Distance measurement device, distance measurement method, and program

Abstract

This distance measurement device comprises: a light-emitting unit having a plurality of light-emitting elements; a light-receiving unit having a plurality of light-receiving elements; a measurement means that creates a histogram on the basis of the time until the light-receiving unit receives light which is emitted by the light-emitting unit and reflected from an object, as well as the intensity of the light received by the light-receiving unit, and measures the distance to the object; and a control means that controls the bin width of the histogram on the basis of the intensity of the light received by the light-receiving unit in the distance measurement process for measuring the distance to the object.

Description

Distance measuring device, distance measuring method, and program

[0001] This disclosure relates to the technology of measuring distance.

[0002] A distance measurement method called the Time-Of-Flight (TOF) method is known, which measures the distance to an object by measuring the time-of-flight (TOF) of light from the time it takes to receive reflected light from the object after emitting light. In the TOF method, a histogram is created relating the frequency with which the light-receiving element receives reflected light and the time-of-flight TOF, and the distance is calculated from the most likely time-of-flight TOF obtained from the histogram. Since the distance measurement result depends on the shape of the histogram, the more reflected light originating from the light source is among the reflected light from the object, and the less noise light such as ambient light is, that is, the higher the ratio of distance measurement light (S) to noise light (N) is, the higher the S-N ratio, the better the distance measurement performance, such as the reliability and accuracy of the measurement. On the other hand, if the reflectivity of the object is low or the distance to the object is far, the amount of reflected light from the object may decrease, which can lead to a decrease in distance measurement performance.

[0003] Patent Document 1 describes a method for improving the signal-to-noise ratio (S / N) by creating a histogram by combining multiple pixels of a light-receiving unit that receives reflected light from an object.

[0004] Japanese Patent Publication No. 2023-78474

[0005] While Patent Document 1 can improve the signal-to-noise ratio, it combines multiple pixels in the light-receiving section into a single pixel, which reduces the resolution of the distance measurement result.

[0006] This disclosure is made in view of the above-mentioned problems, and its purpose is to realize a technology that expands the range that can be measured while suppressing a decrease in the reliability and accuracy of distance measurement.

[0007] To solve the above problems, the distance measuring device of the present disclosure includes a light-emitting unit having a plurality of light-emitting elements, a light-receiving unit having a plurality of light-receiving elements, a measuring means for creating a histogram based on the time from when the light emitted by the light-emitting unit is received by the light-receiving unit after it has been reflected from an object, and the intensity of the light received by the light-receiving unit, and for measuring the distance to the object, and a control means for controlling the bin width of the histogram based on the intensity of the light received by the light-receiving unit in the distance measuring process for measuring the distance to the object.

[0008] According to this disclosure, it is possible to expand the range that can be measured while suppressing a decrease in distance measurement accuracy.

[0009] Other features and advantages of the technical ideas derived from this disclosure will become apparent from the following description with reference to the attached drawings. In the attached drawings, the same or similar components are given the same reference numeral.

[0010] The attached drawings are included in the specification and constitute part thereof, illustrating embodiments in this disclosure and used to explain the technical ideas derived from this disclosure together with their descriptions. These include: a block diagram illustrating the configuration of a distance measuring device according to the first, second, and third embodiments; a schematic diagram illustrating the configuration of a light source unit according to the first, second, and third embodiments; a schematic diagram illustrating the configuration of a light-receiving element array according to the first, second, and third embodiments; and a diagram illustrating the state of projected light according to the first, second, and third embodiments. Figure 5A illustrates the state when projected light is projected onto an object according to the first, second, and third embodiments. Figure 5B illustrates the state when projected light is projected onto an object according to the first, second, and third embodiments. Figure 5C illustrates the state when projected light is projected onto an object according to the first, second, and third embodiments. Figure 5D illustrates the state when projected light is projected onto an object according to the first, second, and third embodiments. Figure 6A is a diagram illustrating histograms according to the first, second, and third embodiments. Figure 6B is a diagram illustrating histograms according to the first, second, and third embodiments. Figure 6C is a diagram illustrating histograms according to the first, second, and third embodiments. Figure 7A is a diagram illustrating histograms according to the distance of an object according to the first, second, and third embodiments. Figure 7B is a diagram illustrating histograms according to the distance of an object according to the first, second, and third embodiments. Figure 8A1 is a diagram illustrating the relationship between the histograms according to the distance of an object according to the first, second, and third embodiments and the threshold. Figure 8A2 is a diagram illustrating the relationship between the histograms according to the distance of an object according to the first, second, and third embodiments and the threshold. Figure 8B1 is a diagram illustrating the relationship between the histograms according to the distance of an object according to the first, second, and third embodiments and the threshold. Figure 8B2 is a diagram illustrating the relationship between the histograms according to the distance of an object according to the distance of an object according to the first, second, and third embodiments and the threshold. This is a block diagram illustrating another configuration of the distance measuring device according to the first, second, and third embodiments. Figure 10A is a diagram illustrating the emission pulse width and histogram spread width according to the first, second, and third embodiments. Figure 10B is a diagram illustrating the emission pulse width and histogram spread width according to the first, second, and third embodiments.Figure 10C is a diagram illustrating the emission pulse width and histogram spread width according to the first, second, and third embodiments. Figure 11A is a diagram illustrating the relationship between the histogram bin width and threshold according to the first, second, and third embodiments. Figure 11B is a diagram illustrating the relationship between the histogram bin width and threshold according to the first, second, and third embodiments. This is a flowchart illustrating the distance measurement process according to the first embodiment. This is a flowchart illustrating the distance measurement process according to the second embodiment. This is a flowchart illustrating the distance measurement process according to the second embodiment. Figure 15A is a flowchart illustrating the distance measurement process according to the third embodiment. Figure 15B is a flowchart illustrating the distance measurement process according to the third embodiment.

