Back rest for a weaving machine.
The invention relates to a back rest for guiding warp
threads in a weaving machine. I n particular, the invention relates
to a back rest comprising a back rest profile resiliently supported
by a force element.
On a weaving machine, the warp threads are unwound
from a warp beam and guided via a back rest towards the heald
frames. The warp threads are to be held with a certain tension,
which is defined by the type of warp threads used and the cloth
to be woven. During weaving, the heald frames move up and
down. During each movement of the heald frames the pulling
force on the warp threads changes. This pulling force causes
undesired tensions in the warp threads, which are compensated
for by providing a back rest on the weaving machine. A good
quality back rest, which may be used both for stiff warp threads,
having low elasticity, as for delicate warp threads, which are
prone to damage, should be held as unstressed or slack as
possible for allowing an undisturbed movement of the warp
threads and at the same time should have a good following
behaviour for enabling the back rest to follow the movement of
the warp threads to keep them tensioned on the one hand and
for keeping contact with the warp threads at all time for avoiding
unwanted tension in the warp threads because of the back rest
and the warp threads not moving together on the other hand.
From the state of the art already different back rests are known.
For example EP 0 409 811 Al discloses a supporting
mechanism for a back rest in a weaving machine with two
supports which support the back rest at its respective ends,
wherein each support consists of two leaf springs mounted next
to one another, which each are attached at one of their ends to
one another and to the weaving machine and at their other ends
are connected with one another to support the back rest.
WO 2008/077383 Al discloses a back rest, wherein a guide
profile is arranged on a leaf spring so as to be able to oscillate.
However, this requires the leaf spring to be fairly large, what
may complicate the use of warp beams with large diameters, so
as to make it possible to use a leaf spring which is soft or slack
enough and provides a sufficiently following behaviour. Such
back rest also has the disadvantage that a certain leaf spring is
only suited to be applied at a certain warp tension. Similar,
DE 2 162 396 Al relates to a leaf spring that functions as a
guide element in a back rest. WO 97/30201 relates to a back
rest arrangement comprising a leaf spring supported on a frame,
wherein the spring behaviour of the leaf spring may be adjusted .
I n accordance with an embodiment the leaf spring is fixed on the
frame using a first element and additionally supported by a
second element, the position of which may by varied for varying
the behaviour or the stiffness of the spring.
It is further known from DE 33 48 030 Al to provide a
resiliently supported guide profile in the form of a pivotally
mounted profile. Warp threads contact the profile at its upper
end. The profile is supported at its upper end by a force element
in the form of a pressure cushion. A similar structure is disclosed
in US 4,121,625, wherein a rigid, moveably arranged guide
profile is supported on a fixed member via a pressure cushion.
GB 4333 shows a moveably arranged rigid guide element made
of cast iron which cooperates with the warp threads opposite the
guiding face of this guide element supported by a helical spring
element.
It is the object of the invention to provide a back rest
being sufficiently soft or slack for avoiding undesired tensioning
of the warp threads and having a good following behaviour for
always keeping contact with the warp threads.
This object is solved by a back rest for guiding warp
threads in a weaving machine comprising a back rest profile
pivotally arranged at a support point and provided with a guide
section for guiding warp threads, wherein the back rest
comprises at least one resilient force element for supporting the
back rest profile, and wherein the location of force application of
the at least one resilient force element on the back rest profile is
arranged between the support point and the guide section and is
distanced from the support point as well as from the guide
section.
Preferred embodiments are defined in the dependent
claims.
The basic idea of the invention is to provide a back rest
comprising a back rest profile pivotally arranged at a support
point on a support element and provided with a guide section for
guiding warp threads and at least one resilient force element for
applying a force to the back rest profile, wherein the point of
force application between the at least one resilient force element
and the back rest profile is arranged between the support point
and the guide section for making use of a leverage between the
forces applied on the back rest profile by the warp threads and
by the least one resilient force element.
The location of force application of the at least one resilient
force element is defined in accordance with the invention as the
area in which forces are applied on the back rest profile by the
resilient force element.
A back rest according to the invention comprising a
pivotally arranged back rest profile and taking advantage of a
leverage in that the resilient force element supports the back
rest profile in between the guide section and the support point
allows for a back rest which is slack enough not to disturb the
warp thread movements, while still sufficient force is applied on
the back rest profile to allow the back rest profile to follow the
warp threads always and keeping the warp threads tensioned.
The back rest according to the invention is advantageous
as due to the leverage provided between forces which are
applied on the back rest profile at the guide section and at the
location of force application of the resilient force element, a low
inertia back rest profile and a stiff resilient force element may be
used, by what a back rest occupying a small space is obtained,
wherein a force applied on the warp threads to keep a desired
warp tension and an elastic compliance of the back rest profile to
avoid undesired tensions by the movement of the heald frames
can be well balanced.
If the resilient force element is situated close to the guide
section of the back rest profile for warp threads, the spring
deflection of the resilient force element has to be essentially
equal to the displacement or deflection path of the warp threads.
Even if such a displacement is small, for example about 5 mm,
due to the high weaving-speed of for example about 800
cycles/min, resilient force elements with a high elasticity and
with a low spring constant are required in order not to cause
additional tensions in the warp threads. On the other hand,
however, the resilient force element should still be strong
enough to move the back rest profile fast for allowing a good
following, thus requiring for a higher spring constant. Therefore,
at least for high-speed weaving applications, the resilient force
element is sufficiently distanced from the guide section of the
back rest profile for the warp threads.
When the resilient force element is positioned far from the
guiding section of the back rest profile for the warp threads, the
resilient force element needs to be comparatively strong or stiff
to move the back rest profile fast enough for following the warp
threads. This requires for a resilient force element with a high
spring constant. Also, the back rest profile has to be stiff enough
to ensure an accurate movement of the guide section of the back
rest profile, resulting in a heavier back rest profile. The resulting
back rest, however, still has to be both slack and light-weight
enough to allow an undisturbed movement of the warp threads.
Therefore, at least for high-speed weaving applications, the
resilient force element is also sufficiently distanced from the
support point of the back rest profile for the warp threads.
According to an embodiment, the resilient force element is
arranged so that the location where force is applied on the back
rest profile is situated essentially halfway between the support
point and the guide section of the back rest profile. Essentially
halfway between the support point and the guide section in
accordance with the invention is defined as a location, which is
distanced from the support point as well as from the guide
section by a distance of at least 30%, preferably at least 40%, of
the distance between the support point and the guide section.
