CORD DRIVING MECHANISM FOR A BLIND

Abstract: A blind is described which includes a cord driving mechanism comprising a pulley (56) having a circumferential, radially outward-facing and toothed groove (18) and a shoe (84), relative to which the pulley (56) rotates, surrounding at least part of the circumferential groove in the pulley. A cord passes around the pulley (56), in the space defined by the circumferential groove (18) and the shoe (84). The cord is retained in the groove (18) by contact with the shoe (84). The dimensions of the groove (18) and/or the spacing between the groove (18) and the shoe (84) and/or the size of the cord is/are selected to provide a desired resistance to rotation of the pulley (56) and/or a desired maximum load which can be exerted on the cord.

Description: CORD DRIVING MECHANISM FOR A BLIND This invention relates to powered blinds of the type which includes an operating cord entrained around a powered driving pulley. In the case of vertical blinds, the cord may operate the open/close function of the blind. Power is delivered to the pulley from an electric motor via a gearbox and rotation of the pulley tends to entrain the cord, thus operating the blind. However, to ensure that the cord is reliably gripped by the pulley, it has hitherto been found necessary to ensure that the cord is tensioned in its passage around the pulley. Clearly, once the pulley begins to drive the cord, there will be a certain amount of tension in the cord upstream of the pulley, but it has been found that tension (additional to that resulting from the weight of the cord itself) is required both upstream and downstream of the pulley to ensure that as the pulley begins to rotate, it takes the cord with it. This will be referred to as "back-tensioning" of the cord. It gives rise to excessive wear on the pulley bearings and increases the drag of the mechanism, thereby increasing the motor current required to drive the blind. Furthermore, the task of assembling the driving mechanism of the blind requires a degree of dexterity, since the cord must be kept properly positioned relative to the pulley until the cord can be tensioned to keep it in place. It is an object of the present invention to address the problems outlined above. According to a first aspect of the present invention, there is provided a cord driving mechanism for a blind comprising a cord driving pulley having a circumferential, radially outward-facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley. The advantages of this arrangement are twofold. Firstly, the shoe will retain the cord positioned correctly with respect to the pulley during the manufacturing process. Secondly, the shoe can be arranged to bear against the cord to ensure that it is properly gripped by the pulley as the pulley begins to rotate in service. The net result is that much less, or no, back-tension is required, the pulley bearings will last longer and the drag of the mechanism will be considerably reduced. For extra security, it is preferred that the shoe should surround at least half of the circumference of the pulley. This has further advantages which will be explained later. In a preferred arrangement, a plurality of nips are distributed around the circumferential groove of the pulley. These nips pinch the cord as it passes around the pulley, ensuring a further improvement in the ability of the pulley to grip the cord. Each of the nips is preferably radial within the groove. The nips are preferably spaced equidistantly around the circumferential groove. To ensure that at least one nip grips the cord at any time, there should be at least four. For example, there may be twelve. To ensure a good grip on both sides of the cord, it is preferred that the nips be defined by formations on both sides of the circumferential groove. For example, the formations defining each nip may be opposite one another on each side of the groove. This arrangement keeps the path of the cord relatively straight and provides unconstricted regions between nips, one advantage of which will be described later. The formations may be triangular teeth and are preferably symmetric, since the pulley will need to drive the cord in both directions. The mechanism is preferably arranged to be self-threading (as will be described later). For reasons which are self-evident, the mechanism will benefit from a doctor arranged adjacent the circumferential groove in the pulley and adapted to guide the cord out of the groove when the pulley is rotated. Again, as two directions of rotation are required, the doctor is preferably substantially symmetric. For reasons which will be explained later, the doctor may define an insertion opening for the cord. According to a second aspect of the invention, there is provided a blind including a cord driving mechanism comprising a pulley having a