Patent GB-1322509-A (GB)
Title: Electrically operated typewriter
IPC: B41J1/24
Filed: 1970-06-24
Abstract: 1322509 Selective printing ECOFON VERKAUFSGESELLSCHAFT PROBST KG 24 June 1970 [26 June 1969] 30738/70 Addition to 1321903 Heading B6F Keyboard construction. An electric typewriter keyboard comprises a printed circuit board 8 (Fig. 2) having a pluarlity of conductive areas (9) respectively aligned with the keyboard keys 3. In Fig. 1, an electrically conductive, rubber foil 6 and a perforated, electrically insulating sheet 7 are interposed between the keys 3 and the printed circuit board 8 so that when a key is depressed the conductive foil 6 passes through an aligned perforation to make a mechanical switch contact with the aligned conductive area (9). The contact parts of the areas 9 and the foil 6 are protected against contamination by dust and against moisture by the sandwich construction of the board 8, plate 7 and rubber foil 6. A magnetic retaining plate may be provided in the keyboard by holding each key 3 in the depressed position, until the signal so produced is accepted by the typewriter selection mechanism. As an alternative, piezoelectric crystals may be arranged above the conductive areas 9 for generating electric potentials when keys are depressed. As a further alternative a thin, electrically polarized insulating layer may be arranged between the printed circuit board 8 and the keys 1 so that when a key is depressed, a signal is produced. Alternatively, an insulating foil may be provided between the electrically conductive foil 6 and the printed circuit board 8. When a key 3 is depressed, the capacitance of the condenser formed by the aligned area (9), the insulating foil and the conductive foil 6 is charged to generate a signal. As seen in (Fig. 2), conductors (10) lead to respective elements (11) of a contact ring 12 comprising a circular array of contact elements. The printed circuit board is flexible so that the contact ring 12 is bent into a vertical plane, Fig. 1. Type-disc printer.-The printing mechanism of the typewriter comprises a circular disc 15 with radial flexible arms which is driven continuously by a motor 20 and pulley system 17, 18, 19. The pulley 17 carries a contact 21 which sweeps the contact ring 12. When the angular position of the type-disc 15 corresponds with a particular depressed key 3, a circuit is completed from the keyboard to an amplifier (Fig. 3) via contact ring 12, contact 21, slip ring 22, contact finger 23 and binding post 24 of the amplifier. This results in the timed action of a single hammer 28 under the force of spring 27 when the electromagnet 25 is released. Magnetic tape recording.-Two additional conductive areas (30, Fig. 2) are provided on the printed circuit board 8. The intervals between the traverse of the contact 21 over the contact elements (11) of the contact ring 12 associated with one of the two conductive areas (30) and the time of a type selecting step are recorded on magnetic tape, the interval being characteristic of and uniquely correlated with each letter. Preferably, a synchronizing pulse is recorded on a separate track simultaneousley with the passage of the sensing contact 21, such a pulse being derived for example from a magnet attached to pulley 17. When transscribing such a tape, the tape transporting motor may be controlled in such a manner that synchronizing pulses stored on the tape occur simultaneously with the synchronising pulses of the typewriter. The tape recording typewriter may be used as a transmitter or receiver in a telegraphic system.