DEVICE AND METHOD FOR INTERMITTENTLY STORING AND RETURNING YARN DURING THE WINDING OF CONICAL BOBBINS FED WITH YARN AT CONSTANT SPEED

Abstract: A device and method for winding conical bobbins (24) with yarn withdrawn at constant speed from individual spinning units, and comprising a deflecting roller, peg, or similar element (5), which is connected to and moved backwards and forwards by a swinging arm (4) which by storing and returning the yarn with swing movement compensates for the different speeds at which the yarn is collected on the conical surface of the bobbin (24) under formation. Said deflecting roller (5) varies the length of the yarn path so as to stabilise the tension of the winding yarn being deposited at a practically constant value during the entire cycle defined by the travel of the yarn guide element from a position corresponding to one end of the bobbin to its return into said position. The value at which the tension of the yarn is stabilised during its winding onto the conical surface derives from the elastic action generated by a spring (6) or similar element. The position of the deflecting roller is determined at every moment by an analog or digital transducer (7, 36). The value of said store must fluctuate within a range extending between preset limits. If a storage value arises which does not lie within the preset range, the transducer generates an output signal the intensity of which is such as to activate, by means of a central unit (8), a drive source (9) which is arranged to vary the extent of elastic deformation impressed on the spring (6) or like elastic element. Said variation corrects the tension of the yarn being wound to a value which is slightly different from the preceding value so as to rapidly return the fluctuating storage to within the preset range.

Description: The invention relates to a yarn tensioning device in a winding unit for conical bobbins fed with yarn at a constant speed from individual spinning units. More particularly, the invention relates to a device in which a store for the supply of yarn and a tension compensator and regulator for the yarn being wound are combined. In the spinning units, the yarn emerges at their outlet at constant speed from feed rollers and must be deposited at a speed which varies between the major diameter and minor diameter of the conical bobbin being formed. In such a working process it is therefore necessary to periodically vary the yarn length in the section between the feed rollers and its point of deposition on the circumference of the conical bobbin. This length variation and the consequent variation in yarn tension are compensated by adjusting the yarn path by means of a winding tension regulator and compensator device. Tension compensators are known in the art. They comprise a deflecting roller connected to a rocker arm. Depending on the instantaneous yarn tension, or rather according to the instantaneous position of the rocker arm, the mobile deflecting roller is deviated to a varying extent from its contact or bearing position, this position being assumed by the action of a force exerted by a counterweight, a spring or a similar elastic element in contrast with the tension exerted by the yarn. These yarn tension compensators have the drawback of exerting an elastic opposing force which cannot be controlled to take account of the tension variations which can occur in the yarn in the case of non-regular storage. In this respect, in said devices a constantly rotating substantially cylindrical drive roller rotates the conical bobbin under formation, the dimensions of which, together with the taper and angle of the winding helix determine the angular swing amplitude of the mobile rocker arm. The swing position of this latter, which keeps the roller connected to it constantly adhering to the yarn, determines the yarn storage, which constantly increases and decreases according to the stage in the progress of the entire yarn storage and release cycle. Any slippage between the bobbin drive roller and the bobbin under formation, which frequently occurs due to the friction drive used, increases the length of yarn stored and changes the swing position of the mobile arm which, under the action of the elastic element acting as a pulling means, is moved in the limit into an abutting position, consequently nullifying the tension of the yarn being collected. Thus without tension, the yarn leaving the winding roller winds with irregular turns, so prejudicing the bobbin formation and in the limit twisting about itself to create knots and tangles such as to comprise the yarn consistency. The tangled yarn also frequently creates obstacles which interrupt yarn continuity, so blocking the spinning process. The high yarn formation rate of spinning units means that any production hold-up in such spinning units assumes considerable importance because of the reduced rate of yarn collection in the form of bobbins. Yarn tension compensators of this type also have the drawback that if the yarn count or thickness, the type of bobbin under formation or the winding helix angle varies, they have to be adapted to this by onerous manual adjustments at the individual spinning stations, or by replacing the elastic element with another elastic element which conforms to the different operating characteristics. These devices are therefore inflexible in use. Devices for storing and intermittently releasing yarn, preferably for textile machines, are also known. These include by way of example the devices described and claimed in DE-A-1785153 and DE-A-2454917. Such devices have numerous drawbacks: they are insensitive to tension and even less to tension variations in the winding yarn because the storage and release element is of a type which, by means of a lever system, is completely controlled by a to-and-fro drive rod which passes along the entire machine face to operate the yarn stores of all the spinning units; they are unable to adjust the yarn