Case Studies

ITS Designs a Cognex VisionPro & Radiation Tolerant Camera Solution for Sellafield Ltd

Sellafield Ltd has installed a new vision system designed by Industrial Technology Systems Ltd (ITS), permitting precision guiding of the cranes which move radioactive waste.

Sellafield Ltd is responsible for the safe delivery of multi-million pound contracts on behalf of the Nuclear Decommissioning Agency, and when the decision was made to replace the Optical Character Recognition (OCR) system in the Encapsulated Product Store 2 (EPS2), which had been operational since 1995, they called on ITS.

The vision system is used to guide the cranes in storage vaults 1 and 2, where access is prohibited because of the hazardous nature of the radioactive environment. Sellafield Ltd required an accurate, reliable new system which could achieve the mean time to repair of four hours, to avoid affecting normal operations.

The key purpose of the two OCR systems is to guide the cranes and align them in a specific position in the vaults, using roof-mounted targets. Once aligned, the crane reads the target plate identification which comprises a string of alphanumeric characters etched into the target. Once aligned the crane can then either pick up or lower a Stillage (a rack of cans containing radioactive waste).

ITS’ solution was to provide a vision application using the PC-based Cognex VisionPro. The Pattern Finding Tool finds the roof target within the camera’s field of view, a Find Circle Tool seeks the alignment circle, calculates the offset for each direction which is passed to the crane’s control system. Once aligned the vision application reads the characters using the OCR tool. The read result is then sent via serial communication to the Vault Inventory Control System (VICS), where the crane’s correct location is verified. A registered fail, indicating that the location is not confirmed, results in Stillages neither being placed nor picked up.

Two new radiation-tolerant cameras with non-browning zoom lenses, from Mirion Technologies, were integral to the solution. Identical but independent systems were supplied for each vault, which interface with a common CCTV System and the VICS.

An initial problem encountered by ITS was the quality of some of the sample target plates. The surfaces contained scratches and oil marks, which can cause problems when trying to read text. To overcome this, the image was filtered to make the surface defects less prominent, resulting in a 100% successful read result.

In order to ensure that the alignment accuracy of the crane was not compromised by any ovality in the laser etched circles on the alignment plates, ITS used a function to find the centre of an ellipse rather than a circle, this increasing the accuracy of alignment with the centre of the actual shape rather than an assumed circle.

This solution allows for accurate alignment of the crane and successful OCR reading every time, irrespective of the condition of the plates, which are an unknown factor because of prohibited access.

A third problem was visibility in the vaults, where there is reduced lighting. The previous OCR system had experienced difficulties reading some of the roof-mounted targets and this difficulty was addressed in the new system by fitting external halogen lights to the R938 cameras, providing a consistent lighting environment.

Sellafield Ltd’s response to the new system has been gratitude for ITS’ effort and work, preparing the system on time without loss of operational time. Throughout the project, ITS adhered to Sellafield Ltd’s Quality Systems, ensuring that both documentation and software were to the required standard and organised in a readily accessible way. Life Time Quality Records were handed over to Sellafield Ltd upon completion of the project, and ITS was praised by the company for “very thorough and very well prepared” test documents.