THREAD CATCHING DEVICES

Abstract: A chuck is adapted to be cantilever-mounted for rotation about a longitudinal axis (20) thereof in a winding ma­ chine for threads such as synthetic plastics filament, glass fibre etc. The chuck comprises an element movable radially thereon between retracted and extended positions under the action of centrifugal force when the chuck is rotated about its longitudinal axis at or above a pre­ determined operating speed in use. The element (l78) has a head portion (l80) which projects radially outwardly from the bobbin tube receiving surface of the chuck when the element is in its extended position, and is located inwardly of that surface when the element is in its re­ tracted position. The head portion (l80) either includes thread catching means adapted to receive and catch a thread to secure the thread to the chuck for winding in­ to a package thereon or is adapted to co-operate in use with a part carried by the chuck in order to form such a thread catching means.

Description: The present invention relates to thread catching devices for high speed winding machines for threads such as syn­ thetic plastics filament, glass fibre strands and the like. In this specification, the term "high speed" refers to linear thread speeds of 3000 m/min. and above, and especially to linear thread speeds above 5000 m/min. Prior Art The chuck (also called "spindle" or "mandrel") of a fila­ ment winder is frequently provided with a thread-catching device built into the chuck structure, for example as shown in US Patents 4 336 9l2, 4 460 l33 and 4 l06 7ll. As shown by these specifications, the chuck itself is commonly cantilevered-mounted, and bobbin tubes, on which thread packages are formed in use, can be placed on and removed from the chuck by moving them axially along the chuck from the free end thereof. When the chuck is designed to carry a plurality of bobbin tubes simultaneously, for simultaneous formation of a corresponding plurality of thread packages, the thread catching device either has to be built into the chuck structure radially inwardly of the outer cylindri­ cal (bobbin tube receiving) surface of the chuck, for example as shown in US Patents 4 0l4 476 and 4 l06 7ll or the device must be mounted on the chuck between neighbouring bobbin tubes, for example as described in US Patents 4 477 034 and 4 482 099. Certain proposals have already been made regarding thread-catching devices movable on the chuck between re­ tracted (radially inward) positions enabling donning of bobbin tubes, and extended (radially outward) operating positions between neighbouring bobbin tubes. For example, European Patent Specification No. 470, and U.S. Patent Specification No. 293l587 cited in connection therewith, show thread catchers mounted on levers which can be pi­ voted by contact with the bobbin tubes themselves. Pro­ posals have also been made for "snagging" devices mo­ vable from retracted to extended positions under the action of centrifugal force. Such a system is shown in U.S. Patent Spec. No. 2998202, but is applicable only to a snagger at the free end of a cantilever-mounted chuck. Another is shown in US Patent Spec. No. 2706090 but this arrangement also is described only as applied to the end of a chuck. Thread severing devices operated by centrifugal force have also been described in German published Patent Spe­ cification (Offenlegungsschrift) No. l760458. However, the arrangement shown in that specification is designed for a radically different spindle type, and is not sui­ table for a winding machine for threads such as synthe­ tic filament and glass fibre. The invention The invention relates to a thread catching device for a chuck adapted to be cantilever-mounted for rotation about a longitudinal axis thereof in a winding machine for threads such as synthetic plastics filament, glass fibre etc. In a first aspect the device comprises an element movable radially between retracted and extended positions under the action of centrifugal force when the chuck is rotated about its longitudinal axis at or above a predetermined operating speed in use. The ele­ ment has a head portion which in use projects radially outwardly from the bobbin tube receiving surface of the chuck when the element is in its extended position, and is located inwardly of that surface when the element is in its retracted position. The head portion may include or be adapted to provide part of thread catching means adapted to receive and catch a thread e.g. as the thread is being moved axially of the chuck. Such catching means may be of a currently conventional type. The head portion may also include thread severing means and/or thread guiding means for guiding axial movement of the thread into the thread catching means. The chuck may include guide means for guiding the radial movement of the element between its retracted and ex­ tended positions. Biassing means may also be provided tending to return the element towards its retracted po­ sition. Means may to exert a force on the ele­ ment urging the head portion, when in its extended po­ sition, into contact with an axial end face on an adja­ cent bobbin tube. The last-named means may be adapted to define a pivoting system for the element, such that when the element is in its extended position, the cen­ trifugal force acting thereon is converted by the pi­ voting system into a turning moment urging the head portion of the element into contact with the bobbin tube. The pivoting system may include abutment surfaces, spaced from pivot point on the chuck and on the element, adapted to engage when the element is in its extended position. The pivoting system may further include a suitable connection means between the element and a biassing means tending to return the element to its re­ tracted position. By way of example, several embodiments of the invention will now be disclosed with reference to the accompanying diagrammatic drawings, in which Fig. l shows a highly simplified side elevation of a winding machine including a chuck in accor­ dance with the invention, Fig. 2 shows a partial cross section through one em­ bodiment of a chuck for use in a machine as shown in Fig. l, Fig. 3 shows a sectioned side elevation of a detail taken from Fig. 2, Fig. 4 shows a detailed side elevation of one em­ bodiment of a thread-catching element in accordance with the invention, Fig. 5 shows an end elevation of the element shown in Fig. 4 Fig. 6 shows a plan view of the element shown in Fig. 4 and 5, Fig. 7 to ll are diagrams representing movement of the ele­ ment shown in Figs. 4 to 6 from its retracted to its extended position in use, Fig. l2 is a side elevation similar to Fig. 3, but showing an alternative form of thread-catching element in a retracted condition, Fig. l3 is a view similar to Fig. l2 but showing the element in an extended condition, Fig. l4 shows a longitudinal section through a ring structure incorporating another form of thread-­ catching element according to the invention, Fig. l5 shows a detail taken from Fig. l4, Fig. l6 is a side elevation similar to Fig. l2 but showing still another form of thread-catching element according to the invention, Fig. l7 is a plan view of the arrangement shown in Fig. l6, Figs. l8 and l9 show a side elevation and end elevation re­ spectively and illustrate yet another form of thread-catching element according to the in­ vention, Figs. 20 and 2l are views corresponding respectively with Figs. l2 and l3 but showing a thread-catching element in accordance with a modification of the em­ bodiment of Figs. 2 to 6, and Figs. 22 and 23 show a modification of the embodiment illustra­ ted in Figs. 20 and 2l General remarks Fig. l shows a winding machine comprising a headstock 300 and a chuck l0 cantilever-mounted at one end (not shown) in the headstock 300. The headstock contains con­ ventional drive systems so that the chuck can be rotated in use about its longitudinal axis 20, at which time the chuck carries an inboard bobbin tube 26 and an outboard bobbin tube 260 upon which respective thread packages are to be formed. A gap 46 