METHOD AND IMPROVED YARN FEEDER SYSTEM AND DEVICE FOR OPTIMISING YARN FEED TO A TEXTILE MACHINE OPERATING HIGHLY DISCONTINUOUSLY OR WITH ALTERNATING MOTION

Abstract

Method and system using a device for feeding yarn to a textile machine, operating discontinuously or with alternating motion, and a device compensating for changes in conditions for feeding or taking up yarn by the textile machine, the compensator device including a movable compensator that performs this compensation to maintain constant yarn tension even when conditions for feeding or taking up yarn change, the movable compensator being rigid and connected to an electric actuator, a control unit of this actuator capable of detecting displacement of the movable compensator from a predetermined resting position when there is a change in take-up or feeding of the yarn and capable of returning the movable compensator to the resting position after such change. Provision is made for continuously detecting yarn tension and operating the electric actuator to maintain tension constant. The compensator device used in this system operating according to the method.

Claims

1. A method for feeding yarns or threads including metal wires to a textile machine at a constant tension, or to a machine processing the metal wire, said feeding taking place discontinuously, that is with sequences of stages in which the yarn moves with at least a first and at least a second condition of feeding or take-up by the machine which differ from each other, said conditions following each other in time, comprising: said feeding being performed by a yarn feeder device having tension detection means, yarn accumulator means driven by its own electric motor, and control means connected to such tension detection means and accumulator means and capable of acting on such accumulator means on the basis of a tension value obtained from said tension detection means, provision being made for a compensator device associated with said feeder device acting together with the yarn coming from said accumulator means before acting together with said tension detection means, said compensator device being able to compensate for changes in the feed or take-up conditions of the yarn at the transition between each first and each second feed or take-up condition following upon the first, this enabling the control means for the feeder device to act on the accumulator means to alter action by the accumulator means on the yarn and maintain the value of the tension detected by the tension detection means constant over time and equal to a set value, said constant tension also being maintained during the stage of changing the feed conditions due to the interaction between said yarn and said compensator device, the compensator device including the movable compensating means supporting a body capable of acting together with the yarn at one free end, said movable compensating means being able to move from a predetermined resting position in the feed direction of yarn when the yarn passes from a condition of lesser take-up to a condition of greater take-up, but moving in the opposite direction when the yarn passes from a condition of greater take-up to a condition of lesser take-up, said compensating means returning to the resting position at the end of such change in take-up, wherein provision is made to control the movement of said compensating means through its own corresponding electric motor directly and rigidly attached to said compensating means and capable of directly controlling the movement of a compensating arm of said compensating means, the compensating arm being controlled according to the set or detected tension of the yarn and the position measured during each stage in which it is fed to the textile machine, said compensating means being rigid.

2. The method according to claim 1, wherein the compensating means and its electric motor that controls the compensating means directly and strictly in movement operate in a passive-dynamic mode, said compensating means being able to move freely, together with the motor, under the force of the yarn but being brought back to the resting position after such movement by the electric motor, said motor generating a torque capable of maintaining said compensating means for yarn in the resting position as yarn is fed to the textile machine.

3. The method according to claim 1, wherein the compensating means and the relative electric motor which controls it in motion operate in an active-predictive mode, said motor moving the compensating means from the resting position to a compensating position corresponding to change in the tension of yarn as soon as such change is detected.

4. The method according to claim 1, wherein it provides for continuous control of the electric motor of the compensator device by a control unit connected directly or indirectly to the tension detection means.

5. The method according to claim 1, wherein provision is alternatively made for said compensating means to rotate about a fixed axis of a drive shaft leaving the electric motor to which said compensating means is rigidly attached, or moves along the compensator device.

6. The method according to claim 1, wherein provision is made for a further accumulation of yarn on the compensator device in addition to the accumulation of yarn on the accumulator means of the feeder device.

7. The method according to claim 1, wherein movement of the compensating means is alternatively angularly limited or unlimited.

