Distance measurement device and distance measurement method

Abstract

This distance measurement device comprises: a light irradiation unit that emits light; a sensor that detects reflected light resulting from the light emitted by the light irradiation unit being reflected by a distance measurement target object; a distance data acquisition unit that generates two-dimensional distance data of a plurality of frames indicating the distance to the distance measurement target object on the basis of the time from when the light irradiation unit emits light to when the sensor detects the reflected light; a received light intensity acquisition unit that acquires the received light intensity of the reflected light detected by the sensor; and a correction calculation unit that changes the number of frames in which the distance measurement values of the two-dimensional distance data between the plurality of frames are integrated, on the basis of the received light intensity of the reflected light for each frame.

Description

Distance Measuring Device and Distance Measuring Method

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

[0002] Conventionally, there has been a technique for measuring the distance to an object by irradiating the object with laser light having a predetermined wavelength, receiving the light reflected by the object, and measuring the distance based on the timing of light irradiation and the timing of light reception. As a sensor using such a distance measuring technique, a ToF (Time of Flight) sensor is known. As a document in which a technique related to a ToF sensor is disclosed, for example, Patent Document 1 can be exemplified.

[0003] Japanese Patent Application Laid-Open No. 2021-18079

[0004] In such a conventional technique, a semiconductor laser such as a vertical cavity surface emitting laser (VCSEL) is used to irradiate the object with laser light. However, there has been a problem that noise or the like is generated in the distance measurement data due to scattered light of the laser light irradiated on the surface of the object, and an appropriate distance measurement value cannot be obtained.

[0005] The present embodiment has been made in view of such a situation, and an object thereof is to provide a distance measuring device and a distance measuring method capable of accurately measuring the distance to an object to be distance-measured.

[0006] One aspect of the present embodiment includes a light irradiation unit that irradiates light, a sensor that detects reflected light obtained by reflecting the light irradiated by the light irradiation unit on a distance measurement target object, and a distance data acquisition unit that generates two-dimensional distance data of a plurality of frames indicating the distance to the distance measurement target object based on the time from when the light irradiation unit irradiates light until the sensor detects the reflected light, a light reception intensity acquisition unit that acquires the light reception intensity of the reflected light detected by the sensor, and a correction calculation unit that changes the number of frames for integrating the distance measurement values of the two-dimensional distance data between the plurality of frames based on the light reception intensity for each frame of the reflected light.

[0007] Furthermore, one aspect of this embodiment is a distance measuring method performed by a distance measuring device comprising a light irradiation unit that irradiates light and a sensor that detects reflected light reflected from an object to be measured by the light irradiation unit, the method comprising generating two-dimensional distance data for multiple frames indicating the distance to the object to be measured based on the time from when the light irradiation unit irradiates light until the sensor detects the reflected light, obtaining the received light intensity of the reflected light detected by the sensor, and changing the number of frames for accumulating the distance values ​​of the two-dimensional distance data between the multiple frames based on the received light intensity for each frame of the reflected light.

[0008] According to this embodiment, the distance to an object can be measured with high accuracy.

[0009] This figure shows an example of the configuration of the distance information acquisition system according to the first embodiment. This figure shows an example of the functional configuration of the calculation unit of this embodiment. This figure explains the calculations performed by the calculation unit of this embodiment. This figure shows an example of the relationship between the received light intensity and the variation in the distance measurement result of this embodiment. This figure shows an example of the correspondence between the received light intensity and the number of integrated frames of this embodiment. This figure shows a first modified example of the correspondence between the received light intensity and the number of integrated frames of this embodiment. This figure shows a second modified example of the correspondence between the received light intensity and the number of integrated frames of this embodiment. This figure shows an example of the operation flow of the distance measuring device of this embodiment. This figure shows an example of the functional configuration of the calculation unit according to the second embodiment. This figure shows an example of the operation flow of the distance measuring device of the second embodiment.

