Tracking Codes and How They Work

> Industrial Traceability

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Introduction

In the past few years, traceability has become a major issue for the industrial sector, since allowing for better tracking and management of products can lead to important cost/savings. Most of the time, this notion of traceability takes the form of barcodes on products. Originally, the well-known, one-dimensional (1D) barcodes were the first barcodes to be created and they have been used ever since due to their simplicity. But due to the limited quantity of information which can be stored in these initial barcodes, a database is needed to interpret the decoded information and to link it to the information of the product. Without the database, the number that is decoded does not mean anything. However, sometimes, a higher density storage of information than the one allowed by 1D codes is needed. So, two-dimensional barcodes were created to store a maximum of information without requiring an accompanying database.

State of the Art Code

By having the capacity to store information in two-dimensions (2D); these barcodes can store such a density of information that a product and its information can be decoded without using an external database. The code itself can contain information like: the brand, the name of the product, the year of fabrication and so forth. For a given industry, the ability to access this critical information at every step of the production process without the use of an accompanying database greatly facilitates the handling of the product.

However, for these codes to be readable by all the subcontractors along the production line, standards for two-dimensional and one-dimensional barcodes needed to be created. Those standards are regulated by associations like the International Organization for Standards (ISO) and the Global Standards 1 (GS1). The ISO is a nongovernmental and international organization that creates norms in various domains. They ensure that the barcodes meet a minimum standard for quality and can fulfil their functions properly. In the barcoding domain, the ISO works in partnership with Global Standards 1 (GS1). The latter is an international organization similar to the ISO, but which specializes in barcodes for products. The GS1 standard demands a particular structure for its barcodes in order to store several types of information. However, before explaining the diverse elements required by these standards, it is important to explain how both two-dimensional and one-dimensional barcodes work.

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Technical Aspects of 2D Codes

Many different structures exist for 2D codes. However, they are all based on the fact that each combination and organization of the black and white pixels is associated with an alphanumeric character. To read a barcode, a photograph is generally taken and analyzed by an image processing software in order to isolate, read and finally interpret the barcode. Among all the different types of two-dimensional codes, there are two main types that are used in most industries: The data matrix (DM) and the quick response (QR) barcode.

Data Matrix

Data matrix codes, as shown in Figure 1A, are delimited by two black lines with one on the left and one on the bottom in order to facilitate the localization of the code by the image processing software. Furthermore, the other two edges of the code consist of alternating black and white pixels. These lines are used by the computer program which analyses the code to get its main spatial frequency which is related to the size of the smallest element. They also indicate the number of columns and lines. These regions do not contain information, but only facilitate the tracking and decoding of the code. They can also be drawn by red edges as shown in Figure 1B.

A B

Fig 1: A) Data matrix example B) Data matrix example with red localization pixels

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Quick Response Code

As shown in Figure 2A and 2B; QR codes have a different structure than data matrices. In this case, localization pixels are arranged differently. There are three squares at the corners and one square inside the code for localization, and two lines of alternating black and white pixels for determining the main spatial frequency.

Size and Requirements

Numerous sizes exist for these two types of barcode. For example, in a QR code with a size of 29 × 29 pixels, 27% of the total number of pixels are used for the localization of the code; whereas for a data matrix code with a size of 22 × 22 pixels, the amount of code used for localization is only 17%. Then, a priori, for a given size, DM codes can store more information than QR codes, because they use a lower percentage of their pixels for localization. Also, it is worth noting that these two kinds of codes are surrounded by a white margin of variable thickness called the quiet zone. This white background is used to facilitate the localization of the code on the image taken by the reading system.

A B

Fig 2: A) QR code example B) QR code example with red localization pixels

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DM vs QR Code

Furthermore, these two types of codes also have redundant pixels that allow a reading system to interpret the code even though some pixels are damaged or illegible. This immunity to the degradation of the code is quantified by the error correction (EC) level. This number represents the maximum percentage of information containing pixels that can be damaged while still allowing the code to be readable. For example, a DM can have an EC level from 14% to 39%, whereas a QR code can have an EC level of 7% to 30%. Thus, an industry with a lot of handling that could cause damage to the barcode, and that therefore needs a reliable barcode, would find the use of data matrices a good choice due to its higher EC levels. However, if only a minimal EC level is needed, then the QR code might be the best option, because of their low end EC level of 7%. The barcode will therefore be smaller. As a matter of fact, the higher the EC level is, the greater the number of pixels is needed, since more information has to be repeated to arrive at a readable code.

