Weft feeder for fluid jet looms

Abstract: In a measuring weft feeder for fluid jet looms - equipped with an electromagnetic yarn stopping device (8) comprising at least one electromagnetic coil (12) and a movable core (13) of ferromagnetic material subject to the contrasting actions of said coil (12) and of a return spring (14), so as to move a rod (9), engaging and stopping the yarn at the outlet of the weft feeder, between a withdrawn rest position and a projecting yarn stopping position in which the end of the rod (9) is positioned into a cavity (10) formed for the purpose on the drum periphery (3), close to its free end - the movable core (13) of the yarn stopping device is formed of a substantially cylindrical hollow head (15) of ferromagnetic material and of a cylindrical rod (9) of ceramic material axially positioned into the hollow of the head (15), and the outer surface of the rod (9) and the inner surface of the hollow head (15) are provided with grooves (17,17A,18,18A) along their directrices, while the remaining hollow part between the head and the rod is filled with plastic material (16) which is pressure injected to block the rod (9) into the head (15). According to the invention, the walls of the drum cavity (10) housing the end of the rod (9) of the yarn stopping device - which are positioned according to the generating lines of the drum - are inclined so as to open outwardly wide apart.

Description: The present invention concerns improvements in the weft feeders for fluid jet looms known as measuring weft feeders, which are apt to measure the weft yarn lengths to be inserted into the loom shed. As known, a weft feeder of this type comprises an electric motor which causes the rotation of a winding arm, and a drum held stationary around which said arm winds up the yarn into even turns, forming a weft yarn reserve the length of which is controlled by means of suitable sensors. The loom nozzle, provided to launch the weft yarn into the warp shed, draws from the weft feeder drum the weft yarn length required for each weft insertion. Said length is measured and controlled by the weft feeder counting the number of unwound turns by suitable means. As soon as the yarn at the outlet of the weft feeder, to be launched into the loom shed, has reached the predetermined length, it is stopped on the drum by means of a device comprising a rod apt to engage the yarn at the outlet of the feeder, said rod being movable between a withdrawn rest position and a projecting working position in which the end of the rod moves into a cavity formed for the purpose on the drum periphery, close to its free end, so as to stop the weft yarn by engaging the same as it unwinds from the drum. Preferably, the weft yarn stopping device is an electromagnetic device, wherein said rod projects from a movable core, which comprises a head of ferromagnetic material subject to the contrasting actions of at least an electromagnetic coil and of a return spring, allowing to move said rod alternatively into the projecting yarn stopping position and into the withdrawn rest position. Such a weft feeder is known from the document EP-A-0 111 308. The present invention concerns improvements in said electromagnetic yarn stopping device and in the cavity formed therefor on the drum periphery, so as to obtain an improved performance of the weft feeder. It should in fact be noted that, while the weft feeder is working, the constant rubbing of the yarn against the rod of the electromagnetic stopping device causes the wear of said rod in the area of yarn engagement, by forming grooves and/or cuts which make said device unutilizable after a short period of use. So far, attempts have been made to overcome this drawback by making the rod of the stopping device of materials - always metallic - apt to stand as far as possible this action of wear. Such rods have also been made of materials with a low wear resistance, but surface treated or coated so as to oppose a valid resistance to wear. Said solutions have however provided no satisfactory results. The present invention has faced and solved the above problem by adopting - in a fully original way - a rod made of ceramic material, suitably fixed to the ferromagnetic core of the device. More precisely, according to the invention, the electromagnetic stopping device in the weft feeder is of the type comprising, mounted inside a housing, at least one electromagnetic coil and a movable core of ferromagnetic material subject to the contrasting actions of said coil and of a return spring, so as to move a yarn stop rod extending axially therefrom in a projecting yarn stopping position and, alternatively, in a withdrawn rest position, and it is characterized in that the movable core is formed of a substantially cylindrical hollow head of ferromagnetic material and of a cylindrical rod of ceramic material, axially positioned into the hollow of the head, and in that the outer surface of the rod and the inner surface of the hollow head are provided with grooves along their directrices, and the remaining hollow part between the head and the rod is filled with plastic material, which is pressure injected in order to block the rod into the head. Suitably, said grooves of the rod and of the hollow head do not coincide when mounting the two parts of the movable core, and the projecting free end of the rod is round-shaped. With a device formed in this way - which, with its many advantages, also has however the inconvenience of making use of a fragile rod, easy to break if under bending stress, especially impact stress - it has been deemed appropriate to give an improved configuration to the cavity on the drum periphery housing the end of the yarn stop rod. It should be noted that the electromagnetic yarn stopping device can be made according to two different principles, namely with the rod, in rest conditions, withdrawn into