10/24: Output: Printers

• Types of printers: laser, inkjet, dot-matrix printers

• Other types: plotters, label printers, digital presses, photo printers, electrostatic printers, LED printers

• How color printing works

• What to look for in a printer

Printers: General

• Printers– two main groups:

impact (dot-matrix, daisy-wheel) & nonimpact (laser, inkjet, thermal)

– other types: plotters, label printers, digital presses, photo printers, large-format printers

– color printing

dot matrix printer image courtesy of epson.com, others courtesy of hp.com

Impact Printers• Dot-Matrix printers: Pins are

pushed by solenoids to hit a ribbon in front of the paper.

• Daisy-Wheel printers: Letters are pushed to hit the ribbon in front of the paper.

• Stamp ink onto the paper.• Advantages: cheap, reliable,

low CPU demand, multiple-form copying

• Disadvantages: loud, slowimages courtesy of How Computers Work and Brother.com

• The ink cartridges have tiny heating elements that cause microdrops of ink to heat up and expand, shooting out of the nozzle and onto the paper.

• Advantage: cheap color printing

images courtesy of HP.com and How Computers Work

Non-Impact: Inkjet Printers

• The ink cartridge(s)– nozzle – firing chamber– path from reservoir – thin-film resistor

Cross-section of a nozzle.

How does the ink get out? One of two ways: The Thermal method or the Piezo-Electric method.

The Ink Cartridge

Nozzle

Firing Chamber

Resistor

How the ink gets out: thermal method

• Used by Hewlett Packard & Canon

• A thin-film resistor is heated by electric current.

• The resistor heats up the ink that is next to it.

How the ink gets out: thermal method

• The ink- now gaseous - expands, forming a bubble.

• The bubble pushes out the rest of the ink in the firing chamber.

Nozzle

Firing Chamber

Resistor

How the ink gets out: thermal method

• The resistor cools, causing the bubble to shrink.

• The shrinking creates a vacuum, which draws new ink from the reservoir.

Nozzle

Firing Chamber

Resistor

• The piezo method uses a flexing, swelling crystal instead of heat to push the ink out.

Laser Printers• Deposit toner onto the paper,

then melt it to make it permanent.

• Cheaper by the day – per page printing costs are very low.

• Faster than inkjet printers.

• Very quiet.

images courtesy of How Computers Work

Laser printing

• The pattern to be printed is set up in a grid of black areas and white areas.

• The laser beams, horizontal line by horizontal line, this grid of dark areas.

Laser printing

• When the drum is hit with the laser beam, it electrically charges the coating at that spot.

• In HP & Canon printers, the coating is positively charged.

Laser printing

• As the drum rolls by, the positively charged parts of the coating on the drum attract the toner particles.

Laser printing

• The sheet of paper touches the drum coated in toner.

• The toner jumps to the paper from the drum because the paper is more strongly charged than the drum.

Laser printing

• The paper, with the toner particles, goes to the fusing rollers. The rollers use pressure and heat to bind the toner to the paper permanently.

How Color Printing Works

• subtractive color– monitors use additive

color: all colors combine to get lighter shades

• printers combine colors to get darker shades

• all colors together create black

Looking at printers in ads

• Go to http://www.buy.com

• things to note when comparison shopping:– what YOU will be using the printer for– ppm (pages per minute) in b&w, color– size limitations of paper– paper tray capacity– price (and price of ink/toner cartridges)– dpi (dots per inch) – print quality capabilities– (inkjets) type of black printing: separate cartridge?