Development of an underwater manipulator mounted for an AUV

Oceans, the familiar environment for us, are an attractive environment because of abundant mineral resources, energy, space, and so on, and underwater research and development are carried out rapidly during recent decades. However, the extreme conditions such as high water pressure, invisibility and non-oxygen become great barriers for human to access directly. Underwater robots are expected and developed as efficient tools for the operation instead of human beings. In order to realize underwater robots, the autonomy and intelligence of robots are one of the most important research topics and AUVs are the new tools for underwater operations. The demand of getting work using AUVs will increase and the missions become more and more complicated. Therefore, manipulators which are mounted on AUVs are expected to play an important role for complex tasks. This paper discusses the dynamics and control of an underwater robot equipped with a manipulator. The motion of multi-body systems in underwater environment has a lot of difficulties because that all bodies are not kept on fixed objects, and the movement of a body effects other bodies and excites each other, etc. The fluid dynamics also makes the problem more complicated matter. The nonlinear forces, such as drag forces and hydraulic forces, act on both the manipulators and the robot vehicle. Recent years, many studies on underwater vehicle-manipulator systems (UYMS) have been examined. We have also studied dynamics and control of a manipulator mounted on a robot in horizontal and vertical plane and proposed a method using resolved acceleration control (RAC). In this paper, kinematics and dynamics of a 2-link underwater manipulator mounted on an AUV "Twin-Burger" which was developed as a testbed for intelligent software development, and a RAC method for underwater manipulator is described. Next, the routing algorithm using the dynamic manipulability of the robot is proposed considering the coordinate action between manipulator and AUV. In order to evaluate effectiveness of the RAC method and the routing algorithm numerical simulations are performed. The simulation results show the good control performance. Based on the simulation, we designed a Manipulator using a CAD system. Magnet coupling method is introduced to transfer torque into the joints in order to realize waterproof mechanism. Finally, we examined the performance of proposed path planning algorithm through experiment