Improved yarn puller

Abstract

A puller 110 for a carpet tuft forming apparatus, the puller comprising: a first leg 111 comprising first jaw 113, a second 112 comprising a second jaw 114, wherein the first leg 111 and the second le

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to a yarn puller suitable for use in weaving carpet on a power loom. BACKGROUND TO THE INVENTION In a power loom for producing woven carpet, in particular for weaving Axminster carpet, a tuft forming apparatus provides the lengths of yarn which, when cut, form the yarn tufts. The pulling and cutting of yarn, and thereby the forming of tufts, occurs at so-called ‘loading points’. The tufts are transferred from these loading points by a tuft carrier and thereafter by a gripper mechanism over to their respective ‘weaving points’ before being woven into place within tensioned warp and weft threads. The result is the production of carpets capable of having complex, multi-coloured and beautiful patterns. Tuft forming apparatus comprise yarn pullers (also known as ‘tuft pullers’) which are specialised devices configured to draw a length of yarn which can then be cut to form a tuft. Several such apparatus are disclosed in EP 1156145 A1. Typically, the tuft length is set by the desired pile height; this determines the distance through which the puller must draw the yarn from a yarn selector wheel (and the bobbin whereon each yarn is wound). The yarn itself is set by the required colour; this determines the angular position of the yarn selector wheel which provides yarns of various colours maintained in channels at angularly discrete positions on the selector rim. The technical problems with pullers in the state-of-the-art highlight significant limitations and challenges encountered in the operation and performance of existing puller designs within existing tuft forming apparatus. For example, known tuft pullers face operational challenges when operating above 16 Hz due to the tendency of the puller legs to bounce open during closure. This problem is exacerbated at these low operating frequencies by leg resonance. This bouncing motion results in a loss of grip on the yarn held between the legs, leading to inconsistent tuft lengths and reduced production efficiency. Additionally, the bias spring between the puller legs experiences rapid wear above 25 Hz, further compromising the reliability and longevity of the puller mechanism. In known puller designs, the use of separate needle rollers for pivot points on the puller legs often leads to the pivot covers becoming loose during operation. This instability in the pivot mechanism contributes to erratic performance and requires frequent maintenance to ensure proper functionality, leading to downtime and decreased productivity in carpet weaving operations. Known puller designs lack also direct control mechanisms for both the opening and closing phases of the puller cycle. Whether utilising a sprung leg system or an integrally formed resilient leg member, the puller operates solely on the inherent mechanical elasticity of these components. This reliance on mechanical properties results in diminished control over the puller jaws, leading to inconsistencies in tuft length and reduced overall performance over time due to wear. It is known that wear or fatigue can lead to unpredictable changes in the mechano-elastic behaviour of the resilient members over time. Existing designs often employ soldering, bolts, or doweling to attach the jaws to the puller legs, resulting in inaccuracies in jaw positioning and frequent detachment during operation. This lack of secure attachment leads to variations in tuft length and uneven pile height in the produced carpets, necessitating frequent repairs and interruptions to production processes, ultimately impacting the overall quality and efficiency of carpet manufacturing. The use of straight driving pins in prior puller designs results in high frictional forces and accelerated wear. This leads to increased maintenance requirements and the need for frequent replacement of worn pins and puller legs, contributing to downtime and production costs in carpet weaving operations. These technical problems underscore the need for innovative technical solutions in tuft pullers to address issues related to operational stability, control mechanisms, pivot reliability, attachment methods, and overall performance in carpet manufacturing processes It is therefore an object of the invention to overcome the aforementioned problems. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a puller for a carpet tuft forming apparatus, the puller comprising: a first leg comprising a first jaw, a second leg comprising a second jaw, wherein the first leg and the second leg are pivotably interconnected so as to permit relative motion of the first leg with respect to the second leg between an open state and a closed state, and wherein the first jaw and the second jaw are usable for engaging a yarn when the legs are in the closed state and for disengaging the yarn when the legs are in the open state; the puller further configured in that: at least one of the first leg and the second leg comprises a guide configured to engage a driving member, and the guide is configured such that, in use, engagement of the guide and the driving member causes relative motion of the first leg with respect to the second leg from the open state to the closed state and from the closed state to the open state. Additionally or alternatively, the guide may be configured such that, in use, when the guide and the driving member engage, relative motion therebetween causes relative motion of the first leg with respect to the second leg between the open state and the closed state, whereby to control opening and closing motion of the legs. In this way, relative motion between the engaged guide and driving member causes the controlled opening and closing of the legs. In this way, the puller legs may operate at speeds of up to 45-65 Hz without bouncing open upon closure, as is a problem in previous puller arrangements. This is particularly beneficial for looms requiring a high rate of puller leg closure associated with high operating speeds, such as in large-scale carpet production. This advantage is achieved, in part, by the replacement of uncontrolled opening and / or closing motions of the legs, often using unreliable resilient members, with controlled opening and closing and, in particular, with a guide which is manoeuvred about the moving driving member so as to actuate the opening and closing motions of the puller legs with precise control and without causing wear or other detriment to the moveable components over time. Typically, the first jaw and the second jaw being usable for engaging a yarn may be understood to mean that the first jaw and the second are configured to engage the yarn when the legs are in the closed state, and the first jaw and the second jaw being usable for disengaging a yarn may be understood to mean that the first jaw and the second jaw are configured such that the yarn is disengaged when the legs are in the open state. In an example of the first aspect, the first leg and the second leg are pivotably interconnected by at least one pivot pin. In this way, the first and second legs may be connected by means of the same pivot mechanism comprising a common pivot, thereby improving alignment and synchronisation between the legs and providing overall smoother opening / closing movements. In other words, the legs may be pivotably connected by means of a single same pivot pin 3 passing through a shaft about which the legs rotate. Such an arrangement has further advantages in reducing the complexity of, and space occupied by, the puller assembly, and in particular the complexity of any cranking that may be necessary to pivot said assembly, and reducing manufacture costs. In an example of the first aspect, the puller comprises one or more further legs with one or more further jaws corresponding thereto. In this way, improved grip on the yarn end is provided by having further jaws whereto the yarn is engaged. In an example of the first aspect, the first leg and the second leg are pivotably interconnected by a first pivot pin engaging the first leg and a second pivot pin engaging the second leg. In this way, different and / or independent rotational movements of the legs may be realised, the likelihood of interference or wear between the legs is mitigated, and the legs may have different positions or orientations in order to distribute load bearing more effectively. Herein, a leg is typically understood to mean any elongate member intended for a mechanical application such as the tuft forming apparatus herein disclosed. The leg may be integrally formed or it may comprise a plurality of segments which are fixedly connected in use. Preferably, the leg is formed of any material of high strength, high stiffness, and low density; exemplary materials include titanium, hardened steel, or various other alloys thereof. The puller comprises at least two legs; however the invention is not limited thereto, and the puller may be extended to more than two legs as will be apparent to the skilled addressee. In preferable examples, the plurality of legs is separately formed, and may be not integrally formed or not connected by resilient means such as a spring, elastic material, or other resilient member. This achieves several advantages as herein described, such as improved precision of control over, and the mechanical longevity of, the rotating members. In some examples, opening and / or closing motion of the legs may not be realised or otherwise influenced by deformation in a component of the puller. The plurality of legs are rotatably interconnected with one another; preferably the legs are pivotably connected, wherein each leg is rotatably connected to the same pivot mechanism (in which case the legs may be considered to be rotatably ‘interconnected’ with respect to each other). The pivot mechanism may comprise a plurality of pivot pins, each pin being rotatably connected to respective legs; alternatively, the pivot mechanism may comprise a single pivot pin to which both legs are each rotatably connected. In at least the latter example, the legs may be separated by a washer, bushing, or other kind of spacer along the pin. Preferably, at least two legs of the plurality of legs each comprise a jaw. The jaw may be arranged at any suitable location on the leg; preferably, the 4 jaws are positioned at corresponding distal ends of their respective legs, whereby the jaws so positioned are usable for engaging a yarn passing therebetween. A distal end of a leg may be understood to mean the end or portion of the leg away from or distal to the pivot. Likewise, a distal end of a puller may be understood to mean the end or portion of the puller (or leg(s) thereof) away from or distal to the pivot. In an example of the first aspect, the first jaw and the second jaw are located at a first distal end of the puller and the guide is located at a second distal end of the puller, wherein the pivot mechanism (preferably, the pivot pin) is located therebetween, wherein the second distal end is at least different to and preferably opposite the first distal end. In this way, the lever action exertable by the driving mechanism is maximised, and the greatest possible control of the jaws is ensured throughout the entire tuft forming cycle. Preferably, a thickness of the legs towards or at least at the first distal end is tapered with respect to a thickness of the legs at the second distal end. In this way, peak stresses in the legs during deflection of the legs are reduced when in the