Measuring device

Abstract

To estimate a light receiving timing and the incident quantity of reflected light even when the incident quantity of reflected light on a light receiving surface is saturated.SOLUTION: A measuring device comprises: a light projecting unit that emits light; a light receiving unit that receives reflected light that is the light emitted from the light projecting unit and reflected by and returning from a measurement object, and has a light receiving surface on which a plurality of photon count type light receiving elements are arranged in an array; and a controller. The controller executes histogram creation processing of creating a histogram on the basis of output values from the plurality of light receiving elements, light receiving timing estimation processing of estimating the timing to receive the reflected light on the basis of a first reaching timing at which the histogram reaches an intermediate value first, which is between the maximum value and the minimum value of the waveform of the histogram, and a second reaching timing at which the histogram reaches the intermediate value next, and output processing of outputting information according to the distance to the measurement object on the basis of a projection timing at which the light projecting unit emits light, and the light receiving timing.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a measurement device. [Background technology]

[0002] With the advancement of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development of LiDAR (Light Detection And Ranging) is being conducted as one of the measurement devices used to grasp the surrounding environment and estimate the vehicle's self-position while driving. LiDAR is equipped with a projector that projects (irradiates) laser light onto the measurement target, and a receiver that receives the reflected light that reflects the laser light back from the measurement target. LiDAR outputs information about the measurement target by measuring the distance to the measurement target based on the difference between the timing when the projector emits the laser light and the timing when the receiver receives the reflected light.

[0003] The light receiver has a light receiving surface on which a plurality of photon counting type light receiving elements (SPAD: Single Photon Avalanche Diode) are arranged in an array. In the measurement device, the output values ​​from a predetermined number of light receiving elements are integrated for a predetermined time, and the integrated value is processed as one pixel to generate a histogram. The timing at which the peak of the generated histogram is detected is regarded as the timing at which the reflected light is received, and the distance to the measurement target is measured (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-91760 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the amount of incident light of reflected light on the light receiving surface may exceed a predetermined upper limit, resulting in a saturated state. In this saturated state, the histogram waveform reaches the upper limit before the peak timing of the amount of incident light of reflected light on the light receiving surface arrives, and the timing at which the histogram waveform first reaches the upper limit is regarded as the timing at which the reflected light is received. Therefore, in the saturated state, the distance to the measurement target may be measured as shorter than the actual distance. Furthermore, in the saturated state, it is not even possible to estimate the amount of incident light of reflected light.

[0006] This specification discloses a technique that can solve at least one of the above problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms.

[0008] (1) A measuring device disclosed in this specification is a measuring device including a light projector that emits light, a light receiver having a light receiving surface on which a plurality of photon counting type light receiving elements are arranged in an array and that receives reflected light that is emitted from the light projector and reflected back to an object to be measured, and a controller, wherein the controller executes a histogram generation process that generates a histogram based on output values ​​from the plurality of light receiving elements, a light receiving timing estimation process that estimates a light receiving timing of the reflected light based on a first arrival timing at which the histogram first reaches an intermediate value between a maximum value and a minimum value of the waveform of the histogram and a second arrival timing at which the histogram next reaches the intermediate value, and an output process that outputs information corresponding to the distance to the object to be measured based on the light projecting timing at which the light projector emits light and the light receiving timing.

[0009] The inventors have newly discovered that the relative relationship between the first arrival timing and the second arrival timing at which the histogram reaches the median value correlates with the peak timing of the incident light amount of the reflected light on the light receiving surface. Therefore, with this measuring device, even when the incident light amount of the reflected light on the light receiving surface becomes saturated, the light receiving timing can be estimated based on the first arrival timing and the second arrival timing.

[0010] (2) In the above measuring device, the controller may be further configured to execute a light receiving timing correction process for correcting the light receiving timing according to the height of the peak of the histogram when the histogram is below the saturation level. The present inventor has newly discovered that the peak timing of the incident light amount of the reflected light on the light receiving surface varies according to the height of the peak of the incident light amount of the reflected light on the light receiving surface. Therefore, in the measuring device, in a non-saturated state in which the histogram peak can be detected, the light receiving timing is corrected according to the height of the histogram peak. Therefore, according to the measuring device, when the histogram is below the saturation level, it is possible to suppress an error in the light receiving timing caused by the high and low peak intensity of the incident light amount of the reflected light on the light receiving surface.

[0011] (3) In the above measuring device, the controller may further be configured to execute a light receiving timing correction process for correcting the light receiving timing according to the length of the time difference between the first arrival timing and the second arrival timing when the histogram exceeds a saturation level. The inventor has newly discovered that the time difference between the first arrival timing and the second arrival timing correlates with the peak intensity of the amount of incident light of the reflected light on the light receiving surface. Therefore, in this measuring device, even in a saturated state in which the peak of the histogram cannot be detected, the light receiving timing is corrected according to the length of the time difference between the first arrival timing and the second arrival timing of the histogram. Therefore, according to this measuring device, when the histogram exceeds the saturation level, it is possible to suppress an error in the light receiving timing caused by the high and low peak intensity of the amount of incident light of the reflected light on the light receiving surface.

