Abstract:
A produce data collector with minimal spectral distortion. The produce data collector includes a light pipe having entrance and exit ends through which a portion of light reflected from a produce item travels, and a spectrometer adjacent the exit end of the light pipe which splits the portion of light into a plurality of wavelengths and which produces signals associated with the wavelengths for identifying the produce item.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to the following commonly assigned and co-pending U.S. application: 
     “Produce Data Collector And Produce Recognition System”, filed Nov. 10, 1998, invented by Gu, and having a Ser. No. 09/189,783. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to product checkout devices and more specifically to a produce data collector and produce recognition system. 
     Bar code readers are well known for their usefulness in retail checkout and inventory control. Bar code readers are capable of identifying and recording most items during a typical transaction since most items are labeled with bar codes. 
     Items which are typically not identified and recorded by a bar code reader are produce items, since produce items are typically not labeled with bar codes. Bar code readers may include a scale for weighing produce items to assist in determining the price of such items. But identification of produce items is still a task for the checkout operator, who must identify a produce item and then manually enter an item identification code. Operator identification methods are slow and inefficient because they typically involve a visual comparison of a produce item with pictures of produce items, or a lookup of text in table. Operator identification methods are also prone to error, on the order of fifteen percent. 
     Therefore, it would be desirable to provide a produce data collector and produce recognition system. It would also be desirable to provide a spectrometer-equipped produce data collector which operates with minimal spectral distortion. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a produce data collector and produce recognition system are is provided. 
     The produce data collector includes a light pipe having entrance and exit ends through which a portion of light reflected from a produce item travels, and a spectrometer adjacent the exit end of the light pipe which splits the portion of light into a plurality of wavelengths and which produces signals associated with the wavelengths for identifying the produce item. 
     The light pipe may be a hollow light pipe or a light rod. 
     An example spectrometer includes a linear variable filter, and a photodetector array adjacent the linear variable filter. 
     The produce data collector may additionally include a lens adjacent an entrance end of the light pipe which focuses the portion of light at the entrance end of the light pipe. 
     It is accordingly an object of the present invention to provide a produce data collector and produce recognition system. 
     It is another object of the present invention to provide a produce data collector which includes a spectrometer and which operates with minimal spectral distortion. 
     It is another object of the present invention to provide a produce data collector which includes a linear variable filter and which operates with minimal spectral distortion. 
     It is another object of the present invention to provide a produce data collector with a reduced field-of- view effect. 
     It is another object of the present invention to provide a produce data collector which uses light pipe to minimize spectral distortion. 
     It is another object of the present invention to provide a produce data collector which uses light pipe to reduce the field-of-view effect and improve the light collection efficiency from a produce item to a linear variable filter without increasing the incident angle of light onto the linear variable filter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a transaction processing system including a produce recognition system; 
     FIG. 2 is a block diagram of a type of produce data collector which collects spectral data; 
     FIG. 3 is a first diagrammatic illustration of the operation of a light pipe within the produce data collector; 
     FIG. 4 is a second diagrammatic illustration of the operation of the light pipe with a condenser lens within the produce data collector; 
     FIG. 5A is a side view illustrating the mounting of the light pipe with a spectrometer; 
     FIG. 5B is a front view illustrating the attachment of the light pipe with the spectrometer; and 
     FIG. 6 is an exploded view of the light pipe. 
     FIG. 7 is a third diagrammatic illustration of the operation of a light pipe within the produce data collector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, transaction processing system  10  includes bar code data collector  12 , produce data collector  14 , and scale  16 . 
     Bar code data collector  12  reads bar code  22  on merchandise item  32  to obtain an item identification number, also know as a price look-up (PLU) number, associated with item  32 . Bar code data collector  12  may be any bar code data collector, including an optical bar code scanner which uses laser beams to read bar codes. Bar code data collector  12  may be located within a checkout counter or mounted on top of a checkout counter. 
