The TV-Trackmeter and the Supervisory-Controlled Underwater Telemanipulation System
Authors: Maddalena D. , Bossi L. , Visentin R. 
Published: October 2008

This paper presents two systems developed by Tecnomare aiming at increasing the efficiency in performing underwater telemanipulation tasks. The first system is a non contact measuring device which, on the bas is of stereoscopic TV image processing, can provide 3D coordinates of points imaged by means of a stereo TV camera, even in case of relative motion between cameras and working scene. Current and future applications of this system are relevant to underwater robotics, navigation, surveys, archaelogy and biology studies. The second system is the supervisory controlled telemanipulation system which includes as key components the TV-Trackmeter and the supervisory control computer. The main features of this telemanipulation system are:–computer aided control of arm movements;–high level man-machine interface;–ability to measure the geometry of the work environment, by means of the TV-Trackmeter;–ability to carry out typical underwater N.D.T. tasks;–automatic compensation for manipulator base movements.

The increase of operational efficiency of this system with respect the traditional master/slave approach is demonstrated by dry and wet laboratory tests performed on a full acale platform node.

INTRODUCTION

The increasing use of R.O.V.'s (Remotely Operated Vehicles) and underwater robotics in the offshore industry for platform inspection/maintenance, for work on deep water subsea well completion etc., is evident. As a matter of fact the use of remotely controlled robot instead of divers means more safety for human beings and better economics especially with reference to saturation diving intervention. Unfortunately the currently available underwater robots cannot fully replace the divers except in a restricted set of simple tasks: divers are still necessary to perform tasks such as close visual inspection, N.D.T. (Non Destructive Test) inspection, maintenance operations, etc. Furthermore, the available underwater telemanipulation systems require extensive training for the operators and the practical execution of tasks generally requires more time than is reasonable to foresee. The basic reason for this is related to the simple master/slave approach used in these systems. In fact, they typically cons is t of a slave underwater arm mounted on an R.O.V.; such an arm is remotely controlled by a master arm which is a scaled replica of the slave and is placed in the R.O.V. control room. The operator uses the master to move the slave and he monitors the task execution by means of one or more TV cameras. Needless to say this approach is rather limited and very often it results in a dangerous and time consuming trial and error process. The system presented in this paper aims at solving such problems in order to dramatically enlarge the applicability of underwater robotics by increasing its efficiency and reliability even in the execution of complex tasks such as N.D.T. inspections. The key components of this system are the TVTrackmeter and the supervisor control computer: basically the TV-Trackmeter provides a geometric modeling of the working scene while the supervisor control computer, on the basis of this geometric modeling, provides a useful interface between operator and robotic arm. With this approach the operator is still in control of the system by means of high level commands such as "fetch the tool A", "clean the node", "move the N.D.T. probe up" and so on, while the computer translates such commands into low level motion commands to be implemented by the robotic arm.