JP2023010254A - Distance measuring device and distance measuring - Google Patents

Abstract

To provide a distance measuring device and a distance measuring method which determine whether or not a multi-path is present and which excel in measurement accuracy.SOLUTION: According to a distance measuring device 100 and a distance measuring method, since an optical pulse has a plurality of different waveform shapes per unit measurement time, it is possible to obtain a plurality of response pulses by a light reception unit 12 in response to reflection from a target object 101. Therefore, it is possible to calculate a distance using the detection timing of the plurality of response pulses included in detection information. A multi-path assessment unit 27 compares the plurality of response pulses with a plurality of optical pulses for each of waveform shapes in order of time sequence and determines whether or not a multi-path is present. It is possible to determine whether or not a multi-path is present, or which one is a response pulse of a detour circuit 52, as the waveform shapes of the optical pluses and response pulses in order of time sequence are similar when a multi-path is not present.SELECTED DRAWING: Figure 9

Description

The disclosure in this specification relates to a ranging device and a ranging method for measuring the distance to a target object.

As a rangefinder, there is a technology that uses light pulses to measure the distance to a target object based on the time of flight (TOF) of the light pulses. Specifically, part of the light emitted from the light source of the range finder is reflected by the target object and returns to the detector of the range finder. Then, the distance to the target object is estimated (see Patent Literature 1, for example).

JP 2017-173298 A

In the distance measuring device described in Patent Literature 1, for example, when there is another reflecting object near the shortest path between the light source and the target object, the light from the light source passes through the reflecting object to reach the target object. Then, a path different from the shortest path directly from the light source to the target object occurs, and a so-called multipath occurs. When multiple identical light pulses are emitted from the light source, multiple response pulses are generated in the normal case where there is no multipath. When a plurality of identical light pulses are emitted from the light source, multiple response pulses are generated in the presence of multipath.

Since a plurality of response pulses are thus generated regardless of the presence or absence of multipath, it is difficult to determine the presence or absence of multipath based on the simple number of response pulses. If the presence or absence of multipath is unknown, and the detected response pulse is the response pulse of the detour route, there is a risk of erroneous measurement of the distance, resulting in a problem of reduced distance measurement accuracy.

Therefore, the object of the disclosure has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a distance measuring apparatus and a distance measuring method that can determine the presence or absence of multipath and have excellent measurement accuracy.

The present disclosure employs the following technical means to achieve the aforementioned objects.

The range finder disclosed herein is a range finder (100) that irradiates a target area with light and measures the distance to a target object (101) in the target area. A light emission control unit (23) for controlling a light emitting unit (11) that emits light toward the target area, and a detection information acquisition unit (24) for acquiring detection information obtained by a light receiving unit (12) for detecting light from a target area. and a distance calculation unit (26) for calculating the distance to the target object using the detection information, and a multipath determination unit (27) for determining the presence or absence of multipath using the detection information, and a light emission control unit controls the light emitting unit to irradiate a plurality of light pulses having different waveform shapes per unit measurement time at different light emission times, and the distance calculation unit generates by reflecting the plurality of light pulses from the target object The distance is calculated using the detection timing of at least one response pulse, and the multipath determination unit uses the order in which the plurality of response pulses are received and the order in which the plurality of light pulses are emitted to determine the response pulses in the same order. This is a distance measuring device that compares waveform shapes with light pulses to determine the presence or absence of multipath.

The ranging method disclosed herein is a ranging method for measuring the distance to a target object (101) in a target region, wherein the processing performed by at least one processor (22) includes a unit measurement A light emitting unit (11) is controlled to irradiate a target region with light pulses having a plurality of different waveform shapes per time at different light emission times, and a light receiving unit (12) for detecting light from the target region is controlled. obtaining the obtained detection information, calculating the distance to the target object using the detection timing of at least one response pulse generated by the light pulse included in the detection information being reflected by the target object, and a plurality of responses Using the order in which pulses are received and the order in which a plurality of light pulses are emitted, the waveform shapes of response pulses and light pulses in the same order are compared to determine the presence or absence of multipath. The method.

According to such a distance measuring device and distance measuring method, the light pulse has a plurality of different waveform shapes and different emission times per unit measurement time. Obtainable. Therefore, the distance can be calculated using the detection timing of the response pulse included in the detection information. Also, the multipath determination unit compares the waveform shapes of the response pulse and the optical pulse in the same order to determine the presence or absence of multipath. When there is no multipath, the waveform shapes of the optical pulse and the response pulse at the same order are similar, so it is possible to determine the presence or absence of the multipath and which response pulse is the detour path. Therefore, since the distance can be measured by the response pulse of the shortest path included in the detection information, it is possible to realize a distance measuring device and a distance measuring method with excellent measurement accuracy.

It should be noted that the symbols in parentheses of each of the means described above are examples showing the correspondence with specific means described in the embodiments described later.

1 is a block diagram showing a distance measuring device 100 according to a first embodiment; FIG. 4 is a diagram showing functional blocks of the signal processing device 20; FIG. The figure which shows the emitted light of 1st Example. The figure explaining a light emission sequence. The figure which shows a response pulse. FIG. 11 shows a saturated response pulse; FIG. 10 is a diagram showing another example of response pulses; 4 is a flowchart showing processing of the signal processing device 20; FIG. 4 is a diagram showing multipath detection processing; Diagram explaining an example of factors that cause multipath 4 is a flowchart showing multipath determination processing; FIG. 10 is a diagram showing response waveforms when the number of effective echoes is 1; 10 is a flowchart showing processing when the number of valid echoes is 2; FIG. 10 is a diagram showing response waveforms when the number of effective echoes is 2; 4 is a flowchart showing processing when the number of valid echoes is 3; FIG. 10 is a diagram showing response waveforms when the number of effective echoes is 3; 4 is a flowchart showing processing when the number of valid echoes is 4; FIG. 10 is a diagram showing response waveforms when the number of effective echoes is 4; 10 is a flowchart showing multipath determination processing according to the second embodiment;

A plurality of embodiments for carrying out the present disclosure will be described below with reference to the drawings. In some cases, portions corresponding to the items described in the preceding embodiments are denoted by the same reference numerals, or one character is added to the preceding reference numerals to omit redundant description. Further, when a part of the configuration is explained in each embodiment, the other part of the configuration is assumed to be the same as the previously explained embodiment. It is possible not only to combine the parts specifically described in each embodiment, but also to partially combine the embodiments if there is no problem with the combination.

