JP6101462B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by ejecting ink from an inkjet head onto a recording medium that is transported on a transport path.

  In an inkjet printing apparatus that forms an image by ejecting ink from a nozzle of an inkjet head onto a recording medium that is conveyed on a conveyance path, an ink chamber that communicates with the nozzle is provided inside the inkjet head, and the volume of the ink chamber is determined by a drive signal. The ink droplets are ejected from the nozzles by changing (expanding and contracting).

  By the way, when the recording medium is transported directly below the ink jet head, an air flow is generated from the upstream to the downstream in the transport direction. Further, when the recording medium is sucked onto the conveying belt with a negative pressure and conveyed at a high speed, the air flow caused by the negative pressure generates an air flow directly under the ink jet head.

  Therefore, in a non-contact printing method in which ink droplets are ejected from a nozzle to a recording medium, the ink droplets are affected by these air currents (hereinafter referred to as conveyance air currents), and the ink droplets are moved downstream in the recording medium conveyance direction. This causes a so-called landing deviation in which the recording medium is displaced from the target trajectory and adheres to the recording medium, causing deterioration in image quality (white stripes, black stripes, color image color change, etc.) due to density unevenness. .

  There exists patent document 1 with respect to such a problem, for example. In the technique of Patent Document 1, when an ink droplet is ejected while relatively moving an inkjet head having a plurality of nozzles and a recording medium in a direction intersecting the nozzle arrangement direction, a droplet having a smaller droplet amount is ejected. Control to increase the speed. Thereby, the landing deviation of the ink droplet due to the conveying airflow is suppressed.

JP 2010-173178 A

  Incidentally, the ink droplets ejected from the nozzles of the inkjet head toward the recording medium may cause a self-air flow. This self-airflow is directed directly under the nozzle in the same direction as the ink droplets are ejected from the nozzle.

  Since this self-airflow includes a directional component that assists the straightness of the ink ejected from the nozzles, depending on the strength, the degree of deviation of the landing of the ink in the conveyance direction of the recording medium due to the above-described conveyance airflow is determined. This may cause a change and hinder the effect of the control that suppresses landing deviation caused by the airflow of conveyance.

  The present invention has been made in view of the above points, and when an image is formed on a recording medium by ejecting ink from each nozzle of an inkjet head above the recording medium conveyed on the conveyance path, An object of the present invention is to provide an image forming apparatus capable of forming a good image in which landing deviation is suppressed even if the self-airflow affects the landing deviation of ink generated by the conveying airflow.

In order to achieve the above object, an image forming apparatus according to the present invention described in claims 1 to 3 includes:
A plurality of nozzles are arranged on the inkjet head arranged above the conveyance path along a main scanning direction orthogonal to the conveyance direction of the recording medium conveyed on the conveyance path, and ink is ejected from each nozzle. In an image forming apparatus for forming an image on the recording medium,
Control means for correcting the propulsive force of the ink ejected from each nozzle based on the ejection density of the ink from each nozzle to the recording medium;
It is characterized by that.

Also, images forming device according to the first exemplary embodiment of the present invention, the driving force of ink discharged respectively from said respective nozzles on the recording medium by ejecting ink to the density unevenness of the image formed on the recording medium In accordance with the present invention, the control unit further corrects the correction contents corresponding to the nozzles by the correction unit based on the ink ejection density from the nozzles to the recording medium. It is characterized by.

Furthermore, the nozzle image forming apparatus according to a second reference example of the image forming equipment and the invention of the present invention as set forth in claim 1, in addition to the configuration described in the introduction, the discharge density is for ejecting ink The number of continuous nozzles in the main scanning direction orthogonal to the transport direction and the number of continuous lines in the transport direction of dots from which the same nozzle ejects ink are determined based on at least one of them. It is characterized by.

The image forming apparatus according to a third reference example of the image forming equipment and the invention of the present invention according to claim 2, in addition to the configuration described in the introduction, the discharge density is the same the same the nozzle It is determined based on the number of drops of ink ejected to the dots.

Further, the image forming apparatus according to a fourth reference example of the image forming equipment and the invention of the present invention according to claim 3, in addition to the configuration described at the beginning, at intervals between said ink jet head and the recording medium Head gap adjusting means for adjusting a certain head gap is further provided, and the control means performs control for adjusting the propulsive force of the ink ejected from the nozzles according to the head gap.

The image forming apparatus according to a fifth reference example of the present invention is an image forming apparatus according to the above first to fourth reference example of the image forming equipment and the invention of the present invention described in each claim, wherein The control content of the propulsive force of the ink ejected from the nozzle is adjusted according to the conveyance speed of the recording medium.

