Application_verification_standards_revB Wp Application Verification Standards

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Application of Data Matrix

Verifi cation Standards

Overview of Data Matrix Quality Standards

and Measured Parameters

Technology White Paper

Technology White Paper

ISO/IEC 16022

The Data Matrix symbology was invented by International Data

Matrix, Inc. The Association for Automatic Identi cation and Mo-

bility (AIM) promulgated the Data Matrix as a public standard in

1996 as “International Symbology Speci cation – Data Matrix.”

This standard was then adopted by ISO as standard ISO/IEC

16022 in May of 2000. The second revision of ISO/IEC 16022

was released in September of 2006. ISO/IEC 16022 Appendix

N contains the  rst public standard for measurement of Data

Matrix symbols. This standard includes measurement of the fol-

lowing parameters:

• Reference Decode

• Symbol Contrast

• Print Growth

• Axial Non-Uniformity

• Unused Error Correction

The lowest of the grades for the above parameters becomes the

overall grade for the Data Matrix, and then the parameters are

combined. The limitations of this standard are its over-reliance

on contrast with regard to the overall quality of a symbol. This

is because the standard is modeled after a guideline for linear

(1D) symbols.

This standard has some application for symbols produced using

black ink on white paper. However, very few marks of this type

are used in the MIL-STD-130 application. The  rst version of

MIL-STD-130 to include veri cation was MIL-STD-130L (October

10, 2003) which stated that marks must be graded as no less

than “B” when generated and no less than “C” through the life

of the mark, by the standards of ISO/IEC 16022.

Lighting requirements for ISO/IEC 16022 veri cation are not

speci ed aside from the need for uniformity across the  eld of

view. However, the standard recommends lighting from two or

more sides at a 45° angle of incidence.

SAE AS9132

The Society of Automotive Engineers (SAE)  rst published

Aerospace Standard (AS)9132 in 2002. This standard differs

from other standards in two signi cant respects. AS9132 cov-

ers three speci c marking methods: dot peen, laser etch, and

electro-chemical etch. Also, AS9132 is a pass or fail standard

that does not lend itself to process control, as there are no in-

termediate steps between success and failure. The parameters

measured by AS9132 are:

Dot Peening

• Cell Fill

• Cell Size

• Dot Size Offset

• Dot Center Offset

• Angle of Distortion

• Dot Ovality

• Matrix Size

Laser and Electro-Chemical Etching

• Cell Fill

• Contrast

• Angle of Distortion

• Matrix Size

• Cell Size

If any one of the measured parameters for a mark fail then the

overall grade for that mark is a failure. There are no lighting or

imaging requirements stated in the AS9132 standard.

ISO/IEC 15415

The  rst ISO/IEC standard designed to address Data Matrix

veri cation was ISO/IEC 15415 (June, 2004). This standard

attempted to correct the insuf ciencies of the previous stan-

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Application of Data Matrix Verifi cation Standards

Data Matrix symbol verifi cation at its most basic level eliminates the subjective quality determination that causes discord between marking

and reading suppliers, and replaces those subjective opinions with objective measurements regarding the quality of the mark. Standards for

verifi cation take this process further to allow an even fi eld of play for all measurement systems, such that cross-company and cross-industry

applications may use an adopted standard to ensure the readability of symbols through their processes by setting limits based upon agreed

standards. Topics of this white paper include:

- An introduction of the following standards:

ISO/IEC 16022

SAE AS9132

ISO/IEC 15415

AIM DPM-1-2006

ISO/IEC 15434 and ISO/IEC 15418

- Parameters measured by each standard

- Examples of standard application, especially regarding the United States Department of Defense Item Unique Identifi cation

initiative MIL-STD-130.

Steve Twaddle, Microscan Systems, Inc.

