Method and tensioning device for stabilizing and regulating the tension of thread being unwound from bobbins

Method and relevant device for stabilizing and regulating the tension of a thread (16) being unwound from a bobbin (18). The method envisages the addition to the unwinding tension (td), of a resistant tension automatically variable in relation to the intensity of the unwinding tension (td).

APPLICATION FIELD

The present invention relates to the method and relevant tensioning device for stabilizing and regulating the tension of thread being unwound from a bobbin or “cop”.

Thread refers to any kind of thread or yarn, obtained from natural, artificial, chemical fibers or mixed fibers. The method and tensioning device according to the present invention, is particularly, but not exclusively, used in four-twisting twisters, or in other textile equipment wherein the thread bobbins are axially unwound (in a “défilé” manner) and at a relatively low rate, both when the unwinding is direct, and when it is effected by means of a reeling machine.

STATE OF THE ART

It is well known that in thread unwinding machines, for example in four-twisting twisters, as described in Italian patent EP 1007773 granted to the Applicant, the thread is axially unwound from a thread bobbin, with remarkable tension variations of the unwound thread.

This tension variation of the unwound thread is due to the gradual reduction of the bobbin diameter and to the shifting of the thread along its unwinding generatrix.

These tension variations are particularly high when the bobbin is substantially cylindrically shaped and, more generally, when the unwinding is effected using a reeling machine, of the known type, which rotates as a result of the action of the unwinding thread.

It is known that tensioning devices are normally used, which brake the moving yarn, thus increasing its tension, in order to give the yarn an adequate tension level and to stabilize the latter in different textile processes, in particular in yarn twisting process.

In the state of the art, e.g. from GB 1.038.504 and DE 1184681, devices for regulating the tension of the double twisting spindles are disclosed.

Said devices are able to add an additional tension but they are unable to counterbalance the variation of the unwinding tension and to give to the exit of the unwinding device a substantially constant tension.

These known tensioning devices generally include a thread tension mechanism consisting of two opposed surfaces which are pushed against each other by weights or springs, between which the thread is passed, such as, for example: washer yarn-braking, charged with weights or springs; piston-tensioner charged with a spring; ball-tensioner.

In recent years, a tensioning device of the so-called “magnetic” type has been developed, which differs from those mentioned above as in this case the tension on the yarn is created by resistance to the rotation of a small wheel on which the yarn is wound and which is slowed down by magnetic hysteresis.

Although both mechanical and magnetic tensioning devices produce an increase in the yarn tension, they do not effectively stabilize the tension itself due to the fact that, as they add a substantially constant value to the tension, they tend to maintain yarn tension irregularities on the yarn tension, which are present at the inlet of the same tensioning devices.

The tensioning devices known in the state of the art are not suitable to ensure a substantially constant tension and they do not meet the requirements of four-twisting spindles, where it is necessary a substantial constant tension in the thread unwound from the feed package. Reference is made, for instance, to a four-twisting spindle according to patent EP 1007773.

These drawbacks have negative consequences on the yarn tension in four-twisting twisters where the known tensioning device is installed, which leads to irregularity and uncontrollability of the balloons, mainly of the descending balloon formed around the packaging container. The operation of a four-twisting spindle requires the formation of two balloons, one inside and the other outside.

For a good operation, the spindle of the four-twisting device requests that every balloons must be stabilized. With reference to the spindle according to the cited patent EP1007773, the rising outer balloon is provided with a reserve pulley, similarly to the traditional double-twisting, while the inner downward balloon does not have space to place a reserve pulley of the thread.
Lacking of a balancing device that gives a substantial constant tension of feed thread, the inner balloon would vary continuously its shape and would interfere with the outer balloon, making the four-twisting spindle not operable.

An objective of the present invention is to provide a balancing device which guarantees the stabilization of the unwound yarn tension and which also allows the consequent regularization and stabilization of the yarn tension downstream of the tensioning device.

