves, and the distance to the target S. If the distance to the target S is short and the radio waves cannot be considered as plane waves, calculation processing of the azimuth spectrum assuming the radio waves as spherical waves is required instead of the normal azimuth FFT. Furthermore, while y(0, k) to y(R-1, k) in the above-mentioned Figure 8(B) are distance spectra for reflected signals from all directions, z(0, θ) to z(R-1, θ) in Figure 8(C) are distance spectra for reflected signals from direction θ.

[0071] In the two-dimensional distance-azimuth signal strength map shown in Figure 8(C) when receiving a reflected wave from an object S at a distance r0 and an orientation θ0, in an ideal state where there is no reflection from unwanted reflection points D2 etc., the maximum signal strength is achieved at a distance of r=r0 and an orientation θ=θ0. In Figure 8(C), the distance spectrum z(r, θ0) extracted from the portion at θ=θ0 matches the distance spectrum in Figure 4, and the orientation spectrum z(r0, θ) extracted from the portion at r=r0 matches the orientation spectrum in Figure 6.

[0072] On the other hand, if a high-intensity unwanted reflected wave from an unwanted reflection point D2 at a direction other than 0 degrees is received in addition to the reflected wave from the desired direction of 0 degrees, the distance spectrum will be a composite of sinc functions, making it impossible to measure the distance correctly. Figure 9 shows a diagram for explaining how to calculate the distance from a map. In Figure 9, the upper part of the figure shows a two-dimensional signal strength map showing the relationship between distance and direction, and the lower part of the figure shows the distance r B 9 shows a map of the relationship between signal strength and direction at range bin r. A , the coordinates of the desired measurement point D1 in the azimuth bin 0 degrees are A, and the distance bin r B , azimuth bin θ B The coordinate of the unwanted reflection point D2 at distance bin r is set to B. B ,Let C be the coordinate in the distance-orientation map corresponding to orientation bin 0 degrees.

[0073] In Figure 9, distance bin r B In the azimuth spectrum of the distance bin r, the side lobe of the unwanted reflection point D2 (corresponding to coordinate C) exists at the azimuth position of 0 degrees. A In the azimuth spectrum of Fig. 1, the main lobe of measurement target point D1 exists at the azimuth position of 0 degrees. In other words, at the azimuth position of 0 degrees, the signal from measurement target point D1, whose distance you want to measure, and the signal from unwanted reflection point D2, which becomes noise, are superimposed, making it difficult to separate and acquire only the signal from measurement target point D1, whose distance you want to measure.

[0074] Fig. 10 is a diagram for explaining calculation of distance from a map. In Fig. 10, the left part shows a two-dimensional signal strength map showing the relationship between distance and direction, and the right part shows the relationship between distance and signal strength at a direction of 0 degrees.

[0075] In other words, if the distance spectrum for the direction of measurement, 0 degrees, is output as shown in the right part of Figure 10, in order to obtain the distance to the measurement target point D1, a different distance (r A , r B) two high-intensity peaks PA and PC appear at points D1 and D2, respectively. If there is a reflection from unwanted reflection point D2 and the side lobe of the signal strength from unwanted reflection point D2 is stronger than the main lobe of measurement target point D1, the distance at coordinate C, i.e., the distance to unwanted reflection point D2, will be erroneously measured as the distance to target S.

[0076] Therefore, if the peak at which the signal strength is greatest exists in the map created by the map creating unit 34 at a point other than near the 0 degree azimuth, the distance measuring unit 36 does not use the map for distance measurement, and if the peak at which the signal strength is greatest exists near the 0 degree azimuth, the distance to the peak is regarded as the distance to the object S.

[0077] Specifically, when the coordinate other than the vicinity of the 0 degree bearing in the two-dimensional bearing-distance signal strength map has the maximum strength, the distance measurement unit 36 determines that the distance to a point other than the object S has been measured, and excludes that measurement value. In the example of Fig. 10, the distance corresponding to the peak PC is excluded, and the distance corresponding to the peak PA is regarded as the distance to the object S.

