UNIFORM, HIGH INTENSITY LIGHT PROJECTOR SUITABLE FOR USE IN MACHINE VISION APPLICATIONS

Abstract: Fruit defects of interest in the production of prunes are identified based on characteristics of illumination reflected by the fruit. Various reflection characteristics can be used in this regard including near infrared reflectivity and polarization state of the reflected illumination. In one embodiment, the apparatus (10) of the present invention includes a transport system (12) for transporting fruit (14) through an inspection zone (16), a reflector type illumination system (18) for illuminating the fruit, a detector system (20) for detecting reflected illumination (21), a sorting system (22) for separating defective fruit from good fruit, and a control system (24) for controlling operation of the sorting system based on signals from the detector system and transport system. In another embodiment, a projector type illumination system (18') provides a uniform, high intensity strip of light that illuminates the fruit. The light projector is suitable for use in other machine vision applications.

Description: UNIFORM, HIGH INTENSITY LIGHT PROJECTOR SUITABLE FOR USE IN MACHINE VISION APPLICATIONS Field of the Invention The present invention relates generally to machine vision applications and with specific reference to the processing of fruit in the production of prunes and, in particular, to a method and an apparatus using a uniform, high intensity light projector that is effective for detecting fruit defects so that defective fruit can be eliminated from a product stream. Background of the Invention In the commercial production of prunes, there are a number of fruit defects that can render the fruit (plum or prune) unacceptable. These include bug bites as well as scabs, cracks, sunburns, and rot. Scabs are formed when the fruit rubs against a branch or other object while on the tree. Cracks may result when a moist growing period is followed by an intense dry period. Sunburn can occur as a consequence of sun exposure, and rot occurs as a consequence of bacterial infection. It is desirable to eliminate fruit having any of these defects prior to packaging. Removal of these defects from the product stream is conventionally done manually by inspectors stationed on both sides of a transport belt. This labor intensive process is expensive and not fully effective. Manual inspection is a tedious process, and it is difficult for an inspector to continuously maintain the degree of concentration necessary to detect the full range of defects identified above, which can sometimes be quite subtle. Although conventional manual sorting is problematic, it is apparent that no fully satisfactory alternative sorting process is available to the industry. Summary of the Invention The present invention is directed to a method and an apparatus using a uniform, high intensity light projector for automatically identifying defects in the production of prunes. The light projector described is also suitable for use in other machine vision applications. It has been recognized that various types of defects of interest in the production of prunes are characterized by reflection properties that differ from the reflection properties of acceptable fruit. In particular, bug bites, scabs, cracks, sunburns, rot, and other defects are exhibited as roughened or irregular surface areas that are distinguishable by analyzing light or other illumination reflected by such surfaces. The present invention takes advantage of this recognition to provide a reliable, automated system for sorting fruit in the context of prune production. According to one aspect of the present invention, a method for identifying fruit defects in the production of prunes entails identifying a reflection characteristic indicative of a fruit defect of interest and determining a reflectance threshold based on the reflection characteristic. The reflection characteristic can relate to the intensity, spectral response, polarization, and/or other properties of the reflected illumination, and the threshold can vary depending on the characteristic under investigation and other factors. For example, the reflection characteristic employed can involve reflectivity in a selected wavelength range such as the near infrared (NIR) wavelength range or can involve variation of the illumination polarization state that results from reflection. In such cases, the threshold can be selected based on intensity or relative intensity of reflected illumination having the identified reflection characteristic. Either a positive or a negative threshold analysis can be employed, i.e. , defects can be identified based on a detected intensity above or below the threshold depending on the methodology employed. Additionally, the analysis can be direct or indirect. That is, defects can be identified directly (by detecting reflected illumination having characteristics indicative of a defect) or indirectly (by detecting reflected illumination not having characteristics indicative of a defect). Preferably, the fruit is actively illuminated in an inspection zone, and a sorting device is provided at or downstream from the inspection zone to