GB2225366A - Roller blind cord lock - Google Patents

Abstract

The cord lock includes a housing 1 containing a pulley 2, for driving connection with the roller, around which a drive cord 14 is looped and passing between a pair of openings 16, 17 defined by cam surfaces 18, 19. If the pulley is turned other than by the drive cord 14 one of the cord tails 14a, 14b jams in one opening and thereby prevents the blind from turning the roller under its own weight. <IMAGE>

Description

ROLLER DRIVE ASSEMBLY This invention is concerned with a drive assembly for winding and unwinding a blind or other sheet material on and off a roller. More specifically, the drive assembly comprises a pulley for driving connection with the roller, a housing for the pulley, and a flexible drive cord looped in driving engagement around the pulley.

In such an assembly there must be some means of preventing the pulley, and hence the roller, from turning under the weight of the sheet material. One early solution to this problem was to locate a separate locking element about the cord tails within the housing. Should the pulley start to rotate other than by the action of the cord, the locking element is carried around with the pulley until i.t causes the assembly to jam. The locking element is automatically freed the next time either cord tail is pulled.

Examples of such arrangements are disclosed in European Patent Specification No. 86 000 and UK Patent Specification No. 2 179 387 A.

There is currently a trend towards reducing the number of components in the assembly, and a more recent solution is disclosed in United Kingdom Patent Specification No. 2 179 907 A. Here the cord tails pass through respective openings which diverge outwardly relative to the axis of the pulley, and the outer edges of the openings have cam surfaces for urging the cord between the cheeks of the pulley. The pulley grips the cord, and on self-rotati.on of the pulley one of the cord tails is carried into engagement with a cord stop formed on the internal surface of the housing between the openings, thereby causing the pulley to jam. In this design the cam surfaces are very prone to wear, and in order to overcome this problem the cam surfaces are provided by metal pins.

This again increases the number of components, and also makes assembly rather difficult.

An alternative solution is proposed in United Kingdom Patent Specification No. 2 180 872 A. In this case the tails pass through a single opening between opposed cam surfaces so that self-rotation of the pulley causes a cord tail to jam against the cam surface associated with the other tail. Whilst this arrangement is generally satisfactory, the use of separate openings is often preferred as giving less risk of snagging and providing a more positive jamming action.

The aim of the present invention is to provide a form of drive assembly which utilises separate openings and yet is less susceptible to wear than the assembly of specification No. 2 179 907.

The present invention provides a drive assembly for a roller having sheet material wound thereon, comprising a pulley for driving connection with the roller, a housing for the pulley, and a drive cord looped around the pulley for winding and unwinding the sheet material on and off the roller, the housing, when viewed in section on a plane perpendicular to the axis of the pulley and passing between the cheeks of the pulley, containing a pair of openings for each receiving a respective cord tail, the openings being outwardly nondivergent (i.e. parallel or convergent) relative to the axis of the pulley, the edge of each opening which is furthest from the other opening being provided with a cam surface for urging the respective cord tail between the internal faces of the pulley, and the pulley having its internal faces arranged to grip the cord such that if the pulley is turned other than by the drive cord one of the cord tails is carried with the pulley towards the other tail causing the pulley to jam and thereby preventing the sheet material from turning the roller under its.own weight.

It has been found that by using non-divergent openings wear on the cam surfaces is substantially reduced, but at the same time the jamming action of the assembly does not appear to be adversely affected in any way.

The cord tail which is carried around with the pulley may travel freely past the portion of the housing between the openings and only jam when it attempts to travel past the opposite cam surface. However, it is preferred to provide a positive cord stop on the interior surface of the housing between the two openings in order to create a positive and more rapid jamming action.

The invention will now be exemplified in the following description to be read in conjunction with the accompanying drawings in which: Figure 1 is a transverse section through a roller drive assembly of the invention taken on a plane passing between the cheeks of the pulley and perpendicular to the axis of the pulley, Figure 2 is a longitudinal section, II-II, through the drive assembly of Fig. 1 with the drive cord omitted for clarity, and Figure 3 is a similar view to Fig. 2 but showing a second drive assembly of the invention.

Referring to Fig. 1, the drive assembly comprises a one-part moulded plastics housing 1 which is generally cup-shaped to receive a moulded plastics pulley 2.

The housing comprises a generally circular rear wall 3 which is surrounded by a forwardly projecting side wall 4, the lower region 4a of which is thickened, as shown.

The rear wall 3 has projecting pins 5, 6 moulded on its external rear surface for retention in complementary holes in a conventional mounting bracket (not shown) secured to a wall, window frame, or other surface. The rear wall also contains a central circular aperture 7 which is surounded by an annular boss 8 projecting internally of the housing from the inner face of wall 3.

