JP4270799B2 - Image recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to detection of an angular deviation of a recording head in an image recording apparatus.
[0002]
[Prior art]
2. Related Art An ink jet type image recording apparatus that forms an image by ejecting ink onto a recording medium is known. An ink jet type image recording apparatus includes, for example, a recording head having a large number of recording elements (ink jet nozzles) arranged in a line. This type of image recording apparatus includes a single recording head for monochrome printing and a plurality of recording heads for color printing. An image recording apparatus having a recording head in which a large number of recording elements are arranged in a line is conventionally known. In such an image recording apparatus, one or more recording heads are attached to a carriage. The carriage can reciprocate (scan) the recording head. The reciprocating direction of the recording head is the main scanning axis. The recording head ejects ink onto the recording medium in accordance with scanning along the main scanning axis. By this ejection, an image along the main scanning axis composed of ink dots is recorded (formed) on the recording medium.
[0003]
The recording medium is intermittently conveyed in a direction (sub-scanning axis) orthogonal to the driving direction (main scanning axis) of the recording head. By this conveyance, the recording head and the recording medium move relatively. The image recording along the main scanning axis is performed while the recording medium is stopped. When the recording of the image along the main scanning axis is completed, the recording medium is conveyed by a predetermined amount in the sub scanning direction and stopped. By repeating these conveyance and recording, the image recording apparatus records, that is, prints an image over the entire recording medium.
[0004]
Further, the image recording apparatus performs printing by various printing methods. This printing method includes, for example, one-pass unidirectional printing. In this one-pass one-way printing, the recording head is driven only in one of the forward path and the backward path, and this one drive is performed once. During this driving, the recording head forms an image along the main scanning axis. When the image is formed, the recording medium is conveyed to form the next image.
[0005]
It should be noted that each of the recording heads or the plurality of recording heads needs to be appropriately adjusted in attachment angle with respect to the carriage. For example, the recording head is attached to the carriage so that the array of recording elements (nozzle array) is arranged along the sub-scanning axis. In this case, the nozzle row extends in a direction along the sub-scanning axis when the attachment angle is properly adjusted.
[0006]
The case where the image recording apparatus in which the mounting angle of the recording head is appropriately adjusted records an image by one-pass one-way printing will be described below with reference to FIG. FIG. 34 is a schematic diagram showing two ink dot rows printed so that the image recording apparatus is arranged along the sub-scanning direction at a position along an arbitrary main scanning axis.
[0007]
Since this image recording apparatus performs recording by one-pass one-way printing, two ink dot rows are recorded by two scans. In the following description, the first scan is the first scan, and the subsequent scan is the second scan. Note that an arrow md shown in FIG. 34 indicates the driving direction of the recording head, and an arrow td indicates the conveyance direction of the recording medium. The image recording apparatus records the ink dot row 1010 in the first scan. Subsequently, the image recording apparatus conveys the recording medium by the nozzle row length dn which is the length of the nozzle row. After the conveyance, the image recording apparatus records the ink dot row 1020 in the second scan. Since the mounting angle of the recording head is adjusted, the ink dot row 1010 and the ink dot row 1020 are linearly arranged along the sub-scanning direction. That is, the recorded ink dot row is recorded so as to substantially coincide with the arrangement direction of the nozzle row.
[0008]
In the image recording apparatus, when the attachment angle is not properly adjusted, the recording head 1030 is inclined with respect to the sub-scanning axis θ as shown in FIG. 35, for example. _ha It will be inclined at. In the present specification, the fact that the recording head is inclined with respect to a predetermined mounting angle is referred to as “angle shift”. Accordingly, the recording head 1030 has an inclination angle θ with respect to a predetermined mounting angle. _ha There is an angle shift. For this reason, the nozzle row 1040 is similarly inclined with respect to the sub-scanning axis.
[0009]
In this state, when the image recording apparatus performs image recording in the same manner as described above, the ink dot row 1010 and the ink dot row 1020 are inclined with respect to the inclination angle θ of the nozzle row 1040 as shown in FIG. _ha Are printed at an inclination similar to the above. In FIG. 36, the ink dot row 1020 has a dot row length that is the length along its own longitudinal axis. This dot row length is substantially the same as the nozzle row length dn.
[0010]
When the ink dot row is inclined as described above, the positions of the upper ink dot 1011 and the lower ink dot 1012 in the ink dot row 1010 in FIG. 36 are shifted along the main scanning axis. The ink dots at the lower end of the ink dot row 1020 are misaligned along the main scanning axis, like the ink dots 1012. For this reason, the ink dots 1011 and the ink dots 1022 are separated along the main scanning axis. That is, when the recording head 1030 has an angle shift, the ink dot row 1010 and the ink dot row 1020 are not aligned linearly along the sub-scanning direction. As described above, a recording head having an angular deviation cannot print a straight line along the sub-scanning axis. In addition, a recording head with an angular deviation causes unevenness when colors are superimposed in color printing. Such angular deviation causes deterioration of the image quality of the recorded image.
[0011]
For this reason, the recording head needs to adjust the attachment angle to the carriage appropriately. Conventionally, the adjustment of the angle deviation is performed as follows, for example.
[0012]
In order to adjust the angle deviation, first, the angle deviation of the recording head is obtained. The inclination angle of the nozzle row and the ink dot row is the inclination angle θ of the recording head. _ha And substantially the same. For this reason, the inclination angle θ of the ink dot row _da To obtain the inclination angle θ of the nozzle row 1040. _ha Ask for. For example, when the recording head is intended to be mounted with the nozzle row along the sub-scanning axis, the inclination angle θ of the ink dot row _da Is obtained by the following equation (10) from the dot row length and the distance th. In the following equation (10), since the dot row length dn is the same as the nozzle row length dn, it is replaced with the nozzle row length. The distance th is a distance between the straight line tb along the sub-scanning axis and passing through the ink dot at one end of the ink dot row and the ink dot at the other end. In addition, the inclination angle θ _da The relationship between the nozzle row length dn and the distance th is shown in FIG.
