Image forming device, determination method

Abstract

To provide an image forming apparatus and a method for determining the image quality of an image formed on a sheet. [Solution] The image forming apparatus 100A includes a detection processing unit that detects edges included in the corresponding region AR10 of each line data DA11, and a determination processing unit that, when an edge is detected, determines a division position for dividing the line data DA11 into first line data used to drive the recording head 36A and second line data used to drive the recording head 36B based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10, and when no edge is detected, randomly determines the division position within the corresponding region AR10.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a determination method.

Background Art

[0002] An inkjet type image forming apparatus including a first ejection unit and a second ejection unit is known. The first ejection unit includes a plurality of first nozzles arranged along a width direction orthogonal to the conveyance direction of the sheet, and ejects ink from each of the first nozzles. The second ejection unit includes a plurality of second nozzles arranged along the width direction, and is arranged such that a part of the plurality of second nozzles overlaps a part of the plurality of first nozzles in the width direction, and ejects the ink from each of the second nozzles.

[0003] In the image forming apparatus, the image data used for driving the first ejection unit and the second ejection unit may be divided into first image data used for driving the first ejection unit and second image data used for driving the second ejection unit. For example, an image forming apparatus is known that determines, as a division position, any position along the main scanning direction in a corresponding region corresponding to an overlapping portion of the plurality of first nozzles and the plurality of second nozzles included in the image data, and divides the position between the first image data and the second image data (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, a configuration is conceivable in which the division position is randomly determined within the corresponding area for each line of line data along the main scanning direction included in the image data. This makes it possible to suppress the generation of muscle images along the transport direction in the image formed on the sheet, compared to a configuration in which the division position is fixed.

[0006] However, in a configuration in which the division position is determined randomly within the corresponding area for each line data, if the image data includes edges that extend in a direction intersecting the main scanning direction, jagged edges may occur in the edges included in the image formed on the sheet.

[0007] The object of the present invention is to provide an image forming apparatus and a method for determining the image quality of an image formed on a sheet. [Means for solving the problem]

[0008] An image forming apparatus according to one aspect of the present invention comprises a first discharge unit, a second discharge unit, a detection processing unit, and a determination processing unit. The first discharge unit includes a plurality of first nozzles arranged along a width direction perpendicular to the sheet transport direction, and discharges ink from each of the first nozzles. The second discharge unit includes a plurality of second nozzles arranged along the width direction, and is arranged such that a portion of the plurality of second nozzles overlaps with a portion of the plurality of first nozzles in the width direction, and discharges the ink from each of the second nozzles. The detection processing unit detects edges included in a corresponding region corresponding to the overlapping portion of the plurality of first nozzles and the plurality of second nozzles in the line data for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first discharge unit and the second discharge unit. If the detection processing unit detects the edge, the determination processing unit determines a division position in which the line data is randomly divided into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density region with a relatively higher density, which is one of two density regions separated by the upstream or downstream edge in a specific direction along the main scanning direction among the edges included in the corresponding region. If the detection processing unit does not detect the edge, the determination processing unit randomly determines the division position within the corresponding region.

[0009] A determination method relating to another aspect of the present invention is performed in an image forming apparatus comprising: a first discharge unit that includes a plurality of first nozzles arranged along a width direction perpendicular to the sheet transport direction and discharges ink from each of the first nozzles; and a second discharge unit that includes a plurality of second nozzles arranged along the width direction and arranged such that a portion of the plurality of second nozzles overlaps with a portion of the plurality of first nozzles in the width direction and discharges the ink from each of the second nozzles, and includes a detection step and a determination step. In the detection step, for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first discharge unit and the second discharge unit, an edge included in the corresponding region corresponding to the overlapping portion of the plurality of first nozzles and the plurality of second nozzles in the line data is detected. In the determination step, if the edge is detected by the detection step, a division position is determined in which the line data is randomly divided into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density region with a relatively higher density, which is separated by the upstream or downstream edge in a specific direction along the main scanning direction among the two density regions of the edge included in the corresponding region. If the edge is not detected by the detection step, the division position is randomly determined within the corresponding region. [Effects of the Invention]

[0010] According to the present invention, it is possible to improve the image quality of the image formed on the sheet. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the configuration of an image forming apparatus according to one embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of the image forming section and the transport unit of the image forming apparatus according to the first embodiment of the present invention. [Figure 3] Figure 3 shows the configuration around the nozzle of an image forming apparatus according to the first embodiment of the present invention. [Figure 4] Figure 4 is a block diagram showing the system configuration of an image forming apparatus according to the first embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing an example of a first data division process performed in an image forming apparatus according to the first embodiment of the present invention. [Figure 6] Figure 6 shows an example of determining the division position for each line data point. [Figure 7] Figure 7 shows the printed images based on each of the line data divided at the division points shown in Figure 6. [Figure 8] Figure 8 shows an example of a division position determined for each line data by an image forming apparatus according to the first embodiment of the present invention. [Figure 9] Figure 9 shows the printed images based on each of the line data divided at the division points shown in Figure 8. [Figure 10] Figure 10 shows an example of a division position determined for each line data by an image forming apparatus according to the first embodiment of the present invention. [Figure 11] Figure 11 shows the printed images based on each line data divided at the division points shown in Figure 10. [Figure 12] Figure 12 is a block diagram showing the system configuration of an image forming apparatus according to a second embodiment of the present invention. [Figure 13] Figure 13 is a flowchart showing an example of a second data division process performed in an image forming apparatus according to a second embodiment of the present invention. [Figure 14] Figure 14 shows an example of a division position determined for each line data by an image forming apparatus according to a second embodiment of the present invention. [Figure 15] Figure 15 shows the printed images based on each line data divided at the division points shown in Figure 14. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of embodying the present invention and do not limit the technical scope of the present invention.

