High-frequency thread-guide device for the production of bobbins with modulated traversing

Abstract

Thread-guide device with modulated traversing with an individual thread-guide having a back-and-forth movement fixed to a flexible element, moved between two pulleys in an alternating clockwise/anticlockwise movement, each driven by its own electric motor, both motors being piloted and coordinated to a control unit.

Description

The present invention relates to the collection of the thread produced or processed by textile machines for winding onto bobbins. In industrial practice, thread collection onto a bobbin is effected on tubes supported by a bobbin-holder arm and resting on a rotating roll, by pulling the thread to be wound onto it. The rotating roll can be activated by a motor, transmitting the rotation movement to the tube onto which the thread is wound, or, in an alternative solution, the roll is idle and is entrained by the bobbin in formation which in turn is driven by a motor. In both cases the function of the roll is to ensure the pressure necessary for forming a sufficiently compact bobbin and with a correct shape. The thread is spirally wound onto the rotating bobbin as the collecting unit is equipped with a thread-guide device which distributes the thread onto the outer surface of the bobbin, with an axial back-and-forth movement, according to a pre-determined cross angle. In industrial practice, the bobbins can have a conical-truncated or cylindrical shape with substantially flat bases, except in some particular cases in which the bobbins are shaped with a marked flaring in the terminal parts.

In traditional bobbin-winding, and especially in automatic bobbin-winding, the most widely-used device for distributing the yarn onto the surface of the bobbin with an axial back-and-forth, i.e. traversing, movement consists in a spiral groove situated on the surface of the rotating roll which allows the yarn to effect an axial excursion of a prefixed length, for a pre-established number of revs of the roll itself and with a prefixed trend of the cross angle of the yarn being wound. In other words, the thread winding and yarn distribution organs operate according to a fixed velocity ratio.

In the present development tendency of yarn processing machines, the thread distribution device on the bobbin must be produced with an autonomous thread-guide device which is independent of the movement of the winding organs.

The thread-distribution device of the yarn on the bobbin must therefore be moved by its own activation organ, with which the frequency of the back-and-forth movement, its run, the length of the spiral wound and the winding cross angle, etc. can be modulated each time and according to necessity.

The patent EP 311,827 describes an individual thread-guide system for a thread collection unit which envisages moving the thread-guide with a closed toothed transmission belt moved with a step-by-step motor controlled by a microprocessor in the traversing movement. The control of the step-by-step motor with a microprocessor allows the desired winding to be effected, with respect to the cross angle, run and traversing frequency. Patent EP 1,209,114 describes belt-tensioner devices for this type of individual thread-guide.

When the yarn collection on the bobbin is effected under severe conditions with the necessity of high-quality bobbins with respect to shape, density and regular unwinding at high speeds, there are considerable problems, for example especially in the most recently conceived automatic bobbin-winders which operate at extremely high collection rates (even over 2,000 m/min), requiring traversing frequencies in the order of 30 Hz and over.

The main problems under these conditions, with thread-guide devices with an alternating movement, derive from the fact that the overall thread-guide and its activation means in any case have a considerable mass and significant inertia at high frequencies and velocities, even when resorting to all the expedients available for reducing the mass of the organs with alternating movements and also deriving from the fact that the times and spaces for the inversion of the movement must in any case be limited (several milliseconds and a few millimeters), to give the bobbin the quality required by the subsequent use, as far as the structure, form and mechanical stability are concerned.

In the intermediate part of its back-and-forth run, the thread-guide is easily activated at the desired velocity, whether said velocity be constant, as in the case of cylindrical bobbins, or when said velocity is variable, as in the case of conical bobbins. In the end sections, close to inversion, the inertia of the thread-guide complex makes it necessary to operate with a lower average speed, with respect to the intermediate excursion section.

As a result of this lower velocity of the thread-guide, the quantity of yarn wound is greater at the two ends of the bobbin. This leads to a greater density at the ends of the bobbin and an irregular profile.

This is minimum when the thread-guide is half-way through its run and maximum when the thread-guide is at the ends of its run.

In order to overcome this problem, it would be necessary to give the traversing device additional power in the movement inversion phases, to reduce the times and distances for braking and acceleration in the opposite direction and re-establish the movement at regime velocity.

