EP1079009A2

EP1079009A2 - Device and method to form the split selvedge in a weaving loom

Info

Publication number: EP1079009A2
Application number: EP00111570A
Authority: EP
Inventors: Dario Pezzoni; Diego Poletti; Adriano Zenoni
Original assignee: NUOVA VAMATEX SpA; Promatech SpA; SOMET Societa Meccanica Tessile SpA; Vamatex Nuova SpA
Current assignee: Promatech SpA
Priority date: 1999-05-31
Filing date: 2000-05-30
Publication date: 2001-02-28
Also published as: EP1079009A3; ITMI991221A1

Abstract

The invention concerns a device and a method to form the split selvedge in a loom, in which the device comprises independent motor means controlled by a central processing unit of the loom on the basis of the actual weaving parameters of each single weft, thereby varying the moment of mutual shifting of the selvedge yarns. It is thus possible to equalize the final tension level of the single wefts, independently from the weaving conditions and from the characteristics of the single weft being inserted, thereby obtaining, after cutting of the split selvedge, a fringe of uniform length even for fabrics woven with different wefts.

Description

The present invention concerns a device and a method to form the split selvedge in weaving looms, particularly gripper looms.
As known to the skilled in the art, in modern looms the split selvedge is used to keep the weft yarns tensioned during and soon after their insertion into the shed, and to allow a regular cutting thereof in order to produce fabrics having a uniform fringe of weft yarn tails. In fact, a group of warp yarns forming the split selvedge is placed at the two sides of the normal warp yarns meant to form the fabric, and at a certain distance therefrom, thereby forming a lateral extension of the warp shed.
Such selvedge yarns are guided by means of at least two yarn-guide elements, which alternately move them in groups in opposite directions, so that said yarns - as an extension of the warp shed formed by the warp yarns meant to form the fabric - are apt to form a lateral warp shed which opens and closes, housing the ends of the weft yarns. These last ones are then tied between the selvedge yarns according to a predetermined pattern, the so-called weave. Once the split selvedge has been thus formed it is possible, by acting thereon with tensioning devices such as the templets, to proceed to the cutting of the weft yarns - in the zone between the fabric and the split selvedge, where no warp yarns are present - at the desired distance from the edge of the fabric, and while the weft yarns are perfectly tensioned; this allows to obtain a lateral fringe of weft yarn tails of perfectly uniform length, and thus particularly appreciated for the high finishing level conferred to the fabric.
The conventional devices to form the split selvedge are moved, through a synchronized mechanism, by the main motion of the loom. This allows to accomplish certain types of weaves, for instance a one-one weave wherein a link is formed at each weft insertion, or else a two-two weave wherein a link is formed at each two successive weft insertions. To change from one weave pattern to another, it is necessary to replace some elements which operate the selvedge forming device - for instance the gearwheels - between the control lever and the main shaft of the loom. This replacement, besides involving a waste of time, forcedly requires to stop the loom thereby determining a slowing down of the production.
Such conventional devices equally allow, by adopting cam mechanisms, to form other weave patterns, for instance one-two weaves, wherein a first weft yarn is tied and the two subsequently inserted weft yarns are then tied together. To change the preset weave pattern, it is of course necessary to replace the cams of the mechanism, with the same inconveniences reported hereabove.
More recently, it has been proposed to adopt selvedge forming devices directly controlled by independent motor means, apt to change the type of weave in a much simpler and faster way. Examples of motors of this type are disclosed in the Patent Application WO96/38608 of Picanol, and in the Patent Applications EP-A-893.522 of Vamatex, and IT-MI99A 000646 of Somet. The contents of these last two patent applications are incorporated herein by way of reference, and are reported as known hereinafter in the description.
In this case, to form the wanted weave for the inserted weft yarns, the yarn-guide elements are moved forward and backward between their end positions by means of the motors described in the aforecited patent applications. Since the movement of such motors is fully independent from the main motion of the loom, it is possible to vary the timing of said motors in respect of the main motion of the loom, so as to obtain any desired weave. For example, if the yarn-guide elements are moved by said motors forward and backward between their end positions at each weaving cycle, a one-one weave is formed in the split selvedge. Whereas, if the forward and backward movement of the yarn-guide elements is completed at each two or three weaving cycles, a two-two or three-three weave is formed. It is also possible to cause such motors to operate alternate cycles between those cited above, so as to obtain a relative motion of the yarn-guide elements apt to form weaves at will, for example a one-two or a one-three weave.
This second type of selvedge forming devices has thus proved to be more versatile. Such devices are currently preferred also because, being free from any mechanical connection to the main motion of the loom, they can be easily mounted on a loom and removed again from the same. Furthermore, they can be applied on the frame of the loom, adjustable in respect of the loom width, so as to be used also in looms weaving fabrics of different widths, or more pieces of fabric.
In their searches on the known-type selvedge forming devices - briefly described hereabove - the inventors of the present invention have discovered the existence of an unpleasant drawback. In fact, in forming the split selvedge on fabrics woven with non-homogeneous wefts - as it typically happens, for example, with coloured fabrics - they were able to discover that, at the end of the weaving operations, the fringe of the finished fabric is not of uniform length, as in the case of a fabric woven with wefts of a single type of yarn.