The lower the required warp tension, the closer to the support
point the force may be applied by the resilient force element.
I n preferred embodiments, the support element for the
back rest profile is mounted on a carrier element for the back
rest. The support element is understood as the element on which
the back rest profile is mounted and with respect to which the
back rest profile is pivoted for following the warp threads. I n one
embodiment, the support element is mounted stationary on the
weaving machine via a carrier element. I n other embodiments,
the support element is arranged moveable with respect to the
weaving machine via a carrier element. I n a preferred
embodiment, the back rest with the support element is mounted
to a carrier element of a weaving machine via an intermediate
element provided with a sensor device for measuring the forces
applied by the warp threads on the back rest. These
measurements can be used as a measure for the warp tension.
I n another embodiment, the warp tension is additionally or
alternatively measured on the warp threads themselves with a
warp thread tension measurement device.
According to preferred embodiments, the back rest profile
is formed as a resiliently deformable plate having preferably a
bended shape, such as a bended plate, in particular the back rest
profile is made of a steel plate, more particular a spring steel
plate, having a thickness of for example between about 0,5 mm
and about 3 mm. The plate can also be entirely or partly formed
from a composite material, for example a fibre-reinforced
wear-resistant synthetic material which for example also has
good sliding properties, for example carbon fibre reinforced
polyethylene or any other fibre reinforced polymer. By providing
a bended back rest profile folded from a metal plate, a
light-weight profile having a low inertia is provided. When
forming the back rest profile from a spring steel plate, a
resiliently or elastically deformable back rest profile is provided,
wherein the total displacement of the guide section of the back
rest profile defining the following behaviour of the back rest
profile is not only obtained by the displacement of the resilient
force element, but wherein the back rest profile, which can be
bent or elastically deformed against its internal counteracting
force, also contributes to the displacement executed by the warp
threads. This is advantageous because a deflection of the
resilient force element, which is necessary for moving the back
rest profile, may be chosen smaller as part of the movement of
the back rest profile results in the deflection or the elastic
deformation of the back rest profile. Therein a resilient force
element with a comparatively smaller elasticity may be used.
The resiliently deformable back rest profile is herein deformed by
the force which is applied on the back rest profile by the warp
threads and the force which is applied on the back rest profile by
the resilient force element, wherein these forces oppose one
another. According to one embodiment, the back rest profile is
only partly deformable, wherein at least the part arranged
beyond or above the point of force application of the resilient
force element is resiliently deformable.
According to another embodiment, the back rest profile is
formed as a plate-shaped profile with a curved free section on
which the guide section for guiding the warp threads is provided .
According to an embodiment the back rest profile is furthermore
formed as a plate-shaped profile, wherein a supported section is
pivotally arranged on the support element and wherein a middle
section, which extends between the supported section and the
free section makes contact with the resilient force element with
its flat side and wherein the free section of the back rest profile
is formed as a curved guide section or guiding area for the warp
threads. This allows an easy and cheap manufacturing of the
back rest profile. By providing such a, preferably integrally
formed, back rest profile, the amount of material used is
minimized and a back rest profile with low inertia can be
obtained, more particularly a hook-shaped back rest profile with
a bent free section.
According to another embodiment, the curved free section
of the back rest profile forming the guide section is curved along
a single arc, making contact with the warp threads along the
entire arc. I n preferred embodiments, the curved free section is
provided with multiple folds, so that the warp threads contact
the back rest profile only at discrete guiding areas forming a
guide section for the warp threads. With such an embodiment, a
frictional resistance between the warp threads and the guide
section is minimized. I n addition, providing multiple folds may
increase the stiffness in the longitudinal direction of the back rest
profile, which can be advantageous to prevent tension
differences between different warp threads.
I n one embodiment, the support point of the back rest
profile is realized using hinges and/or roller bearings. According
to a preferred embodiment, the support point is embodied as a
slot provided on a support element, in which a supported section
of the back rest profile, in particular an edge of the back rest
profile is inserted. The slot extends in the longitudinal direction
of the back rest profile and the supported section is inserted so
that the back rest profile is pivotable about an axis parallel to the
longitudinal direction of the back rest profile. The back rest
profile is held in the slot by the force applied by the warp
threads. After removing the tension in the warp threads, the
back rest profile can easily be removed from the support element
or the back rest profile can be replaced by another back rest
profile, for example by a lighter back rest profile or for example
by a stiffer back rest profile as required for a particular
application.
I n one embodiment, the position of the support point is
adjustable, for example for an adjustment of the position of the
support point of the back rest profile with respect to the location
of the application of force by a resilient force element. According
to another embodiment, the inclination of the back rest profile
with respect to the resilient force element may be set by
adjusting the position of the support point. By changing the
position of the support point and/or of the inclination of the back
rest profile with respect to the resilient force element, the
deformation of the resilient force element may be adapted to the
tension in the warp threads, so that the warp threads are
suitably guided.
According to a preferred embodiment between the
supported section of the back rest profile and the support
element a wear-resistant edge protection can be fitted, for
example a polyurethane cover or a cover in wear-resistant
rubber or in a wear-resistant synthetic material, to protect as
well the edge of the back rest profile as the slot of the support
element from wear. The edge protection preferably is also
electrically conductive to eliminate static electricity charges,
generated by the friction between the warp threads and the back
rest profile. Therefore an electrically conductive rubber or
electrically conductive synthetic material may be chosen, for
example.
According to a preferred embodiment, the resilient force
element is embodied as a pressurized hose filled with a
pressurized fluid, for example compressed air, which is arranged
between the back rest profile and a carrier element for a back
rest, in particular between the back rest profile and a carrier
element arranged on the holding element. Altering the pressure
inside the pressurized hose allows an adjustment of the spring
constant of the resilient force element. Therefore, the force
applied by the resilient force element may easily be set in
dependency of a desired average warp thread tension for specific
warp threads.
When using a pressurized hose as a resilient force element,
it is advantageous that this pressurized hose is arranged
between the carrier element, in particular the carrier element
arranged on the holding element, and the back rest profile in
such a way that the entire pressurized hose may be deformed by
the moving back rest profile without or with only small resistance
due to the support element and/or the holding element. I n other
words, sufficient space should be provided near to the back rest
profile to allow the pressurized hose to deform over its entire
surface. This is advantageous for the lifespan of the pressurized
hose for several reasons. Herein a deformation is not limited to
one single or several specific parts of the pressurized hose, but
the deformation is distributed over a larger part of the
pressurized hose. Secondly, the pressurized hose is able to
create a "rolling" contact with the carrier element or with the
holding element for the pressurized hose arranged on the carrier
element and/or with the back rest profile when the pressurized
hose is deformed, instead of a "frictional" contact when only
limited space is available and the pressurized hose is "squeezed"
between on the one hand the carrier element or the holding
element and on the other hand the back rest profile and for
example is locally pushed out of a holding element into which the
pressurized hose is arranged.