[0078] Here, the vicinity of 0° in azimuth is a range between the negative half-value angle and the positive half-value angle, using a half-value angle determined from the directivity of the array antenna 24. For example, when the half-value angle determined from the directivity of the receiving antenna element 20 is θ A In this case, -θ A Above and +θ A The range is as follows: For example, θ A When the angle θ is 5°, the range of the azimuth from -5° to +5° is near the azimuth θ of 0°.

[0079] Furthermore, when there are multiple peaks with signal strengths equal to or greater than a predetermined threshold at different distances near the 0 degree bearing in the map created by the map creation unit 34, the distance measurement unit 36 may regard the distance to the peak corresponding to the closest distance as the distance to the object S. For example, in the example of FIG. 10 , peak PA is closer than peak PC, so the distance corresponding to peak PA is regarded as the distance to the object S.

[0080] Now, let us assume that the distance to the object S is measured in the same manner as in this embodiment using a single receiving antenna element, such as a horn antenna, that has the same directivity as the array antenna 24. In this case, it is not possible to determine whether the reflected wave is arriving from a direction other than the front of the object S, and the distance will be measured incorrectly. In contrast, in this embodiment, the distance to the object S is measured using the array antenna 24, so the influence of unwanted reflected waves can be eliminated and the distance to the object can be measured with high accuracy.

[0081] A flowchart of the calculation process according to the present disclosure is shown in Fig. 11. The flow of the calculation process executed by the distance measurement device 10 will be described with reference to the flowchart shown in Fig. 11.

[0082] In step S100, the microwave oscillator 12 generates microwaves whose frequency changes linearly by a predetermined sweep frequency F during a predetermined sweep time T.

[0083] In step S101, the microwaves oscillated by the microwave oscillator 12 in step S101 are transmitted from the transmitting antenna element 18. The transmitted waves, which are microwaves transmitted from the transmitting antenna element 18, are reflected by the object S to generate reflected waves, and the reflected waves are received by the multiple receiving antenna elements 20.

[0084] In step S102, a plurality of mixers 26 combine a reference wave corresponding to the transmitted wave SW, which is the microwave oscillated by the microwave oscillator 12 in step S100, with a received wave RW, which is the reflected wave received by the corresponding receiving antenna element 20, to generate a beat wave.

[0085] In step S103, the plurality of IF amplifiers 28 amplify the beat wave generated by the mixer 26 in step S102.

[0086] In step S104, the plurality of AD converters 30 AD convert the beat wave amplified by the IF amplifier 28 in step S103.

[0087] In step S105, the arithmetic processing unit 32 calculates the distance to the target object S by performing distance measurement processing on the digital signal that has been AD converted and output by the AD converter 30 in step S104.

[0088] A flowchart of distance measurement processing according to the present disclosure is shown in Fig. 12. The flow of distance calculation processing in step S105 in Fig. 11 will be described with reference to the flowchart shown in Fig. 12.

[0089] In step S200, the map creation unit 34 performs a distance FFT on each of the multiple digital signals corresponding to the beat waves that have been AD converted and output by the multiple AD converters 30, and calculates the distance spectrum y(0,0) to y(R-1,K-1).

[0090] In step S201, the map creation unit 34 performs an azimuth FFT on the distance spectrum y(0,0) to y(R-1,K-1) calculated in step S200 to calculate the azimuth spectrum z(0,0) to z(R-1,Θ-1). This creates a signal strength map according to the received wave RW, with distance and azimuth as its axes.

[0091] In step S202, the distance measurement unit 36 calculates the distance to the object S based on the map created in step S201. That is, if the signal intensity map shows the maximum intensity at a coordinate other than near the 0 degree azimuth, it determines that the distance to an object other than the object S has been measured, excludes that measurement value, and calculates the distance to the object S as the distance corresponding to the peak near the 0 degree azimuth.

