Control for synchronizing multi-crane lifts

Heavy lifts become more and more important. To increase the lifting capacity, two or more cranes are used. Such multi-crane lifts are commonly called tandem lifts. Only one crane operator controls all cranes synchronously. One crane is defined as the leader crane and the others as the follower cranes. The leader crane is controlled as usual, whereas the additional feature of rotating the load/traverse about a vertical axis can be used. The initial position of a virtual traverse is set by the initial positions of the cranes/hooks. The hooks are precontrolled via Jacobian transformations. The virtual traverse needs to be feedback controlled. There are three objectives of the virtual traverse to be controlled: (i) the horizontal distance, (ii) the vertical distance and (iii) the angle with respect to a vertical axis. A control concept to synchronize the cranes is presented.