The Applicant has studied, experimented and created the present invention, in order to overcome the drawbacks of the known art, to achieve this and other objectives and to obtain further advantages.

INVENTION DISCLOSURE

The present invention is disclosed and characterized in the main claim.

The secondary claims relate to other characteristics of the present invention or variations of the main solution idea.

In accordance with the above objective, the method and tensioning device according to the present invention, envisages the addition of a resistant tension to the yarn unwinding tension, generated by means outside the device, whose amount is automatically variable in relation to the variations of said unwinding tension. In this way, a substantially constant tension on the yarn is obtained, downstream of the device itself.

The amount of resistant tension which is added is generated and controlled by tensioning devices comprising an arm element which oscillates around a rotational axis and which is suitable for winding the thread, within a variable range, onto a cylindrical body, a pulley, for example, coaxial with said rotational axis.

The above-mentioned arm element is subjected to both the unwinding tension of the yarn, increased by the resistant tension due to the at least partial winding of the yarn itself onto said cylindrical body, and to the action of a contrasting force which opposes the yarn unwinding tension, increased by said resistant tension.

According to a characteristic of the present invention, said contrasting force is substantially constant during the entire oscillating range of the arm element and is generated, for example, by a spring or a weight whose value can be regulated.

The arm element is integral with a cylindrical element, consisting, for example, of a small pulley which can rotate around the rotational axis and connected to a flexible hauling element, on which a constant load is applied, which represents said substantially constant contrasting force.

The resistant tension added to the unwinding tension is generated by the friction of the yarn which runs on the cylindrical surface of the cylindrical body, according to the known law of physics
Δt=td(eμα−1)
wherein Δt is the tension increase;tdis the unwinding tension, or, more precisely, the yarn tension in the contact point with the cylindrical body;α is the contact angle of the yarn with the cylindrical body;μ is the friction coefficient between the running yarn and the cylindrical body, and therefore depends on the type of yarn, the material and the finishing degree of the cylindrical body.

For a certain yarn, surface and finishing degree of the cylindrical body, μ is a constant.

In addition to four-twisting (two plus two) twisters, the present invention can also be applied in other twisting systems, for example those called “cabling” or “tyre cord”, in knitwear, or others, and, more generally in all textile processes where bobbins are unwound, both when the unwinding is direct and also when effected by means of a reeling machine.

DESCRIPTION OF SOME PREFERENTIAL EMBODIMENTS

With reference toFIG. 1, a tensioning device10according to the present invention, substantially comprises a radial arm12, oscillating around a rotational axis X and including an end13, shaped as a hook or an eyelet15shown in the nextFIGS. 2 and 5, for example made of ceramic or other material having a low friction coefficient, to guide a yarn16which is unwound from a bobbin18, coaxial to the rotational axis X.

The radial arm12is fixed to an end19of a shaft20coaxial with the rotational axis X and free to rotate with respect to a winding pulley21, also coaxial to the rotational axis X. The winding pulley21has a fixed radius R.

A small pulley23is wedged at the other end22of the shaft20, on which a thin cable25is fixed, to enable the latter to be freely wound onto the peripheral surface of the small pulley23. The thin cable25can be substituted with a rope, a small belt or analogous flexible connecting body. The small pulley23has a fixed radius b.

Moreover, according to a characteristic aspect of the present invention, a constant traction force P is applied to the cable25, obtained, for example, by means of a weight26, arranged vertically, and a counter-pulley29.

A first ceramic- or chromium-plated metal—thread guide ring30, is coaxially positioned with the rotational axis X, above the shaft20, whereas a second thread guide ring31, again in ceramic or in a chromium-plated metal, is positioned coaxially with the rotational axis X, between the shaft20and the bobbin18.

A thread guide element32is fixed outside the winding pulley21so that it lies on a circumferential plane of the latter.

