Sorting machine using dual frequency optical detectors
This application is a continuation-in-part of U.S. patent application Ser. No. 08/377,451, filed Jan. 24, 1995, now U.S. Pat. No. 5,508,512. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to sorting machines that optically sort or separate nonstandard fungible objects from standard objects as they pass a viewing station by viewing such objects in at least two different frequency spectrums and particularly to such sorting machines utilizing detector elements comprised of two or more different photo-sensitive devices. 
     2. Description of prior Art 
     A typical sorting machine of the type utilizing the present invention can be either a gravity-fed channel sorting machine or a belt sorting machine that passes a stream of objects or products to be sorted through an optical viewing station. Typically, the stream is comprised of standard fungible agricultural products, such as coffee beans, tomatoes or the like that are known to be of a standard hue or color in at least two bands of the frequency spectrum. However, if a product is overripe, bruised, or of a different grade from standard, it will have a nonstandard hue or color in at least one of the two bands for which the standard products have a known standard hue or color. Such nonstandard products can be detected and removed or ejected from the stream by optical devices positioned vis-a-vis a viewing station through which the product stream passes. A sorting machine may have a plurality of parallel channels or paths, each with its own optical viewing stations. Moreover, each optical viewing station can have more than one optical sensing device. For example, it is desirable to view the products or objects from different angles so that a spot hidden from view when viewed at a first angle will not be hidden from view when viewed at a second or third angle. However, for purposes of simplicity, each channel or path product stream can be considered as a continuous movement of singulated products that pass by a simplified optical viewing station. 
     An optical viewing station includes one or more lights to illuminate the products in the stream. An illuminated product reflects light and other frequencies, which are sensed by properly positioned photo-sensitive devices for monitoring the predetermined standard frequency spectra discussed above. When a reflection is detected as being below a predetermined threshold value in one of the predetermined standard frequency spectra, an ejection device, such as a strategically located air jet or a mechanical ejection finger is enabled and subsequently activated when the nonstandard product is positioned opposite the ejection device. 
     Alternative to the above operation, the detector can be adjusted to operate the ejector when a reflection deemed to be nonstandard is above a predetermined threshold value in one of the predetermined standard frequency spectra. In such case, standard products would be passed since their reflections would be below the threshold values. 
     It is common in the prior art to use multiple photo or optical detectors for each spectrum, one for each pixel or photo site in a grid of a viewing window. One such system as this is disclosed in U.S. Pat. No. 5,062,532, issued Nov. 5, 1991 in the name of George A. Zivley, which patent is commonly assigned. The RL0256K array of photodiodes made by EG&amp;G Reticon is suggested in the &#39;532 patent for implementing the invention therein disclosed. However, the exemplar photodiodes of this array are wide aperture linear devices used in monochromatic or single frequency spectrum sorting. The invention described in the &#39;532 is not limited to monochromatic sorting, but it is apparent that if bichromatic sorting was involved, first and second arrays with photodiodes tuned to the respective frequency spectrums would have to be physically separated from each other, thereby complicating the ejection firing to distinguish which array was involved in a substandard product detection. Moreover, the sources of illumination of the viewing station would have to be more numerous. 
     U.S. Pat. No. 5,265,732, issued Nov. 30, 1993 in the name of William C. Long, which patent also is commonly assigned, utilizes a detector that permits the detection of multiple spectra at a single location. Shown therein is a prior art scheme utilizing a beam splitter and two filters, one for each of the two frequency spectra used in the sorting. The patent also reveals the use of narrow band lights for illuminating the products in the product stream, rather than ordinary wide band general illumination bulbs. In such a scheme, either a beam splitter and appropriate filters are used with the light sources or the light sources are shown at different angles, with appropriate filters still being required. In all events, the schemes utilize many different and complex optical devices and space requirements to implement such a scheme are a prime consideration. 
     U.S. patent application Ser. No. 08/377,451, filed in the names Calvin G. Gray and Jeffery Stanley Pawley on Jan. 24, 1995, which application is also commonly assigned, describes a photo-optical detector for use in multi-chromatic sorting. The detector utilizes a multi-peak optical interference filter in conjunction with a sandwich type photodiode device of semiconductive materials such as the J16Si Series Silicon/Germanium detectors manufactured by EG&amp;G Judson. This device provides multi-chromatic sorting within a single detector that is compact with relative few components. However, because the number and spectral ranges of available multi-peak filters is limited, the range of sorting applications of this device is likewise limited. 
