Many kinds of electro-hydraulic servo systems are applied to rolling mills such as a hot strip mill, a cold strip mill and a seamless tube mill because of quick response, high power and high positioning accuracy. However when applying an electro-hydraulic servo system to a hot strip downcoiler, it was found that the controlled object has low natural frequency and is lightly damped so that stable control is very difficult. Optimal control theory has been recognized as a powerful tool for system synthesis in such a case. This paper first shows that the existing design method of optimal control is effective for designing an electro-hydraulic servo controller, in which the proper weighting matrices in the quadratic performance function can be determined directly from a physical model. A new design method is then proposed by which the state feedback gains can be obtained directly based on the characteristics of the controlled object. The effectiveness of the controller is demonstrated experimentally.

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In recent years, display devices are being replaced by flat-panel displays such as LCD and plasma displays. Safe transportation methods are required because the glass panels used in the displays are very easily damaged. Problems, such as contamination or damage of the contact area due to stress concentration, during contact-type transportation using, a roller or vacuum pad, have been reported . In order to solve the problems, we focus on a levitation transportation device using swirling flow for transporting objects. A problem has been found in that the levitation precision worsen when the tip of the object passes through the swirl flow generator. In this paper, we experimentally confirmed the cause by measuring the pressure distribution in one swirling flow generator (vortex cup).

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Energy savings have been made in a number of fields due to a shortage of energy resources such as oil and the need to protect the earth’s environment. If an accumulator is coupled with a hydraulic pump unit, intermittent operation of the electric motor powering the pump drive, called “idling stop type operation,” can be attained by using a pressure-holding function. Consequently, a reduction in unneeded power consumption can be realized. In this research, an intermittently operated hydraulic pump unit coupled with an accumulator (ACC pump unit), an inverter control-type hydraulic pump unit (INV pump unit), and a variable displacement-type hydraulic pump unit (VD pump unit) are tested. The relation among electric power consumption, pump output pressure, rotation speed and efficiency for one cycle of an ACC pump unit, an INV pump unit, and a VD pump unit was clarified by experiments conducted using a modeled machine tool. Next, the relation among electricity consumption, efficiency, and duty ratio in the case of supplying working fluid to the load intermittently with a fixed cycle period was investigated, and the predominance of the ACC pump unit was made clear. The ACC pump unit was shown to clearly have the best energy-saving effect. In addition, the static characteristics of each hydraulic pump unit were measured.

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