The applications of pneumatic artificial muscles (PARM) are increasing in the power assist and manipulator systems, since they have advantages such as high power weigh ratio and flexibility. Usually, we have to measure the contract ratio of PARM using a displacement sensor installed near the actuator, which is not preferable from the aspect of preventing dust and water. In this paper, we propose a method of estimating contraction force from the volume change of the PARM, which makes it possible to have a sensor-less actuator. The air charged to and discharged from the PARM is measured by a quick response laminar flow meter. The volume of the PARM is estimated from the flow rate and the pressure measured by a pressure sensor. In order to estimate the contraction force accurately, thin copper wires are stuffed in to the PARM to realize an almost isothermal condition during charge and discharge. The effectiveness of the proposed method is confirmed experimentally.

View full abstract

In the present research, our pump model is designed to visualize the jet flow near a notch (V-shaped groove) of a valve plate in an axial piston pump. The cavitation cloud can be observed clearly using a high-speed video camera from the axial direction and the perpendicular direction to the axis. On the other hand, the CFD (Computational Fluid Dynamics) is employed using a three dimensional DES (Detached Eddy Simulation) turbulent model with cavitation model to estimate the occurrence and the region of the cavitation cloud. The CFD results are found to be in good agreement with the visualization results after the simulated regions of the cavitation cloud are compared with the experimental results for 3, 5 MPa (300, 600rpm). It is found that our CFD method is very useful for estimating the region of the cavitation cloud. Furthermore the cavitation cloud for 24MPa (2400r.p.m.) is obtained using the same CFD methods and the erosion for that case is discussed.

View full abstract

A spool valve is an indispensable component for controlling flow direction as well as flow rate in an oil-hydraulic system. Because an axial flow force sometimes causes an oscillation of the valve, it is important to predict the axial flow force precisely in the design stage. Past representative studies on the axial flow force were based on two-dimensional momentum theory and derived two models, which are an approximated equation model and another detailed model. As real spool valves have three-dimensionally complicated configurations, it is interesting to study the three-dimensional influences on the above equation models. This paper describes high-precision CFD results and the steady/unsteady flow force acting on the spool valve through 3D numerical simulations, compared with the above-mentioned equation models.

View full abstract