Research On AUV Acoustic Guidance And Motion Control Technology For Autonomous Docking

Autonomous underwater vehicle(AUV)plays a big role in underwater exploration by merit of its small size,light weight and high mobility without any restriction of the cable.The exploration of the sea has gone deeper and farer.To fulfill this,higher demands on the range,depth and duration of underwater vehicles must be met.Power supply and data transmission are great challenges for underwater robots with long range,long endurance and large depth.Underwater docking is an effective way to realize underwater charging or data transmission.In this thesis,motion control for underwater docking is studied.The purpose of this study is to realize the precise guidance and motion control of the underwater robot during docking to the recovery platform.The traditional long range AUV has remarkable long distance cruising capability.While the autonomy and accuracy is relatively poor.The precise navigation,accurate path following and precise spot positioning is key for underwater docking.Precise navigation and motion control technology are greatly demanded.This is also the main focus of this thesis.For underwater navigation,the Ultroshort Base Line(USBL)is adopted.First,the orientation and position of AUV relative to the docking system is computed using the acoustic signal transmitted between the positioning array and the transponder.The acoustic signal is filtered to eliminate the noise in the data.Then,the path planning system guides the AUV towards the docking system using the position and orientation acquired in the previous step.The docking can be divided into two processes depending on the distance between the AUV and the docking system.The first process is long range guidance adopting pure fixed point tracking control method.The second process is short range distance control adopting lateral error control guidance method.The propulsion/steering system and the motion control algorithm are optimized through the kinematic and dynamic analysis.This is the focus of this thesis.Depending on the motion state during docking,the motion control can be categorized into three types which is planar path precise following,stable depth adjustment and depth-keeping control,and dynamic spot hovering respectively.These three types of control strategy are all studied in this thesis.The control strategy is simulated and tested in MATLAB/Simulink environment.And those control strategies are also validated through field experiments.The AUV studied in this thesis is of torpedo shape.The length of the vehicle is 8.86m with diameter of 534mm and weight of 2t.The cone shaped docking system with positioning and locking mechanism is adopted to achieve accurate fixing.Also,power Interface is adopted in docking system to underwater power supply and data transmission.Based on lessons learned through field test,the cone shaped docking system is simplified to be square shape to better fulfill its function.And at the base of improvement of the design of navigation and positioning system and the improvement of the precise motion control system,the AUV autonomous docking recovery test is carried out on the lake.It is concluded that the acoustic guidance and motion control technique proposed in this paper can effectively realize the docking of AUV.