JFPS International Journal of Fluid Power System
Online ISSN : 1881-5286
ISSN-L : 1881-5286
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  • Takumi KOBAYASHI, Tetsuya AKAGI, Shujiro DOHTA, Takashi SHINOHARA, So ...
    2021 Volume 14 Issue 1 Pages 1-9
    Published: 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

    In the pneumatic driving system for a soft mechanism, a control valve is the most heavy and expensive device. To realize a compact and inexpensive pneumatic driving system, it is necessary to reduce the size, weight, and cost of the control valve. In the previous study, a low-cost 4-port servo valve that could control the flow rate by changing the bending angle of the buckled tubes was proposed and tested. However, the buckled tube in the valve became the least durable component. The speed at which the valve altered the flow rate was affected by the motor rotational speed and available buckled angular range of the tube. It is necessary to develop a valve that can be operated via a smaller rotational angle, with a durable opening and closing mechanism. In this study, a small-sized servo valve that can control the flow rate via a diaphragm and gate mechanism, driven by a low-cost RC servo motor, is proposed and tested. The tested valve comprises a tiny RC-servo motor, two gate mechanisms, and diaphragms. The gate mechanism contains supply, exhaust, and output ports that connect with each other through a V-shaped groove for the pipeline. Two steel balls are set over the supply and exhaust ports through a diaphragm. By altering the pushing force to both gates using an RC servo motor, the valve can control the supply and exhaust flowrates. In this paper, the construction and operating principle of both valves are described. The output flow rate characteristics of the tested valves are also reported. As a result, it can be confirmed that the tested valve can control the supply and exhaust output flow rate, without any complex mechanical sliding parts, while maintaining a seal.

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  • Ha Tham PHAN, Yasukazu SATO
    2021 Volume 14 Issue 1 Pages 10-18
    Published: 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

    IIn recent years, numerous applications of the variable-speed variable-displacement (VS-VP) hydraulic power unit have been investigated. Especially in a valveless drive system, the necessary hydraulic power could be supplied effectively through a flexible motor speed and pump displacement ratio. This paper presents a control strategy to improve the overall efficiency of a valveless transmission system by regulating motor speed and the displacement ratio simultaneously based on the data of combined overall efficiency maps. In this way, the interaction of the servo motor and hydraulic pump – and whether it affects the overall efficiency of the system – are studied. A numerical simulation is implemented for a series of typical working points of three types of hydraulic power units. The results show that the proposed control strategy achieves better efficiency values in almost all simulation points compared with single-variable power units (variable speed unit (VSFP) and variable displacement unit (FS-VP)). In particular, at a low pressure and low flow rate points, the efficiency of the proposed system is improved by up to 6% and 25%, respectively, compared with the VS-FP and FS-VP power units.

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  • Takashi SHINOHARA, Keichi KUSUNOSE, Tetsuya AKAGI, Shujiro DOHTA, Taku ...
    2021 Volume 14 Issue 1 Pages 19-27
    Published: 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

    In the damp and wet conditions such as water supply pipe, some pipe inspection robots using pneumatic actuators have many advantages such as no electrical leakage and short circuit. In the previous study, an inchworm type pipe inspection robot using extension type flexible pneumatic actuators (“EFPAs” for short) was successfully developed. Also, as a robot for thinner pipe, “wriggling type” and “cilia type” robots were also proposed and tested. The wriggling type robot could move forward by wriggling its body. The cilia type robot could move by using many cilia type plates covered on it. As a result, the cilia type robot could travel in wet pipe and corners by twisting its body toward any direction. In this paper, to improve the mobility of cilia type robot and simplification of driving system, a cilia type robot with automatic wriggling motion is proposed and tested. The automatic wriggling mechanism can be realized by utilizing the pressure delay in serial connected three EFPAs that consist of each tube and orifice. To obtain the suitable diameter of orifice, the analytical model of sliding and bending mechanism using three EFPAs in the robot is proposed. The robot with theoretical suitable orifice is also tested. As a result, it can be confirmed that the tested robot can smoothly travel in a pipe and corner with twice speed compared with the previous one.

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  • Takumi KOBAYASHI, Tetsuya AKAGI, Shujiro DOHTA, Takashi SHINOHARA, So ...
    2021 Volume 14 Issue 1 Pages 28-34
    Published: 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

    In the pneumatic driving system for a soft mechanism, the control valve is the most heavy and expensive device. To realize a compact and inexpensive pneumatic driving system, it is necessary to reduce the size, weight, and cost of the control valve. In the previous study, low-cost and compact flow rate control type servo valves, that uses buckled tubes and a gate mechanism to control the flow rate in an analog way, were proposed and tested. However, in these valves, a drift of the overlap zone was observed owing to plastic deformation of the buckled tubes and lower stiffness of the valve frame. Ideally, the feedback control system using the fluidic parameter of the valve output is useful to solve this problem. However, there is no low-cost flow rate sensor in the market. In this paper, a low-cost pressure control type servo valve using buckled tubes and a gate mechanism, that consists of a low-cost pressure transducer and an on-board tiny-embedded controller, is proposed and tested. The construction and operating principle of both valves have been described. The pressure control performance of the tested valves has also been reported. As a result, it can be confirmed that the tested valve can control the output pressure according to the desired voltage. The dynamic performance of the valves has also been described.

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