You are an expert at summarizing long articles. Proceed to summarize the following text:

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 generally to a window blind assembly and more particularly, to a cord stopper which is detachably and slidably connectable to a lift cord of a window blind assembly.  
           [0003]    2. Description of the Related Art  
           [0004]    Window blind assemblies are intensively used to decorate windows and to shield windows from outside incident light. A window blind assembly constructed according to U.S. Pat. No. 6,453,974 is shown in FIG. 1, comprising a headrail  11 , a bottom rail  12 , a blind supporting system  13  joining the headrail  11  and the bottom rail  12  and mounted with a plurality of slats  14 , two lift cords  15  each having a first portion  152  affixed to one end of the bottom rail  12  and upwardly penetrated through the slats  14  and the headrail  11  and a second portion  151  extended out of the headrail  11  through a lift cord lock  16  near one end of the headrail  11 . The second portion  151  of each lift cord  15  is for pulling by the user to control the elevation of the bottom rail  12 , i.e., changing the length of the second portion  151  of each lift cord  15  relatively control the extending (unfolding) status of the window blind assembly. A window blind assembly of this design is not safe in use. Because the first portion  152  of each lift cord  15  that passes through the slats  13  can easily be pulled by a child, and an accident may occur when a child playing with the first portion  152  of each lift cord  15  for fun and hang the first portion  152  of each lift cord  15  on the neck accidentally. Further, the lift cord lock  16  may fail, thereby causing the slats  14  and the bottom rail  12  to fall suddenly and to further hit a person below accidentally. In order to eliminate these problems, U.S. Pat. No. 6,453,974 uses two cord stoppers  17  to limit stretching of the first portion  152  of each lift cord  15 . According to this design, each cord stopper comprises a locking guider having at least a guiding through slot provided thereon; each locking guider is slidably connected to the respective lift cord by tying an adjustable knot at the guiding through slot; the adjustable knot is constructed by tying the lift cord on the locking guider by forming a loop on the lift cord, passing the loop through the respective guiding through slot and penetrating a free end of the lift cord into the loop so as to form the adjustable knot tying around the locking guider, as shown in FIG. 2. This installation procedure is complicated and inconvenient.  
           [0005]    Therefore, it is desirable to provide a window blind assembly having one or more cord stoppers that eliminate the aforesaid problem.  
         SUMMARY OF THE INVENTION  
         [0006]    It is the primary objective of the present invention to provide a window blind assembly having at least one lift cord stopper, which prevents excessively stretching of the lift cords that pass through the slats.  
           [0007]    It is another objective of the present invention to provide a window blind assembly having at lease one lift cord stopper, which presents falling of the bottom rail from the top position accidentally due to failure of the cord lock.  
           [0008]    It is still another objective of the present invention to provide a window blind assembly having at least one lift cord stopper, which lift cord stopper is easy to install.  
           [0009]    It is still another objective of the present invention to provide a window blind assembly having at least one lift cord stopper, which enables the user to conveniently adjust the position of each cord stopper.  
           [0010]    It is still another objective of the present invention to provide a window blind assembly, which has the tied-up portion of each lift cord kept from sight, causing a sense of beauty.  
           [0011]    To achieve these objectives of the present invention, the window blind assembly comprises a headrail, a bottom rail, a plurality of slats, a supporting unit connected to the headrail, the bottom rail and the slats for supporting the slats between the headrail and the bottom rail, a lift cord lock mounted on the headrail, a pair of lift cords each having an end affixed to the bottom rail, a first portion penetrated through the slats and extended through the headrail, and a second portion extended out of the headrail through the lift cord lock for operation to control elevation of the bottom rail, and at least one cord stopper including a first cover shell having an insertion hole, a second cover shell openably closed to the first cover shell to form a receiving chamber therebetween, and at least one holding down member disposed in the receiving chamber. A part of the second portion of the lift cord is positioned in the receiving chamber of the cord stopper by means of insertion of the second portion of the lift cord through the insertion hole of the cord stopper. The part of the second portion of the lift cord is pressed by the holding down member to hold the cord stopper on the second portion of the lift cord. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a window blind assembly constructed according to U.S. Pat. No. 6,453,974.  
