Design And Control Of Self-insulated Bio-inspired Flexible Parallel Joint

The current live working task is finished mainly through the labor,which will inevitably contribute the physical security of the labor not to be better protected.It can effectively prevent the personal injury accidents and improve the efficiency of live working to accomplish the task by the live working robot instead of the labor.The traditional live working robot has the disadvantages such as large self-weight and high insulation cost.The fundamental cause of these obvious disadvantages of the traditional live working robot is the series drive mode of the embedded motor.The biological motion of human arm is supported by the bones and is driven by the muscles according to anatomy and biological kinematics.The flexible shoulder joint and wrist joint are driven in parallel.Therefore,for the applications of the live work,this project intends to develop a self-insulated bio-inspired robotic arm including the wrist joint,the elbow joint and the shoulder joint by mimicking the human arm.The drive motors and other conductive units are separated from the robotic arm.The scheme actuated by the human arm muscles is replaced by the remote cable-driven strategy.To ensure that the robotic arm has the insulating property,the body of the robotic arm is designed by the insulation materials.The self-insulated bio-inspired robotic arm is a complex multi-body system including the wrist joint mechanism,the elbow joint mechanism and the shoulder joint mechanism.It is necessary to start from the research of the single component mechanism,which is helpful to the subsequent research of the whole self-insulated bio-inspired robotic arm.Its research principle is relatively simple because one degree of freedom(1-DOF)motion of the elbow joint of the human arm is imitated by a two-cable-driven revolute joint mechanism.The elbow joint mechanism is not considered in the dissertation.3-DOF(Roll,Pitch and Yaw)motion of the wrist joint and the shoulder joint for the robotic arm are imitated by the parallel mechanism with a flexible support body driven by multiple cables.The mechanism that produces roll and pitch motions is studied separately because roll,pitch and yaw motions can be decoupled.Therefore,the parallel mechanism with a flexible support body driven by multiple cables is simplified and redesigned as the parallel mechanism with a flexible support body driven by three cables.The proposed self-insulated bio-inspired flexible parallel joint is the parallel mechanism with a flexible support body driven by three cables.Seeing that the research methods of the cable-driven parallel mechanism with the flexible support body is applied in the design of the robotic arm,this dissertation studies the mechanism that imitates the human arm wrist/shoulder joint motion.This dissertation performs an in-depth study for the design,control and insulation characteristic of the mechanism.Firstly,in consideration of the lateral bending characteristic of the flexible supporting body,a method that combines the kinematics with the statics is proposed to solve the kinematics and the statics of the system simultaneously.The simulation analysis shows that the kinematics and static model of the system is reasonable and correct.Based on the kinematics and the statics of the system and the cables position limit constraint and the cable unidirectional drive constraint,the optimal design for the cable placements is carried out to reduce the sizes of the actuators and energy consumption.The optimization results show that closer is better when each end of the cable comes to the upper limit of connecting radius between the cable and the fixed base and the moving platform.Moreover,the workspace of the system is analyzed by the constraint for the positive cable force.The simulation results show that the translational workspace of the mechanism is an inverted cone and its volume increases with the increase of the ratio of the radius(the ratio of the connection radius of the cable and the fixed base and the connection radius of the cable and the moving platform).The simulation results show that the method of the optimal design of the cable placements and workspace analysis are reasonable.Secondly,three dynamical models of the system are established based on Lagrange's equation by considering the coupling principle of the large range motion of the rigid body and the small deformation of the flexible body.The dynamics include the dynamical model that considers the flexible vibration factor,the dynamical model that only considers the radial flexible vibration factor and the dynamical model that neglects the flexible vibration factor.To use less energy to achieve the minimum errors of the flexible system,the linear quadratic optimal control(LQOC)method is applied to design the system controller based on the first dynamical model.To achieve a small system position tracking error while suppressing the flexible vibrations of the system,the nonlinear control(NC)method is applied to design the system controller based on the second system dynamical model.To eliminate the distractions of the system in time and reduce the tracking errors of the system while stabilizing the closed-loop system,PD with feed-forward control(PD-FC)method is applied to design the system controller based on the third system dynamical model.Because of the cable cannot provide the push force,the cable internal force principle is used in PD-FC method to ensure that all cable forces are always positive.The stability of the closed-loop system is proved based on Lyapunov stability theory.The simulation results confirm that the designed controllers can track a desired trajectory while suppressing vibrations of the flexible system.The experiment platform for a bio-inspired flexible parallel joint mainly including system mechanical platform and system electrical platform is designed to verify the rationality of the simulation results still further.The system control experiments that considers the flexible vibration factor,only considers the radial flexible vibration factor and neglects the flexible vibration factor are executed by the experiment platform.The results show that the experimental results of each system control strategy are close to the corresponding simulation results,which proves the rationality of the corresponding system control strategy and the correctness of the corresponding system dynamics modeling.Finally,aiming at one of the key features,self-insulated,of the bio-inspired robotic arm,the insulation characteristic of the bio-inspired flexible joint system has been studied according to theoretical simulations and experiments.The distribution of electric potential and electric field on the surface and surrounding space of the mechanical structure of the system at rated voltage is calculated by finite element method.The results show that the maximum electric field intensity is much lower than disruptive electric field intensity of air and the insulation materials.Therefore,the electric field environment does not have the conditions for electric arc generation.To verify the simulation results still further,3D printing technology is adopted to build an experimental model with the same material,same shape and same scale as the simulation model,and the insulation pressure test is carried out through the established system insulation test platform in this dissertation.The breakdown characteristic of the sample is tested by stepwise boost voltage method.The experiment phenomenon shows that insulation parallel joint is not breakdown and does not have the condition of electric arc generation under the current voltage level.Therefore,the insulation parallel joint in parallel has good insulation property and keep its insulation property under wide range voltage,and the correctness of the simulation conclusion is confirmed.