Even though DM barcodes are the most reliable and compact solution for industrial needs, QR barcodes are still highly desired in some cases. In fact, QR codes can store a greater number of different symbols such as the Japanese alphabet. Nowadays, these codes are very widespread in the mobile phone industry, because they are easier and faster to read by cellphones than other kinds of 2D code. This can be explained by the larger percentage of pixels that are allocated to localization purposes, since even if the camera of the cellphone is not properly aligned, the reading of the code is still possible. However, QR codes are not appropriate for curved products. For example, in the case of a cylindrical object, it is better to use a rectangular code in such a way that its longest dimensional side does not follow the direction of the curvature. This will facilitate the reading of the code later on. However, QR codes can only have a square shape, whereas DM codes can have square or rectangular shapes, which make them the best solution for certain situations.

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Technical Aspects of 1D Codes

Even though two-dimensional barcodes have a lot of advantages in regards to traceability, one- dimensional barcodes are still used in a lot of industries. As a matter of fact, the writing and reading of these codes are much easier than 2D codes. A lot of different structures and standards also exist for these codes. However, they are all based on the fact that each combination of black and white lines is associated with a symbol (alphanumeric or only numeric, depending on the standard). In everyday situations, UPC-A barcodes are the most frequently used, especially in the commercial world. However, this standard only represents numbers and does not include letters which makes this kind of barcode not very well-adapted to all situations of industrial traceability. In fact, such standards as Code 128 and Code 39 are more omnipresent in commercial sectors. Code 128 owes its name to its capacity to store all the characters of the ASCII 128 (American Standard Code for Information Interchange) set; which consists of numbers, letters and punctuation marks. Code 39 is a less compact equivalent to Code 128 and is largely used in the automotive industry and in the defense sector. On the other hand, Code 128 is mainly used in the internal supply chains of industries to assure the maintenance and handling of products.

Fig 3: Example of a 128 code with its different sections: 1. Quiet zone 2. Start/Stop character 3. Code data 4. Validation character

1D Code Structure and Readability

As seen in Figure 3, a barcode using the 128 Code structure is divided into several parts with a total of 108 symbols. Each of these parts contains a certain number of symbols. A symbol is a combination which alternates three black lines and three blank spaces of various widths. Each symbol is associated with a particular alphanumeric character that is part of the ASCII 128 set.

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First of all, the beginning and the end of the barcode are surrounded by the quiet zone, which allows for a better localization of the code during its reading. Then, there are 3 symbols that mark the beginning of the code and the code itself that occupies most of the space with its 103 symbols. After the code, there is a verification symbol that allows the reading instrument to determine if the information in the barcode was read correctly. In fact, each alphanumeric character is associated with a number and a particular calculation is done with the decoded characters. This calculation should be equal to the value of the alphanumeric character of the verification symbol. So, during the reading of the code, if the calculation based on the decoded information is not equal to the verification symbol; then a new data acquisition must be done by the reading system. Finally, the code ends with two symbols that are common to all Code 128 barcodes. These two symbols indicate the end of the information on the barcode to the reading instrument. The fact that there are 3 starting symbols and only 2 ending symbols allows the barcode to be read and decoded forwards and backwards.

The reading of a one-dimensional barcode is based on the fact that black lines reflect less incident light than white lines. So, the reading instrument is made of a laser that scans a particular field of view in which the 1D barcode is placed. A photodetector then measures the quantity of light that is reflected back from the barcode. At any given time, the total reflected energy changes whether the laser/reader is projected onto a black or white line. This photodetector generates an electric current proportional to the incident light power. The variations of the generated current can then be analyzed to extract the alternating black and white lines. Finally, with the help of a database, this series of bits can be associated to a product and to all its information.

