AN ARC WELDING ROBOT SYSTEM TO REALIZE COORDINATED MOTIONS IS DESCRIBED IN THIS PAPER. ONE FEATURE OF THIS ROBOT SYSTEM IS THAT THE TEACHING TASK OF COORDINATED MOTIONS IS SIMPLIFIED BY EMPLOYING A THREE-DIMENSIONAL VISION SENSOR. THE VISION SENSOR DETECTS THE THREE- DIMENSIONAL SHAPE OF THE TARGET WELDING GROOVE AND MODIFIES COORDINATED MOTIONS SO THAT THE IDEAL WELDING CAN BE REALIZED. EXPERIMENTAL RESULTS REVEAL THE APPLICABILITY OF THE ROBOT SYSTEM.