Light detection device, light detection method, and lidar device

A light detection device includes a light projector, a light receiver, a detector, and a controller. The light projector projects light to a predetermined range. The light receiver has a light receiving region in which light is received. The detector detects light by comparing a light reception result by the light receiver with a predetermined threshold. The controller controls the threshold. The controller shifts in turn a range where light is projected from the light projector. The controller, causes the detector to detect light per a portion of the light receiving region, the portion corresponding to a range with light being projected from the light projector, and sets the threshold based on a light reception result by the light receiver in a different portion of the light receiving region from the portion corresponding to the range with light being projected.

This is the U.S. national stage of application No. PCT/JP2019/008021, filed on Mar. 1, 2019. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Application No. 2018-045770 filed Mar. 13, 2018, the disclosure of which is also incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a light detection device, a light detection method, and a lidar device including the light detection device.

BACKGROUND ART

Patent Document 1 discloses an object detection apparatus mounted on a vehicle as a lidar. The object detection apparatus includes: a light emission unit including a light source; a light detector that receives light emitted from the light emission unit and reflected by an object; a signal detector to be input with an output signal of the light detector; and a control unit. A threshold for signal detection is set in the signal detector. The control unit acquires a noise level from output of the light detector when the light emission unit does not emit light, and sets the threshold based on this noise level. Patent Document 1 discloses that it is optimal to set the threshold to the maximum noise level to be expected at the initial state for the system.

CITATION LIST

Patent Document

Patent Document 1: JP 2017-173298 A

SUMMARY

Technical Problem

The inventor of the present application focused on the fact that it is possible to reduce the influence of ambient light from the outside and to enhance the accuracy of light detection of projected light by shortening a time interval from setting of a threshold to detection of reflected light. In Patent Document 1, however, the threshold is set based on the output of the light detector when no light is projected from the light emission unit. Thus, a period during which light projection is not performed is required in addition to a period during which light projection is performed, and it is difficult to perform highly accurate light detection speedily in the related art.

An object of the present disclosure is to provide a light detection device, a light detection method, and a lidar device that can facilitate speedy light detection.

Solution to Problem

A light detection device according to the present disclosure includes a light projector, a light receiver, a detector, and a controller. The light projector projects light to a predetermined range. The light receiver has a light receiving region in which light is received. The detector detects light by comparing a light reception result by the light receiver with a predetermined threshold. The controller controls the threshold. The controller shifts in turn a range where light is projected from the light projector. The controller causes the detector to detect light per a portion of the light receiving region, the portion corresponding to a range with light being projected from the light projector, and sets the threshold based on a light reception result by the light receiver in a different portion of the light receiving region from the portion corresponding to the range with light being projected.

A light detection method according to the present disclosure provides a method by which a light detection device detects light, the light detection device including a light projector that projects light to a predetermined range and a light receiver that has a light receiving region in which light is received.

A lidar device according to the present disclosure includes a light detection device and a distance calculator. The distance calculator calculates a distance through which detected light passes based on a light detection result of the light detection device.

Advantageous Effect

According to the light detection device, the light detection method, and the lidar device according to the present disclosure, the speedy light detection can be facilitated.

DETAILED DESCRIPTION

Hereinafter, embodiments of a light detection device, a light detection method, and a lidar device according to the present disclosure will be described with reference to the accompanying drawings. Note that, the same components are denoted by the same reference signs in each of the following embodiments.

Application Example

An example to which a light detection device according to the present disclosure can be applied will be described with reference toFIG.1.FIG.1is a view for describing an application example of a light detection device1according to the present disclosure.

The light detection device1according to the present disclosure can be applied to, for example, a lidar device2for in-vehicle applications. As illustrated inFIG.1, the light detection device1includes a light projector3that projects light to the outside and a light receiver4that receives light from the outside. The lidar device2a device for measuring a distance to an object reflected the light, by detecting reflected light of the light projected from the light projector3using the light detection device1.

For example, the lidar device2generates a distance image that three-dimensionally illustrates various objects in an external environment of a vehicle on which the lidar device2is mounted.FIG.1illustrates a projection plane R2corresponding to an angle of view of a distance image in the lidar device2. The distance image of the lidar device2illustrates a distance in a depth direction Z for each pixel arrayed in a horizontal direction X and a vertical direction Y. Hereinafter, the +Y side and −Y side are sometimes referred to as the upper side and the lower side, respectively.

