Device and Method for Monitoring a Weft Thread
Description
The invention relates to a device for monitoring a weft thread in a
weaving machine comprising a weft thread detector for providing a
signal when an inserted weft thread exceeds its length by a
predetermined amount and an air guide channel located upstream of the
weft thread detector, wherein the weft thread detector is mounted on a
sley of a weaving machine. The invention further relates to a method for
monitoring a weft thread in a weaving machine.
A weft thread detector arranged at the arrival side of a weaving machine
for monitoring an arrival of an inserted weft thread is known and is called
hereafter first weft thread detector or arrival detector for weft thread.
A weft thread detector for providing a signal when an inserted weft
thread exceeds its length by a predetermined amount is called hereafter
second weft thread detector. The expression "second weft thread
detector" is not to be construed as an indication of the number of weft
thread detectors. In one embodiment, the second weft thread detector is
used as only weft thread detector, i.e. without a first weft thread detector.
The terms "first weft thread detector" and "second weft thread detector"
rather denote an order in which the weft thread detectors are arranged in
the insertion direction. The second weft thread detector is also called
broken-weft thread detector.
A device for monitoring a weft thread in a weaving machine comprising a
first weft thread detector and a second weft thread detector are known in
the prior art.
For example, GB 2 119 8 19 A discloses a device comprising a first weft
thread detector, a suction device for weft thread and a second weft
thread detector fixed in succession on a support of a sley of a weaving
machine. The suction device is provided for catching and stretching
inserted weft threads at the arrival side. A jet of air leaving the suction
device without being deflected does not reach the detection zone of the
second weft thread detector. The device comprises a deflection finger.
The finger is located between the outlet of the suction device and the
second weft thread detector and fixed to the frame of the weaving
machine perpendicular to the insertion path. During beat-up, the finger
is brought in the range of the jet of air and the jet of air is deflected
towards the detection zone of the second weft thread detector. A weft
thread present in the jet of air when the finger is located in the range of
the jet of air, will be deflected towards the second weft thread detector
and will be detected by the second weft thread detector.
US 4,432,399 discloses a device for monitoring a weft thread in a
weaving machine, comprising a first weft thread detector for providing a
stop signal when the inserted weft thread does not reach its normal
length and a second weft thread detector spaced from the first weft
thread detector for providing a signal when the inserted weft thread
exceeds its normal length by a predetermined amount. Between the two
weft thread detectors, an air guide channel is arranged for bridging the
space between the two weft thread detectors, which air guide channel
lies in the extension of the insertion path. The two weft thread detectors
and the air guide channel are arranged in order to move with the reed.
It is the object of the invention to provide a device and a method for
monitoring a weft thread allowing a reliable detection of inserted weft
threads that exceed their length by a predetermined amount, i.e.
inserted weft threads extending too far outside the shed.
This object is solved by a device and a method with the features of
claims 1 and 15.
According to a first aspect of the invention, a device is provided for
monitoring a weft thread in a weaving machine comprising a second weft
thread detector for providing a signal when an inserted weft thread
exceeds its length by a predetermined amount and an air guide channel
located upstream of the second weft thread detector, wherein the
second weft thread detector is mounted on a sley of a weaving machine
and the air guide channel is arranged stationary on the weaving
machine.
In other words, the air guide channel is arranged in a fixed position with
respect to the frame of the weaving machine, whereas the second weft
thread detector is mounted on the sley and moves with the reed during
beat-up.
In preferred embodiments, an arrival detector for weft thread is provided
upstream of the air guide channel, i.e. a weft thread detector for
detecting the arrival of a weft thread is provided, more particularly a first
weft thread detector.
The first weft thread detector and the second weft thread detector are
both mounted on the sley in the extension of the reed, wherein the first
weft thread detector is arranged upstream of the air guide channel and
the second weft thread detector is arranged downstream of the air guide
channel.
Weft thread detectors generally have a limited detection zone. A weft
thread is only detected when the weft thread reaches the detection zone.
The first weft thread detector is arranged close to the end of the reed,
wherein relay nozzles provided for an insertion of a weft thread blow the
weft thread in the detection zone of the first weft thread detector.