In the bobbin-winding of the known art, the greater density at the ends of the bobbin can be reduced by alternating complete traversing runs with shortened traversing runs, or with fixed traversing runs, but with continuous staggering at the two ends.

Patent EP 311,784 envisages accumulating kinetic energy with mechanical activation systems of the thread-guide during the intermediate part of its run and transferring it to the thread-guide in the movement inversion phases.

Patent EP 453,622 describes a method and a thread-guide device—again activated with constraint to a flexible ring-closed element and driven by a motor piloted with an alternating movement by a control unit which controls the position of the thread-guide and applies the step-by-step motor with an overcurrent close to its inversion points, to guarantee the braking and acceleration time values. This document also envisages further increasing the power transmitted in the movement inversion phases with an elastic system which is engaged and disengaged during the thread-guide run.

In patent EP 838,422 a thread-guide is adopted with an oscillating finger which moves according to a circular section around a pin orthogonal to the axis of the bobbin, activated by an electric motor piloted in alternating clockwise/anticlockwise movement. At the two ends of the oscillations of the thread-guide, energy accumulators are positioned consisting of elastic elements which only operate in the brief inversion section, with a repulsing effect.

Patent application EP 1,498,378 describes an analogous thread-guide with an oscillating finger with an energy accumulator having a repulsing effect obtained by positioning permanent magnets in correspondence with the run-end of the oscillating finger, which repel magnets having the same polarity.

Patent application EP 1,159,217 describes a thread-guide with an oscillating finger of the previous type, again activated by an electric motor piloted in an alternating clockwise/anticlockwise movement, in which a torsion spring is used as energy accumulator, in particular a propeller spring, or two springs, with opposing winding directions.

It has been observed that in thread-guides activated with an alternating movement, with a motor rotating alternatingly in a clockwise/anticlockwise direction, of both the closed belt type and oscillating finger type, the torque and inertia of the motor substantially determine the performances of the whole thread-guide system and more specifically the possibility of effecting inversion even at the highest velocities in the necessary times and spaces. It should in fact be taken into account that to obtain the inversion of the movement, in the extremely limited times and spaces available, the motor must brake and restart not only the thread-guide and its kinematic connection chain, but also itself. Consequently, in addition to resorting to all possible expedients for reducing the mass of the alternative movement organs, it is necessary to use motors which can reach the highest acceleration, i.e. the highest ratio between the maximum torque the motor can give in inversion and its own inertia. Generally speaking, in electric motors used for activating alternating movements piloted by a control unit—for example synchronous brushless motors—an increase in the dimensions of the motor, in order to obtain a certain driving torque value produced to give the thread-guide system the required braking and acceleration values, corresponds to a considerable increase in its inertia and a corresponding significant decrease in its acceleration.

For further clarifications, a group of synchronous brushless motors can be considered and their torque and inertia moment compared. This comparison is provided, for example, in Table 1 below.

	TABLE 1
	Type of Motor	Torque (Nm)	Inertia (kg cm2)
	Akm 13	0.44	0.045
	Akm 22	0.88	0.16
	Akm 41	1.88	0.81

From this it derives that the smaller the motor used for the activation of a thread-guide, the higher the acceleration will be, which can be obtained in the inversion and more specifically in the braking and in the subsequent acceleration for moving in an inverse direction.

An objective of the present invention is to produce an individual distribution device of the yarn on the winding bobbin which overcomes the restrictions and drawbacks of the thread-guide devices available in the state of the art and allows extremely high accelerations of the thread-guide in correspondence with the inversion points and consequently to obtain the highest-quality bobbins.

The present invention therefore proposes a thread-guide device for the collection of yarns onto a bobbin, wherein the moving parts are not activated by a single motor which provides the necessary torque, but by at least two motors having smaller dimensions, arranged to as to assist each other in providing the same torque necessary for the moving parts, with an overall lower inertia. The device is also equipped with elastic means which coadjuvate the motors supplying additional energy in correspondence with the inversion points of the movement.

The device according to the invention is defined, in its essential components, in the first claim, whereas its variants and preferred embodiments are specified and defined in the dependent claims.

In order to better illustrate the characteristics and advantages of the present invention, it is described with reference to some of its typical embodiments indicated in the enclosed figures for illustrative and non-limiting purposes.

