To prevent drifting of a hydraulic pressure cylinder by connecting a hydraulic pressure actuator and a hydraulic pressure pump free to rotate in both directions to each other by a pair of conduit runs, connecting a hydraulic pressure tank and the conduit runs through a check valve and preloading the hydraulic pressure pump.
A cylinder rod 26 is driven to the drawing-in side by supplying hydraulic pressure from a head side port 14 of a hydraulic pressure cylinder 12 to the cylinder 12 through a hydraulic pressure pump 1 and a rod side port 16 by positive rotation of an electric motor 6. At this time, a difference by the amount of volume of the rod 26 is made between working liquid quantity from the port 14 and pressure liquid quantity to the port 16, a pilot check valve 20 is opened by pilot pressure from a conduit run 10, and excessive working liquid is discharged to a hydraulic pressure tank 18 from a pipe line 8. Shortage of working liquid is replenished to the line 10 from the tank 18 by opening a pilot check valve 22 by negative pressure of the line 10 by reverse rotation of the motor 6. The valves 20, 22 are opened by working liquid pressure of the tank 18 by an air pressure source 24 by stoppage of the motor 6, and hydraulic pressure is introduced to the cylinder 12. Consequently, it is possible to prevent drifting even when external force is applied on the rod 26.
TAKAGI YOSHITOKU
MATSUO HIDEKI
