EP4600194A1

EP4600194A1 - Device and system for controlling the tension during the unwinding of filaments

Info

Publication number: EP4600194A1
Application number: EP25153900.3A
Authority: EP
Inventors: Marco Brogi
Original assignee: Bromas-Log Srl
Current assignee: Bromas-Log Srl
Priority date: 2024-02-07
Filing date: 2025-01-24
Publication date: 2025-08-13
Also published as: IT202400002542A1

Abstract

A magnetic device and system for regulating the unwinding tension of filaments wound on bobbins capable of decreasing or increasing the rotational speed of said bobbins in a rapid and extremely precise manner, taking advantage of the action of eddy or Foucault's currents generated by first and a second rotating elements (4, 5), co-axial to a shaft (1) of a bobbin carrier (2), wherein said first and second rotating elements (4, 5) alternately comprise conductive material or a magnetic field source and the second rotating element (5) is integrally connected to the proximal end of said shaft (1) by reversible locking means that allow said second rotating element (5) to be translated in the axial direction of said shaft (1) by moving it closer to or further away from said first rotating element (4).

Description

Technical field

The present invention belongs to the field of machinery used in the textile industry for the unwinding of filaments or yarns, particularly for the deroulé unwinding of filaments. Deroulé unwinding, unlike defilé unwinding, prevents the filament from twisting as it is unwound from the bobbin, so it is used generically where ribbon-like filaments, also known as flat tapes or tapes, are used, as is common in the case of metallic or carbon filaments or the like, or otherwise where filaments are used on which twisting is not to be imposed, such as in the case of metallic threads or the like
More precisely, this invention is a magnetic device for controlling the unwinding tension of a filament, which applies the principle of the so-called Foucault's current rotating magnetic brake, also called eddy current brake.

