Auxiliary weft yarns drawing-off device and process, weaving loom equipped with such a device

Abstract

 This device (50), for drawing auxiliary weft yarns (31) out of a fabric (2) on a loom (1), comprises at least one draw-off unit (51) located next to a first longitudinal edge (21) of the fabric and having means (6) to exert, on at least one auxiliary weft yarn (31), a drawing effort. This device also comprises at least one locking unit (52) adapted to hold the fabric (2) in its position along a direction (B-B') substantially parallel to the weft yarns in the fabric (2).

Description

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to a device for drawing auxiliary weft yarns out of a fabric on a loom, that is when the fabric is being woven. This invention also relates to a loom equipped with such a device and to a process for drawing auxiliary weft yarns out of a fabric on a loom.

BACKGROUND OF THE INVENTION

[0002] In the field of weaving machines, and as shown on figure 1, it is known to form loops with some pile warp yarns 1002 around auxiliary weft yarns 1001 that are kept away from a backing fabric 1003 made of ground weft yarns 1004 and ground warp yarns 1005 by lancets 1006 that extend from the back of the shed through the reed to at least the beating point. The auxiliary weft yarns 1001 must be removed and, in practice, they are drawn-off from the fabric.

[0003] BE-A-1 014 269 considers two approaches to draw-off auxiliary wefts from a fabric. According to a first approach, a cutting blade cuts the auxiliary weft yarns in their middle, so that two parts of the weft yarns are pulled out of the fabric, at the level of two longitudinal edges of the fabric, by grippers having a forward and backward movement. In practice, it is difficult to cut the auxiliary weft yarns in the middle and this requires a dedicated knife. This can damage the fabric. According to a second approach, the auxiliary weft yarns are drawn-off at the level of one edge of the fabric. In such a case, as the length of the auxiliary weft yarns corresponds to the total width of the fabric, friction forces apply on a large portion of the yarns. In particular, the loops located on the drawing-off device side may be subjected to overheating and damaged. The friction forces also induce a shear stress in the fabric which may run with an oblique movement, that is deviate from its normally straight path within the loom.

SUMMARY OF THE INVENTION

[0004] The invention aims at solving these problems with a new device for drawing auxiliary weft yarns out of a fabric, without needing to cut the auxiliary weft yarns in the middle, whereas the quality of the fabric can be improved.

[0005] The invention concerns a device for drawing auxiliary weft yarns out of a fabric on a loom, this device comprising at least one draw-off unit located next to a first longitudinal edge of the fabric and having means to exert, on at least one auxiliary weft yarn, a drawing effort. This device is characterized in that it also comprises at least one locking unit adapted to hold the fabric in its position along a direction substantially parallel to the weft yarns in the fabric.

[0006] Thanks to the invention, the locking unit holds the fabric in position, which enables it to resist the friction forces induced by the drawing-off movement of the auxiliary weft yarns on the totality of their length. In other words, the locking unit prevents the fabric from going along an oblique way that could result from the shear stress induced by friction forces generated by the displacement of the auxiliary weft yarns within the loops of the fabric.

[0007] According to further aspects of the invention, which are advantageous but not compulsory, the device for drawing auxiliary weft yarns might incorporate one or several of the following features:

• The locking unit is adapted to exert on the fabric and next to a second longitudinal edge of the fabric a locking effort.
• The locking unit comprises a gripper sub-unit and driving means adapted to move the gripper sub-unit along a direction substantially parallel to the weft yarns in the fabric.
• A sensor is adapted to detect the position of at least one longitudinal edge of the fabric and some means are provided to control the driving means of the locking unit in relation to an output signal of the sensor.
• The gripper sub-unit comprises two rollers and means to press the rollers towards each other. Advantageously, at least one of these rollers is provided with needles adapted to penetrate the fabric.
• The locking unit is offset, along a direction of progression of the fabric in the loom, with respect to the draw-off unit.
• The draw-off unit includes a carriage provided with a hook-forming gripper and moved by driving means along a direction substantially parallel to the weft yarns in the fabric. This enables the drawing effort exerted by the draw-off unit to be substantially parallel to the weft yarns in the fabric.
• The hook-forming gripper is provided with a pulley rotatively supported by a bearing and forming a reception surface for at least one auxiliary weft yarn.
• A winder is dedicated to the winding of a special false selvedge whose weft yarns are formed exclusively by auxiliary weft yarns.