θ _da = Arcsin (th / dn) (10)
In this way, the inclination angle θ _da , The nozzle row length dn is known in advance because it is the total length of the nozzle row. The distance th is measured from the recorded ink dot row. In order to measure this distance th, first, two ink dot rows 1010 and 1020 similar to FIG. 36 are recorded as test patterns. Subsequently, the recorded ink dot rows 1010 and 1020 are read by a CCD mounted on the image recording apparatus, and the barycentric position of each ink dot is obtained from the read images of the ink dot rows 1010 and 1020. A straight line corresponding to each of the ink dot rows 1010 and 1020 is obtained based on the obtained gravity center position of each ink dot. And the distance d1 between straight lines which is the distance between these straight lines is measured.
[0013]
Thereby, the distance between the ink dot 1011 and the ink dot 1022 is obtained. The ink dot 1022 has substantially the same position along the main scanning axis as the ink dot 1012 that is an ink dot at one end of the ink dot row 1010. In general, the distance d1 between the straight lines is very small with respect to the dot row length dn. Therefore, it can be said that the ink dot 1022 is positioned so as to be substantially orthogonal to the sub-scanning direction with respect to the ink dot 1011 that is the ink dot at the other end of the ink dot row 1010.
[0014]
Accordingly, the distance d1 between the straight lines can be substantially regarded as the distance th. Accordingly, the recording head 1030 has an inclination substantially equal to the inclination angle θhd using the distance d1 between the straight lines, the nozzle row length dn that is the dot row length of the ink dot row 1010, and the above equation (10). Angle θ _ha Is required.
The recording head 1030 has an inclination angle θ _ha The angle is adjusted based on the above.
[0015]
[Problems to be solved by the invention]
As described above, a test pattern is recorded when the distance th is obtained. Since this test pattern is composed of dot rows, it was formed when the test pattern was read because dirt or dust in the vicinity of the dot row was mistakenly recognized as a dot, and vice versa. Small dots may be recognized as dust. In addition, image loss may occur due to nozzle omission or landing position deviation. For these reasons, a straight line corresponding to the recorded dot row cannot be obtained accurately, and as a result, the inclination angle θ _ha May not be accurately determined.
[0016]
Further, in order to recognize each dot satisfactorily, it is necessary to increase the reading resolution, and it takes a lot of time to read the test pattern. In addition, since the center-of-gravity position of each dot is obtained, much time is required for the calculation process. Furthermore, in order to increase the accuracy of the obtained linear interval, it is necessary to increase the number of samples (dot rows), which increases the reading time and the calculation processing time.
[0017]
The present invention has been made in consideration of such a situation, and the main purpose of the present invention is to ensure that even if a defect such as dirt or dust on the test pattern or missing nozzles or landing position deviation occurs. Another object of the present invention is to provide an image recording apparatus capable of calculating the angle deviation amount of the recording head based on the mutual relationship. A further object of the present invention is to provide an image recording apparatus capable of calculating the angular deviation of the recording head in a short time.
[0018]
[Means for Solving the Problems]
In order to solve the above problems, an image recording apparatus of the present invention has the following configuration.
An image recording apparatus according to an aspect of the present invention includes: a recording unit that records a plurality of pairs of test patterns configured by different pattern elements for each pair of test patterns on a recording medium; A cross-correlation function between the density data is calculated based on density data of the plurality of pairs of test patterns read by the reading means for reading the density of the test pattern, and the maximum of the cross-correlation function Calculating a relative recording position deviation amount from a position having a value, and calculating an angular deviation amount of the recording means based on the recording position deviation amount.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
First, the image recording apparatus will be described with reference to FIG. As shown in FIG. 1, the image recording apparatus 100 includes a carriage 110 and a sheet holding mechanism 140 that face each other with a space therebetween. A sheet 192 as a recording medium is passed between the carriage 110 and the sheet holding mechanism 140. The sheet 192 is sandwiched between a pair of conveyance rollers composed of a conveyance roller 152 and a nip roller 154 and a pair of sheet discharge rollers composed of a sheet discharge roller 162 and a nip roller 164, and is conveyed from the top to the bottom of the figure by these roller pairs.
[0020]
The sheet holding mechanism 140 includes a platen 142 in which a large number of holes are formed, and a fan 148 for pulling the internal space (platen chamber) 144 of the sheet holding mechanism 140 to a negative pressure. While being conveyed, the sheet 192 is sucked to the platen 142 by the negative pressure generated by the fan 148.
[0021]
The carriage 110 includes a recording unit 120 that is a recording unit for recording an image on a sheet 192 and a CCD unit 130 that is a reading unit for reading an image recorded on the sheet 192. The carriage 110 is supported by a pair of guides 112 so as to be movable along a main scanning axis orthogonal to the paper surface.
[0022]
The image recording apparatus 100 further includes a carriage control unit 170 that controls the carriage 110. The carriage control unit 170 controls the recording unit so that a carriage drive mechanism 172 that is a scanning unit for moving the carriage 110 along the main scanning axis and a test image including a pair of test patterns are recorded on the sheet 192. A relative recording position deviation amount of the pair of test patterns is calculated based on the correlation between the recording control unit 174 serving as a control unit and the density data of the pair of test patterns, and recording is performed based on the recording position deviation amount. And an angle deviation calculation unit 176 which is a calculation unit for calculating the angle deviation amount of the head.
[0023]
The carriage 110 can be moved along the main scanning axis by the carriage driving mechanism 172. While the carriage 110 is moved along the main scanning axis, the recording unit 120 records a test image including a pair of test patterns on the paper 192.
[0024]
The pair of test patterns may be composed of a pair of test patterns or a plurality of pairs of test patterns. That is, each of the pair of test patterns may be composed of a single test pattern or a plurality of test patterns.
[0025]
The recording unit 120 includes one recording head in an image recording apparatus for monochrome printing, and includes a plurality of recording heads in an image recording apparatus for color printing. For example, in an inkjet printer that handles six colors of black, cyan, magenta, light cyan, light magenta, and yellow, the recording unit 120 includes six recording heads for each color. The number of recording heads included in the recording unit 120 is arbitrarily determined according to the image quality required for the image recording apparatus.
[0026]
One recording head included in the recording unit 120 is shown in FIG. As shown in FIG. 2, the recording head 122 is composed of a single unit 210 having a large number of recording elements (inkjet nozzles) arranged in a line along the sub-scanning axis at a constant pitch. In other words, the recording head 122 is composed of a single unit 210 having one nozzle row 212.
