WO2004072342A1 - Optical system for controlling the unbroken condition of warp yarns in a weaving loom - Google Patents

Abstract

Optical system for controlling the unbroken condition of warp yarns in a weaving loom wherein on optical reading device (11) is apt to detect a continuous succession of images of the warp yarns (0) as a whole, or of a subset of the same, and a processing unit (U) is apt to measure in a continuous manner one or more parameters of each of said images. The processing unit (U) sends a stop command to the loom and an eventual alarm signal when one of said parameters relative to the last acquired image differs, by a pre-established quantity, from a predetermined value of said parameter or from the value of such parameter measured in one or more of the images preceding the last acquired image.

Description

"OPTICAL SYSTEM FOR CONTROLLING THE UNBROKEN CONDITION OF WARP YARNS IN A WEAVING LOOM"

The present invention relates to an optical system for controlling warp yarns in a weaving loom. More particularly, the present invention relates to a system for controlling in a continuous manner the unbroken condition of warp yarns during weaving, thus functioning as a "warp stop motion device", as it is commonly referred to in the sector. The warp stop motion device is a device mounted in every type of loom and apt to promptly locate the breaking of a warp yarn, just during weaving, so that the loom can be immediately stopped and the operator can proceed to repair said warp yarn (i.e. to knot the broken ends of the same) before defective fabric is produced.

The breakage of a warp yarn always causes, in fact, a variation in the optimal tension set on said yarn during the weaving process, and said slacking (or, in the worst-possible cases, even lack of yarn) causes, obviously, unacceptable de- fects in the produced fabric.

Current weaving art uses two main types of devices for verifying warp yarns. A first, more widespread, type uses drop wire warp stop motion devices; a second type, used occasionally and only for very simple and low-quality articles, uses, instead, rotating brush warp stop motion devices. These two main types of devices for controlling warp yarns will be now briefly illustrated.

Drop wire warp stop motion devices are provided with a plurality of thin steel blades, which are commonly referred to as "drop wires", each of which is positioned over and around a single warp yarn, from which - due to the tension applied to the warp yarns by the loom - the dropwire is kept lifted above a transversal rod called "bank". Each bank - there are, in fact, usually several parallel banks in a loom - is provided with two conductive, usually metallic, elements consisting of an internal bar and an external shell having a U-shaped section, said conductors being reciprocally isolated, from an electric standpoint, by a film of insulating material. The two bank conductors are connected to an electric control circuit, so that, whenever a warp yarn breaks or slackens, the respective drop wire, no longer held up by the tension of the yarn, falls onto the underlying bank and closes the electric circuit formed by the two conductive ele- ments of the bank. As soon as the drop wire falls down, an apposite electronic control device immediately stops the loom and, at the same time, emits a warning signal for the operator and a signal indicating the bank on which the drop wire has fallen and, sometimes, even the approximate location where the fall has taken place.

While drop wire warp stop motion devices generally have the advantage of providing a prompt intervention upon breaking of the yarn, however, they also show several disadvantages. First of all, they require a long set-up time, since on every one of the thousands of yarns that make up the warp a drop wire must be inserted. Bigger weaving plants are often provided with special automatic machinery for this type of operation, but, in any case, it is a complicated, long and, therefore, very costly operation. Due to the high number of drop wires mounted on a bank - normally thousands or tens of thousands - searching the fallen drop wire, in spite of the numerous electronic and mechanical devices designed to simplify this task - always requires a certain level of expertise by the operator and a relatively long execution time.

Moreover, because of the rubbing caused by the warp yarns relative to the drop wires, wear damage of the drop wires takes place, which drop wires, especially when using highly abrasive yarns, must then be replaced periodically. Furthermore, when using particularly delicate synthetic yarns like, for example, those for high quality lining, organza or other similar products, the rubbing of the drop wire against the yarn causes a damage of the same as well, that can lead to a breakage of the yarn.