  According to the present invention, when ink is ejected from each nozzle of an inkjet head above the recording medium transported on the transport path to form an image on the recording medium, the landing deviation of ink generated by the transport airflow Even if the self-air flow influences, a good image in which landing deviation is suppressed can be formed.

That is, according to the image forming apparatus according to the first exemplary embodiment of the image forming equipment and the invention of the present invention described in claims 1 to 3, the discharge density of the ink by the nozzle of the inkjet head increases, the nozzle The degree of self-air flow generated along the ink ejection direction between the recording medium and the recording medium (conveyance path) increases. When the degree of self-airflow indicating this degree increases, the degree of ink flow caused by the conveyance airflow generated from the upstream side to the downstream side in the conveyance direction accompanying the conveyance of the recording medium decreases, and the ink landing position becomes upstream in the conveyance direction. It will shift to the side.

  On the other hand, the driving force of the ink discharged from each nozzle is controlled by the control unit based on the discharge density of the ink discharged from each nozzle. Therefore, even if the degree to which the ejected ink is caused to flow downstream in the transport direction by the transport airflow changes due to the influence of the self-stream generated along the ink discharge direction, the amount of the ink to be ejected is taken into consideration. By adjusting the propulsive force, it is possible to suppress the landing position of the ink in the transport direction and to form a good image in which landing deviation is suppressed.

In addition, according to the image forming apparatus of the first reference example of the present invention, in the image forming apparatus of the present invention described in claim 1, density unevenness of the image formed on the recording medium by the ink ejected by each nozzle is reduced. When the correction means suppresses by correcting the propulsive force when ejecting ink, even if a change occurs in the degree to which the ink landing position is caused to flow downstream in the transport direction due to the influence of the self-current, the correction by the correction means By further correcting the content, it is possible to suppress the occurrence of landing deviation in the transport direction in the ink ejected from the nozzles and form a good image.

Further, according to the image forming apparatus according to a second reference example of the image forming equipment and the invention of the present invention as set forth in claim 1, in the nozzle row on the upstream side, a nozzle for discharging ink adjacent in the main scanning direction If they are continuous, a plurality of self-airflows are combined and developed into a band shape (wall shape). Thereby, the effect | action that an ink advances linearly against a conveyance airflow rather than one self-airflow becomes large. In addition, when dots that eject ink from the same nozzle continue over a plurality of lines in the transport direction, the period at which the nozzle ejects ink becomes shorter, so the stability of the self-stream generated by the ejection of ink increases, Increased self-flow rate.

  Therefore, the ink discharge density of each nozzle can be determined based on the number of continuous nozzles in the main scanning direction of the ink discharge nozzles and the number of continuous lines in the transport direction of dots from which the same nozzle discharges ink. And by adjusting the propulsive force when ejecting the ink in consideration of the degree of self-airflow according to the determined ejection density, suppressing the occurrence of landing deviation in the transport direction in the ink ejected from the nozzle, A good image can be formed.

According to the image forming apparatus according to a third reference example of the image forming equipment and the invention of the present invention as set forth in claim 2, floor by the number of drops of ink which the same nozzles are to eject to the same dot When adjusting the tone, the greater the number of drops of ink ejected to the same dot, the longer the continuous generation time of the self-air flow. Becomes higher.

  Therefore, not only the number of continuous nozzles in the main scanning direction of the ink ejection nozzles and the number of continuous lines in the transport direction of dots from which the same nozzle ejects ink, but also the number of ink drops ejected by the same nozzle to the same dots In consideration of the above, it is possible to determine the ink discharge density of each nozzle. Based on the determined ejection density, the propulsive force when ejecting ink is adjusted in consideration of the degree of self-flow generation, and landing deviation in the sub-scanning direction is prevented from occurring in the ink ejected from each nozzle. Thus, a good image can be formed.

Further, according to the image forming apparatus according to a fourth reference example of the image forming equipment and the invention of the present invention according to claim 3, for example, when using the recording medium thickness is large envelopes and the like, an ink-jet In order to prevent the recording medium from colliding with the head, the head gap between the inkjet head and the recording medium may be widened by the head gap adjusting means.

  When the head gap increases and the interval between the inkjet head and the recording medium increases, the airflow of the carrier easily flows between the inkjet head and the recording medium. In addition, since the head gap is widened, the flying distance and the flying time of the ink are increased, so that the amount of ink that flows is increased. That is, the ink ejected from each nozzle is likely to be caused to flow in the sub-scanning direction by the transport airflow.