The forces operating on the oscillating arm12, as shown inFIG. 1, are:t1, which is the tension on the thread16at the inlet of the hook13of the oscillating arm12, i.e. at the inlet of the latter, is oriented according to the tangent of the winding pulley21, and is equal to td+Δt;t1, which is the tension on the thread16at the outlet of the hook13of the oscillating arm12, i.e. at the outlet of the latter, and oriented towards the rotational axis X and the centre of the thread guide ring30;P, which is the resisting force applied to the cable25.

The equilibrium with the rotation of the oscillating arm12(with respect to its axis X), under steady or almost steady conditions, regardless of the mechanical frictions, is
t1·R=P·b
as the tension t2does not give components due to the fact that it is directed towards the rotational axis X. Therefore,
t1=b/R·P
which means that, when the haulage force P applied on the cable25and therefore on the small pulley23, is kept constant for the whole winding angle envisaged on the winding pulley21, t1will tend to remain constant, as it is obliged to remain at such.

The oscillating arm12will consequently rotate in one direction or another, in order to maintain the equilibrium between the unwinding tension of the thread16and the resisting moment P·b applied to the small pulley23, so as to create, in relation to the actual unwinding tension of the bobbin18, the amount of resisting tension Δt necessary for maintaining the inlet tension at the hook13constant.

If t1is kept constant however, t2at the outlet of the hook13will also be constant, as:
t2=t1·eμ2α2
wherein:α2is the contact angle of the thread16with the hook13which is constant;μ2is the friction coefficient between the thread16and the hook13, also constant for a given thread16and a given material of the hook13.

Furthermore, under the same conditions, the tension t3will be constant, at the outlet of the upper thread guide ring30, both when the thread16is directed upwards, along the rotational axis X, and also when the thread16is directed downwards to form a possible descending balloon for a four-twisting procedure. In all cases we have:
t3=td·eμα·eμ2α2·eμ3α3=b/R·Peμα+μ2α2+μ3α3
wherein:α3and μ3are the contact angle of the thread16with the upper thread guide30and the friction coefficient between the thread16and the upper thread guide30, respectively.

Tests and experiences of the Applicant have demonstrated that the device10can be advantageously used at rates of at least up to 300 m/min and also up to 450 m/min, with direct unwinding and at least up to 150 m/min and also up to 180 m/min for unwinding with a reeling device.

In addition to stabilizing the tension of the thread16, the device10also allows the tension level requested by the downstream process to be regulated. By varying the value of the load P, the working tension can in fact be proportionally modified.

In practice, however, also the unwinding tension tdcan be increased by means of suitable braking systems, in order to obtain certain levels of working tension.

In the FIGS.1bis and1ter a preferential realization of the balancing device is shown, where the tensioning force is applied by weights.

It has to be considered that the tensioning device10rotates together with the balloons of the thread16, while the feed package is steady.

In the case of the four-twisting spindles, the inner of the bobbin18of doubled thread is available. From pulley23and through two counter-pulleys29, the cable25reverts in an axial position within the spindle. The weight26connected to it is so moving vertically into the tube of the bobbin18.
According to a realization preferred by the invention, a joint25′ is interposed on the cable25that does not allow to transmit to the weight26the rotating movement that affects the tensioning device10.

In FIG.1ter, the joint25′ shown is made of a ball-bearing.

The weights26are therefore on the axis of the twisting spindle and are not affected by centrifugal force.

The number of the wrapping turns of the thread16around the pulley21depends on the stroke available for the weights, while the quantity of the weights26depends on the size of the pulleys21and23, moreover on the desired tension on the thread16.

It has been noted that with the realization of FIG.1bis, the force expended with weight26results are constant and independent based on the extent of the angle α of contact between thread16and pulley21.

As an alternative to the use of the weight26, the constant of the resistant force P can be obtained by the use of suitably applied springs and with systems which compensate the linear variation of the force for the variation, under operating conditions, in the length or angle of said springs.

Among the many possible solutions, one is illustrated as an example, with reference toFIGS. 2,3and4.

