This research proposed using the slit structure instead of the orifice structure to reduce the noise level in the pressure reducing system. The slit structure is comprised of disks similar to a cylinder that has been sliced. The compressed air enters the center of the disk and is exhausted through the slit. Because the pressure reducing is performed by the smooth flow in the slit, this can be performed quietly without causing turbulence flow or generating a shock wave. Parallel and radial type slits were manufactured. The pressure, velocity, and temperature were analyzed,and the silence effect was examined. The results obtained are summarized as follows: (1) In the radial type, the exit average velocity and Reynolds number were lower than the parallel type at the same inlet pressure. (2) The slit structure has the silence effect about 35dB more than an orifice. When the inlet pressure is more than 250KPa, the parallel type has the silence effect about 33dB and the radial type has the silence effect of about 39dB. By the above, the silence effect of the radial type is higher than the parallel type by about 6dB. (3) As a result of the frequency analysis of the noise level of the orifice and the radial types, the drop of the sound pressure level at high frequencies is remarkable.

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Two types of the electrode are designed to control the pressure and the flow rate of the ER (Erectro-rheological) fluids. The shape of the electrode is a circular pipe and some parts of the inner surface of the pipe are the electrode. A liquid crystal mixture is selected for the homogeneous ER fluids and the pressure drop of the circular pipe electrode is measured for a constant flow rate. On the other hands, numerical analysis of the electric fields in the circular pipe electrode is conducted. The relations between the flow rate and the pressure are obtained theoretically for various electric field intensities, which almost agree with experimental results. The distribution of the viscosity of the liquid crystal mixture should be considered to obtain high accuracy when the flow analysis is conducted for high voltages. The ER effect of two electrodes is discussed from the distributions of the electric field intensity.

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It is generally not easy to acquire high positioning accuracy in hydraulic servo control systems, since they have an intense non-linearity, such as a dead zone, which is originally caused by leakage and friction. It is considered that the Neural Network compensator is one of the available options to get over the inherent problem. This paper deals with the effect of dither/PWM signals on the steady position error in the hydraulic motor drive system with a state feedback Neural Network. From the computer simulation and the experiment, it is clarified that the application of the dither/PWM signals to the Neural Network control system improves the positioning performance by accompanying the assistance of the Neural Network capability.

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