  Therefore, even if the head gap is adjusted according to the thickness of the recording medium, etc., by adjusting the control content of the propulsive force of the ink ejected by each nozzle according to the head gap, the head By controlling the propulsive force of the ink ejected by the nozzle according to the gap, it is possible to suppress the landing deviation in the sub-scanning direction of the ink ejected from each nozzle, and to produce a good image. Can be formed.

Further, according to the image forming apparatus of the fifth reference example of the present invention , for example, when the conveyance speed of the recording medium increases, the velocity of the conveyance airflow increases, and the self-airflow generated by each nozzle advances the ink straight. The change corresponding to the increase in the speed of the conveying airflow occurs.

  Therefore, even if the conveyance speed of the recording medium is changed by adjusting the control content of the propulsive force of the ink ejected by each nozzle according to the conveyance speed of the recording medium, the content according to the conveyance speed is changed. By adjusting the propulsive force of the ink ejected by the nozzles, it is possible to suppress the occurrence of landing deviation in the sub-scanning direction in the ink ejected from each nozzle and form a good image. .

1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the control system of the inkjet printing apparatus of FIG. FIG. 2 is a partial enlarged cross-sectional view of a conveyance belt and a plastic template in FIG. 1. It is explanatory drawing which shows arrangement | positioning of the head block of FIG. It is explanatory drawing of the self-air flow which generate | occur | produces in the head block of FIG. FIG. 2 is an explanatory diagram illustrating landing deviation according to the ejection density of ink ejected from the nozzles of the head block of FIG. 1. It is explanatory drawing which shows an example of the test pattern used when determining the correction content of a correction table. It is a flowchart for demonstrating the procedure at the time of determining the correction content of a correction table. It is a flowchart for demonstrating operation | movement of the inkjet printing apparatus at the time of applying the correction content of a correction table, and correct | amending the propulsive force of the ink which the nozzle of correction object discharges. (A) is explanatory drawing which shows the nozzle which ejected the ink in the experiment which shows the relationship between the amount of landing deviations, and the distance between a paper and an ejection surface, (b) is the landing deviation in the subscanning direction in the said experiment. It is explanatory drawing which shows the relationship between a quantity and the distance between a paper and an ejection surface.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiment described below exemplifies an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention is to arrange the components and the like as follows. Not specific. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a control system of the inkjet printing apparatus of FIG. 1, and FIG. FIG. 4 is an explanatory view showing the arrangement of the head block of FIG.

  In the following description, the paper surface direction in FIG. Further, as shown in FIG. 1, the top, bottom, left, and right sides of the paper are defined as the top, bottom, left, and right directions. Further, a path indicated by a broken line in FIG. 1 is a transport path R along which the paper PA that is a recording medium is transported. In the following description, upstream and downstream mean upstream and downstream in the transport path R, respectively.

  As shown in FIGS. 1 and 2, the inkjet printing apparatus 1 includes a paper feeding unit 2, a transport unit 3, a printing unit 4, a control unit 5, and a reading unit 6.

  The paper feeding unit 2 feeds paper PA. The sheet feeding unit 2 includes a sheet feeding table 11, a sheet feeding roller 12, and a registration roller 13. The paper feed table 11 is used for loading paper PA used for printing.

  The paper feed roller 12 picks up the paper PA stacked on the paper feed tray 11 one by one and conveys the paper PA toward the registration roller 13. The paper feed roller 12 is disposed on the upper side of the paper feed tray 11. The paper feed roller 12 is rotationally driven by a motor (not shown).

  The registration roller 13 temporarily stops the paper PA conveyed by the paper supply roller 12 and then conveys the paper PA toward the conveyance unit 3. The registration roller 13 is disposed on the downstream side of the paper feed roller 12. The registration roller 13 is rotationally driven by a motor (not shown).

  The transport unit 3 transports the paper PA transported from the registration rollers 13. The transport unit 3 includes a transport belt 21, a drive roller 22, driven rollers 23 to 25, a belt drive motor 26, a plastic template 27, and a fan 28.

  The conveyor belt 21 is an annular belt that is stretched around the driving roller 22 and the driven rollers 23 to 25. As shown in FIG. 3, the conveyor belt 21 is formed with a number of belt holes 21a that are through holes for attracting and holding the paper PA. The conveyance belt 21 sucks and holds the paper PA on a paper holding surface (corresponding to a medium holding surface in claims) 21b by the suction force generated in the belt hole 21a by driving the fan 28. The sheet holding surface 21 b is an upper surface of the conveyance belt 21 that is substantially horizontal between the driving roller 22 and the driven roller 23.

