Optics: measuring and testing – Inspection of flaws or impurities – Textile inspection
Reexamination Certificate
1999-12-22
2001-01-16
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Textile inspection
C372S043010
Reexamination Certificate
active
06175408
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of German Application DE P 19859274.4 filed Dec. 22, 1998, herein incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to an apparatus for detecting foreign substances in strand-like textile material, such as slivers or yarn.
BACKGROUND OF THE INVENTION
European Patent Disclosure EP 0 643 294 A1 describes the detection of foreign substances in a textile material by illuminating the test product and measuring the light reflected by the test product such that the presence of a foreign substance can be concluded from a change in the reflected light. For detecting foreign substances that are darker than the test product, the test product is projected on a light background on a sensor and, to detect lighter foreign substances, it is projected on a dark background. As lighting elements, light-emitting diodes (conventionally abbreviated “LED”) of a certain color, such as green or red, are used. If the light emitted by the light-emitting diode does not suffice to illuminate the textile material adequately at the material speed required, lighting elements are used that emit a higher quantity of light, such as lasers, flash bulbs, or incandescent bulbs. As an alternative provision for amplifying the emitted light, it is disclosed that the number of LEDs can be increased and that a plurality of LEDs of a certain color can be combined into a so-called multichip LED array. The change in the reflected light, from which the presence of a foreign substance is concluded, comprises a change in the total brightness of the reflected light.
However, the apparatus described in European Patent Disclosure EP 0 643 294 A1 has disadvantages. Since LEDs of a certain color, such as green or red, employ a very narrow wavelength range, certain foreign substances may cause no change in brightness, or may not cause a sufficient change in brightness, thus impairing the reliability of foreign substance detection. Lighting elements with a broader light spectrum, such as lasers, flash bulbs or incandescent bulbs, or with a multichip LED array instead of a single LED, require more parts and considerably more structural space. Yet in certain sensors, such as yarn sensors, only a very limited amount of structural space is available. Also, the energy consumption of an incandescent bulb that is used for instance as an alternative to a single LED is markedly higher.
International Patent Disclosure WO 98/33061 describes the use of different colors or wavelengths. Different colors or wavelengths are intended to prevent the inability to detect contaminated foreign bodies in the test product, or the ability to detect them only poorly. From this Patent Disclosure WO 98/33061 A1, it can be learned that the light intensity of a single LED may be unsatisfactory, and thus to amplify the emitted light quantity and hence, to amplify the electro-optical signal, that a plurality of LEDs should be used instead of a single LED. Using many lighting elements, or using lighting elements that emit light at high intensity, such as arc lamps, however, as already noted above, requires additional components and takes up a considerable portion of the only limited available structural space in a yarn sensor. The apparatus described in Patent Disclosure WO 98/33061 A1 employs a measurement of the total brightness of the reflected light.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an improved apparatus for detecting foreign substances in strand-like textile material by using suitable means.
Briefly summarized, the present invention provides an apparatus for detecting foreign substances in strand-like textile material basically comprising means for generation of light, means for exposing the material to the light, and means for evaluating the light reflected from the material, wherein the aforestated objective is achieved by embodying the light generation means to includes a light-emitting diode for generating colored monochromatic light and a frequency transformer for converting the spectrum of the emitted light into white light.
A light-emitting diode that generates colored monochromatic light and has a frequency transformer that emits white light is often referred to as a white-emitting single-chip LED, and will hereinafter be identified as a white-light LED for shorthand purposes. The white-light LED emits light at a substantially higher intensity than previously known LEDs. At the same time, this light has a broad emission spectrum. Additional LEDs for amplifying the light can be dispensed with. It is also unnecessary to use arrangements of additional lighting elements that emit light of a different color. Compared with conventional lighting elements with a broad wavelength spectrum, such as incandescent bulbs, the lifetime of a white-light LED is up to 20 times that of an incandescent bulb. The white-light LED requires substantially less structural space than lasers, flash bulbs or incandescent bulbs. The use of a single white-light LED thus avoids measurement errors of the kind that occur when more than one LED is used because of the fading in intensity or so-called aging of the light emitted by a given LED, which proceeds at a different rate for each LED. Aging of a single white-light LED can be compensated in a relatively simple way by means of a compensation device, which regulates the current delivered and keeps the light intensity constant. To that end, the intensity of the light emitted by the white-light LED is monitored by a sensor.
Even LEDs straight from the factory each emit light at a different intensity. To prevent erroneous measurements, LEDs are selected in accordance with light intensity in classes, and only LEDs from the same class of intensity are used together. This kind of complicated selection can be dispensed with, when a white-light LED is used.
The differences that occur in the light upon comparison of a plurality of white-light LEDs are substantially less than in conventional LEDs. This improves the replicability of the measurements when an LED is replaced. In a white-light LED, whose light-generating LED furnishes blue light as the colored monochromatic light, the wave length spectrum of the light emitted approaches the composition of sunlight. Thus, for example, like sunlight a white-light LED produces a pronounced proportion of blue light and it is therefore especially well suited for the assessment of textile material. White-light LEDs emit a very homogeneous light that can be readily used for measuring purposes.
A white-light LED, in which the LED, the frequency transformer and a lens are disposed in a common housing, requires extraordinarily little structural space and can easily be installed and removed, in the individual components are especially well protected against mechanical action and soiling. A frequency transformer of an epoxy resin molding material with luminescent pigments distributed therein can be embodied and positioned simply and in numerous ways.
While natural colors have a widely scattered reflection range, in pigment dyestuffs, the reflection encountered is virtually single-wave radiation. Reliable color detection and reliable measurement are possible only by exposure to light of a quite specific wavelength in each case. The light of an LED of a certain color, and optionally in a so-called two-color LED the light of one additional LED in another certain color, cover the required wavelength spectrum for detecting pigment colors only inadequately. The white-light LED improves the excitation of the reflection radiation for pigment dyestuffs. This broadens the range of use and improves color detection and measurement.
Measuring the difference in intensity of the spectra of red light and green light, of blue light and green light, and of red light and blue light, as is possible with three color support points, allows the detection of any incident deviations in color values and any drift or migration of the color values. At the same time, a total br
Birlem Olav
Henze Herbert
Kennedy Covington Lobdell & Hickman L.L.P.
Nguyen Sang H.
Pham Hoa Q.
W. Schlafhorst AG & Co.
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