JP5363262B2 - Image recording apparatus and image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image recorder capable of readily and effectively suppressing a variation of density in a record image caused by a variation in the ejection performance of recording elements, and to provide a method of recording an image. <P>SOLUTION: Output density data indicative of recording density at each recording element is acquired (S12), the output information of the recording element is obtained in accordance with the output density data (S14) and characteristic information at a normal state of the recording element is predetermined and stored in a memory. The ejection information is compared with the characteristic information by the recording element (S18), a content for a correction process to the ejection control of a target recording element is changed in accordance with the comparison result (S20, S22), and then correction with respect to the ejection control of the target recording element is performed based on the content of the changed correction process. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image recording apparatus and an image recording method, and particularly corrects density unevenness due to variations in characteristics of recording elements when an image is recorded on a recording medium using a recording head having a plurality of recording elements. The present invention relates to an image recording apparatus and an image recording method.

  In an image recording apparatus such as an ink jet recording apparatus having a plurality of nozzles, the ejection characteristics between the nozzles vary over time due to the drying of the ink in the nozzle openings, which causes adverse effects on the ink ejection. A deteriorated nozzle and a non-ejection nozzle that cannot eject ink at all are included. The presence of such deteriorated nozzles and non-ejection nozzles is not preferable because it leads to permanent disturbance of the recorded image such as white stripes. For this reason, Patent Document 1 proposes a technique for preventing a recorded image from being disturbed due to a decline in nozzle discharge performance.

  Patent Document 1 discloses an ink jet recording apparatus that records an image on a recording medium by ejecting ink from a plurality of nozzles. In this ink jet recording apparatus, a pattern (shading pattern and non-ejection detection pattern) for measuring the recording characteristics of the recording head is output, the density of the pattern is measured, and the non-ejection state is based on the measurement result. The non-ejection nozzle is specified. Further, a density distribution corresponding to each nozzle is obtained, and convolution integration using VTF (Visual Transfer Function) or PSF (Point Spread Function) is performed on the density distribution. Then, the result of the portion corresponding to the non-ejection nozzle in the obtained density distribution is compared with a predetermined reference setting value, and the color of the ink ejected by the non-ejection nozzle is different based on the comparison result. A complement table for complementing with color ink is determined for each nozzle. The image data corresponding to the non-ejection nozzles is converted into different color ink ejection information ejected from other nozzles based on the complement table determined in this way.

JP 2003-136664 A

  As described above, in the technique disclosed in Patent Document 1, non-ejection information is acquired based on a recording pattern, and when the target nozzle is a non-ejection nozzle, a complementary process is performed with different color inks, while the target nozzle is If it is not a non-ejection nozzle, a shading correction process for correcting density unevenness is performed by adjusting the amount of ink ejected from the target nozzle. In the technique disclosed in Patent Document 1, it is determined based on the non-ejection information whether to deal with the non-ejection complementing process or the shading correction process.

  However, there is a wide range of density unevenness due to deterioration of the nozzle ejection performance, and density deterioration can be achieved only by normal shading correction processing for deteriorated nozzles that have lost the ability to eject the original ink density (ink amount). It can be very difficult to deal with in practice.

  In particular, in the technique disclosed in Patent Document 1, the target nozzle is not detected as a non-ejection nozzle, but cannot be ejected with a sufficient density of ink even by shading correction processing (hereinafter referred to as “abnormal density nozzle”). Even in the case of calling, a normal shading correction process is performed. However, such density unevenness due to the presence of the abnormal density nozzle is not properly improved even by the density process (shading correction process) for increasing the density of ink that increases the amount of ink discharged from the abnormal density nozzle. Quality disturbance cannot be sufficiently prevented.

  In addition, there are a wide variety of types and degrees of nozzle discharge performance deterioration, and it is actually difficult to sufficiently deal with all such deteriorated nozzles by shading correction processing alone, and the processing calculation is complicated. It may be assumed that the calculation time becomes longer or an advanced control device is required.

  Furthermore, in the technique disclosed in Patent Document 1, since the non-ejection nozzle complement process is performed using different color inks, the complement capability is greatly affected by the type and number of different color inks used in the complement process. However, in a normal ink jet recording apparatus, since there are certain limitations on the types and number of inks used, there are cases where the non-ejection nozzle complement process cannot be sufficiently performed. In the technique of Patent Document 1, the shading data for the same color is also calculated for the non-ejection nozzle portion. However, since it is non-ejection, it is not actually output, and as a result, non-ejection supplementation is performed with different color inks. Will be done.

  The present invention has been made in view of the above-described circumstances, and provides an image recording apparatus and an image recording method capable of easily and effectively reducing density unevenness of a recorded image caused by variations in ejection performance of recording elements. The purpose is to provide.

  One embodiment of the present invention relates to an image recording apparatus, and the image recording apparatus transports at least one of the recording head having a plurality of recording elements, the recording head, and the recording medium. Conveying means for relatively moving, density information acquiring means for acquiring output density data indicating the recording density for each recording element, and characteristics for obtaining recording information for each recording element from the output density data acquired by the density information acquiring means Calculation means; characteristic storage means for storing characteristic information at the time of the plurality of recording elements determined in advance; the recording information for each recording element required by the characteristic calculation means; and the characteristics stored in the characteristic storage means Correction processing switching means for switching the content of the correction processing for the ejection control of the target recording element among the plurality of recording elements according to the comparison result with the information; Wherein the correction processing according to the contents of the correction process is switched by the switching means, the record information and the image recording apparatus characterized by comprising a correction means for correcting for the ejection control of the object recording element based on the characteristic information.

  According to this aspect, the recording information relating to the recording density of the recording element is compared with the characteristic information at the appropriate time, and the content of the correction process for the ejection control of each recording element is switched in accordance with the comparison result, so that the correction is performed. Is called. In this way, correction can be easily performed by a simple process of switching the content of the correction process according to the comparison result.

  The “recording element” refers to any unit that performs recording on a recording medium. In the case of an inkjet recording apparatus, a nozzle capable of ejecting ink or an actuator (for example, a piezoelectric element) that provides a driving force for ejecting ink. Or a heating element) constitutes a recording element. The “property characteristic information” refers to characteristic information when the recording element is operating properly, and it is possible to obtain the appropriate characteristic information by experiments or the like.

  The content of the correction process for the ejection control of the target recording element preferably includes an ejection correction process for handling the target recording element as an ejection recording element and a non-ejection correction process for treating the target recording element as a non-ejection recording element. .

  By setting such discharge correction processing and non-discharge correction processing as the content of the correction processing, it is possible to simplify the determination of the content of the correction processing, and it is possible to easily perform the correction processing. “Handling the target recording element as non-ejection” means not only the case where the recording element that cannot perform recording is the target recording element, but also the recording medium that has the ability to perform recording. This includes the case of handling so as not to record.

  The ejection correction process involves controlling the ejection of liquid from the target recording element, and the non-ejection correction process controls the ejection of liquid from other recording elements without ejecting liquid from the target recording element. It is desirable to accompany it.