closed state, the inertia of the legs which has been found to exacerbate wear on the driving mechanism is significantly reduced, and the resonant frequency is increased, which reduces the bouncing effect as previously described. In an example of the first aspect, the first leg is configured to move relative to the second leg in a plane of motion, and wherein the first leg and the second leg are configured to overlap, at least in part, in a plane perpendicular to the plane of motion. In this way, the space requirements of the puller may be reduced by overlapping the legs in the plane perpendicular to the plane of rotational motion of the legs. In an example of the first aspect, the first jaw and the second jaw comprise teeth, the teeth being arranged so as to interlock when the legs are in the closed state. Typically, the teeth comprise a plurality of projecting parts. Preferably, the teeth are configured to interlock when the legs are in the closed state so as to deflect the legs such that the jaws become substantially parallel to each other. In this way, improved grip on the yarn is provided. In an example of the first aspect, the first jaw and the second jaw are integrally formed with the first leg and the second leg respectively. In this way, the jaws are prevented from misaligning with or falling off their respective legs, thereby ensuring a consistent tuft length and pile height. Alternatively, it may be connected to the leg by a mechanical fastening (such as dowels, threaded bolts and nuts, or interlocking tabs and slots) or by subsequent fusing (such as via welding, soldering, brazing, adhesive bonding etc.). Herein, a jaw may be understood to mean any component usable for contacting or otherwise directly engaging a yarn. A jaw may be referred to as a gripping portion. Typically, the combined action of two or more jaws is necessary to engage a yarn; for example, a first jaw contacts a yarn on a first side thereof and a second jaw, facing the first jaw, contacts the yarn on a second side opposite the first side of the yarn in a manner so as to engage, at least momentarily, the yarn between the first jaw and the second jaw. Thereafter, the relative motion between the puller assembly and the yarn selector wheel when the yarn is engaged is such that a predetermined length of yarn is drawn from the bobbin. Preferably, the yarn selector wheel is stationary with respect to the loom during a given cycle whereas the puller assembly may be configured to be moved with respect to said wheel via a driving mechanism. Accordingly, to engage a yarn by a plurality of jaws may be understood as the seizing and / or gripping of the yarn between said jaws. The yarn is typically oriented substantially horizontally from when it is extending from a given channel in the yarn selector to when it is being cut by the cutting mechanism. Depending on the loom, the yarn may be oriented horizontally ± 20°. When the jaws are at a minimum separation (for example, when the jaws are presently engaging a yarn), the legs (and equally the puller) may be said to be in a ‘closed’ state. The jaws may be aligned with respect to each other so as to cause deflection in the legs when in the closed state; in this way, the jaws press together, becoming substantially parallel to each other and thereby improving grip on the engaged yarn. Correspondingly, for a yarn to be disengaged may be understood to mean that the yarn is not engaged by the jaws. When the jaws are at a comparatively greater separation than in the closed state and preferably at a maximum separation (for example, when the jaws disengage the current yarn and return to seize the subsequent yarn in the next tuft forming cycle), the legs (and equally the puller) may be said to be in an ‘open’ state. The separation may be understood to mean the distance between the jaws at a given point during the tuft forming cycle. A state may be understood to mean a particular condition or configuration of the first and second legs at a particular point in the tuft forming cycle (and / or at a particular time); this term is used to describe whether the legs, in particular the yarn-engaging jaws thereof, are open or closed. Accordingly, the open and closed states are typically defined by the maximum and minimum configured separations of the jaws in a given cycle. Said separations may be configured based on one or more of: the diameter of the yarn to be used, the required force to be applied when 6 gripping the yarn to be used, the distance between the side cheeks around which the legs pass during the cycle, the distance to other components in the tuft forming apparatus which the legs are not to interact with during the cyclic motions of the puller, other threshold distances, or they may be determined by other factors apparent to the skilled addressee. As the puller legs are configured to move from a first state (either the open or the closed state) to a second state (respectively, either the closed state of the open state) and back to the first state during one tuft forming cycle, it may be considered that there are one or more intermediate states (that is, states between the open and closed states that are neither fully open or fully closed) wherein the legs are configured to transition between the open and closed states and vice versa. In some cases, no yarn may be presented to the puller, for example, when there is a system fault or when said puller is not presently required during a carpet manufacturing process. In such cases the legs (and equally the puller) may continue to cycle between the closed state when the jaws are at a minimum separation and the open state when the legs are at maximum separation during the tuft forming cycle (in this instance, the cycle may also be referred to as a null cycle or a ‘tuft not-forming’ cycle). There may be several cycles during a given weaving process wherein the null position on the selector is aligned to the puller at the beginning and end of each traversing tuft forming cycle and the tuft forming apparatus is over selector positions where tufts are already present, such as in a repair cycle. It will be apparent to the skilled addressee that, in some examples of the invention, when the yarn is not engaged by the jaws, the yarn may not be disengaged altogether; for example, when the yarn is cut to form a tuft during any given tuft forming cycle, the tuft is released from the puller jaws, whereafter (despite the yarn tuft being disengaged from the puller jaws) a length of the tuft is trapped between side cheeks, an end or a side of the tuft may be subsequently contacted by a pusher or the tuft may be guided by entrained air flow into a ‘pocket’ for transfer to a weaving point, and a fresh tail end of yarn may be positioned within a channel of the selector wheel prior to its being engaged by the puller on the subsequent cycle or, if this particular yarn is not selected during the current cycle, its tail end may remain in the channel for one or more cycles until it is needed for the weave pattern. Accordingly, the tail end of the yarn and the yarn tuft are mechanically supported throughout the tuft forming and weaving processes. However, the yarn is only engaged by the puller jaws while a predetermined length is being pulled from the bobbin and while said length is being cut to form a tuft. In an example of the first aspect, the driving member comprises a driving pin configured to move, relatively to the pivot pin, through a first driving path, the guide being configured such that, in use, motion of the driving pin along the first driving path causes the driving pin to engage with the guide. Herein, a driving member (or ‘actuator’) may be understood to mean any component usable for engaging a guide comprised in the one or more legs of the puller such that relative motion between the guide and the driving member when said elements engage actuates relative motion of the legs, preferably pivoting relative motion. Typically, the driving member is driven, and it imparts said motion onto the puller legs via the guide(s) thereof when the driving member engages in use at least one location in / on the guide(s). Alternatively, the driving member may be stationary with respect to the pivot pin and / or the tuft forming apparatus and the guide may instead be driven, in such examples the guide being configured to impart motion onto the legs when it engages the driving member. In either example of the guide or driving member being driven, relative motion is imparted onto the puller legs upon engagement (typically involving either continuous or discontinuous contact at at least one point during a period of time in the tuft forming cycle) of the guide and the driving member. The combination of at least the guide and the driving member may be referred to as the driving mechanism. Exemplary driving members include a driving pin, a crankarm, a rod, a cam, or any other such component usable for engaging a guide of the puller and thereby imparting relative motion onto the legs of the puller. A driving pin may be a cylindrical shaft or rod mounted in the tuft forming apparatus. In some examples, the driving member is driven by a crank, the crank being connected to a gearbox comprised in the tuft forming apparatus. Preferably, there is a single driving member per puller; in this way, the driving member engages a guide in each leg, actuating the legs between the open and closed states. Alternatively, a respective driving member may be provided for each puller leg which separately engages the guide in each leg in order to impart relative rotation on the legs. Alternatively still, there is a single driving member engaging a guide in one leg, the other leg being fixed relative to the pivot pin and / or the tuft forming apparatus whereto the puller is attached. In an example of the first aspect, the guide is configured for actuation by reciprocating motion of the driving pin through the first driving path, wherein said reciprocating motion permits the legs, in use, to move in a cycle between the open state and the closed state. In this way, the puller may continually form tufts one after the other by realising consecutive tuft forming cycles. Herein, the first driving path may be understood to mean the line traced by the driving member during its motion, wherein the motion of the member through said path facilitates the member engaging the guide. Preferably, said motion comprises reciprocating motion of the driving member with respect to the pivot pin along a vertical axis through the member and the pin. Such motion of the driving member, when engaged with the guide, actuates the legs to move relative to one another in a cycle, said cycle forming part of an overall tuft forming cycle, wherein the jaws move apart into the open state and move together into the closed state. Herein, the second driving path may be understood to mean the line traced by the pivotable interconnection (preferably a pivot pin) during motion of the puller assembly, this interconnection and preferably the pin thereof being a convenient reference point for the motion of the entire puller assembly, wherein the motion of said assembly along said path facilitates the drawing of the engaged yarn, the transporting of the drawn yarn to the location of the cutter, and the returning of the jaws to grip the subsequent yarn end. Preferably, said motion of the puller assembly comprises cyclical or reciprocating motion, thereby forming the overall tuft forming cycle. In an example of the first aspect, the driving member further comprises one or more rollers, wherein the one or more rollers are configured to revolve about the (driving) member. In this way, friction between