         [0013]    [0013]FIG. 2 is an enlarged view of a part of FIG. 1 showing the positioning of one cord stopper in the respective lift cord.  
         [0014]    [0014]FIG. 3 is a perspective view of a window blind assembly constructed according to the present invention.  
         [0015]    [0015]FIG. 4 illustrates the structure of the cord stopper used in the window blind assembly shown in FIG. 3.  
         [0016]    [0016]FIG. 5 is a schematic drawing showing one cord stopper fastened to one lift cord according to the present invention.  
         [0017]    [0017]FIG. 6 is an assembly view of one lift cord and one cord stopper according to the present invention.  
         [0018]    [0018]FIG. 7 is a sectional view taken along line  7 - 7  of FIG. 5.  
         [0019]    [0019]FIG. 8 is a sectional view taken along line  8 - 8  of FIG. 6.  
         [0020]    [0020]FIG. 9 is a schematic drawing showing position adjustment of the cord stopper on the lift accord according to the present invention.  
         [0021]    [0021]FIG. 10 is a schematic drawing showing one of the cord stoppers stopped at the headrail according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    As shown in FIG. 3, a window blind assembly  200  is shown comprising a headrail  22 , a bottom rail  23 , a plurality of slats  21 , a supporting unit including two ladder tapes  24  connected to the headrail  22 , the bottom rail  23  and the slats  21  for spacedly supporting the slats  21  horizontally between the headrail  22  and the bottom rail  23 , a pair of lift cords  25  each having an end (not shown) affixed to the bottom rail  23 , a first portion  252  upwardly penetrated through the slats  21  and then transversely extended through the headrail  22 , and a second portion  251  extended out of the headrail  22  through a lift cord lock  26  that is mounted on the headrail  22 , and two cord stoppers  27  respectively fastened to the second portions  251  of the lift cords  25 .  
         [0023]    As shown in FIG. 4, the cord stopper  27  comprises two symmetrical hollow, elongated, oval-shape cover shells, namely, the first cover shell  271  and the second cover shell  272 . The cover shells  271  and  272  have a respective lateral side integrally hinged to each other such that the cover shells  271  and  272  can be turned relative to each other between a close position as shown in FIG. 6 and an open position as shown in FIG. 5. In addition, the cover shells  271  and  272  have a respective recessed space faced to each other such that a receiving chamber is formed inside of the cord stopper when the two cover shells are turn to the close position. The first cover shell  271  comprises an insertion hole  273  in a first end, a wire notch  275  in a second end, a plurality of holding down members, for example, arched ribs  277  transversely disposed in the recessed space thereof, and two locating grooves  279  bilaterally disposed in the recessed space thereof. The second cover shell  272  comprises two wire notches  274  respectively formed in the two distal ends, a plurality of holding down members, for example, protrusion rods  276  respectively disposed in the recessed space thereof corresponding in location to the arched ribs  277  of the first cover shell  271 , and two locating rods  278  bilaterally disposed in the recessed space thereof for engaging the locating grooves  279  of the first cover shell  271 .  
         [0024]    The installation of the cord stoppers  27  to the lift cords  25  are outlined hereinafter with reference to FIGS. 5-8. For easy understanding of the present invention, the following description only explains the installation of one cord stopper  27  in one lift cord  25 . At first, the first cover shell  271  and the second cover shell  272  are opened, and then a free end (not shown) of the second portion  251  of the lift cord is inserted downwardly through the insertion hole  273  into the inside of the first cover shell  271  and then turned upwards and then downwards and then inserted through the insertion hole  273  into the inside of the first cover shell  271  again to from a loop winding on the first cover shell  271 , and then the free end of the second portion  231  is pulled downwardly out of the recessed space of the first cover shell  271  through the wire notch  275 , and then the second cover shell  272  is covered on the first cover shell  271 , keeping the knot thus made received inside the cord stopper  27  as shown in FIG. 6. When closed, the protrusion rods  276  of the second cover shell  272  are respectively pressed on the second portion  251  of the lift cord against the arched ribs  277  of the first cover shell  271 , securing the cord stopper  27  to the second portion  251  of the lift cord in place as shown in FIG. 7. Further, when closed the cord stopper  27 , the wire notches  274  and  275  accommodate a part of the second portion  251  of the lift cord, and the locating rods  278  of the second cover shell  272  are respectively engaged into the locating grooves  279  of the first cover shell  271 , holding the cord stopper  27  in the closed status as shown in FIG. 8.  