[0008] The invention also concerns a weaving loom equipped with a device as mentioned here above for drawing auxiliary weft yarns out of a fabric when such a fabric is being woven on this loom.

[0009] Such a loom is more reliable and produces fabrics of higher quality than the looms of the prior art.

[0010] According to an advantageous aspect of the invention, such a loom may comprise dedicated means, preferably Leno heddles, to weave a special false selvedge whose weft yarns are formed exclusively by auxiliary weft yarns.

[0011] Finally, the invention concerns a process, which can be implemented with a device as mentioned here-above for drawing auxiliary weft yarns out of a fabric on a loom and where auxiliary weft yarns are all pulled out of the fabric at the level of a first longitudinal edge of the fabric, characterized in that the fabric is held in its position along a direction substantially parallel to the weft yarns in the fabric.

[0012] According to further aspects of the invention, which are advantageous but not compulsory, this process might incorporate one or several of the following features:

• A locking effort is exerted on the fabric next to a second longitudinal edge of the fabric, when at least one auxiliary weft yarn is being pulled out of the fabric.
• When they are pulled out of the fabric, the auxiliary weft yarns remain partly engaged within a false selvedge woven with all auxiliary weft yarns and with some dedicated warp yarns, according to a Leno type weave.
• The auxiliary weft yarns are pulled by a gripper moved, between two end positions, along a direction substantially parallel to the weft yarns in the fabric, with a velocity profile such that its speed increases, from a first value to a second value, when the gripper moves away from the fabric and such that the gripper reaches its second speed value at a position where it has travelled more than 50% of its path between a first end position, next to an edge of the fabric, and a second end position, away from this edge.
• The auxiliary weft yarns are pulled out of the fabric by a hook forming gripper driven by a carriage having a back and forth translation movement on a length which has about the same value as half of the width of the fabric.
• A locking unit adapted to exert the locking effort on the fabric is periodically deactivated and moved towards a center zone of the fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will be better understood on the basis of the following description which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures

• figure 1 is a view illustrating a carpet weaving process with auxiliary weft yarns and lancets,
• figure 2 is a schematic perspective view of some parts of a loom according to the invention incorporating a drawing-off device according to the invention,
• figure 3 is a view on a larger scale of detail III on figure 2,
• figure 4 is a view similar to figure 3 when a carriage of a draw-off unit is in another position,
• figure 5 is a view corresponding to detail V on figure 2, at a larger scale and according to another angle,
• figure 6 is a top view of a hook-forming gripper of the draw-off unit shown on figures 2 to 4, with an auxiliary weft yarn wounded around a pulley,
• figure 7 is an enlarged section along line VII-VII on figure 6,
• figure 8 is an enlarged partial front view of a special selvedge used with the loom of figures 1 to 5,
• figure 9 is a schematic representation of the velocity and position profiles of a carriage of the draw-off unit, as a function of time and
• figure 10 is a top view similar to figure 6 for a hook-forming gripper according to a second embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0014] A carpet weaving loom 1 is partially and schematically represented on figure 2 as seen from its back or feeding side. Loom 1 includes a series of partially represented heddle frames 11 each carrying several heddles 12 only one of which is represented on figure 2 for the sake of simplicity. Frames 11 are driven by non-represented means in order to move binding warp yarns 13 so as to form a ground shed for the backing of a fabric 2 to be woven on loom 1. A non represented rapier introduces ground weft yarns 14 in the ground shed in order to form the backing fabric, with the binding warp yarns 13. The movement of this rapier is represented by arrow A₂.

