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Introduction to Laser Printers
Laser printers are an offshoot of photocopier technology. The first laser printer on the commercial market was produced by Canon Corporation in the 1980's. It was based on a copier engine they were selling at the time called the PC-20. The most well known version of this laser printer is the HP LaserJet (HP licensed the engine design from Canon). The laser printer offered many advantages over the then popular impact printers. It was quieter, it was fast (about 8 pages per minute), and it produced output that was waterproof and archival. It produce excellent graphics (300 DPI). Since their introduction, laser printers have become a staple item in the professional office, replacing impact printers as the printer of choice in document printing.
Recent developments in laser printer technology have merged the laser printer and copier into a single machine. Manufacturers of these machines term them "Mopiers" or "Document Offices" referring to the machines' ability to act as a printer or a copier.
Laser printers are rated by two properties, time to first page out (measured in seconds) which rates how longer the printers processor takes to map the image, and print speed (pages per minute) which measures rate at which the printer can output pages. The amount of memory available in the printer can affect both ratings.
How Laser Printers Work
Laser printers use a "toning" or "development" process to produce output. The process uses a combination of various electrostatic charges to transfer dry-ink (also called toner) from its storage reservoir, form images with the toner and place the toner on paper. The toner is then "fused" to the paper either by heat activated or pressure activated bonding materials mixed in the toner.
The process starts when a print job is received from the computer. The printer process the data and creates a digital map which is the image to be printed. The printer pulls a sheet of paper from the paper tray and begins passing the paper through a charging roller which puts an specific electrostatic charge on the paper to make it more receptive to the toner.At the same time a Photoconductor located in the printer begins spinning slowly. This photoconductor is charged with even electrostatic charge by either a corona wire or primary charge roller, erasing old images from the OPC drum and prepping the charge of the drum to receive new images. As the surface of the drum emerges from the erase/charge process a UV laser begins mapping dots on the drums surface. These dots of light change the electrostatic properties of the areas of the drum they strike making these spots attractive to the toner. The imaged surface of the drum then rotates towards a developer roller.
The developer roller is a specially designed cylinder made of metal or conductive polymer material which carries a thin layer of toner on its surface. The developer roller rotates to pick-up fresh toner from the toner reservoir and bring it close to the Photoconductor. As the toner rotates out of the reservoir on the developer roller surface it passes under a close fitting metering blade which increases the electrical excitement properties of the toner (called "triboelectric charge") by friction. A high voltage current is applied to the developer roller as well to increase this excitement even further. In this excited state the toner is very receptive to the charge created by the laser on the Photoconductor drum surface and is less receptive to the areas which were not truck by the laser. Thus when the toner gets very close to the Photoconductor it transfers itself to the Photoconductor at the points where the laser struck the Photoconductor surface.
At this point the photoconductor has a mirror image of the output on its surface. The paper, meanwhile has been in sync with the drum rotation and the first parts of the image approach the paper as it passes over the transfer corona wire. The transfer corona wire enhances the electrostatic charge on the paper making the surface more receptive to the toner than the Photoconductor. The toner is pulled off of the photoconductor onto the paper. The paper continues forward towards the fuser assembly passing over a set of fine metal teeth which dissipate the electrostatic charge on the paper. As the paper passes through the fuser assembly the waxes and bonding agents mixed with the toner melt and bond the toner to the papers surface. The paper then emerges into the output tray.
In the printer, the print process is completing as the paper reaches the output tray. The photoconductor, still rotating, reaches the wiper blade which removes any remaining toner from the Photoconductors surface and deposits the waste toner in the waste chamber. The drum then rotates back up to the primary corona wire or charge roller where the whole process begins again. This process repeats until the printer has no more pages to print at which point the process will stop immediately.Color Laser Printers
Color laser printers work in a similar manner except that the same paper makes four passes under the photoconductor, once for each color of cyan, magenta, yellow, and black, then passes through the fuser, The fuser not only bonds the toner but also aids in the blending of the toners to form specific colors.
LED Printers
LED Printers function exactly like standard beam laser printers the main difference is that OPC drum mapping is done with a array of tiny LED lights instead of a single laser beam.
Toner & Cartridges
Toner usually consists of a colorant, iron particles (magnetite), plastic and wax polymers, and other additives which keep the material dry and prevents clumping. Toner formulations are dependent on many factors, the polarity of the electrical charges used, dot sizes formed, the page speed of the printer, and the operating temperature of the fuser. Since these factors vary a great deal from printer to printer toner formulas tend to be more exacting than inkjet ink formulations to manufacture. Properties such as particle size distribution, flow control, melting point, triboelectric charge, are all critical in the formulation of toners. Toners commonly used are grouped into three basic categories: mono-component magnetic, mono-component non-magnetic, and dual component toners.
Mono-Component Magnetic - This is the most common toner type, it consists of a single toner mixture containing Ferro-magnetic materials. It is completely consumed by use. This toner is commonly used in HP LaserJet Printers and other "Jumping Development Technology" style printers, where there is a gap between the photoconductor and developer roller.
Mono-Component Non-Magnetic - Similar to its magnetic, cousin this toner is a single mixture but contains no Ferro-magnetic components. It is also completely consumed by use. This is commonly used in Lexmark Optra printers and other "Direct Contact Development Technology" printers where there is no gap between the photoconductor and developer roller.
Dual-Component Toners - Consists of two parts a non magnetic toner mixture and a magnetic carrier. The non-magnetic toner is transferred to the photoconductor using the magnetic carrier. The toner is completely consumed from use. The magnetic carrier is not consumed but becomes less effective over time and must be replaced periodically. Sharp JX-9400 printers use this type of toner.Cartridges are generally independent user replaceable components which contain critical consumable parts used in the laser printer. The primary components of the print engine of any laser printer is it cartridge(s). The primary user replaceable components of most laser printers are: The toner reservoir, the developer roller, the photoconductor, and the toner waste bin. Depending on the design of the cartridge and printer these components may be individually replaceable items or may be housed "all-in-one" cartridge.
Laser printers with different brand names are often similar if not identical in design. They use the same replacement parts and same consumables, although the part numbers are determined by the manufacturer whose name is on the printer. Printers that meet such a criteria are said to have the same Engine Designation. The engine designation allows for easy cross-reference of parts and supplies from various manufacture. In normal use the engine designation of a printer refers to the original designers designation or the primary printer associated with that design. For example the Apple Laserwriter Personal NT, the Canon LBP-4, and the HP LaserJet IIP, all use the same cartridges, and most repair parts are the same. Canon was the original designer of this print engine and gave it the designation LBP-LX (stands for Laser Based Printing LX Series). Thus for cross-referencing most people refer to the engine family of these printers as the Canon LBP-LX Engine or Canon LX Engine. The toner cartridge used in the printers, an "all-in-one" type of cartridge, is referred to as the EP-L (Type L Electrostatic Photo-developer cartridge ) cartridge or just an LX cartridge.