Foreign Object Detection System

Abstract

The problem to be solved by the present invention is to provide a foreign object detection system that can detect foreign objects existing on a runway, etc. and uses multiple radars that can suppress interference between radars. The solution of the present invention is a foreign object detection system 1, comprising: a first radar 11; a second radar 21, which is connected to the first radar 11 via a network 33; and a signal source 31, which sends a synchronization signal to the first radar 11 and the second radar 21 via the network 33, and the time for the synchronization signal to be transmitted from the signal source 31 to the first radar 11 is set to τ 1i , and the time for the synchronization signal to be transmitted from the signal source 31 to the second radar 21 is set to τ 2j When |τ 1i -τ 2j | delay time, thereby preventing interference caused by the radar signal output from the second radar 21 being reflected by the reflective object 37 and input to the first radar 11.

Description

Technical Field

[0001] The present invention relates to a foreign object detection system using a plurality of radars. More specifically, the present invention relates to a foreign object detection system using radars that suppress interference between radars. Background Art

[0002] Japanese Patent Publication No. 2019-055769 discloses a system and method for detecting obstacles in an aircraft inspection system. The system disclosed in this publication equips an aircraft with a radar in order to detect obstacles in flight. The radar disclosed in this publication scans a first airspace in a radial direction.

[0003] The radar described in Japanese Patent Publication No. 2019-055769 is suitable for detecting air obstacles. However, the radar described in this publication scans the first airspace in the radial direction, so it cannot detect foreign objects and obstacles on the runway, etc.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-055769 Summary of the invention

[0007] Problems to be solved by the invention

[0008] An object of an invention described in this specification is to provide a foreign object detection system that can detect foreign objects existing on a runway or the like and uses a plurality of radars that can suppress interference between radars.

[0009] Technical solutions to problems

[0010] An invention described in this specification is based on the following knowledge. When multiple radars connected by a network are used to detect foreign objects, sometimes an artifact is generated due to interference waves between radars. The location where this artifact is generated depends on the time difference (delay) when the signal reaches each radar. Therefore, by controlling this delay, the artifact can be identified, thereby effectively suppressing interference between radars.

[0011] An invention described in this specification relates to a foreign object detection system 1. The foreign object detection system 1 includes: a first radar 11, a second radar 21, and a signal source 31. The second radar 21 is connected to the first radar 11 via a network 33. The signal source 31 is an element connected to the first radar 11 and the second radar 21 via the network 33 and used to send a synchronization signal.

[0012] The time it takes for the synchronization signal to be transmitted from the signal source 31 to the first radar 11 is τ 1i Furthermore, the time for the synchronization signal to be transmitted from the signal source 31 to the second radar 21 is τ 2j .

[0013] Then, the signal source 31 controls the signal equivalent to |τ 1i -τ 2j | Delay time. Thus, the foreign object detection system 1 can prevent interference caused by the radar signal output from the second radar 21 being reflected by the reflective object 37 and input to the first radar 11.

[0014] In the preferred example of the foreign object detection system 1 described above, the first radar 11 and the second radar 21 are radars installed on the ground.

[0015] In the preferred example of the foreign object detection system 1, the measurement limit length of the first radar 11 is set to L m When considering L m And control |τ 1i -τ 2j |. Specifically, it is |τ 1i -τ 2j |>2L m / c mode control|τ 1i -τ 2j |(here c is the signal speed).

[0016] In a preferred example of the above-mentioned foreign object detection system 1, there are: a delay time changing unit 41, which changes the delay time; a changing object determining unit 43, which determines the measurement object whose measurement position changes due to the first radar 11 when the delay time changing unit 41 changes the delay time; and an interference judgment unit 45, which judges the measurement object determined by the changing object determination unit 43 as interference.

[0017] In a preferred example of the foreign object detection system 1 described above, the first radar 11 and the second radar 21 are pulse radars and satisfy the following formula (3).

[0018] t max <mod(Δt ij ,T)·····(3),

[0019] In formula (3), t max 2L max / c,L max is the maximum detection distance of the first radar 11 and the second radar 21, c is the signal speed, Δt ij =|τ 1i -τ 2j |, T is the period of the pulse radar.

[0020] In a preferred example of the foreign object detection system 1 described above, the first radar 11 and the second radar 21 are FMCW radars whose frequency changes in a triangular wave shape with respect to time, and satisfy the following equation (4).

