NL8800022A - IDENTIFICATION LABEL SUITABLE FOR OPTICAL READOUT. - Google Patents

Description

V

-1-

Nedap N.V.

Groenlo

Identification label suitable for optical reading.

The invention relates to an identification label which is suitable for optical transmission of a code, and the device with which this can be done.

The so-called barcodes are known, with which 5 articles, prices and the like can be indicated.

These codes have the drawback that the reading must take place in a predetermined direction relative to the code and also that local pollution can deform or make the code unreadable. A further drawback is that these codes can be deciphered and copied using simple means.

The object of the invention is to overcome these drawbacks and to provide a system with which code carriers can be recognized at arbitrary positions, either directly or indirectly, in a specific space.

These code carriers can be used in the identification of goods, persons or animals.

For these applications, use is currently often made of electronic labels, in which information is stored, which can be read by electromagnetic means, for instance according to the principle, as described in applicant's Dutch patent 176404.

The drawback of the electronic labels is that they are expensive compared to the labels with bar codes.

The optical labels according to the invention offer a high degree of code integrity coupled with a large achievable read distance.

The principle of operation of the labels as well as the operation of the reading device will be explained with reference to a few figures.

The principle of the invention is based on the selective absorption of light in the infrared spectrum, by means of polymers. This absorption could be effected by irradiating labels with an infrared light source which are provided with a thin film of polymer material with a reflector behind it. If the light passes through the thin film of polymeric material and after reflection passes this material again, depending on the chosen material, light is absorbed in certain 40 wavelength bands of the infrared spectrum.

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Depending on and determined by the absorption in the polymer material, each label contains a specific code, which can be determined by the wavelength of the absorbed light, by the degree of absorption or by a combination of the two.

The drawback of the method described above is that, when such labels are read in the receiver, not only light is received that comes from reflections by the labels, but also light that comes either directly or via reflections from the light source and thus does not contain any information. If the labels are rather small, it will no longer be possible to filter the information from these labels from the relatively strong signal that comes directly or indirectly from the light source.

In order to provide a solution for this, in the code carriers according to the invention the infrared light is generated on the label itself, namely by luminescent materials such as, for example, the rare earths neodymium or praseodymium. The luminescence in these 20 materials, in the infrared spectrum, is generated by irradiating them with light from the visible or ultraviolet spectrum.

In this way it is achieved that the receiver only receives light from the spectrum to be considered originating from the luminescent material on an encoded label, which is provided with a specific code via absorption in one or more polymers.

The structure of a label then looks as outlined in figure 1.

The carrier (1) is provided with three layers, which consist successively of a reflector or retro-reflector (2), a layer of luminescent material (3) and a layer consisting of polymer material or materials (4).

Since the light emanating from a label will vary in intensity, depending on the position of this label in the space considered and also depending on the position of this label relative to the exciting light source, a reference must be incorporated in the signal, for example, in the form of an absorption ratio between two 40 wavelengths in the spectrum, which is the same for all possible labels in the system.

The readout unit works as follows:

In the considered space, which is shielded as much as possible from light from other sources, ultraviolet light is emitted by means of mercury lamps, for example. Using filters it is prevented that light from the infrared spectrum enters the considered space.

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If a label with a code is now present in the space considered, the rare earth applied to this label, excited by the ultraviolet radiation, will luminesce in the infrared spectrum.

5 This infrared light is partially absorbed through the film of polymeric material or materials applied to the label and then received directly or via reflections by the receiver.

Using a monochromator or with interference filters 10, the received light is first split into a number of specific wavelengths to be examined, which contain the code information as well as the reference information.

Subsequently, the received signal is amplified such that the amplitude of a preselected reference wavelength has reached a pre-normalized value, after which the code of the label can be read by measuring the amplitude of the received signal on the other characteristic wavelengths. determine. It is of course also possible to work with several reference signals, whereby the amplitude ratio of these signals can then be used as reference.

