Distance measuring device and method for detecting dirt on window of distance measuring device

Abstract

The present invention provides a distance measuring device (20), comprising: a light emitting unit (40), a light receiving unit (60), a computing unit (200), a housing (90) having a window (92), and a determining unit (300) for determining that dirt exists on the window when a predetermined dirt determination condition is satisfied. The dirt determination condition includes a first condition, wherein "for at least one pixel within the field of view of the distance measuring device, the light intensity at a specific flight time corresponding to the distance of the optical path from the light emitting unit to the window is greater than an intensity threshold value".

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority based on Japanese Patent Application No. 2019-183438 filed on October 4, 2019, and Japanese Patent Application No. 2020-159470 filed on September 24, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a technology for detecting dirt on a window of a distance measuring device. Background Art

[0004] JP2016-176750A discloses a distance measuring device that irradiates pulse light, receives reflected light reflected by an external object, and measures the distance to the external object based on the flight time of the light.

[0005] In the above-mentioned distance measuring device, if dirt is attached to the window of the distance measuring device, the S / N ratio is reduced and the distance to the external object cannot be accurately measured. However, in the past, the actual situation is that the technology for detecting whether dirt is attached to the window of the distance measuring device has not been fully studied. Summary of the invention

[0006] According to one embodiment of the present disclosure, a distance measuring device is provided. The distance measuring device comprises: a light emitting unit that emits pulse light; a light receiving unit that receives reflected light of the pulse light reflected by an external object; a calculation unit that uses the flight time of the reflected light received by the light receiving unit to calculate the distance to the external object; a housing that accommodates the light emitting unit and the light receiving unit, and the housing has a window through which the pulse light and the reflected light pass; and a determination unit that determines that there is dirt on the window when a predetermined dirt determination condition is met, and the dirt determination condition includes a first condition, which is "for at least one pixel within the field of view of the distance measuring device, the light intensity at a specific flight time corresponding to the distance of the optical path from the light emitting unit to the window is greater than an intensity threshold value".

[0007] According to this distance measuring device, since it is determined that there is dirt on the window when the dirt detection condition is satisfied for the received light intensity at a specific flight time, it is possible to detect whether there is dirt on the window based on the received light intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic structural diagram of a distance measuring device.

[0009] Figure 2 It is a schematic structural diagram showing the optical system.

[0010] Figure 3 It is an explanatory diagram schematically showing the structure of a light receiving array.

[0011] Figure 4 It is an explanatory diagram schematically showing the structure of a light-receiving element included in a pixel.

[0012] Figure 5 It is a schematic structural diagram of the calculation and judgment unit.

[0013] Figure 6 is the histogram of the initial state when there is no dirt on the window.

[0014] Figure 7 This is the histogram during the window dirt detection process.

[0015] Figure 8 It is an explanatory diagram schematically showing the structure of a light receiving array including pixels for dirt detection.

[0016] Fig. 9 This is an explanatory diagram showing how distance measurement and dirt detection are performed for each pixel block.

[0017] Fig.10 is a flow chart showing the steps of the window dirt detection process.

[0018] Fig.11 This is an explanatory diagram showing a situation where there is dirt on the window at a plurality of pixel positions within the field of view. DETAILED DESCRIPTION

[0019] like Figure 1 As shown, the distance measuring device 20 is housed in a housing 90, which has a window 92 on the front surface. Near the window 92, a cleaning unit 400 is provided for performing a removal action for removing window dirt from the window 92. The cleaning unit 400 of this embodiment includes cleaning units 410, 411, and a heater unit 420. The cleaning units 410, 411 are used to remove dirt on the surface of the window 92 by spraying water onto the surface of the window 92. In this example, a first cleaning unit 410 for removing dirt on the left side of the window 92 and a second cleaning unit 411 for removing dirt on the right side of the window 92 are provided, but more than three cleaning units may also be provided. In other words, a plurality of cleaning units each responsible for removing dirt from a plurality of different regions of the window 92 may also be provided. Alternatively, dirt on the entire window 92 may also be removed by one cleaning unit. Further, air may be sprayed instead of water, and the cleaning unit may also be configured to be capable of spraying both water and air. The heater unit 420 is used to heat the window 92 using a heating wire provided along the window 92 to melt snow and ice attached to the surface of the window 92. As the cleaning unit 400, a structure other than these structures may also be adopted. For example, a wiper unit for wiping the window 92 may also be used as the cleaning unit 400.

[0020] The distance measuring device 20 includes an optical system 30 that emits pulsed light for distance measurement and receives reflected light from an external object, and a calculation and determination unit 100 that processes a signal obtained from the optical system 30. The external object is also referred to as an "object" or "target". The optical system 30 includes a light emitting unit 40 that emits laser light as pulsed light, a scanning unit 50 that scans the laser light within a predetermined field of view 80, and a light receiving unit 60 that receives incident light including reflected light from an external object and disturbance light.

[0021] The distance measuring device 20 is, for example, a vehicle-mounted LiDAR (Laser Imaging Detection and Ranging) mounted on a vehicle such as a car. When the vehicle is traveling on a horizontal road surface, the lateral direction of the field of view 80 coincides with the horizontal direction X, and the longitudinal direction coincides with the vertical direction Y. Information such as the distance measured by the distance measuring device 20 is received and used by a distance receiving unit 500 as an external device. The distance receiving unit 500 has a notification unit 510 for notifying the user of various information. The notification unit 510 is, for example, a display unit, a speaker, etc. provided in the passenger compartment. The distance receiving unit 500 is, for example, a control device including an ECU (Electronic Control Unit) of the vehicle.

[0022] like Figure 2 As shown in the figure, the light emitting unit 40 includes a semiconductor laser element (hereinafter, also simply referred to as a laser element) 41 that emits laser light for distance measurement, a circuit substrate 43 provided with a driving circuit of the laser element 41, and a collimating lens 45 that makes the laser light emitted from the laser element 41 parallel light. The laser element 41 is a laser diode that can oscillate so-called short-pulse laser light. In this embodiment, the laser element 41 forms a rectangular laser light emitting area by arranging a plurality of laser diodes in a vertical direction. The laser element 41 is also referred to as a "light source".