Said figures refer to an embodiment of the thread-guide device according to the invention, suitable for distributing yarn onto the winding bobbin in a yarn collection unit, of which the further fundamental components: yarn, bobbin, driving roll and mandrels of the bobbin-holder arm with respect to the actual thread-guide, are only shown in FIGS. 1A and 1B.

FIGS. 1A and 1B respectively illustrate in a front view and left-side cross-section, the idea of the most general solution of the present invention for activating a thread-guide in an alternating high-frequency movement.

FIGS. 2A, 2B and 2C illustrate alternative embodiments of the scheme of FIGS. 1A and 1B, with particular reference to flexible thread-guide activating elements alternative to the toothed belt of FIGS. 1A and 1B.

FIGS. 3A and 3B illustrate an alternative embodiment to the scheme of FIGS. 1A and 1B, with the insertion of elastic elements for the energy accumulation to be restored in the inversion points of the movement.

FIG. 3C illustrates an alternative embodiment of the scheme of FIGS. 2A and 2B, with the insertion of elastic elements for the energy accumulation to be restored in the inversion points of the movement.

FIGS. 4A-C; 5A-C: 6A-B; 7 and 8 illustrate embodiments of the invention with a repulsing effect at the two ends of the thread-guide run.

FIG. 9 shows for illustrative purposes, the trend of the magnetic field produced by a solenoid with respect to a point external to this, situated on its axis at a certain distance.

FIG. 10 shows for illustrative purposes, the trend of the repulsion force F of the magnetic pole of a solenoid with respect to a point external to this, situated on its axis at a certain distance.

As already specified, the technical solution for activating a thread-guide in a high-frequency alternating movement according to the present invention is illustrated with reference to FIGS. 1A and 1B.

The bobbin 10 being wound is supported by the mandrels 11 of a bobbin-holder arm, for rotating around its axis due to the effect of the contact created by resting on its activation roll 12. The yarn F comes from below diverted by the distance rod 14 and is wound onto the bobbin 10, distributed onto the surface of the bobbin by the thread-guide 15 which moves with a back-and-forth movement parallel to the axis of the roll 12 and along two guide-rods 16.

The thread-guide 15 is shown with a continuous line in its central position and with a dashed line in its end positions in which the traversing movement is inverted.

The thread-guide device 18 according to the embodiment of the invention shown with reference to FIGS. 1A and 1B, envisages that the back-and-forth movement be activated with a closed flexible element 19, which can have a toothed belt, as shown in the figures—or an equivalent known element, for example smooth belts, cords, chains and so forth—to which the thread-guide 15 is fixed with a fixing organ which runs along the guide-rods 16.

In the following description the index “a” indicates the element on the left and the index “b” the element on the right, the right and left elements being symmetrical and specularly equal to each other.

The flexible element 19 is typically moved between two driving pulleys 20a, 20b activated in an alternating clockwise/anticlockwise movement according to the arrows, each with its own electric motor 21a, 21b, both of said motors being piloted by a control unit, not shown in the figure for the sake of simplicity, which coordinates the movement of the two motors 21a, 21b of the device 18, in a known way, to create the desired traversing movement. These motors, driven to move with an alternating movement with a piloted angular excursion, are known in the art.

According to a preferred embodiment of the present invention, synchronous motors 21a, 21b are used, of the so-called brushless or step-by step type, coordinatingly piloted by a control unit of the yarn winding station.

In the embodiment shown in FIGS. 1A and 1B, the flexible element 19 is wound onto two driving pulleys 20a, 20b in a closed circuit and kept tense, with two parallel sections, one upper and the other lower. The idea of the solution can also be embodied by activating only one of the pulleys 20a, 20b with two motors.

The functioning of the device 18 is effected as follows. In its right-to-left movement, the movement of the thread-guide 15 is determined both by the pulling of the upper part of the flexible element 19 towards the left, exerted by the left driving pulley 20a activated in an anticlockwise direction with respect to the motor 21a, and also by the pulling of the lower part of the flexible element 19 towards the right, exerted by the right driving pulley 20b activated in an anticlockwise direction with respect to the motor 21b.

