JP2007144847A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer which is able to realize a reproducible printing with a simple configuration and at a high speed while not generating a banding noise such as an unevenness of density, white line, etc. <P>SOLUTION: A line head 2, wherein a plurality of pressure generation means for discharging a liquid from nozzles are arranged and head chips equipped with nozzle plates and heads with a drive circuit for driving the pressure generation means are alternately arranged in the longitudinal direction while a duplication part where predetermined number of nozzles are superposed between adjoining head chips is formed, constitutes an image printer 1 for forming a picture on a recording medium. In this case, the printer is equipped with an image memory 2411 for storing image data and a control means for changing the image data read from the image memory based on any bit of the addresses of the image memory. <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 an inkjet printing apparatus, an inkjet head is moved in the main scanning direction while ejecting small droplets of ink subjected to ejection control by an image signal from a nozzle of an inkjet head (hereinafter also referred to as a head) to a printing medium. After the image is printed, the print medium is conveyed in the sub-scanning direction 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 one line. There are some which form an image on a print medium by repeating the above.

  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.

  Therefore, a staggered line head has been proposed in which print heads having nozzles arranged on a straight line are arranged in a staggered manner without gaps over the entire width of the print medium in the width direction of the print medium (Patent Document 1). reference).

When the line head is used, a method is adopted in which adjacent heads are arranged in an overlapping manner, and the nozzles are switched and ejected at an intermediate position between the overlapping nozzles. However, if the overlapping nozzles are slightly displaced in the nozzle arrangement direction due to the displacement of the head position, and the nozzle spacing between the heads is wider or narrower than the spacing between the nozzles in the head, printing with the image printing device As a result of printing on the medium, there is a problem that density unevenness and white stripe band noise occur on the print medium at the joints of the heads. In order to solve such problems, there has been proposed an image forming method in which random numbers are generated every time one line is printed, and the switching position of overlapping nozzles is changed based on the random numbers (Patent Document). 2).
Japanese Patent Laid-Open No. 11-34360 Japanese Patent Laid-Open No. 2004-50445

  However, since a random number is generated every time one line is printed and the nozzle switching position is changed based on the random number, the time margin is reduced, and high-speed printing becomes difficult.

  In addition, since a random number table is stored in the storage device in advance and the nozzle switching position is changed based on the random number read from the storage device every time one line is printed, a complicated circuit is required.

  Further, when a plurality of sheets are printed, strictly speaking, since the switching position of the nozzle overlap portion is not constant for each sheet, the print result is different, reproducibility is lost, and precise image evaluation cannot be performed.

  SUMMARY An advantage of some aspects of the invention is that it provides an inkjet printing apparatus capable of performing stable image formation at high speed. In other words, the present invention provides an inkjet printing apparatus in which a plurality of print heads are arranged in a staggered manner, without providing a complicated circuit and without causing uneven density and white stripe band noise. For the purpose. It is another object of the present invention to provide an ink jet printing apparatus in which the nozzle overlap portion switching position is constant and a plurality of prints can be reproduced well.

The object of the present invention is achieved by the following configurations.
(1)
A plurality of pressure generating means for discharging the liquid from the nozzles are disposed, and a head chip having a nozzle plate and a head having a drive circuit for driving the pressure generating means are arranged in a staggered manner in the longitudinal direction and adjacent to each other. In an inkjet printing apparatus for forming an image on a recording medium with a line head in which an overlapping portion in which a predetermined number of nozzles overlap with a head chip is formed,
An image memory for storing image data;
An inkjet printing apparatus comprising: control means for changing image data read from the image memory based on any bit of an address of the image memory.
(2)
The image printing apparatus according to (1), wherein the image memory has image data corresponding to the head and having a width equal to the number of pixels of the head.
(3)
2. The ink jet printing apparatus according to (1) or (2), wherein the image data in the image memory includes overlapping pixels corresponding to overlapping portions of nozzles of adjacent heads.
(4)
The inkjet control apparatus according to any one of (1) to (3), wherein the control unit masks overlapping pixels of image data read from the image memory and transmits the masked pixels to the head.

  According to the present invention, high-definition printing can be performed by one scanning, and there is no need for a complicated mechanism, and density unevenness and white streaks can be prevented from occurring on an image formed on a printing medium. .

