In order to clarify the buffer action of fluid films on the impulse and vibration, the equations considered the viscosity and compressibility of the fluid and the elastic deformation of the sold bodies are derived, and solved numerically. The thickness of the fluid film, the mass and velocity of the impacting body (a cylinder), and the deflection of the impacted bodies (a semi-infinite elastic body and a cantilever) are used as parameters and the calculating results are physically discussed. In this paper, the effects of the buffer action are evaluated mainly by the coefficient of restitution. For case where the impacting velocity is relatively small and the film thickness is comparatively large, the coefficient of restriction becomes small. Considering the deflection of the cantilever, the effects of the buffer action of films become to be clear with thin films.

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The development of hydraulic equipment has shown a tendency to increase the power density (power/weight). To increase the power density of swashplate type axial piston motors (hereinafter referred to as motors), high pressure with a speedy operation are necessary. As for the high pressure state, approximately 40 MPa and over, not only countering the increase in leakage but also the high stiffness of the motors should be achived. Therefore, presently, it is not possible to assume the motors to be rigid at a state of high pressure.
This study has been made to clarify 1) the distortion and stress distribution in the piston balls and hydrostatic slipper bearings (hereinafter referred to as slippers) and 2) oil film thickness and flow rate between slipper seal land and swashplate in motors at a high pressure state. The piston balls and slippers mostly affect volumetric mechanical efficiency of the motors. A number of investigations of these part have been made, but these parts were assumed to be rigid, because the studies were conducted in the low and middle pressure region. This simplified approach ignores the importance of the distortion in these parts. We carried out a structural analysis of these parts by means of the axisymmetric finite element method (hereinafter referred to as FEM), with a swashplate angle of zero and the slipper floating on a film of oil, that is the piston thrust load is equal to the slipper load carrying capacity. The load condition of the FEM analysis, the pressure on sliding part between the slipper and the swashplate were obtained from the Reynolds equation.
In addition, distortion, stress distribution, oil film thickness and flow rate characteristics with change in slipper pad thickness were discussed. The results obtained in the structural analysis have provided the basic technical data to enable the motors to operate at a high pressure state.

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The swash plate type variable delivery axial piston pump is commonly applied in construction machinery and other types of machinery as a power source for hydrostatic transmissions. To guarantee vehicle safety, it is necessary for the swash plate to stop at exactly zero angle, regardless of the control methods of the swash plate angle. Especially, it is required that the swash plate returns to zero angle naturally during manual control.
It is already known that a small moment acts on the swash plate restoring it to zero angle when the swash plate angle is near zero. Studies of this phenomenon, however, have not been performed and the principle of occurrence of the zero angle restoring moment is still not well understood.
The objectives of this study are to clarify the principle of occurrence and improve the characteristics of the zero angle restoring moment.
In this report, the inner states of the pump were investigated experimentally, and a model for analysis was proposed. Furthermore, supplemental experiments were performed and it was ascertained that the experimental results are in good agreement with forecasted results based on the model.

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This paper presents a study on the transient characteristics of a variable-displacement, swash-plate type axial piston pump incorporating a pressure compensator. The effects of design and operating parameters on the surge pressure generated in the outlet line at the time of an instantaneous circuit cutoff, and the settling times of pump discharge pressure and swash-plate angle (i.e., pump flow rate) after instantaneous circuit cutoff and opening were mainly investigated.
It was found that the surge pressure was predominantly influenced by the flow resistances in the passages and the pressure override of the pressure-regulating valve, as well as by the volume of the pump discharge line. In addition, the mathematical model of the pump control system presented in this work, in which all variables were expressed by the state equations, and the numerical calculation method for it could be confirmed to be an effective and generally applicable method for the theoretical analysis of the transient characteristics of these systems.

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A pneumatic actuation is anticipated to be applied to more rigorous servo-type motion controls. Especially, it is possible to construct a novel flexible actuation system using the high compliance due to air compressibility. A newly developed pneumatically driven rubber actuator has been constructed for this purpose. Also, its application to robot manipulators or hands is being actively studied. However, the fundamental control characteristics are yet to be studied in depth, so the knowledge about this actuator is not sufficient for designing a servo system.
In this study, the static and dynamic characteristics are examined experimentally. Also, a position servo system was constructed with this actuator and PWM pressure control valves, of which the control performance is discussed. The principal results can be summarized as follows.
1) Both the displacement and the output force of this actuator are very sensitive to the operating pressure.No dynamic delay exists in the conversion process from pressure to force, and its dynamic characteristic depends only on the operating pressure response. Therefore, to apply this actuator effectively as a servo actuator, a high response and high accuracy pressure control is required.
2) The PWM pressure control valve with the high speed on-off solenoid valve is effective for driving this actuator.
3) Although this actuator has a considerably large hysteresis, even the usual linear controller can provide the almost satisfactory control performance within this experiment.

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