WO2017195754A1

WO2017195754A1 - Surveillance system

Info

Publication number: WO2017195754A1
Application number: PCT/JP2017/017465
Authority: WO
Inventors: 潤一藤田
Original assignee: コニカミノルタ株式会社
Priority date: 2016-05-13
Filing date: 2017-05-09
Publication date: 2017-11-16
Also published as: JP6988797B2; JPWO2017195754A1

Abstract

Provided is a surveillance system that detects an object by background subtraction using reflected light of the highest order, for example, and that is capable of detecting an object over a fence, for example. In this surveillance system, a processing section employs, as a background target, a target that is the farthest from a light projection/reception unit in the same light projection/reception direction, and is capable of measuring the distance of a target closer than the background target as a surveillance target. The processing section is capable of setting a mask region within a discretionary range of a surveillance space, and when reflected light from a target that is present within the mask region has been detected, the processing section sets the distance of the target for which the reflected light has been detected to a predetermined distance.

Description

Monitoring system

The present invention relates to a monitoring system that monitors an object by scanning and projecting laser light or the like, for example.

A monitoring device that uses a distance image has been proposed as a monitoring device for detecting an intruder or the like in a monitoring space. Here, the distance image has distance information as a pixel value. Specifically, as shown in Patent Document 1, a laser beam or the like is sent out to a monitoring space, and monitoring is performed to measure a distance to an object in the monitoring space from a time from the sending to reception of reflected light. The device is known. In such a monitoring apparatus, distance information about a plurality of directions facing the monitoring space can be obtained by sequentially changing the transmission direction of the measurement medium such as laser light and scanning the monitoring space two-dimensionally. A distance image can be formed.

In a monitoring device using a distance image, a distance image (background image) as a background in which no moving object exists is compared with an input distance image (current image), and pixels corresponding to a distance closer to the background image are extracted. Thus, the change area is obtained. Then, based on the size / shape of the change area and the distance information in the current image, it is determined whether or not the moving object is the target detection target.

The distance image includes information such as the direction of the object viewed from the transmitting / receiving unit such as a laser beam and the distance to the object. Therefore, the size and shape of the object can be known from the distance image. For example, in an intruder detection application, it is possible to distinguish a relatively large person in the distance from small animals in the vicinity (such as a frog or a cat). It becomes possible, and the detection accuracy of an intruder can be improved.

JP 2007-122507 A

By the way, in important facilities set up in the back of the mountain, the surroundings of the facilities are often surrounded by fences so that ordinary people cannot easily enter. When unattended monitoring is performed by providing a monitoring device in such a facility, it is preferable that a human action can be detected quickly outside the fence because an alarm can be issued early. On the other hand, since the monitoring device is generally installed in the fence to avoid inadvertent access by humans or the like, the laser light emitted from the monitoring device may pass through the fence depending on the installation location of the monitoring device. The light that travels from the inside toward the outside and is reflected by the object may return through the fence again. However, in the monitoring device of Patent Document 1, the object distance image that is in front of the background distance image is extracted as a change image, that is, only the object at a position closer to the background object is the monitoring object. Therefore, if a fence image is set as a background image, there is a problem that even if an object outside the fence appears over the fence, it cannot be detected.

The present invention has been made in view of the above circumstances, and provides a monitoring system capable of detecting an object such as a fence in a monitoring system that detects an object based on a background difference using the highest-order reflected light, for example. For the purpose.

In order to achieve at least one of the above-described objects, a monitoring system reflecting one aspect of the present invention is provided.
A light projecting / receiving unit comprising: an emitting unit that emits a light beam; a scanning unit that scans the light beam in a monitoring space; and a light receiving unit that receives a light beam reflected from an object in the monitoring space;
A processing system for measuring a distance to the object by processing a signal from the light projecting / receiving unit,
The processing unit can set a reference background in the monitoring space, and can measure the distance as an object to be monitored that is closer to the reference background,
The processing unit can set a mask area in an arbitrary range of the monitoring space, and when detecting reflected light from an object existing in the mask area, the object detecting the reflected light Is set to a predetermined distance.