The lidar device2performs a distance measurement using the light detection device1with an optical scanner21scanning the projection plane R2in the horizontal direction X, for example. The light receiver4of the light detection device1has a light receiving region R1corresponding to a plurality of pixels of the distance image arrayed in the vertical direction Y. The resolution of the distance image, that is, the angle of view for each pixel is, for example, 1.0 to 1.6 degrees in the horizontal direction X and 0.3 to 1.2 degrees in the vertical direction Y.

In the light detection device1of the lidar device2as described above, ambient light caused in the external environment can enter the light receiver4together with the reflected light of the light from the light projector3, and thus, a threshold is set to remove the influence of the ambient light as noise. The detecting accuracy of the light detection device1can be improved by shortening a period from the detection of the ambient light to the distance measurement. To this end, the light detection device1of the application example dynamically sets the threshold by repeating the detection of the ambient light concurrently with the detection of the reflected light when generating the distance image of one frame, for example.

Configuration Example

Hereinafter, embodiments as configuration examples of the light detection device1and the lidar device2will be described.

First Embodiment

The configurations and operations of the lidar device2and the light detection device1according to the first embodiment will be described hereinafter.

The configurations of the lidar device2and the light detection device1according to the present embodiment will be described with reference toFIG.1,FIG.2, andFIG.3.FIG.2is a block diagram illustrating the configuration of the lidar device2.FIG.3is a view illustrating a correspondence between the light projector3and the light receiver4of the light detection device1.

The lidar device2includes an optical scanner21, a light projecting lens22, a magnifying optical system23, a light receiving lens24, and the light detection device1, for example, as illustrated inFIG.1. The lidar device2illustrated inFIG.2includes a scanner20including the optical scanner21, and the light projector3, the light receiver4, a detector5, and a controller10which constitute the light detection device1.

The scanner20includes a scanning drive circuit20aand a displacement feedback circuit20bin addition to the optical scanner21. The optical scanner21includes, for example, a mirror and a rotation mechanism that rotates the mirror around a rotation axis which is along the vertical direction Y. The scanning drive circuit20arotationally drives the mirror of the optical scanner21under the control of the controller10. The displacement feedback circuit20bdetects displacement of the driven optical scanner21such as a rotation angle of the mirror, and outputs a feedback signal indicating a detection result to the controller10.

The light projecting lens22(FIG.1) is e.g. a collimator lens, arranged between the light projector3of the light detection device1and the optical scanner21. The light receiving lens24is e.g. a condenser lens, arranged between the light receiver4of the light detection device1and the optical scanner21. The optical scanner21is arranged to guide the light incident from the light projecting lens22to the magnifying optical system23and guide the light incident from the magnifying optical system23to the light receiving lens24. The magnifying optical system23includes e.g. a lens and a mirror, magnifying a light flux of the light incident from the optical scanner21, to emit the magnified light flux to the outside.

As illustrated inFIG.2, the light projector3includes first to fourth light sources31to34and a light source drive circuit30, for example. Each of the light sources31to34is a light source element such as an LD (laser diode) and an LED. Each of the light sources31to34may include a plurality of light source elements. The light source drive circuit30pulse-drives each of the light sources31to34under the control of the controller10, for example.

FIG.3schematically illustrates a state where the light projector3projects light from the first light source31onto the projection plane R2. For example, the first to fourth light sources31to34are arranged in an array form of one row in the light projector3in order from the upper side in the vertical direction Y.

The light receiver4includes a plurality of photosensors4a.FIG.3illustrates, in an enlarged manner, the light receiving region R1formed by the photosensors4aof the light receiver4. In the light receiver4, the plurality of photosensors4aare arranged, for example, in an array form of one row along the vertical direction Y.

The photosensor4agenerates a light reception signal indicating a light reception result when receiving light. Each of the photosensors4acorresponds to, for example, one pixel of a distance image. The photosensor4ais a sensor element such as a single-photon avalanche photodiode (SPAD). The photosensor4amay be a sensor element such as a photodiode (PD) or an avalanche photodiode (APD).

