Feedback control

The open-loop control techniques, discussed in Chap. 6, are the most widely applied methods for controlling crane systems due to their easy and cost-effective application (i.e., feedback sensors are not required). However, they have serious limitations in dealing with nonlinearities, modeling uncertainties, and external disturbances. Therefore, such systems are feasible for only simple crane operations that can be carried out under controlled environments, for example, within an enclosure (such as a factory), where external disturbances such as wind cannot have significant impacts on the crane system. However, crane systems are also used for field or offshore operations and are exposed to external disturbances such as wind, sea currents, and waves. Furthermore, the repetitive nature of crane operations causes degradation and wear within the constituent parts of the support mechanism, which changes their friction-related properties, consequently resulting in modeling uncertainties. Therefore, to achieve the required performance of the crane in a challenging environment, either hybrid open- and closed-loop or solely feedback control strategies are pursued. First, we will discuss the feedback control strategies applied to crane systems, which mostly utilize the feedback of the sway angle of the payload and the position/velocity of the support mechanism (i.e., the trolley, bridge, boom, etc.) in generating control inputs (either force or torque) to the support mechanisms themselves in achieving both the sway suppression of the payload and the position control of the entire crane.