[0027]
In an image recording apparatus using such a recording head 122, ink dots are usually formed in a region traversed by the nozzle row 212 of the recording head 122 by movement of the carriage 110 along the main scanning axis.
[0028]
For example, in order to record a single straight line extending along the sub-scanning axis, ink dots are formed by ejecting ink from all the ink jet nozzles at a predetermined position on the forward path, and the paper 192 is pitched. The ink is moved along the sub-scanning axis by a distance equivalent to half of the distance, and ink is ejected from all the ink-jet nozzles at the same position in the main scanning direction as the ink dots formed in the forward path in the return path. As a result, a large number of ink dot rows, that is, straight lines, are arranged along the sub-scanning axis without any gap.
[0029]
In such an image recording apparatus provided with one or a plurality of recording heads 122, each recording head 122 or each of the plurality of recording heads 122 needs to adjust the angle of the recording head appropriately. For this reason, one of the pair of test patterns is recorded by the first scan, and the other of the pair of test patterns is recorded by the second scan.
[0030]
Next, an angle deviation detection method for adjusting the angle of the recording head will be described. Hereinafter, one black recording head will be described as a representative. In the following description, it is assumed that the black recording head has 496 inkjet nozzles, and the inkjet nozzles are arranged at a nozzle pitch of 360 dpi. In the present embodiment, the nozzle row 212 is arranged along the sub-scanning axis. For this reason, in this angular deviation detection method, the angular deviation of the recording head with respect to the sub-scanning axis is detected. The angle deviation detection can detect an angle deviation with respect to an arbitrary axis other than the angle deviation with respect to the sub-scanning axis.
[0031]
In the angle deviation detection method, test image recording, test pattern reading, and angle deviation amount calculation are performed.
[0032]
・ Test image recording (printing)
For example, as shown in FIG. 3, the test image includes a pair of test patterns 312 and 314 and a black pattern 316 for black level adjustment described later. The test pattern is recorded by one-pass one-way printing. In FIG. 3, the carriage driving direction md and the paper transport direction td are shown, and the drive direction md and the paper transport direction td are orthogonal to each other. The driving direction md is along the main scanning axis, and the paper transport direction td is along the sub-scanning axis.
[0033]
The recording of the test pattern is schematically shown in FIG. In this test pattern recording, as shown in FIG. 4, a black pattern is formed using the lower half of the nozzle row while moving the recording head 802 (1st) in the first scan in the driving direction md (right side in the figure). Record 316 and record the test pattern 312 using the upper half of the nozzle row. The total length in the longitudinal direction of the nozzle row is the nozzle row length dn.
[0034]
After the recording of the black pattern 316 and the test pattern 312, the paper is conveyed by a distance dn / 2 corresponding to half of the nozzle row length dn. After this conveyance, the test pattern 314 is recorded by the recording head 802 (2nd) using the lower half of the nozzle row in the second scan.
[0035]
The test patterns 312 and 314 are both composed of a single test pattern. A preferred pair of test patterns 312, 314 has a high correlation. Therefore, the test pattern is composed of the same pattern element, for example, a rectangular pattern element having a width of 5 dots. The test patterns 312, 314 are recorded with a shift of 64 dots, for example, along the main scanning axis so as not to overlap each other. The shift amount of the test pattern is not limited to 64 dots, and is arbitrarily set according to the width of the test pattern to be recorded.
Note that the test patterns 312 and 314 do not actually extend along the sub-scanning axis as shown in FIG. 3 due to the inclination of the recording head, but are inclined as shown in FIG.
[0036]
・ Reading test patterns
In the following description, it is assumed that the CCD unit 130 has a reading resolution of 1440 dpi.
[0037]
As shown in FIG. 6, the paper 192 is transported upstream in the paper transport direction. By this conveyance, a test image including the test patterns 312 and 314 and the black pattern 316 is arranged above the CCD unit 130 in the carriage 110. Subsequently, the carriage 110 is moved to place the CCD unit 130 below the black pattern 316.
[0038]
At this position (position shown in FIG. 6), the focus of the CCD unit 130 is adjusted. After the focus adjustment is completed, the white level of the CCD unit 130 is adjusted using the white background portion of the paper at that position. This brightness adjustment is performed by a known method.
[0039]
After the white level adjustment is completed, the sheet 192 is conveyed downstream in the sheet conveyance direction until the CCD unit 130 detects the black pattern 316 while the position of the CCD unit 130 is fixed. As the sheet 192 is conveyed, the imaging area of the CCD unit 130 changes from the white background of the sheet 192 to the black background of the black pattern 316, and the output signal of the CCD unit 130 also changes accordingly. A printer control unit (not shown) recognizes that the CCD unit 130 is facing the black pattern 316 as shown in FIG. The conveyance of 192 is stopped.
[0040]
The black level of the CCD unit 130 is adjusted at a position where the CCD unit 130 faces the black pattern 316. This brightness adjustment is performed by a known method.
After the black level adjustment is completed, in order to read the test pattern, the paper 192 is further transported upstream in the paper transport direction, and the CCD unit 130 is disposed immediately before the lower ends of the test patterns 312 and 314.
[0041]
Thereafter, the paper 192 is transported by a minute transport amount, for example, by a transport amount when the drive pulse of the transport motor is set to 20 pulses (ideally, a distance corresponding to one dot line). The CCD unit 130 reads the test patterns 312 and 314 (more precisely, the brightness of the optical image) for each minute conveyance. Data read by the CCD unit 130 is stored in the memory for each minute conveyance. Until the CCD unit 130 finishes reading the test pattern, the series of operations of paper conveyance, image reading, and data storage are continued.
[0042]
・ Calculation of angular deviation
Here, the angle deviation amount θ of the recording head 122 of the present embodiment. _ha The principle of calculation of will be described. As described above with reference to FIG. 4, the test pattern 312 is recorded using the upper half of the nozzle row in the first scan. After the sheet is transported a distance corresponding to half of the nozzle row length dn, the test pattern 314 is recorded using the lower half of the nozzle row in the second scan.
