Object approach detection device and object approach detection method

An object approach detection device includes: an imager that includes a first and a second lens group which have different focal lengths from each other and are arranged so as to image a same target object and that acquires first and second image information imaged through the first and the second lens group, respectively; an object detector that detects presence or absence of an object; and an object approach determiner that determines that approach of the object has been detected when a time difference between a first time and a second time is equal to or less than an approach determination threshold value, the first time being when the first image information is acquired when the object has been detected based on the first image information, the second time being when the second image information is acquired when the object has been detected based on the second image information.

The entire disclosure of Japanese patent Application No. 2017-032991, filed on Feb. 24, 2017, is incorporated herein by reference in its entirety.

BACKGROUND

Technological Field

The present invention relates to an object approach detection device and an object approach detection method.

Description of the Related Art

Conventionally, as a detection device or a detection method of an approaching object, there has been known one that detects a surrounding object by using a stereo camera or the like and measures the distance to the object.

Moreover, JP 2014-16309 A discloses a device which uses a lens unit constituted by a main lens and a lens array, in which microlenses whose focal lengths can be varied are two-dimensionally arranged, to estimate the distance based on image information corresponding to each focal length.

JP 2014-62748 A discloses a device which uses a multifocal lens having a plurality of focusing lengths to capture an image simultaneously for each of the plurality of focusing lengths to acquire a plurality of images, and detects a position of a moving object in a three-dimensional space based on the plurality of acquired images.

In the device described above in JP 2014-16309 A, the distance estimation is performed based on the image information corresponding to each focal length so that the amount of the calculation for this becomes large, and the power consumption increases.

Moreover, in the device in JP 2014-62748 A, the focal length that best focuses from image information on the plurality of focal lengths, that is, a distance z to the object is estimated and calculated, and the xy position of the object is detected based on this to obtain the three-dimensional position (x, y, z) of the object. Furthermore, the three-dimensional position is detected at each predetermined time to obtain a movement locus of the object. Thus, the amount of the calculation also becomes large, and the power consumption increases.

In recent years, a detection device which detects the approach of an object is also mounted on a small flying machine such as a drone, and thus prevention of a crash due to collision has been intended.

In this small flying machine, it is necessary to detect an approaching object at a wide angle over a wide range in order to detect objects from various directions. However, in order to detect an approaching object at a wide angle, a plurality of cameras are necessary. In a case where a stereo camera is used, the number of camera modules increases, the weight increases, and the flight time becomes short.

Thus, although a monocular system can be considered, focusing is necessary for distance measurement of an approaching object, and focusing takes time so that images cannot be acquired at the same time. Moreover, since a focusing lens and a driving mechanism are necessary, the lens becomes heavy, and the flight time becomes short.

Furthermore, as described above, the amount of the calculation becomes large, and the power consumption increases in the ones that estimate the distance to the object. In addition, the flight time becomes short in a small flying machine with a limited power source capacity.

SUMMARY

The present invention has been made in light of the above problems, and an object of the present invention is to provide an object approach detection device and the method thereof, which can reduce the amount of calculation for detecting an approaching object and reduce power consumption.

To achieve the abovementioned object, according to an aspect of the present invention, an object approach detection device reflecting one aspect of the present invention comprises: an imager that includes a first lens group and a second lens group which have different focal lengths from each other and are arranged so as to image a same target object and that acquires first image information and second image information imaged through the first lens group and the second lens group, respectively; an object detector that detects presence or absence of an object based on the first image information and the second image information; and an object approach determiner that determines that approach of the object has been detected when a time difference between a first time and a second time is equal to or less than an approach determination threshold value, the first time being when the first image information is acquired when the object has been detected based on the first image information, the second time being when the second image information is acquired when the object has been detected based on the second image information.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1shows the schematic configuration of an object approach detection device1according to an embodiment of the present invention.FIG. 2is a diagram showing an example of the functional configuration of an object detector23.FIG. 3shows an example of the hardware configuration of the object approach detection device1.

InFIG. 1, the object approach detection device1has an imager10and a processing unit20.

