JP5698595B2 - Image recording device - Google Patents

Description

  The present invention relates to an image recording apparatus and an image recording apparatus control method, and more particularly to an image recording apparatus and an image recording apparatus control method for suppressing density unevenness due to a temperature change of ink.

  As an image recording apparatus, for example, an ink jet full line type color image recording apparatus is known. In such a full-line color image recording apparatus, for example, a long recording head is provided for each color ink of K (black), C (cyan), M (magenta), and Y (yellow), or KCMY. A plurality of short recording heads are provided for each color to perform color image recording. When a plurality of short recording heads are provided for each color, the plurality of short recording heads are arranged in a direction (main scanning direction) perpendicular to the conveyance direction (sub scanning direction) of the recording medium.

  In a full-line image recording apparatus, nozzle rows (recording heads) are arranged for each ink color at a predetermined interval in the direction of transporting a recording medium (sub-scanning direction). The nozzle rows are a plurality of nozzles for ejecting ink, and are arranged over a length equal to or greater than the width of the recording medium in a direction orthogonal to the sub-scanning direction (main scanning direction). Further, in a full-line image recording apparatus (hereinafter simply referred to as an image recording apparatus), desired characters and images are ejected by discharging ink toward a recording medium conveyed from a plurality of nozzles included in each color nozzle row. Recording processing can be performed at high speed.

  A transport mechanism for transporting the recording medium is provided at a position facing such a long recording head or a plurality of short recording heads. For example, the image recording unit receives job information transmitted from the host device, generates recording data from the received job information, and applies any one of the inks of KCMY from each recording head based on the recording data. An image is recorded on a recording medium that is ejected and conveyed directly under the image recording unit.

  In such an image recording apparatus, heat generated when the recording head is driven increases the temperature of the recording head and its surroundings, which may increase the temperature of the ink. When ink changes in temperature, its viscosity and other characteristics change, which changes the amount of ink droplets ejected. This change in ink temperature causes density unevenness in the recorded image. Yes.

  Some image recording apparatuses include a temperature control unit for adjusting the temperature of the recording head to a constant temperature. In such an image recording apparatus, the nozzle or the recording head has a high gradation value. When dots are formed continuously, temperature control by the temperature control unit is insufficient, and an increase in ink temperature cannot be prevented.

  Therefore, a technique has been proposed in which the ambient temperature around the print head is detected and the drive voltage of the print head is switched according to the detected temperature. (For example, Patent Document 1)

Japanese Patent No. 3750750

  However, in the ink jet printer of Patent Document 1, if the head drive voltage is switched during printing of one or one image, the characteristics of ink ejection from the ink jet nozzle change, and the recording state changes to change the image. The recording voltage may be deteriorated, so that the driving voltage cannot be changed during printing of one or one image.

An image recording apparatus according to one aspect of the present invention includes an image recording unit that records an image by ejecting ink onto a recording medium based on recording data, and an ink temperature acquisition unit that acquires an ink temperature of the image recording unit. From the ink temperature correction table in which the preset ink temperature and the correction value for correcting the gradation value indicating the ink discharge liquid amount are associated with each other, the correction value is obtained using the acquired ink temperature. A correction value acquisition unit to be acquired; a correction unit that corrects a gradation value representing an ink ejection liquid amount for each dot forming the image included in the recording data using the acquired correction value; and the recording An image area in the image is specified based on the data, and when the gradation value of a dot in the image area is equal to or less than a predetermined threshold, the image area is set as a correction value fixed area. An image analysis unit, and wherein said correction unit, while the image recording unit is recording the image in the correction value fixed region, fixing the correction value used for correction of the gradation values, the image The recording unit ejects ink onto the recording medium using the corrected gradation value.

  According to some embodiments of the present invention, it is possible to prevent density unevenness due to a change in ink temperature.

1 is a block diagram illustrating the configuration of an image recording apparatus according to an embodiment of the invention. It is a figure which illustrates arrangement | positioning of the component of the image recording apparatus which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the ink temperature which concerns on one Embodiment of this invention, and the correction value of a gradation value. It is an operation | movement flowchart which shows the correction process which concerns on the 1st Embodiment of this invention. It is a figure explaining the correction process which concerns on the 2nd Embodiment of this invention. It is an operation | movement flowchart which shows the correction process which concerns on the 2nd Embodiment of this invention. It is a figure explaining the correction process which concerns on the 3rd Embodiment of this invention. It is an operation | movement flowchart which shows the temperature correction process which concerns on the 3rd Embodiment of this invention.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol was attached | subjected to the corresponding element in several drawing. In the following description, an example in which an inkjet full-line image recording device is used as the image recording device of the present embodiment will be described. However, the image recording device according to the embodiment of the present invention is an inkjet full-line image recording device. The present invention is not limited to this image recording apparatus, and can be applied to other apparatuses as long as the image recording apparatus uses ink.

