Braking means of self-adjusting thread braking devices for weft feeders

Abstract

 A braking means (15') for self-adjusting thread braking devices (14) of weft feeders which comprises a first frustum-shaped body (150), which is substantially flexible both radially and axially, and a second frustum-shaped body (151) which is fitted over the first one and is arranged axially only in the region downstream of the drum of the feeder, over a portion (T) having a suitable length, and is adapted to give the portion of the body of the braking means (15') the rigidity that is necessary and sufficient to transmit to the region of tangency of the body with the drum of the feeder the action applied by the elastic means which press on the braking means (15').

Description

[0001] The present invention relates to a braking means of self-adjusting thread braking devices in weft feeders for textile machines and particularly for weaving looms of the gripper or bullet type.

[0002] More specifically, the invention relates to self-adjusting braking devices of the type disclosed in Italian patents no. 1,251,209 and 1,259,567, which are referenced hereinafter as conventional devices.

[0003] Weft feeders are devices which typically comprise a fixed cylindrical drum, on which an arm rotating in a fishing-reel fashion winds a plurality of turns of thread which constitute a weft reserve, means for producing the advancement of the turns gradually wound from the base towards the end of the drum, and braking means for braking the thread that unwinds from the drum when requested by the loom and for giving it the proper mechanical tension required for the correct unwinding of the thread.

[0004] In such conventional self-adjusting braking devices, the braking means is substantially constituted by a frustum-shaped braking body which is suspended elastically in front of the fixed drum of the feeder, is pushed against the drum typically by the elastic suspension or by equivalent elastic means, and is tangent to the drum at an exit circumference which is slightly smaller than the maximum circumference of the drum. The thread 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 advancement speed of the thread increases, such axial component of the tension tends to move the braking body in contrast with the elastic action of the suspension means or the like, and causes, or tends to cause, its separation from the drum, with a consequent and corresponding reduction in the braking action, which accordingly adjusts itself automatically according to the advancement speed of the thread and therefore according to the mechanical tension of the thread.

[0005] Moreover, the braking body is typically provided with a metallic ring having a protruding edge which is arranged at the smaller or end section of the body and is adapted to engage the thread so as to divert its path. In this manner, the thread discharges onto the braking body the axial component of its tension also at the end region of the body as well as at the region where it is tangent to the feeder drum, significantly improving the response of the braking device.

[0006] For a correct operation in the specified manner, the frustum-shaped body must have special mechanical characteristics, among which considerable radial elasticity and substantial axial rigidity, combined with low inertia, are particularly important.

[0007] For this purpose, it is known to manufacture the frustum-shaped body by using a fabric impregnated with synthetic resins, preferably of the two-part type, or by using a calendered or laminated component made of typically thermosetting polymeric material, providing it with a wear-resistant metallic cladding on the inner side and substantially at a narrow region which straddles the circumference of contact with the drum.

[0008] Conventional braking bodies of the specified type, though having a substantially satisfactory operation, suffer from drawbacks which in some operating circumstances can compromise their operation unacceptably. This occurs for example when the thickness of the frustum-shaped body is reduced significantly in order to reduce the mass and therefore the inertia of the frustum-shaped body so as to achieve better response of the braking means to thread tension variations (especially in the presence of low-count threads). In this case, the axial strength of the frustum-shaped body in fact degrades accordingly and the body tends to undergo a deformation, flexing below the region where contact with the drum of the feeder occurs and thus losing the ability to transmit to said contact region the elastic force (so-called static tension) with which the elastic suspension means or the like press the braking body against the drum.

[0009] The aim of the present invention, starting from the notion of these drawbacks of conventional braking means, is to eliminate them. Within the scope of this aim, an object of the invention is to provide a braking means in the form of a frustum-shaped body as specified, which is improved so as to have significantly low mass and inertia for a corresponding rapid response to variations in the mechanical tension of the thread while retaining the ability to transmit fully, in the region where the body makes contact with the drum of the feeder, the elastic pressure applied to said body by the suspension means or the like.

[0010] A further object of the invention is to provide a braking means, in the form of a frustum-shaped body, which is highly flexible at the region of contact with the drum of the feeder astride the exit circumference of the drum in order to ensure a gradual braking action adapted even for lower-count threads.

[0011] According to the present invention, this aim and these and other objects which will become better apparent from the following detailed description are achieved with an improved braking means having the specific characteristics stated in the appended claims.

[0012] Substantially, the invention is based on the concept of providing a braking means having a composite structure which is obtained by superimposing on a first frustum-shaped body, which is substantially flexible both radially and axially, a second frustum-shaped body which is arranged axially only in the region downstream of the feeder drum, over a portion which has a convenient length and gives said portion of the braking body the rigidity that is necessary and sufficient to transmit to the region of tangency between the braking body and the drum the action applied by elastic means that press on said braking body.

[0013] Further characteristics and advantages of the braking means according to the present invention will become better apparent from the following detailed description and with reference to the accompanying drawings, given by way of non-limitative example, wherein:

Figure 1 is a lateral elevation view of a weft feeder with the self-adjusting braking device provided with a conventional braking means;

Figure 2 is an enlarged-scale axial sectional view of the braking means according to the present invention;

Figure 3 is an enlarged-scale view of a detail of Figure 2;

Figure 4 is an exploded perspective view of the braking means of Figure 2.