The imager10includes a main lens11, a first lens group13G and a second lens group14G which have different focal lengths from each other and are arranged so as to image the same target object and, and acquires first image information D1and second image information D2imaged through each of the main lens11, the first lens group13G and the second lens group14G.

The main lens11is for collecting light, expanding the target range of the imaging and enlarging the viewing angle (widening angle).

The first lens group13G is a lens array including a plurality of first lenses13,13and so on having a first focal length. The second lens group14G is a lens array including a plurality of second lenses14,14and so on having a second focal length.

The plurality of first lenses13,13and so on and the plurality of second lenses14,14and so on are arranged on one object plane12. In this example, the object plane12is flat and may be a transparent object such as glass or may be a virtual plane. Alternatively, the object plane may be curved instead of being flat.

The imager10further has a first imaging element16S which receives the light having passed through the first lens group13G and outputs the first image information D1and a second imaging element17S which receives the light having passed through the second lens group14G and outputs the second image information D2. The first imaging element16S and the second imaging element17S include imaging elements16and17corresponding to the lenses13and14, respectively, and synthesizes the first image information D1and the second image information D2for each focal length based on the images captured by these elements.

The first imaging element16S and the second imaging element17S are arranged to face the object plane12. That is, they are arranged along a flat imaging plane15facing the object plane12. Note that, although a part of the imaging plane15is the first imaging element16S and the second imaging element17S herein, it is also possible to use the entire imaging plane15as an imaging element and extract a necessary part of image information to be synthesized.

Note that the first lens group13G is a lens group with a long focusing length L and the second lens group14G is a lens group with a short focusing length L in the present embodiment. Suppose that the focusing length of the first lens group13G is L1and the focusing length of the second lens group13G is L2. Then, L1is longer than L2, L1>L2. That is, the first focal length of the first lenses13is longer than the second focal length of the second lenses14.

Therefore, the first lenses13focus on a more distant object and the second lenses14focus on an object closer than the case of the first lenses13. Thus, in a case where the object approaches the imager10from a long distance, the first image information D1focused by the first lens group13G is acquired first, and the second image information D2focused by the second lens group14G is acquired thereafter.

Imaging is performed continuously, that is, periodically by the imager10at predetermined time intervals for a target range of a predetermined viewing angle, and the first image information D1and the second image information D2are acquired at the respective timings. At this time, time stamps (digital time stamps) DTS indicating the timings of imaging are acquired. The time stamp DTS indicates a time t at which each of the first image information D1and the second image information D2is acquired. As an example of the time t, it can be shown as “Jan. 30, 2017 13:10:25 27,” “15:52:18 78,” “17:21:25:66,” or the like.

The time interval of the imaging at the imager10can be, for example, 1/60 seconds, 1/30 seconds, 1/10 seconds, one second, two seconds, or the like. In a case where it is desired to increase the speed of object approach detection, the time interval may be short. In a case where the speed of the detection may be slow, the time interval may be long. Moreover, a moving image with an appropriate frame rate such as 60 frames per second (fps), 30 fps or 25 fps may be acquired, and still images and the like may be extracted from the moving image.

As the imager10, it is possible to use a camera or a video camera in which a lens, an imaging element and the like are integrally formed. The image information D1and D2to be acquired may be RGB color image information or may be monochrome image information, infrared or ultraviolet ray image information, or other image information.

The processing unit20has image storage21and22, an object detector23and an object approach determiner24.

The image storage21and22respectively store the first image information D1and the second image information D2acquired and transferred by the imager10.

The object detector23detects the presence or absence of an object based on the first image information D1and the second image information D2.

As shown well inFIG. 2, the object detector23has, for example, an edge detector231that performs edge detection on the first image information D1and the second image information D2, and detects the presence of the object when the edge is equal to or greater than an edge detection threshold value th11. A first edge image E1and a second edge image E2are stored in storage231A and231B.

The object detector23also has an object recognizer232that performs image recognition based on the first image information D1and the second image information D2to recognize the object. The object approach determiner24can determine that the approach of the object has been detected on the condition that the objects (recognized objects) B recognized by the object recognizer232are the same. A first recognized object B1and a second recognized object B2are stored in storage232A and232B.

