Method and device for feeding weft thread.
The invention concerns a method for feeding weft thread in a
weaving machine. The invention also concerns a device for feeding
weft thread in a weaving machine that is designed for applying a
method according to the invention.
A device for feeding weft thread to a weaving shed of an airjet
weaving machine is known from US 4,947,898 or
WO 2010/006774 A2. The device comprises a storage element for
storing weft thread, which storage element comprises a cavity
delimited by side walls, which cavity has an inlet and an outlet for
weft thread. I n the side walls, openings are provided allowing
compressed air to escape. The device comprises a clamping element
for clamping weft thread, which clamping element is arranged near
the out!et of the cavity. The clamping element can be closed for
storing weft thread and can be opened for removing weft thread.
The c!amping element can also close off the outlet of the cavity for
compressed air. The device also comprises a blowing device to blow
weft thread into the storage element, so that weft thread can be
stored in the storage element. The blowing device is arranged near
the inlet of the storage element and serves for blowing weft thread
to the storage element and for blowing weft thread in the direction
from the inlet to the outlet of the storage element. Further the
device comprises a prewinder for releasing weft thread. The device
allows weft thread to be stored under ow tension in the storage
element, so that weft thread under low tension can be removed from
the storage element, aliowing higher weaving speeds to be reached
or to insert weft thread with Iower air consumption and with iower
tension into the weaving shed. The prewinder allows to release a
weft thread with a suitable length.
A method for feeding weft thread to a weaving shed of an airjet
weaving machine is, for example, known from US 4,947,898 and
WO 2010/006774 A2. Such a method describes the controiling of a
thread holder of a prewinder, a blowing device of a storage element,
a thread holder of a storage element and a main blower. Such a
method has the disadvantage that if a certain weft thread is supplied
too slowly to the storage element, this weft thread will be inserted
too slowly into the weaving shed, so that the weft thread arrives too
late in the weaving cycle at the opposite side of the weaving shed
and a weft fault can occur. Such a method also has the disadvantage
that if a certain weft thread is supplied too fast to the storage
element, this weft will be inserted too fast into the weaving shed, so
that the weft thread arrives too early in the weaving cycle at the
opposite side of the weaving shed and so that the weft thread at
arrival is subjected to a high tension, so that a breaking of the weft
thread can occur.
It is an object of the invention to improve such a method, so
that weft thread is supplied under a relatively low tension and with a
desired speed to the storage element and so that weft thread is
inserted under a relatively low tension and with a desired speed into
the weaving shed.
This object is achieved by a method for feeding weft thread in a
weaving machine, wherein a length of weft thread is released from a
prewinder in order to be inserted into a weaving shed, wherein weft
thread coming from the prewinder is supplied to a storage element
via an inlet of the storage element, wherein weft thread is removed
from the storage element via an outlet of the storage element in
order to be inserted into the weaving shed, wherein before the start
of the insertion of weft thread into the weaving shed weft thread is
stored in the storage element, wherein at least during a part of a
period of the insertion of weft thread into the weaving shed a
simultaneous store and removal of weft thread is carried out,
wherein at least at the end of the simultaneous store and removal of
weft thread, the weft thread stored in the storage element is
removed from the storage element faster than weft thread coming
from the prewinder is supplied to the storage element, so that at a
stretching moment in the weaving cycle during the period of the
insertion of weft thread into the weaving shed the weft thread stored
in the storage element changes from stored condition into stretched
condition, wherein the stretching moment is determined as reference
moment.
I n the context of the description with the term "stretching
moment" is meant the moment in the weaving cycle at which during
the insertion of weft thread into the weaving shed the weft thread
stored in the storage element changes from stored condition into
stretched condition . I n the context of the description with the term
"stored condition" is meant stored in non-stretched condition in the
storage element, for example stored in zigzag form in the storage
element. The "reference moment" is a measure of the "stretching
moment", but as is further evident from the description this
"reference moment" does not necessarily have to coincide exactly
with the "stretching moment".
The invention offers the advantage that by determining a
reference moment that is a measure of the moment in the weaving
cycle at which the weft thread is stretched in the storage element, it
is possible to influence or set specific control parameters for
influencing the reference moment in order to control the reference
moment. I n an embodiment, to control the reference moment, the
speed at which weft thread is supplied to the storage element is
adapted to the speed at which weft thread is inserted into the
weaving shed .
According to a preferred embodiment, the start of the storing of
weft thread in the storage eiement is controlled by an opening of a
second thread holder that is arranged between the prewinder and
the storage element, wherein the opening of the second thread
holder is controlled in function of the reference moment in the
weaving cycle. This means that in dependence of the speed at which
weft thread is supplied to the storage element and in dependence of
the speed at which weft thread is inserted into the weaving shed,
the second thread holder that is arranged between the prewinder
and the storage element is opened at a suitable moment, so that the
weft thread changes from stored condition in the storage element
into stretched condition in the storage element at a desired moment
in the weaving cycle, This also allows keeping the tension in the weft
thread relatively low during the storing in the storage element and
during the insertion into the weaving shed .
According to a preferred embodiment the moment of the
opening of the second thread holder that is arranged between the
prewinder and the storage element is determined so that the
determined reference moment is related to a set moment in the
weaving cycle. The choosing of a set moment in the weaving cycle
allows controlling the moment of opening of the second thread
holder so that the determined reference moment is related to this
set moment. The reference moment in the weaving cycle can be
determined depending on the moment in the weaving cycle at which
the first thread holder that is arranged between the storage element
and the weaving shed is opened and/or the moment in the weaving
cycle at which the weft thread is expected to arrive at the opposite
side of the weaving shed. The method according to the invention has
as result that the opening of the second thread holder is also
influenced by the moment in the weaving cycle at which the weft
thread is expected to arrive at the opposite side of the weaving
shed.
According to an embodiment, a method is provided wherein a
length of weft thread is released from a prewinder in order to be
inserted into a weaving shed, wherein weft thread coming from the
prewinder is supplied to a storage element via an inlet of the storage
element, wherein weft thread is removed from the storage element
via an outlet of the storage element in order to be inserted into the
weaving shed, wherein before the start of the insertion of weft
thread into the weaving shed weft thread is stored for example in
zigzag form in the storage element, wherein at the start of the
insertion of weft thread into the weaving shed weft thread is
simultaneously stored in the storage element and removed from the
storage element, wherein at the end of the insertion of weft thread
into the weaving shed weft thread is inserted into the weaving shed
in stretched condition from a prewinder via the storage element,
wherein the start of the insertion of weft thread into the weaving
shed is controlled by the opening of a first thread holder that is
arranged between the storage element and the weaving shed,
wherein the end of the insertion of weft thread into the weaving
shed is controlled by the closing of a second thread holder that is
arranged between the prewinder and the storage element, wherein
the start of the storing of weft thread in the storage element is
controlled by the opening of the second thread holder that is
arranged between the prewinder and the storage element, wherein a
reference moment in the weaving cycle is determined that is a
measure of the moment in the weaving cycle at which during the
insertion of weft thread into the weaving shed the weft thread stored
in the storage element changes from stored condition into stretched
condition, and wherein the opening of the second thread holder that
is arranged between the prewinder and the storage element is
controlled in function of the determined reference moment in the
weaving cycle.
According to an embodiment, weft thread coming from a
prewinder is blown by means of a blowing device that is arranged
between the prewinder and the storage element via an inlet of the
storage element into the storage element, wherein this blowing
device is activated at a moment in the weaving cycle that is
determined in function of the determined reference moment in the
weaving cycle. This allows that this blowing device is activated so
that the blowing device has already blown on the weft thread over a
short time before opening the second thread holder that is arranged
between the prewinder and the storage element. This allows blowing
weft thread into the storage element from the moment at which the
second thread holder is opened. This means that the opening of the
second thread holder determines the moment in the weaving cycle
at which weft thread is stored in the storage element.