automatically divert defective fruit from a product stream based on the threshold analysis. The inspection zone can be located, for example, on a fruit transport belt, or inspection can be conducted as the fruit is projected through the air. The sorting device can be any suitable mechanical or contact-free device, such as a puff-jet array, for selectively diverting identified defective fruit. An apparatus for implementing this method preferably includes a source of illumination for illuminating fruit in an inspection zone, a detector for detecting illumination reflected by the fruit, a processor for comparing a value related to the detected illumination to a threshold value, and a sorting device for diverting defects from the product stream in response to the comparison. In one implementation, defects are identified by analyzing reflected illumination in the near infrared (NIR) frequency range, i.e., illumination having a wavelength between about 635 run and 1100 nm. Certain defects are difficult to reliably identify by reference to reflected light in the visible spectrum, or under passive or ambient lighting conditions. It has been found that such defects can be more readily identified by illuminating the fruit with illumination having a high intensity of power in the NIR wavelength range and then detecting reflected NIR illumination. In particular, most defects of interest in the production of prunes are characterized under these conditions by a high NIR reflectivity, thereby allowing for a simple and reliable sort. Accordingly, in one embodiment, the apparatus of the present invention includes a source of illumination providing a high intensity of power in the NIR wavelength range and a compatible NIR detector. In another implementation, defects are identified by analyzing the polarization of reflected illumination. As previously noted, many defects of interest in the production of prunes are exhibited as roughened fruit surfaces. It is believed that, under appropriate conditions, these defects can affect the polarization state of illumination in a manner that facilitates defect identification. Accordingly, in one implementation of the present invention, defects are identified by illuminating the fruit with illumination having a first polarization state, and detecting and analyzing reflected illumination having a second polarization state. Preferably, the fruit is illuminated with plane polarized light. The reflected illumination is detected and analyzed in a manner that indicates reflected illumination that is circularly or elliptically polarized, or which otherwise includes a component outside of the plane of the incident illumination. The apparatus for implementing this polarization analysis includes a source of illumination having a first polarization state, a detector for detecting reflected illumination having a second polarization state, a processor for comparing a value relative to the detected illumination to a threshold value, and a sorting device for diverting defective fruit from the product stream. Preferably, the source is a uniform, high intensity light projector associated with a polarizer for transmitting plane polarized illumination, and the detector includes a camera associated with a polarizer acting as a cross-analyzer to block reflected illumination having the transmitted planar polarization. Because of anisotropic effects, the performance of the apparatus can be enhanced by employing monochromatic illumination. In one embodiment, the lamp provides or is filtered to provide substantially monochromatic illumination in the green wavelength range. According to another aspect of the present invention, the fruit is subjected to a spectral response altering treatment to enhance a wavelength dependent sorting process. One difficulty associated with sorting fruit in the production of prunes relates to fruit color variation resulting from varying maturity. Fully mature prunes are characteristically black in color and have a low reflectivity in the NIR wavelength range. Less mature prunes may have a somewhat reddish hue and a higher reflectivity in the NIR wavelength range. Although such less mature prunes are not necessarily considered defective, they are difficult to distinguish from true defective prunes based on a NIR reflection-based sort. It has been found that such sorts can be enhanced by subjecting the prunes under consideration to a treatment that diminishes their chlorophyll response. Vegetable matter containing chlorophyll exhibits a marked reflectivity in the NIR wavelength range in addition to the well-known green reflectivity in the visible spectrum. This chlorophyll response is fragile and can be diminished by many types of treatment, including heating, blanching and freezing. By dimimshing their chlorophyll response, even somewhat immature prunes can be readily distinguished from true defects. The associated method of the present invention includes the steps of subjecting a fruit to a treatment that alters the reflectivity of the fruit within a wavelength range, illuminating the fruit with illumination within the same wavelength range, and analyzing illumination within the same wavelength range reflected by