Distance measuring device, distance measuring method, and movable body

Abstract

To provide a distance measuring device capable of suppressing interference with other distance measuring devices while suppressing a reduction in a frame rate.SOLUTION: A distance measuring device includes a light emission control part for controlling a light emission part for emitting pulse light, a light reception part for detecting reflection light emitted from the light emission part and caused by an object existing in a measurement object area and converting the reflection light into a pulse signal, an exposure period setting part for setting an exposure period for detecting the reflection light, and a frequency distribution generation part for generating frequency distribution information obtained by associating a count value that counts the number of pulse signals with the exposure period. The light emission control part controls a light emission interval of the pulse light. A plurality of light emission intervals include a first light emission interval and a second light emission interval having length different from length of the first light emission interval. At least one of the first light emission interval and the second light emission interval is shorter than a measurement period since the pulse signal is emitted until the reflection light due to the pulse light can be detected.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a distance measuring device, a distance measuring method, and a moving object. [Background technology]

[0002] A conventional distance measurement method known as the Time of Flight (TOF) method is known as one of the distance measurement methods for measuring the distance to an object using light. The TOF method measures the distance to an object based on the time between emitting light toward the object and detecting the light reflected by the object. In an environment where multiple similar distance measurement devices exist, the light emission interval of one distance measurement device may be the same as the light emission interval of another distance measurement device. In this case, there is a problem of interference between devices, where light emitted by another distance measurement device may be mistakenly recognized as light reflected from the object. To solve this problem, the laser radar device disclosed in Patent Document 1 randomly sets the timing of emitting pulsed light from a light projection unit to the object at a distance measurement cycle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-158894 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the laser radar device disclosed in Patent Document 1, when the timing of projecting pulsed light is randomly set, the light projection interval is widened from the shortest light projection interval, which may result in a decrease in frame rate.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a distance measuring device, a distance measuring method, and a moving body that can suppress interference with other distance measuring devices while suppressing a decrease in frame rate. [Means for solving the problem]

[0006] According to one disclosure of the present specification, there is provided a distance measuring device comprising: an emission control unit that controls an emission unit that emits pulsed light; a light receiving unit that detects light emitted from the emission unit and reflected by an object in a measurement area and converts it into a pulse signal; an exposure period setting unit that sets an exposure period for detecting the reflected light; and a frequency distribution generation unit that generates frequency distribution information in which a count value that counts the number of pulse signals corresponds to the exposure period, wherein the emission control unit controls the emission interval of the pulsed light, and the multiple emission intervals include a first emission interval and a second emission interval having a length different from that of the first emission interval, and at least one of the first emission interval and the second emission interval is shorter than the measurement period from when the pulsed light is emitted until the reflected light caused by the pulsed light can be detected.

[0007] According to one disclosure of the present specification, there is provided a distance measurement method comprising an emission control step of controlling a light emitting unit that emits pulsed light; a light receiving step of detecting light emitted from the light emitting unit and reflected by an object in a measurement area and converting the light into a pulse signal; an exposure period setting step of setting an exposure period for detecting the reflected light; and a frequency distribution generating step of generating frequency distribution information in which a count value obtained by counting the number of pulse signals corresponds to the exposure period, wherein the emission control step controls the emission interval of the pulsed light, and the plurality of emission intervals include a first emission interval and a second emission interval having a length different from that of the first emission interval, and at least one of the first emission interval and the second emission interval is shorter than the measurement period from when the pulsed light is emitted until the reflected light caused by the pulsed light can be detected. [Effects of the Invention]

[0008] According to the present invention, it is possible to realize a distance measuring device, a distance measuring method, and a moving body that can suppress a decrease in frame rate while suppressing interference with other distance measuring devices. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a hardware block diagram showing an example of the configuration of a distance measuring device according to a first embodiment. [Figure 2] 1 is a functional block diagram showing an example of the configuration of a light emitting device, a light receiving device, and a signal processing device according to a first embodiment. [Figure 3] 3 is a diagram illustrating a frame period, a sub-frame period, and a micro-frame period according to the first embodiment. FIG. [Figure 4] 4 is a timing chart showing an example of control of a first exposure period and a light emission interval according to the first embodiment. [Figure 5] 6 is a histogram showing the relationship between the first exposure period and the count value of the pulse signal according to the first embodiment. [Figure 6] 6 is a timing chart showing an example of control of a second exposure period and a light emission interval according to the first embodiment. [Figure 7] 10 is a histogram showing the relationship between the second exposure period and the count value of the pulse signal according to the first embodiment. [Figure 8] 10 is a timing chart showing an example of control of a first exposure period and a light emission interval according to the second embodiment. [Figure 9] 10 is a histogram showing the relationship between the first exposure period and the count value of the pulse signal according to the second embodiment. [Figure 10] 13 is a histogram showing the relationship between the first exposure period and the count value of the pulse signal according to a comparative example of the third embodiment. [Figure 11] 11 is a timing chart showing an example of control of a first exposure period and a light emission interval according to the third embodiment. [Figure 12] 11 is a histogram showing the relationship between the first exposure period and the count value of the pulse signal according to the third embodiment. [Figure 13] FIG. 10 is a diagram illustrating an example of the configuration of a moving body according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] A distance measuring device and a distance measuring method according to a first embodiment will be described. The distance measuring device described in this embodiment is a device that uses technology such as LiDAR (Light Detection and Ranging). This distance measuring device measures the distance from the distance measuring device to an object based on the time difference between when light is emitted from a light emitting device toward a measurement target area and when the light reflected by the object included in the measurement target area is received by a light receiving device. This distance measuring device is a so-called time gate type device that switches an exposure period (gate period) according to the distance and measures the distance to the object based on information about the exposure period during which reflected light from the object is received.

[0011] Fig. 1 is a hardware block diagram showing an example configuration of a distance measuring device 100. As shown in Fig. 1, the distance measuring device 100 includes a light emitting device 1, a light receiving device 2, and a signal processing device 3. The light emitting device 1, the light receiving device 2, and the signal processing device 3 are connected to each other.

[0012] FIG. 2 is a functional block diagram showing an example configuration of a light-emitting device 1, a light-receiving device 2, and a signal processing device 3. The light-emitting device 1 is a device that emits light such as laser light, and as shown in FIG. 2, includes a light-emitting unit 11. The light-emitting unit 11 includes a light-emitting element (not shown) and serves to emit pulsed light such as laser light emitted from the light-emitting element toward a measurement target area including an object OJ. The light-emitting element constituting the light-emitting unit 11 may be an element capable of high-speed modulation, such as an LED (Light Emitting Diode) or an LD (Laser Diode). The light-emitting element may be a vertical cavity surface-emitting laser (VCSEL) or a surface-emitting element having such elements arranged in an array. The light-emitting unit 11 is preferably configured to emit a uniform amount of light toward the measurement target area, and may further include an optical element, such as a lens, for optically converting the light emitted from the light-emitting element and emitting the light toward the measurement target area.

[0013] The light-receiving device 2 is a device that receives light and includes a light-receiving unit 21. The light-receiving unit 21 includes one or more light-receiving elements (not shown) and serves to receive light incident from the measurement target area. The multiple light-receiving elements constituting the light-receiving unit 21 are arranged two-dimensionally, for example, in a matrix, and measure the distance to multiple points two-dimensionally by receiving light reflected from the object OJ. Examples of such light-receiving elements include a CMOS (Complementary Metal-Oxide-Semiconductor) sensor and a SPAD (Single Photon Avalanche Diode) sensor. In the case of a SPAD sensor, one pulse is generated in response to one photon incident on an avalanche photodiode. The light incident on the light-receiving unit 21 may include ambient light such as sunlight as well as light reflected by the object OJ in the measurement target area. The light receiving unit 21 detects an optical signal including light emitted from the light emitting unit 11 and reflected by an object OJ in the measurement area, converts it into a pulse signal (electrical signal), and outputs it to the signal processing device 3. The light receiving unit 21 may be configured to further include an optical element, such as a lens, for efficiently guiding the reflected light to the light receiving element.

[0014] The signal processing device 3 controls the light emission interval of the light emitted from the light-emitting device 1 and processes the pulse signal output from the light-receiving device 2. The signal processing device 3 may include a processor that performs arithmetic processing of the digital signal, a memory that stores the digital signal, etc. The signal processing device 3 may be an integrated circuit such as an FPGA (Field-Programmable Gate Array) or an ISP (Image Signal Processor). The signal processing device 3 includes an emission control unit 31, an exposure period setting unit 32, a frequency distribution generation unit 33, a peak detection unit 34, and an output unit 35. The emission control unit 31 is connected to the light-emitting unit 11 and the exposure period setting unit 32. The exposure period setting unit 32 is connected to the light-receiving unit 21, the emission control unit 31, and the frequency distribution generation unit 33. The frequency distribution generation unit 33 is connected to the light-receiving unit 21, the exposure period setting unit 32, and the peak detection unit 34. The peak detection unit 34 is connected to the frequency distribution generation unit 33 and the output unit 35. The output section 35 is connected to the peak detection section 34 and an external device (not shown).

[0015] The light emission control unit 31 has a role of controlling the light emission interval of the light emitting unit 11. The light emission control unit 31 outputs a light emission control signal that controls the timing of light emission to the light emitting unit 11, and controls the light emission interval of the light emitted from the light emitting unit 11.

[0016] The exposure period setting unit 32 has a role of setting one of a plurality of exposure periods determined according to the time from when the light is emitted until when it is detected, for the light receiving unit 21, for each emission of pulsed light. Here, the exposure period is a period during which a signal is generated based on the incident light in the light receiving unit 21. The exposure period setting unit 32 generates an exposure control signal that controls the start and end timing of the exposure period in the light receiving unit 21, and outputs the generated exposure control signal to the light receiving unit 21.