[0010] The distance measuring device according to this embodiment will be described in detail below with reference to the attached drawings, with reference to preferred embodiments. Note that the embodiments described below are merely examples, and this embodiment is not limited to the embodiments described below. Furthermore, "based on XX" in this application means "based on at least XX," and includes cases where it is based on other elements in addition to XX. Also, "based on XX" is not limited to cases where XX is used directly, but also includes cases where calculations or processing have been performed on XX. "XX" is any element (for example, any information). Furthermore, in the following drawings, the scale and numbers of each structure may differ from the scale and numbers of the actual structure in order to make each configuration easier to understand.

[0011] [First Embodiment] Figure 1 is a diagram showing an example of the configuration of the distance information acquisition system 1 according to the first embodiment. The outline of the distance information acquisition system 1 will be described with reference to the same figure. Hereinafter, the positional relationships of the components included in the distance information acquisition system 1 may be shown using a three-dimensional Cartesian coordinate system of the x, y, and z axes.

[0012] The distance information acquisition system 1 comprises a distance measuring device 10 and an information processing device 20. The distance measuring device 10 comprises an illumination unit 11, a lens 12, a ToF sensor 13, a distance measuring unit 14, and a calculation unit 15. The distance measuring device 10 acquires the distance to the target object OB.

[0013] The irradiation unit 11 includes a light-emitting element capable of emitting light such as laser light, and irradiates the target object OB with light. The laser light emitted by the irradiation unit 11 may be visible light or infrared light. The number of light-emitting elements included in the irradiation unit 11 may be multiple. Specifically, the irradiation unit 11 may be a laser diode array such as a VCSEL (Vertical Cavity Surface Emitting Laser). Based on instructions from the distance measuring unit 14, the irradiation unit 11 irradiates laser light in a direction perpendicular to the ToF sensor 13 (the z-axis direction in the figure). In the following description, as an example, the irradiation unit 11 will be described as irradiating infrared laser light.

[0014] In other words, the irradiation unit 11 (light irradiation unit) irradiates light.

[0015] Light emitted by the illumination unit 11 is reflected by the target object OB and enters the ToF sensor 13 via the lens 12. The lens 12 may specifically be an optical lens. The distance measuring unit 14 measures the distance to the target object OB based on the time elapsed from when the illumination unit 11 emits light until the ToF sensor 13 receives the light.

[0016] The ToF sensor 13 has multiple pixels on a two-dimensional coordinate system arranged in the vertical direction (y-axis direction in the figure) and the horizontal direction (x-axis direction in the figure). Each pixel in the ToF sensor 13 detects the timing of light reception. The ToF sensor 13 outputs detection information for each pixel in the two-dimensional coordinate system to the distance measuring unit 14 while scanning.

[0017] In other words, the ToF sensor 13 (sensor) detects the reflected light that is reflected off the target object OB (object to be measured) from the light emitted by the irradiation unit 11.

[0018] The distance measuring unit 14 calculates a distance value for each pixel and generates a distance image DI, which is two-dimensional array data. The distance measuring method for the ToF sensor 13 may be the dToF (Direct Time of Flight) method or the iToF (Indirect Time of Flight) method, etc. In the illustrated example, iToF is used. The distance image DI generated by the distance measuring unit 14 is corrected by the calculation unit 15. The correction calculation performed by the calculation unit 15 is a calculation to correct the distance value that occurs based on the misalignment between the optical axis of the lens 12 and the position of the illumination unit 11. After the correction calculation is performed by the calculation unit 15, the distance image DI generated by the distance measuring unit 14 is output to the information processing device 20 as a corrected distance image CDI, and the information processing device 20 converts it into three-dimensional point cloud data. The information processing device 20 may be an information processing device such as a personal computer or a tablet terminal.

[0019] In this embodiment, the functions of the calculation unit 15 are described as being included in the distance measuring device 10, but the functions corresponding to the calculation unit 15 may be included in the information processing device 20. Furthermore, the functions corresponding to the calculation unit 15 may be included in devices other than the distance measuring device 10 and the information processing device 20. In other words, the distance measuring device 10 may be a configuration that includes the configuration included in the distance measuring device 10 and the functions corresponding to the calculation unit 15 included in the information processing device 20.