the fruit, wherein the reflectivity altering treatment facilitates sorting based on analysis of the reflected illumination. In one implementation, the wavelength range is the NIR wavelength range, and the treatment is a chlorophyll response diminishing treatment. The reflectivity altering method can advantageously be integrated into a process for producing prunes to yield an improved two-step sorting process. The prune production process conventionally includes a heat treatment to dehydrate plums so as to yield prunes. These prunes can be sorted using a reflectivity based analysis as described above. In some cases, the fruit diverted as a result of this initial sort may include immature prunes as well as true defects. This diverted stream is then subjected to a reflectivity altering process and re-sorted in accordance with the present invention to separate acceptable immature prunes from true defects. The present invention thus improves the process for identifying fruit defects in the production of prunes and allows for automation of the sorting process. The invention increases the effectiveness of defect identification including distinguishing acceptable immature prunes from true defects. Production costs are thus reduced and acceptable yield is increased, thereby benefiting the producer and consumer. Brief Description of the Drawings For a more complete understanding of the present invention and further advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the drawings in which: Fig. 1 is a schematic diagram showing a side elevation view of a prune sorting apparatus constructed in accordance with the present invention; Fig. 2 is a perspective view showing the prune sorting apparatus of Fig. 1; Fig. 3 is a graph showing the spectrographic reflectance characteristics for a number of black prunes; Fig. 4 is a graph showing the spectrographic reflectance characteristics for a number of defective, cracked prunes; Fig. 5 is a graph showing the spectrographic reflectance characteristics for a number of defective, rotted prunes; Fig. 6 is a graph showing the spectrographic reflectance characteristics for a number of defective, scabbed prunes; Fig. 7 is a graph showing the spectrographic output characteristics for a NIR lamp that can be used in the prune sorting apparatus of Fig. 1; Fig. 8 is a graph showing the spectrographic reflectance characteristics for a number of red prunes that are not necessarily considered to be defects; Fig. 9 is a graph showing the spectrographic reflectance characteristics for a scabbed prune and a red prune prior to blanching; Fig. 10 is a graph showing the spectrographic reflectance characteristics for a scabbed prune and a red prune after blanching; Fig. 11 is a schematic diagram showing a side elevation view of an alternative prune sorting apparatus that is implemented with a uniform, high intensity light projector constructed in accordance with the present invention; Fig. 12 is an isometric view of the illumination system of the apparatus of Fig. 11; and Figs. 13 A and 13B are respective plan (with a partly cut away lid) and right side elevation views of the illumination system of Fig. 12. Fig. 14 shows the light emission spectral characteristic of a preferred thallium-doped metal halide arc lamp installed in the light projector of Figs. 13A and 13B. Figs. 15A and 15B are respective plan (with lid removed) and right side elevation views of an illuminator housing in which two of the light projectors of Figs. 12, 13A, and 13B are installed. Detailed Description of Preferred Embodiments The present invention entails automatic identification of defects in the production of prunes based on characteristics of reflected illumination. In the following description, the invention is set forth with respect to specific exemplary embodiments and parameters for implementing sorts based on NIR reflectivity and based on polarization phenomena. However, it will be appreciated that various modifications and additions are possible in accordance with the teachings of the present invention. A prune sorting apparatus 10 constructed in accordance with the present invention is shown in Figs. 1 and 2. Generally, the apparatus 10 includes: a transport system 12 for transporting fruit 14 through an inspection zone 16; a reflector type illumination system 18 for illuminating fruit 14 in inspection zone 16; a detector system 20 for detecting reflected illumination 21; a sorting system 22 for separating defective fruit from good fruit; and a control system 24 for controlling the operation of sorting system 22 based on signals from detector system 20 and transport system 12. The illustrated apparatus 10 incorporates a number of optical components including polarizers 26 for polarizing the transmitted illumination 27, a mirror 28 for reflecting illumination 21 from inspection zone 16 and selectively transmitting illumination 21 to detector system 20. Although fruit 14 is inspected on transport system 12 in the illustrated embodiment, it will be appreciated that in- the-air (e.g., off belt) inspection or other techniques may be employed if desired. Transport system 12 includes an endless conveyor belt 32 driven by a drive roller (not