JP2004237604A - Density correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a detection time becomes long when a discharge amount is detected for each recording element more highly accurately, or a head number is increased when executing head shading by the detection of the discharge amount in an image recording apparatus which forms images on a recording medium by a recording head with a plurality of arranged recording elements. <P>SOLUTION: A plurality of density patterns are printed on the recording medium by the plurality of recording elements. The printed density patterns are measured by measurement speeds corresponding to the respective densities. An image formation density for each recording element is corrected on the basis of the obtained measured density values. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
1. Field of the Invention The present invention relates to a technique for correcting unevenness in density due to a variation in the discharge amount of each nozzle in a print head in an image forming apparatus that forms an image by discharging ink from a print head.
[0002]
[Prior art]
With the spread of information processing equipment and communication equipment in recent years, image recording apparatuses that perform digital image recording using a recording head of an ink jet system, a thermal transfer system, or the like are also rapidly spreading. In such an image recording apparatus, a recording head in which a plurality of recording elements are arranged in an integrated manner is generally used to improve the recording speed. For example, in an ink jet recording head, a so-called multi-nozzle head in which a plurality of ink ejection ports and liquid paths are integrated is generally used, and a plurality of heaters are also integrated in a thermal transfer type and a thermal type thermal head, and a mechanical energy type is used. In many piezo heads, a plurality of ejection mechanisms are integrated.
[0003]
In such a recording head, variations in characteristics due to the manufacturing process, variations in characteristics of the head constituent materials, and the like occur, so that it is difficult to manufacture such a plurality of recording elements so as to have uniform characteristics. As a result, a certain degree of variation occurs in the characteristics of each recording element of the recording head. For example, in the case of an ink jet recording head, the shape of a discharge port or a liquid path or the like varies, and in the case of a thermal head, the shape or resistance of a heater varies. Further, in addition to the cause of the limitation of the manufacturing technique, the characteristics among the respective recording elements of the recording head vary due to aging.
[0004]
Such non-uniformity of characteristics between the recording elements in the recording head (for example, uneven ink ejection amount in the case of an ink jet recording head) appears as non-uniformity in the size and density of dots recorded by each recording element. As a result, density unevenness occurs in the recorded image.
[0005]
As described above, variations in the characteristics of each printing element in the printhead significantly deteriorate the quality of a printed image. Therefore, in a conventional image printing apparatus, in order to correct this variation, a print pattern reading unit is provided in the apparatus. There is known a method of reading the current density unevenness by periodically detecting the ejection amount of each element in a print element array range, and creating density unevenness correction data based on the density unevenness data.
[0006]
[Problems to be solved by the invention]
In image recording devices equipped with the above-described recording heads, high-definition ink droplets have been used to meet the demand for higher image quality, and higher definition has been pursued. ing. Further, in order to cope with high-speed printing, a printer having a plurality of heads for the same color has been proposed, and the number of heads formed in one unit has been increased. For this reason, there is a concern that the time required for detecting the ejection density in the print head as described above becomes long.
[0007]
Further, as shown in the above-described conventional example, when detecting the ejection density of the print head, the measurement time by the image reading mechanism 210 is increased (driving speed is reduced) in order to perform more accurate measurement, or A method of increasing the number of measurements is used. However, in this method, the time required for detecting the ejection density becomes long.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and in an image recording apparatus having a recording head, by shortening the detection time of the ejection density in the recording head while maintaining the current configuration, high speed and An object is to realize highly accurate density correction.
[0009]
[Means for Solving the Problems]
As one method for achieving the above object, the density correction method of the present invention includes the following steps.
[0010]
That is, in an image recording apparatus that forms an image on a recording medium by a recording head in which a plurality of recording elements are arranged, a plurality of density patterns are printed on the recording medium by the plurality of recording elements, and each of the printed density is printed. The pattern is measured at a measuring speed corresponding to each density, and the image forming density for each recording element is corrected based on the obtained measured density value.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to an image recording apparatus for forming an image on a recording medium by a recording head having a plurality of recording elements arranged thereon, wherein a plurality of density patterns are printed on the recording medium by the plurality of recording elements, and each of the printed densities is printed. The pattern is measured at a measuring speed corresponding to each density, and the image forming density for each recording element is corrected based on the obtained measured density value.The lower the density pattern, the lower the measuring speed. It is characterized by raising. Further, the density pattern is measured at a measurement speed corresponding to the color.
