A laser printer is a type of printer that makes use of an electrostatic digital printing process. The working of a laser printer is quite similar to that of a photocopy machine. It makes use of static electricity and toner powder in place of liquid ink. The application of toner to specific areas of the paper is determined with the help of the charge difference or static electricity. Laser printers are advantageous as they are comparatively more economical, have a faster rate of operation, and are more efficient. Also, laser printers do not make noise and are more stable. The life span of laser printers is considerably high. The limitations of a laser printer include high initial investment and maintenance costs. The toner cartridge of laser printers is expensive and harmful to the health of humans. Also, the laser printers release ozone into the environment and cause pollution. A laser printer is generally suitable for mass printing.
Components of a Laser Printer
A laser printer consists of three main blocks, namely the scanning unit, toner cartridge unit, and fuser assembly unit. The scanning unit of a laser printer typically consists of a laser diode, a scanning motor, and a polygon mirror. The mirror is connected to a scanning motor and is positioned right above the scanning motor and in front of the laser diode. The scanning unit further consists of two-beam alignment lenses. The toner cartridge unit of the laser printer consists of three drums, namely PCR or primary charging roller, OPC drum or organic photoconductive drum, and an ITR or image transfer roller. Another roller is present in close contact with the printer’s toner cartridge and is known as a transfer roller. The third unit of the laser printer is known as the fuser assembly unit. It consists of a pressure roller and a fuser roller. The fuser roller of the fuser assembly unit contains a heating element.
Working Principle of Laser Printer
A laser printer typically works on the basic principle of conversion of an image from digital format to electrostatic format and finally to physical format. It makes use of a computer program to determine the characteristics of the digital input image that is required to be printed. Initially, the digital image received by the printer gets converted into an electrical signal. The electrical signal is used to excite a ray of light. The light energy further helps in the formation of an invisible electrostatic image. A series of charge transfer operations that take place inside the printer circuitry helps in the formation of a visible image onto a neutral sheet of paper. Finally, pressure and fusing operation lead to the development of a permanent image.
Working of Laser Printer
The laser diode of the laser printer receives the input from the computer and tends to convert the electronic signal into an optical signal. Here, the optical signal is in the form of a highly concentrated laser beam. The scanning unit of the printer consists of a scanning motor that rotates according to the input command received from the computer. The rotation of the scanning motor causes the polygon mirror to rotate with the same velocity at the same angle. The light emitted by the laser diode falls on the face of the polygon mirror and gets reflected. The reflected light falls onto the surface of the beam alignment lens. The main purpose of the beam alignment lens is to couple the reflected rays of light to the toner cartridge unit of the laser printer. The main process of the development of the image takes place inside the toner cartridge unit of the printer. The toner cartridge consists of three rollers, namely the ITR roller, OPC drum, and PCR roller. The light that enters the toner cartridge unit of the laser printer initially falls on the OPC drum. The OPC drum or the organic photoconductive drum is cylindrical in shape and is usually made up of aluminium. It consists of a coating of a photoconductive layer on its surface. The base of the OPC drum is supplied with a positive supply, while the negative supply is given to the PCR. A PCR is an acronym for primary charging roller. It is present in the toner cartridge unit right next to the OPC drum. Due to the force of attraction present between the opposite polarity charges, a negative charge gets deposited on the surface of the OPC drum. The portion of the OPC drum on which the laser beam falls tends to lose charge and get neutralized. This helps in the development of an electrostatic image of the input document on the surface of the drum. This electrostatic image is not visible to the naked eyes. The characters contained by the electrostatic image are reversed or mirror-imaged in nature. Another roller called ITR or image transfer roller is present on the other side of the OPC drum. It is also known as a magnetic rod. The ITR is fully covered with toner powder. The magnetic nature of the rod tends to pass a negative charge to the toner. The continuous rotation of the rollers leads to the deposition of negatively charged toner powder onto the portions of the surface of the OPC drum that are neutralized or discharged. This leads to the development of an image on the surface of the drum that is easily visible to the naked eyes. The positive supply connected to the base of the OPC drum helps to hold the toner in right place. Now, the image formed on the OPC drum can be transferred to the surface of the paper with ease. This transfer of image is performed with the help of the transfer roller. The transfer roller is present outside the printer cartridge and is supplied with a positive supply. The paper inserted into the machine passes through the intersection of the OPC drum and the transfer roller. It should be observed that the image that has been transferred onto the surface of the paper is temporary and still needs to be processed. To fix the characters of the input image on the paper, it is passed through the fuser assembly unit of the laser printer. The paper is made to pass through the intersection of the pressure roller and the fuser roller. The fuser roller contains a heating element and is coated with Teflon material. The Teflon coating on the fuser roller protects the paper from catching fire in case excessive heat is supplied by the heating element. The heat supplied by the heating element increases the temperature of the toner powder, thereby causing it to melt. The pressure caused by the pressure roller helps permanently fuse the characters on the sheet of paper. Finally, the printed version of the digital image is obtained.