How do Color Copiers Work?

Most of us have used color copiers in our professional lives. We load them with blank paper, we lift the top lid, place an original on the glass, and press the big green button. The copier then springs to life and after a few seconds, duplicates of the item we placed on the glass are delivered to the output tray.

Or we sit at our computers and click the “Print” button. By the time we get up from our desk and walk to the copier, there are multiple prints of our documents waiting for us in the output tray.

But have you ever wondered how that color copier works? Many of us take the process for granted. Much like a magical plastic box, the color copier takes our hard copy and electronic document originals and produces extremely accurate duplicates, often in vivid color.

In reality, making color copies and prints on today’s office copiers (more appropriately called Multi-Function Printers or “MFP’s”) is a complex series of processes that work together to produce a finished print. Here are how those processes work:

Input

There are basically two ways to get prints from a color MFP. First of all, you can place paper originals (often called hard copies) in the document handler or copy glass (“platen”). The originals are fed through the document handler, and digitally scanned on the platen. The resulting electronic data that is scanned (called a Raster Image) is then held in the MFP’s memory.

The second way to input images into the MFP is to print them from a computer. Users can select the MFP from their control panel, specify paper size and type, and select the quantity. Upon clicking the “Print” button, electronic data is translated and transmitted – usually wirelessly - from the computer to the MFP. Once the data is received by the MFP, it is converted from the original print file format into a bitmap file called a Raster Image. The processor in the MFP that converts the data is called the Raster Image Processor or “RIP”. The converted Raster Image is then held in the MFP’s memory.

Imaging

The Raster Image is a composite color bitmap of the hard copy original or the printed document(s). The “RIP” then separates the bitmap into its four component colors. These component colors – known as the subtractive primaries – are Cyan, Magenta, Yellow, and Black or simply “CMYK”. Each component color is sent to one of four color imaging units inside the MFP.

Each color imaging unit (one for Cyan, one for Magenta, one for Yellow, and one for Black) consists of the following imaging components:

  • A modulated laser or an LED array
  • A photoreceptor drum with a light sensitive coating
  • A corona wire
  • A developer housing containing colored toner and developer
  • A drum cleaning brush and/or soft cleaning blade (“doctor blade”)

Inside the MFP, the photoreceptor drum has a charge applied to it by the corona wire. The Raster Image data is fed to the laser or LED array, where the latent image is exposed on the drum surface, often by using a rotating mirror. This creates a charge differential on the drum surface in the areas were the image was exposed.

Inside the developer housing, an auger or mixer turns on a spindle, and mixes the colored toner – which are very finely ground plastic particles 3 to 5 microns in diameter – with iron developer pellets. This applies a charge to the toner particles much like rubbing a plastic rod with a wool glove would apply a static charge.

As the drum rotates past the developer housing, the charged toner is exposed to the drum surface and toner adheres to the areas of the drum where the image was created by the laser or LED array. The toner is then transferred to the intermediate transfer belt or “ITB”. This transfer is facilitated by a roller on the back side of the ITB that has an attracting charge applied to it.

Each primary color (C, M, Y, and K) is imaged onto its photoreceptor drum and then transferred onto the ITB by the use of an opposing transfer charge, full-color images are created on the belt. Paper is then fed from the paper tray to the transfer area of the ITB. Using yet another transfer charge roller, the color image is pulled from the ITB and transferred onto the paper.

Fusing

Now that the powdery toner image has been transferred to the paper, a final step must be taken to fix or “fuse” the toner to the paper. The paper is passed through an opposing pair of rollers or belts. One belt or roller is heated, most commonly by high-temperature lamps inside the roller. The second belt or roller is called the pressure roller and it applies pressure to the back of the paper. This heat melts the solid toner into a liquid, and the pressure drives the liquified toner into the surface of the paper. Cooling fans blow across the paper surface which cures the hot toner and paper. This creates a hard, permanent image on the paper.

Producing prints on a color MFP is a complex process using mechanical, chemical, electrical, and data processing technologies. There’s a lot going on inside that MFP for it to deliver those crisp, colorful images that we have come to expect!

To learn more about how color copiers work, click here to have your questions answered by a color copier service expert who can tell you everything you need to know about how office equipment works and how office technology can help you be more efficient and save time and money. We can help you decide which copier is best for you.

 

May 3rd 2021