Device for re-tensioning a weft thread unwinding in a shuttle-less loom

A retensioning device for a shuttle-less loom in which the yarn is drawn from a yarn reserve through a pair of eyelets and a thread brake for insertion, e.g. by lances into the warp, comprises a falt chamber defined between a fixed lower plate and a movable upper plate having an opening through which the head of a nozzle passes in the closed position of the upper plate. The nozzle directs a flat stream of air into the chamber to cause the yarn therein to describe a loop with the sides of the loop nearly parallel to one another, thereby preventing tangling.

FIELD OF THE INVENTION 
The present invention relates to a device for re-tensioning a weft thread 
unwinding in a shuttle-less loom and more precisely a loom in which the 
weft is drawn from a fixed yarn reserve located on one side of the 
machine, by mechanical weft-feed means, such as lances moving 
transversely. 
BACKGROUND OF THE INVENTION 
In a loom of this type, if the weft thread stored on the supply bobbin is 
withdrawn directly, owing to the high speed of the lances and the inertia 
of the weft thread, a "balloon" is formed, i.e. a greater or lesser excess 
length of unwound yarn depending on the density of the yarn. 
When unwinding stops, which takes place at precise points in the cycle of 
the loom, this excess length of weft forms a loop whose two sides may, 
depending on their degree of twisting, join together and wind one around 
the other to form a kink. Generally, this kink cannot come undone itself 
and it will be introduced into the shed when the pulling lance once more 
entrains the weft thread, thereby causing a fault in the fabric. 
A known solution making it possible to eliminate this drawback consists of 
effecting a preliminary unwinding of the weft and storing the unwound 
length provisionally on a device comprising a drum. This device unwinds 
the yarn at virtually constant speed, which reduces the "balloon" effect. 
The winding on a drum generally makes it possible to eliminate the kinks 
in the yarn. The major drawback of this system is its very high cost. 
OBJECT OF THE INVENTION 
The present invention intends to provide simpler and less expensive means 
for preventing the formation of kinks, without resorting to a device for 
preliminary unwinding. 
SUMMARY OF THE INVENTION 
The invention attains the object with a device for re-tensioning a weft 
thread as it unwinds, in a loom of the type in question, which comprises 
means producing a channelled current of air which allows the thread to 
form a loop between two fixed points. 
This device re-tensions the weft thread immediately after each stoppage in 
the unwinding operation, by a blast of air giving the yarn the shape of a 
hairpin between the two fixed points which are, for example, eyelets 
through which the thread passes. 
In a preferred embodiment of this device, for channelling the current of 
air, the latter comprises a chamber of slight depth (i.e. generally flat 
chamber) defined by two parallel plates, one plate being stationary and 
provided with side (lateral) flanges substantially parallel to the 
direction of the air stream and the other being removable. The spacing of 
the two plates should be chosen so as to leave ample space for the passage 
of the yarn, in order that the loop may form freely, while preventing 
kinking of the yarn when the device is stationary. 
The stationary plate advantageously supports an air-ejection nozzle located 
substantially equidistantly from the two side flanges of said plate and 
having its outlet orifice facing the central part of the chamber defined 
by the two plates. Furthermore, the outlet orifice of the nozzle 
preferably has a flat rectangular shape, its height being significantly 
less than its width. This arrangement makes it possible to obtain a 
virtually laminar air stream directed accurately between the two plates 
such that the loop formed by the yarn is roughly symmetrical and has two 
substantially parallel sides, spaced apart to the maximum extent and which 
cannot twist one around the other. 
The removable plate is withdrawn to facilitate introduction of the weft 
thread in the device. To ensure positioning of the removable plate, the 
latter comprises an opening for example which, when this plate is in 
position, is traversed by the top of the nozzle. Advantageously, this 
removable plate is transparent, which makes it possible to observe the 
device during operation and above all when it is regulated, which takes 
place by modifying the air flow. 
In a particular embodiment, the air is supplied through a flexible tube, on 
which is placed a device for regulating the rate of flow. The device acts 
by pinching of the tube to modify the section of the supply tube.

