How an Inkjet Printer Works

Inkjet printers contain hundreds of parts all working together to put millions of microscopic dots onto paper. There are five main components of an inkjet printer: print head, paper feeder, circuit board, power supply, and the case. Of these, the print head and paper feeder are the most interesting.

The Print Head

The print head contains an array of microscopic nozzles that fire drops of ink onto the paper. In some cheap printers, the print head is not even part of the printer, but part of the ink cartridge. There are two main types of print head: thermal ("Bubblejet") and piezoelectric.

Thermal print heads have an array of microscopic nozzles with a small heater filament in each one. When a dot needs to be placed on the paper, current is passed through a filament to boil the ink in that nozzle and create a steam bubble. When the bubble pops, ink is shot out the nozzle end while more ink is sucked into the nozzle, ready for the next firing. This process is repeated thousands of times for every page printed. The term "Bubblejet" is actually a brand name owned by Canon, a major printer manufacturer, and is just another name for these inkjets.

Piezoelectric print heads use a special crystal that vibrates when electrified. This vibrating crystal acts like a plunger, pushing ink out of the nozzles and drawing more ink in. The main advantage over the thermal print heads is the larger range of inks they can use. It also allows for higher resolutions because the ink nozzles are closer together. Almost all inkjet printers made today use a piezoelectric print head.

Both types of print head are stabilized by a solid metal bar, and belt driven by a stepper motor. A stepper motor is special type of electric motor that moves in a precise amount for each electrical pulse it receives. As the print head moves back and forth, the printer fires the ink drops at the right time to form the array of dots that make up a printed shape.

The Paper Feeder

The paper feeder consists of the paper tray, pickup rollers, main rollers, and the stepper motors which drives the rollers. The pickup rollers lift a sheet of paper from the tray and move it into the main rollers. These long rollers, along with a fixed guide, keep the sheet align while it is moving. With each pass of the print head, the rollers move the sheet forward a little, until finally ejecting it after printing has finished.

The print quality depends as much on the type of paper as it does on the resolution. Photo paper has a waxy surface that prevents "feathering", which is the spreading out of ink dots as they are absorbed by the paper. It is important to note that, why many printers have high resolutions, low grade paper can never reach these resolutions due to feathering. Uncoated paper has about half the maximum resolution of coated paper.