  The conveyor belt 21 rotates in the clockwise direction in FIG. Accordingly, the transport belt 21 moves endlessly, thereby transporting the paper PA sucked and held on the paper holding surface 21b in the right direction.

  The driving roller 22 and the driven rollers 23 to 25 are for the conveyance belt 21 to be stretched over. The driving roller 22 is driven to rotate by a belt driving motor 26 and rotates the conveyor belt 21. The driven rollers 23 to 25 are driven by the driving roller 22 via the conveyance belt 21. The driven roller 23 is substantially the same height as the drive roller 22 and is spaced from the drive roller 22 by a predetermined distance in the left-right direction. The driven rollers 24 and 25 are disposed at substantially the same height below the driving roller 22 and the driven roller 23 and spaced apart from each other by a predetermined distance in the left-right direction. The belt drive motor 26 drives the drive roller 22 to rotate.

  The plastic template 27 is disposed below the conveying belt 21 between the driving roller 22 and the driven roller 23, and supports the lower surface of the conveying belt 21 so as to be slidable. The plastic template 27 includes a plurality of concave portions 27a dug down from the upper surface toward the lower surface at a portion where the belt hole 21a passes, and a plurality of suction holes 27b penetrating from the bottom surface of the concave portion 27a to the lower surface of the plastic template 27. Have

  The fan 28 generates a downward airflow. As a result, the fan 28 sucks air through the suction holes 27b and the concave portions 27a of the plastic template 27 and the belt holes 21a of the conveying belt 21 to generate a negative pressure in the belt holes 21a. Adsorb on 21b. The fan 28 is disposed below the plastic template 27.

  The printing unit 4 performs printing on the paper PA conveyed by the conveyance unit 3. The printing unit 4 is provided on the upper side of the transport unit 3. The printing unit 4 is fixed in a housing (not shown) of the inkjet printing apparatus 1. The printing unit 4 includes inkjet heads 31 </ b> C, 31 </ b> K, 31 </ b> M, and 31 </ b> Y, a head holder 32, and a head gap adjustment unit (corresponding to the head gap adjustment means in the claims) 33. Note that alphabetic suffixes (C, K, M, Y) indicating colors in codes may be omitted when there is no need to distinguish colors.

  The inkjet heads 31C, 31K, 31M, and 31Y discharge cyan (C), black (K), magenta (M), and yellow (Y) inks, respectively. The inkjet heads 31C, 31K, 31M, 31Y are arranged in parallel in the left-right direction above the transport unit 3. The inkjet heads 31C, 31K, 31M, and 31Y are line-type inkjet heads, each having six head blocks 35 as shown in FIG.

  In each of the inkjet heads 31C, 31K, 31M, and 31Y, the six head blocks 35 are arranged in a staggered manner. Specifically, the six head blocks 35 are arranged in the front-rear direction (main scanning direction), and every other head block 35 is arranged by shifting the position in the left-right direction (sub-scanning direction).

  As shown in FIG. 1, the head holder 32 holds the head block 35 of the inkjet head 31 above the transport unit 3. The head holder 32 is formed in a hollow, substantially rectangular parallelepiped shape.

  Each head block 35 has a plurality of nozzles 38 on a discharge surface 35a (see FIG. 3) which is a lower surface. The nozzles 38 are arranged at regular intervals with a predetermined pitch P in the main scanning direction. Inside each head block 35, a plurality of ink chambers (not shown) communicating with the respective nozzles 38 are provided. Then, by changing the volume of each ink chamber under the control of the control unit 5, ink in the ink chamber is ejected from the corresponding nozzle.

  In such a share mode type head block 35, for example, the volume of each ink chamber is changed by causing the control unit 5 to drive the piezoelectric member constituting the partition of each ink chamber by a drive signal. This drive signal is a pulse signal, and the control unit 5 can adjust the driving force when ink is ejected from the nozzle 38 by changing the voltage or the waveform.

  Since the ink propulsive force is expressed by ejection speed × ink mass, in this embodiment, the control unit 5 adjusts the ink ejection speed as the propulsive force.

  Further, the control unit 5 can change the number of ink droplets (the number of drops) ejected from one nozzle 38 of each head block 35 to one pixel by changing the waveform of the drive signal described above. , Gradation printing expressing the density by the number of droplets (for example, 1 to 7 drops) is performed.

  The head gap adjustment unit 33 adjusts the head gap H. As shown in FIG. 3, the head gap H is a distance between the paper holding surface 21 b of the transport belt 21 and the ejection surface 35 a of the inkjet head 31. The head gap adjustment unit 33 includes a head gap adjustment mechanism 41, a lift motor 42, and a connection member 43.