According to the present invention, for example, in a monitoring system that detects an object based on a background difference using the highest-order reflected light, it is possible to provide a monitoring system that can detect an object such as a fence.

It is sectional drawing of monitoring apparatus MD concerning this embodiment. It is a figure which shows the state which scans the inside of the monitoring space of the monitoring apparatus MD with the laser spot light SB (it shows by hatching) radiate | emitted according to rotation of the mirror unit MU. (A), (c) is a figure which shows the state which looked at the monitoring space where a background target object exists from the side, (b), (d) is a figure which shows the processing result of the processing circuit PROC, respectively. Yes, the vertical axis represents the reflected light intensity, and the horizontal axis represents the distance. It is a figure which shows the monitoring space where background objects other than fence FS do not exist. (A), (c) is a figure which shows the state which looked at the monitoring space from which the background target object except fence FS does not exist from the side, (b), (d) is the processing result of the processing circuit PROC, respectively. The vertical axis represents the reflected light intensity, and the horizontal axis represents the distance. (A), (c) is a figure which shows the state which looked at the monitoring space which set the mask area | region from the side, (b), (d) is a figure which shows the processing result of the processing circuit PROC, respectively. The vertical axis represents the reflected light intensity, and the horizontal axis represents the distance. It is a flowchart which shows the monitoring control performed in the processing circuit PROC of the monitoring apparatus MD. It is a figure which shows the relationship between the cross-sectional shape of a laser spot light beam, and the magnitude | size of the mesh | network of a fence.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a monitoring device MD as a monitoring system according to the present embodiment. However, the shape and length of components may differ from actual ones. The monitoring device MD is preferably installed in an important facility such as an unmanned observation station in the back of the mountain.

The monitoring device MD includes, for example, a pulse-type semiconductor laser LD that emits a laser beam, a collimating lens CL that converts divergent light from the semiconductor laser LD into parallel light, and laser light that is collimated by the collimating lens CL. A mirror unit MU that scans and projects light toward the monitoring space by a rotating mirror surface, reflects reflected light from the object, and a lens LS that collects reflected light from the object reflected by the mirror unit MU; A photodiode PD that receives the light collected by the lens LS, a processing circuit (processing unit) PROC that obtains distance information according to a time difference between the emission timing of the semiconductor laser LD and the light reception timing of the photodiode PD, and a mirror It has a motor MT that rotationally drives the unit MU, and a housing CS that houses them.

In this embodiment, the semiconductor laser LD and the collimating lens CL constitute an emission part LPS, the lens LS and the photodiode PD constitute a light receiving part RPS, and the mirror unit MU constitutes a scanning part, and further these are used for projection. Configure the light receiving unit. The optical axes of the emission part LPS and the light receiving part RPS are preferably orthogonal to the rotation axis RO of the mirror unit MU.

A box-shaped housing CS fixed to a wall WL or the like of a rigid facility has an upper wall CSa, a lower wall CSb facing the upper wall CSa, and a side wall CSc connecting the upper wall CSa and the lower wall CSb. . An opening CSd is formed in a part of the side wall CSc, and a transparent plate TR is attached to the opening CSd.

The mirror unit MU has a shape in which two quadrangular pyramids are joined together in opposite directions, that is, four pairs of mirror surfaces M1 and M2 tilted in a direction facing each other (but not limited to four pairs). ) The mirror surfaces M1 and M2 are preferably formed by depositing a reflective film on the surface of a resin material (for example, PC) in the shape of a mirror unit.

The mirror unit MU is connected to a shaft MTa of a motor MT fixed to the casing CS and is driven to rotate. In the present embodiment, the axis (rotation axis) of the axis MTa extends in the Z direction which is the vertical direction, and the XY plane formed by the X direction and the Y direction orthogonal to the Z direction is a horizontal plane. The axis of MTa may be inclined with respect to the vertical direction.

