Toner transfer technique

1. A module included in a plurality of tandemly arranged modules in an electrophotographic color printer, said module associated with a process control system, said module comprising:

a photoconductive image-recording member;

a charging device to establish on said photoconductive image-recording member a uniform surface potential having a voltage magnitude adjustable via said process control system;

an exposure device to modulate said uniform surface potential and thereby form a latent image on said photoconductive image-recording member;

a development station to develop said latent image and thereby form a toner image on said photoconductive image-recording member;

a transfer station for electrostatically depositing said toner image onto a receiver member in a transfer nip, said transfer station having a transfer roller and a constant-current power supply for delivering to said transfer roller a transfer current;

a controller responsive to said voltage magnitude, said controller to control said constant-current power supply so as to generate said transfer current according to a functional relationship between said transfer current and a control voltage parameter derived from said voltage magnitude;

wherein in accordance with said functional relationship said transfer current has a predetermined constant magnitude if a magnitude of said control voltage parameter is less than or equal to a critical control voltage magnitude;

wherein in accordance with said functional relationship and if said magnitude of said control voltage parameter is greater than said critical control voltage magnitude, said transfer current has a linear increase of magnitude with increase of said magnitude of said control voltage, said linear increase of said transfer current characterized by a predetermined slope; and

wherein a toner control patch is produced from time to time so as to have a density substantially equal to a reference maximum density, said toner control patch derived from a patch latent image formed on said photoconductive image-recording member by said charging device and said exposure device, said patch latent image developed by said development station, said photoconductive image-recording member having been charged to said voltage magnitude prior to creating said patch latent image thereon.

2. Module of claim 1 , wherein for said magnitude of said control voltage parameter greater than said critical control voltage magnitude, said transfer current has a lowest practical value so as to maintain a useful transfer efficiency and minimize back-transfer.

3. Module of claim 1 , wherein said magnitude of said control voltage parameter is said voltage magnitude.

4. Module of claim 1 , wherein said magnitude of said control voltage parameter is said voltage magnitude minus an offset potential magnitude minus a maximum exposure potential magnitude.

5. Module of claim 1 , wherein said toner image is transferred from said photoconductive image-recording member to an intermediate transfer member and thereafter deposited in said transfer station onto said receiver member, said receiver member adhered to a transport web moved through a transfer nip in said transfer station, said transfer nip formed between said intermediate transfer member and said transfer roller.

6. Module of claim 1 , wherein:

prior to said receiver member entering said transfer nip, said receiver member has moved through at least two of said modules included in said plurality of tandemly arranged modules; and

at least two toner images have been transferred to said receiver member in said at least two of said modules.

7. Module of claim 1 , wherein:

S is speed of said receiver member through said transfer station;

L is length of said transfer nip in said transfer station;

I T is any transfer current determined according to said functional relationship from said control voltage for said speed and for said length;

said predetermined constant magnitude of said transfer current is experimentally determined in said module for said magnitude of said control voltage parameter less than or equal to said critical control voltage magnitude;

said critical control voltage magnitude is experimentally determined in said module;

said predetermined slope is experimentally determined in said module for said magnitude of said control voltage parameter greater than said critical control voltage magnitude;

said module can be adapted for any speed S′ and for any length L′; and

for said any speed S′ and for said any length L′, said any transfer current is scaled to a modified transfer current I T ′, where I T ′ is given by the expression I T ′=(I T )(S′/S)(L′/L).

8. Module of claim 1 , wherein said power supply is addressed so as to provide an increased transfer current greater than said tranfer current generated according to said functional relationship, said increased transfer current provided if said toner image exhibits a certain banding artifact.

9. Method of transferring a toner image to a receiver member in a transfer station, said transfer station included in a module of an electrophotographic printer, said receiver member moved through a plurality of modules tandemly arranged in said electrophotographic printer such that toner images can be successively transferred to said receiver member so as to make an output print, said output print included in a run of prints, said module further including a photoconductive image-recording member, a charging device, an exposure device, and a development station, said module associated with a process control system and a controller, said transfer station inclusive of a transfer roller and a constant-current power supply for delivering to said transfer roller a transfer current established via said controller, said method including the steps of:

establishing on said photoconductive image-recording member, via said charging device, a uniform surface potential having a voltage magnitude adjustable via said process control system;

modulating with said exposure device said uniform surface potential and thereby forming a latent image on said photoconductive image-recording member;

developing, in said development station, said latent image produced by said modulating and thereby forming said toner image on said photoconductive image-recording member;

moving a receiver member through said transfer station;

electrostatically transferring said toner image to said receiver member in said transfer station, said transfer current being controlled by said controller according to a functional relationship between said transfer current and a control voltage parameter derived from said voltage magnitude;

wherein, in the step of electrostatically transferring said toner image to said receiver member according to said functional relationship, if magnitude of said control voltage parameter is less than or equal to a critical control voltage magnitude said transfer current has a predetermined constant magnitude, and if said magnitude of said control voltage parameter is greater than said critical control voltage magnitude said transfer current has a linear increase of magnitude with increase of said magnitude of said control voltage parameter, said linear increase characterized by a predetermined slope; and

wherein a toner control patch is made from time to time such that said toner control patch has a measured optical density substantially equal to a reference maximum density, said toner control patch derived from a patch latent image formed on said photoconductive image-recording member by said charging device and said exposure device, said photoconductive image-recording member having been charged by said charging device to said voltage magnitude prior to creating said patch latent image on said photoconductive image-recording member, said patch latent image developed by said development station, said measured optical density substantially equal to said reference maximum density being obtained by causing said process control system to control operating parameters for at least one of said charging device, said exposure device, and said development station.

10. Method of claim 9 wherein, in said step of electrostatically transferring said toner image to said receiver member in said transfer station with magnitude of said control voltage parameter being greater than said critical control voltage magnitude, said transfer current has a lowest practical value so as to maintain a useful transfer efficiency and minimize back-transfer.

11. Method of claim 9 , wherein if after said step of electrostatically transferring said toner image to said receiver member said output print exhibits a banding artifact associated with said toner image, said step of electrostatically transferring said toner image is modified such that for subsequent prints included in said run of prints, an additional transfer current is added to said transfer current as would otherwise be determined from said magnitude of said control voltage parameter according to said functional relationship.