Method to automatically pull out a broken weft yarn from the shed in air looms and pneumomechanical device used in said method

Abstract: Method to automatically pull out a faulty weft from the shed in air looms. In case of a faulty weft, the cutting of the yarn (2) is prevented and a double weft is simultaneously fed into the shed (3). The loop (7) thus formed is conveyed to the outlet of the shed (3) by an air stream, inside a pneumomechanical device (10) positioned at loom outlet. Said device (10) comprises an inner duct (13) into which blows the air stream conveying the faulty weft yarn, yarn gripping and intermittent drawing members (15) positioned downstream of and across said duct (13), and devices (19, 21) to protect from dirt the yarn detection optical sensor (18).

Description: The present invention concerns a method to pull out a faulty weft from the shed in air looms and, in particular, a method specially suited to successfully pull out the weft yarns which, due to their characteristics (for instance, cotton yarns), get entangled with the warp yarns. The invention also concerns a pneumomechanical device used in said method to pull out the faulty weft. Among the known methods, proposed up to date to solve the problem lying at the basis of the invention, one should remember in particular: a first method, wherein the faulty weft is pulled out by mechanical means from the weft insertion side of the loom (hereinafter simply called loom inlet); a second method, wherein the faulty weft is pulled out by pneumatic means from the weft reception side of the loom (hereinafter simply called loom outlet); and, finally, a third method which is a combination of the two previous ones. In all these methods, the loom comprises a device which controls that the weft yarn has correctly reached loom outlet, and which provides to stop the loom and the working of the weft yarn cutting device whenever the yarn does not reach that position, or reaches it in an irregular way. After this operation - eventually followed by a backward stroke of the loom, to free the weft yarn from the warp yarns if these have already interwoven with the same - those which follow vary according to the different known methods, as better described hereinafter. The first method of prior art provides for a mechanical windup device, positioned at loom inlet, to draw the faulty weft by simply pulling it out from the shed. Said device is in fact inserted along the path of the weft yarn - which, as said above, has not yet been cut - and thus simultaneously winds up both the faulty weft, already inserted in the shed, and new weft yarn fed from the weft feeding devices. As soon as the faulty weft has been pulled out, the yarn is cut, the windup device is freed from the yarn skein wound thereon and moved back to its rest position, and the loom can be started again. This method has the serious drawback lying in the fact that the faulty weft, inserted in the shed and already beaten, shows a high resistance to being pulled out directly from the shed, since it tightly adheres to the warp yarns and to the previous weft yarn, against which it has been beaten. This method can therefore be applied only in few cases, for example with fabrics consisting of synthetic and particularly glossy yarns, which have a very low adherence. In other cases, the excessive pulling stress can cause breakage of the faulty weft yarn, or even of the warp yarns, and anyhow easily determines a misalignment of these last ones, thus possibly giving rise to defects or anyhow to discontinuances in the fabric. According to an improved embodiment of said method, disclosed in EP-A-200168, the windup device is positioned at a certain distance from the weft yarn path, towards the warp beam. In case of a faulty weft, this is deviated in the windup device by means of a compressed air jet. The faulty weft is then pulled out following a certain angle in respect of the weft yarn path and this slightly favours the separation of the faulty weft yarn from the warp yarns. Also in this case however, the mechanical pulling action is too strong and it can easily cause the breakage of the faulty weft yarn or of the warp yarns, or even an undesirable displacement of these last ones. In the second method of prior art, disclosed in NL-A-8602191, the weft yarn feeding device is controlled so as to feed - when the loom stops due to a faulty weft insertion - a double weft, which is launched through the shed thanks to the action of the secondary nozzles, forming a loop which moves towards loom outlet. On this side, there is provided a pneumatic yarn suction device, which sucks in the loop formed by the double weft freely launched through the shed, pulling it slightly. At this point, the weft yarn is cut in correspondence of loom inlet and the yarn is sucked in by the suction device, with a backward pulling action (peeling or adhesive tape effect) on the faulty weft. With this system, the beaten weft can be more easily freed - without damaging the fabric being woven - even when there is a higher adherence between weft and warp yarns. This method therefore allows to work with many types of synthetic yarns, provided that they are suitably drawn and thus not fluffy. The pulling force pneumatically imparted on the weft cannot in fact exceed certain values, whereby this method cannot be used to treat synthetic fluffy yarns or yarns with short fibers, and natural fiber yarns. This second method has also another limitation. In fact, the weft yarn is