| 摘要 |
Actuator for moving a diaphragm grid over photographic film during an X-ray exposure to screen secondary radiations from the film, comprising a drive shaft having thereon a pair of coextensive intersecting helical grooves of opposite hand which merge at their ends to form an endless track, a follower on the grid engaged in said track, and means for rotating said shaft for reciprocating said follower along said track thereby to move said grid over the film.
|
