Abstract:
An anti-tamper assembly ( 40, 40   a ) is provided in order to sense the attempted removal of a body attached to a surface ( 17 ) by a fastener ( 36, 36   a ). The assembly ( 40, 40   a ) includes an anti-tamper access-blocking element ( 42, 42   a ) positioned in an anti-tamper position proximal to the fastener ( 36, 36   a ), along with an anti-tamper switch ( 44, 102 ) operably coupled with the element ( 42, 42   a ) in order to bias the switch ( 44, 102 ) to one switch condition. In the event that the element ( 42, 42   a ) is moved from its anti-tamper position, the switch ( 44, 102 ) moves to another switch condition, which generates an alarm signal. The assembly ( 40, 40   a ) may be used to protect an alarm section ( 16, 16   a ) forming a part of an alarm assembly ( 10, 10   a ). The section ( 16, 16   a ) includes a sensor or switch ( 64 ) operable to detect relative movement between first and second members such as a door ( 12 ) and doorframe ( 14 ). In one embodiment, a magnetically actuatable switch ( 42 ) is employed with a mating access-blocking element ( 42 ) in the form of a magnet. Alternately, a mechanically actuatable switch ( 102 ) having an actuating arm ( 104 ) may be used where the arm ( 104 ) engages access-blocking element ( 42   a ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with anti-tamper assemblies for use in preventing removal of bodies mounted on surfaces through use of a fastener. More particularly, the invention is concerned with such anti-tamper assemblies which may be used in conjunction with proximity or movement-sensing switches and include an access-blocking element such as a plug or magnetic component (e.g., a magnet) located in an anti-tamper position relative to the fastener, together with an anti-tamper switch which is operably coupled with the access-blocking element for actuation of the anti-tamper switch upon movement of the access-blocking element from the anti-tamper position thereof. 
     2. Description of the Prior Art 
     Security alarm systems often make use of magnetically actuatable switches attached to doors and windows for detecting unauthorized openings. One type of switch utilized in this context is a reed switch. However, reed switches are subject to unauthorized manipulation through use of an external magnet. Specifically, a compact high-energy magnet may be positioned in proximity to the reed switch, which will then be operated to either open or close the switch depending upon the control scheme. Once this is accomplished, an intruder may open the door or window without triggering the alarm system. 
     In response to these problems, the Magnasphere Corporation of Waukesha, Wis. has introduced improved switches not subject to external magnetic manipulation. These switches typically include a pair of spaced-apart switch elements with a shiftable body (e.g., a spherical ball) moveable between respective positions corresponding to different switch conditions. Thus, the ball may be in simultaneous contact with the switch elements in one condition, and out of such simultaneous contact in another condition. An alarm circuit is electrically coupled to the switch elements in order to generate an alarm signal upon a change in switch condition. The Magnasphere switches are described in U.S. Pat. Nos. 5,332,992; 5,530,428; 5,673,021; 5,889,659; 5,977,873; 6,087,936; 6,506,987; 6,603,378; 6,803,845; 7,023,308; 7,248,136; and 7,291,794. Other magnetic switches are described in U.S. Pat. Nos. 5,668,533 and 5,877,664. 
     In many instances it is necessary to mount alarm system components on the surfaces of doors or windows to be protected using fasteners such as screws, rather than having these components embedded within the protected structures. Such surface-mounted alarm systems can be vulnerable because the one or more of the switch components may be detached by the simple expedient of removing the fasteners. Accordingly, in order to protect the integrity of surface-mounted alarm systems or more broadly any surface-mounted body, an anti-tamper alarm assembly is required. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above and provides a simplified anti-tamper assembly operable to sense the attempted removal of a body attached to a surface by a fastener (e.g., a screw extending through the body and adjacent mounting surface). Broadly speaking, an anti-tamper assembly in accordance with the invention includes an access-blocking element positioned in an anti-temper position proximal to the fastener, and a mating anti-tamper switch operably (e.g., magnetically or mechanically) coupled with the access-blocking element so that movement of the latter causes the anti-tamper switch to operate. 
