Patent Publication Number: US-2009218832-A1

Title: Door Strike

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of door strikes, and more particularly the field of electric door strikes that can be mounted to a door frame. 
     BACKGROUND OF THE INVENTION 
     A door strike is a device for releasably retaining a latch bolt mounted to a door. Door strikes, particularly the electrically operated variety, are commonly used in office buildings where they provide control over ingress and egress of persons via doors of the building. 
     While existing door strikes are relatively effective at controlling ingress and egress of persons via doors, they can in some instances be susceptible to being tampered with by persons seeking unauthorised access to a building. In this regard, persons seeking unauthorised access may try to completely remove a strike from the doorframe to which it is fitted so that the associated door can be freely opened. In some cases a door strike can be removed from a door frame by simply unscrewing a couple of screws that hold the strike to the frame. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a door strike comprising: 
     a body; 
     a retaining means for retaining a latch bolt, the retaining means being movable with respect to the body between a latch bolt retaining position and a latch bolt releasing position; 
     a locking means for releasably locking the retaining means in the latch bolt retaining position; and 
     detecting means for detecting removal of the body from a door frame. 
     Unlike existing door strikes, an embodiment of the door strike according to the present invention has the advantage of being able to detect removal of the strike body from the door frame, which maybe done by a person trying to gain unauthorised access to a premises by removing the strike in an attempt to easily open a door controlled by the strike. 
     Preferably, the detecting means comprises a switch having an actuator that is arranged to move from a first position to a second position when the body is removed from the door frame. 
     Using the switch in the embodiment of the door strike according to the present invention provides a simple, reliable and cost effective detection mechanism. 
     Alternatively, instead of using the switch it is envisaged that the detecting means could be in the form of, for example, a magnetic reed switch, hall effect device, proximity detector, or photo-electric device. 
     Preferably, the locking means is movable relative to the body from a fail safe position, in which the door strike provides fail safe operation, and a fail secure position, in which the door strike provides a fail secure operation. 
     Allowing the locking means to be moved between the fail safe position and the fail secure position in the embodiment of the door strike according to the present invention provides the advantage of providing a versatile single strike that can operate in either mode (that is; fail safe or fail secure). 
     Preferably, the strike comprises a removable part that is arranged to be fitted to an outer surface of the body and which can be removed from the body to gain access to the locking means so to enable the locking means to be moved between the fail safe position and the fail secure position. 
     Use of the removable part in the embodiment of the strike according to the present invention is advantageous because it provides a cover for the fastening devices (for example, screws) that are used to hold the locking means in position. The fastening devices are such that they can be loosened to allow the locking means to be moved between the fail safe and fail secure modes of operation. By acting as a cover the removable part serves several purposes: first, it protects the fastening devices from any damage that may otherwise occur as the strike is being fitted or removed from a doorframe; second, it makes it a little more difficult for an unauthorised person to gain access to the fastening device(s) (holding the locking means in position), which the person make seek in an attempt to render the strike ineffective. 
    
    
     
       A BRIEF DESCRIPTION OF THE DRAWINGS 
       Notwithstanding any other embodiments that may fall within the scope of the present invention, an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which FIGS. ( 1   a ) to  1 ( h ) provide various illustrations of a door strike according to an embodiment of the present invention. 
     
    
    
