Venetian blind construction

A venetian blind construction for the operation of blind slats which are interconnected by supporting elements comprises a housing with a sprocket wheel rotatably mounted in the housing. A sprocket chain defines a tension member for the blind slats and it has one end adapted to be connected to the lowermost slat and it is engaged over the sprocket wheel and is movable by the driving movement of the sprocket wheel to adjust the blind slats. The housing has first and second chain-guiding passage portions and a sprocket portion overlying the sprocket which effect the guidance of the chain toward and away from the sprocket and around the sprocket without permitting any buckling-out of the chain in its movement path.

FIELD AND BACKGROUND OF THE INVENTION 
This invention relates in general to the construction of venetian blinds 
and, in particular, to a new and useful venetian blind which is equipped 
with tension members for lifting and lowering the blind, which extend in 
lateral casings, act on a bottom bar, and are coupled to a drive shaft. 
DESCRIPTION OF THE PRIOR ART 
Venetian blinds of this kind are known which are frequently equipped with 
endless chains or bands which are passed over an upper wheel receiving its 
motion from a drive shaft, and around a lower, idle return pulley. Bands 
are relatively inexpensive, but they cannot ensure either a reliable 
engagement with the drive shaft or a locking of the blind against 
undesirable pushing-up of the same. Endless chains do prevent the 
last-named disadvantage, but due to their length and the necessity of 
providing a lower return pulley, they are relatively expensive. 
SUMMARY OF THE INVENTION 
The present invention is directed to a venetian blind which is equipped 
with tension members making possible a relatively inexpensive and simple 
construction and, in addition, permits the securing of the blind in the 
lowered position, or any intermediate position, against undesirable 
pushing-up, without necessitating additional locks or the like. 
To this end, in accordance with the invention, the tension members comprise 
open chains which, with the blind lowered, extend by at least one chain 
link beyond the sprocket wheel which is carried on the drive shaft, and 
which are guided, along their entire track of motion and with a small 
play, in a groove, whereby, the chain is prevented from buckling out of 
its track of motion. 
In consequence, the chain, which acts on the bottom bar by means of a 
connecting lever guided in the groove, and preferably on rollers, and 
which cannot buckle at any point of its track of motion more than by the 
small guide play owing to the guide groove, behaves approximately as a 
rigid bar between the bottom bar and the sprocket wheel in any position so 
that a completely or partly lowered blind cannot be pushed up by acting on 
the bottom bar inasmuch as the drive shaft itself cannot be rotated by the 
strand of the chain. 
Because of the small play of the chain in the groove, the possible 
reduction in length due to a small zig-zag buckling of the chain upon an 
attempt to push the blind up is small, but still noticeable. The chain 
links may also get jammed in the groove, whereby, even though this 
counteracts the pushing up, it makes the lowering of the blind difficult 
on some occasions. This problem is satisfactorily solved by the invention. 
For this purpose, the chain is designed in a manner such that it can buckle 
from its stretched position only in the direction in which it is guided 
over the sprocket wheel and not in the opposite direction. Any zig-zag 
buckling of the chain in the guide groove and jamming of the individual 
chain links is thereby prevented. Advantageously, the front side inner 
portion of the chain links which, in the stretched chain strand, is turned 
to the vertical plane passing through the axis of the sprocket wheel, is 
rounded in a usual manner so that, in this direction, i.e., in the 
direction in which the chain is deflected on the sprocket wheel, the chain 
can buckle, while the other, outer, front side portion of the chain links 
following each other with a small play, has a straight edge, so that these 
portions or edges extend parallel to each other and prevent a buckling of 
the chain from its stretched position in the opposite, outward direction. 
For this reason, the stretched, vertical chain strand behaves as a rigid 
bar preventing the blind from being pushed up. 