     Therefore, it is a feature of the present invention to provide an improved photo-optical detector for use in a sorting machine having a sandwich of at least a first and second photo-sensitive material responsive to a composite multi-peak frequency spectrum and having a single multi-peak optical interference filter or a set of multiple optical filter elements for passing at least two defined light frequency spectra, one within the wide frequency sensitivity of the first photo-sensitive material and the other within the wide frequency sensitivity of the second photo-sensitive material. 
     It is another feature of the present invention to provide an improved photo-optical detector of the type described above in which a first photo-sensitive material is silicon and a second photo-sensitive material is germanium or a composite of indium-gallium-arsenide. 
     It is still another feature of the present invention to provide a sorting machine utilizing a sandwich detector of the type generally described above that also includes electronic processor means such as a microprocessor for developing a signal for each separate device of the sandwich or, alternatively, a signal when there is a selected combination of signals from the separate devices so that ejection of a nonstandard product can be made on the existence of a single device signal or one or more selected signal combinations. 
     It is yet another feature of the present invention to provide an improved photo-optical detector of the type generally described above utilizing a sandwich of more than two photo-sensitive materials. 
     It is still another feature of the present invention to provide a sorting machine utilizing a sandwich photo-optical detector having more than two photo-sensitive material devices, a filter or a set of filter elements having more than two defined light frequency spectra, and electronic processor means for selecting one or more combinations of signals from the various devices for activating an ejector to remove nonstandard products from a product stream being sorted. 
     It is yet another feature of the present invention to provide an improved photo-optical detector of the type generally described above utilizing a sandwich of multiple photo-sensitive materials which incorporates at least one filtering element for passing a light defined frequency spectrum within the wide frequency sensitivity of a lower photo-sensitive material. 
     It is still another feature of the present invention to provide a sorting machine utilizing a sandwich photo-optical detector having at least two material devices and at least one filter element having a defined light frequency spectra, a broadband pass interference filter having a broadly defined light frequency spectra and electronic processor means for selecting one or more combinations of signals from the various devices for activating an ejector to remove nonstandard products from a product stream being sorted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above-recited features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, a more particular description of the invention briefly summarized above may be had by reference to the exemplary preferred embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only typical preferred embodiments of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
     In the drawings: 
     FIG. 1 is a side view of an electro-optical sorting machine incorporating the sandwich detectors and electrical processing means in accordance with the present invention. 
     FIG. 2 is a top view of an optical viewing station of an electro-optical sorting machine, such as shown in FIG. 1. 
     FIG. 3 is a cross-sectional side view of a sandwich detector in accordance with the present invention. 
     FIG. 4 is a schematic diagrammatic representation of a simplified version of sorting activity in accordance with the present invention. 
     FIG. 5 is a typical responsivity illustration for the sandwich detector shown in FIG. 3. 
     FIG. 6 is a transmission illustration for the optical filters employed in the present invention. 
     FIG. 7 is a diagrammatic representation of multiple sandwich detectors and multi-peak optical filters in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now referring to the drawings, and first to FIG. 1, a high speed sorter for separating nonstandard fungible products or items from a passing stream or flow of such products is shown. Generally, machine 10 includes one or more channels or chutes or slides 12 at a steep angle, usually over 45° and preferably nearly vertical on the order of 80°. The channels are held in position by a framework 14 and are gravity fed the product to be sorted at the top by a hopper 16 attached to the same framework. The product feeds from hopper 16 through dividing vibratory feeder 18 to channels 12. Although a commercial machine usually has two or more channels 12 operating simultaneously with respect to the products that flow respectively through them, for simplicity of discussion, machine 10 is discussed hereinafter as including only a single channel 12. 
     Moreover, a belt sorter having one or more paths for the product machine can be employed using the invention, if desired. Such a machine has a moving horizontal belt onto which the products are to be sorted or deposited, the belt moving the products through an optical viewing station in much the same manner as a channel sorter. 