     AN EMBODIMENT OF THE INVENTION 
     With reference to  FIG. 1(   a ), which illustrates a door strike  100  in accordance with an embodiment of the present invention, the door strike  100  comprises a body  102  and a retaining means  104  that is pivotally mounted to the body  102 . As can be seen in  FIG. 1(   b ), the door strike  100  also comprises a locking means  106  that is slidably mounted to the body  102  and a detecting means  108  that is mounted to the body  102 . Furthermore, as shown in  FIG. 1(   c ) the door strike  100  also comprises a removable part  110  that is mounted to an outer surface  112  of the body  102 . 
     With reference to  FIG. 1(   d ), the body  102  of the strike  100  is made from a cast metal material and comprises: a front face portion  114 ; two side portions  116  that extend outwardly from the front face portion  114  to define a void  118 , in which the locking means  106  and the detecting means  108  reside; and a mounting portion  120  that extends outwardly from one of the side portions  116   a . As can be seen in  FIG. 1(   a ), each end of the front face portion  114  has an aperture  122  for receiving a screw that is used to secure the body  102  to a door frame. In addition to the apertures  122 , the front face portion  114  also has a recessed portion  124  for receiving a latch bolt mounted to a door. As can be seen in  FIG. 1(   d ), one of the side portions  116   b  has a grooved section  126  for receiving the removable part  110 . 
     With reference to  FIGS. 1(   a ) and  1 ( e ), the retaining means  104  comprises: a cast metal element  128 ; a mounting  130  that is coupled to the body  102 ; a pin  132  that is coupled to the cast metal element  128  and the mounting  130 ; and a spring  134  that is fitted to the pin  132 . The cast metal element  128  is pivotally mounted to the body  102  such that it is pivotally movable with respect to the body  102  between a latch bolt retaining position and a latch bolt releasing position. In the latch bolt retaining position, which is illustrated in  FIG. 1(   f ), the cast metal element  128  obstructs the latch bolt when located in the recessed portion  124  in the front face portion  114  of the body  102  such that it cannot be readily removed from the recessed portion  124 . In the latch bolt releasing position, which is illustrated in  FIG. 1(   g ), the cast metal element  128  is such that it does not obstruct the latch bolt when located in the recessed portion  124  in the front face portion  114  of the body  102  such that it can be readily removed from the recessed portion  124 . 
     In relation to the mounting  130 , which is made of a cast metal, and the pin  132  which is made from machined steel, these components  130  and  132  of the strike  100  are arranged to pivotally mount the cast metal element  128  to the body  102 . The spring  134 , which is made from metal, is fitted over the pin  132  and is arranged to urge the cast metal element  128  from the latch bolt releasing position towards the latch bolt retaining position. 
     Referring to  FIG. 1(   h ), the locking means  106  comprises: a metal base plate  136 , which is mounted to one of the side portions  116   b  of the body  102  and which is located in the void  118 ; an electrically activated solenoid  138  that is fixed to the base plate  136 ; and an obstructing assembly  140 , which comprises a metal obstructing member  142  and a housing  144  that houses the obstructing member  142  and which is secured to the base plate  136 . As can be seen in  FIG. 1(   d ), the base plate  136  is secured to the side portion  116  of the body  102  by two screws  146  that are located in slots  148  in the grooved section  126  of one of the side portions  116   b  of the body  102 . In order to switch the strike  100  between fail safe and fail secure modes of operation, a person needs to first remove the removable part  110  from the grooved section  126  (which effectively involves disassembling the strike  100 ) to gain access to the two screws  146 . To remove the removable part  110  from the grooved section  126  the person unscrews the screw  150 , which secures the removable part  110  to the side portion  116 . Once the person has removed the removable part  110  from the grooved section  126 , the person can loosen the two screws  146  to slide the locking means  106 , relative to the side portion  116  of the body  102 , between a fail safe position and a fail secure position. 
     As mentioned previously, the locking means  106  comprises an electrically activated solenoid  138  (powered from either a 6 volt or 12 volt source). When an electric current passes through the solenoid  138 , the solenoid  138  moves the obstructing member  142  so as to lock the element  128  of the retaining means  104  in the latch bolt retaining position so that a latch bolt located in the recessed portion  124  of the front face portion  114  cannot be readily removed therefrom. In this regard, when the solenoid  138  moves the obstructing member  142  so as to lock the element  128  in the latch bolt retaining position, the locking means  106  provides a fail secure mode of operating. Alternatively, when the electric current passes through the solenoid  138  it can also move the obstructing member  142  out of the path of the element  128  such that the element  128  can be moved from the latch bolt retaining position to the latch bolt releasing position. In this mode of operation, which is referred to as fail secure, the obstructing member  142  is such that it locks the element  128  in the latch bolt retaining position when the solenoid  138  does not have an electric current passing therethrough. 
     As indicated previously, the strike  100  comprises a detecting means  108 . The detecting means  108  is in the form of a single-pole-double-throw (SPDT) micro-switch. With reference to  FIG. 1(   b ), the body  152  of the micro-switch is located in the void  118  of the body  102 , while the actuator  154  of the micro-switch projects outwardly from the void  118 . When the strike  100  is fitted to a doorframe the actuator  154  is ‘sandwiched’ between the doorframe and the front face portion  114  of the body  102  such that the actuator  154  is held in a first position. However, when the strike  100  is removed from the doorframe the actuator  154  moves from the first position to a second position as the actuator  154  is no longer sandwiched between the doorframe and the front face portion  114 . As persons skilled in the art will readily appreciate, movement of the actuator  154  from the first position to the second position causes the electric circuit between the terminals  156  (which can bee seen in  FIGS. 1(   b ) and  1 ( d )) of the micro-switch to change accordingly. It is the change in the electric circuit between the terminals  156  that enable the detecting means  108  to provide an alert that the switch  100  has been removed. In this regard, the micro-switch can be wired to a security console that issues, for example, an alarm (in response to the change in the electric circuit between the terminals  156 ) warning the console operator that the strike  100  has been removed from the doorframe. 
     In order to provide the solenoid  138  with a source of current and to detect a change in the electrical circuit at the terminals  156  of the detecting means  108 , the switch  100  comprises a wiring loom  158 , which can be seen in  FIG. 1(   f ). 
     While the present invention has been described with reference to the aforementioned embodiment, it will be understood by those skilled in the art that alterations, changes and improvements may be made and equivalents may be substituted for the elements thereof and steps thereof without departing from the scope of the present invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the present invention without departing from the central scope thereof. Such alterations, changes, modifications and improvements, though not expressly described above, are nevertheless intended and implied to be within the scope and spirit of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the embodiment for carrying out this invention, but that the invention will include all embodiments falling within the scope of the independent claims. 
     It will be readily appreciated by those skilled in the art that the present invention is not limited to use of a detecting means  108  in the form of a micro-switch. Persons skilled in the art will appreciate that in alternative embodiments the detecting means  108  can be in the form of, for example, a magnetic reed switch, a hall effect device, a proximity detector, or photo-electric device.