[0017] The frequency distribution generating unit 33 has a role of generating frequency distribution information. The frequency distribution generating unit 33 has a counter that counts pulse signals, and counts the number of pulse signals for each exposure period based on the exposure period information output from the exposure period setting unit 32 and the pulse signals output from the light receiving unit 21. The frequency distribution generating unit 33 then generates frequency distribution information in which the count value obtained by counting the number of pulse signals corresponds to the exposure period. That is, the frequency distribution generating unit 33 uses the exposure period as a class and the count value obtained by counting the number of pulse signals as a frequency, and generates frequency distribution information in which the class corresponds to the frequency. The frequency distribution generating unit 33 outputs the generated frequency distribution information to the peak detecting unit 34.

[0018] The peak detection unit 34 has the role of detecting the class with the maximum frequency (peak) from the frequency distribution information. The light incident on the light receiving unit 21 may include ambient light such as sunlight in addition to light reflected by the object OJ. Therefore, the peak detection unit 34 detects peaks from the frequency distribution information and identifies the class (exposure period) corresponding to the frequency of the peak. The identified exposure period is time information corresponding to the flight time of light from when the light emitter 11 emits light toward the measurement target area until the light reflected by the object OJ included in the measurement target area is received by the light receiving unit 21. The peak detection unit 34 outputs exposure period information indicating the identified exposure period to the output unit 35.

[0019] The output unit 35 has a role of outputting to an external device the exposure period information output from the peak detection unit 34. The output unit 35 outputs the exposure period information to the external device, for example, every time one or more frame periods described below have elapsed.

[0020] The external device has a role of calculating the distance, and calculates the distance from the distance measuring device 100 to the object OJ based on the exposure period information output from the output unit 35.

[0021] Next, various periods will be described using FIG. 3. FIG. 3 is a diagram illustrating a frame period, a subframe period, and a microframe period according to this embodiment. FIG. 3 illustrates a frame period for acquiring exposure period information corresponding to one distance measurement result, a subframe period for acquiring subframes used to generate the exposure period information, and a microframe period for acquiring microframes used to generate the subframes. These periods are schematically illustrated by arranging blocks horizontally. The horizontal direction in FIG. 3 indicates the passage of time, and one block represents one frame period, one subframe period, or one microframe period. FIG. 3 also illustrates an emission control signal for controlling the emission period of the light-emitting unit 11 and an exposure control signal for controlling the exposure period of the light-receiving unit 21.

[0022] 3, multiple frame periods FL_1, FL_2, ..., FL_n are shown in the "distance measurement period." "FL_1" indicates the first frame period, "FL_2" indicates the second frame period, and "FL_n" indicates the n-th frame period (n is an integer equal to or greater than 3).

[0023] One frame period is made up of multiple subframe periods. The "frame period" in Fig. 3 shows multiple subframe periods SF1_1, SF1_2, ..., SF1_p included in the first frame period FL_1. "SF1_1" indicates the first subframe period, which is the first subframe period, "SF1_2" indicates the second subframe period, which is the second subframe period, and "SF1_p" indicates the pth subframe period, which is the pth subframe period. In this embodiment, the number of subframe periods in the first frame period FL_1 is p (p is an integer greater than or equal to 3).

[0024] One subframe period is made up of multiple microframe periods. Here, a microframe period is a period during which the light-emitting unit 11 can emit a single pulse of light and the light-receiving unit 21 can detect incident light for a predetermined exposure period. By repeatedly providing microframe periods, reflected light can be received during each exposure period.

[0025] The "subframe period" in FIG. 3 shows multiple microframe periods MF1_1, MF1_2, ..., MF1_q included in the first subframe period SF1_1. "MF1_1" indicates the first microframe period, which is the first microframe period, and "MF1_2" indicates the second microframe period, which is the second microframe period. "MF_q" indicates the qth microframe period, which is the qth microframe period. In this embodiment, the number of microframe periods in the first subframe period SF1_1 is q (q is an integer greater than or equal to 3). This number q of microframe periods corresponds to the number of times the light reception results are accumulated.

[0026] Similarly, multiple microframe periods MF2_1, MF2_2, ..., MF2_r included in the second subframe period SF1_2 are shown. "MF2_1" indicates the first microframe period, "MF2_2" indicates the second microframe period, and "MF_r" indicates the rth microframe period. In this embodiment, the number of microframe periods in the second subframe period SF1_2 is r (r is an integer greater than or equal to 3). This number r of microframes corresponds to the number of times the light reception results are accumulated.

[0027] 3 indicate the light-emitting control signal input to the light-emitting unit 11 and the exposure control signal input to the light-receiving unit 21 during one microframe period. The light-emitting unit 11 emits light during the period when the light-emitting control signal output from the light-emitting control unit 31 is at a high level. The light-receiving unit 21 detects incident light during the exposure period when the exposure control signal output from the exposure period setting unit 32 is at a high level.

[0028] In the first microframe period MF1_1, the light-emitting unit 11 emits light during the first light-emitting period L1_1, and the light-receiving unit 21 receives light during the first exposure period E1_1. In the second microframe period MF1_2, the light-emitting unit 11 emits light during the second light-emitting period L1_2, and the light-receiving unit 21 receives light during the second exposure period E1_2. The light-emitting unit 11 emits light with a light-emitting interval between the first light-emitting period L1_1 and the second light-emitting period L1_2. Because the first microframe period MF1_1 and the second microframe period MF1_2 are included in the same first subframe period SF1_1, the first exposure period E1_1 and the second exposure period E1_2 are set to the same timing from light emission. In other words, the length of the period T_1 from the start of the first light-emitting period L1_1 to the start of the first exposure period E1_1 is the same as the length of the period T_1 from the start of the second light-emitting period L1_2 to the start of the second exposure period E1_2. These periods T_1 correspond to the flight time of light from the light-emitting unit 11 emitting light toward the measurement target area until the reflected light reflected by the object OJ included in the measurement target area is received by the light-receiving unit 21.

[0029] Similarly, in the first microframe period MF2_1, the light-emitting unit 11 emits light during the first light-emitting period L2_1, and the light-receiving unit 21 receives light during the first exposure period E2_1. In the second microframe period MF2_2, the light-emitting unit 11 emits light during the second light-emitting period L2_2, and the light-receiving unit 21 receives light during the second exposure period E2_2. The light-emitting unit 11 emits light with a light-emitting interval between the first light-emitting period L2_1 and the second light-emitting period L2_2. Because the first microframe period MF2_1 and the second microframe period MF2_2 are included in the same second subframe period SF1_2, the first exposure period E2_1 and the second exposure period E2_2 are set to the same timing from the start of the light emission. In other words, the length of the period T_2 from the start of the first light-emitting period L2_1 to the start of the first exposure period E2_1 is the same as the length of the period T_2 from the start of the second light-emitting period L2_2 to the start of the second exposure period E2_2. These periods T_2 correspond to the time of flight of light from when light is emitted from the light-emitting unit 11 toward the measurement area until the light reflected by the object OJ included in the measurement area is received by the light-receiving unit 21. Periods T_1 and T_2 have different subframe periods, and therefore different timing from light emission. The difference between the length of period T_1 and the length of period T_2 matches the length of one exposure period, and a shift of one subframe period shifts the timing of outputting the exposure control signal by the length of one exposure period. However, the relationship between the subframe period and the timing of outputting the exposure control signal is not limited to this.

[0030] Next, an example of controlling the exposure period and the light emission interval will be described in detail. FIG. 4 is a timing chart showing an example of controlling the first exposure period and the light emission interval according to this embodiment. The measurement period Q shown in FIG. 4 is the period from when pulsed light is emitted until reflected light due to the pulsed light can be detected. The measurement period Q is long enough so that the reflected light due to the pulsed light is sufficiently weak so as not to affect other distance measurement results. In this embodiment, the measurement period Q is a period obtained by multiplying the exposure period by an integer (e.g., 10 times). That is, the measurement period Q is a period equivalent to the length of 10 exposure periods ("1" to "10"). The numbers "1" to "10" shown in FIG. 4 indicate values ​​proportional to the distance from when light is emitted from the light-emitting unit 11 toward the measurement target area to when the reflected light reflected by the object OJ included in the measurement target area is received by the light-receiving unit 21. These numbers "1" to "10" can also be considered to be values ​​proportional to the time of flight of light, such as the above-mentioned periods T_1 and T_2. During the exposure periods "1" to "10", the distance to the object OJ can be measured based on the count value obtained by counting the number of pulse signals generated in response to the incidence of light during each exposure period.

[0031] The exposure period setting unit 32 sets one of the exposure periods "1" to "10" (for example, exposure period "1") for each of the plurality of microframe periods in a predetermined subframe period. Thereafter, when moving to the next subframe period, the exposure period setting unit 32 switches to another exposure period (for example, exposure period "2") from the exposure periods "1" to "10" and sets the post-switching exposure period "2" for each of the plurality of microframe periods. The exposure period setting unit 32 performs the same process until all exposure periods have been set.

[0032] 4 illustrates an example in which light reflected from an object OJ located at a distance "1" is received during a first exposure period. The first sub-frame period SF1_1 illustrated in FIG. 4 is a period in which light reflected from an object OJ located at a distance "1" can be received. FIG. 4 illustrates L1_1, L1_2, L1_3, L1_4, and L1_5 as light emission periods, and E1_1, E1_2, E1_3, E1_4, and E1_5 as exposure periods. Also, MF1_1, MF1_2, MF1_3, and MF1_4 as microframe periods.

