A real-time optimal control method for swing-free tower crane motions

Tower cranes are commonly used at construction sites all over the world. These cranes are prone to swinging of the cable suspended payload, resulting in unwanted payload oscillations that have severe effects on the safety on the site as well as on operational speed and accuracy of the payload delivery. The nonlinear nature of the rotating crane motion makes controlling these oscillations a complex task. In this paper, a time-optimal velocity control method is developed to enable fast and swing-free tower crane movements by applying Pontryagin´s maximum principle on a set of decoupled payload pendulum equations. The controller is developed in a feedback form and is implementable in real-time. The performance of the controller is compared with other control methods such as notch filtering and input shaping. Simulations using a detailed tower crane model show that time-optimal swing-free movements can be obtained and payload vibrations are reduced to levels lower than those that can be achieved with the other control methods, while resulting in significantly faster rise times in slew velocity.