Distance measuring device, distance measuring method, and program

Abstract

Improve distance measurement accuracy without reducing the frame rate. [Solution] The distance measuring device includes a light-emitting unit having a plurality of light-emitting elements, a light-receiving unit having a plurality of light-receiving elements, a control means that performs a distance measuring operation by individually emitting light from the plurality of light-emitting elements to project light into a predetermined scanning range, and a measurement means that determines the distance to an object based on the time from when the light emitted by the light-emitting unit is projected onto an object during the distance measuring operation until the light-receiving unit receives the light reflected from the object. The measurement means creates a distance measuring result including distance information to the object at a predetermined frame rate, and the control means determines the number of distance measuring operations in the next frame based on the distance measuring result obtained by the measurement means in the distance measuring operation in the previous frame, so as not to increase the number of distance measuring operations in one frame.

Description

[Technical Field]

[0001] This invention relates to a technique for measuring distance. [Background technology]

[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 of projection until the reflected light from the object is received. In the TOF method, a histogram is created relating the frequency of reflected light reception by the photodetector to 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 distance measurement accuracy improves as the amount of reflected light from the light source among the reflected light from the object increases. On the other hand, if the reflectivity of the object is low or the distance to the object is large, the distance measurement accuracy may decrease if there is little reflected light from the object.

[0003] Patent Document 1 describes a method for improving distance measurement accuracy by reducing the optical scanning speed to increase the amount of light received when the amount of light received falls below a threshold. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-63236 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the TOF method, distance measurement results can be obtained at a predetermined frame rate, but in Patent Document 1, the optical scanning speed is reduced and the distance measurement operation is continued until the amount of received light exceeds a threshold, which may result in a decrease in the frame rate.

[0006] This invention has been made in view of the above problems, and its purpose is to realize a technology that improves distance measurement accuracy without reducing the frame rate. [Means for solving the problem]

[0007] To solve the above problems and achieve the objective, the distance measuring device of the present invention comprises a light-emitting unit having a plurality of light-emitting elements, a light-receiving unit having a plurality of light-receiving elements, a control means for performing a distance measuring operation in which the plurality of light-emitting elements individually emit light and project light into a predetermined scanning range, and a measurement means for determining the distance to an object based on the time from when the light emitted by the light-emitting unit is projected onto an object and when the light-receiving unit receives the light reflected from the object during the distance measuring operation. The measurement means creates a distance measuring result including distance information to the object at a predetermined frame rate, and the control means determines the number of distance measuring operations in the next frame based on the distance measuring result obtained by the measurement means in the distance measuring operation in the previous frame, so as not to increase the number of distance measuring operations in one frame. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve distance measurement accuracy without reducing the frame rate. [Brief explanation of the drawing]

[0009] [Figure 1] A block diagram illustrating the configuration of a distance measuring device according to Embodiment 1. [Figure 2] A schematic diagram illustrating the configuration of the light source unit according to Embodiments 1 to 3. [Figure 3] A schematic diagram illustrating the configuration of the photodetector array according to Embodiments 1 to 3. [Figure 4] A diagram illustrating the state of the projected light according to Embodiments 1 to 3. [Figure 5] A diagram illustrating the state in which projected light is projected onto an object according to Embodiments 1 to 3. [Figure 6] A diagram illustrating the distance measurement operation according to a modified example of Embodiment 1. [Figure 7] A block diagram illustrating the configuration of a distance measuring device according to Embodiment 2. [Figure 8] A diagram illustrating the distance measurement operation according to Embodiment 3.

Embodiments for Carrying out the Invention

[0010] Hereinafter* the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in these embodiments* not all of these plurality of features are essential for the invention* and further* the plurality of features may be arbitrarily combined. Further* in the accompanying drawings* the same or similar configurations are denoted by the same reference numerals* and redundant descriptions are omitted.

[0011] * Hereinafter* an example will be described in which the distance measuring device of the present embodiment obtains distance information to an object based on the time-of-flight TOF (Time-Of-Flight) of light from the time when light is projected onto a predetermined scanning range until the light reflected by one or more objects included in the predetermined scanning range is received.

[0012] Note that the distance measuring device and the distance measuring method of the present embodiment are applicable to* for example* imaging devices such as LiDAR (Light Detection And Ranging)* digital cameras* electronic devices having a camera function (smartphones* game machines* tablet terminals* medical devices* etc.)* vehicles such as automobiles* and moving bodies such as robots.

