The present invention relates to a device and method of feeding warp yarns to a loom.

In the known art, warp yarns are fed to a textile machine by disposing, rotatable within a support, a reel or a cylinder with a plurality of yarns wound parallel on the cylinder .

The yarn bed is then inserted into the loom, which withdraws the necessary yarn quantity as required.

The cylinder is mounted idly on a support such that the loom can withdraw the yarns without any resistance. Alternatively, a brake can be interposed between the cylinder and support to enable the yarns to remain under tension during the feed.

Again alternatively, the cylinder can be driven by a motor which controls its rotational velocity, such that the yarn velocity follows the withdrawal rate of the textile machine in a predetermined ratio.

Feed devices of known type are illustrated for example in the documents EP 2 392 706, EP 0 407 824, EP 1 020 551, US 2002-195160 and EP 0 562 214.

However, feed devices of known type are not able to ensure effective tension control. It is nevertheless of fundamental importance that during yarn feed to the textile machine, the yarn tension and hence, indirectly, also the yarn quantity fed to the textile machine be perfectly controlled, to ensure the quality of the finished product.

An important limit of the currently available motorized or braked solutions is that they do not ensure constant yarn tension, in particular during machine stoppage and subsequent restarts, hence causing a reject zone in the finished product.

Such irregular tensions acting on the yarns can cause serious visual defects in the fabric produced by the loom.

Moreover, it should be noted that known devices need to dialogue with the textile machine with which they are associated to receive, for example, a signal relative to the rate at which the yarn is worked in the machine.

Known devices therefore always depend on the textile machine .

In this situation, the technical aim on which the present invention is based is to propose a device and a method of feeding yarns to a loom which overcome the aforestated drawbacks of the known art.

A particular object of the present invention is to provide a device and a method of feeding yarns to a loom which enable the tension of the fed yarns to be effectively controlled.

A further object of the present invention is to propose a device and a method of feeding warp yarns to a loom which are able to control the yarn feed in a totally automatic manner, without any synchronization with the textile machine .

A further object of the present invention is to propose a device and a method of feeding warp yarns to a loom which are able to be applied to currently available machines which have not been adapted.

A final object of the present invention is to propose a device and a method of feeding warp yarns to a loom which are able to control the yarn tension during all stages of the process, including the stage in which the yarn is not fed to the textile machine.

The stated technical aim and the specified object are substantially attained by a device and a method of feeding yarns to a loom comprising the technical characteristics stated in one or more of the accompanying claims .

Further characteristics and advantages of the present invention will be more apparent from the indicative and therefore non-limiting description of a preferred but not exclusive embodiment of a device and a method of feeding yarns to a loom, as illustrated in the accompanying drawings, in which:

Figures from 1 to 5 represent respective views of five embodiments of a device for feeding warp yarns to a loom, in accordance with the present invention.

With reference to the accompanying figures, the reference numeral 1 indicates overall a device for feeding yarns to a loom, in accordance with the present invention.

The device 1 comprises a support member 2 fixable for example to a weaving loom T, and a cylinder 3 rotatably connected to the support 2 and on which a plurality of warp yarns F can be wound mutually parallel.

In a first embodiment, the device 1 also comprises a motor 4 associated with the cylinder 3 to rotate it about its longitudinal axis of rotation "R" .

At least one tension sensor 5 is positioned downstream of the cylinder 4 and is active on at least one yarn F to measure its tension. In detail, the tension sensor 5 generates a tension signal "ST" representative of the value of the tension acting on the yarn F. In the embodiment of Figure 1, the device 1 comprises a plurality of tension sensors 5, each acting on a single yarn F. The tension sensors 5 are preferably aligned along a direction perpendicular to the yarns F and equispaced apart, such as to uniformly monitor the yarns F unwound from the cylinder 3.

