Charging Systems and Dependent Processes in Xerography

1. Charging Systems and Dependent Processes in Xerography 0

2. OUTLINE • OVERVIEW • - Charging system applications • Product examples • CORONA DEVICES • - Geometry • - Performance criteria • - Capacitive charging model • Device dependent electrical behavior BIAS CHARGING & TRANSFER ROLLS 1

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4. Charging System Applications 3

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7. M Y K C ROS ROS ROS ROS Bias transfer roll (BTR) Intermediate Belt (IBT) BTR Paper Fuser Tandem Architecture – Single Pass Color 6

8. ROS ROS ROS Fuser Image on Image – Single Pass Color Hybrid Scavenge less Development ROS DC&AC Charge scorotrons Photoreceptor Cleaner Preclean dicorotron Acoustic Transfer Assist Pre-transfer discorotron Transfer assist blade Transfer dicorotrons 7

9. Corona Devices and Characteristics 8

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11. Dry Air at Atmospheric Pressure. Positive Needle-Plane Corona 10

12. BareWire Corona Emission 11

13. Corona Devices Corotron: Uses small diameter wire or pin array electrode and is the simplest of all corona devices. Used in many products. (DC and or AC) Wire Scorotron: Small diameter wire electrode behind a screen. Wire and screen voltages are independently set. Typically DC.. Pin Scorotron: Similar to a wire scorotron, except that an array of pins is used for the coronode. Pins eliminate wire vibration, enable width, improve reliability and generate less ozone . Negative DC device. Discorotron: The coronode is a glass-coated wire. The dielectric coating is Xerox-unique technology that enables exceptional uniformity (+/- 5%) and reliability. Dicorotron: a discorotron without the grid (screen). First technology used by Xerox with negative charging belt photoreceptors. 12

14. Device Characteristics Shape Factor 13

15. Device Characteristics Uniformity 14

16. I total Vc I shield I plate V plate Slope= ΔI plate/L Δ V plate I-V Behavior Increasing V wire (Itotal) Iplate/L(length) Bareplate voltage (Vplate) V intercept • The slope and intercept voltage are important attributes of corona devices. 15

17. Corona Devices and Characteristics Capacitive Charging Model 16

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21. DEFINITIONS • Power Supply Operating modes: • Constant Current – Implies constant current delivered to the process independent of device characteristics. • Constant Total Current – Total device corona current is maintained constant. Current delivered to the process may vary. • Constant Coronode Voltage (wire or pins) – Applied voltage is held constant. • Constant Shield Voltage – Unique to dicorotrons. The shield bias is maintained constant. • Constant Grid Voltage – Unique to scorotrons. The grid bias is maintained constant. • Process Operating modes: • Constant Voltage – Charge receiving surface(s) are charged to a constant voltage independent of receiver electrical and mechanical characteristics. Requires high slope, voltage sensitive I-V behavior. • Constant Charge Density – Charge receiving surface(s) are charged to a constant charge density independent of receiver electrical and mechanical characteristics. Requires low slope, voltage insensitive I-V behavior. 20

22. Ideal Capacitive Model 21

23. I total Vc I plate V plate I total J(x) current density Vc Beam Profile (Gx) ∫G(x) = 1 Vinitial Vfinal dielectric Velocity (v) Capacitive Charging Model Slope (S)= ΔI plate/L Δ V plate Iplate/L(length) I=-S (Vintercept-Vplate) Bareplate voltage (Vplate) V intercept J(x) = I G(x) J(x) = -S(Vintercept-Vplate) G(x) Q(x) = CV(x) C = capacitance of charge receiving surface dQ(x)/dt = CdV(x)/dt = J(x) CdV(x)/dt = -S[Vintercept-V(x)] G(x) dt = dx/v CdV(x) v/dx = -S[Vintercept-V(x)] G(x) 22

24. ∞ Vfinal ∫dV(x) / (Vintercept – V(x)) = - S / Cv ∫G(x) dx ∞ Vinitial where ∫G(x) dx 0 0 ∫J(x) dx = J = CvdV(x) (where dV(X) = Vfinal - Vinitial ) J = CvdV(x) = Cv (Vfinal - Vinitial) (substitute for Vfinal) J = Cv(Vintercept – Vinitial) (1-exp-SCv) 0 Final Voltage dV(x) / (Vintercept – V(x)) = - S / CvG(x)d(x) Vfinal = V intercept [1- exp-(S/Cv)] + [exp-(S/Cv)]Vinitial Dynamic Charging Current Q(x) = CV(x) J(x) = (dV(x)/dt)C = C(dV(x)/dx)(dx/dt) J(x) = CvdV(x)/dx ∞ 23

