To develop a very high-speed closed-loop pressure control system, an asymmetric servovalve, whose downstream port width is twice of the upstream one, is proposed here as hardware direct compensations to overcome the response differences in pneumatics where step-down response takes a very long settling time when the gain is adjusted to be suitable for step-up response.
The handmade asymmetric valve achieved -3dB bandwidth of 260Hz, whereas the frequency at phase -90 degree is 190 Hz, and achieved rise time less than 1ms and dead time 0.9ms for a step voltage input which corresponds to spool stroke 0.2mm.The flow capacity of the asymmetric valve at exhaust side (i. e., x=-400μm, w_d=-337NL/min) is twice of that at supply side (i. e., x=400μm, w_u=+191NL/min) for the same valve openings.The spool saturation ranges are also discussed. The flow capacity of the downstream side of asymmetric valve (-337NL/min) is about twice of that of the symmetric valve (-171NL/min). The theoretical results agreed well with the experimental ones.
It is clear experimentally that an asymmetric servovalve is effective for speeding up the step-down response of the closed-loop pressure control system to equalize the step-up and step-down response speeds. For the closed-loop system with the symmetric valve, rise time attained 5.7ms for the step response but 14ms for step-down response. Therefore, an asymmetric valve is proposed to overcome this problem. By using the asymmetric valve and a proportional controller, rise time for the step response was adjusted to be 5.7ms (the same as the case using the symmetric valve) with no overshoot and rise time for the step-down response became 7ms. Rise time for step-down responses improved from 14 to 7ms.

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The purpose of this study is to improve the facilities of BDSP into a more convenient one. As regards the first improvement, we have introduced a high-speed calculation method with a fluid line algorithm using a recursive formula. The recursive formula was derived analytically from each of the modal approximation models of the fluid rigid lines and fluid viscoelastic lines. As regards the second improvement, we have introduced a method for simulating the dynamic responses at the arbitrary position of the fluid line, in stead of the conventional method that allows calculation only at both ends of the fluid line. It could be verified in this study that simulation could be done much faster compared with the conventional ones, without any decrease in accuracy. Consequently, BDSP may be concluded to be a convenient and accurate tool for carrying out hydraulic system simulations.

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It is well known that gas bubbles in liquid can absorb pressure fluctuations as well as flow rate ones. This has led to the idea that a large number of small bubbles enclosed in rubber can reduce the surges and pulsations produced by hydraulic oil flows. With the intention to develop a new method of reducing flow fluctuations, rubber containing many discrete micro-bubbles has been experimentally examined in terms of its ability to absorb fluctuations in actual hydraulic oil flows. The rubber seems to be available for this purpose, indicating that it could be a possible convenient tool in reducing pulsations in oil flows.

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An electro-rheological fluid of dispersion system (ERF) is a type of variable plasticity fluid which behaves like a Bingham fluid in that its yield stress varies according to the magnitude of an applied electric field. Therefore, an actuator by means of the ERF can minutely control the force with a high response. However, from another viewpoint, the ERF is regarded as a nonlinear control device with viscosity varying according to the shear rate. In practice, many researchers has pointed out that the nonlinearity of the ERF gives them great difficulty in applying it to a servo system.
In this paper, a new servo method, Electro-Rheological Motion Control (ERMC), which makes an active use of the nonlinearity of ERF, is proposed and its basic theory is approached. An antagonistic rotary actuator (ERAA) utilizing the ERF is controlled by using the ERMC. The ERAA is so constructed that a freely rotatable secondary cylinder is set concentrically between two primary drums driven by motors at the same speed in the opposite directions each other and the ERF is filled in the gap between the secondary cylinder and the primary drums. Under the ERMC, such an on-off control operation is repeated in the stopping process of the primary drums, that the output direction of an actuating torque is switched positive or negative when the control error is negative or positive, respectively. The reason why this method is adopted is due to fact that the control error occurring in on-off operation decreases as the rotational speed of the primary drum decreases because of the non-linearity of the ERF. As a result of experiments, it is confirmed that a high-precision positioning of the ERAA can be realized stably by the ERMC.

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