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

Huapeng Wu, Heikki Handroos and Pekka Pessi

Institute of Mechatronics and Virtual Engineering, Department of
Mechanical Engineering, Lappeenranta University of Technology
P.O.Box 20, FIN-53851 Lappeenranta, FINLAND

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.

KEYWORDS

Parallel robot, ITER vacuum vessel, Machining/welding, water hydraulic.

INTRODUCTION

ITER sectors require more stringent tolerances than normally expected for the size of structure involved.
The outer walls of ITER sectors are made of 60mm thick stainless steel and are joined together by high
efficiency structural and leak tight welds. In addition to the initial vacuum vessel assembly, sectors may
have to be replaced for repair. Since commercially available machines are too heavy for the required
machining operations and the lifting of a possible e-beam gun column system, a new flexible,
lightweight and mobile robotic machine is being considered.
Traditional industrial robots that have been used as general-purpose positioning devices are open chain
mechanisms that generally have the links actuated in series. These kinds of manipulators are more
suitable for long reach and large workspace, but are inherently not very rigid and have poor dynamic
performance at high speed and high dynamic loading under operating conditions. Compared with open
chain manipulators, parallel mechanisms have high stiffness, high accuracy and high force /torque
capacity in a reduced workspace and have found many applications in manufacturing systems [1][2][3].
Since there are no commercial solutions applicable to the ITER environment, a new robot system, using
water hydraulic drives to achieve the required force density, has been developed by the authors in
IMVE in Lappeenranta University of Technology and a prototype was built for testing.