[0033] The light emission control unit 31 outputs a light emission control signal indicating that light is to be emitted in the first light emission period L1_1 to the light emission unit 11 at a predetermined timing such as when the power of the distance measuring device 100 is turned on. The light emission unit 11 emits light in the first light emission period L1_1 based on the light emission control signal output from the light emission control unit 31. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the first light emission period L1_1 to the exposure period setting unit 32.

[0034] The exposure period setting unit 32 determines a first exposure period E1_1 in the first microframe period MF1_1 for generating the first microframe. The first exposure period E1_1 is a period during which reflected light of light emitted from the light-emitting unit 11 during the first light-emitting period L1_1 can be received. Specifically, the first exposure period E1_1 is a period during which reflected light reflected from the object OJ located at a distance of "1" relative to the first light-emitting period L1_1 can be received. The exposure period setting unit 32 outputs an exposure control signal indicating the first exposure period E1_1 to the light-receiving unit 21 when the start timing of the first exposure period E1_1 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the first exposure period E1_1 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. When the reflected light is not incident on the light receiving unit 21, the light receiving unit 21 does not output a pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs exposure period information indicating that the first exposure period E1_1 has been set for the light receiving unit 21 to the frequency distribution generating unit 33.

[0035] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (first exposure period E1_1) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the first exposure period E1_1 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0036] Next, the second microframe period MF1_2 for generating the second microframe will be described. The second microframe period MF1_2 is the microframe period following the first microframe period MF1_1. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, indicating that light is to be emitted in a predetermined second light-emission period L1_2. At this time, the second light-emission period L1_2 is determined so that the light-emission interval T_11 is shorter than the measurement period Q. Here, the light-emission interval T_11 has a length equivalent to five exposure periods. The light-emission unit 11 emits light in the second light-emission period L1_2 based on the light-emission control signal output from the light-emission control unit 31. The light-emission control unit 31 outputs a light-emission notification to the exposure period setting unit 32, indicating that light emission control has been performed in the second light-emission period L1_2.

[0037] The exposure period setting unit 32 determines the second exposure period E1_2 in the second microframe period MF1_2. The second exposure period E1_2 is a period during which reflected light of light emitted from the light-emitting unit 11 during the second light-emitting period L1_2 can be received. Specifically, the second exposure period E1_2 is a period during which reflected light reflected from the object OJ located at a distance of "1" relative to the second light-emitting period L1_2 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the second exposure period E1_2 to the light-receiving unit 21 when the start timing of the second exposure period E1_2 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the second exposure period E1_2 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the second exposure period E1_2 has been set for the light receiving unit 21.

[0038] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (second exposure period E1_2) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the second exposure period E1_2 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0039] Next, the third microframe period MF1_3 for generating the third microframe will be described. The third microframe period MF1_3 is the microframe period following the second microframe period MF1_2. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, instructing it to emit light during a predetermined third light-emission period L1_3. The third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 from the second light-emission period L1_2 to the third light-emission period L1_3 is shorter than the measurement period Q and different from the length of the light-emission interval T_11. Here, the third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 is four exposure periods shorter than the measurement period Q. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_12 has a length equivalent to six exposure periods. In this way, the light-emission interval T_12 is set to a length different from the light-emission interval T_11, which corresponds to five exposure periods. Specifically, the difference between the light emission interval T_11 and the light emission interval T_12 corresponds to an integral multiple (for example, 1) of the exposure period. That is, the light emission interval T_12 is longer than the light emission interval T_11 by one exposure period. The light emission unit 11 emits light in the third light emission period L1_3 based on the light emission control signal output from the light emission control unit 31. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the third light emission period L1_3 to the exposure period setting unit 32.

[0040] The exposure period setting unit 32 determines a third exposure period E1_3 in the third microframe period MF1_3. The third exposure period E1_3 is a period during which reflected light of light emitted from the light-emitting unit 11 during the third light-emitting period L1_3 can be received. Specifically, the third exposure period E1_3 is a period during which reflected light reflected from the object OJ located at a distance of "1" relative to the third light-emitting period L1_3 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the third exposure period E1_3 to the light-receiving unit 21 when the start timing of the third exposure period E1_3 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the third exposure period E1_3 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the third exposure period E1_3 has been set for the light receiving unit 21.

[0041] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (third exposure period E1_3) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the third exposure period E1_3 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0042] Next, the fourth microframe period MF1_4 for generating the fourth microframe will be described. The fourth microframe period MF1_4 is the microframe period following the third microframe period MF1_3. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, indicating that light is to be emitted in a predetermined fourth light-emission period L1_4. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 from the third light-emission period L1_3 to the fourth light-emission period L1_4 is shorter than the measurement period Q and different from the length of the light-emission interval T_12. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 is shorter than the measurement period Q by five exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_13 has a length equivalent to five exposure periods. In this way, the light-emission interval T_13 is different from the light-emission interval T_12 but is the same as the light-emission interval T_11. The light emitting unit 11 emits light in the fourth light emitting period L1_4 based on the light emitting control signal output from the light emitting control unit 31. The light emitting control unit 31 outputs a light emitting notification indicating that light emitting control has been performed in the fourth light emitting period L1_4 to the exposure period setting unit 32.

[0043] The exposure period setting unit 32 determines a fourth exposure period E1_4 in the fourth microframe period. The fourth exposure period E1_4 is a period during which reflected light of light emitted from the light-emitting unit 11 during the fourth light-emitting period L1_4 can be received. Specifically, the fourth exposure period E1_4 is a period during which reflected light reflected from the object OJ located at a distance of "1" relative to the fourth light-emitting period L1_4 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the fourth exposure period E1_4 to the light-receiving unit 21 when the start timing of the fourth exposure period E1_4 arrives based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the fourth exposure period E1_4 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the fourth exposure period E1_4 has been set for the light receiving unit 21.

[0044] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (fourth exposure period E1_4) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the fourth exposure period E1_4 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0045] Next, a fifth microframe period (not shown) for generating the fifth microframe will be described. The fifth microframe period is the microframe period following the fourth microframe period MF1_4. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, instructing it to emit light in a predetermined fifth light-emission period L1_5. The fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 from the fourth light-emission period L1_4 to the fifth light-emission period L1_5 is shorter than the measurement period Q and different from the length of the light-emission interval T_13. Here, the fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 is four exposure periods shorter than the measurement period Q. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_14 has a length equivalent to six exposure periods. The light-emission interval T_14 is different from the lengths of the light-emission intervals T_11 and T_13, but is the same as the length of the light-emission interval T_12. In this way, the light emission control unit 31 controls the light emission interval so that the first light emission interval (light emission intervals T_11, T_13) and the second light emission interval (light emission intervals T_12, T_14) whose length is different from that of the first light emission interval alternate with each other. In this way, the light emission control unit 31 periodically changes the light emission interval. The light emission unit 11 emits light in the fifth light emission period L1_5 based on the light emission control signal output from the light emission control unit 31. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the fifth light emission period L1_5 to the exposure period setting unit 32.

[0046] The exposure period setting unit 32 determines a fifth exposure period E1_5 in the fifth microframe period. The fifth exposure period E1_5 is a period during which reflected light of light emitted from the light-emitting unit 11 during the fifth light-emitting period L1_5 can be received. Specifically, the fifth exposure period E1_5 is a period during which reflected light reflected from the object OJ located at a distance of "1" relative to the fifth light-emitting period L1_5 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the fifth exposure period E1_5 to the light-receiving unit 21 when the start timing of the fifth exposure period E1_5 arrives based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the fifth exposure period E1_5 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the fifth exposure period E1_5 has been set for the light receiving unit 21.

[0047] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (fifth exposure period E1_5) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the fifth exposure period E1_5 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0048] By setting the light-emission interval T_11 to be shorter than the measurement period Q, the second exposure period E1_2 may also receive reflected light from the object OJ located at a distance of "6" relative to the first light-emission period L1_1. Similarly, the third exposure period E1_3 may also receive reflected light from the object OJ located at a distance of "7" relative to the second light-emission period L1_2. Furthermore, the fourth exposure period E1_4 may also receive reflected light from the object OJ located at a distance of "6" relative to the third light-emission period L1_3. Furthermore, the fifth exposure period E1_5 may also receive reflected light from the object OJ located at a distance of "7" relative to the fourth light-emission period L1_4.

[0049] In the first sub-frame period SF1_1, following the above-mentioned fifth micro-frame period, the same process is repeated up to the q-th micro-frame period MF1_q (q is an integer equal to or greater than 6). In this way, in the first sub-frame period SF1_1, the micro-frame period is repeated q times, and multiple (q) exposure periods are set in which reflected light reflected from the object OJ at a distance of "1" can be received. Furthermore, in the first sub-frame period SF1_1, the light emission intervals T_11, T_12, T_13, T_14, etc. are set to be shorter than the measurement period Q. As a result, multiple exposure periods in which reflected light reflected from the objects OJ at distances of "6" and "7" can be received are also set.

