AU631776B2 - - Google Patents

Description

r AUSTRALIA W 7 Patents Act 1990 COMPLETE SPECIFICATION FOR A PETTY PATENT Name of Applicant: Actual Inventor: UNILINE AUSTRALIA LIMITED MA T T I R U N A L A Address for Service: CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

O 00 0 a,4 Invention Title: "IMPROVEMENTS IN VENETIAN BLIND

ASSEMBLIES"

The following statement is a full description of this invention including the best method of performing it known to us.

This invention is concerned with improvements in operating assemblies for venetian blind system.

The invention is concerned particularly with a clutch mechanism associated with a slat tilting mechanism.

Early types of venetian blinds employed a slat tilting mechanism comprising a drum attached to one end of a rotatable shaft supporting spaced tape rollers. Ladder tapes attached to the tape rollers support the venetian blind slats in a manner such that rotation of the shaft clockwise or od anticlockwise causes the slats to tilt either upwardly or downwardly. In this early tilting mechanism, selective rotation of the shaft was achieved by cords wound onto the J drum at one end of the shaft whereby pulling downwardly on one of the cords caused the drum and shaft to rotate to tilt the ~blind slats as required.

o Of more recent times, the drum and cord tilting mechanism has been replaced by a miniature worm and roller gear set housed in a casing adapted for location within the head box of the venetian blind assembly. The roller gear is 20 connected to the rotatable tape roller shaft and rotation of the shaft is effected by rotating a rod which is suspended from a protruding end of the worm gear.

The major difficulty associated with such venetian blind mechanisms is that the miniature worm and roller gear sets, being of plastics material, were quite fragile and were easily stripped by relatively minor rotational forces applied to the gear set when the tilting mechanism was at either of its tilt angle limits.

To overcome the problem of stripping of these miniature worm and roller (or similar right angle drive) gear sets, a drum friction clutch has been proposed. This friction clutch comprises a pair of hollow cylindrical elements with the outer wall of one cylindrical element frictionally engaging with the inner wall of the other cylindrical element.

The inner element is provided with an aperture to receive the rotatable tape roller shaft which extends through the worm and roller gearset described above. The outer cylindrical element DJ includes a rod-like extension of approximately the same diameter as the tape roller shaft an. this extension is located in an end bearing and thus supports one end of the tape roller shaft in the head box.

The difficulty with this type of friction clutch arises from the fact that it is made from injection moulded plastics such as nylon, acetal etc. To ensure an appropriate degree of friction between the inner and outer clutch elements, very close dimensional tolerances are required.

With variations in operating conditions of the injection moulding apparatus, variations in batches of plastics materials, and progressive wear on the surfaces of the injection moulding dies, wide variations in the degree of frictional engagement of the clutch elements can be expected.

Furthermore, the use of the rod-like extension on the outer clutch element to support the tape roller on one end is likely to lead to breakage as the plastics rod-like extension does not possess the same strength characteristics as the metal tape roller shaft.

I I It is an aim of the present invention to overcome or ameliorate the problems of prior art clutch assemblies for tilting mechanisms in venetian blind assemblies.

According to the invention there is provided a tilting mechanism for a venetian blind assembly, said tilting mechanism comprising:a hollow housing; a worm gear rotatably journalled within said housing; a roller gear rotatably journalled within said housing in association with said worm gear, said mechanism characterised in that said roller gear includes an outer toothed element for operative engagement with said worm gear and an inner element adapted to receivably locate a tape roller shaft, said outer element and said inner element including on respective inner and outer surfaces engageable resilient projections which yield at a predetermined value of relative torque between said inner and outer element to permit slip therebetween.

Preferably said inner and outer elements emit an audible sound when slip occurs therebetween.

,2,Q If required, each said inner and outer elements includes a rotational bearing surface rotatably journalled in respective apertures in said housing.

Suitably each of said inner and outer elements includes an end thrust face rotatable against a respective inner face of opposed side walls of said housing.

In order that the invention may be more fully I T L- L L includes an end thrust face rotatable a respective ns 0 1 u S e m -ig inner face of oppose 'a is of said housing.

described, reference is now made to a preferred embodiment illustrated in the accompanying drawings in which:- FIG 1 shows an inner side elevational view of the tilting mechanism.

FIG 2 shows an exploded view of the clutch assembly associated with the mechanism of FIG 1.

a 0 oo0 S0 In FiG 1 the tilting mechanism comprises a hollow housing 1 conveniently formed in two halves and secured a o:00 together by an adhesive and/or by one or more screws 2.

