Patent Abstract:
A lockable keeper arm extends across an opening of a door strike housing. A pivotally mounted transmission lever releasably engages the keeper arm. A pivotally mounted release lever releasably engages the transmission lever. An actuator engages the release lever at a point between the release lever pivot and the transmission lever and drives the release lever between alternate positions in either fail-safe and fail-secure modes. The actuator engagement point may be closer to the release lever pivot point than the transmission lever engagement point. A stop limits travel of the release lever and may be positioned in alternate positions. In alternate positions, the primary lever unlocks the keeper arm when the actuator is either energized or de-energized, placing the strike in fail-safe or fail-secure modes. Magnets may be mounted inside the housing to attract metal particles. The actuator may be an electric solenoid or a motor.

Full Description:
TECHNICAL FIELD 
     The present invention relates to mechanisms for electrically locking a door in a frame; more particularly, to such mechanisms wherein the electrical mechanism is switchable between fail-safe and fail-secure modes of operation; and most particularly, to a mode-switchable electric door strike wherein the mode is easily selectable by positioning of a stop at one of two alternate positions without requiring movement or repositioning of any other components of the strike. 
     BACKGROUND OF THE INVENTION 
     A distinction exists between modes of operation for electric door openers (referred to generally in the art as “electric strikes”), namely, fail-safe or fail-secure. 
     In fail-safe mode, the strike is unlocked at any time that an actuator, such as a solenoid or motor, is de-energized, thus permitting exit through the door in event of a power failure. 
     In fail-secure mode, the strike is locked at any time that the actuator is de-energized, thus securing the door against opening in event of a power failure. 
     In the older prior art, the two modes of operation have generally required two different basic constructions, resulting in increased costs for manufacture and stocking of the different constructions. Thus, it has been desirable in the art to develop strike mechanisms wherein a basic arrangement may be positioned in either fail-safe or fail-secure mode simply by reconfiguring certain internal strike elements. Unfortunately, such prior art reconfiguring typically requires significant movement of various operating elements, often further requiring the removal of the door strike assembly itself. Thus, the process can be cumbersome, difficult to complete reliably, and/or time-consuming to carry out. Further, at least one prior art device provides a means for changing the positions of internal elements from outside the housing. The ready-accessibility of the means can be undesirable for maintaining securing in a fail-secure mode. 
     U.S. Pat. No. 5,788,295, entitled “Electric Door Opener with Multiple Position Armature Permitting Different Operation Modes”, discloses an electric door opener with a transmission lever (“trimmer”  6 ) pivotable about an axis  16  at a first end to lock and unlock a door latch  4 . The transmission lever is actuable by a release lever (“armature”  8 ) pivotable about an axis  9  at a first end and having a shaped opening for receiving a head  17  of the transmission lever. A solenoid  13  includes a plunger  22  operable at the opposite end of the release lever. The release lever is adjustable by position to release or lock head  17  of the transmission lever. A rotation stop  10  is provided to switch the system between fail safe and fail secure modes by variably positioning the head  17  with respect to the opening. 
     The disclosed apparatus has at least two serious shortcomings. 
     First, the rotation stop to change fail-safe to fail-secure and vice versa, provided in the form of a turnable plug, can be readily tampered with using a simple tool. 
     Second, the contact point of the plunger to the release lever is at the distal end of the release lever from pivot axis  9 , which requires a maximum stroke range of the solenoid plunger over which the internal air gap between the armature of the plunger and the core of the coil, and thus the pulling or holding force of the solenoid, necessarily varies substantially. Thus over some portion of the required range, the force of the solenoid available to hold the latch locked is relatively weak. Further, in a case where the actuating force is provided by a motor and the contact point of the motor&#39;s plunger or linkage is at the distal end of the release lever, the operating stroke of the motor needed to move the lever through its full range is maximized. What is needed is an arrangement wherein the required overall stroke of the actuating solenoid is shortened, thereby minimizing variation in air gap and solenoid strength. In the case of a motor actuated mechanism, what is needed is an arrangement wherein the operating stroke of the motor is minimized. 
