Illumination – Plural light sources – With support
Reexamination Certificate
2000-07-18
2001-09-11
Husar, Stephen (Department: 2875)
Illumination
Plural light sources
With support
C362S283000, C362S347000, C362S350000, C362S800000
Reexamination Certificate
active
06286978
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to illumination systems and methods, and more particularly, to a light array system and method for illumination of objects for machine vision, inspection, and image processing applications, and even more particularly to a light array system and method for illumination of objects to be inspected using one dimensional imaging systems.
BACKGROUND OF THE INVENTION
Inspection of manufactured products helps to reduce the number of defective products introduced into the marketplace. The effectiveness of certain types of inspections, for example inspections of printed circuit boards or printed wiring boards (collectively “PWBs”), is often dependent upon the illumination systems and processes used to provide inspection lighting of the manufactured product during inspection.
This is especially true for automated inspection of PWBs using line scan cameras—the ability to identify, classify, and properly detect defects in the inspected PWBs is greatly affected by the lighting available on the subject PWB. Proper illumination allows for enhanced visibility of PWB manufacturing defects, including raw paste analysis (coverage and volume, missing/mis-aligned/damaged components, bent/missing/lifted leads, bridges and near bridges, alignment gauging, insufficient and excess solder, solder dewets, cold and fractured solder joints, etc.).
Several different illumination methodologies have been used for PWB inspection as well as other inspection tasks. These illumination techniques include highly diffuse (“cloudy day”) illumination, direct illumination, re-directed illumination using fiber optics to distribute the source over a line, projected images of lines, ring lights, coaxial illumination, flood lights, as well as all of the above with some form of additional diffuser. Each of these methods proves inadequate when used for automated inspection of PWBs using a line scan camera for at least one or more of the following reasons: (1) inadequate overall light level; (2) excessive localized blooming or glinting (i.e., saturation of camera imaging elements due to excessive light); (3) insufficient coverage of light to fill shadows; and (4) image shiny, near vertical objects, such as leads.
For example, fixed angle single light sources cannot provide lighting to shadowed areas (such as shorter components surrounded by taller components or areas under vertical leads perpendicular to the scan direction). In order to get the light intensity required for inspection, these fixed angle light sources can also cause “blooming” or very bright spots in the camera (due to the angle of reflection) that prevent inspection of that area because nothing could be discerned from the blooming area. In addition, because solder fillets are “mound-shaped”, regardless of the light angle variation, some reflection in a specular fashion back to the camera will occur. To a line scan camera, the shadow areas often look black while the shiny or blooming areas look white and accurate detection of defects in these areas is difficult or impossible.
SUMMARY OF THE INVENTION
The present invention provides a light array illumination system that substantially eliminates or reduces disadvantages and problems associated with previously developed illumination systems and methods used for automated inspections.
More specifically, the present invention provides a system for illumination from a variety of illumination angles to aid inspection of a product. The illumination system includes a dome light array formed in the shape of a partial cylinder about an imaging axis. The dome light array includes a plurality of rows where each row includes a plurality of lamps arranged in an arc about an imaging axis (so that, each lamp in the row is approximately the same distance from the imaging axis) and all of the lamps in a row point to and illuminate the same point within the image area. The illumination system can include an aperture in the top of the dome light array through which a camera can image the image area on the object. Positioning each row of lamps in an arc about the image point provides various illumination angles to give a relatively uniform wide angle, yet intense, illumination to enhance automated PWB defect inspection. To further provide illumination, a pair of side panel light arrays having a plurality of lamps can be attached to the sides of the dome light array so that the side lamps provide further vertical illumination on the image area from a horizontal side plane.
The present invention provides an important technical advantage by dramatically improving the image quality and speed of inspection through the use of illumination geometry that is unavailable from previous lighting systems. For example, imaging and inspection of solder joints/bridges and defects associated with the vertical edge of package leads can be greatly enhanced using the lighting system of the present invention. The present invention also allows more reliable inspection of small components located between taller components.
The present invention provides another technical advantage by providing direct specular distribution of light over a large range of angles to reduce flare and shadowing, while maintaining light intensity levels required for imaging with a line scan camera.
The present invention provides yet another technical advantage by reducing the error rate (or number of false defects) during component inspections. For example, by limiting the blooming or glare effect between leads, the present invention can reduce the number of false bridge defects induced by light glare.
Other technical advantages of the present invention include the extended life of the light source when incorporating long life LEDs, the reduced cost of the light source, and the reduced weight of the light source as compared to conventional lighting systems.
Yet another technical advantage of the present invention as compared to fibre optic based lighting systems is the ability to remotely locate the power source. Furthermore, the electrical cable associated with the present invention does not break as easily and is easier to manipulate than fibre optic cable.
REFERENCES:
patent: 5038258 (1991-08-01), Koch
patent: 5039868 (1991-08-01), Kobayashi et al.
patent: 5309277 (1994-05-01), Deck
patent: 5920643 (1999-07-01), White
patent: 6161941 (2000-12-01), Tait et al.
DeYong Mark R.
Lewin Alvaro D.
Tait Robert W.
Gray Cary Ware and Freidenrich
Husar Stephen
Intelligent Reasoning Systems, Inc.
Ward John Anthony
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