Optics: measuring and testing – By monitoring of webs or thread
Patent
1991-10-15
1993-05-11
Rosenberger, Richard A.
Optics: measuring and testing
By monitoring of webs or thread
250571, 356138, G01D 1126
Patent
active
052105946
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a process for optically measuring the twist of a textile yarn, in which the yarn is lit up by means of a beam of light, to form a spot of light which corresponds to the light diffracted by the surface fibres of the compact core of this yarn.
It also concerns a device for the application of the process for optically measuring the twist of a textile yarn, comprising means for lighting up the yarn by a beam of light, to form a spot of light which corresponds to the light diffracted by the surface fibres of the compact core of this yarn.
Several methods are known for measuring the twist of a textile yarn which constitutes one of the most important characteristics of the yarn. Indeed, most of the mechanical properties and even the accessibility of the reagents, notably colorants during dyeing depend on this fundamental parameter. The twist is determined by the following formula : d the diameter of the yarn in meters, insofar as the structure is considered as ideal and corresponds to a traditional model comprising spiral coilings of fibres in superposed layers. In this case, the characteristic angle of the spiral coiling defines the twist. One of the well-known methods is called "measure by simple untwisting".
This method consists in untwisting the yarn until the twist is zero and in noting the number of turns necessary to obtain this untwisting. Although this measure is very simple, in practice, difficulties are met as soon as one moves away from classic carded yarns and the yarn is very irregular, because it is then practically impossible to untwist it evenly and to obtain zero twist.
Indeed, in a very irregular structure, whilst certain parts are untwisted, other parts are still twisted and the untwisting of these means the retwisting in the opposite direction of the parts which have already been untwisted.
In order to offset this drawback, the use of a needle has been suggested; the needle should be slid between the fibres over the distance separating the two clips of the torsion meter. This means working on very short test-pieces of around 2.5 cm to 5 cm at the most. Even in this case, this determination is sometimes very difficult to carry out.
Another well-known method is called "measure by untwisting-retwisting".The principle of the measure by untwisting-retwisting in the opposite direction until the initial length is covered, is based on the working theory whereby the shortening caused by a twist is independent of the direction of the twist. This can only be true in the case of the perfect yarn, a yarn composed of ideal fibres with no "memory" of shape imposed by the twist.
In practice, even as a very result of storing, the position of the fibres in the yarn becomes fixed, and, as a result, there is, inevitably, a certain memory of the shape.
A third well-known method is called "measure by multiple untwistings-retwistings with test correction".
Counter-testing has been suggested on several occasions as a means of aiming at a correct estimation of the twist. Determination by counter-testing consists in carrying out an untwisting and a retwisting followed by another untwisting and retwisting in the original direction until the initial length is covered. This measure once again supposes a compensation of the behaviour by untwisting-retwisting in both directions of the twist.
The measure of untwisting-retwisting with quadruple counter-test is a measure for determining the twist which necessitates four successive measures carried out by means of a same meter. To begin with, the test-piece is untwisted then retwisted continuously until it gets back its initial length. It is untwisted by the number of turns necessary to cancel out the twist, then retwisted by the same number of turns necessary for the retwisting in the opposite direction increased by a certain number of turns because of the imperfect symmetry of the operations of untwisting-retwisting, notably of the greater or lesser fixing of the twist on the yarn when the measure is taken.
Another method, which is optical, kno
REFERENCES:
patent: 3985450 (1976-10-01), Plockl
patent: 5030841 (1991-07-01), Wampfler
Passap Knitting Machines Inc.
Rosenberger Richard A.
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