The invention relates to a back rest for guiding warp threads in a weaving machine. In 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 . In 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.

In 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. In one embodiment, the support element is mounted stationary on the weaving machine via a carrier element. In other embodiments, the support element is arranged moveable with respect to the weaving machine via a carrier element. In 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. In 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. In 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. In 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.

In 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.

In 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. In 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 . In 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. In 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. In preferred embodiments, a multi-layer hose is used. In 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. In 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. In 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. In 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. In 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. In 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. In 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. In 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. In 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. In preferred embodiments, a warning signal is generated, when reaching a limit position was detected. In other embodiments, the weaving machine is stopped in such a case. In 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. In 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. In one embodiment, the guiding element is embodied as a profile comprising a rounded guiding surface. In other embodiments, a guide roll is provided as guiding element. In 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. In one embodiment, the warp tension is measured indirectly by measuring the pressure in the pressurized hose.

In 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. In 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.

In 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.

In 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.

In 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. In 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. In 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. In 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. In 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 41 according to an embodiment. In 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. In 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.

In 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. In 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.

In 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.