3. Positioning an imaging subsystem to allow visual inspection of welded 

 joints and structural members. Candidates include still- and motion- 

 picture photography, as well as conventional and solid-state TV. 



4. Attaching a line onto instrument packages or navigation transponders 

 through a hook arrangement to recover such packages from underwater 

 structures or in the vicinity of pipelines on the ocean bottom. 



Similar tasks are envisioned for Navy missions involving search, rescue, 

 and recovery operations. However, the attempt of the research and development 

 effort described here is not to provide a work system for immediate use on a 

 Navy mission, but rather to perform the research necessary to develop the 

 concepts basic to the design of such systems in the future. 



2.2 COMPONENT TRADEOFFS 



The choice of components was dependent upon developing a manipulator 

 capable of underwater operation to 2000 feet and operating on a free-swimming 

 submersible. Thus power efficiency, size, and weight became important factors 

 in the design philosophy. In addition, cost and time restraints forced the 

 use of off-the-shelf components wherever possible. 



2.2.1 Power Source 



The most important decision was the choice between an electrohydraul ic- 

 and an electromechanical-powered manipulator system. An electromechanical 

 system was chosen for the following reasons: 



- Off-the-shelf components for an electrohydraul ic system such as 

 cylinders, pistons, pump, and valves are larger in size and weight and 

 are clumsier than the counterparts for the electromechanical system. 



- The power consumption of a hydraulic system is greater because the pump 

 has to be operated during the entire operating time of the manipulator 

 system, while an electromechanical system consumes energy only during 

 the periods when the linkage and joints need to be actuated. 



- Dc motors start and stop smoothly and both high and low speeds are 

 easily obtained while the movement rate of a fluid system is not easily 

 adjustable during operation. 



- The wiring system is much simpler than an electromechanical system, 

 while complex internal fluid routing plus wiring is required for 

 position feedback devices of an electrohydraul ic manipulator system. 



- The outside mechanical configuration of a manipulator with electric 

 drives tends to be smoother and sleeker than a hydraulic-powered 

 manipulator with external hydraulic lines feeding each motor. A smooth 

 and sleek mechanical design helps prevent entanglement in the 

 underwater work environment. 



2.2.2 Electric Drive Assembly 



At operating depths of 2000 feet, electric drives need to be internally 

 pressurized to balance the external pressure. Otherwise, the sealing of 



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