How Things Work

Download Report

Transcript How Things Work

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
A.
make the shock you’ll get worse
make the shock you’ll get weaker
leave the shock you’ll get unchanged
B.
C.
Xerographic Copiers 3
Observations About Copiers






Copies consist of black powder stuck on paper
After jams, the powder sometimes wipes off
Copiers run out of black powder or “toner “
Copies are often warm after being made
Copies are staticy and clingy
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 does a copier spray charge on a surface?
How does a copier make its copies permanent?
Xerographic Copiers 5
Question 1

How can light arrange black powder on paper?
Xerographic Copiers 6
The Xerographic Concept

The xerographic concept
projects an image of the document onto a surface
 that has been sprayed with electric charges.
 Wherever light hits that surface, the charges escape.
 The remaining charges attracts black toner particles
 which are then attached to paper to produce a copy.


The surface is a photoconductor,
an insulator that turns into a conductor in the light,
 so illumination allows charges to move and escape.

Xerographic Copiers 7
Question 2

How does a copier spray charge on a surface?
Xerographic Copiers 8
Electric Fields (Part 1)


There are two ways to view electric forces
The first view is charge-on-charge,


in which charge 1 pushes directly on charge 2.
The second view is charge-field-charge,
in which charge 1 creates an electric field
 and that electric field pushes on charge 2.


Although this electric field sounds fictional,

it actually exists!
Xerographic Copiers 9
Electric Fields (Part 1)

An electric field
is a structure in space that pushes on electric charge
 and is vector in character: magnitude and direction.


At each point in space, the electric field’s
magnitude is proportional to force on + test charge
 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
The total potential energy of a positive charge
is proportional to the voltage at its location in space,
 so it accelerates toward decreasing voltage.



But a charge accelerates with 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
they can move to minimize their potential energies.
 At equilibrium, the metal has a uniform voltage,
 and there is no electric field inside the metal.


Outside a metal, charges can’t move freely, so
they cannot minimize their potential energies.
 At equilibrium, voltages can vary with location,
 and there can be an electric field outside the metal.

Xerographic Copiers 12
Corona Discharges

Outside a sharp or narrow metal at high voltage,
the voltage varies rapidly with position,
 so that the electric field is very strong
 and it can push charges onto passing air particles.


This phenomenon is a corona discharge
in which the narrow metal sprays charges
 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
A.
make the shock you’ll get worse
make the shock you’ll get weaker
leave the shock you’ll get unchanged
B.
C.
Xerographic Copiers 14
Question 3

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
Those charges precoat a photoconductor
It projects a light onto the photoconductor
The charges escape from illuminated regions
The remaining charges attract toner particles
Those particles are fused to the paper as a copy