  In this case, the ejection correction process is performed by ejecting liquid from the target recording element itself, and the non-ejection correction process is performed by ejecting liquid from a recording element other than the target recording element. The process is executed.

  The correction processing switching means performs correction processing for the discharge control of the target recording element when the target recording element can output an output density of an appropriate value by the discharge correction processing according to the comparison result. The content is the ejection correction process, and when the target recording element cannot output an appropriate output density by the ejection correction process, the content of the correction process for the ejection control of the target recording element is the non-ejection It is desirable to use correction processing.

  As described above, the target recording element that cannot discharge an appropriate amount of liquid even by the discharge correction process is supplemented with the discharge density by another recording element, whereby the density due to the target recording element is obtained. Unevenness can be effectively reduced.

  The density information acquisition unit may acquire the output density data by reading a recording density pattern recorded on the recording medium by the plurality of recording elements.

  By using such a recording density pattern, output density data can be easily obtained. The “recording density pattern” is a pattern image in which the output density is changed, and the density change rate, the type of image pattern, and the like are not particularly limited.

  The recording information and the characteristic information are preferably based on input density data input to the plurality of recording elements and output density data of the plurality of recording elements.

  In this case, since the output density data of the recording information is compared with the output density data of the characteristic information at the appropriate time, it is possible to clarify the variation in the recording performance (output density) with respect to the input density data.

  The correction processing switching means preferably switches the content of the correction processing according to a comparison result between the output density data of the recording information and predetermined critical density data based on the characteristic information.

  Thus, by using the critical density data, it is possible to easily determine whether or not the target recording element is a detection recording element.

  The correction processing switching means preferably switches the content of the correction processing depending on whether or not the output density data of the recording information is included in a predetermined range based on the characteristic information.

  As described above, it is possible to easily determine whether or not the target recording element is the detection recording element by using whether or not the target recording element is included in the predetermined range based on the characteristic information.

  The recording information includes a plurality of the output density data acquired over time, and the correction processing switching unit performs the correction processing according to a comparison result between the plurality of output density data acquired over time. It is desirable to switch the contents.

  As described above, by using the output density data with time as a reference, it is possible to perform appropriate correction even for the recording control of the printing element in which the output density fluctuates with time.

The correction switching means to switch the content of the correction processing according to whether or not the characteristic curve of the output density data for input density data that is derived from the recorded information is increased monotonically desirable.

  As described above, by using the increase rate of the output density represented by the characteristic curve as a reference, it is possible to perform an appropriate correction even for a printing element in which the output density data with respect to the input density data is irregular. is there.

  The plurality of recording elements may be arranged in a range corresponding to a full width of a recording range of the recording medium in the recording head.

  As described above, when the recording head has a so-called line head structure, there is a tendency that the recording unevenness due to the variation in the ejection performance between the recording elements tends to be manifested. The effect can be exhibited, and the recording density unevenness can be effectively reduced.

  The recording head may record an image in a predetermined recording range of the recording medium by one relative movement.

  As described above, when the recording head adopts a so-called single-pass method, recording unevenness due to variations in ejection performance between the recording elements tends to become obvious, and thus each aspect of the present invention is more effective. This effect can be exhibited, and recording density unevenness can be effectively reduced.

  Another aspect of the present invention relates to an image recording method, which is an image recording method for recording an image by controlling a plurality of recording elements, wherein output density data indicating a recording density for each recording element is obtained. A density information acquisition step to be acquired; a characteristic calculation step for obtaining recording information for each recording element from the output density data; the recording information for each recording element; and characteristic information for the plurality of recording elements determined in advance when appropriate And a correction processing switching step for switching the content of the correction processing for the ejection control of the target recording element among the plurality of recording elements, and the content of the correction processing switched in the correction processing switching step. And a correction step for correcting the ejection control of the target recording element.

  According to the present invention, the content of the correction process for the ejection control of the target recording element is switched according to the comparison result between the recording information obtained from the output density data for each recording element and the predetermined characteristic information at the appropriate time. By such simple switching of the correction process, it is possible to effectively cope with variations in the ejection performance of the printing elements, and it is possible to effectively reduce the density unevenness of the printed image.

The relationship between the input image data (input density data) input to eject ink from the nozzles and the output density (output density data) of the ink dots formed on the recording medium is shown. It is a flowchart which shows an example of the correction process of the discharge performance of a nozzle. It is a figure which shows an example of the test chart recorded on the recording medium. It is a graph which shows the characteristic curve of a nozzle. It is a flowchart which shows an example of the determination method whether a target nozzle is a normal nozzle or an abnormal density nozzle. It is a graph which shows the example of a test characteristic curve of a nozzle, and shows the case where an object nozzle is a normal nozzle. It is a graph which shows the test characteristic curve example of a nozzle, and shows the case where an object nozzle is a low concentration nozzle. It is a graph which shows the test characteristic curve example of a nozzle, and shows the case where the discharge performance of an object nozzle fluctuates with time. It is a graph which shows the test characteristic curve example of a nozzle, and shows the case where the test characteristic curve of a target nozzle is not a monotonically increasing curve. It is a graph which shows the example of a test characteristic curve of a nozzle, and is a figure explaining an example of critical concentration. It is a figure which shows an example of a non-ejection correction process. It is explanatory drawing which shows an example of a shading correction process. It is a flowchart which shows an example of the image output process accompanied by a halftone process. It is a flowchart which shows an example of the image output process accompanied by a halftone process. 1 is an overall configuration diagram of an inkjet recording apparatus to which an image processing apparatus according to an embodiment of the present invention is applied. FIG. 16 is a plan view of a main part around a recording head of the ink jet recording apparatus shown in FIG. 15. 17A is a plan perspective view showing an example of the structure of the head, FIG. 17B is an enlarged view of the main part of FIG. 17A, and FIG. 17C is another view of the full-line head. It is a plane perspective view which shows the example of a structure. It is sectional drawing which follows the 18-18 line | wire of Fig.17 (a) and FIG.17 (b). FIG. 18 is an enlarged view showing a nozzle arrangement of the head shown in FIG. It is a principal block diagram showing the system configuration of the ink jet recording apparatus. It is a functional block diagram which shows the control structure relevant to a shading correction process and a non-ejection correction process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, ink discharge correction at the time of image recording of an ink jet recording apparatus including a plurality of nozzles will be described, and then the configuration of the ink jet recording apparatus will be described. In the following embodiments, the case where the present invention is applied to an ink jet recording apparatus that forms a desired image on a recording medium by ejecting ink from a recording head having a plurality of nozzles is illustrated. The present invention is not limited to the recording device.

(Nozzle discharge performance)
FIG. 1 shows the relationship between input image data (input density data) input to eject ink from nozzles and the output density (output density data) of ink dots formed on a recording medium. In FIG. 1, the horizontal axis represents input image data based on gradation values, and the vertical axis represents the output density of ink dots actually formed on a recording medium by ink ejected from nozzles.

