Identification of faulty jets via sensing on customer images

1. A method of monitoring jets of a color imaging device, the jets respectively outputting inks of different colors, the imaging device including a monochromatic sensor that senses images output by the imaging device, the method comprising:

generating a correspondence map between an output color space of the jets and an output gray scale space of the monochromatic sensor;

measuring actual gray scale values of an image output by the imaging device at multiple locations, the image generated from actual image data;

calculating predicted gray scale values of the monochromatic sensor for each of the multiple locations, the predicted gray scale values for each of the multiple locations including predicted gray scale values for multiple different possible operating configurations of the jets, wherein each jet can have an operating state of (i) properly operating or (ii) faulty, the different operating configurations comprising different combinations of properly operating and faulty jets for a predetermined group of the jets, each jet of the predetermined group outputting a different one of the different colors; and

determining whether the jets are (i) operating properly or (ii) faulty, by comparing the measured actual gray scale values of the multiple locations with the corresponding predicted gray scale values for each of the multiple locations.

2. The method of claim 1 , wherein, in the step of generating a correspondence map, the correspondence map is generated based on sensing at least one test patch output by the imaging device.

3. The method of claim 1 , wherein the step of generating a correspondence map includes:

purging all the jets of at least one group of jets comprising one jet of each of the different colors;

printing a plurality of test patches by the purged at least one group of jets, each of the test patches being printed from a different set of test patch color coordinates;

sensing the test patches by the monochromatic sensor to generate corresponding gray scale values; and

storing the sensed gray scale values each with the test patch color coordinates used to print the corresponding test patch.

4. The method of claim 1 , wherein the step of generating a correspondence map includes:

printing a plurality of test patches by a plurality of jet groups each comprising one jet for each of the different colors, each test patch being printed from a set of test patch color coordinates, each set of test patch color coordinates being printed by multiple jet groups of the plurality of jet groups;

sensing the test patches by the monochromatic sensor, the monochromatic sensor outputting sensed gray scale values;

averaging the sensed gray scale values for test patches printed by different jet groups from a same one of the sets of test patch color coordinates to generate averaged gray scale values; and

storing each set of test patch color coordinates used to print the test patches with the corresponding averaged gray scale value.

5. The method of claim 1 , wherein, in the step of determining whether the jets are (i) operating properly or (ii) faulty, the determination is made based on a best match between the measured actual gray scale value and the corresponding predicted gray scale values for each of the multiple locations.

6. The method of claim 1 , wherein the step of determining includes determining, for each of the multiple locations, which operating configuration has a predicted gray scale value having a best match with the corresponding actual measured gray scale value.

7. The method of claim 6 , wherein a determination of whether any jets are faulty is carried out at predetermined intervals.

8. The method of claim 1 , further comprising:

performing a cleaning/purging operation if one or more jets is determined to be faulty.

9. A method of monitoring jets of a color imaging device, the jets respectively outputting inks of different colors, the imaging device including a multichromatic sensor that senses images output by the imaging device, the method comprising:

generating a correspondence map between an output color space of the jets and an output color space of the multichromatic sensor;

measuring actual color values of an image output by the imaging device at multiple locations, the image generated from actual image data;

calculating predicted color values of the multichromatic sensor for each of the multiple locations, the predicted color values for each of the multiple locations including predicted color values for multiple different possible operating configurations of the jets, wherein each jet can have an operating state of (i) properly operating or (ii) faulty, the different operating configurations comprising different combinations of properly operating and faulty jets for a predetermined group of the jets, each jet of the predetermined group outputting a different one of the different colors; and

determining whether the jets are (i) operating properly or (ii) faulty, by comparing the measured actual color values of the multiple locations with the corresponding predicted color values for each of the multiple locations.

10. The method of claim 1 , further comprising:

(1) setting a predicted operating state to properly operating for each jet of a jet group having one jet for each of the different colors;

(2) selecting a color of one of the jets of the jet group that has not previously been set as a target color to be the target color, the step of calculating including calculating predicted gray scale outputs for the multiple locations for the jet group wherein the predicted operating state of the jet of the target color is alternately (i) operating properly and (ii) faulty, the step of determining including determining whether the jet of the target color is operating properly or is faulty by comparing the predicted gray scale outputs with the actual gray scale outputs for the multiple locations;

(3) setting the predicted operating state of the jet of the target color according to the results of the step of determining; and

(4) when at least one of the colors of the jets of the jet group has not been set as the target color, repeating steps (2)-(4).

11. A system for monitoring jets in a color imaging device, the jets each corresponding to different ones of a plurality of colors of the color imaging device, the system comprising:

a sensor that senses images and outputs actual gray scale values;

a memory storing a correspondence map between an output color space of the jets and an output gray scale space of the sensor;

a processing device comprising:

a sensor controlling unit that controls the sensor to measure printed output of the color imaging device at multiple locations in the printed output and to output corresponding actual gray scale values,

a prediction unit that calculates predicted gray scale values of the sensor for each of the multiple locations, the predicted gray scale values for each of the multiple locations including predicted gray scale values for multiple possible operating state configurations of the jets wherein each jet can independently have the operating states of properly operating and faulty, and

a judgment unit that determines, for a predetermined group of jets having jets each of which corresponds to a different one of the plurality of colors, the operating states of the jets based on the predicted gray scale values and the actual gray scale values for the multiple locations.

12. The system of claim 11 , wherein the processing device further comprises:

a correspondence table generation unit that controls jets of the printer to produce test patches from test patch color coordinates and stores each of the test patch color coordinates in association with the corresponding actual gray scale value output by the sensor.

13. The system of claim 11 , further comprising:

an interface that allows a user to specify which jets are to be monitored.

14. The system of claim 11 , further comprising:

a display that indicates the determined operating state for at least one jet.

15. The system of claim 11 , wherein the judgment unit determines the operating states of the jets based on a best match between the measured actual gray scale values and the corresponding predicted gray scale values for each of the multiple locations.

16. The system of claim 15 , wherein the best matches are determined by at least one of a minimum mean squared error and a minimum p-norm error between the actual gray scale values and the corresponding predicted gray scale values for the multiple locations.

17. The system of claim 11 , wherein the monitoring of the jets is carried out at predetermined intervals.

18. The system of claim 11 , wherein the processing device:

(1) sets a predicted operating state to properly operating for each jet of a jet group having one jet for each of the plurality of colors;

(2) selects a color of the plurality of colors that has not yet been set as a target color to be set as the target color, the predication unit calculating predicted gray scale values for the multiple locations for the jet group wherein the predicted operating state of the jet of the target color is alternately (i) operating properly and (ii) faulty, the judgment unit determining whether the jet of the target color is operating properly or is faulty by comparing the predicted gray scale values with the actual gray scale values for the multiple locations;

(3) sets the operating state of the jet of the target color according to the results of the judgment unit; and

(4) when at least one color of the plurality of colors has not been set as the target color, repeats functions (2)-(4).

19. The system of claim 11 , further comprising:

a controller that causes jets determined to be faulty to be purged.

20. A xerographic device including the system of claim 11 .