Device for braking a weft thread in a weaving machine

A thread brake for braking a weft thread in a weaving machine includes a rigid stop and an elastically deformable blade which has a free end supported to press resiliently against the rigid stop. Thread guides are provided to guide weft threads between the rigid stop and the elastically deformable blade. The thread brake is activated when the deformable blade elastically presses against the rigid stop. When contacted by a switching device, however, the elastically deformable blade is pushed against its resilient force and removed from the rigid stop, at least in the region of the switching device, deactivating the thread brake.

BACKGROUND OF THE INVENTION 
This invention concerns a device for braking a weft thread in a weaving 
machine. The device can be used in all types of weaving machines, but is 
particularly intended for rapier weaving machines. 
It is known that in modern, high-speed rapier weaving machines the weft 
threads must be inserted into the shed in a controlled manner, in other 
words, each weft thread must be braked or released at the right moments 
and during particular periods of time in the weft insertion cycle. During 
the insertion movement of the grippers, on the one hand the braking must 
be kept to a minimum, both when the weft threads are being accelerated and 
during their rapid travel, in order to limit the tension in the weft 
thread and so prevent weft breaks. On the other hand, when the rate of 
travel of the grippers and of the weft thread is decelerating, and during 
the standstill of the weft thread, the weft thread must be braked in order 
to keep it taut and prevent weaving faults, or in order to keep the thread 
in a desired position. 
SUMMARY OF THE INVENTION 
The present invention has as its object a device for braking a weft thread, 
whereby the braking on the weft thread can be released entirely at the 
right moments and during the right periods in time of the weft insertion 
cycle, such that the weft thread is not loaded more than necessary. A 
particular advantage of the device according to the invention is that the 
braking force can be supplied or removed instantly. 
The present invention also has as its object a device which allows better 
control over the tensioning of the weft thread during the transfer between 
the feed gripper and the receiving gripper. 
Further, the invention has as its object a device which makes it possible 
to adjust the moment of commencement of the braking of the weft thread at 
the end of the insertion in a very simple way, such that by braking the 
weft thread sooner or later the weft thread is released either more or 
less rapidly from the opened clip of the feed gripper, whereby the waste 
length of the weft thread can be reduced to a minimum by the control of 
the device. 
For these purposes, a thread brake according to the invention includes a 
rigid stop and an elastically deformable blade with a free end which 
presses resiliently against the rigid stop, thread guides to guide a weft 
thread between the rigid stop and the blade which operates in conjunction 
with it, and a switching device which can be moved between two positions 
by means of an electromagnet and which can operate in conjunction with the 
elastically deformable blade. In the first position of the switching 
device, the elastically deformable blade presses against the rigid stop, 
such that the thread brake is activated, while in the second position, the 
elastically deformable blade is removed from the stop by means of the 
switching device, at least in the region of the switching device, such 
that the braking action on the weft thread is removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It is known that, as shown in FIG. 1, each of the weft threads 1 on rapier 
weaving machines can be brought into the path of the feed gripper 6 from a 
yarn package 2, via a thread accumulator device 3 and via a device 4 for 
braking the weft thread 1, by means of a thread presentation device 5. For 
the sake of clarity, the figure shows the supply of only one weft thread 
1. The presented weft thread 1 is gripped in the known manner by means of 
the feed gripper 6 and cut loose by means of a cutter 7 at the cloth edge. 
Next, the feed gripper 6 pulls the weft thread 1 into the shed 9, 
transfers it to the receiving gripper 10 halfway along the shed 9, which 
then takes it to the end 11 of the shed 9. 
The present invention concerns the device 4 for braking the weft thread 1, 
such that the purposes set out in the introduction are met. 
As shown in FIGS. 2 to 5, this device 4 includes a thread brake 12. Thread 
break 12 includes a rigid, i.e. inflexible, stop 13 and an elastically 
deformable blade 14 which co-operates with the rigid stop, and thread 
guides to guide the weft thread 1 between the rigid stop 13 and the 
elastically deformable blade 14 co-operating with it. In the embodiment 
shown in FIGS. 2-5, the thread guides include two thread eyes 15 and 16. 
