Abstract:
A latch mechanism is provided for a door which includes a rotatable latch which is rotated into and held in an open position to allow the door to open, and is released from the open position only when a sensing mechanism provided as a part of the latch mechanism, held in the door, senses the door frame upon a closing of the door. The latch is held in an over center engaged position which it is moved into due to a lost motion connection among some, but not all, elements of the latch mechanism.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a door latch device. In particular, the invention relates to structures and methods for a door latch device used with a panic device for doors wherein the locking as well as the unlocking of the door can be controlled by the door latch device. 
     Panic devices for doors have been in use in buildings for approximately 100 years and provide a useful means for allowing unrestricted escape from the building in situations such as an emergency, while providing a reasonable amount of security against unauthorized access. Panic devices are generally used on single action outward opening doors and provide retention within the door frame either into the threshold, transom or door frame to hold the door in the closed position when not in use. 
     There are numerous types and styles of mechanisms used for operating the panic devices where bolts reciprocate vertically in and out of the door frame and extend from the top and bottom of the door. Most of these mechanisms include or are adapted to include a panic bar release arrangement on the inside of the door for rapid and foolproof actuation of the bolts by merely depressing the panic bar to open the door. Many of such mechanisms include an often desirable feature of permitting manipulation of the panic device to latch the bolts in a retracted position during business hours or the like, whereby the door is free to swing open without operating the panic bar or hitting any other release mechanism. 
     To provide operation of installations of this type, some form of bolt latching mechanism is usually provided which retains the bolts in the retracted position when the interior or exterior actuating device is operated during the time the door is open. This prevents the need to continue pressure on the panic bar or key in order to prevent the bolt from contacting the ground or door frame while the door is swinging during the open and closed cycles. 
     A problem with these types of mechanisms, however, is that these mechanisms use a keeper plate or trip mounted on the door frame which is an added component to the door assembly. Thus, the added component increases the assembly required to install the door, resulting in higher installation costs. Further, the added component increases the chance for the component to fail, resulting in costly repairs, inefficient use of work space, and unsafe conditions. Further, the bolts in these mechanisms commonly fail to remain in the retracted position when the door has been opened, resulting in damage to the frame or threshold since the bolt strikes the frame or threshold upon closing. 
     A need, therefore, exists to safely and clearly open a door with a panic device. The solution, however, must be able to retain the bolting mechanism in the retracted position until the door has completely closed. Further, the solution must be capable of sensing that the door has closed to extend the bolt after the door has completely closed. 
     An example of a current panic device wherein the bolts may be retracted is a key operated lock which also services to lock the bolts in the retracted position. By depressing a panic bar, as described in the United States patent to T. Bejarano, U.S. Pat. No. 3,334,500 the bolts may be retracted. Other examples of such devices wherein the bolts may be retracted by a panic device are described in U.S. Pat. No. 3,993,335 to Schmidt, U.S. Pat. No. 3,940,886 to Ellingson, Jr., and U.S. Pat. No. 4,839,988 to Betts et. al. 
     Currently, other panic devices use Pullman latches which rotate about a horizontal axis and use a spring loaded mechanism. These panic devices usually consist of a mechanical system concealed within the vertical lock stile of the door connected with a surface mounted actuating push bar or pad mounted horizontally across the inside face of the door. The two parts of the system are normally linked mechanically. The mechanism within the door stile operates a latch or bolt system which retains the door in the closed position. In this system, the latch or bolt is retained in a keeper plate which is mounted on the door frame. 
     These mechanisms also do not solve the current need since the bolts often do not stay in the retracted position and drag along the ground or across the door frame. Further it is often the case that the door mounted components are installed by the door manufacture in the door assembly and the frame components such as keeper plates are sent to the site separately to be installed after the door frame has been erected. Frequently, the frame mounted components go astray and often the components are installed with less accuracy than can be achieved in the factory. This can lead to potentially dangerous situations should the device fail to open in an emergency. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved latching device that can keep the latch assembly in the disengaged position until after the door has closed. This leads to improved safety and maintenance on the door and door frame. The present invention can also be used without keeper plates and does not require a separate trip device mounted to the frame. This leads to installation cost reductions and improved safety for the occupants of the building. 
