JP2007130881A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer of a line type with which high-definition printing is made possible at one-time scanning and the position of a printed picture does not shift even if the position wherein a recording medium is laid shifts to a sub-scanning direction somewhat, in viewing the above-mentioned trouble. <P>SOLUTION: The inkjet printer is equipped with a line head wherein a plurality of heads are arranged staggeredly, an image memory for storing image data, a detection means for detecting the end of the main scanning direction of the recording medium, a control means for changing the image data that has been read from the image memory based on the information detected by the detection means and the control means for controlling the output of the line head based on the changed image data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet printing apparatus, and more specifically, a line type in which a plurality of nozzles are arranged in a length corresponding to the width of a printing medium, and an image is printed by discharging ink from the nozzles toward the printing medium. The present invention relates to an inkjet printing apparatus.

  In the inkjet printing apparatus, the inkjet head was moved in the main scanning direction while ejecting small droplets of ink, which were controlled by the image signal from the nozzles of the inkjet head, onto the printing medium, and image printing for one line was performed. Thereafter, the printing medium is conveyed in the sub-scanning direction for one line, and a small droplet of ink is ejected from the nozzle of the inkjet head to the printing medium again to print one line of the image. Some form an image on top.

  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 in the main scanning direction, and image formation can be performed only by transporting the printing medium in the sub-scanning direction orthogonal to the main scanning direction, so that high-speed image formation can be performed. it can.

  However, when image formation is performed with only one transport in the sub-scanning direction for high-speed image formation, the print resolution in the main scanning direction is determined by the nozzle pitch of the line head. Therefore, it is conceivable to reduce the dot pitch by reducing the nozzle pitch of the line head in order to reduce the dot pitch of the print in the main scanning direction, but there is a processing limit to reduce the nozzle pitch. There is a limit to the printing accuracy by reducing the dot pitch, and in the case of a long full line head, if even one nozzle is defective, the line head will be defective, and it will be expensive. There's a problem.

  In view of this, a line head has been proposed in which print heads each having nozzles arranged on a straight line are arranged in a staggered pattern across the entire width of the print medium in the width direction of the print medium (see Patent Document 1).

  When printing on a printing medium with an image printing apparatus using the line head, the image printed is biased on the printing medium depending on the position where the printing medium is installed, or the printing medium is installed obliquely. When printing is performed obliquely with respect to the print medium, or when roll paper is used as the print medium, the image may meander on the print medium due to the meandering of the roll paper.

In order to eliminate such a problem, the posture of the recording paper is detected by the posture detection means, and the print head is moved according to the detection result. When the recording paper is inclined by an angle θ from the original posture, the print head is also rotated to a position inclined by θ from the original position (default position). In addition, if the print head is tilted, the positional relationship between the droplet ejection point on the recording paper and the print head (nozzle) changes from the original positional relationship, so that the print head is aligned with the print direction (the longitudinal direction of the print head). And a method of moving in parallel with the direction (see Patent Document 2).
JP 2003-246092 A JP 2005-88242 A

  However, the line head disclosed in Patent Document 1 prints on a print medium when the installation position of the sheet-like print medium is shifted in the main scanning direction or when the roll-like print medium meanders during transportation. There is a problem that the image to be shifted is shifted in the main scanning direction.

  Further, when the sheet-like print medium is installed obliquely, the print head disclosed in Patent Document 2 is rotated to a position inclined by θ from the original position, but in a staggered manner as in the present invention. In the case of a line head in which the heads are arranged, if the line head is tilted, the adjacent heads overlap in the main scanning direction, the image printed on the recording medium overlaps at the boundary of the head, and the image is reduced in the main scanning direction. There is a problem.

  The object of the present invention has been made in view of the above-mentioned problems. High-definition printing is possible by one scan, and printing is performed even if the position on which the recording medium is placed is slightly shifted in the sub-scanning direction. Another object of the present invention is to provide a line-type inkjet printing apparatus in which the position of the printed image is not displaced.