[0015] Jacquard heddles 15 are driven by a non represented Jacquard mechanism and cooperate with pile warp yarns 16 in order to form the pile shed. Lancets 17 are arranged within the shed and form a support for some auxiliary weft yarns 31 which are introduced within the pile shed by a second non represented rapier whose movement is represented by arrow A₃. One lancet 17 is represented on figure 2, for the sake of clarity. Several lancets are actually used. Therefore, the auxiliary weft yarns can lie on the respective lancets 17, as shown on figure 1.

[0016] Warp yarns 13 and ground weft yarns 14 form together the backing of a fabric 2, for instance a carpet provided with loops. 21 and 22 denote respectively the longitudinal edges of fabric 2 shown respectively on the left and on the right of this fabric on figure 2. 23 denotes the front side of fabric 2 and 24 its backside. Front side 23 is provided with loops similar to the loops 1002 of figure 1.

[0017] A-A' denotes the direction of progression of fabric 2 within loom 1. This direction is rectilinear and vertical on a part of the path of fabric 2 on figure 2 where fabric 2 forms a vertical plane. B-B' denotes a direction perpendicular to direction A-A' and comprised within the plane of fabric 2 when direction A-A' is vertical. Warp yarns 13 extend along direction A-A'. Ground weft yarns 14 and auxiliary weft yarns 31 extend along direction B-B' in the vertical position of fabric 2

[0018] A device 20 is provided on loom 1 and devoted to the weaving of a special false selvedge 25 for fabric 2. Device 20 is represented in a schematic way on figure 2 and comprises heddle 18 as means to move yarns 19 which are woven with the auxiliary weft yarns 31 introduced by the second rapier in the pile shed. In other words, false selvedge 25 is formed by all auxiliary weft yarns 31 and some dedicated warp yarns 19 driven by device 20.

[0019] As known by the people skilled in the art of weaving, device 20 may include two heddles, each provided with lifting heddle and one doup. These two heddles are advantageously driven by the Jacquard mechanism.

[0020] Device 20 can also be formed of a mechanism having discs oscillating about a weft wise axis and provided with apertures for warp yarns 19, or any kind of mechanism that permits to cross warp yarns between them in a weave. As explained here-after with respect to figure 8, a Leno type weaving pattern is used for warp yarns 19, which improves the resistance of false selvedge 25 to an effort applied on weft yarns 31.

[0021] Non represented means are also used to weave standard false selvedges next to each longitudinal edge 21 or 22 with dedicated warp yarns and with ground weft yarns 13. The standard false selvedge 26 close to edge 21 is separated by non represented cutting means downstream the draw-off unit. The standard false selvedge close to edge 22 is not represented since it is cut at the level of the beating point.

[0022] Once fabric 2 has been woven, auxiliary weft yarns 31 extend in the main part of fabric 2, between edges 21 and 22, and up to false selvedge 25. They lie perpendicularly to direction A-A'.

[0023] A device 50 is provided on loom 1 in order to draw-off or pull the auxiliary weft yarns 31 out of fabric 2. This device 50 comprises a draw-off unit 51 mounted next to longitudinal edge 21 of fabric 2 and a locking unit 52 mounted next to longitudinal edge 22.

[0024] Draw-off unit 51 comprises an elongated guide bracket 53 whose longitudinal axis X₅₃ is substantially parallel to the weft yarns 14 and 31 in fabric 2, that is perpendicular to direction A-A' and parallel to direction B-B'.

[0025] A servomotor 54 is mounted on bracket 53 next to its extremity opposite to fabric 2 and drives a belt 55. Belt 55 goes around a idle pulley 56 mounted on bracket 53 in the vicinity of edge 21. A carriage 58 is fast with belt 55 and can be moved between the positions represented respectively on figures 2 and 4, that is between a position close to engine 54 and a position close to edge 21, and vice-versa. Carriage 58 slides on a rail 57 fast with bracket 53 and parallel to axis X₅₃.

