The invention relates to a back rest device for guiding warp
threads coming from a warp beam on a weaving machine, wherein
the back rest device comprises a guiding bar. The invention
further relates to a weaving machine comprising a back rest
device and a method for arranging a back rest device on a
weaving machine.
Back rest devices arranged between a warp beam and shed
forming elements are known from the prior art. For
example US 3,125,128 discloses a back rest device
comprising a warp tensioning beam supported by one or
more springs. The device further comprises a carrier beam
and a shaft, wherein the warp tensioning beam is
rotatably supported by arms connected to the shaft.
Further, an outer tube rotatably supported by the carrier
be amand surrounding the carrier beam, and a rod
connected to the outer tube by means of brackets and
disposed between the warp tensioning beam and the outer
tube are provided. Warp threads unwound from a warp beam
run over the warp tensioning beam. A portion of the warp
threads runs directly from the warp tensioning beam to
shed forming elements, whereas the remaining warp threads
pass beneath the rod disposed between the outer tube and
the warp tensioning beam. Depending on the angle of the
outer tube supporting the rod, these warp threads are
more or less tensioned.
It is the object of the invention to provide a simplified
back rest device allowing for a reliable tensioning of
warp threads. It is further the object of the invention
to provide a weaving machine with a simplified back rest
device and a method for arranging a back rest device on a
weaving machine and for tensioning warp threads.
3
This object is solved by a back rest device with the
features of claim 1, a weaving machine with the features
of claim 13 and a method with the features of claim
14.Preferred embodiments are defined in the dependent
claims.
According to a first aspect, a back rest device for
guiding warp threads coming from a warp beam is provided,
comprising a first guiding bar, a mounting device, which
is arranged for mounting the first guiding bar in a fixed
mounting position and in a non-rotatable manner, a second
guiding bar, which in use is arranged in parallel to the
first guiding bar and upstream of the first guiding bar
for deflecting warp threads coming from the warp beam,
and a supporting device, which is arranged for supporting
the second guiding bar so that in use the longitudinal
axis of the second guiding bar is at least substantially
fixed in position with respect to the longitudinal axis
of the first guiding bar.
The second guiding bar is supported so that in use its
longitudinal axis is at least substantially fixed in
position with respect to the first guiding bar. In other
words, the second guiding bar is mounted fixed in
position with respect to the first guiding bar in a plane
perpendicular to the longitudinal axis of the second
guiding bar. However, the second guiding bar in one
embodiment is moveable with respect to the first guiding
bar in the direction of its longitudinal axis.
The back rest device according to the invention is in
particular suitable for weaving a heavy fabric. In the
context of the application, a fabric having a cover
4
factor in the order of magnitude of forty is defined as a
heavy fabric. In the context of the application, the
cover factor is the ratio of the area of the fabric
covered by the threads to the whole area of the fabric,
in other words the cover factor as expressed by the known
basic model of Pierce. For weaving a heavy fabric, a
first guiding bar having a sufficient rigidity is
provided. Rigid elements made for example of stainless
steel, tend to have a higher weight than less rigid
elements. As the first guiding bar is mounted in a fixed
mounting position, a higher weight is acceptable.
By providing a first guiding bar mounted in a nonrotatable
manner, a tension is applied to the warp
threads guided along the surface of the first guiding
bar. The tension depends among others on a wrap angle. In
the context of the application, the wrap angle is defined
as the contact angle of the warp threads against the
first guiding bar.
A diameter of a warp beam and, hence, a withdrawal angle
of the warp threads from the warp beam is varying over
time due to warp thread consumption. When deflecting the
warp threads coming from the warp beam and supplied to
the first guiding bar by means of the second guiding bar
mounted so that its longitudinal axis is in a fixed
position with respect to the longitudinal axis of the
first guiding bar, the warp threads are supplied to the
first guiding bar from a fixed position and with a fixed
direction. Therefore, with the assumption that the
withdrawal angle of warp threads leaving the first
guiding bar is at least substantially constant, the warp
threads are wrapped around the first guiding bar with a
5
fixed wrap angle. Thereby, a known tension is applied to
the warp threads by means of the first guiding bar during
weaving from a full warp beam to an empty warp beam.In
case the angle of warp threads leaving the second guiding
bar is not constant, the influence of the variation of
this angle on the tension applied to the warp threads by
means of the second guiding bar during weaving is small.
