WO2009014537A1

WO2009014537A1 - Systems and methods for detecting ink mixing

Info

Publication number: WO2009014537A1
Application number: PCT/US2007/074321
Authority: WO
Inventors: Behnam Bastani; Bryan S. Ly; Alejandro Campillo Agusti
Original assignee: Hewlett-Packard Company
Priority date: 2007-07-25
Filing date: 2007-07-25
Publication date: 2009-01-29

Abstract

In one embodiment a system and a method for detecting ink mixing relate to printing test patches of ink with a printing device (408), scanning the test patches with a sensor of the printing device to obtain intensity values (408), correlating the intensity values with human color space values on the printing device to obtain observed human color space values (410), comparing the observed human color space values with expected human color space values (412), and determining whether ink mixing has occurred relative to the comparison (414).

Description

SYSTEMS AND METHODS FOR DETECTING INK MIXING

BACKGROUND

InkJet printers typically comprise one or more ink pens that are used to deposit ink on print media, such as photograph paper. An example of such an ink pen is shown in FIG. 1 and is identified by reference numeral 100. As indicated in FIG. 1 , the ink pen 100 includes an outer housing 102, which is designed to contain one more colors of ink. Provided at an end of the pen 100 is a printhead 104 that is used to selectively eject droplets of ink onto the print media. As is schematically depicted in FIG. 1 , the printhead 104 comprises a plurality of nozzles 106 from which the ink droplets are emitted. As is further depicted in FIG. 1 , the nozzles 106 can be arranged in multiple columns 108, which are either part of a single die or multiple dies. In embodiments in which the ink pen 100 is a multicolor ink pen, individual columns 108 can be dedicated to ejecting particular colors of ink.

When multiple colors of ink are used in a printing device, it is desirable to ensure that the inks do not unintentionally mix. Such ink mixing can occur in at least two ways. In a first situation, barriers or other components within a multicolor ink pen that segregate the various inks contained within the pen become compromised, thereby allowing different colored inks to mix within the pen. Such mixing may be referred to as "internal" mixing. In a second situation, ink ejected from the nozzles mix on the outer surface of the printhead. Such mixing may be referred to as "external" mixing. In some cases of external mixing, ink of a first color ejected by a first column of nozzles mixes with ink of a second color ejected by a second column of nozzles. Such a condition may occur, for example, due to a printhead wiping procedure performed by the printing device in an attempt to clean the printhead.

Irrespective of whether internal or external ink mixing occurs, image quality can suffer given that the ink that the printing device deposits is not the ink that the device "thinks" it is ejecting. For current printing devices, efforts are normally focused on prevention of such mixing as opposed to detection. Accordingly, printing devices typically do not comprise means for detecting ink mixing.

BRIEF DESCRIPTION OF THE DRAWINGS The disclosed systems and methods can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale.

FIG. 1 is a perspective view of a prior art ink pen.

FIG. 2 is block diagram of an embodiment of a printing device in which ink mixing can be detected.

FIGs. 3A and 3B are front and side schematic views, respectively, of an embodiment of a sensor that can be used in an ink mixing detection process.

FIG. 4 is a flow diagram of an embodiment of a method for detecting ink mixing. FIG. 5 is a flow diagram of an embodiment of a method for method for calibrating a printing device.

FIG. 6 is a flow diagram of an embodiment of a method for performing ink mixing detection. DETAILED DESCRIPTION

As described above, ink mixing can negatively impact the quality of images printed by an ink-based printing device. Unfortunately, printing devices typically do not comprise means for affirmatively detecting such mixing and, therefore, undesirable printing results can occur. As is described in the following, however, such occurrences can be decreased or avoided by providing a printing device with an ink mixing detection system. In one embodiment, the detection system includes a sensor that is configured to measure the intensity of light that reflects from printed media and a module that is configured to analyze the intensity data and determine whether or not the printed ink is contaminated by another color. In further embodiments, a determination is made as to whether detected ink mixing comprises internal ink mixing or external ink mixing.

Disclosed herein are embodiments of systems and methods for detecting ink mixing. Although particular embodiments are disclosed, those embodiments are provided for purposes of example only to facilitate description of the disclosed systems and methods. Therefore, the disclosed embodiments are not intended to limit the scope of this disclosure.

