How to Verify DPM Codes
Direct part mark codes are verified against the AIM DPM standard
Direct part mark (DPM) codes can vary in appearance. The substrate (surface) on which a code is marked can exhibit varying optical properties and interfere with the image formation. Direct part marking methods, such as dot peen and laser etching, are prone to producing codes with low contrast, poor cell position, or inconsistent cell size. In addition, the surface being marked can be matted, cast, or highly reflective, and is seldom as clean and uniform as a label. Surfaces can be smooth and shiny, furrowed, striped, streaked, coarse, or granular. Therefore, the verification method for DPM codes must provide reliable and consistent results under all conditions. Controlling the background and proper illumination are both very important for DPM codes, which are verified against the AIM DPM standard.
The verification standard for direct part marks - ISO TR 29158 (AIM DPM) - is very similar to ISO/IEC 15415. One exception is that the standard allows 30- and 90- degree lighting angles in addition to 45-degree lighting. 30- and 90-degree lighting make it possible to illuminate symbols on challenging surfaces such as curved or reflective substrates.
Field of View
How big is the largest barcode being printed? A barcode verifier needs a field of view that is large enough to fit a 2-D DPM barcode and still leave enough space to meet the quiet zone requirements specific to that symbol type.
How small is the smallest module (space or cell) in your code? This measurement is the minimum x-dimension. A verifier must be able to accommodate a code’s minimum x-dimension; otherwise, the camera resolution will not be able to properly capture the image needed to perform the verification.
For 2-D DPM codes on products that vary in shape and size, a verifier with the ability to adjust the camera height to the proper focus is useful. An adjustable height is also ideal for 2-D DPM codes that are printed on a recessed portion of a part. For large barcodes or labels with multiple barcodes that need to be verified at the same time, a desktop “box” style verifier with a field of view up to six inches wide is recommended.
When judging the software component of a barcode verifier, make sure it has the functionality to grade and diagnose issues within the barcode printing process. Things to consider include whether the user interface is easy to use, generates reports, grades against the AIM DPM standard, and shows data formatting errors.