JP2016215391A - Image formation apparatus and control method of the same - Google Patents

Abstract

Density variations due to differences in ink fixing modes are reduced. A recording head that outputs a developer on the surface of a sheet in an image forming apparatus uses a chromatic developer of two colors among the three chromatic developers for the developer that forms the same dot. A nozzle for outputting the developer arranged so that an output position on the paper is shifted by a predetermined amount less than one dot in the sub-scanning direction with respect to an output position of the achromatic developer on the paper; When the chromatic color developer and the achromatic color developer are output to form the same dot, the two colors output at positions shifted by a predetermined amount in the sub-scanning direction with respect to the output position of the achromatic color developer The output position of one chromatic color developer and the output position of one chromatic color developer other than the two chromatic color developers are the achromatic color developer. The output timing of a predetermined developer is controlled so as to be shifted by a predetermined amount in the main scanning direction with respect to the output position of That. [Selection] Figure 8

Description

  The present invention relates to an image forming apparatus and a method for controlling the image forming apparatus.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Among such image processing apparatuses, an ink jet printer is known as a printer used to output an electronic document. An ink jet printer forms an image on the entire surface of a sheet by ejecting ink from the recording head while moving a carriage on which the recording head is mounted in the main scanning direction, and transporting the sheet in the sub-scanning direction.

  As an image formation output method in an ink jet printer, there is a multi-pass method in which ink is ejected at two timings, a timing at which the carriage is scanned in one direction and a timing at which the carriage is scanned in the opposite direction. In the multi-pass method, ink is ejected in one direction (hereinafter referred to as “outward path”) and in the opposite direction (hereinafter referred to as “return path”) depending on the arrangement of nozzles that eject ink. The ink color order may be different. If the color order of the ejected ink is different, a color difference (hereinafter referred to as “bidirectional color difference”) occurs between the forward path and the return path.

  A method of controlling the ink ejection timing so that the landing position of the ink that lands first and the landing position of the ink that lands later are shifted for different color inks that form the same dot for the purpose of reducing bidirectional color difference Has been proposed (see, for example, Patent Document 1).

  In order to reduce the bidirectional color difference, a plurality of nozzles that eject the same color ink are arranged so that the color order of the nozzles that eject chromatic ink is the same in the forward path and the backward path. It is conceivable to discharge chromatic ink and discharge achromatic ink in the opposite direction.

  However, in such a case, for example, a time difference from landing of chromatic ink on the forward path to landing of achromatic ink on the return path (hereinafter referred to as “landing time difference”) differs depending on the position in the main scanning direction on the paper surface. As a result, when the landing time difference is large, the chromatic color ink ejected in the forward path is dried and then the achromatic color ink is ejected in the return path. On the other hand, when the landing time difference is small, achromatic ink is ejected in the return path before the chromatic ink ejected in the outbound path is dried. Therefore, a difference occurs in the fixing mode of the ink, and the density varies.

  In the method disclosed in Patent Document 1, only bidirectional color differences due to two chromatic inks are reduced, and density variations caused by differences in landing times of a plurality of chromatic and achromatic inks are not taken into consideration. .

  The present invention has been made to solve such a problem, and in an image forming apparatus that discharges chromatic color ink and achromatic color ink at different scanning timings in a multi-pass method, due to a difference in ink fixing mode. The purpose is to reduce variation in density.

  In order to solve the above problems, one aspect of the present invention includes a carriage that moves a recording head that outputs a developer on the surface of a sheet in a main scanning direction perpendicular to a direction in which the sheet is conveyed. The reciprocating movement in the main scanning direction and the conveyance of the paper are repeated to output the developer to the entire surface of the paper, and from the recording head in one direction of the reciprocating movement of the carriage, After outputting the three chromatic color developers, an image forming apparatus that outputs the achromatic color developer out of the color developer from the recording head in the opposite direction. An output control unit that controls an output timing of the developer; and the recording head includes two chromatic developers of the three chromatic developers for the developer that forms the same dot. Onto the paper A nozzle for outputting the developer, the output position of which is shifted from the output position of the achromatic developer on the paper by a predetermined amount less than one dot in the sub-scanning direction; When the output control unit outputs the chromatic developer and the achromatic developer to form the same dot, the output control unit is arranged in the sub-scanning direction with respect to the output position of the achromatic developer. The output position of one chromatic developer among the two chromatic developers output to a position shifted by a fixed amount, and the presence of one color other than the two chromatic developers. The output timing is controlled such that the output position of the color developer deviates from the output position of the achromatic developer by the predetermined amount in the main scanning direction.

  According to the present invention, in an image forming apparatus that discharges chromatic color ink and achromatic color ink at different scanning timings by a multi-pass method, it is possible to reduce variation in density due to a difference in ink fixing mode.

