DEVICE FOR REGULATING THE YARN WINDINGS SPEED IN THE FORMATION OF CONICAL BOBBINS IN A ROTOR SPINNING MACHINE

Abstract: This invention relates to a device for regulating the winding seed in the formation of cross-wound conical bobbins where the yarn is withdrawn at constant speed from the rotor spinning unit by a lever system able to displace the friction drive band of the drive roller for the conical bobbin under formation, in order to vary the average resultant value of the varying winding speed during each double stroke of the yarn guide element. Said lever system is operated by a two-direction rotary drive source which is activated when a linear position element, associated rigidly with the yarn storage element, senses by known means that abnormal storage swings persist.

Description: The invention relates to a device for regulating the average winding speed in the formation of conical bobbins in & rotor spinning machine so that the swing of a yarn storage element extends within a preset predetermined range. More particularly the invention relates to a device able to vary the position of effective contact of the bobbin with a rotatable drive roller so as to regulate the intermittent storage and return swing of the yarn storage element should the yarn leave the preset predetermined position range. In rotor spinning units the yarn emerges from the exit of extractor rollers at constant speed and, in forming a frusto-conical package, must be deposited at a speed which varies between the major diameter and minor diameter of said package. In such an operational process it is therefore necessary to periodically vary the yarn length contained in the section between the extractor rollers and the point at which the yarn is deposited 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. Yarn storage elements which compensate for the variation in the yarn winding speed on a frusto-conical surface are known in the art. They largely comprise a deflecting roller connected to a rocker arm. The swing position of this latter, which keeps a roller connected to it constantly bearing against the yarn, represents the amount of stored yarn, which is either increasing or decreasing depending on the stage in the progress of the entire yarn storage and return cycle. Any slippage between the drive roller and the bobbin under formation, which is frequently present due to the fraction drive used, increases the length of yarn stored and changes the swing position of the rocker arm, which then moves outside its normal swing range and in the limit abuts against a stop, consequently nullifying the tension of the yarn being collected. Thus without tension, the yarn leaving the extraction rollers of the spinning unit winds with irregular turns, so prejudicing the bobbin formation and in the limit twisting about itself to create loops and tangles such as to compromise the yarn consistency. In addition, the tangled yarn frequently creates obstacles such as to interrupt yarn continuity, so requiring to halt the spinning process. The high yarn formation rate means that any production hold-ups in a rotor spinning unit assume considerable importance because of the reduced rate of yarn collection on the bobbins. Elements and devices for intermittent yarn storage and return which undergo automatic adjustment when the aforesaid difficulties occur are also known. EP-A-0 284 146 discloses a device of this kind, having the features of the preamble of claim 1. In this known device, the variation of the position of effective contact between the conical bobbin and the drive roller is effected by inclining the axis of the conical bobbin relative to the axis of the drive roller, in that the bobbin carrier arm is pivotally supported about a pin extending perpendicularly to the plane including the axes of the bobbin and of the drive roller. Thus the substantially soft outer surface of the bobbin makes effective contact with the drive roller at a position which lies closer either to the end with the major diameter or to the end with the minor diameter rather than at a central position and the average winding speed correspondingly varies until the normal storage swings are restored. Although said device has certain operational merits, it could well be improved with respect to the automatic adjustment of the extent of the yarn storage swings. For this purpose, a device is provided by the present invention, having the features recited in claim 1. By way of non-limiting example a description is given hereinafter of the device, shown diagrammatically on the accompanying drawing, together with clarification of further details and characteristics. The accompanying drawing shows a diagrammatic isometric view of the regulator device for the yarn winding speed in the formation of cross-wound conical bobbins of the present invention, cooperating with the intermittent yarn storage and return element and with the yarn guide element, and also shows the bobbin under formation driven by the friction band of the drive roller. A connection pin 1 holds the outer end of a spiral elastic element 6. Said pin 1 is rigidly fixed in an integral manner to a mobile arm 2; 1a is the position which the pin 1 assumes in its swing movement in the case the stored yarn length has a normal minimum amount. The mobile arm 2 pertains to the yarn compensation and return lever device in which the arm 2 operates as a linear position element for controlling and monitoring the yarn storage; 2a is the position which the mobile arm 2 assumes at that moment during its swing movement when the length of the stored yarn 18 is a normal minimum. A bush 3 rigidly joins together the mobile arm 2 with a mobile arm 4 of the yarn compensation and return lever device which operates as the actual storage and return element for the yarn 18 while also acting as the tension compensation and adjustment element for the yarn 18 being wound. A mobile deflecting and guide roller 5 is supported at the free end of the mobile arm 4 and is able to rotate about itself so as not to generate grazing friction against the yarn 18 undergoing continuous collection. 15 is the position which the mobile arm 4 with the guide roller 5 assumes at the moment during its swing movement when the length of the stored yarn 18 is a normal minimum; 25 is a non-normal position which the mobile arm 4 with the guide roller 5 could assume during its swing movement outside the lower limit position 15 of the predetermined normal storage range. 