  FIG. 1 is a block diagram illustrating the configuration of an image recording apparatus 1 according to an embodiment of the invention. FIG. 2 is a diagram showing an example of the arrangement of components of the image recording apparatus 1 according to an embodiment of the present invention. Hereinafter, an image recording apparatus 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  An image recording apparatus 1 according to an embodiment of the present invention includes a control unit 2, an image recording unit 3, a feeding unit 4, a transport unit 5, and a storage unit 6.

  The control unit 2 includes, for example, an MPU (Micro Processor Unit) and has a control function and a calculation function. The control unit 2 includes a storage unit 7.

  The control unit 2 determines the timing of ejecting ink from the nozzle row 33 included in the recording head 32 of the image recording unit 3 based on the conveyance distance information generated by the conveyance information generation unit 53. The control unit 2 controls the nozzle row driving unit 31 at a timing at which the recording medium 9 is conveyed to a position facing the nozzle row 33 based on the conveyance distance information, and ejects ink from the nozzle row 33 to perform a recording process. .

  The storage unit 7 stores, for example, a ROM (Read Only Memory) that stores a control program, a RAM (Random Access Memory) that the MPU uses as a working storage area, and various setting values related to the control of the image recording apparatus 1. Includes non-volatile memory.

  The control unit 2 functions as, for example, an ink temperature acquisition unit 21, a correction value acquisition unit 22, a correction unit 23, an image analysis unit 24, and a temperature correction unit 25 by executing a control program stored in the ROM, for example. To do. This control program is stored in advance in a ROM, for example.

  In one embodiment according to the present invention, the storage unit 7 is used to execute correction of print data. For example, the ink corresponding to the ink temperature and the correction value as shown in FIGS. 3A and 3B is used. A temperature correction graph or an ink temperature correction table is recorded in advance.

  The image recording unit 3 includes, for example, a recording head 32 including a nozzle row 33, a nozzle row driving unit 31, and an ink temperature measuring unit 34. The nozzle row 33 is formed by a plurality of nozzles that eject ink. The nozzle row drive unit 31 individually drives a plurality of nozzles included in the nozzle row 33 in accordance with the drive instruction from the control unit 2.

  The ink temperature measurement unit 34 is, for example, a thermometer and measures the ink temperature in the image recording unit 3. There are various values that can be used as the ink temperature, and it is not always necessary to directly measure the ink temperature. The ink temperature may be, for example, the temperature in the vicinity of individual nozzles included in the nozzle row 33 or the temperature of the recording head 32 including a plurality of nozzles. Examples of the ink temperature are not limited to these, and may be any value as long as the value reflects the temperature change of the ink immediately before being ejected from the nozzle.

  The feeding unit 4 includes, for example, a feeding tray 41 on which the recording medium 9 such as paper is stacked, and a feeding roller 42 that carries out the recording medium 9, and drives the feeding roller 42 in accordance with an instruction from the control unit 2. The recording medium 9 is transported to the transport unit 5.

  The transport unit 5 includes a transport member 51 configured by, for example, an endless belt, a transport drive unit 52 and a driven unit 54 that drive the transport member 51, and a transport information generation unit 53 that generates transport distance information of the recording medium 9. The recording medium 9 is conveyed to the storage unit 6.

  The storage unit 6 includes a paper discharge roller 61 and a storage tray 62. The storage unit 6 discharges the recording medium 9 on which the recording process has been performed by the image recording unit 3 to the outside by the paper discharge roller 61 and stores it in the storage tray 62.

  In FIG. 1, the image recording apparatus 1 is connected to a host apparatus 8 such as a personal computer (PC). In one embodiment, the image recording apparatus 1 receives job information from the higher-level apparatus 8, and discharges ink onto the recording medium 9 from a plurality of nozzles based on the received job information to perform a recording process.

  However, the image recording apparatus 1 does not necessarily need to be connected to the host apparatus 8. In another embodiment, for example, a storage medium such as a flash memory is connected to the image recording apparatus 1 and stored in the storage medium. Job information may be generated based on the data and the recording process may be executed.

  Further, the ink temperature acquisition unit 21, the correction value acquisition unit 22, the correction unit 23, the image analysis unit 24, and the temperature correction unit 25 described above are signal processing circuits as hardware controlled by the arithmetic processing unit of the control unit 2. It may be configured.

  In the image recording apparatus 1 exemplified above, the first embodiment according to the present invention will be described below.

<First Embodiment>
In the first embodiment, when the ink temperature changes, the image recording apparatus 1 corrects the gradation value indicating the ejection amount included in the recording data.