[0014] 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 arranged at the base of the drum, winds a weft reserve in the form of a plurality of turns of thread SF. In a per se known manner, the thread F, when requested by the loom or other textile machine (not shown), unwinds from the drum, passing through a thread guide 13 which is coaxial to the drum and is subjected, in its unwinding motion, to the action of a self-adjusting braking device, generally designated by the reference numeral 14, which is designed to keep the thread under tension, automatically modulating the braking action as the advancement speed of the thread varies.

[0015] For this purpose, the device 14, which is interposed between the thread guide 13 and the drum 11, comprises a braking means 15 which is constituted by a frustum-shaped body made of synthetic laminated material or fabric impregnated with polymeric resins typically of the two-part type, which is arranged so as to face the drum 11, to which it is tangent along an exit circumference CU which is slightly smaller than the maximum one. By means of an annular support 16 and an elastic means 17, the body 15 is pressed against the drum 11 in order to brake with a preset elastic force, known as static tension, the thread that unwinds from the drum, and the support 16 is supported by a carriage 18 which can move axially with respect to the drum 11 by way of a screw-type mechanism 19 in order to adjust the static tension.

[0016] In the region of contact with the drum 11, the internal surface of the braking means 15 is provided with a metallic reinforcement lamina (not shown) and at the smaller end section of its frustum-shaped body said braking means is provided with a ring 21 which is adapted to engage the thread F and divert its path towards the thread guide 13; the ring 21 is formed by a conical portion 21a, which is accommodated inside the frustum-shaped body, and by a cylindrical portion 21b, which is external to the body and is screwed like a locking ring onto the portion 21a, clamping the frustum-shaped body of the braking means 15.

[0017] According to the present invention, and in accordance with the stated aim and objects, the improved braking means, designated by the reference numeral 15' in Figure 2, maintains the frustum-like shape of the conventional means 15 but is constituted by a composite structure which comprises a first frustum-shaped body 150, which is substantially flexible both radially and axially and protrudes axially from the ring 21 beyond the region of tangency with the drum 11 formed by the exit circumference CU of said drum. A second frustum-shaped body 151 cooperates with the first frustum-shaped body 150, is fitted over the first one and is arranged axially only in the region downstream of the drum 11 of the feeder, over a portion T of suitable length, for example between 50 and 80% of the distance between the ring 21 and the circumference CU of the drum 11, in order to give such portion of the body of the braking means 15' the rigidity that is necessary and sufficient to transmit to the region of tangency between the body and the drum the action applied by the elastic means 17 that press on the braking means. According to a preferred but non-limitative embodiment of the invention, both said first and second frustum-shaped bodies 150 and 151 are made of the same material, typically fabric or calendered material impregnated with epoxy resins, more generally thermosetting resins, or calendered material made of thermoplastic resins, or sheet steel of suitable thickness. Alternatively, a combination of these materials can be used advantageously; for example, by providing the first frustum-shaped body 150 by using impregnated fabric, which is adapted for the purpose due to its greater elasticity, and by providing the second body 151 by using thermoplastic calendered material, or sheet steel, which is more rigid and therefore more adapted to transmit the elastic contact pressure applied by the braking means 15' to the drum 11. Likewise, the two cooperating frustum-shaped bodies 150-151 can be simply arranged side by side and connected to each other by the clamping action applied by the end ring 21 or can be rigidly coupled to each other beforehand by means of an interposed layer of adhesive.

[0018] Without altering the concept of the invention, the details of execution and the embodiments may of course be changed extensively with respect to what is described and illustrated by way of non-limitative example without thereby abandoning the scope of the protection of the appended claims.

[0019] The disclosures in Italian Patent Application No. TO2000A000514 from which this application claims priority are incorporated herein by reference.

[0020] 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 scope of each element identified by way of example by such reference signs.

Claims

1. A braking means (15') for self-adjusting thread braking devices (14) of weft feeders (10), characterized in that it comprises a first frustum-shaped body (150), which is substantially flexible both radially and axially, and a second frustum-shaped body (151) which is fitted over the first frustum-shaped body and is arranged axially only in the region downstream of the drum (11) of the feeder, over a portion (T) having a suitable length, and is adapted to give said portion (T) of the body of the braking means (15') a rigidity necessary and sufficient to transmit to the region of tangency of said body with said drum (11) of the feeder (10) the action applied by elastic means (17) which press on said braking means (15').

2. The braking means according to claim 1, characterized in that both said first and second frustum-shaped bodies (150-151) are made of the same material or of different materials, chosen among the following group of materials: fabrics and calendered materials impregnated with thermosetting resins, typically epoxy resins, calendered materials made of thermoplastic resins, sheet steel.

3. The braking means according to claim 1, characterized in that the first frustum-shaped body (150) is made of impregnated fabric and the second frustum-shaped body is made of thermoplastic calendered material.

4. The braking means according to the preceding claims, characterized in that said portion (T) of convenient length is equal to 50-80% of the distance between the end ring (21) of the braking means (15') and the exit circumference (CU) of the drum (11) of the feeder (10).

5. The braking means according to the preceding claims, characterized in that said first and second frustum-shaped bodies (150-151) are arranged side by side and connected one to the other by the clamping action applied by said end ring (21).

6. The braking means according to claims 1 to 4, characterized in that said cooperating frustum-shaped bodies (150-151) are rigidly coupled to each other by a layer of interposed adhesive.

Drawing