Importance

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Abstract

A control load such as a cylinder or the like is driven at a constant speed by controlling the flow rate of a variable delivery pump. The control mode is switched to the pressure control to keep the stop pressure constant on the basis of an increase in pressure when the control load stops. A remaining delivery amount which will be necessary to raise the delivery pressure to an object stop pressure when the load stops and an excess delivery volume due to the operation time lag when it is assumed that the delivery by the pump is stopped at the present time are predicted. When they coincide, the delivery amount of the pump is set to zero and the control mode is switched to the pressure control. On the other hand, the product of a load volume and a fluid compressibility is calculated from the increase in pressure when the load stops. The feedback gain of the pressure control is controlled on the basis of the calculated value of this product. Further, the pressure difference and the designated flow rate are compared and either smaller one of them is always set to the designated value of the flow control.

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First Claim