8. A system for feeding yarn, including metal wires or threads, at constant tension to a textile machine or to a metal wire processing machine, said feeding being performed discontinuously or with sequences of stages in which the yarn moves with at least a first and at least a second condition of feeding or take-up by the machine which differ from each other, said conditions following one another in time, said feeding system operating according to the method in claim 1 and including a feeder device for the yarn having tension detection means, yarn accumulator means driven by its own electric motor and control means connected to such tension detection means and accumulator means and capable of acting on said accumulator yarn on the basis of a tension obtained from such tension detection means, provision being made for a compensator device associated with said feeder device acting together with the yarn leaving said accumulator means before it acts together with said tension detection means, said compensator device being able to compensate for changes in the feeding or take-up conditions for the yarn at the transition between each first and each second feeding or take-up condition consecutive upon the first, this enabling the control means for the feeder device to act on the accumulator means to alter their action on the yarn and maintain the value of the tension detected by the tension detection means constant over time and equal to a set value, said constant tension being maintained even during the stages of changes in the feeding conditions thanks to the interaction between said yarn and said compensator device, the compensator device including movable compensating means capable of moving from a predetermined resting position in the feed direction for the yarn when the yarn passes from a condition of lesser take-up by the machine to a condition of greater take-up, but moving in the opposite direction when the yarn passes from a condition of greater take-up to a condition of lesser take-up, said compensating means returning to the resting position at the end of this change in take-up, wherein said compensating means comprises a rigid arm carrying a terminal body able to act together with the yarn, said rigid arm being directly and rigidly connected to its own electric motor which directly controls it in movement according to the set or detected tension in the yarn, said rigid arm being located between said yarn accumulator means and said tension detection means, but being separate from the latter.

9. The system according to claim 8, wherein alternatively the resting position of the compensating means lies within a range of movement of such compensating means having two limiting positions or is defined within a circular path of such means about an axis, said path not being restricted angularly.

10. The system according to claim 8, wherein position detector means are provided to determine the spatial position of the rigid arm, said position detector means being associated with the drive shaft of said electric motor also rigidly carrying said rigid arm.

11. The system according to claim 10, wherein provision is made for a control unit for the electric motor of the compensator device connected to the position detector means and capable of detecting movement of the compensating means from the predetermined resting position through said position detector means and of returning said compensating means to the predetermined resting position through control of the electric motor to which the compensating means is rigidly and directly attached, said control unit being directly or indirectly connected to the yarn tension detection means, said control unit controlling the electric motor on the basis of the tension in the yarn detected while said yarn is fed to the machine.

12. The system according to claim 11, wherein said control unit is alternatively associated with the compensator device and connected to the control means of the feeder device or said control unit is part of the control means for the feeder device.

13. The system according to claim 8, wherein said compensator device is a component independent of the feeder device, said compensator device being removably attached to the feeder device and being located at one end or on one side of said feeder device, said compensator device being fully automatic with respect to said feeder device but being intimately connected to said feeder device when it is connected to it.

14. The system according to claim 8, wherein the compensator device has means rotating about its own axis and capable of receiving, when wound, the yarn in at least one of said machine feeding or take-up conditions.

15. A compensator device suitable for use with a feeder device for yarns including metal wires or threads, at a constant tension to a textile machine or to a wire processing machine, said machine operating discontinuously, said compensator device adapted and configured for being part of the feeding system according to claim 8, said compensator device having movable compensating means capable of acting together with said yarn before it leaves said feeder device, said compensating means being defined by a rigid arm rigidly associated with means for actuating its movement, said rigid arm acting together movably with the yarn, the rigid arm being able to move from a predetermined resting position in the feed direction of the yarn when the yarn passes from a condition of lesser take-up by the machine to a condition of greater take-up, but moving in the opposite direction when the yarn passes from a condition of greater take-up to a condition of lesser take-up, provision being made for position detector means capable of detecting movement from said resting position, said position detector means being connected to a control unit capable of directly or indirectly detecting the tension in the yarn and to control said actuator means on the basis of the set or detected tension to return said rigid arm to the resting position after the movement therefrom, wherein the compensator is an independent device in comparison with the feeder device and is located on a side of said feeder device.

16. The compensator device according to claim 15, wherein it comprises a rotating means capable of receiving the yarn upon it when the machine is stopped or when in the stage of returning the yarn to the feeding process.

17. The compensator device according to claim 15, wherein the means for actuating the movement of the rigid arm are an electric motor, the electric motor being directly connected to said rigid arm through its drive shaft so as to rapidly compensating for any rapid movement of the arm, the arm being freely rotatable about an axis of the drive shaft when drawn by the yarn and being returned to the resting position through the action of the electric motor.

