3.4 Printers and Scanners

3.4.a 2D Printers

There are three types of 2D printers: Laser printer, Inkjet printer and Graphics Plotter.

Lazer Printers

StepOperation on
Paper
Operation On
Drum
1Given electric charge (+).Given (-) electric charge.
The drum starts to spin.
2A laser beam is directed by a mirror and lens, moving across the drum (from left to right) to remove charge.

For each location, if:
* Laser off: Charge remains on drum
* Laser on: Charge removed from the drum.
[Repeat step 1-2, until a full page of electrostatic image is created.]
3Drum is coated with charged (-) toner.
The toner only sticks on the discharged parts of the drum.
4The drum rolls over the paper.
The ink is transferred to the paper.
5The paper pass through heated rollers to fuse the toner particles onto the paper.
6The drum is discharged.
Excess toner is collected.
[Page print complete. Start form step 1 again.]

Inkjet Printers

Smaller in size, cheeper to buy, but quality is poorer.

Process:

  1. The printhead moves across the sheet, deposing ink.
    • Release: Either by thermal bubble or piezoelectric.
    • Ink: Cyan, Magenta, Yellow, and black. (NOT RGB!)
      • By a combination of different ink, any color could be formed.
  2. The paper moves forward a fraction.
  3. Repeat step 1-2.

Print accuracy

Two factors denominate the accuracy:

  • Mechanical Precision
    • e.g. How far to move the paper for every sweep of inched
  • Nozzle accuracy
    • i.e. How many nozzles are in the printhead (>Thousands)

Graphics Plotter

Uses a pen to write on a large sheet of paper. Allows the drawing to created directly from vector files – instead of being bitmapped.

The paper is constrained by sprockets, which moves the paper. The pen can move up and down at any time to draw / not draw.


3D Printers

  1. The design is splitter into layers.
  2. For every layer, the nozzle squirt material onto the previous layer.
    • Some way is ensured that the layers are welded together.
  3. Steps 1 and 2 are repeated.

3.4.b Scanners

For traditional 2-D scanners:

  1. The paper is fixed.
  2. A light source moves from one end of sheet to another.
  3. The reflected light passes through mirror and lenses to a charged-coupled device. (CCD)
    • The CCD has an array of photo-sensitive cells. It creates an electrical response proportional to the light intensity.
    • An analogue-to-digitial converter is required to create the bitmap image.
Next page: 3.5 Sound

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