     Produce data collector  14  collects data for produce item  18  or any other non-barcoded merchandise item. Such data preferably includes color and color distribution data, but may also include size data, shape data, surface texture data, and aromatic data. Reference produce data  30  is collected and stored. 
     During a transaction, operation of produce data collector  14  may be initiated by placement of produce item  18  on scale  16  or in by operator-initiated commands from transaction terminal  20 . 
     Scale  16  determines a weight for produce item  18 . Scale  16  works in connection with bar code data collector  12 , but may be designed to operate and be mounted separately. Scale  16  sends weight information for produce item  18  to transaction terminal  20  so that transaction terminal  20  can determine a price for produce item  18  based upon the weight information. 
     Bar code data collector  12  and produce data collector  14  operate separately from each other, but may be integrated together. Bar code data collector  12  works in conjunction with transaction terminal  20  and transaction server  24 . 
     In the case of bar coded items, transaction terminal  20  obtains the item identification number from bar code data collector  12  and retrieves a corresponding price from PLU data file  28  through transaction server  24 . 
     In the case of non-bar coded produce items, transaction terminal  20  executes produce recognition software  21  which obtains produce characteristics from produce data collector  14 , identifies produce item  18  by comparing produce data in produce data  30  with collected produce data, retrieves an item identification number from produce data  30 , retrieves a corresponding unit price from PLU data file  28  and calculates the total price of produce item  18  with the weight from scale  16 . 
     In an alternative embodiment, identification of produce item  18  may be handled by transaction server  24 . Transaction server  24  receives collected produce characteristics and compares them with produce data in produce data  30 . Following identification, transaction server  24  obtains a price for produce item  18  and forwards it to transaction terminal  20 . 
     Storage medium  26  preferably includes one or more hard disk drives. PLU data file  28  and produce data  30  are stored within storage medium  26 , but either may also be located instead at transaction terminal  20 , or bar code data collector  12 . 
     To assist in proper identification of produce items, produce recognition software  21  may additionally display candidate produce items for operator verification. Produce recognition software  21  preferably arranges the candidate produce items in terms of probability of match and displays them as text and/or color images on an operator display of transaction terminal  20 . The operator may accept the most likely candidate returned by or override it with a different choice. 
     Turning now to FIG. 2, produce data collector  14  primarily includes light source  40 , optional condenser lens  42 , light pipe  44 , spectrometer  51 , control circuitry  56 , transparent window  60 , and housing  62 . 
     Light source  40  produces light  70 . Light source  40  preferably produces a white light spectral distribution, and preferably has a range from four hundred 400 nm to 700 nm, which corresponds to the visible wavelength region of light. 
     Light source  40  preferably includes one or more light emitting diodes (LEDs). A broad-spectrum white light producing LED, such as the one manufactured by Nichia Chemical Industries, Ltd., is preferably employed because of its long life, low power consumption, fast turn-on time, low operating temperature, good directivity. Alternate embodiments include additional LEDs having different colors in narrower wavelength ranges and which are preferably used in combination with the broad-spectrum white light LED to even out variations in the spectral distribution and supplement the spectrum of the broad-spectrum white light LED. 
     Other types of light sources  40  are also envisioned by the present invention, although they may be less advantageous than the broad spectrum white LED. For example, a tungsten-halogen light may be used because of its broad spectrum, but produces more heat. 
     A plurality of different-colored LEDs having different non-overlapping wavelength ranges may be employed, but may provide less than desirable collector performance if gaps exist in the overall spectral distribution. 
     Condenser lens  42  and light pipe  44  reduce spectral distortion by minimizing field-of-view (FOV) effect. 
     Spectrometer  51  includes light separating element  52  and photodetector array  54 . 
     Light separating element  52  splits light  76  in the preferred embodiment into light  80  of a continuous band of wavelengths. Light separating element  52  is preferably a linear variable filter (LVF)  90 , such as the one manufactured Optical Coating Laboratory, Inc. LVF  90  offers continuous spectral coverage within the visible wavelength range (400-700 nm). LVF  90  is preferably mounted on photodetectory array  54 . 