is arranged (by means not shown) between the adjacent axial ends of tubes 26, 260 and a thread guide portion 3l2 is left free at the outer end of the chuck. Before starting package winding, a thread l94A is laid in the gap 46 and a second thread l94B is laid on the guide surface 3l2. The threads are being delivered in a direction assumed to be from top to bottom of Fig. l at a predetermined linear speed. The threads are now moved axially towards the inboard end of chuck 3l0, so that thread l94B moves onto bobbin tube 260 and thread l94A moves onto bobbin tube 26. Be­ fore reaching their respective bobbin tubes, however, the threads are received and caught by respective thread catching and severing devices. Such devices have not been shown in Fig. l but embodiments will be des­ cribed with reference to the other figures. The down­ stream portions of the threads (considered with refe­ rence to the delivery direction) are severed from the remainder, and the upstream portions move onto the res­ pective tube for winding of thread packages. Winding machines of the type generally shown in Fig. l can be seen from U.S. Patent Specification Nos. 4 497 450. In this context, the question of whether the winder has two chucks as shown in US 4 497 450 or one chuck as shown in Fig. l is irrelevant. Arrangements for causing the required movements of the threads rela­ tive to the chuck can be seen from U.S. Patent No. 3 920 l93 and from pending European Patent Application No. 86 l04 646.4 filed on April 4, l985 in the names of Adolf Flüeli, Heinz Oswald and Kurt Schefer. The full disclosure of US Patent Specifications 4 497 450 and 3 920 l93 and of European Patent Application No. 86 l04 646.4 are hereby incorporated in the present spe­ cification by reference. First Embodiment - Copending Application The thread catching devices to be described with refe­ rence to Figures 2 to ll are particularly, but not exclusively, designed for use in a chuck structure in accordance with a copending patent application (herein­ after "the copending application") filed in Great Britain in the name of the present applicants on 2 October l985 under the number 85 24 303 and entitled "Chuck struc­ tures". The full disclosure of that copending applica­ tion is incorporated in the present specification by reference. In order to facilitate coordination of the descriptions in the two applications, the reference numerals used in Figures 2 to ll of this application correspond as far as possible with numerals used for similar parts in the copending application. Fig. 2 shows a section through part of chuck l0 in the region of the gap 46 or of the guide surface 3l2; in all respects relevant to the present invention, the arrange­ ments at gap 46 and guide surface 3l2 are identical, and no distinction will be made between them. The chuck structure includes an outer tubular portion 22 providing simultaneously the main load-bearing element of the cantilevered portion of the chuck and a casing for the other elements thereof. Bobbin tubes 26, 260 are re­ ceived on the cylindrical, outer surface of tubular portion 22 and are located and secured relative thereto by bobbin tube positioning and gripping systems des­ cribed in detail in the copending application. One of the internal components of the chuck structure is a support element l50 which is a smooth sliding fit on the internal, cylindrical surface of tubular portion 22. For reasons not related to the present invention, support element l50 may be formed as a ring in the region of the gap 46 and as a disc in the region of the guide surface 3l2. However, only the circumferential portion of ele­ ment l50 is of particular interest in the present con­ text, and that portion is provided with four slots, one of which is indicated at l55 in Fig. 2. The four slots are equiangularly disposed around the axis 20. Tubular portion 22 has four bores l76 extending radially from its outer (bobbin-receiving) surface to open onto re­ spective slots l55. Each bore/slot combination acts as a guidance and locating means for a respective thread catching and severing device l78. Since the operation of each such device is essentially the same, only one will be referred to in the subsequent description. Generally, as indicated in Fig. 3, device l78 comprises a radially outward head portion l80, an intermediate body portion l82 and a radially inward foot portion l84. Further details of the structure can be seen from Figs. 4 to 6. Foot portion l84 has a pair of oppositely facing, flat side faces 3l8 (Figs. 5 and 6), which engage the oppo­ sitely facing side walls (not indicated) of slot l55 (Fig. 2) and locate device l78 circumferentially of the chuck. The spacing of surfaces 3l8 is such that foot portion l84 is a smooth, sliding fit in slot l55 between a radially inward position (not shown in Figs. 2 and 3) in which the foot portion engages surface l57 at the base of the slot, and a radially outward position which will be further described below. The axial length of foot portion l84 (from right to left as viewed in Fig. 3) is greater than the spacing of the surfaces 3l8. Body portion l82 is cylindrical with a diameter approxi­ mately equal to the spacing of surfaces 3l8. Accordingly, foot portion l84 presents radially-outwardly facing sur­ faces l90A and l90B on opposite sides of body portion l82 as viewed in Figs. 4 and 6. As seen in Fig. 5, at least surface l90 A has a rounded apex forming a blunt "edge" extending axially (P). Head portion l80 comprises a pillar l8l integral with body portion l82 and projecting radially from the outer end thereof. At its own outer end, pillar l8l carries an axially projecting tooth l86 formed with a thread gui­ ding edge l87 (Fig. 6). The form and function of this tooth can be seen from U.S. Patent Specification No. 4l067ll, the disclosure of which is hereby incorporated in the present specification by reference. Body portion l82 has a radial bore l9l (Figs. 4 and 5) which is elongated in the transverse direction between guide faces 3l8. Bore l9l contains a clamping element l88 slidable radially in the bore. When the chuck is rota­ ting in use, element l88 slides radially outwardly in its bore l9l to engage the underside (radially inwardly facing surface) on tooth l86, as shown in Fig. 4 and 5. The zone of engagement between element l88 and the tooth l86 forms a thread clamping position. When the chuck is at a standstill, element l88 is no longer firmly pressed against tooth l86, and a thread previously clamped at the clamping position is either automatically released or can be easily withdrawn. Apart from the form of the element l88, the principle of this operation can be seen from U.S. Patent Specification No.4l067ll referred to above, and will not be further described in this speci­ fication. As indicated in Fig. 4, foot portion l84 has a V-shaped recess 202. The large end of the V opens onto one axial surface of foot portion l84, adjacent surface l90B and the recess extends from that axial surface in a direc­ tion axially opposite to the projection of tooth l86 from its support pillar l8l. Recess 202 enables cooperation of device l78 with a biassing means tending to urge the de­ vice into a retracted (radially inward) position relative to the chuck as will now be described with reference to Fig. 3. Provided within tubular portion 22 adjacent support ele­ ment l50 is a second support element l59. A disc or ring l98 is located in engagement with element l59 and carries four spring arms 200 projecting axially therefrom into respective slots l55. Each arm 200 has a free end remote from the carrier l98, and this free end can seat against the rounded apex of recess 202. Spring arm 200 exerts a bias force on foot portion l84 in a radially inward direction (downwards considered with reference to Fig. 3) tending to urge the foot portion into engagement with surface l57 in slot l55. The spring arm can, however, flex to permit device l78 to move to its operative posi­ tion (Fig. 3) as will now be described with reference to the series of diagrams in Figs. 7 to l2. Operation Fig. 7 shows