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by Scott Sabreen
Question: What exactly are QR codes (I see them everywhere)? How do they differ from Data Matrix codes and can they be laser marked? As a plastics manufacturing company, should we use QR or Data Matrix? I use my cell phone app to read QR codes but I’m not sure if they can be read using industrial grade machine vision systems requiring ISO certification.
Answer: First, let’s examine the basics of machine vision codes. Machine-readable (vision) codes are coded information which can be interpreted through the use of optical scanners or cameras. For 1-dimensional "Barcodes," it is a representation of information, typically dark contrast on a light background, to create high and low reflectance which is converted to 1s and 0s. Barcodes store data in the widths and spacings of printed parallel lines. The maximum number of characters which can be encoded in a 1-D barcode is 19-20.
A 1-dimensional barcode (top), QR and Data Matrix Codes are all encoded with the text "Peterson Publications."
The continuing drive to encode more information, in combination with smaller space requirements, has led to the development of 2-dimensional "Data Matrix" and "QR" Codes. Data Matrix and QR codes cannot be read by a laser (as used with Barcodes) as there is typically no sweep pattern that can encompass the entire symbol. They must be scanned by a camera capture device. The QR code, or "Quick Response" code, was invented in 1994 by Denso Wave, a Japanese company. Both QR and Data Matrix are 2-dimensional codes, possess error correction capabilities on multiple levels and meet ISO/IEC Specifications.
General Structure of QR and Data Matrix Codes
QR and Data Matrix codes both contain specifically located data areas and recognition areas that facilitate detecting and decoding. Both utilize Reed-Solomon arithmetic algorithms to recover any damaged area of a part or product of the information code data. Per MIL-STD130, Data Matrix uses an Error Correction Code (ECC) of 200.
While it may appear that QR Codes have more recognition area than Data Matrix based upon the number of modules in the recognition area, it is the Data Matrix which can be more compact in size (as laser marked) and effectiveness. It uses less area to contain equal amounts of data. Both QR and Data Matrix modules will grow in size as more data is added to the code, albeit the size of the actual mark can be altered using the proper software.
Which Code to Use?
The choice as to which code to use is application- and end-use-specific. A few general guidelines include the following:
- Small, tight laser-marked surface areas containing small encoded alphanumerics are required (ECC200).
- Data Matrix will generally laser mark faster than QR codes; however, speed is somewhat dependent on the software and knowledge of marking machine vision codes, including lighting set-up. Cell module sizes as small as 0.004" and less are achievable.
- Encoding images and logos
- Relatively large product surface areas are available.
- Esthetics of the code are important – often QR codes appear more visually appealing.
- QR codes have several modes of encoding data, some of which can be more compact than the 8-bits per character used by Data Matrix.
Industrial Uses of Machine-Readable Codes
For both QR and Data Matrix codes, the original intent was for industrial applications and inventory/product management. With the advent of Smart Phones, QR codes have become prevalent. They provide quick access to the internet and corporate branding and often are seen on printed paper stock media magazines. Consider the housing market - one often observes a QR code on the "For Sale" sign. Brick and mortar stores are beginning to transition from magnetic cards to QR codes. Not to be overlooked, there are many smart phone apps for Data Matrix.
Data Storage Content
General guidelines of data storage entail arithmetic code information, code size and error correction level. The following is general information that has been published in the public domain. It is recommended to limit the amount of data encoded in each symbol. The amount of data that can be encoded will vary depending upon the type of data, the encoding mode and what the indented scanner can read. In most implementations, the amount of data that can be encoded is significantly decreased due to mode switching between different types of characters, such as between numbers, upper case and lower case letters and punctuation.
QR (ECC dependent):
- Numeric: Max. 7,089 characters (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
- Alphanumeric: Max. 4,296 characters (0-9, A-Z [upper-case only], space, $, %, *, +, -, ., /, :)
- Binary/byte: Max. 2,953 characters (8-bit bytes) (23624 bits)
- Kanji/Kana: Max. 1,817 characters
Data Matrix (ECC200):
- Numeric: Max. 1-3,116 characters
- Alphanumeric: Max. 1-2,335 characters
- Binary/byte: Max. 1,556 characters
Laser Marking of QR and Data Matrix Codes
Both QR and Data Matrix codes are markable using traditional near-infrared (1064nm wavelength) industrial lasers, including Nd:YAG, Vanadate and Fiber. The continuous wave (CW) CO2 lasers operate at a wavelength of 10.6 µm (far infrared spectrum) and generate a much lower peak power, yielding colorless engraving (embossing). Thus, they cannot produce high contrast markings on plastics. Note: CO2 lasers commonly are used for marking barcodes and matrix codes on labels, paper-stock and ink ablation. In certain applications, large size Data Matrix codes marked using CO2 lasers have been achieved.
For plastic products, lasers marking is the preferred method because the process yields high-contrast indelible markings and does not require expensive consumable ink/solvents or post-curing. The mechanism of laser marking is to irradiate the polymer with a localized high-energy radiation source (laser). The radiant energy then is absorbed by the material and converted to thermal energy. The thermal energy induces reactions to occur in the material, i.e., the QR or Data Matrix code. Lasers can mark the smallest size machine vision codes. This is important for micro-marking and when there is limited surface area on a part or component to be marked with alphanumerics, logos or schematic diagrams.
Modern machine-vision systems are not just stand-alone inspection devices. Rather, they are integrated into Six Sigma total manufacturing operations, including statistical quality control metrics programs. Industrial manufacturing requirements for indelible direct part marking containing machine vision codes are growing exponentially. Direct part marking enables tracking a product from the time of manufacturing until the end of its useful life. This demand is driven by the increasing requirements for component traceability and product unique identification (UID). Post 9/11, manufacturers are implementing strategies to establish traceability and thwart product tampering and counterfeiting.
Scott Sabreen is the founder and president of The Sabreen Group, Inc., a plastics engineering consulting firm. He is a board member for the Society of Plastics Engineers Decorating/Assembly Division, technical editor for Plastics Decorating and expert engineer for Omnexus/SpecialChem, Intota-Guideline and Nerac. Sabreen may be reached via email at email@example.com.