  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 in which a plurality of heads installed in the inkjet printing apparatus 1 are arranged in a staggered manner, and a control board 4 and a host PC (Personal Computer) (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 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 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. Ink is ejected from the large number of nozzles onto the printing medium P in accordance with an image signal from a host PC (Personal Computer) (not shown), and the surface of the printing medium P is coupled with the conveyance of the printing medium P in the arrow X direction. An image is formed. 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 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 (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 head drive units 241 to 246, and the address selection unit 26 via the bus 7 in accordance with the processing program described above, and controls the operation of each unit based on the status such as the operation status of each unit. Control.

  The host PCI / F 23 is an interface with a host PC (Personal Computer), and is connected to the host PC by a cable 3. Sends and receives various signals and image data for printing.

  The head drive unit 241 drives an image memory 2411 for storing image data to be printed, a gate 2414 for bit masking image data read from the image memory 2411, a shift register 2412 to which the masked image data is written in parallel, and a head 251. A head control signal generator 2413 for generating a signal to be transmitted. The contents of the shift register 2412 are serially transferred to the head 251. A control signal generated by the head control signal generator 2413 is also transmitted to the head 251. The image data is read by designating an address by an address counter (not shown) in the image memory 2411. The address counter counts up every time one line is printed.

  Similarly to the head driving unit 241, the head driving units 242-246 each include an image memory, a gate, a shift register, and a head control signal generating unit, and transmit image data and control signals to the heads 252-256.

  The address selection unit 26 selects the bit of the address counter of the image memory, and generates input signals of gates 2414 to 2464 which are masked when image data is transmitted in parallel to the shift register.

  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 a diagram showing the positional relationship between the head disposed on the line head and the print medium.

  The odd-numbered heads 251, 253, 255 and the even-numbered heads 252, 254, 256 have nozzle rows arranged in a straight line in the longitudinal direction of the line head (Y direction), and the ends of adjacent heads overlap. It is arranged to do.

  In FIG. 3, as an example, six heads are arranged, but this is not a limitation. The number of heads is determined by the width and resolution of the printing medium P. The printing medium P is conveyed in the X direction.

  FIG. 4 is a flowchart showing an image forming operation according to the present invention.

  The operation of the present invention will be described with reference to FIG.

  In step S1, image data is transmitted from the host PC via the host PCI / F 23. Image data is stored in the image memories 2411 to 2461 for each head. The allocation of the image data in the image memory will be described in detail with reference to FIGS.

  In step S <b> 2, the setting value 1 stored in advance in the control unit 22 is set in the address selection unit 26. The set value 1 indicates a bit of an address counter (not shown) of the image memory. For example, when the address counter is 16 bits, the set value 1 means any bit of MA0, MA1, MA2 to MA15 from the lower digit.

  For example, when the set value 1 is MA0, the address counter value MA0 of the image memory connected to the even-numbered head is input to the address selection unit 26, and the inverted value of the address counter value MA0 of the odd-numbered head is the address. The data is input to the selection unit 26. At the time of printing, when the address counter value MA0 of the even-numbered head becomes 0, that is, when the address of the image memory is an even number, the gate 2424 is opened and the pixel data enters the shift register. Since the gate 2424 is closed when the address is an odd number, 0 is entered in the shift register.

  On the other hand, when the address counter value MA0 of the odd-numbered head becomes 0, that is, when the address of the image memory is odd, the gate 2414 is opened and the pixel data is stored in the shift register. When the number is even, the gate 2414 is closed, so that 0 is entered in the shift register.

  In this way, the nozzles of the odd-numbered and even-numbered heads alternately discharge at the overlapping portion.

  When the set value 1 indicates MA1, the nozzles of the odd-numbered and even-numbered heads alternately discharge every two lines in the overlapping portion.

  In step S3, the transport of the table of the transport mechanism 5 is started.

  In step S4, it is determined whether the table of the transport mechanism 5 has been transported to the print start position of the even-numbered head. If it has been transported to the print start position (step S4: YES), the process proceeds to step S5. If it has not yet reached or passed (step S4: NO), the process proceeds to step S6.

  In step S5, a print start instruction is issued to the head driving units 242, 244, and 246 connected to the even-numbered heads.