Due to a contact with the warp threads, the second
guiding bar will also tension the warp threads. As the
second guiding bar is arranged substantially fixed in
position in a plane perpendicular to its longitudinal
axis, a wrap angle of the warp threads coming from the
warp beam and deflected by the second guiding bar varies
over time due to warp thread consumption. However, the
second guiding bar is arranged so that the tension
applied due to frictional effects is significantly less
than the tension applied by the first guiding bar. For
example, the second guiding bar is arranged rotatable
and/or a supporting surface of the second guiding bar is
chosen smaller in size. As a result, the variance of the
wrap angle around the second guiding bar has no or at
least no relevant influence on the tension applied.
The first guiding bar is mounted in a fixed mounting
position, wherein in one embodiment, the fixed mounting
position is settable for example by means of a support
table.
As mentioned above, the tension depends among others on
the wrap angle against the first guiding bar. In one
embodiment, the second guiding bar is provided in a
position for allowing a wrap angle of the warp threads
6
against the first guiding bar between approximately 120
degrees and approximately 290 degrees.
According to preferred embodiments, the supporting device
is arranged for supporting the second guiding bar with
its longitudinal axis in use in a settable position with
respect to the longitudinal axis of the first guiding
bar. The position of the longitudinal axis of the second
guiding bar with respect to the longitudinal axis of the
first bar defines the wrap angle of the warp threads
against the first guiding bar. By setting a position of
the longitudinal axis of the second guiding bar with
respect to the longitudinal axis of the first guiding
bar, a wrap angle is chosen for applying a defined
tension.
In one embodiment, the second guiding bar is mounted on
the first guiding bar by means of the supporting device.
When mounting the second guiding bar on the first guiding
bar, a relative positioning of the second guiding bar and
the first guiding bar is independent from the absolute
mounting position of the first guiding bar.
The second guiding bar in one embodiment is mounted on
the first guiding bar by two support elements provided at
the two ends of the second guiding bar. Preferably, the
supporting device comprises a plurality of support
elements distributedly arranged over the length of the
first guiding bar for supporting the second guiding bar.
Thereby, a reliable support of a second guiding bar is
ensured even when weaving a heavy fabric and using a
second guiding bar having only a small stiffness or
rigidity.
7
In one embodiment, plate-like elements arranged perpendicular
to the first guiding bar and provided with through holes for
receiving the second guiding bar are provided on the first
guiding bar, wherein the second guiding bar is inserted from
the side into the support elements.
In a preferred embodiment, hooks are provided as support
elements, which hooks are distributedly arranged over the
length of the first guiding bar. The second guiding bar is
attached to or detached from such hooks by a radial and/or
tangential displacement allowing for an easy handling.
According to one embodiment, the second guiding bar is
supported moveably, in particular rotatably, in the
hooks. When supporting the second guiding bar moveably, a
force applied by the second guiding bar on the warp
threads is reduced. When supporting the second guiding
bar in a rotatable manner, for example a reciprocating
rotatable manner, the second guiding bar in some
embodiments is moveable with respect to the first guiding
bar in the direction of its longitudinal axis.
Preferably, limit stops are provided for delimiting or
preventing a movement of the second guiding bar in the
direction of its longitudinal axis.
In one embodiment, the outer circumference of the first
guiding bar is larger than the outer circumference of the
second guiding bar, wherein in particular an outer
circumference of the first guiding bar is larger than
500 mm, in particular between approximately 550 mm and
approximately 800 mm and/or an outer circumference of the
second guiding bar is between approximately 90 mm and
8
approximately 230 mm. In other words, preferably, the
outer circumference of the first guiding bar is larger
than the outer circumference of known guiding bars. The
larger outer circumference results in a more rigid
structure allowing for a stronger tensioning of the warp
threads. On the other hand, the second guiding bar is
provided with a smaller outer circumference. Thereby, a
lightweight product is provided allowing for an easy
handling. In addition, the friction applied by the second
guiding bar on the warp threads is negligible even when
supporting the second guiding bar in a non-rotatable
manner.
Preferably, either or both of the first guiding bar and
the second guiding bar is a tubular element, in
particular a circular tubular element. According to a
variant, the first guiding bar and/or the second guiding
bar has an oval cross-section. However, circular tubular
elements are generally less expensive. In addition, a
circular tubular element may be rotated in the mounting
device prior to closing the mounting device for fixing
the first guiding bar. As will be described in more
detail below, such a rotation allows for a user friendly
installation process. In one embodiment, bearing taps are
provided on a tubular element having a non-circular cross
section for allowing a rotation thereof during mounting.
According one embodiment, a wall thickness of the first
guiding bar is between approximately 8 mm and
approximately 15 mm and/or a wall thickness of the second
guiding bar is between approximately 1 mm and
approximately 5 mm. The wall thickness is chosen in order
9
to reduce material costs and weight of the guiding bars,
while ensuring a sufficient rigidity.
