How a Laser Printer Works
How Does a Laser Printer Work?
A laser printer uses a xerographic printing process where the image to be printed is projected onto a rotating drum coated with selenium or other rare metals which is electrically charged. The charge is removed by photo-conductivity from the areas exposed to light. The toner or dry ink particles are electrostatically picked up by the dark, charged areas and the image is printed onto paper by the drum with heat which fuses the toner to the paper. Laser printers print many copies very quickly and give a highly accurate rendering of an image or text.
The components for this process are the drum, fuser, toner, static electricity and the printer controller. The printer controller communicates with the computer through a network, parallel or USB port and the data is transferred to the printer. The computer first ascertains if a printer is attached and ready and the printer sends a signal back to the computer indicating it is attached and ready for data. The computer will also send any fonts that the printer may need and not have stored in its data bank. The printer chooses how to arrange the data on a piece of paper. Laser printers compose the whole page in memory before transferring it to paper. A page with graphics is usually 512 MB of memory or more, so a good laser printer should have at least 1 GB of memory.
Laser printers with more memory can hold multiple pages which will offload the material quicker from the computer. For this to happen the computer and the printer need to speak the same language which is commonly Printer Command Language (PCL) or PostScript (PS).
The laser printer arranges the margins and graph space. After this, the Raster Image processor (RIP) breaks down the data and stores it in the printer’s memory. The drum must be prepared. It is scanned with red-filtered light in older models or a charged drum in newer models electrostatically cleaning the drum. The data is scanned by a laser and written on the drum, then the laser assembly which includes the mirror, lens and laser moves the beam in such a way that it changes the electrical charge on the image or text that are to be printed to be a negative charge from the blank spaces which have a positive charge.
The paper is grasped by the feed rollers and the toner is picked up at almost the same time. The paper must feed in at exactly the right time when the top of the paper and the laser image are together. The drum revolves and the toner sticks to the negatively charged places of the text or image. A toner cartridge contains a magnetic, rotating, metal-developing cylinder, a toner reservoir and a height control mechanism that controls the amount of toner picked up. Toner or dry ink is plastic resin particles that melt in the heating rollers and stick to the paper and iron oxide which adheres to the magnetic cylinder that presents the toner to the drum. As the drum passes by the cylinder the toner jumps off and clings to the areas with the negative or lesser charge. The paper receives a positive charge from the transfer corona so when it passes the drum, the toner with the negative charge jumps to the positively charged paper. This is also where ozone is produced for higher speed laser printers. This is environmentally bad, but there are some solutions to this toxin. A pair of non-stick rollers, the fuser, heated to almost 365 degrees Fahrenheit, melts the toner to the paper as it passes between them. Each laser printer has sensors for each step to make sure the paper is in the right place for the next step.
Sometimes there are vertical white lines or gray mist appearing on the finished product. To fix these problems the corona wires need to be cleaned. This is a very delicate procedure because the wires are thin and can break easily. They can be cleaned with a felt-lined tool that comes with the printer or a cotton swab dipped in alcohol. The gray mist may also come if the printer’s print density control is on too high of a setting. When the drum is new the setting can be very low. It is also possible it is a bad drum, which in most laser printers is contained within the toner cartridge. Sometimes the easiest fix because of this is to try replacing the toner cartridge.
When the image or text is not dark enough to look good it most likely means the toner is almost finished. This can come in splotched areas on the page or on the whole page. Horizontal black lines on the final print usually mean the roller is dirty or damaged. Since there can be about seven rollers in a laser printer, you need to measure where the black line is on the page then determine which roller may be the problem. Regularly spaced splotches are most likely a scratch or flaw in the drum or a build-up of toner on the fusing roller. A vertical line on the edge of the page usually indicates an empty or faulty cartridge. If the page comes out blank, there is no more toner in the laser printer.