The synchronous motors 21a, 21b are controlled by means of position detectors, currently called encoders, which allow the control unit of the winding unit to reveal the angular position of the motor: on the basis of the indications of the encoder, the control unit controls and drives the two motors 21a, 21b with the relative activations, currently called inverters.

FIG. 2A shows an alternative embodiment in which the flexible element 19 consists of a closed cord, on which four balls 22 are positioned which, as they are inserted in suitable seats situated on the pulleys 20a and 20b, ensure that the elastic element 19 does not slide onto the pulleys, favouring their movement. The closing of the elastic element 19 is effected by means of a closing clamp 23.

FIG. 2B shows an embodiment in which the flexible element 19 consists of an open cord, at whose ends there are two balls 22, inserted in suitable seats situated on the driving pulleys 20a and 20b. Two pulleys 24a, 24b are also coaxially housed on the driving pulleys 20a and 20b, on which the ends of a second open flexible element 29, for example a cord or belt, are hooked, by means of the balls 22.

FIG. 2C shows an embodiment of the invention in which the driving pulleys 20a, 20b are positioned on a leaf-spring 32, which tends to curve opening up the interaxis and moving the driving pulleys 20a and 20b away from each other. This expedient is necessary when a cord is used as flexible element 19, which with time tends to elongate, losing the necessary tensioning. Any elongation of the flexible element 19 does in fact automatically cause the pulleys 20a and 20b to move away from each other, re-establishing the necessary tension.

FIGS. 3A and 3B represent a further alternative embodiment, with a torsion spring with cylindrical winding and with a thread having a round section, applied on the rear side of each motor. Completely similar and equally functional solutions are in any case possible, for example with springs with a thread having a rectangular section, and/or with spiral winding, and/or applied on the front side of the respective motor, said alternative forms being completely equivalent to that shown.

Torsion springs 25a, 25b are inserted between the driving pulley 20a, 20b and the fixed structure of the relative motor 21a, 21b, which, as illustrated in the left-side view of FIG. 3B, have one of the ends 26a, 26b constrained to the rear extension of the driving shaft 28a, 28b and the other end 27a, 27b constrained to the structure of the motor itself 21a, 21b.

During the alternating runs of the thread-guide 15 and flexible element 19, in its right-to-left movement of the thread-guide 15, the spring 25a untwists unloading its torsion and increasing the leftwards pull of the cord 19 and thus assisting the action of the motors, especially during the inversion of the movement. In the meantime, the system is operating in an anticlockwise direction loading the spring 25b which increases its torsion and accumulates elastic energy which is released in the subsequent run from left to right of the cord 19 and thread-guide 15.

As already mentioned, FIGS. 4A-C; 5A-C: 6A-B; 7 and 8 illustrate embodiment variants of the technical solution according to the invention with the insertion of repulsing elements of the run of the thread-guide 15 to provide the necessary torque for at least restarting the thread-guide 15 with a higher acceleration than that of each single motor with the respective pulleys.

FIGS. 4A, 4B and 4C illustrate a repulsing system which uses pairs of permanent magnets situated on both the moveable devices characterized by an alternating movement and on the fixed structure, causing the polarities having the same sign to move towards each other in correspondence with the run-end, which however have the tendency to repel each other, favouring braking and movement inversion.

FIGS. 4A, 4B and 4C show the configuration of the thread-guide device 18 with the thread-guide 15 in a central half-run position, in the left-end and right-end of its traversing run, respectively. Permanent moveable magnets 30a, 30b are situated in the two driving pulleys 20&, 20b, for example their spokes, which follow their alternating angular movement, oscillating between two angular positions L and R, which move integrally with the thread-guide 15, inverting their angular movement when said thread-guide 15 is situated at the left or right end of its traversing run.

Two homologous fixed magnets 31a, 31b are assembled on the fixed structure of the machine, in a position corresponding to the two ends L and R so that, in correspondence with the inversion movement, one of the pairs of bodies 30a, 30b and 31a, 31b, having polarities of the same sign, N or S, are facing each other and therefore repelling each other with a force inversely proportional to the square of their distance. A significant repulsing action between one of the two driving pulleys 20a, 20b and its corresponding fixed magnetic body 31a, 31b is thus exerted near the inversion point, which favours the braking and movement inversion, alternatingly in correspondence with the two run-ends of the thread-guide 15.