[0021] fmax <(2f B ×mod(Δτ ij , T)) / T<2f B -f max ·····(4),

[0022] In formula (4), f max Indicates the upper limit frequency (Hz) of the IF band circuit of the FMCW radar, f B represents the sweep width (Hz) of the FMCW radar, Δτ ij =|τ 1i -τ 2j |, T is the period of FMCW radar.

[0023] In a preferred example of the foreign object detection system 1 , the first radar 11 and the second radar 21 are FMCW radars whose frequency changes with respect to time in a sawtooth wave shape, and satisfy the following formula (5).

[0024] f max <(f B ×mod(Δτ ij , T)) / T<f B -f max ·····(5),

[0025] In formula (5), f max Indicates the upper limit frequency (Hz) of the IF band circuit of the FMCW radar, f B represents the sweep width (Hz) of the FMCW radar, Δτ ij =|τ 1i -τ 2j |, T is the period of FMCW radar.

[0026] Effects of the Invention

[0027] According to the above invention, a foreign object detection system can be provided, which controls the time when the signal reaches each radar, thereby effectively preventing interference between radars. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a conceptual diagram showing an example of the configuration of a foreign object detection system.

[0029] Figure 2 This is a conceptual diagram showing the situation of detecting foreign matter.

[0030] Figure 3 A conceptual diagram used to illustrate a situation where interference occurs due to wireless signals from other radars.

[0031] Figure 4 This is a conceptual diagram showing an example of a control system for delay time in a signal source.

[0032] Figure 5 An example of a flow chart for a foreign object detection system to determine whether a detected signal is caused by a foreign object or a reflective body.

[0033] Figure 6 This is a conceptual diagram showing the relationship between a transmission signal and a reception signal when an FMCW radar is used in which the frequency changes in a triangular wave shape with respect to time.

[0034] Figure 7 This is a conceptual diagram showing the relationship between a transmission signal and a reception signal when an FMCW radar is used in which the frequency changes with respect to time in a sawtooth wave shape. DETAILED DESCRIPTION

[0035] Hereinafter, the mode for implementing the present invention will be described using the drawings. The present invention is not limited to the mode described below, and also includes appropriate modifications within the scope obvious to those skilled in the art from the following mode.

[0036] Figure 1 This is a conceptual diagram showing an example of the structure of a foreign object detection system. Figure 1 As shown, the foreign object detection system 1 includes a first radar 11, a second radar 21 and a signal source 31. The second radar 21 is connected to the first radar 11 via a network 33. The signal source 31 is an element connected to the first radar 11 and the second radar 21 via the network 33 and used to send a synchronization signal.

[0037] The foreign object detection system 1 is a system for detecting foreign objects present on the runway 3 of an aircraft, for example. Examples of foreign objects are obstacles that may hinder the movement of an aircraft, and refer to objects that are not present on the runway 3 under normal conditions and may hinder the safe movement of the aircraft or may be obstructive. In the example of an aircraft, foreign objects are present on the runway 3. That is, foreign objects are generally objects that exist in areas that a vehicle may pass through when it is normally traveling. The following description will focus on the foreign object detection system for an aircraft runway. Of course, this foreign object detection system 1 can be used for various purposes such as a foreign object detection system for roads and a foreign object detection system for navigation. This system can also be set up on a road, and is thereby used to notify an autonomous driving vehicle of the presence of foreign objects.

[0038] The first radar 11 and the second radar 21 can appropriately adopt known radars. The radar can receive a synchronization signal (such as an optical signal), convert the received synchronization signal into a wireless signal through a signal converter, or generate a signal with a transmitter that is synchronized with the synchronization signal, and emit the wireless signal from the wireless output unit. In addition, the radar can receive a wireless signal through its wireless receiving unit, convert the received wireless signal into a signal (such as an optical signal) through a signal conversion unit, and output it from the receiving signal output unit. The radar can be a continuous wave (FMCW) radar or a pulse radar. In the FMCW radar, the transmission wave and the reception wave are input to the mixer in the analysis device 39, and the frequency difference of these waves is measured, thereby calculating the distance from the radar to the foreign object. Fiber wireless technology that overlaps the wireless signal on the optical fiber can also be used. In this case, the synchronization signal is a light modulated by the radar signal waveform itself. The synchronization signal can also use the intermediate frequency band waveform that exists in the middle of the generation process of the radar signal waveform. The synchronization signals sent to multiple radars are synchronized, thereby adjusting the timing. The fiber radio unit and the fiber radio system are known as described in Japanese Patent Application No. 2010 / 001438. The signal source 31 may generate and output the synchronization signal using such a known system.

