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The Science and Technology of Laser Printers and Photocopiers

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Slides presented at Institute of Physics, Academia Sinica, 8/27/2007

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The Science and Technology of Laser Printers and Photocopiers

  1. 1. The Science and Technology of Laser Printers and Photocopiers August 27, 2007 Fa-Gung Fan Xerox Research Center Webster Xerox Corporation Webster, NY http://www.xerox.com/innovation/wcrt.shtml Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  2. 2. Outline of the Talk Part I. General Overview of Xerography • Xerographic Process • Description of Subsystems Part II. Transport, Adhesion/Cohesion, and Removal of Fine Particles (toner) in Xerography • Measuring Toner Charge --- Cage Blowoff, Charge Spectrograph • Electrostatic Adhesion/Detachment of Toner Particles • Measuring Toner Adhesion --- Atomic Force Microscopy (AFM), Centrifuge Detachment, Electric Field Detachment • Measuring Cohesion --- Fluidized Bed Part III. Modeling & Simulation of Xerographic Subsystems • Electro-hydrodynamic Flow (Corona Wind) in Corotron Devices • Charging & Transfer Subsystems Using Biased Rolls • Modeling/Analysis of Electrostatics of Biased Rolls Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  3. 3. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  4. 4. 1 6 1) Charge 2) Expose 2 3) Develop 3 4) Transfer 5 5) Clean photoreceptor 6) Erase drum 4 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  5. 5. Xerox C118 Copier & M118 Desktop Multifunction 18 prints/minute, black-and-white (low end) Xerography is a versatile technology --- scales from desktop, to office, to production machines; black-and-white, hightlight color, and full color. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  6. 6. Office Multifunction Machines DocuColor 40 Pro DocuColor 242/260 40 prints/minute 40 to 60 prints/minute full-color full-color Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  7. 7. DocuTech 180 HighLight Production Publisher 180 prints/minute highlight color Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  8. 8. Xerox iGen3 Digital Production Color Press 110 prints/minute full-color Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  9. 9. iGen3 Xerographic Unit Finisher/Binder Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  10. 10. Subsystems and Components Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  11. 11. Photoreceptor 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  12. 12. Photoreceptor A semiconductor whose conductivity is a strong 0 0 5 Voltage on Surface (V) function of light exposure. light _ _ _ _ _ _ _ _ _ _ _ _+_+ -700 ~ -800V -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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  13. 13. 1. Charging Step 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  14. 14. Charging Subsystem (a corotron) 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  15. 15. 2. Imaging/Exposure Step data input 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  16. 16. Imaging/Exposure original document Traditional Analog Copier Laser Printer Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  17. 17. 3. Development Step 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  18. 18. Development development housing Photoreceptor Photoreceptor Toner Apply E Field E Development roll Development roll Development Development step: Photoreceptor Roll Charge particles triboelectrically Electric field moves Mixing Charging particles from developer roll to photoreceptor Toner Particles + Carrier Beads --- triboelectrification Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  19. 19. Polymer particles loaded with Toner pigment and some other additives Toner characteristics: • Charging • Adhesion/cohesion • Powder flow • Rheology 5-10 microns • Color - hue and density • Pigment dispersion Traditional toner --- produced by mechanical means from breaking down of large polymer chunks. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  20. 20. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  21. 21. Chemical Toners Xerox Emulsion polymerization and Aggregation (EA) Process Bottom-up approach in contrast to the top-down mechanical process that produces traditional toner particles. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  22. 22. 4. Transfer Step 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  23. 23. Transfer Subsystem (a corotron device) transfer corotron Paper Apply E Paper Paper Field & Separate E Photoreceptor Photoreceptor Photoreceptor In the Transfer step: Electric field moves particles from photoreceptor to paper or transparency Detachment field must overcome toner adhesion to photoreceptor Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  24. 