1. Field of the Invention
The present invention relates to a printing apparatus such as a printer, and to an adjustment pattern printing method that is used for the printing apparatus.
2. Description of the Related Art
Japanese Patent Laid-Open No. H10-329381 (1998) discloses a process for adjusting a printing position of dots by inkjet printing (hereafter, this will also be referred to as a printing position adjustment process or registration process). More specifically, a “reference pattern” is printed by a reference nozzle array, after which a plurality of “shifted patterns”, which are printed from a different nozzle array whose printing position is shifted a little at a time from the reference pattern, are printed over the reference pattern. Then based on the amount that the printing position of the shifted pattern is shifted and the position of the inflection point of the optical reflectivity, an amount of landing position error of ink droplets is calculated and the ejection timing that the print head ejects ink is corrected.
However, in the technology disclosed in the publication above, there is a problem in that a relatively large amount of media or ink is required for the registration process, and the processing time is long. There is also a need for a more precise registration process.
An object of the present invention is to provide a printing apparatus and an adjustment pattern printing method that is used for the printing apparatus that is able to reduce the amount of media and ink used, reduce the processing time and improve the adjustment precision when executing a registration process.
The present invention provides a printing apparatus for printing an image by moving a head unit with respect to a print medium, the head unit having first and second print heads being used for printing in a common area, the first print head having a first printing element array formed by a plurality of printing elements configured to print dots, the second print head having a second printing element array being arranged along with the first printing element array and being formed by a plurality of printing elements configured to print dots, including:
a pattern printing unit configured to cause a plurality of printing elements in a partial region of the first printing element array and a plurality of printing elements in a partial region of the second printing element array corresponding to the partial region of the first printing element array to print a plurality of adjustment patterns on a print medium, the plurality of adjustment patterns being for acquiring an amount of printing position shift (error) of the second print head with respect to a printing position of the first print head;
an acquisition unit configured to acquire an amount of relative inclination between the first and second print element arrays; and
a selection unit configured to select positions of the partial regions of the first and second printing element arrays based on the amount of relative inclination between the first and second print element arrays.
With the present invention, it is possible to reduce consumption of media and ink upon a registration process, reduce the amount of time required for the registration process, and improve the adjustment precision.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
In the following, embodiments of the present invention will be explained in detail with reference to the accompanying drawings.
The print head unit 401 comprises an electrothermal transducer and is an inkjet print head that ejects ink using thermal energy. The print head unit 401 prints an image by causing ink to be ejected from the ink ejection ports (nozzles) by utilizing the change in pressure that occurs when air bubbles are grown and contracted by film boiling due to thermal energy that is applied by the electrothermal transducer.
The print head unit 401 is mounted in a carriage 202 such that it is removable. The carriage 202 is supported such that it is can freely slide along a guide rail 204, and is moved back and forth along the guide rail 204 by a driving unit such as a motor (not illustrated in the figure). The print medium S is conveyed in the conveyance direction indicated by the arrow Y by conveyance rollers 203 such that a fixed interval is maintained between the print medium S and the surface of the ejection ports (surface formed by the ink ejection ports) of the print head unit 401.
The print head unit 401 comprises a plurality of print heads 401K, 401C, 401M and 401Y for discharging different inks, and respective nozzle arrays (ejection port arrays). Each nozzle array has 1280 printing elements arranged in the sub scanning direction at 1200 dpi spacing. In this example, the print heads are capable of discharging black (K), cyan (C), magenta (M) and yellow (Y) ink. Each print head is integrated with an ink cartridge for supplying the ink (black, cyan, magenta and yellow ink) to be ejected. The nozzles corresponding to the plurality of print heads 401K 401C, 401M and 401Y are used for printing dots in a common area of the print medium.