[0012] (4) In the above measuring device, the controller may further perform a disturbance light histogram generation process for generating a disturbance light histogram based on output values ​​from the plurality of light receiving elements when the reflected light is not irradiated onto the light receiving surface, and an arrival timing correction process for correcting the second arrival timing according to the height of a peak of the disturbance light histogram. The present inventor has newly discovered that the second arrival timing varies according to the height of a peak of the amount of incident disturbance light. Therefore, in this measuring device, the second arrival timing is corrected according to the height of the peak of the disturbance light histogram. Therefore, according to this measuring device, it is possible to suppress an error in the light receiving timing caused by the high and low peak intensity of the amount of incident disturbance light.

[0013] (5) The measurement device disclosed in this specification includes a projector that emits light, a light receiver that receives the light emitted from the projector and reflected back to a measurement target and has a light receiving surface on which a plurality of photon counting type light receiving elements are arranged in an array, and a controller, in which the controller executes a histogram generation process that generates a histogram based on output values ​​from the plurality of light receiving elements, and a first incident light amount estimation process that estimates the amount of incident light of the reflected light based on the time difference between a first arrival time when the histogram first reaches an intermediate value between the maximum value and the minimum value of the waveform of the histogram and a second arrival time when the histogram next reaches the intermediate value. According to this measurement device, even if the amount of incident light of the reflected light on the light receiving surface is saturated, it is possible to estimate the amount of incident light of the reflected light based on the waveform width of the histogram.

[0014] (6) In the above measurement device, the controller further determines, when the peak of the histogram is lower than a saturation level and the difference between the peak of the histogram and the amount of incident ambient light is equal to or greater than a reference value, the output values ​​from the plurality of light receiving elements, <Expression 1> Amount of reflected light incident on the board = 10 (a×受光素子からの出力値+b) * a and b are coefficients and a second incident light amount estimation process for estimating the amount of incident light of the reflected light based on a logarithmic function represented by: According to this measurement device, when the amount of incident light of the reflected light on the light receiving surface is not saturated, the amount of incident light of the reflected light can be estimated by a relatively simple function.

[0015] (7) In the above measurement device, the controller further determines, when the peak of the histogram is lower than a saturation level and the difference between the peak of the histogram and the amount of incident ambient light is less than a reference value, the output values ​​from the plurality of light receiving elements, <Expression 2> Amount of reflected light incident on the light receiving element = c × output value from the light receiving element + d *c and d are coefficients and a third incident light amount estimation process for estimating the amount of incident light of the reflected light based on a real function represented by: According to this measurement device, when the amount of incident light of the reflected light on the light receiving surface is not saturated, the amount of incident light of the reflected light can be estimated by a relatively simple function.

[0016] (8) In the above measurement device, the controller may further be configured to execute a first coefficient correction process for correcting the coefficient a of the logarithmic function to a smaller value as the amount of incident light of the disturbance light increases. According to this measurement device, when the amount of incident light of the reflected light on the light receiving surface is in a non-saturated state, it is possible to estimate the amount of incident light of the reflected light using a relatively simple function while suppressing the influence of disturbance light.

[0017] (9) In the above measurement device, the controller may further be configured to execute a second coefficient correction process for correcting the coefficient c of the real function to a smaller value as the amount of incident light of the disturbance light increases. According to this measurement device, when the amount of incident light of the reflected light on the light receiving surface is in a non-saturated state, it is possible to estimate the amount of incident light of the reflected light using a relatively simple function while suppressing the influence of disturbance light.

[0018] The techniques disclosed in this specification can be realized in various forms, for example, in the form of a measurement device, a measurement method, and the like. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device 10 according to an embodiment. [Diagram 2] A diagram showing the relationship between the output value of a SPAD that constitutes one pixel and a histogram. [Diagram 3] A flowchart showing the measurement process executed by the TOF measurement device 40 and the control circuit 42. [Figure 4] FIG. 13 is an explanatory diagram illustrating histograms in a non-saturated state and a saturated state; [Diagram 5] FIG. 13 is an explanatory diagram showing the relationship between the level of the incident light amount of the disturbance light L3 and the second arrival timing T2. [Figure 6] FIG. 13 is an explanatory diagram showing the relationship between the level of the incident light amount of the reflected light L2 and the timing of receiving the reflected light L2. [Figure 7] FIG. 13 is an explanatory diagram showing the relationship between the amount of incident light of the reflected light L2 and the peak intensity of the histogram (SPAD output value). [Figure 8] FIG. 11 is an explanatory diagram showing the relationship between the amount of incident reflected light L2 and the peak intensity (SPAD output value) of the histogram for each region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A. Embodiment: A-1. Configuration of the measuring device 10: FIG. 1 is a block diagram showing a schematic configuration of a measuring device 10 in this embodiment. As shown in FIG. 1, the measuring device 10 includes a projector 20 that irradiates an emitted light L1 (e.g., a light beam (laser light)) onto a measuring object W, and a light receiver 30 that receives reflected light L2 (return light) that is reflected by the measuring object W and returns from the emitted light L1, and functions as a LiDAR. The measuring device 10 measures the difference between the timing at which the projector 20 emits the emitted light L1 and the timing at which the light receiver 30 receives the reflected light L2 (time of flight of the laser light, hereinafter referred to as "TOF" (Time of Flight)) to acquire information about the measuring object W.

