Patent GB-1211955-A (GB)
Title: Improvements in ink drop writing systems
IPC: H04N1/034
Filed: 1969-03-13
Abstract: 1,211,955. Correcting timing of drop formation in ink-drop writers. A. B. DICK CO. 13 March, 1969 [13 March, 1968], No. 13382/69. Heading G4H. An ink drop 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 target receiving all the drops in the stream and providing an output, a detector responsive to the output to determine whether or not the phasing the ink drops is correct and control means responsive to the detector when this determines that the drops are not being properly charged by the test signal, to adjust the instant in the cycle at which the ink drops are formed. The ink drop writer moves across the width of the print receiving paper on a screw rotated by a motor through 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 electrodes; extending across the width of the paper, to which the video representative signals are applied. A sensing switch detects when the ink drop writer is in the home position, in which position it is beyond the left-hand end of the deflection plates and aligned instead with the target 84, The drops 22 are formed from a jet 20, the formation being controlled by a transducer 14. As a drop is formed it should be charged by a signal applied to charging tunnel 24. If the drop formation is out of phase with the test signal the drops are uncharged. If the drops are charged, they give up their charge to the target causing a flow of current through resistor 86. The voltage drop is 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 (given by delay 92) the phase control network 94 gives a signal to phase charge network 80 to change by 180 degrees the phase of the 66 KHz signal being applied to the drop control transducer 14. This brings the drops into phase with the charging signals applied to tunnel 24. In the form of Fig. 4 the 66 KHz signal is reduced to 33 KHz by divider 17 before being applied to the charging tunnel 24. Drops are formed as before at 66 KHz so that alternate ones are charged and uncharged. Adjacent charged and uncharged drops combine, striking the target at 33 KHz. If the drops are not properly charged they do not combine in pairs but remain separate. A piezo-electric target may be used to detect the drops, each drop giving a signal. A 33 KHz output indicates that the alternate drops are becoming properly charged and are combining with intermediate ones. This frequency is detected by a filter and an integrator. If the drops are not properly phased they do not combine in pairs and the frequency produced by the piezo-electric target is higher.