METHOD TO CONTROL WEFT YARN INSERTION IN A LOOM

Abstract: In a method to control the operation of weft yarn insertion in a loom, as the end of weft yarn insertion approaches, a controllable yarn deviation brake (B), positioned between the weft feeder (M) and the warp shed (F) of the loom (D), brakes the weft yarn (Y) with a high braking force, causing a deviation thereof, and subsequently smooths down a tension peak of said yarn, thereby at least partially reducing said yarn brake deviation towards the starting position, or position of no deviation of said brake (B), the same function being performed upon cutting of said weft yarn (Y). After braking and reduction of the yarn tension peak, during the weft insertion step, the braking force is reduced to a level correlated to the yarn tension which prevails up to cutting of said weft yarn (Y).

Description: "METHOD TO CONTROL WEFT YARN INSERTION IN A LOOM" ===oOo=== The present invention relates to a method as described in the introductory part of claim 1, as well as to a weft yarn deviation brake. 5 In a method of this type - as disclosed by US-A-4.9ό2,97ό - the magnetic core of an electromagnetic linear control system of the yarn deviation brake is shifted, in order to brake the weft yarn by means of the braking element, with a maximum of deviation. As soon as, with a sharp tension peak, towards the end of weft yarn insertion, the high in- 10 crease in yarn tension takes place due to stopping of the weft yarn drawn from the weft feeder of the loom, the current of the electromagnetic control system is already regulated so that, after a braking, the weft yarn with its reaction force pushes back the braking element, reacting to the braking force, whereby, due to smoothing down of the tension peak, there 15 is an absorption of kinetic energy. In other words, the current is regulated so that the braking element which, to start with, is actually shifted with a maximum deviation (i.e. reaches its position of maximum deviation), can subsequently again be moved backward, at least partially, from its position of maximum deviation, due to the reaction force of the 20 yarn, thereby producing a smoothing down effect. Alternatively, due to shifting of the braking element into its position of maximum deviation or rotation, a higher startup current is temporarily set. In both cases, after smoothing down, the yarn deviation or rotation brake takes up again its position of maximum deviation as a result of the braking force. 25 As disclosed by EP-B-239.055 > when the weft yarn is cut at the end of its insertion into the loom, it is known to prevent said weft yarn - which is tensioned by moving of the reed - from bouncing backward as far as the yarn reserve wound on the drum of the weft feeder, that is, to prevent backward oscillations from being produced in the weft yarn, cau- ' ' ,0 sing the loosening thereof. At the outlet of the weft feeder, in correspondence of the yarn drawing point, there is mounted a yarn deviation element apt to be shifted in a controlled manner along the yarn path, which element, upon cutting of the yarn, is moved into a position of yarn deviation. Friction points are created for the yarn in said position of yarn deviation and the yarn is braked with an increasing braking force, giving rise to a recoil or a spring-back. During weft insertion, said yarn deviation element is kept in a position of no deviation up to the moment of yarn cutting. In any case, this method requires an extremely precise control of the yarn deviation element. The object of the present invention is to therefore supply a method allowing to obtain, in the final step of weft yarn insertion, an extreme- ly precise and delicate control of the weft yarn, apt to be carried out with simple and economic means, and to also supply a weft yarn deviation brake allowing to carry out said method. According to the invention, said object is reached with the characteristics disclosed in the characterizing part of claim 1 , and with the characteristics described in claim 10 of the present application. By reducing the braking force in respect of the braking force applied for braking and damping, in the relatively long period of time in which the reed performs its movement to press the weft yarn in position inside the warp shed, the yarn deviation brake is set in a weaker opera- ting condition in which it is thus allowed to automatically react to the reaction force determined by the yarn tension increase during movement of the reed, before cutting and, subsequently, upon dropping of the yarn tension when cutting takes place, so that - in a particularly advantageous way - it is the actual weft yarn which determines the functional un- winding. This means that the reduced braking force is suitably adjusted or set by the control system at the most appropriate moment, before the actual weft yarn causes the yarn deviation brake to act, in the manner which proves to be advantageous for the precise control of said yarn in the final weft