Patent GB-791009-A (GB)
Title: Improvements in or relating to electrical methods and apparatus for engraving plates
IPC: H04N1/40
Filed: 1955-06-28
Abstract: 791,009. Local copying by scanning. NAAMLOOZE VENNOOTSCHAP PHILIPS GLOEILAMPENFABRIEKEN. June 28, 1955 [July 1, 1954], No. 18647/55. Class 40 (3). In a method of engraving a plate according to an original pattern by a chisel of which the depth of penetration varies as a function of the amplitude of an electrical modulating voltage corresponding to the original and in which the chisel is vibrated at a predetermined frequency, the points of maximum depth of sequential penetrations of the chisel into the plate are equally spaced and the speed of the chisel at right angles to the surface of the plate is constant both during the penetration of the plate and withdrawal therefrom. Two symmetrical triangular voltage waveforms of a frequency half that of the fundamental frequency and mutually displaced by 180 degrees are respectively combined with a stepwise voltage derived from the modulating voltage and having voltage values corresponding to that at each peak of the corresponding triangular voltage. The respective combined voltages are applied to an electronic switch, the output of which controls the movement of the chisel, and the switch is controlled by the proportion of the sum of the stepwise voltages of which the resultant amplitude is so chosen that it has the same value as that of first and second modulated triangular voltages at the moments when they have the same value. In the diagrammatic arrangement, Fig. 1, modulating signals from an original on a drum 1 are passed over conductors 5 to a circuit 6 supplied over conductors 7 with a fundamental frequency derived from a member 8 in conjunction with a wheel 9 on the shaft 3 of the drum 1. The output of the circuit 6 is applied over conductors 11 to a chisel 10 engraving a plate mounted on a drum 2 on the shaft 3. A sinusoidal waveform of the fundamental frequency applied at the terminals of conductors 7 is modified in circuits 12, 13, 14 to provide a square waveform of half the fundamental frequency applied via an integrator 27 to the grid of a valve 28 which produces at its anode and cathode outputs two triangular voltages which are fed to the grids of valves 29, 37 respectively. The pulses from circuit 14 are also fed to a circuit 15 and circuits 16, 17 providing sampling pulses, Figs. 11, 16, displaced at 180 degrees and at half the fundamental frequency of those which are applied to valves 18, 31. Pulses of opposite polarity are applied from the anodes and cathodes of each of the valves 18, 31 to clamping circuits comprising diodes 20, 22 and 32, 33 to which the modulating voltage, Fig. 12, is applied at terminals 5. The diodes are rendered conducting by the pulses from the valves 18, 31 and the stepped voltages corresponding to the waveforms of Figs. 13, 17 are derived from the capacitors 25, 34 and are applied to the grids of valves 26, 35 so that the outputs at the anode resistors 30, 36 correspond to the summed triangular and stepped voltages indicated by Fig. 15 and the unbroken-line waveform of Fig. 19. The stepped voltages from capacitors 25, 34 are also applied to the grids of valves 47, 48 and the output at the cathode resistor 46 is fed to the grid of a valve 45 whose output at resistor 44 is proportional to the combined stepped voltages indicated by the unbroken line in Fig. 20. A proportion of this voltage is taken from potentiometer 43 and applied to the point 49 of the electronic switch comprising the diodes 38, 41 and is arranged to have a value equal to that of the two modulated triangular voltages when they are equal and denoted by the dots of Fig. 19. The control voltage depending on its polarity makes the diodes 38, 41 alternately conducting so that the voltage waveform applied via conductors 11 to the chisel is of the form shown in Fig. 21. The angle of taper of the chisel should be less than the angle at which the chisel penetrates the plate under control of the voltage waveform indicated in Fig. 21.