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Printers. Printers come in two main categories: Impact Older printers used typewriter “letter” heads to strike an ink ribbon and transfer ink to the paper.
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Printers • Printers come in two main categories: • Impact • Older printers used typewriter “letter” heads to strike an ink ribbon and transfer ink to the paper. • Dot Matrix printers used a matrix of print pins to create letters. The fewer the pins, the lower the quality. Many form printers using tractor fed paper are still used today.
Printers • Printers come in two main categories: • Non Impact • Most of today’s printers use a non impact method of transferring ink or toner to the paper.
Printers • There are Four main types of printers: • Dot matrix • Ink jet • Laser • Thermal dye transfer and thermal wax transfer
Printers • Dot Matrix: • Been around since the first PCs. • Use mechanical means to press ink from ribbon onto page. • 9 or 24 pin print head • 9pins == low quality and 24 pin has smaller pins close to each other giving better quality print (Near Letter Quality (NQL). • Various size and shape ribbon cartridges • Multipart forms:Carbonless paper forms keep these printers around. • Tractor feed and friction feed • Uses a sprocket to mesh with holes in the side of continuous form paper. Typewriters use friction feed.
Printers Images by permission: http://creativecommons.org/licenses/by-sa/3.0/
Printers Images by permission: http://creativecommons.org/licenses/by-sa/3.0/
Printers • How it works: • A print-head moves back-and-forth in front of the 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.
Printers • Dot Matrix issues: • Print head - Print heads wear off after a while. The ink from the ribbon can clog the tiny pins. Pins can be bent. Electromagnet can be damaged. Print heads are expensive. • Ribbon - Poor print quality can simply mean that the ribbon needs to be replaced. Cartridges vary from printer to printer thus they are not interchangeable. • Overheating - Dot matrix printers are noisy. They are often kept under a padded, sound proofed cover. Less ventilation lead to overheating. • Paper jams - Big problem. Perforated sides can be ripped off easily, jamming the printer.
Printers • Ink jet • Inkjet technology was developed in the 1960s, but first commercialized by IBM in 1976. • Ink is forced through tiny holes (50 – 60 microns in size). Ink can be a single color, or multi-colors. • The resolution of the dots can be as large (small?) as 1440 x 720. With the proper resolution, color ink and photo paper, you can produce photographic quality prints. • Ink jets are less expensive than color laser printers making them popular in the home market.
Printers Images by permission: http://creativecommons.org/licenses/by-sa/3.0/
Printers Images by permission: http://creativecommons.org/licenses/by-sa/3.0/
Printers • How it works: • Characters and graphics are sprayed line by line 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.
Printers • How it works: • As the bubble expands, it pushes ink through the nozzle to form a droplet at the tip of the nozzle, and 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.
Printers • Ink Jet issues: • Cartridges – Ink can dry out over time. If large amounts of printing is done, the cost can be more than a laser. They are also subject to mold growing in the ink, which forces ink out the nozzle. • Refills - Cartridges can be refilled, but the quality of refill ink is often less than OEM standards, and after a few uses, the nozzles are worn out, and ink drips. • Cost – While the printer is usually cheap, the cartridges can be expensive, and often hard to find. • Paper jams – Moisture in paper often causes paper to misfeed.
Printers • Laser: • Laser printers use a type of dry, powdered, electrically charged ink called toner. The printer places the toner on an electrically charged rotating drum and then deposits the toner on paper as the paper moves through the system at the same speed the drum is turning. This involves a complicated process of optical, electrical, and mechanical systems. • Laser printers have the best quality of print, and are the standard by which other printers are judged. Lasers have long been the most expensive, but costs have continually dropped. • The process of printing is broken down into 6 phases:
Printers Images by permission: http://creativecommons.org/licenses/by-sa/3.0/
Printers • Remember the line "Charlie Can Walk Dance & Talk French". The first letters are in the order of the 6 steps. • Cleaning • Conditioning • 3. Writing • 4. Developing • 5. Transfer • 6. Fusing
Printers 1.Cleaning: Excess toner is scraped from the photoelectric drum. 2.Conditioning: A uniform -600 volt charge is placed on the photoelectric drum by the primary corona. 3.Writing: Laser diodes write an invisible electric image on the photoelectric drum by causing the drum surface to be less negative wherever the laser beam hits. 4.Developing: This is where the transfer roller places the toner on the drum. The toner sticks to the areas that have had the electric charge lessened due to the laser beam. 5.Transfer: The secondary corona uses a positive charge to attract the toner from the drum to the paper. The paper gets charged by corona too. 6.Fusing: The toner is then melted into the paper.
Printers • Dye Sublimation: • 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. • Solid Wax Ink: • These printers contain sticks of wax-like ink that are melted and applied to the paper. The ink then hardens in place.
black grey light grey white Printers • Dithering • Dithering is creating the illusion of new colours and shades by varying the pattern of dots. Many printers dither instead of laying down multiple colors. 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. In printing, dithering is usually called half toning, 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.