the device l78 in its retracted position with the foot portion l84 in engagement with surface l57. Head portion l80, and a radially outer part of body por­ tion l82 lie within the radial depth of bore l76. Device l78 is located axially relative to the chuck by engage­ ment of body portion l82 with the inboard side of bore l76, as at 320 in Fig. 7, and by the engagement of the free end of arm 200 with the apex of recess 202. An in­ board bobbin tube, indicate in dotted lines at 26 in Fig. 7, can be moved axially over the bore l76 without interference from the device l78. The clamping element l88 (Fig. 4) is assumed to be withdrawn into its bore l9l in the diagram of Fig. 7; this assumes the "upright" disposition of device l78 as illustrated in the figure - ­ if the device happened to be disposed "head down", de­ pending upon the rotational disposition of the chuck at standstill, the clamping element l88 might be engaging tooth l86 under its own weight, but without any signifi­ cant thread clamping pressure. When tube 26 has been secured relative to the chuck, and the latter has been set in rotation for acceleration to­ wards its operating speed, centrifugal force begins to act upon the device l78. When this force is sufficient to overcome the bias provided by spring arm 200, device l78 will begin to move away from face to face engagement with the surface l57. At the operating speed of the chuck, device l78 will have reached an operating posi­ tion illustrated in Fig. ll, and Fig. 3. An imaginary sequence of movements of the device l78 from the re­ tracted to the operating position will be described with reference to Figs. 8 to ll. It is not intended to indi­ cate that each device l78 will on all occasions perform such a sequence of movements. The described sequence does, however, indicate the points at which device l78 must have freedom to move and to adapt relative to its guiding and locating systems, and where those systems can be arranged to direct device l78 into the required final operating position. The location of the center of gravity G of the device l78 as viewed in the side elevation of Fig. 4 is of special significance in relation to the movement to be decribed. Center of gravity G is located within the body portion l82, between the apex of recess 202 and the sur­ face l90A. The center of gravity has not been marked on Figs. 5 and 6 because for purposes of the present des­ cription its location relative to those figures is not significant. It will lie in or very close to an axial mid-plane through the foot portion l84 and body portion l82. In the following description, the total centrifugal force acting on device on l78 will be assumed to be lo­ calised and acting radially through the center of gravi­ ty G. Turning now to Fig. 8, it is noted firstly that bore l76 is dimensioned to provide a clearance relative to body portion l82. Thus, when the centrifugal force first be­ comes effective to move device l78, it may tend to tilt the device in a clockwise direction as viewed in Fig. 8 about the zone of contact of arm 200 with the apex re­ gion of recess 202. Such tilting is, however, limited by engagement of the free edge of body portion l82 with the outboard side of bore l76, as shown in Fig. 8. Due to the clearance between body l82 and bore l76, tilting of device l78 in a clockwise direction relative to the figures will occur at the latest after the centri­ fugal force has overcome the bias of arm 200 sufficiently to lift foot portion l84 clear of surface l57. This con­ dition is illustrated in Fig. 9. The effect of this til­ ting movement is to move head portion l80 in the outboard direction clear of the end portion of bobbin tube 26, which cannot therefore interfere with movement of device l78 to its operating position. This tilting movement is limited, if necessary, by engagement of body portion l82 with the radially inner, inboard edge of bore l76, as also illustrated in Fig. 9. As soon as this latter en­ gagement of body portion l82 with the tubular portion 22 occurs, further radially outward movement of device l78 will be accompanied by "straightening up" of body portion l82 in bore l76, so that the device moves to­ wards the condition illustrated in Fig. l0 through in­ creased flexing of the arm 200. In Fig. l0, apex P on surface l90A is assumed to have come into engagement with the internal surface of tubular portion 22 adjacent bore l76. The zone of engagement on this apex P provides a new pivot point about which device l78 will now tend to tilt in the anti-clockwise direction relative to the figures. This new tilting movement must, however, be accompanied by at least slightly increased flexing of arm 200, whereas the previous tilting move­ ment was permitted by the play between arm 200 and its contact surfaces in recess 202. By this stage, the cen­ trifugal force acting on clamping element l88 has in­ creased to a point at which the element is urged out­ wardly against the underside of tooth l86. Apex P ensures sufficiently accurate definition of the new pivot point. Tilting of device l78 about its zone of contact on sur­ face l90A will continue until one of two things happened; a) in the absence of a bobbin tube 26 (condition not illustrated) surface l90B comes into contact with the internal surface of tubular portion 22 on the opposite side of bore l76 from surface l90A, or b) the radially outer end of pillar l8l engages the axial end face on the bobbin tube 26 (Fig. ll), which has been correctly located relative to bore l76, e.g. by the bobbin tube positioning systems described in the copending application. This con­ dition will be reached at or before the operating speed of the chuck. As indicated in Figs. 2 and ll, a circumferential groove l92 is provided in the external surface of tubular por­ tion 22 adjacent but on the outboard side of the bores l76. The thread l94 can now be laid in this groove and then moved axially in the direction of the arrow l96 in Fig. ll underneath (radially inwardly from) tooth l86. The tooth then guides the thread into the clamping po­ sition in a manner described in U.S. Patent Specifica­ tion No. 4l067ll, the thread is severed downstream from the clamping position (as described with reference to Fig. l) and the upstream portion of the thread is trans­ ferred over the tooth and the adjoining portion of support pillar l8l onto the bobbin tube 26. The firm contact between support pillar l8l and the axial end face of bobbin tube 26 ensures that the thread cannot be caught between these parts during transfer from the catching and severing device onto the bobbin tube. Package winding can now begin, but since this operation is not a subject to the present invention, it will not be described herein. When package winding is complete, rotation of the chuck is decelerated. As the effect of the centrifugal force is reduced, the bias force applied by spring arm 200 be­ comes effective to tilt device l78 away from bobbin tube 26, and then to return it to the retracted position illu­ strated in Fig. 7. This sequence of events is substan­ tially the reverse of those described with reference to Figs. 8 to l0, and will not be dealt with in detail. As may seen in Fig. 3, when device l78 is in its operative position, spring arm 200 can be supported against a con­ vex surface 20l on an axial projection provided on the support element l59. If necessary, the support element l50 can be axially movable after return of device l78 to ensure that the device is brought back to the "upright" position illustrated in Fig. 7. Second Embodiment A second embodiment of the invention is illustrated in Figs. l2 and l3. As far as possible, similar reference numerals are used to indicate similar parts. Thus, each of Figs. l2 and l3 shows a tubular portion 22A similar to the portion 22 illustrated in Figs. 2 - ll. Fig. l3 shows an inboard bobbin tube 26 and an outboard bobbin tube 260 as also shown in Fig. l. Within tubular portion 22A there is a support element l50A similar to element l50 in Fig. 2, and provided with four similar slots l55A (only one of which can be seen in