In the present configuration example, the photosensors4aof the light receiver4can be grouped into first to fourth sets of the photosensors41,42,43, and44so as to correspond to the first to fourth light sources31to34of the light projector3, respectively. The number of the photosensors4aper set is, for example, eight.

The above optical systems22to24are arranged such that light, incident onto the light receiver4from the same range as a range R3in which the light projector3can project light on the external projection plane R2, is received in the light receiving region R1. As illustrated inFIG.3, the light projectable range3is divided into first to fourth sections R31to R34along the vertical direction Y.

The first section R31is a range where light is projected by the first light source31, and corresponds to a light receiving region R11of the first photosensor set41. Similarly, second, third, and fourth sections R32, R33, and R34are ranges where light is projected by the second, third, and fourth light sources32,33, and34, respectively, and correspond to light receiving regions R12, R13, and R14of the second, third, and fourth photosensor sets42,43, and44, respectively.

Returning toFIG.2, the light receiver4further includes, for example, a photosensor drive circuit40and a multiplexer45. The photosensor drive circuit40drives the respective photosensor sets41to44. The multiplexer45has first to fourth input terminals i1to i4connected to the respective photosensor sets41to44, an output terminal n for distance measurement, and an output terminal m for threshold determination.

The multiplexer45of the light receiver4connects each of the output terminals n and m to one of the first to fourth input terminals i1to i4according to selection signals Sn and Sm from the controller10. As a result, the light receiver4outputs a light reception signal for one set of the photosensors4afrom each of the output terminals m and n.

The controller10includes, for example, a CPU, a RAM, a ROM, and the like, and controls each component according to various information processing. For example, the controller10reads a program and data stored in the ROM into the RAM, and executes various arithmetic processes to implement various operations.

For example, the controller10generates a selection signal Sn for distance measurement to select, from among the first to fourth input terminals i1to i4of the light receiver4, a connecting terminal with the output terminal n, or generates a selection signal Sm for threshold determination to select a connecting terminal with the output terminal m. The controller10also operates as a threshold determiner10aand a distance calculator10bwhich will be described later. The controller10may include an ASIC, an FPGA, and the like. The threshold determiner10a, the distance calculator10b, and the like may be configured by dedicated hardware circuits, respectively.

The detector5includes, for example, a comparator51and a time/digital converter (TDC)52. The comparator51compares the light reception signal output from the output terminal n for distance measurement in the light receiver4with the threshold determined by the threshold determiner10a, and outputs a signal indicating a comparison result to the TDC52. The TDC52is an example of a time measurement circuit that measures a period from a timing input by the controller10to a timing corresponding to the comparison result of the comparator51. The distance calculator10bcalculates a distance value for each pixel based on the period measured by the TDC52.

In the present embodiment, the light detection device1further includes an analog/digital converter (ADC)11and a digital/analog converter (DAC)12. The ADC11, the DAC12, and the threshold determiner10aof the present embodiment are examples of a threshold setting module that sets the threshold in the light detection device1.

The ADC11converts the light reception signal output from the output terminal m for threshold determination in the light receiver4from an analog value to a digital value, and outputs the converted light reception signal to the threshold determiner10a. The threshold determiner10aexecutes calculation processing for setting the threshold based on the received light reception signal to determine the threshold. The DAC12digitally inputs the threshold determined by the threshold determiner10a, converts the threshold into an analog voltage, and outputs the analog voltage to the comparator51. As a result, the threshold is set in the detector5.

In the present embodiment, the ADC11, the DAC12, the comparator51, and the TDC52in the light detection device1are provided as many as, for example, the number of the photosensors4ain the one set in the light receiver4. With this, the controller10may execute various operations for the one set of the photosensors4ain parallel or sequentially.

The operations of the lidar device2and the light detection device1configured as described above will be described hereinafter.

2-1. Operation of Lidar Device

The operation of the lidar device2according to the present embodiment will be described with reference toFIG.4AandFIG.4B.FIG.4Ais a view for describing scanning of the lidar device2.FIG.4Bis a view for describing the details of scanning of the lidar device2.

In the lidar device2of the present embodiment, the controller10controls the light source drive circuit30of the light projector3to cause the first to fourth light sources31to34to be sequentially turned on (to emit pulses of light) one by one. In addition, the controller10controls the scanning drive circuit20aof the scanner20to cause the optical scanner21to scan the light projected in the horizontal direction X.