25. Photoreceptor Charging and Sample Calculations 24

26. Constant Voltage 25

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29. P/R Charging Current Solution J = Idyn./L=Cv(Vintercept-Vinitial)1-exp-S/Cv Idyn./L = P/R dynamic charging current per unit length (amps/meter) Substitute values: Idyn./L = (.95)(.254)[-2000-(-25)][1-exp-(0.2/(0.95)(0.254)] Idyn./L = -268.5X10- 6 amps/meter Idyn. = Idyn./L x L = -268.5 X 10 - 6 amps/meter x 0.3 m. = 80 x 10– 6 amps 28

30. P/R Charging Problem Statement 2. An AC scorotron will be utilized to charge the same ideal photoreceptor to within 98% of its –800 volt grid potential at the same P/R surface velocity (10 ips.=0.254 m./sec.). The static I-V characteristics show that the intercept voltage is approximately equal to the grid bias as expected. The initial residual photoreceptor potential entering the charge device is 0. What must the voltage sensitivity (slope) of the device be to achieve this function? 29

31. P/R Charging Problem (cont’d) Vfinal = V intercept [1- exp-(s/cv)] + [exp-(s/cv)]Vinitial solving for slope (s): s=-cvln[(Vfinal - Vintercept)/( Vinitial - Vintercept)] Vinitial = 0 Vintercept = Vgrid = -800 volts Vfinal = .98Vgrid = .98(-800) Vfinal = -784 volts C = .95 x 10-6 farads/m2 v = 0.254 m./sec. s=-cvln[(Vfinal - Vintercept)/( Vinitial - Vintercept)] s= - (.95 x 10-6 farads/m2)(.254m./sec.) ln[(-784+800)/(0+800)] s= 0.94x10-6 amps/m-volt 30

32. Electrical Analogy of Photoreceptor Charging 31

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34. Charging Process 33

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36. Current Voltage Sensitivity 35

37. Equivalent Circuits and Corotron Current-Voltage Behavior 36

38. DC Corotrons 37

39. Ozone Generation 38

40. Corona Materials Wire Corotrons/Scorotrons tungsten/oxidized tungsten (3.5 mil + corona; 2mil neg. corona) Platinum (field replacement for + corona in legacy products) Gold coated tungsten (some) neg. corona Pin Corotrons/Scorotrons Beryllium copper, phosphor bronze Dicorotron 3-4 mil diameter triple polished tungsten core with glass overcoat, 9 mil overall diameter (core+glass) Grid Materials 304 stainless steel with Electro dag overcoat to inhibit “Parking Deletions” Corona Compatible Plastics Talc filled Polypropylene is preferred. Dielectric grade Noryl (Polyphenylene oxide with minimum 10% mineral or talc filler) 105A

41. Bias Charging and Transfer Rolls (BCR / BTR) 106

42. Photoreceptor Charging 106A

43. Effect of AC fac=1000Hz • A steady state DC voltage approximately equal to the DC bias • is achieved when the applied AC is high enough to generate • both positive and negative corona. Palghat Ramesh 112

44. BIAS CHARGING ROLL • ADVANTAGES • - Size • - Low Ozone • - Applied voltages are lower than corona devices • - “Doubles” as P/R charge neutralizer (some low end products) • DISADVANTAGES • - “Robust” uniform charging appears to require AC • - AC adds to power supply UMC • - AC capacitive currents can be high • - AC (positive corona ½ cycle) degrades P/R transport layer • LIMITATIONS • Extensibility to higher process speeds? 118

45. REFERENCES (cont’d.) • EXTERNAL ARTICLES • “Pin” Models – (K. Pietrowski, Walsh) • Corona Charging – (K. Pietrowski, et al) • Corona Physics – (C. Gallo, W. Lama) • EXTERNAL REFERENCES • Williams, E.M. (1984), Physics and Technology of • Xerographic Processes, John Wiley and Sons, New York. • Schaffert, R.M. (1975), Electrophotography, 5th ed., Focal • Press, London. 138