Structural design and adaptive tracking control of automatic welding robot for liquefied natural gas containment system

Abstract

Liquefied natural gas (LNG) is commonly transported by LNG carriers and stored in cargo containment systems. The primary barrier of the MARK III cargo containment system is welded to a closed space with corrugated stainless steel plates. To meet the requirements of excellent sealing and thermal insulation for cargo containment, the welding process of the corrugated plate need to be strictly controlled, which poses a challenge to the development of related welding equipment. In this paper, we present a new five-axis automatic welding robot system used for plasma arc welding on corrugated surfaces. The moment transfer scheme of the dual linkage mechanism makes the rotary movement of the robot more accurate and stable which gives the system with simpler control algorithm and better overall force characteristics. To ensure tracking accuracy, a novel sensing method based on a LASER sensor, two contact sensors, and an angle sensor is proposed to implement multiple functions such as tracking the welding arc length, identifying corrugation shapes, and detecting welding gun posture. Based on the devised tracking sensor system and welding robot, a servo-control system with a surface-tracking welding control algorithm is established. The experimental results show that the robot system's welding speed is about 7 times that of hand welding and the welding qualification rate was 99%, significantly improving welding efficiency and quality as a critical equipment technology in the process of corrugated plate welding.

Article Highlights

A new five-axis automatic welding robot system based on a surface tracking control algorithm is designed for plasma arc welding on corrugated surfaces, which can realize flat, horizontal, vertical, and overhead automatic welding in LNG liquid cargo containment.

A novel tracking sensor system based on a laser sensor, two contact sensors, and an angle sensor is proposed to implement multiple functions such as tracking the welding arc length, identifying corrugation shapes, and detecting welding gun posture.

The sensing system can cooperate with the robot servo-control system to complete welding seam tracking, adjustment and control of welding gun spatial posture. The experimental results show that the robot system's welding speed is about 7 times that of hand welding and the welding qualification rate was 99%, which reflects that the robot servo-control system can complete the welding of corrugated structures in the cargo containment with high quality and high efficiency welding.