insertion step. The reduced braking force derives from the fact that the yarn tension increase, due to movement of the reed, is considerably weaker than the previous tension peak which also required to be smoothed down and, furthermore, it is not apt to move, with the reaction force acting on the weft yarn , the yarn deviation brake into a starting position, or position of no deviation, under the highest braking force. Said position of no deviation, or a similar position, is however appropriate to allow withdrawing the weft yarn as much as possible after cut- ting. By adjusting the reduced braking force, the yarn deviation brake is made so sensitive and precise as to automatically react to the weft yarn tension increase occurring during motion of the reed, thereby yielding, up to possibly even moving back into a starting position of no deviation and, in synchronism with yarn cutting, to brake with a new strong devia- tion when the free weft yarn end is simultaneously withdrawn (claim 2). It would be detrimental to leave the yarn deviation brake con.stantly in a position of maximum deviation, starting from the braking action, or from the smoothing down action, up to cutting; and this due to the fact that, after cutting, the free weft yarn end would extend too much beyond the weft insertion nozzle. On the other hand, actively moving back the yarn deviation brake into its position of no deviation, after the braking action or after smoothing down the tension peak, would involve the drawback that said yarn deviation brake would then have to be again shifted in synchronism with the cutting operation, which anyhow takes place in a fairly indefinite manner. The brake would in fact have to start its braking action only and exactly from the precise moment in which the weft yarn is actually cut, neither at an earlier nor at a later moment. According to the method of the present invention, a relatively long period of time is available to reduce the braking force. The weakest braking action of the yarn deviation brake, with said reduced braking force, anyhow automatically comes to an end as soon as the brake is moved back into a starting position of no deviation for the next weft insertion step. In spite of the high degree of precision and reliability required, the method of the present invention can be carried out in a simple way for what concerns the technique of control and operation and it ensures weft insertion steps with no problems or inconveniences, even in the presence of yarn qualities difficult to treat. The yarn deviation brake according to claim 11 performs an important multiple function in that, in spite of the simplicity of the respective control system, it contributes to brake and smooth down the tension peak before the end of weft insertion, as well as to brake the yarn after cutting, and to withdraw the free weft yarn end. These functions - in themselves not tied one to the other - can be performed in a simple way, for what concerns the technique of control, and with precision in a favourable point of the weft yarn path which may, in specific circumstances, find itself even fairly distant from the weft feeder of the loom. The embodiment of the method according to claim 3 starts from the assumption to continue applying, for weft yarn control at the end of insertion, only a fraction of the braking force already set previously, to allow the subsequent automatic operation of the yarn deviation brake. The embodiment of the method according to claim 4 ensures that the weft, yarn reaction force, due to movement of the reed, automatically moves back the yarn deviation brake into the starting position of no deviation, or at least into a position close to said starting position, so that, for the final braking, after cutting, and for the withdrawal of the free weft yarn end, use can be made of an ideally wide stroke of the yarn deviation brake (claim 5)- The embodiment of the method according to claim 6 ensures a sufficiently prompt and precise operation of the yarn deviation brake to cause the shifting of said brake during a weft insertion step. Of the highest braking force stored up at first, only a fraction is kept for the subse- quent requirement to brake the yarn after cutting and to withdraw the free weft yarn end. This proves to be more advantageous than creating again a braking force from naught, even though low. The embodiment of the method according to claim 7 allows to obtain a behaviour of the yarn deviation brake which causes its operation with an immediate response. The startup current allows to reliably overcome any mechanical and inertial influence. The embodiment of the method according to claim 8 allows to obtain a reduced braking force through a signal for drawing the yarn turns issued from the weft feeder; this proves to be simple and precise for what concerns the technique of control and operation. Said signal to draw the yarn turns, with a delay time preferably added for the reduction control signal, represents the position