Textiles: weaving – Warp manipulation – Feeding
Reexamination Certificate
2000-07-07
2001-06-19
Falik, Andy (Department: 3765)
Textiles: weaving
Warp manipulation
Feeding
C028S194000, C242S131100, C139S368000
Reexamination Certificate
active
06247504
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a tensioning and drawing-back device provided for keeping under tension and if necessary drawing back at least one warp yarn led from a bobbin to a weaving machine.
More especially this invention relates to a device which is provided for tensioning and drawing back several warp yarns coming from respective bobbins on a creel to a weaving machine.
These types of devices are generally known and have among others an important application with jacquard weaving machines with different yarn consumption for each individual warp yarn.
Known tensioning and drawing-back devices are for example provided on a creel disposed behind the weaving machine for tensioning and drawing back the warp yarns which during the weaving process are led from the bobbins on this creel to the weaving machine. A creel supports a great number of bobbins or packages. The various warp yarns which are required for weaving a fabric are led from respective bobbins via a number of guiding grids to the weaving machine. In order to prevent these warp yarns from entangling together they must continuously be held under tension. Slack warp yarns in the weaving area must also be absolutely avoided because they adversely affect the fabric quality. They can for example result in an irregular pile formation. In particular warp yarns which on weaving occupy different successive positions in the shed must be capable of being drawn back out of the weaving area in order to keep them under tension.
In a known embodiment each warp yarn unwound from a bobbin is first passed around a guiding spindle disposed behind this bobbin and subsequently brought over the bobbin and a guiding spindle disposed in front of the bobbin. A first and a second drop wire are suspended from the warp yarn, respectively between the bobbin and the rear guiding spindle and between the bobbin and the front guiding spindle, so that these drop wires can press the interjacent piece of warp yarn, which extends above the bobbin, onto the bobbin and in so doing can form a type of band brake on the winding surface of this bobbin. This occurs if the warp yarn is slack.
If the warp yarn tightens during the weaving process, whereby the drop wires are raised, the warp yarn comes into a position whereby it is no longer in contact with the winding surface of the bobbin, so that the braking effect is terminated. Through the further unwinding of the warp yarn the tension can fall away, so that the warp yarn again comes to hang slack. Through the downward movement of the front drop wire the warp yarn is again tensioned and if necessary drawn back out of the weaving area.
A creel provided with such a tensioning and drawing-back device has the disadvantage that the drawing-back effect achieved by the drop wires is dependent on the location of the bobbin in the creel. A drop wire with a bobbin placed at the rear in the creel will have much less effect than one and the same drop wire with a bobbin placed at the front in the creel. The number of points of friction between the drop wire and the weaving area is indeed much greater for the warp yarn which is unwound from the rearmost bobbin.
Another significant disadvantage of this known device is that the replacement of a bobbin is a rather difficult and time-consuming work.
In the European patent application EP 0 742 297 a tensioning and drawing-back device has been described which can be disposed independently of the bobbins and detached from the creel. Each warp yarn is led through a feed-through eye of a strip. This strip is provided capable of sliding up and down in a holder and exerts a tensile force on the warp yarn between two guiding grids. The tensile force is implemented by the own weight of the strip or by means of a retracting spring connected to the strip and a fixed point of the device. Through this tensile force the warp yarn is tensioned and if necessary drawn back out of the weaving area.
Such a device can be disposed at the front in the creel. The replacement of an empty bobbin is easier and less time-consuming with this device than with the above described device. Furthermore in this manner a drawing-back force is achieved which is independent of the location of the bobbin in the creel.
In order to prevent the warp yarns from being pulled out of both the weaving area and from the bobbin to the strip, through which the warp yarn would not be drawn back out of the weaving area in an effective manner and fabrics of less good quality would be woven, with this device, along the side of the bobbin, between the first guiding grid and the bobbin, a leaf spring brake is provided in order to retain the warp yarn. Since tensioning and drawing-back devices are generally implemented for rather large numbers of warp yarns this makes the device much more complex and expensive.
With the embodiments with retracting spring the disadvantage furthermore also exists that the warp yarn tension with the passage of time is subject to too much change through extension of the retracting springs.
SUMMARY OF THE INVENTION
It is a purpose of this invention to provide an effective operational tensioning and drawing-back device which does not have the above mentioned disadvantages, and which enables an easy replacement of a bobbin without interruption of the weaving process.
This objective is according to this invention achieved with a tensioning and drawing-back device with the characteristics mentioned in the first paragraph of this specification, which comprises a supporting body with a curved friction surface in order to support the warp yarn between the bobbin and the weaving machine, and comprises a first and a second tensioning element which exert a tensile force on the warp yarn respectively in front of and behind the curved friction surface.
This tensile force can for example be implemented through the own weight of the tensioning elements and/or through spring elements connected to these tensioning elements.
In the preceding paragraph and in that which follows the use of the words “in front of” and “behind” and the words “first” and “second” is accepted as the direction of view of the direction of movement of the warp yarn led to the weaving machine.
This device works as follows. The warp yarn is pulled on both sides of the friction surface by the tensioning elements into an almost V-shaped path and in so doing the warp yarn is held under tension both in the weaving area and in the section between the friction surface and the bobbin. During weaving the warp yarn is pulled toward the weaving area. Because of this the warp yarn, at least in the V-path behind the friction surface, is moved against the tensile force exerted thereon. This decreases the angle of contact of the warp yarn over the curved friction surface. At the moment that this angle of contact has become so small that insufficient frictional resistance is exerted on the warp yarn in order still to prevent the warp yarn from being fed from the bobbin, the bobbin comes with a jerk to a rotary movement and the warp yarn is unwound. Through inertia of the bobbin often a little too much of the warp yarn is unwound. Because of this the warp yarn under influence of the tensile force exerted thereon will be moved back in the opposite direction until the angle of contact is again great enough to develop a counteracting friction, through which the unwinding from the bobbin ceases. The drawing-back out of the weaving area for compensation of the different positions in the shed occurs by slight upward and downward movements of the warp yarn in the V-path behind the friction surface.
This device works very well and can draw back the warp yarn out of the weaving area better than the known devices. Furthermore this device can be made with simple means and for a relatively low price. Because of the fact that the warp yarn is also held well tensioned in the section between the bobbin and the friction surface, the replacement of a bobbin can occur without interruption or disturbance of the weaving process. This replacement is further
Creighton Wray James
Falik Andy
N.V. Michel Van de Wiele
Narasimhan Meera P.
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