Electric heating – Metal heating – By arc
Patent
1994-08-04
1996-01-23
Shaw, Clifford C.
Electric heating
Metal heating
By arc
2191251, 2191304, B23K 906
Patent
active
054866790
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an arc welding control method for a welding robot, more particularly, to a method of controlling a welding current and a welding voltage at the start of a welding operation.
DESCRIPTION OF THE RELATED ART
The present invention is directed to a welding robot which has a welding torch at a distal end of an arm thereof and in which welding is carried out by moving the welding torch along a taught path. When a welding operation is started, first, a preset welding voltage and current are commanded from a robot control device to a controller of a welding machine. On receiving the command, the welding machine supplies electric power between a workpiece and an electrode of the welding torch. When an arc discharge is generated between the workpiece and the electrode, it is detected by the controller of the welding machine, which then supplies an arc generation signal to the robot control device. On receiving the arc generation signal, the robot control device commands welding voltage and current for normal welding to the controller of the welding machine, and at the same time actuates the robot arm to move the welding torch along the taught path. Usually, the above-described control operation is executed at the start of arc welding using a welding robot.
As described above, when arc welding is started according to the conventional method, a preset welding voltage having a fixed value is applied until an arc is generated. The predetermined voltage to be applied at the start of welding is usually set to a value greater than a minimum voltage necessary for generating an arc so that an arc can be generated without fail. Thus, at the start of welding, an excessive current flows, causing a molten pool to be formed on the workpiece, which deteriorates the quality of the bead. Also, such molten pool causes poor appearance of the finished weld.
When an arc is generated, the welding command voltage and current are respectively switched to the welding voltage and current for normal welding, and at the same time the robot arm starts to be driven to move the welding torch. In general, however, robot motion cannot immediately attain the command speed, and usually the command speed is reached upon lapse of a certain period of time after an acceleration process is executed. Thus, in an initial interval wherein movement of the robot is started following the generation of an arc between the workpiece and the electrode, welding command voltage and current corresponding to the command speed of the robot are set in the controller of the welding machine, even when the command speed is not reached by the robot, and actual voltage and current are controlled to the command voltage and current, respectively, by the controller of the welding machine. This causes a problem that molten metal forms a pool during the robot acceleration period, deteriorating the quality of the bead.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an arc welding control method for a welding robot, by which formation of a bead pool is prevented when arc welding is started.
One embodiment of an arc welding control method according to the present invention comprises the steps of setting a welding command voltage to a predetermined initial voltage value in response to an arc start command, to supply electric power between a workpiece and an electrode, and gradually increasing the welding command voltage from the initial voltage value until an arc is generated between the workpiece and the electrode.
The arc welding control method according to the present invention further comprises setting the welding command voltage to a predetermined stopped-state voltage value and starting movement of the welding robot when an arc is generated between the workpiece and the electrode, gradually increasing the welding command voltage corresponding to the increase in moving speed of the welding robot during an acceleration time until the moving speed of the welding robot reaches a predetermined mo
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patent: 3555239 (1971-01-01), Kerth
patent: 3689734 (1972-09-01), Burley et al.
patent: 4390954 (1983-06-01), Manning
patent: 4618760 (1986-10-01), Murch et al.
patent: 5059765 (1991-10-01), Laing
Hamura Masayuki
Makihata Yuuki
Okuda Mitsuhiro
Fanuc Ltd.
Shaw Clifford C.
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