JP2021020338A - Inkjet printing device - Google Patents

Abstract

To provide a multi drop-type inkjet printing device, which can suppress influence of a satellite generated by a last ink droplet to improve quality of a printed image.SOLUTION: The inkjet printing device comprises: an inkjet head 33 that forms a printed image by discharging ink droplets from a nozzle to a printing medium on the basis of image data; and a head control part 65 that controls a driving voltage of the inkjet head 33 so that ink droplets are discharged from the nozzle and a plurality of ink droplets are discharged continuously from the same nozzle to form one pixel constituting the printed image. The head control part 65 performs satellite-suppression control by which a driving voltage at the time of discharging a last ink droplet to be lastly discharged, of the plurality of ink droplets constituting the one pixel, is set lower than a driving voltage at the time of discharging the other ink droplets so that an ink amount in the last ink droplet is smaller than ink amounts in the other ink droplets.SELECTED DRAWING: Figure 2

Description

The present invention relates to a multi-drop type inkjet printing apparatus.

Conventionally, an inkjet printing apparatus that ejects ink from an inkjet head onto a printing medium to perform printing processing has become widespread.

Further, among such an inkjet printing apparatus, a multi-drop type inkjet printing apparatus capable of ejecting a plurality of ink droplets from one nozzle of an inkjet head to one pixel has been proposed. In a multi-drop type inkjet printing apparatus, gradation printing that expresses density is performed by changing the number of ink droplets (the number of drops) ejected to one pixel.

Here, in the inkjet printing apparatus, a head gap is provided between the inkjet head and the printing medium. The ink ejected from each nozzle of the inkjet head flies through this head gap and lands on the printing medium, but when the ink is ejected from each nozzle, the ink droplets are not rounded and a long tailing occurs. However, a phenomenon may occur in which the tailing is cut off and the main drop and the secondary drop (hereinafter referred to as satellite) are separated.

This satellite has a problem that it is affected by an air flow or the like and lands on a region deviating from the specified landing position of the print medium, thereby degrading the image quality of the printed image.

In the above-mentioned multi-drop method, since a plurality of ink droplets are continuously ejected when forming one pixel, the subsequent ink droplets land while absorbing the satellite of the ink droplets ejected earlier. Can be done.

Japanese Unexamined Patent Publication No. 8-336970

However, even in the multi-drop method, among the plurality of ink droplets forming one pixel, the final ink droplet to be ejected last does not have the ink droplet to be ejected after that, so that the final ink droplet is ejected. The satellites generated by the ink are not absorbed by other ink droplets and land on the print medium, degrading the image quality of the printed image.

FIG. 11 is a diagram showing the ejection state of each ink droplet in chronological order when 5 drops of ink droplets are ejected from one nozzle. As shown in FIG. 11, the tail trail (the portion indicated by the arrow B) of the fifth drop (drop 5), which is the final ink drop, separates to form a satellite and lands on the print medium.

According to Patent Document 1, when a plurality of ink droplets forming one pixel are continuously ejected in a multi-drop type inkjet printing apparatus, the ink droplet ejection speed is controlled to be gradually increased to fly. A method of combining a plurality of ink droplets into the ink droplet has been proposed.

However, it is known that when the ejection speed of the final ink droplet is increased as in Patent Document 1, the tailing becomes longer and satellites are more likely to occur. Further, Patent Document 1 does not propose any method for suppressing satellites generated by ejection of final ink droplets.

In view of the above circumstances, it is an object of the present invention to provide an inkjet printing apparatus capable of suppressing the influence of satellites generated by final ink droplets and improving the quality of printed images in a multi-drop type inkjet printing apparatus. And.

The inkjet printing apparatus of the present invention has an inkjet head that ejects ink droplets from a nozzle onto a printing medium to form a printed image based on image data, and an inkjet head that controls the driving voltage of the inkjet head to eject ink droplets from the nozzle. A plurality of head control units that form one pixel that constitutes a printed image by ejecting and continuously ejecting a plurality of ink droplets from the same nozzle are provided, and the head control unit constitutes one pixel. Of the ink droplets in the above, the ejection speed of the final ink droplet to be ejected is made slower than the ejection speed of the ink droplet when ejecting other ink droplets, and the amount of ink in the final ink droplet is set to the other ink droplets. The satellite suppression control is performed so that the amount of ink is less than the amount of ink in.

