Apparatus for detecting foreign substance in strand-like textile material

An apparatus detects foreign substances in strand-like textile material, such as slivers or yarn, using a white-light LED. The color detection is effected over more than two color support points whereby the detection of foreign substances in the textile material is improved. The apparatus is preferably operated in combination with a yarn cleaner in spinning or bobbin winding machines.

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 brightness signal can be formed,
 which is also evaluated in order to ascertain any deviations.
 The detected measurement values are examined for characteristics that allow
 a conclusion to be drawn about the incidence of foreign substances, such
 as foreign fibers or shell fragments. Foreign fibers are for example
 differently colored, or they react differently to dyeing agents, or their
 surface has a different reflection behavior. Color detection over more
 than two and preferably three color support points allows substantially
 more accurate measurement and evaluation and results in accurate color
 resolution and high reliability of the outcome of measurement. Thus even
 color changes that were heretofore in the tolerance range of fluctuation
 in the measured values and were therefore not detected as a color
 detection can now be detected. With the apparatus of the invention, a
 more-sensitive reaction to fluctuations is possible.
 Further features, details and advantages of the invention will be
 understood and explained in the following disclosure of a preferred
 embodiment with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring now to the accompanying drawings, the measuring apparatus of FIG.
 1 has a white-light LED 1, a yarn 2, and sensors 3, 4, 5 that are embodied
 as photo sensors. Although the invention is described herein in an
 embodiment for use with a yarn, it is to be understood by those persons
 skilled in the art that the invention is equally applicable to any other
 strand-like or indeterminate length textile material.
 The white-light LED 1 comprises a structural unit that has a housing 6, a
 light-emitting diode 9 embodied as an LED chip and connected to a voltage
 source, not shown, via the current conductors 7, 8, a frequency
 transformer 10, and a lens 11. The light-emitting diode, or LED, 9
 generates single-colored light, in this exemplary embodiment blue light,
 which is converted by the frequency transformer 10 and emitted as white
 light with a broad wavelength spectrum comprising a mixture of blue
 radiation and yellow converted radiation. The white light is emitted
 through the lens 11 in the direction of the yarn 2. The frequency
 transformer 10 comprises an epoxy resin molding material with luminescent
 pigments distributed therein. The luminescent pigments are adapted in
 their composition to the light generated by the LED 9.
 The light striking the yarn 2 is reflected by the surface of the yarn 2.
 The sensors 3, 4 detect the reflected light striking them and convert it
 into a signal proportional to the reflected light intensity, and this
 signal is delivered over the lines 12, 13 to a signal processing system
 14. The signal processing system 14 evaluates the incoming signals based
 substantially on the measured intensity values. Changes in the intensity
 of the reflected light, or the exceeding of at least one threshold value,
 allow the conclusion to be drawn that there are foreign bodies in the yarn
 2.
 Improved color detection is attained by using a third sensor 5, embodied as
 a photosensor shown in broken lines in FIG. 1, and is also connected to
 the signal processing system 14 via the line 15. The sensor 5 is located
 at a somewhat lower level than the sensors 3, 4, so that it does not
 impede the course of the beam of light from the white-light LED 1 to the
 yarn 2. A line 16 serves the purpose of communication between the signal
 processing system 14 and data processing or other signal processing
 systems, or serves to control a yarn cleaner, not shown.
 FIG. 2 depicts schematically an exemplary embodiment of a circuit by which
 the signals of three sensors, identified at 17, 18, 19, having spectral
 sensitivity in different ranges, are evaluated. In the circuit of FIG. 2,
 the spectral sensitivity of the sensor 17 is in the red light range, that
 of the sensor 18 is in the green light range, and that of the sensor 19 is
 in the blue light range. The sensors 17, 18, 19 are followed by a
 subtraction stage. The color signal emitted by the respective sensor 17,
 18, 19 is delivered over the associated line 20, 21, 22 to the
 differential signal elements 23, 24, 25, respectively. The sensor 17
 communicates with the differential signal elements 23 and 24 via the line
 20; the sensor 18 communicates with the differential signal elements 23
 and 25 via the line 21; and the sensor 19 communicates with the
 differential signal elements 24 and 25 via the line 22. The differential
 signal element 23 receives a color signal from the sensor 17 that is
 proportional to the intensity of the red light detected, as well as a
 color signal from the sensor 18 that is proportional to the intensity of
 the detected green light. The difference in the light intensity of red
 light and green light is ascertained and carried as a color difference
 signal to a high-pass filter 26. The high-pass filter 26 passes
 high-frequency color difference signals and blocks low-frequency color
 difference signals and thus serves to suppress constant or low-frequency
 differences.
 After passing through the high-pass filter 26, the color difference signal
 is checked in a comparator 29 for whether a predetermined, adjustable
 threshold value has been exceeded. If so, an error signal is generated and
 delivered to a switch element 32.
 In substantially similar manner, the differential signal elements 24 and 25
 deliver respective color difference signals to respectively associated
 high-pass filters 27 and 28 which are also connected to respective
 comparators 30 and 31, whereby the measurement of the difference between
 the intensity of the color signals of red light and blue light and of blue
 light and green light is performed simultaneously and in the same way as
 the measurement of the difference in the intensity of the color signals of
 red light and green light.
 The switch element 32 includes an "OR" circuit and checks whether an error
 signal is present from the comparator 29, the comparator 30, or the
 comparator 31. If there is an error signal from at least one comparator
 29, 30, 31, a foreign body signal is generated. This finction performed by
 the switch element 32 is also known as an "OR" operation on the error
 signals to produce a foreign substance signal. If a foreign substance
 signal is present, for example through the signal processing system 14 via
 the line 10, the cutting device of the yarn cleaner is activated, and/or
 other suitable provisions are initiated for maintaining the desired yarn
 quantity.
 Other details, not explained here, of the design and mode of operation of
 white-light-emitting single-chip LEDs can be obtained from the article,
 entitled "Langlebige Beleuchtung mit hohem Wirkungungsgrad"
 [High-Efficiency, Long-Life Lighting], in Components 5/98.
 It will therefore be readily understood by those persons skilled in the art
 that the present invention is susceptible of broad utility and
 application. Many embodiments and adaptations of the present invention
 other than those herein described, as well as many variations,
 modifications and equivalent arrangements, will be apparent from or
 reasonably suggested by the present invention and the foregoing
 description thereof, without departing from the substance or scope of the
 present invention. Accordingly, while the present invention has been
 described herein in detail in relation to its preferred embodiment, it is
 to be understood that this disclosure is only illustrative and exemplary
 of the present invention and is made merely for purposes of providing a
 full and enabling disclosure of the invention. The foregoing disclosure is
 not intended or to be construed to limit the present invention or
 otherwise to exclude any such other embodiments, adaptations, variations,
 modifications and equivalent arrangements, the present invention being
 limited only by the claims appended hereto and the equivalents thereof.