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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     This invention relates to a mechanism for limiting the travel of a hinged window in a frame, and in particular to an assembly that is releasably and securely fastened to the window and the frame. 
     BACKGROUND OF THE INVENTION 
     A common type of window includes a rectangular frame set into a building wall and a corresponding vent connected to the frame by a hinge assembly. The hinge assembly can be oriented so that the vent can pivot about either a horizontal or a vertical axis. Thus, the vent can be opened by pivoting inward and downward about a horizontal axis. Various means are available for securing the vent at a selectable angle to make the opening larger or smaller. It is often desirable to limit the size of the opening; for example, the window might be located in a school, where it is clearly preferable that the opening not be large enough to permit unauthorized, unintended or accidental entry or exit. Prior hinge assemblies include limit mechanisms, to preclude the vent being opened wider than a desired limit. 
     However, it is also desirable that the vent occasionally be opened wider than the selected limit to permit the window to be cleaned or otherwise maintained from inside the building. Traditionally, the opening of the vent beyond the limited range required dismantling the hinge assembly in both the disassembly and reassembly of the hinge, which can involve an excessive amount of time and labor. 
     Therefore, a need exists to provide a mechanism, which normally limits the opening of the vent but also allows selective opening of the vent beyond a limited range. There is also a need to restrict the selective opening of the vent beyond the predetermined limit. 
     SUMMARY OF THE INVENTION 
     The present invention provides a detachable arm limiting assembly for setting a predetermined operating opening of the vent, and allowing selective maximum opening of the vent. Preferably, the detachable arm limiting assembly can be selectively actuated to permit a full range of motion for the vent. 
     The detachable arm limiting assembly includes a mounting bracket secured to a window frame, a slide assembly secured to a vent and an arm pivotally connected to the slide assembly. The arm is a pivotally attached to a locking plate, which is removably attachable to the mounting bracket. One of the locking plate and the arm includes a loading pin. The mounting bracket has a keyway sized to receive the loading pin. The locking plate has a keyway for receiving a fastening interconnecting the locking plate and the mounting bracket. When the locking plate is in a first position, the keyways can accept the corresponding loading pin and fastener. The keyways are configured to then allow the locking plate to be moved to a second engaged position relative to the mounting plate. The fastener can be actuated, thus securing together the locking plate and the mounting bracket. The slide assembly has an adjustable stop to limit the travel of the arm relative to the vent. 
     When the locking plate is secured to the mounting bracket, the degree to which the vent can be opened is limited. However, all that is required to allow the vent to be fully opened for cleaning or other maintenance is the loosening of the fastener, which allows the locking plate and the mounting plate to be moved from the second engaged position, to the first position, thus allowing ready disengagement of the arm from the mounting bracket. The present assembly has the advantage that while it is normally impractical to open of the vent beyond a selected limit, upon releasing the fastener the vent can quickly and easily be opened beyond this limit by a person having the appropriate tool for loosening the fastener. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general perspective view of a detachable arm assembly, having a mounting bracket, a locking plate and an arm for limiting the opening of a window. 
         FIG. 2  is a perspective view of the window set in a building wall. 
         FIG. 3  is a perspective view showing the bracket affixed to a window frame. 
         FIGS. 4 and 5  show side views of the assembly as attached to the window frame and to a window vent, respectively. 
         FIG. 6  is a perspective view of the bracket. 
         FIG. 7  is a perspective view of the bracket as attached to the window frame. 
         FIG. 8  is a perspective view of a fastener, which engages the bracket. 
         FIGS. 9 and 10  are perspective views of the locking plate observed from opposed directions. 
         FIG. 11  is a perspective view of a loading pin of the assembly. 
         FIG. 12  shows partial cross-sections of the arm and the locking bracket and the engagement of the loading pin therewith. 
         FIG. 13  is a front view showing the engagement of the arm and a slide. 
         FIG. 14  is an end view showing the engagement of the arm and slide. 
         FIG. 15  is a front view showing the engagement of the locking plate and the bracket. 
         FIGS. 16 ,  17  and  18  are side views showing successive steps in the engagement of elements of the assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings,  FIGS. 1 and 2  show a preferred embodiment of a detachable arm limiting assembly  100 , which is used to limit the opening of a window  200 . The window moves relative to a frame  202  which is normally set into a building wall  210 . The window is connected to a vent  204 . The assembly  100  restricts the travel of the vent  204  relative to the frame  202 . The vent  204  is typically rectangular in shape and engages the frame  202  through a conventional hinge mechanism such as a 4 bar hinge  206 . The hinge  206  provides that the vent  204  can pivot about a horizontal axis. As indicated in  FIG. 2 , the vent is disposed so that it opens downward into the building. However, it is understood the axis about which the vent rotates can be horizontal, vertical or an intermediate orientation. 