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are necessary, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0012] The following describes an example in which the distance measuring device of this embodiment determines distance information to an object based on the time-of-flight (TOF) of light from the time it emits light into a predetermined scanning range until it receives light reflected from one or more objects included in that predetermined scanning range.

[0013] Furthermore, the distance measuring device and distance measuring method of this embodiment can be applied to, for example, LiDAR (Light Detection and Ranging), imaging devices such as digital cameras, electronic devices with camera functions (smartphones, game consoles, tablet terminals, medical devices, etc.), vehicles such as automobiles, and mobile objects such as robots.

[0014] [First Embodiment] First, the first embodiment will be described.

[0015] <Device Configuration> Figure 1 is a block diagram illustrating the configuration of the distance measuring device according to this embodiment.

[0016] The distance measuring device 100 of this embodiment includes a light projection unit 110, a measurement unit 120, an image-side telecentric lens 130, a main control unit 140, and a beam splitter 150.

[0017] The light projection unit 110 includes a light source unit 113 including a light-emitting section 111 and optical elements 112, and a light source control unit 114. The light-emitting section 111 includes a light-emitting element array 210 in which a plurality of light-emitting elements 211, which will be described later in Figure 2, are arranged in a two-dimensional manner. The optical elements 112 include a collimator lens array 220 and a microlens array 230, which will be described later in Figure 2.

[0018] The light source control unit 114 controls the driving of the light-emitting element array 210. The light source control unit 114 drives multiple light-emitting elements 211 individually or drives them in specific areas. The light source control unit 114 may include a processor and memory, and the driving of the light-emitting element array 210 may be controlled by the processor of the light source control unit 114 executing a program stored in memory. Alternatively, the light source control unit 114 may control the driving of the light-emitting element array 210 in accordance with instructions from the main control unit 140.

[0019] The measurement unit 120 includes a light receiving unit 121, a TDC (Time-to-Digital Converter) array unit 122, a signal processing unit 123, and a measurement control unit 124. The light receiving unit 121 includes a light receiving element array 310, which will be described later in Figure 3. The light receiving element array 310 includes a plurality of light receiving elements 311 arranged in two dimensions, and each light receiving element 311 includes a plurality of sub-light receiving elements 312.

[0020] The TDC array unit 122 measures the time of flight (TOF) of light based on the light detection signal from the sub-photodetector 312. The signal processing unit 123 creates a histogram for each photodetector based on the TOF measurement results measured by the TDC array unit 122. The signal processing unit 123 also creates a distance measurement result based on the histogram, which includes a count map, which is the count value of multiple photodetectors in one frame, and a distance map, which corresponds to the distance to the object. In this way, the signal processing unit 123 creates the distance measurement result at a predetermined frame rate (e.g., 10 to 30 fps).

[0021] The measurement control unit 124 controls the operation of the light receiving unit 121, the TDC array unit 122, and the signal processing unit 123. The measurement control unit 124 may also include a processor and memory, and the operation of the light receiving unit 121, the TDC array unit 122, and the signal processing unit 123 may be controlled by the processor of the measurement control unit 124 executing a program stored in the memory. Alternatively, the processing of the signal processing unit 123 may be implemented by the processor of the measurement control unit 124 executing a program instead of the signal processing unit 123.

[0022] The main control unit 140 includes, for example, a processor such as a CPU and memory such as RAM or ROM, and controls the overall operation of the distance measuring device 100 by executing a program stored in memory using the processor. Alternatively, the processing performed by the light source control unit 114, the signal processing unit 123, or the measurement control unit 124 in this embodiment may be realized by the main control unit 140 executing a program stored in memory using the processor.

[0023] The general operation of the distance measuring device 100 in this embodiment is as follows.

[0024] The light source unit 113 performs pulsed emission, in which multiple light-emitting elements 211 instantaneously emit light at a constant period. The pulsed light emitted passes through the image-side telecentric lens 130 and is projected into the space in front. The pulsed light emitted from each of the multiple light-emitting elements 211 is projected into different areas within a predetermined scanning range (hereinafter referred to as the field of view). Of the projected light, a portion of the light reflected from objects within the predetermined scanning range passes through the image-side telecentric lens 130 and is received by the light-receiving unit 121. The time from when the pulsed light emitted by the light-emitting elements 211 is received by the light-receiving unit 121 is the time of flight (TOF), and the TOF is measured by the TDC array unit 122. However, in a single measurement, it is not possible to exclude noise components such as ambient light and dark counts, and the measurement circuit of the TDC array unit 122 may be affected by noise, potentially causing large errors in the distance measurement result. Therefore, the time from emission to reception (distance measurement operation) is measured repeatedly, and the signal processing unit 123 creates a histogram based on the time-of-flight (TOF) measurement result, and removes noise components and averages the measurement results. By substituting the time-of-flight (TOF) obtained in this way into the following equation 1, the distance L to the object can be determined with high accuracy. (Equation 1) L = TOF × c / 2 In equation 1, c is the speed of light.

