Machine Vision Technology: Part Location with PatMax

Cognex Patented Geometric Pattern Matching Technology

PatMax®, the industry’s gold standard for part and feature location, provides accuracy and repeatability under the most challenging conditions. Originally patented in 1997 as the first high-accuracy, high-speed, high-yield, object location technology for machine vision, PatMax technology is the basis for such companion tools as PatMax SA, PatMax XLC, Synthetic PatMax, PatInspect®, PatFlex®, OCVMax™ and IDMax® covering the broadest range of pattern matching and inspection in the industry.

PatMax utilizes advanced geometric pattern matching technology to reliably and accurately locate parts. Even under the most challenging conditions, this tool can significantly reduce or eliminate fixturing requirements and cost. For locating parts or features, PatMax provides the maximum vision inspection yield and reliability available in a vision system.

Pattern Matching Technology

The very first step in any machine vision application—and the one that usually determines whether the application succeeds or fails—involves locating the object within the vision camera’s field of view—a process known as pattern matching.

Pattern matching can be extremely challenging, as many variables can alter the way an object appears to a vision system. Traditional pattern matching technology relies upon a pixel-grid analysis process commonly known as normalized correlation. This method looks for statistical similarity between a gray-level model—or reference image—of an object and portions of the image to determine the object’s X/Y position.

Though effective in certain situations, this approach limits both the ability to find objects, and the accuracy with which they can be found, under conditions of varying appearance common to production lines, such as changes in object angle, size, and shading.

To overcome these limitations, Cognex developed Geometric Pattern Matching Technology, marketed under the brand name PatMax. This technology learns an object’s geometry using a set of boundary curves that are not tied to a pixel grid, and then looks for similar shapes in the image without relying on specific gray levels. The result is a revolutionary improvement in the ability to accurately find objects despite changes in angle, size, and shading.

Other machine vision companies have adopted the geometric pattern matching concept. However, each vendor interprets the concept in a proprietary way, so that performance characteristics vary widely. Consequently, it may be difficult to determine the product that is best suited to your application. When evaluating machine vision technologies for pattern matching remember to ask questions regarding yield, accuracy, speed, and pattern training—all factors that make PatMax the leading technology for pattern matching.

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