MOSAGHIMI, Bahman (30 Kingsley Road, Brighton, Sussex BN1 5NH, GB)
| CLAIMS 1. A weft yarn carrier (16, 60) for use with a weaving loom, said carrier comprising a bobbin (24) for holding yarn (26) to be used in a weaving process, a temporary yarn store (25) with guide (36) for dispensing and retracting yarn therefrom and tension control means (46, 66) set to urge the yarn back into the carrier, such that the carrier is operable to retract the yarn to the temporary store (25) when it is tensioned to a level below a threshold tension set by the tension control means and to dispense the yarn from the store (25) when it is tensioned to a level above the threshold tension. 2. A weft yarn carrier (16, 60) according to claim 1 wherein the tension control means (46, 66) is arranged such that the yarn (26) is retracted to or dispensed from the store (25) under approximately the same level of tension. 3. A weft yarn carrier (16, 60) according to claim 1 or 2 wherein the tension control means (46, 66) includes a means (47, 70) for adjustment of its bias strength, whereby the threshold tension may be adjusted. 4. A weft yarn carrier (16, 60) according to any one of claims 1 to 3 wherein the temporary yarn store (25) includes a reel (30) and the guide (36) comprises a winding arm (36) arranged to wind and / or unwind yarn about the reel (30). 5. A weft yarn carrier (16, 60) according to claim 4 wherein the winding arm (36) is connected to the tension control means (46, 66). 6. A weft yarn carrier (16) according to claim 5 wherein the tension control means includes a spring (46) set to apply a tension (T8) to the winding arm (36), whereby stored energy in the spring is increased as the winding arm (36) unwinds the yarn and released to drive the winding arm (36) to wind the yarn. 7. A weft yarn carrier (16) according to claim 6 wherein the tension (T8) in the spring is adjustable by means of a screw (47). 8. A weft yarn carrier (16) according to claim 7 wherein the spring (46) is arranged such that, for an anticipated length of yarn to be retracted to the store (25) during a weaving process, the tension (T8, Tmιn) in the spring does not vary substantially in retracting and dispensing that length. 9. A weft yarn carrier (60) according to claim 5 wherein the tension control means includes a motor (66) set to apply a torque to the winding arm (36) thereby urging the arm (36) to wind the yarn (26) and acting as a brake as the arm (36) unwinds the yarn. 10. A weft yarn carrier (60) according to claim 9 wherein the torque applied by the motor (66) to the winding arm (36) is variable in response to a signal from a tension detector (68), in such a manner than the signal returns towards a preset value. 11. A weft yarn carrier (60) according to any preceding claim wherein the carrier is arranged such that, in the event that the temporary yarn store (25) holds no yarn, yarn (26) is dispensed from the bobbin (24) to exit the carrier (60) via the guide (36). 12. A weft yarn carrier (60) according to claim 11 wherein the carrier (60) includes a second tension control means (47) arranged to apply a frictional force (Tf) to the yarn as it is dispensed from the bobbin (24). 13. A weft yarn carrier (60) according to claim 12 wherein the second tension control means (47) is adjustable in order to vary the frictional force (Tf) that needs to be overcome by the yarn as it is dispensed from the bobbin. 14. A weft yarn carrier (60) according to claim 13 wherein the second tension control means comprises two (34a, 34b) curved discs, with adjustable separation. 15. A weft yarn carrier (60) according to claim 14 wherein the separation is adjustable by means of a screw (34c). 16. A weft yarn carrier (60) according to any one of claims 11 to 15 wherein yarn exiting the shuttle must be under sufficient tension to overcome a force (T8) applied by the first tension control means (46, 66) and, if dispensed from the bobbin (24), a force (Tf) applied by the second tension control means (47). |
This invention relates to apparatus for weaving, particularly, although not exclusively, to 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, a 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. This arrangement causes no particular problems and the techniques for producing seamless woven tubes in this way, using a shuttle loom, are well established and explained with reference to Figures 1A and 1 B.
Figure 1A 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 1 A and a lower set 1 B 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. Shuttles generally incorporate two or three eyelet holes, which act to keep the tension in the weft yarn as it is unwound. 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 1A 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 1A.