[0020] Figure 2 shows an example of the functional configuration of the calculation unit of this embodiment. An example of the functional configuration of the calculation unit 15 will be described with reference to this figure. The calculation unit 15 is composed of a distance data acquisition unit 151, a light reception intensity acquisition unit 152, a correction calculation unit 153, and a storage unit 154. Each of these functional units is implemented, for example, using an electronic circuit. In addition, each functional unit may be equipped with internal storage means such as semiconductor memory or a magnetic hard disk drive, as needed. Furthermore, each function may be implemented by a computer and software.

[0021] The distance data acquisition unit 151 acquires a distance image DI from the distance measuring unit 14. The distance image DI contains the distance value (Depth value) of each point on the two-dimensional coordinate system. This distance value can also be described as the distance value before correction. This distance value is obtained based on the timing of light irradiation by the illumination unit 11, the timing of light reception by the ToF sensor 13, and the speed of light. The distance data acquisition unit 151 outputs the acquired distance image DI to the correction calculation unit 153.

[0022] In other words, the distance data acquisition unit 151 generates a multi-frame distance image DI (two-dimensional distance data) indicating the distance to the target object OB, based on the time from when the irradiation unit 11 irradiates light until the ToF sensor 13 detects the reflected light.

[0023] The light intensity acquisition unit 152 acquires the light intensity of the reflected light that is reflected by the object OB from the light irradiated from the irradiation unit 11. Specifically, the light intensity acquisition unit 152 acquires the light intensity of the reflected light detected by the ToF sensor 13 for each pixel of the ToF sensor 13.

[0024] In other words, the light intensity acquisition unit 152 acquires the light intensity of the reflected light detected by the ToF sensor 13.

[0025] The memory unit 154 stores various types of information necessary for the operation of the calculation unit 15. For example, the memory unit 154 stores correction information for correcting the distance image DI. Note that the memory unit 154 does not necessarily have to be included in the calculation unit 15; the calculation unit 15 may be configured to acquire correction information from an external device.

[0026] Next, a specific example of the distance measurement calculation performed by the distance measuring unit 14 will be described with reference to Figure 3. Note that the configuration of the illumination unit 11 and the distance measuring unit 14 shown in the figure is just one example and is not limited to this.

[0027] Figure 3 is a diagram illustrating the calculations performed by the calculation unit 15 of this embodiment. The figure shows the irradiation unit 11, the first substrate SB1, the lens 12, the ToF sensor 13, the second substrate SB2, the distance measuring unit 14, the flexible cable FL, and the target object OB. In describing this figure, components that have already been described with reference to Figure 1 or Figure 2 may be denoted by the same reference numerals, and their description may be omitted.

[0028] In the illustrated example, the illumination unit 11 is fixed to the first substrate SB1, and the ToF sensor 13 and distance measuring unit 14 are fixed to the second substrate SB2. That is, the illumination unit 11 and the ToF sensor 13 and distance measuring unit 14 are fixed to different substrates. The illumination unit 11 and the distance measuring unit 14 are electrically connected by a flexible cable FL. The flexible cable FL transmits electrical signals from the distance measuring unit 14 to the illumination unit 11. Specifically, the distance measuring unit 14 outputs a light emission pulse LP to the illumination unit 11. The light emission pulse LP contains information about the timing of illuminating the illumination unit 11. The light emission pulse LP may also be a control signal to directly irradiate the illumination unit 11. When the illumination unit 11 receives the light emission pulse LP, it emits light. The distance measuring unit 14 also outputs a shutter pulse SUB to the ToF sensor 13. The shutter pulse SUB is output at the timing when the ToF sensor 13 receives light. When the ToF sensor 13 receives a shutter pulse SUB, it detects the light that has been illuminated by the illumination unit 11 and reflected off the target object OB. The distance measuring unit 14 outputs drive pulses, etc., to scan the detection results from multiple elements arranged in a two-dimensional array on the ToF sensor 13. The distance measuring unit 14 manages the timing from the emission of light from the illumination unit 11 to the reception of light by the ToF sensor 13.