The object detector23also has a spatial frequency detector233that detects spatial frequencies F1and F2of the first image information D1and the second image information D2, and detects the presence of the object when the spatial frequencies F1and F2are equal to or greater than a frequency detection threshold value th12.

At this time, for example, the first image information D1and the second image information D2are each divided into a plurality of regions, and the edge detection or the spatial frequency detection is performed on each region of the image information.

A first spatial frequency F1and a second spatial frequency F2are stored in storage233A and233B.

Moreover, for example, the object detector23detects the presence or absence of an object first based on the image information corresponding to the lens group with the long focusing length L among the first image information D1and the second image information D2, and detects the presence or absence of the object based on other image information only when the presence of the object has been detected.

Note that, in the object detector23, various known techniques can be used for the configuration and a series of processing in the edge detector231, the object recognizer232and the spatial frequency detector233. Moreover, it is also possible to adopt a configuration in which a part of them is omitted.

The object approach determiner24determines that the approach of the object has been detected when a time difference Δt between a first time ta and a second time tb is equal to or less than an approach determination threshold value th1. The first time ta is when the first image information D1is acquired when the object has been detected based on the first image information D1. The second time tb is when the second image information D2is acquired when the object has been detected based on the second image information D2. When the approach of the object is determined to be detected, an object approach signal S1is out.

For example, the object approach determiner24can determine that the approach of the object has been detected on the condition that the region in which the object has been detected corresponds to a region into which the first image information D1and the second image information D2are divided or is a region adjacent thereto.

Moreover, for example, the object approach determiner24can determine that the approach of the object is not detected in a case where the object detector23detects the presence of the object based on the image information corresponding to the lens group with the short focusing length L prior to the image information corresponding to the lens group with the long focusing length L among the first image information D1and the second image information D2.

Furthermore, the object approach determiner24has a high-speed approach determination threshold value th2that is smaller than the approach determination threshold value th1, and determines that the high-speed approach of the object has been detected when the time difference Δt is equal to or less than the high-speed approach determination threshold value th2.

Note that the real objects to be imaged by the imager10are described as “object BT,” “object BT1,” “object BT2,” and the like, and the recognizing objects to be detected or recognized based on the imaged image information D are described as “object B,” “object B1,” “object B2,” and the like. However, the distinction between the real objects and the recognizing objects is not strict.

As shown inFIG. 3, the processing unit20is constituted by, for example, a CPU101, a ROM102, a RAM103, a clock generator104, an external I/F105and the like, which are connected by a bus or the like.

The central processing unit (CPU)101controls each part and the whole of the object approach detection device1according to a program (computer program). For example, the CPU101can be formed by application specific integrated circuit (ASIC). The functions and the like of the processing unit20can be realized by the executing a predetermined program by the CPU101and in cooperation with hardware elements.

The read only memory (ROM)102and the random access memory (RAM)103can be realized by a semiconductor, a magnetic disk, or the like, and store control programs, application programs, data, image information and the like. The RAM103is used as a working memory, and a part thereof is used as the image storage21and22.

The clock generator104generates clocks necessary for the series of processing in the processing unit20and provides, for example, clocks for counting by a counter and the time stamps DTS.

The external I/F105receives and transmits data and signals from and to other devices. For example, the external I/F is connected to an operation control unit and the like of a flying machine such as a drone and can transmit the object approach signal S1, the determination result in the processing unit20, to the operation control unit. The operation control unit may perform, for example, operation for collision avoidance when the object approach signal S1is received.

FIGS. 4 to 6show imagers10B and10C showing other examples of the lens configuration of the object approach detection device1.

InFIG. 4, the imager10B includes a main lens11B, a first lens group13GB constituted by a plurality of first lenses13B,13B and so on having a first focal length, and a second lens group14GB constituted by a plurality of second lenses14B,14B and so on having a second focal length.

In the example inFIG. 4, the surface of the main lens11B is the object plane12, and the lenses13B and14B are arranged along the object plane12. A first imaging element16SB and a second imaging element17SB are arranged on an imaging plane15B facing the object plane12.

InFIG. 5, an imager10C includes a first lens group13GC constituted by a plurality of first lenses13C,13C and so on having a first focal length and a second lens group14GC constituted by a plurality of second lenses14C,14C and so on having a second focal length.