Figs. l2 and l3). For each slot l55A, portion 22A has a corresponding radial bore l76A. The thread catching device (now to be described) in Figs. l2 and l3 differs radically from that shown in Figs. 2 to ll. The device essentially comprises two elements, namely an element 2l0 which is substantially L-shaped as viewed in side elevation, and a retaining element 2l2 in the form of an elongated lever. In order to en­ able illustration of various positions for element 2l0, the full illustration of element 2l2 has been omitted from Fig. l3. However, element 2l2 is represented in the latter figure by a dotted line 2l2A representing the longitudinal axis of the element itself. As illustrated in the sectioned view (Fig. l3), element 2l0 has an opening 2l4 in the region at which the two arms of the L join together. This opening is large enough to receive one end of retaining element 2l2, as indicated by the dotted line illustration in Fig. l2. Elements 2l0 and 2l2 have aligned bores receiving a pin 2l6. The bores and the pin 2l6 together form a pivot joint which connects elements 2l0 and 2l2 together while leaving element 2l0 free to pivot relative to element 2l2 about the longitudinal axis of pin 2l6 which extends at right angles to the plane of the drawing and to the longitudinal axis 2l2A of the retaining element. At its other end, element 2l2 is secured by a second pin 2l8 to the support member l50A. For this purpose, pin 2l8 extends across the slot l55A between the sidewalls there­ of and forms a second pivot joint securing retaining element 2l2 within the slot l55A while leaving the re­ taining element free to pivot about the longitudinal axis of pin 2l8 which is parallel to the longitudinal axis of pin 2l6. Element 2l2 extends away from pin 2l8 in a direction generally longitudinally of the chuck. A bridging member 220 extends across slot l55A at the outer circumference of support member l50A. A com­ pression spring (not shown) extends between bridge mem­ ber 220 and a recess 222 (shown only in Fig. l2) in the radially-outwardly facing surface of retaining element 2l2. The compression spring tends to urge element 2l2 into a retracted (radially-inner) position which is illu­ strated in Fig. l2. In this position, which is adopted by element 2l2 when the chuck is not rotating, element 2l0 is wholly withdrawn within the radially outer cylin­ drical surface of tubular portion 22A, and that surface is free to receive bobbin tubes 26, 260 (Fig. l3) with­ out interference with movement of the bobbin tubes axially along the chuck. From the previous description, it will be apparent that one arm of the L-shaped element 2l0 extends generally radially of the chuck away from the pivot pin 2l6; at its radially outer (free) end, this arm is formed with a bulbous head portion 224. The other arm of element 2l4 extends generally axially of the chuck away from pin 2l6 and the free end of this axial arm is formed with an en­ largement which has a radially outwardly facing surface 226 for a purpose to be described further below. In the withdrawn (retracted) condition, as illustrated in Fig. l2, head portion 224 on the radially-outwardly extending arm of element 2l0 extends into but not through bore l76A. In this condition, which is adopted when the chuck is not rotating, the axially-extending arm of element 2l0 is seated on the base l57A of the slot l55A. In this condition, bobbin tubes 26, 260 (Fig. l3) can be freely moved onto and off the chuck, and when correctly located relative to the chuck they leave a gap 46 in communication with the set of openings l76A. When the chuck starts to rotate about its longitudinal axis 20 (Fig. l) each pair of elements 2l0, 2l2 is sub­ jected to centrifugal force tending to pivot the pair of elements about the axis of its respective pin 2l8 against the biasing force of the compression spring en­ gaging bridge portion 220. The mass of element 2l0 is so distributed that the center of gravity G of this element is located within the axially extending arm between pin 2l6 and the enlargement having surface 226. The centri­ fugal force acting on element 2l0 can again be assumed to act locally at center of gravity G. Accordingly, as element 2l0 moves away from surface l57 A, it tends to rotate in a clockwise direction (as viewed in Figs. l2 and l3) about the axis of pin 2l6 due to the moment created by the centrifugal force at G. In the initial phases of outward movement, therefore, centrifugal force tends to tilt head portion 224 away from bobbin tube 26, so that the radially extending arm can pass freely into the gap 46 between the bobbin tubes. However, the axially extending arm of element 2l0 ex­ tends beyond bore l76A so that surface 226 eventually comes into contact with the internal surface of tubular portion 22A, as illustrated in Fig. l3. Centrifugal force acting on both elements 2l0 and 2l2 is still ten­ ding to urge those elements radially outwardly, so that pin 2l6 tends to continue its radially outward movement. Since the axially extending arm is retained by its con­ tact with tubular portion 22A, element 2l0 now pivots in an anti-clockwise direction (considered with refe­ rence to Fig. l3) about the axis of pin 2l6. Head 224 is therefore pivoted into engagement with the adjacent end of bobbin tube 26. As indicated by the full-line and dotted-line illustrations, the degree of anti-clockwise pivoting of element 2l0 will depend upon the length of bobbin tube 26, which is subject to a degree of variation within specified tolerances which can be allowed for in the design. As may be seen in Fig. l2, the bulbous head 224 forms a rounded bulge to engage the axially-facing end surface on bobbin tube 26. This bulge tends to penetrate into the ma­ terial of tube 26 to at least a limited degree, but never­ theless a wedge-shaped gap 228 (Fig. l3) will be left even after maximum penetration. If, now, a thread (not shown) is laid in this gap it will tend to pass into the narrowest portion of the gap and thereby to be clamped between head 224 and bobbin tube 26. Head 224 is not for­ med with a specific thread severing means; accordingly, severing of the thread must be effected by tearing in­ duced by high tension between the clamping position at head 224 and a package which is to be removed from the machine. This arrangement is therefore primarily suitable for finer, weaker threads. At the completion of the winding operation, reduction of the centrifugal force will permit the compression spring engaging bridge portion 220 to return arm 2l2 towards the withdrawn position. Radially inward movement of pin 2l6 will permit head 224 to pivot away from bobbin tube 26, and thus release the previously clamped thread. When the chuck is stationary, elements 2l0, 2l2 have been returned to the retracted position (Fig. l2) so that bobbin tubes can be moved over the bores l76A without interference. The arrangement shown in Figs. l2 and l3 carries the disadvantage that the thread must be laid accurately in gap 228. Head 224 can be formed with a degree of bulge towards bobbin tube 260, so as to provide a radially out­ wardly facing surface on the head to receive the thread; however, this receiving surface cannot be made very ex­ tensive. As an alternative, the thread could be laid first upon the tube 26, then moved into gap 228, and then returned to tube 26 for winding of a package there­ of. However, such a thread guiding procedure is disadvan­ tageous in that it calls for a reversal in movement of a thread guide. These disadvantages can be avoided by an alternative embodiment in accordance with Figs. l4 and l5. It must be noted, however, that while the embodiment in accordance with Figs. l2 and l3 can be used in a chuck structure in accordance with the copending appli­ cation, an embodiment in accordance with Fig. l5 can be used with such a chuck structure only in limited circum­ stances, which will be further described below. Third embodiment The embodiment illustrated in full lines in Fig. l4 com­ prises a ring structure, generally indicated at 230, supporting four clamping elements one of which can