WEFT ACCUMULATOR FOR WEAVING MACHINES

Abstract: Weft accumulator for weaving machines, with the characteristic that it consists essentially of a combination of a) a means for drawing off a predetermined length of yarn with a predetermined speed from a weft supply package, and b) at least one perforated cylindrical tube 1 fitted with an airblower 2 at one end 3 in order to introduce the yarn 11 into the cylindrical tube 1 in a quantity of a maximum of one pick length, and with at the other end 5 a yarn clamp or yarn stop device 4 through which the yarn 11 is drawn out of the cylindrical tube 1.

Description: This invention concerns a weft accumulator system for weaving machines, namely a device which provides an intermediate supply of yarn when yarn is being led from a bobbin or other weft supply package to the shed. Providing an intermediate supply is common technology, the main object being to ensure a continuous speed of unwinding from the yarn package while yet enabling the pick to be inserted into the shed in a discontinuous manner. Various types of weft accumulator systems are known. These are described below. Certain types of weft accumulators are known in which a free loop is formed in the weft yarn. Such a device is described amongst others in Swiss patent No. 409,816, in which the weft yarn is blown into a free loop by means of an airstream. The next pick insertion then pulls the loop straight again. The main disadvantage of this system is that when the pick is inserted, the thread has to be pulled straight against the force of the airstream, and so has to overcome a fairly strong resistance. Another very common type of weft accumulator uses a weft prewinder. In this system, the weft yarn is wound temporarily on a prewinder drum, and is then taken from the drum when the next pick is inserted. It is well known that the resistance necessary to pull the thread free from the prewinder drum is fairly great, thus limiting the yarn velocity during picking. In yet other known types of weft accumulator system, the weft thread is deposed in a mainly zigzag pattern on a flat surface, in other words forming several free loops. Such a system is described amongst others in French patent No. 519.477, in which the weft thread is placed on a moving belt. The most important disadvantage of this type of accumulator is that the loops offer a large resistance when they are drawn off the belt, since the belt cannot be perfectly smooth. A certain amount of roughness is necessary to prevent the loops slipping off or piling up together when they are laid on the belt. Other disadvantages include wear and tear of the parts, since a mechanical drive is required, and accumulation of dust, since the system is necessarily open. In another system, described in French patent 1.449.084, an intermediate supply is provided by placing the weft yarn in a stretched condition in a perforated tube. One of the objects of the present invention is to avoid all of the above disadvantages. Another object of the invention is to provide a weft accumulator system that guarantees a number of advantageous characteristics. The main such characteristics are: the weft accumulator described in the invention takes up little space; the resistance encountered in drawing off the yarn from the accumulator is so low as to be almost negligible; the yarn cannot become tangled; and the system can be used for most types and thickness of yarn. The present invention also concerns a weft accumulator system for weaving machines with the advantage that it mainly consists of a combination of a) a means of drawing off a predetermined yarn length at a predetermined speed from a supply package, and b) at least one perforated, cylindrical tube, one end of which is fitted with an airblower for blowing a quantity of yarn (maximum length equal to one pick) into the tube, and the other end of which has a yarn clamp or yarn stopper device through which the yarn is led out of the tube. The abovementioned advantages are achieved in particular by means of a preferred embodiment characterized by the use of a perforated cylindrical tube with a very small internal diameter, of the order of 10 mm or smaller. In order to explain the characteristics of the invention, for the sake of example only and without being limitative in any way, the following preferred embodiments a re described below with reference to the accompanying drawings, where: - fig. 1 represents the weft accumulator system of the invention; - fig. 2 shows a cross-section along the line II-II in fig. 1; - fig. 3 shows a cross-section along the line III-III in fig. 2; - fig. 4 shows a cross-section along the line IV-IV in fig. 2; - figs. 5 and 6 illustrate the operation of the system of the the invention; - fig. 7 shows a variant of the accumulator system of the invention, according to a similar view as in fig. 2; - fig. 8 shows a cross-section of a variant of the cylindrical tube; - fig. 9 shows an airblower device which is preferably used for the weft accumulator system of the invention; - fig. 10 shows a special embodiment concerning the holes in the perforated cylindrical tube; - fig. 11 shows a variant of the weft accumulator system of the invention, in