Although most of us take barcodes for granted (if we think of them at all), a poorly printed barcode can wreak havoc in the supply chain, potentially interrupting supply and hampering business performance.
The successful use of these 2D codes, or any barcodes, depends on goodquality markings that are readable across the entire supply chain under various environmental conditions (e.g., different lighting). With this in mind, suppliers, wholesalers and brand owners have urged manufacturing and packaging organizations to have their DataMatrix barcodes graded to maintain a standardized level of quality and operability.
This article will provide a general overview of barcode grading for the pharmaceutical manufacturer and packager. It will discuss how and where it can be implemented, and what can be done to help barcodes meet the industry’s quality expectations. The reader will also understand the issues involved in implementing a successful barcode grading program.
Scanning Versus Grading
First, it is important to recognize the difference between barcode scanning (or reading) and grading (also known as verifying). Scanning is the act of reading data that is embedded in the barcode. For example, if a barcode is encoded with a product NDC (National Drug Code), this information would be displayed when the barcode is scanned. Scanning or reading the barcode provides very little indication of the barcode quality. It is binary: the code either can or cannot be read. In fact, it is possible to successfully read a poor-quality barcode if the environment in which it is scanned is ideal (i.e., good lighting, clear line of site with no interference, and proximity of scanner to the code). Conversely, a good-quality barcode may not be readable under poor environmental conditions (e.g., dim lighting, the code is occluded, or the scanner is far away/at an extreme angle to the code). Thus, simply being able to read a barcode in one location provides no assurance that the code will be readable elsewhere under different conditions. Barcode grading helps account for this nuance and provides a number or letter score that quantifies multiple barcode attributes against known standards. It establishes a baseline for quality which greatly improves the chances for successful barcode scans throughout the supply chain.
To grade or verify a DataMatrix, one should understand where the standards come from and what attributes are evaluated. According to the GS1 DataMatrix Guideline, the GS1 DataMatrix is the ISO/IECrecognized and standardized implementation of the use of the 2D data matrix barcode, with the GS1 standards body working in close cooperation with regulators and the healthcare industry to develop standards for encoding the required serialization information. The GS1 DataMatrix may be printed as a square or rectangular symbol, an ordered grid of dark and light dots in which the data is encoded bordered by a finder pattern.
Grading standards have been developed by various standards organizations (ISO/IEC, ANSI) and include both quality attributes and test conditions. ISO/IEC 15415 is the barcode-symbol print-quality test specification referenced in the GS1 DataMatrix Guideline.
Grading Parameters in Detail
There are seven basic attributes, or parameters, that are evaluated when a barcode is verified. All attributes except one (decode) are graded on a number (4-0 – ISO) or letter (A,B,C,D,F – ANSI) scale. A final single grade is then generated based on the lowest score of any one attribute. ISO 15415 considers 1.5 as a passing grade. However, most pharmaceutical distributors are requiring grades of B (3) or higher. A brief explanation of each parameter follows:
- Decode – The ability of the grader to read the barcode. If decode fails, that means the symbol is not constructed according to its symbol specification. A passing grade is 4 or A. A failing grade is 0/F. A failure of the decode parameter means the overall barcode grade is a failure.
- Contrast – The difference between light and dark squares or dots in the barcode, as measured by the level of reflectance between light and dark. Pure black and bright white provide the best contrast/highest grade. Shades of gray with a lower differential between light and dark produce lower grades.
- Modulation – Variation, or differences, in contrast throughout the barcode. Sharp contrast between light and dark elements across the entire barcode (i.e., all dark squares pure black, all light squares bright white) will yield a higher grade. If contrast varies (i.e., some dark squares black, others gray), the grade will be lower.
- Fixed Pattern Damage– The quality of the squares/dots that form the perimeter of the barcode, plus the presence of the “quiet zone” surrounding the barcode. Every DataMatrix has the same perimeter pattern:
- Bottom row and left-most column of dots the same color (all dark or all light). These elements form an L-shaped “finder pattern” that defines the boundaries of the DataMatrix, providing reference for the scanner to read the variable elements embedded in the code. A finder pattern that has gaps in consistency will lead to a lower grade.
