Abstract:
An electric door strike having a keeper rotatably mounted in a fixed strike case for movement between open and closed positions. The keeper includes dual solenoids with a biasing link between the solenoid plungers to urge the plungers to a non-actuated position. Changing the biasing link in the keeper changes the mode of operation. The application of an actuating signal to a solenoid moving the plungers to an actuated position which can be either the fail-safe or fail-secure mode of operation depending on the biasing link employed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to door locking mechanisms and, in particular, to an electric door strike having a dual locking mechanism which includes internally mounted solenoids for use in the fail-safe or fail-secure modes of operation. 
     An electric door strike typically includes a strike case fixedly mounted in a door jamb. The strike case contains a pivotally mounted keeper for retaining the deadbolt and door latch in the strike case under the control of the door-mounted lock mechanism. In addition to the control provided by the local lock mechanism, the keeper can be used to permit opening or securing of the door in accordance with an electrical actuating signal applied from a remote location. 
     In the fail-secure mode of operation, the premises are secured in the event of a power failure by a locking mechanism that causes the keeper to remain engaged in the strike case in the case of power failure. For the fail-safe operating mode, a power failure results in a release of the keeper thereby allowing a door to be opened without regard to the state (locked or unlocked) of the individual lock thereon. 
     An electrically operated door strike which can provide fail-secure mode of operation is disclosed in U.S. Pat. No. 3,640,560 to Zawadzki et al. In this door strike, the release of the strike keeper is externally controlled by means of a small solenoid located within the strike case. The solenoid interacts with a locking cam to release the keeper upon receipt of the signal. The locking mechanism is contained within the keeper assembly and does not engage the strike case. As a result, there is no direct contact between the doorjamb and the rotatable keeper and the mechanism is not sufficiently durable determined strong forces by one seeking unauthorized entry. 
     The provision of both fail-safe and fail-secure modes of operation in a single locking mechanism is accomplished in the electric strike mechanism disclosed in U.S. Pat. No. 5,484,180 to Helmar. The single solenoid mechanism shown therein utilizes a locking yoke which mechanically controls the rotation of the keeper. The mechanical linkage and single solenoid is contained within the housing. The enhanced versatility of the Helmar &#39;180 mechanism is provided by the use of a reversible plunger enabling the device to function in both modes. 
     Accordingly, the present invention is directed to an electric door strike having dual solenoids to provide engagement between the plungers and the strike case affixed to the door jamb in the fail secure mode of operation. The use of dual solenoids secures the opposing sides of the keeper to reduce the likelihood of a forced entry. In addition, the subject door strike is readily converted to the fail-safe mode of operation without removal of the strike case from its mounting in the doorjamb. Further, the invention employs plungers having a novel latch head that inhibits tampering when the plungers are extended and the keeper is secured. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an electric door strike which includes a strike case for affixation to a doorjamb. The strike case is adapted to receive a bolt from a door lock and a keeper is mounted therein. The keeper is rotatably mounted in the strike case for movement between an open position which allows a lock bolt to exit the strike case and a closed position which secures the lock bolt in the strike case and prevents opening of the door. 
     The keeper is provided with first and second solenoids, each solenoid having an electrical connection for the application of actuating signals thereto. Each solenoid has a plunger with a latch head thereon for engagement with a receiving socket in the strike case. Access is provided to one of the plungers to allow substitution of a plunger having a different latch head thereon for use in the fail-safe operating mode wherein the door can be opened in the absence of an actuating signal. 
     In the fail-secure mode, the application of an actuating signal causes the plungers to retract thereby removing the latch heads from the corresponding receiving sockets in the strike case. The dual plungers are extended in the absence of the actuating signals by the action of a biasing link between the plungers which urges the plungers outwardly for engagement with the receiving sockets thereby establishing the fail-secure mode of operation. 
     The replacement of a plunger used for fail-secure operation with a plunger having a different latch head coupled with a modification of the biasing link provides the fail-safe operating mode for the door strike. The remaining plunger with initial latch head is urged by the biasing link out of engagement with the receiving socket in the absence of an actuating signal. Thus, the present door strike can be utilized as a fail-safe or fail-secure locking mechanism with only minor modification. 
     The fail-secure mode of operation results in two latch heads being received in corresponding sockets in the top and bottom of the strike case. Thus, the security of locking in the absence of power is greatly enhanced. In the fail-safe mode, a single latch head is used to engage the strike case. This latch head is withdrawn upon a power failure to permit the keeper to be rotated to the open position by applying pressure to the door regardless of the state of the door mounted lock. 
     To inhibit a dislodging of the latch head from the adjacent receiving socket by the application of an external force, the outer end of the latch head is provided with a non-orthogonal end surface having an undercut. A mating undercut is provided in the receiving socket. As a result, forces tending to move the latch head laterally result in the undercut portion of the latch head engaging the receiving socket. The novel configuration of the latch head and receiving socket limit lateral movement of the keeper when the plunger is extended to enhance the security of the locking mechanism. 
    
    
     Further features and advantages of the invention will become more readily apparent from the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view in perspective showing a preferred embodiment of the invention. 