Thread brake 12 also includes a switching device, preferably a pusher 18, 
which can be moved between two positions by means of an electromagnet 17 
and which can co-operate with the elastically deformable blade 14, so that 
the latter can be removed from the rigid stop by the pusher at the desired 
moments and during certain periods in the weft insertion cycle. 
Electromagnet 17 is controlled by means of controlling means 19. 
In the embodiment shown, the above-mentioned parts are mounted on a 
structure 20 by means of attachments 21. Structure 20 is suspended from a 
bar 22, which in turn is connected to the frame 23 of the weaving machine 
or a package frame. 
The above-mentioned rigid stop 13 consists of a cylinder. The elastically 
deformable blade 14 is mounted so that its free end presses against the 
cylinder wall of the rigid stop 13. Both the rigid stop 13 and the 
elastically deformable blade 14 are preferably arranged vertically. 
As shown in FIGS. 2 and 3, the device 4 preferably has adjusting means 25 
to adjust the force with which the elastically deformable blade 14 presses 
against the rigid stop 13. For this purpose, the elastically deformable 
blade 14 is fixed at the end 26 opposite the free end 24 to a shaft 27 
which can be rotated by means of a small lever 28 whose position can be 
adjusted by means of the set screw 29. Contact between the small lever 28 
and the set screw 29 is ensured by an elastic means, such as a pressure 
spring 30. By screwing in set screw 29 or by rotating the small lever 28 
from position A to position B, any desired braking force of the 
elastically deformable blade 14 on weft thread 1 can be set. In position 
B, the elastically deformable blade has a shape indicated by reference 31. 
The whole assembly can be mounted in a housing 32. 
The thread eyes 15 and 16 are mounted in supports 33 and 34 connected to 
the basic structure 20, such that a weft thread 1 drawn between them 
passes between the rigid stop 13 and the elastically deformable blade 14, 
approximately in the middle of the elastically deformable blade 14. 
In the embodiment shown, the above-mentioned pusher 18 includes a small bar 
which can make contact with the elastically deformable blade 14. This 
pusher 18 can take two positions. The first is a withdrawn position, 
where, as shown in FIG. 3, the end 35 is removed from the elastically 
deformable blade 14, such that the latter presses against the rigid stop 
13 with full force. The second position is a protruding position where, as 
shown in FIG. 4, the pusher 18 pushes the elastically deformable blade 
away from the rigid stop at least in the region of said pusher. The 
contact-point of the pusher 18 on the elastically deformable blade 14 lies 
on or almost on the contact line 36 in which the elastically deformable 
blade normally presses against the rigid stop 13. This has the advantage 
that the braking force on the weft thread can be applied and removed 
instantaneously. As the contact-point of the pusher 18 lies on the contact 
line 36, the slightest bending of the blade 14 results in the braking 
force being removed. In order to ensure that the pusher 18 can act in the 
above-mentioned contact line 36, the cylinder-shaped rigid stop 13 has a 
local notch 37, which is clearly shown in FIGS. 2, 4 and 5. 
The two positions of the switching device, or in this case the pusher 18, 
are shown in detail in FIGS. 6 and 7. The pusher 18 pushes on the 
elastically deformable blade 14, away from the longitudinal axis 38, with 
the effect that, as shown in FIG. 7, only one side of the elastically 
deformable blade 14 is pushed away from the rigid stop rigid stop 13, 
while the other side remains in contact with it. One of the advantages is 
that, although the weft thread is not braked any more, it is still locked 
in from all sides, such that the thread cannot possibly escape from the 
device 4. 