  The output density of the ink dots ejected from the corresponding nozzle here refers not only to the density of the ink dots ejected from the corresponding nozzle at a time, but also the ink dot group ejected at a plurality of times, for example, ejected from the corresponding nozzle. The average density of the ink dot rows arranged in the relative movement direction with respect to the printed recording medium may be used. That is, a method of expressing a continuous density change by the density and number of ink dots using halftone processing or the like is also included.

  Each nozzle that ejects ink is divided into a “normal nozzle” and an “abnormal density nozzle” according to the ejection performance.

The “normal nozzle” here is a nozzle (see “G _a ” in FIG. 1) capable of ejecting a normal amount (appropriate amount) of ink to the input image data, and normal to the input image data. This is a concept including a nozzle (see “G _b ” in FIG. 1) that cannot eject an amount of ink but can eject a normal amount of ink by a shading correction process (discharge correction process).

On the other hand, an “abnormal density nozzle” is a nozzle (see “G _c ” in FIG. 1) that cannot eject a normal amount of ink even by a shading correction process (discharge correction process) that increases the discharge density (discharge amount). Specifically, low density nozzles and time-varying nozzles described later are included in the abnormal density nozzles (see FIGS. 7 to 9 described later).

  In the following embodiments, it is not performed to detect only nozzles (non-ejection nozzles) that cannot eject ink at all, but such non-ejection nozzles are detected as “abnormal density nozzles”. Will be processed.

  The specific contents of the shading correction process and the non-ejection correction process described here will be described later. The shading correction process (ejection correction process) is performed by adjusting the ink density (ink amount) ejected from the target nozzle. A process of correcting the waveform and size of the drive control signal is included so that a larger amount of ink is ejected, and control is performed to eject ink from the target nozzle. Normally, since the ink discharge amount decreases due to a decline in discharge performance, such shading correction processing increases ink discharge amount, but shading correction processing when an excessive amount of ink is discharged from the target nozzle Is a process for reducing the ink discharge amount.

  On the other hand, the non-ejection correction process is a correction that treats a target nozzle determined to be an abnormal density nozzle as a non-ejection nozzle, and prevents ink from being ejected from such a target nozzle, and from the peripheral nozzles of the target nozzle. The waveform and size of the drive control signal applied to the drive elements corresponding to the target nozzle and its peripheral nozzles are set so that the image recording of the target nozzle treated as non-ejection is covered by the ejection control of the ejected ink. Processing to correct is included.

In the above-described prior art, normal nozzles (G _a , G _b ) can be dealt with by normal shading correction processing, but a normal amount of ink can be ejected by shading correction processing (ejection correction processing). The abnormal density nozzle (G _c ) that is impossible could not be appropriately dealt with, and the disturbance of the recorded image due to such an abnormal density nozzle could not be prevented.

  The following embodiments improve image quality and simplify correction processing by treating such abnormal density nozzles that could not be handled by the prior art as non-ejection nozzles instead of ejection nozzles. To do. The following series of correction processes is mainly performed in the control unit of the ink jet recording apparatus.

(Outline of correction data calculation)
FIG. 2 is a flowchart illustrating an example of correction processing for the ejection performance of the nozzles.

  In this embodiment, a test chart (recording density pattern) is used to determine whether the target nozzle is a normal nozzle or an abnormal density nozzle. That is, a drive control signal based on input image data for a patch (test chart) with changed gradation density corresponds to a drive element corresponding to each of the nozzles (for example, a piezoelectric element including a common electrode 156, an individual electrode 157, and an actuator 158 described later). (S10 in FIG. 2), ink is ejected from each nozzle based on the input image data, and a test chart is output and recorded on the recording medium (S12).

  FIG. 3 is a diagram illustrating an example of a test chart recorded on the recording medium 116. FIG. 3 shows a test chart when the recording head is a so-called line head, and an example in which ink is ejected from each of the nozzles of the recording head provided over substantially the entire width of the recording medium 116 to form a test chart. It is shown. FIG. 3 shows the direction of the nozzle row (nozzle row direction) formed by a plurality of nozzles of the recording head and the width of the nozzle row (nozzle row width), from the top to the bottom of FIG. A plurality of test charts are formed by continuously recording ink dots so that the density gradation value increases stepwise, and the density in the nozzle row direction is substantially constant.

  When such a test chart is recorded on the recording medium, the output density of each nozzle is acquired based on the test chart (S14 in FIG. 2). Although a specific acquisition process will be described later, an OD (Optical Density) value at each position of the test chart (scanned image) is obtained, and each recording element (nozzle, etc.) corresponding to each position is obtained from the OD value of the test chart. Output density data indicating the output recording density is acquired. Note that the test chart is read and acquired by a print detection unit described later.

  Based on the output density data and the input image data obtained in this way, a characteristic curve (test characteristic curve) for each nozzle is obtained (S16).

FIG. 4 is a graph showing the characteristic curve of the nozzle. The vertical axis represents output density data, the horizontal axis represents input image data, and the output density increases as the distance from the origin 0 in the vertical direction increases (the output amount increases). However, the density gradation of the input image data increases as the distance increases. As shown in FIG. 4, the characteristic curve (test curve) G _t of the nozzle obtained from the test chart, for disturbances such as, for ejecting ink of normal weight (appropriate amount) from the nozzle with respect to the input image data If the is usually to draw slightly shifted curves from the resulting characteristic curve (appropriate characteristic curve) G _a, the variations in output density values between the nozzle as indicated by the arrow in FIG. 4 seen.

Thus, test characteristic curves G _t and proper characteristic curve G _a are all based on the output density data of the input density data and the recording element to be input to the recording device (ink ejection actuators), the test characteristic curve G _t represents the information recorded on the recording element, the proper characteristic curve G _a represents the characteristic information when the proper recording device (normal).

Such test characteristic curve G _t of each nozzle obtained in the are compared to the appropriate characteristic curve G _a, according to the comparison result, correction contents for discharge control of the target nozzle, shading correction processing (ejection correction processing) And non-ejection correction processing. That is, target nozzle from the comparison result between the test characteristic curve G _t and proper characteristic curve G _a of the target nozzle is determined whether a normal nozzle (S18 in FIG. 2), YES if target nozzle is normal nozzle (S18 ), The correction data is reflected in the shading information for the shading correction process (S20), and when the target nozzle is an abnormal density nozzle that is not a normal nozzle (NO in S18), the non-ejection information for the non-ejection correction process is corrected. The data is reflected (S22).

When input image data for printing is input from a host computer or the like, correction processing is performed based on the above-described shading information and non-ejection information assigned to each nozzle, and high-quality printing that eliminates density unevenness An image is recorded on a recording medium.
(Determination of normal nozzle and abnormal density nozzle)
Next, a specific example of a method for determining whether the target nozzle is a normal nozzle or an abnormal density nozzle (S18 in FIG. 2) will be described.

  FIG. 5 is a flowchart showing an example of a method for determining whether the target nozzle is a normal nozzle or an abnormal density nozzle. 6 to 9 show examples of nozzle test characteristic curves, FIG. 6 shows a case where the target nozzle is a normal nozzle (appropriate nozzle), FIG. 7 shows a case where the target nozzle is a low-density nozzle, and FIG. Shows a case where the discharge performance of the target nozzle varies with time, and FIG. 9 shows a case where the test characteristic curve of the target nozzle is not a monotonically increasing curve.