According to a preferred embodiment the blowing device is
deactivated at a deactivation moment in the weaving cycle so that
the blowing of the blowing device on the weft thread decreases
before the reference moment. I n other words, the activating of the
blowing device ends before the weft thread changes into stretched
condition in the storage element. This is advantageous to influence
the moment in the weaving cycle that the weft thread in the storage
element changes to stretched condition. A short time before
reaching the stretched condition weft thread is blown only by a
residual airflow of the blowing device with iow speed into the storage
element. To this purpose, the start and the end of blowing of this
blowing device in the weaving cycle are determined in function of
amongst others the speed at which is woven.
According to an embodiment the deactivation moment in the
weaving cycle is determined in function of a set part of weft thread
coming from the prewinder being supplied to a storage element via
an inlet of the storage element.
Further, the force of the blowing of this blowing device is
chosen so that the weft thread is not blown to the outlet of the
storage element when a part of the stored weft thread has already
been removed from the storage element. To this end, for example,
the pressure of the compressed air that is delivered to the blowing
device and the flow rate of compressed air that is delivered via the
blowing device to the storage element are adapted to the type of
weft thread, to the speed at which is woven and/or to other similar
parameters. The force of the air flow of the blowing device has to be
sufficient to blow a weft thread with a desired speed into the storage
element, but has however to be limited so that it is avoided that
weft thread gets entangled during the storing of weft thread into the
storage element.
According to another embodiment, the start of the insertion of
weft thread into the weaving shed is controlled by the opening of a
first thread holder that is arranged between the storage element and
the weaving shed and/or the end of the insertion of weft thread into
the weaving shed is controlled by the closing of a second thread
holder that is arranged between the prewinder and the storage
element. The terms "first" and "second" in the "first thread holder"
and the "second thread holder" are only intended to indicate that
there are two different thread holders and in order to indicate which
of both thread holders is meant.
According to a preferred embodiment, the reference moment is
determined on the basis of signals of a thread detector or a number
of thread detectors that are arranged at the prewinder, more
particularly a so-cailed winding detector that delivers each time a
signal if a winding coming from the drum of the prewinder is moved
past the thread detector. The reference moment in embodiments is
determined on the basis of time differences, average time
differences and/or statistical deviations of time differences between
signals of a thread detector that is arranged at the prewinder.
According to another embodiment, the reference moment is
alternatively or in addition determined on the basis of signals from a
presence sensor or a number of presence sensors that are arranged
at the storage element.
According to another embodiment, the reference moment is
alternatively or in addition determined on the basis of signals of a
tension sensor for weft thread, that is arranged between a prewinder
and a storage element and/or a tension sensor for weft thread, that
is arranged between a storage element and the weaving shed .
According to another embodiment, the reference moment is
alternatively or in addition determined on the basis of signals of a
movement sensor for weft thread, for example a movement sensor
for weft thread that can detect the movement, in particular the
speed of a weft thread moving along the movement sensor. The
movement sensor in preferred embodiments is arranged between a
prewinder and a storage element and/or between a storage element
and the weaving shed.
This object is also achieved by a device with a prewinder, a
storage element for weft thread and a thread holder that is arranged
between the prewinder and the storage element, wherein the thread
holder is controlled by a control unit in function of the determined
reference moment in the weaving cycle. The storage element can be
a storage element that allows to store a weft thread in the storage
element in zigzag form, for example a storage element as known
from WO 2010/006774 A2.
The invention also offers the advantage that weft thread that is
stored in the storage element with a low tension, can be inserted
into the weaving shed with low tension and/or with higher speed.
This allows in airjet weaving machines amongst others to increase
the weaving speed or to decrease the consumption of compressed
air necessary for the insertion of a weft thread. The consumption of
compressed air can be decreased by decreasing the pressure of the
compressed air and/or by decreasing the amount of delivered
compressed air. The amount of delivered compressed air is, for
example, determined amongst others by the flow through opening to
the blowers and/or the time interval of blowing. The invention also
offers the advantage that the influence of an alteration of the air
friendliness of a weft thread on the supplying of weft thread to the
storage element and on the insertion of a weft thread into the shed
can easily be taken into account.
Further features and advantages of the invention emerge from
the following description of the embodiments represented in the
drawings.
Fig. 1 shows a perspective view of a part of a weaving machine
according to the invention with a number of devices for
feeding weft threads.
Fig . 2 shows a cross section according to arrow F2 in Fig. 1 of a
blowing device and a storage element of a device
according to the invention before the storing of a weft
thread in the storage element.
Fig. 3 shows schematically a state before the storing of the
weft thread in the storage element of Fig . 2.
Fig. 4 shows a state during the storing of the weft thread into
the storage element of Fig . 2.
Fig. 5 shows a state at the start of the removing of the weft
thread from the storage element of Fig . 2, while weft
thread is further stored in the storage element of Fig. 2 .
Fig . 6 shows a state before the stretching moment when
further removing the weft thread from the storage
element of Fig. 2.
Fig. 7 shows a state after the stretching moment when further
removing the weft thread from the storage element of
Fig. 2.
Fig . 8 shows a state before the end of the removing of the weft
thread from the storage element of Fig. 2.
Fig. 9 shows a state at the end of the removing of the weft
thread from the storage element of Fig . 2.
Fig. 10 shows schematically a view according to arrow F10 in
Fig. 1 of a drum of a prewinder.
Fig . 11 shows successive signals of thread detectors that are
arranged at a prewinder.
shows a variant of Fig. 2.
shows curves of signals of tension sensors measuring the
tension of the weft thread.
shows a view according to arrow F14 in Fig. 1 of a
further storage element.
shows curves of signals of movement sensors measuring
the movement of the weft thread.
The weaving machine shown in Fig. 1 comprises four devices 1
for feeding weft threads 2. Such a device 1 is known from
WO 2010/006774 A2 of which the description forms part of this
patent application. Each device 1 comprises a prewinder 3 onto
which a weft thread 2 coming from a bobbin 4 is wound. Each device
1 further comprises a main blower 5 that is located next to the
weaving shed 6 and is arranged to blow the weft thread 2 into the
weaving shed 6. The weaving shed 6 is formed by warp threads 7
and 8. Each device 1 also comprises a thread brake , a blowing
device 10 and a storage element 11 that are arranged in order to
guide a weft thread 2 successively from a prewinder 3 via the thread
brake 9, the blowing device 10 and the storage element 11 to a
main blower 5. A number of relay nozzles 12 are shown that can
enter into the weaving shed 6 and that are arranged to support a
weft thread 2 inserted into the weaving shed 6 . In preferred
embodiments, the main blowers 5 and the relay nozzles 12 are
mounted on a sley 13 of the weaving machine to move to and fro
with the sley 13. Near the weaving shed 6 a weft cutter 14 is
positioned . At the end of the weaving shed 6 located opposite to the
main blowers 5 a thread detector 15 is located that is arranged to
detect a weft thread 2 inserted through the weaving shed 6 . The
blowing device 10 comprises a blowing unit 16 and a guide tube 17,
also cailed fill tube, that connects to the storage element 11. The
main blower 5 comprises a blowing unit 18 and a guide tube 19 that
is located near the weaving shed 6. A main b!ower 5 and a blowing
device 10 are, for example, implemented as described in
EP 985.062 Bl.
According to a variant embodiment, the thread brake 9 is
provided on or integrated in the prewinder 3 and/or functions as a
thread compensator or a thread damper. According to a variant
embodiment also an extra thread brake or thread clamp is provided
on or integrated in each of the main blowers 5, for example as
known from EP 1.389.244 Bl or EP 1.389.245 Bl. According to a
variant embodiment, also each main blower 5 is replaced by a
number of main blowers, for example two main blowers arranged in
series that co-operate with an associated weft thread 2.