  For example, the correction of the gradation value indicating the ejection amount of the recording data is performed based on the correspondence between the gradation correction value and the ink temperature as shown in FIG. 3 (details will be described later). In the first embodiment, the ink temperature acquisition unit 21 acquires the ink temperature measured by the ink temperature measurement unit 34 of the image recording unit 3. The correction value acquisition unit 22 of the image recording apparatus 1 uses the ink temperature correction graph in FIG. 3A or the ink temperature correction table in FIG. 3B as the correction value corresponding to the ink temperature acquired by the ink temperature acquisition unit 21. Get by reference. The correction unit 23 uses the acquired correction value to correct the gradation value representing the ink discharge liquid amount for each dot forming the image included in the print data. The image recording unit 3 performs recording on the recording medium 9 using the corrected gradation value.

  These correction values are determined in accordance with the change in the amount of ink droplets ejected from the nozzles due to the change in ink temperature. By correcting the gradation value using this correction value, the ink value It is possible to suppress deterioration in image quality due to a change in the amount of ink discharged due to a change in temperature. Hereinafter, these processes will be described in detail.

  FIG. 3A is an ink temperature correction graph showing a correspondence relationship between the ink temperature and the correction value of the gradation value of the recording data according to an embodiment of the present invention. In FIG. 3A, the change in ink temperature is associated with the correction value. FIG. 3B is an ink temperature correction table showing the correspondence between the ink temperature and the correction value shown in FIG. 3A as a table. The relationship between the ink temperature and the correction value for correcting the gradation value indicating the amount of ink discharged is, for example, the ink characteristics and the ink for one gradation from the nozzle of the image recording unit 3 to be used. May be set in advance based on the discharge liquid amount or the like, and may be stored in the storage unit 7 as a graph or a table, for example. The correction values shown in FIGS. 3A and 3B are the gradation values representing the ink discharge amount for each dot forming the image included in the print data by the correction unit 23 according to the change in the ink temperature. Used to correct.

  In the image recording apparatus 1 according to the present embodiment, each nozzle included in the recording head 32 discharges an ideal discharge liquid amount determined as a design target value at a temperature of 25 ° C. set as a reference temperature. Designed to. Therefore, as shown in FIGS. 3A and 3B, the correction value is 0 in the range of 24 ° C. to 27 ° C., which is the temperature range around 25 ° C., and no correction is actually performed. It will be. However, for example, in the recording process, when ink droplets are ejected from the nozzles and dots with high gradation values are continuously formed, the nozzle drive rate is high, so the temperature around the nozzles rises and the ink temperature rises. Lead. When the ink temperature exceeds 27 ° C., the influence of an increase in the amount of ink droplets caused by the temperature change on the image quality becomes conspicuous. For this reason, −1 is set as the gradation correction value in order to suppress the density of the formed dots from increasing due to an increase in the amount of ejected liquid caused by an increase in the ink temperature. In addition, for example, the temperature of the ink may decrease due to the low temperature depending on the environment. If the temperature drops below 24 ° C., the decrease in the amount of ink droplets will have a noticeable effect on the image quality. become. For this reason, +1 is set as the gradation correction value in order to suppress a decrease in dot density due to a decrease in the amount of discharged liquid caused by a decrease in ink temperature. In this way, in FIGS. 3A and 3B, correction value +3 to -19 ° C, correction value +2 to 19 ° C to 21, correction value +1 to 21 ° C to 24 ° C, and correction value +1 to 24 ° C to 27 ° C. Correction value -1 is set to the value 0, 27 ° C to 29 ° C, correction value-2 is set to 29 ° C to 30 ° C, and correction value -3 is set to 30 ° C to 31 ° C.

  Note that the number of gradations and the amount of ink discharged per gradation (that is, the amount of liquid per drop of ink droplet) vary depending on the image recording apparatus 1. Therefore, the correction values shown in the ink temperature correction graph of FIG. 3A and the ink temperature correction table of FIG. 3B depend on the number of gradations of the image recording apparatus 1 and the amount of ink ejected per gradation. Thus, the ink droplet liquid volume that has been increased or decreased due to changes in the ink temperature is set as a design reference (in this embodiment, the ink droplet liquid volume at 25 ° C., which is the reference temperature as described above). The value is set to return to. In one embodiment, the number of gradations is 8 gradations, and the amount of ink ejected per gradation is 6 pl.

  In some embodiments, the correspondence between the ink temperature and the correction value as shown in FIG. 3A or FIG. 3B is stored in advance in the storage unit 7 as a graph or a table, for example, and the correction unit 23 Is referred to when performing correction.

  FIG. 4 is an operation flowchart showing a correction process according to the first embodiment of the present invention. The flow in FIG. 4 starts when the image recording apparatus 1 receives job information from the upper apparatus 8 or the like, for example. In step S <b> 1, the ink temperature acquisition unit 21 acquires the ink temperature measured by the ink temperature measurement unit 34 such as a thermometer provided in the recording head 32.