[0013] [Embodiment 1] First* the first embodiment will be described.

[0014] [Device Configuration] FIG. 1 is a block diagram illustrating the configuration of the distance measuring device according to the present embodiment.

[0015] The distance measuring device 100 of the present embodiment includes a light projecting unit 110* a measuring unit 120* an image-side telecentric lens 130* a main control unit 140* and a beam splitter 150.

[0016] * *“Hereinafter”在专利文本语境中常翻译为“以下” 。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 two dimensions. The optical elements 112 include a collimator lens array 220 and a microlens array 230, which will be described later in Figure 2.

[0017] 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.

[0018] 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.

[0019] 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 containing the count values ​​of multiple photodetectors in one frame and a distance map corresponding 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).

[0020] 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.

[0021] 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.

[0022] The general operation of the distance measuring device 100 in this embodiment is as follows.

[0023] 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 is projected into the space in front of the image-side telecentric lens 130. 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 is received by the light-receiving unit 121 after passing through the image-side telecentric lens 130. 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, a single measurement cannot 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 significant errors in the distance measurement results. Therefore, the time from light emission to light reception (distance measurement operation) is repeatedly measured, and the signal processing unit 123 creates a histogram based on the time-of-flight (TOF) measurement results, and performs noise component removal and averaging of 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. (Formula 1) L = TOF × c / 2 In Equation 1, c is the speed of light.

[0024] <Configuration of the light source unit> Figure 2 is a schematic diagram illustrating the configuration of a light source unit 113 included in the light projection unit 110 according to this embodiment.

[0025] The light-emitting element array 210 has vertical cavity surface-emitting lasers (VCSELs) arranged two-dimensionally on the substrate as light-emitting elements 211.

[0026] 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 use laser bars arranged one-dimensionally on a substrate, or a laser bar stack arranged two-dimensionally 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 where light-emitting diodes are arranged two-dimensionally on a substrate.

[0027] 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.

[0028] 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 primary 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.

[0029] 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 laser as a light-emitting element 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.

[0030] Light emitted from the vertical-cavity surface-emitting laser (VCSEL) as a light-emitting element 211 becomes divergent light due to diffraction at the aperture of the VCSEL. 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 light-emitting element 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 in cases where the radiation angle from the vertical-cavity surface-emitting laser is small due to the aperture diameter, 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.

[0031] <Photodetector configuration> Figure 3 is a schematic diagram illustrating the configuration of the light-receiving element array 310 according to this embodiment.

[0032] 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.

[0033] In the example shown in Figure 3, the photodetector 311 has three sub-photodetectors 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-photodetectors 312 may be arranged in the horizontal and vertical directions.

[0034] <Relationship between light projection and light reception> FIG. 4 is a diagram illustrating the state of the projected light after the light emitted by the light-emitting element 211 passes through the image-side telecentric lens 130.

[0035] 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 enters 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, but 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.

[0036] Next, referring to FIG. 5, the state where the projected light described in FIG. 4 is projected onto an object will be described.

[0037] Figures 5(a) to 5(c) illustrate the state in which light is projected onto an object 501 by the distance measuring device 100 of this embodiment.

[0038] In the examples in Figures 5(a) to (c), projected light is projected onto object 501 as a projected image 502. Projected image size d in Figures 5(a) to (c) b and the width d of the projected light in Figure 4 b They are equal. Figure 5 illustrates the objects 501 in order of proximity to the image-side telecentric lens 130 as Figures 5(a), (b), and (c). Figure 5(d) illustrates the state in which each of the photodetectors 311 (composed of multiple sub-photodetectors 312) in the photodetector array 310 receives light emitted from a corresponding different light-emitting element 211.

[0039] In the examples in Figures 5(a) to (c), the projection light interval increases as the distance from the image-side telecentric lens 130 increases, but the projection image size d b This does not change. That is, the interval between the light rays that pass through the image-side telecentric lens 130 and are projected onto the object 501 (projection light interval) changes according to the distance to the object 501. On the other hand, the width of each of the multiple projected light rays (projection image size d) does not change. b The TDC does not change depending on the distance to object 501. As a result, the light emitted from a certain light-emitting element 211 can be received only by a specific photodetector 311 in the photodetector array 310, as shown in Figure 5(d), making it possible to establish a one-to-one correspondence between the light-emitting elements 211 and the photodetectors 311. Therefore, selective control is possible, where only a portion of the multiple light-emitting elements 211 emit light, and only the photodetectors 311 corresponding to the emitted light-emitting elements 211 are driven from among the multiple photodetectors 311. As a result, multiple photodetectors 311 can share one TDC, and the pixel size can be reduced, which is effective for increasing resolution.

