JP2017215642A - Monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monitoring system which is configured to detect objects by means of background subtraction using the highest order reflection light, for example, and which is capable of continuing the detection process while avoiding the influence of sunlight and the like as much as possible.SOLUTION: A monitoring system includes a detection device configured to detect intensity of background light in a monitoring space for each pixel. A processing unit is configured to recognize an object as a monitoring target when a difference (A-B) between a distance A from a light transceiving unit to a reference background in a single light transceiving direction and a distance B to the object is greater than a threshold C, where the threshold is set according to the intensity of the background light detected by the detection device.SELECTED DRAWING: Figure 6

Description

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

  As a monitoring device for detecting an intruder or the like in a monitoring space, an apparatus 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 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 obtained in advance, the obtained background image is compared with the input distance image (current image), and the background image A so-called background subtraction method is used in which a pixel corresponding to a closer distance is extracted to obtain a change region. Accordingly, it is possible to determine whether or not the moving object is the target detection target based on the size / shape of the change area and the distance information in the current image.

  The distance image includes information such as the direction of the object viewed from the transmission / reception 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 JP 09-318736 A

  By the way, the sun may enter the surveillance space due to the low altitude of the sun such as early morning or dusk. However, since sunlight generally contains a component in the same band as the laser beam used in the monitoring device, there is a possibility that false detection may occur when sunlight enters the monitoring device. Moreover, even when the sun does not exist in the monitoring space, if the sunlight reflected by the reflector is incident on the monitoring device indirectly, there is a possibility of causing false detection in the same manner.

  On the other hand, in Patent Document 2, when the incident of high-intensity background light (sunlight etc.) that may cause erroneous detection of an object is detected, the driver is alerted or the distance is measured by turning on a fail lamp or the like. An in-vehicle distance measuring device that can be interrupted is disclosed. Here, the distance measuring device of Patent Document 2 is fixed in the sense that it provides as much information as possible to support the driver's determination in in-vehicle applications, in which the decision to avoid danger is ultimately left to the driver. There is utility. However, when the technique of Patent Document 2 is diverted to a monitoring application for monitoring the intrusion of a suspicious person or a suspicious object, particularly a monitoring device for an important facility, if the measurement is interrupted due to the incidence of sunlight, As a result, the monitoring function is lost, which is a problem. That is, in a general monitoring device, it is desirable to continue the detection process as much as possible even under bad conditions where sunlight is incident. Such a problem can be said to occur not only in sunlight but also when relatively high intensity background light is incident.

  The present invention has been made in view of the above circumstances. For example, in a monitoring system that performs object detection based on background difference using the highest-order reflected light, the detection process is continued while avoiding the influence of sunlight or the like as much as possible. An object is to provide a monitoring system capable of performing the above.

The monitoring system of the present invention includes:
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 unit for measuring a distance to the object by processing a signal from the light projecting and receiving unit;
A detection system that detects the intensity of background light in the monitoring space,
The processing unit sets a threshold value C based on the intensity of the background light detected by the detection device, and a distance A from the light projecting / receiving unit to a reference background in the same light projecting / receiving direction and a distance B to the object. If the difference (A−B) exceeds the threshold value C, the object to be monitored is recognized.

  According to the present invention, for example, in a monitoring system that performs object detection based on background difference using the highest-order reflected light, a monitoring system capable of continuing detection processing while avoiding the influence of sunlight or the like as much as possible is provided. be able to.

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) is a figure which shows the state which looked at the monitoring space from the side, (b) is the graph which matched the intensity | strength of reflected light, and distance in the output signal of a certain pixel, and is a background image. It is an example. (A) is a figure which shows the state which looked at the monitoring space from the side, (b) is the graph which matched the intensity | strength of reflected light, and distance in the output signal of a certain pixel, It is an example. These are figures which show the state which looked at the monitoring space from the side, and are examples in which the sun is located in the monitoring space. It is a flowchart which shows the monitoring control performed in the processing circuit PROC of the monitoring apparatus MD.

  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 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 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 that rotationally drives the unit MU, and a housing CS that houses them. The photodiode PD has a plurality of pixels arranged in the Z direction.

  In the present 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, the mirror unit MU constitutes a scanning part, and Constructs a light emitting / 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 rigid wall WL or the like includes 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 (axis of rotation) 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 the axis 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 monitoring space of the monitoring device MD is scanned with the laser spot light SB (shown by hatching) emitted according to the rotation of the mirror unit MU. 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. 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. One 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 of the scanning light flux is transmitted through the transparent plate TR again and incident on the second mirror surface M2 of the mirror unit MU in the housing CS. The light is reflected here, is further reflected by the first mirror surface M1, is collected by the lens LS, and is detected for each pixel 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, a detection algorithm for the monitoring object of the monitoring device MD using the background difference method will be described. 3 (a), 4 (a), and 5 are schematic views showing a state in which the monitoring space is viewed from the side, and FIGS. 3 (b) and 4 (b) are FIGS. It is a graph which shows the signal of the processing circuit PROC which respectively respond | corresponded to a) and processed the output of a certain pixel, and shows the intensity | strength on the vertical axis | shaft and the distance on the horizontal axis.

