| 摘要 |
The invention relates to a method for precisely controlling a light beam which is used in writing text or images, in particular in phototypesetting. Rulings, screenings or gratings consisting of slits (Sa-d) or lines (L1, L2) are provided on the frames of the focal planes and, in some applications, on the optics frame. The light beam and, in some embodiments, one or more reference beams, which have been separated from the writing beam, impinge the rulings (Sa-d) or gratings. The signal thus produced and observed by means of photodetectors conveys information on the relative position of the light beams, the rulings and the focal plane relative to one another. This information is converted by means of electronic circuits into information on the position of the writing beam on the focal plane. This information permits the position of the writing beam to be controlled with high accuracy by means of feedback mechanisms. In addition, the method can be set up for deflecting the beam so that the modulation of the beam can be synchronised with the deflection, and thus the pixel can be positioned accurately at the desired position. <IMAGE>
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