Abstract:
A center of gravity adjustment device installed in a bottom rail of a window blind assembly for adjusting the center of gravity of the bottom rail is disclosed to include an adjustment wheel fastened rotatably with the bottom rail for rotating by a user, a rotating wheel fastened rotatably with the bottom rail and spaced from the adjustment wheel at a distance, a weight movable in the bottom rail between the adjustment wheel and the rotating wheel, and a cord member mounted around the adjustment wheel and the rotating wheel and fastened to the weight for moving the weight in said bottom rail between the adjustment wheel and the rotating wheel upon rotation of the adjustment wheel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to lifting window blinds (roll-up blinds, Venetian blinds) and, more specifically, to a center of gravity adjustable bottom rail for window blind. The invention relates to also to a window blind assembly having a center of gravity adjustable bottom rail. 
     2. Description of the Related Art 
     FIG. 7 shows a roller blind  90  according to the prior art. This structure of roller blind  90  comprises a barrel  91  fastened pivotally with the top of a window (not shown) in transverse direction, a bottom rail  92  arranged in parallel to and spaced below the barrel  91 , flexible slats  93  arranged in parallel between the barrel  91  and the bottom rail  91 , two thin covering sheets  95  respectively covering the slats  93  at front and back sides and connected between the barrel  91  and the bottom rail  92  to join the slats  93 . The covering sheets  95  soften the light passing through the window blind assembly  90 . The user can rotate the barrel  91  (manually or by a motor drive) to roll up the slats  93  and the covering sheets  95  around the periphery of the barrel  91 . 
     The aforesaid roller blind  90  is still not satisfactory in function. Because it is difficult to keep the tension of each covering sheet  95  (which is usually a piece of meshed fabric) in balance at left and right sides, the bottom rail  92  cannot be maintained in horizontal accurately. During fabrication and assembly process of the bottom rail  92  (which is comprised of an aluminum profile and two plastic end caps at two ends of the aluminum profile), it is difficult to have the gravity weight evenly distributed in all directions. When installed in the covering sheets  95 , the bottom rail  92  may not be maintained in horizontal accurately. When the bottom rail  92  lifted to a relatively higher position close to the barrel  91 , it stands in an oblique position sloping downwards toward one lateral side of the blind (see FIG.  8 ), obstructing the sense of beauty of the roller blind  90 . 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a center of gravity adjustment device, which is practical for use in a window blind assembly, such as a roll-up blind, lifting-type blind, etc., for enabling the user to adjust the center of gravity of the bottom rail to keep the bottom rail in horizontal. 
     It is another object of the present invention to provide a window blind assembly having a center of gravity adjustable bottom rail, which enables the user to adjust the center of gravity of the bottom rail, keeping the bottom rail in horizontal. 
     To achieve these objects of the present invention, a center of gravity adjustment device is installed in a bottom rail of a window blind assembly for adjusting the center of gravity of the bottom rail, comprising an adjustment wheel fastened rotatably with the bottom rail for rotating by a user, a rotating wheel fastened rotatably with the bottom rail and spaced from the adjustment wheel at a distance, a weight movable in the bottom rail between the adjustment wheel and the rotating wheel, and a cord member mounted around the adjustment wheel and the rotating wheel and fastened to the weight for moving the weight in said bottom rail between the adjustment wheel and the rotating wheel upon rotation of the adjustment wheel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a window blind assembly constructed according to a preferred embodiment of the present invention. 
     FIG. 2 is an exploded view, in an enlarged scale, of the bottom rail of the window blind assembly shown in FIG.  1 . 
     FIG. 3 is a top view, partially in section, of the bottom rail according to the present invention. 
     FIG. 4 is a front view, partially in section, of the bottom rail according to the present invention. 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG.  3 . 
     FIG. 6 is similar to FIG. 3 but showing the position of the weight changed. 
     FIG. 7 shows a roller blind according to the prior art. 