     U.S. Pat. No. 6,390,520 B1, entitled “Door Opener”, the relevant disclosure of which is herein incorporated by reference, discloses an electric door opening mechanism which is operable in either a fail safe or fail secure mode according to whether electric power is connected or disconnected to a pair of coils acting upon lever-shaped rotatable armatures external to the coil. The disclosure includes provisions for adjustment of internal stops to the rotatable armatures and provisions for changing coil positions relative to the armatures. 
     A shortcoming of this apparatus is that, when changing between fail-safe and fail-secure modes, to properly position the coil and to establish the correct range of rotational stroke of the armature, two elements must be repositioned in two separate operations. The coil must be repositioned relative to the rotational armature and the fixed stop must be removed, inverted, and re-installed. 
     In addition, through the normal operation and usage of a strike and latch mechanism, metal particles abraded from mating metal surfaces, such as from the latch bolt and strike, may collect inside the strike housing and may cause binding of close-fitting components within the housing. For example, a solenoid plunger&#39;s movement can become sluggish or stuck from metal debris entering between the plunger and solenoid body or a motor&#39;s movement may become sluggish or stuck if debris enters the motor mechanism. 
     None of the known prior art discloses the improved device which remedies these shortcomings set forth herein. 
     What is needed in the art is an electric door strike wherein the mechanism may be changed easily between fail-safe and fail-secure modes; wherein the means for changing is not accessible without at least removal of an outer cover plate; wherein no repositioning of an actuator, such as a coil, solenoid or motor, is required to change between operating modes, and wherein binding of closed fitting moving components within the housing, such as a solenoid plunger or motor mechanism, is reduced. 
     It is a principal object of the present invention to simplify, without compromising security, the switching of an electric strike between fail-safe mode and fail-secure mode. 
     SUMMARY OF THE INVENTION 
     Briefly described, an electric door opening mechanism in accordance with the present invention comprises a housing having a central cutout portion with an opening adapted to receive a bolt of a door. First and second keeper arms are pivotably mounted on opposite first and second sides of the opening and have latch elements extending across the opening, and have a first position occluding the opening, which position may be locked or unlocked, and a second position pivotable from the first position which allows the bolt to be withdrawn from the opening past the latch elements. First and second transmission levers pivotally mounted to the housing releasably engage the first and second keeper arms. First and second release levers pivotably mounted to the housing releasably engage the first and second transmission levers, respectively. In one aspect of the invention, first and second solenoid plungers engage the first and second release levers, respectively, at a point close to the rotational axes of the release levers, and drive them between alternate positions in each of the fail-safe and fail-secure modes. Motors may also be used to drive the release levers through contact points close to the rotational axes of the release levers. Stops selectively positioned in the housing limit the actuation range of the release levers. The stops may be positioned in either of alternate positions. In one of such stop positions, the rotational range of the release levers is limited such that the overall linkages serve to unlock the keeper arms when the actuators are de-energized, thus placing the strike in fail-safe mode. In the other of such stop positions, the rotational range of the release levers is limited such that the overall linkages serve to lock the keeper arms when the solenoids are de-energized, thus placing the strike in fail-secure mode. Preferably, the stops are movable from within the housing only after removing a housing cover. 
