WO1999020048A1

WO1999020048A1 - Imaging method and system with elongate inspection zone

Info

Publication number: WO1999020048A1
Application number: PCT/US1998/019054
Authority: WO
Inventors: Timothy P. White; Howard Stern
Original assignee: Northeast Robotics Llc
Priority date: 1997-10-10
Filing date: 1998-09-11
Publication date: 1999-04-22
Also published as: AU9315498A; EP1044565A1; EP1044565A4

Abstract

An elongate inspection system and method for providing a uniform illumination field to a desired inspection zone for inspection of a desired area of an object to be inspected. The elongate inspection system defines an inspection plane extending between an inspection device and the object to be inspected. A primary illumination for the inspection system is provided both from the left (54) and from the right (54) of the inspection plane and a secondary illumination (62) is provided along and coincident with the inspection plane. The primary (54) and secondary (62) illumination combine to provide a contiguous uniform illumination field (27, 29) to facilitate accurate inspection of the desired feature, characteristic or attribute of the object to be inspected.

Description

IMAGING METHOD AND SYSTEM WITH ELONGATE INSPECTION ZONE

FIELD OF THE INVENTION

The invention pertains to a method and apparatus for permitting electronic machine vision inspection of light reflecting objects wherein a true inspection is obtained of an elongate linear portion of the surface being viewed or inspected. The invention also pertains to a method and apparatus for permitting such machine vision inspection of an elongate linear portion of a light reflecting object. DESCRIPTION OF THE RELATED ART An electronic machine vision apparatus is commonly employed in conjunction with an automatic machining, assembly and inspection apparatus, particularly of the robotics type. Television cameras are commonly employed to observe the object being machined, assembled, read, viewed or inspected, and the signal received and transmitted by the camera can be compared to a standard signal or database to determine if the imaged article is properly machined, finished, oriented, assembled, determined, etc. Also, machine vision apparatus is widely used in inspection and flaw detection applications whereby inconsistencies and imperfections in both hard and soft goods can be rapidly ascertained and adjustments or rejections instantaneously effected.

A machine vision apparatus detects abnormalities by comparing the signal generated by the camera with a predetermined signal indicating proper dimensions, appearance, orientation, or the like. In order to achieve consistent and accurate results when using a machine vision apparatus employing an electronic camera, it is very important that consistent and uniform lighting of the imaged object occurs, as the lighting will significantly affect the vision signal generated and may produce irregular signals even though no fault may exist in the object being imaged other than it is not uniformly illuminated.

Illumination problems in machine vision applications are particularly present when the object being imaged has a shiny specular surface. For instance, in the inspection of soldered circuits such as used with printed circuit boards the solder's highly reflective nature and uneven surface geometry makes it very difficult to obtain an accurate electronic signal, and the same machine vision problem occurs when inspecting ball bearings, reflective packaging, and other objects having shiny surfaces, particularly irregular shiny surfaces. A similar problem occurs when attempting to read characters on the labeled area of a letter or package, especially when such area is covered with a glassine or other transparent material which may have specular characteristics when illuminated from various angles. The characters are especially difficult to read when the transparent material is wrinkled, crinkled or otherwise bent or folded which may typically occur during the conventional handling of letters, packages or other mail or through changes in relative humidity and the different coefficients of expansion of paper and glassine, as a function of relative humidity.

When utilizing a machine vision apparatus and techniques in shiny surface applications, it is common to employ complicated lighting systems for illuminating the object being imaged, and it is a purpose of such lighting systems to eliminate glints, shadows, highlights, underlights, reflections and other lighting artifacts caused by shiny convex surface objects. Examples of complex lighting systems for use with a machine vision apparatus are shown in United States Patent Nos. 4,677,473; 4,882,498; 5,051,825; 5,060,065 and 5,072,127. While the devices shown in these patents are capable of generating improved lighting characteristics, such devices do not eliminate erroneous signals resulting from the reflection of windows, openings or orifices defined in the lighting apparatus necessary to permit inspection of the article being viewed, and such apparatus does not eliminate erroneous signals generated due to the reflection of the camera (s) , the openings or the voids from specular objects.

Conventional illuminators for line-scanning image sensors, such as those currently used for printed web inspection or in common office copiers, use "dark field" illumination. That is, the light source is off to one side of the optical axis/plane so that there is no direct reflection of the light source into the optics of the imaging system. While such illumination systems facilitate faithful reproduction of surfaces with diffuse reflecting characteristics, such as common office copy paper, for example, they fail to allow faithful reproduction of specular, i.e. "shiny" surfaces, whether flat or uneven. For example, a document or label including a highly reflective metallic foil as part of its art work, when imaged using common off-axis/plane "dark field" illumination, will have the reflective foil reproduced as a black or dark image, rather than a light image. This effect is exploited by the United States Mint in the new large denomination bills to foil counterfeiters by weaving a reflective strip into the paper that appears black when copied or scanned.

Another deleterious effect caused by the poor lighting in current scanner technology is that the specular surface of a matte-finish photograph, reflective document or other art work will exhibit a myriad of "sparkles" or random point reflections, of the off- axis/plane light source, off the angled facets within the fine-scale surface undulations. These shortcomings fundamentally limit the ability of linear scanners and copiers to faithfully reproduce many types of documents and art work.

Attempts have been made to cure this problem with obtaining accurate visual inspection of objects with uneven specular surfaces by providing a large solid angle of uniform illumination. Under such illumination, all portions of the uneven specular surfaces reflect a uniform intensity of light, and thereby appear uniform and more consistent in appearance.

It is well known in the engineering art of automatic inspection or "machine vision" that uneven specular surfaces are among the most difficult to image. This is because objects containing such surfaces reflect, in a distorted manner, the surrounding inspection environment, and thereby acquire visual characteristics such as glints and shadows which may cause errors in the visual interpretation of images of such objects. The visual inspection of objects with uneven specular surfaces can be greatly improved by providing a large solid angle of uniform illumination. Under such illumination, all portions of the uneven specular surfaces reflect a uniform intensity of light, and thereby appear uniform and more consistent in appearance.

Existing methods of providing a large solid angle of uniform illumination make use of diffusers such as translucent plastic, ground glass, and diffusely reflecting surface coatings to take light from one or more narrow-angle light sources such as LEDs, fiber optic light guides, or round cylindrical light bulbs and spread the light into a continuous uniform field of illumination. The important physical characteristic of such a uniform light field is that photons of light impinge on every point on the object being imaged with equal intensity from every point in the illumination field, i.e. uniform incident illumination intensity for all angle values of azimuth and elevation.

In practice, such wide-angle light sources are designed to provide a seamless uniform illumination field only for an area of specified dimensions corresponding to the maximum inspection area needed to be illuminated. This area is referred to as the "diffuse aperture". At points outside the diffuse aperture, the illumination field is no longer seamless, but rather contains voids or areas from which no light is incident on such points.

Large solid angle light sources constructed with traditional diffusing techniques are extremely inefficient. A significant portion of the photon stream emanating from the original light source or light sources is lost through a number of attenuating processes including internal reflections, surface absorption, and simple waste through illumination of not only the part being imaged, but the surrounding area as well. Commonly used light sources, such as LED arrays and focussed incandescent lights, provide adequate illumination intensity for such wide-angle diffuse light sources when standard 2-D array video cameras are used for imaging or observing an object. With such 2-D array video cameras, the image acquisition integration time is typically in the range of 1/60 to 1/30 of a second. When a 1-D line-scan video camera is used to sequentially acquire individual lines of pixels to makeup images of objects under continuous motion, large solid-angle diffuse light sources do not provide an adequate illumination intensity, i.e. the intensity needs to be increased by a factor typically in the range of between about 100 to about 1,000 times.

SUMMARY OF THE INVENTION It is an object of the invention to provide a method and apparatus for illuminating an object to be imaged by machine vision camera (s) wherein an illumination of the object is produced which is continuous and uniform in nature and is free of dark, bright or void portions capable of generating erroneous vision signals.

Another object of the invention is to provide a method and apparatus for illuminating specular objects to be imaged by electronic machine vision cameras, film cameras, scanners, photocopiers or human observers, where the object is uniformly illuminated by a primary, off-axis inspection source of light having an inspection window or viewing orifice to permit vision access along an inspection axis or plane P that is masked against reflection by the object with a secondary light source being supplied along the inspection axis/plane P.

Another object of the invention is to provide a method and apparatus for illuminating an elongate linear portion or narrow strip or zone of an object to be imaged by a linear scanner, for example, where illumination of the linear portion or zone of the object is produced which is continuous and uniform in nature and is free of dark, bright or void portions capable of generating erroneous vision signals.

Another object of the invention is to provide a method and apparatus for illuminating an elongate linear portion or zone of a specular object to be imaged by an electronic machine vision camera, a film camera, a scanner, a photocopier or a human observer, where the linear portion or zone of the object is uniformly illuminated by an elongate primary, off-axis illumination source , composed of two or more opposed off-axis light sources, having an elongate inspection window or viewing orifice between them to permit vision access along an inspection plane P and an elongate secondary on-axis source.

Another object of the invention is to provide a method and apparatus for illuminating specular objects to be imaged by an electronic machine vision camera where the object is illuminated by a light emitted from an off- inspection plane light source of a shape and size sufficient to provide substantially uniform illumination of the object to be imaged and an on-inspection plane light source, projected through an elongate inspection window, permitting machine vision inspection along the inspection plane P while masking the inspection window against possible reflection from the imaged object surface.

