Method of automatically controlling print quality in digital printing

Abstract

A method of automatically monitoring and controlling print quality in digital printing with a first and second scanner capturing an image from different locations in the printing engine. In an exemplary embodiment, a first scanner captures an image from a surface internal to the print engine while an external scanner captures an image from a printed sheet. If the external print image quality is acceptable, the internally captured image is saved as a reference. The system periodically compares internally captured images with the saved reference and provides automatic image correction if the variation from the reference is within a correctable range. If the image variation is not within a correctable range, the system runs a new test print and creates a new reference image.

Description

BACKGROUND

The present disclosure relates to digital printing and particularly to printing processes in which the physical image-forming material such as, for example, dry powder toner in a xerographic marking engine is rendered into at least a portion of the desired final image on some internal member such as, for example, a photoreceptor or passive receiver element and subsequently transferred to the final substrate. In such printing it has been found difficult to maintain the quality of the printed image, particularly for color prints where slight variation in color or color uniformity can render the print unacceptable to the customer.

A well-known technique for controlling print quality is the rendering of test images of the physical image-forming material and their measurement within the machine. Such measurements are then compared to some desired reference value and any difference used to determine adjustments to the printing process. Such test images may be of greater or lesser extent and may be measured in various ways, as, for example, for average value, or for uniformity over an extended area. The rendering of test images may require the interruption of the printing of the desired images, or may be arranged to take place while printing proceeds, as, for example, by rendering test images between the desired images. The measurement process itself may be affected by variation in the characteristics of the internal member or the sensor used for such measurement.

Such internal measurements may not, however, be capable of monitoring all aspects of print quality for which control is necessary or desired, for example defects due to variation in the transfer of images to the final substrate. A well-known technique for detecting and correcting for such defects is the measurement of test prints. Such measurement can take place using a sensor or sensors within the marking engine disposed so this can take place after the final step in the printing process, such as fusing, or by using an external scanner or other sensor. The production of such test prints requires the interruption of useful printing and therefore results in a reduction in marking engine productivity and consumes substrate material thereby increasing the cost of such measurements.

It has thus been desired to minimize the disadvantages of these two approaches, so as to provide better control of print quality and to reduce the cost, both in substrate material and lost productivity, of such control.

BRIEF DESCRIPTION

The present disclosure addresses the above described disadvantages of known print quality monitoring techniques and describes a digital image printing process in which a print engine is used for printing on print media from a digital image supplied to the print engine. In one exemplary embodiment, the print engine is of the electrostatic type employing a photoreceptor. In another exemplary embodiment, the print engine is generalized and may employ, for example, an ink jet printer. Provision is made for continuously and automatically monitoring the quality of the printing by capturing an image from one location or stage in printing, such as a test print, and capturing an image at the same time from a second location or stage, such as a surface internal to the print engine; and, if the captured image from the one location, such as a test print, is satisfactory, the image captured at the second location, such as an internally captured image, is saved as a reference. Subsequently, images may be captured on a running basis from the internal surface and compared with the reference. If the comparison yields a variation within an acceptable range, no correction is required. If the comparison of the running image from the internal surface is variant from the saved reference image, a control signal is generated to effect digital correction of the imaging to yield a desired print. However, if the comparison yields a variation that is not correctable internally by automatic digital changes, a new test print is run and a new test image is taken from the internal surface and a new reference image is saved. Thus, the system of the present disclosure can automatically monitor and correct deviations of print quality in digital image printing without the need to stop the print job for the purpose of running a test print and separately scanning the image from the test print. The method of the present disclosure thus provides for improved productivity and minimizes waste in a digital printing system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary electrostatic print engine employing the method of the present disclosure;

FIG. 2 is a block flow diagram of the method of the present disclosure; and,

FIG. 3 is an exemplary embodiment of a generalized print engine employing the method of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, a print engine, indicated generally at 10 in dashed outline, is of the type receiving a digital image to be printed into a spatially distributed actuator 12 which is controlled by a controller 14 and actuator 12 may be of the well known raster optical scanner variety for creating an image on a photoreceptor 16. In electrostatic or xerographic printing processes, the image from the photoreceptor 16 is transferred to a print media sheet as denoted at block 17 and is secured thereon by a fuser 18 to produce a final printed image. A sensor 20 is disposed to optically measure an image on an internal surface provided within the print engine 10 and the sensor 20 outputs a signal indicative thereof along line 22 to a controller 14. In the present practice, it has been found suitable to employ a full-width array scanner or reduction optic scanner for sensor 20; however, a single or multiple translatable sensor may also be employed. Optionally, the internal surface may be formed on an intermediate belt denoted by the characters IBT as shown in dashed outline in FIG. 1.

