Compensating for printing non-uniformities using a two dimensional map
Correction data is produced for density errors in prints produced using a printer. While printing a test image, the periods of rotation of one or more rotatable imaging members arranged along a receiver feed path in the printer are measured using respective period sensors. The printed test image is measured in both the cross-track and in-track directions and a two dimensional map of the one or more period sensors is determined. A reproduction error signal representing deviation from aim density is determined. The variations from the data at measured periods in one or both directions are used to produce a correction signal.
1. A method for compensating for imaging defects in an electro-photographic imaging system, the method comprising the steps of:
(a) providing one or more imaging elements that rotates while printing;
(b) determining positions on the one or more imaging elements using a period sensor for each imaging element while printing an image of known target density;
(c) measuring the image density;
(d) determining a two dimensional map of the density for each period sensor; wherein each of the imaging maps corresponds to positions on the one or more imaging elements;
(e) comparing the printed density at each of the positions of the imaging maps to the known target density for determining an error signal;
(f) determining a variation correction signal for each period sensors based on the error signal;
(g) applying all the variation correction signals synchronized to the positions of each period sensor when printing subsequent prints to improve image uniformity; and
wherein two or more imaging elements are rotationally synchronized.
2. The method as in claim 1 , wherein the period of rotation of a first synchronized imaging element is an integer multiple of the period of rotation of a second imaging element.
3. The method as in claim 1 , wherein the imaging element is a rotating imaging loop.
4. The method as in claim 1 , wherein the one or more imaging elements includes both a rotating imaging loop and a rotating toning roller.
5. The method as in claim 1 , wherein measuring the image density includes measuring at one or more cross-track locations and scanning in the in-track location as the image moves past the sensor.
6. The method as in claim 1 , wherein measuring the image density includes printing on a sheet and measuring the image on the sheet with an external scanner.
7. The method as in claim 1 further comprises condensing the correction signal by grouping two or more individual pixels together.
8. A method for compensating for imaging defects in an electro-photographic imaging system, the method comprising the steps of:
(a) providing one or more imaging elements that rotates while printing;
(b) determining positions on the one or more imaging elements using a period sensor for each imaging element while printing an image of known target density;
(c) measuring the image density;
(d) determining a two dimensional map of the density for each period sensor; wherein each of the imaging maps corresponds to positions on the one or more imaging elements;
(e) comparing the printed density at each of the positions of the imaging maps to the known target density for determining an error signal;
(f) determining a variation correction signal for each period sensors based on the error signal;
(g) applying all the variation correction signals synchronized to the positions of each period sensor when printing subsequent prints to improve image uniformity;
wherein the one or more imaging elements includes both the rotating imaging cylinder and the rotating toning roller; and
wherein the imaging cylinder and toning roller are rotationally synchronized.
9. The method as in claim 8 , wherein a period of rotation of the imaging cylinder is an integer multiple of a period of rotation of the toning roller.
10. A method for compensating for imaging defects in an electro-photographic imaging system, the method comprising the steps of:
(a) providing one or more imaging elements that rotates while printing;
(b) determining positions on the one or more imaging elements using a period sensor for each imaging element while printing an image of known target density;
(c) measuring the image density;
(d) determining a two dimensional map of the density for each period sensor; wherein each of the imaging maps corresponds to positions on the one or more imaging elements;
(e) comparing the printed density at each of the positions of the imaging maps to the known target density for determining an error signal;
(f) determining a variation correction signal for each period sensors based on the error signal;
(g) applying all the variation correction signals synchronized to the positions of each period sensor when printing subsequent prints to improve image uniformity;
wherein the one or more imaging elements includes both a rotating imaging loop and a rotating toning roller; and
wherein the imaging loop and toning roller are rotationally synchronized.
11. The method as in claim 10 , wherein a period of rotation of the imaging loop is an integer multiple of a period of rotation of the toning roller.