| 摘要 |
PURPOSE: A hydraulic unit for a drive cylinder is provided to extend the lifetime of products and to improve the safety by preventing a shock in working the hydraulic unit without a load. CONSTITUTION: Oil pressure is given to a cartridge valve(70) if pistons(32,42) of a first and a second hydraulic cylinders(30,40) are moved in the right direction. The piston(42) is not detected from a piston sensor(45b) in a cylinder head unit(41b) of the second hydraulic cylinder(40) while the cartridge valve is pushed down. Also, a solenoid valve(80) is off to prevent hydraulic media from being exhausted to a drain line(3d). However, the solenoid valve is converted into the on state from the off during a specific time before changing the feed direction with a hydraulic pump(60) if the piston(42) is detected from the piston sensor(45b). The cartridge valve is on to exhaust a part of the hydraulic media in a cylinder(31) of a cylinder head unit(31b) centering upon the piston(32) to outside through the drain line. The exhausted amount of the hydraulic media is the same as one introduced into the cylinder(31) of the cylinder head unit(31b) through a buffer line(35b).
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