A photocopier utilizes the principles of light, electricity, and toner to create reproductions of documents. Here’s a breakdown of the core steps involved:
Placement and Illumination:
- You place your document face-down on the photocopier’s glass platen (the flat surface).
- A bright light source, often a halogen lamp, illuminates the document from above.
Reflection and Electrostatic Charge:
- Areas of the document that are dark (text and images) absorb the light, while lighter areas (background) reflect it.
- A photoconductive drum, made of a light-sensitive material like selenium, rotates beneath the document.
- This drum possesses a uniform positive electrical charge.
- Where the light hits the drum (corresponding to the document’s lighter areas), it loses its electrical charge due to the photoconductive property. Essentially, light creates a mirror image of your document’s electrical charge on the drum.
Toner Attraction:
- A developer unit, containing toner (a fine, dry powder), sits near the drum. Toner particles are typically black but can also be colored for color photocopiers.
- These toner particles carry a negative electrical charge.
- As the charged drum rotates past the developer unit, the negatively charged toner particles are attracted to the areas of the drum that remain positively charged (corresponding to the dark areas of your document). The toner sticks to these areas, forming an image of your document on the drum’s surface.
Transfer and Fusing:
- A sheet of paper is fed from the paper tray into the machine.
- This paper is momentarily given a strong positive electrical charge.
- The positively charged paper passes close to the drum. The opposite electrical charges cause the toner image to be transferred from the drum to the paper.
Heating and Finishing:
- The paper with the toner image then travels through a fuser unit.
- This unit uses heated rollers to apply heat and pressure to the paper.
- The heat melts the toner particles, fusing them permanently to the paper fibers. This creates a dry, permanent copy of your original document.
Cleaning:
- After each copy cycle, the drum’s surface is meticulously cleaned by a cleaning blade to remove any residual toner particles, ensuring a clear image for the next copy.
Additional Notes:
- Modern photocopiers offer various features like zooming, duplex copying (copying both sides of a document), and digital image adjustments.
- The core process remains fundamentally the same despite these advancements.
