each pass across the page, the controller sends a signal to the paper feed motors to ad-
vance the paper rollers that pull the paper forward into position for the next printhead
pass. At the end of the bitmap file, a command ejects the paper. If another page is to be
printed, a sheet of paper is loaded and the process starts over.
The paper flow controls are provided in the bitmapped data file used to print the doc-
ument. However, the printer controls some parts of the paper flow process, including
when the printer is out of paper, when a paper jam occurs, and when the printhead is not
moving. In these cases and a few more, the printer’s controller signals the computer,
which in turn signals the application or printer drivers to cease sending the bitmapped
data file and to display an error message to the user.Printer Drivers
The workhorse of the inkjet printing process is the software device drivers that perform
the graphics conversions from RGB to CMYK, perform the calculations used in
halftoningoperations,andmanagetheflowofthebitmappeddatafilefromthecomputer
to the printer. The printer driver controls the applications and hardware with which the
printer will work and manages the communications between the printer and the com-
puter to keep the printing process flowing smoothly.
A printer’s device driver is usually included with the printer on a diskette or
CD-ROM, but newer versions of device drivers are constantly being made available,
along with updated BIOS systems and firmware for the printer. Most manufacturers now
have an alert system that will announce via e-mail or fax when new drivers are available
for a particular printer model.Laser Printers
A laser printer, like the one shown in Figure 17-13, is an electrophotographic (EP) printer
that uses the same basic technology found in a photocopier. In general, the laser printer
has become popular as an office printer, but as prices come down, it is also becoming
popular as a home system printer. Laser printers produce clean documents quietly, two
of the major reasons for its popularity, but its print quality is the primary reason why laser
printers are chosen over other forms of printers.
A laser printer produces a printed document using a focused beam of laser light and a
rotating mirror to reproduce the image of a document as an electrostatic charge on a pho-
tosensitive drum. Toner, the “ink” of the laser printer, is added, and the charge on the
drumattractsandholdsitintheimageofthedocument.Asheetofpaperisfedfromthepa-
per supply and electrostatically charged. The paper is rolled over the drum and picks up
the toner. Heat is then applied to the toner, it fuses with the paper, and the document is
completed and placed on the output rack of the printer. To provide an overview of how
the laser printer works, this process has been overly simplified, but in essence this is what
happens when a document is printed on a laser printer. It is also the same process used
when a document is copied on a photocopier.Chapter 17: Printers^423