As mentioned above, preferably a position of the
longitudinal axis of the second guiding bar with respect
to the longitudinal axis of the first guiding bar is
settable. To this end, in preferred embodiments, markers
and/or limit stops are provided for indicating a
plurality of pre-set positions for the longitudinal axis
of the second guiding bar. This allows an aid for the
operator when setting up the back rest device.
In one embodiment, the first guiding bar is mounted by a
mounting device provided at least partly inside the first
guiding bar. In preferred embodiments, the mounting
device comprises two clamping elements for clamping the
first guiding bar at its ends, in particular at its ends
at the height of its outer circumference. Thereby, a more
rigid mounting structure is provided.
According to a second aspect, a weaving machine
comprising a back rest device arranged near a warp beam,
in particular between a warp beam and shed forming
elements is provided. The weaving machine is preferably
designed to allow the weaving of heavy fabric.
Preferably, when weaving heavy fabric also other parts of
the weaving machine, such as a reed, a reed holder, a
sley drive, healds, heald frames, heald frame drives, the
warp beam, a warp beam drive, a cloth take up drive, and
other elements are designed more rigid and/or more
durable and/or are reinforced.
10
According to a third aspect, a method for arranging a back
rest device comprising a first guiding bar, a mounting device,
a second guiding bar, and a supporting device, on a weaving
machine is provided, wherein the first guiding bar is inserted
into the mounting device, warp threads supplied by a warp beam
are arranged over the first guiding bar, and the second
guiding bar is fixed to the supporting device to deflect the
warp threads.
In a preferred embodiment, the second guiding bar is
mounted on the first guiding bar by means of the
supporting device, wherein after attaching the second
guiding bar to the supporting device, the first guiding
bar is oriented, in particular rotated about its
longitudinal axis, for bringing the longitudinal axis of
the second guiding bar into a set position with respect
to the longitudinal axis of the first guiding bar, and
the first guiding bar is mounted by the mounting device
in a non-rotatable manner after the longitudinal axis of
the second guiding bar is in the set position. In other
words, the first guiding bar is rotated for positioning
the second guiding bar in a plane perpendicular to its
longitudinal axis.
By setting the position, a tension applied to the warp
threads is adjusted.
In the following, embodiments of the invention will be
described in detail based on several schematic drawings
in which
Fig. 1 is a schematic perspective view of a back rest
device;
11
Fig. 2 is a schematic side view of the back rest device
similar to the back rest device of Fig. 1
configured for weaving a heavy fabric;
Fig. 3 is a schematic side view of the back rest device
of Fig. 2before setting up the back rest device;
Fig. 4 is a schematic side view of the back rest device
of Fig. 2set for weaving a very heavy fabric;
Fig. 5 is a schematic perspective view of a hook used
in a supporting device of the back rest device
of Fig. 1;
Fig. 6 is a schematic perspective view of the hook of
Fig. 5 with a fixation element;
Fig. 7 is a schematic cross section of the first
guiding bar with a hook from a first side of the
guiding bar;
Fig. 8 is a schematic side view of the first guiding
bar with a hook from the side opposite to the
first side as in Fig. 7;
Fig. 9 is a schematic front view of a first guiding bar
of the back rest device of Fig. 1;
Fig. 10 is a schematic side view of the back rest device
similar to Fig. 2set for weaving a heavy fabric.
Throughout the drawings, the same or similar elements
will be denoted by the same reference numerals.
Fig.1 is a schematic perspective view of a back rest
device 2 mounted on a weaving machine 1 for guiding warp
threads 7 coming from a warp beam 10. In figure 1, only
one warp thread 7 is schematically shown. Of course, in
use a plurality of warp threads is provided. A warp
detector 12 is provided downstream of the back rest
device 2, whereas the back rest device 2 is provided
12
downstream of the warp beam 10. The back rest device 2
comprises a first guiding bar3, a mounting device 4 at
both side parts 16 of the weaving machine, a second
guiding bar5, and a supporting device6. The back rest
device 2 is arranged near the warp beam 10, in particular
between the warp beam 10 and shed forming elements 15
(schematically shown in Fig. 2).
The first guiding bar 3 is a circular tubular element.
Hence, the first guiding bar 3 is also referred to as
tube. In the embodiment shown, the outer diameter of the
first guiding bar 3 is between approximately 200 mm and
approximately 250 mm. A wall thickness of the first
guiding bar 3 is chosen to allowing for a sufficient
stiffness of the first guiding bar 3. In one embodiment,
the wall thickness is between approximately 10 mm and
approximately 15 mm.
