Abstract:
A tensioning device for the cord loop of a window treatment apparatus includes a cord guide disposed in a housing, a biasing element such as a spring and a locking member that locks the cord guide into an installation position. During installation, the cord guide is fixed so that it cannot move and does not affect the tensioning of the cord. After installation, the locking member is removed and the cord guide can move in one direction or another to properly tension the cord.

Description:
RELATED APPLICATIONS 
     This application claims priority to provisional application Ser. No. 60/347,973 filed Nov. 13, 2001 and incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This application pertains to a device for tensioning the cord used for operating a roller blind or other similar window covering, and more particularly to a tensioning device that is adapted to adjust the tension automatically to adjust for changes in the physical characteristics of the cord. 
     B. Description of the Prior Art 
     Window coverings such as roller blinds, vertical and horizontal Venetian blinds, and so on, are typically operated by control cords that can be pulled in one direction or another. While many window coverings use a cord with two ends, systems are also popular that use a cord forming a closed loop. However, such systems are alleged ti be potentially dangerous to children. Therefore, interested organizations (such as the American National Standards Institute (ANSI) and the Window Covering Manufacturers Association (WCMA)) have developed a specification, in conjunction with the Consumer Products Safety Commission (CPSC), requiring such closed loop cord control systems to be secured by a tensioning device. The tensioning device is used externally of the window covering and is arranged so that it applies a tension in the cord within a predetermined range. 
     These tensioning devices are extremely effective in minimizing the danger to infants and young children resulting from the improper use of these cords. However, one problem with them is that during installation they must be carefully adjusted because if too much tension is applied, the window covering becomes difficult to operate and the additional stress on the window covering components results in a high wear and tear and reduced useful life. In fact, under certain conditions if the tension is high enough, the window covering may stop operating. 
     Strict instructions are normally provided to installers on how to install the window covering and the tensioning device. However, these instructions are frequently ignored, especially if the installer is the homeowner and not a professional. 
     A further problem in existing tensioning devices is that a high tension may develop after the tensioning device is installed due to changes in the physical characteristics of cord. For example, if the cord is made of knit or braided material, its fibers may shrink due to age, temperature and/or humidity changes, resulting in an increased tension. 
     OBJECTIVES AND SUMMARY OF THE INVENTION 
     In view of the disadvantages of the prior art, it is an objective of the present invention to provide a tensioning device that adjusts automatically to maintain tension in a continuous cord to a predetermined level. 
     A further objective is to provide a tensioning device that can be installed easily and quickly without requiring any special tools or techniques. 
     Yet another objective is to provide a tensioning device that does not require any extensive redesign, changes of components or other increased costs. 
     Other objectives and advantages of the invention shall become apparent from the following description. 
     Briefly, a tensioning device adapted to tension a cord loop of a window treatment apparatus includes a housing; a cord guide disposed in said housing and adapted to receive a portion of the cord loop; a biasing member adapted to bias said cord guide to apply tension on said cord loop; and locking means adapted to lock said cord guide in an installation position, said locking means being removable to allow said cord guide to tension said cord loop. The locking means includes a tab removably inserted into said cord guide. The tab may be a flexible tab extending through said housing and said cord guide. In one embodiment, rails defining a path of movement for said cord guide are disposed within said housing, the cord guide being adapted to shift up and down in the housing along the guide to selectively increase or decrease the tension on the cord loop. 
     In another embodiment, the cord guide includes a pulley rotatably disposed in said housing. 