In the example inFIG. 5, the first lenses13C and the second lenses14C are arranged on a circumferential or spherical object plane12C.

A first imaging element16SC and a second imaging element17SC are arranged on a circumferential or spherical imaging plane15C facing the object plane12C.

Moreover, in all of the imagers10,10B and10C, the first lenses13,13B and13C and the second lenses14,14B and14C are arranged alternately, specifically, arranged in zigzag on the object planes12,12B and12C and are arranged in a matrix as a whole.

In the imager10C inFIG. 5, shielding walls18are provided between the first lenses13C and the second lenses14C and the first imaging element16SC and the second imaging element17SC to shield the optical paths to the outside of the corresponding regions.

For example, as shown inFIG. 6, each of the shielding walls18may be block-shaped provided with one light transmission hole18a. Each of the shielding walls18is inserted between the first lenses13C (or the second lenses14C) and the first imaging element16C (or the second imaging element17C).

Note that the shielding wall18may be placoid provided with a large number of light transmission holes18acorresponding to each lens.

FIG. 7shows an example of a flow of a series of processing for the object approach detection in the processing unit20.

InFIG. 7, an image such as a still image or a moving image in a target range is captured by the imager10, the first image information D1and the second image information D2are acquired from the image, and the time stamp DTS is acquired at the same time. A set of the first image information D1and the second image information D2is acquired at predetermined time intervals and sent to the processing unit20sequentially.

In the processing unit20, the edge detection is performed on one set of the first image information D1and the second image information D2, and the first edge image E1and the second edge image E2are acquired. The presence or absence of an object is detected based on these edge images. When an object is detected, the time t is acquired from the time stamp DTS corresponding to that first image information D1or that second image information D2.

Normally, when an object approaches the imager10from a long distance, the first image information D1focused by the first lens group13G is acquired first, and the second image information D2focused by the second lens group14G is acquired thereafter. In this case, for example, the time ta is acquired for the first image information D1and, for example, the time tb is acquired for the second image information D2. The time ta is earlier, and the time tb is later.

In this case, the time difference Δt between the time ta and the time tb is tb−ta, and this time difference Δt is a time taken by the object to move from the focusing length L1of the first lens group13G to the focusing length L2of the second lens group14G. If the focusing lengths L1and L2are each constant, the moving speed of the object becomes faster as the time difference Δt becomes smaller.

Thereupon, the time difference Δt is compared with the approach determination threshold value th1. When the time difference Δt is equal to or less than the approach determination threshold value th1, the approach of the object is determined to be detected, and the object approach signal S1is out.

Moreover, the time difference Δt is compared with the high-speed approach determination threshold value th2as necessary. When the time difference Δt is equal to or less than the high-speed approach determination threshold value th2, the high-speed approach of the object is determined to be detected, and a high-speed object approach signal S2is out. The high-speed approach determination threshold value th2is smaller than the approach determination threshold value th1and may be, for example, equal to or less than half. For example, in a case where the approach determination threshold value th1is one second, the high-speed approach determination threshold value th2can be set to about 0.5 seconds.

This will be described in more detail hereinafter.

FIG. 8Ashows examples of the image information D1and D2, andFIG. 8Bshows examples of the edge images E1and E2thereof.

InFIG. 8A, the image information D1is the image captured by the first lens group13G and focused on the focusing length L1of the first lens group13G. The image information D2is the image captured by the second lens group14G and focused on the focusing length L2of the second lens group14G.

In these image information D1and D2, the different objects (real objects) BT1and BT2are in the background, and the object BT1is arranged farther from the imager10than the object BT2. The farther object BT1is in focus in one image information D1while the closer object BT2is in focus in the other image information D2.

The edge image E1inFIG. 8Bis the result of performing the edge detection on the image information D1, and the edge image E2is the result of performing the edge detection on the image information D2.

