Abstract:
Embodiments of a passive infrared detector can distinguish between an intruder and a small animal passing nearby the detector with a high degree of accuracy without substantially detracting from the ability to detect the intruder within a coverage area farther from the detector. In some embodiments, the passive infrared detector includes a pair of lens assemblies that collect infrared light onto corresponding infrared sensors. Each lens assembly receives light from different spatial regions, which do not overlap near the detector and which substantially overlap farther from the detector. The passive infrared detector also includes a controller that is capable of distinguishing between an intruder and a small animal based on simultaneity of signals from the infrared sensors or by summing the signals from the infrared sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/JP2008/000176, with an international filing date of Feb. 7, 2008, which claims priority to Japanese Patent Application No. 2007-034334, filed Feb. 15, 2007. The entire disclosure of each of the above-referenced applications is hereby incorporated by reference herein and made part of this specification. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present application relates generally to a passive infrared detector for detecting an intruder as a moving object by detecting thermal change of far infrared radiation from a human body using pyroelectric elements. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a passive infrared detector may comprise a housing or container formed by a plurality of mirrors and an optical unit mounted on the tip of a pair of side walls extending from the ends of the housing. The optical unit can include a PCB (printed circuit board) on which pyroelectric elements are mounted and adapted to detect an intruder (e.g., a human body) within a guard coverage area (alert object area) by detecting thermal change of far infrared radiation using pyroelectric elements. 
         [0006]    In such a passive infrared detector, methods are known for improving the resolving power of the guard coverage area (alert object area) to prevent false alarms from being caused by movement of a small animal (including a bird and an insect) within the guard coverage area (alert object area). The passive infrared detector may include a plurality of pyroelectric elements forming separate systems within one optical unit or by using a plurality of optical units for monitoring the guard coverage area (alert object area). Passive infrared detectors of this kind are known, such as those disclosed, e.g., in Japanese Laid-open Patent Publication No. 101376/1997. 
       SUMMARY 
       [0007]    Embodiments of the passive infrared detector described herein can discriminate between an intruder and a small animal passing nearby the detector with a high degree of accuracy without detracting from the ability to detect the intruder within a more distant guard coverage area (alert object area). 
         [0008]    An embodiment of a passive infrared detector for detecting a moving object that emits infrared radiation is provided. The embodiment of the detector comprises a first optical element that comprises a first infrared detector and a first optical assembly. The first optical assembly is configured to collect onto the first infrared detector infrared radiation received from a first alert zone, and the first infrared detector is configured to provide a first signal in response to the collected infrared radiation from the first alert zone. The embodiment of the detector also comprises a second optical element that comprises a second infrared detector and a second optical assembly. The second optical assembly is configured to collect onto the second infrared detector infrared radiation from a second alert zone, and the second infrared detector is configured to provide a second signal in response to the collected infrared radiation from the second alert zone. The second optical element is spaced from the first optical element. The embodiment of the detector also comprises a controller that is configured to receive the first signal and the second signal and output a detection signal based on the first signal and the second signal. The first optical element and the second optical element are configured so that the first alert zone and the second alert zone do not overlap in a first coverage region proximate the detector, and the first alert zone and the second alert zone substantially overlap in a second coverage region that is farther from the detector than the first coverage region. The controller is configured to output the detection signal based on (i) simultaneity of a first feature of the first signal and a second feature of the second signal or (ii) a sum of the first signal and the second signal. 
         [0009]    An embodiment of a method for passively detecting a moving object is described. In this embodiment, the method comprises generating with a first detector a first signal in response to first radiation received from a moving object. The first radiation is received from a first alert zone. The method also comprises generating with a second detector a second signal in response to second radiation received from the moving object. The second radiation is received from a second alert zone. The first alert zone and the second alert zone are not overlapping in a first region adjacent the first detector and the second detector, and the first alert zone and the second alert zone are substantially overlapping in a second region beyond the first region. The method also comprises determining the presence of a moving object based on (i) simultaneity of a first feature of the first signal and a second feature of the second signal or (ii) a sum of the first signal and the second signal. 
