Plotters are basicaly print
ing devices which differ from regular printers by their large-sized printing
possibilities, by their high color quality
and graphic precision
. They are mostly used for professional purposes, there are plotter models that even support network
use. Since their price
s makes them a difficult item to fit in a average family budget
and home, they are rarely used as personal printers.
Plotters are often associated to the output of monochrome CAD engineering drawings and architectural plans, but today the plotter market is not reduced to CAD users anymore. Some shifts are taking place in the plotter marketplace: pen plotters are losing space to other types of plotters, such as inkjet and laser models. Even the plotter designation has been substituted by their manufacturers, now they are referred to as large-format printers.
Color x black and white ploting
Monochrome plotters can only produce black and white images, usually being able to produce numerous shades of grey. This kind of plotters is noted for it output sharp
ness and they tend to be fast
er than color plotters.
Color plotters usually use 4 different color cartridges if they are inkjet or laser type; pen type color plotters use colored pens to produce output. The standard ink cartridge colors are cyan, magenta, yellow and black (CMYK).
Typical Plotter sizes
There are many plotter models sizes, but the typical sizes are: 24 inches, 36 inches, 42 inches, 60 inches or even larger than 60 inches. For example: when a plotter is classificated as a 42 inches model, that means that this plotter com handle sheet sizes up to 42” witdh.
The different plotter types:
Pen Type Plotters
The pen type plotters are the ones usually associated to technical printing. These plotters generate line drawings on wide sheets or rolls of paper with continuous lines, creating high precision graphics with attached pens. The combination of horizontal and vertical pen movement allows the plotter to draw arbitrary lines and curves at a single action, different from inkjet and laser prints which scan horizontally across the page.
The pen type plotters are commonly used in computer aided design applications such as AutoCAD to produce engineering drawings and architectural plans at large scale. Pen type plotters are not considered full-color output devices because they can only switch with the set of pens they have: they are not designed to mix colors and that's the main reason they are practicaly reduced to technical printing.
A pen type plotter may be a flatbed or a drum type: flatbed plotters have a drawing pen that moves both horizontaly and vertically over a flat piece of stationary paper; drum plotters have a drawing pen that moves vertically while the paper, on a drum, rotates under it.
Inkjet and Laser Plotters
Now there are inkjet and laser plotter models that offer better results for those who need high quality color printing, like graphic designers and [advertising} agencies. Their main target is the graphic production market: production of banners, signs and other large-format printouts with full color images. These plotters can even lack support for CAD languages and might not include PostScript support in hardware: sometimes they only support a raw raster format and rely on Windows print drivers, software Raster Images (RIPs) and PostScript interpreters.
Concerning their technology, these plotters are not very different from regular printers that we use at home or at offices.
The inkjet type is similar to regular inkjet printers, but it suports a larger print size, higher resolution and higher print quality than most inkjet printers. These plotters have print heads that contains a series of nozzles which sprays extremelly small droplets of ink onto paper to reproduce photo-quality images. The color images are the result of the combination of four basic ink colours (cyan, magenta, yellow and black - CMYC) that are stored in cartridges assembled to the print head.
There are two different technologies used by printer manufacturers: Thermal bubble and Piezoeletric. The Thermal bubble method uses tiny resistors to creat heat; the heat vaporizes the ink and creates a bubble. As the bubble explands, some of the ink is pushed out of a nozzle onto de paper, and when the bubble collapses a vacuum is created, pulling more ink from the cartridge into de print head. Canon and HP printers uses this technology. The Piezoelectric is a method that uses piezo crystals and it is patented by Epson. A crystal is located at the back of the ink reservoir of each nozzle; it receives a tiny electric charge that makes it vibrate. When the crystal vibrates inward, it forces a small amount of ink out of the nozzle; when the crystal vibrates out, it pulls ink into the reservoir to replace the ink that was just sprayed out.
Both inkjet technologies produce images by the moving of a print head over the paper surface. Laser printers do the same thing, differing in the way that the ink is transfered to the paper. This scanning movement of the print head across the paper has one inconvenient: it may cause problems drawing thin lines accurately.
Laser printers use a rotating disk to reflect laser beams, forming an electrostatic image on a selenium imaging drum. After the pattern is set, the printer coats the drum with positivaly charged toner, which is attracted to the negative discharged areas of the drum only. With the toner powder affixed to the pattern, the drum rolls over the surface of the paper, which is moving along a belt below. The paper is negativily charged before it rolls under the drum with a stronger charge than the negative charge of the the electrostatic image, what makes the paper pull the toner powder away. The paper and the drum moves at the same speed, making it possible for the paper to pick up the image pattern exactly. After that, the printer passes the paper through a pair of heated rollers that will melt the toner powder, which fuses with the papers fibers printing there the pattern image. This printing process allows a high quality color or black and white image reprodution, with a higher precision than the inkjet technology but at higher costs as well.
More details on how do inkjet and laser printers work can be found at howstuffworks.com.