18. The compensator device according to claim 15, wherein the means for actuating the movement of the rigid arm are an electric motor of very low inertia, the electric motor being directly connected to said rigid arm through its drive shaft so as to rapidly compensating for any rapid movement of the arm, the arm being freely rotatable about an axis of the drive shaft when drawn by the yarn and being returned to the resting position through the action of the electric motor.

Description

[0062] For a better understanding of the present invention the following drawings are attached, purely by way of a non-limiting example, in which:

[0063] FIG. 1 shows a front view of a compensator device according to the invention associated with a known feeder device for controlling the tension of a yarn fed to a textile machine;

[0064] FIG. 2 shows a side view of the devices shown in FIG. 1;

[0065] FIG. 3 shows a perspective view of the compensator device according to the invention and the feeder device in FIG. 1;

[0066] FIG. 4 shows a front perspective view of the compensator device according to the invention;

[0067] FIG. 5 shows a side view of the compensator device according to the invention;

[0068] FIGS. 6 to 8 show the compensator device from above and in three different positions of use;

[0069] FIG. 9 shows a view from beneath of the compensator device according to the invention; and

[0070] FIGS. 10A-10C show different block diagrams relating to use of the system according to the invention;

[0071] FIGS. 11A-11C show graphs of the tension of the yarn directed to the textile machine in situations where the device which is the object of the invention is not operational (FIG. 11A) and in two situations where the system according to the invention operates in passive-dynamic mode (FIG. 11B) and in active-predictive mode (FIG. 11C) respectively.

[0072] With reference to the aforesaid figures (where corresponding parts have identical numerical references), and FIG. 1 in particular, a compensator device according to the invention is generically indicated by 1 and is associated with an end 2A (or is located on a side) of a feeder device or simply a feeder 2, which is in itself known, to feed a yarn F (shown as a dashed line in FIG. 1) at constant tension to a textile machine T. Yarn F can also be a metal wire and can be delivered to an operating machine such as a winder. Device 1 is a complete and clearly identifiable element, in terms of both construction and use, in comparison with feeder 2.

[0073] Feeder 2 has a tension sensor 3, a pulley 4 (or equivalent yarn accumulation means) driven by its own electric motor (not shown) and a control unit or electronics 60, preferably with microprocessor (see FIG. 10A-10C), which is in itself known. This control unit or electronics is able to assess the tension in a yarn detected by sensor 3 as it is fed to the textile machine, compare the detected tension with a predetermined value (or SET POINT value) and check and adjust the tension of the yarn (if it differs from the desired value) through acting on the aforesaid electric motor and therefore on pulley 4. This feeder 2 and its parts 3, 4 are of a type and operation which are known and therefore will not be further described.

[0074] The feeder, as mentioned, allows the yarn to be fed to the textile machine at constant tension, said textile machine being a production unit for manufactured products or a machine for processing the yarn.

[0075] Device 1 and feeder 2 define a feeding system for yarn F according to the invention.

[0076] Compensator device 1 according to the invention is able to act together with the yarn after it has passed over pulley 4. This compensator device is therefore within the yarn tension control loop, as may be seen from FIG. 1 and as will be clear from the description of the method according to the invention. Thanks to the present invention it is possible to increase the dynamic performance of the feeder system so that it will be able to compensate instantly for sudden changes in yarn take-up (positive and negative), enabling the pulley motor to change to the new speed to feed the yarn as required by the new take-up situation without causing positive or negative tension peaks in the final yarn tension.

[0077] The presence of compensator device 1 within the control loop always ensures that the tension of the yarn leaving feeder 2 is always the same as the one set.

[0078] Compensator 1 is an independent device in comparison with feeder 2 and comprises an electric motor 8, for example a direct current brush motor, preferably with very low inertia to increase its dynamics. In the embodiment of the invention provided by way of example motor 8 directly moves a drive shaft having two parts projecting from opposite sides of the motor itself. In the figures the first part of the drive shaft is indicated by 7 (see FIGS. 7-9), and the second part indicated by 10 may be seen in FIG. 9; the motor is also inserted within a body 11 of the device. A rigid arm (which is thus attached to the drive shaft itself) is mechanically attached to the first part of the drive shaft. At end 14 of arm 13 there is also an annular body (or one of another shape) of ceramic (or other material) 16 over which the yarn runs.

[0079] Electric motor 8, as mentioned, is preferably of very low inertia to allow rapid movement of arm 13 under the force of the yarn and therefore rapid compensation for this movement without it causing tension peaks in the yarn itself.