         [0010]    An embodiment of a system for detecting a moving object is described. In this embodiment, the system comprises a first radiation detector configured to provide a first signal in response to radiation received from a first region and a second radiation detector configured to provide a second signal in response to radiation received from a second region. The first region is not overlapping with the second region in a first monitored zone, and the first region is substantially overlapping with the second region in a second monitored zone. The first monitored zone is closer to the first radiation detector and the second radiation detector than is the second monitored zone. The system further comprises a processor configured to provide a detection signal indicating the presence of the moving object in the first monitored zone or the second monitored zone if (i) a first feature of the first signal temporally coincides with a second feature of the second signal or (ii) a sum of the first signal and the second signal exceeds a threshold. 
         [0011]    An embodiment of a passive infrared detector for detecting a moving object such as intruder is provided. The detector comprises an optical unit having a PCB (printed circuit board) disposed in front of a base. A plurality of lenses are vertically arranged at predetermined spaces and are mounted on the base. Detecting elements are arranged at positions corresponding to the lenses. The detector comprises a controller for processing signals detected by the detecting elements. The spaces between the plurality of lenses are set so that they are small for a size of a human body and large for a size of a small animal. The controller is adapted to determine whether the moving object is an intruder or a small animal by discriminating the simultaneity of signals detected by the detecting elements or by summing the detected signals. 
         [0012]    In certain embodiments, it is possible to distinguish between an intruder and a small animal passing nearby the detector with a high degree of accuracy without detracting from the performance for detecting the intruder within the guard coverage area (alert object area). Such embodiments thus prevent generation of false alarms caused by the small animal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    Additional advantages and features of certain embodiments will become apparent from the following description and claims, taken in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view showing one embodiment of a passive infrared detector; 
           [0015]      FIG. 2  is a perspective view of the passive infrared detector of  FIG. 1  with a cover removed to show the lens assemblies; 
           [0016]      FIG. 3  is a perspective view of the passive infrared detector of  FIG. 2  with the lens assemblies removed to show the detecting elements; 
           [0017]      FIG. 4  is a block diagram showing an embodiment of a control portion usable with embodiments of the passive infrared detector; 
           [0018]      FIG. 5  is a flowchart showing one example of the operation of the passive infrared detector of  FIG. 1 ; 
           [0019]      FIGS. 6(   a )- 6 ( d ) are graphs of examples of signals from the detecting elements of the passive infrared detector of  FIG. 1 ; 
           [0020]      FIG. 7  is a plan view showing an example arrangement of horizontal alert zones Wa in the guard coverage area (alert object area) W of an embodiment of the passive infrared detector of  FIG. 1 ; 
           [0021]      FIGS. 8(   a ) and  8 ( b ) are side views showing an example arrangement of vertical alert zones Wb in the guard coverage area (alert object area) W of an embodiment of the passive infrared detector of  FIG. 1 ; 
           [0022]      FIG. 9  is a flowchart showing another example of the operation of an embodiment of the passive infrared detector; 
           [0023]      FIG. 10  is a block diagram showing another example of a control portion usable with embodiments of the passive infrared detector; 
           [0024]      FIG. 11  is a flowchart showing an example of the operation of a passive infrared detector comprising an embodiment of the control portion of  FIG. 10 ; and 
           [0025]      FIGS. 12(   a )- 12 ( d ) are graphs of examples of signals from the detecting elements of an embodiment of the passive infrared detector shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    Passive infrared detectors described in the prior art may be effective for preventing false alarms at a position in which a human as a detecting object walks (usually at a position about 2 m-30 m from the passive infrared detector). However, it is difficult for such detectors to maintain a sufficient alert zone while preventing generation of false alarms relating to a small animal moving proximate to the passive infrared detector. Although a passive infrared detector using a plurality of optical units separated by a wide space has been proposed, the goal of the wide space is different from preventing generation of false alarms. The wide space is not sufficient for detecting a small animal, and it is difficult to distinguish a human body (human) and an insect or a bird flying nearby the detector or an insect crawling on a surface of the detector. 
