11. Computer Peripherals – Part III

1. 11. Computer Peripherals – Part III Chapt. 10

2. Plan • Printers • Scanners • Keyboards • Pointing Devices

3. † † Impact (the others are non-impact) Printers • Four main types: • Dot matrix • Laser • Ink jet • Thermal dye transfer and thermal wax transfer

4. Impact vs. Non-Impact • Impact printers physically transfer a dot or shape to the paper • Of those in the preceding slide, only dot-matrix uses impact printing • Non-impact printers spray or lay down the image with impact • Impact printers remain important because they can print multi-part forms

5. Printers • Four main types: • Dot matrix • Laser • Ink jet • Thermal dye transfer and thermal wax transfer

6. How it works A print-head moves back-and-forth in front of forms (paper) on which characters or graphic images are transferred. The print-head contains numerous wires, typically from 9 to 24. Each wire is part of a solenoid-like unit. A pulse applied to the solenoid creates a magnetic field which forces the wire to move briefly forward then backward. As the wire moves forward, it presses against a print ribbon containing ink. The impact transfers an ink dot to the paper. The paper is supported from behind by a platen.

7. Demo (well, sort of)

8. One print wire Side view Dot Matrix Print Head Print wires (e.g., 12) Front view

9. Paper Printwire Platen Ribbon Side view Front view Dot Matrix Impact Printing Side view

10. Specifications • cps • characters per second • Varies by quality of print (e.g., draft vs. final) • lpm • lines per minute (related to cps) • Forms • Maximum number of layers of paper that can by printed simultaneously • Specified as n-part forms (e.g., 4-part forms) • mtbf • Mean time between failure (e.g., 6000 hours)

11. Noise • Dot matrix printers are notoriously noisy! • This is a major disadvantage in many environments

12. Uses • Primarily two: • Any situation that requires multi-part forms • Small printers, such as • Calculators • Adding machines • Point-of-sale terminals

13. Dot Matrix Printer Example - 1 • Specifications • 800 cps • 400 lpm • 6-part forms (max) FormsMaster 8000 by Printek, Inc. http://www.printek.com

14. Dot Matrix Printer Example - 2 • Specifications • Printhead wires: 9 • Printhead life: 200 million characters • Print speed: • near letter quality: 105 cps • utility: 420 cps • high speed draft: 550 cps • Number of copies: 8 • MTBF: 8000 hours @ 25% duty cycle, 35% density Pacemaker 3410 by OKI Data, Inc. http://www.okidata.com

15. Printers • Four main types: • Dot matrix • Laser • Ink jet • Thermal dye transfer and thermal wax transfer

16. Laser Photosensitivedrum Spinningmirror How it works • Four steps • A laser is fired in correspondence to the dots to be printed. A spinning mirror causes the dots to be fanned out across the drum. The drum rotates to the next line, usually 1000th or 1600th of an inch.The drum is photosensitive. As a result of the laser light, the drum becomes electrically charged wherever a dot is to be printed.

17. Laser Photosensitivedrum Spinningmirror Operation of a Laser Printer • Four steps • A laser is fired in correspondence to the dots to be printed. A spinning mirror causes the dots to be fanned out across the drum. The drum rotates to the next line, usually 1000th or 1600th of an inch.The drum is photosensitive. As a result of the laser light, the drum becomes electrically charged wherever a dot is to be printed.

18. Laser Photosensitivedrum Spinningmirror Operation of a Laser Printer • Four steps • A laser is fired in correspondence to the dots to be printed. A spinning mirror causes the dots to be fanned out across the drum. The drum rotates to the next line, usually 1000th or 1600th of an inch.The drum is photosensitive. As a result of the laser light, the drum becomes electrically charged wherever a dot is to be printed.

19. Operation of a Laser Printer 2. As the drum continues to rotate, the charged part of the drum passes through a tank of black powder called toner. Toner sticks to the drum wherever the charge is present. Thus, the pattern of toner on the drum matches the image. Toner

20. Chargewire Paper Operation of a Laser Printer 3. A sheet of paper is fed toward the drum. A charge wire coats the paper with electrical charges. When the paper contacts the drum, it picks up the toner from the drum

21. Fusingsystem Coronawire Operation of a Laser Printer 4. As the paper rolls from the drum, it passes over a heat and pressure area known as the fusing system. The fusing system melts the toner to the paper. The printed page then exits the printer.As the same time, the surface of the drum passes over another wire, called a corona wire. This wire resets the charge on the drum, to ready it for the next page.

