JP6988797B2 - Monitoring system - Google Patents

Description

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

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

In a monitoring device using a distance image, a distance image (background image) that is a background in which a moving object does not exist is compared with an input distance image (current image), and pixels corresponding to a distance closer than the background image are extracted. The change area is obtained. Then, based on the size and shape of the changing region and the distance information in the current image, it is determined whether or not the moving object is the target object to be detected.

The distance image has information of the direction of the object as seen from the transmission / reception unit such as the laser luminous flux and the distance to the object. Therefore, the size and shape of an object can be known from a distance image. For example, in the use of intruder detection, it is possible to distinguish between a relatively large person in the distance and a small animal (cat, cat, etc.) in the vicinity. This makes it possible to improve the detection accuracy of intruders.

Japanese Unexamined Patent Publication No. 2007-122507

By the way, in important facilities and the like provided in the mountains, it is often the case that the surroundings of the facilities are surrounded by fences or the like to prevent the general public from easily entering. When unmanned monitoring is performed by installing a monitoring device in such a facility, it is preferable that human behavior can be detected quickly outside the fence because an alarm can be issued at an early stage. On the other hand, since the monitoring device is generally installed inside the fence to avoid inadvertent access by humans, the laser light emitted from the monitoring device may pass through the fence depending on the installation location of the monitoring device. It travels from the inside to the outside, and the light reflected by the object may return through the fence again. However, in the monitoring device of Patent Document 1, the target distance image 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 targeted for monitoring. Therefore, if the fence image is set as the background image, there is a problem that even if an object outside the fence is visible through the fence, it cannot be detected.

The present invention has been made in view of the above circumstances, and provides, for example, a monitoring system that enables detection of an object such as through a fence in a monitoring system that detects an object by background subtraction using the highest-order reflected light. The purpose is.

In order to achieve at least one of the above-mentioned purposes, a monitoring system that reflects one aspect of the present invention may be used.
A light emitting / receiving unit including an emitting unit that emits a light beam, a scanning unit that scans the light beam in the monitoring space, and a light receiving unit that receives the light beam reflected from an object in the monitoring space.
A monitoring system including a processing unit that measures a distance to an object by processing a signal from the light receiving / receiving unit.
The processing unit sets a reference background in the monitoring space, and can measure the distance of an object closer to the reference background as a monitoring object.
The processing unit can set a mask area in an arbitrary range of the monitoring space, and when it detects reflected light from an object existing in the mask area, the object that has detected the reflected light. The distance is set to a predetermined distance, and an object closer than the predetermined distance is set as the monitoring object.

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

It is sectional drawing of the monitoring apparatus MD which concerns on this embodiment. It is a figure which shows the state which scans in the monitoring space of the monitoring apparatus MD by the laser spot light SB (shown by hatching) which emits with the rotation of a mirror unit MU. (A) and (c) are diagrams showing a state in which the monitoring space in which the background object exists is viewed from the side, and (b) and (d) are diagrams showing the processing results of the processing circuit PROC, respectively. The vertical axis is the reflected light intensity, and the horizontal axis is the distance. It is a figure which shows the monitoring space where there is no background object other than a fence FS. (A) and (c) are diagrams showing a state in which a monitoring space in which no background object other than the fence FS exists is viewed from the side, and (b) and (d) are processing results of the processing circuit PROC, respectively. The vertical axis represents the reflected light intensity and the horizontal axis represents the distance. (A) and (c) are diagrams showing a state in which the monitoring space in which the mask area is set is viewed from the side, and (b) and (d) are diagrams showing the processing results of the processing circuit PROC, respectively. , The vertical axis is the reflected light intensity, and the horizontal axis is the distance. It is a flowchart which shows the monitoring control performed by 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 flux, and the size of the mesh of a fence.

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

The monitoring device MD is, for example, a pulse type semiconductor laser LD that emits a laser light beam, a collimating lens CL that converts divergent light from the semiconductor laser LD into parallel light, and a laser beam that is parallel to the collimating lens CL. A mirror unit MU that scans and projects light toward the surveillance space by a rotating mirror surface and reflects the reflected light from the object, and a lens LS that collects the reflected light from the object reflected by the mirror unit MU. , A photodiode PD that receives light collected by the lens LS, a processing circuit (processing unit) PROC that 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, and a mirror. It has a motor MT for rotationally driving the unit MU and a housing CS for accommodating them.