1 is a block diagram illustrating the overall configuration of an image forming apparatus according to an embodiment of the invention. It is a figure which illustrates the mechanical structure of the image formation output mechanism which concerns on embodiment of this invention. FIG. 6 is a diagram schematically illustrating a configuration of a conventional recording head. It is a figure which illustrates the discharge aspect of the ink which concerns on embodiment of this invention. It is a figure which shows the subject in the case of discharging chromatic color ink and achromatic color ink at a different timing. It is a figure which shows the subject in the case of discharging chromatic color ink and achromatic color ink at a different timing. It is a figure which shows the subject in the case of discharging chromatic color ink and achromatic color ink at a different timing. FIG. 6 is a diagram illustrating a relationship between landing positions of inks of respective colors ejected from a recording head according to an embodiment of the invention. FIG. 4 is a diagram illustrating a positional relationship of nozzle rows of a recording head according to an embodiment of the invention. 4 is a flowchart illustrating an ink discharge control operation from a recording head according to an embodiment of the invention. FIG. 6 is a diagram illustrating a relationship between landing positions of inks of respective colors ejected from a recording head according to an embodiment of the invention. 4 is a flowchart illustrating an ink discharge control operation from a recording head according to an embodiment of the invention. It is a figure which illustrates the gradation value correction table which concerns on embodiment of this invention. 4 is a flowchart illustrating an ink discharge control operation from a recording head according to an embodiment of the invention. It is a figure which illustrates the drive waveform pattern which concerns on embodiment of this invention. It is a figure which illustrates the drive waveform pattern which concerns on embodiment of this invention. It is a figure which illustrates the drive waveform pattern table which concerns on embodiment of this invention. 4 is a flowchart illustrating an ink discharge control operation from a recording head according to an embodiment of the invention. 4 is a flowchart illustrating an ink discharge control operation from a recording head according to an embodiment of the invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, an ink jet printer that discharges (outputs) ink droplets onto the paper surface of a sheet and performs image formation output while reciprocating a carriage on which a recording head that discharges ink droplets is mounted in the main scanning direction. Will be described as an example of an image forming apparatus. In addition, the ink jet printer in the present embodiment is a multi-pass method that discharges ink in both the forward path and the return path of the carriage.

  FIG. 1 is a block diagram illustrating the overall configuration of an image forming apparatus according to this embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a controller 100, an operation panel 110, a sensor group 120, a carriage 130, a main scanning motor 140 and a sub scanning motor 150, a conveyance belt 160 and a charging roller 170. Including.

  The operation panel 110 is a user interface that functions as an operation unit and a display unit for inputting and displaying information necessary for the image forming apparatus 1. The sensor group 120 is various sensors that detect various information in the image forming apparatus 1. Specifically, for example, the sensor group 120 monitors a rotation detection sensor for detecting the rotation of the main scanning motor 140 and the sub-scanning motor 150, an optical sensor for detecting the position of the paper, and a temperature in the apparatus. A thermistor, a sensor for monitoring the voltage of the charging belt, and the like.

  The carriage 130 has a recording head 131 that ejects ink as a developer on the surface of the paper. The carriage 130 is moved in the main scanning direction, which is a direction perpendicular to the sub-scanning direction, which is the conveyance direction of the paper conveyed by the conveyance belt 160 during the image forming output operation.

  The main scanning motor 140 is a motor that supplies power for moving the carriage 130 in the main scanning direction. The sub-scanning motor 150 is a motor that supplies power to a conveyance belt 160 that conveys a sheet on which an image is to be formed in the sub-scanning direction. The charging roller 170 charges the conveyor belt 160 to generate an electrostatic force for attracting the sheet, which is an image output target, to the conveyor belt 160.

  The controller 100 is a control unit that controls the operation of the image forming apparatus 1. As shown in FIG. 1, a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, an NVRAM (Non Volatile RAM) 14, ASIC (Application Specific Integrated Circuit) 15, host I / F 16, print controller 17, head driver 18, main scanning motor driver 19, sub-scan motor driver 20, AC bias supply unit 21, and Includes I / O22.

  The CPU 11 is a calculation means and controls the operation of each part of the controller 100. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The RAM 13 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 11 processes information. The NVRAM 14 is a nonvolatile storage medium capable of reading and writing information, and stores a control program and control parameters.

  The ASIC 15 is a hardware circuit that executes image processing necessary for image formation output. The host I / F 16 is an interface for receiving print data from a host device such as a PC (Personal Computer), and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface.

  The print control unit 17 includes data transfer means for driving and controlling the recording head 131 included in the carriage 130 and drive waveform generation means for generating a drive waveform. The head driver 18 controls the recording head 131 based on image information to be formed and output. The main scanning motor driving unit 19 and the sub scanning motor driving unit 20 drive the main scanning motor 140 and the sub scanning motor 150, respectively, according to the control of the CPU 11.

  The AC bias supply unit 21 supplies an AC bias to the charging roller 170. The I / O 22 is a port for inputting a detection signal from the sensor group 120 to the controller 100.

  Print data from the host such as an information processing device such as a PC, an image reading device such as an image scanner, and an imaging device such as a digital camera is received by the host I / F 16. The CPU 11 reads and analyzes the print data in the reception buffer included in the host I / F 16 and controls the ASIC 15 to execute image processing necessary for image formation output, data rearrangement processing, and the like. The image data processed by the ASIC 15 is transferred to the head driver 18 by the CPU 11 controlling the print control unit 17.

  The generation of dot pattern data for image formation output may be performed, for example, by storing font data in the ROM 12, or the image forming apparatus 1 develops image data into bitmap data by a printer driver on the host side. You may make it input into.

  When the head driver 18 receives image data (dot pattern data) corresponding to one row of the recording head 131, the head driver 18 sends the dot pattern data for one row to the carriage 130 as serial data in synchronization with the clock signal. To do. Further, the head driver 18 sends a latch signal to the carriage 130 at a predetermined timing.

