JP5078179B2 - Method for adjusting droplet ejection position error, droplet ejection control method, and image forming apparatus - Google Patents

Description

  The present invention relates to a droplet ejection position error adjustment method, a droplet ejection control method, and an image forming apparatus, and in particular, ejects ink onto a recording medium from a print head on which a plurality of ink discharge ports (nozzles) are formed. The present invention relates to a droplet ejection position error measuring method suitable for an ink jet recording apparatus that forms the image, an adjustment method for correcting the error, a droplet ejection control method, and an image forming apparatus using the method.

  In an ink jet recording apparatus (ink jet printer) equipped with a print head having a plurality of nozzles, when the print head is mounted at an inclination with respect to a predetermined mounting position (ideal mounting position in design), the desired position is obtained. There is a problem that dots are not formed and the dot recording position (droplet ejection position) is shifted.

  In order to determine the degree to which the print head is inclined with respect to the recording paper conveyance direction, Patent Document 1 discloses a line-segment pattern having a length in which a plurality of ink discharge ports are arranged. A method has been proposed in which a plurality of lines are printed and the print results of these line segment patterns are visually determined to adjust the mounting position of the print head.

  Further, Patent Document 2 discloses a structure of a carriage unit that can adjust the head tilt, and proposes a configuration that corrects the tilt from the correlation between the test recording result and a predetermined tilt correction amount. ing.

  Patent Documents 1 and 2 are serial scan type ink jet recording apparatuses that record images while reciprocating the print head in a direction (main scanning direction) orthogonal to the recording paper transport direction (sub-scanning direction). The assumed technology content.

Japanese Patent Laid-Open No. 11-277721 JP 2001-129983 A

  When the droplet ejection position error due to the tilt of the recording head is examined in more detail, in addition to the problems disclosed in Patent Documents 1 and 2 (print line jaggedness due to dot position deviation between scans of the serial scan method), in particular When the density of the nozzle is increased, there are the following problems.

[1] In a streaky inkjet recording device that occurs at the folded portion of a matrix head, a recording head (so-called matrix head) in which a large number of nozzles are two-dimensionally arranged in a matrix is proposed in order to print high-quality images at high speed. Has been. When droplets are ejected with this matrix head, if the head is mounted at an inclination, the pitch between nozzles that eject adjacent dots on the recording medium is shifted, and the unevenness of the matrix (hereinafter referred to as “straight irregularity”) May be referred to as “matrix folding unevenness”). This phenomenon will be described with reference to FIG.

  FIG. 13 is a perspective plan view schematically showing a part of the matrix head. The left figure of FIG. 13 shows the case where the matrix head is normally attached, and the right figure shows the case where the matrix head is attached by rotating counterclockwise within the paper surface. In FIG. 13, reference numeral 210 denotes a nozzle, and reference numeral 212 denotes a pressure chamber corresponding to each nozzle.

  The pressure chambers 212 corresponding to the respective nozzles 210 communicate with a common flow path (not shown) for supplying ink via individual supply ports (not shown). The chamber 212 is filled with ink. Each pressure chamber 212 is provided with a pressure generating element (not shown) (for example, a piezoelectric element), and ink droplets can be ejected from the nozzle 210 by driving and controlling the pressure generating element in accordance with print data. it can. By controlling the ink ejection timing of each nozzle 210 while conveying the recording medium, a desired image can be recorded on the recording medium.

  As shown in the left diagram of FIG. 13, when the matrix head is normally mounted, the dots recorded on the recording medium are aligned so as to be arranged at equal intervals along the main scanning direction. On the other hand, as shown in the right diagram of FIG. 13, when the matrix head is mounted by rotating counterclockwise on the paper surface, the dot interval of the folded portion of the matrix arrangement is significantly larger than the others. (Denoted as B1 in the figure). Therefore, uneven stripes occur in the folding unit of the matrix array. In the following description, a set of nozzles in the matrix unit in the matrix arrangement (nozzle group indicated by C in the figure) is referred to as a “nozzle block”.

[2] Unevenness generated at the joint of short heads When forming a line head by connecting a plurality of short head modules (short heads), if the joint between the short heads is misaligned, adjacent dots are ejected. As a result, the pitch of the nozzles to be shifted is shifted, and uneven stripes occur at the joints of the short heads (hereinafter, this uneven stripe is referred to as “short head connection unevenness”). This phenomenon will be described with reference to FIG.

The upper diagram of FIG. 14 shows a case where the short heads 221 and 222 are normally mounted. At this time, the dots recorded on the recording medium are aligned so as to be arranged at equal intervals along the main scanning direction. . On the other hand, the lower figure shows a case where the short heads 221 and 222 are attached so as to be displaced from each other (in the figure, the right short head is shifted to the right from the normal mounting position). At this time, the dot interval at the connecting portion of the short head is remarkably open compared to the others (denoted as B2 in the figure). Therefore, uneven stripes occur in the unit of connecting short heads.

  Next, consider the cause of the dot displacement from the desired position. The cause of the positional deviation of the dots is an error inherent to the nozzle in addition to the error due to the mounting failure of the head as described above. The error inherent to the nozzle is due to dirt in the vicinity of the nozzle (non-uniform liquid repellency) or defective manufacturing of the nozzle part, and as a result, the liquid droplets discharged from each nozzle are in the desired direction (usually normal) Will deviate from the direction perpendicular to the nozzle surface. These errors are usually considered to occur independently at each nozzle (ie, there is no correlation between different nozzles).

  In addition, the error inherent to the nozzle includes an error that does not cause a deviation in the ejection direction (for example, an error that the nozzle hole has been opened from a desired position in the manufacturing stage). Most of this does not happen, and the error inherent in the nozzle is mainly the error in the ejection direction deviation. Therefore, in the following, only the error in the ejection direction deviation of the nozzle itself will be considered as the nozzle-specific error.

  In Patent Documents 1 and 2 described above, the amount of head mounting deviation is estimated by actually performing a test print, but this separates the error due to the head mounting failure and the error inherent to the nozzle. This is not sufficient when the head position is precisely adjusted by the test pattern.

  In particular, in order to prevent “matrix folding unevenness” and “short head joining unevenness”, when trying to adjust the head position using a test pattern, the amount of dot misalignment to be measured is on the order of several μm. It becomes equal to the order of the position error specific to the nozzle. For this reason, it is difficult to correctly evaluate the adjustment amount (correction amount) of the head position from the value of the measured positional deviation of the dots.

  The present invention has been made in view of such circumstances, and the cause of the droplet ejection position error is divided into that due to defective mounting of the head and the like and an error inherent to the nozzle (due to deviation in the ejection direction of the nozzle itself). It is an object of the present invention to provide a droplet ejection position error adjustment method, droplet ejection control method, and image forming apparatus that enable more accurate droplet ejection position adjustment (correction).

In order to achieve the above object, according to the method for adjusting a droplet ejection position error according to the present invention, the liquid ejection head in which a plurality of droplet ejection openings are formed and a recording medium are moved relative to each other in a first direction. performs ejection of a droplet from the ejection head, wherein the droplet deposition step of on a recording medium attaching the droplets, the droplet ejection results obtained with the droplet ejection process, the first on the recording surface of the recording medium a droplet deposition position error measuring step of obtaining a droplet deposition position error amount with respect to an ideal droplet ejection position in the second direction is a direction perpendicular to the direction of the second direction of the droplets discharged from the droplet discharge port From the ejection direction measurement step for measuring the ejection direction and the droplet ejection position error amount obtained in the droplet ejection position error measurement step, information on the ejection direction obtained in the ejection direction measurement step is used . with respect to the direction, the phase of the recording medium and the liquid ejection head An error factor separation step of separating a first error component resulting from a defective placement and a second error component resulting from a defective ejection direction of the droplet ejection port, and the separated first and The liquid ejecting head and the liquid ejection head are configured to acquire error information of at least the first error component of the second error component, and correct the error of the first error component based on the acquired error information. The relative arrangement of the recording medium is adjusted.

Droplet ejection control method according to the present invention, while relatively moving the recording medium with a plurality of droplet ejection ports liquid discharge head is formed in a first direction, performs discharge of liquid droplets from the liquid ejection head, wherein A droplet ejection process for attaching droplets on the recording medium, and a second direction that is a direction perpendicular to the first direction on the recording surface of the recording medium based on the droplet ejection result obtained in the droplet ejection process A droplet ejection position error measuring step for obtaining a droplet ejection position error amount with respect to the ideal droplet ejection position, and a discharge direction measuring step for measuring the ejection direction in the second direction of the droplets ejected from the droplet ejection port; The liquid ejection head and the recording medium with respect to the second direction using the ejection direction error information obtained in the ejection direction measurement step from the droplet ejection position error amount obtained in the droplet ejection position error measurement step First error component due to relative placement failure of And an error factor separation step for separating the second error component due to the ejection direction defect of the droplet ejection port, and obtaining error information of the separated second error component The droplet ejection by the liquid ejection head is controlled based on error information so as to reduce the visibility of uneven stripes on the recorded image caused by the error of the second error component.