shown) about a roller 34 mounted on a shaft 36. Belt 32 is driven at a speed selected so that fruit 14 is projected from belt 32 along a trajectory 38 into an accept bin 40, unless deflected (as will be described below) by sorting system 22 into a reject bin 42 along a trajectory 44. Preferably, belt 32 is provided with a black matte or other anti-reflective finish to reduce reflectance and improve the effective signal-to-noise ratio as detected by detector system 20. As shown, fruit 14 may be distributed in an essentially random fashion across the length and width of belt 32. Illumination system 18 of Figs. 1 and 2 provides a stripe of illumination in the inspection zone 16 having a substantially uniform intensity across the width of belt 32. The illustrated illumination system 18 includes a pair of elongate lamps 46 positioned on opposite sides of inspection zone 16 to reduce errors caused by shadowing. The type of lamp employed will depend on the specific reflection characteristic under analysis as will be described below. Each lamp 46 is housed within an elliptical mirrored reflector 48 oriented to focus illumination from lamp 46 on inspection zone 16. An enclosure (not shown) may be provided at the base of reflector 48 to protect the lamp from debris or contaminants that could degrade performance or diminish lamp life and to prevent broken bulbs from falling into the product stream. The illustrated illumination system 18 also includes a linear polarizer 26 associated with each lamp 46 to transmit plane polarized illumination. The illustrated polarizer 26 comprises a conventional polymeric polarizing sheet that includes embedded long-chain particles aligned to define a polarization axis. As shown, polarizer 26 extends across the base of reflector 48. It will thus be appreciated that illumination 27 incident upon fruit 14 in inspection zone 16 will be plane polarized. In the embodiment of Figs. 1 and 2, detector system 20 includes a camera 50. Camera 50 detects any incident reflected illumination 21 and provides an output signal indicative of the intensity of illumination 21 and the associated location of fruit 14 on belt 32. The illustrated camera 50, which may be a black and white or an IR camera manufactured by SRC Vision, Ine,. is a digital camera having a high resolution detector plane, where the radiation sensitive pixels of the detector plane are optically mapped to corresponding locations of inspection zone 16. The detector plane is read out on a periodic basis by appropriate data storage registers or the like. The output signal from camera 50 therefore includes substantially real-time intensity information on a pixel-by-pixel basis. Figs. 11, 12, 13 A, 13B, 14, and 15A and 15B illustrate as an alternative embodiment a sorting apparatus 10' for detecting defective fruit based on polarization phenomena. As shown in Fig. 11, a projection type illumination system 18' and a detector system 20' of apparatus 10' differ from those of the apparatus shown in Figs. 1 and 2. Illumination system 18' is provided as two units positioned approximately 457 mm from belt 32. Details of illumination system 18' are shown in Figs. 12, 13A, 13B, 14, 15A, and 15B. Each unit includes an arc lamp 60 for emitting substantially monochromatic illumination having a wavelength in the green range; a hemi-cylindrical, chrome plated metal reflector 62 disposed behind and partly surrounding lamp 60; a pair of nominally identical substantially hemi-cylindrical lenses 64 for focusing illumination as a bright, straight line stripe on belt 32 in inspection zone 16; a series of optical glass elements or rods 66 for providing a more uniform distribution of illumination across the width of belt 32; and a polarizer sheet 68, such as the ones described above, for transmitting substantially plane polarized illumination from lamp 60 to inspection zone 16. More specifically, a long, thin arc lamp 60 has a length 80 and cooperates with reflector 62 to form an apertured arc lamp source 82 of high intensity light in the form of an oblong shape having its long dimension extending along length of 80 of arc lamp 60. Arc lamp 60 is preferably of a metal halide type doped with thallium, gallium, indium iodide, or sodium. A specific example of a preferred arc lamp 60 is a thallium-doped lamp such as an MBIL S-1000 manufactured by Specialty Discharge Lighting, Bellevue, Ohio. The MBIL S-1000 is a double-ended tubular metal halide arc lamp having a 252 mm contact-to-contact length, a 182 mm lighted length, and a 15 mm bulb diameter that emits 70,000 Lumens of thallium green light. Fig. 14 shows the light emission spectral characteristic of the preferred thallium-doped metal halide arc lamp. Reflector 62 is preferably a 203 mm long, 41 mm inner diameter pipe half-section with a polished chrome-plated interior light reflecting surface. The light of oblong shape emitted by apertured arc lamp source 82 propagates in a direction along an optic axis 86 toward a lens assembly 88 formed by conventional cylindrical lenses 64 functioning as light beam shaping devices and multiple mutually spaced-apart glass rods 66 functioning as optically transmissive light dispersing devices. Each of