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CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon provisional application Serial No. 60/065,617, filed Nov. 18, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Casement windows include a sash hinged to a frame or jamb so that by rotation of the handle the window could be moved to an open position or a closed position. Various structures have been suggested to attempt to provide a firm locking of the sash to the frame. Problems exist, however, regarding the window sagging while in the locked as well as the open condition. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a sag prevention and correcting system for windows, particularly casement windows. 
     A further object of this invention is to provide such a sag prevention system which operates in connection with the locking arrangement. 
     In accordance with this invention the sag prevention system is used with a locking arrangement wherein the sash includes at least one and preferably a pair of spaced keepers of a multi-point locking system. The frame has a tie bar arrangement with a roller for each keeper. When the window is rotated to its closed condition the handle for the tie bar arrangement is moved to slide the rollers upwardly for engagement with the keepers. In accordance with the invention a lifting block is located adjacent one of the keepers to be disposed directly above its roller when the window is in the locked condition. The lifting block may be integral with the keeper or may be a separate member. Any sagging is prevented by the lifting block contacting the roller. 
    
    
     THE DRAWINGS 
     FIG. 1 is a front elevational view of a casement window in the locked condition in accordance with this invention; 
     FIG. 2 is a fragmental front elevational view of the casement window in the unlocked condition; 
     FIG. 3 is a fragmental side elevational view of the window shown in FIG. 2; 
     FIG. 4 is a fragmental front elevational view of a casement window in the locked condition; 
     FIG. 5 is a fragmental side elevational view of the window shown in FIG. 4; 
     FIG. 6 is a fragmental side elevational view of a modified form of keeper/lifting block arrangement in accordance with this invention; 
     FIG. 7 is a fragmental end elevational view of a tie bar having a cylindrical roller; 
     FIG. 8 is a fragmental and elevational view of a tie bar having a shouldered roller and a keeper with a flange; 
     FIG. 9 is a fragmental front elevational view showing a casement window in its unlocked condition having a modified form of link structure; 
     FIG. 10 is a fragmental side elevational view of the arrangement shown in FIG. 9; 
     FIG. 11 is a fragmental side elevational view showing yet another form of vertical adjustment mechanism in accordance with this invention; 
     FIG. 12 is a fragmental end elevational view of the arrangement shown in FIG. 11; 
     FIG. 13 is a fragmental side elevational view showing still yet another form of vertical adjustment mechanism in accordance with this invention; 
     FIG. 14 is a fragmental end elevational view of the arrangement shown in FIG. 13; 
     FIG. 15 is a fragmental side elevational view of yet another form of vertical adjustment mechanism in accordance with this invention; 
     FIG. 16 is an enlarged fragmental end view showing a vertical adjustment mechanism for the link in accordance with this invention; and 
     FIG. 17 is a front elevational view of a gauge used for locating the lifting block in the window of FIGS.  1 - 5 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a casement window  10  which includes a frame or jamb  12  and a sash  14  which extends around the window pane itself. Sash  14  is hinged to frame  12  by hinge arms at the bottom area  16  of the window assembly so that the window can be moved to an open position or a closed position. The rotation is controlled by handle  18  in a known manner and its details are not critical to an understanding of this invention. 
     FIGS. 2-5 illustrate the details of the invention wherein a sag prevention system is incorporated with locking members of a known multi-point locking system on the sash and frame. Reference is made to U.S. Pat. Nos. 5,074,075, 5,118,145 and 5,448,857, the details of which are incorporated herein by reference thereto with regard to the known multi-point locking system with which the invention may be adapted. The invention thus has the advantage of requiring only minor structural additions to the known locking system. 
     As shown in FIGS. 2-3 the various components are in their unlocked condition. FIG. 2 illustrates a tie bar  20  having a pair of spaced rollers or abutment members  22  which may be frusto-conically shaped, as shown in FIG. 2 or may have other types of shapes such as shown in FIGS. 7 and 8. It is to be understood that while the members  22  are referred to as rollers, it is not necessary in the broad practice of the invention that the members  22  actually rotate. What is important is that the members  22  present an abutment surface as later described. Members  22  may be considered first abutment members. The tie bar  20  is mounted to the frame  12 . A pair of second abutment members keepers  24 , 26  is mounted to the sash, as shown in FIG.  3 . Keeper  24  has an inclined cam edge  28  and a vertical guide surface or straight guide edge  30 . Keeper  26  has an inclined cam edge  32  and a straight guide edge  34 . In accordance with this invention a lifting block  36  is disposed outwardly from the upper end of straight edge  34 . Although only one lifting block  36  is illustrated in FIG. 3, it is to be understood that the invention may be practiced with a lifting block for each roller as illustrated in phantom in FIG. 5 by the reference numeral  36 A. Similarly, while a pair of rollers and keepers are illustrated, the invention may be broadly practiced with only a single roller and keeper. 
