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.

This monograph details basic concepts and tools fundamental for the analysis and synthesis of linear systems subject to actuator saturation and developments in recent research. The authors use a state-space approach and focus on stability analysis and the synthesis of stabilizing control laws in both local and global contexts. Different methods of modeling the saturation and behavior of the nonlinear closed-loop system are given special attention. Various kinds of Lyapunov functions are considered to present different stability conditions. Results arising from uncertain systems and treating performance in the presence of saturation are given. The text proposes methods and algorithms, based on the use of linear programming and linear matrix inequalities, for computing estimates of the basin of attraction and for designing control systems accounting for the control bounds and the possibility of saturation. They can be easily implemented with mathematical software packages.

Nonlinear Control Techniques for Electro-Hydraulic Actuators in Robotics Engineering meets the needs of those working in advanced electro-hydraulic controls for modern mechatronic and robotic systems. The non-linear EHS control methods covered are proving to be more effective than traditional controllers, such as PIDs. The control strategies given address parametric uncertainty, unknown external load disturbance, single-rod actuator characteristics, and control saturation. Theoretical and experimental validations are explained, and examples provided. Based on the authors' cutting-edge research, this work is an important resource for engineers, researchers, and students working in EHS.

This thesis deals with innovative working hydraulic systems for mobile machines. Flow control systems are studied as an alternative to load sensing. The fundamental difference is that the pump is controlled based on the operator’s command signals rather than feedback signals from the loads. This control approach enables higher energy efficiency and there is no load pressure feedback causing stability issues. Experimental results show a reduced pump pressure margin and energy saving potential for a wheel loader application. The damping contribution from the inlet and outlet orifice in directional valves is studied. Design rules are developed and verified by experiments. A novel system architecture is proposed where flow control, load sensing and open-centre are merged into a generalized system description. The proposed system is configurable and the operator can realize the characteristics of any of the standard systems without compromising energy efficiency. This can be done non-discretely on-the-fly. Experiments show that it is possible to avoid unnecessary energy losses while improving system response and increasing stability margins compared to load sensing. Static and dynamic differences between different control modes are also demonstrated experimentally.