The first guiding bar 3 is provided with a smooth surface
for preventing any damaging of the warp threads 7. The
first guiding bar 3 is, for example, made of steel. In
one embodiment a surface treatment is provided, so that
the first guiding bar 3 has a hard chrome surface. Such a
first guiding bar 3 is strong and durable. In another
embodiment, the first guiding bar 3 is made of stainless
steel, that is also strong and durable, but more
expensive.
The mounting device 4 is arranged for mounting the first
guiding bar 3 in a fixed mounting position and in a nonrotatable
manner. In the embodiment shown, the mounting
device 4 comprises two clamping elements 40 provided at
both side parts 16 of the weaving machine 1 for clamping
13
the two ends 34of the first guiding bar 3.Each clamping
element 40 comprises a fixed clamping part 41 and a
moveable clamping part 42, between which the first
guiding bar 3 is clamped. Before closing the clamping
element 40 by means of the moveable clamping part 42, the
first guiding bar 3 is rotatably supported by the fixed
clamping part 41 having a semi-circular supporting
surface. After closing the clamping element 40 by means
of the moveable clamping part 42, the first guiding bar 3
is mounted in a non-rotatable manner, in other words is
clamped in a non-rotatable manner. The clamping parts 41,
42 are clamped around the first guiding bar 3, for
example using fastening means 43 such as screw means. The
clamping elements 40 are arranged for allowing the
application of a high clamping force. The position of the
mounting device 4 is adjustable by means of the support
tables 14 or along the support tables 14 of the weaving
machine 1, so that the position is adjustable as well in
horizontal direction as in vertical direction.
The second guiding bar 5in use is arranged in parallel to
the first guiding bar 3 and upstream of the first guiding
bar 3 for deflecting warp threads 7 coming from the warp
beam 10. The supporting device 6 is arranged for
supporting the second guiding bar 5 with its longitudinal
axis in use at least substantially fixed in position
with respect to the longitudinal axis of the first
guiding bar 3. In other words, in a plane perpendicular
to the longitudinal axis of the first guiding bar 3 and
perpendicular to the longitudinal axis of the second
guiding bar 5, the second guiding bar 5 is arranged at
least substantially fixed in position with respect to the
first guiding bar 3.
14
In the embodiment shown in Fig. 1, the second guiding bar
5 is also in the form of a circular tubular element. The
outer diameter of the second guiding bar 5 is
significantly smaller than the outer diameter of the
first guiding bar 3. Preferably, the second guiding bar 5
has an outer diameter that is less than half the outer
diameter of the first guiding bar 3. In particular, the
outer diameter of the second guiding bar 5 is between
approximately 35 mm and approximately 80 mm. In one
embodiment, the wall thickness is between approximately
1 mm and approximately 5 mm. A small second guiding bar 5
takes up less space, so that a warp beam 10 can be
arranged closer to the first guiding bar 3, which usually
allows to use a lager warp beam 10. Hence, the second
guiding bar 5, for example, made of the same material as
the first guiding bar 3, for example of steel, in
particular stainless steel, has a lower weight than the
first guiding bar 3 and can be handled more easily. The
second guiding bar 5 in one embodiment is provided in a
rotatable manner. In other embodiments, the second
guiding bar 5 is provided in a non-rotatable manner,
wherein the warp threads 7 slide over the surface of the
second guiding bar 5. In particular, in case of a
relative movement between the second guiding bar 5 and
the warp threads 7, the second guiding bar 5 has a smooth
surface for guiding the warp threads without damaging the
warp threads 7.
In the embodiment shown, the supporting device 6 has a
plurality of hooks 60 provided as support elements8 for
the second guiding bar 5, namely seven hooks 60,
distributedly arranged over the length of the first
guiding bar 3 for supporting the second guiding bar 5.The
15
second guiding bar 5 is held by the hooks 60 with its
longitudinal axis fixed in position with respect to the
longitudinal axis of the first guiding bar 3.
In the embodiment shown, the second guiding bar 5 is
supported rotatably and moveable in the direction of its
longitudinal axis in the hooks 60. For attaching or
detaching the second guiding bar 5, the second guiding
bar 5 is moveable radially into the hooks 60 or out of
the hooks 60. In use, the second guiding bar 5 is held
substantially fixed in position in the radial direction,
wherein – depending on the orientation of the hooks 60,
the second guiding bar 5 is held in place due to
gravitational forces. In addition, in one embodiment, in
use the warp threads 7 force the second guiding bar 5 in
the hooks 60 against a movement in the radial direction.
The axial movement of the second guiding bar 5 can be
delimited or prevented by limit stops 48, 49 that are
formed in the embodiment shown, respectively, by the ends
52 of the second guiding bar 5 and an associated side
surface of the clamping part 41.
