Noise removal device, object detection device, and noise removal method

Abstract

To remove noise with good accuracy from arrival light that arrives corresponding to emitted light.SOLUTION: A noise rejection device 30 removes noise from arrival light that arrives corresponding to emitted light, measuring the intensity of arrival light by a measurement unit 31, the light coming from a detection direction corresponding to the emission direction of the light emitted toward a prescribed range, along an elapsed time from the emission of light, and extracting a detection time from the emission of light to when the arrival light is detected, and the light emission direction corresponding to the arrival light. When an echo of prescribed strength or greater exists in the arrival light whose strength was measured, a determination unit 32 determines, using the strength of the echo and the detection distance corresponding to the elapsed time, whether or not the echo is the one reflected by a detection object existing in the prescribed range, and the echo detected as not having been reflected by the detection object is removed as noise by a rejection unit 33.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a technique for removing noise that occurs when recognizing a detection target using reflected light. [Background technology]

[0002] There is a known technology that irradiates a predetermined area with light such as infrared light, detects reflected light from a detection target within the area, and recognizes the detection target or measures the distance to the detection target. In such optical measurements, the removal of noise caused by the influence of ambient light, etc., has been considered. For example, in Patent Document 1, the reflected wave is received multiple times and superimposed to remove noise components. In addition, Patent Document 2 proposes removing isolated points that are significantly different in distance from surrounding pixels as noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-9841 A [Patent Document 2] Patent No. 6763992 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there are various problems remaining with such noise removal technology. For one thing, when recognizing a detection target or measuring the distance outdoors optically, it is affected by rainfall and ambient light, and the strength of the reflected wave from raindrops, etc. may be high, and it may not be possible to remove it even if multiple measurement results are overlapped. This problem is remarkable in clutter caused by raindrops or ambient light near the measurement point. In addition, for objects that do not easily reflect the irradiated light, such as a car body painted black, the intensity of the reflected light may be low, and simply raising the threshold value for removing the noise component makes it difficult to recognize the detection target or measure the distance. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms or application examples.

[0006] A first aspect of the present disclosure is a noise removal device (30) that removes noise generated when recognizing a detection target (OJT) using light reflection. This noise removal device includes a measurement unit (31) that measures the intensity of arriving light that arrives from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light, a determination unit (32) that, when an echo of a predetermined intensity or more is present in the measured arriving light, determines whether the echo is reflected by a detection target present in the predetermined range using the intensity of the echo and a detection distance that is a distance corresponding to the elapsed time, and a removal unit (33) that removes the echo determined not to be reflected by the detection target as noise.

[0007] Another aspect of the present disclosure is a method for removing noise that occurs when recognizing a detection target using light reflection. This noise removal method detects arriving light, which is light from a detection direction corresponding to the emission direction of light emitted toward a predetermined range (step S110), extracts a detection time, which is the time from the emission of the light to the detection of the arriving light, and the emission direction of the light corresponding to the arriving light, and if an echo of a predetermined intensity or more is present in the measured arriving light, determines whether the echo is reflected by a detection target present in the predetermined range using the intensity of the echo and the detection distance corresponding to the elapsed time (steps S332 to S336), and removes the echo determined not to have been reflected by the detection target as noise (steps S337 and S338). 。 Yet another aspect of the present disclosure is a noise removal device (30) that removes noise generated when recognizing a detection target using light reflection, the noise removal device including: a measurement unit (31) that measures the intensity of arriving light arriving from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light; a determination unit (32) that, when an echo of a predetermined intensity or more is present in the measured arriving light, determines whether the echo is reflected by a detection target present in the predetermined range using the intensity of the echo and a detection distance that is a distance corresponding to the elapsed time; a removal unit (33) that removes the echo that is determined not to be reflected by the detection target as noise; and a condition setting unit that sets a combination of determination conditions related to the intensity of the echo and the detection distance that is a distance corresponding to the elapsed time when determining that an echo of a predetermined intensity or more is present in the measured arriving light, based on at least one of the environment in which the noise removal device is placed and the characteristics of the measurement unit. Note that the present disclosure can also be implemented as a noise removal method corresponding to this noise removal device. [Brief description of the drawings]

[0008] [Figure 1] FIG. 4 is an explanatory diagram showing how a vehicle performs target recognition; [Diagram 2] 1 is a schematic configuration diagram showing the configuration of a target recognition device incorporating a noise removal device according to a first embodiment. [Figure 3A] FIG. 2 is an explanatory diagram showing a schematic configuration of a light receiving and emitting unit. [Figure 3B] 5 is an explanatory diagram illustrating the relationship between a light emission signal and a light reception signal. [Figure 4] 4 is a flowchart showing an example of a target recognition processing routine. [Diagram 5] 11 is a flowchart showing an example of a two-stage threshold determination process. [Figure 6A] FIG. 4 is an explanatory diagram for explaining an intensity ratio treated as the intensity of a received light signal. [Figure 6B] FIG. 4 is an explanatory diagram showing an outline of processing for echoes contained in a received light signal. [Figure 7] 11 is a flowchart showing an example of a noise removal process. [Figure 8] 1 is an explanatory diagram showing the presence of reflected light from raindrops and black cars in terms of the relationship between the distance to the detection target and the signal strength. [Figure 9] FIG. 11 is an explanatory diagram showing an example of a threshold value for separating noise from an actual signal; [Figure 10] 11 is a flowchart showing an example of an isolated point removal process. [Figure 11] FIG. 4 is an explanatory diagram showing the state of reflected light from a road surface. [Figure 12] 11 is a flowchart showing an example of a process for counting the number of adjacent points. [Figure 13] FIG. 11 is a schematic diagram showing the internal configuration of an object surface recognition device incorporating a noise removal device according to a second embodiment. [Figure 14A] 4 is a flowchart showing a correction coefficient acquisition process routine. [Figure 14B] 13 is a graph showing a schematic diagram of a one-dimensional table for determining a correction coefficient. [Figure 15] 13 is a flowchart showing a two-stage threshold determination process routine in the second embodiment. [Figure 16] 10 is a flowchart showing a first noise removal process in the second embodiment. [Figure 17] FIG. 11 is an explanatory diagram showing a state of noise removal. [Figure 18] FIG. 11 is a schematic configuration diagram of a vehicle equipped with a target recognition device incorporating a noise removal device according to a third embodiment. [Figure 19] 13 is a flowchart showing a noise level calibration process routine in the third embodiment. [Figure 20] FIG. 4 is an explanatory diagram showing an example of a calibration process. [Figure 21] 13 is a flowchart showing a noise determination process according to a fourth embodiment. [Figure 22] FIG. 11 is an explanatory diagram showing how noise removal is performed by switching detection target areas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: (A1) Hardware configuration: FIG. 1 shows an overview of the operation of a target recognition device 10 equipped with a noise removal device 30 according to the first embodiment. As shown in the figure, the target recognition device 10 is mounted on a vehicle 100, and measures the distance to targets present in the vicinity in front of the vehicle 100, such as other vehicles, pedestrians, and buildings, and recognizes the targets. In this embodiment, the target recognition device 10 is configured by LiDAR (Light Detection And Ranging). The target recognition device 10 irradiates a predetermined range SCA with irradiation light Lz, which is a pulsed light, while scanning, and receives reflected light corresponding to the irradiation light Lz. For example, if there is a detection target within the predetermined range SCA, the irradiation light Lz hits the object, and the reflected light from the object is returned. The intensity of the reflected light differs not only depending on the presence or absence of an object, but also between parts of the object surface with different reflectances, such as black parts and white parts. For example, a white line may be recognized by the reflected light from a white line on the road surface. For this reason, such detection and recognition targets may be collectively called "targets."

[0010] The target object recognition device 10 of this embodiment receives this reflected light, removes noise contained in the received light signal obtained corresponding to the reflected light using a noise removal device 90, and then recognizes the distance to the detection object and what the target is. Below, the noise removal device 30 will be described together with the configuration and operation of the target object recognition device 10, but it is also possible to operate the noise removal device 30 independently or as a device other than the target object recognition device 10.

[0011] In FIG. 1, the origin is the emission center position of the irradiated light Lz, the front-rear direction of the vehicle 100 is the Y axis, the width direction of the vehicle 100 passing through the origin is the X axis, and the vertical direction passing through the origin is the Z axis. The front of the vehicle 100 is the +Y direction, the rear of the vehicle 100 is the -Y direction, the right direction of the vehicle 100 is the +X direction, the left direction of the vehicle 100 is the -X direction, the vertical upward direction is the +Z direction, and the vertical downward direction is the -Z direction. The irradiated light Lz is a collection of light from a plurality of light-emitting elements arranged in the Z-axis direction, as described later, and its projection area has a vertically elongated shape along the Z direction. This vertically elongated irradiated light Lz is one-dimensionally scanned in the X-axis direction to irradiate a predetermined range. As shown by the thick solid arrow in FIG. 1, the irradiated light Lz is scanned from left to right toward the forward direction of the vehicle 100, while causing a plurality of light-emitting elements to emit light at a predetermined time interval. The irradiated light Lz is a pulsed light, so it can be considered that it is irradiated to each square shown by a thin solid line in the figure. The scanning speed and pulse interval of this irradiated light Lz, which is a pulsed light, determine the resolution θ1 in the X-axis direction of the target recognition device 10. The resolution in the Z-axis direction of the target recognition device 10 is determined by the interval in the Z direction of the multiple light-emitting elements.

[0012] The target recognition device 10 measures the time from emitting the irradiation light Lz to receiving the reflected light, i.e., the time of flight TOF of the light, and calculates the distance to the target from the time of flight TOF to detect the target as a ranging point cloud. A ranging point means a point indicating a position where at least a part of the target identified by the reflected light may be present within a range where the target recognition device 10 can measure distances. A ranging point cloud means a collection of ranging points in a predetermined period of time. The target recognition device 10 recognizes the target using a shape specified by the three-dimensional coordinates of the detected ranging point cloud and the reflection characteristics of the ranging point cloud.

[0013] 2, the target recognition device 10 includes a CPU 20, a storage device 50, an input / output interface 60, a light emitting unit 70, and a light receiving unit 80. The CPU 20, the storage device 50, and the input / output interface 60 are connected to the CPU 20. The storage device 50 includes semiconductor storage devices such as ROM, RAM, and EEPROM, as well as magnetic storage devices such as hard disks. The light emitting unit 70 and the light receiving unit 80 are connected to the input / output interface 60.