Yet another object of the invention is to provide a method and apparatus for illuminating a machine vision observed specular object with an uniform light where the inspection window is masked against possible reflection from the imaged object surface by the introduction of a light through the window along the inspection axis/plane P of an intensity and character substantially equal to the intensity and character of the primary off-axis light illuminating the object.

Still another object of the invention is to provide a method and apparatus for illuminating a machine vision illuminated object having a light reflecting surface wherein a beam splitter is employed to project light through a camera inspection window along the camera inspection axis/plane P of an intensity and character corresponding to the primary light illuminating the imaged object.

Yet a further object of the invention is to minimize the depth of the on-inspection axis/plane light source assembly by utilizing a either flat or a curved beam splitter.

A further object of the invention is to provide an inspection system which facilitates reading of numerals, letters, characters or other indicia in the label area of a letter or packages, even when such areas are covered with a glassine or transparent material which may have specular characteristics when illuminated from various angles, particularly if the transparent material is wrinkled or crinkled, which typically occurs during the handling of letters or packages.

A still further object of the invention is to provide an illumination field which has a greater solid angle and/or a greater uniformity of illumination then other known illumination products. It is a goal of this invention to provide a large solid angle of unbroken uniform illumination at the intensity levels required for 1-D line-scan inspection. Due to the above described inefficiencies of traditional light diffusing methods, a method and apparatus are described which deliver light with high efficiency from a narrow-angle high-intensity light source, such as a fiberoptic "light line", to the surface of the object being observed with such incident light impinging with a high degree of uniformity as a function of the angle of incidence. To achieve the incident illumination intensity levels required for line-scan inspection, the large solid angle light field is focussed rather than diffused. In addition, the uniformly impinging focussed light field is composed of multiple uniformly impinging light fields which are adjacent to and contiguous with one another and appear to the point or area being observed as a single large solid angle light source of highly uniform character. Many machine imaging devices, such as web inspection machines, line-scanning image sensors, and photocopiers, for example, only image an extremely narrow, e.g. about 0.001 to 0.01 inches wide, elongate linear portion or narrow strip or zone of the object being imaged, that extends across the width of the object being imaged. In order to image the entire surface of the object being viewed, such devices scan the length or width of the object by moving the object being scanned relative to the camera and light source or vice versa allowing sequential scan lines to be built up into a complete two-dimensional image in the memory of the vision processor.

The invention relates to an elongate inspection system for uniformly illuminating a desired area of an object when the object is located at an inspection zone of an object observing location, said illumination system comprising: an inspection device for inspecting an object when located at the object observing location, and an inspection plane being defined between said inspection device and an inspection line within the inspection zone; a primary illumination segment for providing off-axis illumination of said object to be inspected, said off-axis primary illumination segment including a member for concentrating said primary illumination segment at said inspection zone; a secondary illumination segment being supplied to said inspection zone along said inspection plane; and said primary illumination segment and said secondary illumination segment, during use, supply a substantially continuous uniform illumination field to facilitate inspection of a desired area of the object to be inspected when the object is located at the inspection zone.

The invention also relates to a method of using an elongate inspection system to uniformly illuminate a desired inspection zone of an object to be inspected, when the object is located at an object observing location, said method comprising the steps of: defining an inspection plane between an inspection device, for inspecting the object when located at the object observing location, and the object to be inspected; supplying a primary illumination segment for supplying off-axis illumination of said object to be inspected; concentrating said off-axis primary illumination segment at said desired inspection zone to achieve a sufficiently intensity of illumination; supplying a secondary illumination segment along said inspection plane; and, during use of said elongate inspection system, adjusting the intensity of the primary illumination segment and the secondary illumination segment to form a substantially continuous uniform illumination field to facilitate inspection of a desired zone of said object to be inspected when said object is located on the inspection plane.

The term "off-axis", as used in following description and in the appended claims, means a light source or illumination segment which is supplied other than along or coincident with the inspection axis or plane of the system. Each "off-axis" illumination source or segment typically has a wedge-shaped cross section, with an apex at inspection line 29, which has solid angle of illumination of about 60°, more preferably a solid angle of illumination of about 70°, and most preferably a solid angle of illumination of about 90° .

The terms "concentrate" and/or "concentrated", as used in following description and in the appended claims and when referring to an illumination segment, mean that the light from the illumination segment is sufficiently directed, confined, altered or focussed, in some manner, at and toward a desired elongate area or inspection zone so that substantially all of the light from the illumination segment illuminates only the inspection zone and is not spread or illuminates the surrounding environment .

The term "high intensity", as used in following description and in the appended claims, means a light source having an intensity which is sufficiently bright such that it cannot be directly viewed by the human eye without causing the individual to blink or turn away. That is, an intensity of about 100 to about 1,000 times that of conventional illumination devices, e.g. an intensity of at least 5,000 watts/cm²/steradian. In particular, when using a line scan camera to image the object, a greater intensity of illumination is required for sufficiently illuminating the object than that required for a conventional CCD camera.

The term "inspection", as used in following description and in the appended claims, means viewing an objected to perceive accurately a surface finish, orientation, or assembly of the object or any letters, numbers, words, addresses or any other indicia, marking (s) , inconsistency, imperfection (s) , or other feature(s), characteristic (s) , or attribute(s) which is part of or contained on the surface of the object to be imaged. The term "uniform illumination", as used in the following description and appended claims, means that the illumination segments have a uniformity of about ± 25%, more preferably a uniformity of about ± 15%, and most preferably a uniformity of about ± 5 - 10% . To improve the lighting efficiency, it is desirable that one or both of the primary and secondary illumination segments be focussed at or along the inspection zone 27 or an inspection line 29 of the system. If the illumination segments are focussed, this allows the use of conventional lighting fixtures, e.g. 150 watt light bulbs, and minimizes the associated cooling requirements and other associated peripheral equipment which is necessary to cool a much higher powered lighting system which is required when utilizing inefficient diffused primary and secondary illumination segments.

As will be appreciated from the following description, the system permitting the practice of the invention is relatively simple and inexpensive as compared with prior art devices incapable of providing a true continuous solid angle illumination of the desired surface as provided by the invention.

An important aspect of the present invention is to define an inspection plane P between the inspection device and an inspection line 29 extending centrally along the inspection zone 27 of the inspection system. The inspection device is able to view, inspect, perceive and/or determine any indicia, markings or other attributes or characteristics of a surface to be imaged when located at the inspection zone 27. In addition, a first source of off-axis light is supplied from a first side of the inspection plane P and focussed or concentrated from that side at the elongate inspection zone 27. A second source of off-axis light is supplied from the opposite side of the inspection plane P and also focussed or concentrated along the entire inspection zone 27. Finally, a secondary source of illumination is provided along the inspection plane P, and is preferably focussed to increase the lighting efficiency, to illuminate the elongate inspection zone 27. The three light segments combine to provide a sufficiently bright illumination of a surface, when located at or along the inspection zone, to facilitate accurate viewing of any indicia, markings or other features, characteristics, or attributes contained on the surface to be imaged, when viewed by a line scan camera.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned objects and advantages of the invention will be appreciated from the following description and accompanying drawings wherein:

Fig. 1 is a schematic, perspective view of a first embodiment of the linear continuous diffuse illuminator according to the present invention; Fig. 2 is a diagrammatic sectional view of the linear continuous diffuse illuminator of Fig. 1;

Fig. 3 is a diagrammatic sectional view of a second embodiment of the linear continuous diffuse illuminator that has been modified to require only two elongate lamps; Fig. 4 is a sectional view of a third embodiment of the linear continuous diffuse illuminator that has a curved secondary light focussing element;

Fig. 5 is a diagrammatic representation showing a fourth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 6 is a diagrammatic representation showing a fifth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 7 is a diagrammatic representation showing a sixth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 8 is a diagrammatic representation showing a seventh embodiment of the linear continuous diffuse illuminator of the present invention; Fig. 9 is a diagrammatic representation showing the illumination bundles traveling through a transparent or opaque slip plate which also serves as a focussing element, according to the present invention; Fig. 10 is a diagrammatic representation of an eighth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 11 is a diagrammatic representation of a ninth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 12 is a diagrammatic representation of a tenth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 13 is a diagrammatic representation of an eleventh embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 14 is a diagrammatic representation showing a twelfth embodiment of the linear continuous diffuse illuminator of the present invention; Fig. 15 is a diagrammatic representation showing a thirteenth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 16 is a diagrammatic representation showing the illumination bundles traveling through a focussing mechanism, according to the present invention;

Fig. 17 is a diagrammatic representation showing a fourteenth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 18 is a diagrammatic representation showing a fifteenth embodiment of the linear continuous diffuse illuminator of the present invention;

Fig. 19 is a diagrammatic representation showing a sixteenth embodiment of the linear continuous diffuse illuminator of the present invention; and Fig. 20 is a diagrammatic representation showing the vision system, according to the present invention, used in combination with a sorting device.