A recovery unit 207 is provided that faces the surface of the ink ejection ports of the print head unit 401 when the print head unit 401 moves to a non-printing area, which is an area within the range of back-and-forth movement of the print head unit 401, however is outside of the range where the print medium passes. This recovery unit 207 comprises a cap 208 (caps 208K 208C, 208M, 208Y) that can cap the ejection ports of the print head unit 401. The caps 208K, 208C, 208M and 208Y can cap the respective ejection ports that eject black, cyan, magenta and yellow ink. A suction pump is connected to the inside of the cap 208. By applying a negative pressure to the inside of the cap 208 when the cap 208 is capping the ejection ports of the print head unit 401, it possible to suck the ink from the ejection ports of the print head unit 401 into the cap 208. By performing this kind of suction recovery operation, it is possible to maintain the ink ejection performance of the print head unit 401.
The recovery unit 207 also comprises a wiper 209 such as a rubber blade for wiping the ejection port surface of the print head unit 401. By ejecting ink from the print head unit 401 toward the cap 208, it is possible to perform a recovery process (also called “preliminary ejection”) to maintain the ink ejection performance of the print head unit 401.
A reflective optical sensor 500 as illustrated in
This optical sensor 500 measures the printing density of the registration adjustment pattern that is printed on the print medium. By alternately conveying the print medium in the sub scanning direction and moving the carriage unit 2, in which the optical sensor is installed, in the main scanning direction, it is possible to detect the density of an adjustment pattern group that is printed on the print medium.
In the registration process of the embodiments, first a plurality of adjustment patterns are printed on a print medium. Each adjustment pattern comprises a first pattern and a second pattern; however, the relative printing position of the second pattern with respect to the first pattern is different.
The adjustment patterns illustrated in
In
The printing element arrays that are used for forming the reference patterns and shifted patterns are set to correspond with the combination of the ink color or scanning direction that will be the adjustment target. First, the printing element array that will be for the reference is set and reference patterns are formed, then the shifted patterns are formed using the other printing element arrays. In the case of performing position adjustment between different colors, the printing element array that prints black forms the reference pattern, for example, and the printing element arrays for the colors cyan, magenta and yellow form the shifted patterns.
In this embodiment, when forming a pattern, in order to conserve the amount of ink and printing paper used, and to reduce the processing time, patterns as illustrated in
In
Here, for example, the case of using the black print head 704 as a reference, and adjusting the printing position of the print heads 701, 702 and 703 of the other three colors was explained; however, any of the colors could be taken to be the reference.
The print heads scan in the direction of the arrow in
Each adjustment pattern comprises a plurality of patterns 708709, 710 and so on that have different shift amounts between the black reference pattern and the shifted patterns of the other colors. When doing this, it is necessary that the size of an adjustment pattern be a size such that change in density is visibly noticeable, or be a size such that the change in density can be detected when compared with the spot diameter of the sensor.
As illustrated in
However, when relative inclination occurs between two print heads, there is a possibility that the printing position cannot be properly adjusted by the adjustment method illustrated in
Here, referring to
Here, printing position adjustment by the printing apparatus is performed so that printing positions of the center regions of two print heads are aligned. Therefore, when printing is performed using all of the printing elements after printing position adjustment has been performed for magenta (M), regardless of whether or not there is relative inclination between the print head 801 for the reference color black and the print head 803 for magenta, there is no printing position shift between black and magenta. In other words, when the printing position shift is defined as a position shift between center positions of two line segments that are printed by two print heads, the center positions of two line segments that are printed by printing elements in the center regions of two print heads match and no printing position shift occurs.
On the other hand, when relative inclination does not occur between print heads for cyan (C), the center positions of the two print heads are aligned to each other even though printing position adjustment is performed using printing elements in the bottom end region of the print heads, so that no printing position shift occurs. However, when relative inclination occurs between print heads, the center positions of the two print heads are not aligned to each other by a printing position adjustment using only the printing elements in the bottom end region of the print heads, and the printing position shift occurs. For this reason, even when the same inclination occurs for magenta (M) and cyan (C), there is a possibility that color shift of cyan (C) will become large. In other words, even when the amount of inclination of the print heads is the same, the color shift amount becomes different depending on positions of printing elements used for printing position adjustment. In the following, an arrangement for solving this problem will be described in detail.