often successfully freed from the pneumatic action of the suction device throughout its length, except at its tail which gets more easily entangled with the warp yarns, thus opposing the pulling action. According to the third method of prior art - disclosed in EP-309013 - which is meant to overcome the above drawback, the weft yarn is not even cut when the loop formed therefrom has been sucked into the suction device; on the contrary, weft yarn is fed into the shed until suitable detection devices, prearranged in the suction device, have detected the unwinding of the loop and thus the full disentanglement of the faulty weft from the shed. If this should not take place after a predetermined weft yarn length has been fed, or after a predetermined suction time has elapsed (which is an evident sign that the faulty weft is still, at least partly, entangled in the shed), one operates a mechanical pulling device, positioned at loom inlet, which provides to draw out the faulty weft according to the first method described heretofore. In this case, the aforementioned drawbacks connected with this method are less serious, as they only concern one portion (normally the tail portion) of the weft and not the whole length thereof. Nevertheless, defects may still be formed in the fabric; there is, furthermore, a considerable yarn consumption, and no precise information is provided as to the actual yarn length which has not been freed by the pneumatic sucking action. A pneumomechanical device to automatically pull out a faulty weft from the shed in air looms with the features of the preamble of claim 7 is known from US-A-4 890 650. All the aforedescribed known methods, adopting a mechanical device to pull out the faulty weft, also have additional drawbacks due to the fact that the mechanical pulling action cannot be adequately controlled. It hence continues up to complete pullout or breakage of the faulty weft, without it being possible to automatically detect the forming of defects in the shed, such as misalignment of the warp yarns, or the presence of a residual length of faulty weft yarn, if this latter has broken during the pullout operation. A last inconvenience is instead present in all the aforedescribed known devices making use of photoelectric cells to detect the presence or absence of weft yarn, in combination with suction devices. Such photoelectric cells are in fact rapidly soiled by the dust and oily residues present in the compressed air jet, and can easily give wrong indications if they are not subjected to accurate and frequent cleaning operations. The object of the present invention is therefore to supply a method to automatically pull out a faulty weft from the shed in air looms, which guarantees a high reliability - independently from the type of yarn being woven - and which is thus particularly suited to weave highly adherent yarns, as natural fiber yarns. Another object of the present invention is to supply a method as described heretofore, which does not require an excessive use of yarn, or too much compressed air consumption for its operation. A further object of the present invention is to supply a pneumomechanical pullout device, particularly suited to correctly carry out the method according to the invention. In particular, said device does not show the inconveniences of the known devices, as it excludes all possibility of accidental weft yarn breakage, guaranteeing moreover a high and long reliability of the optical sensors detecting said yarn. Said objects are reached with a method to automatically pull out a faulty weft from the shed in air looms according to claim 1. The aforespecified method is preferably carried out with a pneumomechanical device to automatically pull out a faulty weft from the shed in air looms according to claim 7. The invention will be described more in detail hereinafter, with reference to a preferred embodiment thereof, illustrated on the accompanying drawings, in which: Figs. 1 to 8 are diagrammatic views, illustrating the different steps to pull out a faulty weft from the shed of an air loom, according to the method of the present invention; Fig. 9 is a section view, on an enlarged scale, of the pneumomechanical pullout device used in said method; Fig. 10 is a partial view of the device shown in fig. 9, comprising the means to protect the photoelectric cell from dirt; and Fig. 11 is a front view of the device shown in fig. 10. According to the main characteristic of the method object of the present invention, the faulty weft yarn is pulled out from the shed, at loom outlet, by a pneumomechanical device allowing to pull out the faulty weft through the combined action of a suction device and of a mechanical intermittent drawing device. Said pneumomechanical device - as opposed to the known devices - allows to perfectly adjust the power of the maximum pulling force imparted on the weft yarn, thereby preventing its breakage in any condition. Since the faulty weft is pulled out at loom outlet - namely by being pulled backward - one obtains the additional advantage deriving from the peeling or adhesive tape effect, both in the pneumatic pulling out step and in the mechanical drawing step. The Applicant has accomplished the present invention after having considered that the automatic methods to pull out a faulty weft, proposed by prior art, do not guarantee a perfect quality of the fabric. In fact - as seen - with such methods, the pulling out of the faulty weft by means of mechanical devices may end up