the member and the guide surface is minimised, permitting smoother rotational motion of the legs, dramatically reducing wear, and increasing the load bearing capacity of the member compared to known sliding contact mechanisms because the roller inner bore makes contact with the pin and the roller outer surface makes rolling contact with the guide track, whereas a pin against the guide track is limited to making line contact. Further advantages of the roller include quieter operation, the provision of consistent motion control due to the uniform rolling action, and that the roller in the guide avoids impact loads on the guide as the pin may otherwise have discontinuous contact or impact with the opening profile of the guide. In this way, the roller reducing wear will lead to a reduction in impacts and inaccuracies in intended puller opening. Preferably, there is a first roller and a second roller, each roller being configured to rotate about the (same) driving member, wherein the first roller is configured to contact a first guide of the first leg and the second roller is configured to contact a second guide of the second leg. Alternatively, (e.g., in examples where the puller legs are separately driven by distinct driving members) each roller may be configured to rotate about a respective driving member associated with each respective leg, wherein a first roller is configured to contact a first guide of the first leg, and a second roller is configured to contact a second guide of the second leg. In any case, the first and second rollers are configured in use to revolve around the given driving member and typically revolve in use in opposite directions so as to permit relative rotation of the first leg with respect to the second leg and vice versa. Herein, a roller may be understood to mean any component configurable to connect to a first component (such as the driving member) and to roll along - and thereby ‘engage’ - a surface of another component (such as the surface of the guide). The roller may be rotatably connected to the driving member such that, as the roller revolves thereabout, the member is permitted to roll along the guide unimpeded by friction as the outer surface of the roller makes contact with the surface of the guide. The roller may be freely rotatable. The roller may have a circular cross-section and / or a smooth outer surface. When implemented in the example of the driving pin, the roller may be referred to as a roller bearing pin, wherein the pin serves as the axis of revolution for the roller. The roller typically has a larger diameter than the pin to provide stability and reduce contact pressure in order that the roller may freely rotate around the pin axis and thereby roll along the surface of the guide with minimal friction. Preferably, between the roller and the pin, there are bearings, bushings, lubrication and / or the like, configured to facilitate smooth rotation. A roller may comprise a chamfer, wherein the chamfer is optionally configured to permit the roller to make contact with the guide of the puller leg with which it is associated while avoiding contact with any other puller legs. Where there are two rollers, each roller may comprise a chamfer, wherein the chamfer of each is configured to permit the roller to avoid contact with the guide of the other puller leg (i.e. the puller leg associated with the other roller). This permits smoother operation and reduces the wear on the rollers and guides. Herein, a guide may be understood to mean any component comprised in the one or more legs of the puller which is usable for engaging the driving member so as to control, guide, direct, constrain or otherwise actuate relative motion of the legs, preferably pivoting relative motion. Alternatively, the guide may be referred to as a track or a guide mechanism. In an example of the first aspect, the first leg comprises a first guide and the second leg comprises a second guide. In this way, greater control over the motion of the legs and increased gripping force of the jaws on the yarn end are provided. In an example of the first aspect, the guide comprises a slot portion, the slot portion being located in at least one of the first leg and the second leg. In this way, the driving member is more stably connected with the guide during use, thereby providing better alignment, reducing the likelihood of the guide disengaging the guide surface at any point, especially during highspeed loom operation, and increasing the precision with which the movement of the legs is determined. Further advantages include that the slot design distributes the load more evenly across the driving member (or, in some examples, across the roller rotatably connected thereto) resulting in reduced stress concentration and wear, and helping to prolong the service life of the puller assembly. Herein, a slot or slot portion may be understood to mean a groove, indentation or through-hole in a puller leg, whereby the slot or portion thereof is usable to engage the driving member, and is configured such that engagement of the slot and the driving member during relative motion therebetween is configured to control or guide the legs to move between open and closed states. Preferably, each leg comprises a through-hole slot; however, the invention is not limited thereto and, alternatively, one leg may comprise a through-hole and the other leg may comprise an indentation, or indeed any combination contemplated by the skilled addressee depending on the technical constraints at hand. More preferably, the slot has a through-thickness or transverse thickness (that is, a thickness in a direction parallel to the axis of the driving member), wherein said thickness is greater than or equal to a threshold thickness. Advantageously, the load applied by the driving member to the slot is thereby distributed across the surface of the slot. In an example of the first aspect, the slot comprises a double-sided cam track. Preferably, the double-sided cam track comprises a first cam profile and a corresponding second cam profile, wherein the driving member is engaged between the first cam profile and the second cam profile. In this way, the double-sided cam track having corresponding cam profiles on both sides of the track allows for balanced and uniform motion of the driving member. This results in smoother operation and reduced stress / wear on the components, thereby extending the service life of the puller. Further advantages include that a more controlled and precise leg motion profile is facilitated, resulting in improved consistency of tuft formation and pile height. Herein, a cam track may be understood to mean a surface comprising a cam profile adapted for guiding the motion of a cam driver such as the driving member. A cam track may comprise one or more cams, wherein a cam may be referred to as a kink, groove, curved portion of the guide surface, or respective pluralities thereof. Therefore, the cam track may comprise a series of kinks or grooves. The cam track may in some examples further comprise straight line portions; for example, on either or both side(s) of a curved portion of the cam track, straight line portions may be disposed whereby to maintain the legs in the open or closed position at 11 respective opposite ends of the tuft forming cycle. The cam track typically has a non-circular profile which effects the specific opening and closing movements and displacements of the leg as the driving member passes along the track in following its driving path. The shape of the cam track determines the motion profile of the leg, including rotary or oscillatory motion thereof. A single-sided cam track is a type of cam track that has a cam profile on only one side surface. A double-sided cam track is a type of cam track that has cam profiles on two side surfaces. In an example of the first aspect, the slot comprises two longitudinally conjoined elongate portions, wherein longitudinal axes of said elongate portions are offset, wherein an offset of said axes is configured to form at least one cam, engagement of the driving member with the at least one cam being configured to impart, in use, opening and closing motion on the legs, whereby to cause relative motion of the first leg with respect to the second leg from the open state to the closed state and from the closed state to the open state. In this way, the plurality of cams may be configured in a double-sided cam track arrangement. It will be apparent to the skilled addressee that other such arrangements of the guide are capable of forming a double-sided cam track or other cam track arrangements, and such arrangements are not excluded hereby. In an example of the first aspect, the guide is further configured in that, when the legs are in the closed state, the yarn is engaged between the jaws with a predetermined force and / or, when the legs are in the open state, a maximum distance between the legs is less than or equal to a threshold distance or a range of threshold distances (for example, said range depending on the range in diameter of typical yarns). The predetermined force may be determined by the level of overdose of the legs (that is, in some examples, when the legs are in the closed state, the jaws press together in such a way as to cause deflection in the legs) and / or by the force necessary to draw a predetermined length of yarn from a bobbin without slippage between the jaws and the yarn end. The threshold distance may be determined by the maximum acceptable separation of the jaws in the open state and / or by the distance between the side cheeks into which the tuft is released following cutting and through which the puller jaws pass. Additionally or alternatively, the threshold distance may be determined by the distance between adjacent yarn ends provided in adjacent channels on the yarn selector wheel in order that the puller jaws do not disturb other yarn ends adjacent to the selected yarn end. According to a second aspect of the invention, there is provided a puller assembly comprising the puller according to the first aspect, the assembly further comprising: at least one pivot pin, 12 the at least one pivot pin being configured to rotatably interconnect the first leg and the second leg of the puller; and at least one driving member, the at least one driving member being configured to engage the respective at least one guide such that, in use, engagement of the at least one driving member and the respective at least one guide causes relative motion of the first leg and the second leg from the open state to the closed state and from the closed state to the open state. Additionally or alternatively, relative motion between the at least one driving member and the respective at least one guide may cause, in use, relative motion of the first leg and the second leg between the open state and the closed state of the puller, whereby to control opening and closing motion of the legs. In this way, relative motion between the engaged guide and driving member causes the controlled opening and closing of the legs. Herein, a puller assembly may be understood to mean an assembly comprising the puller herein disclosed, and further comprising a pivot pin and a driving member, whereby the puller assembly is adapted to realise a pulling motion so as to draw a predetermined length of yarn from its bobbin. In an example of the second aspect, the at least one driving member is connected to a first crank whereby reciprocating motion of the driving member with respect to the guide is actuated in use. In an example of the second aspect, yarn is supplied to the puller via a yarn selector, the yarn selector configured to convey a tail