The speed control of a pneumatic cylinder is usually of an open loop type, adjusted manually by a flow control valve. In this manner, especially when operated at a low driving speed, the constant speed can barely be obtained due to the friction or variations in the load force.
In this study, for low and constant driving speed, the PWM mode feedback speed control method is proposed in which the piston speed is controlled by the PWM mode being driven by an on-off valve. The control system is constructed by using an automobile-type fuel injection valve with high response and endurance as the valve driven in the PWM mode. The characteristics and performance of the control system are analyzed and discussed to obtain the following results.
1) An electro-pneumatic speed servomechanism can be cheaply constructed and it can easily realize a very low and constant driving speed.
2) The theoretical index for the proper choice of the carrier frequency in the PWM was obtained. The stability and limit of stick-slip generation could be theoretically evaluated. Thus, the design guide of the control system could be derived.

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In a large-scale hydraulic system having high repeated actuation cycle, such as a large type forging press, pressure surges often grow with great shock due to the recombination of the oil column separation in the return line attached to the downstream side of the directional control valve. This leads to restriction of the actuation cycle of the hydraulic system.
In this report, the relations between pressure surges and actuation time to close the valve were studied analytically and experimentally. Two different types of valve operation, that is linear, and break line two-stage were examined using a model hydraulic system having a directional control valve of similar flow characteristic as that of the valve usually used in the large-scale hydraulic system.
It was confirmed that the valve closing time can be shortened without increasing the surge pressure by using the break line two-stage valve operation which has lower operating speed near the closing point. And it was concluded that this type of valve operation is an effective method to increase the total actuation cycle of the hydraulic system.

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