         [0027]    Embodiments of the present disclosure will be hereinafter described with reference to the accompanying drawings.  FIGS. 1-9  show embodiments of a passive infrared detector, wherein  FIG. 1  is a perspective view showing one embodiment of a passive infrared detector;  FIG. 2  is a perspective view of the passive infrared detector of  FIG. 1  with a cover removed to show the lens assemblies;  FIG. 3  is a perspective view of the passive infrared detector of  FIG. 2  with the lens assemblies removed to show the detecting elements;  FIG. 4  is a block diagram showing an embodiment of a control portion usable with embodiments of the passive infrared detector;  FIG. 5  is a flowchart showing one example of the operation of the passive infrared detector of  FIG. 1 ;  FIGS. 6(   a )- 6 ( d ) are graphs of examples of signals from the detecting elements of the passive infrared detector of  FIG. 1 ;  FIG. 7  is a plan view showing an example arrangement of horizontal alert zones Wa in the guard coverage area (alert object area) W of an embodiment of the passive infrared detector of  FIG. 1 ;  FIGS. 8(   a ) and  8 ( b ) are side views showing an example arrangement of vertical alert zones Wb in the guard coverage area (alert object area) W of an embodiment of the passive infrared detector of  FIG. 1 ; and FIG.  9  is a flowchart showing another example of the operation of an embodiment of the passive infrared detector. 
         [0028]    As shown in  FIGS. 1-3 , an embodiment of a passive infrared detector  1  can comprise a rectangular base  2  having longer vertical sides in a front view and adapted to be mounted on a mounting surface such as a wall. The detector  1  can include a cover  3  detachably mounted on the front side of the base  2  and having a window that transmits far infrared radiation. An optical unit  4  may be disposed within the cover  3 . 
         [0029]    The optical unit  4  shown in  FIG. 2  can comprise a housing  6  having a pair of openings  6   a  at vertically separated positions, and a pair of vertically separated lens assemblies  7  disposed within the pair of openings  6   a.  The lens assemblies  7  can comprise a plurality of lenses  7   a  (or a pair of mirror assemblies comprising a plurality of mirrors), and a PCB (printed circuit board)  5  ( FIG. 3 ) arranged within the lens assemblies  7 . A space between the vertically arranged lens assemblies  7  is set so that it is small for a size of a human body (intruder) M and large for a size of a small animal T. The lens assemblies  7  are mounted on the housing  6  and may pivot around a shaft  8 , which allows the lens assemblies  7  to be oriented at the same pivoted angle. As shown in  FIG. 3 , the PCB (printed circuit board)  5  comprises a rectangular printed circuit board of longer vertical sides in a front view. Detecting elements  9   a,    9   b  are mounted on the PCB  5  and can comprise pyroelectric elements each arranged at a position substantially corresponding to the central position of each lens assembly  7 . In addition a control portion (control means)  10  is formed on the PCB (printed circuit board)  5  (or a separately arranged printed circuit board). 
         [0030]    In the embodiment shown in  FIG. 4 , the control portion  10  comprises amplification portions  11   a ,  11   b  connected to the detecting elements  9   a,    9   b  for amplifying signals detected by the detecting elements  9   a,    9   b,  a discriminating portion  12  comprising microcomputers for processing signals (signal  1  and signal  2 ) from the amplifying portions  11   a ,  11   b , and an output portion  13  for outputting discriminated results of the discriminating portion  12 . The control portion  10  can operate in accordance with a program stored in a storing portion (not shown). The program may implement the operations of the example flowchart of  FIG. 5 . 
         [0031]    The passive infrared detector  1  can be mounted, for example, at a predetermined height on a wall  14  in a room to be monitored (see  FIGS. 7 and 8 ). A guard coverage area (alert object area) W comprising a plurality of horizontal alert zones Wa is formed by the pair of vertically arranged detecting elements  9   a,    9   b  and can have a sector configuration as shown in the plan view of  FIG. 7 . The guard coverage area (alert object area) W can comprise a plurality of vertical alert zones Wb as shown in the side views of  FIGS. 8(   a ) and  8 ( b ). The vertical alert zones Wb of the detecting elements  9   a,    9   b  are set so that they are not overlapped in the guard coverage area (alert object area) W 1  and are substantially overlapped in a area W 2  extending away from the guard coverage area (alert object area) W 1 . 
