In a laser printer an image of the page to be printed it transferred by a laser beam onto a statically charges rotating drum. The drum is a photoreceptor, and the static charge is removed from areas on the drum which have been hit by the laser. Toner (or dry ink) particles are then transferred onto the surface of the drum, where they are held in place by the electrostatic charge. The image is then transferred to paper (the paper has a higher charge than the drum), and the image is made permanent by passing through heated rollers, which fuse the ink to the paper.
Unlike impact printers, the speed of laser printers can vary quite widely, and depends on a number of factors, including the quality of the image being written. Fast laser printers can achieve about 200 pages per minute (monochrome). Color models can print up to 100 pages per minute.
However very fast machines like these will be expensive, and typically used for applications such as mass mailings of personalized documents, such as utility and credit card bills. Machines for office and home use will print at much lower rates, but will of course be substantially less expensive.
Xerox employee Gary Starkweather invented the laser printer in 1969, and within three years he had developed a completely functional networked printer system. Starkweather's printer was a modification of a photocopier or xerographic printer. The imaging system in the photocopier was disabled, and replaced with an eight sided spinning, mirrored drum. Light from the laser hit the mirrored drum, and was reflected and focused onto the photoreceptor drum of the photocopy machine. As the spinning drum rotated it moved the spot of light along the photoreceptor drum, and the image could be created by electronically turning the laser light on and off at the appropriate times.
Although the prototype hardware was made in just two weeks, it took over three months to complete the software and computer interface.
In 1975 the IBM model 3800 was the first commercially available laser printer. It was used for high volume printing for items such as invoices and labels for mail shots. Although very large by modern standards, it is designed for a very different purpose (higher volume printing) than modern PC laser printers, and many IBM 3800s are still extant.
The first office laser printer emerged in 1981. The Xerox Star 8010 was expensive, and was out of reach for most organizations, which still had to use machines such as dot matrix printers. Three years later the mass market HP LaserJet was released, and competition rapidly heated up with machines from IBM, Brother and other companies. These first generation machine required rather large photoreceptor drums, whose circumference exceeded the length of the paper. The problem here was the recovery time of the coating on the drum, but once fast recovery coatings were available the drum size was reduced, and machines became even smaller.
Laser printers allow fast and quality text and image printing with a variety of fonts and the cost has reduced so that the low end monochrome printers are now reasonably priced for home PC users.
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