According to an alternative embodiment, the second
guiding bar 5 is clamped in the hooks 60, for example
clamped by means of elastic hooks that act as support
elements. Depending on a clamping force of the hooks, the
second guiding bar 5 may be held in a determined position
or may be held moveable in the direction of its
longitudinal axis and/or rotatable about its longitudinal
axis.
During weaving a diameter of the warp beam 10 and, hence,
a withdrawal angle of the warp threads 7 leaving the warp
16
beam 10 is varying over time due to warp thread
consumption. By means of the second guiding bar 5
arranged upstream of the first guiding bar 3, the warp
threads 7 coming from the warp beam 10 are deflected and
supplied to the first guiding bar 3 with a determined
angle. Therefore, with the assumption that the
withdrawal angle of warp threads leaving the first
guiding bar 3 is at least substantially constant, the
warp threads 7 are wrapped around the first guiding bar3
with a fixed wrap angle.
The warp detector 12 is arranged at a suitable height and
a suitable angle with respect to the back rest device 2
in order to avoid considerable bending of warp threads 7
near the warp detector 12. A known fixed arranged tube 44
can be provided, for example, for guiding superfluous
warp threads or for acting as a support for an operator.
As mentioned above, before closing the clamping element
40, the first guiding bar 3 is supported rotatably about
its longitudinal axis. The hooks 60 are fixed on the
first guiding bar 3. Hence, by rotating the first guiding
bar 3, the position of the hooks 60 and, when attached, a
position of the longitudinal axis of the second guiding
bar 5 with respect to the longitudinal axis of the first
guiding bar 3 is adjustable in a plane perpendicular to
the longitudinal axis of the second guiding bar 5.By
adjusting the position, the wrap angle of the warp
threads 7 against the first guiding bar 3 and, hence, the
tension applied to the warp threads 7 by means of the
first guiding bar 3 is adjustable.
17
Fig. 2 is a schematic side view of a back rest device 2
similar to the back rest device 2 of Fig. 1 configured
for weaving a heavy fabric. The back rest device 2 shown
in Fig. 2 differs from that shown in Fig. 1 in the hooks
60 provided for supporting the second guiding bar 5 on
the first guiding bar 3. Apart from the shape of the
hooks 60, the back rest device 2 shown in Fig. 2
corresponds to that of Fig. 1 and the two embodiments are
described together.
According to the embodiment shown in Fig. 2, a wrap angle
of the warp threads 7 against the first guiding bar 3 of
approximately 170 degrees is provided. Other wrap angles
may be suitable for different fabrics to be woven.
Preferably, wrap angles between approximately 170 degrees
and approximately 270 degrees against the first guiding
bar 3 are chosen, so that sufficient friction is exerted
on the warp threads 7 for tensioning the warp threads 7.
Owing to the second guiding bar 5, the wrap angle of the
warp threads 7 about the first guiding bar 3 is
substantially constant during weaving from a full warp
beam to an empty warp beam.
The diameter of the second guiding bar 5 is substantially
less than the diameter of the first guiding bar 3. In
this way, the friction force exerted by the second
guiding bar 5 is small. In other words, due to the large
diameter of the first guiding bar 3, the warp threads 7
are guided along a long distance against the first
guiding bar 3, so that sufficient frictional forces are
exerted for tensioning the warp threads 7. The friction
exerted by the first guiding bar 3 allows that the
tension in the warp threads 7 upstream of the first
18
guiding bar 3 is small. The diameter of the second
guiding bar 5 is also small so that the friction surface
about the second guiding bar 5 is also small. As the wrap
angle of the warp threads 7 against the second guiding
bar 5 is different for a full warp beam 10 than for an
empty warp beam 10,the friction force exerted by the
second guiding bar 5 will also differ. In Fig. 2 the warp
threads 7 are shown for a full warp beam 10. As shown in
Fig. 2 the warp threads in case of an empty warp beam run
according to line 9.The difference in friction force
exerted by the second guiding bar 5 is small with respect
to the friction force caused by the first guiding bar 3.
The withdrawal angle varies depending on the position of
the warp threads in case of a full warp beam and the
position of the warp threads in case of an empty warp
beam.
As can be seen in Fig. 2, the warp threads 7 are directed
downwards when leaving the first guiding bar 3. In
preferred embodiments, when weaving heavy fabric, a line
of symmetry of the shed is under a line between the area
where the warp threads 7 leave the first guiding bar 3
and the cloth line. This allows for an equal tension of
warp threads moved for crossing of the shed and warp
threads remaining in an extreme positioning as explained
in US 5,273,079 the content of which is herewith
incorporated by reference.