According to the inkjet printing apparatus of the present invention, the drive voltage when ejecting the final ink droplet to be ejected last among the plurality of ink droplets constituting one pixel is set to drive when ejecting other ink droplets. Since satellite suppression control is performed so that the amount of ink in the final ink droplets is lower than the voltage and less than the amount of ink in other ink droplets, the tailing of the final ink droplets can be reduced and the final ink droplets can be reduced. It is possible to suppress the influence of satellites generated by the ink and improve the quality of printed images.

The figure which shows the schematic structure of one Embodiment of the inkjet printing apparatus of this invention. Block diagram showing the schematic configuration of the control unit The figure which shows an example of a head drive voltage switching signal and a head drive voltage The figure which shows the ejection state of each ink drop in time series at the time of ejecting 5 drops of ink from one nozzle. A block diagram showing a schematic configuration of a control unit when ink ejection control of four nozzles is performed. The figure which shows an example of the head drive voltage switching signal of four nozzles The figure which shows an example of the head drive voltage supplied to the driver circuit of each of four nozzles. Flow chart for explaining the processing flow of the head control unit The figure which shows an example of the peripheral part of a print medium A diagram showing an example of a state in which the figure or photographic area straddles the peripheral portion and the central portion of the print medium. A diagram showing the ejection state of each ink droplet in chronological order when 5 drops of ink are ejected from one nozzle (conventional example).

Hereinafter, an embodiment of the inkjet printing apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of the inkjet printing apparatus 1 of the present embodiment. The inkjet printing device 1 of the present embodiment is a multi-drop type inkjet printing device. The vertical and horizontal directions indicated by the arrows in FIG. 1 are the vertical and horizontal directions of the inkjet printing apparatus 1 of the present embodiment. Further, the front side of the paper surface in FIG. 1 is the front direction of the inkjet printing apparatus 1 of the present embodiment, and the back side of the paper surface is the rear direction. Hereinafter, the inkjet printing apparatus 1 of the present embodiment will be described with reference to the drawings, but the drawings include illustrations.

As shown in FIG. 1, the inkjet printing device 1 displays a side paper feeding unit 10, an internal paper feeding unit 20, a printing processing unit 30, a paper ejection unit 40, a reversing unit 50, and a control unit 60. A unit 70 and a transport unit 80 are provided.

The print processing unit 30, the internal paper feed unit 20, the transport unit 80, and the control unit 60 are housed and installed in a housing 100 made of metal, resin, or the like. Further, the side paper feeding unit 10, the paper discharging unit 40, and the reversing unit 50 are installed in a state in which a part of the side feeding unit 10, the paper discharging unit 40, and the reversing unit 50 is housed in the housing 100 and a part of the side feeding unit 10 protrudes outside the housing 100.

The side paper feed unit 10 is a primary paper feed unit that feeds only the paper feed table 11 on which the print medium P is placed and the print medium P at the uppermost position from the paper feed table 11 and conveys them onto the paper feed transfer path FR. A 12 and a secondary paper feeding unit 14 that conveys the print medium P conveyed by the primary paper feeding unit 12 onto the circulation transfer path CR are provided.

The internal paper feed unit 20 is a primary paper feed unit that feeds only the paper feed table 21a on which the print medium P is placed and the print medium P at the uppermost position from the paper feed table 21a and conveys them onto the paper feed transfer path FR. 22a, a paper feed tray 21b on which the print medium P is placed, a primary paper feed unit 22b that feeds out only the print medium P at the uppermost position from the paper feed tray 21b and conveys it onto the paper feed transport path FR, and printing. The paper feed tray 21c on which the medium P is placed, the primary paper feed section 22c that feeds out only the print medium P at the uppermost position from the paper feed tray 21c and conveys it onto the paper feed transfer path FR, and the print medium P are mounted. It is provided with a paper feed table 21d to be placed, and a primary paper feed unit 22d that feeds out only the print medium P at the uppermost position from the paper feed table 21d and conveys it onto the paper feed transfer path FR.

