IDENTIFICATION SYSTEM USING ULTRAVIOLET FLUORESCENT MATERIALS SUMMARY OF THE INVENTION The present invention is directed to a system for recognizing individual objects, and more particularly to a system in which identification is achieved by detecting visible light emitted from an ultraviolet fluorescent material placed on the object to be identified.

Various types of object identification or recognition systems have been proposed where the object is marked with visible indicia and optically scanned. A typical type of such system using bar codes is found in the check-out line of many supermarkets or the like.

While such systems have virtually eliminated the need for human intervention in sorting and identifying objects, there have been certain problems associated with them. For example, conventional identification systems operating under visible light conditions require a contrasting background to the indicia placed on the object to assure reliable sensing. This requires that the indicia placed on the object be visibly distinguishable from the object upon which it is placed. Consequently, the indicia must be individually selected to create the necessary contrast. Often this is accomplished by a sticker or label which is applied to the object which carries with it alternating light and dark areas to provide the necessary contrasting background. Such labels are usually permanently applied to the object, and detract from its appearance. In the case of small objects, it may be impossible to apply suitable indicia to the object itself. Furthermore, in many instances the object itself forms part of a larger assembly which requires subsequent removal of the

indicia.

Another problem which has been encountered in. visible light detection systems is interference from areas or sources adjacent the scanned area. For example, erratic operation of the optical detection system may be caused by reflections from the object itself or its carrier, from movement of objects or personnel near the object being scanned, or from nearby light sources.

The. present invention is directed to an object recognition and identification system which overcomes these problems. In a broad sense, the present invention includes means for marking the objects to produce fluorescent radiation a plurality of spectral bands, means for illuminating the objects to cause the marking means to fluoresce, and detector means for distinguishing between each of the fluorescing marking means. More specifically, the object recognition system of the . present invention includes means for marking the object to be identified with a fluorescent material emitting visible light of a predetermined wavelength when illuminated with ultraviolet light, a source of ultraviolet light, and detector means responsive to the visible light produced by the fluorescent material for producing an electrical output signal when the marking means is detected.

In a preferred embodiment of the invention, each object to be detected is marked with a small area of material which emits visible light of a predetermined wavelength only when illuminated with ultraviolet radiation. Such materials have found application, for example, in marking laundry items, and are described in more detail in U.S. Patent No. 3,066,105, U.S. Patent No. 3,162,642, and U.S. Patent No. 3,164;603. . Such materials are normally colorless in ordinary light but fluoresce with a distinctive visible color in ultraviolet light.

Depending on the particular chemical composition of the material, visible light emission of a large number of spectral bands between yellow and blue may be attained. Furthermore, by proper formulation, the fluorescent materials can be caused to emit visible light at a specific desired wavelength.

In the preferred embodiment described, radiation emitted from the fluorescent material on the object is received by a photodetector which produces a. suitable electrical output signal. The photodetector may be of the type responsive to visible radiation, and may be positioned adjacent to the marked object, or located some distance therefrom. In this latter case, the light emitted by the fluorescent material is focused on the photodetector by means of an optical lens system or through an optical fiber.

To increase the sensitivity and selectivity of the photodetector, a narrow band optical filter matched to the fluorescent characteristics of the marking material may be used. Consequently, only radiation of a spectral band specific to the marking material will be received by the photodetector. Furthermore, a plurality of photodetectors and filters may be used ^' to selectively distinguish between objects marked with fluorescent materials emitting at different wavelengths.

The electrical signal output from the photodetector may be used in any way heretofore associated with object recognition and identification systems. One important application of the present invention is in the field of robotic guidance. For example, the invention finds application in the assemblage of tires to wheel rims which must be oriented with respect to each other in a specified way. By applying a small spot of the fluorescent marking material to the wheel and rim, output signals from the

photodetector can be used to guide the robot in the assembling of the tire to the rim. Another application is the selection of a particular type of component from among a collect-ion of different components moving on a conveyor belt. By marking each type of component with a fluoresent material emitting visible light at a different wavelength when excited by ultraviolet light, an array ^' of photodetectors can be used to distinguish and recognize each of the different types of components. Further features of the invention will become apparent from the- detailed description which follows. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a diagrammatic view of an object recognition system using the inventive principle of the present invention.

Fig. 2 is a diagrammatic view illustrating an alternate imaging arrangement for the object recognition system of the present invention.

Fig. 3 is a graphical representation of the filter response for the green fluorescent material used in connection with the present invention.

DETAILED DESCRIPTION For purposes of an -exemplary showing, a preferred embodiment of the object recognition and identification system of the present invention is illustrated in Fig. 1. It will be observed that the specific application illustrated is for distinguishing among a number of different types of objects illustrated at la and lb moving on a conveyor belt 2. For example, object la might be a particular type of machine part, while object lb might represent a different type of machine part.

Part la is provided with a small spot or area 3 of a fluorescent material or coating such as that described in U.S. Patent No. 3,066,105, U.S. Patent No.

3,162,642, or U.S. Patent No. 3,164,603. Each of these compositions represents a fluorescent pigment which is normally colorless in ordinary light, but distinctively fluorescent at a particular wavelength when excited by ultraviolet light. Normally these compounds are supplied in powder form, and are mixed with a plastic or solvent. At. very low concentrations, i.e. 0.001% - 0.01%, the fluorescent material when applied to the substrate is substantially transparent and non-visible. At higher concentrations, depending upon the particular material used, or where the material is mixed with an opaque binder, the material when applied to the underlying substrate takes on a gray or off-white color. In any .event, in many applications it is desirable that the material when applied to the underlying substrate be unnoticeable.

