Study On The Control System Of A Mobile Welding Robot For Shipbuilding

Ship closure welding is an important process in ship manufacturing engineering, which has direct effect on the quality and efficiency of shipbuilding. Due to the large size of the hull closure seam and the complex welding environment, manual welding is still utilized currently. Manual welding exists many shortcomings includes unstable welding quality and low efficiency. According to the problems above, designing a mobile welding robot for hull three-dimensional curve seam can improve the weld quality and efficiency and has great practical value for shipbuilding. In this paper control system of mobile welding robot was designed and welding experiments were conducted.In this paper mechanical structure and seam position detection system of mobile welding robot were designed firstly. Welding robot can be adsorbed on the ship, and the size of magnet was calculated according to the workload of welding robot. A contact-type displacement sensor and vision sensor were used to detect the position of seam in Z direction and Y direction respectively. A kind of calibration method of vision system was developed and the ideal calibration plane was replaced by the small area near seam. The curvature searching model was used to recognize the feature of seam which made the accuracy of seam identification achieve sub-pixel level.PC+ motion controller was chosen as the architecture of control system, and they used serial to communicate. The circuit board of FPGA-based motion controller was designed and made. The program of motion controller was developed in Quartus II environment which included peripheral device interface module, the FPGA on-chip memory and detection module of seam position in Z direction. A pipeline-based median average filter was designed which had high efficiency and low consumption. The FPGA-based trapezoidal acceleration algorithm and PID control algorithm were designed and simulated.The seam tracking experiments of mobile welding robot viewed that the accuracy of tracking is related to the accuracy of seam detection and the deviation rate of seam(the product of welding speed and seam deviation angle’s tangent). The error of tracking is less than 0.9mm in experiments which can meet the need of practical application.