Device for the self-adjusted braking of the yarn for weft feeders

Abstract: A device (14) comprising a frustum-shaped braking body (15) which is suspended and elastically pushed into tangent contact engagement with the drum of the feeder and comprises a metallic covering lamina (20) which is arranged at its larger cross-section. The frustum-shaped body (15) further comprises a surface (15a) for accommodating the covering lamina (20); the surface is recessed with respect to the plane of the internal surface (15b) of the frustum-shaped body and is provided with a discontinuous surface in order to improve the grip of a layer of adhesive which is interposed between the lamina (20) and the frustum-shaped body (15).

Description: The present invention relates to a device for the self-adjusted braking of units for feeding weft to textile machines, particularly to weaving looms of the gripper and projectile type. More specifically, the invention relates to improvements to braking devices of the type disclosed in prior Italian patents no. 1,251,209 and 1,259,567, which are designated hereinafter as "conventional devices". Weft feeders are units which typically comprise a fixed cylindrical drum, on which a rotating arm winds a plurality of turns of yarn which constitute a weft reserve, means for producing the advancement of the turns from the base toward the end of the drum, and means for braking at the output the yarn that unwinds from the drum when required by the loom. Such conventional self-adjusting braking devices are constituted by a braking body which is substantially frustum-shaped and is suspended elastically in front of the fixed drum of the feeder, to which it is tangent at an output circumference which is slightly smaller than the maximum circumference of said drum. The yarn slides between the drum and the frustum-shaped braking body, onto which it discharges the axial component of its tension. When the tension rises -- as the travel speed of the yarn increases -- said axial component tends to move the braking body in contrast with the action of elastic suspension means and causes, or tends to cause, its spacing from the drum, with a consequent and corresponding reduction in the braking action, which accordingly self-adjusts as a function of the travel speed and therefore of the mechanical tension of the yarn. For correct operation in the above-specified sense, the frustum-shaped braking body must have a high radial elasticity, a substantial axial rigidity and a limited inertia. For this purpose it is known to manufacture said frustum-shaped body by using an impregnated fabric or a laminate of high-strength synthetic fibers, internally providing it with a metallic lining. Typically, said lining covers a limited band of said frustum-shaped body which straddles the output circumference of the drum of the feeder and is constituted by a steel lamina with a thickness between 4 and 9 tenths of a millimeter. It is also known to improve the response of the frustum-shaped braking body to variations in the tension of the yarn by providing it with a metal ring which has a protruding rim and is arranged at the smaller or terminal cross-section of the braking body and is suitable to affect the yarn in order to divert its path. In this manner, the yarn discharges onto the braking body the axial component of its tension not only at the circumference on which the body is in contact with the drum of the feeder but also at the terminal region of the body, and the arrangement significantly improves the elastic response of the braking device. However, in some cases, for example in the presence of low-count yarns such as wool yarns for combed fabrics, the elastic yielding of the frustum-shaped body can be insufficient and accordingly the self-adjusting action of the braking applied to the yarn by the body can be compromised. In particular, the elastic deformability of the frustum-shaped body in a radial direction can be reduced significantly by the presence of said metallic covering lamina, which is usually glued directly onto the internal terminal band of the frustum-shaped body, increasing the resisting thickness of the band and thus reducing its elastic deformability. On the other hand, a generalized reduction in the thickness of the material of the frustum-shaped body cannot exceed preset limits owing to the consequent unacceptable degrading of the axial rigidity of said body. The presence of the protruding metallic ring directly and rigidly coupled to the smaller or terminal cross-section of the frustum-shaped body also helps to reduce the radial elasticity of the body, which thus fully discharges the axial component of the tension affecting the yarn directly onto the elastic suspension means of the body, whose rigidity can be excessive with respect to the weak mechanical tensions that affect lower-count yarns. The aim of the present invention, starting from the awareness of these and other drawbacks of conventional self-adjusting braking devices of the specified type, is to eliminate such drawbacks. In particular, an important object of the present invention is to improve such self-adjusting braking devices by providing them with a frustum-shaped body with a metallic covering lamina as specified which has, for an equal axial rigidity, an improved radial elasticity at said lamina, the adoption of which accordingly does not compromise and does not worsen the response of the frustum-shaped body to variations in the mechanical tension that acts on the yam, even if such tension is