  The print control unit 17 reads pattern data of a drive waveform (head drive signal) stored in the ROM 12, performs D / A conversion to generate a drive waveform of an analog signal, and inputs it to the head driver 18. The head driver 18 inputs the drive waveform input from the print control unit 17 to the carriage 130.

  The carriage 130 includes a shift register, a latch circuit, a level conversion circuit (level shifter), an analog switch array (switch means), and the like. The shift register holds a clock signal input from the head driver 18 and serial data that is image data. The latch circuit latches the register value of the shift register with a latch signal from the head driver 18.

  The level shifter changes the level of the output value of the latch circuit. The analog switch array is turned on / off by this level shifter. The carriage 130 controls the on / off of the analog switch array to selectively apply the required drive waveform included in the drive waveform input from the head driver 18 to the actuator means of the recording head 131 for recording. The head 131 is driven. At this time, the head driver 18 selects a driving pulse constituting the driving waveform, for example, a large droplet (large dot), a medium droplet (medium dot), a small droplet (small dot), etc. Can be sorted out.

  Next, the mechanical configuration of the image forming output mechanism in the image forming apparatus 1 according to the present embodiment will be described. FIG. 2 is a diagram illustrating a state in which the mechanical configuration of the image forming output mechanism according to the present embodiment is viewed from above.

  As shown in FIG. 2, in the image forming output mechanism according to the present embodiment, the sheet S is transported over a transport roller 201 driven by a sub-scanning motor 150 and a tension roller 202 that operates in accordance with the transport roller 201. It is conveyed by the belt 160. This transport direction is the sub-scanning direction. In addition, the sub-scanning motor 150, the transporting roller 201, the timing belt 204 that connects the sub-scanning motor 150 and the transporting roller 201, and the transporting belt 160 are transporting mechanisms for transporting paper.

  A recording head 131 used in the inkjet image forming apparatus 1 is attached to a carriage 130. The carriage 130 reciprocates on the guide rod 205 in a direction perpendicular to the paper transport direction by the driving pulley 203, the driven pulley 206, and the timing belt 204 by driving the main scanning motor 140.

  An ink tube 207 for supplying ink from the ink cartridge 208 to the recording head 131 is connected to the carriage 130. The serial type inkjet printer performs printing on the entire surface of the paper by repeating the scanning of the carriage 130 and the conveyance of the paper.

  Here, the configuration of a conventional recording head mounted on the carriage 130 will be described. FIG. 3 is a diagram schematically showing a configuration of a conventional recording head. As shown in FIG. 3, the recording head includes nozzle rows K1 to K4, C1, C2, M1, M2, Y1, and Y2 that eject inks of CMYK (Cyan, Magenta, Yellow, and KeyPlate) colors.

  In addition, as shown in FIG. 3, two recording heads equipped with a nozzle array that discharges K ink, which is an achromatic developer, are mounted side by side in the sub-scanning direction in order to improve the monochrome image printing speed. Has been. One recording head provided with a nozzle row for discharging K ink is in parallel with a recording head provided with a nozzle row for discharging CMY ink, which is a chromatic color developer.

  In addition, as shown in FIG. 3, the nozzle rows that eject CMY color inks are targeted in the main scanning direction for each color in order to make the color order of ink ejected in the forward path and the backward path the same. Has been placed. With such a configuration, a color difference (hereinafter referred to as “bidirectional color difference”) that occurs due to a difference in the color order of ink ejected in the forward path and the backward path is reduced.

  In addition, as shown in FIG. 3, the nozzle rows are arranged in two rows in each recording head, and the nozzle rows are arranged so as to be shifted by a half of the nozzle pitch. With such a configuration, the resolution in the sub-scanning direction is doubled. When a monochrome image is printed by such a recording head, K ink is ejected from the nozzle rows K1 to K4. On the other hand, when printing a color image, the inks of the nozzle rows K1 to K4 are ejected from the nozzle rows K1 to K4 as the achromatic developer, and the nozzle rows C1, C2, M1, M2, Y1, Y2 to CMY are used as the chromatic developer. Each color ink is ejected.

  However, the nozzle rows for ejecting CMY color inks are arranged for each color in the main scanning direction, whereas the nozzle rows for ejecting K ink and the nozzle rows for ejecting CMY color inks. Is not arranged in the target in the main scanning direction. Therefore, for example, when printing an image of a shadow portion where the amount of K ink used is large, a bidirectional color difference occurs.

  In order to reduce such bidirectional color difference, in the printing mode in which printing of one band image is completed in one scan, after each ink of CMY is ejected in one direction of the reciprocating movement of the carriage 130, in the opposite direction The recording head 131 is controlled so that K ink is ejected. That is, in such control, K ink is ejected from the nozzle rows K3 and K4.

  Next, problems when ink is ejected from a conventional recording head in the above-described control will be described with reference to FIGS. FIG. 4 is a diagram illustrating an ink discharge mode on the paper by the above-described control. As shown in FIG. 4, for example, in the first scanning forward path (lowermost arrow shown on the right side of the paper S), each CMY color ink (hereinafter referred to as “chromatic ink”) ”) Is discharged. Then, in the return pass of the second scan, K ink (hereinafter referred to as “achromatic ink”) is ejected to the bottom one band area of the paper S, and chromatic ink is ejected to the next one band area. The Thereafter, the discharge of the chromatic color ink and the achromatic color ink is repeated similarly.