[0040] <Creating a histogram> In this embodiment, 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 then creates a histogram based on the TOF measurement results from 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.

[0041] Furthermore, the signal processing unit 123 creates a count map showing the count values ​​of multiple photodetectors 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 photodetector 311.

[0042] The light received by the sub-photodetector 312 may include two types of light: reflected light (measuring light) from the light emitted by the light-emitting element 211 that is reflected by an object, and reflected light (ambient light) from external light other than the light emitted by the light-emitting element that is reflected by an object. Therefore, the histogram includes the frequency of TOF occurrences originating from the measuring light (received count) and the frequency of TOF occurrences originating from the ambient light (ambient light count).

[0043] 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.

[0044] <Relationship between the number of distance measurement operations and frame rate> In this embodiment, for example, a distance measurement operation is performed by simultaneously illuminating one row of light-emitting elements 211 in the horizontal direction, and sequentially illuminating one row of light-emitting elements 211 in the vertical direction to scan the entire field of view. In this embodiment, a histogram (count map) and one distance image (distance map) can be obtained by repeating this single distance measurement operation multiple times in one frame. In this case, the period for creating one distance image is the frame rate, but the time that can be used to perform the distance measurement operation multiple times within the field of view is limited from the viewpoint of maintaining the frame rate.

[0045] If Td is the time taken for one distance measurement operation and X [fps] is the frame rate, then the number of distance measurement operations Ntotal per frame can be calculated by dividing the time per frame (1 / X) by the time taken for one distance measurement operation (Td), as shown in Equation 3 below. (Formula 3) Ntotal = 1 / (X·Td) From Equation 3, when the light-emitting elements 211 for one row are illuminated simultaneously and the light-emitting elements 211 for one row are illuminated sequentially in the column direction, the number of distance measurement operations Ni per row for the i-th row (where i is a natural number) can be found by dividing the number of distance measurement operations Ntotal per frame by the number of rows nv, as shown in Equation 4 below, where nv is the number of rows. (Formula 4) Ni = Ntotal / nv In this embodiment, an example was described in which one row of light-emitting elements 211 are illuminated simultaneously and then sequentially in the column direction. However, any light-emitting elements 211 may be illuminated in any order.

[0046] <Relationship between the number of distance measurement operations and distance measurement accuracy> According to this embodiment, the signal processing unit 123 creates a histogram based on the results of multiple distance measurement operations performed within the field of view, and based on the histogram, it creates a count map for one frame and a distance map showing the distance to the object.

[0047] In this case, the probability (frequency) of the light-receiving element 311 receiving reflected light from an object per distance measurement operation differs depending on the object's state, such as its reflectivity and distance. For example, if an object with high reflectivity is at a close distance, it is possible to receive reflected light with a high probability per distance measurement operation. On the other hand, if an object with low reflectivity is at a far distance, the possibility of receiving reflected light per distance measurement operation decreases. Therefore, in this embodiment, when one or more objects are present within the field of view, the number of distance measurement operations (number of measurements) required to improve the distance measurement accuracy is determined according to the state of these objects. Specifically, the state of the objects is determined based on the count map and / or distance map, which are the distance measurement results from the previous frame, and the number of distance measurement operations is changed according to the state of the objects. In the following, the state of an object is defined by its reflectivity and / or the distance to the object. An object with a first reflectivity and / or a distance of first distance is called a low-probability object, and an object with a second reflectivity that is higher than the first reflectivity and / or a distance of second distance that is closer than the first distance is called a high-probability object.

[0048] As shown in Figure 4, the light emitted from each light-emitting element 211 passes through the image-side telecentric lens 130 and is projected in parallel and at different angles. Therefore, the light emitted from each light-emitting element 211 is projected onto different parts of the object within the field of view. Consequently, in this embodiment, by increasing the number of times the light-emitting element 211 corresponds to a low-probability object in one frame, it is possible to improve the distance measurement accuracy for low-probability objects.