According to preferred embodiments, clamp elements are
provided on the support element and/or a holding element
carrying the pressurized hose and/or on the carrier element for
deforming end regions of the pressurized hose, more in
particular regions of the pressurized hose near the side edges of
the back rest profile, by forcing the end regions of pressurized
hose away from the back rest profile. The clamp elements have
several advantages. Firstly, in preferred embodiments, the
pressurized hose is longer than the back rest profile in the
longitudinal direction, so that the back rest profile is entirely
supported and a connecting of the pressurized hose to for
example a compressed air source can be realized easily. Due to
the tension of the warp threads acting on the back rest profile,
the pressurized hose is deformed by the back rest profile.
However, regions of the pressurized hose projecting beyond the
back rest profile are not deformed by the back rest profile.
Therefore, in the area of transition between the deformed and
the undeformed parts of the pressurized hose, side edges of the
back rest profile may damage the pressurized hose because of
the movement of the back rest profile, especially when the back
rest profile is for example formed as a simple steel profile or
plate having sharp side edges. When clamp elements are
provided for deforming end regions of the pressurized hose away
from the back rest profile, the pressurized hose is not exposed to
the moving side edges of the back rest profile. As an alternative,
covers are provided in the end regions of the pressurized hose
for protecting the pressurized hose, for example polyurethane
covers.
Further, in preferred embodiments, the back rest profile is
longer than the maximum width of the plane of warp threads on
the weaving machine. This results in an end zone of the back
rest profile near the side edges of the back rest profile being
unused . I n other words, no warp threads are guided on end
zones near the side edges of the back rest profile. However,
without the use of clamp elements, these end zones are also
supported by the pressurized hose. Therefore, a resulting
deflection force on end zones of the back rest profile
neighbouring the side edges, which is forcing the guide element
towards the warp threads, is higher than in other zones of the
back rest profile. This is disadvantageous for obtaining an even
cloth. Providing clamp elements, which force the pressurized
hose away from the back rest profile in the end zones not
guiding warp threads provides a solution for this problem. I n
preferred embodiments, the pressurized hose is forced, more in
particular pushed away from the back rest profile just enough to
eliminate any excess force on the warp threads and to support
the weight of the unused end zones of the back rest profile.
According to a preferred embodiment, a pressurized hose
made at least partly of a fibre-reinforced material is used. This
allows using a thin-walled pressurized hose which is sufficiently
wear-resistant. A thin-walled pressurized hose, such as a
fire-hose having a side wall of less than about 4 mm, more
particular less than 3 mm, for example about 1,5 mm can be
more easily deformed than a pressurized hose having a thicker
wall. This allows for a more undisturbed movement of the back
rest profile. I n preferred embodiments, a multi-layer hose is
used. I n one embodiment a pressurized hose is provided
comprising a neoprene inner side, a wear-resistant polyurethane
outer side and a polyester fibre-reinforced web there between.
I n still another embodiment a back rest profile having a
plate-shaped profile with a folded middle section contacting the
pressurized hose is used. Thereby, via the pressurized hose, a
resilient force element with a changing spring constant or with a
non-linear spring constant is obtained. A back rest profile having
a small fold contacting the pressurized hose with its outer radius,
in other words a fold "pointing" towards the pressurized hose,
will for example result in a lower spring constant, since less
surface of the back rest profile will contact the pressurized hose.
The shape of the fold may be chosen to affect the linearity of the
spring constant. The less sharp the fold, the more the spring
constant will rise with rising deformation of the pressurized hose.
Changing the spring constant may be advantageous to obtain a
specific back rest behaviour. Using a linear spring constant, on
the other hand, may be advantageous to facilitate a prediction of
the back rest behaviour and, thus may facilitate an electronic
control of the back rest.
According to another embodiment, a manometer and a
manual adjusting device with which the pressure in the
pressurized hose can be set manually are provided. The pressure
may be manually adjusted with the aid of the pressure
manometer. Alternatively, a control unit is provided for an
automatical setting that monitors and/or regulates the pressure.
The control unit may be a separate unit or integrated in a control
unit of the weaving machine. I n preferred embodiments, a
display unit such as a screen is provided for monitoring the
pressure.
With the control device the pressure in the pressurized
hose is for example controlled according to the kind of warp
threads used, the woven pattern, the desired warp tension in the
warp threads, the width of the woven cloth, the number of warp
threads per unity of length etc. I n one embodiment, a control
unit which allows reading and/or writing data to and from a
memory card is used, which allows to use predefined control
data or to transport the control data from one weaving machine
to another weaving machine. When the weaving machine
monitors the warp thread tension, predefined control data
comprises in one embodiment a table defining a pressure in the
pressurized hose for a certain measured and desired warp thread
tension.
According to a next preferred embodiment, a diameter of
the pressurized hose is chosen relatively large with respect to
the movement of the guide section of the back rest profile. For
example with an average warp thread displacement of about
5 mm a pressurized hose is chosen with a diameter of about
4 cm to 6 cm, more in particular a diameter of about 5 cm. Using
a pressurized hose with a relatively large diameter is
advantageous because a relatively smaller deformation of the
pressurized hose is required, limiting the wear of the pressurized
hose and the pressure changes in the pressurized hose, so that a
monitoring of the pressure in the pressurized hose is not
complicated.
According to an embodiment the back rest profile is
provided with a guide section which is formed by a guiding roll
which is arranged on the back rest profile. By providing a guiding
roll as guide section for guiding warp threads a relative
movement between the warp threads and the guide section is
avoided, wherein wear of the warp threads may be reduced.
According to an embodiment the resilient force element is
embodied as a series of springs, for example spiral springs,
which are positioned between the back rest profile and a carrier
element for the back rest according to the longitudinal direction
of the back rest profile, more in particular between the back rest
profile and a carrier element for a support element of the back
rest. According to an embodiment small pins are provided
between the back rest profile and the carrier element, in
particular on the carrier element for the back rest and/or on the
back rest profile, onto which springs are fitted. The resulting
spring constant can be adjusted by varying the number of fitted
springs and/or the type of springs, in particular by the use of
springs with different spring constants.
