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FIELD OF THE INVENTION 
     The present invention generally relates to window coverings and, more particularly, relates to cordless blinds and shades. 
     BACKGROUND OF THE INVENTION 
     A variety of window covering devices currently exist, including retractable shades and venetian blinds. In conventional venetian blinds, a plurality of slats are supported in ladder cords that extend between a head rail and a bottom rail. One or more take-up cords extend from the bottom rail, through the slats, and out of the head rail. Upward force on the take-up cords lifts the bottom rail towards the head rail, gathering the slats, from the lowermost to the uppermost. 
     In such blinds, the take-up cords are manually-operated. More specifically, the take-up cords which extend from the bottom rail, through the slats, and out of the head rail are drawn upon by a user which thereby lifts the bottom rail and hence the slats. A lock is typically provided to secure the take-up cord so that the blinds may be secured at various positions between a lowered, extended position, and a raised, fully retracted, position. 
     More recently, in cordless blind products, a spring motor has been provided that is coupled to a take-up drum to which the take-up cord is secured. The spring motor provides a lifting force to the take-up cord. Such spring motors provide smooth operation of the blind, and avoid lengthy cords extending from the blind which can be unsightly and become tangled thereby inhibiting operation of the blind. 
     With a cordless blind product, balancing of the spring motor force is difficult. As the blind is extended, the slats become supported by the ladder cords, and the weight supported by the spring motor reduces. Conversely, when the blind is retracted, the weight of the bottom rail and all the slats needs to be supported by the spring motor. Unless a spring motor provides a corresponding variable force, a number of problems may occur. For example, if the spring motor does not provide enough lifting force, the blind may not remain in the fully retracted position and may slowly fall downward. If the spring motor provides too much lifting force, the blind may not remain at an extended position, and the blind may slowly creep upward. 
     In practice, constant force spring motors sized to support the expected full weight of the slats may be used and an external mechanism, such as a clutch, may be used to lock the spring motor when the blind is at the desired location. However, such devices typically do not provide smooth operation. 
     Variable force spring motors have therefore been developed and permit the blind to be extended to virtually any position from fully retracted to fully extended. Still, sizing the spring motor is difficult. The variable force can be generated by using a spring member tapered in width, thickness and/or diameter which thus results in a force curve having its greatest force when the blind is retracted, and its lowest force when the blind is extended. Depending on the size and weight of the slats and bottom rail, the spring motor can be sized accordingly, or multiple spring motors may be used. 
     Even with such variables force spring motors, the introduction of friction to the system can be advantageous. Such additional friction creates a wider acceptable operational range for a given size of spring motor. However, if too much friction is added to the system, operation of the spring motor and blind will not be smooth. Moreover, it is desirable for the friction to be added only when the blind is being retracted and for little or no additional friction to be added when the blind is extended. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a window shade is provided which comprises an expandable covering, the covering being movable in a first direction when expanding to cover a window, the covering being movable in a second direction when retracting away from the window, a spring motor operably connected to the expandable covering to move the covering in the second direction, a rotating output connected to the spring motor, and a retarder associated with the rotating output, the retarder introducing resistance to movement of the covering in the second direction while not introducing resistance to movement of the covering in the first direction. 
     In accordance with other aspects of the invention, the retarder includes a one-way bearing or a brake. 
     In accordance with another aspect of the invention, a blind is provided which comprises an expandable covering, the covering being movable in a first direction when expanding, and in a second direction when retracting, a cord connected to the expandable covering, the cord being movable in a first direction when the covering is retracted and in a second direction when the covering is expanded, a spring motor connected to the cord for moving the covering between the retracted position and the expanded position, and a one-way roller in engagement with the cord for adding resistance to the movement of the cord in the first direction. 
     In accordance with another aspect of the invention, a blind is provided comprising an expandable covering, the covering being movable in a first direction when expanding and in a second direction when retracting, a cord connected to the expandable covering, a cord spool connected to the cord, a spring motor connected to the cord spool by a rotatable shaft, and a brake adapted to impart a first force against the shaft when the expandable covering moves in the first direction, and a second, higher, force when the expandable covering moves in the second direction. 
     In accordance with yet another aspect of the invention, a spring motor assembly is provide including a frame, a take-up drum pivotally mounted to the frame, a drive drum pivotally mounted to the frame, a coil spring interconnected between the take-up drum and the drive drum, a rotating member operatively connected to the drive drum, and a retarder associated with the rotating member. The retarder introduces resistance to the rotating member in a first direction of rotation and not in a second direction of rotation. 