In the present embodiment, the semiconductor laser LD and the collimating lens CL form an emitting unit LPS, the lens LS and the photodiode PD form a light receiving unit RPS, and the mirror unit MU constitutes a scanning unit, and these are used for further projection. It constitutes a light receiving unit. It is preferable that the optical axes of the emitting unit LPS and the light receiving unit RPS are orthogonal to the rotation axis RO of the mirror unit MU.

The box-shaped housing CS fixed to the wall WL or the like of a rigid body 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 in opposite directions and integrated, that is, four pairs (but not limited to four pairs) of mirror surfaces M1 and M2 tilted in a pair and facing each other. ) Have. 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 the shaft MTa of the motor MT fixed to the housing CS and is rotationally driven. In the present embodiment, the axis (rotational axis) of the axis MTa extends in the Z direction, which is the vertical direction, and the XY plane formed by the X and Y directions orthogonal to the Z direction is the horizontal plane. The axis of MTa may be tilted with respect to the vertical direction.

Next, the object detection principle of the monitoring device MD will be described. In FIG. 1, the divergent light emitted intermittently in a pulse shape from the semiconductor laser LD is converted into a parallel light beam by the collimating lens CL, is incident on the first mirror surface M1 of the rotating mirror unit MU, and is reflected here. Further, after being reflected by the second mirror surface M2, the light is scanned and projected as laser spot light having a vertically long rectangular cross section, for example, through the transparent plate TR and directed 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 called the light emitting / receiving direction. The laser spot luminous flux traveling in the same light emitting / receiving direction is detected by the same pixel.

FIG. 2 is a diagram showing a state in which the laser spot light SB (indicated by hatching) emitted in response to the rotation of the mirror unit MU scans in the monitoring space of the monitoring device MD, and shows trees behind the fence FS. An example of overgrown TT is shown.

Here, the crossing angles are different in the combination of the first mirror surface M1 and the second mirror surface M2 of the mirror unit MU. The laser beam is sequentially reflected by the rotating first mirror surface M1 and the second mirror surface M2. First, the laser beam reflected by the first pair of mirror surfaces M1 and the second mirror surface M2 horizontally moves from left to right in the uppermost region Ln1 of the monitoring space according to the rotation of the mirror unit MU. Is scanned. Next, the laser beam reflected by the second pair of the first mirror surface M1 and the second mirror surface M2 horizontally covers the second region Ln2 from the top of the monitoring space from the left in accordance with the rotation of the mirror unit MU. Scanned to the right. Next, the laser beam reflected by the third pair of the first mirror surface M1 and the second mirror surface M2 horizontally covers the third region Ln3 from the top of the monitoring space from the left in accordance with the rotation of the mirror unit MU. Scanned to the right. Next, the laser beam reflected by the 4th pair of the first mirror surface M1 and the second mirror surface horizontally moves horizontally from left to right in the lowest region Ln4 of the monitoring space according to the rotation of the mirror unit MU. It is scanned. This completes one scan of the entire monitoring space that can be monitored by the monitoring device MD. One frame FL can be obtained by combining the images obtained by scanning the regions Ln1 to Ln4. Then, if the first pair of first mirror surfaces M1 and the second mirror surface M2 return after one rotation of the mirror unit MU, the area from the top region Ln1 to the bottom region Ln4 of the monitoring space is reached again. The scanning is repeated to obtain the next frame FL.

In FIG. 1, a part of the laser beam reflected by the object (trees TT or fence FS) among the light beams scanned and projected passes through the transparent plate TR again and is the second mirror unit MU in the housing CS. It is incident on the mirror surface M2, reflected here, further reflected by the first mirror surface M1, collected by the lens LS, and detected on the light receiving surface of the photodiode PD, respectively. 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 receiving timing of the photodiode PD. As a result, it is possible to detect an object in the entire area in the surveillance space and obtain a frame FL (see FIG. 2) as a distance image having distance information for each pixel. Such a distance image can be transmitted to a distant monitor via a network (not shown) or the like for display, or can be stored in a storage device.

Next, the detection algorithm of the monitored object of the monitoring device MD will be described. FIG. 3 is a diagram showing 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 reference distance image (reference image) is obtained by the monitoring device MD in a state where a moving object such as a human or an animal does not exist. In the state shown in FIG. 3A, a part of the laser spot light beam SB emitted from the monitoring device MD and directed in the same light emitting / receiving direction is reflected by the fence FS installed on the ground G to become the reflected light RB1. However, the rest passes through the wire mesh of the fence FS, is irradiated to the background object of the trees TT, etc., becomes reflected light RB2, and returns to the monitoring device MD respectively.

