Xerography/Electrophotography: The Technology of Photocopiers and Laser Printers
1. Xerography/Electrophotography:
The Technology of Photocopiers
and Laser Printers
MAE Seminar
April 14, 2003
Fa-Gung Fan
Wilson Center for Research & Technology
Xerox Corporation
Webster, NY
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
2. Outline of the Talk
Part I. General Overview of Xerography
Xerographic Process
Brief Description of Subsystems
Transport, Deposition and Removal of Fine
Particles (Toner) in Xerography
Part II. Modeling of Electrostatics
Charging & Transfer Subsystems Using Biased
Rolls
Modeling the Electrostatics of a Biased Rolls
Modeling a Transfer Subsystem Using A Biased
Transfer Roll
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
3. Part I.
General Overview of Xerography
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
4. Xerographic Process
5
2 Fusing
Exposure
1 6
Cleaning
Charging
4
Transfer
Photoreceptor
SN
SN
Substrate
N
S N
Development
Paper
3
C. Duke, J. Noolandi, T. Thieret, “The surface
science of xerography,” Surface Science, 500, p.
1005, (2002)
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
5. Xerox Phaser 7700 Color Desktop Laser
Printer
22 prints/min, full-color
Xerography is a versatile technology that scales from desktop, to
office, to production machines; black-and-white, hightlight color,
and full color.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
6. DocuColor 40 Pro Color Office
Multifunction Machine
40 prints/min, full-color
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
7. DocuTech 6180 Production Publisher
180 prints/min
Black-and-White
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
8. DocuColor iGen3 Digital Production Color
Press
100 prints/min, full-color
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
9. iGen3
Xerographic Unit
Finisher/Binder
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
10. Photoreceptor
A semiconductor whose
conductivity is a strong 0
0 5
Voltage on Surface (V)
function of light exposure.
_ _ _ _ _ _ _ _ _ _ _
_+_+
-1000
++ + + + + + ++ ++ + + +
Exposure (ergs/cm2)
Electron/hole pairs
• Requirements
– Insulator in the dark.
– Conductor when exposed to light
– Builds up enough voltage.
– Uniform properties
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
11. Charging Subsystem
HV Power HV Power HV Power
Supply (-) Supply (-) Supply (-)
Free ions are attracted Rapidly moving electrons Electrons continue to
to wire; Free electrons are and ions collide with air follow Electric Field lines
repelled. Counter-charges molecules, ionizing them to Photoreceptor until
build up on grounded surfaces. and creating a corona. uniform charge builds up
Positive Ions
Electrons
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
12. Imaging/Exposure
Traditional Analog Copier Laser Printer
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
13. Development
Photoreceptor Photoreceptor
Toner
Apply E
Field E
Development roll Development roll
Development
Photoreceptor
Roll
Charge particles
triboelectrically
Electric field moves
Mixing
Charging particles from developer
roll to photoreceptor
Triboelectrification of
toner particles and carrier
beads
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
14. Toner
• Charging
• Adhesion/cohesion
• Powder flow
• Rheology
5-10 microns
• Color - hue and density
• Pigment dispersion
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
15. Toned Carrier Bead
q ≅ 2 x 104 e
m ≅ 2 x 10-10 gm
q/m ≅ 16 µC/gm
20 µm
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
16. Transfer
Paper
Apply E Paper
Paper Field &
Separate E
Photoreceptor Photoreceptor
Photoreceptor
Electric field moves particles from
photoreceptor to paper or transparency
Detachment field must overcome toner
adhesion to photoreceptor
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
17. Fusing Subsystem
Permanently affix the image to the final substrate
paper of various roughnesses and surface treatment
transparency (plastic)
Apply heat and/or pressure
Hot Roll Fuser: Pressure Roll
Unfused toner Fused toner Paper
Elastomer Heat Roll
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
18. Cleaning and Erase
Removes unwanted residual toner and charge
from photoreceptor before next imaging cycle
Physical agitation removes toner (blade or brush)
Light neutralizes charge by making entire photoreceptor
conductive
Photoreceptor
_
_
_
_
_
Charge
Residual toner
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
19. Particle Transport, Deposition and
