Measuring device, measuring program for measuring device, and computer-readable recording medium

Abstract

This expands the measurable distance while suppressing the increase in memory space required to store the histogram. [Solution] The measuring device comprises a light emitter, a light receiver, a memory, and a controller. The controller (a) emits light from the light emitter and, triggered by the light receiving trigger timing, sequentially reads the received signals from each of the multiple light receiving elements at a sampling period, (b) for each pixel, generates a pixel value for each sampling period based on the read multiple received signals and stores a histogram of the pixel values ​​in memory, and (c) generates information corresponding to the distance to the object to be measured based on the light emission timing of the light emitter, the light receiving trigger timing, and the histogram stored in memory. The controller performs a first measurement operation and a second measurement operation in which at least one of the light receiving trigger timing and sampling period differs from the first measurement operation, and outputs a measurement result corresponding to the distance to the object to be measured.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a measuring device, a measurement program for the measuring device, and a computer-readable recording medium.

Background Art

[0002] With the development of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development of LiDAR (Light Detection And Ranging) is underway as one of the measuring devices used for grasping the surrounding environment and estimating the self-position when a vehicle is running. LiDAR includes a light projector that projects (irradiates) laser light onto a measurement target, and a light receiver that receives the reflected light that returns after the laser light is reflected by the measurement target. LiDAR outputs information regarding the measurement target by measuring the distance to the measurement target based on the difference between the light projection timing when the light projector emits laser light and the light reception timing when the light 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 (for example, SPAD: Single Photon Avalanche Diode) are arranged in an array. In the measuring device, an integrated value obtained by integrating output values from a predetermined number of light receiving elements is processed as one pixel to generate a histogram, and the generated histogram is stored in a memory. The timing at which the peak of the histogram stored in the memory is detected is regarded as the light reception timing of the reflected light, and the distance to the measurement target is measured (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] In conventional measuring devices, the longer the maximum measurable distance, the greater the memory area required to store the histogram. As a result, problems arise, such as the maximum measurable distance being limited by the available memory capacity.

[0006] This specification discloses a technology capable of solving at least one of the problems described above. [Means for solving the problem]

[0007] The technologies disclosed herein can be implemented, for example, in the following forms:

[0008] (1) The measuring apparatus disclosed herein comprises a light emitter that emits light, a light receiver in which a plurality of light-receiving elements are arranged in an array to receive reflected light that has been reflected back from the object to be measured after being emitted from the light emitter, a memory, and a controller, wherein the controller is configured to perform the following measurement operations: (a) Emitting light from the light emitter and, triggered by a light-receiving trigger timing, sequentially reading out the received light signals from each of the plurality of light-receiving elements at a sampling period, and (b) For each pixel, the pixel value for each sampling period based on the plurality of received light signals read out. (c) Generates a histogram of the pixel values ​​and stores the histogram in the memory. Based on the light emission timing of the light emitter, the light receiving trigger timing, and the histogram stored in the memory, the controller generates information corresponding to the distance to the object to be measured. Furthermore, the controller performs a first measurement operation and a second measurement operation at a different time from the first measurement operation, in which at least one of the light receiving trigger timing and the sampling period is different from the first measurement operation, and outputs a measurement result corresponding to the distance to the object to be measured based on the information generated in the first measurement operation and the information generated in the second measurement operation. With this configuration, the measurable distance can be expanded while suppressing an increase in the memory area for storing the histogram.

[0009] (2) In the above measuring device, the second time difference between the light emission timing and the light reception trigger timing in the second measuring operation may be configured to be longer than the first time difference between the light emission timing and the light reception trigger timing in the first measuring operation. This configuration makes it possible to widen the measurable distance while suppressing the expansion of the memory area for storing the histogram.

[0010] (3) In the above measuring device, the second sampling period in the second measurement operation may be configured to be longer than the first sampling period in the first measurement operation. With this configuration, the measurable distance can be expanded without requiring a change in the light reception trigger timing, while suppressing the expansion of the memory area for storing the histogram.

[0011] (4) In the above measuring device, the light emission intensity of the light emitter in the second measurement operation may be set to be higher than the light emission intensity of the light emitter in the first measurement operation. This configuration makes it possible to suppress the decrease in measurement accuracy in the second measurement operation caused by long-distance measurement.

[0012] (5) In the above measuring device, the number of times the pixel value is accumulated in accordance with the number of times (a) and (b) are performed in the second measuring operation may be configured to be greater than the number of times the pixel value is accumulated in accordance with the number of times (a) and (b) are performed in the first measuring operation. With this configuration, it is possible to suppress the decrease in measurement accuracy in the second measuring operation caused by long-distance measurement.