which the cylindrical tube is divided into two parts; - fig. 12 shows yet another variant of the weft accumulator system of the invention, in which two perforated cylindrical tubes are used. As can be seen from figs. 1 to 4, the weft accumulator system of the invention consists in principle of at least one perforated cylindrical tube 1, an airblower 2 mounted on one end 3 of the tube 1 with the nozzle pointing into the tube 1, and a yarn clamp or yarn stopper 4 mounted on the other end 5. A number of yarn supply devices are also provided, eg. the rollers 6. Fig. 1 also shows how the accumulator is positioned with respect to certain other conventional parts of the machine 7, in particular the weft supply package 7A and the main nozzle 7B. The weft accumulator should preferably be constructed so that the blower 2 and the yarn clamp 4 fit on the ends 3 and 5 of the tube 1, and so form the end closures of the tube. The airblower 2 can of course be a conventional injector. The yarn clamp 4 in its simplest form can consist of two rectangular clamping blocks 8A and 8B whose plane of contact 9 lies in the diameter of the tube 1 and is preferably horizontal. The perforations 10 should preferably be distributed evenly over the wall of the tube 1. Thus the openings 10 can be situated in axial planes with respect to the tube 1, so that these planes, are separated from each other by a constant distance A, as shown in fig. 2. The operation of the weft accumulator is described in essence below. A weft length 11 is led via the weft supply rollers 6, where the length should preferably be measured out, to the airblower 2. This blower or injector 2 blows the yarn 11 into the tube 1. The thread piles up at the clamp 4 so as to form coils 12 against the inside wall of the tube 11. The fact that the coils 12 lie neatly and evenly against the inside wall of the tube can be explained as follows. When the tube 1 is empty, as shown in fig. 5, the airstream 13 from the airblower carries all the air to the end 5 of the tube 1. It is therefore clear that, as shown schematically in fig. 5, the greatest quantity of air escapes through the perforations 10 nearest the clamp 4. As a result, the yarn 11 inside the tube 1 begins to coil at the end 5 of the tube 1. This results in slightly less air escaping through the very last perforations, since they are blocked by the coils 12. Since a greater proportion of air is thus force to escape through the still unobstructed perforations, the yarn 11 always comes to lie against the already formed coils 12. The coils 12 are held against the inside wall of the tube 1 by the residual air flow through the perforations 10A against which the thread 11 lies. The warp yarn 11 can then be drawn out of the tube 1 when the clamp 4 is opened. Fig. 7 shows a variant of the invention in which the perforated cylindrical tube has one or more large openings or perf orations 14 at the end 3 nearest the airblower 2. This avoids the air blown in by the airblower 2 not being able to escape when the tube 1 is nearly full, and thus prevents the coils 12 being blown over one another as a result. Excess air can always escape through the relatively large openings 14. The direction in which the yarn 11 should preferably be coiled inside the tube depends on the yarn twist. The yarn 11 should preferably be coiled inside the tube 1 so that it is always partially untwisted. However, if the thread 11 is coiled inside the tube 1 so that it is twisted even more, this will not cause problems; tests have always shown that the direction of the coils in which the yarn 1 is laid inside the tube 1 reverses spontaneously at a certain moment. In order to improve the airflow inside the tube 1, and in particular to encourage the weft yarn 11 to coil in a particular direction, special measures can be taken according to a number of preferred embodiments. In a first variant for this purpose, each perforation 10 in the tube 1 lies at an angle to the corresponding radius 15 of the tube, in a particular direction of rotation, as shown in the cross-sectional diagram in fig. 8.. Another preferred embodiment uses an airblower or injector which has a nozzle with spiral grooves 16 in order to impart a vortex motion to the airstream 13 blown into the tube 1. This vortex motion forces the weft thread 11 to coil in a particular direction. In yet another embodiment, the warp thread 11 is encouraged to coil in a particular direction by positioning the perforations 10 in one or more spiral lines round the wall of the tube 1, for example as shown in fig. 10. If the diameter of the cylindrical tube 1 is made very small, of the order of 1 cm or smaller, preferably as small as 3 mm, this has the added advantage that the yarn 11 can be drawn out of the cylinder 1 with a minimum of resistance, thus giving a weft supply with extremely low tension. The tube 1 can of course be made of a large number of materials. However, it should preferably be made of some transparent material so that the behaviour of the yarn 11 inside the tube 1 can be checked visually. It is well known that at high picking speed the weft yarn 11 must not be braked suddenly while it is being supplied, otherwise there is a real danger of