YARN FEEDING DEVICE

Abstract: Yarn feeding device for projectile or gripper looms, comprising a drum (D) to store the yarn (Y), an inclined annular deflection surface (G) at the free front end of the drum (D), a circumferentially continuous and yielding conical braking surface (B) at the wider end of a hollow conical brake carrier (C), pressed in contact with the deflection surface (G), the brake carrier (C) being supported at its smaller end onto a stationary part (P) and the braking surface (B) being adjustable in respect of the deflection surface (G), according to the yarn unwinding speed, so as to compensate for any tension increase in the yarn (Y), and an annular counterdeflection surface (H) for the yarn (Y), downstream of the deflection surface (G) and coaxial to the drum (D), the inside diameter of the counterdeflection surface (H) being smaller than the outside diameter of the deflection surface (G). The annular counterdeflection surface (H) is stationary, and the braking surface (B) is adjusted exclusively by direct contact of the yarn (Y), through deformation and/or displacement of the brake carrier (C) in respect of the fixed counterdeflection surface (H).

Description: "YARN FEEDING DEVICE" ===o0o=== The invention concerns a yarn feeding device according to the i troductory part of claim 1. In a yarn feeding device as known from US-A-4,θ68,807, the conic yarn braking surface is defined by the inner circumference of an elast synthetic rubber ring, fixed to the base of a rigid frustoconical bra carrier. A yarnguide eyelet, fixed to the small diameter end section said brake carrier, acts as counterdeflection surface. The brake carri is fixed with its small end section into a bearing, mounted axially sl dable - essentially in a direction of the drum axis - into the stationa part of the feeder. A spring acts as preloading element and presses t braking surface in an axial direction against the inclined deflecti surface. A detection device detects yarn tension and adjusts the bra carrier so as to oppose the preloading force and thus reduce the braki effect between the braking surface and the deflection surface, as y tension increases. During unwinding of the yarn, its tension increases proportion to the unwinding speed, and the braking surface thus reduc its braking effect on the yarn so as to compensate for the yarn tens increase resulting from the unwinding speed. The same principle - i.e. to reduce the braking effect between braking surface and the deflection surface, as yarn tension increases is adopted in a yarn feeding device known from the publication "TW INFORMA 92, of L.G.L. ELECTRONICS S.p.A., Gandino, Italy. In this ca the braking surface is defined by the inner circumference of a coni metal plate ring, fixed to the inner side of the wide diameter end s tion of a carbon fiber cone. The counterdeflection surface is defined the conical lining inside the small diameter end section of the cone. cone is mounted with its small end into an annular ring membrane, fi to the stationary part of the feeder and forming the preloading eleme The yarn slides between the braking surface and the deflection surfa and then inwardly and around the counterdeflection surface, transmitt the axial components of its tension, while the cone is simultaneous kept balanced by the membrane. In this way, the axial component of ya tension shifts the braking surface against the action of the membrane, soon as yarn tension increases on rising of the unwinding speed, in ord to reduce the braking action. In view of the ever increasing yarn unwinding speeds of mode projectile or gripper looms, the object of the present invention is supply a yarn feeding device of the aforementioned type, wherein ya tension is detected with high sensitiveness and the braking action exactly adapted to the force vectors of the sliding yarn and efficient adjusted, without perceptibly disturbing yarn movement. According to the invention, this object is reached with the chara teristics specified in the characterizing part of claim 1. It is deemed that this construction, with the fixed counterdefle tion surface separate from the braking surface, prevents the counter flection surface - or the force vectors, generated by the rubbing ya acting on said surface - from affecting the adjustment of the braki action. The braking surface responds, directly and alone, extremely s sitively and promptly to any force vectors generated by the yarn caus friction. So long as the yarn moves at a low unwinding speed, the brak surface and the deflection surface produce an efficient braking effe which is particularly desirable in the case of projectile or grip looms. But if the yarn unwinding speed notably increases, on rising said speed and of the yarn centrifugal force, as the yarn moves aro the deflection surface, a sickle-shaped opening or relief zone is crea between the deflection surface and the braking surface, which ther deforms. Due to said opening or relief zone, the yarn travels with considerably reduced resistance when its unwinding speed is higher. opening or release zone rotates with the yarn unwinding point around deflection surface like a wave distortion which spreads circumferentia along the braking surface. Probably, the sickle-shaped opening or rel zone results from a partial tilting and distorting motion of the defor ble braking surface on the brake carrier, correspondingly elastic, and i relation to the deflection