circumferential, radially outward-facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley and further including a cord which passes around the pulley, in the space defined by the circumferential groove and the shoe. The cord driving mechanism is preferably as described above as being in accordance with the invention. The pulley is adapted to drive the cord which is, in turn, adapted to operate moving parts of the blind, such as the traverse or tilt mechanisms. Preferably, the cord is not back-tensioned in normal use and this can best be achieved by arranging for it to be retained in the groove by contact with the shoe. The dimensions of the groove and/or the spacing between the groove and the shoe and/or the size of the cord may be selected to provide a desired resistance to rotation of the pulley and/or a desired maximum load which can be exerted on the cord. A third aspect of the present invention provides a cord driving pulley for a blind having a circumferential, radially outward-facing groove around which are distributed a plurality of nips. A fourth aspect of the present invention provides a method of installing a cord in a cord driving mechanism of a blind comprising a cord driving pulley having a circumferential, radially outward-facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley, comprising offering a free end of the cord to the space defined by the circumferential groove and the shoe and rotating the pulley to entrain the cord. This is a much simpler method than that currently in use. Because this method is envisaged, it is better for the shoe to surround as much of the circumference of the pulley as will carry cord in normal use, i.e. over half of it. Where the mechanism includes a doctor arranged adjacent the circumferential groove in the pulley and adapted to guide the cord out of the groove when the pulley is rotated, the method will further comprise retrieving the free end of the cord once it has passed around the pulley and is freed by the doctor. Where, as described above, the doctor defines an insertion opening for the cord, the free end of the cord will be offered up to that opening. Similarly, where a plurality of nips are distributed around the circumferential groove, the free end of the cord will be offered up to the region of the groove between two of the nips. The present invention will now be described by way of example with reference to figures 1-5 of the accompanying drawings, in which: figure 1 shows one half of a moulded pulley; figure 2 shows the other half of a moulded pulley; figure 3 is an assembly drawing of the pulley; figure 4 shows a moulded doctor; and figure 5 is an assembly drawing of a gearbox. The half pulley 10 illustrated in figure 1 comprises a flange 12, shaped on one side 14 so as, in cooperation with the other half pulley 16 illustrated in figure 2, to provide a "V"-shaped groove 18 in the finished product, as illustrated in figure 3. A central cylindrical bore 20 is provided in the flange, together with locating features in the form of a pin 22 and a pair of part-cylindrical bosses 24. The side 14 of the flange 12 which forms one half of the "V"-shaped groove includes twelve symmetric, triangular teeth 26. The teeth and the flange have central, relatively shallowly inclined surfaces 28, 30 and distal, relatively sharply inclined surfaces 32, 34. These help the teeth 26 and the groove 18 to grip the cord (not shown) . The half pulley 16 illustrated in figure 2 also comprises a flange 36, shaped on one side 38 so as to cooperate with the other half pulley 10 illustrated in figure 1. A central bearing surface in the form of a cylindrical bore 40 is provided in the flange, continuing into a central boss 58, together with locating features in the form of a recess 42 and a pair of part-cylindrical detents 44. Again, the side 38 of the flange 36 which forms one half of the "V"-shaped groove includes twelve symmetric, triangular teeth 46. The teeth and the flange have central, relatively shallowly inclined surfaces 48, 50 and distal, relatively sharply inclined surfaces 52, 54. The teeth 26, 46 in both pulley halves can be seen to be radially directed. It is for this reason that the pulley is manufactured in two halves 10, 16. If this were not so, there would need to be as many removable cores in the mould as there are teeth on the pulley, twelve in this example. This would increase both tooling and production costs. A two part moulding is used to allow radial teeth, since it is clear that, in a pulley which must grip efficiently and operate in both directions, radial teeth are to be preferred. The assembly of the pulley 56 is shown in figure 3. As will be understood, on assembly, the central boss 58 will be received in the bore 20; the pin 22 will go into the recess 42; and the bosses 24 will go into the detents 44. In this way the teeth 26 