Key Technology For Underwater Self-Reconfigurable Robot

Underwater self-reconfigurable robot(USR)is a new conceptional underwater modular robotic system.It comprises of a number of intelligent modules,which are simply structurized and functionally distributed.These modules are connected together to achieve general function by means of multiply modules' cooperation.In contrast with fixed-shape and highly structurized normal underwater vehicles,the structure and function of USR are highly distributed,each module is an intelligent module which is able to act as an agent with environment perception,motion,detection and working abilities.USR can change its configuration and choose different motion ways according to different environment and its own function and configuration.All of these enhance its adaptability to different and complex environment or tasks.Because of modular design,this system owns good quality in fault recovery,and is easy for maintenance and system expansion.Concerned with underwater self-reconfigurable robotic system,extensive studies on the technologies of general design in modules and robotic system,reconfiguration strategies,underwater docking,theory of underwater swimming for open topological configuration and motion planning strategies for bottom touched gaits have been conducted in this thesis.The prototype modules have been developed and the function and technologies have been verified on the machine by a mass of tank experiments.The basic unit in self-reconfigurable robot is module,which makes module design to be a key point in USR's research.The function of module will directly determine the ability of reconfiguration,reliability of underwater connection,rules of stabilities and dynamics characteristics and strategies of locomotion control and plan.In this thesis,it presents the general rules in USR's general design and module design.The relationship between buoyancy and gravity has been proposed.Solutions in general design,buoyancy adjusting,underwater docking device,bus control strategies have been analyzed in details,all of these provide basis rules and means for USR's general design.Underwater docking a key action in USR.The problem has been divided into three phases,which are preliminary close,short range leading by control system,keeping touch by machinery leading.By docking planning in preliminary close,the dock path has to be take into account to avoid collision problem.The rules have been proposed by the method of self-similar segmentation.A successive approximation method is applied and can avoid module collision effectively.The fine trim for adjusting the pose of the end plane is used based on Jacobian matrix.As basis action,the priority in angle,tangential and normal direction refers to the end plane has been analyzed and tested by photoelectrical leading system,the docking control strategies based on photoelectrical leading and sensor aid plane matching has been researched and the optimization algorithm has resolved the underwater docking problem.In the last,tank tests have verified the validity of the method.Through studying the characteristics of the modules and topology configuration,a graphic topology analysis method of USR was built,and this method was used to analyze the USR system configuration and reconfiguration processes.Based on multi-body dynamics theory and the topology analysis method above-mentioned,kinetic theory was derived for USR open configuration in water.Through dynamics modeling and simulation analysis,swimming gaits of octopus and winding which based on snake-like robot theory,were designed and validated by simulation and water-tank experiments.Based on module behavior and planning analysis,USR gait control method was built,and bottom-touched gaits were designed and implemented with this method for typical configurations(Creeping,Rolling and Quadruped).Through analyzing the adjacent gaits movement process for typical configurations,manipulator mechanism interference could be avoided effectively in motion planning process,thus the preset gaits can be performed with coherent and stable states.To ensure the coordination of gaits,time sequence relation of legs and law of motion were studied;in this moment,movement efficiency of bottom-touched gait could be increased greatly.Simulation and water-tank experiments were used to validate the correctness and effectiveness of bottom-touched gaits.The strategies of docking and gait plan described in this thesis are significant for the reconfiguration and coordinately motion control for USR.It has built a basic theory and research platform for underwater self-reconfigurable robot,and it is also valuable for research and development of other new underwater vehicles.