In this way, the print medium P is conveyed to the secondary paper feed unit 14 from the side paper feed unit 10 or the internal paper feed unit 20, and the print medium P is also conveyed from the reversing unit 50, which will be described later.

Therefore, in front of the secondary paper feed unit 14 in the transport direction, the transport path of the print medium P fed from the internal paper feed section 20 and the print medium P on which one surface conveyed from the reversing section 50 is printed. There is a confluence point where the transportation route of With reference to this confluence, the path on the paper feed mechanism side is called the paper feed transfer path FR, and the other paths are called the circulation transfer path CR.

The print processing unit 30 includes a line head 31 and a head holder 32. Each line head 31 has a plurality of inkjet heads, and prints by ejecting ink from the inkjet head to the print medium P conveyed by the conveying unit 80. In the head holder 32, each inkjet head of each line head 31 is installed.

The print processing unit 30 of the present embodiment has four line heads 31, and the four line heads 31 are arranged at predetermined intervals along the transport path of the print medium P. The four line heads eject inks of different colors (eg, black, cyan, magenta, and yellow).

Each line head 31 has two rows of heads in which three inkjet heads 33 (see FIG. 2) are arranged at equal intervals in a direction orthogonal to the transport direction of the print medium P. The two rows of head rows are arranged so as to be offset by about half a pitch in the orthogonal direction.

Each inkjet head 33 has a plurality of nozzles that eject ink to the print medium P. The plurality of nozzles of each inkjet head 33 are arranged in a direction orthogonal to the transport direction of the print medium P. Each nozzle includes a piezo element 33a and a driver circuit 33b for driving the piezo element 33a. By driving the piezo element 33a by the driver circuit 33b, ink is ejected from each nozzle.

The transport unit 80 includes a platen 81, a fan mechanism 82, a transport belt 83, and the like. The transport unit 80 conveys the print medium P conveyed from the side paper feed unit 10 while maintaining a constant speed in a state of being sucked and attracted to the transfer belt 83. Then, the transport unit 80 transports the printed print medium P to the paper discharge unit 40 after the print process is applied to the print medium P by the inkjet head.

The platen 81 is a plate member provided so as to face the bottom surface of the head holder 32. A plurality of platen suction holes 81a are formed in the platen 81. The platen suction hole 81a is a through hole, and is formed in a two-dimensional shape in a direction orthogonal to the transport direction and the transport direction of the print medium P.

A fan mechanism 82 is provided below the platen 81. The fan mechanism 82 generates suction air in the platen suction hole 81a of the platen 81 by rotating the fan to create a negative pressure in the space below the platen 81.

The transport belt 83 is an annular endless belt that is hung on the platen 81, a drive roller, a driven roller, and the like and slides on the platen 81. The transport belt 83 is made of a material such as rubber or resin that has plasticity and generates an appropriate frictional force with the print medium P. A plurality of belt suction holes (not shown) are formed in the transport belt 83. The belt suction hole is a through hole and is formed in a two-dimensional shape in a direction orthogonal to the transport direction and the transport direction of the print medium P. Due to the generation of the suction air in the platen suction hole 81a of the platen 81 described above, the suction air is also generated in the belt suction hole, which generates the suction force, and the print medium P is sucked and sucked on the transport belt 83.

Then, the print medium P that has been conveyed by the transfer unit 80 and printed by the print processing unit 30 is conveyed on the circulation transfer path CR by a transfer roller or the like arranged on the circulation transfer path CR. The circulation transport path CR is provided with a switching mechanism 49 for switching between guiding the print medium P transported on the circulation transport path CR to the paper ejection unit 40 and recirculating the print medium P on the circulation transport path CR. There is. Specifically, the switching mechanism 49 switches between the transport path on the paper ejection section 40 side and the transport path on the reversing section 50 side.

The paper ejection unit 40 has a tray-shaped paper ejection table 45 protruding from the housing 100 of the inkjet printing apparatus 1, and a pair of paper ejection rollers 48 for ejecting the print medium P on the paper ejection table 45. Then, the print medium P guided to the transport path on the paper ejection unit 40 side by the switching mechanism 49 is ejected to the paper ejection table 45 by the paper ejection roller 48.