         [0032]    For example, the lens assemblies  7  of the optical unit  4  can be oriented so that the respective alert zones Wb are overlapped at a position sufficiently apart from the passive infrared detector  1 . The passive infrared detector  1  is arranged so that each lens assembly  7  can be oriented at the same angle by pivoting the optical unit  4  around the shaft  8 . 
         [0033]      FIG. 5  is a flowchart showing one example of the operation of the passive infrared detector  1 . After the detector  1  is mounted and the lens assemblies  7  are oriented, the program is started (S 100 ), and the program determines whether the signal  1  detected by the detecting element  9   a  exceeds a threshold set in the discriminating portion  12  (S 101 ). The step S 101  is repeated until the signal  1  exceeds the threshold (e.g., it becomes YES). When the signal  1  has become YES at the step S 101 , the program determines whether the signal  2  detected by the detecting element  9   b  exceeds a threshold set in the discriminating portion  12  (S 102 ). The step S 102  is also repeated until the signal  2  exceeds the threshold (e.g., it becomes YES). Peaks of the signals  1 ,  2  are detected (S  103 ) at this point of time when the determination in step S 102  became YES. 
         [0034]    When the peaks are detected at the step S 103 , the program determines whether the peaks of the signals  1 ,  2  occur at the same time (S 104 ). When the step S 104  is YES, the program determines that an intruder is present and an alarm is output (S 105 ) and the program ends (S 106 ). Accordingly, in the example flowchart of  FIG. 5 , the detected moving object (detecting object) is determined to be an intruder M (human body) when the peaks P 1 , P 2  ( FIG. 6(   a )) of the signals  1 ,  2  occur at the same time, e.g., when the moving object within the area W ( FIG. 8(   a )) is detected by both the detecting elements  9   a,    9   b.    
         [0035]    The detected moving object is determined to be a small animal T when only one signal (either the signal  1  or  2 ) is detected as shown in  FIGS. 6(   b ) and  6 ( c ). For example, when a small animal (including an insect or a bird) T within the area W 1  is detected as shown in  FIG. 8(   b ), the peaks P 1 , P 2  do not occur at the same time. The moving object is also judged as a small animal T when the peaks P 1 , P 2  reverse direction relative to each other and do not occur at the same time ( FIG. 6(   d )). Thus, embodiments of the detector  1  have improved detecting accuracy when the intruder M and the small animal T are within the area W 1  proximate to the passive infrared detector  1 . 
         [0036]    In the program implementing the example flowchart of  FIG. 5 , the determination whether the moving object is an intruder M or a small animal T is carried out by discriminating whether the peaks P 1 , P 2  of the signals  1 ,  2  occur at the same time. In other embodiments, it is possible to make this determination based on the simultaneity of the rising time points (or falling time points) of the signals  1 ,  2  as shown in the example flowchart of  FIG. 9 . After start of the program (S 100 ), the rising time points U 1 , U 2  of the signals  1 ,  2  ( FIGS. 6(   a )- 6 ( c )) are detected (S  107 ) when both the signals  1 ,  2  exceed thresholds (S 101 , S 102 ). The program determines whether the rising time points U 1 , U 2  are simultaneous (S 108 ). When the program determines YES at step S 108 , an alarm is output (S 105 ) and the program ends (S 106 ). The moving object is determined to be an intruder M when the rising time points U 1 , U 2  of the signals  1 ,  2  occur at the same time, and the moving object is determined to be a small animal such as an insect or a bird when the rising time points U 1 , U 2  of the signals  1 ,  2  are not the same as shown, for example, in  FIGS. 6(   b )- 6 ( d ). 
         [0037]    Therefore, in one embodiment of the passive infrared detector  1 , the detecting elements  9   a,    9   b  are mounted on the PCB (printed circuit board)  5  so that they correspond to the pair of vertical lens assemblies  7  of the optical unit  4 . The signals detected by the detecting elements  9   a,    9   b  are processed by the control portion  10  to discriminate whether the moving object is an intruder M or a small animal T. In this embodiment, it is possible to detect the small animal T moving within the guard coverage area (alert object area) W 1  proximate to the optical unit  4  without detracting from the ability to detect the intruder M within the guard coverage area (alert object area) W. because the pair of lens assemblies  7  can be oriented at predetermined directions as well as at predetermined positions. 