(First embodiment)
A first embodiment of the present disclosure will be described with reference to FIGS. 1 to 18. FIG. The distance measuring device 100 of this embodiment irradiates a target area with light and measures the distance to the target object 101 in the target area. The distance measuring device 100 includes an optical sensor 10 and a signal processing device 20, as shown in FIG. A distance measuring device 100 of this embodiment is mounted on a vehicle and measures the distance to a target object 101 around the vehicle.

The ranging device 100 is also called a LiDAR (Light Detection and Ranging/Laser Imaging Detection and Ranging) device. The distance measuring device 100 measures the distance to the reflection point by detecting reflected light from the reflection point with respect to irradiation of light. Range finder 100 is installed in a vehicle having at least one of an advanced driving support function and an automatic driving function, for example. The distance measuring device 100 is communicably connected to the in-vehicle ECU 30 via an in-vehicle LAN. The in-vehicle ECU 30 is an electronic control device that uses the measurement result of the distance measuring device 100 for processing such as advanced driving assistance and automatic driving.

The optical sensor 10 detects light irradiation and reflected light. The optical sensor 10 measures the time of flight of light by measuring the time difference between the time the light is emitted from the light source and the time the reflected light arrives. The optical sensor 10 includes a light emitting section 11 , a light receiving section 12 and a control circuit 13 .

The light emitting unit 11 emits light toward the target area. Light emitting unit 11 is a light source that emits laser light toward the outside of the vehicle, and is realized by, for example, a laser element. Under the control of the control circuit 13, the light emitting unit 11 emits intermittent pulsed beams of laser light. The light emitting unit 11 causes the movable optical member to scan the laser light in accordance with the irradiation timing of the laser light.

The light receiving unit 12 detects light from the target area. The light receiving unit 12 is configured to detect light from the surroundings of the vehicle, and has a plurality of light receiving elements. The light-receiving element is an imaging element that detects light including reflected light from the target object 101 with respect to laser light irradiation by the light-emitting unit 11 . The target object 101 is, for example, a feature around the vehicle. In the following, the reflected light from the target object 101 for this laser beam irradiation is simply referred to as "reflected light".

For example, the light receiving element is set to have a high sensitivity to the vicinity of the wavelength of the laser light emitted from the light emitting section 11 . The light receiving elements are arranged in a one-dimensional or two-dimensional array. The number of light receiving elements corresponds to the number of pixels. As an example of the light receiving element, a single photon avalanche diode (SPAD) is adopted. When one or more photons are incident on the SPAD, the electron doubling action due to avalanche doubling produces an electrical pulse. A SPAD can output an electric pulse, which is a digital signal, without going through an AD conversion circuit.

The control circuit 13 performs an irradiation function of scanning laser light and a reflected light detection function of detecting reflected light. In the irradiation function, the control circuit 13 controls irradiation and scanning of the laser light by the light emitting section 11 . In the reflected light detection function, the control circuit 13 reads the electric pulse output by the light receiving element of the light receiving section 12 .

Specifically, the control circuit 13 sequentially exposes and scans each of a plurality of scanning lines of the light-receiving element along with irradiation of the laser light. As a result, the control circuit 13 acquires the number of electric pulses for each time within the exposure time output from each light receiving element as detection data. Then, the control circuit 13 generates detection information that associates the elapsed time from the laser light irradiation time with the detection time of each detection signal within the exposure time indicated by the detection data. The control circuit 13 outputs the generated detection information to the signal processing device 20 .

The signal processing device 20 generates a point cloud image of the target object 101 based on detection information from the optical sensor 10 . The signal processing device 20 is a control device and, as shown in FIG. 1, a computer including at least one memory 21 and at least one processor 22 . The memory 21 non-temporarily stores or stores computer-readable programs and data. The memory 21 is implemented by at least one type of non-transitory tangible storage medium such as semiconductor memory, magnetic medium, and optical medium. The memory 21 stores various programs executed by the processor 22, such as a range finding program and an image processing program, which will be described later.

The processor 22 includes, as a core, at least one type of CPU (Central Processing Unit), GPU (Graphics Processing Unit), RISC (Reduced Instruction Set Computer), etc., for example. Processor 22 executes a plurality of instructions contained in, for example, a ranging program stored in memory 21 . The signal processing device 20 implements a distance measurement method for measuring the distance to the target object 101 in the target area by executing the distance measurement program. The signal processing device 20 also executes image processing for generating a point cloud image of the target object 101 from the detection result of the optical sensor 10 by executing an image processing program. In the signal processing device 20, a plurality of functional units are constructed by causing the processor 22 to execute a plurality of programs and a plurality of instructions. Specifically, the signal processing device 20 has, as functional units, a light emission control unit 23, a distance calculation unit 26, a detection information acquisition unit 24, a multipath determination unit 27, and an image generation unit 25, as shown in FIG.

The light emission control section 23 controls the light emission section 11 . The light emission control unit 23 gives an operation command to the optical sensor 10 . The control circuit 13 controls the light emitting section 11 based on the operation command. The light emission control section 23 controls the number of light pulses emitted by the light emitting section 11 per unit measurement time, the waveform shape, and the light emission intensity. A light pulse emitted by the light emitting unit 11 will be described later.

The detection information acquisition section 24 acquires the detection information obtained by the light receiving section 12 . The detection information acquiring unit 24 determines whether or not the waveform information of the detected reflected wave is valid for the newly acquired detection information. For example, the detection information acquiring unit 24 determines whether the waveform information is valid based on the magnitude of the S/N ratio of the waveform, the amplitude of the waveform, and the like. When determining that the waveform information is not valid, the detection information acquisition unit 24 rejects the acquired detection information. The detection information acquisition unit 24 acquires detection information for all pixels in each control cycle. The detection information acquisition unit 24 sequentially provides each acquired detection information to the distance calculation unit 26 .