     These and other aspects and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a blind according to the invention; 
     FIG. 2 is a top view of FIG. 1; 
     FIG. 3 is an enlarged fragmentary view of FIG.1; 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a sectional view of one embodiment of a one-way bearing according to the invention; 
     FIG. 6 is a sectional view of a second embodiment of a one-way bearing according to the invention; 
     FIG. 7 is a schematic representation of a second embodiment of the invention; 
     FIG. 8 is a schematic representation of a third embodiment of the invention; 
     FIG. 9 is a schematic representation of a fourth embodiment of the invention; 
     FIG. 10 is a schematic representation of a fifth embodiment of the invention; 
     FIG. 11 is a schematic representation of a sixth embodiment of the invention; 
     FIG. 12 is a schematic representation of a seventh embodiment of the invention; 
     FIG. 13 is a schematic representation of an eighth embodiment of the invention; and 
     FIG. 14 is a schematic representation of a ninth embodiment of the invention. 
    
    
     While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and with specific reference to FIG. 1, a blind or shade according to the invention is generally depicted by reference numeral  20 . As shown therein, the blind  20  includes a head rail  22 , a bottom rail  24 , and a window covering material  26  therebetween. In the depicted embodiment, the window covering  26  includes a plurality of slats  28 , but other material, fabrics, and structures may be utilized. 
     In order to raise and lower the bottom rail  24  and slats  28 , and thus move the blind  20  between a retracted upper position and a lowered extended position, the slats  28  are supported by first and second ladder cords forming a series of continuous loops (not shown), and first and second take-up cords  30 ,  32  extend through the slats  28  and connect the base rail  24  to the first and second cord spools  34  and  36 . Rotation of the first and second cord spools  34  and  36  winds and unwinds the first and second take-up cords  30 ,  32  respectively thereon, and thus raises and lowers the blind  20 . As opposed to conventional venetian blinds which extend the take-up cords from the head rail  22  for manually raising and lowering the blind  20 , a cordless blind such as that depicted, includes a spring motor  38  to provide the motive force for raising the blind  20 . 
     More specifically, as shown in FIG. 2, the spring motor  38  includes a take-up drum  40  and a drive drum  42  which are connected by a spring member  44 . The spring member  44  is a coil spring in the form of a ribbon of metal pre-stressed on one side to thus cause the spring member  44  to have a natural or relaxed state in the form of a wound coil. The spring member  44  is wound onto the take-up drum  40  in its relaxed state, and connected to the drive drum  42  such that upon rotation of the drive drum  42 , the spring member  44  is back wound onto the drive drum  42 . Thus, when the drive drum  42  rotates and back winds the spring member  44  onto the drive drum, the spring member  44  is biased to rewind back on to the take-up drum  40 . It is this biasing force which is utilized by the blind  20  to raise the window covering  26 . 
     Referring now to FIGS. 2 and 3, the spring motor  38  is shown positioned between the first and second cord spools  34  and  36 . The cord spools  34  and  36  are intermeshed, as through gears, with the take-up drum  40  and drive drum  42  such that rotation of the cord spools  34  and  36  causes rotation of the drive drum  42  and take-up drum  40 , and thus winding or unwinding motion in the spring member  44 . 
     For example, when the blind  20  is moved from the retracted position to the extended position, the bottom rail  24  is pulled away from the head rail  22 . This in turn pulls the first and second take-up cords  30  and  32  away from the head rail and causes the cord spools  34  and  36  to rotate. The rotation of the first and second cord spools  34  and  36  in turn causes the drive drum  42  to rotate and thus back wind a spring member from the take-up drum  40  to the drive drum  42 . The take-up drum  40  is independently mounted such that rotation of the first and second cord spools  34  and  36  does not directly cause rotation of the take-up drum  40 . 
     Thus, by pulling the bottom rail  24  downwardly away from the head rail  22 , a spring member  44  is back wound onto the drive drum  42  creating biasing force tending to cause the spring member  44  to wind back onto the take-up drum  40  and thus pull the bottom rail toward the head rail. By appropriately sizing the width, thickness and or diameter of the spring member  44 , this biasing force can be graded such that it is greatest when the bottom rail is fully retracted, and least when the bottom rail is fully extended. Otherwise, if a constant spring force member  44  is utilized, a mechanical locking or clamp mechanism must be utilized. 