[0049] However, increasing the number of distance measurements for low-probability objects increases the number of combined distance measurements per frame, which may reduce the frame rate. Therefore, in this embodiment, by increasing the number of distance measurements for low-probability objects and decreasing the number of distance measurements for high-probability objects, the number of combined distance measurements is kept the same or not increased, making it possible to improve the distance measurement accuracy for low-probability objects while maintaining the frame rate.

[0050] In this embodiment, an example was described in which the number of times the light-emitting element flashes (number of distance measurements) is changed according to the state of the object. However, the state of different parts of the object may differ depending on the object's orientation, etc. In such cases, the number of times the light-emitting element flashes (number of distance measurements) may be changed according to the state of each part of the object.

[0051] <How to set the number of distance measurements> Next, we will explain how to set the number of distance measurements Ni that can be taken per line.

[0052] The number of distance measurements Ni(nf) in the i-th row of an nf frame is determined to be proportional to the number of distance measurements Ni(nf-1) in the i-th row of the previous frame, and inversely proportional to the sum of the count values ​​ci(nf-1) in the i-th row of the previous frame, as shown in Equation 5 below, where ci(nf-1) is the sum of the count values ​​in the i-th row of the previous frame, and Ni(nf-1) is the number of distance measurements in the i-th row of the previous frame. In this way, the sum of the count values ​​in each row is the same, and the distance measurement accuracy for low-probability objects can be improved while maintaining the frame rate. (Formula 5) Ni(nf)∝(Ni(nf-1)) / (ci(nf-1)) In Equation 5, (ci(nf-1)) / (Ni(nf-1)) corresponds to the estimated reception probability per light emission in the i-th row of the nf-1 frame.

[0053] In this embodiment, an example was described in which the number of distance measurements for the next frame is determined so that the sum of the count values ​​in each row is the same. However, the average value of the distance information for one row of row i of the previous frame is taken as Li(nf-1), and the number of distance measurements for row i of the next frame may be determined to be proportional to the square of the average value of the distance information for one row of row i of the previous frame, Li(nf-1), as shown in Equation 6 below. (Formula 6) Ni(nf)∝Li(nf-1) 2 In this case, the average value Li(nf-1) of the distance measurement information for one row of row i of the previous frame may be used as the average value of the distance information corresponding only to the main object from the distance information of row i of the previous frame.

[0054] Furthermore, a lower limit and / or upper limit may be set for the number of times the light-emitting element emits light.

[0055] For example, if the number of distance measurements Ni(nf) in the i-th row of the next frame is less than or equal to a predetermined threshold Nmin, a lower limit can be set by setting Ni(nf)=Nmin, or Ni(nf)=0 to prevent light emission in the next nf frame (making the number of light emission zero).

[0056] Furthermore, if the number of distance measurements Ni(nf) in the i-th row of the next frame is greater than or equal to a predetermined threshold Nmax, an upper limit may be set by setting Ni(nf) = Nmax.

[0057] According to Embodiment 1 described above, the number of distance measurements in the next frame is determined based on the distance measurement results of the previous frame, so as not to increase the number of distance measurements (number of times the light-emitting element flashes) in one frame. Specifically, the state of an object is determined based on the count map and / or distance map, which are the distance measurement results of the previous frame, and the number of distance measurements is changed according to the state of the object. When changing the number of distance measurements in the next frame according to the state of the object, the number of distance measurements for high-probability objects is decreased by the same amount as the number of distance measurements for low-probability objects, so that the total number of distance measurements in one frame remains the same or does not increase. This makes it possible to improve the distance measurement accuracy for low-probability objects without reducing the frame rate.

[0058] [Modified example of Embodiment 1] In the embodiment 1 described above, an example was explained in which the number of distance measurements (number of times the light-emitting elements are emitted) in the next frame is changed according to the state of the object. In this case, if the multiple light-emitting elements 211 of the light-emitting element array 210 are emitted sequentially from the first row as shown in Figure 6(a), for example, if low-probability objects are concentrated around row i, an in-field difference of rolling distortion will occur. For this reason, instead of emitting the light-emitting elements sequentially from the first row, the rows in which the light-emitting elements are emitted may be controlled in any order (discretely) as shown in Figure 6(b).

