Textiles: weaving – Weft manipulation – Tensions
Reexamination Certificate
2001-10-19
2003-04-01
Calvert, John J. (Department: 3765)
Textiles: weaving
Weft manipulation
Tensions
C139S453000, C242S421000
Reexamination Certificate
active
06539982
ABSTRACT:
This is a nationalization of PCT/NL00/00047, filed Jan. 21, 2000 and published in English.
FIELD OF THE INVENTION
The present invention relates to a loom with an insertion brake which is disposed between a yarn feeder and the shed of the loom, which insertion brake comprises a movable brake element, which is capable of movement between two fixedly disposed yarn guides from a position of rest on one side of the yarn to an operative position on the other side of the yarn, wherein the movable brake element is connected to a driving motor, the excitation of which is controlled by an electronic system, wherein at least one programme for the time and the position of the movable brake element is incorporated in said electronic system.
BACKGROUND OF THE INVENTION
In looms, in particular air looms, the weft yarn is carried into the shed from a yarn feeder at a high velocity during the insertion process. Near the end of the insertion process, the yarn movement is braked abruptly by a braking element on the yarn feeder, wherein the kinetic energy contained in the weft yarn is converted into tension energy in the yarn. High tension peaks may occur in the yarn thereby, which may have various undesirable consequences and which may in some cases even lead to yarn breakage.
In order to obviate the occurrence of such a tension peak and/or damp it at least partially, EP 0 356 380 discloses a loom wherein an insertion brake is disposed between the yarn feeder and the shed of the loom, which insertion brake comprises a driven, movable brake element, which is capable of movement between two fixed yarn guides from a position of rest, wherein the yarn is not passed over the fixed yarn guides, or only to a small extent, to an operative position, wherein the yarn is passed over the yarn guides to a greater extent. The movable brake element is thereby driven in such a manner that the brake element is first moved from its position of rest to a maximum stroke position at the end of the insertion process or shortly therebefore. Then the brake element is returned from its maximum stroke position to a reduced stroke position under the influence of the reactive force of the yarn, wherein the kinetic energy contained in the yarn is reduced and the occurrence of a tension peak is obviated or at least damped. In the prior art loom all this is according to one embodiment achieved in that the movable brake element comprises an elastic part, which is pressed down by the reactive force of the yarn following a maximum stroke of the brake element, whereby kinetic energy from the yarn is stored in said elastic parts In another embodiment, the brake element is controlled by a linear magnetic motor, which is so controlled that the brake element is only moved to its maximum stroke position upon major excitation of the motor, after which the degree of excitation is reduced and the reactive force of the yarn is capable of returning the brake element against the motor force, whereby reduction of kinetic energy in the yarn takes place again, so that the tension peak is damped in this manner as well. In both embodiments an interaction between the reactive force of the yarn and a mechanical or electrical force of the brake element takes place, therefore. This interaction may lead to malfunction, especially at higher operating speeds of the loom, so that an optimum damping of the tension peak that occurs cannot be achieved.
Another embodiment of a loom of the kind to which the present invention relates is disclosed in EP 0 155 431. In this prior art loom, the brake element which is capable of movement between two fixed guides is a lever, whose movements are controlled by a cam driving unit. A position-time diagram is stored on the circumferential surface of the cam in question, according to which the movable brake element's positions are controlled during the insertion process. Such mechanical control of the movable brake element is satisfactory per se for lower-speed looms, but one drawback is the fact that constantly the same position-time diagram is gone through for each insertion. Generally such mechanical control is not sufficiently flexible for quickly varying operating conditions, whilst it is furthermore difficult to adapt to varying yarn qualities, for example. Furthermore, this mechanical control of the brake element is fairly inelastic (rigid), so that problems may arise in case of sudden thickenings in the yarn.
In order to make a loom of the above kind more flexible and more easily adaptable to varying operating conditions, EP 0 605 531 presents a loom wherein the movable brake element is driven by a fast-response stepping motor or DC motor, which is controlled by an electronic control device, which comprises a programme section incorporating a variable programme for time and position of the brake element, at least between insertions. The connection between the motor and the brake element is inelastic thereby, and the driving force of the motor is larger than the maximum reactive force of the yarn at all times, so that it is possible to go through any position-time diagram for the brake element that may be desired. One drawback of this prior art loom is the fact that the brake element control is still rigid, so that problems may arise after all when sudden thickenings are encountered in the yarn.
From Dutch laid-open patent application No. 6712481 a yarn brake is known which comprises a stationary brake element and a movable brake element. The movable brake element is thereby driven by a moving coil motor, which is excited via an electronic system, wherein a position detection sensor is incorporated in the electronic system, which position detection sensor senses the instantaneous position of the movable brake element. The amount of current being supplied to the moving coil motor thereby depends on the position of the movable brake element as sensed by the position detection sensor, all this in such a manner that the final tension of the yarn will remain constant, also in the case of variations in the initial tension. This yarn brake is a genuine yarn tension regulating device, therefore.
Another device for regulating the yarn tension in looms is disclosed in EP 0 467 059. In this device the movable brake element is a two-armed rotary lever, one end of which is movable between two fixed yarn guides and the other end of which carries a magnet coil, which co-acts with two spaced permanent magnets of a linear electric motor. In a lever position wherein the yarn is passed over the fixed guides, said permanent magnets produce an effect like a spring. The yarn tension thereby exerts a reactive force on the lever, which is compensated by the degree of excitation of the linear electric motor. The instantaneous yarn tension is calculated on the basis of the degree of excitation of the linear electric motor. The electronic control system for the linear motor furthermore includes a position detection sensor, which continuously senses the instantaneous position of the lever. The instantaneous yarn tension calculated from the degree of excitation of the linear motor is compared with a desired yarn tension for each position, and in case of a deviation the degree of excitation of the linear motor is changed. Thus the yarn tension can be regulated in such a manner that it conforms to a specific desired position-tension diagram. Furthermore the linear motor of this prior art device can also be excited in such a manner that the brake element takes up positions which are required for drawing back the yarn at the end of the insertion process.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a loom wherein the movable brake element is controlled in a flexible and very precise manner whilst exhibiting sufficient elasticity to be able to cope with sudden variations in the yarn quality or the yarn thickness.
In order to accomplish that objective, the loom according to the invention is characterized in that the electronic system comprises a position detection sensor for sensing the instantaneous position of
Calvert John J.
Jacobson & Holman PLLC
Muromoto Robert H.
Te Strake Textile B.V.
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