Device for equalizing the warp yarn tension in a loom

A device for equalizing the warp yarn tension in a loom having a movable back rest and a fixed beam spaced therefrom. The back rest is moved to and fro the beam during the weaving operations with the warp yarns extending thereover. A pressure cushion is carried between the back rest and the beam parallel to the back rest and the beam. The pressure cushion is compressed and relaxed as the back rest moves to and fro said beam during the weaving operation for equalizing the warp yarn tension.

BACKGROUND OF THE INVENTION 
The invention refers to a device for equalizing the warp yarn tension in a 
loom having a movably supported back rest. 
For equalizing the warp tension during the weaving process, especially 
during formation of the shed and during beat up of the reed, it is usual 
to arrange the back rest of the loom to be movable. In that case, three 
fundamental suspension systems are known. On the one hand, spring members 
are provided in the back rest suspension, the action of which is directed 
against the force exerted by the warp. On the other hand, the back rest is 
rigidly supported in a suspension which is moved positively in the 
direction of a yielding of the warp in time with the formation of the shed 
or with the beat up of the reed respectively. Finally, combinations of 
both systems are also know, in which the back rest is supported springily 
in a suspension moved positively and in time with the formation of the 
shed or the beat up of the reed respectively. All of the systems have the 
disadvantage in common, that the back rest suspension engages with the 
side frames of the loom at two points. 
Since the warp force is distributed more or less uniformly along the length 
of the back rest from the sum of the forces from the individual warp 
threads, this two-point support demands a back rest resistant to bending 
with a corresponding weight, which is in the way of the above-mentioned 
movements for equalizing the warp tension. 
Complete equalizing of the warp tension without the occurrence of peaks in 
the tension is thereby rendered substantially impossible. 
SUMMARY OF THE INVENTION 
The device in accordance with the invention for equalizing the warp thread 
tension is characterized in that the back rest is supported by at least 
one pressure cushion extending essentially in the direction longitudinal 
to the back rest. 
In one embodiment of the invention as a result of the length of the 
pressure cushion being approximately equal to the width of warp, the back 
rest can be lightly built since no bending stresses arise in the back 
rest. 
The cushion may, at least over one part of its periphery, consist of 
stretchable material such, for example, as soft rubber. 
A solution which is inexpensive and is simple for replacement and repair 
results if the cushion consists of a hoselike body which bears against a 
stationary longitudinal beam of the loom frame, in which case, the 
hoselike body may be filled with a liquid or gaseous substance. In the 
case of such a pressure cushion, the contents may also be connected to a 
source of constant pressure. 
Accordingly, it is an object of the present invention to provide a device 
for equalizing the warp tensions during weaving operation on a loom. 
Another important object of the present invention is to provide a pressure 
cushion between a back rest and a longitudinal beam of a loom for 
equalizing the tension in the warp during weaving. 
These and other objects and advantages of the invention will become 
apparent upon reference to the following specification, attendant claims 
and drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, the warp 1 is shown approaching from the warp 
beam (not shown), which comes over the back rest 4 in the direction of the 
arrow 5 to the heddles (not shown) of a shed-forming device. The back rest 
4 is carried by levers 6 which are supported pivotally on lugs 7 on a 
longitudinal beam 8 of the loom by means of pivots 9. Between the rear 
wall 10 of the half-round hollow back rest 10 illustrated and the rear 
wall 11 of the longitudinal beam 8 is a hoselike cushion 12 having a 
membrane-like jacket 13 which extends along the entire length of the back 
rest 10 and beams. The cushion is filled with a filling of liquid or 
gaseous substance. The filling is at any pressure which may be chosen and 
kept constant by connection of the cushion to a suitable source of 
pressure. Instead of that, the filling may also be enclosed hermetically 
in the pressure cushion. The movements of the back rest have, as a rule, 
modest amplitudes, on account of which it is also sufficient to produce 
the jacket from inextensible material and to enclose the filling 
hermetically in the jacket. In this case, upon the back rest approaching 
the stationary beam 8, a slight rise in pressure takes place in the 
filling, in which case, however, the equalizing of the warp tension is not 
quite total but, in most cases, it is sufficient. Improvement follows if 
the jacket consists of material which is stretchable or has the elasticity 
of rubber. The pressure cushion may also consist in its entirety of a 
material having the elasticity of rubber such, e.g., as plastics, in which 
case, a number of short pressure cushions may be arranged in an 
interrupted row on the rear wall 11 of the longitudinal beam 8. The 
cushion may also contain a solid porous filling material and, in addition, 
be filled with a liquid or gaseous substance. 
While a preferred embodiment of the invention has been described using 
specific terms, such description is for illustrative purposes only, and it 
is to be understood that changes and variations may be made without 
departing from the spirit or scope of the following claims.