Patent Description:
In particular, the device for the automatic removal of wrong weft threads of the invention is started up after the insertion of a wrong weft thread is signalled and the loom consequently stopped, to remove the wrong weft thread from the shed and simultaneously verify that such removal takes place in a correct and complete manner. If the outcome of this test is negative, the consent signal to restart the loom is not sent while instead a warning signal is delivered to activate the operator to perform manual removal, thus avoiding the generation of defects in the produced fabric caused by a weft thread portion possibly entangled in the shed.

In air weaving looms it may happen that the weft thread launched by special nozzles from one side of the loom (usually the left side, seen from the normal working position of a weaver) to cross the shed inside the dedicated channel formed in the reed does not correctly arrive to the opposite (right) side of the loom. The reasons of this wrong weft insertion can be multiple - for example, a wrong supply pressure of the weft transfer system, a wrong timing in the activation of the air jets of the weft transfer system, an interference of the weft thread with mechanical elements located along the reed channel or with the warp threads - but the final outcome comes down to only two specific cases: broken weft or short weft. Such outcome is verified by means of two optical sensors located along the weft thread path, at the right side of the loom, namely a first optical sensor upstream of the expected point of regular arrival of the weft thread free end, and a second optical sensor downstream of such point.

When the weft thread is correctly inserted, the first optical sensor detects the weft arrival within the expected time window, while the second optical sensor does not detect anything, since the advancement of the weft thread is mechanically stopped by acting on the opposite end thereof. On the other hand, in the event of a broken weft thread, the mechanical stop of the weft thread on the left side of the loom has no effect on the broken thread piece, which thus continues its run and is detected, in succession, by both the first and the second optical sensors. In the event of a short weft thread, i.e., a weft thread which has become entangled in the shed, the weft thread tip is instead not detected on the right side of the loom by either of the two optical sensors, at least within set time limits.

In all the above-mentioned cases of wrong weft thread insertion an alarm status is immediately activated when the loom control system detects the error, interrupting the work cycle in progress and starting a procedure for the automatic removal of the weft thread which has been wrongly inserted. Said procedure for the automatic removal of a weft thread left inside the shed consists of a combined and coordinated action of the jets of the auxiliary nozzles for weft thread transfer and of mechanical and/or pneumatic devices for carrying out a pulling action on the weft thread.

Once the automatic removal procedure has been successfully completed and the wrong weft thread has been removed from the shed, the automatic restart of the loom is enabled and therefore no defects remain on the fabric. On the other hand, when the automatic removal procedure does not allow the weft removal to be completed in a set time, the automatic restart of the loom is not activated, and the intervention of an operator is requested for manual removal of the wrong weft thread and manual restart of the loom.

The devices for the automatic removal of wrong weft threads available on the market are divided into two families, which can be identified by the way they interact and pull the weft thread; a first family exclusively consists of pneumatic devices, while a second family additionally comprises mechanical devices for carrying out a pulling action on the weft thread.

In the case of an entirely pneumatic automatic removal procedure, schematically illustrated in <FIG>, the auxiliary nozzles distributed along the reed R channel blow simultaneously and intermittently to cause the weft thread T to progressively shift towards the right side of the weaving loom where the above-mentioned two optical sensors (S1; S2) together with a pneumatic device A are provided. When activated, said pneumatic device A generates a pulling force F on a wrong weft thread coming close to it, so that said weft thread T is progressively removed from the shed thanks to the overall pneumatic dragging action exerted by the whole of these devices thereon. The optical sensor S2, arranged immediately before the pneumatic device A, monitors the running of the weft thread T inside the same, during the extraction, allowing the loom electronic control system to ascertain the outcome of the automatic removal procedure.

As a matter of fact, if the weft thread tail disappears from the control area of the second optical sensor S2 within a set time, the removal procedure is considered as successfully completed, and thus the automatic restart of the loom is enabled. If the weft thread T tail does not disappear from the control area of the second optical sensor S2 within said set time, the automatic removal procedure is considered as failed, and the automatic restart of the loom remains therefore inhibited until manual intervention by an operator.

