EP1526102A1

EP1526102A1 - Braking device of weft feeders for textile machines

Info

Publication number: EP1526102A1
Application number: EP04022315A
Authority: EP
Inventors: Pietro Zenoni; Rosario Castelli
Original assignee: LGL Electronics SpA
Current assignee: LGL Electronics SpA
Priority date: 2003-10-23
Filing date: 2004-09-20
Publication date: 2005-04-27
Anticipated expiration: 2024-09-20
Also published as: DE602004011444D1; CN1609303A; ITTO20030833A1; DE602004011444T2; EP1526102B1; CN1609303B

Abstract

This invention relates to a modulated braking device for weft feeders (10) comprising a drum (11) for storage of a weft reserve (SF) and a frustoconical braking member (16) applying a self-adjusting braking action upon the yarn (F) unwinding from the drum (11). The drum (11) is provided with a cylindrical skirt (M) and with a plane front surface (SP) connected to each other by a rounded annular surface (SR). The surface of the skirt (M) of the drum (11) has different degrees of roughness, with an annular braking band (FF) having a lower degree of roughness and extending along said rounded annular surface (SR), in the area that is to be engaged by the frustoconical braking member (16), and with a residual surface portion of the skirt (M), outside the braking band, having a higher degree of roughness.

Description

The present invention generally relates to weft feeders for textile machines and is concerned with an improvement to modulated braking devices for said weft feeders.
More particularly, this invention relates to weft feeders of the type disclosed in the prior patent No. EP 534 253 of the Applicant, which comprise a stationary drum, on which is stored a weft reserve in form of yarn loops, and a braking member having a circular profile, typically a frustoconical member.
In the weft looms of the above-mentioned type, which are intended to be known to those skilled in the art, the stationary drum has a cylindrical skirt and a plane front surface which is connected to the skirt by a rounded annular surface. The frustoconical braking member is coaxially supported on elastic means in front of the drum of the feeder, and is biased by said elastic means to elastically and adjustably engage said rounded annular surface with its main section, along a tangency circumference of the drum which is slightly smaller in diameter than the main circumference of the drum. The yam runs between the drum and the braking member along a sloping path extending between the tangency circumference of the drum and a yarn-guiding eyelet that is arranged nearby the smaller section of the braking member. The braking member applies a self-adjusting braking action upon the unwinding yarn, whose intensity changes as a function of the variations of the speed and mechanical tension of the yam; the braking action can also be adjusted by means of electric means or linear/rotary electro-dynamical means supplied by a current that is modulated as a function of the variations of the mechanical tension of the yarn.
Typically, the frustoconical braking member is made of a metal sheet, fibers or laminated plastic impregnated with epoxy resins, and has an inner surface having a degree of roughness in the range 0,8 to 1,2 microns, which is to contact the yarn while circularly moving in the braking member. The cylindrical surface of the skirt of the drum is also treated with this relatively high degree of roughness for better accuracy during the unwinding run of the yarn. In fact, al lower degree of roughness results in a higher friction coefficient, due to a higher number of micro-contact points between the yarn and the surface of the drum, so that the accuracy of the circular movement of the yarn along said surface, and eventually the accuracy of the unwinding run of the yarn, are adversely affected. On the contrary, when processing yams made of glass fibers, the degree of roughness of the surface of the cylindrical drum should be reduced to values in the range 0,2 to 0,4 microns, e.g. by polishing, to prevent the yam from cracking while running through the braking device.
Also, a higher friction coefficient between the surface of the cylindrical drum and the yarn results in considerably strengthening the braking action of the frustoconical member; accordingly, the elastic contact pressure, so-called "static pressure", of the frustoconical member can be correspondingly reduced for a longer mechanical life of said member.
However, to this purpose, it is not convenient to polish the overall cylindrical surface of the drum of the feeder, both because it is a complex and expensive treatment and because, as mentioned above, the overall surface, if polished with a low degree of roughness, would adversely affect the accuracy of the unwinding run in case of conventional yams.
A main object of the present invention is to provide an improved braking device which allows the braking action upon the yarn to be considerably strengthened and, at the same time, does not adversely affect the accuracy of the unwinding run of the yarn.
According to this invention, said object is achieved by a modulated braking device characterized in that it has a stationary drum with a cylindrical skirt having an outer surface which has different degrees of roughness, with an annular braking band having a lower degree of roughness and extending along the rounded annular surface, on the area that is to be engaged by the frustoconical braking member; and with the residual surface portion of the skirt, outside the braking band, having a higher degree of roughness.
According to this invention, the higher degree of roughness of said surface portion of the skirt outside the braking band is in the range 0,8 to 1,2 microns, and the degree of roughness of the braking band is in the range 0,2 to 0,4 microns. The braking band is preferably made by polishing a layer of a thick chromium plating, and symmetrically extends on both sides of the tangency circumference of the frustoconical braking member with the drum, along spans having a predetermined width.
This invention will be now described in more detail with reference to the attached drawings, shown by way of non limiting example, wherein:
Fig. 1 is a side elevation view of a weft feeder with an improved braking device according to the present invention;
Fig. 2 is a diagrammatical view to an enlarged scale of a detail of the stationary drum of the braking device of Fig. 1;
Fig. 3 is a transversal, cross-section view along line III-III of Fig. 2.
In Fig. 1, a weft feeder 10 of a known type comprises a drum 11 having a cylindrical skirt M and a plane front surface SP that is connected to the skirt by a rounded annular surface SR. A hollow swivel arm 12 is attached to a rotary disc 13 arranged at the base of the drum and winds a plurality of yarn loops SF on the drum to form a weft reserve. In a way known per se, on request of the loom or other textile machine (not shown), yarn F is unwound from the drum, runs through a yarn-guide eyelet 14 coaxial to the drum and, while unwinding, is subjected to the braking action of a self-adjusting braking part generally referred with 15, which is adapted to keep the yam under tension by automatically modulating the braking action as a function of the running speed of the yarn. To this purpose, braking part 15 comprises a frustoconical braking member 16 made of a metal sheet, synthetic fabric or laminated plastic impregnated with a polymeric resin, which is arranged in front of drum 11. The frustoconical member is tangent to the drum along a tangency circumference of rounded annular surface SR which is slightly smaller in diameter than the main circumference of the drum. By means of an annular support 17 and an elastic suspension, not shown in the figure, frustoconical braking member 16 is biased against drum 11 to brake the yarn unwinding from the drum with a predetermined elastic force, so-called static tension. Support 17 is carried on a slide 18 that is axially movable with respect to drum 11 and is operatable by a screw drive 19 for the purpose of adjusting the static tension.
According to this invention, cylindrical skirt M of stationary drum 11 has an outer surface which has different degrees of roughness, with an annular braking band FF having a lower degree of roughness and extending along rounded annular surface SR, and with a residual surface portion, outside the braking band, which has a higher degree of roughness.
Conveniently, the higher degree of roughness of said surface portion of skirt M outside braking band FF is in the range 0,8 to 1,2 microns, and the degree of roughness of braking band FF is in the range 0,2 to 0,4 microns.
The braking band is preferably made by polishing a layer of a thick chromium plating, has a predetermined width H, e.g. in the range 3 to 7 mm, and symmetrically extends on both sides of the tangency circumference of the drum of the feeder, along equal spans H/2.
A preferred embodiment of the invention has been described herein, but it is evident that many changes may be made by a person skilled in the art, depending on the circumstances, within the scope of the inventive concept.

