US 20050078136 A1
A method and system for calibrating a device having a first fluid source that ejects a first drop quantity and a second fluid source that ejects a second drop quantity by, for example, printing a pattern having a first portion and a second portion; obtaining a relationship between the first drop quantity and the second drop quantity from the pattern; and adjusting data used to determine quantities of fluid to eject from the first or second fluid sources based on the relationship between the first and second drop quantities. Other embodiments of the invention are directed to a calibration apparatus and system.
43. A method of calibrating a device having a first fluid source that ejects a first drop quantity and a second fluid source that ejects a second drop quantity, comprising:
printing a pattern having a first portion and a second portion, wherein the first portion is printed by the first fluid source and the second portion is printed by the second fluid source;
obtaining a drop volume relationship between the first drop quantity and the second drop quantity from the pattern; and
adjusting data used to determine quantities of fluid to eject from the first fluid source or the second fluid source based on the relationship between the first drop quantity and the second drop quantity.
44. The method of
45. The method of
46. The method of
47. The method of
determining an intersection point between a calculated value of the first portion response and the second portion response; and
determining the fill density of the first portion at the intersection point.
48. The method of
creating a fit line along at least a part of the signal response of the test portion; and
adjusting the intersection point to an intersection between the fit line and the calculated value of the reference portion response.
49. The method of
50. The method of
determining a fill density of the second portion corresponding to a fill density of the first portion; and
calculating the second drop quantity from the fill density of the second portion.
51. The method of
52. A method comprising:
printing a test pattern having a reference portion and a test portion, wherein the reference portion is printed by a first fluid source and the test portion is printed by a second fluid source;
obtaining a drop volume relationship between a first drop volume of the first fluid source and a second drop volume of the second fluid source from the test pattern; and
adjusting at least one value in a color map using the drop volume relationship between the first drop volume and the second drop volume.
53. The method of
54. The method of
55. The method of
determining an intersection point between a reference line determined from the reference portion data and the test portion data; and
determining the fill density of the test portion at the intersection point.
56. The method of
57. The method of
58. The method of
determining a fill density of the test portion substantially equal to a fill density of the reference portion; and
calculating the second drop volume from the fill density of the test portion.
59. The method of
60. A calibration apparatus for a device having a first fluid source that ejects a first drop volume and a second fluid source that ejects a second drop volume, comprising:
means for scanning a test pattern having a reference portion and a test portion and generating a sensor output, wherein the reference portion is printed by the first fluid source and the test portion is printed by the second fluid source;
means for obtaining a drop volume relationship between the first drop volume and the second drop volume from the test pattern; and
means for changing a color map using the drop volume relationship.
61. The calibration apparatus of
62. The calibration apparatus of
means for determining a fill density of the test portion corresponding to a fill density of the reference portion; and
means for calculating a drop volume from the fill density of the test portion.
Inkjet printers have become increasingly sophisticated and can generate more complex images than before, including color photographic-quality images. Some inkjet printers have two or more pens, such as a high dye-load pen and a low dye-load pen, or multiple chambers within a single inkjet pen to handle a wide range of colors and hues. Differences in drop volume and/or drop weights between the pens, however, may cause noticeable color variations and/or hue shifts and generate images that do not accurately replicate desired colors.
Accordingly, an embodiment of the invention is directed to a method of calibrating a device having a first fluid source that ejects a first drop quantity and a second fluid source that ejects a second drop quantity. An embodiment of the method comprises printing a pattern having a first portion and a second portion, wherein the first portion is printed by the first fluid source and the second portion is printed by the second fluid source; obtaining a relationship between the first drop quantity and the second drop quantity from the pattern; and adjusting data used to determine quantities of fluid to eject from the first fluid source or the second fluid source based on the relationship between the first drop quantity and the second drop quantity.
Another embodiment of the invention is directed to a calibration apparatus for a device having a first fluid source that ejects a first drop quantity to form a first region and a second fluid source to eject a second drop quantity to form a second region. The apparatus comprises an optical sensor to generate output from scanning the first portion and the second portion; and a processor arranged to receive the output, wherein the processor includes a configuration to determine a relationship between the first drop quantity and the second drop quantity using the output.