cylindrical lenses 64 is offset from optic axis 86 by an angle 90 of preferably 69.8 degrees to form a V-shaped lens assembly having a lens apex region 92 and ends 94. Each cylindrical lens 64 is preferably 173 mm in length and has a 50 mm curved surface radius. Cylindrical lenses 64 are closely spaced apart at their ends in apex lens region 92 and are symmetrically positioned on either side of optic axis 86. Cylindrical lenses 64 in this configuration bring to a line focus and stretch the length beyond the 182 mm length of the light emitted by arc lamp source 82. (One cylindrical lens 64 positioned in front of arc lamp source 82 would be inadequate to achieve the projection length necessary to cover the desired 61 cm width of belt 32 in apparatus 10'.) The angular offset results in a narrow line of high intensity light having a nonuniform light intensity distribution characterized by low intensity and high intensity regions. The low intensity region resides along the line in two portions, and the high intensity region is positioned between the low intensity portions and extends about 85 mm in each direction generally symmetrically about optic axis 86. Glass rods 66 are mutually spaced apart from one another and arranged in two lines that are parallel to cylindrical lenses 64 and thereby form a V-shaped element assembly 96 with an element apex region 98 positioned a distance 100 downstream of element apex region 98. Each glass rod 66 is preferably made of BK-7 glass having a 43 mm length and 9.5 mm radius. An equal number of glass rods 66 is positioned on either side of optic axis 86, with a center-to-center distance 102 of 12 mm between adjacent glass rods and a distance 100 of 17.8 mm. A total of sixteen glass rods 66 laterally disperse a portion of the light incident to them. Glass rods 66 are positioned to contribute an amount of light in the high intensity region to the low intensity portions and cover in the central portion about 50 percent of the full optical projection of arc lamp source 82. The use of cylindrical glass rods 66 and their symmetrical arrangement about optic axis 86 facilitates uniform light distribution. The effect is to homogenize the high intensity light incident on and along the width of belt 32 to within ±5 percent variation. The width of the bright stripe on belt 32 is set primarily by the bulb diameter of arc lamp 60 and the focal lengths of cylindrical lenses 64. In the preferred implementation described above, the output beam measured at 457 mm from element apex region 98 is 20 mw/cm 2 over a 25.4 mm x 610 mm scan. (The scan width of detector system 20 is 1 mm, which is much less than the 25.4 mm width of stripe projected onto belt 32.) Figs. 15A and 15B show plan and right side elevation views of an illuminator housing 110 in which two nominally identical illumination systems 18' are enclosed and positioned side-by-side to project a bright stripe of substantially uniform intensity on a 122 cm wide belt 32. (Fig. 15A shows the interior of housing 110 with its lid removed.) Housing 110 includes two cool air flow channels having separate cool air inlets and a common warm air return outlet. Cool air is delivered from an external source (not shown). An air flow channel 112 receives cool air from an inlet 114 and circulates the cool air in two directions around part of the perimeter of the interior of housing 110. A glass interior barrier window 116 and a window assembly 118 form a portion of air flow channel 112 that is located in front of glass rods 66 of the lens assembly 88 of each illumination system 18'. Window assembly 118 is composed of a thin plastic polarizer 68 positioned at the interface between two optically transparent plastic sheets 120. Cool air flowing in the space between interior barrier window 116 and window assembly 118 prevents polarizer 68 from melting under the intense heat generated by arc lamp source 82. The warm air exiting air flow channel 112 passes through the central part of the interior of housing 110 in the space between illumination systems 18' and to the outside through a warm air return outlet 122. An air flow channel 130 receives cool air from an inlet 132 and circulates the cool air in two directions to two channel openings 134 for delivery into a space 136 behind each illuminator system 18'. Two small holes 138 provided in an enclosure 140 for each illumination system 18' are positioned to direct air flow across a fused quartz-metal seal at each end of arc lamp 60 to prevent cracking of the seal and a consequent loss of lamp tube pressure. (Cracking would otherwise result from the differential heat expansion properties of quartz and metal, the latter having a greater rate of expansion with an increase in heat.) The cool air is not directed toward the lamp tube because the plasma arc provides a more intense light output when the quartz tube remains hot. Warm air exits side vents 142 in enclosure 140 and flows into the central interior portion of enclosure 140 to the outside through warm air return outlet 122. Detector system 20' as shown in Fig. 11 includes analyzer 30 and camera 50. Analyzer 30 can be constructed from a conventional polymeric polarizing sheet similar to