  The head gap adjustment mechanism 41 moves the transport unit 3 up and down with respect to the inkjet head 31. Two head gap adjusting mechanisms 41 are provided apart in the front-rear direction. The head gap adjusting mechanism 41 includes a pair of pulleys 46 and 47, a shaft 48, and wires 49 and 50.

  Pulleys 46 and 47 wind and unwind wires 49 and 50, respectively. The pulleys 46 and 47 are supported in the head holder 32 so as to be spaced apart from each other in the left-right direction.

  The shaft 48 connects a pair of pulleys 46 and 47 to each other. The shaft 48 is made of a long member extending in the left-right direction, and one end is fixed to the pulley 46 and the other end is fixed to the pulley 47. Thereby, a pair of pulleys 46 and 47 are rotated synchronously.

  The wires 49 and 50 suspend and support the transport unit 3. One ends of the wires 49 and 50 are connected to the transport unit 3, and the other ends are wound around pulleys 46 and 47. As the wires 49 and 50 are wound and fed by the rotation of the pulleys 46 and 47, the transport unit 3 moves up and down, and the head gap H changes.

  The lifting motor 42 rotates the pulleys 46 and 47. The connection member 43 is a member that connects the head holder 32 and the transport unit 3. The connecting member 43 is configured such that the length in the vertical direction can be adjusted according to the head gap H.

  The reading unit 6 includes a document feeding device and a document image reading device (both not shown), and reads the image by the reading device while transporting the document set on the tray of the feed device and converts it into data. To do.

  By the way, at the time of printing by the ink jet printing apparatus 1 of the present embodiment, as shown in FIG. 5, the ink droplet 52 is ejected from the head block 35 of the ink jet head 31, and the self heading from the head block 35 toward the paper PA. Airflow W1 is generated. Further, a conveyance air flow W2 that is an air flow in the conveyance direction is generated by the conveyance of the sheet PA by the conveyance unit 3 and the suction of air by the fan 28.

  The transport air flow W2 acts to cause the ink droplets 52 to flow downstream in the transport direction and shift landing. On the other hand, the self-air flow W1 described above improves the straightness of the ink droplet 52 toward the paper PA, and works to reduce the amount of landing deviation of the ink droplet 52 downstream in the transport direction by the transport air flow W2. .

  The self-air flow W1 becomes stronger when a plurality of nozzles 38 that are continuous in the main scanning direction discharge ink. The self-air flow W1 also increases when ink is repeatedly ejected to a plurality of lines of dots where the same nozzle 38 is continuous. Further, the self-air flow W1 is high when the same nozzle 38 repeats ink ejection to the same dot.

  That is, when there is a high discharge density region where the density per unit area (discharge density) of the ink discharged from the nozzles 38 to the paper PA is high, the degree of the self-air flow W1 generated by the ink discharge becomes strong. Therefore, the self-airflow degree indicating the degree of the self-airflow W1 affects the degree to which the ink droplet 52 is landed and shifted to the downstream side in the transport direction of the paper PA by the transport airflow W2.

  For example, as shown in the explanatory diagram of FIG. 6, when ink is ejected from the nozzles of the cyan (C) and magenta (M) head blocks 35 to the same pixel of the paper PA, # 5 to ## Since the cyan (C) and magenta (M) inks are ejected to the pixels corresponding to the seventh nozzle 38 at the same density, there is no ink landing deviation between the colors. However, since cyan (C) is discharged at a lower density than magenta (M) to the pixels corresponding to the nozzles # 1 to # 4, cyan (C) ink having a low discharge density is magenta (M ), The ink landing position is shifted in the sub-scanning direction with respect to magenta (M).

  FIG. 6 shows a case where the discharge densities of cyan (C) and magenta (M) inks are different in the sub-scanning direction. However, the discharge density is different for each dot in the main scanning direction. A similar situation occurs in different cases.

  When the situation shown in FIG. 6 occurs, the driving force when discharging cyan (C) ink corresponding to a pixel having a low discharge density is increased, or the driving force when discharging magenta (M) ink. By reducing the force, landing deviation from magenta (M) ink of the same pixel can be suppressed.

  Therefore, the control unit 5 in FIG. 2 adjusts the driving force of the ink droplets 52 ejected by the nozzles 38 of the head block 35 with respect to the dots in the high ejection density region in accordance with the degree of the self-airflow W1. A correction table is stored in advance.

