GB1210203A - Improvements in ink drop writing systems - Google Patents

Abstract

1,210,203. Selective printing. A. B. DICK CO. 13 March, 1969 [13 March, 1968], No. 13383/69. Heading B6F. [Also in Divisions G4-G6] An ink drop writing system of the kind in which ink drops 22 are formed in a stream in synchronization with synchronization signals, and are charged in accordance with synchronized video representative signals to be subsequently deflected in an electric field by an amount depending upon the charge and then caused to impinge on a writing medium, is provided with means for testing and correcting the phasing of the ink drops relative to the video representative signals. The testing and correcting means comprises means for applying a fixed frequency test signal synchronized with the synchronizing signal for charging the stream of drops in place of the video representative signals, a detector 76 so placed as to receive drops charged by the test signal only when the phasing of the drops is correct and means responsive to the detector output for adjusting the phase of formation of the ink drops so that the detector does receive drops. The ink drop writer moves across the width of the printreceiving paper on a screw (44, Fig. 2) rotated by a motor and gearing first in one direction and then in the other to return the writer to its home position. The stream of ink drops passes between a pair of elongated deflector electrodes 41, extending across the width of the paper, to which the video representative signals are applied. A feeler (74, Fig. 2) operating a sensing switch detects when the ink drop writer is in the home position, in which position it is aligned with the detector 76. The drops 22 are formed from a jet 20, drop formation being controlled by a transducer 14. As a drop is formed it should if correctly timed be charged by a test signal applied to the charging tunnel 24. If while the ink drop writer is in the home position the drop formation is out of phase with the test signal the drops are uncharged or insufficiently charged. If the drops are properly charged, they are deflected by the synchronous signals applied to the electrodes to strike detector 76. The detector may be of piezoelectric material generating a pulse for each drop. These are amplified and applied to an integrator 90. If there is no integrator signal after the ink drop writer has been in the home position for a certain period a phase control circuit changes by 180 degrees the phase of the test signal being applied to the drop control transducer 14. This brings the drops into correct phase with the charging signals applied to tunnel 24. The deflector plates are energized by a 66 KHz signal which may be reduced to 33 KHz before being applied to the charging tunnel 24. Drops are formed at 66 KHz so that alternate ones are charged and uncharged. The uncharged drops reduce interference between the adjacent charged drops. The detector may be some other form of senser e.g. a microswitch.