  In the background subtraction method employed in the present embodiment, a reference image (also referred to as a background image) acquired in advance is used. Specifically, as a pre-monitoring preparation (pre-processing), as shown in FIG. 3A, a monitoring device is used for a background object BG (referred to as a reference background) in which no moving object such as a human or an animal exists. The laser spot beam SB is scanned from the MD. In the state shown in FIG. 3A, the laser spot light beam SB emitted from the monitoring device MD and traveling in the same light projecting / receiving direction is irradiated on the background object BG to be reflected light RB1, and returns to the monitoring device MD.

  In this case, as a result of processing from the processing circuit PROC, as shown in FIG. 3B, a peak P1 (last echo: highest-order reflected light) corresponding to the distance to the background object BG is obtained. Therefore, a reference image (see FIG. 2) can be obtained based on the reflected light RB1 obtained from the background object BG. In the object monitoring algorithm, it is assumed that no object exists behind the peak P1, which is the highest order reflected light. In an object monitoring algorithm using a general background subtraction method, it is assumed that no object exists behind the object that emits the highest-order reflected light (last echo). “Highest-order reflected light” refers to the reflected light from the farthest object within the maximum measurable distance of the monitoring device MD (beyond this, it becomes a measurement impossible point). . 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.

  In actual monitoring, as shown in FIG. 4 (a), when an intruder OBJ appears in front of the background object BG, it is shown in FIG. 4 (b) based on the reflected light RB2 from the intruder OBJ. A peak P2 appears in the processing result. In such a case, the processing circuit PROC compares the distance A to the reference background in FIG. 3B with the distance B to the object in FIG. 4B, and a threshold value having a difference (A−B). When C is exceeded, it is possible to call attention that a monitoring object (intruder OBJ) has appeared. Further, when the intruder OBJ is moving, the position of the peak P2 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.

  Next, the influence of background light in the monitoring space will be described. Here, the background light refers to light incident on the monitoring device MD from the monitoring space regardless of the irradiated laser light. The monitoring device MD in the present embodiment can receive only light from the laser beam emission direction (that is, reflected light) because of its configuration, and thus is relatively resistant to disturbance. However, for example, as shown in FIG. 5, when the sun SN is located in the monitoring space, the level of background light greatly increases due to the influence of sunlight, which may adversely affect object detection. In general, the intensity of reflected light reflected from an object irradiated with a laser beam is weak, so when the background light intensity increases, the reflected light is buried in the background light, and the reliability of the distance measurement value is increased. May fall. According to the examination result of the present inventor, for example, in the case of indoors where the background light intensity is relatively low, the object can be detected with a distance measurement value ± 12 cm (referred to as measurement reproducibility), whereas the background in the outdoors It was found that the measurement reproducibility is reduced to a distance measurement value of about ± 24 cm in an environment where light can easily enter.

  Therefore, in the present embodiment, the background light is detected using the pixel of the photodiode PD as a detection device, and the processing circuit PROC changes the threshold C according to the output signal. In this example, when the sun SN is located in the monitoring space, the intensity of the background light detected by the photodiode PD increases, so the processing circuit PROC detects the output of the photodiode PD and increases the threshold C accordingly. . That is, when the intensity of the background light is high, the risk of erroneous detection is reduced by increasing the threshold value C. Thereby, the detection process can be continued while avoiding the influence of sunlight or the like as much as possible.

  When the threshold C used here is applied to the above example, it is preferably set to 12 cm when detecting an object indoors and set to 24 cm when detecting an object indoors. However, the threshold value can be appropriately increased or decreased in accordance with the environment of the monitoring space in proportion to the intensity of the background light (for example, when the intensity of the background light increases by 30%, the threshold value is increased by 30%). Either of the binary values may be selected depending on whether the sun SN is located in the monitoring space or not. As the threshold value C, an optimum value can be determined through simulations and experiments. The intensity of the background light detected by the detection device may be the maximum intensity or the average intensity of the light received by the pixel, or may be an integrated value. The detection device is not limited to the photodiode PD, and a solar radiation sensor or the like may be used separately.

  On the other hand, the processing circuit PROC can determine that the direct sunlight or the like has been detected when the intensity of the background light is very high in a certain pixel. Therefore, the processing circuit PROC sets a limit value, and when the intensity of the background light exceeds the limit value, the pixel can be excluded from the object as having detected abnormal light.