     In another aspect of the invention, the tensioning device includes a housing having two housing portions; a cord guide movably disposed within said housing and adapted to receive a cord loop; a biasing spring coupled to said cord guide and adapted to apply a biasing force on said cord guide to thereby tension said cord loop; and a locking tab extending through said housing, said locking tab being constructed and arranged to lock said cord guide against movement during installation, said locking tab being removable to release said biasing spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a window covering with a first prior art tensioning device; 
     FIGS. 2 a  and  2   b  show perspective views of other prior art tensioning devices without springs; 
     FIGS. 3A-3C show a side elevational view of a prior art tensioning device with a spring and a pulley in an unmounted position, a mounted and operational position and a mounted and inoperational position, respectively; 
     FIG. 4 shows an exploded view of a tensioning device constructed in accordance with this invention; 
     FIG. 5 shows a side elevational cross sectional view of a tensioning device constructed in accordance with this invention; 
     FIG. 6 shows a front perspective elevational view of a tensioning device constructed in accordance with this invention with the housing closed; 
     FIG. 7 shows a rear perspective elevational view of a tensioning device constructed in accordance with this invention, with the housing closed. 
     FIGS. 8A-8C show a side elevational view of a tensioning device without a pulley constructed in accordance with the present invention in a mounted, a mounted intermediate, and a mounted final position, respectively; 
     FIG. 9 shows a perspective view of an alternate embodiment of the invention with a pulley; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a typical installation of a window treatment apparatus with tensioning means. The window treatment apparatus  10  consists in this case of a folded panel  12  hanging from a cassette  14 . The cassette  14  is secured to a window frame  16 . Incorporated within the cassette  14  there is a mechanism (not shown) which is not part of this invention and which is activated or operated by a cord loop  18 . The cord loop passes through a tension device  20  also secured to the window frame  16  and is adapted to provide tension in cord loop  18 . FIGS. 2A and 2B show two types of tension devices  20 A and  20 B which do not utilize springs or any other active means of generating tension in the loop cord  18 . Hence, the tension in the loop cord  18  is controlled only by the position of the tension devices on the frame  16 . If this position is not selected properly, or if the loop cord  18  shrinks over time, the tension within the loop will increase, possibly to a level that may render the apparatus  10  inoperable. 
     FIGS. 3A-3C show a more advanced tensioning device  20 C for tensioning cord loop  18 . The device  20 C includes a housing  22  supported by a bracket  24 . Inside the housing there is provided a pulley  26  biased in the downward direction by a spring  28 . The cord loop  18  is trained around the pulley, as shown. FIG. 3A shows the tension device  20 C before installation, with the spring  28  being relaxed. FIG. 3B shows the device  20 C installed. Normally, the device  20 C is positioned so that the pulley  26  is raised slightly and pushes upwardly against the spring  28 . In this position, the tension in cord loop  18  is dependent on the force generated by the spring  28 . However, if the device  20 C is installed too low and/or if the cord loop  18  shrinks excessively, the pulley  26  is raised sufficiently to squeeze the spring  28  tightly up against the top  30  of housing  22 . Under these conditions, the spring  28  is in effect disabled and the tension within the cord loop  18  may be high enough to interfere with the operation of, or even disable the respective apparatus. A tensioning device of this type is disclosed in U.S. Pat. No. 6,311,756, incorporated herein by reference. 
     A tensioning apparatus constructed in accordance with the present invention is shown in FIGS. 4-8. In this embodiment, the apparatus  120  includes a housing  122  formed of two housing parts  122 A,  122 B. A through hole  123  passes through the housing parts  122 A,  122 B. A bracket  24  is constructed and arranged to be mounted on a window frame. A straight pin  25  is used to attach housing  122  to the bracket  24  by passing the pin  25  through holes  123  and  125  in bracket  24 . 
     Within the housing  122  there is provided a cord guide  126 . Guide  126  is substantially semicircular with an annular groove  127  for accommodating the cord loop  18 . The cord guide  126  is associated with a spring  128 . More particularly, groove  129  are provided to allow the cord guide  126  to move up and down within the housing  122 . A spring  128  is disposed between the cord guide  126  and a top  130  portion of housing  122 . As in the embodiment of FIGS. 3A-3C, the cord guide is biased downwardly by the spring  128 . Preferably, housing part  122 A is formed with tracks  131 . The cord guide  126  is constructed so that it can move up and down on the tracks  131  within the housing  122 . 