     In order to ensure that a spring member  44  does not cause unwanted motion in the blind  20 , additional friction is added to the system by the present invention by various forms of variable friction mechanisms or retarders. In the description that follows in correspondence to FIGS. 4-14 the various embodiments are depicted to show multiple ways in which friction can be added to the system during one direction of motion of the blind  20 , and not in the opposite direction. However, it is to be understood that these embodiments are listed by way of example only, and not exclusive. 
     First with regard to FIGS. 2-4, the first take-up  30  cord  30  is shown extending from the first cord spool  34  and wrapped around a capstan  46 . The take-up cord  30  extends backward in the direction of the first cord spool  34  and then downwardly through a cord assembly  47  mounted to the head rail  22 . The capstan  46  includes a cylindrical hub  48  with first and second tapered or frusto-conical sections  50  and  52 . The capstan  46  also includes a through hole  54  about which the capstan  46  is able to rotate. As shown in FIG. 4, the capstan  46  is mounted to a frame  56  by an axle  58  and a bearing  60 . A second capstan  46  is similarly provided for the second cord  32 . 
     The bearing  60  is a one-way style of bearing in that it freely rotates in a first direction (clockwise or counterclockwise), but which resists rotation in the opposite direction. By wrapping the first take-up cord  30  around the capstan  46  and providing the one-way bearing  60  in an orientation which freely rotates with the cord  30  when the bottom rail  24  is pulled from the head rail  22 , the capstan  46  will necessarily resist rotation in the opposite direction. This means that friction will be introduced by the one-way bearing  60  when the bottom rail  24  is moved toward the head rail  22 . Since the capstan  46  will not rotate, the frictional drag between the first take-up cord  30  and the cylindrical hub  48  of the capstan  46  will slow movement of the first take-up cord  30  and thus movement of the blind  20 . 
     FIGS. 5 and 6 show two embodiments of one-way bearings which may be utilized by the invention. However, again, such embodiments are by way of example only, and are not exclusive. Referring first to FIG. 5, the one-way bearing  60  is shown to have an outer race  62  having a plurality of locking ramps  64  corresponding in number to the number of balls  66  journalled within an inner race  68 . The outer race  62  is frictionally engaged within the through hole  54  of the capstan  46  such that relative rotation between the outer race  62  and the capstan  46  is not possible. If the capstan  46  is rotated in a clockwise direction as depicted in FIG. 5, the balls  66  rotate clockwise as well, while the axle  58  is stationary. If the capstan  46  attempts to rotate counterclockwise, the balls  66  are frictionally engaged by the locking ramps  64  to prevent such rotation. 
     With regard to FIG. 6, another type of one-way bearing  60  is shown. The bearing  60  includes an outer race  70  frictionally engaged within the through hole  54  of the capstan  46 . A plurality of locking tabs  72  radially extend inwardly from the outer race  70 . The axle  58  shown in FIG. 6 is stationary, but includes a star shape in cross-section formed by a plurality of cam surfaces  74  extending radially outwardly therefrom. More specifically, each cam surface  74  includes an arcuate portion  76  and a locking shoulder  78 . When the capstan  46  and outer race  70  rotate in a clockwise direction, the arcuate portions  76  engage the flexible locking tabs  72  by pushing the locking tabs  72  outwardly and allowing the capstan  46  to rotate. However, when the capstan  46  and outer race  70  attempt to rotate clockwise, the locking tabs  72  engage the locking shoulders  78 , and prevent rotation. 
     FIG. 7 shows a second embodiment of the invention wherein the cord spool  34  is not linearly aligned with the spring motor  38 , but rather is connected to a rotating shaft  80  extending from the spring motor  38 . A roller  82  is provided downstream of the cord spool  34  and is mounted on a one-way bearing  60 . The roller  82  is allowed to rotate in a clockwise direction, but not in a counterclockwise direction. 
     FIG. 8 is a schematic representation of a third embodiment of the invention wherein the roller  82  is mounted onto a tension spring  84 . Again, the roller  82  is downstream of the cord spool  34 , and the roller  82  is mounted on to a one-way bearing  60 . The tension spring  84  adds additional friction to the movement of the take-up cord  30 . 
     FIG. 9 is a schematic representation of a fourth embodiment of the invention wherein the second roller  86  mounted on a second tension spring  88  is disposed so as to oppose the first roller  82 . The first and second rollers  82  and  86  are downstream of the cord spool  34  and are mounted on one-way bearings  60 . First and second tension springs  84  and  88  pinch the cord between the first and second rollers  82  and  86  to add additional friction to the movement of the take-up cord  30 . 