Accordingly, it is an object of the invention to provide a venetian blind 
construction for the operation of blind slats which are interconnected by 
supporting elements, which comprises a housing with a rotatable sprocket 
wheel rotatably mounted in the housing and with a sprocket chain engaged 
over the sprocket wheel which defines a tension member for the blind slats 
and has one end connected to the lowermost slat and which is movable by 
rotation of a sprocket wheel to adjust the blind slats and, wherein, the 
housing includes first and second chain guide passage portions leading 
toward and away from the sprocket wheel and a portion overlying the 
sprocket wheel for guiding the chain in respect to the sprocket wheel and 
toward and away from it so that it does not move out of a path of track 
motion. 
A further object of the invention is to provide a venetian blind which is 
simple in design, rugged in construction and economical to manufacture. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
should be had to the accompanying drawing and descriptive matter in which 
there are illustrated preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in particular, the invention embodied therein in 
FIGS. 1 to 4, comprises a venetian blind construction, generally 
designated 50, which includes a plurality of slats 1 which are 
interconnected by supporting elements 2 and which are raised and lowered 
by a tension member or chain 9 which is advanced by a rotatable sprocket 7 
in a housing 6 having means for guiding the chain into association with 
the sprocket, over the sprocket and away from the sprocket, without it 
coming out of a defined chain pathway. 
FIG. 1 shows a blind 50 with slats 1 suspended from the structure of a 
drive shaft 3, by means of folding supporting members 2. Drive shaft 3 is 
rotatable through a transmission 4, by means of a crank handle 5. A motor 
drive could also be used, of course. At either side of the blind, guide 
casings 6 are provided which are each closed at their tops by a hood 6a 
enclosing a sprocket wheel 7 carried by the shaft 3. Connecting levers 8 
are secured to the bottom bar 1a of the blind, and they project into the 
associated casing 6. One end of an open chain 9 extends upwardly in casing 
6 and is passed over sprocket wheel 7 which is hinged to an associated 
lever 8. With the blind lowered, the other end of the chain 9 is in a 
position close beyond the sprocket wheel (FIG. 2). 
As shown in FIGS. 2, 3 and 4, casing 6 has an approximately inverted 
U-shaped cross-section and comprises two guide grooves or passages 11a, 
11b laterally of a central longitudinal slot, in which the respective 
chain strand is guided with a small lateral play. The connecting lever 8 
of bottom bar 1a projects through longitudinal slot 10 into casing 6 and 
is angled in the direction of passage 11a and guided in this passage by 
means of rollers 8a. FIG. 4 shows that longitudinal slot 10 of casing 6 is 
undercut and cross-bolts 12 are guided in the enlarged space 10a thus 
formed. The bolts 12 are provided on each, or every other, slat 1. This 
makes a blind for exterior use which is wind-resistant. In order to make 
possible the introduction of cross-bolts 12 into narrow slot 10 of casing 
6, passage 11b for the trailing chain strand is designed as a separate 
part 6b of casing 6 and is in the form of a channel section which is 
snapped onto retaining projections 6c provided on casing backwall 30. A 
hood part 6a is aligned with respective passages 11a, 11b and encloses a 
sprocket wheel 7 which also defines a guide channel 11c allowing for only 
a small radial play of chain 9, so that along the entire track of motion 
of chain 9, a buckling of the chain or lifting from sprocket wheel 7 is 
prevented. This ensures that bottom bar 1a and, thereby, the blind, cannot 
be pushed upwardly from its partly or completely lowered position, since 
the chain strand between lever 8 and sprocket wheel 7 behaves as a rigid 
bar, while drive shaft 3 carrying sprocket wheel 7, due to the 
transmission coupled thereto, is self-locking and blocks any rotation of 
the sprocket wheel upon actuation of the chain. On the other hand, the 
blind can be gathered any time by rotating drive shaft 3, and the 
engagement of chain 9 with sprocket wheel 7 is trouble-proof. The chain 9 
is of a length at least long enough so that at least one link always 
extends beyond the rear "or opposite" portion or side of sprocket wheel 7 
and at most slightly greater than the height of the venetian blind 
construction with the blind slats fully lowered. This allows sufficient 
room in channel 11b so that the end of chain 9 wrapped around sprocket 7 
can travel down into channel 11b as the slats are raised. 