polarizers 26. However, analyzer 30 is oriented so that its polarization axis is substantially perpendicular to the polarization plane of the incident plane polarized radiation. That is, polarizer sheets 68 and analyzer 30 are arranged relative to the propagation path of illumination 21, 27 as cross-polarized sheets so that reflected illumination 21 retaining the transmitted plane polarization is substantially blocked from camera 50 disregarding, for the moment, anisotropic effects. As will be understood from the description below, polarizer sheets 68 and analyzer 30 allow for detection based on polarization phenomena associated with fruit defects. The output signal from detector system 20 or 20' is transmitted to control system 24, which contains a microprocessor. Control system 24 also receives information regarding the belt speed of transport system 12. Such rate information may be provided in any suitable form. For example, in the case of constant speed operation, a speed constant can be pre-programmed into control system 24. Alternatively, rate information can be obtained via an interface with a control panel or motor of transport system 12. Where a more positive feedback based indication is desired, a rate signal may be obtained from an encoder, for example, mounted on roller shaft 36. Control system 24 of the illustrated embodiment performs a number of functions. Control system 24 first implements a threshold analysis to identify any fruit defects. Although other arrangements are possible, the illustrated apparatus 10 is configured to conduct a positive threshold analysis, e ^ , to identify defects based on received illumination intensity in excess of a determined threshold. The threshold is determined based on the reflection characteristic (e.g., polarization state) under consideration, the performance of illumination system 18 or 18' and optical components, and certain theoretically and/or empirically derived criteria for accurately distinguishing between good fruit and defective fruit. When the threshold analysis identifies a defect, control system 24 controls the operation of sorting system 22 so as to deflect the defective fruit into reject bin 42. In this regard, control system 24 determines where the defective fruit is located relative to the width of belt 32 and synchronizes operation of sorting system 22 to movement of fruit 14 so that sorting system 22 is activated at the appropriate time. Preferably, sorting system 22 can be selectively activated at discrete locations spaced across the width of belt 32 so that defects can be rejected substantially without affecting adjacent acceptable fruit. Any suitable mechanical, pneumatic, or other deflecting mechanism can be used in this regard. The illustrated sorting system 22 includes a linear array of puff-jets distributed along the length of a control bar 52. Upon activation, each puff-jet provides an instantaneous and highly localized gas discharge sufficient to deflect defective fruit into reject bin 42 as indicated by trajectory 44. Control system 24 uses information regarding the location of the defect relative to the width of belt 32 to determine which puff-jet should be activated. The timing for activating sorting system 22 is determined mathematically based on knowledge of the relative positions of inspection zone 16 and control bar 52, and the operation of transport system 12. Control system 24 uses such timing information to implement an appropriate delay before transmitting an activation signal to sorting system 22. The following discussion sets forth the basis for a positive threshold analysis with respect to NIR and polarization reflection characteristics of prune defects. It will be appreciated that other reflection characteristics and identification criteria can be utilized in accordance with the present invention. Figs. 3-6 show the spectrographic reflection characteristics for, respectively, good black prunes, defective cracked prunes, defective rotted prunes, and defective scabbed prunes. As can be seen, both good fruit and defective fruit exhibit a low reflectivity in the visible spectrum. By contrast, all of the types of defects illustrated exhibit a markedly higher reflectivity in the NIR spectrum, making for a relatively easy sort. In particular, it will be observed that the good black prunes have a maximum reflectivity of less than about 30% throughout the NIR range, and a maximum reflectivity of no more than about 20% in the 750-1000 nm wavelength range. The fruit defects have a reflectivity greater than 30% in the 750-1000 nm range, and even higher reflectivity when the entire NIR range is considered. This demonstrates that an accurate threshold sort can be conducted based on NIR reflectivity and, especially, based on reflectivity in the 750-1000 nm range. In the latter range, a threshold value may be selected based on a reflectivity in the 20-30% range. It will be appreciated that the specific value employed may vary from harvest to harvest or based on other factors. Fig. 7 shows the spectrographic output characteristics of a rare gas Argon lamp that is used in illumination system 18 according to a NIR reflection based implementation of the present