Image forming device and adjustment method

Abstract

To provide an image forming apparatus and adjustment method that can suppress the generation of muscle images without complicating the configuration. [Solution] The image forming apparatus includes a first setting processing unit that, when the separation distance δ is greater than or equal to a threshold, sets the nozzle 72 to the side in a specific direction D13 from among the plurality of nozzles 37B as the usable area for ejecting ink, and when the separation distance δ is less than the threshold, sets the nozzle 73 to the side in a specific direction D13 from among the plurality of nozzles 37B as the usable area; and an adjustment processing unit that, when the separation distance δ is greater than or equal to the threshold, reduces the amount of ink ejected from nozzle 71, and when the separation distance δ is less than the threshold, increases the amount of ink ejected from nozzle 71.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an adjustment 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 a conveyance direction of a 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 a part of the plurality of second nozzles overlaps with a part of the plurality of first nozzles on a specific direction side along the width direction with respect to the first ejection unit, and ejects the ink from each of the second nozzles. In the image forming apparatus, at any position in the width direction in an overlapping portion where the plurality of first nozzles and the plurality of second nozzles overlap, the nozzle that ejects the ink is switched between the first nozzle and the second nozzle.

[0003] In the image forming apparatus, due to an attachment error of the first ejection unit and the second ejection unit or the like, the nozzle interval in a switching portion where the nozzle that ejects the ink in the overlapping portion is switched may deviate from a design value. In this case, streak images along the conveyance direction may occur in an image formed on a sheet. On the other hand, an image forming apparatus that reduces the ejection amount of the ink of either one of the two nozzles included in the switching portion based on a separation distance in the width direction between the first nozzle and the second nozzle included in the switching portion is known as a related art (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, in the image forming apparatus relating to the above-mentioned related technologies, it is necessary to provide a function to excessively reduce the amount of ink ejected from one of the two nozzles included in the switching section, in case the deviation of the spacing distance in the width direction of the two nozzles included in the switching section from the design value is excessively large. Therefore, the configuration of the image forming apparatus becomes complicated.

[0006] The object of the present invention is to provide an image forming apparatus and adjustment method that can suppress the generation of muscle images without complicating the configuration. [Means for solving the problem]

[0007] An image forming apparatus according to one aspect of the present invention comprises a first discharge unit, a second discharge unit, an acquisition processing unit, a first setting processing unit, and an adjustment 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, on a specific side of the width direction from the first discharge unit, and discharges the ink from each of the second nozzles. The acquisition processing unit acquires a first separation distance in the width direction between a third nozzle included in the overlapping portion of the plurality of first nozzles with the plurality of second nozzles, and a fourth nozzle that is closest to the third nozzle among the second nozzles located on a specific side of the third nozzle. The first setting processing unit sets the area from the fourth nozzle on the specific direction side of the plurality of second nozzles to the usage area used for ink ejection if the first separation distance acquired by the acquisition processing unit is greater than or equal to a predetermined threshold, and sets the area from the fifth nozzle adjacent to the fourth nozzle on the specific direction side of the plurality of second nozzles to the usage area if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, and adjusts the amount of ink ejected from either the third nozzle or the fourth nozzle or both based on the first separation distance if the first separation distance is less than the threshold, and increases the amount of ink ejected from either the third nozzle or the fifth nozzle or both based on the second separation distance between the third nozzle and the fifth nozzle in the width direction.

[0008] An adjustment 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 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, on a specific side of the width direction from the first discharge unit, and discharges the ink from each of the second nozzles, and includes an acquisition step, a setting step, and an adjustment step. In the acquisition step, a first separation distance in the width direction is acquired between a third nozzle included in the overlapping portion of the plurality of first nozzles with the plurality of second nozzles and a fourth nozzle that is closest to the third nozzle among the second nozzles located on a specific side of the third nozzle. In the setting step, if the first separation distance obtained by the acquisition step is greater than or equal to a predetermined threshold, the area from the fourth nozzle on the specific direction side of the plurality of second nozzles is set as the usage area used for ink ejection. If the first separation distance is less than the threshold, the area from the fifth nozzle adjacent to the fourth nozzle on the specific direction side of the plurality of second nozzles is set as the usage area. In the adjustment step, if the first separation distance obtained by the acquisition step is greater than or equal to the threshold, the amount of ink ejected from either the third nozzle or the fourth nozzle or both is reduced based on the first separation distance. If the first separation distance is less than the threshold, the amount of ink ejected from either the third nozzle or the fifth nozzle or both is increased based on the second separation distance between the third nozzle and the fifth nozzle in the width direction. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the generation of muscle images without complicating the structure. [Brief explanation of the drawing]

[0010] [Figure 1]Figure 1 shows the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of the image forming section and the transport unit of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 shows the configuration around the nozzle of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing an example of the discharge volume adjustment process performed in an image forming apparatus according to an embodiment of the present invention. [Figure 6] Figure 6 shows an example of the overlap region of an image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0012] [Configuration of the image forming apparatus 100] First, the configuration of the image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Figures 1 to 4. Here, Figure 1 is a cross-sectional view showing the configuration of the image forming apparatus 100. Figure 2 is a plan view showing the configuration of the image forming unit 3 and the transport unit 4. Figure 3 is a cross-sectional view showing the configuration of the nozzle 37, pressurizing chamber 38, piezoelectric element 39, and individual flow path 40. Note that in Figure 1, the sheet transport path R11 is shown by a dashed line. Also, in Figure 2, the overlap region OL10 is shown by a dashed line.