with the breakage thereof (a length of which may remain entangled in the shed), or with the misalignment of the warp yarns, even if a final signal of successful pullout has been issued, thus determining the automatic restart of the weaving operation. In this case therefore, unless there is someone to supervise the operations, the woven fabric will show defects such as the presence of incomplete wefts or of an irregular warp. While this circumstance could be considered acceptable in the case of weaving cheaper or more ordinary fabrics, it is instead an increasingly felt requirement - when weaving high-quality fabrics - to dispose of automatic devices to pull out a faulty weft yarn, which allow the loom to start again only in the absence of any possible defects in the fabric. As will be clear from the following description, the method according to the present invention fully reaches this object, as the mechanical drawing action to pull out the faulty weft is carried only to an extent such as not to break said weft, thereby preventing the presence in the fabric of broken wefts or of other defects. Figures 1 to 8 - which diagrammatically illustrate the weaving zone of an air loom - show the different steps to pull out a faulty weft yarn with the method according to the present invention. The nozzle 1, positioned at loom inlet, is the last member of the device feeding the weft yarn 2. Said weft yarn travels across the shed 3, launched by the action of the main nozzle 1 and of the secondary nozzles 4 positioned along said shed, up to reaching loom outlet. Along its path, the weft yarn 2 is arranged between the warp yarns 5, suitably parted, and is then beaten by a reed (not shown) against the fabric 6 being formed. At loom outlet there is positioned - in known manner - an optical sensor in the form of a photoelectric cell or like, apt to detect the correct arrival of the weft yarn and to send a warning signal, to stop the loom, in case said weft yarn - due to breakage, wrong feeding, or other causes - should not have completed its travelling path across the shed 3. According to the method of the present invention, when the yarn sensor positioned at loom outlet detects a faulty weft insertion (for instance, a short or broken weft, as shown in fig. 1), it simultaneously operates an automatic cycle to pull out the faulty weft, which comprises the following steps. First of all, loom braking is started and the yarn cutting device 11 positioned at loom inlet is simultaneously stopped from working, so that the faulty weft inserted in the shed remains physically connected to the weft yarn 2 being fed through the nozzle 1. At the same time, a weft turn 2a is released from the yarn feeding device, so as to prevent weft yarn breakage between the nozzle 1 and loom inlet, as reed beating up takes place. The turn 2a is held up by a blow device 8, to avoid that any excess yarn may enter the shed, entangling with the warp yarns. As soon as the loom has stopped (normally, before stopping, it performs at least one whole working cycle), it is started again in the opposite direction, so as to take the warp yarns back into the open shed position corresponding to the position of faulty weft insertion; the faulty weft is thus freed from the warp yarns and ready to be pulled out. During this whole step, the blow device 8 is operative while the cutting device 11 is at rest. At this point, the blow device 8 is stopped and the yarn feeding device releases a double weft, which is launched into the shed by the nozzle 1 and by the secondary nozzles 4, thereby forming a loop 7 which emerges from loom outlet and is sucked into the suction mouth 9 of a pneumomechanical pullout device 10 (fig. 2). An optical sensor 18 (figs. 9 and 10) detects the inlet of the loop 7 into the device 10 and operates the cutting device 11, which cuts the yarn downstream of the nozzle 1 (fig. 3) so that said yarn can be sucked into the device 10. The sucking action of the device 10 is now combined with the blowing action of the secondary nozzles 4, which are operated in sequence from the outlet to the inlet of the loom. If this exclusively pneumatic pulling action is sufficient to disentangle the faulty weft from the warp yarns (fig. 4), said weft will be fully sucked into and expelled from the device 10, so that the optical sensor will detect the absence of yarn, allowing the loom to start again. The power of the suction jet is regulated according to the mechanical strength of the weft yarn so as to prevent any possible breakage thereof. If, viceversa, the aforedescribed pneumatic action has not proved sufficient to disentangle the faulty weft from the warp yarns, the optical sensor will continue to detect the presence of weft inside the device 10 (fig. 5). After a certain time, the sucking action of the device 10 and the blowing action of the nozzles 4 are stopped, and the mechanical part of said pneumomechanical device 10 is operated (as shown in fig. 6). According to the method of the present invention, the mechanical action imparted on the weft yarn consists in an intermittent drawing action of modest amplitude (up to 1-2 cm), by which the weft yarn is urged to disentangle from the warp yarns. The amplitude of said intermittent drawing action is regulated according to the characteristics of the yarn being woven, so that in any case (i.e. even when it fails to disentangle) said yarn keeps within the range of its elastic deformations and thus incurs no danger of breakage. The mechanical action