[0029] The illumination unit 11 emits light based on the light emission pulse LP, and the ToF sensor 13 receives reflected light based on the shutter pulse SUB. This operation is performed multiple times, changing the phases of the light emission pulse LP and the shutter pulse SUB, to obtain a distance image DI of one frame. The distance measuring unit 14 obtains multiple distance image DI frames by repeatedly performing the process of obtaining a distance image DI of one frame by outputting the light emission pulse LP and the shutter pulse SUB. In one example of this embodiment, the distance measuring unit 14 obtains 30 distance image DI frames per second.

[0030] In the illustrated example, the center of the effective image range of the ToF sensor 13 coincides with the optical axis of the lens 12. The distance between the optical axis of the lens 12 and the center of the light emission surface of the illumination unit 11 is denoted as distance dV. As shown in Figure 1, if the illumination unit 11 is located above the ToF sensor 13, the left side of Figure 3 is above the camera, and the right side of Figure 3 is below the camera. The ToF sensor 13 is usually located inside the camera body due to the flange back of the lens 12. The distance between the light emission surface of the illumination unit 11 and the light-receiving surface of the ToF sensor 13 is denoted as distance LD. The lens 12 has an entrance pupil position defined. In the illustrated model, the distance from the light-receiving surface of the ToF sensor 13 to the entrance pupil position of the lens 12 is denoted as distance LI. The maximum field of view of the lens is also defined from the entrance pupil position.

[0031] Distance AD ​​is the distance in the optical axis direction from the entrance pupil position of lens 12 to the object OB. Distance YD is the distance from the optical axis to the object OB in the direction of the lower side (right side in the figure) of the camera. In this case, the light emitted from the illumination unit 11 reaches the object OB at distance Da. The light reflected from the object OB reaches the entrance pupil position of lens 12 at distance Db. Here, distance Dc is the distance from the entrance pupil position of lens 12 to the rear principal plane of the lens, and distance Dd is the distance from the rear principal plane to the light-receiving surface of the ToF sensor 13.

[0032] As shown in the figure, distance Dd is an angled distance relative to the ToF sensor 13, depending on the angle of the incident principal ray. If the ToF sensor 13 is a small sensor, such as a 1 / 4-inch sensor, the effective image range of the ToF sensor 13 is small, H3.6 [mm] × V2.7 [mm]. Also, in the case of a C-mount lens, the flange back is short, 17.526 [mm]. In the illustrated example, for the sake of simplicity, the angle between distance Dc and distance Dd is ignored, and Dc + Dd ≈ LI is treated (where the symbol ≈ means approximately equal).

[0033] Alternatively, the distance Dc and distance Dd may be accurately calculated by determining the angle between distance Dc and distance Dd from the distance from the rear principal plane to the light-receiving surface of the ToF sensor 13 and the pixel position of the ToF sensor 13 corresponding to the position of the object OB, and then determining distance Dd. A detailed explanation of the calculation of distance Dc and distance Dd is omitted.

[0034] [About Speckle Noise] Generally, when laser light is shone on the surface of an object OB, some of the light is scattered and reflected on the surface of the object OB, causing a phenomenon called speckle. Speckle introduces errors into the measurement distance of the ToF sensor 13. Speckle is a probabilistic phenomenon, and since a different pattern of reflected light is generated for each measurement frame of the ToF sensor 13, variations occur in the measurement results. When variations in measurement distance occur due to speckle, for example, even with an object OB that has a smooth surface, a problem arises in that undulation-like noise (hereinafter also simply referred to as "undulation") occurs on the surface of the three-dimensional model of the object OB that is the measurement result.

