Winding – tensioning – or guiding – Unidirectional winding and unwinding – Variable number of windings on support
Reexamination Certificate
1999-02-22
2001-04-10
Walsh, Donald P. (Department: 3653)
Winding, tensioning, or guiding
Unidirectional winding and unwinding
Variable number of windings on support
C139S452000
Reexamination Certificate
active
06213419
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a yarn feeder including a housing for a drive motor and a drive shaft, a yarn winding on element which rotates with the drive shaft, a stationary storage drum having a cylindrical, circumferentially closed section, and a stationarily held ring-shaped yarn control element surrounding the circumferential section between a yarn store section and a yarn withdrawal section of the storage drum.
BACKGROUND OF THE INVENTION
In a yarn feeder as known from GB-C-1355518 (FIG. 9) the yarn control element is formed as a stable hollow body supported separately from the storage drum and put over the withdrawal end at the front side of the storage drum. The yarn control element surrounds the cylindrical circumferential section of the storage drum with radial distance by its big diameter cylindrical end portion. In this case the yarn control element minimizes the formation of a balloon during withdrawal of the yarn from the yarn store on the storage drum overhead of the withdrawal region into a withdrawal eyelet positioned in front of and co-axially relative to the storage drum. Among other influences the yarn orbiting around the withdrawal region due to centrifugal force tends to separate in an arch shape from the circumference of the storage drum and to form a spiral shaped ballooning-configuration downstream into the withdrawal eyelet. This known phenomena of the balloon formation leads to strong mechanical loads in the yarn, to an increasing tension in the withdrawn yarn and to yarn breakages, respectively. These disadvantages are eliminated by suppressing the balloon formation by means of the yarn control element. However, due to its distance from the circumferential surface of the storage drum the yarn control element does not suffice to guarantee a uniform and pre-determined basic tension in the withdrawn yarn. For this reason and as mentioned in GB-1355518 in addition to and upstream of the yarn control element frequently a so called brush braking ring is installed at a bracket fixed to the housing, the bristles of which contact the drum and brake the yarn in order to guarantee the necessary yarn withdrawal tension. However, a brush braking ring has, for mechanical reasons, the disadvantage of a speed-dependent braking effect i.e. a braking effect raising the yarn tension with increasing speed. This is a disadvantage, since the withdrawal tension should remain approximately uniform within a broad speed range in order to achieve optimal insertion relations in the weaving machine.
It is an object of the present invention to create a yarn feeder of the kind as disclosed above in which in a structurally simple way an essentially constant yarn withdrawal tension can be achieved in conjunction with the balloon limiting function. This object can be achieved by providing a yarn control element configured as a finite band having a planar cross section, which band is laid on the cylindrical circumferential section with mutually aligned adjacent ends. The band is resistant against extension in circumferential direction of the storage drum and is yieldable in the radial direction of the storage drum, and an elastic tensioning device is provided which preloads the band against the circumferential section.
The yarn is pulled through between the lower side of the band and the cylindrical circumferential section of the storage drum and in addition orbits in the circumferential direction during its withdrawal movement. The mechanical obstacle of the band suppresses the balloon formation tendency of the yarn extremely effectively. Further, a uniform and precisely pre-determinable braking effect is exerted onto the yarn by the contact pressure of the band against the circumferential portion, which braking effect surprisingly remains constant with yarn speed variations. In this way the balloon formation is suppressed by the yarn control element and simultaneously an essentially constant yarn withdrawal tension is achieved. The yarn has to overcome the elastic pre-load spanning or forcing the band onto the circumferential section only at its passing location below the band which in the circumferential area of the passing location remains supported on the circumferential section. Thanks to the yieldability of the band in the radial direction the yarn is forming so to speak an orbiting wave in the band or a sickle shaped free space, respectively, such that at this deformation the deformation resistance of the band remains essentially constant and independent of the speed. Since the perpendicular force on the yarn resulting from the pre-load of the band against the circumferential section remains essentially constant and is independent of speed, and due to the constant friction coefficients between the yarn and the band and the circumferential section, respectively, the advantageous result is that the yarn withdrawal tension remains essentially constant. The reasons for this positive effect of the yarn control element cannot be judged precisely. However, the result of the co-operation between the yarn, the band and the circumferential section, namely an essentially constant yarn withdrawal tension, is convincing. Unexpectedly even the gap between the ends of the band does not disturb the uniform braking effect, apparently since due to the dynamic movement relations the yarn does not feel the circumferential interruption in the band, provided that the yarn direction is inclined in relation to the direction of the circumferential gap.
Suitably the band is of flexible metal or plastic. Furthermore the use of a compound-band is possible having a wear resistant layer and in connection therewith another layer with differing properties.
The band in one embodiment includes a circumferential interruption so that two terminal ends are formed. The terminal ends of the band are parallel to one another and inclined, and the circumferential interruption in the band is as small as possible. The direction of the ends of the band is selected such that the yarn never will pass across the circumferential interruption with parallel orientation.
The band can be elastically pre-loaded by a tensioning device and is positioned on the circumferential section exclusively by frictional contact. The friction at the circumferential section is used to suppress an axial wandering of the band under the drag of the yarn.
The band can be positioned on the storage drum by means of a circumferentially extending shoulder. In this way bands of random widths can be positioned safely and with low tension for sensitive yarn materials.
In one embodiment, the band together with the tensioning device is supported in a holder and is positioned on the circumferential section by means of the holder. The holder, which is oriented parallel to the axis of the storage drum, is adjustable and is mounted in a bracket which is fixed to the housing and extends along the circumference of the storage drum. Thus, the position of the band is assured by the holder, suitably allowing an adjustment of the band in the longitudinal direction of the storage drum, and the holder also takes up occurring axial forces.
At the yarn entrance side of the band, a circumferentially extending depression is provided in the storage drum circumference, or the cylindrical circumference section is configured to project outwardly beyond the storage drum circumference at the yarn entrance side. In accordance with this embodiment, a significantly gentle yarn entrance below the band is achieved.
The tensioning device is provided with a spring element which at least bridges the circumferential interruption between the ends of the band. The spring element is connected with the band at least locally, and preferably is constructed of a tensioned elastomeric material, rubber strip or a tension spring. In this embodiment, tension is brought into the band exclusively by the spring element which at least bridges the circumferential gap of the band and pulls both ends of the band towards each other and produces in this way radial contact pressu
Flynn ,Thiel, Boutell & Tanis, P.C.
Iro AB
Walsh Donald P.
Webb Collin A.
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