As a method of the edge detection, there are, for example, a method of obtaining a density gradient by differentiating the image density (luminance), a method of obtaining a density difference between adjacent pixels, and other methods. In an image of a focused object, the density gradient and the density difference tend to increase at the edges. Therefore, for example, in a case where a ratio of a part of the areas with large density gradient and density difference to the entire image is equal to or greater than a certain value, in a case where the number of pixels with large density gradient and density difference between adjacent pixels is equal to or greater than a certain number or certain ratio, and the like, it is possible to detect the presence of the focused object BT.

In the edge image E1inFIG. 8B, the edges clearly appear on the focused object BT1, and in the edge image E2, the edges clearly appear on the focused object BT2. Therefore, in this case, the object BT1is detected in the image information D1or the edge image E1, and the object BT2is detected in the image information D2or the edge image E2.

FIGS. 9A to 9Cshow how an object is detected from the image information.

FIG. 9Ashows image information D11, D12and D13.FIG. 9Bshows edge images E11, E12and E13obtained from the image information D11, D12and D13, respectively.FIG. 9Cshows frequency distribution curves of density differences ΔG of the adjacent pixels in the edge images E11, E12and E13, respectively.

InFIG. 9A, the image information D11, D12and D13are obtained by imaging the object (real object) BT3arranged at the center of the screen at different distances. Among them, in the image information D12in the center, the object BT3is at the focusing length and focused.

InFIG. 9B, in the edge images E11, E12and E13, the pixels after the edge detection are enlarged to be shown. Among them, the difference of the intensities, that is, the contrast is large in the edge image E12, and the edges are detected most frequently.

InFIG. 9C, each of the horizontal axes represents the density difference ΔG of each pixel, and each of the vertical axes represents the number (pixel number) n. An appropriate position on each of the horizontal axes is set as a threshold value thG, and the total number NTG of the pixels with the density difference ΔG exceeding the threshold value thG is checked. The total number NTG corresponds to the area at the lower part of the curve. It is shown that the edge image E12in the middle has the largest total number NTG.

Therefore, for example, in a case where the threshold value thG indicating the pixels of the edges is set and the total number NTG of pixels exceeding the threshold value thG is equal to or greater than the edge detection threshold value th11, the presence of the object B should be detected in that edge image E or image information D.

Note that, in the image information D, the difference of the intensities becomes larger, that is, the contrast becomes large by including a clear focused image, and the spatial frequency F tends to be high. That is, the focused image information D has the high spatial frequency F.

Thereupon, the spatial frequency F of each of the image information D11, D12and D13may be detected, and the presence of the object may be detected when the spatial frequency F is equal to or greater than the frequency detection threshold value th12.

In this case, the spatial frequencies F1and F2of the first image information D1and the second image information D2are detected respectively by the spatial frequency detector233. The presence of an object should be detected when the spatial frequencies F1and F2are equal to or greater than the frequency detection threshold value th12.

FIGS. 10A and 10Bare diagrams showing a schematic flow of the series of processing in the object approach determiner24.

FIG. 10Ashows how the object BT enters into the viewing field of the imager10and approaches with the time t. The imaging is performed by the imager10at times t1, t2, t3, t4and t5. The object BT is positioned at the focusing length L1of the first lens group13G at the time t2and positioned at the focusing length L2of the second lens group14G at the time t4.

InFIG. 10B, the image information D1and D2imaged at each time t are schematically shown. At the time t1, the unfocused image information D1and the image information D2substantially with nothing are obtained. At the time t2, the focused image information D1and the unfocused image information D2are obtained. At the time t3, the unfocused image information D1and D2are obtained. At the time t4, the unfocused image information D1and the focused image information D2are obtained. At the time t5, the unfocused image information D1and D2are obtained.

From these image information D1and D2, the edge images E1and E2are respectively obtained by the edge detection, and the detection of the object BT is performed. In this example, the objects (recognized objects) B1and B2are detected from the focused image information D1at the time t2and the focused image information D2at the time t4, respectively.

As a result, the object B1is detected at the focusing length L1at the time t2, and the object B2is detected at the focusing length L2at the time t4. That is, the first time ta when the object B1is detected based on the first image information D1is the “time t2,” and the second time tb when the object B2is detected based on the second image information D2is the “time t4.” Therefore, the time difference Δt (=tb−ta) between the first time ta and the second time tb is Δt=t4−t2.