At each prewinder 3 a thread holder 20 is provided that is
formed for example by a bar 2 1 arranged to be actuated by an
actuator 22. The thread holder 20 is also named second thread
holder in this description. I n an embodiment, the actuator 22
consists of an electromagnet, while the bar 21 consists of a pin that
can cooperate with the electromagnet. The prewinder 3 comprises
for example a drum 23 and a winding arm not shown to wind weft
thread 2 on the drum 23. I n the embodiment of Fig. 1 the thread
holder 20 is fixed to the prewinder 3 . The bar 21 is arranged to
move to and from the drum 23 of the prewinder 3. When the bar 2 1
is moved to a position to the drum 23, also called closed position,
the bar 2 1 can prevent that weft thread 2 is released from the
prewinder 3, while when the bar 21 is moved to a position at which
the bar 2 1 is remote from the drum 23, also called opened position,
weft thread 2 can be released from the prewinder 3. In this case the
thread holder 20 is arranged in order to hold the weft thread 2 at a
determined place when the thread holder 20 is in closed position.
Each prewinder 3 a so comprises at least one thread detector 24 that
generates a signal each time when a weft thread 2 which is released
from the drum 23 moves past this thread detector 24.
As explained in Fig. 2 and 3, a weft thread 2 can be blown
through the guide tube 17 of the blowing device 10, via the inlet 25
into the storage element 11 and according to the moving direction B
to the outlet 26 of the storage element 11 located opposite to the
inlet 25. At the outlet 26 of the storage element 11 a thread holder
27 is arranged. The thread holder 27 is also named first thread
holder in this description. The thread holder 27 is arranged to clamp
the weft thread 2 at the outlet 26, more particularly in order to hold
the weft thread 2 at a determined place. Alternatively or in addition,
the thread holder 27 is arranged to essentially hermetically seal the
storage element 11 at the outlet 26 and/or to brake a moving weft
thread 2. I n an embodiment, the thread holder 27 consists of a bar
28 that can be commanded by an actuator 29 and of a stop 30
against which the bar 28 can impact. I n an embodiment, the
actuator 29 consists of an electromagnet, while the bar 28 consists
of a pin that can cooperate with the electromagnet. In this case, a
weft thread 2 can be held by the thread holder 27 by clamping the
weft thread 2 between the bar 28 and the stop 30. During the
clamping, the thread holder 27 is in a closed position . If the thread
holder 27 does not clamp the weft thread 2, more particularly when
the bar 28 is removed from the stop 30, the thread holder 27 is in
opened position .
The weaving machine comprises, as schematically shown in
Fig . 1, a control unit 31 arranged to drive an actuator 22 of a thread
holder 20 via a drive unit 32, to drive an actuator 29 of a thread
holder 27 via a drive unit 33 and to drive the weft cutter 14 via a
drive unit 34. In preferred embodiments, the control unit 31 in
addition provides a blowing unit 16 of a blowing device 10 with
compressed air via a controllable valve system 35 that is connected
to a compressed air source 47. Further, the control unit 31
preferably provides a blowing device 18 of a main blower 5 with
compressed air via a controllable valve system 36 and provides a
relay nozzle 12 with compressed air via a controllable valve system
37. The control unit 31 is arranged to receive signals of a thread
detector 15 and/or to receive signals of the thread detectors 24 of
the prewinders 3.
In the embodiment shown in Fig. 2 and 3, the storage element
11 for the weft thread 2 comprises a cavity 38 located between the
inlet 25 and the outlet 26 that is delimited by side walls 39, 40 and
that has a substantially flat shape. I n this case the transverse width
between the side walls 39, 40 of the cavity 38 decreases from the
inlet 25 to the outlet 26, so that the side walls 39, 40 mutually form
a small angle, for example an angle in the order of magnitude
between 1° and 8°. At a side wall 4 1 of the cavity 38, for example
the upper side wall, several openings 42 are provided that allow
compressed air to escape from the cavity 38, The storage element
11 also comprises a thread guide 43 that is arranged beyond the
thread holder 27, this means between the thread holder 27 and the
main blower 5.
To a blowing device 10 there is delivered compressed air from a
compressed air source 47, for example an air tank that is shown
schematically in Fig. 1, which compressed air source 47 is connected
to the blowing device 10 via a valve system 35. The pressure and/or
the air flow rate with which compressed air is delivered to the
blowing device 10 in preferred embodiments are set and regulated
so that weft thread 2 is supplied to the storage element 11 with a
desired speed. The force with which the blowing device 10 blows has
to be such that weft thread 2 is supplied to the storage element 2
with a sufficient speed. The pressure and/or the flow rate can also
be adapted during weaving, for example in function of measured or
set weaving parameters.
To a main blower 5 and/or relay nozzles 12 there is delivered
compressed air from a compressed air source 48, for example an air
tank that is shown schematically in Fig. 1, which compressed air
source 48 is connected via a valve system 36 or 37 to a main blower
5 and/or a relay nozzle 12. The pressure and/or the flow rate with
which compressed air is delivered to a main blower 5 and/or a relay
nozzle 12 in preferred embodiments are set and regulated so that
the weft thread 2 is inserted into the weaving shed 6 with a desired
speed. The force with which the main blower 5 and the relay nozzles
12 blow has to be such that weft thread 2 is inserted into the
weaving shed 6 with a sufficient speed. The pressure and/or the flow
o rate in further embodiments are adapted during weaving, for
example in function of measured or set weaving parameters, for
example in a way as known from WO 2006/1 14187 or
EP 1272699 Bl .
The thread holders 20, the thread holders 27, the blowing
i s devices 10, the main blowers 5 and the relay nozzles 12 are
controlled according to a method according to the invention via the
control unit 3 1. The operation for feeding weft thread 2 with a device
I according to the invention is further explained using Fig. 3 to 9.
I n Fig. 3 the thread holders 20 and 27 are closed, while the
0 main blower 5, the blowing device 10 as well as the relay nozzles 12
do not blow. I n Fig. 4 the thread holder 20 is opened and the
blowing device 10 blows so that weft thread 2 released from the
drum 23 of the prewinder 3 is supplied to the storage element 11
and is stored according to a zigzag form with a number of loops 49
5 in the storage element 11. In Fig. 5 also the thread holder 27 is
opened and the main blower 5 together with a number of relay
nozzles 12 blow weft thread 2 into the weaving shed 6. I n Fig. 5
simultaneously weft thread 2 is removed from the storage element
via the outlet 26 and weft thread 2 is blown and stored in the
storage element 11 via the inlet 25.
Next, the blowing device 10 stops blowing so that weft thread 2
is only supplied to the storage element 11 by means of a residual air
flow, while stored weft thread 2 is further removed from the storage
element 11. Because the speed at which the weft thread 2 is
removed from the storage element 11 is greater than the speed at
which weft thread 2 is supplied to the storage element 11, at a
certain moment the weft thread 2 will be stretched in the storage
element 11. By stopping the blowing before a weft thread 2 is fully
stored in the storage element 11 it is also easiiy achieved that the
weft thread 2 will be stretched in the storage element 11 while the
weft thread 2 is further inserted into the weaving shed 6. The
moment at which the weft thread 2 is stretched in the storage
element 11 is called the stretching moment.
In the state shown in Fig . 1 and 7, the weft thread 2 that is
stretched between the prewinder 3 and the main blower 5 is further
supplied to the storage element 11 according to the moving direction
B of the weft thread 2 via the inlet 25, while the weft thread 2 is
removed from the storage element 11 via an outlet 26 located
opposite to the inlet 25. I n the state shown in Fig. 8, the thread
holder 20 of the prewinder 3 is closed so that it is prevented by the
thread holder 20 that weft thread 2 is further released from the
prewinder 3 so that the insertion of weft thread 2 into the weaving
shed 6 will end. I n the state shown in Fig. 9, the weft thread 2 is
inserted into the weaving shed 6 and the thread holder 27 is also
closed again . Meanwhile also the main blower 5 and the relay
nozzles 12 stop blowing and the weft thread 2 is cut by the weft
cutter 14. The weft thread 2 can be cut a short time before, while or
a short time after the moment that the thread holder 27 is closed.