said device, or with the rod, in rest conditions, projecting from said device and engaging into the cavity provided therefor in the drum. This second arrangement (in which the rod is normally projecting from the device) is preferred especially in the case of adopting an electromagnetic stopping device provided with a single magnet, in that yarn stopping is guaranteed even when the apparatus is not working. As said - according to modern technique of construction - the drum around which the yarn reserve is wound is mounted idle on the motor shaft and is prevented from rotating (usually thanks to the magnetic field generated by permanent magnets fixed to the drum and opposing other magnets fixed on the body of the measuring weft feeder). This constructive arrangement hence allows, under the action of suitable external forces, the rotation of the drum about its own axis: said rotation may in fact occur, generally in the form of oscillations, when the weft feeder is being set up - owing to the handling which it undergoes - or else during use thereof, when handling the weft feeder drum in order to vary its extension - and thus the length of the yarn reserve wound thereon - if a drum with variable diameter is adopted. Obviously, during the drum rotations or oscillations, the rod of the electromagnetic stopping device can be hit by the walls of the cavity into which its end is housed, with consequent damages both to the rod and to said walls (whereby the rod is very likely to break, if it is fragile as in the case of the present invention). According to the invention, this trifling but tiresome drawback is overcome by forming the walls of the drum cavity - which are positioned according to the generating lines of the drum - inclined so as to open outwardly wide apart. The invention is now described in further detail, with reference to the accompanying drawings, which illustrate a preferred embodiment thereof and in which: Fig. 1 is a lateral view of a measuring weft feeder comprising the improvements according to the present invention; Fig. 2 is a cross section view of a normal electromagnetic yarn stopping device for said weft feeder; Fig. 3 is a lateral part section view of a movable core according to the invention for the electromagnetic stopping device shown in fig. 2; Fig. 4 is a front view, from the outlet end, of the weft feeder shown in fig. 1; Fig. 5 shows the end of the weft feeder drum of fig. 1, seen from the yarn stopping device; and Fig. 6 is a reduced scale perspective view, from the outlet end, of the weft feeder according to the invention. A measuring weft feeder to feed the weft yarn to fluid jet looms essentially comprises an electric motor 1, which causes the rotation of a winding arm 2, and a drum 3 held stationary, around which said arm 2 winds up the weft yarn 4 into even turns, forming a reserve 5 controlled by sensors 6, the length of said turns being adjustable by changing the radial position of columns 7 which allow to vary the diameter of the drum 3. In these measuring weft feeders, the yarn 4 being fed to the loom is stopped after a predetermined length thereof has been withdrawn by the loom nozzle; this operation is accomplished by the electromagnetic device 8, when its rod 9 is moved into the projecting position and introduced into the cavity 10 provided therefor on the periphery of the drum 3, close to its free end, to thereby engage and stop the yarn 4. A normal electromagnetic yarn stopping device is shown in fig. 2. Said device 8 comprises a body 11, fixed to the measuring weft feeder and housing an electromagnetic coil 12, a movable core 13 and a spring 14. The device 8 could besides include even more than one coil and its constructive arrangement could be different from that shown. In the device 8 shown in fig. 2, the coil 12 is meant to withdraw the movable core 13 in a rest position, against the action of the spring 14 which is instead meant to keep the rod 9 of said core in the projecting yarn stopping position into the cavity 10 of the drum 3. It is understood that the spring could alternatively be designed to keep the movable core in the rest position, while the electromagnetic coil could be provided to move said core into the working position with its rod 9 projecting into the drum cavity. Figure 3 shows in greater detail the movable core 13 of the electromagnetic yarn stopping device 8 according to the invention. Said core 13 consists of a substantially cylindrical hollow head 15 of ferromagnetic material, apt to respond to the action of the electromagnetic coil 12, and of a rod 9 of ceramic material having a high rubbing resistance, which is axially blocked into the head 15 and projects therefrom. Always according to the invention, the ceramic rod 9 is fixedly connected to the head 15, being blocked therein by injecting a suitable synthetic plastic material 16 into the hollow part between the head and the rod. To make this connection steadier, into the outer surface of the rod 9 and into the inner surface of the head 15 there are formed grooves 17, 17A and, respectively, 18, 18A, along directrices of said surfaces, so as to create undercuts into which penetrates the injected plastic material, thereby notably improving the grip between the head 15 and the rod 9. The two grooves 17, 17A, formed on the rod portion housed inside the head 15, are arranged so as not to coincide with the grooves 18, 18A of said head, but to be axially offset in respect thereof. The projecting free end of the rod 9 has a round-shaped tip, so as to guarantee its prompt disengagement from the weft yarn 4 when the movable core 13 is withdrawn into the rest position by the coil 12 of the device 8, and the weft yarn 4 has to be fed again to the loom for a new insertion. Since, as known in weaving technique, ceramic materials are apt to provide the best resistance to wear caused by rubbing of yarns, especially