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 1 B and weft tension re-establishes causing the shuttle to commence dispensing weft yarn once more. As the shuttle continues its rightwards movement the weft yarn 2, now represented by the line 5, interweaves with the warp yarns 1 B 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 1 A. 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.
Ideally, in a completed woven seamless article, those parts of the woven piece that formed the edges whilst on the loom should be indistinguishable from the remainder of the woven piece. This is despite their distinctive location on the loom. Accordingly, much care must be taken during the weave at each point in time that the weft is looped round each of the extreme warp ends. That is, at the point the shuttle reverses direction. Any variation of tension at this time in the weave will readily affect the appearance of the finished article. In fact, this consideration should be made during any weaving process, for flat as well as the seamless items described above, although it is more noticeable for seamless articles. The edge of the woven piece on the loom, which is woven as the shuttle direction is reversed, is commonly referred to as the selvedge.
As the shuttle reverses direction, the tension in the weft falls and then re- establishes itself at the start of the next pick. During this reversal process the tension of the weft is inherently unstable, which can in turn affect the quality of the selvedge finish. In a straightforward flat weave there will be two selvedges, one at each longitudinal edge of the woven fabric. The tension in the weft is critical to maintaining selvedge quality. If it is too high, looped warp threads will pull inwards creating a "fishtail" effect. If it is too low then looped sections of thread may be left at the fabric edges.
In a flat weave, the problem of maintaining selvedge quality is generally addressed by giving special treatment to the edges of the weave to render it less sensitive to variations in the weft tension. Normally, the selvedge will comprise a group of at least eight warp yarns joined together to hold the woven weft yarns tight. These yarns may further be held on a separate bobbin, under higher tension and closer together than the remainder of the warp bed. The weave may also be more intricate: for example a leno or chain weave can be used to produce a more robust selvedge that is less likely to fray. Different yarns may also be used at the selvedge position.
The weaver conventionally will control weft tension using an arrangement of eyelets to provide a tortuous path for the yarn to follow through the shuttle before its exit. If a higher yarn tension is needed, the yarn will be threaded through more, or smaller, eyelets. If a lower tension is required, for example if the yarn is thicker, then fewer or larger eyelets will be used. This relatively crude arrangement can be tolerated because the selvedge holds the weft yarns in place and so compensates for any variation in weft tension. For example, 4.5 N (10 g) of warp tension may be absorbed by the selvedge whereas the shuttle operator is liable to introduce a variation of only around 1.5 N (3 g) (weft). That is, for a typical selvedge, warp tension is approximately three times that of the weft. These figures could, of course, be varied according to the yarn count.
In normal weaving, the warp threads that form the selvedge are held on a separate beam (creel) to the main beam that holds the standard warp threads. This allows for the tension of the selvedge warp threads to be controlled independently to that of the main body of warp threads. The selvedges of a flat weave are also generally held in a temple in order to permit a more effective beat. The beat occurs as a reed is pulled along the warp yarns onto the woven area in order to pack the weft threads together. This helps to maintain a square grain: the warp at 90° to the weft, which is essential in order to ensure normal behaviour of the woven fabric. Importantly however, the problem of the woven fabric drawing inwards along its edges is also eliminated.
A problem arises when weaving seamless tubular items in that they lack a selvedge that can be treated differently. To do so would result in one part of the tube having a markedly different appearance, hardly attractive given the desire to be seam-free. That is, only a single warp thread can comprise the selvedge, the appearance of which will be highly sensitive to the tension in the weft yarn. The fishtail effect is a common problem encountered in weaving seamless articles.
The problem is exacerbated if weaving a garment such as that shown in Figure 2. This figure illustrates an 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 is noted that, between the dotted lines A and B, the loom must weave three separate tubes: one for each sleeve and a third for the body. Accordingly, this garment 10 will have, not two, but six selvedges 12a - f, none of which can be adjusted to compensate for variable tension in the weft. Moreover, at least four of these 12a, b, e, f, those on the sleeves, are not fixed, but variable. That is, the sleeves are necessarily at an angle with respect to the direction of the warp threads with the result that a different warp yarn defines the selvedge position as weaving progresses along the sleeve. In other words, any of the warp threads has the potential to become a selvedge thread. Note that the shape of the body may also require a variable selvedge, but the effect is more pronounced in the example illustrated in relation to the sleeves.