The embodiments described above are not intended to be exhaustive and other aspects of the invention will be apparent to those skilled in the art after reviewing the drawings and the detailed description below.
Housing 102 preferably encloses the electrical and mechanical operating mechanisms of the printer 101. Operation is administrated by an electronic processor 103 (such as a microprocessor or application specific integrated circuit (“ASIC”) controlled printed circuit board) connected appropriately to a computer (not shown). If desired, general purpose microprocessors or ASIC-executing firmware or software may be used to program and execute imaging, printing, print media handling, and/or control functions and logic operations. In an embodiment, the processor 103 functions may be performed by the computer, by electronics on-board the printer 101, of by interactions therebetween. The term “processor” as used herein encompasses these functions, whether performed by a computer, the printer 101, an intermediary device therebetween, or by a combined interaction of such elements.
In a preferred embodiment, ink-jet pens 115X may be individually mounted in a movable carriage 109. For example, without limitation, in a “full color” system, inks can be included for subtractive primary colors, i.e., cyan (X=C), yellow (X=Y), magenta (X=M) and true black (X=K). Further, if desired, an ink fixer (X=F) may also be included. However, the invention is not so limited and also contemplates the use of an integrated pen system, such as that in which pens 115X themselves may include one or more chambers (not shown). For instance, an integrated embodiment may include a plurality of pens (e.g., two pens) having a plurality of chambers (e.g., three) per pen. Reusable printhead systems are fluidically coupled by tubing 119 to replaceable or refillable ink reservoirs 117X (generally, in a full color system, inks preferably for the subtractive primary colors, cyan (X=C), yellow (X=Y), magenta (X=M) and true black (X=K) are provided; ink fixer (X=F) solutions are also sometimes provided). In a preferred embodiment, each pen 115X operates using an internal back pressure regulator for allowing transfer of ink from a respective reservoir 117X while maintaining the appropriate back-pressure needed for the operation of each printhead of each pen. If desired, replaceable ink jet cartridges, such as those having a self-contained ink reservoir and back-pressure regulating mechanism, may be employed. Once a printed page is completed, the print medium is typically ejected onto an output tray 121.
Preferably, the embodiments of the invention operate within the printer 101 by comparing drop volumes of two or more pens and/or ink chambers 115X and using this comparison to reduce or remove color imbalances between the pens and/or chambers. In accordance with an embodiment of the invention, the relationship between the drop volumes may be determined without requiring a unique reference or calibration standard. Further, because primary and secondary inks may be printed on the same paper or media, in general, the effects of the paper or media will be relatively negligible. Two ink or fluid sources 115X, such as a high dye-load pen and a low dye-load pen, may be considered in a paired set, but embodiments of the invention may be used in any application that ejects ink from more than one pen (including those of different types) and/or chamber. In an embodiment, one pen is referred to as a “reference pen” and another pen is referred to as a “secondary pen”. The terms “reference” and “secondary” correspond to the portions of a test pattern printed by each pen 115X and do not reflect the relative importance of the pens 115X during an actual printing operation.
In this example, the ratio between the drop quantites of the two pens in a matched pen pair affects the “blue-yellow shift”, or the degree of blue or yellow appearing in a printed image. For example, if the specified functional (e.g., nominal or optimum) drop quantity ratio between the high-dye load pen and the low dye-load pen is 5.0 nanograms/4.4 nanograms to obtain a correct or preferred balance of cyan and magenta to yellow, a ratio higher than the specified functional ratio may create an image that is too yellow, while a ratio lower than the specified functional ratio may create an image that is too blue. Ratio changes may occur if, for example, the drop quantity of either pen deviates from the specified functional drop quantity. If such variations are left uncorrected, the generated chroma values generated by the pen pair may vary from, for example, 0 to 20 for a given color, which may be an unacceptably high variance for some applications.
The pattern 300 starts with a spit bar 302 generated by both pens to clear nozzles in the pens, stabilize pen temperatures, and stabilize drop volumes before generating the remainder of the test pattern. After the spit bar 302, the pattern 300 includes a white space 304, a light absorbing portion 306, and a reference portion 308. The light absorbing portion 306 absorbs stray light and prevents or reduces the influence of unwanted signals on the results of optically scanning. The light absorbing portion 306 in a preferred embodiment is light black and printed in one tile.