Present status of the art

In textile manufacturing, one stage of processing involves the filaments used for weaving being progressively unwound from their respective bobbins and going to feed a weaving loom or warping machine or other similar machinery. In this patent text, the term bobbin, or spool, is used to refer to a filament or a yarn wound on a cylindrical or truncated cone-shaped core.
Special machines, known as "creels," are used to feed the weaving looms, consisting of a fixed frame suitable for supporting tens or hundreds of bobbins arranged in rows. The bobbins are rotationally connected to the frame of the creel and are thus free to rotate about their longitudinal axis, thus facilitating the unwinding of the yarn as it is fed to the weaving loom. The bobbins rotate as a result of the yarn being pulled by the weaving loom.
This unwinding can take place with the yarn moving away from the bobbin along an axis parallel to the longitudinal axis of the latter (defilé), or along an axis transverse to the longitudinal axis of the bobbins (deroul6).
In the former case, the yarn inevitably undergoes twisting, so this type of unwinding is not suitable for flat or ribbon-like filaments, a conformation that is often typical of certain types of filaments used mainly for certain technical fabrics, such as filaments of carbon, Kevlar, aramid or metallic materials that are used in the manufacture of ballistic fabrics, geotextiles or the like. In general, deroulé unwinding is preferable in all cases where no twist is to be imposed on the filament, regardless of the cross section of the filament.
Deroulé unwinding, unlike defilé unwinding, ensures that the flat filament is not subjected to undesirable twisting during unwinding from the respective bobbin, however, even in a deroulé unwinding, it is extremely important to be able to regulate and control the unwinding tension of the filament in order to maintain a good quality of the finished product and to avoid filament breaking or damage, consequently limiting production waste.
For this reason, special braking devices have been developed which are used to control the unwinding tension of the filament as it is unwound from each bobbin, in order to maintain the pulling tension as uniform as possible. Such devices also perform the important function of preventing excessive unwinding of the yarn when the feed to the loom is stopped, by blocking the rotation of the bobbin, which would otherwise continue to rotate about its axis by inertia.
Braking devices of the mechanical type have long been known, called "friction" brakes, comprising a belt, or jaw mechanism, configured to exert frictional torque on the bobbin axis. These devices allow very approximate control of the filament unwinding tension, and in particular do not allow fine adjustment of the desired tension value; moreover, during filament unwinding, it is not possible to intervene to change the braking torque on the bobbin, with the disadvantageous consequence that the actual pull on the filament varies progressively as the outer diameter of the bobbin varies.
Typically, in machines that support a plurality of bobbins, a respective braking device is applied to each individual bobbin. In the most common embodiment, such a device comprises a belt, at least partially elastic, tensioned by means of a spring, which exerts friction on the peripheral surface of a pulley coaxial to the axis of the bobbin.
Over time, continuous belt braking devices have also been developed, in which a single belt exerts its braking action on a plurality of different pulleys, each of which is integral to the axis of respective bobbins. According to a common implementation example, belt tension is increased or decreased by linearly translating a tensioning pulley, supported at the end of a pneumatic actuator. However, the movement induced by the actuator is not so uniform as to ensure sufficiently precise modulation of the unwinding tension. Furthermore, bobbins located close to the tensioning element are generally subjected to greater braking than bobbins located farther away.
All mechanical type devices are affected by problems related to wear and tear caused by the continuous contact (sliding friction) of the braking element with the braked element; moreover, such devices are strongly affected by fluctuations in ambient temperature and are greatly affected by variations in the unwinding speed of the bobbins, which changes as the diameter of the bobbins themselves varies, particularly in the case of bobbins of large diameter and weight. Moreover, systems of this type, being open, collect dirt and are therefore not suitable for performing processing with yarns that can generate dust, or processing that is located in dirty environments.
A further problem affecting the mechanical type devices described so far is related to the so-called "stick-slip" effect, or starting friction, which occurs when the frictional force exerted by the brake changes from static to dynamic, i.e., whenever the bobbin, starting from a standstill, begins to rotate about its axis. In such a case, there is initially a buildup of tension in the brake, which is followed by a sudden release, which triggers a bouncing phenomenon, further amplified by the elasticity of the filament. This issue has particularly negative implications because it causes a very discontinuous feeding of the filament toward the weaving loom, with obvious repercussions on the residual tension of the filament incorporated in the finished fabric and thus on the quality of the latter.