  In step S2, the correction value acquisition unit 22 uses the acquired ink temperature to calculate the ink temperature and the correction value such as the ink temperature correction graph shown in FIG. 3A or the ink temperature correction table shown in FIG. The correction value is acquired by referring to the correspondence relationship.

  In step S3, the correction unit 23 corrects the gradation value of each dot of the image included in the recording data in the job information using the acquired correction value, and the image recording unit 3 calculates the corrected gradation value. Ink is ejected onto the recording medium to form each dot of the image included in the recording data.

  After the gradation value correction and recording process, the flow proceeds to step S4, where it is determined whether or not all the recording processes specified by the job information have been completed. When all the recording processes instructed by the job information have been completed, it is determined as Yes and this flow ends. On the other hand, if the recording process instructed by the job information has not ended, it is determined No, the flow proceeds to step S1, and these processes are repeated until the job ends.

  As described above, there are various values that can be used as the ink temperature, and it is not always necessary to directly measure the ink temperature. For example, the value used as the ink temperature is any value as long as the value changes according to the change in the temperature of the ink in the image recording unit 3 such as the temperature of the recording head 32 or the temperature of each nozzle. There may be.

  Further, when the image recording unit 3 of the image recording apparatus 1 is configured by combining a plurality of short recording heads 32 and the ink temperature measuring unit 34 measures the temperature of the recording head 32 as the ink temperature, for example, FIG. The gradation value correction by the operation flow may be performed for each recording head 32. Further, for example, when the ink temperature measurement unit 34 measures the temperature in units of nozzles as the ink temperature, the gradation value correction by the operation flow of FIG. 4 may be performed for each nozzle.

  As described above, the image recording apparatus 1 according to the present invention monitors the change in the ink temperature, and uses the correction value corresponding to the ink temperature to determine the gradation value of each dot that forms the image of the recording data. Since the correction is performed, it is possible to suppress the density unevenness of the recorded image due to the change in the ink temperature.

  Further, since the correction according to the change in the ink temperature according to the present embodiment is a treatment for the gradation value of the dots forming the image, it can be executed without changing the drive voltage of the recording head. It can be executed even during recording of one image or one image, or during ejection of ink.

<Second Embodiment>
Next, the second embodiment will be described with reference to FIGS. 5 and 6. In the second embodiment, the correction value is fixed to a constant value in an image area composed of dots having a gradation value equal to or lower than a predetermined gradation value. The correction value is fixed in the case of an image area composed of dots having gradation values equal to or lower than a predetermined gradation value, particularly in the case of an image area filled with dots equal to or lower than a predetermined gradation value. If the correction value is changed within the range, the density unevenness due to the change of the correction value becomes noticeable. Therefore, this is performed to prohibit the change of the correction value in such an image area.

  First, specification of the position of the image area will be described. In a general printing apparatus, for example, original data created with a vector image or the like is rasterized into bitmap data when generating job information. Since the bitmap data is composed of data indicating gradation values representing the shade of color for each dot, the bitmap data is an image formed by dots. However, in original data such as a vector image before being converted into bitmap data, a distinction is made between an image area composed of images such as photographs and pictures and a text area composed of text such as characters and symbols. May have been.

  In such a case, image area information indicating the position in which the image area exists in the rasterized bitmap data (for example, represented by the coordinate range of dots in the horizontal and vertical directions of the image area). ), And text area information (for example, represented by the coordinate range of dots in the horizontal and vertical directions of the text area) indicating the position in which the text area is present in the rasterized bitmap data. By including them, the positions of the image area and the text area can be specified based on the job information.

  FIG. 5 shows, as an example, an image area A and an image area B composed of images such as photographs and pictures, and a text area C composed of characters and symbols. The image analysis unit 24 specifies the positions of the image area and the text area based on the image area information and the text area information included in the job information. Further, the image analysis unit 24 uses the position of the image area specified by the image area information to determine whether or not the tone value of the dot in the image area is equal to or less than a predetermined threshold value. When the tone value of a certain dot is equal to or less than a predetermined threshold, the image area is set as a correction value fixed area for fixing the correction value.

  An image area A shown in FIG. 5 is a correction value changeable area in which the gradation value is higher than a predetermined threshold and the correction value can be changed. The image area B is a correction value fixing area in which the correction value is fixed at a gradation value lower than a predetermined threshold value.

  FIG. 6 is an operation flowchart showing a correction process according to the second embodiment of the present invention. In the first embodiment, when the correction value acquisition unit 22 acquires the correction value, the correction unit 23 immediately corrects the gradation value using the correction value (steps S2 to S3 in FIG. 4). However, in the second embodiment, after the correction value acquisition unit 22 acquires the correction value, the gradation is determined depending on whether or not the dot formed by the next ink droplet ejection is within the correction value fixed image region. Whether or not value correction is performed changes.

