This study deals with the application of a Model Reference Adaptive Control (MRAC) theory in discrete time to an electro-hydraulic servo system. MRAC is very useful to control a plant of which parameters are unknown or vary during operation.
An electro-hydraulic servo system is generally a continuous time system. In order to control this system by micro-computer in discrete time, z-transform is used. It should be noted that the plant becomes a non-minimum phase system in discrete time for smaller sampling periods, even if it is a minimum phase system in continuous time, and the plant can no longer be controlled by MRAC in discrete time.
Conditions under which the discrete plant is in non-minimum phase are being investigated. If the sampling period is less than about one half of the natural period of the electro-hydraulic system in continuous time, its discrete system using z-transform becomes a non-minimum phase system.
The output velocity (or state-variable) of the plant is fed back to decrease the natural period. The modified plant is combined with MRAC in discrete time. This indicates that the problem of short sampling time is greatly reduced.

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The movement of pneumatic cylinders tends to be unstable and must be compensated in some manner. If the system is driven with proportional valves, the pole assignment method can be used by operating opening cross-sectional area in the proportional valve with a feeding back of the system state variables. The proposed servo system is driven by charging and discharging high speed switching valves and the valves switch the air up to 200 Hz. The compensation by operating opening time of valves is discussed and tested in this paper. As a result, the usefulness of this compensation is shown theoretically and experimentally.
Furthermore, the observer which estimates the higher order state variables is introduced into this servo system. The observer can estimate the system state variables such as velocity and pressure correctly, therefore allowing the sensors to be replaced.

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This paper concerns newly developed software for manifold block design.
Manifold block has become indispensable to almost every hydraulic system nowadays. However, its design is extremely complicated and difficult. The reasons are firstly that hydraulic circuits have to be very densely placed in the manifold block, and secondly, there is no means to correct a failure in the design or manufacture. In addition, each manifold block is custom designed.
Considering the above, we analyzed the experiences of design engineers and their habitual design processes, and developed a support system for manifold block design using a super-mini computer. With this, we are now able to prove the correctness of a design. The software is easy to operate, it can retrieve past design data, and it is extendable to the production line.
Today, manifold blocks are mostly designed on a super-mini computer and/or CAD. Use of this system is particularly effective with manifold blocks with many holes. More than 2800 manifold blocks have successfully been designed as of now. Many common failures of the past have been completely eliminated.

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Lately, the power density (power/weight) of hydraulic equipment has been increased as a result of research developments. To increase the power density of swashplate type axial piston motors (hereinafter referred to as motors), high pressure and speedy operation are necessary. As for the high pressure state, measures must be taken against increased leakage flow rate and over-rigidity of the motors. Therefore, in the present stage, the motors should not be rigid during application of high pressure.
In the previous report, we described a theoretical analysis of elastohydrostatic lubrication of piston balls and slipper bearings in motors, at a swashplate angle of 0° with slipper floating on the oil film.
In this report, the leakage flow rate between a slipper and swashplate were measured with change in slipper pad thickness and supply pressure, as identification of the theoretical analysis. The measured leakage flow rate was in qualitative agreement with the results of theoretical analysis. Furthermore, the leakage flow rate was measured with change in the swashplate angle. It was found that the tendency of the leakage flow rate with the change in slipper pad thickness at swashplate angle β≠0° was similar to that at β=0°.

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