1. Field of the Invention
The present invention relates to an inkjet recording apparatus which records an image on a recording medium by discharging ink from a recording head thereof, and a recording position adjustment method therefor.
2. Description of the Related Art
Conventionally, as a technique used in an inkjet recording apparatus, there has been known the technique of correcting a deviation of a dot-recorded position (a position where an ink droplet is placed) on a recording medium. Japanese Patent Application Laid-Open No. 11-240146 discusses the technique for controlling ink discharge timing according to the position of a carriage with a recording heat loaded thereon in a scanning direction, thereby accurately correcting a recording position regardless of where the carriage is located in the scanning position even when there is a variation in the distance between the carriage and the recording medium in the scanning direction.
However, an amount of deviation of ink droplet impact position varies within the scanning range of the carriage not only in a case of deviations in the scanning direction but also in a case of deviations in the direction intersecting the scanning direction (conveyance direction). One of the causes thereof is, for example, a change in the posture of the carriage during the scanning operation.
A deviation of an impact position in the scanning direction can be corrected by adjustment of the discharge timing, and therefore it is possible to set adjustment values for respective positions within the scanning range. However, for correcting a deviation of an impact position in the conveyance direction, either data should be shifted in the conveyance direction or the nozzle use range should be changed, therefore it is desirable to use one adjustment value to keep the impact position deviation within the required accuracy range throughout the entire scanning range.
When an impact position deviation in the conveyance direction is adjusted at a recording apparatus equipped with a recording head with three or more nozzle arrays formed thereon, a specific nozzle array is set as a reference array, and an adjustment value is applied to each of other nozzles. For example, it is assumed that there is a reference nozzle array, and a nozzle array A and a nozzle array B are the other nozzle arrays. In this case, optimal adjustment of the impact position of the nozzle array A in the conveyance direction relative to the reference nozzle array may result in a further increased deviation between the impact positions of the nozzle arrays A and B. However, the deviation between the nozzle arrays A and B may have a greater influence on the image than the deviation between the reference nozzle array and the nozzle array A. In this case, the adjustment value to the deviation between the nozzle arrays A and B should be preferentially optimally set. Therefore, when adjustment values for nozzle arrays are determined at a recording apparatus equipped with three or more nozzle arrays, the adjustment values should be determined in consideration of the priority order of those nozzle arrays.
The present invention is directed to a recording apparatus and a recording position adjustment method capable of setting adjustment values for adjusting deviations of impact positions in a conveyance direction to a plurality of nozzle arrays so as to reduce a deviation amount as a whole in each nozzle array throughout a scanning range and adjust the impact positions.
According to an aspect of the present invention, an inkjet recording apparatus is configured to perform recording by driving a recording head, at which a plurality of nozzle arrays for discharging ink are arranged in a predetermined direction, to perform scanning in a scanning direction while conveying a recording medium in a direction which intersects the predetermined direction. The inkjet recording apparatus includes an acquisition unit configured to acquire a deviation amount of a recording position in the intersecting direction for each of the plurality of nozzle arrays, at a plurality positions in the predetermined direction, a determination unit configured to compare the acquired deviation amount of the recording position of each nozzle array with a threshold value to determine a nozzle array exceeding the threshold value, and a setting unit configured to preferentially set an adjustment value for adjusting the recording position of the nozzle array exceeding the threshold value.
According to the present invention, in a recording apparatus using a recording head with a plurality of redundant chips (nozzle arrays), it is possible to prevent overlapping of the regions where dots are recorded with the redundant portions of the colors, thereby reducing occurrence of density nonuniformity.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
The recording apparatus 2 further includes a carriage 4 guided and supported so that the carriage 4 can perform reciprocal scanning in a width direction (the direction indicated by the arrow A, scanning direction) of a recording medium which corresponds to a predetermined direction, and a conveyance roller 70 for conveying a recording medium such as recording paper in the direction indicated by the arrow B (conveyance direction) which intersects the predetermined direction. Further, the recording apparatus 2 includes a carriage motor (not illustrated) and a carriage belt (hereinafter referred to as “belt”) 270 for reciprocating the carriage 4 in the arrow A direction, and recording heads 1 mounted on the carriage 4. Further, the recording apparatus 2 includes a suction type ink recovery unit 9 for supplying ink and preventing an ink discharge failure which otherwise might be caused by clogging of a discharge port of the recording head 1. Further, a linear scale is disposed in the scanning direction. A relative travel distance of the carriage 4 is detected by counting output pulses of an encoder sensor (not illustrated), and ink discharge timing is controlled based on this information.