Not only is the tension required to be sensitively controlled in the weft to avoid a fishtail effect and looping, the variable selvedge also precludes use of a standard temple to stabilise the selvedge. The temple itself would need to be moveable across the warp in order to stretch the different selvedge position, and this is impossible to achieve.
It is clear that the disadvantages of the single yarn, variable selvedge apply not just to the shape of garment shown in Figure 2. All seamless garments will encounter the problem that normal variation in the weft tension cannot be absorbed by the selvedge. Any situation in which it is necessary or desirable to fabricate multiple tubes across the width of the warp bed is additionally likely to encounter the problem of a variable selvedge. For example, in weaving jumpers, dresses, trousers, or prostheses having multiple branches.
A limited-capability tension device for weaving is described in PCT publication no. WO 2007/085872. The shuttle described in this document addresses the problem caused by lack of tension control in the weft yarns as off-centre seamless tubes are woven. This problem occurs primarily when switching pick direction at a loom edge to the far side of the (off- centre) sleeve being woven. As the shuttle continues its journey fully across the loom regardless of whether the underlying warp yarns are incorporated in the weave or not, a length of slack weft yarn will be dispensed from the shuttle once the edge of the sleeve is passed. At the near-side turn, this slack is readily taken up during weaving of the subsequent pick. At the far-side turn however, weft tension is not regained. The yarn will remain slack as it is drawn across the warp threads for the duration of the pick, at which point the warp yarns will engage the weft. There will accordingly be a residual length of weft yarn which remains as a loop extending beyond the end of the sleeve. In the finished product these loops have to be removed or, alternatively as described in WO 2007/085872, some method of rewinding the yarn between picks is employed.
The shuttle described in WO 2007/085872 includes a temporary storage area for the weft yarn and some means of detecting loss of weft tension. If slackening is detected, the slack yarn is retracted back into the shuttle and stored in the temporary storage area. Once tension is regained, retraction stops and the weft yarn is dispensed from the shuttle as before, preferentially from the temporary storage means. Various storage and detection mechanisms are described. For example, a tensioned spring connected to a winding arm is biased against the (tensioned) pull of the weft yarn. If tension is lost in the weft yarn, the force of the spring will cause the winding arm to rotate, which in turn loops the weft yarn around a temporary storage spool. Once the slack is drawn in, tension in the yarn is regained, which acts against the force of the spring stopping the motion of the winding arm. The yarn is then pulled out from the shuttle under tension, as is conventional in the field.
The shuttle described in WO 2007/085872 does not control tension as such. The yarn is retracted as the shuttle retraces its flight, which prevents formation of a trailing yarn. In this way, the yarn is, ideally, at zero tension during retraction, but this depends on the mechanics of the rewinding mechanism. When the weft yarn is dispensed, this shuttle is no different from the prior art. Tension is controlled by passing the yarn through a tortuous path, generally provided by the use of eyelets, between the bobbin and its exit from the shuttle.
For maximum flexibility and to permit weaving of any shape of garment, with fixed or variable selvedges, there is a perceived need to provide a shuttle and method of weaving with improved control of tension than is currently available.
It is an object of the present invention to provide a device for use in weaving, that is, in particular, capable of controlling the tension at which the weft yarn is dispensed and / or retracted and is therefore suitable for reducing the occurrence of a "fishtail" effect in seamless garments. Accordingly, the present invention provides a weft yarn carrier for use with a weaving loom, said carrier comprising a bobbin for holding yarn to be used in a weaving process, a temporary yarn store with guide for dispensing and retracting yarn therefrom and tension control means set to urge the yarn back into the carrier, such that the carrier is operable to retract the yarn to the temporary store when it is tensioned to a level below a threshold tension set by the tension control means and to dispense the yarn from the store when it is tensioned to a level above the threshold tension.
