Rotatable thread arrester for weft feeders for air-jet looms

A rotatable thread arrester, associated with a thread feeder, includes an arrester finger for the thread that is movable with respect to the reel of the feeder under the control of a movement device and engages the thread so as to stop its unwinding from the reel and viceversa in order to damp the peak of the mechanical tension generated on the thread by the contact with the arrester finger. The arrester finger is oscillatably suspended about an axis "x" that is parallel to the axis "y" of the reel and is controlled by the action of a motor which rotates the arrester in the thread unwinding direction, so that the arrester finger, in the arresting position, follows the thread unwinding from the reel.

BACKGROUND OF THE INVENTION 
The present invention relates to a thread arrester for weft feeders for 
air-jet looms. 
It is known that weft feeders are devices that accumulate a reserve of 
thread in the form of turns wound around a fixed reel or drum and feed the 
loom by unwinding the turns in an amount equal to the length L of thread 
required by the loom at each beat, said length being equal to the width of 
the fabric being formed. 
In the specific case of air-jet looms, the pre-feeder lo also has the task 
of pre-measuring the length L, and this task is performed by counting the 
unwound turns of thread, for example by means of a photocell, since: 
EQU L=n.pi.D 
where n is the number of unwound turns and D is the diameter of the fixed 
drum or reel of the feeder. 
The unwinding of the thread is controlled by an electrically-controlled 
arrester, which, by means of a movable finger acting by contact engagement 
with the drum, stops the unwinding of the thread when the n.sup.th turn 
has been reached. 
In conventional weft feeders, in view of the high speed of a modern air-jet 
loom, which can insert approximately 1500 meters of weft per minute, the 
intervention time of the arrester is extremely short and is typically 
comprised between 10 and 20 ms (milliseconds). It is evident that when the 
arrester intervenes, a peak T.sub.1 of the mechanical tension T of the 
thread occurs in the portion of thread downstream of said arrester, said 
tension varying in time t, as shown qualitatively in the diagram of the 
accompanying FIG. 1. 
The peak T.sub.1 of the mechanical tension T must be damped appropriately, 
on penalty of weft thread breakage, which occurs more frequently as the 
count of said thread decreases. Various auxiliary damping means, 
interposed between the weft feeder and the loom, are currently used for 
this purpose. Typically, a conventional tension damping device is 
constituted by at least one set of three rollers, the intermediate roller 
being movable; the weft thread is passed between said rollers along a path 
that forms loops which during thread braking are straightened since the 
intermediate roller or rollers flex, thus allowing the thread to elongate 
and consequently damping said tension peak. 
However, this known auxiliary damping system, and others, based for example 
on the flexing of elastic means, do not yield satisfactory results, mainly 
due to the inertia of the masses of the movable damping elements, which 
produces significant delays in the intervention of the system, thus 
limiting its effectiveness. 
Said auxiliary damping systems are furthermore physically separated from 
the weft feeder and accordingly, in addition to requiring adequate 
installation spaces, they must be selected and adjusted both according to 
the characteristics of the feeder braking device and to the count of the 
thread being processed. 
SUMMARY OF THE INVENTION 
The aim of the present invention is to eliminate these and other drawbacks, 
and within the scope of this general aim it has the important object of 
providing a thread arrester that can eliminate the onset of tension peaks 
on the thread by virtue of a gradual braking action applied to said 
thread, the pre-measured length L whereof is however kept unchanged. 
The device according to the invention thus eliminates the use of auxiliary 
damping devices of any kind and sort interposed between the pre-feeder and 
the loom, does not require accurate adjustment operations when the count 
of the thread being used varies, and entails considerable advantages both 
from an economical point of view and as far as system functionality is 
concerned. 
According to the present invention, this aim and these objects and 
advantages are achieved with a thread arrester having the specific 
features stated in the appended claims. 
The invention is essentially based on the concept of giving the movable 
finger of the braking device a controlled rotation in the direction in 
which the turns of thread unwind. 
This rotation of the device movable finger on one hand does not change the 
number n of the total turns unwound from the drum, and therefore does not 
change the pre-measured length L of the thread, and on the other hand 
produces an effective damping in the braking action and substantially 
eliminates the onset of said tension peak on the thread.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIGS. 2 and 3, the reference numeral 10 generally 
designates a weft feeder for air-jet looms comprising, in a per se known 
manner, a fixed body 11, a fixed drum or reel 12 formed by a plurality of 
rods 13 supported by a hub 14, and a rotatable disk 15 located at the base 
of the reel 12 and driven by a hollow drive shaft 16. A hollow rotating 
arm 15' is rigidly coupled to the disk 15 and is connected to the hollow 
drive shaft; the thread FI originating from the spool runs in the cavity 
of the shaft and of the arm and is wound by the disk 15 on the reel 12 to 
form a reserve of thread turns RF to be fed to the loom. 
At each beat of the loom, a number n of turns of thread, equal to the 
length L of the weft that the loom inserts with said beat, is unwound from 
the reel 12. 
The number of turns that unwind is counted, in a per se known manner, by a 
photoelectric cell (not shown) that cooperates with a counter; when said 
counter reaches the last-but-one turn (n-1), it energizes an arrester, 
generally designated by the reference numeral 17. Said arrester is 
provided with an arresting finger 18 which, by moving downwardly in a 
radial direction, enters the slot 13' of a rod 13" of the reel, stopping 
the unwinding of the thread when the n.sup.th (last) turn is reached. 