[0080] Arm 13 can however freely rotate (causing the motor to rotate) about an axis M (or drive shaft axis) if drawn by yarn F, both when the motor has very low inertia (preferred) and when it has limited inertia; in every case this arm has a zero or initial resting position (for example that seen in FIG. 6) that is adopted when yarn F is taken up by textile machine T without changes in tension and without interruptions. This arm may also adopt other compensation positions, as described below.

[0081] The assembly of arm 13 and motor 8 (i.e. substantially device 1) can operate in two different modes: passive-dynamic mode or active-predictive mode.

[0082] In passive-dynamic mode the motor enables arm 13 (attached to the drive shaft) to be pulled by the yarn and moved from its resting position also causing the motor itself to rotate. However, this motor acts after said movement to return arm 13 to the resting position. In this mode or operating mode the motor substantially operates as a dynamic spring whose force (with which it acts on arm 13) can be programmed by programming and/or controlling the motor torque.

[0083] This force is not however predetermined and fixed (as in the solution in U.S. Pat. No. 4,752,044), but can vary in that it automatically adjusts to changes in the set value of the yarn tension in the various stages of the production process so as to always maintain the arm in its predetermined position whatever the set operating tension of the yarn for each particular stage in the production of a manufactured article. This enables motor 8 to oppose an equal and opposite force to that which moves arm 13 (to which it is always directly connected) from the resting position to maintain this arm in its equilibrium position (for example that at 3 o'clock in FIG. 6).

[0084] The variability of the opposing force or the action of the motor on arm 13 will be described below.

[0085] In active-predictive mode, motor 8 is able to act in advance (in predictive mode) as soon as it detects a change in the yarn tension (detected by sensor 3) due to a change in the operating stage of the machine. In this case motor 8 moves arm 13 carried by the drive shaft to the compensating position capable of compensating for the change in tension: if this tends to increase, motor 8 moves the arm to the compensating position at 6 o'clock in FIG. 7, if the change tends to a decrease in yarn tension (because the textile machine has stopped or slowed down yarn take-up), the motor moves arm 13 to the compensating position at 12 o'clock in FIG. 8. This enables the yarn tension to be kept constant regardless of the operating and production stage of textile machine T.

[0086] FIGS. 11A-11C show the tension curves in situations where motor-arm assembly or device 1 is disabled (FIG. 11A), in passive-dynamic mode (FIG. 11B) or in active-predictive mode (FIG. 11C).

[0087] In the figures, curves or lines F, K, W and Y respectively define the set yarn tension (in a production operating stage, curve F), the measured yarn tension (curve K), the set point position for arm 13 (curve W) and the actual position of arm 13 (curve Y). In the figures, time is the abscissa, the ordinate is the tension measured for F and K, as well as a position value for W and Y.

[0088] As may be seen from comparing the figures, when device 1 is disabled the measured yarn tension has significant peaks and variations in comparison with the other situations in FIGS. 11B, 11C. From comparing FIGS. 11B and 11C it can also be seen that the yarn tension has more limited variations in the situation where device 1 acts in active-predictive mode. Finally, in FIG. 11C it can be seen that the resting position of arm 13 (curve W) is not predetermined, but follows the change in the yarn tension; this resting position is also followed by the present position of the arm during the compensation performed by device 1.

[0089] Second part 10 of the drive shaft supports a magnet 18, which, together with arm 13 associated with motor 8, is free to rotate about its axis M within a specific circular sector (causing the drive shaft to rotate). Alternatively, the assembly comprising arm 13 and magnet 18 can rotate freely, making a complete revolution about axis of rotation M (the axis of the drive shaft); in other words, both arm 13 and magnet 18 are splined onto the drive shaft with the result that both rotate about axis M in the same way, freely or within an angular sector. This enables the position of arm 13 to be immediately known by detecting the position of the magnet.

[0090] For this purpose there are position detectors 19 around the magnet, for example one or more linear Hall sensors 20, capable of generating a position signal addressed, for example, to a control unit 70 of compensator device 1. Thanks to the Hall sensor data this unit 70 is able to transform the motor rotation into two sinusoids offset by 90 (Sine and Cosine) from which it is possible to obtain the absolute position of the shaft and therefore of arm 13 that acts together with the yarn, arm 13 being rigidly attached to the shaft and to magnet 18, in real time.

