Research On Pendubot System Based On Unmodeled Dynamics Compensation

Pendubot (pendulum robot), as a typical nonlinear underactuated mechanical system, is playing a leading role in modern industrial, by reducing the number of the components, lightening the weight of the equipment and lowering the cost. Consequently, there is a high theoretical and practical value in this kind of system.When the Pendubot is at a balance posture, it has a complex characteristics of nonlinearity and underactuated. An excellent robustness and a good dynamic response cannot be guaranteed by traditional linear controllers, because the impact of higher order nonlinear term of the system is not considered. As a result of that, it is necessary to study the uncertainties of the Pendubot system.With the support of State Key Laboratory of Synthetical Automation for Process Industries (Northeastern University), a PD balance control algorithm based on unmodeled dynamics compensation is proposed in order to overcome the drawbacks of the traditional balance control method, and its validity and advantage has been proved by simulations and real-time experiments. The main contributions are summarized are as follows:1. The dynamics model of the Pendubot has been established by using the Lagrange dynamics equation. As the model for controller design, a parallel subsystem form is analyzed based on that dynamics model, which is constituted by a low-level linear term and a higher order nonlinear term.2. A new PD balance control algorithm based on an unmodeled dynamic compensator is proposed because of the higher order nonlinear term in the model. The simulation research of the balance control algorithm proposed in this paper is introduced on MATLAB/Simulink environment, based on the top balance position.The results of the simulation are analyzed in two aspects, which are the range of balance control and the robustness.3. The new balance controllers that designed are applied on Pendubot system, the result of the real-time experiments has been analyzed. The effect of the new method is compared with the LQR balance controller. By analyzing the indicators of swing-up performance, balance performance and anti-jamming performance, it has been shown that the weakness of the traditional balance algorithm, such as the poor anti-interference ability and the small balanced stable interval, is overcame, and the robustness and convergence speed of the system is improved. The validity and advantage of the PD control algorithm with unmodeled dynamics compensation has been proved.