Method for manufacturing measurement device

Abstract

To prevent reduction in the measurement accuracy of a distance to a measurement target due to variations in light emission timing, variations in output timing of a light-receiving signal, or the like from the light-receiving element.SOLUTION: A method for manufacturing a measurement device includes: a preparation step of preparing a sample measurement target with a flat surface; an acquisition step of emitting light from a light emitter toward the flat surface of the sample measurement target, receiving the reflected light reflected on the flat surface on a light-receiving surface of a light receiver, and acquiring a measurement result of a distance for each pixel to the flat surface on the basis of the light-receiving signals of multiple samples output by the respective light-receiving elements; and a correction step of correcting at least one of the light emission timing of the light-emitting elements and the output timing of the light-receiving signals from the light-receiving elements so as to make the measurement result of the distance for each pixel closer to uniformness.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a method for manufacturing a measuring 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 of the laser light reflected off 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 projection timing when the projector emits the laser light and the reception timing when the receiver receives the reflected light. The projector has one or more light-emitting elements, and the receiver has a light-receiving surface on which a plurality of light-receiving elements are arranged in an array (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-91760 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional measuring devices, for example, the distance to the object may not be measured accurately due to variations in the timing of light projection from the light projector or variations in the timing of output of the light reception signal from the light receiving element in the light receiver. Factors causing variations in the timing of light projection include variations in the length of the wiring connected to the multiple light projecting elements and variations in the timing of output of the trigger signal given to the light projector. Factors causing variations in the timing of output of the light reception signal include variations in the length of the wiring connected to the multiple light receiving elements and variations in response characteristics.

[0005] This specification discloses a technique that can solve at least one of the above-mentioned problems. [Means for solving the problem]

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] (1) A method for manufacturing a measuring device disclosed in this specification is a method for manufacturing a measuring device including a projector having one or more light-emitting elements, 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 object that is emitted by the projector, and a controller for controlling the projector and the light-receiver. The method includes a preparation step of preparing a sample measurement object having a flat surface, an acquisition step of emitting light from the projector toward the flat surface of the sample measurement object, receiving the reflected light reflected back from the flat surface at the light-receiving surface of the receiver, and acquiring a measurement result of the distance to the flat surface for each pixel based on a plurality of sample light-receiving signals output from each of the plurality of light-receiving elements, and a correction step of correcting at least one of the emission timing of the light-emitting element and the output timing of the light-receiving signal from the light-receiving element so that the measurement result of the distance for each pixel approaches uniformity.

[0008] According to the manufacturing method of this measuring device, it is possible to suppress a decrease in the measurement accuracy of the distance to the object to be measured, which is caused, for example, by variations in the timing of light projection from the light-projecting device or variations in the output timing of the light-receiving signal from the light-receiving element in the receiver.

[0009] (2) In the above-described method for manufacturing a measuring device, the correction step may change at least one of the length of a wiring connected to the light-emitting element and the length of a wiring connected to the light-receiving element. According to this method for manufacturing a measuring device, a decrease in the measurement accuracy of the distance to the measurement object can be suppressed by adjusting a hardware configuration.

[0010] (3) In the method for manufacturing the measuring device, the correction step may change an output timing of a trigger signal that the controller provides to the light-emitting element. According to this method for manufacturing the measuring device, a decrease in the measurement accuracy of the distance to the measurement object can be suppressed by adjusting a configuration on the projector side.

[0011] (4) In the above-mentioned method for manufacturing a measuring device, the correction step may generate correction information for correcting the measurement results obtained by the controller based on the light receiving signals from the light receiving elements so that the measurement results approach uniformity based on the measurement results of the distance for each pixel. According to this method for manufacturing a measuring device, it is possible to suppress a decrease in the measurement accuracy of the distance to the measurement target by correcting software processing without requiring adjustment of a hardware configuration.

[0012] The techniques disclosed in this specification can be realized in various forms, for example, in the form of a measurement device, a manufacturing method thereof, and the like. [Brief description of the drawings]

[0013] [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] 1 is a flowchart showing a part of a manufacturing process of the measuring device 10. [Figure 4] An explanatory diagram of an example of a correction method using wiring DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] The light receiver 30 includes a light receiving section 32 and a light receiving optical system 34 .

[0022] 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).

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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").

[0027] 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.

