In this paper, the design of a control system for nonlinear plants with a time delay is proposed. It is derived that the control systems of any nonlinear plants with a time delay can be reduced to a simple second-order model. For the identification of nonlinear plants, radial basis function neural networks, which are known for their stable learning capability and fast training, are used. In the simulation study of nonlinear plants with a time delay, it was observed that the steady-stete error between the plant output and the reference model output was small. Moreover, in the experimental study of an actual pneumatic cylinder, it is shown that the proposed method yields a stable tracking performance.

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Differential pressure type air leak testers are widely used in industry due to their suitability for automation, low manufacturing cost, accuracy of 2% FS and applicability for leaks as small as 1.7×10^-10m³/s. We developed a differential pressure type leak tester, modified the circuit and investigated its characteristics. In the previous differential type air leak tester, the temperature recovery time was set to be constant for various test pressures and volumes. We found that different test pressure and volume required a different temperature recovery time to obtain the expected repeatability and accuracy. Detailed investigation showed that the higher the test pressure and the bigger the volume, the longer temperature recovery time was required to obtain the expected repeatability and accuracy. We also demonstrated the effect of temperature recovery time on repeatability by comparing the normal chamber and copper wire stuffed isothermal chamber. The result showed that the copper wire stuffed isothermal chamber suppressed uncertainty.

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In the present research, our pump model is designed to visualize the jet flow near a notch of a valve plate in an axial piston pump. The cavitation cloud can be observed clearly using a high-speed video camera from the perpendicular direction to the axis and the direction of the jet flow and the area of the cavitation cloud are obtained. A valve plate with V-shaped groove type is used and the regions of the occurrence of the cavitation are analyzed using an image processing technique. Furthermore the computational fluid dynamics is employed using the 2-D vortex method combined with boundary element method to estimate the occurrence and the region of the cavitation cloud.

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