Positioning using a pneumatic system is much more difficult compared with that by a hydraulic system for different compressibilities of the working fluids, but for some working conditions, pneumatic systems are more suitable due to their clearness and safety.
To position reliably and accurately without any load, a pneumatic system, in which several cylinders are connected to each other in series and the actions of the cylinders are controlled by a microcomputer, can be used. Especially when the the stroke of each cylinder in some unit varies in a 2^n-1 sequence where n is the integer number beginning from 1, the total displacement of the cylinder series can be any integer in this unit from 0 to 2^N-1 where N is the number of the cylinders used in the system. Such systems have no feedback control and no electrical devices around the actuators, so that extremely high reliabilities and repeatabilities can be expected even when the systems are used under hazardous conditions such as around explosive gases or in a strong magnetic field.
In this research, the basic equations for such systems have been deduced. The experiments and simulations have been carried out by means of a model system without any external load in which four cylinders with strokes of 1cm, 2cm, 4cm, and 8cm were used. This paper reports on the following results obtained from the experiments and the computer simulation. That is, such a system is reliable for digital positionings, and the positioning paths as the outputs of the system can be made smooth by only adjusting suitably the timing according to which the driving signals for the actions of each cylinder are sent from a microcomputer.

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Controlled by a microcomputer, a pneumatic system in which several cylinders are connected to each other in series can be used to realize accurate positioning. Especially when the stroke of each cylinder in some unit varies in a 2^n-1 sequence where n is the integer number beginning from 1, the total displacement of the cylinder series can be any integer in this unit from 0 to 2^N-1 where N is the number of the cylinders used in the system. Such systems have no feedback control and no electrical devices around the actuators, so that extremely high reliabilities and repeatabilities can be expected even when the systems are used under a hazardous condition such as around explosive gas or in a strong magnetic field. Also, as already reported, by using such systems under the conditions without an external load, the digital positionings can be realized smoothly just by adjusting the timing of the driving signals programmed in the microcomputer.
In this research by means of the “model system” in which four cylinders with strokes of 1cm, 2cm, 4cm and 8cm were used, a further investigation has been carried out numerically and experimentally about such systems under the condition of an inertial load. From the research, the following conclusions have been obtained. That is, such systems are reliable for digital positionings even under an inertial load. The vibrations of the “moving bodies” caused by collisions can be controlled by means of the “braking control”. The positioning paths as the outputs of the systems can be made smooth by means of the “timing control”. Also, with consideration given to the collisions, the positionings can also be simulated numerically under an inertial load.

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Gas-charged accumulators are being widely used as energy storage devices in hydraulic systems. During the gas compression and expansion process in the accumulator, the gas temperature varies and the heat is transferred between the charged gas and the accumulator wall. Thermodynamic losses occur during these processes. In this paper, a heat transfer model is considered for the energy balance of bladder-type accumulator. A thermal time constant, which is very important factor for this heat transfer model and influenced by a natural convection of charged gas, is experimentally investigated at constant gas volume after the rapid discharge of oil into the accumulator. A simple model for predicting thermal time constants based on the structure of bladder-type accumulators is proposed. The model can explain quantitatively the correlation between nondimensional gas volumes and nondimensional thermal time constants. Nondimensional gas pressure responses using the proposed model are calculated and compared with the experimental results.

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A poppet valve is used solely as a check valve and also included as a pilot part in various kinds of control valves in oil hydraulic circuits; therefore, it is very important to clarify its characteristics.
The purpose of this paper is to search the behavior during tens ms when it responds to a quick flow change. In this research, a check valve is used as one of the examples of poppet valves. The composition where an oil hammer influences the valve is treated as one of examples of a quick change in pressure and flow velocity. The composition is an important part of the intensifier using an oil hammer which the authors have been developing and also the result will provide fundamental data to clarify the dynamic characteristics of a hydraulic system with a poppet valve.
The transient phenomena are researched by experiments and simulations. For the analysis by simulation, fundamental equations concerning a check valve and those by the characteristics method concerning a pipeline are presented. They are solved simultaneously using the Runge-Kutta methods. The effects of the spring, mass of the poppet, and volume and length at the connective parts on a peak generated pressure is clarified.

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