Ranging device and ranging method

Abstract

[Problem] To improve ranging accuracy. [Solution] This ranging device comprises: a light receiving unit that repeatedly receives a reflected light pulse signal obtained as a result of a light pulse signal being reflected by an object; a histogram generating unit that generates a histogram obtained by classifying the light reception frequency of the reflected light pulse signal for each unit light reception period; and a light emitting unit that repeatedly emits the light pulse signal with a pulse width that is shorter than twice the unit light reception period.

Description

Distance measuring device and distance measuring method

[0001] The present disclosure relates to a distance measuring device and a distance measuring method.

[0002] In autonomous driving technology and the like, LiDAR (Light Detection and Ranging) using a direct time of flight (dToF) method is widely adopted, which measures the distance to an object based on the timing of irradiating light onto the object and the timing of receiving light reflected from the object. For example, a method has been proposed in which a single time-of-flight histogram is formed by adding multiple time-of-flight histograms shifted by one class, and the time-of-flight is detected using the formed single time-of-flight histogram, thereby achieving high resolution in a short distance measurement time (see Patent Document 1).

[0003] International Publication No. 2022 / 264504

[0004] The light receiving unit of the distance measuring device uses, for example, a single photon avalanche diode (SPAD) that detects photons. A SPAD has a characteristic that after detecting a photon, a dead time occurs during which no photons can be detected for a certain period of time.

[0005] Due to this dead time, when a reflected light pulse signal having a predetermined pulse width is received, the probability of the SPAD responding is lower in the latter half of the pulse width than in the first half of the pulse width, which can cause the histogram to slope downward and shift the center of gravity of the histogram, resulting in a pileup phenomenon that deteriorates distance measurement accuracy.

[0006] In particular, when the light intensity of the reflected light pulse signal is high, most SPADs react in the first half of the pulse width, and the dead time described above prevents the SPADs from reacting to photons in the second half of the pulse width, resulting in saturation, in which the light reception frequency of the histogram bins located in the second half of the pulse width drops significantly. In this case, there is a problem that the center of gravity of the histogram shifts significantly, significantly deteriorating the distance measurement accuracy. As such, when an object is located close, the reflectivity of the object is high, or the light emission intensity of the light-emitting element is high, the light intensity of the reflected light pulse signal is likely to be high, and the above-mentioned saturation is likely to occur.

[0007] Patent Document 1 does not disclose anything about the pile-up phenomenon and saturation phenomenon described above, or about countermeasures for them.

[0008] Therefore, the present disclosure provides a distance measuring device and a distance measuring method that can improve distance measurement accuracy.

[0009] In order to solve the above problems, according to the present disclosure, there is provided a distance measuring device including: a light receiving unit that repeatedly receives a reflected light pulse signal that is a light pulse signal reflected by an object; a histogram generating unit that generates a histogram that classifies the reception frequency of the reflected light pulse signal for each unit light receiving period; and a light emitting unit that repeatedly emits the light pulse signal with a pulse width that is shorter than twice the unit light receiving period.

[0010] The light emitting section may repeatedly emit the light pulse signal with a pulse width shorter than the unit light receiving period.

[0011] Furthermore, according to the present disclosure, there is provided a distance measuring device comprising: a light receiving unit that repeatedly receives a reflected light pulse signal that is a light pulse signal reflected by an object; a histogram generating unit that generates a histogram that classifies the frequency of receiving the reflected light pulse signal for each unit light receiving period; and a control unit that controls the light emitting unit to select in turn one of a plurality of pulse widths having different phases and emit the light pulse signal, or that selects in turn one of a plurality of different correspondences between the reception time of the reflected light pulse signal received by the light receiving unit and a plurality of unit light receiving periods that the histogram has, or that selects the plurality of correspondences in parallel.

[0012] The light emitting unit may be configured to select a plurality of pulse widths each having a different phase in turn and emit the optical pulse signal, or to intermittently emit the optical pulse signal having a pulse width of the same phase.

[0013] The light emitting device may further include a light emission timing control section that selects one of a plurality of pulse widths having different phases in turn, and the light emitting section may emit the optical pulse signal with the pulse width selected by the light emission timing control section.

[0014] The light emission timing control unit may select each of the plurality of pulse widths in turn a predetermined number of times, which is equal to or greater than two; the light emission unit may repeat the operation of emitting the light pulse signal of the pulse width selected by the light emission timing control unit the predetermined number of times; the light receiving unit may repeat the operation of receiving the reflected light pulse signal corresponding to the light pulse signal emitted for each of the plurality of pulse widths the predetermined number of times; and the histogram generation unit may generate the histogram based on the reflected light pulse signal corresponding to the light pulse signal emitted by selecting each of the plurality of pulse widths the predetermined number of times.

[0015] The light emission timing control section may switch the selection among the plurality of pulse widths in turn for each light emission operation of the light emitting section.

[0016] The light emission timing control section may shift the phases of the plurality of pulse widths at equal intervals.

[0017] The light emission timing control section may shift the phases of the plurality of pulse widths by the same phase amount that is shorter than the unit light receiving period.

[0018] The plurality of pulse widths may have the same time width.

[0019] The plurality of pulse widths may include n (n is an integer of 1 or greater) pulse widths whose phases are earlier than a reference pulse width, and the n pulse widths whose phases are later than the reference pulse width.

[0020] The plurality of pulse widths may include two or more pulse widths having different time widths.

[0021] The plurality of pulse widths may include n (n is an integer of 1 or more) pulse widths that are shorter than a reference pulse width and the n pulse widths that are longer than the reference pulse width, and the n pulse widths that are shorter than the reference pulse width and the n pulse widths that are longer than the reference pulse width may have the same center of gravity.

[0022] The device may further include a synchronization control unit that synchronizes the light receiving unit and the light emitting unit, and a delay circuit that delays the synchronization signal output by the synchronization control unit by a period shorter than the unit light receiving period for each light emitting operation of the light emitting unit and transmits the delayed signal to the light emitting unit.

[0023] The light-receiving time allocation unit may be configured to select one of a plurality of different correspondences between the light-receiving times of the reflected light pulse signals repeatedly received by the light-receiving unit and a plurality of the unit light-receiving periods included in the histogram, and the histogram generation unit may generate the histogram based on the correspondence selected by the light-receiving time allocation unit.

[0024] The light-receiving time allocation unit may select each of the plurality of correspondences in turn a predetermined number of times, which is equal to or greater than two, and the histogram generation unit may allocate the light-receiving time to a plurality of the unit light-receiving periods for each of the plurality of correspondences selected in turn the predetermined number of times, thereby generating the histogram.

[0025] The plurality of associations may be such that the unit light-receiving periods corresponding to the light-receiving times are shifted at equal intervals.

[0026] The plurality of correspondences may include n (n is an integer of 1 or more) correspondences in which the unit light-reception period corresponding to the light-reception time is earlier than a reference correspondence between the light-reception time and the plurality of unit light-reception periods in the histogram, and the n correspondences in which the unit light-reception period corresponding to the light-reception time is later than the reference correspondence.

[0027] The light-reception time allocation unit may generate the plurality of associations between the light-reception times and the plurality of unit light-reception periods by varying the associations by a time width shorter than the unit light-reception period.

[0028] The present disclosure also provides a distance measurement method that includes repeatedly receiving a reflected light pulse signal that is a light pulse signal reflected by an object, generating a histogram that classifies the reception frequency of the reflected light pulse signal by unit light reception period, and selecting one of a plurality of pulse widths having different phases in turn to emit the light pulse signal, selecting one of a plurality of different correspondences between the reception time of the reflected light pulse signal and a plurality of the unit light reception periods in the histogram in turn, or selecting the plurality of correspondences in parallel.

[0029] FIG. 3 is a block diagram showing the configuration of a ranging device according to a first embodiment of the present disclosure. FIG. 3 is a diagram illustrating a ranging method of the ranging device. FIG. 3A is a diagram illustrating a case where the center of gravity of an RX waveform is at the boundary between bins. FIG. 3B is a diagram illustrating a case where the RX waveform extends beyond two bins only to the right. FIG. 3C is a diagram illustrating a case where the center of gravity of an RX waveform is at the center of a bin. FIG. 3D is a diagram illustrating a case where the RX waveform extends beyond two bins only to the left. FIG. 4A is an image displaying depth representing distance from a plane. FIG. 4B is a diagram illustrating the depth error of FIG. 4A. FIG. 5A is a diagram illustrating a case where the center of gravity position of an RX waveform whose pulse width is a constant multiple of the bin width is the same as FIG. 4A. FIG. 5B is a diagram illustrating a case where the center of gravity position of an RX waveform whose pulse width is a constant multiple of the bin width is the same as FIG. 4B. FIG. 5C is a diagram illustrating a case where the center of gravity position of an RX waveform whose pulse width is a constant multiple of the bin width is the same as FIG. 4C. FIG. 5D is a diagram showing a case where the center of gravity position of an RX waveform in which the pulse width is a constant multiple of the bin width is the same as that in FIG. 4D . FIG. 6A is a diagram showing an ideal RX waveform and histogram when there is no dead time. FIG. 6B is a diagram showing an RX waveform and histogram when the received light intensity is low. FIG. 6C is a diagram showing an RX waveform and histogram when the received light intensity is medium. FIG. 6D is a diagram showing an RX waveform and histogram when the received light intensity is high. A diagram showing a first ranging technique according to the first embodiment of the present disclosure. A diagram showing switching of TX waveforms by a light emitting unit. A diagram showing multiple RX waveforms based on the multiple TX waveforms of FIG. 7. A flowchart explaining the operation of the ranging device according to the first embodiment of the present disclosure. A diagram showing a delay time list. A diagram explaining the influence of cyclic error in the first ranging technique. FIG. 13A is an image showing true depth in a first simulation. FIG. 13B is a diagram showing ranging results when the number of divisions is 1. FIG. 13C is a diagram showing ranging results when the number of divisions is 4. Fig. 13D is a diagram showing the distance measurement results when the number of divisions is 8. Fig. 13E is a diagram showing the distance measurement results when the number of divisions is 16. Fig. 13F is a diagram showing the depth values ​​and depth error values ​​of Figs. 13B to 13E. Fig. 14A is an image showing the true depth in a second simulation. Fig. 14B is a diagram showing the distance measurement results when the number of divisions is 1. Fig. 14C is a diagram showing the distance measurement results when the number of divisions is 4. Fig. 14D is a diagram showing the distance measurement results when the number of divisions is 8. Fig. 14E is a diagram showing the distance measurement results when the number of divisions is 16. Fig. 14F is a diagram showing the depth values ​​and depth error values ​​of Figs. 14B to 14E.FIG. 15A is an image showing true depth in the third simulation. FIG. 15B is a diagram showing distance measurement results when the number of divisions is 1. FIG. 15C is a diagram showing distance measurement results when the number of divisions is 4. FIG. 15D is a diagram showing distance measurement results when the number of divisions is 8. FIG. 15E is a diagram showing distance measurement results when the number of divisions is 16. FIG. 15F is a diagram showing depth values ​​and depth error values ​​of FIGS. 15B to 15E. FIG. 16A is an image showing true depth in the fourth simulation. FIG. 16B is a diagram showing distance measurement results when the number of divisions is 1. FIG. 16C is a diagram showing distance measurement results when the number of divisions is 4. FIG. 16D is a diagram showing distance measurement results when the number of divisions is 8. FIG. 16E is a diagram showing distance measurement results when the number of divisions is 16. FIG. 16F is a diagram showing depth values ​​and depth error values ​​of FIGS. 16B to 16E. A diagram explaining the influence of the pileup phenomenon in the first distance measurement method. 18A is a diagram showing a case where the pulse width of the RX waveform is three times the bin width. FIG. 18B is a diagram showing a case where the pulse width of the RX waveform is less than twice the bin width. FIG. 18C is a diagram showing a case where the pulse width of the RX waveform is less than the bin width. FIG. 19A is a diagram showing a first ranging result of a ranging method according to a comparative example. FIG. 19B is a diagram showing a second ranging result of a ranging method according to a comparative example. FIG. 21A is a diagram showing a relationship between an RX waveform with a long pulse width and a histogram. FIG. 21B is a diagram showing a relationship between an RX waveform with a medium pulse width and a histogram. FIG. 21C is a diagram showing a relationship between an RX waveform with a short pulse width and a histogram. FIG. 21B is a diagram showing a relationship between an RX waveform with a short pulse width and a histogram. FIG. 21C is a diagram showing a ranging method according to a modification of the first embodiment of the present disclosure. A block diagram showing a configuration of a ranging device according to a second embodiment of the present disclosure. A block diagram showing a detailed configuration of a ranging unit according to the second embodiment of the present disclosure. A block diagram showing an example of a schematic configuration of a vehicle control system. FIG. 4 is an explanatory diagram showing an example of the installation positions of an outside-vehicle information detection unit and an imaging unit.