     Tie bar  20  is mounted to a link  38  which in turn is mounted to a pivotable handle  40 . When handle  40  is in the up position the tie bar is in its unlocked condition where the rollers  22  are spaced from the keepers  24 , 26 . When handle  40  is rotated downwardly the tie bar is shifted upwardly and the rollers contact the keepers, as shown in FIGS. 4-5. 
     The sequential contacting of the keepers takes place by the lower roller  22  first contacting and rolling against inclined cam edge  32  of lower keeper  26 . When the lower roller reaches the junction with straight guide edge  34  upper roller  22  begins to contact inclined cam edge  28  of upper keeper  24 . Similarly, where abutment member  22  is a roller, the roller may but need not rotate. In continued upper movement of the rollers, the lower roller  22  rides against straight guide edge  34  while upper roller  22  rides against inclined edge  28  and ultimately straight guide edge  30 . When the rollers are both located at the straight edges the window sash is pulled tightly against the weather seals of the frame. 
     Thus, as described above, each keeper is in the path of movement of the vertically moving roller  22  so that when the rollers  22  contact the inclined and straight edges of each keeper, a locking results. 
     In accordance with this invention lifting block  36  is mounted outwardly of straight edge  34  generally in line with or more accurately across the path of movement of lower roller  22 . Lifting block  36  is illustrated in FIGS. 3 and 5 as being integral with keeper  26  and extending outwardly from guide edge  34 . It is to be understood, however, that the invention may be practiced where the lifting block is a separate element mounted adjacent to and upwardly from keeper  26 . 
     FIGS. 4-5 show the condition of the components in the fully locked position. As shown therein, lower roller  22  is located directly below lifting block  36  when upper roller  22  is along straight guide edge  30  of upper keeper  24 . In the fully locked condition roller  22  would be at the lower edge  44  of block  36 . If there should be any tendency for the sash to sag, such tendency is prevented by lower roller  22  acting as an abutment against edge  44  for lifting block  36  thereby preventing downward movement or sagging of the sash, or lifting the sash if it has sagged while in the open position. 
     Preferably, lifting block  36  is located at lower keeper  26 . The invention, however, may also be practiced by having the lifting block at the upper keeper  24  located directly above the upper roller  22  when the handle  40  is moved to its down position as shown in FIGS. 4-5. The invention may also be practiced by having a lifting block for each keeper, particularly when used with a heavy sash. The preferred practice of the invention is illustrated where there is a single lifting block located at the lower keeper  26  and where the sash is not particularly heavy. 
     As noted, the lifting block  36  may be integral with keeper  26  or may be a separate member located directly above the lower roller  22 . Not only does lifting block  36  prevent sagging and support the sash in its locked position, but also the lifting block corrects minor sag while the sash is in its open position. 
     The invention may be practiced by having one or both keepers or lifting block  36  vertically adjustable in its location on sash  14 . FIG. 3, for example, illustrates a pair of slots  27  to be formed in keeper  26  so that the keeper  26  could be slidably moved up or down and then locked in position by the illustrated screws or fasteners. 
     Any other suitable structure may be used to permit the vertical adjustability of the keepers and/or lifting block. FIG. 6, for example, illustrates the lifting block  36  to include the same type of slot/fastener arrangement so as to be independently movable with respect to keeper  26 . FIG. 6, further illustrates a variation of the invention where the contact surface  35  of lifting block  36  is arcuate to receive cylindrical roller  22 A. The cylindrical roller is also shown in FIG.  7 . 
     FIG. 8 shows a variation of the invention where one of the keepers such as keeper  24  has a flange  25  for contacting roller  22 B which is in the form of a cylinder having an outwardly extending shoulder  23  which rides against flange  25 . 
     Where lifting block  36  is not integral with keeper  26  the two pieces could have mating teeth or cams engaged with each other to effect vertical movement of one piece with respect to the other. Where vertical adjusting structure is used care should be taken to take into account the weight of the window as it might affect the efficiency of performance of the vertical adjusting structure. 
     FIGS. 9-10 show a variation of the invention wherein the link  38 A associated with handle  40  is connected to tie bar  20  by a fork structure  100  wherein the fork arms or prongs  101  are disposed on each side of a pin  102  fixed on tie bar  20 . 
     FIGS. 11-12 illustrate a further vertical adjustment mechanism which may be used in accordance with this invention. As shown therein, the pin  102 A is eccentrically mounted or may be of elliptical form so that upon rotation of the pin the forked end of link  38 A is moved up or down. For example, as shown in FIG. 12, the eccentrically mounted pin  103  is secured to tie bar  20  with a cam disk  105  disposed between link  38 A and tie bar  20 . Rotation of eccentric pin  103  affects the precise location of link  38  at its area of mounting to tie bar  20 . A known mechanism commonly referred to as TORX would provide this type of adjustment. 
