EP1982011A2

EP1982011A2 - Method and apparatus for weaving

Info

Publication number: EP1982011A2
Application number: EP07705349A
Authority: EP
Inventors: Bahman Mostaghimi; John Downie
Original assignee: University of Brighton
Current assignee: University of Brighton
Priority date: 2006-01-24
Filing date: 2007-01-23
Publication date: 2008-10-22
Also published as: WO2007085872A3; WO2007085872A2; GB0601376D0; JP2009523924A; IL192938A0

Abstract

A method of weaving tubular items such as a sleeved garment (10), using a weft yarn carrier such as a shuttle (not shown) which is passed backwards and forwards across the warp yarn bed (1) of a weaving loom. The method comprises detecting slack in the dispensed weft yarn, said slack being due to weft yarn which, although dispensed by the shuttle, is not interwoven with those warp yarns which are beyond the selvedge of the area being woven. The slack yarn is retracted back into the shuttle and is stored in the shuttle for later re-dispensing.

Description

METHOD AND APPARATUS FOR WEAVING

This invention relates to a method and apparatus for weaving, particularly the weaving of tubular items, such as isolated tubes or items comprising tubes such as garments or certain types of prostheses.

For the purpose of weaving tubular items, the weaving loom may be set up with a bed of suitable warp yarns having a width corresponding to the desired flattened width of the item to be woven - in other words all the warp yarns are incorporated in the weave. This arrangement causes no particular problems, and the techniques for producing seamless woven tubes in this way, using a shuttle loom, are well established.

Sometimes it is not possible to utilise the whole width of the warp yarns for weaving the item and this can lead to difficulties if the item being woven is positioned to one side of the centre line of the width of the bed of warp yarns. This will be explained by reference to Figures 1 to 3 of the accompanying drawings.

Figure 1 A is a diagrammatic side view illustrating the structure of the "double cloth" construction conventionally used to fabricate seamless tubes by weaving. The tube comprises an upper set 1A and a lower set 1B of warp yarns about which is woven, in plain weave, a weft yarn 2. The weft yarn 2 is continuous in the sense that, at each end, it passes from the upper set of warp yarns to the lower set of warp yarns or vice versa without a break, so that the ends are truly seamless and, once removed from the constraints of the loom, the upper and lower layers of plain weave thus woven can be formed into a cylindrical tubular shape which has no identifiable seam.

Figure 1 B is a diagrammatic view looking along the warp yarns 1 of a weaving loom in a direction looking back towards the warp beam (not shown), and shows the very beginning of the fabrication of a seamless tube in plain weave, utilising the "double cloth" construction. For the purpose of illustration, the drawing shows a warp bed having a small number of yarns only and it will be seen that the outermost yarns on each side do not take part in the weaving. Thus the extent of the woven tube is shown approximately by the vertical lines 3A, 3B. As is well known, weaving proceeds by moving a shuttle 9 backwards and forwards across the warp bed. Each movement of the shuttle from one side of the warp bed to the other is referred to as a pick. The shuttle carries a bobbin (not shown) on which the weft yarn 2 is wound. The weft yarn is dispensed automatically from the bobbin as the shuttle moves across the warp bed due to the weft yarn being in tension and thus being, in effect, "pulled" out of the shuttle. It will be understood that the shuttle moves across the whole width of the warp bed on each pick, even though the item to be woven is narrower than this.

On the first pick, the shuttle moves right to left across the warp bed dispensing the weft yarn as it travels. The first pick of the weft yarn is shown as the line 4. During the first pick, the weft yarn 4 interweaves with alternate warp yarns 1 A to form an upper layer of plain woven fabric in the conventional way. To achieve this, all of the warp yarns between lines 3A and 3B are moved by the heddles (not shown) to create a shed such that the weft yarn 4 only interweaves with the upper layer of warp yarns 1 A.

