Underwater Flexible Cable Serial Robotic Arm Based On A Floating Platform Design And Planning

Marine resources are rich in variety and huge in reserves.In recent years,people have worked more and more frequently at sea.For the exploration of some complex environmental areas,underwater robots equipped with manipulators play an important role.At present,the driving unit of the manipulator carried by the underwater robot is mostly located at its joints to provide driving force,which greatly increases the overall mass and volume of the manipulator,resulting in excessive inertia of the manipulator and excessive water resistance.And the large mass of the driving unit also occupies the valuable bearing space of the manipulator,and also has a great impact on the control,energy consumption and sealing maintenance of the manipulator.In order to solve the above problems,a lightweight cable-driven underwater manipulator is designed to reduce the influence of excessive mass and volume of the driving motor on the motion of the manipulator.The specific research methods and contents are as follows:Firstly,the design requirements of salvage operation mode are determined,and the material and cable driving mode of the manipulator are determined by analyzing the design requirements.Aiming at the kinematic coupling problem of cable drive,this paper proposes a scheme of combining series and parallel mechanisms,presetting the driving unit of series mechanism and driving the cable of series mechanism to move inside the connecting rod of parallel mechanism.The ball joint and the rotating joint are selected as the joint motion pairs to select the motor and complete the design of the mechanical arm mechanism.The strength of the selected wire rope is checked and the static analysis of the main bearing parts of the manipulator is completed by the Simulation plug-in of Solid Works.Secondly,the improved D-H method and space vector method are used to analyze the kinematics of the manipulator.The improved D-H method is used to complete the kinematics derivation of the manipulator to obtain the forward and inverse kinematics equations,and the mutual mapping relationship between the joint angle and the end position is established.The world coordinate system and the body coordinate system are established in the manipulator system to determine the anchor points connected to the manipulator platform and other related point coordinates on the manipulator,and the relationship between the cable length and the joint angle is established by using the spatial vector position relationship of each point.The relationship among the driving space(cable length),joint space(joint angle)and operation space(end position)of the manipulator is obtained by the above methods.The correctness of the forward and inverse kinematics equations of the manipulator is verified in the Robotics Toolbox.Based on the kinematics of the manipulator,the workspace of the manipulator is obtained and analyzed by Monte Carlo Method.Then,the dynamic model of the underwater cable-driven manipulator is established by Lagrange method.The Lagrange dynamics is deduced,and the torque of the manipulator is solved by using the relevant parameters of the manipulator obtained in Solid Works.The hydrodynamic analysis of the manipulator is carried out by using the slicing principle,and the dynamic model of the manipulator is established.The solution and simulation analysis of the dynamic equation are completed by combining the motion trajectory.Based on the kinematics of the manipulator,the length,velocity and acceleration of the cable during the motion of the manipulator are solved and verified by simulation.The results show that the change of the cable conforms to the motion characteristics of the manipulator.At the same time,the theoretical derivation of the cable tension is carried out,and its value range is discussed.Finally,the trajectory planning of the manipulator is analyzed.In this paper,the linear trajectory and circular trajectory of the manipulator are planned in Cartesian space which can intuitively reflect the motion.Spatial linear trajectory planning is the use of point-by-point interpolation to obtain linear trajectory interpolation functions when the coordinates of the beginning and end of the two points are known.The spatial arc trajectory planning adopts a new coordinate system in the trajectory circle plane,and solves the transformation matrix of the old and new coordinate systems,and transforms the complex spatial three-dimensional problem into a plane two-dimensional problem.Then the position interpolation of the arc trajectory is performed to obtain the interpolation function of the arc planning.The two trajectory planning is simulated and verified in Robotics Toolbox,and the results show that the manipulator runs smoothly.Based on the arc trajectory planning,according to the kinematics of the manipulator,the corresponding relationship between the trajectory of the end of the manipulator and the length of the cable is known,and the change of the cable during the movement is obtained.Through the obtained cable motion parameter curve,the cable motion conforms to the motion characteristics of the manipulator.