     Thus, there is provided by the invention disclosed herein an improved door latch device which overcomes many of the inadequacies of door latches known to the prior art. The invention provides for the mounting of a novel door latch device on the internal side of the door for providing a latch assembly which, rather than vertically extending from the door to engage the door frame, rotatably engages and disengages the door frame. This door latch device, upon mechanical instructions from the actuation of the panic exit device, or other device such as a key lock, is rotated into a disengaging and engaging position, respectively, to allow the door to be opened and to be closed. 
     In an embodiment, the door latch device comprises at least one housing fixed within the door stile and at least one fork positioned inward of the housing and slidably engaged to the housing. The door latch device further comprises a latch assembly rotatably mounted to the housing and mechanically connected to the fork. The latch assembly is rotatable from an engaged position in a first rotational direction to a disengaged position to allow the door to open. The latch assembly also is rotatable from the disengaged position to the engaged position in a second rotational direction to engage the door frame after the door has closed. 
     In an embodiment, the latch assembly comprises a latch rotatably connected to the housing. Additionally, a pair of linkages are positioned below the latch and rotatably connected to the housing. A pair of connecting rods are positioned between the latch and the pair of linkages and are slidably engaged to the pair of linkages. Further, a bias member is fixed to the pair of connecting rods and to the fork. The latch assembly further comprises a rocker element positioned between the housing and the latch wherein the rocker element is rotatably connected to the housing and slidably engaged within the latch. 
     The pair of linkages have a linkage pin positioned in the middle of the linkages while the connecting rods each have a rod slot for receiving the linkage pin. 
     The latch has a projection facing the door stile in the engaged position and rotated downward ninety degrees in the disengaged position. The latch further has a latch aperture positioned opposite the projection wherein the latch aperture is rotatably connected to the housing. The rocker element has a rocker pin positioned to mechanically connect to the projection during the second rotational direction. The rocker element further has a bridge positioned within the door stile in the engaged position and positioned outside the door stile in the disengaged position. 
     The present invention further provides a method of engaging and disengaging a door latch device for a door fitted in a door frame comprised of activating the fork in a downward direction. Thereupon, the latch assembly is rotated from an engaged position in the first rotational direction to a disengaged position to disengage from the door frame. A lost motion arrangement, preferably in the form of slot and pin connections between the housing and the fork permit the latch to be captured in an over center position and held against returning to the latched position while the door remains open. The method also provides for sensing the door frame by the latching mechanism upon the closing of the door. Further, the latch is rotated from the disengaged position to the engaged position in a second rotational direction to engage the door frame after the door frame has been sensed. 
     An advantage of the present invention is to provide a door latch device that efficiently retains and releases a door. 
     Another advantage of the present invention is to provide a latch assembly that moves from an engaged position to a disengaged position when the door is opened. 
     Another advantage provided by the present invention is the automatic sensing of the door frame during a closing movement of the door. 
     Another advantage of the present invention is to provide a latch assembly that automatically moves from the disengaged position to the engaged position when the door frame is sensed. 
     Another advantage is to provide a lost motion effect to prevent the latch from returning to the latched position while the door is open. 
     Another advantage of the present invention is to provide a door latch device eliminating a striker plate and/or a trip mechanism mounted to the door or frame. 
    
    
     Still further advantages will become apparent from a consideration of the following descriptions and drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a door latch device illustrated in an engaged position embodying the principles of the present invention. 
     FIG. 2 is a cross sectional view of the door latch device of FIG. 1 rotated 90 degrees about a vertical axis. 
     FIG. 3 is an isolated cross sectional view of a housing portion of the door latch device of FIG.  1 . 
     FIG. 4 is an isolated cross sectional view of a fork portion of the door latch device of FIG.  1 . 
     FIG. 5 is an isolated cross sectional view of a rocker portion of the door latch device of FIG.  1 . 
     FIG. 6 is a partially assembled side elevational view of the door latch device of FIG.  1 . 
     FIG. 7 is a more complete (than FIG. 6) partially assembled side elevational view of the door latch device of FIG.  1 . 
     FIG. 8 is an isolated cross sectional view of a latch portion of the door latch device of FIG.  1 . 
     FIG. 9 is an isolated cross sectional view of a link portion of the door latch device of FIG.  1 . 
     FIG. 10 is a more complete (than FIG. 7) partially assembled side elevational view of the door latch device of FIG.  1 . 
     FIG. 11 is an isolated cross sectional view of a rod portion of the door latch device of FIG.  1 . 
     FIG. 12 is an isolated cross sectional view of a biasing member portion of the door latch device of FIG.  1 . 