weak. Another particular object of the present invention, again with the goal of improving the self-adjusting response of the braking device in the presence of low-count yarns, is to improve the protruding metallic ring and the method of its coupling to the smaller terminal section of the frustum-shaped body, on the one hand in order to avoid radially stiffening the structure of said frustum-shaped body at said terminal section and on the other hand in order to give said ring a shock-absorbing action which surprisingly and significantly improves the self-adjusting behavior of the braking device even in the presence of very small tensions affecting the yarn. The above aim and objects are achieved by a device for the self-adjusting braking of yarn for weft feeders, according to the present invention, comprising a frustum-shaped braking body which is suspended and elastically pushed into tangent contact with the drum of the feeder along an output circumference of said drum and comprising a metallic covering lamina which is arranged at its larger cross-section, characterized in that said frustum-shaped body further comprises a surface for accommodating said covering lamina, said surface being recessed with respect to the plane of the internal surface of the frustum-shaped body and being provided with a discontinuous surface in order to improve the grip of a layer of adhesive which is interposed between said lamina and said frustum-shaped body. Preferably, according to the invention, said seating surface is formed by means of a surface treatment of the corresponding band of the frustum-shaped body with a laser beam; said treatment simultaneously produces the intended removal of material and the intended surface discontinuity of the band being treated. Another improvement according to the present invention consists in replacing the protruding steel ring which is rigidly glued to the frustum-shaped body with a contoured ring which has a conical portion and a cylindrical portion which are mutually connected by an internal blending region which forms a wide curve, and in detachably and elastically coupling said contoured ring to the frustum-shaped body, clamping said body between the conical portion of the profiled ring and an annular locking element which is screwed onto the cylindrical portion of said ring; a ring made of elastically flexible material being interposed between the annular element and the frustum-shaped body. Further characteristics and advantages of the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, which are given by way of non-limitative example and wherein: Figure 1 is a lateral elevation view of a weft feeder with a conventional self-adjusting braking device; Figure 2 is an enlarged-scale sectional view, taken along an axial plane, of the self-adjusting braking device according to the present invention; Figures 3 and 4 are enlarged-scale views of details of Figure 2. In Figure 1, the reference numeral 10 designates a conventional weft feeder which comprises a fixed drum 11 on which a hollow rotating arm, rigidly coupled to a rotating disk 12 located at the base of the drum, winds a weft reserve in the form of a plurality of turns of yarn SF. In a per se known manner, the yarn F, when required by the loom or other textile machine (not shown), unwinds from the drum, passing through a yarn guide 13 which is coaxial to said drum, and is subjected, during its unwinding motion, to the action of a self-adjusting braking device, generally designated by the reference numeral 14, which is meant to keep said yarn under tension, automatically modulating the braking action as the travel speed of said yarn varies. For this purpose, the device 14, which is interposed between the drum 11 and the yarn guide 12, comprises a frustum-shaped braking body 15 made of fabric or laminated synthetic fibers, impregnated with polymeric resins, which is arranged so as to face the drum 11, to which it is tangent along an output circumference CU which is slightly smaller than the maximum circumference. By means of an annular support 16 and of an elastic suspension 17, the body 15 is pushed so as to engage by elastic contact the drum 11 in order to brake with a preset elastic force the yarn that unwinds from said drum. The annular support 16 is supported by a carriage 18 which can move axially with respect to the drum 11 by means of a screw mechanism 19 in order to vary the static tension that pushes the body 15 against said drum. In the region of contact with the drum 11, the internal surface of the frustum-shaped body 15 is provided with a metallic reinforcement lamina 20, typically a steel lamina between 4 and 9 tenths of a millimeter thick, covering a limited band of the frustum-shaped body 15 which lies on either side of the output circumference CU; the width LA of the band being, for example, between 25 and 30 mm. According to the present invention, and according to the above aim and objects, on the internal surface of the frustum-shaped body 15 and at the metallic lamina 20 there is provided a surface 15a for accommodating the reinforcement lamina. As clearly shown in the detail view of Figure 3, the surface 15a is recessed with respect to the plane of the internal surface 15b of the frustum-shaped body 15, so that the application of the lamina 20, performed by interposing a thin layer of adhesive, does not significantly alter the thickness of the frustum-shaped body and therefore its radial elasticity and its axial rigidity. Advantageously, according to the invention, the surface 