Patent GB-1223498-A (GB)
Title: Printer control system
IPC: G06K15/08
Filed: 1968-09-25
Abstract: 1,223,498. Electric control of printers. MOHAWK DATA SCIENCES CORP. 25 Sept., 1968 [16 Oct., 1967], No. 45599/68. Heading G4H. Printing apparatus comprises means for printing a line of data means for storing the data to be printed in the line scanning means for scanning a segment of the store, representing part of the line means for operating a section of the printing means to print the scanned data and means for preventing the scanning means from scanning any other segment of the store until the data in the scanned segment has been printed. The printer comprises a travelling band 10, carrying 64 different type slugs, and a stationary print hammer in each character position. The hammers are divided into two or more equal zones, the driver circuits 20 being connected in turn to the hammers of each zone by a selector matrix 18. Characters to be printed are received successively in serial bit mode by the input circuit 200. The characters are then passed in turn in parallel mode to data memory 30 to await read-out for printing. Control signals are also received. These are carriage return (CR), line feed (LF), tabulate (TAB) and form feed (FF). They are decoded by circuits 200 and corresponding signals stored in memory 40. Signals from memory 40 control the timing and character position generator 100, the zone selector 18 and the paper feed control 500. Memory 30 is divided into six groups, each having a number of storage positions equal to the number of print hammers in a zone. Control memory 40 has a storage position for each of the groups in memory 30, the corresponding position being addressed together with a group of memory 30. Memory 30 contains three times as many groups as the number of print zones so that the total buffering capacity is three full print lines. Circuit 200 includes a shift register for converting the signals to parallel mode and decodes the incoming characters to indicate whether the character is a character (data) to be printed, a space, or a format control signal CR, LF, TAB or FF. Load control circuits 300 controls the transmission of a data character to memory 30 for storage in a predetermined group. Later this character is read out and compared in comparator 22 with a coded signal provided by the timing and character position generator. If a match is detected the character is printed. Format control signals effect the following control operations: (1) If the control signal is a CR, LF or FF, the group of memory 30 to which the preceding data characters were sent is closed, whether or not it is full and the next received characters are sent to the next group. (2) When a TAB signal is received all the positions in memory 30 after the last received character are filled with internally generated space signals up to the TAB position which is preset on a plugboard. (3) A CR signal causes data to be entered into the position of control memory 40 corresponding to the newly addressed group of memory 30 so that the next received characters will be printed beginning at the left-most position of the print line. (4) An LF signal again causes bits to be entered with control memory 40 corresponding to the newly addressed group of memory 30 and the paper feed control 500 will feed the paper one line space before the printer begins printing. The paper is advanced one line space for each LF signal received. (5) An FF signal causes a data bit to be entered into the position of memory 40 corresponding with the newly addressed group of memory 30 to cause the paper feed control to advance the paper 14 to the first print line of the next form. This is for the case when the paper is a web of connected forms. The printer prints the characters at substantially the same instant they are received and the memory 30 is therefore read out by circuit 400 at the same time as incoming characters are read in. For this purpose timing circuits 100 produce a repetitive sequence of timing pulses, each sequence defining one basic time cycle. The cycles are synchronized with the movement of band 10 and have a high frequency compared with the input data. Each cycle has a first half in which the load control circuits 300 operate and a second half in which the read control circuits 400 operate. Circuits 400 read out each group of memory 30 in turn together with the corresponding position of control memory 40 and each group remains addressed until all the data therein has been printed and all the control operations indicate by the bits stored in the corresponding position of memory 40 have been executed. When a new group is addressed, the control store is scanned and the necessary feeding operations are affected before the characters are printed. When the printer is printing substantially full lines data is taken out of store at about the same rate as it is entered. But when printing short lines, because of the time taken for line spacing operations, data is entered at a greater rate than it is taken out. Normally, the memory 30 provides sufficient buffering capacity to accommodate this difference, but where a long succession of short lines is to be printed the system automatically switches to a different mode of operation, termed the " tail " mode. In this mode of operation format control signals when they are received do not cause a new group to be addressed in memory 30. Instead successive blocks of incoming data are tailed together so as to leave no empty spaces in the memory. The format control signals are replaced by a special character entered into memory 30 which when printed indicates that format control operations had been suspended because the capacity of the buffer memory 30 was in danger of being exceeded. The special character when printed shows where a format control operation should have been made. As described, the printer has 16 print hammers although in practice there may be 80. The hammers are divided into two groups of eight as shown in Fig. 6. The spacing of the characters on the band 10 is one and oneseventh times the hammer spacing so that if character A is under the first hammer of zone 1, character H is under the first hammer of zone 2. This is shown as time TS. At a later instant, time TT character B is under hammer 2 and character I under hammer 10. Successive characters come under successive hammers until after 8 intervals character B is under the first hammer of zone 1 and I is under the first hammer of zone 2. The eight intervals are called major time intervals, together constituting a major time cycle. Each interval is divided by timing circuits into 16 minor time intervals. There are eight hammer driving circuits 20 connected by gates 18 to hammers in the two zones alternately. The circuits 20 are controlled by a comparator 22 which compares the incoming character data, expressed as a six-bit signal, with a similar signal from character generator 100. This consists of a six position master counter advanced by character pulses derived photo-electrically from the movement of the band. It gives a unique output for each of the 64 type slugs on the band. The count is transferred to a slave counter at the second minor time interval of the first major time interval. If printing is in zone 1, one is added to the slave counter. If printing is in zone 2, eight is added. This brings the slave counter count to the appropriate value for defining characters in the first or second zones. These values are compared with the character signals and the print hammers operated where there is agreement. The control system is described in detail with reference to Figs. 3a-3d (not shown).