[0050] FIG. 5 shows a frequency distribution representing the relationship between the first exposure period and the count value of the pulse signal. For the sake of explanation, it is assumed that only light reflected from the object OJ is received. The frequency distribution generating unit 33 generates frequency distribution information representing the relationship between the exposure periods during which light reflected from the object OJ at distances of "1," "6," and "7" can be received and the count value of the pulse signal for each exposure period, as shown in FIG. 5. A count for distance "1" occurs for each light emission, whereas counts for distances "6" and "7" occur less frequently than for distance "1." This is because the light-emitting unit 11 emits light at two different light-emitting intervals (first light-emitting interval and second light-emitting interval), which distributes the count of the pulse signal due to self-interference. Specifically, the light-emitting unit 11 emits light at two different light-emitting intervals: first light-emitting intervals T_11 and T_13, which correspond to the length of five exposure periods, and second light-emitting intervals T_12 and T_14, which correspond to the length of six exposure periods. This is because the count of pulse signals due to self-interference is distributed between two distances: "6" and "7." If the light-emitting unit 11 were to emit light at one of the first and second light-emitting intervals, the count of pulse signals due to self-interference would be concentrated at either the distance "6" or the distance "7," and would not change from the count value for the distance "1." From the second sub-frame period SF1_2 to the p-th sub-frame period SF1_p, reflected light from the object OJ located at the distance "1" is not received. Therefore, when the distance to the object OJ is "1," no counts other than the distances "1," "6," and "7" are generated. The peak detection unit 34 detects a peak from the frequency distribution information shown in FIG. 5 at the end of the first frame period FL_1 and identifies the class (exposure period "1") corresponding to the frequency of the peak.

[0051] Next, an example will be described in which light reflected from an object OJ located at a distance "2" is received during the second exposure period. FIG. 6 is a timing chart showing an example of control of the second exposure period and the light emission interval. The second sub-frame period SF1_2 shown in FIG. 6 is executed after the first sub-frame period SF1_1, and is a period during which light reflected from an object OJ located at a distance "2" can be received. FIG. 6 illustrates L2_1, L2_2, L2_3, L2_4, and L2_5 as light emission periods, and E2_1, E2_2, E2_3, E2_4, and E2_5 as exposure periods. MF2_1, MF2_2, MF2_3, and MF2_4 are also shown as micro-frame periods.

[0052] The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11 instructing the light-emitting unit 11 to emit light in a predetermined first light-emission period L2_1 in the second sub-frame period SF1_2. The light-emitting unit 11 emits light in the first light-emission period L2_1 based on the light-emission control signal output from the light-emission control unit 31. The light-emission control unit 31 outputs a light-emission notification to the exposure period setting unit 32 indicating that light emission control has been performed in the first light-emission period L2_1.

[0053] The exposure period setting unit 32 determines a first exposure period E2_1 in the first microframe period MF2_1 for generating the first microframe. The first exposure period E2_1 is a period during which reflected light of light emitted from the light-emitting unit 11 during the first light-emitting period L2_1 can be received. Specifically, the first exposure period E2_1 is a period during which reflected light reflected from the object OJ located at a distance of "2" relative to the first light-emitting period L2_1 can be received. The exposure period setting unit 32 outputs an exposure control signal indicating the first exposure period E2_1 to the light-receiving unit 21 when the start timing of the first exposure period E2_1 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the first exposure period E2_1 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. When the reflected light is not incident on the light receiving unit 21, the light receiving unit 21 does not output a pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs exposure period information indicating that the first exposure period E2_1 has been set for the light receiving unit 21 to the frequency distribution generating unit 33.

[0054] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (first exposure period E2_1) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the first exposure period E2_1 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0055] Next, the second microframe period MF2_2 for generating the second microframe will be described. The second microframe period MF2_2 is the microframe period following the first microframe period MF2_1. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, indicating that light is to be emitted during a predetermined second light-emission period L2_2. At this time, the second light-emission period L2_2 is determined so that the length of the light-emission interval T_21 is five exposure periods shorter than the measurement period Q, as in the case of the first subframe period SF1_1. That is, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_21 has a length equivalent to five exposure periods. The light-emitting unit 11 emits light during the second light-emission period L2_2 based on the light-emission control signal output from the light-emission control unit 31. The light-emission control unit 31 outputs a light-emission notification to the exposure period setting unit 32, indicating that light emission control has been completed during the second light-emission period L2_2.

[0056] The exposure period setting unit 32 determines the second exposure period E2_2 in the second microframe period MF2_2. The second exposure period E2_2 is a period during which reflected light of light emitted from the light-emitting unit 11 during the second light-emitting period L2_2 can be received. Specifically, the second exposure period E2_2 is a period during which reflected light reflected from the object OJ located at a distance of "2" relative to the second light-emitting period L2_2 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the second exposure period E2_2 to the light-receiving unit 21 when the start timing of the second exposure period E2_2 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the second exposure period E2_2 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the second exposure period E2_2 has been set for the light receiving unit 21.

[0057] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (second exposure period E2_2) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the second exposure period E2_2 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0058] Next, the third microframe period MF2_3 for generating the third microframe will be described. The third microframe period MF2_3 is the microframe period following the second microframe period MF2_2. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, instructing it to emit light during a predetermined third light-emission period L2_3. The third light-emission period L2_3 is determined so that the length of the light-emission interval T_22 from the second light-emission period L2_2 to the third light-emission period L2_3 is shorter than the measurement period Q and different from the length of the light-emission interval T_21. Here, similar to the first subframe period SF1_1, the third light-emission period L2_3 is determined so that the length of the light-emission interval T_22 is four exposure periods shorter than the measurement period Q. That is, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_22 has a length equivalent to six exposure periods. In this way, the light-emission interval T_22 is set to a length different from the light-emission interval T_21, which corresponds to five exposure periods. That is, the light emission interval T_22 is longer than the light emission interval T_21 by one exposure period. The light emission unit 11 emits light in the third light emission period L2_3 based on the light emission control signal output from the light emission control unit 31. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the third light emission period L2_3 to the exposure period setting unit 32.

[0059] The exposure period setting unit 32 determines a third exposure period E2_3 in the third microframe period MF2_3. The third exposure period E2_3 is a period during which reflected light of light emitted from the light-emitting unit 11 during the third light-emitting period L2_3 can be received. Specifically, the third exposure period E2_3 is a period during which reflected light reflected from the object OJ located at a distance of "2" relative to the third light-emitting period L2_3 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the third exposure period E2_3 to the light-receiving unit 21 when the start timing of the third exposure period E2_3 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the third exposure period E2_3 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the third exposure period E2_3 has been set for the light receiving unit 21.

[0060] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (third exposure period E2_3) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the third exposure period E2_3 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0061] Next, the fourth microframe period MF2_4 for generating the fourth microframe will be described. The fourth microframe period MF2_4 is the microframe period following the third microframe period MF2_3. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, instructing it to emit light during a predetermined fourth light-emission period L2_4. The fourth light-emission period L2_4 is determined so that the length of the light-emission interval T_23 from the third light-emission period L2_3 to the fourth light-emission period L2_4 is shorter than the measurement period Q and different from the length of the light-emission interval T_22. Here, the fourth light-emission period L2_4 is determined so that the length of the light-emission interval T_23 is shorter than the measurement period Q by five exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_23 has a length equivalent to five exposure periods. In this way, the light-emission interval T_23 is different from the light-emission interval T_22 but is the same as the light-emission interval T_21. The light emitting unit 11 emits light in the fourth light emitting period L2_4 based on the light emitting control signal output from the light emitting control unit 31. The light emitting control unit 31 outputs a light emitting notification indicating that light emitting control has been performed in the fourth light emitting period L2_4 to the exposure period setting unit 32.

[0062] The exposure period setting unit 32 determines a fourth exposure period E2_4 in the fourth microframe period. The fourth exposure period E2_4 is a period during which reflected light of light emitted from the light-emitting unit 11 during the fourth light-emitting period L2_4 can be received. Specifically, the fourth exposure period E2_4 is a period during which reflected light reflected from the object OJ located at a distance of "2" relative to the fourth light-emitting period L2_4 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the fourth exposure period E2_4 to the light-receiving unit 21 when the start timing of the fourth exposure period E2_4 arrives, based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the fourth exposure period E2_4 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the fourth exposure period E2_4 has been set for the light receiving unit 21.

[0063] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (fourth exposure period E2_4) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the fourth exposure period E2_4 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0064] Next, a fifth microframe period (not shown) for generating the fifth microframe will be described. The fifth microframe period is the microframe period following the fourth microframe period MF2_4. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in a predetermined fifth light-emission period L2_5. The fifth light-emission period L2_5 is determined so that the length of the light-emission interval T_24 from the fourth light-emission period L2_4 to the fifth light-emission period L2_5 is shorter than the measurement period Q and different from the length of the light-emission interval T_23. Here, the fifth light-emission period L2_5 is determined so that the length of the light-emission interval T_24 is four exposure periods shorter than the measurement period Q. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_24 has a length equivalent to six exposure periods. The light-emission interval T_24 is different from the lengths of the light-emission intervals T_21 and T_23, but is the same as the length of the light-emission interval T_22. In this way, the light emission control unit 31 controls the light emission interval so that the first light emission interval (light emission intervals T_21, T_23) and the second light emission interval (light emission intervals T_22, T_24) whose length is different from that of the first light emission interval alternate with each other. In this way, the light emission control unit 31 periodically changes the light emission interval. The light emission unit 11 emits light in the fifth light emission period L2_5 based on the light emission control signal output from the light emission control unit 31. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the fifth light emission period L2_5 to the exposure period setting unit 32.

