Bank for warp stop motion in looms with automatic indication of the yarn breakage zone

Abstract: Bank for warp stop motion in looms, of the type consisting of a pair of parallel electroconductive and reciprocally insulated bars (6, 7) forming the two conductors of an electric circuit, in which a first outer U-shaped bar (6) has a substantially constant resistance in respect of the length, and a second inner flat bar (7) is divided into two or more adjacent and insulated sections, electrically connected through resistors (13) of preset value.

Description: The object of the present invention is a device to transmit electric contacts in the warp stop motion of a loom, known in the weaving field as "bank". As known, a warp stop motion is a device consisting of a series of parallel banks, positioned crosswise above the warp yarns and extending through the slots of a plurality of side-by-side drop-wires. Each warp yarn slides into a second slot formed in each drop-wire and, with its tension, it keeps said drop-wire suspended above the bank; in case of breakage of a warp yarn, the respective drop-wire will fall, by gravity, onto the underlying bank and will thus cause its working. The purpose of a warp stop motion is in fact to automatically indicate the breakage of a warp yarn and also locate its position, at least with a certain precision. Said indication determines the automatic stopping of the loom, allowing to subsequently mend the broken yarn. Loom stopping is obtained by means of an electric or electronic signal, produced by the closing of an electric circuit caused by falling of the drop-wire onto the bank. According to prior art, to reach this object the bank consists of a first rigid bar of electroconductive material, generally U-shaped, and of a second flat bar, also of electroconductive material, inserted into the U-shaped bar and slightly projecting therefrom, but separated from the same by an insulating lining. The falling of the drop-wire, determined by breakage of a warp yarn, puts in contact the first U-shaped bar with the second flat bar, closing the electric circuit and thus sending an electric signal which can be used to indicate yarn breakage. Said signal allows to obtain the immediate stopping of the loom and to locate the bank onto which the drop-wire has fallen, but not to locate the position of the broken yarn along said bank. This leads to a considerable waste of time, as it compels the operator to carry out a manual search among the thousands of drop-wires mounted on a single bank. The search is moreover not always easy, as it requires skill in causing the oscillation of the drop-wires, so as to visually locate the irregular oscillation occurring in correspondence of the fallen drop-wire. The object of the present invention is therefore to supply a bank comprising a signaling system, which allows to locate a limited section of the bank on which to carry out the manual search of the fallen drop-wire. In prior art, the warp stop motion normally comprises more than one bank (from six to eight), since the thickness of the drop-wires does not allow to mount on a single bank as many drop-wires as the total number of warp yarns existing in the loom. A first step of the search thus involves selecting the bank concerned with the falling of the drop-wire, and this can be easily obtained by providing each bank with a separate electric circuit; the electric signal issued upon closing of said circuit is in fact apt to supply an indication to the operator as to the bank on which to carry out the search. A second step involves locating, along the single bank, the position of the broken or loose warp yarn. This has been obtained with different solutions. A first solution contemplates forming, along a same bank, a flat bar consisting of several adjacent and partially superposed sections, separated one from the other by thin layers of insulating material, so that each flat bar section has its own tailpiece which reaches a same end of the bank and is thus apt to form an independent electric signaling circuit. This allows to positively locate the section of the bank on which to carry out the manual search. It can be easily understood how this system allows to restrict the field of search from a magnitude order of a few meters (typical of the size of a bank) to a magnitude order of several decimeters, hence not providing a solution of high precision. Moreover, the system thus conceived involves a very complex structure, which makes it very costly and greatly limits its practical application. A second solution is known from GB-A-2 117 017 which discloses a bank for warp stop motion in looms according to the preamble of claim 1. A third solution of banks with automatic search of the warp yarn breakage point is described in EP-A-276 206, according to which the flat bar is formed by winding a metal conductor into a spiral around an insulating core. One thus obtains a circuit with a linearly variable resistance according to the length of the flat bar, which allows to produce an electric signal proportional to the distance between the