Abstract:
A spectrum analyzer determines the light emission characteristics of an authentication mark that is invisible when illuminated with visible light but is visible when illuminated with IR light. The spectrum analyzer includes an IR light source, a mirror positioned to deflect light from the IR light source in a direction that is substantially perpendicular to a surface of the authentication mark, a first lens for collimating light that is emitted by the authentication mark in response to an illumination by the light from the IR light source, an optical element comprising a prism or a hologram for generating a spectrum from the collimated light, a second lens for imaging the spectrum, an IR light blocking filter, a detector positioned to receive light components of the spectrum after the spectrum has been imaged by the second lens and filtered by the IR light blocking filter, and a control unit connected to the detector and programmed to read the authentication mark based on intensities of the light components received by the detector.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/108,956, filed Nov. 18, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to authentication marks or security marks and, more particularly, a device and method for reading an authentication mark by analyzing the spectrum of visible light that is emitted by the authentication mark when the authentication mark is illuminated with infrared and/or ultraviolet light. 
     2. Description of the Related Art 
     Various techniques have been used to identify articles in an effort to reduce counterfeiting. For collectibles such as art works and sports memorabilia, where a single item may be worth millions of dollars, a technique that is highly refined and virtually impossible to copy is desired. This is because high potential counterfeiting gains will motivate counterfeiters to invest large sums of money and resources to defeat the anti-counterfeit measure. Similarly, the high cost of implementing an anti-counterfeit measure for collectibles is typically accepted by the owner or insurer, because the potential loss from counterfeiting is great. 
     On the other hand, for mass produced items such as apparel, CDs, and audio and video cassettes, cost is a more important factor in implementing an anti-counterfeit measure. The implementation cost must be small enough so that the cost of the protected product will not increase dramatically. Yet, the anti-counterfeit measure must be refined enough so that counterfeiters will be unable to defeat the anti-counterfeit measure in a sufficiently easy manner such that they will be able to economically produce and sell counterfeit goods. 
     Mass produced items also have to be protected against product diversion. Product diversion occurs when a counterfeiter acquires genuine, non-counterfeit goods that are targeted for one market and sells them in a different market. The counterfeiter does this to circumvent the manufacturer&#39;s goal of controlling the supply of his or her goods in a particular market and, as a consequence, benefits from the sales in that limited supply market or in the diverted sales market. 
     In one type of anti-counterfeit and anti-diversion measure, an ultraviolet (UV) ink is used to mark the product with an identifying indicia. One benefit of using the UV ink is that it is typically not visible when illuminated with light in the visible spectrum (380-770 nm), but is visible when illuminated with light in the UV spectrum (200-380 nm). Therefore, counterfeiters will be unable to tell whether the product contains a security mark by merely looking at the product when the product is illuminated with visible light. 
     A number of UV inks are readily available in the security industry and can be obtained at a relatively low cost. Several UV ink types and compositions are described, for example, in U.S. Pat. No. 5,569,317, entitled “Fluorescent and Phosphorescent Tagged Ink for Indicia” the disclosure of which is incorporated by reference herein. This patent discloses a security mark that becomes visible when illuminated with UV light having a wavelength of 254 nm. 
     However, the use of security marks containing a UV ink has seen increased use and counterfeiters have become knowledgeable about their use. It has been a common practice for counterfeiters to examine the UV ink from a product sample, reproduce or procure the same or similar UV ink that matches the characteristics of the UV ink from the product sample, and apply the same security mark on the counterfeit products using the substitute UV ink. 
     In another type of anti-counterfeit and anti-diversion measure, an infrared (IR) ink is used to mark the product with an identifying indicia. As with the UV ink, one benefit of using the IR ink is that it is typically not visible when illuminated with light in the visible spectrum, but is visible when illuminated with light in the IR spectrum (800-1600 nm). An additional benefit of using the IR ink is that it is more difficult to reproduce or procure the matching IR ink by studying a product sample containing the IR security mark. Examples of IR security mark usage are given in U.S. Pat. No. 5,611,958 and U.S. Pat. No. 5,766,324. The disclosures of these patents are incorporated by reference herein. 