  Therefore, at the start position of one scan, the time difference from when the chromatic color ink lands on the paper to when the achromatic color ink lands on the paper (hereinafter referred to as “landing time difference (output time difference)”) is the smallest, The difference in landing time at the end position of one scan is the largest.

  FIG. 5 is a diagram exemplifying different ink fixing modes depending on the landing time difference of the ink on the paper in the case where the K ink is ejected after the CMY inks are ejected by the control described above. FIG. 5A illustrates an ink fixing mode when the landing time difference is relatively small, and FIG. 5B illustrates an ink fixing mode when the landing time difference is relatively large. FIG. 6 is a graph illustrating the relationship between the landing time difference (seconds) and the ink density.

  When the landing time difference is small, the achromatic ink ejected in the return path is landed on the sheet before the chromatic ink ejected in the outbound path and landed on the sheet is dried. For this reason, as the landing time difference is smaller, as shown in FIG. 5A, the achromatic ink tends to penetrate into the inside of the paper, and therefore the ink density tends to be lower as shown in FIG.

  On the other hand, when the landing time difference is large, the achromatic ink ejected in the return path is landed on the sheet while the chromatic ink ejected in the forward path and landed on the sheet is dried. Therefore, as the landing time is longer, as shown in FIG. 5B, the achromatic color ink is less likely to penetrate into the inside of the paper, so that the ink density tends to increase as shown in FIG.

  FIG. 7 is a diagram exemplifying variation in density on the paper that occurs when K ink is ejected after CMY color inks are ejected by the above-described control. As shown in FIG. 7, the ink density is lower at the start position of one scan for discharging achromatic ink (K ink) (the printed image is lighter), and the ink density is higher at the end position of one scan (printed). The image becomes darker). Further, since the scanning direction of the achromatic color ink is changed for each scanning, the density levels at the left and right edges of the paper are also changed. As a result, the density of the ink fixed on the paper varies. The gist of the present embodiment is to reduce such variation in density.

  FIG. 8 shows landing positions of the achromatic color ink and the chromatic color ink ejected to the area where the same dot is formed by the recording head 131 according to this embodiment for solving the above-described problem shown in FIGS. It is a figure which illustrates the relationship of the output position on a paper. The square shown in FIG. 8 is a region where dots are formed by the ink droplets 301 to 304 (hereinafter referred to as “dot region”), and the dot region is divided into a quarter region by dotted lines. Is marked with an “x” mark in the center.

  Each color ink lands at a position centered on each “x” mark. In the case shown in FIG. 8, the ink droplets 301 are achromatic inks, and the ink droplets 302 to 304 are chromatic inks of three colors. As shown in FIG. 8, the landing positions of the two chromatic ink droplets 303 and 304 of the three chromatic inks of CMY are two minutes in the sub-scanning direction with respect to the landing position of the achromatic ink droplet 301. Is shifted by one dot.

  Further, the landing position of one chromatic ink droplet 304 is shifted by a half dot in the main scanning direction with respect to the landing position of the achromatic ink droplet 301. Further, the landing positions of the chromatic ink droplets 302 other than the two chromatic ink droplets 303 and 304 described above are shifted by a half dot in the main scanning direction with respect to the landing positions of the achromatic ink droplets 301. .

  Hereinafter, a configuration for realizing the landing mode of each color ink shown in FIG. 8 will be described. FIG. 9 is a diagram exemplifying a positional relationship between a nozzle array that ejects achromatic ink and a nozzle array that ejects chromatic ink that constitutes the recording head 131 according to the present embodiment. The configuration of the recording head 131 according to the present embodiment is the same as the configuration of the recording head described with reference to FIG. 3 except for the configuration described below with reference to FIG.

  In the following description, the ink droplet 301 shown in FIG. 8 is a K ink droplet, the ink droplet 302 is a C ink droplet, the ink droplet 303 is a Y ink droplet, and the ink droplet 304 is an M ink droplet. A case will be described as an example.

  In the recording head 131 according to the present embodiment, the nozzle row that ejects chromatic ink that is shifted by a half dot in the sub-scanning direction with respect to the landing position of the achromatic color ink is different from the nozzle row that ejects the achromatic color ink. Thus, the position is shifted by the radius of the nozzle row in the sub-scanning direction. For example, as shown in FIG. 8, in the conventional recording head, the nozzle rows for ejecting the ink of the achromatic color ink K3 and the ink of the chromatic color ink M2 in which the ink droplets land at the same position, as shown in FIG. The nozzle row is shifted by a radius p / 2 in the sub-scanning direction.

  Similarly, the nozzle rows that respectively eject the achromatic ink K4 and the chromatic ink M1 are shifted in the sub-scanning direction by the nozzle row radius p / 2. The same applies to the nozzle rows that eject the achromatic ink K3 and the chromatic ink Y1, respectively, and the nozzle rows that eject the achromatic ink K4 and the chromatic ink Y2, respectively. With such a configuration, the landing position of the two chromatic inks can be shifted by a half dot in the sub-scanning direction with respect to the landing position of the achromatic ink.

  Next, an ink ejection control operation from the recording head 131 according to the present embodiment will be described. FIG. 10 is a flowchart illustrating an ink discharge control operation from the recording head 131 according to this embodiment. The operation shown in FIG. 10 is an operation of the CPU 11 that performs an operation according to a program for controlling each part of the image forming apparatus 1, and is a flowchart showing an ink ejection control operation in an image forming output for one page. That is, the CPU 11 functions as an output control unit that controls the output timing of the developer.