FIG.4AandFIG.4Bexemplify a range R30(hereinafter, referred to as a “light projection range”) of the projection plane R2where light is projected from a light source turned on in the light projector3. The light projection range R30on the projection plane R2is shifted in turn among the first to fourth sections R31to R34(FIG.3) at a position in the horizontal direction X during scanning. As a result, the light projection range R30two-dimensionally moves on the projection plane R2as schematically illustrated by the arrow inFIG.4A. As illustrated inFIG.4B, such scanning is performed with the light projection ranges R30before and after the movement in the horizontal direction X overlapped on each other, for example.

The controller10can recognize a position of the light projection range R30in the horizontal direction X based on a signal from the displacement feedback circuit20bof the scanner20, and can recognize a position of the light projection range R30in the vertical direction Y according to the turning-on light source, for example.

The detector5of the light detection device1performs the threshold determination on the light reception signal from the light receiver4to detect reflected light of the projected light. With each of the light projection ranges R30as an object of distance measurement, the detector5measures a period from the time when the light is projected by the light projector3to the time when the reflected light is detected, by the TDC52. Based on the period measured by the TDC52, the distance calculator10bof the lidar device2calculates a distance value of each pixel for each of the light projection ranges R30moving on the projection plane R2. The lidar device2superimposes the light projection ranges R30on each other as illustrated inFIG.4Bto sequentially perform the measurement, and performs calculation processing of averaging on the superposed portion.

As the above scanning of the projection plane R2is repeated, it is possible to sequentially generate distance images at a desired frame rate (for example, 30 fps). In addition, since the plurality of photosensors4ain the light receiver4are grouped for use, the distance image for each frame can be generated at high speed with the circuit area of the light detection device1reduced.

In the light detection device1of the present embodiment, the controller10dynamically sets the threshold, to be used for the detection of reflected light in the detector5, based on the light reception signal indicating the light reception result outside the light projection range R30when light is projected to each of the light projection ranges R30.

2-2. Threshold of Light Detection Device

The threshold in the light detection method of the light detection device1will be described with reference toFIG.5AtoFIG.5E.

FIGS.5A to5Eexemplify light reception signals in various cases. InFIG.5AtoFIG.5E, the horizontal axis represents a time t, and the vertical axis represents a voltage V.

FIG.5Aexemplifies a light reception signal in an ideal case and a preset threshold Vth. The light reception signal includes a reflected light component80corresponding to reflected light of projected light and an ambient light component81corresponding to ambient light. In the example ofFIG.5A, the preset threshold Vth is larger than the ambient light component81of the light reception signal and smaller than the reflected light component80. In this case, the detector5can detect a timing at which the reflected light component80is obtained when the light reception signal exceeds the threshold Vth.

In the lidar device2, for example, it is considered that each intensity of the ambient light component81and the reflected light component80change every moment due to movement of the light projection range R30or a change in the external environment of the vehicle.FIG.5BandFIG.5Cexemplify light reception signals in a case where the ambient light component81gets larger and a case where the reflected light component80gets smaller, from the same setting of the threshold Vth as inFIG.5A.

In the case ofFIG.5B, as the ambient light component81is larger than the threshold Vth, a situation is conceivable where noise caused by ambient light is erroneously detected as reflected light. In the case ofFIG.5C, as the reflected light component80is smaller than the threshold Vth, a situation is conceivable where the reflected light fails to be detected. To solve this, the light detection device1of the present embodiment detects the ambient light component81during distance measurement in the lidar device2to update the threshold Vth according to a detection result.

FIG.5DandFIG.5Eillustrate examples in which the light detection device1of the present embodiment updates the setting of the threshold Vth from the cases similar toFIG.5BandFIG.5C, respectively. The threshold Vth in the example ofFIG.5Dis increased to exceed the ambient light component81from the case ofFIG.5B. The threshold Vth in the example ofFIG.5Eis lowered within a range exceeding the ambient light component81from the case ofFIG.5C. With such update of the setting of the threshold Vth, it is possible to improve the accuracy for detecting the reflected light component80in the light detection device1by avoiding the situations illustrated inFIG.5BandFIG.5C.