[0014] The CPU 20 reads and executes a computer program stored in the storage device 50, thereby functioning as the noise removal device 30, as well as the light emission control unit 22, the distance calculation unit 40, and the target recognition unit 45. The light emission control unit 22, the distance calculation unit 40, and the target recognition unit 45 may be configured as separate devices that operate according to instructions from the CPU 20.

[0015] The light emission control unit 22 transmits a light emission signal to the light emission unit 70 at regular intervals via the input / output interface 60. The light emission unit 70 includes a light emitting element 72 and a scanner 74. The light emitting element 72 is composed of a plurality of laser diodes LD1 to LD8 arranged in the Z direction, as illustrated in FIG. 3A. When a pulsed light emission signal is received, the laser diodes LD1 to LD8 emit light in response to the pulse and emit the irradiation light Lz. The laser diodes LD1 to LD8 emit, for example, infrared light as the irradiation light Lz. The scanner 74 is composed of, for example, a mirror or a DMD (Digital Mirror Device), and scans the irradiation light emitted from the laser diodes LD1 to LD8 from the -x direction to the +x direction at regular intervals. There may be one or more laser diodes. In the case of one or a small number of laser diodes, the scanner 74 may be configured to be able to scan in the Z axis direction in addition to the X axis direction, that is, in two-dimensional directions. In addition, the light emitting elements 72 may be arranged two-dimensionally in the X and Z directions, and scanning by the scanner 74 may be omitted.

[0016] The light receiving unit 80 includes a plurality of light receiving elements 82. As indicated by the symbols SP1 to SP8, eight light receiving elements 82 are arranged in the z direction. Each light receiving element 82 is composed of 5×5 micro SPADs (msp11 to msp55) arranged two-dimensionally, and 25 micro SPADs constitute one light receiving element 82. The micro SPAD is a single photon avalanche diode, and outputs a binary signal indicating whether or not a photon has been incident. The light receiving element 82, which is composed of 25 micro SPADs, can output a signal corresponding to how many of the micro SPADs have detected reflected light, that is, an intensity signal indicating the intensity of the light that has reached the light receiving element 82. The arrangement of the micro SPADs may be another configuration, such as 3×6.

[0017] As shown in FIG. 3B, when the light emission signal LDF is output from the light emission control unit 22 of the CPU 20 and one of the laser diodes LD1 to LD8 constituting the light emitting element 72 emits light, the reflected light of the irradiated light reflected by the detection target OJT enters the light receiving element 82. Then, the light receiving element 82 outputs a signal according to the intensity of the reflected light along with the elapsed time from the emission of the light emitting element 72. Note that most of the light reaching the light receiving element 82 is reflected light of the light emitted from the light emitting element 72 reflected by the object, but external light and stray light reflected multiple times also enter. Since the light receiving element 82 itself cannot detect only the reflected light contained in the reaching light, the noise removal device 30 realized by the CPU 20 removes the influence of external light and the like, and calculates the distance to the detection target OJT and the reflected light intensity based on the reflected light from the detection target OJT.

[0018] If the detection target OJT is something like a wall located at a predetermined distance from the target recognition device 10 and there is nothing between the detection target OJT and the detection target OJT, the light receiving signal will have a peak SS3 at a time TOF corresponding to the distance from the light emission signal LDF to the detection target OJT, as shown in FIG. 3B (A). However, in reality, noise caused by various factors is superimposed on the light receiving signal, and other peaks SS1 and SS2 may appear in the light receiving signal, as shown in FIG. 3B (B). The noise removing device 30, which receives the light receiving signal via the input / output interface 60, removes such noise from the light receiving signal. The noise removing device 30 includes a measuring unit 31 that receives a signal from the light receiving unit 80 and measures the signal strength and elapsed time, a determining unit 32 that determines whether an echo present in the measured light receiving signal is an echo due to reflected light from the detection target, and a removing unit 33 that removes noise. The noise removing process performed by the removing unit 33 will be described in detail later.

[0019] The light reception signal output by the noise removal device 30, i.e., the light reception signal from which noise has been removed, is output to a distance calculation unit 40. The distance calculation unit 40 calculates the distance from the target recognition device 10 to the detection target OJT based on the time (TOF) from light emission to reception of the light reception signal. Specifically, the distance calculation unit 40 calculates the distance D from the target recognition device 10 to the reflection point of the detection target OJT using the time TOF from when the light emitting elements LD1 to LD8 emit the irradiated light Lz until the irradiated light Lz hits the detection target OJT and the reflected light Rz is received by the light receiving element 82 of the light receiving unit 80. If the speed of light is c, the distance D from the target recognition device 10 to the reflection point of the detection target OJT is expressed as follows: D = TOF / (2 c) The target recognition unit 45 receives the calculation result from the distance calculation unit 40, and determines the position of the reflection point of the detection target OJT from the direction of the reflection point of the detection target OJT and the distance D to the reflection point, and recognizes the target from the set of the reflection points.

[0020] The outline of the target recognition process performed by the CPU 20 will be described with reference to the flowchart of Fig. 4. The illustrated target recognition process routine is repeatedly executed at a predetermined interval when an ignition switch (not shown) of the vehicle 100 is turned on and power is supplied to the target recognition device 10. The illustrated routine is roughly divided into three steps: a scanning process (step S100) that scans a predetermined range SCA with a laser beam and collects data on the light reception signals of reflected light at all pixels belonging to the predetermined range SCA, a noise removal process (step S300) that removes noise from the collected light reception signal data, and a recognition process (step S500) that calculates the distance to a target present in the predetermined range SCA after removing noise and recognizes the target.

[0021] When the scanning process (step S100) is started, the scanner 74 is first started and scanning with laser light is started (step S100s). The processes following this scan (steps S110 to S130) are repeated until the end of the scan (step S100e). The process from the start to the end of the scan corresponds to scanning the predetermined range SCA shown in FIG. 1 from the origin to the end point of the diagonal.

[0022] When scanning starts, first, light emission and light reception operations are performed (step S110). As already explained, this process is a process of outputting a light emission signal LDF to one of the light emitting elements 72 at a predetermined time interval and receiving a light reception signal from one of the light receiving elements 82 of the light receiving section 80. The light reception signal is a signal corresponding to one of the pixels constituting the predetermined range SCA. In the light reception signal TS, a mountain-shaped signal waveform having a peak and a predetermined time width appears due to various factors. In the following explanation, the mountain-shaped signal waveform including this peak is called an echo regardless of the magnitude of the peak value. One of the echoes is caused by reflected light from the detection target OJT, but it can also be caused by so-called clutter. A two-stage threshold judgment process (step S120) is performed on this light reception signal to extract an echo TSn contained in the light reception signal according to the intensity of the light reception signal.

[0023] An outline of this two-stage threshold determination process is shown in FIG. 5. The light receiving signal TS to be handled in the two-stage threshold determination process (step S120) is the signal read in step S110. The signal from the light receiving element 82 may be processed as the light receiving signal TS as it is, or may be processed by sequentially reading the signal once stored in the storage device 50. In the two-stage threshold determination process, first, the signal strength RT of the light receiving signal TS is read in chronological order, with the time when the light emission signal LDF is output as time 0 (step S210), and it is determined whether or not there is a point in the signal strength RT of the light receiving signal TS that is greater than the first threshold Th1 (step S220). The signal strength RT of the light receiving signal TS is the strength of the signal obtained from the light receiving element 82 at a point on the time axis, and in this embodiment, it is a signal corresponding to how many of the 25 micro SPADs have detected a photon and activated their output. As shown in FIG. 6A, the intensity of the received light signal TS is determined by the intensity ratio RRn of the actual intensity difference Δrmax, which is the difference between the peak intensity RTn of the echo and the external light intensity Ena, to the maximum intensity difference ΔRmax, which is the difference between the maximum possible intensity RTmax of the received light signal and the external light intensity Ena. In other words, RRn=Δrn / ΔRmax =(RTn-Ena) / (RTmax-Ena) and this may be treated as the intensity of the received light signal.

[0024] The signal strength RT of the received light signal TS read out in time series is RT>Th1 When a period in which the signal strength RT of the received light signal TS is greater than the first threshold value Th1 is found, this period is extracted as an echo TSn (step S230). Here, n is an integer value whose initial value is 1 and is incremented every time a period in which the signal strength RT of the received light signal TS is greater than the first threshold value Th1 is found. This state is shown in column (A) of FIG. 6B. In this example, a period in which the signal strength RT of the received light signal TS is greater than the first threshold value Th1 is extracted as an echo TS1. Here, the first threshold value Th1 is set as a value greater than the external light intensity Ena corresponding to the intensity of the background light detected by the light receiving element 82. It is determined whether the peak intensity RTn of the echo TSn extracted as the signal strength RT of the received light signal TS being greater than the first threshold value Th1 is greater than a second threshold value Th2 that is predetermined as a value greater than the first threshold value Th1 (step S240).

[0025] As a result of the determination in step S240, the echo TSn is RTn>Th2 If the peak intensity RTn of the echo TSn is: RTn>Th2 If not, it cannot be said that the echo TSn is due to reflected light from the target, and it is determined that there is a possibility that it is noise, and the echo TSn is treated as a target for noise determination (step S260). After that, it is determined whether the light receiving signal TS has been read out to the end in chronological order (step S270), and if it has been read out to the end, the process goes to "NEXT" and ends this processing routine, and if it has not been read out to the end, the process returns to step S210 and the above-mentioned process of reading out the light receiving signal TS in chronological order is repeated.

[0026] Normally, if a target exists in the direction of the laser light emitted from the target recognition device 10, there is no reflected light from a target farther away than the target, so there is often only one echo due to the reflected light from the target. However, for example, during rainfall, the received light signal detected by the scanner 74 of the target recognition device 10 may contain multiple echoes TSn, such as echoes due to reflected light from raindrops and echoes due to reflected light from the target of the laser light that has passed through the raindrops. As a result, when the received light signal TS is read out to the end in chronological order, in some cases, multiple echoes TSn (four echoes TS1 to TS4 in the example shown in the figure) are extracted as a period in which the peak intensity RTn exceeds the first threshold value Th1, as shown in column (A) of FIG. 6B. Furthermore, as shown in columns (B) and (C) of the figure, echoes TS2, TS3, and TS4 have peak intensities RT2, RT3, and RT4 that exceed the second threshold value Th2, and are therefore determined not to be subject to noise judgment. On the other hand, echo TS1 has peak intensity RT1 that is between the first threshold value Th1 and the second threshold value Th2, and is therefore subject to the first noise judgment process described below, as shown in column (D) of the figure.

