Central to the ARM Project, the manipulator hardware 1s required to demonstrate the capability of automatically tracking welds on subsea structures for inspection purposes At the outset of the Project, detailed analysis of the kinematics involved was carried out Further modeling work added to the knowledge of the required geometries to be covered by the manipulator This specification has subsequently been developed into the ARM itself
The manipulator is used in conjunction with an associated suction attachment system This latter system enables the carrier ROV to be docked onto the subsea structure and hence provides a reasonably stable work platform The sensory control systems are then utilised to drive the manipulator along the required trajectories to perform the tasks
Further work has demonstrated the probability of increased productivity by using an additional two-function manipulator deployment system This effectively reduces the number of times the system has to be relocated and redocked to ensure total weld coverage
This paper describes the results achieved to date with the prototype ARM system
The ARM Project is based on a list of requirements for cleaning and inspection of a variety of node types of varying chord and brace sizes Gwen the requirements a period of concept design study was embarked upon in order to derive an agreed working specification for the equipment to be developed This work involved analysis of currently available manipulators and display-modeling of operating envelopes with particular assessment of geometries suitable for the envisaged tasks
A manipulator specification was thus developed along with a control/software specification This formed the basis of the project It was intended that the manipulator be part of a package which included an attachment system for the carrier vehicle (ROV) and this was also incorporated into the investigation and specification process Development of actual hardware and software followed and details are discussed In the following sections During the hardware development phase, an additional area of technology was addressed, incorporating the Camera Alive vision equipment A preliminary task based on a Puma 560 was initiated to assess feasibility of the technique for use in the main project The interfacing of all the constituent parts above, will result in live trials with typical nodes at the NDE Centre in London Results thus far are covered at the end of the presentation
The general aim of the ARM Project is to produce a prototype subsea manipulator arm capable of deploying NDT sensors to automate inspection of subsea structural welds To set the requirements for the manipulator, task definitions had to be initially outlined The base areas addressed were :-
1) Cleaning
Weld surfaces need to be cleaned for NDT Inspection
2) Inspection
NDT system types were identified and assessed for potential use with the arm
3) General Purpose Requirements
During any cleaning/inspection operation, other tasks may well crop up The arm should be capable of addressing a variety of these tasks