[0012]
Further, the measurement value characteristics at a predetermined measurement speed are held in advance, and the measurement speed is determined based on the measurement value characteristics. For example, the fastest measurement speed is determined based on the measurement value characteristics. The measured value characteristic is a reference density value obtained as a result of measuring a predetermined reference pattern at a predetermined measurement speed, and detects an image forming density for each recording element based on a difference from the measured density value.
[0013]
Further, when measuring the density pattern, the position information of the recording element is also measured, and the image forming density for each recording element is corrected based on the measured density value and the position information.
[0014]
The recording head forms an image on a recording medium by discharging ink droplets.
[0015]
The present invention can be realized in the configuration and processing specifically shown in the drawings attached to the application corresponding to the following embodiments.
[0016]
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0017]
<First embodiment>
First, a method of correcting unevenness in density, which is generally employed, will be described using an example of an inkjet recording apparatus that forms an image on a recording medium by discharging ink droplets from a recording head. Here, an example is a so-called BJ type recording head in which bubbles are formed in the ink in the ejection ports by the heat generated by the thermoelectric conversion elements attached inside the plurality of ejection ports, and the ink droplets are ejected at the bubble generation pressure. However, the same correction method can be applied to a so-called piezo-type recording head that discharges droplets with mechanical vibration energy.
[0018]
Assuming that such an inkjet recording head can scan a range corresponding to the length of a short side (297 mm) of an A3 size recording medium, for example, at a density of 400 dpi, 128 recording heads in a direction perpendicular to the scanning direction are provided. Discharge ports are arranged. In the case of a color recording apparatus, four cyan heads, magenta heads, yellow heads, and black heads having this configuration are used.
[0019]
In order to correct such ejection unevenness (density unevenness) for each ink ejection port of the recording head, it is necessary that the ink ejection amount from each ink ejection port and the recording density data read by the reading system be correctly associated. It is a premise. Therefore, first, each ejection port of the recording head is driven by a predetermined uniform recording signal, and conditions are changed for each color on the recording medium as shown in FIG. Form. The detection pattern is determined by a recording head in which a plurality of ejection openings are arranged in a line in an upper row (corresponding to 32 pixels in this example) and a middle row (corresponding to 32 pixels in this example) in a printing direction (main scanning direction) from left to right in FIG. This is formed by so-called irregular three-line printing in which three lines in the lower row (corresponding to the same 32 pixels) are printed.
[0020]
FIG. 2 shows the details of this detection pattern. The shaded area at the bottom of FIG. 2 corresponds to one of the detection patterns shown in FIG. 1. For example, when there are 128 ejection openings (128 nozzles), the first line 2a in the upper stage is Printing is performed by discharging ink from the 96th to final 128th discharge ports. Next, in the second line 2b in the middle stage, printing is performed by discharging ink from all the first to 128th discharge ports. In the third line 2c, which is the last lower stage, printing is performed by discharging ink from the first to thirty-second discharge ports at the forefront.
[0021]
FIG. 3 is a diagram for explaining the operation of reading the detection pattern. In the figure, a reading mechanism 210 is provided on a carriage that moves the recording head 20 in the main scanning direction, and a reading element row of the reading mechanism 210 is configured in a direction orthogonal to the head nozzle row direction. The reading mechanism 210 performs detection by moving on the detection pattern in the sub-scanning direction. At this time, as shown in (a), the reading mechanism 210 moves in the sub-scanning direction by being driven by the sub-scanning driving mechanism 211. Alternatively, as shown in (b), the reading mechanism 210 may be stopped at an arbitrary position, and the recording medium 1 may be moved in the sub-scanning direction by the recording medium transport mechanism.
[0022]
Here, FIG. 4 shows a schematic block configuration of the reading mechanism 210. According to the figure, a reading mechanism 210 includes a light source 61 for illuminating a recording medium, a lens 62 for forming an image on a photoelectric conversion element 63 (hereinafter simply referred to as a detection sensor) such as a CCD or a CMOS sensor, and the like. The row information of the image orthogonal to the main scanning direction is read by the number of pixels corresponding to the number of photoelectric conversion elements.
