Research On Trajectory Planning And Coordination Control For Dual-Beam Laser Welding Robot With Multiple Manipulators

In the field of aircraft manufacturing,compared with the traditional riveting method,laser welding lightweight technology could improve the workpiece stiffness and production efficiency.To improve the welding quality of the T-joint of aircraft structural parts,dual beam laser welding robot with multiple manipulators is used to synchronously weld on both sides of the skin truss T-joint,which has good flexibility and could accurately control the position and attitude(PA)of welding joint,with stable welding speed and impact,and high welding efficiency.At present,there have been indepth studies on the trajectory planning of typical industrial single welding manipulators,but there is a lack of systematic and targeted research on the trajectory planning and coordination control of the robot with multiple manipulators,which are the key technologies for the application of the dual beam laser welding process in the field of the aviation industry.This paper focuses on these two aspects.The main research contents include:(1)The particularity of dual beam laser welding process in the aviation field is deeply analyzed,and the requirements of dual beam laser welding process and welding equipment are summarized.The differences and commonalities between the dual beam laser welding robot with multiple manipulators and other industrial manipulators and typical multi robots are analyzed and discussed.Based on the analysis of the composition,main characteristics,functions,and process indexes of the dual beam laser welding robot with multiple manipulators,the theoretical framework of trajectory planning and coordination control of the dual beam laser welding robot with multiple manipulators is proposed,and its implementation process and key enabling technologies involved are described in detail.(2)The modular decomposition and kinematics solution method of kinematic branch chains for the integrated robot with multiple manipulators is proposed.The topological structure of the 18 axes dual beam laser welding robot with multiple manipulators is analyzed,the kinematic chain of the robot is modularized,and the topological structure description of the dual beam laser welding robot with multiple manipulators which has the motion certainty is established.On this basis,the kinematic model of dual beam laser welding robot with multiple manipulators is constructed,and its kinematics analysis is carried out,the forward and inverse kinematics solutions of dual beam laser welding robot with multiple manipulators are obtained,and its correctness is calculated and verified.Based on the kinematics model of dual beam laser welding robot with multiple manipulators,the two kinematics characteristics of workspace and singularity of the robot are calculated,which provides a theoretical and numerical basis for trajectory planning and coordination control of dual beam laser welding robot with multiple manipulators.(3)In order to realize the smooth and efficient motion of the new dual beam laser welding robot with multiple manipulators,the coordination trajectory optimization method is proposed.Firstly,according to the time and space coordination requirements of fuselage T-joint welding and pressing manipulators,the data of bilateral welds and pressing path of T-joint on hyperboloid skin are extracted.According to the path point transformation matrix of the local coordinate system relative to the reference coordinate system,the PA of the robot with multiple manipulators are obtained.Combined with the inverse kinematics model of the dual beam laser welding robot,the quintic B-spline curve is adopted to interpolate the motion of each joint.Taking the speed and acceleration of each joint as the constraint conditions,and the smoothness and efficiency of the dual beam laser welding robot motion as the optimization goal,the multi-objective coordination trajectory optimization model is established.The non dominated sorting genetic algorithm NSGA Ⅲ is used to solve the optimization model.While realizing the consistent change of the speed of the robot end effectors,the optimization scheme is provided to improve the comprehensive performance of motion smoothness and operation efficiency of the dual beam laser welding robot with multiple manipulators.(4)Aiming at the characteristics that the dynamic characteristics of the robot with multiple manipulators vary greatly with its position and attitude(PA)in the process of dual beam laser welding,its PA-natural frequency is evaluated quantitatively,which puts forward the requirements for the stable working conditions of the dual beam laser welding robot with multiple manipulators.Based on the discrete time nodes,the PA models of the robot with multiple manipulators at different times of T-joint welding are constructed respectively.Through the finite element analysis,the variation law of the natural frequency of the robot during welding operation is obtained,and the optimal time node is chosen to reduce the number of tests.Taking the joint working space of Tjoint double beam laser welding as the small joint space,the natural frequency of the robot changing with the PA in the small joint space is obtained based on the DOE method of experimental design,and then the influence of each joint on the natural frequency of the robot in the process of double beam laser welding is obtained through range analysis,to provide guidance for the coordination control of the robot with multiple manipulators.Based on the method of partial least squares PLS fitting regression parameters,the dynamic natural frequency model of the robot with multiple manipulators is constructed.(5)In order to improve the end control accuracy of dual beam laser welding robot with multiple manipulators,a coordination control strategy based on robot end effectors’ error allocation is proposed.According to the structure and kinematics model of the robot,the error model of the robot with multiple manipulators end effectors is established,and the parameters of the control system based on the modal analysis are calculated.Based on hierarchical planning of task space and the introduction of the error allocation coefficient,the double-layer feedback control strategy of the dual beam laser welding robot with multiple manipulators is designed by combining the modelfree joint error compensation with the model-based end effectors error coordinated allocation,so as to avoid the problems of complex and time-consuming closed-loop inverse kinematics control algorithm.A joint simulation platform is built to simulate the dual beam laser welding robot with multiple manipulators,and the effectiveness of the proposed method is verified.