Imaging apparatus and method of predicting the photoreceptor replacement interval

1. A method of predicting a photoreceptor replacement interval, comprising:

measuring a charging current of a charging device;

measuring a grid current from at least one of grid wires and a shield;

measuring a voltage of a photoreceptor charge transport layer of a photoreceptor;

computing a thickness of the photoreceptor charge transport layer based on the measured charging current, the measured grid current, and the measured voltage of the photoreceptor charge transport layer;

determining a replacement interval based on the computed thickness of the photoreceptor charge transport layer; and

at least one of storing or outputting the replacement interval.

2. The method of claim 1 , wherein the charging current is a current that is supplied to coronode wires of a scorotron charge device.

3. The method of claim 2 , wherein the grid current is a current from the at least one of a scorotron grid and a scorotron shield of the scorotron charge device, the scorotron grid being positioned between the coronode wires and the photoreceptor charge transport layer.

4. The method of claim 1 , the measuring the voltage of the photoreceptor charge transport layer further comprising:

measuring a voltage (V initial ) of the photoreceptor charge transport layer after a pre-charge erase of the photoreceptor charge transport layer, wherein

the thickness of the photoreceptor charge transport layer is computed based on the measured charging current, the measured grid current, and V initial .

5. The method of claim 1 , the measuring the voltage of the photoreceptor charge transport layer further comprising:

measuring a voltage (V intercept ) of the photoreceptor charge transport layer after rotating the photoreceptor to consecutively charge the photoreceptor charge transport layer by the charge device with a pre-charge erase device being off, so that charge continues to build through each revolution of the photoreceptor, wherein

the thickness of the photoreceptor charge transport layer is computed based on the measured charging current, the measured grid current, and V intercept .

6. The method of claim 3 , further comprising:

determining a slope (S) of the scorotron charge device between a first data point and a second data point, wherein

the thickness of the photoreceptor charge transport layer is computed based on the measured charging current, the measured grid current, the measured voltage of the photoreceptor charge transport layer, and the slope (S).

7. The method of claim 6 , wherein determining the slope (S) further comprises:

measuring the first data point by rotating the photoreceptor with a pre-charge erase device on, the measuring including:

charging the photoreceptor charge transport layer by the scorotron charging device,

measuring a first charging current,

measuring a first grid current,

determining a dynamic current (I dynamic 1 ) delivered to the photoreceptor charge transport layer as the difference between the first charging current and the first grid current, and

measuring a voltage (V 1 ) of the photoreceptor charge transport layer after charging the photoreceptor charge transport layer, the first data point being (V 1 , I dynamic 1 );

measuring the second data point by rotating the photoreceptor with the pre-charge erase device off, the measuring including:

charging the photoreceptor charge transport layer by the scorotron charging device, the photoreceptor charge transport layer entering a scorotron charging area with a residual charge due to the pre-charge erase device being off,

measuring a second charging current,

measuring a second grid current,

determining a dynamic current (I dynamic 2 ) delivered to the photoreceptor charge transport layer as the difference between the second charging current and the second grid current, and

measuring a voltage (V 2 ) of the photoreceptor charge transport layer after charging the photoreceptor charge transport layer, the second data point being (V 2 , I dynamic 2 ); and

determining the slope (S) as the slope between the first data point and the second data point.

8. The method of claim 7 , further comprising:

measuring a voltage (V initial ) of the photoreceptor charge transport layer after the pre-charge erase of the photoreceptor charge transport layer; and

measuring a voltage (V intercept ) of the photoreceptor charge transport layer after rotating the photoreceptor to consecutively charge the photoreceptor charge transport layer by the scorotron charge device with the pre-charge erase device being off, so that charge continues to build through each revolution of the photoreceptor, wherein

the thickness of the photoreceptor charge transport layer is computed based on the slope (S), V initial , and V intercept .

9. The method of claim 8 , wherein the thickness of the photoreceptor charge transport layer is determined by solving the following equations:

I dynamic 1 =Cv ( V intercept −V initial )(1− e −S/Cv )

C=∈ 0 k/d× 10 6

where

d=the thickness of the photoreceptor charge transport layer that is to be determined,

k=the dielectric constant of the photoreceptor charge transport layer (a known constant),

∈ 0 =permittivity of free space (a constant equal to 8.85×10 −12 ),

C=capacitance per unit area of the photoreceptor charge transport layer in μf/meter 2 (to be determined), and

v=velocity of the surface of the photoreceptor charge transport layer in meters/second (a known constant).

