Visual Feedback Control of a Three-Dimensional Overhead Crane

Overhead cranes are used widely in various industrial fields. Crane transportation load must be transported for the work efficiency and safety to the destination without swinging. As a demand of highly precise and safety rises, automation is thought about as a method corresponding to lack of operator of mastery of skills. A transportation load of an overhead crane swings by a traveling acceleration change while doing up-and-down motion of a rope length change. It is necessary to measure this three-dimensional motion for swing suppression control. When it is installed in an overhead crane, a measurement sensor becomes complicated. In this paper, the trial stereovision device is manufactured which is a non-contact sensor, not an installation sensor and tried to control the overhead crane by vision feedback. The vision sensor is a stereovision device of four degree of freedom for tracking and gazing with two CCD cameras. A position measurement of a transportation load and an experiment of tracking control were done. The three-dimensional position of the transportation load is provided with CCD image data of two cameras, the focus distance, and four-vision device drive angles and is used for crane control. The vision device drive target angles that a point of intersection of two camera optical axes seems to always accord with the transportation load center is obtained using inverse kinematics. With these target angles, the control of tracking and gazing about the transportation load can be done. On the other hand, in an overhead crane model, using measured three-dimensional coordinate values, positioning and vibration suppression control of the transportation load was done. The overhead crane model consists of a trolley running on two perpendicular slide guide rails and a hoisting device of the transportation load. The overhead crane model has five degree of freedom, and they are x, y direction displacements of a trolley, a rope length, a swing angle, a swing direction angle. The variable rope length, the swing angle and the swing direction angle are calculated using the load position measured by the vision sensor. Variable digital gains of the trolley in consideration of the rope length change were pursued by this information, and overhead crane control was done. The experiment result of overhead crane control by vision feedback showed that the used control system was effective.