Patent GB-1156909-A (GB)
Title: Controlled Ink-Jet Copy-Reproducing Apparatus
Inventor: LOUGHREN ARTHUR VIVIAN
IPC: H04N1/034
Filed: 1967-10-18
Abstract: 1,156,909. Copying by scanning. A. V. LOUGHREN. 18 Oct., 1967 [8 Nov.. 1966], No. 47473/67. Heading H4F. In an arrangement for reproducing on a record sheet a copy of a subject corresponding to video signals in serial form by utilizing the latter to control an ink-jet carried by a head arranged to scan the record sheet in synchronism with the video signals the jet is provided with means acting thereon to break-up the link stream into droplets at a substantially constant average frequency the instantaneous timing of the break-up being determined by the magnitude of samples of the video signals taken periodically at the average frequency. The scanning apparatus employed in carrying out the present invention and which is similar to that disclosed in Specification 1,145,653, comprises, as shown in Figs. 1 to 4, a scanning head 22 arranged to scan a record sheet 12 carried by a rotating drum 11, the head carrying a nozzle 26 supplied with ink via a pump 43 from a reservoir 42 and being oscillatable by electromagnetic means 33, 34 to break-up the ink stream into droplets in the vicinity of an electrode 35 to which the video samples are supplied. In the arrangement of Specification 1,145,653, which employed a plurality of nozzles one for each of a plurality of colours, sinusoidal oscillators were supplied to the winding 33 associated with each nozzle to break-up the issuing jets, at regular intervals, into a series of droplets of uniform size and optical characteristics. This arrangement then operated to allow ink to reach the record sheet (e.g. ink stream 26a, Fig. 3) in the absence of video signals on electrode 35 whereas when the droplets in the stream were charged by video signal components supplied to electrode 35 deflecting plates 37, 38, supplied from a unidirectional voltage source, operated to deflect the droplets to a drain 41 whence they returned to the ink reservoir 42. With this arrangement the copy was produced on sheet 12 in a plurality of discrete tonal values in either monochrome or colour. In distinction, the present invention operates to control the size and optical characteristics of each droplet continuously so that the copy is reproduced with a continuous tonal variation. To achieve this a series of double pulses termed anticipation Pulses-A (Fig. 5) and Terminating Pulses-B are produced on the amplitude coincidence of samples of the video signal with a positively-going and with a negatively-going sawtooth wave recurrent at the sampling frequency. Thus, as shown in Fig. 6, samples (G, Fig. 8) of the video signal (F, Fig. 8) from source 50 are produced via circuit 52 and developed across cathode-resistor 55 under the control of timing pulses (E, Fig. 8) from a generator 51 which also controls the two sawtooth generators 56, 57 (waveforms H and I respectively, Fig. 8). The magnitudes of the latter may be adjusted by potentiometers 59, 62 and on amplitude coincidence of the sawtooth waves with the video sample (G, Fig. 8) the pulses A and T (see also Fig. 5) are produced via transformers 60, 63 and generators 64 and 65 respectively. These pulses, the position and spacing of which may be adjusted by potentiometers 59 and 62 are combined in amplifier 66 (detailed in Fig. 7, not shown) and supplied to the winding 33 which produces the oscillation of the ink nozzle. The pulses A are also supplied to a sampling circuit 71 to which the video samples are supplied via a non-linear amplifier 70 (which compensates for variations in the transit times of the droplets due to variations in their masses) and the output samples from circuit 71 are fed to the electrode 35 via a delay device 69 (which compensates for the finite transit time of the droplets) together with the output of a sampling circuit 67 triggered by the pulses-T and developing from a H.V. input at terminal 68 a rectangular wave (J, Fig. 8) the low-potential portions of which allow the passage of droplets to the record sheet 12 whilst the high-potential portions charge the droplets to such a value that the plates 37, 38 deflect them to the drain 41. Thus the droplets which reach the record sheet are those controlled by the video signals and since the position and spacing of the A and T pulses which determine the intervals (B, Figs. 5 and 8) during which the droplets impinge on the record sheet are determined by the amplitude of the video samples a recording with a continuous tonal variation is produced. In a modification of this arrangement the " Negative " sawtooth generator 57 is dispensed with and the pulses T are produced with a fixed delay after the pulses A so that the average durations of the periods B and D are constant (Fig. 11, not shown). Since in the arrangement the droplets are of constant size there is no variation in transit time and the non- linear amplifier 70 is then only required to compensate for variations in the timing of the initiation of the droplets which varies with the amplitudes of the video samples. Instead of using a single ink supply reservoir the nozzle may be fed from two or more ink sources of different optical densities or colours. Thus, as shown in Fig. 10, inks of different optical densities from constant flow control devices 85, 90 are pumped alternately to pipe 96, which communicates with the single nozzle, by electromagnetic means 100 which, under the timing control of generator 51, produces pulses of ink by flexing the surfaces 89, 93 of chambers 87, 92. Because of the finite length of the pipe connection to the nozzle a clean separation between the two inks, e.g. between the dark and light inks 80, 81 (a, Fig. 9) cannot be achieved and intervening portions such as 82 (b, Fig. 9) consisting of a mixture of both inks occur. These portions which produce an intermediate shading may be selected in combination with the other portions for producing the recording by appropriately timing the pulses A and T producing the required portions B and the portions D to be discarded (i.e. directed to the sink). An extension of this method of operation utilizing four sources of ink, i.e. magenta, yellow, cyan, and a " clear " marker (for luminance control) is described in connection with Figs. 12 to 16 (none shown).