In this manner, tension in the yarn is consistently held at a level close to the preset threshold value as it is dispensed from and retracted to the temporary store. This is a far more sophisticated control than offered by the prior art tension control mechanism using eyelets, or similar provision of a tortuous path. Such prior art designs of shuttles are simply not capable of retracting the yarn and therefore cannot exercise such fine control of its tension level.
Tension control such as provided by this invention can be used to great effect when weaving seamless items with variable selvedges. As mentioned above, a standard temple cannot be used to stabilise a variable selvedge. An application of this invention however offers a solution: a full width temple in combination with a shuttle equipped with a variable tension control capability. A full width temple will control the tension of all the warp threads and so responsibility for special treatment of the selvedge is shifted to the weft. A variable tension device is therefore incorporated in the shuttle, which is adjusted before weaving according to the weft yarn count and warp tension. During weaving therefore, a shuttle designed in accordance with the present invention will maintain the pre-selected weft tension in the shuttle.
Ideally, the yarn is under approximately the same tension regardless of whether it is retracted to or dispensed from the store within the carrier. This is in contrast to the prior art shuttle described in the above listed PCT application, which retracts the yarn under zero tension and dispenses it under a tension set in accordance with a tortuous exit path.
During a weaving process, yarn will be retracted to the temporary store as the shuttle turns and then begins a subsequent pick. When the weft starts to become incorporated in the weave during this new pick, the weft yarn will therefore be dispensed from the temporary store. This is the point at which the selvedge is woven. Yarn tension at this point will therefore be governed by the sensitive tension control device, and not by the crude arrangements of the prior art. Such control of tension as afforded by the present invention enables better quality selvedges to be woven in seamless articles. This advantage applies even if the selvedge varies position, for example along a sleeve extending across a warp bed.
It is preferred that the tension control means includes a means for adjustment of its bias strength, whereby the threshold tension level may be adjusted. This permits this design of shuttle to be adapted to weaving different yarns, different weave constructions, used with different warp tensions and other variations commonly found in the field of weaving. It further allows tension to be fine tuned if weaving is commenced and initial inspection reveals that the quality of the selvedges is not satisfactory. That is, fine adjustment may readily be made to the yarn tension without unthreading and rethreading the yarn.
The temporary yarn store may include a reel and the guide may comprise a winding arm arranged to wind and / or unwind yarn about the reel. The winding arm is preferably connected to the tension control means, which permits a relatively straightforward communication of force from the control means to the winding or unwinding yarn.
The tension control means may include a spring set to apply a tension (T 8 ) to the winding arm, whereby energy stored in the spring is increased as the winding arm unwinds the yarn and released to drive the winding arm to wind the yarn. The tension (T 8 ) in the spring is preferably adjustable by means of a threaded screw. The force / tension applied by the spring must be overcome in order for the yarn to be dispensed, which therefore requires the yarn to be dispensed from the temporary store under tension in the region of T 8 . Obviously, the instantaneous tension in the yarn as it is dispensed will depend on the initial spring tension (T 8 ) and the amount by which this is reduced as a result of excess yarn winding about the reel. During retraction, the spring supplies the reverse force / tension (T 8 ), which pulls the yarn back into the carrier.
Preferably the reduction of T 8 as a result of excess yarn being wound on the reel represents only a small fraction of the value Of T 8 . This may be achieved by suitable design of spring, which selected such that only a small reduction in bias strength occurs if the maximum anticipated (for a particular weaving process) length of yarn is retracted to the reel. That is T 8 , under such circumstances, may be considered constant.
Alternatively, the tension control means includes a motor set to apply a torque to the winding arm thereby urging the arm to wind the yarn and acting as a brake as the arm unwinds the yarn. The torque applied by the motor to the winding arm may be variable in response to a signal from a tension detector, in such a manner than the signal returns towards a preset value.
