JP2009073178A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method for preventing the head temperature from rising to the predetermined temperature or more. <P>SOLUTION: This image forming method is provided for changing basic assignment when the temperature detected by any of temperature sensors 61-64 exceeds the predetermined temperature (here, 60°C). Specifically, the temperature of recording heads K1-K4 is detected by the temperature sensors 61-64 every time when completing the forming of an image on one recording medium (here, one label 14). When the detected temperature exceeds 60°C, the association of raster line regions with ink ejection opening arrays (the association of rasters 1-4 and the recording heads K1-K4) under the basic assignment is shifted one by one. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming method and an image forming apparatus for forming an image by ejecting ink onto a recording medium.

  Conventionally, dry electrophotographic printers have been used for printing forms and the like. Recently, however, inkjet printers (inkjet image forming apparatuses) have begun to be used as printers that replace dry electrophotography. This ink jet printer forms an image by ejecting ink droplets onto a recording medium from a plurality of ink ejection openings (nozzle exits) formed in a recording head (printing head). As a technique for ejecting ink droplets, a technique is known in which thermal energy corresponding to a driving pulse is supplied to ink in a nozzle to form bubbles due to film boiling, and ink droplets are ejected from the nozzles by the bubbles. A large number of ink droplets corresponding to the image to be formed are ejected from the nozzles onto the recording medium to form an image.

  In general, such an ink jet printer prints directly on a web (forms an image) so that a large amount of printing processing is possible and the running cost is low. It is suitable for printing various forms such as mail order application forms. However, inkjet printers cannot achieve printing speeds that exceed the maximum drive frequency of the recording head (maximum nominal value: Hz that can repeatedly eject ink per second while maintaining stable image quality). There is a problem that it is not possible to sufficiently meet the market demand for speed improvement. To solve such problems, raster development is performed on image data of the same color using a so-called line printer, the generated raster data is divided, and the divided raster data is assigned to a plurality of recording heads. “Raster division” has been proposed in which printing speed is improved by printing (see, for example, Patent Document 1).

  In the above-described line printer, a single row of ink discharge ports formed of a plurality of ink discharge ports arranged in a direction orthogonal to the recording medium conveyance direction (which is an example of the crossing direction referred to in the present invention) is formed. A recording head is often used. FIG. 9 and FIG. 9 show the case where four such recording heads are arranged in the recording medium conveyance direction, for example, to form an image (four rows of ink discharge ports, which is an example of the arrangement of a plurality of rows referred to in the present invention). This will be described with reference to FIG.

  FIG. 9A is a schematic diagram showing four recording heads K1, K2, K3, and K4 arranged in the recording medium conveyance direction (arrow A direction), and FIG. 9B shows a recording that has landed on the recording medium. It is a schematic diagram which shows the ink droplet from the heads K1-K4. FIG. 10 is a schematic diagram illustrating an example in which the same ruled line K is repeatedly printed on each page of the recording medium P. Here, it is assumed that four recording heads K1, K2, K3, and K4 are arranged in order from the upstream side in the conveyance direction of the recording medium, and printing is performed in this order. In FIG. 9A, the numbers in the circles represent the ink discharge port arrays of the recording heads. In FIG. 9B, the numbers in the circles were discharged from the ink discharge ports of the recording heads. A pixel formed by ink droplets is represented, and a region surrounded by a circle represents a pixel region. Note that the two-point difference line on the recording medium P in FIG. 9B represents a raster line area to be described later, and an area sandwiched between two adjacent two-point difference lines is one raster line referred to in the present invention. It is an area.

After printing by the recording heads K1 to K4 is performed once in this order, printing by the recording head K1 is performed again following the recording head K4, as shown in FIG. Between the print area (one raster line area) by the recording head K1 and the print area by the recording head K4, the recording medium is conveyed by a distance corresponding to the installation interval of the recording heads K1 to K4. Since the printing timing (ink ejection timing) of the recording heads K1 to K4 can be adjusted while confirming the image printed on the recording medium, various proposals have been made for methods of correcting errors by the recording head.
JP 2005-238556 A

  When printing on standard paper such as a form using the above-described line printer, the same ruled line on each page of the recording medium P such as paper (showing pages 1 to 4 in FIG. 10) as shown in FIG. A large amount of printing may be repeated by repeating K. In such a case, raster data obtained by raster development of the image data carrying the ruled line K is divided and assigned to the recording heads K1 to K4 to print this image data. In this printing, only a specific recording head (recording head K1 in the example of FIG. 10) is used intensively, and the temperature (head temperature) of the specific recording head (recording head K1) increases. The head temperature is one of parameters for determining the ink discharge amount, and this point will be described with reference to FIG. FIG. 11 is a graph showing the relationship between the head temperature and the ink discharge amount. The horizontal axis represents the print head temperature, and the vertical axis represents the amount of ink ejected.