In the present embodiment, the case of correcting the adjustment value for adjusting the printing position according to an inclination amount of the print heads and the position of the printing elements used for printing the patterns for a printing position adjustment will be explained.
In the figures, reference number 901 illustrates the printing elements that print a pattern for performing printing position adjustment for the cyan print head, and illustrates how much the position of the printing elements separate from the center (reference position) due to inclination of the print head. Reference number 902 illustrates the same for the black print head. Reference number 903 indicates the used printing elements that are used for printing a pattern, 907 indicates the printing elements on the top end of the used printing elements 903, and 908 indicates the printing elements on the bottom end of the used printing elements 903, where the element numbers (position shift information from the reference position of the printing elements) are taken to be A1 and A2 (A1>A2). The results of performing adjustment uniformly receive the effects of the printing elements used for adjustments, so that the value 904 obtained by projecting the center position between A1 and A2 in the printing element array onto the main scanning axis (correction value B) is the amount of shift of the used printing elements 903 from the center of the print head. The point on the main scanning axis where the very top printing element position of the printing element array is projected is taken to be 905 (X(T)), and the point on the main scanning axis where the very bottom printing element position of the printing element array is projected is taken to be 906 (X(B)). The point where the main scanning axis in
Here, the method for finding the inclination amount S of a print head will be explained in detail. An example of printing patterns for acquiring the inclination amount S is illustrated in
First, a reference pattern is printed on the print medium using the 256 printing elements of the very bottom area of the printing element array for which the inclination amount S is to be obtained. After that, the print head on which that printing element array is mounted is moved relative to the print medium in the sub scanning direction a distance that is the same as the length in the element arrangement direction of the printing element array (approximately one inch in this embodiment). Then, the 256 printing elements on the very top of the printing element array are used to print one non-reference pattern (+6) on the print medium. Similarly, that printing element array is used to print in parallel combinations of the reference pattern and non-reference pattern for the other non-reference patterns, so that seven vertical line patterns are printed on the print medium as illustrated in
The inclination amount S that was obtained is stored in a memory medium through user input to the printing apparatus or the like. Here, the inclination amounts S for the black, cyan, magenta and yellow printing element arrays are taken to be S(i) (i=K, C, M, Y) respectively.
The printing patterns above are an example, and variations are possible such as increasing the output resolution in order to improve the detection precision of the inclination amount, increasing the horizontal size of the printing patterns in order to increase the selected width of the inclination amount, or increasing the number (types) of non-reference patterns. Moreover, changes are possible such as increasing the vertical size of the printing patterns (lengthening the line patterns) in order to improve the visibility of the printed line patterns, or increasing the width of the lines to more than two dots. On the other hand, when the number of printing elements of each printing element array is less than 256 elements, it is necessary to change the image according to the conditions such as reducing the vertical size of the printing pattern.
As a method for obtaining the inclination amount S of the printing element array, is a method of printing a plurality of overlapping adjustment patterns while gradually changing the printing timing of the very top printing element group with respect to printing of the very bottom printing element array, which is the reference, and then determining the density using a sensor or the like.
Next, a method is explained for finding the amount that the adjustment value, which is obtained when printing patterns are printed using a position other than the center of the print heads with inclination occurring in the print heads, is shifted from the adjustment value of the printing position that was originally supposed to be found, or in other words the correction amount. The correction value B can be expressed by Equation 1 below.
This correction value B can be found respectively for black and cyan. Here, black is taken to be the reference element array, so that by taking the adjustment value for cyan with respect to black that was adjusted using the bottom area of the printing element array before correction is performed to be P(C), Equation 2 for finding the corrected adjustment value P′(C) is as given below.
P′(C)=P(C)−2(B(K)−B(C)) Equation 2
By correcting the printing adjustment value P using the correction value B in this way, a more suitable adjustment value is obtained.