[0013] (6) In the above measuring device, the controller may be configured to perform a first mode in which it performs the first measurement operation and outputs the measurement result based on the information generated by the first measurement operation, and a second mode in which it performs the first measurement operation and the second measurement operation and outputs the measurement result based on the information generated by the first measurement operation and the information generated by the second measurement operation. With this configuration, normal measurement and long-distance measurement can be selectively performed by switching modes.

[0014] Furthermore, the technologies disclosed herein can be implemented in various forms, for example, in the form of a measuring device, a measuring method, a measuring program for controlling the measuring device, and a computer-readable recording medium on which the measuring program is stored. [Brief explanation of the drawing]

[0015] [Figure 1] Block diagram schematically showing the configuration of the measuring device in the embodiment. [Figure 2] Block diagram showing the internal structure of the light-receiving chip. [Figure 3] An explanatory diagram showing the light emission and reception timing and histograms in basic measurement operation and delayed measurement operation. [Figure 4] This diagram illustrates the light transmission / reception timing and histograms during basic and low-rate measurement operations. [Figure 5] Flowchart showing the measurement process [Modes for carrying out the invention]

[0016] A. Embodiments: A-1. Configuration of measuring device 10: Figure 1 is a schematic block diagram showing the configuration of the measuring device 10 in this embodiment. As shown in Figure 1, the measuring device 10 includes a light emitter 20 that irradiates the target W to be measured with emitted light L1 (for example, a light beam (laser light)) and a light receiver 30 that receives reflected light L2 (return light) that comes back after the emitted light L1 is reflected from the target W, and functions as a LiDAR. The measuring device 10 obtains information about the target W by measuring the difference between the timing when the light emitter 20 emits 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)).

[0017] The measuring device 10 is installed, for example, in a vehicle (not shown) on which AD or ADAS is implemented. The measuring device 10 assists in detecting objects such as people and other vehicles while the vehicle is in motion, and provides various types of information useful for ensuring the safety of the vehicle driver and those around the vehicle, and for reducing damage to objects in the surrounding area while the vehicle is in motion, to other devices and users.

[0018] The floodlight 20 includes a light source 22, a light projection optical system 24, a light projection control device 26, and a current source 28.

[0019] The light source 22 includes one or more light-emitting elements (not shown) or a light-emitting source having one or more light-emitting element arrays (for example, those in which light-emitting elements are arranged linearly (one-dimensionally) or planar (two-dimensionally)). The light-emitting element is, for example, a laser diode, a surface-emitting type laser light-emitting element (for example, a VCSEL (Vertical Cavity Surface Emitting Laser, hereinafter referred to as a "surface-emitting element")), a surface-emitting element array (for example, a VCSEL array) in which a plurality of surface-emitting elements are arranged one-dimensionally or two-dimensionally on a substrate (semiconductor substrate, ceramic substrate, 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 elements constituting the light source 22. The current source 28 supplies, for example, a periodic square-wave current for turning on and off the current flowing through the light-emitting elements to the light-emitting elements.

[0021] The light projection control device 26 controls the current (drive current) supplied from the current source 28 to the light-emitting elements by generating a control signal for the current source 28 and inputting it to the current source 28. The light projection control device 26 inputs a signal indicating the timing when the light-emitting element emits light (the timing when 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 causes the light-emitting element to emit light periodically and repeatedly, for example, by performing control to periodically repeat the on / off of the current flowing through the light-emitting element.

[0022] The light projection optical system 24 adjusts the light distribution of the emitted light L1, for example, by applying an optical action (refraction, scattering, diffraction, etc.) to the light emitted by the light source 22. The light projection optical system 24 is configured using various optical components such as various lenses such as collimating lenses and mirrors (mirrors).

[0023] The light receiver 30 has a light-receiving portion 32 and a light-receiving optical system 34.

[0024] The light-receiving optical system 34 focuses the reflected light L2 that returns after the light L1 emitted from the light emitter 20 is reflected by the object to be measured W, etc., onto the light-receiving unit 32. The light-receiving optical system 34 is composed of optical components such as various lenses such as focusing lenses, various filters such as wavelength filters, and reflectors (mirrors).

[0025] The light-receiving unit 32 has multiple light-receiving elements. The light-receiving unit 32 generates a light-receiving signal with a current level or voltage level corresponding to the intensity of the reflected light L2 by photoelectric conversion of the reflected light L2 incident from the light-receiving optical system 34. The light-receiving unit 32 inputs a signal indicating the timing at which the light-receiving elements constituting the light-receiving unit 32 received the reflected light L2 (hereinafter referred to as "light-receiving timing"), and the light-receiving signal generated by the light-receiving elements, to the TOF measuring device 40.

