Barcode Verification Reliability
Wednesday, February 27, 2008
Posted in: Barcodes
Gage R & R in Barcode Verification
Whether or not you’ve thought about it, a barcode verifier is a gage. And like any gage, reliability is everything. How is gage reliability assured? In the world of statistical process control (SPC), ISO9000 and Six Sigma, Gage Repeatability and Reproducibility (GR&R) is a method for measuring process variation.
Apologies to those whose belief about barcode verification is “we’ve never had a problem so we don’t need to do anything.” But I can’t honestly say that I hope you are right—because you are wrong. Even if your process is very well controlled, if you don’t measure, you don’t even know how good your process is. And you can’t measure without calibrated gages.
ISO conformance is the test for barcode verifier repeatability and reproducibility. A manufacturer of an ISO-compliant verifier must demonstrate that their instrument meets ISO/IEC 15426-01 specifications for the particular type of barcode that unit tests: for example, Linear Symbols.
The thing about conformance to specification is, there is a third factor that is implied but not explicitly addressed. That third factor is time. Time is the dimension over which change takes place. In the case of an opto-electronic instrument such as a barcode verifier, the change factor itself has at least two dimensions: rate and degree. Poorly designed instruments, or beautifully designed instruments made with poor quality components often exhibit electronic instability that can be to a high degree over relatively short spans of time. The environment in which the instrument is used, or how it is used can also affect instrument stability. Rough handling or haphazard storage during nonuse intervals can also accelerate instrument instability.
Repeatability and reproducibility of results are also a function of how the instrument is used. For example, wand-based barcode verifiers reply on the human operator to move the input device over the symbol. A highly complex and sophisticated timing algorithm extracts bar/space width measurements from the movement of the wand by a human operator. Even the most experienced user cannot move a wand over a barcode at a perfectly steady speed. R & R are compromised, even in a calibrated, compliant instrument. Add to this the additional factors of ambient light and possibly wand angle, and test results are even more un-repeatable and un-reproducible.
These factors are eliminated with the very advanced Quick Check 890 from Honeywell Imaging and Mobility. Wand movement and potential variations are eliminated by the automatic scan path: the QC890 has no moving parts. Scan angle is fixed within the housing, which also eliminates any influence from ambient light. Even test aperture is automatically configured. The QC890 virtually eliminates operator-induced variations in symbol grading. Annual calibration and re-certification closes the loop on R & R.
