Image-Based ID Reader Reads Codes on Printing Plates

  • May 11, 2015
  • Cognex Corporation
  • Feature

Process-free printing plates reduce costs for high volume printers by eliminating the need to maintain and run a processor and reducing the need for chemicals, water and energy. But process-free plates create a major challenge for the automated plate lines that sort and transport the large number of plates used by major printers. Plate lines read codes on plates at multiple points in order to identify them so they can be transported to the proper location. While the codes on conventional plates are clearly visible to the naked eye and relatively easy to read, codes on process-free plates are invisible and much harder to read. Engineers at NELA, the world’s leading producer of plate lines, found that the laser scanner code readers used in the past were unable to read the codes on process free plates even in infrared light. They tried other code readers and found that the Cognex DataMan 300 image-based ID reader is able to provide near 100% read rates. In order to save NELA the trouble of rewriting their control software to communicate with the new readers, Cognex helped NELA engineers write a series of scripts that enable the DataMan 300 to emulate the previous readers so no software changes were needed.

Printing plate advancements

The vast majority of printing plates have a base level of grained aluminum onto which a coating is added. The coating is imaged by a light or heat source, causing the imaged areas to harden or bind together. To prepare the plate for printing, the non-imaged areas need to be removed to expose the underlying grained aluminum. The hardened or linked areas of emulsion then become the areas that carry the ink while the grained aluminum carries fountain solution – a mixture of chemicals dissolved in water -- from the press’s dampening system to stop ink from going to the non-imaged areas. After the plate is imaged, the non-imaged areas have to be removed and the plate stabilized for printing. This is traditionally done through the use of a developing process using special chemistry and wash solutions. Plate processing requires water of very high levels of purity both to wash the plate and in some cases dilute the chemistry. Plate processors also require energy to operate. The chemicals and water also need to be disposed of after use.

Process-free plates, on the other hand, require neither additional chemistry nor a processor. A typical process-free plate works as follows. After imaging the plate is mounted on the press cylinder like any other plate. The fountain and ink rollers are engaged to cover the entire plate with fountain solution and ink. During the startup of the press, the absorption of the fountain solution prepares the un-imaged coating to be physically removed by the tack and shear of the ink. The coating is then transferred from the plate to the blanket and then carried out of the press by a substrate.  Process free plates eliminate the costs of maintaining and running a processor and also achieve better process control by eliminating processing variables.

Cognex DataMan 300 barcode reader set-up at NELA

Plate line operation

Newspaper printing operations often deal with hundreds of printing plates every hour for multiple newspapers and editions that are commonly printed at a common facility. The plates are usually produced in the order that the page content is completed, not in the order that they will be used. Sorting these plates and delivering them to the correct location is a critical task that must be done correctly in order to avoid misprinting or delays. Plate lines collect plates from the platemaking process and deliver them to a network of storage bins or sometimes directly to the presses where they will be used.

NELA is a third-generation family owned company that employs more than 200 people worldwide producing register control and plate automation systems. The company’s VCP plate automation system precisely registers printing plates using two high resolution complementary metal-oxide semiconductor (CMOS) cameras. Once the correct position is confirmed, the printing plates are punched and bent in a one-step operation and placed into the stacking station of the plate line ready for distribution to the proper location.

Either a Code 39 1-D barcode, Code 128 1-D barcode, 2-D data matrix code or QR code is printed onto each plate at the time it is created so it can be identified throughput the handling process. The plate automation system reads this code after registration in order to ensure the legibility of the code. The code is read again numerous times during handling by the plate line so that the plate can be automatically pulled off the sortation line and delivered to the right storage location or press.

Code reading challenge

“We have been using a particular model of laser scanning code reader in our plate lines for a number of years,” said Jeff Benjamin, Engineer for NELA. “But a significant number of our customers are switching over to process-free plates and the laser scanners are unable to read these plates. This is not surprising since you can’t see the codes in the new plates with your eyes. The laser scanners are also unable to read 2D data matrix and QR codes which a few of our customers are starting to use.”

Benjamin concluded that laser scanning based ID readers would be unable to read the codes on the new plates. He talked to several manufacturers of image-based ID readers and asked for a demonstration of their ability to read the new plates.  Image-based ID readers use a series of algorithms to process a captured image to make it easier to read codes regardless of their orientation or print quality. Image-based readers also are able to use a variety of light sources, such as UV light, to read codes that lasers cannot see.  Benjamin tried a number of different image-based readers with mixed results.

Comparison of conventional printing plate (left) and process-free plate (right)

Image-based reader provides near 100% read rates

“The one that worked the best is the Cognex DataMan 300 ID reader with a built-in UV light source which provided near 100% read rates,” Benjamin said. Cognex DataMan barcode readers use the 1DMax software algorithm and Hotbars image analysis technology to handle extreme variations of code degradation and provide high read rates. DataMan barcode readers also provide the 2DMax+ reading algorithm that overcomes challenges such as poor marking quality or damaged clocking patterns on 2D codes. The DataMan 300 also offers 800 by 600 pixel image resolution and built-in Ethernet which makes it easy to communicate with a PLC.

“Our next challenge arose from the fact that we had been developing our control software for years to work with the proprietary scripting language used by the previous laser scanners,” Benjamin said. “Switching over to the new image-based readers offered the uninviting prospect of having to rewrite all of this software to work with a new scripting language.  My goal was to switch over to the Cognex readers without having to change our software. Cognex helped me develop scripts that run on the DataMan 300 readers that cause them to emulate the commands of our old readers. For example, our software is set up to send a “^#^” command to ask the reader to identify its model to confirm the command language it is using. With the new scripts running, the Cognex reader answers that it is the model of laser scanner used in the past. The Cognex script also responds to all other commands provided by the existing software in the same way as the old laser scanner ID reader.

Barcode on a traditional plate

“Overall, we are very happy with the performance provided by the Cognex DataMan 300 image based ID reader,” Benjamin concluded. “This ID reader is the only one that we know of that can consistently read codes on the new process-free plates. It has also expanded the code reading capability of our plate automation systems to 2-D data matrix and QR codes. Cognex also worked with us to write scripts that enable their readers to flawlessly emulate the previous laser scanner readers. These scripts saved a large amount of time by eliminating the need to rewrite our software. As a result, we have been able to provide important new capabilities to the users of our plate lines that will enable them to easily implement process-free plates and 2-D data matrix and QR codes. The support provided by Cognex throughout this process has phenomenal and played a big role in our success.”

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