Investigation On Design And Key Issues For 7R 6-DOF Painting Robot

Driven by the significant need from automobile manufacturing for industrial painting robot with high performance,this dissertation investigates into some key issues in the design of a 7R 6-DOF painting robot in terms of type design,inverse kinematics and singularity analysis,stiffness modeling,structural optimization design,parameter calibration.The following contributions have been made.For the structure innovative design,according to the painting task for the car body,a 7R 6-DOF painting robot is proposed by integrating the 4R 3-DOF wrist and 3R arm.The transmission scheme,key structural parameters and detailed structure are separately designed for the wrist and arm,completing the structure innovative design of the painting robot.For inverse kinematics and singularity analysis,by constructing an equivalent transformation between the 7R 6-DOF robot and the 6R robot with orthogonal spherical wrist,an integrated method to solve the inverse kinematics of the 7R 6-DOF robot is proposed.The analytical solutions of the equivalent 6R robot are utilized to calculate the approximate solutions of the 7R 6-DOF robot,while exact solutions are derived by Jacobian-based iterative algorithm.This integrated method provides reliable initial solutions and has high accuracy and efficiency.Based on geometry of the 7R 6-DOF robot,a one-dimensional iterative inverse kinematics algorithm is presented,and the multiple solutions problem is investigated.Based on the transformation between the 7R6-DOF robot and equivalent 6R robot on velocity level,the singularity conditions for the position singularities and the orientation singularities are identified.The singularity avoidance method is presented,especially the modified twist-decomposition approach is proposed to deal with orientation singularities based on the functional redundancy.For the stiffness modeling,considering the gravity and joint/link stiffness,a stiffness modeling method of the robot is proposed.The stiffness models of the position mechanism and orientation mechanism are constructed with virtual joint method,and the stiffness model of the robot is derived with linear superposition.By force and deformation analysis of the couple joint of the wrist,the stiffness model considers the effects of the couple joint.In order to take into account deformations of the link under its own gravity,the gravity is treated as equivalent pairs of general forces applied on the adjacent joints,and the equivalent transform matrix is derived based on the finite element analysis.A method for computing the stiffness values of the joints and links is presented.Distribution of the deflections of the 7R 6-DOF painting robot end-effector over the entire workspace and contributions of the components to global deflection are analyzed.For the structural optimization design,an integrated structural optimization design method based on the stiffness model is proposed.Based on the stiffness model,deformations of the end-effector are analized,and the robot configurations with maximum position deformation are taken as typical ones to consider the changes of load condition in the workspace.By constructing metamodels directly relating the stiffness and mass of the structure components,the structure optimization design of the robot is divided into part-level topology optimizations and a parametric system optimization,which greatly improved the efficiency.An iterative form is utilized to consider the changes of load condition along the optimization process.The results of the optimization of a 7R 6-DOF painting robot show that the deformations of the robot are reduced with the total mass is the constrain condition,which verified the proposed optimization method.For the parameter calibration,geometrical error model is established based on the MDH convention.According to the compensability and constrains of parameters in the controller,model reduction method is proposed and the redundancy of the model is analyzed.The calibration models for compliance parameters and inertial parameters are separately established.Model reduction and redundancy analysis are completed by considering the properties of the compliance matrix and QR decomposition of the Jacobian matrix.The calibration experiments on a self-developed prototype of the 7R6-DOF painting robot are implemented.The results show that the average position error is reduced from 4.678 mm to 0.831 mm after kinematic calibration,and it can be further reduced to 0.534 mm with kinematic and inertial parameters calibration,while the compliance parameters calibration can effectively reduce the deflection of the robot under external loads,which verified the proposed calibration method.The research work of this dissertation has been employed for the design and establishment of a 7R 6-DOF painting robot.It can enrich the design method and theory of the industrial painting robot,and has important theoretical significance and engineering value for the promotion of self-research and practical application of relative technology and equipment.