S18 as described above with respect of Figure 2, in this embodiment, made from the comparison result between the test characteristic curve G _t and proper characteristic curve G _a of the target nozzle to the target nozzle is determined whether a normal nozzle Specifically, the determination is performed as follows.

First, the output density data with a predetermined threshold density values for each nozzle obtained from the test chart and (critical concentration data) D _c is compared (S30 in FIG. 5). As shown in FIG. 7, when the output density data of the test curve G _t of the target nozzle does not reach the critical concentration value D _c (YES in S30), the non-ejection recording the target nozzle and the corresponding drive device is not discharging ink Treated as an element, non-ejection correction processing is performed (S38).

Critical concentration value D _c is a value determined in advance based on the characteristic information of the proper characteristic curve G _a, for example on the basis of the output density data of the proper characteristic curve G _a to the boundary value not to impair the image quality in visual the value based on may be employed as the critical concentration value D _c.

On the other hand, when the output density data of the test curve G _t of the target nozzle has reached the critical concentration value D _c (NO in S30), the contents of the correction process based on the temporal variation of the output density data of the target nozzle It is switched (S32). That is, a plurality of data of the test curve G _t is time acquired is stored in a storage device such as a magnetic medium as ejection data for each nozzle (printing information). In the example shown in FIG. 8, the output density data of the test characteristic curve G _tn measured at the n-th time acquired most recently and the test characteristic curve acquired in the past (FIG. 8 shows the deterioration of ink discharge performance over time. _Are compared with each other, and the difference between them is calculated based on the input image data. Over time when the difference between the output density between the acquired are tested characteristic curve G _t is equal to or greater than a predetermined value (YES in S32 in FIG. 5), the non-ejection recording the target nozzle and the corresponding drive device is not discharging ink Treated as an element, non-ejection correction processing is performed (S38).

  On the other hand, when the output density difference with time of the target nozzle is smaller than the predetermined value (NO in S32), it is determined whether or not the test characteristic curve is a monotonically increasing curve (S34). The monotone increasing curve here is an increasing curve in which the output density increases (becomes darker) as the tone value of the input image data increases, and the tone value of the input image data increases. It refers to a curve that does not include a portion where the output density decreases (becomes thin) (see, for example, the “R” portion in FIG. 9). Specifically, a differential value of the output density data with respect to the input image data is obtained, and whether or not the output density data of the target nozzle increases together with the input image data is obtained from this differential value. When it is determined from such a differential value that the output density data of the target nozzle does not increase with the input image data and the test characteristic curve is not a monotonically increasing curve (YES in S34 of FIG. 5), the target nozzle and The corresponding drive element is treated as a non-ejection recording element that does not eject ink, and non-ejection correction processing is performed (S38). The “test characteristic curve acquired over time” is a test characteristic curve acquired after a certain time, and the time interval is not particularly limited.

  On the other hand, when it is determined that the test characteristic curve is a monotonically increasing curve (NO in S34), the target nozzle and its corresponding driving element are treated as an ejection recording element capable of ejecting a normal amount of ink, and the target A shading correction process is performed for the ejection control of the nozzles and their corresponding drive elements (S36).

  Note that the determination methods shown in FIGS. 5 to 9 are merely examples, and other determinations may be further added, or one or more of the above determinations (S30, S32, and S34 in FIG. 5) may be omitted. Is possible.

For example, in the example shown in FIG. 7 but critical concentration value D _c is a predetermined value may be changed according to the input image data the critical concentration value D _c as shown in FIG. 10. It varies according to the input image data a constant value of such a critical density value D _c, for example, the difference between the output density value and the critical density value D _c of the characteristic information of the proper characteristic curve G _a is in all of the input image data It can also be determined to be Thus, depending on whether the output density data of the test characteristic curve obtained from the test chart in the predetermined range is included based on the characteristic information of the proper characteristic curve G _a, switching the contents of the correction process of the target nozzle You can also. Incidentally, in determining such a predetermined range may be determined based on the upper critical density value and the lower limit characteristic information of the critical concentration value proper characteristic curve G _a of.

(Non-ejection correction processing and shading correction processing)
Next, the non-ejection correction process will be described with reference to FIG.

  FIG. 11 is a diagram illustrating an example of the non-ejection correction process. When the target nozzle is a non-ejection nozzle, the left and right neighboring nozzles (“non-ejection left neighboring nozzle” and “non-ejection nozzle” in FIG. 11) An example of correcting the ink discharge density from the discharge right adjacent nozzle ") is shown. In FIG. 11, the horizontal axis represents each of a plurality of nozzles arranged in parallel in the nozzle row direction, and the vertical axis represents ink output density (ink amount) ejected from the nozzles.

  In the non-ejection correction process of this example, as shown in FIG. 11, corresponding driving is performed so that ink is not ejected from the target nozzle which is a non-ejection nozzle (that is, the output density of the target nozzle becomes “0.0”). The element is controlled, and the corresponding drive element (piezoelectric drive element or the like) is controlled so that an ink amount larger than the original discharge amount is ejected from the adjacent nozzle of the target nozzle to increase the output density of the adjacent nozzle. . Such control information is stored as non-ejection information and is referred to when the correction process is executed. At this time, the ink color ejected from the adjacent nozzle is the same color as the ink color ejected from the target nozzle.

  In the non-ejection correction process shown in FIG. 11, the ink output density ejected from the left and right adjacent nozzles before the non-ejection correction process is represented by 1.0, and after the non-ejection correction process, the ink is ejected from both the left and right nozzles. The ink output density of the target nozzle increased by non-ejection correction processing is “correction amount” (for example, a correction ratio of “1.5”). It is displayed.

  In FIG. 11, the correction amount of the ink output density for the adjacent nozzles based on the non-ejection correction process is uniform between the adjacent nozzles, but the correction amount for the nozzles adjacent to the target nozzle and their drive elements is appropriately set as necessary. Can be determined. For example, the ratio of the ink output density ejected from the left and right adjacent nozzles after the non-ejection correction process can be appropriately selected within the range of 1.0 to 2.0.

  Further, the non-ejection correction process may be performed using a nozzle (peripheral nozzle) other than the nozzle adjacent to the target nozzle. By performing non-ejection correction processing using nozzles at an angular position of 180 degrees centered on the target nozzle as an adjacent nozzle (peripheral nozzle) on both sides of the target nozzle, the target nozzle treated as a non-ejection nozzle The record can be supplemented from both sides.

  Further, when there is an error in the width direction (nozzle row direction) with respect to the landing position of the ink dot output from the nozzle, the correction ratio (correction amount) is taken into account with this droplet ejection position error (landing position error). May be calculated. For example, the landing position on the recording medium of the ink discharged from the adjacent nozzle is different from the original landing position of the ink discharged from the target nozzle (the landing position at the time of proper discharge) due to such a droplet ejection position error. In the case of being away, the correction ratio may be increased from the normal time. Conversely, if the landing position of the ink ejected from the adjacent nozzle on the recording medium approaches the original landing position of the ink ejected from the target nozzle due to a droplet ejection position error, the correction ratio is normally set. It may be reduced from time.