[0030] Hereinafter, embodiments of a distance measuring device and a distance measuring method will be described with reference to the drawings. The following description will focus on the main components of the distance measuring device and the distance measuring method, but the distance measuring device and the distance measuring method may include components and functions that are not shown or described. The following description does not exclude components and functions that are not shown or described.

[0031] 1 is a block diagram showing the configuration of a distance measuring device 1 according to a first embodiment of the present disclosure. The distance measuring device 1 in Fig. 1 is capable of measuring the distance to an object 10. The distance measuring device 1 includes a light emitting unit 2, a light receiving unit 3, a time-of-flight detecting unit 4, a histogram generating unit 5, a distance detecting unit 6, a light emission timing control unit 11, a clock signal generating unit (synchronization control unit) 12, a delay circuit 13, and a control unit 14.

[0032] The light emitting unit 2 intermittently emits a light pulse (TX: Transmitter exchange) signal toward the object 10. The light receiving unit 3 repeatedly receives a reflected light pulse (RX: Received exchange) signal that is the TX signal reflected by the object 10.

[0033] The light emitting unit 2 has, for example, a plurality of light emitting elements arranged in a two-dimensional direction. Furthermore, under the control of the light emission timing control unit 11, the light emitting unit 2 can adjust the pulse width and phase of each TX signal emitted by the plurality of light emitting elements.

[0034] The light receiving unit 3 includes, for example, multiple SPADs. The multiple SPADs are arranged, for example, two-dimensionally. In this specification, the smallest unit on the light receiving surface of the light receiving unit 3 is sometimes referred to as a pixel. One or more SPADs are arranged in one pixel. For example, a high bias voltage is applied to the SPADs. The SPADs have sensitivity that allows them to respond to a single incident photon. When a SPAD responds to a photon, it generates an electric charge. In this specification, the response of a SPAD to a photon is sometimes referred to as firing. When a SPAD fires, it generates an electric charge. The electric charge is amplified by avalanche multiplication, generating a large current. This causes a sudden drop in the voltage between the cathode and anode of the SPAD (hereinafter referred to as the output voltage). The light receiving unit 3 detects the reception of an RX signal by detecting a drop in the output voltage of each SPAD. The higher the intensity of the incident light, the higher the proportion of firing SPADs among the multiple SPADs in the light receiving unit 3. On the other hand, the lower the light intensity of the incident light, the lower the proportion of spads that ignite among the plurality of spads in the light receiving section 3 .

[0035] Immediately after detecting a photon, the output voltage of the SPAD drops. In order for the SPAD to be able to detect photons again, a recharge operation is required to raise the output voltage of the SPAD to the bias voltage. The period from when the SPAD detects a photon until the recharge operation of the SPAD is completed is a dead time during which the SPAD cannot detect photons.

[0036] The time-of-flight detection unit 4 detects the time of flight from when the light-emitting unit 2 emits the TX signal until when the light-receiving unit 3 receives the RX signal. The histogram generation unit 5 generates a histogram that classifies the frequency of receiving the RX signal for each predetermined unit light-receiving period, based on the time of flight repeatedly detected by the time-of-flight detection unit 4. The distance detection unit 6 detects the distance to the object 10 based on the generated histogram.

[0037] In this specification, the time-of-flight detection unit 4, the histogram generation unit 5, and the distance detection unit 6 are collectively referred to as a distance measurement unit 7.

[0038] In each bin of the histogram, for example, the total number of SPADs that detected photons per unit light-receiving period in each of a plurality of light-emitting periods (hereinafter also referred to as light-receiving frequency) is recorded.

[0039] The light emission timing control unit 11 controls the light emission timing of the light emitting unit 2. The light emission timing control unit 11 may also control the end timing of light emission of the light emitting unit 2. By adjusting the light emission timing and end timing of light emission of the light emitting unit 2, the length of the pulse width of the TX signal can be adjusted. By adjusting the light emission timing of the light emitting unit 2, the phase of the pulse width can be adjusted.

[0040] The clock signal generating unit 12 generates a clock signal (synchronization signal) that synchronizes the light emitting operation of the light emitting unit 2 and the light receiving operation of the light receiving unit 3. The delay circuit 13 delays the timing of transmitting the clock signal to the light emission timing control unit 11.

[0041] The control unit 14 controls the amount of delay by the delay circuit 13. By controlling the amount of delay, the control unit 14 controls the delay of the light emission timing of the light emitting unit 2, and can generate multiple TX signals with different phases. The control method of the control unit 14 will be described in detail later.

[0042] Fig. 2 is a diagram illustrating a ranging method of the ranging device 1. Fig. 2 illustrates a waveform of a TX signal (TX waveform), a waveform of an RX signal (RX waveform), and a histogram formed based on the RX waveform.

[0043] In principle, the distance measuring device 1 can detect the distance to the object 10 by detecting the time of flight from the timing of the light pulse signal emitted by the light emitting unit 2 and the timing and interval of the reflected light pulse signal received by the light receiving unit 3.

[0044] However, various errors are expected to occur in the time of flight. For example, the phase and length of the emission period of the TX signal emitted by the light emitter 2 may fluctuate. Furthermore, the sensitivity of each SPAD in the light receiver 3 to the light intensity of the RX signal may also fluctuate. Furthermore, the light receiver 3 may be subject to noise light, such as sunlight, in addition to the RX signal. Therefore, the distance measuring device 1 emits the TX signal multiple times and repeatedly receives the RX signal for each distance measurement. The histogram generator 5 generates a histogram based on the frequency of reception of the RX signal. The histogram generator 5 generates a histogram whose center of gravity coincides with the center of gravity of the pulse widths T of the multiple RX signals repeatedly received. The distance detector 6 detects the time of flight of the optical pulse signal and the reflected optical pulse signal from the distance between the center of gravity of the pulse widths T of the multiple TX signals repeatedly emitted and the center of gravity of the histogram. In this way, by measuring the time of flight based on the distance between the center of gravity of multiple TX signals and the center of gravity of a histogram generated based on multiple RX signals, the distance to an object can be measured with high accuracy.

[0045] It should be noted that for one RX signal, multiple SPADs may detect photons at multiple different light receiving timings.

[0046] FIG. 3 is a diagram illustrating the first problem of the ranging method of FIG. 2. FIG. 3 illustrates an RX waveform and a histogram generated by the histogram generation unit 5 based on the RX waveform. The horizontal axis of the RX waveform and the histogram represents time. The vertical axis of the RX waveform represents the received light intensity. The vertical axis of the histogram represents the frequency of light reception. FIG. 3 also illustrates multiple bins that make up the histogram. Each of the multiple bins has a bin width b corresponding to a unit light reception period. Hereinafter, the unit light reception period may be referred to as the bin width b.

[0047] The time-of-flight detection unit 4 classifies the timing of light reception by the light receiving unit 3 into one of the bins of the histogram. As a result, the histogram shows the light reception frequency measured in the corresponding bin for each flight distance of the RX signal (i.e., for each distance of the measured object 10).

[0048] For example, if the unit light-receiving period is a period corresponding to a flight distance of 10 cm of the RX signal, the time-of-flight detection unit 4 uses one bin to measure the light-receiving frequency of the RX signal for a flight distance of 100 cm to 110 cm, for example.The time-of-flight detection unit 4 also uses the bin immediately following this one bin to measure the light-receiving frequency of the RX signal for a flight distance of 110 cm to 120 cm.

[0049] Here, the time-of-flight detection unit 4 classifies an RX signal with a flight distance of 101 cm and an RX signal with a flight distance of 109 cm into the same bin. These two RX signals are treated as an RX signal with a flight distance of 105 cm, for example. Therefore, when a large number of RX signals with a flight distance of 101 cm are received, an error (hereinafter also referred to as a positive error) occurs in which the calculated flight distance is longer than the actual flight distance. Furthermore, when a large number of RX signals with a flight distance of 109 cm are received, an error (hereinafter also referred to as a negative error) occurs in which the calculated flight distance is shorter than the actual flight distance.

[0050] On the other hand, if the same number of RX signals with a flight distance of 101 cm and 109 cm are received, the positive error and negative error cancel each other out, and the center of gravity of the histogram can be calculated without error.

[0051] Whether a positive error, a negative error, or a canceling error occurs varies depending on the flight time.

[0052] 3A shows a case where the center of gravity of the RX waveform is on the boundary of a histogram bin. The RX waveform in FIG. 3A extends evenly to the right and left of the two bins. The positive error described above occurs based on the portion of the RX waveform that extends to the right. Furthermore, a negative error occurs based on the portion of the RX waveform that extends to the left. In this case, the light reception frequencies of the two bins of the histogram corresponding to the extended portions become the same (i.e., the positive and negative errors cancel each other out), and the center of gravity of the histogram and the center of gravity of the RX waveform coincide.