     FIG. 13 is a completely assembled side elevational view of the door latch device of FIG. 1 in the latched position. 
     FIG. 14 is a completely assembled side elevational view of the door latch device of FIG. 1 in the unlatched position. 
     FIG. 15 is a partially disassembled side elevational view of the door latch device of FIG. 1 in the unlatched position. 
     FIG. 16 is a completely assembled side elevational view of the door latch device of FIG. 1 in the latched position and including the use of a plate to protect a relatively soft wooden door. 
     FIG. 17 is a cross sectional view of a second embodiment of a door latch device illustrated in an engaged position embodying the principles of the present invention. 
     FIG. 18 is a cross sectional view of the door latch device of FIG. 17 rotated 90 degrees about a vertical axis. 
     FIG. 19 is an isolated cross sectional view of a housing portion of the door latch device of FIG.  17 . 
     FIG. 20 is an isolated cross sectional view of a fork portion of the door latch device of FIG.  17 . 
     FIG. 21 is an isolated cross sectional view of a rocker portion of the door latch device of FIG.  17 . 
     FIG. 22 is a partially assembled side elevational view of the door latch device of FIG.  17 . 
     FIG. 23 is a more complete (than FIG. 22) partially assembled side elevational view of the door latch device of FIG.  17 . 
     FIG. 24 is an isolated cross sectional view of a latch portion of the door latch device of FIG.  17 . 
     FIG. 25 is an isolated cross sectional view of a link portion of the door latch device of FIG.  17 . 
     FIG. 26 is a more complete (than FIG. 23) partially assembled side elevational view of the door latch device of FIG.  17 . 
     FIG. 27 is an isolated cross sectional view of a rod portion of the door latch device of FIG.  17 . 
     FIG. 28 is an isolated cross sectional view of a biasing member portion of the door latch device of FIG.  17 . 
     FIG. 29 is a completely assembled side elevational view of the door latch device of FIG. 17 in the latched position. 
     FIG. 30 is a completely assembled side elevational view of the door latch device of FIG. 17 in the unlatched position. 
     FIG. 31 is a partially disassembled side elevational view of the door latch device of FIG. 17 in the unlatched position. 
     FIG. 32 is a plan view of the plate shown in FIG. 16, here shown in isolation. 
     FIG. 33 is a fragmentary perspective view of a door latch device with a push bar actuator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the present invention may be embodied in many different forms, there is shown in the drawings and discussed herein one or more specific embodiments of a door latch device  20  embodying the principles of the present invention with the understanding that the present disclosure is to be considered only as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. 
     As discussed above, the present invention provides a structure and method to maintain a door latch  22  in a disengaged position until a door  24  which it is mounted on has completely closed. The door latch device  20  of the present invention efficiently and safely retracts and extends the door latch  22  during the opening and closing of the door  24  relative to a door frame  26 . 
     The door latch device  20  of the present invention is to be mounted on the door  24  which has an active style  28  and an inactive style (not shown), it being understood that the term “active style” merely refers to the edge of the door which opens and closes and the inactive style refers generally to the hinged edge of the door. Although the active style  26  as depicted is of a design suitable for specific types of doors, it is within the scope of the invention to mount the door latch device  20  on any type of door having an active style as hereinafter described. 
     FIGS. 1 and 2 illustrate, in cross sectional views, an exemplary door latch device  20  which is used to engage and disengage the door  24  relative to the frame  26 . FIGS. 1 and 2 illustrate the door latch device in a condition where the latch  22  is extended and in FIG. 1 is illustrated as being engaged with the frame  26 . 
     The door latch device  20  is comprised of a plurality of individual components, each of which are shown in detail in isolated views in FIGS. 3-9. 
     FIG. 3 illustrates a housing  30  which is secured to the door style  28 , for example, by threaded fasteners extending into apertures  32  formed in an end wall  34  of the housing  30 . The housing preferably is formed in a U-shape with two side legs  36  and with the wall  34  forming the bight of the U. The two side legs are mirror images of each other and therefore only one of the side legs is shown in FIG.  3 . 
     The side legs are provided with four apertures for receiving pins. A first aperture  38  is in the form of a vertical slot and is located near a lower edge  40  and a free edge  42  of the housing  30 . A second aperture  44  is located above the first aperture and toward the bight wall  34 . The third aperture  46  is above the second aperture and is located adjacent to the free edge  42 . The fourth aperture  48  is located near a top edge  50  of the housing  30  and toward the bight side  34 . 