  The operation flow of FIG. 6 starts when the image recording apparatus 1 receives job information. In step ST <b> 1, the ink temperature acquisition unit 21 acquires the ink temperature from the ink temperature measurement unit 34.

  In step ST2, the correction value acquisition unit 22 acquires a correction value by referring to the correspondence between the ink temperature and the correction value as shown in FIG. 3A or 3B using the ink temperature. .

  Subsequently, the process proceeds to step ST3, and the image analysis unit 24 acquires image area information indicating the position of the image area in the image included in the recording data from the received job information, and uses the image area information, It is determined whether or not the dot formed by the next ink droplet ejection by the image recording unit 3 is in the image area. If there is no dot formed in the image area by the next ink droplet ejected by the image recording unit 3, step ST3 is determined to be No, and the flow proceeds to step ST5.

  On the other hand, when the image recording unit 3 ejects the next ink droplet and the dot to be formed is in the image area, step ST3 is determined to be YES, and the flow proceeds to step ST4. In step ST <b> 4, the image analysis unit 24 determines whether or not the image region including the dots that are formed by ejecting ink droplets next is a correction value fixed region that is configured by dots having a predetermined gradation value or less. To do. If it is the correction value fixed region, it is determined Yes and the flow proceeds to step ST6. On the other hand, if it is not the correction value fixed area but the correction value changeable area, it is determined No and the flow proceeds to step ST5.

  In step ST5, the correction unit 23 corrects the tone value of each dot forming the image included in the recording data using the correction value acquired by the correction value acquisition unit 22 in step ST2. In ST6, the image recording unit 3 executes the recording process using the recording data whose gradation value is corrected by the correcting unit 23.

  Subsequently, the flow proceeds to step ST7, where it is determined whether or not all the recording processes designated by the job information have been completed. If all the recording processes have not been completed, it is determined No, the flow returns to step ST1, and thereafter these processes are repeated until the end of the job. On the other hand, if the recording process instructed by the job information has been completed, the determination is Yes and the flow ends.

  The recording process executed according to the operation flow of FIG. 6 will be described using the example shown in FIG. In FIG. 5, the direction in which the recording process by the image recording apparatus 1 proceeds is indicated by an arrow X.

  When the image recording apparatus 1 receives the job information, it acquires a correction value according to the ink temperature in step ST1 to step ST2 in FIG. Further, since there is no image area at the upper end of the recording medium in FIG. 5, step ST3 is determined as No, and the image included in the job information using the correction value acquired by the correction value acquisition unit 22 in steps ST5 to ST6. The tone value of each dot forming the image is corrected, and using the corrected tone value, the image recording unit 3 starts the recording process from the upper end of the recording medium 9 in the direction of the arrow. Until the recording process reaches the image area A, if there is a change in the ink temperature exceeding a predetermined temperature point, the correction value is changed in steps ST1 to ST2, and the changed correction value is set in steps ST5 to ST6. The tone value is corrected using the corrected tone value, and the recording process proceeds using the corrected tone value.

  When the recording process reaches the image area A, the next dot formed by ejecting ink droplets is in the image area, so that step ST3 is determined to be Yes, but the image area A is corrected as described above. Since the value can be changed, step ST4 is determined as No, and the gradation value is corrected using the correction value in the storage unit 7 in steps ST5 to ST6, and recording is performed using the corrected gradation value. Processing proceeds. In addition, since the ink droplets are ejected from the nozzles of the image recording unit 3 while the image in the image area A is recorded, the image recording unit 3 generates heat and the ink temperature changes. When the change in the ink temperature exceeds a predetermined temperature point, the correction value acquired in step ST1 to step STE2 is changed, and the gradation value is corrected using the changed correction value. Recording processing is executed.

  When the recording process further proceeds and the image area A passes the lower end, step ST3 in FIG. 6 is determined No until the image area B is reached, so the correction value acquisition unit 22 acquires in step ST5 to step ST6. The gradation value is corrected using the corrected value.

  The image area B is a correction value fixed area as described above. Therefore, when the image area B is reached, step ST3 and step ST4 in FIG. 6 are determined as YES, and the recording process proceeds in step ST7 without correcting the gradation value in step ST5. Therefore, while the image recording unit 3 is recording an image in the image area B, the correction of the gradation value using the correction value is not performed, and the gradation value remains the value corrected in the previous correction process. As a result, the correction value used for correcting the gradation value is fixed. That is, in this image area B, since the gradation value is equal to or less than a predetermined threshold value, gradation correction is not performed because gradation unevenness is conspicuous when gradation correction is executed.