35 is a non-normal position which the mobile arm 4 with the guide roller 5 could assume during its swing movement outside the upper limit position of the predetermined normal storage range. The spiral elastic element 6 which stores elastic energy by the tensioning of the yarn 18 consists of a steel strip or wire or similar steel element, wound substantially as a flat Archimedes spiral. Two position transducers 7 and 17 of optical, magnetic, analog or digital type convert the position of the end of the mobile arm 2 into an electrical signal or a series of electrical signals which are sent to a central unit 8 which comprises an electrical comparator with a central electronic microprocessor unit, both of known type. Said central unit 8 processes the data originating from the transducers 7 and 17, to then activate a two-direction rotary drive source 50 when regularizing the storage of yarn 18. A shaft 10 is fixed in proximity of one of its ends to the inner end of the spiral elastic element 6. Fixed yarn deflecting and guide rollers 11 and 12 having a substantially cylindrical profile are connected rigidly to base plates 13 and 19. These latter are fixed to the machine structure, not shown on the figure. A pair of extractor rollers 14 and 16 is 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 at constant speed from a spinning unit of a rotor spinning machine. A solid or hollow shaft 20 of substantially circular cross-section is operated as a control rod for the yarn guide element 26 of each winding station by means of a suitably shaped cam so as to transmit a movement of suitable kinematic and dynamic characteristics to said yarn guide element 26. A drive roller 22 rotates by friction the cross-wound yarn bobbin 24 under formation. The yarn guide element 26 is driven with reciprocating to-and-fro motion by the shaft 20, this latter extending along the entire operational winding face of the winding machine. A friction contact region 28 in the form of a narrow circular band projects slightly from the surface of the drive roller 22. By means of this projection the roller 22 drives the conical bobbin 24. A blade 30 deflects the path of the yarn 18. A bobbin carrier arm 34 rotatably supports the yarn bobbin 24. Cables 38 and 39 connect the transducers 7 and 17 to the central unit 8. 42 indicates the swing path of the mobile arm 4; 44 indicates the reciprocating to-and-fro movement path of the shaft 20. 46 is the pivot about which the intermittent yarn storage and return lever device swings by way of the bush 3. A drive shaft 48 which extends along the entire winding face, is supported in bearings 37. The two-direction rotary drive source 50 consists preferably of a stepping motor which by way of a lever 54 displaces axially the drive roller 22 and consequently the drive band 28 in one direction or the other in order to vary the line of effective contact with the bobbin 24 to consequently obtain a controlled variation in the average winding speed of the yarn 18. The lever 54 is pivotable about a pivot 52 by virtue of the rotary movement of an output shaft of the drive source 50. A support 33 is provided for the pivot 52 and lever 54 which displaces the drive roller 22. A cam 53 is keyed onto the output shaft of the drive source 50. The rotation of said cam 53 determines the angular displacement (arrows 60) of the lever 54, and consequently the axial displacement of the drive roller 22 by means of flanges 55. A key 9 enables the drive roller 22 to slide axially, rigid with the flanges 55, on the shaft 48. Between the flanges 55 there is received a forked end of the lever 54; 56 and 57 are arrows indicating the axial displacements of the drive roller 22, the edge of one end of which varies in position between the lines 27 and 23. A cable 58 connects the central unit 8 to the drive source 50. The operation of the device according to the invention is as follows. The average winding speed corresponds substantially to the spinning speed of the rotor spinning chamber i.e. to the constant yarn withdrawal speed determined by the rollers 14, 16. When the yarn 18 is being collected on the minor diameter of the bobbin 24 the winding speed is less than the speed at which the yarn 18 is fed by the extractor rollers 14 and 16, and the storing lever device 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 due to the yarn being moved 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 which has to be stored and then returned for each complete reciprocating stroke of the yarn guide element 26. Because of the rigid connection between the two mobile arms 2 and 4, the variation in the position of the mobile deflecting roller 5 also varies the position of the end of the arm 2. Said end interacts with the linear position transducers 7 and 17 without the need for mutual contact, these latter generating at their output a signal or several signals of electrical nature which are fed through the connection cables 38 and 39 to the central unit 8 which compares and processes said signals. If during the continuous winding process the storage swing remains within the predetermined limits preset by the position of the two transducers 7 and 17, the central unit 8 confirms that the storage and return cycles of the yarn 18 are normal. Thus no signal is generated at the output of the central unit 8 and no activation signal is therefore fed to the drive source 50. If during the continuous winding process the storage swing strays outside the predetermined preset limits, the corresponding mobile linear position of the end of the arm 2 is such as to cause the transducers 7 and 17 to generate an electrical signal or signals which after suitable comparison and processing in the central unit 8 give instant rise to an instantaneous output signal which activates the drive source 50. Said two-direction rotary drive source 50 having received the activation signal rotates the cam 53 which angularly displaces the corresponding lever 54 pivoted on the pivot 52. By means of its mechanical thrust against the flanges 55, the forked end of the lever 54 causes the drive roller 22 and thus its friction drive band 28 to undergo an axial displacement in one direction or the other, so changing the diameter of effective contact between the conical bobbin 24 and the drive