     In one preferred embodiment the access-blocking element is a magnetic component and the anti-tamper switch is a magnetically actuatable with a shiftable, magnetically responsive component as a part thereof. As used herein, a “magnetically actuatable switch” refers to a switch which is shiftable between first and second different switch positions in response to different magnetic conditions in the region of the switch. The access-blocking element may itself be a magnet while the shiftable component of the mating switch component is responsive to ambient magnetic conditions; alternately, the shiftable switch component may be a magnet while the access-blocking element may be formed of steel or other material attracted to the switch component magnet. In either case, the access-blocking magnetic component interacts with the magnetically responsive anti-tamper switch so that the latter assumes a first switch condition when the access-blocking magnetic component is in the anti-tamper position thereof. The anti-tamper switch is operable to assume a different, second switch condition when the access-blocking magnetic component is moved from the anti-tamper position to a tamper position, permitting access to the fastener for removal thereof. Advantageously, the anti-tamper assembly also has an alarm circuit coupled with the anti-tamper switch and operable to generate an alarm signal in response to the movement of the anti-tamper magnetic component to the tamper position. 
     In preferred forms, the anti-tamper switch is a Magnasphere switch coupled with an anit-tamper magnet. The switch comprises a housing, a pair of spaced-apart switch elements, and a shiftable, electrically conductive, metallic body within the housing and moveable between respective first and second switch conditions under the influence of ambient magnetic conditions. A first magnetic component such as a magnet is associated with the switch housing and serves to bias the shiftable body to one of the switch conditions. However such bias is overcome by the presence of the anti-tamper magnet which moves the shiftable body to the other switch condition. Upon removal of the anti-tamper magnet, the switch housing magnet serves to move the shiftable body to the one switch condition. Normally, one of the switch conditions corresponds to the moveable body being in simultaneous contact with both switch elements, while the other switch conditions correspond to the body being out of simultaneous contact with the switch elements. Depending upon the selected switch control scheme, the alarm circuit may be triggered when the switch is in either of these conditions. 
     In another preferred embodiment, the anti-tamper switch may be a mechanical switch such as a micro-switch, and the access-blocking element may be a plug or block formed of any convenient material. In such a case, the actuating switch has an arm which engages the access-blocking element in order to maintain the switch in a first condition. If the access-blocking element is removed from the anti-tamper position thereof, the switch arm shifts in order to change the condition of the switch, which in turn activates the alarm circuit. 
     One important use for the anti-tamper assemblies of the invention is in the protection of movement or proximity sensors or switches mounted on the surface of a first member and operable to detect movement of a second member from a position in close proximity to the first member to a position remote from the first member. For example, the sensors or switches may be mounted on a window or doorframe, in order to detect opening of the associated door or window. The movement or proximity sensor is also preferably a Magnasphere switch of the type described above, including a housing magnet serving to bias the electrically conductive and moveable body to one of the switch conditions. The second member has a magnet oriented such that, when the second member is adjacent the first member, the second member magnet overcomes the bias of the housing magnet and shifts the moveable body to the other of the switch conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a door protected by a magnetically actuated surface-mounted alarm assembly in accordance with the invention; 
         FIG. 2  is an enlarged, fragmentary view illustrating the sections of the surface-mounted alarm assembly of  FIG. 1 ; 
         FIG. 3  is a sectional view of the preferred magnetically actuatable anti-tamper switch forming a part of the surface-mounted alarm assembly of  FIGS. 1 and 2 ; 
         FIG. 4  is a vertical sectional view of the sections of the surface-mounted alarm assembly of  FIGS. 1 and 2 ; 