end of the yarn to the puller. In an example of the second aspect, the at least one pivot pin is connected to a second crank whereby motion of said pin with respect to the yarn selector is actuated in use so as to pull a length of yarn from the yarn selector when the yarn is engaged. According to a third aspect of the invention, there is provided a carpet tuft forming apparatus comprising the puller assembly according to the second aspect, the apparatus further comprising a cutter assembly configured to sever, when the yarn is engaged by the jaws of the puller, a predetermined length of the yarn whereby to form a tuft. According to a fourth aspect of the invention, there is provided a carpet weaving loom comprising one or more of the carpet tuft forming apparatus according to the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention are hereinafter described by way of non-limiting example and with reference to the accompanying drawings, wherein: Fig. 1 is a diagram of a first puller known in the art; Fig. 2 is a diagram of a second puller known in the art; Fig. 3 is a diagram of a puller according to a first embodiment of the invention; Fig. 4 is a diagram of an exemplary guide according to the invention; Fig. 5 is a diagram of a puller according to a second embodiment of the invention; Fig. 6 is a further diagram of the puller according to the second embodiment; Fig. 7 is a diagram of an exemplary puller assembly according to the invention; and Fig. 8 is a diagram of an exemplary puller assembly according to the invention. DETAILED DESCRIPTION With reference to Fig. 1, there is a first yarn puller known in the art. The first puller comprises a generally U-shaped portion 38 with elongate parallel legs 39, 40 and jaws 41, 42 connected via bolts or dowels at the free ends of the legs 39, 40, wherein the legs 39, 40 are integrally formed at the end opposite their free ends by means of the U-shaped portion 38. The legs 39, 40 (and thereby the jaws 41, 42) are urged together into a closed state by the resilience of the U-shaped portion 38. A driving pin 43 moves up and down with respect to a pair of raised cam surfaces 44, 45 formed on each of the legs 39, 40, whereby relative motion between the legs 39, 40 is permitted between an open state and the closed state. The raised cam surface in each leg may be considered a single-sided cam track. When the pin 43 is moved down between the cam surfaces 44, 45, the legs 39, 40 are actuated into the open state. In the open state, the U-shaped portion 38 is elastically deformed and the separation of the jaws 41, 42 is a maximum so as to permit a yarn to pass therebetween. When the pin 43 is then moved up, out from between the cam surfaces 44, 55 and into the space between the legs and above the cams, the separating force previously imparted by the pin 43 when between said cam surfaces 44, 45 is removed. Consequently, by the mechanical elasticity of the U-shaped portion 38, the legs 39, 40 return back to their closed state when the deforming force is removed. In the closed state, the U-shaped portion 38 is undeformed and the separation of the jaws 41, 42 is at a minimum so as to grip a yarn passing therebetween. As such, the resilience of the U-shaped portion 38 biases the jaws 41, 42 together into the closed state in the absence of the force imparted by the pin 43 against the cams. The first puller is mounted for rotation about a shaft between a forward position with the jaws 41, 42 adjacent a yarn selector wheel (not shown) and a rearward position with the jaws 41, 42 for cutting. A tuft forming cycle for the first puller comprises the first puller rotating about the shaft between the forward position and the rearward position, and back. As the first puller is pivoting towards the forward position, the pin 43 moves down between the cam surfaces 44, 45. Accordingly, the jaws 41, 42 open and permit a free end of yarn to pass between them. As the shaft continues to rotate, the first puller is not substantially pivoting while the pin 43 moves up and out from between the cam surfaces 44, 45. In this way, the resilience of the U-shaped portion 38 returns the legs 39, 40 to the closed state, closing the jaws 41, 42 together, without action of the pin 43 against the cams and the free end of yarn is gripped by the jaws 41,42. As the first puller is pivoting towards the rearward position, the pin 43 is above the cam surfaces 44, 45. Accordingly, the jaws 41, 42 are closed, gripping the end of yarn between them and pulling yarn from the selector wheel. The puller thereby draws a predetermined length of yarn (typically 1 inch, however it may vary from 19.5 mm up to over 30 mm depending on the pile height requirement for the carpet) from the bobbin. Action of a cutting assembly then severs the yarn to form a tuft. As the shaft continues to rotate, the first puller is not substantially pivoting while the pin 43 moves down between the cam surfaces 44, 45. Accordingly, the jaws 41, 42 open and release the tuft. Thereafter, the tuft is guided by entrained air flow into a ‘pocket’ for transfer to a weaving point. A yarn selector motor is then free to rotate the yarn selector wheel into a different angular position to provide the next selected yarn at the loading point adjacent the first puller. Further rotation of the shaft pivots the first puller towards the forward position to grip the next selected yarn during the next tuft forming cycle. With reference to Fig. 2, there is a second yarn puller known in the art. The second puller comprises a pair of elongate parallel legs 102, 103 with jaws 104, 105 connected via soldering, bolting, or an equivalent fusing technique at their lowermost ends, wherein the legs 102, 103 are separately formed. The legs 102, 103 are urged together (and thereby the jaws 104, 105 urged apart) by a resilient member 106 (such as a spring) attached at the uppermost end of the legs 102, 103, whereby to urge the jaws 104, 105 into an open state at the lowermost end. A driving pin 99 moves up and down with respect to a pair of raised cam surfaces 107, 108 formed on each of the legs 102, 103, whereby relative motion between the legs 102, 103 is permitted between the open state and a closed state. The raised cam surface in each leg may be considered a single-sided cam track. When the pin 99 is moved up between the cam surfaces 107, 108, the legs are actuated together at their lowermost end into the closed state. In the closed state, the resilient member 106 is elastically deformed and the separation of the jaws 104,105 is at a minimum so as to grip a yarn passing therebetween. When the pin 99 is then moved down, out from between the cam surfaces 107, 108 and into the space between the legs and beneath the cams, the separating force previously imparted by the pin 99 when between said cam surfaces 107, 108 is removed. Consequently, by the mechanical elasticity of the resilient member 106, the legs 102, 103 return back to their open state at their lowermost end when the deforming force is removed. In the open state, the resilient member 106 is relatively relaxed and the separation of the jaws 104, 105 is so as to permit a yarn to pass therebetween. As such, the resilience of the resilient member 106 biases the jaws 104, 105 apart into the open state in the absence of the force imparted by the pin 99 against the cams. The second puller is mounted for rotation about a shaft between a forward position with the jaws 104, 105 adjacent the yarn selector wheel and a rearward position with the jaws 104, 105 between a pair of side cheeks. A tuft forming cycle for the second puller comprises the second puller rotating about the shaft between the forward position and the rearward position, and back. As the second puller is pivoting towards the forward position, the pin 99 is below the cam surfaces 107, 108. Accordingly, the jaws 104, 105 are open and can permit a free end of yarn to pass between them. As the shaft continues to rotate, the second puller is not substantially pivoting while the pin 99 is moving towards its uppermost position and passing between the cam surfaces 107, 108. In this way, the jaws 104, 105 are actuated to close together and grip the free end of yarn. As the second puller is pivoting towards the rearward position, the pin 99 is above the cam surfaces 107, 108. Accordingly, the jaws 104, 105 are closed, gripping the 16 end of yarn between them and pulling yarn from the selector wheel. The puller thereby draws a predetermined length of yarn (typically as described above in relation to the first puller) from the bobbin. Action of a cutting assembly now severs the yarn to form a tuft. As the shaft continues to rotate, the second puller is not substantially pivoting while the pin 99 is moving towards its lowermost position and passing back between the cam surfaces 107, 108. In this way, the resilience of the resilient member 106 returns the legs 102, 103 to the open state, opening the jaws 104, 105 apart, without action of the pin 99 against the cams and the tuft is released into the side cheeks. Thereafter, the tuft is transferred to a weaving point. A yarn selector motor is then free to rotate the yarn selector wheel into a different angular position to provide the next selected yarn at the loading point adjacent the second puller. Further rotation of the shaft pivots the second puller towards the forward position to grip the next selected yarn during the next tuft forming cycle. In the example of the first puller, when the U-shaped portion 38 is undeformed, the legs 39, 40 are biased together into the closed state. Consequently, the pin 43 actuates the legs 39, 40 into the open state, but the resilience of the U-shaped portion 38 returns the legs 39, 40 to the closed state without action of the pin 43 against the cams. In the example of the second puller, when the resilient member 106 is most relaxed, the legs 108, 107 are biased apart at their lowermost end into the open state. Consequently, the pin 99 actuates the legs 102, 103 into the closed state, but the resilience of the resilient member 106 returns the legs 102, 103 to the open state without action of the pin 99 against the cams. Accordingly, in both examples described hitherto, whether it be for the opening portion of the pin’s cycle (as in the second puller) or for the closing portion of the pin’s cycle (as in the first puller), the puller is not under the direct control of a mechanism but merely responding to inherent mechanical elasticity. Furthermore, in both of said examples, the transition between the open and closed states is uncontrolled, insofar as it is determined chiefly by the elastic properties of the resilient member. This has resulted in the aforementioned problems of lack of fine control over the puller jaws, reduced performance over time as a result of wear or unstable elastic properties of the resilient member (i.e. the spring or the material forming the puller). Further disadvantages of the first and second pullers include that soldering, doweling or bolting the jaws to connect them to the legs results in the jaws often being positioned on the legs inaccurately or falling off during operation, thereby reducing the accuracy of the tuft length, slowing production to make repairs, and producing carpets with an uneven pile height. According to the invention herein disclosed, an improved approach is to operate the puller jaws by deliberately controlling them to begin gradually coming together as the puller jaws move past the ends of the tufts and, likewise, to gradually open apart as the puller jaws move between the side cheeks. In this way, a balance may be struck between several desirable objectives: the closure of the jaws