Patent Application
20130048235
The present invention relates to a mechanism for extending or retracting a covering for an architectural opening, such as venetian blinds, roman shades, pleated window coverings or the like. It includes a drive shaft and a driven cord spool mounted in keyed connection with the drive shaft, about which a lift cord can be wound in order to retract or extend the window covering.
In the art conical spools are known that usually have a first end having a first diameter and a second end having a second diameter, the second diameter being smaller than the first. Such spools generally include a sloping portion where, the diameter of the spool reduces from the first diameter over a predetermined axial length to the second smaller diameter. Alternatively a relatively steep and short sloping portion is followed by a body portion that ends in the second smaller diameter end. The cord is affixed to the smaller diameter end and is guided onto the spool at the larger diameter end. Such spools are described in CH 581,257; EP 0,554,212; DE 195,05,824; EP 1,431,508; EP 1,577,483; U.S. Pat. No. 5,908,062; and WO 2004/048739.
These spools are used in mechanisms where the spool is mounted to rotate with a driven shaft while remaining stationary in axial direction, i.e. the spool is rotatable but does not move in longitudinal direction. The shape of the spool is especially designed to prevent cord windings of the lift cord being wound about the spool from overlapping, while ensuring the axial transport of these windings.
A problem with these known spools when used in the raising and lowering mechanisms is that it has been difficult, in operation, to get identical windings of lift cords on each and every spool.
It has been found that a number of windings will occasionally slip down the slope of the spools. When this will happen is not directly predictable. It has been found that the weight of the blind acting on a cord winding in a first position on the sloped portion of the spool has a relatively small axial force component in a down-hill direction. Additionally a subsequent winding formed on the spool pushes the previous winding out of its first position to move in axial direction to a second position. The resulting total axial force acting on the cord windings may become too big and result in the slippage of a stack of windings. The slippage in turn results in the bottom bar of a blind being pulled or dropped out of its horizontal position. A slanted position of the bottom bar is objectionable from a consumer's point of view. The problem is particularly visible in window coverings with only two cord spools and can only be corrected by completely lowering the bottom bar and thus unwinding the lift cords from their spools.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art. It is also an object of the present invention to provide alternative structures, which are less cumbersome in assembly and operation and which moreover, can be made relatively inexpensively. Alternatively it is an object of the invention to at least provide the public with a useful choice.
To this end the present invention provides a mechanism for extending or retracting for a covering for an architectural opening with respect to an architectural opening the mechanism including a rotatable drive shaft, at least one lift cord, at least one cord spool for winding and unwinding the at least one lift cord, the cord spool being mounted for rotation with the drive shaft while being axially stationary and the cord spool having a first diameter end and a second diameter end and the first diameter being larger than the second diameter and the spool having a first generally conical circumferential spool portion between the first and second end and the first spool portion having a plurality of steps, each step having a tread.
By having steps extending axially from the first diameter end a cord on such a step will no longer be subject to the combined two axial force components as previously described, but only to the axial “pushing” force component that is caused by each new winding being formed. The axial force component of the weight acting on a cord winding resting on a sloped surface is no longer present. By thus reducing the total axial force acting on each winding the problem of the unwanted and unpredictable slippage of one or more windings is solved.
Advantageously the tread of each step is axially long enough to accommodate a single cord winding but not long enough to accommodate two cord windings, such that in use a newly formed winding will be formed on the first step adjacent the first diameter end and in the process of being formed will push a previous formed cord winding toward the smaller diameter end and off the first step.
According to a further advantage the tread of each step is horizontal in axial direction. Also each tread advantageously has the same axial length.
A further advantage of the invention is to have a formula by which the preceding claims wherein the number of steps in the first spool portion is defined as follows
Advantageously a second spool portion extends between the first spool portion and the second diameter end.
According to a further advantage the second spool portion is conical at a smaller taper than the first spool portion.
Also advantageously the second spool portion can be generally cylindrical. Further advantageously the second spool portion has a plurality of strips extending axially between the end of the first spool section and the second spool end.
Alternatively for the cylindrical second spool portion advantageously the circumferential surface of the second spool portion is shaped to have at least one elongated strip-like body portion having a shape consistent with a radius that is larger than the actual spool radius such that the circumferential surface of the strips lies somewhat inwardly from the rest of the circumferential surface of the spool. Advantageously the radius of the at least on strip reduces along the axial length of the second spool section such that the radius of the at least one strip is larger adjacent first spool section and smaller adjacent the second spool end.