[0026] The measuring device 10 further includes a TOF measuring device 40, a control circuit 42, and a communication I / F (Interface) 50. In this embodiment, the TOF measuring device 40 and the control circuit 42 are examples of controllers.

[0027] The TOF measuring device 40 determines the time of flight (TOF) based on a signal indicating the light emission timing input from the light emission control device 26 and a signal indicating the light reception timing input from the light receiving unit 32. The TOF measuring device 40 has, for example, a time measurement IC (integrated circuit) equipped with a TDC (Time to Digital Converter) circuit. The TOF measuring device 40 inputs the determined 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 (CPU (Central Processing Unit), MPU (Micro Processing Unit), ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), DSP (Digital Signal Processor), etc.). Based on the received light signal and TOF input from the TOF measuring device 40, the control circuit 42 generates information used for various measurements such as detection of the target W and distance measurement. This information includes, for example, a histogram used in time-correlated single-photon counting, the distance to each point of the target W, and a point cloud. The control circuit 42 also controls the light projection control device 26 and the light receiving unit 32. For example, by controlling the light projection control device 26 and the light receiving unit 32, the control circuit 42 controls the aforementioned light projection timing and light receiving timing so that the processing for histogram generation is accelerated or optimized. The information generated by the control circuit 42 is provided (transmitted) to devices that utilize the information (hereinafter referred to as "various utilization devices 60") via the communication I / F 50.

[0029] Various devices 60 perform tasks such as creating environmental maps using point clouds and self-localization (SLAM (Simultaneous Localization and Mapping)) using scan matching algorithms (NDT (Normal Distributions Transform), ICP (Iterative Closest Point), etc.).

[0030] A-2. Internal configuration of the light-receiving chip 31: Figure 2 is a block diagram showing the internal configuration of the light-receiving chip 31. The light-receiving chip 31 is a semiconductor chip that includes a light-receiving unit 32 and a TOF measuring device 40. Specifically, in the light-receiving chip 31, various electronic components and circuits that constitute the light-receiving unit 32 and the TOF measuring device 40 are mounted on a common circuit board 41, integrating them into a single chip. The light-receiving chip 31 (various electronic components and circuits that constitute the light-receiving unit 32 and the TOF measuring device 40) is composed of, for example, FPGAs and DSPs.

[0031] In this embodiment, the light-receiving unit 32 has a light-receiving surface 32A in which a plurality of light-receiving elements are arranged in an array-like linear (one-dimensional) or planar (two-dimensional) configuration. In this embodiment, the light-receiving element is a SPAD, which is an example of a photon-counting type light-receiving element. The SPAD responds with a predetermined probability (e.g., 20%) when a photon is incident on it, and outputs one pulse when it detects a photon.

[0032] In the light-receiving unit 32 that utilizes SPADs, one pixel in the image acquired based on the light-receiving signal from the SPADs (hereinafter referred to as the "received image") is defined by the "SPAD unit number M" and the "SPAD integration count U". The SPAD unit number M is the number of adjacent SPADs on the light-receiving surface 32A. For example, in a configuration where multiple SPADs are arranged two-dimensionally on the light-receiving surface 32A, the SPAD unit number M is 9 (=3×3) or 16 (=4×4). The larger the SPAD unit number M, the lower the resolution of the received image. The SPAD integration count U is the number of times the output value of each SPAD is integrated at predetermined sampling timings. A larger SPAD integration count U means that the integration time of the SPAD output value is longer. The larger the SPAD integration count U, the lower the frame rate of the received image (the number of images (frames) that make up one second of video). Note that the SPAD integration count U is an example of the number of times pixel values ​​are integrated.

[0033] As shown in Figure 2, the light receiving unit 32 includes a SPAD array 72, a timing control circuit 74, a drive circuit 76, and an output circuit 78.

[0034] The SPAD array 72 has multiple SPADs 70 arranged in a two-dimensional grid. Pixel drive lines LD (in the left-right direction in Figure 2) are connected to each column of the multiple SPADs 70, and output signal lines LS (in the up-down direction in Figure 2) are connected to each row. One end of the pixel drive line LD is connected to the output terminal of the drive circuit 76 corresponding to each column, and one end of the output signal line LS is connected to the input terminal of the output circuit 78 corresponding to each row.