Then, when the time difference Δt=t4−t2is less than the approach determination threshold value th1, that is, when Δt<th1, the approach of the object is determined to be detected, and the object approach signal S1is out.

Moreover, when the time difference Δt=t4−t2is less than the high-speed approach determination threshold value th2, that is, Δt<th2, the high-speed approach of the object is determined to be detected, and the high-speed object approach signal S2is out.

Note that, the determination of the detection of the object approach may include a case where the time difference Δt is equal to the threshold values th1or th2.

Next, various conditions for the determination of the detection of the object approach will be described.

First, in the examples shown inFIGS. 10A and 10B, since the same single object BT is imaged, the detected object B1(the first recognized object) and the object B2(the second recognized object) are determined to be the same in the object recognizer232.

In this case, the object approach determiner24can determine that the approach of the object has been detected on the condition that the objects B1and B2recognized by the object recognizer232are the same. That is, in a case where such determination is performed, the approach of the object is determined to be not detected if the objects B1and B2are different from each other. Therefore, the object approach signal S1is not out.

Next,FIG. 11shows how the approach of the object is detected by dividing the region of the image information D.

In the example inFIG. 11, 300 vertical pixels and 300 horizontal pixels are aligned in a matrix on the imaging plane15. The imaging plane15includes the first imaging element16SC and the second imaging element17SC. For example, 150 vertical pixels and 150 horizontal pixels are assigned as the first imaging element16SC and the second imaging element17SC, and the first image information image D1and the second image information image D2are obtained, respectively.

In the first imaging element16SC and the second imaging element17SC, the first image information image D1and the second image information image D2are divided into regions AE with a predetermined size. In this example, the images are divided into the matrix regions AE, each with 10 vertical pixels and 10 horizontal pixels. In the first image information image D1and the second image information image D2, the positional relationships of the regions AE correspond to each other.

Then, the object approach determiner24can determine that the approach of the object has been detected on the condition that each of the detected regions AE corresponds to a region AE into which the first image information D1and the second image information D2are divided or is a region AE adjacent thereto in a case where the objects B1and B2have been detected.

That is, in this case, in the second image information D2shown inFIG. 11, the approach of the object is determined to be detected only in a case where the object B2has been detected in a region AE1in which the object B1has been detected in the first image information D1, or in any one of the eight regions AE adjacent to this region AE1from the top, bottom, left and right. Thus, the approach of the object can be detected with higher accuracy.

Moreover, since the region AE in which the objects B1and B2have been detected can be identified, the spatial positions of the objects B1and B2can also be identified.

Note that the size and setting method of the region AE in this case may be various.

FIG. 12shows an example of a case where the approach is determined to be not detected even when the object is detected. InFIG. 12, the image information D1and D2imaged at each time t are schematically shown.

That is, the imaging is performed at the times t1, t2and t3by the imager10. At the time t1, no object is detected from image information D1, and the object B3is detected from the image information D2. At the time t2, the object B1is detected from the image information D1, and the object B3is detected from the image information D2. At the time t3, no object is detected from the image information D1, and the two objects (recognized objects) B2and B3are detected from the image information D2.

In such a case, since the presence of the object B3has been detected at the time t1based on the second image information D2corresponding to the lens group with the short focusing length L2prior to the first image information D1corresponding to the lens group with the long focusing length L1, the approach of the object is determined to be not detected, and the object approach signal S1is not out.

That is, the object B3detected based on the second image information D2is detected at all of the times t1, t2and t3, and this is a case where there is an object different from the object BT which should be detected at a position of the focusing length L2, other objects have been crossed, or the like, leading to erroneous detection. Thus, the object approach signal S1is not out herein.

What can be considered for such a situation is, for example, a case where the position of the imager10attached to the flying machine is close to the airframe or the like and a part of the airframe is imaged or a case where the imager10is attached to image the lower side and the image of the ground is always captured.

Note that, in this case, if the object B3is not detected based on the second image information D2, the object B1is detected at the time t2, and the object B2is detected at the time t3. Thus, the time difference Δt is t3−t2. When the time difference Δt is equal to or less than the approach determination threshold value th1, the approach of the object is determined to be detected, and the object approach signal S1is out.