The distance calculator 26 calculates the distance to the target object 101 using the detection information. The distance calculator 26 calculates the distance using detection timings of a plurality of response pulses generated by reflection of the light pulse from the target object 101 . Specifically, the distance calculator 26 calculates the distance to the reflection point. A reflection point is a point where laser light irradiation is reflected by the target object 101 . A reflection point can also be said to be an emission point of reflected light. The distance calculation unit 26 sequentially provides the calculated distance value to the reflection point to the image generation unit 25 .

The image generator 25 converts the distance value to the reflection point calculated by the distance calculator 26 into three-dimensional coordinate information. The image generator 25 converts the distance value into a three-dimensional coordinate value based on the focal length of the optical system, the number of light receiving elements, the size of the light receiving elements, and the like. A three-dimensional coordinate value is a coordinate system centered on the distance measuring device 100 . The image generation unit 25 converts all the distance values into a three-dimensional coordinate system and generates a point cloud image including coordinate information of the reflection points corresponding to the respective light receiving elements.

Next, the light pulse emitted by the light emitting section 11 will be described with reference to FIGS. 3 and 4. FIG. As shown in the first embodiment of FIG. 3, the emitted light has a plurality of light pulses, two in this embodiment, which have different light emission intensities and waveform shapes per unit measurement time and different light emission times. It is characterized by points. A unit measurement time is the generation time of one histogram. The unit measurement time is the time set for receiving the reflected light after the light is emitted. The unit measurement time is set based on, for example, the upper limit of distance measurement. In the first embodiment, the light emission intensity of the preceding optical pulse is greater than that of the latter optical pulse. Further, the light emission time of the light pulse in the former stage and the light pulse in the latter stage do not overlap and are shifted in terms of time. Hereinafter, the former-stage optical pulse is sometimes referred to as the first emitted pulse 41 and the latter-stage optical pulse is sometimes referred to as the second emitted pulse 42 . The first embodiment is also characterized in that the first emitted pulse 41 and the second emitted pulse 42 have different waveform shapes. The second emitted pulse 42 has a flatter shape than the first emitted pulse 41 and is left-right asymmetrical. In contrast, in the first comparative example, there is only one light pulse per unit measurement time.

Also, as shown in FIG. 4, a light emission time is assigned to each pixel. Light emission is controlled so that all pixels have the same light emission pattern. The light emission pattern is a combination of the number of light pulses per unit measurement time, the light emission intensity of the light pulses, and the waveform shape of the light pulses. Therefore, for example, the period for the first pixel p and the period for the second pixel p+1 are controlled to have the same light emission pattern. As described above, there are two light pulses within the generation time of one histogram, and the light emission is performed a plurality of times, for example, N times.

Next, a response pulse of reflected light will be described with reference to FIGS. 5 to 7. FIG. Since the emitted light has two light pulses as described above, under ideal conditions the reflected light also has two response pulses, as shown in FIG. Hereinafter, the front-stage response pulse may be referred to as a first response pulse 43 and the rear-stage response pulse may be referred to as a second response pulse 44 .

5 to 7, the vertical axis indicates the response power. Response power corresponds to light intensity. In this embodiment, the light receiving element is a SPAD, so the response power corresponds to the number of responses. The light-receiving unit 12 has a structure in which, when one or more photons, which are light particles, are incident on a pixel, SPADs are arranged for each pixel to output one large electric pulse signal by multiplication like an avalanche. Since one photon can be multiplied into many electrons, one photon can be detected, and the number of output electrical pulse signals is the number of responses.

When detecting the distance, it is desirable to use the detection time of the peak value of each response pulse. This is because the distance can be calculated with high accuracy based on the time difference between the peak value of each light pulse of the emitted light and the peak value of each response pulse. As shown in FIG. 4, peak values are obtained by sampling. The control circuit 13 counts the number of electric pulses output from each light receiving element at each sampling. The control circuit 13 then generates a histogram that records the number of electrical pulses for each sampling. Each class of the histogram indicates the time of flight (TOF) of light, which is the elapsed time for each sampling from the emission time of the light emitting unit 11 . The sampling frequency therefore corresponds to the time resolution of the TOF measurement.

When the peak value can be detected by sampling, as shown in FIG. 5, the peak value is used to calculate the distance. Further, as shown in FIG. 6, since the first response pulse 43 is saturated and the peak value cannot be detected with high accuracy, the peak value of the second response pulse 44 is used to calculate the distance.

Saturation as shown in FIG. 6 means the upper limit of the received light intensity of each light receiving element. When each light receiving element is a SPAD, the received light intensity corresponding to the number of responses of the SPAD in each light receiving element is obtained. If the distance is calculated using the saturated first response pulse 43, the distance is calculated by regarding the sampling time when the maximum number of responses is obtained as the peak value.

Also, FIG. 7 shows an example of a response pulse when emitted light has two light pulses within the generation time of one histogram, and the light emission is performed N=1 times. When N=1, the maximum number of responses to saturate is smaller than in FIG. Even when N=1, a peak value or saturation occurs in the response power, so the distance can be calculated even when N=1.

Next, a method for determining saturation will be described. Whether or not it is saturated can be determined using sampling values. For example, (1) when there are a predetermined number of K1 or more maximum responses, (2) when there are a predetermined number of K2 or more maximum responses, and when the half-value width is a predetermined T1 [ns] or more, and (3 ) When there are K3 or more maximum responses and the bottom width is equal to or greater than a predetermined T2 [ns], it is determined that saturation has occurred. The determination conditions (1) to (3) may be used individually, or may be used in combination. Also, the values of K1, K2 and K3 may be different or the same. Also, the values of T1 and T2 may be different or the same. These values are determined, for example, by preliminary experiments and simulations.

In order to determine whether the response pulse of the reflected light has an appropriate waveform with little noise, the distance calculator 26 calculates the signal-to-noise ratio (S/N ratio) of the first response pulse 43 and the second response pulse 44. calculate. If the calculated signal-to-noise ratio (hereinafter sometimes simply referred to as SN) satisfies a predetermined condition, it is assumed that the waveform is suitable with little noise. It can be judged that the noise becomes less as the SN becomes larger. SN can be calculated by the following equations (1) to (4).

