Mechanical Design And Simulation Of Mobile Welding Robot For The Main Girder Of Bridge Crane

Based on the analysis of welding process of box girder of bridge crane, this paper proposed a mobile welding robot for two long seams of box girder, which accomplished the automatic welding of the two long seams.By the analysis of two long seams and its trajectory, PPR-3DOF concept of mechanical deployment for the mobile welding robot was proposed, which include prismatic pair for frame's horizontal movement, prismatic pair for lift platform's vertical movement, and revolute pair for welding torch's rotational movement. This Mechanical scheme satisfied the welding requirement of two long seams of double-girder bridge crane girder, and horizontal available welding size is22.5 meters. Specific mechanism realization of each DOF and the way of power supply was selected. According to the mechanism realization of each DOF, the robot was divided into three modules, each module's mechanism design, power calculation and motor selection was accomplished.Based on the theory of robot kinematics, D-H coordinate system was established, the forward kinematics and inverse kinematics were analyzed. Trajectory planning of the two seams is accomplished. According to the analysis of differential equation's numerical solution, linear replacement was taken to the arch seam, and its reasonableness was verified, each motor's rotation rate of linear seam welding was calculated by algebraic algorithm.Three-dimensional solid model of mobile welding robot was created through Creo Parametric software, the model was transferred to Adams/view software to implement the two seam's kinematic simulation, and simulation curves exported from Adams/Postprocess module was analyzed, the results show that displacement and velocity curves were correspond to expectations, maximum error of arch seam is 0.0861 mm while linear seam is 0.356 mm, both velocity error is less than 0.001mm/s, simulation error is allowable, so mobile welding robot kinematics modeling is reasonable.Causes of trajectory error were analyzed, and one-dimensional-PSD-based error detection method was proposed, the monitored data was researched in two cases: delayed and advanced,robotic end-trajectory equation with error attenuation function was established, the error was compensated while inverse kinematics solution was input in controller, and reasonableness of the compensation strategy was verified by MATLAB simulation. While coefficient K is low, it compensates more quickly.