Barcodes have become an inseparable part of trade and one of the most important elements of the logistics supply chain. Labels used on transport packaging and palletized load units should ensure full identification of the shipment and streamline work across all links of the supply chain. A label that is an integral part of packaging or a load unit, in addition to climatic exposure, is subjected to mechanical stress during transport, which causes changes in the quality of barcode prints. Optical changes to the barcode (changes in bar contrast, the appearance of gaps in bar continuity, reduced edge sharpness) and dimensional changes to the code (bar reduction) may occur. The magnitude of these changes depends primarily on the technical condition of the vehicle, the condition of the road surface, driving speed, and the method of securing loads in the semi-trailer or on the railway platform. The above can lead to the loss of the basic informational functions of the labels.
In order to assess the quality of barcodes, their verification is carried out using the traditional (dimensional) method or the ANSI (American National Standards Institute) method. It is advisable to use the ANSI method, which provides accurate and unambiguous results. This method is primarily used for rapid quality assessment of the code, detecting sources of incorrect barcode symbol readings, and defining the symbol’s readability by scanners. It was initially introduced in the United States as the ANSI X3.182 standard (published in 1990), and subsequently defined in the European standard (EN 1635 of 1995) and the international standard (ISO/IEC 15416). Currently, the ISO/IEC 15416:2000 standard is in force worldwide, which is based on a detailed analysis of the “Scan Reflectance Profile” (SRP). Unlike the traditional method, the ANSI method is subject to standardization; therefore, verifiers from different manufacturers will provide similar, comparable results of code quality analysis (this assumption holds true provided the devices are correctly calibrated). According to this method, each code is assigned a grade in the form of a letter or number, depending on the measurement results (Table 1). Each code must achieve a designated minimum and acceptable grade value. The profile analyzed in the ANSI method constitutes a graph of the relationship between the light reflectance coefficient (expressed in %) of the barcode symbol and the linear distance across the symbol. The light reflectance coefficient values are placed on the ordinate axis, and linear distances within the code are on the abscissa axis. Light bars (spaces) and light margins (present at both ends of the graph) are characterized by a high light reflectance coefficient, while dark bars are characterized by a low value. Verifiers automatically analyze the obtained graph.
In an analysis compliant with the PN-EN ISO/IEC 15416:2004 standard, seven parameters are examined to assess the quality of a barcode:
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decoding algorithm specified in the standard for a given symbology, e.g., ISO/IEC 15417 for Code 128 (decoding is strictly required during the initial measurement of symbol quality)
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symbol contrast (SC), which is the difference between the highest (Rmax.) and lowest (Rmin.) light reflectance coefficient values
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minimum light reflectance coefficient (Rmin.), which should be no greater than 0.5 Rmax.
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minimum edge contrast (ECmin.), which is the smallest contrast value between an adjacent space and a dark bar throughout the entire SRP
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modulation (MOD) as the ratio between the minimum edge contrast and the symbol contrast
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decodability (V) defining the accuracy of the printed code’s dimensions relative to the nominal dimensions of the code
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defects, i.e., irregularities in the light reflectance coefficient values present within bars, margins, or spaces.
All the quantities mentioned above are measured by the verifier, and the resulting code grade is equal to the lowest result of any parameter. This grade serves as a determinant of barcode quality. Table 2 shows how the values of the examined parameters affect the quality grade of barcodes.
The aim of the study was to examine the abrasion resistance of barcode symbols depending on the printing technique used. The study examined the resistance of barcode prints applied using various techniques on collective and transport packaging. Most samples were taken from cardboard transport packaging. Samples printed directly on film and logistics labels were also used. Undamaged codes, whose quality was visually beyond reproach, were selected for the tests. Labels printed exclusively for the use of the Institute of Logistics and Warehousing in Poznań were also examined.
The article comes from the magazine “Logistyka” 1/2011.