is then followed by a new pneumatic cycle (fig. 7) - equal to that previously described - and these cycles can be alternated several times, up to obtaining the full release of the faulty weft yarn, which is sucked into and expelled from the device 10 (fig. 8). The loom can then be started again, after having been suitably reset. If, after a predetermined number of pneumomechanical cycles, the optical sensor still detects the presence of weft yarn in the device 10, a stop signal is issued, requiring the presence of an operator. This allows to obtain a very high working reliability for what concerns the final quality of the fabric. The faulty weft is in fact automatically pulled out only when this can be done without breaking the same, or anyhow stressing it to an extent such as to disturb the arrangement of the warp yarns. In spite of this, thanks to the combined pneumatic and mechanical pulling actions, the yarn is successfully pulled out in a number of cases which can well be compared to that of the devices of prior art, without however presenting the drawbacks thereof. The pneumomechanical device 10 according to the present invention is illustrated in further detail in fig. 9. It consists of a casing 12, provided with a cylindrical cavity or duct 13 into which can be produced, by any known means, an air stream in the direction of arrow F. Such a result can be obtained for example by means of a suitably inclined blow device 14, leading into the duct 13. This latter is connected, at one end, to the already described suction mouth 9 - opening towards the shed 3, so as to easily suck in the loop 7 formed by the weft yarn 2 coming out from the shed 3 - and, at the other end, to the intermittent mechanical drawing device forming part of the pneumomechanical device 10. Said intermittent mechanical device consists of a pair of grippers 15, hinged onto a support 16. The grippers 15 can be closed by means of an electric or pneumatic control. The support 16 is apt to translate in a direction parallel to the axis of the duct 13, between a rest position 16 and a working position 16a (shown in dashes in fig. 9), under the control of a linear actuator 17, preferably of pneumatic type. The drawing stroke of the actuator 17 can be adjusted according to the elasticity of the yarn - as previously pointed out - so that the alternate pulling stress imparted on said yarn may always keep below its breaking value, with a fair margin of safety. As already mentioned above, the device 10 comprises - in known manner - an optical sensor, for instance in the form of a photoelectric cell 18, to detect the presence of weft yarn 2 inside said device. According to the present invention, means are provided to protect the photoelectric cell 18 from dirt, so as to guarantee a reliable working thereof for long periods of time and, at the same time, facilitate its cleaning. Said protection means mainly consist of a shutter 19 - illustrated in figs. 10 and 11 - movable between a working position 19 and a rest position 19a (shown in dashes in fig. 11), under the control of a preferably pneumatic linear actuator 20. In the working position, the shutter 19 fully closes the suction mouth 9 of the device 10, preventing the loom air stream from penetrating therein and depositing dust and oily residues on the surface of the photoelectric cell 18. The shutter 19 is operated simultaneously with the blow device 14 so as to keep the duct 13 open only for the time strictly required to allow the passage of the weft yarn. Said protection means can moreover comprise a device to screen the photoelectric cell 18, which will hence not come in direct contact with the air stream blowing through the duct 13. Said screening preferably consists of an antistatic glass tube 21, which has an inner section equal to that of the duct 13 and which faces the photoelectric cell 18. The inner surface of said tube can be very rapidly cleaned, whenever required, by simply introducing a brush into the suction mouth 9. It will be appreciated, from the previous description, how the method according to the present invention has fully reached the intended objects. It in fact allows to pull out a faulty weft yarn with a backward pull (peeling or adhesive tape effect) throughout the weft yarn length, including the weft tail. The power of the pulling action can moreover be controlled, both in the pneumatic and in the mechanical cycle, by suitably adjusting a power reducer of the blow device 14 and, respectively, the stroke of the linear actuator 17, according to the count and other physical characteristics of the yarn being woven. This hence allows to automatically pull out the faulty weft, without any inconveniences, even when weaving natural fiber yarns and, in particular, cotton fibers which combine a high adherence with a scarce mechanical resistance. It will be noted, furthermore, that the amount of weft yarn used up in this automatic operation is only that strictly required for the loopformed by the weft freely launched through the shed - to reach the pullout device, with considerable yarn saving in respect of the devices of known type. It is evident, from the previous description, that the present invention cannot be limited to the single embodiment described heretofore. It is in fact possible to change the type and positioning of pneumomechanical device, for instance by using friction windup devices or the like, without thereby departing from the scope of the invention as defined in the attached claims.

