The position-measuring vision system for industrial robots, newly developed by Hyundai Electro-Mechanical Research Institute (HEMRI), can measure six-degree-of-freedom (6-DOF) position and orientation of a car body on a continuously moving conveyor.

Vision System for Sealing Robots
HEMRI¡¯s vision-guided robotic sealing system consists of a continuously moving overhanging conveyor, two sealing robots and three stereo visions, as shown below.

Procedure for measuring 6- DOF position and orientation of car body:

1. User Coordinate Setup
Set up a common coordinate system between left-hand side and right-hand side robots.

2. Identifying the Position of Gauge Holes of Reference Car Body and Vision Calibration Boards
Select three gauge holes to be measured on the reference car body, and find their threedimensional position data in the common coordinate system by moving the robot tip to the center of each hole. Then, teach the robots for each camera to get the corresponding gauge hole image in its field-of-view.
Attach the camera calibration board near the gauge hole and move the robot tip to the predefined three points on the board to obtain three-dimensional position data of each hole. Repeat the procedure for all selected gauge holes.

3. Camera Calibration
In the camera calibration step, the camera matrices from left and right cameras are obtained by using the calibration pattern.

4. 3-D Coordinate Reconstruction from 2-D Stereo Image Coordinates
In this step, the image coordinate-based threedimensional coordinate values are reconstructed by using the triangulation from the stereo matching points and the calculated camera matrices.

5. Calculation of 6-DOF Position and Orientation of Reference Car Body
A calibration board coordinate system is created for each hole by using position data, obtained in Step 2, of three points on the calibration board.
By transforming the reconstructed three-dimensional coordinates obtained in Step 4 into calibration board coordinates, three-dimensional positions of gauge holes in the robot coordinate system are obtained.
6-DOF position and orientation of the reference car body is calculated from three-dimensional positions of three gauge holes. Following Steps 1 to 5, a preparatory stage is completed for production.

6. Measuring and Robot Sealing in Production Stage
In the production stage, 6- DOF position and orientation of every incoming car is estimated by measuring the position of the gauge holes with the vision system. The robots perform sealing work along the trajectory corrected by the amount of difference in position and orientation between the reference and the incoming car body.

Conclusion
Machine vision is a key factor in intelligent robot application. The need for vision-guided robotic automation systems will increase rapidly in the near future. Hyundai Heavy Industries will continue its cutting- edge research in this field to develop robot and vision solutions that meet our customers' needs.