Abstract:
A drape or blind assembly having a headrail in which there is disposed a shaft, on rotation of which the position of the drapes or blind slats is adjusted, and a transmission mechanism having a housing and a drive gear supported by the housing in the headrail with the drive gear coaxial with the axis of the shaft and a rigid one piece coaxial coupling coupled between the shaft and the gear so that normal rotation of the drive gear causes rotation of the shaft. If, however, the drive gear is rotated past a predetermined rotational position, a stop member generally provided on the coupling engages an abutment member to prevent further rotation of the shaft. To prevent damage to the mechanism in such a situation, the mechanism includes a recess defined by first drive surfaces and resilient arms having complementary second drive surfaces. On continued rotation of the drive gear after the stop member has engaged the abutment member, the resilient arms flex to permit relative rotation of the first and second drive surfaces. Bearings are provided in the headrail for rotatably supporting the shaft, and retaining it in position.

Description:
FIELD OF THE INVENTION 
     The invention relates window covering assemblies such as drapes or blends and to a coupling for use in transmission mechanisms, and also to a novel form of bearing assembly and method of assembling such drapes and blinds using such bearing assemblies. This application is a continuation in part of U.S. patent application Ser. No. 07/733,652 filed Jul. 22, 1991, U.S. Pat. No. 5,139,072, entitled Coupling and Transmission Mechanism for Drape or Blind Assembly, inventor Norbert Marocco, which was a continuation-in-part of U.S. patent application Ser. No. 475,734 filed Feb. 7, 1990 entitled Coupling and Transmission Mechanism for Drape or Blind Assembly, inventor Norbert Marocco (now abandoned). 
    
    
     BACKGROUND OF THE INVENTION 
     Window coverings such as venetian blinds are well known in which a so-called headrail or channel supports a horizontal shaft. The horizontal shaft carries the tapes or cords on which the slats of the venetian blind are supported. Rotation of the rod in one direction or the other will tilt the slats one way or the other, thus closing and opening the blind. 
     Operation of the control rod may be through a pulley and continuous chain, or may be by means of a worm and wheel, and a wand rotating the worm, so as to thereby rotate the shaft. 
     The shaft on which the tapes or cords are wound, can only be rotated a certain distance in either direction, and will then stop. If, however, excessive torque is applied to the shaft, the blind can be damaged. 
     Accordingly, it is desirable to incorporate a torque limiting device so that if the continuous chain or wand is rotated beyond the point at which the shaft must stop, the chain or wand will simply rotate, and the torque limiting device will prevent the rotation being transmitted to the shaft. Various different types of clutch devices have been proposed, in most cases being of considerable degrees of complexity requiring costly tooling, and time-consuming assembly. In addition, as the design of venetian blinds becomes further and further refined, the space available for incorporating such a torque limiting device becomes more and more restricted. 
     In window coverings in many case a worm and gear wheel drive is used, axis of the wheel in the mechanism is offset with respect to the axis of the shaft. As a result, it is also necessary to incorporate some form of flexible coupling, to take into account the lack of alignment, and this further complicates the incorporation of a torque-limiting device. 
     However, in one case a flexible drive was used having a drive shaft coupling secured to one end, and a gear coupling at the other end, which did incorporate a form of torque limiting device, but it was relatively expensive. 
     In some window covering assemblies, a rotatable shaft is provided in the headrail for raising and lowering the drapes or blind slats. In such assemblies, it is also desirable to provide a transmission or clutch mechanism for limiting rotation of such shaft beyond certain limiting positions. 
     This invention provides a transmission mechanism for use in window covering assemblies of the type including a headrail having disposed therein a control shaft on rotation of which the positions of the drapes or blind slats may be adjusted and in which the transmission mechanism is operative to limit rotation of such a shaft while preventing accidental damage to the drive or transmission mechanisms if a person operates the drive mechanism in an attempt to move the shaft beyond such limiting positions. 
     This invention provides a novel coupling for use in such a transmission mechanism. 
     This invention also provides a novel form of bearing for supporting the shaft in the headrail. 
     One design of such venetian blind assemblies is shown in U.S. Pat. No. 4,531,563. 