[0027] After the above-described two-stage threshold determination process is performed, the signal strength RTn of the echo contained in the received light signal at the scanned position and the detection distance of that echo, that is, the detection distance LTn corresponding to the time from when the light emission signal LDF is output to when the peak of the echo TSn is detected, are associated with each other and temporarily stored in the storage device 50 (step S130). The above-described process (steps S110 to S130) is repeated until the scan is completed for the entire range of the predetermined range SCA (step S100e). When the scan process is completed for the entire range of the predetermined range SCA, a noise removal process (step S300) is then performed.

[0028] (A2) Overview of noise reduction process: The noise removal process (step S300) will be described. In this embodiment, the CPU 20 that executes the noise removal process (step S300) corresponds to the noise removal device 30, but hardware corresponding to the noise removal device 30 may be prepared separately from the CPU 20. Electrical noise is also superimposed on the light receiving signal obtained from the light receiving element 82, but the noise that the noise removal device 30 of this embodiment is trying to remove is not electrical noise but clutter. Here, clutter refers to signal waveforms that are generated in the light receiving element 82 by light from the predetermined range SCA and that are unnecessary for target recognition. Various lights, including not only light reflected from the detection target OJT of the laser light emitted by the light emitting element 72 in response to the light emission signal LDF, but also background light, are incident on the light receiving element 82. For example, if it is raining, part of the laser light may be reflected by raindrops and this may enter the light receiving element 82. In addition, light (stray light) that is reflected multiple times by an object present in the predetermined range SCA may enter. Since the micro-SPAD of the photodetector 82 has the sensitivity to detect even a single photon, the received photon signal may have only one peak for the OJT to be detected, as shown in FIG. 3B (A), or it may have a waveform with multiple peaks along the time axis (B).

[0029] In terms of Fig. 3B, in Fig. 3A, the received light signal contains one echo (SS0), but in Fig. 3B, the received light signal contains five echoes, SS1 to SS5. In the latter case, a process is required to identify the echo to be eliminated as noise and identify the echo that corresponds to the detection target. This is the noise removal process.

[0030] The noise removal process (step S300) includes a first noise removal process (step S330) for removing clutter noise generated by nearby raindrops, etc., and a second noise removal process (step S340) for removing isolated point noise. In this embodiment, the first noise removal process (step S330) and the second noise removal process (step S340) are executed consecutively, but each may be executed separately. Both processes have in common that they determine whether or not the echo included in the received light signal is due to reflected light from the detection target based on the intensity of the received light signal and the detection distance. When the noise removal process (step S300) is started, the following processes (steps S320 to S340) are repeated (steps S300s to S300e) for all pixels within the predetermined range SCA stored in the storage device 50 by the scan process (step S100). First, it is determined whether or not to perform noise determination (step S320). If the target pixel includes an echo TSn that is determined to be a noise-determined echo by the above-mentioned two-stage threshold determination process (step S120), the first noise removal process (step S330) is performed on the echo TSn, and then the second noise removal process is performed. For echoes TS2 to TS4 shown in FIG. 6B that are determined to be reflected light from the detection target, the first noise removal process (step S330) is not performed, and the second noise removal process (step S340) is performed. On the other hand, if it is determined that there is an echo that should be determined to be a noise-determined echo, the first noise removal process (step S330) and the second noise removal process (step S340) are performed. It is also possible to perform the first noise removal process (step S330) and the second noise removal process (step S340) on all echoes without performing the determination in step S320.

[0031] (A3) First noise reduction process: The first noise removal process (step S330) will be described with reference to FIG. 7. The first noise removal process is a process for removing clutter noise caused by light reflected by nearby raindrops, etc. When this process is started, first, an echo TSn (n's initial value is 1) to be subjected to noise determination is identified (step S331). Next, a determination is made as to whether a detection distance LTn corresponding to the time from when the light emission signal LDF is output until the peak of the echo TSn is detected is equal to or less than a predetermined first distance threshold TL1 (step S332). If the echo TSn is a signal due to light reflected from the detection target, the detection distance LTn, which is the distance to the detection target, is calculated as follows, where tn is the time from the light emission signal LDF to the echo peak, and c / sec is the speed of light: LTn=c tn / 2 However, in signal processing, the detection distance may be treated as a time equivalent to the detection distance (hereinafter, referred to as detection time tn).

[0032] If the detection distance LTn of the echo TSn is not equal to or less than the first distance threshold TL1 (for example, about 10 m) in the determination of step S332, the echo TSn is not determined to be noise because it is far away, and the following process is not performed. On the other hand, if the detection distance LTn of the echo TSn is equal to or less than the first distance threshold TL1 (step S332: "YES"), it is determined whether or not an echo exists behind the focused echo TSn (step S333). The existence of an echo behind refers to, for example, the case where a second echo TS2, etc. exists behind the first echo TS1, which is the subject of noise determination, on the time axis, that is, far away as viewed from the target recognition device 10, as shown in FIG. 6B. In FIG. 6B, only the first echo TS1 is the subject of noise determination, but if the second echo TS2 is greater than the first threshold Th1 and less than the second threshold Th2, the second echo TS2 is the subject of noise determination, and the third echo TS3, etc. behind it are treated as echoes existing behind it.

[0033] If there is an echo that is not subject to noise judgment behind the echo TSn that is subject to noise judgment (step S333: "YES"), it is further determined whether the detection distance LTn of the echo TSn that is subject to judgment is smaller than a second distance threshold TL2 that is larger than the first distance threshold TL1 (step S334). If the result of this series of determinations (steps S332 to S334) is that the detection distance LTn of the echo TSn that is subject to noise judgment processing is closer than the first distance threshold TL1 (step S332: "YES"), there is another echo behind the echo TSn (step S333: "YES"), and the detection distance LTn of the echo TSn is smaller than the second distance threshold TL2 (step S334: "YES"), the echo TSn is removed as noise (step S338).

[0034] On the other hand, even if the judgment in either step S333 or S334 is not "YES", the echo TSn is similarly determined to be noise and is removed in step S338 in the following cases. The judgment process is performed as follows. That is, if the detection distance LTn of the echo TSn that is the target of the noise judgment process is closer than the first distance threshold TL1 (step S332: "YES") and there is no further echo behind the echo TSn (step S333: "NO"), the noise judgment threshold TR is set to a small threshold TrS (step S350), and on the other hand, even if there is a further echo behind the echo TSn (step S333: "YES"), if the detection distance LTn of the echo TSn is not smaller than the second distance threshold TL2 (step S334: "NO"), the noise judgment threshold TR is set to a large threshold TrL that is larger than the small threshold TrS (step S360). Then, it is determined whether the peak intensity RTn of the echo TSn that is the subject of the noise determination is equal to or less than the noise determination threshold TR (step S337), and if the peak intensity RTn of the echo TSn of interest is equal to or less than the noise determination threshold TR (step S337: "YES"), the echo TSn is removed as noise (step S338). The method of determining the large threshold TrL and the small threshold TrS used in this determination will be described in detail later.

[0035] In cases other than the above, that is, when the detection distance LTn of the echo TSn is not within the first distance threshold TL1 (step S332: "NO"), or when the peak intensity RTn of the focused echo TSn is not equal to or less than the noise determination threshold TR (step S337: "NO"), the echo TSn is deemed not to be noise, and the process proceeds to step S339. In step S339, if all the determinations for the extracted echo TSn have not been completed, the process returns to step S331 and the above-mentioned process (steps S331 to S338) is repeated, and if all the determinations for the extracted echo TSn have been completed, the noise removal process ends.

[0036] The above-described process determines that echoes TSn generated by light reflected by raindrops are clutter noise, and that echoes TSn generated by light reflected from a detection target such as a black vehicle are not noise. This utilizes the fact that light reflected by raindrops and the like and light reflected from a detection target have the characteristics described below. The first distance threshold TL1, the second distance threshold TL2, the small threshold TrS, and the large threshold TrL used in the above process are set based on the characteristics of the reflected light. FIG. 8 is an explanatory diagram showing the relationship between the distance LT from the target recognition device 10, that is, the vehicle 100, and the signal strength RT of the received light signal. The graphs RNav, RNav+σ, RNav+2σ, and RNav+3σ shown in FIG. 8 show the distribution range of the reflected signal from raindrops, which is the cause of the noise to be removed in the noise removal process. The graphs BCav, BCav-σ, and BCav-2σ show the distribution range of the reflected signal from a black vehicle, which is an example of a detection target that may be difficult to detect visually at night, rather than being noise.

[0037] Here, "σ" in each graph is the standard deviation in the intensity distribution of the reflected light from the raindrops or the black vehicle. The intensity of the reflected light from the raindrops is not uniform even if the distance to the raindrops is constant, but varies depending on the size of the raindrops and the positional relationship between the laser light emitted from the light emitting element 72 and the raindrops, but statistically it can be regarded as a distribution within a certain range. The graph RNav indicates the upper limit of the range in which the reflected light from the raindrops is distributed up to the average value. Similarly, the graph RNav+3σ indicates the upper limit of the distribution range of the reflected light up to three times the standard deviation σ. In other words, if the distribution of the reflected light from the raindrops is a normal distribution, the probability that the intensity of the reflected light falls within the range with the graph RNav+σ as the upper limit is about 67%, the probability that the intensity of the reflected light falls within the range with the graph RNav+2σ as the upper limit is about 95%, and the probability that the intensity of the reflected light falls within the range with the graph RNav+3σ as the upper limit is about 99.7%.

[0038] The intensity of reflected light from a detection target such as a black vehicle can be statistically seen as a distribution within a certain range, but since the detection target is an object to be detected, it is necessary to take into consideration the distribution on the side where the intensity of reflected light is weak. In order to correctly detect even weak reflected light from a detection target such as a black vehicle, we considered what kind of distribution the reflected light with low signal intensity from the detection target takes. The graph BCav in FIG. 8 indicates the lower limit of the range in which the reflected light from the detection target is distributed up to the average reflected light intensity. Similarly, the graph BCav+2σ indicates the lower limit of the distribution range of reflected light up to twice the standard deviation σ on the lower side of the reflected light intensity. In other words, if the distribution of reflected light from the detection target is a normal distribution, the probability that the intensity of reflected light falls within the range with the graph BCav+σ as the lower limit is about 67%, and the probability that the intensity of reflected light falls within the range with the graph BCav+2σ as the lower limit is about 95%. Although not shown in FIG. 8, if the range with the graph BCav+3σ as the lower limit is considered, the probability that the intensity of reflected light from the detection target falls within this range is about 99.7%.