An image forming apparatus according to the present invention includes a liquid discharge head in which a plurality of liquid droplet discharge ports are formed, and droplets from the liquid discharge head while relatively moving the liquid discharge head and the recording medium in a first direction. for discharge was, the the droplet ejection control means for controlling the deposition of liquid droplets on a recording medium, reads the position of the dots printed on the recording medium, ideal droplet deposition position on the recording surface of the recording medium A droplet ejection position error measuring unit that measures a droplet ejection position error amount, a discharge direction measuring unit that measures a discharge direction of the second direction of a droplet ejected from the droplet ejection port, and the droplet ejection position error Relative arrangement of the liquid ejection head and the recording medium with respect to the second direction by using information on the ejection direction obtained by the ejection direction measurement unit from the droplet ejection position error amount obtained by the measurement unit First due to defects Based on the error factor separation means for separating the difference component and the second error component due to the ejection direction defect of the droplet ejection port, and the error information of the first error component separated by the error factor separation means. The adjustment amount calculation means for calculating the adjustment amount of the relative arrangement of the liquid ejection head and the recording medium, which is necessary for correcting the error of the first error component, and the adjustment amount calculation means. And a position adjusting means for adjusting the relative arrangement of the liquid ejection head and the recording medium according to the adjustment amount.

An image forming apparatus according to another aspect of the present invention includes a liquid discharge head having a plurality of droplet discharge ports, and the liquid discharge head while relatively moving the liquid discharge head and the recording medium in a first direction. by ejecting droplets from the a droplet ejection control means for controlling the deposition of liquid droplets on a recording medium, it reads the position of the dots printed on the recording medium, ideal on the recording surface of the recording medium A droplet ejection position error measuring unit that measures a droplet ejection position error amount with respect to a droplet ejection position, a discharge direction measuring unit that measures a discharge direction of the second direction of a droplet discharged from the droplet discharge port, The liquid ejection head and the recording medium with respect to the second direction using the ejection direction error information obtained by the ejection direction measurement means from the droplet ejection position error amount obtained by the droplet ejection position error measurement means Due to poor relative placement of Error factor separating means for separating the first error component and the second error component resulting from the defective ejection direction of the droplet discharge port, and the second error component separated by the error factor separating means. Droplet placement determining means for determining the droplet placement by the liquid ejection head based on error information so as to reduce the visibility of uneven stripes on the recorded image due to the error of the second error component. It is characterized by having.

  The present specification also discloses the following invention.

  According to a first aspect of the present invention, there is provided a droplet ejection position error measuring method in which a droplet is ejected from a liquid ejection head in which a plurality of droplet ejection ports are formed, and the droplet is deposited on a recording medium. From the droplet ejection results obtained in the droplet ejection process, the droplet ejection position error measurement step for measuring the droplet ejection position error amount relative to the ideal droplet ejection position on the recording surface of the recording medium, and the measured droplet ejection position error amount An error factor separation step for separating a first error component caused by a relative arrangement failure between the liquid discharge head and the recording medium and a second error component caused by a discharge direction failure of the droplet discharge port; And error information of at least one of the first and second error components is acquired.

  According to the present invention, the actual droplet ejection position on the recording medium is grasped from the droplet ejection result on the recording medium, and an error (droplet ejection position error) from the ideal droplet ejection position is specified. The error measured at this time includes a first error component caused by a relative disposition of the head and the recording medium, and a second error component caused by a defective ejection direction unique to the nozzle (droplet ejection port). It is included. Therefore, it is possible to separate a first error component and a second error component by performing a plurality of measurements, detections, and the like under different conditions, and combining these pieces of information, and to evaluate an error due to each factor.

  By using the error value for each factor obtained in this way, it is possible to effectively perform adjustment for correcting the relative disposition of the head and the recording medium, and correction for suppressing deterioration in image quality due to defective ejection direction. It becomes possible.

  Examples of the relative arrangement failure between the liquid discharge head and the recording medium include, for example, a head mounting position failure (mounting failure), a skew / meandering due to a transfer failure of the recording medium transfer system (transfer device improper installation), and the like. .

  For the measurement of the droplet ejection position error, a print detection means (for example, a CCD scanner) having an image sensor (an image sensor such as a line sensor or an area sensor) for imaging the print result of the test print (or practical print) is used. Can be used. The test pattern is read by the print detection means, and the obtained image signal is analyzed (processed) to obtain the amount of deviation from the ideal droplet ejection position.

  The recording medium at the time of measurement is preferably a medium with a low degree of bleeding (for example, a medium having a porous image receiving layer, an inkjet-dedicated photographic paper, etc.). By using such a medium, a clean dot shape is reproduced on the medium, so that the measurement accuracy of the position error increases.

  Alternatively, a mode in which the conveyance belt itself for holding and conveying the recording medium is also used as the medium is possible. That is, a mode in which the test pattern is directly printed on the conveyance belt is also possible. In this case, in addition to the advantage that a useless medium is not consumed, there are also the following advantages.

  In the mode of printing the test pattern on the conveyance belt, the droplet ejection distance is the longest, and hence the amount of droplet ejection position deviation due to oblique flight is large (when a test printing medium is placed on the conveyance belt, Since the flight distance is shortened by the thickness, the distance between the ejection surface and the medium is maximized when printing on a transport belt on which nothing is placed. Therefore, it is easy to measure the droplet ejection position error in the print detection unit. In the case where the print detection means is mounted at a predetermined position of the apparatus, the observation distance by the sensor of the print detection means is a fixed value (the distance between the sensor and the belt is a fixed value). The depth of focus may be shallow.

  For the measurement of the distance between the nozzle surface and the medium, for example, a distance measuring unit that performs distance measurement using a pulse laser can be used. Further, the thickness information of the medium may be given from the user interface.

  A second aspect of the present invention is an aspect of the method for measuring a droplet ejection position error according to the first aspect of the invention, and the first recording medium located at the first distance from the ejection surface of the liquid ejection head in which a plurality of droplet ejection openings are formed. On the other hand, from the first droplet ejection step of ejecting droplets from the liquid ejection head and depositing the droplets on the first recording medium, and the droplet ejection results obtained in the first droplet ejection step, What is the first droplet ejection position error measurement step for measuring the first droplet ejection position error amount with respect to the ideal droplet ejection position on the recording surface of the first recording medium, and the first distance from the ejection surface? A second droplet ejecting step of ejecting droplets from the liquid ejection head to a second recording medium at a different second distance, and depositing the droplets on the second recording medium; From the droplet ejection results obtained in the droplet ejection process of No. 2, the ideal droplet ejection position on the recording surface of the second recording medium From the second recording position error measurement step for measuring the second droplet ejection position error amount, and the first and second droplet ejection position error amounts measured in the first and second recording position error measurement steps, An operation for separating a first error component caused by a relative arrangement failure between the liquid discharge head and the first and second recording media, and a second error component caused by a discharge direction failure of the droplet discharge port. An error factor separation step of performing at least one of the first and second error components, and acquiring error information of at least one of the first and second error components.

  By performing droplet ejection a plurality of times while changing the distance between the ejection surface of the liquid ejection head and the recording surface, the error factor can be easily separated from the droplet ejection results.

  Invention 3 is an aspect of a method for measuring a droplet ejection position error according to Invention 1, in which droplets are ejected from a liquid ejection head in which a plurality of droplet ejection openings are formed, and the droplets are deposited on a recording medium. A droplet ejection step, a droplet ejection position error measurement step for obtaining a droplet ejection position error amount with respect to an ideal droplet ejection position on the recording surface of the recording medium from a droplet ejection result obtained in the droplet ejection step, and the droplet From the ejection direction measurement step for measuring the ejection direction of the droplets ejected from the ejection port and the droplet ejection position error amount obtained in the droplet ejection position error measurement step, information on the ejection direction obtained in the ejection direction measurement step is obtained. Utilizing the error factor separation, the first error component caused by the relative disposition of the liquid ejection head and the recording medium is separated from the second error component caused by the ejection direction defect of the droplet ejection port. And including a first error component and a second error component. And obtaining at least one of error information.

