A LOCKING DEVICE FOR ROLLER BLINDS

Abstract: A ratchet mechanism which uses balls lets the balls fall down radially according to the prior art, for locking between the drum (1) which is fitted to the roller blind tube and the immobilised shaft (2). According to the invention the drum (1) is provided with changed depressions which have protrusions (4', 5', 6') for prevention of this movement. The protrusions partly support the ball which at any given instant is topmost and hence enables a slow rotation.

Description: A locking device for roller blinds. The invention relates to a locking mechanism for roller blinds comprising a non-rotating shaft with a first set of radial depressions having inclined surfaces and an intermittently rotating drum with a second set of radial depressions mounted in a spring driven roller blind tube and provided with balls adapted for providing an interlocking of the shaft and the drum by jamming between said first and second set of depressions. This type of locking of a roller blind replaced a construction using ratchets and ratchet wheels which permitted the pulling of the roller blind during tightening of the spring fitted inside the tube and locking. The ratchets were mounted on journals on the drum, and by sufficiently rapid rotation they were flung outwards and held at a distance from the ratchet wheel. During slow rotation gravity caused re-engagement. The construction using balls caused expensive manufacture of ratchets and ratchet wheels and the wear and friction on the bearings of the ratchets were replaced by balls which established locking between the stationary shaft and the drum by falling into the radial depressions in the stationary shaft. Due to the small diameter of a roller blind tube and the need for a suitable mass for the balls, so that they can overcome possible dust and still provide a reliable movement, fairly large balls have been used and only two first radial depressions which cooperate with three second radial depressions. This provides for sufficient possibilities of locking in practice. However, in particular this advantageous construction gives problems, if the stationary shaft cannot be securely placed in a position so that one of the two first depressions is upwards turned (and consequently the other is facing 2 downwards) . When such a depression faces upwards, three lockings are ensured per revolution, whereas if the two first depressions are facing sideways (i.e. at right angles to the first position described above) , then coincidences will determine if a ball rolls into the space between the shaft and drum and creates a locking thereby. This has the effect that the known, otherwise useful construction does not have the freedom of orientation which is required by modern building techniques. It is required that a roller blind tube can be mounted in their mountings, irrespective of whether they are mounted on a wall or in the ceiling, and hence 4 depressions in the shaft are required in practice. Modern locking devices are disposed such that the balls obtain a free run towards the centre of the shaft. This means that the moment the component of gravity is larger than the component of the centripetal acceleration the ball will roll towards the centre of the shaft and thereby lock the drum. Thereby the rotational velocity which must be overcome is only dependent on the distance of the ball from the centre of rotation and by the rotational velocity for a fixed placement of the locking depressions in the shaft. This means that the spring must be tightened to such a degree that the necessary rotational velocity will be obtained at the latest after 1/3 revolution, in order that the mechanism is released and the roller blind moved upwards. This requires a large tightening of the spring and causes the roller blind to move upwards at high velocity. It is the purpose of the invention to avoid these disadvantages, and this is obtained in that the second set of radial depressions is provided with projections in the direction of rolling-up as a partial support for the balls and in order to create a release direction for the balls which is not directed towards the centre of rotation. Thereby "pockets" are so to speak created in the drum for 3 the balls which support the balls partly, so that a part of the force with which gravity influences the ball which is at any one instant the top one, is taken up by the drum. Hereby the force which forces the ball against the locking surface on the shaft is reduced. In this manner a reduction of the rotational speed which is required to keep the balls in the drum is obtained. Thereby the spring does not need to be tightened as in the prior art, and the roller blind may move much slower before the ball is locked. Thereby a given spring mechanism obtains a larger capacity and may be used for larger roller blinds than in known constructions. An embodiment of the invention is particular in that surfaces have been provided at the second set of radial depressions such that the jamming of a ball occurs with a force which is directed at an angle with respect to the tangent to the shaft at the ball in question. Another way of expressing this is that the inclined surfaces are oriented differently from the usual where the force is essentially directed tangentially. The increased radial force is no disadvantage, and the advantage of the inclined surfaces is furthermore that the balls may "roll" from the second set of radial depressions whithout being dependent on a purely ' radial movement. Hereby it becomes possible under certain circumstances to provide only two first radial depressions. A further embodiment of the invention is particular in that the bottoms of the second set of radial depressions are shaped as a part of a spherical surface with a radius essentially equal to the radius of the balls. Such spherical surfaces are disposed in the bottom on either side of the protrusions, so that the balls are not only jammed between edges on the first and second set of depressions, but are also supported by a part of a spherical surface. The projections in the second set of radial depressions are reinforced by the spherical transfer to the bottom, and the 4 strenght increases. Thereby a greater security is obtained against deformation and wear. A further embodiment is particular in that also the first set of radial depressions are provided with bottoms which are parts of spherical surfaces with a radius essentially equal to the radius of the balls. This enables a less solid construction of the walls between the axial depressions (first set of radial depressions) in the shaft, whereby more depressions may be fitted for a given axial diameter. The invention will be described in greater detail in the following with reference to the drawing, in which Fig. 1 shows a known construction in cross section through the balls and depressions, Fig. 2 shows an embodiment of the invention, and Fig. 3 shows an embodiment with a reinforcement of the protrusions . In Fig. 1 is shown a blocking mechanism according to the prior art where a drum 1 with a bearing which is not shown is fitted rotatably around a stationary shaft 2. The shaft is provided with a profile 3 at the end which may lock against rotation to the support bracket. The drum is provided with 3 radial depressions 4, 5, 6 which are capable of containing balls 7 such that they do not engage the depressions 8, 9 in the shaft 2. During rotation this condition is maintained as long as the balls are flung outwards with sufficient force, and it is this condition which is shown in the figure. The surface which during rotation presses against the ball is directed towards the centre of the movement. The borderline case obtains when a depression 4, 5, 6 with a ball is directly above the shaft, while the sides of the depression contributes to holding the balls in other angular positions. When a ball falls down to touch a depression 8, 9 it jams between the slanted surfaces, and blocking occurs. In Fig. 2 is seen an embodiment of the invention in which the depressions 4, 5, 6 are differently shaped, in that there are provided protrusions 4', 5', 6' which partly support the ball which is at any time the topmost ball, even during slow rotation. The shaft is provided with the depressions 8, 9, 10, 11. In the figure there is schematically shown a ball in the depression 4 and another ball which performs blocking at the depression 5, 5' . In Fig. 3 is seen the shape of one of the depressions in the second set of radial depressions in perspective detail. Using the same reference numerals as in Fig. 2, the edge or protrusion 4' is seen between the depression with the greatest radial distance to the centre 4 and the depression 4" which is to cooperate with a ball 7 and one of the first set of depressions 8, 9 on the stationary shaft 2. The bottom of the depressions in the drum 1 is given a spherical shape, i.e. the depressions have a spherical surface as the transfer to a plane perpendicular to the axis of the drum. Compared to the situation where the depressions are constituted as cylindrical surfaces which intersect in the protrusion 4', a reinforcement is obtained of the edge which is created, because it thicker near the bottom while retaining a shape which corresponds to the ball 7, namely a circular arc 4c which is seen from the edge in Fig. 3. This reinforcement of the edge has shown itself to have a beneficial influence on the durability of the edge or protrusion. A part of the reason is that there is a surface contact sphere-against-sphere against the ball 7 instead of just a circle, as in the case ball against cylinder.