     The design disclosed in this patent involves the use of a headrail of channel shaped construction, having two edge flanges. The tilt rod was supported on two or more bearing assemblies. Each of the bearing assemblies consisted of generally U-shaped rectangular metal components which could be snap fitted in the headrail and secured in position by frictional engagement with edge flanges on the headrail. 
     In this design, however, it was necessary to provide additional rod retention components also of a generally inverted U-shaped sheet metal construction, which could be snap fitted into the headrail after the insertion of the tilt rod in the bearing assemblies, and then retaining the tilt rod in position in the bearing assemblies. 
     Thus each of the bearing assemblies consisted of two separate components. Each of the components had to be snap fitted into the blind headrail at separate times, requiring two distinct operations for the completion of each bearing assembly. 
     In addition, since the components illustrated in that patent were formed of sheet metal, their construction was relatively expensive. As a result that design, while having met with considerable commercial success in the past, is nevertheless relatively expensive in terms of the actual components themselves and is also relatively costly in terms of the abandoned required for assembly. 
     In addition to these features of this earlier design, the tilt rod itself was retained at one end in a tilt control drive mechanism, of a type which is generally well known in the-art, although different designs are provided by different manufacturers. 
     However, in order to retain the tilt rod in position in engagement with the drive assembly, it was necessary in this earlier design to provide a form of stop mechanism engaging the free end of the tilt rod remote from the gear drive, to retain the one end of the tilt rod in engagement with the tilt drive. This meant that yet another component again formed of sheet metal, had to be designed and manufactured and supplied and then assembled in order to provide a complete functional blind. 
     A further design of tilt rod bearing for venetian blinds is illustrated in U.S. Pat. No. 4,333,510. In that form of bearing, the bearing assembly consisted of a one piece integral moulded structure. The structure incorporated two U-shaped bearings for the tilt rod. One of the U-shaped structures incorporation abutments to retain the tilt rod in position. 
     In that form of structure, the bearing assembly had lower leg portions adapted to extend through the lower central web of the headrail, and had tooth formations engaging either side of an opening in the lower web portion of the headrail. 
     In that form of bearing, openings were provided in the lower portion of the bearing structure for passage of the tilt elements and the suspension elements but without the provision of any antifriction bearing. As a result, extensive use would cause wear on the plastic around the openings. 
     A still further form of blind assembly is illustrated generally in U.S. Pat. No. 4,945,970 issued Aug. 7, 1990 entitled CORD LOCK UNIT FOR DRAPE OR BLIND ASSEMBLY. 
     However, no details of the bearing assembly are illustrated in that patent. 
     It is, therefore, apparent that it is desirable to provide such a venetian blind assembly in which the tilt rod is supported in bearings of integral one piece moulded construction, which bearings both support the tilt rod and also retain it in the headrail, and in which the bearings are securely held relative to the headrail against movement, and in which the bearing assemblies incorporate antifriction means for passage of the flexible tilt elements and flexible support element. 
     Other objects of the invention will become apparent as the description herein proceeds. 
     BRIEF SUMMARY OF THE INVENTION 
     Broadly, the present invention provides a window covering assembly of the type including a headrail having drapes or blind slats suspended therefrom and having disposed therein a shaft on rotation of which the positions of the drapes or blind slats may be adjusted and which transmission mechanism comprises a housing adapted to be disposed in such a headrail, a drive gear rotatably supported in the housing for rotation about a first axis, support means on the housing whereby it is non-rotatably disposed in the headrail with the axis of said drive gear coaxial with the axis of said shaft within said headrail, an integral one-piece rigid coupling coupled coaxially to said drive gear and to said-shaft for transmitting rotational movement of said drive gear to said shaft, a stop member, and an abutment member adapted to engage the stop member on rotation of said coupling to a predetermined rotational position thereby then to prevent further rotation of said coupling, said transmission mechanism including a recess having internal first surfaces, and resilient arm means extending into said recess and having second surfaces complementary to said first surfaces and adapted normally to engage said first surfaces to transmit rotational movement therebetween and whereby, upon rotation of said shaft to said predetermined rotational position and engagement of said stop member with said abutment member, and if excessive torque is thereafter applied to said resilient arm means on continued rotation of said drive gear, to cause said arm means to flex thereby in turn to permit one of said first and second drive surfaces to continue to rotate past the other of said first and second drive surfaces. 
