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This application claims the benefit of provisional application Ser. No. 60/557,862 to Geringer et al., which was filed on Mar. 30, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to door locks, and in particular to electric door locks that can be operated in both the fail-safe and fail-secure mode. 
   2. Description of the Related Art 
   Security doors to prevent theft or vandalism have evolved over the years from simple doors with heavy duty locks to more sophisticated egress and access control devices. Hardware and systems for limiting and controlling egress and access through doors are generally utilized for theft-prevention or to establish a secured area into which (or from which) entry is limited. For example, retail stores use such secured doors in certain departments (such as, for example, the automotive department) which may not always be manned to prevent thieves from escaping through the door with valuable merchandise. In addition, industrial companies also use such secured exit doors to prevent pilferage of valuable equipment and merchandise. 
   One type of door lock which has been used in the past to control egress and access through a door is an electromagnetic system which utilizes an electromagnet mounted on a door jamb, with an armature mounted on the door held by the electromagnet to retain the door in the closed position when the electromagnet is actuated. Such locking mechanisms are illustrated in U.S. Pat. No. 4,439,808, to Gillham, U.S. Pat. No. 4,609,910, to Geringer et al., U.S. Pat. No. 4,652,028, to Logan et al., U.S. Pat. No. 4,720,128 to Logan, Jr., et al., and U.S. Pat. No. 5,000,497, to Geringer et al. All of these references utilize an electromagnet mounted in or on a door jamb and an armature on the door held by the electromagnet to retain the door in the closed position. Such electromagnetic locking systems are quite effective at controlling egress and access through the door they are installed on. Unfortunately, however, such systems are quite expensive, and require a fairly complex installation, often with the electromagnet being mounted in the door jamb. 
   Another type of system which is known in the art is the electric door strike release mechanism, in which a latch bolt located in and extending from a locking mechanism located in a door is receivable in an electrically operable door strike mounted in the frame of the door. The door may be opened either by retracting the latch bolt into the locking mechanism to thereby disengage it from the door strike, or by electrically actuating the door strike mechanism to cause it to open and to thereby release the extended latch bolt from the door strike mechanism. Typically, such electrically operable door strikes pivot to allow the door to close without the door strike mechanism being electrically actuated. Such door strike mechanisms are illustrated in U.S. Pat. No. 4,017,107, to Hanchett, U.S. Pat. No. 4,626,010, to Hanchett et al., and in U.S. Pat. No. 5,484,180, to Helmar. Like the electromagnet/armature systems discussed above, electrically operated door strike systems are also expensive, and require a significant installation into the door jamb, which must usually be reinforced. 
   Electrically operable door locks have also been developed that can be installed on a door through which access is to be controlled by an electrically operable security system. Such a lock is disclosed in U.S. Pat. No. 5,876,073 to Geringer et al. The door opening mechanism of the door lock is selectively locked and unlocked by controlling the supply of electricity to the door lock to thereby control access or egress through the door. The electrically operable door lock uses an electromagnetic actuator to drive a locking member between a locked position in which it engages a latch actuating member to prevent it from being rotated to retract a latch bolt to open a door, and an unlocked position in which it is disengaged from the latch actuating member to allow it to be rotated to retract the latch bolt to open the door. By reversing the position of the electromagnetic actuator in the door lock apparatus, the system may operate in either a fail secure mode in which the electromagnetic actuator must be powered to unlock the door, or a fail safe mode in which the electromagnetic actuator must be powered to lock the door. 
   SUMMARY OF THE INVENTION 
   One embodiment of an electric door lock according to the present invention is interchangeable between fail safe and fail secure modes and comprises a housing for receiving a plurality of internal components of the door lock. A window is included in the housing, the window allowing access to the internal components to change the operation of the lock between fail safe and fail secure modes. 
   Another embodiment of an electric door lock according to the present invention that is interchangeable between fail safe and fail secure modes also comprises a housing for receiving a plurality of internal components of the door lock. The housing has a removable cover plate. A switching mechanism is included for altering the internal components to change the operation of the lock between fail safe and fail secure modes without removing the cover plate. 