Figure 2 schematically shows the operation of a possible embodiment of the reading device.

Lamp (5) mainly emits ultraviolet light.

Filter (6) ensures that no light of the infrared spectrum to be considered is present with this emitted light.

The rare earth (3), which is located on the label (1), will luminesce in the infrared spectrum. Reflector (2) ensures that as much light as possible is reflected by the label. This effect can be further improved by making this reflector retro-reflective and placing the receiver in the vicinity of the light source. The film (4) of polymeric material or materials, which can for instance be built up of hydrocarbon compounds such as, for example, amines, imides and phenols, ensures that specific wavelengths in the spectrum are absorbed to a greater or lesser extent, so that the code of the label is determined.

Monochromator (7) splits the infrared light (8) into these specific wavelengths (9), after which this light is collected serially with the aid of a 40 chopper and one sensor, or in parallel with several sensors (10).

All signals are amplified via amplifiers (11) such that the amplitude of the reference signal (12) has reached a predetermined fixed reference value (13).

45 Code (14) can now be determined from the other signals via comparators (15) and decoding circuit (16).

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The code can be applied in this way in the form of or without absorption at one or more of the characteristic wavelengths, but also in the form of variation in the degree of absorption at these wavelengths.

Instead of a monochromator, in another embodiment of the receiver according to the invention, a rotating filter disc for a single detector can also be used, through which the wavelengths to be considered from the spectrum are successively filtered.

The advantage of this is that only one channel is required, so that, for example, dark current, noise and offset influences of the detector and the amplifier can be more easily compensated.

The advantage of the above-described identification system compared to bar codes is that, even with partial contamination of the label, the complete code is still present and readable and that the orientation of the label in the space considered is not important, provided that the light source and detector are visually in communication with the label either directly or indirectly, for example via reflecting mirrors.

. 880 002.2.

Claims (7)

An identification system consisting of coded labels and a device for reading these coded labels, characterized in that the code is formed by the degree of absorption of light at one or more predetermined wavelengths of the spectrum in a film of, for example, polymeric material or materials, which is applied to each label belonging to the system, the wavelengths of this spectrum being chosen such that they normally do not or hardly occur in the space considered. Identification system according to claim 1, characterized in that the light source is a luminescent material, such as, for example, a rare earth, which is excited by ambient light or by a light source 15 with a spectrum which does not overlap the spectrum to be considered and which is provided on the label, behind the absorbent film that acts as a code carrier. 3. Identification system according to one or both of the preceding claims, characterized in that a reflector or a retro-reflector is arranged behind the code carrier on the label or behind the luminescent material in such a way that the intensity of the reflected or emitted light is of the spectrum to be considered, is increased, Identification system according to one or more of the preceding claims, characterized in that the receiving device is provided with a monochromator or a number of interference filters, with which the received spectrum is divided into a number of wavelengths to be considered and wherein one or more of these wavelengths act or act as a reference signal in order to compensate for the influence of the intensity caused by the light source, the position of the label in the space considered, as well as the sensitivity of the receiver, 880002.2 v -6- ► Identification system according to one or more of the preceding claims, characterized in that the code is formed by or without absorption in a number of predetermined wavelengths of the considered spectrum 5 and / or by a number of predetermined absorption levels per wavelength of this spectrum, these levels being chosen so that they can be clearly distinguished from each other by the receiver, Identification system according to one or more of the preceding claims, characterized in that the luminescent material applied to the label is charged by ambient light and the charged energy is only released in the form of luminescence at the moment, that the label and thereby the luminescent material is excited by light of a wavelength range specific for this material, for example in the ultraviolet spectrum. Identification system according to one or more of the preceding claims, characterized in that the luminescent material on the label is a material which is afterglow or phosphorescent, the light source and the detector being switched on and off alternately in order to to prevent light from the light source from being received by the receiver. 8800022