Patent GB-432795-A (GB)
Title: Improvements in or relating to a method of and apparatus for reproducing a picture or the like on the surface of a printing plate or other body
IPC: B41C1/04
Filed: 1933-11-30
Abstract: 432,795. Engraving; printing - surfaces; copying - telegraphy. LOSIER, M. L., 124, North Grove Street, East Orange, and HUGHES, W. A., 605, Broad Street, Newark, both in New Jersey, U.S.A.-(Assignees of Losier, G. E.) Nov. 30, 1933, Nos. 33676 and 33677. Convention dates, Dec. 2, 1932 and Dec. 19, 1932. [Class 100 (ii)] [See also Groups XXXV and XL] In a method and apparatus for reproducing a picture or the like on the surface of a printing- plate or other body, the original is scanned by a light source which controls a light-sensitive element in accordance with the light and shade of the original, and the output of the lightsensitive element serves to control the volume of light delivered from a given source, this light being intermittently interrupted and serving to energize a second light-sensitive element which controls an engraving-tool operating on the surface of the printing-plate &c. The engraving-tool preferably has two cutting edges which taper away from each other from a common point. The original picture 36, Fig. 1, is mounted on a table 14, and the plate 81 to receive the reproduction is supported by a table 15, the tables being connected together by pivoted links 19, 22 and an adjustable rod 24, and being reciprocated along guides 11 by means of an electric motor. The picture 36 is scanned by a device 35 which includes an adjustably-mounted light source and lens system for projecting a beam of light on to the picture, whence it is reflected on to a photoelectric cell mounted within the device 35 and connected by leads 181, 182 to an amplifier 180, the output of which passes through a screening system 190, which controls a second photoelectric cell 198 connected through an amplifier 212 to the cutting-tool 80. The tool 80 and scanning-device 35 are reciprocated transversely of the tables 14, 15 by chains 83, 66 connected to the cutting and scanning devices respectively, and driven by pulleys 85, 63 and gearing from the motor which reciprocates the tables, and the cutter is made operative during the forward stroke only, a commutator being arranged to complete the circuit of an electromagnet 99, Fig. 5, during the back stroke ; this electromagnet acts to hold the cutting-tool raised above the plate 81 by attracting an armature 104 which is carried by the cutter unit, the whole of which is supported on a pivoted arm 103. The cutter unit comprises a magnet yoke 108 carrying an electromagnet 109 which is energized during the machine operation, and between the pole pieces is rigidly supported a coil 125, to which are connected the output leads of the amplifier 212. An armature 127 is supported in the opening of the coil 125 so as to possess a small rotative movement about an axis which is the median of the coil 125, and this movement serves to operate the tool-holder 130, which is connected at its upper end to the armature by a flexible link 131 while at its lower end, which carries the tool 133, a flexible diaphragm 136 is provided attached by bolts to a bar 138 carried by the yoke 108. This bar 138 also serves as a guide for a slidable tube 146 having a passage way 147 which is connected to openings provided in the tube 146 adjacent the cutting-tool, and through which the chips &c. are drawn by suction, a brush being provided to facilitate this. The tube 146 carries a roller which serves to support the cutter unit and, by means of a rack and pinion, the tube 146 can be adjusted relatively to the member 138, with consequential adjustment of the position of the yoke 108 and of the cutting-tool 130 relative to the work 81. The cutting-tool 133 is shown in detail in Figs. 8 and 9, and has cutting- edges 167 which serve to produce a printing- plate surface having pyramid-shaped depressions therein, the depths of which vary according to the currents produced by the scanning- device 35. For a light part of the picture, the depressions are made deepest and the printing- surface smallest when a positive copy of an original is being made, but when a negative copy is required the reverse is the case. The screening system 190 may take one of three described forms, which operate in different ways. (1) The leads 188, 192, Fig. 10, may be connected to the moving coil of a galvanometer, and a light beam reflected from the mirror 194 carried by the coil is reflected on to the photoelectric cell 198 connected to the amplifier 212. The beam is brought to a focus by a lens 199 at a point between the teeth of a wheel 200, which is driven through a chain or equivalent 203 by the reciprocating table 15. Alternatively a toothed band may replace the wheel 200. When the part of the picture being scanned is midway between black and white, the focus of the beam is midway between the top and bottom of the notches but according to the current which flows in the coil of the galvanometer, the beam of light reflected by the mirror is displaced relatively to the teeth of the wheel 200, so that light passes to the cell 198 for a longer or shorter time, and therefore the maximum current through the cell flows for a longer or shorter time, with a corresponding effect on the coil 125, so that the tool 133 operates for a time and cuts to a depth which depends upon the light intensity of the point being scanned. (2) The leads 188, 192 may be connected to a glow lamp, the light emission of which varies directly with the current flowing therethrough. The light emitted is allowed to fall on the photo-electric cell 198, through a band or disc which is driven from the cutting- table 15 and has alternate transparent and opaque sections. By this means, the magnitude of the current emitted by the cell varies according to the point scanned, the increased current impulses enduring, however, for periods which are constant and depend upon the width of the opaque and transparent sections of the scanning means. (3) The leads 188, 192 are connected to a light valve and the current flowing therein serves to control the amount of light passing from a steady source through a scanning-device to the photo-electric cell 198. The printing- plate produced may be used for preparing prints or for making matts of mouldable material from which duplicates may be prepared by casting. By suitable adjustments of the apparatus, positive or negative copies of the picture 36 to an enlarged or reduced scale may be obtained, and the scanning and reproducing means may be mounted either at the same place or at a distance from one another, the impulses being transmitted either by wire connections or by a wireless system. A number of cutting- heads may be controlled by the one scanning means.