Measurement device and measurement method for measurement device

Abstract

To measure a distance to a measurement object while reducing the memory capacity for storing received light data.SOLUTION: A controller executes: update processing of repeatedly executing the update operation that writes received light data output from multiple light-receiving elements into memory after the light emission timing of a light emitter, and overwrites the memory with the received light data subsequently output from the multiple light-receiving elements when the writing amount of the received light data reaches a reference value of the memory; and measurement processing of measuring a distance to a measurement object by taking out a received light data group including reflected light received light data when the reflected light received light data being the received light data corresponding to the reflected light is written into the memory.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] With the progress 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 for grasping the surrounding environment and estimating the vehicle's self-position while driving. LiDAR includes a projector that projects (irradiates) laser light onto a measurement target, and a receiver that receives the reflected light that is reflected back from the measurement target by the laser light. 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 (see, for example, Patent Document 1).

[0003] Conventional measuring devices are configured to write into memory all of a group of received light data for an estimated time period from when light is emitted from a projector, reflected by a measurement target, and returned to a receiver. [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] Conventional measuring devices require a large-capacity memory capable of storing all of the light reception data for an estimated time period. Conversely, reducing the memory capacity shortens the distance that can be measured by the measuring device.

[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 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 reflected light that is returned from a measurement target after the light emitted from the projector is reflected, a controller, and a memory. The controller executes an update process that writes light reception data output from the plurality of light receiving elements to the memory after a light emission timing of the projector, and when an amount of the light reception data written reaches a reference value of the memory, repeatedly executes an update operation of overwriting the memory with the light reception data output from the plurality of light receiving elements thereafter, and a measurement process that, when reflected light reception data, which is the light reception data corresponding to the reflected light, is written to the memory, extracts a light reception data group including the reflected light reception data and measures a distance to the measurement target.

[0009] With this measuring device, it is possible to measure the distance to the object to be measured while reducing the memory capacity required to store the light reception data, compared to a configuration in which light reception data for the estimated time it takes for light to be emitted from the light source, reflected by the object to be measured, and returned to the receiver is written into memory.

[0010] (2) In the measurement device, the controller may further execute a reference value changing process for changing the reference value of the memory. According to this measurement device, the upper limit of the memory for storing the light reception data can be appropriately changed.

[0011] (3) In the above measurement device, the controller may be configured to stop the update process when the reflected light reception data is written to the memory. With this measurement device, it is possible to prevent the light reception data from being stored unnecessarily even after the reflected light is detected.

[0012] (4) In the above measurement device, when the update process for a first pixel in the optical receiver is stopped, the controller may use a memory area allocated to the first pixel for updating the light reception data for a second pixel. According to this measurement device, after reflected light is detected for the first pixel, the memory area for the first pixel can be effectively used for storing the light reception data for the second pixel.

[0013] The techniques disclosed in this specification can be realized in various forms, for example, in the form of a light source, a measurement device including the light source, a measurement method, and the like. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a measurement device 10 according to an embodiment. [Diagram 2] FIG. 11 is an explanatory diagram showing the variation in the timing of light projection and the timing of light reception signal output and the result of distance measurement. [Diagram 3] Flowchart showing part of memory processing [Figure 4] FIG. 1 is an explanatory diagram illustrating memory processing in an embodiment and a comparative example; [Diagram 5] FIG. 1 is an explanatory diagram illustrating memory processing of a first pixel and a second pixel; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A. First 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The light receiver 30 includes a light receiving section 32 and a light receiving optical system 34 .

[0023] 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).

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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").

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] A-3.Memory handling: 3 is a flowchart showing a part of the memory process. This memory process is a process for measuring the distance to the measurement target W while reducing the memory capacity for storing the received light data. The TOF measurement device 40 uses a memory 44 for storing the received light data (output values) output from the multiple SPADs.

[0034] As shown in Fig. 3, the TOF measurement device 40 determines the memory area to be used (S110). The memory area to be used is an area of ​​the memory 44 to be used for storing received light data, and is determined by a reference value. The reference value is an upper limit of the memory area to be used (used memory capacity) of the memory 44. The memory area to be used can be changed by changing the reference value (an example of a reference value changing process). The reference value may be set to a value corresponding to the entire memory area of ​​the memory 44, or may be set to a value corresponding to a part of the memory area of ​​the memory 44.

[0035] Next, the TOF measurement device 40 starts an update process, triggered by the light projection timing of the projector 20. In the update process, the TOF measurement device 40 writes the light reception data output from the multiple SPADs to the usable memory area of ​​the memory 44 after the light projection timing of the projector 20, and when the amount of written light reception data reaches the above-mentioned reference value, repeatedly executes an update operation of overwriting the usable memory area with the light reception data output from the multiple SPADs thereafter.

[0036] Specifically, the TOF measurement device 40 first starts a process of writing the light reception data (histogram) output from the multiple SPADs to the usable memory area of ​​the memory 44 (S120). Next, the TOF measurement device 40 judges whether or not the reflected light L2 is detected based on the light reception data (histogram) written in the usable memory area (S130). Specifically, the TOF measurement device 40 compares the light reception data (histogram) written in the usable memory area with a signal detection threshold to judge whether or not the reflected light reception data, which is the light reception data corresponding to the reflected light L2, is included.

