Patent GB-692349-A (GB)
IPC: B41C1/04
Filed: 1949-07-21
Abstract: 692,349. Copying by scanning. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. July 21, 1949 [July 24, 1948], No. 19249/49. Class 40 (iii). In a machine for producing a screened relief pattern plate from a sheet bearing an image, comprising a reciprocable carriage supporting an electro-optical pick-up system and a synchronously moved reciprocating carriage carrying a plate-deforming tool, the transmitting sheet and recording plate being mounted on synchronously rotated cylinders, the pick-up system comprises a light-source and a source of pulsating current connected to modulate the light-source. In particular, the screen frequency is produced by an electrical generator comprising a rotor element driven synchronously with the cylinders and an independently rotatable stator element driven at a speed much lower than that of the rotor. The photo-electric scanning members comprising a light-source 22a andphoto-cell 22c are mounted on a carriage 22 which is adjustably clamped to the upper run of a belt 27 of which the lower run is attached to a carriage 23 on which the balanced armature engraving unit 30 is mounted so that the carriages 22, 23 are moved in opposite direction on supporting bars 38, 39. The cylinders 10, 12 carrying the plate 11 to be engraved and sheet 12 bearing the image to be transmitted are secured to shafts 14a, 14b which are connected for simultaneous rotation by coupling discs 15a, 15b. The shaft 14a is driven from a motor 16 through worm-wheel gearing 18, 19 and an over-running clutch 20. The belt 27 is carried by pulleys 25, 26, the former being driven from the shaft 14a by means of gearing 46, 47 and 48, 49. The shaft 14a carries a relatively heavy fly-wheel 21 utilized to smooth out minor pulsations in the rotary motion, and also a rotor member 40a associated with a stator member 40b rotated at a relatively slow speed by pulleys 41, 44, 45 and a belt 43 connected at 43a to the tool-actuating carriage 23. The signal generator constituted by the members 40a, 40b is utilized to produce an interrupting frequency applied to the scanning light 22a and to the actuating coils of the engraving tool 30 in order to provide a screen pattern on the printing-plate 11. In the arrangement shown, the stylus is heated and the printing-plate is formed of decomposable material, such as cellulose nitrate. The actuating unit 30 is carried by a platform 34 pivotally secured to the carriage 23 and forming the armature of an electromagnet 37 mounted on the carriage. The unit 30 is held in operative position when the magnet 37 is energized, but is moved to an inoperative position by a U-shaped spring 36 engaging the platform 34 and a portion of the carriage when the magnet is de-energized. The rest position of the tool 24 relative to the plate 11 is adjusted by a rotatable spindle in threaded engagement with one arm of a spring 31 having a second arm carrying a shoe 32 in engagement with the sheet 11 and engaged by the end of the spindle. The adjustment of the apparatus for obtaining desired depths of engraving corresponding to black- and white is facilitated by a microscope 60 mounted in a housing 64 provided with a light-source 65 and carried on an adjustable arm 61, the arrangement being that a marginal portion on the image sheet including black-andwhite portions is reproduced, and adjustments made consequent upon the results observed through the microscope 60. Circuit arrangements. The output of the photo-cell 22c of the electron-multiplier type is fed to an amplifier 73, part of the output of which is fed back through a low-pass network 75 arranged to prevent fluctuation of output corresponding to the mean brightness of the image on the sheet 13 from varying the mean position of the stylus 24. The output from the screen generator 40 is fed via amplifiers 77, 79 and amplifiers 84, 87 in parallel to the scanning light 22a and the lamp 65 of the adjustment device. The outputs of the amplifiers 73, 77 are also fed through resistances 74, 89 pivoted with adjustable tapping points 90, 91 so that the combined outputs in desired proportions can be applied via amplifiers 94, 95 to the primary of a transformer 96, the secondary of the transformer being connected to the coils 30c, 30d of the unit 30. Adjustable voltages derived from a resistance 99 across the secondary of the transformer and from a resistance 97 in series with the coil 30c, 30d are combined and fed back to the input of the power amplifier 95 for linearizing the overall characteristics of the amplifier and actuating mechanism 30 and controlling the output impedance of the amplifier to provide damping of the mechanism 30. The system is set into operation by actuation of a switch 113 which connects an A.C. supply to a tube 128 which operates a heater 56 for the stylus and the heaters of various amplifier valves. A con. tact-closing member 116 associated with a relay 37 is initially held in position manually until the motor 16 has been set into operation. The output from the screen amplifier 79 fed to a valve 121 operates relay 120 to close contacts 119 so that the relay 37 is automatically held energized whilst the apparatus is in operation. The recording apparatus can be operated from a distant transmitter by actuating a switch 105 connecting an input terminal 106 in lieu of the output terminal of the electro-optical pick-up and the amplifier 73. Specification 692,400 is referred to.