Measuring device

Abstract

To measure the distance to a measurement object while changing reflected light detection performance or the like.SOLUTION: A controller executes: first measuring processing of, for a plurality of light receiving elements arranged in a target area which is at least part of a light receiving surface, acquiring output values from the plurality of light receiving elements, with a first acquisition unit defined by the number of the light receiving elements constituting one pixel and the integrated number of times of output values from the light receiving elements, and measuring the distance to a measurement object on the basis of an obtained output result; and second measuring processing of, for the plurality of light receiving elements arranged in the target area, acquiring the output values from the plurality of light receiving elements, with a second acquisition unit different from the first acquisition unit in at least one of the number of the light receiving elements constituting one pixel and the integrated number of times of output values from the light receiving elements, and measuring the distance to the measurement object on the basis of an obtained output result.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 time 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 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, and the light receiving timing is determined based on the histogram (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] In the above conventional measuring device, the number of light receiving elements constituting one pixel and the number of times the output signals of the light receiving elements are integrated are both fixed. Therefore, for example, it is not possible to change the reflected light detection performance or the image resolution, and there is room for improvement. Note that this problem is not limited to photon counting type light receiving elements, but is also a common problem in measuring devices in which multiple analog output type light receiving elements are arranged in an array.

[0006] This specification discloses a technique that can solve the above-mentioned 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 measurement device disclosed in this specification includes a light projector that emits light, a light receiver having a light receiving surface in which a plurality of light receiving elements are arranged in an array to receive light reflected back from a measurement target that is the light projected by the light projector, and a controller, wherein the controller executes a first measurement process of acquiring output values ​​of the light receiving elements arranged in at least a part of a target area of ​​the light receiving surface in a first acquisition unit determined by the number of the light receiving elements constituting one pixel and the number of times of integration of the output values ​​of the light receiving elements, and measuring a distance to the measurement target based on the obtained output result, and a second measurement process of acquiring output values ​​of the light receiving elements arranged in the target area in a second acquisition unit in which at least one of the number of the light receiving elements constituting one pixel and the number of times of integration of the output values ​​of the light receiving elements is different from the first acquisition unit, and measuring a distance to the measurement target based on the obtained output result.

[0009] According to this measuring device, for example, by changing at least one of the number of light receiving elements constituting one pixel and the number of times the output values ​​of the light receiving elements constituting one pixel are integrated, it is possible to change the detection performance of reflected light, the resolution, and the frame rate. This makes it possible to measure the distance to the measurement target while changing the detection performance of reflected light, etc.

[0010] (2) In the above-mentioned measuring device, the second acquisition unit may have a larger output sum value than the first acquisition unit, the sum value being determined based on the number of the light receiving elements constituting one pixel and the number of times the output values ​​of the light receiving elements are integrated, and the controller may switch to the second measurement process when a switching condition is satisfied during the execution of the first measurement process. According to this measuring device, when a predetermined switching condition is satisfied, the first acquisition unit is switched to the second acquisition unit having a higher detection performance for reflected light, and the measurement process is performed. This makes it possible to measure the distance to the measurement target while changing the detection performance for reflected light according to various situations.

[0011] (3) In the above-mentioned measuring device, the second acquisition unit may be configured to have a larger number of the light receiving elements constituting one pixel than the first acquisition unit, and to have the same or less number of integration times of the output values ​​of the light receiving elements. According to this measuring device, when a switching condition is satisfied, the measurement process is performed by switching from the first acquisition unit to the second acquisition unit having a lower resolution while suppressing a decrease in frame rate. This makes it possible to measure the distance to the measurement object while changing the resolution according to various situations.

[0012] (4) In the above-mentioned measuring device, the second acquisition unit may be configured to have the same or less number of light receiving elements constituting one pixel as the first acquisition unit, and to have a larger number of integration times of the output values ​​of the light receiving elements. According to this measuring device, when a switching condition is satisfied, the first acquisition unit is switched to the second acquisition unit having a lower frame rate while suppressing a decrease in resolution, and a measurement process is performed. This makes it possible to measure the distance to the measurement target while changing the frame rate according to various situations.

