Recentry, various studies on positioning with pneumatic pistons have been carried out by using proportional valves or pulse method, etc., but the accuracies of positioning by these methods are still insufficient. A new electro-pneumatic servo-system is proposed to realize higher accuracy. The system has an analogue proportional control circiut which uses a new electro-pneumatic converter. The converter is composed of a flapper driven by solenoid, a pneumatic micrometer and a pneumatic relay. A high converting gain with wide linear range can be obtained by the device, and it can be less expensive.
The reproducibility of positioning of the servo-system was tested with a 50mm bore and 50mm stroke piston cylinder. As a result, standard deviations of the stopping position could be reduced to less than 0.004mmin the best condition of friction with replaced piston seals.

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Solenoid has been widely used as a highly reliable and short stroke actuator. However, the main defects are the delay of the actuator motion and its low driving efficiency. Analyzing the various driving parameters, three major factors of solenoid delay are found: mechanical delay caused by movable inertia, current delay by solenoid inductance, and magnetic flux delay by eddy-current. This paper introduces two improvement methods: a driving circuit which utilizes the constant current of a choke coil to make the solenoid current response faster, and a ferrite core which is widely used as a radio frequency magnetic material to decrease the eddy-current loss. These ideas reduce both current delay and magnetic flux delay and also improve the driving efficiency of the actuator. The resulting motion indicates a very small dead time, which is considered very good for servoactuator.
High speed solenoid actuator is applied to develop a direct-drive servo-valve and a linear hydraulic servo system. A lthought here is room for improvementt, h e results indicatet he capability of this solenoid actuator to the highly efficient servo system.

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The speed control of a pneumatic motor is usually of an open loop type, adjusted manually by a flow control valve. Using it for the automatic control, the closed loop control is desired.
In this paper, the feedback speed control of a radial piston motor with an electro-pneumatic proportional valve is studied. To realize satisfactory control without sacrificing the low cost of pneumatics, the I-PD control scheme in which the controller is simply installed by proportional, integral and derivative elements is employed. The design of control system is based on the partially model matching method. The performance of the control system is discussed to obtain the following results.
1) By employingth e I -PDc ontrol, a satisfactoryc losedl oop speedc ontrols ystemf or a pneumatic motor can be cheaply constructed.
2) In this system, if either the reference speed or the load torque is increased up to the saturation point of the proportional valve opening, the step response becomes more oscillatory.
3)The derivativer eference speed feedforward is effective to improve the starting characteristics of the system.

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