Referring now in more detail to the drawings, in which like numerals indicate corresponding parts throughout the several views, FIG. 2 illustrates an example printing device 200. It is noted that the printing device 200 need not be limited to printing functionality. For example, in some embodiments, the printing device 200 can provide further functionalities such as copying, faxing, and emailing. In such a case, the printing device 100 may be described as a multi-functional printing device. As is indicated in FIG. 2, the printing device 200 comprises one or more controllers 202, memory 204, one or more user interface devices 206, a print engine 208, and at least one input/output (I/O) device 210.

The controller 202 is adapted to execute commands stored in memory 204 and can comprise a general-purpose processor, a microprocessor, one or more application-specific integrated circuits (ASICs), a plurality of suitably configured digital logic gates, and other electrical configurations comprised of discrete elements both individually and in various combinations that coordinate the overall operation of the printing device 200. The memory 202 comprises any one or a combination of volatile memory elements (e.g., random access memory (RAM)) and nonvolatile memory elements (e.g., read-only memory (ROM), flash memory, hard disk, etc.).

The user interface devices 206 comprise those components with which a human user can interact with the printing device 200 and input selections. In cases in which the printing device 200 comprises a printer, the user interface devices 206 can comprise a control panel that includes one or more of a liquid crystal display

(LCD) and input buttons.

The print engine 208, which may also be referred to as the print mechanism, includes the various components that are used to perform printing, including ink pens, such as those described in relation to FIG. 1. As indicated in FIG. 2, the print engine 208 further includes a sensor 218 that can be used to provide information that can be used to detect ink mixing. In some embodiments, the sensor comprises a densitometer.

The one or more I/O devices 210 facilitate communications between the printing device 200 and other devices and/or networks. Therefore, the i/O devices 210 may enable connection of the printing device 200 to a host computer and/or a network.

The memory 204 includes various programs (or program modules) including an operating system 212, a calibration module 214, and an ink mixing detection module 216. The operating system 212 generally controls operation of the printing device 200 and its various components, including the print engine 208 and the sensor 218. As described in greater detail in relation to FIG. 5, the calibration module 214 is configured to calibrate the printing device 200 so that manufacturing variations can be taken into account when the sensor is used for ink mixing detection. Once such calibration has been performed, ink mixing determinations can be performed by the ink mixing detection module 216, as described in relation to FIG. 6.

Various programs (i.e. logic) have been described herein. Those programs can be stored on any computer-readable medium for use by or in connection with any computer-related system or method. In the context of this document, a computer- readable medium is an electronic, magnetic, optical, or other physical device or means that contains or stores a computer program for use by or in connection with a computer-related system or method. Those programs can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor- containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions.

FIGs. 3A and 3B schematically illustrate an embodiment for the sensor 218. Beginning with FIG. 3A, the sensor 218 generally comprises a housing 300 that contains or supports one or more light sources 302 and one or more photodetectors 304. In the embodiment of FIG. 3A, four light sources 302 and two photodetectors 304 are provided. The light sources 302 are configured to selectively and independently emit visible light toward print media when the media passes the sensor 218. In some embodiments, each light source 302 comprises a light-emitting diode (LED) that emits a different color. In such a case, the colors can include, for example, blue, green, orange, and red.

With reference to FIG. 3B, the light emitted by the light sources 302 is directed toward the print media 308 and is reflected by the print media to the photodetectors 304. As indicated in FIG. 3B, the sensor 218 can, in at least some embodiments, further include a lens system, represented by lens 306, that focuses the reflected light onto the photodetectors 304. The photodetectors 304 are configured to detect the intensity of the light reflected by the print media 308. In some embodiments, each photodetector 304 measures a different aspect of light intensity. For example, one photodetector 304 can measure diffuse reflectance and the other photodetector 304 can measure spectral reflectance. By way of example, the photodetectors 308 each comprise a phototransistor. In further embodiments, a filter (not shown) can be provided between the optical system 306 and the photodetectors 304 to filter out light radiation that may interfere with detection of light reflected by the print media 308. An example of a suitable sensor is the Tetris sensor from Vishay Intertechnology, Inc.

Irrespective of its particular construction, the sensor 218 is positioned within the printing device 100 at a location at which it can readily obtain the desired intensity information. By way of example, the sensor 218 is mounted adjacent the ink pens of the print engine 208 to enable convenient evaluation of patterns or "patches" of ink that have been printed on the print media by the ink pens. In some embodiments, the sensor 218 is mounted to an internal carriage (not shown) of the printing device 200 that supports the ink pens.

