"What Impact Printers are good for"

In this section, we'll discuss three types of printers: line matrix, serial dot matrix, and band printers, all of which are frequently lumped together as "impact" printers. While there are many similarities among these technologies the differences are even greater.

Band printers print by impact the same way typewriters do - with fully formed embossed characters like you'd find on the ball of an old Selectric typewriter. This approach prohibits band printers from printing graphical output or varying the size of a printed character, and as a result, the use of band printers is decreasing dramatically.

While line matrix and serial dot matrix printers both form characters by impact printing of dots, they too, have very little else in common. Line matrix printers print the dot arrays for their characters by moving the paper vertically past a hammerbank, which shuttles back and forth horizontally across a small space. Since the hammers in the bank cover the full line width, the shuttle motion makes one row of dots in each character array to be printed on the line. As the paper moves upward, the print head progressively builds these rows of dots from top to bottom of the characters. When all the rows have been formed, the cycle is complete and a full line of characters has been printed. Then the paper moves down to the next line and the array-forming cycle is repeated.

In contrast, serial matrix printers use a moveable print head, which has an array of pins. The print head moves horizontally across the paper and prints characters - one at a time - to complete the line. Then, the paper advances and characters are again printed horizontally across the page. Because of their design differences, line matrix printers are much faster than serial dot matrix printers, and their print mechanisms are far more reliable. Both line matrix and serial dot matrix printers produce dots that are larger than those produced by laser and thermal technologies, dot spacing being in the range of 100 to 200 dpi.

To be continued with "Thermal Printers"...

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