DEVELOPMENT OF A TELEROBOTIC UNDERWATER MANIPULATOR

For more than the past decade, Remotely Operated Vehicles (ROVs) have been utilised in the oil industry for a plethora of tasks associated w ith offshore oil exploration and production. Initially, they were only used for observation but with the advent of the larger more sophistic ated working class ROVs their functions have expanded to include inter vention tasks, such as valve operation and component replacement. In a further attempt to replace divers with ROVs for subsea operations, Mo bil North Sea Limited has been involved with developing means for perf orming non-destructive testing inspections of the welds joining struct ural members on offshore production platforms. The paper discusses the design of a special-purpose manipulator developed to place various ty pes of NDT devices on or near welds with sufficient accuracy to find s urface and near-surface fatigue cracks with a high probability of dete ction. Special computer software was developed to accurately model the work piece in situ, define the intersection of the structural members and to compute the trajectory that the manipulator must follow to acc urately track the welds. The software interfaces with the manipulator controls to provide command signals to guide the NDT device along the computed trajectory, thus allowing the inspection to be performed; a t ask that would be virtually impossible if required to be accomplished using conventional master/slave control. Three-dimensional video feedb ack is provided to the manipulator control system to correct the path of the NDT device along the desired track. The system also incorporate d teach and learn techniques, collision avoidance and automatic manipu lator parking. Test results of the system trials are provided.