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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a bracket for a window blind and more specifically, to a bracket assembly for a window blind, which has means for horizontal calibration.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional window blind, for example, a roller blind comprises generally a bracket for fastening to the top side of a window, a roller pivotally mounted in the bracket, a blind shade, which has a top side fastened to the periphery of the roller such that the roller can be rotated to roll up or let off the blind shade, a bottom rod fastened to and extended along the bottom hem of the blind shade, and an operating cord for operation by the user to rotate the roller. When operating the operating cord to rotate the roller in one direction, the roller rolls up the blind shade. On the contrary, when operating the operating cord to rotate the roller in the reversed direction, the roller lets off the blind shade. The bottom rod imparts a downward drag force to the blind shade, and therefore the blind shade is kept smoothly suspended from the roller when extended out.  
         [0005]     In order to cause a sense of beauty, the roller is set in parallel to the bracket. However, it is difficult to set the bracket in horizontal accurately during installation. If the bracket is not accurately kept in horizontal, the roller cannot be maintained in horizontal. At this time, the bottom rod slopes in one direction, imparting an unbalanced drag force to the bottom side of the blind shade. When rotating the roller to roll up the blind shade, the blind shade will be received to the roller in a wrinkled status, obstructing the sense of beauty of the roller blind. This problem may occur in other window blinds such as Venetian blind, Roman shade, honeycomb shade, resulting in an unbalanced status of the slats or blind shade.  
       SUMMARY OF THE INVENTION  
       [0006]     It is the primary objective of the present invention to provide a bracket assembly, which has means for horizontal calibration during installation.  
         [0007]     To achieve this objectives of the present invention, the bracket assembly comprises a bracket provided with a coupling portion, a locating frame provided with a coupling portion connectable to the coupling portion of the bracket, and a level mounted on the locating frame for showing whether the bracket is in level after connection of the coupling portion of the locating frame to the coupling portion of the bracket. In an alternate form of the present invention, the locating frame is eliminated, and the level is directly mounted to the bracket. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a front view of a roller blind constructed according to the present invention.  
         [0009]      FIG. 2  is a perspective partial view of a bracket assembly according to a first preferred embodiment of the present invention.  
         [0010]      FIG. 3  is a front view in an enlarged scale of a part of the bracket assembly according to the first preferred embodiment of the present invention.  
         [0011]      FIG. 4  is a schematic side view in an enlarged scale of a part of the first preferred embodiment of the present invention showing the relationship between the coupling portion at the bracket and the coupling portion at the locating frame.  
         [0012]      FIG. 5  is perspective partial view of a bracket assembly according to a second preferred embodiment of the present invention.  
         [0013]      FIG. 6  is a front view in an enlarged scale of a part of the bracket assembly according to the second embodiment of the present invention.  
         [0014]      FIG. 7  is a schematic side view in an enlarged scale of a part of the second preferred embodiment of the present invention showing the relationship between the coupling portion at the bracket and the coupling portion at the locating frame. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     Referring to  FIG. 1 , a roller blind is shown comprising a bracket  10  affixed to the top side of a window (not shown), a roller  20  pivotally situated within and arranged in parallel to the bracket  10 , a blind shade  30  wound round the roller  20 , a bottom rod  40  fastened to the bottom hem of the blind shade  30 , and an operating cord  50  coupled to the roller  20  for operation by the user to rotate the roller  20  forwards and backwards. When operating the operating cord  50  to rotate the roller  20  in one direction, the roller  20  rolls up the blind shade  30 . On the contrary, when operating the operating cord  50  to rotate the roller  20  in the reversed direction, the roller  20  lets off the blind shade  30 . The bottom rod  40  imparts a downward drag force to the blind shade  30 , and therefore the blind shade  30  is kept smoothly suspended from the roller  20  when extended out.  
         [0016]     Referring to  FIGS. 2-4 , a bracket assembly in accordance with the first preferred embodiment of the present invention is shown comprised of the bracket  10 , a locating frame  60 , and a level  70 . The bracket  10  is a flat, elongated, substantially L-shaped member comprising a top wall  11  and a sidewall  12  arranged at right angles and extended in longitudinal direction, an angled top flange  13  upwardly protruded from the top wall  11  and extended along the length of the top wall  11 , and a coupling portion  131  defined within the space surrounded by the top wall  11  and the angled top flange  13 . The coupling portion  131  comprises a top edge  132 , a bottom edge  133 , and an opening  134  facing the rear side of the bracket  10 . The bottom edge  133  forms a part of the top surface of the top wall  11 . The top edge  132  and the bottom edge  133  are substantially arranged in parallel and spaced from each other by a gap. The bracket  10  further comprises two end plates  14  at the two distal ends of the top wall  11  and the sidewall  12  (see also  FIG. 1 ). The end plates  14  each have a pivot hole  141 . The roller  20  is pivotally coupled to the pivot holes  141  of the end plates  14 . The axis, which passes through the pivot holes  141  of the end plates  14 , is substantially in parallel to the top wall  11  of the bracket  10  (the length of the bracket  10 ).  
