Flexible or portable closure – partition – or panel – Plural strip – slat – or panel type – Venetian blind type
Reexamination Certificate
1998-12-18
2001-07-03
Purol, David M. (Department: 3634)
Flexible or portable closure, partition, or panel
Plural strip, slat, or panel type
Venetian blind type
C160S319000
Reexamination Certificate
active
06253822
ABSTRACT:
FIELD OF THE INVENTION
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.
BACKGROUND
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 blinds
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 no the pulley until the cord can be tensioned to keep it in place.
SUMMARY
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.
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Bromberg & Sunstein LLP
Eclipse Blind Systems Limited
Purol David M.
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