Another inconvenience is then represented by false stops of the loom, an inconvenience that is particularly evident in weaving delicate yarns, where a low tension of the warp yarns is required. In fact it is possible, in these cases, that the typical oscillation of the drop wires, due to the rhythmic movement of the warp, is sufficiently broad to generate at times false contacts on the bank, with the consequent stop of the loom, even in the absence of any breakage or slacking of a warp yarn. A similar inconvenience, i.e. the stop of the loom caused by false contacts signalled by the bank control circuit, can occur as well because of bunching of electrostatic charges on the warp yarns - phenomenon caused by the rubbing of warp yarns against the drop wires and particularly evident when synthetic yarns are woven - which cause in an unpredictable manner discharge currents on the banks. These currents close the bank electric circuit momentarily and, therefore, give a temporary false indication of breakage of the warp yarns . The bunching of electrostatic charges on the warp yarns is also responsible for a further inconvenience that is present in the drop wire warp stop motion device, i.e. that of the electrostatic adhesion of one or more warp yarns. The electrostatic adhesion force is in fact sometimes sufficient to exceed the weight of a drop wire so that, even in the case of a breakage of a warp yarn, the relative drop wire is held up by the adjacent yarns and the breakage is not detected.

The rotating brush warp stop motion devices (shown in Figures 2 and 3) include a device G transversally positioned under the warp yarns - comprising a linear bristle brush C and a harmonic yarn D stretched in a position diametrically opposite to that of the brush C - that rotates continuously at a low speed, periodically brushing the warp yarns. In case one of the warp yarns breaks, the brush C is apt to "capture" the same during its rotation and to drag it therewith by wrapping the broken yarn around the rotation axis of the device G. During this anomalous movement of the broken warp yarn E, the yarn itself exerts a progressive pressure upon the harmonic yarn D so that said yarn takes the deformed configuration shown in Figure 3A and, therefore, by shortening, activates a traction contact H that stops the loom.

The rotating brush warp stop motion devices offer the advantage of avoiding altogether the presence of drop wires along with relative inconveniences, but are characterized by the big drawback of being unable to promptly signal the breakage of the yarn, signal that, as a matter of fact, takes place with a delay depending from the relative position of the brush in respect of the warp yarns at the moment of breakage of the yarn. So it can happen that the stopping of the loom, following the breakage of the yarn, takes place only after several tens of beatings, causing thus obvious and serious defects in the fabric.

An improvement of this type of warp stop motion device has been obtained using, along with the brush and instead of the harmonic yarn, the ray of an optical device, such as a photoelectric cell or a laser, that "intercepts" and pinpoints ^' more rapidly the broken yarn captured by the brush. Even in this improved type of warp stop motion device, though to a lesser degree, the problem of a delay in the signalling and relative stopping of the loom still exists, so that the brush warp stop motion device is used, as already mentioned, exclusively for the weaving of products in which the quality of the fabric is not so important, like, for example, for lining.

Object of the present invention is, therefore, to provide a new type of optical system for controlling the unbroken condition of the warp yarns in a weaving loom, apt to promptly signal the breakage or slacking of warp yarns, so as to avoid any warp defect in the fabric, and to eliminate the above discussed main inconveniences of the drop wire warp stop motion devices, i.e.: long set-up time, drop wire wear, warp yarn deterioration, false signals of broken warp yarns or, on the other hand, missed signals of said breakage due to electrostatic adhesion phenomena between the yarns.

In particular, an important object of the present invention is to eliminate the presence of metallic drop wires associated with every warp yarn. This way, both the warp long initial set-up step and the negative consequences due to the rubbing physical contact between drop wires and warp yarns would be automatically eliminated.

A system for controlling warp of this type would meet a highly-demanded need in the sector, a need that up till today has not been addressed, i.e. the possibility to have a warp stop motion device that has the same effectiveness in terms of a quick breakage detection, than the drop wire warp stop motion device, but that presents lower operational costs and that considerably contributes to the reduction of total num- ber of stops of the loom, just like the brush warp stop motion device does.

Such object is achieved, according to the present invention, through an optical system for controlling the unbroken condition of the warp yarns in a weaving loom having the fea- tures disclosed in claim 1) , appended below.