In the light detection device1, by inputting the light reception signal considered not to include the reflected light component80, the controller10as the threshold determiner10acan detect the intensity of the ambient light component81and determine the threshold. For example, the threshold determiner10acalculates a value larger than the ambient light component81by a predetermined width as the threshold Vth. The threshold determiner10amay calculate an average to derive the threshold Vth. Hereinafter, details of the operation of the light detection device1will be described.

2-3. Operation of Light Detection Device

The operation of the light detection device1according to the present embodiment will be described with reference toFIG.6toFIG.8D.

FIG.6is a flowchart illustrating the operation of the light detection device1. Each process according to the flowchart ofFIG.6is executed by the controller10of the light detection device1.FIG.7AtoFIG.7Jare timing charts illustrating an operation example of the light detection device1.FIG.8AtoFIG.8Dare views for describing the operation example of the light detection device1.

FIG.7A,FIG.7B,FIG.7C, andFIG.7Dillustrate lighting timings of the first, second, third, and fourth light sources31to34, respectively.FIG.7Eillustrates a control timing of the selection signal Sn for distance measurement.FIG.7Fillustrates a control timing of the selection signal Sm for threshold determination.FIG.7G,FIG.7H,FIG.7I, andFIG.7Jillustrate output timings of the first, second, third, and fourth photosensors41to44, respectively.

In the flowchart ofFIG.6, first, the controller10controls the scanner20to start driving the optical scanner21(S1). In addition, the controller10controls the light projector3to turn on only the fourth light source34at time t0inFIG.7D(S2). The projection plane R2at time t0is illustrated inFIG.8A.

On the projection plane R2ofFIG.8A, light is projected from the light projector3to the fourth section R34among the first to fourth sections R31to R34corresponding to the respective photosensor sets41to44. From the first to third sections R31to R33, ambient light is incident to the first to third photosensor sets41to43.

The controller10acquires a light reception result by the first photosensor set41(S3). For example, the controller10outputs a light reception signal of the first photosensor set41from the light receiver4to the ADC11(FIG.2) with the initial setting of the output terminal m for threshold determination (FIG.7E). The ADC11converts the received light reception signal into a digital value and outputs the digital value to the controller10.

Next, the controller10operates as the threshold determiner10ato set the threshold according to the acquired light reception result (S4). The controller10detects the intensity of ambient light based on the light reception signal from the ADC11, and calculates the threshold according to a detection result. The controller10sets the calculated threshold in the detector5via the DAC12. By the processing of Steps S2to S5, the threshold is set according to the ambient light in the current first section R31.

In addition, regarding a variable N (=1 to 4) for distance measurement and a variable M (=1 to 4) for threshold determination, the controller10sets N=1 and M=2, respectively (S5). For example, the controller10generates the selection signal Sn so as to control a connecting terminal with the output terminal m for distance measurement to the first input terminal it (FIG.7E), and generates the selection signal Sm so as to control a connecting terminal with the output terminal m for threshold determination to the second input terminal i2(FIG.7F).

Furthermore, the controller10turns on only an N-th light source among the plurality of light sources31to34of the light projector3based on the set variable N for distance measurement (S6). For example, the controller10turns on the first light source31at time t1after Step S5as illustrated inFIG.7A(S6). The projection plane R2at time t1is illustrated inFIG.8B.

On the projection plane R2ofFIG.8B, light is projected from the light projector3to the first section R31. Then, reflected light of the light from the light projector3is received by the first photosensor set41. At this time, the light receiver4outputs a light reception signal from the first photosensor set41to the detector5in response to the selection signal Sn of N=1 (S5) (FIGS.7E and7G).

The controller10acquires a measured period by the TDC52from the detector5(S7). For example, the controller10causes the TDC52to start measuring the period at the time of executing Step S6. The detector5causes the comparator51to compare the input light reception signal with the set threshold. The detector5causes the TDC52to output a signal indicating the measured period when the light reception signal in the comparator51exceeds the threshold.

Next, the controller10operates as the distance calculator10bto perform an calculation processing for distance measurement in the projected N-th section based on the measured period thus acquired (S8). For example, the controller10calculates a distance value by multiplying the measured period indicated by the signal from the TDC52and a speed of light. The controller10stores the distance value for each pixel in association with a position in the horizontal direction X and the vertical direction Y.