surface, as well as from an oval bend in t normally circular braking surface. Before and after the sickle-shap opening, in the direction of rotation, the braking surface is kept biased contact with the deflection surface, so that said opening rotat smoothly and without appraisable vibrations around the braking surfac As soon as yarn unwinding speed decreases, the braking surface automat cally moves back into its original position on the deflection surfac under the influence of the biasing member and due to its own elasticit so that it tends to establish again - as far as possible - a circul zone or line of contact with the deflection surface. During tiltin distorting and deforming of the braking surface, the downstream yarn permanently guided by the fixed counterdeflection surface. It is deeme furthermore, that the sickle-shaped opening or relief zone, which disti guishes itself for the extremely narrow radiusing angle with the circul circumference of the deflection surface, results from the scarce resis ance to tilting and distortion of the braking surface and from its radi deformability in the zone of yarn contact, although - or for the ve fact that - the braking surface remains biased on the deflection surfa over the rest of its inner circumference. The yarn actually slid through the sickle-shaped opening or relief zone, at an increasi unwinding speed, with a decreasing resistance. It should also be tak into account that. in the dynamic phase of yarn unwinding at highe speed, the mechanical effect deriving from yarn contact on the braki surface and on the deflection surface and from the yarn friction forc acting thereon, leads to an unexpected yielding of the braking surfa and to an unforeseen reduction of the braking effect. In modern loom the rotation speed of the yarn unwinding point is so high that, in t dynamic phase, the whole braking surface can be lifted and the inertia the system is no longer sufficient to press the braking surface again the deflection surface, inasmuch as the deformation work of the braki surface and that of the brake carrier greatly absorb precompressio Another explanation of the effect is that the yarn friction force displ ces a circumferential section of the braking surface, in respect of t remaining part thereof, in the yarn unwinding direction. In fact, th circumferential section of the braking surface, which undergoes so to s a distortion, performs a tilting movement in respect of the front end the yarn storage drum; the contact line between the braking surface a the deflection surface is slightly shifted towards the front end of t storage drum, considering that the braking surface is conical and the d flection surface is rounded. Since, due to said displacement, the leng of the contact line between the braking surface and the curved deflecti surface of the drum is reduced, and since the braking surface is radial deformable, the contact pressure of said surface on the deflection surf ce thereby decreases. It can even happen that the braking surface may lifted from the deflection surface. Yarn braking diminishes or cease During this local displacement of the contact line onto a smaller diam ter of the deflection surface, and due to the slight tilting movement this circumferential section of the braking surface, the yarn conta point with the braking surface gets closer to the axis of the stora drum. The lever arm of the reaction force by friction of the yarn again the braking surface consequently becomes shorter, thereby reducing t braking torque which opposes the rotary motion of the yarn unwindi point. It should moreover be considered that the yarn sliding through t braking space, which yarn has a specific elasticity of its own and compressible, gets less and less compressed as its unwinding speed in reases, in that the braking surface and the deflection surface have le and less time to squeeze the yarn as its unwinding speed becomes highe The deformation work which brakes the yarn decreases; due to the ya being less and less compressed, the tilting and distortion of the braki surface increases even further, and also its parting from the deflecti surface, thereby increasing the local displacement of the contact li between the braking surface and the deflection surface over a smal L diameter of this last surface. This in turn Leads to a further wideni of the sickle-shaped opening or relief zone in which the yarn finds i self. It may even be that with a top yarn unwinding speed, in the prese ce of the already cited wave distortion which spreads circumferentiall a fairly stable condition may be created in the braking surface, with reduced braking action on the yarn. Seen that the counterdeflection su face no longer forms part of the brake carrier, nor does it have to supported by the same, the brake carrier can be made extremely ligh weighted and yielding practically in every direction, or according to a degrees of freedom, except in an axial direction, which improves the se sitiveness of the braking surface adjustment according to yarn unwindi speed. This means that the braking effect is reduced when there is a hi increase in the unwinding speed; but it again increases when yarn unwin ing speed drops down. The yieldable braking surface - which automatical reacts with the brake carrier under the effect of yarn contact - is ap in cooperation with said brake carrier, to respond to unwinding cond tions which are critical for the yarn, i.e. to