[0035] The drive circuit 76 includes a shift register and an address decoder, and drives each SPAD 70 of the SPAD array 72, either simultaneously for all pixels or in column units. The drive circuit 76 selects the SPAD 70 to be used to detect photon incidence in column units by applying a selection control voltage to the pixel drive line LD corresponding to the column to be read. The received light signals (signals output based on the detection of photon incidence) output from each SPAD 70 of the column selected and scanned by the drive circuit 76 are input to the output circuit 78 through each of the output signal lines LS. The output circuit 78 outputs the received light signals input from each SPAD 70 to the adder circuit 44 provided for each pixel.

[0036] The timing control circuit 74 includes a timing generator that generates various timing signals, and controls the drive circuit 76 and the output circuit 78 based on the various timing signals generated by the timing generator. The timing control circuit 74 is communicated to the control circuit 42 via the input terminal 43.

[0037] The TOF measuring device 40 includes an adder circuit 44, a histogram processing circuit 46, and an arithmetic circuit 48.

[0038] The summing circuit 44 measures the time-of-flight (TOF) for each detected photon based on the light-receiving signals input from one or more SPADs 70 constituting a single pixel, and adds the number of detected photons to each of the multiple time slots arranged in a time series based on the measured TOF. The summing circuit 44 then outputs the aggregated number of detected photons for each time slot as a pixel value to the histogram processing circuit 46.

[0039] The histogram processing circuit 46 creates a histogram from the pixel values ​​obtained for each of the one or more SPADs 70. The horizontal axis of the histogram is the BIN number (BININDEX) corresponding to the number indicating the sampling order for each sampling period SP (the time slot mentioned above), and the vertical axis of the histogram is the pixel value. The histogram processing circuit 46 has a memory 47. The histogram processing circuit 46 stores the data group that constitutes the histogram in the memory 47. For example, SRAM (Static Random Access Memory) or DRAM (Dynamic Random Access Memory) can be used for the memory 47.

[0040] The calculation circuit 48 identifies the time of flight when the pixel value peaks from the histogram created by the histogram processing circuit 46. Based on the identified time of flight, the calculation circuit 48 estimates or calculates the distance from the measuring device 10 or the device on which it is mounted to an object within the ranging range. The calculation circuit 48 then outputs the estimated or calculated distance information to, for example, the control circuit 42 via the output terminal 45.

[0041] A3. Measurement operation: The TOF measuring device 40, with the configuration described above, can repeatedly perform the measurement operation. The measurement operation is an operation that sequentially performs the following processes (a) to (c). (a) Readout process: The control circuit 42 emits light L1 from the light emitter 20, and the adder circuit 44 uses the light receiving trigger timing TR(TR1,TR2) as a trigger to sequentially read out the received signals from each of the multiple SPADs 70 with a sampling period SP(SP1,SP2). (b) Histogram generation process: The histogram processing circuit 46 generates pixel values ​​for each pixel based on the multiple light-receiving signals read out, and stores the histogram of the pixel values ​​for each pixel in the memory 47. (c) Peak detection processing: The calculation circuit 48 generates information corresponding to the peak detection timing TS (TS1, TS2, TS3) of the histogram, based on the light emission timing TP of the light emitter 20, the light reception trigger timing TR, and the histogram stored in the memory 47. The information corresponding to the peak detection timing TS of the histogram is an example of information corresponding to the distance to the measurement target.

[0042] The TOF measuring device 40 is capable of selectively performing a plurality of measurement operations in which at least one of the light-receiving trigger timing TR and sampling period SP differs from one another, based on control by the control circuit 42. In this embodiment, the TOF measuring device 40 is capable of selectively performing a basic measurement operation, a delayed measurement operation, and a low-rate measurement operation. The basic measurement operation is an example of a first measurement operation, and the delayed measurement operation and the low-rate measurement operation are examples of second measurement operations.

[0043] Figure 3 is an explanatory diagram showing the light emission and reception timings and histograms in the basic measurement operation and the delayed measurement operation. As shown on the left side of Figure 3(A), in the basic measurement operation, during the readout process, the light emitter 20 emits light L1 with a first light emission intensity P1 at the light emission timing (light emission trigger timing) TP. The summing circuit 44 of the light receiver 30 uses the first light reception trigger timing TR1, which approximately coincides with the light emission timing TP, as a trigger to sequentially read the received signals from each of the multiple SPADs 70 with a first sampling period SP1 (e.g., 1 ns, with a measurement distance resolution of 15 cm). The number of SPAD integrations U is, for example, 1. The first receivable period TC1 in the basic measurement operation is the period from the light emission timing TP (first light reception trigger timing TR1) to the first end timing TE1. As a result, a histogram like the one shown on the right side of Figure 3(A) is generated and stored in the memory 47.

