Tracking control with enhanced coupling for 5-DOF tower cranes using new block backstepping

Considering the increasing popularity of tower cranes in buildings, there is gradually more research on them. However, because tower cranes are underactuated and highly complex, many control problems remain to be solved, such as eliminating swing and reducing the tracking error. Many control strategies for tower crane systems have emerged in recent years, but a superior feedback approach, which is called backstepping, has not become mature in this field. In this regard, a tracking controller using a new block backstepping approach is developed for 5-DOF tower crane systems, which provides a new control idea for this field. A simple state transformation is designed to couple the actuated and non-actuated states, so that the swing angles are eliminated when the jib and cart reach stability. Then, a bounded time function that affects the controller gain is added to the controller to slow the actuator start and suppress the swing angles. An integral state is introduced, which integrates the carefully designed state transformation and consequently reduces the steady-state errors. The stability is guaranteed by rigorous theories based on Lyapunov's theorems. Finally, three sets of substantial hardware experiments ensure the superiority of the developed method.