| 摘要 |
<p>1452490 Document copying apparatus XEROX CORP 21 Dec 1973 59539/73 Heading G2A In a photo-copying apparatus which operates on the scanning principle, the intensity of the light source is adjusted according to the reflectance of the original, as determined by a preliminary scan. Fig. 1 shows an electro-photographic copying apparatus of the type disclosed in Specification 1436899, in which the light source 15 and mirror 12 scan across the document 11 which is being copied, the light eventually being reflected on to a rotating photo-receptor 18. A slit 19 in a coverplate 20 limits the image field and compensates for the uneven light distribution from the lamp 15. In order to adjust the intensity of the lamp to a suitable value, a preliminary scan is carried out. A light intensity detector 21 (of which there may be more than one) is mounted on the plate 20. The output from detector 21 is compared with a predetermined reference voltage, and the resultant led to a memory capacitor and a lamp drive circuit (35, 37), Fig. 3 (not shown). If the detector voltage is higher than the reference voltage, the current to lamp 15 is automatically reduced until these two voltages are equal, after which the capacitor ceases discharging. Instead of controlling the illumination intensity, the same effect may be obtained by controlling the width of a slot in the optical system.</p> |