[0043]
When the recording head 122 has no angular deviation, the test patterns 312 and 314 are parallel to the sub-scanning axis as shown in FIG. The test patterns 312, 314 are separated from each other by 64 dots along the main scanning axis so as not to overlap. However, when the recording head 122 has an angular deviation, the test patterns 312 and 314 are inclined with respect to the sub-scanning axis as shown in FIG. FIG. 5 shows, as an example, test patterns 312 and 314 recorded by a recording head in which an angular deviation is caused clockwise about the center of gravity of the nozzle row. In FIG. 8, in order to compare the test patterns 312 and 314 with and without an angle shift, the test patterns 312 and 314 in FIG. FIG. In FIG. 8, a solid line 822 indicates a recording area when an image is also recorded in the upper half nozzle row together with the test pattern 312 when the angular deviation is present. A test pattern 312 is included in this recording area. A solid line 824 indicates a recording area when an image is also recorded in the lower half nozzle row together with the test pattern 314 in the case where the angular deviation is present. A test pattern 314 is included in this recording area. A broken line 832 indicates a recording area when an image is also recorded in the upper half nozzle row together with the test pattern 312 when there is no angular deviation. A broken line 834 indicates a recording area when an image is also recorded in the lower half nozzle row together with the test pattern 314 when there is no angular deviation. For this reason, these recording areas have the same longitudinal dimension as the nozzle row length dn.
[0044]
As shown in FIG. 8, when there is no angular deviation, the recording area indicated by the broken lines 832 and 834 has the central portion and the end portion along the longitudinal direction located at the same position along the main scanning axis. Yes. From this, it can be seen that the lower end of the test pattern 312 shown in FIG. 3 and the lower end of the test pattern 314 can maintain 64 dots, which is a predetermined separation distance.
[0045]
However, when there is an angle shift, the recording areas indicated by the solid lines 822 and 824 are located at different positions along the main scanning axis between the central portion and the end portion along the longitudinal direction. This angular deviation occurs because the recording head rotates clockwise around the center of gravity of the nozzle row. For this reason, the central portion of the recording area indicated by the solid lines 822 and 824 is substantially the same in position along the main scanning axis as the central portion of the storage area when there is no angular deviation. However, the end portions of the recording area indicated by the solid lines 822 and 824 are substantially displaced along the main scanning axis with respect to the end position of the storage area when there is no angular deviation. That is, the recording position deviation amount γ at the end of the recording area indicated by the solid lines 822 and 824 with respect to the end of the storage area when there is no angular deviation. _tm Is obtained by an increase / decrease with respect to the predetermined separation distance of 64 dots. Specifically, this recording position deviation amount γ _tm Is obtained by increasing or decreasing the distance between the central portion of the recording area indicated by the solid line 822 and the end portion of the recording area indicated by the solid line 824 with respect to the predetermined separation distance of 64 dots.
[0046]
When the angular deviation is counterclockwise, the interval between the central portion of the recording area indicated by the solid line 822 and the lower end portion of the recording area indicated by the solid line 824 is wide. Conversely, when the angular deviation is clockwise, the interval between the central portion of the recording area indicated by the solid line 822 and the lower end portion of the recording area indicated by the solid line 824 becomes narrow.
[0047]
In the present embodiment, the central portion of the recording area indicated by the solid line 822 is the lower end portion of the test pattern 312. The lower end portion of the recording area indicated by the solid line 824 is the lower end portion of the test pattern 314. Therefore, a value obtained by subtracting 64 dots, which is the predetermined separation distance, from the separation distance along the main scanning axis between the test pattern 312 and the test pattern 314 is the recording position deviation amount γ. _tm It becomes. That is, the relative positional deviation amount along the main scanning axis of the pair of test patterns is the recording positional deviation amount γ. _tm It is. A method of calculating the separation distance along the main scanning axis between the test pattern 312 and the test pattern 314 will be described in detail later.
[0048]
Recording position deviation amount γ _tm Is the distance along the main scanning axis from the center to the end of the recording area, as described above. The distance from the center of the recording area to the end is dn / 2 because it is half the nozzle row length dn. The inclination angle of the recording area is the inclination angle (angle deviation amount θ) due to the angle deviation of the recording head. _ha ). For this reason, the amount of angular deviation _ha Can be expressed by the following equation (9).
θ _ha = arcsin (γ _tm / (Dn / 2)) (9)
A description will be given of the calculation of the relative recording position deviation amount along the main scanning axis of the pair of test patterns 312, 314 when calculating the recording position deviation amount of the pair of test patterns. In this embodiment, the amount of deviation is calculated using a cross-correlation function.
[0049]
Two signals r ₁ (X), r ₂ For (x), these cross-correlation functions Φ12 (τ) are expressed by the following equation (1).
Φ12 (τ) = ∫r ₁ (X) r ₂ (X 1 τ) dx (1)
Here, τ indicates the distance between the two signals. Φ12 (τ) is the signal r ₁ (X) and signal r ₂ The maximum value is taken when (x) matches.
[0050]
In the actual processing, as shown in FIG. 9, the optical images 312i and 314i of the test patterns 312 and 314 read by the CCD unit 130 are used as the optical image 312i and the second optical image 312i of the test pattern 312 recorded by the first scanning. And the optical image 314i of the test pattern 314 recorded by the scanning of the above. Since the resolution at the time of recording is 360 dpi and the CCD resolution is 1440 dpi, the optical image division width is expressed by the following formula when the shift amount between the test pattern 312 and the test pattern 314 at the time of test pattern recording is 64 dots. It becomes like (2).
Optical image division width = 64 dots × (1440 dpi ÷ 360 dpi) (2)
Next, the data of the respective optical images 312i and 314i are summed in the sub-scanning direction (the reading direction of the CCD unit 130), and the added density data (FIG. 10) of the optical image 312i and the added density data of the optical image 314i ( FIG. 11) is obtained.
[0051]
Subsequently, the addition density data in the sub-scanning direction of the optical image 312i is expressed as r. ₁ (X) r represents the addition data in the sub-scanning direction of the optical image 314i. ₂ A cross-correlation function is obtained as (x), and a position where the cross-correlation function shows a maximum value is calculated.
[0052]
Specifically, the cross correlation of the test pattern is examined as follows using the cross correlation function. FIG. 12 shows the respective added density data 712 and 714 of the pair of optical images 312i and 314i that are targets of the recording position deviation amount to be obtained, and their relative positional relationships. The cross-correlation function Φ between the two added density data 712 and the added density data 714 ₁₂ FIG. 13 shows (τ) calculated and shown.