Rotatably journalled within housing 1 is a worm gear 3 journalled on axle portions 4 and 5 respectively. Axle °oo portion 5 extends outwardly of housing 1 and includes an ei.larged portion 6 with an aperture 7 which, in use, is 0.00, engagable by a hooked rod (not shown) which is rotatable to e00o operate the venetian blind tilting mechanism.

0. Also journalled within the housing 1 is a roller gear 8 which operatively engages worm gear 3 whereby rotation of worm gear 3 causes rotation of roller gear 8.

Roller gear 8 comprises an outer element 9 havin toothed projections 10 which engage worm gear 3. Outer element 9 is formed as a hollow cylinder with a plurality of toothed projections 11 on the inner surface thereof, the toothed projection 11 extending parallel to the rotational axis of roller gear 8.

~Y~

6 Located within outer element 9 is an inner element 12 having on its outer surface toothed projections 13 also extending parallel to the rotational axis fo roller gear 8.

Inner element 12 includes a central aperture 14 to receivably locate a tape roller shaft (not shown) having a cross sectional shape complementary to that of aperture 14.

FIG 2 shows an exploded view of roller gear 8 illustrating more clearly the end thrust faces 15 and 16 of outer and inner element 9 and 12 respectively. These thrust faces bear on respective adjacent inner faces of housing 1.

0 Associated with each of thrust faces 15 and 16 are o0 0 projecting bushes 17 which are rotatably journalled in o oo apertures 18 (shown in FIG 1) in the opposed side walls of housing 1.

Inner and outer elements 9 and 12 respectively of roller gear 8 are comprised of the same or different plastics material and respective toothed projections 11 and 13 are 0ooo formed with dimensions of height and thickness as well as cross sectional shape to permit a resilient yield when a predetermined value of relative torque is applied between inner and outer elements 9 and 12. The predetermined value of torque is such that when excessive rotational torque is applied by worm gear 3 to roller gear 8, slippage occurs between inner and outer element 9 and 12 to prevent stripping of the worm and roller gear set.

It will be clear to a skilled addressee that depending on the characteristics of rigidity, resilience and internal lubricity of the or each of the polymeric materials

I

I N~chosen for the inner and outer elements 9 and 12, the characteristics of height, thickness and cross-sectional shape of toothed projection 11 and 13 as well as the relative numbers thereof may be readily determined to achieve slippage at a predetermined relative torque between those elements.

Preferably, the nature of the polymeric materials employed and the shape and dimension of toothed projections 11 and 13 are chosen to achieve an audible "clicking" noise as slippage occurs between the inner and outer elements 9 and 12.

13 By providing an audible indication of slippage between the clutch elements 9 and 12, an operator of the tilting mechanism fitted to a venetian blind assembly is immediately aware that the limits of the tilting mechanism have been reached or that an attempt is being made to operate the tilting mechanism in the wrong direction thus avoiding damage to the tilting mechanism.

Other advantages over prior art venetian blind clutch mechanisms are that only a single mechanism is required for both tilting and controlled slippage ease of assembly of the venetian blind operating assembly and the ability to support the metal tape roller shaft on its own opposed ends thus increasing the physical strength of the assembly.

It will be apparent to a skilled addres6ee that many modifications and variation may be made to the tilting mechanism according to the invention without departing from the spirit and scope thereof.

Claims (3)

1. A tilting mechanism for a venetian blind assembly, said tilting mechanism comprising:- a hollow housing; a worm gear rotatably journalled within said housing; a roller gear rotatably journalled within said housing in association with said worm gear, said mechanism characterised in that said roller gear includes an outer tootbad element for operative engagement with said worm gear and an inner element adapted to receivably locate a tape roller shaft, said outer element and said inner element including on respective inner and outer surfaces engageable resilient projections which yield at a predetermined value of relative torque between said inner and outer element to permit slip therebetween.

2. A tilting mechanism as claimed in claim 1 or claim 2 wherein said inner and outer elements emit an audible sound when slip occurs therebetween.

3. A tilting mechanism for a venetian blind assembly substantially as hereinbefore described with reference to the 2Q, accompanying drawings. DATED this seventh day of October 1992 UNILINE AUSTRALIA LIMITED By their Patent Attorney CULLEN CO I ABSTRACT A venetian blind tilting mechanism comprises a worm and roller gear set with a clutch mechanism between the roller gear and a tape roller shaft normally driven directly by the roller gear The roller gear comprises inner and outer elements (12,9) each with toothed projections (13,11) which coact to rotate the tape roller shaft but allow slip therebetween at a predetermined value of relative torque between the inner and outer elements (12,9) by resilient yield oo, between the coacting toothed projections (13,11). 0000 Soo o 400 o oa I, 0 r i 0 0 ii