[0025] <Configuration of the light source unit> Figure 2 is a schematic diagram illustrating the configuration of the light source unit 113 included in the light projection unit 110 according to this embodiment.

[0026] The light-emitting element array 210 has vertical cavity surface-emitting lasers (VCSELs) arranged two-dimensionally on a substrate as light-emitting elements 211.

[0027] While the light-emitting element 211 is not intended to be limited to a vertical-cavity surface-emitting laser, it is desirable that it be able to be integrated in one or two dimensions. Examples of light-emitting elements 211 include end-face-emitting lasers and LEDs (light-emitting diodes). When using end-face-emitting lasers as the light-emitting elements 211, the light-emitting element array 210 can also use laser bars arranged in one dimension on a substrate, or a laser bar stack arranged in two dimensions by stacking laser bars. Furthermore, when using light-emitting diodes (LEDs) as the light-emitting elements 211, the light-emitting element array 210 can be used in a configuration in which light-emitting diodes are arranged in two dimensions on a substrate.

[0028] In this embodiment, it is desirable that the wavelength of light emitted by the light-emitting element 211 of the distance measuring device 100 be in the near-infrared band in order to suppress the influence of ambient light. However, it is not intended to be limited to this, and light in other bands may be used as long as the influence of ambient light can be suppressed.

[0029] Vertical-cavity surface-emitting lasers are fabricated using semiconductor processes with materials similar to those used in edge-emitting and surface-emitting lasers. For configurations that emit light in the near-infrared wavelength range, GaAs-based semiconductor materials can be used as the main material. In this case, the dielectric multilayer film forming the DBR (distributed reflection) mirror of the vertical-cavity surface-emitting laser can be constructed by alternately and periodically stacking two thin films made of materials with different refractive indices (GaAs / AlGaAs). The wavelength of the emitted light can be changed by adjusting the elemental combination and composition of the compound semiconductor.

[0030] The vertical-cavity surface-emitting laser is equipped with electrodes for injecting current and holes into the active layer, and by controlling the injection timing with the light source control unit 114, it is possible to emit arbitrary pulsed light or modulated light. The light source control unit 114 can, for example, individually drive the vertical-cavity surface-emitting lasers as light-emitting elements 211, or drive the vertical-cavity surface-emitting lasers in the row direction, column direction, or specific area direction of a VCSEL array in which vertical-cavity surface-emitting lasers are arranged in a two-dimensional manner.

[0031] Light emitted from the vertical-cavity surface-emitting laser (CEL) as a light-emitting element 211 becomes divergent light due to diffraction at the aperture of the CEL. Therefore, a collimator lens array 220, in which collimator lenses 221 are arranged in a two-dimensional manner, is placed (between the light-emitting element array 210 and the microlens array 230 described later) to control the divergence angle of the divergent light or to convert it into parallel light. In this embodiment, the collimator lenses 221 constituting the collimator lens array 220 are arranged in a one-to-one correspondence with each of the light-emitting elements 211. The light emitted from the VCSEL array, collimated by the collimator lens array 220, is converted, for example, into parallel light perpendicular to the VCSEL array substrate. Note that, depending on the aperture diameter, if the radiation angle from the CEL is small, the collimator lenses 221 may be omitted. The microlens array 230 includes a plurality of microlenses 231 arranged in a two-dimensional manner. The light emitted by the light-emitting element 211 is converted to a predetermined emission diameter by the microlens 231 and projected through the image-side telecentric lens 130.

[0032] <Configuration of light-receiving elements> Figure 3 is a schematic diagram illustrating the configuration of the light-receiving element array 310 according to this embodiment.

[0033] The light-receiving element array 310 includes a plurality of light-receiving elements 311 arranged in a two-dimensional manner. Each light-receiving element 311 also includes a plurality of sub-light-receiving elements 312 arranged in a two-dimensional manner. Each of the sub-light-receiving elements can be driven individually.

[0034] In the example shown in Figure 3, the light-receiving element 311 has three sub-light-receiving elements arranged in a 3x3 configuration, with three in each of the horizontal (row) and vertical (column) directions, but any number of m x n (where m and n are natural numbers) sub-light-receiving elements 312 may be arranged in the horizontal and vertical directions.

[0035] <Relationship between light emission and light reception> Figure 4 illustrates the state of the emitted light after the light emitted by the light-emitting element 211 has passed through the image-side telecentric lens 130.