[0013] (5) In the above-mentioned measuring device, when the switching condition and the area restriction condition are satisfied during the execution of the first measuring process, the controller may be configured to execute the second measuring process on a specific area that is a part of the light receiving surface, and execute the first measuring process on the other area of ​​the light receiving surface excluding the specific area. With this measuring device, it is possible to change the resolution and detection performance only in the specific area of ​​the light receiving surface.

[0014] 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]

[0015] [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 showing the difference in the number of SPAD integrations U between the reference measurement process and the low frame rate measurement process. [Diagram 5] FIG. 13 is an explanatory diagram showing the difference in the number M of SPAD units between the reference measurement process and the low-resolution measurement process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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 a 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 when the projector 20 emits the emitted light L1 and the timing when 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The light receiver 30 includes a light receiving section 32 and a light receiving optical system 34 .

[0024] 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).

[0025] The light receiving unit 32 has a plurality of light receiving elements. The light receiving elements are, for example, photodiodes, SPADs (Single Photon Avalanche Diodes), balanced photodetectors, etc. The light receiving unit 32 photoelectrically converts the reflected light L2 incident from the light receiving optical system 34 to generate a light receiving signal having a current level or a voltage level according to the intensity of the reflected light L2. 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.

[0026] 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.

[0027] 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.

[0028] 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").

[0029] 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.

[0030] 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 the following, a configuration in which the light receiving element is a SPAD as an example of a photon counting type light receiving element will be described as an example. When a photon is incident on the SPAD, the SPAD responds with a predetermined probability (e.g., 20%) and outputs one pulse when a photon is detected.

[0031] 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 defined 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 large number of integrations of the output value of the SPAD. 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.

[0032] 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.

[0033] 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 determines the light receiving timing based on the timing corresponding to the waveform showing a relatively high peak in the histogram H.

[0034] A-3. Measurement process: 3 is a flowchart showing the measurement process executed by the TOF measurement device 40 and the control circuit 42. In this measurement process, the TOF can be measured while changing at least one of the number M of SPAD units constituting one pixel and the number of SPAD integrations U.

[0035] (Reference measurement process): 3, the TOF measurement device 40 executes a reference measurement process at the beginning of measurement (S110). In the reference measurement process, output values ​​of a plurality of light receiving elements arranged over the entire light receiving surface 32A are acquired in a reference unit in which the number of SPAD units M and the number of SPAD integration times U are set to predetermined values ​​(initial values), and the distance to the measurement target W is measured based on the acquired output results. The reference unit is an example of a first acquisition unit, and the reference measurement process is an example of a first measurement process.

[0036] Next, the TOF measurement device 40 judges whether the detection performance improvement condition is satisfied (S120). The detection performance means the detection accuracy of the presence or absence of the reflected light L2 in one pixel. The more the number M of SPAD units constituting one pixel, the more the output values ​​of the SPADs that detect photons when the reflected light L2 is irradiated on the light receiving surface 32A are superimposed in terms of area, and the peak intensity of the histogram becomes relatively higher. As a result, the detection performance for the reflected light L2 is improved. Also, the more the number U of integration times of the SPADs constituting one pixel, the more the output values ​​of the SPADs that detect photons when the reflected light L2 is irradiated on the light receiving surface 32A are superimposed in terms of time, and the peak intensity of the histogram becomes relatively higher. As a result, the detection performance for the reflected light L2 is improved. The detection performance improvement condition is an example of a switching condition.

[0037] Examples of conditions for improving detection performance include the following. (1) The measurement results of the reference measurement process showed a predetermined change pattern (for example, a change pattern indicating the detection of the measurement object W, a change pattern indicating the detection of an abnormal image, etc.). (2) The relative speed between the measuring device 10 and the object to be measured W (for example, the moving speed of the vehicle on which the measuring device 10 is mounted) exceeds a predetermined speed or falls below a predetermined speed. (3) A signal indicating an instruction to improve detection performance is received from outside (for example, a control unit of a vehicle in which the measuring device 10 is mounted).

[0038] When the TOF measurement device 40 determines that the detection performance improvement condition is not satisfied (S120: NO), it continues the reference measurement process. On the other hand, when the TOF measurement device 40 determines that the detection performance improvement condition is satisfied (S120: YES), it determines whether or not the frame rate restriction condition is satisfied (S130). The frame rate restriction condition is a condition for restricting the reduction of the frame rate, and examples thereof include the following: (1) The relative speed between the measuring device 10 and the object to be measured W (for example, the moving speed of a vehicle on which the measuring device 10 is mounted) becomes equal to or exceeds a predetermined speed. (2) The current frame rate has reached a specified lower limit.