In addition, the controller10acquires a light reception result of an M-th photosensor in the light receiver4(S9). For example, the light receiver4outputs a light reception signal from the second photosensor set32to the controller10via the ADC11in response to the selection signal Sm of M=2 at time t1(S5) (FIG.7FandFIG.7H). As illustrated inFIG.8B, the light reception signal indicates a result of receiving the ambient light in the second section R32where light is not projected.

Next, the controller10sets the threshold based on the acquired light reception result of the M-th photosensor (S10). The process of Step S10is performed in the same manner as Step S5. The newly set threshold is used when executing the next Steps S6to S7. For example, the controller10executes Steps S7to S8and Steps S9to S10in parallel.

Next, the controller10updates the variable N for distance measurement (S11to S13). For example, the controller10determines whether the set variable N reaches “4” (S11), and in the case of not reaching N=4 (No in S11), increments the variable N to “N+1” (S12). On the other hand, in the case of reaching N=4 (Yes in S11), the controller10updates the variable N to “1” (S13). The controller10generates the selection signal Sn according to the updated variable N, and switches a connecting terminal with the output terminal n for distance measurement (FIG.7E).

Then, the controller10updates the variable M for threshold determination (S14to S16). The processes of Steps S14to S16are executed in the same manner as Steps S11to S13, for example. As a result, the selection signal Sm according to the updated variable M is generated, and a connecting terminal with the output terminal m for threshold determination is switched (FIG.7F).

The controller10repeats the processing after Step S6in a predetermined cycle (for example, 10 μsec) based on the updated variables N and M.

For example, the controller10turns on the second, third, and fourth light sources42to44at times t2, t3, and t4as illustrated inFIG.7B,FIG.7C, andFIG.7D(S6) to execute the processes of Steps S7to S10sequentially. The projection planes R2at times t2and t3are illustrated inFIG.8CandFIG.8D, respectively. Note that a region for which distance measurement has been performed is shaded inFIG.8CandFIG.8D.

With the above processing, for example, the first light source31is turned on at time t1(S6), and the distance measurement of the first section R31where light is projected is executed (FIGS.7G, S7, and S8). At this time, the threshold is updated by detecting ambient light of the second section R32where light is not projected (FIGS.7H, S9, and S10).

After turning off the first light source31, the second light source32is turned on at time t2(S6), and the distance measurement of the second section R32is executed using the updated threshold (FIGS.7H, S7, and S8). The second section R32at time t2, which is an object of the distance measurement, is same as the second section R32at time t1, which is used for the threshold determination, except for the shift of scanning in the horizontal direction as illustrated inFIG.8C. In this manner, a situation for the ambient light can be approximated both temporally and spatially among the distance measurement and the threshold determination, so that the detection accuracy of the light detection device1can be improved.

In addition, measuring the distance in the N-th section, where light is being projected, and setting the threshold with detection of the ambient light of the M-th section, where light is to be projected next, are repeatedly executed in a simultaneous and parallel manner as illustrated inFIG.7GtoFIG.7J. As a result, a highly accurate distance image can be efficiently obtained without reserving a lot of periods only for detecting ambient light until the distance measurement reaches the entire projection plane R2of the distance image.

As described above, the light detection device1according to the present embodiment includes the light projector3, the light receiver4, the detector5, and the controller10. The light projector3projects light to the light projection range R30. The light receiver4has the light receiving region R1for receiving light. The detector5detects light by comparing a light reception result by the light receiver4with a predetermined threshold. The controller10controls the threshold. The controller10shifts in turn the light projection range R30among the first to fourth sections R31to R34in the light projectable range R3. The controller10causes the detector5to detect light per a portion corresponding to a range with light being projected from the light projector3in the light receiving region R1, and sets the threshold based on a light reception result by the light receiver4in a different portion of the light receiving region from the portion corresponding to the range with light being projected (S6to S10).

According to the above light detection device1, it is possible to set the threshold by acquiring a light reception result of a section where light is not projected with the detector5detecting light for each section where light is being projected from the light projector3. As a result, it is possible to facilitate the speedy light detection as compared to a case where a light reception result for setting a threshold is obtained during a period in which no light is projected from the light projector3.