[0023]
After reading the image for a predetermined width, the reading mechanism 210 is driven in the reverse direction of the sub-scanning direction, thereby returning to the initial position. Next, the carriage is driven in the main scanning direction to move the reading mechanism 210 to the next pattern, and the entire image is read by repeating the above measurement procedure.
[0024]
Next, an example of reading a detection pattern of a certain color formed as shown in FIG. 2 will be described.
[0025]
As shown on the lower left side of FIG. 2, the detection pattern 2 of a certain color is read by the image reading mechanism 210 from the reading start position S to the reading end position F in the arrow Y direction (sub scanning direction), and the read density distribution data is read. They are temporarily stored in the memory in the device in the order of reading.
[0026]
By the way, in a general image recording apparatus, the recording density of the ink jet recording system and the resolution of the image reading mechanism 210 are often the same, for example, 400 dpi. In that case, the dots of the ink ejected from each ink ejection port correspond to one pixel of the reading system. Further, if the density distribution data read and stored in the memory is represented by 256 gradations, the print density by the discharge port can be expressed by associating one discharge port with one byte area in the memory. This means that one byte is composed of binary 8 bits, and the number of combinations is 2 ⁸ = 256. Therefore, the threshold value D _TH Is set, the section (the number of bytes) of the density data exceeding the threshold value coincides with the ejection section in the reading direction of the detection pattern.
[0027]
In the graph shown in the upper part of FIG. 2, X1 to X2 are detected as the sections of the above detection pattern, but since X1 and X2 are obtained as address information on the memory, the first to 128th outlets are calculated by the address calculation. The storage address of the density data is calculated, and the density unevenness correction amount is calculated based on the density data.
[0028]
Note that the image reading mechanism 210 is driven at a constant speed. Generally, the measurement signal level of a high-density pattern is reduced because the amount of reflected light is reduced, and it is difficult to determine the high-density pattern due to the influence of signal noise. Is set to be a speed (or measurement time) suitable for measuring the entire pattern.
[0029]
Hereinafter, a method for detecting the ejection amount of the print head according to the present embodiment will be described in detail.
[0030]
FIG. 5 is a diagram illustrating a configuration example of a recording head in the inkjet recording apparatus according to the present embodiment.
[0031]
In the figure, reference numeral 20 denotes an ink jet head (recording head) of a type that discharges ink onto recording paper using bubbles generated by thermal energy or a head that discharges ink with mechanical energy. It is integrally attached to. An ink jet head cartridge 21 is constituted by the integrated head 20 and the ink tank 10, and this cartridge 21 is detachably attached to a recording apparatus.
[0032]
In the ink jet head cartridge 21 of the present embodiment, as can be seen from FIG. 5, the tip of the ink jet head 20 projects slightly from the front surface of the ink tank 10. The cartridge 21 is of a replaceable type, and is configured to be detachably fixedly supported by a carriage mounted on a drive mechanism 201 of an ink jet recording apparatus main body to be described later. The ink tank 10 storing the ink to be supplied to the inkjet head 20 includes an ink absorber, a container for inserting the ink absorber, and a lid member for sealing the ink absorber (both are not shown). ing. The ink is filled in the ink tank 10, and the ink is sequentially supplied to the head 20 according to the ejection of the ink from the head 20.
[0033]
The ink jet head cartridge 21 configured as described above is removably mounted on a carriage of an ink jet recording apparatus driving mechanism 201 described below in a predetermined manner, and the carriage and the recording member are input by a predetermined recording signal. A desired recorded image is formed by controlling the relative movement with respect to.
[0034]
FIG. 6 is an external perspective view illustrating a configuration example of an inkjet recording apparatus including a mechanism for head shading processing according to the present embodiment.
[0035]
In the figure, reference numeral 16 denotes a carriage for holding the ink jet head cartridge 21 shown in FIG. The carriage 16 is connected to a part of a drive belt 18 that transmits a driving force of a drive motor 17, and is slidably attached to two guide shafts 19A and 19B disposed in parallel with each other. As a result, the recording head 20 can freely reciprocate over the entire width of the recording medium. The recording head 20 records an image corresponding to the received data on a recording medium during the reciprocating movement. Each time one scan (main scan) for recording by the recording head 20 is completed, the recording paper is conveyed by a predetermined amount in a direction orthogonal to the main scan direction, that is, a sub-scan is performed.