  When the recording process passes through the image area B, there is no image area thereafter. Therefore, if the ink temperature changes beyond a predetermined temperature point, the correction value is changed in steps ST1 to ST2, and in steps ST5 to ST6. The gradation value is corrected using the changed correction value, and the recording process proceeds using the corrected gradation value. In the present embodiment, the text area is a correction value changeable area. This is because in the text area, even if there is some variation in the ink discharge liquid amount, it is not so noticeable. Therefore, in the present embodiment, in the text area C, when the ink temperature changes beyond a predetermined temperature point, the correction value is changed, and the gradation value is corrected using the changed correction value. .

  As described above, in the second embodiment, while the image recording unit 3 records an image in the correction value fixed region, which is an image region having a gradation value equal to or less than a predetermined threshold, the correction unit No correction is performed on the gradation value 23, and the gradation value is not updated by the correction. Therefore, while an image is recorded in the correction value fixed area, the correction value used for correcting the gradation value is fixed and kept constant. Thereby, it is possible to suppress density unevenness caused by changing the correction value in the image area having the gradation value equal to or less than the threshold value.

<Third Embodiment>
Next, a third embodiment according to the present invention will be described with reference to FIGS. In the third embodiment, an image included in print data is analyzed, and the direction of change in ink temperature frequently changes based on the distribution of dots with high gradation values and dots with low gradation values in the image. The region is estimated, and in the region where the direction of change in the ink temperature changes frequently, the ink temperature measured by the temperature measurement unit is corrected, and the fluctuation of the correction value is moderated.

  First, estimation of an area where the direction of change in ink temperature frequently changes will be described. As described above, when the recording head is driven, heat is generated. Therefore, in the recording process, it is presumed that the ink temperature in the vicinity of the nozzle that records an image area in which dots having a high gradation and a large number of ink droplet ejections are continuously formed for a predetermined number of times or more increases. Is done. Further, in the recording process, a dot with a low gradation and a small number of ink droplet ejections is immediately after an image area where dots having a high gradation and a large number of ink droplet ejections are continuously formed for a predetermined number of times or more. When the image area continuously formed more than the number of times continues, the ink temperature rises in the high gradation area and then immediately falls in the low gradation area.

  In such an area in which an image area in which dots with low gradation are continuously formed for a predetermined number of times immediately follows an image area in which dots with high gradation are continuously formed for a predetermined number of times or more, the ink temperature Since the direction of the change in the vertical direction changes in a short time, if the ink temperature acquired by the ink temperature acquisition unit 21 is used as it is and the correction value is acquired with reference to the ink temperature correction graph or the ink temperature correction table, the correction value becomes frequent. In contrast, the density unevenness may be conspicuous.

  Therefore, in the third embodiment, the image analysis unit 24 analyzes the image included in the recording data in advance before executing the recording process by the image recording unit 3, and in the recording process, a dot having a high gradation is determined in advance. A region where an image region in which dots having low gradation are continuously formed for a predetermined number of times immediately after an image region continuously formed for the number of times is extracted as a temperature correction region.

  A dot having a high gradation value is a dot having a gradation value higher than a predetermined threshold. For example, the number of gradations is 8 gradations, and the amount of ink ejected per gradation is 6 pl. If the image recording apparatus 1 is assumed, the threshold value may be set so that the gradation value is 6 or more. In this case, if the gradation value is 6, 7, or 8, the dot has a high gradation value.

  Similarly, a dot having a low gradation value is a dot having a gradation value lower than a predetermined threshold value. For example, the number of gradations is 8 gradations, and the amount of ink ejected per gradation is 8 Assuming that the image recording apparatus 1 is 6 pl, the threshold value may be set to a gradation value of 2 or less. In this case, if the gradation value is 0, 1, and 2, the dot has a low gradation value.

  Note that the “predetermined number of times”, which is the number of consecutive high-tone dots or low-tone dots used for extraction of the temperature correction region, is also referred to as the continuous dot formation number in the following description. The number of continuous dot formations for high gradation dots and the number of continuous dot formations for low gradation dots may be the same or different.

  The example shown in FIG. 7 is an example in which the temperature correction region is extracted by setting the number of continuous dot formation times of the image region having a high gradation and the image region having a low gradation to 100 times, which is used for extraction of the temperature correction region. In the third embodiment, the temperature measured by the ink temperature measurement unit 34 is corrected in the extracted temperature correction region. In FIG. 7, the direction in which the recording process proceeds is indicated by an arrow X.

  FIG. 8 is an operation flowchart showing temperature correction processing according to the third embodiment. In the third embodiment, as in the first embodiment, the gradation value is corrected according to the operation flow shown in FIG. 4, but in the third embodiment, the ink executed in step S1 in FIG. The ink temperature is acquired by the temperature acquisition unit 21 according to the operation flow of FIG.

  The operation flow of FIG. 8 starts when the operation flow shown in FIG. 4 proceeds to step S1. In step STE1 of FIG. 8, the ink temperature acquisition unit 21 acquires the ink temperature, and the flow proceeds to step STE2.