DESCRIPTION OF THE INVENTION

A first embodiment of the inventive concept of the present invention is shown in Fig. 1. In that Figure, an elongate primary illuminator 10 comprises a pair of elongate primary light sources 21 and a pair of elongate primary diffusers 23 each disposed at an acute angle relative to the surface of the object O being imaged, as seen in Fig. 2, to provide primary diffuse off-axis illumination of a linear portion or zone 27 of the surface of the object O being imaged. The elongate primary illuminator 10 has an inspection window 25 formed therein that is elongate to provide vision access along an inspection plane P of the linear portion or zone 27 of the object 0 being imaged by the camera 12.

The elongate light projector 14 also comprises a secondary elongate light source 34, an elongate translucent secondary diffuser 32, an elongate beam splitter 26, and an elongate light absorption panel 38. An elongate linear light projector 14 effectively "fills" the elongate "hole" in the linear primary diffuse light source created by the inspection window 25 with the secondary diffused light supplied along the inspection plane P. The illumination characteristics of the light sources can be adjusted, via rheostats 40, such that the secondary diffuse light source is substantially equal in intensity and character to that provided by the primary diffuse light source. By this arrangement, the inspection window is filled with diffused light and masked by the light projector. The light sources 21, 34 may consist of an elongate array of lamps, diodes, LEDs or optical fibers, or a single elongate florescent, incandescent, or electroluminescent lamp capable of generating relatively uniform light which is cast upon the secondary diffuser 32. The intensity of each of the light sources 21, 34 can be controlled using separate rheostats 40 or other suitable control devices. By adjusting the intensity of the light sources 21, 34 until the intensity of the light projected by the light projector through the inspection window is substantially the same as the intensity and character of the diffused primary light source, the inspection window is completely masked. Lastly, when the illumination sources employ laser diodes or light emitting diodes, the relative integrated intensity of the sources, such as 21 and 34 of Fig. 2, may be adjusted by pulsing the sources with differing "on" times.

The elongate illuminator of Figs. 1 and 2 is preferably of a length sufficient to span and illuminate the entire width of the area of the surface of the object O to be imaged, i.e. an elongate strip extending entirely across the object O to be viewed, for inspection by the camera 12. In order to image the entire desired surface of the object 0 being imaged, i.e. the length and the width, the object is moved relative to the elongate illuminator, as indicated by arrow S, such that the illuminator scans the entire desired length of the object 0. The linear continuous diffuse illuminator is designed for use with linear scanners, such as line scan cameras and photocopiers, and provides a continuous diffuse illumination environment for a linear area to be imaged. With the basic geometry of the continuous diffuse illuminator disclosed above, the illumination field of a scanner or a copier can be made continuous and uniform, allowing accurate reproduction of documents and art work with unseen and/or specular surface finishes as well as those with diffuse surfaces. With such uniform diffuse lighting, smooth and uneven specular surfaces appear uniformly bright. Uneven textured photographic surfaces are made to appear glint-free. The linear continuous diffuse illuminator allows linear scanning devices of all kinds to faithfully reproduce subject matter with both specular and diffuse surface textures by nullifying the effects of uneven surface geometry of specular surfaces.

A second embodiment of an elongate illuminator is schematically illustrated in Fig. 3 in diagrammatic cross section. In this embodiment, one of the primary light sources 21 of the previous embodiment has been combined with the light projector light source 34 to form a single light source 36, thereby reducing the number of light sources from three to two. The number of diffusers is likewise reduced from three to two by combining one of the primary light diffusers 23 with the light projector secondary diffuser 32 to form a single combined diffuser 41. The combined diffuser 41 has two sections, a primary diffuser section 23 and a secondary diffuser section 32. A portion of the light emitted from the combined light source 36 is diffused by the primary diffuser section 23 and provides direct, primary illumination of a desired area or zone of the object being imaged. Second portion of the light emitted from the combined light source 36 is diffused by the secondary section 32 and is reflected by the beam splitter 26 to illuminate, along the inspection plane P, an elongate portion of the object being imaged. Reducing the number of light sources and diffusers lowers the power requirement and manufacturing costs of the elongate illuminator and also assists with providing a more compact unit.

The secondary diffuser section 32 is thinner than the primary diffuser section 23. The relative thinness of the secondary diffuser section 32, in comparison to the primary diffuser section 23, is selected so as to compensate for the partial reflectivity of the beam splitter 26 and the greater optical distance of the diffuser 32 to the object surface O as compared to the optical distance of diffuser 41 to the object surface O and thereby light reflected by the beam splitter through the inspection window of substantially the same intensity as that illuminating the object via the primary diffuser section 23 of the combined diffuser 41. Alternatively, the intensity of the light may be balanced by forming the primary diffuser section 23 more opaque than the secondary diffuser section 32. Lastly, adjustment of the rheostats 40 or pulsing of the light sources can also facilitate such balancing as well.

In this embodiment, the illumination device may communicate, via the wiring or cabling, with a computer 44, containing a central processing unit, a RAM, a ROM and a memory, which can control, if desired, operation of the illumination device, e.g. automatically control the rheostats 40, to control the focus of a lens incorporated in the camera. The camera 12, used in combination with the illumination device, generates and supplies an input of the sensed image to the computer 44, via suitable wiring or cabling. The computer 44 is also connected, via suitable wiring or cabling, to a scanning or conveying apparatus or means 46 which conveys the object 0 to be imaged relative to the illumination device and the camera 12, as can be seen Fig. 3. It is to be appreciated that, if desired, the illumination device and the camera 12 can be moved relative to the object by the scanning or conveying apparatus or means 46. The computer 44 then transmits, via suitable wiring or cabling, the sensed image to a reproducing device 48, such as a printer, a thermal inspection device or the like where a reproduction of the inspected or sensed image is outputted as a reproduction 49. Alternatively, the sensed image may be sent to some other device where the sensed image is further processed in some manner, e.g. the sensed image is compared to a test image of the object or otherwise read or decoded. Finally, the sensed image can be utilized for handling or sorting of the inspected object, e.g. sorting mail depending upon the indicia carried by the letter or package.

A third embodiment of an elongate illuminator is schematically illustrated in cross section in Fig. 4. In this embodiment, the planar elongate translucent diffuser 32 is replaced by a curved elongate reflective diffuser 32 having an elongate concave face disposed toward both the elongate secondary light source 34 and the elongate beam splitter 26. The light emitting by the secondary elongate light source 34 is received and reflected by the curved reflector 32, have partial diffused characteristic, e.g. a Venetian blind surface, toward the beam splitter 26. The beam splitter 26, in turn, reflects the partially diffused light along the inspection plane P for filling the elongate inspection window with secondary diffused light. This configuration provides an increased range of incident angles for the diffused light provided along the inspection plane P while, at the same time, reduces the required height of the illumination device above the object O being inspected. In this embodiment, panel 42 and the two diffusers 32, 23 are arranged such that light emitting from the secondary elongate light source 34 is prevented from directly illuminating the desired portion or zone 27 of the object 0 being imaged. Thus no direct non-diffuse illumination of the object can occur and only uniform diffuse illumination of the desired portion or zone 27 of the object O to be imaged is ensured.

When the elongated illumination device is incorporated into a scanner or a photocopier machine, the illumination device is fixedly secured to a camera 12 and forms an integrated unit 50. The camera 12 provides an input to a computer 44, via suitable wiring or cabling. The computer 44 is also connected, via suitable wiring or cabling, to a scanning or conveying apparatus or means 46 which conveys the integrated unit 50 relative to the object O to be imaged, i.e. the object 0 remains stationary, as shown in Fig. 4. Alternatively, the object O can be moved relative to integrated unit 50 by the scanning or conveying apparatus or means 46. The computer 44 then transmits, via suitable wiring or cabling, the sensed image to a reproducing device 48, such as a printer, a thermal inspection device or the like where a reproduction of the observed image is outputted as a reproduction 49. Alternatively, the sensed image may be sent to some other device where the sensed image is further processed in some fashion, e.g. the sensed image is compared to a test image of the object or determined and then used to sort the product. It is to be appreciated that the relative movement between the illumination device and the object to be imaged can be achieved in the variety of different ways. Further the combination of the elongated diffuse illumination device, the computer, the camera and the conveying apparatus may be incorporated into a combined system 51 for one of inspection and reproduction of the object to be imaged.

With reference to Fig. 5, a fourth variation of the continuous illumination system, according to the present invention, is shown. The following embodiments, of the continuous diffuse illuminator, are similar to the previous embodiments except that the primary difference is that the supplied light is either concentrated or focussed, in some manner, along the elongate inspection zone 27 to increase the intensity of the illumination, e.g. to increase the intensity by about 100 to about 1,000 times over conventional illumination devices, and facilitate a more accurate inspection or viewing of the object to be imaged in certain desired applications.

As can be seen in this Figure, the linear continuous diffuse illuminator comprises a left off-axis illumination assembly 52 and a right off-axis illumination assembly 52. As both off-axis illumination assemblies 52 are identical to one another but are merely mirror images of one another, a detailed description concerning only one of the off-axis illumination assemblies is provided. The right off-axis illumination assembly 52 comprises an elongate light source 54, such as a high intensity linear fiberoptic light source, having an elongate outlet 55 supplying a light segment to a rear surface of an elongate diffuser elongate 56 . The opposed front surface of the elongate diffuser 56 transmits the supplied light to an elongate focussing mechanism or member 58, such as an acrylic dowel having a diameter of between 0.5 to 6 inches. The received light, from the elongate diffuser 56, passes through the elongate focussing member 58 and is concentrated or focussed at and along an elongate inspection zone 27 of a surface to be inspected, which is coincident with the inspection plane P of the inspection system.