be seen at 232. The use of a ring structure to support clamping elements is well known in the design of chucks and has been described, for example, in published Euro­ pean Patent Applications Nos. l27822 and l39897. The clamping element, and corresponding features of the ring structure, were however different in those prior published applications. The ring structure 230 shown in Fig. l4 comprises a first ring element 234 and a second ring element 236 joined by securing screws 238. Screws 238 draw elements 234, 236 into firm, mating contact at a joining plane indicated at 240. Element 236 is formed with a peripheral groove 242 adjoi­ ning the plane 240. The groove is endless, but is best seen in the lower half of Fig. l4. Furthermore, element 236 has four recesses, one only of which can be seen at 244 in the upper half of Fig. l4. These recesses are formed in the end face of element 236 at the joining plane 240, and they are of limited angular extent and equiangularly disposed about the axis 246 of the ring structure. Each recess 244 opens onto both an outer cy­ lindrical surface 248 and an inner cylindrical surface 250 of ring element 236; both the surfaces are coaxial with the ring structure. Ring element 234 also has an outer cylindrical surface 252 and an inner cylindrical surface 254 coaxial with the ring structure. Four recesses, only one of which can be seen at 256 in the upper half of Fig. l4, are formed in element 234 in alignment with respective re­ cesses 244 in element 236. Each recess 256 opens onto the internal surface 254 of the element 234, and also onto the joining plane 240, but extends only part way through the radial thickness of element 234. Each pair of recesses 244, 256 forms an L-shaped re­ ceiving chamber to receive a respective clamping element 232, which is correspondingly L-shaped as viewed in elevation in Fig. l4. The horizontal bar of the L is lo­ cated in recess 256 of the chamber, and the vertical bar is located in the corresponding recess 244. As clearly seen in Fig. l4, when the horizontal bar of the L engages the radially facing surface 258 within recess 256, the vertical bar of the L is long enough to extend close to, but within, the outer cylindrical sur­ face 248 of element 236. The distribution of mass in each clamping element 232 is such that the center of gravity G of the clamping element is located in the junction re­ gion of the two bars of the element and within recess 244. The dimensions of clamping element 232 in relation to its receiving chamber are such that the clamping ele­ ment has limited freedom of movement in all directions within the chamber, but cannot be ejected radially out­ wardly therefrom. Retention of the element against ra­ dially inward movement will be referred to again later in the description. Ring structure 230 is built into a chuck with the axis 246 of the ring structure coaxial with the axis 20 (Fig. l) of the chuck. As the chuck is driven into rotation about its longitudinal axis, centrifugal force acting on each element 232 immediately drives it radially out­ wardly into contact with the surface 258 in the corres­ ponding receiving chamber. Since the center of gravity G lies within recess 244, however, element 232 tends to tilt about the zone 260 at the junction of joining plane 240 and surface 258. In order to ensure that this til­ ting takes place, surface 258 might be given a slight inclination to the axis 246 so that zone 260 is slightly wedge-shaped. Alternatively, or in addition, the corres­ ponding contact surfaces on clamping element 232 may be shaped to ensure that the desired tilting movement occurs. The result of this tilting movement is indicated in an exaggerated fashion in Fig. l5. As may be seen in Fig. l5, the radially outer end of the vertical bar of element 232 has a rounded surface 262 facing element 234. When element 232 is tilted as des­ cribed above, this rounded surface is driven into con­ tact with the axially facing surface of element 234 in the joining plane 240, for example as indicated at 264 in Fig. l5. The zone of contact may not be exactly at the indicated position 264 because of the freedom of movement of element 232 within its receiving chamber. However, the rounded surface 262 ensures that for all possible engaging positions of clamping element 232, a wedge-shaped gap 266 will be formed so as to converge from the outer cylindrical surface 248 (Fig. l4) to the contact zone 264. Cylindrical surface 248 forms a thread-receiving sur­ face, which may have a thread receiving groove (not shown) similar to the groove l92 in Fig. ll. When the thread is moved axially on surface 248 towards unit 234, the thread remains on surface 248 until it reaches the groove 242. As may be seen in Fig. l5, a rounded surface 262 is such that a thread arriving at groove 242, is al­ ready aligned with the outermost portion of rounded sur­ face 262; when the thread falls into groove 242, it is guided by surface 262 radially inwardly into the wedge-­ shaped gap 266 in which it is eventually clamped in a manner similar to the clamping of the thread in the em­ bodiment of Figs. l2 and l3. It is not essential that the thread immediately passes on to rounded surface 262 as soon as it falls into the groove 242, but the di­ mensions of the parts should be such that the thread cannot fall into the recess 244 between clamping ele­ ment 232 and ring element 248. The ring structure shown in Fig. l4 can be used in two different ways. In the first way, the ring is built in­ to the chuck itself. Arrangements for doing this, have not been specifically illustrated in Fig. l4, but they are well-known in the chuck design art: examples of such arrangements are shown in US Patent 4l067ll. In this case, surfaces 252 and 248 will lie in an imagina­ ry cylinder which also contains the outer surface of the chuck casing. In use, a bobbin tube, such as tube 26 shown in Fig. l4 is passed over the chuck as previously described, and the thread clamping structure presents no interference because all of its elements lie within the outermost cylindrical surface of the chuck casing. Such an arrangement cannot be used in the chuck structure according to the copending patent application referred to above. The disadvantage of this arrangement is that the thread clamping positions 264, 266 (Fig. l5) have a significant spacing radially inwardly from the outer surface of bobbin tube 26. The thread must therefore "climb" from its clamping position onto the tube sur­ face; this is acceptable in some circumstances, but not in others. In the latter event, a second mode of use may be adopted, in which ring structure 230 is mounted between adjacent bobbin tubes. This is indicated diagrammatically by the dotted line illustration 26A of a bobbin tube engaging an axial face on ring element 234; it is emphasized, however, that this illustration is provided only to show the principle involved, since both ring elements 234 and 236 would need modification to enable their use between bobbin tubes. Such modification is also known in the art and is shown, for example, in US Patents 4477034 and 4482099. Such an arrangement could be used with a chuck structure in accordance with the previously mentioned co-pending patent application, since the bobbin tubes and ring structures are moved together onto the outer cylindrical surface of the chuck. In this second mode of use, the thread does not have to climb from the clamping position onto the bobbin tube, but the rings have to be removed from the chuck along with the tubes. In both modes of use, the thread end should be released by the clamping element 232 when the chuck comes to a standstill. In the absence of centrifugal force, the clamping pressure on the thread end will be so light that it can easily withdrawn from the clamping position if it has not already been released therefrom. In any event, removal of a package carried by bobbin tube 26 in Fig. l4 by movement of the bobbin tube from left to right as viewed in that figure, will tend to open the clamp on the associated thread end even if there is a tendency for that