[0065] The exposure period setting unit 32 determines a fifth exposure period E2_5 in the fifth microframe period. The fifth exposure period E2_5 is a period during which reflected light of light emitted from the light-emitting unit 11 during the fifth light-emitting period L2_5 can be received. Specifically, the fifth exposure period E2_5 is a period during which reflected light reflected from the object OJ located at a distance of "2" from the fifth light-emitting period L2_5 can be received, as in the previous period. The exposure period setting unit 32 outputs an exposure control signal indicating the fifth exposure period E2_5 to the light-receiving unit 21 when the start timing of the fifth exposure period E2_5 arrives based on the light-emission notification output from the light-emission control unit 31. When reflected light reflected from the object OJ is incident during the fifth exposure period E2_5 indicated by the exposure control signal output from the exposure period setting unit 32, the light-receiving unit 21 converts the received light into an electrical pulse signal and outputs the converted pulse signal to the frequency distribution generating unit 33. The exposure period setting unit 32 outputs to the frequency distribution generating unit 33 exposure period information indicating that the fifth exposure period E2_5 has been set for the light receiving unit 21.

[0066] The frequency distribution generating unit 33 counts the pulse signals for each exposure period based on the pulse signals output from the light receiving unit 21 and the exposure period information (fifth exposure period E2_5) output from the exposure period setting unit 32. Then, the frequency distribution generating unit 33 sets the fifth exposure period E2_5 as a class, sets the count value obtained by counting the number of pulse signals as a frequency, and generates and stores frequency distribution information in which the classes and the frequencies are associated with each other.

[0067] By setting the light-emission interval T_21 to be shorter than the measurement period Q, the second exposure period E2_2 may also receive reflected light from an object OJ located at a distance of "7" relative to the first light-emission period L2_1. Similarly, the third exposure period E2_3 may also receive reflected light from an object OJ located at a distance of "8" relative to the second light-emission period L2_2. Furthermore, the fourth exposure period E2_4 may also receive reflected light from an object OJ located at a distance of "7" relative to the third light-emission period L2_3. Furthermore, the fifth exposure period E2_5 may also receive reflected light from an object OJ located at a distance of "8" relative to the fourth light-emission period L2_4.

[0068] In the second sub-frame period SF1_2, following the above-mentioned fifth micro-frame period, the same process is repeated up to the q-th micro-frame period MF2_r (r is an integer equal to or greater than 6). In this way, in the second sub-frame period SF1_2, the micro-frame period is repeated r times, and multiple (r) exposure periods are set in which reflected light reflected from the object OJ at a distance of "2" can be received. Furthermore, in the second sub-frame period SF1_2, the light emission intervals T_21, T_22, T_23, T_24, etc. are set to be shorter than the measurement period Q. As a result, multiple exposure periods in which reflected light reflected from the objects OJ at distances of "7" and "8" can be received are also set.

[0069] FIG. 7 shows a frequency distribution representing the relationship between the second exposure period and the count value of the pulse signal. For the sake of explanation, it is assumed that only light reflected from the object OJ is received. The frequency distribution generating unit 33 generates frequency distribution information representing the relationship between the exposure periods during which light reflected from the object OJ at distances of "2," "7," and "8" can be received and the count value of the pulse signal for each exposure period, as shown in FIG. 7. A count for the distance "2" occurs for each light emission, whereas counts for the other distances "7" and "8" occur less frequently than for the distance "2." This is because the light-emitting unit 11 emits light at two different light-emitting intervals (first light-emitting interval and second light-emitting interval), which distributes the count of the pulse signal due to self-interference. Specifically, the light-emitting unit 11 emits light at two different light-emitting intervals: first light-emitting intervals T_21 and T_23, which correspond to the length of five exposure periods, and second light-emitting intervals T_22 and T_24, which correspond to the length of six exposure periods. This is because the count of pulse signals due to self-interference is distributed between two distances: "7" and "8." If the light-emitting unit 11 were to emit light at one of the first and second light-emitting intervals, the count of pulse signals due to self-interference would be concentrated at either the distance "7" or the distance "8," and would not change from the count value at the distance "2." During the first sub-frame period SF1_1 and the third to p-th sub-frame periods SF1_3 to SF1_p, reflected light from the object OJ located at the distance "2" is not received. Therefore, when the distance to the object OJ is "2," no counts other than those for distances "2," "7," and "8" are generated. The peak detection unit 34 detects peaks from the frequency distribution information shown in FIG. 7 and identifies the class (exposure period "2") corresponding to the frequency of the peak.

[0070] As described above, the distance measuring device 100 according to this embodiment includes the light-emission control unit 31, the light-receiving unit 21, the exposure period setting unit 32, and the frequency distribution generating unit 33. The light-emission control unit 31 controls the light-emitting unit 11, which emits pulsed light. The light-receiving unit 21 detects light emitted from the light-emitting unit 11 and reflected by an object OJ in the measurement area and converts the light into a pulse signal. The exposure period setting unit 32 sets the exposure period for detecting the reflected light. The frequency distribution generating unit 33 generates frequency distribution information in which a count value obtained by counting the number of pulse signals corresponds to the exposure period. The light-emission control unit 31 controls the emission interval of the pulsed light. In this configuration, the multiple emission intervals include a first emission interval and a second emission interval having a length different from the first emission interval. At least one of the first emission interval and the second emission interval is shorter than the measurement period Q, which is the period from when the pulsed light is emitted until when reflected light resulting from the pulsed light can be detected. With this configuration, the distance measuring device 100 can suppress a decrease in frame rate by making the emission interval shorter than the measurement period Q. Furthermore, by including a light emission interval whose length is different from the lengths of other light emission intervals, the distance measuring device 100 can suppress interference with other distance measuring devices whose light emission intervals are constant. Furthermore, by including a light emission interval whose length is different from the lengths of other light emission intervals, the distance measuring device 100 can distribute the counting of pulse signals due to self-interference, thereby suppressing erroneous distance measurements due to self-interference.

[0071] Furthermore, in the distance measuring device 100 according to this embodiment, the light emission control unit 31 controls the light emission interval so that the first light emission interval and the second light emission interval alternate. With this configuration, the distance measuring device 100 can evenly distribute the count of pulse signals due to self-interference, and can properly detect peaks.

[0072] The distance measurement method according to this embodiment includes an emission control step, a light receiving step, an exposure period setting step, and a frequency distribution generating step. The emission control step controls the light emitter 11, which emits pulsed light. The light receiving step detects light emitted from the light emitter 11 and reflected by an object OJ in the measurement area and converts it into a pulse signal. The exposure period setting step sets an exposure period for detecting the reflected light. The frequency distribution generating step generates frequency distribution information in which a count value obtained by counting the number of pulse signals corresponds to the exposure period. The emission control step controls the emission interval of the pulsed light. The multiple emission intervals include a first emission interval and a second emission interval having a length different from the first emission interval. At least one of the first emission interval and the second emission interval is shorter than the measurement period Q from when the pulsed light is emitted until when reflected light resulting from the pulsed light can be detected. This enables the distance measurement method to suppress interference between distance measurement devices while suppressing a decrease in frame rate.

[0073] [Second embodiment] A distance measuring device 100 according to a second embodiment will be described. This embodiment differs from the distance measuring device 100 according to the first embodiment in that the length of the light emission interval is changed randomly. Note that the same components as those in the distance measuring device 100 according to the first embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0074] Figure 8 is a timing chart showing an example of control of the first exposure period and light emission interval. Figure 8 shows L1_1, L1_2, L1_3, L1_4, and L1_5 as light emission periods, E1_1, E1_2, E1_3, E1_4, and E1_5 as exposure periods, and MF1_1, MF1_2, MF1_3, and MF1_4 as microframe periods.

[0075] The light emission control unit 31 outputs a light emission control signal to the light emission unit 11 in the first microframe period MF1_1, indicating that light emission is to be performed in the first light emission period L1_1. The light emission control unit 31 also outputs a light emission notification indicating that light emission control has been performed in the first light emission period L1_1 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the first exposure period E1_1 to the light receiving unit 21 when the start timing of the first exposure period E1_1 arrives.

[0076] Next, the second microframe period MF1_2 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in the second light-emission period L1_2. Here, the second light-emission period L1_2 is determined so that the length of the light-emission interval T_11 from the first light-emission period L1_1 to the second light-emission period L1_2 is shorter than the measurement period Q. At this time, the second light-emission period L1_2 is determined randomly so that the length of the light-emission interval T_11 is an integer multiple of one exposure period. Here, determining the light-emission period randomly means determining the light-emission period randomly. By randomly determining the second light-emission period L1_2, the length of the light-emission interval T_11 is also determined randomly. Here, the second light-emission period L1_2 is determined so that the length of the light-emission interval T_11 is shorter than the measurement period Q by five exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_11 has a length equivalent to five exposure periods. The light-emission control unit 31 outputs a light-emission notification indicating that light emission control has been performed in the second light-emission period L1_2 to the exposure period setting unit 32. Based on the light-emission notification output from the light-emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the second exposure period E1_2 to the light-receiving unit 21 when the start timing of the second exposure period E1_2 arrives.

[0077] Next, the third microframe period MF1_3 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in the third light-emission period L1_3. Here, the third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 from the second light-emission period L1_2 to the third light-emission period L1_3 is shorter than the measurement period Q and different from the length of the light-emission interval T_11. At this time, the third light-emission period L1_3 is determined randomly so that the length of the light-emission interval T_12 is an integer multiple of one exposure period. By randomly determining the third light-emission period L1_3, the length of the light-emission interval T_12 is also determined randomly. Here, the third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 is three exposure periods shorter than the measurement period Q. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_12 has a length equivalent to seven exposure periods. In this way, the light emission interval T_12 has a length different from the light emission interval T_11. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the third light emission period L1_3 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the third exposure period E1_3 to the light receiving unit 21 when the start timing of the third exposure period E1_3 arrives.

