Granted Patent B2

US 11,878,530 · App. 17/661,708 · Granted Jan 23, 2024

Inventor: Stuart A Schweid (Pittsford, NY)

Assignee: Xerox Corporation

B41J2/1652

Abstract

Claims (84)

1. A method of scheduling a purge operation for a printhead having a plurality of inkjets in an inkjet printer comprising:

comparing a spatial distribution of inoperative inkjets in the printhead to a predicted random distribution of inoperative inkjets in the printhead; and

generating a signal indicating the printhead is ready for a purge when the spatial distribution of the inoperative inkjets is denser than the predicted random distribution.

2. The method of claim 1 further comprising:

generating an inkjet status vector that identifies each inkjet in the plurality of inkjets in the printhead as being operational or inoperative;

applying a filter having an integer number of elements to the inkjet status vector;

generating a first histogram of the filtered inkjet status vector to identify the spatial distribution of the inoperative inkjets in the printhead;

generating a first probability distribution for each element of the filter using an acceptable probability failure rate;

generating a second histogram for the printhead using the first probability distribution rate and a total number of inkjets in the plurality of inkjets;

comparing corresponding terms in the first and second histograms; and

generating a signal indicating the printhead is ready for a purge when one term in the first histogram is equal to or greater than the corresponding term in the second histogram.

3. The method of claim 2 wherein the filter is a rectangular filter.

4. The method of claim 3 wherein the rectangular filter has five filter elements.

5. The method of claim 2 further comprising:

identifying a standard deviation for the second histogram;

generating a first percentile histogram using the second histogram and a portion of a first probability distribution corresponding to a first percentile of the first probability distribution;

comparing terms in the first histogram to corresponding terms in the first percentile histogram; and

generating the signal when one term in the first histogram is equal to or greater than the corresponding term in the first percentile histogram.

6. The method of claim 5 wherein the first probability distribution is a Poisson probability distribution.

7. The method of claim 6 wherein the percentile histogram is a 99th percentile histogram.

8. The method of claim 7 wherein the percentile of the first probability distribution is 2.4 times the standard deviation of the second histogram.

9. The method of claim 5 further comprising:

generating a third histogram for the printhead using the first probability distribution and a number of inkjets in the plurality of inkjets that is less than the total number of inkjets in the plurality of inkjets;

identifying a standard deviation for the third histogram;

generating a second percentile histogram using the third histogram and a portion of a second probability distribution corresponding to the percentile of the second probability distribution;

generating a fourth histogram of a inkjet status vector for the number of inkjets that is less than the total number of inkjets;

comparing terms in the fourth histogram to corresponding terms in the second percentile histogram; and

generating the signal when one term in the fourth histogram is equal to or greater than the corresponding term in the second percentile histogram.

10. The method of claim 9 further comprising:

generating a fifth histogram for the printhead using a first probability in the first probability distribution and a probability of zero for the remaining probabilities in the first probability distribution;

generating a sixth histogram by subtracting terms of the third histogram from corresponding terms in the second percentile histogram;

generating a first cumulative sum histogram using the terms of the sixth histogram;

generating a second cumulative sum histogram using the terms of the first histogram;

comparing terms in the second cumulative sum histogram to corresponding terms in the first cumulative sum histogram; and

generating the signal when one term in the second cumulative sum histogram is equal to or greater than the corresponding term in the first cumulative sum histogram.

11. The method of claim 10 further comprising:

generating a single streakiness threshold using differences between the terms of the second percentile histogram and the corresponding terms of the fifth histogram and a first weighting of the differences;

generating a single streakiness measurement using differences between the terms of the second percentile histogram and the corresponding terms of the first histogram and a second weighting of the differences;

comparing the single streakiness measurement to the single streakiness threshold; and

generating the signal when the single streakiness measurement is equal to or greater than the single streakiness threshold.

12. The method of claim 11 wherein the first weighting of the differences is the Manahalnobis distance of the terms of the second percentile histogram and the terms of fifth histogram and the second weighting of the differences is the Manahalanobis distance of the terms of the second percentile histogram and the terms of the first histogram.