breaking it. Figs. 11 and 12 show embodiments of the weft accumulator of the invention which offer a particular solution to this problem. In the embodiment shown in fig. 11, the perforated cylindrical tube 1 is divided into two in-line sections 1A and 1B by an adjustable yarn brake 17 mounted approximately in the middle of the tube 1. This yarn brake 17 can consist for example of two brake shoes 18 and 19 which form a complete closure. The yarn clamp 4 and the yarn brake 17 are worked in such a way that the following operation cycle is repeated throughout the weaving process. When the yarn clamp 4 is closed, section 1B of the cylinder is filled. At a certain moment the yarn brake 17 is closed, so that section 1B then contains an initial length of yarn L2 equal to the length which has to be provided during acceleration of the pick plus the remainder of the pick at normal picking speed. An additional length L1 is next introduced into section 1A of the cylinder 1, equal to the length which has to be inserted into the shed during the deceleration stage. To start the pick, the yarn clamp 4 is opened, and the initial yarn length L2 is taken from section 1B, accelerated and led through the shed. The brake 17 excercises a relatively light braking force on the weft yarn 11. This provides the necessary braking when the last length of weft yarn to be inserted into the shed is drawn from the accumulator, ie. the length contained in the first section 1A of the cylinder 1. In a variant of the embodiment shown in fig. 11, two accumulators of the type shown in fig. 1 can be placed in series, for example as shown in fig. 12. However, in this case the first accumulator is fitted with a yarn brake 17 and the second with a yarn clamp 4. The operation of the configuration shown in fig. 12 may be analogous to that of the variant shown in fig. 11. In each of these figures, corresponding parts are indicated with the same numbers. It is clear that the term "perforated cylindrical tube" must be taken to include all tubes with a circular section as well as other tubes with a regularly curved inside wall, eg. with an elliptical section. The present invention is not limited to the embodiments described herein by way of example and shown in the accompanying figures; on the contrary, such weft accumulators for weaving machines, together with their components, can be made in all forms and dimensions while still remaining within the scope of the invention.

Claims: 1. Weft accumulator for weaving machines, with the characteristic that it consists essentially of a combination of a) a means for drawing off a predetermined length of yarn with a predetermined speed form a weft supply package, and b) at least one perforated cylindrical tube 1 fitted with an airblower 2 at one end 3 in order to introduce the yarn 11 into the cylindrical tube 1 in a quantity of a maximum of one pick length, and with at the other end 5 a yarn clamp or yarn stop device 4 through which the yarn 11 is drawn out of the cylindrical tube 1. 2. Weft accumulator as in claim 1, with the characteristic that the yarn brake 4 consists of two brake shoes (8A and 8B) which close the cylindrical tube 1. 3. Weft accumulator as in claims 1 or 2, with the characteristic that at the end 3 nearest the airblower 2 the perforated cylindrical tube has openings which allow a relatively larger air escape than do the normal perforations in the wall of the cylindrical tube. 4. Weft accumulator as in any of the preceding claims, with the characteristic that the perforations 10 in the cylindrical tube 1 are at an angle relative to the corresponding radii 15 of the cylindrical tube and in a particular sense of rotation. 5. Weft accumulator as in any of the preceding claims, with the characteristic that the perforations 10 in the cylindrical tube 1 are distributed around the circumference of the tube 1 in at least one spiral line. 6. Weft accumulator as in one of the preceding claims, with the characteristic that the nozzle of the airblower 2 has spiral grooves 16 in it. 7. Weft accumulator as in any of the preceding claims, with the characteristic that the perforated tube 1 is divided into two in-line sections (1A, 1B) by means of an adjustable weft brake 17. 8. Weft accumulator as in any of claims 1 to 6, with the characteristic that it consists essentially of two perforated, in-line cylindrical tubes 1 in series with each other, each of which has at one end 3 an airblower 2 in order to introduce the yarn 11 into the corresponding tube 1, and at the other end 5 a yarn brake 17 and a yarn clamp 4 respectively. 9. Weft accumulator as in any of the preceding claims, with the characteristic that the perforated cylindrical tubes 1 consist of transparent material. 10. Weft accumulator as in any of the preceding claims, with the characteristic that the perforated cylindrical tubes 1 have an internal diameter of the order of 1 cm or less. 11. Weft accumulator for weaving machines, essentially as described above and shown in the accompanying figures.

Inventors: AMPE, FRANK, MARKEY, HUGO, VAN BOGAERT, PHILIPPE, VERHULST, JOZEF, WEYMEELS,LUC
Applicants: PICANOL N.V.
Application year: 1987
Main classification: D03D47
IPC codes: D03D47, B65H51