Patent ID: 7863539

Claim:
A positioning method of spot welding robot comprising a welding gun having a movable electrode tip capable of being moved forward and backward by means of a servo motor and an opposition electrode tip opposed to said movable electrode tip so as to sandwich a work piece, for positioning said opposition electrode tip at a position of a spot welding point in contact with a lower surface of said work piece, said method comprising: (A) moving said welding gun with a separation between said opposition electrode tip and said movable electrode tip kept open and larger than a preset plate thickness of said work piece so as to position said opposition electrode tip and said movable electrode tip on both sides of said work piece in a plate-thickness direction of said work piece, respectively, and temporarily positioning said opposition electrode tip at a stand-by position; (B) moving said movable electrode tip in a direction approaching toward said opposition electrode tip while monitoring a current value of said servo motor driving said movable electrode tip, and when said current value exceeds a prescribed value, determining that a distal end of said movable electrode tip has been brought into contact with said work piece, stopping a movement of said movable electrode tip, and measuring an open separation of two opposing tips between said movable electrode tip and said opposition electrode tip that has been temporarily positioned at said stand-by position; and, (C) determining a difference value by subtracting said preset plate thickness of said work piece from said open separation of said two opposing tips, and moving said opposition electrode tip in a direction approaching toward said movable electrode tip from said stand-by position to said position of said spot welding point to finally position said opposition electrode tip, by using said difference value as an amount of movement of said opposition electrode tip.