A second weft thread detector for detecting weft threads that extend too
far outside a shed, for example broken weft threads, is also called
broken-weft thread detector. Such a second weft thread detector is
arranged downstream of the first weft thread detector in the insertion
direction. By providing an air guide channel, the air flow is directed to an
area allowing the second weft thread detector to detect a weft thread
transported by the air flow. In accordance with the invention, the air
guide channel is arranged stationary. Therefore, the weft thread end
leaving the air guide channel is presented at a presenting area allowing
a more reliable detection. The presenting area is determined by the
shape and/or position of the air guide channel. The shape and/or
position may be chosen to minimize the influence of the movement of
the weft thread through the air guide channel and/or to minimize forces
acting on the weft thread moving through the air guide channel at least
in a zone of the air guide channel. Hence, an insertion of a weft thread
upstream of the air guide channel is not or only slightly influenced by the
transport of the weft thread through the air guide channel. In addition, a
movement of the second weft thread detector with respect to the
presented weft thread does not or only slightly influence the insertion of
weft threads upstream of the air guide channel.
According to an embodiment, the air guide channel is configured to
present a weft thread in a presenting area traversed by a detection zone
of the second weft thread detector during beat-up. To this end, in one
embodiment an air flow leaving the outlet opening of the air guide
channel is channelled to the presenting area, which is chosen so that the
detection zone of the second weft thread detector traverses the air flow
leaving the outlet opening during beat-up. An end of for example a
broken weft thread transported by the air flow will be presented in the
presenting area. The second weft thread detector is mounted on the
sley and moves during beat-up, wherein the detection zone traverses
the presenting area. In result, an effective detection zone of the second
weft thread detector is traversed. Therefore, a more reliable detection
is ensured. In other words, during insertion the air guide channel does
not necessarily guide the air flow towards the detection zone of the
second weft thread detector, but rather to a presenting area in front of
the detection zone during insertion, wherein during beat-up the detection
zone is moved towards and across this presenting area and in this way
traverses the presenting area. In the context of the application, a
"presenting area in front of the detection zone" is defined an area that is
located opposite the side of the second weft thread detector that in use
is directed to the fabric and where a leading end-part of a weft thread
extending outside the air guide channel can be located.
In one embodiment, a weft thread stretching device is provided in the
extension of an insertion path of the weft thread upstream of the air
guide channel, which weft thread stretching device is configured for
catching end-parts of inserted weft threads, wherein preferably the air
guide channel bridges at least 50%, more preferably at least 70%, in
particular at least 80% of the distance between the weft thread
stretching device and the second weft thread detector. In one
embodiment the weft thread stretching device comprises a suction
nozzle, more in particular a ring-jet suction nozzle. In the context of the
application, a ring-jet suction nozzle is defined as a suction device,
wherein a suction effect is obtained by blowing compressed air into the
suction device. Compressed air used for catching inserted weft threads
is used to transport a weft thread through the air guide channel. The air
guide channel is in preferred embodiments provided in the extension of
the cross-section of the suction nozzle at an outlet side of the suction
nozzle.
In one embodiment, the air guide channel fits well with the outlet
opening of the weft thread stretching device, more particularly with the
outlet opening of the suction nozzle of the weft thread stretching device.
In this case, efficient use of the air flow through the suction nozzle is
made to transport the weft thread towards the presenting area, in
particular to a presenting area in front of the detection zone of the
second weft thread detector.
In preferred embodiments, the air guide channel comprises a tube, in
particular a straight tube. The tube provides a closed air guide channel,
wherein an air flow through the tube is not or only slightly disturbed by
external influences. In addition, when providing a straight tube, forces
acting on the weft thread while the weft thread is moving through the
tube are minimised and the movement of the weft thread through the
tube does not or only slightly influences an insertion of the weft threads
upstream of the tube. The air guide channel also allows guiding a weft
thread through the air guide channel.
According to an embodiment, the tube has an inlet opening having a
circular cross-section. In particular when providing a ring-jet suction
nozzle a tube having a circular cross-section allows a smooth transition
of the air flow from the suction nozzle to the air guide channel.