     Importantly, the housing part  122 B is formed with a horizontal slot  132 . A similar slot  134  is provided in the cord guide  126  and a third slot  136  is formed in the housing part  122 A as shown. The cord guide  126  can be positioned between the housing portions  122 A,  122 B so that the three slots  132 ,  134 ,  136  are aligned to receive and accommodate a tab  140 . As seen in FIG. 4, the tab  140  is formed of a front portion  142  which is relatively flat and an intermediate portion  144  and a rear portion  146 . The front and rear portions  142 ,  146  are substantially parallel and the intermediate portion  144  is perpendicular to the end portion and is sized and shaped to fit through slots  132 ,  134 ,  136 . The front portion  142  is large enough so that it can be imprinted with some instructions. 
     When the tensioning device  120  is completely assembled, the front and rear portions  142 ,  146  of tab  140  are abutting the housing portions  122 B, 122 A, respectively, with the intermediate portion  144  extending through the housing portions  122 B,  122 A and the cord guide  126 , as seen in FIGS. 7 and 8. As shown in FIG. 5, in this position the cord guide  126  is pushing upwardly against the spring  128  so that the spring is somewhat compressed. Thus, tab  140  defines an installation position for the cord guide  126  in which the guide can travel a large distance vertically upward before coil  128  is completely compressed. 
     The tensioning device  120  is shipped with the tab  140  in place and the cord guide  126  locked in the installation position, as defined above, and shown in FIG.  8 A. When the tensioning device  120  is received, it is first installed on its bracket  24  while the tab  140  is in place, as shown in FIG.  8 B. The installer is instructed to insure that the bracket should be positioned to insure that the cord loop  18  is relatively taught, not loose. Because the tab  140  prevents movement of the cord guide  126 , the spring  128  does not yet apply any force on the cord loop  18 . 
     The tab  140  is made of an elastic material so that as the front portion  142  is pulled forward, the rear portion  144  is bent and can be retrieved through the slots  132 ,  134 ,  136 . The tab  140  can be made of paper or plastic. Once the tensioning device  120  is properly installed, the tab  140  is removed, as shown in FIG.  8 C. As soon as the tab is removed, the cord guide  126  is pushed down by the spring  128  thereby tensioning the cord loop  18  to the proper level. Moreover, if the cord loop  18  gets shorter because of shrinkage or other reason, the cord guide  126  automatically rises to compensate for this effect. However, because in its initial or installation position, the cord guide  126  is positioned at the bottom of the housing  120 , there is sufficient room in the housing to allow the cord guide  126  to rise applying excessive tension on the cord loop  18  and disabling the whole apparatus. 
     In the embodiment of FIGS. 4-8, the cord guide  126  provides groove  127  through which the cord loop  18  can slip. In order to reduce friction, the cord guide  126  can incorporate a pulley  126 A, as shown in FIG.  9 . The pulley  126 A is formed with a slot  134 A to accommodate a tab as described above. In addition, as shown in FIG. 9, instead of a compression-type spring  18 , a tension spring  28 A can be used to bias the pulley  126  downwardly. Of course, a similar tension spring  28 A may also be used for the embodiments of FIGS. 4-8. 
     The pulley  126 A is rotatably supported by a bracket  133  which is then connected to the end of spring  128 A. The slot  134 A may be provided in the bracket  133  rather than the pulley  126 A. 
     The tensioning device described herein is advantageous because it insures that the cord loop is properly tensioned at installation. Moreover, if the tension on the cord loop changes, for example, due to changes in the physical characteristics of the cord loop, the device automatically adjusts itself by allowing the cord guide or pulley to shift. 
     The tab can also be made of a relatively stiff material, in which case it is inserted into the housing through the slots and can be selectively removed therefrom without necessary bending any of its portions. 
     While the invention has been described with reference to several particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles of the invention. Accordingly, the embodiments described in particular should be considered as exemplary, not limiting, with respect to the following claims.