  According to the third aspect of the present invention, the actual droplet ejection position on the recording medium is grasped from the droplet ejection result on the recording medium, and an error (droplet ejection position error) from the ideal droplet ejection position is specified. The error measured at this time includes a first error component caused by a relative disposition of the head and the recording medium, and a second error component caused by a defective ejection direction unique to the nozzle (droplet ejection port). It is included. By observing the state of droplets being ejected from the droplet ejection port, etc., by grasping the droplet ejection direction (flying direction), it is due to the ejection direction defect of the droplet ejection port from the ejection angle A droplet ejection position error (second error component) can be specified. Therefore, based on the information on the second error component and the information on the droplet deposition position error (error with respect to the ideal droplet deposition position) measured from the droplet ejection result, the relative disposition of the liquid ejection head and the recording medium is caused. The resulting first error component can be identified.

  The invention which concerns on invention 4 provides the adjustment method of the droplet deposition position error for achieving the said objective. That is, the droplet ejection position error adjustment method according to the invention 4 obtains error information of the first error component according to the recording position error measurement method according to any one of the inventions 1 to 3, The relative arrangement of the liquid ejection head and the recording medium is adjusted so as to correct the error of the first error component based on the acquired error information.

  For example, the head mounting position is adjusted for poor head mounting, and the position of the transport device is adjusted for transport failure in the recording medium transport system. Thereby, the error due to the relative arrangement failure can be corrected appropriately.

  The invention which concerns on the invention 5 provides the droplet ejection control method which achieves the said objective. That is, the droplet ejection control method according to the fifth aspect of the present invention obtains the error information of the second error component according to the droplet ejection position error measurement method according to any one of the first to third aspects, and obtains this error information. The droplet ejection by the liquid ejection head is controlled based on error information so as to reduce the visibility of uneven stripes on the recorded image caused by the error of the second error component.

  By correctly grasping the component of the droplet ejection position error (second error component) caused by defective ejection direction and correcting the droplet ejection arrangement (dot arrangement) from the viewpoint of suppressing the occurrence of unevenness caused by such factors, Quality image formation can be realized.

  For example, based on the information on the second error component, the image data is corrected from the viewpoint of suppressing the occurrence of unevenness due to the second error component, and halftone processing (halftoning is performed on the corrected data. Process) to obtain droplet placement (dot placement) data. Further, by controlling droplet ejection by the liquid ejection head according to the droplet ejection arrangement data, good image formation is possible.

  The invention according to a sixth aspect provides an image forming apparatus that achieves the above object. That is, an image forming apparatus according to a sixth aspect of the present invention performs a control for controlling a liquid discharge head in which a plurality of liquid droplet discharge ports are formed and a liquid droplet to be discharged from the liquid discharge head and attached to a recording medium. A droplet control unit, a droplet ejection position error measurement unit that reads a position of a dot recorded on the recording medium, and measures a droplet ejection position error amount with respect to an ideal droplet ejection position on the recording surface of the recording medium; From the droplet ejection position error amount obtained by the droplet ejection position error measuring means, the first error component caused by the relative disposition of the liquid ejection head and the recording medium and the ejection direction defect of the droplet ejection port are determined. Based on the error information of the first error component separated by the error factor separation means and error factor separation means for separating the second error component caused by the error, the error of the first error component is corrected. Necessary for the liquid discharge Adjustment amount calculating means for calculating the adjustment amount of the relative arrangement of the print head and the recording medium, and adjusting the relative arrangement of the liquid ejection head and the recording medium according to the adjustment amount calculated by the adjustment amount calculation means. And a position adjusting means.

An image forming apparatus according to a seventh aspect of the invention includes a liquid discharge head in which a plurality of liquid droplet discharge ports are formed, and a control for discharging droplets from the liquid discharge head and attaching the droplets onto a recording medium. A droplet control unit; a recording position error measuring unit that reads a position of a dot recorded on the recording medium and measures an amount of droplet ejection position error with respect to an ideal droplet ejection position on the recording surface of the recording medium; From the droplet ejection position error amount obtained by the droplet position error measuring means, the first error component caused by the relative disposition of the liquid ejection head and the recording medium, and the ejection direction defect of the droplet ejection port Error factor separation means for separating the second error component to be recorded, and recording caused by the error of the second error component based on the error information of the second error component separated by the error factor separation means Visibility of stripes on images As reduced, characterized in that and a droplet deposition arrangement determining means for determining the droplet deposition arrangement according to the liquid ejection head.

  An invention according to an eighth aspect is an aspect of the image forming apparatus according to the sixth or seventh aspect, and includes a discharge direction measuring unit that measures a discharge direction of a droplet discharged from the droplet discharge port, and the error factor The separating means uses the information on the ejection direction obtained by the ejection direction measuring means from the recording position error amount measured by the recording position error measuring means, and uses the first error component and the second error. An operation for separating the components is performed.

  An ink jet recording apparatus as one aspect of an image forming apparatus according to inventions 6 to 8 includes a nozzle for discharging ink droplets for forming dots and a pressure generating means (such as a piezoelectric element or a heating element) for generating discharge pressure. A liquid ejection head (recording head) having a liquid droplet ejection element array in which a plurality of liquid droplet ejection elements are arranged, and droplet ejection from the recording head based on droplet ejection arrangement data generated from image data An ejection control means, and an image is formed on a recording medium by droplets ejected from the nozzle.

  As a configuration example of the recording head, a full line type head in which a plurality of nozzles are arranged over a length corresponding to the entire width of the recording medium can be used. In this case, a combination of a plurality of relatively short recording head modules having nozzle rows that are less than the length corresponding to the entire width of the recording medium, and connecting them together, the nozzle having a length corresponding to the entire width of the recording medium as a whole. There is an aspect that constitutes a column.

  A full-line type head is usually arranged along a direction perpendicular to the relative feeding direction (relative conveyance direction) of the recording medium, but has a certain angle with respect to the direction perpendicular to the conveyance direction. There may be a mode in which the recording head is arranged along the oblique direction.

  The “recording medium” is a medium to which liquid ejected from a liquid ejection head (recording head) adheres, and receives an image recording by the action of the recording head. That is, the “recording medium” can be called a printing medium, an image forming medium, a recording medium, an image receiving medium, an ejected medium, and the like, a continuous sheet, a cut sheet, a seal sheet, a resin sheet such as an OHP sheet, Various media are included regardless of the material and shape, such as a printed board on which a film, cloth, wiring pattern, or the like is formed, an intermediate transfer medium, and the like.

  “Conveyance means” means a mode in which the recording medium is transported to a stopped (fixed) recording head, a mode in which the recording head is moved relative to the stopped recording medium, or a movement of both the recording head and the recording medium Any of the embodiments are included.

  When a color image is formed by an inkjet head, a recording head may be arranged for each color of a plurality of colors (recording liquids), or a configuration in which a plurality of colors of ink can be discharged from one recording head may be adopted. .

  The present invention is not limited to the full-line head described above, but can also be applied to shuttle scan type recording heads (recording heads that perform droplet ejection while reciprocating in a direction substantially perpendicular to the recording medium conveyance direction). It is.

  According to the present invention, the first error component due to the relative disposition of the liquid discharge head and the recording medium is separated from the second error component due to the discharge direction defect of the droplet discharge port, Error information corresponding to the factor can be acquired. As a result, appropriate apparatus adjustment and droplet ejection control can be realized, and high-quality image formation can be achieved.

The figure which illustrated droplet ejection position deviation | shift amount (DELTA) X from the ideal position for every nozzle block in a matrix head The figure which illustrated droplet deposition position deviation | shift amount (DELTA) X from the ideal position in the head structure which connected the short head. Schematic diagram showing a correction example of droplet placement that reduces the visibility of uneven stripes 1 is a diagram illustrating the overall composition of an ink jet recording apparatus showing a first embodiment of an image forming apparatus according to the present invention; FIG. 4 is a plan view of the main part around the printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing structural example of head Enlarged view of the main part of Fig. 6 (a) Plane perspective view showing another structure example of a full-line head Sectional drawing which follows the 7-7 line in Drawing 6 (a) The enlarged view which shows the nozzle arrangement of the head shown to Fig.6 (a) 1 is a principal block diagram showing a system configuration of an ink jet recording apparatus according to a first embodiment. 7 is a flowchart showing a control procedure when measuring a droplet ejection position error in the ink jet recording apparatus according to the first embodiment. FIG. 5 is a block diagram of a main part showing a system configuration of an ink jet recording apparatus according to a second embodiment of the present invention. 7 is a flowchart showing a control procedure when measuring a droplet ejection position error in the ink jet recording apparatus according to the second embodiment. Schematic diagram used to explain the phenomenon in which a droplet ejection position error occurs due to a defective mounting angle of the matrix head Schematic diagram used to explain the phenomenon in which the droplet ejection position error occurs due to a short head mounting position failure

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Principle of measurement]
First, the principle of measurement of the droplet deposition position error according to the embodiment of the present invention will be described. In the following description, the ideal position in the main scanning direction of dots recorded on the recording medium is X0, and the actual position is X. Further, assuming that the error due to head mounting failure is δXH, and the error due to deviation in the ejection direction of the nozzle itself is δXD, the following equation is assumed.

