Patent GB-1328763-A (GB)
Title: Optical system
IPC: G06K15/22
Filed: 1972-04-10
Abstract: 1328763 Photographic drawing apparatus INTERNATIONAL BUSINESS MACHINES CORP 10 April 1972 [1 June 1971] 16362/72 Heading G2A In apparatus for tracing a line on photo-sensitive material, there is provided means for producing a beam of light, means for providing relative movement between the beam and the material, a reticle 33, Fig. 5, defining the line to be traced and positioned in the beam, a plurality of field shutters, and means for moving the shutters for covering and uncovering the reticle, in which the movement of the shutters is synchronized with the relative movement between the light beam and the material to provide a uniform exposure of the latter. As shown the field shutters consist of a pair of independently rotatable shutter cylinders 28, 29 arranged in telescoping fashion adjacent the recticle 7 each cylinder having a helical edge perpendicular to the reticle which edges will traverse across the reticle 33 when the cylinders are rotated. A light source 30, condenser lens 31 and mirror 32 are mounted inside the cylinders 28, 29 for producing the light beam. Preferably the reticle is rectangular and the shutters are moved at a constant velocity, each shutter moving such that its image moves at the same velocity as the relative velocity. Preferably the photo-sensitive material is moved by means of an x-y table drive Fig. 3 (not shown) and the light source remains stationary. In the embodiment of Fig.1 (a-d) (not shown) the field shutters are formed by a pair of shutter blades both movable back and forth across the reticle. In alternative forms, Figs. 6, 7 (not shown), different driving arrangements for pairs of linearly movable shutter blades are shown. The field shutters may consist of a single rotatable disc (72), Fig. 8 (not shown) mounted adjacent to and having a crenelated periphery overlapping the reticle (75) such that upon rotation of the disc the edges of the crenelations will move across the reticle to start and finish line tracing. A further embodiment of the field shutters consists of a pair of independently rotatable circular discs 134, Fig, 9, having identical profiles of a constant velocity cam. The optical exposure head shown in detail in Fig. 9 is part of a photo-tracing machine, Fig. 10 (not shown) and is mounted for rotation through 90 degrees in either direction, whereby tracing may be carried out at both 0 and 90 degree orientations. The head includes a reticle index wheel 152, the periphery of which is adjacent the shutters 134, and the wheel carrying a plurality of holders 162 each containing a reticle 132 having a pattern for defining a different size line to be traced. The wheel 152 is rotatable to position a selected reticle adjacent the shutters, there being means 163 for moving the holder of the selected reticle radially outwards to position the reticle in the light beam. A variable neutral density filter 136 is provided to compensate for variations in light intensity due to lamp aging. Projection lens 133 is mounted in a constant focus air bearing 138 to minimize focusing errors due to variations in the contours of the photo-sensitive material 111. Photo-cells (123, 125), Fig. 10 (not shown) sense the feed of the photo-sensitive material in x-y  directions and provide output pulses which are used for synchronization purposes, so that the position of the field shutter in relation to the photo-sensitive material is known at any instant. A control system, Fig. 19 (not shown) is provided for this purpose.