[0023] The scanning unit 50 is composed of a so-called one-dimensional scanner. The scanning unit 50 includes a reflector 54, a rotary solenoid 58, and a rotating unit 56. The reflector 54 reflects the laser light that has passed through the collimating lens 45 and has become parallel light. The rotary solenoid 58 receives a control signal from the calculation and determination unit 100 and repeatedly rotates forward and reverse within a predetermined angle range. The rotating unit 56 is driven by the rotary solenoid 58 to repeatedly rotate forward and reverse with the vertical direction as the axial rotation axis, so that the reflector 54 scans in one direction along the horizontal direction. The laser light incident from the laser element 41 via the collimating lens 45 is reflected by the reflector 54 and scanned in the horizontal direction by the rotation of the reflector 54. Figure 1The field of view 80 shown corresponds to the scanning range of the irradiation light. Since the light intensity is obtained at each pixel position in the field of view 80, the distribution of the light intensity in the field of view 80 constitutes an image. Therefore, the field of view 80 can also be called an "image area". In addition, the scanning unit 50 can be omitted, and the pulse light is emitted from the light emitting unit 40 throughout the entire field of view 80, and the reflected light throughout the entire field of view 80 is received by the light receiving unit 60. The collection of data representing the distribution of the light intensity in the field of view 80 is also called a "frame". Distance measurement is performed for each frame.

[0024] If there is an external object such as a person or a car, the laser light output from the distance measuring device 20 is diffusely reflected on the surface of the external object, and a part of the laser light returns as reflected light to the reflector 54 of the scanning unit 50. The reflected light is reflected by the reflector 54, and is incident on the light receiving lens 61 of the light receiving unit 60 together with the disturbance light as incident light, and is focused by the light receiving lens 61 and incident on the light receiving array 65.

[0025] like Figure 3 As shown, the light receiving array 65 is composed of a plurality of pixels 66 arranged two-dimensionally. Figure 4 As shown, one pixel 66 is composed of a plurality of light receiving elements 68 arranged in H numbers in the horizontal direction and V numbers in the vertical direction. H and V are integers greater than 1, respectively. In the present embodiment, H=V=5, and it is composed of 5 light receiving elements 68 in the horizontal direction and 5 light receiving elements 68 in the vertical direction, respectively. However, the pixel 66 can be composed of any number of light receiving elements 68, or it can be composed of one light receiving element 68. In the present embodiment, the number of light receiving elements 68 (H×V) constituting one pixel 66 is also referred to as "pixel size". In the present embodiment, SPAD (Single Photon Avalanche Diode) is used as the light receiving element 68, but other types of light receiving elements such as PIN photodiodes can also be used. The light receiving result of one pixel 66 is the light receiving intensity at one pixel position within the field of view 80. As can be seen from this description, the "pixel 66" constituting the light receiving array 65 refers to hardware, and is used in a different meaning from the "pixel" constituting the field of view 80. However, since the light reception result of the pixel 66 is used as the light reception intensity of one pixel within the field of view range 80, there is a corresponding relationship between the two.

[0026] Each photosensitive element 68 is connected in series with a quenching resistor Rq and an avalanche diode Da between a power supply Vcc and a ground line, and the voltage at their connection point is input to an inversion element INV, which is converted into a digital signal after the voltage level is inverted. The output of the inversion element INV is input to one input terminal of the AND circuit SW. A selection signal Sc is input to another input terminal of the AND circuit SW. The selection signal Sc is used to specify which photosensitive element 68 of the photosensitive array 65 is to read the signal. That is, if the selection signal Sc for selecting a certain photosensitive element 68 is switched from a low level to a high level, an output signal Sout reflecting the state of the avalanche diode Da is output from the photosensitive element 68. The timing of switching the selection signal Sc to a high level is equivalent to the flight time of the reflected light. Therefore, after a pulse of light is emitted, the selection signal Sc is switched from a low level to a high level at multiple timings corresponding to multiple flight times.

[0027] The output signal Sout is a pulse signal generated by receiving incident light, including reflected light and disturbance light. The output signals Sout of the light receiving element 68 at multiple flight times are sequentially input to the calculation and determination unit 100.

[0028] like Figure 5 As shown, the calculation and determination unit 100 includes a calculation unit 200, a determination unit 300, and a storage unit 310. The calculation unit 200 calculates the distance D from the external object OBJ using the flight time Tf of the reflected light received by the light receiving unit 60. The calculation unit 200 includes a control unit 210 that controls the calculation and determination unit 100 as a whole, an addition unit 220, a histogram generation unit 230, a peak detection unit 240, and a distance calculation unit 250.

[0029] The adding section 220 is a circuit that adds the outputs of the light receiving elements 68 included in the pixels 66 constituting the light receiving array 65. If an incident light pulse is incident on a pixel 66, each light receiving element 68 included in the pixel 66 operates. As described above, in the present embodiment, a SPAD is used as the light receiving element 68, and a plurality of SPADs constitute the pixel 66. For a SPAD, it can detect as long as one photon is incident, but the detection of the SPAD using the limited light from the external object OBJ is necessarily probabilistic. The adding section 220 adds the output signals Sout from the SPADs that can only probabilistically detect the incident light.

[0030] The histogram generation unit 230 generates a histogram of the light intensity by adding the addition results of the addition unit 220 multiple times, and outputs the histogram to the peak detection unit 240. The histogram is a graph showing the light intensity at each of the multiple flight times. The light intensity is the total number of SPADs receiving light within a pixel 66. The multiple flight times are set at certain intervals. The peak detection unit 240 analyzes the light intensity of the histogram input from the histogram generation unit 230, detects the peak of the light intensity, and determines the flight time of the detected peak. The flight time of the detected peak is equivalent to the flight time Tf of the light reflected by the external object OBJ. The distance calculation unit 250 uses the flight time Tf of the light to calculate the distance D from the external object OBJ.

