Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-09-01
2001-07-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339060, C250S227230
Reexamination Certificate
active
06262419
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method according to the preamble to claim
1
and to a device for carrying out this method.
BACKGROUND ART
On-line measuring technology preferably makes use of NIR spectrometry, which is capable of operating rapidly and also without contact. However, for some applications this wavelength range is not suitable, e.g. if carbon black or graphite are used as pigments, when the method is to be surface sensitive or when foreign atoms, such for example as nitrogen, are to be recognized. In these cases operation must be at wavelengths of greater than 2.5 &mgr;m, i.e. in MIR. In this range Fourier transformation infra-red (FTIR) spectrometers are the means used until now for selection. By means of FTIR spectrometers however only full spectra can be recorded over a wide wavelength range of about 2.5-25 &mgr;m. This requires a relatively long measuring period. In this wavelength range also the room temperature background radiation (about 10 &mgr;m), is found, whose influence can only be suppressed by expensive measures such as cooled diaphragms and filters or by modulation of the illuminating radiation. FTIR spectrometers also use moving parts, so that their range of applicability is restricted. Furthermore it is difficult to use them at a large distance from the substances to be investigated. Finally, their manufacturing costs are also extremely high.
A method for routine identification of the material of plastic parts with the aid of infra-red spectroscopy is already known from DE 43 40 914 A1. In this case an infra-red reflection spectrum is recorded from the surface of a plastic part to be investigated, and is compared with a set of reference spectra. The reflection spectrum used lies in the MIR range at a wave number range between 400 and 4000 cm
−1
. This area still partly lies in the range of heat radiation. In order that this has no disturbing effect on the measuring procedure, it is necessary to modulate the radiation before it impinges on the plastic part. According to DE 43 40 914 A1, an interferometer is used for this purpose, in which the radiation emitted by an IR light source is subjected to intensity modulation. The optical transmission of such an interferometer is however limited and the power of its output radiation is low in relation to the power of its input radiation. Therefore the output radiation lies at only a few watts, so that the signal-to-noise ratio is low. In order however to be able to investigate carbon-containing plastics in a routine manner by radiation in the MIR range, the document DE 43 40 914 A1 proposes to position the plastic part to be investigated with the aid of a video device. In this way it can be assured that the plastic part is located in a correct measuring position.
Thus however the known method has the disadvantages that it requires an expensive device for positioning, and that it operates relatively slowly due to the positioning procedure.
If a surface irradiator is used as a radiation source, it can be operated at a maximum temperature of 1000° C. Therefore an increase in power can only be achieved by corresponding enlargement of its surface area. This is difficult in the case of a subsequently-incorporated interferometer, so that for this reason the radiation power is restricted to a maximum of 50 watts.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to indicate a method and a device for recognizing organic substances in solid bodies by spectral detection of radiation reflected or transmitted from the substances, by means of which a rapid measurement is possible and which is versatile and may be used extremely cost-effectively and at a larger distance from the object to be measured.
This object is achieved according to the invention by the feature given in the characterizing part of claim
1
.
Advantageous further developments of the method according to the invention and devices for carrying out this method will become apparent from the sub-claims.
By virtue of the fact that a wavelength range of about 2.4-4 &mgr;m is used for radiation, only an extremely restricted wavelength range is used for the investigation, whose information content however surprisingly proves sufficient for many applications. This wavelength range is at a clear distance from the disturbing heat radiation, so that the radiation impinging on the solid body can be unmodulated. Therefore there is no longer any necessity for an interferometer or spectrometer between the radiation source and the solid body to be investigated. As the power restriction caused by this is eliminated, the solid body can be illuminated at a high radiation power, which can extend into the kilowatt range. Due to this high power, positioning of the solid body is omitted, and these can even be scanned in a moving condition, this scanning being without contact and from a larger distance, for example with a distance of 50 cm between the radiation source and the solid body. In this way the measurement can be carried out rapidly, so that it is suitable for on-line operation.
More sensitive detectors may also be used, which likewise contribute to rapid measurement. As in the wavelength range below 4 &mgr;m the room temperature background radiation is still relatively negligible, no special measures are necessary to suppress it.
The output power of the radiation source should come to at least 50 watts and its spacing from the solid body investigated in the case of direct irradiation should be at least 10 cm. In order to compensate for surface irregularities in the solid body, the irradiated surface thereon should come to at least 1 cm
2
, or should have a minimum diameter of 1 cm.
The method according to the invention is particularly suitable for sorting articles of various plastics, which are moved past the radiation source on a continuously driven conveyor belt.
Within the named wavelength range, recognition is carried out with reference to the absorption bands of the extension oscillations of C—H-bonds and any present extension oscillations of N—H-bonds. In many cases of application these may be clearly distinguished from one another, so that they are sufficient for perfect recognition of specific organic substances.
As light sources emitting in a narrow band with a wavelength range of 2-4 &mgr;m are scarcely obtainable or are difficult to produce, it is appropriate in order to irradiate the substances to be recognized, to use a wide-band radiation and to pass the radiation reflected from or transmitted by the substances through a narrow-band filter whose transmittance frequency is preferably variable. Suitable for this is an acousto-optical filter, which can consist of a TeO
2
-crystal, upon which is secured an oscillator crystal (piezo-crystal). This latter may be advantageously energized by a digitally programmable high frequency source in order to pass through the transmission wavelength range of about 2-4 &mgr;m.
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patent: 4631408 (1986-12-01), Zelmanovic et al.
patent: 4880979 (1989-11-01), Yoshida
patent: 4883963 (1989-11-01), Kemeny et al.
patent: 5216484 (1993-06-01), Chao et al.
patent: 5510619 (1996-04-01), Zachmann et al.
patent: 5747806 (1998-05-01), Khalil et al.
patent: 5841546 (1998-11-01), Carangelo et al.
patent: 43 40 914 A1 (1995-06-01), None
patent: 0 250 070 A1 (1987-12-01), None
patent: 2 217 838 (1989-11-01), None
patent: WO 94/11126 (1994-05-01), None
Feldhoff Roger
Huth-Fehre Thomas
Kantimm Thomas
Kowol Frank
Gabor Otilia
Hannaher Constantine
Institut fuer Chemo-und Biosensorik Muenster E.V.
Marshall & Melhorn LLC
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