In the embodiment according to FIGS. 5 and 6, guide casings 16 are provided 
at each side of a blind (not shown), which are each closed at their tops 
by a corresponding guide hood portion 16a of the casing which encloses a 
sprocket wheel 17 affixed to drive shaft 13 of the blind. Connecting 
levers 18 are secured to a bottom bar 1a' of the blind, and they project 
into the associated casing 16. One end of the levers 18 are connected to 
an open chain 19 which is trained to run upwardly in casing 16 over 
sprocket wheel 17. With the blind lowered, the trailing portion (link 19b) 
of the chain ends close beyond the sprocket wheel 17 (FIG. 5). Casing 16 
has an approximately U-shape cross-section and comprises two guide 
passages 21a and 21b which are provided on respective sides of a central 
longitudinal slot in which the respective chain strand 19 is guided with a 
small lateral play. In contradistinction to the first embodiment of the 
invention, the chain 19 is assembled of chain links 19a which are of 
symmetrical shape relative to the central plane of the chain in which, 
with the chain stretched, hinge axes 20 of joint plates 19b, connecting 
chain links 19a are situated. While the outside of chain links 19a is a 
flat surface 22 which is parallel to the central plane of the chain and 
the front portions or edges of the links which are adjacent and 
perpendicular thereto are also flat surfaces 23, the inside of the chain 
links in the zone of hinge axes 20 is rounded and the adjacent 
intermediate front face portions 24 are beveled. The front face portions 
23 which are parallel to and oppose each other with a small play, prevent 
any buckling of the chain toward the outside (toward the lefthand side of 
FIG. 5), while the flat outside surface 22 of the chain links provide a 
trouble-proof sliding guidance for the chains within passages 21a and 21b. 
On the other hand, the oblique surface portions 24 ofthe chain links permit 
an easy buckling of the chain toward the inside, so that a quite 
satisfactory run of the chain over sprocket wheel 17 is ensured. Further, 
covering hood 16a is provided with a central rib 25 intended for holding 
down the chain, by which, in cooperation with hinge pins 20 of the chain, 
any lifting of chain 19 from sprocket wheel 17 is prevented. 
Due to the described design of the chain and guidance, no buckling or 
jamming of the chain in groove 21a is possible. In connection with rib 25 
and the self-locking drive of shaft 13, it is also ensured that the blind 
can never be unintentionally pushed up. 
Thus, a venetian blind construction is presented for the operation of 
raisable and lowerable blind slats which are interconnected by supporting 
elements between a first position in which the blind slats are fully 
lowered and a second position in which the blind slats are fully raised 
comprising a pair of housings, a rotatable sprocket wheel rotatably 
mounted in each of said housings, a pair of open ended sprocket chains 
having two ends, each chain defining a pull member for the blind slats, 
each chain having one end adapted to be connected to one end of the 
lowermost slat, and an opposite end being engaged over one side of each of 
the sprocket wheels and being movable by the sprocket wheels to raise and 
lower the blind slats. Each of the opposite ends of the open sprocket 
chains extends by at least one chain link beyond an opposite side of each 
of the sprocket wheels respectively between the first and the second 
positions. Each of the housings has first and second chain guide passage 
portions and a housing portion overlying the sprocket wheel mounted in the 
housing for guiding one of the sprocket chains toward and away from the 
sprocket wheels respectively, in a defined trackway and preventing the 
chains from buckling out of the trackway. Each of the chains has a length 
in the first position in which the blind slats are fully lowered, at most 
slightly greater than the height of the fully lowered venetian blinds. 
The construction of the actuating mechanism of the inventive venetian blind 
is simple, resistant to disturbances, omits expensive locking means and is 
secured against undesired manipulation from the side of the bottom bar in 
any position. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.