| 摘要 |
A scanning system includes a scanner mirror driven in a substantially linear pivoting movement by a galvanometer excited with a substantially sawtooth current waveform, the mirror directing a pilot beam in a scanning movement along a photographic film located upon a diffraction grid which forms a part of a holder of the film. The film is transparent to the pilot beam, and is encircled by a frame defining a window for viewing the film. The grid is composed of a repeating sequence of groups of rulings oriented in different directions resulting in correspondingly different directions of the diffracted beam, upon illumination of the grid by the pilot beam. An array of detectors detects the direction of the diffracted beam, which is employed as a feedback signal to accurately locate the pilot beam, to provide fine position data of the pilot beam. One or more data beams for either writing or reading image data upon the film are also scanned by the mirror concurrently with the scanning of the pilot beam for accurate positioning of each write (or read) beam. Blind scanning, with location based on galvanometer current, is employed near an edge of a scan line wherein the diffraction grid may not be illuminated by the pilot beam. Circuitry responsive to transitions between diffracted beams during a scanning of the pilot beam across the grid withholds timing pulses during instances of possible jitter for improved printing and reading of the film.
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