[0031] The determination unit 300 uses the light intensity received in the light receiving unit 60 to perform a dirt detection process for the window 92. In the present embodiment, the determination unit 300 uses the histogram generated by the histogram generating unit 230 as information indicating the light intensity received in the light receiving unit 60. The details of the dirt detection process for the window 92 will be described later. When it is determined that there is dirt on the window 92, the cleaning unit 400 performs a removal operation for removing the dirt from the window 92 according to an instruction from the determination unit 300. A temperature sensor 320 for measuring the temperature of the external air is connected to the determination unit 300. However, the temperature sensor 320 may be omitted.

[0032] The storage unit 310 stores the distribution of threshold setting values ​​within the field of view 80 of the distance measuring device 20. The so-called "threshold setting value" is a value for determining the intensity threshold used in the window dirt detection process, which is pre-set and stored in the storage unit 310. The intensity threshold and the threshold setting value will be further described later.

[0033] like Figure 6 as well as Figure 7 As shown in FIG. 1 , the histogram generated by the histogram generating unit 230 is a graph showing the received light intensity I at each of the plurality of flight times Tf. Figure 6 An example of a histogram showing an initial state in which there is no dirt on the window 92, Figure 7 An example of a histogram showing the window dirt detection process. Figure 6 as well as Figure 7 The meanings of the reference numerals used in the following are as follows. In addition, reference numerals ending with "0" indicate the initial state, and reference numerals ending with "1" indicate the window dirt detection process. Figure 7 The meanings of the reference numerals in the window dirt detection process shown are explained.

[0034] (1) CL0, CL1: clutter peak

[0035] The clutter peak CL1 is a peak of the received light intensity that appears at a specific flight time Tc corresponding to the distance of the optical path from the light emitting unit 40 to the window 92. The reflected light from the window 92 is referred to as "clutter light".

[0036] (2) Tc: Flight time of clutter peak

[0037] The flight time Tc of the clutter peak is a specific flight time corresponding to the distance of the optical path from the light emitting unit 40 to the window 92 .

[0038] (3) TP0, TP1: target peak

[0039] The target peak value TP1 is a peak value corresponding to the received light intensity of the reflected light from the external object.

[0040] (4) Tt: Flight time of target peak

[0041] The flight time Tt of the target peak is the flight time corresponding to the distance from the light emitting section 40 to the external object.

[0042] (5) Imax: The maximum value of the light intensity I

[0043] The maximum value Imax that the light intensity I can take is the total number of light receiving elements 68 for each pixel used when creating the histogram. Figure 4 As described in , one pixel 66 is composed of H×V light receiving elements 68. When N is an integer greater than 2, when the light receiving results of N times of light emission are totaled and a histogram is created, the maximum value Imax that the light receiving intensity I can take is equal to N×H×V.

[0044] (6) H0, H1: clutter peak level

[0045] The clutter peak level H1 is the absolute value of the height of the clutter peak CL1. Hereinafter, the clutter peak level H1 is also simply referred to as "peak level H1" or "received light intensity H1".

[0046] (7) It0, It1: intensity threshold of clutter peak

[0047] The intensity threshold It1 of the clutter peak CL1 is used to determine whether the first condition in the dirt detection condition, "for at least one pixel within the field of view 80 of the distance measuring device 20, the light intensity at the specific flight time Tc is greater than the intensity threshold It1", is satisfied. The intensity threshold It1 is usually set to a value less than the maximum value Imax of the light intensity I, but can also be set to a value equal to the maximum value Imax. The method for determining the intensity threshold It1 during the window dirt detection process will be described later.

[0048] (8) BL0, BL1: Baseline level of histogram

[0049] The base level BL1 of the histogram is the average value of signal values ​​other than the peak value in the histogram.

[0050] (9) α: Threshold setting value

[0051] The threshold setting value α is a value obtained by subtracting the baseline level BL1 from the intensity threshold It1. In other words, the intensity threshold It1 can be determined by adding the threshold setting value α to the baseline level BL1. However, as described later, the intensity threshold It1 can also be determined by other methods.

[0052] (10) (Imax0-BL0), (Imax-BL1): effective signal range width

[0053] The effective signal range width (Imax-BL1) is a value obtained by subtracting the baseline level BL1 from the maximum value Imax that the received light intensity I can take.

[0054] like Figure 6 As shown, in a typical histogram in an initial state where there is no dirt on the window 92, a target peak TP0 corresponding to the reflected light from the external object appears. The distance to the external object is determined based on the flight time Tt of the target peak TP0. Figure 6 The histogram also includes a noise peak CL0 as the peak of the reflected light on the window 92. The noise peak CL0 is the intensity of the received light at a specific flight time Tc corresponding to the distance of the optical path from the light emitting unit 40 to the window 92. The noise peak CL0 has a peak level H0 (hereinafter referred to as "initial noise peak level H0") when the window 92 is free of dirt, such as when it is shipped from the factory. In addition, the specific flight time Tc at which the noise peak CL0 appears is different for each pixel position within the field of view range 80. The reason for this is that Figure 1 In the embodiment, the optical path length of the optical path from the light emitting unit 40 to the window 92 is different for each pixel position in the field of view range 80. In addition, generally, the initial clutter peak level H0 at each pixel position is also different for each pixel position.

[0055] In addition, in a conventional distance measuring device, since the position where the window 92 exists is not a distance measuring object, it is not necessary to obtain a measured value of the light intensity I at a specific flight time Tc where the clutter peak CL1 appears. In the present embodiment, one feature is that in order to detect dirt on the window 92 using the clutter peak CL1, a measured value of the light intensity I is obtained at a specific flight time Tc.

[0056] like Figure 7As shown in the example of FIG. 1 , the target peak TP1 and the clutter peak CL1 in the histogram during the window dirt detection process are generally different from the target peak TP0 and the clutter peak CL0 in the initial state. For example, when there is dirt on the window 92, the clutter peak level H1 becomes higher than the initial clutter peak level H0. In addition, when there is dirt on the window 92, the target peak TP1 level for the same external object often becomes lower.

