Bond Graph Modelling and Simulation Techniques Applied to a Three Axis Driven Pendulum

Abstract

A pendulum of three meter length, which can be controlled in three perpendicular axes, is used in experiments for strap-down navigation components. In the first measurements with accelerometers attached to the pendulum not only the pendulum frequency but also some higher frequencies were detected. By means of modelling and simulation the causes of the higher frequencies are found. In this contribution the modelling techniques and some simulation results will be described. It will be shown how the bond graph modelling technique can give a clear description of the system not only for the two dimensional case, with rotation around ono axis, but also for the case where the pendulum is controlled at the three axes. First the model will be restricted for clearity roasons, to one axis. The general set up of the pendulum and drive system will be shown, then step by step the model is extended. Adding torsion in the drive axis will show the first additional frequency. A simple model of the pendulum construction showing the bending of this construction will add higher frequencies to the system. Finally the model for the three dimensional movement will be treated. The bond graph of such a system shows clearly all the interactions in tho system. It can be concluded that the system tic way of setting up a model of a rotating body is one of the advantages using bond graphs.