Design of a heave compensation system with a redundant hydraulic manipulator

Abstract

Waves cause problems when operating in big sea because of their constant movement. Many operations, as moving cargo from ship to ship or from ship to a fixed platform, demands stable working conditions, and this is often difficult to achieve when the waves becomes too big. The use of active heave compensation can greatly reduce this disturbance. To overcome the movement of the waves, different applications can be applied. The 6 degrees of freedom Stewart platform can be used to compensate, as it can compensate for all motions, translative and orientational. It can also be used as a test platform to create artificial waves/movements which can be used to test/develope new heave compensating equipment. By solving the kinematics for both the Stewart platform and the hydraulic manipulator, creating a dynamic model for the manipulator using simulation software, the machines are analyzed. They are modeled and simulated in different software as SimulationX and MATLAB/Simulink. A model of a hydraulic manipulator is created to compensate wave motion when we place the manipulator on top of the Stewart platform. The manipulators has a redundant configuration and the properties of this is explore in regards to heave compensation. A physical experiments shows that the end effector of the hydraulic manipulator follows a straight line as if it heave compensating. In order to detect changes in position and orientations, an Inertial Measurement Unit is designed. This can detect fast angles changes in roll and pitch due to sensor fusion using an accelerometer and a gyroscope. A solution for removing position drifting by introducing a Spring-Damper-System is also presented. Further research concerning wave prediction may increase the accuracy of measuring position using the accelerometer. By creating these models and test them in real life, we will have a great tool for further research concerning heave compensation. Our new simulation of compensation indicates that many different applications for wave compensation can be developed and tested using the Stewart platform, which gives a real life testing environment. By having this complete heave compensation laboratory many new ideas and product can be created.