[0013] [First Embodiment] First, the configuration of an image forming apparatus 100A according to a first embodiment of the present invention will be described while referring to FIGS. 1 to 4. Here, FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 100A. FIG. 2 is a plan view showing the configurations of the image forming unit 3 and the conveyance unit 4. FIG. 3 is a cross-sectional view showing the configurations of the nozzle 37, the pressure chamber 38, the piezoelectric element 39, and the individual flow path 40. In FIG. 1, the sheet conveyance path R11 is indicated by a two-dot chain line. In FIG. 2, the overlap region OL10 is indicated by a broken line.

[0014] The image forming apparatus 100A is a printer capable of forming an image on a sheet by an inkjet method. Note that the present invention may be applied to a facsimile apparatus, a copying machine, a multifunction machine, or the like capable of forming an image on a sheet by an inkjet method.

[0015] As shown in FIGS. 1 and 4, the image forming apparatus 100A includes a housing 1, a sheet conveyance unit 2, an image forming unit 3, a conveyance unit 4, an operation display unit 5, a storage unit 6, a main control unit 7, and an engine control unit 8.

[0016] The housing 1 houses each component of the image forming apparatus 100A. A paper feed cassette 11 (see FIG. 1) is detachably provided in the housing 1. Sheets on which images are to be formed are stored in the paper feed cassette 11. A paper discharge tray 12 (see FIG. 1) is provided on the outer surface of the housing 1. Sheets on which images are formed by the image forming unit 3 are discharged onto the paper discharge tray 12. Inside the housing 1, the sheets stored in the paper feed cassette 11 are conveyed along a sheet conveyance path R11 (see FIG. 1) that passes through the image forming position of the image forming unit 3 and reaches the paper discharge tray 12.

[0017] The sheet transport unit 2 transports the sheets stored in the paper feed cassette 11 along the sheet transport path R11 (see Figure 1). As shown in Figure 1, the sheet transport unit 2 includes a pickup roller 21 and a plurality of transport rollers 22. The pickup roller 21 picks up the top sheet from the sheet bundle stored in the paper feed cassette 11 and sends the sheet along the sheet transport path R11. The plurality of transport rollers 22 are arranged in a line along the sheet transport path R11. Each of the transport rollers 22 transports a sheet along the sheet transport path R11. Each of the transport rollers 22 transports a sheet in the transport direction D11 (see Figure 1) from the paper feed cassette 11 to the output tray 12.

[0018] The image forming unit 3 forms an image on a sheet conveyed by the sheet conveying unit 2. As shown in Figures 1 and 2, the image forming unit 3 comprises four line heads 30 (31-34) and a head frame 35.

[0019] As shown in Figure 2, each line head 30 is elongated in the width direction D12, which is perpendicular to the transport direction D11. Specifically, each line head 30 has a length in the width direction D12 that corresponds to the width of the largest sheet that can be accommodated in the paper feed cassette 11. The four line heads 30 are arranged at equal intervals along the transport direction D11.

[0020] As shown in Figure 2, each line head 30 has multiple recording heads 36. Each recording head 36 ejects an ink droplet toward a sheet being transported by the transport unit 4. Each recording head 36 on line head 31 ejects a black ink droplet. Each recording head 36 on line head 32 ejects a cyan ink droplet. Each recording head 36 on line head 33 ejects a magenta ink droplet. Each recording head 36 on line head 34 ejects a yellow ink droplet.

[0021] Each recording head 36 is equipped with a plurality of nozzles 37 (see Figures 2 and 3) that eject ink droplets onto a sheet. Each nozzle 37 is located on the surface of the recording head 36 that faces the sheet being transported by the transport unit 4. For example, in the image forming apparatus 100A, small, medium, or large ink droplets are ejected from the nozzles 37.

[0022] Each recording head 36 is equipped with a pressurized chamber 38 (see Figure 3), a piezoelectric element 39 (see Figure 3), and an individual flow path 40 (see Figure 3) corresponding to each nozzle 37. The pressurized chamber 38 communicates with the nozzle 37 and contains ink. The piezoelectric element 39 causes ink droplets to be ejected from the nozzle 37 by changing the pressure inside the pressurized chamber 38 in response to the input of a drive signal. The individual flow path 40 is an ink flow path provided between the pressurized chamber 38 and a common flow path (not shown) that is common to the multiple nozzles 37. Multiple individual flow paths 40 corresponding to the multiple nozzles 37 are connected to the common flow path. The common flow path is connected to an ink supply unit (not shown) that supplies ink to each of the pressurized chambers 38.

[0023] As shown in Figure 2, the line head 31 has three recording heads 36 (36A, 36B, and 36C).

[0024] The recording head 36A includes a plurality of nozzles 37A (see Figure 2) arranged along the width direction D12 perpendicular to the transport direction D11, and ejects ink from each of the nozzles 37A. The recording head 36B includes a plurality of nozzles 37B (see Figure 2) arranged along the width direction D12, and ejects ink from each of the nozzles 37B. The recording head 36C includes a plurality of nozzles 37C (see Figure 2) arranged along the width direction D12, and ejects ink from each of the nozzles 37C.

[0025] The three recording heads 36 included in the line head 31 are arranged in a staggered pattern along the width direction D12.