24. 5. Fusing Step 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  25. 25. Fusing Subsystem Fusing step: 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 Fused toner Paper Elastomer Heat Roll Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  26. 26. 6. Cleaning & Erase Step 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  27. 27. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  28. 28. Part II. Transport, Adhesion/Cohesion, and Removal of Fine Particles (toner) in Xerography Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  29. 29. Transport, Adhesion/Cohesion and Removal of Fine Particles (Toner) in Xerography photoreceptor development housing drum Toner must flow smoothly down dispenser Toner must develop DC40 Pro onto roll uniformly Toner must transfer from roll to paper carrier bead paper Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  30. 30. Transport, Adhesion/Cohesion and Removal of Fine Particles (Toner) in Xerography photoreceptor development housing drum Toner must flow smoothly down dispenser Toner must develop onto roll uniformly Mag. roll Toner must transfer from roll to paper P/R drum carrier bead paper Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  31. 31. Toner Charge Measurements Blowoff Tribo Air 50 40 Q/M (µC/gm) 30 Blow toner µ from toned 20 beads in cage 10 Measure charge & mass 0 difference 0 1 2 3 4 Calculate Toner Concentration (%) average Q/M Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  32. 32. Toner Charge Measurements Charge Spectrograph 1.5 99% 95% q/D (fC/µm) 1 90% Air Flow µ 80% E Field 50% 0.5 Lycopodium 0 Inject toner 0 5 10 15 20 25 30 35 Displacement ∝ q/D -0.5 Diameter (µm) µ Measure D --- diameter of toner particle position & size of particles Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  33. 33. Toner Adhesion Forces Fa Particle adhesion depends on: ++ + ++ + Size, shape, & roughness E + Materials + + + + Flow agents ++ ++ Charge Surface charge Fad distribution on particle Detachment when Fa > Fad Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  34. 34. 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 Coulomb polarization αQ Ed ≅ ≈ 1 V / µm β 16 π ε o R 2 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  35. 35. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  36. 36. Additives Control Adhesion Changing type of additive modifies adhesion Atomic Force Microscopy results Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  37. 37. Atomic Force Microscopy (AFM) Bring toner Push toner Retract toner until near surface against surface probe releases 200 µm 20 µm Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  38. 38. AFM Measure Single Particle Adhesion Laser Photodetector Particle Cantilever Piezoelectric: moves up and down Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  39. 39. Centrifuge Detachment Measure Many Particle Adhesion Putt, putt, putt,... Vroom, vroom,... Whoosh,... Observe Donor Plate after Each Spin H. Mizes, “Adhesion of Small Particle”, Electro. Soc. Amer. Univ. of Rochester, 6/23/95 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  40. 40. Electric Field Detachment 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  41. 41. Electrical Field Detachment of Charged Toner Detachment Cell Adhesion of Triboelectrically Charged Toner 1 Transferred Fraction 0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 12 14 16 18 Detachment Field (V/µm) µ Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  42. 42. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  43. 43. Fluidized Bed Measure Powder Cohesion Stresses on the toner bed τ σ α α h σ ∆P Tension Compression σ = ρ (1−ε) gh cos α − ∆ P (1− Shear (1− τ = ρ (1−ε) gh sin α P.K. Watson, “Yield Locus of Cohesive Granular Materials”, Workshop on Dynamics of Granular Materials: Understanding & Control, Univ. of Chicago, 5/11/95 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  44. 44. 70 Te nsi on 60 C ompression Less Additives τ , She ar Stre s s (N/m2 ) 50 More Additives 40 30 20 10 0 -30 -20 -10 0 10 20 30 40 50 60 70 σ , Compre s s ive Stre s s (N/m2 ) Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  45. 45. Summary I. General Overview of Xerography • Xerographic Process • Subsystems & Components II. Transport, Adhesion/Cohesion, and Removal of Fine Particles (toner) in Xerography • Measuring Toner Charge • Electrostatic Adhesion/Detachment of Toner Particles • Measuring Toner Adhesion • Measuring Cohesion Part III. Modeling & Simulation of Xerographic Subsystems • Electro-hydrodynamic Flow (Corona Wind) in Corotrons • Charging & Transfer Subsystems Using Biased Rolls • Modeling/Analysis of Electrostatics of Biased Rolls Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  46. 