[0035] Conventionally, to suppress such undulations, methods have been proposed to reduce noise (e.g., smoothing) by performing integration processing such as moving averages using distance image DIs from multiple frames, given that speckle is a probabilistic phenomenon. However, when the subject object OB is moving, motion vectors are generated between multiple frames, resulting in side effects such as so-called "tailing."

[0036] The correction calculation unit 153 of this embodiment reduces the noise generated in the distance image DI due to the speckle described above. A specific example of noise reduction by the correction calculation unit 153 will be described. In the ToF sensor 13, the distance value (Depth value) is calculated based on the ratio of the received intensity of reflected light. Therefore, among the pixels of the ToF sensor 13, pixels with low received intensity of reflected light have more noise than pixels with high received intensity of reflected light. The received intensity of reflected light changes depending on the distance from the ToF sensor 13 to the object OB. For example, if the distance from the ToF sensor 13 to the object OB is relatively far, the received intensity of reflected light will be relatively low. In other words, the farther the distance from the ToF sensor 13 to the object OB, the lower the received intensity of reflected light. For this reason, the further the distance from the ToF sensor 13 to the object OB, the greater the noise, and the greater the error and variation in the distance value (Depth value).

[0037] Figure 4 shows an example of the relationship between light reception intensity and the variation in distance measurement results in this embodiment. In the example shown in the figure, in the region where the distance from the ToF sensor 13 to the object OB is far and the light reception intensity is relatively low (for example, region Ra), the difference in depth position (i.e., variation in distance values) is relatively large. In the region where the distance from the ToF sensor 13 to the object OB is close and the light reception intensity is relatively high (for example, region Rb), the difference in depth position (i.e., variation in distance values) is relatively small. In this embodiment, the region is divided into two areas: region Ra, where the light reception intensity is relatively low, and region Rb, where the light reception intensity is relatively high. However, there may be three or more regions.

[0038] Here, if there is movement in the object out of bounds (OB), the closer the distance from the ToF sensor 13 to the object out of bounds, the greater the amount of variation within the field of view of the ToF sensor 13. Conversely, the farther the distance from the ToF sensor 13 to the object out of bounds, the smaller the amount of variation within the field of view of the ToF sensor 13. Therefore, when performing integration processing such as moving average using multiple frames of distance image DI to reduce noise due to speckle, if the distance from the ToF sensor 13 to the object out of bounds is short, increasing the number of frames to be integrated makes it more likely for a trailing pattern to occur. On the other hand, if the distance from the ToF sensor 13 to the object out of bounds is far, a trailing pattern is less likely to occur even if the number of frames to be integrated is increased.

[0039] Therefore, in this embodiment, the correction calculation unit 153 increases the number of integrated frames to enhance the noise reduction effect when the noise is relatively large and trailing is unlikely to occur, that is, when the distance from the ToF sensor 13 to the object OB is large. Conversely, when the noise is relatively small and trailing is likely to occur, that is, when the distance from the ToF sensor 13 to the object OB is small, the correction calculation unit 153 reduces the number of integrated frames to reduce the occurrence of trailing. With the distance measuring device 10 configured in this way, it is possible to achieve both noise reduction and trailing reduction depending on the distance to the object OB.

[0040] More specifically, the correction calculation unit 153 obtains the light reception intensity for each pixel of the ToF sensor 13 from the light reception intensity acquisition unit 152 for each frame. Based on the light reception intensity for each pixel of the ToF sensor 13, the correction calculation unit 153 determines the number of integrated frames for each pixel. Based on the determined number of integrated frames, the correction calculation unit 153 smooths the distance measurement values ​​by integrating the distance measurement values ​​of the distance image DI across multiple frames.

[0041] In other words, the correction calculation unit 153 smooths the distance measurement values ​​by changing the number of frames for which the distance measurement values ​​of the distance image DI are accumulated between multiple frames, based on the received light intensity for each frame of reflected light.

[0042] The correction calculation unit 153 outputs the smoothed distance image DI as a corrected distance image CDI to the information processing device 20.