       FIGS. 4 and 5  show the general disposition of the assembly  100  with the frame  202  and vent  204 .  FIG. 4  shows the attachment of the assembly  100  and the hinge mechanism  206  to the frame  202 , while  FIG. 5  shows the attachment to the vent  204 . 
     The assembly  100  includes a mounting bracket  110 , a locking plate  140  and an arm  170 . The mounting bracket  110  has fastening portions such as ends  112  and a coupling portion such as mid-portion  114 . Though not required, the coupling portion is disposed in a plane spaced from the fastening portion. As seen in  FIG. 5 , each end portion  112  has an attachment hole  116 , which can accept an attachment means  118  for securing the mounting bracket to the frame  202 . The attachment means  118  is typically a threaded fastener such as a screw or a bolt or rivet. The mid-portion  114  has a threaded aperture  128  and a first keyway  130 . The threaded aperture  128  accepts a fastener which is typically a screw  120  with a screw head  122  configured to receive a corresponding tool for adjusting its position. Preferably, the screw  120  is a security type fastener capable of being driven by only a select driver configuration. 
     A preferred configuration of the screw head  122  is shown in FIG.  7 . The head  122  has a hexagonal hole  124  with a central pin  126 , which precludes the screw from being adjusted with a conventional Allen wrench, regular or Phillips screw driver. A less conventional hexagonal tool is required, which corresponds with the hexagonal hole but has an opening to accept the pin  126 . Such a tool is unlikely to be carried by an unauthorized person. Therefore, as will be understood later, an unauthorized person would be most unlikely to be able to enter or exit the window  200  either by accident or intentionally. 
     Although the screw  120  can be removably attached to the threaded aperture  128 , for convenience the screw is preferably swaged to be permanently attached to the mounting bracket  110 , while retaining a desired degree of adjustability between a release position and a locking position. 
     In the normal vertical orientation of the mounting bracket  110  on the frame  202 , the keyway  130  is below the threaded aperture  128 . As evident from  FIGS. 5 and 6 , the mounting bracket  110  is configured so that when the mounting bracket is attached to the frame  202 , a space remains between the mid-portion  114  and the frame  202 . The keyway  130  has a bulbous section  132  and slot section  134  extending downward from the bulbous section  132 . 
     The locking plate  140  ( FIGS. 8 and 9 ) is generally step-shaped, having a frame-proximate portion  142  and a vent-proximate portion  144 . In the intended, generally vertical, orientation of the locking plate  140 , the frame-proximate portion  142  is uppermost and has a second keyway  150 . The vent-proximate portion  144  has an aperture  156  for a loading pin  160 . The second keyway  150  has a bulbous section  152  and a narrower slot section  154  extending upward from the wide portion  152 . Bounding the slot section  154  is a generally circular recess or shoulder  158  sized to approximately the same diameter as the screw head. The recess  158  is on the side of the frame-proximate portion  142  intended to face the vent  204 . 
     The loading pin  160  ( FIG. 10 ) has a center flange  162  and an end flange  164  spaced therefrom. As seen in  FIG. 11 , to secure together the arm  170  and the locking plate  140 , the pin  160  first through an aperture  172  near one end of the arm  170  and then through the aperture  156  of the locking plate  140 , until the center flange  162  comes up against the arm  170 . The formation of a swaged end  166  on the loading pin  160  permanently secures the locking plate  140  and the arm  170  in a pivotal relationship. 
     The opposed end of the arm  170  is pivotally and permanently connected to a generally rectangular shoe  180 , which slidably engages an elongate track  182  as show in  FIGS. 13 and 14 . The shoe  180  can travel along the track  182  between limits defined by a permanent stop  184  and an adjustable stop  186 . The same surface of the arm  170  faces both the shoe  180  and the locking plate  140 . The adjustable stop  186  can be a metal plate with a hole  188 . Prior to installation of the assembly  100 , the stop  186  is free to slide along the track  182 . Once the assembly is installed, the stop  186  can be located in a preferred position as will be shown later. A limit screw  194  is provided in the slide shoe  180 . Limiting the angle through which the arm  170  can pivot when disengaged from the bracket  110 , assists in precluding the vent  204  from opening too far and stressing the hinge  206 . 