  As shown in FIG. 11, when the amount of ink ejected as the temperature of the recording head increases, the image quality deteriorates. Therefore, the increase or decrease in the ink ejection amount due to the change in the head temperature changes the pulse width. It is suppressed by that. However, with this technique, when the temperature of the recording head is equal to or higher than a certain temperature (in the example of FIG. 11, the temperature of the recording head is 60 ° or higher), it becomes difficult to control the ink ejection amount, and a stable image is obtained. There is a problem that it becomes difficult to obtain.

  In view of the above circumstances, an object of the present invention is to provide an image forming method and an image forming apparatus in which the head temperature is not raised above a predetermined temperature.

In order to achieve the above object, an image forming method according to the present invention includes a plurality of ink ejection port arrays, each including a plurality of ink ejection ports arranged in a crossing direction intersecting a conveyance direction of a recording medium, along the conveyance direction. The plurality of ink discharge port arrays arranged in a row toward one raster line region in which a plurality of pixel regions on a recording medium on which one pixel is formed are arranged in the intersecting direction. In an image forming method for forming an image on a recording medium by repeatedly discharging ink from one of the ink discharge port arrays,
(1) To which raster line area of the plurality of raster line areas on the recording medium is assigned in advance to which ink discharge port array from among the plurality of ink discharge port arrays As a basic assignment,
(2) detecting the temperature of each of the plurality of ink ejection port arrays during image formation on the recording medium;
(3) The basic assignment is changed based on the detected temperature.

here,
(4) The basic assignment may be changed when the detected temperature exceeds a predetermined temperature.

Also,
(5) The basic allocation is changed when the difference between the maximum temperature and the minimum temperature among the detected temperatures of the plurality of ink discharge port arrays exceeds a predetermined value. May be.

further,
(6) The basic assignment may be changed every time an image is formed on one recording medium.

Furthermore,
(7) Each time an image is formed on a single recording medium, the correspondence between the raster line area and the ink ejection port array in the basic allocation may be shifted one by one.

Furthermore,
(8) Prior to forming an image on a recording medium, the number of ink ejection dots from each of the plurality of ink ejection port arrays is detected,
(9) The basic assignment may be changed based on the detected number of dots.

According to another aspect of the present invention, there is provided an image forming apparatus according to the present invention, wherein an ink ejection port array including a plurality of ink ejection ports arranged in a crossing direction intersecting a transporting direction of the recording medium is provided along the transporting direction. And a plurality of rows of ink discharge ports, and one pixel region on a recording medium on which one pixel is formed is directed toward one raster line region formed by arranging a plurality of pixel regions in the intersecting direction. In an image forming apparatus that repeatedly discharges ink from one of the plurality of ink discharge port arrays to form an image on a recording medium,
(10) To which raster line region of the plurality of raster line regions on the recording medium is assigned in advance from which ink discharge port row of the plurality of ink discharge port rows Basic allocation storage means for storing the basic allocation,
(11) Temperature detection means for detecting the temperature of each of the plurality of ink ejection port arrays during image formation on a recording medium;
(12) A basic allocation changing means for changing the basic allocation based on the temperature detected by the temperature detecting means is provided.

here,
(13) The basic allocation changing unit may change the basic allocation when a temperature detected by the temperature detecting unit exceeds a predetermined temperature.

further,
(14) In the basic allocation changing unit, the difference between the maximum temperature and the minimum temperature among the temperatures of the plurality of ink ejection port arrays detected by the temperature detection unit exceeds a predetermined value. The basic assignment may be changed at the same time.

Furthermore,
(15) The basic allocation changing unit may change the basic allocation every time an image is formed on one recording medium.

Furthermore,
(16) The basic allocation changing means shifts the correspondence between the raster line area and the ink ejection port array in the basic allocation one by one every time an image is formed on one recording medium. Also good.

Furthermore,
(17) comprising dot number detection means for detecting the number of ink ejection dots from each of the plurality of ink ejection port arrays prior to forming an image on a recording medium;
(18) The basic allocation changing unit may change the basic allocation based on the number of dots detected by the dot number detecting unit.

According to another image forming method of the present invention for achieving the above object, an ink ejection port array comprising a plurality of ink ejection ports arranged in a crossing direction intersecting a transporting direction of a recording medium is provided in the transporting direction. Are arranged in a plurality of columns along one line, and one pixel area on a recording medium on which one pixel is formed is arranged in the plurality of columns toward one raster line area formed by arranging a plurality of pixel areas in the intersecting direction. In an image forming method for forming an image on a recording medium by repeatedly discharging ink from any one of the ink discharge port arrays,
(19) To which raster line area of the plurality of raster line areas on the recording medium is assigned in advance from which ink discharge port array of the plurality of ink discharge port arrays The basic allocation is set, and a temperature increase of each of the plurality of ink ejection port arrays is predicted, and the basic allocation is changed based on the predicted temperature.

here,
(20) Prior to forming an image on a recording medium, the number of ink ejection dots from each of the plurality of ink ejection port arrays is detected, and the basic allocation is changed based on the detected number of dots. Also good.