undesirable increases yarn tension determined by the unwinding speed, and is consequently in position to automatically adjust itself, so as to reduce the braki action on which yarn tension ultimately depends. The braking surface c be made extremely flexible in a radial and torsional direction. It he reacts with high sensitiveness to yarn contact, although it remains s ported by the deflection surface along a contact length of more than h of a complete circle. However, the bearing of the braking surface co ressed in an axial direction by the deflection surface, does not aff negatively the formation of the sickle-shaped opening or reLief zone, that, ahead of and behind the yarn unwinding point, the bearing press is automatically reduced or even disappears when the yarn unwinding po rotates about the storage drum at a higher yarn unwinding speed. resistance of the braking surface to opening of the sickle-shaped int space might become so low that, under the effect of the yarn centrifu force, the braking surface might even be lifted from the deflection s face. In other words, as yarn speed increases, the yarn drags along fric ion force, approximately in the unwinding direction, at least circumferential section of the braking surface, till the contact li between the braking surface and the deflection surface is partial shifted towards the drum axis and the braking surface clears the way f the yarn in the sickle-shaped opening or relief zone, with a remarkab reduced resistance. Further preferred embodiments can be found in the depending claim The characteristics and advantages of the yarn feeding device the present invention will anyhow be more evident from the followi detailed description of some preferred embodiments thereof, given by w of example and illustrated on the accompanying drawings, in which: Fig. 1 is a diagrammatic side view of a loom yarn feeding device; Fig. 2 is an axial section view, on an enlarged scale, with a re pective cross section, of the device shown in fig. 1; Fig. 3 s a perspective sectional view of a practical embodiment the yarn feeder according to the invention, with some parts removed; an Fig. 4 shows means to adjust the pre-loading force on the ya braking element in the yarn feeder according to the invention. As shown in fig. 1, in a system to feed weft yarn to a loom, t yarn Y is withdrawn from a spool S and is tangentially wound into turns by means of a winding device operated by a motor - around the outer s face of a storage drum D of the yarn feeding device. The yarn Y is us by a loom L which draws it "in defile" from the front end of the stora drum D, by means of a weft picking member K. The front end of the stora drum D terminates into a circular and rounded deflection surface G. braking element R, in the form of a frustoconical ring, surrounds deflection surface G. The inner face of the braking element R define circumferentially continuous conical braking surface B of predetermi axial length. The braking element R is pressed in a substantially ax direction against the storage drum D with a pre-loading force imparted a pre-loading element. A line of contact Z - at least theoretica circular - is formed between the braking surface B and the deflect surface G. The diameter on the left side of the braking surface B wider than the diameter of the contact line Z. The diameter on the rig side of the braking surface B is smaller than that of the contact line The braking element R is carried by a suitably conical, holl brake carrier C, which is supported by a stationary part P downstream the front end of the storage drum D. The braking element R is fixed i the wider end of the brake carrier C. Said brake carrier C is relativ rigid in an axial direction - so as to transmit the pre-loading impar by the pre-loading element - while being instead deformable in ev other direction. The brake carrier can form itself the pre-loading e ment. It can however also be conceived to axially compress the smal end of the brake carrier C by means of a pre-loading element supported the stationary part P. Downstream of the front end of the storage drum D, an annular s tionary counterdeflection surface H is provided - suitably in the form a fixed yarnguide eyelet - the inside diameter of which is considera smaller than that of the braking surface B. Downstream of the counter flection surface H, the yarn Y can be gripped by a weft picking membe of the loom (projectile or gripper loom), which inserts the yarn into shed. On unwinding, the yarn Y is drawn from the tangential turns wo on the storage drum D and slides over the deflection surface G and un the braking surface B, before deviating in an oblique direction towa the drum axis and sliding with a new deviation, more or less in a dir tion of the drum axis, over the counterdeflection surface H. Fig. 2 shows how the braking surface B is tilted and distorted, sliding of the yarn Y, in a limited peripheral zone, thereby shift from the position indicated in full lines to an offset and distor position Bl indicated by dashed lines. This displacement of the brak surface B derives from the fact that said surface cannot extend in a c cumferential direction, to clear the way for the yarn Y, but is shif under the pressure of the yarn Y being unwound and thus sliding aro the deflection surface G. The braking surface B undergoes only a lo deformation ahead of and behind the yarn unwinding poin , whereby t normally circular contact