[0026] Device 50 also includes an electrical winder 59 adapted to wind the special false selvedge 25 when it comes out of a guide member 60 located next to edge 21 and held in position by a bracket 62. In other words, the false selvedge 25 enters guide member 60 and is then pulled by winder 59, which enables to separate false selvedge 25 from the main part of fabric 2.

[0027] False selvedge 25 can then be directed towards a bin 61.

[0028] On figures 2 to 4, auxiliary weft yarns 31, which are fast with false selvedge 25, are only partially represented. In particular, auxiliary weft yarns 31 are not represented on the part of false selvedge 25 which is separated from the main part of fabric 2. On figures 2 and 3, only one such auxiliary weft yarn 31 is represented, namely an auxiliary weft yarns being pulled out of fabric 2.

[0029] Carriage 58 is provided with a hook-forming gripper 65 which comprises an arm 66 fixed by screws 67 on carriage 58 and a hook part 68 located at the end of arm 66 directed towards edge 21 and where an idle pulley 69 is rotatively mounted around an axis X₆₉ which is oblique with respect to the longitudinal axis X₆₆ of arm 66. Axis X₆₉ is defined by a support member 70 fast with arm 66. Pulley 69 is mounted with respect to member 70 thanks to a roller bearing 71, which facilitates rotation of pulley 69 around axis X₆₉. Instead of roller bearing 71, one can also use a needle bearing or a ball bearing.

[0030] On figure 2, for the sake of clarity, hook part 68 is represented in a simplified way, as a hook. The structure of this part can be derived from figures 4, 6 and 7.

[0031] A deflector 72 is also mounted at the end of arm 66 next to pulley 69, at the level of hook part 68. Deflector 72 aims at guiding an auxiliary weft yarn 31 towards the radial external surface 69A of pulley 69 when carriage 58 moves arm 66 towards edge 21, in such a way that deflector 72 comes into contact with this yarn. In other words, due to the binding of false selvedge 25 at the level of guide member 60, one auxiliary weft yarn extending between this false selvedge and the main part of fabric 2 is on the path of hook part 68, so that it can be partly wounded around surface 69A after it has been guided by deflector 72. Then, when carriage 58 is moved by belt 55 towards servomotor 54, auxiliary weft yarn 31 is pulled by hook part 68 out of fabric 2. Since a part of this auxiliary weft yarn is fast within false selvedge 25, the traction effort T₁ exerted on a weft yarn 31 by pulley 69 is such that the part of the yarn 31, which is still engaged in the loops of fabric 2, is pulled out of these loops. Effort T₁ is substantially parallel to weft yarns in fabric 2, that is to direction B-B', which facilitates pulling of auxiliary weft yarns 31 out of fabric 2.

[0032] When the carriage 58 moves from the position of figure 4 to the position of figure 2, the yarn 31 makes a loop between false selvedge 25 and edge 21, so that the length L₅₈ of the path of carriage 58 between its two extreme positions is about the same as half of the width ℓ₂ of fabric 2 taken between its two edges 21 and 22. The fact that the value of length L₅₈ is about half of the value of width 1₂ means that the difference between L₅₈ and I₂/2 is less than 20%. In other words, with a movement of the carriage 58 slightly larger than half of width ℓ₂, it is possible to pull a weft yarn 31 completely out of fabric 2, from edge 21.

[0033] Carriage 58 is provided with no positively driven accessory. Therefore, carriage 58 does not need to be fed with power and can be very light, as compared to the case where it would carry a clamp.

[0034] Friction forces resist the extraction of a weft yarn 31 out of fabric 2. These friction forces could locally deform fabric 2 and cause it to deviate from its path.

[0035] In order to avoid this, locking unit 52 comprises two rollers 81 and 82 respectively mounted on two arms 83 and 84 of a clamp 85. Both rollers rotate around axes X₈₁ and X₈₂ that are parallel to direction B-B'. Clamp 85 can press rollers 81 and 82 one against the other.