  According to the present invention, since the basic allocation (predetermined recording head to which raster data is allocated) can be changed based on the temperature of each of the ink ejection port arrays during image formation, the ink ejection ports that exceed a predetermined temperature When a row is detected, the basic assignment can be changed so that ink is not ejected from this ink ejection port row (or the amount of ink ejected is reduced). As a result, the amount of ink ejected from the detected ink ejection port array is reduced and the temperature is lowered. As described above, since the basic assignment is changed so that ink is not ejected from the ink ejection port array exceeding the predetermined temperature (or the amount of ejected ink is reduced), the temperature of each ink ejection port array is set in advance. Does not rise above the specified temperature. For this reason, it is possible to prevent a decrease in image quality due to an increase in the temperature of the ink discharge port array, and it is possible to stabilize the print quality.

  The present invention has been realized in a line printer having four recording heads of the same color.

  An example of the image forming apparatus of the present invention will be described with reference to FIG.

  FIG. 1 is a perspective view showing an outline of a line printer which is an example of an image forming apparatus of the present invention.

  A line printer (hereinafter referred to as a printer) 10 includes recording heads K1, K2, K3, and K4 that form images by ejecting ink onto a plurality of labels 14 (an example of a recording medium). The plurality of labels 14 are temporarily attached to the surface of the mount 12 wound in a roll shape. The recording heads K1 to K4 remain stationary and do not move during image formation. Further, black ink droplets are ejected from the recording heads K1 to K4. The label 14 together with the mount 12 is transported at a constant speed in the direction of arrow A by transport rollers 18 and 20 driven by a transport motor 16.

  Each of the recording heads K1, K2, K3, and K4 has a row of ink that includes a plurality of ink discharge ports arranged in a direction perpendicular to the conveyance direction of the recording medium (an example of a crossing direction in the present invention). A discharge port array is formed. Here, the four recording heads K1, K2, K3, and K4 are arranged in the conveyance direction (arrow A direction) of the recording medium (four ink ejection port arrays, which is an example of the multiple-row arrangement referred to in the present invention). Form an image.

  A leading edge detection sensor 22 that detects the leading edge of the label 14 is disposed upstream of the recording head K1 in the transport direction (upstream in the direction of arrow A). When the leading edge detection sensor 22 detects the leading edge of the label 14, the recording heads K <b> 1 to K <b> 4 start ejecting ink at a predetermined timing, and printing is sequentially performed on each label 14. Note that a leading edge detection sensor 24 that detects the leading edge of the label 14 is also disposed downstream of the recording head K4 in the transport direction (downstream in the direction of arrow A), and the leading edge detection sensor 24 is jammed. Used for detection of

  The electrical system of the printer 10 in FIG. 1 will be described with reference to FIG.

  FIG. 2 is a block diagram showing an electrical system of the printer of FIG.

  Data of an image formed on the mount 12 (see FIG. 1) is created by the host PC 100. The created image data is transferred to the interface controller 30 and then transmitted to the memory controller 32. The memory controller 32 sends received data (image data) to the VRAM 36 in accordance with an instruction from the CPU 34 (an example of basic allocation changing means and basic allocation storage means according to the present invention and also an example of dot number detecting means according to the present invention). Write once at high speed. After a predetermined amount of recording data is written in the VRAM 36, the CPU 34 starts preparation for an image forming operation by the recording heads K1 to K4.

  First, the head U / D motor 40 and the capping motor 42 are operated with each other via the drive unit 38, and the recording heads K1 to K4, which are blocked by a cap mechanism (not shown), are moved to the recording position. To do. During this movement, the recording heads K1 to K4 move in the vertical direction, and the cap mechanism (not shown) moves in parallel with the transport direction (the direction of arrow A in FIG. 1). Subsequently, the transport motor 16 is driven by the drive unit 44 to start transporting the mount 12. The start of the conveyance motor 16 is triggered by the speed instruction value of the conveyance motor 16 being written from the CPU 34 to the servo logic circuit 46.

  Thereafter, the output of the rotary encoder 48 is fed back to the servo logic circuit 46, and the conveyance speed of the mount 12 is controlled at a constant speed by the feedback loop of the drive unit 44 to the conveyance motor 16 to the rotary encoder 48 to the servo logic circuit 46. The servo logic circuit 46 converts the output of the rotary encoder 48 into a transport position pulse and outputs it, and this output data is used as a cutout signal for each recording head K1 to K4 to perform raster recording.

  When the leading edge detection sensor 22 detects the leading edge of the label 14, the recording head control circuit 48 receives a transport position pulse corresponding to the distance from the leading edge detection sensor 22 to each of the recording heads K to K4. Reading of the image buffer is started from 32, and the read image buffer is transferred to the recording head control circuit 48. The recording head control circuit 48 tries to generate recording data for all the rasters having different cut-out timings in the recording heads K1 to K4. In the transfer output unit to the recording heads K1 to K4, the recording heads K1 to K4. Masks the recording data for rasters not handled by (3 rasters out of 4 rasters).

