Patent GB-1292485-A (GB)
Title: Electro-junction printing systems
IPC: H04N1/40
Filed: 1970-04-21
Abstract: 1292485 Facsimile apparatus; transistor pulse circuits PHONOCOPY Inc 21 April 1970 [5 June 1969] 19002/70 Headings H3T and H4F In a printing process which employs a conductive electrode 27 in electrical and thermal contact with a thin metallic foil the undersurface of which is contacted by a heat responsive printing system 29, a high current secondary 24 of a pulse transformer 22 is connected across the electro-junction formed between the electrode and foil, and the primary 21 of the transformer is driven with a train at information controlled print pulses each comprising a plurality of timespaced wave alternations. The current driver circuit includes a series resonant circuit having an inductor L and a capacitor C, serially connected with a parallel arrangement of SCR 15 and diode 16 between terminals 12 and 13 of a D.C. power supply 11. The control electrode 17 of SCR 15 is connected to a transformer winding 16, the other terminal of which is supplied from negative bias source 14 of supply 11 i.e. SCR 15 is non-conductive except when the A.C. signal in winding 16 is supplied to overcome the bias from terminal 14. Pulse generation is controlled by supplying trigger pulses to transformer 33 which has its primary winding connected to a modulator 34 which generates a plurality of trigger pulses for each input pulse on line 35 with the time interval between the trigger pulses controlled to vary in accordance with the length of the print pulse input in line 35, e.g. a facsimile input pulse train. For the shortest pulse duration on line 35, e.g. corresponding to a black dot, at least two trigger pulses are produced at the output of modulator 34 which trigger the SCR 15 to conduct. For longer print pulses a succession of trigger pulses are applied to SCR 15. Specifically the print pulses on line 35 are converted in modulator 34 into pulses shown in Fig. 2A and the output of the modulator provides a series of trigger pulses as shown in Fig. 2B the line interval between successive pulses being in accordance with the amplitude of the wave shown in Fig. 2A. With this arrangement a small dot or continuous line may be accurately printed. During each trigger pulse of Fig. 2B the circuit goes through one oscillator cycle as shown in Fig. 2C. When the trigger impulse occurs in the secondary winding 16 the SCR conducts and the D.C. charge on condenser C from supply 11 discharges so that the voltage across inductor L appears as the waveform 36 in Fig. 2C. When a succession of trigger pulses according to Fig. 2B are applied to the SCR 15 the total energy transmitted to the electrode 27 comprises the sum of the constant quantum energies associated with a single oscillatory cycle at Fig. 2C. At the end of the oscillatory cycle the energy contained in the magnetic field of transformer 22 acts as a voltage source in winding 21 and by means of diode 23 is applied to capacitor C with proper polarity to add to the voltage from the supply 11. Thus after a succession of print pulses the total voltage charge on capacitor C builds up so that in effect the series circuit LC is charged to a higher voltage level than the supply voltage from power supply 11. Thus a smaller power supply 11 may be utilized. Modulator 34 is described with reference to Fig. 3 (not shown).