     FIG. 2 is a side view of the embodiment of FIG. 1, showing the keeper in a closed position; 
     FIG. 3 is a top view of the embodiment shown in FIG. 2; 
     FIG. 4 is cross-sectional view taken along line  4 — 4  of FIG. 3 of the embodiment adapted for fail-secure operation; 
     FIG. 5 is a side view of the keeper of the embodiment shown in FIGS.  2  and FIG. 3; 
     FIG. 6 is a cross-sectional view taken along line  4 — 4  of FIG. 3 of the embodiment adapted for fail-safe operation; 
     FIG. 7 is an exploded view in perspective of a latch head and insert in the embodiment of FIG. 1; and 
     FIGS. 8 and 9 are side views of the latch heads shown in FIG.  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the embodiment of FIG. 1, an electric door strike is shown comprising a strike case  11  dimensioned for mounting in a receptacle in a door jamb (not shown) and secured by threaded fasteners positioned in the slots in flanges  12 . 
     A keeper  15  is mounted in the strike case for rotation about an axis defined by axial rods  36 ,  37  which extend between from the top and bottom end members of strike case  11 . A pair of springs  17 ,  18  are located about the spaced axial rods  36 ,  37  to provide a biasing force which urges the keeper to a normally open position and places the return member  20  in the position shown in FIG. 1 where the member  20  is positioned at a right angle to the inside surface of the keeper  15 . As noted from FIG. 5, the return member  20  is mounted for rotation on the axial rods  36  and  37 . 
     An extension  21  is affixed to the return member  20  by fasteners  22  and is shown extending forwardly and outwardly of the member  20 . The extension arm is positioned to contact a dead bolt  31  extending from the edge of door  29  as it moves in the direction of the arrow in FIG.  1 . The extension arm enables the closure of the door  29  with the dead bolt extended to rotate the keeper  15  to the return or closed position. During normal operation of the electrically actuated locking mechanism, the release of the keeper enables the door to be opened and the keeper rotates to the position as shown FIG.  1 . The action of the spring  18  of FIG. 6 urges the keeper to the open position. The combination of extension arm  21  and return member  20  cause the keeper to close by contact with the deadbolt. If the door lock includes only a beveled latch bolt, the extension arm  21  is removed and the return member  20  is secured to the strike case. The biasing force of spring  17  of FIG. 5 urges the keeper to a closed position when the keeper  11  has been opened by the latch bolt alone. The keeper  15  is provided with a plurality of chamfered surfaces  24  on the external surface so that the beveled surface of a latch bolt readily travels thereacross in the return to the strike case. 
     The keeper  15  is shown in the closed position in FIG. 2 with the return member  20  and extension arm  21  located in the interior of the strike case  11 . The strike case is shown in the top view of FIG. 3 in the closed position with a receiving socket  30  located on the top surface. A like socket is located on the bottom surface of the strike case  11 . The axial rods  36  and  37  extend into mating openings in the adjacent surfaces of the strike case and define the axis of rotation of the keeper. 
     The keeper assembly is shown in the cross-sectional view of FIG. 4 taken along the corresponding lines of FIG.  3  and the side view of FIG. 5 showing the keeper removed from the strike case. In FIG. 5, the placement of springs  17  and  18  on the axial rods  36  and  37  is shown. Spring  18  extends outwardly at free end  26  to contact the strike case and urge the keeper to an open position. In the fail secure mode, the keeper is closed by the bolt of the door mounted mechanism contacting the extension arm mounted on return member  20  and is maintained in that position by the protruding end  34  of the latch heads which enter the receiving sockets  30  of the strike case. The spring  17  is located on axial rod  36  and provides a restoring force for maintaining the keeper and return member  20  at a right angle position. 
     The axial rods  36 ,  37  are provided with collars  38 ,  39  respectively which secure the rods in the keeper  15  and limit axial movement to that needed to assemble the keeper in the strike case and to facilitate replacement of a plunger. The keeper is provided with a central slot  41  between the ends of rods  36 ,  37  to serve as a passageway for wire pairs  42  which extend inwardly to the solenoids  44 ,  45  seen in FIG.  4 . The keeper  15  is shown positioned within the strike case  11  in the secure position in FIG.  4 . 
     The solenoids  44 ,  45  each contain a plunger  46 ,  47  in axial alignment with a biasing link  49  located therebetween. In both fail-secure and fail-safe modes of operation, the link provides a force urging a plunger outwardly of the respective solenoid. As shown, solenoid tube  50  having a coil spacer  51  and flux washer  52  at the opposing ends houses the windings  53  of the solenoid. A solenoid spacer  58  is interposed between the adjacently spaced solenoids. The spacer is provided with tapered sockets which receive the tapered ends of the plungers and limit lateral movement thereof. The solenoids are maintained in the aligned position in the keeper by a shoulder  59  formed on the interior surface of the keeper and a removable insert  60  at the opposing end of the keeper. The insert  60  extends inwardly to contact the flux washer  52 . 
