Xerographic Copiers 1 Xerographic Copiers

Xerographic Copiers 2 Introductory Question You are covered with static electricity. If you hold a sharp pin in your hand as you reach out for a doorknob, the pin will You are covered with static electricity. If you hold a sharp pin in your hand as you reach out for a doorknob, the pin will A. make the shock you’ll get worse B. make the shock you’ll get weaker C. leave the shock you’ll get unchanged

Xerographic Copiers 3 Observations About Copiers Copies consist of black powder stuck on paper Copies consist of black powder stuck on paper After jams, the powder sometimes wipes off After jams, the powder sometimes wipes off Copiers run out of black powder or “toner “ Copiers run out of black powder or “toner “ Copies are often warm after being made Copies are often warm after being made Copies are staticy and clingy Copies are staticy and clingy Some copiers scan a light, some use a flash Some copiers scan a light, some use a flash

Xerographic Copiers 4 3 Questions about Xerographic Copiers How can light arrange black powder on paper? How can light arrange black powder on paper? How does a copier spray charge on a surface? How does a copier spray charge on a surface? How does a copier make its copies permanent? How does a copier make its copies permanent?

Xerographic Copiers 5 Question 1 How can light arrange black powder on paper? How can light arrange black powder on paper?

Xerographic Copiers 6 The Xerographic Concept The xerographic concept The xerographic concept projects an image of the document onto a surface projects an image of the document onto a surface that has been sprayed with electric charges. that has been sprayed with electric charges. Wherever light hits that surface, the charges escape. Wherever light hits that surface, the charges escape. The remaining charges attracts black toner particles The remaining charges attracts black toner particles which are then attached to paper to produce a copy. which are then attached to paper to produce a copy. The surface is a photoconductor, The surface is a photoconductor, an insulator that turns into a conductor in the light, an insulator that turns into a conductor in the light, so illumination allows charges to move and escape. so illumination allows charges to move and escape.

Xerographic Copiers 7 Question 2 How does a copier spray charge on a surface? How does a copier spray charge on a surface?

Xerographic Copiers 8 Electric Fields (Part 1) There are two ways to view electric forces There are two ways to view electric forces The first view is charge-on-charge, The first view is charge-on-charge, in which charge 1 pushes directly on charge 2. in which charge 1 pushes directly on charge 2. The second view is charge-field-charge, The second view is charge-field-charge, in which charge 1 creates an electric field in which charge 1 creates an electric field and that electric field pushes on charge 2. and that electric field pushes on charge 2. Although this electric field sounds fictional, Although this electric field sounds fictional, it actually exists! it actually exists!

Xerographic Copiers 9 Electric Fields (Part 1) An electric field An electric field is a structure in space that pushes on electric charge is a structure in space that pushes on electric charge and is vector in character: magnitude and direction. and is vector in character: magnitude and direction. At each point in space, the electric field’s At each point in space, the electric field’s magnitude is proportional to force on + test charge magnitude is proportional to force on + test charge and direction is direction of that force. and direction is direction of that force.

Xerographic Copiers 10 Voltage Gradients and Electric Fields Objects always accelerate so as to reduce their total potential energies as quickly as possible Objects always accelerate so as to reduce their total potential energies as quickly as possible The total potential energy of a positive charge The total potential energy of a positive charge is proportional to the voltage at its location in space, is proportional to the voltage at its location in space, so it accelerates toward decreasing voltage. so it accelerates toward decreasing voltage. But a charge accelerates with an electric field, But a charge accelerates with an electric field, so a voltage gradient (a slope) is an electric field! so a voltage gradient (a slope) is an electric field!

Xerographic Copiers 11 Electric Fields In and Around Metals Inside a metal, charges can move freely, so Inside a metal, charges can move freely, so they can move to minimize their potential energies. they can move to minimize their potential energies. At equilibrium, the metal has a uniform voltage, At equilibrium, the metal has a uniform voltage, and there is no electric field inside the metal. and there is no electric field inside the metal. Outside a metal, charges can’t move freely, so Outside a metal, charges can’t move freely, so they cannot minimize their potential energies. they cannot minimize their potential energies. At equilibrium, voltages can vary with location, At equilibrium, voltages can vary with location, and there can be an electric field outside the metal. and there can be an electric field outside the metal.

Xerographic Copiers 12 Corona Discharges Outside a sharp or narrow metal at high voltage, Outside a sharp or narrow metal at high voltage, the voltage varies rapidly with position, the voltage varies rapidly with position, so that the electric field is very strong so that the electric field is very strong and it can push charges onto passing air particles. and it can push charges onto passing air particles. This phenomenon is a corona discharge This phenomenon is a corona discharge in which the narrow metal sprays charges in which the narrow metal sprays charges and can easily deposit or dissipate static electricity. and can easily deposit or dissipate static electricity.

Xerographic Copiers 13 Introductory Question (revisited) You are covered with static electricity. If you hold a sharp pin in your hand as you reach out for a doorknob, the pin will You are covered with static electricity. If you hold a sharp pin in your hand as you reach out for a doorknob, the pin will A. make the shock you’ll get worse B. make the shock you’ll get weaker C. leave the shock you’ll get unchanged

Xerographic Copiers 14 Question 3 How does a copier make its copies permanent? How does a copier make its copies permanent?

Xerographic Copiers 15 Xerographic Process

Xerographic Copiers 16 Copier Structure

Xerographic Copiers 17 Summary about Xerographic Copiers It sprays charges from a corona discharge It sprays charges from a corona discharge Those charges precoat a photoconductor Those charges precoat a photoconductor It projects a light onto the photoconductor It projects a light onto the photoconductor The charges escape from illuminated regions The charges escape from illuminated regions The remaining charges attract toner particles The remaining charges attract toner particles Those particles are fused to the paper as a copy Those particles are fused to the paper as a copy