13. An inkjet printer comprising:

a printhead having a plurality of inkjets; and

a controller operatively connected to the printhead, the controller being configured to:

compare a spatial distribution of inoperative inkjets in the printhead to a predicted random distribution of inoperative inkjets in the printhead; and

generate a signal indicating the printhead is ready for a purge when the spatial distribution of the inoperative inkjets is denser than the predicted random distribution.

14. The inkjet printer of claim 13 , the controller being further configured to:

generate an inkjet status vector that identifies each inkjet in the plurality of inkjets in the printhead as being operational or inoperative;

apply a filter having an integer number of elements to the inkjet status vector;

generate a first histogram of the filtered inkjet status vector to identify the spatial distribution of the inoperative inkjets in the printhead;

generate a first probability distribution for each element of the filter using an acceptable probability failure rate;

generate a second histogram for the printhead using the first probability distribution rate and a total number of inkjets in the plurality of inkjets;

compare corresponding terms in the first and second histograms; and

generate a signal indicating the printhead is ready for a purge when one term in the first histogram is equal to or greater than the corresponding term in the second histogram.

15. The inkjet printer of claim 14 wherein the filter is a rectangular filter.

16. The inkjet printer of claim 15 wherein the rectangular filter has five filter elements.

17. The inkjet printer of claim 14 , the controller being further configured to:

identify a standard deviation for the second histogram;

generate a first percentile histogram using the second histogram and a portion of a first probability distribution corresponding to a first percentile of the first probability distribution;

compare terms in the first histogram to corresponding terms in the first percentile histogram; and

generate the signal when one term in the first histogram is equal to or greater than the corresponding term in the first percentile histogram.

18. The inkjet printer of claim 17 wherein the first probability distribution is a Poisson probability distribution.

19. The inkjet printer of claim 18 wherein the percentile histogram is a 99th percentile histogram.

20. The inkjet printer of claim 19 wherein the percentile of the probability distribution is 2.4 times the standard deviation of the second histogram.

21. The inkjet printer of claim 17 , the controller being further configured to:

generate a third histogram for the printhead using the first probability distribution and a number of inkjets in the plurality of inkjets that is less than the total number of inkjets in the plurality of inkjets;

identify a standard deviation for the third histogram;

generating a second percentile histogram using the third histogram and a portion of a second probability distribution corresponding to the percentile of the second probability distribution;

generate a fourth histogram of a inkjet status vector for the number of inkjets that is less than the total number of inkjets;

compare terms in the fourth histogram to corresponding terms in the second percentile histogram; and

generate the signal when one term in the fourth histogram is equal to or greater than the corresponding term in the second percentile histogram.

22. The inkjet printer of claim 21 , the controller being further configured to:

generate a fifth histogram for the printhead using a first probability in the first probability distribution and a probability of zero for the remaining probabilities in the first probability distribution;

generate a sixth histogram by subtracting terms of the third histogram from corresponding terms in the second percentile histogram;

generate a first cumulative sum histogram using the terms of the sixth histogram;

generate a second cumulative sum histogram using the terms of the first histogram;

compare terms in the second cumulative sum histogram to corresponding terms in the first cumulative sum histogram; and

generate the signal when one term in the second cumulative sum histogram is equal to or greater than the corresponding term in the first cumulative sum histogram.

23. The inkjet printer of claim 22 , the controller being further configured to:

generate a single streakiness threshold using differences between the terms of the second percentile histogram and the corresponding terms of the fifth histogram and a first weighting of the differences;

generate a single streakiness measurement using differences between the terms of the second percentile histogram and the corresponding terms of the first histogram and a second weighting of the differences;

compare the single streakiness measurement to the single streakiness threshold; and

generate the signal when the single streakiness measurement is equal to or greater than the single streakiness threshold.

24. The inkjet printer of claim 23 wherein the first weighting of the differences is the Manahalnobis distance of the terms of the second percentile histogram and the terms of fifth histogram and the second weighting of the differences is the Manahalanobis distance of the terms of the second percentile histogram and the terms of the first histogram.

Assignments (8)

Continuity (1)