ABSTRACT

Sonsub North Sea Ltd IS a part of the Sonsub group of companies which has been involved in the application of remote systems technology to the subsea environment for a number of years.

Primarily, Sonsub has been supporting the various requirements of the Offshore oil and Gas Exploration and Production industry. The use of robotics and other remote systems technology to successfully complete work tasks In the subsea environment, has presented challenges that have required an innovative approach to the use of telerobotics.

Remotely Operated Vehicles (ROV's) are a form of robotics that have been utilised In the Offshore oil and Gas Industry since the early 1970's. However, until recently, their use has been restricted to observation and light manipulator work, utilising a variety of rate feed, spatially correspondent or tactile feedback manipulator systems.

The Challenge remains to develop systems that have the ability to carry out human equivalent tasks presently performed by divers, thus enabling personnel to be removed from this hazardous environment. There are numerous difficulties to be overcome In meeting this challenge and this paper addresses a particular philosophy and methodology adopted by one company to service the needs of its customers.

The Problems

Taking telerobotics and remote handling technology into the subsea environment presents its own unique problems. The most obvious problem is ensuring that all electric, electronic and mechanical components are suitably protected against seawater and the pressures encountered when working at depth. Other less obvious, but equally critical problems related to the operating environment are as follows.

Sea Surface Conditions

This affects the launch and recovery of the relevant ROV systems and can cause considerable delay to operations whilst waiting for weather conditions within the system's launch and recovery limits. If work IS taking place from a floating vessel rather than a fixed offshore structure, unfavourable surface conditions can also have a dramatic effect on the station-keeping ability of the vessel. The need to carry out repair and maintenance to quite sophisticated electronic equipment on the deck of a heaving vessel In a severe storm, can challenge the skill and patience of the most qualified and experienced Technician.

Ocean Currents

The business end of an ROV system IS basically a vehicle which IS able to "fly" through water on the end of a control tether or umbilical carrying all power, signal and data conductors. An ROV is flown In a similar fashion to a helicopter, In that it IS free to move In all planes and has the ability to hover. The ROV IS subject to prevailing ocean currents as a helicopter is subject to prevailing winds. One major difference IS that the helicopter pilot has the advantage of "presence" and a feel for the conditions affecting the machine.

The ROV pilot does not have this added dimension and can only fly and operate manipulators by vision with limited assistance from tactile sensors. It IS this lack of direct "presence" or "feel" that can make the performance of manipulative tasks extremely difficult.

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