| 摘要 |
A teaching machine for selectively reproducing the respective audio tracks on a record drum lengthwise thereof has a servo-controlled track selector wherein a drive motor rotates the drum through a slip-clutch, and a series of ratchet wheels on the shaft of the drum are offset by fractional tooth differences and are engageable by respective pawls to stop the drum at as many different positions as the number of ratchet wheels times the number of teeth on each ratchet wheel. The pawls are actuated by respective solenoids controlled by a commutator operated by the drum shaft. The commutator has radially spaced brushes connected respectively to the solenoids, and has as many segments as the teeth on each ratchet wheel. Further, the portions of each segment engageable by the respective brushes are offset the same as are the teeth of the ratchet wheels. By selecting the circuits of the respective brushes and segments, the solenoids are actuated selectively to cause the drum to be indexed. By also selecting between one or another of two side-by-side heads spaced by an odd multiple of one-half the distance between successive index positions, the number of audio tracks which can be selected is doubled.
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