clamp to "stick" shut. The arrangement shown in Fig. l4 has the advantage, in relation to the embodiment shown in Figs. l2 and l3, that the clamping element does not tend to dig into the axially facing end of the bobbin tube, and furthermore is not dependent upon an adequate radial thickness of the end face on the bobbin tube. It has the disadvan­ tage that it cannot be used in the preferred chuck structure in accordance with the copending application except in the form of a "push-on" ring. This disadvan­ tage can be avoided by arrangements in accordance with Figs. l6 to l9. Fourth and fifth embodiments A further embodiment is illustrated in Figs. l6 and l7 and represents a modification of the device shown in Figs. l2 and l3. As far as possible, the reference nume­ rals used in the description of Figs. l2 and l3 will be used again to indicate similar parts in the description of Figs. l6 and l7. Accordingly, the tube representing the outer casing of the chuck is indicated at 22A, and the inboard bobbin tube is indicated at 26. The support element l50A in Fig. l6 is similar to the corresponding element in Fig. l2, and in particular is provided with slots l55A (only one of which can be seen in Fig. l6) each having a radially facing surface l57A. In each slot l55A there is a cross pin 2l8 supporting a lever 2l2, similar to the correspondingly numbered ele­ ments in Fig. l2. A compression spring 223 extends bet­ ween a recess 222 in lever 2l2 and a recess 225 in the tube 22A. At its end remote from pin 2l8, lever 2l2 has a fork provided by extensions 2l3 (Fig. l7) supporting a cross pin 2l6 similar to the correspondingly numbered pin in Fig. l2. However, the elements 270, 272 supported by pin 2l6 in Fig. l6 are radically different from ele­ ment 2l0 illustrated in Fig. l2. Element 270 comprises a bulbous head portion 274 at the outer, free end of a single support leg 276. Element 272 also has a head portion 278 at the outer, free end of two supporting legs, one of which is indicated at 280. The radially inner end of each support leg (276 and 280) is enlarged and provided with a through bore to receive pin 2l6. Each element can rotate about the longitudinal axis of the retaining pin 2l6. Leg 276 fits on to a cen­ tral portion of pin 2l6 (containing the longitudinal axis 2l2A of lever 2l2), and the legs 280 of element 272 are engaged with the pin to either side of leg 276. For rea­ sons which will be explained later in the description, each extension on each leg 276 and 280 has a projection extending generally radially inwardly, the projection on leg 276 being indicated at 282, and the projection on the illustrated leg 280 being indicated at 284. Each of these projections forms a generally rounded apex pointing away from pin 2l6. The projection 282 on leg 276 lies radially inwardly from element 272, while the projections 284 on legs 280 lie radially inwardly from element 270. The full-line illustration in Fig. l6 represents the de­ vice in its extended or operative condition. In this con­ dition, centrifugal force acting on the device has al­ ready rotated lever 2l2 in a clockwise direction as viewed in the figure against the bias applied by the com­ pression spring 223. This rotation has continued until an abutment 2l3 on lever 2l2 has engaged the internal surface of tube 22A. Elements 270, 272 therefore project radially outwardly from the external surface of tube 22A into the gap (not indicated in Fig. l6) between the in­ board tube 26 and an outboard tube (also not indicated in this figure, but apparent from Fig. l3). Although the center of gravity of element 270 has not been marked on Fig. l6, it is apparent that it will be located to the left of the longitudinal axis of pin 2l6, as viewed in that figure. Similarly, the center of gra­ vity of element 272 will be located to the right of the longitudinal axis of pin 2l6 as viewed in Fig. l6. Accordingly, centrifugal force acting on element 270 will tend to rotate that element in a clockwise direction as viewed in the figure, while a centrifugal force acting on element 272 will tend to urge that element in an anti-­ clockwise direction. The mass of element 272 is made greater than that of element 270, so that the pair of elements tend to rotate in a anti-clockwise direction about the axis of pin 2l6. Accordingly, one axially-­ facing surface (to the left as viewed in Fig.l6) on head-­ portion 274 of element 270 is forced into contact with the adjacent axially facing end surface on inboard bobbin tube 26. This tube-engaging face on head 274 is formed as a plane surface which will be referred to further later in this description. The axially opposite face of head 274 has a bulge facing and making firm contact with a rounded surface on head portion 278 similar to the rounded surface 262 previous­ ly described with reference to Fig. l5. Accordingly, a wedge-shaped gap 286 is formed between these two head portions leading into a nip 288 (Fig. l7) where the head portions make contact. This forms a thread clamping position similar to that previously described at 264 in the embodiment of Fig. l5. During deceleration of the chuck, as the centrifugal force acting on the thread catching device is reduced, spring 223 pivots lever 2l2 in an anti-clockwise direction around pin 2l8. Elements 270, 272 are therefore drawn radially inwardly of tube 22A through the radial bore l76A similar to that previous­ ly described with reference to Fig. l2. When the chuck is rotationally at a standstill, the projections 282, 284 engage surface l57A as indicated in dash-dotted line in Fig. l6. Reduction of centrifugal force during return of the device to its retracted position reduces the clamping effect applied to the thread by nip 288. The thread is therefore free to be drawn out of the nip as tube 26, now bearing a wound package, is removed from the chuck. In any case, engagement of the pro­ jections 282, 284 with surface l57A applies opposed turning moments to elements 270, 272 tending to draw the head portions 274, 278 apart and positively open nip 288. This opening effect is limited by engagement of the respective head portions with the surface defin­ ing bore l76A. As shown by the dash-dotted line illu­ stration, the radially outer ends of head portions 274, 278 lie wholly within bore l76A when in the retracted positions, so that there is no interference with removal of tube 26 and a package wound thereon. As previously mentioned, the bobbin tube engaging sur­ face on head portion 274 is provided by a plane face, and not by an edge as described for the embodiment illu­ strated in Figs. 2 to 6. Accordingly, a wedge-shaped gap (of relatively small dimensions compared with gap 286) will be formed at the Junction of head 274 with tube 26. Such an arrangement is considered acceptable provided the axial speed of the thread as it moves from the clamping nip 288 onto the bobbin tube 26 is sufficiently high - this corresponds to an adequate angle of incli­ nation of the thread to the chuck axis (or, in Fig. l7, the axis 2l2A of lever 2l2) as the thread moves onto tube 26. This high axial thread speed (inclination to the chuck axis) can be obtained by an arrangement as disclosed in U.S. Patent Application Ser. No. 06/72398l previously referred to. The arrangement shown in Figs. l6 and l7 is therefore particularly designed for use with a thread guiding system as disclosed in that U.S. Patent Application. If the axial speed of movement of the thread is relatively low as it passes on to bobbin tube 26, then head 274 can be provided with an edge to avoid formation of a thread-clamping gap at the zone of contact between head 274 and bobbin tube 26. Bore l76A and bobbin tube 26 (when correctly mounted on the chuck) must be so arranged that the bobbin tube will not interfere with the radially outward movement of ele­ ments 270, 272 as the device shown in Fig. l6 moves to its extended position. The locating means (not illu­ strated) which locates bobbin tube 26 relative to the chuck must therefore ensure that the outboard end of the bobbin tube does not project over the inboard edge of