[0036] Roller 81 lies against the front side 23 of fabric 2, whereas roller 82 lies against its backside 24. Roller 82 is provided with needles 82A which can at least superficially penetrate within fabric 2, thus ensuring efficient guiding of fabric 2 by the pair of rollers 81 and 82.

[0037] When they are pressed against each other, rollers 81 and 82 exert a locking effort E on fabric 2 that can only move along direction A-A' but is locked along direction B-B'. This effort E prevents the fabric to run obliquely due to the friction forces occurring when one yarn 31 is pulled out of the loops of a row of loops on front side 23.

[0038] Effort E is basically a pinching effort.

[0039] In other words, thanks to unit 52, it is possible to resist friction forces between yarns 31 and loops of fabric 2 that could be prejudicial to the handling of the fabric 2 in the loom.

[0040] However and since the effort E must be limited to avoid that the needles 82A damage the fabric 2, clamp 85 forms a gripper sub-unit which is movable parallely to direction B-B' and is piloted by a linear actuator 86 in order to correct the position of the fabric along the direction B-B' in case it deviates from its normal path.

[0041] A contact sensor 90 is provided on bracket 53. Sensor 90 delivers to an electronic control unit 100, a signal S₉₀ representative of the position of edge 21 along direction B-B', next to pulley 56. Unit 100 generates, on the basis of signal S₉₀, an electronic control signal S₁₀₀ which is sent to actuator 86 in order to position clamp 85 along direction B-B' in relation with the actual position of edge 21. The clamp 85 is moved by the actuator 86 along direction B-B' with the amount of the shift of position of edge 21 so that edge 21, recovers its normal position. In other words, it is possible to react, with unit 52, to a movement of edge 21 towards servomotor 54 by sending to actuator 86 a signal S₁₀₀ to pull clamp 85 backwards on figure 4, that is away from bracket 53, which induces that a traction effort T₂ is exerted on fabric 2, next to edge 22, so that edge 21 is brought back to a rectilinear configuration. Effort T₂ is parallel to direction B-B'

[0042] Thanks to effort E, it is possible to pull on fabric 2, in order to resist the friction forces that tend to deviate fabric 2 towards bracket 53.

[0043] By successively applying this shift of position of unit 52, clamp 85 moves towards edge 22 and comes to a point where it is necessary to bring it back to a position that is closer to the opposite edge 21 of fabric 2, in order to avoid that the rollers 81 and 82 leave the fabric, which would make effort E inefficient. To this end, unit 52 is periodically deactivated and clamp 85 is opened. Then rollers 81 and 82 are moved by actuator 86 towards a center zone of fabric 2, that is towards edge 21. Clamp is then closed so that effort E is exerted closer to the center of fabric 2. Alternatively, a sensor, e.g. a switch, can be used to detect when rollers 81 and 82 come close to edge 22 and send a signal to unit 100 which then controls clamp 85 and actuator 86 to deactivate unit 52 and move the rollers towards the center of fabric 2.

[0044] A protecting cover 87 is arranged between a beam 88 supporting actuator 86 and the back side 24 of fabric 2, in order to avoid direct contact with the needles 82A.

[0045] Draw-off unit 51 and locking unit 52 are offset from each other along direction A-A'. More precisely, rollers 81 and 82 are offset with respect to hook-forming part 68 along direction A-A', so that locking effort E is exerted on a part of fabric 2 whose auxiliary weft yarns 31 have already been pulled out. One notes Δ₅ the distance between items 68, next to edge 21, and 81-82, next to edge 22, along direction A-A'. Distance Δ₅ can have a value between 10 and 40 mm, for a fabric having a width ℓ₂ between 2 and 4 m.

[0046] Unit 52 is located upward of unit 51, so that effort E is exerted on a part of fabric 8 where auxiliary weft yarns 31 have already been drawn-off by unit 51. Therefore, effort E does not brake or lock weft yarns 31 when they are pulled out of fabric 2 by gripper 65. In particular, needles 82A do not interfere with weft yarns 31.