[0039] like Figure 1 As shown in FIG. 1 , it is preferred that radars are arranged at predetermined intervals on both ends of the runway 3. In this case, the radar group only needs to be present near the runway 3 away from the taxiing portion of the aircraft. For example, the radar group (first radar group) present at one end of the runway 3 is denoted as RAU 1j (j is 1, 2, ...), the radar group (second radar group) existing at the other end of runway 3 is denoted as RAU 2i (i is 1, 2, ...). Radars are also installed in vehicles (aircraft, cars, motorcycles, bicycles, helicopters, drones). On the other hand, in the present invention, Figure 1 As shown, it is preferred that the first radar 11 and the second radar 21 are radars installed on the ground. It is preferred that the first radar 11 and the second radar 21 are radars respectively present at both ends of the runway 3. In other words, it is preferred that there is a positional relationship of the runway 3 between the first radar 11 and the second radar 21. Examples of the distance between the radars present in each group may be 1m to 5km, 10m to 1km, 100m to 1km, 200m to 1km, or 10m to 100m.

[0040] The signal source 31 is an element connected to the first radar 11 and the second radar 21 through the network 33 and used to send a synchronization signal. The synchronization signal output from the signal source 31 reaches the first radar 11 and the second radar 21 through the network 33, and becomes a radar signal based on the synchronization signal from the first radar 11 and the second radar 21.

[0041] An example of the network 33 is an optical fiber network. Each element connected to the optical fiber network can send and receive information via optical fibers. In the optical fiber network, for example, well-known elements such as routers and amplifiers can be appropriately installed.

[0042] Figure 2 : is a conceptual diagram showing a situation of detecting a foreign object. For example, a wireless signal 13 output from a first radar 11 hits a foreign object 35. Then, the wireless signal is reflected by the foreign object 35. The reflected wireless signal 15 (or a part thereof) returns to the first radar 11. The first radar 11 receives the wireless signal 15 reflected and returned by the foreign object 35. Then, the first radar 11 appropriately converts the received wireless signal and outputs it as a detection signal. An analysis device 39 connected to the network 33 (which may be located in the same device as the signal source 31) receives the detection signal transmitted through the network 33. Then, the analysis device 39 analyzes the received detection signal. The speed of the wireless signal is stored in the storage unit. In this way, the analysis device 39 can, for example, use the time when the first radar 11 outputs the radar signal and the time when the first radar 11 receives the wireless signal 15 to find the distance from the first radar 11 to the foreign object 35. There are multiple radars in this system, so the distance from each radar to the foreign object 35 can be found. In this way, the position information of the plurality of radars and the distance information from each radar to the foreign object 35 can be used to determine the position of the foreign object 35 (for example, the position of the foreign object 35 on the runway 3 ).

[0043] Figure 3A conceptual diagram for explaining a situation where interference is caused by wireless signals from other radars. In this example, interference based on wireless signals from other radars is caused by the presence of a reflector 37. The reflector 37 is an object that does not affect the normal navigation of the vehicle, but there is a concern that the system may misidentify the wireless signal from the radar due to the reflection of the object. For example, sometimes an aircraft 37 is on standby outside the runway 3. In this way, for example, the wireless signal 23 from the second radar 21 will be reflected by the body of the aircraft 37, and the reflected wireless signal 25 will reach the first radar 11. In this way, the timing of the wireless signal 25 reaching the first radar 11 is the same as the timing of the wireless signal output from the first radar 11 being reflected by the foreign object 35 and returning, and arrives at the first radar 11. In this way, there will be a situation where the analysis device 39 determines that the foreign object 35 exists. In this case, the first radar 11 will observe an artifact as if there is a foreign object 35. Since the foreign object 35 is received as a signal with incorrect distance in multiple radars, it is expected that the position of the foreign object 35 cannot be determined, and the system is confused. On the other hand, for example, the optical path length from the signal source 31 to the first radar 11 is maintained, and the optical path length from the signal source 31 to the second radar 21 is changed. In this way, if the signal received by the first radar 11 is from the foreign object 35, the timing of receiving the signal from the foreign object 35 will not change because the optical path length of the first radar 11 has not changed. On the other hand, for the signal output from the second radar 21, reflected by the reflector 37 and received by the first radar 11, the timing of receiving the signal will change as the optical path length from the signal source 31 to the second radar 21 changes. In this way, the first radar 11 will receive a signal that seems to be a change in the distance between the pseudo image and the first radar 11. That is, by changing the difference in the timing of receiving the optical signal between the radar of an observed object and other radars, it can be determined whether the received signal is a pseudo image or a signal from the foreign object 35.