- The top row and right-most column of dots, known as the “Clock Track,” alternate between light and dark elements. This defines the basic structure of the symbol and can also help determine size and distortion. If this is interrupted (missing light or dark elements), a lower grade will be generated.
- Quiet Zone directly outside of the perimeter defined by the Fixed Pattern. This area must be devoid of any markings. Any extraneous printing or marks in the quiet zone will lead to a lower grade.
- Grid Non-Uniformity – The adherence of the barcode to fit within specified horizontal and vertical boundaries of the code. For example, if a square barcode is specified but actually printed as a rectangle, this would lead to a lower grade.
- Axial Non-Uniformity – The alignment of the barcode with the horizontal and vertical axes. Scenarios that would cause lower grades include square codes that print out (or have their images captured) as trapezoids or nonrectangular parallelograms.
- Unused Error Correction – This indicates the amount of available Error Correction in a symbol. Error Correction is a method of reconstructing data that is lost via damage, erasure of the symbol, or poor printing. One hundred percent unused Error Correction is the ideal case. The higher the amount of error correction used (i.e., due to damaged/ missing elements), the lower the grade.
Conditions for barcode grading are also specified in the standards. These include light intensity/wavelength, size of the measuring aperture, angle of illumination, barcode substrate orientation relative to the image sensor (should be perpendicular), and number of scans. When multiple scans are performed, the final grade is determined by taking the average of all the final grades from each of the scans. Whenever possible, the barcode should be graded in its final configuration (i.e., label on bottle or case).
To facilitate grading, barcode verifiers are available that control and maintain the conditions listed above while capturing the barcode image and performing analyses for each parameter. These graders are typically off-line devices (i.e., desktop or tabletop units) that capture the image of the barcode under static, controlled conditions. These machines are calibrated using calibration conformance test cards – cards printed with 2D codes with known grades (from planned defects) that are placed on the verifier, requiring the verifier to display the expected grades to pass calibration. In practice, the packages or labels with actual barcodes are placed on the verifier, images are captured and analyzed for the seven grading parameters, and a grade is generated. The verifier also generates a report that lists, among other items, the grades of each individual parameter for each scan. This report enables a detailed evaluation of the barcode quality and optimization of the printing/packaging system. Handheld/portable graders are also available for capturing images in the field (e.g., pallet label in warehouse).
On-line grading is also possible, although maintaining the test conditions specified by the grading standards is challenging. Dedicated on-line grading systems are available that use the same design principles of the off-line graders but can be mounted directly onto a packaging line. Alternatively, on-line vision systems used to verify product information can also perform grading since they are already capturing the barcode images and can analyze the parameters.
There are no definitive standards or guidelines specifying when to use off-line or on-line grading as part of a company’s barcode quality management program. GS1 references the use of both in combination. This approach makes sense from a practical standpoint because there are positives and negatives with both methods, and they can complement each other.
There are several important reasons why off-line grading should be utilized. It provides tight control and repeatability of the test conditions per the ISO standard. The package/label can be placed in the correct location every time and does not move, so image capture is optimized. The off-line grader is easily calibrated using the test cards. Of course, a drawback of off-line grading is the requirement to pull samples from the line and bring them to the grader. This takes extra effort and does not allow 100 percent verification of all codes. If a failing or below-spec grade occurs, a procedure must be in place to address product coded since the most recent passing grade.