     Combination security marks have also been proposed. In U.S. Pat. No. 5,360,628 and U.S. Pat. No. 5,599,578, the disclosures of both of which are incorporated by reference herein, a security mark comprising a visible component and an invisible component made up of a combination of a UV dye and a biologic marker, or a combination of an IR dye and a biologic marker is proposed. Also, in U.S. Pat. No. 5,698,397, the disclosure of which is incorporated by reference herein, a security mark containing two different types of up-converting phosphors is proposed. 
     The detection of invisible security marks is performed automatically using a photodiode, for example, or manually by observing the fluorescence that results from illumination with a UV or IR light source. Sometimes, an invisible security mark is printed as an invisible bar code, as in U.S. Pat. No. 5,502,304, U.S. Pat. No. 5,525,798, U.S. Pat. No. 5,542,971, and U.S. Pat. No. 5,766,324, and is read using a bar code reader. However, there has been no system for automatically determining the characteristics of light that is emitted from an invisible security mark as a result of illumination with a UV or an IR light source. For example, an IR ink may emit a green light in response to illumination with IR light, but the automatic reading systems described above merely look for any emission above a certain threshold and do not distinguish between a green light emission and any other spectral characteristic. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a system and method for determining the light emission characteristics of an authentication mark that is invisible when illuminated with visible light but is visible when illuminated with either UV or IR light. As used herein, an “invisible” mark is a mark that is not visible with the human eye when illuminated with light in the visible spectrum. 
     The above and other objects of the invention are achieved by a spectrum analyzer having an IR light source, a mirror positioned to deflect light from the IR light source in a direction that is substantially perpendicular to a surface of the authentication mark, a first lens for collimating light that is emitted by the authentication mark in response to an illumination by the light from the IR light source, an optical element comprising a prism or a hologram for generating a spectrum from the collimated light, a second lens for imaging the spectrum, an IR light blocking filter, a detector positioned to receive light components of the spectrum after the spectrum has been imaged by the second lens and filtered by the IR light blocking filter, and a control unit connected to the detector and programmed to read the authentication mark based on intensities of the light components received by the detector. 
     The detector comprises an array of photodiodes or charged-coupled devices (CCDs) each positioned to receive a different one of the imaged light components. Alternatively, a single aperture-photodiode assembly may be used. When the single aperture-photodiode assembly is used, the assembly can be controlled to be moved to a plurality of positions so that the photodiode receives a different one of the imaged light components through the aperture at each of the plurality of positions of the assembly or the optical element can be controlled to be rotated to a plurality of positions such that the photodiode receives a different one of the light component through the aperture at each of the plurality of positions of the optical element. 
     The spectrum analyzer according to the invention may further comprise a beam splitter positioned between the object lens and the prism, a reticle positioned to image light deflected by the beam splitter, and a movable stage on which the authentication mark is mounted. The movable stage can be controlled in accordance with the image formed by the reticle to align the authentication mark. 
     Additional objects, features and advantages of the invention will be set forth in the description of preferred embodiments which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail herein with reference to the drawings in which: 
     FIG. 1 illustrates a spectrum analyzer according to a first embodiment of the invention; 
     FIG. 2 is a diagram illustrating a shift in the imaged portion of the authentication mark based on the incidence angle of the illumination beam; 
     FIG. 3 illustrates a spectrum analyzer according to a second embodiment of the invention; 
     FIG. 4 illustrates the steps of reading the authentication mark according to the invention; and 
     FIG. 5 is a flow diagram illustrating the steps for verifying the authentication mark according to the invention. 
    
    
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred exemplary embodiments of the invention, and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a spectrum analyzer  10  according to a first preferred embodiment. The spectrum analyzer  10  illuminates an authentication mark  20  using an infrared (IR) light that is generated by a light source  30 , passed through a focusing lens  40 , and deflected by a mirror  50 . The mirror  50  is positioned directly above the mark  20  and angled such that the IR light generated by the light source  30  is deflected towards the mark  20  at an angle generally normal to the authentication mark surface. 
     The mark  20  includes an IR ink containing an up-converting phosphor that responds to an IR light excitation by fluorescing, i.e., emitting light in the visible spectrum. The up-converting phosphor used in the preferred embodiments is an up-converting phosphor “PTIR545” which is available from Phosphor Technology Ltd. This phosphor fluoresces when it is excited by an IR light having a wavelength of about 960 nm. Other up-converting phosphors may be used in the invention so long as the light source  30  produces an IR light having the necessary wavelength to cause the up-converting phosphor to fluoresce. The light source  30  of the preferred embodiments is a semiconductor laser that is capable of generating an IR laser having a wavelength of about 960 nm. 
