A STUDY ON ARC CHARACTERISTICS AND ITS APPLICATION TO HEIGHT CONTROL IN PLASMA-ARC CUTTING

When cutting curved or thin plates, which can,be easily deformed during plasma arc cutting, it is indispensable to control the motion of the torch to keep a constant electrode tip-to-workpiece distance (arc length). In this study, the characteristics of the arc were analyzed and the results were used for detecting the electrode tip-to-workpiece distance during cutting. Analyzing the frequency power spectrum of the arc voltage signal as measured with a FFT analyzer, the first dominant frequency component was found to be 360 Hz, due to the current ripples of the rectified three-phase power source, and the second dominant frequency was 19 kHz, due to the anode spot motion. The arc voltage signal, detected from the lower peak value and filtered by the moving averaging method, increased almost linearly with the increase in electrode tip-to-workpiece distance. This arc characteristic could be effectively used to realize a reliable height control system for plasma arc cutting processes.