Development of a dynamic positioning system for unmanned mud sampling vessels using variable structure control

Morito, Makoto*; Yoshimura, Koki*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa   

We study control systems for an Unmanned Surface Vehicle for mud extraction. Mud sampling USV is equipped with a mud sampler, which is lowered to the seabed by a winch for sampling and surveying. During mud sampling surveys, the cable between the hull and the mud sampler should be slackened so that the mud sampler and the hull do not influence each other through the cable. Strong winds blow in the area to be surveyed during the winter months and many momentary gusts are observed. This requires strong position and angle control (Dynamic Positioning) to prevent wind effects for the USV to extract mud. The USV has main thrusters for forward and backward travel and bow thrusters/stern thrusters for left-right travel and turning. During mud extraction, the main thrusters are used to move the vessel forward and backward, and the bow and stern thrusters are used to move left and right to maintain the position of the hull in which the mud extraction is carried out. During DP (Dynamic Positioning), the bow thruster and stern thruster are used to hold the bow heading of the USV constant, preventing the twisting of the cable connecting the USV to the mud sampler. Therefore, when the USV performs DP, it is necessary to properly perform three controls: Surge control, Sway control, and Yaw control. At this time, both Sway and Yaw control of the USV using bow and stern thrusters.