| 摘要 |
A preferred embodiment of the graduated filter comprises two bearings for the rotary axles of the two filter discs. The rotary axles are driven by a motor via a belt drive. The belt drive comprises a double belt pulley at the drive shaft of the motor and two toothed belts which wrap around respective toothed-belt pulleys mounted at the rotary axles. Compared with known toothed-wheel gearing, the belt drive is less expensive, more practical, wear-resisting and lighter in weight. The plane of the intersecting axes of rotation of the rotary axles is slightly inclined with respect to the direction of the optical axis of the graduated filter. By virtue of the angular adjustment of the axes of rotation of the rotary axles of the two filter discs, it is rendered possible that the toothed belts snugly fit the running surfaces of the respective toothed-belt pulleys, so that the latter and the toothed belts are uniformly loaded, thus increasing service life thereof and ensuring constant transmission of force.
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