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Industry Standards |
In DPM verification applications, the quality of Data Matrix marks
are typically verified to specifications set forth by the International
Standards Organization (ISO) and other recognized industry groups
such as SAE. There are three different areas addressed by ISO standards:
symbology, print quality and conformance testing specifications. Industry-specific
application specifications reference these ISO as well as other specifications
to guide users on how to mark and verify print quality of the mark
on a part. It is important to understand the three different areas
defined by ISO specifications, and how the various industry application
standards reference them as they are all targeted at accomplishing
something different.
Symbology specification – Defines what the code is, the code
structure, symbol formats, error correction rules, and decoding algorithm.
In the case of Data Matrix, the ISO specification is ISO 16022.
Print quality test specification – Defines the underlying quality
assessment metrics, methods and grading used to analyze code quality.
ISO defines “print” as any method to put a code on a substrate.
For Data Matrix, the ISO specification is ISO 15415. However, because
this standard was originally developed for codes marked on paper labels,
its usefulness has been limited in direct part mark 2D code applications.
Because a 2D print quality specification did not exist when ISO 16022
was created, this standard provided quality assessment metrics as
part of its appendix. These metrics are often referred to as “AIM”
metrics. SAE AS9132 Standard “Data Matrix Coding Quality Requirements
for Parts Marking” is an aerospace industry standard designed
to address the unique aspects of DPM relative to metallic parts.
Conformance specification – Defines the testing that a DPM verification
supplier needs to perform on its systems to ensure that results are
within a certain tolerance of the expected results of the ISO print
quality standard. For Data Matrix, the ISO specification is ISO 15426-2.
Because conformance is reliant on a fundamentally sound “print”
(i.e. mark) quality specification, a new print quality test specification
which is currently being developed by AIM must be completed before
conformance can be achieved.
Application standards – Application standards are industry-specific,
and define the symbol type that should be used in various industries
and the data content. Application standards also provide general guidance
on what is considered a “good” or “passing”
mark within various industry applications. For example, MIL-STD-130
defines code and quality requirements for marking parts supplied to
the U.S. Department of Defense. This standard defines Data Matrix
as the symbology, what data needs to be encoded, how the data should
be encoded, and the mark quality requirements. Similar application
standards and/or guidelines exist for other industries.
It is important to note that certain verification standards that exist
today for printed, high-contrast 2D marks are frequently not useful
in the verification of DPM 2D marks. Today, verifiers will provide
results based on the quality assessment metrics defined in the following
three standards and specifications:
- The SAE AS9132 standard defines metrics for
dot peen, laser, and electrochemical etch marking methods for metallic
parts. In the case of dot peen, the standard calls for measurements
of dot size, dot position, and dot ovality to indicate whether a
mark is acceptable or unacceptable. AS9132 provides guidelines for
first article inspection performed by an inspector with magnification
aids, and subsequent process monitoring as defined by a quality
assurance plan. AS9132 measurements can alternatively be performed
using electro-optical devices.
- ISO 16022 “International Symbology Specification
– Data Matrix” – This is the international symbology
specification for Data Matrix. Reference verification criteria are
provided for measuring symbol contrast, print growth, axial non-uniformity,
and unused error correction. Marks are graded using an A-F scale
where A is excellent and F is fail.
- ISO 15415 “Bar code print test specification”
– This specification provides print quality test specification
for 2D symbols, including Data Matrix. ISO 15415 encompasses a subset
of the metrics defined by the ISO 16022 such as symbol contrast,
unused error correction and axial non-uniformity, with the addition
of metrics for modulation, grid non-uniformity, and fixed
pattern damage.
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