line Z is locally shifted towards the front of the storage drum D. Consequently - since, the diameter of the defle ion surface G is rapidly reduced on account of the curvature - said sh ting results into a shorter contact line Zl, whereby in this zone braking surface B yields outwardly and deforms, taking up an oval sha A syckle-shaped opening or relief zone X is thus formed between the b king surface B, in its position Bl, and the deflection surface G, that, in spite of the axial biasing force of the braking surface B, yarn speed rises the braking action on the yarn is reduced. The br carrier C allows, or follows, the local deformation or displacement the braking element R (indicated in dashes by Cl). The sickle-sha opening X and the shifting of the contact line Z into the position Zl shown in detail in fig. 2. Due to shifting of the contact line in position Zl, also the yarn clamping point between the braking surfac and the deflection surface G gets closer to the axis of the storage d D, thereby reducing the lever arm of the reaction force due to yarn fr tion. There ensues a decreasing resistance for the rotation movement the yarn unwinding point around the deflection surface G. This a involves a reduced braking action on rising of the yarn unwinding spe which compensates for - i.e. reduces - the high yarn tension level high yarn unwinding speeds. Fig. 2 shows the pre-loading element M in form of a spring between the brake carrier C and the stationary part P In the practical embodiment of the invention shown in fig. 3; braking element R is a ring formed by a metal (or metal alloy) pl having a smooth and highly wearproof surface. The ring is fixed to inner surface of the wider end of the brake carrier C - or even fo part of said brake carrier - which has a frustoconical shape and is ma for example, from thin sheet steel for springs. The brake carrier C provided with a plurality of openings 2 adjacent to the braking surfac - for instance in the form of axial or S-shaped slits - extending as as its smaller diameter end section, which define spring tongues 1. - δ - tongues 1 extend between the braking surface B and the smaller end of t brake carrier C, where the free ends of at least some of the adjace tongues 1 (but possibly also all) can be interconnected. The stationa part P has the shape of a cup 4• anchored with its base into a fix support arm 5- Into the base of the cup 4 there is fixed a yarngui eyelet 6 which defines the counterdeflection surface H, for example ceramic yarnguide eyelet. The outer edge of the cup 4 > facing the fro end of the storage drum D, abuts on the outer sides of the tongues 1 as to transmit the axial biasing force to the braking element R. Into t cup 4 there are fixed a plurality of equally spaced axial coupling p 8. Each coupling pin 8 extends through one of the openings 2 - as suitably widened opening 2a - or through a hole of a tongue 1 , into brake carrier C. At the ends of the coupling pins 8 there, is fixed a r element 7, acting as stop, which is in contact with the inner surface the tongues 1. Due to pressure on the deflection surface G, the tongue are apt to bend so that, when the biasing force acts, the brake carrie takes up the shape more or less of a cup. In spite of this, the wider of the brake carrier C is likely to undergo together with the brak surface B. with a slight strain strength, a local tilting and distorti A screw can be provided between the support arm 5 and the cup 4 to adj the pre-loading force. It can however also be conceived to axially m the support arm 5 by means of an adjusting screw, not shown. Fig. 4 illustrates an arrangement to adjust the pre-loading for by which the braking surface B of the brake carrier C is pressed agai the front end of the storage drum D. According to this arrangement, a knob or screw HI and a spr system H3 are held by a ring F into the fixed support arm 5- An in thread of the knob HI engages into an outer thread of a hub part 4A the cup support 4- A tooth H2 projecting from the fixed support ar engages into a longitudinal groove or slit S in the knob HI . so as obtain an axial movement of the cup support 4 when the knob HI is be turned. In this way, by rotating the knob HI it is possible to axia shift the cup support 4 > and this determines an increase or a reducti in the pre-loading force by which the brake carrier C and the braki surface B are compressed against the front end of the drum D. Nevertheless, instead of adopting the solution shown in fig. 4- is also possible to adjust the pre-loading force by more conventio means, with a so-called guide device or slider, known per se. In th case the whole support arm 5, into which is fixed the cup support 4, be axially shifted forward and backward in respect of the front end the drum D, preferably also by means of an adjusting screw or knob, wh determines the axial position of a slider carrying the support arm said slider being axially movable with the arm 5 into a fixed longitu nal bracket, of the yarn feeding device, extending along the whole dru and even beyond its front end. Fig. 1 also shows the possibility to dispose of a device T upstr of the braking element .R, to limit or remove "balloons", suppor independently from said braking element and from the brake carrier C. According to the invention, due to the reduced braking action yarn unwinding speed increases, it is possible to obtain a relativ constant and limited varn tension level.