The air guide channel is shaped to channel the air flow towards the
presenting area. For this purpose, in one embodiment, the air guide
channel comprises a nozzle-shaped end-part arranged at an outlet side
of the air guide channel. In order to limit the presenting area of the air
flow leaving the air guide channel, in preferred embodiments, the
nozzle-shaped end-part has a flattened outlet opening, in particular an
outlet opening with an oval cross-section. In the context of the
application, the height of the outlet opening is defined as the dimension
in the direction perpendicular to the insertion path of a weft thread and
perpendicular to the beat-up direction.
In one embodiment, the nozzle-shaped end-part and the tube are
manufactured as separate parts and fixed to each other. The
nozzle-shaped end-part in one embodiment is detachably fixed to the
tube, allowing for a replacement of the end-part. In other embodiments,
the nozzle-shaped end-part is permanently fixed to the tube, in particular
glued or welded to the tube. In still another embodiment, the
nozzle-shaped end-part and the tube are formed in one piece.
The shape of the air guide channel is preferably optimized for minimizing
a contact of internal walls with the weft thread. However, a weft thread
may still make contact with the internal wall of the air guide channel, in
particular at an end-part of the air guide channel. Therefore, in one
embodiment at least in the vicinity of the internal wall of the air guide
channel a wear-resistant coating and/or a wear-resistant insert is
provided in a weft thread contact area of the air guide channel, more in
particular in an area of the air guide channel directed to the fabric.
In one embodiment, the air guide channel is at least partly made, in
particular at least in the vicinity of the internal wall, of a material having a
low frictional resistance to air and weft threads, in particular a synthetic
material, for example a polyvinyl chloride reinforced with fillers.
In still another embodiment, the first weft thread detector for detecting
the arrival of a weft thread and the second weft thread detector for
providing a signal when an inserted weft thread exceeds its length by a
predetermined amount are configured for optically monitoring the weft
thread. In preferred embodiments, both weft thread detectors work on
the same operating principle. In particular, optical weft thread detectors
as described in EP 0 943 024 B 1 are used, the content of which is
herewith incorporated by reference.
In one embodiment, a detection zone of a first and/or second weft thread
detector extends between an upper part and a lower part of the weft
thread detector. In the context of the application, the upper part and the
lower part of the weft thread detector are defined as parts of the weft
thread detector arranged above and below an insertion path as seen in a
direction approximately perpendicular to a fabric, i.e. in the direction of
the height of the air guide channel.
According to a second aspect, a method is provided for monitoring a
weft thread with a device comprising a second weft thread detector for
providing a signal when an inserted weft thread exceeds its length by a
predetermined amount which is mounted on a sley of a weaving
machine and an air guide channel, which air guide channel is located
upstream of the second weft thread detector, wherein the air guide
channel is arranged stationary on the weaving machine and channels an
air flow to a presenting area, and a detection zone of the second weft
thread detector is moved through the presenting area during beat-up.
Further features and advantages of the invention will emerge from the
following description of the embodiments illustrated in the drawings,
wherein
is a schematic top view of a part of a weaving machine with a
device according to an embodiment of the invention;
is a perspective view of a part of the weaving machine
shown in figure 1 in a position during insertion of a weft
thread;
is a front view of an embodiment of a nozzle-shaped
end-part;
is a cross-section along a line A-A in figure 3;
is a front view of a weft thread detector and the
nozzle-shaped end-part during insertion;
is a front view of a weft thread detector and the
nozzle-shaped end-part of figure 5 during beat-up;
is a front view of a weft thread detector and the
nozzle-shaped end-part of figure 6 during further beat-up;
figure 8: is a perspective view of a part of the weaving machine
shown in figure 2 in a position during beat-up of a weft
thread;
figures 9 and 10; figures 11 and 12, figures 13 and 14;
figures 15 and 16; and figures 17 and 18
are respectively variant embodiments of figures 3 and 4;
figure 19: is a top view of an air guide channel provided with the
nozzle-shaped end-part of figures 17 and 18;
figure 20 is a perspective view of figure 19.
Figure 1 is a schematic top view of a part of a weaving machine, more
particularly of an air-jet weaving machine, with a device 1 for monitoring
a weft thread comprising a second weft thread detector 10 according to
a first embodiment of the invention during insertion of a weft thread 2.
Fig. 2 shows a perspective view of a part of a weaving machine similar
to Fig. 1.