[0021] The measuring device 10 is mounted on, for example, a vehicle (not shown) equipped with AD or ADAS. For example, while the vehicle is traveling, the measuring device 10 assists in the detection of objects such as people and other vehicles, and provides various types of information to other devices and users that are useful for ensuring the safety of the driver of the vehicle and those around the vehicle, and for reducing damage to surrounding objects while the vehicle is being driven.

[0022] The light projector 20 includes a light source 22, a light projecting optical system 24, a light projecting control device 26, and a current source 28.

[0023] The light source 22 includes a light emitting source having one or a plurality of light emitting elements (not shown), or one or a plurality of light emitting element arrays (e.g., light emitting elements arranged linearly (one-dimensionally) or planarly (two-dimensionally)). The light emitting element is, for example, a laser diode, a surface-emitting type laser light emitting element (e.g., VCSEL (Vertical Cavity Surface Emitting Laser, hereinafter referred to as a "surface light emitting element"), a surface light emitting element array (e.g., a VCSEL array) in which a plurality of surface light emitting elements are arranged one-dimensionally or two-dimensionally on a substrate (semiconductor substrate, ceramic substrate, etc.), etc.

[0024] The current source 28 supplies a current corresponding to a control signal input from the light projection control device 26 to the light emitting element constituting the light source 22. The current source 28 supplies, for example, a periodic square wave current to the light emitting element for turning on and off the current flowing through the light emitting element.

[0025] The light-projection control device 26 generates a control signal for the current source 28 and inputs it to the current source 28, thereby controlling the current (drive current) supplied from the current source 28 to the light-emitting element. The light-projection control device 26 inputs a signal indicating the timing at which the light-emitting element emits light (the timing at which the light-emitting element emits light; hereinafter, referred to as "light-projection timing") to the TOF measurement device 40. The light-projection control device 26 periodically and repeatedly controls the on-off of a current flowing through the light-emitting element, for example, thereby causing the light-emitting element to periodically and repeatedly emit light.

[0026] The light projection optical system 24 adjusts the light distribution of the emitted light L1, for example, by applying an optical effect (such as refraction, scattering, or diffraction) to the light emitted by the light source 22. The light projection optical system 24 is configured using optical components, for example, various lenses such as a collimator lens, a reflector (mirror), and the like.

[0027] The light receiver 30 includes a light receiving section 32 and a light receiving optical system 34 .

[0028] The light receiving optical system 34 collects reflected light L2, which is light emitted from the projector 20 and reflected by the measurement target W or the like and returns, onto the light receiving unit 32. The light receiving optical system 34 is configured using optical components, such as various lenses such as a collecting lens, various filters such as a wavelength filter, and a reflecting mirror (mirror).

[0029] The light receiving unit 32 has a plurality of light receiving elements. The light receiving unit 32 generates a light receiving signal having a current level or a voltage level according to the intensity of the reflected light L2 by photoelectrically converting the reflected light L2 incident from the light receiving optical system 34. The light receiving unit 32 inputs to the TOF measurement device 40 a signal indicating the timing at which the light receiving elements constituting the light receiving unit 32 receive the reflected light L2 (hereinafter referred to as "light receiving timing") and the light receiving signal generated by the light receiving elements.

[0030] The measurement apparatus 10 further includes a TOF measurement device 40, a control circuit 42, and a communication I / F (Interface) 50. In this embodiment, the TOF measurement device 40 and the control circuit 42 are an example of a controller.

[0031] The TOF measurement device 40 obtains the TOF based on a signal indicating the light projection timing input from the light projection control device 26 and a signal indicating the light reception timing input from the light receiving unit 32. The TOF measurement device 40 has, for example, a time measurement IC (Integrated Circuit) equipped with a TDC (Time to Digital Converter) circuit. The TOF measurement device 40 inputs the obtained TOF and the light reception signal input from the light receiving unit 32 to the control circuit 42.

[0032] The control circuit 42 has a processor (such as a central processing unit (CPU), a micro processing unit (MPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and a digital signal processor (DSP)). Based on the light receiving signal and the TOF input from the TOF measurement device 40, the control circuit 42 generates information used for various measurements such as detection and distance measurement of the measurement target W. The information is, for example, a histogram used in time correlated single photon counting, a distance to each point of the measurement target W, a point cloud (point cloud information), and the like. The control circuit 42 also controls the light projection control device 26 and the light receiving unit 32. For example, the control circuit 42 controls the light projection timing and the light receiving timing described above so that the process for generating the histogram is accelerated or optimized by controlling the light projection control device 26 and the light receiving unit 32. The information generated by the control circuit 42 is provided (transmitted) via the communication I / F 50 to a device that uses the information (hereinafter, referred to as "various use devices 60").