In the present embodiment, the controller10sets the threshold based on the light reception result at the portion of the light receiving region R1corresponding to the range where the light projector3projects light in next turn (seeFIG.7AtoFIG.7J). As a result, a state in which ambient light is detected for the threshold setting is in terms of time closer to a state in which light is detected by the detector5, so that the threshold according to the ambient light can be accurately set.

In addition, the detector5may detect light when the portion used for the threshold setting in the light receiving region R1corresponds to the range where light is projected by the light projector3based on the set threshold (seeFIG.8AtoFIG.8D). As a result, a state in which ambient light is detected for the threshold setting is spatially closer to a state in which light is detected by the detector5, so that the threshold according to the ambient light can be accurately set.

In the present embodiment, the light projector3includes the plurality of light sources31to34arrayed in a row. The controller10shifts the light projection range R30by causing the first to fourth light sources31to34to emit light in turn (S6). As a result, the light projection range R30can be shifted with a simple configuration.

In the present embodiment, the light detection device1may further include the optical scanner21. The optical scanner21scans the light projected by the light projector3in the horizontal direction X crossing the vertical direction Y in which the first to fourth light sources31to34are arrayed (S1). The controller10causes the detector5to detect the light during scanning by the optical scanner21. As a result, the light detection of the entire projection plane R2can be sequentially performed.

In the present embodiment, the light receiver4includes the plurality of photosensors4athat form the light receiving region R1. The controller10causes the detector5to detect light for each of the sets41to44of the photosensors4arespectively corresponding to the ranges where light is projected from the light sources31to34of the light projector3among the plurality of photosensors4a(S6to S8). As a result, the light detection can be efficiently performed for each of the sets41to44of the photosensors4a.

In the present embodiment, the detector5includes the TDC52that measures the period from the timing at which the light projector3projects light to the timing at which the light is detected based on the threshold. With the TDC52, the distance measurement can be performed by measuring the period during which reflected light of the projected light is obtained.

In addition, the lidar device2according to the present embodiment includes the light detection device1and the distance calculator10b. The distance calculator10bcalculates a distance that detected light has passed based on a light detection result of the light detection device1. According to the lidar device2of the present embodiment, the operation of the light detection device1facilitates the speedy light detection for distance measurement.

In addition, the light detection method according to the present embodiment is a method by which the light detection device1including the light projector3and the light receiver4detects light. This method includes: shifting in turn a range where light is projected from the light projector3; detecting light by comparing a light reception result by the light receiver4with a predetermined threshold per a portion of the light receiving region corresponding to a range where light is being projected from the light projector3; and setting the threshold based on a light reception result by the light receiver4in a portion other than the portion corresponding to the range where light is being projected in the light receiving region. According to this method, the speedy light detection can be facilitated.

Other Embodiments

In the first embodiment, the threshold is set based on the light reception result of the portion of the light receiving region R1corresponding to the range where the light projector3next projects light (seeFIG.7). In the present embodiment, the threshold may be set based on a light reception result of a portion corresponding to the range where the light projector3projects light at a time subsequent to the next time. For example, the setting in Step S3ofFIG.6may be changed such that a difference between the variable N for distance measurement and the variable M for threshold determination is two or more. In this case, the controller10appropriately stores the determined threshold in an internal memory such as a RAM.

In addition, the example in which the light projector3includes the first to fourth light sources31to34has been described in each of the above embodiments. The number of light sources of the light projector3of the present embodiment is not limited to four. The light projector3may include two or more light sources, and each light source may be sequentially turned on. In addition, the light projector3may switch the light projection range R30using a mechanism or the like that changes a light projection direction in the vertical direction Y. The grouping of the photosensors4aof the light receiver4may be appropriately changed depending on how the light projection range R30is switched by the light projector3.

In addition, the detector5of the light detection device1includes the TDC52in each of the above embodiments, but the detector5is not necessarily provided. The detector5can detect various kinds of light exceeding the threshold based on the comparison result of the comparator51. The light detection device1may be used together with an externally configured TDC, or may be used in a configuration that adopts an ADC instead of the TDC.

In addition, the example in which the light detection device1includes the ADC11and the DAC12that constitute the threshold setting module and the controller10operates as the threshold determiner10ahas been described in each of the above embodiments. The light detection device1of the present embodiment is not limited thereto, and for example, an analog circuit or the like that implements the operation of the threshold setting module may be provided instead of the ADC11and the DAC12.