A method for installing the back rest device 2 on a
weaving machine 1 is described with reference to Figs. 2
to 4, showing a schematic side view of the back rest
device 2 during weaving a fabric, before installation of
19
the back rest device and during weaving a very heavy
fabric, respectively.
When installing the back rest device 2, the first guiding
bar 3 is moved in the mounting device 4 without fixing
the first guiding bar 3 in the mounting device 4. The
warp threads 7 are arranged over the first guiding bar 3.
The hooks 60 extend through the warp threads 7 as shown
in Fig. 3. Before moving the first guiding bar 3 with the
hooks 60 to the position shown in Fig. 3, the tube 44 is
removed. Then the second guiding bar 5 is arranged in the
hooks 60.
After arranging the second guiding bar 5, the first
guiding bar 3 is rotated from the position as shown in
Fig. 3 according to direction R, wherein the warp threads
7 are moved along with the second guiding bar 5 and wound
in a defined wrap angle against the first guiding bar 3.
The first guiding bar 3 is hereby oriented in angular
position in order to bring the second guiding bar 5 into
a desired position, for example the position as shown in
Fig. 2.
Fig. 4 is a schematic side view of the back rest device 2
of Fig. 2 configured for weaving a very heavy fabric. In
this embodiment, a wrap angle of the warp threads 7
against the first guiding bar 3 is approximately 270
degrees.
As mentioned above, when weaving a heavy fabric, at least
a wrap angle as shown in Fig. 2 is preferably provided.
In order to obtain that as well as for a full warp beam
as for an empty warp beam still a wrap angle is present
20
around the second guiding bar 5, the second guiding bar 5
has to be arranged at least past the line 11shown in
Fig. 2, which line 11 indicates the direct connection
between the empty warp beam 10 and the first guiding
bar 3.
In one embodiment, markers45 (shown in Fig. 1) are
provided on the first guiding bar 3 and/or markers 46, 47
are provided on the mounting device 4 to allow to
position and to fix the first guiding bar 3 in several
pre-set positions, for example markers45 indicating wrap
angles from 0 degrees to 360 degrees and/or markers 46,
47 indicating respectively vertical and horizontal
positions of the first guiding bar 3 with respect to the
mounting device 4. Hereby, it is possible based on the
markers 45 to determine the angular position of the first
guiding bar 3, and based on the markers 46 and 47 to
determine the vertical and horizontal position of the
first guiding bar 3.
In one embodiment, a warp tension sensor (not shown) is
provided that measures the tension of the warp threads 7.
For example, a separate warp tension measurement device
is provided that measures the tension in some or all of
the warp threads 7 directly on the warp threads.
Preferably, such a sensor is provided between the back
rest device 2 and the warp detector 12.In another
embodiment, the warp tension is measured indirectly by
measuring the forces of the first guiding bar 3 acting in
the region of the mounting device 4. In both cases, a
measured tension can be used for bringing the warp
tension to a desired value.
21
Fig. 5 to 8 schematically show a hook 60 and support
elements 8 used in a supporting device6 of the back rest
device 2 of Fig. 1, whereas Fig. 7 to 9 schematically
show an associated first guiding bar 3.
As shown in Fig. 9, the first guiding bar 3 is provided
at its two ends 34 with bearing taps 36 that can be
received in the clamping elements 40 of the mounting
device 4 shown in Fig. 1. The bearing taps 36, for
example, are formed by machining.
The hook 60 shown in Fig.5 is provided with a curved part
600 for receiving the second guiding bar 5. The hook 60
can be fixed with its distal end 601 near the first
guiding bar 3. In an embodiment as shown in Figs. 5 to 8,
a fixation element 61 is fixed with bolts 62 to the hook
60, wherein the bolts 62 extend through openings 602 in
the hook 60. The fixation element 61 is fixed with bolts
63 to the first guiding bar 3, which first guiding bar 3
is provided to this end with a bore hole 603 having screw
thread. Further a pin 64 is provided for positioning the
fixation element 61 in an accurate position with respect
to the hook 60, which pin 64 can co-operate with a slot
604 in the hook 60. Further a pin 65 is provided to set
the fixation element 61 in an accurate position with
respect to the first guiding bar 3, which pin 65 can cooperate
with a bore hole 605 in the first guiding bar 3.
According to an embodiment the fixation element 61 has a
shape that makes contact with the outer circumference of
the first guiding bar 3. According to a variant
embodiment the fixation element 61 has a flat wall that
in use makes contact with a flat part that is provided at
22
the height of the bore hole 603 on the first guiding
bar 3, which flat part is made, for example, with a
milling machine.