[0059] [Embodiment 2] In the above-described Embodiment 1, an example was described in which one row of light-emitting elements is emitted simultaneously, and one row of light-emitting elements 211 are emitted sequentially in the column direction. In contrast, the distance measuring device 700 of Embodiment 2, as shown in Figure 7, has a main control unit 140 which includes a light-emitting element determination unit 721, and further includes an object detection unit 710. In Embodiment 2, the object detection unit 710 detects an object of interest from an image captured by the imaging unit 711, and the light-emitting element determination unit 721 determines which light-emitting elements to emit in relation to the object of interest. The other configurations and functions of the distance measuring device 700 of Embodiment 2 are the same as those in Figure 1 of Embodiment 1.

[0060] As a result, the projected light emitted by the image-side telecentric lens 130 is projected only onto the object of interest, making it possible to perform distance measurement only on the object of interest. By performing distance measurement only on the object of interest in this way, it becomes possible to allocate the total number of distance measurements per frame (Ntotal) only to the area of ​​the object of interest, thereby increasing the number of distance measurements taken on the object of interest and improving the distance measurement accuracy for that object.

[0061] [Embodiment 3] In Embodiment 1 described above, an example was explained in which the number of distance measurements (number of times the light-emitting element flashes) in the next frame is changed according to the state of the object. In contrast, Embodiment 3 improves the distance measurement accuracy by changing the pulse width of the light emitted by the light-emitting element 211 (changing the light emission energy).

[0062] In this embodiment, based on the count value ci(nf-1) of the i-th row of the previous frame (the sum of the count values ​​for one row), the emission pulse width is lengthened according to the count value ci for low-probability objects, as shown in Figure 8(a), and shortened according to the count value ci for high-probability objects, as shown in Figure 8(b). This improves the distance measurement accuracy for low-probability objects while satisfying eye-safe conditions to protect the human eye.

[0063] [Other embodiments] This embodiment can also be implemented by supplying a program that implements one or more of the functions of the above-described embodiment 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 implemented by a circuit (e.g., an ASIC) that implements one or more functions.

[0064] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention.