According to another embodiment, a holding element is
provided on a carrier element of the back rest for holding the
resilient force element, wherein the design and/or size of the
holding element are adapted to the type of resilient force
element used. I n one embodiment, a channel-shaped holding
element is provided for holding the pressurized hose stably while
sufficient space is provided to allow the pressurized hose to
deform in response to force applied by the back rest profile. I n
another embodiment, wherein the resilient force element is
configured as a series of springs, for example spiral springs, a
holding element is provided with a series of pins onto which the
springs may be attached on the holding element.
According to an embodiment the holding element is
arranged moveable on a carrier element for holding the resilient
force element. For example the carrier element is provided with
some discrete positions onto which the holding element can be
arranged on the carrier element, for example using connection
elements, such as bolts and corresponding boreholes, to set
and/or change the location where the resilient force element
applies force on the back rest profile. I n this way the operating
range of a back rest according to the invention can be extended
additionally with respect to what is possible by regulating the
pressure in the pressurized hose and/or the spring constant of
the springs.
According to still another embodiment, a stop element is
provided on the carrier element and/or the holding element for
limiting the movement of the back rest profile. I n one
embodiment, employing a pressurized hose as a resilient force
element, the stop element is configured for supporting the back
rest profile in a defined position, for example a position where
the back rest profile is located when the pressure in the
pressurized hose is released. To this end, the stop element is
configured in one embodiment as a longitudinal profile upon
which the back rest profile abuts.
According to another embodiment, a safety device is
provided for detecting excessive movement of the back rest
profile. I n preferred embodiments, a proximity detector, a laser
beam and/or any other type of position detector is used to detect
for example the presence of the back rest profile beyond a limit
position. I n preferred embodiments, a warning signal is
generated, when reaching a limit position was detected. I n other
embodiments, the weaving machine is stopped in such a case. I n
further embodiments, several limit positions are defined, which
result in different solution-strategies. With a safety device a
punctured pressurized hose may also be identified. I n one
embodiment, the safety device is arranged on the stop element,
so that when the back rest profile abuts against the stop element
the safety device generates a respective signal.
When the warp threads are unwound from a warp beam,
the angle under which the back rest profile is approached
changes with the reduction of remaining warp threads wound on
the warp beam. Consequently, the direction of the resulting force
on the back rest profile varies. To compensate the change in
force, in one embodiment the pressure in the pressurized hose is
adapted.
Alternatively or in addition, in another embodiment, a
guiding element is provided near the support element upstream
of the back rest profile in the moving direction of the warp
threads. When providing a guiding element upstream of the back
rest profile, in particular in a region of the support point, the
warp threads wound off the warp beam travel via the guiding
element to the back rest profile, and so the direction of the force
applied to the back rest profile is kept constant. I n one
embodiment, the guiding element is embodied as a profile
comprising a rounded guiding surface. I n other embodiments, a
guide roll is provided as guiding element. I n one embodiment,
the position of the guiding element is adjustable in the horizontal
and/or the vertical direction.
According to another embodiment, a sensor device is
provided for determining the warp tension, wherein the sensor
device cooperates with the pressurized hose. I n one
embodiment, the warp tension is measured indirectly by
measuring the pressure in the pressurized hose.
I n the following, embodiments of the invention will be
described in detail based on several schematic drawings in which
Fig. 1 shows a schematic side view of an embodiment of a
back rest according to the invention;
Fig. 2 shows a schematic perspective view of a further
embodiment of a back rest according to the
invention;
Fig. 3 shows a schematic side view of a still further
embodiment of a back rest according to the
invention;
Fig. 4 shows a schematic perspective view of the back rest
according to figure 3;
Fig. 5 to 11 show a schematic side view of further embodiments
of a back rest according to the invention;
Fig. 12 shows a partially cut schematic perspective view of
the back rest according to figure 11;
Fig. 13 and 14 show a schematic side view of further
embodiments of a back rest according to the
invention;
Fig. 15 shows a detail of a possible deformation of a back
rest according to the invention;
Fig. 16 to 18 show a schematic side view of other embodiments
of a back rest according to the invention;
Fig. 19 shows a schematic perspective view of the
embodiment of figure 18;
Fig. 20 shows a schematic side view of a variant
embodiment of figure 18.
The figures schematically show different embodiments of a
back rest according to the invention. Throughout the drawings,
the same elements will be denoted by the same reference
numerals. A repeated detailed description of the same elements
present in different embodiments is omitted . Elements of
different embodiments may be combined to realize further
embodiments.
Figure 1 shows a first embodiment of a back rest 1
according to the invention comprising a back rest profile 2 and a
resilient force element 3 for supporting the back rest profile 2.
The back rest profile 2 has a relatively low weight and is formed
by a spring steel plate with a thickness of about 1,5 mm, which
has been bent according to a certain shape. The back rest 1
further comprises a support element 4 attached to a carrier
element 5, for example using a bolt connection. The carrier
element 5 is for example embodied as a support beam being part
of the frame of the weaving machine. The support element 4
comprises at the end situated opposite the carrier element 5 a
slot 6 which forms a support point 7 for the back rest profile 2.
I n this embodiment the slot 6 is integrally formed with the
support element 4 .
The back rest profile 2 is positioned in the slot 6 which
forms a support point 7 for the back rest profile 2, wherein the
support point 7 allows the back rest profile 2 to pivot about a
certain angle with respect to the support point 7 about an axis
parallel with the longitudinal direction of the back rest profile 2.
The supported section 8 of the back rest profile 2 which is
supported at the support point 7 which is positioned in the slot 6
cooperates with a wear-resistant and electrically conductive
protection 9, for example a polyurethane cover, which is
arranged between the edge of the supported section 8 and the
slot 6. During weaving warp threads 10 which are guided by the
back rest profile 2, contact the back rest profile 2 in a guide
section 11 at a free section 12 of the back rest profile 2, which
free section 12 shows a curved form. The back rest profile 2 can
pivot around the support point 7 in a reaction to the forces
applied by the warp threads 10 against the force of the resilient
force element 3. Therefore the warp threads 10 which are guided
along the guide section 11 are kept under sufficient tension.