Example systems having been described above, operation of the systems will now be discussed. In the discussions that follow, flow diagrams are provided. Process steps or blocks in these flow diagrams may represent modules, segments, or portions of code that include one or more executable instructions for implementing specific logical functions or steps in the process. Although particular example process steps are described, alternative implementations are feasible. Moreover, steps may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved.

FIG. 4 illustrates an example method for detecting ink mixing. In this embodiment, calibration of the printing device on which ink mixing will be detected (e.g., printing device 200) is performed before ink mixing detection. By way of example, such calibration can be performed at the factory at which the printing device was built prior to shipment of the device. As an initial step in the calibration process, human color space values are measured for control test patches of ink, as indicated in block 400. In some embodiments, one or more control test patches are printed by a designated control printer for each primary color of ink that will be used in the printing device on which ink mixing detection will be performed. By way of example, black, gray, magenta, yellow, and light magenta test patches are printed by the control printer. The human color space values comprise measure values that characterize the hues of the various patches in terms of human cone reflectance. Once the human color space values have been measured, they are stored in the memory of the printing device, as indicated in block 402. The values can be designated as "expected" values given that the same or similar values will be expected when test patches of the same colors of ink printed by the printing device are evaluated.

Next, the control test patches are scanned by the sensor (e.g., sensor 218) of the printing device to obtain light intensity values, as indicated in block 404. In some embodiments, an intensity value is obtained for each control test patch when independently illuminated by multiple light source of the sensor, such that each test patch is separately illuminated by multiple light sources and the intensity value for each form of illumination is observed. A correlation between the intensity values and a human color space can then be determined and stored on the printing device for later use, as indicated in block 406.

At this point, the calibration has been completed and ink mixing detection can be performed by the printing device. In some embodiments, the detection process is performed by the printing device on a continual, intermittent basis throughout its useful life. By way of example, the process can be performed on a periodic basis, each time a predetermined number of pages have been printed, or combinations thereof. When the detection process is to be performed, new test patches are printed and scanned by the printing device to obtain new intensity values, as indicated in block 408. At least one test patch is printed for each color of ink used in the printing device and, again, the intensity values are obtained by separately illuminating each patch with multiple ones of the light sources individually. Once the intensity values have been obtained, they are correlated to observed human color space values ("observed values"), as indicated in block 410. The observed values are then compared to the expected values (from block 402), as indicated in block 412, and an ink mixing determination is made relative to the results of the comparison, as indicated in block 414. In some embodiments, if the observed values differ from the expected values to a degree that exceeds a predetermined threshold, ink mixing is determined and appropriate notification and/or remediation steps can be taken.

FIG. 5 describes an example method for calibrating a printing device as described above in greater detail, which can, at least in part, be performed by the calibration module 214 (FIG. 2). Beginning with block 500, control test patches are printed with a control printer. Again, at least one patch is printed for each color of ink that will be used in a printing device on which ink mixing detection is to be performed. In other words, at least one patch is printed for each primary color printed by the printing device. In some embodiments, a control printer with known and reliable characteristics is used to calibrate multiple printing devices to obtain uniformity across those printing devices.

Once the control test patches have been printed, International Commission on Illumination, or Commission Internationale de I'Eclairage (CIE), L*a*b* values are measured for each test patch using a color measurement tool, as indicated in block 502. By way of example, the color measurement tool comprises a colorimeter. With such values, the color or hue of each patch can be defined relative to the human color space. The CIE L*a*b* values are then stored in the memory of the printing device as the expected values, as indicated in block 504. Next, the control test patches are input into the printing device to be calibrated and the patches are scanned by the sensor (e.g., sensor 218) of the printing device to obtain intensity values for the patches, as indicated in block 506. In some embodiments, an intensity value is obtained for each control test patch when independently illuminated by multiple light sources of the sensor on an independent basis. In addition, as indicated in block 508, the unprinted media (e.g., white paper) is scanned by the sensor and the intensity values obtained from that scanning are used to normalize the intensity values obtained by scanning the various patches. That normalization produces normalized intensity values that take into account manufacturing variations in the sensor (e.g., LED reflectance variation) as well as variations in printing device, such as the distance from the media at which the sensor is mounted in the printing device.

