Optics: measuring and testing – Inspection of flaws or impurities – Textile inspection
Reexamination Certificate
1999-07-26
2001-03-13
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Textile inspection
C356S430000
Reexamination Certificate
active
06201602
ABSTRACT:
A detector of foreign fibres according to the present invention can be used for the detection of foreign fibres and foreign materials in the textile industry, for example in yarns, slivers and unformed fibre bands on, for example (though not exclusively), weaving machines, ring spinning machines, open-end spinning machines, air-jet spinning machines or chemical spinning machines, bobbin winding machines, doubling machines, cards, drawing benches, combing machines, bobbin frames, texturing machines, . . . .
In the rest of the description of the invention, yarns, slivers, unformed fibre bands and the like are referred to as the measurement object.
Existing detectors of foreign fibres are based on one of the following methods:
Detection of discoloration by detection in two or more spectral bands.
A method of this kind is described in WO 95/29396 (CSIRO). The measurement object is placed in front of a light-absorbing background, and at least one light source allows light with at least two different wavelengths to be incident on the measurement object, which reflects light. The light reflected by the measurement object contains at least two different wavelengths. The quantities of light of each wavelength are measured by one or more detectors, and these measured quantities of light are used to generate signals which are a function of the colour (or discoloration) of the measurement object. A similar approach is to be found in CH-A5-674379 (SCHEINHÜTTE), which document furthermore specifies that the influence of the diameter of the yarn on the reflected light is the same for both wavelengths and can in this way be eliminated.
Detection of contrast between the yarn and a matched background.
In EP-A-0 197 763 (CSIRO), the yarn to be examined is held in front of a background which is selected in such a way that it has a reflectivity which is approximately equal to that of the yarn itself. Diffused light illuminates the yarn and the background. The total quantity of light reflected by the yarn and by the background is measured at one location. If the background has been selected correctly, this quantity is virtually independent of the dimensions of the yarn to be examined. A change in the reflected light measured indicates the presence of contamination, and not a change in the dimensions of the yarn. As an alternative to a background of the same reflectivity as that of the yarn, the possibility is put forward of using a semi-transparent material as the background and illuminating through this material, so that the brightness detected by the receiver resulting from the background corresponds to the brightness resulting from the light reflected onto the yarn. This possibility is expanded on, inter alia, in EP-0,553,445 A2 (LOEPFE).
Detection of reflected light, normalized using diameter information.
A method of this kind is described, inter alia, in WO 93/13407 (SIEGFRIED PEYER AG). In this method, modulated light is directed from a light source onto the moving yarn. A first and a second sensor are provided, the first sensor receiving light which is reflected by the yarn, and the second sensor at the same time receiving light which is transmitted through the yarn. The transmitted light and the reflected light have opposite reactions to variations in the diameter of the yarn. The signals from the two sensors are combined with the aid of electronic means so that a signal is present at the output if there is a foreign fibre in the yarn and so that the effect of diameter variations is largely suppressed. Another embodiment of this method is described in WO 93/19359 (ZELLWEGER USTER AG).
EP-A-0,533,446 (GEBRÜDER LOEPFE AG) describes a method and an apparatus for the detection of contamination in yarns. In this method, a first sensor is used to measure light reflected by the yarn, resulting in a first measurement signal which is dependent on the magnitude of any contamination arising and on the diameter of the yarn. In order to eliminate the dependence on the diameter, a second measurement signal is recorded, which is dependent essentially only on the diameter of the yarn. A combination of the two measurement signals is used to compensate for the influence of the diameter of the yarn in the first measurement signal.
The principle of detecting foreign fibres and foreign materials on the basis of a colour measurement has the drawback that certain colours and discolorations with specific spectral reflection properties are not detected.
The principle based on contrast measurement against a background has the drawbacks that the background has to be matched to the yarn and also that this principle is unable to eliminate the influence of diameter variations of the measurement object itself to a sufficient extent. This drawback also applies to the principle according to which the reflection on the measurement object is normalized using diameter information. As a result, the sensitivity of these methods to foreign fibres and foreign materials is lower than desired.
The object of the detector according to the present invention is to provide a solution to the abovementioned drawbacks.
Principle
The detection method for detecting foreign fibres or foreign materials according to the invention is based on measuring the absorption of light which fills a measurement volume within which a measurement object is situated. Said absorption of light is measured without separately driving light sources for reflection and transmission, and without separately detecting signals representative for reflection and transmission. The spectrum of the light which is used for this purpose is selected in such a way that the measurement object does not absorb this light to a significant extent. Use is made of the fact that in that case foreign fibres and foreign materials will have a greater absorption coefficient for the spectrum of the light used than the measurement object itself.
The method is preferably carried out by introducing light into the measurement volume, in which the measurement object to be examined is situated, via at least one light source. Photodetection takes place in or around this measurement volume, with the result that all the light, or a representative sample of the light, inside the measurement volume is measured and converted into a proportional electrical signal. Comparison of this signal with a signal measured when the measurement volume was empty provides the absorption in the measurement volume, and interpretation of this provides the level of contamination of the measurement object.
The essential feature of the principle is the detection of all the light in the measurement volume, or of a representative sample thereof which is taken uniformly over the entire measurement volume. Furthermore, there are no specific conditions placed on the illumination, detection and measurement volume, in contrast to the principles currently used for the detection of foreign fibres and foreign materials, the correct functioning of which depends on the selection of the background, the setting of the background illumination or on an auxiliary signal for normalization.
In addition the present invention includes detection of foreign materials in a yarn on an open-end spinning machine, characterized in that the detection takes place at the level of the spinning tube. The detector used for the detection may be as described above. The elements of the detector may be arranged directly on the circumference of the spinning tube. The elements of the detector may also be arranged on a support which is attached to the outer wall of the spinning tube. The present invention also includes detection of foreign materials in a sliver at the level of the breaker or at the level of the rotor entry on an open-end spinning machine as well as detection of foreign materials in a sliver at the exit of a card or detection of foreign materials in a sliver at the entry to or exit from a drawing bench.
Operation
When the measurement volume is empty, there is no absorption of light in the measurement volume and all the light which is situated in
Barco B.V.
Font Frank G.
Lauchman Layla
Pillsbury Madison & Sutro LLP
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