In addition, a central secondary illumination assembly 60 comprises a light source 62 which supplies a light segment, via an elongate outlet 61, to an exterior concave surface 65 of a cylindrical reflective diffuser or mirror 66. The cylindrical reflective diffuser or mirror 66, in turn, reflects the supplied light toward an inwardly facing convex surface 67 of a cylindrical beam splitter 68. The cylindrical beam splitter 68 typical reflects a desired amount of the supplied light, e.g. between 20% to about 80% and preferably about 50% of the supplied light, along the inspection plane P and focusses the reflected light at and along the elongate inspection zone 27 which is coincident with the desired area of the object O to be inspected. The cylindrical beam splitter 68 also allows the camera to view the object O to be inspected along the inspection plane P, i.e. the cylindrical beam splitter 68 allows a desired amount of reflected light, typically between 20% to about 80% and preferably about 50%, to pass therethrough along the inspection plane P to be viewed by the camera 12.

As can be seen in Fig. 5, the pair of elongate off- axis illumination assemblies 52, 52 supply light segments from the right and from the left of the inspection plane P while the central illumination assembly 60 supplies a light segment along the inspection plane P to facilitate illumination of the entire elongate inspection zone 27.

Each one of the light sources 54, 62 of the inspection system is connected to a rheostat 68, or some other adjustable component, to facilitate balancing of the intensity and/or the character of the supplied light from each of the right, the left and the central illumination assemblies 52, 52, 60 along the inspection plane P to create the required uniform illumination field so that accurate vision, observation and/or inspection of the desired area of the object O to be imaged is achieved.

Turning now to Fig. 6, a fifth embodiment of the present invention will now be described. In this embodiment, the linear continuous diffused illuminator consists only of focussing and reflecting optical elements. As can be seen in this Figure, there is a left and a right off-axis illumination assembly, both being designated with the numeral 52. As both off-axis illumination assemblies 52 are identical to one another but are merely mirror images of one another, a detail description concerning only one of the off-axis illumination assemblies 52 is provided. The right off- axis illumination assembly 52 comprises an elongate light source 54 having an elongate outlet 55 supplying a light segment to a rear surface of an elongate diffuser 64, such as a holographic diffuser. The opposite front surface of the elongate diffuser 64 transmits the supplied light to a pair of elongate parallel, opposed cylindrical lens 72, 74. The light strikes and enters an outwardly facing surface of the first opposed cylinder lens 72 which, in turn, transmits the light to the second opposed cylinder lens 74. The outer surface of the second opposed cylinder lens 74 projects and focusses an image of the supplied linear light source at and along the elongate inspection line or zone 27.

A central secondary illumination source 60 comprises an illumination source 62 which supplies a light segment, via an elongate outlet 61, to a rear surface of a holographic diffuser 64. The front surface of the holographic diffuser 64 illuminates a pair of opposed plano-convex cylinder lens 76, 78. The light passes through the pair of opposed plano-convex cylinder lens 76, 78 and is focussed toward a mirror 80. The supplied light is reflected by the mirror 80 toward a beam splitter 82. The beam splitter 82 is located along the inspection plane P, at an oblique angle thereto, e.g. a 45° angle, to reflect a portion of the supplied light along the inspection plane P toward the inspection zone 27. The beam splitter 82 reflects a desired amount of light, e.g. between about 20% to about 80% and preferably about 50%, which is supplied by the mirror 80. The beam splitter 82 also allows the inspection device 12 to view the object O to be inspected along the inspection plane P through the beam splitter 82. The holographic diffusers 64, located immediately adjacent to but in front of the outlet of each linear light source 54, 54, 62, expand and homogenize the projected light field for greater uniformity and coverage at the focal point along the inspection zone 27.

A sixth embodiment of the present invention will now be described with reference to Fig. 7. As can be seen in this Figure, there is a left and a right off-axis illumination assembly, both being designated with the numeral 52. As both off-axis illumination assemblies 52 are identical to one another but are merely mirror images of one another, a detail description concerning only one of the off-axis illumination assemblies 52 is provided. The right off-axis illumination assembly 52 comprises an elongate light source 54 having an elongate outlet 55 supplying a light segment toward a rear surface of a first of a solid glass or plastic lens, a holographic lens, a fresnel lens or a positive cylinder lens 84. The light strikes and enters the rear surface of the first positive cylinder lens 84, passes therethrough, and an image of the linear light source is focussed, by the front surface of the first positive cylinder lens 84, at and along the elongate inspection zone 27.

A central secondary illumination source 60 comprises an illumination source 62 which supplies a light segment, via an elongate outlet 61, to a rear surface of a second of a solid glass or plastic lens, a holographic lens, a fresnel lens or a positive cylinder lens 86. The light strikes and enters the rear surface of the second positive cylinder lens 86, passes therethrough, and an image of the linear light source is supplied to a flat mirror 88. The supplied light is reflected by the mirror 88 toward a flat beam splitter 90. The beam splitter 90 is located along the inspection plane P, at an oblique angle thereto, e.g. a 45° angle, to reflect a portion of the supplied light along the inspection axis toward the inspection zone 27. The beam splitter 90 reflects a desired amount of light, e.g. between about 20% to about 80% and preferably about 50%, which is supplied by the mirror 88. The light reflected from the beam splitter 90 is supplied along the inspection plane P and illuminates the elongate inspection zone 27 or is focussed along an elongate inspection line 29. The beam splitter 90 also allows the inspection device 12 to view the object O to be inspected along the inspection plane P. With reference to Fig. 8, a seventh embodiment of the linear continuous illumination system, according to the present invention, can be seen. As can be seen in Fig. 8, a linear array camera 12 observes an inspection zone 27 of a moving object O along the inspection plane P. A single linear light source 92 emits a high intensity illumination field 94 from a linear outlet or aperture 96. The emitted illumination field is collimated by a positive cylinder lens 98 into a collimated light illumination field 100. The collimated illumination field 100 is directed at a flat first beam splitter 102 which reflects about 75% of the illumination field toward a mirror 108 while the remaining approximately 25% of the collimated illumination field pass through the first beam splitter 102 as collimated light bundle 103 which continues toward a first focussing lens assembly 106. The first focussing lens assembly 106 focusses the light bundle 103, in the form of focussed light bundle 101 passing through slip plate 118 (see Fig. 9) , onto and along the inspection zone 27 where the inspection plane P intersects with the desired area of the object O being imaged.

The reflected illumination bundle 105 is reflected by the mirror 108 toward a flat second beam splitter 110. The second beam splitter 110 reflects about 67% of the illumination bundle 105, as illumination bundle 111, toward a curved beam splitter 112. The remaining light, about 33% of illumination bundle 105 passes through the second beam splitter 110, as light bundle 107, and continues toward another focussing lens assembly 106 which is identical to focussing lens assembly 106, but is a reversed right-to-left focussing lens assembly. The focussing lens assembly 106 focusses the light bundle 107, in the form of focussed light bundle 115 passing through slip plate 118, at and along the inspection zone 27 of the camera 12 where the inspection plane P intersects the desired area of the object 0 being imaged.

The focussing lens assemblies 106 comprise a lens which assists with focussing of the light bundles 103, 107 at the inspection zone 127. A variety of different lens can be utilized to assist with focussing the supplied light bundles 103, 107 at and along the inspection zone 127 or an inspection line. As such teaching is well known in the art, further detailed discussion concerning the same is not provided. The reflected illumination bundle 111, directed toward the curved beam splitter 112, is reflected by the curved beam splitter 112, as reflected light bundle 116, which comes into focus at and along the inspection zone 27 or an inspection line. The three focussed illumination bundles 101, 115, and 116 (Fig. 9), are adjacent, uniform, and contiguous with one another and together constitute a single uniform wide-angle illumination field converging at and along inspection zone 27. If desired, a glass slip plate 118 can space the light sources from the object O being imaged. The curved beam splitter 112 also allows the camera 12 to view the object O to be inspected along the inspection plane P and through the curved beam splitter 112. As can be seen in Fig. 8, a pressure roller 119 is provided for engaging an undersurface of the object O to be imaged, e.g. a mail envelope. The pressure roller 119 is driven by a drive mechanism, not shown in detail, which conveys the object O relative to the inspection system so that the desired indicia, e.g. an address, on the object O can be viewed and determined to facilitate sorting of the mail, for example. As such pressure roller conveying feature is well known to those skilled in this art, a further detailed description concerning the same is not provided herein.

A detailed cross-sectional view showing the illumination characteristics, as the light bundles passing through the slip plate 118, can be seen in Fig. 9. As can be seen in this Figure, the left off-axis illumination bundle 101 passes through the slip plate 118 and is directed at the inspection zone 27 at an angle which is substantially equal and opposite to the supplied angle of the right illumination bundle 115. In addition, the central secondary illumination bundle 116 is supplied along the inspection axis and focussed at the inspection zone 27 or along an inspection line. All three illumination bundles 101, 115, 116 form a uniform contiguous illumination light source which provides substantially uniform illumination of the desired area of the object O to be imaged.

