JP2007168267A - Inkjet printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printing apparatus capable of forming an image at a precise position on a printing medium without requiring a large capacity of an image memory and without requiring a complicated adjusting mechanism, and capable of forming the image with a high quality generating no color deviation and no positional deviation of the image. <P>SOLUTION: A plurality of heads having one or a plurality of nozzle lines are arranged over the whole width of the printing medium in a line head. The inkjet printing apparatus has a plurality of the line heads and forms the image on the moving printing medium by delivering ink from the nozzle lines. The inkjet printing apparatus has a conveying apparatus for moving the printing medium, a plurality of first detecting means for detecting passing-through of the printing medium, and a controlling means for controlling a timing for starting printing of the line head based on the detected result by the first detecting means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color line printer using a plurality of inkjet line heads and a high-speed line printer.

  In an inkjet printing apparatus, a small droplet of ink subjected to ejection control by an image signal from a nozzle of an inkjet head (hereinafter also referred to as a head) is ejected to a printing medium while the inkjet head is perpendicular to the printing medium conveyance direction. After moving the image for one line, the print medium is conveyed for one line, and a small droplet of ink is ejected from the nozzles of the inkjet head to the print medium again to print the image for one line. There is a so-called shuttle type printer that forms an image on a printing medium by repeating this process.

  As another inkjet printing apparatus, an inkjet head is configured in a long shape in which nozzles for ejecting ink are arranged at an equal interval pitch in the length of the substantially maximum printing width of the printing medium, and is fixed to the apparatus main body. Some have line heads. According to this configuration, it is not necessary to move the inkjet head, and image formation can be performed only by transporting the printing medium, so that high-speed image formation can be performed.

  In recent years, inkjet color printers that print a color image by arranging a plurality of line heads in the print medium transport direction and discharge different color inks, and high-speed printers that discharge the same color ink and print at high speed have been developed. ing.

  Since each line head is shifted in the printing medium conveyance direction, it is necessary to shift the printing start time according to the position. In other words, the print start of the line head located downstream of the line head upstream in the print medium transport direction is delayed so that the color image on the print medium does not cause color misalignment or the high speed printer does not cause landing misalignment. To be formed. In order to delay the start of printing, there is a method in which non-ejection data is written in the image memory for each line head by an amount corresponding to the positional deviation, and ejection is not performed while the non-ejection data is being read.

Also, a detecting means for detecting the leading edge of the printing medium is provided upstream of the line head, and the time for which the printing medium is conveyed to the position where printing is started after the leading edge of the printing medium is detected is set for each line head by a timer or the like. There has been proposed a method of counting and starting the printing from the time point up. (For example, see Patent Document 1)
JP 2001-253066 A

  However, in the method of inserting non-ejection data into the image memory by an amount corresponding to the positional deviation between the line heads, an image memory larger than the actual image is required and expensive because the non-ejection data is inserted. .

  Further, when reading from the image memory, processing is performed for each image. Therefore, printing of all line head images is completed and processing for one image is completed. For this reason, when roll paper is used as the printing medium, a gap is required between the printed images, and continuous printing cannot be performed.

  When printing is started using a detection means that detects the leading edge of the printing medium upstream of the line head, if the position between the line heads is shifted from the correct position, color misalignment or image misalignment occurs. There was a problem to say. For this reason, for example, when the line head is replaced in the market, it becomes a device with a complicated adjustment mechanism, or a jig is required for position adjustment, resulting in an increase in cost.

  Further, even if the detecting means is accurately installed, if unevenness in the conveyance speed of the printing medium occurs after the leading edge of the printing medium is detected by the detecting means, color misregistration or image positional deviation occurs.

  Therefore, the present invention does not require a large-capacity image memory, can form an image at a precise position on a printing medium without the need for a complicated adjustment mechanism, and has high image quality that does not cause color misalignment or image misalignment. An object of the present invention is to provide an ink jet printing apparatus for forming a clear image.