ここで図５に示すように、ｌｍａｘは、受光素子が取り得る最大値であり、ｌｐｅａｋは、応答パルスのピーク値であり、ｌａｍｂは、応答パルスの最小値である。たとえば式（１）によって算出されたＳＮが、適正な信頼値である所定のしきい値以上の場合には、雑音が少ない適切な応答パルスと判断する。また数式（１）～（４）のＳＮの算出方法は、個別に用いてもよく、これらを組み合わせて判断してもよい。

Here, as shown in FIG. 5, lmax is the maximum value that the light receiving element can take, lpeak is the peak value of the response pulse, and lamb is the minimum value of the response pulse. For example, when the SN calculated by equation (1) is equal to or greater than a predetermined threshold value, which is an appropriate reliability value, it is determined that the response pulse is an appropriate response pulse with little noise. Further, the SN calculation methods of formulas (1) to (4) may be used individually or may be determined by combining them.

Next, specific processing of the distance calculation unit 26 will be described. The flowchart of FIG. 8 shows processing of a distance measurement program that is repeatedly executed in a short period of time by the distance calculation unit 26 when the power of the distance measurement device 100 is turned on. In FIG. 8, the first response pulse 43 is called Echo A and the second response pulse 44 is called Echo B. FIG.

In step S1, it is determined whether or not the echo A is saturated. If saturated, the process proceeds to step S2, and if not saturated, the process proceeds to step S10. In step S2, it is determined whether or not the echo B is saturated. If saturated, the process proceeds to step S3, and if not saturated, the process proceeds to step S5. The saturation determination method described above is used to determine saturation.

In step S3, both echo A and echo B are saturated, so the distance is calculated using echo A and echo B, and the process proceeds to step S4. Since both response pulses are saturated, the distance is calculated at each response pulse and the distance is calculated by averaging or the like. In step S4, a first flag is given, and this flow ends. Flags will be described later.

In step S5, it is determined whether or not the SN of echo B is equal to or greater than the threshold. If the SN is equal to or greater than the threshold, the process proceeds to step S6. . In step S8, since echo B is not saturated and the reliability of SN is high, echo B is used to calculate the distance, and the process proceeds to step S7. In step S7, a second flag is given, and this flow ends.

In step S8, echo B is not saturated, but the reliability of SN is low, so the saturated echo A is used to calculate the distance, and the process proceeds to step S9. In step S9, a third flag is given, and this flow ends.

In step S10, since echo A is not saturated, it is determined whether or not the SN of echo B is above the threshold. Otherwise, the process moves to step S13. In step S11, Echo A and Echo B are not saturated and the reliability of SN of Echo B is high, so the distance is calculated using Echo A and Echo B, and the process proceeds to Step S12. Since the first emitted pulse 41 has a higher emission intensity, it is estimated that the echo B based on the second emitted pulse 42 is not saturated when the echo A based on the first emitted pulse 41 is not saturated. there is In step S12, a fourth flag is given, and this flow ends.

In step S13, echo A is not saturated, but the SN of echo B is not above the threshold. Therefore, it is determined whether the SN of echo A is above the threshold. If not, the process moves to step S14, and if it is not equal to or greater than the threshold value, the process moves to step S16. In step S14, Echo A and Echo B are not saturated, but the SN reliability of Echo B is low and the SN reliability of Echo A is high. Therefore, only Echo A is used to calculate the distance. move to In step S15, a fifth flag is given, and this flow ends.

In step S16, echo A and echo B are not saturated, but since the reliability of SN of echo A and echo B is low, it is determined that there is no target object 101, and the process proceeds to step S17. In step S17, a sixth flag is given, and this flow ends.

In this way, there are six distance calculation patterns depending on the presence or absence of saturation of Echo A and Echo B and the presence or absence of reliability based on the SN of Echo A and Echo B. FIG. Also, different flags are assigned to the respective patterns.

The first to sixth flags are response pulse information regarding Echo A and Echo B. The response pulse information includes information such as the detection timing of each echo, received light intensity and SN. In this embodiment, the response pulse information is indicated by six flags. The first to sixth flags are given as information for roughly classifying the reflection intensity from the target object 101 for use in subsequent processing. The reflection intensity becomes weaker in order from the first flag to the sixth flag. For example, in the first flag, since echo A and echo B are saturated, the reflection intensity is the strongest, and there is a high possibility that the target object 101 is a high-brightness object, so using saturated echo A and echo B calculating the distance.

As shown in FIG. 8, the distance calculator 26 calculates the distance using the detection timing of the response pulse having a peak value below the upper detection limit of the light receiver 12 among the multiple response pulses included in the detection information. A response pulse having a peak value below the upper limit of detection is synonymous with a non-saturated response pulse. Specifically, as shown in steps S6, S11 and S14 in FIG. 8, when echo A and echo B are not saturated, the distance is calculated using the response pulse that is not saturated. This is for improving the distance measurement accuracy.

Further, as shown in FIG. 8, the distance calculation unit 26 selects, among a plurality of response pulses included in the detection information, response pulses having a peak value below the upper detection limit of the light receiving unit 12 and having a signal-to-noise ratio of a predetermined value. The distance is calculated using the detection timing of the response pulse greater than the confidence value. Specifically, as shown in steps S6, S11 and S14 in FIG. 8, the distance is calculated when SN is equal to or greater than the threshold value. This is because response pulses with less noise are used to improve distance measurement accuracy.

Furthermore, as shown in FIG. 8, the distance calculation unit 26 determines that, among the plurality of response pulses included in the detection information, if there is no response pulse having a peak value below the upper detection limit of the light receiving unit 12, The distance is calculated using the detection timing of all response pulses. Specifically, as shown in step S3 of FIG. 8, echo A and echo B are saturated, so echo A and echo B are used to calculate the distance. A saturated echo lowers the detection accuracy, but the use of two echoes can suppress the lowering of the detection accuracy.