[0036]
A reading mechanism 210 is configured adjacent to the carriage 16. The reading mechanism 210 can be driven in the main scanning direction similarly to the recording head 20. Although FIG. 6 shows an example in which the reading mechanism 210 is adjacent to the recording head 20 in the main scanning direction, the present invention is not limited to this example as long as it can be driven in the main scanning direction and the pattern can be detected. As shown in FIG. 3, a sub-scanning drive unit 211 may be configured to drive the reading mechanism 210 in the sub-scanning direction, or a method of transporting a recording medium by a recording medium transport system may be used.
[0037]
Reference numeral 26 denotes a head recovery device, which is disposed at one end of the movement path of the recording head 20 (for example, at a position facing the home position). The head recovery device 26 is driven by the motor 22 via the transmission mechanism 23 to cap the recording head 20. The head recovery device 26 has a cap portion 26A. The cap portion 26A is fitted to the recording head 20, and a suction operation (suction recovery) is performed by suction means (a suction pump or the like) provided appropriately in the head recovery device 26. Perform By this suction operation, ink is forcibly discharged from each of the ejection ports of the recording head 20, and attached substances such as thickened ink and dust around each of the ejection ports existing in each of the ejection ports of the recording head 20 are removed. Thus, the ejection recovery processing is realized. In addition, when the recording operation is not performed for a relatively long time such as after the recording is completed, the recording head 20 can be protected from drying, dust adhesion, and the like by capping the recording head 20 with the cap portion 26A. Such an ejection recovery process is performed when the power is turned on, when the print head is replaced, or when the printing operation is not performed for a certain period of time or longer.
[0038]
Reference numeral 31 denotes a blade disposed on a side surface of the head recovery device 26 and formed as a wiping member made of silicone rubber. The blade 31 is held in a cantilever form by a blade holding member 31 </ b> A, and is operated by a motor 22 and a transmission mechanism 23, similarly to the head recovery device 26, and slides on the ejection surface of the recording head 20. Therefore, by causing the blade 31 to protrude into the movement path of the recording head 20 at an appropriate timing during the recording operation of the recording head 20 or after the ejection recovery processing using the head recovery device 26, the blade 31 is moved. By rubbing the discharge surface of No. 20, it is possible to wipe off the adhered matter such as dew, wet or dust adhering to the discharge surface.
[0039]
In the example of FIG. 6, for the sake of simplicity, the configuration of a single-color printing apparatus to which one ink jet head cartridge 21 is attached is shown. , Magenta, yellow, and black ink jet head cartridges are attached, and the structure is basically the same as that of FIG.
[0040]
FIG. 7 is a block diagram illustrating a configuration example of a reading system and a recording system in the inkjet recording apparatus of the present embodiment.
[0041]
The recording unit 100 includes a recording head 20, a head driver 110 that supplies a signal for heating adjustment of the recording head 20 to a constant temperature and an ejection pulse for ejecting ink to a heating medium in each ejection port, and a recording head. A print / temperature control circuit that adjusts the temperature adjustment signal output from the head driver 110 and the pulse width of the ejection pulse so that the printhead 20 is maintained at a predetermined temperature by obtaining temperature information from a temperature sensor (not shown) in the print head 20. And an adjustment control unit 120. The printing / temperature adjustment control unit 120 controls the printing section for each printing color.
[0042]
The image data input to the recording unit 100 is a binarized signal indicating whether or not to eject ink to each ink ejection port. When the binarized image data is input to the head driver 110 controlled by the print / temperature adjustment controller 120, ink is ejected from each ejection port of the corresponding recording head 20.
[0043]
It is also possible to cause ink to be ejected from the ejection port without inputting image data. This is used by the print / temperature adjustment control unit 120 to adjust the temperature from the head driver 110 to a specific ejection port. This can be performed by applying a heating pulse for a longer time than during normal temperature adjustment.
[0044]
By using such an ejection method, for example, a pattern for detecting an ejection port position can be printed. For example, ink is ejected only from a specific ejection port of the recording head 20 by a drive signal of the print / temperature adjustment control unit 120, and a linear ejection port position detection pattern is printed on the right side of each density unevenness detection pattern. be able to.