  In step S6, it is determined whether the table of the transport mechanism 5 has been transported to the print start position of the odd-numbered head. If it has been conveyed to the print start position (step S6: YES), the process proceeds to step S7, and if it has not reached yet (step S6: NO), the process proceeds to step S4.

  In step S7, an instruction to start printing is issued to the head driving units 241, 243, and 245 connected to the odd-numbered heads.

  In response to the even-numbered head printing start instruction, the head driving units 242, 244 and 246 each perform the following operations.

  In step S11, image data is read from the image memory and transferred in parallel to the shift register. At this time, the image data is bit-masked by the gates 2424, 2444 (not shown) and 2464 and transferred in parallel to the shift registers 2422, 2442 (not shown) and 2462.

  In step S12, the contents of the shift register are serially transferred to the head, and the transfer clock, latch clock, drive ON signal, etc. generated by the head control signal generators 2423, 2443 (not shown) and 2463 are transmitted to the head.

  In step S13, the heads 252, 254, 256 eject ink from the nozzles based on the contents of the shift register, and print one line. After printing one line, the address counter of the image memory is counted up.

  In step S14, it is determined whether printing for one page has been completed. If the printing for one page is finished (step S14: YES), the operation is finished. If not completed (step S14: NO), the process returns to step S11 and printing is continued.

  In response to the odd-numbered head printing start instruction, the head driving units 241, 243 (not shown) and 245 (not shown) respectively perform the following operations.

  The steps S11 to 14 described above are applied to the head drive units connected to the even-numbered heads, but the steps S21 to 24 are not applied to the head drive units connected to the odd-numbered heads. Since the same operation is performed, the description is omitted.

  In reading out the image data to be printed from the image memory, the address counter of the image memory connected to the even-numbered head starts counting at the same time (the even-numbered head printing start instruction in step S5). The address counter of the image memory connected to the second image memory starts counting at the same time (the odd-numbered head print start instruction in step S7), and thus has the same value.

  FIG. 5 is a diagram showing the pixel allocation of the image memory when the odd-numbered head and the even-numbered head according to the present invention overlap one nozzle. The number of nozzles of each head and the width of the number of pixels indicated by the pixel number of the image memory are the same.

  In the drawing, the pixel allocation for the image memory 2411 related to the head 251, the image memory 2421 related to the head 252, and the image memory 2431 related to the head 253 is shown, but the image memory 2441 to 2461 related to the heads 254 to 256 is omitted. is doing. Pixel numbers 0, 1, 2 to a have the same width as the number of nozzles of the head. The pixels indicated by pixel numbers 0 to a are transferred to the head by one serial transfer. The address is one page from address 0000, and the image data at the address pointed to by the address counter described above is read out.

  In this case, the overlapping portion shown in FIG. 3 is a single nozzle. The pixel number 0 of the image memory 2411 in FIG. 5 and the pixel number a of the image memory 2421 are overlapping pixels, and the same data is stored redundantly in the overlapping pixels for one page from the address 0000. Yes. Similarly, the pixel number 0 in the image memory 2421 and the pixel number a in the image memory 2431 are overlapping pixels, and the same data is stored in the overlapping pixels from the address 0000 for one page.

  FIG. 6 is a diagram showing the pixel allocation of the image memory when the odd-numbered head and the even-numbered head according to the present invention overlap with 8 nozzles.

  When the overlapping portion has 8 nozzles, the gate 2414 in FIG. 2 has 8 gates, and the gate 2424 requires two sets of 8 gates.

  The pixel numbers 0 to 7 in the image memory 2411 and the pixel numbers a to h in the image memory 2421 in FIG. 6 are duplicated pixels, and the same data is duplicated and stored in the duplicated pixels for one page from the address 0000. Has been. Similarly, pixels having the pixel numbers 0 to 7 in the image memory 2421 and the pixel numbers a to h in the image memory 2431 are overlapped, and the same data is stored redundantly in the overlapped pixels for one page from the address 0000. Has been.

  FIG. 7 is a diagram showing the relationship recorded in the print medium and the overlap of nozzles of adjacent heads according to the present invention.

  For example, black dots are dots ejected by the nozzles of the head 251, and white dots are dots ejected by the nozzles of the head 252.