Next, the shape of the response pulse will be explained. As shown in FIG. 9, in the emitted light of the first example, the shapes of the first emitted pulse 41 and the second emitted pulse 42 are different, and in the emitted light of the second comparative example, the first emitted pulse 41 and the second emitted pulse The shape of the pulse 42 is similar. In other words, the light emission control unit 23 controls the light emission unit 11 to irradiate a plurality of light pulses having different light emission intensities and the same waveform shape per unit measurement time. Here, the same waveform shape also includes a similar shape.

In the first embodiment and the second comparative example, the reflected light has the same shape as the outgoing light if it is a single pass. On the other hand, in the case of multipath, as shown in FIG. 9, the reflected light and the emitted light are different in the first embodiment. Specifically, the multipath determination unit 27 compares the waveform shapes of the plurality of response pulses included in the detection information and the plurality of light pulses emitted by the light emitting unit 11 in chronological order. More specifically, the time-series order is used to compare the waveform shapes of response pulses and light pulses in the same order using the order in which the plurality of response pulses are received and the order in which the plurality of light pulses are irradiated. Therefore, the waveform shapes of the first irradiated light pulse and the first received response pulse are compared, and the waveform shapes of the second irradiated light pulse and the second received response pulse are compared. Then, the multipath determination unit 27 determines whether or not there is a multipath. In the first embodiment, in the case of multipath, the waveform shapes of the first output pulse 41 and the first response pulse 43 are the same, and the waveform shapes of the second output pulse 42 and the second response pulse 44 are different. In the second comparative example, in the case of multipath, the waveform shapes of the first output pulse 41 and the first response pulse 43 are the same, and the waveform shapes of the second output pulse 42 and the second response pulse 44 are also the same.

Therefore, the multipath determination unit 27 can determine whether or not there is multipath based on the emitted light of the first embodiment. This is because, in the case of multipath, the reflected light from the bypass path 52 indicated by the dashed line has a long path length, so that it arrives at the light receiving section 12 later than the second response pulse 44 on the shortest path 51 indicated by the solid line. This is because the first response pulse 43a of the detour route 52 indicated by the dashed line may arrive early.

Next, determination of waveform similarity by the multipath determination unit 27 will be described. The multipath determination unit 27 determines whether or not the two pulses have the same waveform shape, for example, (1) within a range of values in which there is a difference in the area (sum) of the pulses; (3) Within a range of values with a difference in pulse peak heights (4) Within a range of values with a difference in pulse widths (5) Within a range of values with a difference in pulse tail widths They are judged to be the same if they are within a certain range of values. Therefore, the same waveform is not limited to being completely the same, but includes a certain similarity range. The similarity determination conditions (1) to (5) may be used individually or in combination.

FIG. 10 is a diagram illustrating an example of factors that cause multipath. As shown in FIG. 10, when the vehicle behind is equipped with the range finder 100 and the vehicle ahead is irradiated with light, if there is a puddle on the route, a detour route 52 reflected by the puddle is formed. Occur. The puddle is an out-of-range object 103 because it lies outside the region of interest. Due to such detour path 52, the response pulse is affected. When a multipath such as shown in FIG. 10 occurs, if it can be determined that the multipath exists as described above, it is possible to output information about the multipath and distance information. As a result, the other control device can improve the estimation accuracy of estimating that the road surface is wet from the information on the multipath and the information on the distance to the forward vehicle.

Besides multipath, other factors that affect the response pulse include, for example, internal reflections. However, echoes due to internal reflections (clutter) are less likely to occur than multipath occurrences, or echoes due to internal reflections can be removed separately. Therefore, detecting the presence or absence of multipath is more important than dealing with internal reflection echoes. Also, as multipaths, two routes, the shortest route 51 and the detour route 52, often occur, and the possibility of three or more routes occurring is low. Therefore, it is assumed that there are two multipaths, and the presence or absence of multipaths is determined.

Next, the case where the number of effective echoes is 1 to 4 will be explained. The number of effective echoes is the number of response pulses that are not saturated and have an appropriate waveform with little noise among the response pulses included in the detection information. When two light pulses are emitted as in the first embodiment, two response pulses are generated in the normal shortest path 51 and two response pulses are detected in the detour path 52. The maximum number of response pulses can be detected. is the case. Therefore, in this embodiment, the maximum number of effective echoes is four.

Processing according to the number of valid echoes will be described with reference to FIG. The flowchart shown in FIG. 11 is executed by the multipath determination unit 27 after counting the number of valid echoes. In step S21, it is determined whether or not the number of effective echoes is 0. If the number is 0, the process proceeds to step S22. If not, the process proceeds to step S24. In step S22, since the number of effective echoes is 0, it is determined that there is no target object 101, and the process proceeds to step S23.

In step S24, it is determined whether or not the number of valid echoes is one. If the number is one, the process proceeds to step S25. In step S25, since the number of effective echoes is 1, it is determined that there is no multipath, and the process proceeds to step S23.

FIG. 11 shows an example of waveforms when the number of effective echoes is one. As shown in FIG. 12, when the number of effective echoes is 1, there is only the first response pulse 43 and there is no second response pulse 44 . In this case, the second response pulse 44 is not returned, probably because the target object 101 is far away, so it can be determined that there is no multipath.

At step S26, it is determined whether or not the number of valid echoes is two. If the number is two, the process proceeds to step S27. In step S27, since the number of effective echoes is 2, processing for the number of effective echoes of 2, which will be described later, is executed, and the process proceeds to step S23.

At step S28, it is determined whether or not the number of valid echoes is three. If the number is three, the process proceeds to step S29. In step S29, since the number of effective echoes is 3, processing for the number of effective echoes of 3, which will be described later, is executed, and the process proceeds to step S23.

At step S210, it is determined whether or not the number of valid echoes is four. If the number is four, the process proceeds to step S211. In step S211, since the number of effective echoes is 4, processing for the number of effective echoes of 4, which will be described later, is executed, and the process proceeds to step S23. In step S212, since the number of effective echoes is 5 or more, it is judged as an error, and the process proceeds to step S23.