[0092] Alternatively, if there are multiple peaks with signal strengths above a predetermined threshold at different distances near an orientation of 0 degrees, the distance to the peak corresponding to the closest distance is calculated as the distance to the object S.

[0093] The functions of the arithmetic processing unit 32 can be realized by a program for causing a computer to function.

[0094] Fig. 13 is a block diagram showing the hardware configuration of a processing unit according to the present disclosure. Fig. 13 illustrates an example of the physical configuration of a computer 1 used as the processing unit 32. As shown in Fig. 13, the computer 1 can be configured by a computer including a bus 510, a processor 501, a main memory 502, an auxiliary memory 503, a communication interface 504, and an input / output interface 505. The processor 501, the main memory 502, the auxiliary memory 503, the communication interface 504, and the input / output interface 505 are connected to one another via the bus 510. An input device 506 and an output device 507 are connected to the input / output interface 505.

[0095] The processor 501 may be, for example, a CPU (Central Processing Unit), a microprocessor, a digital signal processor, a microcontroller, or a combination of these.

[0096] The main memory 502 may be, for example, a semiconductor RAM (random access memory).

[0097] For example, a flash memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination of these may be used as the auxiliary memory 503. A program for causing the processor 501 to execute the operations of the above-described arithmetic processing unit 32 is stored in the auxiliary memory 503. The processor 501 loads the program stored in the auxiliary memory 503 onto the main memory 502 and executes each instruction included in the loaded program.

[0098] The communication interface 504 is an interface for connecting to a network.

[0099] The input / output interface 505 may be, for example, a USB interface, a short-range communication interface such as infrared or Bluetooth (registered trademark), or a combination of these.

[0100] The input device 506 may be, for example, a keyboard, a mouse, a touchpad, a microphone, or a combination thereof. The output device 507 may be, for example, a display, a printer, a speaker, or a combination thereof.

[0101] When the functions of the arithmetic processing unit 32 are realized by a program for causing a computer to function, the functions described in the above embodiment are realized by executing the program by the processor 501 and main memory 502.

[0102] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0103] Furthermore, some or all of the functions of the above-described blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the above-described control blocks is formed is also included in the scope of the present invention.

[0104] Furthermore, some or all of the functions of each of the above blocks may be operated by the above device, or may be operated by another device (for example, an edge computer or a cloud server).

[0105] (Example)

[0106] Distance was measured using an FMCW radar with an array antenna, with steel material as the target. The distance from the array antenna to the target was 1710 to 1730 mm. Figure 14 shows the measured distance-azimuth signal strength distribution. The values in the bars BA represent the absolute values of the results of a 2D FFT of distance and azimuth. As shown in Figure 14, a main lobe ML1 of the measurement target point is located at approximately 0 degrees azimuth, and a side lobe SL of an unwanted reflection point is also located. Furthermore, a main lobe ML2 of an unwanted reflection point is located at -20 degrees azimuth.

[0107] Figure 15 also shows examples of azimuth spectra at distances of 1714 mm and 1771 mm. The azimuth spectrum at a distance of 1714 mm has peak P1 at a position approximately at an azimuth of 0 degrees. On the other hand, the azimuth spectrum at a distance of 1771 mm has peak P2 at an azimuth of -20 degrees, which has a signal strength approximately twice as strong. Of these two peaks P1 and P2, peak P1 represents the target point to be measured, and peak P2 represents the target's unwanted reflection point. In this case, the distance to the unwanted reflection point is 1771 mm, which may result in an erroneous measurement that makes the target appear 57 mm farther away than the actual distance. However, the azimuth at which the signal strength is greatest is -20 degrees, which is clearly different from the azimuth from which the desired reflected wave arrives. Therefore, the signal strength of peak P2 is excluded from the calculation to determine the distance. This allows the distance to the target to be determined as 1771 mm, demonstrating that the distance to the target can be determined with high accuracy.