     Preferably, one or more permanent magnets are included within the housing to collect metal particles generated by wear of the latch over the lifetime of the assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an isometric view from the right front showing a first embodiment of the present invention with the cover removed for clarity (cover is removed and not shown in all views herein); 
         FIG. 1A  is a detailed view of the area shown in circle  1 A in  FIG. 1 ; 
         FIG. 1B  is a detailed view of the area shown in circle  1 B in  FIG. 1 ; 
         FIG. 2  is a plan view of the first embodiment shown in  FIG. 1 ; 
         FIG. 2A  is a detailed view of the area shown in circle  2 A in  FIG. 2 ; 
         FIG. 2B  is a detailed view of the area shown in circle  2 B in  FIG. 2 ; 
         FIG. 3  is an isometric view from the left front of the first embodiment shown in  FIG. 1 ; 
         FIG. 3A  is a detailed view of the area shown in circle  3 A in  FIG. 3 ; 
         FIG. 3B  is a detailed view of the area shown in circle  3 B in  FIG. 3 ; 
         FIG. 4A  is an isometric view of the release and transmission levers in an unlocked position in fail-safe mode; 
         FIG. 4B  is an isometric view of the release and transmission levers in a locked position; 
         FIG. 4C  is an isometric view of the release and transmission levers in an unlocked position in fail-secure mode; 
         FIG. 5  is an isometric view from the right front showing a second embodiment of the present invention; 
         FIG. 5A  is a detailed view of the area shown in circle  5 A in  FIG. 5 ; 
         FIG. 6  is an isometric view from the right rear of the second embodiment shown in  FIG. 5 ; 
         FIG. 6A  is a detailed view of the area shown in circle  6 A in  FIG. 6 ; 
         FIG. 6B  is a detailed view of the area shown in circle  6 B in  FIG. 6 ; 
         FIG. 7  is a plan view of the second embodiment shown in  FIG. 5 ; 
         FIG. 7A  is a detailed view of the area shown in circle  7 A in  FIG. 7 ; 
         FIG. 7B  is a detailed view of the area shown in circle  7 B in  FIG. 7 ; 
         FIG. 8A  is a schematic drawing of a portion of the first embodiment showing the release lever in an unlocked fail-secure position when the solenoid is energized; 
         FIG. 8B  is a schematic drawing of a portion of the first embodiment showing the release lever in a locked fail-secure position when the solenoid is de-energized; 
         FIG. 9A  is a schematic drawing of a portion of the first embodiment showing the release lever in a locked fail-safe position when the solenoid is energized; and 
         FIG. 9B  is a schematic drawing of a portion of the first embodiment showing the release lever in an unlocked fail-safe position when the solenoid is de-energized. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1 through 4 , a first embodiment  10  of a mode-switchable electric door strike in accordance with the present invention comprises a housing  12  mountable to a door jamb (not shown). Such mounting may be either surface mounting or recessed mounting, as is well known in the prior art. A cover (not shown) protects the interior of housing  12  from tampering as well as from dirt, dust, and the like. Housing  12  includes a cutout portion  14  adapted to receive a bolt (not shown) of a door (not shown) as is also known in the prior art. 
     A mode-switchable electric door strike in accordance with the present invention preferably comprises first and second mirror-image locking mechanisms  16  mounted to housing  12  and disposed symmetrically about cutout portion  14  as shown in the following disclosure and discussion. For simplicity and clarity in presentation, general reference may be made to only one of the two mirror-image mechanisms  16 , but such reference should be considered as being equally applicable to both except as may be noted. The use of a pair of keeper arms  18  is presently preferred over a single keeper arm as each keeper arm of the pair is subject to only half of any incoming force which, in turn, means that the strength of the device is essentially doubled. However, it should be noted that, while the drawings depict a strike with first and second mirror-image locking mechanisms, the invention contemplates use of a single keeper arm  18  and locking mechanism  16  if desired. 
     Opposing keeper arms  18  are mounted at keeper arm pivots  20  positioned proximate the midpoint of keeper arms  18  and are positioned proximate to cutout portion  14 . When keeper arms  18  are oriented in a closed position, latch portions  22  of arms  18  extend into and occlude cutout portion  14  thereby retaining the door bolt within cutout portion  14 . As is known in the prior art, when the door is moved closed, the door bolt is free to be received by cutout portion  14 , even when keeper arms  18  are in closed positions. That is, when the door is shut into a frame supporting strike  10 , the door bolt moves to allow passage past latch portions  22  but then snaps into cutout portion  14 . Once in cutout portion  14  and when keeper arms  18  are in closed positions, the bolt is trapped in cutout portion  14  and the door cannot be opened. Such keeper and strike action are well known in the art and the operation thereof will not be further discussed herein. 
     Keeper arms  18  are adapted to engage with transmission levers  24  mounted to housing  12  by transmission lever pivots  26 . The axes of rotation of transmission lever pivots  26  are parallel to and aligned vertically with the axes of keeper arm pivots  20 . 
     Prong  28  is positioned on each keeper arm  18  opposite latch portion  22 . Prong  28  is received within a fork  30  positioned on a corresponding side of transmission lever  24  when keeper arm  18  is in a closed position. 
