Research On Impedance Control Of Underwater Manipulator

Along with the quickening of ocean developing process, the requirement of underwater working equipment is increasing day by day. The intelligent working level of underwater manipulator is raising due to the complex mission of underwater exploration, salvage, pipeline inspection and repair. The force control study has important theoretical study significance and practical application value to improve underwater working ability and intelligent level.Due to the ocean environment, coupling influence between the environment and the ship and also the restriction of underwater communication technique, it is hard to carry out manual intervention and monitoring. The control technology, including position and force control, is basic and critical one of underwater manipulator's autonomous operation.According to the fact that the original underwater manipulator can't realize attitude control, the degrees of freedom of manipulator have been improved. The kinematics model of the modified underwater manipulator has been established. The operation space has also been analyzed. The underwater manipulator of being installed on the movable vehicle can implement larger range operation. Therefore the kinematics model of underwater vehicle-manipulator system is established, and inverse kinematics is also studied.On the condition of constrained environment, the manipulator's dynamic characteristics is analyzed, and according to underwater environment, the effect of ocean current,water resistance,additional mass force on system dynamics is also analyzed. The force control system of underwater manipulator is established, which is based on impedance control. This system combines force control and position control into a framework. The target impedance is realized through double closed-loop including position inner loop and force external loop. The effect of target impedance parameter on the performance of force control is discussed and the impedance parameter regulation law is summarized.Through the adjustment of the reference trajectory, impedance control indirectly achieves force control. Taking the uncertainty or unknown of underwater environment into account, it is difficult to given right reference trajectory. In this paper, an off-line estimation method is presented. Using this method estimates the uncertainty parameters of a single environment and can draw a comparatively precise position and stiffness of the environment, in order to get the reference trajectory. A new parameter estimation method is proposed according to uncertain environment. This online method is based on force and position feedback information to estimate the environment parameters. Without needing mission plan, this method would get a reference position to move manipulator. Underwater manipulator can follow the surface of an unknown environment with the hope contact force. Through computer simulation experiments verified force tracking capability of the proposed control strategy.Taking the underwater 3 joint manipulator as experimental carrier, the position and stance control experiment is carried on, and grasping target object is realized. The force tracking experiment of manipulator under multi-constrained environment is completed. The validating experiment is carried on aiming at reference trajectory estimation. The result validates the validity and feasibility of the control strategy and method.