invention. As shown, the power output of the rare gas Argon lamp is highly concentrated in the 750-1000 nm wavelength range corresponding to wavelength range noted above where good fruit is readily distinguished from defective fruit. The NIR implementation of the illustrated embodiment thus involves illuminating fruit 14 in inspection zone 16 using a lamp 46 that has a high intensity of power in the NIR, detecting illumination in the NIR range using an appropriate detector, and operating sorting system 22 to reject fruit when the detected illumination exceeds an appropriately selected threshold. It will be appreciated that such a sort can be conducted without the illustrated polarizers 26. However, it has been found that the irregular surface of a prune results in glints of illumination that interfere with the threshold analysis. The effect of these glints can be reduced by employing polarizers 26 as shown. Polarizers 26 also tend to block extraneous illumination (e.g., reflected by belt 32) thereby improving the effective signal-to-noise ratio as detected by detector system 20. One difficulty associated with the NIR sorting process as described above relates to less mature or so-called red prunes. These prunes are not considered defective but may have NIR reflection characteristics, as shown in Fig. 8, that are difficult to distinguish from those of defective fruit. As a result, when a particular harvest yields a large number of red prunes, the NIR sort alone could reject an unacceptable quantity of good fruit. This problem is addressed in accordance with the present invention by subjecting suspect fruit to a treatment to diminish the chlorophyll response of the fruit. Figs. 9 and 10 show a comparison of the spectrographic reflectance characteristics of a good red prune and a defective scabbed fruit before (Fig. 9) and after (Fig. 10) such a treatment. The treatment employed in this case entailed blanching the fruit at 210°F for two minutes. As shown in Fig. 9, the good red fruit initially had a higher reflectivity than the defective scabbed fruit in the NIR range. After the treatment, the reflectivity of the good red fruit is reduced and the reflectivity of the defective scabbed fruit is increased as shown in Fig. 10, thereby allowing for a positive threshold sort as described above. This chlorophyll response treatment can be implemented in the context of the present invention as follows. Initially, all fruit is sorted using the NIR threshold analysis as described above. When there is a concern regarding possible rejection of good red prunes, the contents of reject bin 42 are subjected to blanching or other treatment for affecting the chlorophyll response of the fruit. In practice, a conveyor belt can be provided at the base of the reject bin to continuously deliver rejected fruit to a chlorophyll response treatment station. The treated fruit is then returned to the transport system for a second pass through inspection zone 16. In this manner, fruit yield is improved without unnecessarily treating good black prunes, which are accepted on the first pass. As an alternative to the NIR reflectivity based analysis as described above, fruit 14 can be sorted based on analysis of the polarization state of the reflected illumination. It has been noted that the roughened fruit surfaces associated with various defects tend to alter the polarization state of incident illumination, whereas acceptable fruit is less likely to produce such an effect. As described above, polarizers 26 transmit substantially plane polarized illumination. When such illumination is reflected by good fruit, the reflected radiation which is unaltered by the good fruit is largely blocked by analyzer 30, such that detector system 20 detects little intensity. However, a portion of the plane polarized illumination reflected by defective fruit will be altered and will not be plane polarized, and will therefore pass through analyzer 30 with some intensity. This effect can be utilized to conduct a positive threshold sort as described above. Ideally, this polarization analysis could be implemented with virtually any type of lamp 46. In practice, though, it has been found beneficial to employ monochromatic illumination due to anisotropic performance characteristics of apparatus 10. Excellent results have been obtained by employing a thallium lamp, the light emission spectrum of which is shown in Fig. 14, to provide substantially monochromatic illumination having a green wavelength. Under these conditions, the fruit substantially disappears except for defects from the perspective of the camera, thus allowing for an easy and accurate sort. While various embodiments or implementations of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. For example, one or more of the polarizers may be omitted, depending on the type of specimen under inspection. Moreover, the intense, uniform light emitted by the illumination system shown in Figs. 12, 13A, 13B, 14, and 15A and 15B can be used in other machine vision applications such as wood veneer defect clipping control and inspection of other fruit products including, for example, peaches. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.