[0044] In the delayed measurement operation, the light reception trigger timing TR and the emission intensity of the emitted light L1 differ from those of the basic measurement operation. That is, as shown on the left side of Figure 3(B), in the delayed measurement operation, during the readout process, the light emitter 20 emits emitted light L1 with a second emission intensity P2 (for example, 1.5 times or more the first emission intensity P1) that is higher than the first emission intensity P1 at the light emission timing TP. The summing circuit 44 of the light receiver 30 uses the second light reception trigger timing TR2, which is delayed by a delay time ΔTD from the light emission timing TP, as a trigger to sequentially read the received signals from each of the multiple SPADs 70 at the first sampling period SP1. The second light reception period TC2 in the delayed measurement operation is the period from the second light reception trigger timing TR2 to the second end timing TE2. As a result, a histogram like the one shown on the right side of Figure 3(B) is generated and stored in the memory 47.

[0045] The length of the second light-receivable period TC2 in the delayed measurement operation may be the same as the length of the first light-receivable period TC1 in the basic measurement operation, or it may be shorter than the length of the first light-receivable period TC1. The first light-receivable period TC1 and the second light-receivable period TC2 may partially overlap with each other. Specifically, the second light-receiving trigger timing TR2 of the second light-receivable period TC2 may be earlier than the first end timing TE1 of the first light-receivable period TC1. This suppresses the occurrence of a period during which distance measurement is impossible between the first light-receivable period TC1 and the second light-receivable period TC2.

[0046] Figure 4 is an explanatory diagram showing the light emission and reception timings and histograms for the basic measurement operation and the low-rate measurement operation. The low-rate measurement operation differs from the basic measurement operation in the sampling period SP and the number of SPAD integrations U. That is, as shown on the left side of Figure 4(B), in the low-rate measurement operation, in the readout process, similar to the basic measurement operation, the light emitter 20 emits light L1 with a first light emission intensity P1 at the light emission timing TP. The summing circuit 44 of the light receiver 30 is triggered by the first light reception trigger timing TR1 and sequentially reads the received signals from each of the multiple SPADs 70 with a second sampling period SP2 (e.g., 2ns, with a measurement distance resolution of 30cm) which is longer than the first sampling period SP1. The third light-receivable period TC3 in the low-rate measurement operation is the period from the first light reception trigger timing TR1 to the third end timing TE3. The third termination timing TE3 is later than the first termination timing TE1 of the first light-receivable period TC1. The number of SPAD integrations U (e.g., 2) in the low-rate measurement operation is greater than the number of SPAD integrations U in the basic measurement operation. As a result, a histogram like the one shown on the right side of Figure 4(B) is generated and stored in memory 47.

[0047] A4. Measurement process: Figure 5 is a flowchart of the measurement process. For example, when the measuring device 10 is powered on and a measurement start instruction is received from, for example, the user device 60, the control circuit 42 executes the measurement process shown in Figure 5. The measurement process performs at least one of the following: a basic measurement operation, a delayed measurement operation, and a low-rate measurement operation, and outputs a measurement result corresponding to the distance to the object to be measured based on the information generated by the executed measurement operation.

[0048] In this embodiment, the measuring device 10 is configured to allow setting between a normal measurement mode and a long-distance measurement mode. The control circuit 42 selectively sets between the normal measurement mode and the long-distance measurement mode based on mode selection information received, for example, from the user device 60. The normal measurement mode is a mode that performs distance measurement where the maximum measurable distance is a first upper limit distance (e.g., 300m). The long-distance measurement mode is a mode that performs distance measurement where the maximum measurable distance is a second upper limit distance (e.g., 600m) that is longer than the first upper limit distance. The normal measurement mode is an example of the first mode, and the long-distance measurement mode is an example of the second mode.

[0049] The control circuit 42 determines whether or not it is set to long-distance measurement mode (S110). If the control circuit 42 determines that it is set to normal measurement mode (S110: NO), it causes the TOF measuring device 40 to perform basic measurement operations (see Figures 3(A) and 4(A)) (S150). In the examples of Figures 3(A) and 4(A), the first light reception timing TS1 at the light receiver 30 (histogram peak detection timing) is the timing after a first waiting time ΔTS1 has elapsed from the first light reception trigger timing TR1. Therefore, in the peak detection process in the basic measurement operation, the calculation circuit 48 generates first generated information corresponding to the first light reception timing TS1 (for example, including a BIN number corresponding to the first light reception timing TS1).

