| 摘要 |
PURPOSE:To aim at enhancing the accuracy of positioning in a device for preventing vibration which is generated in an elevating column having a static pressure holding circuit upon deceleration, by disposing a pair of variable restricting valves in the supply and discharge pipes of a hydraulic cylinder so that the open degree of each valve is controlled in accordance with the position of the column. CONSTITUTION:A ball-screw shaft 15 is driven when a drive motor 16 is operated, and therefore, an arm 13 and a column 12 ascend and descend along a guide surface 11. A piston rod 19 in a hydraulic cylinder 18 is connected to the lower end of the column 12, and the hydraulic cylinder 18 is parted into two of upper and lower chambers by a piston 20 for holding the column under static pressure. A pair of passages 22, 23 which are communicated with an oil reservoir 21, are connected to the hydraulic cylinder 18, and check valves 33, 34 and variable restricting valves 29, 30 which are respectivey arranged in parallel with each other, are disposed in the intermediate parts of the passages 22, 23. When the column 12 comes to a position near to a set value of stopping, the open degrees of the variable restricting valves 29, 30 are made small, thereby the force of viscous resistance is enhanced, and the open degrees of the variable restricting valves 29, 30 are made equal to zero at the set value. |