In an attempt to overcome the disadvantages of traditional mechanical friction brakes, magnetic braking devices have been developed over time, which allow the bobbin to be slowed down by generating eddy currents (also called Foucault's currents) by electromagnetic induction. A typical implementation example involves the use of a disc of metal that is a good conductor of electricity and is integrally connected to the axis of the bobbin, said disc, as it rotates, passes through a magnetic field generated by special electromagnets or fixed, i.e., non-rotating, permanent magnets integral to the frame supporting the bobbins. Due to the effect of the movement within the magnetic field, induced voltages are created in the metal disk that generate eddy currents, and these in turn generate a magnetic field that, opposing that generated by the fixed magnets, performs a braking function on the disk, which consequently loses kinetic energy, dissipating it in the form of the heat generated by the eddy currents. The braking force acts without contact between the different parts, so these devices are essentially wear-free.
U.S. Patent Application US1825061A describes an eddy-current magnetic brake for controlling the unwinding tension of a filament wound on a bobbin, in which the metal rotor of conductive material is arranged between the two poles of a electromagnet which is fixed with respect to a support frame. The rotor of conductive material is integrally connected to a spindle, which in turn is configured to coaxially support the bobbin, which is mechanically connected to said spindle. In such a device, the braking torque is fixed and depends on the characteristics of the magnets and the rotor, as well as their distance from each other, and it is never possible to modulate the braking torque during unwinding.
European patent application EP2509904A1 relates to a device for controlling the pulling tension of a filament equipped with an eddy-current magnetic brake and incorporating a self-compensating mechanism that allows for an albeit limited linear translation of the bobbin in a transverse direction with respect to the axis of rotation of the bobbin itself, so that any variations in the pulling tension of the filament can be accommodated while maintaining as uniform a tension as possible in the filament itself. Again, the magnets are fixed with respect to a support frame, while the disk of conductive material rotates in solidarity with the axis of the bobbin. The modulation of braking torque that can be achieved is very modest because it results from the limited oscillation of the compensating means, and therefore it is not possible to maintain a constant braking torque as the size and weight of the bobbin decreases (resulting in an increase in unwinding speed) during the unwinding of the yarn, especially in the case of bobbins that are initially large and/or made of composite materials with a high specific weight.
PCT patent application WO2008138318A1 describes a similar eddy-current magnetic braking device comprising an arm swinging about an axis parallel to the axis of rotation of the bobbin, to the distal end of which is attached a pair of magnetic elements, facing each other; in the space between the two magnets is inserted the disk of conductive material which is integral to the axis of rotation of the bobbin. Any tension peaks caused by the unwinding of the continuous material are compensated for by a torsion spring built into the support of the swing arm, the spring allows for an albeit limited oscillation of the arm about its axis, in this way bringing the magnetic elements slightly closer to or further away from the axis of the disk of conductive material.
All currently known magnetic brakes comprise a static element, to which magnets are integrally connected, and a moving element, consisting of a disk made of conductive material. The braking effect on the moving element is due to the eddy currents that are produced in the moving element itself due to the movement of the latter with respect to the fixed element, and more particularly due to the movement of the moving element within the magnetic field generated by the magnets that are integral to the fixed element. This characteristic of the known type of magnetic systems makes them unsuitable for use in weaving operations in which the feeding of the yarn to the loom is very slow and, consequently, the speed of rotation of the bobbin is equally low; in fact, in such cases the braking torque generated is very close to zero. In any case, even when these devices are used for fast unwinding applications, it is not possible to maintain braking during the stopping phase of bobbin rotation, all the more so when this is rapid, producing severe slack in the filaments being unwound, especially when the rotating masses have a high inertia.
Another disadvantage of magnetic devices of the aforementioned type is that the braking torque can be modulated only after stopping the unwinding and weaving process: the braking torque is adjusted by bringing the fixed element and the moving element closer together or farther apart, or by changing the type of the elements that make up the brake assembly, for example, by using magnets of different types or employing discs of different metal materials. In any case, it is not possible to vary the braking torque continuously and progressively as the bobbin unwinds.
Other examples of magnetic braking devices are described in patent applications EP2813456A1 and DE4318294A1 , however, none of these devices allow the filament unwinding tension to be modulated in a sufficiently fast and precise manner, by adjusting the distance between the two moving elements according to the desired braking level.
More recently, electronic braking systems have been developed, which, while exhibiting a good range of braking values, are not sufficiently sensitive at low levels of tension; moreover, their high weight makes them unsuitable for unwindings having pulse-like progressions or for unwinding processes characterized by frequent changes in speed. Another problem inherent in electronic braking devices is their high cost of construction and maintenance, in addition to their considerable power consumption and the considerable heat transfer to the surrounding environment due to the large amount of heat energy dissipated.