     FIG. 8 is a schematic view showing the bottom rail lifted to a relatively higher position close to the barrel of the prior art roller blind shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a window blind assembly  10  in accordance with the present invention is shown comprised of a barrel  11  fastened pivotally with the top side of a window (not shown), a bottom rail  12  arranged in parallel to and spaced below the barrel  11 , a plurality of flexible slats  13  arranged in parallel between the barrel  11  and the bottom rail  12 , two ladder tapes  14  bilaterally and vertically connected between the barrel  11  and the bottom rail  12  and joining the slats  13 , and a flexible covering sheet  15 . The covering sheet  15  has a first half disposed at the front side of the slats  13 , a second half disposed at the back side of the slats  13 , and a middle part connected between the first half and the second half below the bottom rail  12 . The top sides of the first and second halves of the covering sheet  15  are respectively connected to the barrel  11 . Because the aforesaid basic structure of the window blind assembly is not within the scope of the claims of the present invention, no further detailed description in this regard is necessary. 
     Referring to FIG.  2  and FIG. 1 again, the main feature of the present invention is at the bottom rail  12 . The bottom rail  12  is a hollow elongated flat member extruded from aluminum, having a flat top surface, a convex bottom surface, and a longitudinally extended middle partition wall  16 . The partition wall  16  divides the internal space of the bottom rail  12  a longitudinally extended front chamber  17  and a longitudinally extended back chamber  18 . Further, the partition wall  16  has two end notches  19  respectively formed in the two distal ends on the middle. 
     Referring to FIGS.  3 ˜ 5  and FIGS. 1 and 2 again, two end caps  21  are respectively fastened to the two ends of the bottom rail  12 . The end caps  21  are L-shaped cover members respectively injection-molded from plastics, each having a vertical wall  22  and a horizontal wall  23  connected at right angles, and two insertion blocks  24  bilaterally perpendicularly extended from the vertical wall  22  and suspending above the horizontal wall  23 . By mans of plugging the insertion blocks  24  into the longitudinally extended front chamber  17  and longitudinally extended back chamber  18  of the bottom rail  12 , the end caps  21  are fastened to the ends of the bottom rail  12 . When the end caps  21  installed, the vertical walls  22  of the end caps  21  close the ends of the bottom rail  12 , and the horizontal walls  23  of the end caps  21  are suspended below the bottom rail  12  and spaced from the bottom surface of the bottom rail  12  at a distance (for the passing of the covering sheet  15 ). Further, the vertical wall  22  of each end cap  21  has a horizontally extended elongated slot  25  corresponding to the longitudinally extended front chamber  17  of the bottom rail  12 . In order to save manufacturing cost, the end caps  21  are made having two frames of line formed of dents and disposed in the respective vertical wall  22  corresponding to the longitudinally extended front chamber  17  and the longitudinally extended back chamber  18 . Therefore, the user can remove the area within one frame of line and keep the area within the other frame of line intact. By means of selectively piercing one frame of line, a horizontally extended elongated slot  25  is formed in each end cap  21  corresponding to the longitudinally extended front chamber  17 . 
     As illustrated in FIG. 1, two identical center of gravity adjustment devices  30  are symmetrically mounted in the two ends of the bottom rail  12 . FIGS.  2 ˜ 6  show only one center of gravity adjustment device  30 . Each center of gravity adjustment device  30  comprises a track  40 , an adjustment wheel  50 , a rotating wheel  60 , a weight  70 , and a cord member  80 . 
     The track  40  is an elongated flat bar having a longitudinally extended center opening  41 , two end holes  42  and  43  formed in the two ends in communication with the center opening  41 , and a retaining portion  44  protruded from one end. The track  40  is inserted into the longitudinally extended front chamber  17  of the bottom rail  12  to engage the retaining portion  44  into one end notch  19  of the partition wall  16 . When the retaining portion  44  engaged into one end notch  19  of the partition wall  16 , the track  40  is set in position and maintained in flush with one end of the bottom rail  12 . 
     The adjustment wheel  50  is a flat circular wheel having an endless groove  51  around the periphery. The surface of the endless groove  51  is coarsened or embossed with a pattern (not shown). The adjustment wheel  50  is pivotally mounted in the outer end hole  42  of the track  40  by a pin  52 . When installed, the adjustment wheel  50  has a part disposed outside the outer end of the track  40  (i.e., outside one end of the bottom rail  12 ) and projecting out of the elongated slot  25  of the corresponding end cap  21 . Therefore, the user can rotate the adjustment wheel  50  with the thumb conveniently. 
     The rotating wheel  60  is same as the adjustment wheel  50  in shape, having an endless groove  61  around the periphery. The rotating wheel  60  is pivotally mounted in the inner end hole  42  of the track  40  by a pin  62 . 