The thread holder 27 is, for example, closed while the weft thread 2
is beaten up by the sley 13. Subsequently the above mentioned
cycle of Fig. 3 to 9 can be repeated.
According to a variant embodiment, the thread holder 27 can
also be closed a short time before the state shown in Fig. 8 with a
small force, so that the weft thread 2 is decelerated a short time
before the state shown in Fig, 8. I t is clear that if a thread brake 9,
as shown in Fig , 1, is provided between the prewinder 3 and the
storage element 1 that this thread brake 9 can be controlled, for
example, at the end of the insertion of weft thread 2 into the
weaving shed 6, in other words in such way that the thread brake 9
decelerates the weft thread 2 a short time before the state shown in
Fig. 8 . I f a thread brake is provided near the main blower 5, this
thread brake can decelerate the weft thread 2 similarly a short time
before the state of Fig . 8. The decelerating or braking of a weft
thread 2 a short time before the end of the insertion into the
weaving shed 6 of the weft thread 2 is advantageous to limit the
tension in the weft thread 2 when this weft thread 2 makes contact
with the bar 2 1 of the thread holder 20.
In the embodiment shown, the valve system 36 of the main
blower 5 and the valve system 37 of a relay nozzle 12 are controlled
in a known way during a weaving cycle. In this case the opening of
the first thread holder 27 is also controiled in a known way, which
thread holder 27 determines the start of the insertion of weft thread
2 into the weaving shed 6 . If, for example, the length of weft thread
2 consists of four windings 50 that were stored on the drum 23 of
the prewinder 3 and that were released from the drum 23, then the
closing of the thread holder 20 can take place in a known way, for
example the thread holder 20 can be brought to a closed position
after the penultimate winding 50, in this case the third winding 50
has passed the thread detector 24. According to the embodiment
shown, the second thread holder 20 and the thread detector 24 are
arranged so that a weft thread 2 only passes by the thread detector
24 each time when a winding is released from the drum 23 almost
completely. The closing of the first thread holder 27 has to take
place after the weft thread 2 is inserted into the weaving shed 6 and
before a following weft thread 2 is stored in the storage element 11
If weaving is carried out with two devices 1 according to the
invention, there is always sufficient time available to close the
thread holder 27 and the closing, for example, takes place at the
moment that the inserted weft thread 2 is beaten up against the
fabric 51. The cutting of the weft thread 2 for example takes place a
short time before the thread holder 27 is closed.
According to a preferred embodiment of the invention the
subsequent signals of a thread detector 24 are used to control the
valve system 35 of the blowing unit 18 and to control the opening of
the thread holder 20. Based on the moments of the subsequent
signals of a thread detector 24, also named winding moments, it is
possible to determine when a weft thread 2 changes from stored
condition in the storage element 11 to stretched condition, more
particularly when the stretching moment takes place. If storing of
the weft thread 2 in the storage element 1 takes longer than the
insertion of the weft thread 2 into the weaving shed 6, then the time
difference lapsed between two subsequent signals of a thread
detector 24, also called winding time, will be larger during the
storing of weft thread 2 in the storage element 11 than during the
insertion of weft thread 2 into the weaving shed 6 with the weft
thread 2 passing in stretched condition through the storage element
11. I n this embodiment, the time difference that lapses between the
opening of the thread holder 20 and the signal that is generated by
the passing of the first winding past the thread detector 24 is called
the winding time of the first winding, The winding times for the three
subsequent windings are determined by the time differences that
pass between the four respective subsequent signals of the thread
detector 24. If for example a weft thread 2 for one insertion is
formed by four windings 50 and the stretching moment takes place
during the third winding, then the winding time for the first three
windings will be substantially larger than the winding time for the
fourth winding, If the stretching moment takes place during the
second winding, then the winding time of the first and the second
winding will be substantially larger than the winding time of the third
and the fourth winding . I f the stretching moment takes place during
the fourth winding then the winding time of the fourth winding will
not be substantially smaller than the winding time of the previous
windings.
Using the winding moments and/or the winding times, it is
possible to determine at which moment in the weaving cycle the
stretching moment takes place. By comparing subsequent winding
moments and/or winding times, a reference moment can be
determined that is a measure of the stretching moment. The
reference moment can for example be determined as follows. If, for
example, it is determined that the stretching moment takes place
during the third winding, then the reference moment during the third
winding can be determined further starting from the winding times
of the second, third and fourth winding. To this end use can be made
for example of the rule of three to determine if the stretching
moment takes place near the start, the middle or the end of the
third winding. This means if the winding time of the third winding
differs only slightly from the winding time of the second winding,
implying that the third winding is mainly stored in the storage
element 11, the stretching moment takes place near the end of the
third winding. If the winding time of the third winding differs only
slightly from the winding time of the fourth winding, implying that
the third winding passes mainly stretched through the storage
element 11, the stretching moment takes place near the start of the
third winding . I f the winding time of the third winding is the average
of the winding time of second and the fourth winding, the stretching
moment takes place near the middle of the third winding. The
comparing of the winding times and/or the winding moments allows
determining a reference moment in the weaving cycle that is a
measure of the stretching moment.
According to an embodiment of the invention, the opening of
the second thread holder 20 that is positioned between the
prewinder 3 and the storage element 11 is controlled as a function of
the determined reference moment in the weaving cycle. I n this
embodiment, the moment at which the second thread holder 20 is
opened is chosen or set so that the reference moment coincides with
a desired moment during the weaving cycle, for example near the
middle of the third winding in case a weft thread 2 for one insertion
is formed by four windings 50. This means that the opening of the
second thread holder 20 during the weaving cycle is controlled to a
moment earlier or later in the weaving cycle so that the determined
reference moment that is a measure of the stretching moment is
shifted to a desired moment in the weaving cycle. If in the example
shown, it is determined that the third winding time is approximately
equal to the second winding time, then in an embodiment the thread
holder 20 is opened stepwise later in the weaving cycle, until the
third winding time is the average of the second and the fourth
winding time. If it is determined that in the example shown the third
winding time is approximately equal to the fourth winding time, then
in an embodiment the thread holder 20 is opened stepwise earlier in
the weaving cycle, until the third winding time is the average of the
second and the fourth winding time.
In this case the determined reference moment can also be
compared with a desired or set moment in the weaving cycle, and
the thread holder 20 can be opened earlier or later in the weaving
cycle until the determined reference moment coincides with the
desired or set moment in the weaving cycle. This allows controlling
the start of the storing of weft thread 2 in the storage element 11 by
the opening of the thread holder 20, so that the stretching moment
for which the reference moment is a measure takes place at a
desired or set moment in the weaving cycle.
According to the invention, the reference moment is not
necessarily determined based on winding times and/or winding
moments. I n other embodiments, the reference moment
alternatively or in addition is determined in a similar way based on
average winding times, based on statistical deviations of winding
times, based on average winding moments and/or based on
statistical deviations of winding moments.
In addition, according to an embodiment of the invention the
blowing device 10 is activated at a moment in the weaving cycle that
is determined in function of the determined reference moment in the
weaving cycle. The moment for activating the blowing device 10 is
determined in a similar way as the moment in the weaving cycle that
the thread holder 20 opens, and for example is influenced so that
the blowing device 10 is activated in order to blow slightly earlier in
the weaving cycle than the opening of the thread holder 20, for
example a few millisecond earlier. This allows that the blowing
device 10 already blows on the weft thread 2 when the thread holder
20 opens.