[0026] Specifically, as shown in Figure 2, the recording head 36B is arranged such that a portion of the multiple nozzles 37B overlaps with a portion of the multiple nozzles 37A in the width direction D12. Similarly, the recording head 36C is arranged such that a portion of the multiple nozzles 37C overlaps with a portion of the multiple nozzles 37B in the width direction D12. In this specification, the overlapping region in the width direction D12 between a plurality of nozzles 37 included in one of the three recording heads 36 and a plurality of nozzles 37 included in another recording head 36 is referred to as the "overlap region OL10" (see Figure 2). Recording head 36A is an example of the first discharge unit of the present invention. Nozzle 37A is an example of the first nozzle of the present invention. Recording head 36B is an example of the second discharge unit of the present invention. Nozzle 37B is an example of the second nozzle of the present invention.

[0027] Line heads 32-34 have three recording heads 36 arranged similarly to line head 31.

[0028] Furthermore, the number of recording heads 36 provided on each line head 30 is not limited to three.

[0029] The head frame 35 supports four line heads 30. The head frame 35 is supported by the housing 1. Note that the number of line heads 30 provided in the image forming unit 3 is not limited to four.

[0030] As shown in Figure 1, the transport unit 4 is positioned below the four line heads 30. The transport unit 4 transports the sheet while facing the recording head 36. As shown in Figure 1, the transport unit 4 comprises a transport belt 41 on which the sheet is placed, a first tension roller 42, a second tension roller 43, and a third tension roller 44 that tension the transport belt 41, and a transport frame 45 that supports them. The gap between the transport belt 41 and the recording head 36 is adjusted so that the gap between the surface of the sheet and the recording head 36 during image formation is a predetermined distance (e.g., 1 mm).

[0031] The first tension roller 42 is rotationally driven by a rotational driving force supplied from a motor (not shown). This causes the conveyor belt 41 to rotate in a direction that allows the sheet to be conveyed in the conveying direction D11 (see Figure 1). The conveying unit 4 is also equipped with a suction unit (not shown) that draws in air through numerous through holes formed in the conveyor belt 41 in order to attract the sheet to the conveyor belt 41. In addition, a pressure roller 46 is provided above the first tension roller 42 to press the sheet against the conveyor belt 41 for conveyance.

[0032] The operation display unit 5 includes a display unit such as a liquid crystal display that displays various information in response to control instructions from the main control unit 7, and an operation unit such as operation keys or a touch panel that inputs various information to the main control unit 7 in response to user operations.

[0033] The memory unit 6 is a non-volatile memory device. For example, the memory unit 6 is a non-volatile memory such as flash memory.

[0034] The main control unit 7 comprehensively controls the image forming apparatus 100A. As shown in Figure 4, the main control unit 7 includes a CPU 51, a ROM 52, and a RAM 53. The CPU 51 is a processor that performs various arithmetic operations. The ROM 52 is a non-volatile memory device in which information such as control programs for causing the CPU 51 to perform various operations is pre-stored. The RAM 53 is a volatile or non-volatile memory device used as temporary storage memory (work area) for the various operations performed by the CPU 51. The CPU 51 comprehensively controls the image forming apparatus 100A by executing various control programs pre-stored in the ROM 52.

[0035] The engine control unit 8 controls the sheet transport unit 2, the image forming unit 3, and the transport unit 4. For example, the engine control unit 8 is composed of electronic circuits such as integrated circuits (ASIC, DSP).

[0036] Furthermore, the engine control unit 8 performs image processing on the image data for one page of the document to be printed. For example, the image processing includes a decomposition process that separates the image data into monochrome image data corresponding to black, cyan, magenta, and yellow.

[0037] Furthermore, the image processing includes a conversion process that converts the monochrome image data into print data DA10 (see Figure 6) used to drive the three recording heads 36 included in the line head 30. The print data DA10 corresponds to each of the nozzles 37 and includes ejection amount data DA12 (see Figure 6) indicating the amount of ink ejected from the nozzle 37. The print data DA10 is an example of image data of the present invention.

[0038] For example, the ejection volume data DA12 is data that represents one of the values ​​"0", "1", "2", or "3". When the recording head 36 receives an input of ejection volume data DA12 with a value of "3", it ejects a large ink droplet from the nozzle 37 corresponding to that ejection volume data DA12. When the recording head 36 receives an input of ejection volume data DA12 with a value of "2", it ejects a medium-sized ink droplet from the nozzle 37 corresponding to that ejection volume data DA12. When the recording head 36 receives an input of ejection volume data DA12 with a value of "1", it ejects a small ink droplet from the nozzle 37 corresponding to that ejection volume data DA12. When the recording head 36 receives an input of ejection volume data DA12 with a value of "0", it does not eject an ink droplet from the nozzle 37 corresponding to that ejection volume data DA12. Note that in Figure 6, the ejection volume data DA12 that represents a value of "1", "2", or "3" is hatched.

[0039] Incidentally, a configuration is known in which any position along the main scanning direction D20 (see Figure 6) in the corresponding area AR10 (see Figure 6), which corresponds to the overlap area OL10 (see Figure 6), which is the overlapping portion of multiple nozzles 37A (see Figure 6) and multiple nozzles 37B (see Figure 6) contained in the print data DA10 (see Figure 6), is determined as a division position for dividing the data into data used to drive the recording head 36A and data used to drive the recording head 36B. The main scanning direction D20 is the direction corresponding to the width direction D12.