The weft thread 2 is inserted in a shed formed by selectively raising and
lowering warp threads 3. During insertion, the weft thread 2 is supported
by relay nozzles 4 and guided in an insertion channel 509 (see Fig. 2)
through a reed 5. The insertion channel 509 mainly determines the
insertion path of the weft thread. In the embodiment shown, a first weft
thread detector 6, also called arrival detector for weft thread, is arranged
on the sley 500 (see Fig. 2) at the end of the insertion channel 509 next
to the reed 5 in order to detect the arrival of the weft thread 2.
The leading end-part 2f of the inserted weft thread 2 is caught and
stretched with a predetermined tension by a weft thread stretching
device 7, such as a suction nozzle. As schematically shown, the weft
thread stretching device 7 is arranged stationary on the weaving
machine in an extension of an insertion path of the weft thread 2, for
example by means of a support beam 700.
The reed 5 is attached to the sley 500 and is moved in beat-up direction
B towards a beat-up line 800 of a fabric 8 for a beat-up movement, in
short beat-up. The weft thread 2, of which the leading end-part 2f is
caught and stretched by the weft thread stretching device 7, as
schematically shown in Fig. 1, is moved with the reed 5 towards the
beat-up line 800 and is beaten-up into the fabric 8.
In accordance with the embodiment shown in Fig. 1, a weft thread
holding device 9 is arranged stationary on the weaving machine in an
area of a beat-up line 800 for holding the leading end-parts of a number
of beaten-up weft threads 2d. As mentioned above, the weft thread
stretching device 7 is also arranged stationary on the weaving machine,
at a distance from the beat-up line 800 in the extension of an insertion
path of the weft thread 2. In one embodiment, a movable guiding device
9 1 is provided for guiding the caught leading end-part 2f of the weft
thread 2 towards the weft thread holding device 9. The guiding device
9 1 is fixed on the sley 500. A cutting device 92 is provided between a
fabric edge 801 of the fabric 8 and the weft thread holding device 9 for
cutting the ends of the weft threads after they are bound by the warp
threads 3. The cutting device 92 is arranged close to the fabric edge
801 for minimizing the length of the ends of the bound weft threads
protruding from the fabric 8. The cut-off ends are removed via a duct
(not-shown) provided to the weft thread holding device 9. Further also an
optional suction device 12 for removing faulty inserted weft threads is
shown schematically.
In the embodiment shown, the weft thread stretching device 7 is a
ring-jet suction nozzle. The weft thread stretching device 7 is connected
to a compressed-air tank (not shown) in order to obtain a suction effect.
The device 1 for monitoring a weft thread according to the invention
comprises a second weft thread detector 10 for providing a signal when
an inserted weft thread exceeds its length by a predetermined amount.
The second weft thread detector 10 is mounted on the sley 500 of the
weaving machine and moves together with the sley 500. In the
embodiment shown, the second weft thread detector 10 is mounted on
the sley 500 in line with the first weft thread detector 6.
Further, an air guide channel 11 is provided, which is located upstream
of the second weft thread detector 10 seen in the insertion direction of
the weft thread. The air guide channel 11 is arranged fixed in a position
with respect to the frame of the weaving machine.
As schematically shown, the air guide channel 11 is arranged at the
outlet side of the weft thread stretching device 7, in an extension of an
insertion path of the weft thread 2 by means of a support beam 700. In
the embodiment, the air guide channel 11 fits well with an outlet opening
of the weft thread stretching device 7 configured as suction nozzle. The
air guide channel 11 bridges mainly the distance between the weft
thread stretching device 7 and the second weft thread detector 10, more
in particular bridges at least 80% of the distance between the weft
thread stretching device 7 and weft thread detector 10.
In an embodiment shown, the air guide channel 11 comprises a straight
tube 110 having an inlet opening having a circular cross-section and a
nozzle-shaped end-part 112 arranged at the outlet side of the air guide
channel 11. In the embodiment shown, the nozzle-shaped end-part 112
is mounted on the straight tube 110. The air guide channel 11 is
manufactured at least at the vicinity of the internal wall of a material
having a low frictional resistance to air and a low frictional resistance to
weft threads, for example a synthetic material.
Fig. 3 shows a front view and Fig. 4 a cross-section along a line A-A in
Fig. 3 of an embodiment of a nozzle-shaped end-part 112. Other
exemplary embodiments of nozzle-shaped end-parts 112 are shown in
Figures 9 to 18 and will be described with reference to these figures
below.
