GB1422835A - Echo check circuit - Google Patents

Abstract

1422835 Printers XEROX CORP 22 Nov 1973 [24 Nov 1972] 54231/73 Heading G4H [Also in Divisions H2 and H3] In a non-impact character printer employing a plurality of flash lamps to illuminate selected characters from character sets moved relative to the lamps, an echo check signal indicating a lamp has flashed is generated in response to a signal which changes in amplitude between limits within a time that determines the duration of the echo check signal. Each lamp covers say 4 or 6 character positions along the line, a character set being provided circumferentially on a rotating drum for each position, the sets for a given lamp occupying different sectors of the drum. The lamps are flashed to project character images for electrostatic printing at times determined by comparing character data from a computer with a drum position counter to produce flash command pulses. The echo check signals are supplied to the computer to cause abort, reprint and/or flagging of line or page if an echo check signal is produced without a flash command pulse or vice versa. Figs. 4a, 4b, show a circuit provided for each lamp. A flash command pulse 26 at the left goes via a transistor switch 31 and an isolation transformer 32 to turn on transistor 34 to discharge a capacitor 38 into the gate of an SCR 35. (31, 34 and 35 are reverse-biased for noise-rejection.) SCR 35 fires so that a capacitor 39 discharges via a transformer 40 to energize sparker and trigger electrodes 43, 44 in the lamp 4 which flashes with discharge through it of a capacitor 50. A pulse is produced via a transformer 51 to cut off transistors 55, 56 and turn on transistor 57. A ramp voltage is produced by 57 in conjunction with a capacitor 58 and resistor 59 to feed a NAND gate 63 also fed from transistor 56. The output of NAND 63 is inverted 67 to provide the echo check pulse 65.