On the second pick, the shuttle moves left to right across the warp yarns, and the shed is set up so that the weft yarn now interweaves with the lower set of warp yarns 1 B between the lines 3A, 3B. Due to excess yarn having been dispensed by the shuttle 9 during its leftwards passage across the leftmost warp yarns not involved in the weaving, the tension in the weft yarn drops and, for the first part of the second pick, no further warp yarn is dispensed by the shuttle. As the shuttle travels from left to right, the trailing weft yarn eventually engages the leftmost warp yarn 1B and weft tension re-establishes causing the shuttle to commence dispensing weft yarn once more. As the shuttle continues its rightwards movement the weft yam 2, now represented by the line 5, interweaves with the warp yarns 1B to form a lower layer of plain woven fabric. At the end of the second pick the shuttle 9 travels across the rightmost warp yarns not involved in weaving and weft yarn continues to be dispensed during this period, as illustrated.

The shuttle now commences the third pick, moving back towards the left, the shed having been set up once again so that the weft yarn interweaves with the warp yarns 1A. As with the beginning of the second pick, the weft yarn tension drops during the first part of the third pick and the dispensing of weft yarn by the shuttle ceases until such time as the tension rises again, following engagement of the trailing weft yarn by the warp yarns 1A.

Thus it will be seen that this weaving process creates a seamless tube of the type illustrated in Figure 1A in the approximate centre of the width of the bed of warp yarns 1. When seen in plan the tube created by such a process will extend lengthwise in the direction of the warp yarns. Such a tube (but with a lower number of warp yarns) is diagrammatically illustrated in plan in Figure 2A as a dotted rectangle 7. It will be noted that the tube 7 is symmetrical about the centre line 8 of the bed of warp lines 1. In Figure 2B, by contrast, the tube 7 is displaced to the left with respect to the centre line 8, but still overlaps the centre line. In Figure 2C (which has a wider warp bed) the tube 7 is displaced so far to the left that no part of it overlaps the centre line.

The purpose of the series of drawings in Figure 2 is to explain how the excess weft yarn, created as the shuttle continues to dispense yarn as it travels beyond the area of the tube 7 on each pick, is handled in the conventional weaving process.

Referring to Figure 2A, it will be clear from the description of Figure 1 that the excess weft yarn dispensed on each pick is used up on the following pick. This is because, on every pick, the weft yarn will re-tension - A -

itself before the shuttle reaches the end of its travel. For a very narrow tube 7, this re-tensioning will not occur until very close to the end of the shuttle travel, but nevertheless, it does occur. This means that, on the next pick, the length of excess weft yarn can never be greater than half the width of the warp bed and therefore the excess weft yarn is taken up before the end of the pick.

Thus, when weaving a tube which is symmetrically placed about the centre line, the excess weft yarn will be the same for each pick, and the yarn will use up the excess and re-tension itself before the end of the pick. When weaving a tube which is not symmetrically placed, but does cross the centre line as shown in Figure 2B, the situation is similar, except that the amount of excess yarn will increase and decrease on alternate picks. However, even the increased length can never be long enough to cause the weft yarn not to re-tension itself at the end of the pick. As the centre line of the tube 7 is moved further and further from the centre line 8 of the warp bed, so the point at which re-tensioning occurs on each pick gets closer and closer to the end of the pick. The limit point is when the tube is positioned such that one of its edges is actually coincident with the centre line 8 of the warp bed. Figure 2C illustrates the situation beyond this limit point. From the above detailed description of Figure 1 B, it will be seen that, during each pick involving movement of the shuttle from right to left, a length L1 of excess weft yarn will be dispensed. As already explained, when the shuttle returns on its next pick the tension in the weft yarn drops because the weft is not immediately engaged with the leftmost warp yarns, but does not in fact engage the warp yarns until the left hand edge of the tube 7. It will thus be seen that the relatively short excess weft yarn L1 will fairly soon be used up on the next pick, and the weft yarn will re-tension itself at that point, and will re-commence dispensing weft yarn. By the end of the rightwards movement of the next pick, a length l_2 of weft yarn will have been dispensed. Thus, at the start of the next movement of the shuttle from right to left there is a considerable excess to take up before re- tensioning can occur. Unfortunately this excess does not even start to be taken up until the shuttle reaches the right hand edge of tube 7, at which point the warp yarns engage the weft yarn. Thus it will be seen that, by the time that the shuttle reaches the end of the pick, the excess yarn L2 will not have been used up, and there will be a residual length Lr of weft yarn which remains as a loop extending beyond the right hand edge of tube 7 when the shuttle reaches the end of the pick. As already explained, at the end of each pick, the shed changes over from one layer of the tube 7 to the other, and acts to interweave the warp and weft yarns, thus trapping the loop at the left hand edge of the tube 7.