In the present invention, the cable25has one of its ends,25a(FIG. 3 and 4) integral with the small pulley23, and another end25bintegral with the small pulley23, and another end25bintegral with a cam40, which can rotate on a hinge41, parallel to the rotational axis X. The cam40develops in a substantially linear mode with an angle β, passing from a radius A1to a radius A2, and the amount of this development is substantially equal to the circumference of the pulley23.

The Head of a spring42of the flexional type, with a high number of coils (20, for example) is fixed to the cam40, and arranged coaxially with the hinge41(FIG. 2,3and4). The other end of the spring42is fixed to a supporting plate45(FIG. 2) of the device10.

In this solution, the spring42acts on the same radial arm12through the cam40and the small cable25, which partially coils around the same and partially around the small pulley23. The cam40, as the spring42, when operating, linearly increases its charge, also proportionally increases the distance of the cable25from the axis of the hinge41. In this way, the tension P on the cable25is always the same, for any angular position of the cam40and the radial arm12.

If, for example, the envisaged working angle of the radial arm12is 360°, the angle β of the cam40and therefore of the spring42is 180°, the spring42is precharged for 180°, and the radius A2is equal to the double of the radius A1, as the spring42doubles its charge, the cam40will therefore accomplish the linear doubling of the cable distance from the axis of the hinge41for 180° of its development, ensuring the constancy of the charge P for the whole 360° rotation of the radial arm12, to which an analogous rotation of the small shaft20corresponds, as shown inFIGS. 3 and 4.

A stop pin35(FIG. 2) is vertically placed on the upper part of the winding pulley21, to limit the rotation of the radial arm12and prevent the spring42discharging over a certain value. The latter can be directly fixed on the winding pulley21, in which case the rotation angle of the radial arm12can be of a maximum of 360°, or a little less, or mounted on an element which can twist for a certain arc, around the rotational axis X with respect to the winding pulley21, in which case the rotation angle of the radial arm12can be over 360°.

According to the embodiment of the device10shown inFIG. 2, the pulley21is fixed to the support plate45, which, in turn, is fastened to a fixed containment structure46, or container, placed coaxially with the bobbin18. A ball bearing50is interposed between the pulley21and small shaft20.

Moreover, a lateral upright element51is indirectly fixed to the supporting plate45and supports a thread guide group130, consisting of a fixed base52, a rotating disk53, with in between a ball bearing55. The thread guide group130has the same function as the thread guide ring30.

A pre-charge ball56is placed above the second thread guide ring31, in order to vary the value of the unwinding tension td.

According to another embodiment shown inFIG. 5, the device10is mounted on a reeling machine60, rotating around the rotational axis X. The reeling machine60includes an arm61equipped, at one end, with a thread guide62.

In this case, the supporting plate45, together with the structure mounted on it, which is analogous to that previously described with reference toFIG. 2, rotates together with the reeling machine60with respect to the container46placed around the bobbin18.

The supporting plate45is integral with a short tube63mounted so that can twist around a fixed pin65, with in between the ball bearing66.

A brake of known type67, equipped with a weight69for the regulation of the unwinding tension td, is associated to the short tube63.

For all the above, it is clear that the method according to the present invention, for stabilizing and regulating the tension of a thread being unwound from a bobbin, envisages that an amount of tension Δt, automatically variable, is added to the thread unwinding tension tdapplied by a body external to the device according to the invention, so as to have, downstream the device itself, a constant tension on the thread.

It is clear, however, that the device10herein described, which has been applied, for illustrative purposes, to a four-twisting twister, can be modified and/or parts can be added to it, or can be adapted for other applications, without being excluded from the scope of the present invention. For example, the device according to the present invention can be used for other types of textile machines.

It is also clear that, even if the invention has been described making reference to specific examples, any person skilled in the field can surely found other equivalent forms of tensioning devices, all of them included within the scope of the present invention.