Advancing material of indeterminate length – With material-responsive control means – To regulate longitudinal movement of material
Patent
1998-04-02
2000-01-04
Walsh, Donald P.
Advancing material of indeterminate length
With material-responsive control means
To regulate longitudinal movement of material
226 45, 2423657, 2424181, 66211, 66146, B23Q 1500
Patent
active
060100524
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates generally to a yarn supply apparatus, and more particularly to a yarn supply apparatus for supplying elastic and inelastic (hard) yarns, ribbons, strands, and the like.
BACKGROUND OF THE INVENTION
Yarn supply apparatuses in knitting machines have the task of supplying the corresponding knitting stations with yarn of the requisite tension and in the desired quantity at the correct time in each case. The constancy of the yarn tension substantially determines the uniformity of the knitted product produced.
Fluctuations in the tension of the supplied yarn, especially when they recur systematically in one row of loops after another, can cause a marked impairment of quality of the resultant knitted goods. Fluctuations in yarn tension can occur when the yarn demand abruptly changes over time. This is the case for instance in flatbed knitting machines when at the turning point of the yarn guide there is suddenly no yarn consumption. If the yarn tension then fluctuates, the result is different loop widths at the edges of the resultant knitted goods than in the middle.
Especially with hard yarns, because of the nonexistent capability of the yarn to expand, the yarn tension depends on the yarn supply quantity, which should match yarn consumption as closely as possible at the particular current time.
For applications with yarn consumption that fluctuates over time, the yarn supply apparatus known from German Patent DE 36 27 731 C1 was developed; it has a yarn wheel driven by a stepping motor. The yarn wheel carries the yarn, drawn from a yarn bobbin, to the applicable knitting station via a yarn brake. The yarn supplied by the yarn wheel travels through a terminal eyelet of a lever supported pivotably on its other end. The eyelet represents a turning point, at which the yarn is rerouted at an acute angle. To adjust a constant yarn tension, the pivot lever is acted upon by a constant torque by means of a direct current motor. The pivot lever is also connected to a position transducer, which detects its pivoted position and readjusts the stepping motor accordingly. The pivot lever, in cooperation with the sensor device, thus serves to detect the existing yarn supply.
A closed-loop controller compares the position of the pivot lever with a command value and accelerates or decelerates the motor if the command value is exceeded or undershot. To compensate for sudden changes in demand, which the motor cannot follow instantaneously because of its moment of inertia, the pivot lever forms a yarn store, which can temporarily store a limited length of yarn.
On sudden changes in yarn demand, the pivot lever must be speeded up. The moment of mass inertia of the pivot lever has an effect on the yarn tension and impairs the constancy thereof.
From German Patent DE 38 20 618 C2, the yarn supply apparatus for kinky and other effect yarns is known, which has two rotationally driven yarn wheels, rotating in opposite directions, around which the yarn to be supplied is wrapped multiple times in a figure eight. An arm carrying an eyelet on its end and acted upon by torque in a predetermined direction of rotation acts as a yarn store for temporarily storing yarn intermittently not drawn off by the knitting stations. The yarn travels at an acute angle through its terminal eyelet, and for temporary storage it is deposited on bolts or posts located along a circle around the arm.
Frictional effects that affect yarn travel occur both on the bolts or posts forming a temporary store and at the eyelet of the arm through which the yarn travels at an acute angle.
From German Patent Disclosure DE 42 06 607 A1, a yarn supply apparatus for simultaneously supplying two yarns to a knitting machine is known, in which a yarn supply wheel is driven by a disk rotor motor. At least one yarn travels from the yarn supply wheel through the longitudinal opening of a helical spring wound in a conical or trumpet shape. A permanent magnet and a Hall sensor are provided on a bearing that pivotably holds the helical spri
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Fecker Josef
Ketterer Ludwig
Leins Eberhard
Schmodde Hermann
Weber Friedrich
Memminger-Iro GmbH
Pham Minh-Chau
Walsh Donald P.
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