In step S23, each flag is given and this flow is terminated. Each flag is a multipath flag set in the processing up to step S23, or a flag corresponding to the determination result such as no object, no multipath, and error. This causes different flags to be set in each case. Therefore, by referring to the flag, it is possible to output judgment material in multipath judgment processing to another device. Also, by using flags, the amount of information can be suppressed. In other words, since the flag information corresponding to each flag is set in advance, other devices can refer to the associated flag information by designating the flag.

Next, processing corresponding to the number of effective echoes will be described with reference to FIGS. 13 to 18. FIG. In FIGS. 14, 16 and 18, the response pulse of detour path 52 is indicated by dashed lines. 13, 15 and 17, the first emitted pulse 41 is indicated as template A, the second emitted pulse 42 is indicated as template B, the response pulse with early arrival time is indicated as echo A, and the response pulse with late arrival time is indicated as echo B. are doing. Also, in FIGS. 13 to 18, the multipath flag is described as the M flag. The multipath flag is a flag that is set to output information about the multipath when there is a multipath. In this embodiment, as the multipath flags, the first to seventh multipath flags are set in advance. Information related to multipath includes, for example, the number of effective echoes, waveform similarity, response pulse intensity, and response pulse arrival time.

First, the processing when the number of valid echoes is two will be described. The process shown in FIG. 13 is started when the process moves to step S27 in FIG. In step S31, the waveform shapes of the plurality of response pulses and the plurality of output pulses are compared in chronological order, and the process proceeds to step S32.

In step S32, it is determined whether or not the echo B and the template B are similar. If they are similar, the process proceeds to step S33. Whether or not the waveforms are similar is determined by the similarity determination of the waveforms described above.

In step S33, since echo B and template B are similar, it is determined that there is no multipath, and this flow ends. FIG. 14 shows an example of waveforms when the number of effective echoes is two. As shown in FIG. 12, when the number of effective echoes is 2, there are cases where there are multipaths and there are cases where there are no multipaths. If there is no multipath, the waveform shapes of the second output pulse 42 and the second response pulse 44 are the same.

In step S34, it is determined whether or not the echo B and the template A are similar. If they are similar, the process proceeds to step S35. In step S33, since echo B and template A are similar, it is determined that there is multipath, the first multipath flag is set, and this flow ends. In step S36, it is determined that there is a multipath, a second multipath flag is set, and this flow ends.

As shown in FIG. 14, the waveform shapes of the second output pulse 42 and the second response pulse 44 are different when there is multipath. In the case of the first multipath flag of FIG. 12, the second response pulse 44 is similar in shape to the first output pulse 41, so the second response pulse 44 is determined to be the response pulse of the bypass route 52. FIG. In the case of the second multipath flag in FIG. 12, the second response pulse 44 is determined to be the response pulse of the detour path 52 because the shape of the second response pulse 44 is not similar to that of the first output pulse 41 . In the case of the first multipath flag, for example, the target object 101 is a low-reflection object, and the out-of-range object 103 contributing to multipath generation is also a low-reflection object. In the case of the second multipath flag, for example, the target object 101 is a normal reflecting object, and the out-of-range object 103 contributing to multipath generation is also a low reflecting object. Depending on the position and reflectance of such an out-of-range object 103, the detection timing of response pulses in multipaths differs.

Next, processing when the number of valid echoes is three will be described. The process shown in FIG. 15 is started when the process moves to step S29 in FIG. In step S41, the waveform shapes of the plurality of response pulses and the plurality of output pulses are compared in chronological order, and the process proceeds to step S42.

In step S42, it is determined whether or not the time interval between echo A and echo B is equal to or less than a predetermined set value T3. The process moves to step S44. The set value T3 is a value for determining whether or not the out-of-range object 103 is close when the number of effective echoes is three. The set value T3 is set by prior experiments or simulations, and is set smaller than the time interval between the first emitted pulse 41 and the second emitted pulse 42 . In step S43, since the time interval between echo A and echo B is equal to or less than the set value T3, it is determined that multipath exists, the third multipath flag is set, and this flow ends.

In step S44, it is determined whether or not the echo B and the template B are similar. If they are similar, the process proceeds to step S45. In step S43, since echo B and template B are similar, it is determined that there is multipath, the fourth multipath flag is set, and this flow ends. In step S46, it is determined that there is a multipath, a fifth multipath flag is set, and this flow ends.

As shown in FIG. 16, when the number of effective echoes is 3, there are 3 patterns, all of which have multipath. If the number of effective echoes is three, it is larger than the number of emitted light pulses, so it is determined that there is multipath. In the case of the third multipath flag in FIG. 16, the first response pulse 43 and the second response pulse 44 of the shortest path 51 are detected, and the first response pulse 43a of the detour path 52 is detected. The first response pulse 43 on the shortest path 51, the first response pulse 43a on the detour path 52, and the second response pulse 44 on the shortest path 51 are detected in this order. In this case, it becomes a factor for determining that the out-of-range object 103 is close.

In the case of the fourth multipath flag in FIG. 16, the second response pulse 44 of the shortest path 51 and the first response pulse 43a of the detour path 52 are superimposed. The first response pulse 43 on the shortest path 51, the superimposed pulse, and the second response pulse 44a on the detour path 52 are detected in this order. In this case, the out-of-range object 103 is determined to be farther than in the case of the third multipath flag.

Further, in the case of the fifth multipath flag in FIG. 16, the first response pulse 43 and the second response pulse 44 of the shortest route 51 are detected, and the first response pulse 43a of the detour route 52 is detected. The first response pulse 43 of the shortest path 51, the second response pulse 44 of the shortest path 51, and the first response pulse 43a of the detour path 52 are detected in this order. In this case, it is a factor in determining that the out-of-range object 103 is farther than the fourth multipath flag.

Next, processing when the number of valid echoes is four will be described. The processing shown in FIG. 17 is started when moving to step S211 in FIG. In step S51, the waveform shapes of the plurality of response pulses and the plurality of output pulses are compared in chronological order, and the process proceeds to step S52.

In step S52, it is determined whether or not the time interval between echo A and echo B is equal to or less than a predetermined set value T4. The process moves to step S54. The set value T3 is a value for determining whether or not the out-of-range object 103 is close when the number of effective echoes is four. The set value T4 is set by prior experiments or simulations, and is set smaller than the time interval between the first emitted pulse 41 and the second emitted pulse 42 .