The carrier itself may further be arranged such that, in the event that the temporary yarn store holds no yarn, yarn is dispensed from the bobbin to exit the carrier via the guide. That is, weaving continues once the temporary store is empty with the weft yarn being pulled directly from the bobbin. The yarn must still however pass through the same guide that controls yarn exiting the temporary store. For embodiments in which passage through the guide is the means by which tension is communication to the yarn from the tension control means, the yarn taken directly from the bobbin must also overcome any force applied through the guide. That is, yarn dispensed directly from the bobbin must also be pulled from the carrier under a tension that is sufficient to overcome the bias of the tension control device.
The carrier preferably includes a second tension control means arranged to apply a frictional force (T f ) to the yarn as it is dispensed from the bobbin. In this way, yarn pulled from the carrier that comes directly from the bobbin must be pulled under sufficient tension to overcome the forces applied by both the tension control devices. That is, during the bulk of the weave, the weft is woven into the warp at a higher tension than at the selvedges.
The second tension control means is preferably also adjustable in order to vary the frictional force (T f ) that needs to be overcome by the yarn as it is dispensed from the bobbin. Ideally, the second tension control means comprises two curved discs, with adjustable separation. The separation may further be adjustable by means of a screw. Many alternative designs of frictional controllers are available, but this arrangement, with curving disc surfaces, is less likely to snap the yarn if knots or other imperfections are present.
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings.
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 1A.
Figure 2 is a diagrammatic plan view of the warp yarn bed of a weaving loom, showing the weaving of a sleeved garment. Figure 3 is a side view illustrating relevant components of an embodiment of a weft yarn carrier in the form of a shuttle in accordance with the present invention.
Figures 4A, 4B and 4C are partial views of the shuttle of Figure 3 on an enlarged scale.
Figure 5 is a side view illustrating relevant components of a second embodiment of a weft yarn carrier in the form of a shuttle in accordance with the present invention.
Figures 6A and 6B are partial views of the shuttle of Figure 5 on an enlarged scale.
Referring first to Figures 3 and 4, there is shown a modified flying shuttle according to a first embodiment of the invention. Figure 3 shows the majority of the shuttle 16, whilst Figures 4A, 4B and 4C show, from different viewpoints, the internal mechanism at the left-hand side at an enlarged scale. It will be seen from Figure 3 that the shuttle 16 has an elongate body 20, having pointed ends (of which one 21 is shown) 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 and, in particular, the method used for moving the shuttle across the warp bed.
The body 20 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. Two situations are to be distinguished in weaving using this design of shuttle. During the majority of the weaving process, yarn 26 is unwound directly from the pirn 24, guided by an eye 28, which is in line with the axis of the pirn, and exits the shuttle. The storage mechanism 25 plays little part in this situation and is to some extent bypassed by the path taken by the yarn 26 through the shuttle. At certain stages of the weaving process however, as the shuttle changes direction between picks, yarn is wound onto and then dispensed from the storage mechanism 25. The storage mechanism 25 comprises (see Fig 4A) a fixed reel 30, about which a variable quantity of yarn 26 may be wound, and support structure 32. The reel 30 is tapered so has to have a larger diameter at the end of the shuttle remote from the pirn 24. This encourages the yarn to slip back towards the pirn end of the reel, if space is available, as it is wound. The guiding eye 28 is held at the end of a wire 28a that is fixed to the support structure 32. The support structure 32 includes an adjustable friction dampener 34, which in this embodiment is a pair 34a, 34b of curved tension discs whose separation can be adjusted by a screw 34c. The screw 34c can be set according to yarn thickness and strength to provide a suitable holding force. The friction dampener 34 holds the yarn in place under tension as it passes under the support 32. Thereafter, if the reel 30 contains a store of yarn, the yarn 26 is wound about the reel 30 and threaded through a winder arm 36. The winder arm 36 is operable, as will be described in greater detail below, to wind the weft yarn 26 about the tapered reel 30 and to guide the unwinding yarn. From the winder arm 36 the yarn emerges from the shuttle body via an exit guide 38. The emerging yarn 26 is used to create the weft during weaving, as described above.