   These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of one embodiment of a lock according to the present invention with its cover removed so that its internal components are visible; 
       FIG. 2  is a plan view of one embodiment of a lock according to the present invention with its cover removed so that its internal components are visible; 
       FIG. 3  is a plan view of a portion of the locking arm and cam mechanism shown in  FIGS. 1 and 2 ; 
       FIG. 4  is a plan view of one embodiment of a cover plate according to the present invention; 
       FIG. 5  is a perspective view of one embodiment of a locking arm according to the present invention. 
       FIG. 6  is a perspective view of one embodiment of a locking arm and solenoid arrangement according to the present invention; 
       FIG. 7  is a perspective view of one embodiment of a lock according to the present invention with its cover in place; and 
       FIG. 8  is a perspective view of a door utilizing a lock according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The inventions herein are described with reference to a particular lock but it should be understood that the inventions can be similarly used in other types of locks and other devices unrelated to locks. The components described herein can have many different shapes and sizes beyond those shown and can be arranged in many different ways beyond those described herein. 
   One embodiment of a fail safe/fail secure lock according to the present invention comprises an electrically operable lock that can be changed to operate in either the fail safe mode or fail secure mode. It is generally understood in the industry that the fail safe mode of a lock describes a mode wherein the door can be opened by the lock doorknob when power to the lock is turned off or interrupted (i.e. power failure). Conversely, the fail secure mode describes a mode wherein the door cannot be opened by the doorknob when power to the lock is off or lost. 
   The lock generally comprises a lock housing holding the lock&#39;s internal components, which include a mechanism for allowing the lock to be changed between the fail safe and fail secure modes. In conventional locks, changing between the fail safe and fail secure modes requires opening the housing, such as by removing the cover, to access the internal components and manipulating the internal components. This can be an overly complex and inconvenient procedure and can result in damage to the internal components or lost internal components. Locks according to the present invention comprise a mechanism for allowing the lock to be changed without opening the lock housing. Different mechanisms can be used according to the present invention, with one mechanism being an access window that allows access to a limited section of the lock&#39;s internal components. The internal components can be accessed through the window to change the lock between fail safe and fail secure modes. The window and the lock&#39;s internal components are also arranged such that they remain secure and will not fall out of the lock housing through the access window. The lock also includes internal components that allow for improved reliability and extended life. 
   It will be understood that when an element is referred to as being “on”, “connected to”, “coupled to” or “in contact with” another element or layer, it can be directly on, connected or coupled to, or in contact with the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on”, “directly connected to”, “directly coupled to” or “directly in contact with” another element or layer, there are no intervening elements or layers present. 
     FIGS. 1 and 2  show one embodiment of a lock  10  according to the present invention that can be quickly and easily changed to operate in either the fail safe or fail secure mode, without opening the housing. The lock  10  generally comprises a housing  12  that can be many different shapes and sizes, but has a height, width and depth so that it can be mounted within a door and is large enough to securely hold the lock&#39;s internal components described below. The housing can be made of many different rigid and durable materials, with a preferred material being a metal. The housing  12  is shown in  FIGS. 1 and 2  with its cover plate removed so that the internal lock components are shown to facilitate explanation of the operation of the lock&#39;s internal components. The lock  10  in  FIG. 1  is also shown with a portion of the back of housing cutaway so that the internal components can be viewed for ease of explanation. It is understood, however, that when the lock  10  is finally assembled (as shown in  FIG. 7 ), the housing is complete with its cover plate installed such that the housing  12  and its cover plate surround and hold the internal lock components. 
   The housing  12  comprises a back plate  13  to which many of the lock&#39;s internal components are mounted. The lock further comprises a front plate  14  that is arranged so that when the lock  10  is installed in the door, the front plate  14  is flush with the leading edge of the door. A latch bolt  16  is mounted within the housing  12  and a pivotally mounted retraction lever  18  is also mounted within the housing  12  in proximity to the latch bolt  16 . A doorknob or opening lever (“doorknob”) can be mounted to the lock  10  at the retraction lever  18  such that rotation of the doorknob causes rotation of the retraction lever  18 . In most embodiments an inside and outside doorknob can be mounted to the retraction lever  18  with the doorknobs being on opposite sides of the lock  10 . The latch bolt  16  is urged to the extended position by the bias of latch bolt spring  24 , and the retraction lever  18  has a retraction finger  20  that is mechanically coupled to the latch bolt rod  22  so that rotational movement of the retraction lever  18  overcome the bias of spring  24 . This in turn causes the latch bolt  16  to retract into the housing  12 . 