[0036] The microlens 231 and the image-side telecentric lens 130 form an afocal optical system where parallel light incident on the lens exits the lens as parallel light. In an afocal system, since the object and the image are conjugate at infinity, a parallel light beam is incident on the microlens 231 and a parallel light beam is emitted from the image-side telecentric lens 130. That is, the light projected from the image-side telecentric lens 130 is projected at an angle corresponding to the image height (the positional relationship between the microlens 231 and the image-side telecentric lens 130) and is projected parallelly. Therefore, the width d ｂ (thickness in three dimensions) of the projected light is projected with the same width (thickness in three dimensions) at any distance from the object side as viewed from the image-side telecentric lens 130 (independent of the distance to the object). However, let the emission diameter at the microlens 231 be p, the focal length of the microlens 231 be f Ｍ , and the focal length of the image-side telecentric lens 130 be f Ｌ . Then, the width d ｂ of the projected light is obtained by the following formula 2. However, when the emission diameter p at the microlens 231 is larger than the pitch of the microlens 231, the emission diameter p is limited by the pitch of the microlens 231. Also, when the width d ｂ of the projected light is larger than the pupil diameter of the image-side telecentric lens 130, the width d ｂ of the projected light is limited by the pupil diameter. (Formula 2) d ｂ = (p · f Ｌ ) / f Ｍ In the example of FIG. 4, the collimator lens 221 is omitted. However, when the spread of the light emitted from the light-emitting element 211 is large, a collimator lens 221 may be interposed between the light-emitting element 211 and the microlens 231 for collimation.

[0037] Next, referring to FIGS. 5A - 5D, the state where the projected light described in FIG. 4 is projected onto an object will be described.

[0038] FIGS. 5A - 5C are diagrams illustrating the state where the projected light is projected onto the object 501 by the distance measuring device 100 of the present embodiment.

[0039] In the example of FIGS. 5A - 5C, the projected light is projected onto the object 501 as a projected image 502. The projected image size d in FIGS. 5A - 5C ｂ is equal to the width d of the projected light in FIG. 4 ｂ . FIG. 5 illustrates the object 501 in the order from closest to the image-side telecentric lens 130 as FIGS. 5A, FIG. 5B, and FIG. 5C. FIG. 5D illustrates a state in which each of the light-receiving elements 311 (constituted by a plurality of sub-light-receiving elements 312) in the light-receiving element array 310 receives the light emitted from a corresponding different light-emitting element 211.

[0040] In the example of FIGS. 5A - 5C, the projected light interval increases as the distance from the image-side telecentric lens 130 increases, but the projected image size d ｂ does not change. That is, the interval of the light projected onto the object 501 through the image-side telecentric lens 130 (projected light interval) changes according to the distance to the object 501. On the other hand, the width of each of the plurality of projected lights (projected image size d ｂ [[ID=Eleven]] ) does not change according to the distance to the object 501. Thereby, the light emitted from a certain light-emitting element 211 can be made to be received only by a specific light-receiving element 311 in the light-receiving element array 310 as shown in FIG. 5D, and it is possible to make the light-emitting element 211 and the light-receiving element 311 correspond one-to-one. For this reason, it is possible to perform alternative control in which only a part of the plurality of light-emitting elements 211 emits light and only the light-receiving element 311 corresponding to the light-emitting element 211 that emits light among the plurality of light-receiving elements 311 is driven. Thereby, one TDC can be shared by the plurality of light-receiving elements 311, and the pixel size can be reduced, which is effective for increasing the resolution.

[0041] <Distance measurement operation> As a light emission sequence of the light-emitting element array 210, for example, it is possible to simultaneously emit light from the light-emitting elements 211 for one row and scan within the angular field by sequentially emitting light in the column direction to obtain one distance measurement image. By repeatedly executing such an operation of scanning within the angular field at a predetermined frame rate, a distance measurement image is generated for each frame.

[0042] <Histogram> In this embodiment, the TDC array unit 122 measures the time of flight (TOF) of light based on the light detection signal of the sub-photodetector 312. The signal processing unit 123 then creates a histogram based on the TOF measurement results by the TDC array unit 122. The histogram is statistical information that shows the relationship between the time of flight (TOF) of light until the photodetector 311 receives reflected light from an object, and the count value, which is the frequency with which the photodetector 311 receives reflected light from an object. The count value can also be rephrased as the intensity (signal intensity) of the light reflected from an object that the photodetector 311 receives.

[0043] Furthermore, the signal processing unit 123 creates a count map showing the count values ​​of multiple light-receiving elements 311 in one frame, and a distance map showing the distance to one or more objects within the field of view, based on the histogram for each light-receiving element 311.

[0044] The light received by the sub-photodetector 312 may include two types of light: reflected light (measuring light) from the light emitted from the light-emitting element 211 that is reflected by an object, and reflected light (ambient light) from external light other than the light emitted from the light-emitting element that is reflected by an object. Therefore, the histogram includes the frequency of TOF occurrences originating from the measuring light (measuring light count) and the frequency of TOF occurrences originating from the ambient light (ambient light count).

[0045] Methods for calculating the distance to an object from a histogram include extracting the peaks from the histogram or fitting the area around the peaks of the histogram.

[0046] Figures 6A-6C illustrate histograms. Figure 6A illustrates a histogram consisting only of photons originating from ranging light. Figure 6B illustrates a histogram consisting only of photons originating from ambient light.

