Barcodes, and more recently QR codes, are an incredibly common part of human life. We can find them on practically every product in a store, and increasingly on books in libraries, where they save time in indexing collections, as well as on documents. 1D/2D codes play a similar role in industrial applications, serving as a quick way to classify objects. QR technology is used not only for indexing but also for general encoding of character strings, such as various links and references to websites.
Reading 1D/2D codes can be achieved using a standard “PC-based” vision system, or through compact readers specially designed for this task. 1D/2D inspection systems can operate on different principles. Historically, laser and diode readers were popular, but now “image-based” devices, which utilize image sensors, are decidedly displacing them. Image-based readers are essentially smart cameras, equipped with an appropriate sensor, processor, and recognition algorithm. This is a very convenient solution, capable of guaranteeing speeds of even several hundred reads per second. Reading codes using a “PC-based” system, on the other hand, will be useful for non-standard applications.
How can one most simply understand 1D/2D inspection? Just read a QR code with a smartphone. In both cases, the operating principle is practically identical; only the tool used to perform the task changes. Although dedicated devices and systems will carry out inspections much faster and with better quality, smartphones can also be called smart cameras – they are also compact devices containing a camera, processor, and software.
Laser and Diode Readers
Older, increasingly less common technology for reading barcodes includes laser readers. These devices emit a longitudinal laser beam, which is projected onto the code being read, perpendicular to the direction of its lines. This beam is reflected from the gaps between the code lines and directed to a mirror (or lens), from where it then goes to a photodetector, where it is converted into electrical pulses. The longitudinal laser beam is created using an oscillating or rotating mirror, which can make readers based on this technology more prone to failure and less resistant to shocks. It was not by chance that only barcodes were mentioned at the beginning of the paragraph, as laser readers do not allow for reading “Data Matrix” type codes. Another disadvantage is that they require barcodes of fairly good quality, because the scanned line is very thin.
Diode readers operate on a similar principle, except that here, instead of a laser, the light source is LED diodes. These devices do not have moving parts, which are needed to generate the longitudinal laser beam, making them more resistant to shocks and drops, and consuming less energy, which is more significant for mobile devices. The advantage of laser readers, on the other hand, is a greater range. Currently, however, both technologies are being superseded by a more functional and reliable method based on camera image analysis.
“Linear Imager” and “Area Imager” Scanners
The widespread adoption of 2D codes in the market created a need for appropriate devices to verify them. For this reason, readers whose operating principle is based on typical machine vision solutions were developed. “Linear imager” devices with a linear sensor and “area imager” devices with an area sensor are compact vision systems, composed of a photosensitive sensor and a processor – algorithms read the code from the image recorded by the sensor. Thanks to this approach, readers based on the new technology can provide greater functionality than laser readers and are becoming more attractive for all industrial uses. Code readers based on “PC-based” vision systems operate on an identical principle, with the difference that here the camera and processor are two separate devices.
Reading codes using image sensors as well as typical “PC-based” vision systems allows for the greatest efficiency and functionality among all solutions used.
When discussing the technology of image-based code readers, it is impossible not to mention their greatest advantage, which is reliability (the ratio of correctly read codes to the number of attempts made). New devices, unlike the previous generation, do not just see a single line but the entire code image. This allows processing algorithms to select an appropriate part of the code or to eliminate distortions in the image, such as noise, overexposure, or poor perspective. The openness to various forms of lighting (no need for a laser) allows for entirely new applications, such as reading codes printed with UV ink. Thanks to the technologies used, image-based code readers provide greater scanning fluidity and reduce costs allocated to manually reading codes deemed incorrect and requiring human intervention.
Another advantage of the new solution is the ability to read codes in any orientation. Algorithms detect the edges of the code in the image and ensure its proper alignment. While, as mentioned above, such codes can also be read using laser readers, it would require projecting many laser lines. Additionally, image-based readers can recognize multiple codes simultaneously within their field of view, which would not be possible with older technology.
All types of 1D/2D codes are extremely popular, from industrial and scientific applications to retail checkouts and document identification.
“Area imager” readers are adapted to read 2D codes, which are increasingly popular in industrial and other applications. Furthermore, a single device has the ability to read both 1D and 2D codes, even interchangeably.
The previously mentioned “linear imager” readers have an analogous operating principle to image-based devices, with the difference that a linear sensor is used for image acquisition. Such a solution is not capable of reading “Data Matrix” codes, but it compensates with a lower price.
Linear readers boast similar reliability to image-based devices because the read line is slightly thicker than with laser readers, allowing the software to select an appropriate segment. “Linear imager” systems and readers feature the same high speed as “area imager” technology.
“Linear imager” and “area imager” readers have one more advantage over laser readers – they are not equipped with moving parts, such as a vibrating mirror, making them more fault-tolerant and resistant to falls. These and other advantages make the new solution increasingly common in the market.
Thanks to the multitude of available solutions, it’s easy to choose the right system for a given application. There are systems for verifying single codes, for reading dozens of codes at once located in the sensor’s field of view, or for reading low-quality codes. Universal algorithms can decode 1D/2D IDs written in various standards.
For typical, as well as more advanced solutions, ready-made systems from companies like Cognex can be successfully utilized. Dataman series image readers are complete solutions for 1D/2D inspection that only require proper connection and simple configuration. These devices are equipped with exceptionally versatile algorithms that can detect everything from single barcodes to multiple QR codes at once.
For exceptionally advanced and unusual applications, typical “PC-based” vision systems, equipped with a camera and a processor, can also be used. Such a configuration allows for appropriate customization and optimization of the system for a given application, but it is also less economical than ready-made solutions.
