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Chain and Band Printers
Daisy Wheel Printers

Fire Controlman Volume 03-Digital Data Systems
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Figure  12-7.—Band,  paper,  ribbon,  and  hammer  relationship in a typical band printer. changing the size of the fonts is not possible because each column printed must have its own print hammer. Band and chain printer characters are generally printed at 10 characters per inch (cpi), although a few printers have been manufactured to print 12 cpi. Chain   and   band   printers   are   medium-   and high-speed printers. They print over 300 lines per minute. CHARACTER  PRINTERS Character  printers  print  one  character  at  a  time. Most character printers are impact-type printers. The notable exception to this is the ink jet printer, which sprays  ink  on  the  paper  to  print  characters.  The common impact character printers are the dot matrix and the daisy wheel printers. Dot Matrix Printers A dot matrix printer forms characters by printing a series of small dots. The heart of the dot matrix printer is the print head. The print head contains a series of print wires, small pins that strike the page to create characters and graphics. The quality of print from a dot matrix printer is directly related to the number of print wires in the print head. The most common print heads use 9 or 24 print wires. Figure 12-8 illustrates the nine-pin print head. Figure  12-8.—A  single  column,  nine-pin  print  head. The print wires in the print head are independently driven by individual solenoids. A pulse applied to the selected solenoid forces the print wire into the ribbon and the paper. The print wire is returned to its normal position by a spring that holds it in the print head. The firing of the print wires can occur over 300 times per second. The print wire solenoid driver pulse generates heat. The print head is usually mounted on a heat sink because of the speed at which the print head operates. The heat sink uses ambient air to disperse heat that, if left unchecked, would damage the print wires. The quality of print generated by dot matrix printers has  improved  greatly  over  time.  Older  printers contained only seven print wires and the dots were clearly visible. Because of this, dot matrix printers were often used for only draft work and the final document was reprinted on a daisy wheel-type printer or manually typed. Today, many dot matrix printers have a print mode refereed to as near letter quality (NLQ). Letter quality refers to the quality of print typically generated by a typewriter. Near letter quality print has become acceptable   for   all   but   the   most   formal   of communications. A dot matrix printer using the nine-pin print head shown in figure 12-8, will initially print a character in the draft mode. The paper is then advanced one-half dot space and the character is printed again. This will fill in the space between the dots and the characters will appear  smoother. A 24-pin print head prints near letter quality faster because it has two vertical columns of print wires. The print wires in column two are slightly offset from 12-9






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