This paper presents trajectory tracking control of ROV-which is used for lifting and transporting large and heavy objects. The ROV is expected to have relatively complicated con∼ figuration due to large thrusters, and its dynamics is highly nonlinear. Sliding mode technique which can handle the nonlinear dynamics was employed. Experiments were conducted using a small ROV model with four thrusters. Surge and Yaw are· controlled by two horizontal thrusters. Heave and Sway are controlled by diagonal thrusters. The ROV model used in the experiments was relatively small, and high accuracy was required for the positioning sensor system. An ultrasonic ranging system whose accuracy is lmm order was developed for the basin test.


In offshore oil development in deep waters and construction of huge offshore platforms for ocean space utilization, time for underwater operation become very long. Direct human activities are limited due to safety and cost of long time operations. Especially in deep waters, environments are hazardous for human and ROVs become useful tools. ROVs developed so far a.re mostly platforms of sensors and used for" data collection such as inspection. Few ROVs have trajectory tracking ability which is important for long time operation[l4]. One of a few systems which has such ability is JASON system[4]. Work horse ROVs which have trajectory tracking ability are needed for lifting heavy objects for installation and repair of offshore structure. Computer controlled trajectory tracking ability of ROV will dramatically reduce the load on operator. In transporting stage, operator have only to give information about trajectory to ROV. This enables the long time operation in deep waters. One problem arisen

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