     As shown in FIG. 4, plungers  46 ,  47  are each provided with a hollow core for receiving a latch head  62  press fit therein. The latch heads are urged to a secure position as shown by the biasing link  49  which extends therebetween through the spacer  58 . When the solenoids are actuated by the application of signals to external connector  64 , the plungers retract the latch heads from within the receiving sockets  30  of the strike case and the keeper is then free to rotate about axial rods  36 ,  37  to the open position. 
     The protruding end of the latch head  15  provided with an inclined end surface  70  having an undercut located beneath one edge. The incline provides an end surface that is nonorthogonal to the axis of the plunger. As a result, the latch head is urged inwardly by the strike case upon closure. Also, the latch head is provided with an undercut that faces an undercut  71  in the receiving socket. The application of an external force to the keeper in the direction to open the keeper, when the keeper is secured drives the mating surfaces of the undercuts into contact reducing the ability of an intruder to defeat the security of the keeper by the use of an implement or by the direct application of force. 
     As shown in the fail-secure mode of FIG. 4, the keeper is provided with identical latch heads  62  press fit into the corresponding plungers  46 ,  47 . The plungers are coupled together by a biasing link  49  comprised of a spring extending between recesses in the adjacent inner ends of the plungers. The spring urges the latch heads to the position shown. The mode of operation of the electric door strike is changed to the fail-safe mode of operation by the replacement of a latch head and biasing link as seen in FIG.  6 . Replacement is effected by decoupling the keeper  15  from the strike case by means of compressing one or both of the axial rods. 
     Upon removal of the keeper, the insert  60  is withdrawn from the keeper thereby allowing the plunger  47  to be withdrawn from solenoid  44 . The latch head  62  is removed from the end of the plunger and replaced with a latch head  72  having a blunt end without the offset engaging end of latch head  62 . Alternatively, replacement of the plunger and latchhead as a single unit can be made. Also, the biasing link which had comprised spring  49  in the fail-secure mode is removed and replaced by linking rod  73 . Rod  73  is threaded at each end so that it is first threaded into plunger  47  before placement into solenoid  44 . A biasing spring  74  placed over the solenoid and moved into position against the blunt end of latch head  72  supplies the biasing force for both latch heads in the fail-safe mode shown in FIG.  6 . After placement of the plunger into the solenoid with the rod  73  threaded into plunger  47  and the spring  74  in position about latch head  72 , the latch head is rotated so that rod  73  threads into plunger  46 . As a result, the plungers are linked to move in the same direction. In the absence of an actuating signal applied to solenoid  44 , the spring  74  maintains latch head  62  in the withdrawn position as shown in FIG. 6 with the inner end of plunger  46  adjacent to the spacer  58 . The modifications made to the biasing link and the substitution of a blunt latch head to provide fail safe operation are accompanied by the application of an actuating signal to conductor pair  41 . Control of the actuating signals can be provided by a microprocessor located at a central station which typically serves a number of portals located throughout a large building. 
     As discussed herein, the preferred embodiment utilizes a keeper having a removable end insert  60  shown in FIGS. 1 and 6. This embodiment enables the electric door strike to be readily converted between fail-secure and fail-safe modes of operation. The insert  60  is shown in FIG. 7 with an offset opening  76  that receives end  34  of latch head  62 . As mentioned, latch head  62  is fitted into plunger  47 . The end  34  is offset mounted on the latch head  62  to correspond with the offset of opening  76  in the insert  60 . The offset enables the plunger  47  to be axially aligned with the solenoid  44  and causes the undercut in end  70  to align with the undercut  71  in the receiving socket. The insert is held in position by set screws (not shown) located in the wall  80  of the keeper and entering the positioning slots  81  in the insert. 
     The latch head  62  is provided with travel limit pin  77  which limits the latch head from extending too far beyond insert  60 . A similar pin is utilized on the latch head at the opposing end of the keeper. Since the blunt end of latch head  72  lacks an engaging end, no registration pin is located thereon. 
     When converting the keeper to fail safe operation, the latch head  72  of FIG. 9 has a blunt end substituted for the latch head of FIG.  8 . When the plunger encircled by spring  74  is inserted into the solenoid and secured by linking rod  73  to the adjacent plunger  46  as shown in FIG. 6, the insert  60  is placed in the strike case and secured. The non-actuated position of FIG. 6 is changed upon the application of an actuating signal to solenoid  44 . 
     In operation, the application of the appropriate actuating signal to the subject door strike causes one or both of the solenoids to be energized and causes the corresponding plunger or plungers to overcome the force of the biasing link and either free or secure the keeper to the strike case. The double latch head security of the invention in the fail-secure mode makes the electric door strike extremely difficult to defeat. Furthermore, the undercut of the engaging head resists tampering by the application of force to the interface between the keeper and strike case by urging the undercut into contact with a corresponding undercut in the strike case. The transition between fail-secure and fail-safe modes of operation is accomplished by removal of the keeper with access to the interior thereof provided by the removable insert located at one end of the keeper. Thus, the present invention provides a durable and versatile electric door strike that is extremely difficult to defeat. 
     While the foregoing description has been with reference to a preferred embodiment of the invention, it is to be noted that variations and modifications may be made therein without departing from the scope of the invention.