laser printing

laser printing
Name	Laser printing
Inventor	Gary Starkweather
Invented	1969
Company	Xerox
Related	Xerox 9700

laser printing is a digital printing process that produces high-quality text and graphics by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image. The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated to permanently fuse the text or imagery. As a non-impact, PostScript-compatible method, it differs from analog xerography and has become the dominant technology for office and personal printing.

History

The technology was invented in 1969 at Xerox by researcher Gary Starkweather, who modified an existing Xerox 7000 copier. The first commercial implementation was the Xerox 9700 Electronic printing system, introduced in 1977. The first desktop laser printer was the Xerox Star workstation system in 1981, but the market was revolutionized by the 1984 release of the HP LaserJet, which used a controller developed by Canon Inc. under the Canon CX engine. This partnership established the LaserJet series as an industry standard, with subsequent competition from companies like Brother Industries, Lexmark, and Kyocera.

Technology

The core component is an organic photoconductive drum, typically coated with selenium or other photoconductive materials. A laser assembly, often using a laser diode and a rotating polygon mirror, scans the drum line by line. This process is managed by a raster image processor interpreting Page Description Language data, commonly PostScript or PCL. The system also includes a precision fuser assembly, a high-voltage corona wire or primary charge roller for charging the drum, and a developer unit containing a mixture of toner and magnetic carrier beads. The entire mechanism is precisely timed by the printer's main controller board.

Process

The printing cycle, known as the Xerography process, involves several distinct steps. First, the photoconductor drum is given a uniform negative electrostatic charge by the primary charge roller. The laser then discharges specific points on the drum, creating an electrostatic latent image. In the developing stage, positively charged toner particles are attracted to the discharged areas on the drum. The transfer roller then applies a positive charge to the paper, pulling the toner from the drum onto the paper's surface. Finally, the paper passes through the fuser unit, where heated rollers melt and press the toner into the paper fiber.

Applications

Laser printers are ubiquitous in office environments for producing documents, reports, and correspondence, with major manufacturers including HP Inc., Canon Inc., and Ricoh. They are critical in data center operations for printing logs and batch reports. The technology is also used in Direct mail production, Transaction printing for bills and statements, and publishing for proofs and short runs. High-volume production printers from companies like Xerox and Konica Minolta are used in commercial print shops and in-plant printing facilities.

Comparison with other printing methods

Compared to inkjet printing, laser printing generally offers faster speeds for text, lower cost-per-page for high-volume printing, and water-resistant output, though often at a higher initial hardware cost. When contrasted with solid ink printers, such as those historically made by Tektronix, laser printers typically have superior text sharpness. Against LED printer technology, which uses an LED array instead of a laser, the differences are minimal for most users, though LED printer designs can be more compact. For very high-volume commercial work, laser printing competes with offset printing, which becomes more economical for very large runs.

Environmental considerations

The production and disposal of toner cartridges, often containing plastic and residual toner, generate significant waste, leading to programs like HP Planet Partners for recycling. Energy consumption during operation and in standby mode is a concern addressed by standards like ENERGY STAR. Emissions of ultrafine particles and volatile organic compounds from the fusing process have been studied by organizations like the German Environmental Protection Agency. The long lifespan and durability of laser-printed documents can reduce the need for reprints, potentially offering an offsetting environmental benefit.

Category:Printing