Claims: Method to automatically pull out a faulty weft from the shed in air looms comprising a main nozzle (1) and a plurality of secondary nozzles (4), of the type in which, when the weft yarn (2) does not reach loom outlet, the following steps are provided: to prevent the cutting of the weft yarn (2), and simultaneously to stop the loom; to reset the loom in the position of insertion of the faulty weft; to launch a free double weft through the shed (3), to let emerge from the outlet of the loom a loop (7) formed by the weft yarn (2), and to pneumatically suck or mechanically draw the weft yarn (2) characterized in that the pneumatic and mechanical pulling out actions on the weft yarn (2), are both performed at the outlet side of the loom, after a cutting device (11) has cut the weft yarn (2) at loom inlet, and in that said mechanical pulling out action is obtained by intermittently drawing the weft yarn (2). Method as in claim 1), wherein the pneumatic pulling out action is obtained by means of an air stream formed into an inner duct (13) of a pneumomechanical device (10), and by operating in sequence said secondary nozzles (4) from the outlet to the inlet of the loom. Method as in claim 1), wherein said intermittent drawing action has an amplitude such as not to stress the weft yarn (2) beyond its elasticity limit, in the event it should remain entangled in the warp. Method as in claims 1) and 2), wherein said pneumomechanical device (10) comprises weft yarn gripping members (15), positioned downstream of said duct (13), to impart said mechanical drawing action. Method as in claims 1) and 2), wherein the power of the air stream and the drawing stroke of the pneumomechanical device (10) are adjustable at will, according to the count and other characteristics of the yarns being woven. Method as in any one of the preceding claims comprising moreover - just after having detected the insertion of a faulty weft and having started to brake the loom - the step of releasing a weft yarn turn (2a) from the respective yarn feeding device and deviating said turn by means of an air jet towards a zone out of the shed (3). Pneumomechanical device to automatically pull out a faulty weft from the shed in air looms, at the outlet thereof, of the type comprising a suction mouth (9), apt to suck in the loop (7) formed by a double weft freely launched through the shed (3), an inner duct (13) connected to said suction mouth (9) into which there is formed a suction air stream, a sensor (18) facing said duct (13) to detect the presence of yarn, and yarn gripping members (15) positioned downstream and across said duct (13), characterized in that said yarn gripping members are movable in a direction parallel to the axis of said duct (13) to intermittently draw the yarn. Pneumomechanical device as in claim 8), wherein said yarn clamping members consist of a pair of grippers (15), hinged onto a support (16), alternately movable in a direction parallel to the axis of said duct (13), under the control of a pneumatic actuator (17). Pneumomechanical device as in claim 7), wherein said sensor (18) is an optical sensor and further comprising means to protect from dirt said yarn optical sensor (18), consisting in one or both of: a movable shutter (19) for said suction mouth (9), controlled by a pneumatic actuator (20). a screening for said optical sensor (18) in the form of an antistatic glass tube (21). Pneumomechanical device as in claim 7), wherein said suction air stream is produced by an inclined blow device (14) leading into said duct (13), the power of which can be regulated. Pneumomechanical device as in any one of claims 7) to 10), wherein the power of the air stream inside the duct (13) and the drawing stroke of the gripping members (15) are adjustable at will, according to the count and other characteristics of the yarns being woven.

Inventors: GRANELLI RENATO, GRANELLI, RENATO
Applicants: SOMET SOC MEC TESSILE, SOMET SOCIETA' MECCANICA TESSILE S.P.A.
Application year: 1992
Main classification: D03D51
IPC codes: D03D51