The reversing unit 50 conveys the print medium P from the reversing table 51 that inverts the print medium P and the circulation transfer path CR to the reversal table 51, and transfers the print medium P conveyed to the inversion table 51 on the circulation transfer path CR. It is provided with a reversing roller 52 that returns to.

The print medium P guided to the reversing section 50 by the switching mechanism 49 is conveyed from the circulation transport path CR to the reversing table 51 by the reversing roller 52, and is returned from the reversing table 51 to the circulation transport path CR again, so that the front and back sides are reversed. In this state, it is transported on the circulation transport path CR. Then, the print medium P whose front and back sides are reversed is conveyed again toward the print processing unit 30 by a plurality of rollers such as a transfer roller 53 provided on the circulation transfer path CR.

The control unit 60 controls each part of the above-mentioned inkjet printing device 1 and controls the entire inkjet printing device 1. FIG. 2 is a block diagram showing a schematic configuration of the control unit 60 of the present embodiment. Since the inkjet printing apparatus 1 of the present embodiment is characterized by the control of the inkjet head 33, FIG. 2 mainly shows the configuration related to the control of the inkjet head 33.

As shown in FIG. 2, the control unit 60 includes a CPU (Central Processing Unit) 61, a semiconductor memory 62, an external I / F (Interface) 63, an image processing unit 64, and a head control unit 65.

The CPU controls each part of the inkjet printing apparatus 1 including the inkjet head 33. The semiconductor memory 62 temporarily stores the image data input via the external I / F 63. The external I / F 63 communicates with, for example, a computer (not shown) in which a printer driver is installed, and acquires image data output from the computer.

The image processing unit 64 performs predetermined image processing on the image data temporarily stored in the semiconductor memory.

The head control unit 65 controls ink ejection from each nozzle of the inkjet head 33 based on the image processed image data output from the image processing unit 64, and forms a printed image on the print medium P. The head control unit 65 of the present embodiment performs so-called multi-drop control in which a plurality of ink droplets are continuously ejected from the same nozzle to form one pixel constituting a printed image.

Further, the head control unit 65 of the present embodiment sets the drive voltage when ejecting the final ink droplet to be ejected last among the plurality of ink droplets constituting one pixel when ejecting another ink droplet. Satellite suppression control is performed so that the amount of ink in the final ink droplet is smaller than the amount of ink in other ink droplets, which is lower than the driving voltage of.

Specifically, as shown in FIG. 2, the head control unit 65 includes a drop data generation unit 66, a drive voltage switching signal generation unit 67, a drive voltage supply unit 68, and a drive voltage switching unit 69. There is. Although only one nozzle (piezo element 33a and driver circuit 33b) is shown in FIG. 2 for the sake of clarity, in reality, as described above, each inkjet head 33 has a large number of nozzles. There are as many drive voltage switching units 69 as there are nozzles.

The drop data generation unit 66 performs RIP processing on the image data that has been image-processed to generate raster data, and generates ink drop data based on the raster data. The ink drop data is data used for ink ejection control of each inkjet head, and is data indicating the number of ink drops ejected from each nozzle of each inkjet head.

The drive voltage switching signal generation unit 67 generates a head drive voltage switching signal based on the ink drop data generated by the drop data generation unit 66. Specifically, the drive voltage switching signal generation unit 67 identifies the final ink droplet to be ejected last among the plurality of ink droplets forming each pixel based on the ink drop data, and the identified final ink. A head drive voltage switching signal is generated such that the drive voltage supplied to the nozzle when the drops are ejected is lower than the drive voltage supplied to the nozzle when other ink droplets are ejected.

FIG. 3A is a diagram showing an example of a head drive voltage switching signal. FIG. 3A is an example of a head drive voltage switching signal when, for example, the ink drop data supplied to the driver circuit 33b of a predetermined nozzle is 5-drop data. When the ink drop data is 5 drops data, the 5th drop is specified as the final ink drop. Then, as shown in FIG. 3A, a head drive voltage switching signal is generated such that the 1st drop to the 4th drop is a Law signal and the 5th drop is a High signal. The head drive voltage switching signal is output to the drive voltage switching unit 69.

