Design for robust stability is one of the most important issues in nonlinear systems theory. The validity of linear system design in a small neighborhood is not a sufficient criterion for systems that undergo parametric variations and have strong nonlinear characteristics. With rapid growth in the systems theory, the design of nonlinear systems using bifurcation theory-based procedures has been one of the key developments. Servo-hydraulic systems are one of the most commonly used actuation and control devices, due to their force to weight ratio. They also are highly nonlinear in nature and hence provide considerable difficulty in the design and analysis of these systems and their control algorithms. The goal of this dissertation is to tackle some of the issues of the nonlinear systems theory with applications to servo-hydraulic systems. The use of bifurcation theory for the design and analysis of a nonlinear system is illustrated, and a detailed investigation into the dynamics associated with the servo-hydraulic systems is done. Further, the model decomposition/reduction strategy for parametric study in the nonlinear system is suggested. The idea of control-induced bifurcation is introduced and explained in light of servo-hydraulic systems. The servo-hydraulic system nonlinearities are explained and their effects on the robust stability are highlighted. This numerical work is also complemented with the experimental results on the servo-hydraulic circuits. This general procedure for robust stability design and control design, under the influence of nonlinearities, presented in this work can be used for any nonlinear system. The limitations of bifurcation theory based tools are also highlighted.

This up-to-date book details the basic concepts of many recent developments of nonlinear identification and nonlinear control, and their application to hydraulic servo-systems. It is very application-oriented and provides the reader with detailed working procedures and hints for implementation routines and software tools.

Hydraulic power systems find a wide range of applications varying from high power transmission as in heavy machinery to accurate control as in robotics and flight control actuators, and in mobile systems like agricultural machines. Hydraulic systems have many advantages. They have a high power to weight ratio and the system can be controlled electronically. Therefore they are flexible and are efficient in transferring and controlling power. Hydraulic systems are highly nonlinear in nature and exhibit dynamic fluctuations in parameters such as pressure and velocity. These effects, if not controlled, would lead to large scale oscillations that would damage system components. This work is focused on the robust parametric stability analysis a servo-hydraulic system in two-parameter space. A higher order linear controller and a nonlinear controller using feedback linearization technique are designed. State and input/output transformation were used to reduce the order of the inner-loop feedback linearized plant. In this thesis, the stable-unstable boundary for two-parameter variations is obtained by non-linear analysis and is verified by experimentation. These stability boundaries are used as a tool to study the robustness of the system by measure of distance to instability from the nominal parameters. The control strategies were implemented using Matlab/Simulink and the real time control was implemented using WinCon software developed by Quanser.

Stability is imperative in the design of hydraulic systems. Servo-hydraulic systems are inherently non-linear creating various nuances when analyzing the stability of the system. Friction, port flow, saturation, impact loading, line dynamics, and boundary conditions are a few of the many non-linearities found in servo-hydraulic systems which are to be analyzed using advanced non-linear stability analysis techniques. Some effects of instabilities induced by non-linearities such as pressure oscillations, noise, etc., can be detrimental to the stability or operation of hydraulic systems especially when the design is near the envelope of stability. This thesis presents preliminary research on the various non-linearities found in hydraulic systems. A test stand has been developed to test the hydraulic cylinder system dynamics, with the inclusion of a mass-spring-damper system. An experimental modal analysis was performed on the hydraulic test stand to provide helpful information regarding the natural frequencies of the structure to insure that these frequencies do not lie near the natural frequencies of the hydraulic systems. Initial non-linear dynamic testing was completed on two hydraulic cylinders, consisting of finding the breakaway friction forces of the hydraulic cylinders.