Development of a vision-based measurement system for relative motion compensation

Abstract

Motion compensation is used in many applications where no relative motion between two objects is desired. In the offshore industry, motion compensation systems are used to increase the operational window during load transfers like crane operations or positioning of gangways for personell transfer. In most systems one or more motion reference units (MRU) are used to measure motion with respect to a world reference frame and compensate for this motion. For motion compensation between two independently moving objects, a MRU-based solution becomes complex when measurements must be exchanged and combined. Vision systems have existed for a long time and are utilized in a wide specter of functions. In this thesis a vision-based system for measuring the relative motion between objects is developed. A camera is fixed to one object, while a pattern is fixed to the other object. Images are acquired of a scene containing the pattern, and the relative motion between the camera and the pattern is computed. Experiments have shown that under static conditions the vision based measurement system detects the heave distance between pattern and camera with less than 0.5 mm deviation at a distance of 2.3 m, and roll and pitch angles of the pattern is computed with less than 0.2_ deviation.