In this section, you will probably learn more about printers than you ever wanted to. There are several different types of printers and you will need to know their print processes and common issues. First we'll take a look at the common connection types and then dive into the various different types of printers.
Very old printers utilized a RS-232 connection that was either a 9 or 25 pin serial port and cable. The cable should be less than 50 feet long (15.25 meters). These connections required that the port be configured with parity type, speed, protocol and character frame.
This connection type was eventually replaced with a higher speed parallel connection which have recently become obselete. Parallel connections utilize a DB-25 port on the computer to connect to the printer. The newest parallel ports were Extended Capability Ports (ECP) which offered increased performance over previous parallel standards. Both the computer's parallel port and the peripheral's port had to support ECP in order to take advantage of the higher speeds. Parallel cables are limited to less than 10 feet (3 meters) in length.
Most current printers use USB, firewire, or ethernet (RJ-45) network connections. More expensive models are available that offer WI-Fi or Bluetooth connections. USB and Firewire connected printers can be shared over a network, however, the host computer that it is connected to must be left on in order for others to print to the printer. This is an advantage of the newer network printers which do not have this limitation.
Dot Matrix printers for home use are nearly obselete having been replaced with faster, higher quality varieties, however, you may still come across them at some businesses. In fact, most cash registers use a dot matrix printer for printing out receipts. Dot Matrix printers use an impact printing process whereby a matrix of pins imprint an image on a ribbon. The ink from this ribbon is transplanted to the paper. Very old dot matrix printers used a pin feeding system that used paper with a series of holes along the sides of the paper (see image to the right). After printing the perforated edges with the holes are torn off. Newer models of dot matrix printers typically use a friction feed (rollers) mechanism.
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.
These are not a very common printer type, however, you will run across them in use for specialty applications. Thermal wax printers use a roll of cellophane like film that is made up of colored wax panels. These panels are either cyan, magenta, and yellow (CMY) or cyan, magenta, yellow, and black (CMYK). This film is rolled past a printhead containing thousands of heated elements that burn the wax from the film onto the paper. When the roll is all used up, simply replace it with a new one. These printers are very slow because the ribbon prints each color separately so it takes 3 or 4 (depending on the roll type) panels to pass a page to complete it. These printers typically print 300 dpi at about 1 ppm.
The print process is very similar to the thermal wax printers, however, there are a couple of differences. Dye-sublimation printers use film that contains dye rather than wax and must be used with specially coated paper. Second, dye-sub printers do not melt wax from the ribbon to the paper; the printhead turns the dye into gas which then solidifies on the paper. Most 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 depending on the heat output by each element on the printhead. This is in contrast to the use of a dithering process like other print processes. For this reason, dye-sub printers can produce photographic quality output and are used for desktop publishing, medical imaging, and other high-end applications. The image to the right shows an example of a large poster-size dye-sub printer.
Ink jet printers are the most common types of printers for home use because of their good quality and affordable price. The image to the right shows the printhead of an ink jet printer. This particular one has an extra black cartridge, however, most have CMYK cartridges. Each of these cartridges contains liquid ink that is sprayed onto the paper through very tiny nozzles in the printhead. The printhead makes a pass across the width of the page printing a strip. Then the paper is fed a little and the printhead passes back across the page printing another strip. This process continues until the whole page is printed. Ink jets can print 2400+ dpi at 24+ ppm which is a big part of their attraction.
Occasionally, the nozzles on the printhead can become clogged. Most printers have a software program built into the driver that will tell the printer to do a printhead cleaning. In some cases this can/must be activated from the front panel of the printer. Do not run this process unless necessary as it uses a lot of ink. If the printer has a bin for collecting the excess ink from the cleaning process, make sure you empty it.
If the output is disfigured or wavy, make sure that the paper thickness level is in the correct position, if applicable. If it is, then the paper feed rollers probably need to be replaced.
Solid Ink printers were invented by Tektronix which is now owned by Xerox. Solid ink printers are very fast and offer vibrant colors because of the inks that they use, and a printing process that produces continuous tone output. These printers use solid blocks of wax ink that are melted down into the printhead that sprays the ink onto a drum. The paper is then rolled over the drum which transfers the ink to the paper. These printers are pretty expensive.
Clogged jets - The most common problem with solid ink printer also occurs on ink jets. Occasionally some of the jets on the printhead get clogged. To remedy this, run the cleaning procedure from the front panel or driver of the printer. Like ink jets, this uses a lot of ink.
