Photocopying Machine also known as copier or copy machine, that produces exact reproduction of the original documents on paper.
Photocopying Machine makes paper copies of documents and other visual images quickly and cheaply. Most current Photocopying Machine uses a technology called xerography, a dry process using heat.
Photocopying Machine – Introduction
XEROGRAPHY was invented by CHESTER CARLSON IN 1938. 10-22-38 ASTORIA, this is the first word he printed on paper.
Gradually printing technology improved to Thermal Printer, Thermal Transfer Printer,Inkjet Printer, LED Printer, Laser Printer.
Almost all photocopying machine employs the principles of Xerography, Photo conductivity and The Universal Law of Attraction and Repulsion.
XEROGRAPHY was derived from the Greek words XEROS meaning DRY, GRAPHEIN to write.
Photocopying Machine – Working Principle – Charge
This process involves application of positive charge to the photoreceptor surface. This operation must be done in darkness. Because the selenium drum or photoreceptor retains charge only in darkness.
The machine components involved at this stage are Photoreceptor which is an aluminum drum coated with a layer of selenium and oxides of selenium.
Photocopying Machine – Working Principle – Expose
The purpose of this function is to transport the reflected image of the original document to the drum. The machine component involved at this stages are, Platen glass, Exposure lamp usually a halogen lamp, Lens and mirror assemble and photoreceptor or drum.
When original document is placed on the platen glass, exposure lamp is used to illuminate the original. The non-image area of original reflects light and image area observes light. Light is reflected from original document to drum using lens and mirror assembly.
This reflected light falls on drum and dissipates charge. Image area of original absorbs light and hence that corresponding portion of the drum is still in darkness.
Therefore the surface of the drum corresponding to image area of original retains a strong positive charge.
Photocopying Machine – Working Principle – Develop
Components involved at this stage are, Toner, Carrier and Drum. Toner is made of combination of carbon, resin and thermo plastic material.
Toner has a property whereby on contact and friction with the carrier, develops an opposite charge. Toner and carrier constitutes Developer.
Carrier consists of ferrite beads with a small positive charge. Ferrite is a magnetic material. Carrier and toner are simultaneously released from their respective places and allowed to mix.
A negative charge is induced in the toner. Since carrier carries a positive charge, toner clings to carrier. This mix is applied to drum.
The positively charged latent image of drum pulls the negatively charged toner particles, Since the positive charge on drum is higher than that on developer.
Photocopying Machine – Working Principle – Transfer
Components involved at this stage are Drum, Paper, Transfer Corotron wire. Transfer Corotron applies positive charge on paper which is stronger that that on drum.
This charge on paper is static in nature. The copy paper is then bought in contact with drum. The toner in the drum unit now clings onto the paper. But still some residual toner remains on the drum.
Photocopying Machine – Working Principle – Fuse
During the early transfer process image on the drum is transferred on the paper which form a visible image, but it is not fixed permanently on paper. During this fusing process loosely bound toner image on paper is made permanent.
The thermoplastic toner is melted to its melting point in the fusing chamber. Simultaneously pressure is applied on the toner so that the toner is ingrained onto the paper.
Photocopying Machine – Working Principle – Clean
The purpose of this function is to clean the drum of residual toner and hence make the drum ready for next copy. Otherwise the residual image will be copied on to the subsequent copy.
The pre-clean corotron loosens the residual image from drum making removal of residual toner easier. Removal is carried out by means of plastic scrapper blade, which is held against the surface of the drum.
As the drum rotates, the residual toner is scraped off by the cleaning blade thereby ensuring that there is no left over toner and the surface of the drum is clean and ready for fresh charge.
Residual toner scraped from the drum is thrown away and not re-used as it may be contaminated by paper dust.