A+ Core 1 (220-1101) Cram Notes

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4. Printers

4.1 Explain the differences between the various printer types and summarize the associated imaging process

1. Laser printers

  • The following are the 6 steps in the ElectroPhotographic (EP) print process of Laser Printer:

    • Cleaning: Cleaning the photosensitive drum includes residual toner left on the drum and removing the electrical charges left out on the drum. The physical cleaning is done with a rubber blade and the electrical charge cleaning is done with erasure lamps.

    • Charging: The next step in printing, is to charge the photo sensitive drum with high negative charge, this is done with the help of a corona wire.

    • Writing: A laser (type 3) sweeps the entire length of the drum, creating the static image of the matter to be printed. The places where the laser travel, the highly charges are neutralized. Other places of the drum, it remains highly negatively charged.

    • Developing: Now drum gets in close proximity to the toner. Because the toner is negatively charged, it gets attracted to the areas where the drum is neutral. It will not be attracted to the places where the drum is highly negatively charged. Thus the image of the page to be printed formed on the photosensitive drum.

    • Transferring: Now, the toner on the drum gets attracted toward the paper, by using highly positive charges developed on the surface of the paper. The "transfer corona" is used to generate highly positive charge on the paper surface and to attract the toner from the drum. Thus the image of the page to be printed formed on the paper. But still, the toner is loose and can get easily smeared.

    • Fusing: In order to permanently bond the toner particles to the paper, the paper is passed through rollers. One of the rollers, the non stick roller is heated by a high intensity lamp, generating the heat necessary to bond the toner to the surface of the paper.

  • Problems associated with laser printers and probable causes:

    • Speckled pages: The causes for this may be

      • The failure to clean the drum after printing properly, or

      • The drum might have developed scratches.

    • Blank pages: The causes for white pages may be

      • The toner would have dried out, replace the toner.

      • The transfer corona, that is responsible for transferring the toner to the drum might have failed.

      • The High Voltage Power Supply (HVPS) failure will also result in white pages.

    • Ghosted Images: Ghosting occurs when previously printed pages are printed again, though much lighter than the present image. The most likely cause is that the erasure lamp might not be working properly, thus leaving some charges representing the earlier image left on the photosensitive drum before new image is written. Also check the cleaning blade, which is responsible for scraping the residual toner.

    • Smudged images: If the fusing fails, the toner will not bond with the paper. Check the halogen lamp responsible for heating.

  • Typically, a laser printer maintenance kit consists of fuser fixing assembly, pickup rollers, transfer roller, gloves, and instruction manual./p>

2. Impact printers

  • Impact printers are capable of printing multipart forms, since they can give necessary impact to print to multiple forms simultaneously.

  • ECP (Extended Capability Port) has less control overhead and best suited for transferring large chunks of data, such as between the computer and laser printer.

3. InkJet Printers

InkJet Printers is the generic name given for contact less printing using ink. Friction feed is most commonly used with laser printers, and Inkjet printers. One needs to check the calibration for the inkject printer if it is not printing properly. If it doesn't help, then check the ink cartridge if it requires replacement.

4. Thermal printers

Thermal printers require a special kind of paper, called thermal paper. This paper is sensitive to heat, and the printing is produced by thermal heat applied on the paper by the print head.

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