| 摘要 |
PURPOSE:To securely prevent a vertical shaft from falling due to a drop or loss of air pressure by judging the variation direction of in-cylinder pressure and the moving direction of the vertical shaft and operating a lock mechanism. CONSTITUTION:The vertical shaft 12 is supported on an X- and a Y-axially movable member 11 so that the shaft is elevated freely in a Z-axial direction. The elevation position of the vertical shaft 12 is detected by a displacement detector 13. Further, an air balance device 21 consisting of a cylinder 2 united with the shaft 12, a piston inserted into the cylinder 23, and a piston rod 25 fixed to the member 11 is provided in the hollow hole 17 in the vertical shaft 12. Variation in the pressure in the chamber 41 of the cylinder 23 is detected by a detector 45 and sent to a controller 47 together with the output of the detector 13. The controller 47 judges an abnormal state when the pressure in the chamber 41 drops and the vertical shaft 12 moves down, and operates the lock mechanism 31.
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