tension to one or more predetermined values preset according to the type of yarn being collected or of the bobbin under formation; they present considerable difficulty in adjusting the value preset for the storage of the yarn being wound, as this adjustment must be made manually by an operator by adjusting the length of the connecting rods or the positions of the lever pivots in order to vary the lever arms, and is therefore lengthy, laborious and variable according to the geometrical characteristics of the bobbin under formation and the winding helix angle; they also have a rather high inertia force due to the presence of several lever systems which are mobile simultaneously but intermittently, and tend to trigger uncontrollable vibratory oscillations and at the same time limit the collection rate; they also set limits on the machine length and therefore on the number of spinning units as their operation relies on drive rods which have to extend along the face of the collection units and are subjected to large numbers of to-and-fro movement strokes. These devices are also rather bulky and inefficient when slippage is present between the conical bobbin under formation and the drive roller. This slippage, which is more or less accentuated, is often present because the conical bobbin being cross-wound continuously rests against a drive roller which on a determined but narrow part of its surface possesses a friction band used for friction drive purposes. A further drawback of such devices is the presence of mobile members, such as rods or shafts, which have to be provided and mounted during the machine construction, and cannot be fitted later. Said mobile members control the operation of several storage devices and extend along the entire winding face from a position at the head of the machine. Because of the principle on which they are constructed, these devices are therefore inflexible and unadaptable to pre-existing spinning stations or stations not provided with the aforesaid mobile members which pass along the front structure of the entire collection face. Tensioning devices having a tension compensator arm are further known, wherein the yarn tension is controlled as a function of the angular position of the arm. A device of this kind and having the structural and functional features recited in the preamble of claim 1 is known from GB-A-2 125 072. In this known device, a change in the angular position of the tension compensator arm determines, through the electronic comparator and control unit, the adjustment of a yarn tensioner located upstream of the arm, so as to increase or decrease the yarn tension and therefore restore the previous angular position of the arm. Such a device is however not suitable where a yarn storage is intermittently required like in the case of winding conical bobbins, because the compensator arm of the known device cannot perform yarn storing and releasing movements without simultaneously intervening on the yarn tensioner and causing yarn tension variations opposing such movements. An object of the present invention is to obviate the aforesaid drawbacks by providing a yarn tensioning device in a winding unit for conical bobbins fed with yarn at constant speed, which device: enables the stored yarn length to be always maintained within a preset range of values with only limited variations in yarn tension; allows the immediate takeup of any additional yarn lengths accidentally present due to slippage between the drive roller and the conical bobbin under formation; does not limit the yarn collection speed in the formation of conical bobbins; does not set limits on the machine length and thus does not limit the number of winding units to be positioned side by side, as these do not require for their operation any drive member extending along the entire winding face, and therefore do not possess further masses moving longitudinally to the machine and connected to drive rods subjected to reciprocating to-and-fro movements; does not limit the diameter of the bobbins obtainable and does not require laborious adjustment to be made when changing the taper of the bobbins under formation; has extreme operational flexibility such as to allow a range of application enabling sort or compact bobbins to be made up within a vast range of yarn counts without the need for laborious mechanical adjustments; can be applied without the need for extensive demounting and remounting of the component parts of the winding machine if this, being already set for forming cylindrical bobbins, is to be converted for forming conical bobbins; can be easily disengaged so as to make it possible to form both conical and cylindrical bobbins on the same machine. A further object of the present invention is to provide a yarn tensioning device in which a store for the intermittent feed of yarn and a tension compensator and regulator for the yarn being wound are combined, in a manner requiring very little maintenance. These and further objects are all attained by a yarn tensioning device having the features claimed in claim 1. The device according to the invention has the advantage, for any variation in the type of yarn and for any variation in the geometrical characteristics of the winding or of the bobbin to be obtained, of automatically adjusting and setting the tension of the yarn being collected to a corresponding value for obtaining regular storage and release swings in accordance with the preset values and limits. A further advantage of the device according to the invention is that it allows the response and speed of operation of the drive source when angularly rotating the shaft to obtain an increase in the preloadlng of the elastic element to be greater than the response and speed of operation of the drive source when angularly rotating the shaft to obtain a reduction in the preloading or a slackening of the elastic element. A further advantage of the invention is that it ensures that once actuated by the drive