[0078] Next, the fourth microframe period MF1_4 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in the fourth light-emission period L1_4. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 from the third light-emission period L1_3 to the fourth light-emission period L1_4 is shorter than the measurement period Q and different from the lengths of the light-emission intervals T_11 and T_12. At this time, the fourth light-emission period L1_4 is determined randomly so that the length of the light-emission interval T_13 is an integer multiple of one exposure period. By randomly determining the fourth light-emission period L1_4, the length of the light-emission interval T_13 is also determined randomly. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 is shorter than the measurement period Q by six exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_13 has a length equivalent to four exposure periods. In this way, the light emission interval T_13 has a length different from the light emission intervals T_11 and T_12. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the fourth light emission period L1_4 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the fourth exposure period E1_4 to the light receiving unit 21 when the start timing of the fourth exposure period E1_4 arrives.

[0079] Next, the fifth microframe period (not shown) will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, indicating that light is to be emitted in the fifth light-emission period L1_5. Here, the fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 from the fourth light-emission period L1_4 to the fifth light-emission period L1_5 is shorter than the measurement period Q and different from the lengths of the light-emission intervals T_11, T_12, and T_13. At this time, the fifth light-emission period L1_5 is determined randomly so that the length of the light-emission interval T_14 is an integer multiple of one exposure period. By randomly determining the fifth light-emission period L1_5, the length of the light-emission interval T_14 is also determined randomly. Here, the fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 is four exposure periods shorter than the measurement period Q. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_14 has a length equivalent to six exposure periods. In this way, the light emission interval T_14 has a length different from the light emission intervals T_11, T_12, and T_13. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the fifth light emission period L1_5 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the fifth exposure period E1_5 to the light receiving unit 21 when the start timing of the fifth exposure period E1_5 arrives.

[0080] By setting the light-emission interval T_11 to be shorter than the measurement period Q, the second exposure period E1_2 can also receive reflected light from the object OJ located at a distance of "6" relative to the first light-emission period L1_1. Similarly, the third exposure period E1_3 can also receive reflected light from the object OJ located at a distance of "8" relative to the second light-emission period L1_2. Furthermore, the fourth exposure period E1_4 can also receive reflected light from the object OJ located at a distance of "5" relative to the third light-emission period L1_3. Furthermore, the fifth exposure period E1_5 can also receive reflected light from the object OJ located at a distance of "7" relative to the fourth light-emission period L1_4.

[0081] In the first sub-frame period SF1_1, following the above-mentioned fifth micro-frame period, the same process is repeated up to the q-th micro-frame period MF1_q (q is an integer equal to or greater than 6). In this way, in the first sub-frame period SF1_1, the micro-frame period is repeated q times, and multiple (q) exposure periods are set in which reflected light reflected from an object OJ at a distance of "1" can be received. Furthermore, in the first sub-frame period SF1_1, the light emission intervals T_11, T_12, T_13, T_14, etc. are set randomly so as to be shorter than the measurement period Q. As a result, exposure periods in which reflected light reflected from an object OJ at a distance of "5," "6," "8," etc. can be received are also set.

[0082] FIG. 9 shows a frequency distribution representing the relationship between the first exposure period and the count value of the pulse signal. For the sake of explanation, it is assumed that only light reflected from the object OJ is received. The frequency distribution generation unit 33 generates frequency distribution information representing the relationship between the exposure periods during which light reflected from the object OJ at distances of "1," "5," "6," and "8" can be received and the count value of the pulse signal for each exposure period, as shown in FIG. 9. A count for distance "1" occurs with each light emission, whereas counts for distances "5," "6," and "8" occur less frequently than for distance "1." This is because the light-emitting unit 11 emits light at random intervals, so the counts of the pulse signal due to self-interference are distributed among distances "5," "6," and "8." The peak detection unit 34 detects peaks from the frequency distribution information shown in FIG. 9 and identifies the class (exposure period "1") corresponding to the frequency of the peak.

[0083] As described above, in the distance measuring device 100 according to this embodiment, the light emission control unit 31 randomly changes the light emission interval. This configuration allows the distance measuring device 100 to increase the number of light emission interval patterns, thereby further suppressing interference with other distance measuring devices and self-interference.

[0084] [Third embodiment] A distance measuring device 100 according to the third embodiment will now be described. This embodiment differs from the distance measuring device 100 according to the first and second embodiments in that the light emission interval is changed when there are multiple peak candidates detected by the peak detection unit 34. Note that the same components as those in the distance measuring device 100 according to the first and second embodiments are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0085] FIG. 10 shows a frequency distribution representing the relationship between the first exposure period and the count value of the pulse signal in a comparative example of this embodiment. The frequency distribution information shown in FIG. 10 was generated by the frequency distribution generator 33 when distance measurement was performed using the method shown in FIG. 4 during the first subframe period SF1_1, which is a period during which reflected light from the object OJ at a distance of "1" can be received. For the sake of explanation, it is assumed that only reflected light from the object OJ is received. As shown in FIG. 10, the frequency distribution generator 33 generates frequency distribution information representing the relationship between the exposure periods during which reflected light from the object OJ at distances of "1," "6," and "7" can be received and the count value of the pulse signal during each exposure period. In this embodiment, the first subframe period SF1_1 is assumed to consist of 100 microframe periods. FIG. 10 also shows "Th1," which indicates the maximum counter value, and "Th2," which indicates a threshold value for determining peaks in the frequency distribution information. Here, the maximum counter value Th1 is set to "64," and the threshold value Th2 for determining peaks is set to "40."

[0086] The frequency distribution information shown in FIG. 10 illustrates an example of detection when the reflected light from the object OJ is relatively strong. When the light-emitting unit 11 emits light 100 times, the light reflected from the object OJ is received 100 times during exposure period “1.” During exposure periods “6” and “7,” the light reflected from the object OJ is received half as many times (50 times) due to self-interference. As a result, the count value of the pulse signal during exposure period “1” is “100,” exceeding the maximum value Th1 of the counter. Furthermore, the count values ​​of the pulse signal during exposure periods “6” and “7” are “50,” respectively, which are less than the maximum value Th1 of the counter. Furthermore, the count values ​​of the pulse signal during exposure periods “1,” “6,” and “7” are greater than or equal to the peak determination threshold Th2. In other words, there are three peak candidates detected by the peak detection unit 34. If there are multiple peak candidates at the end of one frame period, the peak detection unit 34 outputs a notification to the light-emission control unit 31 indicating that the number of light-emission interval patterns should be increased.

[0087] The light emission control unit 31 increases the number of light emission interval patterns based on the notification output from the peak detection unit 34. In the example shown in Fig. 4, the light emission unit 11 is controlled to emit light in two light emission interval patterns: a first light emission interval T_11, T_13 corresponding to five exposure periods, and a second light emission interval T_12, T_14 corresponding to six exposure periods. In this control, since there are multiple peak candidates, the light emission control unit 31 increases the number of light emission interval patterns from two to three.

[0088] Fig. 11 is a timing chart showing an example of control of the first exposure period and light emission interval in the first sub-frame period SF1_1 when the number of light emission interval patterns is increased to three. Fig. 11 shows L1_1, L1_2, L1_3, L1_4, and L1_5 as light emission periods, and E1_1, E1_2, E1_3, E1_4, and E1_5 as exposure periods. Also shown are MF1_1, MF1_2, MF1_3, and MF1_4 as micro-frame periods.

[0089] The light emission control unit 31 outputs a light emission control signal to the light emission unit 11 during the first microframe period MF1_1, indicating that light emission is to be performed during a predetermined first light emission period L1_1. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed during the first light emission period L1_1 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the first exposure period E1_1 to the light receiving unit 21 when the start timing of the first exposure period E1_1 arrives.

[0090] Next, the second microframe period MF1_2 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in a predetermined second light-emission period L1_2. Here, the second light-emission period L1_2 is determined so that the light-emission interval T_11 from the first light-emission period L1_1 to the second light-emission period L1_2 is shorter than the measurement period Q. Here, the second light-emission period L1_2 is determined so that the light-emission interval T_11 is shorter than the measurement period Q by five exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_11 has a length equivalent to five exposure periods. The light-emission control unit 31 outputs a light-emission notification to the exposure period setting unit 32, which indicates that light emission control has been performed in the second light-emission period L1_2. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the second exposure period E1_2 to the light receiving unit 21 when the start timing of the second exposure period E1_2 arrives.

[0091] Next, the third microframe period MF1_3 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in a predetermined third light-emission period L1_3. Here, the third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 from the second light-emission period L1_2 to the third light-emission period L1_3 is shorter than the measurement period Q and different from the length of the light-emission interval T_11. Here, the third light-emission period L1_3 is determined so that the length of the light-emission interval T_12 is shorter than the measurement period Q by four exposure periods. That is, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_12 has a length equivalent to six exposure periods. In this way, the light-emission interval T_12 is set to a length different from the light-emission interval T_11, which corresponds to five exposure periods. That is, the light-emission interval T_12 is longer than the light-emission interval T_11 by one exposure period. The light-emission control unit 31 outputs a light-emission notification indicating that light emission control has been performed in the third light-emission period L1_3 to the exposure period setting unit 32. Based on the light-emission notification output from the light-emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the third exposure period E1_3 to the light-receiving unit 21 when the start timing of the third exposure period E1_3 arrives.