Objects and summary of the invention

The magnetic device that is the subject of the present invention makes it possible to control and regulate the unwinding tension of a filament wound on a bobbin when the latter is fed to a loom or other textile machinery, such as a warping machine or similar machines. The device supports a bobbin and is rotationally connected to a fixed frame so that the traction applied to the extremity of the filament causes the bobbin to rotate about its own axis. Unwinding takes place in deroulé, that is, the filament moves away in a direction transverse to the axis of rotation of the bobbin.
The objective of the present invention is to provide a magnetic device for controlling the unwinding tension of a filament wound on a bobbin, which is capable of decreasing or increasing the rotational speed of said bobbin in an extremely rapid, precise and continuous manner, taking advantage of the action of eddy currents generated by electromagnetic induction, regardless of the mass and diameter of the bobbin, i.e., the amount of filament wound on it.
A further objective of the present invention is to provide an eddy-current magnetic device which is capable of exerting a constant braking or accelerating torque on a bobbin which is put into rotation about its axis by the traction applied to the end of the filament wound on it, even when the conditions of ambient temperature or humidity change, or in the presence of dirt, as well as when the unwinding speed of the filament changes.
A further objective of the present invention is to provide an eddy-current magnetic device of the aforesaid type that is capable of exerting a braking torque on the bobbin even when the rotational speed of the latter is zero.
These and other objectives that will become clear from reading the present text are achieved by the object of the present invention, which consists of an eddy current magnetic device suitable for controlling and regulating the tension of the deroulé-type unwinding of a filament wound around a bobbin.
In a preferred embodiment, the device which is the subject of the present invention includes a cylindrical bobbin carrier coaxial to a shaft, means of rotational coupling of said shaft with a fixed frame such as a creel or similar machine, a magnetic rotating element, a conductive rotating element, means for transmitting a rotational motion to one of said rotating elements, the latter being both capable of rotating about the same axis of rotation, coincident with the axis of rotation of said shaft to which the bobbin carrier is integrally connected.
Only one of the two rotating elements, i.e., depending on the possible embodiments, either the magnetic element or the conductive element, is idlingly coupled to the bobbin carrier shaft and is equipped with organs for receiving rotational motion from said means for transmitting motion, while the second rotating element, respectively the conductive element or the magnetic element, is rotationally integral with the shaft of the bobbin carrier, the latter rotates as a result of the tensile force applied to the extremity of the filament being gradually fed to the weaving frame. The rotation between the magnetic element and the conductive element generates a torque that, depending on the relative movement of the magnetic element and the conductive element, may oppose or may favor the unwinding of the filament: if the direction of rotation of the two elements is opposite, a braking effect on the bobbin carrier will be achieved; otherwise, in case the direction of rotation is the same, an acceleration of the rotation of the bobbin carrier will be achieved.
Advantageously, the magnetic device which is the subject of the present invention makes it possible to adjust the braking or accelerating torque acting on the bobbin carrier, consequently increasing or decreasing the unwinding tension of the filament, in a manner completely independent from the mass and diameter of the bobbin.
In particular, the present magnetic device makes it possible to maintain a constant braking or accelerating torque as the filament unwinding speed varies, even when said speed is zero or close to zero, regardless of any changes in temperature and humidity or whether any dirt such as machining residue is present.
The device which is the subject of the present invention is not affected by stick-slip phenomena typical of mechanical braking systems; moreover, it is completely immune to abrasive wear caused by friction between the parts of conventional mechanical brakes and is not affected by problems of eccentricity, ovalization or asymmetrical wear, which are characteristic of mechanical brakes.
A plurality of magnetic control devices may be installed on the same frame where several groups of magnetic devices of the aforesaid type are each connected by the same means of rotational motion transmission, the latter placing in rotation the idler rotating elements of the different devices belonging to the same group.

Brief description of the drawings

The invention will be better understood by following the description and drawings, which show practical non-limiting embodiments of the invention itself.

Fig. 1 shows a side view of an embodiment of the magnetic device that is the subject of the present invention; the A-A cutting plane line is shown.
Fig. 2 shows a view of the magnetic device from the back side.
Fig. 3 shows section A-A of the magnetic device in Fig. 1.
Fig. 4 shows an exploded view of the device.
Fig. 5 shows a group of three devices each supporting a bobbin in which the respective motion-receiving organs of each device are set in rotation by a single flexible mechanical transmission element (7), which in turn receives motion from a single drive means (8); a device (9) that measures the tension of the filaments is also visible.
Fig. 6 shows a group of devices with their respective bobbins rotationally coupled to the same fixed frame (A) and put into rotation by the same flexible mechanical transmission element (7). The C-C cutting plane line is shown.
Fig. 7 shows the section C-C of Fig. 6.
Fig. 8 shows a system comprising a plurality of groups of magnetic devices each group being rotationally coupled to a post of a fixed frame (A). A single drive means (8), via a transmission kinematics, transfers motion to several flexible mechanical transmission elements (7), each of which transfers motion to the motion receiving organs (6) of the magnetic devices of the respective group.
Fig. 9 shows a top view of a system like the one in Figure 8 in which the different posts, each supporting a group of magnetic devices, are not aligned in the same vertical plane but are offset from each other.