[0091] In one embodiment, the control unit also advantageously comprises systems (in themselves known) to drive the electric motor to control its rotation speed and applied torque.

[0092] Preferably, provision is also made for real-time data exchange between control electronics 60 of feeder 2 and control unit 70 of compensator device 1 so as to be able to set the desired torque for the motor of this device 1 and then control its rotation and read its position (and consequently, in a direct and immediate way, that of arm 13). The torque setting is dynamic and not fixed as it depends on the set yarn tension or that detected by sensor 3.

[0093] Information exchange may take place in one of the following ways: through any serial bus, through digital or PWM signals, or through analog signals.

[0094] It is therefore clear that feeder 2 (through its control electronics), which acts together with said compensator device 1, is able to know the position of arm in real time, in a secure and immediate way, and adjust the torque/shift/speed applied to the motor of compensator device 1. This is because of the direct connection between the drive shaft and said arm or because of the direct action of this motor on the arm.

[0095] By appropriately managing the received position signal for arm 13 and by appropriately controlling the motor acting on this arm, the feeder system for yarn F according to the invention is therefore able to close a second control loop for the position of arm 13 in an almost immediate way to keep it in the desired position, for example in its central position (3 o'clock), as the set tension varies. This is to compensate for movement of the yarn and changes in its tension linked to the various operating stages of the textile machine.

[0096] With reference to FIGS. 10A, 10B, the system can be implemented in different ways: [0097] 1. Compensator device 1 has its own control unit 70 which is intended to receive from control electronics 60 of feeder 2 a resting position reference (indicated by block 80 in FIGS. 10A and 10B) which the arm must maintain as the set or detected tension of yarn F varies. Control unit 70 acts together with the means (magnet 18) for measuring the position of arm 13 and driving motor 8 (blocks 81 and 82). The control unit thus closes the control loop for the position of arm 13. [0098] 2. Alternatively, and preferably, it is control electronics 60 of feeder 2 that receive the data relating to the position of arm 13 from magnet 18 and consequently set a torque value for motor 8 to close the control loop for that position (on the basis of the set or detected yarn tension). In this case, the drive means for motor 8 may be located in control unit 70 of compensator device 1 (to which a reference is passed by the feeder) or in the electronics 60 of feeder 2 (as described below). This solution is preferable because control electronics 60 of feeder 2 not only know the position of the arm, but also know directly the measured tension of the yarn (being connected to tension sensor 3) and can then use the two items of information to optimise the performance of the system. For example, if such electronics detect that the yarn tension is increasing due to a sudden request for yarn from textile machine T, they may decide to automatically change the position set point for arm 13, for example by moving it from 3 o'clock to 6 o'clock. This is in accordance with the active-predictive operating mode of the assembly of motor 8 and arm 13 indicated above.

[0099] This function also allows for further reduction in the peak tension because use is made of not only the low inertia of motor 8 but also its dynamics to compensate for the situation. The same obviously applies to the stage of a sudden slowdown in take-up. All this may in fact be seen from FIG. 11C and comparison with FIG. 11B previously mentioned.

[0100] The electronics of the feeder system (i.e. control unit 70 of compensator device 1 or control electronics 60 of feeder 2, as described above), by continuing to read the position of arm 13 (depending on the tension detected in yarn F) and by suitably controlling the torque of the motor acting together with arm 13, are able to hold the position of compensating arm 13 at the desired value. This torque value will therefore allow arm 13 to be kept in equilibrium in its resting position, for example at 3 o'clock, by applying a force equal and contrary to the feed tension of the yarn to the arm, directly through the drive shaft. This is without any delay in the action on arm 13, as instead happens in the solution in WO 2013/064879.

[0101] Thus an increase or decrease in yarn tension will cause arm 13 to move from its balanced position, always keeping the yarn at the set working tension, as for example indicated below:

a) in the case where the set yarn tension needs to be increased during processing, arm 13 will obviously tend to fall (moving towards the 6 o'clock position in FIG. 7) and the system electronics (i.e. control unit 70 of device 1 or control electronics 60 of feeder 2) reading this change in position will calculate the new torque to be applied to motor 8 to bring arm 13 back to the resting position;
b) in the case where the set tension needs to be decreased during processing, arm 13 will obviously tend to rise (moving towards the 12 o'clock position in FIG. 8) and the control unit or the electronics of the feeder reading this change in position will calculate the new torque to be applied to motor 8 to bring arm 13 back to the resting position.