[0092] Next, the fourth microframe period MF1_4 will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in a predetermined fourth light-emission period L1_4. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 from the third light-emission period L1_3 to the fourth light-emission period L1_4 is shorter than the measurement period Q and different from the lengths of the light-emission intervals T_11 and T_12. Here, the fourth light-emission period L1_4 is determined so that the length of the light-emission interval T_13 is shorter than the measurement period Q by three exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_13 has a length equivalent to seven exposure periods. In this way, the light-emission interval T_13 is different from the lengths of the light-emission intervals T_11 and T_12. The light-emission control unit 31 outputs a light-emission notification to the exposure period setting unit 32, which indicates that light emission control has been performed in the fourth light-emission period L1_4. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the fourth exposure period E1_4 to the light receiving unit 21 when the start timing of the fourth exposure period E1_4 arrives.

[0093] Next, the fifth microframe period (not shown) will be described. The light-emission control unit 31 outputs a light-emission control signal to the light-emitting unit 11, which indicates that light is to be emitted in a predetermined fifth light-emission period L1_5. Here, the fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 from the fourth light-emission period L1_4 to the fifth light-emission period L1_5 is shorter than the measurement period Q and different from the lengths of the light-emission intervals T_12 and T_13. Here, the fifth light-emission period L1_5 is determined so that the length of the light-emission interval T_14 is shorter than the measurement period Q by five exposure periods. In other words, since the measurement period Q has a length equivalent to ten exposure periods, the light-emission interval T_14 has a length equivalent to five exposure periods. In this way, the light-emission interval T_14 is different from the lengths of the light-emission intervals T_12 and T_13, but is the same as the length of the light-emission interval T_11. The light emission control unit 31 outputs a light emission notification indicating that light emission control has been performed in the fifth light emission period L1_5 to the exposure period setting unit 32. Based on the light emission notification output from the light emission control unit 31, the exposure period setting unit 32 outputs an exposure control signal indicating the fifth exposure period E1_5 to the light receiving unit 21 when the start timing of the fifth exposure period E1_5 arrives.

[0094] By setting the light-emission interval T_11 to be shorter than the measurement period Q, the second exposure period E1_2 may also receive reflected light from the object OJ located at a distance of "6" relative to the first light-emission period L1_1. Similarly, the third exposure period E1_3 may also receive reflected light from the object OJ located at a distance of "7" relative to the second light-emission period L1_2. Furthermore, the fourth exposure period E1_4 may also receive reflected light from the object OJ located at a distance of "8" relative to the third light-emission period L1_3. Furthermore, the fifth exposure period E1_5 may also receive reflected light from the object OJ located at a distance of "6" relative to the fourth light-emission period L1_4.

[0095] In the first sub-frame period SF1_1, following the above-mentioned fifth micro-frame period, the same process is repeated up to the q-th micro-frame period MF1_q (q is an integer equal to or greater than 6). In this way, in the first sub-frame period SF1_1, the micro-frame period is repeated q times, and multiple (q) exposure periods are set in which reflected light reflected from the object OJ at a distance of "1" can be received. Furthermore, in the first sub-frame period SF1_1, the light emission intervals T_11, T_12, T_13, T_14, etc. are set to be shorter than the measurement period Q. As a result, multiple exposure periods in which reflected light reflected from the objects OJ at distances of "6," "7," and "8" can be received are also set.

[0096] In this embodiment, the number of light-emission interval patterns is increased from two to three. Specifically, the number of light-emission interval patterns is increased to three: light-emission intervals T_11 and T_14, which correspond to five exposure periods; light-emission interval T_12, which corresponds to six exposure periods; and light-emission interval T_13, which corresponds to seven exposure periods. As a result, as shown in FIG. 12 , in addition to receiving reflected light from the object OJ at distances of "1," light reflected from the object OJ at distances of "6," "7," and "8" is also received. In this case, if the light-emitting unit 11 emits light 100 times, the reflected light from the object OJ is received 100 times during exposure period "1," and 33 times (one-third of that) during exposure periods "6," "7," and "8." In this way, the number of exposure periods counted due to self-interference caused by setting the light-emission interval shorter than the measurement period Q is increased from two to three, thereby enabling better dispersion. As a result, the count value of the pulse signal in exposure period "1" is equal to or greater than the threshold value Th2 for peak determination. At this time, the count values ​​of the pulse signal in exposure periods "6," "7," and "8" are less than the threshold value Th2 for peak determination. In this way, there is only one peak in the frequency distribution information. This allows the peak detection unit 34 to properly identify the class (exposure period "1") corresponding to the frequency of the peak.

[0097] As described above, in the distance measuring device 100 according to this embodiment, the first light-emitting interval T_11 and the second light-emitting interval T_12 are continuous. The exposure period E1_1 in the first light-emitting interval T_11 and the exposure period E1_2 in the second light-emitting interval T_12 are included in a single measurement period Q. When multiple exposure periods are included in such a measurement period Q, the peak detection unit 34 detects a peak candidate if the count value of the number of pulse signals is equal to or greater than the threshold value Th2. If multiple peak candidates exist, the peak detection unit 34 outputs a notification to the light-emitting control unit 31 indicating that the number of light-emitting interval patterns should be increased. The light-emitting control unit 31 increases the number of light-emitting interval patterns based on the notification output from the peak detection unit 34. After increasing the number of light-emitting interval patterns, the light-emitting control unit 31 controls the light-emitting unit 11 based on the increased light-emitting interval patterns. In this way, the light-emitting control unit 31 changes the light-emitting interval based on the result of comparing the count value of the pulse signals with the threshold value Th2. With this configuration, when multiple peak candidates are detected, the distance measuring device 100 can further distribute the exposure periods counted due to self-interference. This allows the distance measuring device 100 to reduce the count value of the exposure periods counted due to self-interference. As a result, the distance measuring device 100 can properly detect the peak even when multiple peak candidates are detected when the reflected light from the object OJ is relatively strong.

[0098] [Fourth embodiment] Next, a moving body according to the fourth embodiment will be described with reference to Fig. 13. Fig. 13 is a diagram showing an example of the configuration of a moving body according to the fourth embodiment.

[0099] 13(a) shows an example of the configuration of a device mounted on a vehicle as an on-board camera. The device 300 has a distance measurement unit 303 that measures the distance to an object, and a collision determination unit 304 that determines whether or not there is a possibility of collision based on the distance measured by the distance measurement unit 303. The distance measurement unit 303 is configured from the distance measuring device 100 described in the first to third embodiments. Here, the distance measurement unit 303 is an example of a distance information acquisition means that acquires distance information to the object. In other words, the distance information is information related to the distance to the object, etc.

[0100] The device 300 is connected to a vehicle information acquisition device 310 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. The device 300 is also connected to a control ECU 320, which is a control device that outputs a control signal to generate a braking force for the vehicle based on the determination result of the collision determination unit 304. The device 300 is also connected to an alarm device 330 that issues an alarm to the driver based on the determination result of the collision determination unit 304. For example, if the collision determination unit 304 determines that a collision is highly likely, the control ECU 320 performs vehicle control to avoid a collision and mitigate damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 330 warns the user by sounding an alarm, displaying alarm information on a screen of a car navigation system, etc., or vibrating a seat belt or steering wheel. These devices of the device 300 function as a mobile object control unit that controls the operation of controlling the vehicle as described above.

[0101] In this embodiment, the device 300 measures the distance around the vehicle, for example, the front or rear. Fig. 13(b) shows the device when measuring the distance in front of the vehicle (distance measurement range 350). The vehicle information acquisition device 310, which serves as a distance measurement control means, sends an instruction to the device 300 or the distance measurement unit 303 to perform a distance measurement operation. This configuration can further improve the accuracy of distance measurement.

[0102] Although the above describes an example of control to prevent collision with other vehicles, the present invention can also be applied to control of automatic driving by following other vehicles, control of automatic driving to prevent deviation from a lane, etc. Furthermore, the present invention is not limited to vehicles such as automobiles, but can be applied to moving objects (moving devices) such as ships, aircraft, artificial satellites, industrial robots, and consumer robots. In addition, the present invention can be applied to a wide range of devices that use object recognition or biometric recognition, such as intelligent transport systems (ITS) and surveillance systems, without being limited to moving objects.

[0103] [Modified embodiment] The present invention is not limited to the above-described embodiments and can be modified in various ways. For example, an example in which part of the configuration of one embodiment is added to another embodiment, or an example in which part of the configuration of another embodiment is replaced with another embodiment, is also an embodiment of the present invention.

[0104] For example, although the present embodiment shows an example in which measurements are made for the same exposure period in one subframe, measurements may be made for multiple different exposure periods.Furthermore, the light emission intervals are not limited to the multiple light emission intervals shown in Figures 4 and 6, and other light emission intervals may also be used.

[0105] The plurality of light emission intervals may include a first light emission interval, a second light emission interval following the first light emission interval, and a third light emission interval following the second light emission interval. In this case, the light emission control unit 31 may control the light emission intervals so that the difference between the second light emission interval and the third light emission interval is greater than the difference between the first light emission interval and the second light emission interval. The light emission control unit 31 may also control the light emission intervals so that the difference between the second light emission interval and the third light emission interval is smaller than the difference between the first light emission interval and the second light emission interval.

[0106] Furthermore, although an example has been described in which all of the multiple light emission intervals are shorter than the measurement period Q, this is not limiting. For example, the multiple light emission intervals may include both light emission intervals shorter than the measurement period Q and light emission intervals longer than the measurement period Q. In other words, at least one light emission interval of the multiple light emission intervals may be longer than the measurement period Q. In this case, multiple exposure periods may not be included in one measurement period.

[0107] In addition, an example has been described in which the light emission control unit 31 changes the light emission interval based on the result of comparing the count value with the threshold value Th2, but this is not limited to this, and the light emission interval may be changed based on, for example, the frequency distribution of the count value.