source or actuator, the angular rotations in both directions for the purpose of varying the preloading of the elastic element are perfectly irreversible so that the thrust of the elastic element against the shaft or the vibration of the machine when in operation are unable to minimally modify the extent of said actuated rotations. A preferred embodiment of the device of the present invention is described hereinafter by way of non-limiting example with reference to the single accompanying drawing figure. This is a diagrammatic isometric view of the device of the present invention cooperating with a yarn guide element, the bobbin under formation being driven by the friction band of a drive roller, the figure showing the moment of maximum storage in the yarn travel while the yarn guide element is moving in the increasing diameter direction of the cross-wound bobbin. A pin 1 is rigidly fixed to a mobile shaped arm 2 of a yarn compensation and release lever system, which operates as the linear position element of a system for controlling and monitoring the effective length of the yarn 18 stored. 2a is the position which the mobile arm 2 assumes at that moment during its swing moment when the stored length of the yarn 18 is zero or a minimum. A bush or ring 3 rigidly joins together one end of the mobile arm 2 and one end of a second shaped arm 4 of the yarn storage and release lever system. The arm 4 operates as the actual storage and release element for the yarn 18 while also acting as the tension compensation and adjustment element for the yarn 18 being wound. 4a is the position which the mobile arm 4 assumes at that moment during its swing movement when the stored length of yarn 18 is zero or a minimum. A yarn deflecting and guide roller 5 moves with swing movement by being carried by the free end of the mobile arm 4 but is able to rotate about its own axis so as not to generate grazing friction against the yarn 18 undergoing continuous collection. The roller 5 has a substantially cylindrical profile. 5a is the position which the mobile yarn deflecting and guide roller 5 assumes at that moment during its swing movement when the stored yarn length is zero or a minimum. A preloaded spiral elastic element 6 having one end secured to the pin 1 stores drive energy by means of appropriate deformation resulting from its loading by angular rotation applied by a shaft 10. The elastic element 6 consists of a steel strip or wire or a like steel element, wound substantially as a flat Archimedes spiral and exerts a reaction force opposing and balancing the force produced by the tension of the yarn 18 on the arm 4. A coil 7 of an analog or digital transducer or other optical or magnetic position sensor serves to continuously detect the angular position of the lever system through an arcuate projection 36 of the mobile arm 2 and to convert said position into an electric signal or a series of electric signals which are fed to an electronic control unit 8 which comprises an electrical comparator and an electronic microprocessor. Said control unit 8 processes the data originating from the analog or digital transducer comprising the coil 7 and mobile projection 36, to then activate a drive source 9 for regularizing the yarn storage. A drive source 9 operates the shaft 10 and consists of a pneumatic, hydraulic or electrical actuator (like a stepping motor) or a combination of two or more of these types. The shaft 10 is rotatably supported to be rotated angularly by the drive source 9 to vary the preloading of the spiral elastic element 6 for the purpose of regularizing the yarn storage if this has strayed outside the range of preset values. The shaft 10 is fixed or hinged, at or in proximity to its end, to the inner end of the spiral elastic element 6. A yarn deflecting and guide roller 11 having a substantially cylindrical profile is connected to a base plate 13. The roller 11 is free to rotate about its axis in order not to generate grazing friction against the yarn 18 undergoing continuous collection movement. A yarn deflecting and guide roller 12 of substantially cylindrical profile is connected to a base plate 15. The roller 12 is free to rotate about its axis. The base plate 13 for the roller 11 is fixed to the machine structure which is otherwise not shown. The base plate 15 for the roller 12 is also fixed to the machine structure. A pair of rollers 14 and 16 are positioned along the path of the yarn 18, both rollers being pressed against each other with said yarn 18 passing between them to withdraw it from a spinning unit of a rotor spinning machine and feed it towards the compensator device of the present invention at constant speed. A solid or hollow shaft 20 of substantially circular cross-section is operated as a control rod for a yarn guide element 26 by means of a suitably shaped cam so as to transmit a reciprocating movement of suitable kinematic and dynamic characteristics to the yarn guide element 26. A drive roller 22 rotates the conical bobbin 24 at a friction region 28 in the form of a circular band of limited width. The bobbin 24 is rotatably supported by a bobbin carrier arm 34. The shaft 20 extends along the entire operational winding face of the machine. A blade 30 deflects the path of the yarn 18 upstream of the yarn guide element 26. Said blade can be linear or shaped with more or less accentuated profiles already known in the art. A base plate 32 supports the coil 7 of the analog or digital transducer. This coil surrounds the arcuate projection 36 provided at the free end of the mobile arm 2, said projection forming the mobile core of the analog or digital transducer. 36a is the position which the projection 36 assumes at that moment during its swing movement when the stored length of the yarn 18 is zero or a minimum. A connection cable 38 connects the transducer, which generates electrical signals proportional to the linear position of the projection 36, with the control unit 8. A connection cable 40 connects the control unit 8 with the drive source 9. 