[0102] The feeder electronics will therefore be able to control the position of compensating arm 13, automatically and quickly, precisely because the arm is attached to the drive shaft, thus enabling the operator to modify the working tension at will during processing, for example, to make graduations in tension during the production cycle for a manufactured article (for example graduated compression on medical socks, etc.). Each change in tension involves a change in the motor torque applied to arm 13 that will always adopt the resting position (for example 3 o'clock) or will be brought back to it to keep constant the present tension of the yarn or the tension that the yarn takes up during the particular feed stage required for that particular production stage.

[0103] In other words, the feeder system is provided with a control unit (device 1 or feeder 2), incorporating for example a microprocessor, which controls operation of the motor that directly moves arm 13. However this arm, together with the drive shaft to which it is connected, can initially move freely about axis M (causing the motor to rotate) when the textile machine's take-up or feed conditions vary with consequent change in the tension of the yarn passing through annular body 16 supported by arm 13.

[0104] Any change in the position of arm 13 (with respect to a predetermined reference or resting position, e.g. 3 o'clock) is detected by the control unit of the feeder system through signals coming from position detection means 19. These data are supplied to said electronic control unit (60, 70) for the feeder system to close the control loop.

[0105] Control unit 70 of device 1, in particular, is able to detect by how much (angularly) arm 13 has moved from the reference position and on the basis of this value control electronics 60 of feeder 2 can monitor, change and control the power supply to the motor of pulley 4 so that it changes its rotation speed to compensate for the angular movement of arm 13 with respect to the reference position. In this way feeder 2 makes use of information on the position of arm 13 to anticipate the change (acceleration/deceleration of pulley 4), further improving the quality of the delivery tension. This is in accordance with the active-predictive operating mode described above.

[0106] Also in this case, (as in the case of EP2262940) compensator device 1 therefore acts as a balance and the electronics of the feeder system will in real time calculate the torque to be applied to motor 8 that acts together with arm 13 to keep it always in balance in a wholly automatic way. This depends on the present tension of yarn F (obviously to maintain the predetermined tension).

[0107] Controlling the position of arm 13 in this way will also have a compensating effect on the delivery tension, which will lead to total elimination or drastic reduction in tension peaks and slackening of the yarn itself. In fact when textile machine T increases its demand for yarn F suddenly and the dynamics of the motor driving pulley 4 is insufficient to compensate for such change, arm 13 will tend to fall (moving towards the 6 o'clock position) increasing the quantity of yarn F sent to machine T; this until the motor of pulley 4 reaches the necessary rotation speed to eliminate or reduce the tension peak. At this point the arm will return to its initial or resting position automatically.

[0108] On the contrary, when the textile machine decreases its demand for yarn suddenly and the dynamics of the motor driving pulley 4 is insufficient to compensate for such change, arm 13 will tend to rise (moving towards the 12 o'clock position in FIG. 8) decreasing the quantity of yarn F sent to machine T, until the motor of pulley 4 reaches the necessary rotation speed to eliminate or reduce slackening of the yarn. At this point the arm will return to its initial or resting position automatically (FIG. 6).

[0109] In its first embodiment the resting position of arm 13 lies within a range of movement of compensating means or arm 13 which has two limiting positions (that is 6 o'clock and 12 o'clock).

[0110] Also, knowing the position of compensating arm 13 precisely and in real time the electronics of feeder 2 can use this information to accelerate or slow the rotation of pulley 4 to minimize the time for settling into the new ideal speed to obtain a constant preset value of the tension of yarn F and maintain it, further limiting the amplitude of the tension peak or slackening in yarn F.

[0111] Also, knowing the position of compensating arm 13 and the value of the tension measured through sensor 3 precisely and in real time during transients (changes in take-up), the feeder system can change the drive of motor 8 that acts together with arm 13 to reduce the change in the delivery tension of feeder 2 even more; for example: i) during the sudden acceleration stage, arm 13 will tend to fall (moving towards the 6 o'clock compensation position in FIG. 7) and the measured yarn tension will tend to rise; in this case the electronics of the feeder system may decide to:

[0112] 1) interrupt closing of the loop controlling the position of arm 13 or reduce its effect so that the yarn can lower arm 13 until the yarn tension is within the predetermined limits, thus using this interval to move from 3 o'clock to 6 o'clock as a stock of yarn F to be fed;

