| 摘要 |
PURPOSE:To prevent an excessive vibration load from being placed on the mirror by providing mechanical stoppers which have an overloading preventing function above and below the mirror. CONSTITUTION:When the mirror 1 abuts on a movable body 5 or 6 with a smaller force than a threshold value, the mirror 1 does not move any more. When the mirror 1 abuts on the movable body 5 or 6 with a larger force than the threshold value, on the other hand, springs 7a and 7b shrink to move up the movable body 5 and move down the movable body 6. The threshold value is set smaller than the force which deforms harmfully or breaks the mirror 1 and then the movement quantity of the mirror 1 is minimized within the range wherein the mirror 1 neither deforms harmfully nor breaks. Consequently, the vibration quantity of the mirror due to an earthquake is minimized and the deformation of the mirror itself is minimized. |
