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Optical character recognition for mother plate life cycle optimization

Client : Xstrata Affinerie CCR

Our client, a copper and precious metals refinery, performs the last step in copper refining using an electroplating process. During the process, the copper is deposited on stainless steel plates known as mother plates. After over 10 years of use, the 85,000 mother plates had started showing signs of surface corrosion, which affected the physical quality of the copper cathodes and slowed production. Our client therefore decided to restore them at a rate of about 300 mother plates a week. However, the client had to be able to identify the mother plates to track which ones had been repaired and aid process improvement.

Our task was to develop a custom optical system, because conventional character recognition methods could not be used on mother plates for the following reasons:

  • The engraved numbers are copper on copper, resulting in poor contrast.
  • The surface is uneven and presents numerous defects (scratches, stains, marks).
  • The numbers are not always engraved in the same location, which means a broader field of vision is required, reducing image resolution.

The development project was conducted in three main phases. Phase one consisted of ensuring the project’s feasibility and developing a preliminary design for a reading system. At the end of this phase, we were sufficiently confident it could achieve the stated goal of 95% reading accuracy, and CCR decided to go forward with the project.

Phase two consisted of installing a temporary image acquisition system in the plant. The findings in this phase prompted changes to the system’s geometry: positioning of lighting modules and cameras, and use of hydrophobic windows to reduce the effects of the surrounding vapor.

Phase three entailed completing development of the vision system and commissioning three systems. While the systems were being physically installed, we were able to optimize the character recognition algorithm using the images obtained with the first machine. We tested multiple versions of the software before arriving at a definitive version.

After restoring over 5,000 mother plates, our client noticed an improvement in the quality of electroplating on repaired mother plates, easier cathode stripping, and fewer machine blockages, which cut down on operator intervention and the risks of accidents.

 

The high level of cooperation between Xstrata Affinerie CCR, INO, and the other project partners was critical to its success. Moreover, the optical system we have delivered has paved the way for our client to implement other process improvement projects.

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