A shaft (not shown) runs in bearings supported axially through the centre of the reel 30 and support structure 32. The winder arm 36 is mounted on a knob 40 (Fig 4B) fixed to one end of the shaft, remote from the support structure 32. The arm 36 initially extends in a radial direction, but then turns through 90° to an axial direction and terminates in a winder eye 42. Rotatably mounted on the support structure 32 (Fig. 4C), on the opposite side to the reel 30 and separate from the friction dampener 34 and therefore not in contact with the yarn 26, is a hollow drum 44. The shaft extends through the support structure 32 to emerge centrally within the drum 44. The drum contains a spiral clock spring 46 that serves as a tensioning device. The centre of the spring 46 is attached to the shaft and its outer end to the hollow drum 44. The drum 44 has a gear ring fixed to its outer surface, which meshes with a screw adjuster 47 partly mounted on the support structure 32. The screw adjuster 47 can accordingly be tightened or loosened to rotate the hollow drum 44 and so to adjust the tension in the spring 46. When the desired tension is set, the screw adjuster 47 holds the drum 44 in place. This sets the biasing force that may be exerted by the spring 36.
The shaft extending from the centre of the spring 46 to the winder arm 36 ensures communication between the two. That is, the sense of the spring 46 is such that energy is stored as the winder arm 36 rotates to unwind the yarn 36. Conversely therefore, the spring relaxes as the winder arm 36 places yarn 26 on the reel 30.
When weaving with this shuttle 16, the shaft is initially held fixed and the screw adjuster 47 is set to give the spring its required tension (T 8 ). The appropriate weaving tension will depend on various factors including yarn thickness, tension in the warp yarns, weave construction and position in the loom. The yarn 26 is threaded from the pirn 24 via the friction dampener 34 and through winder arm 36. The friction dampener 34 is also adjusted to set a holding force (T f ) appropriate to the yarn type and weave.
Once the shuttle 16 is threaded, and before weaving commences, the shaft is released. At this stage the yarn must be held under tension in order to overcome the bias T 8 of the spring. Alternatively, the winder arm 36 is free to rotate under the bias T 8 exerted by the spring 46. Rotation will continue as the spring 46 relaxes and, consequently, yarn 26 is wound a number of times about the reel 30.
Consider the first alternative above. Starting tension in the yarn must match the bias of the spring 46; that is, yarn is initially under tension T 8 . The shuttle is then moved rapidly across the warp bed and tension in the yarn increases. In this initial period, once the tension in the yarn is sufficient to overcome both the bias of the spring 46 and the force of the friction dampener 34, the yarn 26 will be pulled directly from the pirn 24. That is, weft thread will be dispensed under a tension T 8 + T f .
In the other alternative, consider the tension in the yarn 26 increasing gradually from zero. Almost immediately, once a small force is exerted that is sufficient to begin winding the spring, the winder arm 36 will be rotated in order to remove yarn 26 from the reel 30. Yarn 26 is therefore dispensed from the shuttle under the (instantaneous) tension set by the spring (0, rising to T 8 ).
Once all the yarn stored on the reel 30 has been unwound, yarn 26 is then taken directly from the pirn 24. At this stage, the spring 46 is fully wound and so exerts a bias T 8 on the winder arm 36 to wind yarn back on the reel 30. As before therefore tension is the yarn as it is dispensed from the pirn 24 must therefore be sufficient to maintain the winder arm 36 against the force of the spring and to overcome the resistance of the friction dampener i.e. T 8 + T f .
Of course in a practical weaving situation, the initial starting tension may be held anywhere between 0 and T 8 , with the shortfall from T 8 being taken up in windings around the reel.
Consider now a situation during the weaving process in which the tension in the yarn drops. This would occur if the speed of the shuttle's flight is slowed during a pick, for example, as the shuttle approaches the end of a pick and prepares to stop. Once the tension drops, the yarn tension is no longer sufficient to counter the bias of the spring 46 and it ceases to be able to hold the winding arm 36. The spring 46 will relax to release its stored energy, which rotates the shaft and therefore, in turn, the winder arm 36. As the winder arm 36 rotates, it winds excess yarn 26 onto the reel 30 and so retracts the yarn back into the shuttle.
