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Feature Articles

2D Symbol Readers in Manufacturing Industries. . . .by Nello Zuech, President, Vision Systems International, Consultancy

by Nello Zuech, Contributing Editor - AIA

Machine vision is now firmly entrenched as the approach for reading most 2D symbols. In this country three different 2D symbols have emerged as de facto standards. PDF-417, a stacked 1D code widely used for paper trail traceability in shipping and receiving applications. A rastering laser scanner best reads it. Maxicode looks like a honeycomb with a bull’s eye target in the middle and is widely used in parcel sortation applications. A machine vision-based scanner best reads it. Data Matrix is a checkerboard-like code and most widely adopted by manufacturing industries. Again, a machine vision-based scanner best reads it. In Japan one will find that the QR code is popular. This symbol has locator patterns in three corners and is also best read by machine vision-based system. All of these 2D symbol readers come in fixed mounted or hand held versions. This list is not meant to be a comprehensive list of all 2D symbols, just those most popular in this country.

In addition to smaller footprint and higher data density, 2D codes enjoy other advantages: they have no orientation restrictions and few contrast limitations. They can be applied many different ways and have a rigorous form of error correction. Many also have redundancy built into the code making it possible to read codes that have been partially obliterated. They are also reasonably tolerant of distortions.

Industrial applications are driving 2D code adoption. Fundamentally, 2D code readers are data acquisition systems and lend themselves to integration into management information systems that optimize manufacturing productivity and quality. They are being used for process error-proofing, work-in-progress monitoring and for post-production tracing. A standardized format for marking components too small for conventional bar codes is critical for telecommunications, automotive, semiconductor, and other electronic manufacturers especially where unit traceability of parts is required. These industries have established space-constrained marking standards based on two-dimensional (2D) symbology.  Small product marking is also critical to the medical device and pharmaceutical industries. In this case, the Uniform Code Council (UCC) has developed a multi-industry standard.

A major driver for the adoption of Data Matrix code readers has been part traceability. Because the Data Matrix code can be printed as individual squares or dots it can be directly etched, stamped, ink jet printed, laser scribed or peened onto metal, plastic and other materials. Direct part marking is becoming widespread as the means of tracing parts since many parts do not lend themselves to label attachment. The Data Matrix code is favored because it does not take up much space and, therefore, does not impact the functionality, integrity or the aesthetics of a part.

Two-dimensional bar code readers or matrix code readers typically incorporate features associated with machine vision applications: find routines to locate the code, enhancement routines to sharpen markings, and analysis routines to decode and read the code. While hand-held readers exist for reading matrix codes, the matrix code reader often is designed for overhead reading at a fixed location.

The matrix code readers are essentially machine vision systems and/or application-specific smart cameras. These systems integrate the CCD area imager, image processing hardware/software for image enhancement, ‘‘find’‘ and de-coding, as well as the necessary lighting and optics into a single package. Machine vision-based 2D symbol readers typically use an area imager to take a picture of the entire symbol. Typical machine vision algorithms are used to enhance the image, locate the symbol based on the symbol’s fiducials, segment the image and apply decoding algorithms to read the code.

As smart camera implementations they are becoming similar in packaging and use to their linear/laser equivalents and now at about the same cost. Being machine vision systems some have the capability to perform OCR/OCV functions simultaneously, which is an added advantage in some applications.

Some of the industries that have typical applications for which direct part marking has become routine or required by law include:

  • Aerospace – engine parts, turbine blades and other fabricated parts and assemblies
  • Semiconductor – wafers, packages
  • Electronics – bare and assembled boards
  • Automotive – engines and other fabricated parts and assemblies
  • Medical devices – medical implants, tools, medical test kits, vials
  • Pharmaceutical – labels, containers, blister packs
  • Security – identification of parts to prevent counterfeiting or tampering.

Direct part marking makes it possible to track a product until it is scrapped. Direct part marking is used when a part has to be marked permanently. Via a part tracking database it is possible to maintain an accurate history of the part: when and how it was made, where it has been, who has had possession of it, for how long, etc. In industries like the semiconductor industry, in addition to generating a record of the manufacturing history of every component, product tracking also provides optimal control over the entire fabrication process – from processing to packaging. In the case of certain aerospace components and military and medical equipment, the law requires direct part marking.