[0053] As shown in Figure 3A, as the time of flight increases, the center of gravity of the RX waveform moves to the right relative to the bin boundary. Figure 3B shows a case where the RX waveform extends beyond two bins to the right only. From Figure 3A to Figure 3B, as the time of flight increases, the light reception frequency of the bin corresponding to the portion extending to the right increases, and it no longer extends to the left, so the light reception frequency of the corresponding bin becomes zero. As a result, the RX waveform extends beyond the two bins to the right only, and the center of gravity of the histogram shifts to the right of the center of gravity of the RX waveform. Figure 3B shows the deviation (Error) of the center of gravity between the RX waveform and the histogram. This deviation of the center of gravity deteriorates ranging accuracy.

[0054] Figure 3C shows the case where the center of gravity of the RX waveform is in the center of the bin. Figure 3C shows the case where the time of flight is further increased from Figure 3B. By transitioning from Figure 3B to Figure 3C, the amount of light protruding to the right and the amount of light protruding to the left of one bin become equal. In this case, the light reception frequency of the two bins of the histogram corresponding to the protruding portions becomes the same, and the center of gravity of the histogram and the center of gravity of the RX waveform coincide.

[0055] Fig. 3D shows the case where the RX waveform extends beyond the two bins only to the left. Fig. 3D shows the case where the flight time is further increased from Fig. 3C. In the transition from Fig. 3C to Fig. 4D, the RX waveform extends beyond the two bins only to the left, and the center of gravity of the histogram shifts to the left of the center of gravity of the RX waveform.

[0056] From FIG. 3D, if the flight time is further increased, the state shown in FIG. 3A is reached.

[0057] The error between the center of gravity of the RX waveform and the center of gravity of the histogram shown in FIGS. 3A to 3D changes periodically as the flight time increases or decreases, and is therefore also called a periodic error (cyclic error).

[0058] 4A is an image displaying depth, which represents the distance from a plane to the dToF sensor. The dToF sensor emits a TX signal toward the center of the plane (i.e., the center of FIG. 4A). The center of FIG. 4A represents the shortest flight distance. The flight distance increases as the distance from the center of FIG. 4A increases.

[0059] 4B is a diagram showing depth error on a plane when the plane of FIG. 4A is photographed using a dToF sensor or the like. As shown in FIG. 4B, cyclic error occurs as the flight distance increases. In this case, the cyclic error can be seen as a periodic concentric stripe pattern.

[0060] Figure 5 shows one solution to the first problem in Figure 3. Cyclic errors can be suppressed by making the pulse width T of the RX waveform a constant multiple (more precisely, a natural number multiple) of the bin width b. Figure 5 shows an example in which the pulse width T of the RX waveform is twice the bin width b (i.e., T = 2b). The center of gravity positions of the RX waveforms in Figures 5A to 5D are the same as the center of gravity positions of the RX waveforms in Figures 3A to 3D, respectively.

[0061] The RX waveforms shown in Figures 5A to 5D can make the center of gravity of the histogram and the center of gravity of the RX waveform approximately coincident even if the center of gravity of the RX waveform is not on the boundary of a bin or at the center of gravity of a bin, thereby preventing the occurrence of cyclic errors.

[0062] Therefore, one possible method for solving the first problem is to suppress the occurrence of cyclic errors by making the light-emitting pulse width T of the light-emitting unit 2 a constant multiple of the bin width b. However, the pulse width T of the RX waveform varies with temperature. Therefore, depending on the environment, the pulse width T of the RX waveform may not become a constant multiple of the bin width b despite control of the light-emitting unit 2, which may result in the occurrence of cyclic errors as shown in FIG. 3.

[0063] 6 is a diagram illustrating the second problem of the ranging method of FIG. 2. As described above, SPAD has a dead time after detecting a photon, during which the photon cannot be detected. The dead time is usually longer than the bin width b, and may be several times or more the bin width b.

[0064] Fig. 6A shows an ideal RX waveform and histogram when there is no dead time. The RX waveform in Fig. 6A has a substantially uniform received light intensity over the entire pulse width T. In this case, the SPAD receives light at a uniform frequency over the pulse width T, resulting in a flat histogram like the histogram in Fig. 6A.

[0065] More specifically, the RX waveform in Fig. 6A spans three unit light-reception periods. Accordingly, three bins are generated in the histogram. In the example of Fig. 6A, the RX signal is incident during the same period in each of the three unit light-reception periods, so the three bins have the same light-reception frequency. Note that, depending on the phase of the RX waveform, there may be differences in the periods in which the RX signal is incident among the three unit light-reception periods, which may result in differences in the light-reception frequencies of the three bins.

[0066] FIG. 6B shows an RX waveform and histogram when a dead time is present. The RX waveform in FIG. 6B has a substantially uniform light-receiving intensity, similar to FIG. 6A . However, the SPAD that received the photon is unable to receive photons during the dead time, so the light-receiving frequency is lower in the latter half of the pulse width T of the RX waveform compared to the first half. This can cause the histogram to slope downward. In this case, an error occurs between the center of gravity of the histogram and the center of gravity of the RX waveform, deteriorating ranging accuracy. The phenomenon of a difference in light-receiving frequency between the first and second halves of the pulse width T due to the dead time, as shown in FIG. 6B , is also known as a pile-up phenomenon.

[0067] FIG. 6B shows an example in which a histogram with a downward slope is generated due to the pile-up phenomenon, but depending on the phase of the RX waveform, a mountain-shaped histogram may be generated due to the pile-up phenomenon.

[0068] Fig. 6C shows an example in which the received light intensity of the RX waveform is increased compared to Fig. 6B. When the received light intensity of the RX waveform is increased, more SPADs receive photons in the first half of the pulse width T. As a result, the number of SPADs that cannot receive light increases in the second half of the pulse width T. As a result, the histogram in Fig. 6C has a stronger downward trend compared to the histogram in Fig. 6B, and the deviation between the center of gravity of the histogram and the center of gravity of the RX waveform becomes larger.

[0069] 6C, the higher the received light intensity of the RX waveform, the worse the distance measurement accuracy. The received light intensity of the RX waveform becomes high when the object 10 has high reflectivity, when the object 10 is close, etc.

[0070] When the received light intensity is high, a saturation phenomenon may occur. Figure 6D shows an example in which the received light intensity of the RX waveform is higher than that of Figure 6C. The difference is that Figure 6A to Figure 6C generate three bins in the histogram, but Figure 6D generates only two bins.

[0071] 6D occurs, for example, when all of the SPADs in the light-receiving unit 3 receive light in the first half of the pulse width T (the first and second unit light-receiving periods). In this case, there are no SPADs that can receive light in the third unit light-receiving period, so the light-receiving frequency becomes 0 and no bins are generated. The phenomenon in which the number of bins in the histogram decreases due to almost all of the SPADs receiving light in the first half of the pulse width T is also called saturation. When saturation occurs, the distance measurement accuracy deteriorates significantly.

[0072] The ranging device 1 according to the first embodiment of the present disclosure is characterized by its ability to solve the first problem of deterioration in ranging accuracy due to cyclic errors, and the second problem of deterioration in ranging accuracy due to pile-up and saturation phenomena.

[0073] The distance measuring device 1 according to the first embodiment of the present disclosure has at least one of the following two features. The first feature is that the light emitting unit 2 emits a TX signal having a TX waveform whose pulse width T is shorter than twice the bin width b (i.e., the unit light receiving period). The second feature is that the light emitting unit 2 emits multiple TX signals in sequence, each having a TX waveform with a different phase.

[0074] An example in which the distance measuring device 1 has both the first and second features will be described below. Note that the distance measuring device 1 may have a configuration that does not have either the first or second feature. That is, the light emitting unit 2 may set the pulse width T of the TX waveform to be at least twice the bin width b. Furthermore, the light emitting unit 2 may repeatedly emit a TX signal having a TX waveform with the same phase.

[0075] 7 is a diagram illustrating a first ranging technique according to the first embodiment of the present disclosure. The light emitting unit 2, for example, emits four TX signals in sequence, each having a first to fourth TX waveform shown in FIG. The first to fourth TX waveforms are TX waveforms with different phases from one another.

[0076] The first TX waveform has a phase shift of A in the forward direction of the time axis from the bin boundary (i.e., a phase difference of "-A"). The second TX waveform has a phase shift of A / 3 in the forward direction of the time axis from the bin boundary (i.e., a phase difference of "-A / 3"). The third TX waveform has a phase shift of A / 3 in the backward direction of the time axis from the bin boundary (i.e., a phase difference of "+A / 3"). The fourth TX waveform has a phase shift of A in the backward direction of the time axis from the bin boundary (i.e., a phase difference of "+A").

[0077] 7, the phase differences (absolute values) "A" and "A / 3" are smaller than the bin width b. In this specification, the phase difference relative to the bin boundary is also referred to as the offset.

[0078] 7 also illustrates a reference TX waveform. The reference TX waveform is a TX waveform that has no phase difference with the bin boundaries and corresponds to the TX waveform in FIG. 2. In this specification, an example will be described in which the light-emitting unit 2 does not emit a TX signal having a TX waveform that has no phase difference with the bin boundaries (the same phase as the reference TX waveform). Note that the multiple TX waveforms in the TX signal emitted by the light-emitting unit 2 may include a TX waveform that has no phase difference with the bin boundaries.

[0079] The first to fourth TX waveforms and the reference TX waveform all have the same pulse width T.

[0080] 7 can be generated by, for example, the delay circuit 13 in Fig. 1. The time-of-flight detection unit 4 classifies the RX signal received by the light receiving unit 3 into one of a plurality of bins based on the clock signal obtained from the clock signal generation unit 12. The boundary between the bins is, for example, the timing at which the time-of-flight detection unit 4 obtains the clock signal. Alternatively, the boundary between the bins may be a timing shifted by a predetermined delay amount from the timing at which the clock signal is obtained.

[0081] The delay circuit 13 obtains a clock signal from the clock signal generation unit 12. The delay circuit 13 delays the clock signal and inputs the delayed clock signal to the light emission timing control unit 11. This causes the light emitting unit 2 to emit a TX signal having a TX waveform corresponding to the delayed clock signal. The delay circuit 13 delays the clock signal to generate an offset of the TX waveform (i.e., a phase difference with respect to the bin boundary).

[0082] In addition, when the delay circuit 13 does not delay the clock signal, or when the delay amount of the clock signal is set to a delay amount corresponding to the bin width b, the light emitting unit 2 can emit a TX signal having the reference TX waveform of Figure 7.

[0083] The light-emitting unit 2 switches the phase of the TX waveform for each light emission, for example. Fig. 8 is a diagram showing the switching of the TX waveform by the light-emitting unit 2. In this specification, the interval between each light emission by the light-emitting unit 2 is also referred to as the pulse repetition interval (PRI). As shown in Fig. 8, the light-emitting unit 2 emits the first to fourth TX waveforms in turn, for example, in this order.

[0084] The control unit 14 in Figure 1 controls the delay amount of the delay circuit 13 so that the light emitting unit 2 emits a TX signal by selecting one of a plurality of TX waveforms (first to fourth TX waveforms in the example of Figure 8) each having a different phase in turn.