of the weft yarn in the yarn path and in the shed, starting from which a new yarn tension increase will be produced due to movement of the reed, so that, for a further reliability of the method, said reduction control signal may reckon a sufficient lapse of time before cutting. Alternatively, according to the embodiment of the method described in claim 9, said reduced braking force could also be obtained with a signal external to the loom (or to the device for the control and operation thereof, and/or according to the position, by means of an encoder); and in a specially advantageous way, with the particularly simple external signal of derivability according to the embodiment of the method described in claim 10. The weft yarn deviation brake according to claim 12 makes use of a proportional rotation magnet which allows an extremely precise adjustment of the braking force, or of the reduced braking force, and which reacts in a practically immediate way to controls of the current regulation circuit, or to the current reduction for said reduced braking force. Some preferred embodiments of the invention shall now be described hereinafter with reference to the accompanying drawings, in which: Fig. 1 shows diagrammatically a system of weft yarn insertion in a loom; Figs. 2A to 2F illustrate different working conditions of the weft yarn deviation brake shown in fig. 1 ; and Figs. 3A to 3D are four diagrams illustrating the yarn tension trend, the movement of the yarn deviation brake, the current absorbed, and a chain of signals, step after step according to the time or angle of rotation of the loom. The fundamental components of a weft yarn insertion system as shown in fig. 1, conceived to carry out the method according to the invention, are a loom D with a warp shed F and a movable reed R, operated in known manner, a weft feeder M to feed a weft yarn Y to the loom D, a weft insertion nozzle N and a controllable yarn deviation brake B. To the same loom D there could be simultaneously associated more weft feeders M, apt to feed to the weft insertion nozzle N different or similar yarns to be inserted in the warp shed F. The weft feeder M for the loom D is a so-called measuring weft feeder, on the storage drum 2 of which there is kept available a yarn reserve of suitable consistency, wound into turns, from which reserve the loom D then provides, time after time, to intermittently draw a predetermined weft yarn length according to the pattern being woven. Said weft yarn length is set by a stop device 1 associated to the storage drum 2 , which allows to draw, time after time, in a non-operating condition, only a predetermined number of yarn turns, before stopping the wef yarn Y and blocking it in order to prevent a further drawing thereof. A sensor 3 for the yarn turns cooperates with said stop device 1 and, at the passage of each yarn turn being drawn, it issues a signal - sending it for instance to a control device C of the weft feeder M - to allow the prompt opera- tion of said stop device 1. Between the weft insertion nozzle N and the warp shed F there is provided a cutting device S which cuts, time after time, the weft yarn Y after its insertion. The yarn deviation brake B has various fixed deviation points , on one side of the yarn path , and a braking element 5 with respective deviation elements (two in this parti- cular embodiment) which can be shifted between said fixed deviation points 4 ^ transversely to the yarn path, by means of a rotation control member 6 - preferably an electromagnetic proportional actuator - from the shown starting position of no deviation, to the braking position of yarn deviation shown in dashed lines. To said rotation control member 6 there is associated a current regulation circuit 7, to which a reduction control signal X can be sent, for instance through a control device CU (or else directly from the weft feeder M or from the loom D), in order to set the highest braking force to a reduced braking force level , by reducing the current for said rotation control member 6, said reduced braking force corresponding to a fraction of said highest braking force of yarn deviation. The control device CU can be connected to the control device C of the weft feeder M, and/or to the loom D, in order to promptly operate the yarn deviation brake B during a weft insertion step. Suitably, a transducer or indicator 8 (encoder) of the loom is alternatively provided, which - according to a specific position of rotation, for instance of the main shaft of the loom D - issues an external signal, acting as reduction control signal X (claim 12). Figs. 2A to 2F illustrate different working positions of the yarn deviation brake B of fig. 1 , said positions being adjustable - according to the method of the present invention - at each weft insertion step, or being determined by the reaction force of the deviated weft yarn Y. During the main phase of the weft insertion step (with the stop device 1 at rest ) , the weft yarn Y in the yarn deviation