[0047] As shown in Figure 6A, the histogram consisting only of photons derived from the ranging light shows the number of photons accumulating within a time (distance) range corresponding to the emission time of the light-emitting element 211, whereas the ambient light shows the number of photons counted randomly over time (distance).

[0048] In the example in Figures 6A-6B, the histograms consisting only of photons from the ranging light and the histogram consisting only of photons from the ambient light are shown separately. However, in reality, ranging light and ambient light cannot be distinguished. Therefore, as shown in Figure 6C, the histogram is a combination of the histograms in Figure 6A and Figure 6B.

[0049] <Reliability of Distance Measurement (Errors) and Histograms> Figure 7A shows an example of a histogram when the distance between objects is short, and Figure 7B shows an example of a histogram when the distance between objects is long.

[0050] In the example shown in Figures 7A-7B, for the sake of explanation, the counts derived from the ranging light and the counts derived from the ambient light are shown separately, but in reality, the histograms obtained do not allow for the distinction between the two.

[0051] As shown in Figure 7A, when the object is close, the bin where the count derived from the ranging light is detected is the bin with the maximum count, so the object's distance can be accurately calculated. For example, the distance indicated by the bin with the maximum count may be taken as the object's distance, or the object's distance may be calculated from the bins before and after the bin with the maximum count as shown in Equation 3 below, or the object's distance may be calculated by other methods. (Equation 3) LSB ｐｅａｋ =LSBC0 × 1 / 2 × (C1 - C2) / ((C1 - C0) - (C0 - C2)) In Equation 3, LSB ｐｅａｋ The result is the distance measurement. LSBC0 is the distance indicated by the bin where the count is at its maximum. C0 is the maximum count (the count value of the bin LSBC0). C1 and C2 are the count values ​​of the bins before and after LSBC0.

[0052] In contrast, as shown in Figure 7B, when the object is far away, the bin where the count originating from ambient light is detected is the bin with the maximum count. Therefore, calculating the object's distance from the count value of that bin may result in an erroneous measurement, where the object's distance is calculated incorrectly.

[0053] The mismeasurements described above can be suppressed by setting a threshold Sth for the histogram count. For example, if there are sufficient counts originating from the ranging light, as in the histogram in Figure 8A1, extracting only the counts above the threshold Sth results in a histogram like Figure 8A2, and only the counts originating from the ranging light can be used for ranging. On the other hand, as in Figure 8B1, if the counts originating from the ranging light are equal to or less than the counts originating from ambient light, extracting only those above the threshold Sth results in zero counts, as in Figure 8B2. In this case, the reduction in reliability due to mismeasurements can be suppressed by considering it impossible to measure the distance.

[0054] A larger threshold Sth suppresses mismeasurement (reduced reliability), but at the same time discards counts originating from the measuring light, increasing the likelihood of mismeasurement being impossible under conditions where it is difficult to obtain counts originating from the measuring light, such as with objects at great distances. On the other hand, a smaller threshold Sth reduces the likelihood of mismeasurement but increases the likelihood of mismeasurement (reduced reliability). It is desirable to set the threshold Sth considering the light emission energy of the light-emitting element 211, the pupil diameter of the image-side telecentric lens 130, and the quantum efficiency of the photodetector 311.

[0055] Since ambient light is affected by weather and location, the threshold Sth may be set to be variable, taking into account the influence of ambient light. For example, the main control unit 140 may control the light source control unit 114 and the measurement control unit 124, and by taking measurements while the light source unit 113 is not emitting light, a histogram of ambient light only may be obtained, and the threshold Sth may be set from the histogram of ambient light only. Alternatively, as shown in Figure 9, the distance measuring device 100 may be equipped with a photometric unit 900 including a photometric unit 901 and a photometric control unit 902, which directly measures the influence of ambient light, and the threshold Sth may be set from the measurement results.

[0056] <Distance Measurement Accuracy and Histogram Bin Width> Since distance measurement accuracy depends on the histogram bin width (sampling width relative to distance), it is desirable to reduce the bin width if you want to increase the distance measurement accuracy. However, reducing the bin width reduces the number of photons counted per bin, so for distant objects, the count from ambient light may be higher than the count from the ranging light.

[0057] As shown in Figure 10A, when the light-emitting element 211 emits light with a pulse width Tp, the histogram calculated by the signal processing unit 123 will have a spread width Th that reflects the pulse width Tp of the light-emitting element 211, as shown in Figure 10B. In other words, the histogram spread width Th will be greater than or equal to the pulse width Tp (Th ≥ Tp) when there are enough photons returned that the TDC does not pile up. However, when there are close objects or when there are enough photons returned that the TDC piles up, if the light-receiving element 311 is a SPAD element, only the photons that returned earlier within the pulse width Tp can be detected due to the effect of dead time. For this reason, the histogram may be biased towards the closer distance side, as shown in Figure 10C. In such cases, the histogram spread width Th may be less than or equal to the pulse width Tp (Th ≤ Tp).

