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Because horizontal motion of a rotary crane generates undesirable two-dimensional load sway, skillful operators are needed to control the crane's motion; for this purpose, various types of control schemes have been proposed. Because natural frequency of the rope-load oscillation system affects the stability and performance of the control system, the controller design should consider robustness with respect to rope length. If the control system considers the effect of rope length variance, the crane's motion can be controlled without a sensor system for measuring it. This paper presents a control method based on linear matrix inequality optimization for achieving robustness with respect to rope length variance. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.

Horizontal motion of booms in rotary cranes typically generates undesirable twodimensional load-sway; therefore, crane operators must be highly skilled to control the crane's motion. To reduce the burden on human operators, automatic control systems that can simultaneously control the boom's position while suppressing unwanted loadsway have been widely investigated. In most existing control schemes, both horizontal and vertical boom motion must be used to suppress load-sway. However, it would be less energy intensive and indeed safer if a control scheme could be developed that only utilized horizontal boom motion, i.e. without the need for any vertical motion. In this paper, we present a nonlinear controller design that enables both boom positioning and load-sway suppression using only horizontal boom motion. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.