     In such a transmission mechanism, the aforementioned recess can be provided in the drive member with the resilient arm means being integrally formed with the coupling. Alternatively, the recess can be provided in the coupling with the resilient arm means being integrally formed with the drive member. 
     Such resilient arm means can comprise a pair of mutually spaced apart arms separated by an axially extending slot whereby said arms will be flexed toward each other when sufficient torque is applied thereto but will spring apart from each other when such an excessive torque is no longer applied. 
     The stop member provided in such a transmission mechanism will generally be integrally formed with the coupling to project therefrom. The abutment member can be integrally formed with the housing to project therefrom or may be provided as a separate component adapted to be secured to the headrail of such a drape or blind assembly. 
     The coupling forming part of a transmission mechanism in accordance with this invention may also include an axial recess coaxial with said arms and extending into the coupling for receiving the shaft of the drape or blind assembly. 
     One embodiment of a transmission mechanism in accordance with this invention also comprises a worm drive gear carried by a drive shaft rotatably supported in the housing, said worm drive gear engaging said drive gear whereby rotation of said worm drive gear causes rotation of said drive gear. In such an embodiment, the housing preferably comprises a boss portion adapted to extend through an opening in the headrail of the drape or blind assembly with a drive shaft extending through the boss portion and a tongue portion extending downwardly from said housing spaced from said boss, to engage the base of said headrail and support said housing with said gear coaxial with said shaft. 
     As already indicated, the present invention also provides a novel coupling for use in a transmission mechanism in a window covering assembly of the type hereinbefore described. Such a coupling can be broadly defined as comprising an integral one piece rigid body adapted to be coupled coaxially to the shaft of the drape or blind assembly for co-rotation therewith and having integrally formed therewith resilient arm means having second surfaces complementary to the surfaces within a recess of a drive member forming part of such a transmission mechanism and coaxial with said drive gear and said shaft, and a stop member on said body adapted, upon rotation of said coupling to a predetermined rotational position, to engage an abutment member so that if excessive torque is then applied to said resilient arm means by continued rotation of said drive gear such torque causes said arm means to flex thereby in turn to permit said drive gear to continue to rotate with said first surfaces rotating past said second surfaces without transmitting torque to said shaft. 
     Such a coupling finds use in the manufacture of drape and blind assemblies incorporating existing forms of transmission mechanisms. For example, such a coupling can be used with a transmission mechanism in which the end of the shaft is normally received in an axial recess in the drive member or gear of the transmission mechanism. It will be understood that the housing of such an existing transmission mechanism will not be provided with an abutment member for engaging the stop member on the coupling. This can, however, be resolved by providing a separate abutment member adapted to be secured in an appropriate position on the headrail of the assembly. 
     A coupling as provided by this invention will be provided in its body member with an acircular axial recess adapted to receive the end of the shaft of such a drape or blind assembly for transmitting rotational movement from the coupling to such a shaft. 
     In another embodiment of the invention, the invention broadly comprises a venetian blind assembly in turn comprising a headrail channel member of generally three sided U-shaped channel construction, and defining edge retaining formations on the two free edges thereof, tilt rod means in said headrail channel, and drive means for rotating said tilt rod means, said tilt rod means being axially moveable relative to said drive means, a plurality of bearing means each of said bearing means being of integral one piece construction, each said bearing means defining bearing recess means for receiving said tilt rod, and rod retaining means for retaining said tilt rod in said bearing recess means, formed as a single integral unit, and, means for securing flexible tilt control elements to said tilt rod, and means for guiding flexible slat support, elements, for movement within said headrail. 
     In a preferred embodiment of the bearing assembly, the bearing comprises an integral one piece thermoplastic structure having two upstanding bearing wall portions, and a junction portion extending between them. A generally upwardly open U-shaped bearing is formed in one of the bearing walls, and a bearing through-opening is formed in the other of the bearing walls, having a bridge portion extending thereacross. The bridge portion is adapted to retain the shaft of the drape or blind assembly in position. 
     The bearing assembly is also preferably provided with shoulders, adapted to make a snap fit within the two side edges of the headrail, so as to retain the bearing assembly in position. 