  According to the correction table, the amount of landing deviation of the ink flowed in the conveying airflow W2 changes in accordance with the degree of the self-airflow W1 (the amount of landing deviation decreases when the degree of the self-airflow W1 is large, and the amount of landing deviation decreases when the degree is small. In consideration of the fact that the amount of ink is small), the table defines the adjustment amount of the ink propulsive force with respect to the reference propulsive force according to the ink ejection density that affects the self-airflow degree, which is the degree of occurrence of the self-airflow W1. is there.

  Here, the ink ejection density can be represented by, for example, a printing rate indicating an area ratio of an actually printed region to a printable region of the paper PA. The printing rate can be defined in a one-dimensional or two-dimensional range by one or both of the number of continuous ink ejection dots in the main scanning direction and the number of ink continuous ejection dots in the sub-scanning direction.

  Then, the control unit 5 of the present embodiment actually ejects ink with respect to a reference driving force according to a printing rate defined in a two-dimensional range by the number of continuous ejection dots of ink in both main scanning and sub-scanning directions. A correction table that divides and defines the adjustment amount of the propulsive force at the time of the control is stored in the control unit 5 and used.

  Even if the adjustment amount for the reference value of the propulsive force of the ink defined in the correction table is classified according to the ink ejection density (printing rate) in consideration of the number of ink drops ejected to the same dot by the same nozzle 38. Good.

  In the inkjet printing apparatus 1 according to the present embodiment having the above-described configuration, the nozzles 38 of the head blocks 35 of the inkjet heads 31C, 31K, 31M, and 31Y of the respective colors discharge the inks of the respective colors. Therefore, the adjustment of the ink ejection driving force by the control unit 5 using the correction table described above is performed on the nozzles 38 of the head blocks 35 of the ink jet heads 31C, 31K, 31M, and 31Y of the respective colors.

  In addition, when determining the correction contents to be applied to each nozzle 38 by using the correction table every time the nozzles 38 eject ink, the printing rate of the nozzles 38 is determined as follows. For example, it can be determined as follows.

  That is, for example, in each head block 35, the ejection pattern (in which the nozzles 38 to be corrected and the nozzles 38 adjacent in the main scanning direction ejected to dots over the past predetermined lines (for example, 30 lines) ( Main scanning direction, sub-scanning direction, same dot). Of course, the target of the nozzle 38 that refers to the ink ejection pattern to determine the printing rate may be further expanded in the main scanning direction.

  In addition, the correction content of each classification according to the printing rate is, for example, from the test pattern according to the printing rate (ink discharge density) printed by the inkjet printing apparatus 1, the landing deviation of the ink in the sub-scanning direction by the self-air flow W1. The degree can be grasped and determined based on it.

  In the present embodiment, the correction content corresponding to the printing rate is determined for each nozzle 38. For this reason, as a test pattern to be printed by the inkjet printing apparatus 1 when determining the correction contents of each section according to the printing rate, all the nozzles 38 have different printing rates (discharges) in the main scanning direction and the sub-scanning direction. It is preferable that a large number of patterns in which ink is ejected at a density) are included.

  In this embodiment, since the number of ink drops ejected to the same dot by the same nozzle 38 is added to the printing rate (ejection density), a pattern in which the number of ink drops ejected to the same dot is different is included. It is preferable.

  Therefore, the test pattern shown in the explanatory diagram of FIG. 7 may be used. In this test pattern, there are three groups in which the number of continuous nozzles 38 that eject ink is large, medium, and small ("wide", "medium", and "narrow" in the figure). To do. Each group has three patterns in which the number of continuous ink ejections from each nozzle 38 in the sub-scanning direction is large, medium, and small. Each of the three groups and three patterns is provided with four regions in which the number of ink drops ejected to the same dot is large, small, medium, and large (in order from the left side in the drawing).

  By using such a test pattern, the self-airflow W1 can be changed according to the printing rate by adding the number of drops of ink ejected to the same dot to the two-dimensional printing rate (dot density) including both main scanning and sub-scanning directions. The degree of landing deviation of the ink in the sub-scanning direction due to the influence can be grasped, and the correction content can be determined based on the degree.

  Next, a procedure for determining the correction contents of a correction table (not shown) stored in, for example, the hard disk of the control unit 5 will be described.

  FIG. 8 is a flowchart for explaining the operation of the inkjet printing apparatus 1 when determining the correction content of the additional correction table. The process of the flowchart of FIG. 8 is started when the image data of the test pattern of FIG.

