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 twobeam 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.