         [0017]     The locating frame  60  is a substantially inverted U-shaped member comprising a top wall  61 , a first sidewall  62  at the front side of the top wall  61 , a second sidewall  63  at the rear side of the top wall  61 , and a coupling portion  631  forwardly extended from the bottom side of the second sidewall  63 . The coupling portion  631  is a coupling block comprising a top edge  632  and a bottom edge  633 . The top edge  632  and the bottom edge  633  are arranged in parallel. The distance between the top edge  632  and the bottom edge  633  is approximately equal to the gap between the top edge  132  and bottom edge  133  of the coupling portion  131  of the bracket  10 .  
         [0018]     The level  70  is disposed at the bottom side of the first sidewall  62 . Further, the level  70  can be a bubble level or electronic level.  
         [0019]     By means of coupling the coupling portion  631  of the locating frame  60  to the coupling portion  131  of the bracket  10 , i.e., by means of attaching the top edge  632  and bottom edge  633  of the locating frame  60  to the top edge  132  and bottom edge  133  of the coupling portion  131  of the bracket  10  respectively, the locating frame  60  is fastened to the front side of the top wall  11  of the bracket  10 . After installation of the locating frame  60  in the bracket  10 , the level  70  is maintained in parallel to the bracket  10 . By means of the indication of the level  70 , the bracket  10  can easily be adjusted to horizontal during installation of the bracket assembly in the window.  
         [0020]      FIGS. 5-7  show a bracket assembly according to the second preferred embodiment of the present invention. According to this embodiment, the bracket assembly is comprised of a bracket  80 , a locating frame  90 , and a level  70 .  
         [0021]     The bracket  80  is a flat rail set in vertical, comprising an angled flange  81  protruded from the front side near the top and extended along the length thereof, and a coupling portion  811  defined in the space between the front side of the bracket  80  and the angled flange  81 . The coupling portion  811  comprises a left-side edge  812 , a right-side edge  813  and an upward opening  814 . The left-side edge  812  and the right-side edge  813  are arranged in parallel and spaced from each other by a gap. The bracket  80  further comprises two end plates  82  respectively perpendicularly extended from the two distal ends thereof. The end plates  82  each have a pivot hole  821  (see  FIG. 5 ). The roller  20  (not shown) is pivotally connected to the pivot holes  821  of the end plates  82  and arranged in parallel to the bracket  80 . The axis, which passes through the pivot holes  821  of the end plates  82 , is substantially in parallel to the bracket  80  (the length of the bracket  80 ).  
         [0022]     The locating frame  90  is a plate member comprising a top wall  91  and a coupling portion  92 . The coupling portion  92  is a coupling block downwardly extended from the rear side of the top wall  91 , comprising a left-side edge  921  and a right-side edge  922 . The left-side edge  921  and the right-side edge  922  are substantially arranged in parallel. The distance between the left-side edge  921  and the right-side edge  922  is substantially equal to the gap between the left-side edge  812  and right-side edge  813  of the coupling portion  811  of the bracket  80 .  
         [0023]     The level  70  is disposed at the front side of the top wall  91 . The use of this second embodiment is substantially similar to the aforesaid first embodiment.  
         [0024]     In order to cause a sense of beauty, the roller is arranged in parallel to the bracket. Therefore, the roller is maintained in horizontal after installation and horizontal calibration of the bracket in the top side of the window. When rotating the roller to roll up and let off the blind shade, the two opposite lateral sides of the blind shade receive a balanced tensile force, and therefore the blind shade is maintained smoothly wound round the roller without wrinkles when received to the roller.  
         [0025]     After installation of the bracket assembly in the top side of the window, the level with the locating frame can be removed from the bracket for use to calibrate the horizontal status of another bracket. Therefore, one level and locating frame combination can be used with a number of brackets for different windows to save the installation cost. Alternatively, the level can be directly affixed to the bracket without the locating frame. Further, the invention can also be employed to any of a variety of other window blinds such as Venetian blind, Roman shade, etc.  
         [0026]     Although a particularly embodiment of the present invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Summary:
A bracket assembly includes a bracket provided with a coupling portion, a locating frame provided with a coupling portion connectable to the coupling portion of the bracket, and a level mounted on the locating frame for showing whether the bracket is in level after connection of the coupling portion of the locating frame to the coupling portion of the bracket. By means of the indication of the level, the bracket can easily be adjusted to horizontal during installation of the bracket assembly in a window.