AAUC, Mechtronics Lab
Marine fouling on ship hulls requires constant maintenance in inspection and maintenance. Yet, various underwater structures and facilities demand even more technical inspection and maintenance.
In the past few years, some hull cleaning robots can propel themselves in free water to approach then attach to the ship hull by suspending their bodies with wheels or caterpillar tread. The advantages on the dual-mode configuration are summarized :
- Increased access and adaptability to complex topography by attaching/detaching the surface.
- Improved mobility achieved by switching to swimming mode.
The Searazor is designed as a universal platform to perform inspection and maintenance on various curved surfaces such as ship hulls and other underwater structures. The vehicle is capable of locomotion both in free-water and on ferromagnetic surfaces with two wheels and two vectored thrusters.
The Searazor prototype aims to transition between the two disciplines of swimming and climbing, in order to roam about complex curvatures, especially at stern, bow or even on the propeller. This design is expected to expand the operation range to inaccessible areas for state-of-the-art underwater vehicles.
Its primary locomotion mode, climbing mode, consists of attaching to the ship hull with two magnetic wheels, accompanied by a pair of vectored thrusters to propel and balance the body. The Searazor’s secondary locomotion mode, swimming mode, is used when the robot is firstly deployed or detached from the surface, during which the robot can manoeuvre in free water using its thrusters.
Achievements and Challenges
The Searazor platform is a mechatronic system, which inherits strong dynamic characteristics and demands advanced control schemes. Therefore, simulations have been be carried out prior to the design.
The simulation model is built with bond graph method. A servo control system that governs the attitude and steering is also implemented. These models are then assembled to a rigid body under the force input from thruster, wheels and environmental factors. The resulting motion of the vehicle under human manoeuvring input is simulated in 20-sim software.
The simulation currently provides support for the Searazor prototype design. The entire model will be the simulation framework for developing and testing control algorithms for maneuvring the vehicle in complex marine environments.
The dual-mode configuration is regarded as the key feature of robotic platform. The issues brought by the transition of locomotion mode exist mainly in the control schemes. In the control system, the transition reflects problems in switching between two schemes in dealing with sensor information, actuators and maneuver.
Besides the control system, our research and development team also need to encounter common problems in underwater measurement, communication and navigation.
The project is funded by Aalesund University College and Regionale Forskingsfond Midt-Norge. The research is supervised by Prof. Hand Petter Hildre and Prof. Houxiang Zhang, and conducted by the doctorate candidate Cong Liu. Two students Kenneth Strandabø and Lars Reidar Brekke are also involved in the development.
Up to May, 2013, our research team has been engaged in the detailed design of the first Searazor prototype. The preliminary experiment and test are planned to carried out in Autumn 2013 in the new towling tank at Aalesund Univeristy College.