MODELLING AND CONTROL OF FLEXIBLE ROBOTS

Abstract

In this thesis, modelling and control of rotational/translational flexible link robots are studied. Three different modelling approaches are investigated for a single-link flexible robot, including the two most generally used modelling methods, say the Assumed Modes Method (AMM) and the Finite Element Method (FEM), and a newly developed lumping method. For all the three methods, it is shown that different dynamic models (linear or nonlinear) can be obtained through different representations of the position of the flexible link. By comparisons between the AMM models and the FEM models, and the simulations in later study of controller design, all the derived models are shown to be able to provide reasonably good approximations to the original flexible robot system. The work of control design consists of four parts. Firstly, a simplest model, in which the flexible link is lumped to an equivalent concentrated mass connecting to a weightless linear spring, is investigated to design a two-loop PD type controller for end-point tracking of the flexible robot; then, the most generally used models from AMM and FEM are used to develop two nonlinear controllers, which show quite good robustness to payload variations; thirdly, the control problem is studied with an energy-based approach for both single- and multi-link flexible robot systems, and the approach does not need system dynamics in stability proof and is thus actually non-model-based; and finally, the variable structure technique is applied to controller design based on the partial differential equations of the systems. The controllers presented in the last two parts are able to overcome the drawbacks associated with the truncated-model-based ones, such as the control/ observation spillovers, from which the controllers developed in the first two parts have suffered.