[0039] For signals that should be removed as noise, such as light reflected by raindrops, the distribution of the high signal strength side of the variation in the reflected light from raindrops is considered, while for signals that should be treated as detection targets, such as black vehicles, the distribution of the low signal strength side is considered, and conditions for separating the two were considered. As illustrated in FIG. 8, the intensity distribution of the reflected light from raindrops that should be determined as noise rapidly narrows its appearance range as the distance LT from the vehicle 100 increases, and at a certain distance or more, it becomes equal to or less than a constant signal strength RT. On the other hand, the signal strength RT of the reflected light from a detection target that should not be determined as noise expands its appearance range to the high side of the signal strength RT as the distance LT from the vehicle 100 decreases. Therefore, the first distance threshold TL1 and the second distance threshold TL2 are set as the upper and lower distances of the range in which the distribution range of the intensity of the received light signal caused by reflection from raindrops and the distribution range of the intensity signal caused by reflection from the detection target can be distinguished by the magnitude of the signal strength RT, as shown in the figure. For example, the second distance threshold TL2 can be assumed to be about 2 to 4 m, and the first distance threshold TL1 can be assumed to be about 8 to 10 m, and these can be determined by experiments or simulations. On the other hand, the small threshold TrS and the large threshold TrL are thresholds for distinguishing the distribution range of the intensity signal caused by the reflection by raindrops from the distribution range of the intensity signal caused by the reflection by the detection target, and when an echo TSn exists in the rear, the large threshold TrL is set to a value higher than the graph RNav+3σ when the distance LT is between the second threshold Th2 and the first threshold Th1, so that the echo TSn caused by the reflected light from the raindrops is reliably determined to be noise. Also, when there is no echo TSn in the rear, the small threshold TrS is set to a value approximately equal to the graph RNav+3σ when the distance LT is between the second threshold Th2 and the first threshold Th1, so that the echo TSn is less likely to be erroneously determined to be noise. As an example, Condition 1: The target echo TSn is closer than the second distance threshold TL2 and there is no echo behind it, or the target echo TSn is between the second distance threshold TL2 and the first distance threshold TL1 and there is no echo behind it. The small threshold TrS is determined to be a value large enough to distinguish between the distribution of signals from raindrops (RNav+2σ) and the distribution of signals from black vehicles (BCav-2σ). Condition 2: The target echo TSn is between the second distance threshold TL2 and the first distance threshold TL1, and there is an echo behind it. The large threshold TrL is determined to be a value that allows the distribution of signals from raindrops, RNav+3σ, and the distribution of signals from black vehicles, BCav-2σ, to be distinguished from each other.

[0040] As a result, the echo TSn is determined as follows: [1] If the distance from the vehicle 100 is equal to or greater than a first distance threshold TL1 (e.g., 10 m), the echo TSn is determined not to be noise and is not removed (step S332). [2] If the distance from the vehicle 100 is smaller than the first distance threshold TL1 and equal to or greater than the second distance threshold TL2, the echo is compared with a threshold (small threshold TrS or large threshold TrL) that varies depending on whether or not there is an echo behind. If the echo is smaller than the threshold, it is determined to be noise and is removed (steps S332 to S338). If the echo is larger than the threshold, it is determined not to be noise and is not removed (steps S332 to S337). [3] If there is an echo behind the vehicle 100 and the distance from the vehicle 100 is less than the second distance threshold TL2, the echo TSn is determined to be noise and is removed (steps S332, S333, S334, S338). [4] If there is no echo behind and the distance from vehicle 100 is less than the second distance threshold TL2, it is compared with the small threshold TrS (steps S332, S333, S335, S337). If it is less than the threshold, it is determined to be noise and removed (step S338). If it is greater than the small threshold TrS, it is determined not to be noise and is not removed (steps S337, S339).

[0041] As a result, the reflected light from raindrops in the vicinity of the vehicle 100 (within the second threshold Th2) is removed as noise if there is no echo behind, and if there is an echo behind, whether it is removed as noise or not is determined by the magnitude of the small threshold TrS, and the echo TSn from a range a predetermined distance away from the vehicle 100 (from the second threshold Th2 to the first threshold Th1) is correctly discriminated as noise or reflected light from the detection target by the small threshold TrS and the large threshold TrL. In the above embodiment, the small threshold TrS and the large threshold TrL are constant regardless of the distance LT from the vehicle 100, but as shown in FIG. 9, they may be set as values ​​that gradually decrease as the distance LT increases. This is because the reflection intensity from raindrops is small enough to be distinguished from the reflection intensity from the detection target at or above the second threshold Th2, but tends to decrease according to the distance LT. In this way, the discrimination accuracy of noise can be further improved when the detection distance LTn corresponding to the echo TSn is equal to or greater than the second threshold Th2 and less than the first threshold Th1. Although not shown in the figure, when it is not raining, the distribution of reflected light in the area below the second distance threshold TL2 is not significantly different from the distribution between the second distance threshold TL2 and the first distance threshold TL1, and the noise distribution is only slightly wider toward the higher intensity side. Therefore, when it is not raining, clutter noise is hardly generated, and noise can be removed by the above-mentioned algorithm (Figure 7). In the above judgment, the small threshold TrS and the large threshold TrL are determined based on the intensity distribution of reflected light from raindrops and the intensity distribution of reflected light from a black vehicle. It is assumed that signals from any reflected light fall into the respective distribution ranges with a certain probability, and in reality, there may be cases where exceptionally large reflected signals are brought about by raindrops. When there is such an exceptionally large echo, it may be judged not to be noise according to the judgment shown in Figure 7, but such echoes become isolated points, and are removed as noise by the second noise removal process described below.

[0042] (A4) Second noise reduction process: Next, the second noise removal process (step S340) performed following the first noise removal process (FIG. 4, step S330) will be described. The second noise removal process is a process for removing an echo TSn as noise if it is from an isolated point. Note that even if the echo TSn is determined not to be the target of the first noise removal process (step S320: "NO"), or if the echo TSn is determined to be from a point farther away than the first threshold Th1 in the first noise removal process illustrated in FIG. 7 and treated as being due to reflected light from a detection target (step S332: "NO"), it is removed as noise if it is determined to be an isolated point by this second noise removal process (step S340). If it is determined not to be an isolated point by the second noise removal process, it is finally treated as reflected light from a target.

[0043] An example of the second noise removal process will be described with reference to the flowchart of Fig. 10. In the second noise removal process, the upper left corner of the predetermined range SCA scanned by the target recognition device 10 is set as the origin, and the following processes (steps S410 to S490) are sequentially performed for all pixels belonging to the predetermined range SCA. The pixel being processed is called the target point N (initial value 1). When this process is started, first, data stored in the storage device 50 for the pixel corresponding to the target point N is read out, and the peak intensity RTn of the reflected light from the pixel corresponding to the target point N is identified (step S410). This peak intensity RTn is the signal intensity of the echo TSn that was not determined to be noise.

[0044] Next, it is determined whether the peak intensity RTn of the reflected light of the target point N is equal to or less than a third threshold Th3 (step S420). The third threshold Th3 is set as a threshold value that is, for example, greater than the second threshold Th2 and is a level at which it is determined whether the reflected light should be treated as significant even if it is an isolated point. If the peak intensity RTn of the echo TSn is equal to or less than the third threshold Th3 (step S420: "YES"), it is determined whether the target point N is an isolated point, and the following process is performed. First, the detection distance LTn to the target point N that is the object being determined is obtained (step S430). Next, a nearby point corresponding to ±m pixels above and below the pixel of the target point N is searched for (step S440).

[0045] The neighboring points above and below a pixel refer to the above and below of a predetermined range SCA in FIG. 1. If reflected light from the road surface is detected as shown in FIG. 11, the neighboring points are near and far from the viewpoint of the vehicle 100. Of course, if reflected light from the ceiling of a tunnel is detected, the neighboring points are near and far from the viewpoint of the vehicle 100. FIG. 11 shows an example in which four neighboring points, −2, −1, +1, and +2, are found in the vertical direction as neighboring points of the target point N. In step S440, the neighboring points in the vertical direction are searched for, but the neighboring points in the horizontal direction (X-axis direction in FIG. 1) may also be searched for. Of course, the search is not limited to one of the X-axis direction and the Z-axis direction, and the search may be for neighboring points in any direction in the XZ plane. The search direction is not limited to one, and multiple searches may also be performed. Moreover, m may be a value of 1 or a value of 3 or more. Moreover, instead of ±m from the target point, m may be in a specific direction from the target point.

[0046] After searching for ±m neighboring points of the pixel of the target point N, it is then determined whether the change in distance between the target point and the neighboring points arranged vertically is a monotonous increase or decrease (step S450). If the change is monotonous (step S450: "YES"), the distance threshold ΔLh is set to a first distance threshold LL (step S460), and if the change is not monotonous (step S450: "NO"), the distance threshold ΔLh is set to a second distance threshold LS smaller than the first distance threshold (step S465). This distance threshold ΔLh is referred to in the subsequent counting process of predetermined neighboring points (step S600).

[0047] The details of the counting process of the predetermined adjacent points (step S600) will be described with reference to the flowchart of FIG. 12. In this process, after initializing the value of the counter CNT to 0 (step S605), the process is repeated m-1 times while decrementing the variable m indicating the adjacent point (steps S610s to S610e). In this embodiment, the process from step S620 to S640 is repeated for m=2, 1, -1, -2. First, the distance difference DLm between the target point N and the adjacent point N+m is calculated (step S620). FIG. 11 shows an example of the distance difference DLm between the target point N and the adjacent point N+1. Next, it is determined whether or not this distance difference DLm is equal to or less than the distance threshold ΔLh set in the previous process (step S460 or S465) (step S630), and if the distance difference DLm is equal to or less than the distance threshold ΔLh, it is determined that the two are adjacent to each other, and the counter CNT is incremented by 1 (step S640). If the distance difference DLm is greater than the distance threshold ΔLh, the counter CNT is not incremented.

[0048] The above process is repeated by changing the variable m, and after making a judgment for all variables m and making a process of incrementing or not incrementing the counter, the process exits to "NEXT" and ends this processing routine. Then, returning to the second noise removal process shown in Fig. 10, it is judged whether the value of the counter CNT is equal to or less than a predetermined score threshold Thc (step S470), and if the value of the counter CNT is equal to or less than the score threshold Thc, the target point N is removed as noise (step S480). On the other hand, if the value of the counter CNT is greater than the score threshold Thc (step S470: "NO"), the target point N cannot be judged as noise, and nothing is done.