     FIGS. 13-14 illustrate yet another form of vertical adjustment mechanism wherein a hexagonal cam disk  105 A is mounted to pin  103  so that rotation of pin  103  causes pin  102  disposed between the fork arms of link  38 A to move the arms upwardly or downwardly. Such adjustment may be easily achieved by using a conventional adjustment wrench W. 
     FIG. 15 illustrates yet another manner of adjustment wherein the link  38 B is made of two parts  39 A and  39 B which are connected together by a suitable fastener  41  extending through elongated slot  43  thereby controlling the degree of overlap of link parts  39 A and  39 B. 
     FIG. 16 illustrates yet another form of adjustment where link  20 A is provided with teeth  31  for engagement with complementary teeth  33  on link  38 C. A suitable threaded fastener  29  and nut  29 B may be manipulated to move the mating teeth  31 , 33  into and out of engagement with each other. 
     FIG. 17 illustrates a gauge  42  which may be used for properly positioning the lifting block and more particularly its lower edge  44  on the sash. As shown therein gauge  42  is of two piece construction for locating the bottom keeper lifter on casement windows with multi-point locking systems. A pair of sliding members  46 , 48  comprise gauge  42 . Each member includes a slot  50  into which pins  52 , 52  of the other member are slidably mounted. The members  46 , 48  can be locked together in any suitable manner once the proper height adjustment can be achieved. 
     Lower member  48  includes a lower surface  54  which would be placed on the bottom hinge track of frame  12 . A side wall  56  is dimensioned to correspond to the stack height of the hinge and spacers, if used. Such height might, for example, be {fraction (7/16)} inches. Surface  58  would be set in the bottom sash arm mounting surface. A cutout  60  avoids contact with weld flash. For example, the cut out  60  includes a relief notch  59  with a recess  61  to accommodate any weld flash at the corner of the window frame F, shown in phantom. Surface  62  of upper member  46  would correspond to the top tangent surface of the bottom roller in the locked position. This would also correspond to the lower edge  44  or  35  of lifting block  36 . A similar surface  64  in line with surface  62  is provided also to correspond to the tangible surface of the bottom roller. Either of the surfaces  62 , 64  could be used for determining where the lifting block  36  should be located with regard to its lower surface. 
     Thus, in use the surface  54  would be placed on the bottom hinge track. Members  46 , 48  would be slidably adjusted so that surface  62  or  64  would be tangent to the bottom roller  22  in the locked position. Members  46 , 48  would then be locked to fix this distance. Surface  58  would be set in the bottom hinge sash arm mounting surfaces. By the proper placement and selection of the various surfaces in gauge  42 , accurate placement of the lifting block  36  can be assured. 
     The above procedure allows for the proper placement and location of the lifting block  36  with respect to roller  22 . If it is more desirable to adjust the location of the roller in order to obtain the proper alignment and positioning with respect to the lifting block  36  the following procedure can be used. Surface  58  of gauge  42  would be set in the bottom hinge sash arm surface. Slide members  46 , 48  would be selectively adjusted so that surface  62  or  64  would correspond to the location of surface  44  or  35  of lifting block  36 . Members  46 , 48  would then be locked to fix this distance. Surface  54  would be placed on the bottom hinge track surface. Roller  22  would then be adjusted so that roller  22  would be tangent to surface  62  or  64 . This adjustment of the location of roller  22  could be made by using the various techniques shown in FIGS. 11-14 and/or  17 . 
     Gauge  42  is useful not only in retrofitting existing windows to add a separate lifting block, but could also be used in original manufactured windows to be sure of proper location of the roller and the lifting block whether the lifting block is integral with the lower keeper or is a separate member. 
     It is to be understood that the invention may be practiced in manners other than specifically shown and described. For example, the tie bar may be mounted to either the sash or the frame with the fixed abutment member mounted on the other of the sash or the frame. The tie bar may have the roller as its movable abutment member, as described, or the keeper may be mounted on the tie bar and be an abutment member with the roller or abutment member on the other of the sash or the frame. Where the keeper is mounted on the tie bar, the keeper may be considered as a second abutment member and the roller would be a first abutment member. In these variations the lifting block would be disposed across the path of movement of the movable or second abutment member so as to be contacted by the second abutment member when the window assembly is in its locked position to minimize sag and to correct for sag.

Summary:
A casement window utilizes a multi-locking system having a pair of spaced keepers and a tie bar with a corresponding pair of rollers. In the locking action the rollers ride against the inclined and straight vertical surfaces of the keepers. A lifting block is located immediately above the lower roller when the locking system is in its locked condition. The lifting block prevents sagging and supports the sash in the locked condition. The provision of a lifting block in combination with the known multi-point locking system takes advantage of the locking system components to prevent sagging.