In this recording apparatus 2, the carriage 4 includes four recording heads 1 each integrally including three colors of ink so as to make twelve colors of ink in total so that the recording apparatus 2 can record data on a recording medium in full color. The recording apparatus 2 configured as mentioned above performs recording, after the conveyance roller 70 conveys the recording medium to a predetermined recording start position, by repeating the operation of scanning of the recording heads 1 in a main scanning direction by driving the carriage 4 and the operation of conveyance of a recording medium in a sub-scanning direction by the conveyance roller 70.
More specifically, the carriage 4 is moved in the arrow A direction illustrated in
Further, the carriage 4 includes a reflection type optical sensor 30 (not illustrated), which functions to detect a density of an adjustment pattern recorded on a recording medium (sheet) in order to detect a deviation of a recording position. Combining the scanning of the carriage 4 in the scanning direction and the sheet conveyance operation in the sub-scanning direction enables the optical sensor 30 to detect the density of the adjustment pattern recorded on the sheet. The reflection type optical sensor 30 may be used for detecting an end of a sheet.
In the present exemplary embodiment, it is assumed that a white light-emitting diode (LED) or 3-color LED is used as the light emitting unit 11, and a photodiode having sensitivity in a visible light region is used as the light receiving unit 12 so that registration adjustment can be performed for the heads which discharge all ink including main ink such as cyan (C), magenta (M), yellow (Y), and black (K), and special color ink. However, for adjustment of nozzle arrays of different kinds of ink in a case of detecting the relationship between their relative recording positions and the density of dots recorded in a superimposed manner, it is more preferable to use a 3-color LED that enables selection of a color having high detection sensitivity. As will be described in more detail later, for detection of the density of an image recorded on the recording medium 3, the sensor 30 does not have to detect an absolute value of the density, but only has to detect the relative density. Further, the sensor 30 may have any degree of detection resolution as long as the detection resolution is sufficient to enable detection of the relative density difference in each pattern (also referred to as “patch”) belonging to an adjustment pattern group which will be described later.
Further, a detection system including the reflection type optical sensor 30 may have any degree of stability as long as the detection system is stable enough to have no influence on the detection density difference until a completion of the detection of the adjustment pattern group. At the time of the sensitivity adjustment, for example, the optical sensor 30 is moved to an unrecorded portion of a sheet. As a sensitivity adjustment the light emission intensity of the light emitting unit 11 is adjusted, or a gain of a detection amplifier is adjusted in the light receiving unit 12, so as to realize the detection level of an upper limit value. While not essential, the sensitivity adjustment is preferable for increasing the detection accuracy by improving the signal/noise (S/N) ratio.
Desirably, the space resolution of the reflection type optical sensor 30 is set to a level that enables detection of an area smaller than a recording area of one adjustment pattern. In multipass recording that completes recording of a predetermined area by performing recording and scanning a plurality of times, when adjustment pattern groups are recorded in such a manner that two pattern groups can be adjacent to each other in the respective scanning direction and sub-scanning direction, a recording width of the sub-scanning direction is reduced according to the number of passes. Therefore, the sensor resolution is limited by the number of recording passes. The number of recording passes (recording width) may be determined based on the sensor resolution. Further, a change in the distance between a recording medium and the reflection type optical sensor 30 causes a change in the amount of light received by a phototransistor, thereby enabling detection of the distance between a recording medium and the carriage 4 (corresponding to the distance between a recording medium and the recording head).
Ahead driver 440 is a driver for driving a discharge heater in the recording head 1 according to, for example, print data. The head driver 440 includes a shift register for arranging print data so as to correspond to the position of the discharge heater, and a latch circuit for performing latching at appropriate timing. The head driver 440 further includes, for example, a logical circuit element for actuating the discharge heater in synchronization with a driving timing signal, and a timing setting unit for appropriately setting driving timing (discharge timing) for adjustment of a dot recording position.
Hereinafter, the recording position adjustment method according to the present exemplary embodiment will be described in detail.
Next, the method of acquiring impact position deviations of the colors by generating test patterns will be described. If adjustment values are acquired by generating test patterns throughout the entire region in the scanning direction with respect to each of all combinations of the eleven colors, this will require a large number of recoding media and a great deal of time. Therefore, instead of that, the present exemplary embodiment employs the following method which enables easier acquisition of the adjustment values.
The adjustment pattern 13 for acquiring an deviation amount in the conveyance direction may be embodied by any of conventionally known various patterns. For example, a deviation amount between two target colors can be acquired by drawing lines with different deviation amounts between the colors in a plurality of stages and obtaining the deviation amount based on the deviation amount when two lines are the closest to forming a straight line. Alternatively, a deviation amount between two target colors can be acquired by forming a plurality of blocks with different deviation amounts between the colors so that the catoptrics density is changed, and obtaining the deviation amount based on the change in the catoptrics density.