will line up exactly with the teeth 46, to provide a series of nips 60, separated by spaces 62. The finished pulley has an integral gear 64, moulded integrally with the second half 16. The two halves may be ultrasonically welded together, although care must be taken to prevent distortion, or may be glued together. In either case, the amount of pressure applied will vary the separation between the teeth 26, 46, which may be significant. The choice of material for the pulley and the choice of material for the cord are important. A balance must be struck between the need for good grip between the pulley and the cord and a desire to reduce abrasion of the cord. The presently preferred material for the pulley is DuPont's Minion 23B1, a 37% mineral-glass-reinforced PA (nylon) 66 (28% mineral, 9% glass). This combines well with a 2.5 mm nominal diameter smooth braided polyester cord with polyester filler, such as are well known to those skilled in the art of blind making. An important advantage of the present invention can be appreciated from its ability to use unmodified polyester cords. Most motorised blinds use a drive train which can be described as incorporating a "positive drive" member. This member may take the form of a ball chain or an apertured tape or a helical drive shaft. The present invention takes advantage of unmodified cords, which it is able to do by virtue of its unique non-tensioned and self- threading construction. It is therefore applicable to the conversion of manual blinds to motorised form, not so much as an after-market accessory, but rather as a convenient way for manufacturers to modify their own products. This carries with it substantial development cost advantages, as there is not need to modify the perfectly good mechanism of a manual blind to accommodate any modified motorised drive train. Figure 4 illustrates a doctor 66. The doctor 66 includes a blade 68 which goes between the two parts 10, 16 of the pulley 56 to guide the cord out of the groove 18. It also includes a pair of wings 70, the purpose of which will become apparen . Figure 5 shows an assembled gearbox 72. A spindle 74 is driven by a motor (not shown) . Attached to the spindle 74 is a worm 76, which drives a helical gear 78. The helical gear then transmits drive via a reduction gear 80 and an idle gear 82 to the gear 64 on the pulley 56. Closely surrounding over one half of the circumference of the pulley 56 is a shoe 84, the two free ends of which run parallel and close to the edges of the wings 70 of the doctor 66. The doctor blade 68 is located in the "V"- shaped groove of the pulley 56. The wings 70 of the doctor 66 define, in conjunction with the gearbox housing and the shoe 84, an insertion aperture for the cord on each side of the pulley 56. Installing the cord onto the pulley is simplicity itself. The free end of the cord is offered up to the insertion aperture (under the appropriate wing 70) and the spindle 74 is rotated. The free end of the cord will then be trapped by a nip 60 in the pulley and between the pulley 56 and the shoe 84 and will begin to wind onto the pulley 56. If the cord does not come free of the pulley once it reaches the other side of the doctor 66, the doctor blade 68 will strip it out of the groove 18. In this sense, the mechanism can be described as self-threading. As has been explained in detail in the introduction to this application, the use of the pulley and shoe combination described obviates the need for "back-tensioning" of the cord. In addition, the dimensions of the groove and the distance between the pulley and the shoe can be optimised to provide a desired degree of resistance to rotation of the pulley or a desired maximum load rating. Clearly, the first should be as low as possible so as not to overload the motor; the second should be reasonably high to prevent slippage of the cord in normal use. With the material and cord specifications as discussed above, a number of different groove sizes were experimented with, to give an indication of the amount of leeway available. The groove widths were varied by applying different amounts of pressure to the two halves of the pulley 56 during assembly. The results observed were as follows. "HEIGHT" indicates the maximum and minimum thicknesses of the complete pulley (an indicator of groove width); "TEST CURRENT" is the current draw required to drive the gearbox alone; "CORD CURRENT" is the lowest current draw required to drive the gearbox and cord; "SLIP CURRENT" is the current at which the cord slips in the groove, if held fast; and "LOAD" is the load in the cord at which the onset of slippage was seen. 9.40 50 57 60 400-600 80 9.55 50 57 60 SLIPPED SLIPPED From these figures, it can be seen that a compromise between good grip and low current draw can be achieved, in this case with a pulley thickness of 9.10 - 9.25 mm.