     The products to be separated or sorted by machine 10 are small fungible items, such as coffee beans. Coffee beans, it will be appreciated, are individually identifiable by color in one or more spectral bands. The feed from the hopper via the vibratory feeder and down the channel is all by gravity action. The flow of the products is only slowed from free fall by the friction caused by the bends and the surfaces of the path. The products do move, however, at a fast rate and in large quantity, as is well known in the art. 
     An optical viewer or sensor 20, described more fully below, is located toward the bottom part of the channel. As the flow of products passes past the sensor, nonstandard or substandard products are sensed or detected. It will be appreciated that such sensing or detection requires the substandard products to be distinguished both from the standard products and the background. Typically a substandard item, such as a coffee bean, is detectable on the basis of its being darker or lighter or of a different color or hue from an acceptable range of darkness, lightness or color predetermined for standard or acceptable items. This sensing can be in a single spectral range for monochromatic detection, in two separated spectral ranges for bichromatic detection, or in a plurality of spectral ranges for multi-chromatic detection. It is understood that a &#34;spectral range&#34; can be wholly or partially in the visual spectrum or can be wholly or partially in the nonvisual spectrum. For example, sensing in the infrared range is commonly done. When a substandard product or item is sensed, an electrical signal is produced that results in an ejection of the substandard item by the actuation of an ejector mechanism. 
     An ejector 36 located underneath and adjacent optical sensor means 20 is actuated by the actuation electrical signal just mentioned to produce an air blast to remove the unwanted substandard product from the flow of products in the product stream. The ejector can be a mechanical ejector, if desired. When the actuation signal occurs, typically, a solenoid valve is operated to release or emit an air blast at the product stream to timely remove the substandard item. The delay in actuation is very short following the time of sensing, the timing being such to produce the desired expelling of the detected substandard item and is accomplished in a manner well known in the art. The items thus removed in the process fall down into reject accumulator 28 for subsequent disposal. The items not removed continue down channel extension 30 to be gathered or packaged as quality products passing the preset standards and avoiding removal. The control of the flow and the sensitivity of the sensors are controlled by preset controls that are well-known in the art. 
     Now referring to FIG. 2, the viewing or optical sensor and related components of the machine are illustrated as seen from above. Sensor means 20 generally is a ring-like structure with a center opening 32, the flow of the products to be separated or sorted as discussed above passing through the opening at a &#34;window&#34; location or plane. This is the electro-optical viewing station for the machine. The optical or viewing mechanism is well-known and generally includes three evenly, peripherally spaced individual sensors 37, which include a photocell, photodiode, or other photo-optical detector. At least three lamps 38 are included in the plane, one for each individual sensor. Each lamp 38 projects a beam against a separate background plate 40, the reflection therefrom and from any products flowing between the background plate and the photocell sensor being detected by the sensor. The reason that three sensors are employed is to ensure sensing a substandard item that is detectable from only one direction and not necessarily from another direction. Only one lamp 38 is shown for each viewing combination of photocell sensor 37 and background plate 40. In actual practice, there are usually multiple lamps 38 for illuminating the product stream uniformly and the same or additional multiple lamps for illuminating the background plate uniformly. 
     FIG. 3 illustrates a modified J16 Si Series silicon/germanium &#34;sandwich&#34; detector 51 manufactured by EG&amp;G Judson of Montgomeryville, Pa. Of course, any other two or more element device having responsive semiconductor materials similar to such a device can be employed. This two-color detector consists of a high performance silicon photodiode device 50 mounted in a &#34;sandwich&#34; configuration over a germanium photodiode device 52 with filter element 53 located between these photodiode devices. Filter 53 is a layer of material having the desired optical filtering properties of restricting the passing light to a spectrum within the responsive region of the lower photodiode device 52, and is preferably attached to the underside of upper photodiode device 50. It will be seen that radiation enters window 54 to cause a nominal response in silicon device 50 at 800 nm. Longer wavelengths of the radiation pass through the silicon material and filter element 53 and cause a nominal response in germanium device 52 at 1300 nm. Actually, the responsivity of the two devices is more accurately portrayed in FIG. 5, each device being somewhat broadband over a spectrum of frequencies. 