It is to be appreciated that the slip plate 118 can have a variety of different configurations. The principle feature of the slip plate 118 is that a contiguous central groove 120 with an optically clear surface, at which the illumination can converge at and along the elongate area being imaged, is achieved. The purpose of the groove 120 is to prevent abrasions to the bottom surface of the slip plate by the moving object O at the point where the inspection plane P passes therethrough and an image of the object is acquired. Depending upon the mechanical properties of the inspection process involved, the slip plate groove 120 may take a number of different cross-sectional profile geometries. For example, the slip plate groove may be provided with a curved surface, combined convexed and/or concave curved surfaces or flat sloping edges. Because the slip plate 118 may be made out of glass, some other transparent material, or a metal plate having an elongate opening therein, it may exhibit optical refracting properties and its design will be governed by the final geometry of the other elements of the focussing lens assemblies 106. The important aspect of the slip plate 118 is that it maintains a constant distance between the surface being observed and the camera 12.

Fig. 10 show an eighth embodiment of the present invention. In this embodiment, a linear array camera 12 observes an inspection zone 27 of a moving object O along an inspection plane P. A single linear light source 92 emits a high intensity illumination field 94 from a linear outlet or aperture 96. The emitted illumination field is collimated by a positive cylinder first lens 98 into a collimated light illumination field 100. The collimated illumination field 100 is directed at a flat first beam splitter 102 which reflects about 75% of the illumination field toward a first mirror 108, as illumination bundle 105, while the remaining approximately 25% of the collimated illumination field 100 passes through the first beam splitter 102, as collimated light bundle 103, which continues toward a first focussing lens assembly 106. The first focussing lens assembly 106 focusses the light bundle 103, in the form of focussed light bundle 101, onto and along the inspection zone 27 or an inspection line where the inspection plane P intersects the desired area of the object O being imaged.

A second beam splitter 109, located between the first beam splitter 102 and the first mirror 108, reflects about 33% of the illumination bundle 105, as illumination bundle 107, toward a second focussing lens assembly 106 which is identical to focussing lens assembly 106, but is a reversed right-to-left focussing lens assembly. The second focussing lens assembly 106 focusses the light bundle 107, in the form of focussed light bundle 115, onto and along the inspection zone 27 of the camera 12 where the optical plane P intersects the desired area of the object O being imaged. The unreflected light passes through the second beam splitter 109 and is reflected by first mirror 108 toward a second mirror 122. The second mirror 122 reflects the supplied light to a rear surface of a second lens 124 and the supplied light passes through the second lens 124 and is directed toward a flat third beam splitter 126. The flat third beam splitter 126 is located along the inspection plane P, at an oblique angle thereto, e.g. a 45° angle. The flat third beam splitter 126 reflects a desired amount of the supplied light, e.g. between 20% to about 80% and preferably about 50% of the supplied light, along the inspection plane P and focusses the reflected light, as reflected light bundle 116, along the elongate inspection zone 27 of the desired area of the object O to be inspected. A light trap 180 is provided to absorb any light that passes through the third beam splitter 126. The three illumination bundles 101, 115, and 116, are adjacent, uniform, and contiguous with one another and together constitute a single uniform wide-angle illumination field converging at and along inspection zone 27. If desired, a tempered glass slip plate 118 can separate the light sources from the object O being imaged.

With reference to Fig. 11, a ninth embodiment of the present invention is shown. In this embodiment, a linear array camera 12 observes an inspection zone 27 or an inspection line of a moving object O along an inspection plane P. A pair of linear light sources 92, 128 emit a high intensity illumination field 94, 130 from linear outlets or apertures 96, 132. The first emitted illumination field 94 is collimated by a first pair of opposed positive cylinder lenses 98 into a collimated light illumination field 100. The collimated illumination field 100 passes through a flat first beam splitter 102 which reflects about 50% of the illumination field toward a first mirror 108 while the remaining approximately 50% of the collimated illumination field passes through the beam splitter 102, as collimated light bundle 103, which continues toward a first focussing lens assembly 106. The first focussing lens assembly 106 focusses the light bundle 103, in the form of focussed light bundle 101, onto and along the inspection zone 27 or inspection line where the inspection plane P intersects the desired area of the object O being imaged.

The first mirror 108 reflects 100% of the illumination bundle 105, as light bundle 107, toward a second focussing lens assembly 106, which is identical to the first focussing lens assembly 106 but is a reversed right-to-left focussing lens assembly. The focussing lens assembly 106 focusses the light bundle 105, as focussed illumination bundle 115, onto and along the inspection zone 27 or inspection line of the camera 12 where the optical plane P intersects the desired area of the object O being inspected.

The second light source 128 supplies light toward second mirror 134 where the supplied light is reflected, via the second mirror 134, toward a rear surface of a second pair of opposed lenses 136, 138. The supplied light passes through the second pair of lenses 136, 138 and is directed, as illumination bundle 111, toward a flat second beam splitter 126. The flat second beam splitter 126 is located along the inspection plane P, at an oblique angle thereto, e.g. a 45° angle. The flat beam splitter 126 reflects a desired amount of the supplied light, e.g. between 20% to about 80% and preferably about 50% of the supplied light, along the inspection plane P and focusses the reflected light, as reflected light bundle 116, at and along the elongate inspection zone 27 or inspection line of the desired area of the object O to be inspected. The second beam splitter 126 also allows the inspection device to view the object 0 to be inspected along the inspection plane P through the second beam splitter 126.

The three illumination bundles 101, 115, and 116, are adjacent, uniform, and contiguous with one another and together constitute a single uniform wide-angle illumination field converging at and along the inspection zone 27. If desired, a metal or glass slip plate 118 can separate the illumination assembly from the object O being imaged. Turning now to Fig. 12, a tenth embodiment of the present invention can be seen. In this embodiment, a plurality of light sources 140 direct light at a rear surface of a plurality of lenses 142. The plurality of lenses 142 each focus an illumination bundle 144 at and along the inspection zone 27, or an elongate inspection line. As can be seen in this Figure, three light sources 140 are provided to illuminate the inspection zone 27, or an elongate inspection line, from the left of the inspection plane P while three similar light sources 140 are arranged to provide light to the inspection zone 27, or an elongate inspection line, from the right of the inspection plane P.

In addition, a central secondary illumination source 146 provides light to a rear surface of another focussing lens 148. The light passes through the focussing lens 148, as illumination bundle 152, and is directed toward a flat beam splitter 150. The flat beam splitter 150 is located along the inspection plane P, at an oblique angle thereto, e.g. a 45° angle. The flat beam splitter 150 reflects a desired amount of the supplied light, e.g. between 20% and about 80% and preferably about 50% of the supplied light, and allows a desired amount of illumination bundle 152 to pass therethrough, as illumination bundle 116 focussed at and along the elongate inspection zone 27, or an elongate inspection line, of the object O to be inspected. The camera 12 is located off-set and views the object O to be inspected along the observation plane P altered by a mirror 154 and a flat beam splitter 150, i.e. the inspection plane P extends from the camera 12 to the mirror 154, the flat beam splitter 150, and finally to the object O to be inspected. Turning now to Fig. 13, an eleventh embodiment of the present invention will now be discussed. As can be seen in this embodiment, an optical plane P is defined between the camera 12 and an inspection zone 27 of the desired area of the object O to be imaged, e.g., the indicia or markings contained on a postal envelope. As can be seen in this Figure, the linear high intensity continuous diffuse illuminator comprises a left off-axis illumination 160 and a right off-axis illumination assembly 160. As both off-axis illumination assemblies are identical to one another and are merely mirror images of one another, a detailed description concerning only one of the off-axis illumination assemblies 160 is now provided. As can be seen in Fig. 13, the illumination assembly 160 comprises a high intensity fiber optic light source 162 having an elongate opening 164. The opening supplies a light segment to a first end surface 166 of an elongate light guide 168. The light guide 168 supplies the light along the length of the light guide, toward a second opposed end surface 170. The light guide 168 may be, for example, a 1/8 inch thick piece of clear Lucite^®. The second opposed end surface 170 of the light guide 168 is provided with an end diffuser 172 for diffusing the transmitted light. The light guide exit end surface 170 will be evenly illuminated since the exit end surface 170 appears to be illuminated by an array of elongate sources, one for each internal reflection of light rays inside the light guide, as clearly explained in pages 263-265 of Modern Optical Engineering , second edition, by Warren J. Smith .

The second end surface 170 of both light guides 168 can be supported by a steel shoe 174 having an aperture 176 extending therethrough. The aperture 176 of the steel shoe 174 is aligned along and coincident with the inspection plane P of the system. A camera 12 is also aligned along the inspection plane P and a beam splitter 178 is located along and normal to the inspection plane P, e.g. a 90° angle. The beam splitter 178 allows a desired amount of light to pass therethrough for viewing by the camera 12, e.g. between about 20% to about 80% and preferably about 50%, while reflecting the remaining portion of the light back along or toward the inspection plane P.