         FIG. 5  is a fragmentary, sectional view of the anti-tamper switch of the surface-mounted alarm assembly of  FIGS. 1 and 2 , shown in an actuated condition upon attempted removal of the alarm section thereof; 
         FIG. 6  is a vertical sectional view taken along lines  6 - 6  of  FIG. 4 ; 
         FIG. 7  is a vertical sectional view similar to that of  FIG. 6 , but showing the parts of the anti-tamper assembly of  FIGS. 1 and 2  in exploded relation; 
         FIG. 8  is a vertical sectional view of another embodiment of the invention, using a mechanically actuated anti-tamper switch; 
         FIG. 9  is a view similar to that of  FIG. 7 , but illustrating the actuation of the anti-tamper switch upon removal of the access-blocking element; and 
         FIG. 10  is a fragmentary vertical sectional view depicting the orientation of the mechanical anti-tamper switch in the alarm condition thereof upon removal of the access-blocking element. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment of FIGS.  1 - 7  Using Magnetically Actuated Anti-Tamper Switch 
     Turning now to  FIG. 1 , an anti-tamper alarm assembly  10  is illustrated in operative position for protecting a door  12  mounted in a doorframe  14 . The alarm assembly  10  broadly includes an alarm section  16  mounted on the outer surface  17  of doorframe  14 , as well as a magnetic section  18  mounted on the adjacent outer surface  19  of door  12 . Broadly, the assembly  10  is designed to trigger an alarm upon unauthorized opening of door  12 . Moreover, the assembly  10  is provided with specialized anti-tamper structure which likewise triggers an alarm in the event that an intruder attempts to remove the alarm section  16  from doorframe  14 . 
     In more detail, the alarm section  16  includes a box-like housing  20  having an outer wall  22 , inner wall  24 , top and bottom walls  26 ,  28 , and end walls  29 ,  29   a . The inner wall  24  abuts surface  17  as shown. A total of three long screws  30  extend through suitable openings provided in the walls  22 ,  24  and through the outer surface  17  of doorframe  14  and into the interior of the latter. Additionally, the housing  20  has a larger passageway  32  extending through outer wall  22  and which is aligned with a smaller, screw-receiving opening  34  provided through inner wall  24 . A short screw  36  extends through the opening  34 , and passes through surface  17  and into the interior of doorframe  14 . A removable plug  38  is situated within passageway  32  as shown in  FIGS. 2 ,  4 , and  6 . The interior of section  16  has a synthetic fill  39  which fills the entirety of the section save for the operative and connective components therein, and the passageway  32 . 
     The section  16  further includes an anti-tamper assembly  40  designed to initiate an alarm in the event that an intruder attempts to remove the alarm section  16  from doorframe  14  by removal of screws  30  and  36 . Generally, the assembly  40  comprises an anti-tamper access-blocking element  42  in the form of a cylindrical magnet positioned in proximity to the head of screw  36  beneath plug  38 , and a magnetically actuatable anti-tamper switch  44  operably coupled with the element  42 . 
     In preferred forms, the anti-tamper switch  44  is a Magnasphere switch  46  of the type illustrated in  FIG. 3 . Such a switch includes a conductive housing  48  with a dielectric plug  50  closing the open end of the housing. A pair of first and second switch elements or electrodes  52  and  54  form a part of switch  46 , with the element  52  passing centrally through plug  50 , whereas element  54  is operably connected with conductive housing  48 . The switch  46  also includes a shiftable, electrically conductive ball  56  within housing  48  and moveable therein under the influence ambient magnetic conditions between respective switch conditions; one switch condition illustrated in phantom in  FIG. 3  is when the ball  56  is in simultaneous electrical contact with the housing  48  (and thus switch element  54 ) and central switch element  52 , whereas the other switch condition illustrated in full lines in  FIG. 3  is when the ball  56  is out of such simultaneous contact. The ball  56  is preferably formed of a magnetic metallic material. A magnetic biasing ring  57  is located about housing  48  as shown and serves to magnetically bias the ball  56  to the full line position thereof in the absence of a stronger or opposing magnetic field. Of course, other types of magnetically actuatable switches could be employed such as reed switches or switches of the type described in U.S. Pat. Nos. 5,877,664 and 5,668,533. However, the ensuing description will describe the use of a Magnasphere switch  46  as the anti-tamper switch  44 . 
