Applying Machine Vision to Verification and Testing

Machine vision is a superior replacement for human vision in applications such as high-speed verification and testing. We review trends and issues in applying machine vision. In the last few years, machine vision systems have improved dramatically in performance, ease-of-use, intelligence, and cost. Applying machine vision to verification and testing is now relatively easy and inexpensive. Successful application of machine vision requires care in the selection of the vision vendor, the vision system, and other components in your system, and in integrating the vision system into your production process. Introducing Machine Vision Machine vision uses cameras, computers and algorithms to replace human vision in inspection tasks that require precise, repetitive, high-speed verification and testing. Humans are not good at making precise measures “by eye” and their performance quickly decreases when doing repetitive or highspeed visual tasks. On the other hand, the human visual system is unmatched for understanding complex visual scenes, quickly learning new visual tasks, and making subtle judgments based on limited evidence. Machine vision still must be limited to verifying and testing well-specified parts in controlled environments. As an example of the differences in human and machine capability, Figure 1 shows a dot-matrix barcode. A defect is a missing dot, which could be caused by two dots touching each other or a dot with the wrong size. Can you see the defect? How many dots are there? What are the dot areas in microns? Figure 1. Dot inspection – a good task for a machine vision system The defect is 29 bars from the right, where top two dots are touching. There are over 1300 dots, so counting them is slow and difficult. Precise dimensional measure of each dot is impossible for us to do – our visual system is not a calibrated measuring tool – although we can point out dots that touch or look too big or too small.