The resilient force element 3 is positioned so that a force is
applied on the back rest profile 2 on a location 13 between the
support point 7 and the guide section 11, in the embodiment
shown essentially halfway between the support point 7 and the
guide section 11. This means a certain distance away from the
support point 7 and a certain distance away from the guide
section 11, wherein both distances are almost equal. The
resilient force element 3 which can apply a force on the back rest
profile 2 on a location 13 between the guide section 11 and the
support point 7 allows to use a resilient force element 3 having a
spring deflection which is smaller than the deflection of the back
rest profile 2 at the guide section 11 and allows to apply enough
force to move the back rest profile 2 fast, while still a lightweight
back rest profile 2 may be used. Forces acting on the back rest
profile 2 in the guide section 11 resulting from contact with the
warp threads 10 are balanced by the resilient force element 3,
wherein the back rest profile 2 acts as a lever. By the leverage
forces applied by the warp threads 10 are balanced by larger
forces applied by the resilient force element 3. Therefore the
back rest profile 2 is able to yield better in contact with the warp
threads, even with a relatively stiff resilient force element 3
which applies large forces to allow a good following behaviour of
the back rest profile 2 with the warp threads 10.
I n this way the arrangement allows a back rest 1 which at
the guiding section is slack or soft enough not to disturb a
movement of the warp threads 10. On the other hand, when
using a back rest profile 2 having a low inertia and a relatively
strong resilient force element 3, the back rest profile 2 is able to
follow the warp threads 10 fast and keep these tensioned.
I n this embodiment of a back rest 1 according to the
invention the resilient force element 3 is embodied as a
pressurized hose 14 which may be supplied with a fluid, for
example compressed air. The pressurized hose 14 is arranged in
a channel-shaped holding element 15. The holding element 15 is
fitted on the carrier element 5, for example using a bolt
connection. The pressurized hose 14 supports the back rest
profile 2 about halfway between the guide section 11 and the
support point 7 of the back rest profile 2 at the middle section 16
of the back rest profile 2. Herein the middle section 16 of the
back rest profile 2 is embodied flat, more in particular as a flat
plate section. A certain play is provided between the holding
element 15 and the pressurized hose 14 to easily allow the
deforming of the pressurized hose 14. To increase the
deformation of the pressurized hose 14 and the wear resistance
of the pressurized hose 14, the pressurized hose 14 is embodied
thin-walled, in a material suited therefore and/or with a
relatively large diameter.
The adaptation of the pressure of the fluid, for example of
the compressed air inside the pressurized hose 14 allows an
adaptation of the spring constant of the pressurized hose 14.
Therefore the force which is applied by the pressurized hose 14
may be adapted easily. Preferably a control unit 17 is provided
for an automatically setting, monitoring and/or regulating of the
pressure inside the pressurized hose 14. Herein compressed air
is guided from a compressed air source 18 via the control unit
17, which for example comprises a controllable pressure
regulator, and via a supply duct 19 at a certain pressure to the
pressurized hose 14. The pressure in the pressurized hose 14 is
for example set or adjusted corresponding to the kind of warp
threads used, the pattern woven, etc. The control unit 17
cooperates with a pressure sensor 20 for measuring the pressure
inside the pressurized hose 14 and allows to regulate the
pressure in the pressurized hose 14 automatically so that the
pressure measured becomes equal to a desired pressure. The
pressure sensor 20 is arranged for example at the supply duct
19. Instead of an automatic control unit 17 for regulating the
pressure in the pressurized hose 14 also a manual regulating
device may be provided for regulating the pressure inside the
pressurized hose 14.
I n this embodiment an additional guiding element 21 is
provided, which is arranged in the support element 4, for
example using a bolt connection. The guiding element 21 is
arranged upstream of the guide section 11 in a direction of
movement B of the warp threads 10 from a warp beam towards
heald frames. The guiding surface 22 of the guiding element 21
is essentially positioned in a region of the supported section 8 of
the back rest profile 2. During weaving, warp threads 10 are
unwound off a warp beam and guided towards the heald frames
via the back rest 1. Herein the warp threads 10 which are
unwound from the warp beam move via the guiding element 21
towards the back rest profile 2. Since the guiding element 21 is
arranged so that the warp threads 10 always remain in contact
with the guiding element 21, the direction of the force applied on
the back rest profile 2 by the warp threads 10 is kept almost
constant. The position of the guiding element 21 defines in this
case the angle with which the warp threads 10 are guided
towards the back rest profile 2.
Further a stop element 23 is provided that in this
embodiment is arranged close to the back rest profile 2 on the
channel-shaped holding element 15. The stop element 23 is
herein formed as an elongated profile, for example formed in a
wear resistant material and is arranged for stopping the back
rest profile 2 at a defined, for example minimal distance from the
carrier element 5 and/or from the support element 4, regardless
of the forces applied by the warp threads 10. According to a
variant, the stop element 23 can be arranged on another part of
the back rest 1, for example on the carrier element 5.
Figure 2 shows a perspective view of an embodiment
comparable to the embodiment of figure 1. Herein the back rest
profile 2 comprises a middle section 16 with a fold 24 which
makes contact with the pressurized hose 14. The fold 24 makes
contact with the pressurized hose 14 at the outer radius 25 of
the fold 24. Compared to the embodiment of figure 1 the contact
at the fold 24 results in a lower effective spring constant of the
back rest 1, since less surface of the back rest profile 2 makes
contact with the pressurized hose 14 than is the case with the
back rest profile 2 in figure 1. Herein the spring constant
changes also considerably when the back rest profile 2 is pressed
more or less into the pressurized hose 14. Herein the changing
of the spring constant may be enlarged, compensated or
diminished by changing the pressure inside the pressurized hose
14 suitably. As can be seen in figure 2, the pressurized hose 14
is longer than the back rest profile 2 in the longitudinal
direction L of the back rest 1. Therefore the side edges 26 of the
back rest profile 2 contact the pressurized hose 14 and deform
the pressurized hose 14 locally. The stop element 23 is in this
embodiment integrally formed with or makes part of an edge of
the holding element 15.
According to the embodiment of figures 3 and 4, clamp
elements 27 are provided next to and close to both side edges
26 of the back rest profile 2 which deform the pressurized hose
14, as is schematically shown in figure 4 . I n this embodiment the
clamp elements 27 are fitted to the channel-shaped holding
element 15 which carries the pressurized hose 14 and serve to
deform the end regions 28 of the pressurized hose 14 which
therefore do not contact the back rest profile 2. As a result the
pressurized hose 14 is not exposed to the side edges 26 of the
back rest profile 2. It has to be noted that the deformation
caused by the clamp elements 27 at the end regions 28 is
preferably deeper than a deformation caused by pivoting the
back rest profile 2 about a certain angle. The clamp elements 27
consist for example of two elements 29 and 30 fixed to one
another, which are fixed to another with a bolt connection. The
clamp elements 27 are arranged along the holding element 15 in
this embodiment and can form a clamping connection with the
holding element 15. The pressurized hose 14 can push the clamp
elements 27 with a force against the holding element 15. Such a
clamp connection allows to displace the clamp elements 27 along
the longitudinal direction L of the back rest 1 and to position the
clamp elements 27 in a desired radial position with respect to the
pressurized hose 14. The clamping elements 27 can be arranged
in other ways according to other variants, for example can be
fixed to the carrier element 5 with a bolt connection.