[0050] The control circuit 42 generates a measurement result corresponding to the distance to the object to be measured based on the first generated information and outputs it to the user device 60 (S160), thereby ending the measurement process. In the examples of Figures 3(A) and 4(A), the first distance to the object to be measured is calculated by the following formula. First distance = (speed of light) × [(rank of BIN number corresponding to the first light reception timing TS1) × (first sampling period SP1)] / 2 As mentioned above, the maximum measurable distance in normal measurement mode is the first upper limit distance (e.g., 300m).

[0051] If the control circuit 42 determines that it is set to long-distance measurement mode (S110: YES), it will perform a basic measurement operation (S120), and then perform either a delayed measurement operation (see Figure 3(B)) or a low-rate measurement operation (see Figure 4(B)) (S130). The control circuit 42 may also decide whether to perform a delayed measurement operation or a low-rate measurement operation based on measurement operation selection information included in the mode selection information received from the user device 60, for example.

[0052] In the delayed measurement operation, during the waiting period from the light emission timing TP until the delay time ΔTD has elapsed, the summing circuit 44 of the light receiver 30 does not read the received signal from the SPAD array 72 (see Figure 3(B)). Therefore, the histogram processing circuit 46 does not generate a histogram and does not use the memory 47. Next, when the second light reception trigger timing TR2 arrives, the summing circuit 44 starts reading the received signal from the SPAD array 72. Therefore, the histogram processing circuit 46 uses the memory 47 to generate a histogram. In other words, in the delayed measurement operation, the summing circuit 44 reads the received signal from the SPAD array 72 only for the second light reception period TC2 (equal to or less than the first light reception period TC1), and the histogram processing circuit 46 uses the memory 47 to store the histogram. Therefore, the storage area of ​​the memory 47 used in the delayed measurement operation is the same as the storage area of ​​the memory 47 used in the basic measurement operation. The measurable distance in delayed measurement operation differs from the measurable distance in basic measurement operation; for example, it is between 300m and 600m.

[0053] In the example shown in Figure 3(B), the second light reception timing TS2 (histogram peak detection timing) at the light receiver 30 is the timing after a second waiting time ΔTS2 has elapsed from the second light reception trigger timing TR2. Therefore, in the peak detection process during the delayed measurement operation, the calculation circuit 48 generates second generated information corresponding to the second light reception timing TS2 (for example, a BIN number corresponding to the second light reception timing TS2).

[0054] In low-rate measurement operation, the summing circuit 44 of the photodetector 30 starts reading the received signal from the SPAD array 72 at the light emission timing TP (see Figure 4(B)). Therefore, in low-rate measurement operation, the summing circuit 44 reads the received signal from the SPAD array 72 over the third receivable period TC3 (twice the length of the first receivable period TC1), and the histogram processing circuit 46 uses the memory 47 to store the histogram. The measurable distance in low-rate measurement operation is twice the measurable distance in basic measurement operation (for example, 0m or more and 600m or less).

[0055] However, in the example shown in Figure 4(B), the second sampling period SP2 in the low-rate measurement operation is twice the first sampling period SP1 in the basic measurement operation. Therefore, the storage area of ​​memory 47 used in the low-rate measurement operation is the same as the storage area of ​​memory 47 used in the basic measurement operation.

[0056] In the example shown in Figure 4(B), the third light reception timing TS3 (histogram peak detection timing) at the light receiver 30 is the timing after a third waiting time ΔTS3 has elapsed from the first light reception trigger timing TR1. Therefore, in the peak detection process during low-rate measurement operation, the calculation circuit 48 generates third generated information corresponding to the third light reception timing TS3 (for example, a BIN number corresponding to the third light reception timing TS3).

[0057] The control circuit 42 outputs a measurement result corresponding to the distance to the object to be measured to the user device 60 (S140) based on the first generated information generated by the basic measurement operation and the second generated information generated by the delayed measurement operation or the third generated information generated by the low-rate measurement operation, and then terminates the measurement process.

[0058] In the example shown in Figure 3(B), where a delayed measurement operation is performed in long-distance measurement mode, the second distance to the object being measured is calculated using the following formula. Second distance = (speed of light) × [(delay time ΔTD) + (rank of BIN number corresponding to the second light reception timing TS2) × (first sampling period SP1)] / 2 In this case, the control circuit 42 outputs a first distance as a measurement result when the measurable distance is between 0m and 300m, and outputs a second distance as a measurement result when the measurable distance is between 300m and 600m. This allows the long-distance measurement mode to expand the measurable distance while suppressing the expansion of the memory area for storing the histogram compared to the normal measurement mode. Furthermore, by performing a delayed measurement operation in the long-distance measurement mode, the sampling period SP can be kept constant, and the distance to the target can be measured with uniform measurement accuracy (time resolution) within the measurable distance range.

