Sway Control Technology and Its Application for Overhead Traveling Cranes

cranes and gantry cranes occupy a crucial role within industry. They are used throughout the world in thousands of factories, steel mills, foundries, ship yards, warehouses, nuclear power plants, waste recycling facilities and other industrial complexes. In many manufacturing operations, operator controlled cranes account for as much as 20% of the production cycle. Material handling engineers have long sought systems to dampen loads and improve load spotting as a way to improve production throughput and operational safety. Even experienced crane operators have diffi culty controlling load sway. Furthermore, the trend in industry is to remove the operator from the crane cab in order to free him up to perform other functions, to have less experienced workers at each work station hitch and independently move their loads, or to automate the handling system and eliminate manual operation entirely. In this paper, we will examine the problems of controlling load sway as well as the various methods that can be employed to control sway. A typical overhead crane is a 3-axis machine having a bridge (X-axis), trolley (Y-axis) and hoist (Z-axis) as shown in Figure 1. The load is suspended from a moveable trolley by means of cables, and behaves much like a pure pendulum. Figure 1 illustrates bi-axial swing of the load caused by simultaneous motion of both trolley and bridge. When displaced to an initial angle and released, the pendulum will swing back and forth with periodic motion until dampened by gravity or other external forces. The time it takes for a pendulum to make one complete swing is called the period of the pendulum. mg l l y x x y x, y, 0