     FIG. 4 illustrates a fork  52  which also may be formed in a U-shape with two mirror image legs  54  and a lower bight wall  56  of the U. An adapter  58 , in the form of an internally threaded nut is captured on the bight wall  56  by an appropriate crimping operation. The fork  52  is received within the housing  30  and, as seen best in FIG. 2, a lower portion of the fork legs  60  is provided with sliding clearance within the side legs  36  of the housing. This portion of the fork legs includes an aperture  62  for receiving a pin that also extends through the slot  38  of the housing as described below. 
     Fork side leg  54  has an inward jog section  64  and a vertical upper section  66  spaced slightly inwardly of the side legs  36  of the housing as seen in FIG.  2 . In the upper section  66  of the leg  54 , there is provided a vertical slot  68  which receives a pin (described below) that also extends through aperture  44  in the housing. Near a top end  70  of the upper section  66  is a horizontal slot  72  to receive a pin to be described below. 
     FIG. 5 illustrates a rocker member  74  which has two legs  76  which are mirror shaped and may be connected by a bridge  78  extending between an upper end  80  of the two legs  76 . Alternatively, two separate rockers may be provided which have an inturned portion corresponding to the bridge  78 , which, however, do not extend across the full distance between the two separate rockers. An aperture  82  is provided near a lower end  83  of the rocker leg  76  for receiving a pin (described below) that also extends through aperture  44  in the housing and slot  68  in the fork. Near the upper end  80  of the rocker leg  76  is provided a generally horizontal slot  84  to receive a pin also extending through aperture  48  in the housing. Positioned below the slot is an aperture  86  to receive a rocker pin as described below. 
     FIG. 6 is a cross section illustrating the arrangement of the rocker  74  relative to the housing  30  and illustrating a pin  90  extending through the aperture  82  in the rocker and aperture  44  in the housing, as well as a pin  92  extending through the slot  84  in the rocker  74  and the aperture  48  in the housing. The rocker  74  is arranged to pivot about the pin  90  through a range constrained by the length of the slot  84  which receives the pin  92 . As illustrated, the rocker  74  is pivoted counter clockwise so that the pin  92  rests against a right hand edge  93  of the slot  84 . 
     FIG. 7 illustrates the placement of the fork  52  into assembly with the housing  30  and the rocker  74 . Here it is seen that the pin  90  is further received in the slot  68  of the fork  52  and that a pin  94  is received in the aperture  62  in the fork and also in the slot  38  of the housing  30 . The fork  52  can slide vertically within the housing, constrained by the dimension of the slot  68  and the slot  38 . As illustrated in FIG. 7, the fork  52  is slid upwardly to the greatest extent possible within the housing  30  such that the pin  90  rests on a bottom  95  of the slot  68  and the pin  94  engages a top  96  of the slot  38  of the housing. 
     FIG. 8 illustrates the latch  22  which has a first aperture  98  for pivotally receiving the pin  92  which extends through the housing  30  and the rocker  74 . A second aperture  100  is provided for receiving a pin described below. The latch  22  has a curved top portion  102  which extends the full width of the latch  22 . At an end of the leg  97  opposite the aperture  98  is a projection  104  which protrudes slightly beyond the curved portion  102 . 
     FIG. 9 illustrates one of two link members  106 . Each link member has a first aperture  108  near one end to receive a pin (described below) extending through the housing aperture  46 , a second aperture  110  near an opposite end to receive a pin (described below) extending through the slot  72  in the fork  52  and a third, central aperture  111  to receive a link pin as described below. 
     FIG. 10 illustrates the placement of the latch  22  and the link  106  onto the assembly of the housing  30 , the rocker  74  and the fork  52 . Here it is seen that the latch  22  is pivotally mounted on the pin  92  and is free to rotate about that pin. The link  106  is pivotally received on a pin  112  which is received in the aperture  46  of the housing  30 . The aperture  110  receives a pin  114  which is received in the slot  72  of the fork  52 . The link  106  is free to pivot about the pin  112  and is constrained only due to the connection of the link  106  to the fork  52  through the pin  114 , with the fork  52  being limited in its vertical motion by the pins  90  and  94  received in the slots  68  and  38  as described above. As illustrated, the link  106  is rotated about the pin  112  to its counter clockwisemost position since the fork  52  is in its uppermost position relative to the housing  30 . 