[0057] The baseline level BL1 during the window dirt detection process is affected by the external environment such as the presence or absence of an external light source such as the sun. For example, when there is strong sunlight, the baseline level BL1 shows an extremely high value. At this time, the clutter peak level H1 also rises in the same manner. Therefore, it is preferable to appropriately determine the intensity threshold It1 during the window dirt detection process in consideration of the influence of such an external environment. This point will be further described later.

[0058] As a method for determining the intensity threshold value It1 during the window contamination detection process, for example, the following methods A to C are conceivable.

[0059] <Method A for determining intensity threshold>

[0060] The intensity threshold It1 during the window dirt detection process is set to a constant value.

[0061] In this case, the intensity threshold It1 may be set to a value common to all pixels within the field of view 80, or the intensity threshold It1 may be set for each pixel within the field of view 80 and stored as a threshold setting value in the storage unit 310. In the former case, the storage unit 310 may be omitted. However, if the intensity threshold It1 is set for each pixel within the field of view 80, the intensity threshold It1 higher than the initial clutter peak level H0 of each pixel can be set, so there is an advantage that the window dirt detection process can be performed more accurately.

[0062] <Method B for determining intensity threshold>

[0063] A value obtained by adding a threshold setting value α, which is a fixed value, to the base line level BL1 of the histogram is defined as an intensity threshold value It1 in the window contamination detection process.

[0064] It1=BL1+α…(1)

[0065] Here, the threshold setting value α is a value that is preset so that the calculation result (BL0+α) when the above formula (1) is applied in the initial state is sufficiently larger than the initial clutter peak level H0. The threshold setting value α may be set to a value shared by all pixels within the field of view 80, or an intensity fixed value α may be set for each pixel within the field of view 80 and stored in the storage unit 310.

[0066] According to this method B, it is possible to appropriately determine the intensity threshold It1 during the window dirt detection process by taking into account the influence of the external environment such as the presence or absence of an external light source. In addition, the threshold setting value α can also be determined based on the pixel size (H×V) and the number of light emission times N when generating a histogram. For example, the threshold setting value α can also be determined using any of the following formulas.

[0067] α=α0×(H×V)

[0068] α=α0×N

[0069] α=α0×(H×V)×N

[0070] Here, α0 is a predetermined constant value. The pixel size (H×V) is as shown in Figure 4 As described in , this is the number of SPADs included in one pixel 66.

[0071] <Method C for determining intensity threshold>

[0072] The effective signal range width (Imax-BL1) is multiplied by the threshold setting value β, and the value obtained by adding the baseline level BL1 to the multiplication result is set as the intensity threshold It1 during the window dirt detection process, where the threshold setting value β is a coefficient less than 1.

[0073] In this case, the intensity threshold It1 during the window dirt detection process can be calculated by the following formula.

[0074] It1=(Imax-BL1)×β+BL1…(2)

[0075] Here, the threshold setting value β is pre-set to a value that is sufficiently larger than the initial noise peak level H0 when the calculation result {(Imax-BL0)×β+BL0} when the above formula (2) is applied in the initial state. The threshold setting value β can also be set to a value shared by all pixels within the field of view 80, or it can be set for each pixel within the field of view 80 and stored in the storage unit 310. According to this method C, as with the above-mentioned method B, there is an advantage that the intensity threshold value It1 during the window dirt detection process can be appropriately determined by considering the influence of the external environment. In addition, this method C also has the following advantages: since the intensity threshold value It1 during the window dirt detection process can be maintained at a value less than the maximum value Imax of the received light intensity when the light from the outside is extremely strong and the baseline level BL1 becomes high, the window dirt detection process can be performed more accurately.

[0076] Furthermore, when the threshold setting value for determining the intensity threshold It1 is different for each pixel in the field of view 80, it is preferable to store the distribution of the threshold setting values ​​in the field of view 80 in the storage unit 310. It is preferable to store the threshold setting values ​​at all pixel positions in the field of view 80, but it is also possible to store the threshold setting values ​​only at the pixel positions after the interval is extended, thereby storing the distribution of the threshold setting values ​​in the field of view 80. In the latter case, when calculating the intensity threshold It1 at each pixel position, the threshold setting value at each pixel position can be determined by interpolation.

[0077] like Figure 8 As shown in the example, a light receiving array 65a including pixels 67 for dirt detection in addition to the pixels 66 for distance measurement may be used. That is, the light receiving unit 60 may also include pixels 67 for dirt detection in the window 92 in addition to the pixels 66 for distance measurement. The pixels 67 for dirt detection are arranged near the pixels 66 for distance measurement. Specifically, it is preferred that the pixels 67 for dirt detection are arranged so that no clutter light is applied to the pixels 67 for dirt detection when there is no dirt on the window 92, and clutter light is applied to the pixels 67 for dirt detection when there is dirt on the window 92. When there is dirt on the window 92, the clutter peak value increases in the pixel 66 for distance measurement, and the clutter light to its surroundings increases. If the pixel 67 for dirt detection is arranged at this position, the presence or absence of dirt can be determined by whether there is light input to the pixel 67, and there is an advantage that dirt detection can be achieved with simpler calculations.

[0078] In addition, if Fig. 9 As shown, the plurality of pixels 66 included in the light receiving array 65 may be divided into a plurality of pixel blocks and time-division processing may be performed to perform distance measurement and dirt detection at the same timing. Fig. 9 In the example of FIG. 1 , the plurality of pixels 66 are divided into two pixel blocks, pixel block A and pixel block B. When one pixel block is used for distance measurement, the other pixel block is used for dirt detection in parallel. The plurality of pixels 66 included in the light receiving array 65 may also be divided into three or more pixel blocks. In this case, at least one pixel block can be used for dirt detection, and the other pixel block can be used for distance measurement.

[0079] Fig.10 The window dirt detection process shown is executed under the control of the control unit 210. In step S100, it is determined whether the processing timing of the window dirt detection process has been reached. The processing timing of the window dirt detection process may be set, for example, to each predetermined period in the normal distance measurement operation of the distance measuring device 20. Alternatively, the processing timing of the window dirt detection process may be set within a predetermined self-diagnosis period of the distance measuring device 20.