[0040] Here, a configuration is conceivable in which, for each line data DA11 (see Figure 6) along the main scanning direction D20 included in the print data DA10, the division position is randomly determined within the corresponding region AR10 (see Figure 6) in the line data DA11. This makes it possible to suppress the generation of streaky images along the transport direction D11 in the image formed on the sheet, compared to a configuration in which the division position is fixed.

[0041] However, in a configuration where the division position is determined randomly within the corresponding area AR10 for each line data DA11, if the print data DA10 includes an edge that extends in a direction intersecting the main scanning direction D20, jagged edges may occur in the image formed on the sheet.

[0042] Specifically, in the image forming apparatus 100A, the positional relationship between recording heads 36A and 36B in the width direction D12 may deviate from the ideal state. Figure 6 shows nozzles 37A and 37B when the positional relationship between recording heads 36A and 36B in the width direction D12 is ideal. Figure 7 shows nozzles 37A and 37B when the positional relationship between recording heads 36A and 36B in the width direction D12 deviates from the ideal state.

[0043] When the positional relationship between recording heads 36A and 36B in the width direction D12 is ideal, as shown in Figure 6, the distance Δ between a specific nozzle X1 (see Figure 6) included in recording head 36A and a specific nozzle X2 (see Figure 6) included in recording head 36B in the width direction D12 is the distance of one dot (the nozzle spacing in recording head 36). Here, specific nozzle X1 is one of the multiple nozzles 37A included in recording head 36A that are included in the overlap region OL10. Also, specific nozzle X2 is the nozzle closest to specific nozzle X1 among the nozzles 37B located downstream of specific nozzle X1 in the first direction D13 (see Figure 6). The first direction D13 is the direction from recording head 36A to recording head 36B along the width direction D12.

[0044] If the relative positions of recording head 36A and recording head 36B in the width direction D12 deviate from the ideal state, the distance Δ between specific nozzle X1 (see Figure 7) and specific nozzle X2 (see Figure 7) will be less than the distance of one dot, as shown in Figure 7.

[0045] When the relative positions of recording heads 36A and 36B in the width direction D12 deviate from the ideal state, and the division position is randomly determined within the corresponding area AR10 for each line data DA11 as shown in Figure 6, jaggedness occurs in the edges of the line images extending in a direction intersecting the width direction D12, as shown in Figure 7, in the image IM10 (see Figure 7) formed on the sheet. In Figure 6, the division position randomly determined for each line data DA11 is shown by a thick black line.

[0046] In contrast, the image forming apparatus 100A according to the first embodiment of the present invention can improve the image quality of the image formed on the sheet, as will be explained below.

[0047] Specifically, the engine control unit 8 includes the detection processing unit 61A and the determination processing unit 62A shown in Figure 4.

[0048] In addition, the main control unit 7 may include a detection processing unit 61A and a decision processing unit 62A instead of the engine control unit 8. Specifically, the CPU 51 of the main control unit 7 may function as each of the above-mentioned processing units by executing the control program stored in the ROM 52 in advance.

[0049] The detection processing unit 61A detects edges included in the corresponding region AR10 within each line data DA11 contained in the print data DA10.

[0050] For example, the detection processing unit 61A detects as an edge a portion where a column of ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is zero is adjacent to a column of ejection amount data DA12 indicating that the ink ejection amount is not zero. For example, the detection processing unit 61A detects as an edge a portion where a column containing three or more consecutive ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is zero is adjacent to a column containing two or more consecutive ejection amount data DA12 indicating that the ink ejection amount is not zero.

[0051] For example, the detection processing unit 61A performs a first detection process to detect a first edge in which the amount of ink ejected increases along a second direction D21 (see Figure 8) along the main scanning direction D20, and a second detection process to detect a second edge in which the amount of ink ejected increases along a direction opposite to the second direction D21, in the order of the first detection process and the second detection process. Alternatively, the detection processing unit 61A may perform the first detection process and the second detection process in the order of the second detection process and the first detection process.

[0052] For example, the detection processing unit 61A detects edges included in the corresponding region AR10 using a pattern matching method that employs a pattern for detecting edges.

[0053] The detection processing unit 61A may detect edges included in the corresponding region AR10 using conventionally known methods.

[0054] When an edge is detected by the detection processing unit 61A, the determination processing unit 62A determines a division position in which the line data DA11 is divided into first line data used to drive the recording head 36A and second line data used to drive the recording head 36B, based on the position of the upstream or downstream edge in the second direction D21 (see Figure 8) (an example of a specific direction in the present invention) along the main scanning direction D20, among the edges included in the corresponding region AR10.

[0055] For example, when an edge is detected by the detection processing unit 61A, the determination processing unit 62A determines the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 as the division position (see Figure 8).

[0056] For example, if the first edge is detected by the first detection process, the determination processing unit 62A determines the position of the uppermost first edge in the second direction D21 as the division position. If the first edge is not detected by the first detection process and the second edge is detected by the second detection process, the determination processing unit 62A determines the position of the lowermost second edge in the second direction D21 as the division position.

[0057] Furthermore, if no edge is detected by the detection processing unit 61A, the determination processing unit 62A randomly determines the division position within the corresponding region AR10 (see Figure 8).

[0058] For example, the decision processing unit 62A uses a random number table to determine the division position within the corresponding region AR10.

[0059] The second direction D21 can be any direction along the main scanning direction D20.

[0060] [First data splitting process] Next, with reference to Figure 5, the determination method of the present invention will be described along with an example of the procedure for the first data division process executed by the engine control unit 8. Here, steps S11, S12, etc. represent the processing procedure (step) numbers executed by the engine control unit 8. The engine control unit 8 executes the first data division process when performing a printing process to print a document. The engine control unit 8 also executes the first data division process for each color: black, cyan, magenta, and yellow.