     The J16 Si Series detector has been employed in fiber optic power measurements and in two-color temperature sensing applications. The manufacturer states that each silicon device or element and the germanium device or element requires a preamplifier in practice, which are respectively connected to terminals 56 and 58. 
     A very simplified schematic representation of the essential parts of the invention are shown in FIG. 4. Products 59 pass through the optical viewing station and are illuminated by one or more light sources 61. Typically, a light source is a wide band incandescent or fluorescent light. Radiation reflections from the products pass through a viewing window 63 to be received by a twin peak optical interference filter (not shown) placed in front of sandwich detector 51. However, it has been found that there are many types of products for which optical sorting is desired, but for which a multi-peak interference filter having corresponding transmission properties is not available or known. An alternative is to utilize a combination of interference filters in order to obtain transmission properties within the standard color spectra of the product. Conventional optical filter 65 has transmission characteristics such as shown in FIG. 6, wherein the percentage of transmission is described by peak 69 over a range of wavelengths. The desired spectrum of light passed by filter 65 is one that is sufficiently broad to encompass the relatively narrow spectra for the standard colors of the product, and further, which provides maximum transmission responses at those relatively narrow spectra. A second filter, filter element 53, is attached to the underside of upper photodiode device 50 or placed between photodiode devices 50 and 52 and has the transmission response described in FIG. 6 by peak 71. The desired spectrum of light passed by filter element 71 is relatively narrow, near the maximum in the responsive region of the lower photodiode device 52. The transmission responses of filters 65 and 53 are not normally the same value, although they could be. 
     Returning to FIG. 4, device 50 is connected to a preamplifier/amplifier 60 and device 52 is connected to a preamplifier/amplifier 62 to produce the outputs that are then subjected to threshold detection in threshold detectors 64 and 66, respectively. Since the transmission response peaks are not necessarily the same, the threshold detection levels can be set at different levels, as shown in FIG. 6. That is, the level may be set at a nominal value of 80 for the first peak which has a higher peak than the second, while the threshold level may be set at 60 for the second peak. 
     In operation, an effective signal 68 is produced from detector 64 when a classifier interpreter means determines that a threshold level has been exceeded by the input to detector 64 and an effective signal 70 is produced from detector 66 when a classifier interpretation means determines that a threshold level has been exceeded by the input to detector 66. Actually, the classifier interpretation means typically is located in a subsequent microprocessor, but the threshold level development and signal production scheme can best be understood from the just described functional operation of FIG. 4. 
     Signals 68 and 70 are utilized in a suitable electronic processing means, typically a microprocessor, to result in an eventual ejection activation signal as previously discussed and which is well known in the art. Perhaps the most simple logic operation of such a processing means is to cause an ejection activation signal when either signal 68 or 70 is produced. However, the logic can be established to cause an ejection signal only when both signals are present. 
     As previously mentioned, it is common to view the product stream from multiple angles, such as diagrammatically illustrated in FIG. 7. In this diagram, three sandwich detectors 51 are located at 120° positions with respect to the product stream when viewed from the top. Each detector 51a, 51b and 51c are associated with similar related components, such as discussed in connection with FIG. 4, although not all components are shown in FIG. 7. In any event, six inputs are applied to microprocessor 80, namely, inputs 68a and 70a from detector 51a, inputs 68b and 70b from detector 51b, and inputs 68c and 70c from detector 51c. The microprocessor can be programmed to result in an ejection signal 81 when any one of the six inputs are present or any combination of the six inputs are present. 
     By using two or more filter elements and incorporating one or more of those elements into the sandwich of photodiodes, this invention allows for the possibility of sorting many more types of products without increasing the size or optical complexity of the overall device. In fact, the scanning capabilities of this invention are limited only by the availability of photodiode materials and their responsivities. Once the standard colors and corresponding spectra of a product are known, an optical detector can be designed utilizing the appropriate combination of photodiodes and filtering elements. 
     Further additional optional embodiments can be chosen by using detectors 51 having more than two photo-sensitive semiconductive materials with general responsivity spectral ranges different from one another and using two or more optical filters. However, the general principles of operation are applicable as discussed above even though the combinations available are more complex. Thus, while several embodiments have been discussed and other embodiments have been generally described, it is understood that the invention is not limited thereto, since many modifications may be made and will become apparent to those skilled in the art.