Up to now, there has been a lot of researches on the sliding mode control which has insensitive characteristics to the variations of plant parameters, nonlinearities, and external disturbances. One difficulty in applying the sliding mode control is the need for knowledge on full-state vector. The use of an state observer is a natural step towards the relaxation of this condition. However, it is impossible to show the essential effect of the sliding mode because an exact plant modeling is needed. Recently, there has been a remarkable advance in microprocessors and one can construct a controller, formerly unrealizable due to hardware restrictions in the past. Therefore in this paper, the PID sliding mode controller which has only one output feedback signal is suggested by means of a microprocessor, and the performance of an electro-hydraulic servosystem compensated with this controller is verified.

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The refrigerated dryer mentioned in this paper is one of the most popular ones among compressed air dryers. It consists of a precool-reheater, a main cooler and a refrigerator. The steam contained in the compressed air condenses due to cooling in the main cooler and the precooling side of the precool-reheater. If the condensate is not completely separated and drained, the dew point of the compressed air at the dryer outlet will increase, not allowing for the expected air condition to occur. In this paper, the effect of separation and drainage of the condensate regarding dehumidification of a refrigerated dryer is clarified in relation to the rating capacity of each heat exchanger and air temperature in the dryer through theoretical and experimental investigations.

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Recently, hydraulic servo systems with electro-hydraulic servovalves are being applied to various kinds of manufacturing systems. These hydraulic servo systems often need to have dual performance, by that is meant quick traversing and high positioning accuracy. Therefore, in the closed-loop system, gains of some devices change according to each performance. Therefore it is desirable that the servovalve of a hydraulic system has a non-linear flow gain to provide stability to the system. In other words, it is more effective for a servovalve to have a lower flow gain near its neutral spool position than one at the other spool position.
A hybrid-type servovalve has been newly created for this purpose so as to provide this non-linear flow gain. It has an underlap at oil support port and an overlap at oil return port in the spoolvalve. This servovalve is able to have a desirable non-linear flow gain to the spool position by selecting a suitable underlap and overlap for spool valve.
In this paper, the static characteristics (i.e., pressure gain characteristics and output flow characteristics) of a hybrid-type servovalve have been analyzed with realistic assumptions (i.e., a uniform radial clearance and rounded corners in the spool valve). In addition, the theoretical characteristics of the hybrid-type servovalve have been compared with the experimental results.

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The uninterrupted supply of electric power requires that high-voltage power distribution maintenance work be done in a live-line state, and for this purpose a manipulator for power distribution line work has been developed that allows an operator to work by remote control. The manipulator must be light-weight and high-output, because it is installed on the relatively unstable end of an insulated crane boom of a “cherry picker” truck and must handle heavy objects such as power distribution machinery and materials. Under such conditions, a hydraulic drive system has more advantages than an electrical drive system, but from the standpoint of control performance, a hydraulic manipulator has some characteristic problems not found in an electric manipulator. The stiffness is also low because most of it is made of plastic in order to ensure electrical insulation performance.
In this research we are studying the positional precision of the end of the arm regarding robustness with respect to changes in the system parameters of a 6-axes hydraulic manipulator that has such unstable characteristics. In particular, cooperation of the various axes becomes important for improving the positional precision, and position disturbance estimation and compensation by an observer is applied and evaluated by an independent servo-system for each joint. As a result, it was verified by an experiment that robust, stable positional precision can always be achieved against fluctuations in the moment of inertia caused by changes in the attitude of the arm, and against nonlinear disturbances, such as axis interference, that are characteristic of multi-jointed arms.

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For the development of an ultra-high pressure pump with high control ability, instead of the conventional three-plunger pump we designed and tested a new rotating swash plate, seven-piston pump.
As a result, this pump shows good practical flow performance in the range of 0-200MPa.
But, over the above pressure domain, flow characteristics deteriorate considerably, and flow becomes zero in the range of 350-400MPa.
The reason for this is assumed to come from the fact that leakage from piston clearance is predominant until a pressure of about 200MPa, but delay effect of suction and delivery valve becomes the main factor of flow reduction at high pressures over 200MPa.

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