[0037] When the TOF measurement device 40 determines that the reflected light L2 has not been detected (S130: NO), it determines whether the amount of written light reception data has reached the reference value (S150). When the TOF measurement device 40 determines that the amount of written light reception data has not reached the reference value (S150: NO), it returns to S130 and continues writing the light reception data to the memory area to be used. On the other hand, when the TOF measurement device 40 determines that the amount of written light reception data has reached the reference value (S150: YES), it starts a process of overwriting the light reception data output from the multiple SPADs in the memory area to be used (S160). In short, the light reception data group (histogram) that does not include the reflected light reception data is basically not used to measure the distance to the measurement target W, so there is no problem even if it is lost by overwriting. After starting the overwriting process, the TOF measurement device 40 adds 1 to the number of overwrites N (S170) and returns to S130. That is, the TOF measurement device 40 counts the number of overwrites.

[0038] On the other hand, when the TOF measurement device 40 determines that the reflected light L2 has been detected (S130: YES), it copies and extracts the light reception data group (histogram) contained in the reflected light reception data and outputs it to the control circuit 42 (S140), and the control circuit 42 measures the distance to the measurement object W based on the extracted light reception data group and the number of overwrites N.

[0039] 4 is an explanatory diagram illustrating memory processing in the embodiment and the comparative example. The memory processing in the comparative example is a process in which all light reception data output from a plurality of SPADs is continuously written to the memory without overwriting until the reflected light L2 is detected. For example, in order to be able to measure the distance to the measurement target W up to 200 m away, a large memory capacity M is required that can store all of the light reception data groups for the estimated time from when light is emitted from the projector 20 to when it is reflected by the measurement target W up to 200 m away and returns to the light receiver 30. For this reason, it is necessary to secure a memory area for that memory capacity M in the memory 44.

[0040] On the other hand, in the memory processing of the embodiment, the light reception data output from the multiple SPADs is written to a usable memory area of ​​memory capacity m(K) smaller than the memory capacity M, and when the amount of written light reception data reaches the upper limit of the memory capacity m(K), the usable memory area is overwritten. In the example of Fig. 4, since reflected light reception data exceeding the signal detection threshold is included during the third and fourth overwriting processes, the third and fourth light reception data groups are output to the control circuit 42. Therefore, in the memory processing of the embodiment, if a memory area of ​​memory capacity m(K) is secured in the memory 44, it is possible to measure the distance to the measurement target W up to 200 m away.

[0041] After outputting the light reception data group including the reflected light reception data (S140), the TOF measurement device 40 stops the update process, releases the memory area for memory processing for other pixels (S180), and ends this memory process. FIG. 5 is an explanatory diagram illustrating memory processing for the first pixel and the second pixel. As shown in FIG. 5, when the reflected light L2 is detected for a relatively short period ΔTS for the first pixel and the update process is stopped, the memory area for the first pixel is not used for the remaining time Δtf. Therefore, the memory area for the first pixel is released for update processing for the second pixel. As a result, the memory area for the second pixel is expanded, so that the time until the reflected light L2 is detected after the light projection timing is extended, and the distance to the measurement target W that is farther away can be measured.

[0042] A-4. Advantages of this embodiment: As described above, according to the measuring device 10 of this embodiment, it is possible to measure the distance to the measurement object W while reducing the memory capacity required to store the light reception data, compared to a configuration in which light reception data for the estimated time from when light is emitted from the light source 20, reflected by the measurement object W, and returned to the receiver 30 is written into memory.

[0043] 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.

[0044] The configuration of the measuring device 10 in the above embodiment is merely an example, and various modifications are possible.

[0045] In the flow chart of the measurement process in the above embodiment, it is not necessary to execute either the process of S110 or the process of S180. [Explanation of symbols]

[0046] 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 44: Memory 60: Utilization device

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 controller; A measurement device comprising: The controller: an update process for repeatedly executing an update operation in which, after a light emission timing of the light emitter, light reception data output from the plurality of light receiving elements is written into the memory, and when an amount of the light reception data written reaches a reference value of the memory, the light reception data output from the plurality of light receiving elements is subsequently overwritten into the memory; When reflected light reception data, which is the light reception data corresponding to the reflected light, is written to the memory, a measurement process is performed to extract a light reception data group including the reflected light reception data and measure the distance to the measurement object.

2. 2. The measuring device according to claim 1, The controller further comprises: The measurement device executes a reference value changing process for changing the reference value in the memory.

3. 2. The measuring device according to claim 1, The controller stops the update process when the reflected light reception data is written to the memory.

4. The measuring device according to claim 3, A measurement device wherein, when the controller stops the update process for a first pixel in the optical receiver, the controller uses the memory area allocated to the first pixel for updating the light reception data for a second pixel.

5. A measurement method for a measurement device including a light projector that emits light, a light receiver having a light receiving surface on which a plurality of light receiving elements are arranged in an array that receives reflected light that is emitted from the light projector and reflected back from a measurement target, and a memory, comprising: an updating step of writing the light reception data output from the plurality of light receiving elements into the memory after a light projection timing of the light projector, and when an amount of the light reception data written reaches a reference value of the memory, repeatedly executing an updating operation of overwriting the light reception data output from the plurality of light receiving elements into the memory; a measurement step of extracting a group of light reception data including the reflected light reception data, which is the light reception data corresponding to the reflected light, and measuring the distance to the measurement object when the reflected light reception data is written to the memory.

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