X = X0 + .delta.XH + .delta.XD [Formula 1]
For convenience of calculation, ΔX = X−X0.

  As a measurement procedure, first, a predetermined test pattern is printed. The test pattern to be printed may be one dot from each nozzle. However, since the position error in the main scanning direction is a problem as described above, a dot row parallel to the sub-scanning direction by continuous ejection from each nozzle. (Line) may be formed.

  Next, the position X of the dot ejected with the test pattern is measured by an image reading device such as a scanner. Examples of graphs showing the relationship between the ideal droplet ejection position (corresponding to the “ideal droplet ejection position”) X0 of the droplets ejected from each nozzle and the error ΔX are shown in FIGS.

  FIG. 1 shows ΔX calculated when two nozzle blocks (each nozzle block has 49 nozzles) are tilted by 0.02 degrees in the matrix head. If there is no deviation in the ejection direction of the nozzle itself, ΔX becomes a straight line having a certain inclination for each nozzle block (FIG. 1A). However, in actuality, there is a deviation in the ejection direction of the nozzle itself, and δXD is different for each nozzle, so ΔX is as shown in FIG. It is difficult to calculate an accurate head adjustment amount from the result of ΔX as shown in FIG.

  FIG. 2 shows a line head constituted by connecting a plurality of short heads (here, the short head 1 and the short head 2). The short head 1 is mounted with a shift of +4 μm from the ideal position in the main scanning direction. ΔX is calculated when the head 2 is mounted with a deviation of −2.5 μm in the main scanning direction.

  If there is no deviation in the ejection direction of the nozzle itself, ΔX has a constant value for each short head (FIG. 2A). However, since there is actually a deviation in the ejection direction of the nozzle itself and δXD is different for each nozzle, ΔX is as shown in FIG. 2B. In this case as well, it is difficult to calculate an accurate head adjustment amount. is there.

  Therefore, in the present embodiment, processing for separating δXD and δXH from the error ΔX is performed. Hereinafter, an example of a method for calculating δXD and δXH will be described.

  [Calculation method 1] The test pattern (second time) is set so that the distance from the nozzle to the recording medium is k times (where k> 0 and k ≠ 1) as compared with the above (first time) test pattern ejection. ). The position X ′ of the dots ejected by the second test pattern is measured by an image reading device such as a scanner. The dot position X ′ at this time is represented by the following equation.

X ′ = X0 + δXH + k × δXD [Formula 2]
That is, the error δXH due to the head mounting failure does not change, but the error due to the ejection direction deviation becomes k times.

  ΔXH and δXD are obtained from the above [Expression 1] and [Expression 2], and the rotation angle of the head or the shift amount of the joint portion (that is, the adjustment amount of the head) is calculated based on the derived δXH.

  The head position is adjusted according to the value of the adjustment amount thus obtained. As a means for adjusting the position of the head, for example, in the case of a matrix head, a rotational movement mechanism is provided. In the case of a configuration in which short heads are connected, an inter-head distance moving mechanism that varies the distance between the short heads is provided.

  The specific structure of these moving mechanisms is not particularly limited, and a known configuration that achieves a target movable function can be applied. In the case of a line head configured by connecting short heads in a matrix arrangement, a configuration including both a rotational movement mechanism and a movement mechanism that varies the distance between the short heads is preferable. In this case, it is a preferable adjustment procedure to adjust the rotation after first adjusting the position (shift amount) between the short heads.

  [Calculation Method 2] Since δXD is due to the displacement of the discharge angle, the discharge state is photographed with a high-speed camera or the like, and the image is analyzed to calculate the displacement amount of the discharge angle. From this calculated value (displacement amount of the discharge angle) and the distance from the nozzle to the recording medium, δXD can be calculated, and δXH can be calculated from this δXD and the above [Equation 1].

  Next, an example of a correction method for the error δXD due to the ejection direction deviation will be described.

  Consider the error δXD specific to each nozzle. In particular, if there is a deviation in the flight direction in the main scanning direction, stripes parallel to the sub-scanning direction are generated, which causes a significant deterioration in image quality. In the following, a method for preventing this unevenness by changing the droplet ejection rate of each nozzle will be described. An example is shown below.

  FIG. 3 is a schematic diagram of the droplet ejection arrangement when the nozzle pitch (density) is 1200 npi (nozzle per inch). The nozzles may be arranged in a matrix structure, but in this example, the nozzles are schematically shown as an array in a row as illustrated.

  In FIG. 3A, the nozzles nz3 and nz4 have deviations in the ejection direction and have droplet ejection position errors (landing position deviations) of −5 μm and +5 μm in the main scanning direction on the recording surface, respectively (however, In the figure, the right direction is positive). For this reason, white stripes are present between the nozzles nz3 and nz4 (area indicated by B in the figure).

  FIG. 3B shows the corrected white stripe. That is, in order to reduce the visibility of white stripes generated between the nozzles nz3 and nz4 (the region indicated by the symbol B in FIG. 3A), the dots ejected from the nozzles nz3 and nz4 in FIG. Are increased one by one and at the same time, the dots from the adjacent nozzles nz2 and nz5 are decreased one by one. In the figure, dots indicated by symbols α1 and α2 are added dots, and white dot circles indicated by symbols β1 and β2 are reduced (recording is omitted).

  By correcting the droplet placement in this way, it is possible to reduce the visibility of white stripes while maintaining the average density value.

  In carrying out the present invention, the method for correcting the droplet placement using the information on the droplet deposition position error is not limited to the above example, and various methods including known methods can be used. .

[Configuration of inkjet recording apparatus]
Next, an ink jet recording apparatus as a specific example of the image forming apparatus according to the present invention will be described.

  FIG. 4 is an overall configuration diagram of the ink jet recording apparatus showing the first embodiment of the image forming apparatus according to the present invention. As shown in the figure, the ink jet recording apparatus 110 includes a plurality of ink jet recording heads (hereinafter referred to as “ink jet recording heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 112 having 112K, 112C, 112M, and 112Y, an ink storage / loading unit 114 that stores ink to be supplied to each of the heads 112K, 112C, 112M, and 112Y, and recording paper as a recording medium The paper feeding unit 118 that supplies the paper 116, the decurling unit 120 that removes curl of the recording paper 116, and the nozzle surface (ink ejection surface) of the printing unit 112 are disposed so as to improve the flatness of the recording paper 116. By the belt conveyance unit 122 that conveys the recording paper 116 while being held, the distance measurement unit 123 that measures the distance to the recording surface, and the printing unit 112 A print determination unit 124 which reads the characters results, and a paper output unit 126 for discharging the recorded recording paper (printed matter) to the outside.

  The ink storage / loading unit 114 includes ink tanks that store inks of colors corresponding to the heads 112K, 112C, 112M, and 112Y, and the tanks are connected to the heads 112K, 112C, 112M, and 112Y via a required pipe line. Communicated with. Further, the ink storage / loading unit 114 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In FIG. 4, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 118, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When a plurality of types of recording media (media) can be used, an information recording body such as a barcode or a wireless tag that records media type information is attached to a magazine, and information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of recording medium to be used (media type) and to perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The recording paper 116 delivered from the paper supply unit 118 retains curl due to having been loaded in the magazine. In order to remove this curl, the decurling unit 120 applies heat to the recording paper 116 by the heating drum 130 in the direction opposite to the curl direction of the magazine. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration using roll paper, a cutter (first cutter) 128 is provided as shown in FIG. 4, and the roll paper is cut into a desired size by the cutter 128. Note that the cutter 128 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 116 is sent to the belt conveyance unit 122. The belt conveyance unit 122 has a structure in which an endless belt (corresponding to a conveyance belt) 133 is wound between rollers 131 and 132, and faces at least the nozzle surface of the printing unit 112 and the sensor surface of the printing detection unit 124. The portion to be formed is a horizontal surface (flat surface).

  The belt 133 has a width that is greater than the width of the recording paper 116, and a plurality of suction holes (not shown) are formed on the belt surface. Further, in the case of a configuration in which a test pattern for measuring the amount of droplet ejection position deviation is directly recorded on the belt 133, a test pattern printing area is provided on the belt 133.

  As shown in FIG. 4, an adsorption chamber 134 is provided at a position facing the nozzle surface of the printing unit 112 and the sensor surface of the printing detection unit 124 inside the belt 133 spanned between the rollers 131 and 132. The recording paper 116 is sucked and held on the belt 133 by sucking the suction chamber 134 with a fan 135 to a negative pressure. In place of the suction adsorption method, an electrostatic adsorption method may be adopted.

