Electronic device for maintaining the scanning raster of a flying-spot scanner in register with the film frames

摘要

714,345. Photo electric control system. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 11, 1952 [Oct. 5, 1951], No. 23271/51. Class 40 (3) In a device for maintaining the raster of a flying spot film scanner in register with the frame, means are provided for projecting a patch of light on to a part of the film which includes at least a part of a sprocket hole, light reflected from this part producing in a detector an output which depends on the relative position of the sprocket hole and the patch of light and is used to adjust the position of the scanning raster. As shown, the scanning raster is produced by a cathode ray tube and is imaged on to the film plane FP. The light spot which i'luminates the sprocket hole is produced by an auxiliary cathode ray tube AT and the overlapping portions A, B, and sprocket hole SH are shown in Fig. 4. Photo-electric cells PESP1/SP, PE' each receive light from one of the areas A, B, and feed a differential amplifier DA the output of which is applied to a servo system SS to adjust the light patch relatively to the sprocket hole and at the same time the position of the scanning raster of tube F.S. In a modification (Fig. 2, not shown) the cathode ray tube AT is replaced by a small projector lamp, light from which is reflected into the region of the sprocket hole by a mirror the angular position of which is adjustable. The mirror may be carried by a loud speaker speech coil. In a further embodiment (Fig. 3 not shown) the beam produced by cathode ray tube AT oscillates across one edge of the sprocket hole thus producing in a single photo-electric cell a number of square pulses whose width depends on the degree of overlap of the trace with the hole, and whose average value varies in sense and magnitude according to the duration and extent of misalignment.