[0028] A-2. Variation in timing of light emission and output of light receiving signal: 2 is an explanatory diagram showing the variation in the timing of projecting light and the output timing of the light receiving signal, and the result of distance measurement. In the projector 20 of this embodiment, light emitting elements are arranged in a line, and the vertical pixel NO is a number given to each pixel composed of a predetermined number of light emitting elements. In the following, the case where the number of units is one will be described as an example, but the number of units may be multiple.

[0029] Fig. 2(b) shows the time from input of a trigger signal to light emission for each of the multiple light-emitting elements (VCSELs) in projector 20. As shown in Fig. 2(b), the light-projection timing of the multiple light-emitting elements varies. Causes of the variation in light-projection timing include variation in the length of the wiring connected to the multiple light-projecting elements and variation in the output timing of the trigger signal given to projector 20.

[0030] Fig. 2(c) shows the time from input of a trigger signal to output of a light receiving signal for each of the multiple light receiving elements (SPAD) of the light receiver 30. As shown in Fig. 2(c), the output timing of the light receiving signals from the multiple light receiving elements varies. Factors that cause the variation in the output timing of the light receiving signals include the length of the wiring connected to the multiple light receiving elements and the variation in response characteristics.

[0031] FIG. 2(a) shows the result of measuring the distance to the measurement object W in the presence of variations in the timing of projecting light and the timing of outputting the light receiving signal. This measurement object W has, for example, a flat surface. The light projector 20 emits light L1 toward the flat surface, and the light receiver 30 receives the reflected light L2 reflected by the flat surface. The distance between each of the light-emitting elements and the flat surface is uniform, and the distance between each of the light-receiving elements and the flat surface is also uniform. In this case, the distance from W should be uniform for all pixels. However, in FIG. 2(a), the measurement result of the distance to the measurement object W varies for each pixel. This is due to variations in the timing of projecting light and the timing of outputting the light receiving signal.

[0032] A-3. Manufacturing method of the measuring device 10: 3 is a flowchart showing a part of the manufacturing process of the measuring device 10. First, the measuring device 10 is assembled (S110). Note that the assembly of the measuring device 10 does not need to be completed at this point, as long as it is possible to execute an acquisition process for acquiring a sample light receiving signal, which will be described later.

[0033] Next, a sample measurement object having a flat surface is prepared (S120). This step S120 is an example of a preparation step. The sample measurement object is, for example, a plate-like body and has a flat surface. The flat surface has a uniform reflectance as a whole.

[0034] Next, a plurality of sample light receiving signals are acquired (S130). This step S130 is an example of an acquisition step. Specifically, emitted light L1 is irradiated from a plurality of light emitting elements of the projector 20 toward the flat surface, and reflected light L2 reflected and returned from the flat surface is received by a plurality of light receiving elements of the light receiver 30, and a plurality of sample light receiving signals output from each of the plurality of light receiving elements are acquired. It is assumed that the distance between each of the plurality of light emitting elements and the flat surface is uniform, and the distance between each of the plurality of light receiving elements and the flat surface is also uniform. Based on the acquired plurality of sample light receiving signals, the distance to the flat surface for each pixel is measured, and an image reflecting the measurement result (hereinafter, referred to as a "measurement result image") is obtained. Here, if there is no variation in the timing of projecting light or the timing of outputting the light receiving signal, the measurement result image will be a monochromatic image without unevenness. On the other hand, if there is variation in the timing of projecting light or the timing of outputting the light receiving signal (see FIG. 2(a) above), the measurement result image will have shading for each pixel, resulting in an uneven mixed-color image.

[0035] Therefore, the timing of projecting light and the timing of outputting the light receiving signal are corrected (S140). This step S140 is an example of a correction step. At least one of the timing of light emission of the light emitting element and the timing of outputting the light receiving signal from the light receiving element is corrected so that the measurement results of the distance for each pixel become closer to uniform. Specifically, there are a correction method using wiring, a correction method using a light emission trigger signal, and a correction method using the measurement results.

[0036] (1) Wiring correction method The wiring correction method is a method of changing at least one of the wiring length connected to the light-emitting element and the wiring length connected to the light-receiving element. FIG. 4 is an explanatory diagram of an example of the wiring correction method. In FIG. 4, the current source 28 is omitted. FIG. 4(a) shows the wiring state before correction on the projector 20 side. Each of the multiple light-emitting elements (V1, V2, V3, etc.) is electrically connected to the light-projection control device 26 via wiring (L1, L2, L3, etc.). The lengths of the wiring (L1, L2, L3, etc.) connected to each of the multiple light-emitting elements are the same. The light-projection control device 26 sequentially outputs trigger signals to the multiple light-emitting elements at uniform time intervals ΔT. However, as shown on the right side of FIG. 4(a), the light-projection timing intervals of the multiple light-emitting elements vary due to variations in response performance of the multiple light-emitting elements, etc. The light projection timing interval ΔT1 between the light emitting elements V1 and V2 is longer than the time interval ΔT, and the light projection timing interval ΔT2 between the light emitting elements V2 and V3 is shorter than the time interval ΔT.