The light supplied from the light sources 162 enters the first end surfaces 166 of the light guides 168. The light travels along the light guides 168 and exits the second opposed end surfaces 170 of the light guides 168. The supplied light passes through the diffusers 172 and some of the light passes through the aperture 176 in the steel shoe 174 while a remaining portion of the light reflects off the opposite end surface of the diffuser and/or the beam splitter and is then reflected through the aperture 176. In addition, some of the light is reflected off the beam splitter 178 back through the aperture 176 in the steel shoe. The pair of spaced apart diffusers 172 and the beam splitter 178 and the surface being inspected together from an elongate illumination integration chamber for illuminating the desired area or zone 27 of the object O to be observed or, e.g. an address area of an envelope. When the indicia, e.g. address area, of an envelope passes through the system and is located along the inspection plane P, it is sufficiently illuminated by the light sources 162 so that the camera 12 can view the indicia and determine the indicia for further handling of the object to be imaged, e.g. sorting of the mail. With reference to Fig. 14, a slight variation of the embodiment of Fig. 13 is shown. As can be seen in this Figure, a third fiber optic light source 162 is provided. It supplies a light segment, via an elongate opening 164 of the light source 162, to a first end surface 166 of a light guide 169. The light travels along the light guide 169 and exits from the second opposed end surface 171 of the light guide 169. From there, the supplied light passes through a diffuser 173 and is reflected by the beam splitter 178 along the inspection plane P. In this embodiment, the beam splitter 178 is arranged at an oblique angle with respect to the inspection plane P, e.g. a 45° angle, instead of being normal to the inspection plane P as with the previous embodiment. The beam splitter 178 reflects a desired amount of the supplied light, e.g. between about 20% to about 80% and preferably about 50%, along the inspection plane P while a remainder of the light passes through the beam splitter 178 and is absorbed by a light trap 180. The flat beam splitter 178 also allows the camera 12 to view the object O to be inspected along the inspection plane P through the beam splitter 178.

With reference to Fig. 15, a further variation of the embodiment of Fig. 13 is shown. As can be seen in this Figure, a single movable fiber optic light source 162 is utilized. This single light source 162 supplies a light segment, via an elongate opening 164 of the light source 162, to first end surfaces 166 of three adjacent, stacked light guides 168. The light travels along each of the light guides 168 and exits from the second opposed end surfaces 170 thereof. The second end surfaces 170 of the three light guides 168 are supported by a steel shoe 174 having an aperture 176 extending therethrough. The aperture 176 of the steel shoe 174 is aligned along the inspection plane P of the inspection system. The supplied light from the top and bottom light guides 168 passes through the diffusers 172 and is directed through the aperture 176 in the steel shoe 174 at the desired area of the object O to be observed. According to this embodiment the second ends of the light guides 168 are oriented toward the inspection zone 27 to provide greater illumination of the desired area of the object O to be inspected.

The supplied light from the intermediate light guide 168 exits from the second opposed surface 170 of the light guide 168 and passes through a diffuser 172. The diffused light is then reflected by the beam splitter 178 down along the inspection plane P. In this embodiment, the beam splitter 178 is arranged at an oblique angle with respect to the inspection plane P, e.g. a 45° angle. The beam splitter 178 reflects a desired amount of the supplied light, e.g. between about 20% to about 80% and preferably about 50%, along the inspection plane P while a remainder of the light passes through the beam splitter 178 and is absorbed a light trap 180. The beam splitter 178 also allows the camera 12 to view the object O to be inspected along the inspection plane P through the beam splitter.

Turning now to Fig. 16, another embodiment of the focussing assembly of the present invention will now be described. As can be seen in this Figure, both off-axis illumination assemblies 52 are identical to one another but are merely mirror images of one another. Accordingly, a detail description concerning only one of the off-axis illumination assemblies is provided. Light from the right off-axis illumination assembly 52 is supplied to an elongate focussing member mechanism 58A, such as a partial portion of a concave lens with a surface curvature specified in relation to the design of other optical elements to provide the required uniform illumination.

The supplied light passes through a front surface of a elongate convex lens focussing member 58A and exists from a rear surface thereof. The light is then supplied to a front surface of a Fresnel Lens 58B. The light passes through the Fresnel Lens 58B and exists from a rear surface thereof. The light exiting from the rear surface of the Fresnel Lens 58B and is directed, focussed or concentrated, through the inspection window provided in the slip plate 118, at and along the illumination zone 27 or along an elongate inspection line 29. Secondly, light from the central secondary illumination assembly is supplied along the inspection plane P and focussed at and along the elongate inspection zone 27, or an elongate inspection line 29, of the desired area of the object O to be inspected through the inspection window provided in the slip plate, if provided. The rheostats facilitate balancing of the intensity and/or character of the supplied light from each of the right, the left and the central illumination assemblies to create the required uniform illumination field so that accurate vision, observation and/or inspection of the desired area of the object to be imaged is achieved.

A pair of opposed rollers 190, 192, which are driven by a drive mechanism not shown in detail, are provided for conveying the object O to be inspected. A first of the conveying rollers 190 is a stationary roller which is fixedly supported with respect to the system, while the second roller 192 is spring biased, by a conventional spring mechanism 194, toward the fixed roller 190 to pinch the object O to be inspected, e.g. an envelope, and facilitate conveying of that object O relative to the inspection system. A second pair of similarly arranged rollers 190, 192 are located on the other side of the inspection system to further assist with conveying of the object O to be inspected. The two pairs of rollers 190, 192 are synchronized to rotate at the same speed, and such synchronization is well known in the art. Accordingly, a further detailed description concerning the same is not provided.

As indicated above, if the supplied light is focussed along the elongate inspection line 29, rather than being dispersed over the area surrounding the inspection line 29 the power requirements of the illumination system are significantly reduced. Nevertheless, it is still possible to obtain acceptable illumination results by utilizing lights with significantly higher power requirements, in combination with diffusers, and concentrating the supplied diffused light along the illumination zone or area 27 rather than along the elongate inspection line.

Turning now to Fig. 17, a fourteenth embodiment of the present invention will now be discussed. This Figure shows a high efficiency light guide solution in which the light guides' 168 output ends 170 are aimed to intersect at the illuminated area or zone 27. This illumination arrangement directs most of the light towards the target area or zone 27 and reduces the need for the end diffusers 172, shown in Figs. 13 and 14. In the region of each light guide's output end surface 170, the light guides upper surface 195, lower surface 197 and its optical axis 199 all extend parallel to one another and extend orthogonal to output end surface 170. The light guide end surfaces 170 are brought as close to the region or zone 27 as possible without blocking the camera's 12 line of sight along the inspection plane. A separate elongate central illumination source 162 supplies light, via an elongate opening 164 of the light source 162, to a rear surface of an associated lens 193 which focusses the light toward a beam splitter 178. The beam splitter 178 is arranged at an oblique angle with respect to the inspection plane P, e.g. a 45° angle. The beam splitter 178 reflects a desired amount of the supplied light, e.g. between about 20% to about 80% and preferably about 50%, along the inspection plane P while a remainder of the light passes through the beam splitter 178 and can be absorbed by a light trap, for example. The light supplied by the beam splitter 178 provides the target area or zone 27, or an inspection line, with equal illumination from the directions approximately along the camera's optical axis, which direction of illumination cannot be provided by the light guides 168 of Fig. 17.

Turning now to Fig. 18, a preferred embodiment of the present invention will now be discussed. As can be seen in this embodiment, an optical plane P is defined between the camera 12 and an inspection zone 27 of the desired area of the object O to be imaged, e.g. the indicia or markings contained on a postal envelope. The linear high intensity continuous diffuse illuminator comprises a left off-axis illumination assembly 200 and a right off-axis illumination assembly 200. As both off-axis illumination assemblies are identical to one another and are merely mirror images of one another, a detailed description concerning only one of the off-axis illumination assemblies 200 is now provided. As can be seen in Fig. 18, the illumination assembly 200 comprises a high intensity fiber optic light source 202 having an elongate opening 204. The opening 204 supplies a light segment to a first end surface 206 of an elongate light guide 208. The light guide 208 supplies the light along the length of the light guide 208, toward a second opposed end surface 210. The light guide 208 may be, for example, a 1/8 inch thick piece of clear Lucite^® plastic. The light guide 208 may be curved or bent when it is advantageous to do so; for instance, when it is desired to avoid a structural element or an optical path within the assembly. The light guide exit end surface 210 will be evenly illuminated since the exit end surface 210 appears to be illuminated by an array of elongate sources, one for each internal reflection of light rays inside the light guide, as briefly discussed above. In addition, the second end surfaces 210 can be made either diffusing or focussing. Alternatively, the second end surface 210, of this embodiment as well as the any of the other embodiments, e.g. Figs. 13-15, 17 and 18, can be altered, varied or have optically active materials applied thereto, e.g. a holographic diffuser material, to more efficiently and uniformly cast light upon the inspection line 29. The second end surface 210 of both light guides 208 can be supported by a slip plate 212 which has a central aperture 214 extending therethrough. The aperture 214 of the slip plate 212 is aligned along and coincident with the inspection plane P of the system.

The light supplied from the light sources 202 enters the first end surface 206 of the light guide 208. The light travels along the light guide 208 and exits the second opposed end surface 210 of the light guide 208. The supplied light is then directed downwardly through the aperture 214 of the slip plate 212 toward the object O to be observed. It is desirable to have the two opposed end surfaces 210 of the light guides 208 located as close as possible to the inspection zone 27, or the elongate inspection line 29, without affecting the line of sight of the camera 12.

