| 摘要 |
An automatic high speed microfilm searching system is disclosed for locating a desired frame of microfilm. Each frame consists of information data and index data. The index data comprises a sequence of vertically-aligned data bar groups, each representing a half character of a sequence of characters of a unique index code for the associated frame. A pair of synchronization bars, each half the width of a data bar, is vertically aligned with each data bar group. Additional synchronization pulses both precede and follow the data bar groups. Depending on which direction the microfilm is moving, the leading synchronization bars are sensed by a bar sensing unit on the left or on the right of the viewing screen. Each sensing bar unit comprises a plurality of vertically-aligned data bar sensors and synchronization bar sensors, with three sensors assigned to each vertical bar in a data bar group, and three sensors assigned to reading the synchronization bars. If the data bars are centrally located each of the three synchronization bar sensors senses the leading synchronization bar; if the data bars are high, only one or two of the central and high synchronization bar sensors senses the leading synchronization bar; if the data bars are low, only one or two of the central and low synchronization bar sensors senses the leading synchronization bar. A bar position determining means is responsive to the three synchronization bar sensors to determine whether the data bars are high, centrally positioned or low. The transition between synchronization bar pairs is used to latch the correctly-read character data into storage. After two half characters are stored they are transferred to a computer for comparison with the desired frame index code. When the available frame index code corresponds with the desired frame index code, the microfilm is stopped to project the desired frame onto the viewing screen.
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