Design And Research Of Wall Climbing Robot For Weld Inspection Of Large Pressure Vessel

As special equipment in-service pressure vessels operate under corrosive,lowtemperature,high-temperature or high-pressure conditions for a long time,the vessel welds are prone to cracking and creep,fatigue fracture and other defects,causing safety hazards,which require regular weld inspection.In view of the current manual weld inspection is cumbersome,inefficient and other shortcomings,this paper researches and designs a miniaturized four-wheeled permanent magnetic adsorption wall crawling robot that can replace manual inspection and has the ability to adapt to different curvature radius walls,which carries a magnetic particle inspection instrument to move along the weld on the vessel wall autonomously and carry out weld surface defect detection.The details of the study are as follows.Firstly,through the analysis of the functional requirements and execution scheme of the robot,the permanent magnet adsorption and wheel movement solution were determined.Based on this,a permanent magnetic wheel with integrated adsorption and mobility capabilities and a flexible mobile mechanism were designed independently for the mechanical body of the wall climbing robot.By establishing statics models for critical adsorption and direct motion state analysis,the minimum value of individual magnetic wheel adsorption force is 527.7N and the minimum value of motor torque is9.9N·m,which provides theoretical support for the reliable adsorption and movement of the robot.Secondly,the weld seam images acquired by the robot are grayed out and gaussian filtered,and the center position of the weld seam is extracted using a combination of canny edge detection,probabilistic hough linear detection and least squares linear fitting.On this basis,the robot’s posture is corrected using the integral separation PID control algorithm to complete the robot’s autonomous weld seam tracking.Based on the principle and process of magnetic particle inspection of the weld seam,we carried out the inspection of weld seam surface defects in a simulated robot operation environment,aiming to test the robot’s weld seam defect detection capability.Thirdly,a master-slave control system is designed for the robot body side and the remote control side at the hardware and software levels.The hardware modules such as buck circuit,master controller,motor motion control and communication are designed for the robot body side.The robot is able to track the weld seam by parsing the command data and controlling the motion of the robot.A multi-threaded approach was used to complete the upper computer interface of the remote console for humancomputer interaction,weld seam and magnetic particle image visualization.Finally,the experimental prototype of the weld inspection wall-climbing robot was built,and experimental tests were conducted in three aspects: hardware and software system,robot operation performance,and human-computer interaction interface.The experimental results show that the output voltage ripple coefficient of each buck circuit is less than 5%,which meets the normal power supply requirements;the robot can cross the weld seam with a height of 3mm～5mm,and the discrepancy between the robot and the center of the weld seam fluctuates within ±2mm,which meets the requirements of barrier crossing and weld seam tracking;the communication distance is 100 m,the wireless local area network transmission time delay is within the range of 0.33s～0.42 s,and the weld seam and magnetic powder images are clearly displayed and the weld seam is accurately identified.The weld detection wall climbing robot system meets all design targets and has good prospects for industrial applications.