Removal in Xerography
Toner must flow smoothly
down dispenser
Toner must develop
onto roll uniformly
Toner must transfer from
roll to paper
paper
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
20. Toner Adhesion Forces
Fa Particle adhesion
depends on:
++ + ++
+ Size, shape, &
roughness
+ Materials
+
+
+ + Flow agents
++ ++
Charge
Surface charge
Fad distribution on
particle
Detachment when Fa > Fad
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
21. Electrostatic Image Force Model
Q
Fa σ=
E R 4 π R2
Fi
Image Force Applied Force
Q2
Fi = − α Fa = β QE − γ π ε o R 2 E 2
16 π ε o R2
αQ
Ed ≅ ≈ 1 V / µm
β 16 π ε o R 2
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
22. Charge Patch Adhesion Model
Q = σ At
Fa
Ac
Ac
Fad f =
At
2
σ
F ad = − A c − W A c
2 εo
σ W
= −Qf
2ε +
o σ
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
23. Electric Field Detachment of Fine Particles
Measure Many Particle Adhesion
transparent
conductive
electrodes
Donor Receiver
V
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,
10th Int. Cong. on Non-Impact Printing, 142-146
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
24. Toner Transferred
When FE > FAD
FE
-
-
Donor Surface
- -
FAD
E. Eklund, W. Wayman, L. Brillson, D. Hays, 1994 IS&T Proc.,
10th Int. Cong. on Non-Impact Printing, 142-146
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
25. Adhesion Control Additives
Changing type of additive modifies adhesion
Atomic Force Microscopy results
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
26. Part II.
Modeling of Electrostatics
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
27. Xerographic Machine Using Drum
Photoreceptor and Biased Rolls
Biased Charging Roll
1
6
1) Charge
2) Expose
2 3) Develop
3
4) Transfer
5 5) Clean
6) Erase
4
Paper or
Intermediate Belt
Biased Transfer Roll
J. Swift and S. Badesha, Surface
Science, 500, p.1024, (2002)
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
28. Biased Charging/Transfer Rolls
(BCR/BTR)
pre-nip nip post-nip Applications of Biased Rolls:
VA Charging
Transfer
Roller Drum
Shaft Insulator
Elastomer Ground plane
Field probe
C. DiRubio, G. Fletcher, Proceedings of IS&T NIP 12:
International Conference on Digital Printing Technologies,
p.334, 1996.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
29. Basic Equations
2 ρ
Electrical Potential ∇ φ =− (1)
ε
Interface Condition ∂φ ∂φ σ
− k = − k + (2)
∂n matl 2 ∂n matl1 ε 0
Electric Conduction j = γ (| E |) E where E = −∇φ (3)
Conservation of ∂σ ∂σ ∂ 2φ
+v = γ s 2 + j matl1 ⋅ n − j matl 2 ⋅ n (4)
Surface Charge ∂t ∂s ∂s
Ref. P. Ramesh, private communication
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
30. KEY Requirements for the Integrated
Model:
1. Allows Implementation volume and surface
charge density
2. Solves Poisson equation for composite
domain, and obtain electric field
3. Calculates current density
4. Solves surface charge transport
5. Handles air breakdown
In our integrated model, 1 and 2 are done in
ABAQUS/Standard (version 5.7), and 3 to 5 are
implemented as an in-house C program.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
31. Flowchart of the Integrated Model
Start
Input/Pre
child process ABAQUS
check to see if ABAQUS job is completed
UNIX fork() parent process
UNIX shell
script
Check if
air breakdown
occurs Handling air breakdown σ brk = ε 0 (Eairgap − EPaschen )
(5)
Update & solve
surface charge
Y
t < tmax
N
Stop/Post
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
32. Modeling of Biased Charging Roll (BCR) &
Comparison with Field Probe Measurement
C. DiRubio, G. Fletcher, “Field profile Parameters used in the field probe
measurements in biased charging experiment:
systems,” Proceedings of Image
Science &Technology NIP 12, p.334, Elastomer:
1996 outer diameter = 37.83 mm
inner diameter = 25.24 mm
pre-nip nip post-nip dielectric constant = 4.4
resistivity = 5.0E+9 ohm-cm
VA
Insulator (kapton tape):
thickness = 33 microns
dielectric constant = 2.7
Roller Drum Field Probe (magnet wire):
Shaft Insulator diameter = 1.72 mm
Elastomer Ground plane
Field probe
Nip Width (contact) = 2.7 mm
Schematic of the nip region
of the experimental Charge Relaxation Time = 0.22 sec
apparatus.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
33. σ probe
Eair = (6)
ε0 30
Τ=32
25 Τ=1
where σ probe = Q / Aprobe
20
Eair (V/µ m)
15
Τ=0.35
dwell time based on effective nip width
10
T= Τ=0.13
charge relaxation time
5
0
T roll surface -3 -2 -1 0
x (mm)
1 2 3
speed, v
(mm/sec)
32 0.656 The field profiles for different values of T.