[0059] As described above, the measurable distance in the delayed measurement operation is longer than that in the basic measurement operation. Therefore, the light intensity of the reflected light L2 incident on the receiver 30 in the delayed measurement operation is lower than that of the reflected light L2 incident on the receiver 30 in the basic measurement operation. However, the second light emission intensity P2 of the emitter 20 in the delayed measurement operation is higher than the first light emission intensity P1 of the emitter 20 in the basic measurement operation. Therefore, the decrease in accuracy of distance measurement caused by the attenuation of reflected light L2 in long-distance measurements is suppressed.

[0060] In the example shown in Figure 4(B), where a low-rate measurement operation is performed in long-distance measurement mode, the third distance to the object being measured is calculated using the following formula. Third distance = (speed of light) × [(rank of BIN number corresponding to the third light reception timing TS3) × (second sampling period SP2)] / 2 In this case, the control circuit 42 outputs a first distance as a measurement result when the measurable distance is between 0m and 300m, and outputs a third distance as a measurement result when the measurable distance is between 300m and 600m. That is, for measurable distances between 0m and 300m, the measurement results of the basic measurement operation, which has higher measurement accuracy than the low-rate measurement operation, are used. As a result, in the long-distance measurement mode, the measurable distance can be expanded while suppressing the expansion of the memory area for storing the histogram compared to the normal measurement mode. In addition, by performing the low-rate measurement operation in the long-distance measurement mode, the distance to the measurement target at a distance can be measured without delaying the light reception trigger timing TR.

[0061] As described above, the measurable distance in low-rate measurement operation includes a longer distance than the measurable distance in basic measurement operation. Therefore, the light intensity of reflected light L2 incident on the photodetector 30 in delayed measurement operation may be lower than the light intensity of reflected light L2 incident on the photodetector 30 in basic measurement operation. However, the number of SPAD integrations U in delayed measurement operation is greater than the number of SPAD integrations U in basic measurement operation. Therefore, the decrease in accuracy of distance measurement due to attenuation of reflected light L2 in long-distance measurements is suppressed.

[0062] B. Variations: The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible.

[0063] The configuration of the measuring 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 was used as an example of a photodetector, but it is not limited to this, and other photon-counting type photodetectors (e.g., MPPC (Multi-Pixel Photon Counter)) or photodetectors other than photon-counting type photodetectors (e.g., photodiodes or phototransistors) may also be used. Furthermore, in the above embodiment, the signal output by the SPAD 70 based on the detection of photons was used as an example of a light-receiving signal from the photodetector, but it is not limited to this, and for example, if the photodetector is not of the photon-counting type, it may be a signal output by the photodetector based on light reception (an analog signal or digital signal corresponding to the amount of light received).

[0064] The light-receiving chip 31 may not be configured in a way that integrates the light-receiving unit 32 and the TOF measuring device 40 into a single chip. The memory is not limited to the memory 47 in the histogram processing circuit 46, but may be a memory provided outside the histogram processing circuit 46. The measuring device 10 may not perform either delayed measurement operation or low-rate measurement operation. The measuring device 10 may perform only the long-distance measurement mode without performing the normal measurement mode.

[0065] The flowchart of the measurement process in the above embodiment is merely an example and can be modified in various ways. For example, the sampling period SP in the delayed measurement operation may be longer or shorter than the first sampling period SP1 in the basic measurement operation. The light emission intensity of the light emitter 20 in the delayed measurement operation may be the same as the first light emission intensity P1 in the basic measurement operation. The number of SPAD integrations U in the delayed measurement operation may be more or less than the number of SPAD integrations U in the basic measurement operation.

[0066] The light-receiving trigger timing TR in the low-rate measurement operation may be later than the first light-receiving trigger timing TR1 in the basic measurement operation. Also, the light emission intensity of the light emitter 20 in the low-rate measurement operation may be higher than the first light emission intensity P1 in the basic measurement operation. The number of SPAD integrations U in the low-rate measurement operation may be the same as the number of SPAD integrations U in the basic measurement operation. [Explanation of Symbols]

[0067] 10: Measuring device 20: Light emitter 30: Light receiver 31: Light receiving chip 32: Light receiving unit 40: TOF measuring device 41: Circuit board 42: Control circuit 44: Adder circuit 46: Histogram processing circuit 47: Memory 48: Arithmetic circuit 70: SPAD W: Measurement target

