Siemens SIMATIC MV500 - 3.2.3 Verification methods for different application scenarios; 3.2.3.1 Verification of printed labels; 3.2.3.2 Verification of direct part marks

Image processing
3.2 Code verification
SIMATIC MV500
Operating Instructions, 03/2021, C79000-G8976-C494-05
47
Example
The reader is aligned at an angle to the surface of the marked object which distorts the
marking in the image acquisition. The quality feature "Axial non-uniformity" is therefore
generally evaluated with a quality grade 1, which means the quality of the entire marking can
never be better than 1. If compliance with an ISO standard is not required, however, "Axial
non-uniformity" can be removed from the evaluation to make a meaningful statement about
the marking quality using the remaining quality features.
3.2.3 Verification methods for different application scenarios
3.2.3.1 Verification of printed labels
In 1996, the "Association for Automatic Identification and Mobility" (AIM) published the data
matrix symbology specification with an evaluation procedure for print quality. According to
this evaluation procedure, test systems could evaluate a symbol according to its degree of
acceptability (4 to 0).
The specification later became the ISO/IEC 16022 standard. This type of test was developed
for paper labels with high contrast.
It allows a quantitative measurement of the print quality and allows the testing of printed 2D
codes based on a quality standard. Here, the important fact is that the printing of a data
matrix code on paper is a high-quality process.
White paper is printed with black ink to achieve a high contrast. With this background, the
threshold values for grading in the ISO/IEC 16022 standard are very restrictive because the
marking quality is so high.
Less exacting requirements are neither suitable nor useful in the printing industry. The AIM
standard identifies the following typical errors:
• Blocked ink jets
• Too much or too little ink
• Inconsistent application of the ink
• Inadequate contrast due to a combination of ink color and background color
3.2.3.2 Verification of direct part marks
Test procedure
In contrast to printed labels, most workpieces are not optimized for marking but rather for
their primary purpose. It is, for example, more difficult to apply a laser marking to bare
aluminum than to stainless steel. Aluminum is, however, more suitable in the production of
parts for aircraft because it is lighter. The weight is therefore more important than
markability. A test object with a marking on aluminum does not normally pass the test
according to the ISO/IEC 16022 standard due to the low degree of contrast.