[0053]
In FIG. 13, d1 giving the maximum value of the cross-correlation function indicates the separation distance between the optical images 312i and 314i. That is, the position value calculated in this way is the recording position deviation amount γ of the optical images 312i and 314i of the pair of test patterns 312 and 314. _tp1440 Represents.
[0054]
The recording position deviation amount γ thus calculated _tp1440 Is for the optical images 312i and 314i read at a resolution of 1440 dpi, and therefore, the recording position shift amount γ of the actual test patterns 312 and 314 recorded at a resolution of 360 dpi. _tp360 Is represented by the following equation (3).
γ _tp360 = Γ _tp1440 ÷ (1440 dpi ÷ 360 dpi) (3)
Recording position deviation γ _tp360 Includes a shift amount given in order to avoid mutual overlap when the test patterns 312 and 314 are recorded. Therefore, the recording position deviation amount γ to be obtained _tm Is the previously obtained recording position deviation amount γ _tp360 The value obtained by subtracting 64 dots for recording at the time of recording. That is, the recording position deviation amount γ to be obtained _tm Is represented by the following equation (4).
γ _tm = Γ _tp360 -64 (4)
In this embodiment, since the relative recording position deviation amount of the pair of test patterns recorded for adjusting the ink ejection timing is obtained using the cross-correlation function of the density data of the pair of test patterns, the recording is performed. The amount of displacement can be calculated in a short time and with high accuracy.
[0055]
(Second Embodiment)
The image recording apparatus according to the second embodiment will be described below. This embodiment is different from the first embodiment only in the shape and number of test patterns, and the apparatus configuration and the like are the same as those in the first embodiment.
[0056]
As described above, the pair of test patterns is not limited to a pair of test patterns. The pair of test patterns may be composed of a plurality of pairs of test patterns.
[0057]
Specifically, in this embodiment, any one of (1) increasing the number of test patterns, (2) using a plurality of test patterns having different widths, and (3) adding a test pattern in the sub-scanning direction A test pattern using is used.
[0058]
(1) Increase the number of test patterns.
The test pattern of the method (1) includes a pair of test patterns 332 and 334, another pair of test patterns 336 and 338, and another pair of test patterns 340 and 342 as shown in FIG. Contains. Test patterns 332, 336, and 340 included in one of the pair of test patterns are recorded by, for example, a first scan, and test patterns 334, 338, and 342 included in the other of the pair of test patterns are recorded by a second scan. The
[0059]
The test patterns 332, 334, 336, 338, 340, and 342 are recorded with a shift of, for example, 64 dots along the main scanning axis so as not to overlap each other. In other words, the test patterns 332, 334, 336, 338, 340, 342 are arranged at a pitch of 64 dots along the main scanning axis.
[0060]
The test patterns 332, 334, 336, 338, 340, and 342 are all composed of the same pattern element, for example, a rectangular pattern element having a width of 5 dots. The test patterns 332, 334, 336, 338, 340, 342 may be recorded so that all of them fall within the reading width of the CCD unit 130.
[0061]
The width of the rectangular pattern element of the test pattern is not limited to 5 dots. Also, the number of test patterns is not limited to six. Further, the shift amount of the test pattern is not limited to 64 dots. The width of the rectangular pattern element, the number of test patterns 6 and the amount of test pattern shift are arbitrary under the conditions that the test patterns do not overlap each other, preferably under the condition that all the test patterns fit within the reading width of the CCD unit 130. May be changed to
[0062]
As shown in FIG. 16, the data read by the CCD unit 130 includes optical images 332i, 336i, and 340i of the test patterns 332, 336, and 340 recorded on the forward path constituting one of the pair of test patterns. It is divided into optical images 334i, 338i, and 342i of test patterns 334, 338, and 342 recorded on the return path constituting the other of the pair of test patterns.
[0063]
The recording position deviation amount of a pair of test patterns is calculated, for example, by using the cross-correlation function for each of a plurality of pairs of test patterns, using the cross-correlation function. Then, the calculated plurality of recording position deviation amounts are averaged, and the angle deviation amount is obtained based on the average value.
[0064]
Alternatively, the recording position shift amount of the pair of test patterns is obtained by using the cross-correlation function by the above-described method for the test pattern group recorded in the first scan and the test pattern group recorded in the second scan. May be required.
According to this embodiment, since the number of samples is large, it is effective for improving the accuracy of the required recording position deviation amount.
[0065]
(2) A plurality of test patterns having different widths are used.
The plurality of test patterns need not all be composed of the same pattern element. The plurality of test patterns may be composed of different pattern elements for each pair of test patterns.
[0066]
In the method (2), as shown in FIG. 19, the pair of test patterns is a pair of test patterns 362 and 364 composed of rectangular pattern elements having a width of 5 dots and a rectangle having a width of 10 dots. It includes another pair of test patterns 366 and 368 composed of pattern elements, and yet another pair of test patterns 370 and 372 composed of rectangular pattern elements having a width of 4 dots. These six test patterns 362, 364, 366, 368, 370, 372 are arranged at a pitch of 64 dots along the main scanning axis.
[0067]
This method has the following advantages compared to the test pattern of the method (1).
[0068]
In the test pattern of the method (1), for example, as shown in FIG. 16, one test pattern 342 out of six test patterns 332, 334, 336, 338, 340, 342 is lost. think of. In this case, as shown in FIG. 17, the addition density data 332n, 334n, 336n, 338n, and 340n of the test patterns 332, 334, 336, 338, and 340n are obtained, but the addition density data 342n of the missing test pattern 342 is obtained. (Indicated by the dashed line) is not obtained. In FIG. 17, the addition density data 332n, 336n, and 340n corresponding to the test patterns 332, 336, and 340 recorded in the first scan correspond to the test patterns 334 and 338 recorded in the second scan. The added density data 334n and 338n to be displayed are shown on the lower side.
