Introduction

For years impact printers have played a major role in the office. Since the first typewriters were introduced in the 1800's impact printers have provided a fast efficient method tho produce easy to read text output.

The introduction of computers into the office environment expanded the role of impact printers significantly. Now large volume printing was possible and day-to-day business tasks such as billing, shipping, and letter writing could be processed on a larger scale by machines.

Impact printers produce output by several methods. The most common is by striking or impacting a inked ribbon which is positioned between the output media and the impact head. The ink is driven into the media and the output is formed. Other less common impact printing methods include inkwheels which pre-ink the impact head (common found in calculators and cash registers) and direct impact on pressure sensitive paper (which changes color under pressure).

Most Impact printers determine speed in "cps", characters per second. Impact printers are noted for their noise, which in some cases require that they be kept in sound dampening blocks.

Impact printers can accept paper in the form of individual sheets, rolls, or fanfold. They are used primarily for text printing, although dot matrix printers can create simple graphics.

Types of Impact Printers

Block Impact

Block impact printers produce out put from pre-shaped fixed characters mounted on blocks. The blocks may be mounted on a spinning wheel (also known as daisywheel), or a globe shaped single block, bands of blocks,or individual blocks. The blocks can vary in thickness and size. The selected characters are projected towards the output media by some physical impact force such as an electromagnetic hammer, lever, or in the case of old manual typewriters by brute force.
Block impact printers provide letter quality (these types of printers are the origin of the term "letter quality") print. Block impact provides limited type faces and letter sizes.

Dot Matrix

The dot matrix printer is the more common type of impact printer in use today. The main component of the dot matrix printer is a printhead consisting of rows of electromagnetically activated pins which which create tiny dots on the output media. The pin arrangements most commonly used are 9, 24, 48 pins arranged in rows.
Dot matrix printers are capable of producing more varied output than block impact printers as the pin design permits printing in different fonts, font sizes, print densities, and even allows the printer to produce crude graphic images.
Like the block impact printer, dot matrix printers are noisy and larger continously printing machines are usually kept in sound dampening boxes.

Ribbons & Rolls

Unless the type of paper being used is pressure sensitive, Impact printers require some form ink to create the output. The most common used supplies are described below.

Inked Ribbons

Inked ribbons are found in a wide variety of types and designs. They consist of a cartridge or spool which holds a long length of nylon or mylar ribbon which is coated with ink.
Nylon ribbons are usually woven like cloth from strands of nylon and coated with a vegetable-oil based ink. The density and texture of the nylon weave as well as the thickness of the nylon strands are important factors in determining how much ink the ribbon can hold and how well the ribbon will stand up to repeated impact strikes. The type of inks are also important for the application in which the printer is being used. Standard dot matrix ink is a zero solids lubricating material which not only provides the outputs appearance but also lubricates the pins on the printhead. However standard dot matrix ink offers poor water resistance and archival qualities. For impact printers which are used to print record documents, ribbons are coated with inks containg 5-10% carbon solids which increase the archival quality of the output.
In dot matrix printers, nylon ribbons are generally recirculated to use as much of the ink as possible and are replaced when the printed output shows signs of fading. Cartridge versions provide a continous loop of ribbon while spool versions usually reverse direction when they reach the end of the spool.
Mylar ribbons are much different from nylon ribbons although the general appearance is the same. Mylar ribbons are also found in cartridges and spools. However, Mylar ribbons are non-woven plastic which is coated with a dry black carbon. The carbon is water and fade resistant and provides sharp output on most paper. Mylar ribbons are single pass ribbons and must be replaced when the ribbon reaches the end.