According to a preferred embodiment of the invention, the
blowing device 10 is deactivated at a deactivation moment in the
weaving cycle, wherein the deactivation moment is set so that the
blowing of the blowing device 10 on the weft thread 2 decreases
before the weft thread 2 in the storage element 11 changes to
stretched condition . If the reference moment, and thus also the
stretching moment, in the embodiment in which a weft thread 2 for
one insertion consists of four windings, takes place during the third
winding, then the blowing device 10 in an embodiment is
deactivated after the signal of the second winding in such a way that
also the blowing decreases after the second winding. This method
offers also the advantage that mainly only two windings are stored
in the storage element 11, so that the reference moment can be
determined based on for example the time difference between the
third and the fourth winding time. By the advanced deactivating of
the blowing device 10 it is avoided that loops of the weft thread 2
are blown over one another in the storage element 11 a short time
before the stretching moment. By the advanced deactivating of the
blowing device 10 it is also assured that the stretching moment
takes place before the third winding passes at the thread detector
24, in other words before the fourth winding 50 is removed from the
drum 23.
Of course the device 1 according to the invention allows to
further use known methods for controlling for example the thread
brake 9. Because in the described example the fourth winding is
removed directly from the prewinder 3, the insertion of the fourth
winding will take place in a similar way as in a weaving machine
wherein no storage element 11 is provided. Hereby the thread brake
9 can be activated in a known way a certain time after the passing of
the penultimate winding at the thread detector 24. The device 1 also
allows to control based on signals of the thread detector 24, for
example signals for the first winding and for the second winding, the
relay nozzles 12 in a way as known from WO 2007/057217 Al,
despite the signals of the thread detector 24 for the first and second
winding not being determined during the insertion of this weft thread
2 into the weaving shed 6. Nevertheless, these signals are
representative for the speed with which the same weft thread 2 will
be inserted into the weaving shed 6, because these signals are
measured on the same part of the weft thread 2 that later will be
inserted into the weaving shed 6.
I n another embodiment, the pressure and/or the flow rate of
the compressed air delivered to the main blowers 5 are controlled in
a known way in function of signals of the thread detector 15 that
detects when a weft thread 2 arrives in the weaving cycle at the
opposite side of the weaving shed 6. I n a similar way, in another
embodiment the pressure and/or the flow rate of the compressed air
delivered to the blowing device 10 are controlled in function of
signals of the thread detector 15, so that the pressure and/or the
flow rate of the compressed air delivered to the blowing device 10
also alters with an alteration of the pressure and/or flow rate of the
compressed air delivered to the main blowers 5. The pressure and/or
flow rate of the compressed air delivered to the blowing device 10
can also be altered so that for example during a weaving cycle the
time for the removing from a prewinder 3 of the first two windings
50 from the drum 23 remains approximately constant. Also the
opening of the thread holder 27 can be controlled in a know way
during a weaving cycle, for example in a way as a thread holder 20
of the prewinder 3 is opened in an airjet weaving machine without
storage element 11.
I n the embodiment described, wherein a weft thread 2 for one
insertion is formed by four windings 50 and the stretching moment
takes place during the third winding, this means during the
penultimate winding, the advantage is obtained that the weft thread
2 can be inserted in a safe manner into the weaving shed 6, more
particularly in a way in which the weft thread 2 can be braked in a
known way during the end of the insertion, but the weft thread 2 can
still be inserted into the weaving shed 6 at high speed and low
tension during the largest part and from the start of the insertion.
In Fig . 10 the mutual position of the thread holder 20 and the
thread detector 24 is shown wherein with arrow R the direction is
indicated in which during the weaving cycle the weft thread 2 is
removed from the prewinder 3. Here, the thread holder 20 and the
thread detector 24 are mutually located so that the thread detector
24 delivers a first signal when the first winding has been removed
from the prewinder 3, delivers a second signal when the second
winding has been removed from the prewinder 3, delivers a third
signal when the third winding has been removed from the prewinder
3 and a fourth signal when the fourth winding has been removed
from the prewinder 3. The fourth signal is delivered a short time
before the weft thread 2 is stopped by the thread holder 20.
According to an embodiment as shown in Fig. 10, also a second
thread detector 52 is provided at each prewinder 3 in addition to the
thread detector 24, which for example with respect to the
circumference of the drum 23 is arranged opposite to the thread
detector 24. This allows during the removing of a winding 50 of a
prewinder 3 to obtain two signals, in other words one signal of the
thread detector 24 and one signal of the second thread detector 52.
I n the example, wherein a weft thread 2 for one insertion consists of
four windings, during a weaving cycle eight signals are generated
that occur each time at the removal of a subsequent half winding. I n
this case according to the invention the activating of the thread
holder 20 can be controlled so that the stretching moment or the
reference moment that is a measure of the stretching moment for
example takes piace after "3,25" windings, in other words a short
time after the third signal of the thread detector 24 and a short time
before the fourth signal of the thread detector 52.
According to a further embodiment along the circumference of
the drum 23 several thread detectors are arranged that each can
detect the passing of a winding, for example four thread detectors
that are shifted by 90°, more particularly the thread detectors 24
and 52 and two further thread detectors 53 and 54 shown in dashed
lines in Fig , 10. In this case a reference moment can be determined
based on time differences between subsequent signals of thread
detectors 24, 53, 52 and 54. To this end there can be determined
subsequently time differences 55 between signals of the thread
detectors 24 and 53, time differences 56 between signals of the
thread detectors 53 and 52, time differences 57 between signals of
the thread detectors 52 and 54 and time differences 58 between
signals of the thread detectors 54 and 24. Such time differences 55,
56, 57, 58 are set out in Fig. 11 wherein electrical signals of the
thread detectors 24, 53, 52 and 54 are set out according to a time
scale. The reference moment can be determined as the moment in
the weaving cycle a short time before the moment at which a
substantial drop in the subsequent time differences 55, 56, 57, 58
takes place, as indicated with moment 59 in Fig . 11. This allows to
determine a reference moment according to the invention with a
comparatively higher accuracy, than the reference moment
determined in a way as described above based on signals of only
one thread detector 24.
According to a variant, a first value of a reference moment is
determined as described above based on only signals of the thread
detector 24, while based on only signals of the thread detector 52,
the thread detector 53 and the thread detector 54 respectively a
second, third and fourth value for a reference moment are
determined. Subsequently, a reference moment according to the
invention in an embodiment is determined statistically, for example
as an average of the first, second, third or fourth value for the
reference moment. According to a variant not shown for example
also three thread detectors are provided along the circumference of
the drum 23 that are for example mutually shifted by 120°.
As shown in Fig. 12, in an embodiment a presence sensor 44,
for example an optical sensor, is provided at the storage element 11
for observing the storing, this means the filling up of the storage
element 11 with weft thread 2 and/or the removing of weft thread 2
from the storage element 11. If a stretched weft thread 2 is present
in the storage element 11, the presence sensor 44 in an
embodiment generates a low signal, while if a weft thread 2 stored
in zigzag form is present in the storage element 11, the presence
sensor 44 generates a high signal . Other embodiments are feasible.
I n an embodiment several presence sensors 45 and 46, designed
similarly as presence sensor 44, are arranged at the storage element
in order to observe the presence of a weft thread that is whether
or not in stretched condition in the storage element 11.