brake B is neither deviated nor subjected to friction, in order to prevent slowing down the movement of the weft yarn being inserted into the loom shed. The yarn deviation brake B thus finds itself in its position of no deviation, or starting position. The braking element 5 is withdrawn. The weft yarn Y is inserted by the nozzle N into the warp shed F of the loom D in the direction indicated by the arrow (fig. 2A) . More or less when the stop device 1 starts to operate, on reaching of the preset weft yarn length to be drawn, the yarn deviation brake B is shifted in the braking position of maximum deviation, as shown in fig. 2B. Due to the friction applied on the yarn and to the deviating action, the weft yarn Y is thus braked, so as to prevent the stop device 1 from being left to slow down by itself the whole free weft yarn mass. The braking points are indicated by the single arrows pointing upwards. When the weft yarn Y is intercepted in correspondence of the stop device 1, due to sudden slowing down of the yarn, a very high tension peak is produced therein. The highest braking force of the yarn deviation brake B is actually regulated at that intensity, thereby allowing the reaction force of the weft yarn, produced at that point, to at least partially reduce the deviation caused by the braking element 5 , as indicated by the arrows pointing downward in fig. 2C. While the deviation is being reduced, there is an absorption of kinetic energy and a smoothing down effect is produced on the weft yarn, which is appropriate to prevent weft yarn breakages. Just after the smoothing down action, obtained through said reduced deviation, and after reduction of the yarn tension peak, the weft yarn Y, which at this point has already practically stopped - as indicated by 0 in fig. 2D - is no longer able to oppose the braking force; as a result of the highest braking force, the braking element thus moves back into its position of maximum deviation, as shown in fig. 2B. It is more or less at this time (t , in fig. 3C) that the braking force is dropped to the level of a reduced braking force. In the working step illustrated in fig. 2E - due to movement of the reed R which leads to pressure of the yarn against the edge of the fabric being woven, and due to changing of the yarn pattern in that point - a tension increase is again produced in the yarn, being anyhow lower than the tension increase produced in correspondence of said tension peak. Due to said tension increase, the reaction force produced in the weft yarn moves the braking element, kept in said position of deviation by the reduced braking force, back into its starting position of no deviation, or into a position close to this latter, against the reduced braking force. Subsequently, as shown in fig. 2F, the cutting device S is operated to cut off the tensioned weft yarn. This produces a sudden fall of yarn tension. The reduced braking force again causes a further shifting of the braking element 5 into its position of maximum deviation. Friction points are thus created, to prevent backward oscillations or a spring-back of the weft yarn towards the weft feeder M. At the same time, thanks to said shifting of the yarn deviation brake into its position of maximum deviation, the free weft yarn end in the insertion nozzle N is withdrawn in such a way as to prevent it from colliding with other yarns or from flapping around, thereby getting damaged due to the blowing action of the nozzle N. Thus, in a subsequent phase - before the start of a new weft insertion step - the yarn deviation brake B is again moved back, by the rotation control member 6, into its starting position of no deviation. The diagrams shown in figs. 3A to 3 illustrate the relationship between the weft yarn tension, the movement of the yarn deviation brake B, the current fed by the rotation control member 6, and the control signals to operate said yarn deviation brake. As shown in fig. 3A (yarn tension trend, according to the time t or the angle of rotation of the loom) , following the action of the stop device 1, towards the end of weft yarn insertion, a very high tension peak is produced (curve 9)- Said tension peak is then followed by a sudden fall of yarn tension, after which the tension again rises due to movement of the reed; finally, the tension practically drops (down to a minimum level corresponding to the tension produced by the residual tractive force of the insertion nozzle) at the moment of weft yarn cutting. The continuous curve 9 places in evidence the tension trend without a controllable yarn deviation brake B. The curve 9' ? drawn in dashes, shows how the yarn deviation brake B reduces the tension peak 9. The insertion is finally concluded some degrees of rotation angle of the main shaft of the loom before 0° (i.e. 360°). As shown in fig. 3B, the yarn deviation brake is at first rapidly shifted from its starting position to its position of maximum deviation, and this with the highest braking force (for instance a braking