  When the power of the motor (reference numeral 188 in FIG. 9) is transmitted to at least one of the rollers 131 and 132 around which the belt 133 is wound, the belt 133 is driven in the clockwise direction in FIG. The held recording paper 116 is conveyed from left to right in FIG.

  When a test pattern for measuring the amount of droplet ejection position deviation is printed on a predetermined area (test pattern printing area) on the belt 133 or a borderless print is printed, the ink also adheres to the belt 133. As a cleaning unit for the belt 133, a belt cleaning unit 136 is provided at a predetermined position other than the printing area.

  In the example of FIG. 4, a belt cleaning unit 136 is disposed at a subsequent stage of the print detection unit 124 and in front of the conveyance roller 137. Although details of the configuration of the belt cleaning unit 136 are not illustrated, for example, there are a method of niping a brush roll, a water absorption roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism in place of the belt conveyance unit 122 is also conceivable, if the roller / nip conveyance is performed in the printing area, the image is likely to blur because the roller contacts the printing surface of the sheet immediately after printing. There's a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 140 is provided on the upstream side of the printing unit 112 on the paper conveyance path formed by the belt conveyance unit 122. The heating fan 140 heats the recording paper 116 by blowing heated air onto the recording paper 116 before printing. Heating the recording paper 116 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 112K, 112C, 112M, and 112Y of the printing unit 112 has a length corresponding to the maximum paper width of the recording paper 116 targeted by the inkjet recording device 110, and the nozzle surface has a recording medium of the maximum size. The head is a full-line type in which a plurality of nozzles for ejecting ink are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 5).

  The heads 112K, 112C, 112M, and 112Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 116. 112K, 112C, 112M, and 112Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 116.

  A color image can be formed on the recording paper 116 by discharging different colors of ink from the heads 112K, 112C, 112M, and 112Y while the recording paper 116 is being conveyed by the belt conveyance unit 122.

  As described above, according to the configuration in which the full-line heads 112K, 112C, 112M, and 112Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 116 and the printing unit in the paper feeding direction (sub-scanning direction). An image can be recorded on the entire surface of the recording paper 116 by performing the operation of relatively moving the 112 once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited.

  The distance measuring unit 123 shown in FIG. 4 is means for measuring the distance to the recording surface with a pulse laser, and obtains distance information between the nozzle surfaces of the heads 112K, 112C, 112M, and 112Y and the recording surface from the measurement result. . As a means for specifying the distance between the ejection surface and the recording surface (distance specifying means), a measuring means for actually measuring the distance may be used, or a means for acquiring information on the thickness of the recording medium used. It may be used. As a means for acquiring information on the thickness of the recording medium, in addition to means for actually measuring the thickness, a mode in which the thickness information is input using a user interface, a container (magazine, cassette) containing the recording medium is used. And the like may be read from the information recording unit attached to the above.

  Means for varying the distance between the nozzle surface and the recording surface include the presence or absence of a recording medium (recording paper 116) or the use of a recording medium (recording paper 116) having a different thickness, as well as the heads 112K, 112C, and 112M. , 112Y is provided with a head moving means (moving means for moving the heads 112K, 112C, 112M, 112Y up and down in the case of FIG. 4) that moves the head 112K closer to or away from the medium support surface 122A of the belt conveyance unit 122. Alternatively, belt conveying unit moving means (FIG. 5) moves the belt conveying unit 122 so that the medium support surface 122A of the belt conveying unit 122 approaches or moves away from the nozzle surfaces of the heads 112K, 112C, 112M, and 112Y. 4 is provided with a moving means for moving the belt conveyance unit 122 up and down, or an appropriate combination thereof. That.

  The print detection unit 124 includes an image sensor (line sensor or area sensor) for imaging the droplet ejection result of the print unit 112, and nozzle clogging, droplet ejection position error, etc. from the droplet ejection image read by the image sensor. It functions as a means for checking the discharge characteristics. Test patterns or practical images printed by the heads 112K, 112C, 112M, and 112Y of the respective colors are read by the print detection unit 124, and ejection determination of each head is performed. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position (droplet ejection position), and the like.

  The printed matter recorded by the printing unit 112 is discharged from the paper discharge unit 126. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 110 is provided with a sorting means (not shown) that switches the paper discharge path in order to select the prints of the main image and the prints of the test print and send them to the discharge units 126A and 126B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by the cutter (second cutter) 148. Although not shown in FIG. 4, the paper output unit 126A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the respective heads 112K, 112C, 112M, and 112Y for each color are common, the heads are represented by reference numeral 150 in the following.

  6A is a plan perspective view showing an example of the structure of the head 150, and FIG. 6B is an enlarged view of a part thereof. FIG. 6C is a plan perspective view showing another example of the structure of the head 150, and FIG. 7 shows a three-dimensional configuration of a droplet discharge element for one channel (an ink chamber unit corresponding to one nozzle 151). It is sectional drawing (sectional drawing in alignment with line 7-7 in Fig.6 (a)).

  In order to increase the dot pitch printed on the recording paper 116, it is necessary to increase the nozzle pitch in the head 150. As shown in FIGS. 6A and 6B, the head 150 of this example includes a plurality of ink chamber units (liquid chambers) including nozzles 151 that are ink discharge ports, pressure chambers 152 corresponding to the nozzles 151, and the like. Droplet ejecting elements) 153 are arranged in a zigzag matrix (two-dimensionally), and thus are projected so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density of nozzle spacing (projection nozzle pitch) is achieved.

  The configuration in which one or more nozzle rows are formed over a length corresponding to the entire width of the recording paper 116 in a direction substantially orthogonal to the feeding direction of the recording paper 116 is not limited to this example. For example, instead of the configuration of FIG. 6 (a), as shown in FIG. 6 (c), short head modules 150 ′ in which a plurality of nozzles 151 are two-dimensionally arranged are arranged in a staggered manner and connected. A line head having a nozzle row having a length corresponding to the entire width of the recording paper 116 may be configured.

  The pressure chamber 152 provided corresponding to each nozzle 151 has a substantially square planar shape (see FIGS. 6 (a) and 6 (b)), and the nozzle 151 is provided at one of the diagonal corners. An outlet for supplying ink (supply port) 154 is provided on the other side. The shape of the pressure chamber 152 is not limited to this example, and the planar shape may have various forms such as a quadrangle (rhombus, rectangle, etc.), a pentagon, a hexagon, other polygons, a circle, and an ellipse.

  As shown in FIG. 7, each pressure chamber 152 communicates with the common flow path 155 through the supply port 154. The common channel 155 communicates with an ink tank (not shown) as an ink supply source, and the ink supplied from the ink tank is distributed and supplied to each pressure chamber 152 via the common channel 155.

  An actuator 158 having an individual electrode 157 is joined to a pressure plate (vibrating plate also serving as a common electrode) 156 constituting a part of the pressure chamber 152 (the top surface in FIG. 7). By applying a driving voltage between the individual electrode 157 and the common electrode, the actuator 158 is deformed to change the volume of the pressure chamber 152, and ink is ejected from the nozzle 151 due to the pressure change accompanying this. For the actuator 158, a piezoelectric element using a piezoelectric body such as lead zirconate titanate or barium titanate is preferably used. When the displacement of the actuator 158 returns to its original state after ink ejection, new ink is refilled into the pressure chamber 152 from the common flow path 155 through the supply port 154.

  In addition, a liquid repellent layer 159 is provided on the nozzle surface 150A of the head 150 from the viewpoint of improving the discharge stability and the cleaning performance of the discharge surface (nozzle surface 150A). The method for imparting liquid repellency to the nozzle surface 150A (liquid repellent treatment method) is not particularly limited. For example, a method of applying a fluorine-based liquid repellent material or a liquid repellent such as fluorine-based polymer particles (PTFE). There is a method of depositing a material in vacuum and forming a thin layer on the surface.

By controlling the driving of the actuator 158 corresponding to each nozzle 151 in accordance with droplet ejection arrangement data generated from the input image, ink droplets can be ejected from the nozzles 151. As described with reference to FIG. 4, the recording paper 116 as a recording medium is conveyed in the sub-scanning direction at a constant speed, and the ink ejection timing of each nozzle 151 is controlled according to the conveyance speed. It is possible to record a desired image.

  As shown in FIG. 8, the ink chamber units 153 having the above-described structure are arranged in a constant arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern.

  That is, with a structure in which a plurality of ink chamber units 153 are arranged at a constant pitch d along the direction of an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 151 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction.

