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How Photocopiers Work

Analogue Photocopiers

Analogue photocopiers use traditional xenography processes to duplicate a document, using the process of combining static electricity with a dry plastic chemical powder called ‘toner’. This is the process by which analogue photocopying takes place:

  1. The original is placed on a clear glass plate
  2. When the user initiates the process using a button, the copy paper is collected from the paper cassette using the paper feed, and inserted into the paper transport, while a fluorescent or incandescent lamp is turned on underneath the glass
  3. The light from the exposure lamp shining on a strip of the original image through the glass carries a reflection of the portion of image onto a mirror. In this way, the lamp is shifted along the document to light a portion of the image at a time
  4. The mirror is positioned to project the image light into a rotating photoconductive drum
  5. As the photosensitive film on the drum reacts to the light, the Charge Corona applies a negative charge to the drum to create static electricity where the light has formed an active image representation on the drum
  6. As the drum rotates passed the development toner unit, the toner powder consisting of negatively charged developer material is attracted to the drum surface where the image is arranged in the form of negative charge
  7. The toner attaches to the drum in the arrangement of the image, and is carried by the drum to where it meets the copy paper
  8. The Transfer Corona then separates the charges by attracting the toner away from the drum and onto the paper, forming the image on the paper as the drum rotates passed the corona.
  9. The drum continues to rotate on and passes a cleaning unit, which collects residue toner and developer left on the drum, and removes any residue charge from the drum to be clean for the next copy
  10. The paper with the toner is passed on to the Fuser Unit, which uses the heating element on the upper roller to melt the toner plastic and release the ink pigment onto the paper, and press it onto the paper.
  11. The paper is then transported on, and often brushed for any residue, before exiting the copier onto the paper/catch tray

Digital Photocopiers

Digital photocopiers are not so dissimilar in process to analogue copiers when you consider the printing element of producing a copy. However, there are commonly two types of printing mechanisms in copiers: Inkjet and Laser.

For either type, digital copiers can be considered as having a laser scanner component to copy and digitise the original, and a printer element with either of two mechanisms The scanning component is the fundamentally digital part of a digital copier, and takes the following process:

  1. The original document is placed on a clear glass plate
  2. The user can manipulate the number of copies, scale and other attributes using a digital control panel
  3. Once the user initiates the copying process using a start button, the copy paper is collected from the paper cassette using the paper feed and inserted into the paper transport, while a fluorescent or incandescent lamp is turned on underneath the glass
  4. The light from the exposure lamp shining on a strip of the original image through the glass carries a reflection of the portion of image onto a mirror. In this way, the lamp is shifted along the document to light a portion of the image at a time
  5. The CCD panel converts each strip of image light into a signal of information for each row of a raster
  6. The signal is passed through an analogue to digital converter for the Raster Image Processor (RIP), which creates a raster image copy of the original, storing it in memory
  7. The raster image can then undergo image processing for the attributes set by the user before initiating the copy, and any other advanced image processing such as orientation correction

Digital copiers ‘memorize’ an image very quickly, and as a result of storing it in memory, multiple copies can be produced very quickly, as shifting the lamp along the original is the most time consuming part of the process.

After any image processing and image handling is completed, the RIP outputs the signal to the printing section of the copier.

In laser photocopiers, the signal is passed through a laser gun, which then acts as the light source to project each line of image information onto the rotating photosensitive drum to recreate the image on the drum as an arrangement of static electricity. This then follows the same printing process as an analogue photocopier. This laser-induced printing process is also similar to what happens in a laser printer.

In inkjet photocopiers, the RIP passes the signal through electrical circuitry that controls the horizontal movement of the printhead across the paper and the heat to set the ink at the positions required on each line, just like it does for inkjet printers.