42 represents the swing path of the mobile arm 4 and 44 represents the reciprocating to-and-fro movement path of the shaft 20. A shaft 46 is the pivot axis about which the yarn storage and intermittent release lever system swings by way of the bush coupling 3 which is pivotally mounted on the shaft 46. The drive shaft 48 which rigidly supports the drive roller 22, extends along the entire winding face of the machine. The operation of the device according to the invention is as follows. The purpose of the storage and release device for the yarn 18 being wound onto the conical bobbin 24 is to adapt the varying winding speed deriving from the taper of the bobbin 24 to the constant outlet speed from the feed rollers 16 and 14. The average winding speed corresponds substantially to the spinning speed of the spinning chamber. When the yarn 18 is being collected on the minor diameter of the bobbin 24 the winding speed is less than the feed speed from the rollers 14 and 16, and the lever system by means of its mobile arm 4 stores a suitable length of yarn 18. This stored length is returned gradually as the collection speed increases on moving the yarn 18 towards the major diameter of the bobbin 24 by means of the yarn guide element 26. The ratio of the minor diameter to the major diameter of the bobbin 24 under formation determines the maximum length of yarn 18 which has to be stored and then released for each complete cycle of the yarn guide element 26. As said ratio decreases continuously with increasing fullness of the bobbin 24 under formation, the amplitude of the swing movement of the mobile yarn deflecting and guide roller 5 also decreases for decreasing storage of yarn 18. The mobile deflecting roller 5 generates a loop by deflecting the yarn 18 from its path between the two spaced fixed guide means defined by the rollers 11, 12. This loop therefore has a continuously varying amplitude and the device of the present invention automatically controls this loop by acting as a compensator for the periodic tension variations which arise as a result of the periodic winding speed variations in the formation of a conical bobbin. In order to compensate said tension variations to which the collected yarn 18 is subjected and level them out to a substantially constant value, the mobile deflecting roller 5, which drags the yarn into a temporary storage loop by means of the swing movement of the mobile arm 4 between a plurality of yarn storage and release positions, has to assume different positions within a certain range of swing movement positions, relative to the fixed deflecting guide rollers 11 and 12. These latter, which are rotatable, provide precise guiding of the yarn 18 by virtue of their shape. Because of the rigid connection between the two mobile arms 2 and 4, this variation in the position of the mobile deflecting roller 5 also varies the position of the projection 36 of the lever Said variation generates a signal or several signals of electrical nature which are fed through the connecting cable 38 to the central unit 8 which compares said signals with at least one reference signal which is assigned to swings of the lever system within a regular swing range corresponding to a regular yarn tension. If during the continuous winding process the storage swings remain within predetermined preset limits defining said regular swing range corresponding to the regular yarn tension, the instantaneous mobile linear position of the projection 36 generates electrical signals which when processed in the control unit 8 confirm that the storage and release cycles of the yarn 18 are regular. Thus no signal is generated at the output of the control unit 8 and no activation signal is therefore fed to the drive source 9. If during the continuous winding process the storage swings of the lever system stray outside or beyond the predetermined preset limits, the corresponding mobile linear position of the projection 36 generates an electrical signal or signals which after suitable comparison and processing in the control unit 8 results to be different from said at least one reference signal, and this gives instant rise to an output electric control signal which activates the drive source 9. This latter angularly rotates the shaft 10 to increase or decrease the preloading of the spiral elastic element 6 in order to restore the swings of the lever system within the limits of the predetermined preset range and to adjust the lever system to a yarn tension value slightly higher or lower than its previous value. This latter operation can be further clarified as follows. If the mobile deflecting roller 5 causes the loop in the yarn 18 to assume a position which exceeds the maximum storage limit allowed by the predetermined range of swing for regular operation, the drive source 9 is operated and rotates the shaft 10 angularly in the direction which slightly reduces the amount of preloading of the spiral elastic element 6. This latter element therefore slackens and compels the yarn 18, by means of the lever system 2,3, 4 and 5, to collect on the conical bobbin 24 under an average tension which is slightly lower than the preceding situation. This reduction in the average tension of the yarn 18 being continuously wound must be sufficiently gradual to not allow the formation of knots tangles or similar defects which if collected on the bobbin would reduce its quality. By only slightly decreasing the average tension of the yarn 18 being wound, the yarn slackens and becomes less inserted into the already deposited layers of yarn, and therefore proceeds to wind in the form of turns having a slightly greater diameter. These turns rapidly and progressively take up the excessive storage created by a multiplicity of factors. If the mobile deflecting roller 5 causes the loop in the yarn 18 to assume a position below the minimum storage limit allowed by the predetermined range of