The object of the present invention can be achieved by the following constitution.
(1)
A line head in which a plurality of heads having one or a plurality of nozzle rows are arranged across the entire width of the printing medium, the head having a plurality of the line heads, and ejecting ink from the nozzle rows to the moving printing medium. In an inkjet printing apparatus for forming an image,
A transport device for moving the printing medium;
A plurality of first detection means for detecting passage of the print medium;
An inkjet printing apparatus comprising: a control unit that controls a print start timing of the line head based on a detection result of the first detection unit.
(2)
The ink jet printing apparatus according to (1), wherein the control unit controls the print start timing to be delayed and the delay amount to be changed.
(3)
The inkjet printing apparatus according to (2), wherein the control unit changes the delay amount in units of ink ejection time.
(4)
The inkjet printing apparatus according to (2), wherein the control unit changes the delay amount based on a movement amount of moving the printing medium.
(5)
The inkjet printing apparatus according to (4), wherein the movement amount is a value based on position information detected by the second detection unit.
(6)
The ink jet printing apparatus according to (5), wherein the second detection unit is arranged for each line head.
(7)
The ink jet printing apparatus according to any one of (1) to (6), wherein the first detection unit detects a leading end of a printing medium.
(8)
The inkjet printing apparatus according to any one of (1) to (7), wherein the first detection unit detects a mark printed in advance on a printing medium.
(9)
The control means controls the print start timing based on a detection result obtained by detecting the mark printed on the print medium by the upstream line head by the first detection means (1) to ( The inkjet printing apparatus according to any one of 8).

  By controlling the printing start timing of the line head based on the detection result of the first detection means for detecting the passage of the printing medium arranged for each line head, printing is performed from an accurate position on the printing medium of each line head. Since it can be started, it is possible to form a high-quality image with no color shift or image position shift of images printed by a plurality of line heads.

  Although the example of embodiment regarding this invention is shown below, the aspect of this invention is not limited to these.

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

  FIG. 1 is a perspective view showing a main part of an inkjet printing apparatus according to the present invention. The line-type inkjet printing apparatus can perform image printing by relatively moving the line head and the printing medium in a direction orthogonal to the nozzle row of the line head. Here, the relative movement between the line head and the printing medium will be described by taking as an example a mode in which the line head is fixed and the printing medium is moved in a direction perpendicular to the nozzle row of the line head, but conversely, the line head May be moved.

  In the figure, reference numeral 2 denotes a line head in which a plurality of heads installed in the inkjet printing apparatus 1 are arranged in a staggered manner, and a head drive substrate 4 and a main body control unit (not shown) are connected by a cable 3. The line head 2 is covered by a cover 200 except for the surface facing the print medium P. In the case of performing full-color image printing, for example, a line head for ejecting ink of each color of YMC is arranged for each color. Here, a description will be given of an apparatus provided with one line head 2.

  The print medium P is placed on a table on the print medium transport mechanism 5 that transports the print medium P, and is transported at a constant speed in the direction indicated by the arrow X in the drawing.

  The line head 2 is disposed so as to face the surface of the printing medium P as shown in the figure, and the longitudinal direction thereof extends in the direction of arrow Y in the figure orthogonal to the conveyance direction of the printing medium P indicated by the arrow X direction.

  In the line head 2, a number of nozzles are arranged at equal intervals along the Y direction in a length corresponding to the width of the print medium P on a hidden surface in the drawing facing the surface of the print medium P. ing. By transporting ink to the print medium P in accordance with an image signal transmitted from a host PC (Personal Computer) (not shown) from a large number of nozzles via a main body control unit (not shown), the print medium P is conveyed in the direction of arrow X. Together with this, an image is formed on the surface of the printing medium P. That is, image formation is performed at a high speed by completing the printing process of a predetermined image forming area in one transport.

  The first detection means 7 comprises a photo detector, detects the passage of the printing medium, and transmits the detection result to the main body control unit via the head drive substrate 4.

  The line head 2 is supplied with ink from an intermediate tank (not shown) through an ink supply pipe 6.

  FIG. 2 is a schematic diagram in which three sets of line heads according to the present invention are arranged.

  In the line heads 21 to 23, heads 211 to 214, 221 to 224, and 231 to 234 are arranged in a staggered manner with the head drive substrates 41 to 43 interposed therebetween, and the line heads are, for example, Y, M, A color image is formed on the printing medium P by ejecting C ink.

  The first detection means 71 to 73 are located slightly upstream in the print medium transport direction from the nozzle row of the head, and detect and detect the tip of the print medium P or the mark M printed on the print medium P. The result is transmitted to the main body control unit 8.

  The head drive substrates 41 to 43 convert the image signal to voltage and drive the head pressure generating means to discharge ink. Further, the output of the first detection means is A / D converted and transmitted to the main body control unit 8.

  The main body control unit 8 distributes image data transmitted from the PC to the head, transports the recording medium P, and controls the inkjet printing apparatus as a whole.

<First Embodiment>
FIG. 3 is a block diagram of the main body control unit showing the first embodiment according to the present invention.