In order for the normalized intensity values obtained from the sensor to have meaning in terms of human perception of hue, the values must be correlated to human color space. For example, if the normalized color values can be translated into CIE L*a*b* values, they could be compared with the expected CIE L*a*b* values to determine whether or not the inks exhibit signs of contamination by other inks. Unfortunately, the CIE L*a*b* color space is highly nonlinear coordinate system and it is therefore difficult to develop a direct correlation between the sensor intensity values and CIE L*a*b* values. However, the CIE XYZ space is generally linear relative to light intensity. Accordingly, correlation between sensor intensity values and CIE XYZ coordinates is less complicated and can be performed with greater ease. In some embodiments, the correlation can be performed through standard linear regression processes. With reference next to block 510, the normalized intensity values are mapped to the CIE XYZ coordinate system using the above-described correlation process. The mapping is then stored in printing device memory as a correlation, as indicated in block 512, and will be available for later use in ink mixing detection procedures. By way of example, the correlation comprises a linear matrix that improves the speed and efficiency of mixing determinations. A linear matrix can be used given that the relationship between the CIE XYZ space and the reflectance energy is substantially linear. At this point printing device calibration has been completed and ink mixing detection can be performed. FIG. 6 describes an example method for performing ink mixing detection, i.e., testing to determine whether ink mixing has occurred. Again, such testing can be performed on an intermittent basis relative to one or more threshold criteria (e.g., time, number of printed pages, etc.). Beginning with block 600, test patches are printed with the printing device on which ink mixing detection is to be performed. In some embodiments, 5 to 10 test patches can be printed for each primary color of ink used by the printing device. Next, the printed test patches are scanned by the printing device's sensor to obtain intensity values, as indicated in block 602. Then, as indicated block 604, the unprinted media (e.g., white paper) is scanned by the sensor and the intensity values obtained from that scanning are used to normalize the intensity values obtained by scanning the various patches in similar manner to that described above in relation to FIG. 5. Normalized intensity values that account for variation between printing devices and their components results.

Referring next to block 606, the normalized intensity values are mapped to the CIE XYZ coordinate system using the correlation that was stored during the calibration process to obtain CIE XYZ coordinates (block 512, FIG. 5). At this point, the CIE XYZ coordinates are translated into CIE L*a*b* values by, for example, performing reverse transformation. In the forward transformation (XYZ to CIE L^*a^*b^*), the following relations are used:

L^* = 116f(Y/y_n)-16 [Equation 1]

a* = 500[f(X/X_n)-f (YZY_n)] [Equation 2]

b* = 200[f(Y/Y_n)-f (ZZZ_n)] [Equation 3]

where

f (t) = ft for t > 0.008856 [Equation 4]

f (t) = 7.787f +16/116 otherwise [Equation 5]

and X_n, Y_n, and Z_n are the reference CIE XYZ values of the media. The division of the f(t) function into two domains is performed to prevent an infinite slope at t = 0. The function f(t) is assumed to be linear below some t = to, and is assumed to match the { ' ³ part of the function at to in both value and slope. In other words:

t(^z - at_o +b (match in value) [Equation 6]

1/1 Ztft J = a (match in slope) [Equation 7] The value of b is chosen to be 16/116. The above two equations can then be solved for a and to'.

a = 1/(3£²) = 7.787037 •■• [Equation 8]

t_Q = S³ = 0.008856 • • • [Equation 9]

where δ = 6 / 29. Note that 16 / 116 = 2δ / 3.

In the reverse transformation, with δ = 6 / 29 as mentioned above, the following steps are performed:

