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Printing Process Tutorial


No computer is complete without a printer. At some point, you're going to want to print photos scan a document. A good, reliable, feature-rich printer can make these tasks simple as well as fun. The two primary types are inkjet and laser. A laser printer produces much sharper prints than an inkjet. Photo printers are inkjets designed specifically for producing high quality pictures. We'll take a look at the printing process for both of these types of printers.

Inkjet Printing Process:
The main Components of an inkjet printer are as follows:
  • Cartridges - The container that holds the ink. Some contain the print head.
  • Print Head Assembly - Contains the nozzles for ink spraying.
  • Rollers - Moves the paper as it's printing.
  • Print Head Steppor Motor - Moves the cartridges and head back and forth. Some have a park motor to prevent the head assembly from moving when it's not being used.
  • Paper Feed Steppor Motor - Powers the rollers.
  • Belt - Connects the assembly to the motor.
  • Stabilizer Bar - Makes sure the roller movement is consistent and the printing is precise.
The primary method for inkjet printing is the Thermal Bubble method (aka Bubble Jet). As the name implies, a bubble is formed in the cartridge as heat made by resistors is vaporized. As the bubble grows, it forces ink through the nozzles. When the bubble bursts, it causes oil from the cartridge to enter the print head.

Another method is the Piezoelectric method. This technique uses a piezo crystal positioned at the back of each nozzle. An electric current vibrates the crystal. When it vibrates inward, oil is pushed out of the nozzle. Vibrating outward draws in more ink to replace what was used.

Laser Print Process:
The main Components of a laser printer are as follows:
  • Laser Assembly (Contains the Laser, Mirror, & Lenses) - Draws Image.
  • Photoreceptor (Drum) - Contains the image.
  • Charged Roller (Older Printers used a Primary Corona Wire) - Charges the drum.
  • Toner - Plastic, Pigmented Powder.
  • Toner Hopper - Contains the Toner.
  • Developer Assembly - Unit that attracts the toner so it can be transferred to paper.
  • Fuser (Heated Rollers) - Melts ink.
The printing process for a laser printer is much more complex. But before we do let's take a quick look at how a laser printer communicates with a computer when you click "OK to print.

A laser printer uses a Page Description Language (PDL) to talk to a PC. The two most popular are Postscript (from Adobe) and Printer Command Language (PCL from Hewlett Packard). These use vectors to represent the page layout which are then converted to a bitmap image. Afterwards, the page is arranged - the margins are set, the text is put in place, and anything else that pertains to the particular page that is to be printed. Then, the Raster Image Processor (RIP) converts the page data into dots, transfers it to the printer's memory, and the actual printing is ready to begin.

The charged roller (corona wire on older printers) is responsible for giving the drum a positive or negative charge. In this explanation I'm going to use a positive charge. The laser beam fires through a moving mirror and lenses and draws the image to be printed on the drum. This image is given a negative charge. Next, positively charged toner is applied to the image. The toner is located in a container called a toner hopper. The developer is a set of negatively charged beads on the developer roller that attracts the toner as the roller moves them through the hopper. Since the negative charge on the image is a lot stronger than the negative charge on the beads, the toner is drawn away from the beads onto the drum. Then, the drum rolls onto the charged paper, and the paper grabs the toner. The paper is immediately discharged by another corona wire to keep it from sticking to the drum. But even at this point, the toner is just sitting on the paper. It only becomes bonded after passing through the fuser rollers, melting the toner into the paper.

At one time, printers were one-dimensional - they printed and that was all. Now, there are many All-In One printers on the market, having the ability to fax, scan, and copy. When looking to buy, more than likely you'll see the following major printer specifications.

Resolution:
Just as monitor resolution is how clear a screen image is, printer resolution is how clear a printout is and is measured in dots per inch (DPI). However, many times the DPI is listed as two numbers such as 2400 x 600, so in reality it's really dots per square inch. The higher the DPI, the sharper the image. This is especially relevant when you need the best image quality possible.

Print Speed:
Print speed is how many pages printed per minute (PPM) and varies with manufacturer and model. There is usually a different PPM for black and color cartridges on the same printer. Keep in mind, however, that on any particular machine, these numbers are theoretical and other factors have a significant effect on how fast pages print-such as the print mode used and whether or not you're printing text or a photo. But overall, a 22-PPM printer will print faster than one at 16 PPM.

Duplex Printing:
Duplex printing is the ability to automatically print on both sides of a sheet of paper. Some higher end models have 2 print heads and can do this simultaneously.

Maximum Duty Cycle:
This is a measure of how "strong" a printer is. In other words, the number of pages that can be printed per month before physical damage occurs. These numbers can run up into the thousands. Laser printers typically have a much higher duty cycle than inkjets, with some as high as 30,000 pages or more. Since the average home user doesn't print nearly that many pages per month, you can pretty much overlook this number.

Connectivity:
Most printers today support at least two types of connectors. They connect via USB, Ethernet, Wi-Fi, Bluetooth, pictbridge, and memory cards. Pictbridge allows a camera to connect directly to a printer without a computer. Both devices have to be pictbridge compliant to take advantage of this feature. Those that contain memory card slots allow you to insert your camera's card and print directly without the computer.

Memory:
Printers contain their own memory. When you tell a computer to print, the data is sent to the printer's memory. If you have to print long documents, make sure there is plenty of memory to handle the job. A printer with at least 64MB of memory is a good start.

What to Buy:
Should you get an inkjet or laser? Well, if you're not going to be doing much printing and real sharp image quality isn't an issue, an inkjet is sufficient. Otherwise, a laser would be better. Ink cartridges are expensive, and heavy printing can have you buying cartridges often. You wouldn't want an inkjet for printing large numbers of pages. A single cartridge can be over $30, and some printers use multiple cartridges. So before buying an inkjet, make sure you know the price of the cartridge(s) for a particular model.

If photography is your thing, then go ahead and get a photo printer. Are you on the go? There are portable printers available. Print in your car, outdoors, anywhere you like. Some of the top manufacturers include Canon, Brother, Hewlett Packard, and Lexmark. All produce a variety of inkjets and lasers.







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