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FIELD OF THE INVENTION 
     This invention relates to the field of consumer and industrial fixtures designed for operating doors. A push-pull type door latch allows an individual to unlatch a door from either side. A push type door assembly permits conveying a signal activating or de-activating a functional apparatus on the opposite side of a door. The invention makes it possible to adjust the height and vary the position of the door fixtures without penetrating the body of the door itself, which has wide-spread applications in both consumer use and industrial contexts such as nursing homes, hospitals, and manufacturing plants. 
     BACKGROUND OF THE INVENTION 
     Most bi-functional door latches have handles on either side of the door, a latching mechanism consisting of a bolt contained in a cavity that can alternately be extended into or retracted from an aligned orifice in the door jamb, and an opening in the door beneath the handle position communicating with the bolt cavity. Conventional door latches operate by simultaneous turning of a door knob in either direction to retract the bolt, and pushing or pulling to open the door. In push-pull type latches a push on the handle from the inside of the door and a pull on the handle from the outside of the door releases the bolt and opens the door in one continuous motion. Typically, the door opening between the handles contains a mechanism which translates the turning motion of the knob or the push-pull force on the handle into horizontal action to retract the bolt. 
     U.S. Pat. Nos. 6,293,598 and 7,258,374 disclose a push-pull type latch in which motion of the handle is translated to the bolt by a cam configured to engage a planar surface of the handle. Deflection of the handle is restricted by a stop, which is said to reduce wear on the moving components of the latch. The handle is under spring-loaded pressure so that when a pushed handle is released, the handle returns to its original position. Similarly, U.S. Pat. No. 4,629,228 discloses a complicated internal latch mechanism for displacing a bolt, utilizing a rotating cam responsive to deflection of the handle, and translated to the bolt by engagement of a driver tab on a slide member. U.S. Pat. Nos. 6,196,599, 5,085,474, and 4,003,593 describe further embodiments of push-pull type latches that utilize rotational components, such as a crank or cam internal to the door to translate push-pull vertical motion into horizontal movement of the bolt. 
     The afore-mentioned background art represent devices with several features in common, distinguishable from the present invention. These inventions all utilize mechanically sophisticated mechanisms internal to the door having moving parts to translate push-pull force on the handle to horizontal displacement of the bolt. This necessitates providing two holes in the door itself, one through the door to accommodate access of the handles to the motion translation mechanisms, and other hole to retain the bolt situated at a right angle to the first and communicating therewith. A second common feature is a requirement that the latch on either side of the door must be in the same corresponding geometric plane position on the door. Finally, these holes must be made very precisely in order to assure proper alignment of the latch components, so that installation thereof is not trivial or routinely performable by the end user. 
     SUMMARY OF THE INVENTION 
     Push-pull type door latches have an advantage over other convention door opening mechanisms in that opening is effected by a single continuous motion. This feature has particular efficacy in situations, as in food handling facilities or hospitals, where a person is carrying an object occupying both hands. Such person entering a space with an inward opening door need only press on the latch handle with a wrist, elbow, or shoulder to gain entry. A disadvantage to conventional push-pull latches is that the position of the handles is predetermined by the place in the door where the access holes are bored. Repositioning the latch members necessitates reboring the holes, and constrains the position of the latch on either side of the door to the same position. 
     It is therefore an objective of the present invention to provide flexibility in the positioning of the latch handles, and to allow latches on either side of a door to be asymmetrically situated with respect to both horizontal and vertical dimensions. 
     It is a further objective to mount a door latch without penetrating the body of the door itself, thus permitting readjustment of the position of the latch handles at will. This feature also provides for ease of installation without professional intervention. In a still further objective, the novel latch permits control of a functional apparatus mounted on one side of a door from the opposite side. 