The present invention will, anyway, be better understood through the following description of some of its preferred embodiments, shown in the appended drawings, wherein:

Figure 1 is a schematic side view of a loom, wherein a schematic block diagram of the optical system for controlling the unbroken condition of warp yarns according to the present invention is inserted;

Figure 2A is a front view of a prior art device of a brush warp stop motion device;

Figure 2B is a side view of the warp stop motion device of Figure 2A, inserted among the main elements of a loom with which it works;

Figures 3A and 3B are views corresponding to Figures 2A and 2B during the detection of a broken warp yarn.

In Figure 1, following the direction of the fabric as it is woven, are shown: warp beam S, warp yarn cylinder F, warp yarns 0, heald frames Q, comb P and fabric cylinder R of woven fabric T. According to the innovative basic idea of the present invention, the control of the unbroken condition of warp yarns is obtained by examining an image of the warp yarns as a whole, or of a subset of the same, through an optical reading device 1 and by then processing in an appropriate way the images acquired by said reader through a process- ing unit U, that can usefully be the same processing unit currently used for controlling the operation of the loom.

Preferably, the optical reader 1 is mounted above the plane formed by warp yarns 0, so that a plan view of the same is taken, i.e. an image in which all warp yarns are clearly visible. The image definition can be improved by having, in correspondence of the optical reader and on the opposite side of warp yarns 0, a light source L so as to increase, in the acquired image, the contrast between warp yarns 0 and the background of the image itself. As mentioned above, the ac- quired image can comprise the warp yarns as a whole or a subset of the same; in the latter case, i.e. when the shooting field of the optical reader 1 does not comprise all warp yarns, the complete monitoring of the same is achieved by using several appropriately offset optical readers. The optical reader can be both a spot type such as, for example, a video camera, and a linear type such as, for example, a continuous bar of optical readers of the type used for scanners . A preferred position, particularly from a mechanic point of view, for the installation of the optical reader and the relative light source is the one shown in the drawing, i.e. immediately upstream of the group of heald-frames in the direction of movement of the fabric; this area, in fact, is sufficiently free of other service devices and other loom accessories. The fact that in that area the warp yarns are subjected to a strong and periodic spreading apart, caused by heald-frames Q for shed formation, does not constitute any. problem. In fact, it is possible, first of all, to make coin- cide the image-taking time with the shed-closing time, when warp yarns 0 are all perfectly aligned. Alternatively, it is possible to freely chose the image-taking time, particularly when it is preferred to have a image-taking frequency higher that the beating frequency of the loom, by suitably adapting the optical reader depth of field.

The position of the optical reader 1 is not, anyway, critical for the operation of the present invention. Where textile or installations reasons so request, it is, therefore, possible to install the same in other positions as well. In the drawing two other possible installation positions of the optical reader are shown: position 2, immediately downstream of the weft yarn cylinder F and position 3, immediately upstream of the comb P.

The images of warp yarns 0 are sequentially acquired by the optical reader with a minimum frequency equal to the working frequency of the loom, so that if a warp defect is detected, the loom can be stopped at the latest during the first or second beating after the detection of the defect and the defect can, therefore, quickly be eliminated after even- tually executing a corresponding number of reverse beatings of the loom.

According to the invention, the presence of a warp defect, such as, for example, a broken warp yarn or a slackened warp yarn, is detected by the processing unit U by measuring one or more parameters of the last acquired image and by comparing each of said parameters with a predetermined value for that parameter, or with the value that the same parameter had in one or more of the images before the last acquired image. In a first embodiment, the considered parameter is the number of warp yarns. The processing unit U counts, on the image acquired by the optical reader 1, the number of warp yarns and then compares the result of such calculation with a predetermined value that, in this case, is the total number of warp yarns mounted on the loom (or the total number of warp yarns the group of warp yarns resulting from the image, if the image does ^'not include the warp yarns as a whole). The predetermined value of the number of warp yarns can be known to the weaver and he can manually enter it into the process- ing unit U, or the unit itself can use the result of the calculation made on the first acquired image, at the very beginning of the weaving process and preferably when the loom is standstill, i.e. when all warp yarn are still perfectly unbroken. When, during the analysis the last acquired image, the processing unit detects that the number of warp yarns is different, by a pre-established quantity, from the above- mentioned predetermined value, it sends a stop command to the loom main engine M and, simultaneously, emits an alarm signal A to alert the weaver that a manual repair operation of the loom is requested. The above pre-established quantity that causes the alarm mechanism to sound is usually equal to 1.