  The processing of the CPU 34 depends on the control program written in the FlashROM 50 (which is an example of the storage means in the present invention), but the RAM 52 is also used for work. The EEPROM 54 is a non-volatile memory that stores numerical values unique to the apparatus, such as an adjustment value for electrically adjusting a minute recording position (registration) between the recording heads K1 to K4. The printer 10 is provided with an operation panel 56 including a display device such as an LCD and keys for temporarily suspending, resuming, and emergency stop of a recording operation, and writing display data and turning keys on via an input / output port 58. / OFF state can be read.

  Each of the recording heads K1 to K4 incorporates temperature detection sensors 61 to 64 (which are an example of temperature detection means in the present invention) that detect the temperature of each ink discharge port array. The temperatures detected by the temperature detection sensors 61 to 64 and the output analog values of the detection signals detected by the tip detection sensors 22 and 24 are read out almost in real time via the AD converter 66. The pump motor 68 supplies ink to the recording heads K1 to K4 from an ink tank (not shown), or pressurizes the inside of the recording heads K1 to K4 to forcibly discharge ink from the ink discharge ports. And a pump (not shown) used to restore sound recording performance.

  An image forming method by the printer 10 having the above configuration will be described with reference to FIG. FIG. 3 is a flowchart showing the first embodiment of the image forming method of the present invention. In this example, as shown in FIG. 9, raster 1 is associated with recording head K1, raster 2 is associated with recording head K2, raster 3 is associated with recording head K3, and raster 4 is associated with recording head K4. To correspond.

  The flow shown in FIG. 3 changes the basic assignment when the temperature detected by any of the temperature sensors 61 to 64 (see FIG. 2) exceeds a predetermined temperature (here, 60 ° C.). Specifically, each time an image is formed on one recording medium (here, one label 14), the temperature of the recording heads K1 to K4 is changed by the temperature sensors 61 to 64. When the detected temperature exceeds 60 ° C., the correspondence between the raster line area and the ink ejection port array in the basic allocation (correspondence between the rasters 1 to 4 and the recording heads K1 to K4) is shifted one by one. It is.

  This flow is started when a print start signal is input from the host PC 100 (see FIG. 2) to the CPU 34 (S301), and is executed by the CPU 34 in accordance with a program stored in the Flash ROM 50 (see FIG. 2). First, data input from the host PC 100 (see FIG. 2) is raster-divided, and rasters 1 to 4 are assigned to each head (S302). This assignment is a basic assignment and is stored in advance in the FlashROM 50. Subsequently, one page is printed (S303), and it is determined whether or not to continue printing (whether or not the second page is printed) (S304). If it is determined that printing is not continued, printing is terminated (S322). When it is determined to continue printing, the temperature of the recording heads K1 to K4 is detected by the temperature sensors 61 to 64 (S305), and it is determined whether or not the detected temperature exceeds 60 ° C. (S306). When any of the temperature sensors 61 to 64 detects a temperature of 60 ° C. or lower, the second page is printed (S308). When the temperature detected by any of the temperature sensors 61 to 64 exceeds 60 ° C., the raster allocation is moved one by one (the correspondence between the rasters 1 to 4 and the recording heads K1 to K4 is shifted one by one). (S307). Specifically, raster 1 is associated with recording head K2, raster 2 is associated with recording head K3, raster 3 is associated with recording head K4, and raster 4 is associated with recording head K1. That is, in the basic allocation, ink is ejected from the recording head K1 to the raster line area 1, but after the allocation is changed, ink is ejected from the recording head K2 to the raster line area 1. Similarly, in the basic allocation, ink is ejected from the recording head K2 to the raster line area 2, but after the allocation is changed, ink is ejected from the recording head K3 to the raster line area 2, and in the basic allocation, the raster line is Ink was ejected from the recording head K3 to the area 3, but after changing the allocation, ink was ejected from the recording head K4 to the raster line area 3. In the basic allocation, ink was ejected from the recording head K4 to the raster line area 4. However, after the allocation is changed, ink is ejected from the recording head K1 to the raster line area 4. In this way, by changing the basic allocation, the amount of ink ejected from the recording head having a high head temperature can be reduced, so that an increase in the temperature of the recording head can be prevented.

  Since the temperature of the recording heads K1 to K4 is detected after printing one page as described above, the amount of ink ejected from the recording head exceeding the predetermined temperature can be reduced (or ink can be prevented from being ejected). The temperature of the recording head exceeding the predetermined temperature can be lowered. For this reason, it is possible to prevent the image quality from being lowered due to the temperature rise of the recording head and to stabilize the print quality. In S306, for example, when the temperatures of the recording heads K1 and K2 both exceed 60 ° C., the temperature of the recording head K2 is not lowered even if the allocation change shown in S307 is performed, but in S311 described later, the same as S306. Therefore, the temperature rise of the recording head K2 can be suppressed.

