Device and method for detecting fluorescent and...

Radiant energy – Luminophor irradiation – With ultraviolet source

Reexamination Certificate

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Details

C250S458100

Reexamination Certificate

active

06297509

ABSTRACT:

This invention describes an apparatus and method for detecting fluorescently and phosphorescently emitted light from sheet material such as papers of value or bank notes.
Such an apparatus is already known from U.S. Pat. No. 3,473,027. The apparatus described therein has an illuminating device for illuminating sheet material with ultraviolet excitation light. The sheet material is preferably illuminated continuously by ultraviolet excitation light. If required, clocked illumination of the sheet material is also possible. The light emitted by the sheet material is detected by a sensor. For this purpose the emitted light is imaged by a lens system onto a prism which then decomposes the emitted light into certain wave ranges. The individual wave ranges are each imaged by a further lens system onto a separate detector which then emits an electric signal proportional to the intensity of the wave range. To permit the sheet material to be detected along a track with a desired resolution, the sheet material is transported by a transport system along a transport direction past the illuminating device and sensor.
A disadvantage of the known apparatus is that the light emitted by the sheet material cannot be divided into fluorescent and phosphorescent fractions.
An apparatus and method for detecting fluorescently and phosphorescently emitted light from an identification mark on a parcel is known from U.S. Pat. No. 3,592,326. This print describes, in connection with a parcel singulating and orienting apparatus, an optical scanning means including an illuminating device wherein the parcels transported on conveyor belts are illuminated in clocked fashion during the transport motion by lamps focused on a scanning line. The light emitted by the parcel or identification mark is supplied via a rotating mirror assembly, whose rotary axis extends parallel to the transport direction and which is located exactly above said scanning line, via two prisms and associated filters to one of two sensors in each case. One sensor is in charge of detecting reflection and fluorescence when the illumination is switched on, and the other sensor for ascertaining phosphorescently emitted light when the illumination is switched off.
The known apparatus firstly has an elaborate structure and secondly requires at least two sensors, involving corresponding adjustment, calibration and servicing effort. Due to the illumination and scanning oriented toward the scanning line, the excitation of the phosphorescently glowing identification mark is low so that little intensity is available for detecting phosphorescently emitted light and no exact, reproducible measurement is ensured.
The invention is therefore based on the problem of providing a very exactly measuring apparatus and method for detecting fluorescent and phosphorescent light from sheet material wherein the light emitted by the sheet material can be divided into a fluorescent and a phosphorescent fraction with one common sensor.
This problem is solved by the features in the characterizing parts of the main claim and the independent claim.
According to the invention, the sensor detects one intensity of emitted light during the light phase of clocked excitation light and a further intensity of emitted light during the dark phase of clocked excitation light. In an evaluation device an intensity of fluorescently emitted light and an intensity of phosphorescently emitted light are derived from the intensities detected in the light phase and dark phase of clocked excitation light. The intensity of phosphorescently emitted light corresponds to the intensity of the dark phase, and the intensity of fluorescently emitted light is derived as the difference of intensity in the light phase and intensity in the dark phase. Furthermore, the sensor detects the intensities of emitted light within, and toward the end (in the transport direction) of, the area of the sheet material illuminated by the illuminating device. Additionally, the area of the sheet material illuminated by the illuminating device is selected to be so great that it is a multiple of the desired resolution.
This permits the intensity of phosphorescently emitted light to be relatively great since it ensures long preillumination with high intensity.


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patent: 6024202 (2000-02-01), Potter
patent: 002097916-A (1982-11-01), None
patent: 2 240 947 A (1991-08-01), None
patent: 06308032-A (1994-11-01), None

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