  FIG. 7A shows a state in which the nozzles eject ink onto the printing medium when the adjacent head overlaps one nozzle, and FIG. 7B shows the nozzles and printing when the adjacent head overlaps eight nozzles. A state in which the nozzles eject ink onto the medium is shown. For example, in FIG. 7A, the head 251 and the head 252 have an overlapping portion of one nozzle, and in the ejection result M01, the address selection unit 26 selects the address counter MA0. The head 252 alternately discharges from overlapping nozzles. In the ejection result M11, the address selection unit 26 selects the address counter MA1, and therefore, in the ejection result M21, the address selection unit 26 selects the address counter MA2 in the ejection result M21. In 252, discharge is alternately performed from the overlapping nozzles.

  In FIG. 7B, the head 251 and the head 252 have an overlapping portion of 8 nozzles, and in the discharge result M02, the head 251 and the head 252 alternately discharge from the overlapping nozzle for each line. Similarly, in the discharge result M12, the head 251 and the head 252 alternately discharge from the overlapping nozzles every two lines and in M22 every four lines.

  The number of overlapping nozzles is not limited to 1 and 8 described above.

  FIG. 8 is an enlarged view of the periphery of the shift registers 2412 and 2422 in the block diagram of FIG. The overlapping part of the heads 251 and 252 has 4 nozzles.

  8 shows an example in which the output from the address selection unit 26 is connected to the gate input differently from that in FIG.

  The gate 2414 is described in detail as four gates 24141 to 24144, and the gate 2424 is described in detail as four gates 24241 to 24244 and four gates 24245 to 24248. Image data from the image memories 2411 and 2421 is input to one input terminal of each gate, and a signal from the address selection unit 26 is input to the other input terminal.

  Since the address selection unit output 261 enters the input terminals of the gates 24142 and 24144 and the gates 24241, 24243, 24245, and 24247, and the address selection output 262 enters the input terminals of the gates 24141 and 24143 and the gates 24242, 24244, 24246, and 24248, The discharge results are discharged from the heads 251 and 252 every other nozzle at the nozzle overlap portion.

  FIG. 9 shows the discharge result. As described above with reference to FIG. 7, in the discharge result M03, the head 251 and the head 252 alternately discharge from overlapping nozzles for each line. In the discharge result M13, the head 251 and the head 252 alternately discharge from the overlapping nozzles every two lines and in the discharge result M23 every four lines.

  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 block diagram of control board 4 concerning the present invention. It is a figure which shows the positional relationship of the head arrange | positioned at a line head, and a printing medium. 3 is a flowchart showing an image forming operation according to the present invention. It is the figure which showed pixel allocation of the image memory when the odd-numbered head and even-numbered head which concern on this invention overlap 1 nozzle. It is the figure which showed pixel allocation of the image memory when the odd-numbered head and even-numbered head which concern on this invention overlap 8 nozzles. It is a figure which shows the relationship recorded on the printing medium and the overlap of the nozzle of the adjacent head which concerns on this invention. FIG. 3 is an enlarged view of the periphery of shift registers 2412 and 2422 in the block diagram of FIG. 2. It is the result discharged to the printing medium in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Line head 3 Cable 4 Control board 5 Print medium conveyance mechanism 22 Control part 26 Address selection part 241 Head drive part 2411 Image memory 2412 Shift register 2413 Head control signal generation part 2414 Gate 251-256 Head

Claims (4)

A plurality of pressure generating means for discharging the liquid from the nozzles are disposed, and a head chip having a nozzle plate and a head having a drive circuit for driving the pressure generating means are arranged in a staggered manner in the longitudinal direction and adjacent to each other. In an inkjet printing apparatus for forming an image on a recording medium with a line head in which an overlapping portion in which a predetermined number of nozzles overlap with a head chip is formed,
An image memory for storing image data;
An inkjet printing apparatus comprising: control means for changing image data read from the image memory based on any bit of an address of the image memory. 2. The ink jet printing apparatus according to claim 1, wherein the image memory has image data corresponding to the head and having a width of the same number of pixels as the number of nozzles of the head. 3. The ink jet printing apparatus according to claim 1, wherein the image data in the image memory includes overlapping pixels corresponding to overlapping portions of nozzles of adjacent heads. 4. 4. The inkjet printing apparatus according to claim 1, wherein the control unit masks overlapping pixels of the image data read from the image memory and transmits the masked data to the head. 5.

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