     The weight  70  is an elongated flat heavy metal plate smaller than the longitudinally extended center opening  41  of the track  40 , having two longitudinal slots  71  cut through the top and bottom sides and arranged in parallel, and two pairs of end holes  72  aligned in the two ends in communication with the longitudinal slots  71 . The weight  70  is longitudinally movably suspended in the longitudinally extended center opening  41  of the track  40 . 
     The cord member  80  is mounted around the endless groove  51  of the adjustment wheel  50  and the endless groove  61  of the rotating wheel  60  and inserted through the back end holes  72  of the weight  70  and the corresponding longitudinal slot  71 , having two ends respectively inserted through the front end holes  72  of the weight  70  into the corresponding longitudinal slot  71  and then respectively tied in a knot  81  or  82 . The two knots  81  and  82  of the cord member  80  are respectively stopped in connection areas between the front end holes  72  of the weight  70  and the corresponding longitudinal slot  71 . The friction resistance between the wheels  50  and  60  and the cord member  80  enables the cord member  80  to be moved to carry the weight  70  leftwards or rightwards upon rotary motion of the adjustment wheel  50 . For example, when the user rotating the adjustment wheel  50  clockwise, the cord member  80  is turned with the adjustment wheel  50 , thereby causing the left knot  81  to pull the weight  70  leftwards (at the same time, the right knot  82  pushes the weight  70  leftwards) to the position shown in FIG.  6 . 
     The aforesaid description explains the structure and function of the bottom rail  12 . During installation, the adjustment wheel  50  and the rotating wheel  60  are respectively pivotally mounted in the two ends of the track  40  at first, and then the weight  70  is put in the longitudinally extended center opening  41  of the track  40 , and then one end of the cord member  80  is tied in a knot  82 , and then the other end of the cord member  80  is inserted from the front longitudinal slot  71  of the weight  70  through one front end hole  72  of the weight  70  and then extended over the endless groove  61  of the rotating wheel  60  and inserted through the back end holes  72  and back longitudinal slot  71  of the weight  70  and then extended over the endless groove  51  of the adjustment wheel  50  and then inserted through the other front end hole  72  of the weight  70  into the longitudinally extended center opening  41  of the track  40  and then tied in a knot  81 . Thereafter, the two center of gravity adjustment devices  30  are respectively mounted in the bottom rail  12 , and then the end caps  21  are fastened to the ends of the bottom rail  12 . 
     When the bottom rail  12  installed in the window blind assembly  10 , the user can rotate the adjustment wheel  50  of each center of gravity adjustment device  30  to adjust the position of the respective weight  70  in the respective track  40 , so as to further adjust the center of gravity of the bottom rail  12 , keeping the bottom rail  12  in horizontal accurately. For example, if the bottom rail  12  sloping downwards from the left side toward the right sight, the user can rotate the adjustment wheel  50  of the left center of gravity adjustment device  30  to adjust the position of the respective weight  70  leftwards (the user may adjust the two center of gravity adjustment devices  30  if necessary), so as to further shift the center of gravity of the bottom rail  12  leftwards, enabling the bottom rail  12  to be held in horizontal. 
     According to the aforesaid embodiment of the present invention, the center of gravity adjustment devices  30  are mounted in the bottom rail  12  near the front side of the bottom rail  12 . When the user rotating the barrel  11  to roll up the covering sheet  15  and the slats  13 , the bottom rail  12  is gradually turned from a horizontal position to a vertical position, i.e., the back side of the bottom rail  12  is gradually turned upwards and the front side of the bottom rail  12  is gradually turned downwards. Because the center of gravity adjustment devices  30  are mounted in the bottom rail  12  near the front side of the bottom rail  12 , the center of gravity of the bottom rail  12  can smoothly be shifted to the bottom side to stretch the cover sheet  15  when turned from the horizontal position to the vertical position. 
     While only one embodiment of the present invention has been shown and described, it will be understood that various modifications and changes could be made thereunto without departing from the spirit of the invention. For example, the bottom rail can be made having only one center of gravity adjustment device on the middle for adjustment, and the center of gravity adjustment device of the present invention can be installed in the bottom rail of any type of window blind assembly, such as roller blind, Venetian blind, pleated blind, etc. Accordingly, the invention is not to be limited except as by the appended claims.