Vertical Thrusters Research Articles

Thruster fault-tolerant control of a hovering AUV with four horizontal and two vertical thrusters

This paper deals with the motion control of a hovering autonomous underwater vehicle (AUV) with four horizontal and two vertical thrusters, when one or more thrusters are completely malfunctioned. Three thruster fault cases are considered: one horizontal thruster is faulty; two horizontal thrusters are faulty; and one vertical thruster is faulty. Through a series of simulations and an experiment, it is validated that the AUV can track a planned path in a 3-D space with minimally three thrusters (two are horizontal ones); however, some cases require the changes of the vehicle’s preferred direction of motion and its movement manner. Additionally, when the number of active horizontal thrusters is less than the required degree-of-freedom, a continuous state feedback control law does not exist due to the non-holonomic constraint. This paper highlights that the hovering AUV can overcome the non-holonomic constraint if using the feature that their translational and rotational motions can be controlled independently.

Experimental Verification of Lifting Force of Underwater Robot with Thrusters Using Passive Posture Maintenance

An underwater robot is developed that can be used for environmental protection work in the sea near Okinawa (e.g., removing crown-of-thorns starfish). When a submerged object is raised with the aid of an underwater robot, the conventional method of using fixed thrusters presents difficulties in raising the object straight upward because of the change in the robot’s attitude. Therefore, we propose “thrusters that employ a passive posture maintenance mechanism.” By using this mechanism, the vertical thrusters are able to maintain an upward posture, and the underwater robot is able to raise a submerged object straight upward relatively easily. Moreover, the attitude stability of an underwater robot and the work efficiency of its thrusters are important in water. Hence, we examine the attitude stability and the efficiency of the lifting force of an underwater robot using our proposed passive fixed mechanism for thrusters. We describe the design and fabrication of the proposedmechanismand experimentally verify the effectiveness of our proposed mechanism.

2A2-N04 受動型スラスタ姿勢維持機構を用いた水中ロボットの引上力の検討(水中ロボット・メカトロニクス)

In recent years, coral predation by crown-of-thorns starfish has become a serious problem. Therefore, authors have been developing an underwater robot to capture the starfish. The robot has two vertical thrusters, which are used for vertical movement control of the robot. The robot can lift a underwater object by a thrust of the thruster. In the case of conventional fixation method, however, lifting force is lost. Because the vertical thruster is locked rigidly to body of the robot. For that reason, we propose the passivity posture maintenance mechanism for a thruster, in order to use a thrust of the vertical thruster effectively. In the lifting force measurement experiment, we confirmed the effectiveness of this mechanism.

Design of low-cost unmanned underwater vehicle for shallow waters

Unmanned underwater vehicles (UUVs) have received worldwide attention and been widely used in various applications. In this paper, a recently developed low cost UUV prototype at the University of Canterbury is introduced, which is designed specifically for shallow water tasks, especially for inspecting and cleaning sea chests of ships for bio-security purpose. The main hull of the UUV is made of polyvinyl chloride (PVC), with a 400 mm diameter and 800 mm length. External frames mount two horizontal propellers, four vertical thrusters and power is derived from onboard batteries. The maximum thrust force of up to 10 kg that is provided by the propellers can generate a forward/backward speed of up to 1.4 m/s for the 112 kg UUV. The vertical thrusters provide depth control with a max thrust force of 20 kg. The UUV is equipped with a range of sensors capable of sensing its instantaneous temperature, depth, attitude and surrounding environment. Costing less than US$10,000 for a prototype, it provides an excellent platform for further underwater vehicle development targeting shallow water tasks with a working depth up to 20m.