[0108] Although the example of increasing the number of light emission interval patterns when multiple peaks exist at the end of one frame period has been described, this is not limiting. For example, if multiple peak candidates are detected during one frame period, the light emission control unit 31 may increase the number of light emission interval patterns without performing processing from the middle of that frame period onwards, and then move on to the next frame period. In this case, the frequency distribution generation unit 33 stops generating frequency distribution information and starts generating frequency distribution information after the light emission interval has been changed. This prevents a decrease in processing speed.

[0109] Furthermore, although an example has been described in which the measurement period Q is divided into 10 periods (exposure periods) from "1" to "10", the present invention is not limited to this and the measurement period Q may be divided into other periods.

[0110] Furthermore, while the above embodiments have been described with respect to a distance measuring device, the algorithms described in the above embodiments can also be applied to an information processing device for processing distance data indicating the distance to an object. In this case, the light emission control unit 31, exposure period setting unit 32, frequency distribution generation unit 33, peak detection unit 34, and output unit 35 of the distance measuring device 100 shown in FIG. 2 can be configured by an information processing device. The information processing device can be a device such as a personal computer including a processor (e.g., a CPU or MPU). Alternatively, the information processing device can be a circuit such as an ASIC that realizes the functions of the exposure period setting unit 32, light emission control unit 31, exposure period setting unit 32, frequency distribution generation unit 33, peak detection unit 34, and output unit 35.

[0111] Furthermore, although the example has been described in which the function of calculating the distance to the object OJ is provided in an external device, the present invention is not limited to this, and the function may be provided in the distance measuring device 100, for example.

[0112] The disclosure of the above embodiment includes the following configurations and methods. (Configuration 1) a light emission control unit that controls a light emitting unit that emits pulsed light; a light receiving unit that detects light emitted from the light emitting unit and reflected by an object in a measurement target area and converts the light into a pulse signal; an exposure period setting unit that sets an exposure period for detecting the reflected light; a frequency distribution generating unit that generates frequency distribution information in which a count value obtained by counting the number of the pulse signals is associated with the exposure period, the light emission control unit controls the light emission interval of the pulsed light, the plurality of light emitting intervals include a first light emitting interval and a second light emitting interval having a length different from a length of the first light emitting interval; A distance measuring device characterized in that at least one of the first light emission interval and the second light emission interval is shorter than the measurement period from when the pulsed light is emitted until when the reflected light caused by the pulsed light can be detected. (Configuration 2) the first light emitting interval and the second light emitting interval are continuous, 2. The distance measuring device according to configuration 1, wherein the exposure period in the first light emission interval and the exposure period in the second light emission interval are included in one measurement period. (Configuration 3) 3. The distance measuring device according to configuration 1 or 2, wherein the light emission control unit controls the light emission interval so that the first light emission interval and the second light emission interval alternate. (Configuration 4) 4. The distance measuring device according to any one of configurations 1 to 3, wherein the difference between the first light emission interval and the second light emission interval corresponds to an integer multiple of the exposure period. (Configuration 5) 5. The distance measuring device according to any one of configurations 1, 2, and 4, wherein the light emission control unit randomly changes the light emission interval. (Configuration 6) 5. The distance measuring device according to any one of configurations 1 to 4, wherein the light emission control unit periodically changes the light emission interval. (Configuration 7) the plurality of light emission intervals include a third light emission interval that follows the second light emission interval, The distance measuring device according to any one of configurations 1 to 6, wherein the light emission control unit controls the light emission interval so that the difference between the second light emission interval and the third light emission interval is greater than the difference between the first light emission interval and the second light emission interval. (Configuration 8) the plurality of light emission intervals include a third light emission interval that follows the second light emission interval, The distance measuring device according to any one of configurations 1 to 6, wherein the light emission control unit controls the light emission interval so that the difference between the second light emission interval and the third light emission interval is smaller than the difference between the first light emission interval and the second light emission interval. (Configuration 9) 9. The distance measuring device according to any one of configurations 1 to 8, wherein the light emission control unit changes the light emission interval when there are multiple candidates for the peak of the count value. (Configuration 10) 10. The distance measuring device according to any one of configurations 1 to 9, wherein the light emission control unit changes the light emission interval based on a result of comparing the count value with a predetermined threshold value. (Configuration 11) 10. The distance measuring device according to any one of configurations 1 to 9, wherein the light emission control unit changes the light emission interval based on a frequency distribution of the count value. (Configuration 12) 13. The distance measuring device according to any one of configurations 1 to 12, wherein, when there are multiple candidates for the peak of the count value, the frequency distribution generation unit stops generating the frequency distribution information, and starts generating the frequency distribution information after the light emission interval is changed. (Configuration 13) 13. The distance measuring device according to any one of configurations 1 to 12, wherein at least one of the plurality of light emission intervals is longer than the measurement period. (Configuration 14) A mobile object, a distance measuring device according to any one of configurations 1 to 13; and a control means for controlling the moving body based on the distance information acquired by the distance measuring device. (Configuration 15) a light emission control step of controlling a light emitting unit that emits pulsed light; a light receiving step of detecting light emitted from the light emitting unit and reflected by an object in a measurement target area and converting the light into a pulse signal; an exposure period setting step of setting an exposure period for detecting the reflected light; a frequency distribution generating step of generating frequency distribution information in which a count value obtained by counting the number of the pulse signals is associated with the exposure period, the light emission control step controls a light emission interval of the pulsed light; the plurality of light emitting intervals include a first light emitting interval and a second light emitting interval having a length different from a length of the first light emitting interval; A distance measuring method characterized in that at least one of the first light emission interval and the second light emission interval is shorter than the measurement period from when the pulsed light is emitted until when the reflected light caused by the pulsed light can be detected. [Explanation of symbols]

[0113] 11...Light emitting part 21...Light receiving section 31...Light emission control unit 32...Exposure period setting unit 33...Frequency distribution generator 34...Peak detector 100...Distance measuring device

Claims

1. a light emission control unit that controls a light emitting unit that emits pulsed light; a light receiving unit that detects light emitted from the light emitting unit and reflected by an object in a measurement target area and converts the light into a pulse signal; an exposure period setting unit that sets an exposure period for detecting the reflected light; a frequency distribution generating unit that generates frequency distribution information in which a count value obtained by counting the number of the pulse signals is associated with the exposure period, the light emission control unit controls the light emission interval of the pulsed light, the plurality of light emitting intervals include a first light emitting interval and a second light emitting interval having a length different from a length of the first light emitting interval; A distance measuring device characterized in that at least one of the first light emission interval and the second light emission interval is shorter than the measurement period from when the pulsed light is emitted until when the reflected light caused by the pulsed light can be detected.

2. the first light emitting interval and the second light emitting interval are continuous, 2. The distance measuring device according to claim 1, wherein the exposure period in the first light emission interval and the exposure period in the second light emission interval are included in one measurement period.

3. 2. The distance measuring device according to claim 1, wherein the light emission control unit controls the light emission interval so that the first light emission interval and the second light emission interval alternate.

4. 2. The distance measuring device according to claim 1, wherein the difference between the first light emission interval and the second light emission interval corresponds to an integral multiple of the exposure period.

5. 2. The distance measuring device according to claim 1, wherein the light emission control unit randomly changes the light emission interval.

6. 2. The distance measuring device according to claim 1, wherein the light emission control unit periodically changes the light emission interval.

7. the plurality of light emitting intervals include a third light emitting interval that follows the second light emitting interval, 2. The distance measuring device according to claim 1, wherein the light emission control unit controls the light emission interval so that the difference between the second light emission interval and the third light emission interval is greater than the difference between the first light emission interval and the second light emission interval.

8. the plurality of light emitting intervals include a third light emitting interval that follows the second light emitting interval, 2. The distance measuring device according to claim 1, wherein the light emission control unit controls the light emission interval so that the difference between the second light emission interval and the third light emission interval is smaller than the difference between the first light emission interval and the second light emission interval.

9. 2. The distance measuring device according to claim 1, wherein the light emission control unit changes the light emission interval when there are a plurality of candidates for the peak of the count value.

10. 2. The distance measuring device according to claim 1, wherein the light emission control unit changes the light emission interval based on a result of comparison between the count value and a predetermined threshold value.

11. 2. The distance measuring device according to claim 1, wherein the light emission control unit changes the light emission interval based on a frequency distribution of the count value.

12. The distance measuring device according to claim 1, characterized in that if there are multiple candidates for the peak of the count value, the frequency distribution generation unit stops generating the frequency distribution information, and starts generating the frequency distribution information after the light emission interval is changed.

13. 2. The distance measuring device according to claim 1, wherein at least one of the plurality of light emission intervals is longer than the measurement period.

14. A mobile object, The distance measuring device according to claim 1 ; and a control means for controlling the moving body based on the distance information acquired by the distance measuring device.

15. a light emission control step of controlling a light emitting unit that emits pulsed light; a light receiving step of detecting light emitted from the light emitting unit and reflected by an object in a measurement target area and converting the light into a pulse signal; an exposure period setting step of setting an exposure period for detecting the reflected light; a frequency distribution generating step of generating frequency distribution information in which a count value obtained by counting the number of the pulse signals is associated with the exposure period, the light emission control step controls a light emission interval of the pulsed light; the plurality of light emitting intervals include a first light emitting interval and a second light emitting interval having a length different from a length of the first light emitting interval; A distance measuring method characterized in that at least one of the first light emission interval and the second light emission interval is shorter than the measurement period from when the pulsed light is emitted until when the reflected light caused by the pulsed light can be detected.

Images