For example, there is six colors PM, M, MBk, Y, C, and PC at the left recording heads, and linear approximation can be substantially established among the deviation amounts of these six colors (refer to the lower graph of
Next, in step S3-2, threshold values corresponding to the respective combinations of the colors are applied to the generated impact position deviation profile. In the present exemplary embodiment, 1.5 is set as the threshold value for a combination of two colors related to a light color or yellow, and 1.0 is set as the threshold value for a combination of the other colors. These threshold values are values set to determine whether an impact position deviation between colors is within an acceptable range. A small value (1.0) is set as the threshold value for a combination of frequently superimposed colors or a combination of conspicuous colors, thereby narrowing the acceptable range for the deviation amount therebetween to maintain high-quality image recording. The combination of frequently superimposed colors may be not only a combination of light colors but also a combination of dark colors.
Next, in step S3-3, each of the all combinations of the eleven colors is determined whether it has a deviation amount equal to or smaller than the threshold value therefor, or exceeding the threshold value therefor. As mentioned above, in the present exemplary embodiment, eleven combinations all exceed the threshold value therefor. If there is no combination that exceeds the threshold value, since the impact positions do not need to be adjusted, the controller 400 does not perform position adjustment in step S3-5. On the other hand, if a specific combination exceeds the threshold value therefor (YES in step S3-3), the adjustment priority order of this combination is changed, so that the impact position deviations can be optimally adjusted for all of the eleven colors.
Next, in step S3-4, a higher priority order is assigned to the combination exceeding the threshold value so that the adjustment value for this combination is preferentially determined. In the present exemplary embodiment, PBk is set as the reference color, and therefore, first, the adjustment values are determined for the combinations of PBk-cyan C, magenta M, and photo cyan PC which are the combinations exceeding the respective threshold values, out of the combinations including the reference color (PBk). Next, adjustment values are determined for the colors exceeding the threshold value based on the adjustment colors cyan C and magenta M. This is because priority is given to the basic colors (C, M, Y, and K) of color overprinting. The adjustment value for the color K out of these basic colors is most preferentially determined. The adjustment value for the color Y is less preferentially determined than the colors C and M due to its low visibility. Therefore, in the present exemplary embodiment, next, the adjustment value for the color Gy is determined based on the relationship of Gy to C and M, and then the adjustment value for B is determined based on the relationship of B to C and M. Further, the adjustment value for G is determined based on the relationship of G to C and M, and G, and then the adjustment value for R is determined based on the relationship of R to C and M.
Now, the adjustment value determination method will be described in further detail.
On the other hand, in step S3-5, the impact positions are adjusted in a set normal order for the combinations that do not exceed the threshold value. In the present exemplary embodiment, this corresponds to determination of the adjustment values between the remaining colors and the reference color (PBk). In the present exemplary embodiment, the impact position adjustments are performed according to the following order.
(1) Adjust PBk-C, and determine the impact adjustment value of C.
(2) Adjust PBk-M, and determine the impact adjustment value of M.
(3) Adjust PBk-PC, and determine the impact adjustment value of PC.
(4) Adjust M-C-Gy, and determine the impact adjustment value of Gy.
(5) Adjust M-C-B, and determine the impact adjustment value of B.
(6) Adjust M-C-R, and determine the impact adjustment value of R.
(7) Adjust M-C-G, and determine the impact adjustment value of G.
(8) Adjust the remaining colors (PM, PGy, and Y) based on PBk (reference color).
A concrete description will be given of the method for determining the impact position adjustment values for the plurality of colors that has been described above with reference to
First, in step S18-1, the controller 400 of the recording apparatus 2 sets adjustment target colors. In the present exemplary embodiment, the controller 400 sets A, B, and C as the adjustment target colors. If this flow process is applied to the example illustrated in
Next, in step S18-2, the controller 400 acquires an average deviation value of the adjustment target color in the carriage direction (CR direction). Then, the controller 400 determines the adjustment value based on the average deviation value, and corrects the position.