Next, the object detection principle of the monitoring device MD will be described. In FIG. 1, divergent light intermittently emitted in a pulse form from a semiconductor laser LD is converted into a parallel light beam by a collimating lens CL, enters a first mirror surface M1 of a rotating mirror unit MU, and is reflected there. Further, after being reflected by the second mirror surface M2, the light is scanned and projected as a laser spot light having, for example, a vertically long rectangular cross section through the transparent plate TR and toward the external monitoring space. The direction in which the emitted laser spot light is reflected by the object and returned as reflected light is referred to as the light projecting / receiving direction. Laser spot beams traveling in the same light projecting / receiving direction are detected by the same pixel.

FIG. 2 is a diagram illustrating a state in which the laser spot light SB (indicated by hatching) emitted in accordance with the rotation of the mirror unit MU scans the monitoring space of the monitoring device MD, and trees are arranged behind the fence FS. An example in which TT is thick is shown.

Here, in the combination of the first mirror surface M1 and the second mirror surface M2 of the mirror unit MU, the crossing angles are different from each other. The laser light is sequentially reflected by the rotating first mirror surface M1 and second mirror surface M2. First, the laser light reflected by the first pair of the first mirror surface M1 and the second mirror surface M2 moves from the left to the right in the horizontal direction in the uppermost area Ln1 in accordance with the rotation of the mirror unit MU. Is scanned. Next, the laser light reflected by the second pair of the first mirror surface M1 and the second mirror surface M2 moves from the left in the horizontal direction to the second region Ln2 from the top of the monitoring space according to the rotation of the mirror unit MU. Scan to the right. Next, the laser light reflected by the third pair of the first mirror surface M1 and the second mirror surface M2 passes through the third region Ln3 from the top in the monitoring space in accordance with the rotation of the mirror unit MU from the left in the horizontal direction. Scan to the right. Next, the laser beams reflected by the fourth pair of the first mirror surface M1 and the second mirror surface are moved horizontally from left to right in the lowermost region Ln4 of the monitoring space according to the rotation of the mirror unit MU. Scanned. Thus, one scan of the entire monitoring space that can be monitored by the monitoring device MD is completed. A single frame FL is obtained by combining images obtained by scanning the regions Ln1 to Ln4. If the first pair of the first mirror surface M1 and the second mirror surface M2 return after one rotation of the mirror unit MU, the region from the uppermost region Ln1 to the lowermost region Ln4 is again displayed. Scanning is repeated to obtain the next frame FL.

In FIG. 1, part of the laser light reflected by the object (trees TT or fence FS) out of the projected light beam is transmitted again through the transparent plate TR and the second mirror unit MU in the housing CS. The light enters the mirror surface M2, is reflected here, is further reflected by the first mirror surface M1, is collected by the lens LS, and is detected by the light receiving surface of the photodiode PD. Further, the processing circuit PROC, which is a processing unit, obtains distance information according to the time difference between the emission timing of the semiconductor laser LD and the light reception timing of the photodiode PD. Thereby, the object is detected in the entire area in the monitoring space, and a frame FL (see FIG. 2) as a distance image having distance information for each pixel can be obtained. Such a distance image can be transmitted to a remote monitor via a network (not shown) or the like and displayed, or can be stored in a storage device.

Next, the detection algorithm for the monitoring object of the monitoring device MD will be described. FIG. 3 is a diagram illustrating a state in which the monitoring space is viewed from the side in association with the processing result of the processing circuit PROC. Here, as a preparation for monitoring, as shown in FIG. 3A, a distance image (reference image) serving as a reference is obtained by the monitoring device MD in the absence of a moving object such as a human being or an animal. In the state shown in FIG. 3A, a part of the laser spot light beam SB emitted from the monitoring device MD and traveling in the same light projecting / receiving direction is reflected by the fence FS installed on the ground G to become reflected light RB1. However, the rest passes through the wire mesh of the fence FS, is irradiated on the background object of the trees TT, etc., becomes reflected light RB2, and returns to the monitoring device MD.