According to the embodiment shown in Fig . 12, a number of
presence sensors 44, 45 and 46 are arranged distributed along the
length of the storage element 11 in order to determine a reference
moment according to the invention. If for example a weft thread 2 is
stored in the area of such a presence sensor 44, 45 or 46 in zigzag
form, the presence sensor generates a high signal, while if weft
thread 2 passes in stretched condition by such a presence sensor 44,
45 or 46, the presence sensor generates a ow signal. This means
that before the storing of weft thread 2 in the storage element 11
the presence sensors 44, 45 and 46 each deliver a low signal. If
during the weaving cycle at least one of the presence sensors 44, 45
or 46 generates a high signal and at a certain moment delivers a low
signal again, this indicates that at this presence sensor the weft
thread 2 stored in zigzag form has become stretched . The presence
sensors 44, 45 and 46 can for example be arranged so that normally
the presence sensors 44 and 45 during the weaving cycle generate a
high signal, while the presence sensor 46 never generates a high
signal. The signal of the presence sensor 46 is then used as a
verification signal.
A reference moment according to the invention in one example
is determined as follows. If for a weft thread 2 only the presence
sensor 45 generates a high signal during a certain time, for example
during a period of 3msec, followed by a low signal, then the
reference moment can be determined as a certain time, for example
2msec, after the moment that the signal of the presence sensor 45
got low again, I f for a weft thread 2 as well the presence sensor 45
as the presence sensor 44 both generate a high signal and then
again a low signal, then the reference moment can be determined as
a certain time, for example 2msec, after the moment that the signal
of the presence sensor 44 got low again. According to a possibility
the moment that the signal of the presence sensor 45 got low again
can also be taken into account. During the storing of a weft thread 2
in the storage element 11, the signal of the presence sensor 45 will
get low again a certain time, for example 2msec, before the signal of
the presence sensor 44. In this case the reference moment is for
example determined as a short time after the moment that the
signal of the presence sensor 44 gets low again, if the signal of the
presence sensor 45 got low again slightly before, for example
2msec. This allows with a great certainty to determine a reference
moment according to the invention and excludes for example that an
alteration of a signal of a presence sensor caused by a weft thread
not correctly stored in zigzag form is interpreted incorrectly as a
weft thread being stretched. If as well the presence sensors 44, 45
as 46 generate a high signal and then again a low signal, the
reference moment can be determined as a moment a certain time
after the signal of the presence sensor 46 got low, if successively the
signals of the presence sensors 45 and 44 got low again a short time
there before.
I n accordance with an embodiment, the thread holder 20 is
subsequently controlled according to the determined reference
moment. To this end the thread holder 20 can be controlled for
example so that during the storing of weft thread 2 in the storage
element 11 the presence sensors 44 and 45 generate a high signal
during the weaving cycle, while the presence sensor 46 never
generates a high signal, wherein the stretching moment can be
determined as the moment at which the generated signals of the
presence sensors 45 and 44 alter from a high signal to a low signal
short time one after another. This embodiment allows determining
the reference moment according to the invention relatively accurate,
which allows the opening of the thread holder 20 to be controlled in
function of this reference moment. If this reference moment takes
place for example too early in the weaving cycle on average, which
implies that few weft thread 2 is stored in zigzag form in the storage
element 11, for a next insertion of weft thread 2, in an embodiment
the thread holder 20 is opened earlier in the weaving cycle. If this
reference moment takes place for example too late in the weaving
cycle on average, which impiies that much weft thread 2 is stored in
zigzag form in the storage element 11, for a next insertion of weft
thread 2 the thread holder 20 in an embodiment is opened later in
the weaving cycle.
The reference moment determined with signals of the presence
sensors 44, 45 or 46 can of course also be used to control the valve
system 35 of the blowing device 10, as well as to control the valve
system 36 of a main blower 5 or the valve system 37 of a relay
nozzle 12.
According to another embodiment as shown in Fig. 12, a tension
sensor 60 for the weft thread 2 is arranged at the thread guide 43
and a tension sensor 6 1 for the weft thread 2 is arranged at the
blowing device 10. Each tension sensor 60, 6 1 delivers a signal that
is a measure of the tension in the weft thread 2. I n Fig. 13 with
curves 62 and 63 examples of electrical signals of the tension
sensors 60, 61, respectively, during the insertion of a weft thread 2
are shown as a function of the weaving machine angle. As shown the
signal of the tension sensor 60 increases at a moment 68, while also
the signal of the tension sensor 61 increases at the same moment.
Such an increase of tension is due to the stretching of the weft
thread 2 at a stretching moment and the moment of this increase
determines the reference moment according to the invention.
According to a further embodiment as shown in Fig. 14, a
movement sensor 64 for the weft thread 2 is arranged at the thread
guide 43 and a movement sensor 65 for the weft thread 2 is
arranged at the blowing device 10. Each movement sensor 64, 65
delivers a signal that is a measure of the movement course and/or
the speed of movement of the weft thread 2. I n Fig. 15 with curves
66 and 67 examples of electrical signals of the movement sensors
64, 65, respectively, during the insertion of a weft thread 2 are
shown as a function of the weaving machine angle. As shown, the
signal of the movement sensor 64 increases at a moment 69, while
the signal of the movement sensor 65 decreases at the same
moment. Such alteration in speed of the weft thread 2 is due to the
stretching of the weft thread 2 at the stretching moment and the
moment of this alteration determines the reference moment
according to the invention.
According to an embodiment the stretching moment is for
example chosen during the last winding, at the fourth winding in the
example with a weft thread 2 for one insertion formed by four
windings 50, which allows to weave at high speed, but with the risk
that the decelerating of the weft thread 2 can happen less
controlled. With such a setting of the weaving machine, the use of at
least one tension sensor 60, 61 and/or at least one movement
sensor 64, 65 in order to determine the reference moment is
particularly suitable in order to allow the stretching moment to take
place as late as possible in the weaving cycle. I n this case, the
reference moment can be determined accurately, more particularly
the stretching moment can be determined easily even when the
stretching moment takes place at the end of the insertion of the weft
thread 2 in the weaving shed 6.
I t is known that successive weft threads 2 from a same bobbin
4 can have an air friendliness that alters and that the force
necessary to draw a weft thread from a bobbin 4 can alter slowly
according to the diameter of the bobbin 4 . As a resu!t, weft threads
coming from a same bobbin 4 supplied using the same setting of the
pressure and/or the air flow rate of the blowing unit 16 during the
storing in the storage element 11 can be stored with a different
speed. Further, as a result weft threads coming from the same
bobbin 4 inserted using the same setting of the pressure and/or the
air flow rate of the blowing unit 18 during the insertion into the shed
6 can move with a different speed. In a device 1 according to the
invention, in preferred embodiments a weft thread 2 is accelerated
at the start of the insertion into the shed 6, then further inserted
with an approximately constant speed into the weaving shed 6 and
decelerated or braked at the end of the insertion into the shed 6.
The determining of a reference moment according to the invention
and the use of a reference moment according to the invention for
controlling the opening of the thread holder 20 is especially suitable
to be used for the weaving of weft thread 2 wherein the air
friendliness of successive weft threads 2 inserted alters. This
particular advantage of the invention will be explained more in detaii
hereafter.
During the weaving, the drive unit 33 of the thread holder 27 is
opened for example at a certain moment in the weaving cycle, which
moment is in preferred embodiments set in function of the moment
at which a weaving shed 6 is formed. The valve system 36 of the
main blower 5 is in preferred embodiments set so that a weft thread
2 arrives at a desired moment in the weaving cycie at the thread
detector 15, for example as known from EP 0.239. 137 Bl . The valve
system 37 for the relay nozzles 12 is in preferred embodiments set
so that the weft thread 2 is supported by the air flow from the relay
nozzles 12, for example as known from EP 2.163.670 Al or
WO 2007/057.217 Al .