[0044] The synchronization signal is transmitted from the signal source 31 to the first radar 11, and the time is τ 1i Furthermore, the time it takes for the synchronization signal to be transmitted from the signal source 31 to the second radar 21 is τ 2j Then, the signal source 31 controls the signal equivalent to |τ 1i -τ 2j | delay time. Thus, the foreign object detection system 1 can prevent interference generated by the radar signal output from the second radar 21 being reflected by the reflector 37 and input to the first radar 11. For example, when the delay time is changed, if the distance from the first radar 11 or the second radar 21 to the observed object changes, it is sufficient to determine that the signal is not derived from the foreign object 35 but from the reflector 37, and not process as if the foreign object 35 exists.

[0045] In the case where the wireless signal output by the second radar 21 is directly received by the first radar 11, the output timing of the wireless signals of the first radar 11 and the second radar 21 is adjusted, thereby preventing interference. That is, the position of each radar, the distance from one radar to other radars, and the timing of the wireless signal output from each radar are stored in the storage unit of the analysis device 39. Then, the speed of the wireless signal is also stored in the storage unit. Therefore, when a radar receives a wireless signal, the distance from the radar to other radars and the speed of the wireless signal are used to find the time when the wireless signal reaches the radar from other radars, and the information related to the time when the wireless signal is emitted from the radar and other radars is used to analyze whether the wireless signal received by the radar is a signal sent from other radars and directly received by the radar.

[0046] Figure 4 This is a conceptual diagram showing an example of a control system for delay time in a signal source. This control system for delay time is a combination of an optical switch 51 and a plurality of types of delay lines 53, 55, 57. Each of the delay lines 53, 55, 57 has a different length, for example, and the time required for the optical signal to pass through may be different. Therefore, by selecting the delay line 53, 55, 57 by the optical switch 51, the time for the synchronization signal to reach the second radar 21 can be controlled. The above example is an example of delay control. For example, the refractive index of the core can be changed by applying an external force (such as pressure and temperature) to the optical fiber, thereby changing the speed of the synchronization signal transmitted in the optical fiber, thereby controlling the delay time.

[0047] In the preferred example of the foreign object detection system 1, the measurement limit length of the first radar 11 is set to L m When considering L m And control |τ 1i -τ 2j |. Specifically, to become |τ 1i -τ 2j |>2L m / c (where c is the signal speed) to control |τ 1i -τ 2j |. The signal speed means the speed of the wireless signal output from the radar. For example, the distance l1 from the signal source 31 to the first radar 11 (l1 may change due to a switch, for example) and the distance l2 from the signal source 31 to the second radar 21 (l2 may change due to a switch, for example) are taken into account to take into account the transmission speed of the synchronization signal in the network 33 and become |τ 1i -τ 2j |>2L m / c method to control the distance l1 and the distance l2. This can effectively prevent the interference of optical signals.

[0048] In a preferred example of the foreign object detection system 1, there are: a delay time changing unit 41 that changes the delay time; a variable object determining unit 43 that determines the measurement object whose measurement position is changed by the first radar 11 when the delay time changing unit 41 changes the delay time; and an interference judging unit 45 that judges the measurement object determined by the variable object determining unit 43 as interference. These elements may also exist in the above-mentioned analysis device 39. This analysis device 39 is based on a computer, for example. An example of the delay time changing unit 41 is to change the delay lines 53, 55, and 57 connected to the optical switch 51 by the instruction of the analysis device 39.