Equations 1 and 2 are described such that they correspond to the number of nozzles and the shifting direction of the print heads used in the present embodiment. When the number of nozzles mounted in the print heads is different than in the present embodiment, or when the number of nozzles that are mounted in each print head is different, or when the definition of the shifting direction is different, the equations above can be easily changed and optimized for each respective form.
By calculating the correction value as described above from the size of the inclination of the print heads between two head for which printing adjustment is performed, and from the position of the element arrays that print the adjustment patterns, and then correcting the adjustment value according to that correction value, it is possible to reduce the effect of the inclination of the print head and the position of the elements that print the patterns, and it is possible to obtain a more suitable printing position adjustment value.
In first embodiment, an arrangement for correcting the printing position adjustment value was described. However, in the second embodiment, instead of correcting the printing position adjustment value, the position of printing elements used for printing the adjustment patterns is changed according to the amount of inclination of the print head so that a more accurate printing position adjustment value is obtained.
As described in detail in the explanation of the first embodiment with reference to
As described in the first embodiment, a deviation of the adjustment value caused by the inclination of the print heads at a position for adjustment with respect to the center region can be expressed by equation 1. As a result of adjustment without correction, the predicted amounts of the printing position shifts between the reference printing element array (black) and the printing element arrays (cyan, magenta, yellow) to be adjusted (that is, a relative inclination between two print heads) can be expressed as B(k)−B(i) (i=C, M, Y). Therefore, for printing element arrays for which this value exceeds a certain threshold value, performing adjustment using the center region of the print heads is preferred.
The predicted amount of printing position shift and the threshold value will be explained in detail below. The deviation of the adjustment value obtained from Equation 1 is calculated from the position of the printing element group that is used for printing adjustment patterns and from the amount of inclination of the print head. The position of the printing array group can be freely set; however, here, the adjustment pattern is set as illustrated in
A flow for selecting the position of the element arrays for printing the adjustment patterns will be described with reference to
In this embodiment, there where three colors C, M and Y for which adjustment is performed, so that flow is such that when the top region is used, printing is performed using the bottom region. However, in the case of setting the position of the element groups to be used in printing the adjustment patterns for six kinds of element arrays, for example, two kinds of element arrays can be applied for each of the three locations, top region, center region and bottom region, and two lines can be printed.
Moreover, in the present embodiment, the position of the element arrays used in adjustment was divided into three regions, and because the top region and the bottom region are symmetrically located, comparison of the amount of printing position shift is performed only once. However, the position can be divided into five divisions, or four regions having different widths, and in that case, more complicated processing flow is necessary for determining which position is suitable to be set.
Next, a method for properly setting the threshold value Z above will be explained. The threshold value Z is a value used in determining whether the deviation in the adjustment value between printing element arrays caused by inclination of print heads is large or small, so can be set according to the required adjustment precision. For example, in the present embodiment, the printing resolution in printing position adjustment between printing element arrays is 1200 dpi, and the adjustment resolution is 4800 dpi. Therefore, there may be always approximately 5.3 μm of error as quantization error. Taking into consideration the shift that occurs when determining the amount of dispersion in adjustment or the amount of inclination when performing printing position adjustment, the threshold value Z should be preferably set so that the necessary precision is obtained. Changing the threshold value Z according to conditions such as the type of paper used during adjustment and the distance between the print head and the paper is also effective.
As described above, by changing the position of the printing elements in each print head that are used in printing adjustment patterns according to the amount of printing position shift caused by relative inclination between print heads for which printing position adjustment is performed, it is possible to obtain higher printing position adjustment precision.
In the second embodiment, when there was a large amount of shift caused by relative inclination of the print heads, the position of the element groups used for printing the adjustment patterns was the center region. In this embodiment, construction is such that, using the same judgment, when a deviation of printing position adjustment value is large, an adjustment pattern is added that will correct that deviation.