The object of the present invention is achieved by the following configurations.
(1)
A line head in which a plurality of heads are arranged in a staggered manner;
An image memory for storing image data;
Detecting means for detecting an end of the printing medium in the main scanning direction;
Control means for changing the image data read from the image memory based on the information detected by the detection means, and for controlling the output of the line head based on the changed image data. Inkjet printing device.
(2)
The inkjet printing apparatus includes a shift register that shifts image data read from the image memory,
The inkjet printing apparatus according to (1), wherein the control unit controls an operation of the shift register based on information detected by the detection unit.
(3)
The information detected by the detection means is an amount of deviation from a predetermined position of the print medium in the main scanning direction. The inkjet printing apparatus according to (1) or (2),
(4)
The size of the image memory is represented by the number of pixels, and the number of pixels in the main scanning direction is smaller than the number of nozzles of the head. The inkjet printing apparatus as described.

  According to the present invention, an inkjet printing apparatus that can perform high-definition printing by one scan, does not require a complicated mechanism, and does not shift the position of the printed image even if the setting position of the printing medium is slightly shifted. Can be provided.

  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. Note that the line-type inkjet printing apparatus can perform image printing by relatively moving the line head and the printing medium in the sub-scanning direction (movement direction). Here, the relative movement of the line head and the print medium in the sub-scanning direction will be described by taking an example in which the line head is fixed and the print medium is moved in the sub-scanning direction. It may be moved in the sub scanning direction.

  In the figure, reference numeral 2 denotes a line head installed in the inkjet printing apparatus 1, and a host PC (Personal Computer) (not shown) and a control board 4 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 addition, when full-color image printing is performed, for example, a line head for ejecting ink of each color of YMCK 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 drawing, and the length direction thereof extends in the arrow Y direction in the drawing 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. The ink is ejected from the large number of nozzles onto the printing medium P in accordance with the image signal from the host PC, whereby an image is formed on the surface of the printing medium P in combination with the conveyance of the printing medium P in the arrow X direction. 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 CCD sensor 8 detects the end of the printing medium P in the main scanning direction and measures how far the printing medium P is placed from a predetermined position (a normal position on which the printing medium is placed). . The measured value is amplified and A / D converted by the detection means (21 in FIG. 2), and transmitted to the control means on the control board 4 (22 in FIG. 2, hereinafter referred to as a control unit).

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

  FIG. 2 is a block diagram of the control board 4 according to the present invention.

  The control unit 22 includes, for example, a CPU 221, a ROM 222, and a RAM 223. The processing program recorded in the ROM 222 is expanded on the RAM 223 and is executed by the CPU 221.

  The control unit 22 is connected to the host PCI / F 23, the detection unit 21, the head drive units 241 to 246, and the shift clock generation unit 26 through the bus 7 in accordance with the processing program described above, and based on the status of the operation state of each unit. Control the operation of each part.

  As described above, the detection unit 21 detects the amount of placement deviation of the printing medium P and transmits it to the control unit 22.

  The host PCI / F 23 is an interface with a host PC (Personal Computer), and transmits and receives various signals and image data for printing.

  The head drive unit 241 includes an image memory 2411 that stores image data to be printed, a shift register 2412 that shifts the image data, and a head control signal generation unit 2413 that generates a signal for driving the head 251. To 251.

  Similarly, the head drive units 242 to 246 include an image memory, a shift register, and a head control signal generation unit, and transmit the generated signals to the heads 252 to 256.

  The shift clock generation unit 26 generates a shift clock when the image data is shifted by the shift registers 2412 to 2462.

  The heads 251 to 256 are ink jet heads, and eject ink according to the image data transmitted from the head driving units 241 to 246 to form an image on the printing medium.

  FIG. 3 is an example of a diagram showing the positional relationship between the heads 251 to 256 constituting the line head 2, the detection means 21, and the printing medium P.

  This is a case where the printing medium P is placed at a normal position with respect to the line head 2. This is a case where the printing medium P ′ is placed with an inclination θ. The detection means 21 detects the edge of the print medium in the main scanning direction in real time during conveyance of the print medium, measures the amount of deviation between the print media P and P ′, and transmits it to the control unit 22.

  FIG. 4 is an enlarged view of the positional relationship between the print medium and the detection means 21. As shown in FIG. FIG. 4A shows the state of the print medium P ′ placed at an inclination with respect to the print medium P when placed at a regular position. FIG. 4B shows the state of the print medium P ′ placed in parallel with the print medium P when placed at a regular position. The recording medium is conveyed in the direction of arrow X. The end portion in the main scanning direction of the print medium placed at the normal position overlaps with the vertical broken line of the detection means 21. The distance between the edge of the print medium P ′ and the vertical broken line is the amount of deviation. For example, in FIG. 4A, the distance is 211, and in FIG. 4B, the distance 212 is the shift amount.