As the yarn is retracted, tension in the yarn outside of the shuttle is increased and the biasing force of the spring is reduced as the spring unwinds / relaxes. Very quickly therefore, these forces will equalise and the yarn is again held under tension in accordance with the biasing force of the spring. As weaving progresses, yarn 26 is taken from the shuttle as before: first from the reel 30 and thereafter from the pirn 24.
The situation is similar if the shuttle is moved backwards. This will first cause a drop in yarn tension as its forward motion is reduced. The yarn will be pulled backwards as the spring bias causes the winder arm 36 to rotate and so to store excess yarn on the reel 30. If the shuttle is moved in reverse, tension will continue to drop and, for so long as this tension is maintained at a level just below the instantaneous bias of the spring 46, retraction will also continue.
During a practical weaving situation it is not anticipated that there will be sufficient slack thread to fully unwind the spring. That is, the bias exerted by the spring in winding and unwinding from the reel will vary between T mιn and T 8 , where T mιn is the tension resulting from the maximum anticipated number of windings. Suitable design of spring 46 can ensure that T mιn ~ T 8 , during the anticipated operating range.
Regardless of whether the yarn 26 is being dispensed or retracted from the reel, tension in the yarn is maintained as a result of the balance of forces between the wound spring and outward pull of the yarn. If the yarn is dispensed, the outward pull on the yarn results from the flight of the shuttle across the loom. If the flight slows, excess yarn is wound onto the reel 30 in order to re-establish exit tension. Once the excess begins to be used in the weaving process, yarn exit tension will increase in line with the increased energy stored in the spring. Once the excess has been re-used, yarn tension will return to T 8 . Dispensing will thereafter continue at a tension T 8 + T f , as yarn will now be taken directly from the pirn, but at a lower rate as a result of the speed reduction. As the yarn is retracted, the winding arm 36 is essentially pulling with a tension T 8 against the fixed position of the woven yarn.
The friction dampener 34 also contributes to the tension in the yarn as it is dispensed directly from the pirn, which will be the case during the majority of the weaving process. This contribution T f must be sufficient to overcome the friction provided by the plates 34a, b. Such a device, utilising the pair of friction plates with adjustable separation, is commonly used in sewing machines to tension the thread.
As the change in forces is always gradual and produces an instantaneous reaction, there is no significant loss of tension in the yarn. In the prior art, as the shuttle turns between picks, the tension in the yarn falls to zero before retraction begins. In the present invention, the tension in the yarn is maintained between T mιn and T 8 as the shuttle slows and as it turns and at T 8 + T f thereafter.
In weaving a fabric therefore, it is clear that the yarn 26 can be dispensed from or retracted to the storage device 25 under essentially constant tension. At the end of, and throughout each pick, this shuttle 16 maintains tension in the weft yarn. This includes the time at which the yarn is looped around the selvedge, therefore reducing the likelihood of formation of loops or a fishtail effect.
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 of the mechanism. A full width temple may be used in combination with the variable-tension shuttle of the present invention. A full width temple will control the tension of all the warp threads and so responsibility for special treatment of the selvedge is shifted to the weft. The variable tensions in the shuttle T 8 , T f must be adjusted before weaving begins. The settings will depend on factors such as yarn count and tension in the warp threads. It is envisaged that in most weaving applications T 8 ~ T f . Typically, examination of the first few woven weft rows will confirm whether or not the tensions have been set correctly. If not, further adjustment can be made and weaving recommenced. Once the correct range has been established however, there should be no need for further manual intervention. Weaving at the critical selvedges will be with the weft under a tension in the range T mιn to T 8 . Suitable design of spring 46 can ensure that this range is appropriately narrow.
It is clear that many alternative components to those described in relation to the above embodiment exist. What is important is that a tensioning device is included in the shuttle that ensures the yarn is dispensed or retracted, as required, whilst maintaining tension. This is to be contrasted with the prior art shuttle disclosed in the above mentioned PCT application, in which yarn is only retracted once the tension falls to zero.
