Hybrid Parallel Robot for the Assembling of ITER

The international thermonuclear experimental reactor (ITER) is a joint international research and development project that aims to demonstrate the scientific and technical feasibility of fusion power. The reactor tokomak (vacuum vessel) is made of stainless steel, and contains nine sectors welded together; each sector has about the size of 10 meter high and 6 meter wide. The sectors of ITER vacuum vessel (VV) (Fig. 1) require more stringent tolerance (±5mm) than normally expected for the size of the structure involved. The walls (inner wall and outer wall) of ITER sectors are of 60mm thick and are joined by high quality leak tight welds. In addition to the initial vacuum vessel assembly, the sectors may have to be replaced for repair. Meanwhile, the machining operations and lifting of a possible e-beam gun column system require extreme stiffness property and good accuracy for a machine tool. The payload to weight ratio also has to be significantly better than it is in the commercial industrial robots. The conventional robots, providing a high nominal payload, are lack of stiffness and accuracy in such machining condition. Since commercially available machines capable of handling large payloads require floor mounting and their workspaces are insufficient for reaching the cross section at a single mounting position, a special robot is needed. Parallel robots have high stiffness, high dynamic performance and good payload to weight ratio in comparison with the conventional serial robots. Stewart [1] presented the novel idea of sixdegree-of-freedom parallel robot in 1960’s. A remarkable number of research articles and books about parallel manipulators have been published during the last two decades. There are also a number of successful industrial applications developed [2], [3], [4], [7]. The parallel manipulators have many potential advantages compared with the conventional serial link manipulators. Parallel manipulators are closed-loop mechanism presenting good performances in terms of accuracy, rigidity, high speed, and ability to handle large loads. They are becoming popular in applications such as machining, welding, assembly, flight and vehicle simulators, mining machines, and pointing devices [2], [3], [4], [7]. The most important drawback of parallel robots is the small workspace, which can be made larger by adding additional serial axes in the robot. For the assembly of the ITER vacuum vessel sector, the precise positioning of welding endeffectors at some distance in a confined space from the available supports will be required, Source: Parallel Manipulators, Towards New Applications, Book edited by: Huapeng Wu, ISBN 978-3-902613-40-0, pp. 506, April 2008, I-Tech Education and Publishing, Vienna, Austria O pe n A cc es s D at ab as e w w w .in te hw eb .c om