As can be seen from figure 4, the back rest profile 2 is
longer than the width of the plane of warp threads 10 on the
back rest profile 2. This results in that the end zones 31 of the
back rest profile 2 near the side edges 26 are unused by the
warp threads 10. These end zones 31 can however also be
supported by the pressurized hose 14. By providing the clamp
elements 27, which force the pressurized hose 14 away from the
back rest profile 2, the end zones 31 of the back rest profile 2
are not loaded by the pressurized hose 14 and therefore unequal
loads by the warp threads 10 over the longitudinal direction L of
the back rest profile 2 are compensated for.
As shown in figure 3 the support element 4 that is formed
by a curved plate is fixed to the carrier element 5 via an
intermediate piece 32 with bolt connections. The curved support
element 4 comprises a slot 6 for the back rest profile 2 defining
the position of the support point 7. Herein the position of the
support point 7 can for example in horizontal and/or vertical
position be adjusted by setting the support element 4 in a
different position with respect to the plate-formed intermediate
piece 32, as is for example shown in dashed line in figure 3. By
adjusting that position of the support element 4 in horizontal
and/or vertical direction the inclination of the back rest profile 2
can as well be adjusted. For this purpose, according to a variant
also the intermediate piece 32 can be set in multiple positions
with respect to the carrier element 5.
Figure 5 shows an embodiment comparable to the
embodiment of figures 3 and 4, wherein a guiding element 21 is
provided upstream of the back rest profile 2 which is embodied
as a guiding roll 33. I n this embodiment the carrier element 5 is
connected to the frame 35 of the weaving machine via a resilient
intermediate element 34, so that the carrier element 5 is
arranged moveable with respect to the frame 35 of the weaving
machine. The intermediate element 34 is provided with a sensor
device 36 which allows to measure forces which are defined by
the tension in the warp threads 10. Herein the signal of a sensor
device 36 may be applied to control the rotating movement of
the warp beam and/or to control the pressure in the pressurized
hose 14 via a control unit 17. I n this embodiment the guiding roll
33 is fitted to the frame 35 of the weaving machine. Herein the
sensor device 36 measures essentially only the forces which are
applied on the back rest profile 2. By fitting the guiding roll 33 to
the frame 35 the direction of the forces measured by the sensor
device 36 stays almost equal, regardless of the size and/or
position of a warp beam. I n this embodiment the control unit 17
can cooperate with a input unit 37 for entering data and a
display unit 38 for displaying data.
Figure 6 shows an embodiment comparable to the one
shown in figure 1, wherein a guide section 11 is arranged on a
guiding roll 39 which is arranged on the back rest profile 2.
Herein the guiding roll 39 which is arranged on the back rest
profile 2 provides the guide section 11 arranged on the back rest
profile 2 for the guiding of the warp threads 10. The guiding roll
39 is embodied so that its weight is minimised. Therefore the
guiding roll 39 comprises for example a hollow, thin-walled roll
element 40 which is supported in a holder 42 by journal bearings
4 1 according to an embodiment. I n the embodiment shown the
guiding roll 39 is arranged on a back rest profile 2 comprising a
fold 24 via the holder 42. The force applied by the pressurized
hose 14 is applied essentially halfway between a guide section
11 and a support point 7. Herein the warp threads 10 are guided
directly from the warp beam to the back rest 1, wherein the
direction of the warp threads 10 is defined by the diameter of
the warp beam. Herein the support element 4 comprises a front
guiding zone 43 which can shield the warp threads 10 from the
support point 7 of the back rest profile 2.
Figure 7 shows another embodiment, comprising a guiding
roll 39 provided on a plate-formed back rest profile 2 comprising
at the middle section 16 a plate-formed flat section 44 which
makes contact with the pressurized hose 14. As shown in
figure 7 two guiding rolls 39 and 33 are provided for guiding the
warp threads 10 which are embodied essentially equal. A guiding
roll 39 is fitted to the back rest profile 2 and is moved with the
back rest profile 2 to keep contact with the warp threads 10. The
other guiding roll 33 functions as a guiding element 21 upstream
of the back rest profile 2 and is installed stationary on the
intermediate piece 32 via a supporting plate 45. I n this
embodiment as well the guiding roll 39 as the guiding roll 33 are
supported by roller bearings 46. Herein also a stop element 23 is
arranged on the back rest profile 2 which can cooperate with the
holding element 15.
Figure 8 shows an embodiment wherein the holding
element 15 can be arranged in a number of positions with
respect to the carrier element 5. Herein a first position of the
holding element 15 is shown in full line, while a second position
of the holding element 15 is shown in dashed line. By setting the
position wherein the holding element 15 is arranged on the
carrier element 5, the location 13 where the resilient force
element 3, more in particular the pressurized hose 14, acts on
the back rest profile 2 can be set. Therefore a number of
boreholes 47 provided with screw thread are arranged in the
carrier element 5 for example, which can cooperate with bolts 48
extending through the holding element 15 and which allow to set
the holding element 15 in different positions with regard to the
carrier element 5.
Figure 9 shows an embodiment wherein a safety device 49
is provided for detecting an excessive movement of the back rest
profile 2. The safety device 49 shown comprises a sensor 50
allowing to detect if the back rest profile 2 reaches a defined
limit position. The sensor 50 is arranged for example near the
stop element 23 at a side edge 26 of the back rest profile 2 on
the carrier element 5, so that the sensor 50 can generate a
signal when the back rest profile 2 approaches the stop element
23. This signal can be used for example to stop the weaving
machine or to give a warning signal, for example via the control
unit 17 and/or the display unit 38.
