Abstract:
An electromechanical sensor for use with an alarm system, comprises a housing containing upper and lower conductive components, for example flanged washers. The upper and lower conductive components are elastically separated and are compressibly displaceable from a first closed circuit position to a second open circuit position by the installation and tightening of a bolt through the sensor. The upper and lower conductive components are electrically isolated from the housing by at least one non-conducting sleeve when the conductive components are compressed into the second open circuit position by the bolt tightening. At least one of the upper and lower conductive components comes into conductive contact with the housing when the bolt is withdrawn, compression reduced and the conductive components are allowed to expand into the first closed circuit position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims the priority date of U.S. Provisional Application 60/222,767, filed Aug. 3, 2000, in accordance with 35 USC §119(e). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to sensors for use in security systems. More particularly, the sensors of the present invention relate to sensors for detecting tampering with bolts of the kind used in industrial and heavy equipment environments.  
         BACKGROUND OF THE INVENTION  
         [0003]    There is a need for assuring the security of heavy construction equipment. For example, it is desirable to bolt down the hood of a bulldozer, so that if left overnight, and not otherwise secured, the hood cannot be easily raised in order to steal expensive parts. Attempts have been made in the past to provide apparatus for detecting tampering with bolts but the known methods have not proven equal to the task of either [1] delaying the thiefs access to the target until help arrives; [2] resisting attempts of would-be thieves to bypass the tamper sensor and thereby prevent an alarm from being given; or [3] both of these objectives.  
           [0004]    An example of a prior art device is disclosed in U.S. Pat. No. 4,713,506 to Klink. The disclosure teaches a device for detecting when a screw is withdrawn from its place between electrical contacts. However, the article protected by such a device would not be secure from an attacker who removes the head of the screw while leaving the body of the screw intact within the monitoring circuit. In the case of heavy equipment, all of the screws could be thus disabled with no alarm being raised until all the screws had been disabled and only when the truck hood is lifted, or the generator lifted onto the thieves&#39; trucks would the alarm begin to sound. The thieves would have maximum getaway time.  
           [0005]    Another example of the prior art devices is disclosed in U.S. Pat. No. 4,329,681 however the disclosed sensor would not withstand a brute force attack by which the sensor with bolt head encased therein is simply pried over and snapped off or sawn off. Alternatively, a drill could be applied through the casing and bolt head. In any case, a resourceful thief that merely wants maximum getaway time can easily bypass such a defense and when the stakes are high enough, they usually do succeed. Moreover, since the circuit is protecting the bolt but not vice versa, and thus is exposed, it may possible to tap into and electronically fool the circuitry into failing to detect a change in resistance, thereby bypassing the alarm circuitry and successfully removing all bolts without the alarm being activated until it is too late.  
         SUMMARY OF THE PRESENT INVENTION  
         [0006]    Thus the present invention seeks to provide a mechanism whereby equipment in general and heavy equipment in particular are protected using tamper sensors through which heavy bolts are passed through. The bolts actually hold the spring-loaded, expandible sensor in place. Because the sensor has two potential contacts which are shielded by the sensor housing as well as the bolt above and the secured article below, any attempt to shift the sensor housing or the bolt head relative to one another or the secured article, results in closing of the circuit and the alarm being raised. In fact, in a situation where the secured article is so large that lifting of the article is not expected, and the sensors can be placed between the large article and the mounting surface upon which it will rest, then bolts may not be necessary. However, it is also recognized that in such a scenario, any prospective thieves simply need to complete the loading process and drive away before security forces arrive. Ideally, a large plurality of the inventive combination of bolts and sensors are used so that significant effort, and therefore time, are consumed in breaking through all of them before beginning the getaway.  