According to another possibility the pin 65 can cooperate
with a bore hole 606 in the first guiding bar 3.
This allows to arrange the hook 60 in a position 180
degrees turned. Because as shown in Fig. 9, the first
guiding bar 3 is designed symmetrical around an axis of
symmetry 35, the first guiding bar 3 can be turned around
its axis of symmetry 35 over 180 degrees. In case the
first guiding bar 3 is worn due to contact with warp
threads 7, the other side of the first guiding bar 3 can
be used to make contact with the warp threads 7. This
allows to double the lifetime of the first guiding bar 3,
in particular when the warp threads 7 are guided over
less than 180 degrees over the first guiding bar 3.
It is preferred to fix the hooks 60 accurately with
respect to the first guiding bar 3. In other embodiments,
the hooks 60 are fixed in any other suitable way to the
first guiding bar 3, or are welded to the first guiding
bar 3.
The hooks 60 are flat, this means have a comparatively
small extension in the direction of the longitudinal axis
of the second guiding bar 5. Such hooks 60 do not open
the plane of warp threads substantially, so that no
“stripes” in the fabric will occur. The fixation elements
61, the bolts 62 and 63, and the pins 64 and 65 do not
come into contact with the warp threads 7.
23
As mentioned above, the second guiding bar 5 is
preferably of low weight and has a comparatively small
outer diameter. Due to the small dimensioning, the second
guiding bar 5 in one embodiment has only a limited
rigidity. A sufficient number of hooks 60 is provided in
order to avoid or at least delimit a bending of the
second guiding bar 5 caused by the tension in the warp
threads7.
As mentioned above, in one embodiment, the second guiding
bar 5 is not clamped in the hooks 60, but held in a
moveable manner. In order to avoid a too extensive
shifting movement of the second guiding bar 5 in a
longitudinal direction, in one embodiment, limit stops 48
are arranged at the ends 52 of the second guiding bar 5
to avoid or delimit such shifting. The curved part 600
allows a movement of the second guiding bar 5relative to
the hooks 60 in a radial direction for attaching or
detaching the second guiding bar 5. In one embodiment,
closure elements are provided closing the opening of the
curved part 600 for avoiding a displacement of the second
guiding bar 5 in radial direction and/or in tangential
direction.
According to a variant (not shown), a second guiding bar
5 having a higher rigidity is provided, wherein the
number of support elements can be reduced. To this end,
in one embodiment a dimension of the second guiding bar
is increased.
Fig. 10 shows another embodiment, wherein a second
guiding bar 105 having an oval cross-section supported in
support elements 8 such as hooks 160 is provided. The
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orientation of the second guiding bar 105 in this
embodiment is chosen so that the warp threads7 exert a
force on the second guiding bar 105 in a direction where
the second guiding bar 105 is more rigid against bending.
As the second guiding bar 105 having an oval crosssection
is prevented from rotating in the support
elements 8, a frictional force is exerted on the warp
threads 7 by means of the second guiding bar 105 which
may be slightly higher than that exerted by the second
guiding bar 5 shown in Figs. 1 to 4.Apart from the shape
of the second guiding bar 105 and the associated hooks
160, the back rest device 2 shown in Fig. 10 corresponds
to that of Fig. 2 and for a detailed description,
reference is made to Fig. 2.
As shown in Fig. 1, at the height of both side parts 16
the first clamping part 41 is fixed via a fixation block
50 to the support table 14. In the clamping part 41, as
schematically shown in Figs. 2, 3, 4 and 10, different
bore holes 51 are arranged to be able to position the
clamping part 41 via the fixation block 50 in different
positions with respect to the support table 14. This
allows to set the first guiding bar 3 in a desired
position. Of course this setting of position can be done
in other known ways.
In the context of the application “first” and “second” are
only used to distinguish between the first guiding bar 3 and
the second guiding bar 5. It is, for example, also possible to
call the first guiding bar 3 that is mounted fixedly “back
rest bar” or “back rest roller”, and the second guiding bar 5
“tension bar” or “tension roller”.
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The warp threads 7 move from the warp beam 10 firstly via the
second guiding bar 5 and subsequently via the first guiding
bar 3 to shed forming elements 15, so that in use according to
the movement direction of the warp threads 7 from the warp
beam 10, the second guiding bar 5 is arranged upstream of the
first guiding bar 3, in other words the first guiding bar 3 is
arranged downstream of the second guiding bar 5.