Claims: CLAIMS 1. A cord driving mechanism for a blind comprising a cord driving pulley having a circumferential, radially outward- facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley. 2. A mechanism according to claim 1 in which the shoe surrounds at least half of the circumference of the pulley. 3. A mechanism according to claim 1 or claim 2 in which a plurality of nips are distributed around the circumferential groove. 4. A mechanism according to claim 3 in which each of the nips is radial within the groove. 5. A mechanism according to any one of claims 1-4 in which the nips are equidistantly spaced around the circumferential groove. 6. A mechanism according to any one of claims 1-5 in which the nips are at least four in number. 7. A mechanism according to claim 6 in which nips are twelve in number. 8. A mechanism according to any preceding claim in which the nips are defined by formations on both sides of the circumferential groove. 9. A mechanism according to claim 8 in which the formations defining each nip are opposite one another on each side of the groove. 10. A mechanism according to claim 8 or claim 9 in which the formations are triangular teeth. 11. A mechanism according to any one of claims 8-10 in which the formations are symmetric. 12. A self-threading cord driving mechanism for a blind according to any one of claims 1-11. 13. A mechanism according to any preceding claim further including a doctor arranged adjacent the circumferential groove in the pulley and adapted to guide the cord out of the groove when the pulley is rotated. 14. A mechanism according to claim 13 in which the doctor is substantially symmetric. 15. A mechanism according to claim 13 or claim 14 in which the doctor defines an insertion opening for the cord. 16. A blind including a cord driving mechanism comprising a pulley having a circumferential, radially outward-facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley and further including a cord which passes around the pulley, in the space defined by the circumferential groove and the shoe. 17. A blind according to claim 16 in which the pulley is adapted to drive the cord and the cord is, in turn, adapted to operate moving parts of the blind. 18. A blind according to claim 16 or claim 17 in which the cord driving mechanism is as defined in any one of claims 1-13. 19. A blind according to any one of claims 16-18 in which the cord is not back-tensioned in normal use. 20. A blind according to any one of claims 16-19 in which the cord is retained in the groove by contact with the shoe. 21. A blind according to claim 20 in which the dimensions of the groove and/or the spacing between the groove and the shoe and/or the size of the cord is/are selected to provide a desired resistance to rotation of the pulley and/or a desired maximum load which can be exerted on the cord. 22. A cord driving pulley for a blind having a circumferential, radially outward-facing groove around which are distributed a plurality of nips. 23. A pulley according to claim 22 in which each of the nips is radial within the groove. 24. A pulley according to claim 22 or claim 23 in which the nips are equidistantly spaced around the circumferential groove. 25. A pulley according to any one of claims 22-24 in which the nips are at least four in number. 26. A pulley according to claim 25 in which nips are twelve in number. 27. A pulley according to any one of claims 22-26 in which the nips are defined by formations on both sides of the circumferential groove. 28. A pulley according to claim 27 in which the formations defining each nip are opposite one another on each side of the groove. 29. A pulley according to claim 27 or claim 28 in which the formations are triangular teeth. 30. A pulley according to any one of claims 27-29 in which the formations are symmetric. 31. A method of installing a cord in a cord driving mechanism of a blind comprising a cord driving pulley having a circumferential, radially outward-facing groove and a shoe, relative to which the pulley rotates, surrounding at least part of the circumferential groove in the pulley, comprising offering a free end of the cord to the space defined by the circumferential groove and the shoe and rotating the pulley to entrain the cord. 32. A method according to claim 31 in which the mechanism includes a doctor arranged adjacent the circumferential groove in the pulley and adapted to guide the cord out of the groove when the pulley is rotated, further comprising retrieving the free end of the cord once it has passed around the pulley and is freed by the doctor. 33. A method according to claim 32 in which the doctor defines an insertion opening for the cord and the free end of the cord is offered up to that opening. 34. A method according to any one of claims 31-33 in which a plurality of nips are distributed around the circumferential groove and the free end of the cord is offered up to the region of the groove between two of the nips. 35. A cord driving mechanism for a blind as described herein with reference to the accompanying drawings. 36. A blind as described herein with reference to the accompanying drawings. 37. A cord driving pulley for a blind as described herein with reference to the accompanying drawings. 38. A method of installing a cord in a cord driving mechanism of a blind as described herein with reference to the accompanying drawings.

Inventors: WOOTTON MALCOLM JAMES, WOOTTON, MALCOLM, JAMES
Applicants: ECLIPSE BLIND SYSTEMS PLC, WOOTTON MALCOLM JAMES, WOOTTON, MALCOLM, JAMES
Application year: 1997
Main classification: E06B9
IPC codes: E06B9