In carrying out studies to find the cause for this drawback, they discovered that it depends on the fact that wefts having different weaving parameters (as count, volume, twisting degree, and the like) are stopped in slightly different times by the closing selvedge yarns. Consequently, the weft yarns are not all tensioned likewise, since those that are tied by the selvedge yarns in advance or delay in respect of the moment of maximum elastic stretching of the yarn, turn out to be more loose. In such conditions, when the split selvedge is removed from the fabric with a cutting device, the looser wefts are deviated from said device and are hence cut to a longer extent than the other wefts.
The object of the present invention is to thus overcome the aforementioned drawback, by supplying a device and a method to form the split selvedge, which allows to tie all the wefts with the same tension so that the fringe of the fabric, once it has been removed from the split selvedge, turns out to be of a perfectly uniform length.
According to the invention, said object is reached by means of a device as in the characterizing portion of Claim 1, and by means of a method as in the characterizing portion of Claim 6.
The invention will now be described in further detail hereinafter, with reference to the accompanying drawings, in which:
Fig. 1 is a diagrammatic front elevation view showing a gripper loom equipped with selvedge forming devices; and
Fig. 2 is a block diagram illustrating the device and the method to form the split selvedge, according to the present invention.
Fig. 1 diagrammatically illustrates a weaving loom T, of the type with grippers P and a weft yarn presenting device S, meant for weaving two pieces of fabric C. The top part of the loom comprises - fixed in an adjustable position to an upper crosspiece F of the loom - devices to form the split selvedge A and devices to form the leno heald weave B, all equipped with autonomous motor means, for example of the type described in the introductory part of the present description.
Each device to form the split selvedge A comprises at least one pair of yarn-guide elements, apt to move alternately and in opposite directions the warp yarns O_A meant to form the split selvedge A, just as done by the heald frames in respect of the warp yarns O_C meant to form the fabric C.
According to the present invention, by using the selvedge forming devices operated by means of linear motors or step-by-step motors of the aforedescribed type, it is possible to cause the moment of mutual shifting of the selvedge yarns to coincide with a very precise time of the weaving cycle, not only in a constant manner for a specific fabric, but individually on each inserted weft, thereby allowing to obtain a punctual and precise control on the stopping modes of each single weft.
To reach this result, the logic functions of the loom are modified as per the block diagram of fig. 2. According to this diagram, each time the central processing and control unit U of the loom sends instructions to the weft presenting device S to select a special weft, it contextually provides to interrogate a parametric table R, previously stored into a storage area of the same unit U, obtaining therefrom a default value of the moment of mutual shifting of the selvedge yarns, which is most appropriate for that particular weft. It then sends corresponding instructions to the selvedge forming devices A, to obtain the mutual shifting of the selvedge yarns exactly with the wanted delay or advance of the closing time, thereby varying the moment of mutual shifting of the selvedge yarns according to the weaving parameters of each single weft, and of the loom.
The parametric table R can, for example, be prearranged so as to contain all the possible sets of weaving parameters of the different wefts woven on the loom and of the different working conditions of the loom, associating to each of said sets a default value of the moment of mutual shifting of the selvedge yarns. The moment of mutual shifting of the selvedge yarns can thus be adapted to any weaving cycle, according to the type of weft, to the way in which the weft is inserted, to the preset channel of weft insertion, to the weaving speed, and to other variable working parameters of the loom. As an alternative, the parametric table R can be replaced by an appropriate algorithm which, on the basis of the weaving parameters concerning each single weft insertion, reckons each time the exact value of the moment of mutual shifting of the selvedge yarns. In this case, said algorithm can be provided with self-learning functions - well known to a technician skilled in the art - so as to optimize the reckoned result according to the results previously obtained in the same parametric conditions.
The two systems can of course be combined, selecting the most appropriate mode for each weaving parameter to be placed under control.
The selvedge forming device according to the present invention also allows, with a fully similar logic, to modify the type of weave not only for each fabric being woven - as done so far in known technique - but also for each weft or group of wefts. With the same modes described heretofore, it is in fact possible to control the motor means which operate the selvedge forming device A; said motor means are thus controlled to modify the length of their complete cycle, independently from the modifications concerning the moment of mutual shifting of the selvedge yarns, so as to change the weave according to the type of weft being woven, thereby achieving another important result to improve the weaving capacities of the loom.
In the previous description, reference has been made - for the sake of simplicity - to selvedge forming devices adopting one pair of yarn-guide elements, but it is obvious that the invention can equally include other embodiments wherein the selvedge forming device comprises more than two yarn-guide elements which, time after time, are controlled by a driving motor. For example, four yarn-guide elements can be provided which form each time a set of two yarn-guide elements moving in opposite directions. Each set is then controlled by an autonomous motor and by an autonomous drive shaft. This allows to form special weaves with more selvedge yarns.
From the above description, it clearly results that the present invention has fully reached the intended object, namely to be able to control the final tension level of each single weft, by adjusting for each single weft the moment of mutual shifting of the selvedge yarns. Such an adjustment can be carried out in any wanted manner, even by differentiating the closing times of the right-hand and left-hand selvedge of the fabric - always within the scope of the present invention - associating thereto also the most appropriate type of weave, without requiring any mechanical interventions or stops of the loom.