Detailed description of an embodiment of the invention

It should be noted that in the present patent text the term filament is used to refer to thread-like or ribbon-like material, not necessarily formed from an assembly of fibers.
The magnetic device for regulating the deroulé unwinding tension of a filament wound on a bobbin, which is the object of the present invention, comprises a braking or accelerating device of the eddy current type in which a disk of conductive material, preferably non-ferromagnetic metal, rotates within a magnetic field generated by one or more permanent magnets, the latter being integral with an annular support, which is also rotating in the opposite direction to the conductive metal disk, should braking action be desired, or in the same direction and at a greater speed than the conductive material disk, should accelerating action be desired.
As will be apparent to the person skilled in the art, the traction applied to the extremity of the filament, when it is fed to a textile machine, induces a rotation of the bobbin. With the device that is the subject of the present invention, the tension of the filament as it unwinds from the bobbin can be controlled by applying a braking (i.e., opposing bobbin rotation) or accelerating (i.e., enhancing bobbin rotation) torque to the bobbin.
In a preferred embodiment of the invention, the magnetic device that is the subject of the present invention includes:

a shaft (1) to the distal portion of which is integrally connected a cylindrical bobbin carrier (2), the latter being suitable for supporting a bobbin of filamentous material which is attached to said bobbin carrier by inserting said bobbin carrier within the cylindrical cavity defined by the inner surface of the bobbin core in such a manner as to make it integral with it, for example by means of suitable protrusions projecting from the side surface of the bobbin carrier which press against the inner surface of the cylindrical core. The proximal portion of said shaft (1) is rotationally coupled to a fixed frame (A) of a textile machine, e.g., the frame of a creel, by means of rotational coupling means (3), the latter comprising a bearing and, in a particularly effective embodiment of the invention, a ratchet mechanism such as a freewheeling mechanism that allows the shaft to rotate only in one direction, i.e., that in which the filament is unwound, but prevents rotation in the opposite direction, in order to prevent the bobbin carrier from rotating freely in the direction opposite to the normal direction of unwinding in the event that the filament breaks;
a first rotating element (4) coaxial to said shaft (1) and idlingly coupled to the proximal portion of the latter, so that said first rotating element is free to rotate about said shaft, but not to translate relative to it; said first rotating element (4) also includes an organ (6), which in the attached figures is represented by a pulley, suitable for receiving a rotational motion transmitted by appropriate transmission means (7);
a second rotating element (5), also coaxial to said shaft (1), is integrally connected to the proximal end of said shaft (1) by means of reversible locking means, by acting on which said second rotating element (5) can be translated along the axis of the shaft. In the attached figures, such reversible locking means comprise a male thread defined at the proximal end of the shaft (1) onto which a corresponding female thread defined in said second rotating element (5) is screwed; an end locknut is screwed onto the male thread, firmly locking said second rotating element (5) in place. After unscrewing the lock nut, screwing or unscrewing the second rotating element (5) on the threaded end of the shaft (1) brings the second rotating element closer to or further away from the first rotating element (4), thereby increasing or decreasing the magnetic interaction between the two elements. This feature, while not essential, is useful for calibrating the device in the initial setting phase in order to adjust the desired braking level;
a motion receiving organ (6) integral to said first rotating element (4) and suitable for receiving a rotational motion by means of flexible mechanical transmission means (7), which in turn receive motion from drive means (9).

