Abstract:
A simple high optical efficiency reflective optical sensor for bill validator uses an inexpensive bulb having a case which is transparent to efficient luminous radiation. This case is used as a wave guide to return reflected radiation to at least one photo detector situated directly under the transparent bottom of the case. The bulb emits a narrow beam of light and is positioned in close proximity and perpendicular to a bill surface and illuminates it. The light reflected or fluoresced by the bill is collected widely with a convex lens end of the bulb case and this collected radiation is transmitted through the bulb case to the at least one photo detector. Preferably, the bulb is a light emitting diode.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to bill validators, having an optical sensor means for measuring the reflectance and transmittance of paper bills as they move past the optical sensor. The sensor includes a radiation emitter which also acts to direct reflected radiation to a photodetector. This sensor may also be used as common reflective sensor for detection of various index marks with relatively small space dependence.  
       BACKGROUND OF THE INVENTION  
       [0002]     Bill validators used in vending machines and the like typically utilize various styles of reflective optical sensors to obtain measurements from an inserted bill to determine authenticity, denomination and location. Typically, the bill is transported past at least one photosensor, having a light-emitting diode (LED) and photodetector (photodiode or phototransistor).  
         [0003]     Some factors that adversely affect the bill measurements include the following: inserted bills are of different denominations, cleanliness and quality; bill may be creased or crumpled, and the bill location and inclination across passageway may strongly vary. In addition, the output power of LED can vary due to age and/or ambient conditions. Furthermore, there are normal production variations in LED optical power output and detector sensitivity, which can lead to sensors having varying current and voltage requirements in order to operate effectively. In order to partially offset these factors, optical sensor measurements are taken over a large dynamic range. As power of LED and sensitivity of photodetector are limited, the optical efficiency should be high to improve the performance of the sensors.  
         [0004]     In the art, many embodiments of reflective optical sensors are known. The simple sensors comprise at least one photo emitter and one photo detector with relatively wide spatial diagrams (U.S. Pat. Nos. 4,348,656; 4,628,194; 5,222,584; 5,476,169; 5,692,067; 5,751,840; 5,855,268; 5,889,883; 5,909,503; 5,960,103). Such sensors have low optical efficiency and their output signal strongly depends on bill location and inclination across passageway. The space required to mount the sensors (footprint) slightly exceeds the total area of the emitters and detectors.  
         [0005]     To improve optical efficiency, many sensors mount the emitters and detectors at an angle to one another and converging on the bill surface (U.S. Pat. Nos. 4,041,456; 4,628,194; 4,973,851; 5,420,406; 5,467,405; 5,483,069; 5,918,960; 5,992,601; 6,028,951; 6,073,744). These sensors require special optical heads, receptacles etc. The footprint for these sensors significantly exceeds the total area of emitters and detectors due to the various mounting and carrying paths. Even with this more complicated design, the output signal from these sensors strongly depends on bill location and inclination across passageway.  
         [0006]     Advanced sensors in addition to plurality of LED&#39;s and photo detectors comprise various focusing, light guiding and reflecting elements, including fiber optic “fish tails” and splitters (U.S. Pat. Nos. 5,308,992; 5,381,019; 5,616,915; 6,044,952; 6,104,036; 6,163,036; 6,188,080; 6,359,287; 6,392,863). These sensors are more complicated, large and expensive, require special optical parts and often require additional alignment during validator assembly. The output signal of these advanced sensors continues to be largely dependent on bill location and inclination across passageway.  
         [0007]     Some special optical sensors conduct bill scanning by means of LED&#39;s and detectors arrays with special lenses or by direct TV image or light beam scanning (U.S. Pat. Nos.  4 , 179 , 685 ;  4 , 197 , 584 ;  4 , 293 , 776 ;  6 , 363 , 164 ). This technology is expensive and is not suitable for mass production and utilization.  
         [0008]     Some optical shadow on a bill may occur with the majority of prior art sensors because of bill inclination, illumination or observation.  
         [0009]     It is a general object of the present invention to provide a simple reflective space efficient sensor having high optical efficiency for bill examination and other applications.  
         [0010]     The present invention overcomes a number of the disadvantages described above with respect to the prior art sensors.  