[0085] 8 shows an example in which the light-emitting unit 2 switches the phase of the TX waveform for each PRI. However, the present invention is not limited to this, and the light-emitting unit 2 may switch the phase of the TX waveform for each of a plurality of PRIs.

[0086] Fig. 9 is a diagram showing multiple RX waveforms based on the multiple TX waveforms of Fig. 7. Fig. 9 illustrates first to fourth RX waveforms based on the first to fourth TX waveforms, a reference RX waveform based on a reference TX waveform, and a histogram generated based on the first to fourth RX waveforms. The reference RX waveform of Fig. 9 corresponds to the RX waveform of Fig. 2, etc. The first to fourth RX waveforms have the same offset from the reference RX waveform as the first to fourth TX waveforms.

[0087] The histogram generator 5 integrates the light reception frequencies of the RX signals having each of the first to fourth RX waveforms to generate the histogram shown in Fig. 9. The histogram in Fig. 9 has bins the number of which corresponds to the pulse width T of the first to fourth RX waveforms and the offsets "-A" to "+A" of the first to fourth RX waveforms.

[0088] For example, if the pulse width T is twice the bin width b (i.e., T=2b), the histogram may have four bins: two bins Ba corresponding to the pulse width T, one bin Bb (the bin for the first unit light-reception period) corresponding to the offset "-A" in the forward direction of the time axis, and one bin Bc (the bin for the second unit light-reception period) corresponding to the offset "+A" in the backward direction of the time axis. In the example of FIG. 7, the bin Bb for the first unit light-reception period is formed based on the first RX waveform, etc. In the example of FIG. 7, the bin Bc for the second unit light-reception period is formed based on the fourth RX waveform, etc.

[0089] The first to fourth TX waveforms in FIG. 7 are adjusted to be 0 (i.e., (-A) + (-1 / 3A) + 1 / 3A + A = 0). The sum of the offsets of the first to fourth RX waveforms corresponding to the first to fourth TX waveforms, respectively, also becomes 0. This allows the center of gravity of the histogram in FIG. 9 to be approximately aligned with the center of gravity of the reference RX waveform. That is, as in FIG. 2, the time of flight can be detected from the center of gravity of the histogram and the center of gravity of the TX waveform (reference TX waveform).

[0090] The phases of the first to fourth TX waveforms in Figure 7 are shifted at equal intervals by the same phase amount. More specifically, the phase difference between the first TX waveform and the second TX waveform, the phase difference between the second TX waveform and the third TX waveform, and the phase difference between the third TX waveform and the fourth TX waveform are all 2 / 3 A. This allows the first to fourth RX waveforms to be evenly distributed on the time axis. Furthermore, when accumulating the light reception frequencies of the first to fourth RX waveforms, it is possible to prevent the light reception frequencies from concentrating and accumulating in a specific bin of the histogram.

[0091] That is, the multiple TX waveforms of the TX signal include n TX waveforms (n=2 in the example of FIG. 7) whose phases are earlier than the reference TX waveform, and n TX waveforms whose phases are later than the reference TX waveform. Furthermore, the n TX waveforms whose phases are earlier than the reference TX waveform and the n TX waveforms whose phases are later than the reference TX waveform include n pairs of TX waveforms whose phase differences from the reference TX waveform have the same absolute value.

[0092] 10 is a flowchart illustrating the operation of the distance measuring device 1 according to the first embodiment of the present disclosure. First, the control unit 14 sets a division number N and generates a delay time list based on the division number N (step S1). The division number N is the number of types of TX waveforms. The light emitting unit 2 divides the number of light emissions for one distance measurement into each type of TX waveform.

[0093] 7, the number of divisions N for the first to fourth TX waveforms is 4. If the light emitting unit 2 emits light 1000 times in one distance measurement, the light emitting unit 2 emits TX signals having the first to fourth TX waveforms 250 times each.

[0094] Fig. 11 is a diagram showing a delay time list. The delay time list in Fig. 11 stores the relationship between i%N, which calculates the remainder when a light emission period counter i described below is divided by N, and an offset (delay time) that indicates the amount by which the phase of the TX waveform is shifted. The delay time list is stored, for example, in a predetermined memory unit or the like in the distance measuring device 1.

[0095] Next, the control unit 14 initializes a light emission period counter i (step S2). For example, the control unit 14 sets the light emission period counter i to 0. The light emission period counter i is a count value for counting PRIs.

[0096] The control unit 14 obtains an offset from the delay time list (step S3). As described above, the control unit 14 calculates the remainder when the light emission period counter i is divided by the division number N, and obtains the offset based on the obtained value. For example, if i=0, the offset "-A" in the delay time list of FIG. 11 is obtained.

[0097] Next, the distance measuring device 1 performs light emission and light reception operations (step S4). The control unit 14 transmits the acquired offset to the delay circuit 13. The delay circuit 13 delays the light emission of the light emitting unit 2 based on the offset transmitted from the control unit 14. The light emitting unit 2 emits a TX signal having, for example, a first TX waveform. The light receiving unit 3 receives an RX signal having, for example, a first RX waveform. Based on this, the time-of-flight detection unit 4 classifies the light reception timing into one of multiple bins.

[0098] The control unit 14 determines whether the light emitting unit 2 has emitted light the number of times required for one distance measurement (for example, 1,000 times) (step S5). The control unit 14 determines, for example, whether the light emission period counter i is equal to or greater than the required number of times.

[0099] If the number of times the light emitting unit 2 has emitted light has not reached the required number (for example, i<1000), the control unit 14 increments the light emitting period counter i (i→i+1) (step S6).

[0100] Next, in step S3, the control unit 14 acquires an offset based on the incremented light-emitting period counter i. For example, if i=1, the offset "-A / 3" in the delay time list of Fig. 11 is acquired. This causes the light-emitting unit 2 to emit a TX signal with the second TX waveform, and the light-receiving unit 3 to receive an RX signal with the second RX waveform.

[0101] That is, the control unit 14 can select multiple TX waveforms with different phases in rotation for each light emission based on the delay time list in Fig. 11. Furthermore, after the light emitting unit 2 emits a TX signal in which the first to fourth TX waveforms are selected once each in steps S3 to S6, it again emits a TX signal in which the first to fourth TX waveforms are selected once each. That is, the control unit 14 selects the first to fourth TX waveforms in rotation two or more predetermined times (for example, 250 times).

[0102] When the number of times that the light-emitting unit 2 has emitted light reaches the required number (for example, i≧1000), the light-emitting unit 2 stops emitting light. The histogram generating unit 5 generates a histogram. The distance detecting unit 6 detects the distance to the object 10 based on calculation of the center of gravity of the histogram (step S7). This allows the distance measuring device 1 to measure the distance to the object 10.

[0103] 12 is a diagram illustrating the influence of cyclic errors in the ranging method according to the first embodiment of the present disclosure. Even in the ranging method according to the present disclosure, the pulse widths T of the first to fourth RX waveforms may not be a constant multiple of the bin width b.

[0104] Figure 12 shows the same case as Figure 3B where the reference RX waveform extends beyond the bin boundary to the right, resulting in a positive error in the histogram.

[0105] In the example of Figure 3B, errors are accumulated in the bins corresponding to the portions of the RX waveform that extend to the right. For example, the number of times an RX signal is received with a flight distance of approximately 101 cm is accumulated in the bin indicating a flight distance of 105 cm. In this example, a positive error of approximately +4 cm is repeatedly accumulated according to the number of times the RX signal is received. In the example of Figure 3B, since the phase of the RX signal does not change, if an RX signal with a flight distance of approximately 101 cm is received 1,000 times, an error of approximately +4 cm for 1,000 times is accumulated in the bin indicating the flight distance of 105 cm, and the error between the center of gravity of the RX signal and the center of gravity of the histogram becomes large.

[0106] In contrast, the multiple RX waveforms disclosed herein include RX waveforms with phases earlier than the reference RX waveform and RX waveforms with phases later than the reference RX waveform. This allows the error between the centroid position of the RX signal and the centroid position of the histogram to be changed for each RX waveform with a different phase. Therefore, by repeatedly receiving multiple times while changing the phase of the RX waveform in turn, the histogram bins corresponding to the centroids of the RX waveforms are distributed among multiple bins. As a whole, the error between the centroid position of the RX signal and the centroid position of the histogram can be reduced, thereby reducing cyclic errors.

[0107] The larger the division number N, the more effective it is at reducing cyclic errors.

[0108] The inventors have confirmed the effect of reducing cyclic errors through simulations using the distance measuring device 1 of the present disclosure. 13 to 16 illustrate a ground truth depth (GT_depth) image, a depth image of the distance measurement result (measured depth), an image showing the distance measurement error, and a waveform diagram of the distance measurement error.

[0109] In the simulation, the distance to the subject (i.e., object 10) is 1 m. The field of view (FOV) of the distance measuring device 1 is 70 degrees. A pinhole camera without lens distortion is used for the distance measuring device 1. For a bin width b, the maximum phase difference between the multiple TX waveforms is +3 / 4b, and the minimum phase difference is -3 / 4b. The pulse width T of the TX waveform is different in each of Figures 13 to 16. Figures 13 to 16 also illustrate the simulation results when the number of divisions N is 1, 4, 8, and 16. The phase differences between the multiple TX waveforms are set to be equally spaced based on the number of divisions N and the above-mentioned maximum and minimum phase differences.

[0110] The simulation with the division number N = 1 is a conventional simulation. When the division number N = 1, the distance measuring device 1 repeatedly emits a TX signal having a reference TX waveform shown in Fig. 7 and the like.

[0111] FIG. 13 is a diagram showing the simulation results when the pulse width T=2b.

[0112] 13A shows a true depth (GT depth [m]) image, which illustrates the depth as a function of the true distance from the plane to the dToF sensor measured in the simulation.

[0113] 13B to 13E are diagrams showing simulation results when the number of divisions N is 1, 4, 8, and 16, respectively. That is, FIG. 13B shows the simulation results of a general-purpose distance measurement process. The first row of FIG. 13B to 13E shows depth images (measured depth [m]) of the distance measurement results. The second row of FIG. 13B to 13E shows images of the distance measurement error (depth error [m]).

[0114] The third rows of Figures 13B to 13E show waveforms of the distance measurement error (depth error [m]). The waveforms on the third rows of Figures 13B to 13E include the distance measurement error in the dotted line portions on the first and second rows of Figures 13B to 13E. The horizontal axis of the waveform diagrams on the third rows of Figures 13B to 13E indicates the position (index) of the dotted line portions on the first and second rows of Figures 13B to 13E, and the vertical axis indicates the distance measurement error.

[0115] As described above, the simulation in Figure 13 is a simulation in which the pulse width T of the TX waveform is a constant multiple of the bin width b. In this case, cyclic errors are suppressed as shown in Figure 5. Therefore, almost no errors occur in any of Figures 13B to 13E.

