The present invention relates to a method for making Venetian blinds with double crossbands where the slats of the blind are inserted between a lower carrying crossband and an upper crossband preventing lifting of the slats.

It is the objective of such an embodiment to prevent the slats from being blown up and standing on edge in the ladder band when the Venetian blind is installed in a place with strong ventilation or other wind effects. Besides, the design which is often called a ladder lock has a si¬ lencing effect compared to a standard ladder band without double crossbands as the slats cannot touch each other. The disadvantage of prior art ladder bands with double crossbands is that the width of the ladder band and the distance between the interacting crossbands have to be in¬ creased in order to insert a slat between the lower and up¬ per crossbands. This also results in a poorer function of the double ladder. Further, the speed of inserting a slat between the interacting crossbands during mounting in the ladder band will have to be reduced in order to be able to steer the slat safely during insertion. Special instru¬ ments have been developed for this purpose, cf. e.g. DK-A- 3364/83, DE-B-2003304 and EP-A2-0319190.

The objective of the present invention is to show a method of the said nature where slats in Venetian blinds can be inserted without a special embodiment of the instru¬ ment used, without the speed or safety of insertion being reduced compared to production of Venetian blinds without a ladder lock. It must also be possible to obtain a ladder lock with narrow tolerances (height/width) whereby the function of the ladder lock is improved considerably.

This is achieved according to the invention by insert- ing the slats in a known manner in ladder bands, each com¬ prising two standard ladders while the crossbands are

paired off at the same level, by one standard ladder being then lowered until its crossbands lock the underlying slat, and by the lowered ladder being fixed to the lower strip of the Venetian blind while the ladder carrying the slats is fixed to the upper strip of the Venetian blind.

The invention also relates to a ladder band to be used for carrying out the method as claimed in Claim 1. Such a ladder band is described in Claim 2.

In Venetian blinds both with and without a double lad- der the slats are normally locked in the longitudinal di¬ rection by a hoisting cord used for raising the Venetian blind and passed through holes in the slats close to the ladder band in such a way that each consecutive crossband - or double crossband - is placed on either side of the hoisting cord.

As the double ladder according to the described method is formed after slats have been inserted in the ladder band, an even better locking of the slats in the longitudi¬ nal direction is obtained as the ladder on which a slat rests and the ladder which prevents the slat from being lifted can be placed on either side of the hoisting cord alternately.

For esthetic reasons, it is preferred that the two ladders should be connected. It is thus expedient according to the invention that the two ladders should be intertwined, or that the two lad¬ ders should be interconnected by flexible threads at suit¬ able intervals.

In the following, the invention is described further in connection with the drawing where

Fig. 1 shows a prior art ladder band with a ladder lock, Fig. 2 in perspective a first embodiment of a ladder band according to the invention, and Fig. 3a another embodiment of a ladder band according to the invention,

the same prepared for insertion of slats not shown, the same, but after locking of the slats not shown, part of a Venetian blind with a double ladder band and hoisting cord, the same seen from in front, part of another Venetian blind with double ladder bands and hoisting cord, and the same seen from in front, a third embodiment of a ladder band according to the invention seen from in front and in¬ cluding two standard ladders with a common leg and shown before joining of the two lad- ders, the same seen from above, the same seen from in front and prepared for insertion of slats not shown, the same after locking of the inserted slats, a modification of the ladder band shown in

Figs. 6a-6d, seen from in front and prepared for insertion of slats not shown,

Fig. 7b the same after locking of the inserted slats,

Fig. 8a a modification of the ladder band shown in Figs. 3a-3c, seen from in front and prepared for insertion of slats not shown, and Fig. 8b the same after locking of the inserted slats. Fig. 1 shows a prior art ladder band with double lad¬ der bands for Venetian blinds whose slats are inserted be- tween a lower carrying crossband C-D and an upper crossband A-B preventing slats from being lifted. In order to allow mechanical insertion of slats between the two crossbands in the normal way, the width of the ladder band and the dis¬ tance between the two crossbands have so far been increased and/or a specially designed instrument has been used for assembly of the socalled slat package, i.e. slats and lad-

der bands as well as any hoisting cord.

Fig. 2 shows a ladder band consisting of two inter¬ twined standard ladders. The crossband C-D of one ladder thus constitutes the lower slat-carrying crossband, while the crosband A-B of the other ladder constitutes the upper crossband which prevents lifting of the slats. One ladder is fixed in the normal way to the top strip of the Venetian blind, while the other ladder is fixed to the bottom strip of the Venetian blind. When the slats have been inserted in the double crossbands which during insertion may have a large mutual distance, one ladder is pulled upwards, while the other ladder is pulled downwards by the bottom strip so that a safe slat lock is produced with a short distance be¬ tween the crossbands. A corresponding function is obtained by the embodiment shown in Figs. 3a-c where the ladder band consists of two mutually parallel standard ladders. To fix the ladder band relative to a hoisting cord not shown which may have been passed through holes in the slats between the two ladders, the ladders can as shown be interconnected by flexible threads at suitable intervals.

Fig. 4a shows, in perspective, part of a Venetian blind with a double adder band and a hoisting cord passed through holes in the slats close to the ladder band in such a way that the interacting pairs of crossbands are placed alternately on either side of the hoisting cord.

Fig. 5a shows, also in perspective, part of a Venetian blind made by a method according to the present invention, and where better locking of the slats in the longitudinal direction is obtained by the crossband carrying a given slat being placed on one side of the hoisting cord, while the crossband preventing the slat from being lifted and the crossbands carrying the two adjacent slats are placed on the other side of the hoisting cord (see Fig. 5b).

Fig. 6a shows a ladder band consisting of two standard ladders intertwined so that one of the legs is common to the two ladders. The ladder band is prepared for insertion of slats by placing one ladder over the other as shown in Fig. 6c. The common leg of the two ladders is fixed to both the top strip and the bottom strip of the Venetian blind.

Figs. 7a and 7b show a modification where one ladder opposite to every crossband and possibly as an extension of it, has a loop at the leg which is not common and grips the not common leg of the other ladder.

Figs. 8a and 8b show a modification of the ladder band shown in Figs. 3a-3c where the interconnection of the stan¬ dard ladders by flexible threads is replaced by loops as shown in Figs. 7a and 7b, but at both ends of the cross- bands of one ladder.