[0049] When the peak intensity RTn of the echo TSn is judged to be equal to or greater than the third threshold Th3 (step S420: "YES"), or when the target point is removed as noise (step S480) or when the value of the counter CNT is greater than the point threshold Thc (step S470: "NO"), the process proceeds to step S490, where it is judged whether the second noise removal process for removing isolated points is completed for all pixels in the predetermined range SCA (step S490), and the above-mentioned processes from step S410 to S490 are repeated until the process is completed. When the second noise removal process is completed for all pixels, the process goes to "NEXT" and ends.

[0050] In this way, if the distance to the nearby points existing in the vicinity of the target point N increases or decreases monotonically, the points are counted as nearby points even if the distance difference to the nearby points is large. On the other hand, if the distance to the nearby points existing in the vicinity of the target point N does not increase or decrease monotonically, only the points with a small distance difference to the nearby points are counted as nearby points. As a result, it becomes possible to take into consideration the presence of targets that tend to be a series of points continuing in a predetermined direction, such as a road surface or a wall, in determining isolated points. The score threshold Thc used in the determination in the above step S470 may be a uniform value or a value according to the distance. The value according to the distance may be a value that is smaller as the distance to the target point N increases. The score threshold may be a function of the distance, or may be switched between multiple levels, such as two or three levels, before and after a predetermined distance. The magnitude of the score threshold may be all points (2·m if m=2), or may be a value that is about 80% of that.

[0051] Thereafter, the points that are determined to have reflected light, excluding those that are removed as noise, are subjected to the target recognition process (step S500) shown in Fig. 4. In the target recognition process, first, the detection distance LTn to the target point N is calculated based on the timing of detection of reflected light at each target point N, or if it has already been calculated and stored in the storage device 50, it is read out, and the detection target OJT is recognized from the distance to the target point N. Specifically, target recognition such as extraction of the road surface, recognition of white lines, or clustering and tracking of targets is performed using the detection point from which noise has been removed and nearby points.

[0052] According to the noise removal device 30 of the first embodiment described above, clutter noise caused by raindrops, dust, etc. can be removed using the echo intensity and detection distance. In addition, instead of simply removing isolated points that have a different detection distance from surrounding points, points in a specific arrangement relationship are not considered to be noise, so that flexible decisions can be made such as removing isolated points that are not targets as noise while not removing white lines, etc. As a result, raindrops during rainfall can be distinguished from detection target OJT such as black-painted vehicles, reducing the possibility of overlooking the detection target OJT.

[0053] B. Second embodiment: A schematic configuration of a target recognition device 10A equipped with a noise removal device 30 of the second embodiment is shown in Fig. 13. As shown in the figure, this target recognition device 10A has a configuration almost similar to that of the target recognition device 10 of the first embodiment, but differs in that the internal processing of the noise removal device 30A is different, various sensors that detect environmental conditions for the processing are provided, and a calibration unit for calibrating the light receiving unit 80 is further provided.

[0054] In the second embodiment, a condition setting unit 121 is provided inside the CPU 20. The condition setting unit 121 is realized by the CPU 20 executing a program described later, similar to the noise removal device 30A and the like. The condition setting unit 121 is connected to an illuminance sensor 111 for detecting environmental conditions, a weather sensor 112, a time detector 113, and the like. The illuminance sensor 111 detects the brightness (illuminance) of the environment of the target recognition device 10A. The illuminance may be detected as an analog value, or may be detected as an index indicating multiple stages such as "bright", "dim", "dark", and "completely dark".

[0055] The weather sensor 112 is a sensor that detects weather conditions such as "sunny", "cloudy", "rainy", etc. The weather sensor 112 may be realized by combining sensors that detect illuminance and raindrops, etc., or may acquire weather conditions by wirelessly connecting to a site that detects local weather conditions and provides them on request. The time detector 113 can be easily realized by a real-time clock, etc., but may also be configured to acquire time information included in an external reference clock, for example, a GPS, or a radio-controlled clock.

[0056] In the embodiment, the following description will be given assuming that these three sensors are provided, but the number of sensors may be one or two. In addition, other necessary sensors that detect the environment in which the vehicle 100 is placed, such as a humidity sensor, a wind speed sensor, a snowfall detector, a fog or gas detector, a sensor that detects the flooding of the road surface by reflected light, etc., may also be provided.

[0057] The operation of the condition setting unit 121 will be described. Fig. 14A is a flowchart showing a correction coefficient acquisition processing routine realized by the condition setting unit 121. As will be described later, the condition setting unit 121 acquires a correction coefficient from an environmental condition, and modifies a judgment condition for noise removal in the noise removal device 30A using the correction coefficient.

[0058] When the illustrated correction coefficient acquisition process is started, first, parameters are acquired from the various sensors 111 to 113 connected to the condition setting unit 121 (step S710). The parameters are illuminance B if the illuminance sensor 111 is used, meteorological information M if the weather sensor 112 is used, and time T if the time detector 113 is used. After the parameters are acquired, a process is performed to acquire the correction coefficient by referring to a map (step S720). The concept of the map to be referred to is shown in FIG. 14B. The illustrated map is conceptual, and the relationship between the actual parameters and the correction coefficient may be determined experimentally or empirically.

[0059] In this example, multiple correction coefficients a1, a2, b1, b2, c1, and c2 are acquired for illuminance M, weather M, and time T. The significance and use of the correction coefficients will be described later, but it is not necessary to acquire all the correction coefficients, and only some of the correction coefficients may be acquired using the map. In the example shown in the figure, the lower the illuminance B, the larger the correction coefficient value, the higher the illuminance B, the smaller the correction coefficient value, the closer the weather M is to the rainy side, the larger the correction coefficient value, the closer the weather M is to the sunny side, the larger the correction coefficient value is, and the closer the time T is to night (0:00 in 24-hour notation), the smaller the correction coefficient value is. In this example, the correction coefficient value for each parameter is shown in an analog manner, but the correction coefficient may be a map that takes a constant value for a predetermined range of the parameter. When multiple parameters are used, multiple correction coefficients are obtained corresponding to the parameters, and the smallest value of the multiple correction coefficients may be used. In this way, the correction coefficient can be set according to the most influential condition. Of course, it is also possible to use the average value, and when the correction coefficient is 3 or more, it is also possible to use the median value.

[0060] Next, the application of the correction coefficient will be described. FIG. 15 is a flowchart showing a processing routine in the second embodiment corresponding to the two-stage threshold judgment process shown in FIG. 5 of the first embodiment. Each step corresponds to FIG. 5, and is the same except for steps S220a and S240a with the suffix a. In step S220a, the first threshold Th1 is multiplied by the correction coefficient a1, and in step S240a, the second threshold Th2 is multiplied by the correction coefficient a2, which is different from the first embodiment. For this reason, for example, when the illuminance B is high, when the weather M is fine, or when the time T is daytime, the correction coefficients a1 and a2 are smaller than 1.0. As a result, the signal strength range (see FIG. 6B) for determining that an echo with a signal strength RT is treated as a target for noise judgment (step S260) is set to a low strength range. Note that the correction coefficients a1 and a2 do not need to be the same value, and the set signal strength range (Th1 to Th2) can be widened or narrowed. Alternatively, only one of the correction coefficients a1 and a2 may be determined based on the illuminance B, etc., and the other may remain a fixed value. In any case, the range of whether or not to treat as a target for noise determination can be freely set based on parameters such as the illuminance B, weather M, and time T. Of course, the correction coefficients a1 and a2 may be set using one or two of the illuminance B, weather M, and time T.

[0061] In this manner, the same effect as in the first embodiment of narrowing down the targets for noise judgment using a two-stage threshold can be achieved, and the noise judgment process (step S260) can more appropriately determine whether or not the detected echo should be subject to noise judgment in accordance with the environment in which the target recognition device 10A is located.

[0062] Similarly, the first distance threshold TL1, the second distance threshold TL2, the small threshold TrS, and the large threshold TrL in the first noise removal process can be corrected by the illuminance B, the weather M, the time T, and the like. This example is shown in FIG. 16. FIG. 16 is a flowchart showing a processing routine in the second embodiment corresponding to the first noise removal process shown in FIG. 7 of the first embodiment. Each step corresponds to FIG. 7, and is the same except for steps S332b, S334b, S335b, and S336b with the suffix b. This differs from the first embodiment in that in step S332b, the first distance threshold TL1 is multiplied by a correction coefficient b1, in step S334b, the second distance threshold TL2 is multiplied by a correction coefficient b2, in step S335b, the small threshold TrS is multiplied by a correction coefficient c1, and in step S336b, the large threshold TrS is multiplied by a correction coefficient c2.

[0063] Similar to the correction coefficients a1 and a2 in the two-stage threshold judgment process (FIG. 15), these correction coefficients b1, b2, c1, and c2 are set by parameters such as illuminance B, weather M, and time T. Also, it is not necessary to set all correction coefficients, and various settings are possible, similar to the two-stage threshold judgment process (FIG. 15), regarding which of illuminance B, weather M, and time T to use, how to set them when multiple are used, and the magnitude relationship between parameters such as illuminance B and correction coefficient b1, etc.

[0064] An example of how noise determination is performed by the process shown in FIG. 16 is shown in FIG. 17. The upper part of the figure shows the case of rainy weather, and the lower part shows the case of fine weather. In the table shown in FIG. 14B, the correction coefficient b1 is set to a value close to 1.0 in the case of rainy weather, and is set to a smaller value in the case of fine weather. For this reason, the threshold value b1×TL1 used for determination in step S332b is set to the dashed line rr1 in the case of rainy weather, and to the lower dashed line ss1 in the case of fine weather. As a result, assuming a case in which the echoes TSS2, TSS3, and TSS1 are included in the signal in descending order of magnitude, in rainy weather, the threshold value is set high, so that clutter noise TSS3 due to raindrops is removed, and in fine weather, the threshold value is set relatively low, so that the echo TSS3 from the target can be detected.

[0065] In this way, by correcting the first distance threshold TL1, the second distance threshold TL2, the small threshold TrS and the large threshold TrL in the first noise removal process using parameters such as illuminance B, weather M, and time T as parameters, using Table 2, an example of which is shown in Figure 14B, it is possible to achieve the same effect as in the first embodiment according to the environment in which the target recognition device 10A is placed, and furthermore, to perform even more appropriate noise removal.

