No abstract

No abstract

In this paper, we present a method for calculating reaction forces for a crane mounted on a ship moving in waves. The method is used to calculate the reaction forces between the crane base and the vessel deck. This includes the case where the crane is mounted on the platform that keeps the base of the crane horizontal when the vessel is moving in roll and pitch. The wave motion of the ship is modeled with force response amplitude operators (RAOs) based on the JONSWAP wave spectrum. The combined equations of motion for a vessel and a crane are derived using Kane’s equations of motion, where velocities and angular velocities are formulated in terms of twists, and the associated partial velocities and partial angular velocities are given as lines in Plücker coordinates. The unknown reaction forces are represented as wrenches and are determined using screw transformations. The method is used to study the effect of the roll and pitch compensation platform in numerical simulations. The efficiency of the platform is evaluated in terms of the magnitude of reaction forces and crane payload sway angles.

A vision-based controller for a knuckle boom crane is presented. The controller is used to control the motion of the crane tip and at the same time, compensate for payload oscillations. The oscillations of the payload are measured with three cameras that are fixed to the crane king and are used to track two spherical markers fixed to the payload cable. Based on color and size information, each camera identifies the image points corresponding to the markers. The payload angles are then determined using linear triangulation of the image points. An extended Kalman filter is used for the estimation of payload angles and angular velocity. The length of the payload cable is also estimated using the least-squares technique with projection. The crane is controlled by a linear cascade controller where the inner control loop is designed to damp out the pendulum oscillation, and the crane tip is controlled by the outer loop. The control variable of the controller is the commanded crane tip acceleration, which is converted to a velocity command using a velocity loop. The performance of the control system is studied experimentally using a scaled laboratory version of a knuckle boom crane.

This paper presents a modeling technique and a controller for an underactuated crane payload. The crane payload is modeled as a bifilar pendulum. The payload is attached to a sheave block, such that a cable can freely run to either side. This configuration is often used in different types of cranes, including offshore cranes. To achieve asymptotic stability in the absence of damping, we propose a controller based on an energy approach and the passivity properties of the system. We prove stability of the system with the proposed controller using LaSalle's invariance principle. The control performance is studied in the numerical simulations. The simulation results show that all the states of the closed-loop system with coupled sway and skew dynamics converge to the origin.