1. Light Exposure:
- The photocopying process begins with the placement of the original document on the glass surface of the photocopier. When you press the copy button, a bright light is shone onto the document. This light source illuminates the entire surface of the document, creating a precise representation of its content.
2. Reflective Scanning:
- A system of mirrors and lenses directs the light reflected off the document onto a photosensitive drum. This drum is typically coated with a semiconductor material like selenium or a photoconductive material like amorphous silicon.
3. Charging the Drum:
- Before exposure to light, the drum is given an overall positive charge. The light from the document causes areas on the drum’s surface to discharge, creating an electrostatic image that mirrors the content of the original document.
4. Developing the Image:
- The next step involves the application of toner, a fine powder made of pigment and plastic particles with an electrostatic charge opposite to that of the charged areas on the drum. The toner is attracted to the discharged areas, forming a visible image on the drum.
5. Transfer to Paper:
- A sheet of paper is passed close to the drum. As the paper moves, it receives a negative charge from a corona wire or roller. This negative charge attracts the positively charged toner from the drum, transferring the image onto the paper.
6. Fusing the Toner:
- The paper, now carrying the toner image, passes through a fuser unit. This unit uses heat and pressure to melt the toner particles into the fibers of the paper, ensuring a permanent bond. The result is a dry and smudge-resistant copy.
7. Cleaning and Discharging:
- Any remaining toner on the drum is removed by a cleaning blade or roller. Additionally, the drum is exposed to a bright light or discharged using a discharge lamp to prepare it for the next copy cycle.
8. Duplexing (Optional):
- Some advanced photocopiers support duplex printing, allowing for double-sided copying. In these machines, the paper may be directed through a duplex path, where it undergoes a second imaging and fusing process for the reverse side.
In summary, a photocopier uses a combination of light exposure, photoconductive drum technology, toner application, and paper handling to reproduce the content of an original document. The electrostatic principles involved in the process result in an accurate and high-quality copy of the original.