An external sensor 24 optically measures the image printed on a test sheet and outputs a signal indicative thereof along line 26 to the controller 14. In the present practice, sensor 24 may comprise a full-width array, reduction optics, or a translatable single or multiple sensor arrangement.

Referring to FIG. 2, the method of operation of the print engine system 10 of FIG. 1 is indicated, wherein the spatially distributed actuator 12 is initialized at step 30. The system proceeds to create a print target and inter-document zone (IDZ) target image at step 32; and, while printing the target image in step 32, proceeds to step 34 and measures the IDZ target with the sensor 20.

The system then proceeds to step 36 and measures the target print using external sensor 24. The system then proceeds to step 38 and determines the print quality defect level in the signal outputted from sensor 24.

The system then proceeds to step 40 and makes a determination as to whether the print quality defect (PQ) level determined in step 38 is within an acceptable range. If the determination in step 40 is in the affirmative, the system proceeds to step 42 and saves the internal sensor measurement of step 34 as a Reference Signal. If the determination in step 40 is negative, the system proceeds to step 44 and calculates a control signal to reduce the print quality defect; and, the control signal of step 44 is then loaded at step 46 into the actuator 12 by returning to step 32; and, the system repeats the process through to step 40 until the determination there is affirmative. The system then proceeds from step 42 to print the customer job at step 48.

While printing the customer job, the system at step 50 periodically renders an IDZ target and proceeds to step 52 to measure the target using the internal sensor 20. The result of the target measuring step 52 is then compared with the Reference Signal saved at step 42.

The system then proceeds to step 56 and asks the question whether the difference between the measured comparison of step 54 is within an acceptable range; and, if the answer is affirmative, the system then returns to step 50.

However, if the determination at step 56 is negative, the system proceeds to step 58 and asks whether the difference is internally correctable. If the determination at step 58 is affirmative, the system then calculates at step 60 a control signal to reduce the print quality defect; and, at step 64 loads the control signal of step 62 into the actuator and returns to step 50.

However, if the determination at step 58 is negative, the system returns to step 32.

Referring to FIG. 3, a more generalized exemplary version of the method of the present disclosure is illustrated wherein a print engine 100 is employed which may be any of the solid ink print engine, multiple engine printing system and of the type employing an ink jet or laser printer. A spatially distributed actuator 102 receives the digital image to be printed, such as, for example, by electronic input by a computer or a scanner (not shown). The image is marked at a first location 104 within the print engine, or at a first stage in the printing process; and, a first image measurement is taken thereupon at step 106 by a suitable second sensor. The measurement taken at step 106 is then inputted along line 108 to a controller at step 110.

The printing process is continued from step 104 to a second location at step 112 and a second image measurement is then taken by a second sensor at step 114 and this measurement is also inputted along a line 116 to the controller at step 110. Either of the first or second sensor may be a full width array sensor, a reduction optic sensor, a translating array sensor, a multiple array sensor, or a two-dimensional array sensor. The controller at step 110 then is operative to establish one of the first and second measurements as a reference and to initiate a control signal along line 118 for controlling the actuator at step 102. Also, at step 110, the measurement of the image at one of the first and second location is held as a reference. The choice of measurement location for the reference may be based upon which measurement location is upstream in the printing process and to thereby provide greater and earlier opportunity for correction of quality defects by the controller.

The present disclosure thus describes a method of automatically monitoring digital image printing for print quality and correcting the print image internally within the print engine without interrupting the print job.

