Automatic measurement and control of the attitude of crane lifters - Lifter-attitude measurement and control

The spreaders and lifters on cranes are usually controlled to stop at the same time as their trolleys are stopped. Despite the use of adequate control systems, however, the lifters usually have comparatively large sway movements, due to their free suspension from the trolleys through pulleys, hooks and cables. It is therefore important to accurately measure the attitude of the lifters, in order to suppress such sways by means of secondary control. The authors have previously proposed a maintenance-free automatic measurement and control system which accurately measures the lifter's attitude, using a servo-type accelerometer and a double-rigid-body pendulum model for the system, and completely eliminates the sway of the lifter. However, the measurement/control system takes action only after the trolleys are stopped. This paper extends the previous approach, and presents an on-line automatic measurement and control system that enables the lifters to stop at the same time as the trolleys are first stopped. (C) 1998 Elsevier Science Ltd. All rights reserved.