Abstract:
A brake for loom weft yarn feeding device is arranged between a front portion of the drum, on which the yarn coming from a conventional bobbin is wound, and a space defined by a hollow enclosing and covering element. The covering element has a front orifice and is positioned in front of the drum. The element has a substantially cone-shaped or spherical cap configuration, wherein a brake is provided comprising a body of round, oval or possibly even quadrangular plan, consisting of one or more intermediate segmental rings, within approximately semicircular profile, which are fitted with at least one head in a portion of lesser diameter than those of the segmental rings at either end. The weft yarn is comprised and compressed between the rim of one of the heads and the inner wall of the hall element, immediately before exiting therefrom through the orifice.

Description:
FIELD OF THE INVENTION 
     The invention relates to a loom weft yarn feeding device having a storing drum from which yarn is removed and a brake for braking the yarn. 
     BACKGROUND OF THE RELATED ART 
     Brakes on loom weft yarn feeding devices are suitable for maintaining a desirable tension profile in the weft yarn unwinding from the weft feeder drum, thereby preventing it from breaking. A weft yarn feeder is intended to feed weft yarn coming from a bobbin to a loom. Traditionally, a weft yarn feeder is provided with a braking member placed in the vicinity of the storing drum and acting in the direction of the drum to which the weft yarn is conveyed before exiting therefrom. The braking member has the function of keeping the weft yarn tension as constant as possible, and of preventing the yarn from breaking, which would inevitably cause at least a temporary interruption of the production cycle. 
     Known brakes for loom weft yarn feeding devices of the lever or ring type are built in such a way as to act systematically in the direction of the drum, and unfortunately possess a number of important disadvantages. The braking member, generally consisting of a disk acting counter to the weft yarn unwinding direction, tends to become deformed in time and then is no longer able to couple with the drum with the required precision. Moreover, during rotation of the withdrawn weft yarn, centrifugal forces tend to lift the weft yarn off the drum whereas the braking member tends to contrast it in the opposite direction. As a result, weft yarn tension, especially at higher withdrawal speeds and higher rotation speeds, increases considerably. The weft yarn itself thus becomes easily subject to breaking, or does not enable a reliable changeover between the loom pincers, e.g. in a rapier loom. 
     Another drawback with a known braking device using a brake cap generally produced from a plastic material is that the force exerted on the brake cap results in deformations of and wear spots at certain parts of the brake cap. Consequently, the yarn is no longer braked uniformly and exists from the weft yarn feeding device under braking that is not constant. This increases the danger of stretching and breaking the weft yarn. 
     The brake body of a brake as known from GB 14 25 900, FIG. 8, is an annular tube of circular cross-section made of rubber or plastic material. Said tube is inflated by pressurized air and is seated on a ring provided in the interior of the annular tube. Said ring is mounted to the drum front end portion of the storage drum such that a circumferential region of said annular tube is defining a circumferentially continuous braking rim which is radially held in contact with the covering element inner wall. In operation, supposedly due to the radially oriented force pressing the braking rim against the covering element inner wall such that the braking rim is acting cross-wise or even slightly opposite to the weft yarn withdrawal direction and/or due to the stiffness of the inflated tube, the weft yarn tension occurring in the weft yarn downstream the braking zone significantly varies with varying weft yarn speeds. In another embodiment (GB 1 425 900, FIG. 3), an annular brake body with axially oriented bristles is mounted in the space confined by the cone-shaped covering element. Tips of the bristles radially contact the covering element inner wall. Said bristles define an indefinite plurality of discrete braking tips, but no circumferentially continuous braking rim. This does not allow to achieve a relatively constant downstream tension in the weft yarn when the withdrawal speed of the weft yarn varies, since the friction between the braking tips of the bristles and the yarn progressively increases with increasing weft yarn withdrawal speed. 
     An object of this invention is to produce a loom weft yarn feeding device having a brake apt to guarantee optimal and constant tension of the weft yarn fed to the loom and to avoid the possibility of yarn breakages. 
     A further object of the invention is to produce a loom weft yarn feeding device having a brake in which the braking member provided for yarn braking is not subject to local deformation and/or wear which could prevent that the yarn passes the brake under constant braking conditions. 
     A further object of the invention is to put a brake in a loom weft yarn feeding device at the disposal of users, designed such that it is able to ensure high level resistance and dependability in time, while also being simple and economical to manufacture. 