[0037] Therefore, the length of the wiring is changed so as to suppress the variation in the light projection timing intervals of the multiple light-emitting elements. For example, as shown in Fig. 4(B), the wiring L2a connected to the light-emitting element V2 is made shorter than the wiring L1 connected to the light-emitting element V1, and the wiring L3a connected to the light-emitting element V3 is made longer than the wiring L1 connected to the light-emitting element V1. This suppresses the variation in the light projection timing intervals of the multiple light-emitting elements, as shown on the right side of Fig. 4(b). According to the wiring correction method, the hardware configuration can be adjusted to suppress a decrease in the measurement accuracy of the distance to the measurement target W.

[0038] (2) Correction method using light emission trigger signal The correction method using a light emission trigger signal changes the output timing of a trigger signal that the light projection control device 26 gives to the light-emitting element. In the example of Fig. 4(a), the output timing of the trigger signal output by the light projection control device 26 is changed without changing the wiring length so as to suppress variation in the light projection timing intervals of multiple light-emitting elements. According to the correction method using a light emission trigger signal, by adjusting the configuration on the projector 20 side, it is possible to suppress a decrease in the measurement accuracy of the distance to the measurement target W.

[0039] (3) Correction method based on measurement results The correction method based on the measurement results generates correction information for correcting the measurement results obtained by the TOF measurement device 40 and the control circuit 42 based on the light receiving signals from the light receiving elements so that the measurement results approach uniformity based on the measurement results of the distance for each pixel. The correction information is, for example, a correction value that offsets the error in the distance measurement between the pixels in FIG. 2(a). The correction method based on the measurement results makes it possible to prevent a decrease in the measurement accuracy of the distance to the measurement target W by correcting software processing without requiring adjustment work for the hardware configuration.

[0040] A-4. Advantages of this embodiment: As described above, it is possible to prevent a decrease in the measurement accuracy of the distance to the measurement object W due to, for example, variations in the timing of light projection from the light-projector 20 or variations in the output timing of the light-receiving signal from the light-receiving element in the light-receiver 30.

[0041] 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.

[0042] The configuration of the measuring device 10 in the above embodiment is merely an example, and various modifications are possible.

[0043] The flow chart of the manufacturing method of the measurement process in the above embodiment is an example and can be modified in various ways. [Explanation of symbols]

[0044] 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 34: Light receiving optical system 40: TOF measuring device 42: Control circuit 60: Utilizing device IC: Time measurement L2: Reflected light W: Measurement object

Claims

1. A method for manufacturing a measuring device including: a light projector having one or more light emitting elements; a light receiver having a light receiving surface on which a plurality of light receiving elements are arranged in an array to receive reflected light emitted by the light projector and returned from a measurement target; and a controller for controlling the light projector and the light receiver, A preparation step of preparing a sample measurement object having a flat surface; an acquisition step of emitting light from the light projector toward the flat surface of the sample measurement target, receiving the reflected light reflected by the flat surface and returning at the light receiving surface of the light receiver, and acquiring a measurement result of the distance to the flat surface for each pixel based on a plurality of sample light receiving signals output from each of the plurality of light receiving elements; A method for manufacturing a measuring device, comprising: a correction step of correcting at least one of the light emission timing of the light-emitting element and the output timing of the light-receiving signal from the light-receiving element so that the distance measurement results for each pixel approach uniformity.

2. A method for manufacturing the measuring device according to claim 1, comprising the steps of: The method for manufacturing a measuring device, wherein the correction step changes at least one of a length of a wiring connected to the light-emitting element and a length of a wiring connected to the light-receiving element.

3. A method for manufacturing the measuring device according to claim 1, comprising the steps of: The correction step changes an output timing of a trigger signal that the controller provides to the light-emitting element.

4. A method for manufacturing the measuring device according to claim 1, comprising the steps of: A method for manufacturing a measuring device, in which the correction process generates correction information for correcting the measurement results obtained by the controller based on the light receiving signal from the light receiving element so that the measurement results approach uniformity based on the distance measurement results for each pixel.

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