[0033] The various utilization devices 60 perform, for example, creating an environmental map using a point cloud, self-position estimation (SLAM (Simultaneous Localization and Mapping)) using a scan matching algorithm (NDT (Normal Distributions Transform), ICP (Iterative Closest Point), etc.), and the like.

[0034] A-2. Signal Processing in TOF Measurement Device 40: In this embodiment, the photoreceiver 30 (light receiving section 32) has a light receiving surface 32A on which a plurality of light receiving elements are arranged in a linear (one-dimensional) array or a planar (two-dimensional) array. In this embodiment, the light receiving elements are SPADs, which are an example of photon counting type light receiving elements. The SPAD responds with a certain probability (e.g., 20%) when a photon is incident, and outputs one pulse when a photon is detected.

[0035] In the light receiving unit 32 using SPADs, one pixel in an image (hereinafter referred to as a "received light image") acquired based on a light receiving signal from the SPAD is determined by the "number of SPAD units M" and the "number of SPAD integrations U". The number of SPAD units M is the number of SPADs adjacent to each other on the light receiving surface 32A. For example, in a configuration in which a plurality of SPADs are two-dimensionally arranged on the light receiving surface 32A, the number of SPAD units M is 9 (=3×3) or 16 (=4×4). The larger the number of SPAD units M, the lower the resolution of the received light image. The number of SPAD integrations U is the number of times the output value of each SPAD is integrated at a predetermined sampling timing. A large number of SPAD integrations U means a long integration time of the SPAD output values. The larger the number of SPAD integrations U, the lower the frame rate of the received light image (the number of images (frames) that make up a video per second). The TOF measurement device 40 generates a histogram for each pixel based on the output values ​​of the SPAD that constitutes each pixel.

[0036] FIG. 2 is an explanatory diagram showing the relationship between the output value of the SPAD constituting one pixel and a histogram. The upper part of FIG. 2 shows the time change of the output value of each SPAD. The lower part of FIG. 2 shows a graph G showing the time change of the incident light amount (received light intensity, irradiation intensity) per unit area of ​​the light (including the reflected light L2 and the disturbance light (background light) L3) irradiated to one pixel of the light receiving surface 32A, and a histogram H generated by the TOF measurement device 40. Q1 in FIG. 2 means one pulse output when each SPAD detects a photon when the reflected light L2 is incident, and Q2 means one pulse output when each SPAD detects a photon when the reflected light L2 is not incident and only the disturbance light L3 is incident.

[0037] In the graph G, the waveform showing a relatively high peak intensity is the waveform when the reflected light L2 is incident on the light receiving surface 32A, and the waveform showing a relatively low peak intensity is the waveform when the reflected light L2 is not incident and only the disturbance light L3 is incident on the light receiving surface 32A. The incident light amount of the reflected light L2 is higher than the incident light amount of the disturbance light L3. Therefore, as shown in the histogram H, when the reflected light L2 is incident on the light receiving surface 32A, the number of detected photons in one pixel is statistically large, and when the reflected light L2 is not incident and only the disturbance light L3 is incident on the light receiving surface 32A, the number of detected photons in one pixel is statistically small. The TOF measurement device 40 estimates the light receiving timing based on the timing corresponding to the waveform showing a relatively high peak in the histogram H.

[0038] A-3. Estimation process of the timing of receiving reflected light L2 and the reflectance of the measurement target W: 3 is a flowchart showing a measurement process executed by the TOF measurement device 40 and the control circuit 42. In this measurement process, the timing of receiving the reflected light L2 and the reflectance of the measurement object W are estimated.

[0039] (Estimation of reception timing of reflected light L2): As shown in FIG. 3, the TOF measurement device 40 executes a histogram generation process to generate a histogram based on output values ​​from a plurality of SPADs (S110). The TOF measurement device 40 sequentially stores the output values ​​from the plurality of SPADs in a predetermined memory area. The TOF measurement device 40 reads the output values ​​from the plurality of SPADs recorded in the memory area at each predetermined sampling timing and sequentially generates a histogram for each pixel. The TOF measurement device 40 extracts a histogram including a signal waveform of the reflected light L2 based on a comparison between the sequentially generated histograms and a signal detection threshold. In this embodiment, the signal detection threshold is the same value as the determination threshold for determining the presence or absence of the reflected light L2, but may be a value lower than the determination threshold.