     Photodetector array  54  produces waveform signals  82  containing spectral data. The pixels of the array spatially sample the continuous band of wavelengths produced by light separating element  52 , and produce a set of discrete signal levels. Photodetector array  54  is preferably a complimentary metal oxide semiconductor (CMOS) array, but could be a Charge Coupled Device (CCD) array. 
     Control circuitry  56  controls operation of produce data collector  14  and produces digitized produce data waveform signals  84 . For this purpose, control circuitry  56  includes an analog-to-digital (A/D) converter. A twelve bit A/D converter with a sampling rate of 22-44 kHz produces acceptable results. 
     Transparent window  60  may include an anti-reflective coating to reduce the reflection of light  72 , which may add background light noise to light  74 . 
     Housing  62  contains light source  40 , condenser lens  42 , light pipe  44 , spectrometer  51 , photodetector array  54 , control circuitry  56 , and transparent window  60 . 
     In operation, an operator places produce item  18  on window  60 . Control circuitry  56  turns on light source  40 . Light separating element  52  separates reflected light  74  into different wavelengths to produce light  80  of a continuous band of wavelengths. Photodetector array  54  produces waveform signals  82  containing produce data. Control circuitry  56  produces digitized produce data signals  84  which it sends to transaction terminal  20 . Control circuitry  56  turns off light source  40  and goes into a wait state. 
     Transaction terminal  20  uses produce data in digitized produce data signals  84  to identify produce item  18 . Here, produce data consists of digitized waveforms which transaction terminal  20  compares to reference digitized waveforms stored within produce data  30 . After identification, transaction terminal  20  obtains a unit price from PLU data file  28  and a weight from scale  16  in order to calculate a total cost of produce item  18 . Transaction terminal  20  enters the total cost into the transaction. 
     With reference to FIGS. 3 and 4, an LVF-equipped spectrometer  51  is shown in more detail. One important characteristic of such an LVF-equipped spectrometer  51  is that the physical position along the length of LVF  90  corresponds to wavelengths. This characteristic results in a field-of-view (FOV) effect. 
     In simple terms, a window of finite size causes distortion in a measured waveform. This distortion is mainly caused by two factors: 1) the arrival of rays from one point on window  60  at different points on LVF  90  with different distances and incident angles (radiometric effect), and 2) the wavelength shift of the filtering band of LVF  90  for non-normal incident rays. 
     Such distortion could be very significant when the distance between window  60  and LVF  90  is small. However, for optimal efficiency and compactness, it would be desirable to place LVF  90  as close to window  60  as possible. To reduce the FOV effect, the distance between window  60  and LVF  90  must be many times larger than both the sizes of window  60  and LVF  90 . 
     With reference to FIG. 3, the present invention reduces the FOV effect and hence improves the performance. The incident angles of all rays will not change when they travel through light pipe  44 , but the position of rays with different incident angles from any given point at window  60  will be mixed at exit face  92  of light pipe  44 . Making light pipe  44  longer improves mixing. Though the optical path traveled by light  74  is increased by light pipe  44 , the length of light pipe  44  itself does not reduce efficiency. The physical dimensions of produce data collector  14  can be reduced by folding the optical path of light  74  by folding light pipe  44 . 
     With reference to FIG. 4, light pipe  44  may be used with or without condenser lens  42 . Condenser lens  42  improves efficiency by focusing light  74  at entrance surface  94  of light pipe  44 , but increases the range of incident angles of light  74  onto the LVF. However, due to the mixing effect of light pipe  44 , the FOV effect at exit face  92  of light pipe  44  is reduced to a pure smoothing effect on the spectrum. This is equivalent to a reduced spectral resolution of LVF  90 . If the spectra from produce item  18  are smooth and continuous, a slightly lower wavelength resolution may still be adequate. The smoothing effect can be controlled by limiting the maximum incident angle θ max . For example, the maximum incident angle can be set to the acceptance angle of the light separating element  52 , in which case the smoothing effect will be negligible. 