     According to the present invention, a universal push-pull type door latch is adapted for securing a door in secured closed position within a door casing. The door has a front opening side and a back side surface which abbuts a doorjamb on its closing edge. The edged surface conventionally closes within the door casing. The latch has a substantially horizontal mounting bracket with a base portion mounted on each side of the door, and an upper and lower flange portion extending horizontally and perpendicularly to the base portion. The flanges have bores aligned to receive one or a plurality of pivot pins. The door latch has a master pull handle and a slave push handle. The master pull handle, having an inner and an outer surface, comprises a substantially triangular portion and a gripping portion extending in a direction towards the door cases. A bushing to accommodate a pivot pin is positioned in the triangular corner of the handle at the corner proximate to the door edge surface. The handle is sized to fit within the flanges of the mounting bracket, and is secured in place by the pivot pin passing through the bushing and the aligned bracket bores. This provides an axis of rotation for the handle, which moves through an arc as the master handle is pulled forward. Protruding from the outer surface of the master handle triangular portion is a pawl engageable with grooves in a strike plate mounted on the casing or doorjamb in secured closed position. A torsion spring is disposed in the handle to urge pressure to the pawl in the strike plate groove. 
     On the opposite, back side of the door a mounting bracket is placed at any desired location. A slave push handle which may be identical in design to the master handle is mounted through its bushing and aligned bracket bores, only in opposite configuration from the master handle with the gripping portion extending in a direction away from the door casing. The slave handle thus rotates about an axis of rotation on the inner side of the substantially triangular portion of the handle. 
     A two ended flexible motion transfer belt is disposed between the master and salve handles circumscribing the edged door surface and anchored at one end on the outer surface of the master pull handle triangular portion and at the other end anchored on the inner surface of the slave handle to provide mechanical advantage to remotely disengage the paul from the strike plate groove when the slave push handle is inwardly deflected. On the master handle side of the door, the pawl is disengaged from the strike plate groove when the handle to which is attached is outwardly deflected. 
     The push-lull latch of the present invention is readily adapted to incorporate a locking assembly which disables the push handle by creating slack in the motion transfer belt. In locking mode, the distance of travel of the slave handle is too short to translate its motion to the master handle. The locking assembly has a rotatable idler arm bearing a substantially vertical slot. It is secured to the mounting bracket by a pivot pin passing through a bushing mounted thereon on the opposite end of the mounting bracket from which the master handle is mounted The idler arm bushing is aligned with bores in the upper and lower bracket flanges on the opening side of a door to provide an axis of rotation. The upper or lower bracket flange has a beveled locking tab projecting vertically, so that the motion transfer belt passing through the idler arm slot, disposed between the master and slave handles is tautened sufficiently for motion transfer to occur when the idler arm is in locking engagement with the flange locking tab. Sufficient space is designed between the tab and the base portion of the mounting bracket to allow interposition of the idler arm. There is enough space between the pin and bushing of the idler arm to permit traverse of the idler arm lower edge over the beveled tab. 
     The principles of the present invention may be generally applied to situations in which its is desirable to convey mechanical advantage from the back side surface of a door abutting a doorjamb on its closing edge to the opening side front surface. Such a push-type door assembly has a spring loaded push pedal having an inner and outer surface and comprising a functionally triangular portion mounted in a bracket by mounting means. This portion of the pedal has a bushing at its inner leg to accommodate a pivot pin at the distal triangular corner of the triangular portion from the door edge to provide an axis of rotation for the pedal. A functional apparatus, such as a bell, light, or other appliance capable of activation or inactivation by lateral force is mounted on the opening side surface of the door. Communication between pedal and the functional apparatus is effected by a two ended flexible motion transfer belt disposed between the inner surface of the pedal, circumscribing the door edge, and attached to a switch or motion arm, capable of responding to deflection of the pedal transmitted through the motion transfer belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective partially exploded drawing of a push-pull door latch as viewed from the edge of a door. 
       FIGS.  2 A and  2 B.are perspective views of the locking assembly in locked position ( 2 A) and closed position ( 2 B). 
         FIG. 3  is a perspective view of the pull handle showing engagement of the pawl in the strike plate. 
         FIG. 4  is a perspective view of the pull side of the latch having a cover plate for disguising a previously drilled door hole. 