[0040] Next, the TOF measurement device 40 acquires a first arrival time T1 and a second arrival time T2 in a histogram including the signal waveform of the extracted reflected light L2 (S120). The first arrival time T1 is the timing when the waveform of the histogram first reaches the median value Lh, and the second arrival time T2 is the timing when the waveform of the histogram next reaches the median value Lh. The median value Lh is a value between the maximum value (corresponding to the peak of the signal waveform of the reflected light L2) and the average value (corresponding to the signal waveform of the disturbance light L3) of the waveform of the histogram. In addition, it is preferable that the median value Lh is a value obtained by adding a height value of a predetermined ratio to the difference between the maximum value and the minimum value to the minimum value. In this embodiment, the predetermined ratio is 1 / 2, but is not limited to this, and may be, for example, 3 / 4.

[0041] Fig. 4 is an explanatory diagram illustrating histograms in a non-saturated state and a saturated state. The non-saturated state is a state in which the peak intensity Lp of the histogram is less than a predetermined saturation level Lq, as shown in Fig. 4(a), and the saturated state is a state in which the peak intensity Lp of the histogram reaches a predetermined saturation level Lq, as shown in Fig. 4(b). In the non-saturated state, the peak timing at which the peak intensity is reached can be identified from the waveform of the histogram and estimated as the light receiving timing.

[0042] On the other hand, in a saturated state, the histogram waveform reaches the saturation level Lq and becomes flat before the peak timing of the incident light amount of the reflected light L2 on the light receiving surface 32A (hereinafter referred to as the "light receiving timing of the reflected light L2") arrives, and since there are multiple timings at which the histogram waveform reaches a peak, it is not possible to identify the peak timing. If the timing at which the histogram waveform first reaches the saturation level Lq is taken as the light receiving timing of the reflected light L2, a problem occurs in that the distance to the measurement target W is measured as shorter than the actual distance.

[0043] In response to this, the inventor of the present invention has newly discovered that the temporal relationship between the first arrival timing T1 and the second arrival timing T2 in the histogram correlates with the timing of receiving the reflected light L2. That is, the timing of receiving the reflected light L2 can be estimated based on the first arrival timing T1 and the time difference ΔT between the first arrival timing T1 and the second arrival timing T2. Therefore, in this embodiment, the timing of receiving the reflected light L2 can be estimated not only in a non-saturated state but also in a saturated state.

[0044] Next, the TOF measurement device 40 executes an arrival timing correction process (S130). The arrival timing correction process is a process for correcting the second arrival timing T2 depending on the level of the incident light amount of the disturbance light L3 on the light receiving surface 32A. Specifically, when the light receiving surface 32A is not irradiated with the reflected light L2 and only the disturbance light L3 is irradiated with it, the TOF measurement device 40 appropriately executes a disturbance light histogram generation process for generating a disturbance light histogram based on output values ​​from a plurality of SPADs. The TOF measurement device 40 corrects the second arrival timing T2 depending on the height of the average value of the disturbance light histogram generated in the disturbance light histogram generation process.

[0045] FIG. 5 is an explanatory diagram showing the relationship between the amount of incident light of the disturbance light L3 and the second arrival timing T2. References Hg1 to Hg5 in FIG. 5 are disturbance light histograms with different amounts of incident light of the disturbance light L3. Reference R1 is an approximation line of a plurality of first arrival timings T1 under a situation where the amount of incident light of the reflected light L2 is the same and the amount of incident light of the disturbance light L3 is different. Reference R2 is an approximation line of a plurality of second arrival timings T2 under a situation where the amount of incident light of the reflected light L2 is the same and the amount of incident light of the disturbance light L3 is different. As can be seen from FIG. 5, the first arrival timing T1 is constant regardless of the amount of incident light of the disturbance light L3 as long as the amount of incident light of the reflected light L2 is the same. On the other hand, the second arrival timing T2 is closer to the first arrival timing T1 as the amount of incident light of the disturbance light L3 is higher, even if the amount of incident light of the reflected light L2 is the same. Therefore, the TOF measurement device 40 corrects the second arrival time T2 to a later time (a time further away from the first arrival time T1) as the amount of incident light in the disturbance light histogram increases, based on a linear function of the approximate straight line R2.

[0046] Next, the TOF measurement device 40 executes a light reception timing estimation process (S140). The TOF measurement device 40 estimates the light reception timing of the reflected light L2 based on the first arrival timing T1 and the second arrival timing T2 (or the corrected second arrival timing T2). For example, the timing obtained by adding a value obtained by multiplying the time difference ΔT between the first arrival timing T1 and the second arrival timing T2 by a predetermined time ratio (for example, 1 / 2, 3 / 8, etc.) to the first arrival timing T1 is set to be the light reception timing of the reflected light L2.

[0047] Next, the TOF measurement device 40 executes a light-receiving timing correction process (S150). The light-receiving timing correction process is a process for correcting the light-receiving timing of the reflected light L2 depending on the level of the incident light amount of the reflected light L2 on the light-receiving surface 32A.

