The first step of pattern matching always includes a learning process. A “gold” master is used to create a template. This template is used for identification purposes on all subsequent parts. A score is generated depending on how well the object or feature under inspection matches the original template. You can take advantage of pattern matching in applications that include alignment, gauging, and inspection, as reported in “PCBased Software for Pattern, Color, and Color Pattern Matching”, Photonics Tech Briefs (only in select issues of NASA Tech Briefs), June 2003, page 10a.

Pattern matching software makes it possible to find patterns and fiducials easily on semiconductor wafers, printed circuit boards, and automotive parts, allowing for quick prototyping without programming.

Alignment determines the position and orientation of a known object by locating alignment marks, or a fiducial, a predefined alignment pattern such as two intersecting lines. You can then use the fiducials as points of reference on the object. An example is searching an image that contains a microarray used for drug discovery. A fiducial is typically placed in one of the corners of the microarray. The machine vision application uses the marks to align the microarray in preparation for a motion control system to perform a raster scan of the device in order to inspect each array. Also, by knowing the exact size of the fiducial mark, the system can perform vision-motion calibration, which maps pixel values to encoder counts in the motion control system.

Relying on learning algorithms, this software module — NI Vision Development Module - enables high-speed pattern matching for locating objects of various size and orientation. The module includes an interactive environment for quickly prototyping vision applications without programming (IMAQ Vision Builder), and a library of functions for image processing (IMAQ Vision). IMAQ Vision Builder can automatically generate an IMAQ Vision block diagram that contains the same functionality as the series of operations users already prototyped in IMAQ Vision Builder. The diagram can be integrated into the users automation or production test application, which may include motion control, instrument control, and data acquisition.

This work was done by Jason Mulliner, Vision product manager, for National Instruments. For more information call (512) 683-0100 or visit National Instruments online at  NI Vision Development Module is a development tool for LabVIEW, LabWindows/CVI, and Measurement Studio.