To develop and test, under simulated operating conditions , a new computer assisted underwater telemanipulation system aimed at the execution of tasks now performed by divers, and not feasible by means of the existing directly controlled underwater manipulators mounted onboard ROVs (Remotely Operated Vehicles).
Typical tasks include inspection of nodes of offshore platforms and light manipulation on submarine wellheads.
See project TH./07077/89/IT.
The lab tests were carried out simulating a docked vehicle placing the skid in front of a full size structural node, and a hovering vehicle mounting the manipulator base and the TV-Trackmeter csmeras on a moving base placed close to a well head mock-up.
The test results showed a faster and safer task execution with the supervisory control: the close visual inspection was carried out in a time two to five times shorter than the master/slave, the optimal water jet cleaning of the weld node was performed automatically, the NDT (Eddy Current) inspection was reliably carried out automatically keeping the probe with the proper alignment (this task is simply impossible with the master/slave approach). Furthermore the moving base trials demonstrated the feasibility of tasks such as valves actuation, insertion of a guide line or a transporter, cutting of a wire rope, due to the automatic base motion compensation implemented using the TV-Trackmeter.
The overall system is composed of a console (including processing units) and a skid which is to be mounted on a Remote Operated Vehicle (ROV). The skid includes the remote arm, the tool package and the TV cameras. The console includes the supervisory computer, a graphic system which shows simulations and an elarged view of the remote scene, a touch panel to select functions and tasks, joystick and master arm. Furthermore a computer vision system (TV-Trackmeter ), fitted with stereoscopic underwater TV cameras, provides a geometric modelling of the remote environment.
The main system functions include :
- fully automatic task execution (e. g. cleaning of a node weld with a water-jet tool);
- computer assisted operations (e. g. Non Destructive Test probe motion according the joystick commands with automatic probe alignment along the weld direction; this operation mode is referred to as "resolved motion");
- manual operation (i. e. master/slave).
Since the TV-Trackmeter can provide the coordinates of working scene points even if it is moving, the system is able to perform tasks with a loose docking or a hovering vehicle.