Patent GB-166917-A (GB)
Title: Improvements in and relating to the production of facsimiles of documents, pictures,drawings, and the like
IPC: H04N1/23
Filed: 1920-01-20
Abstract: 166,917. Bartholomew, H. G. Jan. 20, 1920. Photo-mechanical printing-surfaces.-Relates to the method of producing facsimiles of documents &c., in which the surface to be copied is enlarged and divided into small areas which are classified in respect of tone by the eye or otherwise, the results of the classification being embodied in a code message in accordance with which the reproducing instrument is controlled. In the reproducing instrument, a light-sensitive surface is moved in a stepwise manner in relation to means whereby successive areas mav be more or less exposed according to the tone to be reproduced. Where a shutter is used, it may be designed to give varying exposures ur a variable number of fixed exposures in a given time, or a fixed exposure, the variations being provided by movement of the sensitive surface. Alternatively an electric lamp may be made to glow for varying periods. In another method the intensity of the light is varied either by varying the strength of the source or by interposing between it and the surface a variable number of screens. A further method consists in varying the amount of surface exposed at any instant by means of an iris or other diaphragm. The resulting photograph may be used in the half tone process without the use of a ruled screen. In an example, a tube carrying lenses projects a spot of light on to the sensitive surface. Between the source of light and the tube are arranged the diaphragms 7 - - 7<d>, Fig. 2, and the shutter 10. Each diaphragm has a large hole 8 and a small hole 9, the holes 8 being normally in register along the axis of the tube through the action of the springs 16 - - 16<d>. The energization of one of the magnets 20 - - 20d causes the corresponding diaphragm to move so that its small hole registers. with the large holes of the others. If the shutter is now opened by means of its electromagnet 21, an area will be exposed corresponding to the aperture in the diaphragm. The sensitive surface is carried on a carriage 26, Fig. 3, which travels along the screws 37, 28. The latter carries at its end a square-toothed ratchet wheel 29 to which a rotation of one tooth is imparted by means of an electromagnet each time the platform has completed its travel along the screw 37. A continuously rotating pulley 39 is revolubly mounted on the spindle 40 which forms part of the screw 37. The pulley is normally pressed by the spring 42 into engagement with the disc 43 fixed to the spindle 40 and carrying a pin 44 which co-operates with the stops 45, 46 carried by the lever 47, Fig. 5. With the lever 47 in the position shown, the screw 37 is free to revolve counter clockwise carrying with it the cam 53. The latter by means of the lever 54, Fig. 6, completes the circuit of the magnet 53 and the stop 46 engages the pin 44. The can 53 is now in the position shown and the lever 54 completes a circuit through the shutter magnet 21, thus making the exposure. This cycle of operations is repeated until a complete zone of exposures has been made, when the direction of rotation of the screw 37 is reversed in any suitable manner and the table 26 returned to its first position, the lever 58 being moved to hold the pins 44, 45, 46 out of engagement. The closing of the circuits of the diaphragm magnets may be affected manually by keys or automatically by suitably perforated slip passing over a tracker mechanism and running synchronously with the device for moving the sensitive surface.