Since the laser spot light beam spreads away from the monitoring device MD, the relationship between the cross-sectional shape of the laser spot light beam and the mesh size of the fence FS varies depending on the distance to the fence FS. For example, in FIG. 8, when the length of one side of the mesh of the fence FS is L = 40 mm and the thickness is t = 4 mm, and the distance between the monitoring device MD and the fence FS is 3 m, the size of the laser spot light beam SB1 When the distance between the monitoring device MD and the fence FS is 10 m, the fence FS is irradiated with the size of the laser spot light beam SB2.

In this case, as shown in FIG. 3B, the processing result from the processing circuit PROC is obtained from the peak P1 (first echo) corresponding to the distance to the fence FS and the background object (referred to as the reference background). A peak P2 (last echo: highest order reflected light) corresponding to the distance is obtained. In the object monitoring algorithm using the background subtraction method, it is assumed that no object exists behind the peak P2, which is the highest order reflected light. A background image is set by recognizing the background object using the highest order reflected light, and by detecting the detected object using the highest order reflected light during actual monitoring, rain, snow, fog, etc. The impact can be avoided. Here, “the highest order reflected light” is within the maximum measurable distance of the monitoring device MD (beyond this, it becomes an unmeasurable point), and the reflected light from the farthest object is It shall be said.

Here, as shown in FIG. 3C, when an intruder OBJ appears in front of the background object, as shown in FIG. 3D, in the processing result from the processing circuit PROC, the peak P1 and the peak A peak P3 corresponding to the reflected light RB3 from the intruder OBJ appears between P2 and P2. At this measurement point, the peak P3 becomes the last echo instead of the peak P2. The processing circuit PROC compares the processing result of FIG. 3B with the processing result of FIG. When a predetermined distance difference from P3 occurs, attention can be alerted. Further, when the intruder OBJ is moving, the position of the peak P3 changes in the frame obtained by repeating the scanning, so that the processing circuit PROC tracks the intruder OBJ to obtain the moving direction and speed (moving object detection). It can be performed. For example, when the position of the peak P3 comes before the peak P1, the processing circuit PROC can determine that the intruder OBJ has exceeded the fence FS, and can issue an alarm or the like via an alarm device (not shown). .

On the other hand, in the monitoring space, as shown in FIG. 4, there may be no object other than the fence FS in the monitorable range of the monitoring device, such as a space where the other side of the fence FS is opened. FIG. 5 is a diagram showing a state in which such a monitoring space is viewed from the side in association with the processing result of the processing circuit PROC.

Also in this example, as a preparation for monitoring, as shown in FIG. 5A, a distance image (reference image) serving as a reference is obtained by the monitoring device MD in a state where there is no moving object such as a human being or an animal. However, in the state shown in FIG. 5A, a part of the laser spot light beam SB emitted from the monitoring device MD and traveling in the same light projecting / receiving direction is reflected by the fence FS installed on the ground G and reflected light RB1. However, since the remainder passes through the fence FS and travels toward infinity, as shown in FIG. 5B, only the reflected light beam RB1 returns to the monitoring device MD. Therefore, when the above-described monitoring object detection algorithm is used in such a monitoring space, the reflected light beam RB1 becomes the last echo, so the background image uses the fence FS.

In such a case, as shown in FIG. 5C, when an intruder OBJ appears in the back side of the fence FS, in the processing result from the processing circuit PROC, as shown in FIG. Then, a peak P3 corresponding to the reflected light RB3 from the intruder OBJ appears. Here, the processing circuit PROC compares the processing result of FIG. 5B and the processing result of FIG. 5D, but if the background image is set with the reflected light RB1 from the fence FS as the last echo, the background difference In the detection algorithm using the method, it is not assumed that the reflected light returns from the monitoring object at the back side from the last echo, and as a result, the processing circuit PROC cannot detect the intruder OBJ at the back side of the fence FS. It will be. If the intruder OBJ gets over the fence FS, the processing circuit PROC can detect it, but the detection timing may be too late.