can be slowed and more controlled in order to prevent the jaws from bouncing back open upon closure, while being fast enough to grip onto the selected yarn firmly and before the puller pivots by any significant distance away from the selected yarn. With reference to Fig. 3, there is provided a yarn puller 110 according to a first embodiment of the invention. The puller 110 comprises a first leg 111 comprising a first jaw 113 and a second leg 112 comprising a second jaw 114. As in Fig. 3, the firstjaw 113 and the second jaw 114 are located at a first distal end of the puller 110 (the lowermost end in Fig. 3) and the guide 116 is located at a second distal end of the puller 110 (the uppermost end in Fig. 3) with the pivotable interconnection (about axis 115) located therebetween. In this way, the lever action of the driving mechanism (116, 118, shown in Fig. 7) is maximised, and the greatest possible control of the jaws 113, 114 is thereby ensured. However, the invention is not limited thereto and the pivotable interconnection (and, therefore, axis 115) may be located at the second distal end, with the guide 116 being located between the first and second distal ends. Preferably, a thickness of legs 111, 112 at the first distal end is tapered with respect to a thickness of the legs 111, 112 at the second distal end. The first leg 111 and the second leg 112 are pivotably interconnected so as to permit relative motion of the first leg 111 with respect to the second leg 112 between an open state and a closed state. As in Fig. 3, the legs 111, 112 are both pivoted about an axis 115 parallel to a shaft passing through both legs 111, 112. Particularly, the legs 111, 112 are pivoted about the same axis 115 and the shaft comprises a circular hole in each leg 111, 112, said holes having equal circumferences and being aligned so as to form a through-hole. However, the invention is not limited thereto and the legs 111, 112 may be pivoted about distinct axes, comprise holes of unequal circumferences, and / or not be axially aligned as described in later alternative examples. Preferably, the first leg and the second leg are pivotably interconnected by means of a single same pivot pin passing through the shaft about which the legs 111, 112 rotate. The legs 111, 112 are thereby constrained from relative translation and permitted to rotate relative 18 to one another about the pivot pin, subject to the action of the driving mechanism (116, 118), that is, the relative motion of a driving member (118) and the guide 116. In Fig. 3, the first leg 111 moves relative to the second leg 112 in a plane of motion perpendicular to the axis 115 and the legs overlap in part in the plane of the axis 155, that is, perpendicular to the plane of motion. When the legs 111, 112 share at least one of the guide and the pivot, the legs 111, 112 overlap. However, when the legs 111, 112 share neither the guide nor the pivot, the legs 111, 112 may or may not overlap. The first jaw 113 and the second jaw 114 are configured in use to engage a yarn when the legs 111, 112 are in the closed state and configured such that the yarn is disengaged when the legs 111, 112 are in the open state. In the closed state, the jaws 113, 114 are urged together; in the open state, they are urged apart. As in Fig. 3, the first jaw 113 and the second jaw 114 optionally comprise teeth 117 on their inner faces, the teeth 117 being arranged so as to interlock when in the closed state, thereby providing improved grip on the yarn passing therebetween. Additionally, the jaws 113, 114 may be integrally formed with the respective legs 111, 112 by manufacturing them in one piece; and the jaws 113, 114 may be aligned with respect to each other so as to cause deflection in the legs 111, 112 when in the closed state. The puller 110 is further configured in that at least one of the first leg 111 and the second leg 112 comprises a guide 116 configured to engage the driving member. The guide 116 is configured such that, when the guide 116 and the driving member engage, relative motion therebetween causes relative motion of the first leg 111 with respect to the second leg 112 between the open state and the closed state. As in Fig. 3, preferably each of the legs 111, 112 comprises a respective guide 116a, 116b, that is, the first leg 111 comprises a first guide 116a and the second leg 112 comprises a second guide 116b. However, the invention is not limited thereto and, alternatively, only one of the legs 111, 112 may include the guide 116. The guide 116 is described in detail hereafter with reference to Fig. 4. With reference to Fig. 4, there is provided an exemplary guide 116b according to some embodiments of the invention. The guide 116b comprises a slot located in the second leg 112, the slot comprising a doublesided cam track as shown. Preferably, the double-sided cam track comprises a first cam profile (that is, the cam profile on the lefthand inner surface of the guide 116b) and a corresponding 19 second cam profile (that is, the cam profile on the righthand inner surface of the guide 116b), wherein the driving member is engaged therebetween. More preferably, the slot further comprises two or more longitudinally conjoined elongate portions, with at least one upper portion (w - x) and one lower portion (y - z), wherein longitudinal axes of said elongate portions are offset, wherein an offset of said axes is configured to form a plurality of cams 121a, 121b at the conjoining portion (x - y) of said elongate portions. The plurality of cams 121a, 121b are configured such that engagement of the driving member with the cams 121a, 121b is so as to impart, in use, rotation on the leg 112 and thereby opening and closing motion on the legs in concert. In this way, a double-side cam track is formed in the guide. Said cams 121a, 121b may comprise one or more kinks, grooves, or curved portions arranged in the surface of guide which contacts the driving member. For example, said longitudinal axes may be substantially parallel and laterally offset by a fixed transverse distance or, alternatively, said axes may not be parallel and instead be offset by a fixed angle. The latter example is illustrated in Fig. 4, wherein an angular offset between upper and lower portions is 3.2 degrees. In either example, the angular and / or lateral offset between the two or more elongate portions (w - x), (y - z) forms, at the conjoining portion (x - y) between said elongate portions, cams 121a, 121b on either side of the slot. Preferably, and as in Fig. 4, the cams 121a, 121b correspond to one another insofar as the cam 121a is characterised by a curving of the lefthand inner guide surface and the cam 121b is characterised by the same curve reproduced on the righthand inner guide surface. Alternatively, they may not correspond and may have different curvatures in order to manipulate the movement of the legs in a different way. It will be apparent to the skilled addressee that other such arrangements of the guide 116b may be capable of forming a double-sided cam track and such arrangements are not excluded hereby. For example, the slot may be replaced by a groove or indentation in the body of the puller leg 112. During the tuft forming cycle, the driving member reciprocates back and forth with respect to the puller while interacting with the guide 116b so as to actuate cyclic motion of the legs between an open and a closed state. In preferable examples, the interactions of the driving member and the guide 116b are characterised by rolling motion of a roller connected to the member along the surface of the guide 116b. Each leg 111, 112 may be in rolling contact with a roller configured to engage the respective guides 116a, 116b of each respective leg 111, 112, wherein the rollers are configured to revolve around the driving member (118) whereto the rollers are rotatably connected. In respect of the puller assembly, that is, the puller legs working in concert with the pivot mechanism (119, shown in Fig. 7) and the driving mechanism (116, 118, shown in Fig. 7), the tuft forming cycle comprises four stages described hereinafter: (1) closing motion, (2) the closed state, (3) opening motion, and (4) the open state. (1) Closing motion is associated with the legs 111, 112 moving through one or more intermediate states from an open state to a closed state. As the driving member moves upward, it begins to be engaged with the cams 121b, 121a in the conjoining portion (x - y) of the guide 116b which, by the (typically normal) contact forces associated with such an engagement, causes the leg 112 to rotate anticlockwise about an axis 115 passing perpendicularly through the page. Anticlockwise rotation of leg 112 when coupled with relative clockwise rotation of leg 111 is associated with closing motion, wherein the jaws move together, and the free end of yarn is seized. In this way, the double-sided cam track engages the driving member on both sides thereof, and thereby controls the pivotable motion of the leg throughout the entire closing motion of the jaws. By controlling the jaws as such, they are prevented from closing prematurely (resulting in the jaws pushing the yarn end into the selector wheel which would prevent the jaws from seizing it) or closing belatedly (resulting in the jaws seizing the yarn improperly and at a reduced tuft length). Preferably, the closing motion of the tuft forming cycle has a minimum duration (that is, closing motion may be performed rapidly), wherein the minimum duration is determined by a duration of a maximum acceptable angular displacement of the puller assembly. In this way, the closing motion of the jaws is minimally disrupted by the concurrently pivoting puller assembly. (2) The closed state is associated with the jaws engaging a yarn or a tuft while the driving member is engaged with the upper portion (w - x). As the driving member moves upward into the upper portion (w-x), it remains engaged with the guide 116b but no longer engaged with the cams 121a, 121b. Accordingly, the jaws are maintained in the closed state at a minimum separation therebetween. During the closed state, the relative motion of the puller assembly away from the yarn selector wheel causes a predetermined length of yarn to be drawn from the bobbin, said length subsequently being cut to form a tuft. Optionally, the upper portion (w - x) of the guide 116b may be further configured in that, when the jaws are in the closed state, the yarn is engaged between the jaws with a predetermined force. Additionally, the jaws may be aligned with respect to each other so as to cause deflection in the legs when in the closed state. The extent of deflection in the legs may be determined by said predetermined force between the jaws. Such a closed state may be referred to as an overdosed state. In this way, when the jaws press together (and the teeth thereof 21 interlock), the legs are configured to deflect (i.e. elastically deform) in such a way that the jaws become substantially parallel. This improves grip on the yarn end and, since the deflection is well within the elastic limit of the legs, fatiguing of the legs is prevented. The duration of the closed state of the tuft forming cycle is determined, in part, by the desired tuft length; that is, a longer duration permits the jaws to draw a longer length of yarn from the bobbin. The duration is also determined, in part, by the speed of the puller movement and, therefore, the frequency of the tuft generation cycle. (3) Opening motion is associated with the legs 111, 112 moving back through the one or more intermediate states from a closed state to an open state. As the driving member moves downward, it begins once again to be