     A further object of the invention is to create a loom weft yarn feeding device with a brake having an elastically deformable braking rim wherein the brake has an improved behavior in operation, leading to a relatively constant tension profile in the weft yarn, i.e. avoiding critical tension variations with varying weft yarn speed in weft yarn feeders for different types of looms, like projectile looms, rapier looms, and even jet looms. The brake ought to have an extremely simple design, should operate without changing its braking behavior due to wear and should be suitable for a broad variety of different yarn qualities. The operational behavior of the brake should lead to a self-compensating effect, which means that the brake automatically reduces the braking effect with increasing yarn speed or during temporary acceleration phases and vice versa. 
     SUMMARY OF THE INVENTION 
     These and yet further objects are achieved with a loom weft yarn feeding device having an elastically deformable brake body having a radially deformable lip defining a braking rim. 
     The yarn is compressed between the rim provided on one of the heads and the inner wall of the hollow covering element immediately before exiting therefrom through the front orifice of the covering element. The covering element simultaneously fulfills the function of a balloon limiting structure and a counter-braking surface co-operating with the braking rim in a circumferentially continuous braking zone arranged essentially perpendicular to the axis of the covering element and the storing drum of the weft yarn feeding device. 
     A self-adjusting traction brake can be achieved by the important fact that the braking rim is axially pressed against the covering element inner wall in essentially the same direction in which the weft yarn is withdrawn from the weft yarn storing device. This means that the braking rim in the brake does not act significantly cross-wise or even counter to the withdrawal direction of the yarn and thus is able to smoothly yield when the yarn circulating inside the covering element is passing the braking zone simultaneous with predominant circulating motion and linear withdrawal speed. Since the weft yarn locally is deforming the braking rim which brakes the yarn against the covering element inner wall in a circumferentially continuous fashion, significant wear of the braking rim can be avoided. If, nevertheless, wear of the braking rim will take place, said wear is extremely uniformly distributed along the circumferentially continuous braking rim so that no local and remaining deformations or wear spots occur in the braking rim. The brake has an extremely simple design and does not significantly suffer from wear but is suitable for a big variety of yarn qualities. From the smooth cooperation between the covering element inner wall and the circumferentially continuous, at least radially deformable braking rim predominantly loaded by contact pressure in essentially the same direction as the weft yarn is withdrawn (traction type brake), results a desirable self-compensating effect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will be described with the help of the drawings. In the drawing is: 
     FIG.  1 : a schematic partial longitudinal section of a loom weft yarn feeding device equipped with a weft yarn brake. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1 a storing drum  12  of a loom weft yarn feeding device (not shown in detail) is indicated, terminating in a drum front end portion  13 . A weft yarn  14 , coming from a bobbin (not shown) is wound in adjacent windings by means of a not shown winding-on element onto storing drum  12 . In the embodiment shown, storing drum  12  can be a stationary storing drum. Over the drum front end portion  13 , a hollow cone-shaped covering element  16  is extending in axial and radial overlapping fashion with a radial clearance between drum front end section  13  and an inner wall  17  of said covering element  16 . Covering element  16  is fixed by known means stationarily in relation to drum  12 , is provided in its smaller diameter front portion with an orifice  18  and is confining with its inner wall  17  a space in front of said drum front end portion  13 . The weft yarn  14  is withdrawn for consumption (e.g. by insertion means of a loom, not shown) from a weft yarn supply on storing drum  12  overhead of drum front end portion  13 , further through the space inside covering element  16  and is then exiting through orifice  18  towards the loom. 
     In front of drum front end portion  13 , a brake  10  for the withdrawn weft yarn  14  is provided. According to the invention, in the space defined by covering element or cone  16  and arranged at the same axis as cone  16  an element is provided forming a brake body  20 , formed to advantage by a tubular body with different diameters. In the embodiment shown, said brake body  20  has an accordion-like or bellows-like design and is round, oval, or even quadrangular in its longitudinal sectional configuration. Said brake body  20  is comprised by a plurality of ring portions  21  with each having an approximately semi-circular profile. Furthermore, said brake body  20  has rear and front heads  22 ,  24 , each of which is defined by a circular plane portion, e.g. with a diameter smaller than the diameters of the intermediate ring portions  21 . The brake body  20  as a whole, i.e. including the rear and front heads  22 ,  24 , is made preferably of rubber, a plastic material, or a metallic sheet material permitting elastic deformation of the brake body  20  lengthwise and/or crosswise, i.e., deformations in axial and/or radial directions. 
