| 摘要 |
A flying spot scanner is used to expose a photosensitive surface to an intensity modulated beam of light to build up an image on the photosensitive surface. Such a scanner includes a position sensor comprising an elongate grating (14), means to take part of the beam of light from the scanning head (8) of the flying spot scanner and apply it to the grating (14) so that it scans in a direction along the grating, the rulings of the grating forming an oblique angle with the direction of scanning of the part of the beam of light, a photodetector (17) arranged to monitor the interaction of the part of the beam of light with the grating, means (13, 16) to produce a signal representative of the position of the beam of light in its direction of scanning, and means (20) to mix the output signal from the photodetector (17) with the signal representative of the position of the part of the beam of light to provide a phase modulated output signal, the phase modulation of which gives an indication of the position of the scanning beam of light in a direction transverse to its scanning direction. Preferably the means to produce a signal representative of the position of the beam in its direction of scanning includes a second grating (13) and photodetector (16). |
