Study On Dynamic Characteristics Of Underwater Exoskeleton Robots

Research on exoskeleton robots technology to enhance the ability of individual can be traced back to 1960 s.Considerable research results have been obtained in the recent 50 years.Underwater exoskeleton robots are defined as a wearable mechanical device for underwater operations.The application of exoskeleton robots to enhance the ability of the frogman in underwater environment is rarely at domestic and abroad.This thesis focuses on a series of studies on the dynamics of underwater exoskeleton robots.Based on the basic principle of D-H parameter method and coordinate system transformation,the coordinate system of underwater exoskeleton robot and its simplified structure are established.The D-H parameters of all the connecting rods of the robot and the transformation matrix of two adjacent coordinate systems are deduced.In order to ensure good man-machine harmony when the diver wears the exoskeleton robot,the body's standard freestyle swimming posture is studied and the ideal motion curves of the hip joint and knee joint are obtained as the moving target curve of the underwater exoskeleton robot.Based on the computational efficiency of the algorithm,the advantage of the Newton-Euler dynamic iterative algorithm is demonstrated.According to the geometric model of the robot,the inertia tensor of the leg is calculated.According to the extrapolated iterative process of the Newton-Euler algorithm is applied to derive the inertia force and inertia moment of thigh and caliber from motion posture of hip joint and knee joint.The force analysis of the robot underwater is mainly concerned.The pressure distribution from the water along the leg is assumed and further is equivalent to a concentrated force and a moment acting at the end of the connecting rod.In terms of the robot's motion,the torque,the power and the hydraulic driving force required for the hip joint and the knee joint are calculated via the inverse iterative process of the Newton-Euler algorithm.Based on the established kinetic model,the influence on the dynamic performance of the leg length is taken into account.The kinetic parameters required for the different underwater velocity of the robot are also discussed.The Fluent dynamic grid technique is used to solve the liquid pressure distribution during the movement of the robot leg.The numerical results show that the dynamic pressure distribution along the leg direction is in agreement with the water resistance distribution assumed in dynamic modeling.The inverse problem of the underwater robot dynamics is simulated via the multi-body dynamics software Adams.Inputing the joint angle function and considering the effect of the equivalent fluid resistance on the robot,the joint torque is numerically obtained.The simulated results are in good accordance with the results obtained from the dynamic model.