drop-wire fallen onto the bank and an end of the same bank. The theoretical precision of this system is no doubt greater than that provided by the previously described system and it is the greater, the higher the specific resistance per length unit of the conductive flat bar. For this reason, the spiral winding of the conductor, or other similar methods to artificially lengthen the path of the conductor - the length of the flat bar being unvaried - are particularly fit for this type of structure of the bank. Another way to obtain a bank with a fine precision, suited for a satisfactory practical use and not too complicated from the constructive point of view, is by spreading a conductive material of high resistivity over and along the flat bar. This method is described in the Italian Utility Model application MI91U-000593, of the same Applicant, wherein the flat bar consists of a support of insulating material onto which there is applied, by a painting or printing process, an heterogeneous liquid curable material having a particularly high electric resistivity. Nevertheless, the systems described both in EP-A-276 206 and in MI91U-000593 suffer from some drawbacks. The greatest problem involving the flat bar obtained by the combination of an insulating support and of a thin lining of conductive material - whether it be wound into a spiral or linearly applied - lies in the fact that the circuit is actually too fragile to stand the repeated impacts and abrasive action of the drop-wires, as well as any impacts which the linings of conductive material may undergo during assembly and disassembly of the whole warp stop motion device on the loom. The possibility that the continuity of the conductive material may be interrupted in some point represents a particular danger, since the whole area of the bank beyond said point would be cut off from the circuit, whereby the automatic stopping of the loom would not be guaranteed in case of breakage of a warp yarn in that area. A second equally important problem is determined by the changes of resistance due to dust depositing on the flat bar. Such dust deposits - in weaving environments not equipped with specific air cleaners - are very consistent and may vary, even considerably, the resistivity of said bar. This notably reduces the precision of the warp stop motion device in locating the position of the fallen drop-wire, thereby prejudicing the essential characteristic of these systems, unless one should make use of electronic devices to compensate for this "dust effect", which however increase the cost of the warp stop motion device to a very considerable extent. Said solutions therefore, though providing an optimal theoretical precision in determining the drop-wire falling point on the bank, end up by not guaranteeing the necessary reliability of the whole system and, consequently, do not provide a fully satisfactory practical application. It would hence be preferable, in a wide number of applications, to be able to dispose of a bank which, though not providing a high precision in locating the position of the drop-wire fallen on said bank, is however apt to indicate without fail a limited zone of the bank concerned with the falling of said drop-wire, and is also apt to positively guarantee the stopping of the loom in case of breakage or loosening of the warp yarns, independently from any misusages which the bank may have undergone while handling the same. Another important object of the present invention is to moreover supply a bank of the aforementioned type, which involves low costs and a sufficiently simple construction. These results are obtained with a bank according to claim 1. Further characteristics and advantages of the device according to the present invention will anyhow be more evident from the following detailed description of a preferred embodiment thereof, given by way of example and illustrated on the accompanying drawings, in which: Fig. 1 is a partial diagrammatic perspective view of a warp stop motion conceived according to the invention; Fig. 2 is a side elevation view of a preferred embodiment of a bank according to the invention; Fig. 3 is a cross-section view along the line III-III of fig. 2, on an enlarged scale, of one of said banks and of a drop-wire cooperating therewith; Fig. 3a is a section view similar to that of fig. 3, but showing only the bank (without drop-wire) on an even more enlarged scale; Fig. 4 shows, on an enlarged scale, the detail of fig. 2 enclosed in the circle IV; and Fig. 5 shows, on an enlarged scale, the detail of fig. 2 enclosed in the circle V. As shown in fig. 1, the electronic warp stop motion to which the invention is applied consists of a plurality of banks 5 (six in the drawing, but up to eight can be provided), the end sections of which engage into a pair of control blocks 3 (only one of them being shown in fig. 1) of the fast coupling type; each bank 5 comprises independent electric circuits for every single half thereof, apt to generate signal lights on indicators 1 and 2. A plurality of drop-wires 4 is mounted on each bank 5 which crosses