  FIG. 5 is a diagram showing a result of printing on a print medium with a line head.

  FIG. 5A shows the result of printing in the state of FIG. 4A, the printing result of the printing medium P (placed at the normal position), and FIG. 5B shows the printing medium P ′ (inclined). This is the result of printing.

  In FIG. 5B, characters are printed on the print medium P 'gradually on the left. There is a risk that it will eventually protrude to the left of the print medium P ′.

  Further, FIG. 5C shows the result of printing in the state of FIG. 4B, the printing result of the printing medium P (placed at the regular position), and FIG. 5D shows the printing medium P ′. It is a printing result of (placed in parallel).

  In FIG. 5D, the characters are shifted to the left as a whole with respect to the printing result of FIG.

  FIG. 6 shows a printing result to which the present invention is applied. FIG. 6A shows the result of printing on the printing medium P (placed at a normal position). When the present invention is applied to the printing medium P ′ (placed in parallel), characters are printed at the same position. The

  FIG. 6B shows a result of printing by applying the present invention to the printing medium P ′ (tilted and placed).

  FIG. 7 is a diagram in which image data according to the present invention is assigned to the nozzles of the head. The heads 251 to 256 are arranged side by side as shown in FIG. In the figure, one box corresponds to one nozzle. Each head has 16 nozzles for convenience.

  Here, the shift operation according to the present invention will be described with reference to FIGS.

  In FIG. 2, the image data in the image memory 241 is latched in the shift register 2412 in parallel. The number of bits of the shift register 2412 is the same as the number of nozzles of the head 251 and is larger than the width of the image memory 2411 (number of pixels in the main scanning direction). The image data is latched at the center of the shift register 2412. At this time, 0 is placed at both ends of the shift register 2412.

  In the control unit 22 that has received the distance between the predetermined position detected by the detection means 21 (the position of the end when the print medium is placed at the normal position) and the end of the placed print medium, the distance The shift clock is generated by the shift clock generator 26 by the number obtained by dividing the value by the nozzle pitch of the head 251. The shift clock generated by the shift clock generator 26 is sent to shift registers 2412 to 2462 (not shown). For example, if the nozzle pitch is 100 μm and the value detected by the detecting means 21 is 100 μm (in the case of 212 in FIG. 4), one right shift clock is reversely detected and the value detected in the opposite direction is −200 μm (211 in FIG. 4). 2), two left shift clocks are generated.

  The shift registers 2412 to 2462 that have received the shift clock shift the image data to the right or left by the number of right or left shift clocks. Shift is performed, and 0 is entered in the vacant bits.

  The image data shifted by the shift register is serially transferred to the heads 251 to 256 using the transfer clock generated by the head control signal generators 2413 to 2463 (not shown) as a clock.

  FIG. 7 shows a state in which image data is transferred to the nozzles of the heads 251 to 254.

  1. In the normal position of the print medium, the print medium is placed at a normal position, and the end of the print medium detected by the detection means 21 and the predetermined position (the position of the print medium normally placed) are not displaced. The image data is transferred to the head. The nozzles 1 to C are image data. The two nozzles at both ends of the head are 0 because they are not shifted right or left by the shift register.

  On the other hand, 2. When the printing medium is placed with one dot shifted to the right, the contents of the shift register 2412 are shifted to the right by one pixel, so the nozzles 1 to C become image data, the leftmost three nozzles are 0, and the rightmost one The nozzle is zero. Similarly, the heads 252 to 254 are also shifted rightward by one pixel, so that the entire image is shifted rightward by one pixel and discharged. With these operations, even if the printing medium is placed shifted by one dot to the right, the image is printed at a normal position on the printing medium.

  Furthermore, 3. In the case where the print medium is placed with a two-dot shift to the left, the image data is similarly discharged to the left by two dots.

  FIG. 8 is a flowchart showing the flow of operation for correcting the displacement of the print medium.

  This flowchart is started by a print command after receiving image data from the host PC.

  In step S1, the image data in the image memory is transferred in parallel to the shift register.

