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Machine Vision for Process Control
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The most common control function implemented with machine vision is guidance. Robot guidance and alignment are two typical implementations. Robot guidance usually requires 3-D vision while alignment is typically 2-D. To align parts for processing unique patterns must be identified during training that can be used by the vision system to register subsequent parts. Best results are obtained from specifically designed locating registration marks called fiducials. Solid circles are often preferred for their rotation insensitivity and easy centroid definition. Fiducial shape, size and location are defined for surface mount printed circuit boards for both board alignment and part placement in IPC-SM-782. To align a part in X, Y and Theta, or rotation, requires two fiducials or patterns. To get sufficient precision in Theta the two fiducials should not be in the same camera image. Either two cameras or a moveable camera are required. |