It can readily be shown that: Lr = 2 x L2 - Wb where Wb = width of warp bed

Thus it can be seen, at the limit condition mentioned above, where L2 = Wb/2, the residual yarn length Lr is zero. Also, it can be seen that, if length L2 is less than Wb/2, then the value of Lr becomes negative, corresponding to the condition shown in Figure 2B in which excess yarn is generated, but is used up before the end of the pick, so that further weft yarn has to be displaced by the shuttle.

Because the residual excess yarn is not drawn through the shed on each leftwards pick, the excess weft yarn on the next (rightwards) pick is never more than length L1 , and so can readily be used up on the rightwards pick. Thus, the residual loops only form on the right side, and not on the left. As weaving proceeds, a series of loops, corresponding to the excess weft yarn created on each pick are formed on the right hand edge of the tube 7.

In the finished product, these loops have to be removed and this can be achieved by cutting them, and then seaming the edge to prevent fraying; however, if this is done, the tube can no longer be said to be seamless.

Of course, this problem can be avoided by appropriate positioning of the tube being woven with respect to the centre line of the warp bed. However, this is not always possible. If it is necessary to fabricate multiple tubes across the width of the warp bed, for example, in the weaving of such items as garments having sleeves or trouser legs, or prostheses having multiple branches, it is possible that the physical requirements of the finished article may require that at least one of the tubes to be woven is off- centre. To illustrate this, reference is now made to Figure 3 which shows the outline 10 of a sleeved garment to be woven on a bed of warp yarns 1. The drawing is diagrammatic - in practice there would be many more warp yarns than is shown.

It will be noted that, between the dotted lines A and B, the loom must weave three separate tubes: one for each of the left hand and right hand sleeves, and one for the body. Above the line A and below the line B, the loom weaves only a single tube. It is in the section between lines A and B that the problem arises because, even if the garment as a whole is centrally positioned with respect to the axis 8, the left and right hand sleeves will be considerably off centre.

Weaving of the section between lines A and B is carried out with three shuttles: one for weaving the body, and one for weaving each of the sleeves. Thus it will be seen that the weaving of the sleeves will result in the formation of loops, as described above. In the present invention we enable the weaving of true seamless tubular items, which may be positioned anywhere across the width of the warp yarns, by retracting excess weft yarn back into the shuttle or other weft yarn carrier and temporarily storing such excess yarn so that it can be dispensed later, as needed. Thus, according to a first aspect of the invention, there is provided a method of weaving tubular items, using a weft yarn carrier moved backwards and forwards across a bed of warp yarns in order to dispense weft yarn to be interwoven with the warp yarns, said method comprising detecting slack in the dispensed weft yarn, retracting the slack yarn back into the carrier and storing the retracted slack yarn on the carrier for later re-dispensing.

In practice, the weft yarn dispensed by the carrier is interwoven with the warp yarns only in that area of the warp yarn bed where the item is being woven. Thus, the slack weft yarn comprises that excess yarn which is created as the carrier moves beyond the item being woven into that area of the warp yarn bed in which the weft yarn is not being interwoven with the warp yarn.

Using the method of the invention, it will be seen that tubes can be woven, even if they are positioned considerably off-centre with respect to the warp bed, without creating loops at the selvedges. This in turn enables the fabrication of relatively complex items containing bifurcated tubes, such as garments and bifurcated prostheses. For example, a garment having a body and two sleeves such as illustrated in Figure 3 is effectively a multiple bifurcated tube, and can be woven using three shuttles, one of which is used for weaving each of the sleeves, and one for the body. At least the shuttles which weave the sleeves utilise the method of the invention, but all three shuttles may do so if, for example, the whole garment is positioned off-centre. It will be seen that multiple items can be woven simultaneously by positioning the items across the width of the warp bed and using an appropriate number of shuttles, for example, in order to fabricate two garments such as shown in Figure 3 positioned across the width of the warp bed, six shuttles will be needed, three for each garment.

During weaving, each shuttle is passed in turn across the warp bed, and the shed is adjusted so that weft yarn is woven into only those warp yarns which are within that part of the garment outline which that particular shuttle is weaving. The next pick, using a different shuttle, will require a re-adjustment of the shed to cater for the different part of the garment which the shuttle is weaving. In addition, as weaving proceeds, the particular warp yarns with which the weft yarn is woven may change, for example because the edges of the sleeves are not parallel with the warp direction, but are at a slight angle to it.