  As shown in FIG. 10, the CPU 11 acquires CMYK format image data input to the image forming apparatus 1 via the host I / F 16 (S1001). Thereby, the CPU 11 starts the ink ejection by controlling the recording head 131 so as to form the dots constituting the acquired image data in the scanning order. CPU11 which acquired image data determines whether the value of K which comprises the dot of the formation object of the acquired image data is 0 (S1002).

  When the value of K is 0 (S1002 / YES), there is no landing time difference between the chromatic color ink and the achromatic color ink, so the CPU 11 proceeds to the processing of S1005 without correcting the ejection timing. On the other hand, when the value of K is not 0 (S1002 / NO), the CPU 11 determines whether or not the values of C, M, and Y constituting the dot to be formed are all 0 (S1003).

  When the values of C, M, and Y are all 0 (S1003 / YES), there is no landing time difference between the chromatic color ink and the achromatic color ink, so the CPU 11 does not correct the ejection timing, and does not correct the ejection timing. Proceed to the process. On the other hand, when any one or more of the values of C, M, and Y is not 0 (S1002 / YES), the CPU 11 corrects the ink ejection timing from the recording head 131 (S1004).

  Specifically, the CPU 11 corrects the discharge timing of the chromatic color ink shifted by a half dot in the main scanning direction with respect to the landing position of the achromatic color ink. For example, the CPU 11 causes the landing positions of the achromatic ink K3 where ink droplets land at the same position in the recording head shown in FIG. 8 and the chromatic inks M2 and C1 to be shifted by a half dot in the main scanning direction. The ejection timing from the nozzle rows of M2 and C1 is corrected.

  Similarly, the CPU 11 corrects the ejection timing from the C1 nozzle row so that the landing positions of the achromatic color ink K4 and the chromatic color inks M1 and C2 are shifted by a half dot in the main scanning direction.

  The CPU 11 that has corrected the ejection timing determines whether or not the processing for all the formation target dots of the acquired image data has been completed (S1005). When the processing for all dots is not completed (S1005 / NO), the CPU 11 repeats the processing from S1002 for other dots to be formed, and when the processing for all dots is completed (S1005 / YES), the processing ends. To do.

  Note that the CPU 11 may perform processing for restricting the total amount of ink adhering to the paper when performing ink ejection control, or may reflect image characteristics of the image forming apparatus and user preferences. You may correct | amend etc.

  As described above, in the recording head 131 of the image forming apparatus 1 according to the present embodiment, the nozzle row that ejects predetermined two chromatic inks in the sub-scanning direction with respect to the nozzle row that ejects achromatic ink. It is configured to be shifted by the radius of the nozzle row. Further, in the image forming apparatus 1 according to the present embodiment, the predetermined two colors so that the landing position of the predetermined two chromatic inks and the landing position of the achromatic ink are shifted by a half dot in the main scanning direction. The discharge timing of the chromatic color ink is adjusted.

  As a result, when one or more chromatic color inks and achromatic color inks are ejected in order to form the same dot, each ink droplet lands at a position shifted by a half dot from each other in the dot formation region. As a result, the overlapping portion of each ink droplet is reduced. Therefore, according to the present embodiment, in the image forming apparatus 1 that discharges chromatic color ink and achromatic color ink at different scanning timings by the multi-pass method, it is possible to reduce the density variation due to the difference in the ink fixing mode. become.

  In the above embodiment, the color of the chromatic ink droplets 302, 303, and 304 shown in FIG. 8 is not limited, but the chromatic color ink droplet 304 that is diagonal to the achromatic ink droplet 301 is not present. The ink droplets may be limited to M ink droplets having the largest color difference from the chromatic ink. FIG. 11 is a diagram illustrating the relationship between the landing positions of the respective color inks when the chromatic color ink droplets diagonal to the achromatic color ink droplets are limited to M ink.

  As shown in FIG. 11, an overlapping portion (a portion hatched with a vertical line) between the achromatic ink droplet 301 and the chromatic ink droplet 304 on the diagonal line is an achromatic ink droplet 301 and another chromatic ink droplet 302. , 303 is smaller than the overlapping portion. Therefore, by making the chromatic ink droplet 304 the M ink droplet having the largest color difference from the achromatic ink droplet 301, the influence of the difference in the fixing state of the ink due to the landing time difference is further reduced, and the density variation is further increased. It becomes possible to reduce.

  Further, the ejection timing control in the above embodiment may be performed according to the resolution of the image to be imaged. When dots are formed with a plurality of colors of ink in a relatively low resolution image, a shift in the landing position of each color of ink appears as a loss of gray balance. In order to prevent such a loss of gray balance, the CPU 11 determines whether or not to correct the ejection timing according to the resolution of the image.

  FIG. 12 is a flowchart illustrating an ink discharge control operation according to the resolution of an image. As illustrated in FIG. 12, the CPU 11 performs processes similar to the processes of S1001 to S1003 illustrated in FIG. 10 in S1201 to S1203. When any one or more of the values of C, M, and Y is not 0 (S1203 / NO), the CPU 11 acquires the resolution of the image data acquired in S1201 (S1204).

