OUTPUT DEVICES: PRINTING DEVICES

• Output devices take data produced by a computer and turn it into a human-readable form (such as a printed document or an image on a screen)
• Output from a computer is sometimes used to operate another device (e.g. a loudspeaker or an actuator)
• The most common output devices are: printers, screens, loudspeakers and multimedia projectors

Printing Devices

Inkjet printers

2 types of inkjet printers:

• Thermal bubble
• Piezoelectric crystal

Thermal bubble

• Droplets of ink are produced using a thermal bubble
• Behind hundreds of print nozzles, there are tiny resistors that create heat (the temperature momentarily exceeds 1000°C)
• The heat causes the ink to vaporize and form tiny bubbles
• As each bubble expands, ink is ejected onto the paper
• As it cools, the bubble collapses and draws in fresh ink and the process continues until the page is printed

Piezoelectric crystal

• A small piezoelectric crystal is located at the rear of each ink reservoir of each nozzle
• When the crystal receives a small electric current, it begins to vibrate in and out
• As it vibrates inwards, ink is ejected onto the paper
• As it vibrates outwards again, new ink is drawn in to replace it

Printer interrupts

There are 2 types of interrupts:

Hardware and software 

• Interrupts are signals sent to the processor that cause it to stop what it’s doing in order to service the interrupt, for example:
  • When a printer makes a request for more data to be sent, it sends out an interrupt and the processor acts on the request
  • Or, if the printer runs out of paper it also sends an interrupt which the processor services and sends a message to the printer driver to display an error message on the screen

Drivers and buffers

Printer drivers

• Software that converts the data to be printed in a form specific to a given printer
• Their purpose is to allow applications to carry out the print job without needing to be aware of the specific format details of the printer being used

Printer buffer

• Temporary memory which stores data until it is ready to be used (in this case, to be printed)
• This allows the processor to carry out other tasks whilst the relatively slow printing process can carry on in the background

Laser printers

• Laser printers use dry toner rather than liquid ink as in inkjet printers
• They rely heavily on the use of electrostatic charges to produce text and images on paper
• Unlike inkjet printers, they produce a whole page at a time rather than print line-by-line
• Although no faster than an inkjet when producing one-off documents, they are better suited to large print jobs (e.g. 5000 leaflets)

Dot matrix printers

• Dot matrix printers are sometimes known as impact printers. Similar to a typewriter, they strike an inked ribbon which imprints dots to form letters on the page
• Useful where multipart stationery is required
• Can work effectively in damp or dirty atmospheres
• Noisy, poor print quality and expensive to buy

3D Printers

• 3D printers can print using plastic filament, powdered resin, ceramic or metal powder, or paper
• Intricate objects can be printed, including hollow areas

Uses of 3D printing:

• Education
• Prototyping and Manufacturing
• Medicine
• Construction
• Art and Jewelry

Additive and subtractive manufacturing

• Additive manufacturing builds up an object layer by layer
• This is very different to subtractive manufacturing where an object is made by removing material (such as a sculptor or a lathe)
• For example, a statue could be made from powdered stone and built up layer by layer
• A sculptor could otherwise remove stone from a large block to make the same statue

Direct and binder printing

• Direct 3D printing is based on inkjet printer technology
• With 3D printers, the print head doesn’t just move left to right, but it also moves up and down to create the 3D model
• Binder 3D printing involves two passes to produce each layer of the object
• One pass sprays dry powder and another pass sprays a binder (a type of glue) which makes the powder stick together to build a solid object

Applications in medicine

1. Manufacturing of prosthetic limbs or orthotics
   1. Huge reduction in cost and greater accuracy in matching limb to individual patient
2. Reconstructive surgery or general surgery
   1. Surgeons can “try out” a procedure first to ensure actual surgery is more accurate; can produce very accurate parts for surgical procedures

Applications in manufacturing and art

• Manufacturing parts for cars
• Very old cars are very likely to need parts no longer manufactured; by using an existing part as a blueprint it is possible to print new components at a fraction of the cost
• Prototyping for design, fashion, and art can save huge costs