  When driving a nozzle with a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and the nozzles are sequentially driven from one side to the other for each block, etc., and one line (1 in the width direction of the paper (direction perpendicular to the paper conveyance direction)) Driving a nozzle that prints a line of dots in a row or a line consisting of dots in a plurality of rows is defined as main scanning.

  In particular, when driving the nozzles 151 arranged in a matrix as shown in FIG. 8, the main scanning as described in the above (3) is preferable. That is, nozzles 151-11, 151-12, 151-13, 151-14, 151-15, 151-16 are made into one block (other nozzles 151-21,..., 151-26 are made into one block, Nozzles 151-31,..., 151-36 as one block,..., And by sequentially driving the nozzles 151-11, 151-12,. One line is printed in the width direction of 116.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. This is defined as sub-scanning.

  The direction indicated by one line (or the longitudinal direction of the belt-like region) recorded by the main scanning is referred to as a main scanning direction, and the direction in which the sub scanning is performed is referred to as a sub scanning direction. In other words, in the present embodiment, the conveyance direction of the recording paper 116 is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In this embodiment, a method of ejecting ink droplets by deformation of an actuator 158 typified by a piezo element (piezoelectric element) is adopted. However, the method of ejecting ink is not particularly limited in implementing the present invention. Instead of the piezo jet method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Explanation of control system]
FIG. 9 is a block diagram showing a system configuration of the inkjet recording apparatus 110. As shown in the figure, the inkjet recording apparatus 110 includes a communication interface 170, a system controller 172, a nozzle surface-medium distance information acquisition unit 173, an image memory 174, a ROM 175, a motor driver 176, a heater driver 178, and a print control unit. 180, an image buffer memory 182, a head driver 184, a head position adjusting mechanism 185, and the like.

  The communication interface 170 is an interface unit (image input unit) that functions as an image input unit that receives image data sent from the host computer 186. As the communication interface 170, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 186 is taken into the inkjet recording apparatus 110 via the communication interface 170 and temporarily stored in the image memory 174. The image memory 174 is a storage unit that stores an image input via the communication interface 170, and data is read and written through the system controller 172. The image memory 174 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 172 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 110 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 172 controls the communication interface 170, the image memory 174, the motor driver 176, the heater driver 178, and the like, and performs communication control with the host computer 186, read / write control of the image memory 174 and ROM 175, and the like. At the same time, a control signal for controlling the motor 188 and the heater 189 of the transport system is generated.

  Further, the system controller 172 performs a calculation process for generating droplet ejection position error data from the distance information obtained from the nozzle surface-medium distance information acquisition unit 173 and the test pattern read data read from the print detection unit 124. A drop error measurement calculation unit 172A, a density correction coefficient calculation unit 172B that calculates a density correction coefficient from error component information (δXD) caused by a nozzle-specific ejection direction shift of the measured position error, and a measured position error And a head adjustment amount calculation unit 172C that calculates an adjustment amount of the head from information (δXH) of an error component caused by the head mounting deviation. The processing functions of the droplet ejection error measurement calculation unit 172A, the density correction coefficient calculation unit 172B, and the head adjustment amount calculation unit 172C can be realized by ASIC, software, or an appropriate combination.

  The density correction coefficient calculation unit 172B calculates a density correction coefficient from each δXD for each nozzle. The density correction coefficient data obtained by the density correction coefficient calculation unit 172B is stored in the density correction coefficient storage unit 190.

  Further, the head mounting position is adjusted by moving the head position adjustment mechanism 185 according to the value of the head adjustment amount obtained by the head adjustment amount calculation unit 172C. The head position adjustment mechanism 185 may be configured to be automatically controlled using an electric drive unit typified by a motor or the like, or the value of the head adjustment amount obtained by the head adjustment amount calculation unit 172C is not illustrated. A configuration in which the head mounting position is adjusted by manually operating the head position adjusting mechanism 185 based on the display on a display or the like is also possible.

  A method for obtaining the density correction coefficient from the value of δXD in the density correction coefficient calculation unit 172B and a method of obtaining the head adjustment amount from the value of δXH in the head adjustment amount calculation unit 172C are calculated using an arithmetic expression (correlation is shown). Function), or a lookup table or the like may be used.

  The nozzle surface-medium distance information acquisition unit 173 includes an aspect such as the distance measurement unit 123 described with reference to FIG. 4 or a user interface for the user to input the thickness information of the recording medium (recording paper 116).

  The ROM 175 stores programs executed by the CPU of the system controller 172 and various data necessary for control (for example, test pattern data for measuring droplet ejection position errors, equations necessary for calculating droplet ejection position deviation amounts, and lookups). Table). The ROM 175 may be a non-rewritable storage means. However, when updating the droplet ejection position error information, it is preferable to use a rewritable storage means such as an EEPROM. Further, by utilizing the storage area of the ROM 175, a configuration in which the ROM 175 is also used as the density correction coefficient storage unit 190 is possible.

  The image memory 174 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 176 is a driver (driving circuit) that drives the conveyance motor 188 in accordance with an instruction from the system controller 172. The heater driver 178 is a driver that drives the heater 189 such as a post-drying unit in accordance with an instruction from the system controller 172.

  In accordance with the control of the system controller 172, the print control unit 180 performs various processes, corrections, and the like for generating a droplet ejection control signal from image data (multi-value input image data) in the image memory 174. In addition to functioning as a signal processing unit, it functions as an ejection control unit that supplies the generated ink ejection data to the head driver 184 to control ejection driving of the head 150.

  That is, the print control unit 180 includes a density data generation unit 180A, a correction processing unit 180B, an ink ejection data generation unit 180C, and a drive waveform generation unit 180D. Each of these functional blocks (180A to 180D) can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit 180A is a signal processing unit that generates density data for each ink color from input image data, and performs density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion processing. Do.

  The correction processing unit 180B is a processing unit that performs density correction calculation using the density correction coefficient stored in the density correction coefficient storage unit 190.

  The ink ejection data generation unit 180C performs halftoning processing (intermediate gradation processing) for converting the corrected density data generated by the correction processing unit 180B into binary (or multivalued) droplet ejection arrangement data (dot data). Signal processing means including means.

  Here, an image processing flow in the print control unit 180 will be described. The data format of the input image is not particularly limited, and is, for example, 24-bit RGB data. The input image is subjected to density conversion processing using a lookup table, and converted to density data D (i, j) corresponding to the ink color of the printer. Note that (i, j) represents the position of the pixel, and density data is assigned to each pixel.

  In this example, it is assumed that the resolution of the input image matches the resolution of the printer (nozzle resolution). If they do not match, pixel number conversion processing is performed on the input image in accordance with the printer resolution.

  The density conversion process is a general process, and includes an undercolor removal (UCR) process or a process of distributing to light ink in a system using light ink (same color light ink).

  For example, in the case of a three-color ink configuration of C (cyan), M (magenta), and Y (yellow), it is converted into CMY density data D (i, j). Alternatively, in the case of a system including other inks such as K (black), LC (light cyan), and LM (light magenta) in addition to the above three colors, the density data D (i, j) including the ink color is included. Converted.

  The density data D (i, j) generation process is performed in the density data generation unit 180A shown in FIG.

  The correction processing unit 180B performs correction processing on the density data D (i, j) obtained through the above density conversion processing. Here, calculation is performed by multiplying the density data D (i, j) by the density correction coefficient (droplet ejection rate correction coefficient) di corresponding to the corresponding nozzle.

That is, the pixel position (i, j) on the image is specified by the position (main scanning direction position) i and the sub-scanning direction position j of the nozzle nzi, and density data D (i, j) is given for each pixel. When correction processing is performed for a nozzle that is responsible for droplet ejection in a neighboring pixel row at a white streak (straight line) occurrence position indicated by reference character B in FIG. 3, corrected density data D ′ (i, j ) Is:
D ′ (i, j) = D (i, j) + di × D (i, j)
Calculated by In this way, corrected density data D ′ (i, j) is obtained.

  The process of generating D ′ (i, j) corrected by the above calculation formula is performed in the correction processing unit 180B of FIG.

Thereafter, by performing halftoning processing from the corrected density data D ′ (i, j), a dot type on / off signal (binary data) or a size type (when dot size modulation is included) Converted to multi-value data including dot size selection). The method of halftoning is not particularly limited, and a known binary (multi-value) method such as an error diffusion method or a dither method can be used.

  Ink ejection (droplet ejection) data for each nozzle is generated based on the binary (multilevel) signal thus obtained. The ink ejection data generation process including the halftoning process is performed in the ink ejection data generation unit 180C in FIG.

  The ink discharge data generated by the ink discharge data generation unit 180C is given to the head driver 184, and the ink discharge operation of the head 150 is controlled.