[0066] C. Third embodiment: Next, a third embodiment will be described. As shown in FIG. 18, a target recognition device 10B of the third embodiment is provided in a vehicle 100B. This target recognition device 10B has a configuration similar to that of the target recognition device 10 of the first embodiment, and is different in that it includes a calibration unit 130 and an instruction unit 131, and that the processing in the noise elimination device 30B includes a calibration process described later. In this embodiment, when the instruction unit 131 receives an instruction from a user and outputs an instruction to perform the calibration process, the calibration unit 130 causes the noise elimination device 30B to perform the calibration process, and drives the light emitting unit 70 via the input / output interface 60 for the calibration process. The calibration process will be described below.

[0067] 19 is a flow chart showing a noise level calibration process routine. In this process, when an echo of a predetermined intensity or more exists, that is, when it is determined that the signal is not noise, a judgment condition is set by the characteristics of a measurement unit that measures the signal in the noise removal device, here the light receiving unit 80. Prior to carrying out the illustrated process, the user of the vehicle 100B parks the vehicle 100 in a place where the calibration plate CAL is grounded, such as a garage. The calibration plate CAL is for calibrating the characteristics of the light emitting unit 70 and the light receiving unit 80, and is a plate that is painted uniformly in a color with high reflectivity, for example, white. The user of the vehicle 100B places such a calibration plate CAL on a wall or the like in a parking lot.

[0068] When the illustrated noise level calibration process is started, first, it is determined whether or not a calibration command has been input (step S751). When the user operates the command unit 131, the noise removal device 30B determines that a calibration command has been input, and executes the measurement process (step S752). Specifically, a laser pulse is output within a measurable range using the light-emitting unit 70, and the measurement unit 31 detects the reflected light using the light-receiving unit 80. When the vehicle 100B is stopped at a position where the front of the vehicle 100B faces the CAL, the command unit 131 is operated, and the measurement process is performed, the light received by the light-receiving unit 80 is reflected light from the uniform white calibration plate CAL, and therefore comes from a fixed distance.

[0069] Therefore, focusing on this point, it is judged whether reflected light from the calibration plate CAL is detected (step S753). If the detected object is from a uniform distance, it is judged to be the calibration plate CAL, and if it is not from a uniform distance, it is judged not to be the calibration plate CAL. If it is judged to be the calibration plate CAL, the entire area is scanned (step S754). If reflected light from the calibration plate CAL is detected, total reflection by a uniform white light at a uniform distance is detected, so if the intensity of the laser light pulse emitted from the light-emitting unit 70 is constant regardless of the scanning position and the sensitivity of light reception by the light-receiving unit 80 is constant regardless of the light-receiving position, a uniform image should be obtained. An image obtained under such ideal conditions is shown in the upper part of FIG. 20.

[0070] On the other hand, the image actually obtained is an uneven image as shown in the lower part of the figure. This is because the intensity of the laser light pulse emitted from the light emitting unit 70 is not uniform depending on the scanning position, and the sensitivity of the light receiving unit 80 to receive the light may differ depending on the light receiving position. This is not due to raindrops or the like, but clutter caused by hardware, and does not change every time a measurement is made, and is reproducible. Even if the sensitivity of each light receiving element is adjusted so that there is no such clutter at the time of shipment, clutter may occur due to aging or the like. Therefore, the content of the clutter is next determined to determine whether it is clutter caused by hardware (step S760), and if it is determined to be clutter caused by hardware (step S755: "YES"), a calibration value CRTn is set (step S756), and this routine ends.

[0071] The calibration value CRTn is a threshold value set corresponding to the scan position, and when determining the peak intensity RTn of the reflected light, is used to subtract the calibration value CRTn from the peak intensity RTn of the echo TSn detected by the light-receiving unit 80. The peak intensity RTn of the echo TSn in the two-stage threshold determination process (FIGS. 5 and 15), the first noise removal process (FIGS. 7 and 16), and the second noise removal process (FIG. 10) is a value obtained by subtracting the calibration value CRTn from the peak intensity RTn detected by the light-receiving unit 80.

[0072] This makes it possible to eliminate or reduce the influence of clutter caused by uneven sensitivity of hardware in the light receiving unit 80, etc. Such calibration processing may be performed when the vehicle 100B or the target object recognition device 10B is shipped from the factory, or may be performed at the time of vehicle inspection, etc. Also, a calibration plate CAL may be provided as an accessory, and the user may install the calibration plate CAL on the parking lot and perform the calibration processing periodically or at any timing.

[0073] In the above embodiment, the calibration value CRTn is set to detect the location where clutter occurs and reduce its influence. However, if it is known that the emission intensity of the light-emitting unit 70 near the left and right ends of the measurement range is low as a characteristic of the light-emitting unit 70 or the light-receiving unit 80, the calibration value CRTn near the left and right ends of the measurement range may be set to a small value or a negative value without measurement. In this way, the decrease in detection sensitivity near the left and right ends of the measurement range can be eliminated. Such correction is not limited to the left and right ends, but may be performed at a location required by the characteristics of the light-emitting unit 70 or the light-receiving unit 80. In the above embodiment, the sensitivity is corrected by setting the calibration value CRTn and subtracting it from the peak intensity RTn of the detected echo TSn. However, the first and second threshold values ​​Th1 and Th2 to be compared when detecting the echo may be corrected according to the intensity of the clutter or the location of the measurement range.

[0074] D: Fourth embodiment: Next, a fourth embodiment will be described. The target recognition device 10 and the noise removal device 30 of the fourth embodiment have the same hardware configuration as those of the first embodiment, and only a part of the process performed by the noise removal device 30 is different. In the first embodiment, a two-stage threshold determination process (FIG. 5) is used to determine whether an echo TSn included in a received light signal is treated as a reflected signal from a target rather than as noise (step S250), or whether it is to be determined whether it is noise or not (step S260). In the fourth embodiment, the following process is additionally performed in order to reduce the echoes TSn to be determined whether they are noise or not.

[0075] The noise determination process routine additionally performed by the noise removal device 30 is shown in the flowchart of FIG. 21. The process shown in FIG. 21 corresponds to the process of step S260 in FIG. 5, that is, the process of "treating as a target for noise determination." As shown in FIG. 5, the two-stage threshold determination process determines that an echo TSn whose peak intensity RTn is greater than the first threshold Th1 and less than the second threshold Th2 is to be a target for noise determination (step S260). More specifically, as shown in FIG. 21, after confirming that it is a target for noise determination (step S261: "YES"), the noise removal device 30 performs a process of narrowing the read range of the signal from the light receiving unit 80, that is, the detection target region ROI of the echo TSn (step S262). In this embodiment, the process of narrowing the detection target region ROI is performed by narrowing the range in which the measurement unit 31 of the noise removal device 30 reads out the light receiving signal from the light receiving unit 80. The process of narrowing the detection target region ROI can also be achieved by directly controlling the light emitting unit 70 and the light receiving unit 80 by hardware.

[0076] After narrowing the detection target region ROI, the noise removal device 30 performs a process of detecting the echo TSn again (step S263). This state is shown in FIG. 22. The upper part of the figure shows an example of detection in a normal state before narrowing the detection target region ROI. The detection target region ROI is the maximum range ROI1 in the light receiving section 80, and at this time, the dynamic range of detection is wide and there is a lot of noise. There are four apparent echoes TSa, TSb, TSc, and TSd. Of these echoes, echoes TSb and TSd are the echoes that are treated as targets for noise judgment by the two-stage threshold judgment process shown in FIG. 5.

[0077] In response to this determination, the detection target region ROI is narrowed to ROI2 in step S262 and detection is performed again. As a result, the dynamic range is reduced due to the narrowing of the detection range, as shown in the lower part of Fig. 22, and the echoes TSb and TSd disappear. In such a case, the determination in step S264 is "YES", that is, it can be determined that the noise has disappeared, so it is determined that there is no noise (step S265). On the other hand, if the noise has not disappeared, it is determined that the echoes TSb and TSd may be noise (step S266). Thereafter, a process is performed to return the detection target region ROI to its original state (step S267), and this routine ends.

[0078] In the fourth embodiment described above, by switching the size of the detection target area ROI when detecting an echo between wide and narrow, and switching the dynamic range between large and small, it is possible to realize both a wide detection target area ROI and noise removal. As a result, it is possible to reduce the number of objects to be judged as being noise or not, and to shorten the time required for processing.

[0079] In this embodiment, when an echo to be subjected to noise judgment is found after the two-stage threshold judgment process, the detection target area ROI is switched to a narrow range and noise is removed if it is noise. However, noise removal by narrowing the detection target area ROI may be performed before the two-stage judgment. In addition, the detection target area ROI may be switched to a wide range each time a measurement is performed, and detections in a wide detection target area ROI and a narrow detection target area ROI may be performed in pairs to achieve both noise reduction and a wide detection target area ROI. Except for the above points, the target recognition device 10 and the noise removal device 30 of this embodiment have the same effects as those of the first embodiment.

[0080] E. Other embodiments: (1) The following embodiment is also possible as a noise removal device that removes noise generated when recognizing a detection target using light reflection. This noise removal device includes a measurement unit that measures the intensity of arriving light that arrives from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light, a determination unit that, when an echo of a predetermined intensity or more is present in the measured arriving light, determines whether the echo is reflected by a detection target present in the predetermined range using the intensity of the echo and a detection distance that is a distance corresponding to the elapsed time, and a removal unit that removes the echo that is determined not to be reflected by the detection target as noise. In this way, since the determination is made using the intensity of the echo and the detection distance that is a distance corresponding to the elapsed time, it is possible to increase the accuracy of noise removal without simply determining that an echo with a weak intensity is noise. Here, as a process, instead of using the detection distance, the determination may be made using an elapsed time equivalent to the detection distance. When using the echo intensity and the detection distance, which is a distance corresponding to the elapsed time, to determine whether an echo has been reflected by a detection target present within a specified range, a judgment may be made combining the echo intensity and the detection distance to determine whether it is noise or not, or both may be mapped in advance and the map may be referred to using the echo intensity and detection distance to determine whether it is noise or not.

[0081] This device may be used alone for noise removal, or the signal after noise removal may be output to a target recognition device and used for target recognition. The light irradiated to the predetermined range may be laser light or infrared light from a light emitting diode or the like. Irradiation of the predetermined range may be performed by scanning the predetermined range with light from a point light source, and the scanning may be performed in a two-dimensional direction. Also, a plurality of light emitting units that emit light may be arranged in one direction, and one-dimensional scanning may be performed in a direction intersecting this direction to detect the intensity of the light arriving from within the predetermined range. Furthermore, a large number of light emitting units may be arranged two-dimensionally, and the light arriving from the predetermined range may be detected by one irradiation.