     The magnetically actuatable anti-tamper switch  46  includes leads  58  and  60  respectively coupled with switch elements  52  and  54 . The leads  58 ,  60  extend through the interior of housing  20  then pass through conduit  62 , and form a part of an alarm circuit designed to initiate an alarm when the ball  56  is moved from one to the other of its switch positions as described below. 
     The section  16  also includes a separate movement sensor  64  ( FIG. 4 ) located in laterally spaced relationship to anti-tamper switch  46  and adjacent the bottom wall  28  of housing  20 . The sensor  64  is preferably a Magnasphere magnetically actuatable proximity switch of the type illustrated and described in  FIG. 3  of pending application for U.S. Letters patent Ser. No. 12/172,788 filed Jul. 14, 2008, entitled TAMPER-RESISTANT ALARM SWITCH ASSEMBLY; this application is fully incorporated by reference herein. The sensor or switch  64  is very similar to anti-tamper switch  46  and includes a conductive housing  66  with a dielectric plug  68  and first and second switch elements  70  and  72 . An electrically conductive, magnetically responsive, shiftable metallic ball  74  is within housing  66  and is moveable between respective switch positions where ball  74  is in simultaneous contact with the switch elements  70 ,  72 , and out of such simultaneous contact. However, in lieu of a biasing ring, the sensor or switch  64  has an associated magnet  76  located adjacent the upper surface of housing  66 . The magnet  76  is of sufficient strength to move ball  74  to its position out of simultaneous contact with switch elements  70 ,  72 , in the absence of a stronger ambient magnetic field. The sensor or switch  64  also has leads  78  and  80  respectively connected with the switch elements  70 ,  72  and passing through housing  20  into conduit  62 . The leads  78 ,  80  form a part of an alarm circuit. 
     The magnetic section  18  includes a housing  82  with upper and lower walls  84 ,  86 , inner and outer walls  88 ,  90  and end walls  92 ,  94 , and has an internal synthetic fill  96 . The housing  82  is secured to surface  19  of door  12  by means of four long screws  98  extending through the outer wall  90 , fill  96 , inner wall  88 , surface  19  and into the interior of door  12 . Internally, the section  18  also includes a large magnet  100  located, when door  12  is closed, directly beneath the sensor or switch  64 . In this position, the magnet  100  is of sufficient strength to overcome the bias of magnet  76 , thus moving ball  74  to the switch position where the ball  74  is in simultaneous contact with housing  66  (and thus switch element  72 ) and central switch element  70 . 
     In the event that door  12  is opened while the alarm assembly  10  is armed, movement of the magnet  100  away from sensor or switch  64  causes the ball  74  to move under the influence of magnet  76 , to thus change the switch condition of sensor or switch  64 . This generates an alarm signal indicating the unauthorized door opening. However, an intruder may seek to defeat alarm assembly  10  by removing the alarm section  16  from doorframe  14  by removing the screws  30  and  36 . While the screws  30  can be easily removed, detachment of the screw  36  requires that plug  38  be removed from passageway  32  and access-blocking magnet  42  pulled from its original position, thereby allowing access to screw  36 . However, the movement of magnet  42  from its initial anti-tamper position adjacent the head of screw  36  causes actuation of the anti-tamper switch  46 . Specifically, in the original anti-tamper position of magnet  42 , the latter serves to overcome the bias of ring  57 , moving the ball  56  to the  FIG. 6  position in simultaneous contact with switch elements  52  and  54 . However, upon removal of magnet  42 , the magnetic field of biasing ring  57  moves the ball  56  to the  FIG. 7  position thereof. This generates an alarm signal indicating the attempted tampering with alarm section  16 . 