[0039] (Low frame rate measurement process): When the TOF measurement device 40 determines that the frame rate limiting condition is not satisfied (S130: NO), it executes a low frame rate measurement process (S140). In the low frame rate measurement process, output values ​​of a plurality of SPADs arranged over the entire light receiving surface 32A are acquired in low frame rate units, and the distance to the measurement target W is measured based on the acquired output results. In the low frame rate unit, the number M of SPAD units is the same as that of the reference unit, and the number of SPAD integration times U is large. The low frame rate unit is an example of a second acquisition unit, and the low frame rate measurement process is an example of a second measurement process.

[0040] 4 is an explanatory diagram showing the difference in the SPAD integration count U between the reference measurement process and the low frame rate measurement process. Since the reference measurement process and the low frame rate measurement process have the same number of SPAD units M, in both cases, a histogram (hereinafter referred to as a "unit histogram") is generated in which the output values ​​of SPADs with the number of SPAD units M are area-wise superimposed for each sampling timing (sampling period).

[0041] Here, the number of SPAD integrations U in the reference measurement process is, for example, "1". In this case, as shown in FIG. 4(a), the TOF measurement device 40 outputs a unit histogram according to the amount of incident light on the light receiving surface 32A as data for one pixel at each sampling timing, and the control circuit 42 judges the presence or absence of the reflected light L2 based on a comparison between the unit histogram and a judgment threshold value. At each sampling timing, the signal waveform corresponding to the reflected light L2 is relatively small, so the SN ratio is low. The SN ratio here is the magnification of the peak value S of the signal corresponding to the reflected light L2 to the peak value N of the signal corresponding to the disturbance light L3. Thus, in the reference measurement process, the SN ratio is low, and therefore the peak intensity of the unit histogram constituting one pixel is relatively low, so the detection performance for the reflected light L2 is relatively low.

[0042] On the other hand, the number of SPAD integrations U in the low frame rate measurement process is, for example, "3". In this case, as shown in FIG. 4(b), the TOF measurement device 40 generates a histogram (hereinafter referred to as a "superimposed histogram") by superimposing unit histograms generated at three sampling timings, and outputs the superimposed histogram as data for one pixel. The control circuit 42 judges the presence or absence of the reflected light L2 based on a comparison between the superimposed histogram and a judgment threshold value. Since the signal waveform corresponding to the reflected light L2 superimposed at three sampling timings is relatively large, the SN ratio is high. Thus, in the low frame rate measurement process, the SN ratio is high, and accordingly, the peak intensity of the superimposed histogram constituting one pixel is relatively high, so the detection performance for the reflected light L2 is relatively high. However, in the low frame rate measurement process, the frame rate of the received light image is lower than that in the reference measurement process.

[0043] For example, when a vehicle equipped with the measuring device 10 is moving at a low speed (moving speed less than a predetermined speed), the possibility of overlooking an image is relatively low even if the frame rate is reduced, so it is preferable to improve the detection performance for the reflected light L2 by performing a low frame rate measurement process. Note that in the low frame rate measurement process, the number of SPAD units M may be made smaller than that in the reference measurement process to increase the resolution of the received light image. Also, the number of SPAD integration times U for each of the reference measurement process and the low frame rate measurement process is not limited to the number in the example of FIG. 4 and can be changed as appropriate.

[0044] (Low resolution measurement processing): When the TOF measurement device 40 determines that the frame rate limiting condition is satisfied (S130: YES), it executes a low-resolution measurement process (S150). In the low-resolution measurement process, output values ​​of a plurality of light receiving elements arranged over the entire light receiving surface 32A are acquired in a low-resolution unit, and the distance to the measurement target W is measured based on the acquired output results. The low-resolution unit has a larger number of SPAD units M than the above-mentioned reference unit, and has the same number of SPAD accumulations U. The low-resolution unit is an example of a second acquisition unit, and the low-resolution measurement process is an example of a second measurement process.