[0116] 14A and 14B show simulation results when the pulse width T is set to 2.25b. As shown in FIG. 14B, concentric cyclic errors are observed in the distance measurement results. Furthermore, as shown in FIG. 14C, when the distance measurement method of the present disclosure is applied, the cyclic errors are reduced. Furthermore, as shown in FIGS. 14D and 14E, the larger the division number N, the greater the effect of reducing the cyclic errors.

[0117] Fig. 15 shows the simulation results when the pulse width T is 2.5b. Fig. 16 shows the simulation results when the pulse width T is 2.75b. As in Fig. 14, Figs. 15 and 16 also show the reduction in cyclic error.

[0118] As shown in FIGS. 13 to 16, the distance measuring device 1 according to the first embodiment of the present disclosure can suppress the cyclic error, which is the first problem described above.

[0119] 17 is a diagram illustrating the influence of the pile-up phenomenon in the ranging method according to the first embodiment of the present disclosure. As shown in FIG. 17, in the ranging method according to the present disclosure, the portion of the first to fourth RX waveforms where the SPAD light reception frequency is concentrated due to the pile-up phenomenon can be distributed to multiple bins in the histogram. This makes it possible to reduce errors due to the pile-up phenomenon.

[0120] Ranging errors due to the pile-up phenomenon and the saturation phenomenon can also be reduced by reducing the pulse width T of the TX waveform. Fig. 18 is a diagram illustrating reduction in ranging errors due to the pile-up phenomenon and the saturation phenomenon in the ranging method according to the first embodiment of the present disclosure.

[0121] Fig. 18A is a diagram showing a case where the pulse width T of the RX waveform is three times the bin width b (T = 3b). In the example of Fig. 18A, an RX signal is incident during three unit light-reception periods. In Fig. 18A, during the third unit light-reception period from the front on the time axis, the RX signal cannot be received due to a saturation phenomenon, and no bin is generated.

[0122] 18B shows a case where the pulse width T of the RX waveform is less than twice the bin width b (T<2b). Compared to FIG. 18A, FIG. 18B is characterized by a reduced number of unit light-reception periods in which the RX waveform is incident. In FIG. 18B, there is no third unit light-reception period that would be affected by saturation. This prevents the occurrence of saturation.

[0123] As shown in Figure 18B, when the pulse width T of the RX waveform is less than twice the bin width b (i.e., when the pulse width T of the TX waveform is less than twice the bin width b), the probability of saturation can be significantly reduced, and the influence of ranging errors due to pileup can also be reduced.

[0124] 18C is a diagram showing a case where the pulse width T of the RX waveform is less than the bin width b (T<b). In FIG. 18C, there is one unit light-receiving period in which the RX signal is incident. In a case like FIG. 18C, in principle, saturation and pile-up do not occur.

[0125] As shown in FIG. 18C, when the pulse width T of the TX waveform is set to be less than the bin width b, the influence of ranging errors due to the saturation phenomenon and pile-up phenomenon can be significantly reduced.

[0126] Fig. 19 is a diagram showing a ranging technique according to a first comparative example. In the ranging technique according to the first comparative example, the pulse width T of the TX waveform is set to be less than the bin width b, as in Fig. 18 . On the other hand, the ranging technique of Fig. 19 does not emit a TX signal having multiple TX waveforms with different phases, as shown in Fig. 7 . In other words, in the ranging technique of Fig. 19 , a TX signal having a TX waveform with a single phase is repeatedly emitted.

[0127] As shown in Figures 19A and 19B, when the pulse width T of the RX waveform is less than the bin width b, the histogram may generate only one bin. In this case, the center of gravity of the single bin becomes the center of gravity of the histogram, regardless of the center of gravity of the RX waveform. In Figures 19A and 19B, the center of gravity of the RX waveform is different from each other, but the center of gravity of the histogram is the same. This may result in a deterioration in the ranging accuracy of the ranging method of Figure 19.

[0128] Furthermore, even if the light emitting unit 2 is controlled to emit a TX signal having a TX waveform with a bin width of b or more, the pulse width T of the RX waveform may become less than the bin width b depending on the temperature. In this case, the ranging accuracy also deteriorates, as in the case of FIG.

[0129] As a second comparative example, an example can be considered in which the pulse width T of the TX waveform is made larger than the bin width b. Furthermore, to prevent cyclic errors, an example can be considered in which the pulse width T is made a constant multiple (e.g., two or three times) of the bin width b. However, in the second comparative example, it is not possible to reduce ranging errors due to the saturation phenomenon and pile-up phenomenon shown in FIG. 18 .

[0130] 20 is a diagram illustrating a second ranging technique according to the first embodiment of the present disclosure. In the ranging technique of FIG. 20, the light-emitting unit 2 emits TX signals having first to fourth TX waveforms whose pulse width T is less than the bin width b. As a result, the light-receiving unit 3 receives RX signals having first to fourth RX waveforms whose pulse width T is less than the bin width b. The first to fourth RX waveforms in FIG. 20 have the same phase difference with respect to the reference RX waveform as in FIG. 7.

[0131] The histogram in Fig. 20 has bins whose number corresponds to the pulse width T of the first to fourth RX waveforms and the offsets of the first to fourth RX waveforms. This results in two or more bins in the histogram, which can prevent the occurrence of the error shown in Fig. 19.

[0132] In addition, the ranging method of Fig. 20 can reduce ranging errors due to the saturation phenomenon and pile-up phenomenon, similar to Fig. 18C. Although Fig. 20 describes an example in which the pulse width T is less than the bin width b, even when the pulse width T is less than twice the bin width b, it is possible to reduce ranging errors due to the saturation phenomenon and pile-up phenomenon, similar to Fig. 18B.

[0133] Furthermore, in the ranging method of Fig. 20, cyclic errors can be suppressed, similarly to the example of Fig. 12. This eliminates the need to set the pulse width T to a constant multiple of the bin width b, and therefore the pulse width T can be set to be less than the bin width b.

[0134] Note that the ranging device 1 according to the first embodiment of the present disclosure may suppress the ranging error in Fig. 19 using a method other than the ranging method in Fig. 20. For example, the ranging device 1 may measure the temperature of the imaging environment and, based on the measured temperature, control the light emission of the light-emitting unit 2 so that the pulse width T of the RX waveform is approximately equal to the bin width b or greater than or equal to the bin width b (for example, twice the bin width b). In this case, the light-emitting unit 2 may intermittently emit a TX signal having a TX waveform (for example, the reference TX waveform in Fig. 7) with the same phase.

[0135] 21A and 21B are diagrams showing the relationship between the pulse width T of the RX waveform and the histogram. １ is, for example, 2.3 times the bin width b. The pulse width T ２ is, for example, 1.15 times the bin width b. The pulse width T ３ is, for example, 0.46 times the bin width b.

[0136] In Fig. 21A, for example, the light emitting unit 2 is controlled to emit a TX signal having a TX waveform with a pulse width T twice the bin width b. In Figs. 21B and 21C, for example, the light emitting unit 2 is controlled to emit a TX signal having a TX waveform with a pulse width T that is approximately the same as the bin width b. However, due to temperature changes, the above-mentioned pulse width T in each of Figs. 21A to 21C １ , T ２ , and T ３ It is assumed that an RX signal having the following RX waveform is received.

[0137] In Figures 21A and 21B, the maximum and minimum phase differences of the first to fourth RX waveforms relative to the reference RX waveform are ±0.5b. In Figure 21C, the maximum and minimum phase differences of the first to fourth RX waveforms relative to the reference RX waveform are ±b.

[0138] 21A to 21C, the smaller the pulse width T of the RX waveform, the narrower the histogram width, making it easier to identify the center of gravity, thereby reducing ranging errors due to saturation and pile-up.Furthermore, as shown in FIG. 21C, if the histogram can be flattened, ranging errors due to saturation and pile-up can be further reduced.

[0139] Fig. 22 is a diagram illustrating a ranging technique according to a modification of the first embodiment of the present disclosure. The ranging technique in Fig. 22 differs from the ranging technique in Fig. 7 in that the pulse widths of the first to fourth TX waveforms are different from each other.

[0140] For example, the pulse width of the reference TX waveform is T ０ The pulse width of the first TX waveform is T ０ The pulse width of the second TX waveform is T ０ The pulse width of the third TX waveform is T ０ +A / 3. The pulse width of the fourth TX waveform is T ０ +A. The phase difference A is, for example, 1 / 2 of the bin width b.

[0141] The centers of gravity of the first to fourth TX waveforms are substantially the same as the center of gravity of the reference TX waveform. The multiple TX waveforms emitted by the light-emitting unit 2 include n TX waveforms (n=2 in the example of FIG. 7) with pulse widths shorter than the reference TX waveform, and n TX waveforms with pulse widths longer than the reference TX waveform.

[0142] 9, the histogram generator 5 can generate a histogram having a center of gravity substantially identical to that of the reference RX waveform. As with the ranging method of FIG. 7, the ranging method of FIG. 22 can also reduce ranging errors due to cyclic errors, saturation phenomena, and pile-up phenomena.

[0143] As described above, the distance measuring device 1 according to the first embodiment of the present disclosure has a first feature of emitting a TX signal having a TX waveform with a pulse width T shorter than twice the unit light-reception period, and a second feature of emitting a TX signal by switching in sequence among a plurality of TX waveforms with different phases. This allows the distance measuring device 1 to solve both the first and second problems described above and improve distance measurement accuracy.

[0144] Specifically, when the light intensity of the received light is high, the second problem of saturation and pile-up may occur. In response to this problem, the first feature can reduce the number of bins where saturation and pile-up may occur, thereby preventing a deterioration in ranging accuracy. Furthermore, if the pulse width T of the TX waveform is made shorter than the unit light-receiving period, the occurrence of saturation and pile-up can be prevented in principle, and ranging accuracy can be significantly improved.

[0145] The second feature allows the number of bins in the histogram to be two or more even when the pulse width T of the RX waveform is shorter than the unit light-receiving period, thereby preventing a deterioration in distance measurement accuracy.

[0146] The second feature is that even if a pile-up phenomenon occurs, the period during which light reception by the SPAD is concentrated can be distributed among multiple bins, thereby suppressing deterioration in distance measurement accuracy due to the pile-up phenomenon.

[0147] Furthermore, the second feature can offset the error due to cyclic error, which is the first problem. By increasing the number of phase types of the TX waveform, the error due to cyclic error can be more effectively offset, improving ranging accuracy.

[0148] 7 , errors due to cyclic error, pile-up phenomenon, and saturation phenomenon are dispersed to each bin of the histogram by controlling the light-emitting unit 2. This dispersion of the distance measurement errors can also be achieved by controlling the distance measurement unit 7. The second embodiment of the present disclosure is characterized in that the distance measurement errors are dispersed by controlling the distance measurement unit 7.

[0149] Fig. 23 is a block diagram showing the configuration of a distance measuring device 1a according to a second embodiment of the present disclosure. Fig. 24 is a block diagram showing the detailed configuration of a distance measuring unit 7a according to the second embodiment of the present disclosure. The distance measuring device 1a in Fig. 23 differs from the distance measuring device 1 in Fig. 1 in that it does not have the delay circuit 13 in Fig. 1. A time-of-flight detection unit (light-reception time allocation unit) 4a in Fig. 24 is configured using, for example, a TDC (Time to Digital Converter), but its processing operation is different from that of the time-of-flight detection unit 4 in Fig. 1.