     In order to facilitate insertion the bearing assembly is further preferably provided with generally wedge shaped side surfaces, so that as it is forced downwardly into the headrail, it progressively spreads the walls of the headrail apart. 
     In a further preferred form of the bearing, openings are provided through the junction wall of the bearing assembly, for passage of the cords and tapes and the like, and roller bearing means are provided supported adjacent to such opening, to provide antifriction guides for the cords or tapes so as to prolong the life of the drape or blind assembly. 
     The invention further comprises such a venetian blind assembly wherein the bearing means comprises opening means for said flexible support elements, bearing support means on either side of said opening means, and, antifriction means supported in said bearing support means and extending from side to side of said opening means, whereby to guide said flexible support elements from said bearing means through said opening means. 
     The invention further comprises such a venetian blind assembly and further including a clamp member inter-engageable with and rotatable with said tilt rod, whereby to lock the same against axial movement relative to said drive means. 
     The invention further comprises such a venetian blind assembly and wherein said walls of said U-shaped channel of said headrail are resiliently moveable relative to one another whereby to spread apart and to close, and including wedging surfaces on said bearing means, whereby said bearing means may be press fitted downwardly between said walls of said U-shaped rail, spreading the same progressively apart, and including abutment means formed on said bearing means, for inter-engagement with said retention means on said free edges of said wall means. 
     Other features of the invention and the advantages presented thereby will become apparent as the description herein proceeds. 
     The various features of novelty which characterize the invention are pointed out with more particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective illustration of a venetian blind assembly showing one embodiment of a transmission mechanism in accordance with this invention in position therein; 
     FIG. 1A is a fragmentary perspective illustration of a venetian blind assembly showing a similar embodiment to FIG. 1, and illustrating two bearing assemblies spaced apart along the headrail; 
     FIG. 2 is an exploded perspective view partially cut away of the transmission mechanism of FIG. 1; 
     FIG. 3 is an axial sectional view when taken as indicated by the arrows 3--3 of FIG. 2 with the component parts in their assembled positions; 
     FIG. 4 is a transverse section when taken as indicated by the arrows 4--4 of FIG. 3; 
     FIG. 5 is a perspective illustration similar to that of FIG. 1 but showing an alternative embodiment of the invention; 
     FIG. 6 is an axial sectional view through the transmission mechanism of FIG. 5 when taken as indicated by the arrows 6--6 of that figure; 
     FIG. 7 is a transverse section when taken as indicated by the arrows 7--7 of FIG. 6; 
     FIG. 8 is a section along the line 8--6 of FIG. 6 and 
     FIG. 9 is an axial sectional view through yet another embodiment of a transmission mechanism in accordance with this invention; 
     FIG. 10 is an exploded perspective illustration of a bearing assembly and the tilt rod of the venetian blind assembly of FIG. 1A, 
     FIG. 11 is a section along the line 11--11 of FIG. 1A showing the insertion of a bearing assembly into the blind track, and, 
     FIG. 12 is an exploded perspective illustration of one end of the venetian blind assembly of FIG. 1A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first of all to FIGS. 1 and 1A, it will be noted that the invention is shown there used for the sake of example in association with A1 a venetian blind assembly of the type having a headrail indicated generally as 10, having a bottom wall 12, and side walls 14 and 15 in turn having their upper edges folded over inwardly to provide top edge retaining means on lips 14a and 15a respectively. A shaft 16 having a hexagonal cross-sectional configuration extends along the interior of the headrail 10, being supported by bearings 18. The individual surfaces of the shaft 16 are indicated by the legend 17. 
     A plurality of blind slats 20 are supported on tapes or cords 211-, in a manner known per say. 
     The cords or tapes 22 extend upwardly through the bottom wall 12 of the headrail 10, and are wound around a sleeve 24 keyed to the shaft 16. 
     In addition, as in other venetian blinds, further cords C are provided extending centrally through the slats 20, by means of which the slats 20 may be raised or lowered. Those cords C and the cord-locking mechanism L (FIG. 1A) associated therewith are known per se, and detailed illustrations are omitted for the sake of clarity. 