     Keeper arms  18  are resiliently urged to the closed position by springs (not visible) which may be mounted on pivots  20 . One arm of each spring engages a keeper arm  18  on its prong side and the other arm engages a sidewall of cutout portion  14 . Thus, when prongs  28  are released from forks  30 , keeper arms  18  are held in the closed position only by the springs. To open the door, a user simply pushes against the door, causing the bolt to rotate keeper arms  18  against the springs. Once the bolt clears keeper arms  18 , the keeper arms rotate back to the closed position under the urging of the springs. Further, to best position each transmission lever  24  to receive prong  28 , a compression spring (not shown) may be mounted on one end thereof to fork  30  (in recess  32 ,  FIGS. 4A-4C ) and at the other end thereof to housing  12  proximate fork  30 . The compression springs urge transmission levers  24  rotatably away from housing  12  to best position fork  30  to receive prong  28 . 
     A release lever  34  is used to control the motion of each transmission lever  24  from a rotatable state to a locked state. Release lever  34  is mounted at one end thereof to housing  12  by release lever pivot  36 . The axes of rotation of release lever pivots  36  are parallel to but offset laterally from the axes of both keeper arm pivots  20  and transmission lever pivots  26 . The other ends of release levers  34  engage ends  38  of transmission levers  24  opposite forks  30 . 
     As best seen in  FIGS. 4A ,  4 B, and  4 C, the end of transmission lever  24  opposite fork  30  is provided with a pair of opposing laterally extending rectangular channels  40  which cut across transmission lever  24 . Sidewalls  42  of channels  40  in combination with the bottoms  43  of channels  40  form a T-shaped key  44 . A corresponding T-shaped opening  46  is provided in release lever  34 . A base  48  of T-shaped opening  46  is sized to allow a base  50  of key  44  to move freely therethrough. 
     The embodiment described provides three positions for release lever  34  with respect to transmission lever  24 . 
     In the first position (unlocked fail-safe) seen in  FIG. 4A , release lever  34  is completely disengaged from transmission lever  24 , whereby transmission lever  24  is allowed to rotate freely to the unlocked position as described above. 
     In the second position (locked in fail-safe and fail-secure modes) seen in  FIG. 4B , the arms of key  44  are positioned within the arms of opening  46 . In this position, key arms  44  cannot move out via opening  46 , whereby rotation of transmission lever  24  is prevented. With transmission lever  24  thus locked in place, keeper arms  18  are held in the locked position and the door cannot be opened. 
     In the third position (unlocked fail-secure) seen in  FIG. 4C , release lever  34  is positioned whereby the base  50  ( FIG. 4A ) of T-shaped key  44  is positioned within the arms of T-shaped opening  46 . Since key base  50  can freely move through opening  46 , transmission lever  24  can freely rotate to an unlocked position thereby allowing the door to be opened as desired. 
     Referring again to  FIGS. 1-4 , to control the movement of release lever  34 , a solenoid  52  is mounted proximate thereto on housing  12  by mounting screw  54  engaging a correspondingly threaded hole. Solenoid plunger  56  extends through an opening  58  in release lever  34  adjacent release lever pivot  36  and is retained therein by annular groove  59  formed in plunger  56 . Thus, whenever, solenoid  52  is energized, release lever  34  is drawn thereto, in the direction shown by arrow  57  in  FIG. 4A . A reverse force is provided by a spring (not visible) preferably within solenoid  52  which resiliently urges release lever  34  away from solenoid  52 . 
     Note that in the present invention, solenoid plunger  56  engages release lever  34  at a point between T-shaped opening  46  and pivot  36 , close to the pivot, whereas in U.S. Pat. No. 5,788,295, as described above the solenoid plunger engages the release is lever well distal of the lever&#39;s pivot. That is, the opening for receiving the transmission (trimmer) lever is placed between the engagement point of the plunger and the release lever pivot, making the engagement point necessarily remote from the pivot and thus engendering an undesirable range of stroke of the solenoid armature. 
     Moreover, in accordance with the present invention, the fail-safe and fail-secure modes of strike operation are regulated simply by repositioning a singular lever stop. The solenoid does not have to be repositioned as the coil had to be in U.S. Pat. No. 6,390,520. 