In the case of a device with combined pneumatic and mechanical operation, which is schematically illustrated in <FIG>, the extraction cycle is substantially the same, except for how the weft thread T is pulled once its tip has reached the pneumatic device A. In fact, after being initially dragged by the pneumatic action of device A, in a completely analogous way to that of the device described above, in this combined device the tip of the weft thread being extracted is trapped between a pair of oppositely rotating cylinders C, which close on said tip with a set contact force and exert, by rotating in the opposite direction, a mechanical pulling force which is added to the pneumatic force generated by device A. Such automatic removal device with combined pneumatic and mechanical action obviously guarantees greater efficiency in the extraction of the weft thread T, especially in situations when the weft thread is heavily entangled within the shed.

However, both the above-described types of devices for the automatic removal of wrong weft threads have a common drawback, i.e. that they do not allow the integrity of the wrong weft thread T to be checked during the extraction phase. In situations where the weft thread T is heavily entangled in the shed, therefore, the probability increases that the mechanical traction device causes its unwanted breakage, which breakage is also completely out of control. In fact, even after an unwanted breakage of the weft thread T, the extraction device continues to pull the free end of the weft thread T and sends a positive outcome of the automatic removal procedure to the loom control system when the tail of the weft thread C extracted from the shed is detected by the sensor S2, thus consequently enabling the automatic restart of the loom. However, the broken portion of the weft thread C which remained entangled in the shed is not detected and it is not removed, thus reducing the efficiency of the automatic removal device, and resulting in a textile defect which is only detectable when the fabric is finished.

Other solutions are available on the market, which can be implemented on the left side of the machine, i.e., by extracting the wrong weft thread from its side of insertion. However, even in these different solutions it is not possible to check the integrity of the weft thread T during its extraction from inside the shed, thus leaving open the possibility that pieces of a broken weft thread are left inside the shed, thereby generating defects on the final fabric when the loom is automatically restarted.

In one of these latter solutions, disclosed in <CIT>, it is also proposed the additional use of a mechanism apt to measure the tension of the weft thread during its extraction step, so as to interrupt the extraction operation if such a tension exceeds a set threshold value. This document represents the prior art closest to the invention, which prior art is in fact reported in the preamble of the independent claims.

Considering the market demand to maintain high-quality standards of fabrics made with air weaving looms, the technical problem addressed by the present invention is to improve the reliability of the currently used devices for the automatic removal of wrong weft threads, making it possible to detect any conditions of weft thread unwanted breakage which may occur during the automatic extraction of a wrong weft thread from the shed.

A weft thread breakage during the extraction step from the shed occurs if the pulling force generated on the weft thread by the automatic removal device exceeds the tensile strength of the weft thread. Each type of weft thread, based on the type of material and the mechanical features imparted in the spinning process, has in fact a well-defined tensile strength.

In the context of solving the above technical problem, a first object of the present invention is thus to set up a device detecting the variations of tension of a wrong weft thread during its extraction from the shed, without interfering with normal weaving operations.

A second object of the present invention is to provide a method of interpreting the above-mentioned variations of tension of said weft thread, so that its possible occurred breakage, or in any case its high possibility of breakage, during the above-mentioned extraction of the wrong weft thread from the shed, can be deduced without being visually detected.

This problem is solved, and these objects achieved, by means of a device for the automatic removal of wrong weft threads from the shed of an air weaving loom having the features defined in claim <NUM>, and by a method for the automatic removal of wrong weft threads having the features defined in claim <NUM>. Other preferred features of the above-mentioned device are defined in the dependent claims.

Further features and advantages of the device for the automatic removal of wrong weft threads from the shed of an air weaving loom, according to the present invention will anyhow become more evident from the following detailed description of a preferred embodiment of the same, given by mere way of nonlimiting example and illustrated in the accompanying drawings, wherein:.

According to the present invention, to solve the problem highlighted above by means of a simple and immediately applicable solution, a known device D for the extraction of wrong weft threads, with combined pneumatic and mechanical operation, for example of the type schematically illustrated in <FIG>, is supplemented with a sensor apt to detect the tension of the wrong weft thread during its extraction from the shed. For the sake of simplicity, such a tension sensor will be hereinafter referred to as tensiometer. Based on the data provided by said tensiometer and on an appropriate interpretation mode of said data, the present invention has been finalized.

To achieve the objects of the invention, a tensiometer <NUM>, mounted on a carriage which can be moved in a direction perpendicular to the weft threads, is preferably positioned between the optical sensor S2 closest to the right end of the loom and the pneumo-mechanical device D for the extraction of a wrong weft thread. The tensiometer <NUM> can consist of any electronic device measuring the tension of a thread running inside the same and generating an electrical signal proportional to said tension.

