This paper deals with a new bondgraphs representation method for pneumatic systems. A pneumatic system has compressible fluid-flow and thermal fields. In constructing bondgraphs model for such a system, fluid and thermal power bonds have been employed. In addition to it, multi-port C and multi-port R elements have been frequently used. Therefore, the resulting bondgraphs model becomes complicated, and it is difficult to understand how energy flows branch off or join together. From this viewpoint, a bondgraphs representation for such a system is incorporated into the present study by introducing a new concept of effort and flow in both compressible fluid-flow and thermal fields. In this bondgraphs representation, the product of effort and flow is power, which means that true bondgraphs are being used. Furthermore, only 1-port C and 1-port R elements are used for modeling of this system. Therefore, the energy flows can be easily understood from the resulting bondgraphs representation. To confirm the usefulness of this representation for a simple pneumatic system, simulation was carried out. By comparing the simulated results obtained with the experimental ones, the usefulness of this representation is clarified. In simulation, a simulation program named BGSP was employed without modifying it so as to use multi-port elements. It is a great achievement that the modification of BGSP is not needed when this representation is used in modeling a pneumatic system.

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In this paper, the characteristics of disk-type hydrostatic thrust bearings, simulating the major bearing/seal parts of water hydraulic pumps and motors, have been provided. The bearings are made up by combination of stainless steel/ stainless steel and stainless steel/plastics. The characteristics are evaluated by the relationship among the load capacity, pocket pressure, film thickness and leakage flow rate. The main results obtained are as follows : 1) the load capacity expressed by the ratio of hydrostatic balance is not only dependent of the supply pressure (with the same restrictor) but also of the elastic modulus of materials, 2) effects of inlet pressure drop into the bearing landing are much smaller than those of elastic deformation, especially in plastics, 3) Young's modulus of plastics is dependent of stress acting on their surfaces and is not a constant such as metals.

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In this paper, the characteristics of disk-type hydrostatic thrust bearings are discussed theoretical point of view. The bearing/seal parts are made up by combining stainless steel/stainless steel and stainless steel/plastics. The characteristics evaluated by the relationship among the load capacity, pocket pressure, film thickness and leakage flow rate are shown numerically. The main results are as follows : 1) the load capacity expressed by the ratio of hydrostatic balance is dependent not only on the supply pressure (with the same restrictor) but also on the elastic modulus of materials; 2) effects of pressure drop at the outlet land of pocket are much smaller than those of elastic deformation; and 3) the calculated results are in good agreement with the experimental results reported in a previous paper.

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This paper concerns estimation of system parameters in a hydraulic system and figuring out the variety of the failures. The system is assumed to be disturbed and its parameters are estimated using the Extended Kalman Filter (EKF).
The hydraulic system consists of a pump, a pressure regulator, pipes and an accumulator and is modeled with nonlinear differential equations, The parameters of the model are extended to the state variables and then are estimated with EKF. Since the parameters have a correlation with the failures, the variety of failures can be figured out by observing the parameters. The proposed methodology showed its effetiveness through an experiment of internal leakage in the pump and the pipe, The leakage magnitude could be expected from the magnitude change of the estimated parameters.

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