     FIGS. 10 and 11 show fifth and sixth embodiments wherein resistance is added to the rotation of the shaft  80 , as opposed to the take-up cord  30 . More specifically, in FIG. 10, a brake arm  90  is disposed at an angle to the shaft  80 . The brake arm  90  includes a cam surface  92  and a braking surface  94 . The brake arm  90  is biased into engagement with the shaft  80  by a tension spring  96 . When the shaft  80  rotates in a clockwise direction as shown in FIG. 10, the shaft  80  engages the cam surface  92  which pushes the brake arm  90  away, against the force of the tension spring  96 . However, when the shaft  80  attempts to rotate in a counterclockwise direction, as shown in FIG. 10, the tension spring  96  forces the braking surface  94  into engagement with the shaft  80  and thus resists rotation. 
     FIG. 11 is similar to FIG. 10 in that a brake arm  90  is utilized, however the embodiment of FIG. 11 includes three brake arms  90 , all of which are mounted to the shaft  80 . In addition, the shaft  80  and brake arms  90  are mounted within a cylinder  98 . The brake arms  90  are pivotally attached to the shaft  80  at pivots  100  such that rotation of the shaft  80 , in a counterclockwise direction, will cause the cam surfaces  92  to engage the cylinder  98  and force the brake arms  90  radially inwardly toward the shaft  80 . As a result, rotation of the shaft  80  will not be impeded. However, if the shaft  80  attempts to rotate in a clockwise direction, the brake surfaces  94  of the brake arms  90  engage the cylinder  98  and resist rotation of the shaft  80 . 
     FIG. 12 depicts a seventh embodiment of the invention wherein a first roller  102 , having a fixed pivot  104 , is provided adjacent a second roller  106  mounted on a tension spring  108 . The take-up cord  30  is trained around the second roller  106  between the first roller  102  and second roller  106 . If the take-up cord  30  is pulled downwardly, the tension spring  108  compresses, moving the cord  30  out of engagement with the first roller  102 . The first roller  102  is thereby able to rotate with little friction being added to the motion of the take-up cord  30 . However, when the take-up cord  30  attempts to move upwardly, the tension spring  108  forces the take-up cord  30  into pinching engagement between the first and second rollers  102  and  106 , thereby adding friction and drag to the movement of the take-up cord  30 . 
     FIGS. 13 and 14 depict eighth and ninth embodiments of the invention wherein first and second pulleys  110  and  112  are mounted outside the spring motor  38  with a belt  114  being trained around the first and second pulleys  110  and  112 . 
     In FIG. 13, the first and second pulleys are mounted concentric with the first and second cord spools  34  and  36  with the first pulley  110  being mounted onto a one-way bearing  60 . It is to be understood that, alternatively, the second pulley  112  could be mounted on a one-way bearing. As a result, rotation of the cord spools in one direction is not impeded by the one-way bearing  60 , whereas rotation of the cord spools  34  and  36  in the opposite direction is impeded by the one-way bearing  60 . 
     FIG. 14 is similar to FIG. 13 but for the addition of a belt tension adjustment mechanism  116 . The belt tension adjustment mechanism  116  is provided in a form of a roller  118  mounted to a pivot arm  120 . As can be appreciated from FIG. 14, the roller  118  is able to travel an arcuate pathway  122  as the pivot arm  120  pivots about arcuate pathway  122 . In so doing, the diameter of the belt  114  can be increased or decreased and thus increase or decrease the tension within the belt  114 . The belt tension adjustment mechanism  116  adds a constant amount of friction to the belt  114  regardless of the direction of rotation of the belt  114 . As a result, at least one of the pulleys  110  and  112  is mounted on a one-way bearing  60 . 
     From the foregoing, it can therefore be seen that the invention provides a spring motor, and window blind driven by a spring motor, with a mechanism for adding resistance to rotation of the spring motor in one direction and not the opposite direction.

Summary:
A cordless blind having a mechanism for introducing a variable amount of friction into the operation of the cordless blind is disclosed. The cordless blind includes a spring motor operatively connected to a cord connected to the window covering of the blind. Pulling and releasing the cord expands and retracts the blind. In order to introduce additional resistance to movement into the system when retracting the blind and not when expanding the blind, variable friction mechanisms or retarders, including one-way bearings, and one-way braking arms, are used for introducing friction into the system only when desired.