| 摘要 |
A ratchet assembly properly positions selected film frames at a film gate aperture of a photographic printer. The ratchet assembly includes a ratchet wheel rotatably attached to a base having a plurality of ratchet teeth. Each tooth has a rotation-prevention edge and a ramped edge with the ramped edge being inclined toward the rotation-prevention edge of an adjacent tooth. A positioning pawl is pivotally attached to the base proximate a first end and has a head portion proximate a second end. The head portion has a first edge adapted to slidably engage the ramped edge of the ratchet wheel. The head portion of the positioning pawl is biased against the ratchet wheel such that if the ratchet wheel is indexed too far and does not properly position the selected film frame at the print gate aperture, the head portion forces the ratchet wheel to move back by slidably engaging the ramped surface of the ratchet wheel until an alignment pawl engages a notch located on the periphery of the disc film unit. The notch is in a precisely defined spatial relationship to the selected film frame at the print gate aperture and the alignment pawl ensures that the selected film frame is optically centered.
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