Page 177 - Graphic Design and Print Production Fundamentals

6.3 Electrophotography

Roberto Medeiros

Electrophotography (also known as xerography) is a complex process commonly used in copiers and
faxes, as well as in digital printers. It is an imaging technology that takes a digital file and utilizes a
photoreceptor, light source, electrostatic principles, and toner to produce the printed output. Before this
process was used for digital printing, it was extensively used in analog copiers where a lamp illuminated
the page being copied, and then a series of mirrors reflected the page directly onto the surface of a drum.
Digital copiers replaced the direct light path with a sensor that converts the analog image into digital
information, then a laser or an LED array writes the image onto the drum. Many digital printers today
are based on the same platform as digital copiers. The technology has seen many improvements over the
years, but the electrophotographic process at its core remains relatively unchanged.

Photoreceptor

The photoreceptor is commonly referred to as a drum. It is a cylinder coated with a material that becomes
conductive when exposed to light. Areas that are not exposed have a high resistance which allows these
areas to hold the electrostatic charge necessary for the process.

Light Source

Light sources used in digital printing include LED arrays or, more commonly, lasers. VCSEL (vertical
cavity surface emitting laser) is an advanced type of laser used in the most current digital presses in the
market. A VCSEL array can position its beam with high accuracy (addressability) for optimal clarity,
resolution, and image positioning. This makes it ideally suited for a digital press.

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