Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
1999-06-14
2001-03-27
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
C356S124000
Reexamination Certificate
active
06208412
ABSTRACT:
TECHNICAL FIELD
The invention relates to an apparatus and method for determining optical quality of a transparent product, wherein the apparatus and method involve passing one or more gray-scale patterns through the product.
BACKGROUND OF THE INVENTION
A prior method for determining optical quality of a transparent product, such as a front windshield for a motor vehicle, involves projecting an array of dots through the product and onto a screen. The dots are then measured manually, and the measurements are compared with predetermined, standard measurements to evaluate optical distortion of the product.
Because the dots are measured manually, this method is rather time-consuming, fatiguing and error prone. Furthermore, the method provides limited coverage of the product. For example, distortion occurring between dots is not detected.
Another method for determining optical quality of a transparent product involves using a test pattern comprising a plurality of diamonds or equivalent pattern. A moveable light source is positioned behind the test pattern, and its movement is synchronized with a moveable line-scan camera positioned in front of the test pattern. As the light source and camera move with respect to the product, the camera views images of the test pattern as seen through the product. Measurements of diamonds detected in the images are compared with undistorted diamonds to evaluate distortion of the product. This method also provides limited coverage of the product. Furthermore, the apparatus used to practice the method is relatively slow, complex and costly.
DISCLOSURE OF INVENTION
The invention overcomes the shortcomings of the prior art by providing a method and apparatus for determining optical quality of a transparent product at any and all points on the product. Furthermore, the method and apparatus provide accurate and repeatable results.
Under the invention, a method of determining optical quality of a transparent product includes passing a first gray-scale pattern through the product; obtaining a first image of the first pattern with an image pickup device after the first pattern has passed through the product; and determining optical quality of the product based on data obtained from the first image.
Exemplary gray-scale patterns that may be used to practice the method include sinusoidal gratings as well as sawtooth gratings. Advantageously, the gray-scale patterns may be projected through the product, or generated behind the product. Consequently, the method may be used with a variety of product and apparatus configurations.
More specifically, the method includes determining a phase for each of a plurality of pixels of the first image, wherein each pixel corresponds to a particular point on the product. One or more optical characteristics are then determined for each of a plurality of points on the product based on the phase at the corresponding pixel.
An apparatus according to the invention for determining optical quality of a transparent product includes an image generating device for generating a gray-scale pattern such that the gray-scale pattern may be passed through the product. The apparatus further includes an image pickup device for obtaining an image of the gray-scale pattern after the pattern has passed through the product, and an image analyzing device in communication with the image pickup device. The image analyzing device includes instructions for determining optical quality of the product based on the image of the gray-scale pattern.
These and other objects, features and advantages of the invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings.
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Rosenberger Richard A.
Shelton Larry I.
Visteon Global Technologies Inc.
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