Poppet valve circuits are liable to be unstable and various kinds of oscillations induced. This paper deals with chaotic oscillations occurring in a direct-acting poppet valve circuit with a long pipeline on the basis of a distributed parameter model with average pipeline friction. Then, the influence of pipeline friction on chaotic oscillations was examined taking the pipeline length as a control parameter by using the method of numerical simulation. Simulation results are qualitatively in better agreement with experimental results than the case of a frictionless pipeline model.

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In this paper the load capacity, power losses and stiffness of disk-type hydrostatic thrust bearings including the case of eccentric loading are discussed theoretically. The bearing/seal parts are made up by combining stainless steel/stainless steel and stainless steel/plastics. The main results are as follows :
1) For the elastic materials, the maximum stiffness derived from the minimum film thickness is larger than that of the rigid material at the large ratio of pocket pressure and hydrostatic balance.
2) The stiffness increases with the supply pressure. The power loss due to leakage flow is mainly affected by the supply pressure and that due to frictional torque by eccentric loading.
3) For the case of water, the power loss due to leakage flow is a little larger but that due to frictional torque is much smaller than the case of hydraulic oil. Then, the total power loss is much smaller than that of hydraulic oil.

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Even for disk-type hydrostatic bearings supporting concentric loads, cavitation can occur in the case of dynamic loading.
In this paper the load-film thickness characteristics of hydrostatic bearings under cavitating condition due to squeeze film effects are analyzed both experimentally and theoretically. Theoretical results, newly developed as a type of bubble models, are compared with the conventional treatments, where the liquid film pressure does not decrease below the atmospheric pressure and the liquid film has enough tensile strength, and also with experimental results.

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In this paper, a two-degree-of-freedom control method is applied for position control of a pneumatic motor driving system. The control system consists of the I-PD controller, Smith's time delay compensator and disturbance compensator. The design procedure is essentially based on partial model matching which offers a reasonable way to simplify the design and controller configuration under disturbance rejection. Computer simulations by MATLAB and experiments of the position control were carried out under various conditions. The results obtained are summarized as follows : (1) Reference tracking performance for changes in trajectory or load mass was good, and steady-state positioning accuracies of within ± 0.4mm could be obtained. (2) Excellent control performance for step or trapezoidal disturbances was obtained. (3) Robustness of the control system for characteristics change of the control object could be maintained.

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