     The mounting bracket  110  and the locking plate  140 , are configured so that the screw  120  and the bulbous section  132  of the first keyway  130  are spaced apart by the same distance as the loading pin  160  and the bulbous section  152  of the second keyway  150 . The first keyway  130  can now engage the loading pin  160 , and the second keyway  150  can engage the fastener  120 , since the corresponding bulbous sections  132  and  152  are sized respectively to allow passage of the loading pin end flange  164  and of the screw head  122 . Once such passage has occurred, the locking plate  140  is in a first or release position. It can be translated relative to the mounting bracket  110  to a second or locked position, wherein the loading pin  160  and the screw  120  are in alignment with the slots  134  and  154  of the corresponding keyways  130  and  150 .  FIG. 15  shows the locking plate in the locked position, other elements of the assembly  100  being omitted for clarity. 
     The mounting bracket  110 , the locking plate  140  and the arm  170  are typically fabricated from a metal such as stainless steel about 0.1″ (2.5 mm) thick. The track is composed of similar material with a thickness of about 0.06″ (1.5 mm). The slide shoe  180  is typically a composite of a sheet metal pressed to conform to the profile of the track and a plastic contact member of high lubricity such as Teflon. 
     When the assembly  100  is installed in its intended position as illustrated in  FIGS. 4 and 5 , the bracket  110  is affixed vertically to the frame  202 , using suitable fasteners such as screws. The track  182  is correspondingly screwed or otherwise mounted to the vent  204 . Once the track  182  is attached to the vent  204 , the hole  188  can be selectably aligned with one of a plurality of corresponding holes  190  in the track and secured in this position with a fastener which passes through the holes  188  and  190  and into the frame  202 . The position of the adjustable stop  186  defines the uppermost limit of travel of the slide shoe  180  in the track. 
     Upon operable installation of the assembly  100 , and that the locking plate  140  and bracket  110  the assembly disengaged, it is used according to steps illustrated in  FIGS. 16 ,  17  and  18 , as follows. The vent  204  is disposed at a suitable angle relative to the frame  202  and the slide shoe  180  positioned along the track  182  so that a user can align the wide portion  152  of the second keyway  150  with the screw head  122 , the screw  120  being in the release position. At this point, if the locking plate  140  is not closely aligned with the orientation of the mounting bracket  110 , the locking plate  140  is pivoted about the loading pin  160  until it is correctly aligned. Preferably, the locking plate  140  can be pivoted by hand, without freely pivoting under gravity alone. 
     The locking plate  140  being correctly aligned with the bracket  110 , the user engages the locking plate  140  and the screw  120 . As indicated previously, the wide portion  132  of the second keyway  150  accepts the screw head  122  and the wide portion  132  of the first keyway  130  accepts the end flange  164  of the loading pin  160 . Once the screw head  122  and the end flange  164  have cleared the locking plate  140  and the bracket  110  respectively, the locking plate  140  is in the release position and is then translated downward into the interlock position. The screw  120  is then adjusted to the closed position, the screw head  122  being tightened into the recess  158  to secure the locking plate  140  to the bracket  110 . 
     At this point, the arm  170  is still free to pivot about the loading pin  160  and also relative to the slide shoe  180 . Thus, the vent  204  can be closed into the frame  202 , or opened to a limit predetermined by setting of the adjustable stop  186 . While the fastener secures the locking plate  140  against the bracket  110 , the load exerted by the vent  204  when open is borne primarily by the loading pin  160  which in turn exerts the load downward onto the mounting bracket  110 . 
     To permit cleaning or other maintenance work on the vent  204 , the screw  120  is loosened and the locking plate  140  separated from the mounting bracket  110  by reversing the above-described procedure. Otherwise, as long as the locking plate  140  remains secured to the mounting bracket  110 , the window  200  cannot now be opened beyond the predetermined limit. Since any person not having the proper tool would be unable to loosen the screw  120 , accidental or unauthorized exit or entry through the window would be largely precluded. This is particularly important in a setting such as a school, where primary and elementary students might otherwise be especially vulnerable to accidents. 
     The interconnect or limiting assembly of this invention finds most practical use with a bottom-pivoted window vent that opens into the building, since it is desirable that work such as cleaning be done from inside the building. However, it could equally well be used if the vent opened outward. Furthermore, if the orientations of both keyways  130  and  150  were reversed, the invention could be used with a top-pivoted window vent. 
     While the invention has been described in connection with a preferred embodiment, nevertheless numerous and extensive departures may be made therein without however departing from the spirit of the invention and the scope of the appended claims.

Summary:
A mechanism which selectably limits the opening of a hinged window vent. The mechanism has a releasable arm that permits the vent to be conveniently opened beyond the selected limit. An assembly is disclosed for limiting travel of a vent relative to a frame. The assembly includes a security fastener for restricting transition of the assembly between a locked configuration and an unlocked configuration. An arm is pivotally connected to a mounting bracket by a locking plate and a loading pin.