  In S307, the raster assignment is moved one by one, and then two pages are printed (S308). After this printing, as in S304, it is determined whether or not to continue printing (whether or not the third page is printed) (S309). If it is determined that printing is not continued, printing is terminated (S322). When it is determined that printing is to be continued, the temperature of the recording heads K1 to K4 is detected by the temperature sensors 61 to 64 (S310), and it is determined whether or not the detected temperature exceeds 60 ° C. (S311). When any of the temperature sensors 61 to 64 detects a temperature of 60 ° C. or lower, the third page is printed (S313). When the temperature detected by any of the temperature sensors 61 to 64 exceeds 60 ° C., the raster allocation is moved one by one (the correspondence between the rasters 1 to 4 and the recording heads K1 to K4 is shifted one by one). (S312). Specifically, raster 1 is associated with recording head K3, raster 2 is associated with recording head K4, raster 3 is associated with recording head K1, and raster 4 is associated with recording head K2. That is, in the basic allocation, ink is ejected from the recording head K1 to the raster line area 1, but after the second allocation change, ink is ejected from the recording head K3 to the raster line area 1. Similarly, ink is ejected from the recording head K2 to the raster line area 2 in the basic allocation, but after changing the second allocation, ink is ejected from the recording head K4 to the raster line area 2. Ink was ejected from the recording head K3 to the raster line area 3, but after the second allocation change, ink was ejected from the recording head K1 to the raster line area 3, and recording was performed to the raster line area 4 in the basic allocation. Ink was ejected from the head K4, but after the second allocation change, ink is ejected from the recording head K2 to the raster line area 4. In this way, by changing the basic allocation, the amount of ink ejected from the recording head having a high head temperature can be reduced, so that an increase in the temperature of the recording head can be prevented.

  After shifting the raster assignment one by one in S312, three pages are printed (S313). After this printing, it is determined whether or not to continue printing (whether or not the fourth page is printed) (S314). If it is determined that printing is not continued, printing is terminated (S322). When it is determined that printing is to be continued, the temperatures of the recording heads K1 to K4 are detected by the temperature sensors 61 to 64 (S315), and it is determined whether or not the detected temperature exceeds 60 ° C. (S316). When any of the temperature sensors 61 to 64 detects a temperature of 60 ° C. or lower, the fourth page is printed (S318). When the temperature detected by any of the temperature sensors 61 to 64 exceeds 60 ° C., the raster allocation is moved one by one (the correspondence between the rasters 1 to 4 and the recording heads K1 to K4 is shifted one by one). (S317). Specifically, raster 1 is associated with recording head K4, raster 2 is associated with recording head K1, raster 3 is associated with recording head K2, and raster 4 is associated with recording head K3. That is, in the basic allocation, ink is ejected from the recording head K1 to the raster line area 1, but after the third change of allocation, ink is ejected from the recording head K4 to the raster line area 1. Similarly, in the basic allocation, ink is ejected from the recording head K2 to the raster line area 2, but after the third allocation change, ink is ejected from the recording head K1 to the raster line area 2. Ink was ejected from the recording head K3 to the raster line area 3, but after the third allocation change, ink was ejected from the recording head K2 to the raster line area 3, and recording was performed to the raster line area 4 in the basic allocation. Ink was ejected from the head K4, but after the third allocation change, ink is ejected from the recording head K3 to the raster line area 4. In this way, by changing the basic allocation, the amount of ink ejected from the recording head having a high head temperature can be reduced, so that an increase in the temperature of the recording head can be prevented.

  In S317, the raster assignment is moved one by one, and then four pages are printed (S318). After this printing, it is determined whether or not to continue printing (whether or not the fifth page is printed) (S319). If it is determined that printing is not continued, printing is terminated (S322). When it is determined that printing is to be continued, the temperature of the recording heads K1 to K4 is detected by the temperature sensors 61 to 64 (S320), and it is determined whether or not the detected temperature exceeds 60 ° C. (S321). When any of the temperature sensors 61 to 64 detects a temperature of 60 ° C. or lower, the fifth page is printed (not shown). When the temperature detected by any of the temperature sensors 61 to 64 exceeds 60 ° C., the raster allocation is moved one by one (the correspondence between the rasters 1 to 4 and the recording heads K1 to K4 is shifted one by one). (Not shown). In this case, it returns to the basic allocation (same as S302).

  As described above, by shifting the raster allocation each time the head temperature becomes a certain level or more, it avoids the intensive use of a specific recording head, equalizes the temperature of each recording head, and uniforms the discharge amount. It becomes possible to become.

  Another example of the image forming method by the printer 10 having the above configuration will be described with reference to FIG. FIG. 4 is a flowchart showing Embodiment 2 of the image forming method of the present invention. In this example, as shown in FIG. 9, raster 1 is associated with recording head K1, raster 2 is associated with recording head K2, raster 3 is associated with recording head K3, and raster 4 is associated with recording head K4. To correspond.

  The flow shown in FIG. 4 detects the number of ink ejection dots from the recording heads K1 to K4 prior to forming an image on the recording medium (here, the label 14), and based on the detected number of dots. Specifically, the basic assignment is changed, and more specifically, by arbitrarily assigning the raster for each page, the head temperature is set for the raster having the largest number of ink ejection dots in the page. Assign the lowest recording head. Conversely, a raster having the smallest number of ejected dots in a page is assigned to the recording head having the highest head temperature. This makes it possible to suppress an increase in head temperature.