  In step S <b> 1 of FIG. 8, the control unit 5 prints, for example, a test pattern (including large, medium, and small image portions) read from the hard disk by the printing unit 4. At this time, the control unit 5 uses the correction table already stored in the hard disk, and the nozzle 38 of the head block 35 of each color is equivalent to the amount of ink landing deviation downstream in the sub-scanning direction due to the transport airflow W2. The ink ejection propulsive force is corrected so as to be higher than the standard propulsive force when there is no conveyance air flow W2.

  If the test pattern has been printed on the paper PA, it is confirmed whether or not ink landing deviation has occurred on the test pattern image on the printed paper PA (step S3).

  If landing deviation has occurred (YES in step S3), a correction value for eliminating landing deviation by a user operation on an operation panel (not shown) or the like (for example, change in voltage of drive signal or waveform pattern). Is updated and input to the inkjet printing apparatus 1 (step S5). Then, the updated correction value is temporarily stored in a hard disk (not shown) of the control unit 5 as a correction value of the ink ejection driving force at the corresponding dot density of the corresponding color (step S7), and the process returns to step S1. To do.

  If no landing deviation has occurred in step S3 (NO), the correction value temporarily stored in the hard disk or the like (for example, the voltage of the drive signal or the change in waveform pattern) corresponds to the corresponding color. The correction value for the ink ejection driving force at the dot density is stored again in the hard disk or the like (step S9), and the procedure is terminated.

  The test pattern image is read by the reading device of the reading unit 6, the control unit 5 determines the presence or absence of landing deviation, and based on the result, the control unit 5 performs the update input of the correction value, so that the test pattern The control unit 5 may determine the correction contents of the correction table without repeating the user's input operation or the like while repeating printing and image reading.

  Next, the operation of the inkjet printing apparatus 1 when correcting the propulsive force when each nozzle 38 discharges ink according to the ink discharge density by applying the correction contents of the correction table will be described.

  FIG. 9 is a flowchart for explaining the operation of the inkjet printing apparatus 1 when correcting the propulsive force of the ink ejected by the correction target nozzle by applying the correction content of the correction table (not shown). The process of the flowchart in FIG. 9 is performed by dropping image data to be printed into the inkjet printing apparatus 1, and drop data that is image data in a format corresponding to printing by the inkjet head 31 from image data in RGB format by the control unit 5. Is generated when is generated.

  In step S11 of FIG. 9, when the pixel corresponding to one nozzle 38 of the drop data is set as the target pixel for each color, the control unit 5 and its surroundings (both sides in the main scanning direction and upstream in the sub scanning direction). Whether the dot density of the pixel of interest belongs to large, medium, or small is determined from the drop data with the other pixel.

  Next, the control unit 5 determines the correction content corresponding to the dot density (large, medium, small) determined in step S11 of the target pixel, that is, the printing rate, using a correction table (not shown). Then, the driving force when ink is ejected from the nozzle 38 corresponding to the target pixel is switched to the driving force determined by a correction table (not shown) (step S13).

  Therefore, the controller 5 causes the target nozzle 38 to eject the ink having the number of drops corresponding to the image data with the propulsive force after switching (step S15).

  Increasing the propulsive force (velocity) when ejecting ink shortens the ink flight time until it reaches the paper PA, so that the ink landing position is shifted upstream in the sub-scanning direction. On the other hand, if the propulsive force (speed) is decreased, the ink flying time until it reaches the paper PA becomes longer, so that the ink landing position is shifted downstream in the sub-scanning direction.

  For this reason, for example, even when ink of each color is ejected to the same dot at different ejection densities, the self-occurrence that occurs in ink ejection of each color by shifting the landing position in the sub-scanning direction by adjusting the ink ejection driving force It is possible to suppress landing deviation between the two inks due to the difference in the airflow W1. Accordingly, even when the degree of the self-air flow W1 is different, the landing positions of the respective inks in the sub-scanning direction can be brought close to each other, and a good image can be formed in which the occurrence of a color change in the color image due to density unevenness is suppressed.

  Incidentally, the amount of landing deviation increases as the distance between the paper PA and the ejection surface 35a increases. The distance between the paper PA and the ejection surface 35a corresponds to the distance obtained by removing the thickness of the paper PA from the head gap H. For the same type of paper PA (having the same thickness), the larger the head gap H, the greater the distance between the paper PA and the ejection surface 35a.

  However, for example, when a plurality of types of paper PAs having different thicknesses are mixed in the paper PA used for printing, the head gap H is maintained at a size that matches the thickness of the thick paper PA. Therefore, when the thin paper PA passes just below the ejection surface 35a, the distance between the paper PA and the ejection surface 35a may be increased.