A central secondary illumination assemblies 216 comprises a central illumination source 218 which supplies a light segment, via an elongate outlet 220, to a mirror 222 which reflects the supplied light at a first surface of a pair of opposed plano-convex cylinder lens 224, 226. The light passes through the pair of opposed plano-convex cylinder lens 224, 226, exits a rear surface of the second plano-convex cylinder lens 226, and is focussed toward the beam splitter 228. The beam splitter 228 is located along the inspection plane P, at an oblique angle thereto, e.g. at a 45° angle, to reflect a portion of the supplied light along the inspection plane P toward the inspection zone 27. The beam splitter 228 reflects a desired amount of light, e.g. between about 20% to about 80% and preferably about 50%, which is supplied by a mirror 222. The beam splitter 228 also allows the inspection device 12 to view the object O to be inspected along the inspection plane P through the beam splitter 228. The beam splitter 228 redirects the focussed light rays at the object O to be observed along the elongate inspection line 29 to improve the illumination efficiency of the inspection system. When the indicia of an envelope, or other object to be observed, passes through the system and is located along the inspection plane P, it is sufficiently illuminated by the three illumination sources 200, 200, 216 so that the camera 12 can view the indicia and determine the indicia for further manipulation or handling of the object to be imaged, e.g. sorting of the mail.

As with the embodiment of Fig. 8, a pressure roller 119 is provided for engaging an undersurface of the object 0 to be imaged, e.g. a mail envelope. The pressure roller 119 is driven by a drive mechanism, not shown in detail, which conveys the object O relative to the inspection system so that the desired indicia, e.g. an address, on the object O can be viewed and determined to facilitate sorting of the mail, for example. In Fig. 19, a second preferred embodiment of the present invention can be seen. According to this embodiment, the illumination source 230 comprises three separate but closely arranged light bulbs 232, e.g. 150 watt light bulbs, which are all directed to illuminate one or more end surfaces 234 of one or more elongate light guides 235, e.g. three of which are shown in this Figure. The opposed second end of each one of the three light guides 235 is connected to an inlet of a fiber optic randomizer 236. The fiber optic randomizer 236 which is designed to provide substantial uniform illumination at the outlet or outlets thereof. In the shown embodiment, there are seven outlets which are not specifically designated. Three left light guide strands 237 are connected to three of the outlets of the fiber optic randomizer 236. The supplied light, from the outlets of the fiber optic randomizer 236, flows along the left light guide strands 237 and exits at each elongate light guide outlet or end surface 238 of each light guide strand 237. Three right light guide strands 239 are connected to three additional outlets of the fiber optic randomizer 236. The supplied light, from the outlets of the fiber optic randomizer 236, flows along the right light guide strands 239 and exits via an elongate light guide outlet or end surface 240 of each light guide strand 239.

The elongate light guide outlets or end surfaces 238, of the three separate left light guide strands 237, provide off-axis illumination from the left (as can be seen in this Figure) . The elongate light guide outlets or end surfaces 240, of the three separate right light guide strands 239, provide off-axis illumination from the right (as can be seen in this Figure) .

A larger, central single light guide strand 241 is connected to the seventh outlet of the fiber optic randomizer 236. The supplied light, from the outlet of the fiber optic randomizer 236, flows along the central light guide strand 241 and exits via an elongate light guide outlet or end surface 242 thereof which provides on-axis illumination to the inspection system. As the supplied light passes along the light guides 235 or light guide strands 237, 239 or 241, it bounces and/or is reflected numerous times off the inner wall of the light guides 235 or light guide strands 237, 239 or 241.

The three left light guide strands 237 and the three right light guide strands 239 all have the same transverse cross-sectional areas so that all six of those light guide strands will each individually supply substantially equal illumination from their respective end surfaces 238 and 240. The central light guide strand 241, however, has a transverse cross-sectional area which is about two and one-half times the cross-sectional area of the left and right light guide strands 237 and 239. The reason for this increase in cross-sectional area is that the central light guide strand 241 must supply excess light because approximately 60% of the supplied light from the central light guide strand 241 is loss due to the inefficient optics of the inspection system, e.g. some light passes through the beam splitter and is not reflected at the object while some of the light reflected by the object is reflected by the beam splitter away from the camera 12 and thus does not pass therethrough. Also some light is absorbed by the beam splitter. The wider cross sectional area of the central light guide strand 241 helps to supply excess light which compensates for these optical inefficiencies .

Secondly, when the three light bulbs 232 are all working, they generally supply excess illumination to the light guides 235 and thus the intensity of the light bulbs

232 can be reduced to increase their operating life. Due to this arrangement, if one of the light bulbs 232 is defective or burns out, for example, the rheostats 68 of the remaining light bulbs 232 can be increased to provide sufficient illumination at the light guide outlets or end surfaces 238, 240, 242 without having to shut down the inspection system. Thereafter, the defective or burn out light bulb 232 can be replaced at the convenience of the machine operator. This arrangement also eliminates the need to balance the left off-axis, the right off-axis and the central on-axis light sources, when a light bulb is replaced, to provide the desired continuous and uniform illumination of the inspection zone 27 or inspection line 29. A portion of the supplied light exits from each of the three second opposed outlets or end surfaces 238 of the left light guide strands 237 and is directed at a rear surface of a pair of opposed focussing cylinder lens 243, 244. The light passes therethrough and is focussed by each of the pair of opposed focussing cylinder lens 243, 244 at an inspection zone 27 or along an inspection line 29. In addition, a portion of the supplied light exits from each of the three outlets or end surfaces 240 of the left light guide strands 239 and is directed at a rear surface of a pair of opposed focussing cylinder lens 243, 244. The light passes therethrough and is focussed by each of the pair of focussing cylinder lens 243, 244 at an inspection zone 27 or along an inspection line 29.

Lastly, a portion of the supplied light from elongate light guide outlet or end surface 242, of the central light guide strand 240, is reflected by a first mirror 245 at a rear surface of a pair of opposed focussing cylinder lens 246, 247. The light passes through the pair of opposed focussing cylinder lens 246, 247 and is focussed at a beam splitter 228. The beam splitter 228 reflects the supplied light at or along an inspection zone 27 or an elongate line 29. The beam splitter 228 is located along the inspection plane P, at an oblique angle thereto, e.g. at a 45° angle, to reflect a portion of the supplied light along the inspection plane P toward the inspection zone 27 or along an inspection line 29 while a light trap 180 absorbs the light that passes therethrough. The beam splitter 228 reflects a desired amount of light, e.g. between about 20% to about 80% and preferably about 50%, which is supplied by the opposed lens 246, 247. The beam splitter 228 also allows the inspection device 12 to view the object O to be inspected along the inspection plane P through the beam splitter 228.

An important aspect of each embodiment of the present invention is to achieve the following three features. First, the illumination system must provide an increased solid angle of illumination, which is preferably a wedge of illumination having an illumination angle extending over an angle of at least about 90°, preferably an illumination angle extending over an angle of more than about 120°, and more preferably an illumination angle extending over an angle approaching about 175°. Secondly, the increased solid angle of illumination must be substantially uniform, as a function of incident angle with respect to the inspection line 29, from one side of the illumination source to the opposite side of the illumination source as well as at locations within the illumination source. That is, the illumination intensity of the illumination source should only fluctuate about ± 10% and preferably about ± 5%. Thirdly, the increased solid angle of illumination must be substantially contiguous from one side of the illumination source to the opposite side of the illumination source as well as at locations within the illumination source. That is, only a small or slight break or interruption in the increased solid angle of illumination, which is not visibly perceived by the inspection device, can be tolerated. Generally, a small or slight break or interruption can be tolerated only as long as the interruption is not perceived by the camera as an interruption in the contiguous illumination field.

With reference now to Fig. 20, a diagrammatic drawing showing use of the vision system 256, according to the present invention, is shown for a mail sorting application. It is to be appreciated that the vision system 256, shown in this Figure, is a combination of any one of the linear continuous diffuse illuminators 258, shown in the previous embodiments, an observation means 12, such as a camera, and associated processing hardware and software. Accordingly, these elements are only diagrammatically shown in this Figure. It is to be appreciated that the diagrammatically depicted illumination source comprises both light supplied along the observation axis as well as light supplied off-axis.

The camera 12 is connected to a vision processor 260 which receives information perceived by the camera 12 and, in turn, processes that information by conventional technology well known in the art to render a determination, e.g. the numerical address or indicia is deciphered, the object is either "acceptable" or "unacceptable", the object is either "conforming" or "non-conforming", etc. The purpose of the vision processor 260 is to reduce the amount of information or data, supplied by the camera 12, which is ultimately conveyed to the industrial computer 262 so that the conveyed information is in a simpler and more readily utilizable format, e.g. the deciphered mailing address, which can then be used for further conveying or sorting of the envelope E, e.g. a simple pass/fail signal and the like. The computer 262 is connected to the vision processor 260 to receive information therefrom and, based upon internal processing of the information received from the vision processor 260, the computer 262 outputs a signal which typically is one of the following three outputs .

In the event that the vision processor 260 is able to decipher the indicia and/or characters contained on the envelope E, e.g. read the mailing address, then this information is accurately conveyed to the computer 262 by the vision processor 260. The computer 262 then outputs a signal, e.g. a parallel or a serial signal, to a printer 264 which directly prints the deciphered indicia on the envelope E in a bar code format, for example. Thereafter, as the envelope E is conveyed along the mail sorting system, the printed bar code is easily read by conventional bar code reading equipment to facilitate further manipulation of the envelope E. Alternatively, in the event that the vision system 256 is not able to completely decipher the indicia contained on the envelope E, the computer 262 then outputs a signal to a diverter 266 which diverts that particular envelope E to an area where the indicia of the envelope E is read by an operator viewing the indicia. Once this has occurred, the operator causes an appropriate bar code to be applied to the envelope E and the envelope E then reenters the mail sorting system for further sorting, handling or processing based upon the added bar code.