In a second embodiment of the present invention, the considered parameter is the overall pattern formed by the warp yarns of the acquired image. The processing unit U, in this case, compares, pixel by pixel, the last acquired image with the one immediately preceding the same - or an image obtained by the average values of the last acquired n images - causing the loom to stop only when the number of pixel deviations between the two images is higher than a pre-established quantity. Such a quantity will, in this case, have to be determined experimentally, according to the type of yarns used and other weaving conditions as well; in particular, such quantity will have to be high enough to exclude small lateral movements which warp yarns may undergo as possible causes of alarm conditions, and low enough to allow the signalling of deviations which a warp yarn undergoes due to slacking or breakage of the same. It should then be considered that by having completely eliminated - according to the present invention - metal drop wires of traditional warp stop motion devices, all electrostatic phenomena caused by the rubbing between warp yarns and such drop wires have correspondingly all the same been elimi- nated. It is, therefore, clear that in case of breakage or slaking of a warp yarn, said yarn will position itself in a much more deformed configuration than in a loom with a traditional drop wire warp stop motion device.

In a third embodiment of the optical control system of the warp yarns according to the present invention, the considered parameter is the parallelism of warp yarns. The position of every warp yarn detected in the image is, therefore, compared with that of an ideal yarn placed according to a predetermined direction, and the deviation between the two images is determined. The predetermined direction can be manually input into the processing unit U; on the contrary, it can be automatically detected by the same, based on the direction of the warp yarns when the loom is standstill, before the beginning of weaving operations. The deviation can, for example, be calculated as pixel percentage of the image of every single warp yarn that is aligned along said predetermined direction, by causing the loom to stop only when the value of said percentage is lower than a pre-established quantity. Even said pre-established quantity will have to be experimentally determined according to the weaving type and conditions, and will have to be high enough to exclude error signals caused by small angular variations which warp yarns undergo due to movement of heald- frames, and instead low enough to comprise every possible deviation from said predetermined direction which a warp yarn undergoes due to slacking or breakage of the same.

In a fourth embodiment, the considered parameter is the position of every warp yarn, and such position is compared with that taken by the same warp yarn in the previous image, or in an image formed by the average data of the last previous n images, by detecting the deviation between the two images as the number of pixels of the representation of every single yarn which do not coincide with the ones of the previ- ous image. To make the breakage or slacking of the warp yarns more easily detectable from the possible small lateral and angular movements of said yarns caused by normal weaving operations, it is possible to give a higher weight to the deviation of every single pixel as larger the lateral distance relative to the position of the warp yarn of the previous image, or when the deviations are bilateral instead of monolat- eral.

The stop function of the loom and the determination of the predetermined deviation quantity above which such func- tion is determined are similar to those described in the above-mentioned third embodiment and are not, for the sake of brevity, further described herewith.

Differently from what happens in the second embodiment, the stop command of the loom in the third and fourth embodi- ments is given following a verification of the deviation in respect of the predetermined values measured on every single warp yarn, instead of on the entire acquired image. It is therefore generally possible, in these embodiments, to dis- tinguish with a higher precision degree between small movements of warp yarns due to normal weaving operations and larger movements caused instead by a breakage or slaking of the yarns themselves.

In a fifth and last embodiment, currently preferred, the considered parameter is the theoretical diameter of the warp yarns. In this case, a bar linear optical reader having a high number of optical readers is used, so that resolution is at least equal to the theoretical diameter of the warp yarn and preferably 1/2 or, even better, 1/4 of the same. An opti- cal reader of this type is in fact capable of detecting not only the presence or absence of the yarn, but also of detecting a progressive thinning thereof - when a breakage occurs not all of a sudden but due to a progressive wear of the yarn - by anticipating therefore the error signal and the stop of the loom in respect of the moment of breakage.