           [0007]    This is accomplished by providing an electromechanical sensor body which comprises a conductive housing within which are disposed upper and lower conductive components. The upper and lower conductive components are separated from one another elastically by a conductive compressible element and are compressibly displaceable from a first closed circuit position to a second open circuit position. The upper and lower conductive components are electrically isolated from the conductive housing by at least one electrically non-conductive sleeve when conductive components are compressed into the second open circuit position. At least one of the upper and lower conductive components must come into conductive contact with the housing, possibly by direct contact with a contact surface thereon, when at least one of the conductive components is in the first closed circuit position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    In order to understand the invention and to see how it may be carried out in practice, an exemplary embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0009]    [0009]FIG. 1 is a partial cross-sectional view of a bolt tamper sensor installation, wherein the bolt is fully tightened into place, in accordance with an exemplary embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a partial cross-sectional view of a bolt tamper sensor installation, wherein the bolt is partially screwed into place, but not tightened, in accordance with an exemplary embodiment of the present invention; and  
         [0011]    [0011]FIG. 3 is a partial cross-sectional view of a bolt tamper sensor installation, wherein the bolt is substantially not screwed into place, in accordance with an exemplary embodiment of the present invention; and  
         [0012]    [0012]FIG. 4 is a schematic illustration of a comparator circuit, in accordance with an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0013]    The sensor of the present invention is specifically designed for securing important parts, such as electric motors, pumps, hydraulic components, air hammers, generators, etch, against loosening and/or unauthorized opening. The sensor is installed by simply inserting the bolt, whose security is to be assured, through the sensor, and tightening the bolt in place.  
         [0014]    The sensor is intended to give instant warning and can be adapted to trigger an alarm system.  
         [0015]    [0015]FIGS. 1 through 3 illustrate the electromechanical features of the installation of bolt  80  and sensor  22 .  
         [0016]    Sensor  22  may be manufactured in practically and size and cross-sectional shape. Each sensor  22  can be provided in a range of sizes corresponding to a range of several bolt sizes.  
         [0017]    Sensor  22  protects bolt  80  by triggering an alarm if the sensor is tampered with in any one of the following ways, for example:  
         [0018]    against unauthorized opening;  
         [0019]    against loosening;  
         [0020]    against loosening even if the complete sensor  22  is held against the head of bolt  80  as the bolt  80  is withdrawn or against secured article  42  in which bolt  80  is installed; and  
         [0021]    against shorting or disconnecting of any of the wires  25  or  26  of sensor  22  (“hotwires”).  
         [0022]    [0022]FIG. 1 is a partial cross-sectional view, of bolt tamper sensor  22  installation, wherein bolt  80  is fully tightened into place, in accordance with an exemplary embodiment of the present invention. In FIG. 1, gap  76  is closed and does not appear, in contrast to FIG. 2 and FIG. 3 where gap  76  is substantial. However, gaps  70  and  72  form, and create an open circuit.  
         [0023]    [0023]FIG. 2 is a partial cross-sectional view, of bolt tamper sensor  22  installation, wherein bolt  80  is partially screwed into place, but not tightened, in accordance with an exemplary embodiment of the present invention. In FIG. 2, gap  76  between bolt head washer  90  and washer  62  is partially closed.  
         [0024]    [0024]FIG. 3 is a partial cross-sectional view, of bolt tamper sensor  22  installed, wherein bolt  80  is not fully screwed into place, in accordance with an exemplary embodiment of the present invention. FIG. 3 shows a gap  76  between bolt head washer  90  and insulating washer  62 .  
         [0025]    Bolt  80  passes through a sensor housing  50 , tightening together other mechanical parts of sensor  22 , as well as the secured article  42  into which bolt  80  is screwed, as described hereinbelow. Bolt  80  is electrically insulated from sensor  22  and does not form part of the comparator circuit.  
