Method for Inspection and Detection of Defects on Surfaces of Disc-Shaped Objects and Computer System with a Software Product for Carrying out the Method
First Claim
1. A method for inspecting and detecting defects on surfaces of disc-shaped objects, comprising the following steps:
- capturing an image of the respective disc-shaped object, wherein the entire surface is captured with a plurality of fields;
deriving a defect-free reference of a pre-defined size from plural fields equal in size on the surface of the disc-shaped object;
generating a difference image of the surface of the disc-shaped object, wherein the derived reference is subtracted from each field on the surface of the disc-shaped object;
applying a color transformation to the difference image, wherein, by a suitable choice of transformation, signals in one channel are maximized, while undesired variations of the fields, caused by the production, are moved to a different channel;
evaluating the signals, wherein a mean value, a variance, a maximum value and a minimum value are determined for each field;
determining a distribution of the signals for each pixel of a field and a distribution of the signals for each defect to be examined, wherein the distribution is determined for each combination of transformation and detection channel used; and
selecting that combination of transformation and detection channel, for which the largest number of pixels of a field with the defect to be found lie outside the spread of the pixels of the respective field on the surface of the respective disc-shaped object from production, and which results in the largest signals for the defect.
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Accused Products
Abstract
An image (30) of a disc-shaped object (100) is recorded, wherein the entire surface (100O) is captured with a plurality of fields (60). A difference image (31) is formed, by subtracting a reference from each field (60) of the surface (100O) of the disc-shaped object (100), and subject to a color transformation, wherein by a suitable choice of transformation signals in one channel are maximized, while at the same time undesired variations, caused by production, of the fields (60) are moved to a different channel. That combination of transformation and detection channel is chosen for which the largest number of pixels of a field (60) with the defect to be found are located outside the spread of the pixels of the respective field (60) on the surface (100O) of the respective disc-shaped object (100) from production and provide the largest signals for the defect.
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Citations
23 Claims
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1. A method for inspecting and detecting defects on surfaces of disc-shaped objects, comprising the following steps:
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capturing an image of the respective disc-shaped object, wherein the entire surface is captured with a plurality of fields; deriving a defect-free reference of a pre-defined size from plural fields equal in size on the surface of the disc-shaped object; generating a difference image of the surface of the disc-shaped object, wherein the derived reference is subtracted from each field on the surface of the disc-shaped object; applying a color transformation to the difference image, wherein, by a suitable choice of transformation, signals in one channel are maximized, while undesired variations of the fields, caused by the production, are moved to a different channel; evaluating the signals, wherein a mean value, a variance, a maximum value and a minimum value are determined for each field; determining a distribution of the signals for each pixel of a field and a distribution of the signals for each defect to be examined, wherein the distribution is determined for each combination of transformation and detection channel used; and selecting that combination of transformation and detection channel, for which the largest number of pixels of a field with the defect to be found lie outside the spread of the pixels of the respective field on the surface of the respective disc-shaped object from production, and which results in the largest signals for the defect. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18)
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11. The method of claim 11, wherein the threshold is a function of the distance from a center of mass of the disc-shaped object.
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19. A computer system with a software product, wherein the software product together with the computer system carries out an inspection and detection of defects on surfaces of disc-shaped objects, wherein the software product comprises the following steps:
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capturing an image of the respective disc-shaped object with a camera of a system, wherein the entire surface of the disc-shaped object is captured with a plurality of fields, and wherein an image capturing window of the camera essentially corresponds to the size of the field; forming a defect-free reference of a pre-defined size from plural fields, equal in size, of the surface of the disc-shaped object; generating a difference image of the surface of the disc-shaped object, wherein the formed reference is subtracted from every field of the surface of the disc-shaped object; applying a color transformation to the difference image, wherein by a suitable choice of the transformation signals in one channel are maximized, while at the same time undesired variations, caused by production, of the fields are moved to a different channel; evaluating the signals, wherein a mean value, a variance, a maximum value and a minimum value are determined for each field; determining a distribution of the signals for each pixel of a field and a distribution of the signals for each defect to be examined, wherein the distribution is determined for each combination of transformation used and detection channel used; and selecting that combination of transformation and detection channel, for which the largest number of pixels of a field with the defect to be found are located outside the spread of the pixels of the respective field on the surface of the respective disc-shaped object from production, and which yields the largest signals for the defect. - View Dependent Claims (20, 21, 22, 23)
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Specification