[0049] The computer has an input unit, an output unit, a control unit, a computing unit, and a storage unit. Each element is connected by a bus, etc., and can send and receive information. For example, the storage unit can store a control program and various information. When predetermined information is input from the input unit, the control unit reads the control program stored in the storage unit. Then, the control unit appropriately reads the information stored in the storage unit and transmits it to the computing unit. In addition, the control unit transmits the appropriately input information to the computing unit. The computing unit uses the various information received to perform computing processing and stores it in the storage unit. The control unit reads the calculation results stored in the storage unit and outputs them from the output unit. In this way, various processing can be performed.

[0050] Figure 5 An example of a flow chart for a foreign object detection system to determine whether a detected signal is caused by a foreign object or a reflective body. Figure 5 In the example of FIG. 1 , the first radar 11 receives a wireless signal ( S101 ).

[0051] The analysis device 39 analyzes whether the received signal is a wireless signal output from other radars and reaches the first radar 11 (S102). The distance from the first radar 11 to the other radars and the transmission timing of the synchronization signal from the signal source 31 to the first radar 11 and the transmission timing to the other radars are stored in the storage unit of the analysis device 39. Therefore, the analysis device 39 only needs to read the information related to the above timing stored in the storage unit to analyze whether the signal received by the first radar 11 is a wireless signal output from other radars and reaches the first radar 11 directly.

[0052] The analyzing device 39 determines that the wireless signal reaching the first radar 11 is a wireless signal output from another radar and directly reaching the first radar 11 ( S103 ), and the foreign object 35 is not detected.

[0053] When the analysis device 39 determines that the wireless signal reaching the first radar 11 is not a wireless signal output from other radars and directly reaching the first radar 11, it will evaluate whether the wireless signal originates from the signal of the foreign object 35 or the artifact originating from the reflector 37 (S104). In this case, for example, the difference between the optical path length from the signal source 31 to the first radar 11 and the optical path length from the signal source 31 to the other radars is changed. In a specific example, the delay time change unit 41 issues an instruction to the optical switch 51 to change the delay path, thereby changing the optical path length from the signal source 31 to the specific radar. Then, it is analyzed whether the distance from the first radar 11 to the detected object has changed. For example, the computer monitors the distance from the object (candidate for the foreign object 35) to the first radar 11 based on the signal from the first radar 11, and stores it in the storage unit. Then, as described above, the distance from the first radar 11 to the object after the distance from the signal source 31 to the other radars is changed is calculated and stored in the storage unit. Then, the analysis device 39 reads the distance from the first radar 11 to the object before and after the delay time is changed from the storage unit and compares them. When the distance from the first radar 11 to the object changes, or when the change is consistent with the change obtained from the change in the delay time, the received signal is determined to be caused by interference. The measurement object whose measurement position changes due to the first radar 11 is determined to be a reflective object 37. In addition, when the distance from the first radar 11 to the object does not change, the object is determined to be a foreign object 35.

[0054] That is, when the distance to the object changes (S105), the detection signal is analyzed as a signal originating from the reflector 37. On the other hand, when the distance from the first radar 11 to the detected object does not change (S106), the detection signal is analyzed as a signal originating from the foreign object 35. When the analysis device 39 analyzes the signal as originating from the foreign object 35, it uses the information of the distance to the foreign object 35 observed by other radars and the position information of each radar to find the position of the foreign object. Then, an alarm is appropriately output to draw attention.

[0055] 1. Positional relationship between multiple radars and signal delay

[0056] The RAU 1j As the jth remote antenna unit (radar) in row 1, RAU 2i as the i-th remote antenna unit (radar) in row 2. Then, τ 1j and τ 2i As from RAU 1j and RAU 2i The deviation of the reference time of transmitting radar waves, L ij As RAU 1j With RAU 2i The distance between.

[0057] The speed of the radio wave is set to c, and the radar signal passes through RAU 1j Arriving at RAU 2i The time taken is L ij / c. The synchronization signal output from the signal source reaches the RAU 2i The timing of the synchronization signal output from the signal source passes through the RAU 1j The output is a radar signal and the radar signal reaches the RAU 2i The time taken for the two to be synchronized is |τ if the timing deviation of the synchronization signal is taken into account. 2i -τ 1j +L ij / c|≡Δt ij .

[0058] On the other hand, the synchronization signal output from the signal source reaches the RAU 1j The timing of the synchronization signal output from the signal source passes through the RAU 2i The output is a radar signal and the radar signal reaches the RAU 1j The time taken, the difference between the two is also |τ 1j -τ 2i +L ij / c|≡Δt ji .