During the procedure for the automatic removal of a wrong weft thread, when the tip of the weft thread (T) being extracted has reached the extraction device D and has been clamped by the cylinders C, the tensiometer <NUM> is approached and brought into contact with the weft thread T, thus deviating the same from its straight trajectory, in order to measure the overall pulling force F applied by the cylinders C and the pneumatic device A to the weft thread T in its running direction. A schematic representation of the tensiometer <NUM> is depicted in <FIG>, wherein the tensiometer <NUM> elements causing the deviation of the weft thread T from its straight path are represented by guide rollers <NUM>, and wherein the tensiometer <NUM> sensitive element is a roller feeler <NUM> interposed between said guide rollers <NUM>, said roller feeler <NUM> being integral with a load cell <NUM> detecting the force exerted on the roller feeler <NUM> by the weft thread T. When a wrong weft thread is detected, the tensiometer <NUM> is made to advance towards the wrong weft thread T until bringing the guide rollers <NUM> and the roller feeler <NUM> into their operative position in contact with the weft thread T. This operation is facilitated by a V-shaped fork, integral with said tensiometer <NUM>, which, during the approaching step of the tensiometer <NUM>, intercepts the weft thread T and precisely directs it onto said guide rollers <NUM> and onto said roller feeler <NUM>.

The guide rollers <NUM> cause a moderately wavy pattern of the weft thread T trajectory, as schematically illustrated in <FIG>, and the roller feeler <NUM> is mounted at the middle portion of such wavy pattern, in a direction perpendicular to the weft thread T running direction. Thanks to this, as the tension of the weft thread T varies, the force applied to the roller feeler <NUM> varies too, and such variation is detected by the load cell <NUM> and translated into an electric signal proportional to the actual tension of the weft thread T. The present explanation of how the tensiometer <NUM> operates is obviously provided by mere way of example and thus it does not limit in any way the present invention wherein, in fact, any type of tensiometer apt to provide an electrical measurement of the tension of a weft thread can be used, regardless of how this measure is obtained.

The variations of the tension F of the weft thread T, as detected by the load cell <NUM>, are then immediately processed by a processing unit - which can indifferently be a dedicated processing unit associated with the tensiometer <NUM>, or the same central processing unit of the loom - to verify whether, during the entire cycle of extraction of the wrong weft thread, threshold conditions which are set on the basis of the features of the weft thread and/or of the actual textile operation are exceeded. Exceeding one of said threshold conditions is considered as a probable occurred breakage of the weft thread T.

This latter information is then used by the loom control system, in addition to the already provided checks, to determine with greater reliability the final outcome of the automatic weft thread removal procedure. As a matter of fact, if the procedure is successfully completed according to the criteria of the prior art solution, and furthermore the device of the present invention has detected no probable breakage of the weft thread, the automatic restart of the loom can be enabled. If, on the other hand, the device of the present invention has detected a probable breakage of the weft thread, the automatic restart of the loom is inhibited - even in the presence of a positive outcome of the check according to the criteria of the known device for the removal of wrong weft threads - and at the same time a request for intervention of an operator is signalled, for him to directly visually check and possibly manually remove the piece(s) of weft thread left inside the shed, and subsequently restart the loom. In this latter case, by avoiding the automatic restart of the machine, the device of the invention allows to generate no defects on the finished fabric. Consequently, the device for the automatic removal of wrong weft threads according to the invention offers a higher overall reliability than known devices.

Several possible modes are now described of processing and analysing the data on the tension T of the weft thread, as detected by the tensiometer <NUM>, to evaluate whether a probable breakage of the weft thread is occurred during the cycle of extraction of the same from the shed.

A first mode is based on comparison between the value of the signal emitted by the tensiometer <NUM> - suitably processed to represent the overall tension F applied to the weft thread being extracted - and the tensile strength value of the weft thread itself.

Said tensile strength is known to vary depending on the type of textile material the weft thread is made with, and its value is not constant over the entire length of the weft thread, but it rather depends on the mechanical features introduced through the spinning process as well as on the ambient operating conditions. A breaking tension Fb of the weft thread T in operation, and a safety tension Ft less than or equal to the breaking tension Fb are thereby identified, such as to create therebetween a control band of the weft thread tension F, within which there is statistically a high probability that the weft thread will break.