Claims: 6 P A T E N T C L A I M S 1. A locking mechanism for roller blinds comprising a non-rotating shaft (2) with a first set of radial depressions (8, 9) having inclined surfaces and an intermittently rotating drum (1) with a second set of radial depressions (4, 5, 6) mounted in a spring driven roller blind tube and provided with balls (7) adapted for providing an interlocking of the shaft and the drum by jamming between said first and second set of depressions c h a r a c t e r i s e d i n that the second set of radial depressions (4, 5, 6) is provided with projections (4', 5', 6') in the direction of rolling-up as a partial support for the balls (7) and in order to create a release direction for the balls which is not directed towards the centre of rotation. 2. A locking mechanism for roller blinds according to claim 1, c h a r a c t e r i s e d i n that surfaces have been provided at the second set of radial depressions (4, 5, 6) such that the jamming of a ball (7) occurs with a force which is directed at an angle with respect to the tangent to the shaft at the ball in question. 3. A locking mechanism according to claim 2, c h a r a c t e r i s e d i n that the bottoms of the second set of radial depressions (4, 5, 6) are shaped as a part of a spherical surface with a radius essentially equal to the radius of the balls (7) . 4. A locking device according to claim 3, c h a r a c t e r i s e d i n that also the first set of radial depressions (8, 9) are provided with bottoms which are parts of spherical surfaces with a radius essentially equal to the radius of the balls (7) .

Inventors: RYSHOLT KIM, RYSHOLT, KIM
Applicants: FABERS FAB AS C, RYSHOLT KIM, A/S CHR. FABERS FABRIKER, RYSHOLT, KIM
Application year: 1999
Main classification: E06B9
IPC codes: E06B9