[0058] As described above, the maximum distance that can be measured appropriately without mismeasurement (measurable range) for counts derived from the ranging light decreases. Therefore, it is desirable to set the bin width to a value that balances the measuring accuracy and the measurable range. For example, under the condition of bin width Tb as shown in Figure 11A, the maximum value Smax of the count derived from the ranging light does not exceed the threshold Sth, so measurement is not possible and the measurable range is reduced. However, by setting the bin width to Tb' (>Tb) as shown in Figure 11B, at least the maximum value Cmax of the count exceeds the threshold Sth, so measurement becomes possible and the measurable range is expanded. However, since the Cmax bin may contain a combination of counts derived from the ranging light and counts derived from ambient light, the Cmax bin does not necessarily represent the appropriate distance to the object.

[0059] In this case, even if the bin width Tb2 is made larger than the emission pulse width Tp of the light-emitting element 211, the effect of increasing the count from ambient light will outweigh the effect of increasing the count from the ranging light, and therefore it will not contribute to expanding the measurable range. For this reason, it is desirable that the bin width Tb' be less than or equal to the emission pulse width Tp (Tb' ≤ Tp).

[0060] Based on the above, in this embodiment, by appropriately controlling the bin width of the histogram based on the count value of the histogram obtained by the distance measurement operation (the intensity of light received from reflected light from an object), the range in which distance can be measured is expanded while suppressing a decrease in the reliability and accuracy of the distance measurement.

[0061] <Distance Measurement Process> Figure 12 is a flowchart illustrating the process of controlling the bin width in the distance measurement process according to the first embodiment.

[0062] The distance measurement process shown in Figure 12 is executed repeatedly for each frame, and is achieved by the main control unit 140 executing a program stored in memory to control the light projection unit 110 and the measurement unit 120. Alternatively, the processing of the main control unit 140 in this embodiment may be achieved by the light source control unit 114 of the light projection unit 110, or the signal processing unit 123 or measurement control unit 124 of the measurement unit 120 executing a program stored in memory. The bin width Tb can be controlled, for example, by changing the sampling (clock) frequency in the measurement unit 120, or by not using specific (lower) bits in the data obtained by sampling. The same applies to the second and third embodiments described later.

[0063] When processing starts in step S1200, in step S1201 the bin width Tb is set to Tb0 (< pulse width Tp), and in step S1202 the distance measurement process is performed with the bin width Tb0 set in step S1201. In step 1203 it is determined whether distance measurement is possible with bin width Tb0, and if distance measurement is possible, the process proceeds to step S1206 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step 1204, the bin width Tb is set from Tb0 to Tb1 (Tb0 ≤ Tb1 ≤ pulse width Tp), then distance measurement is performed in step S1205, and the process ends in step S1206.

[0064] As described above, according to the first embodiment, when the histogram count does not exceed the threshold St and therefore distance measurement is not possible, the bin width Tb is increased within a range that does not exceed the emission pulse width Tp, thereby making it possible to expand the range in which distance measurement is possible while suppressing a decrease in the reliability and accuracy of distance measurement.

[0065] [Second Embodiment] Next, a second embodiment will be described.

[0066] In the first embodiment, when distance measurement was not possible with bin width Tb0, the measurable distance was increased by increasing the bin width Tb from Tb0 to Tb1. However, increasing the bin width Tb reduces the distance resolution and thus the distance measurement accuracy. Therefore, in the second embodiment, in addition to the configuration of the first embodiment, it is possible to set either a high-precision mode that prioritizes distance measurement accuracy or a high-reliability mode that prioritizes the reliability of distance measurement. Then, as shown in Figure 13 in the high-precision mode or as shown in Figure 14 in the high-reliability mode, even if distance measurement is not possible with bin width Tb0, the bin width Tb is not increased to suppress the decrease in distance measurement accuracy and terminate the distance measurement.

[0067] Figure 13 is a flowchart illustrating the distance measurement process according to the high-precision mode of the second embodiment.

[0068] When processing starts in step S1300, the bin width Tb is set to Tb0 (< pulse width Tp) in step S1301, and distance measurement processing is performed in step S1302. In step 1303, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step S1307 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step 1304 and it is determined whether high-precision distance measurement mode is set. If high-precision distance measurement mode is set, the process proceeds to step S1307 and ends without controlling the bin width Tb. If high-precision distance measurement mode is not set, the process proceeds to step S1305, the bin width is set from Tb0 to Tb1 (Tb0 ≤ Tb1 ≤ pulse width Tp), distance measurement processing is performed in step 1306, and the process ends in step S1307.

[0069] Figure 14 is a flowchart illustrating the distance measurement process according to the high-reliability mode of the second embodiment.

[0070] When processing starts in step S1400, the bin width Tb is set to Tb0 (< pulse width Tp) in step S1401, and distance measurement processing is performed in step S1402. In step 1403, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step S1407 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step 1404 and it is determined whether high reliability mode is set. If high reliability mode is set, the process proceeds to step S1407 and ends without controlling the threshold Sth. If high reliability mode is not set, the process proceeds to step S1405, the threshold Sth is relaxed to increase, distance measurement processing is performed in step 1406, and the process ends in step S1407.