[0045]
The density unevenness detection pattern is printed by inputting the fixed values (80H) of cyan, magenta, yellow, and black from the memory 250 to the γ conversion unit 270 of the image processing unit 200, thereby forming a halftone pattern. To be recorded.
[0046]
Hereinafter, the outline of the density detection method according to the present embodiment will be described first.
[0047]
In order to correct the ink ejection amount of the recording head of the image recording apparatus (head shading), it is necessary to detect the current density unevenness state. In this embodiment, prior to detecting the density unevenness, FIG. The reference data is obtained by measuring the reference pattern of each density. FIG. 8 shows a state where three reference patterns are formed side by side in the main scanning direction on a recording medium. In the present embodiment, the density of the reference pattern is detected by driving the reading mechanism 210 with respect to the recording medium while measuring in the sub-scanning direction. After the measurement, the reading mechanism 210 is driven in the reverse direction of the sub-scan and returns to the initial position. Next, the reading mechanism 210 is driven in the main scanning direction, and moves to the measurement start point of the next pattern. Thereafter, similarly, the driving in the sub-scanning direction, the sub-scanning reverse direction, the main scanning direction,...
[0048]
In the present embodiment, the speed of the drive unit in the sub-scanning direction of the reading mechanism 210 is made variable, and the drive time (speed) and the measured density value at the time of measurement are simultaneously captured and recorded in a memory (not shown).
[0049]
FIG. 9 shows patterns of densities A, B, and C (A <B <C) shown in FIG. 8 when the scanning speed of the reading mechanism 210 is changed to V1, V2, and V3 (V1>V2> V3). Shows the measured density value d. In general, since the pattern of the density A, which is a low density, has a large amount of reflected light to the detection sensor, the measured value d is higher than the other densities B and C, and when the driving speed of the reading mechanism 210 is further reduced. The measurement value is higher because the measurement time is longer.
[0050]
By the way, in FIG. 9, if the measured value is 2 / d or less, the influence of signal noise is large, and it is difficult to determine the signal of the measurement result. Therefore, if the measured value is 2 / d or more, relatively stable determination can be performed. Therefore, in the present embodiment, a density read value at a drive speed (measurement time) at a signal level effective for each ink density is stored in the memory as reference data. In the example shown in FIG. 9, a measured value of d / 2 or more is obtained as reference data (A1, V1), (B1, V1), (A2, V2), (B2, V2), (C2, V2). , (A3, V3), (B3, V3), and (C3, V3).
[0051]
Next, a detection pattern for density unevenness detection is measured based on the reference data obtained as described above. It is assumed that the detection pattern used in the present embodiment is the same as that shown in FIG.
[0052]
In the present embodiment, the measurement conditions are determined according to the type and density of the ink in the detection pattern, that is, based on the above-described reference data. For example, for the pattern of the density A, V1 which is the fastest driving speed at which stable detection is possible is selected as the measurement speed, and the corresponding measurement value A1 is set as a target value. The density is detected based on the difference between the measured values. Similarly, the measurement speed V1 and the target value B1 are set for the density B pattern, and the measurement speed V2 and the target value C2 are set for the density C pattern. At this time, if the actual measurement value is lower than expected, the measurement is performed only under the measurement condition under the condition that the measurement speed is further reduced.
[0053]
As described above, in the present embodiment, while selecting the fastest driving speed according to the density of each detection pattern, the density detection of the detection patterns formed on the entire recording medium is performed, thereby minimizing the measurement time as a whole. It can be.
[0054]
Hereinafter, density unevenness correction, that is, head shading (HS) according to the present embodiment will be described with reference to the flowcharts of FIGS.
[0055]
In FIG. 10, first, at step S1, the detection conditions in the reading mechanism 210 are calibrated. Specifically, a predetermined calibration pattern is measured in advance, and the variation between pixels is corrected from the measurement data. This calibration process is performed at the initial stage of the detection sensor and at an arbitrary calibration time, but may be performed for each head shading process. When the calibration is completed, the reference pattern shown in FIG. 8 is read with the measurement time variable, and the reference data is obtained.