Since the laser spot luminous flux spreads as the distance from the monitoring device MD increases, the relationship between the cross-sectional shape of the laser spot luminous flux and the size of the mesh of the fence FS differs 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 luminous flux SB1. When the distance between the monitoring device MD and the fence FS is 10 m, the fence FS is irradiated with the magnitude of the laser spot luminous flux SB2.

In this case, as shown in FIG. 3B, the processing result from the processing circuit PROC is up to the peak P1 (first echo) corresponding to the distance to the fence FS and the background object (reference background). The peak P2 (last echo: highest-order reflected light) corresponding to the distance can be obtained. According to the object monitoring algorithm using the background subtraction method, it is assumed that there is no object behind the peak P2 which is the highest-order reflected light. By recognizing the background object using the highest-order reflected light and setting the background image, and by recognizing the detected object using the highest-order reflected light during actual monitoring, rain, snow, fog, etc. The effect can be avoided. Here, the "highest-order reflected light" refers to the reflected light from the farthest object within the maximum measurable distance of the monitoring device MD (when it exceeds this, it becomes an unmeasurable point). 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, the peak P1 and the peak are shown in the processing result from the processing circuit PROC. 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, and the processing circuit PROC compares the processing result of FIG. 3 (b) with the processing result of FIG. 3 (d), and peaks P2 and peak. When a predetermined distance difference occurs with P3, attention can be drawn. Further, when the intruder OBJ is moving, the position of the peak P3 changes in the frame obtained by repeating the scan. Therefore, the processing circuit PROC tracks the intruder OBJ and obtains the moving direction and speed (moving object detection). It can be performed. For example, when the position of the peak P3 is in front of the peak P1, the processing circuit PROC can determine that the intruder OBJ has crossed the fence FS and issue an alarm via an alarm (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 when the other side of the fence FS is an open space. 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 reference distance image (reference image) is obtained by the monitoring device MD in the absence of moving objects such as humans and animals. However, in the state shown in FIG. 5A, a part of the laser spot light flux SB emitted from the monitoring device MD and heading in the same light emitting / receiving direction is reflected by the fence FS installed on the ground G and the reflected light RB1. However, since the rest passes through the fence FS and heads for infinity, only the reflected luminous flux RB1 returns to the monitoring device MD as shown in FIG. 5 (b). Therefore, when the above-mentioned detection algorithm for the monitored object is used in such a monitoring space, the reflected light flux RB1 becomes the last echo, so that the background image uses the fence FS.

In such a case, when an intruder OBJ appears on the back side of the fence FS as shown in FIG. 5 (c), as shown in FIG. 5 (d), in the processing result from the processing circuit PROC, the back side of the peak P1. In addition, the 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 with the processing result of FIG. 5D, but when the background image is set with the reflected light RB1 from the fence FS as the last echo, background subtraction is performed. Since the detection algorithm using the method does not assume that the reflected light returns from the monitored object on the back side of the last echo, as a result, the processing circuit PROC cannot detect the intruder OBJ on 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 that may delay the detection timing too much.

An algorithm for detecting an object to be monitored by the monitoring device MD that can deal with such a problem will be described. FIG. 6 is a diagram showing a state in which the same monitoring space as in FIG. 4 is viewed from the side, in association with the processing result of the processing circuit PROC.

Again, as a preparatory step for monitoring, as shown in FIG. 6A, a reference distance image (reference image) is obtained by the monitoring device MD in the absence of moving objects such as humans and animals. At this time, as in the example shown in FIG. 5A, the laser beam that has passed through the fence FS goes to infinity, so that the reflected light RB1 is generated only from the fence FS.

Therefore, in the present embodiment, the fence FS is masked so that the fence FS has 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 inputs to the processing device PROC via an interface (not shown), so that the fence FS can be used in the monitoring space. It is possible to set a mask area MA (which can take any three-dimensional shape) that surrounds all of them. In such a case, the processing device PROC forcibly sets the three-dimensional coordinates of the object (including the fence FS) reflected from the mask region MA to a predetermined distance, that is, an infinite distance (or an unmeasurable point). That is, the distance obtained based on the reflected light from the fence FS existing in the mask region MA is replaced with the distance from the monitoring device MD to the infinity (or the unmeasurable point). As a result, the fence FS can be ignored in the object detection algorithm and can be prevented from becoming an obstacle to object detection. The "predetermined distance" is preferably an infinite distance (or an unmeasurable point), but if a background object exists behind the mask region, it may be the distance of the background object.