[0061] <Step S11> First, in step S11, the engine control unit 8 selects one line data DA11 to be divided from among the multiple line data DA11 included in the print data DA10 to be printed.

[0062] <Step S12> In step S12, the engine control unit 8 detects edges in the line data DA11 to be divided that are included in the corresponding region AR10, which corresponds to the overlap region OL10 where the recording heads 36A and 36B overlap. The processing in step S12 is an example of the detection step of the present invention and is performed by the detection processing unit 61A of the engine control unit 8.

[0063] Specifically, the engine control unit 8 detects as an edge a portion where a column containing three or more consecutive ejection amount data DA12 indicating zero ink ejection amount in the corresponding region AR10 is adjacent to a column containing two or more consecutive ejection amount data DA12 indicating that the ink ejection amount is not zero. The engine control unit 8 also executes the first detection process and the second detection process in the order of the first detection process and the second detection process.

[0064] <Step S13> In step S13, the engine control unit 8 determines whether or not an edge has been detected by the processing in step S12.

[0065] If the engine control unit 8 determines that an edge has been detected (Yes in S13), it proceeds to step S14. If no edge has been detected (No in S13), the engine control unit 8 proceeds to step S15.

[0066] <Step S14> In step S14, the engine control unit 8 determines the division position based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 corresponding to the overlap region OL10 where the recording head 36A and the recording head 36B overlap. The processing in step S14 is an example of the determination step of the present invention and is performed by the determination processing unit 62A of the engine control unit 8.

[0067] Specifically, if the first edge is detected by the first detection process, the engine control unit 8 determines the position of the upstreammost first edge in the second direction D21 as the division position. If the first edge is not detected by the first detection process and the second edge is detected by the second detection process, the engine control unit 8 determines the position of the downstreammost second edge in the second direction D21 as the division position.

[0068] <Step S15> In step S15, the engine control unit 8 randomly determines the division position within the corresponding region AR10 that corresponds to the overlap region OL10 where the recording head 36A and the recording head 36B overlap. The process in step S15 is an example of the determination step of the present invention and is performed by the determination processing unit 62A of the engine control unit 8.

[0069] <Step S16> In step S16, the engine control unit 8 detects edges in the line data DA11 to be divided that are included in the corresponding region AR10, which corresponds to the overlap region OL10 where the recording heads 36B and 36C overlap, using the same method as in step S12. The process in step S16 is an example of the detection step of the present invention and is performed by the detection processing unit 61A of the engine control unit 8.

[0070] <Step S17> In step S17, the engine control unit 8 determines whether or not an edge has been detected by the processing in step S16.

[0071] If the engine control unit 8 determines that an edge has been detected (Yes in S17), it proceeds to step S18. If no edge has been detected (No in S17), the engine control unit 8 proceeds to step S19.

[0072] <Step S18> In step S18, the engine control unit 8 determines the division position based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 corresponding to the overlap region OL10 where the recording heads 36B and 36C overlap, using the same method as in step S14. The process in step S18 is an example of the determination step of the present invention and is performed by the determination processing unit 62A of the engine control unit 8.

[0073] <Step S19> In step S19, the engine control unit 8 randomly determines the division position within the corresponding region AR10 that corresponds to the overlap region OL10 where the recording head 36B and the recording head 36C overlap. The process in step S19 is an example of the determination step of the present invention and is performed by the determination processing unit 62A of the engine control unit 8.

[0074] <Step S20> In step S20, the engine control unit 8 divides the line data DA11 to be divided into the first line data, the second line data, and the third line data used to drive the recording head 36C, based on the division position determined by the processing in step S14 or step S15, and the division position determined by the processing in step S18 or step S19.

[0075] The first line data, the second line data, and the third line data, which are divided by the processing in step S20, are used to drive the three recording heads 36 included in the line head 30. As a result, an image corresponding to the line data DA11 is formed on the sheet.

[0076] <Step S21> In step S21, the engine control unit 8 determines whether all line data DA11 included in the print data DA10 to be printed have been selected by the processing in step S11.

[0077] At this point, if the engine control unit 8 determines that all line data DA11 have been selected (Yes side of S21), it terminates the first data division process. If not all line data DA11 have been selected (No side of S21), the engine control unit 8 proceeds to step S11.

[0078] Figure 8 shows the division positions determined by the first data division process when the print data DA10 shown in Figure 6 is printed. Figure 9 shows the image IM10 formed on the sheet based on the first line data and the second line data divided by the first data division process. As shown in Figure 9, by setting the division position to the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10, jagged edges of the line image extending in a direction intersecting the width direction D12 included in the image IM10 formed on the sheet are suppressed.

[0079] In this way, the image forming apparatus 100A detects edges included in the corresponding region AR10 of the line data DA11 contained in the print data DA10. When an edge is detected, the division position is determined based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10. This makes it possible to avoid the situation shown in Figure 6 where the division position is set on one side of the region enclosing the edge in one line and on the other side of the region enclosing the edge in another line. Therefore, it is possible to suppress the occurrence of jagged edges in the image contained in the image formed on the sheet.

[0080] Furthermore, in the image forming apparatus 100A, if no edge is detected, the division position is determined randomly within the corresponding region AR10. This makes it possible to suppress the generation of muscle images along the transport direction D11 in the image formed on the sheet.

[0081] Therefore, the image forming apparatus 100A can improve the image quality of the image formed on the sheet.

