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The Best Standard for Grading Dot Peen Codes

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Dot peen codes are generated using a marking pin to stamp a series of closely spaced dots to add numbers, text, or data matrix symbols directly onto a part. Monitoring the quality of symbols marked by dot peen is crucial to ensure that pin, pressure, and speed remain consistent in creating readable codes.

However, selecting the right standard to grade dot peen code quality is not always easy. Many manufacturers that make components requiring barcodes often opt for AS9132, which is only used on data matrix symbols that are directly marked onto parts with dot peening. However, AS9132 along with several other standards, don’t always get the job done.

In this post, we’ll break down the various barcode grading standard options, why certain standards aren’t suitable for dot peen, and why ISO 29158 is usually the smartest choice.

Choosing the Right Standard to Grade Dot Peen Code Quality

What is AS9132?

AS9132 (2002) was developed by the Society of Automotive Engineers (SAE) and is an aerospace standard (AS). It specifies print quality and technical parameters for data matrix symbols that are direct part marked (DPM)specifically dot peen marked. Those parameters are:

  1. Quiet Zone: an unmarked perimeter of at least one element wide

  2. Symbol Contrast: the reflective difference of light and dark areas

  3. Cell Size: cells must be within 60-105% of the x-dimension

  4. Dot Center Offset: element placement error or inaccuracy

  5. Dot Ovality: degree of non-roundness

  6. Angle of Distortion: an early version of Grid non-uniformity

 

Even though the AS9132 standard checks for many dot peen specific parameters, it’s not always the best solution when it comes to grading your dot peen marking applications.

 

Why should AS9132 not be used to grade dot peen code quality?

 

  • There is no defined method for calculating metrics, whereas 15415 and AIM DPM specify that an image should be captured and analyzed. Instead, AS9132 only checks the shape of the dots markednot the symbol as a whole, which includes the unmarked background or substrate.

  • While AS9132 is a better tool for monitoring or calibrating the marking settings and needle quality, it’s not suitable for assessing the readability of the code.

  • The standard reference decode algorithm is not used to determine decodability, which causes inconsistent results between implementations of AS9132 grading.

  • AS9132 does not specify lighting angle, which is another cause of implementation inconsistency, so results from one manufacturer to another can be inconsistent.

  • The 105% size limit is too stringent for laser etched codes.

  • AS9132 does not test for other important quality attributes, such as fixed pattern damage and modulation.

Dot peen code quality can also be graded using one of the ISO standards for barcode verification.

Dot peen codes

ISO Standards for Barcode Verification

When grading barcodes, there are numerous ISO certification standards you can use and each one solves varied application challenges. The information on different standards below will help you choose the best inspection method for your barcode grading needs.

ISO 16022 

  • ISO 16022 (2006) only defines the creation of the data matrix code, print or marking method, and code structure and decode algorithms.

  • Prior to the existence of 15415, 16022 specified a limited set of quality parameters.

  • ISO 16022 is not intended to be a verification specification that determines quality, in fact, 10622 now references 15415 for quality.

ISO 15415

  • ISO 15415 (2011) expands upon ISO 16022 by adding modulation, Grid Non-uniformity and fixed pattern damage grading parameters.

  • ISO 15415 does not accommodate codes created from dots.

  • ISO 15415 originally required a 5-scan average to produce a grade; ISO 15415 (2016) corrects this. 

  • ISO 15415 assumes the symbol is always marked on a diffusely reflective surface (non-shiny) and does not account for the variety of surface substrates DPM codes are often found on.

  • The only permitted lighting angle is 45-degrees, which does not accommodate the numerous marking methods, materials, and non-white reflectance conditions often used.

Why is ISO 29158 the best option?

  • ISO 29158 is based on the ISO 15415 standard but has been altered to accommodate the challenges of obtaining an ideal image of a code printed on substrates other than flat white paper (diffuse reflection vs. specular reflection).

  • ISO 29158 actively inspects acceptable lighting position angles as well as varying the type of lighting have been added. The standard allows 30, 45, 90, and dome lighting angles from 1, 2, or 4 sides.

  • The algorithms have been adjusted to calculate modulation values differently, so the reflectance levels are attainable with darker, textured, or reflective backgrounds.

  • Camera settings are modified to capture a brighter or optimized image exposure.

  • ISO 29158 checks a crucial set of quality parameters, which provide feedback to better estimate readability. Those quality parameters include:

  • Cell contrast (CC): The difference in reflectivity between the brightest module and the darkest module.

  • Cell modulation (CM):This is a grade based on the amount of variability in reflectivity of the modules.

  • Distributed Damage (DD): This parameter takes into account the effect of multiple segments of the fixed pattern having imperfections.

  • Minimum Reflectance (MR):Checks that the darkness of the dark modules is sufficient.

  • Axial Non-Uniformity (ANU):Tests for uneven scaling of the symbol.

  • Grid Non-uniformity (GNU):Identifies when module grid alignment is not centered based on the calculated grid.

  • Decode (DEC):Reports whether the 2D Symbol was decoded in accordance with the reference decode algorithm with the specified aperture.

Ultimately, the choice of which standard to use may come down to what is written in the application standard each company is asked to follow. Companies that have the power to switch to the ISO 29158 standard for dot peen codes will find their quality monitoring to be more detailed and easier to manage. For this reason, along with its many quality parameter checks, the ISO 29158 standard is often the best method for reliable dot peen code grading needs. 

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