As shown in Figs. 3 and 4, the nozzle-shaped end-part 112 has a
flattened outlet opening 112a. In the embodiment shown the outlet
opening 112a has an oval cross-section. At the inlet opening 112b the
nozzle-shaped end-part 112 has a circular cross-section that fits well
with the cross-section of the tube shown in Fig. 2. A channel 112c is
provided between the inlet opening 112b having a circular cross-section
and the flattened outlet opening 112a. In the context of the application,
the length of the nozzle-shaped end-part 112 is defined as the
dimension in the direction of an insertion path of a weft thread. The
width of the nozzle-shaped end-part 112 is defined as the dimension in
the beat-up direction B, i.e. in the direction of a movement path of the
weft thread during beat-up. The height of the nozzle-shaped end-part
112 is defined as the dimension in the direction perpendicular to the
insertion path and perpendicular to the beat-up direction B. As shown in
the cross-section of Fig. 3, in this embodiment, a width of the channel
112c is approximately constant over the length of the nozzle-shaped
end-part 112. A height of the channel 112c through the nozzle-shaped
end-part 112 decreases for channelling the air flow through the
nozzle-shaped end-part 112 to a presenting area. As seen in Fig. 3, the
flattened outlet opening 112a is slightly curved upwards with respect to a
center line in order to adapt the course of the flattened outlet opening
112a to the beat-up direction B.
For fixing the nozzle-shaped end-part 112 an annular space 112d for
receiving the tube 110 (see Fig. 2) is provided at the inlet side of the
nozzle-shaped end-part 112. Further, an insert 112e, for example a rod,
near the outlet opening 112a, is provided. The insert 112e is made
wear-resistant, for example, comprises a wear-resistant coating and/or is
made of a wear-resistant material. The insert 112e can co-operate
during beat-up with an end-part 2f (see Fig. 1) of a weft thread 2
extending between the nozzle-shaped end-part 112 and the second weft
thread detector 10. Herewith the wear-resistant insert 112e is provided
in a weft thread contact area of the air guide channel 11, more in
particular in an area of the air guide channel 11 directed to the fabric 8.
During beat-up, the second weft thread detector 10 and the first weft
thread detector 6 which are both mounted on the sley 500, are moved in
the beat-up direction B as shown in Fig. 1.
Figs. 5 to 7 show a front view of a second weft thread detector 10 and
the nozzle-shaped end-part 112 during the beat-up direction B at
successive instants in time. The second weft thread detector 10 is
configured for optically monitoring weft threads. The second weft thread
detector 10 is, in a known way, fixed by fixation means 15 to the sley
500 (see Fig. 1) . In the embodiment shown, the second weft thread
detector 10 is provided with a guiding opening 10a arranged in the
extension of the insertion channel 509 of the reed 5 (see Fig. 2). The
shape of the guiding opening 10a of the second weft thread detector 10
is similar to the shape of the dents of the reed 5. The guiding opening
10a is limited by an upper leg 10b and a lower leg 10c, wherein light
rays are directed transversely through the guiding opening 10a between
the upper leg 10b and the lower leg 10c. In other words, a detection
zone of the second weft thread detector 10 extends between an upper
part and a lower part of the weft thread detector 10 perpendicular to an
insertion path. The first weft thread detector 6 is, for example, configured
similar to the second weft thread detector 10. Examples of weft thread
detectors suitable to be used as the second weft thread detector 10
and/or the first weft detector 6 are described in EP 0 943 024 B 1.
The air guide channel 11, more in particular the nozzle-shaped end-part
112, is configured to present the weft thread in a presenting area. As
shown in Figs. 5 to 7, the presenting area is chosen such that it is
traversed by the detection zone of the second weft thread detector 10
during beat-up. As described above, the presenting area at which a weft
thread is presented to the second weft thread detector 10 is determined
by the position and/or the shape of the air guide channel 11. In the
context of the application, the presenting area is determined by the area
of the leading end-part 2f extending beyond the nozzle-shaped end-part
112. In the embodiment of Fig. 5, for example, the leading end-part 2f
determining the presenting area is located approximately beyond the
centre of the nozzle-shaped end-part 112. The presenting area is
traversed in this embodiment by the detection zone of the second weft
thread detector 10 in positions located near the positions shown in Figs.