Claims

1. A measuring device, A floodlight that emits light, A light receiver comprising multiple light-receiving elements arranged in an array, which receives reflected light that is returned after being reflected off the object to be measured from the aforementioned light emitter, Memory and Controller and Equipped with, The controller is configured to perform the following measurement operations: (a) to (c), (a) Light is emitted from the light emitter, and the light receiving trigger timing is used as a trigger to sequentially read out the light receiving signals from each of the plurality of light receiving elements at the sampling period, (b) For each pixel, generate a pixel value for each sampling period based on the multiple light-receiving signals read out, and store a histogram of the pixel values ​​in the memory. (c) Based on the light emission timing of the light emitter, the light receiving trigger timing, and the histogram stored in the memory, information corresponding to the distance to the object to be measured is generated. Furthermore, the controller, A first measurement operation is performed, and a second measurement operation is performed at a different time from the first measurement operation, wherein at least one of the light reception trigger timing and the sampling period is different from the first measurement operation. Based on the information generated in the first measurement operation and the information generated in the second measurement operation, a measurement result corresponding to the distance to the object to be measured is output. Measuring device.

2. A measuring device according to claim 1, The second time difference between the light emission timing and the light reception trigger timing in the second measurement operation is longer than the first time difference between the light emission timing and the light reception trigger timing in the first measurement operation. Measuring device.

3. A measuring device according to claim 1, The second sampling period in the second measurement operation is longer than the first sampling period in the first measurement operation. Measuring device.

4. A measuring device according to claim 2 or claim 3, The light emission intensity of the floodlight in the second measurement operation is higher than the light emission intensity of the floodlight in the first measurement operation. Measuring device.

5. A measuring device according to claim 2 or claim 3, The number of times the pixel value is accumulated in accordance with the number of times (a) and (b) are performed in the second measurement operation is greater than the number of times the pixel value is accumulated in accordance with the number of times (a) and (b) are performed in the first measurement operation. Measuring device.

6. A measuring device according to any one of claims 1 to 3, The aforementioned controller, A first mode that performs the first measurement operation and outputs the measurement result based on the information generated by the first measurement operation, The system is configured to perform a second mode in which the first measurement operation and the second measurement operation are performed, and the measurement result is output based on the information generated by the first measurement operation and the information generated by the second measurement operation. Measuring device.

7. A computer in a measuring device comprising a light emitter that emits light, a light receiver with multiple light-receiving elements arranged in an array that receives reflected light that has been reflected back from the object to be measured after being emitted from the light emitter, and a memory, Perform the following measurement operations (a) to (c): (a) Light is emitted from the light emitter, and the light receiving trigger timing is used as a trigger to sequentially read out the light receiving signals from each of the plurality of light receiving elements at the sampling period, (b) For each pixel, generate a pixel value for each sampling period based on the multiple light-receiving signals read out, and store a histogram of the pixel values ​​in the memory. (c) Based on the light emission timing of the light emitter, the light receiving trigger timing, and the histogram stored in the memory, information corresponding to the distance to the object to be measured is generated. Furthermore, the computer, A first measurement operation is performed, and a second measurement operation is performed at a different time from the first measurement operation, wherein at least one of the light reception trigger timing and the sampling period is different from the first measurement operation. Based on the information generated in the first measurement operation and the information generated in the second measurement operation, a measurement result corresponding to the distance to the object to be measured is output. Measurement program for a measuring device.

8. A computer-readable recording medium that stores a measurement program for controlling a measuring device comprising: a light emitter that emits light; a light receiver having multiple light-receiving elements arranged in an array that receive reflected light that has been reflected back from the object to be measured after being emitted from the light emitter; and a memory. On the computer, Perform the following measurement operations (a) to (c): (a) Light is emitted from the light emitter, and the light receiving trigger timing is used as a trigger to sequentially read out the light receiving signals from each of the plurality of light receiving elements at the sampling period, (b) For each pixel, generate a pixel value for each sampling period based on the multiple light-receiving signals read out, and store a histogram of the pixel values ​​in the memory. (c) Based on the light emission timing of the light emitter, the light receiving trigger timing, and the histogram stored in the memory, information corresponding to the distance to the object to be measured is generated. Furthermore, the computer, A first measurement operation is performed, and a second measurement operation is performed at a different time from the first measurement operation, wherein at least one of the light reception trigger timing and the sampling period is different from the first measurement operation. Based on the information generated in the first measurement operation and the information generated in the second measurement operation, a measurement result corresponding to the distance to the object to be measured is output. A computer-readable recording medium.

Images