Optical: systems and elements – Lens – Telecentric system
Reexamination Certificate
1999-05-19
2001-09-18
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
Telecentric system
C359S821000
Reexamination Certificate
active
06292306
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a metrological apparatus, and more particularly to apparatus of the type employed for automated optical inspection of manufactured objects, particularly in regard to the determination of precise dimensional measurements of such objects. Even more particularly this invention relates to an improved variable magnification optical system and associated video camera for accurately performing computerized image analysis and dimensional measurements of such objects.
Metrological apparatus of the type described normally includes a support for the object upon which dimensional measurements are to be made, and some means for precisely moving either the object or the associated video camera which is employed for recording or displaying a magnified image of the object that is being inspected. Such apparatus in addition to being able to perform measurements in a horizontal or X-Y plane, also may include autofocus means for determining heights of the object in the Z direction normal to the X-Y plane. In this manner such apparatus is capable of producing a full, three-dimensional inspection of the object.
Heretofore, as described for example in U.S. Pat. No. 5,389,774, it has been customary normally to employ in a video inspection system of the type described a conventional zoom lens mechanism to vary focal length and to maintain focus. Typical such zoom lenses are not telecentric, so that the position of the object within the depth of focus significantly affects apparent size of the object, particularly at lower magnifications and at larger fields.
One object of this invention is to provide for an inspection system of the type described a telecentric zoom lens device that covers a broad range of magnifications, has a large collimated space for insertion of an illumination means, has large working distance, and allows for use with interchangeable infinity corrected objectives.
Another object of this invention is to provide a telecentric zoom lens device of the type described having an F-number or aperture which is intentionally nearly constant at the image, thereby presenting uniform intensity and resolution throughout the magnification range.
Other objects of the invention will be apparent hereinafter from the specification and recital of the appended claims, particularly when read in the light of the accompanying drawings.
SUMMARY OF THE INVENTION
The work to be inspected is positioned on the surface of a table beneath a series of imaging lenses that are secured to a system support that overlies the work. The lenses have an optical axis disposed vertically and includes a coaxial adjustable telecentric stop or iris diaphragm and two moving groups of lenses for performing magnification zooming, where these are controlled by cam and slot means as in conventional zoom lenses. The complete system may also include a substage collimator or illuminator to offer a silhouette image of the object, while a beamsplitter within the lens system can be used to inject surface inspection illumination in the opposing direction.
In addition, the lens systems support is mounted for vertical adjustment on a vertical slide, so that the entire assembly (the camera, the diaphragm, the imaging lens system, and the surface illuminator) can be moved as a unit vertically relative to the work, whereby magnification variation is achieved and focus maintained by cam actuated positioning of the lens groups within the zoom lens assembly, while the object plane can be relocated by moving the entire system thereon relative to the work. The lens system incorporates telecentricity and consistent precise image resolution so as to maximize measurement accuracy. This is accomplished through the use of the variable aperture of the iris diaphragm positioned at the back focus of the front objective lens. That lens serves in an optical relay to present an intermediate image to an optical zoom, which is a novel means for achieving improved performance in this class of apparatus.
REFERENCES:
patent: 5619031 (1997-04-01), Choate
patent: 5668665 (1997-09-01), Choate
patent: 5745236 (1998-04-01), Haga
Optical Gaging Products, Inc.
Schwartz Jordan M.
Shlesinger Fitzsimmons & Shlesinger
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