6 and 7, such as the position of Fig. 8.
Figs. 9 to 18 show exemplary embodiments of nozzle-shaped end-parts
112. The nozzle-shaped end-parts 112 shown in Figs. 3 to 4 and 9 to 18
are similar in shape and common reference numbers will be used for
similar or common elements. In all embodiments, the nozzle-shaped
end-part 112 has a flattened outlet opening 112a with an oval
cross-section and an inlet opening 112b with a circular cross-section that
fits well on the cross-section of the tube 110 shown in Fig. 2. A channel
112c is provided between the inlet opening 112b and the flattened outlet
opening 112a. The presenting area at which weft threads are presented
to the second weft thread detector 10 is determined by the shape of the
outlet opening 112a, its width, its height and its position with respect to
the insertion path.
As mentioned above, the presenting area is chosen such that the
presenting area is traversed by the detection zone of the second weft
thread detector 10 during beat-up. Therefore, the height of the flattened
outlet opening 112a is chosen in order that the presenting area is
located between the upper leg 10b and the lower leg 10c of the second
weft thread detector 10 during beat-up (see Figs. 5 to 7). However,
within these boundary conditions, it is possible to vary the height. The
width of the flattened outlet opening 112a and/or its offset with respect to
a longitudinal axis of the weft thread stretching device 7 (see Fig. 2) in
the beat-up direction B can also be varied in order to ensure that the
presenting area is traversed by the detection zone of the second weft
thread detector 10.
As the comparison of Figs. 3 and 4 and Figs. 9 and 10 shows, the
embodiment of Fig. 9 differs from the embodiment of Fig. 3 in that a
height of the flattened outlet opening 112a is decreased for decreasing
the presenting area. However, a width of the channel 112c to the
nozzle-shaped end-part 112 is kept constant.
In the context of the application, the area of the channel 112c arranged
closer to the beat-up line 800 (see Fig. 1) is referred to as front area,
whereas the opposing area of the channel 112c is referred to as rear
area. In the embodiment of Figs. 11 and 12, a sidewall of the channel
112c through the nozzle-shaped end-part 112 is provided with a convex
bulge in the front area. By providing a convex bulge in the front area, an
air flow flowing in the front area is deflected towards the rear area.
Figs. 13 and 14 show an embodiment of the nozzle-shaped end-part 112
similar to that of Figs. 11 and 12. In the embodiment shown in Figs. 13
and 14, a sidewall of the channel 112c through the nozzle-shaped
end-part 112 is also provided with a convex bulge in the front area of the
nozzle-shaped end-part 112, wherein a height of the flattening outlet
opening 112a is decreased compared to the embodiment of Figs. 11 and
12.
Figs. 15 and 16 show a further embodiment of a nozzle-shaped end-part
112, wherein a channel 112c through the nozzle-shaped end-part 112 is
curved towards a beat-up line 800 (see Fig. 1) in order to provide a
presenting area which is closer to the beat-up line 800. In the
embodiment shown, a curvature of the sidewalls of the channel 112c is
not uniform. Rather, an area of the channel 112c closer to the beat-up
line 800 is provided with a more pronounced concave curvature for
guiding an air flow towards to the rear area of the channel 112c.
Figs. 17 and 18 show an embodiment of a nozzle-shaped end-part 112
similar to that shown in Fig. 15 and 16. In the embodiment shown in
Figs. 17 and 18, a curvature towards the beat-up line 800 is
considerably more pronounced for bringing the presenting area closer to
the beat-up line 800 (see Fig. 1) .
Figs. 19 and 20 show an air guide channel 11 with a tube 110, for
example a straight tube, which is provided with a number of openings
115 for escaping compressed air out of the tube 110. In order to easy
the fixing, the tube 110 is also provided with recesses 116 in the vicinity
of the inlet opening where the tube 110 is intended to be fixed to the weft
thread stretching device 7. The openings in the tube 110 can be
arranged according to a variant not shown in other positions along the
tube 110, for example similar as with a tube known from EP 0 273 473.
The device and the method according to the invention are not limited to
the embodiments described and illustrated in the drawings by way of
example. The device and the method can also be configured within the
claims according to variant embodiments, shapes and dimensions.