   As shown, the front portion of the latch bolt  16  extends through a bolt opening  26  in the front plate  14  in its extended position and is arranged to engage a strike plate (not shown) in a door frame. The latch bolt  16  can also be retracted as described above so that all or most of the latch bolt&#39;s front portion is retracted into the housing  12 . In normal use, door lock  10  is mounted in a door to allow a user to operate a doorknob and the latch bolt  16  to release the door. When the door is locked by the door lock  10  the latch bolt  16  extends from front plate  14  to engage a strike plate (shown in  FIG. 8 ). When the door can be opened, the latch bolt  16  is retracted and disengages from the strike plate. 
   An auxiliary latch  28  is mounted within the housing  12  parallel to the latch bolt  16 , and comprises a front portion that extends from auxiliary latch opening  30  in the front plate  14 . The auxiliary latch  28  is urged by the auxiliary latch spring  32  to the extended position, and the auxiliary latch  28  can be moved to a retracted position within the housing  10 , against the force of spring  32 , by a force applied to the end of auxiliary latch  28 . In operation, the auxiliary latch  28  and spring  32  cooperate to hold the latch bolt  16  at a predetermined position. In one embodiment according to the present invention, the auxiliary latch  28  is arranged such that when in its retracted position, the latch bolt  16  can only be retracted by the inside doorknob and the key cylinder. When the auxiliary latch  28  is in its extended position the latch bolt  16  can be retracted. In operation, when the door is closed, the auxiliary latch  28  can be compressed by the frame of the door or the strike plate, and holds the latch bolt  16  at its extended position such that the latch bolt  16  is blocked against operation driven by the outside doorknob. 
   A key cylinder (not shown) can be mounted within cylinder opening  34  and a bolt lever  36  extends between the latch bolt rod  22  and the key cylinder. Operation of the key cylinder causes the bolt lever  36  to move about a bolt lever pin  38  such that when the proper key is inserted in the key cylinder and rotated, the bolt lever  36  is rotated about the bolt lever pin  38 . When the end of the bolt lever  36  at the latch bolt  16  moves away from the front plate  14 , the bolt lever  36  operates on the latch bolt  16  such that the latch bolt  16  retracts into the lock housing  12 . 
   The lock  10  also comprises a solenoid  40 , a locking arm  42 , and a locking cam  44 , all of which cooperate to allow or block the retraction lever  18  from operating under force of doorknob to retract the latch  16 . This allows the lock  10  to operate in the fail safe and fail secure modes. The retraction lever  18  has a locking tab  46  that mates with a locking slot  48  in the locking cam  44 . When the locking tab  46  is mated with the locking slot  48 , the retraction lever  18  is blocked from retracting the latch bolt  16 . Conversely, when the locking tab  46  is not mated with the locking slot  48  the retracting lever can retract the latch bolt  16 . 
   The solenoid  40  is mounted near the top of the housing  10  at a solenoid holder  50 . The solenoid  40  comprises a solenoid body  52  and a plunger  54 , with the solenoid body  52  having an internal coil (not shown) that can be energized to create a magnetic field that operates to pull the plunger  54  within the solenoid body  52 . The plunger  54  also comprises a plunger tip  56  with a plunger spring  58  arranged on the plunger  54 , between the plunger tip  56  and solenoid body  52 . When the solenoid  40  is energized, the plunger is drawn into the solenoid body  52  against the force of the spring  58 , compressing the spring  58  between the solenoid body  52  and the plunger tip  56 . When the solenoid  40  is not energized (such as in a power failure) the coil is not energized and the plunger  54  at least partially extends from the solenoid body  52  under force of the spring  58 . 
   The plunger  54  is connected to one end of the locking arm  42  and as the plunger  54  goes though the movement of being drawn into and extending from the solenoid body  52 , the locking arm  42  is pulled toward or pushed away from the solenoid body  52 . First and second bushings  57   a  and  57   b  (shown in  FIG. 2 ) are arranged within the housing  12  and adjacent to the locking arm  42  so that the locking arm  42  is substantially prevented from sliding toward the front plate  14 . Instead, its primary motion is sliding back and forth under the force of, and in relation to, the solenoid  40 . 