     The latch  22  is free to pivot about the pin  92  through an arc where at the clockwisemost position, the projection  104  will engage an inturned tab  116  on the housing  30  and, in a counter clockwisemost position, an edge  118  of the latch  22  will engage a pin  120  carried in the aperture  86  of the rocker  74 . As illustrated in FIG. 10, the latch  22  is in its clockwisemost (engaged) position. 
     FIG. 11 illustrates one of two identical rod members  126 . The rod member  126  has a first aperture  128  near a top end  130  which receives a latch pin (described below) carried in the latch aperture  100 . The rod member  126  has a vertical slot  132  positioned toward, but spaced above a bottom end  134  for receiving a pin (described below) carried in the aperture  111  of the link  106  as described below. The rod member  126  further has an aperture  136  near the bottom end  134 . 
     FIG. 12 illustrates a biasing member  140  which may be in the form of a coil spring. The coil spring has a first eye  142  for receiving the pin  94  which extends through the housing  30  and the fork  52 . An eye  144  is located at the opposite end of the biasing member  140  and is received in the aperture  136  in the rod member  126 . 
     FIG. 13 illustrates the further assembly of the rod member  126  and the biasing member  140  on to the assembly illustrated in FIG.  10 . Here it is seen that the biasing member  140  is captured at the lower end eye  142  by the pin  94  and at its upper end eye  144  by the aperture  136  in the rod  126 . The rod  126  is pivotally captured on a latch pin  150  which is received in the latch aperture  100 . A link pin  152  is received in the slot  132  of the rod member  126  and also extends into the aperture  111  of the link  106 . Thus, FIG. 13 illustrates the door latch mechanism  20 , and each of its component parts, in the latched position in which the latch  22  would be engaged with the door frame  26 . 
     The door latch mechanism  20  is moved to an unlatched position by operation of a panic bar or push bar  155  shown in FIG.  33  and described in U.S. Pat. No. 3,993,335 incorporated herein by reference which causes a threaded rod  156  (FIGS. 1 and 2) to move downwardly, the threaded rod  156  being threadingly engaged in the adapter  58 , thereby causing the fork  52  to move downwardly relative to the housing  30 . This downward movement of the fork  52  carries the pin  94  downwardly, as well as the pin  114 , thereby pulling the biasing member  140  downwardly and rotating the link  106  in a clockwise direction about the pin  112 . This pivotal movement of the link  106  and the downward force provided by the biasing member  140  moves the rod member  126  downwardly, thereby causing the latch  22  to pivot about the pin  92  in a counter clockwise direction until the edge  118  of the latch engages the rocker pin  120 . The engagement of the edge  118  with the rocker pin  120  will cause the rocker  74  to pivot about the pin  90  in a clockwise direction, thus resulting in the bridge  78  protruding beyond an inner face  160  of the door  28 . This resulting condition of the latch mechanism is illustrated in FIG.  14 . 
     When the pressure on the panic bar is released, there no longer is a downward force being exerted by the threaded rod  156 , and therefore the biasing member  140  exerts an upward force on the pin  94  to move the fork  52  upwardly relative to the housing  30 . However, the projection  104  of the latch  22  engages the links  106  in an over center condition preventing clockwise rotation of the latch  22  and thereby stopping the upward movement of the fork  52  due to the rod member  126  and its connection to the latch at pin  150  and the link  106  connection at the pin  114  to the fork  52 . The slots  68  in the fork  52  and  38  in the housing  30  allow for lost motion to occur, permitting a slight upward movement of the fork  52  relative to the housing  30  before the projection  104  engages the links  106 . 
     FIG. 15 illustrates the engagement of the latch  22  with the links  106 , with visibility blocking components removed. In this manner, the latch  22  will be retained in its unlatched position while the door remains open, even though pressure has been released on the panic bar. 
     When the door  24  returns to its closed position relative to the door frame  26 , the bridge  78 , which is now projecting beyond the face  160  of the door, will engage the door frame  26  and will cause the rocker  74  to pivot about the pin  90 , causing the rocker pin  120  to press against the edge  116  of the latch  22  until the projection  104  moves past “dead center” on the links  106 , which will then release the restraint preventing the biasing member  140  from pulling upwardly on the pin  94 . With this restraint released, pin  94  will be drawn upwardly, thereby carrying the fork  52  upwardly and pivoting the links  106  about the pin  112 , the upward movement of the pin  114  thereby carrying the rod member  126  upwardly, causing the latch  22  to pivot about the pin  92  through the connection of the rod member  126  at the pin  150  to the latch member  22 . The end result of this movement will be a return to the latched condition as illustrated in FIG.  1 . Therefore, it is seen that the door latch mechanism of the present invention utilizes a lost motion arrangement in order to trap the latch  22  against returning to the latched position upon a release of the panic push bar. Also, the present invention utilizes the concept of rotating the latch  22  beyond a top dead center relative to the links  106  to trap the latch  22  against returning to the latched position upon release of the panic exit bar. 