engaged with the cams 121b, 121a in the conjoining portion (x - y) which, by the normal contact forces associated with such an engagement, causes the leg 112 to rotate clockwise about an axis 115 passing perpendicularly through the page. Clockwise rotation of leg 112 when coupled with relative anticlockwise rotation of leg 111 is associated with opening motion, wherein the jaws move apart, and the tuft is released into the side cheeks. In this way, the double-sided cam track engages the driving member on both sides thereof, and thereby controls the pivotable motion of the leg throughout the entire opening motion. By controlling the jaws as such, they are prevented from opening prematurely or opening belatedly, both of which can result in the yarn not being cut (thereby forming no tuft) or being cut at a reduced tuft length (thereby causing an uneven pile height in the final carpet). Preferably, the opening motion of the tuft forming cycle has a minimum duration, wherein the minimum duration is determined by a duration of a maximum acceptable angular displacement of the puller assembly. In this way, the opening motion of the jaws is least disrupted by the concurrently pivoting puller assembly. (4) The open state is associated with the jaws not being engaged with a yarn or a tuft while the driving member is engaged with the lower portion (y - z). As the driving member continues to move downward into the lower portion (y - z), it remains engaged with the guide 116b but no longer engaged with the cams 121a, 121b. Accordingly, the jaws are maintained in the open state at a maximum separation therebetween. During the open state, the relative motion of the puller assembly towards the yarn selector wheel takes the puller to the loading point, wherefrom the next free end of yarn is drawn, and the cycle begins from stage (1) once again. Optionally, the lower potion (y - z) of the guide 116b may be further configured such that, when the legs are in the open state, a distance between the legs is greater than or equal to a first threshold distance, wherein the first 22 threshold distance is determined by the distance between the side cheeks (preferably the distance between the respective outside edges of the side cheeks) whereabout the puller jaws pass upon releasing the cut tuft, and a distance between the jaws is less than or equal to a second threshold distance, wherein the second threshold distance is determined by either the width of the channel on the yarn selector wheel wherethrough the puller jaws pass when engaging the next yarn end. Accordingly, the distance between the legs and the distance between the jaws may not be equal and may be determined by different limiting factors. The tufts are held in a radial orientation in the selector of about 5 mm spacing, so preferably the tips of the jaws are 5 mm apart as they pass between the yarn ends in order to avoid disturbing the yarn ends either side of the selected yarn (by being too wide apart) or disturbing the selected yarn (by being too close together). The duration of the open state of the tuft forming cycle is determined, in part, by the desired tuft length; that is, a longer duration permits the jaws in use to engage the yarn end at a position that is further forward than otherwise, thereby engaging a longer length of yarn. The duration is also determined, in part, by the speed of the puller movement and, therefore, the frequency of the tuft generation cycle. It will be apparent to the skilled addressee that the foregoing descriptions in respect of a guide 116b for leg 112 may be applied analogously in respect of a guide 116a for leg 111 without departing from the invention. For example, the guide 116a of the leg 111 may be a mirror image of the guide 116b shown in Fig. 4 reflected about a line passing through the lefthand edge of the leg 112 in Fig. 4. Alternatively, the guide 116a for leg 111 may have an angular offset of -3.2 degree, another angular and / or lateral offset, or indeed any cam or guide arrangement contemplated by the skilled addressee and appropriate to realise the stages of the tuft forming cycle described hitherto. In the foregoing, it can be learned that the desired tuft length, upon cutting, is achieved in part by configuring the duration of the closed and / or open states, that is, having longer such durations will achieve long tuft lengths and having shorter such durations will achieve short tuft lengths. In addition to this setting, the tuft length can be set by adjusting a puller crank radius as described with reference to Fig. 8. With reference to Figs. 5 and 6, there is provided a yarn puller 120 according to a second embodiment of the invention. The puller 120 comprises a first leg 111 comprising a first jaw 113 and a second leg 112 comprising a second jaw 114. As in Figs. 5 and 6, the first jaw 113 and the second jaw 114 are located at a first distal end of the puller 120 (the lowermost end in Figs. 5 and 6) and the guide 116 is located at a second distal end of the puller 120 (the uppermost end) with the pivotable interconnection located therebetween. In this way, the lever action of the driving mechanism (116, 118) is maximised, and the greatest possible control of the jaws 113, 114 is thereby ensured. However, the invention is not limited thereto and the pivotable interconnection may be located at the second distal end, with the guide 116 being located between the first and second distal ends. Preferably, a thickness of legs 111, 112 at the first distal end is tapered with respect to a thickness of the legs 111, 112 at the second distal end. The first leg 111 and the second leg 112 are pivotably interconnected so as to permit relative motion of the first leg 111 with respect to the second leg 112 between an open state (shown in Fig. 6) and a closed state (shown in Fig. 5). As in Figs. 5 and 6, the legs 111, 112 are pivoted about parallel and laterally offset axes 115a, 115b passing through each leg (perpendicular to the page) at their respective locations shown. Particularly, the legs 111, 112 are pivoted about axes 115a, 115b by means of the shaft comprising a circular hole formed in each leg 111, 112, said holes having equal circumferences and being laterally shifted by a fixed distance, preventing relative translation of the legs 111, 112 but permitting translation in concert when drawing the yarn. Preferably, the first leg and the second leg are pivotably interconnected by a first pivot pin 119a engaging the first leg 111 and a second pivot pin 119b engaging the second leg 112. The legs 111, 112 are thereby constrained from relative translation and permitted to rotate relative to one another about the respective pivot pins 119a, 119b, subject to the action of the driving mechanism (116, 118), that is, the relative motion of a driving member (118) and the guide 116. In Figs. 5 and 6, the first leg 111 moves relative to the second leg 112 in a plane of motion perpendicular to the axes 115a, 115b and the legs overlap in part in the plane of said axes, that is, perpendicular to the plane of motion. The first jaw 113 and the second jaw 114 are usable for engaging a yarn when the legs 111, 112 are in the closed state and for disengaging the yarn when the legs 111, 112 are in the open state. For example, the jaws 113, 114 may be configured or adapted to directly engage a yarn 24 in the closed state when a yarn is presented to the puller and the jaws 113, 114 may be further configured or adapted such that in the open state (or at least in a state such as one of the intermediate states so that said state is not the closed state) the yarn becomes disengaged following cutting thereof. In the closed state, the jaws 113, 114 are urged together; in the open state, they are urged apart. Though not shown in Figs. 5 and 6, the jaws may comprise teeth and / or be integrally formed with their respective legs as in the first embodiment. The puller 120 is further configured in that at least one of the first leg 111 and the second leg 112 comprises a guide 116 configured to engage the driving member 118. The guide 116 is configured such that, when the guide 116 and the driving member 118 engage, relative motion therebetween causes relative motion of the first leg 111 with respect to the second leg 112 between the open state and the closed state. As in Figs. 5 and 6, both of the legs 111, 112 comprise a guide 116, that is, the first leg 111 comprises a first guide 116a and the second leg 112 comprises a second guide 116b. However, the invention is not limited thereto and alternatively only one of the legs 111,112 may include the guide 116. As with the embodiments of Figs. 3 and 4, each leg 111, 112 may be in rolling contact with a roller configured to engage the respective guides 116a, 116b of each respective leg 111, 112, wherein the rollers are configured to revolve around the driving member 118 whereto the rollers are rotatably connected. With reference to Fig. 7, there is provided a puller assembly 130 according to some embodiments of the invention. The assembly 130 preferably comprises the yarn puller 110 according to the first embodiment of the invention, and further comprises a pivot pin 119 and a driving member 118. In Fig. 7, the puller 110 is in the open state with the jaws 113, 114 actuated open by the driving mechanism (116, 118). In alternative examples, the puller assembly may comprise the yarn puller 120 according to the second embodiment, wherein the puller assembly comprises two pivot pins, each pivot pin corresponding to a respective leg. In further alternatives, the puller assembly may comprise two driving members, each driving member corresponding to a respective leg. In any case, aspects of the driving mechanism are not repeated again and may be as hitherto described. The pivot pin 119 is configured to rotatably interconnect the legs 111, 112 of the puller 110. Preferably, the pivot pin 119 extends through both of the puller legs 111, 112, whereby independent rotational motion of the legs 111,112 about the pin 119 is permitted, such rotations 25 occurring in the same plane of motion perpendicular to the axis of the pin 119. As such, independent translational motion of the legs (that is, not including translational motion in concert) is not permitted. Alternatively, the pivot pin 119 does not extend through the entire thickness of both of the puller legs 111, 112 and extends through one or none of the puller legs 111, 112, the pin 119 instead resting between the legs 111, 112 within a groove or other indentation formed in one or both of the legs 111, 112 such that, from at least one side of the puller 110, the pivot pin 119 is not visible. In any case, the puller legs 111, 112 may be separated by a washer, bushing, or other kind of spacer along the pin 119. Preferably, each leg is rotatably connected to the same pivot pin 119 and, consequently, the legs 111, 112 are rotatably interconnected as such. Alternatively, the legs 111, 112 may be rotatably interconnected by a pivot mechanism comprising one or more pins, wherein each leg is independently pivoted on a distinct pin of the pivot mechanism. Preferably, the pivot pin 119 is located between distal ends of the puller legs 111, 112, that is, between the guide 116 located at the uppermost distal end of the puller 110 and the jaws 113, 114 located at the lowermost distal end of the puller 110. In such examples, the puller legs 111, 112 are pivoted about a point substantially equidistant between the first and second distal ends. In this way, the reciprocating driving member 118 may, for the same force exerted in use on the guide 116 at the opposite distal end to the jaws 113, 114, impart the greatest lever moment at the