[0113] 2) automatically set a working set point for arm 13 to a lower position to provide more yarn F to textile machine T until the critical condition is overcome. (ii) during the sudden deceleration stage, arm 13 will tend to rise (moving to the 12 o'clock compensation position in FIG. 8) and the measured tension will tend to fall; in this case the feeder system may decide to:

[0114] 1) interrupt closing of the position control loop or reduce its effect so that arm 13 can recover yarn F until its tension lies within the predetermined limits, thus using the interval to move from 3 o'clock to 12 o'clock, acting to recover the excess fed yarn;

[0115] 2) automatically set a working set point or resting position for arm 13 to a higher position to provide less yarn F to textile machine T until the critical condition is overcome.

[0116] The set point or reference value for the position control loop for compensating arm 13, hitherto considered for example to be the 3 o'clock value (FIG. 6), may instead be variable and suitably dynamically managed by the feeder electronics in order (for example) to provide for a possible subsequent feeding stage; for example, during the stage in which the yarn is slowed down and then stopped by the textile machine the set point could automatically pass to the 12 o'clock position so that there is a greater stock of yarn F to provide for the next acceleration on restarting, further reducing the next peak.

[0117] In a further embodiment of the invention (already included in the figures), there is also associated with compensating arm 13 a drum or cylinder 26 on which yarn is deposited during the recovery stage, thus increasing the quantity of yarn F stored, because the amplitude of the angular rotation sector has increased, and in this case will no longer be restricted to between 6 o'clock and 12 o'clock but will be able to rotate freely about axis of rotation M.

[0118] The drum where the yarn is deposited may be attached to arm 13 or free to rotate on bearings that make its rotation independent. The diameter of the drum determines the maximum quantity of yarn F that can be recovered from the device 1/feeder 2 system. This drum may therefore have different dimensions depending on the quantity of yarn F that is desired to be recovered on it. This drum may be cylindrical, semicylindrical or have a shape with a variable cross-section.

[0119] The compensator device may work without mechanical stops preventing it from rotating beyond the 6 o'clock to 12 o'clock arc, allowing arm 13 to rotate without restriction about the axis during the recovery stage. In this case arm 13 is free to deposit a much larger quantity of yarn stored during the recovery stage on drum 26, which will then be fed back to the textile machine at the next restart.

[0120] This brings about a double reservoir of yarn, that is drum 26 in addition to pulley 4.

[0121] Thanks to the present invention a single system is able to work at even very different feed tensions, without the need for any action by the operator. This system is able to compensate for sudden changes in feed without giving rise to tension peaks or slackening of the yarn, as well as, to a small extent, to recover greater quantities of yarn F than in the solutions previously described in the state of the art.

[0122] Various embodiments of the invention have been described. Of course yet others are possible. For example, the annular ceramic body on arm 13 may be replaced by a body made of any other material having slip characteristics appropriate to the application. In addition, the text describes the use of a direct current motor with brushes, but it is obvious that any type of electric motor or actuator (brushless, stepper, etc.) and also pneumatic could be used.

[0123] The use of an encoder with Hall sensors to detect rotation of the drive shaft has been described, but any encoder on the market may also be used or a Hall sensor may be incorporated in the motor; in this case there is no need to have the drive shaft projecting on both sides.

[0124] In addition, arm 13 is rigid, although it may have its own minimal flexibility, so as to further cushion the compensating effect, such flexibility deriving from the material or cross-section with which the arm is made. Furthermore, this compensating arm is described as rotating, but it may be replaced by an arm that follows a linear motion using a linear actuator or motor moving longitudinally through positions equivalent to 6, 3 and 12 o'clock.

[0125] Finally, the existence of a control unit for device 1 acting together with the control electronics for feeder 2 has been described. Obviously this control unit may be the one for feeder 2 (that is it may be part of its control electronics) and act automatically when body 11 of device 1 is attached to feeder 2, automatically recognising the presence of device 1 (the presence of body 11 being detected by suitable connectors, not shown, through which the control unit acts together with the motor of device 1 and the encoder or position sensor means for the drive shaft associated with arm 13). This solution is shown in FIG. 10C.

[0126] The invention applies to the feeding of textile yarns, but also metal wires.

[0127] These variants are also to be regarded as being included within the scope of the invention as defined by the following claims.