According to different embodiments of the invention, said first rotating element (4) may comprise conductive material or alternately a magnetic field source, while said second rotating element (5) respectively comprises a magnetic field source or alternately conductive material, such that mutual rotation of said first (4) and second (5) rotating elements generates eddy currents in the conductive material.
In the embodiment illustrated in the attached figures, said first rotating element (4) comprises a disc of conductive metallic material (41) and is rotationally coupled by means of a bearing to the proximal portion of the shaft (1). The disk of conductive material (41) is integral with the motion-receiving organ (6), which in this case is represented by a pulley having a groove suitable for accommodating flexible means of mechanical transmission (7), in this case a belt or the like, the latter in turn receiving motion from said drive means (8), which in the figures are represented by a motor. Equivalent solutions to the belt are, of course, possible, such as a chain, in which case the motion-receiving organs are conformed like toothed crowns.
The second rotating element (5) comprises an annular element (51), to which permanent magnets (52) are integrally connected, and a ferromagnetic disk (53), advantageously made of an alloy having low residual induction and high magnetic permeability, preferably made of ferrite, adjacent to said annular element (51) on the side of said annular element (51) opposite to the side facing toward said first rotating element (4). Said permanent magnets (52) are arranged on said annular element (51) with one pole facing toward the conductive disk (41) of said first rotating element (4) while the second pole is in contact with said ferromagnetic disk (53); each magnet is arranged on the annular element (51) with opposite polarity to the adjacent magnet. The annular element (51) is integrally connected to said shaft (1) by means of a female thread that engages in the male thread defined at the proximal end of said shaft; a lock nut locks the annular element in place, preventing its longitudinal translation, as well as its rotation with respect to the shaft.
In a second embodiment, alternative to the one above described, however falling within the same inventive concept, said first rotating element (4) comprises an annular support element to which permanent magnets are integrally connected, and a disc of ferromagnetic material, advantageously made of an alloy having low residual induction and high magnetic permeability, preferably made of ferrite, adjacent to the annular element on the side of the latter opposite to that facing toward said second rotating element (5). The magnets are arranged on said annular element with one pole facing toward the second rotating element (5) and the second pole in contact with the ferromagnetic disk; each magnet is arranged on the annular element with opposite polarity to the adjacent magnet.
In this second embodiment, said second rotating element (5) comprises a disk made of conductive metallic material the latter is integrally connected to the shaft (1) by means of a female thread which engages in the male thread defined at the proximal end of said shaft, a lock nut prevents the longitudinal translation of said conductive disk as well as its rotation with respect to the shaft (1).
As already explained, the device object of the present invention operates by always maintaining a difference between the rotational speed of the first rotating element and that of the second rotating element, this difference determining the torque applied on the bobbin. The device can operate either negatively, creating a braking effect, in the case where the first rotating element rotates in the direction opposite to the direction of unwinding of the bobbin, or positively, favoring unwinding, in the case where the first rotating element rotates with a higher angular velocity than that of unwinding and in the same direction of rotation as the bobbin.
Also included in the same inventive concept is a system for regulating the deroulé unwinding tension of a plurality of bobbins, in which a plurality of magnetic devices of the aforementioned type are rotationally coupled to a fixed frame (A). In such a system said bobbins are divided into groups, and all the bobbins in the same group share the same means of transmitting rotational motion, in other words, referring to the embodiment shown in the attached figures, a single flexible mechanical transmission element (7) sets the pulleys (6) of all the devices belonging to the same group in rotation. A single motor (8) can drive a plurality of flexible elements (7) of different groups of magnetic devices, for example, by means of suitable angular transmission kinematics that receive motion from the motor and transmit it to a corresponding flexible element, which in turn transmits rotation to the pulleys of the devices of the same group.
A typical application involves, for each group of devices, a single transmission driving two sets of mechanical devices arranged on the same vertical post, the motion being transmitted by a single belt to the individual devices placed in series with each other, which makes it economical and simple to implement this system. This configuration takes advantage of a minimum number of elements in relation to the number of devices mounted on a column, alternatively it is possible to arrange the devices only on one side of the post, in which case it is also necessary to provide an end pulley for transmission.
Depending on the processing requirements, the different posts, each of which supports a respective group of magnetic devices, may lie aligned in the same vertical plane or may be staggered with each other in order to cover a wider field orthogonally. When the system is applied to feed a textile loom, the distribution of the filaments across its width should cover the width of the fabric to be made, generally 140 to 180 cm. The configuration with staggered posts is particularly useful in deroulé processing in which tapes that do not tolerate deflections in direction, such as in the case of carbon fibers, are used, allowing the width of the fabric to be covered while at the same time ensuring an unwinding of each filament substantially orthogonal to the axis of the respective bobbin.
In a particularly complete embodiment, the system includes a device (9) that measures the tension of the filaments, or the cumulative tension of the filaments of the different bobbins, through a load cell or other similar devices, e.g., piezoelectric devices.

