CAPA Part 2: Linear Barcodes

You have a barcode problem.

A press is stopped, a customer is unhappy, a supply chain is broken…it’s an expensive, stressful nightmare. You need a solution—now.

Barcodes are Visual

Barcodes are visual images. Each image has a set of properties with tolerances. Those properties and tolerances are defined by international standards, established and maintained by the ISO.

Corrective actions for a non-working barcode are based on the applicable ISO standard for the barcode involved. ISO 15415 covers linear barcodes—parallel lines and spaces. ISO 15415 covers matrix or 2D barcodes.

Determining why a barcode is not working, or working poorly, is done with a verifier. The ISO standards enumerate a set of attributes and tolerances, each of which affects whether and how well a scanner can read and decode the barcode. Testing the performance of a barcode with a scanner is meaningless. Even though scanners are manufactured to comply with related ISO standards, scanners of different types, conditions and ages perform differently. Testing a barcode with a smartphone is even less informative since it uses a non-compliant light source and decode algorithm. Only an ISO compliant verifier can predict scanning success.

The key to determining corrective action is the verification report, since each ISO attribute is graded separately. Here is a sample linear barcode ISO 15416 verification report.

The red highlighted fields signal problems in this barcode. The upper left Summary window displays the final grade, an ISO 0.0 or ANSI F.

The Summary window also summarizes the state of this barcode. Average Bar Gain is 26%, and the tolerance is +27.9%. Printing used all and more of the plus-side bar width tolerance. That’s not good, and the right window tells you why.

The right window displays the individual attributes for this linear barcode, and the grade for each:

  • Symbol Contrast is a C. This attribute measures and evaluates the amount of reflectance difference between the barcode and the background. That’s not great but it’s acceptable.

When Symbol Contrast is downgraded, it’s because either the dark (RMin) value (bars) are not dark enough, or the light (RMax) background, which includes the quiet zones and spaces, is not light enough. Correct one or both reflectance values.

  • Edge Contrast is an A. That’s great. Edge Contrast grades the lowest (worst) difference in contrast between a dark element (bar) and the adjacent light element (space). Edge Contrast is a “worst case scenario” which is where a scanner is most likely to have a problem scanning it. If edge contrast is downgraded, find the problem area on the Scan Reflectance Profile and then look for it on the barcode image.
  • Modulation is a D. Modulation grades the uniformity of the two reflectance values. Remember, a barcode should only have two reflectance values: light and dark. Each should be uniform. When they are not, it confuses the scanner and downgrades the verification report.

Look for patterns in the RMax areas or unevenness in the bars. Look for and correct (eliminate) patterns in the RMax areas or unevenness in the bars.

  • Defects is a D. This attribute grades extraneous artifacts that can confuse the scanner; voids in bars, spots in spaces.Defects are caused by ink jet nozzle splatter, dirty or dusty substrate, particulate on impression rollers or other stray artifacts. Poor housekeeping is a common cause.
  • Decodability is a D. Decodability grades the dimensional accuracy of the placement and width of the bars and spaces.

Scanner expect bars and spaces to be a specific width and positioned accurately to each other. Excessive gain spreads bars and squeezes spaces, putting the centers and edges in unpredictable places. Design file resolution (DPI) must be compatible with printer resolution. When it is not, the printer interpolates the data, relocating bars and spaces and modifying widths.

  • Decode is a pass/fail attribute. Notice the Scan Reflectance Profile at the bottom of the report. The blue horizontal line is where the scanner decodes the barcode. Each transition through this line represents a bar and space. The scanner identifies the symbol type—in this case a UPC-A barcode—by counting the transitions and the width of the bars and spaces.

When a bar-to-space transition fails to cross the blue scan line, the count is thrown off and the scanner cannot decode the barcode. Excessive gain is a common cause of a decode failure.

Corrective Actions

Suggested corrections for each ISO attribute are italicized above.

Gain is not the only issue that can cause barcode problems, but it is the most common cause, and should always be the first thing to look for.

Your questions and comments are always welcome. Contact us here. You can schedule a free 15 minute consultation here.

Recommended Posts

3db Barcode Testimonial

Our company (an advanced software company) recently worked with Barcode Test to source a barcode verifier.  Not long ago, we were awarded a contract requiring products to be marked with IUIDs in accordance with MIL-STD-130.  For that standard, marking labels must pass a verification test that evaluates many variables (contrast, size, clarity, syntax, modularity, and more).  After a thorough search, we reduced our options to a select few.

In our search for a verifier, the Axicon line caught our attention.  Barcode Test is our regional reseller for this product.   From the beginning, they were very prompt with their responses.  We ended up having a quick call with John Nachtrieb to go over our needs.  John was extremely easy to work with and provided a lot of great information.  He was very knowledgeable on the matter and was quick to offer up a demo unit (free of charge).

Upon receiving the demo verifier and testing it, a few questions arose.  John joined a call with us and answered all our questions.  Ultimately, the Axicon verifier wasn’t the best fit for us, so we shipped the demo back.  John was completely understanding.  A few weeks later, Barcode Test reached back out with another possible verifier for us to try.  While they didn’t sell that brand, they just wanted to help us find the best option that met our needs. They even offered to send us the unit that they have in-house to see if it worked to our liking. 

Barcode Test is truly a great company to work with.  Their service and willingness to help the customer are far beyond what you typically get from other companies.  They are experts in barcode quality assurance and seem willing to help in any way they can (even if that means not getting a sale and recommending another option that better fits the customer’s needs).  If anyone is in the market for barcode verification/scanning services or products, I would highly recommend giving Barcode Test a call.

Regards,

Production Manager