   The locking arm  42  is connected between the plunger  54  and the locking cam  44  and the locking arm  42  cooperates with the locking cam  44  to allow the lock  10  to operate in either the fail safe or fail secure mode. The locking arm  44  and locking cam  42  have cooperating switching mechanisms that can be manipulated to change the operation of the lock between fail safe and fail secure modes depending upon how the locking arm  42  is connected to the locking cam  44 . Many different mechanisms can be utilized according to the present invention, and in one embodiment, the locking cam  44  has a slot that can be engaged by locking arm  42  using different engagement mechanisms, such as a screw, pin, rod, clamp, etc. The locking arm  42  has two engagement locations for mounting the engagement mechanism, with one of the two locations allowing engagement with the slot for operation of the lock in fail safe mode and the other for operation in the fail secure mode. 
   In one embodiment according to the present invention, and as shown in  FIGS. 1 and 2 , the two engagement locations on the locking arm  42  comprise a threaded fail safe hole  60  and a threaded fail secure hole  62 . The engagement mechanism comprises a slot screw  64  that is also threaded to mate with the holes  60 ,  62 . The holes  60 ,  62  are arranged over a V-shaped slot  66  in the locking cam  44  such that when the slot screw  64  is threaded into one of the holes  60 ,  62 , the screw  64  passes into the slot  66 . 
   Operation of the solenoid  50  causes the locking arm  42  to move forward and back with the action of the solenoid plunger  54 , which in turn causes the screw  64  to slide within slot  66 . As described above, the locking arm  42  does not substantially move toward the front plate  14  so that the sliding action of the screw  64  in the slot  66  causes the locking cam  44  to move forward and back in relation to the front plate  14 . When the screw  64  is in the fail safe hole  60  as shown in  FIG. 1 , and power is off to the solenoid (or there is a power failure), the plunger  54  extends from the solenoid body  52  under the force of the spring  58  and the locking arm  42  is pushed toward the bottom plate of the housing  12 . At the same time, the screw  64  slides within the slot  66 , moving the locking cam  44  away from the front plate  14 . This action moves the retraction lever&#39;s locking tab  46  out of the cam&#39;s locking slot  48 , which in turn allows the retraction lever  18  to operate to retract the latch bolt  16 . Accordingly, in this arrangement the lock  10  operates in fail safe mode by allowing the lock to operate when power is off or lost. 
   Referring now to  FIG. 3 , the screw  64  is threaded into the fail secure hole  62 . When power is off or there is a power failure, the locking arm is pushed down by the plunger  54 . This causes the screw  64  to slide in the slot  66 , but instead of moving the cam  44  away from the front plate  14 , the cam is pushed toward the front plate. This causes the locking tab  46  to mate with the locking slot  48 , which prevents the retraction lever  18  from retracting the latch bolt  16 . In this arrangement the lock  10  operates in fail secure mode by not allowing the lock to operate when power is off or lost. 
     FIG. 4  shows one embodiment of a lock cover plate  70  according to the present invention that is arranged to fit over the lock  10  such that the housing  12  and cover plate  70  provide an enclosure for the lock&#39;s internal components. The plate comprises a key cylinder opening  72  so that a key can operate on the key cylinder, and a doorknob opening  74  so that a doorknob can be mounted to the retraction lever. The plate  70  also comprises several smaller holes  76  that can be used for mounting or to hold pins within the lock  10 . 
   The plate  70  also comprises an access window  78  that is arranged over the screw  64 , and the fail safe and fail secure holes  60 ,  62  (shown in  FIGS. 1-3 ). The holes  60 ,  62  can be accessed through the window so that the screw  64  can be threaded into one of the holes without removing the plate  70 . Similarly, the screw  62  can be removed from one of the holes  60 ,  62  through the window  78  and turned into the other of the holes  60 ,  62 . This allows the lock  10  to be quickly and easily changed between the fail safe and fail secure modes without removing the front plate. This also allows the mode of the lock to be changed without the danger of damaging or misplacing the lock&#39;s internal components. 