jaws 113, 114, thereby permitting tighter grip on the engaged yarn and more control over the actuation of the jaws 113, 114. Alternatively, the pivot pin 119 may be located at the uppermost distal end of the puller 110, the jaws 113, 114 located at the lowermost distal end of the puller 110, and the guide 116 located therebetween. Preferably, the pivot mechanism comprises the pivot pin 119 within a pivot bush. In such examples, the pivot bush is a cylindrical component preferably made of hardened steel or another durable material. Such a bush is insertable into the puller legs 111, 112 in order to provide a bearing surface and support for the legs 111, 112 and the pin 119 about which the legs 111, 112 are pivoted. The bush typically does not rotate relative to the pivot pin 119. The puller legs may pivot freely on the (fixed) puller leg pivot bush and the legs may make contact with an outer surface of the bush (the inner surface making contact with the pin). In this way, the legs 111,112 can smoothly rotate about the pin 119. Furthermore, the bush helps to reduce friction and wear between the rotating components and the pin 119, thereby extending the lifespan of the carpet tuft forming apparatus. Bushing also minimises vibration and misalignment issues. Alternatively, the pivot pin 119 is rotatably connected to each leg 111, 112 (and the legs 111, 112 thereby rotatably interconnected) via a bearing mechanism other than a pivot bush. Examples of such bearing mechanisms include plain bearings, roller bearings, and ball bearings. It will be apparent to the skilled addressee that any such alternative mechanism providing a low-friction interface between the pin 119 and the legs may instead be implemented. The choice of alternative may depend on factors such as required speed or frequency of opening / closing, space constraints, and environmental conditions. In some examples of the invention, the assembly comprises two pivot pins for use in relation to the second embodiment of the invention, as aforementioned. In such examples, a first pivot pin permits rotation of the first leg 111 thereabout and a second pivot pin permits rotation of the second leg 112 thereabout, each leg thereby being engaged with a separate pivot pin. The first and second pins may be axially aligned but distinct pins or, alternatively, the pins may have parallel but laterally shifted axes. In this way, rotation of each leg about its respective pivot may be controlled independently (to the extent limited by the adjoining guide and driving member). Preferably, the at least one pivot pin 119 is cranked such that reciprocating motion of the pin 119, and thereby the entirety of the puller assembly 130 itself, causes a predetermined length of yarn to be pulled or otherwise drawn from a yarn selector wheel supplying the yarn and, in turn, the bobbin whereupon the yarn is wound. Such motion of the pin 119 is along a second driving path. As will now be appreciated, there are a number of components which, in use, move relatively to one another in order that the apparatus can form tufts. Such motions include: the motion of the driving pin 118 with respect to the guide 116 (and thereby by the relative motion of the legs 111, 112) required to provide opening and closing movements of the jaws 113, 114 to precisely control engagement and disengagement of the yarn respectively, and the motion of the pivot pin (the thereby the relative motion of the puller assembly 130 and the yarn) required to provide the forward and backward movements of the assembly 130 to pull yarn from the selector wheel (and in turn from the creel and a particular bobbin thereof). These motions are driven from a gearbox comprised in the tuft forming apparatus. The gearbox may be driven by a servomotor under the control of a computer, and in this way, it can be ensured that the timing of the puller assembly 130 and cutter assembly movements can be synchronised with the rotation of the 27 selector wheel. Alternatively, a separate computer-controlled servomotor may be provided to drive each motion of the cutter and puller and, in this example, the computer ensures the appropriate timing of these motions in synchronism with the discrete rotations of the selector wheel. Further details of such motions may be learned from Fig. 8. With reference to Fig. 8, there is provided a puller assembly 140 according to some embodiments of the invention. The assembly 140 preferably comprises the yarn puller 110 according to the first embodiment of the invention, and further comprises a pivot pin 119, a driving member 118, an axis 131, a puller assembly body 132, a mount 133, and a rod 134. In Fig. 8, the puller 110 is in the open state with the jaws 113, 114 actuated open by the driving mechanism (116, 118). In alternative examples, the puller assembly may comprise the yarn puller 120 according to the second embodiment, wherein the puller assembly comprises two pivot pins, each pivot pin corresponding to a respective leg. In further alternatives, the puller assembly may comprise two driving members, each driving member corresponding to a respective leg. As hitherto described, the driving member(s) 118 may comprise one or more rollers (not shown) configured to maintain rolling contact with the guide 116 (or which each respective guide) of the puller legs. The motion of the rollers includes the motion with respect to the driving member(s) 118 to which they are rotatably connected (and typically about which they can revolve in opposite directions by means of bearings or otherwise) and the motion with respect of the guide 116 (or each respective guide) with which they are in rolling contact. In any case, aspects of the driving mechanism (116, 118) are not repeated again and may be as hitherto described. The axis of the rod 134 is perpendicular to the axis of the driving member 118 and the axis of the pivot pin 119, the axis of the driving member 118 and the pivot pin 119 being parallel to each other. The axis of the rod is substantially parallel to the axis of the legs 111, 112 and to the axis of the puller assembly body 132, the axes of the legs 111, 112 and the puller assembly body 132 being substantially parallel to each other. The axis 131 is perpendicular to both the axis of the rod 134 and the axis of the driving member 118. The pivot pin 119 is mounted to the puller assembly body 132. The driving member 118 is mounted to the rod 134 by means of mount 133. The mount 133 may be movably connected to the rod 134, wherein the mount 133 is configured to slide along the rod 134 in a direction parallel to the axis of the rod 134 (for example, using a ball bearing for rolling contact between 28 the mount 133 and the surface of the rod 134), and wherein the rod 134 is fixedly connected to the puller assembly body 132. Alternatively, the mount 133 may be fixedly connected to the rod 134, wherein the rod 134 is configured to slide within the puller assembly body in a direction parallel to the axis of the rod 134 (for example, using a journal bearing for sliding contact between the puller assembly body 132 and the surface of the rod 134). In either case, the mount 133 or alternatively the rod 134 is configured to be actuated using a pinion (not shown) connected to the gearbox. In this way, relative motion of the driving member 118 fixedly connected to the mount 133 is actuated with respect to the pivotable interconnection (in this embodiment, the pivot pin 119), whereby opening and closing motion is imparted on one or more of the puller legs 111, 112. The puller leg pivot pin 119 provides the location for the pivot. The pin 119 is located within accurate bores comprised in the puller body (i.e. the leg(s) thereof) and in a puller leg cover plate (not shown) which is configured to attach to or at least in part cover a side of the puller facing away from the rod 134. As hitherto described, a puller leg pivot bush may be accurately located around the puller leg pivot pin 119, wherein said bush may be trapped between the puller leg cover plate and a puller wear plate (not shown) which is configured to attach to or at least in part cover a side of the puller facing toward the rod 134. Accordingly, the puller is typically fixedly positioned between the cover plate and the wear plate. The bush typically does not rotate relative to the pivot pin 119. The puller legs may pivot freely on the (fixed) puller leg pivot bush. The reason for the two components (i.e. the bush and the pin 119) is that it is difficult to make the assembly with the required tolerances such that the puller legs 111, 112 are free to move laterally to open and close but are constrained by the space between the puller leg cover plate and the puller wear plate. This limits the movement of the legs 111, 112 away from or towards the puller body to maintain accurate positioning of the jaws 113, 114 and hence accurate tuft lengths. The space for the legs 111, 112 is set by only the length of the puller leg pivot bush and a puller leg spacer block (not shown) which are both easy to manufacture to high accuracy. Otherwise the pivot pin 119 would need to be a very accurate length and the counterbores in both the puller leg cover plate and the puller body would need to have very accurate depths as well as the puller wear plate having very accurate thickness - i.e. there are too many components requiring too high accuracy with a build-up of errors easily leading to the gap for the legs 111, 112 being insufficient so they will not open and close, or the gap being too large and the legs 111, 112 not being adequately constrained. Simultaneously to said opening and closing motions, relative motion of the jaws 113, 114 is actuated with respect to the yarn selector wheel (not shown) by rotation about axis 131. The puller assembly 140 is mounted for rotation about a shaft intersecting and parallel with the axis 131. The puller assembly 140 is mounted to said shaft via a rotatable connection at the distal end of the puller assembly body 132 opposite the distal end whereat the pivot pin 119 attaches the puller 110 to the puller assembly body 132. In this way, the puller assembly 140 (and thereby the at least one pivot pin 119 thereof) is cranked such that reciprocating motion of the pin 119 (and thereby the entirety of the puller assembly 140 itself) causes a predetermined length of yarn to be pulled or otherwise drawn from a yarn selector wheel supplying the yarn and, in turn, the bobbin whereupon the yarn is wound. Such motion of the pin 119 is along a second driving path and includes rotation between a forward (i.e. rightward in Fig. 8) position with the jaws 113, 114 adjacent the yarn selector wheel (not shown) and a rearward (i.e. leftwardin Fig. 8) position with the jaws 113, 114 for cutting of desired length of tail end yarn. A tuft forming cycle for the first puller comprises the first puller rotating about the axis 131 from the forward position to the rearward position, and back to the forward position. The desired cut tuft length may be varied by adjusting the puller crank radius, that is, the distance from the axis 131 to the pivot pin 119 or, alternatively, to the jaw tips. The foregoing descriptions are mere examples of the invention and are not intended to limit the protection scope of the invention. Though the description of each embodiment has its own emphasis, for any aspect that is not described in relation to one embodiment, reference may be made to related descriptions of any other embodiments. Any variation, replacement or other embodiment within the scope of the claims appended hereto and readily contemplated by the skilled addressee shall fall within the protection scope of the invention.