The drive voltage supply unit 68 includes two power sources, a first head drive power source 68a and a second head drive power source 68b, and is connected to the first head drive power source 68a or the second head drive power source 68b via the drive voltage switching unit 69. The generated head drive voltage is supplied to the driver circuit 33b of the nozzle of the inkjet head 33.

The first head drive power supply 68a generates the first head drive voltage supplied to the inkjet head when the final ink droplets described above are ejected, and the second head drive power supply 68b has ink droplets other than the final ink droplets. It generates a second head drive voltage that is supplied to the inkjet head when it is ejected. In the present embodiment, as described above, the head drive voltage when ejecting the final ink droplet is lower than the head drive voltage when ejecting other ink droplets, so that the first head drive voltage is the first. It is set lower than the 2-head drive voltage. However, if the magnitude of the first head drive voltage is made too low, the amount of ink in the final ink droplets becomes smaller than necessary, which may affect the pixel density. Therefore, the first head drive voltage V1 and the second head drive voltage V2 are preferably, for example, about V1: V2 = 5: 6. However, the ratio is not limited to this, and other ratios may be set within a range that does not affect the pixel density.

By setting the head drive voltage when ejecting the final ink droplets low in this way, the amount of ink in the final ink droplets can be made smaller than the amount of ink in the other ink droplets, and the ejection speed of the final ink droplets. Can be made slower than the ejection speed of other ink droplets, so that the tailing of the final ink droplets described above can be shortened.

FIG. 4 is a diagram showing the ejection state of each ink droplet in chronological order when 5 drops of ink droplets are ejected from one nozzle. As shown in FIG. 4, the tailing (the portion indicated by the arrow A) of the fifth drop (drop 5), which is the final ink drop, can be shortened.

By shortening the tailing of the final ink droplet in this way, it is possible to suppress the satellite generated by the ejection of the final ink droplet, and it is possible to suppress the deterioration of the print image quality due to the impact deviation of the satellite.

The drive voltage switching unit 69 is composed of a selector circuit, and includes a first head drive voltage generated by the first head drive power supply 68a and a second head drive voltage generated by the second head drive power supply 68b. Is supplied.

Then, the drive voltage switching unit 69 switches between supplying the first head drive voltage to the driver circuit 33b of the inkjet head 33 and supplying the second head drive voltage based on the input head drive voltage switching signal.

Specifically, when the head drive voltage switching signal as shown in FIG. 3A is input, the drive voltage switching unit 69 supplies the head drive voltage as shown in FIG. 3B to the driver circuit 33b of the inkjet head 33, for example. .. That is, the drive voltage switching unit 69 drives the second head generated by the second head drive power supply 68b in response to the Law signal of the head drive voltage switching signal at the time of ink ejection from the first drop to the fourth drop. The voltage V2 is supplied to the driver circuit 33b. Then, the drive voltage switching unit 69 receives the first head generated by the first head drive power supply 68a in response to the High signal of the head drive voltage switching signal at the time of ejecting the ink of the fifth drop which is the final ink droplet. The drive voltage V1 is supplied to the driver circuit 33b.

The driver circuit 33b drives the piezo element 33a based on the input first head drive voltage V1 or second head drive voltage V2 and ink drop data to eject ink from the nozzle.

In addition, in FIG. 2, FIG. 3A and FIG. 3B, in order to make the explanation easy to understand, ink ejection control from one nozzle has been described, but as described above, in reality, each inkjet head 33 has a plurality of nozzles. Ink ejection control similar to the above is performed for each nozzle. FIG. 5 is a diagram showing an example of a schematic configuration of a control unit 60 when ink ejection control of four nozzles (nozzles 1 to 4) is performed. Further, FIG. 6 is a diagram showing an example of head drive voltage switching signals of four nozzles (nozzles 1 to 4). Further, FIG. 7 is a diagram showing an example of head drive voltages supplied to the driver circuits 34a to 34d of the four nozzles (nozzles 1 to 4), respectively.