Technology White Paper

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dards by addressing the components of direct part marking. The

parameters measured by ISO/IEC 15415 are:

• Symbol Contrast

• Axial Non-Uniformity

• Grid Non-Uniformity

• Unused Error Correction

• Fixed Pattern Damage

• Modulation

• Reference Decode

• Print Growth (may be reported but is not included as a

grade component)

ISO/IEC 15415 speci es that the veri cation report must in-

clude the following information, with each element separated by

a forward-slash character:

• Grade (Arithmetic mean to one decimal place of the grades

measured from all images)

• Aperture (Diameter of the arti cial aperture to the nearest

thousandth of an inch)

• Light (Wavelength in nanometers)

• Angle (Assumed to be 45° and only reported if different

than 45°)

One of the requirements of ISO/IEC 15415 is capturing  ve

images each taken at 72° (± 5°) from each other, such that the

symbol is measured at  ve orientations through one complete

rotation. Another limitation of ISO/IEC 15415 is its over-sen-

sitivity to minute changes in grayscale across the symbol and

quiet zone, resulting in failing grades for modulation and  xed

pattern damage on many easy-to-read parts.

AIM DPM-1-2006

The AIM Direct Part Mark Quality Guideline was released in

December 2006. The basic differences between ISO/IEC 15415

and AIM DPM-1-2006 are enumerated in Sections 5.1 and 5.2

of the guideline as follows:

5.1 Process Differences from ISO/IEC 15415

All parameters in the symbology and print quality speci cations

apply except for:

• A different method for setting the image contrast.

• A different method for creating the binary image.

• A new method for choosing the aperture size.

• An image pre-process methodology for joining disconnected

modules in a symbol.

• A different process for determining the Modulation param-

eter renamed Cell Modulation.

• A different process for determining the Symbol Contrast

parameter which has been renamed Cell Contrast.

• A different process for computing Fixed Pattern Damage.

• A new parameter called Minimum Re ectance.

This guideline explains how to specify and report quality grades

in a manner complementary to, yet distinct from, the method in

ISO/IEC 15415.

5.2 Lighting

This guideline recommends three speci c lighting environments

consisting of two forms of diffuse (non-directional) lighting:

• Diffuse on-axis illumination uses a diffuse light source illu-

minating the symbol approximately perpendicular to its sur-

face (nominally parallel to the optical axis of the camera).

• Diffuse off-axis illumination uses light from an array of LEDs

re ected from the inside of a diffusely re ecting surface of

a hemisphere, with the symbol at its center, to provide even

incident illumination from all directions.

• Directional illumination is oriented at a low angle (approxi-

mately 30 degrees) to the mark surface.

The parameters measured by AIM DPM-1-2006 are:

• Cell Contrast

• Axial Non-Uniformity

• Grid Non-Uniformity

• Unused Error Correction

• Fixed Pattern Damage

• Cell Modulation

• Reference Decode

• Minimum Re ectance

As with other standards, the overall grade is the lowest of any of

the sub-grades. Highlights of the physical setup for AIM DPM-1-

2006 are:

• The image sensor plane must be parallel to the surface of

the part although no tolerance is speci ed for the

parallelism.

• The symbol must be oriented such that one edge is parallel

to the side of the image sensor (±5°).

• A speci c set of lights must be used for this veri cation

type: 90° (90), dome (D), 30° from four directions (30Q),

30° from two directions (30T) and 30° from one direction

(30S).

• The image must be in the best possible focus, but there is

no stated focus tolerance.

ISO/IEC 15434 and ISO/IEC 15418

These standards concern the syntax and semantics (formatting)

of the string for Data Matrix symbols used in the IUID program

as speci ed by the MIL-STD-130. The string must start with the

characters “[)>” followed by a Record Separator (ASCII decimal

30) and ends with the Record Separator and the End of Trans-

mission (ASCII decimal 4). The string may be formatted using

one of three formats:

• Application Identi ers (AI)

• Data Identi ers (DI)

• Text Element Identi ers (TEI)

All data elements in the string include a data quali er specify-

ing what type of information follows, and the Group Separator

(ASCII decimal 29) separates individual elements. Unique Item

Identi er (UII) strings using the AI or DI format may use a macro

that replaces the leading “[)>R

S05G

S” or “[)>R

S06G

S” and trailing

“R

S

E

OT” with a single byte, thus saving data capacity in the Data

Matrix symbol.

