Verification

 

Since bar code print quality is rarely obvious to the human eye, checking the quality of the printed symbol against bar code standards is a critical step that ensures good scannability.  Failing to verify bar code symbols frequently results in unscannable bar codes that reduce the efficiency of data exchange between customer and supplier. A visual inspection of the label is also important.  The bar code labels on packaging are a reflection of the company shipping the material, so check for errors like misspelled words, incorrect formats, and poor alignment of the symbols and text.

There are many parameters of a bar code that contribute to successful scanning. These include:

• Print contrast - the difference in reflectance between the white spaces and the black bars. The greater the difference, the better the bar code.
• Bar width measurements and ratios - the relationships between the wide elements (bars or spaces) and narrow the narrow elements must be maintained according to the symbology specification.
• Elimination of defects - spots and voids in the symbol.
• Decodability - the ease with which a scanner can decode the symbol.

In addition, 2D verifiers look at the parameter of unused error correction.  It should be remembered that 2D symbologies have complex data formats which must be checked for compliance.

Verifier Selection

Consider the following when selecting a verifier:

• Verifiers, depending on price, have different features.
  • If you are printing symbols then you need more information about the bar code than if you are just receiving the bar codes and checking them for compliance.
• Verifiers require different aperture diameters (focusing elements) depending on the X-dimension of the symbol being tested and different illumination wavelengths.
  • Ensure that the verifier you purchase works with all of the symbols you need to test.
  • For accurate results, verifiers must analyze the bar code using the same illumination wavelength as the reading device.
• Choose a verifier that supports your application standard.
  • If you need to support more than one application standard, can additional label application standards be programmed into your verifier?
• Ensure that your verifier's results are repeatable.
  • Does it have some type of calibration tool?
  • Is there a set of calibration symbols to validate accuracy?
• The verifier should comply with the ANSI X3.182 "Guideline for Bar Code Print Quality."

Most industry-specific bar code applicationstandards and guidelines require conformance to the "ANSI Bar Code Print Quality Guideline" (X3.182). Even if you are not following a specific application standard, the ANSI X3.182  is recommended for accurate verification results. The ANSI print quality parameters are based on bar and space reflectance values, ratios, defects, and decodability, and provide a letter grade of A, B,C,D, or F. You can order a copy of the ANSI guidelines at www.ansi.org.

Ongoing Verification Process

A consistent verification process is necessary to ensure continuous bar code print quality. In many cases it is not possible to verify every bar code printed or received. Therefore, this process should conform to standard statistical practices based on knowledge learned and applied during early analysis of symbol quality.  In the early stages of a verification program, bar codes should be verified as often as possible during each print run. With the experience gained from the verification results, the bar code analysis can be limited to the beginning, middle, and end of each print run. Bar codes should always be verified after changing the ribbon, toner or ink; when label stock is changed; and after maintenance is performed on the printing equipment.