Plastics Decorating - January/February 2008 - (Page 28) TECHNOLOGY FEATURE by Scott R. Sabreen, The Sabreen Group, Inc. Industrial manufacturing requirements for indelible direct part marking containing machine vision codes are growing exponentially. Direct part marking enables tracking a product from the time of manufacturing until the end of its useful life. This demand is driven by the increasing requirements for component traceability and product unique identification (UID). Post 9/11, manufacturers are implementing strategies to establish traceability and thwart product tampering and counterfeiting. The U.S. Department of Defense (DoD) has MIL-STD-130M as the standard practice on military property. Beyond DoD military requirements, manufacturers of commercial industrial products ranging from automotive, packaging, pharmaceutical, electronic, and consumer goods are aggressively adopting similar standards. Direct part marking containing unique identification information necessitates digital process technology such as inkjet, dot peen, and laser marking. For many three-dimensional plastic products, lasers are the preferred method because the process yields high-contrast indelible markings and does not require expensive consumable ink costs/solvents or post-curing. Further, lasers can mark the smallest-size machine vision codes. This is important for micro-marking, or when there is limited surface area on a part or component to be marked with alphanumerics, logos, or schematic diagrams. Robust six-sigma manufacturing operations require all products to be 100 percent human or machine vision readable regardless of the size and detail complexity of the actual marking. What are Machine Vision Codes? Machine-readable (vision) codes are coded information that can be interpreted through the use of optical scanners or cameras. A familiar example is one-dimensional “Bar“Bar code” which is a representation of information, typically dark contrast on a light background, to create high and low reflectance that is converted to 1s and 0s. The most common formats of barcodes store data in the widths and spacings of printed parallel lines (black and white stripes). However, newer patterns of dots, concentric circles, and text codes hidden within images also are used. Within the United States, the UPC (Universal Product Code) is the best-known and most widespread use of barcodes in retail and consumer products. Although modern barcode schemes can contain the ASCII character set, there are needs in the manufacturing sectors, 28 electronic, aerospace, automotive, pharmaceutical, etc., in which significantly more advanced machine vision codes are required. The continuing drive to encode more information in combination with smaller space requirements has led to the development of two-dimensional “Data Matrix” codes. Data Matrix codes cannot be read by a laser (used in Barcodes) as typically, there is no sweep pattern that can encompass the entire symbol. They must be scanned by a camera capture device. 2D Data Matrix is the revolutionary machine-readable code specifically designed to address the limitations of barcodes. Figure 1 demonstrates the differences between 2D Data Matrix v. Barcode. 2D Code Bar Code Contains data Contains data AND /OR Figure 1 Comparison between 2D Code and Barcode 2D Data Matrix codes are ideal for small parts marking and are designed to survive harsh industrial environments. The size of Data Matrix codes is only 1/10 to 1/100 of Barcode given equal encoded data. Thus, very little space on a part is needed which can contain significant manufacturing data for product traceability. Every code is about half black and half white, resulting in a 50/50 chance that cell damage will not harm readability. Data Matrix’s high degree of redundancy (data is scattered throughout the symbol) and resistance to printing defects makes it highly reliable. Error correction schemes built into the algorithm optimize the ability to recover from symbol damage. Figure 2 compares Data Matrix Code v. Barcode.
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