[0080] When the predetermined processing timing of the window dirt detection process is reached, the process proceeds to step S200 , and the determination unit 300 acquires the peak level H1 of the clutter peak CL1 from the histogram of the received light intensity.

[0081] In step S300, the determination unit 300 determines whether a predetermined contamination determination condition is satisfied. If the contamination determination condition is not satisfied, the process returns to step S100 and waits until the next processing timing. On the other hand, if the contamination determination condition is satisfied, the process proceeds to step S400 described below.

[0082] As the contamination determination condition, for example, any one of various contamination determination conditions described below can be used.

[0083] <Fouling judgment condition 1>

[0084] When only the following first condition C1 is satisfied, it is determined that dirt is present on the window 92 .

[0085] First condition C1: "For at least one pixel within the field of view 80 of the distance measuring device 20, the light intensity H1 at a specific flight time Tc corresponding to the distance of the optical path from the light emitting unit 40 to the window 92 is greater than or equal to the intensity threshold It1"

[0086] This contamination determination condition 1 is a looser condition than other contamination determination conditions described later, and therefore has the advantage that the possibility of missing contamination of the window 92 is low. In addition, it is preferable to determine whether the first condition C1 is satisfied regardless of whether the histogram includes the target peak TP1. If so, there is an advantage that contamination of the window 92 can be detected even when the histogram includes the target peak TP1.

[0087] <Fouling judgment condition 2>

[0088] When both the first condition C1 and the second condition C2a described below are satisfied, it is determined that dirt is present on the window 92 .

[0089] Second condition C2a: "In the field of view 80, the number of pixels whose light intensity H1 at a specific flight time Tc is greater than or equal to the intensity threshold It1 is greater than or equal to the number threshold, where the number threshold is an integer greater than or equal to 2"

[0090] For the fouling judgment condition 2, Figure 7 In the example, when there are a plurality of pixels having a peak level H1 of a clutter peak CL1 equal to or greater than the intensity threshold It1 within the field of view 80 , it is determined that dirt is present on the window 92 . This has the advantage that dirt on the window 92 can be determined more reliably.

[0091] <Fouling judgment condition 3>

[0092] When both the first condition C1 described above and the second condition C2 b described below are satisfied, it is determined that dirt is present on the window 92 .

[0093] Second condition C2b: "In the field of view 80, there exists a pixel group in which a plurality of pixels are continuous and the light intensity H1 at a specific flight time Tc is greater than the intensity threshold It1, and the number of pixels in the pixel group is greater than a predetermined number threshold."

[0094] For the fouling judgment condition 3, if Fig.11 As shown in FIG. 1 , it is assumed that due to the dirt on the window 92, a plurality of pixels whose light intensity H1 at a specific flight time Tc is greater than the intensity threshold It1 are continuous within the field of view 80 and constitute a pixel assembly PA. In addition, the phrase "two pixels are continuous" means that one pixel exists in any of the four adjacent positions above, below, left, and right of the other pixel. When there is dirt on the window 92, the dirt often adheres to a concentrated area within the window 92, so as Fig.11 As shown, a plurality of pixels whose light intensity H1 at a specific flight time Tc is greater than the intensity threshold It1 generally constitute the pixel assembly PA within the field of view 80. Therefore, in the contamination determination condition 3, there is an advantage that the contamination of the window 92 can be determined more reliably than in the contamination determination condition 2 described above.

[0095] The determination of whether the dirt determination condition is satisfied can also be implemented over multiple frames. For example, when N is set to a predetermined integer greater than 2, it is also possible to determine that there is dirt in the window 92 when the dirt determination condition is satisfied continuously over N consecutive frames. In addition, when N is set to an integer greater than 3 and M is set to an integer greater than 2 and less than N, it is also possible to determine that there is dirt in the window 92 when the dirt determination condition is satisfied in M ​​frames out of N consecutive frames. Alternatively, when N is set to a predetermined integer greater than 2, it is also possible to use the total value or average value of the light intensity H1 and the intensity threshold It1 over N consecutive frames to determine whether the dirt determination condition is satisfied. If these methods are adopted, there is the advantage of being able to stably determine the presence or absence of dirt and prevent false detection.

[0096] When the dirt determination condition is met, the process proceeds to step S400 and performs the window dirt removal operation. According to the instruction from the determination unit 300, the cleaning unit 400 performs the window dirt removal operation. Specifically, for example, the cleaning units 410 and 411 spray at least one of water and air onto the surface of the window 92 to remove the dirt on the surface of the window 92. In addition, when the outside air temperature measured by the temperature sensor 320 indicates a temperature at which snow or ice may adhere to the window 92, the heater unit 420 heats the window 92 through a heating line provided along the window 92 to melt the snow or ice attached to the surface of the window 92.

[0097] In addition, it is also possible to select one of the multiple cleaning methods and execute the method according to the position of the dirt of the window 92. For example, it is also possible to use multiple cleaning units 410, 411 that are responsible for removing the dirt of multiple different areas of the window 92 respectively, and according to the area where the dirt is present, only the cleaning unit responsible for removing the dirt in the area is selected and the cleaning unit is started. Alternatively, it is also possible to configure two cleaning units 410, 411 on one of the two sides of the window 92, and set the first cleaning unit 410 to have a slower fluid discharge speed and a lower dirt removal ability, and set the second cleaning unit 411 to have a faster fluid discharge speed and a higher dirt removal ability. In this case, when there is dirt in the area closer to the side of the window 92 configured with two cleaning units, the first cleaning unit 410 with a lower dirt removal ability is used to perform dirt removal, and when there is dirt in the area closer to the other side, the second cleaning unit 411 is used to perform dirt removal because it has a higher dirt removal ability.

[0098] In addition, a cleaning method may be selected and executed according to the degree of contamination. As a contamination index value indicating the degree of contamination, for example, any of the following index values ​​may be used.

[0099] (1) Dirt index value D1

[0100] The contamination index value D1 is the difference between the received light intensity H1 and the intensity threshold value It1.