         [0026]    The functional requirements of sensor  22  may in an exemplary embodiment be provided by embodiments or alternatives to the following electromechanical components:  
         [0027]    sensor housing  50 , which may be composed of metal or some electrically conductive rigid material and has a known resistance, has connected thereto or embedded therein, a resistor  102 , both of which are in a constant state of short circuit, via lead  25  as a part of a comparator circuit  20 . The remainder of the comparator circuit  20  may be located at a distance from the sensor  22 , or it may be provided as an IC (integrated circuit) within a microchip located within a chamber  104  inside the wall of sensor housing  50 . Lead  26 , shown connected to flanged washer  56  could just as well be connected to flange washer  54  or spring  66 . Furthermore, as an alternative embodiment, there could be located in chamber  104  a small power source and a transmitter for sending detected changes in the overall circuit resistance to a central monitoring station and to initiate alarm activation;  
         [0028]    upward facing flanged metal washer  54  and downward facing flanged washer  56 , both of which move inside sensor housing  50  and are separated by a conductive compressible element, such as spring  66 . An “armed” state is initiated when flanged washers  54  and  56  are compressed by bolt  80 , thereby opening the circuit by disconnecting them from sensor housing  50 ;  
         [0029]    insulating washers  62  and  64  which may be fabricated from Delrin or TEFE, for example, respectively insulate the head of bolt  80  from sensor housing  50 , and sensor housing  50  from any metal parts which may also be in contact with the bolt stem  60 . Set against the head of bolt  80 , they have the following functions:  
         [0030]    a) to maintain flanged washers  54  and  56  inside sensor housing  50  yet allowing no electrical contact when bolt  80  is screwed in, and by being screwed in, thereby pressing together the parts of sensor  22 ;  
         [0031]    b) to allow adaptation of sensor housing  50  to the size of bolt  80 , permitting the size to be adjusted by simple drilling;  
         [0032]    insulating sleeve  68  which may be fabricated from Delrin or TEFE, for example, provides the following:  
         [0033]    a) insulates the conductive compressible element, spring  66  from sensor housing  50 ;  
         [0034]    b) allows movement of flanged washers  54  and  56  within it; and  
         [0035]    c) insulates sensor housing  50  from flanged washers  54  and  56  when bolt  80  is screwed in fully.  
         [0036]    Washer  100 , which is preferably integrally formed with or securely attached to the head of bolt  80  together with bolt head washer  90  and bolt stem  60  is provided to prevent tampering with flanged washer  54  by attempting to force a screwdriver or some other object in from the side. Additionally, washer  100 , which is sized to fit within insulating washer  62 , is in actual contact with flanged washer  54  and presses thereagainst up to the depth permitted by compression of bolt head washer  90  against insulating washer  62 ; and  
         [0037]    cylindrical washer  94 , which not only maintains sleeve  68  in place, it also serves as a potential contact point to conduct current between flanged washer  54  and sensor housing  50 . Instead of being a separate component, housing  50  could be shaped to have a cross-sectional profile resembling double brackets, i.e., [ ] such that an insulator layer could be provided on its inner surface between spring  66  and housing  50 . For example if one first formed a flange  106  in the bottom of a cylinder intended to form a housing  50 , coated the inner surface of the wall portion with an insulator coating, then inserted a downward facing flanged washer  56 , followed by a spring  66  and then the upward facing flanged washer  54  and then bent in and over the top edge of the cylinder to form a flange at the top, one could form a self-contained unit combining the aforementioned components.  
         [0038]    In one alternative embodiment of the present invention, an RF (radio frequency) transmitter is located in sensor housing  50  and a battery can be located adjacent thereto or in flanged washer  54  (among other possible locations).  
         [0039]    With particular reference to FIG. 3, bolt  80  and sensor  22  are assembled as follows. Insulating sleeve  68  is inserted into sensor housing  50 . Downward facing flanged washer  56  is then inserted and insulating washer  64  is applied to the bottom annular groove  98  between sensor housing  50  and washer  56 . Insulating washer  64  is provided with a minimum thickness such that it barely electrically isolates sensor housing  50  from contact with secured article  42 . The distance between the bottom of sensor housing  50  from secured article  42  should be as small as possible, such that it would be difficult to drill through or cut away from insulating washer  64  without grounding sensor housing  50  by contact with either the drill bit or saw, for example. Spring  66  is inserted followed by upward facing flanged washer  54 . Cylindrical washer  94  is then inserted and screwed into place to slightly compress flanged washers  54  and  56  together with spring  66 . Insulating washer  62  is applied into annular groove  96  and bolt  80  is now screwed into place.  