The "unmeasurable point" means a point where the reflected light of the laser beam on the object is equal to or less than 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 ahead, the distance of the object in the mask region MA can be replaced with, for example, 50 m or more. Then, the peak P1 of the reflected light RB1 of the fence FS shown by the dotted line in FIG. 6B is shifted to the unmeasurable point or more, so that it is excluded from the background image in the object detection algorithm.

With such a setting, when an intruder OBJ appears in the monitoring space as shown in FIG. 6 (c), an intruder appears in the processing result from the processing circuit PROC as shown in FIG. 6 (d). A peak P3 corresponding to the reflected light RB3 from the person OBJ appears, but this is recognized as the last echo in the detection algorithm. Therefore, the processing circuit PROC can compare the processing result of FIG. 6 (b) with the processing result of FIG. 6 (d), determine that a new peak P3 has occurred, and call attention. For example, if an intruder OBJ is included in the mask area MA, it may be excluded from the monitored object on the detection algorithm. However, since the mask area MA can be arbitrarily set three-dimensionally, for example, intrusion. When the person OBJ tries to get over the fence FS, it protrudes above the mask area MA, so that the monitoring device MD can detect this and issue an alarm or the like.

The monitoring control of the monitoring device MD using the above detection algorithm will be described with reference to the drawings. Here, the processing circuit PROC arbitrarily sets the mask area according to the user's specification via an interface (not shown).

FIG. 7 is a flowchart showing monitoring control performed by the processing circuit PROC of the monitoring device MD. First, in step S101 of FIG. 7, the processing circuit PROC determines whether or not to set the mask region MA. Specifically, for example, when the user inputs the data (three-dimensional coordinates) of the mask area MA including the fence in the monitoring space, it is determined that the processing circuit PROC sets the mask area MA accordingly, and step S102. Specifies the mask area MA based on the input data. On the other hand, if the inputted data of the mask area MA is, the flow since the bypassing step S102, does not processing circuit PROC sets the mask area MA.

Next, in step S103, the processing circuit PROC scans the laser beam from the light emitting / receiving unit of the monitoring device MD, receives the reflected light, and obtains N distance data (distance images) 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 this belongs to the mask region MA based on the three-dimensional coordinates of the Nth measurement point.

When it is determined that the coordinates of the Nth measurement point exist in the mask region 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 actually calculates the distance of the measurement point. Use as a value.

In step S107, the processing circuit PROC determines whether or not all the measurement points in the frame are present in the mask region MA, and if it is determined that the determination has not been completed, the processing circuit PROC determines in step S108. With N = N + 1, the flow is returned to step S105. On the other hand, when it is determined that it has been determined whether or not all the measurement points in the frame exist in the mask region MA, the processing circuit PROC further performs a background image by the user using an interface (not shown) in step S109. Determine if it has been updated. When 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 detects the monitored object by using the new background image (current frame). 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. do. If it is determined that a suspicious object exists, 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, and performs the next laser light scan to perform the next. Get a distance image for the frame of. 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 present specification, and the inclusion of other embodiments / modifications is to those skilled in the art from the embodiments and technical ideas described in the present specification. it is obvious. The description and embodiments of the specification are for illustration purposes only, and the scope of the present invention is set forth by the claims described below. For example, not only a fence but also a glass plate that transmits a part of laser light can be surrounded by a mask area. Further, by rotating the wall WL to which the monitoring device MD is attached in the vertical direction, the laser beam emitted from the light emitting / receiving unit can be directed in all directions by 360 °. The mask area can be set even when a fence or the like exists 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 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 (6)

A light emitting / receiving unit including an emitting unit that emits a light beam, a scanning unit that scans the light beam in the monitoring space, and a light receiving unit that receives the light beam reflected from an object in the monitoring space.
A monitoring system including a processing unit that measures a distance to an object by processing a signal from the light receiving / receiving unit.
The processing unit sets a reference background in the monitoring space, and can measure the distance of an object closer to the reference background in the same light emitting / receiving direction from the light emitting / receiving unit as a monitoring object.
The processing unit can set a mask area in an arbitrary range of the monitoring space, and when it detects reflected light from an object existing in the mask area, the object that has detected the reflected light. A monitoring system in which the distance is set to a predetermined distance, and an object closer than the predetermined distance is set as the monitoring object. Wherein the predetermined distance is the distance to the reference background or infinity Moshiku monitoring system according to claim 1 which is unmeasurable 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 has a monitoring range as a three-dimensional space, and the mask area can be set three-dimensionally within the monitoring range. Claims 1 to 5 detect the monitored object whose position has changed between the time-preceding scan of the luminous flux by the scanning unit and the time-following scanning by the scanning unit as a moving object. The monitoring system described in any of.

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