     Brake body  20  is mounted to drum front end portion  13 . For this purpose, a recess  32  is made centrally in the front face of said drum front end portion  13  to which the cone or covering element  16  is associated, e.g. held by an external support or a fixture at a mounting bracket (not shown) of the housing of the feeding device. At said drum front end portion  13  in recess  32 , a seat  26 ′ is made. For this purpose, a back wall  26  of said recess  32  may define ring-shaped seat  26 ′ or a plate embossment (not shown) of a shape complementary to that of rear head  22  of brake body  20 , so that brake body  20  may be stably positioned and centered by means of its rear head  22  at the storing drum  12 , e.g. prior to securing the cone or covering element  16  in relation to said drum  12  at the feeding device. 
     The front head  24  provided at the opposite end of brake body  20  comes into direct contact with weft yarn  14  withdrawn from the outer periphery of storing drum  12  overhead via the rounded drum front end portion  13  and before the weft yarn  14  exits from covering element  16  through orifice  18 . The front head  24  of brake body  20  defines in the shown preferred embodiment a lip  25  running essentially parallel to the longitudinal axis of covering element  16  and drum  12  and also to the direction in which the weft yarn  14  exits through orifice  18 , as indicated by arrow X. A given flexibility or deformability of front head  24 , which is one of the properties of the material the entire brake body  20  is made of permits exact adjustment of the edge or braking rim  23  of said front head  24  to the profile of the inner wall  27  of covering element  16 , of which said inner wall  17  is systematically run up against. The weft yarn  14 , leaving the drum  12  and obligatorily unwinding according to a cone-shape spiral pattern when leaving the storing drum  12  and later also covering element  16 , thus is kept under constant yarn tension between the edge or braking rim  23  of front head  24  and the inner wall  17  of covering element  16 . Apparently, said weft yarn  14  will be braked depending on the continuous contact between the axially yieldably loaded braking rim  23  and the inner wall  17  of covering element  16 . 
     The thrust of the brake body  20  transferred by braking rim  23  onto inner wall  17  is internal to the conical spiral path formed by the weft yarn  14  and is directed toward the center of the spiral according to the direction of the movement of the weft yarn  14  in a diameter smaller than the outer diameter of storing drum  12 . This allows that the inertia of the weft yarn  14  forms angles, e.g. when passing through the braking zone, differing in function of the weft yarn speed and of the axial position of the braking zone or contact zone between the brake body braking rim  23  and inner wall  17 . Upstream said braking zone, the weft yarn  14  is free to move as necessary along its spiral path and with rotation about the axis of storing drum  12 . However, covering element  16  there fulfills a balloon limiting function as well as downstream of said braking zone. 
     In FIG. 1, the weft yarn  14  unwinding according to the above-mentioned cone-shaped spiral pattern is shown as running with a slight distance from the inner wall  17  of covering element  16 . However, the weft yarn  14  then apparently will be pushed by the edge or braking rim  23  of front head  24  of brake body  20  in the direction towards inner wall  17 . Brake body  20  therefore is acting as a calibrated brake  10  for the weft yarn  14  and is acting in the weft direction, namely along the direction of feeding of the weft yarn  14  to the loom which is the direction indicated by the arrows X. 
     Bending or elastic deformation of brake body  20  means both, namely the front lip  25  formed by the front head  24 , which lip is capable of bending backwards and inwards to adjust to the profile of the inner wall  17 , and also the more rear part of brake body  20  on account of its intermediate ring portions  21  with semi-circular profiles each which ring portions  21  act like an accordion and as an absorber of vibrations and tension. As a result, the weft yarn  14  downstream the braking zone is remaining at essentially constant yarn tension measured in the position immediately behind the orifice  18  where the weft yarn  14  is existing from covering element  16 . Pressing said braking rim against inner wall  17  in essentially the same axial direction as said weft yarn  14  is withdrawn (arrows X) as well as the deformability of the braking rim  23  and lip  25  where the rotating yarn is passing the braking zone as well as the adaptability of braking rim  23  to the profile of inner wall  17  and the integrated absorber of vibrations and tension, lead in combination to a traction type braking avoiding significant tension fluctuations in the withdrawn weft-yarn  14  which fluctuations could cause yarn breakages. 
     In the embodiment shown in FIG. 1, the outer contours of ring portions  21  (which also could be of zigzag configuration) are essentially parallel to the axis of covering element  16 . However, the contour of brake body  20  with its ring portions  21 —in a longitudinal section—could be round, oval or even conical, e.g. with a similar conicity as inner wall  17 . 