After weaving, the unused warp yarns are cut away to reveal a seamless garment.

In a second aspect of the invention there is provided a weft yarn carrier for use in a weaving loom, said carrier comprising a bobbin for holding yarn, to be used as weft yarn in a weaving process, and means for dispensing said yarn from the carrier during such weaving process, said carrier being characterised by means for detecting slack in the dispensed weft yarn, means for retracting the slack yarn into the carrier and means for storing the retracted yarn on the carrier for later re-dispensing.

The presence of slack yarn can be detected by monitoring the tension of the yarn being dispensed by the carrier. If the tension drops below a predetermined level, set for example by an electronic circuit or a physical spring, then this causes the slack yarn to be retracted into the carrier and stored, thus re-tensioning the yarn.

Advantageously, the arrangement is such that yarn dispensed by the carrier is taken preferentially from the storing means and only if this is empty will yarn be taken from the bobbin. To achieve this, the yarn storing means may be situated in the yarn path between the bobbin and the carrier dispensing means. The carrier dispensing means is likely to be a hole or channel formed in the body of the carrier through which yarn is guided to the exterior of the carrier.

Thus it will be understood that the yarn storage means is intended as a temporary store for yarn which has been dispensed, but has subsequently lost tension and become slack. Such excess yarn is held in the storage means until such time as the carrier needs to dispense more weft yarn, at which time the yarn storage means is emptied first, before yarn is taken from the bobbin. As will be apparent from the descriptions given above of excess weft yarn produced during the weaving of a narrow tube positioned off-centre, the length of excess yarn produced can be quite considerable - typically 40 to 50cm - and the yarn storage means has to be designed in such a way as to be able to store at least the expected maximum likely length of excess.

The yarn storage means may comprise, for example, a cylindrical reel onto which excess yarn is coiled up. In one embodiment, means are provided for rotating the reel to coil up the yarn. The rotating means may be controlled by mechanical means such as a spring, or can be controlled by electronic circuitry which drives a small electric motor mounted on the weft yarn carrier. In a preferred embodiment, the reel does not rotate, and the excess weft yarn is coiled onto the stationary reel by means of a flyer, namely a winder arm having a yarn guide which rotates relative to the reel to coil the yarn onto the reel. Various arrangements are possible for the flyer, but the main advantage of using a flyer to coil yarn onto the reel, as distinct from rotating the reel itself, is that the flyer can have a lightweight construction, exhibiting minimum inertia, and is thus capable of rapid reciprocating movement which would be necessary in a high speed loom. In an embodiment, the flyer comprises a sleeve which is rotatable about the axis of the reel, which sleeve carries a winder arm which terminates in a yarn guide in the form of a winder eye through which the yarn is passed. The winder arm extends generally radially from the sleeve, and then bends over the yarn-carrying surface of the reel so that the yarn may be guided onto the surface as the sleeve rotates relative to the reel. As before, movement of the sleeve can be controlled by mechanical means such as a spring, or can be controlled by electronic circuitry which drives a small electric motor mounted on the weft yarn carrier.

Another alternative yarn storage means is a variable tortuous path structure, through which yarn emerging from the bobbin passes before being dispensed from the carrier. Such structures can be varied by altering the path of yarn through the structure to make it longer or shorter, or by varying the size of the structure. In either case, the result is to enable variation in the amount of yarn which is "stored" in such a structure. An example of a tortuous path structure is a structure which forces the yarn to follow a multiple zigzag path in which the magnitude of the zigzag deflections can be varied so as to alter the amount of yarn traversing through the structure. This can form a very rapid acting variable storage structure for yarn.

If an electronic version is used the possibility opens up of intelligently controlling the weft yarn dispensed by the shuttle. Thus a microprocessor and associated memory could be mounted within the shuttle and used to control dispensing of yarn in accordance with a preset program and/or external control signals, these latter being generated as a result of monitoring instantaneous weaving conditions.

An important factor in the design of the yarn storage means is its physical size since, without major loom modification, the size of the weft yarn carrier is dictated by the size of the shed which is formed during weaving and through which the weft yarn carrier has to pass.