[0101] (2) Dirt index value D2

[0102] The dirt index value D2 is the number of pixels where dirt exists.

[0103] (3) Dirt index value D3

[0104] The dirt index value D3 is a summed value obtained by adding the difference between the received light intensity H1 and the intensity threshold value It1 for a plurality of pixels within the viewing area 80 .

[0105] The larger the contamination index values ​​D1 to D3 are, the higher the degree of contamination is. The determination unit 300 may calculate any one of the contamination index values ​​D1 to D3 and notify the cleaning unit 400 of the contamination index value.

[0106] The cleaning unit 400 can select and execute one of a plurality of cleaning methods with different dirt removal capabilities according to the degree of dirt represented by the dirt index value. For example, the degree of dirt can be pre-divided into a plurality of dirt stages, and one of the following three cleaning methods can be used in each dirt stage.

[0107] (1) Cleaning method C1

[0108] Perform cleaning of the purge section using only air.

[0109] (2) Cleaning method C2

[0110] Perform cleaning of the cleaning section using both air and water.

[0111] (3) Cleaning method C3

[0112] Perform cleaning using both the washing section and the wiper section.

[0113] The dirt removal capabilities of the three cleaning methods C1 to C3 gradually increase, and they are selected and applied in the order from low to high degree of dirt.

[0114] In addition, step S400 may be omitted. In addition, when the window 92 is dirty, it is preferred that the determination unit 300 informs the occupants of the vehicle equipped with the distance measuring device 20 that there is dirt on the window 92 of the distance measuring device 20. For example, such a notification unit 510 such as a display unit or a speaker provided in the passenger compartment may be used for such notification. When notifying of the dirt, it is preferred that the location where the dirt is present in the window 92 is notified to the outside. In addition, the calculation unit 200 may not output the distance data of the area where the dirt is present in the window 92 to the outside, but may only output the distance data of the area where the dirt is not present to the outside.

[0115] Furthermore, when the above-mentioned <Content Judgment Condition 2> or <Content Judgment Condition 3> is used, when the number of pixels whose light intensity H1 at a specific flight time Tc is greater than the intensity threshold It1 is greater than the first number threshold, (a) when the number of pixels is greater than the second number threshold, the cleaning unit 400 is not caused to perform a removal operation but only to perform a notification, wherein the second number threshold is greater than the first number threshold, and (b) when the number of pixels is less than the second number threshold, the cleaning unit 400 is caused to perform a removal operation. In this way, it can be determined whether the dirt is of a size that cannot be removed by the cleaning unit 400.

[0116] In addition, when the window 92 is not contaminated, the determination unit 300 may also update the threshold setting value by calculating a new threshold setting value corresponding to the light intensity H1 and storing it in the storage unit 310. In this case, the cleaning unit 400 may also be driven to perform the removal action, and the light intensity H1 obtained after the removal action may be used to calculate a new threshold setting value. For example, the new threshold setting value may be calculated using the original light intensity H0 and the light intensity H1. According to this method, it is possible to cope with the aging of the light, the deformation of the window 92, etc., and to prevent dirt from being missed.

[0117] Furthermore, during normal vehicle travel, when the vehicle ends travel without being judged as dirt, the threshold setting value may be updated by calculating a new threshold setting value corresponding to the light intensity H1 obtained during this period and storing it in the storage unit 310. This method can cope with aging of the light emission, deformation of the window 92, etc., and can prevent dirt from being missed.

[0118] As described above, according to this embodiment, when the predetermined contamination detection condition for the received light intensity H1 at the specific flight time Tc is satisfied, it is determined that there is contamination on the window 92 , so that it is possible to detect whether there is contamination on the window based on the received light intensity.

[0119] The control unit and method described in the present disclosure may also be implemented by a special-purpose computer, which is provided by a processor and a memory programmed to execute one or more functions concretized by a computer program. Alternatively, the control unit and method described in the present disclosure may also be implemented by a special-purpose computer, which is provided by a processor constituted by one or more special-purpose hardware logic circuits. Alternatively, the control unit and method described in the present disclosure may also be implemented by one or more special-purpose computers consisting of a processor and a memory programmed to execute one or more functions and a processor composed of one or more hardware logic circuits. In addition, the computer program may also be stored as an instruction executed by a computer in a computer-readable non-transient tangible recording medium.

[0120] The present disclosure is not limited to the above-described embodiments and their modifications, and can be implemented in various forms within the scope of the gist thereof. In addition, the above-described various characteristic structures can be arbitrarily combined and adopted as long as they do not contradict each other.

Claims

1. A distance measuring device, comprising: A light emitting part, emitting pulse light; A light receiving part receives reflected light of the pulse light reflected by an external object; a calculation unit that uses the flight time of the reflected light received by the light receiving unit to calculate the distance to the external object; a housing that accommodates the light emitting unit and the light receiving unit, wherein the housing has a window through which the pulse light and the reflected light pass; and The determination unit determines that dirt exists on the window when a predetermined dirt determination condition is met. The dirt determination condition includes a first condition, which is "for at least one pixel within the field of view of the distance measuring device, the light intensity at a specific flight time corresponding to the distance of the light path from the light emitting unit to the window is greater than an intensity threshold value", The computing unit is configured to create a histogram representing the intensity of received light at each of the plurality of flight times, and to provide the histogram to the determining unit. The determination unit is configured to calculate the intensity threshold by adding a threshold setting value to a baseline level of the histogram, in, The baseline level of the histogram is the average value of the signal values ​​other than the peak value in the histogram, and the threshold setting value is a fixed value. The distance measuring device further includes a storage unit, wherein the storage unit stores a distribution of the threshold setting values ​​within the field of view. The determination unit calculates the intensity threshold value for each pixel in the field of view using the threshold setting value stored in the storage unit.

2. The distance measuring device according to claim 1, in, The above-mentioned fouling determination condition further includes a second condition, which is: "Within the above-mentioned field of view, the number of pixels whose light intensity at the above-mentioned specific flight time is above the above-mentioned intensity threshold is above a predetermined first number threshold", or "Within the above-mentioned field of view, there exists a pixel cluster in which a plurality of pixels are continuous with each other and the light intensity at the above-mentioned specific flight time is above the above-mentioned intensity threshold, and the number of pixels in the above-mentioned pixel cluster is above a predetermined first number threshold." 3. The distance measuring device according to claim 1 or 2, in, The light receiving unit includes pixels for detecting window dirt in addition to pixels for distance measurement.