[0082] (2) In such a configuration, the determination unit may determine that the first echo is not reflected by a detection object present in the predetermined range when the arriving light measured by the measurement unit includes a first echo and a second echo having a longer elapsed time than the first echo, and the first echo is from within a predetermined first distance range. In this way, when a single arriving light includes multiple echoes, and the first echo and the second echo having a longer elapsed time than the first echo are from within the predetermined first distance range, it can be determined that the first echo is not reflected by a detection object present in the predetermined range. When the arriving light from a direction corresponding to one emission direction includes multiple echoes, reflections by raindrops and reflections of light that has passed through raindrops are assumed, so that if the first echo, which is the closer echo, is from within the predetermined first distance range, the first echo is determined to be noise. The first distance range is not uniform depending on the location where the noise removal device is used, but can be a range of several meters when mounted on a vehicle, for example. Of course, when a radar dome or the like is installed and used to detect a long-distance target, the range may be about 10 meters or more. The first echo does not have to be the first of multiple echoes, and if there are three or more echoes, the second echo may be the first echo and the third echo may be the second echo for the above judgment. This also applies to the following configurations.

[0083] (3) In the configuration of (1) or (2) above, the determination unit may be configured to compare the intensity of the first echo with a predetermined intensity threshold of a first value when the measurement unit detects a first echo and a second echo having a longer elapsed time than the first echo as the echoes contained in the arriving light, and to compare the intensity of the first echo with an intensity threshold of a second value smaller than the first value when the measurement unit does not detect a second echo having a longer elapsed time than the first echo as the echoes contained in the arriving light, and to determine that the first echo is not reflected by a detection target present in the predetermined range when the intensity of the first echo is smaller than the intensity threshold. In this way, the magnitude of the intensity threshold for comparing the intensity of the first echo is changed depending on whether or not there is a second echo behind the first echo, thereby improving the accuracy of determining that the first echo is not reflected by a detection target. If there is a second echo behind, there is a high possibility that the first echo is due to reflected light from raindrops or the like, so by comparing the intensity of the first echo with a first value that is greater than the second value set as the intensity threshold when there is no echo behind, the possibility of determining that the light is not reflected from the detection target is increased. The first and second values ​​set as the intensity threshold may be preset values, or the second value may be determined as a ratio, such as 80% of the first value. Also, the second value may be changed according to the intensity of the background light or the like.

[0084] (4) In the configurations (1) to (3) above, the measurement unit detects, as the echo, an echo included in the arriving light from a target point that is one point in the predetermined range and an echo included in the arriving light from at least two nearby points that are close to the target point, and the judgment unit may be configured to judge that the echo included in the arriving light from the target point is not reflected by a detection target present in the predetermined range when the number of nearby points, which is the number of nearby points where the distance difference corresponding to the difference between the elapsed time of the echo included in the arriving light from the target point and the elapsed time of the echo included in the arriving light at the nearby point is equal to or less than a predetermined distance threshold, is equal to or less than a predetermined point number threshold. In this way, it is possible to accurately determine whether the target point of interest is an isolated point or is arriving light from some detection target including a nearby point and is not an isolated point. Of course, whether the target point is an isolated point or not may be judged by other methods. For example, it may be judged by whether the change in the detection distance of the target point and the change in the detection distance of the nearby point are synchronized. Alternatively, the determination may be made based on whether or not there is a certain relationship between the ratio of the intensity of the light arriving from the target point or the nearby point and the ratio of the detection distance.

[0085] (5) In the above configuration (4), the target point and the adjacent point may be arranged in a predetermined direction, and the predetermined direction may include at least one of a vertical component and a horizontal component. In this way, when the target point or the adjacent point includes a vertical or horizontal component, it can be easily determined that it belongs to the detection target. Such detection targets can be, for example, road surfaces, walls, white lines or steps on a road, guardrails, etc. The components included in the predetermined direction may be either vertical or horizontal components, or both.

[0086] (6) In the configuration of (4) or (5) above, the determination unit may set the distance threshold to be compared with the distance difference to determine the number of adjacent points as a first distance threshold when a first condition is satisfied in which the detection distances corresponding to the elapsed times of the echoes included in the light arriving from the target point and the adjacent point, respectively, monotonically increase or decrease in this order when the target point and the adjacent point are lined up in order along a predetermined direction, and set the distance threshold to be compared with the distance difference to determine the number of adjacent points as a second distance threshold smaller than the first distance threshold in cases other than when the first condition is satisfied. In this way, it is possible to determine that a target point on a linear detection target such as the above-mentioned white line is not an isolated point more easily than when the adjacent points are not lined up in one direction relative to the target point.

[0087] (7) In the configurations (4) to (6) above, the score threshold may be increased or decreased in at least two stages depending on whether the detection distance corresponding to the elapsed time is short or long. In this way, when the target point is far away, the score threshold is reduced, so that even if the target point is far away, it is easy to determine that it is not an isolated point. Such a score threshold may be set in advance to two or more stages and switched between the set values, or may be increased or decreased at a predetermined ratio.

[0088] (8) In the first embodiment described above, as shown in the flowchart of Fig. 10, the first distance threshold LL or the second distance threshold LS is set as the distance threshold ΔLh depending on whether the detected distance to the target point or the adjacent point is monotonically increasing or decreasing (steps S450 to S465), and then the number of points whose distance difference DLm is smaller than the distance threshold ΔLh is counted (Fig. 12), and it is determined whether the target point is to be subject to noise determination (Fig. 10, step S470). In contrast, as described below, the determination regarding the number of adjacent points may be made with priority over the determination of whether the distance is monotonically increasing or decreasing. That is, the judgment unit may sequentially change the target point, which is one point in the predetermined range, and judge whether the number of adjacent points is equal to or less than the number threshold, and even if the judgment has already determined that the number of adjacent points of other target points in the predetermined range is equal to or less than the number threshold, if the target point and the adjacent points are arranged in order along a predetermined direction and the detection distances corresponding to the elapsed times of the echoes included in the arriving light from the target point and the adjacent point are monotonically increasing or decreasing in this order, the judgment unit may judge that the echoes included in the arriving light from the other target points are reflected by a detection target existing in the predetermined range. Explaining with reference to Fig. 10, the judgment of step S450 is moved to after step S470, and if the detection distances of the target point and the adjacent point are monotonically increasing or decreasing in this order, the processing of step S480 is not performed. In this way, if the detection distances of the target point and the nearby points are monotonically increasing or decreasing in this order, even if the number of nearby points is small and it has already been determined that the echo contained in the arriving light from that point is not reflected by a detection target present in the specified range, the target point can be determined not to be an isolated point. Note that, in the processing order of Figure 10, if it is determined that there is a monotonous increase or decrease, it is not necessary to make a determination regarding the number of nearby points. Of course, after making a determination regarding the number of nearby points, if the detection distances to the target point and the nearby points are monotonically increasing or decreasing in this order, the result of the determination regarding the number of nearby points may be overturned.

[0089] (9) In the first embodiment described above, as shown in FIG. 5 and FIG. 6B, an echo having a signal intensity equal to or greater than the first threshold value Th1, which is the lower limit, and less than the second threshold value Th2, which is the upper limit, is determined to be a target for noise determination (FIG. 5, steps S220, S240). However, a determination may be made only for the second threshold value Th2, which is the upper limit. In this case, the determination unit may compare the intensity of the echo included in the arriving light with an upper limit value, which is a predetermined intensity threshold, and may exclude the echo from the determination when the intensity of the echo is equal to or greater than the upper limit. In this way, the number of echoes that are subject to noise determination can be reduced by simple determination, and the noise determination process can be accelerated. In addition, the intensity may be determined by a peak value, or may be determined by the width (e.g., half-width) of the echo where the intensity is equal to or greater than a predetermined value, or the area where the intensity of the echo is equal to or greater than a predetermined value.

[0090] (10) In the configuration of (9) above, the determination unit may compare the intensity of the echo included in the arriving light with the upper limit and a lower limit that is smaller than the upper limit, and may determine an echo having an intensity equal to or greater than the lower limit and less than the upper limit as the object of the determination. In this way, it is possible to further reduce the number of echoes for which it is determined whether or not they are from a detection target, and to further speed up the noise removal process. Of course, it may be determined that an echo having an intensity equal to or less than a predetermined intensity is the object of noise determination.

[0091] (11) In the configurations (1) to (9) above, the determination unit may treat, in the determination, the intensity ratio of the actual intensity difference, which is the difference between the peak intensity of the echo and the external light intensity, to the maximum intensity difference, which is the difference between the maximum intensity that the echo can have and the external light intensity, as the intensity of the echo. In this way, it is possible to reduce the influence of the external light intensity. Of course, the peak intensity of the echo may be used as it is.

[0092] (12) As another configuration of the present disclosure, a noise removal device that removes noise generated when recognizing a detection target using light reflection is possible. This noise removal device includes a measurement unit that measures the intensity of arriving light that arrives from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light, a determination unit that, when an echo of a predetermined intensity or more is present in the measured arriving light, determines whether the echo is reflected by a detection target present in the predetermined range using the intensity of the echo and a detection distance that is a distance corresponding to the elapsed time, a removal unit that removes the echo that is determined not to be reflected by the detection target as noise, and a condition setting unit that sets a determination condition for determining whether an echo of the predetermined intensity or more is present in the measured arriving light based on at least one of the environment in which the noise removal device is placed and the characteristics of the measurement unit. In this way, it is possible to determine whether an echo of the predetermined intensity or more is present in the measured arriving light while reducing the influence of the environment in which the noise removal device is placed and the characteristics of the measurement unit.

[0093] The environment in which such a noise removal device is placed includes the illuminance, weather, and time of day of the object measured by the measurement unit of the noise removal device, which affect the detection of echoes. Of course, it is not limited to these, and humidity, wind speed, snowfall, fog, gas, flooding of the road surface, and the like may also be taken into consideration. In addition, the characteristics of the measurement unit may include differences in sensitivity for each measurement point of the measurement unit, and the distribution of noise intensity as electrical noise. Since the characteristics of such a measurement unit may vary not only at the time of shipment from the factory but also over time and with aging, the characteristic values ​​may be acquired and set periodically or after each usage time.

