Laser printers were introduced in 1984 as a method for producing crisp, quality print much sharper than the dot-matrix printers. Featuring up to 1200 dpi( dots per inch) resolution, laser printers cost more on the front end than ink-jet printers, their chief rival. But ink-jet printers require expensive ink cartridges whereas laser printers use much cheaper toner powder.
        Laser printers operation is best described with the aid of Figure 2.27.The heart of the printer is the organic photoconductive, or OPC, drum. On the surface of this drum is a special coating that will hold an electrostatic charge. The surface is also photoconductive. meaning a spot on the drum hit by light will be discharged. To begin, a portion of the drum passed under a negatively charged wire known as the charge corona wire, This wire’s large negative charge induces a positive charge on the drum just under the wire. Next, the image to be printed is delivered to tis charged region of the drum by a finely crafted laser and spinning mirror combination. Wherever the laser light strikes the OPC drum, the photoconductive material is discharged. The drum then rolls past a toner dispenser. The toner is a fine black powder that is given a positive charge. It is thus drawn to those portions of the drum that have been discharged by the laser. Meanwhile, paper is fed through the printer ah the same speed as the drum. It passes over a positively charged wire (the transfer corona wire) that gives the paper a strong negative charge just prior to its contact with the drum. The positively charged toner powder on the drum is transferred to the stronger negative charge on the paper. The paper is then passed near a negatively charge wire (the detac corona wire) that removes the negative charge from the paper and therefore prevents it from statically clinging to the drum. The paper and loose toner powder are then passed through heated fuser rollers, where the powder melts into the paper fiber. The warm paper then exits the printer. The drum continues rolling, passing through a high-intensity light that discharges all the photoconductors, thereby erasing the image from the drum and making it ready for application of a positive charge again from the charge corona wire.
        The technology of laser printers continues to improve and their prices continue to drop. Advanced printers are now available that can print in color by running the page through separate printing operations, each with a different color toner powder


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