(^430) PC Hardware: A Beginner’s Guide
Primary corona Also called the main corona or the primary grid, this device
forms an electrical field that uniformly charges the photosensitive drum to a
negative 600V prior to the image of the document being placed on the drum
by the light source.
Transfer corona This mechanism causes the page image to move from the
drum to the paper. The transfer corona charges the back of the paper, and the
charge pulls the toner from the drum onto the front of the paper. As the paper
exits the transfer corona, a static charge eliminator strip reduces the charge on
the paper so that it won’t stick to the drum. Not all printers use a transfer corona;
some use a transfer roller instead.
Fusing rollers The toner is melted permanently to the page by the fusing rollers
through pressure and heat, usually between 165 and 180 degrees Celsius. The
fuser, and not the laser, is why the pages coming out of a laser printer are hot.
Controller The controller is effectively the motherboard of the laser printer.
It communicates with the PC, houses the memory in the printer, and forms
the image printed on the page. The controller board also holds the memory
of the printer. The memory on a laser printer can be expanded and adding
memory allows the printer to reproduce larger documents or graphics in
higher resolutions or to support additional soft fonts.
Color Laser Printers
Monochromelaserprintersusethesamehalftoningtechniquesasthemonochromeinkjet
printer (see “The Inkjet Printing Process” earlier in the chapter). The difference, of course,
is that the image of the document to be printed is detailed onto the print drum all at once
instead of as a series of printhead passes. However, before this can be done, the print
commands and image data must be converted into the pattern of dots that will produce
the document.Printing Color Documents
The Raster Image Processor (RIP), which is part of the internal control circuitry of the la-
ser printer, translates the string of characters and printing commands sent to the printer
by the computer into the dots that make up the image the printer will transfer to paper.
The RIP computes the position of each dot on the page and creates an image of the docu-
ment in the printer’s memory, where one bit of memory corresponds to each dot position
of the image.
The controller than directs the use of the laser (or LED or LCD) light source to create
the dot pattern on the drum. In a laser printer, the laser beam is focused on a multisided
mirrorthatdirectsthebeamontothedrum.Eachplacethebeamtouchesrepresentsadotin
theimage.LEDandLCDprintersturntheirlightsourcesonandoffforeachofthedotpo-
sitions on the drum.
The number of dots in use to create printed pages varies with price and manufacturer.
Laser printers commonly offer resolutions of 400 to 1200dpi (dots per inch), with 600dpi