46. Part III. Modeling & Simulation of Xerographic Subsystems Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  47. 47. Corona Wind in Corotrons 5 2 Fusing Exposure 1 6 Cleaning Charging 4 Transfer Photoreceptor SN SN Substrate N S N Development Paper 3 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  48. 48. Corona Wind Corona wind phenomenon is a coupling of electrical and fluid-dynamic problems. The study of this subject belongs to a branch of fluid mechanics called electrohydrodynamics (or EHD). Corotron Device Charging of a Photoreceptor Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  49. 49. Governing Equations (2-D, steady- state)  ∂ 2V ∂ 2V  Gauss’ Law ε0 2 + 2  ∂x  = −q   ∂y  Conservation of Charge ∂q ∂q  ∂ 2 q ∂ 2 q   ∂  ∂V  ∂  ∂V  u +v = D 2 + 2  + b   q  ∂x  + q    ∂x ∂y  ∂y   ∂x  ∂x   ∂y  ∂y  charge convection Conservation of Mass ∂u ∂v + =0 ∂x ∂y EHD Conservation of Momentum pumping  ∂u ∂u  ∂p  ∂ 2u ∂ 2u  ρ  u + v  = − + µ  2 + 2  + qE x  ∂x  ∂y   ∂x  ∂x  ∂y    ∂v ∂v  ∂p  ∂ 2v ∂ 2v  ρ  u + v  = − + µ  2 + 2  + qE y   ∂x ∂y   ∂y   ∂x ∂y   Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  50. 50. Kaptsov’s Condition at Coronating Wire Surface 1 E onset = ( A + B ) Peek’s law Rw Condition at Moving Substrate ∂σ ∂V V u paper = bq σ = ε0 ∂x ∂y td Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  51. 51. Electrical Potential Charge Density Air Flow Patterns Zamankhan et al., J. Imaging Sci. Technol., 50, pp. 375–385, 2006 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  52. 52. Control of Air Flow in Corotrons Fan et al., US Patent 7085512 Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  53. 53. Machines that Use Biased Rolls 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 DocuColor 40 Pro Office Biased Transfer Roll Color Multifunction Machine Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  54. 54. Electrostatics of Biased Charging/Transfer Rolls 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  55. 55. Basic Equations 2 ρ Electrical Potential ∇ φ =− ε Interface Condition  ∂φ   ∂φ  σ − k  = − k  +  ∂n matl 2  ∂n  matl1 ε 0 Electric Conduction j =γ E where E = −∇φ Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  56. 56. Modeling of Biased Charging Roll & Comparison with Field Probe Measurement Parameters used in the field probe C. DiRubio, G. Fletcher, “Field profile experiment: measurements in biased charging systems,” Proceedings of Image Science Elastomer: &Technology NIP 12, p.334, 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  57. 57. σ probe Eair = 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  58. 58. The computational mesh used. (yellow -- elastomer; white -- air gap; blue -- insulator on the drum) Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  59. 59. Potential map for T=32. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  60. 60. Potential map for T=1. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  61. 61. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  62. 62. Potential map for T=0.13. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  63. 63. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  64. 64. Transfer Subsystem Using A Biased Transfer Roll Photoreceptor Post-Nip Pre-Nip Intermediate Belt V Biased Transfer Roll Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  65. 65. Air Breakdown & Paschen Curve 50 45 Paschen Curve 40 Eair (V= -200) 35 Eair (V= -400) Eair (V/µ m) 30 Eair (V= -600) Eair (V= -800) 25 20 15 10 5 0 0 50 100 150 200 dair (µm) µ Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  66. 66. The field profile in the ITB-PR air gap. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  67. 67. The field profile in the BTR-ITB air gap. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  68. 68. 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 Academia Sinica, Taipei, Taiwan, 8/27/2007
  69. 69. increase in resistivity The I-V curves for different values of BTR resistivities. Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007
  70. 70. Summary I. General Overview of Xerography • Xerographic Process • Subsystems & Components II. Transport, Adhesion/Cohesion, and Removal of Fine Particles (toner) in Xerography • Measuring Toner Charge • Electrostatic Adhesion/Detachment of Toner Particles • Measuring Toner Adhesion • Measuring Cohesion Part III. Modeling & Simulation of Xerographic Subsystems • Electro-hydrodynamic Flow (Corona Wind) in Corotrons • Charging & Transfer Subsystems Using Biased Rolls • Modeling/Analysis of Electrostatics of Biased Rolls Fa-Gung Fan, Xerox Corporation Academia Sinica, Taipei, Taiwan, 8/27/2007

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