By Hanieh Ghassabian G.
To operate inside the vacuum vessel of the RFX-mod2 machine, a team of researchers developed sophisticated robots combined with virtual reality simulations, enabling operators to control and perform remote interventions with precision and safety.
RFX-mod2 is an Italian research infrastructure of high strategic priority dedicated to the study of plasma physics and magnetic plasma confinement using the configuration known as the Reversed Field Pinch (RFP). The RFX-mod2 machine, developed as an evolution of the previous RFX-mod, is a toroidal device — meaning doughnut-shaped — designed to confine plasma through magnetic fields.
RFX-mod2 represents an advanced device in the field of nuclear fusion research, built to improve the understanding of plasma dynamics and to test new control and confinement scenarios, with the goal of contributing to the development of clean and sustainable energy sources.
Robot manipulator testing
The RFX-mod2 machine requires highly specialized maintenance operations inside the vacuum vessel, which can only be accessed through openings just 150 millimeters in diameter; direct human intervention is impossible. This is where the collaboration with a team of researchers from the University of Naples Federico II, led by Professor Giuseppe Di Gironimo, comes into play for the development of an innovative manipulator robot within the framework of the Nefertari project.
The technological upgrade of the robotic system
“At the heart of the innovation is a robotic manipulator arm capable of being inserted through the narrow openings of the vacuum vessel and performing delicate operations such as gripping and replacing graphite tiles, the protective lining of the inner wall closest to the plasma.” explains dott. Michele Fadone, researcher of the Consorzio RFX and head of the activity.
As early as the 1990s, a robotic arm had already been developed for this task in the original RFX machine, but over time technological limitations emerged in terms of mobility and maintenance. For this reason, a new and more advanced robotic arm was developed, equipped with an additional degree of freedom that allows it to reach the same position through multiple configurations, thereby increasing precision and flexibility.
Since it is impossible to install cameras directly inside the vacuum vessel due to darkness and limited space, the team developed a digital twin of the robot.
“Thanks to virtual reality software,” explains Professor Di Gironimo, “an operator can wear a VR headset and see in real time what the robot is doing inside the core of the machine, as if opening a ‘virtual window’ into the interior.”
This approach not only improves control and safety but also facilitates operator training in a dedicated facility where both the robot and the machine are replicated.
The new manipulator robot is also more compact thanks to the use of smaller motors integrated directly onto the vertical axes, eliminating bulky gears and external cabling typical of the 1990s.
The cabling has in fact been integrated within the arm components themselves, improving flexibility and reducing failures.
“To grasp the graphite tiles, the robot uses an intelligent gripper with movable fingers that latch into the component,” Professor Di Gironimo explains. “Release is achieved through a ‘key’ mechanism requiring a 90-degree rotation and a compression force of 150 Newtons to ensure stable fastening.”
After grasping the tile, the robotic arm passes it to a second robot — nicknamed by the team the “robot pizzaiolo” — positioned at another opening in the vessel. This second robot is responsible for transporting or positioning the tile outside the vessel for maintenance or inspection.
The operation of the two robots is coordinated and can be carried out simultaneously through trajectory planning. However, in the event of minor misalignments or unexpected situations, the operator intervenes through teleoperation using a haptic device that provides tactile feedback, allowing them to feel the applied pressure and thus improving both control and safety.
The project represents a significant advancement in the use of robotics for precision maintenance in complex machines, paving the way for safer and more efficient interventions in extreme environments.
The combination of advanced mechanics, digital simulation, and remote control through virtual reality constitutes a model that could inspire future developments across numerous industrial and scientific sectors.