High read rates for a traceability monitoring system

20 March 2012

A German-based industrial product manufacturer has specified Cognex In-Sight 5100 ID readers to create a continuous monitoring system for traceability at several of its facilities across the globe.

The company, ETO Magnetic, is able produce several million defect-free parts for the automotive industry with just a few seconds between steps in the production process. A factor in this success is the continuous monitoring of parts on their way to a finished product, based on intelligent vision systems. Laser-etched and dot peen 2D codes provide a way to create an individual fingerprint for quality assurance. Since the introduction of this traceability solution, the pseudo-failure rate has been reduced from 4% to almost zero.

Identification with obstacles
Laser-etched codes provide good contrast and can be read reliably, whereas dot peen codes on metal parts present the last generation of code readers with a much more difficult reading task. During the production process, metal components are thermally and mechanically distorted to the extent that these 2D codes suffer collateral damage. When stamping the tiny 6x6 mm identification areas in the dot peen process, tool wear can lead to differences in impression depths and angles of the individual marking points.

The previous code readers used by the company identified around 4% of the parts as having unreadable codes. "This rate was clearly too high," said process planner, Klaus Schwanz of ETO Magnetic. "In our manufacturing processes, a product with an unreadable code is treated as a reject. In a plant handling several million parts, our old ID readers were simply not up to scratch. So we looked for a better system and found it in the In-Sight 5110 from Cognex."

An intelligent solution
It was only when ETO Magnetic began to use In-Sight 5110 fixed-mount ID readers on their manufacturing lines that the 2D dot peen codes could be identified with 100% certainty. "A decisive advantage of the change to the new system is its combination of lighting, camera, ID software, processor and communications interface," said Bruno Halter, senior application engineer at Cognex.

An essential contribution was also the know-how of the vision specialist, who eliminated possible illumination problem points. For metal surfaces that were, in part, highly reflective and particularly difficult to identify, the developers at ETO Magnetic used flat white lighting. "Earlier, we tried to read dot peen 2D codes in the same way as printed codes. In particularly difficult cases, reflective behaviour of the dot peen codes rendered this method ineffective. To address this challenge, we lit the relevant areas uniformly with white light and were able to recognise the impressions of the dot peen code reliably as black spots," explained Halter.

The decoding cannot be optimised with additional lighting in every case. In many industrial environments, space limitations often leave room only for the ID reader itself. For this reason, Cognex In-Sight ID readers are equipped with the Cognex IDMax data matrix code reading software, based on the company’s PatMax technology which is said to guarantee reliable and stable decoding even under difficult conditions. A digital, high-speed recognition system, DSP architecture and optimised reader algorithms ensure high reading rates at all times in identification applications with labels and direct marking, even on the fastest production lines.

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