[0048] FIG. 6 is an explanatory diagram showing the relationship between the level of the incident light amount of the reflected light L2 and the light receiving timing of the reflected light L2. Symbols Hh to Hl in FIG. 6 are histograms with different incident light amounts of the reflected light L2. Symbol Gp is ​​an approximation line of a plurality of light receiving timings (peak timings of the incident light amount of the reflected light L2) under conditions with different incident light amounts of the reflected light L2. As can be seen from FIG. 6, the light receiving timing becomes earlier as the incident light amount of the reflected light L2 becomes higher. Therefore, the TOF measurement device 40 corrects the second arrival timing T2 to a later timing as the peak intensity of the histogram becomes higher based on a linear function of the approximation line Gp.

[0049] Here, the inventor newly discovered that the time difference ΔT between the first arrival timing T1 and the second arrival timing T2 correlates with the peak intensity (height) of the amount of incident light of the reflected light L2 on the light receiving surface 32A. That is, the higher the peak intensity of the amount of incident light of the reflected light L2, the wider the width of the waveform of the histogram becomes, and accordingly, the time difference ΔT between the first arrival timing T1 and the second arrival timing T2 becomes larger. Therefore, even in a saturated state, for example, the peak intensity of the amount of incident light of the reflected light L2 can be estimated based on the time difference ΔT between the first arrival timing T1 and the second arrival timing T2. The TOF measurement device 40 corrects the second arrival timing T2 to a later timing based on the linear function of the approximation straight line Gp, as the time difference ΔT between the first arrival timing T1 and the second arrival timing T2 becomes longer.

[0050] Thereafter, the TOF measurement device 40 measures the distance to the measurement target W based on the light receiving timing (or the corrected light receiving timing), and outputs information corresponding to the distance to the utilization device 60 (S160). The process of S160 is an example of output processing. As a result, the TOF measurement device 40 can measure the distance to the measurement target W by the following formula A. <Formula A> Distance (m) = [A x "Bin number corresponding to the first arrival time T1" + B x ("Bin number corresponding to the second arrival time T2" ​​+ C x BG intensity)] + (D x peak intensity) + E] x F A, B: Weighting coefficients C: Correction coefficient for arrival timing correction process BG intensity: Intensity of ambient light L3 D: Correction coefficient for light reception timing correction process E: Overall offset coefficient (e.g., correction coefficient for offsetting deviations in light projection timing, etc.) F: Coefficient for converting the bin number of the histogram into the distance (m) to the measurement target W It should be noted that A to F can be changed appropriately according to individual differences in the measuring device 10 and changes in the surrounding environment.

[0051] (Estimation of reflectance of object W): Next, the TOF measurement device 40 executes a process for estimating the reflectance of the object W to be measured. The reflectance ρ of the measurement object W can be estimated using the following equation B (LiDAR equation): <Formula B> P RX =P TX ρ (D RX / 2R) 2 ·γ P RX : Amount of reflected light L2 P TX : Amount of emitted light L1 ρ: reflectance of the measurement target W D RX : Diameter of the light receiving surface 32A R: Distance to the measurement target W γ: Light transmittance of the optical system (light projecting optical system 24 and light receiving optical system 34) That is, the amount of incident light P RX If it can be estimated, the reflectance ρ of the measurement object W can be estimated from the above formula B.

[0052] 7 is an explanatory diagram showing the relationship between the amount of incident light of reflected light L2 and the peak intensity of the histogram (SPAD output value) when reflected light L2 is incident on the light receiving surface 32A. As shown in FIG. 7, in a measurement device using a photon count type light receiving element (SPAD), unlike a measurement device using an analog output type light receiving element, the correlation between the amount of incident light of reflected light L2 and the peak intensity of the histogram is nonlinear. Therefore, in this embodiment, the amount of incident light of reflected light L2 is estimated by different estimation methods depending on whether the amount of incident light of reflected light L2 belongs to the "first region E1", "second region E2", or "third region E3". "First region E1": Saturation region (peak intensity of histogram = saturation level Lq, incident light amount of reflected light L2 ≧ saturation level Lq) "Second region E2": Non-saturated region (difference in peak intensity between histogram and ambient light L3 ≧ reference value, incident light amount of reflected light L2 < saturation level Lq) "Third region E3": Non-saturated region (difference in peak intensity between histogram and ambient light L3 < reference value, incident light amount of reflected light L2 < saturation level Lq) FIG. 8 shows the relationship between the amount of incident reflected light L2 and the peak intensity (SPAD output value) of the histogram for each region.

[0053] The TOF measurement device 40 judges whether the incident light amount of the reflected light L2 is saturated or not based on the histogram when the reflected light L2 is incident on the light receiving surface 32A (S170). When the TOF measurement device 40 judges that the incident light amount is saturated (S170: YES), the TOF measurement device 40 estimates the peak intensity of the incident light amount of the reflected light L2 based on the time difference ΔT between the first arrival timing T1 and the second arrival timing T2, similar to the above-mentioned light receiving timing correction process (S180). This process of S180 is an example of a first incident light amount estimation process. Specifically, the peak intensity of the incident light amount of the reflected light L2 is estimated using the following formula C. <Formula C> Amount of reflected light L2 = 10 (e·ΔT+f) e, f: Variables determined according to the magnitude of ambient light L3 8 shows a logarithmic graph indicating the relationship between the time difference ΔT and the amount of incident light of reflected light L2 in the first region E1. On the logarithmic graph, the relationship between the time difference ΔT and the amount of incident light of reflected light L2 is approximately linear, and the smaller the amount of incident light of disturbance light L3, the larger the time difference ΔT (see graphs G1a (less disturbance light L3) to G1c (more disturbance light L3)).