[0108] FIG. 16 shows a trend graph of distance measurements. FIG. 16 is a trend graph showing the trends of distances measured when measurements with peaks of maximum signal strength outside the range of -5° to +5° in azimuth are excluded (measurements when the technology of the present disclosure is applied), and distances measured when measurements with peaks of maximum signal strength outside the range of -5° to +5° in azimuth are not excluded (measurements when the technology of the present disclosure is not applied). As shown in FIG. 16, when the distance to an object is measured without applying the technology of the present disclosure, many of the measured values appear in the range of approximately 1750 to 1820 mm, i.e., in an obviously erroneous range. In contrast, when the distance to an object is measured using the technology of the present disclosure, the measured values are concentrated around 1720 mm, and it was found that the frequency of measurements in the obviously erroneous range decreases.

[0109] Although the present embodiment has been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and applications are possible within the scope of the gist of the present disclosure.

[0110] Furthermore, the configuration of the distance measurement device 10 described in the above embodiment (see Figure 1) is just one example, and it goes without saying that unnecessary parts may be deleted or new parts may be added within the scope of the present disclosure.

[0111] The following notes are provided regarding the technology of the present disclosure.

[0112] <Additional Notes> (Appendix 1) A distance measuring device for measuring a distance to an object having a plane, an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; and The arithmetic processing unit a map creating unit that creates a map of signal strength according to the received waves, with distance and an orientation along the array direction as axes; a distance measurement unit that does not use the map for distance measurement when a peak with maximum signal strength exists in a position other than near an azimuth of 0 degrees in the map, and that considers the distance to the peak as the distance to the object when a peak with maximum signal strength exists in a position near an azimuth of 0 degrees in the map; A distance measuring device having: (Appendix 2) A distance measuring device for measuring a distance to an object having a plane, an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; and The arithmetic processing unit a map creating unit that creates a map of signal strength according to the received waves, with distance and an orientation along the array direction as axes; a distance measurement unit that, when a plurality of peaks having signal intensities equal to or greater than a predetermined threshold exist at different distances in the vicinity of an orientation of 0 degrees in the map, determines the distance to the peak corresponding to the closest distance as the distance to the object; A distance measuring device having: (Appendix 3) A distance measuring device as described in Appendix 1 or 2, wherein the vicinity of 0 degrees azimuth is a range greater than or equal to the negative half-value angle of azimuth and less than or equal to the positive half-value angle of azimuth, using a half-value angle determined from the directivity of the array antenna. (Appendix 4) The distance measurement device according to any one of appendices 1 to 3, wherein the map creation unit calculates a distance spectrum by performing a fast Fourier transform on a signal based on the received wave, calculates an orientation spectrum by performing a fast Fourier transform on the calculated distance spectrum, and creates the map based on the distance spectrum and the orientation spectrum. (Appendix 5) A distance measurement method for measuring a distance to an object having a plane, comprising: an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; A distance measuring device having Using the arithmetic processing unit, a map creation step of creating a map of signal strength according to the received waves, with distance and an azimuth along the array direction as axes; a distance measurement step in which, if the peak with the maximum signal strength exists in the map other than near the 0 degree azimuth, the map is not used for distance measurement, and, if the peak with the maximum signal strength exists in the 0 degree azimuth, the distance to the peak is regarded as the distance to the object; A distance measurement method having the following. (Appendix 6) A distance measurement method for measuring a distance to an object having a plane, comprising: an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; A distance measuring device having Using the arithmetic processing unit, a map creation step of creating a map of signal strength according to the received waves, with distance and an azimuth along the array direction as axes; a distance measurement step of determining, in the case where a plurality of peaks having signal intensities equal to or greater than a predetermined threshold exist at different distances in the vicinity of a 0 degree bearing in the map, the distance to the peak corresponding to the closest distance as the distance to the object; A distance measurement method having the following. (Appendix 7) A distance measurement method as described in Appendix 5 or 6, wherein the vicinity of 0 degrees azimuth is a range greater than or equal to the negative half-value angle of azimuth and less than or equal to the positive half-value angle of azimuth, using a half-value angle determined from the directivity of the array antenna. (Appendix 8) The distance measurement method according to any one of appendices 5 to 7, wherein the map creation step calculates a distance spectrum by performing a fast Fourier transform on a signal based on the received wave, calculates an orientation spectrum by performing a fast Fourier transform on the calculated distance spectrum, and creates the map based on the distance spectrum and the orientation spectrum. [Explanation of symbols]