d^ef / . \

1. define f_y = (L +16) /116

def

2. define f_x = f +a /500 def

3. define f_z = f_y - b* /200

4. if f_y > δ then Y = Y_nf_y ³ else Y = {f_y -λQlλ λ0)3δ²Y_n

5. if f_x > δ then X = Xf_x else X = (f_χ - 16/116) 3^²X_n

6. f_z > δ then Z = Z// else Z = (f_z -16/116) 3δ²Z_n

Once CIE L*a*b* values, i.e., observed CIE L*a*b* values, have been determined, they can be compared to the expected CIE L*a*b* values that were stored during the calibration process (block 504, FIG. 5), as indicated in block 610. Through such comparison, it can be determined whether or not ink mixing has occurred. Therefore, with reference to decision block 612, flow depends from this point upon whether a threshold has been exceeded. In some embodiments, the threshold pertains to the degree to which the hue angle, which is defined by the a and b values of the CIE L^*a*b* values, differs from the hue angle of the expected CIE L*a*b* values. If the threshold is not exceeded, ink mixing is not detected and flow for the detection session is terminated. If, on the other, the threshold is exceeded, meaning that the hue of a test patch significantly differs from the hue of the control test patch, the ink on the print media has been contaminated by another color of ink. In such a case, an error notification can be generated, as indicated in block 614. In some embodiments, the error notification can be internal and can signal the printing device to perform a printhead cleaning operation. In other embodiments, the error notification can be external and can signal a need for a service call.

FIG. 7 describes a further example method for performing ink mixing detection. In this method, however, the type of ink mixing is determined. Beginning with block 700, multiple sequential test patches for the same color ink are printed with the printing device. By way of example, five test patches are printed. Next, with reference to block 702, normalized intensity values are determined for each patch and translated into observed CIE L*a*b* values in similar manner to that described above in relation to FIG. 6. The observed CIE l_*a*b* values are then compared with the expected CIE L*a*b* values as to each patch, as indicated in block 704, such that each patch can be evaluated relative to the color (hue) that should have been deposited on the print media.

Referring to decision block 706, if the variation between the observed and expected CIE L*a*b* values does not exceed a predetermined threshold, flow for the detection session is terminated. If the variation exceeds the threshold, however, flow continues to decision block 706 at which it is determined whether the variation decreases across the sequence of patches. If not, there is no significant variation across the sequence, the hue is generally constant, and internal ink mixing is indicated (block 710). If there is significant decrease from patch to patch in the sequence, continued use of the printhead nozzles is clearing the contaminating ink from the printhead, and external mixing is indicated (block 712).. In either case, an appropriate error notification can be generated, as indicated in block 714. In some embodiments, detection of internal mixing will result in a service call and pen replacement and detection of external mixing will result in a printhead cleaning process being performed.

Claims

CLAIMSWhat is claimed is:

1. A method for detecting ink mixing, the method comprising: printing test patches of ink with a printing device (408); scanning the test patches with a sensor of the printing device to obtain intensity values (408); correlating the intensity values with human color space values on the printing device to obtain observed human color space values (410); comparing the observed human color space values with expected human color space values (412); and determining whether ink mixing has occurred relative to the comparison (414).

2. The method of claim 1 , wherein printing test patches comprises printing test patches of each primary color of ink used by the printing device.

3. The method of claim 1 , wherein scanning the test patches comprising individually scanning each test patch with a sensor that separately illuminates the test patches with multiple light sources of different colors.

4. The method of claim 1 , wherein correlating the intensity values comprises correlating the intensity values to CIE XYZ coordinates.

5. The method of claim 4, wherein correlating the intensity values further comprises translating the CIE YXZ coordinates into CIE L*a*b^* values.

6. The method of claim 5, wherein comparing the observed human color space values with expected human color space values comprises comparing the CIE L*a*b^* values with expected CIE L*a*b* values.

7. The method of claim 1 , further comprising calibrating the printing device by printing control test patches of ink with a separate control printer and measuring human color space values for each of the control test patches with a color measurement tool.

8. The method of claim 7, wherein calibrating the printing device further comprises storing the measured human color space values on the printing device as the expected human color space values.

9. The method of claim 8, wherein calibrating the printing device further comprises separately scanning each control test patch with the sensor of the printing device to obtain intensity values, mapping those intensity values to a human color space, and storing a mapping between those intensity values and the human color space on the printing device, wherein correlating the intensity values is performed using the stored mapping.

10. A printing device (200) comprising: a print engine (208) including multiple ink pens of different colors and a sensor (218) having multiple light sources of different colors, the sensor being configured to individually illuminate printed patches of ink with the light sources and measure intensity values of reflected light; memory (204) including an ink mixing detection module (216) configured to obtain intensity values from the sensor that result from scanning printed test patches, to correlate the intensity values with human color space values on the printing device to obtain observed human color space values, and to compare the observed human color space values with expected human color space values.