  CPU11 which acquired the resolution determines whether the acquired resolution is more than a predetermined threshold value (S1205). When the resolution is less than the threshold value (S1205 / NO), the CPU 11 proceeds to the processing of S1207 without correcting the ejection timing in order to prevent the gray balance from being lost due to the deviation of the landing positions of the inks of the respective colors.

  On the other hand, when the resolution is equal to or higher than the threshold (S1205 / YES), the CPU 11 performs the same processing as S1004 shown in FIG. 10 (S1206). The CPU 11 that has corrected the ejection timing determines whether or not the processing for all the formation target dots of the acquired image data has been completed (S1207). If the processing for all dots has not been completed (S1207 / NO), the CPU 11 repeats the processing from S1202 for other dots to be formed, and if the processing for all dots has been completed (S1207 / YES), the processing is terminated. To do.

  With such a configuration, it is possible to reduce the variation in density due to the difference in the ink fixing mode while giving priority to preventing the gray balance from being lost due to the deviation of the landing positions of the inks of the respective colors.

  Further, in the above embodiment, in addition to shifting the landing position of each color ink, the gradation value may be corrected according to the landing time difference. FIG. 13 is a diagram illustrating a tone value correction table that defines the relationship between the landing time difference and the tone value correction value. The gradation value correction table is stored in, for example, the ROM 12 of the image forming apparatus 1. As shown in FIG. 13, the gradation value correction table is information in which the correction value of each gradation value is associated with each landing time difference range.

  As described above with reference to FIGS. 5 and 6, the ink density tends to increase as the landing time difference increases. Therefore, as shown in FIG. 13, in the gradation value correction table, when the landing time difference is equal to or greater than a predetermined value (for example, 0.5 seconds), the gradation value decreases as the landing time difference increases (ink The concentration is low).

  Further, as shown in FIG. 6, when the landing time difference becomes a certain value or more, the ink density does not change. Therefore, the gradation value correction table is determined to correct with the same gradation value when the landing time difference is equal to or greater than a predetermined value (for example, 1.5 seconds).

  FIG. 14 is a flowchart illustrating an ink discharge control operation in the case where the gradation value is corrected based on the gradation value correction table shown in FIG. As illustrated in FIG. 14, the CPU 11 performs processes similar to the processes of S1001 to S1003 illustrated in FIG. 10 in S1401 to S1403.

  When any one or more of the values of C, M, and Y is not 0 (S1403 / NO), the CPU 11 acquires the landing time difference at the dot position to be formed (S1404). That is, the CPU 11 functions as an output time difference acquisition unit that acquires an output time difference that is a time difference from when the chromatic color developer is output onto the paper to when the achromatic color developer is output onto the paper. The landing time difference is obtained based on, for example, the formation target dot position and the moving speed of the recording head 131.

  The CPU 11 that acquired the landing time difference refers to the gradation value correction table shown in FIG. 13, and associates the gradation value of the image at the dot position to be formed with the range of the landing time difference that includes the acquired landing time difference. The tone value is corrected (S1405). That is, the CPU 11 functions as a gradation value correction unit. The CPU 11 having corrected the gradation value performs the same process as S1004 shown in FIG. 10 (S1406).

  Through the processing of S1405 and S1406, each color ink is ejected from the recording head 131 so that dots are formed with the corrected gradation value, and the landing position of each chromatic color ink is equal to the landing position of the achromatic ink by a predetermined amount. Each color ink is ejected so as to shift.

  With such a configuration, not only the landing position of each color ink is shifted, but also the gradation value is corrected according to the landing time difference and the ink density is made uniform, so that it is possible to further reduce the density variation. The range of the landing time difference in the gradation value correction table shown in FIG. 13 is an example, and may be determined in a different range. As the range is finely classified, the gradation value correction accuracy is improved.

  In the above embodiment, in addition to shifting the landing position of each color ink, a driving waveform pattern for driving the recording head 131 may be selected according to the landing time difference. 15 and 16 are diagrams exemplifying drive waveform patterns generated by the drive waveform generation means described above. As shown in FIG. 15, the drive waveform is composed of, for example, a waveform element that falls from the reference potential Ve and a waveform element that rises from the state after the fall in one printing cycle (one drive cycle). It consists of eight drive pulses P1 to P8. One printing cycle is determined by the maximum driving frequency.

  Also, as shown in FIG. 16, the drive waveform has different voltage rise and fall amounts depending on the pattern, and the greater the rise and fall amounts, the greater the amount of ink that is ejected. That is, when the recording head 131 is driven by the drive waveform of the pattern 1 indicated by the alternate long and short dash line in FIG. 16, the amount of ejected ink is the largest, and the recording head 131 is driven by the drive waveform of the pattern 3 indicated by the dotted line. In this case, the amount of ink ejected is minimized.

  FIG. 17 is a diagram illustrating a drive waveform pattern table that defines the relationship between the landing time difference and the drive waveform pattern. For example, the drive waveform pattern table is stored in the ROM 12 of the image forming apparatus 1. As shown in FIG. 17, the drive waveform pattern table is information in which a drive waveform pattern is associated with each landing time difference range.

  As described above with reference to FIGS. 5 and 6, the ink density tends to increase as the landing time difference increases. Therefore, as shown in FIG. 13, in the drive waveform pattern table, when the landing time difference is equal to or greater than a predetermined value (for example, 0.5 seconds), the larger the landing time difference, the smaller the ink ejection amount (ink). The drive waveform pattern is selected so that the density becomes low.

