Will Automatically Permit The Spring To Adjust Itself To The Correct Tension

The roller is rotatable relative to the spindle

. A torsion spring is disposed around thespindle and is connected at one end thereof to the spindle and by its other end to the interior of the roller. Thus rotation of the roller in one direction relative to the spring acts to wind up the spring which is maintained in a wound up state bymeans of a pawl on the roller which engages with a ratchet connected to the spindle.

It is a common occurrence that roller blind is damaged, or will not function properly because the user does not pre-set the torsion spring to the correct tension. If the spring is not wound to the correct tension the roller blind will notoperate effectively and if overwound the spring may be strained or broken. Overwinding can occur for example in use if the roller is removed from its support brackets either intentionally (e.g. for cleaning) or if it is allowed to unwind so abruptlythat the roller is knocked out of its brackets, and is then re-wound by hand.

Therefore the mechanism will not function satisfactorily unless the torsion spring is pretensioned. This usually is done by manually rolling the shade on to the roller, placing the roller in the brackets and then pulling down the shade to impartan initial torque in the spring. Without releasing the pawl the roller is taken out of the brackets and rolled up again by hand, replaced on the brackets and pulled down again to impart a further torque in the spring. Thus, when the pawl is thenreleased and the roller rewinds the shade, the initial torque will be retained in the spring.

To rewind the shade it is pulled downwards for ashort distance to release the pawl from the ratchet and when the shade is released, the spring will unwind to rotate the roller in a shade winding direction. The spring tension must be sufficient to rotate the roller fast enough for the pawls to remaindisengaged by centrifugal force while the shade is being wound up.
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It is an object of the invention to overcome the aforesaid problems and to provide a device for association with a roller blind which device will prevent the torsion spring from becoming damaged by overwinding and which, if the spring isovertensioned, will automatically permit the spring to adjust itself to the correct tension.

When in use the roller blind is mounted in brackets on the window frame, and when the shade is extended by unwinding it from the roller this causes the roller to rotaterelative to the spindle to impart a torque in the spring. The pawl and ratchet arrangement operates to hold the shade against the torque of the spring in a desired unwound extended position of the shade.

Thus, in accordance with a further embodiment the invention provides a roller blind comprising an axially elongate cylindrical roller, a spindle axially disposed within a housingat one end of the roller and terminating in a flat pin which extends beyond the end of the roller, a torsion spring disposed around the spindle with one end of the torsion spring attached to the spindle, and wherein the other end of the torsion spring isconnected to a collar rotatable about the spindle, and wherein means are provided to resist rotation of the collar on the spindle when the torque exerted by the torsion spring is at or below a predetermined level but said means being operable to permitrotation of the collar when the tension in the torsion spring exceeds said predetermined level thereby permitting unwinding of the torsion spring until the tension in the torsion spring is again at or below said predetermined level.

According to the invention a roller blind has associated therewith a slip coupling which normally acts to resist unwinding of the torsion spring when the tension in the torsion spring is at or below a predetermined tension but which when thetension spring is overstressed is adapted to slip to permit unwinding of the torsion spring until the tension in the torsion spring is again at or below said predetermined tension. The slip mechanism can be disposed on or within the roller or may beincorporated in a support bracket for the roller.

In a preferred embodiment the spring is comprised of a length of wire of suitable resilience retained in a substantially diametrically disposed channel in a face of the bearing, opposite ends of the wire extending from the channel to engage withstops formed in the face of the bracket. Preferably, the ends of the wire extend substantially at a tangent from the edge of the bearing, and means are provided on the bearing to dampen oscillation in the ends of the wire.

The resistance meansmay comprise a resilient spring attached to the collar and rotatable therewith but which is normally prevented from rotating by means of a stop or stops on the interior of the roller housing but which, when the force exerted by the torsion spring exceedsa predetermined limit, is caused to flex to override the stop or stops and permit unwinding of the torsion spring.

Although the slip coupling of the invention has been described with reference to a roller blind, it can also be used to prevent overwinding of other spring-powered devices such as alarm clocks and clockwork toys.

by: erin

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