Keivan Torabi Z. - Professor, Faculty of Mechanical Engineering, University of Kashan
Amir Ali Amiri Moghadam - Ph.D. Student, Faculty of Mechanical Engineering, Ferdowsi University of Mashhad
Mehdi Maarefdoost - Ph.D. Student, Faculty of Mechanical Engineering, Islamic Azad University- Gonabad Branch

In this paper, application of Quantitative Feedback Theory (QFT) to design optimal robust PID controllers for robot arm manipulators is proposed. In reality robots have uncertain mathematical models. Uncertainties in the models are caused by lack of knowledge about the dynamics of the robot, external disturbance, pay load changes, and friction, etc. Thus application of robust control methods for high precise control of robots is inevitable. As robot arm manipulators have multivariable nonlinear coupled transfer functions, therefore, using QFT technique at first converts the nonlinear plant into a family of linear and uncertain plants. This is achieved using fixed-point theorem and then for illumination of cross-coupling effect between degrees of freedom suitable disturbance rejection bounds will be designed. An optimal robust PID controller will be designed for the linear processes. In order to illustrate the algorithm the authors applied a two degree of freedom robot and the optimal robust PID controller is designed for tracking problem. Finally, the robustness and optimality of the design will be checked by means of a nonlinear simulation in tracking different trajectories.

QFT, Robot arm manipulators, Robust PID, Uncertainty, Nonlinear simulation