[0043] In the following description, the number of frames integrated by the correction calculation unit 153 is also referred to as the number of frames for smoothing the distance measurement value, or simply the integrated frame number.

[0044] FIG. 5 is a diagram showing an example of the correspondence relationship between the received light intensity and the integrated frame number in the present embodiment. In this example, in pixels in a region where the distance from the ToF sensor 13 to the object OB is far and the received light intensity is relatively low (for example, region Ra), the difference in the depth position (that is, the variation in the distance value) is relatively large. In pixels in a region where the distance from the ToF sensor 13 to the object OB is close and the received light intensity is relatively high (for example, region Rb), the difference in the depth position (that is, the variation in the distance value) is relatively small.

[0045] As shown in the figure, the correction calculation unit 153 relatively increases the number of integrated frames for pixels in region Ra, and relatively decreases the number of integrated frames for pixels in region Rb. The pixels in region Ra and the pixels in region Rb may be composed of one pixel, or may be composed in units of a plurality of pixels.

[0046] That is, the correction calculation unit 153 increases the number of frames for integrating the distance measurement value of the distance image DI as the received light intensity of the reflected light is lower, and decreases the number of frames for integrating the distance measurement value of the distance image DI as the received light intensity of the reflected light is higher.

[0047] In this case, the correction calculation unit 153 may determine the number of frames to be integrated based on whether the received light intensity of the reflected light is less than a predetermined threshold value or not less than the threshold value. For example, when the received light intensity of the reflected light is less than the threshold value th1, the correction calculation unit 153 increases the number of frames to be integrated, and when the received light intensity of the reflected light is not less than the threshold value th1, the correction calculation unit 153 decreases the number of frames to be integrated.

[0048] That is, when the received light intensity of the reflected light is less than a predetermined threshold value, the correction calculation unit 153 increases the number of frames for integrating the distance measurement value of the distance image DI, and when it is not less than the threshold value, the correction calculation unit 153 decreases the number of frames for integrating the distance measurement value of the distance image DI.

[0049] As an example, the correction calculation unit 153 sets the number of integrated frames to the upper limit value LU when the reflected light intensity is less than the threshold th1 (i.e., region Ra). Also, the correction calculation unit 153 sets the number of integrated frames to less than the upper limit value LU when the reflected light intensity is greater than or equal to the threshold th1 (i.e., region Rb).

[0050] As shown in the figure, the correction calculation unit 153 may also gradually decrease the number of integrated frames in response to an increase in the received intensity of reflected light. For example, in the region Rb, in the range where the received intensity is less than the threshold th2 (i.e., region Rb1), the correction calculation unit 153 linearly decreases the number of integrated frames from the upper limit LU to the lower limit LL. In the range where the received intensity is greater than or equal to the threshold th2 (i.e., region Rb2), the correction calculation unit 153 sets the number of integrated frames to the lower limit LL. The upper limit LU of the number of integrated frames is, for example, 20 frames. The lower limit LL of the number of integrated frames is, for example, 2 frames.

[0051] The threshold values ​​th1, th2, upper limit LU, and lower limit LL shown in the figure may all be pre-stored as correction information in the storage unit 154. In this case, the correction calculation unit 153 may read the correction information (i.e., threshold values ​​th1, th2, upper limit LU, and lower limit LL) from the storage unit 154 and calculate the number of integrated frames with respect to the received light intensity of the reflected light.

[0052] In the example described above, the correction calculation unit 153 linearly decreases the number of integrated frames as the received intensity of the reflected light increases, but it is not limited to this. The correction calculation unit 153 may change the number of integrated frames curvilinearly or in a stepwise manner.

[0053] Figure 6 shows a first modified example of the correspondence between the received light intensity and the number of integrated frames in this embodiment. In this modified example, the correction calculation unit 153 gradually decreases the number of integrated frames in a curve as the received light intensity of the reflected light increases.

[0054] Figure 7 shows a second modified example of the correspondence between the received light intensity and the number of integrated frames in this embodiment. In this modified example, the correction calculation unit 153 gradually reduces the number of integrated frames in a stepwise manner as the received light intensity of the reflected light increases.