22. Specifications • ppm • Pages per minute • Typically 4-10 ppm • dpi • Dots per inch • Typically 600-1200 dpi

23. Laser Printer Example Laserjet 5000 Series from Hewlett Packard Co. (http://www.hp.com)

24. Printers • Four main types: • Dot matrix • Laser • Ink jet • Thermal dye transfer and thermal wax transfer

25. Background • Inkjet technology was developed in the 1960s • First commercialized by IBM in 1976 with the 6640 printer • Cannon and Hewlett Packard developed similar technology • Also called bubble jet

26. How it works Characters and graphics are 'painted‘ line by line to from a pattern of dots as a print head scans horizontally across the paper. An ink-filled print cartridge is attached to the inkjet's print head. The print head contains 50 or more ink-filled chambers, each attached to a nozzle. An electrical pulse flows through thin resistors at the bottom of each chamber. When current flows through a resistor, the resistor heats a thin layer of ink at the bottom of the chamber to more than 900 degrees Fahrenheit for several millionths of a second . The ink boils and forms a bubble of vapour. As the vapour bubble expands, it pushes ink through the nozzle to form a droplet at the tip of the nozzle. The droplet sprays onto the paper. The volume of the ejected ink is about one millionth that of a drop of water from an eye-dropper. A typical character is formed by an array of these drops 20 across and 20 high. As the resistor cools, the bubble collapses. The resulting suction pulls fresh ink from the attached reservoir into the firing chamber.

27. Inkjet Printer Example

28. Printers • Four main types: • Dot matrix • Laser • Ink jet • Thermal dye transfer and thermal wax transfer

29. How it works Thermal dye transfer printers, also called dye sublimation printers, heat ribbons containing dye and then diffuse the dyes onto specially coated paper or transparencies. These printers are the most expensive and slowest, but they produce continuous-tone images that mimic actual photographs. Note that you need special paper, which is quite expensive. A new breed of thermal dye transfer printers, called snapshot printers, produce small photographic snapshots and are much less expensive than their full-size cousins. Thermal wax transfer printers use wax-based inks that are melted and then laid down on regular paper or transparencies. Unlike thermal dye transfer printers, these printers print images as dots, which means that images must be dithered first. As a result images are not quite photo-realistic, although they are very good. The big advantages of these printers over thermal dye transfer printers are that they don't require special paper and they are faster.

30. black grey light grey white Dithering Dithering is creating the illusion of new colours and shades by varying the pattern of dots. Newspaper photographs, for example, are dithered. If you look closely, you can see that different shades of grey are produced by varying the patterns of black and white dots. There are no grey dots at all. The more dither patterns that a device or program supports, the more shades of grey it can represent. In printing, dithering is usually called halftoning, and shades of grey are called halftones. Note that dithering differs from grey scaling. In grey scaling, each individual dot can have a different shade of grey.

31. Plan • Printers • Scanners • Keyboards • Pointing Devices

32. How it works A scanner works by digitizing an image. A scanning mechanism consists of a light source and a row of light sensors. As light is reflected from individual points on the page, it is received by the light sensors and translated to digital signals that correspond to the brightness of each point. Colour filters can be used to produce colour images, either by providing multiple sensors or by scanning the image three times with a separate colour filter for each pass. The resolution of scanners is similar to that of printers, approximately 300-600 dpi (dots per inch).

33. Scanners • Three main types • Flatbed • Sheet-fed • Handheld

34. Flatbed Scanner Example

35. Sheet-fed Scanner Example OfficeJet Series 700 from Hewlett Packard Co (http://www.hp.com)

36. Handheld Scanner Example QuickScan GP Bar Code Scanner from PSC, Inc. (http://www.pscnet.com)

37. Plan • Printers • Scanners • Keyboards • Pointing Devices

38. Examples Natural keyboard by Microsoft Internet keyboard by Microsoft

39. Keyboard Connectors

40. Plan • Printers • Scanners • Keyboards • Pointing Devices

41. Examples

42. Thank you Next topic