Charge roller positioning

1. A method comprising:

positioning a first end of a charge roller to a first plurality of index positions;

determining a capacitance between the charge roller and a photoconductor imaging plate at each of the first plurality of index positions;

calculating a change in capacitance for each of the first plurality of index positions based upon the capacitances that are determined; and

calibrating a position of the charge roller based upon the calculated change in capacitance for each of the first plurality of index positions.

2. The method of claim 1 , wherein the capacitance is determined based upon a measurement of an alternating current in a circuit comprising the charge roller and the photoconductor imaging plate.

3. The method of claim 2 , wherein the alternating current is measured by:

measuring a voltage in a circuit comprising the charge roller and the photoconductor imaging plate via a coil transformer; and

applying the voltage to an integrator through a rectifier.

4. The method of claim 1 , wherein the positioning comprises:

positioning the charge roller in contact with the photoconductor imaging plate; and

raising the first end of the charge roller through the first plurality of index positions.

5. The method of claim 1 , further comprising:

calculating a change in capacitance for each of the first plurality of index positions based upon the capacitance that is measured between the charge roller and the photoconductor imaging plate at each of the first plurality of index positions.

6. The method of claim 1 , wherein the calibrating the position of the charge roller comprises:

setting the first end of the charge roller to an operating position, based upon an offset from a first index position.

7. The method of claim 1 , further comprising:

raising a second end of the charge roller to a second plurality of index positions;

measuring a capacitance between the charge roller and the photoconductor imaging plate at each of the plurality of second index positions; and

calculating a change in capacitance for each of the second plurality of index positions based upon the measured capacitances at each of the plurality of second index positions.

8. The method of claim 7 , wherein the calibrating the position of the charge roller is further based upon a second index position.

9. The method of claim 8 , wherein the calibrating the position of the charge roller comprises:

setting the first end of the charge roller to a first operating index position, based upon a first offset from the first index position; and

setting the second end of the charge roller to a second operating index position, based upon a second offset from the second index position.

10. The method of claim 7 , further comprising determining a second index position of the plurality of index positions with a greatest change in capacitance.

11. The method of claim 1 , further comprising determining a first index position of the first plurality of index positions with a greatest change in capacitance.

12. The method of claim 11 , wherein the first index position is used to calibrate the position of the charge roller.

13. A method for adjusting a position of a charge roller comprising:

measuring an alternating current in a printing device, wherein the printing device comprises a charge roller and a photoconductor imaging plate;

determining a capacitance between the charge roller and the photoconductor imaging plate, wherein the capacitance is determined based upon a measurement of the alternating current;

calculating a distance between the charge roller and the photoconductor imaging plate based upon the capacitance; and

adjusting a position of the charge roller based upon the distance that is calculated.

14. The method of claim 13 , wherein the measuring the alternating current is performed by:

measuring a voltage in a circuit comprising the charge roller and the photoconductor imaging plate via a coil transformer; and

applying the voltage to an integrator through a rectifier.

15. The method of claim 13 , wherein determining the capacitance is in accordance with: C=I/(ωV), where I is an alternating current, V is a voltage, and ω is an angular velocity, and wherein the distance is calculated in accordance with: C=(2π·e 0 ·L)/(cos h −1 (1+g/R)), where C is the capacitance, L is a length of the charge roller, g is a separation distance between the charge roller and the photoconductor imaging plate, R is a radius of the charge roller, and e 0 is a permittivity of free space.

16. The method of claim 13 , wherein determining the capacitance is further based upon a voltage of a power supply.

17. A device comprising:

a charge roller;

a photoconductor imaging plate;

at least one positioning unit for positioning at least a first end of the charge roller to a first plurality of index positions;

a current sensor, for measuring an alternating current in a circuit comprising the charge roller and the photoconductor imaging plate when the at least the first end of the charge roller is at each of the first plurality of index positions, wherein the alternating current is proportional to a capacitance between the charge roller and the photoconductor imaging plate; and

a controller to:

calculate a change in capacitance for each of the first plurality of index positions based upon the measurement of the alternating current; and

calibrating a position of the charge roller based upon the change in capacitance for each of the first plurality of index positions.

18. The device of claim 17 , wherein the controller is further for:

sending instructions to the at least one positioning unit to position the at least the first end of the charge roller to the first plurality of index positions; and

sending instructions to the current sensor to measure the alternating current when the at least the first end of the charge roller is at each of the first plurality of index positions.

19. The device of claim 17 , wherein the controller is further to determine a first index position of the first plurality of index positions with a greatest change in capacitance.

20. The device of claim 19 , wherein the first index position is used to calibrate the position of the charge roller.