Textiles: weaving – Weft manipulation – Weaving with stationary weft supply
Reexamination Certificate
2000-04-17
2001-08-07
Falik, Andy (Department: 3741)
Textiles: weaving
Weft manipulation
Weaving with stationary weft supply
C242S365400
Reexamination Certificate
active
06269843
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a yarn braking device in yarn feeders and to an annular brake element for said device.
DESCRIPTION OF THE RELATED ART
Yarn braking devices, as disclosed in EP-A-0 686 128 and EP-A-0 534 263, are equipped on the inner side of the braking portion of the brake element with a circumferentially continuous lining, or metallic layer, defining a frustoconical brake band. Yarn braking devices of this type guarantee a self-adjusting or self-compensating effect, i.e., they automatically reduce the braking effect as yarn speed increases, and viceversa, so as to achieve a tension profile in the yarn being withdrawn which has only small fluctuations, i.e., a relatively constant yarn tension level.
In a yarn braking device as disclosed in U.S. Pat. No. 4,926,912, individually bendable laminae, interconnected by a circumferentially extending base section of the annular brake element, are used to directly transmit the axial load of the brake element onto the withdrawal rim of the yarn storage drum, and on the yarn itself. The withdrawn yarn, unwinding along the withdrawal rim, subsequently lifts the various laminae and becomes tensioned. An increase in the withdrawal speed hence leads to a progressive increase of the yarn tension, and the yarn braking device is thus unable to accomplish a self-adjusting or self-compensating braking effect.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to provide a yarn braking device and an annular brake element of the type described heretofore, having a self-adjusting or self-compensating effect and an improved operating behavior resulting into a highly reduced number of operating inconveniences, particularly of yarn breakages.
According to the invention, said object is reached with a yarn braking device having the characteristics disclosed in a first embodiment, and with an annular brake element as in a second embodiment.
According to the first embodiment, said yarn braking device essentially comprises an annular brake element having a substantially conical and circumferentially continuous braking portion, of which at least the radial flexibility is significant and which is positioned coaxial to a body shaped as a drum around which is wound a weft yarn reserve under an axial spring load and in peripheral contact, along an essentially circular braking zone, with a rim of said drum from which the yarn is withdrawn, and a flexible and wearproof friction surface structure provided on said braking portion in said braking zone, and is characterized in that said friction surface structure is formed by a plurality of separate elements contacting said braking portion in said braking zone and movable one in respect of the other.
Since separate elements, positioned along said braking zone, are used to transmit the forces between the braking portion and the yarn withdrawal rim, or the yarn respectively, said separate elements being movable in relation to each other and being backed-up by the braking portion, it is not possible for such elements to accomplish a significant spring action or deformation resistance, apt to interfere with the mutual cooperation between the braking portion and the yarn withdrawal rim, or the yarn respectively. In fact, the separate elements behave extremely passively and do not undesirably disturb the constant and smooth transmission of forces between the braking portion, and the yarn withdrawal rim and the yarn. The separate elements merely fulfil the task of providing a predetermined coefficient of friction and an effective wear protection for the braking portion. Failing, therefore, a circumferentially continuous structure with undesirable spring properties and deformation resistance, it is possible to obtain a performance of the braking device similar to that which would be obtained if the radially flexible braking portion were in direct contact with the yarn withdrawal rim, and with the yarn. Even at high speeds, in modern projectile or gripper looms, and with delicate yarn qualities, it is possible to obtain an efficient self-adjustment or self-compensation of the braking effect, which results into a significantly reduced number of operating inconveniences, such as yarn breakages. For example, a coarse denim yarn can be safely woven with a yarn feeder and a gripper loom working at high speed.
According to another embodiment, all said separate elements are movably interconnected within a unitary body. This of course simplifies securing the elements to the braking portion, which must be done in such a way that, in the braking zone, said elements are separated one from the other.
According to another embodiment, said separate elements are not totally interconnected, but are secured to the braking portion one by one. They anyhow provide the required wear resistance and friction coefficient and are apt to prevent the braking portion from contacting the yarn, but do not have any disturbing effect on the mutual cooperation between the braking portion and the yarn. Said elements might even be secured to the braking portion in the braking zone, i.e., directly behind the braking zone.
According to another embodiment, the separate elements are easy to manufacture and have a long-lasting operation, a high wear-resistance and a uniform passive behavior. A solution fo the present invention could also be to adopt a light braking body comprising laminae and to support such laminae at the back—when they are lifted by the yarn unwound in “defile” along a spiral-shaped path—at least on the braking zone, by means of a circumferentially continuous, flexible and pre-loaded braking portion, acting as backup member.
According to another embodiment, the laminae could be positioned in an essentially radial direction, if wishing to operate in both rotation senses of the yarn feeder. If the laminae are positioned obliquely in respect of a radial direction, they can be used to operate only in one rotation sense, i.e., in the sense in which the laminae are inclined.
In another embodiment, a single unitary strip with a base section connecting the laminae, is advantageous from a manufacturing point of view. The base section connecting the laminae is of course positioned at a distance from the braking zone and has no negative effects on the passive flexibility and relative mobility of said laminae. The main purpose of the base section is to keep the laminae in a predetermined positioning, for instance with small interspaces in which the yarn cannot touch the braking portion supporting them at the back.
According to another embodiment, the single unitary strip is manufactured in a flat condition, the laminae are formed by cutting interspaces therein, and the strip is subsequently bent into the shape corresponding to the shape of the braking portion in operating conditions.
Another embodiment provides for a relatively large number of laminae, which is advantageous for their extreme flexibility and passive behavior during operation of the device.
According to yet another embodiment, the braking portion extends close to the free tips of the laminae, which is even more advantageous in order to support said laminae over the full length thereof. It is important for the braking portion to support the laminae at the back, at least behind the braking zone, so that said laminae do not behave as active springs. An extension of the braking portion beyond the free tips of the laminae might be advantageous to prevent an undesired contact of the withdrawn yarn with said free tips.
According to another embodiment, said separate elements are particles applied onto the braking portion, in the braking zone. Said separate elements may define an almost continuous surface, but are nevertheless movable in respect of each other so as not to determine an undesirable spring behavior or resistance to deformation in the mutual cooperation between the yarn and the flexible braking portion.
According to another embodiment, the braking portion is part of an essentially annular elastic membrane apt to transmit the required f
Falik Andy
Nuova Roj Electrotex S.r.l.
Young & Thompson
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