[0055] Even with the distance measuring device 10 configured as in these modified examples, noise reduction and trail reduction can be achieved simultaneously by adjusting the number of integrated frames for smoothing according to the distance to the target object OB.

[0056] Figure 8 shows an example of the operation flow of the distance measuring device 10 of this embodiment.

[0057] (Step S10) The irradiation unit 11 irradiates the target object OB with laser light. The ToF sensor 13 detects the reflected light from the target object OB. Step S10 can also be rephrased as detecting the reflected light of the irradiated laser light and detecting the presence of the target object OB by the reflected light.

[0058] (Step S20) The distance measuring unit 14 calculates a distance value for each pixel of the ToF sensor 13 and generates a distance image DI (i.e., two-dimensional distance data), which is two-dimensional array data.

[0059] (Step S30) The light intensity acquisition unit 152 acquires the light intensity of the reflected light detected by the ToF sensor 13 for each pixel of the ToF sensor 13.

[0060] (Step S40) The correction calculation unit 153 calculates the number of integrated frames for each pixel of the ToF sensor 13 based on the received intensity of the reflected light.

[0061] (Step S50) The correction calculation unit 153 smooths the distance image DI by integrating the distance image DI of multiple frames pixel by pixel based on the number of integrated frames per pixel calculated in step S40. The correction calculation unit 153 outputs the smoothed distance image DI as a corrected distance image CDI.

[0062] The distance measuring device 10 sequentially generates a corrected distance image CDI by repeatedly executing steps S10 to S50 described above for each frame. The processing in steps S20 to S50 may be performed on the entire pixel of the ToF sensor 13, or on the range in the pixel of the ToF sensor 13 where reflected light from the object OB is received.

[0063] With the distance measuring device 10 configured in this way, noise reduction and trail reduction can be achieved simultaneously by adjusting the number of integrated frames for smoothing according to the distance to the target object's out-of-bounds area. Therefore, the distance measuring device 10 can accurately measure the distance to the target object.

[0064] [Second Embodiment] Figure 9 shows an example of the functional configuration of the calculation unit 15a according to the second embodiment. The calculation unit 15a of this embodiment differs from the calculation unit 15 of the first embodiment described above in that it includes a motion determination unit 155.

[0065] The motion determination unit 155 determines whether the object OB is a moving object based on the pixel-by-pixel detection results from the ToF sensor 13. The motion determination unit 155 performs motion determination based on one of the known methods. For example, the motion determination unit 155 extracts feature points of the object OB from the pixel-by-pixel detection results from the ToF sensor 13. The motion determination unit 155 calculates a motion vector based on the positional changes between frames for the extracted feature points. The motion determination unit 155 determines that the object OB is a moving object if the magnitude of the motion vector of the feature points exceeds a predetermined threshold.

[0066] In other words, the motion determination unit 155 determines that the object OB is a moving object. A moving object includes an object that is moving relative to the distance information acquisition system 1.

[0067] The correction calculation unit 153 reduces the number of frames for integrating the distance measurement values ​​of the distance image DI when the target object OB is a moving object. The correction calculation unit 153 further adjusts the number of integration frames to be reduced from the number of integration frames determined by the received light intensity when the target object OB is a moving object.

[0068] Furthermore, if the object OB is a moving object, the correction calculation unit 153 reduces the number of frames for accumulating the distance measurement value of the distance image DI as the magnitude of the movement of the object OB increases. A large magnitude of movement means that the movement per unit time is large relative to the distance information acquisition system 1. The correction calculation unit 153 further adjusts the number of accumulation frames determined by the received light intensity to be even smaller as the magnitude of the movement of the object OB increases.

[0069] Figure 10 shows an example of the operation flow of the distance measuring device 10 of the second embodiment.

[0070] The operation flow shown in Figure 10 differs from the operation flow shown in Figure 8 in that the processing in step S45 is added.