     As illustrated in FIG. 1, the bearing 18 will be seen to comprise first and second bearing portions 18a and 18b, of integral one piece construction, typically being formed of moulded thermo-plastic material. Bearing portion 18a is formed with a generally upwardly open U-shaped recess 19a, and bearing portion 18b is formed with a bearing in the form of through-opening 19b, bearing portion 13b having a bridge portion 18c extending thereover, whereby to prevent the escape of the rod 16 thereform. 
     The bearing 18 is retained in position, within the headrail 15, by means of shoulders 18d, engaging the top edge lips 14a and 15a of the headrail. 
     As explained above (and illustrated in FIG. (1A), there will (usually) be more than one bearing 18. The bearings 18 also provide for the passage of the cords 22, and the cords C, in a manner which will be readily understood, but which is omitted from FIG. 1A for the sake of clarity. 
     Detailed illustration of a preferred form of bearing assembly is shown in FIG. 10. 
     It will, of course, be appreciated that as in all venetian blinds, at least two pairs of the cords 22, (FIG. 1A) and sometimes more, are provided at spaced intervals along the headrail 10, for supporting the slats 20 at two or more spaced-apart positions. However, only one such pair of cords 22 is shown (in FIG. 1) for the sake of clarity. 
     The transmission mechanism in accordance with the invention is indicated generally as 26. Transmission mechanism 26 is provided to control the angle of tilt of the slats 20. The angle of tilt is controlled or adjusted, by simply rotating the tilt shaft 16 either clockwise or anti-clockwise. 
     The transmission mechanism 26 is shown in more detail in FIGS. 2, 3, and 4. It will be seen to comprise a housing 28, housing a drive member or gear 30, and a worm drive gear 32. 
     Worm drive gear 32 is, in turn, mounted on a shaft 34, which is formed at its free end with a wand connection 36. The wand is omitted from the drawing for the sake of clarity. 
     Drive gear 30 is formed with a plurality of exterior teeth 38 adapted to be engaged by the worm drive gear 32. 
     In this embodiment, an interior recess 40 is formed as a through-bore through drive gear 30 along its central axis and drive surfaces 42 are formed inside recess 40 of regular shape along the length of the through-bore or recess 40 for reasons yet to be described. 
     Housing 28 is positioned and secured in headrail 10, by means described below, so that the central axis of gear 30 is coaxial with tilt shaft 16. 
     In order to couple the drive gear 30 to the shaft 16, an integral one-piece torque-limiting coupling generally indicated at 44 is provided. Coupling 44 comprises a generally cylindrical integral one piece rigid body portion 46 having an interior axial shaft recess 48. Drive surfaces 50 are formed within shaft recess 48 for receiving an end of the shaft 16, the surfaces 17 of the shaft 16 being complementary to the drive surfaces 50 whereby the shaft 16 may be drivingly received in the recess coaxially therewith. 
     Coupling 44 further comprises a generally U-shaped end member generally indicated at 51 and including a pair of arms 52. The arms 52 are separated by a slot 54. They are preferably formed of thermoplastic material and are, to some degree, resilient such that they may be flexed towards each other and will, when released, spring apart from one another. 
     Arms 52 are formed integrally with the body portion 46 through a reduced diameter neck portion 56. Arms 52 and define a plurality of drive surfaces 58. Surfaces 58 are complementary to surfaces 42 in the recess 40 of drive gear 30 and are coaxial with recess 40 and with shaft 16, all on a common axis. 
     Rotation of gear 30 will thus be transmitted through the drive surfaces 42, and 58 to the coupling 44 and through drive surfaces 48, and 51 to the shaft 16, all on a common axis. 
     It is necessary that means shall be provided to limit rotation of the tilt shaft 16 in both directions, in turn to restrict the tilting of the slats 20 in both directions. 
     In this particular embodiment, abutment members 60 are formed on each side of the housing 28 and a stop member or flange 62 is formed on the cylindrical body 46 of the coupling 44. In this way, rotation of the coupling will be limited by contact of the stop flange 62 with one of the abutment members 60 regardless of the direction of rotation. 
     Two abutment members 60 are provided (FIG. 1), one on each side of the housing 28 to permit the housing 28 to be used at either end of the headrail 10. 
     Referring again to FIG. 1, it will be noted that the housing 28 is formed with a downwardly dependent boss or leg 64 which extends through aligned openings in the bottom wall 12 and the front side wall 14 of the headrail 10. A recess 66 is provided in the housing 28 to receive top edge lip 14a of the side wall 14. 
