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Printers
There are several different types of printers and you will need to know their print processes and common issues.
Feed Mechanisms:
- Pin Feed - Paper has perforated strip on each side that contains holes that fit onto pins that are rotated by a motor in the printer.
- Friction Feed - Typically uses rollers that press against the platen or drum that rotate forcing the paper through the printer.
Thermal Wax - Thermal wax printers use a roll of cellophane like film that has colored panels on it. The file is rolled past a print head containing thousands of heated elements that burn the wax from the film onto the paper.
Dye-Sublimation - The print process is very similar to the thermal wax printers, however, there are a few differences. Dye-sublimation printers use film that contains dye rather than wax and must be used with specially coated paper. More importantly, they offer extremely high quality due to their continuous tone printing. Continuous tone refers to the fact that the dots put down by the printer can vary in size and intensity rather than using a dithering process like other print processes. For this reason, dye-sub printers can product photographic quality output.
Dot Matrix - Uses an impact printing process whereby a matrix of pins imprint an image. Uses a Ribbon. ROM programs the Fonts.
Troubleshooting:
- Smudges can be caused by the ribbon tension being too high
- Broken printhead pins can cause incomplete or missing characters.
- If the tops of characters are missing, the printhead is misaligned with the platen and needs to be reseated or the printhead carriage may need to be adjusted.
- If the print gets lighter on the page from left to right, the printhead distance from the plate is uneven and will need to be adjusted.
Ink Jet(or Bubble Jet) - No contact therefore quiet. Works by spraying ink onto the paper in a sequential fashion. Similar in operation to a dot matrix printer.
Troubleshooting:
- Never refill cartridges which are causing problems. The head is part of the cartridge so replace the entire cartridge.
- If the output is disfigured or wavy, make sure that the paper thickness level is in the correct position. If it is, then the paper feed rollers probably need to be replaced.
Laser Printers - Uses a Page Description Language (PDL) to print a page at a time. Main components are:
- Cleaning Blade - This rubber blade removes excess toner off the drum after the print process has completed.
- Photosensitive Drum - The core of the electrophotographic process. This component should not be exposed to light.
- Primary Corona Wire - Highly negatively charged wire erases the charge on the Photosensitive drum to make it ready for another image.
- Transfer Corona - A roller that contains a positively charged wire to pull the toner off the photosensitive drum and place it on the page.
- Toner - Plastic Resin. Naturally Negatively charged
- Fusing Rollers - Bonds the toner particles to prevent smearing. Uses heat to bond. A thermal fuse prevents the fuser from overheating.
Troubleshooting:
- Blank Pages - Can be caused by No Toner, Transfer Corona Failure or HVPS Failure.
- Speckled Pages - Due to a failure in the cleaning step of the EP Process. Or a scratch on the EP drum.
- Ghosted Images - Caused if the erasure lamp doesn’t erase all of the image from the EP drum before the next page is printed.
- Smudged Images - The fusing process must have failed. The heating elements in the fusing rollers may be faulty.
- Dark spots - Can indicated toner buildup at some point in the paper path. Running blank sheets through it may clear problem.
- Jams in laser printers usually occur in the paper pickup area, the fuser or the registration area. They can be caused by incorrect paper settings or media types.
Electrophotographic Print Process(EP):
The process concerned with putting the image on the page. Follows Six processes.
- Cleaning - The Drum is cleaned and electrically erased.
- Charging - The Drum is negatively charged to -5000Vdc. Done by the Primary Corona.
- Writing - The Laser sweeps the length of the drum applying the image. The Laser reduces the negative charge on the drum where the image is going to be.
- Developing - The Toner is transferred to the area on the drum which has been swept by the laser.
- Transferring - Once the image is on the drum the paper is fed through and the transfer corona wire attracts the image from the drum to the paper.
- Fusing - The Fusing rollers heat up and pass the paper through bonding the toner to the paper. Uses a Non stick roller surface.
Physical Connections:
Older printers utilize a RS-232 connection that can either be 9 or 25 pin serial port and cable. The cable should be less than 50 feet long (15.25 meters). Serial configuration requires that the port be configured with parity type, speed, protocol and character frame must be configured.
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Parallel connections utilize a DB-25 port(left) on the computer to connect to the printer. Parallel cables should be less than 10 feet(3 meters). Most parallel ports are now Extended Capability Ports (ECP) which offers increased performance over previous standards. Both the computer's parallel port and the peripheral's port must support ECP in order to use it. |
Many newer printers use USB connections and higher-end printers have rj-45 network connections and can be integrated with standard networks. Older models may have coaxial network connections. Another popular connection solution is the print server such as a Jet-Direct interface that connects to the printers parallel port and has an RJ-45 connection at the other end.
Further Reference:
http://www.techtutorials.com/tutorials/printing.shtml
http://www.techtutorials.com/Hardware/Printers/
Font Types:
- Bitmap - composed of dots called pixels.
- Vector - Uses mathematical formulas to plot lines. Requires less storage space than bitmap.
- TrueType - Outline fonts for Windows only.
Scanners
Scanners are comprised of a Charge Coupled Device(CCD) array. This array is like a series of "eyes" that read and record light intensities and stores them in digital form. This is achieved when the scanners internal light source passes over the image that is being scanned.
Scanners come in three basic types. The simplest type of scanner is the hand held in which the scanning device is moved across images or text. The scanner reads the information directly. A Page scanner works by inserting a page into the top of the scanner which is pulled via rollers through the scanner. The most common type of scanner is the flatbed scanner which allows you to place a image or document on the top of its surface, much like a photocopier. Scanner quality is measured in DPI or dots per inch. 300 DPI is usually adequate for normal scanning, however, modern scanners can scan at resolutions of 9600 DPI and higher. The higher the resolution, the larger the resultant scanned file will be.
Scanners are connected to the system board via a SCSI, Parallel or other proprietary connection method depending on the scanner model.
Further Reference:
http://www.pctechguide.com/18scanners.htm
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