       SUMMARY OF THE INVENTION  
       [0011]     A validation device for sensing the authenticity of bills according to the present invention comprises a bill passageway, an optical sensing arrangement to one side of the passageway and opening onto the passageway for directing radiation onto a bill as it moves past the sensor and for receiving radiation reflected from the bill; an arrangement for processing an output signal of the optical sensing arrangement produces an eluation signal. An evaluation system uses the evaluation signal and based thereon, makes a prediction of the authenticity of the bill. The optical sensing arrangement includes a bulb emitter encased in a case transparent to luminous radiation and at least one photodetector is situated to receive radiation emitted by the bulb emitter and reflected by a bill and returned to the photodetector by passing through the plastic case of the bulb emitter.  
         [0012]     According to an aspect of the invention, the bulb emitter is a light emitting diode device preferably with a plastic case.  
         [0013]     According to yet a further aspect of the invention, the case of the light emitting diode device includes a convex end which faces the bill passageway and acts as a lens to direct emitted radiation onto the bill and to receive and direct radiation impinging on the convex lens through the case to the photodetector.  
         [0014]     In yet a further aspect of the invention, the plastic case has a generally flat transparent base adjacent the photodetector and the photodetector is located below the base.  
         [0015]     In yet a further aspect of the invention, the convex end of the case is immediately adjacent the bill passageway.  
         [0016]     In yet a further aspect of the invention, the convex end of the case is of a width greater than the spacing between the convex end and the center line of the bill passageway.  
         [0017]     In yet a further aspect of the invention, the case acts as a light guide for focusing radiation emitted by the bulb emitter and reflected from the bill onto the photodetector.  
         [0018]     In yet a further aspect of the invention, the light emitting diode is a directional emitter directing emitted radiation generally through the convex end of the case.  
         [0019]     In yet a further aspect of the invention, the light emitting diode is designed to emit ultraviolet radiation.  
         [0020]     In yet a further aspect of the invention, a validation device comprises the ultraviolet absorbing thin film filter between light emitting diode base and photo detector.  
         [0021]     In yet a further aspect of the invention, the opposite to light emitting diode part of outlying passageway wall is made from white non luminescent material.  
         [0022]     In yet a further aspect of the invention, the optical sensor includes white light emitting diode and at least two photo detectors with band-pass or rejection colored thin film filters between light emitting diode base and said photo detectors.  
         [0023]     In yet a further aspect of the invention, the optical sensor includes multicolor multi chip light emitting diode with at least one photo detector adjacent to light emitting diode base.  
         [0024]     In yet a further aspect of the invention, optical sensor includes the opaque cap round said light emitting diode with end slit for bar-code reading and bill edge detection.  
         [0025]     Additionally in accordance with preferred embodiment of the present invention, there is provided a method of bill ultraviolet examination including perpendicular narrow-beam illumination of a portion of a bill surface by means of a transparent body bulb ultraviolet light emitting diode, and collection of the mirror and diffuse reflected ultraviolet light and fluorescent light from the illuminated bill portion by light emitting diode convex end, and transmission of this collected light throw transparent light emitting diode body to at least one photo detector adjacent to said light emitting diode base and filtering of said transmitted light with an ultraviolet absorption filter between said light emitting diode base and detector, and detection of transmitted light with planar PIN photo diodes, and processing of output photo signal for bill identification and validation.  
         [0026]     Also provided, in accordance with preferred embodiment of the present invention, is a method for simultaneous evaluation of optical characteristics of a bill including perpendicular narrow-beam illumination of part of a bill surface by means of a white light emitting diode with a transparent bulb body having a convex end, and collection of the mirror and diffuse reflected light from the illuminated bill part using the convex end of the light emitting diode, and transmission of collected light through the transparent light emitting diode body to photo detectors adjacent to a base of the light emitting diode and filtering of transmitted light with absorption and/or bend-pass filters, and detection with planar PIN-photodiodes, and separate processing of steady and alternate photo signal components from each photo detector for bill identification and validation.  
         [0027]     Further provided, in accordance with preferred embodiment of the present invention, is a method for sequential evaluation of optical characteristics of a bill including: sequential perpendicular narrow-beam illumination of part of a bill surface with varicolored light by means of a transparent body bulb multi color multi chip light emitting diode, and collection of mirror and diffuse reflected light from the illuminated bill part by means of a convex end of the light emitting diode, and transmission of collected light through the transparent body of the light emitting diode to a photo detector adjacent to a base of the light emitting diode, and sequential detection and processing of said varicolored light components for bill identification and validation.  