  The drive waveform generation unit 180D is a unit that generates a drive signal waveform for driving the actuator 158 (see FIG. 7) corresponding to each nozzle 151 of the head 150, and the signal generated by the drive waveform generation unit 180D. (Drive waveform) is supplied to the head driver 184. The signal output from the drive waveform generator 180D may be digital waveform data or an analog voltage signal.

  As shown in FIG. 9, the print control unit 180 includes an image buffer memory 182, and image data, parameters, and other data are temporarily stored in the image buffer memory 182 when image data is processed in the print control unit 180. Is done. In FIG. 9, the image buffer memory 182 is shown in a form associated with the print control unit 180, but it can also be used as the image memory 174. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  An outline of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 170 and stored in the image memory 174. At this stage, for example, RGB multivalued image data is stored in the image memory 174.

  In the ink jet recording apparatus 110, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory 174 is sent to the print control unit 180 via the system controller 172, and the density data generation unit 180A, the correction processing unit 180B of the print control unit 180, the ink It is converted into dot data for each ink color via the ejection data generation unit 180C.

  That is, the print control unit 180 performs a process of converting the input RGB image data into dot data of four colors K, C, M, and Y. Thus, the dot data generated by the print control unit 180 is stored in the image buffer memory 182. This dot data for each color is converted into CMYK droplet ejection arrangement data for ejecting ink from the nozzles of the head 150, and the ink ejection data to be printed is determined.

  The head driver 184 outputs a drive signal for driving the actuator 158 corresponding to each nozzle 151 of the head 150 in accordance with the print contents based on the ink ejection data and the drive waveform signal given from the print control unit 180. The head driver 184 may include a feedback control system for keeping the head driving condition constant.

  In this way, when the drive signal output from the head driver 184 is applied to the head 150, ink is ejected from the corresponding nozzle 151. An image is formed on the recording paper 116 by controlling ink ejection from the head 150 in synchronization with the conveyance speed of the recording paper 116.

  As described above, based on the ink discharge data and the drive signal waveform generated through the required signal processing in the print control unit 180, control of the discharge amount and discharge timing of the ink droplets from each nozzle through the head driver 184. Is done. Thereby, a desired dot size and dot arrangement are realized. Also, in this example, image data is corrected in consideration of the droplet ejection position error before the halftoning process (intermediate gradation process), so that unevenness caused by the droplet ejection position error is accurately detected. It can be corrected.

  As described with reference to FIG. 4, the print detection unit 124 is a block including an image sensor. The print detection unit 124 reads an image printed on the recording paper 116, performs necessary signal processing, and the like to perform a printing situation (whether ejection is performed, droplet ejection). Variation in droplet ejection position, optical density, etc.) and the detection result is provided to the print controller 180 and the system controller 172.

  The print control unit 180 performs various corrections on the head 150 based on information obtained from the print detection unit 124 as necessary, and performs cleaning operations (nozzle recovery operation) such as preliminary ejection, suction, and wiping as necessary. Perform the controls to be implemented.

  In this example, the combination of the system controller 172 and the print controller 180 corresponds to the “droplet ejection control unit”, and the combination of the print detection unit 124 and the droplet ejection error measurement calculation unit 172A becomes the “droplet ejection position error measurement unit”. Equivalent to. Further, the droplet ejection error measurement calculation unit 172A of this example includes a function as “error factor separating means”. The head adjustment amount calculation unit 172C corresponds to “adjustment amount calculation means”, and the head position adjustment mechanism 185 corresponds to “position adjustment means”.

  FIG. 10 is a flowchart showing a control procedure when measuring the droplet deposition position error in the inkjet recording apparatus 110 according to the present embodiment.

  The start timing of the measurement flow of the droplet ejection position error shown in the figure is not particularly limited. At the time of manufacturing the device, at the time of head replacement, at the time of maintenance, at the time of startup of the device, the predetermined timing based on the management of the accumulated operating time, or at any time by the operator There may be various cases such as the designated timing.

  When the droplet deposition position error measurement flow is started (step S10), first, the distance between the nozzle surface and the medium is set to the first distance (Y1) (step S12), and printing of a predetermined test pattern is executed (step S12). Step S14). The test pattern printing process (first time) in step S14 corresponds to the “droplet deposition process” in Invention 1 or the “first droplet ejection process” in Invention 2.

  Thereafter, the droplet ejection result of the test pattern in step S14 is read, and the error amount (ΔX1 = X−X0) from the ideal position is measured (step S16). The error amount measurement process (first time) in step S16 corresponds to the “droplet position error measurement step” in Invention 1 or the “first droplet position error measurement process” in Invention 2, and the error amount (Δ X1) corresponds to the “droplet position error amount” referred to in Invention 1 or the “first droplet position error amount” referred to in Invention 2.

The information on the first distance (Y1) in step S12 and the information on the error amount (ΔX1) obtained in step S16 are stored in storage means such as a memory.

  Subsequently, the distance between the nozzle surface and the medium is changed to the second distance (Y2) (step S18). At this time, the second distance (Y2) is k times the first distance (Y1) (Y2 = k × Y1).

  Then, at the second distance (Y2), a predetermined test pattern (a test pattern by the same drive control as in step S14) is printed (step S20). The test pattern printing process (second time) in step S20 corresponds to the “droplet deposition process” in Invention 1 or the “second droplet ejection process” in Invention 2.

  Thereafter, the droplet ejection result of the test pattern in step S20 is read, and the error amount (ΔX2 = X′−X0) from the ideal position is measured (step S22). The error amount measuring step (second time) in step S22 corresponds to the “droplet position error measuring step” in Invention 1 or the “second droplet position error measuring step” in Invention 2, and the error amount (Δ X2) corresponds to the “droplet position error amount” referred to in Invention 1 or the “second droplet discharge position error amount” referred to in Invention 2.

  The information on the second distance (Y2) in step S18 and the information on the error amount (ΔX2) obtained in step S22 are stored in storage means such as a memory.

  Next, from the error amount information (ΔX1, ΔX2) obtained in steps S16 and S22, equations [Expression 1] and [Expression 2] are solved to calculate δXH and δXD (step S24). The calculation process in step S24 corresponds to an “error factor separation process”.

  Then, the head adjustment amount is obtained from δXH obtained in step S24 (step S26), and the measurement process is terminated (step S28).

  The head position is adjusted according to the head adjustment amount obtained by the above measurement flow. Further, the density correction coefficient is determined using the information of δXD obtained by the above measurement flow.

  In this embodiment, both δXH and δXD are obtained. However, only one of the values is calculated, and either the head mounting position adjustment or the droplet ejection arrangement correction is performed. Is also possible.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  FIG. 11 is a block diagram showing a configuration of an ink jet recording apparatus according to the second embodiment of the present invention. In FIG. 11, the same or similar elements as those shown in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted.

  The ink jet recording apparatus 110 ′ shown in FIG. 11 is a configuration example of an embodiment that implements [Calculation method 2] described in the above description of [Measurement principle].

  That is, the ink jet recording apparatus 110 ′ shown in FIG. 11 is equipped with a high speed camera 194 as means for photographing the discharge state from each nozzle of the head 150. Further, an image analysis unit 172D is provided in the system controller 172 as means for performing signal processing for analyzing an image signal obtained from the high-speed camera 194 and calculating a droplet discharge angle and the like.

  The high-speed camera 194 has a photographing speed of, for example, about 100,000 frames / second for the purpose of photographing the flight of droplets by inkjet. The image analysis unit 172D may be realized by software or may be configured by a dedicated image processing IC. ΔXD is calculated from the discharge angle information obtained by the image analysis unit 172D and the nozzle surface-medium distance information, and δXH is calculated from the δXD and the above [Equation 1].

  In the case of the configuration illustrated in FIG. 11, the combination of the high-speed camera 194 and the image analysis unit 172D corresponds to the “ejection direction measuring unit”, and the combination of the image analysis unit 172D and the droplet ejection error measurement calculation unit 172A is “error factor separation”. It corresponds to “means”.

  FIG. 12 is a flowchart showing a control procedure when measuring the droplet ejection position error in the inkjet recording apparatus 110 ′ shown in FIG. 11.

  The start timing of the measurement flow of the droplet ejection position error shown in the figure is not particularly limited. At the time of manufacturing the device, at the time of head replacement, at the time of maintenance, at the time of startup of the device, the predetermined timing based on the management of the accumulated operating time, or at any time by the operator There may be various cases such as the designated timing.

  When the measurement flow of the droplet ejection position error starts (step S30), first, the distance between the nozzle surface and the medium is set to a predetermined distance (for example, Y1) (step S32), and a predetermined test pattern is printed. (Step S34). The test pattern printing process in step S34 corresponds to the “droplet ejection process” in the first or third aspect.