the drop-wires through an elongated slot thereof allowing them to freely move verticalwise. The warp yarns, which run parallel to each other below the warp stop motion and transversely to the longitudinal axis of the banks 5, cross a second slot of said drop-wires 4 keeping them lifted and thus not in contact - during regular working of the loom - with the upper edge of the flat bar 7 of the respective bank 5. In this way the drop-wires 4, though adhering to the outer conductive surface of the U-shaped bar 6 of the bank 5, do not determine the closing of the respective circuit in that, being lifted by the warp yarns, they do not come in contact with the inner flat bar 7 of the bank 5; as soon as the breakage or loosening of a warp yarn causes the falling, by gravity, of a drop-wire 4, this latter closes the circuit between the inner flat bar 7 of the bank 5 and its outer U-shaped bar 6, producing the required electric signal. For this purpose, according to a preferred embodiment of the present invention and as clearly shown in figs. 3 and 3a, the bank 5 consists of: a continuous outer U-shaped bar 6 made from a metallic conductive material, whose top profile 6' is shown in fig. 4; a continuous U-shaped intermediate lining 8 of insulating material, whose top profile 8' is shown in fig. 4; and an inner flat bar 7, also made from a metallic conductive material - whose top profile 10, fret-shaped, is shown in fig. 4 - which is divided into two or more adjacent sections, interconnected by junctions of the type shown in the circles IV and V of fig. 2 and, in greater detail, in figs. 4 and 5. The outer U-shaped bar 6, the insulating lining 8 and the inner flat bar 7 are joined together by drawing of the outer bar 6 in correspondence of holes 14 formed into the inner flat bar 7, bushes 15 of a stiff insulating material and of depth equal to the thickness of the flat bar 7 having been previously housed into said holes 14. The inner flat bar 7 is split across its center line - as shown by IV in figs. 2 and 4 - into two sections of equal length, forming two independent electric circuits. Each of said sections is in turn divided into a number (for example from two to four) of sub-sections, which are series connected through junctions of the type shown by V in figs. 2 and 5. The splitting of the bar 7 into two reciprocally insulated sections allows to form in the bank 5 two independent electric circuits, each leading to a respective control block 3, and to thus immediately locate in which of the two circuits - and thus in which half - of each bank the falling of the drop-wire has occurred. The junction point between the two halves of the bar 7 (shown by IV) consists of a slanting cut 9, formed in the middle of the longitudinal axis of said flat bar, which allows to interpose a thin layer of insulating material apt to electrically separate the circuits of the two bar sections. It should be noted that - as stated hereinafter with reference to the junctions between the sub-sections of the bar 7 (shown by V) - the thickness of said insulating material, namely the distance between the adjacent sections of the flat bar 7, close to the upper edge of said bar, should be as small as possible in order to avoid that a drop-wire, which has fallen just in correspondence of the cut 9, may fail to be electrically detected. According to the invention, and as stated hereabove, to reduce even further the length of the bank 5 on which to carry out the search of the broken or loosened yarn, the two sections of the flat bar 7 are in turn divided into a number of sub-sections, having a length of a few decimeters, which are series connected with the interposition of discrete value resistors and through special junction elements of the type V shown in figs. 2 and 5. Thus, while along a given sub-section the resistance of the bar 7 is deemed to be substantially constant, between one sub-section and the next the value of the electric resistance changes considerably and abruptly - according to the value of said resistors - and consequently, there will be an easily perceptible variation in the value of the current intensity running through the circuit. It is evident that, by reading said current intensity, one can easily identify the sub-section in which the closing of the circuit has taken place. Said current intensity can also be read with low-resolution instruments, seen the high ratio between the value of the resistors interposed between one sub-section and the next and the neglectable inner resistance of the flat bar 7. The electric signal thus detected is not only apt to determine a stopping of the loom, but also to generate a double signal light by means of an indicator 1, which evidences the bank and its right or left section onto which the drop-wire has fallen, and of an indicator 2, which evidences the drop-wire falling zone along said bank. In the event of loosening of a warp yarn with intermittent release of the corresponding drop-wire, the signal light will be intermittent but will anyhow allow to locate the zone wherein to search the loosened yarn. According