On-line grading offers 100 percent inspection of every barcode that is printed. Any degradation in barcode quality is immediately detectable and can be addressed. However, it is virtually impossible to replicate ISO-specified conditions with a system mounted on an active line. As a result, any grade that is generated by the on-line system may not match a grade obtained using a calibrated off-line table-top verifier. It is also likely that on-line conditions would typically be inferior to those found using an off-line grader (e.g., ambient lighting, mechanical vibration/ product movement, line speed precluding multiple scans), so on-line grading may generate worse results (false negatives – additional rejects) than an off-line system. For these reasons, a good approach would start with an off-line grader to establish a baseline, traceable barcode quality verification process. Then, if possible, simultaneously use an on-line verification system to provide continuous comparative checks of each barcode. This verification system should detect changes in barcode quality and trigger alerts and/or action limits based on certain minimum grading requirements. Manufacturers and packagers should evolve and refine their grading programs/procedures as data is gathered and experience gained.
Printing and Substrates
The final piece to the puzzle to achieve a well-graded barcode is, of course, the physical barcode itself. If the quality of the actual DataMatrix is poor, then a poor grade will be generated no matter how well the image capture and analyses are controlled. Matching the right printing technology with the right packaging substrate, and knowing how to properly set up and maintain the printing system, will help ensure that high-quality barcodes are placed on each package. Lab/bench testing of printing methods on the proposed label/packaging material is a good idea before the equipment and packaging components are committed to.
There are three primary types of systems used to print/mark barcodes and human-readable data – thermal transfer, inkjet and laser ablation/ marking. Thermal transfer operates on the principle of applying heat to an ink-laden ribbon which causes the transfer of the heated ink onto a substrate. The heat is applied to only the areas of ink on the ribbon that must be printed on the substrate to create the specified image and text. Thermal transfer is a very common method for printing on labels that are on a web. The web can be held firmly against the thermal transfer ribbon to achieve good transfer of the ink onto the label before the label is applied to a bottle. Thermal transfer systems have parts (print head, backing plate) and consumables (ribbon) that must be carefully maintained. A poorly maintained thermal transfer system could result in lighter print (resulting in lower contrast and/or modulation) or missing elements (failed decode, lower fixed pattern, and unused error correction grades).
Inkjet printers use a series of very small nozzles to spray drops of ink directly on the substrate. Inkjet is often used for printing directly onto cartons and labels. The nozzles must be kept clean and ink level must be monitored/maintained. The carton material should also be unvarnished to allow the ink to effectively dry and adhere to the substrate. Dirty nozzles could result in missing and/or incorrectly marked dots (failed decode, lower fixed pattern, error correction). Low ink could lead to missing or lightly printed elements potentially impacting parameters.
When printing directly onto a carton, it is important for the carton conveying/handling system to maintain positive control of the carton. This will minimize potential for skewed positioning and vibration that could cause an imprecisely shaped barcode (affecting grid/axial nonuniformity), wrongly positioned barcode (causing an inadequate quiet zone), or poorly defined elements.
Laser ablation is the process of removing a coated material from a surface by irradiating it with a laser beam. On pharmaceutical packaging materials, a section of the substrate is coated with a dark or light material that is “burned” off in the shape of the code and text to reveal the substrate below. The substrate color is the opposite of the coating color, creating the necessary contrast for the markings to be read. Laser marking is the process of irradiating a reactive layer of material, which changes color to create the required markings. These laser printing processes are very precise and do not consume any materials, and are applicable to labels and cartons. A large contrast in color between the coating material and underlying substrate is needed to get good grades for contrast and modulation using laser ablation. For laser marking, the color change of the substrate when irradiated must be sufficiently dark to contrast the lighter substrate. Quality of the substrate and proper handling/positioning of the package are again important.
In summary, the use of the 2D DataMatrix will increase dramatically with the advent of prescription drug anti-counterfeiting regulations throughout the world mandating a unique serial number on each saleable packaging unit and shipper label. Manufacturers and packagers will need to ensure that the barcodes used to carry critical product authentication data are precisely and accurately marked and verified. Good packaging and artwork design, properly selected and maintained printing systems, and an effective barcode verification process will all be needed to keep product moving safely and efficiently throughout the global supply chain.