  During printing of this test pattern, the ejection state is photographed by the high-speed camera 194 (see FIG. 11), and the obtained image data (data indicating the flight trajectory of the droplet) is analyzed to measure the deviation amount of the ejection angle. (Step S36 in FIG. 12). The process in step S36 corresponds to the “ejection direction measuring process” referred to in the invention 3.

  Then, the droplet ejection position error component δXD caused by the ejection angle deviation is calculated from the value of the ejection angle deviation amount obtained in step S36 and the value of the nozzle surface-medium distance obtained from step S32 (step S38). .

  Further, the test pattern droplet ejection result in step S34 is read, and the error amount (ΔX = X−X0) from the ideal position is measured (step S40). The error amount measurement step (first time) in step S40 corresponds to the “droplet position error measurement step” in the first or third aspect, and the error amount (ΔX) corresponds to the “droplet position error amount”. .

  Subsequently, from the error amount information (ΔX) obtained in step S40 and the information of δXD obtained in step S38, δXH is calculated using [Equation 1] (step S42). The calculation process in step S42 corresponds to an “error factor separation process”.

  Then, the head adjustment amount is obtained from δXH obtained in step S42 (step S44), and the measurement process is terminated (step S46).

  The head position is adjusted according to the head adjustment amount obtained by the above measurement flow. Further, the density correction coefficient is determined using the information of δXD obtained by the above measurement flow.

[Modification 1]
The droplet ejection error measurement calculation unit 172A, the density correction coefficient calculation unit 172B, the head adjustment amount calculation unit 172C, the image analysis unit 172D, the density data generation unit 180A, and the correction processing unit 180B described with reference to FIG. 9 or FIG. A mode in which all or a part is mounted on the host computer 186 side is also possible.

  Further, the application of the present invention is not limited to a line head type printer, but can be effectively applied to a shuttle scan type printer.

[Modification 2]
In the above-described embodiment, the mounting failure of the head is exemplified as the relative disposition of the liquid ejection head and the recording medium. However, in addition to the head mounting failure, the transport unit is not installed correctly (for example, the head attached at the normal mounting position). On the other hand, the present invention can also be applied to a droplet ejection position error when reproducible skew / meander occurs due to a case where a recording medium transport belt is mounted obliquely). In this case, means (mechanism) for adjusting the position of the conveying means is provided in place of or in combination with the head position adjusting mechanism 185.

  DESCRIPTION OF SYMBOLS 110 ... Inkjet recording device, 112 ... Printing part, 112K, 112C, 112M, 112Y ... Head, 114 ... Ink storage / loading part, 116 ... Recording paper (recording medium), 122 ... Belt conveying part (conveying means), 123 ... Distance measuring unit 124 ... printing detection unit 150 ... head 151 ... nozzle 152 ... pressure chamber 153 ... ink chamber unit 158 ... actuator 172 ... system controller 172A ... drop ejection error measurement calculating unit 172B ... density Correction coefficient calculation unit, 172C ... head adjustment amount calculation unit, 172D ... image analysis unit, 173 ... nozzle surface-medium distance information acquisition unit, 175 ... ROM, 180 ... print control unit, 180A ... density data generation unit, 180B ... Correction processing unit, 180C... Ink ejection data generation unit, 180D... Drive waveform generation unit, 184. De driver, 185 ... head position adjustment mechanism, 194 ... high-speed camera

Claims (6)

While a plurality of droplet discharge port that is formed liquid discharge head recording medium are relatively moved in a first direction, it performs discharge of liquid droplets from the liquid ejection head to deposit a droplet on the recording medium hitting A drip process;
From the droplet ejection result obtained in the droplet ejection step, the droplet ejection position error amount with respect to the ideal droplet ejection position in the second direction that is perpendicular to the first direction on the recording surface of the recording medium is obtained. Drop position error measurement process,
A discharge direction measuring step of measuring a discharge direction of the second direction of the droplet discharged from the droplet discharge port;
The liquid ejection head and the recording medium with respect to the second direction using the ejection direction error information obtained in the ejection direction measurement step from the droplet ejection position error amount obtained in the droplet ejection position error measurement step An error factor separation step of separating a first error component caused by a relative arrangement failure of the first and a second error component caused by a defective ejection direction of the droplet ejection port;
Error information of at least the first error component of the separated first and second error components is obtained, and the error of the first error component is calculated based on the obtained error information. A method for adjusting a droplet ejection position error, wherein the relative arrangement of the liquid ejection head and the recording medium is adjusted so as to correct. While a plurality of droplet discharge port that is formed liquid discharge head recording medium are relatively moved in a first direction, it performs discharge of liquid droplets from the liquid ejection head to deposit a droplet on the recording medium hitting A drip process;
From the droplet ejection result obtained in the droplet ejection step, the droplet ejection position error amount with respect to the ideal droplet ejection position in the second direction that is perpendicular to the first direction on the recording surface of the recording medium is obtained. Drop position error measurement process,
A discharge direction measuring step of measuring a discharge direction of the second direction of the droplet discharged from the droplet discharge port;
The liquid ejection head and the recording medium with respect to the second direction using the ejection direction error information obtained in the ejection direction measurement step from the droplet ejection position error amount obtained in the droplet ejection position error measurement step An error factor separation step of separating a first error component caused by a relative arrangement failure of the first and a second error component caused by a defective ejection direction of the droplet ejection port;
Error information of the separated second error component is acquired, and the visibility of the stripe unevenness on the recorded image due to the error of the second error component is reduced based on the acquired error information Thus, a droplet ejection control method comprising controlling droplet ejection by the liquid ejection head.   The error information of the second error component is acquired according to the error factor separation step in the droplet ejection position error adjustment method according to claim 1, and the second error component is acquired based on the acquired error information. A droplet ejection control method, wherein droplet ejection by the liquid ejection head is controlled so as to reduce the visibility of uneven stripes on a recorded image due to the error of the above. A liquid discharge head in which a plurality of droplet discharge ports are formed;
While relatively moving the recording medium and the liquid ejection head in the first direction, by ejecting droplets from the liquid ejection head, a droplet ejection control means for controlling the deposition of liquid droplets on the recording medium,
A droplet ejection position error measuring unit that reads a position of a dot recorded on the recording medium and measures a droplet ejection position error amount with respect to an ideal droplet ejection position on the recording surface of the recording medium;
A discharge direction measuring means for measuring a discharge direction of the second direction of the droplet discharged from the droplet discharge port;
From the droplet ejection position error amount obtained by the droplet ejection position error measuring means, the information on the ejection direction obtained by the ejection direction measuring means is used to make the liquid ejection head and the recording in the second direction. Error factor separation means for separating a first error component caused by a poor relative arrangement of the medium and a second error component caused by a defective ejection direction of the droplet ejection port;
Relative arrangement of the liquid ejection head and the recording medium necessary for correcting the error of the first error component based on the error information of the first error component separated by the error factor separation means Adjustment amount calculating means for calculating the adjustment amount of
Position adjusting means for adjusting the relative arrangement of the liquid ejection head and the recording medium in accordance with the adjustment amount calculated by the adjustment amount calculating means;
An image forming apparatus comprising: A liquid discharge head in which a plurality of droplet discharge ports are formed;
While relatively moving the recording medium and the liquid ejection head in the first direction, by ejecting droplets from the liquid ejection head, a droplet ejection control means for controlling the deposition of liquid droplets on the recording medium,
A droplet ejection position error measuring unit that reads a position of a dot recorded on the recording medium and measures a droplet ejection position error amount with respect to an ideal droplet ejection position on the recording surface of the recording medium;
A discharge direction measuring means for measuring a discharge direction of the second direction of the droplet discharged from the droplet discharge port;
From the droplet ejection position error amount obtained by the droplet ejection position error measuring means, the information on the ejection direction obtained by the ejection direction measuring means is used to make the liquid ejection head and the recording in the second direction. Error factor separation means for separating a first error component caused by a poor relative arrangement of the medium and a second error component caused by a defective ejection direction of the droplet ejection port;
Based on the error information of the second error component separated by the error factor separation means, the liquid ejection is performed so as to reduce the visibility of uneven stripes on the recorded image due to the error of the second error component. Droplet ejection arrangement determining means for determining the droplet ejection arrangement by the head;
An image forming apparatus comprising:   Based on the error information of the second error component separated by the error factor separation means, the liquid ejection is performed so as to reduce the visibility of uneven stripes on the recorded image due to the error of the second error component. The image forming apparatus according to claim 4, further comprising a droplet ejection arrangement determining unit that determines a droplet ejection arrangement by the head.

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