When PID control or optimal control is used for pneumatic servo systems, it is not always easy to get a good response under a wide range of working positions, because exact models for the pneumatic actuators cannot be obtained and because their dynamics is very nonlinear. The Time Delay Control (TDC), however, can rapidly compensate for the modeling error and nonlinearity using a simple control scheme.
In this paper, TDC was applied to a pneumatic position control system consisting of a pneumatic cylinder and on-off type reed valves driven by PWM. The effectiveness of the pneumatic system controlled by TDC was confirmed with simulations and experiments. The main results are as follows :
1. A simple TDC controller was designed, in which the piston position, velocity, acceleration and derivative of acceleration are used as state variables.
2. TDC can rapidly compensate for the nonlinearity in dynamics due to gas compressibility.
3. This system always has a good response for any reference position and for any piston moving direction.
4. The system is strong against modeling errors occurring at high frequencies due to the friction effect and so on if an estimated input gain of a plant is made larger than the real value.
This study utilizing TDC demonstrates that a pneumatic position control system can be designed even by rough parameter identification, and that it always has a good response under a wide range of operating conditions.

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Lubrication condition between a piston and cylinder produces a large influence on the performance of swashplate-type axial pistons pump and motors. It is desirable to have fluid lubrication for these sliding parts so as to decrease friction and abrasion. Understanding the lubrication between piston and cylinder is extreme importance to have efficient fluid lubrication for larger operating ranges. Therefore, we advocate the necessity of observing and evaluating the degree of metal contact and separation based on fluid film between a piston and cylinder under mixed lubrication condition.
In this report, we attempted to measure piston spinning, and observed and evaluated the lubrication between a free-spinning piston and cylinder. Then, the influence of the spin on a piston is examined. Further more, the influence of radial clearance and effect of the forced lubrication are measured at the time the piston is spinning.

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The thermodynamic method for measuring the efficiency is introduced for two oil-hydraulic gear pumps having rating pressure of 20 MPa, and their efficiencies are compared with the ones which are given mechanically by measuring the pressure difference, rate of flow and power input.
Conclusions obtained are as follows :
(1) Stable values of the efficiency can be given by the thermodynamic methods adopted under the condition of constant heat transfer with the surroundings through the casing walls.
(2) The efficiencies obtained by the thermodynamic methods are two or three percent larger than the ones measured mechanically even under the condition that there is no temperature difference between the pump casing and the surroundings. So, it is supposed that there are some heat transfer and heat accumulation which cannot be detected in the experimental apparatus.
(3) The heat transfer and heat conduction with the surroundings through the casing walls have direct effects on the values of efficiencies measured by the thermodynamic methods, and it is necessary for a more precise efficiency measurement to establish how to compensate for the effects of the heat outflow in the surrounding area.
(4) The means of inserting the plastic boards between the casing wall and the bracket or the Blacket and the common base minimize the effects of heat conduction. The means of covering the inlet/outlet pipes and the temperature measuring block by the glass-wool also minimize the effects of heat conduction.

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Velocity distributions of converging oil flows in a pipe with a cross-sectional change in which the Reynolds numbers are much less than those of air or water due to high viscosity of oil have been measured with LDV. The measurements have also been compared with the numerical predictions by the laminar flow theory, giving fairly good agreement between the two. As a result, the findings are as follows : (1) Regardless of the convergence ratio and Reynolds number, the convergent flow region reaches the axial direction as far as the pipe radius upstream from the changing cross-section. (2) Within the Reynolds numbers employed in the present experiments, which have been as high as about 5000, distinct turbulence has not appeared in the convergent flow. Actually, the flow convergence rather helps reduce turbulence produced at and transmitted from upstream. (3) After convergence the flow is restored to a Poiseuille one in a downstream pipe when the Reynolds number is smaller than 2000. The restoration distance depends on Re, of which relation is substantially predicted by FUJIMOTO's empiric equation.

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