Patent Publication Number: US-2010117383-A1

Title: Door strike

Description:
TECHNICAL FIELD 
     This invention relates to a door strike. 
     BACKGROUND TO THE INVENTION 
     Door strikes are used for controlling access through doors such as fire doors or tenancy entrance doors. A door strike is typically installed into a door jamb and engages with a door latch by way of a keeper. If the keeper is free to move then the door can be opened. If the keeper is not free to move then the strike is said to be “locked”. The keeper traps the door latch and the door can only be opened if the latch can be retracted such as by using a door handle or key. Door strikes are typically electrically powered and utilise a solenoid to actuate the strike mechanism. 
     An electric door strike can operate in one of two modes “power to look” and “power to open”. In the power to lock mode the keeper is free to move when no power is supplied and becomes locked upon supplying power. In this mode persons are free to pass through doors in the event of a power outage or the like. In the power to open mode the keeper is free to move only when power is supplied and in the absence of power the keeper becomes locked. 
     SUMMARY OF THE INVENTION 
     The present invention provides a door strike including: a latch retainer for retaining a door latch; a lock actuator which operates when power is applied; a mode selector rotatable between at least two positions; in a first position of the mode selector the strike adopts a power to open mode, in the second position of the mode selector the strike adopts a power to lock mode. 
     The mode selector may include at least two recesses which cooperate with a lug associated with the latch retainer. 
     The recesses may be provided about a generally cylindrical portion of the mode selector. 
     The mode selector may include at least two grooves which dictate the at least two positions of the mode selector. 
     At least one set screw may sit in either of the grooves to retain the mode selector in either of the at least two positions. 
     The latch retainer may be pivotally mounted in the door strike. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a door strike according to an embodiment of the invention; 
         FIG. 2  is a cross sectional view illustrating mounting of a door strike in a door frame; 
         FIG. 3  is a rear view of the strike of  FIG. 1  with rear cover removed to expose moving parts of the strike and shown in the power to lock mode with no power applied; 
         FIG. 4  shows the capstan and keeper of the strike of  FIG. 3  in isolation and in a perspective view; 
         FIG. 5  shows the door strike of  FIG. 3  in the power to lock mode with power applied; 
         FIG. 6  illustrates the door strike of  FIG. 3  being changed to the power to open mode; 
         FIG. 7  shows the door strike of  FIG. 3  in the power to open mode with no power applied; 
         FIG. 8  shows the door strike of  FIG. 3  in the power to open mode with power applied; 
         FIG. 9  is a cross sectional view of the strike of  FIG. 3  along line A-A; 
         FIG. 10  is an illustration of the capstan screw and stopper; 
         FIG. 11  is a cross sectional view similar to  FIG. 9 , but showing set screw loosened; 
         FIG. 12  is a perspective view of an alternative version of capstan for use in a lock according to a further embodiment of the invention; and 
         FIG. 13  depicts the capstan of  FIG. 12  in another position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a door strike  10  is shown in perspective view. The door strike is installed in a door frame in use (see  FIG. 2 ) and receives a door latch in a recess bounded on one side by a latch retainer in the form of keeper  12 . If keeper is free to move, then the door can be opened without retracting the door latch. If the keeper is not free to move, then the door latch must be retracted to allow the door to open. This may necessitate the use of a key or the like to withdraw the door latch. 
     Referring to  FIG. 3 , door strike  10  is shown including keeper  12  for retaining a door latch. Strike  10  further includes a mode selector in the form of capstan  14 , and a lock actuator in the form of solenoid  16 . The capstan  14  is rotatable between two positions to switch the strike between a power to open mode and a power to lock mode as will later be described. 
     Capstan  14  sits in housing  18  in which it is free to rotate, and also free to move to the left and the right upon activation or deactivation of solenoid  16 . Solenoid  16  includes a plunger  20  which is urged to the left in the drawings when electric power is applied which in turn causes lateral movement of capstan  14  against the pressure of spring  24  of microswitch  22 . Spring  24  biases the capstan  14  and plunger  20  to the right as seen in the drawings and operates to return capstan  14  and plunger  20  to their original positions when power to the solenoid is interrupted. 