Figure 10 shows an embodiment with a back rest profile 2
comparable to figure 3 wherein the carrier element 5 can be
moved back and forth during weaving by a drive device 51, for
example an eccentric drive to give the back rest profile 2 a so
called "easing motion" movement. The drive device 51 can
comprise an eccentric 52 and linking rods 53, 54 and 55,
wherein the linking rod 55 is fitted to the frame 35 of the
weaving machine via a support 56, for example. Herein the back
rest profile 2 moves together with the carrier element 5 and the
linking rod 54 and the back rest profile 2 moves with regard to
the carrier element 5 by pivoting the back rest profile 2 with
regard to the support element 4 . Herein also warp threads 10
are shown which are guided from a warp beam 57 via the back
rest 1 to schematically shown heald frames 58. Additionally or
alternatively the carrier element 5 can also be installed resiliently
to allow for an additional movement of the back rest profile 2,
for example using the spring 59 shown in dashed line. If in this
case the eccentric 52 is not driven or the linking rod 53 is fitted
fixedly to the frame 35, the carrier element 5 is only installed
resiliently via the spring 59. If the spring 59 is not provided and
the linking rod 55 is fitted fixedly to the frame 35, the carrier
element 5 is only driveable via the driving device 51.
Figures 11 and 12 show a resilient force element 3 which is
embodied as a series of springs 60, for example spiral springs,
which are each installed on two pins 61 and 62, wherein a pin 62
is fixed to the back rest profile 2 and a pin 61 is fixed to the
carrier element 5. The pins 61 are arranged on a holding
element 15, wherein the holding element 15 can be fixed to the
carrier element 5 in defined positions with regard to the carrier
element 5. The pins 62 are also arranged on a holder 63 which is
fitted to the back rest profile 2. De springs 60 are installed with a
suitable inclination, corresponding to a position of the back rest
profile 2 and the warp threads 10. As can be seen in figure 12,
the different springs 60 are installed next to one another along
the longitudinal direction L of the back rest profile 2. The number
and/or the type of springs 60 is chosen for realising a required
force to be applied by the force element 3 between the carrier
element 5 and the back rest profile 2. Herein the number of
springs 60 preferably is arranged divided according to the
longitudinal direction L of the back rest profile 2.
I n figure 13 the resilient force element 3 is embodied as a
number of pressurized hoses 64 which are installed in parallel to
one another and function together similarly as the pressurized
hose 14. The different pressurized hoses 64 can be arranged in
an envelope 65 which is arranged in the holding element 15 and
makes contact with the back rest profile 2. Herein the pressure
inside each of the different pressurized hoses 64 can be set
suitably by a control unit 17 or regulated to obtain a desired
force on and a desired position of the back rest profile 2 at a
certain warp tension of the warp threads 10.
Figure 14 shows a back rest 1 which can be applied for
weaving for example fantasy cloth wherein the warp threads 10
are woven at a relatively low warp tension or for weaving terry
cloth wherein warp threads are woven with a relatively low warp
tension from one of the warp beams. Herein warp threads 10 are
guided via a guiding element 21 and the guide section 11 of the
back rest profile 2 according to the direction of movement B
towards the heald frames. I n this embodiment the warp threads
10 are guided almost about an angle of 90° around the guide
section 11. The supported section 8 is supported at the support
point 7 and is situated almost above the free section 12 with the
guide section 11. If the required warp tension is relatively low,
the location 13 where the force is applied by the resilient force
element 3 can be chosen relatively close to the support point 7.
Therefore the pressurized hose 14 with the holder 15 is installed
relatively close to the support element 4 .
I n figure 15 a back rest profile 2 and a pressurized hose 14
are shown in full line at a certain tension in the warp threads 10,
while in dashed line the back rest profile 2 and the pressurized
hose 14 are shown at a higher tension in the warp threads 10.
By the higher tension in the warp threads 10 as well the back
rest profile 2 as the pressurized hose 14 deforms. By the
deformation of the pressurized hose 14 the location 13 where
the back rest profile 2 makes contact with the pressurized hose
14 is displaced in a direction towards the holding element 15 by
what the guide section 11 of the back rest profile 2 deflects in
the direction towards the pressurized hose 14. Because
furthermore the back rest profile 2 bends around the pressurized
hose 14 by the force Fl of the warp threads 10, an additional
elastic deformation is imposed to the back rest profile 2, so that
the back rest profile 2 is deflected even more towards the
pressurized hose 14 and shows a shape as indicated in dashed
line. The force Fl herein is counteracted by the force F2 at the
location 13 and by the forces F3 and F4 at the support point 7.
Herein the location 13 of applying the force F2 by the resilient
force element 3 on the back rest profile 2 is situated between the
support point 7 where the forces F3 and F4 are applied and the
location 66 at the guide section 11 where the force Fl is applied
by the warp threads 10. The location 13 herein is distanced as
well from the support point 7 as from the location 66. The
location 13 herein is situated essentially halfway between the
support point 7 and the location 66.
Figure 16 shows a back rest 1 wherein warp threads 10 are
woven at a first warp tension and warp threads 75 are woven at
a second warp tension, for example for weaving fantasy cloth or
for weaving terry cloth. For this purpose, in addition to a back
rest 1 similar to the back rest 1 of figure 1, a second back rest
67 is provided with a back rest profile 68 on which several
holders 69 are arranged along the longitudinal direction of a
guide element 70, for example a guiding roller, for supporting
the guide element 70 providing a guide section 11. Each holder
69 has a small width in the longitudinal direction of the guide
element 70 and is able to protrude between warp threads 10 and
warp threads 75. The back rest profile 69 has two profile
sections 71 and 72 arranged almost perpendicular to each other.
The profile section 71 is contacting a pressurized hose 74 at a
location 83, while the profile section 72 is contacting the
pressurized hose 74 at a location 84. The pressurized hose 74 is
acting as a resilient force element 3. Each location 83 and 84 is
arranged between the support point 7 and the guide section 11
and distanced from both the support point 7 and the guide
section 11. The pressurized hose 74 is also held by a holding
element 73 and is supported by a support element 76 via a
wear-resistant protection 9. The second back rest 67 is
supported on a support element 77.
Figure 17 shows a backrest 67 similar to the back rest 67
of figure 16, wherein the back rest profile 68 is contacting the
pressurized hose 74 at one location 13, similar to the back rest
profile 2 of figure 1 contacting the pressurizes hose 74 at one
location 13. The backrest 67 of figures 16 and 17 can also be
combined with clamp elements 27 of figures 3 to 5, with a stop
element of figure 1, with a safety device of figure 9 or with parts
of other embodiments.
