Welding control apparatus for pulse arc welding of consumed electrode type, arc length control method for use with the same, and welding system including the welding control apparatus

A welding control apparatus for use in pulse arc welding of consumed electrode type using, as shield gas, carbon dioxide or a gas mixture containing carbon dioxide as a main component, the welding control apparatus comprising:

• a current detector for detecting a welding current of a welding power supply;
• a voltage detector for detecting a welding voltage of the welding power supply;
• a constriction detector for detecting a constriction of a droplet of molten metal based on at least one of the detected welding current and welding voltage;
• a waveform generator for, during one pulse cycle made up of a first pulse period including a peak period and a base period of a first pulse waveform and a second pulse period including a peak period and a base period of a second pulse waveform, alternately generating two types of pulse waveforms differing in at least one of a pulse peak current and a pulse width to be output to the welding power supply based on preset waveform parameters such that the first pulse waveform for releasing the droplet from a wire distal end and the second pulse waveform for shaping the droplet are output as the two types of pulse waveforms in order named for transfer of one droplet, the waveform generator immediately changing over, when the constriction of the droplet is detected, a current value of a first pulse to a predetermined value lower than a current value at the time of detection of the constriction;
• an integrator for receiving, as parameters in a formula (1), inputs of preset various data of information regarding a gradient Ks of an external characteristic of the welding power supply, a welding current setting value Is2 in the second pulse period, and a welding voltage setting value Vs2 in the second pulse period, and further receiving inputs of various data of information regarding an instantaneous value Io2 of the welding current detected in the second pulse period and an instantaneous value Vo2 of the welding voltage detected in the second pulse period, the integrator starting calculation of a voltage error integral value Sv2 expressed by the formula (1) from a time when the first pulse period ends and the second pulse period starts in the pulse cycle and bringing the calculation to an end at a time when a result of the calculation has become 0;
• and
• a comparator for comparatively determining whether a value of the voltage error integral value Sv2 provided as the calculation result has become 0,
• wherein, for each pulse cycle, the waveform generator terminates a relevant pulse cycle and starts a next pulse cycle at a time when the value of the voltage error integral value Sv2 has become 0, where
• Sv2=∫{Ks(Io2−Is2)+Vs2−Vo2}dt (1).