bore l76A. Tolerances in the bobbin tube length will therefore be taken up by additional pivoting of elements 270, 272 in an anti-clockwise direction about pin 2l6 relative to the position shown in full lines in Fig. l6. However, where a thread moving and guiding system in accordance with the U.S. Patent Application Ser. No. 06/72398l is used, it is preferable to define as close­ ly as possible the axial location of the point at which the thread is caught. In order to enable this, the axial location of the clamping point must be made independent of the axial end face of bobbin tube 26, since va­ riation in the length of bobbin tubes is unavoidable. This implies the possibility of a small gap between the radially outer portion of the thread catching device and the end face of the bobbin tube. Such a gap is to­ lerable provided the axial speed of movement of the thread as it moves on to bobbin tube 26 is high enough. An arrangement which assumes the achievement of this condition is illustrated in Figs. l8 and l9, and again the same reference numerals have been used to illustrate the same parts. Accordingly, Figs. l8 and l9 also show an inboard bobbin tube 26, a tube 22A forming the chuck casing, a bore l76A forming a guide for the thread catching device which will be described below, a support element l50A within the chuck, a slot l55A in the ele­ ment l50A and a radially facing surface l57A within the slot. The thread catching device shown in Figs. l8 and l9 com­ prises two generally L-shaped elements 286, 288 respec­ tively. Element 286 (the "support element") has an axially-extending leg 290 located in slot l55A, and a radially extending leg 292 which is located in bore l76A. A recess 294 in leg 290 receives a compression spring 296 which acts against the radially inner surface of tube 22A and tends to urge the device into the retrac­ ted position (not illustrated). In the latter condition, the radially inward facing surface (not specifically indicated) on leg 290 contacts the face l57A. In the ex­ tended condition of the device, as actually illustrated, the radially outwardly facing surface (not specifically indicated) on leg 290 contacts the internal surface of tube 22A and limits radially outward movement of the device under the effects of centrifugal force. When the device is in its retracted condition, the ra­ dially outer end of leg 292 lies wholly within bore l76A, so that this leg does not interfere with movement of tube 26 onto and off the chuck. As element 286 is moved radially outwardly under the effect of centrifugal force, leg 292 runs smoothly in the cylindrical surface defining bore l76A, and guides movement of the device to its fully extended position as illustrated. As in the case of the embodiment described with reference to Fig. l6, bobbin tube 26, when correctly mounted on the chuck, is so located relative to bore l76A, that it does not interfere with the radially outward movement of leg 292. In fact, since there is no tilting movement of leg 292 during this outward movement, a gap S can be created bet­ ween bobbin tube 26 and leg 292; the maximum dimensions of this gap S will be dependent upon the maximum per­ missible tolerances in the length of bobbin tube 26. On its side facing away from bobbin tube 26, element 286 has a generally L-shaped recess 298 receiving the ele­ ment 288. A cross pin 300 extends across this recess at right angles to the length of leg 292, and the axial leg 302 of element 288 is pivotally mounted on pin 300. The radially extending leg 304 of element 288 has a bulge 306 at its radially outer end, the bulge projecting to­ wards bobbin tube 26. Under the effect of centrifugal action, element 288 tends to rotate in an anti-clockwise direction about pin 300 as viewed in Fig. l8, so that bulge 306 is urged into engagement with the adjacent sur­ face on leg 292. Thus a wedge-shaped gap 308 and a clamping nip (not specifically illustrated) are created as already described with reference to Figs. l5, l6 and l7. Leg 292 of element 286 has a transverse slot 3l0, similar to the groove 242 shown in Fig. l4, enabling access of the thread to the clamping nip produced bet­ ween bulge 306 and the leg 292. As seen in Fig. l8, the axially extending leg 302 of element 288 may have a free end projecting slightly ra­ dially inwardly from element 286 when the device is in its extended position, with bulge 306 pivoted into clam­ ping contact with leg 292. As the device is returned to its retracted position, this free end of leg 302 engages surface l57A first, and causes pivoting of element 288 about pin 300 in a clockwise direction as viewed in Fig. l8. This will ensure opening of the clamping nip. How­ ever, this special projection of the leg 302 in Fig. l8, and the special projections 282, 284 described with re­ ference to Fig. l6 are safety measures intended to deal with any tendency for, say, sticky substances to hold the nip closed; in many circumstances, they could be omitted without undesirable effects. Sixth embodiment From the description of Figs. l8 and l9, it will be appreciated that the embodiment of Figs. 2 to 6 could be modified if the axial speed of movement of the thread onto the bobbin tube 26 can be made sufficiently high. Such an arrangement is shown in Figs. 20 and 2l, which correspond respectively with Figs. 7 and ll illustrating the unmodified embodiment. Parts in Figs. 20 and 2l identical with parts already described with reference to Figs. 2 to ll are indicated by the same reference nume­ rals, and will not be specifically described again with reference to Figs. 20 and 2l. The modified parts are the head portion l80A in Fig. 20, in particular the pillar l8lA (Fig. 2l) and the bore l76B (Fig. 20). Referring first to the latter modification, the dimensions of the bore have been reduced so that bore l76B is a closer fit round the body portion l82 of element l78. Body portion l82 is now a smooth sliding fit in the bore, so that element l78A can move bodily radially between the re­ tracted position (Fig. 20) and the extended position (Fig. 2l). The element is located in the latter position by en­ gagement of foot portion l84 with the internal surface of tube 22. As described with reference to the preceding em­ bodiments, the locating means (not shown) for bobbin tube 26 must maintain the adjacent end of the bobbin tube clear of bore l76B, so that there is no interference with radial movement of element l78 to its extended position. Tilting of element l78 during this radial movement is now minimal. The pillar l8l described with reference to Fig. 4 is mo­ dified in that the relatively sharp, bobbin-engaging edge thereon has been eliminated. Pillar l8lA (Fig. 2l) has a generally plane face l83 directed towards the ad­ jacent axial end of bobbin tube 26. As in the case of the embodiment of Fig. l8, a small gap S can be created, the maximum dimensions of which are dependent upon the per­ missible tolerances in the length of bobbin tube 26. The remaining features of the embodiment of Figs. 20 and 2l are identical to those previously described for the em­ bodiment of Figs. 2 to ll. The apex P described with re­ ference to Fig. 5 could, however, be omitted provided the surfaces l90A and l90B adequately locate the modified element in its extended position by contact with the chuck casing 22. Seventh embodiment Figures 22 and 23 illustrate a modified version of the arrangement shown in Figures 20 and 2l, Figure 22 being a view corresponding to Fig. 2 and Figure 23 being a view corresponding to Fig. 20. Once again, similar parts have been indicated by similar reference numer­ als. The major modification relates to the creation of a biassing force tending to return element l78B to its retracted position (Fig. 23). As will be described, in this embodiment the biassing force on each element l78B is created by a respective permanent magnet and the biassing springs provided in the previous embodi­ ments are eliminated. The foot portion of each element l78B is therefore considerably simplified, as is the task of assembling the unit in the chuck portion 22. The bore