     The housing 28 is also formed with an outward projection 68 which, when the housing 28 is in position in the headrail 10, is received under the top edge lip 15a as will readily be understood by reference to FIG. 1. A resilient tongue 70 also integrally formed with the housing 28, extends downwardly from housing 28 and presses against the bottom wall 12 of the headrail to ensure a snug non-rotatable fit of the transmission mechanism 26 in the headrail 10. The boss 64, and tongue 70 raise the housing in headrail and locate the housing with the axis of the gear 30 coaxial with the shaft 16. 
     In normal operation, the wand (not shown) rotates the shaft 34 which, in turn, through the coupling 44 rotates the shaft 16, until the desired angle of tilt for the slats 20 has been achieved. Once the stop flange 62 has contacted an abutment member 60, no further rotation of the shaft 16 can take place. However, in the event that excessive torque is applied to the drive gear 30, after the stop flange 62 has contacted the abutment member 60, by, for example, someone continuing to rotate the wand, or by some other misuse, then the arms 52 will flex toward each other, disengaging the driven surfaces 58 of the arms 52 from the drive surfaces 42 of the gear 30. The gear 30 will thus rotate, while the coupling 44 will remain stationary. 
     It will thus be noted that a one piece integral simple yet highly effective form of coaxial torque-limiting coupling device, is provided, and that a simple straight-forward in-line coupling is provided in a manner which makes it economical to manufacture and assemble. 
     Reference will next be made to FIGS. 5, 6 and 7 of the accompanying drawings in which there is indicated generally at 72 a transmission mechanism including a housing 74 for driving a shaft 76 of a blind assembly generally indicated at 73. 
     The blind assembly 78 is almost identical to the blind assembly 10 hereinbefore described, but differs therefrom in that the shaft 76 is generally cylindrical, except that it has a longitudinally extending semi-cylindrical recess or notch 80 (FIG. 7). A semi-cylindrical key 82 is formed in an axial recess 84 of a drive gear 86 corresponding to the drive gear 30 of the mechanism already described. 
     To permit the use of a torque limiting coupling similar to the coupling 44 already described in this modified form of blind assembly, the transmission mechanism utilizes a modified torque-limiting coupling 88 and an adaptor 90. 
     Additionally, a separate abutment member 92 (FIG. 5) is provided for reasons to be described below. Such an abutment member is adapted to be secured in any convenient manner to the side wall 15 of the headrail 10. 
     The coupling 88 is provided, at one end, with a generally cylindrical axial recess 94 having a semi-cylindrical key 96 for engagement with the notch 80 in the shaft 76. It will be understood that the recess 94 has the same transverse sectional configuration and dimensions as the shaft 76. 
     The coupling 88 comprises, at its opposite end, a coaxial extension 98 having arms 99 defining an hexagonal cross-sectional configuration corresponding to that of the coupling 44. Coupling 88 also has a stop member 97 formed thereon. 
     The adaptor 90 comprises, at one end, an axial extension 100 having a transverse sectional configuration and notch 101 identical in shape to that of the shaft 76 (FIG. 7). This extension 100 is received in the axial recess 84 of the drive gear 86 so that rotation of that drive gear 36 will cause rotation of the adaptor 90. 
     At its opposite end, the adaptor 90 is formed with an axial recess 102 having a hexagonal transverse sectional configuration identical in shape to that of the recess 40 provided in the drive gear 30 of the mechanism already described with reference to FIGS. 1 to 4 of the drawings. 
     The U-shaped arms 99 of the coupling 88 are received in the recess 102 for conjoint rotation of the coupling 88 and the adaptor 90 until such time as the stop member 97 engages the abutment member 92. After such engagement, if rotation of the drive gear 86 is continued, the arms 99 of the coupling 83 will flex toward each other so permitting the adaptor 90 to continue to rotate while the coupling 88 and the shaft 76 remain stationary. 
     It will now be understood that the use of the coaxial coupling 83 and coaxial adaptor 90 permits the use of the invention in a blind assembly in which the configuration of the shaft 76 and the axial recess 84 in the drive gear 36 are different from the configurations of the recess 48 and the U-shaped end member 51 of the coupling 44. 
