Research On Precise Localisation,Task Planning And Feedback Control In The Mobile Robotic Welding

High-precision machining of large-sized workpiece is one key issue of the national advanced manufacturing.The mainstream method is to use the base-fixed robotic arm to perform multiple local operations through the teaching-playback pipeline,which cannot satisfy the demands of mobility,automation,precision and efficiency.Therefore,it is a new trend to perform joint operation by using mobile robot equipped with robotic manipulator.This paper introduces a novel mobile welding robot consisting of a six degree-of-freedom PRP-RRR robotic arm mounted on a hexapod mobile robot.One special part is that it applies 3-limbs parallel mechanism for each leg,which improves the overall rigidity,accuracy and workload capability,thus enabling it to carry various operation equipment.Moreover,the robotic arm is also specially designed and characterized by motion decoupling of the end-effector,and so it has excellent adaptability to various weldseams.This paper mainly focuses on the visual localisation,welding task planning,feedback control and control system,et.al.The experiments were performed to verify these researches.The major contents are listed as follows:1.We proposed a novel method to calibrate the hand-eye matrix of the linear laser sensor and the homogeneous transformation matrix of the base coordinates through an intermediate coordinate system,which allowed a universal coordinate representation of object posture.2.We discussed the different performance requirements of the visual localisation algorithm for the two stages: during robot walking and standing still in front of the workpiece.To satisfy the requirements,we proposed the workpiece real-time rough localisation algorithm and the weldseam offline precise localisation algorithm,so that the robot has visual sensing capability.3.We proposed the hexapod robot posture fine-tuning strategy.The strategy tunes the posture of the hexapod robot,so that the relative posture of the welding arm and the weldseam satisfies specific relationship.According to the numerical analysis of the control precision index,this strategy makes full use of the motion decoupling characteristic of the welding arm.4.We analyzed the workspace,velocity,workload and error performance of the welding arm,based on which,the welding task planning method of different weldseams was introduced.5.We analyzed and built the mathematical models for the arc length and side shift features.Besides,we designed a 1-2-order hybrid fuzzy controller to compensate the deviation of the controlled features,thus improving the weld formation quality.6.We developed the robot control system,including the hardwares,the supporting softwares and control algorithms.Based on the system,the control strategy and operation logic were derived.7.Apart from the theoretical analysis,the prototype was built and a lot of experiments were performed to verify all the researches,including: 1)testing experiments of the visual localisation algorithms;2)verifying experiments of the task planning methods;3)open-loop welding experiments;4)closed-loop welding experiments.