FIGS. 5A, 5B and 5C illustrate a further perfected embodiment of the thread-guide activation device according to the scheme of FIGS. 4A-C.

Analogously to FIGS. 4A, 4B and 4C, FIGS. 5A-C also respectively show the configuration of the thread-guide device 18 with the thread-guide 15 in a central half-run position as in FIG. 5A, in the left-end of its traversing run as in FIG. 5B and in the right-end as in FIG. 5C. As in the embodiment according to FIGS. 4A-C, also in the embodiment according to FIGS. 5A-C, permanent magnets 30a, 30b, are situated on the two driving pulleys 20a, 20b, which oscillate between two angular positions L and R, in correspondence with the thread-guide 15 completely to the left and completely to the right, respectively.

A pair of fixed magnetic bodies 41a, 41b, for example permanent magnets, are assembled on the fixed structure of the motor chassis, in a position corresponding to the two ends L and R so that, in correspondence with the movement inversion points, both of the moveable magnetic bodies 30a, 30b are facing the corresponding fixed magnetic body 41a, 41b, having polarities of the same sign, N or S, and therefore repelling each other with a force inversely proportional to the square of their distance.

As illustrated in FIGS. 5B and 5C, with each inversion of the traversing movement, both of the pairs of magnetic bodies 30a, 30b and 41a, 41b face each other to act as a repellent, no longer alternatingly but jointly, therefore exerting a double action with respect to the embodiment of the technical solution of FIGS. 4A-C.

In the embodiment according to FIGS. 4A-C and 5A-C, the variation in the traversing run can be effected by coherently providing the motors 21a, 21b with a piloting command for limited run or inversion point values.

FIGS. 6A and 6B show a further embodiment of the invention, respectively illustrating the configuration of the thread-guide device 18 with the thread-guide 15 in a central half-run position, indicated with a continuous line, whereas the end positions of the thread-guide to the left and right of its traversing run, are indicated with a dashed line. A permanent moveable magnet 30 is situated on the body of the thread-guide 15, which integrally follows the alternating movement of the thread-guide 15 as far as the inversion positions to the left and right.

In FIG. 6A, two fixed permanent magnets 31a, 31b, analogous to those of FIGS. 4A-C and 5A-C, are assembled on the fixed structure of the machine, in a position corresponding to the two ends of the traversing run so that, in correspondence with the movement inversion, the magnetic body 30 is facing one of the fixed magnetic bodies, having polarities of the same sign, N or S, and therefore repelling each other with a force inversely proportional to the square of their distance. In FIG. 6B, the fixed magnetic bodies, on the other hand, consist of bobbins 42a, 42b stimulated by two feeding lines 43a, 43b. This type of embodiment allows the repulsion force exerted in correspondence with the run-end, to be regulated with the feeding of the bobbin 42a, 42b, the bobbin 42a, 42b acting as a solenoid.

It is in fact known that a solenoid is a cylindrically-shaped bobbin consisting of a series of circular coils very close to each other and produced with a single wire of conductor material. By passing an electric current having an intensity i in the wire, a magnetic field is created, both inside and outside the solenoid, directly proportional to the total number of coils, at the current intensity and with magnetic permeability and inversely proportional to the length of the solenoid. In the case of a solenoid of this type, situated in a physical medium (in the present case, air), the modulus of the magnetic induction vector B proves to be

$B=\mu \frac{N}{I}i$

with N the total number of coils, μ the magnetic permeability of the medium, l the length of the solenoid and i the intensity of the electric current. The magnetic field produced by a solenoid can be schematized as if it were obtained by a continuous distribution of coils, through which the same current passes. Considering the formula for calculating the magnetic field of a coil with respect to a point lying at a distance x from the centre of the coil, on the axis orthogonal to the plane of the coil itself and passing through its centre, it can be seen that the magnetic field drops with an increase in the distance from the coil itself with the quadratic law.

In particular, considering the outer coil of one of the sides of the solenoid, the magnetic field produced with respect to a point outside the solenoid, situated on the axis of the solenoid at a distance x from the centre of the coil, is given by the formula:

$B=\frac{{\mu }_0}{2}I\frac{R^{\angle }}{{\left(R^2+x^2\right)}^{3/2}}$

wherein μ₀ indicates the magnetic permeability in the vacuum, I the intensity of the electric current, R the radius of the coil. The trend of the magnetic field B with respect to x is shown in FIG. 9 (in which the distance x is indicated on the axis of the abscissa and the value of the magnetic field B is indicated on the ordinate).

