In recent years, the drive current applied to acting on nozzle flapper valves has been reduced to save the electric power and the drive force acting on flappers has been lowered to approximate the level of the amount of flow jet force on flapper. As a result, the dynamic characteristics of pneumatic nozzle flapper are influenced, because the flow jet force changes the flapper displacement. So it is necessary to analyze the influences of flow jet force on nozzle flapper system.
In this paper a simplified model of flow jet force on flapper is proposed. The model is coincides with results of experiments in certain conditions. The influences of flow jet force on flappers have been experimentally measured by frequency response tests. The results of experiment, the effects of flow jet force on flapper reduce in high frequency domain. Indicate the model we proposed is practical. We think this model will be beneficial to analysis and design of nozzle flapper valves.

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A sampled-data H_∞ control is applied for a pneumatic cylinder system and its effectiveness is examined experimentally. Compared to the conventional continuous-based H_∞ control, the experimental results show that the sampled-data control achieves superior performance not only for long sampling periods but also for short sampling periods.

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The hydraulic cylinder system is a nonlinear system with variable parameters. It is difficult to meet control demands or obtain satisfactory performance by adopting traditional tuning techniques. This paper presents a Fuzzy Model Reference Learning Controller (FMRLC) for positioning control of an electro-hydraulic servo system. FMRLC has three main parts: the fuzzy controller, the reference model and the learning mechanism. The learning mechanism tunes the rule base of the direct fuzzy controller by changing the centers of the output membership functions so that the closed loop system behaves like the reference model. These rule base modifications are made by observing data from the controlled process, the reference model and the fuzzy controller. The effectiveness of the proposed control was confirmed through simulations and experiments using the servo valve controlled cylinder system.

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A design method of a robust force controller for a water-hydraulic moulding press is proposed. Force control is one of the key technologies used for the press. The control performance is affected by flow characteristics, stiffness of the press, and pipe length. Considering the uncertain factors as modelling error of a nominal model, a method of designing a robust force controller is proposed by applying H∞ control theory. The robust force controller is examined using an experimental water-hydraulic servo system. It has been shown that the force control system can be successfully built considering the robustness against the uncertain factors including various pipe lengths.

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