Claims

1. A puller for a carpet tuft forming apparatus, the puller comprising:a first leg comprising a first jaw,a second leg comprising a second jaw,wherein the first leg and the second leg are pivotably interconnected so as to permit relative motion of the first leg with respect to the second leg between an open state and a closed state, andwherein the first jaw and the second jaw are usable for engaging a yarn when the legs are in the closed state and for disengaging the yarn when the legs are in the open state;the puller further configured in that:at least one of the first leg and the second leg comprises a guide configured to engage a driving member, andthe guide is configured such that, in use, engagement of the guide and the driving member causes relative motion of the first leg with respect to the second leg from the open state to the closed state and from the closed state to the open state.

2. The puller of claim 1, wherein the first leg and the second leg are pivotably interconnected by at least one pivot pin.

3. The puller of claim 2, wherein the driving member comprises a driving pin configured to move, relatively to the pivot pin, through a driving path, the guide being configured such that, in use, motion of the driving pin along the driving path causes the driving pin to engage with the guide.

4. The puller of claim 3, wherein the driving member further comprises one or more rollers, wherein the one or more rollers are configured to revolve about the driving pin.

5. The puller of claim 3 or claim 4, wherein the guide is configured for actuation by reciprocating motion of the driving pin through the driving path, wherein said reciprocating motion permits the legs, in use, to move in a cycle between the open state and the closed state.

6. The puller of any of claims 2 to 5, wherein the first jaw and the second jaw are located at a first distal end of the puller, the guide is located at a second distal end of the puller, and the pivot pin is located therebetween.

7. The puller of any preceding claim, wherein the guide comprises a slot, the slot being located in at least one of the first leg and the second leg.

8. The puller of claim 7, wherein the slot comprises a double-sided cam track.

9. The puller of claim 8, wherein the slot comprises two longitudinally conjoined elongate portions, wherein longitudinal axes of said elongate portions are offset, wherein an offset of said axes is configured to form a plurality of cams, engagement of the driving member with the plurality of cams being configured to impart, in use, opening and closing motion on the legs, whereby to cause relative motion of the first leg with respect to the second leg from the open state to the closed state and from the closed state to the open state.

10. The puller of any preceding claim, wherein the guide is further configured in that, when the legs are in the closed state, the yarn is engaged between the jaws with a predetermined force.

11. The puller of any preceding claim, wherein the guide is further configured in that, when the legs are in the open state, a maximum distance between the legs is less than or equal to a threshold distance.

12. The puller of any preceding claim, wherein the first leg is configured to move relative to the second leg in a plane of motion, and wherein the first leg and the second leg are configured to overlap, at least in part, in a plane perpendicular to the plane of motion.

13. The puller of any preceding claim, wherein the first jaw and the second jaw comprise teeth, the teeth being arranged so as to interlock when in the closed state.

14. The puller of any preceding claim, wherein the first jaw and the second jaw are integrally formed with the first leg and the second leg respectively.

15. The puller of any preceding claim, wherein the puller comprises one or more further legs with one or more further jaws corresponding thereto.

16. The puller of any preceding claim, wherein the first leg comprises a first guide and the second leg comprises a second guide.

17. The puller of any preceding claim, wherein the first leg and the second leg are pivotably interconnected by a first pivot pin engaging the first leg and a second pivot pin engaging the second leg.

18. A puller assembly comprising the puller of any preceding claim, the assembly further comprising:at least one pivot pin, the at least one pivot pin being configured to rotatably interconnect the first leg and the second leg of the puller; andat least one driving member, the at least one driving member being configured to engage the respective at least one guide such that, in use, engagement of the at least one driving member and the respective at least one guide causes relative motion of the first leg and the second leg from the open state to the closed state and from the closed state to the open state.

19. The puller assembly of claim 18, wherein the at least one driving member is connected to a first crank whereby reciprocating motion of the driving member with respect to the guide is actuated in use.

20. The puller assembly of claims 18 or 19, wherein yarn is supplied to the puller via a yarn selector, the yarn selector configured to convey a tail end of the yarn to the puller.

21. The puller assembly of claim 20, wherein the at least one pivot pin is connected to a second crank whereby relative motion of said pin with respect to the yarn selector is actuated in use so as to pull a predetermined length of yarn from the yarn selector when the yarn is engaged.

22. A carpet tuft forming apparatus comprising the puller assembly of any of claims 18 to 21, the apparatus further comprising a cutter assembly configured to sever, when the yarn is engaged by the jaws of the puller, a length of the yarn whereby to form a tuft.3323. A carpet weaving loom comprising one or more of the carpet tuft forming apparatus of claim19.s

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