[0082] Furthermore, in the image forming apparatus 100A, when an edge included in the corresponding region AR10 is detected, the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 is determined as the division position. This makes it possible to make the change in density at the division position less noticeable compared to a configuration in which the division position is set within any of the density regions separated by the edge.

[0083] Furthermore, in the image forming apparatus 100A, the portion where a column of ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is zero is adjacent to a column of ejection amount data DA12 indicating that the ink ejection amount is not zero is detected as an edge. This makes it possible to suppress a decrease in the reproducibility of edge density compared to a configuration in which the portion where a column of ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is a first amount greater than zero is adjacent to a column of ejection amount data DA12 indicating that the ink ejection amount is a second amount greater than the first amount is also detected as an edge.

[0084] The detection processing unit 61A may also detect as an edge a portion where a column of ejection amount data DA12 indicating that the amount of ink ejected in the corresponding area AR10 is equal to or greater than a predetermined threshold is adjacent to a column of ejection amount data DA12 indicating that the amount of ink ejected is less than the threshold.

[0085] Furthermore, when an edge is detected by the detection processing unit 61A, the determination processing unit 62A may randomly determine the division position within the relatively lower concentration region of two concentration regions separated by the upstream or downstream edge in the second direction D21, among the edges included in the corresponding region AR10. For example, if the first edge is detected by the first detection process, the determination processing unit 62A may randomly determine the division position within the relatively lower concentration region of two concentration regions separated by the uppermost first edge in the second direction D21. If the first edge is not detected by the first detection process and the second edge is detected by the second detection process, the determination processing unit 62A may randomly determine the division position within the relatively lower concentration region of two concentration regions separated by the downstream second edge in the second direction D21.

[0086] Furthermore, when an edge is detected by the detection processing unit 61A, the determination processing unit 62A may determine the division position according to a predetermined determination method within the relatively lower density region of the two density regions separated by the upstream or downstream edge in the second direction D21, among the edges included in the corresponding region AR10. In this case, it is desirable that the portion where a column of ejection amount data DA12 indicating that the ink ejection amount in the corresponding region AR10 is zero is adjacent to a column of ejection amount data DA12 indicating that the ink ejection amount is not zero is detected as an edge. For example, if the first edge is detected by the first detection process, the determination processing unit 62A may determine the division position according to the determination method within the relatively lower density region of the two density regions separated by the uppermost first edge in the second direction D21. If the first edge is not detected by the first detection process and the second edge is detected by the second detection process, the determination processing unit 62A may determine the division position according to the determination method within the relatively lower density region of the two density regions separated by the downstream second edge in the second direction D21.

[0087] Furthermore, the detection processing unit 61A may detect edges included in the region corresponding to the overlap region OL10 in the line data for each line data included in the monochrome image data (another example of the image data of the present invention).

[0088] By the way, in a configuration where the division position is determined by the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10, or by the position within the density region with a relatively lower density among the two density regions separated by said edge, if there is a white line (see Figure 10) extending in a direction intersecting the main scanning direction D20 within the corresponding region AR10, the line width of the white line formed on the sheet becomes thinner than it should be, as shown in Figure 11. In other words, in the above configuration, the reproducibility of white lines extending in a direction intersecting the main scanning direction D20 within the corresponding region AR10 is reduced.

[0089] In contrast, the image forming apparatus 100B according to the second embodiment of the present invention can suppress a decrease in the reproducibility of white lines extending in a direction intersecting the main scanning direction D20 within the corresponding region AR10, as will be explained below.

[0090] [Second Embodiment] The configuration of the image forming apparatus 100B according to the second embodiment of the present invention will be described below with reference to Figure 12.

[0091] As shown in Figures 4 and 12, the configuration of the engine control unit 8 in the image forming apparatus 100B differs from that of the image forming apparatus 100A. Specifically, the engine control unit 8 of the image forming apparatus 100B includes a detection processing unit 61B, a determination processing unit 62B, and a modification processing unit 63, instead of the detection processing unit 61A and the determination processing unit 62A. The other configurations are common to both the image forming apparatus 100A and the image forming apparatus 100B. Below, only the differences in the configuration of the image forming apparatus 100B compared to the image forming apparatus 100A will be described.

[0092] The detection processing unit 61B detects edges included in the corresponding region AR10 within each line data DA11 contained in the print data DA10.

[0093] For example, the detection processing unit 61B detects as an edge a portion where a column of ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is greater than or equal to the threshold is adjacent to a column of ejection amount data DA12 indicating that the ink ejection amount is less than the threshold. For example, the detection processing unit 61B detects as an edge a portion where a column containing three or more consecutive ejection amount data DA12 indicating that the ink ejection amount in the corresponding area AR10 is greater than or equal to the threshold is adjacent to a column containing two or more consecutive ejection amount data DA12 indicating that the ink ejection amount is less than the threshold. For example, the threshold is "1".

[0094] When an edge is detected by the detection processing unit 61B, the determination processing unit 62B randomly determines the division position within the concentration region with a relatively higher concentration among the two concentration regions separated by the upstream or downstream edge in the second direction D21, from among the edges included in the corresponding region AR10.

[0095] For example, the decision processing unit 62B uses a random number table to determine the division position within the density region with a relatively higher density among the two density regions that are separated by the uppermost or lowermost edge in the second direction D21 among the edges included in the corresponding region AR10.

[0096] Furthermore, if no edge is detected by the detection processing unit 61B, the determination processing unit 62B randomly determines the division position within the corresponding region AR10.