  In step STE 2, the ink temperature acquisition unit 21 determines whether or not the dot formed by the next ink droplet ejection by the image recording unit 3 is within the temperature correction region extracted by the image analysis unit 24. If there is no dot in the temperature correction area formed by the next ink droplet ejected by the image recording unit 3, the determination is No and the flow proceeds to step STE3, and the ink measured by the ink temperature acquisition unit 21 in step STE3. The temperature is directly acquired as the ink temperature, and this flow ends.

  On the other hand, if the image recording unit 3 ejects the next ink droplet and the dot to be formed is within the temperature correction region, the determination is Yes and the flow proceeds to step STE4.

  In step STE4, the temperature correction unit 25 corrects the ink temperature acquired by the ink temperature measurement unit. In this correction, for example, the ink temperature measured by the temperature measurement unit 34 is corrected based on a preset temperature correction coefficient so that the deviation from the reference temperature becomes small. For example, this may be performed by calculating {(measured ink temperature−reference temperature) × temperature correction coefficient + reference temperature}. Here, the “reference temperature” is a temperature determined as a reference in the design of the nozzle, and in the present embodiment, the “reference temperature” is the same as described above in the description of FIGS. 3A and 3B. Is 25 ° C. The temperature correction coefficient is a predetermined value in consideration of the influence of the correction value variation on the image quality in the region where the direction of the temperature change of the ink temperature frequently changes. It may be set to a value between 0 and 1, and is 0.5 in the example of FIG.

  In the temperature correction area, the corrected value is acquired as the ink temperature and used in the processing after step S2 in FIG.

  For example, when the temperature acquired in step STE1 is 28 ° C., and there is no dot in the temperature correction area formed by the next ink droplet being ejected by the image recording unit 3, 28 ° C. is used as it is as the ink temperature. The correction value acquired in step S2 of FIG. 4 is −1 from the correspondence between the ink temperature and the correction value shown in FIG. 3A or 3B.

  However, if the temperature acquired in step STE1 is 28 ° C. and the dots formed by the next ink droplet ejection by the image recording unit 3 are in the temperature correction region, the temperature correction is executed in step STE4. , {(28 ° C.−25 ° C.) × 0.5 + 25 ° C.}, 26.5 ° C. is acquired as the ink temperature. Therefore, the correction value acquired in step S2 in FIG. 4 becomes 0 based on the correspondence between the ink temperature and the correction value shown in FIG. 3A or 3B.

  As described above, in the third embodiment, the temperature correction region estimated that the direction of change in the ink temperature frequently changes up and down is extracted. In the temperature correction region, for example, a preset temperature correction coefficient is extracted. Based on the above, the measured ink temperature is corrected so that the deviation from the reference temperature becomes small. Therefore, the correction value can be gradually changed even in an area where the change direction of the ink temperature is estimated to change frequently in a short period, thereby suppressing density unevenness.

  In the third embodiment, the process of gradually changing the correction value in the region where the change direction of the ink temperature changes frequently is not limited to these examples. For example, dots with low gradation are extracted continuously in a predetermined number of times immediately after an image area that has been extracted in the same manner as the temperature correction region described above and where dots with high gradation are continuously formed over a predetermined number of times. In the area where the formed image area continues, another table in which the correction value of the ink temperature correction table shown in FIG. 3B is reduced may be used. For example, in such another table, the correction values are 2, ink temperature to 20 ° C., 2 to 20 ° C. to 23 ° C., 1, 23 to 28 ° C., 0 to 28 ° C. to 30 ° C., 1, 30 ° C. to It may be set to -2 at 31 ° C.

  Further, the correction of the gradation value according to some embodiments of the present invention is not limited to that described in the above-described embodiment. For example, a correction coefficient is stored in a table as a correction value, and the correction coefficient is The gradation value may be corrected by multiplication. For example, in such a table, correction values used as ink temperature correction coefficients are 1.3 for ink temperature to 19 ° C., 1.2 for 19 ° C. to 21 ° C., 1.1 for 21 ° C. to 24 ° C., It may be set to 1.0 at 24 ° C to 27 ° C, 0.9 at 27 ° C to 29 ° C, 0.8 at 29 ° C to 30 ° C, 0.7 at 30 ° C to 31 ° C. In this case, the correction unit 23 obtains a value obtained by multiplying the correction coefficient acquired based on the ink temperature by the gradation value indicating the ink discharge liquid amount for each dot forming the image included in the print data. For example, rounding may be performed, and the image recording unit 3 may execute the recording process using the gradation value closest to the obtained value.

  In the above-described embodiments, the correction value is obtained from the ink temperature using only one correspondence between the ink temperature and the correction value shown in FIG. 3A or 3B. . However, the embodiment of the present invention is not limited to this. For example, the variation in the amount of ink discharged due to the variation in ink temperature varies depending on the type of ink. Therefore, for example, the ink temperature correction graph or the ink temperature correction table that associates the ink temperature and the correction value in FIG. 3 may be stored in the storage unit 7 for each ink type.