In FIG. 6, the ink drop data supplied to the driver circuit 34a of the nozzle 1 is 5 drops data, the ink drop data supplied to the driver circuit 34b of the nozzle 2 is 4 drops data, and the nozzle 3 An example of a head drive voltage switching signal when the ink drop data supplied to the driver circuit 34c of the above is 2-drop data and the ink drop data supplied to the driver circuit 34d of the nozzle 4 is 7-drop data. Is.

As shown in FIGS. 6A to 6D, for each of the nozzles 1 to 4, the Law signal is obtained until the timing when the ink droplet immediately before the final ink droplet is ejected, and the High signal is obtained at the timing when the final ink droplet is ejected. Head drive voltage switching signals such as the above are generated and output to the drive voltage switching units 69a to 69d, respectively.

Then, as shown in FIGS. 7A to 7D, the second head drive voltage V2 is supplied to the driver circuits 34a to 34d in response to the Law signal of the head drive voltage switching signal for the nozzles 1 to 4, and the head drive voltage is switched. The first head drive voltage V1 is supplied to the driver circuits 34a to 34d, respectively, according to the high signal of the signal.

As a result, the tailing of the final ink droplets of each of the nozzles 1 to 4 can be shortened. By shortening the tailing of the final ink droplet in this way, it is possible to suppress the satellite generated by the ejection of the final ink droplet, and it is possible to suppress the deterioration of the print image quality due to the impact deviation of the satellite.

Returning to FIG. 1, the display unit 70 is composed of a touch panel having a liquid crystal display, displays various setting input screens, and receives various setting inputs such as an instruction input for starting printing.

Next, the processing flow of the head control unit 65 will be described with reference to the flowchart shown in FIG.

First, the head control unit 65 receives image data that has undergone predetermined image processing in the image processing unit 64 as described above (S10).

Then, the drop data generation unit 66 generates drop data for each nozzle based on the input image data (S12), and specifies the number of final ink droplet drops for each nozzle (S14).

Then, when the head control unit 65 outputs the ink drop data of each nozzle to the driver circuit of each nozzle and outputs the ink drop data of the ink droplets other than the final ink droplet (S16, NO), the drive voltage When the Raw signal is output as the head drive voltage switching signal from the switching signal generation unit 67 (S18) and the ink drop data of the final ink droplet is output (S16, YES), the head drive is performed from the drive voltage switching signal generation unit 67. A High signal is output as a voltage switching signal (S20).

When the drive voltage switching signal is a Law signal, the first head drive voltage is supplied from the drive voltage switching unit 69 to the driver circuit of each nozzle (S22), and when the drive voltage switching signal is a High signal. Is supplied with the second head drive voltage from the drive voltage switching unit 69 to the driver circuit of each nozzle (S24).

The driver circuit of each nozzle drives the piezo element based on the input first head drive voltage or second head drive voltage and ink drop data, and ejects ink from each nozzle (S26).

According to the inkjet printing apparatus 1 of the above embodiment, when the drive voltage at the time of ejecting the final ink droplet to be ejected last among the plurality of ink droplets constituting one pixel is set, when the other ink droplets are ejected. Since satellite suppression control is performed so that the amount of ink in the final ink droplets is lower than the drive voltage of the other ink droplets, the tailing of the final ink droplets can be reduced, and the final ink droplets can be reduced. It is possible to suppress the influence of satellites generated by ink droplets and improve the quality of printed images.

In addition, unlike the inkjet printing apparatus 1 of the present embodiment, not only the driving voltage at the time of ejecting the final ink droplets is lowered, but also for each ink droplet between the first ejected ink droplets and the final ink droplets. A method of sequentially lowering the ejection speed is conceivable, but in the case of such control, the amount of ink of a plurality of ink droplets other than the ink droplets ejected first is reduced, and as a result, the total ink forming one pixel is formed. Since the amount is considerably reduced, it affects the density of the pixels.

On the other hand, in the inkjet printing apparatus 1 of the present embodiment, since only the driving voltage at the time of ejecting the final ink droplet is lowered, there is almost no influence on the pixel density.

Further, in the inkjet printing apparatus 1 of the above embodiment, when forming all the pixels included in the printed image, the satellite suppression control is performed by the head control unit 65 described above, but the present invention is not limited to this, for example. Since characters are easily affected by satellites, the head control unit 65 may perform the satellite suppression control described above only when forming a printed image of a character area.