  The controller 85 includes, for example, a CPU, a ROM, a RAM, and a non-volatile memory. A processing program recorded in the ROM is expanded on the RAM, and the processing program is executed by the CPU. The nonvolatile memory stores delay information, image memory configuration, head driving conditions, and the like.

  The host PCI / F 84 is an interface with a host PC (Personal Computer), and transmits and receives various signals for printing, image data, status of the inkjet printing apparatus, and the like.

  The image memories 831 to 833 store image data to be printed by the line heads 21 to 23.

  The read / write controllers 821 to 823 write the image data received from the PC to the image memory, or read the image data from the image memory and distribute it to each head of the line head.

  The delay circuits 811 to 813 delay the detection result (the leading edge detection signal of the print medium or the mark M detection signal) detected by the first detection unit by a predetermined time and send it to the read / write control unit.

  The conveyance driving unit 86 drives a driving roller 87 that conveys the printing medium P.

  The drive roller 87 is, for example, a roller for nipping and transporting the printing medium P, transporting a transport belt, or transporting an XY stage table.

  The operation of the first embodiment will be described with reference to FIG.

  FIG. 4 is a schematic diagram showing the temporal relationship between the positions of the line head, the first detection means, and the printing medium according to the first and second embodiments of the present invention.

  The ejection clock is a pulse generated every time one line is printed. The printing medium P is conveyed in the direction of the arrow, and the mark M is detected by the first detection means 71. The image data 1a is read from the image memory (831 in FIG. 3) and transmitted to the line head 21 using the output of the first detection means 71 as a trigger. The nozzle row of the line head 21 is displaced from the first detection means 71 by a distance a. In other words, the print medium is conveyed to the nozzle row of the head 21 after a delay a in terms of the print medium conveyance time. The image data 1a is ejected at the rising edge of the ejection clock 1. Next, the image data 2 a is ejected by the ejection clock 2. Thereafter, the image data is sequentially read and discharged as discharge clocks 3 and 4.

  Here, the delay a is set to one discharge clock, but this is not limited. If the distance a is large, the delay time becomes longer by the time during which the print medium is conveyed. However, it is necessary to adjust the distance a so as to be a multiple of the ejection clock period. The same applies to the delays b and c.

  The printing medium P is further conveyed, and the mark M is detected by the first detection means 72. The image data 1b of the line head 22 is read from the image memory (832 in FIG. 3) and transmitted to the line head 22 using the output of the first detection means 72 as a trigger. As described above, the image data 1b is ejected by the ejection clock 5, and the image data 2b is ejected by the ejection clock 6. Thereafter, the image data is sequentially read out and discharged by the discharge clocks 7 and 8.

  The printing medium P is further conveyed, and the image data 1c and 2c are ejected by the line head 23 as described above.

  In the present embodiment, the mark is detected by the first detection means, but the leading edge of the printing medium may be detected instead of the mark.

  As described above, since the first detection means is arranged in each line head, the position of the nozzle array of the line head is close to the first detection means. For this reason, each first detection means starts printing with a short delay time after detecting the leading edge of the printing medium or the mark on the printing medium. Fewer image quality can be formed.

<Second Embodiment>
FIG. 5 is a block diagram of a main body control unit showing a second embodiment according to the present invention.

  The input unit 88 includes a display unit such as an LCD and an input button, and inputs a delay amount to each line head using the input button. The input delay amount is transmitted to the delay circuits 811 to 813 via the controller 85.

  The position information acquisition unit 89 that is the second detection unit counts the output of a rotary encoder (not shown) that is the position information of the drive roller 87 and detects the amount of movement of the print medium P. The pitch of the rotary encoder is set to discharge resolution or its multiplication.

  The operation of the second embodiment will be described with reference to FIG.

  In the first embodiment, an ejection clock is used as an ejection signal, whereas in the second embodiment, ejection is performed in synchronization with the rotary encoder output described above.

  In advance, the moving amount of the printing medium, which is the delay amount from the first detection means 71 of the mark M to the ejection from the input unit 88, is inputted in units of the number of pulses of the rotary encoder.

  The input delay amount is transmitted to the delay circuits 811 to 813 via the controller 85. The delay circuits 811 to 813 store the transmitted delay amount in a register.

  When the printing medium P starts to be conveyed, the rotary encoder output is transferred to the delay circuits 811 to 813 via the controller 85.

  After the print medium P is conveyed and the mark M is detected by the first detection means 71, the delay circuit 811 counts the rotary encoder output and counts up to the delay amount stored in the register. Is transmitted to the line head 21. The sent image data 1a is discharged in synchronization with the next rotary encoder output (for example, encoder output 1). Next, the image data 2 a is ejected in synchronization with the encoder output 2. Thereafter, image data is sequentially discharged.

