Pekka Pessi

Utilization of virtual prototyping in development of CMM

The characteristic advantages of hydraulics (high power density, simple construction and reliability) together with the characteristics of water as the pressure medium (fire and environmentally safe, chemically neutral, not activated nor affected by radiation) are highlighted in critical applications such as remote handling operations in International Thermonuclear Experimental Reactor (ITER). However, component cost and lack of wide selection of water hydraulic components make it difficult to build and to test complex water hydraulic systems. The use of virtual prototyping for the development of water hydraulic tools can be used to address this problem. Rapidly increased computational power has created conditions for extensive numerical calculations, enabling computer aided virtual prototyping to replace physical prototype phases in product development.

Mobile parallel robot for assembly and repair of ITER vacuum vessel

Purpose – The purpose of this paper is to build up a parallel robot for assembling, machining and repairing of the vacuum vessel of the international thermonuclear experimental reactor (ITER).Design/methodology/approach – The process of assembling and machining of the vacuum vessel need a special robot. By studying the structure of the vacuum vessel, a novel parallel robot is built, which has ten degrees of freedom driven by water hydraulic cylinders and electrical servo motors. Kinematic models for the redundant degree robot have been defined. A prototype has been built. Experiments for machine cutting and laser welding were carried out.Findings – The parallel robot is capable of holding all necessary machining tools and welding end‐effectors in all positions accurately and stably inside the vacuum vessel sector. The kinematic models appeared to be complex because of the redundant structure of the robot, and an optimization algorithm ensuring the maximum stiffness during the robot motion helps to find th...

MECHATRONICS DESIGN AND DEVELOPMENT TOWARDS A HEAVY-DUTY WATERHDRAULIC WELDING/CUTTING ROBOT

ABSTRACT This paper presents a special robot, able to carry out welding and machining processes from inside the ITER vacuum vessel, consisting of a five-degree-of-freedom parallel mechanism mounted on a carriage driven by two electric motors on a rack. The kinematic design of the robot has been optimised for ITER access and a hydraulically actuated pre-prototype built. A hybrid controller is designed for the robot, including position, speed and pressure feedback loops to achieve high accuracy and high dynamic performances. Finally, the experimental tests are given and discussed.

Modeling and Control of Water Hydraulic Driven Parallel Robot

This paper presents a novel mobile parallel robot, which is able to carry welding and machining processes from inside the international thermonuclear experimental reactor (ITER) vacuum vessel (VV). The kinematics design of the robot has been optimized for ITER access. Kinematics modeling is given in the paper, and control algorithm is designed for water hydraulic.

A Hybrid Parallel Robot

This paper presents a novel mobile parallel robot carries out welding and machining processes in assembly and repair of vacuum vessel (VV) of reactor (ITER). The kinematics of the robot has been optimized for the ITERs access. The kinematics analysis of the robot construction is given in the paper and the welding and machining experiments are demonstrated by a limited prototype.

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

A Mobile Hybrid Parallel Robot with Redundant Kinematic Structure

This paper presents a novel mobile parallel robot, which is able to carry welding and machining processes from inside the international thermonuclear experimental reactor (ITER) vacuum vessel (VV). The kinematic design of the robot has been optimized for ITER access. Kinematic analysis is given in the paper, and control algorithm is designed for water hydraulic.