         [0028]     Additionally provided, in accordance with preferred embodiment of the present invention, is method for bar code reading and bill edge detection including perpendicular narrow-beam illumination of separate bar or bill edge throw slit in opaque light emitting diode cap, and collection of the mirror and diffuse reflected light from illuminated surface throw said slit by means of light emitting diode convex end, and transmission of the collected light throw transparent light emitting diode body to photo detector adjacent to light emitting diode base, and detection of transmitted light with planar photo detector, and processing of alternate photo signal component from photo detector for bar code identification and bill edge location.  
         [0029]     In operation light emitting diode with narrow diagram is positioned perpendicularly and in close proximity to the bill surface to illuminate part thereof. The illuminated part of the bill surface is practically equal to from the size of the light beam emitted from the light emitting diode. The power of the light reflected back in a particular direction is proportional to the degree of specularity and the diffuse behavior of the bill surface. Bills contain both specular and diffuse surfaces as part of their design and material properties with the main surface being predominantly diffuse. Use of highly reflective devices such as plastic blazed holograms, metallized labels and threads creates areas of specular reflection. Additionally, the bill (substrate or/and dye) often emits fluorescent light of a certain wavelength (or several wavelengths) when irradiated with ultraviolet light. To obtain good optical information about the bill under investigation, all light components outgoing from the illuminated bill surface should be collected. Under perpendicular illumination specular reflected light propagates in exactly opposite direction. Diffuse and fluorescent components propagate more uniformly (in general according to so-called cosine law). Due to small gap between the light emitting diode and the bill, most of the outgoing light from the illuminated bill surface is collected with the convex end of the light emitting diode and is transmitted to the photo detector through the transparent light emitting diode body. With this arrangement, the light emitting diode body is used as a total reflection light guide and collector without any additional optical parts. Such an arrangement has low sensitivity to bill vibration and inclination in the passageway at inclination angles up to the maximum light emitting diode beam aperture (commonly 8-12°) by reason of insignificant variations of perpendicular to bill light power within this angle aperture. Additionally, due to the narrow light emitting diode aperture, ambient light-striking the bill surface is also insignificant for bill testing.  
         [0030]     Transmitted light through the light emitting diode body is detected with broad band and selective photo detectors situated under the transparent light emitting diode base. Low-cost thin film band-pass or absorption rejection filters are used in conjunction with hardware/software subtraction provides an integrated intensity and separate color (including ultraviolet reflection) signals from the bill under investigation.  
         [0031]     Using an opaque cap round light emitting diode with an end slit in conjunction with its narrow diagram and alternate signal component processing provides stable contrast signal under bar-code reading and bill edge detection.  
         [0032]     Several embodiments of the present invention will now be described by way of example with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]     Preferred embodiments of the invention are shown in the drawings, wherein:  
         [0034]      FIG. 1  is an enlarged side view of optical sensor for bill ultraviolet testing;  
         [0035]      FIG. 2  is an exploded enlarged perspective assembly view of optical sensor for bar-code reading and bill edge detection;  
         [0036]     FIG. 3  is a block diagram of hardware component processing of signals in ultraviolet optical sensor;  
         [0037]      FIG. 4  is a typical signal of genuine bill ultraviolet scanning in  FIG. 1  embodiment;  
         [0038]      FIG. 5  is a typical signal of counterfeit bill ultraviolet scanning in  FIG. 1  embodiment; and  
         [0039]      FIG. 6  is a typical signal of bar code scanning in  FIG. 2  embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     The optical sensor  2  shown in  FIG. 1  is positioned for emitting radiation to eradiate the bill  12 . The surface characteristics of the bill alter the radiation which is reflected from the bill and returned to the optical sensor. The bill  12  is transported through the bill passageway  20  defined by an exterior wall  13  and a light transparent wall  11 .  
         [0041]     The optical sensor  2  has a light emitting diode (LED)  4 , positioned to one side of the passageway  20  and located immediately adjacent the transparent wall  11 . The light emitting diode  4  has a transparent case  6  with a generally cylindrical portion terminating at one end in the convex lens portion  10  and closed at the other end by the quasi planar base  14 . The case  6  is preferably of a plastic or other light transmitting material. Radiation produced by the LED  4  passes through the plastic case. Generally centered within the case is a luminous chip  16  centrally located in a non light transmitting concave recess  18 . The luminous chip  16  is connected by a pair of leads  22  to a power source. Radiation from the luminous chip  16  generally passes in a parallel manner through the convex lens  10  of the plastic case  6 . The radiation produced by the LED is generally through the end of the LED and produces a narrow beam of radiation for eradiating the bill  12 . The radiation produced by the LED strikes the bill and depending upon the characteristics of the bill, is reflected from the surface thereof. A portion of this reflected radiation strikes the convex lens  10  of the LED and passes therethrough and is guided to the base  14  of the LED and through the base to photodetectors  25  and  26  located exterior to the based of the LED.  