The weft yarn carrier will normally take the form of a conventional shuttle, but it should be understood that the term shuttle is used herein in its broadest sense as meaning a device which carries its own weft yarn, for example on a bobbin or pirn, and which has means, for example in the form of holes or channels, for dispensing the yarn during weaving. Conventional shuttles have a generally tubular shape, usually with pointed ends to maximise their aerodynamic efficiency, but the yarn carrier of the present invention does not need to have such a shape, although it may do so, depending on the circumstances of use. Likewise, conventional shuttles are often of a relatively heavy construction in order to give the shuttle the maximum momentum during its movement across the warp bed. This is to ensure the smooth dispensing of yarn from the shuttle, since any small irregularities or snagging can be overcome by the momentum of the shuttle. However, in the present invention, with its closer control of the dispensing of warp yarn from the carrier, the carrier does not necessarily need to be of heavy construction, and this gives much greater flexibility in the design of the carrier. To assist clarity, the term shuttle is used extensively in this specification in view of its universal usage in the weaving industry. However, the term is intended to be given a broad interpretation as specified above.

The shuttle may be moved backwards and forwards across the warp bed by any of the known means, for example mechanical means, pneumatic or hydraulic means or electromagnetic means. The mode of travel may be by flying through the air or, if greater control is needed, some form of remote guidance system may be used such as magnetic levitation, air levitation or water levitation. Systems such as magnetic or water levitation can provide both propulsion and guidance to the shuttle; for example angled air or water jets along the route of the shuttle could be used to propel the shuttle across the warp bed. The jets could be moveable to direct the shuttle in both directions, as needed, or two sets of fixed jets could be provided, each angled to propel the shuttle in one direction or the other.

This invention is applicable to any suitable type of weaving loom. Jacquard looms are particularly suitable for weaving items such as prostheses and garments due to the close control of weaving given by individual control of the heddles. In order that the invention may be better understood, several embodi merits thereof will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 A is a diagrammatic side view to illustrate the structure of a conventional seamless woven tube as it comes off the loom; Figure 1 B is a diagrammatic view of the warp yarns in a weaving loom set up for weaving a tube of the type shown in Figure 1 A;

Figure 2 is a series of diagrammatic plan views A, B and C of the warp yarn bed of a weaving loom, showing three different potential positions of a tube to be woven by the loom; Figure 3 is a diagrammatic plan view of the warp yarn bed of a weaving loom, showing the weaving of a sleeved garment;

Figure 4 is a side view of an embodiment of a weft yarn carrier in the form of a shuttle, suitable for use in the method of the present invention; Figures 5A and 5B are partial views of the shuttle of Figure 4 on an enlarged scale;

Figures 6, 7A and 7B correspond to Figures 4, 5A and 5B respectively, illustrating a further embodiment;

Figure 8 is a perspective view of a weft yarn carrier in the form of a shuttle, showing a still further embodiment of the invention;

Figures 9A and 9B are partial views of the shuttle of Figure 8 on an enlarged scale; and

Figure 10 is a simplified outline block diagram of the circuitry within the shuttle of Figures 8 and 9. Referring firstly to Figures 4 and 5, there is shown a modified flying shuttle according to a first embodiment of the invention. Figure 4 shows the whole shuttle, whilst Figures 5A and 5B show the mechanism at the left-hand side at an enlarged scale. It will be seen from Figure 4 that the shuttle has an elongate body 20, having pointed ends 21 , 22 to improve its aerodynamic performance. The shuttle is typically made of wood, possibly with brass ends to take up wear, so as to endow the shuttle, when in motion, with a significant momentum. This momentum is desirable in order to ensure that the weft yarn dispenses smoothly. However, although described in relation to shuttles of this general type, it should be made clear that alternative shuttle structures and materials are possible, depending upon the circumstances, in particular the method used for moving the shuttle across the warp bed.

The body has a hollow interior 23, which may or may not be closed by means of a door or lid (not shown). Within the interior 23 is mounted a bobbin or pirn 24 which is the primary source of weft yarn, and a take-up and storage mechanism 25. During weaving, yarn is unwound from the pirn 24, passes through the storage mechanism 25, to be described, and emerges from the shuttle body via a hole extending from the interior 23 through to the exterior. The emerging yarn 26 is used to create the weft during weaving, as described above.