In step S53, since the time interval between Echo A and Echo B is equal to or less than the set value T4, it is determined that multipath exists, the sixth multipath flag is set, and this flow ends. In step S54, since the time interval between echo A and echo B is not equal to or less than the set value T4, it is determined that multipath exists, the seventh multipath flag is set, and this flow ends.

As shown in FIG. 18, when the number of effective echoes is four, there are two patterns, all of which have multipath. In the case of the sixth multipath flag in FIG. 18, the first response pulse 43 and the second response pulse 44 of the shortest path 51 are detected, and the first response pulse 43a and the second response pulse 44a of the detour path 52 are detected. is the case. The first response pulse 43 of the shortest path 51, the first response pulse 43a of the detour path 52, the second response pulse 44 of the shortest path 51, and the second response pulse 44a of the detour path 52 are detected in this order. In this case, it becomes a factor for determining that the out-of-range object 103 is close.

In the case of the seventh multipath flag in FIG. 18, similarly, the first response pulse 43 and the second response pulse 44 of the shortest path 51 are detected, and the first response pulse 43a and the second response pulse 44a of the detour path 52 are detected. is detected. The first response pulse 43 of the shortest path 51, the second response pulse 44 of the shortest path 51, the first response pulse 43a of the detour path 52, and the second response pulse 44a of the detour path 52 are detected in this order. In this case, it is a factor in determining that the out-of-range object 103 is farther than the sixth multipath flag.

As described above, according to the distance measuring device 100 and the distance measuring method of the present embodiment, the light pulse has a plurality of different waveform shapes per unit measurement time. 12 can obtain multiple response pulses. Therefore, the distance can be calculated using the detection timings of a plurality of response pulses included in the detection information. The multipath determination unit 27 also compares the waveform shapes of the plurality of response pulses and the plurality of optical pulses in chronological order to determine the presence or absence of multipath. When there is no multipath, the time-series waveform shapes of the optical pulse and the response pulse are similar, so it is possible to determine the presence or absence of the multipath and which response pulse is the detour path 52 . Therefore, since the distance can be measured by the response pulse of the shortest path 51, the distance measuring device 100 and the distance measuring method with excellent measurement accuracy can be realized.

In this embodiment, the multipath determination unit 27 determines that multipath exists when the number of response pulses included in the detection information is greater than the number of light pulses emitted by the light emitting unit 11 per unit measurement time. do. As described with reference to FIG. 11, for example, when the number of output pulses is two, it is determined that multipath exists when the number of response pulses is three or more. This is because, if there is no multipath, the number of response pulses should be 2 or less. This makes it possible to determine whether or not there is a multipath together with whether or not the waveform shapes are similar.

Furthermore, in the present embodiment, the multipath determination unit 27 determines that the number of response pulses is two or more and that the waveform shape of the second optical pulse and the waveform shape of the second response pulse are different. Judge that there is a pass. As described with reference to FIG. 9 and the like, since the waveform shapes of the first output pulse 41 and the second output pulse 42 are different, the presence or absence of multipath can be determined based on the waveform shape of the second response pulse.

Further, in the present embodiment, the multipath judgment unit 27 judges the presence or absence of multipath by using a response pulse having a peak value below the detection upper limit of the light receiving unit 12 among the plurality of response pulses. Since waveform shapes are compared by response pulses having peak values, the presence or absence of multipath can be determined with high accuracy.

Furthermore, in the present embodiment, the multipath determination unit 27 compares only response pulses with a signal-to-noise ratio equal to or higher than a predetermined reliability value among the plurality of response pulses with the optical pulse. As a result, the waveform shape is compared by the response pulse whose SN is higher than the reliability value and the reliability is high, so the presence or absence of multipath can be determined with high accuracy.

Further, in the present embodiment, the distance measurement method includes controlling the light emitting unit 11 to irradiate the target area with light pulses having a plurality of different waveform shapes per unit measurement time, and detecting the light from the target area. The distance to the target object 101 is obtained using the detection timing of at least one response pulse generated by the reflection of the light pulse included in the detection information from the target object 101. calculating, and comparing multiple response pulses included in the detection information with multiple waveform shapes emitted by the light emitting unit 11 in chronological order to determine the presence or absence of multipath. As a result, the distance can be calculated with high accuracy as described above.

(Second embodiment)
Next, a second embodiment of the present disclosure will be described using FIG. 19 . This embodiment is characterized by the process of determining the presence or absence of multipath. Processing according to the number of valid echoes in this embodiment will be described with reference to FIG. The flowchart shown in FIG. 19 is executed by the multipath determination unit 27 after counting the number of valid echoes.

In step S61, it is determined whether or not the number of effective echoes is 0. If the number is 0, the process proceeds to step S62. If not, the process proceeds to step S64. In step S62, since the number of effective echoes is 0, it is determined that there is no target object 101, and the process proceeds to step S63.

At step S64, it is determined whether or not the number of valid echoes is one. If the number is one, the process proceeds to step S65. In step S65, since the number of valid echoes is 1, it is determined that there is no multipath, and the process proceeds to step S63.

At step S66, it is determined whether or not the number of valid echoes is two. If the number is two, the process proceeds to step S67. In step S67, it is determined whether or not echo B and template B are similar. If they are similar, the process proceeds to step S68.

In step S68, since echo B and template B are similar, it is determined that there is no multipath, and the process proceeds to step S63. In step S69, since echo B and template B are not similar, it is determined that there is multipath, and the process proceeds to step S63. In step S610, since the number of effective echoes is 3 or more, it is determined that there is multipath, and the process proceeds to step S63.

In step S63, each flag is given and this flow is terminated. The flags in this embodiment are flags set in the processing up to step S63, or flags corresponding to no object, no multipath, presence of multipath, and the number of effective echoes.

As described above, in this embodiment, the cases are classified into five cases according to the number of effective echoes and the similarity judgment of waveform shapes. In the flowchart shown in FIG. 11 described above, there are 11 cases including subroutine processing, whereas in the present embodiment there are five cases, so the processing can be simplified.