Moreover, the object B3is detected based on the second image information D2at the time t1at first. Since the object B1is detected at the time t2and the object B2is detected at the time t3, the determination of the presence or absence of the approach of the object by the time difference Δt is performed on the condition that that the object B1and the object B2are the same. In a case where the condition is met, the object approach signal S1is out.

Furthermore, if the object B3detected based on the second image information D2is identified by the object recognizer232and clarified that the object B3is different from the object BT which should be detected, the determination of the presence or absence of the approach based on the detection of the objects B1and B2may be performed even in this case.

Further, for example, in case where the object B3is detected based on the second image information D2only at the time t1and the object B3is not detected at the times t2and t3, the object B3is also considered to be different from the object BT which should be detected. In such a case, that is, in a case where the presence of the object B3is detected first based on the second image information D2corresponding to the lens group with the short focusing length L2, the detection of the object B1can be not detected for a certain period of time thereafter. In this case, only in a case where the presence or absence of the object is detected first based on the first image information D1corresponding to the lens group with the long focusing length L1, the detection of the presence or absence of the object based on the second image information D2is performed.

In addition, the detection of the object based on the second image information D2may be not performed until the object is detected from the first image information D1. In this way, the amount of computation is reduced, and the power consumption is reduced.

In the embodiments described above, the two image information images D1and D2are acquired by the two imaging elements, the first imaging element16SC and the second imaging element17SC, in the imagers10,10B and10C. However, embodiments are not limited to this, and three or more image information images D may be acquired by using three or more imaging elements, and the detection of the presence or absence of an object and the detection of the approach of an object may be performed based on these images D.

That is, such an imager10D includes, for example, N (N is an integer of 3 or more) lens groups which have different focal lengths from each other and are arranged so as to image the same target object, and N pieces of image information D1to DN, which include the first image information D1, the second image information D2, the third image information D3and so on to the N-th image information DN, are acquired by the N lens groups.

Then, for example, in the object detector23, the presence or absence of an object is detected based on the N pieces of image information D1to DN. The object approach determiner24determines the approach of the object has been detected when a time difference Δt between a time ta and a time tb is equal to or less than the approach determination threshold value th1. The time ta is when the image information is acquired when an object has been detected based on any one of the image information D1to DN among the N pieces of image information D1to DN. The time tb is when the image information is acquired when an object has been detected based on other image information.

Next, a schematic flow of a series of processing in the object approach detection device1will be described based on the flowchart shown inFIG. 13.

InFIG. 13, the first image information D1is acquired by the imager10(#11). The presence or absence of an object from the first image information D1is checked (#12). When an object is detected (YES in #12), the first time ta is acquired from the time stamp DTS or the like (#13). The second image information D2is acquired (#14), and the presence or absence of the object is checked (#15). When an object is detected (YES in #15), the second time tb is acquired (#16).

The time difference Δt between the first time ta and the second time tb is obtained and compared with the approach determination threshold value th1(#17). When the time difference Δt is equal to or less than the approach determination threshold value th1, the approach of the object is determined to be detected, and the object approach signal S1and the like are out (#18).

According to the embodiment described above, since the presence or absence of the approach is determined by performing the detection of an object to obtain the time difference Δt and comparing the time difference Δt with the approach determination threshold value th1, the amount of calculation is small, and thus the power consumption can be reduced. Incidentally, when the distance to the object is estimated as in the conventional case, the amount of calculation is large, and thus the power consumption cannot be reduced.

Therefore, according to the object approach detection device1of the present embodiment, when the object approach detection device1is mounted on a small flying machine such as a drone, the flight time thereof can be made longer.

When a combination of the main lens11, the first lens group13G and the second lens group14G is used as the imager10, the target range of the imaging is enlarged and the viewing angle is widened so that an object can be detected from various directions with lightweight equipment.

In the embodiments described above, the configuration, structure, combination, size, number, material, arrangement, content of a series of processing, order, threshold values th and the like of the whole or each part of the imagers10,10B and10C, the processing unit20and the object approach detection device1can be changed as appropriate in accordance with the gist of the present invention.