| 摘要 |
PROBLEM TO BE SOLVED: To enable centering regulation with high accuracy by disposing a rotation preventive means which has a differential screw thread mechanism consisting of first screw threads engaging at a first pitch with a fixing part and second screw threads for supporting a movable part by engaging at a second pitch with the first screw threads and prevents the rotation of the second screw threads. SOLUTION: The rotation preventive means which has the differential screw thread mechanism consisting of the first screw threads engaging at the first pitch with the fixing part and the second screw threads for supporting the movable part by engaging at the second pitch with the first screw threads and prevents the rotation of the second screw threads is disposed. The internal threads of the bore part of a cylindrical screw 152 which is the first screw threads are screwed to a supporting member 150 which is the second screw threads on the movable part 120 side and is screwed to a hexagonal socket head cap screw 153 on the opposite side thereof. When the hexagonal socket head cap screw 153 is rotated, the cylindrical screw 152 rotates together as well. In such a case, the supporting member 150 is movable in the axial direction of the supporting member 150 by rotation of the cylindrical screw 152 but the rotation of the supporting member 150 itself around its axis does not occur.
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