15a for accommodating the lamina 20 is obtained by treating the material of the frustum-shaped body with a laser beam; this treatment, in addition to producing the removal of material, recessing the surface 15a with respect to the surface 15b, generates a surface discontinuity, dressing the surface 15a in order to improve the grip of the layer of adhesive suitable to rigidly couple the lamina 20 to the body 15. Although it is advantageous and preferable, the surface treatment with a laser beam is not limitative: the accommodation surface 15a can also be treated mechanically, for example by sanding. As shown in Figure 2, the frustum-shaped body 15 has, in addition to the lamina 20, a metal ring which is arranged at the smaller terminal section of the frustum-shaped body and is suitable to affect the yarn and divert its path toward the terminal yarn guide 13. According to the present invention and in order to achieve the above aim and objects, the metal ring, generally designated by the reference numeral 30, has the improved structure shown in the detail view of Figure 4. Such improved structure is composed of a profiled ring, preferably made of chromed aluminum, which has a conical portion 31 accommodated inside the frustum-shaped body 15 and a cylindrical portion 32 which protrudes axially from the body 15; those two portions 31 and 32 are connected by a blending portion 33 which forms a wide curve. The cylindrical portion 32 is provided with a threaded region which is meant to receive a correspondingly threaded annular locking element 34, preferably made of plastics and suitable to clamp, with a ring 35 of an elastomeric material of the O-ring type interposed, the frustum-shaped body 15 between the conical portion 31 of the ling and the annular element 34. As clearly shown in the figure, an annular gap L is formed between the annular locking element 13 and the frustum-shaped body 15 and ensures elastic contact between the body 15 and the elastomeric ring 35, which accordingly provides a shock-absorbing action, improving the overall elastic response of the braking device. Without altering the basic concept of the invention, the details of execution and the embodiments may of course be altered extensively with respect to what has been described and illustrated by way of non-limitative example without thereby abandoning the scope of the invention. The disclosures in Italian Patent Application No. TO98A000402 from which this application claims priority are incorporated herein by reference. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims: A device (14) for the self-adjusting braking of yarn for weft feeders (10), comprising a frustum-shaped braking body (15) which is suspended and elastically pushed into tangent contact with the drum (11) of the feeder (10) along an output circumference (CU) of said drum and comprising a metallic covering lamina (20) which is arranged at its larger cross-section, characterized in that said frustum-shaped body (15) further comprises a surface (15a) for accommodating said covering lamina (20), said surface being recessed with respect to the plane of the internal surface (15b) of the frustum-shaped body and being provided with a discontinuous surface in order to improve the grip of a layer of adhesive which is interposed between said lamina (20) and said frustum-shaped body (15). The device (14) according to claim 1, characterized in that the surface (15a) for accommodating the lamina (20) is obtained by means of a surface laser treatment of the material of the frustum-shaped body (15). The device according to claims 1 and 2, characterized in that said surface (15a) for accommodating the lamina (20) covers a band of the internal surface of the frustum-shaped body (15) which straddles the output circumference (CU) along which the frustum-shaped body (15) is tangent to the drum (11) of the feeder (10). The device (14) according to claim 1, further comprising a metal ring (30) arranged at the smaller terminal section of the frustum-shaped body, which is suitable to affect and divert the yarn that unwinds from said drum (11), characterized in that said ring (30) is profiled and comprises a conical portion (31), which is accommodated inside the frustum-shaped body (15), and a cylindrical portion (32), which protrudes axially from said body (15), said portions (31;32) being mutually connected by an internal blending portion (33) which forms a wide curve. The device according to claim 4, characterized in that the cylindrical portion (32) is provided with a threaded region which is meant to receive a correspondingly threaded annular locking element (34), suitable to elastically clamp, with a ring (35) of elastomeric material of the O-Ring type interposed, the frustum-shaped body (15) between said conical portion (31) of the ring (30) and said annular locking element (34). The device (14) according to claim 4, characterized in that said profiled ring (30) is made of chromed aluminum. The device according to claim 5, characterized in that said annular locking element (34) is made of plastics. The device according to claim 5, characterized in that it comprises an annular gap (L) which is delimited between the annular locking element (34) and the frustum-shaped body (15) and is suitable to ensure elastic contact between said frustum-shaped body (15) and said elastomeric ring (35).

Inventors: CASTELLI ROSARIO, ZENONI PIETRO, CASTELLI, ROSARIO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1999
Main classification: B65H51
IPC codes: D03D47, B65H51