[0045] 5 is an explanatory diagram showing the difference between the number of SPAD units M between the reference measurement process and the low resolution measurement process. Since the reference measurement process and the low resolution measurement process have the same SPAD integration count U, the frame rates are the same.

[0046] Here, the number M of SPAD units in the reference measurement process is, for example, "2 x 2". In this case, as shown in the upper right of FIG. 5, the TOF measurement device 40 outputs a unit histogram according to the amount of incident light in the "2 x 2" SPAD arrangement area as data for one pixel, and the control circuit 42 judges the presence or absence of reflected light L2 based on a comparison between the unit histogram and a judgment threshold. In the "2 x 2" SPAD arrangement area, the signal waveform corresponding to the reflected light L2 is relatively small, so the S / N ratio is low. Thus, in the reference measurement process, the S / N ratio is low, and therefore the peak intensity of the unit histogram constituting one pixel is relatively low, so the detection performance for the reflected light L2 is relatively low.

[0047] On the other hand, the number M of SPAD units in the low-resolution measurement process is, for example, "4 x 4". In this case, as shown in the lower right of FIG. 5, the TOF measurement device 40 outputs a unit histogram according to the amount of incident light in the "4 x 4" SPAD arrangement area as data for one pixel, and the control circuit 42 judges the presence or absence of reflected light L2 based on a comparison between the unit histogram and a judgment threshold. In the "4 x 4" SPAD arrangement area, the signal waveform corresponding to the reflected light L2 is relatively large, so the S / N ratio is low. Thus, in the low-resolution measurement process, the S / N ratio is high, and therefore the peak intensity of the unit histogram constituting one pixel is relatively high, so the detection performance for the reflected light L2 is relatively high. However, in the low-resolution measurement process, the resolution of the received light image is lower than that in the reference measurement process.

[0048] For example, when the vehicle on which the measuring device 10 is mounted is moving at high speed (moving speed is equal to or higher than a predetermined speed), it is not preferable to perform low frame rate measurement processing because if the frame rate is increased, the possibility of overlooking the image increases. In this case, it is preferable to perform low resolution measurement processing to improve the detection performance for the reflected light L2. In the low resolution measurement processing, the SPAD integration number U may be reduced compared to the reference measurement processing to increase the frame rate of the received light image. In addition, the number of SPAD units M in each of the reference measurement processing and the low resolution measurement processing is not limited to the example shown in FIG. 5 and can be changed as appropriate. After the TOF measuring device 40 executes the low frame rate measurement processing or the low resolution measurement processing for a predetermined time, for example, the TOF measuring device 40 returns to S120.

[0049] A-4. Generation of decision threshold: It is preferable that the judgment threshold is appropriately corrected according to the average value of the histogram. Here, when the presence or absence of the reflected light L2 is judged based on a comparison between the superimposed histogram and the judgment threshold, for example, the following comparative example is a method for generating the judgment threshold. This is a method in which the average value of the unit histogram is calculated at each sampling timing, the average values ​​of the unit histograms for multiple times are summed, and the judgment threshold is corrected according to the sum of the average values. In this method, a rounding error occurs due to fractional processing each time the average value of the unit histogram is calculated, and the average values ​​of the unit histograms for multiple times including the rounding error are summed. In short, the sum of the average values ​​includes the rounding errors for multiple times. Therefore, there is a risk that the judgment threshold cannot be accurately corrected with the sum of the average values ​​including such multiple rounding errors.

[0050] In contrast, in this embodiment, before calculating the average value, the unit histograms are integrated multiple times, and the average value of the superimposed histogram obtained by the integration is used to correct the judgment threshold. In the method of this embodiment, the rounding error occurs only once in the calculation of the average value used to correct the judgment threshold. Therefore, in the method of this embodiment, the influence of the rounding error is suppressed compared to the method of the comparative example, and the judgment threshold can be corrected with high accuracy.

[0051] In this embodiment, it is preferable to calculate the average value used for correcting the determination threshold value based on a histogram generated 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 fluctuation (fluctuation) of the histogram is mainly due to the fluctuation of the disturbance light L3. Therefore, with the method of this embodiment, it is possible to eliminate the influence of the reflected light L2 and accurately correct the determination threshold value according to the fluctuation of the disturbance light L3, compared to the case where the average value is calculated based on a histogram generated when the reflected light L2 is irradiated with the light receiving surface 32A.