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

1. A method of automatically controlling digital printing of a document print job on media sheets comprising: (a) providing a print engine;(b) disposing a first sensor for measuring an image on a printed sheet;(c) disposing a second sensor for measuring an image on a surface internal to the print engine;(d) measuring an image on a printed sheet with the first sensor;(e) measuring an image on a surface internal to the print engine with the second sensor;(f) determining a performance metric of the image on the printed sheet and, if acceptable, saving the measurement of the image on the surface internal to the print engine from the second sensor as a reference, and if not acceptable, calculating and applying a control signal and repeating steps (d)-(f);(g) executing the print job and periodically measuring an image on the surface internal to the print engine using the second sensor and comparing with the saved reference; and,(h) repeating steps (d)-(f) if the comparison in step (g) is not within an acceptable range; and, continuing the print job if the comparison of step (g) is within an acceptable range.

2. The method defined in claim 1, wherein the step of disposing a first and second sensor includes disposing two dimensional array image sensing devices.

3. The method defined in claim 2, wherein the step of disposing a first and second sensor includes disposing one of: a full width array sensor, a reduction optics sensor, a translating array sensor, and a multi-array sensor.

4. The method defined in claim 1, wherein the step of measuring an image on the printed sheet and the step of measuring an image on an internal surface includes measuring the same image at different locations in the printing process.

5. The method defined in claim 4, wherein the step of disposing a first and second sensor includes disposing two dimensional array image sensing devices.

6. The method defined in claim 1, wherein if the comparison in step (g) is within an acceptable range, calculating a control signal based upon the deviation of the image on the internal surface from the saved reference image applying the control signal and continuing the print job.

7. The method described in claim 1, wherein the step of measuring an image on a surface internal to a print engine includes measuring without interrupting the print job.

8. The method of claim 1, wherein the step of disposing a second sensor includes disposing a sensor on one of a photoreceptor drum, a photoreceptor belt, an intermediate drum, an intermediate belt, an imaging drum, an imaging belt, and print media.

9. The method of claim 1, wherein the step of providing a print engine includes providing one of a xerographic print engine, a solid ink print engine, and a multiple engine printing system.

10. A system for controlling digital printing comprising: (a) a print engine; and,(b) a plurality of two-dimensional array image sensing devices disposed for measuring an image during the printing process at different locations.

11. The system defined in claim 10, wherein one of the image sensing devices is disposed internally of the print engine and one is disposed externally.

12. The system defined in claim 10, wherein the print engine includes a photoreceptor.

13. The system defined in claim 10, wherein the print engine includes one of an ink jet printer and a laser printer.

14. The system of claim 10, wherein the print engine is at least one of: a xerographic print engine, a solid ink print engine, and a multiple engine printing system.

15. The system defined in claim 10, wherein the step of disposing a first and second sensor includes disposing at least one of: a full width array sensor, a reduction optics sensor, a translating array sensor, and a multi-array sensor.

16. A method of measuring digital printing of an image comprising: (a) providing a print engine with multiple locations to sense an image during printing;(b) disposing a first sensor and measuring an image at a first location in during printing;(c) disposing a second sensor and measuring an image at a second location during printing;(d) measuring a printed image at the first location in the printing process with the first sensor; and,(e) measuring the printed image at a second location in the printing process using the second sensor.

17. The method defined in claim 16, wherein the step of disposing a first and second sensor includes disposing two dimensional array image sensing devices.

18. The method defined in claim 16, wherein the step of disposing a first and second sensor includes disposing at least one of: a full width array sensor, a reduction optics sensor, a translating array sensor, and a multi-array sensor.

19. The method of claim 16, wherein the step of disposing a first sensor includes disposing a sensor on one of a photoreceptor drum, a photoreceptor belt, an intermediate drum, an intermediate belt, an imaging drum, an imaging belt, and print media.

20. The method of claim 16, wherein the step of disposing a first and second sensor includes disposing point sensors.

21. The method of claim 16, wherein the step of disposing a first and second sensor includes disposing at least one of: a reflectance measuring sensor, a density sensor, and a color parameter measuring sensor.

22. The method of claim 16, wherein the print engine is at least one of: a xerographic print engine, a solid ink print engine, and a multiple engine printing system.

23. The method defined in claim 16 further comprising: (a) calculating a control signal based on measurements of a printed image obtained from the first sensor at the first location and from the second sensor at the second location; and,(b) applying the control signal to the printing and improving a performance metric of the printing process.

24. The method defined in claim 16, wherein the step of measuring a printed image at a fixed location in the printing process and the step of measuring a printed image at a second location in the printing process includes measuring the same image.