Engineering news
Modular manoeuvres: Joysticks provide control for each individual joint
James Fisher Nuclear has produced a modular, six-degrees-of-freedom robotic arm that can be deployed through a standard-size penetration port for radiological cells.
The arm has been tested at the company's test facility in Cumbria, and it now hopes to export the technology for decommissioning work abroad.
Current commercial robotic manipulators are largely inadequate for nuclear decommissioning tasks owing to limitations in radiation tolerance, dexterity, working range, and payload. A fundamental difficulty for many arms is that they cannot be inserted into a standard diameter penetration port (smaller than 300 mm) adopted by the nuclear industry.
In response, James Fisher developed its cost-effective modular manipulator to use for a range of remote handling and decommissioning tasks. The ModuMan 100 provides a functional 2.3-metre reach and a payload capacity of 100kg at full stretch.
The arm can be deployed through a standard-size penetration port for radiological cells or by using a carrier system, and is compatible with a range of tooling. The construction materials selected mean the arm can handle the heat, humidity, caustic or acidic fumes encountered during decommissioning tasks, and the link lengths have been designed to give optimum dexterity to navigate restricted environments.
“Our goals included making the manipulator modular, cost-effective, and maintainable, while making best use of off-the-shelf solutions,” said Carwyn Jones, system design manager at James Fisher. “We designed the system with both in-cell and out-cell components.
“In-cell – the inaccessible area within harsh environments – the arm uses multiple hydraulic actuators to power the joint motion, and out-cell, it powers a dual servo motor arrangement that drives the shoulder to rotate. All the hydraulic sensors and drives are located out-cell to provide ease of maintenance and to minimise downtime,” he said.
At the end of the arm, a jaw picks out debris or grasps tools such as shears, drills, and wash-down equipment to aid in decommissioning activities.
The robotic arm is controlled using National Instruments’ CompactRIO hardware and LabVIEW system design software and robotics module. To navigate the environment, the operator uses two three-axis joysticks, which provide proportional control for each individual joint.
The system has undergone inhouse and cross-site testing and is being used for operator training and longevity trials in a simulated environment.
“This process provided us with confidence in the equipment and real operator feedback. The feedback highlighted how quick and easy it is for operators to train and master the system, which is a result of our intuitive user interface,” said Jones.
So far, the arm has undergone 1,200 hours of non-irradiated testing. “The trials have been successful and we are confident the manipulator will continue to perform well,” he said.
He also thinks the arm could be developed to become even more technically capable. “If a customer wanted a collision avoidance function, then we would implement it.”
And Jones sees potential in export markets, particularly in the US. “The modular nature of the arm means that it’s no huge deal if the penetration holes are slightly smaller, as is the case in the States.”