[0047] In order for the hook part 68 of arm 66 to efficiently pull a weft yarn 31 out of fabric 2, it is necessary that the part of this weft yarn that belongs to false selvedge 25 is not pulled out of this false selvedge. In other words, false selvedge 25 must hold one end of each yarn 31 strongly enough the resist the traction T₁ exerted by the hook part 68.

[0048] To this purpose, and as shown on figure 8, auxiliary weft yarns are woven with two series of warp yarns 19A and 19B. A first series of warp yarns 19A extends substantially perpendicularly to the auxiliary weft yarns 31 and on a same side of these yarns, on the backside of these yarns on the example of figure 8.

[0049] A second series of warp yarns 19B extend around weft yarns 31 and warp yarns 19A. More precisely, each warp yarn 19B crosses each weft yarn 31 on the side opposite to warp yarns 19A. That is, if the warp yarns 19A are on the backside of the weft yarns 31 on figure 8, the warp yarns 19B cross weft yarns 31 on their front side. Moreover, the warp yarns 19B go around the warp yarns 19A on their backside, that is on their side opposite the weft yarns 31. In the weaving process, warp yarns 19A and 19B follow a Leno type weave.

[0050] If one weaves a false selvedge 25 in the way represented on figure 8, this induces a strong holding of the weft yarns 31 by the two series of warp yarns 19A and 19B.

[0051] As shown on figure 9, and in order to take into account the specificities of the forces exerted on the weft yarns 31, the speed S of carriage 58 in its movement from the position of figure 4 to the position of figure 2 progressively increases from a first value S₀ equal to 0 to a second maximum value S_max. This takes place in a first part M1 of the movement of carriage 58. Indeed, carriage 58 moves with a relatively low speed when high friction forces exist between an auxiliary weft yarn 31 and the loops of fabric 2 due to the fact that weft yarn 31 is held within the loops on most of its length. Yarn 31 is then subjected to a low jerk. Then, as the weft yarn 31 comes out of the loops of fabric 2, friction forces decrease and the speed of carriage 58 increases. Therefore, auxiliary weft yarns 31 are extracted from the main part of the fabric 2 in a progressive way.

[0052] After a predetermined period of time Δt₁ which corresponds to the first part M1 of its movement, carriage 58 reaches a maximum speed S_max where weft yarn 31 can be pulled out rapidly from the loops since only a relatively small part of each weft yarn 31 is still engaged within some of the loops. Carriage 58 keeps this maximum speed during a second part M2 of its movement, for a period of time Δt₂. In a third part M3 of the carriage movement, the carriage reverses its direction of travel and, in a fourth part M4, it decelerates on its way back to the position of figure 4. The duration Δt₃ and Δt₄ of the third and fourth parts M3 and M4 of the carriage movement can be short since the inertia of carriage 58 is low. The maximum speed S'_max reached by the carriage 58 on its way back to its position of figure 4 has a value higher than S_max, since no auxiliary weft yarn is handled during third and fourth parts M3 and M4 of its movement.

[0053] On figure 9, the lower curve represents, as a function of time, the position P of carriage 58 and gripper 65 between a first end position P₁ where they are next to edge 21, as shown on figure 4, and a second end position P₂ where they are away from fabric 2, as shown on figure 2.

[0054] As shown by curve P, the position of carriage 58, and hence of gripper 65 and hook part 68, has smooth transitions.

[0055] At the end of the first part M1 of the movement, the carriage 58 reaches an intermediate position P_A which is closer to position P₂ than to position P₁. The path between positions P₁ and P_A corresponds to more than 50% of the total path between position P₁ and position P₂.

[0056] In other words, the carriage 58 and the gripper 65 reach their maximum speed S_max after Δt₁, that is when the carriage has reached position P_A where it has travelled more than 50% of its path between the end positions P₁ and P₂.