The particular chemical composition of the fuorescent material is chosen so that when it is excited by a suitable source of ultraviolet light, the emitted visible light occurs at any one of a number of specific wavelengths. For example, one class of compounds particularly useful with the present invention may be summarized by the following chemical formula:

wherein X represents either oxygen or sulfur, Y represents NHCO and NHCO Z2, and Z-_ represents hydrogen, a 1-8 carbon chain aliphatic, and a radical represented by the formula:

^" This composition produces a colorless compound which fluo-resces yellow to orange in ultraviolet light. Other substitutions of the radicals will produce various other visible output color emissions lying between yellow and blue, i.e. between about 450-620 nm.

The size of the spot area 3 applied to the substrate will depend upon the particular geometry of the • underlying object and the detector installation, as will be described in more detail hereinafter. Furthermore, the spot 3 may be applied to a particular face or side of the underlying substrate such that the orientation of the object on the conveyor belt may be determined. In any event, it will be understood that one part la may be . marked with a material 3 which fluoresces at one visible wavelength, while another part lb may be provided with a different fluorescent compound 4 fluorescing at a different visible light wavelength. In this manner, part la may be distinguished from part lb.

The fluorescent material 3 or 4 is excited by means of an ultraviolet light source 5 positioned adjacent conveyor belt 2. For purposes of an exemplary showing, light 5 produces ultraviolet light at a wavelength of 356nm. It.will be understood that ultraviolet light sources having different wavelengths may be utilized in order to obtain the maximum visible light intensity from the particular fluorescent material.

The detection means used in connection with the preferred embodiment of the present invention is illustrated generally at 6 in Fig. 1. Detector means 6 includes a fiber optic bundle 7 having one end 7a positioned adjacent and directed toward part la so as to receive light emitted from fluorescent material 3. The opposite end 7b of the fiber optical bundle may be positioned at some distance from the part depending upon the specific conditions of the particular application.

The terminal end 7b of the fiber optic bundle is directed toward a photodetector 8 having a spectral response in the visible region matched to the fluorescent wavelength of fluorescent material 3. To further increase the sensitivty and selectivity of photocell 8, an optical filter 9 having a narrow pass band at the fluorescent wavelength of fluorescent material 3 may be provided between the terminal end 7b of the fiber optic bundle and photodetector 8. The electrical signal produced by photodetector 8 on ouitput line 10 may be provided to a suitable utilization device 11 such as a sorting mechanism, a robot arm, a diverter or the like. Such utilization means may cause the part to be reoriented, removed from the belt, or assembled in a particular orientation to another part or assembly.

It will be observed that this arrangement greatly reduces the possibility of erratic operation of detector means 6 caused by spurious light sources or reflections. Because of the unique nature of the radiation emitted by the fluorescent material 3 coupled with the relatively narrow pass band of filter 9 and the spectral response of the photodetector, the system of the present invention is sensitive only to a very narrow range of visible, light wavelengths. Consequently, the system will not respond to visible light having wavelengths outside its response band. Furthermore, since the fluorescent material may be caused to fluoresce only when irradiated by a suitable ultraviolet light source, the marking means themselves are relatively insensitive to ambient conditions. Finally, the intensity of the fluorescing material provides good contrast to the background substrate of the parts la pr lb.

In some instances, it may be desirable to provide electrical outputs responsive to a plurality of

wavelengths. In this situation, a branch 12 may be added to fiber optic .7, with the output end 13 of branch 12 located adjacent a second photodetector 14. A second- optical filter, having a pass band different from optical filter 9 , may be interposed between the output end 13 of the fiber optic bundle and the second photodetector 14. The electrical output on line 16 from the second photodetector is applied to utilization means 11. In one application of the system just described, optical filter 9 may have a pass band matched to the visible light output from fluorescent material 3, while optical filter 15 may have a pass band matched to the visible light output from fluorescent material 4. In this manner, detection means 6 may be caused to distinguish between objects marked with different fluorescent materials.

Alternately, the optical pass bands of the filters may be set to recognize the same visible color from a particular fluorescent marking. For example, as illustrated in Fig. 3, a fluorescent material having a green color may be separated through the use of separate filters into separate optical bands of blue and yellow. The electrical outputs from each of photodetectors 8 and 14 may then be used independently or in combination as recognition signals for this particular color. In any event,, in this embodiment the detection means includes a plurality of filters passing to an associated one of the photodetectors the different spectral bands emitted by the marking means. An alternate arrangement for the focusing optics is illustrated in Fig. 2. In this arrangement, the emitted light from the fluorescent material 3 is focused through a collimating lens 17. and an optical filter 18 having a narrow pass band, and applied to a photocell 19. The electrical output 20 from the

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photocell may then be applied to utilization means 11 as ' previously described. This arrangement permits the lens or lenses to be placed further away from the area being scanned in order to give a greater depth of field. Such an arrangement finds particular application where the detection means must be located some distance from the objects being scanned, for example on a packaging line.

It will be understood that various changes in the steps, materials, and arrangements of parts, may be made without departing from the spirit of the invention as expressed in the appended claims. For example, in some applications the focusing optics, fiber optics or collimating lens, may be dispensed with and the photodetector placed directly adjacent to the objects to be scanned.

Furthermore, each object may be provided with a plurality of fluorescent markings. In this situation, a corresponding number of photodetectors and filters may be used to individually recognize and distinguish between the markings on the objects.