1 23.65 (DiRubio and Fletcher)
0.35 65.8
0.13 251.6
(data from C. DiRubio)
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
34. The computational mesh used. (yellow mesh --- elastomer; white mesh --- air gap;
blue mesh --- insulator on the drum).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
35. Potential map for T=32. The color scale is from 0V (dark blue) to 400V (red).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
36. Potential map for T=1. The color scale in this figure is from 0V (dark blue) to
697V (red).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
37. Nip
The blow-up of the nip region shown in previous slide. The contours represent equal
electrical potentials (for T=1). The field lines are orthogonal to these equi-potential
lines.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
38. Potential map for T=0.13. The color scale in this figure is from 0V (dark blue) to
822V (red).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
39. Pre-Nip Nip Post-Nip
The model predictions of field profile for various values of T as evaluated from Eq.(6).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
40. 30
Τ=32
25 Τ=1
20
Eair (V/µ m)
15
Τ=0.35
10
Τ=0.13
5
0
-3 -2 -1 0 1 2 3
x (mm)
The field profiles for different values
of T as measured with 1.72mm probe.
The field profiles seen by a 1.72mm probe as (DiRubio and Fletcher)
predicted by the model. (The high-resolution field profiles
from the model were first averaged with a circular area of 1.72mm
diameter, and then shifted so that the position of the peak field for
each curve is at x=0.) The profiles on this figure should
be compared with the measured ones (at the right).
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
41. Transfer Subsystem Using A Biased
Transfer Roll
Photoreceptor
(PR)
Photoreceptor:
ITB:
BTR Elastomer:
Nip
Post-Nip
Pre-Nip
Intermediate Transfer Belt (ITB)
v = Belt speed
Bias Transfer
Roll (BTR)
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
43. The region that is included in the model and the computational mesh used. (yellow
mesh --- BTR elastomer; magenta mesh --- ITB; cyan mesh --- PR material coated on
the drum; white mesh --- air gap)
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
44. The steady-state potential map of the modeled domain. The contours displayed in this
figure are the equi-potential contours.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
45. Post-Nip Nip Pre-Nip
Field profile in the ITB-PR air gap. The Paschen breakdown limit for
the air gap is also plotted.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
46. Post-Nip Nip Pre-Nip
The field profile in the BTR-ITB air gap.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
47. Nip
The variations of charge densities on different surfaces. The relevant surfaces shown
here are the photoreceptor surface, the upper surface of ITB, the lower surface of
ITB, and the BTR surface.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
48. Transfer Subsystem I-V Curves
increase in
resistivity
I-V curves for different values of BTR resistivities.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
49. Transfer Subsystem I-V Curves
I-V curves for four different field-dependent BTR
resistivities.
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003
50. Summary:
We discussed:
Part I. General Overview of Xerography
Xerographic Process
Brief Description of Subsystems
Transport, Deposition and Removal of Fine Particles (Toner)
in Xerography
Part II. Modeling of Electrostatics
Charging & Transfer Subsystems Using Biased Rolls
Modeling the Electrostatics of Biased Rolls
Modeling a Transfer Subsystem Using A Biased Transfer
Roll
Fa-Gung Fan, Xerox Corporation MAE Dept. Seminar, Clarkson University, 4/14/2003