   In one embodiment according to the present invention, the window is sized so that the screw  64  can be removed by a screwdriver or other similar tool. Other embodiments according to the present invention can have different sized windows, such as a window large enough to remove the screw using a larger tool, or by hand. In still other embodiments, the cover plate can have more than one window, such as two windows allowing the screw  64  to be removed from one of the holes through one window and inserted into the other hole through the second window. 
     FIGS. 5 and 6  show one embodiment of a locking arm  80  according to the present invention, with the locking arm  80  coupled to the plunger  82  of a solenoid  84  as shown in  FIG. 6 . Like the solenoid described above, solenoid  84  has a spring to bias the plunger  82  in the extended position when the solenoid is not energized (power off or failure). The plunger end  86  of the locking arm  80  attaches to the solenoid plunger  82  (shown in  FIG. 1 ). At the other end, the locking arm comprises a tab  87  having fail safe and fail secure holes  88 ,  90  as described in  FIG. 1 . A linking section  92  extends between the plunger end  86  and tab  87 , and a stop  94  prevents the arm from extending too far down under action of the solenoid. 
   The locking arm  80  comprises an improvement over the prior art in that the prior locking arm comprises a surface that can be in contact with the lock&#39;s back (reference number  13  in  FIGS. 1 and 2 ). This contact can cause a significant point of friction that can result in an added load to the operation of the solenoid. Any added load can reduce the life of a solenoid thereby reducing the overall life of the lock. The locking arm  80  contacts the back plate  13  along one edge  96  that results in much less friction between the arm  80  and back plate  13 . The locking arm  80  also has less mass compared to prior mechanisms, such that the solenoid  84  can more easily move the locking arm  80  compared to prior mechanisms. This results in a reduced load on the solenoid  84 , which further enhances reliability and lifespan of the solenoid  84 . 
     FIG. 7  shows one embodiment of a lock  100  according to the present invention after the cover plate  102  has been mounted in place to the lock housing  104 ′. The cover plate  102  has an access window  106  which allows for the lock  100  to be changed between the fail safe and fail secure modes as described above by changing the location of the slot screw between the fail safe and fail secure holes. In this embodiment, this is accomplished by accessing the slot screw with a screwdriver through the access window  106 . This is typically done before the lock  100  is installed in a door. The lock is then installed in a door and connected to electrical conductors that carry a power and control signals to control whether the lock can be opened. When power from the conductors is off or lost, a fail condition exists and depending on the location of the slot screw, the lock will either be “safe” to be operated to open its door, or “secure” such that it cannot be operated to open its door. 
     FIG. 8  shows one embodiment of a door system  110  that can utilize a lock according to the present invention. The door system  110  comprises a door  112  mounted in a door frame, usually by hinges, such that the door  112  can swing open and closed on the hinges. A lock  116  according to the present invention, is mounted in the door  112  such that the lock&#39;s front plate  118  is flush with the door&#39;s leading edge  120 . The latch bolt extends from the lock  116  and door  112  though the front plate  118  and is arranged to engage a strike plate  124  in the door frame  114  to hold the door closed. Electrical power and control signals are transmitted over conductors  126  that typically run from the door system controller (not shown), through the door frame  114  near the hinges, through the door  112  and into the lock  116 . The lock  116  is configured to work in the fail safe or fail secure mode such that when power to the lock is interrupted, the lock will either be operable or not. If the lock is in the fail safe mode and door  112  is closed with the latch bolt  122  engaging the strike plate at the time power is interrupted, the lock will be operable at the handle  126  to open the door. If it is in the fail secure mode when power is interrupted, the handle  126  will not be operable to open the door  112 . 
   Although the present invention has been described in considerable detail with references to certain preferred configurations thereof, other versions are possible. The invention can be used in different locks and different components can be used in the locks described above. Many different solenoids can be used in the lock including single or multiple stage coils that are operable with different voltages, such as 12 or 24 volts. The steps taken above to interchange the lock between fail safe and fail secure modes can be taken in different order and different steps can be used. Therefore the spirit and scope of the claims should not be limited to the preferred version contained herein.

Summary:
An electric door lock interchangeable between fail safe and fail secure modes comprising a housing for receiving a plurality of internal components of the door lock. A window is included in the housing, the window allowing access to the internal components to change the operation of the lock between fail safe an fail secure modes.