  This flow is activated when a print start signal is input from the host PC 100 (see FIG. 2) to the CPU 34 (S401), and is executed by the CPU 34 in accordance with a program stored in the Flash ROM 50 (see FIG. 2). First, data input from the host PC 100 (see FIG. 2) is raster-divided, and rasters 1 to 4 are assigned to each head (S402). This assignment is a basic assignment and is stored in advance in the FlashROM 50. Subsequently, dot count for each raster (S403) is performed. That is, prior to printing one page, the number of ink droplets ejected from the recording heads K1 to K4 (each ink ejection port array) when printing this one page is calculated for each recording head K1 to K4. Keep (seek). Subsequently, the temperature of each of the recording heads K1 to K4 is detected by the temperature sensors 61 to 64 (see FIG. 2) (S404), and a raster with a small dot count is assigned in order from the recording head with the highest temperature (S405). Is printed (S406).

  After printing one page, the raster allocation executed in S405 is reset (S407). Thereafter, it is determined whether or not two pages are printed (S408). If there is no printing, the printing is terminated (S409). When the second page is printed, the process returns to S402, and the number of ink droplets ejected from the recording heads K1 to K4 (each ink ejection port array) when printing the second page is determined for each recording head K1 to K4. (S403). Thereafter, the same procedure as above is repeated until printing is completed.

  As described above, to which raster line area of the plurality of raster line areas on the recording medium is assigned in advance from which ink discharge port array of the plurality of ink discharge port arrays Before the image is formed on the recording medium, the number of ink ejection dots from each of the plurality of ink ejection port arrays is detected, and the basic allocation is performed based on the detected number of dots and the head temperature. Therefore, it is possible to avoid intensive use of a specific recording head, and it is possible to stabilize the print quality by making the temperature of each recording head uniform and making the discharge amount uniform.

  In the example described above, an example in which a single ink discharge port array is formed in one recording head is shown. However, as shown in FIG. 5, a plurality of ink discharge port arrays (nozzle arrays) N1, N2, N3, and N4 are provided. Even if it is formed on one recording head K, the same applies.

  A third embodiment of the present invention will be described with reference to FIG.

  FIG. 6 is a flowchart showing the third embodiment of the image forming method of the present invention, in which a part of the flow shown in FIG. 3 is changed. This changed portion is a portion surrounded by a broken line in FIG. 6, and the procedure before and after the portion is the same as that in FIG. 3, and thus a part thereof is omitted in FIG. Further, “S601” and “S602” are added in FIG. 6 after “N” in S306, S311, S316, and S321 shown in FIG.

  In the first embodiment, in S306, S311, S316, and S321, attention is paid only to the maximum temperature 60 ° C. of each recording head K1 to K4, but attention is paid to the difference between the maximum temperature and the minimum temperature among the recording heads K1 to K4. Thus, the basic assignment may be changed when the difference exceeds a predetermined value. This is because even if the maximum temperature does not exceed 60 ° C., if the difference between the maximum temperature and the minimum temperature of each recording head exceeds 20 ° C., wait until the maximum temperature exceeds 60 ° C. This is because it takes a long time to reduce the difference even if the raster allocation is changed. Therefore, even when the maximum temperature does not exceed 60 ° C., when the difference between the maximum temperature and the minimum temperature among the recording heads K1 to K4 is not less than a predetermined value (20 ° C. in this embodiment) determined by the head. By changing the raster allocation, it is possible to average the temperature between the heads by preventing the protruding heads having the highest temperature from appearing. The procedure will be described with reference to FIG. As described above, FIG. 6 is different from FIG.

  6 is a determination as to whether the maximum temperature is 60 ° C. in S306, S311, S316, and S321 of the flow chart 3. Ka, Kb, Kc, and Kd indicate arbitrary heads. In the case of “YES”, an operation that is the same as that in the flowchart of the first embodiment (FIG. 3) is executed. However, in the case of “NO”, a portion surrounded by a broken line is added. That is, it is determined whether the maximum and minimum temperature difference between the heads is 20 ° C. or more (S601), and in the case of NO, the flow chart is the same as in FIG. However, if “YES” in S601, the basic allocation is changed. This change can reduce the amount of ink ejected from the recording head having the highest temperature, thereby preventing the temperature of the recording head from rising to 60 ° C. or higher.

  In the first to third embodiments, the temperature of each recording head is actually measured after printing (after measurement), and the basic assignment is changed. In the fourth embodiment, the temperature of each recording head (temperature after printing) is changed. An example will be described in which prediction is made based on print data (image data) and the basic assignment is changed based on the predicted temperature. A fourth embodiment will be described with reference to FIGS.

  FIG. 7 is a graph showing how the recording head rises in temperature according to the number of continuous prints (as the number of continuous prints increases). The horizontal axis in FIG. 7 represents the number of continuous prints, and the vertical axis represents what the print head is. Indicates whether the temperature has risen by a certain degree. FIG. 8 is a flowchart illustrating the image forming method according to the fourth embodiment. Curves 701, 702, 703, 704, and 705 shown in FIG. 7 indicate the degree of temperature rise (temperature) of the recording head when the number of shots (ink discharge amount print duty) is different even when the number of continuously printed sheets is the same. The difference is shown, and the higher the driving amount (the higher the printing duty), the higher the temperature of the recording head.

