The present invention relates to a welding robot control apparatus, or more in particular to a control apparatus suitable for a welding robot of such a type as to perform the welding work by moving both a welding torch and a workpiece.
In arc welding, a welding bead is formed while moving a welding torch in relative fashion along a welding line on a workpiece. In stopping the robot instantaneously, therefore, the welding operation is required to be halted from the standpoint of maintaining the welding quality. Such a stoppage of the welding operation will hereinafter be referred to as a provisional stoppage.
In the case where welding is stopped in the middle of a welding operation, however, a dent is likely to occur in the bead and the workpiece, and due to a cutting off of the supply of a shield gas, an oxide layer (solidified slug) of a high electrical resistance is deposited on the dent. If the welding operation is restarted under this condition, arc vanishing is likely to occur, and even if the arc is generated, a problem of reduced welding strength results due to the remnant of the dent.
FIG. 1 is a diagram for explaining this problem. In FIG. 1, reference numeral 1 designates a workpiece, and numeral 2 a torch. The hatched part represents a bead (soldified weld metal) formed as a result of the welding. If an arc is turned on at point A to proceed with the welding operation to a point C, provisional stoppage of welding at a mid-point B would cause a dent in the bead and the workpiece as shown. Upon the arc being turned off, a shield gas which has been supplied so far is also cut off, which causes an oxide layer (solidified slug) of a high electrical resistance to be deposited on the surface of the molten weld metal which is deposited on the dent. As a result, in restarting the welding operation from point B by turning on the arc, there is a case where the arc would not be generated. Even if the arc is generated, sufficient welding strength may not be obtained since the dent cannot be completely removed.
A conventional technique for resolving the problem described above is disclosed in JP-A-63-278675.