[0065] The disclosures herein include the following distance measuring devices, distance measuring methods, and programs. [Item 1] A light-emitting unit having multiple light-emitting elements, A light-receiving unit having multiple light-receiving elements, A control means that performs a distance measuring operation by individually emitting light from the plurality of light-emitting elements and projecting light into a predetermined scanning range, The distance measurement operation includes a measuring means that determines the distance to an object based on the time it takes for the light emitted by the light-emitting unit to be projected onto the object and for the light-receiving unit to receive the light reflected from the object. The measurement means creates a distance measurement result including distance information to the object at a predetermined frame rate. The distance measuring device is characterized in that the control means determines the number of distance measuring operations in the next frame based on the distance measuring result obtained by the measuring means in the distance measuring operation in the previous frame, so as not to increase the number of distance measuring operations in one frame. [Item 2] The control means performs the distance measurement operation multiple times in the previous frame and determines the number of distance measurement operations in the next frame based on the distance measurement results obtained by the measurement means. The distance measuring device according to item 1, characterized in that the number of distance measuring operations in the following frame includes zero. [Item 3] The distance measuring device according to item 1 or 2, characterized in that the control means determines the state of an object included in the predetermined scanning range based on the distance measurement result obtained by the measuring means in the distance measuring operation in the previous frame, and determines the number of distance measuring operations in the next frame according to the state of the object. [Item 4] The state of the object is the reflectance of the object and / or the distance to the object. The distance measuring device according to item 3, characterized in that the control means increases the number of distance measuring operations for an object with a first reflectance and / or a first distance, and decreases the number of distance measuring operations for an object with a second reflectance that is higher than the first reflectance and / or a second distance that is closer than the first distance by the amount by which the number of distance measuring operations for an object with the first reflectance was increased. [Item 5] The measurement means creates a histogram as the distance measurement result for one frame, showing the relationship between the time of flight of light until the light receiving element receives reflected light from the object and the count value which is the frequency with which the light receiving element receives reflected light from the object. A distance measuring device according to any one of items 1 to 4, characterized in that it creates a count map of the count values ​​of the plurality of light-receiving elements in one frame and a distance map corresponding to the distance to the object, based on the histogram of each light-receiving element. [Item 6] The distance measuring device according to item 5, characterized in that the control means determines the number of distance measuring operations in the next frame based on the distance map and / or the count map obtained in the previous frame. [Item 7] The light-emitting section is arranged in a two-dimensional manner in the row and column directions, with the plurality of light-emitting elements arranged in mutually orthogonal directions. The distance measuring device according to item 6, characterized in that the distance measuring operation includes simultaneously illuminating a row of light-emitting elements and sequentially illuminating the row of light-emitting elements in the column direction. [Item 8] The distance measuring device according to item 7, characterized in that the control means determines the number of times the light-emitting element per row illuminates in the next frame based on the number of times the light-emitting element per row illuminates in the previous frame and the count value. [Item 9] The distance measuring device according to item 8, characterized in that the control means calculates the estimated light reception probability for one emission of light by the i-th row light-emitting element from the number of times the i-th row (where i is a natural number) light-emitting element emits light in the previous frame and the sum of the count values ​​of the i-th row light-emitting element in the previous frame, and determines the number of times the i-th row light-emitting element emits light in the next frame based on the estimated light reception probability. [Item 10] The distance measuring device according to item 9, characterized in that the control means determines the number of times the i-th row light-emitting element lights up in the next frame in proportion to the number of times the i-th row light-emitting element lights up in the previous frame, and inversely proportional to the sum of the count values ​​of the i-th row light-emitting elements in the previous frame. [Item 11] The distance measuring device according to item 7, characterized in that the control means determines the number of times the i-th row light-emitting element is illuminated in the next frame in proportion to the square of the average value of the distance measurement results for the i-th row in the previous frame. [Item 12] The distance measuring device according to any one of items 7 to 11, characterized in that the control means controls the rows in which the light-emitting element emits light in no particular order. [Item 13] The distance measuring device according to any one of items 7 to 12, characterized in that the number of times the light-emitting element is illuminated is provided with a lower limit and / or an upper limit. [Item 14] An imaging means for imaging the predetermined scanning range, The system includes a detection means for detecting a predetermined object from an image generated by the imaging means, The distance measuring device according to item 1 or 2, characterized in that the control means controls the light-emitting unit so that the light emitted by the light-emitting unit is projected onto the predetermined object during the distance measuring operation. [Item 15] The distance measuring device according to any one of items 7 to 14, characterized in that the control means controls the pulse width for which the light-emitting element emits light instead of the number of times the light-emitting element emits light. [Item 16] The distance measuring device according to any one of items 1 to 15, 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. [Item 17] The distance measuring device according to item 16, characterized in that it has a beam splitter that guides the light emitted from the light-emitting unit to the image-side telecentric lens and guides the light reflected from the object to the light-receiving unit. [Item 18] The distance measuring device according to item 16 or 17, 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 on the image-side telecentric lens as parallel light. [Item 19] 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, A control step of performing a distance measuring operation in which the plurality of light-emitting elements are individually made to emit light and project light into a predetermined scanning range, The distance measurement operation includes a measurement step of determining the distance to an object based on the time it takes for the light emitted by the light-emitting unit to be projected onto an object and for the light-receiving unit to receive the light reflected from the object. In the measurement step, a distance measurement result including distance information to the object is created at a predetermined frame rate. The control step is characterized in that the number of distance measurement operations in the next frame is determined based on the distance measurement result obtained in the measurement step during the distance measurement operation in the previous frame, so as not to increase the number of distance measurement operations in one frame. [Item 20] A program to cause a computer to function as a distance measuring device as described in any of items 1 through 18. [Explanation of Symbols]

[0066] 100, 700... 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 light-emitting unit having multiple light-emitting elements, A light-receiving unit having multiple light-receiving elements, A control means that performs a distance measuring operation by individually emitting light from the plurality of light-emitting elements and projecting light into a predetermined scanning range, The distance measurement operation includes a measuring means that determines the distance to an object based on the time it takes for the light emitted by the light-emitting unit to be projected onto the object and for the light-receiving unit to receive the light reflected from the object. The measurement means creates a distance measurement result including distance information to the object at a predetermined frame rate. The distance measuring device is characterized in that the control means determines the number of distance measuring operations in the next frame based on the distance measuring result obtained by the measuring means in the distance measuring operation in the previous frame, so as not to increase the number of distance measuring operations in one frame.

2. The control means performs the distance measurement operation multiple times in the previous frame and determines the number of distance measurement operations in the next frame based on the distance measurement results obtained by the measurement means. The distance measuring device according to claim 1, characterized in that the number of distance measuring operations in the following frame includes zero.