Preferably, after the light absorbing portion 306 is printed, the reference portion 308 is printed by the reference pen at a known reference fill density. The reference fill density can have a value that is between the maximum and minimum fill density of the secondary pen. In an embodiment, the reference fill density is selected so that the calculated (e.g., average) response of the reference pen at the reference fill density will correspond to a point between the minimum and maximum fill densities of the secondary pen. For example, if the minimum fill density of a secondary pen is 14% and the maximum fill density is 41%, the reference fill density could lie between 14% and 41%. Of course, other minimum, maximum, and reference fill density values can be selected for alternate embodiments.
The color of the reference portion 308 is selected based on, for example, a spectral response of an optical sensor or scanner to be used for scanning the test pattern 300. In one example, the test pattern 300 will eventually be scanned with an optical sensor having a light source with a light output between 420 nm and 470 nm. To accommodate light sources in this range, a high dye-load reference pen may eject, for example, 19 parts magenta ink and 12 parts yellow ink to generate a reference portion 308 having a fill density of 19% magenta and 12% yellow. If the test pattern 300 will be scanned using a 420-470 nm light source, cyan ink is preferably not used to generate the reference portion 308 because cyan ink may not absorb the light from the light source as well and therefore may yield less useful information during the scanning process. Further, although a combination of two colors is used to generate the reference portion 308 in this embodiment, the reference portion 308 may be a single color or incorporate different color combinations depending on the specific characteristics of the light source. In an embodiment, the reference portion 308 color is selected to better ensure that the spectral response generated by the reference portion 308 will remain sufficiently consistent even if there are small variations between the optical sensors generating the response for the same test pattern 300.
In a preferred embodiment, after the reference pen prints the reference portion 308, the secondary pen prints a test portion 310 containing one or more test tiles 311. In an embodiment, the test portion 310 has a smooth ink gradation representing increasing fill densities generated by the secondary pen. The secondary pen may generate the ink gradation over multiple test tiles 311, each test tile 311 having a fill density that is greater than the previous test tile 311. To do this, the secondary pen may fire ink at increasing fill densities along each increment 301 to form each test tile 311. For example, if each test tile 311 is represented by the 10×10 deposition point grid (such as noted above), the first test tile 311 may have 14 out of its 100 ink deposition points printed with ink (i.e., a fill density of 14%), while subsequent test tiles 311 may have fill densities increasing at a rate of 1% per test tile 311 along the test portion 310 up to 41% or some other selected or predetermined ending point.
Note that other starting and ending levels may also be used to print the test portion 310. In an embodiment, the starting and ending drop volume and fill density levels corresponding to a minimum and a maximum fill density for the secondary pen. The maximum fill density may correspond to, for example, a saturation threshold at which an increase in fill density would not change the optical sensor response. Further, the minimum fill density may be chosen to cover an expected or anticipated drop volume variation (e.g. based on manufacturing tolerances) between different pens. Regardless of the specific starting and ending values and the fill density increment between each test tile 311, the response of the secondary pen in generating the test tiles 311 will determine where the secondary pen drop volume corresponds with the reference pen drop volume to obtain the drop quantity ratio (e.g., 5.0 nanograms reference/4.4 nanograms secondary).
In an embodiment, the secondary pen is a low dye-load pen and the test tiles 211 are printed with black ink from the low dye-load pen. Black low dye-load ink often provides a preferred specified or an optimum signal response for certain light sources, such as the 420-470 nm light source noted in the example above. In short, the example described herein assumes that the 19% magenta/12% yellow ink reference combination represents the drop quantity of the reference pen and that the black ink represents the drop quantity of the secondary pen.
Referring back to the method shown in
Preferably, once the entire test pattern 300 has been scanned (block 204), the processor 103 compares the calculated (e.g., average) signal response of the reference portion 400 with the signal response of the test portion 402 (block 206) and finds an intersection point 404 between the calculated (e.g., average) reference portion signal response 400 with the test portion signal response 402 (block 208). In an embodiment, the starting and ending portions of the reference portion signal response are trimmed before calculating the calculated signal response 400 to better ensure that the calculated signal response 400 is calculated or determined from a more stable signal and not transient data generated as the optical sensor measures the start and end of the reference portion 400. For example, without limitation, the invention may scan a subject pattern a plurality of times (e.g., four) and then average the associated signals at each position. In an embodiment, the average signal response of the scans can then be used in connection with a line fitting technique or other mathematical technique. However, it is important to note that the invention is not limited to a specified number of scans and any number of scans can be employed.