Further aspects of the invention will be apparent from the detailed description below of a particular embodiment and the drawings thereof, in which:
The cord spools 7, 9 each have a first or larger diameter end 21, 27, and a second or smaller diameter end 23, 29 as well as a first spool portion 33 (not visible in
The cord spools 7, 9 are fixed on the driven shaft 5 and upon rotation of the shaft the spools also rotate. The spools are also fixed with respect to the headrail in respective left and right axial positions by left and right spool support members 47, 47B which are anchored to the head rail such that the support members are aligned with the respective openings in the head rail through which the lift cords 11, 13 are guided onto the spools inside the head rail. Thus the spools are rotatably but do not move in elongated or axial direction. A spool support member 47 (as best visible in
Formula 1 will determine the number of steps is as follows
is “Nsteps=(Lslope*(1/cos α))/Lstep”. Formula 1
It is of course then also possible to calculate the height of the riser of each step Hriser with Formula 2.
is “Hriser=((Lslope/cos α)* sin α)/Nsteps”. Formula 2
The rate of progression of the windings in axial direction along the spool can thus be influenced by altering the slope angle a of the sloped portion 33. As shown above changing the angle while keeping the other variables the same will result in a higher riser. A cord winding on the second step will experience reduced friction compared to a winding on the first step, and likewise on each subsequent step further down the friction is less because the diameter of the spool at each step is reduced compared to that of the previous step.
The last step (45) may be chosen to be of different size to function as a transfer portion between the sloped portion 33 and the second spool portion 25.
In use upon pulling one of the front or rear lengths 17A, 17B of the ball chain 17, the operator 25 will drive shaft 5 to rotate. The spools will also rotate and when the direction of rotation is for lifting the blind the lift cords 11, 13 will be wound about the spools 7, 9. After a few initial turns of the spool during which the lift cord is first wound about the spool the windings will start to form in a first position on the first tread 35A of the spool 7. Each subsequent winding will be formed in the same first position, i.e. on the first tread 35A of the first step 35 and in the process will push the previously formed winding axially away, off the first tread and into a second position on the tread 37A of the second step 37. In moving from the first to the second position this previously formed cord winding pushes the winding that was on the second tread 37A to the third tread 39A. This means that each subsequent winding formed as the cord is wound about the spool pushes each previous winding to the next lower tread of the next step, while the horizontal treads of the steps prevent the cord windings from slipping down the slope. Once windings are also present on the second spool portion, these windings will also be pushed axially, i.e. towards the second spool end. As the windings form on the spool the tension in the cord windings that is present as a result of the weight of the blind acting on the lift cord is gradually reduced to zero. After a certain number of windings are present on the spool the windings closest to the second diameter end will experience zero tension in the winding and the only resistance these windings experience to axial movement is frictional since the weight of the blind no longer directly acts on these windings.
It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. The invention is further limited by the terms of the claims and not limited to the embodiment herein described, as such it will be clear that the device is not limited to use in a Roman shade. When used in a venetian blind the support member for the cord spool will be differently shaped and the camming member will be differently placed. The slope angle, then number of steps, the length of the sloped section of the spool can all be altered to suit the blind in which the device is used. Alternatively the whole spool body can be conical and formed in steps each having a tread and a riser. Although in the example only two cord spools are present in the window covering, in larger window coverings more spools can be used. Ideally for each lift cord a spool is provided.
Other means for driving the shaft 5 then the ball chain operator 15 can be provided, e.g. a motor, a spring motor, a crank shaft, a single pull cord drive system etc.
In an alternative embodiment the second spool portion may be conical like the first spool portion but with a smaller taper.
Directional and positional expressions, such as upper, lower, top, bottom, left, right, above, below, vertical, horizontal, clockwise, counter clockwise or like are generally used only to assist in understanding of the present invention as illustrated in the accompanying drawing figures. None of this should be construed to create limitations, as to position, orientation in actual use of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10004038.5 | Apr 2010 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/001656 | 4/1/2011 | WO | 00 | 11/8/2012 |