  Further, as shown in FIG. 6, when the landing time difference becomes a certain value or more, the ink density does not change. Therefore, the drive waveform pattern table is determined so that the same drive waveform pattern is selected when the landing time difference is equal to or greater than a predetermined value (for example, 1.5 seconds). That is, in the drive waveform pattern of the drive waveform pattern table shown in FIG. 17, the voltage rise and fall amount decreases in the order of pattern 1 to pattern n.

  FIG. 18 is a flowchart illustrating an ink discharge control operation when a drive waveform is selected based on the drive waveform pattern table shown in FIG. As illustrated in FIG. 18, the CPU 11 performs processes similar to the processes of S1401 to S1404 illustrated in FIG. 14 in S1801 to S1804.

  The CPU 11 that acquired the landing time difference refers to the driving waveform pattern table shown in FIG. 17 and selects a driving waveform of a pattern associated with the landing time difference range that includes the acquired landing time difference to drive the recording head 131. The print control unit 17 is controlled to do so (S1805). That is, the CPU 11 functions as a drive waveform acquisition unit that acquires a drive waveform. The CPU 11 that has selected the drive waveform pattern performs the same processing as S1004 shown in FIG. 10 (S1806).

  Through the processing of S1805 and S1806, each color ink is ejected from the recording head 131 with an output amount corresponding to the landing time difference by the selected drive waveform pattern, and the landing position of each chromatic color ink is the same as the landing position of the achromatic color ink. Each color ink is ejected so as to shift by a fixed amount.

  With such a configuration, not only the landing position of each color ink is shifted, but also the ink density is made uniform by adjusting the ink discharge amount according to the landing time difference, so that it is possible to further reduce the density variation. . Note that the range of the landing time difference in the drive waveform pattern table shown in FIG. 17 is an exemplification, and may be determined in a different range. As the range is finely classified, the gradation value correction accuracy is improved.

  Further, the control of the ejection timing in the above embodiment may be performed according to the brightness of the dot area to be formed, that is, the brightness of the image to be formed. The dot area to be formed includes a shadow area and a highlight area. When the dot area to be formed is from the highlight area to the intermediate color area (the area between the highlight area and the shadow area), the deviation of the landing positions of the inks of the respective colors appears as the collapse of the gray balance. In order to prevent such a loss of gray balance, the CPU 11 determines whether or not to correct the ejection timing according to the brightness of the dot area to be formed.

  FIG. 19 is a flowchart illustrating an ink discharge control operation according to the brightness of the dot area to be formed. As illustrated in FIG. 19, the CPU 11 performs processes similar to the processes of S1001 to S1003 illustrated in FIG. 10 in S1901 to S1903. If any one or more of the C, M, and Y values is not 0 (S1903 / NO), the CPU 11 determines in advance the sum of the C, M, Y, and K gradation values that form the dot to be formed. It is determined whether or not it is equal to or less than the threshold value (S1904).

  When the sum of the gradation values of C, M, Y, and K is larger than the threshold value (S1904 / NO), the CPU 11 prevents the formation of the gray balance from the highlight area to the intermediate color area. Therefore, the process proceeds to S1906 without correcting the ejection timing. On the other hand, when the sum of the C, M, Y, and K gradation values is equal to or smaller than the threshold value (S1904 / YES), the CPU 11 performs the same process as S1004 shown in FIG. 10 (S1905).

  The CPU 11 that has corrected the ejection timing determines whether or not the processing for all the formation target dots of the acquired image data has been completed (S1906). If the processing for all dots has not been completed (S1906 / NO), the CPU 11 repeats the processing from S1902 for other dots to be formed, and if the processing for all dots has been completed (S1906 / YES), terminates the processing. To do.

  With such a configuration, it is possible to reduce the variation in density due to the difference in the fixing mode of the ink while giving priority to preventing the gray balance from being lost due to the deviation of the landing positions of the inks of the respective colors.

  In the embodiment illustrated in FIG. 19, the CPU 11 has been described as an example in which the brightness of the dot area to be formed is determined based on the sum of C, M, Y, and K gradation values. However, this is merely an example, and any mode may be used as long as the brightness of the dot region to be formed can be determined. For example, the CPU 11 may determine the brightness of the dot area based on the sum of the ink adhesion amounts of the respective colors from the C, M, Y, and K gradation values. In addition, for example, the CPU 11 may determine the brightness of the dot region based on the ratio between the adhesion amount of K ink and the adhesion amount of CMY inks in the ink adhesion amount of each color.

  In these embodiments, the case where the deviation amount of the landing position of each color ink droplet described with reference to FIG. 8 is a half dot has been described as an example. However, this is an example, and a predetermined amount less than one dot size, such as one-third dot and three-quarter dots, may be used.

  Further, the configuration of the recording head 131 according to these embodiments is not limited to the configuration shown in FIG. For example, a recording head that constitutes a nozzle row that ejects K3 and K4 inks may be mounted on the opposite side of the recording head that constitutes a nozzle row that ejects K1 and K2 inks in the sub-scanning direction. Also, for example, if the nozzle rows that eject CMY color inks are arranged for each color in the main scanning direction, the order of the nozzle rows that eject the color inks is an order other than FIG. There may be.

