ITER Articulated Inspection Arm (AIA): Geometric calibration issues of a long-reach flexible robot

Abstract

This paper is part of the Remote Handling (RH) activities for the future fusion reactor ITER. Specifically it relates to the possibility to carry out close inspection tasks of the Vacuum Vessel first wall using a long reach robot called the “Articulated Inspection Arm” (AIA). Early studies for this device identified the need of improving the accuracy of the end-effector position in such robot structures. Therefore, the aim of this R&D program performed under the European Fusion Development Agreement (EFDA) work program is to develop a flexible parametric model with localised compliances of an AIA-like system, in order to compensate for its flexibilities. The geometric calibration is performed using a non-linear multivariable optimisation technique, which minimizes the average error between the simulated and real robot position. The optimised set of parameters, tested on the first segment of the robot, enables to divide by 3 the error on the end-effector position, in comparison to a rigid model. We expect better prediction after mechanical improvements to reduce the serious backlash in the joints. The prediction model applied to the whole arm will enable errors to be reduced from more than 1 m, in some configurations, to a final accuracy of a few centimetres.