[0094] (13) In the configuration of (12) above, when the condition setting unit determines that the environment is rainy in the first case, sunny in the second case, cloudy in the third case, or nighttime in the fourth case, for at least two of these cases, it sets at least one of a first threshold value for comparing with the intensity of the echo and a second threshold value for comparing with the detection distance. In the i-th case and the j-th case (i < j, i, j = 1 to 4), in the i-th case, it may perform at least one of a first setting for setting the first threshold value to a value larger than that in the j-th case and a second setting for setting the second threshold value to a distance closer than that in the j-th case. By doing so, the influence of factors such as weather can be reduced. The classification is not limited to the first to fourth cases, and it may be a smaller number of classifications or a larger number of classifications than this.

[0095] (14) In the configuration of (12) or (13) above, the condition setting unit may correct the determination condition according to the magnitude of the noise detected or learned in advance at the measurement position of the measurement unit so as to reduce the influence of the noise. By doing so, the influence of the noise at the measurement position of the measurement unit can be reduced. Such so-called calibration processing may be performed at the time of factory shipment of the noise removal device, or may be performed during vehicle inspection or the like. Also, the calibration processing may be performed regularly or at an arbitrary timing.

[0096] (15) In the configuration of (12) to (14) above, further, a detection range switching unit is provided that switches the range for reading the intensity of the arriving light from the measurement range measurable by the measurement unit into a first range and a second range narrower than the first range. The condition setting unit may select either the first range or the second range as the determination condition. By doing so, since the dynamic range of detection changes depending on the width of the detection range, the detectability of noise can be changed. Therefore, the detection range may be switched to easily determine whether an echo suspected of being noise is actually noise.

[0097] (16) In the configuration of (15) above, the detection range may be switched at a specific timing, for example, when an echo is detected that is to be judged as noise or not, or may be switched dynamically. In the latter case, since it is switched dynamically, it is not necessary to perform a process for judging whether it is the timing to switch the detection range each time.

[0098] (17) The present disclosure may be implemented as an object detection device including any one of the above-mentioned noise removal devices and an object detection unit that detects an object based on the echo included in the signal from which the noise has been removed by the noise removal device. In this way, the object is detected after the noise is removed with high accuracy, so that the detection accuracy of the object can be improved. The object may be detected as a collection of points that exist within a detection distance by removing noise from echoes included in light that reaches the noise detection device from the direction of light irradiated to a predetermined range. Furthermore, target recognition may be performed to recognize the object as one of a vehicle, a two-wheeled vehicle, a pedestrian, a drone, a sign, a guardrail, a white line on a road surface, a plant, and a fence based on the external shape and movement of the object.

[0099] (18) The present disclosure can also be implemented as a method for removing noise that occurs when a detection target is recognized using light reflection. This noise removal method measures the intensity of arriving light that arrives from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light, and when an echo of a predetermined intensity or more is present in the measured arriving light, the intensity of the echo and the detection distance, which is the distance corresponding to the elapsed time, are used to determine whether the echo is reflected by a detection target present in the predetermined range, and the echo that is determined not to be reflected by the detection target is removed as noise. In this way, since the determination is made using the intensity of the echo and the detection distance, which is the distance corresponding to the elapsed time, it is possible to increase the accuracy of noise removal without simply determining that an echo with a weak intensity is noise. Here, as a process, instead of using the detection distance, the determination may be made using an elapsed time equivalent to the detection distance, and the method described for the noise removal device described above can also be applied to the noise removal method. For example, when using the intensity of the echo and the detection distance, which is the distance corresponding to the elapsed time, to determine whether or not the echo is light arriving from a detection target existing within a predetermined range, a determination may be made by combining the intensity of the echo and the detection distance to determine whether or not it is noise, or both may be mapped in advance, and the map may be referenced based on the intensity of the echo and the detection distance to determine whether or not it is noise.

[0100] (19) In each of the above embodiments, a part of the configuration realized by hardware may be replaced by software. At least a part of the configuration realized by software may be realized by a discrete circuit configuration. In addition, when a part or all of the functions of the present disclosure are realized by software, the software (computer program) may be provided in a form stored in a computer-readable recording medium. The term "computer-readable recording medium" is not limited to portable recording media such as flexible disks and CD-ROMs, but also includes internal storage devices in a computer such as various RAMs and ROMs, and external storage devices fixed to a computer such as a hard disk. In other words, the term "computer-readable recording medium" has a broad meaning including any recording medium to which a data packet can be fixed, not temporarily.

[0101] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention column can be appropriately replaced or combined to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0102] 10, 10A, 10B... target recognition device, 20... CPU, 22... light emission control unit, 30, 30A, 30B... noise removal device, 31... measurement unit, 32... judgment unit, 33... removal unit, 40... distance calculation unit, 45... target recognition unit, 50... storage device, 60... input / output interface, 70... light emission unit, 72... light emission element, 74... scanner, 80... light receiving unit, 82... light receiving element, 90... noise removal device, 100, 100B... vehicle, 111... illuminance sensor, 112... weather sensor, 113... time detector, 121... condition setting unit, 131... instruction unit, 132... calibration unit, CAL... calibration plate, TS... light receiving signal, TSn... echo, RT... signal strength, RTn... peak strength, LTn... detection distance

Claims

1. A noise removal device (30) for removing noise generated when recognizing a detection target using reflection of light, comprising: a measuring unit (31) that measures the intensity of light arriving from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light; a determination unit (32) that, when an echo having an intensity equal to or greater than a predetermined level is present in the measured arriving light, determines whether or not the echo has been reflected by a detection target present within the predetermined range, using the intensity of the echo and a detection distance that is a distance corresponding to the elapsed time; a removal unit (33) that removes, as noise, the echo that is determined not to have been reflected by the detection target; Equipped with The determination unit is When the measurement unit detects a first echo and a second echo having a longer elapsed time than the first echo as the echoes included in the arriving light, the measurement unit compares the intensity of the first echo with a predetermined intensity threshold value of a first value; When the measurement unit does not detect a second echo having a longer elapsed time than the first echo as the echo included in the arriving light, the measurement unit compares the intensity of the first echo with an intensity threshold value of a second value smaller than the first value; When the intensity of the first echo is smaller than the intensity threshold, the first echo is determined not to have been reflected by a detection target present within the predetermined range. Noise removal device.

2. the determining unit, when the arriving light measured by the measuring unit includes a first echo and a second echo having a longer elapsed time than the first echo, and the first echo is from within a predetermined first distance range, determines that the first echo is not reflected by a detection target present within the predetermined range. The noise removal device according to claim 1 .

3. The noise removal device according to claim 1 or 2, the measurement unit detects, as the echo, an echo contained in the light arriving from a target point that is one point in the predetermined range, and echoes contained in the light arriving from at least two nearby points that are close to the target point; The noise removal device, wherein the judgment unit judges that the echo contained in the arriving light from the target point is not reflected by a detection target present in the specified range when the number of nearby points, which is the number of nearby points where the distance difference corresponding to the difference between the elapsed time of the echo contained in the arriving light from the target point and the elapsed time of the echo contained in the arriving light at the nearby point is less than a predetermined distance threshold, is less than a predetermined point number threshold.

4. The noise removal device according to claim 3 , wherein the target point and the neighboring point are aligned in a predetermined direction, the predetermined direction including at least one of a vertical component and a horizontal component.

5. The determination unit is a first distance threshold is set as the distance threshold to be compared with the distance difference in order to determine the number of nearby points when a first condition is satisfied in which, with the target point and the nearby point being lined up in order along a predetermined direction, the detection distances corresponding to the elapsed times of the echoes contained in the light arriving from the target point and the nearby point, respectively, monotonically increase or decrease in this order; When the first condition is not satisfied, the distance threshold value to be compared with the distance difference in order to obtain the number of neighboring points is set to a second distance threshold value that is smaller than the first distance threshold value. The noise removal device according to claim 3.

6. The noise removal device according to claim 3 , wherein the score threshold is increased or decreased in at least two stages depending on whether the detection distance corresponding to the elapsed time is short or long.

7. The determination unit is Sequentially changing the target point, which is one point in the predetermined range, and determining whether the number of neighboring points is equal to or less than the point number threshold; 4. The noise removal device according to claim 3, wherein even if the judgment has already determined that the number of nearby points for other target points within the specified range is equal to or less than the number threshold, if a first condition is satisfied in which the target point and the nearby point are lined up in order along a specified direction and the detection distances corresponding to the elapsed times of the echoes contained in the arriving light from the target point and the nearby point respectively monotonically increase or decrease in this order, the noise removal device judges that the echoes contained in the arriving light from the other target points have been reflected by a detection target present in the specified range.

8. 3. The noise removal device according to claim 1, wherein the judgment unit compares the intensity of the echo contained in the arriving light with an upper limit value that is a predetermined intensity threshold, and if the intensity of the echo is equal to or greater than the upper limit value, excludes the echo from the judgment.

9. 9. The noise removal device according to claim 8, wherein the judgment unit compares an intensity of the echo contained in the arriving light with the upper limit value and a lower limit value that is smaller than the upper limit value, and determines an echo whose intensity is equal to or greater than the lower limit value and less than the upper limit value as the subject of the judgment.

10. 3. The noise removal device according to claim 1, wherein the judgment unit, in the judgment, treats an intensity ratio of an actual intensity difference, which is a difference between a peak intensity of the echo and an external light intensity, to a maximum intensity difference, which is a difference between a maximum intensity that the echo can have and an external light intensity, as the intensity of the echo.

11. A noise removal device (30, 30A, 30B) according to claim 1 or 2, an object detection unit (40, 45) for detecting an object based on the echo included in the signal from which the noise has been removed by the noise removal device; An object detection device (10, 10A, 10B) comprising:

12. A method for removing noise that occurs when recognizing a detection target using light reflection, comprising: measuring the intensity of light arriving from a direction corresponding to the emission direction of light emitted toward a predetermined range along with the elapsed time from the emission of the light; When an echo having an intensity equal to or greater than a predetermined level is present in the measured arriving light, the intensity of the echo and a detection distance corresponding to the elapsed time are used to determine whether or not the echo has been reflected by a detection target present within the predetermined range, and in this determination, When a first echo and a second echo having a longer elapsed time than the first echo are detected as the echoes included in the arriving light, the intensity of the first echo is compared with a predetermined intensity threshold value of a first value; When a second echo having a longer elapsed time than the first echo is not detected as the echo included in the arriving light, the intensity of the first echo is compared with an intensity threshold having a second value smaller than the first value; If the intensity of the first echo is smaller than the intensity threshold, the first echo is determined to not have been reflected by a detection target present within the predetermined range; removing the echo determined not to have been reflected by the detection target as noise; Noise removal methods.

Images