Arc sensor for simultaneous detection of torch aiming deviation and gap width. Development of high-frequency oscillation arc (2nd report)

摘要

This paper describes horizontal fillet welding experiments to determine the characteristics of an arc sensor using the high-frequency oscillation arc and compares the performance with conventional sine wave oscillation. Efforts made to use numerical calculations to determine welding current waveforms suitable for detection of a groove with gap are discussed. Also outlined is the development of a high-frequency oscillation arc sensor for simultaneous detection of torch aiming deviation and gap width based on the numerical analysis results obtained. The results obtained may be summarised as follows.The welding current-voltage characteristics of the high-frequency oscillation arc have coexisting dynamic and static states. The former dynamic characteristics occur when the arc moves at high speed inside the groove, resulting in the arc self-regulation effect being unable to track the change in tip-base metal distance L. The latter static characteristics occur when tip-base metal distance L is constant at the end of oscillation. The welding current-voltage characteristics of the high-frequency oscillation arc are controlled by the arc self-regulation effect.The frequency characteristics (amplitude in groove welding) of the high-frequency oscillation arc are clarified. The amplitude of the welding current is maximised in the low-frequency domain and monotonically decreases with an increasing frequency. No effect comparable with resonant frequency f_c occurring in sine wave oscillation is found. During sine wave oscillation, however, the amplitude of the welding voltage monotonically increases with an increasing frequency, whereas that of the high-frequency oscillation arc is virtually constant, with no frequency dependence being found. These characteristics are due to the specific oscillation pattern of the high-frequency oscillation arc involving the arc stopping at both ends of oscillation and moving at high speed between both ends.The numerical analysis results indicate the feasibility of an arc sensor for simultaneous detection of torch aiming deviation and gap width by the high-frequency oscillation arc method. Through application of the welding current when the arc stops at the end of oscillation as an information source, torch aiming deviation detection can be performed regardless of whether or not any gap is present in the groove. The change in the welding current at the oscillation centre is also well correlated with the gap, and gap width detection can be performed from the relative difference between the mean welding current at both ends of oscillation and the minimum welding current at eh oscillation centre.The developed high-frequency oscillation arc sensor is used to perform seam tracking with a feedback control system operating in the arm of an actual welding robot. Simultaneous gap width detection is found possible when the gap is continuously varied in the 03.5 mm range.