current of 0,7A) or even with a startup current far higher than normal, in order to overcome any possible mechanical or inertial influences (for instance, more than 0,7A for 3 to 9 ms). Following the tension peak in the curve 9, the yarn deviation brake B is at least partially moved back towards its starting position, so as to have an absorption of kinetic energy (tension curve 9' in fig. 3A), before being again shifted into its position of maximum deviation (as shown in fig. 3-B) due to the highest braking force which continues to act (for instance 0,7A). When the subsequent yarn tension increase occurs, due to movement of the reed, the yarn deviation brake is again caused to move back, by the actual weft yarn, into its starting position, or at least into a position close to said starting position, where - thanks to the already cited reduction control signal X - in correspondence of t only a reduced braking force (for instance 0,3A to 0,4A) is set. At this point, the weft yarn is tensioned. Cutting of the weft yarn then takes place, which practically produces a prompt weft yarn tension drop. Under the action of the reduced bra- king force (for instance 0,3A to 0,4A), the yarn deviation brake rapidly moves back into a position of maximum deviation and, in so doing, it stops the tendency of the weft yarn to spring backward and, furthermore, it withdraws the free weft yarn end. Subsequently, the yarn deviation brake is shifted back into its starting position and it remains in said position for most of the successive weft insertion step. As illustrated in fig. 3C, in correspondence of a time t , for the proportional rotation magnet forming the control member 6 of the yarn deviation brake B, a maximum startup current I (for instance over 0,7A) is set , so as to rapidly shift the yarn deviation brake into a position of maximum deviation. In the case of a heavy or thick quality yarn, said current 1 is maintained up to a time t , in that such a heavy quality weft yarn is anyhow apt to move back the yarn deviation brake, at least partially, towards its starting position of no deviation, even in the presence of the highest braking force, when the tension peak occurs, so as to reduce its effects. Whereas, in the case of a lighter quality yarn, in correspondence of the time t (for instance after 3 to 9 ms), the startup current I is reduced to the current I ' , for the highest braking force (for instance to 0,7A), so as to put the light quality weft yarn in the condition to move back, at least partially, the yarn deviation brake towards its starting position of no deviation, when the tension peak occurs. Said current I' , equally as the startup current I , is however so strong that the highest braking force produced by it is substantially higher than the reaction force which the weft yarn can oppose during the subsequent motion of the reed, under the effect of the tension increase. For this reason, a reduction control signal X is generated in correspondence of the time t and the current I is consequently regulated, this current being substantially weaker than the startup current I or than the actual current I 1 (for instance, only 0.3A to 0.4A). Said time t is sufficiently spaced from the time t , in correspondence of which the weft yarn is cut. The current I is kept beyond said time t until, after the free cut weft yarn end has been duly withdrawn, the current I (a negati- e current) is set in correspondence of the time t , this last current being apt to move back the yarn deviation brake actively in its starting position of no deviation. To carry out the aforedescribed working steps, the curve of the current trend 11 (fig. 3C) is adapted to the conditions or parameters depending on the yarn quality, on the type of loom and on the operating modes of the system. As shown in fig. 3D, to reduce the current to I in correspondence of the time t , the reduction control signal X is derived from the signals to draw the yarn turns, or of yarn unwinding, issued by the sensor 3 of yarn passage positioned on the weft feeder M. More exactly, said reduction control signal X is derived from a predetermined signal (for instance, from the signal c) forming part of the signals a, b, c, to draw the yarn turns, generated in sequence. Furthermore, as soon as said preselected signal c to draw the yarn turns is generated, one takes into account a predetermined delay time d, so as to generate said reduction control signal X exactly in correspondence of said time t , namely in correspondence of a specific angle of rotation of the loom, that is, after the tension peak has been reduced due to braking and sufficiently in advance in respect of the time t in correspondence of which the weft yarn is cut. The reduction control signal X could besides be even genera- ted by the loom D - by way of the signal transducer 8, in function of a predetermined position of rotation, for instance of the main shaft of the loom - and/or by the device for the control and operation of the loom.