Usually the pirn 24 does not rotate but is fixed firmly, but in such a way that it can readily be removed for replenishing, on a post 27 mounted axially in the interior 23. However, the use of a rotating pirn is not excluded. The storage mechanism 25 is supported on a small plate 28 mounted across the interior 23 of shuttle body. Fixedly mounted on the plate 28 is a hollow axle (not visible) through which weft yarn 29 enters the mechanism from the pirn 24. Rotatably mounted on the axle is a sleeve 30 which carries a winder arm 31. The arm 31 initially extends in a radial direction, but then turns through 90° to an axial direction, and terminates in a winder eye 32. Fixedly mounted on the end of the hollow axle is a spool 33 having a yarn carrying surface 36. Thus it will be understood that the spool 33 cannot rotate with respect to the shuttle body. Extending from the centre of the spool 33, and communicating with the interior of the hollow axle, is a radially extending bore 37 which opens onto the yarn carrying surface 36. A coil spring 34 is mounted with its inner end attached to the sleeve 30, and its outer end attached to a post 35 mounted on the plate 28.

As made clear in the previous discussion of Figures 1 and 2 in particular, the shuttle normally operates with the emerging weft yarn under tension. It is common practice to maintain this tension by taking the yarn through a tortuous path as it travels from the pirn to the exterior of the shuttle. In the shuttle of Figures 4 and 5, the situation with the yarn under tension is illustrated in Figure 5A. It will be seen that yarn 29 emerging from the pirn 24 enters the hollow axle and re-emerges from the end of bore 37 to pass through the winder eye 32. The yarn continues in an approximately axial direction to an eye 38 attached to the body of the shuttle and thence exits the shuttle at reference 26.

In the position shown in Figure 5A, the coil spring 34 is in the wound condition and is thus biasing the sleeve 30 and arm 31 to rotate in the direction of arrow A. However, the arrangement is such that the normal weft yarn tension existing in the yarn 29 extending between the bore 37 and fixed eye 38 is sufficient to hold the arm 31 and prevent it rotating under the pressure of spring 34.

Thus it will be seen that, provided sufficient tension is maintained in the weft yarn being dispensed from the shuttle, the arm 31 will be held in the position shown in Figure 5A against the force of the spring. If, however, the weft yarn goes slack, for example under the circumstances outlined above with reference to Figures 1 and 2, then the force of spring 34 will cause the sleeve 30 to rotate which will in turn carry the arm 31 in the direction of arrow A. The winder eye 32 thus moves around and just above the yarn carrying surface 36 of spool 33, taking with it any excess weft yarn resulting from the loss of tension. During this process, excess weft yarn 39 from outside the shuttle is retracted back into the shuttle and is wound around the spool 33 which thus acts as a temporary yarn store - see Figure 5B. When further weft yarn is demanded, the weft yarn tension is reestablished. This tensions the length of yarn 29 between the winder eye 32 and fixed eye 38 and starts to pull yarn off the spool 33, thus driving the sleeve 30 and winder arm 31 to rotate in the direction opposite to that of arrow A. It will be seen that, during this process, the spring 34 becomes re-tensioned. In this way, any yarn which is wound around spool 33 is dispensed initially, until the spool returns to the empty condition shown in Figure 5A. Once the position shown in Figure 5A is reached, and the spool 33 is once again empty, further weft yarn is withdrawn from the pirn 24. Since the above operation is required to be carried out at high speed - typically several times per second - low rotational inertia is essential in the rotating components 30, 31 of the mechanism.

Reference is now made to Figures 6 and 7 which show a geared version of the shuttle shown in Figures 4 and 5. In this second version, the sleeve 30 is joined to a gear 40 which is driven from a gear 41 , which latter is rotatably mounted on the hollow axle separately from the gear 40/sleeve 30. The inner end of coil spring 34 is attached to the gear 41 whilst its outer end is attached, as before, to the plate 28.

The gears 40 and 41 are mechanically linked by a pair of gears 42, 43 freely rotatably mounted on a shaft 44 attached to the plate 28. Gear 41 meshes with gear 43 and gear 40 meshes with gear 42. Thus gear 41 drives gear 40 via gear 43 and 42 with a step-up ratio, and this in turn means that the winder arm 31 is able, for a given spring specification, to travel a longer distance and at greater speed than with the embodiment of Figures 4 and 5. On the other hand, the spring will have to be made stronger if the arm 31 is to exert the same force on the yarn 29 at the winder eye 32.