[0150] The light emitting unit 2a in FIG. 23 intermittently emits a TX signal with the same phase and pulse width (for example, a TX signal having the reference TX waveform in FIG. 7).

[0151] The operation of the distance measuring device 1a in Fig. 23 is similar to that in the flowchart of Fig. 10. However, the distance measuring device 1a in Fig. 23 differs from the distance measuring device 1 in Fig. 1 in the operation of step S4 in Fig. 10.

[0152] The control unit 14a in Fig. 24 transmits the offset (delay time) acquired in step S3 in Fig. 10 to the time-of-flight detection unit 4a. Note that the time-of-flight detection unit 4a may acquire the offset from the delay time list in Fig. 11 based on the light emission period counter i.

[0153] The time-of-flight detection unit 4a acquires the time (hereinafter also referred to as the light reception time) from when the light-emitting unit 2a emits the TX signal to when the light-receiving unit 3 receives the RX signal based on the clock signal acquired from the clock signal generation unit 12 and the pixel signal acquired from the light-receiving unit 3.

[0154] The time-of-flight detection unit 4a adds an offset (for example, the offset in FIG. 11 ) to the light-reception time to calculate a phase-shifted light-reception time. The time-of-flight detection unit 4a assigns the phase-shifted light-reception time to one of multiple bins in the histogram and transmits the assigned number (bin_index) to the histogram generation unit 5. The histogram generation unit 5 increments the number of times light is received in the bin specified by the assigned number. In this way, the time-of-flight detection unit 4a associates the light-reception time with one of multiple bins in the histogram.

[0155] Even if the time-of-flight detection unit 4a acquires the same light-reception time from the light-receiving unit 3, the time-of-flight detection unit 4a may assign the light-reception time to a bin with a different assigned number depending on the value of the offset. The offset is selected in rotation, as in Fig. 8. That is, the time-of-flight detection unit 4a selects in rotation one of a plurality of different correspondences between the light-reception time of the RX waveform repeatedly received by the light-receiving unit 3 and a plurality of unit light-reception periods included in the histogram.

[0156] The histogram generating unit 5 generates a histogram based on the assigned numbers, thereby generating a histogram similar to that shown in FIG.

[0157] The delay time list can be set with offsets similar to those in Fig. 11. That is, the time-of-flight detection unit 4a can use a delay time list with an equal number of positive and negative offsets, which are adjusted so that the sum of the offsets is 0. Furthermore, the time-of-flight detection unit 4a can use offsets that are shorter than the unit light-receiving period and are shifted at equal intervals by the same phase amount.

[0158] In the distance measuring device 1a according to the second embodiment, at least part of the light emitting unit 2a, the light receiving unit 3, the light emission timing control unit 11, or the clock signal generating unit 12 may be provided external to the distance measuring device 1a. In this case, the distance measuring unit 7a may generate a histogram and calculate the center of gravity based on pixel signals transferred from the externally provided light receiving unit 3, etc. Alternatively, the time-of-flight detection unit 4a may be controlled by, for example, an information processing device downstream of the distance measuring device 1a. This simplifies the configuration of the distance measuring device 1a.

[0159] The light emitting unit 2 according to the first embodiment may be applied to the distance measuring device 1a. That is, the light emitting unit 2a may be configured to emit TX signals having the first to fourth waveforms in turn in Fig. 7. The light emitting unit 2a may also emit a TX signal having a TX waveform in which the pulse width T is less than twice the bin width b or less than the bin width b.

[0160] In this way, in the distance measuring device 1a according to the second embodiment of the present disclosure, the distance measurement error is dispersed by controlling the distance measuring unit 7. As a result, like the distance measuring device 1 according to the first embodiment, distance measurement errors due to cyclic errors, pile-up phenomena, and saturation phenomena can be suppressed. Furthermore, compared to the distance measuring device 1 according to the first embodiment, the distance measuring device 1a according to the second embodiment does not require complex light emission control. For example, the configuration of the distance measuring device 1a can be simplified by implementing the control of the time-of-flight detection unit 4a in a downstream information processing device or the like.

[0161] At least a part of the distance measuring device 1 or 1a described in the above-described embodiment may be configured as hardware or software. When configured as software, a program that realizes at least a part of the functions of the information processing device may be stored on a recording medium such as a flexible disk or CD-ROM, and may be read and executed by a computer. The recording medium is not limited to removable media such as magnetic disks and optical disks, but may also be fixed recording media such as hard disk drives and memories.

[0162] A program that realizes at least part of the functions of the distance measuring device 1 or 1a may be distributed via a communication line (including wireless communication) such as the Internet. Furthermore, the program may be encrypted, modulated, or compressed and distributed via a wired or wireless line such as the Internet, or stored on a recording medium.

[0163] (Application Examples) The technology according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, a robot, construction machinery, or agricultural machinery (tractor).

[0164] 25 is a block diagram showing a schematic configuration example of a vehicle control system 7000, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied. The vehicle control system 7000 includes a plurality of electronic control units connected via a communication network 7010. In the example shown in FIG. 25 , the vehicle control system 7000 includes a drive system control unit 7100, a body system control unit 7200, a battery control unit 7300, an outside-vehicle information detection unit 7400, an inside-vehicle information detection unit 7500, and an integrated control unit 7600. The communication network 7010 connecting these multiple control units may be an in-vehicle communication network conforming to any standard, such as a Controller Area Network (CAN), a Local Interconnect Network (LIN), a Local Area Network (LAN), or FlexRay (registered trademark).

[0165] Each control unit includes a microcomputer that performs arithmetic processing according to various programs, a memory unit that stores the programs executed by the microcomputer or parameters used in various calculations, and a drive circuit that drives various controlled devices. Each control unit includes a network I / F for communicating with other control units via a communication network 7010, and a communication I / F for communicating with devices or sensors inside and outside the vehicle via wired or wireless communication. Figure 25 illustrates the functional configuration of the integrated control unit 7600, including a microcomputer 7610, a general-purpose communication I / F 7620, a dedicated communication I / F 7630, a positioning unit 7640, a beacon receiving unit 7650, an in-vehicle device I / F 7660, an audio / video output unit 7670, an in-vehicle network I / F 7680, and a memory unit 7690. The other control units also include a microcomputer, a communication I / F, a memory unit, and the like.

[0166] The drivetrain control unit 7100 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 7100 functions as a control device for a drive force generating device for generating drive force for the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating braking force for the vehicle. The drivetrain control unit 7100 may also function as a control device for an ABS (Antilock Brake System) or an ESC (Electronic Stability Control), etc.

[0167] A vehicle state detection unit 7110 is connected to the drivetrain control unit 7100. The vehicle state detection unit 7110 includes at least one of a gyro sensor that detects the angular velocity of the axial rotational motion of the vehicle body, an acceleration sensor that detects the acceleration of the vehicle, or a sensor that detects the amount of operation of the accelerator pedal, the amount of operation of the brake pedal, the steering angle of the steering wheel, the engine rotation speed, the rotation speed of the wheels, etc. The drivetrain control unit 7100 performs arithmetic processing using signals input from the vehicle state detection unit 7110, and controls the internal combustion engine, the drive motor, the electric power steering device, the brake device, etc.

[0168] The body system control unit 7200 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 7200 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 7200. The body system control unit 7200 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0169] The battery control unit 7300 controls the secondary battery 7310, which is the power supply source for the drive motor, in accordance with various programs. For example, information such as battery temperature, battery output voltage, or remaining battery capacity is input to the battery control unit 7300 from a battery device equipped with the secondary battery 7310. The battery control unit 7300 performs arithmetic processing using these signals, and controls the temperature regulation of the secondary battery 7310 or a cooling device or the like equipped in the battery device.

[0170] The outside vehicle information detection unit 7400 detects information outside the vehicle equipped with the vehicle control system 7000. For example, at least one of an imaging unit 7410 and an outside vehicle information detection unit 7420 is connected to the outside vehicle information detection unit 7400. The imaging unit 7410 includes at least one of a time-of-flight (ToF) camera, a stereo camera, a monocular camera, an infrared camera, and other cameras. The outside vehicle information detection unit 7420 includes at least one of an environmental sensor for detecting the current weather or climate, or a surrounding information detection sensor for detecting other vehicles, obstacles, pedestrians, etc. around the vehicle equipped with the vehicle control system 7000.

[0171] The environmental sensor may be, for example, at least one of a raindrop sensor that detects rain, a fog sensor that detects fog, a sunshine sensor that detects the degree of sunshine, and a snow sensor that detects snowfall. The surrounding information detection sensor may be at least one of an ultrasonic sensor, a radar device, and a LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) device. The imaging unit 7410 and the outside vehicle information detection unit 7420 may each be provided as an independent sensor or device, or may be provided as a device in which multiple sensors or devices are integrated.

[0172] 26 shows an example of the installation positions of the imaging unit 7410 and the vehicle exterior information detection unit 7420. The imaging units 7910, 7912, 7914, 7916, and 7918 are provided, for example, at least one of the front nose, side mirrors, rear bumper, back door, and upper part of the windshield inside the vehicle cabin of the vehicle 7900. The imaging unit 7910 provided on the front nose and the imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 7900. The imaging units 7912 and 7914 provided on the side mirrors mainly acquire images of the sides of the vehicle 7900. The imaging unit 7916 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 7900. The imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin is mainly used to detect leading vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0173] 26 shows an example of the imaging ranges of the imaging units 7910, 7912, 7914, and 7916. Imaging range a indicates the imaging range of the imaging unit 7910 provided on the front nose, imaging ranges b and c indicate the imaging ranges of the imaging units 7912 and 7914 provided on the side mirrors, respectively, and imaging range d indicates the imaging range of the imaging unit 7916 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 7910, 7912, 7914, and 7916, a bird's-eye view image of the vehicle 7900 viewed from above can be obtained.

[0174] The outside vehicle information detection units 7920, 7922, 7924, 7926, 7928, and 7930 provided on the front, rear, sides, corners, and above the windshield inside the vehicle cabin of the vehicle 7900 may be, for example, ultrasonic sensors or radar devices. The outside vehicle information detection units 7920, 7926, and 7930 provided on the front nose, rear bumper, back door, and above the windshield inside the vehicle cabin of the vehicle 7900 may be, for example, LIDAR devices. These outside vehicle information detection units 7920 to 7930 are mainly used to detect preceding vehicles, pedestrians, obstacles, etc.