  Here, FIG. 10 shows an experimental result showing the relationship between the landing deviation amount and the distance between the paper PA and the ejection surface 35a. In FIG. 10A, a plurality of adjacent nozzles 38 that ejected ink in this experiment are shown in black. FIG. 10B shows the relationship between the average value of the amount of landing deviation in the sub-scanning direction at the nozzle 38 and the distance between the paper PA and the ejection surface 35a. As shown in FIG. 10B, as the distance between the paper PA and the ejection surface 35a increases, the amount of ink landing deviation in the sub-scanning direction increases.

  Therefore, the correction content of the ink ejection propulsion force defined by a correction table (not shown) is further classified according to the size of the head gap H. The coefficient may be increased.

  Moreover, the conveyance air flow W2 becomes stronger as the wind speed is higher. Since the wind speed of the transport air flow W2 increases as the transport speed of the paper PA by the transport section 3 increases, the correction content of the ink ejection driving force specified by a correction table (not shown) depends on the transport speed of the paper PA by the transport section 3. Further, the correction content (correction coefficient) for increasing the propulsive force at the time of discharge may be increased as the conveyance speed is higher.

  In the above-described embodiment, in consideration of the change in the landing deviation amount in the sub-scanning direction due to the influence of the self-airflow W1, the landing deviation of the ink is caused to flow downstream in the sub-scanning direction. The case where the correction content of the ink ejection driving force used for eliminating the density unevenness caused by this is additionally changed has been described. However, the present invention can be widely applied to the case where the ink ejection driving force is controlled in accordance with the degree of generation of the airflow W2 and the self-airflow W1 (self-airflow degree) based on the ink ejection density.

  In the above-described embodiment, the case where the inkjet head 31 is configured by arranging a plurality (six) of the head blocks 35 in a staggered manner in the main scanning direction has been described. However, the present invention is also applicable to the case where the nozzle row that covers the print width in the main scanning direction is provided in the single-unit inkjet head 31.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Paper feed part 3 Conveyance part 4 Printing part 5 Control part 6 Reading part 11 Paper feed stand 12 Paper feed roller 13 Registration roller 21 Conveyance belt 21a Belt hole 21b Paper holding surface 22 Drive roller 23-25 Followed roller 26 Belt drive motor 27 Plastic template 27a Recessed portion 27b Suction hole 28 Fan 31, 31C, 31K, 31M, 31Y Inkjet head 32 Head holder 33 Head gap adjusting unit 35 Head block 35a Discharge surface 38 Nozzle 41 Head gap adjusting mechanism 42 Lifting motor 43 Connection Member 46, 47 Pulley 48 Shaft 49, 50 Wire 52 Ink droplet H Head gap P Pitch PA Paper R Transport path W1 Self-air flow W2 Transport air-flow

Claims (3)

A plurality of nozzles are arranged on the inkjet head arranged above the conveyance path along a main scanning direction orthogonal to the conveyance direction of the recording medium conveyed on the conveyance path, and ink is ejected from each nozzle. In an image forming apparatus for forming an image on the recording medium,
Control means for correcting the propulsive force of the ink ejected from each nozzle based on the ejection density of the ink from each nozzle to the recording medium;
The ejection density is at least one of the number of continuous nozzles in the main scanning direction orthogonal to the transport direction of the nozzles that eject ink and the number of continuous lines in the transport direction of dots from which the same nozzle ejects ink. Is determined based on one side,
An image forming apparatus. A plurality of nozzles are arranged on the inkjet head arranged above the conveyance path along a main scanning direction orthogonal to the conveyance direction of the recording medium conveyed on the conveyance path, and ink is ejected from each nozzle. In an image forming apparatus for forming an image on the recording medium,
Control means for correcting the propulsive force of the ink ejected from each nozzle based on the ejection density of the ink from each nozzle to the recording medium;
The discharge density is determined based on the number of ink drops discharged from the same nozzle to the same dot.
An image forming apparatus. A plurality of nozzles are arranged on the inkjet head arranged above the conveyance path along a main scanning direction orthogonal to the conveyance direction of the recording medium conveyed on the conveyance path, and ink is ejected from each nozzle. In an image forming apparatus for forming an image on the recording medium,
Control means for correcting the propulsive force of the ink ejected from each nozzle based on the ejection density of the ink from each nozzle to the recording medium;
A head gap adjusting means for adjusting a head gap which is an interval between the inkjet head and the recording medium;
The control means performs control to adjust the propulsive force of the ink by the nozzle according to the head gap.
Imaging equipment, characterized in that.