l76B in tubular portion 22, the head portion l80A of element l78B and the body portion l82 of ele­ ment l78B are as shown in and described with reference to Figs. 20 and 2l. Thus, when element l78B is in its extended position (Fig. 22), the relationship of body l82 to bore l76B and of head portion l80A to bobbin tube 26 is as shown in and described with reference to Fig. 2l. However, the relatively heavy and complex foot portion l84 of the previous embodiments is replaced in Figs. 22 and 23 by a simple plate l84A which projects in all directions beyond the body part l82. The slot l55B in support member l50B is therefore widened slightly re­ lative to that shown in Fig. 2, in order to take the increased width of the foot portion l84A, and is shallower (radial direction) than the slot in the pre­ vious embodiments, corresponding to the decreased (radial) depth of the foot portion. A suitable blind bore (not particularly referenced) is provided in support member l50B, being axially aligned with bore l76B in chuck tubular portion 22 and opening at one end onto surface l57 of slot l55B. This blind bore is filled by a permanent magnet 330 secured in its receiving bore by adhesive so that the outer end face of the magnet is flush with sur­ face l57. Element l78B (or at least part thereof) is made of a ferromagnetic material so that magnet 330 tends to draw element l78B radially inwards until foot plate l84A rests on surface l57 (Fig. 23). Support member l50B is preferably made of a material having a low magnetic permeability, e.g. aluminium. The action of centrifugal force on the element l78B is substantially the same as on the element l78A of the previous embodiment. When the level of the centri­ fugal force is sufficient to overcome the magnetic force tending to hold plate l84A in contact with mag­ net 330, element l78B moves radially outwardly until plate l84A engages tubular portion 22 (Fig. 22). Ele­ ment l76B is then in its operative or extended posi­ tion. The magnet must be arranged so that element l76B is still subjected to an adequate biassing force (ra­ dially inward) even when in the extended position, so that the element returns to the retracted position as the centrifugal force is reduced after completion of winding. The use of magnetic means to create a biassing force is not of course limited to the illustrated embodiment - it could equally be applied to any of the preceding embodiments, or wherever a returning force is needed to retract an element initially moved out under centri­ fugal force. It is not essential to provide a permanent magnet - selectively energisable electromagnetic means could be used. A permanent magnet will normally be far simpler, however. The radially movable thread clamping element shown in Figs. 22 and 23 is identical to the element l88 shown in Figs. 4 and 2l. This element could, however, be cylin­ drical e.g. in the form of a pin. The opening receiving this clamping element (whether as actually illustrated or in pin-form) could pass completely through the ele­ ment l78 from end to end thereof. Suitable permanent magnets are available from Maurer Magnetic AG of CH - 8627 Grüningen, Switzerland. By way of example only, a suitable magnet is in disc-form (dia­ meter l2 mm, axial length 6 mm) and is magnetised in the axial direction to give a remanence of 3600 Gauss and a coercive force of 2000 Oersted. The magnet can exert an axially directed force 3 N on a ferromagnetic body in contact therewith and an axial force of IN on the same body at an axial spacing of l mm from the magnet. Reference has already been made to use of the chuck in a winder as shown in US 4 497 540 (European Patent Application 73 930), but the invention is certainly not limited to this type of winder. Alternative multi-­ chuck winders are shown in US 4 298 l7l and 4 007 884. Single-chuck winders can also include the present in­ vention. The term "cantilever-mounted" is not intended to limit the claims to any specific form of support structure for the chuck. British Patent Application No. 85 24 303 referred to in the introduction as "copending application" corresponds with European Patent Application No. 86 ll3 l04.3, filed 24.9.l986.

Claims: 1. A chuck adapted to be cantilever-mounted for rota­ tion about a longitudinal axis thereof in a winding machine for threads such as synthetic plastics fila­ ment, glass fibre etc., the chuck comprising an ele­ ment movable radially thereon between retracted and extended positions under the action of centrifugal force when the chuck is rotated about its longitu­ dinal axis at or above a predetermined operating speed in use, the element having a head portion which projects radially outwardly from the bobbin tube receiving surface of the chuck when the ele­ ment is in its extended position, and is located inwardly of that surface when the element is in its retracted position, the head portion either inclu­ ding thread catching means adapted to receive and catch a thread to secure the thread to the chuck for winding into a package thereon or being adapted to co-operate in use with a part carried by the chuck in order to form such a thread catching means. 2. A chuck as claimed in claim l, wherein the head portion also includes thread severing means and/or thread guiding means for guiding axial movement of the thread into the thread catching means. 3. A chuck as claimed in claim l or claim 2 including guide means for guiding the radial movement of the element between its retracted and extended positions. 4. A chuck as claimed in any preceding claim including biassing means tending to return the element to­ wards its retracted position. 5. A chuck as claimed in any preceding claim including means to exert a force on the element urging the head portion, when in its extended position, into contact with an axial end face on an adjacent bobbin tube. 6. A chuck as claimed in claim 5 wherein said force - ­ exerting means is adapted to define a pivoting system for the element, such that when the element is in its extended position, the centrifugal force acting thereon is converted by the pivoting system into a turning moment urging the head portion of the element into contact with the bobbin tube. 7. A chuck as claimed in claim 6 wherein the pivoting system includes abutment surfaces, on the chuck and on the element, adapted to engage when the element is in its extended position. 8. A chuck as claimed in claim 7 wherein the pivoting system further includes a connection means bet­ ween the element and a biassing means tending to return the element to its retracted position. 9. A chuck as claimed in any preceding claim wherein the thread catching means is adapted to receive a thread being moved axially of the chuck. l0. A chuck as claimed in any of the claims l to 8 wherein the thread catching means is adapted to receive a thread being moved radially of the chuck. 11. A chuck as claimed in claim 9 or claim l0 wherein the thread catching means is adapted to catch the thread by clamping it. 12. A thread catching device for use in combination with a chuck of a winding machine for winding thread com­ prising an element mounted for pivotal movement under the action of centrifugal force in use to urge a head portion of the element in a direction substantially axially of the chuck into engagement with a counterpart to form a thread clamp between contacting surfaces of the head portion and the counterpart. 13. A device as claimed in claim l2 wherein the counter­ part is provided by another element of the device. 14. A device as claimed in claim l3 wherein said other element is also pivotable under the action of cen­ trifugal force. 15. A device as claimed in claim l3 wherein said other element is fixed against pivotal movement under the action of centrifugal force. 16. A device as claimed in claim l2 wherein the counter­ part is provided in use by the axial end face of an adjacent bobbin tube.

Inventors: BUSENHART, PETER, OSWALD, HEINZ, SCHNEEBERGER, RUEDI
Applicants: MASCHINENFABRIK RIETER AG
Application year: 1987
Main classification: B65H65
IPC codes: B65H65, D01D7