A magnetic pole is created in the outer side of the coil of a solenoid through which an electric current passes, whose repulsion force F is given by:

$F\left(x,i\right)=\frac{1}{g}\mu \left(\frac{}{x}B_0\left(x,i\right)\right)$

wherein F(x,i) indicates the force of the solenoid in relation to the current i and distance x, with μ indicating the magnetic dipole moment (calculated as a ratio between the intensity of the magnetic field of the magnet on the thread-guide and the volume of the magnet on the thread-guide), g indicates the gravity acceleration (9.8 m/s²) and B₀(x,i) indicates the magnetic field on the axis of the solenoid. The trend of the repulsion force F with respect to x is shown in figure 10 (in which the distance x is indicated on the axis of the abscissa and the value of the repulsion force F is indicated on the ordinate).

The repulsion force is considerably high, close to the outer coil, and drops significantly after a few millimetres. By varying the supply current of the coil, the repulsion force of the solenoid can be varied, within certain values. The graph of FIG. 10 shows two force trends with two different current values. Analogously, in order to vary the discarding, i.e. reduce the inversion space, it is sufficient to stimulate the bobbin or solenoid with a different current.

For substantial variations in the run according to FIGS. 6A-B, the variation can be effected by modifying the positions of the fixed magnetic bodies 31a, 31b or 42a, 42b, as shown in FIG. 7. According to this illustrative embodiment, the axial position of the two fixed magnetic bodies 31a, 31b is regulated by assembling these bodies on a fixed guide in an axial direction and moving them axially with a worm screw 35a, 35b moved in rotation in a clockwise/anticlockwise direction with a motorization 36, to move the two magnetic bodies 31a, 31b towards or away from each other, respectively.

With the same arrangement as FIG. 7, it is also possible to offset the traversing runs, by or by not varying the width of the run, modifying the axial coordinate of the right and left inversion points, giving the worm screws 35a, 35b a clockwise or anticlockwise rotation, by means of the motorization 36.

In the embodiment illustrated in FIG. 8, the scheme of FIGS. 6A and 6B is modified by inserting, instead of fixed magnetic bodies, mechanical shock absorber elements 45a, 45b in a position corresponding to the two ends of the traversing run of the thread-guide 15 so that, in correspondence with the inversion of the movement, the thread-guide 15 discharges its kinetic energy by coming into contact with a repelling element 45a, 45b, which in turn accumulates it and returns it after the movement inversion. This repelling element can be a gas, hydraulic, spring decelerator, positioned at the two ends of the traversing run. This pair of repelling elements 45a, 45b can come into contact directly with the thread-guide 15 or with elements fixed to the flexible element 19 on the two parts of the thread-guide 15, so that the stress exerted by the repellents does not damage the thread-guide itself or its connection to the flexible element. The use, by the activation of the two driving pulleys 20a, 20b to which the flexible element 19 which moves the thread-guide 15 is fixed, of at least two motors, arranged so as to assist each other in providing torque to the moving parts, offers the advantage of being able to select motors having smaller dimensions with respect to those necessary if the necessary torque were assigned to only one motor, with the consequence of being able to exploit the fact that said motors with reduced dimensions have a lower inertia and can therefore provide greater acceleration in correspondence with the inversion of the movement direction. In this way, it is possible to obtain the optimization of the ratio between the torque supplied and the inertia of the system.

Furthermore, the use of separate motors for the two driving pulleys also allows the inertia of the parts moved by the motors to be subdivided, and at the same time to distribute the points in which the torque is supplied, subjecting the system as a whole to less stress.

The action of the elastic means which, when present, assist the motors providing their additional energy in correspondence with the movement inversion points, has the fundamental role of assisting the motors when these are subjected to most stress. The device is consequently able to give the thread-guide greater acceleration, providing the further advantage of obtaining higher production rates.

The present invention is described for illustrative but non-limiting purposes, according to its preferred embodiments, but variations and/or modifications can obviously be applied by experts in the field, all included in the protection scope, as defined in the enclosed claims.