     Referring now to  FIG. 4 , capstan  14  and keeper  12  are shown in isolation and are in the same positions as in  FIG. 1 . The cylindrical part of capstan  14  bears two recesses  28  and  29 . In use the position of either of recesses in relation to keeper  12  dictates whether or not keeper is free to move. If one or other of recesses  28 ,  29  is aligned with lug  34  of keeper  12  then the lug is free to pass by the capstan by way of the recess and thus the keeper is allowed to rotate. 
     Referring again to  FIG. 3 , recess  28  is aligned with lug  34  and thus the keeper is free to rotate. The strike is thus in the power to lock mode. 
     Referring now to  FIG. 5 , power is being applied to solenoid  16  and it can be seen that plunger  20  of solenoid has moved capstan  14  to the left as shown in the drawings. Recess  28  now does not align with lug  34 . Instead, capstan  14  obstructs lug  34  and so keeper  12  is not free to rotate and the strike is locked. 
     Referring now to  FIGS. 9 ,  10  and  11 , capstan  14  is rotatable between two positions to provide either power to lock or power to open modes of operation. Capstan  14  is maintained in either of the two positions by way of set screws  36  sitting in either of grooves  30  or  32 . The set screws are mounted in threaded holes provided in the body of the strike.  FIG. 9  shows set screw  36  sitting in groove  30 . Each of set screws  36  have a shoulder  38  which abuts against stop  40  provided in each of the threaded holes to limit the depth of insertion of set screws  36  into the body of the strike. In  FIG. 9  screw  36  is fully inserted with shoulder  38  abutting stop  40 . In this position, the tip of the set screw sits in groove  30  with about 0.5 mm clearance between the tip of screw  36  and the capstan  14 . Thus, even when fully inserted, screws  36  do not press onto capstan  14  and capstan  14  remains free to move to the left and right upon activation of solenoid  16 . In order to rotate capstan  14 , set screws  36  must first be withdrawn a number of turns until the tip of screw  36  is out of engagement with groove  30 . Capstan  14  has a series of castellations  42  about one end. A small tool such as a screwdriver can be inserted through a slot in the strike to rotate capstan  14  by pushing on castellations  44 . 
     Referring to  FIG. 6 , the process of switching the strike from power to lock mode to power to open mode is illustrated. At step  1  two set screws  36  are loosened to bring them out of groove  30 . At step  2  a small screwdriver is used to rotate capstan  14  through 180 degrees by way of castellations  42  to line groove  32  up with set screws  36  (see detail A). At step  3  set screws  36  are screwed back into the strike to sit in groove  32  (See detail B). The strike is now in the power to open mode (See Detail C). 
     Referring to  FIG. 7 , strike  10  is shown in the power to open mode with no power applied. It can be seen that recess  29  does not align with lug  34 . Instead, capstan  14  obstructs lug and so keeper cannot move. 
     Referring to  FIG. 8 , strike  10  is shown in the power to open mode with power applied to solenoid  16 . It can be seen that recess  29  aligns with lug  34  and keeper is free to rotate to allow the door to open. 
     Referring to  FIGS. 12 and 13 , an alternative version of capstan  114  is shown rotatably mounted in a housing  118 . This version of capstan  114  differs to the one described above in that it features an aligning means which includes two arms in the form of elongated castellations  130 ,  132  which cooperate with a stop  134  to align either of grooves  130 ,  132  with the set screws to improve ease of switching modes of the lock as will now be described. 
     In  FIG. 12  it can be seen that elongated castellation  132  abuts stop  134 . In this position groove  130  is aligned with set screws (not shown). The capstan is now only permitted to turn anticlockwise as indicated by arrow A. If capstan is turned in the direction of arrow A then the other elongate castellation  130  comes around to abut the other side of stop  134  as shown in  FIG. 13 . When castellation  130  abuts stop  134  the set screws (not shown) are aligned with groove  132 . Now, capstan may only rotate clockwise in the direction shown by arrow B. In this way, a user is not required to visually align the grooves with the capstan screws as was the case with the lock described above. Instead the user simply loosens the set screws and rotates the capstan in whichever direction it is permitted to rotate until the capstan comes up against a stop and then re-tightens the capstan screws. 
     In a still further embodiment, the alignment means takes to the form of one elongated castellation and two stops. The capstan is allowed to rotate between the two stops and when it is at either stop the lock is either in the power to open or power to lock mode and the set screws are aligned with the appropriate one of the grooves on the capstan. 
     Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated. 
     Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.