During the extraction cycle, the weft thread can be repeatedly entangled and released in the shed, and the tension F of the weft thread T accordingly increases and decreases. All such variations of tension F of the weft thread T are accurately detected by the tensiometer <NUM>. <FIG> depicts four typical diagrams of different trends of the tension F of the weft thread T versus time during the extraction of the wrong weft thread from the shed, said diagrams being representative of four different, statistically significant, situations of the weft thread T, as better explained below.

If the measured signal representing the tension F always remains below the threshold value of the safety tension Ft (curve A), the extracted weft thread T is considered intact, and the automatic restart of the loom is therefore enabled at the end of the operation of automatic removal of the wrong weft thread T. Conversely, if at any instant of the extraction cycle the tension F detected by the tensiometer <NUM> exceeds the safety tension Ft or even the breaking tension Fb (curve B), this circumstance is identified as a probable breakage of the weft thread T and consequently the automatic restart of the loom is inhibited. If during the extraction cycle the value measured by the tensiometer <NUM> progressively increases and then abruptly and quickly collapses during the extraction phase (curve C), this circumstance is identified as a probable breakage of the weft thread, even when the breaking tension Fb has not been exceeded, and thus the automatic restart of the loom is inhibited also in this case. In completely similar circumstances, if the tension F value progressively decreases after a high peak, until recovering its initial values (curve D), this is considered instead as a condition wherein the weft thread has become untangled and is still intact, despite the safety tension Ft has been exceeded, so that the automatic restart of the loom is authorized upon completion of the extraction cycle.

An additional way of interpreting the data of the tension F of the weft thread T, which is illustrated in <FIG>, uses a mixed approach, further adding to the control described above the analysis of the derivative dF of the tension F of the weft thread versus time, the value of such derivative dF being constantly monitored during the extraction cycle of the weft thread. When the extraction of the weft thread T from the shed takes place without serious entanglement conditions of the weft thread T, the value of tension of the weft thread T is approximately constant and therefore the value for the derivative against time of such tension is about zero. If, on the contrary, conditions of entanglement of the weft thread T occur, the value of the tension F measured by the tensiometer <NUM> progressively increases and the signal of the derivative dF consequently deviates from the zero value.

Small variations of the derivative dF, in the presence of a non-zero value of the tension F signal from the tensiometer <NUM> in the instants following a peak of variation (curve D), can therefore be interpreted as conditions of a weft thread becoming untangled and being still intact (curve H). Negative peaks in the signal of the derivative dF (curve G) are instead indicators of potential sudden breakage of the weft thread, even in the presence of a non-zero signal from the tensiometer <NUM> in the instants following the sudden variation (curve C). Interpreting the data of the tension F of the weft thread T by this mixed approach makes it possible to define a more stringent criterion, according to a precautionary purpose, to determine the probable occurred breakage of the weft thread T during the extraction cycle, and therefore avoid a possible defect on the final fabric at the automatic restart of the machine.

The introduction of a tensiometer <NUM> for measuring the tension F of the weft thread T during the extraction of a wrong weft thread from the shed, and the described processing and interpreting modes of the signal generated by the same, allow therefore to significantly improve the quality of the manufactured fabric, avoiding defects caused by incomplete removal of a wrong weft thread by the automatic removal device carrying out this operation.

Claim 1:
Device for the automatic removal of wrong weft threads from the shed of an air weaving loom, of the type comprising a pneumatic or pneumo-mechanical extraction device (D) of a wrong weft thread (T), a tensiometer (<NUM>), arranged upstream of said extraction device (D), which detects the variations of a tension (F) imparted on the weft thread (T) by said extraction device (D) during the extraction step of the weft thread (T) from the shed, and a processing unit which processes the variations of tension (F) of the weft thread (T) and disables the automatic restart of the loom when said variations of tension (F) satisfy set threshold conditions, characterized in that said tensiometer (<NUM>) comprises guide elements (<NUM>), which deviate the weft thread (T) from its straight trajectory, and a sensitive element (<NUM>, <NUM>), interposed between said guide elements (<NUM>), which detects said variations of tension (F) of the weft thread (T), and in that said tensiometer (<NUM>) is mounted on a carriage which can be moved in a direction perpendicular to the direction of insertion of the weft threads, and in that said tensiometer (<NUM>), when the insertion of a wrong weft thread is detected, is made to approach the weft thread (T) until bringing said guide elements (<NUM>) and said sensitive element (<NUM>, <NUM>) into contact with the wrong weft thread (T).