In the previous report, a method in which energy savings in pneumatic systems were possible was proposed. It is a method using the meter-in circuit drive for cutting off the supply pressure when the piston reached the stroke end. A drastic reduction in air consumption is possible when this driving method is adopting. In this study, some problems in adopting this method were examined. The exhaust side initial pressure lowers further than the supply pressure. The possibility in which this effect appeared in the response initial stage piston was examined. The result showed that a drive equal to the conventional drive was possible. The response in adopting the meter-in a circuit drive at low speed was examined. It was proven that a large difference was not seen in comparison with the result of the meter-out circuit drive.

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This study deals with the trajectory control of a three degree-of-freedom hydraulic parallel mechanism. The hydraulic parallel mechanism is useful in a working field where high power and high accuracy are necessary. In the previous report of this study, applying a sliding mode control to the mechanism by using a disturbance observer, we confirmed through experiments a good response of the end effector. However, the response of each hydraulic servo system was accompanied with a certain magnitude of time delay from the reference input. Therefore, as a method for overcoming this problem, we propose a modified sliding mode control such that the system's transfer function is well represented by a dead time characteristic when the system is in the sliding mode. The dynamic performance of the trajectory control of the designed mechanism was investigated by experiments. As a result, we confirmed the validity of the applied method.

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In a pneumatic cylinder, a conveying load is supported at the sliding part between the piston and cylinder. The dynamic behavior of the frictional force that is generated at this part during operation greatly depends on its lubrication condition. This lubrication condition is principally governed by oil film thickness, pressure, and temperature. For that reason, further knowledge is required on the factors involved when a pneumatic cylinder is actually used in order to obtain a deeper understanding of frictional characteristics.
Measurement of temperature changes caused by sliding at the friction surface of a pneumatic cylinder is conducted in this paper. The temperature of the lubricant is related to its viscosity, and the viscosity has an effect on the ability to form an oil film and viscous resistance. Therefore, the dependency of friction surface temperature on velocity and loads is first investigated, and their physical processes are discussed to verify the measurement results by referring to hydrodynamic lubrication theory. Next, regarding the friction surface temperature approximately as the oil film temperature, the cause of the frictional force reduction occurring with temperature rise that is observed in the measurement results is elucidated according to a theoretical equation of frictional force in hydrodynamic lubrication by taking account of viscosity changes due to temperature changes. From this examination, it is also shown that variations in frictional force tend to depend highly on velocity at higher velocity ranges.

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At the maximum supply pressure of 55 MPa (the maximum load of 15 kN), circular hydrostatic thrust bearings are investigated in mixed to fluid film lubrication experimentally and theoretically. The effect of elastic deformation on the tribological characteristics is examined and the optimal criterion for high-pressure or tap-water hydraulic pumps and motors is discussed. The bearing diameter was 20 mm and the recess radius ratio was 0.5. The bearings tested were made of carbon steel, bearing steel and plastics (polyetheretherketone; PEEK), whose surface roughness was finished from 0.05 to 3.6μmRa. Hydraulic fluid with ISO VG 32 was used as the test liquid. Frictional torque and leakage flow rate were measured and power loss was assessed in a wide range of operating conditions. As regards the specimens with rough surface, the power loss minimized when the hydrostatic balance ratio, defined by the ratio of the load to the maximum hydrostatic load-carrying capacity, was set close to unity. By contrast, for the specimens with smooth surface, the ratio exceeded unity as the supply pressure increased. The elastic effect became notable when the supply pressure and the load were established higher and/or the specimens were made of plastics. The experimental data was in good agreement with the theoretical results considering elastic analysis.

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