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
In the specific case of air-jet looms, the pre-feeder 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:
L = n π 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 nth turn has been
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&sub1; 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 figure 1.
The peak T&sub1; 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.
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.
Further characteristics and advantages of the device according to
the present invention will become apparent from the following detailed description
and with reference to the accompanying drawings, given by way of non-limitative
- figure 1 is a plot of the mechanical tension of the thread as a function of
- figure 2 is a partially sectional partial view of a feeder for air-jet looms
equipped with the thread arrester according to an embodiment of the present invention;
- figure 3 is a front view, taken along the direction of the arrows III-III of
- figure 4 is a partially sectional view of an air-jet loom feeder with the thread
arrester according to an embodiment of the present invention;
- figure 4a is an enlarged-scale view of a detail of figure 4;
- figure 5 is a front view, taken in the direction of the arrows V-V of figure
- figure 6 is a diagram of the motion rule of the movable finger of the thread
arrester shown in figure 4;
- figure 7 is a partial sectional view, similar to figure 4a, of another embodiment
of the invention;
- figure 8 is a view taken in the direction of the arrows VIII-VIII of figure
With reference to figures 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 nth
(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
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 figure
3, in the thread advancement direction, remaining however inside the slot 13',
and this causes an effective damping of the tension peak T&sub1; (figure 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 figures 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 µP, 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 figure 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 figure 5) and reaches this position at
the end of the unwinding of the nth 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
µP; 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 figure
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 figure 1.
The reverse rotation of the motor 132, performed according to any
motion rule by the microprocessor µP following an actuation signal "t" from the
loom, moves the bar 118 into the release position when said loom inserts a new
According to the embodiment of figures 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 90o, 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
20-22o 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 figure 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.
Where technical features mentioned in any claim are followed by reference
signs, those reference signs have been included for the sole purpose of increasing
the intelligibility of the claims and accordingly such reference signs do not
have any limiting effect on the interpretation of each element identified by way
of example by such reference signs.