Image analysis – Pattern recognition – Feature extraction
Reexamination Certificate
1998-12-18
2001-06-26
Johns, Andrew W. (Department: 2621)
Image analysis
Pattern recognition
Feature extraction
Reexamination Certificate
active
06252986
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to machine vision, and particularly to machine vision systems specialized for finding a particular class of objects in an image.
BACKGROUND OF THE INVENTION
Many machine vision systems use a model of an object for locating and/or inspecting objects in an image.
In the field of semiconductor device manufacturing, a vacuum nozzle is used to pick up semiconductor chips. In manufacturing facilities using machine vision, it is sometimes necessary to inspect the nozzle to ensure that the nozzle will function reliably. To inspect the nozzle, an image of the nozzle is acquired by the machine vision system, and the image is searched with a model of the nozzle to find, and then inspect the nozzle.
It is known to use the Generalized Hough Transform (GHT), specialized to find circles, to create a GHT circular model of the nozzle, given the diameter of the nozzle. However, this approach can only find circular profiles of the nozzle that scale uniformly, and is therefore typically only used to find one ring or profile of the image of the nozzle, typically only the outer ring. Further, sometimes this approach does not provide sufficient accuracy regarding the position of the nozzle for some applications. Moreover, certain aspects of the relationship between the inner and outer profiles of the image of the nozzle cannot be inspected at all, such as concentricity, and bent nozzle conditions.
SUMMARY OF THE INVENTION
In a first general aspect of the invention, a method is provided for finding an image of an object having a concentric profile, wherein the concentric profile has an inner profile and an outer profile, and wherein the inner profile is in concentric relationship with the outer profile. The method includes the steps of creating a single model of the object using the inner profile and the outer profile; creating a compound model of the object having an inner sub-model based on the inner profile, and an outer sub-model based on the outer profile; in a coarse search phase, searching for the object using the single model to provide coarse location information; and in a fine search phase, searching for the object using the coarse location information and the compound model to provide fine object location and object scale information.
In a preferred embodiment, the fine object scale information includes: an inner profile diameter and an outer profile diameter. In another preferred embodiment, each sub-model of the compound model is a closed two-vertex curvilinear shape that spans 180 degrees. In other preferred embodiments, each sub-model includes information representing polarity.
In another general aspect of the invention, a method is provided for finding an image of an object having a concentric profile, the concentric profile having a plurality of constituent profiles, wherein the profiles are in concentric relationship with each other. Here, the method includes creating a single model of the object using the plurality of constituent profiles; creating a compound model of the object having a sub-model for each profile of the plurality of constitutent profiles; in a coarse search phase, searching for the object using the single model to provide coarse location information; and in a fine search phase, searching for the object using the coarse location information and the compound model to provide fine object location and object scale information. In a preferred embodiment, each of the profiles of the plurality of constituent profiles scales independently in the fine search phase.
The methods of the invention can find circular profiles of a nozzle that scale non-uniformly as well as that scale uniformly, and is therefore can be used to find one or more rings or profiles of the image of a nozzle. Further, the methods of the invention can provide superior accuracy regarding the position of the nozzle for many applications. Moreover, certain aspects of the relationship between the inner and outer profiles of the image of the nozzle, such as a bent nozzle condition, can be effectively inspected by the methods of the invention.
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Azarian Seyed H.
Cognex Corporation
Johns Andrew W.
Weinzimmer Russ
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