A Three-Dimensional Position Measurement Method Using Two Pan-Tilt Cameras

We have developed a 3D measuring system that uses two pan-tilt cameras to accurately measure the position of a robot’s hand. With this system, a target is set up at the tip of the robot’s hand. The pan-tilt cameras are controlled so that the midpoint of the target view is centered within the camera frames. Then, its 3D position is calculated using a triangulation method from the azimuth and elevation angles of the two cameras and the distance between them. Because measurement precision is essential to such a system, we proposed a new method of the target with the concentric circle patterns, for which the center was measured precisely from the gravity centers of those circles. As a result, we achieved a high degree of precision (within 0.03 mm) with a single camera, for a camera-target distance of between 200 and 1000 mm, and where the tilt angle of the target relative to the camera was less than 70°. It was verified, by experiment, that the 3D measurement precision of the trial system is 0.15 mm for a 500-mm cube.