Ever wonder why the word “laser” is in the term “Laser Printer”? Is it an actual laser, or is this just some gimmick to sell more printers?
To find out, I painstakingly disassembled the guts of a 1990’s era Apple Laserwriter 16/600 printer. My approach: keep removing hunks of metal, motors and plastic until I found the laser. This activity served to kill an otherwise unoccupied afternoon during a break in business school. Click for photos and a detailed breakdown.
Indeed, there is a laser, which is part of an assembly of mirrors, motors and lenses:
So whats going on here? A laser printer, much like a photocopier, works by creating a static charge on a rotating drum. This drum is then exposed to fine dust which collects where the charge is, and then the dust is fused onto the paper by heating coil. In a regular office photocopier, a system of lenses takes the reflection of your original document and shines this light on the drum. In a laser printer, this task is handled by a small laser.
Here is the close-up of the laser:
This laser is pointed at a spinning octagonal mirror:
As you can see, the mirror part is on the edges of this spinning disc.
My guess is that this scatters the laser light against the a series of lenses which project the light on the drum.
Software inside the printer must generate a signal of laser pulses based on where the disk is known to be at any given instant. I guess the principal is very much like the scanning electron beam in a television set. The dot moves so quickly that it effectivly paints an image against the drum.