The tension sensor 5 can be active on a group of mutually adjacent yarns F such as to obtain a mean value of the tension acting on the yarns F of said group. In this case, the tension signal "ST" is representative of the mean value of the tension acting on the yarns F of the group .

Advantageously, the device 1 can comprise a plurality of tension sensors 5, each active on a group of mutually adjacent yarns F. The tension sensors 5 are preferably aligned along a direction perpendicular to the yarns F and equispaced apart such as to uniformly monitor the yarns F unwound from the cylinder 3.

In the embodiment of Figure 2, the device 1 comprises two tension sensors 5 acting on respective groups of yarns F disposed along opposite sides of the bed of yarns F unwinding from the cylinder 3.

In the embodiment of Figure 3, the device 1 comprises a single tension sensor 5 which acts on all the yarns F unwinding from the cylinder 3. In such a case, the tension signal "ST" is representative of the mean value of the tension acting on all yarns F. In this case the tension sensor 5 is disposed in a direction perpendicular to the yarns F.

All the tension sensors 5 are, by way of example, load cells . According to the invention, the device 1 also comprises a control unit 6 connected to the tension sensor 5 to receive the tension signal "ST" or the tension signals "ST" if the device 1 comprises a plurality of tension sensors 5.

The control unit 6 comprises a comparison subunit 7 which compares the instantaneous measured tension value represented by the tension signal "ST" with a predetermined reference tension value preset by a user to generate a displacement signal "SS" representative of the difference between the measured tension value and the predetermined tension value.

If the device 1 comprises a plurality of tension sensors 5, the comparison subunit 7 firstly determines a mean instantaneous measured tension value and compares it in a manner similar to the predetermined tension value, to generate the displacement signal "SS" representative of the difference between the mean measured tension value and the predetermined tension value.

The displacement signal "SS" is sent to a command subunit 8 of the control unit 6 which determines the velocity to be set for the cylinder 3 such that the measured tension value (absolute or mean) is maintained constant and equal to the predetermined tension value.

The command subunit 8 then generates a command signal "SC" representative of the instantaneous value of the velocity of the cylinder 3.

The control unit 6 is functionally connected to the motor 4 such that the command signal "SC" can be sent to the motor 4. In this manner, the value of the tension acting on the monitored yarns F is maintained constant with time by virtue of a closed loop control.

In detail, when the measured tension value (absolute or mean) exceeds the predetermined tension value, the velocity of the cylinder 3 is increased such that the measured tension value decreases until it reaches the predetermined tension value. Likewise, when the measured tension value is less than the predetermined tension value, the velocity of the cylinder 3 is decreased such that the measured tension value increases until it reaches the predetermined tension value.

From the aforegoing description, it is therefore apparent that the device of the present invention is able to operate totally automatically without any signal of synchronization with the textile machine and can also maintain the yarn tension constant even during machine stoppage .

In this respect, it must be added that in the control unit 6 a tension threshold value can be set representative of a minimum tension value below which a slackening of the bed of yarns F takes place, these hence lying slack downstream of the cylinder.

If the tension value measured by the tension sensor (or tension sensors) 5 is less than the tension threshold value, the control unit 6 generates the command signal "SC" representative of a negative direction of rotation of the cylinder 3. In other words, the command signal "SC" is representative of a negative value of the instantaneous velocity of the cylinder 3. In that case, the motor 4 reverses its rotation such as to recover the slack portions of the yarns F and again attain the predetermined tension value.

In a preferred embodiment, the tension threshold value, representative of a minimum tension value below which a slackening of the bed of yarns F takes place, coincides with the predetermined tension value.

In those embodiments in which the device 1 comprises a plurality of tension sensors 5, the control unit 6 also comprises a comparison subunit 9 which receives the plurality of tension signals "ST" originating from each tension sensor 5.

The comparison subunit 9 compares the tension signals "ST" to calculate differences between the measured tension values (absolute or mean) .