  FIG. 6 is a flowchart showing the monitoring control performed by the processing circuit PROC of the monitoring device MD. First, in step S101 of FIG. 6, the processing circuit PROC receives output signals from all the pixels of the photodiode PD, and individually acquires the background light intensity.

  Next, in step S102, the processing circuit PROC determines whether or not the user updates the reference background image using an interface (not shown). If it is determined that the background image has been updated, the processing circuit PROC registers a new background image in step S103 and uses this to detect the monitoring object. On the other hand, if the processing circuit PROC does not determine that the background image has been updated, the flow bypasses step S103.

  Further, N = 1 is set in step S104, and in subsequent step S105, the processing circuit PROC determines whether or not the obtained background light intensity exceeds the limit value. If it is determined that the calculated background light intensity exceeds the limit value, the processing circuit PROC excludes the Nth pixel from the detection processing target data in step S106. In this case, the processing circuit PROC can recognize the pixel as a non-measurable point on the distance image.

  On the other hand, when it is determined that the obtained background light intensity is equal to or less than the limit value, the processing circuit PROC employs the Nth pixel as detection processing target data in step S107.

  In subsequent step S108, the processing circuit PROC determines the threshold value Cn as described above according to the background light intensity of the Nth pixel. Thereafter, in step S109, the processing circuit PROC obtains a difference for the Nth pixel, that is, (background image distance An−current frame object distance Bn).

  In step S110, the processing circuit PROC compares the difference (An−Bn) with the threshold Cn for the Nth pixel. If the difference (An−Bn) exceeds the threshold Cn, the processing circuit PROC compares the difference with the Nth pixel in step S111. Extract (store) pixels. On the other hand, if the difference (An−Bn) does not exceed the threshold value Cn, the process bypasses step S111 and does not store the Nth pixel.

  Further, in step S112, the processing circuit PROC determines whether or not the difference and the threshold have been compared for all the pixels in the frame. If it is determined that the comparison has not been completed, N = N + 1 in step S113. Is returned to step S105. On the other hand, if it is determined that the difference and the threshold have been compared for all the pixels in the frame, the processing circuit PROC performs a clustering process on the extracted pixels in step S114. The clustering process is a process for finding a group of pixels in the extracted pixels, that is, a process necessary for determining whether or not the extracted pixels correspond to an object to be monitored. Here, the number of pixel groups in a lump is called the number of cluster pixels. When this number exceeds a predetermined value D, it can be determined that the monitoring object has a certain size. Therefore, the predetermined value D is set to an optimum value depending on the size of the object to be detected. For example, if the detected object is a human, a predetermined value D based on the size of the human is set. As a result, it is possible to avoid misreporting by small animals that are not detected.

  In step S115, the processing circuit PROC determines whether or not the obtained number of cluster pixels exceeds a predetermined value D. If it exceeds the predetermined value D, the processing circuit PROC outputs an alarm signal in step S116, displays an alarm on a monitor (not shown), returns the flow to step S101, and performs the next laser beam scanning. To obtain a distance image for the next frame. On the other hand, if the obtained number of cluster pixels does not exceed the predetermined value D, the processing circuit PROC determines that the background image remains unchanged, and 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 apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims. For example, as an example of background light, an example of light that is incident from an object when the sun is located in the monitoring space is given, but the present invention is not limited to this. Can handle.

BG Background object CL Collimating lens CS Housing CSa Upper wall CSb Lower wall CSc Side wall CSd Opening FL Frame LD Semiconductor laser LPS Emitting part LS Lens M1, M2 Mirror surface MD Monitoring device MT Motor MTa Axis MU Mirror unit OBJ Intruder PD Photo Diode PROC Processing circuit RB1, RB2 Reflected light RO Rotating axis RPS Light receiving part SB Laser spot light TR Transparent plate WL Wall

Claims (4)

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 unit for measuring a distance to the object by processing a signal from the light projecting and receiving unit;
A detection system that detects the intensity of background light in the monitoring space,
The processing unit sets a threshold value C based on the intensity of the background light detected by the detection device, and a distance A from the light projecting / receiving unit to a reference background in the same light projecting / receiving direction and a distance B to the object. When the difference (A−B) exceeds the threshold C, the monitoring system recognizes the object to be monitored.   The monitoring system according to claim 1, wherein the processing unit increases the threshold value as the intensity of the background light increases.   3. The processing unit according to claim 1 or 2, wherein when the intensity of the background light detected by the detection device exceeds a limit value, the processing unit determines that abnormal light has been detected and excludes it from the monitoring target. The monitoring system described.   The monitoring system according to claim 1, wherein the detection device is the light receiving unit.

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