         FIG. 5  is a perspective view of the push side of the latch featuring a housing. 
         FIG. 6  shows one side of the latch assembly with an interchangeable ornamental accessory for the handle. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The push-pull door latch of the present invention allows easy installation on a new or existing door, and eliminates the internal mechanism in conventional latches that converts the push or pull motion of the handles into horizontal movement for engagement and disengagement of a bolt in a door casing oriface.  FIG. 1  shows a door  10  having a front opening side  12  and an edge  14 . The components for the pull side are shown on the left  100  and those for the push side are shown on the right  200 . The pull latch includes a mounting bracket  102  consisting of a base portion  104 , an upper flange portion  106 , and lower flange portion  108 . Both flange portions have bores  118  aligned in upper and lower registration to receive one or a plurality of pivot pins  120 . The mounting bracket  102  is may be mounted horizontally, but does not require precise leveling. This embodiment is shown with a mounting bracket tab  122  with a slot  124  through which a mounting screw  126  can be inserted and tightened to secure the bracket  102 . However, mounting the bracket  102  by mechanical means is optional. Preferably an adhesive or double sided adhesive tape is used instead to secure the bracket  102  without making screw holes. 
     The master pull handle  116 , having an inner and an outer surface, comprises a generally triangular portion  112  having and a gripping portion  110 . In the corner closest to the door casing (not shown) is a bushing  114  aligned to receive a pivot pin  120 . When assembled, the pull handle  116  fits between the upper flange portion  106  and the lower flange portion  108  of the mounting bracket  102 , and the pivot pin  102  is inserted through the pivot bore  130 , the bushing  114 , and the lower pivot bore  132 . Preferably the pivot pins have heads larger than the pivot bores so they are held in place by gravity. The master pull handle  116  has a pawl  128  protruding from it which engages a vertical groove in a strike plate embedded in the door casing. Parenthetically referring to  FIG. 3 , this top view shows the pawl  128  engaged in a groove  402  of the strike plate  400  embedded in a doorjamb  16 . Preferably, the strike plate  16  is embedded so that its outer surface is flush with the door jamb  16 . To maintain the pawl  128  in its groove, a torsion spring  146  urges a constant pressure against the master handle  116  outer surface using its free prong as leverage against the mounting bracket base portion  104 . The torsion spring  146  is positioned in alignment with the flange bores  130  and  132 , and circles the pivot pin  120 . 
     Referring to the right side of  FIG. 1   200 , the components of the slave handle side are illustrated. The push slave handle  216  is identical to the master pull handle  116  but is assembled in a  180  degree rotational position, and has a slot  218  in the triangular leg of the slave handle  216  facing the door. The mounting bracket  202  is identical to the mounting bracket  102 . When assembled the bushing  214  will be aligned with the flange bore  230  of the mounting bracket  202  and be secured at the fulcrum of the triangular handle portion  216  by a pivot pin  220 . 
       FIG. 1  also partly illustrates the configuration of some components of an optional locking assembly with respect to the overall latch assembly. The locking feature utilizes a rotatable idler arm body  134  having a bushing  138 , and a slot  136 . The idler arm body  134  is assembled as for the handles by aligning the arm body  134  with the upper  118  and lower flange bores (not visible in this view) and inserting a pivot pin  140 . 
     A key feature of the present invention is the means for releasing the pawl  128  from the strike plate groove, as more fully described hereafter. On the master pull side  100  the pawl release occurs directly when the master handle  116  is pulled because the pawl  128  is attached to it. On the push side  200  release of the pawl  128  is obtained through a flexible motion transfer belt  300  which extends from the inside surface of the slave handle triangular portion  112  through a slot  218 , then around the edge of the door and terminates on the outer side of the master handle  116 . When the slave handle is pushed, motion is transferred via the motion transfer belt  300  to create a pulling action on the master handle  116 , thereby releasing the pawl  128  remotely. If the latch assembly is equipped with a locking assembly, partly described above, the motion transfer belt  300  also passes through a slot  136  in the idler arm  134 . Referring to the “triangular” aspect of the master and slave handles, this means only that the motion transfer belt  300  is placed at its ends at points on the handles where a mechanical advantage is obtained. Since mechanical advantage is exerted to cause movement through an arc about an axis of rotation at the pivot pin, thus defining a functional triangulation, the handles are characterized as “triangular”. Even though the actual shape of the handles is depicted as triangular, there is no absolute requirement for this, so long as functional triangularity is embodied in the device. 