3. The distance measuring device according to claim 1, characterized in that the control means determines the state of an object included in the predetermined scanning range based on the distance measurement result obtained by the measuring means in the distance measuring operation in the previous frame, and determines the number of distance measuring operations in the next frame according to the state of the object.

4. The state of the object is the reflectance of the object and / or the distance to the object. The distance measuring device according to claim 3, characterized in that the control means increases the number of distance measuring operations for an object with a first reflectance and / or a first distance, and decreases the number of distance measuring operations for an object with a second reflectance that is higher than the first reflectance and / or a second distance that is closer than the first distance by the amount by which the number of distance measuring operations for an object with the first reflectance was increased.

5. The measurement means creates a histogram as the distance measurement result for one frame, showing the relationship between the time of flight of light until the light receiving element receives reflected light from the object and the count value which is the frequency with which the light receiving element receives reflected light from the object. The distance measuring device according to claim 1, characterized in that it creates a count map of the count values ​​of the plurality of light-receiving elements in one frame and a distance map corresponding to the distance to the object, based on the histogram for each of the light-receiving elements.

6. The distance measuring device according to claim 5, wherein the control means determines the number of distance measuring operations in the next frame based on the distance map and / or count map obtained in the previous frame.

7. The light-emitting section is arranged in a two-dimensional manner in the row and column directions, with the plurality of light-emitting elements arranged in mutually orthogonal directions. The distance measuring device according to claim 6, characterized in that the distance measuring operation includes simultaneously illuminating a row of light-emitting elements and sequentially illuminating the row of light-emitting elements in the column direction.

8. The distance measuring device according to claim 7, characterized in that the control means determines the number of times the light-emitting element per row illuminates in the next frame based on the number of times the light-emitting element per row illuminates in the previous frame and the count value.

9. The distance measuring device according to claim 8, characterized in that the control means calculates an estimated light reception probability for one emission of light by the i-th row light-emitting element from the number of times the i-th row (where i is a natural number) light-emitting element emits light in the previous frame and the sum of the count values ​​of the i-th row light-emitting element in the previous frame, and determines the number of times the i-th row light-emitting element emits light in the next frame based on the estimated light reception probability.

10. The distance measuring device according to claim 9, characterized in that the control means determines the number of times the i-th light-emitting element in the i-th row illuminates in the next frame in proportion to the number of times the i-th row light-emitting element illuminates in the previous frame, and inversely proportional to the sum of the count values ​​of the i-th row light-emitting elements in the previous frame.

11. The distance measuring device according to claim 7, characterized in that the control means determines the number of times the i-th row light-emitting element is illuminated in the next frame in proportion to the square of the average value of the distance measurement results for the i-th row in the previous frame.

12. The distance measuring device according to claim 7, characterized in that the control means controls the rows in which the light-emitting elements emit light in no particular order.

13. The distance measuring device according to claim 7, characterized in that the number of times the light-emitting element is illuminated is provided with a lower limit and / or an upper limit.

14. An imaging means for imaging the predetermined scanning range, The system includes a detection means for detecting a predetermined object from an image generated by the imaging means, The distance measuring device according to claim 1, characterized in that the control means controls the light-emitting unit so that the light emitted by the light-emitting unit is projected onto the predetermined object during the distance measuring operation.

15. The distance measuring device according to claim 7, characterized in that the control means controls the pulse width for causing the light-emitting element to emit light instead of the number of times the light-emitting element emits light.

16. The distance measuring device according to claim 1, 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.

17. The distance measuring device according to claim 16, further comprising a beam splitter that guides the light emitted from the light-emitting unit to the image-side telecentric lens and guides the light reflected from the object to the light-receiving unit.

18. The distance measuring device according to claim 16, 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.

19. 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, A control step of performing a distance measuring operation in which the plurality of light-emitting elements are individually made to emit light and project light into a predetermined scanning range, The distance measurement operation includes a measurement step of determining the distance to an object based on the time it takes for the light emitted by the light-emitting unit to be projected onto an object and for the light-receiving unit to receive the light reflected from the object. In the measurement step, a distance measurement result including distance information to the object is created at a predetermined frame rate. The control step is characterized in that the number of distance measurement operations in the next frame is determined based on the distance measurement result obtained in the measurement step during the distance measurement operation in the previous frame, so as not to increase the number of distance measurement operations in one frame.

20. A program for causing a computer to function as a distance measuring device according to any one of claims 1 to 18.

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