In
As described above, by determining the amount of printing position shift from the inclination of the print heads and the position of the printing element groups that print the adjustment patterns, it is possible to obtain adjustment values that can more accurately set the printing position.
In the embodiments 1 to 3 above, the explanation centered mainly on a printing position shift between different colors; however, needless to say the same effect is obtained in the case of element arrays of the same color that have different inclinations. Moreover, the amount of inclination was detected for all element arrays; however, in the case of a plurality of element arrays in the same print head, it is possible to detect the amount of inclination of one of those arrays, and presume that the other element arrays in the same print head have the same amount of inclination.
In the printing apparatus, of the two printing operations that are the object of the registration adjustment process, the timing of one of the printing operations is controlled, and an adjustment value for aligning the printing positions of the two printing operations is saved. In the case where this adjustment value does not need to be updated, the adjustment value can be set as a default value during the inspection process at the factory at the time of shipping, and ROM that stores that value can be mounted in the printing apparatus. However, when the registration process is performed according to an instruction from a user, or by a repairperson or by taking the printing apparatus to a repair center, by storing the adjustment value in an EEPROM, the value can be suitably updated. In this case, the timing of one printing operation is controlled based on the adjustment value stored in the printing apparatus and an adjustment pattern is printed, and timing information for a printing operation that will minimize a relative position shift in elements is obtained. Then, a new adjustment value is set based on the printing timing that minimizes the amount of shifting from the printing timing when printing the adjustment patterns and that adjustment value is stored in the EEPROM. In either case, the adjustment value is referenced as a printing timing correction value when printing an image.
The configuration and number of nozzle arrays or print heads described above, and the kinds and number of ink colors are only examples, and needless to say that any appropriate ones could be used. For example, in the example above, a form of using the four colors Bk, C, M and Y was presented; however, a form of also using special colors such as light cyan and like magenta having a low density, or using red and green is also possible. In addition, in each of the embodiments above, the case of applying the present invention to an inkjet printing apparatus that forms images by discharging ink from print heads onto a print medium was explained. However, the present invention can be applied to any kind of printing apparatus regardless of type as long as dots are formed and printed while there is relative movement between the print head and printing paper.
Moreover, an example of detecting the density using an optical sensor was given as the method for detecting shifting of the printing position adjustment patterns; however, the construction of the present invention is not limited to this. Construction is also possible in which the user visually selects an optimum pattern and acquires an adjustment value by inputting the selected pattern.
In the embodiments above, an example of the case of using inkjet printing elements as the printing elements was presented; however it is also possible to apply the present invention to elements other than inkjet printing elements as long as the printing elements can print dots.
In the embodiments above, an example of a printer that causes the print heads to scan in a main scanning direction and conveys the print medium in a sub scanning direction was given; however the present invention is not limited to this and can also be applied to a so-called line type inkjet printer.
In the above second embodiment, in case where a relative inclination between two print heads is equal to or smaller than a threshold value, top end region or bottom end region of the printing heads are selected as a partial region for printing an adjustment pattern, and in case where the relative inclination between two print heads is greater than the threshold value, center regions of the print heads are selected as the partial region for printing an adjustment pattern. However, the present invention is not limited to this configuration. For example, a configuration can be employed as below. A relative inclination of the printing element array for cyan with respect to the printing element array for black is compared with a relative inclination of the printing element array for yellow with respect to the printing element array for black. Next, in case where the relative inclination of the printing element array for cyan is smaller than the relative inclination of the printing element array for yellow, center regions of the printing element arrays for yellow and black are selected as a first partial region and top end region or bottom end region of the printing element arrays for cyan and black are selected as a second partial region. Contrary, in case where the relative inclination of the printing element array for cyan is greater than the relative inclination of the printing element array for yellow, center regions of the printing element arrays for cyan and black are selected as a first partial region and top end region or bottom end region of the printing element arrays for yellow and black are selected as a second partial region.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2011-000628, filed Jan. 5, 2011, which is hereby incorporated by reference herein in its entirety.
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