[0071] As described above, according to the second embodiment, when the high-precision mode or high-reliability mode is on, the bin width Tp is not controlled, thereby enabling distance measurement in a highly accurate or highly reliable state (with suppressed mismeasurement). When the high-precision mode or high-reliability mode is off, the bin width Tb can be increased or the threshold value St can be relaxed, thereby expanding the measurable range while suppressing a decrease in the reliability and accuracy of the distance measurement.

[0072] [Third Embodiment] Next, a third embodiment will be described.

[0073] In the second embodiment, when the high-precision mode or high-reliability mode is set, the decrease in distance measurement accuracy is suppressed, and when the high-precision mode or high-reliability mode is off, the distance that can be measured is improved by increasing the bin width Tb. In contrast, in the third embodiment, in addition to the configuration of the first embodiment, both the high-precision mode and the high-reliability mode can be set.

[0074] Figure 15A is a flowchart illustrating the distance measurement process prioritizing the high-precision mode according to the third embodiment.

[0075] In Figure 15A, when processing starts in step S1500, the bin width Tb is set to Tb0 (< pulse width Tp) in step S1501, and distance measurement processing is performed in step S1502. In step 1503, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step S1511 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step 1504 and it is determined whether high-precision mode is set. If high-precision mode is set, the process proceeds to step S1511 and ends without controlling the bin width Tb. If high-precision distance measurement mode is not set, the process proceeds to step S1505, the bin width Tb is set from Tb0 to Tb1 (Tb0 ≤ Tb1 ≤ pulse width Tp), and then distance measurement processing is performed in step 1306. Next, in step S1507, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step S1511 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step S1508 and it is determined whether high reliability mode is set. If high reliability mode is set, the process proceeds to step S1511 and ends without controlling the threshold Sth. If high reliability mode is not set, the process proceeds to step S1509, the threshold Sth is relaxed to increase, distance measurement is performed in step 1510, and the process ends in step S1511.

[0076] Figure 15B is a flowchart illustrating the distance measurement process prioritizing the high-reliability mode according to the third embodiment.

[0077] In Figure 15B, when processing starts in step S1520, the bin width Tb is set to Tb0 (< pulse width Tp) in step S1521, and distance measurement processing is performed in step S1522. In step 1523, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step 1531 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step 1524 and it is determined whether high reliability mode is set. If high reliability mode is set, the process proceeds to step S1531 and ends without controlling the threshold Sth. If high reliability mode is not set, the process proceeds to step S1525, the threshold Sth is relaxed to increase, and then distance measurement processing is performed in step 1526. Next, in step S1527, it is determined whether distance measurement is possible. If distance measurement is possible, the process proceeds to step S1531 and ends without controlling the bin width Tb. If distance measurement is not possible, the process proceeds to step S1528 and it is determined whether high accuracy mode is set. If high-precision mode is set, the process proceeds to step S1531 and ends without controlling the bin width Tb. If high-precision mode is not set, the process proceeds to step S1529, where the bin width Tb is set from Tb0 to Tb1 (Tb0 ≤ Tb1 ≤ pulse width Tp), then distance measurement is performed in step 1530, and the process ends in step S1531.

[0078] As described above, according to the third embodiment, when the high-precision mode or high-reliability mode is on, the control of the bin width Tp is not performed, thereby suppressing a decrease in distance measurement accuracy or reliability. Furthermore, when the high-precision mode and high-reliability mode are off, the range that can be measured can be expanded while suppressing a decrease in the reliability and accuracy of distance measurement by increasing the bin width Tb or relaxing the threshold Sth.

[0079] [Other Embodiments] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more functions.

[0080] The technical ideas derived from this disclosure are not limited to the exemplary embodiments disclosed, but are intended to encompass various modifications of the exemplary embodiments, or substitutions with equivalent structures or functions. The scope of the following claims should be interpreted in the broadest way to encompass all such modifications and equivalent structures and functions.

[0081] This application claims priority based on Japanese Patent Application No. 2025-018541, filed on February 6, 2025, and all of its contents are incorporated herein by reference.

[0082] 100... Distance measuring device, 111... Light-emitting unit, 113... Light source unit, 120... Measurement unit, 121... Light-receiving unit, 122... TDC array unit, 123... Signal processing unit, 140... Main control unit

Claims

1. A distance measuring device comprising: a light-emitting unit having a plurality of light-emitting elements; a light-receiving unit having a plurality of light-receiving elements; a measuring means for creating a histogram based on the time from when the light emitted by the light-emitting unit is received by the light-receiving unit and the intensity of the light received by the light-receiving unit, and for measuring the distance to the object; and a control means for controlling the bin width of the histogram based on the intensity of the light received by the light-receiving unit in a distance measuring process for measuring the distance to the object.

2. The distance measuring device according to claim 1, characterized in that the control means sets the bin width of the histogram to a first bin width and performs the distance measuring process, determines whether or not the distance to the object can be measured, and if the distance to the object cannot be measured with the first bin width, controls the control to set the bin width of the histogram to a second bin width that is larger than the first bin width and perform the distance measuring process.

3. The distance measuring device according to claim 2, characterized in that the control means controls the histogram bin width not to be set to a second bin width that is larger than the first bin width when the distance to the object can be measured with the first bin width.