Jams - Most jams are caused by dirty rollers. These can be cleaned with isopropyl alcohol and a lint-free cloth.
Waste Ink - Some solid ink printers have an ink waste bin where excess ink goes. This needs to be emptied periodically or it may overflow.
Laser printers are very popular in offices, but not so much for home use due to their initial cost and cost of consumables (items which must be periodically replaced). Laser printers use dry ink, called toner, static electricity, and heat to place and bond the ink onto the paper. This is known as the electro-photographic process. Before we exam the steps of this process, let's first take a look at some of the components of a laser printer:
Cleaning Blade - This rubber blade or felt pad removes excess toner off the drum after the print process has completed.
Photosensitive Drum - The core of the electro-photographic process. This component should not be exposed to light and needs to be replaced periodically. Also known as an "imaging unit" or "imaging kit". See image
Primary Corona Wire - Highly negatively charged wire erases the charge on the Photosensitive drum to make it ready for another image. Needs to be cleaned periodically.
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 that is the ink for a laser printer. Naturally negatively charged. See image
Fusing unit - Bonds the toner particles to prevent smearing. Uses heat to bond. Needs to be replaced periodically as the fusing platens (rollers) get worn down. Often the thermal fuse will blow and then you will know it is time to replace the unit because it will no longer heat up. Note: Fusers can reach temperatures over 200 degrees - make sure you let it cool before handling it. See image
Although slightly repetitive, let's go through the 6 steps of the electro-photographic process:
Cleaning - The drum is cleaned by the cleaning blade and the excess toner goes into a waste bin. The drum is electrically erased by the erase lamp leaving the drum electrically neutral.
Charging - The photosensitive drum is negatively charged by the primary corona.
Writing - The Laser sweeps the length of the drum removing the negative charge where the toner should be applied.
Developing - The toner is transferred to the area on the drum which has been swept by the laser. Remember that toner is negatively charged and like charges repel. This means that toner will not be applied to areas where the laser did not remove the negative charge made by the primary corona.
Transferring - Once the image is on the drum the paper is fed through. The transfer corona uses a positive electrical charge to attract the negatively charged toner and pull it off the photosensitive drum onto the paper.
Fusing - The paper passes through the fuser unit. The non-stick fusing rollers use heat and pressure to bond the toner to the paper.
Blank Pages - Can be caused by no toner, transfer corona failure or a power supply failure. If you have installed new toner cartridges, make sure that you remove the seal. If the toner cartridges aren't empty, try reseating them. If still having the problem, look at the photosensitive drum and if the image is still there, it means the transfer corona or power supply has failed.
Speckled Pages - Due to a failure in the cleaning step of the EP process, or a scratch on the photosensitive drum.
Ghosted Images - Ghosting usually occurs with images that require a large amount of toner. When the toner cartridge canít provide sufficient toner, a residual electrical charge can be left on the drum that will repeat down the length of the page. If your printer has a toner density setting, try reducing the density. Laser printers can be very particular about the paper being used. Try higher quality paper. Also make sure that the humidity is reasonable.
Smudged Images - The fusing process must have failed. The heating elements in the fusing rollers may be faulty.
Dark spots - Can indicate toner buildup at some point in the paper path. If the spots repeat at regular intervals, there may be toner built up on the fuser rollers. Running blank sheets through it may clear problem. It is important to periodically clean the printer. The best way is with a low static vacuum. Canned air will work, but will blow toner everywhere.
Unfused Toner - If pages come out with loose toner that can be smudged, it means that the toner isn't being fused to the paper. First try media that meets the printer's specifications. If still having a problem, replace the fuser.
Jams in laser printers usually occur in the paper pickup area, the fuser or the registration area. They can be caused by dirty rollers, incorrect paper settings, media types, or environmental conditions.
Page Description Languages:
PDLs are programming languages used to "describe" the contents of a page in terms that a printer can understand. Adobe's PostScript and HP's Printer Control Language (PCL) are the 2 most common PDLs used in desktop publishing. When sent to the printer, a document is parsed by the driver which converts the document into the language that the printer understands and instructs the printer how to format the document. This is why it is so important to use the correct driver for your printer. If you use a PCL driver for a PostScript printer, most likely a bunch of garbled text or nothing will print out.