Claims

1. A thread-guide device (18) for the collection of yarns on a bobbin (10), wherein the yarn (F) is distributed on the surface of the bobbin by a thread-guide (15) which moves with a back-and-forth movement parallel to the axis of the supporting roll (12) of the bobbin (10), and the thread-guide device (18) is driven with a back-and-forth movement by means of a flexible element (19), to which the thread-guide (15) is fixed, the flexible element (19) being moved between two pulleys (20a, 20b) which move with an alternating clockwise/anticlockwise movement by the activation of an electric motor piloted by a control unit, characterized in that the pulleys (20a, 20b) are activated by at least two electric motors (21a, 21b), the motors (21a, 21b) being controlled by at least one position detector and piloted by said control unit, which coordinates the piloting of said motors (21a, 21b) to produce the desired traversing movement.

2. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that said pulleys (20a, 20b) are driving pulleys each activated by at least one of its own electric motors (21a, 21b).

3. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that the motors (21a, 21b) are synchronous motors of the brushless or step-by-step type.

4. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that elastic elements for the accumulation of elastic energy, to be returned in the movement inversion points, are inserted between the fixed structure of each motor (21a, 21b) and the corresponding moving parts of the motor itself.

5. The thread-guide device for the collection of yarns on a bobbin according to claim 4, characterized in that said elastic elements are torsion springs (25a, 25b), each of which is constrained with one of its ends (26a, 26b) to the driving shaft (28a, 28b) and with the other end (27a, 27b) to the fixed structure of the motor itself (21a, 21b).

6. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that the pulleys (20a, 20b) are toothed pulleys and the flexible element (19) consists of a closed toothed belt.

7. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that the flexible element (19) consists of a cord, which is wound onto two pulleys (20a, 20b), to which it is physically fixed with constraints (22).

8. The thread-guide device for the collection of yarns on a bobbin according to claim 7, characterized in that the flexible element (19) consists of a cord which forms a closed circuit.

9. The thread-guide device for the collection of yarns on a bobbin according to claim 7, characterized in that the flexible element (19) consists of a cord which forms an open circuit.

10. The thread-guide device for the collection of yarns on a bobbin according to claim 1, characterized in that fixed repulsing elements (31a, 31b; 41a, 41b; 42a, 42b; 45a, 45b) are inserted in the device in correspondence with the ends of the traversing run of the thread-guide (15) to favour the movement inversion.

11. The thread-guide device for the collection of yarns on a bobbin according to claim 10, characterized in that fixed repulsing elements are inserted in the device, consisting of permanent moveable magnets (30; 30a, 30b), which integrally follow the alternating movement of the thread-guide (15), and fixed magnetic bodies (31a, 31b, 41a, 41b; 42a, 42b), and said fixed and moveable magnetic bodies face each other in correspondence with the inversion points of the movements, having polarities of the same sign among each other.

12. The thread-guide device for the collection of yarns on a bobbin according to claim 11, characterized in that the fixed magnetic bodies (31a, 31b, 41a, 41b) are permanent magnets.

13. The thread-guide device for the collection of yarns on a bobbin according to claim 11, characterized in that the fixed magnetic bodies (42a, 42b) are bobbins.

14. The thread-guide device for the collection of yarns on a bobbin according to claim 11, characterized in that the variation in the traversing run is effected by modifying the positions of the fixed magnetic bodies (31a, 31b; 41a, 41b; 42a, 42b).

15. The thread-guide device for the collection of yarns on a bobbin according to claim 14, characterized in that the variation in the traversing run is effected by modifying the angular positions of the fixed magnetic bodies (31a, 31b; 41a, 41b), the permanent moveable magnets being constrained to the pulleys (20a, 20b).

16. The thread-guide device for the collection of yarns on a bobbin according to claim 15, characterized in that the variation in the traversing run is effected by modifying the axial positions of the fixed magnetic bodies (31a, 31b; 42a, 42b), the permanent moveable magnet (30) being assembled on the body of the thread-guide (15) integrally following its alternating movement.

17. The thread-guide device for the collection of yarns on a bobbin according to claim 10, characterized in that mechanical shock-absorber elements (45a, 45b) are inserted in the device in a position corresponding to the two ends of the traversing run of the thread-guide (15).