Impedance control of secondary regulated hydraulic crane in the water entry phase

Abstract

During the water entry phase in heavy lift marine operations, the involved crane system must satisfy stringent safety requirements. A hydraulic crane driven by a secondary controlled unit that has the advantage of high dynamic behavior and energy efficiency is investigated in this paper. The detailed models of the crane system and the offshore operating conditions are established. To guarantee functionality of the crane system under harsh sea conditions, a cascade control structure is constructed. In the outer loop, an extended state observer is used to estimate the unmeasured payload states. Then, an impedance controller is designed to realize trajectory tracking and impedance regulation of the payload. In the inner loop, the reference trajectory is provided by the impedance controller. An indirect adaptive robust control approach is applied to maximize the achievable tracking performance and to obtain accurate parameter estimates of the secondary controlled unit in the presence of parametric uncertainties and unknown disturbances. The proposed controller can lower a payload to a desired position, and keep the values of the hydrodynamic forces and wire tension within acceptable bounds at the same time. Comparative simulation results verify the effectiveness of the proposed control method.