Inside an Inkjet Photo Printer

The Fine Print Every time you hit “print,” this $100 inkjet lays down thousands of droplets per inch of paper, with microscopic precision Ted Kinsman/Photo Researchers

Even today’s budget-priced home printers churn out quality photos that a few years ago you could have gotten only from a professional printing house. Key to the high quality are steady improvements in print heads, which can eject smaller and smaller droplets of ink with ever-greater precision.

A decade ago, eight-picoliter drops (that’s eight trillionths of a liter) were considered small. These days, inkjet printers deliver drops as tiny as one picoliter through thousands of nozzles—some less than half the width of a human hair.

To make prints that look like photos instead of finger paintings, the printer must precisely control how much ink comes out of every nozzle, every time, at a rate of up to 22,000 drops per second.

Putting Ink to Paper

Two types of technology can squeeze ink through the nozzles.

Using Heat: Canon and HP use a thermal process. The printer’s electronics send precise charges to a resistor at the back of the nozzle, which heats the ink until it bubbles out  John MacNeill

Using Pressure: Epson printers use disks made of a piezoelectric material, which flexes when current is applied--first drawing fresh ink into the nozzle, then pushing it onto the paper  John MacNeill