     To provide the fail-safe position shown in  FIG. 4A , a stop  60 , in the form of a post, is mounted on housing  12  as shown in  FIGS. 1A ,  2 B, and  3 B on the solenoid-facing side of release lever  34 . When solenoid  52  is de-energized, the solenoid spring urges release lever  34  away from stop  60  and to the unlocked fail-safe position shown in  FIGS. 4A and 9B . In the fail-safe mode, upon energizing of solenoid  52 , stop  60  limits the solenoid inward stroke and corresponding motion of release lever  34  to the locked position shown in  FIGS. 4B and 9A . Thus in fail-safe mode, the stroke of plunger  56  and rotation of release lever  34  are limited between positions  4 A (solenoid de-energized) and  4 B (solenoid energized). 
     To provide a fail-secure position of release lever  34 , stop  60  is moved to a second location on the opposite side of release lever  34  as shown in  FIGS. 1B ,  2 A, and  3 A. In this stop location, the outward de-energized stroke of plunger  56  and rotation of release lever  34  are limited by stop  60  to the locked position shown in  FIG. 4B . When solenoid  52  is energized, plunger  56  pulls release lever  34  away from stop  60  and into the third position shown in  FIGS. 4C and 8A , thereby permitting transmission lever  24  to rotate and to allow keeper arm  18  to release the door bolt from cutout portion  14 . This is the fail-secure mode whereby when the power is off, release lever  34  returns to rest against stop  60  and into a position as shown in  FIGS. 4B and 8B , thereby locking transmission lever  24  and keeping the door from being opened. 
     Stop  60  may take any one of several forms. In first embodiment  10 , stop  60  is preferably a post  62 , such as a shoulder screw, secured to housing  12  from within the strike cover accessible only by removing the housing cover, or from the rear of housing  12  (not shown) after first removing the entire strike housing from its mount. In either case, a mode change can be made by simply repositioning a stop. Note that a mode change cannot be made without at least removing the housing cover thereby substantially reducing the tamperability of the mode switching feature. 
     Referring now to  FIGS. 5-7 , in a second embodiment  10 ′ wherein all elements are identical with those of first embodiment  10  except a stop  60 ′ is formed as an inverted U-shaped bracket having a central opening or gate  64 . Stop  60 ′ may be secured by one or more screws  66  that are accessible from either within the housing or from the rear of housing  12 . The width of gate  64  is selected such that a side  68  of the gate limits motion of release lever  34  when the solenoid is energized (position  4 B—fail-safe mode) when stop  60 ′ is mounted at a first location as shown in  FIG. 7A , and a side  68  of the gate limits motion of release lever  34  when the solenoid is de-energized (position  4 B—fail-secure mode) when stop  60 ′ is mounted at a second location as shown in  FIG. 7B . (Note: In  FIGS. 1 through 3  and  5  though  7 , for illustrative purposes only, stops  60 ,  60 ′ are shown in both fail-safe and fail-secure modes in opposite locking mechanisms  16 ,  16 ′ within a single device. 
     Other stop configurations are fully anticipated by the present invention. For example, a U-shaped element (not shown) having legs the same distance apart as gate sides  68  of stop  60 ′ may be inserted through appropriately-spaced holes  9  (not shown) in the base of housing  12 . 
     Referring now to  FIG. 2 , a known problem in use of electric strikes is that latch components such as portions  22  undergo significant wear from being abraded by the latch bolt during the working life of a strike, which can produce metal particles that migrate and undesirably cause binding of moving components within the strike such as, for example, the solenoid plunger. Such particles typically are ferromagnetic and therefore can be attracted to magnets. To quarantine such particles, first and second large button magnets  70  and small button magnets  72  are mounted to the housing exemplarily as shown in  FIG. 2 . Obviously, other locations may be used. 
     While the invention has been described herein utilizing solenoids to drive the release levers through their alternate positions, it is understood that motors may be used to drive the release levers, through linkages or direct, and wherein the motors may be any type, such as for example, electric, vacuum, pneumatic or hydraulic and may act linearly or rotationally to drive the levers. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.

Technology Classification (CPC): 8