  Further, as described above, there are various values that can be used as the ink temperature. For example, when the temperature near each nozzle is acquired as the ink temperature, the correction value is acquired for each nozzle. However, when a common ink temperature is acquired for a plurality of nozzles, for example, the temperature of the recording head 32 is acquired as the ink temperature, one ink temperature acquired for the recording head 32 is used. The acquired one ink temperature is used for correcting the gradation value for the dots formed by the plurality of nozzles included in the recording head 32, as used for the plurality of nozzles included in the recording head 32. Also good.

  Further, in the extraction of the temperature correction area in the third embodiment, when the temperature of the recording head 32 is acquired as the ink temperature, a dot with a high gradation value is extracted from a plurality of nozzles included in one recording head. The gradation values of a plurality of dots formed by ink droplets ejected simultaneously from each of them may be averaged, and if the average value is higher than a predetermined threshold, it may be determined that the dot has a high gradation value. Similarly, a dot having a low gradation value also averages the gradation values of a plurality of dots formed by ink droplets simultaneously ejected from each of a plurality of nozzles included in one recording head, and the average value thereof. May be determined to be a dot having a low gradation value.

  Several embodiments have been described. However, the embodiments according to the present invention are not limited to the above-described embodiments, but should be understood as including various modifications and alternative forms of the above-described embodiments. For example, it will be understood that various embodiments can be embodied by modifying the components without departing from the spirit and scope thereof. Further, it will be understood that various embodiments according to the present invention can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. Alternatively, various implementations according to the present invention may be made by deleting or replacing some components from all the components shown in the embodiment, or adding some components to the components shown in the embodiment. One skilled in the art will appreciate that the form may be implemented.

DESCRIPTION OF SYMBOLS 1 Image recording device 2 Control part 3 Image recording part 4 Feeding part 5 Conveying part 6 Storage part 7 Storage part 8 High-order apparatus 9 Recording medium 21 Ink temperature acquisition part 22 Correction value acquisition part 23 Correction part 24 Image analysis part 25 Temperature correction Unit 31 Nozzle row drive unit 32 Recording head 33 Nozzle row 34 Ink temperature measurement unit 41 Feed tray 42 Feed roller 51 Transport member 52 Transport drive unit 53 Transport information generation unit 54 Drive unit 61 Paper discharge roller 62 Storage tray

Claims (3)

An image recording device,
An image recording unit for recording an image by ejecting ink to a recording medium based on the recording data;
An ink temperature acquisition unit for acquiring the ink temperature of the image recording unit;
A correction value is acquired using the acquired ink temperature from an ink temperature correction table in which a preset ink temperature and a correction value for correcting a gradation value indicating the ink discharge liquid amount are associated with each other. A correction value acquisition unit to perform,
A correction unit that corrects a gradation value representing an ink discharge amount for each dot forming the image included in the recording data, using the acquired correction value;
An image analysis that identifies an image area in the image based on the recording data and sets the image area as a correction value fixed area when the tone value of a dot in the image area is equal to or less than a predetermined threshold value With parts, and
The correction unit fixes the correction value used for correcting the gradation value while the image recording unit records an image in the correction value fixing region,
The image recording unit ejects ink onto the recording medium using the corrected gradation value;
An image recording apparatus. An image recording device,
An image recording unit for recording an image by ejecting ink to a recording medium based on the recording data;
An ink temperature acquisition unit for acquiring the ink temperature of the image recording unit;
An image analysis unit that extracts, as a temperature correction region, a region in which the direction of change in the ink temperature frequently changes based on a distribution of a high gradation portion and a low gradation portion of the image;
While the image recording unit records an image in the temperature correction region, the ink temperature acquired by the ink temperature acquisition unit is less shifted from the reference temperature based on a preset temperature correction coefficient. A temperature correction unit that corrects so that
The ink temperature corrected by the temperature correction unit is used from an ink temperature correction table in which a preset ink temperature and a correction value for correcting a gradation value indicating the ink discharge liquid amount are associated with each other. A correction value acquisition unit for acquiring correction values by
A correction unit that corrects a gradation value representing an ink ejection liquid amount for each dot forming the image included in the recording data using a correction value acquired by the correction value acquisition unit;
The image recording unit ejects ink onto the recording medium using the corrected gradation value;
An image recording apparatus. In the extraction of the temperature correction region by the image analysis unit, an image region in which dots having high gradation are continuously formed for a predetermined first number of times or more immediately after the image region by the recording process by the image recording unit. 3. The image recording apparatus according to claim 2, wherein two continuous regions are extracted from the image, each of which includes a continuous image region in which dots having low gradation are continuously formed a predetermined second number of times or more .