[0056]
In step S2, a detection pattern for density unevenness detection is printed. In step S3, the printed detection pattern is read, density data corresponding to each measurement point is calculated, and the density data and the ejection port are compared. Perform association. In step S4, the density shading correction data (HS data) is calculated based on the measured density data of the detection pattern, thereby ending the head shading processing. By correcting the image information drive signal based on the HS data, an image without density unevenness is recorded.
[0057]
FIG. 11 is a flowchart showing the reference data acquisition process after the detection sensor calibration in step S1 of FIG.
[0058]
First, in step S11, a reference pattern to be read is set. For example, a pattern corresponding to each pixel resolution of the detection sensor is prepared as a reference pattern. Then, in step S12, the number of measurements for the same pattern is specified. Note that it is also possible to designate one measurement as the number of measurements. Then, in step S13, by detecting the reference pattern selected in step S11 by the detection sensor, detection sensitivity, light amount adjustment, density variation between pixels, and the like are detected for each pixel. Hereinafter, the values detected here are collectively referred to as ejection conditions.
[0059]
In the present embodiment, the reference data is obtained by calculating the measurement condition using the calibration data of the detection sensor and the correction value of each pixel based on the detection result of the ejection condition one or more times. In step S14, if the number of measurements has reached the upper limit of the number of measurements determined in step S12, the process proceeds to step S15. If not, the number of measurements is incremented in step S19, and then the ejection condition is detected in step S13. .
[0060]
In step S15, it is determined whether the ejection conditions obtained so far are sufficient to perform the correction value calculation, that is, whether all the ejection conditions for each printing element have been detected. If it is determined in step S15 that the condition is not sufficient, the process returns to step S11 to optimize the condition of the reference pattern. Then, after changing the measurement conditions, the density detection processing in steps S12 to S15 is repeated.
[0061]
If it is determined in step S15 that the ejection conditions for each printing element have been sufficiently detected, the process proceeds to step S16, where reference data is calculated based on the obtained ejection conditions, and is used as HS reference data. Along with pattern conditions
(↑ The reference data and ejection pattern conditions are separate items. Please check!)
Store in memory. Then, after changing the measurement time for acquiring the reference data, that is, the measurement speed in step S17, the processes in steps S11 to S16 are repeated.
[0062]
Further, in step S18, the processing of steps S11 to S17 is repeated for the types of printhead constituent colors to be evaluated, whereby reference data of each color is obtained. Note that this embodiment shows an example in which the recording head has a four-color configuration.
[0063]
FIG. 12 is a flowchart showing the detection pattern printing process in step S2 of FIG.
[0064]
First, in step S21, the detection pattern shown in FIG. 1 is printed based on the ejection pattern conditions acquired by the processing shown in FIG. At this time, a positioning pattern (position detection pattern) is printed adjacent to the density pattern for each recording element. Then, in step S22, the detection pattern is printed a plurality of times in consideration of the change in the ejection condition. Then, in step S23, printing is performed for the constituent colors of the recording head (for the four colors in the present embodiment).
[0065]
FIG. 13 is a flowchart showing the detection pattern reading process in step S3 of FIG.
[0066]
First, in step S31, it is checked whether or not there is a change in the measurement conditions such as the measurement speed based on the already acquired reference data. If there is no change, the process proceeds to step S33. If there is a change, the measurement condition is set in step S32.
[0067]
In step S33, the measurement start position of each detection pattern is detected by moving the detection sensor in the main scanning direction. At this time, the pattern number and pattern position of the detected pattern are recorded in the memory. In step S34, the patterns (position detection patterns and density patterns) arranged on the main scanning line are measured based on the detection conditions (calibrated sensor conditions and reference data) obtained in step S1, and stored in the memory. . As a result, a density value of the density pattern (hereinafter, referred to as a pattern density) and nozzle position data are obtained.
[0068]
When the detection process for one pattern is completed, in step S35, the detection sensor is driven in the main scanning direction to the start point of the next pattern until all the patterns in the main scanning direction are completed. Further, in step S36, after the measurement on one scanning line is completed, the detection sensor is transported in the sub-scanning direction.
[0069]
In step S37, the same detection processing is repeated for a predetermined number of patterns, and in step S38, the above sequence is similarly repeated for the four colors constituting the print head.
[0070]
FIG. 14 is a flowchart showing the HS data calculation processing in step S4 of FIG.