         [0025]    Referring to FIG. 9, when adjusting the lifting range of the bottom rail  23  subject to one&#39;s desire or favorite, the position of the cord stoppers  27  should be relatively adjusted, preventing excessive stretching of the first portion  252  of each lift cord  25 . The present invention enables the user to conveniently adjust the position of the cord stoppers  27  relative to the lift cords  25 . The position adjustment of the cord stoppers  27  is easy. At first, open each cord stopper  27  by force (this can easily be achieved by an adult person). Because each lift cord  25  is fastened to the respective cord stopper  27  by a slip knot, the cord stopper  27  can easily be moved upwards or downwards on the respective lift cord  25  after opened the second cover shell  272  from the first cover shell  271 . After adjustment, the first cover shell  271  and the second cover shell  272  are closed again.  
         [0026]    Normally, the invention controls the sliding status of the lift cords  25  by means of the lift cord lock  26 . If the lift cord lock  26  failed, the slats  21  and the bottom rail  23  forced to fall by their gravity weight. Falling of the bottom rail  23  drives the lift cords  25 , causing the second portions  251  of the lift cords  25  to move toward the lift cord lock  26 , and at the same time the cord stoppers  27  are respectively moved with the second portions  251  of the lift cords  25  and then stopped at the lift cord lock  26  where the cord stoppers  27  lock up the downward falling movement of the bottom rail  23 .  
         [0027]    As shown in FIG. 10, if a child pulled the first portion  252  of one lift cord  25  between two adjacent slats  21  for fin, the respective cord stopper  27  will be moved upwards and stopped at the lift cord lock  26  in case the lift cord lock  26  failed at this time, preventing excessive stretching of the first portion  252 .  
         [0028]    As indicated above, the invention has numerous advantages as outlined hereinafter.  
         [0029]    1. By means of the cord stoppers  27 , the invention limits sliding of the lift cords  25  even if the lift cord lock  26  fails.  
         [0030]    2. By means of inserting the second portion  251  through the insertion hole  273  of the first cover shell  271 , the cord stopper  27  is easily fastened to the respective lift cord  25 .  
         [0031]    3. By means of the cord stoppers  27 , the moving distance of the bottom rail or the stretching distance of the lift cords is well controlled, preventing an accident.  
         [0032]    4. The protrusion rods  276  of the second cover shell  272  are respectively pressed on the second portion  251  of the lift cord against the arched ribs  277  of the first cover shell  271 , securing the cord stopper  27  to the second portion  251  of the lift cord in place.  
         [0033]    5. After installation, the user can adjust the elevational position of the cord stoppers  27  relative to the second portions  251  of the lift cords  25  simply by opening each cord stopper  27  and then moving each cord stopper  27  relative to the respective lift cord  25  to the desired elevation and then closing each cord stopper  27  again.  
         [0034]    6. The cord stoppers can be used in a conventional window blind assembly without making any structural change of the window blind assembly.  
         [0035]    7. Because the knot of each lift cord  25  is received inside the respective cord stopper  27 , the sense of beauty of the window blind assembly is maintained intact.  
         [0036]    Although a particular embodiment of the 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 cord stopper for use in slidably and detachably connecting a lift cord of a window blind assembly includes a first cover shell having an insertion hole for insertion of the lift cord, a second cover shell openably closed to the first cover shell to form a receiving chamber therebetween, and a plurality of holding down members disposed in the receiving chamber for pressing the lift cord that is inserted through the insertion hole of the first cover shell to hold the cord stopper on the lift cord.