GB1277922A - Photo-optical drawing heads for use in automatic drawing machines - Google Patents

Abstract

1277922 Photographic apparatus G CORADI A G 18 Aug 1969 [19 Aug 1968] 41173/69 Heading G2A A photo-optical drawing head containing a light source 11 is provided with a first shutter 18, operable by electro-motive or electromagnetic means, and a second shutter 15, before the first shutter, for controlling the intensity of light emitted by the head, the second shutter being an electro-optical or a magneto-optical shutter. The head forms part of an automatic drawing machine having a drawing board 1 movable relatively to the head. Light from the source 11 and a concave reflector 12 is imaged at infinity by a first auxiliary condenser system 13, and the parallel beam so formed is reflected by a cold light mirror 14 into the second shutter 15. Light passing therethrough falls on a second auxiliary condenser system 16 which forms a real image of the source 11 at the aperture of an apertured diaphragm 17, and from there, when the first shutter 18 is open, light is focused by a main condenser 19 on the aperture of an apertured diaphragm or mask 20, the final image being reproduced on photo-sensitive material 3 by a lens system 21. As the head and/or a carriage 6 are moved in response to control impulses from a storage medium, the light beam passing through the mask 20 traces out a pattern on the material 3. The intensity of this light beam is adjusted by the second shutter 15 according to the drawing speed. The second shutter may comprise a Kerr-cell Fig.2 (not shown), light plane polarized by a polorizer (22) entering a cylinder (24) filled with nitrobenzene or chloroform. On leaving the cylinder the light enters an analyzer (26) turned through 90 degrees relative to the polarizer (22), where it is mostly extinguished voltage being applied to electrodes (27, 28) only when the head moves relative to the drawing board. The Kerr cell may be replaced by a Faraday cell or by an ammonium-dihydrogenphosphate or potassiumdihydrogenphosphate cell. The apertured mask 20 is advantageously a rotary diaphragm having a plurality of different sized apertures. In another embodiment, Fig. 5 (not shown), the head remains stationary and the drawing board moves. The cold-light mirror (50) is situated after the second shutter (15) and reflectes long wavelength light therefrom to a photo-cell (51) which is coupled back to the shutter (15). The provision of the second shutter ensures that the exposure can be commenced and terminated accurately.