Measurement of three-dimensional welding torch orientation for manual arc welding process

Abstract

Torch orientation plays an important role in welding quality control for a manual arc welding process. The detection of the torch orientation can facilitate weld monitoring, welder training, and may also open a door to many other interesting and useful applications. Yet, little research has been done in measuring the torch orientation in the manual arc welding process. This paper introduces a torch orientation measurement scheme that can be conveniently incorporated both in a real manual arc welding process and in a welder training system. The proposed measurement employs a miniature wireless inertial measurement unit (WIMU), which includes a tri-axial accelerometer and a tri-axial gyroscope. A quaternion-based unscented Kalman filter (UKF) has been designed to estimate the three-dimensional (3D) torch orientation, in which the quaternion associated with the orientation is included in the state vector, as is the angular rate measured by the gyroscope. In addition, an auto-nulling procedure has been developed where the WIMU drift and measurement noise are captured and adaptively compensated in-line to ensure the measurement accuracy. The performance of the proposed scheme has been evaluated by simulations and welding experiments with different types of processes and fit-ups. The simulation results show that the inclination (x- and y-axes) of the torch has been accurately measured with a root-mean-square error (RMSE) in the order of 0.3°. The major error obtained in the heading (z-axis) measurement has been reduced significantly by the proposed auto-nulling procedure. Statistics from welding experiments indicate the proposed scheme is able to provide a complete 3D orientation measurement with the RMSE in the order of 3°.