Testing direct part marks
Rick Nelson, Chief Editor -- Test & Measurement World, 10/1/2005
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| A Data Matrix symbol includes a finder (L) pattern (red), a clock track (blue), and data modules or cells (black), whose quality must be verified. The colors are for illustration purposes only; the actual symbol would be monochromatic. Adapted from Ref. 2. |
But if you've determined that permanent DPM (as opposed to the use of a removable label) is right for you, you'll need a way to ensure that the mark you affix is of sufficient quality to remain readable throughout the manufacturing process and beyond. According to a 16-page report from Cognex (Ref. 2), "Because the quality of a direct marked 2-D code is so critical to the success of lifetime part traceability, many manufacturers view the 2-D mark as a critical attribute of the part itself."
Ensuring code quality requires verification of the various matrix segments, including the finder pattern, clock track, and data region (figure), as well as the "quiet area," or the clear area that surrounds the pattern on all four sides.
The Cognex report provides details on what you need to know about symbol quality, presenting topics ranging from a standards overview (including information on the ISO 15415 print-quality specification and its limitations for DPM applications), to implementation issues (including camera resolution, lighting, and fixturing). It also describes available DPM verification systems, including in-line, stand-alone, and handheld models.
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