  Further, after the printing medium P is conveyed and the first detection means 72 detects the mark M, the delay circuit 812 counts the rotary encoder output and counts up to the delay amount stored in the register. The image data 1b is read and transmitted to the line head 22. The sent image data 1b is discharged in synchronization with the next rotary encoder output (for example, encoder output 5). Next, the image data 2 b is ejected in synchronization with the encoder output 6. Thereafter, image data is sequentially discharged.

  Further, when the print medium P is conveyed and the mark M is detected by the first detection unit 73, the same operation as described above is performed.

  In the present embodiment, the delay amount from when the mark is detected by the first detection means 71 to 73 to when the image data is ejected from the heads 21 to 23 is set as one pulse of the encoder, but this is not restrictive. If the distances a, b, and c between the detection means 71 to 73 and the nozzle rows of the line heads 21 to 23 are large, the number of pulses is input from the input unit 88 by that distance. However, the distances a, b, and c need to be matched so that the encoder pitch is multiplied.

  As described above, since the first detection means is arranged in each line head, the position of the nozzle array of the line head is close to the first detection means. Therefore, after each first detection means detects the leading edge of the printing medium or the mark on the printing medium, printing is started with a short movement amount of the printing medium. High-quality image formation with little displacement is possible.

<Third Embodiment>
FIG. 6 is a block diagram of a main body control unit showing a third embodiment according to the present invention.

  FIG. 7 is a schematic diagram showing the temporal relationship between the position of the line head, the first detection means, and the print medium according to the third embodiment of the present invention.

  FIGS. 6 and 7 are configurations in which the first detection means 71 and the delay circuit 811 are removed from FIGS.

  The operation of the third embodiment will be described with reference to FIG.

  In this embodiment, roll paper is used as the printing medium. The host PC instructs the controller 85 to start printing via the host PCI / F 84. The controller 85 starts conveying the roll paper and issues a print trigger to the read / write control unit 821. In response to the print trigger, the read / write control unit 821 reads the image data 1 a (here, the data of the mark M) from the image memory 831 and transmits it to the line head 21. The sent image data 1a is discharged in synchronization with the next encoder output (for example, encoder output 1). Next, the image data 2 a is ejected in synchronization with the encoder output 2. Thereafter, image data is sequentially discharged.

  Further, after the printing medium P is conveyed and the first detection means 72 detects the mark M printed by the head 21, the image data 1 b is ejected in synchronization with the encoder output 5. Thereafter, image data is sequentially discharged.

  Further, after the printing medium P is conveyed and the first detection means 73 detects the mark M printed by the head 21, the image data 1 c is ejected in synchronization with the encoder output 9. Thereafter, image data is sequentially discharged.

  Since the mark printed by the upstream line head is detected and discharged by the downstream line head based on the detection result, it is possible to form an accurate image without any color shift or image shift at any position on the print medium.

<Fourth embodiment>
FIG. 8 is a perspective view showing a main part of an inkjet printing apparatus using a linear encoder. A linear scale 91 is affixed on the table (or belt) of the photographic print medium transport mechanism 5. Encoder sensors 891 to 893, which are second detection means, are arranged downstream of the first detection means 71 to 73 in the print medium conveyance direction for each line head. The encoder sensors 891 to 893 are made of a photo detector and detect the slit of the linear scale 91 to generate a pulse.

  FIG. 9 is a block diagram of the main body control unit showing the fourth embodiment.

  The linear scale 91 affixed on the table (or belt) of the photographic print medium transport mechanism 5 is detected by the encode sensors 891 to 893, and position information as detection results is input to the delay circuits 811 to 813.

  FIG. 10 is a schematic diagram showing the temporal relationship between the position of the line head, the first detection means, and the print medium according to the fourth embodiment.

  The operation of the fourth embodiment will be described with reference to FIGS.

  In the present embodiment, as an example, a case where the mark M is printed on a printing medium in advance will be described.

  The linear scale movement amount, which is the delay amount from the first detection means 71 of the mark M to the ejection from the input unit 88, is input in advance in units of slits of the linear scale.

  The input delay amount is transmitted to the delay circuits 811 to 813 via the controller 85. The delay circuits 811 to 813 store the transmitted delay amount in a register.

  When the printing medium P starts to be conveyed, the outputs of the encoder sensors 891 to 893 that have detected the slits of the linear scale are transferred to the delay circuits 811 to 813.

