Designing Labels for Effective Quality Inspection
By Miles Kroner, Vision and Serialization Business Manager at Mettler-Toledo
Product labels are a critical component of product packaging, offering manufacturers a chance to convince consumers of the quality of a product, and providing the last opportunity to impart information such as allergen warnings, expiration date and instructions for use. Less immediately apparent is the importance of product labeling with regard to inventory management, itemization, traceability and product tracking: crucial information in the event of a product recall.
In order to understand the most effective way to create a print and label quality inspection program, it is important to know how automated inspection equipment works, what codes are and the factors that can influence inspection effectiveness.
There are three basic ways codes are presented on product packaging: alphanumeric strings, such as expiration dates which are readable by human eye, 1D barcodes that contain information about the product or price, and 2D barcodes which combines multiple pieces of information.
Reading codes relies on the contrast between filled and empty space. With automated vision systems, a camera captures an image and separate vision processing software analyzes and decodes. The displayed image can be further analyzed based on how easy the code was to read and assign a ‘grade’ – so if a printer is running out of ink and beginning to print faintly, the system can notify an operator once the code drops below a certain grade. A process known as optical character recognition (OCR) or optical character verification (OCV) is used to read alphanumeric strings. Because there are greater opportunities for variation in printed text compared to a barcode, this can be more challenging.
Design Elements to Consider
The method by which a vision system is able to pick out things like characters or codes on a label surface is reliant on the contrast between the printed character and the background upon which the character is printed. All too often more ambitious label designs can result in a frustratingly difficult reading situation,.. Choose print colors which stand out against the label background in order to avoid this problem – and remember that black and white are the preferred colors for barcodes, though if this is impossible choose colors which sufficiently contrast from one another.
Contrast may be king when it comes to label design, but it is far from the only factor to consider. The label material can also be a factor in determining how easy inspection can be – reflective materials (such as foils) can cause problems and require a custom lighting solution to accurately perform the inspection. Alphanumeric codes should be printed at a size which cameras can easily read; the width of the smallest character should be no smaller than three pixels, and the total area of a given character should consist of some 20-25 pixels. The space between characters also needs to be sufficient for the system to distinguish between characters: two pixels of space at least.
There are other things to consider when producing alphanumeric codes. The advantage of a barcode over alphanumeric codes is partially due to the uniformity of appearance while fonts are far more varied. This allows codes to have standardized quality grades which make creating effective designs far more easily. These quality grades are determined by analyzing the reflectance of the barcode, the edge contrast, the symbol contrast, the modulation, the decodability and any defects in the code. Each of these elements are graded separately on a scale from A to F, and an average of these grades determines the overall score of the code. Generally, a grade of C or higher will be readable by most barcode scanners, although obviously the higher the grade the less-likely there will be any reading errors.
Reading Codes Properly is a Process
It is a well-known fact that product labels are important as a means of communication with consumers, but the contents of a label are equally important for manufacturers and retailers. Product codes are necessary for identifying and tracking products, making them critical for a smooth transportation and distribution process – to say nothing of their role in making a product recall go smoothly. Any problems which may arise as a result of a poorly-printed code reflect poorly on the manufacturer and, depending on the industry, could lead to serious problems. It is critical for manufacturers to know ahead of time what the standards for their industry are, and what their own internal standards will be. Pharmaceutical companies, for example, may wish to only produce barcodes with a grade of B or higher to minimize the number of times a code may need to be re-scanned before a successful read, while other applications (such as a UPC) may be able to afford a C grade, as re-scanning a code is not necessarily as troublesome in a retail situation.
There are a lot of things which go into ensuring product codes are readable – everything from the type of printer to the print surface to how you choose to read the codes has to be taken into consideration in order to ensure a high-quality and readable code on product labeling and packaging. Manufacturers who choose to take all of these factors into account, however, will be rewarded with a higher quality product and fewer customer complaints.