You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention has to do with electric strikes which can be used to electrically release or lock a door lock. In particular, the invention has to do with a surface mounted electric strike which can be installed on a doorjamb without cutting the doorjamb.  
         [0003]     2. The Related Art  
         [0004]     Surface mounted electric strikes that can be installed on a door jamb without cutting the door jamb provide a flexible and cost effective solution to the need for an electric strike. One such strike is described in U.S. Pat. No. 6,390,520 which discloses an electric door opener which can be used in either a fail safe or fail secure mode.  
         [0005]     It is an object of the present invention to provide a surface mounted electric strike having a simplified operating mechanism and a strengthened locking mechanism.  
       SUMMARY OF THE INVENTION  
       [0006]     The electric strike of the present invention employs a locking mechanism whereby two latches are pivotally mounted to a housing and releasably engaged by a single yoke. The yoke is pivotally mounted to the housing and is directly actuated by a cam. The cam is actuated electrically such as by a solenoid, a miniature motor and screw drive or the like.  
         [0007]     The cam can be designed to cause operation of the strike in a fail secure mode or a fail safe mode depending upon which side of the cam faces the yoke. To switch from one mode to another, the cam is simply removed, turned upside down and reinstalled. In the fail secure mode, the yoke is in the locking position unless it is moved to the unlocking position by the cam. In the unlocking position the latches are free to move and they will open when pressure is applied to them by the bolt of a door as the door is opened. When the cam is returned to its locking position, a spring urges the yoke back to its locking position when the latches have returned to their locked positions. Each latch is provided with a spring which urges the latches to return to their locked positions when they pivot out of their locked positions as the bolt is pulled out of the strike.  
         [0008]     In fail safe operation, the cam is installed to maintain the yoke in its unlocking position. When the electrical solenoid is actuated, the cam is moved to its locking position and the yoke spring causes the yoke to move to its locking position, thereby maintaining the latches in their locking positions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Fig. I is a perspective view of the present invention with the back cover removed.  
         [0010]     Fig. II is perspective top view of the active components of the present invention in a locked position.  
         [0011]     Fig. III is a perspective bottom view of the active components of the invention in a locked position.  
         [0012]     Fig. IV is a perspective top view of the active components of the invention in an unlocked position.  
         [0013]     Fig. V is an expanded perspective view of the product of the invention.  
         [0014]     Fig. VI is a front perspective view of the product of the invention.  
         [0015]     Fig. VII is a back perspective view of the product of the invention.  
         [0016]     Figs. VII A and B illustrate an embodiment of the invention which operates in a fail secure mode.  
         [0017]     Figs. IX A and B illustrate an embodiment of the invention which operates in a fail safe mode.  
         [0018]     Fig. X illustrates the product of the invention mounted on a door jamb.  
         [0019]     Fig. XI A illustrates the cam  20  of the invention in perspective and Fig. XI B illustrates the cam of Fig. XI A rotated about axis y-y.  
         [0020]     Fig. XII illustrates a motor and screw drive, as an alternative electrical actuator, connected to the cam  20 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring to Figs. I-V and X, surface mounted electric strike  1  comprises a housing  2 , and a cover  3  which support and protect the active components. The cover  3  can be in more than one piece such as  3   a  and  3   b  as illustrated in Fig. V. Cutout portions  5  and  6  in the housing  2  and cover  3 , respectively, are adapted to receive the bolt  7  of a door  8 . The cover  3  is held in place by screws  26 . The strike  1  is mounted on door jamb  9  using installation screws  10   a  and  10   b  which optionally are held in place by set screws  11   a  and  11   b . The set screws prevent the installation screws from loosening as a result of the pounding caused by the opening and closing of the door. As a further option or another option, pins  30  can be employed to stabilize the installation and also prevent the early loosening of the installation screws.  
         [0022]     Latches  12   a  and  12   b  are mounted on pivots  13   a  and  13   b  and the latches are held in the locked position by yoke  14 . The yoke  14  is comprised of legs  14   a  and  14   b , edge  14   c  and arm  14   d  having tapered edge  14   e . The latches are unlocked when solenoid  15  is actuated by electrical current in the conventional manner known in the art. When the solenoid  15  is activated, shaft  16  moves in the direction of arrow  17  and the pin  18  mounted in shaft  16  causes the arm  19  of cam  20  to move in the direction of arrow  17  thereby rotating cam  20  about pin  21 . This causes cam  20  to push against tapered edge  14   e  and cause yoke  14  to pivot on edge  14   c  thereby moving legs  14   a  and  14   b  downwardly to disengage latches  12   a  and  12   b . The latches  12   a  and  12   b  then are free to move to open positions when one pulls on the door  8  causing the bolt  7  to be pulled out of the strike  1 . Latch springs  22   a  and  22   b  cause latches  12   a  and  12   b  to return to their closed positions after the bolt  7  is pulled out of the strike  1 . The bolt  7  retracts into the door  8  as the bolt  7  passes the latches  12   a  and  12   b  when the door closes.  
         [0023]     Electrical devices other than a solenoid can be used to lock or unlock the latches. For example, an electric motor  28  and screw drive  29  can be used as illustrated in Fig. XII.  
         [0024]     Figs. I-III illustrate the active components in their locked positions and Fig. IV illustrates the active components in their unlocked positions. When the electrical current to the solenoid  15  is turned off, shaft  16  is returned to its original position by spring  23  as best illustrated in Fig. IV. The yoke  14  then is returned to its locked position by lock spring  24  provided that the latches  12   a  and  12   b  have returned to their locked positions. Lock spring  24  is held in place by screw  27 . The yoke  14  can be pivotally mounted to housing  2  by suitable means such as screw  25 . Screw  25  is installed with sufficient clearance relative to yoke  14  to permit the yoke to freely move from a locked to an unlocked position and back while preventing the yoke from moving out of its operating position. Housing  2 , in cooperation with set screw  25 , also serves to maintain the yoke in its operating position.  
         [0025]     An expanded view of the components of the invention is provided in Fig. V.  
         [0026]     Figs. I-IV illustrate the strike  1  of the invention configured to operate in a fail secure mode where the door  8  is locked unless the solenoid  15  is actuated. However, the strike  1  can easily be made to work in a fail safe mode (where the door  8  is unlocked unless the solenoid  15  is actuated) by simply removing cam  20  from a first installation position, turning it upside down and reinstalling it in a second installation position. Figs. VIII A and B, IX A and B and XI A and B illustrate the cam  20  in more detail with Fig. VIII A showing the cam  20  installed in the fail secure operating mode with solenoid  15  energized showing the yoke  14  in its unlocked position and Fig. VIII B showing the same components with solenoid  15  de-energized showing yoke  14  in its locked position. Fig. IX A illustrates the cam  20  installed in the failsafe operating mode with solenoid  15  de-energized and the yoke in its unlocked position and Fig. IX B shows the same components with solenoid  15  energized showing the yoke in its locked position. Fig. XI A illustrates the cam  20  by itself in perspective and Fig. XI B illustrates the cam  20  of Fig. XI A after it has been rotated approximately 180° about axis y-y.

Summary:
A surface mounted electric strike which can be installed on a door jamb without cutting the door jamb. The strike employs a simplified locking mechanism whereby two latches are releasably engaged by a single yoke. An electrical solenoid actuates a cam which directly actuates the yoke. The strike can operate in a fail safe mode or a fail secure mode.