Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-12-24
2001-05-29
Epps, Georgia (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339110
Reexamination Certificate
active
06239436
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and systems for inspecting a low gloss surface of an object at a vision station and, in particular, to methods and systems for inspecting a low gloss surface of an object at a vision station utilizing radiation having a wavelength longer than the wavelength of visible light, but shorter than the dimension of a surface defect to be detected.
BACKGROUND ART
The non-contact inspection of a surface is often most easily accomplished by probing or illuminating the surface with light from a light source and sensing its reflected component as illustrated in FIG.
1
. Deviations from surface flatness and other surface irregularities can be detected by noticing distortions and discontinuities in the reflected image. The light source typically has a known structure (so-called structured lighting).
This technique of probing a surface with a structured light source is extremely sensitive. An article by Lippincott and Stark entitled “Optical-Digital Detection of Dents and Scratches on Specular Metal Surfaces”, Aug. 15, 1982, v. 21 (16),
APPLIED OPTICS
, describes a technique of imaging a series of regularly spaced lines through reflection from a specular surface. Apparatus embodying related ideas are described in U.S. Pat. Nos. 4,792,232; 5,436,726; and 5,237,404.
Automatic processing of images of structured lighting is desirable in an industrial setting. U.S. Pat. Nos. 4,792,232; 4,629,319; and 4,686,374 describe the electronic analog and digital processing of such images. Optical Fourier plane processing (or optical/digital processing) of images of structure lighting is also natural where the images contain periodic structures. U.S. Pat. No. 4,629,319 discloses a panel surface inspection system including an infrared (i.e. IR) source in the form of a CO
2
laser and an IR retro-reflective material to form an image on a pair of adjacent infrared detectors in a pyroelectric vidicon.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and system for inspecting a low gloss surface of an object at a vision station utilizing a regular, extended pattern of radiation having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect.
Another object of the present invention is to provide a method and system for inspecting a low gloss surface of an object at a vision station utilizing infrared radiation such as broadband infrared radiation.
Yet, still another object of the present invention is to provide a method and system for inspecting a low gloss surface of an object at a vision station utilizing a regular, extended pattern of radiation having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect to automatically locate the surface defect.
Still another object of the present invention is to provide a relatively inexpensive method and system for inspecting a low gloss surface of an object at a vision station in a factory environment by using an extended source of structured infrared radiation.
Yet, still another object of the present invention is to provide a method and system for inspecting a low gloss surface of an object at a vision station to automatically locate a surface defect in the object utilizing a signal processing method which detects pattern distortions and correlates such pattern distortions between multiple images.
In carrying out the above objects and other objects of the present invention, a method is provided for inspecting a low gloss surface of an object at a vision station to automatically locate a surface defect in the object. The method includes the step of directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal. The method also includes the step of imaging the reflected light signal at the vision station to generate a first set of electrical signals representing the surface defect to be located. The method finally includes the step of processing the first set of electrical signals to obtain a second set of electrical signals representing pattern distortions in the reflected radiation signal caused by the surface defect to locate the surface defect in the object.
Further in carrying out the above objects and other objects of the present invention, a system is provided for inspecting a low gloss surface of an object at a vision station to automatically locate a surface defect in the object. The system includes a structured radiation source located at the vision station for directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal. The system also includes an imaging detector having an image plane located at the vision station for imaging the reflected radiation signal and to generate a first set of electrical signals representing the surface defect to be located. The system finally includes a signal processor coupled to the imaging detector for processing the first set of electrical signals to obtain a second set of electrical signals representing pattern distortions in the reflected radiation signal caused by the surface defect to locate the surface defect in the object.
Preferably, the radiation is infrared radiation, the source is an infrared source, and the imaging detector is an infrared camera.
Still further in carrying out the above objects and other objects of the present invention, a method is provided for inspecting a low gloss surface of an object located at a vision station. The method includes the step of directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal. The method also includes the step of converting the reflected radiation signal into a visible image for visual observation of pattern distortions in the reflected radiation signal caused by the surface defect.
Yet, still further in carrying out the above objects and other objects of the present invention, a system is provided for inspecting a low gloss surface of an object located at a vision station. The system includes a structured radiation source located at the vision station for directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal. The system also includes an image converter located at the vision station for converting the reflected radiation signal into a visible image for visual observation of pattern distortions in the reflected radiation signal caused by the surface defect.
Preferably, the radiation is infrared radiation, the source is an infrared source and the converter is an infrared image converter.
The improved method and system described herein use structured electromagnetic radiation having a longer wavelength than visible light to probe or inspect a surface. The radiation reflected from the surface being inspected is imaged by means of a sensor capable of responding to this wavelength. Since a surface appears glossy when the characteristic wavelength of its surface roughness is much shorter than that of the probing radiation, increasing the wavelength of probing radiation has the effect of making a diffusing surface more glossy. Thus, the technique of detecting surface irregularities or defects by noticing distortions and discontinuities in the reflected image of a light source having a known structure can be applied to surfaces which appear gloss-less to the naked eye.
The
Czubko Myron
Haven Neil
Parker Jeffrey B
Brooks & Kushman P.C.
Epps Georgia
Hanig Richard
Perceptron, Inc.
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