Research On Trajectory Planning Method Of Robot Spot Welding Operation For Car Curved Body-in-White Parts

With the rapid development of welding automation technology,automatic lines with spot welding robots as the core equipment have been widely used in various fields of machinery production,and the increasing number of automated equipment and production materials make the welding workstation environment increasingly complex.Therefore,while ensuring production efficiency and welding quality,the path and trajectory planning of spot welding robots for complex tasks has become the focus of current research.The paper investigates robot obstacle avoidance,collision avoidance and singularity avoidance welding path and trajectory planning methods,using the curved Body-in-White welding parts as the object of study.The proposed planning methods are demonstrated by simulation analysis and example verification.The main research are as follows.1.Taking C-type welding tongs as an example,the coordinate transformation matrix of welding tongs,robot,welding parts and welding joints are established.Based on the analysis of the welding movement characteristics for Body-in-White curved surface workpiece,the forward and inverse kinematics model of the robot is established,the motion constraint conditions of collision free welding are constructed.According to the structural characteristics of complex surface welding parts,the welding part model is built in 3D grid space.The swept sphere volume(SSV)method is used to model the structured obstacles other than welding parts and robots.Meanwhile,the robot are modeled by the capsule envelope method.The above modeling method is helpful to improve the computational efficiency of the subsequent obstacle avoidance and collision detection.2.A hybrid obstacle avoidance path planning method based on the Memetic algorithm framework is proposed for the welding process of curved Body-in-White parts.the improved A~* algorithm is used to obtain the optimal set of smooth and collision-free paths between welding joints,and construct the objective function to traverse the welding joints with the shortest path length and the highest smoothness,Multi-objective Elitist Simulated Annealing Genetic Algorithm(MESAGA)is used to plan the welding sequence of the welding joints,so as to obtain the smooth optimal welding path for obstacle avoidance under the curved Body-in-White part.3.According to the characteristics of obstacles in the workstation,a time-optimal obstacle avoidance trajectory planning method based on the improved Whale Optimization Algorithm(IWOA)is proposed,and the singularity avoidance operation is carried out for the straight-line trajectory passing through the singularity region.An improved RRT~*algorithm based on target offset and target preference expansion strategy under repulsion field is used to find the obstacle-free path,and penalty terms are used to limit the robot velocity,acceleration and jerk.The time between nodes is used as the location dimension information of the IWOA,so as to complete the time-optimal trajectory planning for obstacle avoidance and singularity configuration in complex workstation environments.4.Taking the car side inner panel with curved structure as the object of study,a method of dual robot spot welding task assignment and welding sequence planning considering welding quality and welding deformation,and a method of dual robot collision avoidance trajectory planning based on optimal layout are proposed.The welding joints are divided into four priorities with the minimum sum and minimum difference of the two robot welding paths as the optimization objectives,the Non-dominated Sorting Genetic Algorithm-Ⅱ(NSGA-Ⅱ)is used to obtain the Pareto optimal solution set for the dual robot welding sequence.The evaluation system is constructed with the static performance index and motion performance index.With the layout position of the two robots as the optimization objective,the improved chicken swarm optimization(CSO)algorithm is used to solve the collision avoidance trajectory under the optimal layout of dual robots.5.The planned paths and trajectories are imported into the automotive automatic production line simulation software Process Designer & Process Simulate to verify the effectiveness of the proposed path and trajectory planning method for spot welding robots in this paper.Firstly,interference analysis of the welding path in the rear floor workstation is carried out,and after discussing the welding joint accessibility,a smooth obstacle avoidance welding path is formed in the rear seat beam assembly workstation.Secondly,the analysis of operation timing and layout optimization of the two robots responsible for the welding of the car side inner panel.Collision detection is carried out by using the motion envelope of dual robots,and the motion performance of the robot is analyzed to generate a collision avoidance welding trajectory of dual robots based on optimal layout.Finally,the off-line control command is output to the robot,and the robot is debugged to complete the welding operation.Verification results show that the path and trajectory planning method proposed in this paper can achieve the purpose of shortening the development cycle of new products and reducing production costs,providing the process planner with ideas for debugging or simulating the spot welding robot.