     The present invention utilizes a frame sensor, in the form of the rocker  74  with its rocker pin  120 , to reactivate the latch  22  and move it back to the latched position by pushing the latch  22  over the top dead center position relative to the link  106 . 
     The present invention does not require a separate striker plate or trip mechanism mounted on the door frame in order to reactivate the latch mechanism. 
     Although the invention is illustrated in FIGS. 1 and 2 as being located within a metal door, it can also be utilized in other doors, for example, wood doors. In such an arrangement it may be necessary to utilize an additional plate  161  mounted at the top of the door to protect the relatively soft material of the door frame. The plate  161  is shown in place in FIG.  16  and in an isolated view in FIG. 32, where it is seen that it has a large central aperture  162  to allow the latch  22  to extend through the plate into the latching position and its also includes several apertures  164  for receiving fasteners to secure the plate  161  to the door  24 . A tab  166  may be provided to prevent damage to the door frame  26  when the bridge  78  of the rocker  74  engages the door frame  26 . The tabs  166  is positioned a set distance from aperture  162  in order that free play is minimized between the door and frame when the latch is engaged. 
     An alternative embodiment of the present invention is shown in FIGS. 17-34 which includes a door latch device  220  embodying the principles of the present invention. 
     As discussed above, the present invention provides a structure and method to maintain a door latch  222  in a disengaged position until a door  224  which it is mounted on has completely closed. The door latch device  220  of the present invention efficiently and safely retracts and extends the door latch  222  during the opening and closing of the door  224  relative to a door frame  226 . 
     The door latch device  220  of this embodiment is to be mounted on the door  224  which has an active style  228  and an inactive style (not shown), it being understood that the term “active style” merely refers to the edge of the door which opens and closes and the inactive style refers generally to the hinged edge of the door. Although the active style  226  as depicted is of a design suitable for specific types of doors, it is within the scope of the invention to mount the door latch device  220  on any type of door having an active style as hereinafter described. 
     FIGS. 17 and 18 illustrate, in cross sectional views, an exemplary door latch device  220  which is used to engage and disengage the door  224  relative to the frame  226 . FIGS. 17 and 18 illustrate the door latch device  220  in a condition where the latch  222  is extended and in FIG. 17 is illustrated as being engaged with the frame  226 . 
     The door latch device  220  is comprised of a plurality of individual components, each of which are shown in detail in isolated views in FIGS. 19-28. 
     FIG. 19 illustrates a housing  230  which is secured to the door style  228 , for example, by threaded fasteners extending into apertures  232  formed in an end wall  234  of the housing  230 . The housing preferably is formed in a U-shape with two side legs  236  and with the wall  234  forming the bight of the U. The two side legs are mirror images of each other and therefore only one of the side legs is shown in FIG.  19 . 
     The side legs  236  are provided with four apertures for receiving pins. A first aperture  238  is in the form of a vertical slot and is located near a lower edge  240  and a free edge  242  of the housing  230 . A second aperture  244  is located above the first aperture and toward the bight wall  234  and is also in the form of a vertical slot. The third aperture  246  is above the second aperture and is located adjacent to the bight wall  234 . The fourth aperture  248  is located near a top edge  250  of the housing  230  and toward the bight wall  234 . 
     FIG. 20 illustrates a fork  252  which also may be formed in a U-shape with two mirror image legs  254  and a lower bight wall  256  of the U. An adapter  258 , in the form of an internally threaded nut is captured on the bight wall  256  by an appropriate crimping operation. The fork  252  is received within the housing  230  and, as seen best in FIG. 18, the fork legs  254  are provided with sliding clearance within the side legs  236  of the housing  230 . The fork legs  254  include an aperture  262  for receiving a pin that also extends through the slot  238  of the housing  230  as described below. 
     In an upper section of the legs  254 , there is provided an aperture  268  which receives a pin (described below) that also extends through aperture  244  in the housing. Near a top end  270  of the legs  254  is a horizontal slot  272  to receive a pin to be described below. 