If the air friendliness of successive weft threads 2 coming from
a certain bobbin 4 increases during weaving from this bobbin 4, at
equal setting of the valve system 35 of the blowing device 10 a weft
thread 2 will be stored faster in the storage element 11. If the
thread holder 27 is opened at the same moment in the weaving
cycle, at this moment a large part of the weft thread 2 will already
be stored in the storage element 11, so that a large part of the weft
thread 2 also is inserted with large speed from the storage element
11 into the weaving shed 6 before the weft thread 2 in the storage
element 11 is stretched, so that then only a small remaining part of
the weft thread 2 is inserted with lower speed directly from the
prewinder 3. Due to this effect, when weaving with a more air
friendiy weft thread 2, this means a weft thread moving faster with a
same blowing force, the speed with which the weft thread 2 is
transported through the weaving shed 6 is additionally raised
because this weft thread 2 is stored over a larger part in the storage
element 11. This means that the stretching moment for a fast weft
thread 2 will take place later in the weaving cycle than the stretching
moment for a slower weft thread 2. If according to the invention the
reference moment is determined that is a measure of the stretching
moment and in case the actual stretching moment takes place later
in the weaving cycle, at a following insertion of weft thread 2 the
moment that the thread holder 20 is opened can be controlled in
function of this determined reference moment, and so that the
control is carried out so that if the reference moment takes place
later in the weaving cycle, the moment that the thread holder 20 is
opened is controlled later in the weaving cycle. Due to the opening
of the thread holder 20 later at a following insertion of weft thread 2,
less weft thread 2 will be stored in the storage element 11, so that
less weft thread 2 previously stored in the storage element 11 is
inserted into the weaving shed 6 and more weft thread 2 will be
inserted directly and, thus, slower from the prewinder 3. With the
invention it is possible during the insertion of a fast weft thread 2
into a weaving shed 6 to decelerate this weft thread 2 earlier, so
that the effect of the fast weft thread 2 is opposed.
I f the air friendliness of successive weft threads 2 coming from
a certain bobbin 4 decreases during the weaving from this bobbin 4,
at equal setting of the valve system 35 of the blowing device 10 a
weft thread 2 will be stored slower in the storage element 11. If the
thread holder 27 is opened at the same moment in the weaving
cycle, at this moment only a small part of the weft thread 2 will be
stored in the storing element 11, so that a small part of the weft
thread 2 is inserted with large speed from the storage element 11
into the weaving shed 6 before the weft thread 2 in the storage
element 11 is stretched, so that then a large remaining part of the
weft thread 2 is inserted with lower speed directly from the
prewinder 3. Due to this effect, when weaving with a less air friendly
weft thread, this means a weft thread moving slower with a same
blowing force, the speed with which the weft thread is transported
through the weaving shed 6 is additionally lowered because for one
insertion only a smaller part of this weft thread is previously stored
in the storage element 11. This means that the stretching moment
for a slow weft thread 2 will take place earlier in the weaving cycle
than the stretching moment for a faster weft thread 2. If according
to the invention the reference moment is determined that is a
measure of the stretching moment and in case the actual stretching
moment takes place earlier in the weaving cycle, at a following
insertion of weft thread 2 the moment that the thread holder 20 is
opened can be controlled in function of this determined reference
moment, and so that the control is carried out so that if the
reference moment takes place earlier in the weaving cycle, the
moment that the thread holder 20 is opened is controlled earlier in
the weaving cycle. Due to the opening of the thread holder 20 earlier
at a following insertion of weft thread 2, more weft thread 2 will be
stored in the storage element 11, so that for one insertion more weft
thread 2 previously stored in the storage element 11 is inserted into
the weaving shed 6 and less weft thread 2 will be inserted directly
and thus slower from the prewinder 3. With the invention it is
possible during the insertion of a slow weft thread 2 into a weaving
shed 6 to decelerate this weft thread 2 later, so that the effect of the
slow weft thread 2 is opposed.
By controlling the moment that the thread holder 20 is opened
in function of the reference moment in the weaving cycle that is a
measure of the stretching of the weft thread 2 in the storage
element 11, it is possible to oppose the effect of a fast or a slow weft
thread, more particularly to decelerate a fast weft thread 2 more
and to decelerate a slow weft thread 2 less. The invention also
allows further using all regulations and settings of the valve systems
36 and 37 that are used in a device 1 in which no storage element
11 is provided. The valve system 35 in an embodiment is activated
so that the blowing device 10 blows approximately at the moment of
the opening of the thread holder 20, for example slightly before the
opening of the thread holder 20 so that the blowing device 10
already blows on the weft thread 2 while the weft thread 2 is
released by the thread holder 20. Of course the valve system 35 of
the main blower 5 can also be controlled in a known way so that a
weft thread 2 passes at a thread detector 15 at a desired moment in
the weaving cycle.
According to the invention it is also possible to regulate the
valve system 35 of the blowing device 10 so that the reference
moment takes place or is in relation to the removing of a certain
winding 50 from a prewinder 3. The invention in preferred
embodiments is carried out with a setting so that the reference
moment takes place during the removal of the penultimate winding .
According to another possibility the invention is used with a
reference moment during the removal of the last winding, which
allows to weave faster but implies more risk for the braking of the
weft thread 2.
According to an embodiment, the blowing device 10 blows on
the weft thread 2 during a certain time interval. According to
another embodiment, the blowing device 10 blows on the weft
thread 2 until a set moment in the weaving cycle. According to a
preferred embodiment of the invention the blowing device 10 is
deactivated at a deactivation moment in the weaving cycle, which is
defined as a moment at which a certain part of weft thread 2 coming
from the prewinder 3 is supplied to the storage element 11 via an
inlet 25 of the storage eiement 11, for example a certain time after
two windings 50 are removed from the prewinder 3. The
deactivation moment is for example in the shown embodiment
determined in function of the second signal of the thread detector 24
and/or in function of the moment that the presence sensor 45
generates a high signal. This means that for a fast weft thread 2,
wherein for example a certain time after two windings 50 are
removed takes place earlier in the weaving cycle than the set time
or the set moment in the weaving cycle until which moment the
blowing device 10 normally blows, the blowing device 10 stops
blowing at an earlier moment in the weaving cycle than the set time
or the set moment in the weaving cycle. Due to this, the blowing
device 10 blows during a shorter time interval on a fast weft thread
2, so that the amount of stored weft thread 2 in the storage element
11 is limited and so that also the speed with which a fast weft thread
2 is inserted into the weaving shed 6 is limited . Due to this also the
stretching moment or the reference moment according to the
invention takes place earlier than in case the blowing device 10
blows as set. For a slow weft thread 2 the blowing device 10 for
example blows as set, so that as much weft thread 2 as possible is
stored in the storage element 11 and the insertion of slow weft
thread 2 into the weaving shed 6 can still happen with sufficient
speed . Due to this, also a fast weft thread 2 is braked earlier in the
weaving cycle and a slow weft thread 2 is braked later in the
weaving cycle. I n order to avoid that a fast weft thread 2 is inserted
too fast and that a slow weft thread 2 is inserted too slow, according
to the invention the blowing device 10 is not activated any more
from the moment that a certain length of weft thread 2 is stored in
the storage element 11. This embodiment is particularly
advantageous in order to oppose the influence of random fast or
slow weft threads.
Despite the first winding times and/or winding moments, more
particularly the winding times and/or winding moments of the
windings that are stored in the storage element 11 before the
reference moment, are not influenced by the insertion of weft thread
2 into the weaving shed 6, these winding times and/or winding
moments are representative for the air friendliness of the weft
thread 2 concerned. Therefore, it may be assumed that if the first
winding times are short, the weft thread 2 will be inserted into the
weaving shed 6 relatively fast, and that if the first winding times are
long, the weft thread 2 will be inserted into the weaving shed 6
relatively slow. This also allows that the first winding times and/or
winding moments determined with a device 1 according to the
invention can also be used for a method according to
WO 2007/057.217 Al.
Notwithstanding in the embodiments shown a weft thread 2 for
one insertion is formed by four windings 50, it is of course possible
that a weft thread 2 for one insertion is formed by another number
of windings 50, for example five or more windings 50. In this case
the described method can be adapted suitably, for example so that
in the description the first and the second winding are retained and
in the description the third and fourth winding are respectively
replaced by the penultimate and ultimate winding. Other variants
are possible.