  In the flow shown in FIG. 8, prior to forming an image on a recording medium (for example, the label 14 (see FIG. 1)), the number of ink ejection dots is calculated in advance for each raster based on the print data. Based on the calculated number of dots, the ejection amount (ink ejection amount) of each raster is calculated in advance, the print head temperature (head temperature) is predicted with reference to the graph of FIG. 7, and based on the predicted head temperature. Therefore, the basic allocation is changed so as to suppress an increase in the head temperature (so as not to exceed a certain temperature). Specifically, when printing a certain amount of pages (m pages) (after printing), it is predicted that the head temperature will be raised most (raster with the highest print duty when printing m pages). Changes the basic allocation so that the recording head having the lowest head temperature is allocated before printing. In other words, a print head that is expected to have the highest head temperature (after printing) when printing a certain amount of pages (m pages) has a raster with the lowest print duty when printing m pages. Assign. As a result, it is possible to suppress an increase in head temperature of each recording head.

  8 starts when a print start signal is input from the host PC 100 (see FIG. 2) to the CPU 34 (S801), and the CPU 34 executes this flow according to a program stored in the Flash ROM 50 (see FIG. 2). Execute. First, print data (image data) input from the host PC 100 (see FIG. 2) is divided into pages of a certain amount (a certain number of pages, m pages) (S802), and the temperatures of the recording heads K1 to K4 are measured (actual measurement). (S803). Subsequently, the print data in a certain amount of pages is raster-divided (S804).

Subsequently, the dot count is performed for each divided raster (here, rasters 1 to 4) (print duty is calculated) (S805). That is, prior to printing a certain amount of pages, the number of ink droplets of each raster 1 to 4 is calculated in advance for each raster 1 to 4 when a certain amount of page is printed (calculated beforehand). ). Subsequently, referring to the profile (corresponding to the graph of FIG. 7) stored in the Flash ROM 50 (see FIG. 2) (S806), when the image corresponding to each of the rasters 1 to 4 has been formed, the recording head Is predicted to rise (S807). With reference to the recording heads K1 to K4 measured in S803, the recording heads K1 to K4 to which the rasters 1 to 4 are assigned are determined. Here, the recording head having the highest temperature measured in S803 includes:
In S807, the raster having the smallest temperature rise (the lowest print duty) is assigned. That is, the raster having the smallest temperature rise of the recording head when the image corresponding to the raster has been formed is assigned to the recording head having the highest temperature measured in S803. Similarly, a raster having the second lowest print duty is assigned to the recording head having the second highest temperature measured in S803. Similarly, a raster having the third lowest print duty is assigned to the recording head having the third highest temperature measured in S803. Similarly, the raster having the highest print duty is assigned to the recording head having the lowest temperature measured in S803 (S808). The combination of the raster and the print head that is assigned first in S808 is the basic assignment. In this way, the rasters 1 to 4 are assigned to the recording heads 1 to 4, and a certain amount of pages are printed (S809).

  After printing a certain amount of pages in S809, the raster allocation executed in S808 is reset (S810). Thereafter, it is determined whether or not there is the next printing (S811), and if there is no next printing, the printing is terminated (S812). When there is the next printing, the process returns to S803, the temperature of the recording heads K1 to K4 is measured, the process proceeds to S804, and the print data for the next m pages is raster-divided. Thereafter, the same procedure as above is repeated until printing is completed.

  In the above example, an example of raster division composed of a plurality of recording heads has been shown. However, as shown in FIG. 5, single-color ink ejection rows (nozzle rows) N1, N2, N3, and N4 are provided in one head. The same applies to the head.

  According to the image forming method of Embodiment 4 described above, the basic assignment can be changed so that the raster that is predicted to have the lowest temperature rise in this image formation is assigned to the recording head having the highest temperature before the image formation. As a result, the degree of temperature rise of each recording head during image formation can be suppressed, so that deterioration in image quality due to temperature rise of the recording head can be reduced, and printing quality can be stabilized.

1 is a perspective view illustrating an outline of a line printer which is an example of an image forming apparatus of the present invention. It is a block diagram which shows the electric system of the printer of FIG. It is a flowchart which shows Example 1 of the image forming method of this invention. It is a flowchart which shows Example 2 of the image forming method of this invention. 2 is a perspective view showing an outline of one recording head K on which a plurality of ink discharge port arrays (nozzle arrays) N1, N2, N3, and N4 are formed. FIG. It is a flowchart which shows the principal part of Example 3 which added the temperature difference between heads to Example 1. FIG. It is a graph which shows a mode that a recording head heats up according to the number of continuous printing, a horizontal axis represents the number of continuous printing, and a vertical axis | shaft represents the temperature of a recording head. It is a flowchart which shows an example of the image forming method of this invention. (A) is a schematic diagram illustrating four recording heads K1, K2, K3, and K4 arranged in the conveyance direction (arrow A direction) of the recording medium, and (b) is a recording head K1 that has landed on the recording medium. It is a schematic diagram which shows the ink droplet from -K4. 6 is a schematic diagram illustrating an example in which the same ruled line K is repeatedly printed on each page of the recording medium P. FIG. 4 is a graph showing the relationship between the head temperature and the ink discharge amount, where the horizontal axis represents the print head temperature, and the vertical axis represents the amount of ink discharged.