     FIG. 21 illustrates a rocker member  274  which has two legs  276  which are mirror shaped and may be connected by a bridge  278  extending between an upper end  280  of the two legs  276 . Alternatively, two separate rockers may be provided which have an inturned portion corresponding to the bridge  278 , which, however, do not extend across the full distance between the two separate rockers. An aperture  282  is provided near a lower end  283  of the rocker leg  276  for receiving a pin (described below) that also extends through hole  246  in the housing  230 . Near the upper end  280  of the rocker leg  276  is provided a generally horizontal slot  284  to receive a pin also extending through aperture  248  in the housing. Positioned below the slot is an aperture  286  to receive a rocker pin as described below. 
     FIG. 22 is a cross section illustrating the arrangement of the rocker  274  relative to the housing  230  and illustrating a pin  290  extending through the aperture  282  in the rocker and aperture  246  in the housing, as well as a pin  292  extending through the slot  284  in the rocker  274  and the aperture  248  in the housing. The rocker  274  is arranged to pivot about the pin  290  through a range constrained by the length of the slot  284  which receives the pin  292 . As illustrated, the rocker  274  is pivoted counter clockwise so that the pin  292  rests against a right hand edge  293  of the slot  284 . 
     FIG. 23 illustrates the placement of the fork  252  into assembly with the housing  230  and the rocker  274 . Here it is seen that a pin  293  is received in the aperture  268  of the fork  52  and also in the slot  244  of the housing  230 . A pin  294  is received in the aperture  262  in the fork and also in the slot  238  of the housing  230 . The fork  252  can slide vertically within the housing, constrained by the dimension of the slot  244  and the slot  238 . As illustrated in FIG. 23, the fork  252  is slid upwardly to the greatest extent possible within the housing  230  such that the pin  293  rests on a top of the slot  244  and the pin  294  engages a top of the slot  238  of the housing. 
     FIG. 24 illustrates the latch  222  which has a first aperture  298  for pivotally receiving the pin  292  which extends through the housing  230  and the rocker  274 . A second aperture  300  is provided for receiving a pin described below. The latch  222  has a curved top portion  302  which extends the full width of the latch  222 . At an end of a leg  303  opposite the aperture  298  is a projection  304  which protrudes slightly beyond the curved portion  302 . 
     FIG. 25 illustrates one of two link members  306 . Each link member has a first aperture  308  near one end to receive a pin (described below) extending through the housing aperture  246 , a second aperture  310  near an opposite end to receive a pin (described below) extending through the slot  272  in the fork  252  and a third, central aperture  311  to receive a link pin as described below. The link members  306  also include a projection  313  formed on one edge between the apertures  308  and  310 . 
     FIG. 26 illustrates the placement of the latch  222  and the link  306  onto the assembly of the housing  230 , the rocker  274  and the fork  252 . Here it is seen that the latch  222  is pivotally mounted on the pin  292  and is free to rotate about that pin. The link  306 , via aperture  308 , is pivotally received on the pin  290  about which the rocker pivots. The aperture  310  receives a pin  312  which is received in the slot  272  of the fork  252 . The link  306  is free to pivot about the pin  290  and is constrained only due to the connection of the link  306  to the fork  252  through the pin  312 , with the fork  252  being limited in its vertical motion by the pins  293  and  294  received in the slots  244  and  238  as described above. As illustrated, the link  306  is rotated about the pin  290  to its clockwisemost position since the fork  252  is in its uppermost position relative to the housing  230 . 
     The latch  222  is free to pivot about the pin  292  through an arc where at the clockwisemost position, the projection  304  will engage an inturned tab  316  on the housing  230  and, in a counter clockwisemost position, an edge  318  of the latch  222  will engage a pin  320  carried in the aperture  286  of the rocker  274 . As illustrated in FIG. 26, the latch  222  is in its clockwisemost position. 
     FIG. 27 illustrates one of two identical rod members  326 . The rod member  326  has a first aperture  328  near a top end  330  which receives a latch pin (described below) carried in the latch aperture  300 . The rod member  326  has a vertical slot  332  positioned toward, but spaced above a bottom end  334  for receiving a pin (described below) carried in the aperture  311  of the link  306  as described below. The rod member  326  further has an aperture  336  near the bottom end  334 . 
     FIG. 28 illustrates a biasing member  340  which may be in the form of a coil spring. The coil spring has a first eye  342  for receiving the pin  294  which extends through the housing  230  and the fork  252 . An eye  344  is located at the opposite end of the biasing member  340  and is received in the aperture  336  in the rod member  326 . 
