Stand-alone code and label reading vision systems are readily available and well-established. However the track and trace requirements of many production lines, particularly in the pharmaceutical, healthcare and food industries throw up challenges that cannot be met by ‘off the shelf’ systems
Factors such as the reading speed required, or the contrast available between the printed characters and the label, combined with regulatory requirements often mean that the code reading systems need to be configured by vision experts to meet the individual application. In many cases, the vision system needs to be fully integrated into the production line to provide appropriate reject mechanisms for labels and/or product that do not meet the specified criteria. For example labels with partial print, missing print or smudged print may need to be removed from the line before they are applied to the product or packaging.
Eliminating background effects
In many cases, the colour or surface finish of the label makes it difficult to read the codes. This may be because the code is printed onto a coloured label or onto a reflective surface, or the surface may be creased. In these cases, it is generally critical to get the illumination correct in order to generate the required contrast to allow the codes to be read. In a recent application, Olmec developed a vision system for the inspection of a medical product in a foil packaging which simultaneously had to confirm that the product was in the correct position in the foil prior to sealing while verifying the batch code printed on the foil surface. This required illumination from above, but both the product and the foil reflected the light strongly making it difficult to check the product position. By using polarising filters, reflections from the foil were suppressed giving a black background against a light product for the positional check (Figure 1), while on-axis illumination was used for the code reading application (Figure 2). This application highlighted the importance of complete integration of the vision system with the process line, since it was essential that the foil material was flat and under tension to ensure it was evenly illuminated. This necessitated changing the path of the foil and supporting it correctly as it passed under the camera to prevent it from sagging and casting shadows over the code.
Code reading tasks can include fully validated character recognition, character verification and robust 2D data matrix handling and grading. Code verification systems can help eliminate variables that affect the readability of a code, and confirm that the printing is good from the start. Typically there could be a requirement to verify a 2D code according to the parameters of ISO 15415 with automatic rejection of the label or packaging if the 2D code is unreadable or missing, or if the text is missing or incorrect. These test parameters include axial non-uniformity of the code, fixed pattern damage and print growth, where the actual element size within the code may be larger or smaller than expected due to insufficient or excess ink being applied during printing. Reading tasks could include simultaneously detecting changing batch code orientation and differing quantities and location of characters on a label. There may be requirements for code reading to a variety of different standards. In the pharmaceutical industry, there is a wide range of national codification standards across Europe, the most widely used being the 13 digit GS1 GTIN code structure, used in 17 countries including the UK and Ireland. However since January 1st 2011 all pharmaceutical products distributed in France are required to conform to French CIP13. This means they must have an ECC200 Data Matrix barcode that incorporates the CIP13 code, a batch number, expiration date and human readable text. In a new development, the EU ‘Falsified Medicines Directive’ (2011/62/EU) has been set up to ensure that medicines are safe and that the trade in medicines is rigorously controlled in order to improve the protection of public health.
One aspect of this directive is looking specifically at introducing obligatory ‘safety features’ to allow, amongst other things, verification of the authenticity of medicinal products using a ‘unique identifier’. The consultation period to decide what form this unique identifier will take closes on 27 April and the adoption of the unique identifier is scheduled for 2014.
Keeping up to speed
Another key challenge facing code reading vision systems is the speed at which the line is operating. In order to integrate a code reading system into the production line control system to ensure 100 per cent inspection, it is essential to undertake a detailed analysis of the existing control system functions including triggering and reject reconciliation to ensure that the appropriate image acquisition, reading and processing times can be met for the particular application. For example, Olmec has recently designed a vision system for a leading healthcare manufacturer, which provides 100 per cent reading and verification of codes on cartons. The system reads the 2D code and text that is printed onto the carton as it leaves the cartoning machine at read rates up to 1,200 cartons/min with automatic rejection of cartons if the 2D code is unreadable or missing, or if the text is missing or incorrect.
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