US 5,673,334 AGranted

Method and apparatus for inspection of characteristics on non-rigid packages

AssigneeCognex Corporation

InventorsSanjay Nichani, David Li

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Abstract

A method and apparatus to search, locate and inspect an object or characteristic of interest on a non-rigid package. First, a model of patterns of interest are stored to train the system with a model of the characteristics of interest. A minimum spanning forest (MSF) is generated defining the characteristics of interest as vertices with each vertex referencing a vertex closest to itself in order to minimize the sum of the distances between vertices in each minimum spanning tree (MST) of the MSF. At run time two coarse alignment features that the system has been trained to identify are located to determine rotation and coarse position of a non-rigid package being inspected. Local alignment then determines the exact position of local alignment points each of which is a starting vertex associated with one or more characteristics of interest as vertices in that starting vertexes MST. When the exact position of each local alignment point is determined the approximate position of associated characteristics is then known. Fine alignment determines the exact position of the characteristics of interest. The fine alignment process uses the minimum spanning forrest ("MSF") to locate each characteristic of interest in a selected order by reference to another, nearest, previously located characteristic.

A method of implementing a machine vision system to locate and inspect at least one alignment feature and at least two characteristics of interest on a surface of an object, said method comprising the steps of:

storing information related to a model of said object, said at least one alignment feature, and each of said at least two characteristics of interest in memory accessible to said vision system, said information related to said model of said object including an image of said object, said information related to said at least one alignment feature including ideal position information of said at least one alignment feature on said model of said object, and said information related to said at least two characteristics of interest including an ideal position of each of said at least two characteristics of interest on said model of said object;
inter-relating in said memory said at least one alignment feature and each of said at least two characteristics of interest to effect an order of locating and inspecting each of said at least two characteristics of interest by reference to a respective nearest one of said at least two characteristics of interest, said order requiring that a first one of said at least two characteristics of interest located nearest said at least one alignment point is located first in said order and a second one of said at least two characteristics of interest located nearest said first one is located second in said order;
and
sequentially locating with said machine vision system each of said at least two characteristics of interest on said surface of said object by determining an actual location of said at least one alignment feature, and determining an actual location of said first one of said at least two characteristics of interest as a function of said ideal position information of said at least one alignment feature and said actual location of said at least one alignment feature, and determining an actual location of said second one of said at least two characteristics of interest as a function of said ideal position of said first one of said at least two characteristics of interest and said actual location of said first one of said at least two characteristics of interest.

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Abstract

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