It should be clear that the present invention has been described with particular reference to some preferred embodiments of the same, whose aim is however merely illustrative of some possible working ways of the invention, without, how- ever, that the present invention should be considered as limited to such embodiments. There should be, therefore, foreseen other possible embodiments in which the above-described parameters can, for example, be variously combined or combined with or substituted by other parameters according to combinations that will, based on each situation, be considered more convenient or practical for the single specific applications, without departing from the scope of the invention as it is defined by the appended claims.

Claims

1) Optical system for controlling the unbroken condition of warp yarns in a loom characterized in that it comprises an optical reading device apt to detect a continuous succession of images of the warp yarns as a whole, or of a subset of the same, and a processing unit apt to measure in a continuous manner one or more parameters of each of said images, and in that the processing unit sends a stop command to the loom and an eventual alarm signal when one of said parameters relative to the last acquired image differs, by a pre-established quantity, from a predetermined value of said parameter or from the value for such parameter measured in one or more of the images preceding the last acquired image.

2) Optical system as in Claim 1), wherein said parameter is the warp yarn theoretical diameter.

3) Optical system as in Claim 2) , wherein said optical reading device is a linear optical reader with resolution at least equal to the yarn theoretical diameter and ^' preferably equal to 1/2 or, even more preferably, 1/4 of said diameter.

4) Optical system as in Claim 1), wherein said parameter is the number of warp yarns and said pre-established quantity is equal to or greater than 1.

5) Optical system as in Claim 4), wherein said predeter- - mined value of the number of warp yarns is manually input into the processing unit.

6) Optical system as in Claim 4), wherein said predeter- mined value of the number of warp yarns is automatically set by the processing unit as being equal to the number of warp yarns detected in the first acquired image.

7) Optical system as in Claim 1), wherein said parameter is the overall pattern formed, at pixel level, by the warp yarns in the acquired image, and said pre-established quantity is a number of pixel deviations experimentally determined, according to weaving type and conditions, high enough to exclude small lateral movements which warp yarns undergo during weaving and low enough to comprise the deviations which a warp yarn undergoes due to slacking or breakage of the same.

8) Optical system as in Claim 7), wherein said measured value is the pattern formed by the warp yarns in the image preceding the last acquired image.

9) Optical system as in Claim 7), wherein said measured value is a pattern formed by the average data of the warp yarn patterns in the n images preceding the last acquired image . 10) Optical system as in Claim 1), wherein said parameter is the parallelism of the warp yarns, determined as pixel percentage of the image of every single warp yarn which are aligned along a same predetermined direction, and said pre- established quantity is a pixel percentage deviation, deter- mined experimentally according to weaving type and conditions, high enough to exclude small angular deviations which warp yarns undergo due to the movement of the heald- frames and low enough to comprise the deviations from said predetermined direction which a warp yarn undergoes due to slacking or breakage of the same.

11) Optical system as in Claim 10), wherein said predetermined direction of the warp yarns is manually input into the processing unit.

12) Optical system as in Claim 10), wherein said prede- termined direction of the warp yarns is automatically set by the processing unit as being equal to the average direction of the warp yarns in the first acquired image.

13) Optical system as in Claim 1) , wherein said parameter is the position of the warp yarns, determined for every single warp yarn with reference to a previous image of the same warp yarn, and said pre-established quantity is a number of pixel deviations, determined experimentally according to weaving type and conditions, high enough to exclude small movements or angular deviations which warp yarns undergo during normal weaving operations and low enough to comprise the deviations from said position in the previous image which a warp yarn undergoes due to slacking or breakage of the same.

14) Optical system as in Claim 13), wherein said previ- ous image of the warp yarn is an image formed by the average data of n images of the warp yarn preceding the last acquired image .

15) Optical system as in Claim 13) , wherein in determining said number of deviations a bigger weight is given to any deviation as larger its lateral distance relative to the warp yarn position in the previous image, or when said deviations are bilateral instead of monolateral.