swing far regular operation, the drive source 9 is operated and rotates the shaft 10 angularly in the direction which slightly increases the amount of preloading of the spiral elastic element 6. This latter element therefore tightens and compels the yarn 18, by means of the lever system 2, 3, 4 and 5, to collect on the conical bobbin 24 under an average tension which is slightly higher than the preceding situation. This increase in the average tension of the yarn 18 being continuously wound can be substantially rapid as there is no danger of forming knots, tangles or similar defects. By only slightly increasing the average tension of the yarn 18 being wound, the yarn tightens and becomes more inserted into the already deposited layers of yarn, and therefore proceeds to wind as turns having a slightly smaller diameter. Such turns rapidly and progressively cause the yarn to store in the form of an increasingly larger loop, with the result that the intermittent swing of the mobile arm 4 again falls within the limits of the range of swing for regular operation. The width of said regular range is predetermined and preset by the geometrical characteristics of the winding being made and the geometrical characteristics of the conical bobbin 24 under formation. It has been found that the described device for intermittently storing and releasing yarn during the winding of conical bobbins fed with yarn at constant speed operates very reliably and periodically compensates the variations in yarn tension without the mobile deflecting roller 5 undergoing uncontrollable swings. As is apparent from the foregoing, the lever system is swingable independently from the reciprocating movement of the rod 20 and the yarn guide element 26. The use of the device according to the invention is not limited to the winding of conical bobbins produced on a rotor spinning unit, but can also be advantageously applied to winding units of any winding apparatus on which conical bobbins are wound. A preferred embodiment has been described herein but it is apparent that other embodiments are possible which fall within the scope of the appendant claims. Thus the positions of the operating lever systems can vary; different drive arrangements can be provided; it is also possible to vary the shapes and dimensions of the yarn deflecting-storages roller together with the arms which undergo swing movement; ratios and dimensions of the various operational elements can also vary; modifications of a practical applicational nature can be made; thus for example a mechanical-pneumatic transducer can be used instead of an electromechanical transducer; the position of the storage lever system can also be sensed by an optical rod or bar, or by one or more optical sensors in cooperation with bar codes; this latter position, which is converted into an electric signal and processed as heretofore described, can also be sensed on a circumferential are close to the axis of rotation of the storage lever mechanism so as not to be influenced by any small vibrations which arise during passage of the yarn.

Claims: A yarn tensioning device in a winding unit for conical bobbins (24) fed with yarn at a constant speed, comprising: a lever system having two shaped arms (2,4) rigidly connected to each other at one end by a bush (3) pivotally mounted about an axis (46), one (4) of said shaped arms (2,4) carrying at its free end a yarn guide means (5) and acting as a tension compensator deflecting the yarn path between two spaced fixed guide means (11,12); elastic means (6) acting on said lever system for generating a force opposing and balancing the force produced by the tension of the yarn (18) on said one shaped arm (4); a sensor (coil 7) cooperating with the other (2) of said arms (2,4) for continuously detecting the angular position of said lever system and for generating electrical signals as a function of said angular position; an electronic comparator and control unit (8) receiving said electrical signals and including comparator and processor means for comparing said electrical signals with at least one reference signal corresponding to a regular yarn tension and for generating an electric control signal when from the comparison arises a signal which is different from said at least one reference signal; a drive source (9) activated by said electrical control signal for restoring said regular yarn tension; characterised in that: said lever system is swingable between a plurality of yarn storage and release positions within and beyond a regular range of swing corresponding to said regular yarn tension and said reference signal is assigned to swings within said regular range of swing; and in that said elastic means comprise a preloaded spiral elastic element (6) having one end engaged with said other arm (2) and another end operatively connected with said drive source (9), whereby said activated drive source (9) increases or decreases the preloading of said spiral elastic element (6) to adjust the lever system to a yarn tensioning value slightly higher or lower than its previous value and to restore the swing of the lever system within said regular swing range. A device as claimed in claim 1, characterised in that said sensor comprises an electromagnetic sensor including a coil (7) surrounding an arcuate projection (36) of said other arm (2) provided at the free end of said other arm (2). A device as claimed in claim 1, characterised in that said lever system is swingable independently from the reciprocating movement of a yarn distributing means (20,26) associated to the conical bobbin (24). A device as claimed in claim 1, characterised in that said drive source (9) is a stepping motor having its output shaft connected with a shaft (10) engaging said another end of said preloaded spiral elastic element (6).

Inventors: BOLLER, GIORGIO, COLLI, LUIGI, MONTALI, SERGIO
Applicants: SAVIO S.P.A.
Application year: 1988
Main classification: B65H59
IPC codes: B65H59, B65H54