| 摘要 |
PURPOSE:To prevent the degradation in the accuracy of the reflecting surfaces of the polygon mirror by thermal expansion while adopting the constitution to fix the polygon mirror by using screws to the seat of a revolving shaft by providing mounting holes in which external threads pass and spaces which are not used as the mounting holes on approximately the concentrical region of the rotary polygon mirror. CONSTITUTION:For example, 8 pieces of small holes 12 are formed at equal angular intervals on the approximate circle around the center of the polygon mirror 1 on the outer side of a hole 11. These holes maintain the coaxiality with the hole 11. Of 8 pieces of the small holes 12, the four small holes 12a existing at every other point are used as the mounting holes with internal threads cut in which the screws 4 pass. The spaces not used as the mounting holes are provided together with the mounting holes 12a on the polygon mirror 1. The form of suppressing the strains occurring in the difference in the degree of thermal expansion and to relieve stresses is, therefore, attained, even when the polygon mirror 1 expands thermally. The accuracy of the reflecting surfaces of the polygon mirror 1 is maintained as constant as possible and the fluctuation in the scanning position of a beam is suppressed as far as possible. |