In addition, the lidar device2and the light detection device1that use the optical scanner21have been described in each of the above embodiments, but the optical scanner21may be omitted as appropriate. For example, when the light sources of the light projector3and the photosensors4aof the light receiver4are arranged in a two-dimensional array form, the distance measurement and the ambient light detection similar to those in the first embodiment can be performed without using the optical scanner21.

In addition, the light detection device1uses the detection result of ambient light for setting of the threshold of the detector5in each of the above embodiments. The light detection device1of the present embodiment may perform imaging of an external environment using the detection result of ambient light. For example, the controller10may generate a captured image of the external environment based on a light reception signal from the ADC11.

In addition, the example in which the distance calculator10bgenerates the distance image has been described in each of the above embodiments. Without being limited to the distance image, the distance calculator10bof the present embodiment may generate information indicating a distance in various formats, for example, may generate three-dimensional point cloud data.

In addition, the example in which the controller10of the light detection device1in the lidar device2operates as the distance calculator10bhas been described in each of the above embodiments. In the lidar device2of the present embodiment, the distance calculator10bmay be provided separately from the light detection device1.

In addition, the configuration example of the lidar device2and the light detection device1for in-vehicle applications have been described in each of the above embodiments. The lidar device2and the light detection device1according to the present disclosure are applicable not only to the in-vehicle applications but also to various applications.

APPENDIX

As described above, various embodiments of the present disclosure have been described, but the present disclosure is not limited to the above contents, and various modifications can be made within a range where the technical idea is substantially the same. Hereinafter, various aspects according to the present disclosure will be additionally described.

A first aspect according to the present disclosure is a light detection device (1) including a light projector (3), a light receiver (4), a detector (5), and a controller (10). The light projector projects light to a predetermined range (R30). The light receiver has a light receiving region (R1) in which light is received. The detector detects light by comparing a light reception result by the light receiver with a predetermined threshold. The controller controls the threshold. The controller shifts in turn a range where light is projected from the light projector (S6), causes the detector to detect light per a portion of the light receiving region, the portion corresponding to a range with light being projected from the light projector (S7and S8), and sets the threshold based on a light reception result by the light receiver in a different portion of the light receiving region from the portion corresponding to the range with light being projected (S9and S10).

As a second aspect, in the light detection device of the first aspect, the controller sets the threshold based on a light reception result at a portion of the light receiving region corresponding to a range where light is in next turn to be projected from the light projector.

As a third aspect, in the light detection device according to the first or second aspect, the light projector includes a plurality of light sources (31to34) arrayed in a row. The controller shifts the range where light is projected by causing the light sources to emit light in turn.

As a fourth aspect, the light detection device of the third aspect further includes an optical scanner (21) that scans the light projected by the light projector in a direction crossing a direction in which the light sources are arrayed. The controller causes the detector to detect light during the scanning by the optical scanner.

As a fifth aspect, in the light detection device according to the third or fourth aspect, the light receiver includes a plurality of photosensors (4a) forming the light receiving region. The controller causes the detector to detect light per a set of the photosensors corresponding, among the plurality of the photosensors, to a range where light is projected from each light source in the light projector.

As a sixth aspect, in the light detection device according to any one of the first to fifth aspects, the detector includes a time measurement circuit (52) that measures a period from a timing at which the light projector projects light to a timing at which light is detected based on the threshold.

A seventh aspect is a lidar device including the light detection device according to any one of the first to sixth aspects and a distance calculator (10b). The distance calculator calculates a distance through which detected light passes based on a light detection result of the light detection device.

An eighth aspect is a light detection method by which a light detection device (1) detects light, the light detection device (1) including a light projector (3) that projects light to a predetermined range (R30) and a light receiver (4) that has a light receiving region (R1) in which light is received. This method includes: shifting in turn a range where light is projected from the light projector (S6); detecting light by comparing a light reception result by the light receiver with a predetermined threshold per a portion of the light receiving region, the portion corresponding to a range with light being projected from the light projector (S7and S8); and setting the threshold based on a light reception result by the light receiver in a different portion of the light receiving region from the portion corresponding to the range with light being projected (S9and S10).

REFERENCE SIGNS LIST