[0097] The change processing unit 63 changes the threshold value according to a predetermined change operation.

[0098] For example, the change processing unit 63 displays a change operation screen used to accept the change operation on the operation display unit 5 in accordance with a predetermined operation on the operation display unit 5. Then, when the change processing unit 63 accepts the change operation on the change operation screen, it changes the threshold value in accordance with the accepted change operation.

[0099] [Second data splitting process] Next, with reference to Figure 13, the determination method of the present invention will be described along with an example of the procedure for the second data division process performed by the engine control unit 8. The engine control unit 8 performs the second data division process when executing the printing process. Furthermore, the engine control unit 8 performs the second data division process for each color: black, cyan, magenta, and yellow.

[0100] <Step S31> First, in step S31, the engine control unit 8 selects one line data DA11 to be divided from among the multiple line data DA11 included in the print data DA10 to be printed.

[0101] <Step S32> In step S32, the engine control unit 8 detects edges in the line data DA11 to be divided that are included in the corresponding region AR10, which corresponds to the overlap region OL10 where the recording head 36A and the recording head 36B overlap. The processing in step S32 is an example of the detection step of the present invention and is performed by the detection processing unit 61B of the engine control unit 8.

[0102] Specifically, the engine control unit 8 detects as an edge a portion where a column containing three or more consecutive ejection amount data DA12 indicating that the ink ejection amount in the corresponding region AR10 is equal to or greater than the threshold is adjacent to a column containing two or more consecutive ejection amount data DA12 indicating that the ink ejection amount is less than the threshold.

[0103] <Step S33> In step S33, the engine control unit 8 determines whether or not an edge has been detected by the processing in step S32.

[0104] If the engine control unit 8 determines that an edge has been detected (Yes in S33), it proceeds to step S34. If no edge has been detected (No in S33), the engine control unit 8 proceeds to step S35.

[0105] <Step S34> In step S34, the engine control unit 8 determines the division position based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 corresponding to the overlap region OL10 where the recording head 36A and the recording head 36B overlap. The processing in step S34 is an example of the determination step of the present invention and is performed by the determination processing unit 62B of the engine control unit 8.

[0106] Specifically, the engine control unit 8 randomly determines the division position within the concentration region with a relatively higher concentration among the two concentration regions separated by the uppermost edge in the second direction D21 among the edges included in the corresponding region AR10.

[0107] <Step S35> In step S35, the engine control unit 8 randomly determines the division position within the corresponding region AR10 that corresponds to the overlap region OL10 where the recording head 36A and the recording head 36B overlap. The process in step S35 is an example of the determination step of the present invention and is performed by the determination processing unit 62B of the engine control unit 8.

[0108] <Step S36> In step S36, the engine control unit 8 detects edges in the line data DA11 to be divided that are included in the corresponding region AR10, which corresponds to the overlap region OL10 where the recording head 36B and the recording head 36C overlap, using the same method as in step S32. The process in step S36 is an example of the detection step of the present invention and is performed by the detection processing unit 61B of the engine control unit 8.

[0109] <Step S37> In step S37, the engine control unit 8 determines whether or not an edge was detected by the processing in step S36.

[0110] If the engine control unit 8 determines that an edge has been detected (Yes in S37), it proceeds to step S38. If no edge has been detected (No in S37), the engine control unit 8 proceeds to step S39.

[0111] <Step S38> In step S38, the engine control unit 8 determines the division position based on the position of the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10 corresponding to the overlap region OL10 where the recording head 36B and the recording head 36C overlap, using the same method as in step S34. The process in step S38 is an example of the determination step of the present invention and is performed by the determination processing unit 62B of the engine control unit 8.

[0112] <Step S39> In step S39, the engine control unit 8 randomly determines the division position within the corresponding region AR10 that corresponds to the overlap region OL10 where the recording head 36B and the recording head 36C overlap. The process in step S39 is an example of the determination step of the present invention and is performed by the determination processing unit 62B of the engine control unit 8.

[0113] <Step S40> In step S40, the engine control unit 8 divides the line data DA11 to be divided into the first line data, the second line data, and the third line data based on the division position determined by the processing in step S34 or step S35, and the division position determined by the processing in step S38 or step S39.

[0114] The first line data, the second line data, and the third line data, which are divided by the processing in step S40, are used to drive the three recording heads 36 included in the line head 30. As a result, an image corresponding to the line data DA11 is formed on the sheet.

[0115] <Step S41> In step S41, the engine control unit 8 determines whether all line data DA11 included in the print data DA10 to be printed have been selected by the processing in step S31.

[0116] At this point, if the engine control unit 8 determines that all line data DA11 have been selected (Yes side of S41), it terminates the second data division process. If not all line data DA11 have been selected (No side of S41), the engine control unit 8 proceeds to step S31.

[0117] Figure 14 shows the division positions determined by the second data division process when the print data DA10 shown in Figure 10 is printed. Figure 15 shows the image IM10 formed on the sheet based on the first line data and the second line data divided by the second data division process. As shown in Figure 15, by randomly determining the division positions within the density region with relatively higher density among two density regions separated by the upstream or downstream edge in the second direction D21 among the edges included in the corresponding region AR10, the decrease in the reproducibility of the white line image extending in the direction intersecting the width direction D12 included in the image IM10 formed on the sheet is suppressed.

[0118] Thus, the image forming apparatus 100B can suppress the occurrence of jagged edges in the image formed on the sheet, and can also suppress a decrease in the reproducibility of white lines extending in a direction intersecting the main scanning direction D20 within the corresponding region AR10.