  Non-ejection correction based on this correction ratio (correction amount) is a process of changing image data so as to increase or decrease the number of alternative droplets ejected from the peripheral nozzles of the target nozzle treated as non-ejection, or is ejected from the peripheral nozzles. This process is performed by increasing or decreasing the ink droplet size.

  The “adjacent nozzle” or “peripheral nozzle” in this example relates to the ink dots formed on the recording medium, and is present in the ink dots adjacent to or on the periphery of the ink dots recorded by the target nozzle. This is a nozzle for forming ink dots. Therefore, when the nozzle row is formed in one row in the recording head, it is general that the nozzles arranged adjacent to or around the target nozzle in the recording head are adjacent nozzles or peripheral nozzles. In addition, when a plurality of nozzles have an irregular arrangement such as the matrix arrangement described later in the print head, the nozzles arranged adjacent to or around the target nozzle in the print head are not necessarily relative to the target nozzle. Does not apply to adjacent nozzles or peripheral nozzles.

  As described above, according to the present embodiment, it is possible to eject not only the nozzle from which ink cannot be ejected at all, but also the ink from the test chart (see FIG. 3), but the shading correction process (ejection correction process). ), An abnormal density nozzle (see FIGS. 7 to 9) that cannot eject a normal amount of ink is also treated as a non-ejection nozzle. Accordingly, the abnormal density nozzle capable of ejecting ink and its corresponding recording element are controlled so that ink is not ejected, while the drive control signal for the nozzle adjacent to the abnormal density nozzle and its corresponding recording element is used. On the other hand, correction processing as shown in FIG. 11 is performed.

  Next, the shading correction process will be described with reference to FIG. FIG. 12 is an explanatory diagram illustrating an example of shading correction processing.

  In the above determination of whether the target nozzle is a normal nozzle or an abnormal density nozzle (see FIG. 5), if it is determined that the target nozzle and its corresponding driving element are treated as normal recording elements (ejection recording elements), The shading correction process is performed (see S36 in FIG. 5).

  As shown in S200 of FIG. 12, a resolution conversion curve indicating the correspondence between the pixel position (density measurement position) of the scanner and the nozzle position is measured in advance and stored, and according to this resolution curve, the test chart Each density measurement position (for example, 400 dpi resolution) in the scanned image is converted into a corresponding nozzle position (for example, 1200 dpi resolution) in the recording head.

  The nozzle position obtained in this way and the density measurement value (output density value) D1 in the test chart corresponding to the nozzle position are associated with each other as shown in S202 of FIG. The difference between the target density value D0 and the density measurement value (output density value) D1 is calculated. The target density value D0 used here is a target value of the ink density to be ejected from the target nozzle, and can be appropriately determined as necessary. For example, the average density of ink ejected from a predetermined nozzle range may be calculated and stored as the target density value D0.

  Then, as shown in S204 of FIG. 12, the measured density value (output density value) D1 and the target density value according to the pixel value-density value curve indicating the correspondence between the pixel value and the density value obtained experimentally in advance. Output pixel values (“pixel value” in S204) P0 and P1 corresponding to D0 (“density value” in S204) are obtained. The output pixel value difference amount (P0-P1) is stored as a density correction value for each nozzle position (shading information) (S206 in FIG. 12), and is referred to when the correction process is executed.

  In the example of FIG. 12, correction processing for increasing / decreasing the number of droplets ejected from the target nozzle (pixel value) is shown, but processing for increasing / decreasing the size of the ink droplets ejected from the target nozzle may be used.

  The non-ejection correction process and the shading correction process described above are merely examples, and other non-ejection correction processes and shading correction processes may be performed.

(Correction processing and image output)
High quality that effectively eliminates density unevenness by applying correction processing based on shading information and non-ejection information obtained as described above to the input image data for desired image formation for each nozzle. Can be formed on a recording medium. The above correction processing is also effective at the time of image output with halftone processing.

  13 and 14 are flowcharts illustrating an example of an image output process that accompanies a halftone process.

  In each example shown in FIGS. 13 and 14, input image data for forming a desired image is input, so-called halftone processing is performed based on the input image data, and the data after halftone processing is converted into data. This is common in that the image output is performed based on (S50, S54 and S56 in FIG. 13, S60, S62 and S66 in FIG. 14). However, the examples shown in FIGS. 13 and 14 are different in that the timing at which the above correction processing (shading correction processing, non-ejection correction density) is performed is before or after the halftone processing. That is, the above correction processing (shading correction processing, non-ejection correction density) may be performed before the halftone processing as shown in FIG. 13, or may be performed after the halftone processing as shown in FIG. Good. Considering the complexity of the calculation of the halftone process, the calculation process becomes simpler when the above correction process (shading correction process, non-ejection correction density) is performed after the halftone process as shown in FIG. It is possible to shorten the time.

  Note that the timing for calculating the correction value of the correction process (shading correction process, non-ejection correction density) is arbitrary. For example, the correction value is calculated by outputting a test chart to the margin of the recording medium every time the image is output. Or the above correction value may be calculated when there is a periodic maintenance or an instruction from the user.

  Further, detection of normal nozzles and abnormal density nozzles may be performed for each output of the test chart. In addition, information on nozzles detected as abnormal density nozzles (non-ejection information) is held in a storage device, and nozzles detected as abnormal density nozzles in the past with reference to non-ejection information during subsequent detection By treating it as an abnormal density nozzle, it is possible to omit the detection process of whether it is a normal nozzle or an abnormal density nozzle. However, even if the nozzle is determined to be an abnormal density nozzle, the ejection performance may be recovered by head cleaning or image recording, etc., so a detection process of whether the nozzle is normal or abnormal density is performed every time the test chart is output. Therefore, accurate correction processing can be performed.

(Effect of correction processing)
In this way, when the density measurement test chart output to the recording medium is measured and density correction (shading correction) is performed based on the measurement result, a characteristic curve of the input value-output image density of each nozzle is created, When a predetermined condition is satisfied for the characteristics of the characteristic curve of each nozzle, the nozzle is set as a non-ejection nozzle, and an image corresponding to the nozzle is set to white (that is, an image is formed without ejecting ink). Non-ejection correction is performed by peripheral nozzles (without forming ink dots for).

  That is, according to the present embodiment, the correction content is switched between “normal nozzle handling” and “non-ejection nozzle handling” based on the characteristic curve regarding the ejection performance of the target nozzle. As a result, it is possible to perform an appropriate correction process even for an abnormal density nozzle (a nozzle that is not a non-ejection nozzle but is not capable of ejecting a sufficient density of ink even by a shading correction process) that was difficult to cope with in the prior art. This can effectively prevent image quality disturbance.