[0071]
First, in step S41, the pattern density and nozzle position data obtained in step S34 of FIG. 13 are obtained. In step S42, density data of the same pattern is calculated from this pattern density based on the reference data. The data is associated with each nozzle.
[0072]
In step S44, corrected density data, that is, HS data, is calculated from the speed data and the target value in the reference data.
[0073]
Then, in step S45, the HS data is calculated using the density data of the detection pattern.
[0074]
In step S46, the above processing is performed on a plurality of detection patterns, and in step S47, the above processing is repeated for four colors, thereby ending the calculation routine.
[0075]
In the present embodiment, an example in which HS data for a plurality of detection patterns is calculated for one color has been described. However, an average of these HS data may be used as HS data used for density unevenness correction. Values may be used.
[0076]
As described above, according to the head shading processing of the present embodiment, since the density data of the density unevenness detection pattern is accurately associated with each ejection port, appropriate density unevenness correction data (HS data) is obtained. Can be calculated. As a result, high-quality image recording without density unevenness becomes possible.
[0077]
Note that the present invention is not limited to a recording apparatus using an ink-jet method, and can be similarly applied to a thermal transfer method, a heat-sensitive method, and the like.
[0078]
<Modification>
In the above embodiments, the description has been made assuming that the liquid droplets ejected from the recording head are ink, and the liquid contained in the ink tank is ink, but the contained matter is not limited to ink. Absent. For example, an ink tank may contain a processing liquid discharged to a recording medium in order to improve the fixing property and water resistance of the recorded image or to improve the image quality.
[0079]
The above-described embodiment includes a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for causing ink to be ejected, particularly in an ink jet recording system. By using a method that causes a change in the state, it is possible to achieve higher density and higher definition of recording.
[0080]
Regarding the typical configuration and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). Applying at least one drive signal corresponding to recording information and providing a rapid temperature rise exceeding nucleate boiling to the electrothermal transducer, thereby causing the electrothermal transducer to generate heat energy, and This is effective because a film in the liquid (ink) corresponding to this drive signal can be formed on a one-to-one basis by causing film boiling on the heat acting surface. By discharging the liquid (ink) through the discharge opening by the growth and contraction of the bubble, at least one droplet is formed. When the drive signal is formed in a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of the liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable.
[0081]
As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.
[0082]
As the configuration of the recording head, in addition to the combination of the discharge port, the liquid path, and the electrothermal converter (the linear liquid flow path or the right-angled liquid flow path) as disclosed in each of the above-mentioned specifications, a heat acting surface A configuration using U.S. Pat. No. 4,558,333 and U.S. Pat. No. 4,459,600, which disclose a configuration in which is disposed in a bending region, is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slot is used as a discharge portion of an electrothermal converter for a plurality of electrothermal converters, or an opening for absorbing a pressure wave of thermal energy is discharged. A configuration based on JP-A-59-138461, which discloses a configuration corresponding to each unit, may be adopted.
[0083]
Further, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is satisfied by a combination of a plurality of recording heads as disclosed in the above specification. Either the configuration or the configuration as one recording head integrally formed may be used.
[0084]
In addition, not only the cartridge-type recording head in which the ink tank is provided integrally with the recording head itself described in the above embodiment, but also the electrical connection with the apparatus main body by being mounted on the apparatus main body. A replaceable chip-type recording head that can supply ink from the apparatus main body may be used.
[0085]
It is preferable to add recovery means for the printhead, preliminary auxiliary means, and the like to the configuration of the printing apparatus described above because the printing operation can be further stabilized. Specific examples thereof include capping means for the recording head, cleaning means, pressurizing or sucking means, preheating means using an electrothermal transducer or another heating element or a combination thereof. It is also effective to provide a preliminary ejection mode for performing ejection that is different from printing, in order to perform stable printing.
[0086]
Further, the printing mode of the printing apparatus is not limited to a printing mode of only a mainstream color such as black, and may be a printing head integrally formed or a combination of a plurality of printing heads. The device may be provided with at least one of the full colors.
[0087]
In the above-described embodiment, the description has been made on the assumption that the ink is a liquid.However, even if the ink solidifies at room temperature or below, an ink that softens or liquefies at room temperature may be used. Alternatively, in the ink jet system, the temperature of the ink itself is controlled within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. It is sufficient if the ink is sometimes in a liquid state.