4. The distance measuring device according to claim 1 or 2, in, A set of data representing the distribution of the light intensity within the field of view is called a frame, and when N is an integer greater than 2, the determination unit determines whether there is dirt on the window using the light intensity in N consecutive frames and the intensity threshold.

5. The distance measuring device according to claim 4, in, When the contamination determination condition is continuously satisfied over the N consecutive frames, the determination unit determines that there is contamination on the window.

6. The distance measuring device according to claim 4, in, When N is an integer greater than or equal to 3 and M is an integer greater than or equal to 2 and less than or equal to N, the determination unit determines that there is dirt on the window when the contamination determination condition is satisfied in M ​​frames among the continuous N frames.

7. The distance measuring device according to claim 4, in, The determination unit determines whether the contamination determination condition is satisfied using a total value or an average value of the received light intensity and the intensity threshold value over the N consecutive frames.

8. The distance measuring device according to claim 1 or 2, in, A cleaning unit is further provided, and when it is determined that dirt is present on the window, the cleaning unit performs a removal operation for removing the dirt from the window.

9. The distance measuring device according to claim 8, in, The cleaning unit selects one of a plurality of cleaning methods according to a location where dirt exists on the window, and performs the selected cleaning method.

10. The distance measuring device according to claim 9, in, The cleaning unit has a plurality of cleaning units, each of which is responsible for removing dirt from a plurality of different regions of the window. The cleaning unit responsible for removing dirt is selected and cleaning is performed according to the region where the dirt exists in the plurality of different regions.

11. The distance measuring device according to claim 8, in, The cleaning unit selects one of a plurality of cleaning methods having different dirt removal capabilities according to the degree of dirt on the window, and executes the selected cleaning method.

12. The distance measuring device according to claim 11, in, The determination unit calculates any one of the following index values ​​as a contamination index value indicating the degree of contamination on the window: A first dirt index value represents a difference between the light intensity and the intensity threshold; A second dirt index value indicates the number of pixels where the above dirt exists; as well as The third dirt index value represents a summed value obtained by adding the difference between the light receiving intensity and the intensity threshold value for a plurality of pixels within the field of view. The dirt index value is notified to the cleaning unit.

13. The distance measuring device according to claim 8 as appended to claim 2, in, When the number of pixels whose light intensity at the specific flight time is greater than or equal to the intensity threshold is greater than or equal to the first number threshold, the determination unit performs the following operations: (a) when the number of pixels is greater than a second number threshold, the cleaning unit does not perform a removal operation, but instead performs a notification indicating that dirt is present on the window, wherein the second number threshold is greater than the first number threshold, (b) when the number of pixels is less than the second number threshold, causing the cleaning unit to perform the removal operation.

14. The distance measuring device according to claim 8, in, In a state where it is not determined that dirt is present on the window, the determination unit updates the threshold setting value by calculating a new threshold setting value based on the received light intensity and storing the new threshold setting value in the storage unit.

15. The distance measuring device according to claim 1 or 2, in, The determination unit notifies the outside of a position where the dirt is present on the window.

16. The distance measuring device according to claim 1 or 2, in, The calculation unit does not notify the outside of the distance obtained in the area where the dirt exists in the window, but outputs the distance obtained in the area where the dirt does not exist to the outside.

17. A distance measuring device comprising: A light emitting part, emitting pulse light; A light receiving part receives reflected light of the pulse light reflected by an external object; a calculation unit that uses the flight time of the reflected light received by the light receiving unit to calculate the distance to the external object; a housing that accommodates the light emitting unit and the light receiving unit, wherein the housing has a window through which the pulse light and the reflected light pass; and The determination unit determines that dirt exists on the window when a predetermined dirt determination condition is met. The dirt determination condition includes a first condition, which is "for at least one pixel within the field of view of the distance measuring device, the light intensity at a specific flight time corresponding to the distance of the light path from the light emitting unit to the window is greater than an intensity threshold value", The computing unit is configured to create a histogram representing the intensity of received light at each of the plurality of flight times, and to provide the histogram to the determining unit. In the above histogram, when the value obtained by subtracting the baseline level of the above histogram from the maximum value that the received light intensity can take is called the effective signal range width, in, The maximum value of the light receiving intensity is the total number of light receiving elements of each pixel used when creating the histogram. The baseline level of the histogram is the average value of the signal values ​​other than the peak value in the histogram. The determination unit is configured to calculate the intensity threshold by multiplying the effective signal range width by a threshold setting value and adding the baseline level to the multiplication result, wherein the threshold setting value is a coefficient less than 1. The distance measuring device further includes a storage unit, wherein the storage unit stores a distribution of the threshold setting values ​​within the field of view. The determination unit calculates the intensity threshold value for each pixel in the field of view using the threshold setting value stored in the storage unit.

18. The distance measuring device according to claim 17, in, The above-mentioned fouling determination condition further includes a second condition, which is: "Within the above-mentioned field of view, the number of pixels whose light intensity at the above-mentioned specific flight time is above the above-mentioned intensity threshold is above a predetermined first number threshold", or "Within the above-mentioned field of view, there exists a pixel cluster in which a plurality of pixels are continuous with each other and the light intensity at the above-mentioned specific flight time is above the above-mentioned intensity threshold, and the number of pixels in the above-mentioned pixel cluster is above a predetermined first number threshold." 19. The distance measuring device according to claim 17 or 18, in, The light receiving unit includes pixels for detecting window dirt in addition to pixels for distance measurement.

20. The distance measuring device according to claim 17 or 18, in, A set of data representing the distribution of the light intensity within the field of view is called a frame, and when N is an integer greater than 2, the determination unit determines whether there is dirt on the window using the light intensity in N consecutive frames and the intensity threshold.