I t is clear that the controlling of the moment to open the thread
holder 20 does not necessary have to happen continuously, but can
happen in steps, for example steps of 2msec, I f the determined
reference moment in the weaving cycle, for example, alters on
average less than 2msec from weft thread to weft thread, then in an
embodiment the moment of opening of the thread holder 20 is not
adjusted. If the determined reference moment is altered for example
more than 2msec, then the moment of opening in an embodiment is
adjusted with a step of 2msec, more particularly advanced or
delayed.
By the invention it is achieved that the opening of the thread
holder 20 takes place early enough in the weaving cycle, so that a
sufficient length weft thread 2 is stored in the storage element 11,
which length allows inserting the weft thread 2 with high speed and
with low tension into the weaving shed 6. By the invention it is also
5 achieved that the opening of the thread holder 20 takes place late
enough in the weaving cycle, so that during the insertion of weft
thread 2 into the weaving shed 6 the stored weft thread 2 in the
storage element 11 is stretched and so that the weft thread 2 during
the insertion of the last part of weft thread 2 into the weaving shed
o 6 is removed directly from the prewinder 3 and in this way is
braked.
The invention also offers the advantage that when weaving with
several devices 1 according to the invention that feed weft thread 2
into the weaving shed 6 according to a pattern, the storing of weft
i s thread 2 in the storage element 11 can already take place during the
insertion of a weft thread 2 from another device 1. This means that
in an embodiment the storing of weft thread 2 in a storage element
11 takes place during several weaving cycles, while the removing of
weft thread 2 from the storage element 11 takes place only during
one single weaving cycle.
According to an embodiment not shown, the thread holder 27
shown in the drawings is replaced by a thread holder that is
arranged near the main blower 5 and that is arranged to command
the releasing of weft thread 2 at the start of the insertion of a weft
thread 2.
When weaving with several weft threads according to a pattern
and if several weft threads are woven with other weaving
parameters, for example as known from WO 01/79597 Al, it is also
possible for each weft thread to combine a method according to the
0 invention with a method as known from WO 01/79597 Al. A method
according to the invention can of course also be combined with a
method as known from WO 2006/1 14187 Al, more particularly in an
embodiment the reference moment is determined as an average of a
number of reference moments, whereby the number of reference
moments that is used to determine the average reference moment is
for example determined based on the number of alterations that is
carried out with respect to the moment for the opening of the thread
holder 20.
It is of course also possible to store no weft thread 2 in the
storage element 11 and to weave with a device 1 according to the
invention in a known classical way, wherein weft thread 2 is always
removed directly form the prewinder 3, I n this case the method
according to the invention is also not used.
Notwithstanding that in the weaving machine shown four
devices according to the invention are used, in other embodiments
use is made of only one device according to the invention or of
another number of devices according to the invention. If a weft
thread 2 is not suitable for being stored in a storage element the
blowing device 10 can be used together with a main blower 5 in
order to remove a weft thread 2 from the prewinder 3 and to insert
the weft thread 2 into a weaving shed 6.
The shown embodiments only serve to explain the invention .
Variants are possible, in particular with respect to the embodiments
of the blowing device, the storage element, the thread holders and
the sensors. Also combinations of the shown embodiments are
possible that fall under the claims.
Claims,
1. Method for feeding weft thread (2) in a weaving machine,
wherein a length of weft thread (2) is released from a prewinder (3)
in order to be inserted into a weaving shed (6), wherein weft thread
(2) coming from the prewinder (3) is supplied to a storage element
( 11) via an inlet (25) of the storage element (11), wherein weft
thread (2) is removed from the storage element ( 11) via an outlet
(26) of the storage element ( 11) in order to be inserted into the
10 weaving shed (6), wherein before the start of the insertion of weft
thread (2) into the weaving shed (6) weft thread (2) is stored in the
storage element ( 11), wherein at least during a part of a period of
the insertion of the weft thread (2) into the weaving shed (6) a
simultaneous store and removal of weft thread (2) is carried out,
characterised in that at least at the end of the simultaneous store
and removal of weft thread (2), the weft thread (2) stored in the
storage element ( 11) is removed from the storage element (11)
faster than weft thread (2) coming from the prewinder (3) is
supplied to the storage element ( 11), so that at a stretching
20 moment in the weaving cycle during the period of the insertion of
weft thread (2) into the weaving shed (6) the weft thread (2) stored
in the storage element (11) changes from stored condition into
stretched condition, wherein a reference moment is determined that
is a measure of the stretching moment.
25
2 , Method according to claim 1, characterised in that the start of
the storing of weft thread (2) in the storage element ( 11) is
controlied by an opening of a second thread holder (20) that is
arranged between the prewinder (3) and the storage element (11),
3 wherein the opening of the second thread holder (20) is controlled in
function of the reference moment in the weaving cycle.
3. Method according to claim 2, characterised in that the moment
of the opening of the second thread holder (20) that is arranged
between the prewinder (3) and the storage element ( 11) is
determined so that the determined reference moment is related to a
set moment in the weaving cycle.
4 . Method according to claim 1, 2 or 3, characterised in that weft
thread (2) coming from the prewinder (3) is blown into a storage
element ( 11) by means of a blowing device ( 10) that is arranged
between the prewinder (3) and the storage element ( 11) via an inlet
(25) of a storage element ( 11), wherein this blowing device (10) is
activated at a moment in the weaving cycle that is determined in
function of the reference moment in the weaving cycle.
5. Method according to claim 4, characterised in that the blowing
device (10) is de-activated at a de-activation moment in the weaving
cycle so that the blowing of the blowing device ( 10) on the weft
thread (2) decreases before the reference moment.
6. Method according to claim 5, characterised in that the
de-activating is determined in function of a set part of weft thread
(2) coming from the prewinder (3) being supplied to a storage
element ( 11).
7. Method according to any one of claims 1 to 6, characterised in
that the start of the insertion of weft thread (2) into the weaving
shed (6) is controlled by the opening of a first thread holder (27)
that is arranged between the storage element (11) and the weaving
shed (6) and/or the end of the insertion of weft thread (2) into the
weaving shed (6) is controlled by the closing of a second thread
holder (20) that is arranged between the prewinder (3) and the
storage element (11).
8. Method according to any one of claims 1 to 7, characterised in
that the reference moment is determined based on signals of at least
one thread detector (24, 52, 53, 54) that is arranged at the
prewinder (3).
9. Method according to claim 8, characterised in that the thread
detector (24, 52, 53, 54) delivers each time a signal if a winding
(50) coming from the drum (23) of the prewinder (3) is moved past
the thread detector (24, 52, 53, 54).
10. Method according to any one of claims 1 to 7, characterised in
that the reference moment is determined based on signals from at
least one presence sensor (44, 45, 46) that is arranged at the
storage element (11).
11. Method according to any one of claims 1 to 7, characterised in
that the reference moment is determined based on signals of a
tension sensor (60, 61) for weft thread (2).
12. Method according to any one of claims 1 to 7, characterised in
that the reference moment is determined based on signals of a
movement sensor (64, 65) for weft thread (2), for example a
movement sensor (64, 65) for weft thread (2) that can detect the
movement of a weft thread (2) moving along the movement sensor
(64, 65).
13. Device for applying a method according to any one of claims 1
to 12, characterised in that the device (1) comprises a prewinder
(3), a storage element ( 11) for weft thread (2) and a thread holder
(20) that is arranged between the prewinder (3) and the storage
element (11), wherein the thread holder (20) is controlled by a
control unit (31) as a function of the determined reference moment
in the weaving cycle.
14. Device according to claim 13, characterised in that the storage
element ( 11) is a storage element ( 11) in which a weft thread (2) is
stored in zigzag form.