More specifically, the controller 400 calculates an average value of the deviation amounts in the entire region of the CR direction for each color. This can be performed by calculating an average of the deviation amounts measured at a plurality of positions in the CR direction as indicated in
Next, in step S18-3, the controller 400 calculates the deviation amounts of the adjustment target colors A, B, and C in an initial state, i.e., when only the adjustment value based on the reference color is applied thereto. More specifically, the controller 400 uses a variable N, and sets 1 as N, A as An, B as Bn, and C as Cn (N=1, An=A, Bn=B, and Cn=C). An, Bn, and Cn represent the adjustment values of the respective colors. A is the impact deviation amount of the reference color for each carriage position, B is the impact deviation amount of the adjustment color 1 for each carriage position, and C is the impact deviation amount of the adjustment color 2 for each carriage position. In other words, this is the state that the adjustment value calculated only in consideration of a single deviation amount of the color is set to each color.
Next, in step S18-4, the controller 400 calculates the largest deviation amount for each CR position with respect to An, Bn, and Cn. In the example illustrated in
Next, in step S18-5, the controller 400 calculates the largest deviation amount (Rn) throughout the entire CR region. In the example illustrated in
Next, in step S18-6, it is determined whether N is equal to 5 (N=5). If N is not equal to 5 (NO in step S18-6), the processing proceeds to step S18-7 in which N is incremented by 1, and then the processing returns to step S18-4. This is because, in this process flow, cases N=1 to 5 are prepared, and the largest deviation amount is calculated for each of the cases. The cases N=1 to 5 are prepared as follows. In the case of N=1, An=A, Bn=B, and Cn=C. In the case of N=2, An=A, Bn=B+1, and Cn=C. In the case of N=3, An=A, Bn=B, and Cn=C+1. In the case of N=4, An=A, Bn=B−1, and Cn=C. In the case of N=5, An=A, Bn=B, and Cn=C−1.
The number “1”, which is added to or subtracted from B or C in the above equations, corresponds to the adjustment resolution of the impact position adjustment (1200 dpi: 21 μm).
In other words, according to this process flow, in the case of N=1, the controller 400 calculates the largest impact position deviation amount among the adjustment target colors in the initial state (the adjustment value is determined only in consideration of the deviation of each color). Further, in the case of N=2, the controller 400 calculates the largest impact position deviation amount in such a state that the adjustment value of +1 is applied to the color B (adjustment color 1) out of the adjustment target colors 3. Similarly, the controller 400 can calculate the largest deviation amount in such a state that the adjustment value of +1 or −1 is applied to B (adjustment color 1) or C (adjustment color 2). In this way, in step S18-4, the controller 400 calculates the largest deviation amount for each CR position with respect to An, Bn, and Cn in the all cases except for the case of N=1 (step S18-5).
In step S18-9, the controller 400 sets the adjustment values An, Bn, and Cn that provide the smallest Rn. In this example, the largest deviation amount Rn is 35 μm when N is 5, and this is smaller than those when N is 1 or the other numbers. Therefore, in this case, the controller 400 selects the adjustment values An=A, Bn=B, and Cn=C−1 that realize the smallest impact deviation amount to the all of the combinations among the three adjustment target colors throughout the entire carriage scanning region.
In this way, in terms of the impact position deviation amount among a plurality of colors and for each carriage position, the optimum impact adjustment value is not necessarily the value which minimizes the deviation amount of each color relative to the reference color. In other words, adjustment of a plurality of colors based on the reference color may deteriorate the impact position deviation among the plurality of colors. When the adjustment values are determined according to the present exemplary embodiment, all of the adjustment target colors (three colors in the present exemplary embodiment) can be adjusted to reduce the deviation amount.
As mentioned above, in the present exemplary embodiment, the deviation amounts of the respective combinations of the plurality of nozzle arrays are compared to the threshold value. Then, the adjustment value for the combination exceeding the threshold value is preferentially determined, whereby the total of the deviation amounts among the plurality of nozzle arrays can be reduced. Further, as illustrated in
The adjustment values acquired in the above-mentioned manner are basically determined based on the impact deviation amounts throughout the entire carriage region and the combinations of the ink colors. However, if there is a change in the recording range where the carriage is driven to perform scanning for recording (for example, the size of a recording medium is changed), the adjustment values may be changed according to the print region.
On the other hand,
Further, in the above description, the deviation amount in the conveyance direction is determined with use of the pattern. However, since the deviation in the conveyance direction is mainly caused by a change in the posture of the carriage, the deviation amount of the recording position may be estimated by directly detecting a change in the carriage rail.
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 modifications, equivalent structures, and functions.
Number | Date | Country | Kind |
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2010-019447 | Jan 2010 | JP | national |
This application is a Divisional of U.S. patent application Ser. No. 13/014,666 filed on Jan. 26, 2011 which claims the benefit of Japanese Patent Application No. 2010-019447 filed Jan. 29, 2010, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | |
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Parent | 13014666 | Jan 2011 | US |
Child | 14103075 | US |