Constraint Control of a Boom Crane System

Boom cranes are among the most used cranes to lift heavy loads. Although fairly simple mechanically, from the control viewpoint this kind of crane is a nonlinear underactuated system which presents several challenges, especially when con-trolled in the presence of constraints. To solve this problem, we propose an approach based on the Explicit Reference Governor (ERG), which does not require any online optimization, thus making it computationally inexpensive. The proposed control scheme is able to steer the crane to a desired position ensuring the respect of limited joint ranges, maximum oscillation angle, and the avoidance of static obstacles.Comment: The paper was published in 37th International Symposium on Automation and Robotics in Construction (ISARC 2020

Modeling and control of 5-DoF boom crane

Automation of cranes can have a direct impact on the productivity of construction projects. In this paper, we focus on the control of one of the most used cranes, the boom crane. Tower cranes and overhead cranes have been widely studied in the literature, whereas the control of boom cranes has been investigated only by a few works. Typically, these works make use of simple models making use of a large number of simplifying assumptions (e.g. fixed length cable, assuming certain dynamics are uncoupled, etc.) A first result of this paper is to present a fairly complete nonlinear dynamic model of a boom crane taking into account all coupling dynamics and where the only simplifying assumption is that the cable is considered as rigid. The boom crane involves pitching and rotational movements, which generate complicated centrifugal forces, and consequently, equations of motion highly nonlinear. On the basis of this model, a control law has been developed able to perform position control of the crane while actively damping the oscillations of the load. The effectiveness of the approach has been tested in simulation with realistic physical parameters and tested in the presence of wind disturbances.Comment: the paper was published in 37th International Symposium on Automation and Robotics in Construction (ISARC 2020

Modelling and Control of a Knuckle Boom Crane

Cranes come in various sizes and designs to perform different tasks. Depending on their dynamic properties, they can be classified as gantry cranes and rotary cranes. In this paper we will focus on the so called 'knuckle boom' cranes which are among the most common types of rotary cranes. Compared with the other kinds of cranes (e.g. boom cranes, tower cranes, overhead cranes, etc), the study of knuckle cranes is still at an early stage and very few control strategies for this kind of crane have been proposed in the literature. Although fairly simple mechanically, from the control viewpoint the knuckle cranes present several challenges. A first result of this paper is to present for the first time a complete mathematical model for this kind of crane where it is possible to control the three rotations of the crane (known as luff, slew, and jib movement), and the cable length. The only simplifying assumption of the model is that the cable is considered rigid. On the basis of this model, we propose a nonlinear control law based on energy considerations which is able to perform position control of the crane while actively damping the oscillations of the load. The corresponding stability and convergence analysis is carefully proved using the LaSalle's invariance principle. The effectiveness of the proposed control approach has been tested in simulation with realistic physical parameters and in the presence of model mismatch.Comment: This paper has been accepted to International Journal of Control on March 29th 2021. arXiv admin note: text overlap with arXiv:2103.0250

Real-Time Motion Compensation in Ship-to-Ship Load Handling

DoktorgradsavhandlingLike the automotive industry, the maritime industry is facing a higher demand for autonomous offshore operations. It is therefore in the author’s belief that the marine industry has to develop and implement new technology for both existing and new products to meet the increased autonomy demand. This thesis aims at presenting a unified understanding of the motions and the accompanying load handling issue in ship-to-ship operations. The ship-to-ship kinematics is modeled and a crane operator assistant is developed as a possible solution to increase the so-called weather window of ship-to-ship load transfers. The weather window is today determined by the significant wave height, and the current limitation of such operations is at 2.5m significant wave height. Proposing new methods capable of assisting the crane operator when transferring the load from one ship onto another is believed to further relax the weather window criteria, as well as increasing both the safety and efficiency of the operation itself. A novel ship-to-ship estimation algorithm using the well known Extended Kalman Filter (EKF) is developed and experimentally investigated in the Norwegian Motion Laboratory. In addition to the ship-to-ship observer, an observer for measuring the suspended load motions is developed. These estimators are used to form the novel crane operator assistant presented at the end of this thesis. The presented assistant consists of a wire-length assistant and an anti-swing assistant, which both aim at assisting the crane operator in ship-to-ship load transfers by adjusting the crane operator inputs slightly in real-time. The expected outcome is increased repeatability and efficiency, as well as reduced risk in general. The developed methods are described using a common and consistent mathematical notation for both the observers and the kinematic control systems. The appended papers at the end of this thesis have experimentally investigated and validated the proposed methods using several experiments which have been carried out in the Norwegian Motion Laborator