[0054] When the TOF measurement device 40 judges that the state is not saturated (S170: NO), it judges whether the peak intensity difference between the histogram and the ambient light L3 is equal to or greater than a reference value (S190). The reference value can be changed as appropriate. When the TOF measurement device 40 judges that the peak intensity difference is equal to or greater than a reference value (S190: YES), it estimates the peak intensity of the incident light amount of the reflected light L2 based on the peak intensity (SPAD output value) of the histogram and the following logarithmic function (Equation D) (S200). The process of S200 is an example of a second incident light amount estimation process. Specifically, the peak intensity of the incident light amount of the reflected light L2 is estimated using the following Equation D. <Formula D> Amount of reflected light incident on the board = 10 (a×受光素子からの出力値+b) * a and b are coefficients 8 shows a logarithmic graph indicating the relationship between the peak intensity (SPAD output value) of the histogram and the amount of incident light of the reflected light L2 in the second region E2. On the logarithmic graph, the relationship between the peak intensity of the histogram and the amount of incident light of the reflected light L2 is approximately linear, and the greater the amount of incident light of the disturbance light L3, the gentler the slope becomes (see graphs G2a (low disturbance light L3) to G2c (high disturbance light L3)). A first coefficient correction process may be executed to correct the coefficient a of the logarithmic function to a smaller value as the amount of incident light of the disturbance light L3 increases.

[0055] When the TOF measurement device 40 determines that the peak intensity difference is less than the reference value (S190: NO), it estimates the peak intensity of the incident light amount of the reflected light L2 based on the peak intensity (SPAD output value) of the histogram and the following real function (Equation E) (S210). This process of S210 is an example of a third incident light amount estimation process. Specifically, the peak intensity of the incident light amount of the reflected light L2 is estimated using the following Equation E. <Formula E> Amount of reflected light incident on the light receiving element = c × output value from the light receiving element + d *c and d are coefficients 8 shows a real number graph indicating the relationship between the peak intensity (SPAD output value) of the histogram and the amount of incident light of the reflected light L2 in the third region E3. On the real number graph, the relationship between the peak intensity of the histogram and the amount of incident light of the reflected light L2 is approximately linear, and the greater the amount of incident light of the disturbance light L3, the gentler the slope becomes (see graphs G3a (low disturbance light L3) to G3c (high disturbance light L3)). A second coefficient correction process may be executed to correct the coefficient c of the real number function to a smaller value as the amount of incident light of the disturbance light L3 increases.

[0056] Thereafter, the TOF measurement device 40 calculates the peak intensity of the incident light amount of the reflected light L2 (the incident light amount P RX ), the distance (R) measured in S160, and the above equation B (LiDAR equation), the reflectance ρ of the measurement object W is estimated (S220), and the process returns to S110.

[0057] A-4. Estimation process of reflectance of measurement target W at pixels where reflected light L2 is not detected: In the measurement process shown in FIG. 3, the reflectance ρ of the measurement target W was estimated using equation B (LiDAR equation). However, this estimation method is premised on the ability to estimate the amount of incident light of reflected light L2. On the light receiving surface 32A, there may be pixels where reflected light L2 is detected (hereinafter referred to as "detection pixels") and pixels where reflected light L2 is not detected (hereinafter referred to as "non-detection pixels"). For the detection pixels, the reflectance ρ of the measurement target W can be estimated by the measurement process of FIG. 3. However, for the non-detection pixels, the amount of incident light of reflected light L2 cannot be estimated, and therefore the reflectance ρ of the measurement target W cannot be estimated by the measurement process of FIG. 3.

[0058] Therefore, in this embodiment, the control circuit 42 estimates the reflectance ρ of the measurement target W for the non-detection pixel based on the reflectance ρ of the measurement target W estimated for the detection pixel and the ratio of the amount of disturbance light L3 incident on the non-detection pixel to the detection pixel. It is assumed that the disturbance light L3 is uniformly irradiated over the entire light receiving surface 32A, and that the amount of disturbance light L3 incident on the light receiving surface 32A is independent of the distance from the measurement target W. For example, if the reflectance ρ at the detection pixel is 80% and the ratio of the amount of disturbance light L3 incident on the non-detection pixel to the amount of disturbance light L3 incident on the detection pixel is 1 / 2, the reflectance ρ at the non-detection pixel is estimated to be 40% (=80%×(1 / 2)).

