Inline Barcode Verifier Systems: Validating Test Results

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Recently I ran across an excellent article* about Measurement Systems Analysis. The opening paragraph caught my attention:

“Despite a persistent and incremental march toward automation, people are still necessary for much of manufacturing…..Understanding variation is important whether the process is manual, automated, or…..an amalgam of the two,” writes the article author, Jon Quigley, President and Co-founder of Value Transformation LLC, a North Carolina consultancy focused on product development and cost improvement. I contacted Mr. Quigley, asking him to help me understand  if and how standard measurement validation methods could apply to inline barcode verification systems.

While inline barcode verification is not exactly manufacturing, inline systems claim to be “verification”, and emphasize claimed advantages of automation, but people are a necessary part of making it work. Automatically shunting non-compliant barcodes to a rework area is not a total solution. People are still involved in solving problems.

Gauge Repeatability and Reproducibility (Gauge R & R) are a common technique for Measurement Systems Analysis (MSA), and relies upon identifying common cause and special cause variation in the process. Consider inline barcode verification as the process.

Gauge repeatability and reproducibility

Jon Quigley

“Common cause variation is predictable variation associated with the material, product and processes,” states Quigley.

Predictable, common cause variations in an inline barcode verifier system include:

  • Conveyor speed
  • Distance from scanner to barcode
  • Barcode orientation
  • symbology
  • X dimension
  • wide/narrow ratio
  • Bumps or vibrations in conveyor transport system

…and barcode imaging faults if print and apply are included in the conveyor system.

 

Unpredictable, special cause variations include:

  • Barcode substrate variations
  • Ambient light variations
  • Line voltage variations which could affect system light values, strobe timing, loss of system or scanner configuration settings
  • Scanner positioning due to change out, accidental contact

Additionally, there are other factors, which are neither predictable nor unpredictable. We classify them as unknown. For example, a super aggressive scanner that incorrectly interpolates data from a damaged or inherently poor quality barcode. Is that a predictable variation? It is probably an unpredictable variation, but because it apparently scanned the barcode successfully, the system reported no variation.

Misreads by overly aggressive scanners are unreported special cause variation

Repeatability measures whether the same person will get the same result from the same gauge. Reproducibility measures whether different people obtain the same results with the same gauge. Repeatability and reproducibility do not really apply to inline systems, although inline systems purport to measure and report statistical process control metrics that are inherently stable. Are they correct? Testing accuracy does not magically appear just because the data file is huge.

If Gauge R & R does not apply to inline barcode verification systems, how can such systems be validated?

Consider the common cause variations in an offline barcode verification:

  • Out of date calibration
  • Out of date ISO certification

Calibration and certification data is easily tracked in the offline verifier software.

Unpredictable, special cause variations include:

  • Verification device damage. We cannot think of any others, can you?

User reflectance recalibration and ISO recertification reliably re-establishes offline verifier accuracy. No such recalibration or re-certification protocols exist for any inline verifier systems. Why? Because they are not ISO compliant: calibration would be meaningless–there is no standard against which to re-certify.

No calibration or re-certification protocols exist for inline verifiers because they are inherently non-compliant

Offline verifiers are highly accurate, and produce highly repeatable and reproducible results. Gauge R & R techniques authoritatively establish the repeatability and reproducibility of ISO compliant offline verification tools.  An offline verifier provides the essential tool for validating inline verifiers.

Routinely validate inline barcode verification systems using an ISO compliant offline barcode verifier

*See the article here.

#barcode #barcode verifier #inline verifier #barcode quality

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