     In the embodiment of FIG. 3, maximum incident angle θ max  is limited by the acceptable minimum distance from window  60  to LVF  90  for a certain window size. 
     In the embodiment shown in FIG. 4, maximum incident angle θ max  is determined by the size of lens  42  and the distance from lens  42  to the entrance of light pipe  44 . 
     A practical light pipe design for embodiments Of FIGS. 3 and 4 is illustrated in FIGS. 5A,  5 B, and  6 . With reference to FIGS. 5A and 5B, LVF  90 , photodetector array  54 , and light pipe  44  are mounted to printed circuit board  96 . 
     With reference to FIG. 6, light pipe  44  is hollow and includes two halves  98  and  100 . The inner surfaces of halves  98  and  100  are of optical quality and are highly reflective. The inner surfaces include a reflective coating  108 , such as enhanced aluminum. The outer surfaces have no optical functional requirements. The seams where halves  98  and  100  join should be orientated perpendicular to the linear dimension of LVF  90  in order to minimally effect the accuracy of LVF  90 . 
     Fabrication can be simple and cost-effective. Halves  98  and  100  can be formed from injection molding pr compression molding. Reflective coating  108  may be applied using evaporative coating techniques. 
     As shown in FIG. 6, the two halves can be the same mechanical part. Pins  102  and holes  104  are arranged diagonally. Adhesive can be used to keep halves  98  and  100  together. Screws may also be used to fasten halves  98  and  100  together. Snap-in features may be added to the halves  98  and  100  so that they can be snapped together. Each of halves  98  and  100  has holes  106 , which may be threaded, for fastening light pipe  44  to printed circuit board  96 . 
     Referring now to FIG. 7, a third embodiment uses light pipe  44  itself to limit the maximum incident angle θ max  onto LVF  90 . Since the acceptance angle of LVF  90  is usually less than twenty degrees, a polished glass cylinder or rod may be used as light pipe  44 , utilizing its total internal reflection. In this embodiment, light pipe  44  is a light rod made of optical material with an index of refraction n 1 , such as optical glass or optical plastic. The outer surface of the solid pipe is optically smooth and coated with a thin layer  110  of another material of slightly lower index of refraction n 2 . When a light ray strikes the interface of the two materials it will undergo total internal reflection (TIR) if its angle is less than maximum incident angle θ max , where θ max  (in degrees) is given by          θ   max     =     90   -         sin     -   1            (       n   2       n   1       )       .                              
     All rays that have angles greater than θ max  will transmit through the interface and preferably be absorbed by the light absorbing material. In this embodiment, light pipe  44  can be positioned much closer to window  60  because light with large angles is filtered out by light pipe  44 . Light collection efficiency is much higher. 
     For all three embodiments, the diameter of light pipe  44  should be slightly larger than the length of LVF  90 . LVF  90  should be placed as close as possible to, optimally adjacent to, exit face  92 . 
     Optimal length L of light pipe  44 , is determined by three factors: 1) maximum incident angle θ max , 2) diameter D of light pipe  44 , and 3) light pipe folding factor N:            (     N   -   1     )          D   L       =     tan                     θ   max     .                              
     Light pipe folding factor N is a measure of mixing. If the ray with the largest incident angle is folded N-1 times in light pipe  44 , the rays will be mixed approximately N times at exit face  92 . For any given point on window  60 , there are N rays with different incident angles that will be mixed at any given point on LVF  90 . Without light pipe  44 , there is no mixing; only one ray goes from a given point on window  60  to a given point on LVF  90 . A light pipe folding factor greater than four significantly reduces the FOV effect. 
     The discussion above is also valid for skewed rays. 
     Although the invention has been described with particular reference to certain preferred embodiments thereof, variations and modifications of the present invention can be effected within the spirit and scope of the following claims.