21. The distance measuring device according to claim 20, in, When the contamination determination condition is continuously satisfied over the N consecutive frames, the determination unit determines that there is contamination on the window.

22. The distance measuring device according to claim 20, in, When N is an integer greater than or equal to 3 and M is an integer greater than or equal to 2 and less than or equal to N, the determination unit determines that there is dirt on the window when the contamination determination condition is satisfied in M ​​frames among the continuous N frames.

23. The distance measuring device according to claim 20, in, The determination unit determines whether the contamination determination condition is satisfied using a total value or an average value of the received light intensity and the intensity threshold value over the N consecutive frames.

24. The distance measuring device according to claim 17 or 18, in, A cleaning unit is further provided, and when it is determined that dirt is present on the window, the cleaning unit performs a removal operation for removing the dirt from the window.

25. The distance measuring device according to claim 24, in, The cleaning unit selects one of a plurality of cleaning methods according to a location where dirt exists on the window, and performs the selected cleaning method.

26. The distance measuring device according to claim 25, in, The cleaning unit has a plurality of cleaning units, each of which is responsible for removing dirt from a plurality of different regions of the window. The cleaning unit responsible for removing dirt is selected and cleaning is performed according to the region where the dirt exists in the plurality of different regions.

27. The distance measuring device according to claim 24, in, The cleaning unit selects one of a plurality of cleaning methods having different dirt removal capabilities according to the degree of dirt on the window, and executes the selected cleaning method.

28. The distance measuring device according to claim 27, in, The determination unit calculates any one of the following index values ​​as a contamination index value indicating the degree of contamination on the window: A first dirt index value represents a difference between the light intensity and the intensity threshold; A second dirt index value indicates the number of pixels where the above dirt exists; as well as The third dirt index value represents a summed value obtained by adding the difference between the light receiving intensity and the intensity threshold value for a plurality of pixels within the field of view. The dirt index value is notified to the cleaning unit.

29. The distance measuring device according to claim 24 as appended to claim 18, in, When the number of pixels whose light intensity at the specific flight time is greater than or equal to the intensity threshold is greater than or equal to the first number threshold, the determination unit performs the following operations: (a) when the number of pixels is greater than a second number threshold, the cleaning unit does not perform a removal operation, but instead performs a notification indicating that dirt is present on the window, wherein the second number threshold is greater than the first number threshold, (b) when the number of pixels is less than the second number threshold, causing the cleaning unit to perform the removal operation.

30. The distance measuring device according to claim 24, in, In a state where it is not determined that dirt is present on the window, the determination unit updates the threshold setting value by calculating a new threshold setting value based on the received light intensity and storing the new threshold setting value in the storage unit.

31. The distance measuring device according to claim 17 or 18, in, The determination unit notifies the outside of a position where the dirt is present on the window.

32. The distance measuring device according to claim 17 or 18, in, The calculation unit does not notify the outside of the distance obtained in the area where the dirt exists in the window, but outputs the distance obtained in the area where the dirt does not exist to the outside.

33. A method for detecting dirt on a window of a distance measuring device, in, The above-mentioned distance measuring device has: A light emitting part, emitting pulse light; A light receiving part receives reflected light of the pulse light reflected by an external object; a calculation unit that calculates the distance to the external object using the flight time of the reflected light received by the light receiving unit; and The housing is a housing for accommodating the light emitting unit and the light receiving unit, and the housing has a window for allowing the pulse light and the reflected light to pass through. The above method comprises the following steps: (a) using the output of the light receiving unit to obtain the intensity of received light at a specific flight time corresponding to the distance of the optical path from the light emitting unit to the window; and (b) when a dirt determination condition is satisfied, determining that dirt is present on the window, wherein the dirt determination condition includes a first condition, the first condition being "for at least one pixel within the field of view of the distance measuring device, the light intensity at the specific flight time is greater than an intensity threshold value", The computing unit is configured to create a histogram representing the intensity of received light at each of the plurality of flight times. The step (b) includes the step of calculating the intensity threshold by adding a threshold setting value to a baseline level of the histogram, wherein the baseline level of the histogram is an average value of signal values ​​other than a peak value in the histogram, and the threshold setting value is a fixed value. The distance measuring device further includes a storage unit, wherein the storage unit stores a distribution of the threshold setting values ​​within the field of view. In the step (b), the intensity threshold is calculated for each pixel in the field of view using the threshold setting value stored in the storage unit.

34. A method for detecting dirt on a window of a distance measuring device, in, The above-mentioned distance measuring device has: A light emitting part, emitting pulse light; A light receiving part receives reflected light of the pulse light reflected by an external object; a calculation unit that calculates the distance to the external object using the flight time of the reflected light received by the light receiving unit; and The housing is a housing for accommodating the light emitting unit and the light receiving unit, and the housing has a window for allowing the pulse light and the reflected light to pass through. The above method comprises the following steps: (a) using the output of the light receiving unit to obtain the intensity of received light at a specific flight time corresponding to the distance of the optical path from the light emitting unit to the window; and (b) when a dirt determination condition is satisfied, determining that dirt is present on the window, wherein the dirt determination condition includes a first condition, the first condition being "for at least one pixel within the field of view of the distance measuring device, the light intensity at the specific flight time is greater than an intensity threshold value", The computing unit is configured to create a histogram representing the intensity of received light at each of the plurality of flight times. In the above histogram, when the value obtained by subtracting the baseline level of the histogram from the maximum value that the received light intensity can take is called the effective signal range width, wherein the maximum value that the received light intensity can take is the total number of light receiving elements per pixel used when creating the above histogram, and the baseline level of the histogram is the average value of signal values ​​other than the peak value in the histogram, The step (b) comprises calculating the intensity threshold by multiplying the effective signal range width by a threshold setting value and adding the multiplication result to the baseline level, wherein the threshold setting value is a coefficient less than 1. The distance measuring device further includes a storage unit, wherein the storage unit stores a distribution of the threshold setting values ​​within the field of view. In the step (b), the intensity threshold is calculated for each pixel in the field of view using the threshold setting value stored in the storage unit.

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