     The IR ink containing the PTIR545 phosphor is formed by mixing this up-converting phosphor with a binder resin, which may be any acrylic or urethane resin that is thermoplastic. For cost reasons, only small quantities of the up-converting phosphor are used to form the IR ink. Hence, a diffuse IR light source will be unable to cause significant fluorescence intensity to be easily detected. Rather, a concentrated IR laser source directed at the particular location of the IR mark is necessary. In the preferred embodiments, the light source  30  has a power output of 20 mW. The power output can be adjusted up or down based on the amount of up-converting phosphor that is used in the IR ink. 
     The emitted light is collimated by an objective lens  60 , and dispersed into its spectral components by an optical element  70 . The optical element  70  may be a prism, a holographic optical element (HOE), or any other optical element that is capable of separating light into its spectral components. The spectral components are imaged by an imaging lens  80  and the imaged spectral components are passed through an IR light blocking filter  90  onto a photodetector array  100 , which produces electrical signals that are proportional to the intensities of the light falling thereon. These electrical signals are amplified by an amplifier  110  and supplied to the microprocessor control unit  120  for processing. Alternative to the photodetector array  100 , a charged coupled device (CCD) array may be provided. 
     The spectral components of the emitted light represent the characteristic features of the up-converting phosphor used in the mark  20 . The relative intensities of each of these spectral components are converted into electrical signals using the photodetector array  100 , and the control unit  120  identifies the characteristic features of the emitted light based on these electrical signals. For example, if the mark  20  emits a green light in response to IR illumination, the green component of the emitted light will be imaged onto a corresponding portion of the photodetector array  100 , e.g., middle section of the photodetector array  100 , and the control unit  120  will identify the emitted light as being “green” upon receipt of an electrical signal from the middle section of the photodetector array  100 . 
     Preferably, the photodetector array  100  comprises 64-128 photodiodes and an amplifier  110  is provided for each photodiodes. In FIG. 1, only one amplifier  110  is illustrate for simplicity. The outputs of the amplifiers are multiplexed into a plurality of corresponding channels and the multiplexed signal is supplied to the control unit  120  for processing. 
     The IR light blocking filter  90  is provided because the light in the return path contains a substantial amount of IR reflections from the illuminating IR light. Without the filter  90 , the useful signals that are generated at the photodetector array  100  by the up-converted emitted light is too small relative to the noise signals that are generated at the photodetector array  100  by the reflections of the illuminating IR light. Also, the filter  90  is shown in FIG. 1 to be in intimate contact with the photodetector array  100 . The invention may be practiced with the filter  90  positioned anywhere along the optical path of the emitted light, but the other positions are less desirable because IR light tends to leak around the filter  90  the further away it is positioned from the photodetector array  100 . If too much ambient light is a problem, the light source  30  is modulated (e.g., by the control unit  120 ) to produce IR light at a predetermined frequency and the electrical signals corresponding to the intensities of the spectral components of the emitted light are demodulated at the control unit  120 . 
     If the mark  20  is not in alignment with the illuminating IR light, a movable stage  130  is repositioned until the mark  20  comes into alignment with the illuminating IR light. The alignment is performed with the aid of an image formed at a reticle lens  140  based on light deflections from a beam splitter  150 . 
     In the present invention, the mirror  50  is angled so that the optical axis of the deflected illumination beam is coaxial with the optical axis of the object lens  60 . This coaxial arrangement is desired because it results in a greater depth of field and insensitivity to object texture and/or surface inconsistencies. For example, if the mark  20  is applied on a non-uniform surface (e.g., a fabric) and the illuminating beam axis is offset (i.e., not coaxial) with respect to the optical axis of the object lens, the illumination point of the mark  20  moves up and down depending on the microscopic surface contours of the surface to cause the image formed at the detector  100  to be shifted right and left. 
