GB1385165A - Line drawing photoexposure device with image rotating means - Google Patents

Abstract

1385165 Photo-plotting apparatus; optical projection GERBER SCIENTIFIC INSTRUMENT CO 16 April 1973 [24 July 1972] 18240/73 Headings G2A and G2J A photo-exposure mechanism for exposing lines by moving a light spot over a photo-sensitive surface comprises a support surface 14 for the photo-sensitive material 16 and a photo-exposure device 20 mounted for movement in a plane parallel to the surface 14 and comprising means 34-48 which illuminate an aperture e.g. in wheel 50, and an optical imaging system 54-58 which forms an image of the aperture on the photosensitive surface, this image constituting the light spot 53, the path of the light rays through the system having at least one zone of non-parallel rays in which a non-restricted image rotator 58 (defined below) is located for rotating the image relative to, and in the plane of, the sensitive surface 16. A non-restricted image rotator is one which will rotate an image without causing dispersion of the image rays even if the incoming rays are not parallel. The rotator shown in Figs. 5 and 6 comprises a mirror assembly having three reflecting surfaces 84, 86, 88 mounted on first and second support members 94, 96. These members are mounted in a barrel member 62 which rotates in a frame 68 about a centre line 64. The support members 94, 96 and thus the reflecting surfaces are adjusted by screws 98, 104 to bring the optical axis of the departing rays a and f colinear with the centre line 64. As shown in Fig. 6 on passing through the assembly rays a and b are rotated through 180 degrees. If the barrel member 62 is rotated through 90 degrees counter-clockwise, Fig. 5, the common plane of a and b becomes parallel to the surface 86 and no rotation about line 64 occurs. Thus to maintain a given axis of the projected light spot perpendicular to the path of travel of the spot the mirror assembly is rotated through one half the angular change of direction of the line of travel of the spot. In alternative embodiments the mirror assembly is replaced by a rotatable prism, e.g. a Peehan or reversion prism, in which the entrance and exit faces of the prism are perpendicular to the optical axis of the entering and departing rays and which has an odd number of reflecting surfaces.