[0069]
FIG. 19 shows a cross-correlation function obtained for the added density data shown in FIG. As shown in FIG. 18, this cross-correlation function has a pair of peaks 352 and 354 showing the same maximum value. In FIG. 17, the added density data 332n and 336n are obtained by shifting the lower added density data 334n and 338n by 64 dots to the left along the main scanning axis with respect to the upper added density data 332n, 336n and 340n. And the addition density data 334n and 338n and the addition density data 334n and 338n are added by shifting 256 dots to the right along the main scanning axis (64 dots (see FIG. 18) as the resolution at the time of test pattern recording). This is because the density data 336n and 340n and the added density data 334n and 338n have the same correlation.
[0070]
As described above, in the test pattern of the method (1) shown in FIG. 15, when a part of the plurality of the same test patterns is lost, a pair of peaks 352 and 354 whose cross correlation functions show the same maximum value. Therefore, it is difficult to distinguish the peak representing the original recording position deviation amount.
[0071]
On the other hand, as shown in FIG. 19, the test pattern using the present method includes a pair of test patterns 362 and 364 each composed of a rectangular pattern element having a width of 5 dots, and another pair of test patterns 366. 368 is composed of a rectangular pattern element having a width of 10 dots, and another pair of test patterns 370 and 372 are both composed of a rectangular pattern having a width of 4 dots.
[0072]
Since the width of the pattern element is different for each pair of test patterns in this way, the correlation between two test patterns included in a different pair of test patterns is the correlation between the two test patterns constituting the same pair of test patterns. Compared to the lower one. Accordingly, the obtained cross-correlation function has only one peak indicating the maximum value, and the recording position deviation amount can be calculated stably and easily.
The number of test patterns and the width of the rectangular pattern are not limited to the values described above, and may be arbitrarily changed.
[0073]
(3) A test pattern is added in the sub-scanning direction.
As shown in FIG. 20, a test pattern 412 recorded in the upper half of the nozzle row in the first scan is recorded as a test pattern using this method. At the same time, test patterns 414 and 416 are recorded in the second scan. The test pattern 414 is shifted by 64 dots along the main scanning axis so as not to overlap the test pattern 412. The test pattern 416 is recorded at the same position along the main scanning axis as the test pattern 412.
[0074]
Compared with the methods (1) and (2), the method (3) has the following advantages. In all the test patterns using the methods (1) to (3), the paper is transported between the first scan and the second scan. If skew occurs in the paper transport direction, the test pattern recording position is shifted due to the skew. When the test patterns recorded by the methods (1) and (2) are used for calculating the recording position deviation amount, the recording position deviation directly becomes a measurement error. However, with the method (3), it is possible to calculate the amount of positional deviation along the main scanning direction of the optical images 412n and 416n of the test patterns 412 and 416 shown in FIG. For this reason, the skew amount of the sheet can be obtained by using the equation (9) described in the first embodiment. For this reason, after correcting the skew amount, it is possible to calculate the positional deviation amount of the test patterns 412 and 414. For this reason, the method (3) can calculate the recording position deviation amount with high accuracy even when the paper is skewed. Therefore, the test pattern of the method (3) is useful for improving the accuracy of calculating the recording head angular deviation.
[0075]
(Third embodiment)
The image recording apparatus according to the third embodiment will be described below. This embodiment is different from the first embodiment only in the method of calculating the recording position deviation amount, and the apparatus configuration and the like are the same as those of the first embodiment. Further, the modified example of the test pattern described in the second embodiment can be applied to the present embodiment as it is.
[0076]
In the present embodiment, the relative value of the density data of the pair of test patterns is relatively changed, and the integrated value of the density data is sequentially calculated based on the correlation of the density data of each other. Then, the relative recording position deviation amount of the pair of test patterns is calculated.
Specifically, (1) the integrated value of the logical product of the binarized density data, (2) the integrated value of the logical sum of the binarized density data, and (3) the multi-value density data The integrated value of the comparison minimum value group, (4) the integrated value of the difference between the multi-value density data, (5) the integrated value of the product of the multi-value density data, and the peak value obtained The amount of recording position deviation is calculated.
[0077]
(1) Calculation based on the integrated value of the logical product of binarized density data.
First, the addition density data of a pair of test patterns that are targets of the recording position deviation amount to be obtained is obtained, and binarized to obtain a pair of density data 612 and 614 as shown in FIG. Ask for. Binarization is an operation of comparing density data with a predetermined threshold, and converting density data above the threshold to 1 and density data below the threshold to 0.
[0078]
For a pair of binarized density data 612 and 614, the logical product (AND) is taken at an arbitrary value of x, and as shown in FIG. The logical product 622 is obtained, and the area of the logical product 622 is obtained (that is, the integral value is obtained). This operation is performed for an arbitrary d1. That is, in FIG. 23, the above-described series of calculations are performed while shifting the binarized density data 612 in the + x direction. As a result, as shown in FIG. 25, a graph showing the relationship between the shift between the pair of binarized density data 612 and 614 and the integral value of the logical product 622 is obtained.
[0079]
The integrated value of the logical product of the binarized density data is a value as the overlap of the pair of binarized density data 612 and 614 increases while the binarized density data 612 is shifted in the + x direction. Increases as the overlap decreases. That is, the integrated value of the logical product of a pair of binarized density data takes the maximum value when the pair of binarized density data overlaps most.
In FIG. 25, the value of d1 giving the maximum area indicates the recording position deviation amount of the pair of test patterns corresponding to the pair of binarized density data 612 and 614. Therefore, the recording position shift amount of the pair of test patterns is obtained based on the graph of FIG.
[0080]
(2) Calculation based on the integrated value of the logical sum of binarized density data.
First, similarly to the calculation of the recording position deviation amount based on the logical product described above, the addition density data of a pair of test patterns is obtained and binarized, and as shown in FIG. The obtained density data 612 and 614 are obtained.
[0081]
For a pair of binarized density data 612 and 614, the logical sum (OR) is taken at an arbitrary value of x, and as shown in FIG. The logical sum 632 is obtained, and the area of the logical sum 632 is obtained (that is, the integral value is obtained). This operation is performed for an arbitrary d1. That is, in FIG. 23, the above-described series of calculations are performed while shifting the binarized density data 612 in the + x direction. As a result, as shown in FIG. 27, a graph showing the relationship between the shift between the pair of binarized density data 612 and 614 and the integrated value of the logical sum 632 is obtained.