With reference to the position of the tension sensors 5, the comparison subunit 9 determines, on the basis of the difference between the received tension values, an angular value relative to the misalignment of the cylinder 3 with respect to an angular reference position. In other words, in the presence of an unexpected misalignment of the cylinder 3, the tension acting on the yarns F is no longer uniform in space, and a different tension acts on different yarns.

Thus the comparison subunit 9 calculates the angular value of the misalignment of the cylinder 3 with respect to a reference angular position based on the measurement of the unevenness of the tensions acting on the yarns F. Consequently, the comparison subunit 9 generates a misalignment signal "SD" representative of the angular value of the misalignment of the cylinder 3 with respect to an angular reference position. In the embodiments illustrated in Figures 1 and 2, the device 1 also comprises alignment means 10 active on the cylinder 3 to cause it to rotate about an alignment axis perpendicular to the rotation axis R of the cylinder 3 and perpendicular to a plane in which the yarns F unwinding towards the loom T lie.

By way of example, the support member 2 comprises a fixed portion and a rotatable portion rotatably secured to the fixed portion. The rotatable portion rotates relative to the fixed portion about the alignment axis.

In this case, the alignment means 10 comprise an actuator (not illustrated) associated with the cylinder 3. The actuator acts on the rotatable portion of the support member 2.

In greater detail, the actuator rotates the rotatable portion through an angle equal to the angular value of the misalignment of the cylinder 3, obtained from the comparison subunit 9.

In this respect, the control unit 6 is connected to the alignment means 10 to send the misalignment signal "SD" to the alignment means 10. More precisely, the comparison subunit 9 of the control unit 6 is connected to the alignment means 10 to send the misalignment signal "SD" to the alignment means 10.

According to the embodiment shown in Figure 4, the device 1 comprises two motors 5 disposed on opposite ends of the cylinder 3. The motors 4 can be controlled independently of each other.

In this embodiment, the command subunit 8 of the control unit 6 generates two command signals "SC" each sent to a respective motor 4. Again in this case, the support member 2 comprises the fixed portion and the rotatable portion rotatably secured to the fixed portion. The rotatable portion rotates relative to the fixed portion about the alignment axis. In this case, the control unit 6 comprises a correction subunit 11 connected to the comparison subunit 9 to receive the misalignment signal SD.

The correction subunit 11 determines at least one corrective value for the rotational velocity of one or both the motors 4 such as to determine a twisting torque on the cylinder 3 about the alignment axis.

The value of this twisting torque determines a rotation of the cylinder 3 about the alignment axis equal to the angular value of the misalignment of the cylinder 3 with respect to its reference angular position. In this manner, the cylinder 3 undergoes alignment until all the monitored yarns F are subjected to the same tension, hence obtaining tension uniformity.

In this respect, the correction subunit 11 generates a correction signal "SA" representative of the corrective value of the rotational velocity of the motor 4.

Alternatively, the correction subunit 11 generates two correction signals "SA" representative of the corrective value of the rotational velocity of each motor 4.

The correction subunit 11 is evidently functionally associated with the motors 4 to transmit the correction signals "SA" to them.

In the embodiment of Figure 5, the misalignment signal "SD" is sent directly to the command subunit 8 which consequently corrects the command signals SC, suitably differentiating them to differentiate the rotational velocities of the motors 4 and generate the twisting torque .

The invention also relates to a method of feeding yarns to a loom in accordance with the operation of the device 1 in the aforedescribed embodiments.

The invention hence attains the specified object.

In this respect, the closed loop control operation enables the yarn tension to be maintained constant with time at a tension value suitable for the productive requirements of the loom, which could vary depending on the operative stages themselves (tension during stoppage, during starting, during working, etc.) .

The tension could also be spatially controlled, to maintain it uniform in all the yarns fed.

It should further be noted that the device according to the present invention feeds the warp yarns to the loom in an active manner independently of the loom itself. In other words the device is not electrically coaxial with the loom.