Though an electro-hydraulic servomechanism is rigid at the connecting part, its velocity is affected by the changes of load and inertia. Therefore referential velocity cannot be obtained accurately. This defect has been overcome by a method of load insensitivity and a robust mechanism. There is also the feedforward control method using an observer.
In this paper a rotary electro-hydraulic servomechanism is treated. An observer which estimates and measures the disturbance of load and inertia is constructed and applied to this servo system. Its frequency and indicial responses are tested theoretically and experimentally. As the result, it is clarified theoretically and experimentally that the variation of velocity caused by the disturbance of load and inertia is decreased markedly by this observer without depending on a feedback loop.

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Blood pressure measuring technique using a pneumatic cuff is most important noninvasive method to determine the blood pressure. In this method cuff-pneumatic pressure is at first set higher than systolic blood pressure and then decreased gradually. In this process, blood pressure is determined by start and end of Korotokoff sound or characteristic pattern of cuff-pressure amplitude of oscillation. As the signals of sound or pressure oscillation are obtained intermittently, the cuff-pressure decreasing velocity is needed to be controlled at about 3 mmHg/s to assume the accuracy of measurement. But the velocity is affected by a size of an arm or its stiffness and, hence, it does not become constant when a simple restriction is used to release air of the cuff. In this research a control technique to decrease the cuff-pressure at constant velocity using a simple pneumatic control valve is proposed. The analytical results obtained in this research agreed well with experimental results, and usefulness of this method is known.

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Low-damping and low-robustness characteristics of pneumatic servo systems are sometimes troublesome for the ordinary control systems, but if the pneumatic system is applied to a fatigue tester, and worked near the resonant frequency, then a quick and energy-saving fatigue test can be implemented. For this purpose, it is necessary to know the frequency characteristics of the fatigue tester with a test object. However, because of its strong nonlinearity, the conventional sinusoidal input analysis method is too time-consuming.
This paper proposes a new method, which adopts the advantage of both M-sequence and sinusoidal signals. With this method, a quick and precise frequency characteristics analysis can be achieved. First, the time response of the system to M-sequence input is calculated, then through the FFT analysis of both the input and output signals, the system frequency characteristics can be obtained. Then, coordinated by the sinusoidal input calculation at some special frequencies, the optimal test frequency can be determined. At the frequency for the same amplitude under the same load, the air consumption of the tester for one cycle would be kept to a minimum. Comparisons have been made between the experiment and simulation for six pieces of test object samples. The results show that the optimal frequencies predicted by the simulation agree well with experimental ones. Finally, the load influence on the optimal test frequency is illustrated.
In the paper, comparisons have been also made between the frequency characteristics obtained with sinusoidal and M-sequence inputs for different signal amplitudes. Also the influence of Coulomb friction on the characteristics is discussed.

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A new type of precision positioning system by combined use of a pneumatic actuator and a linear type ultrasonic actuator has been proposed and constructed to realize an ultra-high linear positioning accuracy The system is composed of a feeding pneumatic cylinder controlled by pneumatic on-off valves and an active locking mechanism driven by the ultrasonic linear actuator. The main function of the pneumatic cylinder is to feed and position a positioning object quickly and roughly near a target point. The ultrasonic linear actuator plays the important function of a precise positioning at the target point. The operation principles and the performance of the system are discussed. It has been demonstrated by experiments that the developed system has linear positioning accuracy of better that ± 2μm and a positioning time of better than 0.41s over a traveling stroke of 30mm.

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