[0175] Returning to FIG. 25 , the explanation will be continued. The outside-vehicle information detection unit 7400 causes the imaging unit 7410 to capture an image outside the vehicle and receives the captured image data. The outside-vehicle information detection unit 7400 also receives detection information from the connected outside-vehicle information detection unit 7420. If the outside-vehicle information detection unit 7420 is an ultrasonic sensor, a radar device, or a LIDAR device, the outside-vehicle information detection unit 7400 emits ultrasonic waves or electromagnetic waves and receives information on the received reflected waves. Based on the received information, the outside-vehicle information detection unit 7400 may perform object detection processing or distance detection processing for people, vehicles, obstacles, signs, text on the road, etc. Based on the received information, the outside-vehicle information detection unit 7400 may also perform environment recognition processing for recognizing rainfall, fog, road conditions, etc. Based on the received information, the outside-vehicle information detection unit 7400 may also calculate the distance to an object outside the vehicle.

[0176] The outside vehicle information detection unit 7400 may also perform image recognition processing or distance detection processing to recognize people, vehicles, obstacles, signs, or characters on the road surface based on the received image data. The outside vehicle information detection unit 7400 may perform processing such as distortion correction or alignment on the received image data, and may also generate an overhead image or a panoramic image by combining image data captured by different image capturing units 7410. The outside vehicle information detection unit 7400 may also perform viewpoint conversion processing using image data captured by different image capturing units 7410.

[0177] The interior information detection unit 7500 detects information inside the vehicle. A driver state detection unit 7510 that detects the driver's state is connected to the interior information detection unit 7500, for example. The driver state detection unit 7510 may include a camera that captures an image of the driver, a biosensor that detects the driver's biometric information, or a microphone that collects sound from within the vehicle cabin. The biosensor is provided, for example, on the seat or steering wheel, and detects the biometric information of a passenger sitting in the seat or the driver gripping the steering wheel. The interior information detection unit 7500 may calculate the driver's level of fatigue or concentration based on the detection information input from the driver state detection unit 7510, or may determine whether the driver is dozing off. The interior information detection unit 7500 may perform processing such as noise canceling on the collected audio signal.

[0178] The integrated control unit 7600 controls the overall operation of the vehicle control system 7000 according to various programs. An input unit 7800 is connected to the integrated control unit 7600. The input unit 7800 may be implemented by a device that can be operated by a passenger, such as a touch panel, a button, a microphone, a switch, or a lever. Data obtained by voice recognition of a voice input through a microphone may be input to the integrated control unit 7600. The input unit 7800 may be, for example, a remote control device using infrared or other radio waves, or an externally connected device such as a mobile phone or a personal digital assistant (PDA) that can operate the vehicle control system 7000. The input unit 7800 may be, for example, a camera, in which case the passenger can input information using gestures. Alternatively, data obtained by detecting the movement of a wearable device worn by the passenger may be input. Furthermore, the input unit 7800 may include, for example, an input control circuit that generates an input signal based on information input by the passenger using the input unit 7800 and outputs the input signal to the integrated control unit 7600. Passengers and the like operate this input unit 7800 to input various data to the vehicle control system 7000 and to instruct processing operations.

[0179] The storage unit 7690 may include a ROM (Read Only Memory) that stores various programs executed by the microcomputer, and a RAM (Random Access Memory) that stores various parameters, calculation results, sensor values, etc. The storage unit 7690 may also be realized by a magnetic storage device such as an HDD (Hard Disc Drive), a semiconductor storage device, an optical storage device, a magneto-optical storage device, or the like.

[0180] The general-purpose communication I / F 7620 is a general-purpose communication I / F that mediates communication with various devices present in the external environment 7750. The general-purpose communication I / F 7620 may implement a cellular communication protocol such as GSM (Global System of Mobile communications), WiMAX (registered trademark), LTE (Long Term Evolution), or LTE-Advanced (LTE-A), or other wireless communication protocols such as a wireless LAN (also referred to as Wi-Fi (registered trademark)) or Bluetooth (registered trademark). The general-purpose communication I / F 7620 may connect to a device (e.g., an application server or a control server) present on an external network (e.g., the Internet, a cloud network, or an operator-specific network) via, for example, a base station or an access point. In addition, the general-purpose communication I / F 7620 may connect to a terminal located near the vehicle (e.g., a terminal of a driver, pedestrian, or store, or an MTC (Machine Type Communication) terminal) using, for example, P2P (Peer To Peer) technology.

[0181] The dedicated communication I / F 7630 is a communication I / F that supports a communication protocol designed for use in vehicles. The dedicated communication I / F 7630 may implement a standard protocol such as WAVE (Wireless Access in Vehicle Environment), which is a combination of a lower layer IEEE 802.11p and an upper layer IEEE 1609, DSRC (Dedicated Short Range Communications), or a cellular communication protocol. The dedicated communication I / F 7630 typically performs V2X communication, which is a concept including one or more of vehicle-to-vehicle communication, vehicle-to-infrastructure communication, vehicle-to-home communication, and vehicle-to-pedestrian communication.

[0182] The positioning unit 7640 performs positioning by receiving, for example, GNSS signals from GNSS (Global Navigation Satellite System) satellites (for example, GPS signals from GPS (Global Positioning System) satellites), and generates position information including the latitude, longitude, and altitude of the vehicle. Note that the positioning unit 7640 may identify the current position by exchanging signals with a wireless access point, or may obtain position information from a terminal such as a mobile phone, PHS, or smartphone that has a positioning function.

[0183] The beacon receiving unit 7650 receives, for example, radio waves or electromagnetic waves transmitted from radio stations or the like installed on the road, and acquires information such as the current location, congestion, road closures, required travel time, etc. The function of the beacon receiving unit 7650 may be included in the dedicated communication I / F 7630 described above.

[0184] The in-vehicle device I / F 7660 is a communication interface that mediates connections between the microcomputer 7610 and various in-vehicle devices 7760 present in the vehicle. The in-vehicle device I / F 7660 may establish wireless connections using wireless communication protocols such as wireless LAN, Bluetooth (registered trademark), NFC (Near Field Communication), or WUSB (Wireless USB). Furthermore, the in-vehicle device I / F 7660 may establish a wired connection such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), or MHL (Mobile High-Definition Link) via a connection terminal (and a cable, if necessary) not shown. The in-vehicle device 7760 may include, for example, at least one of a mobile device or a wearable device owned by a passenger, or an information device carried into or attached to the vehicle. The in-vehicle device 7760 may also include a navigation device that searches for a route to an arbitrary destination. The in-vehicle device I / F 7660 exchanges control signals or data signals with these in-vehicle devices 7760.

[0185] The in-vehicle network I / F 7680 is an interface that mediates communication between the microcomputer 7610 and the communication network 7010. The in-vehicle network I / F 7680 transmits and receives signals in accordance with a predetermined protocol supported by the communication network 7010.

[0186] The microcomputer 7610 of the integrated control unit 7600 controls the vehicle control system 7000 in accordance with various programs based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. For example, the microcomputer 7610 may calculate control target values ​​for the driving force generating device, the steering mechanism, or the braking device based on the acquired information inside and outside the vehicle, and output control commands to the drivetrain control unit 7100. For example, the microcomputer 7610 may perform cooperative control aimed at realizing functions of an Advanced Driver Assistance System (ADAS), including vehicle collision avoidance or impact mitigation, following driving based on the following distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc. In addition, the microcomputer 7610 may perform cooperative control for the purpose of autonomous driving, in which the vehicle travels autonomously without relying on driver operation, by controlling a driving force generating device, a steering mechanism, a braking device, etc. based on information acquired about the vehicle's surroundings.

[0187] The microcomputer 7610 may generate three-dimensional distance information between the vehicle and objects such as surrounding structures and people, and create local map information including information about the vicinity of the vehicle's current location, based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. Furthermore, the microcomputer 7610 may predict dangers, such as a vehicle collision, the approach of a pedestrian, or entry into a closed road, based on the acquired information, and generate a warning signal. The warning signal may be, for example, a signal for generating a warning sound or turning on a warning lamp.

[0188] The audio / image output unit 7670 transmits at least one of audio and image output signals to an output device capable of visually or audibly notifying vehicle occupants or the outside of the vehicle of information. In the example of FIG. 25 , an audio speaker 7710, a display unit 7720, and an instrument panel 7730 are illustrated as output devices. The display unit 7720 may include, for example, at least one of an on-board display and a head-up display. The display unit 7720 may have an AR (Augmented Reality) display function. The output device may also be other devices, such as headphones, a wearable device such as an eyeglass-type display worn by the occupant, a projector, or a lamp. When the output device is a display device, the display device visually displays results obtained by various processes performed by the microcomputer 7610 or information received from other control units in various formats, such as text, images, tables, and graphs. When the output device is an audio output device, the audio output device converts audio signals, such as reproduced audio data or acoustic data, into analog signals and audibly outputs the analog signals.

[0189] In the example shown in FIG. 25 , at least two control units connected via the communication network 7010 may be integrated into a single control unit. Alternatively, each control unit may be composed of multiple control units. Furthermore, the vehicle control system 7000 may include another control unit not shown. In the above description, some or all of the functions performed by one of the control units may be performed by another control unit. In other words, as long as information is transmitted and received via the communication network 7010, predetermined arithmetic processing may be performed by one of the control units. Similarly, a sensor or device connected to one of the control units may be connected to another control unit, and multiple control units may transmit and receive detection information to and from each other via the communication network 7010.

[0190] A computer program for realizing each function of the distance measuring device 1 according to this embodiment described with reference to FIG. 1 can be implemented in any control unit or the like. A computer-readable recording medium storing such a computer program can also be provided. Examples of the recording medium include a magnetic disk, an optical disk, a magneto-optical disk, and a flash memory. The computer program may also be distributed, for example, via a network without using a recording medium.

[0191] In the vehicle control system 7000 described above, the distance measuring device 1 according to this embodiment described with reference to Fig. 1 can be applied to the image capturing unit 7410 of the application example shown in Fig. 25. This allows for highly accurate distance measurement even when the subject is at a short distance or when the subject is highly reflective.

[0192] Furthermore, at least some of the components of the distance measuring device 1 described using Fig. 1 may be realized in a module (for example, an integrated circuit module configured on a single die) for the integrated control unit 7600 shown in Fig. 25. Alternatively, the distance measuring device 1 described using Fig. 1 may be realized by multiple control units of the vehicle control system 7000 shown in Fig. 25.