Combinations of the illustrated embodiments that come under the claims
are also possible.
Claims
Device for monitoring a weft thread in a weaving machine
comprising a second weft thread detector ( 10) for providing a
signal when an inserted weft thread exceeds its length by a
predetermined amount and an air guide channel ( 1 1) located
upstream of the second weft thread detector ( 10), wherein the
second weft thread detector ( 10) is mounted on a sley (500) of the
weaving machine
characterized in that
the air guide channel ( 1 1) is arranged stationary on the weaving
machine.
Device for monitoring a weft thread according to claim 1,
characterized in that the air guide channel ( 1 1) is configured to
present a weft thread (2) in a presenting area traversed by a
detection zone of the second weft thread detector ( 10) during
beat-up.
Device for monitoring a weft thread according to claim 1 or 2,
characterized in that a weft thread stretching device (7) is provided
in the extension of an insertion path of the weft thread (2)
upstream of the air guide channel ( 1 1) , which weft thread
stretching device (7) is configured for catching end-parts (2f) of the
inserted weft threads (2).
Device for monitoring a weft thread according to claim 3,
characterized in that the air guide channel ( 1 1) bridges at least
80% of the distance between the weft thread stretching device (7)
and the second weft thread detector ( 10).
5. Device for monitoring a weft thread according to claim 4,
characterized in that the air guide channel ( 1 1) fits well on the
outlet opening ( 1 12a) of the weft thread stretching device (7).
6. Device for monitoring a weft thread according to any one of claims
1 to 5, characterized in that the air guide channel ( 1 1) comprises a
tube ( 1 10), in particular a straight tube ( 1 10), wherein the tube
( 1 10) preferably comprises an opening with a circular
cross-section at the inlet side.
7. Device for monitoring a weft thread according to any one of claims
1 to 6, characterized in that the air guide channel ( 1 1) comprises a
nozzle-shaped end-part ( 1 12) arranged at an outlet side of the air
guide channel ( 1 1) .
8. Device for monitoring a weft thread according to claim 7,
characterized in that the nozzle-shaped end-part ( 1 12) has a
flattened outlet opening ( 1 12a), in particular an outlet opening
( 1 12a) with an oval cross-section.
9. Device for monitoring a weft thread according to claim 7 or 8,
characterized in that the nozzle-shaped end-part ( 1 12) and the
tube ( 1 10) are formed in one piece.
10. Device for monitoring a weft thread according to any one of claims
1 to 9, characterized in that a wear-resistant insert ( 1 12e) is
provided in a weft thread contact area of the air guide channel
( 1 1) , more in particular in an area of the air guide channel ( 1 1)
directed to the fabric (8).
11. Device for monitoring a weft thread according to any one of claims
1 to 10, characterized in that the air guide channel ( 1 1) is at least
in the vicinity of the internal wall made of a material having a low
frictional resistance to air and weft threads, in particular a
synthetic material.
12. Device for monitoring a weft thread according to any one of claims
1 to 11, characterized in that a first weft thread detector (6) for
detecting the arrival of a weft thread is provided, wherein the first
weft thread detector (6) is mounted on the sley (500) of the
weaving machine upstream of the air guide channel ( 1 1) .
13. Device for monitoring a weft thread according to any one of claims
1 to 12, characterized in that the first weft thread detector (6) for
detecting the arrival of a weft thread and the second weft thread
detector ( 10) for providing a signal when an inserted weft thread
exceeds its length by a predetermined amount, are configured for
optically monitoring a weft thread.
14. Device for monitoring a weft thread according to claim 13,
characterized in that a detection zone of a weft thread detector
(6, 10) extends between an upper part and a lower part of the weft
thread detector (6, 10).
Method for monitoring a weft thread with a device according to any
one of claims 1 to 14 comprising a second weft thread detector
( 10) for providing a signal when an inserted weft thread exceeds
its length by a predetermined amount which is mounted on a sley
(500) of a weaving machine and an air guide channel ( 1 1) located
upstream of the second weft thread detector ( 1 0),
characterized in that
the air guide channel ( 1 1) which is arranged stationary on the
weaving machine channelling an air flow to a presenting area, and
that a detection zone of the second weft thread detector ( 10) is
moved through the presenting area during beat-up.