[0059] A-5. Advantages of this embodiment: The inventors have newly discovered that the relative relationship between the first arrival timing T1 and the second arrival timing T2 in the histogram correlates with the peak timing of the incident light amount of the reflected light L2 on the light receiving surface 32A. Therefore, according to this embodiment, even if the incident light amount of the reflected light L2 on the light receiving surface 32A becomes saturated, the light receiving timing can be estimated based on the first arrival timing T1 and the second arrival timing T2 (see S110 to S150 in FIG. 3).

[0060] The inventor also newly discovered that the time difference ΔT between the first arrival time T1 and the second arrival time T2 correlates with the peak intensity of the incident light amount of the reflected light L2 on the light receiving surface 32A. Therefore, in this embodiment, even in a saturated state in which the histogram peak cannot be detected, the peak intensity of the incident light amount of the reflected light L2 can be estimated based on the time difference ΔT of the histogram (see S180 in FIG. 3).

[0061] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0062] The configuration of the measuring device 10 in the above embodiment is merely an example, and various modifications are possible.

[0063] In the flow chart of the measurement process in the above embodiment, the correction process of either the process of S130 or the process of S150 does not have to be executed. [Explanation of symbols]

[0064] 10: Measuring device 20: Light projector 22: Light source 24: Light projection optical system 26: Light projection control device 28: Current source 30: Light receiver 32: Light receiving section 32A: Light receiving surface 34: Light receiving optical system 40: TOF measuring device 42: Control circuit 60: Utilization device E1: First region E2: Second region E3: Third region L1: Emitted light L2: Reflected light L3: Ambient light Lh: Intermediate value Lp: Peak intensity

Claims

1. A floodlight that emits light; a light receiver having a light receiving surface on which a plurality of photon counting type light receiving elements are arranged in an array, the light receiving surface receiving light being reflected back from the measurement object by the light projector; A measurement device comprising: The controller: a histogram generation process for generating a histogram based on output values ​​from the plurality of light receiving elements; a light receiving timing estimation process for estimating a light receiving timing of the reflected light based on a first reaching timing when the histogram first reaches an intermediate value between a maximum value and a minimum value of the waveform of the histogram and a second reaching timing when the histogram next reaches the intermediate value; and output processing for outputting information corresponding to the distance to the measurement object based on a light projection timing at which the light projector emits light and a light reception timing.

2. 2. The measuring device according to claim 1, The controller further comprises: When the histogram is below a saturation level, the measurement apparatus executes a light-receiving timing correction process for correcting the light-receiving timing according to a height of a peak of the histogram.

3. The measuring device according to claim 1 or 2, The controller further comprises: When the histogram exceeds a saturation level, the measurement apparatus executes a light-receiving timing correction process for correcting the light-receiving timing in accordance with a time difference between the first arrival time and the second arrival time.

4. The measuring device according to claim 1 or 2, The controller further comprises: a disturbance light histogram generation process for generating a disturbance light histogram based on output values ​​from the plurality of light receiving elements when the reflected light is not irradiated onto the light receiving surface; an arrival timing correction process for correcting the second arrival timing in accordance with a height of a peak of the disturbance light histogram.

5. A floodlight that emits light; a light receiver having a light receiving surface on which a plurality of photon counting type light receiving elements are arranged in an array, the light receiving surface receiving light being reflected back from the measurement object by the light projector; A measurement device comprising: The controller: a histogram generation process for generating a histogram based on output values ​​from the plurality of light receiving elements; a first incident light amount estimation process that estimates the amount of incident light of the reflected light based on the time difference between a first arrival timing at which the histogram first reaches an intermediate value between the maximum and minimum values ​​of the waveform of the histogram and a second arrival timing at which the histogram next reaches the intermediate value.

6. The measuring device according to claim 5, The controller further comprises: When the peak of the histogram is lower than the saturation level and the difference between the peak of the histogram and the amount of incident ambient light is equal to or greater than a reference value, output values ​​from the plurality of light receiving elements; <Formula 1> Amount of incident light of reflected light = 10 （ａ×受光素子からの出力値＋ｂ） * a and b are coefficients and a second incident light amount estimation process for estimating the amount of incident light of the reflected light based on a logarithmic function represented by:

7. The measuring device according to claim 5 or 6, The controller further comprises: When the peak of the histogram is lower than the saturation level and the difference between the peak of the histogram and the amount of incident ambient light is less than a reference value, output values ​​from the plurality of light receiving elements; <Formula 2> Amount of reflected light incident on the light receiving element = c x output value from the light receiving element + d *c and d are coefficients and a third incident light amount estimation process for estimating the amount of incident light of the reflected light based on a real function represented by

8. The measuring device according to claim 6, The controller further comprises: The measurement apparatus executes a first coefficient correction process for correcting the coefficient a of the logarithmic function to a smaller value as the amount of incident disturbance light increases.

9. The measuring device according to claim 7, The controller further comprises: The measurement apparatus executes a second coefficient correction process for correcting the coefficient c of the real function to a smaller value as the amount of incident disturbance light increases.

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