  In particular, by treating an abnormal density nozzle as a non-ejection nozzle, it is possible not only to perform appropriate correction processing, but also to simplify correction amount calculation processing.

  Further, unlike the conventional technique in which density unevenness detection by reducing the amount of ink discharged from the nozzles and detection of non-ejection nozzles are separated and performed as separate detection processes, this embodiment uses a single test chart. By the processing, it is possible to cope with both density unevenness due to the presence of non-ejection nozzles and density unevenness due to ink discharge amount reduction. In particular, in the present embodiment, it is not necessary to detect whether or not the target nozzle is a non-ejection nozzle that cannot eject ink at all, and it is complicated such as convolution integration using VTF or PSF as in the prior art. Therefore, the correction process can be performed easily.

  It should be noted that it is also possible to appropriately detect whether or not the target nozzle is a non-ejection nozzle that cannot eject ink at all, separately from the correction process.

(Configuration of inkjet recording apparatus)
Next, the configuration of the ink jet recording apparatus according to the present embodiment will be described. In addition, about the content which overlaps with said description, it abbreviate | omits below.

  FIG. 15 is an overall configuration diagram of an ink jet recording apparatus to which an image processing apparatus according to an embodiment of the present invention is applied. As shown in the figure, the inkjet recording apparatus 110 according to the present embodiment includes a plurality of inkjets provided corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A recording head 112 having recording heads (hereinafter referred to as heads) 112K, 112C, 112M, and 112Y; an ink storage / loading unit 114 that stores ink to be supplied to the heads 112K, 112C, 112M, and 112Y; A paper feeding unit 118 that supplies recording paper (recording medium) 116 as a medium, a decurling unit 120 that removes curl of the recording paper 116, and a nozzle surface (ink ejection surface) of the recording head 112 are disposed. Read the print result by the belt transport unit 122 that transports the recording paper 116 while maintaining the flatness of the recording paper 116, and the recording head 112. That the print determination unit 124, 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. 16, 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, etc. 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, 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 133 is wound between rollers 131 and 132, and at least a portion facing the nozzle surface of the recording head 112 and the sensor surface of the print detection unit 124 is a horizontal plane (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. As shown in FIG. 15, an adsorption chamber 134 is provided at a position facing the nozzle surface of the recording head 112 and the sensor surface of the print 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. 20) 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.

  Since ink adheres to the belt 133 when a borderless print or the like is printed, the belt cleaning unit 136 is provided at a predetermined position outside the belt 133 (an appropriate position other than the print region). 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 recording head 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 recording head 112 has a length corresponding to the maximum paper width of the recording paper 116 targeted by the ink jet recording apparatus 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 ink ejection are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 16).

  Therefore, the nozzle row formed by the plurality of nozzles 151 is arranged in a range corresponding to the entire width of the recording range of the recording medium 116 in the recording head 112. The recording head 112 employs a single-pass method capable of recording a desired image over the entire recording range of the recording medium 116 by a single relative movement with the recording medium 116.

  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 recording head 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 print detection unit 124 shown in FIG. 15 includes an image sensor (line sensor or area sensor) for imaging the droplet ejection result of the recording head 112. From the droplet ejection image read by the image sensor, nozzle clogging or It functions as a means for checking ejection characteristics such as landing position errors. A test chart or a practical image printed by the heads 112K, 112C, 112M, and 112Y of each color is 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, and the like.

  Note that the print detection unit 124 of the present embodiment reads the above-described test chart (see FIG. 3).

  A post-drying unit 142 is provided following the print detection unit 124. The post-drying unit 142 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 144 is provided following the post-drying unit 142. The heating / pressurizing unit 144 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 145 having a predetermined uneven surface shape while heating the image surface, and transfers the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output 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. 15, 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.

  FIG. 17A is a plan perspective view showing a structural example of the head 150, and FIG. 17B is an enlarged view of a part of FIG. FIG. 17C is a plan perspective view showing another structure example of the head 150, and FIG. 18 is a cross-sectional view showing the configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 151). It is sectional drawing which follows the 18-18 line of Fig.17 (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. 17A and 17B, the head 150 of this example includes a plurality of ink chamber units each including a nozzle 151 that is an ink discharge port, a pressure chamber 152 corresponding to each nozzle 151, and the like. (Droplet ejection elements) 153 has a structure in which the 153 is arranged in a zigzag matrix (two-dimensionally), and is thereby projected so as to be aligned along the longitudinal direction of the head (direction perpendicular to the paper feed direction). High density of substantial nozzle interval (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. 17A, as shown in FIG. 17C, 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. 17A and 17B), and is located at one of the diagonal corners. An outlet to the nozzle 151 is provided, and an inlet (supply port) 154 for supply ink 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. 18, 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 that also serves as a common electrode) 156 constituting a part of the pressure chamber 152 (the top surface in FIG. 18). 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.

  Note that each recording element of this embodiment includes a common electrode 156, an individual electrode 157, an actuator 158, and a nozzle 151.

  As shown in FIG. 19, the ink chamber unit 153 having the structure described above has a constant arrangement pattern along the row direction along the main scanning direction and the oblique column direction having a constant angle θ not orthogonal to the main scanning direction. Thus, the high-density nozzle head of this example is realized by arranging a large number in a grid pattern.

  That is, with a structure in which a plurality of ink chamber units 153 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be arranged 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, for example, the number of nozzle rows projected so as to be aligned in the main scanning direction is 2400 per inch (2400 nozzles / inch).

  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. 19, 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 the recording paper 116 by sequentially driving the nozzles 151-11, 151-12,. One line is printed in the width direction of 116.

  On the other hand, by moving the full line head and the paper relative to each other, it is possible to repeatedly print one line formed by the main scanning described above (a line composed of a single row of dots or a line composed of a plurality of rows of dots). 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 the main scanning direction, and the direction in which the sub scanning is performed is referred to as the 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.

(Description of control system)
FIG. 20 is a block diagram illustrating a system configuration of the inkjet recording apparatus 110.

  As shown in FIG. 20, the ink jet recording apparatus 110 includes a communication interface 170, a system controller 172, an image memory 174, a storage device 175, a motor driver 176, a heater driver 178, a print control unit 180, an image buffer memory 182, and a head driver 184. Etc.

  The communication interface 170 is an interface unit (image input means) 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 each unit such as 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 the storage device 175, and the like. And a drive control signal for controlling the motor 188 and the heater 189 of the transport system is generated.

  The storage device 175 stores a program executed by the CPU of the system controller 172 and various data necessary for control (including data of a non-ejection detection test chart and a density measurement test chart). The storage device 175 may be a non-rewritable storage unit such as a ROM, or may be a rewritable storage unit such as an EEPROM.

  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 the post-drying unit 142 in accordance with an instruction from the system controller 172.

  The print control unit 180 performs processing such as various processing and correction for generating a droplet ejection control signal from image data (multi-value input image data) in the image memory 174 in accordance with the control of the system controller 172. In addition to functioning as signal processing means, it also functions as drive control means for controlling the ejection drive of the head 150 by supplying the generated ink ejection data to the head driver 184.