     FIG. 29 illustrates the further assembly of the rod member  326  and the biasing member  340  onto the assembly illustrated in FIG.  26 . Here it is seen that the biasing member  340  is captured at the lower end eye  342  by the pin  294  and at its upper end eye  344  by the aperture  336  in the rod  326 . The rod  326  is pivotally captured on a latch pin  350  which is received in the latch aperture  300 . A link pin  352  is received in the slot  332  of the rod member  326  and also extends into the aperture  311  of the link  306 . Thus, FIG. 29 illustrates the door latch mechanism  220 , and each of its component parts, in the latched position in which the latch  222  would be engaged with the door frame  226 . 
     The door latch mechanism  220  is moved to an unlatched position by operation of a panic bar or push bar (not illustrated, but which is shown and described in U.S. Pat. No. 3,993,335 incorporated herein by reference) which causes a threaded rod  356  (FIGS. 17 and 18) to move downwardly, the threaded rod  356  being threadingly engaged in the adapter  258 , thereby causing the fork  252  to move downwardly relative to the housing  230 . This downward movement of the fork  252  carries the pin  294  downwardly, as well as the pin  312 , thereby pulling the biasing member  340  downwardly and rotating the link  306  in a counterclockwise direction about the pin  290 . This pivotal movement of the link  306  and the downward force provided by the biasing member  340  moves the rod member  326  downwardly, thereby causing the latch  222  to pivot about the pin  292  in a counter clockwise direction until the edge  318  of the latch engages the rocker pin  320 . The engagement of the edge  318  with the rocker pin  320  will cause the rocker  274  to pivot about the pin  290  in a clockwise direction, thus resulting in the bridge  278  protruding beyond an inner face  360  of the door  228 . This resulting condition of the latch mechanism is illustrated in FIG.  30 . 
     When the pressure on the panic bar is released, there no longer is a downward force being exerted by the threaded rod  356 , and therefore the biasing member  340  exerts an upward force on the pin  294  to move the fork  252  upwardly relative to the housing  230 . However, the projection  304  of the latch  222  engages the projections  313  on the links  306  in an over center condition preventing clockwise rotation of the latch  222  and thereby stopping the upward movement of the fork  252  due to the rod member  326  and its connection to the latch at pin  350  and the link  306  connection at the pin  312  to the fork  252 . The slots  244  and  238  in the housing  230  allow for lost motion to occur, permitting a slight upward movement of the fork  252  relative to the housing  230  before the projection  304  engages the links  306 . 
     FIG. 31 illustrates the engagement of the latch  222  with the links  306 , with visibility blocking components removed. In this manner, the latch  222  will be retained in its unlatched position while the door remains open, even though pressure has been released on the panic bar. 
     When the door  224  returns to its closed position relative to the door frame  226 , the bridge  278 , which is now projecting beyond the face  360  of the door, will engage the door frame  226  and will cause the rocker  274  to pivot about the pin  290 , causing the rocker pin  320  to press against the edge  316  of the latch  222  until the latch projection  304  moves past “dead center” on the links  306  and out of engagement with the projections  313  on the links  306 , which will then release the restraint preventing the biasing member  340  from pulling upwardly on the pin  294 . With this restraint released, pin  294  will be drawn upwardly, thereby carrying the fork  252  upwardly and pivoting the links  306  about the pin  290 , the upward movement of the pin  352  thereby carrying the rod member  326  upwardly, causing the latch  222  to pivot about the pin  292  through the connection of the rod member  326  at the pin  350  to the latch member  222 . The end result of this movement will be a return to the latched condition as illustrated in FIG.  17 . Therefore, it is seen that the door latch mechanism of the present invention utilizes a lost motion arrangement in order to trap the latch  222  against returning to the latched position upon a release of the panic push bar. Also, the present invention utilizes the concept of rotating the latch  222  beyond a top dead center relative to the links  306  to trap the latch  222  against returning to the latched position upon release of the panic exit bar. 
     In this embodiment, the present invention utilizes a frame sensor, in the form of the rocker  274  with its rocker pin  320 , to reactivate the latch  222  and move it back to the latched position by pushing the latch  222  over the top dead center position relative to the link  306 . 
     The present invention does not require a separate striker plate or trip mechanism mounted on the door frame in order to reactivate the latch mechanism. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.