A Vision-Based 6-DOF Displacement Measurement Method for Assembling PC Bridge Structures Using a Planar Marker

Abstract

Precast concrete (PC) is used in many construction sites around the world, which is delivered after it is totally made on the plant. This is because it can reduce the rate of structural defection and building time. While in construction, many of PC materials are moved by a crane operator to specific positions just by looking. And the workers use hand gestures to fit a shear pin on the lower beam with an upper part. In this paper, a vision-guided method that is more efficient and faster than the conventional PC assembly methods is proposed. A vision-based 6-DOF displacement estimation method measures the relative displacement between the camera located in an upper slab and the marker located at the shear pin on the lower beam. Usually, PC slab has a quite long width, and it is not easy to estimate a precise 6-DOF information with just a pair of a camera and a marker. To mitigate this problem, multiple pairs of cameras and markers can be configured for large PC member and the beam. This paper deals with 6-DOF displacement estimation by using vision-based localization with a planar maker for PC construction sites. A camera detects the corner of the planar marker at first, and sub-pixel information is obtained for the corner and then the data are transferred to a main computer via Bluetooth communication. The main computer calculates 6-DOF displacement with corresponding points in the world coordinate frame. To show feasibility and robustness of the proposed method, some experiments are performed with varying distances.