Air bubbles mixed in the hydraulic oil of hydraulic power transmission systems causes deterioration of the dynamic characteristics of the system, component erosion, accelerated deterioration of the hydraulic oil, reduced heat dissipation, and vibration noise. In this paper, a method to controlling air bubble content by a swirling flow of working oil has been proposed and developed. The amount of air bubbles in the oil flowing out of a bubble separation device can be adjusted by controlling the opening and closing of the valve on a vent port of the device. The air bubble concentration exiting the output port of the bubble separation device is controlled by the opening time duration of the vent valve. The validity of the proposed method has been experimentally verified.

In this paper, for the purpose of developing a pipe inspection robot that can catch pipes whose diameter has changed due to rust generated inside, the pipe holding mechanism that can flexibly catch various size of pipes was prototyped. A novel pipe holding mechanism using three extension type flexible pneumatic actuators (EFPAs) that holds the pipe while bending radially was proposed and tested. Also, the holding characteristics for various pipes of the tested mechanism was investigated. Furthermore, the inchworm-type robot using the tested holding mechanism was also proposed and tested. As a result, it could be confirmed that the robot could travel on the straight pipes and complicated pipes that consists of different pipes. In addition, a novel propulsion mechanism using only two holding mechanisms was also proposed and tested. It was also confirmed that a speed of 4.5 mm/s was obtained and that it could travel in a curved pipe.

In order to enhance energy efficiency of excavators for global environment conservation, an Open Center System (OC-System) as a power source has been improved in the world. However, total system efficiency including the internal combustion engine (ICE) has not been thoroughly considered. On the other hand, a Constant Pressure System (CP-System) enabling the engine to be driven optimally is developed but is not accepted in the industry due to the complexity of the required components. Thus, in this research, a hybrid system combining an OC-System with a CP-System is proposed by using a proposed design guideline and analyzing measurement data of a dig and dump cycle. It is indispensable to consider the nominal gas volume and pressure level for an accumulator in terms of energy saving and initial cost. Therefore, the influences of accumulator volume and pressure level are also discussed in this paper.

Pressure pulsation in oil-hydraulic system is generated due to the use of a positive displacement pump and it causes oscillation, noise and so on. An accumulator is generally employed to suppress the pressure pulsation. However, accumulator needs regular maintenance to prevent its performance deterioration due to gas leakage from it. Furthermore, there is a case where it is difficult to make the size of oil-hydraulic system compact due to the size of accumulator. Therefore, it seems to be necessary for an innovation of an oil-hydraulic system to develop a new oil-hydraulic component to reduce pressure pulsation. In this study, an oil-hydraulic component to reduce pressure pulsation is proposed. The feature of this component is that the structure is simple and the movement of an elastic tube is utilized to suppress pressure pulsation. The component is fabricated and some experiments are carried out to verify the mechanism to reduce pressure pulsation and to make clear its basic characteristics. Consequently, it is made clear that the proposed component and its mechanism are effective to reduce pressure pulsation. In addition to it, it is known that the proposed component can reduce the pressure pulsation of the downstream side of the component by about 43 % of that of the upstream side of it when the average pressure at pump discharge port is 3.5 MPa by setting both the gap width of the component and the hardness of the urethan rubber tube to suitable values.

Based on elderly society and decreasing birth rates in Japan, the rehabilitation device that can be used in home or hospital without assistance has been desired. In the previous study, a tetrahedral shaped flexible actuator using three extension type flexible pneumatic actuators was proposed and tested as a wrist rehabilitation device. The tetrahedral shaped actuator can extend longitudinally and bend toward any radial direction. In this study, a mobile robot using six tetrahedral shaped actuators that can use a core training and amusement for patients and elderly is proposed and tested. In this paper, the construction and operating principle of the tested robot was described. The control system using a micro-computer and 18 on/off valves was also described. In addition, the walking and rotating tests using the tested robot was carried out.