[0082]
The integrated value of the logical sum of the binarized density data becomes smaller as the overlap of the pair of binarized density data 612 and 614 increases while the binarized density data 612 is shifted in the + x direction. And increases as the overlap decreases. That is, the integrated value of the logical sum of a pair of binarized density data takes the minimum value when the pair of binarized density data overlaps most.
[0083]
In FIG. 27, the value of d1 giving the minimum area indicates the recording position shift amount of the pair of test patterns corresponding to the pair of binarized density data 612 and 614. Accordingly, the recording position deviation amount of the pair of test patterns is obtained based on the graph of FIG.
[0084]
(3) Calculation based on the integral value of the comparison minimum value group of multi-value density data.
First, as shown in FIG. 28, the addition density data 712 and 714 of a pair of test patterns which are targets of the recording position deviation amount to be obtained are obtained. The added density data 712 and 714 are multi-value density data.
[0085]
Next, as shown in FIG. 29, a comparison minimum value group 722 of a pair of multi-value addition density data 712 and 714 is taken. Here, the comparison minimum value means that density data at an arbitrary x of a pair of multi-value added density data 712 and 714 is compared to obtain a smaller density data value (minimum value). Then, the comparative minimum value is acquired in the x direction, and the integral value of the minimum value group 722 is taken. Therefore, taking the integral value of the comparative minimum value group 722 of the pair of multi-valued addition density data 712 and 714 is to superimpose the pair of multi-value addition density data 712 and 714 and obtain the area of the overlapping portion. It corresponds to.
[0086]
This operation is performed for an arbitrary d2. That is, in FIG. 28, the above-described series of calculations is performed while shifting the multi-value added density data 712 in the + x direction. As a result, as shown in FIG. 30, a graph showing the relationship between the shift amount of the pair of additional density data 712 and 714 and the integrated value of the comparison minimum value group 722 is obtained.
[0087]
The integrated value of the comparison minimum value group between the density data increases as the overlap of the pair of additional density data 712 and 714 increases while the added density data 712 is shifted in the + x direction, and decreases as the overlap decreases. That is, the integral value of the comparison minimum value group of the pair of density data takes the maximum value when the density data overlap each other most.
[0088]
In FIG. 30, the value of d2 giving the maximum area indicates the recording position shift amount of the pair of test patterns corresponding to the pair of multi-value added density data 712 and 714. Therefore, the recording position deviation amount of the pair of test patterns is obtained based on the graph of FIG.
[0089]
(4) Calculation based on the integrated value of the difference between multi-value density data.
First, similarly to the calculation of the recording position deviation amount based on the integrated value of the comparison minimum value group between the density data described above, as shown in FIG. 28, the pair of test patterns that are the targets of the recording position deviation amount to be obtained are shown. Addition density data 712 and 714 are obtained. The added density data 712 and 714 are multi-value density data.
[0090]
Next, as shown in FIG. 31, the absolute value 742 of the density difference at an arbitrary x of the pair of multi-value added density data 712 and 714 is taken. Further, the integral value of the absolute value 742 of the difference between the pair of multi-value added density data 712 and 714 is taken.
This operation is performed for an arbitrary d2. That is, in FIG. 28, the above-described series of calculations is performed while shifting the multi-value added density data 712 in the + x direction. As a result, as shown in FIG. 32, a graph showing the relationship between the shift amount of the pair of additional density data 712 and 714 and the integral value of the absolute value 742 of the difference between them is obtained.
[0091]
The integral value of the absolute value 742 of the difference between the density data decreases as the overlap of the pair of additional density data 712 and 714 increases while the added density data 712 is shifted in the + x direction, and increases as the overlap decreases. That is, the integral value of the absolute value of the difference between the pair of density data takes the minimum value when the pair of density data overlaps most.
[0092]
In FIG. 32, the value of d2 giving the minimum area indicates the recording position shift amount of the pair of test patterns corresponding to the pair of multi-value added density data 712 and 714. Therefore, the recording position shift amount of the pair of test patterns is obtained based on the graph of FIG.
[0093]
(5) Calculation based on the integral value of the product of multi-value density data.
First, similarly to the calculation of the recording position deviation amount based on the integrated value of the comparison minimum value group between the density data described above, as shown in FIG. 28, the pair of test patterns that are the targets of the recording position deviation amount to be obtained are shown. Addition density data 712 and 714 are obtained. The added density data 712 and 714 are multi-value density data.
[0094]
Next, as shown in FIG. 33, a product 752 of density at an arbitrary x of a pair of multi-value added density data 712 and 714 is taken. Further, the integral value of the product 752 of the pair of multi-value added density data 712 and 714 is taken.
This operation is performed for an arbitrary d2. That is, in FIG. 28, the above-described series of calculations is performed while shifting the multi-valued addition density data 712 in the + x direction. As a result, as shown in FIG. 34, a graph showing the relationship between the shift amount of the pair of additional density data 712 and 714 and the integral value of their product 752 is obtained.
[0095]
The integrated value of the product 752 of the density data increases as the overlap of the pair of added density data 712 and 714 increases while the added density data 712 is shifted in the + x direction, and decreases as the overlap decreases. That is, the integral value of the product of the pair of density data takes the maximum value when the pair of density data overlaps most.
[0096]
In FIG. 34, the value of d2 giving the maximum area indicates the recording position shift amount of the pair of test patterns corresponding to the pair of multi-value added density data 712 and 714. Therefore, the recording position shift amount of the pair of test patterns is obtained based on the graph of FIG.
[0097]
The recording position deviation amount obtained as described above is the deviation amount in FIGS. 23 and 28, and the recording position deviation amount to be finally obtained is the deviation amount given at the time of test pattern recording from the recording position deviation amount obtained here. Is calculated by subtracting
[0098]
In the present embodiment, since the relative recording position deviation amount of the pair of test patterns is obtained by using the correlation between the density data of the pair of test patterns, the recording position deviation amount can be obtained in a short time and with high accuracy. Can be calculated.
Although several embodiments have been specifically described so far with reference to the drawings, the present invention is not limited to the above-described embodiments, and all the embodiments performed without departing from the scope of the invention are not limited thereto. Including implementation.