As before, low rotational inertia is a desirable feature of the mechanism 25, including that of the gear assembly. Reference is now made to Figures 8 and 9 which show an electronic version of the take-up and storage mechanism 25. In this embodiment the sleeve 30 is internally threaded to engage with a fine external thread 50 formed on the exterior of the hollow axle. As before, the spool 33 is fixedly mounted on the distal end of the hollow axle and its bore 37 communicates with the hollow interior of the axle. It will be seen that the threaded connection between the hollow axle and the sleeve 30 causes the sleeve 30, and hence the winder arm 31 , to move axially as the sleeve rotates. This causes the laid-down yarn to be guided over the width of the yarn carrying surface 36 of the spool 33. The sleeve 30 is attached to a gear 51 which is driven by a pinion

52 attached to the output shaft of a small electric motor 53. It will be seen that the sleeve 30/gear 51 combination will move axially as it rotates and, to cater for this, the pinion 52 has a sufficient length, in the axial direction, to ensure that the gear 51 and pinion 52 remain in secure engagement. The motor 53 is powered from a drive circuit mounted on a printed circuit board 54.

A tension sensor 55 is mounted close to the point at which the yarn 29 exits from the cavity 23 within the shuttle and is arranged so as to monitor the tension of the yarn as it exits from the shuttle. The electrical output from the sensor 55 is passed to a control circuit mounted on the printed circuit board 54, and controls the motor 53 in a feedback control circuit, a simplified block diagram of which is given in Figure 10.

The route taken by the yarn 29 when in tension is illustrated in Figure 9A. Under loss of tension due to excess yarn outside the shuttle the tension sensor 55 actuates and sends an appropriate signal to control electronics 56 (see Figure 10) mounted on the printed circuit board 54. This in turn sends a control signal to the motor drive circuit to operate the motor 53 to drive pinion 52 and gear 51. Activated thus, the yarn winder arm 31 rotates about the spool 33 laying up a spiral of yarn taken from the excess outside the shuttle. The axial motion of the arm 31 during this process ensures that the full width of the yarn carrying surface 36 is utilised - see Figure 9B.

When the yarn tension is restored the increase of tension is detected by the sensor 55 which sends a further signal to the control electronics to de-activate the motor 53. As explained previously, the tension in the yarn now causes the winder arm 31 to be driven back in a direction so as to unwind the excess yarn and dispense it from the shuttle. Once the laid-up yarn on spool 33 is exhausted, and assuming that weft yarn tension is still being maintained, then further yarn is dispensed from the pirn 24, as illustrated in Figure 9A.

As with the previous embodiments, low rotational inertia is desirable in the rotating components because of the very rapid operation of the device in use.

The motor and electronic circuitry obtains its power from a small battery or storage capacitor (not shown) which may for convenience be mounted on the printed circuit board 54. Various ways can be devised for charging the battery or capacitor. In one embodiment, illustrated in Figures 8 and 9, charging is carried out by means of the reciprocating motion of a permanent magnet slug (not shown) which is mounted within a guide tube 57. As the shuttle reverses its motion at each end of each pick the slug is accelerated along the tube and, as it does so, induces a current in a coil 58 wound around the exterior of the tube 57 near its centre. Motion of the slug within the tube is limited by end stops, the left-hand one of which is shown under reference 59 in Figures 9A and 9B. The coil 58 is connected via suitable circuitry to the capacitor or battery so as to maintain same in charge.

Claims

1. A method of weaving tubular items, using a weft yarn carrier moved backwards and forwards across a bed of warp yarns in order to dispense weft yarn to be interwoven with the warp yarns, said method comprising detecting slack in the dispensed weft yarn, retracting the slack yarn back into the carrier and storing the retracted slack yarn on the carrier for later re-dispensing.

2. A method as claimed in claim 1 in which the weft yarn dispensed by the carrier is interwoven with the warp yarns only in that area of the warp yarn bed where the item is being woven, and wherein the slack weft yarn comprises that excess yarn which is created as the carrier moves beyond the item being woven into that area of the warp yarn bed in which the weft yarn is not being interwoven with the warp yarn.

