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The line printer is a form of high speed impact printer used in high volume printing in which one line of type is printed at a time. They are associated with the early days of computing, although the technology is still in use. Print speeds of 600 to 1 200 lines per minute (10 to 20 pages per minute) were achieved.

Four principal designs existed:

BAR PRINTERS

Bar printers were similar to chain printers but were slow and less expensive. Rather than a chain moving continuously in one direction, the characters were on fingers mounted on a bar that moved left-to-right and then right-to-left in front of the paper.

In all three designs, timing of the hammers (the so-called “flight time”) was critical, and was adjustable as part of the servicing of the printer. For drum printers, incorrect timing of the hammer resulted in printed lines that wandered vertically, although with character correctly aligned horizontally in their columns. For train and bar printers, incorrect timing of the hammers resulted in characters shifting horizontally, although on vertically-level printed lines. Most drum, chain, and bar printers were capable of printing up to 132 columns, but a few designs could only print 80 columns as others printed up to 160 columns.

 Business cards, flyers, Folders,  Invoice books, Posters,  Magazines, Booklets, Desk  pads, Calendars, Note pads,  Letter heads, Newspapers,  Stickers, Banded corporate gifts  and clothing, NCR Books

COMB PRINTERS

Also known as line matrix printers, these printers  represent the fourth  major design.  These printers were a hybrid of dot matrix printers and line printing. In these printers a comb of hammers printed a portion of a row of pixels at one time (eg every 8th pixel) By shifting the comb back and forth slightly, the entire pixel row could be printed (continuing the example, in 8 cycles. The paper then advanced and the next pixel row was printed. Because far less print head motion was involved than in a conventional dot matrix printer,. these printers were much faster than dot matrix printers and achieved high volumes of printing .  They  were competitive in speed with formed character line printers while also being able to print dot matrix graphics as well as variable –sized characters.

All line printers used paper provided in boxes of continuous fan-fold forms rather than cut-sheets.  The paper was usually perforated to tear  into cut sheets if desired and was commonly printed with alternating white and light-green areas, allowing the reader to easily follow a line of text across the page. The high-speed motion of the paper often developed large electrostatic charges. Line printers frequently used a variety of discharge brushes and active static eliminators to discharge these accumulated discharges.

DRUM PRINTER

In a typical drum printer design, a fixed font character set is engraved onto  the periphery of a number of print wheels, the number matching the number of columns (Letters in a line) the printer could print.  The wheels, joined to form large drum (cylinder) spin at high speed and paper and an inked ribbon is  moved past the print position to achieve high volume printing.. As the desired character for each column passes the print position, a hammer strikes the paper from the back and presses the paper against the ribbon and the drum, causing the desired character to be recorded on the continuous paper.  Because the drum carrying the characters remain in constant motion, the strike-and-retreat action of the hammers had to be very fast to achieve high volume printing.  They were driven by coils mounted on the moving part of the hammer.

CHAIN PRINTER

Chain (also known as train) printers placed the type on moving bars (a horizontally moving chain) As with the drum printer, as the correct character passed by each column, a hammer was fired from behind the paper. Compared to drum printer chain printer had the advantage that the type chain could usually be changed by the operator, resulting in high volume printing . A further  advantage was that vertical registration of characters in a line was much improved over drum printers, which needed extremely precise hammer timing to achieve a reasonably straight line of print. By selecting chains that had a smaller character set (just numbers or a few punctuation marks, the printer could print much faster that if the chain contained the entire upper and low case alphabet, number and all special symbols.

Band printers are a variation of chain printers where a thin steel band is used in stead of a chain with the characters embossed on the band.  Different bands were generally available with a different mix of character, so a character set best matched to the characters commonly printed could be chosen.

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Business cards, flyers, Folders, Invoice books, Posters, Magazines, Booklets, Desk pads, Calendars, Note pads, Letter heads, Newspapers, Stickers, Banded corporate gifts and clothing, NCR Books

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