Study On Critical Control Issues For AUV Docking Applications

Under water recovery of AUV including its autonomous homing and docking operation.Thus,it is easy to build physical connection between ocean mobile observation node and deep-sea fixed base station.After the research on the academic results of relevant fields,it could be concluded that AUV recovery is facing many control problems.The main problems are as follows:local navigation,that is position relationship between AUV and the dock;homing path planning under constraints;3-dimensional trajectory tracking control with complex disturbance of current;the trial technology of AUV’s recovery,etc.Facing the above problems,solutions are as follows:Firstly,a local navigation system is built which is based on underwater light vision navigation.The system compromises data from both light vision navigation and dead reckoning navigation and gives relatively frequency band and decimeter level precision of navigation data.The light vision navigation system is composed of four LED light sources which are located in the entrance edge of tapered docking station,binocular camera equipped on AUVs,image collection card below and navigation computers both working on PC 104 bus.Active exposure control method of image collection was adopted to improve underwater imaging quality.Series of ways such as image enhancement,pseudo-lights out,sign matching,were employed to extract the point information of image.Aaptive fusion method of monocular and binocular location results was used to improve light vision location precision.Using fuzzy R matrixes adjusting method,kalman filtering was adopted to improve navigation precision and guarantee the steady output.Secondly,homing path planning method was put forward,which solved the difficulties brought by constrained condition in finite 3 dimensions space.Simultaneously,it gave an optimal homing path on considering the effect of current.Cubic B-spline curve theory representing a path was put forward.Control points were operated to change geometrical path features.Maneuvering feature of underactuated AUV was analyzed and it concluded constrained path condition from AUV motion and path ends.Consuming model under current disturbance was built based on semi-physical simulation platform.With constrain information and optimizing information expressed by the fitness function,evolution operation of genetic algorithm obtained feasible and optimal path.Path calculation and tracking experiment was performed on semi-physical simulation platform.It proved the algorithm to be high efficient running and also provided a path that meet AUV’s motion ability and task requirement.Thirdly,a hierarchical control structure was put forward based on decoupling control,which eliminating tracking errors by connection of guidance control and state control.It solved 3-dimensionally trajectory tracking control in spite of current disturbance.Take straight line tracking in horizontal plane as example,guidance controller adopts intelligent PID algorithm whose input is transverse error and output refers to reference handing angel.For the state controller,S algorithm was adopted with parameters adjusted adaptively refers to maneuvering model to track varying reference handing angel.Stability of control system is conjointly decided by the guidance controller and the state controller.Sufficient experiment were conducted,trials in lake and at sea proved the stability and reliability of the designed controller,the precision is 2.0m under a stiff current environment.At last,pool experiment was designed and carried out to verify key techniques.The AUV carrier was reformed,and a dock in the shape of "horn mouth" was also designed in matching the carrier.Individual test on navigation and control are performed firstly,the systematical experiment on docking secondly.Based on a previous AUV of 180kg degree,the unidirectional docking system was designed of "horn mouth" shape,applied the integrated structure of fiber reinforced polymer,of good friction and impact-resistant performance.Four LED lights were distributed at the edge of the entrance as mark points.AUV was equipped with binocular system which could illustrate the relative location to the dock.Overall,under pool environment,the control system make sure successful docking in various starting status of the testing AUV.