Data Matrix

A Data Matrix code is a two-dimensional matrix barcode consisting of black and white square modules arranged in either a square or rectangular pattern. The information to be encoded can be text or raw data. Usual data size is from a few bytes up to 2 kilobytes. The length of the encoded data depends on the symbol dimension used. Error correction codes are added to increase symbol strength: even if they are partially damaged, they can still be read. A Data Matrix symbol can store up to 2,335 alphanumeric characters.

Data Matrix symbols are square and made of cells, that is little squares that represent bits. Depending on the situation a white module is a 0 and a black module is a 1, or vice versa. Every Data Matrix is composed of at least two finder patterns or handles and two syncs. Handles are two perpendicular lines, coloured the same way as 1 modules, while syncs are like handles with the difference that they are made of alternating black and white modules. Handles achieve a good alignment with the symbol, while syncs sample modules correctly. If the matrix dimension grows, more syncs and handles are added up to 8 both horizontally and vertically. Symbol sizes vary from 8×8 to 144×144.

Applications

File:Matrix-36.PNG

Four symbols

The most popular application for Data Matrix is marking small items, due to the code’s ability to encode fifty characters in a symbol that is readable at 2 or 3 mm² and the fact that the code can be read with only a 20% contrast ratio.

The Electronic Industries Alliance (EIA) recommends using Data Matrix for labeling small electronic components^[1].

Data Matrix codes are part of a new traceability drive in many industries, particularly aerospace where quality control is tight and a black market exists for counterfeit or non-servicable parts. Data Matrix codes (and accompanying alpha-numeric data) identify details of the component, including manufacturer ID, part number and a unique serial number. The United States Department of Defense aims to have all components of every new aircraft identified by Data Matrix codes within a tight deadline.^{[citation needed]}

Technical Specifications

Data Matrix symbols are made up of square modules arranged within a perimeter finder pattern. It can encode up to 3,116 characters from the entire ASCII character set (with extensions). The symbol consists of data regions which contain square modules set out in a regular array. Large symbols contain several regions. Each data region is delimited by a finder pattern, and this is surrounded on all four sides by a quiet zone border (margin).

Symbols have an even number of rows and an even number of columns. Most of the symbols are square with sizes from 10×10 to 144×144. Some symbols however are rectangular with sizes from 8×18 to 16×48. All symbols can be recognized by the upper right corner module being light (binary 0).

ECC200 is the newest version of Data Matrix and supports advanced encoding error checking and correction algorithms (such as Reed-Solomon). This algorithm allows the recognition of barcodes that are up to 60% damaged.

Data Matrix applications

A data matrix on a Mini PCI card, encoding the serial number

Data Matrix codes are becoming common on printed media such as labels and letters. The code can be read quickly by a scanner which allows the media to be tracked, for example when a parcel has been dispatched to the recipient.

For industrial engineering purposes, Data Matrix codes can be marked directly onto components, ensuring that only the intended component is identified with the Data Matrix encoded data. The codes can be marked onto components with various methods, but within the aerospace industry these are commonly industrial ink-jet, dot-pen marking, laser marking, and electrolytic chemical etching (ECE). These methods give a permanent mark which should last the lifetime of the component.

After creation of the Data Matrix code, the code is usually verified using specialist camera equipment and software. This verification ensures the code conforms to the relevant standards, and ensures it will be readable for the lifetime of the component. After the component enters service, the Data Matrix code can then be read by a reader camera, which decodes the Data Matrix data which can then be used for a number of purposes, such as movement tracking or inventory stock checks.

Standards

Data Matrix was invented by RVSI/Acuity CiMatrix [1], who was acquired by Siemens AG in October, 2005. Datamatrix is covered today by an ISO standard, ISO/IEC16022—International Symbology Specification, Data Matrix, and is in the public domain, which means it can be used free of any licensing or royalties.

ISO/IEC 15418:1999 – Symbol Data Format Semantics
ISO/IEC 15434:1999 – Symbol Data Format Syntax
ISO/IEC 15415 – 2-D Print Quality Standard

How it Works

Although this is a free standard, there are no free documents that explain the encoding process. For C coders, there is example code .

Patent Issues

Acacia Technologies claims that Data Matrix is at least partially covered by their US patent 5,612,524. This claim is being challenged in the United States District Court for the District of Minnesota.^[2]

From Cognex, the company leading the fight against Acacia:

"Cognex has investigated the '524 patent, and has determined that the assertions being made by Acacia with respect to this patent, are completely without basis." [2]

Patent US patent 5,612,524 expired in November 2007, and so current usage is unencumbered by it, though previous usage in the event the patent was upheld would still be covered.

A German Patent Application DE 4107020 was filed in 1991, and published in 1992. This patent is not cited in the above US patent applications and might invalidate them.

External links

References

^ Stevenson, Rick (December 2005). "Laser Marking Matrix Codes on PCBs" (PDF). Printed Circuit Design and Manufacture. Retrieved 2007-05-31.
^ Kirby, Jason. Patent troll or producer? National Post at canada.com. Published on January 14, 2006. Retrieved on April 21, 2007.

[Stevenson-1] Stevenson, Rick (December 2005). "Laser Marking Matrix Codes on PCBs" (PDF). Printed Circuit Design and Manufacture. Retrieved 2007-05-31.

[fp_acacia-2] Kirby, Jason. Patent troll or producer? National Post at canada.com. Published on January 14, 2006. Retrieved on April 21, 2007.

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