  After the printing medium P is conveyed and the first detection means 71 detects the mark M, the delay circuit 811 counts the output of the encoder sensor 891 and counts up to the delay amount stored in the register. Image data is read and transmitted to the line head 21. The sent image data 1a is discharged in synchronization with the next encoder sensor output (for example, encoder output 1). Next, the image data 2 a is ejected in synchronization with the encoder output 2. Thereafter, image data is sequentially discharged.

  Further, after the printing medium P is conveyed and the first detection means 72 detects the mark M, the delay circuit 812 counts the output of the encoder sensor 892 and counts up to the delay amount stored in the register. The image data 1 b is read out from the image data and transmitted to the line head 22. The sent image data 1b is discharged in synchronization with the next encoder sensor output (for example, encoder output 5). Next, the image data 2 b is ejected in synchronization with the encoder output 6. Thereafter, image data is sequentially discharged.

  Further, when the print medium P is conveyed and the mark M is detected by the first detection unit 73, the same operation as described above is performed.

  In this embodiment, the delay amount from when the mark is detected by the first detection means 71 to 73 to when the image data is ejected from the heads 21 to 23 is set to one pitch of the linear scale, but this is not restrictive. If the distances a, b, and c between the detection means 71 to 73 and the nozzle rows of the line heads 21 to 23 are large, the number of pulses is input from the input unit 88 by that distance. However, the distances a, b, and c need to be matched so that the encoder pitch is multiplied.

  Since the first detection means 71 to 73 and the encoder sensors 891 to 893 as the second detection means are arranged close to each other for each line head, fluctuations in the conveyance speed of the print medium, linearity, etc. Even if the scale expands or contracts, the print start timing is the same for the print media between the line heads, and there is no line shift, so there is no color shift or image position shift. Is possible.

  In addition, the detailed configuration and detailed operation of each component constituting the inkjet printing apparatus can be changed as appropriate without departing from the spirit of the present invention.

1 is a perspective view showing a main part of an ink jet printing apparatus according to the present invention. It is a schematic diagram in which three sets of line heads according to the present invention are arranged. It is a block diagram of the main body control part which shows the 1st Embodiment concerning this invention. FIG. 4 is a schematic diagram showing a temporal relationship between the position of the line head, the first detection unit, and the print medium according to the first and second embodiments of the present invention. It is a block diagram of the main body control part which shows the 2nd Embodiment concerning this invention. It is a block diagram of the main body control part which shows the 3rd Embodiment concerning this invention. It is the schematic diagram which showed the time relationship with the position of the line head regarding the 3rd Embodiment concerning this invention, a 1st detection means, and a printing medium. 1 is a perspective view showing a main part of an inkjet printing apparatus using a linear encoder according to the present invention. It is a block diagram of the main body control part which shows the 4th Embodiment concerning this invention. It is the model which showed the temporal relationship with the position of the line head regarding the 4th Embodiment concerning this invention, a 1st detection means, and a printing medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Line head 4 Head drive part 5 Print medium conveyance mechanism 7 1st detection means 8 Main body control part 21-23 Line heads 71-73 1st detection means 811-813 Delay circuit 831-833 Image memory 89 Rotary encoder 891-893 Encoder sensor 91 Linear scale

Claims (9)

A line head in which a plurality of heads having one or a plurality of nozzle rows are arranged across the entire width of the printing medium, the head having a plurality of the line heads, and ejecting ink from the nozzle rows to the moving printing medium. In an inkjet printing apparatus for forming an image,
A transport device for moving the printing medium;
A plurality of first detection means for detecting passage of the print medium;
An inkjet printing apparatus comprising: a control unit that controls a print start timing of the line head based on a detection result of the first detection unit. 2. The ink jet printing apparatus according to claim 1, wherein the control means controls to delay the print start timing and change a delay amount. The inkjet printing apparatus according to claim 2, wherein the control unit changes the delay amount in units of ink ejection time. The inkjet printing apparatus according to claim 2, wherein the control unit changes the delay amount based on a moving amount of moving the printing medium. The inkjet printing apparatus according to claim 4, wherein the amount of movement is a value based on position information detected by the second detection unit. 6. The inkjet printing apparatus according to claim 5, wherein the second detection unit is arranged for each line head. The inkjet printing apparatus according to claim 1, wherein the first detection unit detects a leading end of a printing medium. The inkjet printing apparatus according to claim 1, wherein the first detection unit detects a mark printed in advance on a printing medium. The control means controls the print start timing based on a detection result obtained by detecting a mark printed on a print medium by an upstream line head by the first detection means. The inkjet printing apparatus according to any one of the above.

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