[0057] With such velocity and position profiles, each auxiliary weft yarn 31 is progressively drawn out of the fabric 2, in particular in part M1 of its movement where it undergoes a high tension since it goes through many loops. Since the path between P₀ and P_A represents more than 50% of the total path between P₁ and P₂, an auxiliary weft yarn reaches its maximum extraction speed S_max when it is already more than 50% out of the fabric, that is when its tension has decreased. Heating of the auxiliary weft yarns is thus relatively low, as compared to what happens with looms of the prior art, and the risk that the auxiliary weft yarn cuts one or several loops, which can result from the speed and tension of the weft yarns in the prior art, is reduced.

[0058] In the second embodiment of the invention represented on figure 10, the gripper arm 66 is provided with a hook part 68 where a pulley 69 is incorporated within a support member 70. The external surface 69A of the pulley 69 is adapted to receive an auxiliary weft yarn 31. Pulley 69 is mounted on arm 66 thanks to a roller bearing. Its axis of rotation X₆₉ is perpendicular to a longitudinal axis X₆₆ of arm 66.

[0059] This invention induces several advantages. The carriage 58 is "passive", in so far as it does not carry any actuator to drive a clamp or anything similar. Therefore, carriage 58 can be light and move at a high speed. One does not need a cutting device to be used in the middle of the fabric, which avoids quality problems in the center of the fabric. Thanks to the locking unit 52, no movement along the direction B-B' results from the friction forces induced by the sliding movement of the auxiliary weft yarns 31 within the loops. The movement of the carriage is inline with the auxiliary weft yarns 31 in the fabric, so that friction between the auxiliary weft yarns and the loops can be minimized. The use of a roller bearing 71 between items 69 and 70 induces lower friction forces on the weft yarn 31 at the level of hook part 68 and, hence, relatively low forces on the false selvedge 25, so that the risk of brakeage of yarns 31 is diminished. The fact that one uses a hook forming gripper 65 induces that the total path L₅₈ of the carriage can be roughly half the width ℓ₂ of the fabric 2. Only one special false selvedge 25 is provided next to one edge 21 of the fabric which induces that not much material is wasted. Thanks to the speed profile M1-M4 adapted for the movement of carriage 58, the draw-off cycle is not twice as long as in the case where only half of an auxiliary weft yarn is taken out of the fabric next to each longitudinal edge. Moreover, as explained here-above, overheating of the auxiliary weft yarns is prevented, and risks to cut the loops with the auxiliary weft yarns are low.

[0060] According to some embodiments of the invention, the draw-off unit can be located on the taker-rapier side of the weaving machine, whereas the locking unit is located on the bringer-rapier side. Alternatively, the draw-off unit can be located on the bringer-rapier side, whereas the locking unit is located on the taker-rapier side.

[0061] The invention has been represented on a single-piece loom 1. It can also be implemented with a face-to-face weaving loom where loop-carpets or loop-and-pile carpets can be woven. In the case of face-to-face weaving, the device can include two draw-off units next to one edge of the fabric and one or two locking unit next to the other edge.

[0062] The contact sensor 90 may be located next to edge 21 or next to edge 22 or two sensors can be used. Sensor 90 is represented on the figures as a mechanical sensor. However, other kinds of sensor can be used, e.g. optical sensors.

[0063] Instead of one weft yarn 31, the gripper 65 can pull several such yarns at a time, e.g. five or six.

[0064] Instead of, or in addition to, the special weaving pattern for false selvedge 25, one can use melt-yarns or ultrasonic welding to make the auxiliary weft yarns fast with this selvedge.

[0065] Instead of a servomotor 54 and a belt 55, any other type of electrical, hydraulic or pneumatic linear actuator may be used to drive the hook forming gripper 65.