[0052] A-5. Advantages of this embodiment: As described above, according to the measuring device 10 of this embodiment, the detection performance, resolution, and frame rate of the reflected light L2 can be changed by changing at least one of the number M of SPAD units constituting one pixel and the number of integration times U of the SPADs constituting one pixel. This makes it possible to measure the distance to the measurement target W while changing the detection performance of the reflected light L2, etc.

[0053] 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.

[0054] The configuration of the measurement device 10 in the above embodiment is merely an example and can be modified in various ways. For example, in the above embodiment, a SPAD is used as the light receiving element, but the present invention is not limited to this and an analog output type light receiving element may be used.

[0055] In the above embodiment, the detection performance improvement condition is exemplified as the switching condition, but the switching condition is not limited thereto, and may be other conditions, such as receiving a switching instruction signal from the outside. In the flow chart of the measurement process in the above embodiment, the process of S140 or S150 may be executed without making the decision of S130. The second measurement process may have a larger number of light receiving elements and a smaller number of integration times of the output values ​​of the light receiving elements than the first measurement process, or may have a smaller number of light receiving elements and a larger number of integration times of the output values ​​of the light receiving elements than the first measurement process.

[0056] In the above embodiment, the second measurement process (low frame rate measurement process, low resolution measurement process) is performed on the entire light receiving surface 32A, but the second measurement process may be performed on only a part of the light receiving surface 32A. For example, in the flow chart of the measurement process in the above embodiment, when the detection performance improvement condition is satisfied and the area restriction condition is satisfied, the low resolution measurement process may be performed on a specific area that is a part of the light receiving surface 32A, and the reference measurement process may be continued on the other areas of the light receiving surface 32A excluding the specific area. The area restriction condition is, for example, receiving a signal instructing area restriction from the outside, or appearing a predetermined change pattern (for example, a change pattern indicating the detection of the measurement object W, a change pattern indicating the detection of an abnormal image, etc.) in the image acquired during the reference measurement process (detecting the measurement object W or an abnormal image). [Explanation of symbols]

[0057] 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 50: Communication I / F (Inter face) 60: Device to be used G: Graph H: Histogram L1: Emitted light L2: Reflected light L3: Ambient light W: Measurement object

Claims

1. A floodlight that emits light; a light receiver having a light receiving surface on which a plurality of light receiving elements are arranged in an array to receive light that is emitted from the light projector and reflected by a measurement object and returns; A measurement device comprising: The controller: a first measurement process for acquiring output values ​​of a plurality of light receiving elements arranged in at least a part of a target area of ​​the light receiving surface in a first acquisition unit determined by the number of the light receiving elements constituting one pixel and the number of times the output values ​​of the light receiving elements are integrated, and measuring a distance to the measurement target based on the acquired output results; a second measurement process for acquiring output values ​​of the plurality of light receiving elements arranged in the target area in a second acquisition unit in which at least one of the number of the light receiving elements constituting one pixel and the number of times the output values ​​of the light receiving elements are accumulated is different from the first acquisition unit, and measuring the distance to the measurement target based on the obtained output result.

2. 2. The measuring device according to claim 1, the second acquisition unit has a larger output sum value determined according to the number of the light receiving elements constituting one pixel and the number of times the output values ​​of the light receiving elements are integrated, than the first acquisition unit; The measurement device, wherein the controller switches to and executes the second measurement process when a switching condition is satisfied during execution of the first measurement process.

3. The measuring device according to claim 1 or 2, A measuring device in which the second acquisition unit has a larger number of the light receiving elements constituting one pixel than the first acquisition unit and the number of integration times of the output values ​​of the light receiving elements is equal to or less than that of the first acquisition unit.

4. The measuring device according to claim 1 or 2, A measuring device in which the second acquisition unit has the same or smaller number of light receiving elements constituting one pixel as the first acquisition unit and has a larger number of integration times of the output values ​​of the light receiving elements than the first acquisition unit.

5. The measuring device according to claim 1 or 2, The controller: A measuring device that, when a switching condition is satisfied and an area restriction condition is satisfied during execution of the first measurement process, executes the second measurement process on a specific area that is part of the light receiving surface, and executes the first measurement process on other areas of the light receiving surface excluding the specific area.

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