roller 22. The winding speed of the yarn 18 thus undergoes suitable variation, which returns the storage swing to within the range of values corresponding to normal storage. This latter operation can be further clarified as follows. If the mobile arm 4 with the deflecting roller 5 deflects the yarn 18 to a position 35 which exceeds the maximum preset storage limit, the position of the mobile arm 2 is such as to cause the transducer 7 to generate an output signal corresponding to said position. Said electrical output signal is fed to the central unit 8 via the connection cable 39. The central unit 8 having identified the type of electrical signal arriving from the transducer 7 correspondingly produces a specific output command signal which via the connection cable 58 activates the two-direction rotary drive source 50. Said drive source operates the cam 53 and the lever 54 to axially displace the drive roller 22 in the direction indicated by the arrow 57. Consequently, the drive band 28 operates on decreasing diameters of the conical winding surface, ie it is displaced and positioned in the direction of the minor base of the conical bobbin 24. The average winding speed consequently increases, ie it assumes an average value slightly higher than the previous average value, so leading to rapid and progressive take-up of the excessive stored yarn 18, which will have arisen due to a multiplicity of factors in play. Said average value of the yarn winding speed is the average value of the entire instantaneous differing winding speeds during one complete reciprocating stroke of the yarn guide element 26. When the drive band 28 of the drive roller 22 moves in the direction 57 towards the minor diameter of the conical bobbin 24, the average winding speed of this latter increases because its r.p.m. increases. The drive roller 22 is rotated at constant r.p.m. by the drive shaft 48 extending along the entire winding face. If the mobile deflecting roller 5 deflects the yarn 18 to a position 25 outside the minimum preset storage limit position 15, the position of the mobile arm 2 is such as to cause the transducer 17 to generate an output signal corresponding to said position. Said electrical output signal from the transducer 17 is fed to the central unit 8 via the connection cable 38. The central unit 8 having identified the type of electrical signal arriving from the transducer 17 correspondingly produces a specific output command signal which via the connection cable 58 activates the two-direction rotary drive source 50. Said drive source operates the cam 53 and the lever 54 to axially displace the drive roller 22 in the direction indicated by the arrow 56. Consequently, the drive band 28 operates on increasing diameters of the conical winding surface, ie it is displaced and positioned in the direction of the major base of the conical bobbin 24. The average winding speed consequently decreases, ie it assumes an average value slightly lower than the previous average value, so leading to rapid and progressive storage of yarn in the form of a loop of increasing size, and the intermittent swing of the mobile arm 4 again falls within the limit positions of the preset predetermined normal swing range. The width of the normal swing range is determined by the geometrical characteristics of the winding under way and the characteristics of the yarn 18 and of the conical bobbin 24 under formation. In this latter operating situation, when the drive band 28 of the drive roller 22 moves in the direction 56 towards the major diameter of the conical bobbin 24, the average winding speed of this latter decreases because its r.p.m. decreases. The layer of yarn 18 present on the conical tube on which the yarn is wound is sufficiently soft and deformable to enable the diameter of contact to change gradually, in line with the gradual operation of the drive source 50. A preferred embodiment has been described. The operating lever device can be of different configuration; different drive arrangements can be provided; it is also possible to vary and modify the drive source 50 and the lever 54 which axially displaces the drive roller 22; the rotary drive source 50 can be replaced by pneumatic or electropneumatic actuators or similar actuators able to act directly on the drive roller 22 rather than by way of levers or mechanical elements.

Claims: A device for regulating the winding speed of the yarn (18) in the formation of a cross-wound conical bobbin (24), wherein the bobbin (24) is rotated by contact with a friction drive band (28) of a rotatable drive roller (22) and the yarn is withdrawn at constant speed from the rotor of a spinning unit and is distributed along the conical bobbin (24) by a reciprocating yarn guide element (26), comprising a swinging lever device (2-6) deviating the yarn path and defining a yarn storage and return means for compensating the cyclically varying yarn winding speed during the reciprocating strokes of the yarn guide element (26) to maintain an average value of the yarn winding speed corresponding to the constant yarn withdrawal speed, two position transducers (7, 17) interacting with a linear position element (arm 2) of said lever device (2-6) at the ends of a normal storage and return swing range thereof, and a two-direction drive source (50) activated for varying the position of effective contact of the conical bobbin (24) with the drive roller (22) in order to restore said average speed value when the position transducers (7, 17) sense persisting swings of said linear position element (arm 2) beyond the normal swing range thereof, characterised in that the two-direction drive source (50) is operatively connected with the drive roller (22) and the drive roller (22) is axially displaceable on its shaft (48) relative to the conical bobbin (24) by the two-direction drive source (50). A device according to claim 1, characterised in that the two-direction drive source (50) comprises a rotatable output shaft having a cam (53) rigid therewith, the cam (53) engaging one end of a pivotable control lever (54) the other end of which is received between a pair of flanges (55) rigid with the drive roller (22) and axially slidable on the shaft (48) of the drive roller (22).

Inventors: COLLI, LUIGI, FERRO, FRANCESCO, MONTALI, SERGIO
Applicants: SAVIO S.P.A.
Application year: 1989
Main classification: B65H59
IPC codes: B65H59