Claims

1. A device (50) for drawing auxiliary weft yarns (31) out of a fabric (2) on a loom (1), this device comprising at least one draw-off unit (51) located next to a first longitudinal edge (21) of the fabric and having means (65) to exert, on at least one auxiliary weft yarn, a drawing effort (T₁), characterized in that this device also comprises at least one locking unit (52) adapted to hold the fabric in its position along a direction (B-B') substantially parallel to the weft yarns (31) in the fabric (2).

2. Device according to claim 1, characterized in that the locking unit (52) is adapted to exert, on the fabric (2) and next to a second longitudinal edge (22) of the fabric, a locking effort (E).

3. Device according to one of claims 1 or 2, characterized in that the locking unit (52) comprises a gripper sub-unit (85) and driving means (86) adapted to move the gripper sub-unit along a direction (B-B') substantially parallel to the weft yarns (31) in the fabric (2).

4. Device according to claim 3, characterized in that it comprises a sensor (90) adapted to detect the position of at least one longitudinal edge (21, 22) of the fabric (2) and means (100) adapted to control (S₁₀₀) the driving means (86) of the locking unit (85) in relation to an output signal (S₉₀) of the sensor.

5. Device according to one of claims 3 or 4, characterized in that the gripper sub-unit (85) comprises two rollers (81, 82) and means (85) to press the rollers towards each other.

6. Device according to one of the previous claims, characterized in that the locking unit (52) is offset (Δ₅), along a direction of progression (A-A') of the fabric in the loom (1), with respect to the draw-off unit (51).

7. Device according to one of the previous claims, characterized in that the draw-off unit (51) includes a carriage (58) provided with a hook-forming gripper (65) and moved by driving means (54, 55) along a direction (X₅₃, B-B') substantially parallel to the weft yarns (14, 31) in the fabric (2).

8. Device according to claim 7, characterized in that the hook-forming gripper (65) is provided with a pulley (69) rotatively supported by a bearing (71) and forming a reception surface (69A) for at least one auxiliary weft yarn (31).

9. Device according to one of the previous claims, characterized in that it includes a winder (59) dedicated to the winding of a special false selvedge (25) whose weft yarns are formed exclusively by auxiliary weft yarns (31).

10. A weaving loom (1) equipped with an auxiliary weft yarns drawing-off device (50) according to one of the previous claims.

11. A process for drawing auxiliary weft yarns (31) out of a fabric (2) on a loom (1), where all auxiliary weft yarns are pulled out of the fabric at the level of a first longitudinal edge (21) of the fabric, characterized in that the fabric is held in its position along a direction (B-B') substantially parallel to weft yarns (51) in the fabric (2).

12. Process according to claim 11, characterized in that a locking effort (E) is exerted on the fabric (2) next to a second longitudinal edge (22) of the fabric when at least one auxiliary weft yarn is being pulled out (T₁) of the fabric.

13. Process according to one of claims 11 and 12, characterized in that when they are pulled out of the fabric, the auxiliary weft yarns (31) remain partly engaged within a false selvedge (25) woven with all auxiliary weft yarns (31) and with some dedicated warp yarns (19A, 19B), according to a Leno type weave.

14. Process according to one of claims 11 to 13, characterized in that the auxiliary weft yarns are pulled by a gripper (65) moved, between two end positions (P₁, P₂), along a direction (X₅₃) substantially parallel to the weft yarns (14, 31) in the fabric (2) with a velocity profile (M1-M4) such that its speed increases from a first value (S₀) to a second value (S_max) when the gripper moves away from the fabric and such that the gripper reaches it second speed value (S_max) at a position (P_A) where it has travelled more than 50% of its path between a first end position (P₁) of the gripper (65), next to an edge (21) of the fabric, and a second end position (P₂), of the gripper away from this edge.

15. Process according to one of claims 11 to 14, characterized in that the auxiliary weft yarns (31) are pulled out of the fabric (2) by a hook forming gripper (65) driven by a carriage (58) having a back and forth translation movement with a length (L₅₈) which has about the same value as half of the width (I₂) of the fabric (2).

Drawing