Winding – tensioning – or guiding – Unidirectional winding and unwinding – Variable number of windings on support
Reexamination Certificate
1999-11-15
2001-11-27
Mansen, Michael R. (Department: 3653)
Winding, tensioning, or guiding
Unidirectional winding and unwinding
Variable number of windings on support
C139S452000
Reexamination Certificate
active
06322016
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a yarn feeding device having a storage body with a withdrawal rim which cooperates with a braking band of a yarn brake to form a yarn braking zone. The invention also relates to a yarn brake for use in such a yarn feeding device.
BACKGROUND OF THE INVENTION
In a yarn brake on a yarn feeding device as known from PCT/EP 94/00476, the braking band is glued into the small diameter end portion of a generally conical rubber membrane circumscribing the storage body and being supported at its large diameter end in the stationary support to pull the braking band inner side against the withdrawal rim of the storage body. Such yarn brakes are extensively used at yarn feeding devices for projectile and rapier weaving machines. The membrane commonly constitutes the braking band carrier, and the spring element transmits the axial pressing force onto the braking band without disturbing the local radial deformability of the braking band. Even though it is intended to make the membrane as homogenous as possible nevertheless in operation of the yarn brake the pressing force of the braking band against the withdrawal rim may vary in the circumferential direction. This causes undesirable fluctuation of the withdrawal tension level of the yarn pulled through between the inner side of the braking band and the withdrawal rim and is simultaneously orbiting in the circumferential direction. Gluing the braking band to the braking band carrier is time-consuming and costly. The junction region creates an inhomogeneity which negatively influences a uniform distribution of the pressing force of the brake band along the braking zone. In addition, the friction of the yarn orbiting during withdrawal is transmitted by the braking band into the membrane, which generates a torsional tension in the membrane as the membrane is firmly secured in the large diameter end portion in the support. Said effect caused by the yarn may additionally complicate the uniformity of pressing the braking band against the withdrawal rim. The known yarn brake, however, fulfills a particularly desirable self-compensating effect since it automatically decreases its braking effect with increasing or high withdrawal speed of the yarn and an increase in the yarn tension or a high yarn tension level caused by said withdrawal speed, but the circumferentially varying pressing force of the braking band is disturbing, particularly in the case of sensitive yarn qualities and in modern high performance weaving machines operating with high insertion frequency and extreme insertion speed variations.
A self-regulating yarn brake having a radially deformable braking band with the shape of a frustocone for the first time has been disclosed in EP-A-0 534 263. Said braking band is firmly glued to the inner side of a frustoconical braking band carrier which is radially deformable but axially stiff and is axially loaded in the stationary support by means of a spring assembly. The gluing junction area between the braking band and the braking band carrier has to be made precisely and uniformly and may influence the uniform pressing force distribution of the braking band.
In order to replace the braking band in such yarn brakes having a durable, firm connection between the braking band and the braking band carrier, the braking band carrier has to be disassembled as well and has to be discarded.
It is an object of the invention to create a yarn feeding device of the kind as disclosed as well as a yarn brake for such a yarn feeding device wherein the important advantage of the self-compensating effect is maintained, a negative influencing of the yarn withdrawal tension level due to a circumferentially varying pressing force can be avoided, and wherein the yarn brake is easy to manufacture and handle.
This object can be achieved by supporting the braking band in a floating manner relative to the braking band carrier and the withdrawal rim.
Due to the holding of the braking band in a floating manner, a labour and cost intensive gluing connection between the braking band and the braking band carrier is avoided. In connection therewith the almost unavoidable inhomogeneity of a gluing connection in the force transmission is avoided. The braking band is pressed against the withdrawal rim circumferentially uniformly and regularly. The torsional force generated by the orbiting motion of the yarn and the friction contact of the yarn with the inner side of the braking band is not or not significantly transmitted into the braking band carrier such that the negative influence of such torsional force on the contact between the braking band and the withdrawal rim is avoided. The braking band may move in relation to the braking band carrier during operation and could even rotate. A floating holding of the braking band means a positive engagement which hinders losing the braking band in case of missed contact with the withdrawal rim. However, there is no structural connection between both components but only some sort of a loose trapping. This contributes to the uniformity of the contact pressure. In case that the braking has to be replaced, e.g. due to wear or for adaptation to particular yarn qualities, this can be made easily. The braking band carrier can be used longer and does not need to be disassembled. In order to provide an optimum self-centering of the braking band on the withdrawal rim it can be expedient to support the braking band carrier in a self-centering Cardanic fashion.
The yarn brake can be manufactured with fair costs and in a simple fashion; mounting and maintenance are easy to carry out. The pressing contact relationships between the braking band and the withdrawal rim are optimum thanks to the floating holding, since there is no structural connection between the braking band carrier and the braking band which causes a disturbance when transmitting the axial pre-load force.
The braking band is apt to position itself at least in tangential directions and relative to the normally rounded withdrawal rim, i.e. the braking band is apt to rotate about the axis of the storage body and to displace itself also in the direction of the generatrix of the frustocone or, respectively, to tilt in the braking zone without the necessity that the braking band carrier follow such movements or suppress such movements.
In contradiction to the conventional principle of a circumferentially uniform contact between the braking band carrier and the braking band, the advantage of the floating holding of the braking band is optimized. In the circumferential direction suspension ranges axially pressing against the braking band alternate with ranges not pressing or only pressing with reduced extent. Due to its elastic behaviour the braking is compensating for such differences in the pressing behaviour in an effective manner, particularly with higher yarn speeds. Occasionally the yarn may feel differences in the pressing force of the braking band in the braking zone with low yarn speed. However, this leads to the advantage of relatively high basic yarn tension in the yarn at low yarn speeds and under the axial pre-load of the braking band, which pre-load occasionally and nominally can be lower than in case of a full circumferential pressing relation. Thanks to the self-compensating effect fulfilled by the floating or suspended braking band the difference of the yarn tension between slow and highest yarn speeds remains desirably small, since the braking band does reduce the braking effect automatically with increasing yarn speed. Such a reduced axial pre-load nevertheless leads to a sufficiently high basic yarn tension and relieves the components of the yarn brake and improves the durability.
In one embodiment, the braking band carrier includes a plurality of circumferentially distributed suspension ranges separated by interspaces which contribute to a regular varying braking effect (digital plucking) and to a high basic yarn tension level already with moderate axial pre-load.
The suspension ranges may be formed resiliently in order to
Jacobsson Kurt Arne Gunnar
Ohlson Per
Flynn ,Thiel, Boutell & Tanis, P.C.
Iro AB
Mansen Michael R.
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