Specifically, the above is performed only when the image processing unit 64 determines the character area included in the input image data and the head control unit 65 forms a printed image of the character area based on the determination result. The satellite suppression control may be performed. In this case, the image processing unit 64 corresponds to the character area determination unit of the present invention. Further, a known method can be used for determining the character area.

In this way, by performing the satellite suppression control only when the head control unit 65 forms the print image of the character area, it is possible to suppress the satellite when forming the print image of the character area. It can be printed more clearly. Further, when forming a printed image other than the character area, the head control unit 65 does not perform satellite suppression control, so that the ink amount of the final ink droplet does not decrease and the density of each pixel is increased. Can be maintained.

Further, in the inkjet printing apparatus 1 of the above-described embodiment, when a printed image is formed on the peripheral portion PP of the printing medium P as shown in FIG. 9, the peripheral portion PP is generated in the belt suction hole of the transport belt 88. The above-mentioned satellites are likely to be generated and affected by the suction wind.

Therefore, the head control unit 65 may perform satellite suppression control only when the print image is formed on the peripheral portion PP of the print medium P as shown in FIG. 9, for example.

In this way, the head control unit 65 suppresses the influence of satellites caused by the suction wind of the belt suction hole by performing satellite suppression control only when the print image is formed on the peripheral edge PP of the print medium P. Can be done. Further, when forming a printed image other than the peripheral portion PP, the head control unit 65 does not perform satellite suppression control, so that the ink amount of the final ink droplet does not decrease and the density of each pixel does not decrease. Can be maintained.

The range of the peripheral PP can be arbitrarily set in advance depending on the wind generation status and the satellite generation status in the peripheral PP. As an example, the range of the peripheral edge portion PP may be set so that the distance d from the edge edge of the print medium P is 0 cm <d ≦ 2 cm.

Further, the inkjet printing apparatus 1 of the above-described embodiment employs a suction transport method in which the print medium is suction-adsorbed and transported to the transport belt 88, but the present invention is not limited to this, and the print medium is attracted to the transport belt by static electricity. The electrostatic transport method may be adopted. Also in the case of the electrostatic transfer method, wind is generated by the movement of the transfer belt itself, and the peripheral portion PP of the print medium P is easily affected by the satellite due to the wind.

Therefore, even in the case of the electrostatic transfer method, the satellite suppression control may be performed only when the printed image is formed on the peripheral edge PP of the print medium P.

Further, when the head control unit 65 performs satellite suppression control as described above, the amount of ink in the final ink droplet is smaller than the amount of ink in the other ink droplets. Therefore, for example, when printing figures and photographs that are easily affected by changes in shading, the image quality of those figures and photographs may deteriorate.

Therefore, for example, the image processing unit 64 determines the figure or photographic area included in the image data, and the figure or photographic area GR determines the peripheral portion PP of the above-mentioned print medium P and its peripheral edge as shown in FIG. When the head control unit 65 forms a printed image of the figure or the photographic area GR when straddling both the central portion other than the portion PP, the satellite suppression control may not be performed. In this case, the image processing unit 64 corresponds to the object determination unit of the present invention. A known method can be used for determining the figure or photographic area.

As a result, the influence of satellites on the peripheral edge PP can be suppressed without degrading the image quality of the printed image of the figure or the photographic area GR that straddles both the peripheral edge PP and the central portion of the print medium P.

Further, in the inkjet printing apparatus 1 of the above embodiment, satellite suppression control is performed on the inkjet heads 33 of all colors, but not necessarily all colors (C, M, Y, K in this embodiment). It is not necessary to perform satellite suppression control on the inkjet head 33 (4 colors).

For example, since it is the K ink that the influence of the satellite is easily noticeable on the printed image, the satellite suppression control may be performed only on the K inkjet head 33. The order of colors in which mist is conspicuous is K, M, C, Y (or K, C, M, Y). Therefore, the head control unit 65 may perform satellite suppression control only on, for example, the K and M or C inkjet heads 33, or may perform satellite suppression control only on the K, M and C inkjet heads 33. May be done.

