Introduction to Xerography

Introduction to Xerography

• Xerography is a process used in many office machines like fax machines, printers, and copiers.
• It involves putting images on paper.

Inventor of Xerography

• Chester Carlson, a patent attorney, invented xerography in 1938.

Xerography Process Overview

• Xerox equipment and most copiers use a xerographic process.
• Laser printers also use this process.
• Plain paper fax machines also use this technology.
• The process knowledge serves as a base for understanding future Xerox-related subjects.

Basic Intake Course ASP Engineer Objectives

• Participants will understand xerography, its operations, and processes.
• Participants will learn the difference between analog and digital systems and their advantages.
• Participants will learn the basic procedures for safely handling the machine.
• Participants will be able to analyze machine processes using schematic diagrams and fault isolation procedures.

Photoreceptor Components

• Photoreceptor is the core of the machine.
• It receives, processes, and transfers images using static electricity.
• Most small copiers use a drum-type photoreceptor.
• Larger equipment uses a belt-type photoreceptor.
• The key ingredients are light-sensitive materials.
• A photoreceptor has four layers:
  • Substrate: connects the photoreceptor to the ground, completing an electrical circuit.
  • Oxide layer: connects the photoconductive layer to the substrate.
  • Photoconductive layer: is affected by light. In darkness, it insulates, maintaining charge on the trapping layer.
  • Trapping layer: stores the static charge.

Exposure

• When light hits the photoreceptor, the photoconductive layer becomes conductive (allowing current flow).
• This allows the charge on the trapping layer to flow through the oxide layer to the substrate.
• Where light doesn't hit, the charge remains. This creates a latent image on the photoreceptor, with charged and discharged areas.

Charging

• The photoreceptor is charged in darkness.
• The charge dissipates when exposed to light.
• A charge corotron places a uniform positive charge on the photoreceptor surface.
• Ionized air causes the air near the corotron to become positively charged.
• This positively charged air removes electrons from the photoreceptor, making it positively charged.

Developing

• Carrier beads carry toner to the photoreceptor. Carrier beads are heavier than toner.
• Toner is attracted to the carrier beads due to static electricity.
• Toner is negatively-charged
• A mixture of toner and carrier beads (developer) is created
• The magnetic brush or cascading process transfers developer to the photoreceptor.
• The output is a developed image on the photoreceptor, with toner attracted to the charged areas.

Transferring

• Paper is positioned over the developed image on the photoreceptor.
• Another corotron adheres the paper to the photoreceptor.
• Toner also strongly adheres to the paper.
• The toner on the paper is now transferred from the photoreceptor to the paper.
• The output is a copied image on the paper.

Fusing

• Toner still exists as a fine powder on the paper, and can be easily smudged.
• Heat and/or pressure melt the toner into the paper fibers.
• The output is a permanent image on the paper.

Cleaning

• The photoreceptor is cleaned to prepare for the next cycle.
• Residual charges and toner are removed to prepare to accept the new image.
• Two steps:
  • Remove residual charges using AC corotron to neutralize positive charges on the photoreceptor as well as the negative charges on the residual toner
  • Remove residual toner using a flexible cleaning blade

Digital Exposure

• Modern copiers, unlike printers, don't use hard copy originals.
• Copiers have an optical scanning device to convert images to digital information before digital-image processing.
• Data storage and easier document handling are benefits of digital exposure.

Color Xerography

• Color documents use a digitized method for the color copiers/printers
• The information controls the color filtering during exposure and the four developer housings
• Developer housings contain different color toners (magenta, yellow, cyan and black)
• Multiple cycles are required to generate a color copy