  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. In FIG. 20, the image buffer memory 182 is shown in a mode associated with the print control unit 180, but it can also be used as the image memory 174 or the storage device 175. Also possible is an aspect in which the print controller 180 and the system controller 172 are integrated and configured with one processor.

  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. The dot data for each color is converted into CMYK droplet ejection 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 control 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 control 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 control signal waveform generated through the required signal processing in the print control unit 180, the ink droplet discharge amount and discharge timing of each nozzle via the head driver 184 are determined. Control is performed. Thereby, a desired dot size and dot arrangement are realized.

  As described with reference to FIG. 15, 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 print status (whether ejection is performed, droplet ejection Variation, 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.

(Control system for correction processing)
Next, a control configuration related to the shading correction process and the non-ejection correction process will be described with reference to FIG. FIG. 21 is a functional block diagram showing a control configuration related to the correction process.

  A correction processing control unit 100 shown in FIG. 21 is a unit that controls the above-described shading correction processing and non-ejection correction processing. The system controller 172, print control unit 180, image memory 174, storage device 175, and image buffer in FIG. The memory 182 and other devices are used. The following units included in the correction processing control unit 100 are captured by a functional configuration, and these hardware devices are realized singly or in combination.

  The correction processing control unit 100 includes an output data reading unit 30, a nozzle determination unit 36, a correction calculation unit 40, a scanner control unit 56, and a head driver 184. The output data reading unit 30 includes a nozzle position specifying unit 32 and a measured density measuring unit 34, the correction calculation unit 40 includes a shading correction processing unit 42 and a non-ejection correction processing unit 44, and the data output unit 50 includes a correction image output unit. 52 and an image output unit 54 for printing.

  The print detection unit 124 functions as a density information acquisition unit that acquires output density data (image reading data) of each recording element by scanning a test chart (see FIG. 3) indicating the recording density formed for each recording element. To do. The print detection unit 124 transmits the acquired image reading data of the test chart to the output data reading unit 30.

  The output data reading unit 30 functions as density information acquisition means for acquiring output density data indicating the recording density for each recording element based on the test chart image reading data sent from the print detection unit 124. The output data reading unit 30 includes a nozzle position specifying unit 32 that obtains the position of the corresponding nozzle from the measurement position in the test chart, and a measurement density measurement unit 34 that detects the ink output density at the measurement position in the test chart.

The nozzle determination unit 36 functions as a characteristic calculation unit that obtains ejection information (recording information) for each recording element from the output density data acquired by the output data reading unit 30 based on the test chart. Specifically, based on the output density data for each printing element sent from the output data reading unit 30 and the input image data for test chart output sent from the data output unit 50, the nozzle discrimination unit 36. Finds discharge information (test characteristic curve G _t ) for each nozzle.

  Further, the nozzle discrimination unit 36 functions as a characteristic storage unit that stores predetermined normal characteristic information (proper characteristic curve Ga) of the printing element, and compares this characteristic information with the discharge information for each printing element. It also functions as a correction process switching means for switching the content of the correction process for ejection control of the target recording element according to the comparison result. Specifically, the nozzle determination unit 36 performs ejection correction processing (shading correction processing) that treats the target recording element as a normal recording element (ejection recording element), and treats the target recording element as an abnormal density recording element (non-ejection recording element). The content of the correction process for the discharge control of the target recording element is switched between the non-discharge correction process to be handled. This switching criterion is based on the comparison result between the ejection information and the characteristic information, and when a normal amount of ink can be ejected from the target recording element by the ejection correction process (shading correction process), The content of the correction process for the discharge control is referred to as a discharge correction process. Further, when it is impossible to discharge a normal amount of liquid from the target recording element by the discharge correction process, the content of the correction process for the discharge control of the target recording element is set as the non-discharge correction process.

For example, as shown in FIG. 7 or FIG. 10, the nozzle discrimination unit 36 performs correction processing according to the comparison result between the output density data (G _t ) of the ejection information and the predetermined critical density data D _c based on the characteristic information. The contents can be switched. That is, the nozzle determination unit 36 can switch the content of the correction process depending on whether or not the output density data of the ejection information is included in a predetermined range based on the characteristic information. Further, as shown in FIG. 8, the nozzle determination unit 36 can also switch the content of the correction process according to the comparison result between a plurality of output density data acquired over time. Further, as shown in FIG. 9, the nozzle determination unit 36 can also switch the content of the correction process depending on whether or not the test characteristic curve of the output density data with respect to the input density data derived from the ejection information monotonously increases.

  The correction calculation unit 40 functions as a correction unit that corrects the discharge control of the target recording element based on the discharge information and the characteristic information (the test characteristic curve and the appropriate characteristic curve) according to the content of the correction process switched by the nozzle determination unit 36. To do. The discharge information and the characteristic information are sent from the nozzle determination unit 36 to the correction calculation unit 40.

  The shading correction processing unit 42 of the correction calculation unit 40 calculates a shading correction value so that an appropriate shading correction process as shown in FIG. 12 is performed on the recording element switched to the shading correction process in the nozzle determination unit 36. To do. Further, the non-ejection correction processing unit 44 of the correction calculation unit 40 does not perform an appropriate non-ejection correction process as shown in FIG. 11 on the recording element switched to the non-ejection correction process in the nozzle discrimination unit 36. A discharge correction value is calculated.

  The data output unit 50 functions as a correction unit that corrects the ejection control of the target recording element based on the content of the correction process (shading correction process, non-discharge correction process) switched by the correction calculation unit 40. The correction image output unit 52 of the data output unit 50 outputs input image data for forming a test chart on a recording medium. The print image output unit 54 of the data output unit 50 outputs input image data for forming a desired image on a recording medium.

  The correction image output unit 52 transmits input image data for forming a test chart to the head driver 184 every time a desired image is printed or based on an instruction from the user via the host computer 186. When recording the test chart, the data output unit 50 notifies the scanner control unit 56 that controls the print detection unit 124 that the test chart is recorded, and the scanner control unit 56 notifies the notification. The print detection unit 124 may be controlled so that a scan image of the recorded test chart is acquired based on the above. Also, the input image data for forming the test chart is notified to the nozzle discriminating unit 36, and is used for determining whether the target nozzle in the nozzle discriminating unit 36 is a normal nozzle or an abnormal density nozzle.

  The print image output unit 54 performs a shading correction process or a non-ejection correction process based on the correction information sent from the correction calculation unit 40 on the input image data related to the recording of the desired image sent from the host computer 186. This is performed for each recording element, and the input image data subjected to such correction is output to the head driver 184.

  The head driver 184 sends a drive control signal based on the input image data sent from the data output unit 50 to the head 150 (actuator 158 and the like) and various devices related to driving the head 150, and sends it from the data output unit 50. An image based on the input image data is formed on a recording medium. In this way, a test chart for correction determination and a print image desired by the user are recorded on the recording medium.

  In this embodiment, the print detection unit (scanner) 124 is provided in the inkjet recording apparatus 110. However, a print detection unit for reading a test chart may be provided separately from the inkjet recording apparatus 110.

