| 摘要 |
An indexing mechanism for a typewriter provides a signal controlled transfer to a fast paper advance rate, say for semi-automatic paper insertion, while storing the last operator-selected rate. Two cams are employed which influence, through a follower, the engagement point of a pawl of a pawl and ratchet platen drive. One cam is operator positionable to change the portion of its cam profile that is tracked by the follower and, attendantly, the paper advance rate. By arranging a signal-controlled actuator to deflect the positionable cam from operative engagement with the follower, the outer cam, which has a less prominent profile, is enabled to influence the pawl engagement point and provides high speed paper advance. Upon removal of the actuator signal the positionable cam is automatically returned to its operative position i.e., the last operator selected position.
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