Therefore, in the present embodiment, it is possible to determine the presence or absence of multipath through simpler processing than in the first embodiment. This makes it possible to speed up the processing and reduce the load due to the processing.

(Other embodiments)
Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present disclosure.

The structures of the above-described embodiments are merely examples, and the scope of the present disclosure is not limited to the scope of these descriptions. The scope of the present disclosure is indicated by the description of the claims, and further includes all changes within the meaning and range of equivalents to the description of the claims.

In the first embodiment described above, there are two large and small optical pulses of emitted light, but the number is not limited to two, and may be three or more. Also, the emission intensity of the light pulses of the emitted light may be the same. Further, although the light receiving unit 12 is configured using a SPAD, it is not limited to the SPAD, and may be another image sensor such as a CMOS sensor.

The functions realized by the signal processing device 20 in the first embodiment described above may be realized by hardware and software different from those described above, or a combination thereof. The signal processor 20 may, for example, communicate with other controllers, and the other controllers may perform some or all of the processing. When signal processor 20 is implemented by electronic circuitry, it can be implemented by digital circuitry, including numerous logic circuits, or by analog circuitry. Specifically, the signal processing device 20 may be a locator ECU that estimates the vehicle's own position. The signal processing device 20 may be an ECU that controls advanced driving assistance or automatic driving of the vehicle. The signal processing device 20 may be an ECU that controls communication between the vehicle and the outside world.

The signal processing device 20 may further include an FPGA (Field-Programmable Gate Array), an NPU (Neural network Processing Unit), and an IP core having other dedicated functions. Such a signal processing device 20 may be individually mounted on a printed circuit board, or may be mounted on an ASIC (Application Specific Integrated Circuit), FPGA, or the like.

In the first embodiment described above, the distance measuring device 100 is used in a vehicle, but it is not limited to being mounted in the vehicle, and at least part of it may not be mounted in the vehicle.

DESCRIPTION OF SYMBOLS 10... Optical sensor 11... Light-emitting part 12... Light-receiving part 13... Control circuit 14... Pixel 20... Signal processing apparatus 21... Memory 22... Processor 23... Light emission control part 24... Detection information acquisition part 25... Image generation part 26... Distance calculation Part 27 Multipath determination part 30 In-vehicle ECU 41 First emitted pulse 42 Second emitted pulse 43 First response pulse 44 Second response pulse 51 Shortest path 52 Detour path 100 Ranging device 101 Target object 103 ... out-of-range object

Claims (9)

A distance measuring device (100) for measuring a distance to a target object (101) in the target region by irradiating light toward the target region,
a light emission control unit (23) for controlling a light emission unit (11) that emits light toward the target area;
a detection information acquisition unit (24) for acquiring detection information obtained by a light receiving unit (12) for detecting light from the target area;
a distance calculation unit (26) for calculating the distance to the target object using the detection information;
a multipath determination unit (27) that determines the presence or absence of multipath using the detection information,
The light emission control unit controls the light emitting unit to irradiate light pulses having a plurality of different waveform shapes per unit measurement time at different light emission times,
The distance calculation unit calculates the distance using detection timing of at least one response pulse generated by reflection of the plurality of light pulses from the target object,
The multipath determination unit uses the order in which the plurality of response pulses are received and the order in which the plurality of light pulses are emitted to compare the waveform shapes of the response pulses and the light pulses in the same order. , a ranging device that determines the presence or absence of multipath. When the number of response pulses included in the detection information detected per unit measurement time is greater than the number of light pulses emitted by the light emitting unit per unit measurement time, the multipath determination unit 2. The distance measuring device according to claim 1, wherein it determines that there is multipath. When the number of response pulses included in the detection information is two or more and the waveform shape of the second optical pulse is different from the waveform shape of the second response pulse, the multipath determination unit 3. The distance measuring device according to claim 1, wherein the determination is that there is a multipath. The light emission control unit controls the light emitting unit to irradiate a plurality of light pulses having different light emission intensities and different waveform shapes per unit measurement time,
1-, wherein the multipath judgment unit judges the presence or absence of multipath by using the response pulse having a peak value below the upper detection limit of the light receiving unit among the plurality of response pulses included in the detection information. 4. The distance measuring device according to any one of 3. 2. The multipath determination unit compares only the response pulses with a signal-to-noise ratio equal to or higher than a predetermined reliability value among the plurality of response pulses included in the detection information with the optical pulse. 5. The distance measuring device according to any one of 4. The range finder according to any one of claims 1 to 5, wherein the distance calculator outputs response pulse information regarding a plurality of response pulses included in the detection information. The light emission control unit controls the light emitting unit to irradiate two light pulses having different light emission intensities, different light emission times, and different waveform shapes per unit measurement time,
The distance calculation unit is configured such that the number of response pulses included in the detection information is three, and the first and second response pulses are detected among the plurality of response pulses included in the detection information. 7. The distance measuring apparatus according to claim 6, wherein different response pulse information is output depending on whether the interval of detection time from said response pulse detected is equal to or less than a predetermined set value and when it is greater than said set value. The light emission control unit controls the light emitting unit to irradiate two light pulses having different light emission intensities, different light emission times, and different waveform shapes per unit measurement time,
The distance calculation unit is configured such that the number of response pulses included in the detection information is four, and the first and second response pulses are detected among the plurality of response pulses included in the detection information. 7. The distance measuring apparatus according to claim 6, wherein different response pulse information is output depending on whether the interval of detection time from said response pulse detected is equal to or less than a predetermined set value and when it is greater than said set value. A ranging method for measuring a distance to a target object (101) in a target area, comprising:
In the processing performed by at least one processor (22),
controlling the light emitting unit (11) to irradiate the target region with light pulses having a plurality of different waveform shapes per unit measurement time at different light emission times;
Acquiring detection information obtained by a light receiving unit (12) that detects light from the target area;
calculating the distance to the target object using the detection timing of at least one response pulse generated by the reflection of the light pulse included in the detection information from the target object;
Using the order in which the plurality of response pulses are received and the order in which the plurality of light pulses are emitted, the waveform shapes of the response pulses and the light pulses in the same order are compared to determine the presence or absence of multipath. Ranging methods, including:

Images