[0088]
In addition, to prevent the temperature rise due to thermal energy from being used as the energy of the state change of the ink from the solid state to the liquid state, or to prevent the ink from evaporating, the ink solidifies in a standing state. Alternatively, ink that liquefies by heating may be used. In any case, the application of heat energy causes the ink to be liquefied by application of the heat energy according to the recording signal and the liquid ink to be ejected, or to start to solidify when reaching the recording medium. The present invention is also applicable to a case where an ink having a property of liquefying for the first time is used. In such a case, as described in JP-A-54-56847 or JP-A-60-71260, the ink is held in a liquid state or a solid state in the concave portion or through hole of the porous sheet. It is good also as a form which opposes an electrothermal transducer. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.
[0089]
<Other embodiments>
The form of the ink jet recording apparatus of the present invention is not only used as an image output terminal of an information processing apparatus such as a computer, but also adopts a form of a copying apparatus combined with a reader or the like, or a facsimile apparatus having a transmission / reception function. You may.
[0090]
The present invention can take embodiments as a system, an apparatus, a method, a program, a storage medium, or the like. Specifically, even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, and the like), a device including one device (for example, a copier, a facsimile, Device, etc.).
[0091]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading out and executing the program code stored in the.
[0092]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0093]
As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. I can do it.
[0094]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a case where a part of the actual processing is performed and the function of the above-described embodiment is realized by the processing is also included.
[0095]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0096]
【The invention's effect】
As described above, according to the present invention, in an image recording apparatus equipped with a recording head, high-speed and high-precision density correction can be performed by shortening the detection time of the ejection density in the recording head while maintaining the current configuration. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a detection pattern formed on a recording medium in one embodiment according to the present invention.
FIG. 2 is a diagram illustrating a relationship between density data obtained by reading a detection pattern and an address on a memory;
FIG. 3 is a diagram for explaining an operation of a reading mechanism.
FIG. 4 is a block diagram illustrating a schematic configuration of a reading mechanism.
FIG. 5 is a perspective view illustrating a configuration example of a recording head in an ink jet recording apparatus to which the embodiment is applied.
FIG. 6 is a perspective view showing an example of an internal configuration of a main part in an ink jet recording apparatus to which the embodiment is applied.
FIG. 7 is a block diagram illustrating a configuration example of a reading system and a recording system according to the embodiment.
FIG. 8 is a diagram showing an outline of pattern detection in the present embodiment.
FIG. 9 is a diagram illustrating an example of reference data indicating a relationship between a measurement speed and a density value.
FIG. 10 is a flowchart illustrating head shading in the present embodiment.
FIG. 11 is a flowchart showing reference data acquisition processing.
FIG. 12 is a flowchart illustrating density unevenness detection pattern printing processing.
FIG. 13 is a flowchart illustrating a process of reading a density unevenness detection pattern.
FIG. 14 is a flowchart illustrating a process of creating head shading data.

Claims (10)

In an image recording apparatus that forms an image on a recording medium by a recording head in which a plurality of recording elements are arranged,
By the plurality of printing elements, printing a plurality of density patterns on a printing medium,
Measure each printed density pattern at a measurement speed corresponding to each density,
A density correction method, comprising: correcting an image forming density for each recording element based on the obtained measured density value. 2. The density correction method according to claim 1, wherein the measurement speed is increased as the density pattern is lower. 2. The density correction method according to claim 1, further comprising measuring the density pattern at a measurement speed corresponding to the color. Holding the measurement value characteristics at a predetermined measurement speed in advance,
The density correction method according to claim 1, wherein the measurement speed is determined based on the measurement value characteristics. 5. The density correction method according to claim 4, wherein the fastest measurement speed is determined based on the measured value characteristics. 5. The density correction method according to claim 4, wherein the measured value characteristic is a reference density value obtained as a result of measuring a predetermined reference pattern at a predetermined measurement speed. 7. The density correction method according to claim 6, wherein an image forming density for each recording element is detected based on a difference between the measured density value and the reference density value. The method according to claim 1, wherein the recording head forms an image on a recording medium by discharging ink droplets. A non-transitory computer-readable storage medium storing a program for causing an image forming apparatus to execute the density correction according to claim 1. A recording medium on which the program according to claim 9 is recorded.

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