  Further, the processing of the input density data may be performed by an image processing apparatus separate from the ink jet recording apparatus 110.

  In the above embodiment, the case where the present invention is applied to an ink jet recording apparatus has been described. However, the scope of the present invention is not limited to this. That is, the present invention relates to an image recording apparatus of a type other than an ink jet recording apparatus, for example, a thermal transfer recording apparatus including a recording head using a thermal element as a recording element, and an LED electrophotography including a recording head including an LED element as a recording element. The present invention can also be applied to a printer and a silver halide photographic printer having an LED line exposure head.

  DESCRIPTION OF SYMBOLS 30 ... Output data reading part, 32 ... Nozzle position specific | specification part, 34 ... Measurement density measurement part, 36 ... Nozzle discrimination | determination part, 40 ... Correction calculating part, 42 ... Shading correction process part, 44 ... Non-ejection correction process part, 50 ... Data output unit 52 ... Image output unit for correction 54 ... Image output unit for printing 56 ... Scanner control unit 100 ... Correction control unit 110 ... Inkjet recording device 112 ... Recording head 114 ... Ink storage / loading 116, recording medium, 118, paper feeding unit, 120 ... decurling unit, 122 ... belt conveying unit, 124 ... print detection unit, 126 ... paper discharge unit, 126A ... paper discharge unit, 128 ... cutter, 130 ... heating drum 131 ... Roller, 133 ... Belt, 134 ... Adsorption chamber, 135 ... Fan, 136 ... Belt cleaning unit, 140 ... Heating fan, 142 ... Post-drying unit, 144 Pressure unit, 145 ... pressure roller, 150 ... head, 151 ... nozzle, 152 ... pressure chamber, 153 ... ink chamber unit, 154 ... supply port, 155 ... common channel, 156 ... common electrode, 157 ... individual electrode, 158 ... Actuator, 170 ... Communication interface, 172 ... System controller, 174 ... Image memory, 175 ... Storage device, 176 ... Motor driver, 178 ... Heater driver, 180 ... Print control unit, 182 ... Image buffer memory, 184 ... Head driver 186: Host computer, 188 ... Motor, 189 ... Heater

Claims (12)

A recording head having a plurality of recording elements;
Conveying means for conveying at least one of the recording head and the recording medium to relatively move the recording head and the recording medium;
Density information acquisition means for acquiring output density data indicating a recording density for each recording element;
Characteristic calculating means for obtaining recording information for each recording element from the output density data acquired by the density information acquiring means;
Characteristic storage means for storing characteristic information at the time of the plurality of recording elements determined in advance;
Correction processing for ejection control of the target recording element among the plurality of recording elements according to a comparison result between the recording information for each recording element obtained by the characteristic calculation unit and the characteristic information stored by the characteristic storage unit Correction processing switching means for switching the contents of
Correction means for correcting the ejection control of the target recording element based on the recording information and the characteristic information according to the content of the correction process switched by the correction process switching means ,
The recording information includes a plurality of the output density data acquired over time,
The image recording apparatus characterized in that the correction processing switching means switches the content of the correction processing in accordance with a comparison result between the plurality of output density data acquired over time . A recording head having a plurality of recording elements;
Conveying means for conveying at least one of the recording head and the recording medium to relatively move the recording head and the recording medium;
Density information acquisition means for acquiring output density data indicating a recording density for each recording element;
Characteristic calculating means for obtaining recording information for each recording element from the output density data acquired by the density information acquiring means;
Characteristic storage means for storing characteristic information at the time of the plurality of recording elements determined in advance;
Correction processing for ejection control of the target recording element among the plurality of recording elements according to a comparison result between the recording information for each recording element obtained by the characteristic calculation unit and the characteristic information stored by the characteristic storage unit Correction processing switching means for switching the contents of
Correction means for correcting the ejection control of the target recording element based on the recording information and the characteristic information according to the content of the correction process switched by the correction process switching means,
The image recording apparatus according to claim 1, wherein the correction processing switching means switches the content of the correction processing according to whether or not a characteristic curve of the output density data with respect to input density data derived from the recording information increases monotonously. The content of the correction process for the ejection control of the target recording element includes an ejection correction process in which the target recording element is handled as an ejection recording element, and a non-ejection correction process in which the target recording element is treated as a non-ejection recording element. The image recording apparatus according to claim 1 or 2 . The ejection correction process involves controlling the ejection of liquid from the target recording element,
The image recording apparatus according to claim 3 , wherein the non-ejection correction process includes control of ejection of liquid from another recording element without ejecting liquid from the target recording element . The correction processing switching means performs correction processing for the discharge control of the target recording element when the target recording element can output an output density of an appropriate value by the discharge correction processing according to the comparison result. The content is the ejection correction process, and when the target recording element cannot output an appropriate output density by the ejection correction process, the content of the correction process for the ejection control of the target recording element is the non-ejection The image recording apparatus according to claim 4 , wherein correction processing is performed . 6. The recording information and the characteristic information are based on input density data input to the plurality of recording elements and output density data of the plurality of recording elements. The image recording apparatus described. The correction processing switching means switches the content of the correction processing according to a comparison result between the output density data of the recording information and predetermined critical density data based on the characteristic information. The image recording apparatus described. The correction processing switching means switches the content of the correction processing depending on whether or not the output density data of the recording information is included in a predetermined range based on the characteristic information. The image recording apparatus described in 1. 9. The image recording apparatus according to claim 1, wherein the plurality of recording elements are arranged in a range corresponding to a full width of a recording range of the recording medium in the recording head . The image recording apparatus according to claim 1, wherein the recording head records an image in a predetermined recording range of the recording medium by performing the relative movement once . An image recording method for recording an image by controlling a plurality of recording elements,
A density information acquisition step for acquiring output density data indicating a recording density for each recording element;
A characteristic calculation step for obtaining recording information for each recording element from the output density data;
According to the comparison result between the recording information for each recording element and the characteristic information at the time of the plurality of recording elements determined in advance, the correction processing for the ejection control of the target recording element among the plurality of recording elements Correction processing switching step for switching the contents,
A correction step for correcting the ejection control of the target recording element based on the content of the correction process switched in the correction process switching step,
The recording information includes a plurality of the output density data acquired over time,
In the correction processing switching step, the content of the correction processing is switched according to a comparison result between the plurality of output density data acquired over time. An image recording method for recording an image by controlling a plurality of recording elements,
A density information acquisition step for acquiring output density data indicating a recording density for each recording element;
A characteristic calculation step for obtaining recording information for each recording element from the output density data;
According to the comparison result between the recording information for each recording element and the characteristic information at the time of the plurality of recording elements determined in advance, the correction processing for the ejection control of the target recording element among the plurality of recording elements Correction processing switching step for switching the contents,
A correction step for correcting the ejection control of the target recording element based on the content of the correction process switched in the correction process switching step,
In the correction processing switching step, the content of the correction processing is switched according to whether or not the characteristic curve of the output density data with respect to the input density data derived from the recording information monotonously increases. .