Figure 18 and 19 show a back rest 1 wherein the
pressurized hose 14 is supported by a sensor element 78
contacting the pressurized hose 14 over a small length in the
longitudinal direction of the pressurized hose 14. The sensor
element 78 has a contact element 79 and a support plate 80
fixed with fixing elements 81 to the carrier element 5. Between
the support plate 80 and the contact element 79 a sensor 82 is
provided, which sensor 82 also supports the contact element 79
with respect to the support plate 80. The contact element 79
extends through an opening 86 in the holding element 15. The
sensor 82 is, for example, a metal block onto which strain
gauges for measuring the tension in the block are provided . The
measured tension in the metal block is a measure for the force
exerted by the pressure hose 14 on the contact element 79,
which is a measure of the tension in the warp threads 10. The
sensor device 78 allows to obtain a measure for the warp tension
and cooperates with the pressurized hose 2 by contacting the
pressurized hose 2. With a sensor element 78 the warp tension
can be measured without hindering or interfering with the warp
threads 10, for example by introducing additional friction or
bending. Fixing the sensor element 78 to the carrier element 5 is
advantageous to keep the sensor element 78 away from the
warp threads 10 and the back rest profile 2. This way the sensor
82 is protected from undesired influences from its environment
and additional space for arranging a warp tension measurement
system is not needed. Using a sensor element 78 does not
require an operator to count the number of warp threads 10 onto
which the tension is measured, as is the case with sensor
elements designed to be in direct contact with the warp threads
10. A number of such sensor elements 78 can be used, for
example several sensors arranged across the longitudinal
direction of the pressurized hose 14. This can be used, for
example to measure the warp tension in warp threads from
different warp beams arranged next to one another, or to
measure the warp tension in different areas across a longitudinal
direction of the back rest 1.
Figure 20 shows an alternative embodiment of the device
of figure 18 wherein the contact element 79 of the sensor
element 78 is supported by the sensor 82 relative to the
intermediate piece 32 of the back rest 1. The contact element 79
extends through an opening 85 in the holding element 15 and
contacts the pressurized hose 14.
According to another embodiment, a sensor element, for
example a piezo-sensor element can be arranged on the holding
element 15, 73 or on the back rest profile 2, 68 contacting the
pressurized hose 14, 74 for measuring the force exerted due to
the tension in the warp threads 10, 75. A sensor element 78 can
also be used in combination with a back rest 67 as shown in
figures 16 and 17.
Since the back rest profile 2 is able to pivot about the
support point 7, the back rest profile 2 is also able to deform
between the support point 7 and the location 13, by what the
guide section 11 deflects more towards the pressurized hose 14.
Furthermore the back rest profile 2 is able to deform between
the location 13 and the guide section 11 by what the guide
section 11 deflects still even more. This means that because of a
leverage the guide section 11 is displaced more than the location
13 and that still an additional displacement is obtained by the
deformation of the back rest profile 2, wherein the back rest
profile 2 is able as well to pivot at the support point 7 as to be
bent around the pressurized hose 14. A similar deformation of as
well the resilient force element 3 as of the back rest profile 2 can
be obtained if a number of springs 60 is used as resilient force
element 3 or if a number of pressurized hoses 64 is used as
resilient force element 3.
The back rest according to the invention shown in the
claims is not limited to the described embodiments shown and
described as example, but may also comprise variants and
combinations of these exemplary embodiments which fall under
the claims.
Claims.
1. Back rest for guiding warp threads (10, 75) in a weaving
machine comprising a back rest profile (2, 68) provided with a
guide section (11) for guiding warp threads (10, 75), wherein
the back rest (1) comprises a resilient force element (3) for
supporting the back rest profile (2), characterized in that the
back rest profile (2) is arranged pivotable at a support point (7)
and that a location (13, 83, 84) of application of force (F2) by
the resilient force element (3) on the back rest profile (2) is
arranged between the support point (7) and the guide section
(11) and is distanced from both the support point (7) and the
guide section (11).
2. Back rest according to claim 1, characterized in that the
location (13, 83, 84) of application of force (F2) of the resilient
force element (3) on the back rest profile (2, 68) is arranged
essentially halfway between the support point (7) and the guide
section (11).
3. Back rest according to claim 1 or 2, characterized in that
the back rest profile (2) is formed as an elastically deformable
plate having a thickness of between about 0,5 mm and about
3 mm.
4 . Back rest according to one of the claims 1 to 3,
characterized in that the back rest profile (2) is embodied with a
curved free section (12) onto which the guide section (11) for
guiding the warp threads (10) is provided.
5. Back rest according to one of the claims 1 to 4,
characterized in that the supported section (8) of the back rest
profile (2) is pivotably arranged at a support point (7) in a
support element (4).
6. Back rest according to claim 5, characterized in that the
position of the support element (4) is settable.
7. Back rest according to claim 5 or 6, characterized in that
between the supported section (8) of the back rest profile (2)
and the support element (4) a wear-resistant protection (9) is
arranged to protect both the supported section (8) of the back
rest profile (2) and the support element (4) against wear.
8. Back rest according to one of the claims 1 to 7,
characterized in that the resilient force element (3) comprises a
series of springs (60) installed along the longitudinal direction
(L) of the back rest profile (2).
9. Back rest according to one of the claims 1 to 7,
characterized in that the resilient force element (3) comprises at
least one pressurized hose (14, 64, 74).
10. Back rest according to claim 9, characterized in that a
clamp element (27) is provided which deforms the pressurized
hose (14, 64, 74) by forcing an end region (28) of the
pressurized hose (14, 64, 74) away from the back rest profile
(2).
11. Back rest according to claim 9 or 10, characterized in that
the back rest profile (2) comprises a folded middle section (16)
which makes contact with the pressurized hose (14, 64, 74).
12. Back rest according to one of the claims 1 to 11,
characterized in that a control unit (17) is provided for
automatical setting, adjusting and/or regulating the pressure
inside a pressurized hose (14, 64, 74).
13. Back rest according to one of the claims 1 to 12,
characterized in that a holding element (15) is provided for
holding the resilient force element (3) in a defined position.
14. Back rest according to one of the claims 1 to 13,
characterized in that a stop element (23) is provided for limiting
a movement of the back rest profile (2, 68).
15. Back rest according to one of the claims 1 to 14,
characterized in that a safety device (49) is provided for
detecting an excessive movement of the back rest profile
(2, 68).
16. Back rest according to any one of the claims 9 to 15,
characterized in that a sensor device (78) for determining the
warp tension is provided that cooperates with the pressurized
hose (2, 64, 74).