Developing unit and density control method in electrophotography

1. An ink developing unit comprising:

a) a developer roll comprising a developer roll surface and a first voltage is applied to said developer roll surface;

b) a charge depositor, wherein said charge depositor is positioned to maintain a gap with said developer roll and a second voltage is applied to said depositor;

c) a cleaning device for said developer roll, wherein said cleaning device is in contact with the developer roll surface or an ink layer plated on the developer roll surface; and

d) an ink container, wherein said developer roll, said depositor and said cleaning device are inside said ink container,

wherein a current measuring device is present to measure current flow between said depositor and said developer roll, or a voltage meter is present to measure a voltage across a known resistor that is in series with a power supply to the depositor.

2. A developing unit according to claim 1 , further comprising a skive device.

3. A developing unit according to claim 2 , wherein said skive device comprises a skive roll.

4. A developing unit according to claim 2 , wherein said skive device comprises a skive blade.

5. A developing unit according to claim 1 , further comprising a positively charged ink.

6. A developing unit according to claim 1 , further comprising a negatively charged ink.

7. A developing unit according to claim 1 , wherein said developer roll comprises a roll.

8. A developing unit according to claim 1 , wherein said developer roll comprises overall volume resistivity being less than or equal to 10 3 Ω-cm.

9. A developing unit according to claim 1 , wherein said developer roll comprises overall volume resistivity being at least 10 5 Ω-cm.

10. A developing unit according to claim 1 , wherein said depositor comprises overall volume resistivity being less then or equal to 10 3 Ω-cm.

11. A developing unit according to claim 1 , wherein said depositor comprises a roll.

12. A developing unit according to claim 1 , wherein said cleaning device comprises a roll.

13. A developing unit according to claim 1 further comprises a current measuring means connected to said depositor and said developer roll for measuring current flow between said depositor and said developer roll.

14. An ink developing unit comprising:

a) a developer roll comprising a developer roll surface and a first voltage is applied to said developer roll surface;

b) a charge depositor, wherein said charge depositor is positioned to maintain a gap with said developer roll and a second voltage is applied to said depositor;

c) a cleaning device for said developer roll, wherein said cleaning device is in contact with the developer roll surface or an ink layer plated on the developer roll surface;

d) an ink container, wherein said developer roll, said depositor and said cleaning device are inside said ink container; and

e) a skive device;

wherein a current measuring device is present to measure current flow between said depositor and said developer roll, or a voltage meter is present to measure a voltage across a known resistor that is in series with a power supply to the depositor wherein said second voltage is applied to said skive device which comprises a conductive material.

15. A method for maintaining constant density in an electrophotographic imaging process comprising the steps of:

a. Providing a developing unit comprising a developer, a depositor, a cleaning device, and an ink container, wherein said developer, said depositor and said cleaning device are inside said ink container;

b. Providing an ink in said ink container;

c. Applying a first voltage to said developer;

d. Moving said developer;

e. Applying a second voltage to said depositor; and

f. Controlling a plating current between said developer and said depositor to obtain a constant thickness of ink plated on a surface of said developer by adjusting said first voltage, said second voltage, or a combination thereof.

16. A method for maintaining constant density according to claim 15 , wherein at least one of said first voltage and said second voltage is determined by reference to at least one lookup table.

17. A method for maintaining constant density according to claim 15 , wherein said second voltage is greater than said first voltage when said ink is a positively charged ink.

18. A method for maintaining constant density according to claim 15 , wherein said first voltage is greater than said second voltage when said ink is a negatively charged ink.

19. An ink developing unit comprising:

a) a developer roll comprising a developer roll surface and a first voltage is applied to said developer roll surface;

b) a charge depositor, wherein said charge depositor is positioned to maintain a gap with said developer roll and a second voltage is applied to said depositor;

c) a cleaning device for said developer roll, wherein said cleaning device is in contact with the developer roll surface or an ink layer plated on the developer roll surface;

d) a skive device; and

e) an ink container, wherein said developer roll, said depositor and said cleaning device are inside said ink container,

wherein a current measuring device is present to measure current flow between said depositor and said developer roll, or a voltage meter is present to measure a voltage across a known resistor that is in series with a power supply to the depositor, and wherein the results of measuring the current or the voltage direct control of a plating current between said developer roll and said depositor to obtain a constant thickness of ink plated on a surface of said developer roll by adjusting at least one said first voltage, said second voltage, or a combination thereof.