         [0040]    With particular reference to FIGS.  1   2  and  3 , operation of sensor  22  when bolt  80  is installed and tightened:  
         [0041]    when bolt  80  passes through sensor  22 , and is tightened, all the parts of sensor  22  are pressed together;  
         [0042]    a conductive compressible element, in the exemplary embodiment, a spring  66  is compressed between flanged washers  54  and  56  as they slide inside sleeve  68 , thereby creating gaps  70  and  72  between washer flange contact points  84  or  86  with housing contact points  82  and  88 , thereby isolating sensor housing  50  from flanged washers  54  and  56  as well as spring  66 . In the state aforementioned the sensor housing  50  forms a part of comparator circuit  20  with a constant resistance of value R;  
         [0043]    bolt  80  is insulated from sensor housing  50  by insulating washers  62  and  64  and provides constant contact between flanged washers  54  and  56 , spring  66 , and secured article  42  into which bolt  80  is screwed; and  
         [0044]    any attempt to loosen or remove bolt  80  from its place, shorting or disconnecting any wire in comparator circuit  20 , causes imbalance in circuit  20  and triggering of alarm  36 .  
         [0045]    The operation of sensor  22  when bolt  80  is loosened proceeds as follows:  
         [0046]    sensor housing  50  moves along the outside of sleeve  68  and is insulated from spring  66 , while spring  66  pushes flanged washers  54  and  56  toward the open position;  
         [0047]    flanged washers  54  and  56  slide inside sleeve  68 , while spring  66  pushes them apart until flange shoulders  84  and  86  make contact with cylindrical washer  94  at contact point  82  and sensor housing  50  at contact point  88 , respectively, thereby creating a short circuit and triggering the alarm; and  
         [0048]    insulating washers  62  and  64  insulate bolt  80  from metal parts in contact with sensor housing  50 ; and  
         [0049]    once the bolt is tightened, loosening the bolt  80  results in a short circuit which causes a change in resistance and an alarm.  
         [0050]    Reference is now made to FIG. 4, which illustrates a comparator circuit  20 , in accordance with an exemplary embodiment of the present invention. In one exemplary variation a sensor electrical component  22  is comprised of a group of sensors, sensor  1  through sensor N, connected in parallel  24 , with a combined constant resistance  70  equal to R. Sensor  22  is, in turn, connected by conductor  26  to comparator circuit  20 . A comparator is defined as a control system that continuously monitors the value of a quantity, that quantity here being the resistance, in relation to the expected value.  
         [0051]    In the most common configuration, comparator circuits  20  are implemented with positive feedback, with resistor R 1   28  and resistor R 2   30  providing hysteresis. In electronics, hysteresis connotes a double-valued function, in which different values are obtained depending on whether the independent variable, i.e., the resistance, increases or decreases. The amount of hysteresis affects the input/output relationship of comparator  20 . Also, signals and noise always coexist in analog relationships. Increased hysteresis prevents comparator  20  output from “ringing” when an analog signal with superimposed noise approaches the comparison level.  
         [0052]    A common design goal is to provide a hysteresis large enough to prevent a spurious alarm, while simultaneously keeping it low enough to achieve maximum sensitivity. The threshold values derived from Vcc  32  and Vref  34  are: 
           V   TH+   =R   1 ×( V   CC   −V   REF )/( R   1   +R   2 )(upper threshold) 
         [0053]    and 
           V   TH+   =R   1   ×V   REF /( R   1   +R   2 )(lower threshold). 
         [0054]    Thus, any change in the value of resistance  70  of sensor  22  beyond the threshold values, especially in the extreme cases of a short-circuit or a broken circuit, causes imbalance in comparator circuit  20 , and triggers an alarm signal  36 .  
         [0055]    Interconnecting via conductor  26  a number of sensors  22 , in parallel  24 , or in series  38  to comparator  20 , and balancing the circuit, results in a system in which there is no way of shorting or disconnecting any sensor  22  without triggering alarm  36 . All interconnecting wires are “hotwires.” For either configuration the combined equivalent resistance  70  is R.