Claims: CLAIMS 1 ) Method to control weft yarn insertion in looms - wherein . as the end of weft yarn insertion approaches, a controllable yarn deviation brake, positioned between the weft feeder and the warp shed of the loom, breaks the weft yarn with a high braking force, causing a deviation thereof, and subsequently reduces at least one tension peak of said yarn while, due to said yarn tension, the yarn brake deviation is at least partially reduced towards the starting position, or position of no deviation of said brake, before the weft yarn is subsequently cut in respect of the weft yarn length inserted in the warp shed of the loom, so as to be pressed by the reed against the edge of the fabric being woven - characterized in that, after braking and reduction of the yarn tension peak, during the weft insertion step, the braking force is reduced to a level correlated to the yarn tension which prevails up to cutting of said weft yarn. 2) Method as in claim 1), characterized in that, after cutting, the weft yarn is braked by the same yarn deviation brake, through deviation thereof, said brake automatically reacting to the tension fall of the yarn upon cutting thereof under said reduced braking force. 3) Method as in claim l), characterized in that said reduced braking force is set to a level corresponding only to a fraction of the highest braking force and is kept at that level till after cutting has taken place. 4) Method as in claim 1), characterized in that said reduced braking force is weaker than the weft yarn reaction force active in the yarn deviation brake and determined by the increase of yarn tension due to movement of the reed which leads to pressure of said yarn. 5) Method as in claim 4) ? characterized in that said reduced braking force is correlated to the weft yarn reaction force, so that the weft yarn is apt to move back the yarn deviation brake almost in the starting position of no deviation, up to the moment of yarn cutting. 6) Method as in any one of the previous claims 1) to 5), characte- rized in that said yarn deviation brake is controlled by an electromagnetic actuator of proportional rotation, to be shifted between the starting position, corresponding to no yarn deviation, and a position of maximum deviation and braking, the shifting force of said actuator depen- ding on the current fed or voltage applied to the same, and in that, for the whole lasting period of said reduced braking force, said electromagnetic actuator of proportional rotation is fed with a current which is considerably weaker than the current corresponding to the highest braking force. 7) Method as in claim 6), characterized in that, just before feeding the braking current, a controlled startup current of further intensity is fed. 8 ) Method as in claim 61 , characterized in that the current for the reduced braking force is regulated with a reduction control signal, deri- ved from a predetermined signal for drawing the yarn turns from the weft feeder, apt to send signals to draw the yarn turns, generated according to the movement of weft yarn insertion, preferably with the addition of a predetermined delay time of said reduction control signal , according to the specific conditions of the system. 9) Method as in claim 6), characterized in that the current for the reduced braking force is regulated with a reduction control signal external to the loom. 10) Method as in claim 9), characterized in that said external signal is generated upon reaching, or before reaching, a specific position of rotation, preferably of the main shaft of the loom. 11) Weft yarn deviation brake, particularly to carry out the method as in any one of the previous claims 1) to 10), consisting of a braking element apt to be shifted, under control, between a starting position of no deviation and a position of maximum deviation, during the weft yarn insertion step, characterized in that it comprises a device to regulate a braking force which is considerably reduced in respect of the highest braking force, said device simultaneously acting so as to withdraw the weft yarn and perform a reverse current braking. 12) Weft yarn deviation brake as in claim 11), characterized in that it comprises a braking element, apt to be shifted between a starting position not deviating the weft yarn and a braking position to deviate the weft yarn, and an actuator for said braking element in the form of a proportional rotation magnet, preferably a proportional magnet apt to be shifted bidirectionally, with a circuit to regulate the current for different current intensities, and in that said current regulation circuit is associated to a transducer for a reduction control signal and is apt to react to said reduction control signal by regulation and maintenance of a current for the reduced braking force which is weaker in respect of the current for the highest braking force.

Inventors: COVELLI MARCO, COVELLI, MARCO
Applicants: COVELLI MARCO, ROJ ELECTROTEX NUOVA SRL, COVELLI, MARCO, NUOVA ROJ ELECTROTEX S.R.L.
Application year: 1997
Main classification: D03D47
IPC codes: D03D47