Turning now to the second embodiment of this invention illustrated in Figures 5 and 6. Figure 5 shows the internal components 60 of this alternative design of shuttle, whereas Figures 6A and 6B show in more detail and from different viewpoints, the relevant components towards the exit end. Components of this embodiment that are also shown in previous figures are like referenced. As before, within the interior of this shuttle 60 is mounted a bobbin or pirn 24 which is the primary source of weft yarn, and a take-up and storage mechanism 25. During the majority of the weaving process, yarn 26 is unwound directly from the pirn 24, guided by an eye 28, which is in line with the axis of the pirn, and exits the shuttle. The storage mechanism 25 comprises (see Fig 6A) a fixed reel 30, about which a variable quantity of yarn 26 is wound, and support structure 32. The reel 30 is tapered so has to have a larger diameter at the end of the shuttle remote from the pirn 24. This encourages the yarn to slip back towards the pirn end of the reel, if space is available, as it is wound. The support structure 32 includes an adjustable friction dampener 34, through which the yarn 26 passes after exiting the guiding eye 28. Thereafter, the yarn 26 is threaded through a winder arm 36, which is operable to wind and unwind the weft yarn 26 about the tapered reel 30. From the winder arm 36 the yarn emerges from the shuttle body via an exit guide 38. The emerging yarn 26 is used to create the weft during weaving.
A shaft (not shown) runs in bearings supported axially through the centre of the reel 30 and support structure 32. The winder arm 36, shaped as before, is mounted on a knob 40 (Fig 6B) fixed to one end of the shaft, remote from the support structure 32. This second embodiment differs from the first in that in place of the hollow drum 44 attached to the support structure 32 (Fig. 6A), on the opposite side to the reel 30, is a gear wheel 64. The gear wheel 64 is centrally located on the shaft and is driven by a permanent magnet torque motor 66 via a pinion gear 66a. A tension detecting sensor 68 is located about the yarn 26 in the vicinity of the exit guide 38. A feedback and control circuit 70 is arranged to operate the motor 66 in response to a signal generated at the tension detecting sensor 68.
The control circuit board 70 includes a small battery or charge capacitor (not shown) and a metal wire coiled around a hollow tube 72. Within the tube 72 a cylindrical magnet (not shown) is free to slide under the movement of the shuttle. Each pass of the magnet through the coil induces an electrical pulse in the coil, which is rectified and then supplied to the battery or capacitor. In this way, the battery or capacitor is charged by the weaving motion of the shuttle. This in turn supplies electrical power to the circuit board 70, and hence motor 66. Tension is maintained in the yarn 26 by applying torque through the motor 66, via the gears 66a, 64 to the winder guide 36. This is analogous to the action of the clock spring in the previous embodiment.
Operation of this embodiment of the invention can again be appreciated by considering increasing the tension in the yarn, for example as it begins to be pulled from the reel to exit the shuttle. The motor is off, or at least held stationary, which causes tension in the yarn 26 to increase. Once this tension reaches a set level, as detected by the tension sensor 68, the motor 66 is switched on. The motor 66 effectively brakes, via the gear 64, the unwinding of the winder guide 36 by applying a suitable torque. The motor is thereafter driven with more or less torque in response to the signal from the tension detector 68: if the tension falls, the torque is increased and some yarn retracted, allowing re-establishment of the preset tension. Conversely, if the tension rises, winder speed is permitted to increase, i.e. braking reduced, allowing the tension in the yarn 26 to fall back to its preset level. In this way, tension in the yarn is maintained, albeit with minor fluctuations depending on the response time of the feedback loop.
As before, during the majority of the weaving process, the yarn will be pulled directly from the pirn under a tension set by both the motor and the friction dampener.
The components on the circuit board can be set to permit overall control of tension depending on the yarn and nature of the weave.
In an alternative embodiment, the friction dampener 34 is arranged to guide the yarn only and it is replaced with an alternative tension control device located in the path of the yarn after the exit guide 38. In this embodiment, the friction tension T f therefore needs to be overcome for the yarn to be both dispensed and retracted, regardless of whether the yarn is taken from the reel or the pirn. There will accordingly be a bigger difference between dispensing tension T f + T 8 and retraction tension T 8 - T f .