Winding – tensioning – or guiding – Unidirectional winding and unwinding – Variable number of windings on support
Patent
1998-08-06
2000-08-01
Mansen, Michael R.
Winding, tensioning, or guiding
Unidirectional winding and unwinding
Variable number of windings on support
7386269, 139452, 242150M, 2424191, B65H 5120, D03D 4736, G01L 125
Patent
active
060954493
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a device for controlling tension of a running yarn subjected to rapidly varying stresses to a yarn feeder for feeding yarn to a weaving machine, and to a method for measuring the tension of a yarn at the outlet of a yarn feeder.
BACKGROUND OF THE INVENTION
Controlling yarn tension is very important in order to achieve maximum effectiveness in many weaving operations, such as insertion of the weft yarn in a high-performance loom, like the modern shuttleless looms, or feeding of a group of yarns to a warping machine, or still other operations. In all these activities, the way in which the yarn is drawn off is such that yarn tension may vary considerably. A particular case is insertion of weft yarn in a shuttleless loom, where the yarn is fed in at extremely high and extremely variable speed, causing tension peaks in the yarn that may even result in the yarn breaking.
Mechanical devices are known which control yarn braking in relation to yarn tension, so as to maintain a substantially constant tension in the yarn, far from very high values and exempt from sharp variations. These are equipped with brakes that react mechanically to the tension existing at any moment in the yarn, so that the braking force exerted by the brake on the yarn decreases as the tension increases and, conversely. Braking is mechanically modulated in relation to the yarn tension value. Mechanical devices generally have a slow response time in detecting variations of tension occurring at high frequency. These drawbacks derive from the fact that the yarn tension is detected to modulate braking by using mechanical parts engaging with the yarn and that are prone to move during the yarn tension variations. Though of very small mass, these mechanical parts nevertheless have an inertia and an elasticity that are such that, they interact dynamically with the yarn exchanging kinetic and elastic energy with it, especially in cases of a sudden variation in yarn tension. These dynamic variations slow down the response and diminish the efficaciousness of these devices to control the brake and, as a result, the yarn tension. Moreover, the dynamic interaction of mechanical parts and yarn has an unsettling effect on existing yarn status, and may thus considerably modify yarn tension, especially when the tension varies extremely rapidly and the dynamic interactions between these mechanical parts and the yarn occur continuously. These known devices are, in addition to their slow speed of reaction to tension variations, never completely passive with respect to the yarn in detecting its tension and always alter its value to a certain extent, thereby reducing efficaciousness of braking modulation. Furthermore, these known devices do not measure the absolute or numeric value of yarn tension but are limited to detecting relative variations of tension in order to control yarn braking.
As known devices do not possess a feature whereby the effective tension value is visualised this prevents these devices from being set accurately and permits only an empirical regulation (generally performed `by feel` by an operator).
U.S. Pat. No. 5,316,051 shows a truncated cone-shaped cap fitted on the front end of the drum of a yarn feeder to press directly on the yarn coming from the reserve and passing between cap and drum. This brake exerts a braking force on the yarn that is responsive to the tension in the yarn when exiting from the brake itself. In fact, this exiting yarn tension gives rise to a tension component oriented axially and apt to act retroactively on the cap for being subtracted from the braking force exerted by the cap on the yarn. The axial tension component causes a reduction of the braking force. Therefore, if yarn tension tends to rise, the brake reduces its braking force proportionally. This brake reduces yarn tension peaks and smoothes the tension pattern, but cannot completely cease from braking on the yarn, i.e. the yarn can never be disengaged from the brake completely to reduce yarn tension as muc
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Gallo Mario
Toso Giovanni
Iro AB
Mansen Michael R.
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