     In order not to allow the weft yarn  14  to get caught by the structure of the peripheries of ring portions  21 , a sleeve-like protector  29  could be provided outside of braking body  20 , e.g. of elastic material so that the deformability and the vibration absorption of the brake body  20  is not disturbed. Furthermore, the outer diameter of rear and front heads  22  and  24  are shown to be smaller than the outer diameter of the contour of said ring portions  21 . In alternative embodiments, the outer diameter of at least the front head  24  could be bigger than shown and even as large or larger as the outer diameter of the profiles of ring portions  21 . This also can be said for the outer diameter of rear head  22 . There the outer diameter could even be bigger than the outer diameter of the contour of ring portions  21 . 
     In a further alternative embodiment, brake body  20  could have a quadrangular longitudinal sectional configuration, i.e., could be a straight section of a tube, e.g. with open front end  31 . The front and rear heads  22 ,  24  then could be integrated into said tube section, even with the same or smaller diameters, or could be carried by said tube section. The longitudinal sectional configuration of brake body  20  in further non-shown embodiments could be round, oval, conical or of other geometrical design. The brake body  20  with its rear and front heads  22 ,  24  can be a unitary structure, e.g. an injection-molded rubber or plastic part or a unitary part made from sheet metal. However, since the brake body  20  should have a certain capability for vibration absorption and should be soft, it even might be desirable to form the front lip  25  or even front head  24  from another material having more stiffness and being more wear-proof than the material in the region of ring portions  21 . In another alternative embodiment, an annular reinforcement body (indicated at  27 ) could be mounted, e.g. glued, onto front head  24 , then, e.g., defining braking rim  23 . Said reinforcement ring could be also be fixed at the front-most ring portions  21  instead of front head  24 . Most preferably, brake body  20  with its front and rear heads  24 ,  22  is open on both ends in order to assure the necessary deformability of the ring portions  21  and particularly of the front head  24  with its braking rim  23 . However, in order to hinder lint and contaminations being collected inside brake body  20 , it may be desirable to close at least the front end of brake body  20 , e.g. by a deformable partition wall  28 . In order not to disturb the movability of lip  25  with its braking rim  23 , the transition  28 ′ from said separation wall  28  into the braking body  20  could be set back in relation to braking rim  23  (indicated in FIG. 1 in dotted lines). 
     Regardless of the position the weft yarn  14  is assuming as it moves through covering element  16 , it systematically has to encounter the edge or braking rim of front head  24  of brake body  20 , i.e. has to pass braking zone between braking rim  23  and inner wall  17 . Due to the cooperation between braking edge  23  and inner wall  17 , the yarn is maintained at constant tension. 
     Since the active braking member, namely front head  24  with its braking rim  23 , is part of brake body  20  and is acting in the same direction as the weft yarn  14  is fed to the loom; furthermore, since there are ring portions of the brake body  20  with substantially semi-circular profile providing an overall bellows-like structure, any vibrations will be absorbed without deteriorating the effect of constant braking on the weft yarn  14 . 
     The brake body  20  could have any profile and outer diameter. It even might be cone-shaped to match at least in part with the inner wall  17  of covering element  16 . Said ring portions  21  have not necessarily to be of semi-circular profile, because other profile forms could be used as well. In certain cases the ring portion outer contour could, at least in part, conform to the shape of the inner wall  17 . The brake body  20  then could even form several or numerous points of contact for the weft yarn  14  and with the inner wall  17  so that several braking zones will be formed in a series of at least two of them. In another embodiment, brake body  20  could be made of two ore more parts, at least one of which then is elastically deformable. Both parts could be separated by elastic means, such as, e.g. spiral springs or similar spring components. 
     Covering element  16  is shown with an essentially frustoconical jacket format. However, covering element  16  could be of different configuration, e.g. could have a spherical cap shape and internally accommodate a correspondingly shaped brake body  20  of complementary or smaller diameter. 
     One important feature of the invention is that the brake body  20  is designed with its longitudinal cross-sectional configuration so as to press the braking rim  23  essentially in the axial weft yarn withdrawal direction X against the covering element inner wall  17 . In connection with the circumferentially continuous braking rim  23  formed by an at least radially deformable portion of brake body  20 , this leads to a desirable traction type brake in which said braking rim  23  does not act counter or significantly cross-wise in relation to the axial weft yarn withdrawal direction.