Further, although the inkjet printing apparatus 1 of the above embodiment uses a piezo element for the inkjet head 33, the piezo element is not limited to the piezo element, and other piezoelectric elements may be used.

The following additional notes are further disclosed with respect to the inkjet printing apparatus of the present invention.
(Additional note)
Further, in the inkjet printing apparatus of the present invention, the head control unit determines the driving voltage at the time of ejecting the final ink droplet to be ejected last among the plurality of ink droplets constituting one pixel at the time of satellite suppression control. , It can be made lower than the drive voltage when ejecting other ink droplets.

The inkjet printing apparatus of the present invention can be provided with a character area determination unit that determines a character area included in image data, and the head control unit performs satellite suppression control only when forming a printed image of the character area. be able to.

The inkjet printing apparatus of the present invention may be provided with a transport belt that is provided so as to face the inkjet head and conveys the print medium, and the head control unit is provided only when a printed image is formed on the peripheral edge of the print medium. Satellite suppression control can be performed.

The inkjet printing apparatus of the present invention may include an object determination unit for determining a figure or photographic area included in image data, and the head control unit has a figure or photographic area as a peripheral portion of a print medium and the peripheral portion thereof. When forming a printed image of a figure or a photographic area when straddling both of the central portion other than the above, satellite suppression control can be omitted.

1 Inkjet printing device 10 Side paper feed unit 11 Paper feed table 12 Primary paper feed unit 14 Secondary paper feed unit 20 Internal paper feed unit 21a-21d Paper feed table 22a-22d Primary paper feed unit 30 Print processing unit 31 line Head 32 Head holder 33 Inkjet head 33a Piezo element 33b Driver circuit 34a-34d Driver circuit 40 Paper discharge unit 45 Paper discharge table 48 Paper discharge roller 49 Switching mechanism 50 Reversing unit 51 Reversing table 52 Reversing roller 53 Transfer roller 60 Control unit 62 Semiconductor Memory 63 External I / F
64 Image processing unit 65 Head control unit 66 Drop data generation unit 67 Drive voltage switching signal generation unit 68 Drive voltage supply unit 69 Drive voltage switching unit 69a to 69d Drive voltage switching unit 70 Display unit 80 Transport unit 81 Platen 81a Platen suction hole 82 Fan mechanism 83 Conveyance belt 88 Conveyance belt 100 Housing CR Circulation transport path FR Paper feed transport path GR Photo area P Print medium PP Peripheral part

Claims (5)

An inkjet head that forms a printed image by ejecting ink droplets from a nozzle onto a print medium based on image data.
A head that forms one pixel constituting the printed image by controlling the driving voltage of the inkjet head to eject ink droplets from the nozzles and continuously ejecting a plurality of ink droplets from the same nozzle. Equipped with a control unit
The head control unit makes the ejection speed of the final ink droplet to be ejected last among the plurality of ink droplets constituting the one pixel slower than the ejection speed of the ink droplet when ejecting other ink droplets. An inkjet printing device that controls satellite suppression to reduce the amount of ink in the final ink droplets to be smaller than the amount of ink in the other ink droplets. During the satellite suppression control, the head control unit discharges the drive voltage at which the final ink droplet to be ejected last among the plurality of ink droplets constituting the one pixel is ejected, and the other ink droplets are ejected. The inkjet printing apparatus according to claim 1, wherein the voltage is lower than the driving voltage at the time of printing. A character area determination unit for determining a character area included in the image data is provided.
The inkjet printing apparatus according to claim 1 or 2, wherein the satellite suppression control is performed only when the head control unit forms a printed image of the character region. A transport belt provided facing the inkjet head and sucking and transporting the print medium is provided.
The inkjet printing apparatus according to any one of claims 1 to 3, wherein the head control unit performs satellite suppression control only when the head control unit forms a printed image on the peripheral edge of the print medium. It is provided with an object determination unit that determines a figure or photographic area included in the image data.
When the figure or photographic area extends over both the peripheral portion of the print medium and the central portion other than the peripheral portion, the head control unit forms a printed image of the figure or photographic area. The inkjet printing apparatus according to claim 4, wherein the satellite suppression control is not performed.