[0119] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0120] <Note 1> A first discharge unit that includes a plurality of first nozzles arranged along the width direction perpendicular to the sheet transport direction, and ejects ink from each of the first nozzles; a second discharge unit that includes a plurality of second nozzles arranged along the width direction, with a portion of the plurality of second nozzles overlapping with a portion of the plurality of first nozzles in the width direction, and ejects the ink from each of the second nozzles; and for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first discharge unit and the second discharge unit, the corresponding portion of the overlap between the plurality of first nozzles and the plurality of second nozzles in the line data. An image forming apparatus comprising: a detection processing unit for detecting edges included in a corresponding region; and, when the detection processing unit detects an edge, a determination processing unit for randomly dividing the line data into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density region with a relatively higher density among two density regions separated by the upstream or downstream edge of the edge included in the corresponding region in a specific direction along the main scanning direction, and when the detection processing unit does not detect an edge, a determination processing unit for randomly determining the division position within the corresponding region.

[0121] <Note 2> The image forming apparatus according to Appendix 1, wherein the line data corresponds to each nozzle and includes discharge amount data indicating the amount of ink discharged from the nozzle, and the detection processing unit detects as the edge a portion where a column of discharge amount data indicating that the amount of ink discharged in the corresponding area is greater than or equal to a predetermined threshold and a column of discharge amount data indicating that the amount of ink discharged is less than the threshold are adjacent.

[0122] <Note 3> The image forming apparatus according to Appendix 2, comprising a change processing unit that changes the threshold in accordance with a predetermined change operation.

[0123] <Note 4> A determination method performed in an image forming apparatus comprising: a first discharge unit that includes a plurality of first nozzles arranged along a width direction perpendicular to the sheet transport direction and discharges ink from each of the first nozzles; and a second discharge unit that includes a plurality of second nozzles arranged along the width direction and arranged such that a portion of the plurality of second nozzles overlaps with a portion of the plurality of first nozzles in the width direction and discharges ink from each of the second nozzles, wherein for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first discharge unit and the second discharge unit, the plurality of first nozzles and the plurality of second nozzles in the line data A determination method comprising: a detection step of detecting an edge included in a corresponding area corresponding to the overlapping portion of; if the edge is detected by the detection step, determining a division position in which the line data is randomly divided into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density area with a relatively higher density among two density areas separated by the upstream or downstream edge of the edge included in the corresponding area in a specific direction along the main scanning direction; and if the edge is not detected by the detection step, determining the division position randomly within the corresponding area. [Explanation of Symbols]

[0124] 1 cabinet 2 Sheet transport section 3 Image forming unit 4. Transport Unit 5 Operation display section 6 Memory section 7 Main Control Unit 8. Engine Control Unit 30 line heads 36 Recording head 37 nozzles 61A Detection Processing Unit 61B Detection Processing Unit 62A Decision Processing Unit 62B Decision Processing Unit 63 Change Processing Unit 100A Image forming apparatus 100B Image forming device

Claims

1. A first discharge unit includes a plurality of first nozzles arranged along the width direction perpendicular to the sheet transport direction, and discharges ink from each of the first nozzles, A second discharge unit includes a plurality of second nozzles arranged along the width direction, wherein a portion of the plurality of second nozzles is arranged to overlap with a portion of the plurality of first nozzles in the width direction, and the second discharge unit discharges the ink from each of the second nozzles, A detection processing unit detects, for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first and second discharge units, an edge included in the corresponding region corresponding to the overlapping portion of the plurality of first nozzles and the plurality of second nozzles in the line data, If the detection processing unit detects the edge, the determination processing unit determines a division position in which the line data is randomly divided into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density region with a relatively higher density among the two density regions separated by the upstream or downstream edge in a specific direction along the main scanning direction among the edges included in the corresponding region; if the detection processing unit does not detect the edge, the determination processing unit determines the division position randomly within the corresponding region. An image forming apparatus equipped with the following features.

2. The line data corresponds to each nozzle and includes discharge amount data indicating the amount of ink discharged from the nozzle. The detection processing unit detects as an edge a portion where a column of ejection amount data indicating that the amount of ink ejected in the corresponding region is greater than or equal to a predetermined threshold is adjacent to a column of ejection amount data indicating that the amount of ink ejected is less than the threshold. The image forming apparatus according to claim 1.

3. The system includes a change processing unit that changes the threshold according to a predetermined change operation. The image forming apparatus according to claim 2.

4. A determination method performed in an image forming apparatus comprising: a first discharge unit that includes a plurality of first nozzles arranged along a width direction perpendicular to the sheet transport direction and discharges ink from each of the first nozzles; and a second discharge unit that includes a plurality of second nozzles arranged along the width direction, wherein a portion of the plurality of second nozzles overlaps with a portion of the plurality of first nozzles in the width direction and discharges the ink from each of the second nozzles; A detection step for detecting edges included in a corresponding region corresponding to the overlapping portion of a plurality of first nozzles and a plurality of second nozzles in line data for each line of line data along the main scanning direction corresponding to the width direction included in the image data used to drive the first discharge unit and the second discharge unit, If the edge is detected by the detection step, a division position is determined in which the line data is randomly divided into first line data used to drive the first discharge unit and second line data used to drive the second discharge unit within the density region with a relatively higher density among the two density regions separated by the upstream or downstream edge in a specific direction along the main scanning direction among the edges included in the corresponding region; if the edge is not detected by the detection step, a determination step is performed to randomly determine the division position within the corresponding region. A decision method that includes this.

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