  In step S2, the amount of deviation from a predetermined position (position of the normally placed print medium) at the end in the main scanning direction of the print medium is detected by a CCD sensor as detection means. The detection data is transmitted to the control unit.

  In step S3, the deviation amount is divided by the nozzle pitch. The divided value is rounded off to a natural number and stored in register A.

  In step S4, it is determined whether the absolute value of the contents of register A is greater than a predetermined value. If the content of the register A is larger than the predetermined value (step S4: YES), the process proceeds to step S12. If the content is smaller (step S4: NO), the process proceeds to step S5. Here, the predetermined value is a preset deviation amount. For example, when the printing medium is placed at an inclination (or shifted), it is the limit value of the deviation amount in the direction of arrow Y in FIG.

  In step S5, it is determined whether or not the contents of register A are equal to zero. If equal (step S5: YES), the process proceeds to step S10. If not equal (step S5: NO), the process proceeds to step S6. Here, if it is equal to 0, the shift register is not shifted, so steps S6 to S9 are skipped.

  In step S6, it is determined whether the content of register A is greater than zero. If large (step S6: YES), the process proceeds to step S7. If small (step S6: NO), the process proceeds to step S8.

  In step S7, right shift clocks are generated by the number of contents of the register A.

  In step S8, the left shift clock is generated by the number of contents of the register A.

  In step S9, the contents of the shift register are shifted to the right or left by the right or left shift clock.

  In step S10, the head control signal generator generates a transfer clock, a latch clock, and a drive ON signal. The contents of the shift register are serially transferred to the head using the transfer clock as a clock. The contents of the shift register are serially transferred to the head, and then temporarily stored in another register in the head by a latch clock, and then the piezoelectric element is driven by the drive ON signal based on the contents (image data). Ink is ejected.

  In step S11, it is determined whether ejection of image data for one page has been completed. If completed (step S11: YES), printing is terminated. If the printing for one page has not been completed yet (step S11: NO), the process proceeds to step S1, and the printing is repeated.

  In step S12, the control unit notifies the host PC of the “print medium placement error” via the host PCI / F.

  In this way, printing is performed while correcting the displacement of the print medium line by line.

  In the present embodiment, the printer using sheet paper is described as an example of the ink jet image forming apparatus, but the present invention can also be applied to an ink jet image forming apparatus such as a printer using roll paper.

  In addition, the detailed configuration and detailed operation of each component constituting the inkjet image forming 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 block diagram of a control board concerning the present invention. FIG. 3 is an example of a diagram showing a positional relationship between each of the heads 251 to 256 and the detection unit 21 and the printing medium P that constitute the line head 2 according to the present invention. FIG. 3 is an enlarged view of a positional relationship between a printing medium according to the present invention and detection means 21. It is a figure which shows the printing result printed on the printing medium with the line head which concerns on this invention. It is a figure which shows the printing result printed on the printing medium by applying this invention. It is the figure which allocated image data concerning the present invention to a nozzle of a head. 3 is a flowchart showing a flow of operations for correcting a displacement of a printing medium according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Line head 3 Cable 4 Control board 5 Print medium conveyance mechanism 6 Ink supply pipe 7 Bus 8 CCD sensor 21 Detection means 22 Control part 23 Host PCI / F
26 Shift clock generation unit 241 to 246 Head drive unit 2411 Image memory 2412 Shift register 2413 Head control signal generation unit 251 to 256 Head P Printing medium P ′ Printing medium

Claims (4)

A line head in which a plurality of heads are arranged in a staggered manner;
An image memory for storing image data;
Detecting means for detecting an end of the printing medium in the main scanning direction;
Control means for changing the image data read from the image memory based on the information detected by the detection means, and for controlling the output of the line head based on the changed image data. Inkjet printing device. The inkjet printing apparatus includes a shift register that shifts image data read from the image memory,
2. The ink jet printing apparatus according to claim 1, wherein the control unit controls an operation of the shift register based on information detected by the detection unit. 3. The ink jet printing apparatus according to claim 1, wherein the information detected by the detecting means is a deviation amount from a predetermined position of the print medium in the main scanning direction. The size of the image memory is expressed by the number of pixels, and the number of pixels in the main scanning direction is smaller than the number of nozzles of the head. Inkjet printing device.

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