[0113] 10 Distance measuring device 12 Microwave Oscillator 14 Circulator 16 Power Amplifier 18 Transmitting Antenna Element 20 receiving antenna element 24 Array Antenna 26 Mixer 28 IF amplifier 30 AD converter 32 Processing unit 34 Map Creation Department 36 Distance measurement unit

Claims

1. A distance measuring device for measuring a distance to an object having a plane, an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; and The arithmetic processing unit a map creating unit that creates a map of signal strength according to the received waves, with distance and an orientation along the array direction as axes; a distance measurement unit that does not use the map for distance measurement when a peak with maximum signal strength exists in a position other than near an azimuth of 0 degrees in the map, and that considers the distance to the peak as the distance to the object when a peak with maximum signal strength exists in a position near an azimuth of 0 degrees in the map; A distance measuring device having:

2. A distance measuring device for measuring a distance to an object having a plane, an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; and The arithmetic processing unit a map creating unit that creates a map of signal strength according to the received waves, with distance and an orientation along the array direction as axes; a distance measurement unit that, when a plurality of peaks having signal intensities equal to or greater than a predetermined threshold exist at different distances in the vicinity of an orientation of 0 degrees in the map, determines the distance to the peak corresponding to the closest distance as the distance to the object; A distance measuring device having:

3. 3. The distance measuring device according to claim 1, wherein the vicinity of 0 degrees azimuth is a range of a negative azimuth half angle or more and a positive azimuth half angle or less, using a half angle determined by the directivity of the array antenna.

4. 3. The distance measuring device according to claim 1, wherein the map creation unit calculates a distance spectrum by performing a fast Fourier transform on a signal based on the received wave, calculates an orientation spectrum by performing a fast Fourier transform on the calculated distance spectrum, and creates the map based on the distance spectrum and the orientation spectrum.

5. A distance measurement method for measuring a distance to an object having a plane, comprising: an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; A distance measuring device having Using the arithmetic processing unit, a map creation step of creating a map of signal strength according to the received waves, with distance and an azimuth along the array direction as axes; a distance measurement step in which, if the peak with the maximum signal strength exists in the map other than near the 0 degree azimuth, the map is not used for distance measurement, and, if the peak with the maximum signal strength exists in the 0 degree azimuth, the distance to the peak is regarded as the distance to the object; A distance measurement method having the following.

6. A distance measurement method for measuring a distance to an object having a plane, comprising: an array antenna in which a transmitting antenna element that transmits microwaves toward a plane defined by the object and a plurality of receiving antenna elements that receive the reflected microwaves as received waves are arranged along an arrangement direction parallel to the plane defined by the object; a processing unit for measuring the distance to the object based on the received wave; A distance measuring device having Using the arithmetic processing unit, a map creation step of creating a map of signal strength according to the received waves, with distance and an azimuth along the array direction as axes; a distance measurement step of determining, in the case where a plurality of peaks having signal intensities equal to or greater than a predetermined threshold exist at different distances in the vicinity of an orientation of 0 degrees in the map, the distance to the peak corresponding to the closest distance as the distance to the object; A distance measurement method having the following.

7. 7. The distance measurement method according to claim 5, wherein the vicinity of 0 degrees azimuth is a range of more than a negative half-value angle and less than a positive half-value angle of azimuth, using a half-value angle determined from the directivity of the array antenna.

8. 7. The distance measurement method according to claim 5, wherein the map creation step calculates a distance spectrum by performing a fast Fourier transform on a signal based on the received wave, calculates an orientation spectrum by performing a fast Fourier transform on the calculated distance spectrum, and creates the map based on the distance spectrum and the orientation spectrum.

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