Laser Printer Applications Manual

An Intel 80960SA computer chip controls both the memory and the printing
mechanism in the printer, called the print engine. The printer stores a whole
page in RAM before printing it. (If a page is so dense that it overflows
memory —amost unlikelyevent—the Star LaserPrinter4HI printsthe page
on two sheets.)
1.1.5 The Print engine
It’sthe printengine thatforms the actualcharacters and graphics. The engine
directs its laser, a pinpoint stream of lightpulses, through mirrors and lenses
onto the surface of a positively-charged rotating drum.
r“i””r
Lens
Laser beam
Scanningmirror
ctor laserdiode
~Photosensitive drum
As the laser scans, it“draws” the page-map stored in your printer’s memory.
Wherever a light pulse strikes, that tiny part of the drum drops to a neutral
electricalcharge. That spotthen attractsfinetonerpowder asthedrum rotates
past the powder compartment.
As the drum rotates further it meets the paper. The paper itself is negatively
charged by passing by a fine corona wire. Since opposite charges attract, the
negative paper clings to the positive drum. Then heat and pressure from a
roller melt or,fusethe dotsof toner onto the paper, precisely reproducing the
image.
Finally the paper slides intothe output bin.The paper usually comes out face
dowmso it stacks in the correct sequence.
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