Jouni Mattila (Source) - Tampere University of Technology
Hannu Saarinen (Source) - VTT Technical Research Centre of Finland
Generating Energy from Fusion
ITER is an international project for developing fusion as a clean, sustainable energy source. ITER tests key technologies that a demonstration fusion power plant uses to show that it is possible to capture fusion energy for commercial use. The power plant design is based on the Tokamak principle, in which plasma is maintained at the very high temperature of 100 million °C within a toroidal vacuum chamber surrounded by a magnetic field.
ITER Remote Maintenance Challenge
A major issue for the successful operation of ITER is the maintenance and exchange of in-vessel components by remote handling methods. When operation begins, it is impossible to make changes, conduct inspections, or repair any of the Tokamak components in the radioactive areas by any other method than remote handling. The ITER machine contains thousands of in-vessel components, but to limit the complexity of remote handling activities, the ITER maintenance concept relies on the removal and installation of relatively large modular systems.
To meet the requirement for modular replacement, the diverter comprises 54 cassettes independently mounted on toroidal rails fixed to the inside of the reactor vessel. Each cassette weighs approximately 9 tons, with external dimensions of approximately 3.5 m long by 2.1 m high by 0.8 m wide. We remove cassettes from the vessel using remote handling devices called cassette movers.
Maintenance operations are demanding due to the weight of the components and the constricted space around them. The operations require high position accuracy, high forces, and compact actuator size.
Using NI LabVIEW for Developing the Remote Handling Devices
The ITER diverter test platform 2 (DTP2) remote maintenance development and test laboratory is located at the VTT research center in Finland.We developed two remote maintenance devices for testing the technology before implementation in ITER using NI LabVIEW, LabVIEW Real-Time and NI data acquisition devices for their control systems. LabVIEW offers a flexible environment to interface with different sensors, actuators, and software environments used in the remote maintenance systems. The multicore programming capabilities of LabVIEW facilitate the development of such complex systems.
GUI for the DTP2 Control Room
Because of its ease of use and powerful programming capabilities, LabVIEW was used by VTT to implement the main user interface for the DTP2 control room. The user interface is easy to implement in LabVIEW, which is a big advantage compared to text-based programming languages. From the user interface in the main control room, we initialized the DTP2 system and set up parameters for running maintenance operations.
To view system status, we used LabVIEW front-panel components. Typical monitored parameters include the status of the manipulator joints, pressure information from the hydraulics, and the absolute and relative positions of the robot. The user interface monitors all error, alarm, and warning information from the diagnostics system.
Developing a Controller for the Cassette Multifunctional Mover
In ITER, the cassette multifunctional mover (CMM) device transports the 9-ton diverter cassettes along a complex trajectory to negotiate the path along the diverter access duct from the transfer cask to the plasma chamber. This process requires high accuracy because delicate plasma-facing elements must pass within a few centimeters of the vacuum vessel surfaces.
To control the CMM, we designed a high-level control (HLC) system based on a multicore LabVIEW Real-Time desktop target. The HLC calculates the CMM motion references and passes them via CAN bus to the lower-level servo control system. For system diagnostics, the HLC monitors all system inputs and handles emergency stop signals. Additionally, the HLC based on LabVIEW Real-Time communicates system information back to our 3D simulation environment and real-time simulator that runs the dynamic robot model.
Water Hydraulic Manipulator for CMM
The Department of Intelligent Hydraulics and Automation at Tampere University of Technology created a water hydraulic manipulator (WHMAN). It performs other remote handling operations inside the ITER diverter, such as cutting, bending, and welding pipes; locking and unlocking cassettes; and assisting the CMM during cassette installation and removal. The WHMAN is installed on top of the CMM to assist with remote handling operations. The manipulator has eight degrees of freedom in joint space, which provides the dexterity to cope with the constricted space in the ITER maintenance tunnel.
We control the WHMAN using LabVIEW Real-Time and NI data acquisition devices in a desktop target. An NI PCI-6031E multifunction DAQ board measures many types of sensors such as pressure, linear-voltage differential transformer, temperature, and POT3. The analog output channels on the same device control the servo drives and valves of the WHMAN system. We can extend the number of control channels using an NI PCI-6703 board. We use an NI PCI-6514 industrial digital I/O board as a general-purpose input and output device to access I/O from different subsystems. One of the force sensors requires a specific interface card to operate. Because the card was not shipped with a LabVIEW driver, we easily developed a driver using LabVIEW.
Author: Samuli Bergstrom
Marketing Engineer - National Instruments Finland