Although in the embodiments shown, as well as the first
guiding bar 3 as the second guiding bar 5 are executed as a
hollow guide bar, in other words as a tubular element,
according to a variant, it is also possible to execute at
least one of the guiding bars 3, 5 as a solid guiding bar, for
example the second guiding bar 5.
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WE CLAIM :
1. Back rest device for guiding warp threads (7) coming
from a warp beam (10) comprising a first guiding bar
(3), characterized in that the back rest device (2)
further comprises a mounting device (4), which is
arranged for mounting the first guiding bar (3) in a
fixed mounting position and in a non-rotatable
manner, a second guiding bar(5, 105), which in use
is arranged in parallel to the first guiding bar (3)
and upstream of the first guiding bar (3) for
deflecting warp threads (7) coming from the warp
beam (10), and a supporting device (6), which is
arranged for supporting the second guiding bar
(5, 105)so that in use the longitudinal axis of the
second guiding bar (5, 105) is at least
substantially fixed in position with respect to the
longitudinal axis of the first guiding bar (3).
2. Back rest device according to claim 1, characterized
in that the supporting device (6) is arranged for
supporting the second guiding bar (5, 105)with its
longitudinal axis in use in a settable position with
respect to the longitudinal axis of the first
guiding bar (3).
3. Back rest device according to claim 1 or 2,
characterized in that the second guiding bar
(5, 105)is mounted on the first guiding bar (3) by
means of the supporting device (6).
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4. Back rest device according to claim 3, characterized
in that the supporting device (6) comprises a
plurality of support elements (8) distributedly
arranged over the length of the first guiding bar
(3) for supporting the second guiding bar(5, 105).
5. Back rest device according to claim 4, characterized
in that hooks (60, 160)are provided as support
elements (8), which hooks (60, 160)are distributedly
arranged over the length of the first guiding bar
(3).
6. Back rest device according to claim 5, characterized
in that the second guiding bar (5, 105)is supported
moveably, in particular rotatably, in the
hooks(60, 160).
7. Back rest device according to any one of claims1 to
6, characterized in that limit stops (48, 49) are
provided for delimiting or preventing a movement of
the second guiding bar (5, 105)in the direction of
its longitudinal axis.
8. Back rest device according to any one of claims 1to
7, characterized in that the outer circumference of
the first guiding bar (3) is larger than the outer
circumference of the second guiding bar(5, 105),
wherein in particular an outer circumference of the
first guiding bar (3) is larger than 500 mm, in
particular between approximately 550 mm and
approximately 800 mm and/or an outer circumference
of the second guiding bar (5, 105)is between
approximately 90 mm and approximately 230 mm.
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9. Back rest device according to any one of claims 1 to
8, characterized in that either or both of the first
guiding bar (3) and the second guiding bar
(5, 105)is a tubular element, in particular a
circular tubular element.
10. Back rest device according to claim 9, characterized
in that a wall thickness of the first guiding bar
(3) is between approximately 8 mm and approximately
15 mm and/or a wall thickness of the second guiding
bar (5, 105)is between approximately 1 mm and
approximately 5 mm.
11. Back rest device according to any one of claims 2 to
10, characterized in that markers (45, 46, 47) are
provided for indicating a plurality of pre-set
positions for the longitudinal axis of the second
guiding bar(5, 105).
12. Back rest device according to any one of claims 1 to
11, characterized in that the mounting device (4)
comprises two clamping elements (40) for clamping
the first guiding bar (3) at its ends (34).
13. Weaving machine comprising a back rest device
according to any one of claims 1 to 12,
characterized in that the back rest device (2) is
arranged near a warp beam (10), in particular
between a warp beam (10) and shed forming elements
(15).
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14. Method for arranging a back rest device according to
any one of claims 1 to 12comprising a first guiding
bar (3), a mounting device (4), a second guiding
bar(5, 105), and a supporting device (6), on a
weaving machine (1), wherein the first guiding bar
(3) is inserted into the mounting device (4),warp
threads (7) supplied by a warp beam (10) are
arranged over the first guiding bar (3), and the
second guiding bar (5, 105)is attached to the
supporting device (6) to deflect the warp threads
(7).
15. Method according to claim 14, characterized in that
the second guiding bar (5, 105)is mounted on the
first guiding bar (3) by means of the supporting
device (6), wherein after attaching the second
guiding bar (5, 105)to the supporting device(6), the
first guiding bar (3) is oriented, in particular
rotated about its longitudinal axis, for bringing
the longitudinal axis of the second guiding bar
(5, 105)into a set position with respect to the
longitudinal axis of the first guiding bar (3), and
the first guiding bar (3) is mounted by the mounting
device (4) in a non-rotatable manner after the
second guiding bar (5, 105)is in the set position.