[0071] (Step S45) The motion determination unit 155 adjusts the number of cumulative frames per pixel calculated in step S40 according to the movement of the object OB.

[0072] (Step S50) The correction calculation unit 153 smooths the distance image DI by integrating the distance image DI of multiple frames pixel by pixel based on the number of integrated frames per pixel adjusted in step S45.

[0073] In Figure 10, a process may be added at any time, such as after step S40, to determine whether or not there is movement in the object OB based on the determination result of the motion determination unit 155. If this determination determines that there is no movement in the object OB, the process is performed without step S45. If it determines that there is movement in the object OB, the process is performed including step S45.

[0074] As mentioned above, increasing the number of integrated frames for smoothing enhances the noise reduction effect, but it also makes trailing more likely. This is especially true when the target object (OB) is a moving object.

[0075] According to the distance measuring device 10 of this embodiment, it is possible to determine whether the target object OB is a moving object, and if the target object OB is a moving object, the number of integrated frames for smoothing can be reduced, thereby reducing the occurrence of trailing. Therefore, the distance measuring device 10 can accurately measure the distance to the target object.

[0076] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the above embodiments may be combined as appropriate.

[0077] It can be applied to so-called laser rangefinders, etc.

[0078] 1...Distance information acquisition system, 10...Distance measuring device, 11...Irradiation unit, 13...ToF sensor, 14...Distance measuring unit, 15...Calculation unit, 151...Distance data acquisition unit, 152...Light reception intensity acquisition unit, 153...Correction calculation unit, 154...Storage unit, 155...Motion detection unit, DI...Distance image, CDI...Corrected distance image

Claims

1. A distance measuring device comprising: a light irradiation unit that irradiates light; a sensor that detects reflected light reflected from an object to be measured by the light irradiation unit; a distance data acquisition unit that generates two-dimensional distance data for multiple frames indicating the distance to the object to be measured based on the time from when the light irradiation unit irradiates light until the sensor detects the reflected light; a light reception intensity acquisition unit that acquires the light reception intensity of the reflected light detected by the sensor; and a correction calculation unit that changes the number of frames for accumulating the distance values ​​of the two-dimensional distance data between the multiple frames based on the light reception intensity for each frame of the reflected light.

2. The distance measuring device according to claim 1, wherein the correction calculation unit increases the number of frames for integrating the distance measurement values ​​of the two-dimensional distance data as the intensity of the reflected light reception decreases, and decreases the number of frames for integrating the distance measurement values ​​of the two-dimensional distance data as the intensity of the reflected light reception increases.

3. The distance measuring device according to claim 1, wherein the correction calculation unit increases the number of frames for accumulating the distance measurement values ​​of the two-dimensional distance data when the received light intensity of the reflected light is less than a predetermined threshold, and decreases the number of frames for accumulating the distance measurement values ​​of the two-dimensional distance data when it is equal to or greater than the threshold.

4. The distance measuring device according to claim 2 or 3, further comprising a motion determination unit that determines whether the object to be measured is a moving object, wherein the correction calculation unit reduces the number of frames for accumulating the distance values ​​of the two-dimensional distance data when the object to be measured is a moving object.

5. The distance measuring device according to claim 4, wherein the motion determination unit further determines the magnitude of the movement of the object to be measured, and the correction calculation unit, when the object to be measured is a moving object, reduces the number of frames for accumulating the distance values ​​of the two-dimensional distance data as the magnitude of the movement of the object to be measured increases.

6. A distance measuring method performed by a distance measuring device comprising a light irradiation unit that irradiates light and a sensor that detects reflected light reflected from an object to be measured by the light irradiation unit, the method comprising: generating two-dimensional distance data for multiple frames indicating the distance to the object to be measured based on the time from when the light irradiation unit irradiates light until the sensor detects the reflected light; obtaining the received light intensity of the reflected light detected by the sensor; and changing the number of frames for accumulating the distance values ​​of the two-dimensional distance data between the multiple frames based on the received light intensity for each frame of the reflected light.

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