The detection algorithm of the monitoring target object of the monitoring device MD that can cope with such a problem will be described. FIG. 6 is a diagram illustrating a state in which a monitoring space similar to that in FIG. 4 is viewed from the side in association with the processing result of the processing circuit PROC.

Also here, as a preparation for monitoring, as shown in FIG. 6A, a distance image (reference image) serving as a reference is obtained by the monitoring device MD in a state where there is no moving object such as a human being or an animal. At this time, similarly to the example shown in FIG. 5A, the laser light that has passed through the fence FS travels toward infinity, and thus the reflected light RB1 is generated only from the fence FS.

Therefore, in this embodiment, the mask process is performed on the fence FS so as to have a predetermined distance different from the actual distance. Specifically, since the position (distance and direction) of the fence FS with respect to the monitoring device MD is known in advance, the user can input the fence FS in the monitoring space by inputting to the processing device PROC via an interface (not shown). It is possible to set a mask area MA (which can take an arbitrary three-dimensional shape) that completely surrounds the mask area MA. In such a case, the processing apparatus PROC forcibly sets the three-dimensional coordinates of the object (including the fence FS) reflected from the mask area MA to a predetermined distance, that is, an infinite distance (or an unmeasurable point). In other words, the distance obtained based on the reflected light from the fence FS existing in the mask area MA is replaced with the distance from the monitoring device MD to infinity (or a measurement impossible point). Accordingly, the fence FS can be ignored in the object detection algorithm, and the object detection can be prevented from being an obstacle. The “predetermined distance” is preferably infinitely far (or an unmeasurable point), but when a background object exists on the back side of the mask area, the distance of the background object may be used.

Note that the “unmeasurable point” refers to a point where the reflected light of the laser beam on the object is below the detection limit value of the photodiode PD because it is too far from the monitoring device MD. For example, when the unmeasurable point is 50 m away, the distance of the object in the mask area MA can be replaced with, for example, 50 m or more. Then, the peak P1 of the reflected light RB1 of the fence FS indicated by the dotted line in FIG. 6B is shifted beyond the unmeasurable point, and is excluded from the background image in the object detection algorithm.

When such setting is performed, when an intruder OBJ appears in the monitoring space as shown in FIG. 6C, intrusion occurs in the processing result from the processing circuit PROC as shown in FIG. 6D. The peak P3 corresponding to the reflected light RB3 from the person OBJ appears, but this is recognized as the last echo on the detection algorithm. Therefore, the processing circuit PROC compares the processing result of FIG. 6B and the processing result of FIG. 6D, determines that a new peak P3 has occurred, and can call attention. For example, if the intruder OBJ is included in the mask area MA, there is a risk that it will be excluded from the monitoring object on the detection algorithm, but the mask area MA can be arbitrarily set in three dimensions. When the person OBJ tries to get over the fence FS, it will protrude above the mask area MA, so that the monitoring device MD can detect this and issue an alarm.

The monitoring control of the monitoring device MD using the above detection algorithm will be described with reference to the drawings. Here, it is assumed that the processing circuit PROC arbitrarily sets a mask area in accordance with a user's designation through an interface (not shown).

FIG. 7 is a flowchart showing the monitoring control performed by the processing circuit PROC of the monitoring device MD. First, in step S101 in FIG. 7, the processing circuit PROC determines whether or not to set the mask area MA. Specifically, for example, when the user inputs data (three-dimensional coordinates) of the mask area MA including a fence or the like in the monitoring space, the processing circuit PROC determines that the mask area MA is set in response to this, and step S102 Thus, the mask area MA is designated based on the input data. On the other hand, if the data of the mask area MA is not input, the flow bypasses step S102, so that the processing circuit PROC does not set the mask area MA.

Next, in step S103, the processing circuit PROC scans the laser beam from the light projecting / receiving unit of the monitoring device MD, receives the reflected light, and obtains N distance data (distance image) for one frame in the monitoring space. obtain. Here, the processing circuit PROC first sets N = 1 in step S104, and further determines in step S105 whether or not it belongs to the mask area MA based on the three-dimensional coordinates of the Nth measurement point.

