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The paper describes a low-cost industrial inspection system (MAQVIS) developed by the authors and based on a personal computer equipped with a simple frame grabber and a digital input/output controller. Originally developed under a contract with an industrial partner for inspecting text and symbols printed on electronic components, MAQVIS can be applied to many inspection tasks since it is based on a generic template matching algorithm. The task of inspection is broken down into two steps; first, location of the symbols that must be verified in the image and second, verification of the symbols using criteria previously defined by the operator during the set-up phase. The first step is important in many applications where it is impossible, due to lack of mechanical precision, to guarantee that the object being inspected (or the symbols printed upon it) will always appear in the same position relative to the camera. The second step produces a pass/fail result for each symbol and finally for the component itself. MAQVIS can be programmed to display failed symbols on-screen and indicate the reason for the failure, or simply divert the offending component to the reject bin. Both the location and the verification steps are performed on gray-level images using algorithms specifically developed for this application. Statistical information about the number of failed components and the failure rate of individual symbols is generated and can be used to trace problems in the manufacturing process. The paper describes the system in general, and specifically the template matching algorithm used to locate symbols in the image and also the verification algorithm that validates each symbol as it is found. Results of tests performed using the system on the production line of an electronic components manufacturer are also presented.
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