Technology White Paper

Application of Verifi cation Standards in MIL-STD-130

During the various releases of the MIL-STD-130, the de nition of acceptable Data Matrix marking quality has gone through several

stages, and has used parts of each of the standards mentioned earlier in this document. The table below describes the standards

referenced in MIL-STD-130 and how they are applied.

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Parameters Used in Verifi cation

Below is a brief description of the parameters used in measur-

ing Data Matrix symbols. Many of these measurements use the

concept of the “ideal grid.” This is the equally spaced array of

line segments formed by using the four corners and dividing

the entire Data Matrix by the number of rows horizontally and

columns vertically.

Angle of Distortion – The difference from perpendicular of the

two solid edges of the Data Matrix, measured in degrees.

Axial Non-Uniformity – The difference between the height and

the width with respect to the rows and columns.

Cell Contrast – In AIM DPM-1-2006, the difference in the

population of dark pixels to the population of light pixels (see

histogram) using the sample principle as “Symbol Contrast”

with modi ed de nition.

Cell Size – The overall width divided by the number of columns

or the overall height divided by the number of rows.

Cell Modulation – In AIM DPM-1-2006, a measurement of the

uniformity of the color of the dark areas and the light areas of

the Data Matrix (see histogram) similar to “Modulation” but dif-

fering in implementation.

Dot Center Offset – The linear difference of the location of the

center of the cell compared to the center of the ideal grid center

calculated as a percentage of the nominal cell size.

Dot Size Offset – The difference in the apparent size of each

individual data element in the Data Matrix.

Fixed Pattern Damage – A measurement of the errors in the

borders of the Data Matrix as well as any errors in the quiet

zone around the symbol necessary for the decoding process.

Grid Non-Uniformity – The difference of the measured grid in

relation to the ideal grid formed from the four corners of the

Data Matrix.

Matrix Size – The overall size of the symbol as measured lin-

early across the width or height.

Minimum Refl ectance – Lowest re ectance of any sample area

in the Data Matrix.

Modulation – In ISO/IEC 15415, a measurement of the unifor-

mity of the color of the dark areas and the light areas of the

Data Matrix (see histogram) similar to “Cell Modulation” but

differing in implementation.

Module Fill – The percentage of completeness of the ideal grid.

Nominal Module Size – The scalable X-dimension of a typical

symbol cell.

Dot Ovality – The difference of the widest part of a round cell

versus the narrowest part of the cell.

1. Exceptions to ISO/IEC 15415 in MIL-STD-130:

• No rotational averaging

• Contrast and Modulation grades allowed to be as low as “C”

• 660nm lighting requirement

2. Exceptions to AIM DPM-1-2006 in MIL-STD-130:

• Dome light not allowed

• Quad-directional 45° medium-angle light from ISO/IEC

15415 allowed

• Only applies to direct part marks – not labels

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Print Growth – The positive or negative size relation of the cells

as printed with respect to the ideal grid.

Reference Decode – This is a pass/fail measurement of the

Data Matrix based upon a binary image of the symbol as speci-

 ed in ISO/IEC 16022 (First edition – 2000, Second edition –

2006).

Symbol Contrast – The difference in the population of dark

pixels to the population of light pixels (see histogram) similar to

AIM DPM-1-2006 “Cell Contrast”.

Unused Error Correction – The amount of error correction that

can be read incorrectly when the symbol is still readable that is

currently being read correctly, expressed as a percentage.

Histogram showing pixel color populations for a bimodal distribution typically found in the Data Matrix symbology.

Technology White Paper

Verifi cation Parameters vs. Standards

5

Standard Date

ISO/IEC 16022 May 2000

ISO/IEC 15415 June 2004

AS9132 Laser Etch Feb. 2002

AS9132 Dot Peen Feb. 2002

AS9132 Electrochem Etch Feb. 2002

AIM DPM-1-2006 Dec. 2006

Applicability MIL-STD-130

Labels 130L

All 130L Chg.1/130M

Laser DPM 130L Chg.1/130M

Dot DPM 130L Chg.1/130M

EC Etch DPM 130L Chg.1/130M

DPM 130M Chg.1/130N

©2012 Microscan Systems, Inc. 06/12

www.microscan.com

North America (Corporate Headquarters)

Email: info@microscan.com

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Email: emea@microscan.com

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