In an embodiment, a line 406 representing the calculated reference portion signal response 400 is extended until it crosses the test portion signal response 402 at the intersection point 404. The optical sensor processor then creates a fit line 408 based on a selected number of data points before and after the intersection point 404. The fit line 408 may also be generated using a variety of mathematical equations and/or approximation computations, however, a least squares fit method is preferred to better ensure that stray data points in the test portion signal response 402 do not give an undesirably skewed or an inaccurate representation of the actual test portion signal response 402. In an embodiment, for example, the sensor samples every fourth data point among 600 data points before and 600 data points after the intersection point 404. The fit line 408 is then generated from the sampled data points, and the intersection point 404 is re-evaluated and, if needed, re-adjusted to correspond with the point at which the calculated (e.g., average) reference portion signal response 406 intersects with the fit line 408.
In a preferred embodiment, once the intersection point 404 has been found, the processor 103 determines the position in the test portion 300 at which the intersection takes place to calculate a corresponding fill density for a secondary pen (block 210). Preferably, the optical sensor stores a corresponding position for each signal response. Further, the starting point of the test portion 310 and the increment size 301 of each test tile 311 is known (or can be determined). By correlating the intersection point 404 with a given position on the x-axis of the test pattern 300 generated by the optical sensor and determining the fill density of the test tile 311 in the test pattern 300 corresponding to that position, the fill density of a secondary pen at that position can be determined. In the particular example shown in
The fill density of the secondary pen at the intersection point 404 is then converted into a relative drop quantity value that reflects a relationship between the secondary pen and the reference pen such as a drop volume difference between the secondary pen and the reference pen (block 212). In an embodiment, the drop volumes of the reference and secondary pens, in nanograms X 1000, are represented as follows:
Illustrative equations (1) and (2) above are linear equations, and therefore the estimated drop quantity for both the reference and secondary pens can be represented by straight lines, as shown in
As noted above, the scanning process and various calculations can be conducted using an optical sensor that, in an embodiment, sends its data to a printer controller for processing.
In an embodiment, inkjet nozzles of the printheads are generally in-line with the sensor 600 in the x-axis by fixedly mounting the sensor 600 appropriately on the carriage 109 (
Although some optical sensors in other applications may use multiple filters, an optical sensor 600 used in an embodiment of the invention may, if desired, include only one filter because embodiments of the invention measures spectral response of the test pattern 300 using a narrow band light source (e.g., 420-470 nm in the example described above). The embodiment would therefore use a filter covering the narrow band and would not need multiple filters to accommodate one or more light sources covering a broad band.
The illuminating beam 606 from the LED 602 is transmitted to the test pattern 300 and thereafter it is reflected off the test pattern 300 as a reflected light beam 610. In an embodiment, the area illuminated by the LED 602 is slightly larger than the viewing field of the photodetector 604 to better illuminate a selected viewing region by the LED 602. The reflected light beam 610 then enters a condenser lens 612, which focuses the reflected light beam 610 into the photodetector 604. In an embodiment, the condenser lens 612 has a focal length of approximately 5 mm (millimeters), but other focal lengths may also be selected in other optical sensor configurations and implementations having different packaging and placements of the sensor components. The photodetector 604 then generates an output signal to the printer controller 102 for analysis to generate the test pattern scan, such as the test pattern scan in
Although the description above focuses on detecting drop quantity variations between pens in a multiple-pen or multi-chamber printhead, embodiments of the invention may be used to detect variations between multiple chambers in a single pen as well. Embodiments of the invention can be applied to, for example, a six-ink printer with one pen having high dye-load cyan, yellow and magenta ink and one pen having low dye-load cyan and magenta inks and a black ink. Embodiments of the invention can be used in any application that uses multiple ink sources to balance drop volume difference between two ink sources to give a correct hue of the color output.
While embodiments of the present invention have been particularly shown and described, it should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of embodiments of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.