         [0038]    Embodiments of the control portion  10  can provide accurate discrimination of moving objects without being complicated, because the control portion  10  can use simplified processing of the two signals detected by the detectors  9   a,    9   b.  For example, the control portion  10  may be configured to detect the peaks P 1 , P 2  or the rising time points U 1 , U 2  of signals and to detect whether the two signals occur simultaneously. Accordingly, it is possible to provide a high degree of discrimination between a small animal T such as an insect flying nearby the passive infrared detector  1  or crawling on the cover  3  thereof and an intruder M. Therefore, the control portion  10  prevents false alarms from being generated by the passive infrared detector  1 . 
         [0039]    Embodiments of the passive infrared detector  1  may also further improve the discriminating accuracy of moving objects proximate to the passive infrared detector  1 . For example, in the optical unit  4  the pair of lens assemblies  7  can comprise a multiple of the same lenses  7   a  arranged so that they have the same position relation relative to the respective detecting elements  9   a,    9   b.  Also, the space between the pair of vertical lens assemblies  7  is set small for the human body (intruder M) and large for the small animal T in the guard coverage area (alert object area). In addition, since a plurality of vertically arranged lenses  7   a  are used in the lens assemblies  7  of the optical unit  4 , it is possible to detect infrared rays within the guard coverage area (alert object area) W. Accordingly, embodiments of the detector  1  can be used as a passive infrared detector for detecting an intruder. 
         [0040]      FIG. 10  is a block diagram showing another example of a control portion  10  usable with embodiments of the passive infrared detector  1 ;  FIG. 11  is a flowchart showing an example of the operation of a passive infrared detector  1  comprising an embodiment of the control portion of  FIG. 10 ; and  FIGS. 12(   a )- 12 ( d ) are graphs of examples of signals from the detecting elements of an embodiment of the passive infrared detector shown in  FIG. 10 . The same reference numerals are used in these embodiments as those used in the embodiments described with reference to  FIGS. 1-9 . In these embodiments, the detector  1  can discriminate whether a moving object is an intruder M or a small animal T by summing signals  1 ,  2  detected by detecting elements  9   a,    9   b.  The control portion (control means)  10  comprises amplification portions  11   a ,  11   b , a summing operation portion  15  for summing the signals  1 ,  2  amplified by the amplification portions  11   a ,  11   b , a discriminating portion  12  for discriminating a signal S summed by the summing operation portion  15 , and an output portion  13 . 
         [0041]    As shown in  FIG. 11 , after the program is started (S 200 ), the program determines whether the summed signal S exceeds a threshold previously set in the discriminating portion  12  (S 201 ). The step S 201  is repeated until the signal S exceeds the threshold (e.g., step S 201  becomes YES). When step S 201  has become YES, an alarm is output (S  202 ) and the program ends (S 203 ). In this embodiment, the moving object is determined to be an intruder M when the summed signal S of the signals  1 ,  2  exceeds an upper or a lower threshold as shown in  FIG. 12(   a ). The moving object is determined to be a small animal T when the summed signal S does not exceed the upper or the lower threshold as shown in  FIGS. 12(   b )- 12 ( d ). Thus, the discrimination provided by this program can be similar to the discrimination provided by the embodiments described above. 
         [0042]    Embodiments of the passive infrared detector have been described. Modifications and alternations will occur to those of ordinary skill in the art upon reading and understanding the preceding detailed description. For example, the configuration, orientation, etc. of the lenses  7   a  itself may be appropriately modified in accordance with configurations of the guard coverage area (alert object area) W. More than two detecting elements may be used. It is also possible to further improve the detecting accuracy within the guard coverage area (alert object area) W irrespective of the distance from the passive infrared detector by using multiple detectors for each detecting element  9   a,    9   b  or by monitoring each alert zone Wa, Wb of the guard coverage area (alert object area) W with a plurality of optical units. 
         [0043]    Further, embodiments of the passive infrared detector  1  not only can be mounted on a wall in a room but also can be mounted on an upper wall surface or a ceiling, either inside or outside of the room.