10. The method of claim 8 , wherein at least one of the voltage measurements V initial , V intercept , V 1 , and V 2 is measured using at least one of (1) a pre-development electrostatic voltmeter positioned between an exposure device and a development device and (2) a pre-charge electrostatic voltmeter positioned between the pre-charge erase device and the scorotron charge device.

11. The method of claim 1 , wherein the thickness of the photoreceptor charge transport layer is determined during a test mode.

12. The method of claim 1 , wherein the thickness of the photoreceptor charge transport layer is determined between printing of subsequent customer images of a single job where a circumference of the photoreceptor charge transport layer is greater than a length of a customer image, the determination being made with respect to a portion of the photoreceptor charge transport layer not contacting the customer image.

13. The method of claim 1 , further comprising:

storing a previously determined thickness of the photoreceptor charge transport layer; and

determining the replacement interval based on a comparison of the computed thickness of the photoreceptor charge transport layer to the previously stored thickness of the photoreceptor charge transport layer.

14. A system for predicting a photoreceptor replacement interval, the system comprising:

a first current measuring device that measures charge current supplied to coronode wires and outputs a first current value;

a second current measuring device that measures grid current delivered to at least one of grid wires and a shield and outputs a second current value;

a voltage measuring device that measures voltage of the photoreceptor charge transport layer and outputs a photoreceptor charge transport layer voltage value;

a processor that

receives the first current value, the second current value, and the photoreceptor charge transport layer voltage value, and

determines a photoreceptor replacement interval based on a thickness of the photoreceptor charge transport layer, wherein the determined thickness of the photoreceptor charge transport layer is based on the first current value, the second current value, and the photoreceptor charge transport layer voltage value;

a storage device for storing the photoreceptor replacement interval; and

a display device for displaying the photoreceptor replacement interval.

15. The system of claim 14 , further comprising

a scorotron charge device including coronode wires, a scorotron shield, and a scorotron grid positioned between the coronode wires and the photoreceptor charge transport layer.

16. The system of claim 15 , further comprising:

a pre-charge erase device; and

a controller that controls the voltage measuring device, the controller configured to control the voltage measuring device to measure at least one of an initial voltage (V initial ) of the photoreceptor charge transport layer after a pre-charge erase of the photoreceptor, and an intercept voltage (V intercept ) of the photoreceptor charge transport layer after rotating the photoreceptor to consecutively charge the photoreceptor charge transport layer by the scorotron charge device with the pre-charge erase device being off, so that charge continues to build through each revolution of the photoreceptor, wherein

the processor determines the thickness of the photoreceptor charge transport layer based on the first current value, the second current value, and the at least one of V initial and V intercept .

17. The system of claim 15 , wherein

the controller further controls the first current measuring device and the second current measuring device, and

the controller is configured to control the first current measuring device, the second current measuring device, and the voltage measuring device to measure data corresponding to a first data point and a second data point, each data point including a current and a voltage, wherein

the processor is configured to receive the first data point measurements and the second data point measurements and calculate a slope (S) of the scorotron charge device between the first data point and the second data point, the processor determining the thickness of the photoreceptor charge transport layer based on the slope (S) and at least one of V initial and V intercept .

18. The system of claim 17 , wherein

the controller is further configured to control the first current measuring device and the second current measuring device to determine a dynamic current (I dynamic ) delivered to the photoreceptor charge transport layer as the difference between the first current value and the second current value, wherein

the processor determines the thickness of the photoreceptor charge transport layer by solving the equations:

I dynamic 1 =Cv ( V intercept −V initial )(1− e −S/Cv )

C=∈ 0 k/d× 10 6

where

d=the thickness of the photoreceptor charge transport layer that is to be determined,

k=the dielectric constant of the photoreceptor charge transport layer (a known constant),

∈ 0 =permittivity of free space (a constant equal to 8.85×10 −12 ),

C=capacitance per unit area of the photoreceptor charge transport layer in μf/meter 2 (to be determined), and

v=velocity of the surface of the photoreceptor charge transport layer in meters/second (a known constant).

19. The system of claim 17 , further comprising:

at least one of (1) a pre-charge electrostatic voltmeter positioned between the pre-charge erase device and the scorotron charge device and (2) a pre-development electrostatic voltmeter positioned between an exposure device and a development device, the at least on of the pre-charge and pre-development electrostatic voltmeters comprising the voltage measuring device.

20. A xerographic image forming device including the system of claim 14 .