The hydraulic servo actuator system is generally dealt with as a second order delay element. The self-excited oscillation method has the advantage that it enables easy estimation of the dynamic parameters of the approximated second order transfer function without valuable measuring instruments such as a FFT analyzer. This study utilizing the self-excited oscillation method suggests the real-time identification algorithm. In order to demonstrate the method's effectiveness, the proposed method was experimentally compared with the frequency response characteristics. Results indicate that both method shows good coincident. It was also confirmed that when the supply pressure and additional torque are continuously changed in the hydraulic system, the damping coefficient and undamped natural frequency were updated on the PC monitor. In addition, amplitude and frequency correction coefficients are analytically obtained from the describing function considering the phase shift, and compared with the simulation results.

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When tap water is used as a pressure medium, the structure and material of an oil hydraulic high-speed solenoid valve can not be used because internal leakage and rust can occur. Accordingly, the authors have proposed a novel water hydraulic high-speed solenoid valve. This study is mainly concerned with the development of direct-driven water hydraulic high-speed solenoid valve. Through the investigation of soft magnetic material which has anti-corrosion and low eddy current characteristic, a solenoid design method using soft magnetic stainless steel instead of soft magnetic iron was established. Furthermore, a high-speed driving circuit, which compulsively imprints over-excitation voltage and demagnetization voltage onto the solenoid, is used in order to reduce the switching time of the water hydraulic high-speed solenoid valve. From the linear characteristics of Duty and mean flow, as well as fast switching time within 1.5ms, the validity of solenoid and direct driven valve design method for water hydraulics is verified.

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ER Fluid (ERF) is a functional substance that can change its apparent viscoelastic properties by the application of an electric field. This is called the ER effect. The Applications of ERF to mechanical devices have been anticipated. However, separation and sedimentation of ER particles over long term use, which reduces the ER effect and results in low stability of ER devices, has been an obstacle to such application. To solve these problems, an ER gel was developed and the basic characteristics of ER gel were experimentally analyzed. A thin sheet of ER gel was sandwiched between a pair of plate electrodes and the variation of shear force between the ER gel sheet and the electrode was measured under variated of electric field intensity. The developed ER gel produced extremely high shear force and showed a slip phenomenon at the contact surface of the electrode under high electric field intensity. These results suggest that the developed ER gel has a different shear stress occurrence mechanism from conventional ERF. In this study, the shear stress occurrence mechanism in ER gel was also experimentally analyzed.

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A novel hydraulic actuator with built-in compound control function of displacement and thrust, and a method to improve the dynamic performance of an actuator were studied. Fundamental experiments and numerical analysis were conducted to examine the dynamic characteristics of the prototype hydraulic actuator. A sleeve orifice was introduced to improve the response of spool valve and a cylinder orifice was introduced to improve stability of the system, then their effectiveness was investigated by simulation study. From the experimental results with orifices, it was confirmed that the response of spool valve in thrust and displacement control and the stability of the system in displacement control were improved by orifices. Furthermore, the experimental results showed that adjusting the orifices was also effective in improving precision of the hydraulic actuator.

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