Claims: CLAIMS 1 ) Yarn feeding device - particularly for projectile or grippe looms - comprising a drum (D) to store the yarn (Y), which is tangential ly wound thereon into turns and unwound therefrom in "defile" over a inclined annular deflection surface (G) at the free front end of th storage drum (D) and under a circumfereritially continuous and yieldin conical braking surface (B) at the wider end of a hollow conical brak carrier (C), said braking surface (B) being pressed in contact with th deflection surface (G), through the brake carrier (C), with an approxi mately axial elastic preloading force imparted by a preloading element the brake carrier (C) being supported at its smaller end by a stationar part (P) positioned downstream of the front end of the drum (D), and th braking surface (B) being adjustable in respect of the deflection surfac (G) , at least approximately in a direction of the drum axis, according t yarn unwinding speed, so as to reduce the braking action and compensat for any tension increases in the yarn (Y) determined by the yarn unwin ing speed as it increases, an annular counterdeflection surface (H) bei provided for the yarn (Y) downstream of the deflection surface (G) a coaxial to the drum (D), the inside diameter of said counterdeflecti surface (H) being considerably smaller than the outside diameter of t deflection surface (G), characterized in that the annular counterdefle tion surface (H) is stationary, and in that the braking surface (B) adjustable exclusively by direct contact of the yarn (Y) through deform tion and/or displacement of the brake carrier (C) in respect of the st tionary counterdeflection surface (H). 2) Yarn feeding device as in claim 1 ) , characterized in that t braking surface (B) is formed as an inner smooth and abrasionproof fa of a braking element (R) , it is shaped as a conical metal or plast ring, and it extends in and against the unwinding direction of the ya over the line of contact (Z, Z 1 ) with the deflection surface (G). 3) Yarn feeding device as in claim 1), characterized in that t hollow conical brake carrier (C) is provided with openings (2). suitab formed as slits, defining separate spring tongues (l) ending in corre pondence of the braking surface (B), in that the tongues (l) extend up the smaller end of the brake carrier (C), and in that the tongues (l) a connected to the stationary part (P). 4) Yarn feeding device as in claim 3)» characterized in that t tongues (1) are firmly connected to the stationary part (P) and they least partly form the preloading element, acting by elastic deformatio for the braking surface (B). 5) Yarn feeding device as in claim 3) , characterized in that dynamic geometrical coupling is provided between the tongues ( 1) and t stationary part (P), said coupling being in the form of a universal joi movable in the direction of the drum axis. 6) Yarn feeding device as in claim 3) , characterized in that t ends of at least some adjacent tongues (l) are interconnected, in circumferential direction, at the smaller end of the brake carrier (C in that the smaller end of the brake carrier (C) is connected to an ann lar body (4) of the stationary part (P), which body abuts on the out sides of the tongues (1) , and in that, on the stationary part (P) the is mounted at least a coupling pin (8), which engages into one of t openings (2) or into the hole of a tongue (1 ) and with which coopera means to prevent the brake carrier (C) from slipping out of said pin (8 7) Yarn feeding device as in claim 6), characterized in that t stationary part (P) is in the form of cup (4) creating a passage for t yarn (Y) , into which are provided coupling pins (8) - for instance ei - equally spaced and apt to engage with slack into the brake carrier ( and in that a ring (7) is fixed to the ends of the coupling pins ( inside the brake carrier (C) . 8) Yarn feeding device as in claim 7), characterized in that counterdeflection surface (H) and the brake carrier (C) of the brak surface (B) are supported into a common stationary part (P). 9) Yarn feeding device as in claims 8), characterized in th upstream of the braking surface (B), there is provided a device (T) limit or remove "balloons", which is supported independently from t braking surface (B). 10) Yarn feeding device as in claim 9) characterized in that, Least one device to adjust the preloading element (M) is provided in t stationary part (P) . - 1.

Inventors: MAINA BRUNO, MAINA, BRUNO
Applicants: MAINA BRUNO, ROJ ELECTROTEX NUOVA SRL, MAINA, BRUNO, NUOVA ROJ ELECTROTEX S.R.L.
Application year: 1993
Main classification: B65H51
IPC codes: B65H51, D03D47