         [0042]     From the above, it can be appreciated that the casing of the LED acts as a light guide for directing reflected radiation from the bill, which strikes the convex end of the plastic case of the LED to the photodetectors located below and outside of the LED. Both the LED  4  and the photodetectors  25  and  26  are mounted on the printed circuit board  7  and the signals from the photodetectors are processed by circuitry on the printed circuit board.  
         [0043]     The diameter of the cylindrical walls  8  of the LED are of the order of 5 mm and the radiation produced by the LED is generally of this width and it is generally directed in a perpendicular manner towards the surface of the bill  12 . The bill  12  is spaced from the convex end  10  of the LED up to approximately 3.5 mm. It can thus be appreciated that the beam of radiation is wide relative to the distance of separation from the LED to the bill. The convex end  10  serves to focus reflected radiation back onto the photo diodes  25  and  26 . With this arrangement, most of the outgoing radiation which serves to illuminate the bill surface and is reflected therefrom, is collected by the LED convex lens and transmitted to the photodetectors. It has generally been found that this arrangement results in a reflected signal which is maintained within a much tighter tolerance even with changes in location of the bill in the passageway, the condition of the bill and the inclination thereof.  
         [0044]     It has been found that the reflected signal is typically in the range of 60% to 85% of the produced signal. Thus the optical signal would change up to approximately 30% under bill displacement across the passageway of up to 2 mm. The beam of radiation produced by the LED is relatively narrow, typically between 8 and 12 degrees. The close positioning of the LED to the bill and the use of the LED as a wave guide to return the reflected radiation, results in a signal which is less sensitive to bill inclination in the passageway.  
         [0045]     The embodiment shown in  FIG. 1  also includes a filter arrangement  28  between the base  14  and the photodetector  25 . This preferably is an ultraviolet absorbing film filter. With this arrangement, the LED is preferably a 5 mm bulb ultraviolet LED under the trademark HUUV-5102L sold by Roithner Lasertechnic or general equivalent. Thus the bill  12  is exposed to ultraviolet radiation with the reflected signal and any luminous signals of the bill returning through the LED to the photodetectors  25  and  26 . Photodetector  26  receives the entire signal whereas the signal received by photodetector  25  is absent any ultraviolet portion.  
         [0046]     The embodiment of  FIG. 1  produces a signal at photodetector  26  which is a result of all light radiation striking the detector. In contrast, photodetector  25  is a similar signal but with the UV component removed. Ambient light can also influence photodetectors, however, the positioning of the photodetectors beneath the LED and the plastic casing of the LED acting as a light transmitting guide to the photodetectors, reduces problems associated with ambient light. Furthermore, ambient light is generally associated with the bill passageway  20  and the structure of the optical sensor locates the photodetectors, a significant distance away from the passageway. In this way, the photodetectors are not as sensitive to ambient light in the passageway.  
         [0047]     Optical sensor  2  is located in its own casing having its own transparent wall  11  which forms part of the passageway. This forms a module with the printed circuit board and the LED located within a housing typically formed of a non transparent plastic with the exception of the transparent wall  11 . The elongate form of the optical sensor advantageously uses the LED to not only produce radiation for illuminating the bill but it also uses the LED as a light guide for directing the reflected radiation to the photodetectors located beneath the LED. Opposite passageway wall  13  is made from white non fluorescent ABS plastic. Reflection signal from this wall is used for apparatus self calibration when bill is absent in passageway.  
         [0048]      FIG. 2  is a perspective view of an alternate embodiment of the optical sensor. The optical sensor  100  is positioned adjacent the transparent wall  110  in the bill passageway  120  having an exterior wall  113 . The bill  112  or other document is shown having a bar code  115 . The optical sensor  100  includes a printed circuit board  107  having a photodetector  105  mounted thereon. The photodetector  105  is exposed to the reflected radiation which will pass back through the LED  101 . This LED has a transparent outer casing  104  made up of a cylindrical portion  106 , a convex end portion  108 , and a generally planar transparent base  109 . The LED includes its own light source  111  within the LED which is designed to direct radiation out through the convex end  108 . Connectors  130  and  132  support the light source  111  generally centered within the LED and connected and provides power to it from the printed circuit board  107 .  