The nature of the arrester 17 is non-limitative as regards the scope of the 
present invention. In the illustrated example, it is of the electrodynamic 
type disclosed in the prior European patent publication no. 0581745, and 
comprises a permanent magnet 19, contained in a cylindrical skirt 20, 
which extends in a cylindrical axial pivot 21 that delimits an annular air 
gap 22 together with a circular opening of the skirt 20. A movable fixture 
23 is loosely slideably fitted on the cylindrical pivot 21 and is provided 
with a winding 24 arranged at the gap 22. 
The movable fixture 23 is elastically suspended by two annular flat springs 
25 and is provided at its free end with the arresting finger 18. An 
energization current I, supplied by a source G under the control of the 
counter associated with the photoelectric cell that counts the turns, is 
made to circulate in the winding 24. Due to the energization current I, 
the finger 18 moves downwardly, engaging inside an accommodation slot 13' 
of the underlying rod 13" of the reel 12 in order to engage the turns of 
thread that unwind from said reel. 
According to the present invention, the skirt 20, which constitutes the 
body of the device 17, is provided with two diametrically opposite 
external supports 27 and 28 that oscillatably suspend said device about an 
axis "x" parallel to the axis "y" of the reel 12. 
The support 27 is freely rotatably engaged on a respective supporting pivot 
29 supported by a structure 30 rigidly coupled to the fixed body 11 of the 
feeder. The support 28 is fitted on, and keyed to, the drive shaft 31 of a 
step motor 32, also supported by the fixed structure 30. The energization 
current I is fed to the motor 32, so that when the arrester 17 is 
energized and the finger 18 moves downwardly to engage the unwinding 
thread, the motor 32 is also supplied and turns by one or more steps in 
the thread unwinding direction, designated by the arrow F, following the 
movement of the finger 18. 
Accordingly, the finger 18 moves, as shown in dashed lines in FIG. 3, in 
the thread advancement direction, remaining however inside the slot 13', 
and this causes an effective damping of the tension peak T.sub.1 (FIG. 1), 
which would apply stress to the thread FI, suddenly braked by the finger 
18, if the arrester 17 did not move. 
According to the embodiment of FIGS. 4 and 5, the arrester 170 comprises an 
electric motor 132 also of the step type which is suspended from a bracket 
130 above the reel 12 and is orientated so that its axis is parallel to 
the axis of said reel. A hub 120 is keyed on the shaft of the motor 132 
and is provided with a radial bar 118 directed towards the reel 12. 
Due to the rotation of the shaft of the motor 132, controlled for example 
by a microprocessor .mu.P, with which a power interface I is associated, 
the radial bar 118 can oscillate by moving in reverse with respect to the 
thread turn unwinding direction, designated by the arrow F, from an 
angular position for engaging the unwinding turns, shown in solid lines in 
FIG. 5 (six-o'clock position), to a position for releasing said turns, 
shown in dashed lines in the same figure (four-o'clock position), and vice 
versa. 
In the engagement position, the free end of the bar 118 is accommodated in 
a corresponding accommodation slot 13' to prevent the sliding of the 
unwinding turns on the rod 13". During turn unwinding, the bar 118 is in 
the release position, and when the last-but-one unwinding turn is reached, 
the bar starts moving in the same direction as the turn unwinding 
direction F towards the engagement position (for example, clockwise with 
reference to FIG. 5) and reaches this position at the end of the unwinding 
of the n.sup.th last turn. 
The bar moves gradually from the release position to the engagement 
position according to a rule of motion that is controlled by the 
microprocessor .mu.P; this gradual motion effectively damps the mechanical 
tension peak generated on the thread as a consequence of the engagement of 
the thread with said bar. For this purpose, the motor 132 is powered so as 
to move the bar 118 from the release position to the engagement position 
with a uniformly decelerating motion starting from an initial peripheral 
speed of said bar that is substantially equal to that of the unwinding 
thread. 
This motion rule is qualitatively represented in the chart of FIG. 6, 
showing that the bar 118 initially undergoes a quick acceleration a, which 
brings it up to an initial peripheral speed Vi substantially equal to the 
unwinding speed of the turns of thread, and then undergoes a constant 
deceleration a', which makes it stop in the final engagement position. The 
initial contact of the thread with the bar 118 occurs when said bar 
reaches the accommodation slot 13' with a peripheral speed Vi, so that 
said contact generates practically no mechanical tension at all on said 
thread, whereas during the subsequent deceleration step the bar gradually 
stops the thread, effectively damping the tension peak T1 shown in FIG. 1. 
The reverse rotation of the motor 132, performed according to any motion 
rule by the microprocessor .mu.P following an actuation signal "t" from 
the loom, moves the bar 118 into the release position when said loom 
inserts a new weft beat. 
According to the embodiment of FIGS. 7 and 8, the arrester 270 uses two or 
more bars, for example four bars 218 supported by the hub 220 of the motor 
232 and spaced by an angle of 90.degree., which move in a single 
rotational direction that matches the thread unwinding direction F, and 
move alternately between the engagement position (six-o'clock position) 
and the release position. This last position is reached by the generic bar 
218' after a rotation of the hub 220 of the motor 232 that is equal to 
approximately one quarter of the angle formed between two consecutive 
bars; in the illustrated example, after approximately 
20.degree.-22.degree. of rotation (approximately seven-thirty position). 
Correspondingly, the subsequent bar 218" moves into an intermediate 
position, wherein it does not interfere with the thread, and wherefrom the 
thread arresting stroke begins, moving said bar into the corresponding 
engagement position with the same motion rule as in FIG. 6. 
The details of execution and the embodiments may of course be altered 
extensively with respect to what has been described and illustrated by way 
of non-limitative example without altering the concept of the invention 
and without thereby abandoning the scope of the invention defined by the 
appended claims, wherein the reference numerals are provided only for the 
sake of better comprehension.