In this research, f or controllingt he waveform displacement, a direct digitalcontrol is employed for the electro-hydraulic servo system's linear model with follow-up control.
In this control system, the variable feed back gains of the velocity, the acceleration and its derivative at every sampling time are calculated by means of a digital computer, with the observed state variables of the electro-hydraulic servo system, and the manipulating signal is generated by the digital computer.
Since the calculations of the variable feed back gains are simple, the follow-up control of the reference model can be carried out without any difficulty, when compared with the ordinary electro-hydraulic servo system.
This control method was applied to an analog simulation circuit of a hydraulic servo motor and an experimental apparatus for verification, and the results were as follows:
(1) As a reference model of the controlled object, an electro-hydraulic servo motor, the linear first and second order models can be used. From this discussion, arbitrary nth order reference model could be applied.
(2) The input amplitude dependency of the dynamic characteristics on the electro-hydraulic servo system can be diminished.
(3) Using the straight line approximation of the load pressure vs. flow characteristics of the spool valve, the calculating time can be shortened.

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Recentlyt he social demands for energy conservation and product safety of hydraulic equipments are becoming higher and higher. Water-based fire-resistant hydraulic operating fluids are thought to fit to these demands.
In this research some effects of the water contents of water-glycola nd O/W emulsion, w hich are typical water-based fire-resistant hydraulic operating fluids, on the characteristics of a fixeddelivery vane pump, made to be used mainly with the petroleum-based hydraulic operating fluids, were studied. Following are some of the results of the experimental research presented in this report.
(1) Total efficiency of the test pump was found to remain unchanged practically and to be more than or equal to 70% during its test drive of 250 hours using the water-glycol having less than or equal to 80 wt% water contents.
(2) Test pump damage due to abrasion etc. was hardly found during the 250 hours test drive with water-glycol having less than or equal to 70 wt% water content except for the exceeding small and temporary damage at the beginning of the test.

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