SPECIFIC DESCRIPTION 
The invention relates to a shuttle-less loom in which the weft thread 1, 
coming from a stationary supply bobbin 2 located on one side of the 
machine, is entrained by a lance (not shown) in the direction of arrow 3 
in FIG. 1, the yarn passing through yarn-guide eyelets 4, 5 and 6 as well 
as between braking plates 7, known per se. In the device of the invention, 
the bobbin 2 is surrounded by a casing 8 shown partly in FIGS. 2 and 3, 
the purpose of which is to prevent the weft thread, while unwinding and 
forming the above-mentioned "balloon," from becoming attached to any part 
of the machine. 
The device according to the invention, designated generally by the 
reference numeral 9, is located between the first eyelet 4, through which 
the yarn passes from the casing 8 and the second eyelet 5. It comprises a 
lower plate 10 and an upper plate 11, the lower plate 10 comprising two 
parallel flanges 12 directed upwards in order to define with the upper 
plate 11, a chamber 13 of slight thickness as shown clearly in FIG. 3. 
The lower plate 10 is constituted by a fixed metal part whose flanges 12 
extend in a direction at right-angles to the straight line joining the two 
eyelets 4 and 5. This plate 10 supports an air-ejection nozzle 14, located 
in front of the eyelets 4 and 5 and at equal distances from the latter, 
i.e. along the axis of the device 9. The nozzle 14 is connected to a 
turbine-operated fan 15 by means of a flexible tube 16, as shown in FIG. 
3. 
The upper plate 11 is a transparent part, made for example from Derspex. It 
is removable and has a circular opening 17 through which, when the plate 
is in position, the upper part of the nozzle 14 passes. 
The outlet orifice 18 of the nozzle 14 is directed to face the central part 
of the chamber 13 defined by the plates 10 and 11. This orifice has a flat 
rectangular shape, as shown in FIGS. 4 and 5, its height H clearly being 
less than its width L. 
When the loom in question is operating, the blower 15 continuously sends a 
flow of air into the tube 16, which air escapes through the outlet orifice 
18 of the nozzle 14. Owing to the flattened shape of this orifice, to its 
position and its orientation, there is obtained between the plates 10 and 
11 a laminar air stream, represented by the arrows 19 of FIG. 1, whose 
direction is at right-angles to the straight line joining the eyelets 4 
and 5, which stream travels through the device 9 from front to back, in 
order to escape at the open end of the latter opposite the nozzle 14. 
During the periods, depending on the cycle of the loom, when the weft 
thread 1 is not withdrawn, the latter is retained between the braking 
plates 7. However, the thread may still unwind under the effect of inertia 
and gravity and consequently become slack and it is here that the device 9 
according to the invention intervenes. 
Assuming that the thread is slack between the bobbin 2 and the braking 
plates 7, the air stream passing through the chamber 13 tends to entrain 
the yarn and cause the yarn to describe a loop 20 of variable length 
between the eyelets 4 and 5, inside the chamber 13 located between the 
plates 10 and 11. The laminar distribution of air makes it possible to 
obtain a virtually symmetrical loop 20, the two sides of which are 
substantially parallel to the flanges 12 of the plate 11 and very close to 
these flanges, the sides of the loop being therefore spaced apart to the 
maximum extent, which makes it possible to re-tension the yarn and prevent 
its kinking. 
The flow of air passing through the flexible tube 16 and should be able to 
be regulated depending on the size of the weft thread 1, an equilibrium 
having to be found in order to re-tension the yarn without unwinding the 
bobbin 2. To this end, a device for regulating the rate of flow is located 
on the tube 16. This device, shown in FIG. 3, is based on the principle of 
pinching the tube and it comprises a tubular body 21, surrounding the tube 
16, which comprises a screw 22 acting on a small plate 23 pressed against 
the tube. The transparency of the of the upper plate 11 facilitates 
regulation of the rate of flow, thus facilitating checking of the effect 
obtained. It is also possible to act on the spacing of the two plates 10 
and 11 to obtain correct adjustment. 
The description of the device 9 according to the invention was hitherto 
made considering a single weft thread 1, but the invention relates to 
machines making it possible to weave with several weft threads, in which 
case the device 9 is a multichamber device, however the blower 15 being 
common to them all. 
Naturally and as is apparent from the aforesaid, the invention is not 
limited to the single embodiment of this device for re-tensioning a weft 
thread, which was described above by way of example. On the contrary, it 
includes all variations of construction and application. 
Thus, in particular, in the case of slightly twisted weft threads, the 
removable plate 11 may possibly be eliminated, the laminar air stream 
remaining in contact with the single fixed plate 10 and making it possible 
to obtain the desired result by means of the shape and direction of the 
orifice of the nozzle 14, as well as by the shape of the plate 10 and its 
flanges 12.