4. The distance measuring device according to claim 2, characterized in that a first mode prioritizing measurement accuracy can be set, and the control means controls the histogram bin width to a second bin width that is larger than the first bin width and to perform the distance measuring process when the distance to the object cannot be measured with the first bin width, or when the first mode is not set.

5. The distance measuring device according to claim 4, characterized in that the control means controls the histogram bin width not to be set to a second bin width that is larger than the first bin width when the distance to the object can be measured with the first bin width.

6. The distance measuring device according to claim 4 or 5, characterized in that, when the control means is set to the first mode, it controls not to set the bin width of the histogram to a second bin width that is larger than the first bin width.

7. The distance measuring device according to claim 2, wherein a second mode prioritizing the reliability of distance measurement is set, and the control means relaxes the threshold of the intensity of light received by the light receiving unit used when measuring the distance to the object when the distance to the object cannot be measured with the first bin width, or when the second mode is not set.

8. The distance measuring device according to claim 7, characterized in that the control means controls the threshold not to relax when the distance to the object can be measured with the first bin width.

9. The distance measuring device according to claim 7 or 8, characterized in that the control means controls the threshold so as not to relax it when set to the second mode.

10. The distance measuring device according to claim 2, characterized in that it is possible to set a first mode that prioritizes distance measuring accuracy and a second mode that prioritizes distance measuring reliability, and the control means sets the bin width of the histogram to a second bin width that is larger than the first bin width when the distance to the object cannot be measured with the first bin width and the first mode is not set, and determines whether or not the distance to the object can be measured, and relaxes the threshold of the intensity of light received by the light receiving unit used when measuring the distance to the object when the distance to the object cannot be measured with the second bin width and the second mode is not set.

11. The distance measuring device according to claim 10, characterized in that, when the distance to the object can be measured with the first bin width, the control means does not set the bin width of the histogram to a second bin width that is larger than the first bin width, and does not relax the threshold.

12. The distance measuring device according to claim 10 or 11, characterized in that when the control means is set to the first mode, it does not set the bin width of the histogram to a second bin width that is larger than the first bin width, and when it is set to the second mode, it controls not to relax the threshold.

13. The distance measuring device according to claim 2, wherein it is possible to set a first mode that prioritizes distance measuring accuracy and a second mode that prioritizes distance measuring reliability, and the control means relaxes the threshold of the intensity of light received by the light receiving unit used when measuring the distance to the object if the distance to the object cannot be measured with the first bin width and the second mode is not set, and sets the bin width of the histogram to a second bin width that is larger than the first bin width.

14. The distance measuring device according to claim 13, characterized in that, when the distance to the object can be measured with the first bin width, the control means does not relax the threshold and controls the bin width of the histogram not to be set to a second bin width that is larger than the first bin width.

15. The distance measuring device according to claim 13 or 14, characterized in that the control means does not relax the threshold when set to the second mode, and when set to the first mode, controls not to set the bin width of the histogram to a second bin width that is greater than the first bin width.

16. The distance measuring device according to any one of claims 7 to 15, characterized in that the measuring means measures the distance to the object based on the intensity of light that exceeds the threshold among the light received by the light receiving unit.

17. The distance measuring device according to any one of claims 7 to 16, wherein the threshold is set based on the intensity of light reflected by an object other than the light emitted by the light-emitting unit.

18. The distance measuring device according to any one of claims 1 to 17, characterized in that the bin width is set so as not to exceed the light emission pulse width in the light emission unit.

19. The distance measuring device according to any one of claims 1 to 18, characterized in that the light received by the light receiving unit includes light reflected from an object from light emitted by the light emitting unit and light reflected from an object other than the light emitted by the light emitting unit.

20. The distance measuring device according to any one of claims 1 to 19, characterized in that the intensity of light received by the light receiving unit is information indicating a count value which is the frequency with which the light receiving unit receives light reflected from the object.

21. The distance measuring device according to any one of claims 1 to 20, characterized in that the light emitted by the light-emitting unit is projected onto the object via the image-side telecentric lens, and the light-receiving unit receives the light reflected from the object via the image-side telecentric lens.

22. The distance measuring device according to claim 21, characterized in that it has a beam splitter that guides the light emitted by the light-emitting unit to the image-side telecentric lens and guides the light reflected from the object to the light-receiving unit.

23. The distance measuring device according to claim 21, characterized in that the light-emitting unit incident parallel light onto the image-side telecentric lens, and the image-side telecentric lens emits the parallel light incident onto the image-side telecentric lens as parallel light.

24. A distance measuring method performed by a distance measuring device comprising a light-emitting unit having a plurality of light-emitting elements and a light-receiving unit having a plurality of light-receiving elements, the method comprising: creating a histogram based on the time from when the light emitted by the light-emitting unit is received by the light-receiving unit after it has been reflected from an object, and the intensity of the light received by the light-receiving unit, and measuring the distance to the object; and in the distance measuring process for measuring the distance to the object, the step of controlling the bin width of the histogram based on the intensity of the light received by the light-receiving unit.

25. A program for causing a computer to function as a distance measuring device according to any one of claims 1 to 23.

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