Patent GB-1311167-A (GB)
Title: Control for chain printer
IPC: B41J7/36
Filed: 1970-07-15
Abstract: 1311167 Digital printer control MOHAWK DATA SCIENCES CORP 15 July 1970 [17 Nov 1969] 34383/70 Heading G4H A control system for a line printer of the kind having a type carrier 30 (Figs. 2, 6) moving parallel to the print line the types thereon being spaced by a distance Y greater than the space W between print positions comprises a shift register 70 (Fig. 3) storing a line of coded characters, a memory address counter 152 (Fig. 4) cycling with the shift register and being driven through 4 complete cycles during the time the carrier 30 moves a distance Y, a character generator arranged at the beginning of each cycle to give a code representing the type character on the carrier next coming into alignment with a reference position, a phase counter 166 counting 1-4, being advanced at each address counter cycle, means for advancing the character generator at each advance of the address counter, except when the output of the lowest two orders of address counter equals the output of the phase counter, a comparator 120 for comparing the codes read out of the shift register with those generated by the character generator and for operating a print hammer when the codes agree, the comparator output being gated out only when the lowest two orders of the address counter agree with the value of the phase counter. The type band is mounted on pulleys 34, 36 (Fig. 2), the latter being driven by a motor 22. A disc 24 revolving with pulleys 36 carries marks 38 which are sensed at 46 to provide clock pulses CP. Pulses at one-eighth the frequency are generated by head 44 sensing marks 40. Head 42 senses an end-of-font mark on the band to generate signal IND. The character generator counter 110 (Fig. 3) receives the clock pulses CP as the band moves, generates character codes indicating which character is in a reference position and is reset to zero at the end of the font by the signal IND. If character A is in position 1, Fig. 6, character D is in position 5 and so on, so that if these characters are to be printed in these positions, the corresponding print solenoids are energized. To determine whether a printing stroke is necessary the line of coded characters in shift register 70 is recycled at high speed, the reference character, e.g. A, being entered in a slave counter 114 which is advanced in step with the shift register. By this means the line of characters in shift-register 70 is compared with the characters in corresponding positions along the printing line. When the comparator 120 detects agreement a print signal TR is sent to gates 174-1 to 174-9 (Fig. 4) passing the outputs from decode circuit 172. This decode circuit and another, 170, decode the outputs of the address counter 152 to form column and row outputs C1-C16 and S1-S9. These in combination select one of the print gates 60-1 to 60-144. An output TR from comparator 120 therefore causes a corresponding flip-flop 61-1 to 62-144 to be set. The difference of spacing between the types and the printing positions is accommodated by preventing one in four of the advance pulses from reaching the  slave counter 114. This is effected by a comparator which compares the A1, A2 outputs of counter 152 with the #1, #2 outputs of counter 166. Upon agreement (once in each group of four) gate 94 provides a signal inverted at 98 to disable gate 100. This signal also opens gate 122 to read-out the comparator signal. The hammer drive circuits which are primed by setting the corresponding flip-flops 62-1 to 62-144 are fired at the correct instant, i.e. when the type is opposite the hammer, by firing signals F1-F4 derived from the decoded outputs #1, #2 of the phase counter 166.