3. A method as claimed in either one of claims 1 or 2 wherein slack is detected by monitoring the tension of the weft yarn dispensed by the carrier, and retracting the slack yarn if the tension of the weft yarn drops below a predetermined level.

4. A method as claimed in any one of claims 1 , 2 or 3 wherein the carrier comprises a bobbin for holding the weft yarn and a temporary storage means for storing the retracted yarn, and wherein the weft yarn dispensed by the carrier is taken preferentially from the temporary storage means.

5. A method as claimed in claim 4 wherein the weft yarn dispensed by the carrier is taken from the bobbin only once the amount of yarn stored by the temporary storage means has fallen below a predetermined level or has become zero.

6. A method as claimed in any one of the preceding claims in which the items to be woven comprise multiple tubes positioned across the warp yarn bed, said method comprising utilising a number of weft yarn carriers at least equal to the number of said tubes to be woven, and wherein said weft yarn carriers are moved across the bed in sequence, each weaving just one of said tubes.

7. A method as claimed in claim 6 wherein each weft yarn carrier is moved across the whole width of the warp bed but only interweaves its weft yarn with those warp yarns in that area of the warp yarn bed where that tube which the weft yarn carrier is weaving is positioned.

8. A weft yarn carrier for use in a weaving loom for the weaving of tubular items, said carrier comprising a bobbin for holding yarn, to be used as weft yarn in the weaving process, and means for dispensing said yarn from the carrier during the weaving process, said carrier being characterised by means for detecting slack in the dispensed weft yarn, means for retracting the slack yarn into the carrier and means for storing the retracted yarn on the carrier for later re-dispensing.

9. A weft yarn carrier as claimed in claim 8 wherein the means for detecting slack comprises means for monitoring the tension of the dispensed weft yarn and wherein the yarn retracting means operates to retract yarn when the tension drops below a predetermined level.

10. A weft yarn carrier as claimed in claim 9 including spring means for setting the tension below which weft yarn is retracted by said yarn retracting means.

11. A weft yarn carrier as claimed in claim 9 including an electronic circuit for setting the tension below which weft yarn is retracted by said yarn retracting means.

12. A weft yarn carrier as claimed in any one of claims 8 to 11 wherein the yarn storing means is situated in the yarn path between the bobbin and the carrier dispensing means so that weft yarn is dispensed preferentially from the yarn storing means.

13. A weft yarn carrier as claimed in any one of claims 8 to 12 wherein the yarn storing means comprises a cylindrical reel, means for guiding the excess weft yarn onto the cylindrical surface of the reel for storage, and means for rotating the reel and the guiding means relative to one another.

14. A weft yarn carrier as claimed in claim 13 wherein the rotating means comprises a spring.

15. A weft yarn carrier as claimed in claim 13 wherein the rotating means comprises an electric motor controlled by an electronic circuit.

16. A weft yarn carrier as claimed in any one of claims 13 to 15 wherein the rotating means is operable to rotate the reel, and the yarn guiding means is non-rotatable.

17. A weft yarn carrier as claimed in any one of claims 13 to 15 wherein the rotating means is operable to rotate the yarn guiding means, and the reel is non-rotatable.

18. A weft yarn carrier as claimed in claim 17 wherein the yarn guiding means comprises a winder arm which is mounted for rotation about the axis of the cylindrical reel, which winder arm has a yarn guide to guide the yarn onto the cylindrical surface of the reel.

19. A weft yarn carrier as claimed in claim 18 wherein said yarn guide comprises a winder eye through which the yarn passes so as to be guided thereby.

20. A weft yarn carrier as claimed in any one of claims 8 to 12 wherein the yarn storing means comprises a variable tortuous path structure through which the weft yarn emerging from the bobbin is arranged to pass before being dispensed from the carrier, and means for altering the path of yarn through the structure to thereby alter the amount of yarn which is stored within the structure.

21. A weaving loom incorporating a weft yarn carrier as claimed in any one of claims 8 to 20.

22. A weaving loom as claimed in claim 21 wherein said carrier takes the form of a shuttle.

23. A weaving loom as claimed in either one of claims 21 or 22 wherein the loom is of the jacquard type.