1D vs 2D Codes

From a machine’s perspective, reading a 1D barcode is easier than reading a 2D barcode. As a matter of fact, for the case of a 1D barcode, the incoming signal containing the information is an electric current; while for the case of a 2D barcode, it is a picture. This latter barcode is much more complex to measure and analyse. So it requires an image processing software that takes more time to read. Furthermore, due to their simplicity, 1D reading systems are a lot cheaper than those for 2D barcodes. Also, the reading and the writing of 1D barcodes are generally faster. This can be explained by the fact that 1D barcodes contain a lot less dense information. So they require less detailed writing in their creation, which also makes them cheaper. The fact that 1D barcodes need a connection to a database, contrarily to 2D barcodes, is not necessarily a limiting factor in certain cases. In fact, in certain situations, it is possible that the product information needs to be updated continuously in real time. In these cases, the use of a database is mandatory, because the database can be changed constantly whereas the information on a 2D barcode remains fixed. So, in some cases the use of a two-dimensional code is not advantageous.

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However in cases where the information is complex or needs to travel with the product and not be maintained separately from the product, these cases are probably better for a 2D barcode.

Tracking Codes and Global Standards (GS1)

As explained before and in order to normalize their barcodes, businesses can have their products approved by the GS1. The latter verifies that the codes respect certain standards and have a particular structure. For example, the presence of a HRI (Human Readable Interpretation) of the code is mandatory. This takes the form of a series of numbers written under the barcode that is readable by a human. It contains the same information that is encoded in the two-dimensional or the one-dimensional code. The presence of a HRI for a barcode is essential in order to allow the code information to be collectable even when severely damaged. Also, the standards state that the HRI part of the code must be a certain size and that it must not interfere with the quiet zone of the barcode. The contrast is also evaluated. This consists of the difference between the grayscale value of the whitest and blackest pixels on an image of the barcode. Thus, the higher the contrast is, the easier it is to read the code. Modulation of the printing of the symbol is also evaluated. This represents the consistency of the printing of the barcode and any change in contrast values for every pixel. This measure is preferably low in order to have a maximum contrast. Furthermore, the size of the quiet zone is also regulated to be sure that it is big enough to allow for the localization and isolation of the code by the reading system. For 2D barcodes, the robustness of the code to a deterioration of its matrix is also an important point. In fact, a GS1 code will verify that the error correction of the code is respected by checking if it is still readable even if a particular percentage of its information pixels are damaged.

Conclusion

The advent of 1D and particularly 2D barcodes allow for the storage of information in really compact ways, while giving considerable immunity to potential damage with the presence of EC and HRI functionality. Several marking techniques used for these barcodes have had to be developed and improved. These techniques also have to be applicable to different types of materials. As a matter of fact, with industries requiring such dense levels of information on their barcodes; precise and fast marking techniques involving a high level of automation are needed more than ever. These techniques also respond to the growing requirement of traceability in many industries. For example, laser marking has particularly stood out during the past few years. This marking technology can indeed be used for a lot of material types such as aluminum, wood, plastic, ceramic and so forth. Thus, it can be used in a wide variety of diverse businesses.

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Furthermore, laser marking’s high level of automation makes it an easily adaptable solution for changing conditions, which is an important factor in barcode marking.

About Laserax Laserax is a laser systems manufacturer that provides efficient, high-performing and safe solutions for most demanding industrial applications. Our customers range from upstream to downstream in the aluminum manufacturing value chain, including metal and alloy transformation plus other manufacturing industries. Laserax provides a complete range of products from OEM, to custom and turnkey laser solutions. With us you can also rely on a team of laser technology experts that will insure the safety of your laser applications and provide proper safety training to your team.

Sources

The 2D Revolution, Ahearn & Soper inc., accessed 2016 November 2

Two-dimensional (2D) barcodes, GS1, accessed 2016 November 2

QR Codes Versus Data Matrix, QRworld, accessed 2016 November 2

Datamatrix and QR codes: why 2D codes are still relevant in 2016, Matthews, accessed 2016 November 2

ExpoTools 1D Barcode Encoding Guide, ExpoTools, accessed 2016 November 17

Types of Barcodes: Choosing the right barcode: EAN, UPC, Code128, ITF-14 or Code39?, Scandit, accessed 2016 November 17

Borgwarner Drivetrain Group, Parts Identification & Tracking Application Standard: 2D Direct Part Marking Specifications

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