Textiles: knitting – Stopping – Needle cooperating element controlled
Patent
1994-11-23
1996-06-11
Calvert, John J.
Textiles: knitting
Stopping
Needle cooperating element controlled
66157, 25055929, D04B 3518
Patent
active
055244602
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to knitting machines and particularly to devices for continuously monitoring the needles used in such machines.
FIG. 1 of the annexed drawings shows, by way of example, two typical failures of a needle of a type used in such knitting machines.
FIG. 1 shows a needle 1 of the so called "tab-type" or "automatic-type", comprising a stem 2 ending with a hook 3 and a tab 4 pivoted in 5 to stem 2 and movable between an open position, shown in the figure, and a closed position, in which it defines the needle eye together with the hook 3.
Such needles are subject to a continuous mechanical stress, due to the pulling action exerted by the needle on the yarn; this stress, which takes place with every action of the needle on the yarn, causes a fatigue condition which may lead to the failure of the needle. This failure usually takes place in the area of hook 3, as visible in FIG. 1, and may be preceded by a stage of relevant deformation of the shape of the hook, usually consisting in a torsion deformation and in an opening movement of the hook.
The failure of a needle of a knitting machine during operation thereof has the consequence of a production of faulty fabric due to the absence of the loop corresponding to the broken needle. This results in an economical damage which may be very relevant, considering the very high production speed of the piece or cloth of fabric by the machine, as well as the fact that quite often the faulty fabric cannot be used.
BACKGROUND ART
In the absence of automatic control devices, the production of the faulty fabric goes on until the fault is visually noticed by the machine operators. This happens with a delay depending accidentally upon various factors, since the operator usually attends to various machines and to various tasks on each machine, beside controlling the product quality.
In the endeavour to overcome this drawback, there have been provided devices for the continuous and automatic check of the needles during the operation of a knitting machine. Most of the devices which are being presently marketed are based on electro-optical techniques which exploit the principle of the optical reflection.
Devices of this kind are described for example in U.S. Pat. Nos. 4,027,982 and 3,937,038.
Such reflection-type devices comprise a light emitting device, able to direct a light beam in the direction of a detecting area which is crossed in sequence by the needles during the operation of the machine, and a receiving device, which receives the light reflected by the needles. If the needles are not correctly positioned, are deformed or broken, the quantity of reflected light energy changes, and this is detected, at least theoretically, by the receiving device.
The electro-optical devices based on the principle of the optical reflection, however, have a number of drawbacks. First of all, installing the detector is difficult because of the need to search critical alignment conditions with respect to the path of the needles, conditions which may be kept with difficulty.
Furthermore, the device is not precise, since it tends to overview broken needles or to consider unbroken needles as being broken. Consequently, wrong decisions are taken in controlling the operation of the machine.
Finally, the performance of the device depends in an unacceptable way from the cleanness condition of the detector.
Solutions have also been tested based on the principle of the optical transmission, as, for example, the devices disclosed in U.S. Pat. Nos. 3,659,346 and 3,946,578.
For instance, the device disclosed in U.S. Pat. No. 3,946,578 comprises a light emitting device, able to direct a light beam in the direction of a detection area crossed by the needles, and two (or more) receiving devices (or surfaces) which receive the light emitted by the emitting device.
The needles, travelling across the detection area, intercept part of the light directed towards the receiving devices. In this manner, such receiving devices are able to show when the respective portions o
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Michetti Andrea
Michetti Paolo
Calvert John J.
Microtex Sas di Dott. L. Michetti
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