Kinematic And Dynamic Contorl Of Variable Geometric Truss ARM

Variable Geometry Truss(VGT)manpulator is proposed as a kind of promising hyper-redundant manipulator(HRM).It has higher stiffness and dexterity than traditional serial arm and is more capable of fulfill complicated tasks.VGT arm has been widely used in remote space,underwater and industrial operations.In this thesis,the kinematics and dynamics of a VGT manipulator with symmetric octahedral structure is studied.Based on the requirement of accurate and real-time kinematic planning,inverse kinematics(IK)solution is both very important and fundamental.However,because of the nonlinearity and coupling between displacement vector and normal vector in each VGT section,fast IK algorithm is very difficult to obtain.Thus,a novel analytical inverse kinematics algorithm is proposed in this thesis in order to provide VGT real-time kinematic planning capability.Firstly,in order to obtain the analytical IK solution,a new rotation matrix representation other than the traditional Euler angle and D-H parameters is proposed to better revealing the symmetric structure property in VGT manipulator.A novel inverse kinematics(IK)algorithm based on the requirements of real-time computation and high accuracy is proposed afterwards.The proposed IK algorithm decouples the nonlinear constraint equation system into several simple analytical equations with the help of the new rotation matrix representation and two auxiliary coordinate frames.The proposed IK algorithm can provide real-time computation update and analytical accuracy in the experiment.In addition,due to manufacture tolerance,joint clearance,actuator error and structural elasticity,large model error is inevitable in real operation.The model error significantly reduces end-effector precise positioning capability,so in this thesis,an error compensation scheme is proposed to improve positioning accuracy.The error compensation scheme was transformed into a discrete control system and error is compensated by a proposed control algorithm.The error compensation control calculates the end-effector position and direction correction value with measurement input from an eye-in-hand camera and drives the end-effector toward correct position and pointing direction after several adjustments.The control scheme is proven stable.In real experiments,positioning and pointing error is significantly reduced.Finally,because of the complex structure of VGT manipulator compared with traditional arm,VGT dynamics and control is both challenging and important for an accurate speed and position control.Therefore,the dynamic model of the VGT manipulator is derived based on Lagrange's equations of motion and SimMechanics software.In order to accurately control the end-effector speed and position,a PD based controller is proposed.Simulation results shows that the controller can drive the VGT manipulator into desired position and pointing direction.The dynamic modeling work in this thesis laid the foundation of more advanced control scheme in the futureExperiments and simulations verifies the work in this thesis.The proposed IK algorithm and error compensation control have been implemented on test device in our lab.Based on simulation and experiment results,the proposed IK algorithm was proven correct and effective.As a result,our test device is now capable of on-line path planning.Error compensate successfully drove the end-effector of our test device into desired position and pointing direction.The positioning error is reduced within 1mm.Finally,PD controller was tested in the simulation environment in SimMechanics,and the controller accurately follow the position and speed command.