     It will also be understood that the coupling 88 and adaptor will not be required if the shaft 76 is identical to the shaft having a hexagonal cross-sectional configuration and is used with an existing housing (without an abutment member) and a drive gear with a correspondingly configured axial recess and a co-axial coupling 44. In such a situation, it will simply be necessary to attach an abutment member 92 at an appropriate position on the side wall 15 of the headrail. 
     Finally, reference will be made to FIG. 9 of the accompanying drawings in which there is shown generally at 104 part of yet another embodiment of a transmission mechanism in accordance with this invention. The mechanism 104 is shown as being used for driving a shaft 76 identical to shaft 76 already described. In this particular embodiment, resilient arm means generally indicated at 106 are integrally formed with a drive gear 108 having teeth 110. Since the arm means are identical to that already described with reference to FIGS. 1 to 4, the component parts will not be separately identified. 
     The mechanism 104 also comprises a rigid one-piece coupling generally indicated at 112 including, at one end, an essentially cylindrical axial recess 114 is provided with a semi-cylindrical key 116 and is adapted to receive the end of the shaft 76 for co-rotation therewith (as described in the embodiment of FIGS. 5 8. At its opposite end, the coupling 112 is formed with a co-axial recess 118 having a hexagonal transverse sectional configuration as already described in connection with FIGS. 1-4. 
     A stop member 120 is integrally formed with the coupling 112 and projects radially outwardly therefrom. 
     It is believed that the manner of operation of the transmission mechanism 104 shown in FIG. 9 will easily be understood by comparison with that of the preceding figures and that, therefore, no further description need be provided herein. 
     It will of course be appreciated that while the embodiment of FIG. 9 is illustrated in association with a cylindrical shaft 76, and acircular recess 114 having a rib 116, this is by way merely an example. This embodiment of the invention will equally be applicable to a shaft having a hexagonal or other cross section, and the recess 114 would then of course be modified to suit. 
     A preferred form of bearing assembly 18 will now be described in more detail in connection with FIG. 10. As already explained in relation to FIGS. 1 and 1A, the bearing assembly 18 is of integral one piece thermoplastic construction. The two walls 18A and 18B are joined by a junction wall 130 having side channel walls 132 on either side therefore for greater strength. 
     In the embodiment of FIG. 10 the U-shaped recess in wall 18A is preferably provided with inturned abutment portions 134 on either side, so as to enclose slightly more than a 180 deg. of arc. 
     The through-opening in wall 18b is formed with a bridge formation already described extending completely thereacross and thereby providing a entirely enclosed through-opening for retention of the shaft therein. 
     In order to provide for passage of the cords and tapes and the like, openings 136 and 138 are formed in walls 18a and 18b.  In order for downward guidance of those cords or tapes extending downwardly from the bearing assembly 18, a downwardly open slot 140 is formed in function portion 130. Adjacent slot 140, a roller bearing 142 is supported in end channel support 144, located on respective side walls 132. 
     The sleeve indicated as 24 in FIGS. 1 and 1A comprises a generally cylindrical metallic tube having tongues 146 adapted to be crimped over the ends of the tapes or cords as shown. 
     The sleeve 146 is in turn mounted on a bearing sleeve body 148 formed of thermoplastic material. Body 148 is formed with a through-bore having formations adapted to conform to the shape of the particular drive shaft 16 in the particular drape or blind assembly. 
     The bearing sleeve 148 defines free ends extending from either end of the metallic sleeve 146. The bearing sleeve 148 thus provides bushings for retention in the bearing walls 18A and 18B, and thus provides for an extended working life of the drape or blind assembly. 
     In order to prevent endwise movement of the shaft 16, relative to the headrail, a stop sleeve 150 is provided. Sleeve 150 is formed of thermoplastic material. In this embodiment it has a generally partially cylindrical exterior, and is formed with an axial slot 152, shaped and adapted to conform to the shape of the shaft 16. It is sized and adapted to make a tight friction fit on the shaft 16. 
     Once in position as shown in FIG. 1A, the sleeve 110 will effectively prevent axial movement of the shaft relative to the drive assembly 13. This will ensure that the shaft does not inadvertently become disengaged from the drive assembly 28, or from the coupling 44. 
     The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the appended claims.