yarns sliding onto a narrow surface, a rod 9 made of ceramic material - which has never been adopted so far, also due to the difficulty of fixing it into a head of ferromagnetic material, to form the movable core of the device - notably improves the properties of endurance and reliability of the yarn stopping device of the invention adopting said rod, in respect of the conventional yarn stopping devices. Furthermore, the firm and safe fixing of the rod 9 into the head 15 - as obtained according to the invention - prevents any possible damage which could be caused to such a mechanically fragile material, as the ceramic one, by vibrations, oscillations and possible impacts. Said fixing also helps to most efficiently oppose the effects of the high forces of inertia determined by the high speed of the movable core, which would tend to expel the rod from said core. Figures 4 to 6 show the yarn stopping device 8 in a working position, with the rod 9 penetrating into the cavity 10 provided therefor on the drum 3. According to the invention, the cavity 10 - formed as a wide slit perpendicular to the axis of the drum 3, along a directrix of its cylindrical surface - has its head walls 21 and 22, positioned according to the generating lines of said drum, considerably inclined and opening outwardly wide apart. Said walls may suitably consist of simple inclined flat surfaces - as in the embodiment shown in the drawings - but they could also consist of any other similarly inclined surface having one or more curvatures. With a cavity 10 having the aforespecified characteristics, when the drum 3 rotates about its own axis (marked A in the drawings), the end of the rod 9 comes into contact with one of the two inclined walls 21 or 22 of said cavity 10 generating a force component directed along the axis of said rod 9. Said component causes the lifting of the rod 9, which is facilitated by the smooth contact of its round-shaped tip with said inclined wall. The walls of the cavity 10 are thus not apt to prevent the rotation of the drum 3, nor is the end of the rod 9 likely to undergo damage, in that there is no actual impact, but rather a gradual sliding contact which protects the integrity both of the rod 9 and of the cavity 10. It should also be noted that the configuration of the other parts of the drum 3 allows it to fully rotate about its axis: the adjustable columns 7 are in fact - in their position of maximum extension - contained inside a circle C with centre in A, while the free end of the rod 9, even when it is in a position projecting from the respective device 8, keeps external to the circle C, avoiding all possibility of impact against the adjustable columns 7. These characteristics finally allow to notably increase the reliability of the weft feeder and to protect it from improper use, thereby solving a problem which was greatly felt by loom constructors and users and which the fact of equipping the electromagnetic yarn stopping device with a fragile rod - for instance a ceramic rod, as in the case of the present invention - would have made even more serious.

Claims: Weft feeder for fluid jet looms - of the type apt to measure the weft yarn (4) lengths to be inserted into the loom shed (measuring weft feeder), consisting of an electric motor (1) causing the rotation of a winding arm (2), of a drum (3) held stationary around which said arm (2) winds up the yarn (4) into even turns, forming a weft yarn reserve (5) the length of which is controlled by suitable sensors (6), and of an electromagnetic yarn stopping device (8) comprising at least one electromagnetic coil (12) and a movable core (13) of ferromagnatic material subject to the contrasting actions of said coil and of a return spring (14), so as to move a yarn stop rod (9), apt to engage and stop the yarn (4) at the outlet of the weft feeder, between a withdrawn rest position and a projecting yarn stopping position in which the end of the rod (9) is positioned into a cavity (10) formed for the purpose on the drum periphery, close to its free end - characterized in that, the movable core (13) of the yarn stopping device (8) is formed of a substantially cylindrical hollow head (15) of ferromagnetic material and of a cylindrical rod (9) of ceramic material, axially positioned into the hollow of the head, and in that, the outer surface of the rod and the inner surface of the hollow head are provided with grooves (17, 17A, 18, 18A) along their directrices, and the remaining hollow part (16) between the head and the rod is filled with plastic material, which is pressure injected to block the rod into the head. Weft feeder as in claim 1), wherein said grooves (17, 17A, 18, 18A) of the rod (9) and of the hollow head (15) of the yarn stopping device (8) do not coincide when mounting the two parts of the movable core (13). Weft feeder as in claim 1), wherein the projecting free end of said rod (9) is round-shaped. Weft feeder as in claim 1), wherein the walls (21, 22) of the drum cavity (10) housing the end of the rod (9) of the yarn stopping device (8) - which are positioned according to the generating lines of the drum - are inclined so as to open outwardly wide apart. Weft feeder as in claim 4), wherein said inclined walls (21, 22) of the drum cavity (10) housing the end of the rod (9) of the yarn stopping device (8) are inclined flat surfaces. Weft feeder as in claim 4), of the type having a drum (3) with columns (7) adjustably projecting from a cylindrical body, wherein said columns (7) - in their position of maximum projection - are contained inside a circle (C) having as centre (A) the drum rotation axis, said rod (9) of the yarn stopping device (8) always keeping external to said circle (C).

Inventors: MAINA BRUNO, MAINA, BRUNO
Applicants: ROY ELECTROTEX SPA, ROJ ELECTROTEX S.P.A.
Application year: 1990
Main classification: D03D47
IPC codes: D03D47, B65H51