In the case of the aerospace industry, the Air Transport Association of America has issued guidelines in their ATA SPEC2000 document (Chapter 9). In summary they suggest that permanent parts identification ‘‘allow for ‘cradle-to-grave’ tracking of serialized parts and to facilitate the use of automated processes in parts handling, this specification allows the use of multiple bar code symbology to permanently mark an aircraft part. The model for this specification was the license plate concept for registration. License plates are simply pointers to a database of unlimited fields of tracked information. Similarly, the part number and serial number uniquely identify aircraft parts and become the pointer. Airlines use part numbers and serial numbers of repairable components in many daily business activities. These include provisioning, processing warranty claims, tracking part flight hours and landings, tracking part installation and removal time, and monitoring regulatory agency compliance.’‘ It is projected that marks will be on every single component in an airplane by 2005.

In the automotive industry the Automotive Industry Action Group supports the Data Matrix code. They have issued a specification requiring DataMatrix for all automotive parts marking. They have also finalized a second-generation shipping label standard that supports 2D codes. Component vendors are using 2D to track keyless entry systems, radio components, air-bag system subassembly, pistons, torque converters, fuel injectors, etc.

(EIA) introduced a standard (ANSI/EIA-706) that specifies the use of DataMatrix ECC200 protocol for use in all inter-industry component marking. EIA's 556B standard also specifies the use PDF 417 and MaxiCode for shipping labels. Marking a printed circuit board at the beginning of a production run with a 2D code permits tracing and monitoring the part throughout the production run. In assembly operations, automatic pick and place machines can read the 2D code and set up the machine’s program to place the correct chips on the board. An automatic sorter can use the 2D mark to convey the assembled board to the correct test station.  After inspection and test, a file can use the 2D code to track boards that pass or fail.

The semiconductor industry is rapidly substituting Data Matrix codes for 1D bar codes because as the value of the patterned wafers they produce increases (larger diameter wafers and finer line widths lead to more dense patterned wafers) real estate on wafers has become more valuable. One SEMI standard is SEMI T70997 – Specification for Back Surface Monitoring of Double Side Polished Wafers with a Two Dimensional Matrix Code Symbol.’‘ 

A Data Matrix code that is 0.1’‘ on as side can carry a 5 or 6 digit value and permit wafer traceability throughout the manufacturing processes as well as throughout the packaging operations. In packaging one can find 2D codes on strips, wafers or the die itself. Packaging equipment that support die tracing are those tools that process by site, such as die attach and inspection, lead bond and inspection, laser mark and inspection and test handlers. Die level trace allows a manufacturer to tie the semiconductor fab and back-end test together. After packaging, test results can be correlated to a specific site on a wafer. In addition, unique product markings and product traceability can quickly lead to the identification of counterfeit, stolen or mislabeled copies. 

In the pharmaceutical industry, the Health Industry Business Communication Council has approved 2D application specifications for Data Matrix symbology. Again it was selected because it is space-efficient and can fit onto more small packages than any other bar code. The idea for bar coding is to allow for immediate product verification and ultimately to assure patient safety associated with drug dispensing through pharmacies and in hospitals.
The application of 2D symbol readers can be just as tricky as that of any other machine vision system. The various methods of ‘‘printing’‘ a code yield wide variation in the quality of the image. Some of these require special lighting arrangements to normalize the background and/or enhance the presence of the code. Depth-of-field may become a consideration in some applications. Hence, some applications may benefit from the use of telecentric optical arrangements. Significantly, the machine vision industry is conversant in the ‘‘tricks-of-the-trade’‘ required to make 2D readers reliable even when faced with specular and low contrast applications.

The use of machine vision-based Data Matrix code readers in conjunction with direct part marking applications is becoming widespread throughout many manufacturing industries. In addition to ‘‘cradle-to-grave part tracking’‘ such systems can be an invaluable tool for work-in-process inventory management and traceability and for sorting look-alike parts for automation and shipping accuracy. One can now find and will continue to see increased use of 2D codes throughout manufacturing industries.

Some companies offering Data Matrix 2D symbol readers being used in direct part marking applications include:

 

Company

Website

Fixed Scanner

Hand-Held Scanner

AccuSort

 www.accusort.com

X

 

Cognex 

www.cognex.com

X

 

DVT

www.dvtsensors.com

X

 

Microscan

 www.microscan.com 

X

 

Omron

www.omron.com

X

 

RVSI

www.rvsi.com

X

X

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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