| 摘要 |
PROBLEM TO BE SOLVED: To effectively prevent damage to the periphery of an embedded groove of a main screw shaft, in which a stopper pin is embedded, an auxiliary screw cylinder, or the like even when excessive torque is applied to the stopper pin.SOLUTION: An embedded groove 15c is provided in an upper part of a main screw shaft 15 in a radial direction toward the central axis of the main screw shaft 15. A stopper pin 16 is embedded into the embedded groove 15c. The central axis of the main screw 15c and the central axis of the stopper pin 16 substantially match with each other. A contact surface 16c passing the central axis of the stopper pin 16 is provided at a portion which is a tip part of the stopper pin 16 and protrudes from an outer peripheral surface of the main screw shaft 15. An auxiliary screw cylinder 19 rises with the rotation of the main screw shaft 15. When the auxiliary screw cylinder 19 reaches a rise limit, the contact surface 16b of the stopper pin 16 embedded in the embedded groove 15c of the main screw shaft 15 comes into contact with a start end surface 19a1 in an upper part of an auxiliary screw inner peripheral screw part 19a on an inner peripheral surface of the auxiliary screw cylinder 19.SELECTED DRAWING: Figure 16 |
