Modeling and control of electrohydraulic robot manipulator

Abstract

This thesis is concerned with the mathematical modeling and the position tracking control of hydraulic manipulators. Hydraulically actuated manipulators are widely used in a number of applications including manufacturing and assembly since they provide high power to weight ratio and short response time. To increase the performance of the manipulators, it is essential to control the system well. However, in spite of their advantages, hydraulic manipulators are more complicated in nature due to the nonlinear characteristic of the mechanical linkage and the hydraulic actuator dynamics, parameter variations, payload uncertainties and strong couplings among various joints. The control problem of this system consists of obtaining the physical dynamic model and specifying the corresponding control strategy so that it tracks a predefined desired trajectory as closely as possible at all times. In this thesis, an integrated mathematical dynamic model of a hydraulically driven revolute robot manipulator in state variable form is presented. The integrated model comprises of the dynamic model of the manipulator mechanical links as well as the actuators dynamics. The formulation represents a more realistic dynamic model, thus provides a better and much more suitable model for the purpose of dynamic analysis and controller synthesis. Proportional Integral Sliding Mode Control (PISMC) strategy is adopted to provide the position tracking control for the system. The technique takes the advantages of zero steady error due to the integral term and robustness offered by the Sliding Mode Control (SMC). It is shown mathematically that the proposed controller does not only make the system insensitive to parameter variations, uncertainties and couplings; but also guarantees stability in the large based on Lyapunov theory. The performance of the proposed approach is evaluated and compared with the existing Independent Joint Linear Control (IJC) technique through computer simulation. A 3 DOF revolute robot is used in this study. The results prove that the controller has successfully provided the necessary position tracking control for the hydraulic robot manipulator system