Thirdly, the computer 262 can output an signal to a conveying mechanism 268 which controls conveyance of the envelope E to a desired mail pile, mail bag, mail bin, storage location, etc., depending upon the content of the deciphered indicia.

It is to be appreciated that the relative movement between the illumination system and the object O to be imaged can be achieved in the variety of different ways. Further, the elongated diffuse illumination system, a computer, the camera and a conveying apparatus may be incorporated into a combined unit for one of inspection, reproduction and/or determining of information carried by the object 0 to be imaged.

The light projector is similar in many respects to that shown in United States Patent No. 5,187,611, the contents of which are incorporated herein by reference, and the beam splitter concepts shown in that patent are applicable in the instant disclosure. The beam splitter surfaces and/or the mirror surfaces are conventionally provided with silvered strips, or otherwise treated, wherein the mirror constitutes both a reflective surface and a light pervious surface in which light may pass through the mirror from the object for inspection by the camera, and the mirror also reflects the light generated by the beam splitter light source. Alternatively, the beam splitter mirror can be formed by a half silvered membrane pellicle of nitrocellulose or plastic material, such as "MYLAR", which has advantageous beam splitting characteristics in certain applications.

The beam splitter mirrors, may be provided in a curved configuration having a concave face disposed towards both the object 0 and the secondary light source and a convex face disposed towards the inspection device, which may be a machine vision camera. This configuration provides an increased range of incident angles for the on-axis inspection diffused light source while, at the same time, reducing the required height of the light projector above the object O being viewed.

The diffuser can be formed of treated glass, plastic, or some other light translucent material capable of evenly diffusing light cast upon the diffuser by the light source. The light source may consist of a plurality of lamps, diodes, LEDs or optical fibers, or a single fluorescent or incandescent lamp capable of generating a relatively uniform panel of light cast upon the diffuser. The preferred linear light source is a 150 watt DC light source, such as a DC light source manufactured by Fostec Corp. of Auburn, New York.

It is to be appreciated that if a TDI (Time Delay Integration line scan camera) inspection device 12 is utilized, less light is required to be supplied to the inspection zone 27 to be adequately illuminate the object O to be observed by the inspection device 12. If a single line CCD camera is utilized, however, the illumination requirements are generally much higher to insure adequate illumination of the desired area of the object 0 to be observed for viewing by the single line CDD camera .

The inventors have discovered that when using a high intensity linear fiber optic light source, typically the central 20° of the wedge of illumination coming from the light source is substantially uniform and can be utilized, as the primary illumination segment or the secondary illumination segment, to illuminate the inspection zone.

Since certain changes may be made in the above described illumination device, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.

Claims

We claim:

1. An elongate inspection system for uniformly illuminating a desired area of an object when the object is located at an inspection zone of an object observing location, said illumination system comprising: an inspection device for inspecting an object when located at the object observing location, and an inspection plane being defined between said inspection device and an inspection line within the inspection zone; a primary illumination segment for providing off-axis illumination of said object to be inspected, said off-axis primary illumination segment including a member for concentrating said primary illumination segment at said inspection zone; a secondary illumination segment being supplied to said inspection zone along said inspection plane; and said primary illumination segment and said secondary illumination segment, during use, supply a substantially continuous uniform illumination field to facilitate inspection of a desired area of the object to be inspected when the object is located at the inspection zone.

2. The elongate inspection system according to claim 1, wherein said primary illumination segment comprises a left off-axis illumination segment and a right off-axis illumination segment and both said left off-axis illumination segment and said right off-axis illumination segment are arranged to illuminate said inspection zone.

3. The elongate inspection system according to claim 1, wherein said system comprises a mechanism for controlling at least one of the intensity and character of at least one of said primary illumination segment and said secondary illumination segment to provide a substantially uniform illumination field for illuminating said inspection zone.

4. The elongate inspection system according to claim 1, wherein a single light source supplies light for providing both said primary illumination segment and said secondary illumination segment.

5. The elongate inspection system according to claim 1, wherein at least one light source provides said primary illumination segment and at least one other light source provides said secondary illumination segment.

6. The elongate inspection system according to claim 2, wherein a slip plate, having an aperture provided therein, is located along the inspection plane and separates a remainder of said elongate inspection system from the object to be inspected, and said aperture is coincident with the inspection plane.

7. The elongate inspection system according to claim 2, wherein a diffuser is located between a light source of said primary illumination segment and said member for concentrating said primary illumination segment for diffusing light supplied by said light source.

8. The elongate inspection system according to claim 2, wherein said member for concentrating said primary illumination segment is a lens.

9. The elongate inspection system according to claim 8, wherein a beam splitter is located along said inspection plane, between said inspection device and the object to be inspected, and said beam splitter reflects a portion of said secondary illumination segment along said inspection plane and allows a portion of the light reflected by said object to be inspected to be sensed by said inspection device.

10. The elongate inspection system according to claim 2, wherein light from at least one of said primary illumination segment and said secondary illumination segment is conveyed to said inspection zone by a light guide.

11. The elongate inspection system according to claim 2, wherein said elongate inspection system is stationary and said inspection system further includes a mechanism for conveying the object to be inspected relative to said elongate inspection system.

12. The elongate inspection system according to claim 2, further comprising a computing mechanism which is electrically coupled to said elongate inspection system, and a conveying mechanism which is electrically coupled to said computing mechanism, and said inspection device supplies a sensed image of the object to be inspected to said computing mechanism which determines a feature of the object to be inspected and outputs a signal to said conveying mechanism to control further manipulation of the object to be inspected based upon the determined feature.

13. An elongate inspection system for uniformly illuminating a desired area of an object when the object is located at an inspection zone of an object observing location, said illumination system comprising: an inspection device for inspecting an object when located at the object observing location, and an inspection plane being defined between said inspection device and the inspection zone; a first primary illumination segment for providing left off-axis illumination of said object to be inspected, said left off-axis primary illumination segment including a member for focussing said primary illumination segment at said inspection zone; a second primary illumination segment for providing right off-axis illumination of said object to be inspected, said right off-axis primary illumination segment including a member for focussing said primary illumination segment at said inspection zone; a secondary illumination segment for supplying illumination of said object to be inspected along said inspection plane; and said first and second primary illumination segments and said secondary illumination segment, during use, supply a substantially continuous uniform illumination field to facilitate inspection of a desired area of the object to be inspected when the object is located at the inspection zone.

14. The elongate inspection system according to claim 13, wherein said system comprises a mechanism for controlling at least one of the intensity and character of at least one of said first and second primary illumination segments and said secondary illumination segment to provide a substantially uniform illumination field for illuminating said inspection zone.

15. The elongate inspection system according to claim 13, a slip plate, which has an aperture provided therein, is located along the inspection plane and separates a remainder of said elongate inspection system from the object to be inspected, and said aperture is coincident with the inspection plane.

16. The elongate inspection system according to claim 13, wherein a beam splitter is located along said inspection plane, between said inspection device and the object to be inspected, and said beam splitter reflects a portion of said secondary illumination segment along said inspection plane and allows a portion of the light reflected by said object to be inspected to be sensed by said inspection device.

17. The elongate inspection system according to claim 13, wherein light from both said first and second primary illumination segments is conveyed to said inspection zone by at least one light guide; said primary and secondary illumination segments are both supplied from the same light source which comprises a plurality of light elements located to supply light to a randomizer; and said randomizer having at least one outlet for supplying light for said primary illumination segment and at least one outlet for supplying light for said secondary illumination segment whereby said randomizer ensures that any variation in intensity of the light source equally effects the intensity of both said primary and said secondary illumination segments.

18. The elongate inspection system according to claim 13, further comprising a computing mechanism which is electrically coupled to said elongate inspection system, and a conveying mechanism which is electrically coupled to said computing mechanism, and said inspection device supplies a sensed image of the object to be inspected to said computing mechanism which determines a feature of the object to be inspected and outputs a signal to said conveying mechanism to control further manipulation of the object to be inspected based upon the determined feature.

19. A method of using an elongate inspection system to uniformly illuminate a desired inspection zone of an object to be inspected, when the object is located at an object observing location, said method comprising the steps of: defining an inspection plane between an inspection device, for inspecting the object when located at the object observing location, and the object to be inspected; supplying a primary illumination segment for supplying off-axis illumination of said object to be inspected; concentrating said off-axis primary illumination segment at said desired inspection zone to achieve a sufficiently intensity of illumination; supplying a secondary illumination segment along said inspection plane; and, during use of said elongate inspection system, adjusting the intensity of the primary illumination segment and the secondary illumination segment to form a substantially continuous uniform illumination field to facilitate inspection of a desired zone of said object to be inspected when said object is located on the inspection plane.

20. The method according to claim 19, further comprising the step of forming said primary illumination segment of a left off-axis illumination segment and a right off-axis illumination segment and both said left off-axis illumination segment and said right off-axis illumination segment are arranged to illuminate said inspection zone.