     It will be apparent to those skilled in the art that the motion transfer belt permits provides substantial flexibility by eliminating fixed position holes in the door. Thus, there is versatility in placing either side of the latch in virtually any horizontal or vertical position on the door. Each latch half can be at a different height and distance from the door edge 
     The motion belt  300  may be any thin flexible tape, belt, wire, cable, or fabric capable of overcoming the friction generated at the door edge during motion transfer. Experiments have shown that this means of remotely operating the master handle  116  from the push side  200  has universal efficacy with conventional doors. The door itself and the door casing are parallel when the door is closed. As the door opens, the angle between the door edge and the casing changes and requires more space between the door edge and the door to clear the casing. If the fit of the door to its casing is tight enough to cause binding of the motion transfer belt, it is too tight for the door to open at all. 
     Referring again to the locking assembly of the present invention,  FIGS. 2A and 2B  illustrate the operation of the locking function in its closed and open positions respectively. In closed position, the latch assembly is unlocked; in the open position, the latch assembly is locked, in the sense that the slave push handle is disabled.  FIG. 2A  shows the closed (unlocked) configuration of parts. The rotatable idler arm  134  fits between the upper  106  and lower  108  flanges of the mounting bracket  102  of the master handle assembly  100 , and secured by a pivot pin (not shown) passing through a pivot bore  118 , the bushing  118  (shown in dotted line relief), and a pivot port on the lower flange  108 .(not shown). To achieve the closed position, the idler arm  134  is rotated past a beveled locking tab  142  projecting vertically from the lower flange  108 . The space between the beveled locking tab  142  and the base portion  104  of the mounting bracket  102  is sufficient to accommodate the thickness of the idler arm  134 . The directionality of the bevel is upwards from the outer portion of the lower or upper flanges  106  and  108 . Although shown in  FIG. 2A  as placed on the lower flange  108 , the locking tab  142  may be on either the upper or lower such flange. 
       FIG. 2B  illustrates the locking assembly in the open position. The idler arm  134  is rotated so that it is positioned in front of and distal to the locking tab  142  (shown in dotted line relief). This loosens the motion transfer belt  300  creating a slack, so that when the slave handle is pushed, release of the pawl is disabled, thereby locking out access from the slave handle side  200  of the latch assembly. 
       FIG. 4  shows the latch of the present invention with an oval underplate  148 . This component may take any decorative shape and size, and is intended to disguise a pre-existing hole in a door being converted to the present latch assembly. It&#39;s sole function is to create a more aesthetic presentation of the latch in a door previously fitted with a conventional latch or door knob.  FIG. 5  illustrates a housing  150  which is an enclosure that fits over and substantially covers the latch mechanism, leaving holes  152  in the side-panels  154  to permit access to the handles and the motion transfer belt  300 .  FIG. 6  illustrates an example of a decorative handle cover  156 . The example shown is somewhat ornate, but many styles may be adopted to appeal to individual user&#39;s tastes. The curvature and length of the handle cover  156  is made to conform to the contours of the handle body on the side facing the user. To ensure that it remains in place without bolts, screws, or other fasteners, the handle cover  156  preferably has a lip  160  at the end of the handle, and a second lip  158  engaging the first curved portion of the handle.

Summary:
A push-pull type door latch opens a door by applying direct mechanical force on the pull side, and by remote action on the push side through conveying a force through a motion transfer belt that connects the two handles. The latch involves no access holes in the door so each handle may be situated at offset positions with respect to each other.