Printers

The printer is used to make a paper copy (called a "hard copy") of the documents that you create on the computer. To print, you need to attach and install a printer. Printers fall into two major classifications:

• Impact Printers - An impact printer produces printouts much in a simular way as typewriters. Characters are formed by a hammer or pin striking a ribbon saturated with ink against the paper.

• Non-Impact Printers - A non-impact printer does not require contact to the surface of the paper to produce a printed image or character. There are several methods used to print pages such as ink spray, laser heat, or photocopying . Since the non-impact printer has fewer moving parts, it is the fastest and quietest of printers available.

Impact Printers Most impact printers are Dot Matrix; however, there may still be a few Daisy Wheel printers left.

Dot Matrix

The dot matrix is one of the oldest types of printer and has been around for many years. It is sometimes known as an "impact printer" as a printer ribbon (akin to a typewriter) is "pressed" (or impacted) upon the paper.

The printer head is made up of a row of pins - usually 9 or 25 pins forming a vertical bar. To form a letter, the pins are "fired" in quick succession to press the ribbon against the paper. If you look closely at a sample of output from a dot matrix printer you can see the "dots" that make up the characters.

Technology improves this technique by making the print head shift slightly so that the gaps between dots could be filled in (if you own a dot matrix printer and you print in "final" quality, you will notice that the printer head passes over a line of text twice - the second time is the "fill in" pass).

The more dots you have, the better the resolution, and 25-pin printers can produce reasonable output. One advantage that a dot matrix printer has over all other types is that it can use multi-part stationery. You cannot use multi-part stationery on the other types of printers mentioned here as neither an ink jet nor a laser impacts on the paper.

Dot matrix printers can handle graphics output by firing pins where pixels are set although shading can mean the paper crinkles and it is difficult to get a true "black." Also see http://mimech.com/printers/

Daisy Wheel Printers This type printer produces a printed page by using a print wheel. The name Daisy Wheel comes from the fact the print wheel resembles a daisy flower. A raised character is placed on the tip of each of the daisy wheels petals. To print, the wheel is spun until the desired character is in front of a hammer.

The hammer then strikes the character against an inked ribbon, the ribbon hits the paper, and an imprint of the character is left on the paper. These printers are commonly referred to as " Letter Quality Printers" as the print quality is as good as that of a typewriter. These printers are usually very slow because of the time required to rotate the print wheel for each character desired.

Non-Impact Printers Laser printers – built for speed

Laser printers are the fastest and most popular printers on the market today. They produce extremely high quality images – some near photo quality. Let’s take a closer look at how they do that.

As we mentioned, laser printers use Electrophotography, or an electrophotostatic process, to form images on paper. The basis of the principles involved here is the science of atoms – oppositely-charged atoms are attracted to each other, so opposite static electricity fields cling together. It’s hard to imagine that this has anything to do with printing, but in actuality, this is precisely what makes laser printers work.

Inside the laser printer is a drum, or photoreceptor. It’s made of highly photoconductive material that reacts to light, and is electrically charged by the corona wire. As the drum turns, a laser beam shines on it, discharging specific areas. This pattern of discharged areas is ultimately what determines the images that’ll be printed.

The next step is to coat this pattern with a fine black powder called toner. The toner has been given a positive charge, which allows it to stick just to the pattern, and not the rest of the area. The pattern of toner is then attracted magnetically onto the paper, which is passing the drum on a belt. Then the paper is discharged, which releases it from the drum.

Now that the image or pattern is on the paper, we have to make sure it stays there. That’s done by heated rollers, called the fuser, which melt the toner particles right into the paper. The paper is then pushed into the output tray, and you have your printed page.

This process, although it sounds complicated, happens very quickly, printing many copies per minute. But it’s kind of cool to understand it, don’t you think?

Some of the advantages laser printers have over dot matrix printers are:

• Print different styles of printing in the same document.

• Print Scanned photos or high resolution graphics.

Inkjet printers – let us spray

Inkjet printers literally spray liquid ink through a miniature nozzle similar to your garden hose nozzle. These printers are very quiet and are moderately priced. And the print quality rivals that of a laser printer. Here’s how they do that.

The printhead contains 4 cartridges of different colored ink: cyan (blue), magenta, yellow and black (CMYK). It moves along a bar from one side of the paper to the other, writing as it goes. The formatting information and data sent to it activates the chambers of the ink cartridges.

When the designated nozzle is selected, an electrical pulse flows through thin resistors in the ink chambers that form the character to be printed. The resistor is heated and used to heat a thin layer of ink in each selected chamber, causing the ink to boil or expand to form a bubble of vapor.

This expansion causes pressure on the ink, which pushes it through the nozzle onto the paper. Your page is printed.

An inkjet printer is any printer that places extremely small droplets of ink onto paper to create an image. If you ever look at a piece of paper that has come out of an inkjet printer, you know that:

• The dots are extremely small (usually between 50 and 60 microns in diameter), so small that they are tinier than the diameter of a human hair (70 microns)!
• The dots are positioned very precisely, with resolutions of up to 1440x720 dots per inch (dpi).
• The dots can have different colors combined together to create photo-quality images.

Colour

This is where ink jets come into their own. By using two cartridges - one colour and one black, an ink jet can produce high quality colour output at an affordable price. There are a couple of points to bear in mind when using colour ink jets.

• The paper is fed into the printer engine. The paper is held against a ribbon coated with colored ink (cyan, magenta, yellow, or black).

• As the paper moves through the paper feeders, it presses against the cyan bank of the ribbon. One or more heating elements are turned on, and they melt small dots of the cyan dye. The melted dots are then pressed against the paper.

• The paper continues to move through the paper feeders until the paper peels away from the ribbon. As it peels, the unmelted ink remains on the ribbon, and the melted dye sticks to the paper.

• The paper is pulled back into the printer, and the next color (magenta) band goes through the same process. This repeated for the magenta, yellow, and black.

• After all color cycles, the paper is ejected into the paper tray at the exit.

• No matter what type of printer you use the printer cable goes from the printer to a printer port LPT1 (a DB25 female connector) on the back of the computer.

• The printer port can be either a parallel port or a serial port.

• With a serial connection (COM port) the data is sent one bit at a time

• With a parallel connection (LPT port) the data is sent one byte (8 bits) at a time.

• All color from printers is from a mixture of colors.

• All colors are mixed as dots of different colors.

• Each printed color is a mixture of 4 colors (black, magenta, yellow, and blue).

• Color thermal printers are higher quality than laser or ink jet printers because the heated wax does not bleet into each other or soak into the special paper.

See also How print catridge works