     It will be appreciated that the anti-tamper switch  46  be positioned at a variety of different orientations within section  16 , with the illustrated position being merely exemplary. Moreover, the attractive components of switch  46  and the access-blocking element  42  may be reversed, i.e., the shiftable ball  56  may be formed of magnetic material while the element  42  is formed of a material which is magnetically attracted to the ball  56 . Furthermore, while the switches  46  and  64  are depicted as within a single housing  20 , it would be possible to provide separate, interconnected switch housings. If desired an anti-tamper switch could be provided for the section  18 . That is, an appropriate anti-tamper switch  46  and access-blocking element can be provided within housing  66  adjacent one of the fastening screws serving to attach the housing  66  to door  14  or any other surface, which would generate an alarm signal in the event of attempted removal of section  18 . 
     Finally, while the anti-tamper assembly  40  has been shown in the context of the alarm section  16 , the invention is not so limited. Broadly, the assembly  40  may be used to sense the attempted removal of virtually any type of body attached to a surface by a fastener. 
     Embodiment of FIGS.  8 - 10  Using Mechanically Actuated Anti-Tamper Switch 
     The alarm assembly  10   a  can if desired make use of an alarm section  16   a  employing a mechanically actuated anti-tamper switch in lieu of the magnetically actuatable switch of the first embodiment. The assembly  10   a  has an alarm section  16   a  mounted on the exterior surface  17  of door frame  14 , and a complemental magnetic section (not shown) identical with previously described section  18 . 
     In more detail, the alarm section  16   a  includes a box-like housing  20   a  having an outer wall  22   a , inner wall  24   a , top and bottom walls  26   a ,  28   a , and end walls  29   b . The inner wall  24   a  abuts surface  17  as shown. A total of three long screws  30   a  extend through suitable openings provided in the walls  22   a ,  24   a  and through the outer surface  17  of doorframe  14  and into the interior of the latter. Additionally, the housing  20   a  has a larger passageway  32   a  extending through outer wall  22   a  and which is aligned with a smaller, screw-receiving opening  34   a  provided through inner wall  24   a . A short screw  36   a  extends through the opening  34   a , and passes through surface  17  and into the interior of doorframe  14 . The interior of section  16   a  has a synthetic fill  39   a  which fills the entirety of the section save for the operative and connective components therein, and the passageway  32   a.    
     The section  16   a  further includes an anti-tamper assembly  40   a  designed to initiate an alarm in the event that an intruder attempts to remove the alarm section  16   a  from doorframe  14  by removal of screws  30   a  and  36   a . Generally, the assembly  40   a  comprises an anti-tamper access-blocking element  42   a  in the form of a plug-like cylindrical body positioned in proximity to the head of screw  36   a , and a mechanically actuatable anti-tamper switch  102  operably coupled with the access-blocking element  42   a . The switch  102  is preferably a conventional micro-switch having a shiftable, biased actuating arm  104 . As illustrated in  FIG. 8 , when the access-blocking element  42   a  is properly positioned within passageway  32   a , the arm  104  is depressed, causing the micro-switch  102  to assume a first switch condition. However, in the event that an intruder attempts to detach section  16   a  from doorframe  14  by removal of the screws  30   a  and  36   a , pulling the element  42   a  from passageway  32   a  causes arm  104  to move (see  FIGS. 9 and 10 ) so that the micro-switch  102  assumes a second switch condition Although not shown, it will be appreciated that the micro-switch  102  is connected to an alarm circuit including electrical leads such as the leads  58  and  60  of the first embodiment. Accordingly, movement of the switch arm  104  initiates an alarm indicating the attempted tampering. 
     Inasmuch as the switch  102  does not rely upon ambient magnetic conditions for actuation thereof, the access-blocking element  42   a  may be formed of any suitable material such as metal or synthetic resin.