to a preferred embodiment of the invention, the flat bar 7 is obtained by forming its sub-sections into a suitable metallic material. The profile 10 of the upper edge of the bar 7 is fret-shaped so that, during the oscillations imparted manually on the bank while searching the fallen drop-wire, this latter can be easily led to follow the oscillating movement, and thus be evidenced among the thousands of adjacent drop-wires along the bank. Fig. 5 shows an embodiment of the junction between two sub-sections of the flat bar 7, of the type V. A first element 11 of conductive material is engaged, on one side, with the end of a first sub-section of the flat bar 7 through a dovetail joint, and on the other side, with two identical cross elements 12 of insulating material which are apt to connect, always by way of dovetail joints, said first element 11 and a second identical element 11a of conductive material, positioned specularly to the first and engaged, on the other side, with the end of a second sub-section of the flat bar 7. Such a junction is apt to guarantee a very solid assembly of the whole device, while providing a perfect electric insulation between the different sub-sections of the bank. To restore the continuity of the electric circuit, a resistor 13 of preset value is interposed, by welding, between the two conductive junction elements 11-11a, said resistor being housed into the space formed between two opposite arms of said two cross elements 12. To facilitate the welding process, the two elements 11-11a are made of brass or of similar materials having good characteristics of weldability. Along the upper edge of the junction V, the two conductive junction elements 11-11a should remain separate, but quite close, so that the distance d between them does not exceed a few millimeter tenths, for the same reasons explained heretofore in respect of the junction IV. The bank conceived according to the present invention has proved to possess a very stout structure, such as not to undergo any damage during handling thereof - which is often done without taking particular care - and, even less, to undergo damages due to abrasion or impact by the drop-wires; furthermore, its functionality can by no means be altered by any eventual dust deposits. A further advantage of the bank according to the present invention lies in the relatively low costs both of the materials used to produce the same and of its manufacturing process, which requires no special equipment either to obtain the inner flat conductive bar 7, or to form the junctions IV and V, which can in fact be easily assembled on the bench.

Claims: Bank for warp stop motion in looms, extending through the slots of a plurality of drop-wires (4) cooperating with respective warp yarns, of the type consisting of a pair of parallel electroconductive and reciprocally insulated bars (6, 7) forming the two conductors of an electric circuit, said bars (6, 7) being electrically connected by one of said drop-wires (4) in case of breakage of the respective warp yarn, so as to close said circuit and send a signal to stop the loom, wherein a first bar (6) has a substantially constant resistance in respect of the length, and a second bar (7) is divided into two or more adjacent and insulated sections, characterized in that, said insulated sections are electrically connected through resistors (13) of preset value. Bank for warp stop motion as in claim 1), wherein said first bar (6) is an outer U-shaped bar, and said second bar (7) is an inner flat bar. Bank for warp stop motion as in claim 1) or 2), wherein the junction (V) between two adjacent sections of said second bar (7) is formed by at least one element (12) of insulating material, and by two elements (11-11a) of conductive material having good characteristics of weldability, the terminals of said resistor (13) being welded to these last two elements (11-11a). Bank for warp stop motion as in claim 3), wherein the elements (12) of insulating material are two, formed as a cross, and positioned one above the other at a distance sufficient to allow housing between them said resistor (13). Bank for warp stop motion as in claims 3) and 4), wherein said elements (11-11a) of conductive material are of brass, they have an identical profile apt to house by fitting the lateral arms or said insulating cross elements (12), and they are specularly mounted and fitted into the adjacent ends of said sections. Bank for warp stop motion as in claims 4) and 5), wherein said elements (11-11a, 12) joining the sections are reciprocally engaged, and engaged with the ends of said sections, by way of dovetail joints. Bank for warp stop motion as in claim 1) or 2), wherein said second bar (7) has an upper edge with a fret-shaped profile (10). Bank for warp stop motion as in any one of the preceding claims, wherein said second bar (7) comprises moreover an insulating junction point (IV) in correspondence of its center line.

Inventors: BERNARDI LUIGI, BERNARDI, LUIGI
Applicants: ACTEX SPA, ACTEX S.P.A.
Application year: 1995
Main classification: D03D51
IPC codes: D03D51