Method and device for detecting foreign matter in...

Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet

Reexamination Certificate

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C356S238200

Reexamination Certificate

active

06380548

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of German Application DE P 19939711.2 filed Aug. 21, 1999, herein incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a method and a device for detecting foreign bodies in longitudinally traveling yarn, and more particularly to such a method and device wherein light is directed on the yarn and is reflected by its surface, the reflected light is detected by a sensor and is converted into signals, the signals are subsequently evaluated and, depending on the outcome of this evaluation, an interruption of the yarn travel may be actuated.
BACKGROUND OF THE INVENTION
The fiber material supplied to a textile yarn spinning device can contain impurities, foreign materials and foreign fibers, which may lead to visible, undesired irregularities in the finished product and/or to improper or poor cohesion between the fibers and, in turn, may ultimately result in a yarn break during the subsequent finishing processes. Such foreign matter causes monetary losses in cases of inferior quality or waste goods, and in additional costs when increased production outlay is necessary, for example, in case replacement yarn must be produced or provided. It is therefore customary to employ devices by means of which such foreign matter can be removed from the yarn.
European Patent Publication EP 0 643 294 discloses a method for detecting foreign material in yarn, wherein the yarn is illuminated, the light reflected by the yarn is measured and the presence of a foreign material is inferred from a change in the reflected light. If a threshold value for lighter foreign materials is exceeded, or a threshold value for darker foreign materials is not reached, a foreign material signal is generated and a cleaning cut of the yarn is actuated to remove the affected section of yarn.
A device for the visual detection of impurities, foreign materials and foreign fibers in textile fiber materials is known from European Patent Publication EP 0 399 945 which generates an output signal for actuating a cleaning cut of the yarn in case of sudden color changes in the reflected light.
Changes in color, as well as changes in brightness or reflectivity, however, do not only occur because of foreign fibers but, with cotton yarns for example, also result from the presence of shell and stem particles, as well as leaf fragments, contained in the yarn along with the cotton fibers. When such foreign materials are detected, output signals are also transmitted to the yarn cleaner in order to actuate cleaning cuts of the affected yarn areas. Unfortunately, the proportion of such undesired plant components in the fiber material of yarns can be considerable, due to the already extensive and still increasing automation of the picking process when harvesting cotton, and the attendant factor that an insufficient consideration is often given to the optimal degree of ripeness of the cotton in determining the correct time for harvesting cotton. A portion of the foreign plant material remains in the fiber material and is supplied to the spinning station in spite of great cleaning efforts in the opening room and cleaning during carding. The foreign materials are ultimately detected in the yarn after spinning, resulting in a multitude of cleaning cuts being actuated. Each of the cleaning cuts requires the performance of a yarn piecing or connecting process. A large number of cleaning yarn cuts and yarn piecing operations, which in unfavorable circumstances may be increased if it is necessary to repeat any of the individual piecing operations, lowers the efficiency of the yarn producing or processing operation. In addition, it is also disadvantageous that each yarn piecing or connection inevitably produces a relatively prominent thickened and/or weakened location in the yarn, which impairs the desired uniformity in strength and appearance of the yarn.
OBJECT AND SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to reduce the above mentioned disadvantages and to improve yarn production and processing.
This objective is addressed by providing a method and a device which basically classifies whether or not a foreign body in a yarn can be tolerated. More specifically, in accordance with the present invention, the method and device is adapted to detect foreign matter in a longitudinally traveling yarn and to either actuate or suppress an interruption of the yarn travel according to an evaluation of the detected foreign matter. For this purpose, the method and device utilize a light source for directing light on the yarn so as to be reflected thereby. The light reflected by the yarn is detected, e.g., by a suitable sensor, and signals representative of the reflected light are generated. Certain criteria are predetermined which distinguish the typical properties of foreign matter which can be tolerated in the yarn from the respective properties of foreign matter which cannot be tolerated in the yarn. In the device of the present invention, this criteria is stored, e.g., in a data memory. The signals generated according to the light reflected by the traveling yarn are evaluated by comparing the signals with the predetermined criteria utilizing an evaluation unit connected with the data memory. In turn, a yarn interruption is either actuated or suppressed according to whether the predetermined criteria has been met.
The type and nature of a yarn interruption may take different forms. For example, a cleaning cut of the yarn, such as by a yarn cleaner device, is one contemplated form of a yarn interruption. In a spinning operation, the spinning process may also be interrupted, for example, by stopping the spinning rotor. By suppressing yarn interruptions, a yarn interruption is not triggered with every signal indicating foreign matter, and it is possible in this manner to noticeably reduce the number of cleaning cuts or other yarn interruptions, and in turn reduce the disadvantages caused by piecing or other yarn connections.
Reductions in the visible appearance or in the stability of the finished yarn product as a result of the presence of foreign matter can be negligibly small in certain circumstances, for example, in the case where the foreign matter which is detected is very small. If it will be possible to remove the foreign matter in the course of a subsequent production or processing operation, for example, by stripping the foreign matter at a guide eye, or by washing the foreign matter out of a fabric material, no reduction in quality or suitability of the yarn or the finished product to be made from the yarn, in particular the visual properties thereof, will occur. Such removable foreign materials are particularly suitable for classification as tolerable foreign matter. The criteria are advantageously established such that they define such foreign matter as being tolerable.
In case of a signal indicating a foreign matter is present, a yarn interruption is preferably suppressed if several criteria are simultaneously met at one lengthwise location of the yarn in the detection area. In particular, for example, even though the detected brightness of the light reflected by the yarn may deviate from a predetermined reference value by more than a predetermined amount, if this brightness deviation does not occur for greater than a predetermined length of the yarn, while at the same time a variation of the brightness signal is detected in the affected longitudinal area of the yarn having the brightness deviation, a yarn interruption may be suppressed because, for example, such criteria may indicate the characteristic or typical range of brightness or color values for shell particles. A high degree of dependability in detecting tolerable foreign matter can be achieved by means of meeting several criteria simultaneously. The dependability of detection of tolerable foreign matter can additionally be increased by continuously detecting the yarn diameter and evaluating it as an additional signal.
The values established for the pr

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