Explanation of symbols

10 Printer 34 CPU
50 FlashROM
K1, K2, K3, K4 Recording head

Claims (14)

A recording medium in which a single pixel is formed by arranging a plurality of ink ejection port arrays composed of a plurality of ink ejection ports arranged in a crossing direction intersecting the transporting direction of the recording medium along the transporting direction. Ink is ejected from one of the plurality of ink ejection port arrays toward one raster line region in which a plurality of upper pixel regions are arranged in the intersecting direction. In an image forming method for repeatedly forming an image on a recording medium,
To which raster line area of the plurality of raster line areas on the recording medium the ink ejection port array from which the plurality of ink ejection port arrays are to be ejected is assigned in advance and assigned as a basic allocation. As
During the image formation on the recording medium, the temperature of each of the plurality of ink ejection port arrays is detected,
An image forming method, wherein the basic assignment is changed based on the detected temperature. The image forming method according to claim 1, wherein the basic assignment is changed when the detected temperature exceeds a predetermined temperature. The basic assignment is changed when a difference between a maximum temperature and a minimum temperature among the detected temperatures of the plurality of ink discharge port arrays exceeds a predetermined value. The image forming method according to claim 1. The image forming method according to claim 1, wherein the basic assignment is changed every time an image is formed on a single recording medium. 2. The image forming method according to claim 1, wherein each time an image is formed on a single recording medium, the correspondence between the raster line area and the ink ejection port array in the basic allocation is shifted one by one. . Prior to forming an image on a recording medium, the number of ink ejection dots from each of the plurality of ink ejection port arrays is detected,
7. The image forming method according to claim 1, wherein the basic assignment is changed based on the detected number of dots. An ink discharge port array comprising a plurality of ink discharge ports arranged in a crossing direction that intersects the transport direction of the recording medium includes a plurality of ink discharge port arrays arranged along the transport direction. Any one of the plurality of ink discharge port rows toward one raster line region formed by arranging a plurality of pixel regions on the formed recording medium in the intersecting direction. In an image forming apparatus that forms an image on a recording medium by repeatedly ejecting ink from a row,
Basic allocation in which the ink discharge port array from which the plurality of ink discharge port arrays discharge ink to which raster line region of the plurality of raster line regions on the recording medium is allocated in advance. Basic allocation storage means for storing
Temperature detecting means for detecting the temperature of each of the plurality of ink ejection port arrays during image formation on a recording medium;
An image forming apparatus comprising: a basic allocation changing unit that changes the basic allocation based on a temperature detected by the temperature detecting unit. The basic allocation changing means includes
The image forming apparatus according to claim 7, wherein the basic assignment is changed when a temperature detected by the temperature detecting unit exceeds a predetermined temperature. The basic allocation changing means includes
The basic assignment is changed when the difference between the maximum temperature and the minimum temperature among the temperatures of the plurality of ink ejection port arrays detected by the temperature detection means exceeds a predetermined value. The image forming apparatus according to claim 7, wherein the image forming apparatus is an image forming apparatus. The basic allocation changing means includes
The image forming apparatus according to claim 7, wherein the basic assignment is changed every time an image is formed on a single recording medium. The basic allocation changing means includes
8. The method according to claim 7, wherein each time an image has been formed on a single recording medium, the correspondence between the raster line area and the ink ejection port array in the basic allocation is shifted one by one. Image forming apparatus. Prior to forming an image on a recording medium, the image forming apparatus includes dot number detection means for detecting the number of ink ejection dots from each of the plurality of ink ejection port arrays,
12. The basic allocation changing unit changes the basic allocation based on the number of dots detected by the dot number detection unit. 12. Image forming apparatus. A recording medium in which a single pixel is formed by arranging a plurality of ink ejection port arrays composed of a plurality of ink ejection ports arranged in a crossing direction intersecting the transporting direction of the recording medium along the transporting direction. Ink is ejected from one of the plurality of ink ejection port arrays toward one raster line region in which a plurality of upper pixel regions are arranged in the intersecting direction. In an image forming method for repeatedly forming an image on a recording medium,
To which raster line area of the plurality of raster line areas on the recording medium the ink ejection port array from which the plurality of ink ejection port arrays are to be ejected is assigned in advance and assigned as a basic allocation. An image forming method comprising: predicting a temperature rise of each of the plurality of ink ejection port arrays and changing the basic assignment based on the predicted temperature. Prior to forming an image on a recording medium, the number of ink ejection dots from each of the plurality of ink ejection port arrays is detected, and the basic assignment is changed based on the detected number of dots. The image forming method according to claim 13.

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