Control apparatus for short-circuit arc welding

Claim 1

A short-circuit metal transfer arc welding apparatus for applying short-circuit welds to a base metal comprising: a welding electrode; first means, connected to said welding electrode and to said base metal, for establishing a welding arc between said welding electrode and said base metal by supplying a substantially constant voltage between said base metal and said welding electrode; a pulse responsive feeding motor, mechanically linked to said welding electrode through electrode feed-roll means, for feeding said welding electrode into regular alternate shortcircuit and arcing engagement with said base metal; detection means comprising a first resistor and a first Zener diode, connected in series between said welding electrode and said base metal, and a second Zener diode, connected to the junction point of said first Zener diode and said first resistor, for detecting an arc-on period of said arc, said arcon period extending from the moment of arc ignition to the moment of arc extinction, said detection means producing an output voltage during said arc-on period; pulse means for generating pulses having a prescribed duration; switching means comprising second and third resistors connected in series, across one end of said second Zener diode and one end of said first Zener diode, a transistor having a base, an emitter, and a collector, the base of said transistor being connected to the junction of said second and third resistors, while the emitter of said transistor is connected to said third resistor, and said pulse means being connected to the emitter of said transistor, said switching means causing said pulses, generated by said pulse means, to be switched therethrough during the arc-on period in response to said output voltage of said detection means; and means, responsive to the pulses switched through said switching means, for energizing said pulse responsive feeding motor, to feed said welding electrode towards engagement with said base metal.