It is clear that the construction of the electromagnet 17 can be of various 
kinds. In the example according to FIG. 3 electromagnet 17 includes a 
solenoid 39, wound round a core 40, such that supplying a voltage to the 
solenoid causes an armature 41 connected the pusher 18 to be pulled 
towards the core 40. When the electromagnet is de-energized, the pusher 18 
is returned by means of return spring 42. 
In the variant according to FIGS. 8 and 10, the above-mentioned rigid stop 
13 consists of a cylinder which can rotate round a shaft 43, such that 
dust particles 44 are removed as a result of the rotating movement through 
the thread brake 12. It is clear that the thread guides and cylinder must 
be positioned such that the movement of the weft thread 1 causes the 
desired rotation. For this purpose, the thread eyes are arranged so that, 
as shown in FIG. 10, the weft thread 1 is bent through a small angle over 
the cylinder-shaped surface 45. In order to prevent the rigid yet 
rotatable stop 13 from rotating too far due to its inertia when the weft 
thread is braked, the elastically deformable blade 14 is divided into two 
parts 47 and 48 by means of a longitudinal notch 46. As shown in FIG. 9, 
part 47 is the brake blade for the weft thread 1 which, by means of the 
pusher 18 or another similar switching device, can be pushed away from the 
rotatable stop 13. The second part 48, in contrast, is a brake blade whose 
flat side, regardless of the position of the pusher 18, always remains in 
contact with the rotatable stop 13 and so brakes it constantly. In order 
to improve the dust removal, a small fan formed by a paddle wheel 49 can 
be mounted on the rotatable stop 13, such that an air stream is created in 
the direction of the longitudinal axis of the rotatable stop 13. 
The operation of the device 4 can be simply deduced from the figures. As 
described above, the weft thread 1 is guided through the thread brake 12 
and will then be braked or not depending on whether the electromagnet 17 
is switched off or on. The braking force can be adjusted by means of the 
adjusting device 25, which is done mechanically and manually, after which 
the adjustment is not changed during the operation of the weaving machine. 
The control means 19 ensure that the electromagnet 17 is switched on 
during preset periods of time. 
It is clear that the control means 19 can be of various types. In the first 
place, the intention is for the weft tension variations for a particular 
weft thread 1 to be repeated during each weaving cycle. For this purpose, 
the periods during which the electromagnet 17 must be energized, as a 
function of the weft insertion cycle or in other words the number of crank 
angle degrees of the weaving machine, must be input or programmed 
beforehand by means of an input unit 50. In order to make the braking 
cycles run simultaneously with the drive of the weaving machine, the 
controlling means 19 can for example be triggered by means of a pulse 
generator 52 mounted on the main shaft 51 of the weaving machine. The main 
drive of the weaving machine is indicated schematically by reference 53. 
Control of the thread brake 12 is preferably as shown in FIG. 11, in which 
the braking force K is shown as a function of the rotation of the main 
axis, measured in crank angle degrees X. The weft thread 1 is braked 
between X0 and X1, between X2 and X3 and from X4 onwards. It is clear that 
for this purpose the electromagnet 17 is energized during the periods 
X1-X2 and X3-X4. During the period X0-X1 the weft thread 1 is picked up by 
the feed gripper, while during the period X2-X3 the weft thread 1 is 
handed over to the receiving gripper. It is clear that during these 
periods the brake must be activated in order to ensure that the thread is 
kept taut. At the end of the insertion, at X4, the thread is also braked. 
By choosing a different value for moment X4, the amount of thread waste 54 
can be changed. By activating the brake earlier, it becomes possible for 
the weft thread to be released more quickly from the opened clip of the 
receiving gripper 10. X1 is preferably situated between 50 and 100 crank 
angle degrees, X2 between 160 and 180 crank angle degrees, X3 between 180 
and 200 crank angle degrees and X4 between 270 and 310 crank angle 
degrees. 
The present invention is not limited to the embodiments described by way of 
example and shown in the figures; on the contrary, such a device for 
braking a weft thread in a weaving machine can be made in all sorts of 
forms and dimensions while still remaining within the scope of the 
invention.