     This point is illustrated in FIG.  2 . In FIG. 2, line  210  represents the assumed surface of the mark  20  at one point. Lines  220  and  230  represent respectively a surface of the mark  20  at two other points. These surfaces are above and below the surface  210  because of surface inconsistencies. Line  240  represents an illumination beam that is offset with respect to a line  245  which represents the optical axis of the objective lens  60 . When the mark  20  lies on the surface  210 , a point  250  is imaged. However, when adjacent portions of the mark  20  lie above or below the surface  210 , e.g., on the surface  220  or  230  respectively, as a result of texture changes or surface inconsistencies, a point  260  which is to the right of the point  250  is imaged or a point  270  which is to the left of the point  250  is imaged. Assuming the point  250  was the intended object, by virtue of having an illumination beam that is offset with respect to the optical axis of the objective lens  60 , the image formed at the detector  100  is shifted right and left. On the other hand, if the illumination beam is coaxial with the optical axis  245  of the objective lens  60 , the changes in the surface from  210  to  220  or  230  do not cause the image formed at the detector  100  to be shift right and left and may be more easily accommodated with the depth of field of the imaging system. 
     FIG. 3 illustrates a spectrum analyzer  10  according to a second preferred embodiment. The second embodiment is identical to the first embodiment except that a movable assembly including an aperture  102  and a photodetector  104  is provided instead of the photodetector array  100 . The movable assembly is positioned by the control unit  120  for receipt of each spectral component imaged by the imaging lens  80  in a sequential manner. When all of the spectral components have been accounted for in this manner, the series of signals produced by the photodetector  104  are processed at the control unit  120  to identify the characteristic features of the emitted light based on these signals. Instead of moving the assembly  102 / 104 , the prism  70  can be rotated about a fixed axis to cause different spectral components to be imaged at the photodetector  104  until all spectral components have been accounted for. 
     FIG. 4 illustrates the steps of reading the authentication mark according to the invention. The light source  30  is triggered in Step  410  to produce visible light for aligning the mark  20 . In Step  420 , the mark  20  is viewed through the reticle lens  140  and the movable stage  130  is positioned until the mark  20  comes into alignment with the visible light produced by the light source  30 . 
     Once the mark  20  has been aligned, the light source  30  is triggered in Step  430  to produce modulated IR light for illuminating the mark  20 . In Step  440 , the IR light is deflected onto the mark  20 . In Step  450 , the light emitted by the up-converting phosphor contained in the mark  20  as a result of IR illumination is collimated and, in Step  460 , the collimated light is dispersed into its spectral components. The spectral components are filtered and imaged onto the photodetector array  100  in Step  470 , and the electrical signals produced by the photodetector array  100  are amplified in Step  480  and then processed in Step  495 . 
     The flow diagram for processing the amplified electrical signals to verify the mark  20  is shown in FIG.  5 . First, in Step  500 , the multiplexed signal is demultiplexed and demodulated and the intensity signal in each of the channels is compared in Step  510  against a threshold. The threshold is set for each channel corresponding to each spectral component. If the signal exceeds the threshold, a “1” is assigned (Step  520 ). Otherwise, a “0” is assigned (Step  530 ). The series of 1&#39;s and 0&#39;s constitute an intensity signature of the spectral components of the emitted light. The program loops back to Step  510  until all channels have been processed in this manner (Step  540 ). Then, the completed intensity signature is compared in Step  550  with the series of 1&#39;s and 0&#39;s stored in memory corresponding to a reference intensity signature. The mark  20  is verified with a match (Step  550 ) but is not verified without a match (Step  560 ). 
     While particular embodiments according to the invention have been illustrated and described above, it will be clear that the invention can take a variety of forms and embodiments within the scope of the appended claims. 
     For example, instead of an IR light source and up-converting inks used in the authentication mark, UV light and down-converting inks may be used, or a combination of IR and UV inks with one or more light sources used simultaneously or sequentially. 
     Further, it is envisioned that an IR light source may be arranged directly along the optical axis of the system at the position of mirror  50  and thereby eliminating the need for the mirror  50 . In this embodiment, an IR optical system generates the IR beam directly on to the surface of the authentication mark. 
     Also, the alignment of the IR light beam with respect to the mark  20  may be achieved by moving the spectral analyzer  10  with respect to the mark  20 , instead of providing a movable stage  130  for moving the mark  20  with respect to the spectral analyzer  10 . 
     Most importantly, the IR ink, when it fluoresces, may appear to the human eye to be a certain color when illuminated with IR light, but in fact contains a definite spectral signature which is known by the manufacturer of the authentication mark. Counterfeiters may attempt to reproduce the same overall color, but will find it very difficult to reproduce the exact same spectral signature which is determined by the exact selection of up-converting inks and their relative composition strengths.