Claims: Claims 1. A method for use in identifying fruit defects in the production of prunes, comprising the steps of: identifying an illumination reflection characteristic indicative of a fruit defect of interest in the production of prunes; determining a reflectance threshold relative to the identified reflection characteristic; detecting illumination reflected by a fruit; and analyzing the reflected illumination relative to the reflectance threshold to identify any fruit defects of interest in the production of prunes. 2. The method of claim 1 in which the identified reflection characteristic involves reflectance in the near infrared spectral range and the step of determining a reflectance threshold comprises identifying an intensity level of reflected illumination in the near infrared spectral range so that defective fruit can be distinguished from good fruit relative to the intensity level. 3. The method of claim 1 in which the identified reflection characteristic involves a polarization phenomenon and the step of determining a reflectance threshold comprises identifying an intensity level of reflected illumination having a selected polarization characteristic so that defective fruit can be distinguished from good fruit relative to the intensity level. 4. The method of claim 1 in which the step of analyzing comprises conducting a positive threshold analysis such that fruit defects are identified based on a reflected illumination intensity in excess of the reflectance threshold. 5. The method of claim 1 in which the step of illuminating comprises illuminating the fruit with transmitted illumination having a high intensity of power in the near infrared range by employing a near infrared lamp. 6. The method of claim 5 in which the step of illuminating comprises transmitting illumination having an incident first polarization state. 7. The method of claim 6 in which the step of detecting comprises detecting reflected illumination having a second polarization state different from said incident first polarization state. 8. The method of claim 1, further comprising the step of subjecting the fruit to a treatment to diminish the chlorophyll response of the fruit. 9. The method of claim 1, further comprising the steps of selectively removing the fruit from a product stream based on said step of analyzing, subjecting the removed fruit to a treatment to diminish chlorophyll response of the fruit, and detecting illumination reflected by the fruit after the step of subjecting the removed fruit to a treatment. 10. A light projector from which light propagates to form a high intensity line of light having a substantially uniform intensity distribution over a target surface positioned a distance from the light projector, comprising: a source of high intensity light formed in an oblong shape and propagating in a direction along an optic axis toward a target surface; and a lens assembly positioned to receive the high intensity light and including a light beam shaping device and an optically transmissive light dispersing device, the light beam shaping device concentrating the high intensity light in a narrow line of high intensity light having a nonuniform intensity distribution characterized by low intensity and high intensity regions distributed along the line, and the optically transmissive light dispersing device positioned to receive from the light beam shaping device light propagating from the high intensity region of the line, the light dispersing device redirecting and thereby contributing a portion of the light from the high intensity region laterally toward the low intensity region to make substantially uniform the distribution of light energy along the line of light as it propagates toward the target surface. 11. The light projector of claim 10 in which the source of high intensity light comprises a thin, long apertured arc lamp. 12. The light projector of claim 11 in which the arc lamp is of a metal halide type that is doped with thallium, gallium, indium iodide, or sodium. 13. The light projector of claim 11 in which the apertured arc lamp comprises a long, thin tubular arc lamp partly surrounded by an elongate curved reflector. 14. The light projector of claim 11 in which the light beam shaping device includes two cylindrical lenses positioned to form a V-shaped lens assembly having two ends and a lens apex region, the lens apex region being farther from the source of high intensity light than are the two ends and the optic axis extending through the lens apex region. 15. The light projector of claim 11 in which the optic axis extends through the high intensity region of the line and the low intensity region of the line is divided into two portions positioned on either side of the high intensity region, the optically transmissive light dispersing device comprising multiple spaced-apart light transmissive elements positioned on either side of the optic axis. 16. The light projector of claim 15 in which the multiple light transmissive elements include glass rods. 17. The light projector of claim 16 in which the glass rods are of cylindrical shape. 18. The light projector of claim 15 in which the multiple light transmissive elements are positioned to form a V-shaped element assembly having two ends and an element apex region, the element apex region being farther from the source of high intensity light than are the two ends and the optic axis extending through the element apex region. 19. The light projector of claim 11 in which the source of high intensity light has a length and the lens assembly is nonlinear with a length greater than that of the high intensity light to extend the narrow line of high intensity light beyond the length of the source of high intensity light. 20. The light projector of claim 19 in which the light beam shaping device includes a cylindrical lens and the optically transmissive light dispersing device includes multiple spaced-apart light transmissive elements positioned near and on either side of the optic axis.

Inventors: CAMPBELL DUNCAN, LEIDECKER CLIFF, SQUYRES PARKS, CAMPBELL, DUNCAN, LEIDECKER, CLIFF, SQUYRES, PARKS
Applicants: CAMPBELL DUNCAN, LEIDECKER CLIFF, SQUYRES PARKS, SRC VISION INC, CAMPBELL, DUNCAN, LEIDECKER, CLIFF, SQUYRES, PARKS, SRC VISION, INC.
Application year: 1997
Main classification: B07C5
IPC codes: B07C5, G01N21, G01N33