The Model Reference Adaptive Control (MRAC) does not need exact precision as regards the control system, and this interesting feature is very useful for controlling the pneumatic servo system whose characteristics often change and are not capable of being estimated easily.
When high adaptive gain of MRAC is yielded to obtain rapid and accurate adaptation, saturation of the control parameters occurs and the control system of the pneumatic servo tends to oscillate. For realization of accurate and stable control, switching the adaptive gain method of MRAC is presented in this report. In the region, the cylinder speed is slow and the frictional force changes rapidly; the adaptive gain is switched to high so as to avoid any delay in the adaptive response. As a result of the fundamental effects of switching the adaptive gain in MRAC of the pneumatic position of the servo system can be tested experimentally, and then, the usefulness of this method is specified using an inverted pendulum driven by a pneumatic rodless cylinder.

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This paper deals with the dynamic behavior and stability of a hydraulic system subjected to solid friction of a typical friction model, for example, the “negative slope” characteristic. Numerical simulation reveals a particular phenomenon in which hard self-excited vibration occurs for a disturbance beyond some critical value, despite the fact that the neutral operating point of the system is stable for the whole region of the supply pressure. Vibratory waveform is stick-slip for a smaller disturbance or sinusoidal for a larger disturbance. This multi-structural stability can occur for any friction model studied here, and can be confirmed experimentally.

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In this study, a simulation program for hydraulic control systems has been developed. By using this program, the operator is capable of simulating the dynamic performance of systems without the need of any special knowledge as regards software or control engineering. The program was developed for use on personal computers that are most commonly used today. The simulation is carried out according to each operation in a very simple manner based on the block diagram representation of the systems. For these procedures, a graphical user inter-face was successfully incorporated into the program. Regarding the main features or functions of the program, it is possible to simulate pipeline elements, various kinds of nonlinear elements and even discrete time control systems.

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Structure vibration modes of an oil-hydraulic pump bolted onto fixed bracket, like under real operating conditions, are investigated using FEM and an experimental modal analysis so as to obtain fundamental design data for reducing the pump audible noise level by the vibration control technique. Particular attention has been paid to the FEM analysis by assigning appropriate coupling conditions for the contact surface between the bolted flanges and bracket and the appropriate element attributes for carrying out accurate three-dimensional modeling of solid structures.
The natural frequencies and mode shapes simulated by FEM agree with those obtained by the experimental modal analysis with a sufficient accuracy for practical usage for almost all vibration modes up to around 4 kHz. It has also been shown that the standard size axial piston pump has broadly, at the relatively low frequency range up to around 2 kHz, the vibration modes (1st and 2nd vertical bending, 1st and 2nd horizontal bending, 1st longitudinal and 1st torsional vibration modes) due to the pump casing regarded as the cantilever supported resiliently to the bracket, and, in the relatively high frequency range over 2 kHz, local vibration modes mainly due to the various members of pump structural framework.

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