[0193] The present technology may be configured as follows: (1) A distance measuring device including: a light receiving unit that repeatedly receives a reflected light pulse signal obtained by reflecting a light pulse signal from an object; a histogram generating unit that generates a histogram in which the reception frequency of the reflected light pulse signal is classified for each unit light receiving period; and a light emitting unit that repeatedly emits the light pulse signal with a pulse width that is shorter than twice the unit light receiving period. (2) The distance measuring device according to (1), wherein the light emitting unit repeatedly emits the light pulse signal with a pulse width that is shorter than the unit light receiving period. (3) A distance measuring device comprising: a light receiving unit that repeatedly receives a reflected light pulse signal obtained by reflecting a light pulse signal off an object; a histogram generating unit that generates a histogram in which the reception frequencies of the reflected light pulse signal are classified for each unit light receiving period; and a control unit that controls the light emitting unit to select one of a plurality of pulse widths having different phases in turn to emit the light pulse signal, or to select one of a plurality of different correspondences between the reception times of the reflected light pulse signal received by the light receiving unit and the plurality of unit light receiving periods in the histogram in turn, or to select the plurality of correspondences in parallel. (4) A distance measuring device according to any one of (1) to (3), comprising the light emitting unit that selects in turn a plurality of pulse widths having different phases in turn to emit the light pulse signal, or to intermittently emit the light pulse signal with a pulse width of the same phase. (5) A distance measuring device as described in (4), further comprising an emission timing control unit that selects one of a plurality of pulse widths having different phases in turn, and the light emitting unit emits the optical pulse signal at the pulse width selected by the emission timing control unit.(6) The distance measuring device according to (5), wherein the light emission timing control unit selects each of the plurality of pulse widths in rotation a predetermined number of times or more, the light emitter repeats the operation of emitting the light pulse signal of the pulse width selected by the light emission timing control unit the predetermined number of times, the light receiver repeats the operation of receiving the reflected light pulse signal corresponding to the light pulse signal emitted for each of the plurality of pulse widths the predetermined number of times, and the histogram generator generates the histogram based on the reflected light pulse signal corresponding to the light pulse signal emitted by selecting each of the plurality of pulse widths the predetermined number of times. (7) The distance measuring device according to (5) or (6), wherein the light emission timing control unit switches the selection of the plurality of pulse widths in rotation for each light emission operation of the light emitter. (8) The distance measuring device according to any one of (5) to (7), wherein the light emission timing control unit shifts the phases of the plurality of pulse widths at equal intervals. (9) The distance measuring device according to (8), wherein the light emission timing control unit shifts the phases of the multiple pulse widths by the same phase amount shorter than the unit light reception period. (10) The distance measuring device according to any one of (3) to (9), wherein the multiple pulse widths have the same time width. (11) The distance measuring device according to (10), wherein the multiple pulse widths include n (n is an integer greater than or equal to 1) pulse widths whose phases are earlier than a reference pulse width and the n pulse widths whose phases are later than the reference pulse width. (12) The distance measuring device according to any one of (3) to (9), wherein the multiple pulse widths include two or more pulse widths whose time widths are different from each other. (13) The distance measuring device described in (12), wherein the plurality of pulse widths include n (n is an integer greater than or equal to 1) pulse widths that are shorter than a reference pulse width and the n pulse widths that are longer than the reference pulse width, and the n pulse widths that are shorter than the reference pulse width and the n pulse widths that are longer than the reference pulse width have the same center of gravity.(14) The distance measuring device according to any one of (1) to (13), further comprising: a synchronization control unit that synchronizes the light receiving unit and the light emitting unit; and a delay circuit that delays the synchronization signal output by the synchronization control unit by a period shorter than the unit light receiving period for each light emitting operation of the light emitting unit and transmits the delayed synchronization signal to the light emitting unit. (15) The distance measuring device according to (3) or (4), further comprising: a light receiving time allocation unit that selects in turn one of a plurality of different correspondences between the light receiving times of the reflected light pulse signals repeatedly received by the light receiving unit and a plurality of the unit light receiving periods included in the histogram, and the histogram generation unit generates the histogram based on the correspondence selected by the light receiving time allocation unit. (16) The distance measuring device according to (15), wherein the light-reception time allocation unit selects each of the plurality of associations in rotation a predetermined number of times of two or more, and the histogram generation unit allocates the light-reception time to a plurality of unit light-reception periods for each of the plurality of associations selected in rotation the predetermined number of times to generate the histogram. (17) The distance measuring device according to (15) or (16), wherein the unit light-reception periods corresponding to the light-reception times are shifted at equal intervals in the plurality of associations. (18) The distance measuring device according to any one of (15) to (17), wherein the plurality of associations include n (n is an integer of 1 or more) associations in which the unit light-reception period corresponding to the light-reception time is earlier than a reference association between the light-reception time and the plurality of unit light-reception periods in the histogram, and the n associations in which the unit light-reception period corresponding to the light-reception time is later than the reference association. (19) The distance measuring device described in any one of (15) to (18), wherein the light-receiving time allocation unit generates the plurality of associations by changing the association between the light-receiving time and the plurality of unit light-receiving periods by a time width shorter than the unit light-receiving period.(20) A distance measurement method, which comprises repeatedly receiving a reflected light pulse signal that is a light pulse signal reflected by an object, generating a histogram that classifies the reception frequency of the reflected light pulse signal by unit light reception period, and selecting one of a plurality of pulse widths having different phases in turn to emit the light pulse signal, selecting one of a plurality of different correspondences between the reception time of the reflected light pulse signal and a plurality of the unit light reception periods in the histogram in turn, or selecting the plurality of correspondences in parallel.

[0194] The aspects of the present disclosure are not limited to the individual embodiments described above, but include various modifications that may be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the above-described contents. In other words, various additions, modifications, and partial deletions are possible within the scope of the conceptual idea and spirit of the present disclosure, which is derived from the contents defined in the claims and their equivalents.

[0195] REFERENCE SIGNS LIST 1, 1a Distance measuring device, 2, 2a Light emitting unit, 3 Light receiving unit, 4, 4a Time of flight detection unit, 5 Histogram generating unit, 6 Distance detecting unit, 7, 7a Distance measuring unit, 10 Object, 11 Light emitting timing control unit, 12 Clock signal generating unit, 13 Delay circuit, 14, 14a Control unit

Claims

1. A distance measuring device comprising: a light receiving unit that repeatedly receives a reflected light pulse signal that is a light pulse signal reflected by an object; a histogram generating unit that generates a histogram that classifies the reception frequency of the reflected light pulse signal for each unit light receiving period; and a light emitting unit that repeatedly emits the light pulse signal with a pulse width that is shorter than twice the unit light receiving period.

2. The distance measuring device according to claim 1, wherein the light emitting unit repeatedly emits the optical pulse signal with a pulse width shorter than the unit light receiving period.

3. A distance measuring device comprising: a light receiving unit that repeatedly receives a reflected light pulse signal that is a light pulse signal reflected by an object; a histogram generating unit that generates a histogram in which the frequency of receiving the reflected light pulse signal is classified by unit light receiving period; and a control unit that controls the light emitting unit to select one of a plurality of pulse widths having different phases in turn and emit the light pulse signal, or to select one of a plurality of different correspondences between the reception time of the reflected light pulse signal received by the light receiving unit and a plurality of unit light receiving periods in the histogram in turn, or to select the plurality of correspondences in parallel.

4. A distance measuring device according to claim 3, comprising the light emitting unit which selects in turn a plurality of pulse widths each having a different phase and emits the optical pulse signal, or which intermittently emits the optical pulse signal having a pulse width of the same phase.

5. A distance measuring device as described in claim 4, further comprising an emission timing control section that selects one of a plurality of pulse widths having different phases in turn, and the light emitting section emits the optical pulse signal at the pulse width selected by the emission timing control section.

6. The distance measuring device of claim 5, wherein the light emission timing control unit selects each of the plurality of pulse widths in turn a predetermined number of times, the light emission unit repeats the operation of emitting the light pulse signal of the pulse width selected by the light emission timing control unit a predetermined number of times, the light receiving unit repeats the operation of receiving the reflected light pulse signal corresponding to the light pulse signal emitted for each of the plurality of pulse widths a predetermined number of times, and the histogram generation unit generates the histogram based on the reflected light pulse signal corresponding to the light pulse signal emitted by selecting each of the plurality of pulse widths a predetermined number of times.

7. The distance measuring device according to claim 5, wherein the light emission timing control section switches the selection of the plurality of pulse widths in turn for each light emission operation of the light emitting section.

8. The distance measuring device according to claim 5, wherein the light emission timing control section shifts the phases of the plurality of pulse widths at equal intervals.

9. The distance measuring device according to claim 8, wherein the light emission timing control section shifts the phases of the plurality of pulse widths by the same phase amount that is shorter than the unit light receiving period.

10. The distance measuring device according to claim 3, wherein the plurality of pulse widths have the same time width.

11. The distance measuring device according to claim 10, wherein the plurality of pulse widths include n (n is an integer of 1 or greater) pulse widths whose phases are earlier than a reference pulse width, and the n pulse widths whose phases are later than the reference pulse width.

12. The distance measuring device according to claim 3, wherein the plurality of pulse widths include two or more pulse widths having different time widths.

13. The distance measuring device according to claim 12, wherein the plurality of pulse widths include n (n is an integer of 1 or greater) pulse widths that are shorter than a reference pulse width and the n pulse widths that are longer than the reference pulse width, and the n pulse widths that are shorter than the reference pulse width and the n pulse widths that are longer than the reference pulse width have the same center of gravity.

14. The distance measuring device according to claim 1, further comprising: a synchronization control unit that synchronizes the light receiving unit and the light emitting unit; and a delay circuit that delays the synchronization signal output by the synchronization control unit by a period shorter than the unit light receiving period for each light emitting operation of the light emitting unit and transmits the delayed signal to the light emitting unit.

15. A distance measuring device as described in claim 3, further comprising a light-receiving time allocation unit that selects in turn one of a plurality of different correspondences between the light-receiving times of the reflected light pulse signals repeatedly received by the light-receiving unit and a plurality of the unit light-receiving periods contained in the histogram, and the histogram generation unit generates the histogram based on the correspondence selected by the light-receiving time allocation unit.

16. The distance measuring device of claim 15, wherein the light-receiving time allocation unit selects each of the plurality of correspondences in rotation a predetermined number of times, and the histogram generation unit allocates the light-receiving time to a plurality of the unit light-receiving periods for each of the plurality of correspondences selected in rotation a predetermined number of times to generate the histogram.

17. The distance measuring device according to claim 15, wherein the unit light-receiving periods corresponding to the light-receiving times are shifted at equal intervals in the plurality of associations.

18. The distance measuring device of claim 15, wherein the multiple correspondences include n (n is an integer of 1 or more) correspondences in which the unit light-reception period corresponding to the light-reception time is earlier than a reference correspondence between the light-reception time and the multiple unit light-reception periods in the histogram, and the n correspondences in which the unit light-reception period corresponding to the light-reception time is later than the reference correspondence.

19. The distance measuring device according to claim 15, wherein the light-reception time allocation unit generates the plurality of associations between the light-reception times and the plurality of unit light-reception periods by varying the associations between the light-reception times and the plurality of unit light-reception periods by a time width shorter than the unit light-reception period.

20. A distance measurement method comprising: repeatedly receiving a reflected light pulse signal obtained by reflecting a light pulse signal from an object; generating a histogram in which the frequency of receiving the reflected light pulse signal is classified by unit light-receiving period; and selecting one of a plurality of pulse widths having different phases in turn to emit the light pulse signal; selecting one of a plurality of different correspondences between the receiving time of the reflected light pulse signal and a plurality of unit light-receiving periods in the histogram in turn; or selecting the plurality of correspondences in parallel.

Images