Claims

A modulated braking device for weft feeders (10) comprising a drum (11) for storage of a weft reserve (SF), and a frustoconical braking member (16) applying a self-adjusting braking action upon the yam (F) unwinding from the drum (11), and in which said drum (11) is provided with a cylindrical skirt (M) and with a plane front surface (SP) connected to each other by a rounded annular surface (SR), characterized in that the surface of the skirt (M) of the drum (11) has different degrees of roughness, with an annular braking band (FF) having a lower degree of roughness and extending along said rounded annular surface (SR), in the area that is to be engaged by the frustoconical braking member (16), and with a residual surface portion of the skirt (M), outside the braking band, having a higher degree of roughness.
The device according to claim 1, characterized in that said higher degree of roughness of the surface portion of the skirt (M) outside the braking band (FF) is in the range 0,8 to 1,2 microns, and in that the degree of roughness of the braking band (FF) is in the range 0,2 to 0,4 microns.
The device according to claim 1 or 2, characterized in that the braking band (FF) is made by polishing a layer of a thick chromium plating, has a predetermined width (H) and symmetrically extends on both sides of the tangency circumference of the frustoconical braking member (16) with the drum (11) of the feeder, along equal spans (H/2).
The device according to claim 3, characterized in that said predetermined width (H) is in the range 3 to 7 mm.