[0059] 2. About pulse radar

[0060] The following evaluates the case of using a pulse wave as a radar signal. The pulse wave period (that is, the repetition period of the radar transmission wave) is set to T (seconds). max As the maximum detection distance of the radar. As c as the speed of the wireless signal (radar signal). Then, t max Set to 2L max / c.

[0061] In this way, t max <Δt ij <T·····(1),

[0062] t max +NT<Δt ij <T(N+1)·····(2),

[0063] (Here, N is an integer.)

[0064] When the above conditions are met, the interference signal becomes outside the time range of measuring the radar signal, and the influence of the interference can be suppressed.

[0065] The following formula can be derived from formula (1) and formula (2).

[0066] t max <mod(Δtij ,T)·····(3),

[0067] Here, mod(A, B) is the remainder obtained by dividing A by B, and T is the period of the pulse radar.

[0068] L p For example, let L max A specific integer multiple such as 3 times, 5 times, 10 times, etc.

[0069] In this way, relative to L ij <L p The range of (i, j) is preferably adjusted to satisfy equation (3). 1j and τ 2i This relationship is applicable not only to two radars in different radar groups, but also to two radars in the same radar group.

[0070] RAU 1j and RAU 2i When connected to the network, τ 2i =L 2i ×n / c l (Here, L 2i For signal source to RAU 2i The optical path length, n is the effective refractive index of the network (e.g. 1.5 for optical fiber), c l As mentioned above, by adjusting the fiber length, τ can be adjusted. 2i and delay time.

[0071] 3. FMCW radar

[0072] Next, a case where the radar uses an FMCW radar in which the frequency changes in a triangular wave shape with respect to time will be described.

[0073] Figure 6 This is a conceptual diagram showing the relationship between the transmitted signal and the received signal when using an FMCW radar whose frequency changes in a triangular wave shape with respect to time. The frequency changes in a triangular wave shape with respect to time means that the value of the radar frequency changes with time and forms a triangular wave state when the horizontal axis is time and the vertical axis is frequency.

[0074] T represents the period of FMCW radar (seconds). B is the sweep width of the FMCW radar (Hz). max Indicates the upper frequency limit (Hz) of the IF band circuit of the FMCW radar. The IF band circuit is a circuit for amplifying the lowest frequency component (difference frequency component between the transmission signal and the reception signal) of the output obtained by multiplying the transmitted radar signal and the received radar signal by the mixer. maxSynonymous with the previous statement. Thus, f max / t max Equal to 2f B / T. Therefore, for FMCW radar, if Δτ is adjusted to satisfy the following equation (4): ij , the signal caused by the interference will become a component exceeding the upper limit frequency of the IF band circuit, and its influence can be suppressed.

[0075] f max <(2f B ×mod(Δτ ij , T)) / T<2f B -f max ·····(4),

[0076] Next, a case where the radar uses an FMCW radar in which the frequency changes in a sawtooth wave shape with respect to time will be described.

[0077] Figure 7 This is a conceptual diagram showing the relationship between a transmission signal and a reception signal when an FMCW radar is used in which the frequency changes with respect to time in a sawtooth wave shape.

[0078] The first radar 11 and the second radar 21 are FMCW radars whose frequency changes with respect to time in a sawtooth wave shape, and satisfy the following equation (5).

[0079] f max <(f B ×mod(Δτ ij , T)) / T<f B -f max ·····(5),

[0080] (In formula (5), f max Indicates the upper limit frequency (Hz) of the IF band circuit of the FMCW radar, f B represents the sweep width (Hz) of the FMCW radar, Δτ ij =|τ 1i -τ 2j |, T is the period of FMCW radar.

[0081] Industrial Applicability

[0082] The invention described in this specification relates to a foreign object detection system and can therefore be used in, for example, the information and communication industry and the construction industry.

[0083] Description of Reference Numerals

[0084] 1 Foreign Object Detection System

[0085] 11 First Radar

[0086] 21 Second Radar

[0087] 31 Signal Source

[0088] 33 Network

[0089] 35 Foreign matter

[0090] 37 Reflector

[0091] 39 Analysis device

[0092] 41 Delay time change section

[0093] 43 Change object determination department

[0094] 45 Interference Judgment Unit

[0095] 51 Optical switch

[0096] 53, 55, 57 Delay lines.