  Moreover, you may combine each embodiment mentioned above. For example, when the resolution is less than the threshold value in the embodiment illustrated in FIG. 12, the CPU 11 may perform the gradation value correction in the embodiment illustrated in FIG. 14 and may not perform the ejection timing correction. Similarly, for example, when the resolution is less than the threshold value in the embodiment illustrated in FIG. 12, the CPU 11 selects the drive waveform pattern in the embodiment illustrated in FIG. 18 and does not perform the ejection timing correction. It may be.

  Similarly, the embodiment shown in FIG. 19 may be combined with the embodiment shown in FIG. 14 or the embodiment shown in FIG. In addition, the embodiment shown in FIG. 12 and the embodiment shown in FIG. 19 may be combined to determine whether or not to perform ejection timing correction.

1 Image forming apparatus 11 CPU
12 ROM
13 RAM
14 NVRAM
15 ASIC
16 Host I / F
17 Print Control Unit 18 Head Driver 19 Main Scan Motor Drive Unit 20 Sub Scan Motor Drive Unit 21 AC Bias Supply Unit 22 I / O
DESCRIPTION OF SYMBOLS 100 Controller 110 Operation panel 120 Sensor group 130 Carriage 131 Recording head 140 Main scanning motor 150 Sub scanning motor 160 Conveyance belt 170 Charging roller 201 Conveyance roller 202 Tension roller 203 Driving pulley 204 Timing belt 205 Guide rod 206 Followed pulley 207 Ink tube 208 Ink cartridge

JP 2013-52631 A

Claims (7)

A carriage that moves a recording head that outputs a developer on the surface of the sheet in a main scanning direction perpendicular to the direction in which the sheet is conveyed, and repeats the reciprocating movement of the carriage in the main scanning direction and the conveyance of the sheet. The developer is output to the entire surface of the paper, and the chromatic developer of the three colors of the developer is output from the recording head in one direction of the reciprocating movement of the carriage. An image forming apparatus that outputs an achromatic developer among the developers from the recording head in a direction,
An output control unit that controls output timing of the predetermined developer from the recording head;
In the recording head, for the developer forming the same dot, the output position of the chromatic developer of two colors among the chromatic developer of the three colors on the paper is the achromatic developer. A nozzle for outputting the developer arranged to deviate by a predetermined amount less than one dot size in the sub-scanning direction with respect to the output position on the paper;
The output control unit, when outputting the chromatic developer and the achromatic developer to form the same dot, in the sub-scanning direction with respect to the output position of the achromatic developer. Of the two chromatic color developers that are output at a position shifted by a predetermined amount, the output position of one chromatic color developer and the one color other than the two chromatic color developers. An image forming apparatus, wherein an output timing is controlled so that the output position of the chromatic color developer is shifted by the predetermined amount in a main scanning direction with respect to the output position of the achromatic color developer. The chromatic color developer that is output at a position shifted by the predetermined amount in the sub-scanning direction and the main scanning direction with respect to the output position of the achromatic color developer has the largest color difference from the achromatic color developer. The image forming apparatus according to claim 1, wherein the image forming apparatus is a color developer. 3. The output control unit according to claim 1, wherein the output control unit controls the output timing of the predetermined developer when the resolution of the image to be formed is equal to or higher than a predetermined threshold value. 4. Image forming apparatus. An output time difference acquisition unit that acquires an output time difference that is a time difference from when the chromatic color developer is output onto the paper to when the achromatic color developer is output onto the paper;
A gradation value correction unit that corrects the gradation value of the image to be imaged according to the acquired output time difference, and
The image according to any one of claims 1 to 3, wherein the output control unit controls an output timing of the predetermined developer that is output based on the corrected gradation value. Forming equipment. An output time difference acquisition unit that acquires an output time difference that is a time difference from when the chromatic color developer is output onto the paper to when the achromatic color developer is output onto the paper;
A drive waveform acquisition unit that acquires a drive waveform for driving the recording head by controlling the amount of the developer output from the recording head in accordance with the acquired output time difference, and
The said output control part controls the output timing of the said predetermined developer by which the output amount was controlled based on the acquired said drive waveform. The any one of Claims 1-3 characterized by the above-mentioned. Image forming apparatus. The output control unit controls the output timing of the predetermined developer when the brightness of an image to be formed is equal to or lower than a predetermined brightness. The image forming apparatus according to claim 1. A carriage that moves a recording head that outputs a developer on the surface of the sheet in a main scanning direction perpendicular to the direction in which the sheet is conveyed, and repeats the reciprocating movement of the carriage in the main scanning direction and the conveyance of the sheet. The developer is output to the entire surface of the paper, and the chromatic developer of the three colors of the developer is output from the recording head in one direction of the reciprocating movement of the carriage. A method for controlling an image forming apparatus that outputs an achromatic developer among the developers from the recording head in a direction,
In the recording head, for the developer forming the same dot, the output position of the chromatic developer of two colors among the chromatic developer of the three colors on the paper is the achromatic developer. A nozzle for outputting the developer arranged to deviate by a predetermined amount less than one dot size in the sub-scanning direction with respect to the output position on the paper;
When the chromatic color developer and the achromatic color developer are output to form the same dot, the output position of the achromatic color developer is shifted by the predetermined amount in the sub-scanning direction. Of the two chromatic color developers to be output, the output position of the chromatic color developer of one color, and the chromatic color developer of one color other than the two chromatic color developers A control method for an image forming apparatus, wherein the output timing of the predetermined developer is controlled so that the output position is shifted by the predetermined amount in the main scanning direction with respect to the output position of the achromatic developer.