If it is determined that the coordinates of the Nth measurement point exist in the mask area MA, the processing circuit PROC sets the distance of the measurement point to infinity in step S106. On the other hand, when the mask area MA is not set or the coordinates of the measurement point of the object do not exist in the mask area MA, the flow bypasses step S106, and the processing circuit PROC calculates the actual distance of the measurement point. Value.

In step S107, the processing circuit PROC determines whether or not all the measurement points in the frame have been determined to exist in the mask area MA. If it is determined that the determination has not been completed, the processing circuit PROC determines in step S108. As N = N + 1, the flow returns to step S105. On the other hand, if it is determined that all the measurement points in the frame are present in the mask area MA, the processing circuit PROC further uses the interface (not shown) to display the background image in step S109. It is determined whether or not it has been updated. If it is determined that the background image has been updated, the processing circuit PROC registers a new background image (current frame) in step S110 and uses this to detect the monitoring object. If it is determined that the background image has not been updated, the flow bypasses step S110.

Further, after acquiring the distance data, the processing circuit PROC compares the obtained distance image for one frame with the background image in step S111, and determines whether or not a suspicious object (moving object) has appeared in step S112. To do. If it is determined that there is a suspicious object, the processing circuit PROC outputs an alarm signal in step S113, displays an alarm on a monitor (not shown), returns the flow to step S101, performs the next laser light scan, and then A distance image is obtained for each frame. On the other hand, when it is determined that there is no suspicious object. The processing circuit PROC returns the flow to step S101 without outputting an alarm signal.

The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are included for those skilled in the art from the embodiments and technical ideas described in the present specification. it is obvious. The description and the embodiments are for illustrative purposes only, and the scope of the present invention is indicated by the following claims. For example, not only the fence but also a glass plate that transmits a part of the laser beam can be surrounded by the mask region. Further, by rotating the wall WL to which the monitoring device MD is attached about the vertical direction, the laser light emitted from the light projecting / receiving unit can be directed in all directions of 360 °. The mask area can also be set when a fence or the like is present in front of the background object within the measurable range.

CL Collimating lens CS Housing CSa Upper wall CSb Lower wall CSc Side wall CSd Opening FL Frame FS Fence G Ground LD Semiconductor laser LPS Emitting part LS Lens M1, M2 Mirror surface MA Mask area MD Monitoring device MT Motor MTa Axis MU Mirror unit OBJ Intrusion Person PD Photodiode PROC Processing circuit RB1, RB2, RB3 Reflected light RO Rotating axis RPS Light receiving part SB Laser spot light TR Transparent plate WL Wall

Claims

A light projecting / receiving unit comprising: an emitting unit that emits a light beam; a scanning unit that scans the light beam in a monitoring space; and a light receiving unit that receives a light beam reflected from an object in the monitoring space;
A processing system for measuring a distance to the object by processing a signal from the light projecting / receiving unit,
The processing unit is capable of setting a reference background in the monitoring space, and measuring the distance from the light projecting / receiving unit as an object to be monitored that is closer to the reference background in the same light projecting / receiving direction,
The processing unit can set a mask area in an arbitrary range of the monitoring space, and when detecting reflected light from an object existing in the mask area, the object detecting the reflected light Monitoring system that sets the distance of a certain distance.
The monitoring system according to claim 1, wherein the predetermined distance is a distance to the reference background, an infinite distance, or a measurement impossible point.
The monitoring system according to claim 1, wherein the processing unit recognizes an object that reflects the highest-order reflected light as the reference background or an object to be detected.
The monitoring system according to any one of claims 1 to 3, wherein the object in the mask area is a fence.
The monitoring system according to any one of claims 1 to 4, wherein the processing unit can set a monitoring range as a three-dimensional space and set the mask region in the monitoring range three-dimensionally.
The processing unit detects, as a moving object, the monitoring object whose position has changed between a scanning preceding the light beam in time by the scanning unit and a scanning succeeding in time. A monitoring system according to any one of the above.