Textiles: knitting – Feeding – Positive
Patent
1990-01-04
1991-09-24
Reynolds, W. C.
Textiles: knitting
Feeding
Positive
242 4701, D04B 1550
Patent
active
050504053
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of positively feeding elastic yarn to a knitting machine and to a circular knitting machine.
BACKGROUND OF THE INVENTION
In a method for positively feeding an elastic yarn to the knitting system of a circular knitting machine as known from PCT/EP86/00305, the start and stop signals for the control unit are derived from the movements of the yarn guide for the lead-in and take-out, respectively, of the elastic yarn. On appearance of the lead-in signal, the control unit starts the drive motor of the yarn feeder apparatus at a predetermined speed. The speed is modulated within a predetermined range in response to the successively generated position signals of the circular knitting machine to thereby achieve an accurately synchronized positive yarn feed to the knitting system, taking into account the operating stroke of the needles. Independent of the speed control of the drive motor, the appearance of the take-out signal causes the control unit to generate a stop signal for stopping the drive motor, so that the positive yarn feed terminates with the take-out of the yarn. During the knitting operation, the yarn between the yarn feeding apparatus and the knitting system may be under considerable tension, because the tension of the yarn is still further increased from the take-out instant until the yarn is cut off, due to the drive motor having been stopped, it is extremely difficult to retain the cut-off yarn in the customary yarn clamps (mechanical and/or vacuum-operated). This is due to the tension of the yarn and its compressibility which cause the yarn to slip from the yarn clamp, so that it is no longer available for the next lead-in operation.
Known from DE-OS 19 00 722, is a method for positively feeding an elastic yarn to the knitting system of a circular knitting machine. The yarn is temporarily fed at an increased speed after it has been taken out and before it is cut off, to thereby substantially release the tension of the yarn, so that it is safely retained by the yarn clamp. In this case, however, the operating principle of the purely mechanical yarn feeding apparatus is mechanically derived from the operation of the circular knitting machine, resulting in several disadvantages. The yarn feeder apparatus is only stopped by releasing a clutch after the yarn has been cut off. While the accelerated yarn feeding operation has been initiated at the take-out instant, the accelerated yarn feeding operation is not dictated by the characteristics of the yarn, i.e. its elasticity and smoothness, and the length of the yarn between the yarn feeder apparatus and the knitting system. Feeding is dictated exclusively by the interval between the take-out operation and an instant after the yarn has been cut off, and by the operating speed of the circular knitting machine. The actual tension of the yarn to be relaxed has thus no immediate influence. Although this known method at least partially solves the problems concerning the clamping of the elastic yarn, it is practically impossible to adjust the surplus yarn feed relative to the characteristics of the yarn and to its length between the yarn feeder apparatus and the knitting system. This method is also immediately dependent on a mechanical drive transmission between the knitting machine and the yarn feeder apparatus, which is no longer practicable in the case of a circular knitting machine with an electronically controlled yarn feeder apparatus. The mechanical principle employed in this method, namely, to stop the yarn feeder apparatus only after the yarn has been cut off, and to continue the drive transmission up to this instant, even at an increased yarn feeding speed, is totally unsuitable. This is particularly true when knitting machines are refitted or equipped with electronically controlled yarn feeder devices. The control unit has to perform control functions in response to the take-out signal, and is thus dependant on the timely apprearance of the take-out signal. It is an object of the p
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Calvert John J.
Iro AB
Reynolds W. C.
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