Claims

Device to form the split selvedge in a loom, of the type comprising at least two yarn-guide elements for the selvedge yarns, alternately moving in opposite directions to form a warp shed for the selvedge yarns according to a predetermined weave pattern, characterized in that it also comprises independent motor means to operate said yarn-guide elements, said motor means being controlled by a processing unit apt to vary the moment of mutual shifting of the selvedge yarns into every single weft insertion cycle, and/or the selvedge weave, according to the weaving parameters of said cycle.
Device as in claim 1), wherein said motors are step-by-step or linear motors.
Device as in claim 1), wherein said weaving parameters include the parameters characteristic of the weft yarn and the weaving conditions of said weft.
Device as in claim 1), wherein the default values of the moment of mutual shifting of the selvedge yarns and/or the type of weave are previously stored into a storage area of the central processing unit of the loom, according to the possible different sets of values of said weaving parameters.
Device as in claim 1), wherein the default values of the moment of mutual shifting of the selvedge yarns and/or the type of weave are reckoned, time after time for each weft insertion cycle, by the central processing unit of the loom, on the basis of the set of values of the weaving parameters of said cycle.
Method to form the split selvedge in a loom, of the type equipped with a central processing unit, in which a selvedge forming device comprising independent motor means alternately moves in opposite directions at least two yarn-guide elements for the selvedge yarns, forming a warp shed according to a predetermined weave pattern, characterized in that said central processing unit detects the set of weaving parameters concerning each single weft insertion, associates to said set of parameters a default value of the moment of mutual shifting of the selvedge yarns and/or a type of selvedge weave, and operates said motor means to obtain a movement of said yarn-guide elements for the selvedge yarns, apt to cause said value of the moment of mutual shifting of the selvedge yarns and/or said type of weave.
Method as in claim 6) wherein, into a storage area of said central processing unit there is previously stored a parametric table in which, to each set of possible weaving parameters for each single weft insertion cycle there corresponds at least a default value of the moment of mutual shifting of the selvedge yarns and/or a type of selvedge weave, and wherein said central processing unit detects the weaving parameters of each single weft insertion cycle, compares said parameters with those stored in said parametric table, and associates to said parameters the corresponding default value of the moment of mutual shifting of the selvedge yarns and/or said type of weave.
Method as in claim 6), wherein said central processing unit detects the weaving parameters of each single weft insertion cycle, reckons a default value of the moment of mutual shifting of the selvedge yarns and/or the type of selvedge weave, and associates to said parameters said reckoned value of the moment of mutual shifting of the selvedge yarns and/or said type of weave.
Method as in any one of claims 6) to 8), wherein said motors are step-by-step or linear motors.
Method as in any one of claims 6) to 8), wherein said weaving parameters include the parameters characteristic of the weft yarn and the weaving conditions of said weft.
Method as in any one of claims 6) to 8), wherein the default values of the moment of mutual shifting of the selvedge yarns and/or the type of weave are previously stored into a storage area of the central processing unit of the loom, according to the possible different sets of values of said weaving parameters.
Method as in any one of claims 6) to 8), wherein the default values of the moment of mutual shifting of the selvedge yarns and/or the type of weave are reckoned, time after time for each weft insertion cycle, by the central processing unit of the loom, on the basis of the set of values of the weaving parameters of said cycle.