A Bond Graph Approach for Modelling Systems of Rigid Bodies in Spatial Motion

Abstract

The research presented in this thesis seeks to improve the current state and technique for dynamic modelling of systems of rigid bodies in spatial motion. The research have been focused around modelling of underwater vehicles and robotic manipulators. Dynamic modelling of such systems are of growing importance as the demand for precise motion control with an increasing degree of autonomy continue to grow. This thesis presents a modelling framework which enables model developers to create a basic bond graph template for a system of rigid bodies in spatial motion. This template can be used as a base for further model development, on which the developer can utilize the modularity virtue of the bond graph by interfacing sub models of various systems. An effective method for developing and implementing such a basic template in bond graph software is presented. Then the virtues of this approach is demonstrated through two case studies. In the first case study a simulator for a seven degrees of freedom manipulator is created, onto which a high fidelity hydraulic actuator system is developed and connected seamlessly. Then a control system, taking input from a joystick is developed for the manipulator. The second case study presents a dynamic model of a remotely operated vehicle equipped with a robotic manipulator. First a basic template for this system is developed, according to the method presented in this thesis. The basic template is then extended by integrating an advanced thruster system and a motion control system to the vehicle. Hydrodynamic added mass and damping is also included to both the manipulator and the vehicle, and the manipulator is equipped with a control system. Finally, an interface to the external world through the manipulator end effector is developed. This external interface is used in order to create a simulation where the vehicle and manipulator system lifts an object, relocates it and places it down at the new location. Simulation results from this is provided.