         [0049]     A non transparent shield  140  covers the end of the LED and has a slit opening  150  for allowing the radiation to pass therethrough. As can be appreciated, some of the radiation will be reflected off the end wall  142  of the end cap, however, this will be a constant signal back to the photodetector  105  where various arrangements can be used to reduce this radiation component. A portion of the produced radiation will pass through the slot  150  and will provide a narrow radiation source for illuminating the individual bars of the bar code  115  as they pass by the optical sensor. The signal which is returned to the photodetector through the LED  104  acting as a wave guide and through the transparent base  109  to the photodetector will vary in accordance with the bar code  115 . This arrangement has proven to provide a very effective means for reading of the bar code and providing good quality results with the various possible misorientations of the bar code within the passageway  120 . As can be appreciated, the optical sensor  100  and the transparent wall  110  can be integrated into a single module which is inserted in a suitable port in the wall of the bill passageway of a validator or other sensing device.  
         [0050]     The arrangement of  FIG. 2  is also effective in identifying a bill edge. This is particularly useful for detecting a leading or trailing edge of a bill as it moves past the sensor.  
         [0051]     With the embodiment of  FIG. 2 , the beam of light eradiating the bill has a small angle of divergence so the light divergence on the bill surface does not exceed 0.3 mm. A red LED LTL2F3VEKNT by LITE-ON Inc. and IC photo detector S7184 or S7815 by HAMAMATSU Co. can be used in the bar-code detector.  
         [0052]      FIG. 3  is a block diagram of hardware components used to process signals in an ultraviolet optical sensor. Light  10  reflected from the bill surface is received by photodiode  6  (integral light detector) and is received by photodiode  5  (detector of visible light) after passing through UV absorbing filter  4 . Signal U int , proportional to visible light intensity, proceeds from the output  20  of amplifier  17 . This signal describes the fluorescent properties of the bill paper and dyes. Signal−(U int +U UV ), proportional to total light outgoing from bill, proceeds from the output of amplifier  18  to resistor adder  19 . Under equal transfer constants of amplifiers  17 ,  18  and resistors R in adder unit  19  at the output  21 , outgoing signal ½[U int −(U int +U UV )]=−½ U UV  is developed. This signal describes the ultraviolet reflection of bill surface. Signals from outputs  20 ,  21  are used in a processor module for bill authorization and discrimination. For example, a large value of U int  signal indicates that bill may be counterfeit—i.e. a photocopy on a wood-based paper.  
         [0053]      FIG. 4  is a typical signal U int  of genuine bill ultraviolet scanning in  FIG. 1  embodiment. Scanning speed is about 300 mm/sec. Point  22  indicates the moment of bill leading edge passing by optical sensor. Point  23  indicates the moment of bill trailing edge passing by optical sensor. The signal at  24  (bill is absent in passageway) is caused by back wall  13  reflectance of blue components of illuminating light and by light reflected from all transparent interfaces (about 6% on each)—boundaries between LED and air, air and wall  11 , wall  11  and air. The signal at  24  is used for apparatus self calibration. Signal U int  between points  22  and  23  is caused by bill paper and dyes fluorescence and reflectance of blue components of illuminating light.  
         [0054]      FIG. 5  is a typical signal U int  of a counterfeit bill (similar to previous genuine bill) ultraviolet scanning in  FIG. 1  embodiment. Scanning speed is about 300 mm/sec. Points  22 - 24  indicate the same as in previous illustration. Bands  25  indicate strong fluorescence from leading and trailing bill borders. Band  26  indicates the strong fluorescence from paper bill surface in the watermark zone. Signal U int  strongly differs on genuine and counterfeit bills and is easily used in the processor module to identify counterfeit bills.  
         [0055]      FIG. 6  is a typical signal of bar code scanning in  FIG. 2  embodiment. The slit  15  in opaque cap  14  is 5 mm length and 0.4 mm wide. Scanning speed is about 300 mm/sec. This arrangement provides a good spatial resolution with bar distance and width less then 0.5 mm.  
         [0056]     The present invention is described herein in the context of a banknote application used in a verification device, automatic cash machine or other bills handling device, in a bank, postal facility, supermarket, casino or transportation facility. However, it is appreciated that the embodiments shown and described herein may also be useful for checking other objects, particularly flat objects, such as cards, films, paper sheets and paintings. The checking device may be stationary or portable, battery powered or powered by connection to an electric outlet.  
         [0057]     It is appreciated that various features of the invention, which are, for clarity, described in the contexts of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination.  
         [0058]     Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.