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This month, we are going to do something that's a little different: rather than dealing with specific servicing problems and solutions, we are going to present a brief overview of computer printers and how they work. Note that some of the following information was sent to my Web site by others; in those cases, I have given credit to the original contributor.
Let's start off by taking a look at dot-matrix printers. In that printer, a set of steel pins - as few as 9 and as many as 24 - strike the paper through a fabric or carbon-film ribbon. The pins are activated by solenoids that are controlled by the printer's control logic. Multiple passes are sometimes used to increase the effective number of pins and improve print quality (letter versus draft mode).
For text, an internal character generator (ROM) converts ASCII codes to pin-firing patterns. For arbitrary graphics, the actual bitmap is read out and used to control the pin drive. The paper, carriage, and sometimes ribbon movement are all controlled by stepper motors. Those motors, their drivers, or the interconnect cables, are the most common problem areas. Note that dot-matrix printers are about the only type of impact printers still in wide use, and fewer and fewer are being sold each year.
Ink-Jet Printer Basics
Much of what follows on ink-jet printers comes from Tony Hardman (firstname.lastname@example.org): There is a US publication called The Hard Copy OBSERVER from Lyra Research Inc., Tel: 617-322-0708. It discusses the latest technologies and who does what. It may not cover the print-head technology in very great detail, but it is still a good read if you are into print technology in general. There are many companies that sell variable print processes. One I have heard of is RALFLATAC. They publish a brochure that presents an excellent brief of most technologies available for printing. They have locations in the UK (and around Europe) and the US. By telephone, you can reach them in the UK at 01732-583661, and in the US at 704684-3931. I have no idea if you can get copies of either publication from them, so here is a very brief description:
There are two main types of ink-jet printing - continuous ink jet (CIJ) and drop-on-demand (DOD) impulse printing. Each of those can …