Patent GB-1283574-A (GB)
Title: Line printing with proportional spacing or with proportional spacing and justification
IPC: B41J7/36
Filed: 1969-10-28
Abstract: 1283574 Justifying printers MOWHAWK DATA SCIENCES CORP 28 Oct 1969 [21 Nov 1968] 52798/69 Heading G4H [Also in Division B6] In a printing machine adapted to print justified lines of characters, signals representing a line of characters are stored in a character memory at locations determined by the width of the characters; means for sequentially reading out the memory locations and for printing characters as they are read out, means for shifting the print medium in the direction of the print line whereby successive positions along the line are brought into registration with the print means, the read-out means being operated in timed relation with the shifting means whereby the characters are printed at positions dependent upon their respective storage locations in the memory. A complete print line is divided into 640 character position increments. The widest character (w) is eight increments wide. Characters to be printed are entered by input circuit 10, Fig. 1, via gates 400 and a one-character register to one of 640 character locations of memory 20. The first character is entered in location 1 of memory 20 under the control of addressing ring 40 which is advanced a number of steps equal to the width of the first character. It then addresses the corresponding storage location for the second character and is advanced again by a number corresponding to the width of the second character. This process continues until a space character is detected after the addressing ring 40 has advanced into the justification zone i.e. the maximum number of increments at the right hand end of a line which will have to be filled up during the justification cycle. This is selected to be 80 increments long, an average of twenty characters, making it almost certain that a space will occur in this zone and stop the entry process. The justification process now begins, controlled by a pair of counters in justification control circuit 300. These are called the "shift counter" and the "pad counter". They are set to a count indicative of the number of increments between the position of the last-loaded character and the right-hand margin. This count is entered by initially loading a count of 80 and decrementing for each increment inside the justification zone. The first operation of the justifying cycle causes addressing ring 40 to be stepped down, addressing the locations of memory 20 in reverse sequence until a stored character is detected. It then stops, the detected character being loaded into the one character register in gate circuits 400. The ring 40 is now advanced towards the right-hand storage location 640 the shift counter being decremented in step with the advance of the ring 40. When it reaches a count of zero, the ring 40 stops and the character in the one-character register is loaded into the memory location then addressed by the ring. This corresponds to the extreme right-hand margin of the print line, the character being entered at a location depending on its width, at location 638 if it has a width of 2 and so on. When the last character of the line has been shifted to the margin location, the pad counter is  decremented by one, and the number then standing in the pad counter is entered into the shift counter. The sequence of operations is repeated until the number in the pad counter is zero. This justification process serves to shift the last character to the right-hand margin and each preceding character is moved sequentially to the right and stored in such a location that an additional increment is added to the space between characters. When all the spare character position increments are taken up in this way the process stops, the pad counter then reading zero. Printer, Fig. 3.-A line of eighty print hammers 503-1 to 503-80 co-operates with a print drum 501 carrying a complete font for each hammer. The width of a character Em is measured from the right-hand edge, to a position two increments beyond the left-hand edge. All the right-hand edges of the characters in a font are in line. The drum rotates continuously, printing being by timed operation of a hammer through its drive circuit HD1-4D80. The paper has edge perforations engaged over sprockets 509 which step to feed the paper to the next line printing position. The sprockets 509 are mounted on a laterally shiftable shaft 511, loaded by spring 519 to bear against a cam 515 driven through gear 525 from the shaft of the printing drum. This cam has eight circular camming segments each occupying one tenth of a revolution and each displacing the paper one increment more than the one before. The maximum displacement is Em, eight increments. The lower segment, as shown; permits the shaft 511 to remain in the home position for one revolution. The cam advances while a blank zone on the printing drum passes the printing hammers. Magnetic marks 533, 535 on the drum are sensed to obtain incremental pulses for providing a coded representation of the angular position of the drum. During a printing cycle the drum 501 rotates eight times, in each position the representation of the angular position is compared with certain of the stored characters. In the first drum rotation, with the paper carriage in the home position the 80 character storage locations 1, 8, 15, 22 &c. are scanned and where agreement is found between the stored character and the drum position signals, the corresponding character is printed by firing the print hammer. The paper carriage then shifts one place and the next 80 storage locations 2, 9, 16, 23 &c. are scanned out. This process is repeated until all the storage locations are read out and printed. During the next two revolutions of drum 501 the paper carriage returns to its initial position and the sprockets rotate to advance the paper to the next line position. By this means the lines of characters printed are justified and the spacing between characters outside the justification zone is always two increments.