Claims

1. A foreign body detection system, characterized in that: Include: First Radar; a second radar connected to the first radar via a network; and a signal source, which is independent of the first radar and the second radar, and sends a synchronization signal to the first radar and the second radar through the network, The time for transmitting the synchronization signal from the signal source to the first radar is τ 1i , and the time for the synchronization signal to be transmitted from the signal source to the second radar is set to τ 2j When |τ 1i -τ 2j |Delay time, This prevents interference caused by the radar signal output from the second radar being reflected by a reflective object and input to the first radar. The first radar and the second radar are radars installed on the ground, so as to become |τ 1i -τ 2j |>2L m / c to control the |τ 1i -τ 2j |, c is the signal speed, L m is the measurement limit length of the first radar.

2. A foreign body detection system, characterized in that: Include: First Radar; a second radar connected to the first radar via a network; and a signal source, which is independent of the first radar and the second radar, and sends a synchronization signal to the first radar and the second radar through the network, The time for transmitting the synchronization signal from the signal source to the first radar is τ 1i , and the time for the synchronization signal to be transmitted from the signal source to the second radar is set to τ 2j When |τ 1i -τ 2j |Delay time, This prevents interference caused by the radar signal output from the second radar being reflected by a reflective object and input to the first radar. The foreign object detection system further comprises: a delay time changing unit that changes the delay time; a changing object identifying unit that identifies a measurement object whose measurement position is changed by the first radar when the delay time changing unit changes the delay time; as well as The interference determination unit determines that the measurement object determined by the changing object determination unit is the interference.

3. A foreign body detection system, characterized in that: Include: First Radar; a second radar connected to the first radar via a network; and a signal source, which is independent of the first radar and the second radar, and sends a synchronization signal to the first radar and the second radar through the network, The time for transmitting the synchronization signal from the signal source to the first radar is τ 1i , and the time for the synchronization signal to be transmitted from the signal source to the second radar is set to τ 2j When |τ 1i -τ 2j |Delay time, This prevents interference caused by the radar signal output from the second radar being reflected by a reflective object and input to the first radar. The first radar and the second radar are pulse radars and satisfy the following equation (3): t max <mod(Δt ij ,T)·····(3), In formula (3), t max 2L max / c,L max is the maximum detection distance of the first radar and the second radar, c is the signal speed, Δt ij =|τ 1i－ τ 2j |, T is the period of the pulse radar.

4. A foreign body detection system, characterized in that: Include: First Radar; a second radar connected to the first radar via a network; and a signal source, which is independent of the first radar and the second radar, and sends a synchronization signal to the first radar and the second radar through the network, The time for transmitting the synchronization signal from the signal source to the first radar is τ 1i , and the time for the synchronization signal to be transmitted from the signal source to the second radar is set to τ 2j When |τ 1i -τ 2j |Delay time, This prevents interference caused by the radar signal output from the second radar being reflected by a reflective object and input to the first radar. The first radar and the second radar are FMCW radars whose frequency changes in a triangular wave shape with respect to time, and satisfy the following equation (4): f max <(2f B ×mod(Δτ ij ,T)) / T<2f B -f max ·····(4), In formula (4), f max represents the upper limit frequency of the IF band circuit of the FMCW radar, f B represents the sweep width of the FMCW radar, Δτ ij =|τ 1i -τ 2j |, T is the period of FMCW radar.

5. A foreign body detection system, characterized in that: Include: First Radar; a second radar connected to the first radar via a network; and a signal source, which is independent of the first radar and the second radar, and sends a synchronization signal to the first radar and the second radar through the network, The time for transmitting the synchronization signal from the signal source to the first radar is τ 1i , and the time for the synchronization signal to be transmitted from the signal source to the second radar is set to τ 2j When |τ 1i -τ 2j |Delay time, This prevents interference caused by the radar signal output from the second radar being reflected by a reflective object and input to the first radar. The first radar and the second radar are FMCW radars whose frequency changes with respect to time in a sawtooth wave shape, and satisfy the following equation (5): f max <(f B ×mod(Δτ ij ,T)) / T<f B -f max ·····(5), In formula (5), f max represents the upper limit frequency of the IF band circuit of the FMCW radar, f B represents the sweep width of the FMCW radar, Δτ ij =|τ 1i－ τ 2j |, T is the period of FMCW radar.

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