[0099]
In addition, according to the present embodiment, even if a defect such as dirt or dust on the test pattern or missing nozzle or landing position deviation occurs, the angle deviation amount of the recording head is accurately calculated based on the mutual relationship. Provide for possible angular misalignment detection of images. Further, it is possible to provide image misregistration detection capable of calculating the angular misalignment of the recording head in a short time.
[0100]
【The invention's effect】
According to the present invention, an image recording that can accurately calculate the amount of angular deviation of the recording head based on the mutual relationship even if a stain or dust on the test pattern, or a defect such as missing nozzle or landing position deviation occurs. An apparatus may be provided. Furthermore, the present invention can provide an image recording apparatus that can calculate the angular deviation of the recording head in a short time.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an image recording apparatus according to the present invention.
FIG. 2 is a front view showing one recording head included in the recording unit shown in FIG.
FIG. 3 is a diagram illustrating a test image including a pair of test patterns and a black pattern.
4 is a schematic diagram illustrating a process of forming the test pattern of FIG.
FIG. 5 is a diagram illustrating a test pattern having an angular deviation.
FIG. 6 is a diagram showing a positional relationship of the CCD unit with respect to the image shown in FIG. 5 during focus adjustment and white level adjustment.
FIG. 7 is a diagram showing a positional relationship of the CCD unit with respect to the image shown in FIG. 5 at the time of black level adjustment.
FIG. 8 is a diagram for comparing a test pattern having an angular deviation with a test pattern having no angular deviation.
FIG. 9 is a diagram showing an optical image of a pair of test patterns shown in FIG. 6 read by a CCD unit.
FIG. 10 is a diagram showing the added density data of the optical image of the left test pattern shown in FIG. 6;
11 is a diagram showing added density data of the optical image of the right test pattern shown in FIG. 6; FIG.
FIG. 12 is a diagram showing added density data obtained for the optical image shown in FIG. 9;
FIG. 13 is a graph showing the cross-correlation of a pair of multi-value added density data shown in FIG. 12 by a cross-correlation function.
FIG. 14 is a diagram showing a test pattern using the method (1).
FIG. 15 is a diagram showing an optical image of the six pattern blocks shown in FIG. 14 read by the CCD unit.
FIG. 16 is a diagram illustrating a state where one of the six pattern blocks illustrated in FIG. 14 is lost.
FIG. 17 is a diagram showing added density data obtained for the pattern block shown in FIG. 16;
FIG. 18 is a diagram showing a cross-correlation function obtained for the added density data shown in FIG.
FIG. 19 is a diagram showing a test pattern using the method (2).
FIG. 20 is a diagram illustrating a test pattern using the method of (3).
FIG. 21 is a diagram showing added density data of the test pattern of FIG. 21;
FIG. 22 shows binarized density data of a pair of test patterns for which the recording position deviation amount should be obtained.
FIG. 23 shows a logical product (AND) of a pair of binarized density data shown in FIG.
FIG. 24 is a graph showing a relationship between a shift amount of a pair of binarized density data shown in FIG. 22 and an integral value of their logical product.
FIG. 25 shows a logical sum (OR) of a pair of binarized density data shown in FIG.
FIG. 26 is a graph showing a relationship between a shift amount of a pair of binarized density data shown in FIG. 22 and an integrated value of their logical sums.
FIG. 27 shows the added density data of a pair of test patterns for which the recording position deviation amount should be obtained.
FIG. 28 shows a comparison minimum value group of a pair of multi-value density data shown in FIG.
FIG. 29 is a graph showing a relationship between a shift amount of a pair of multi-value density data shown in FIG. 27 and an integral value of a comparison minimum value group.
30 is a diagram showing an absolute value of a difference between a pair of multi-value density data shown in FIG. 27. FIG.
FIG. 31 is a graph showing the relationship between the shift amount of the pair of multi-value density data shown in FIG. 27 and the integral value of the absolute value of the difference between them.
32 is a diagram showing a product of a pair of multi-value density data shown in FIG. 27. FIG.
FIG. 33 is a graph showing a relationship between a shift amount of a pair of multi-value density data shown in FIG. 27 and an integral value of their products.
FIG. 34 is a schematic diagram showing two ink dot rows printed so that the image recording apparatus is aligned along the sub-scanning direction at a position along an arbitrary main scanning axis.
FIG. 35 is a front view showing a recording head with an angular deviation.
FIG. 36 is a diagram illustrating an ink dot row recorded by a recording head having an angular deviation.
FIG. 37 is a diagram illustrating a relationship between an inclination angle and a nozzle row length.
[Explanation of symbols]
100 Image recording apparatus
110 Carriage
112 Guide
120 Recording unit
130 CCD unit
140 Paper holding mechanism
170 Carriage controller
172 Carriage drive mechanism
174 Recording control unit
176 calculator
192 paper

Claims (4)

Recording means for recording a plurality of pairs of test patterns configured with different pattern elements for each pair of test patterns on a recording medium;
Reading means for reading the densities of the plurality of pairs of test patterns recorded by the recording means;
Based on the density data of the plurality of pairs of test patterns read by the reading means, a cross-correlation function between the density data is calculated, and a relative recording position shift from a position having the maximum value of the cross-correlation function Calculating means for calculating an angle deviation amount of the recording means based on the recording position deviation amount;
An image recording apparatus comprising:   The image recording apparatus according to claim 1, wherein the plurality of pairs of test patterns are configured so that the widths of the pattern elements are different for each pair of test patterns.   The image recording apparatus according to claim 2, wherein the pair of test patterns are recorded on the recording medium along a main scanning direction. While moving the inkjet head in the main scanning direction, one pattern element of each pair in the plurality of pairs of test patterns is recorded on the recording medium in the upper half of the nozzle row of the inkjet head,
The recording medium is conveyed in the sub-scanning direction by a distance corresponding to half of the nozzle row,
While moving the inkjet head in the main scanning direction, the other half of each pair of test patterns in a plurality of pairs of test patterns is recorded in the lower half of the nozzle row of the inkjet head,
Read the density of the plurality of pairs of test patterns recorded by the inkjet head;
Based on the read density data of the plurality of pairs of test patterns, a cross-correlation function between the density data is calculated, and a relative recording position shift amount is calculated from a position having the maximum value of the cross-correlation function. An image recording apparatus characterized by calculating an angle deviation amount of the recording means based on the recording position deviation amount.

Images