An integral axle 9 projects axially from one side of the pulley 2, and this is rotatably received as a close fit in the aperture 7. Though not essential, the axle extends beyond the rear face of wall 3 for reception in a complementary aperture in the mounting braket. The opposite side of the pulley has an integral spigot 10 which projects axially from the open side of the housing for connection with a tubular roller (not shown) having a sheet of material such as a blind wound upon it. The spigot will usually be of cruciform transverse section to provide a better driving engagement with the roller and reduce the amount of plastics material required. The pulley 2 is enclosed within the housing 1 and is axially located between, on the one side, the boss 8, and on the opposite side, by an inwardly directed bead 11 running around the forward edge of the side wall 4.Whilst being sufficient to retain the pulley within the housing the bead 11 is nevertheless small enough to permit the pulley to be snapped into the housing 1.

Referring now to Fig. 2, the pulley 2 normally has a cord 14 looped around it. The cord is a tight fit between the inner cheeks of the pulley, and in order to enhance the grip of the pulley on the cord both internal faces of the pulley may, for example, carry generally radially extending ribs 15 which are circumferentially spaced around the pulley. The thickened lower portion of the side wall 4 contains two mutually spaced generally straight openings 16, 17 through each of which a respective cord tail 14a, 14b passes. The openings 16, 17 are parallel with each other and with a plane that passes mid way between them and includes the axis of the pulley 2. The side of each opening furthest from this plane is gently curved so that the wall of the opening merges smoothly into the internal face of the side wall 4, and these curved portions form cam surfaces 18, 19 in contact with the cord 14. The opposite, mutally adjacent faces of the two openings 16, 17 angularly meet the internal surface of the wall 3, and a rectangular stop element 20 projects radially inwards from the wall 3 half way between the two openings.

If the cord 14 is in the form of an endless loop the openings 16, 17 will be required to open towards the front side of the housing to enable to pulley with the cord looped around it to be inserted into the housing.

The openings could alternatively be joined together by a slot which travels via the rear wall 3. The cord tails 14a and 14b could have free ends provided with suitable weights, in which case the openings could be completely closed and the cord tails threaded through the openings before the pulley is inserted into the housing. The free ends of the cord could alternatively be joined together after threading through the openings. The housing could also be in two snap-fi.t halves each including a portion of the two openings, but this would increase the number of moulded components required.

In normal operation the cord tails 14a and 14b hang vertically down through the respective openings 16, 17.

If either tail is pulled the pulley is caused to rotate and the cord is wound off the pulley through the respective opening. At the other opening the cord is wound onto the pulley, being urged between its cheeks by the respective cam surface 18 or 19. Once the blind has been adjusted to the required position and the cord tails are released, any tendency for the roller to turn the pulley under the weight of the blind will cause one or other of the cord tails to be carried past the respective opening towards the other opening by virtue of the fact that the cord is gripped by the pulley, so that the cord tends to double back upon itself.

However, upon engaging the angular corners associated with the cord stop 20 the cord jams preventing the pulley from turning any further. Pulling either cord tail will cause the cord to be freed so that the pulley can once again be turned by the cord.

The drive assembly of Fig. 3 is similar to that of Fig. 2 except that the openings 16 and 17 mutually converge away from the axis of the pulley. It will be noted that each cord tail adopts an even straighter configuration when passing over the cam surfaces 18, 19 so that the wear on these surfaces is even less than in the device of Fig. 2.

In both of the illustrated drive assemblies the necessary jamming action is perfectly satisfactory, but at the same time the wear on the cam surfaces 18 and 19 is very low and is not detectable even after a considerable period of use. In fact it would be possible to reduce the wear still further by adapting the mounting bracket so that the locating pins 5 and 6 are received in slots disposed circumferentially of the axle 9 allowing the housing a small degree of rotational movement about the axis of the pulley.

Thus, when either of the cord tails are pulled the housing will tend to rotate so that the cord tail which is being wound off the pulley adopts a more linear configuration during passage through the respective opening. This will produce even less wear on the associated cam surface i8 or 19 at the expense of slightly greater back-wind when a cord tail is released..

Claims (2)

1. A drive assembly for a roller having sheet material wound thereon, comprising a pulley for driving connection with the roller, a housing for the pulley, and a drive cord looped around the pulley for winding and unwinding the sheet material on and off the roller, the housing, when viewed in section on a plane perpendicular to the axis of the pulley and passing between the cheeks of the pulley, containing a pair of openings for each receiving a respective cord tail, the openings being outwardly non-divergent (i.e. parallel or convergent) relative to the axis of the pulley, the edge of each opening which is furthest from the other opening being provided with a cam surface for urging the respective cord tail between the internal faces of the pulley, and the pulley having its internal faces arranged to grip the cord such that if the pulley is turned other than by the drive cord one of the cord tails is carried with the pulley towards the other tail causing the pulley to jam and thereby preventing the sheet material from turning the roller under its own weight.

2. A drive assembly for a roller having sheet material wound thereon, substantially as described with reference to the drawings.