Claims

A magnetic device for regulating the tension of the deroulé unwinding of a filament wound on a bobbin, comprising:
- a shaft (1) the proximal portion of which is rotationally coupled to a fixed frame (A) by rotational coupling means (3) and to the distal portion of which is integrally connected a bobbin carrier (2) suitable for integrally supporting said bobbin;

- a first rotating element (4) coaxial to said shaft (1) and idlingly coupled to the proximal portion of said shaft (1);

- a second rotating element (5) coaxial to said shaft (1) and integrally connected to the proximal end of said shaft (1);

- an organ (6) for receiving rotational motion integrally connected to said first rotating element (4) and suitable for receiving motion from mechanical transmission means (7) which in turn are suitable for receiving motion from drive means (8);
wherein said first rotating element (4) and second rotating element (5) alternately comprise conductive material or a magnetic field source, so that by mutual rotation of said first and second rotating elements, electromagnetic induction generates eddy currents in the element comprising conductive material; said magnetic device being characterized in that said second rotating element (5) is integrally connected to the proximal end of said shaft (1) by reversible locking means that allow said second rotating element (5) to be translated in the axial direction of said shaft (1) by moving it closer to or further away from said first rotating element (4).
A magnetic device according to claim 1 characterized in that said first rotating element (4) comprises a disk made of conductive material, and in that said second rotating element (5) comprises an annular element supporting a plurality of permanent magnets and a ferromagnetic disk (53) made of material having low residual induction and high magnetic permeability adjacent to said annular element on the side of said annular element opposite to that facing said conductive disk of said first rotating element (4), said permanent magnets being arranged on said annular element with one pole facing toward said disk of conductive material and the second pole in contact with said ferromagnetic disk, each with opposite polarity with respect to the adjacent magnet.
A magnetic device according to claim 1 characterized in that said second rotating element (5) comprises a disk made of conductive material, and in that said first rotating element (4) comprises an annular element supporting a plurality of permanent magnets and a ferromagnetic disk made of material having low residual induction and high magnetic permeability adjacent to said annular element on the side of said annular element opposite to that facing said conductive disk of said second rotating element (5), said permanent magnets being arranged on said annular element with one pole facing toward said disk of conductive material and the second pole in contact with said ferromagnetic disk, each with opposite polarity with respect to the adjacent magnet.
A magnetic device according to claim 2 or 3 characterized in that said ferromagnetic disk includes ferrite.
A magnetic device according to one of the preceding claims characterized in that said organs (6) for receiving rotational motion comprise a pulley suitable for receiving motion from a belt which in turn is driven by a motor.
A magnetic device according to one of the preceding claims characterized in that said rotational coupling means (3) comprise a free-wheel mechanism.
A system for regulating the tension of the deroulé unwinding of filaments wound on bobbins comprising a plurality of magnetic devices according to one of the preceding claims characterized in that it comprises one or more of groups of magnetic devices in which the magnetic devices belonging to the same group are rotationally coupled to the same fixed frame (A) and the motion-receiving organs (6) of each magnetic device of the same group are put into rotation by the same mechanical transmission means.
A system according to the preceding claim characterized in that it comprises a drive means suitable for transmitting motion to a plurality of mechanical transmission means each of which in turn transfers motion to respective receiving organs (6) of the magnetic devices of a corresponding group.