[0013] The image forming apparatus 100 is a printer capable of forming images on a sheet using an inkjet method. The present invention may also be applied to fax machines, copiers, and multifunction devices capable of forming images on a sheet using an inkjet method.

[0014] As shown in Figures 1 and 4, the image forming apparatus 100 comprises a housing 1, a sheet transport unit 2, an image forming unit 3, a transport unit 4, an operation display unit 5, a storage unit 6, a main control unit 7, and an engine control unit 8.

[0015] The housing 1 houses the various components of the image forming apparatus 100. A paper feed cassette 11 (see Figure 1) is detachably provided in the housing 1. The paper feed cassette 11 contains sheets on which images are formed. A paper output tray 12 (see Figure 1) is provided on the outer surface of the housing 1. Sheets on which images have been formed by the image forming unit 3 are discharged into the paper output tray 12. Inside the housing 1, the sheets contained in the paper feed cassette 11 are transported along a sheet transport path R11 (see Figure 1) that passes through the image forming position by the image forming unit 3 and leads to the paper output tray 12.

[0016] 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.

[0017] 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.

[0018] As shown in FIG. 2, each line head 30 is long in the width direction D12 orthogonal to the conveyance direction D11. Specifically, each line head 30 has a length corresponding to the width of the largest-sized sheet among the sheets that can be accommodated in the paper feed cassette 11 in the width direction D12. The four line heads 30 are provided side by side at equal intervals along the conveyance direction D11.

[0019] As shown in FIG. 2, each line head 30 has a plurality of recording heads 36. Each recording head 36 discharges ink droplets toward the sheet conveyed by the conveyance unit 4. Each recording head 36 provided in the line head 31 discharges black ink droplets. Each recording head 36 provided in the line head 32 discharges cyan ink droplets. Each recording head 36 provided in the line head 33 discharges magenta ink droplets. Each recording head 36 provided in the line head 34 discharges yellow ink droplets.

[0020] Each recording head 36 includes a plurality of nozzles 37 (see FIGS. 2 and 3) that discharge ink droplets onto the sheet. Each nozzle 37 is provided on the opposing surface of the recording head 36 with respect to the sheet conveyed by the conveyance unit 4. For example, in the image forming apparatus 100, small-sized, medium-sized, or large-sized ink droplets are discharged from the nozzles 37.

[0021] Each recording head 36 also includes a pressure chamber 38 (see FIG. 3), a piezoelectric element 39 (see FIG. 3), and an individual flow path 40 (see FIG. 3) corresponding to each nozzle 37. The pressure chamber 38 communicates with the nozzle 37 and stores ink. The piezoelectric element 39 changes the pressure in the pressure chamber 38 in response to the input of a drive signal, thereby discharging ink droplets from the nozzle 37. The individual flow path 40 is an ink flow path provided between the pressure chamber 38 and a common flow path (not shown) common to the plurality of nozzles 37. A plurality of individual flow paths 40 corresponding to the plurality of 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 pressure chamber 38.

[0022] As shown in Figure 2, the line head 31 has three recording heads 36 (36A, 36B, and 36C).

[0023] 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.

[0024] The three recording heads 36 included in the line head 31 are arranged in a staggered pattern along the width direction D12.

[0025] Specifically, as shown in Figure 2, the recording head 36B is positioned such that, in the width direction D12, a portion of the multiple nozzles 37B overlaps with a portion of the multiple nozzles 37A, on the side of a specific direction D13 (see Figure 2) along the width direction D12, compared to the recording head 36A. Similarly, the recording head 36C is positioned such that, in the width direction D12, a portion of the multiple nozzles 37C overlaps with a portion of the multiple nozzles 37B, on the side of a specific direction D13, compared to the recording head 36B. In this specification, the overlapping region in the width direction D12 between a portion of multiple nozzles 37 included in one of the three recording heads 36 and a portion of multiple nozzles 37 included in another recording head 36 is referred to as the "overlap region OL10" (see Figure 2). The recording head 36A is an example of the first discharge unit of the present invention. The nozzle 37A is an example of the first nozzle of the present invention. The recording head 36B is an example of the second discharge unit of the present invention. The nozzle 37B is an example of the second nozzle of the present invention.

[0026] Line heads 32-34 have three recording heads 36 arranged similarly to line head 31.

[0027] Furthermore, the number of recording heads 36 provided on each line head 30 is not limited to three.

[0028] 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.

[0029] 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).

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The main control unit 7 comprehensively controls the image forming apparatus 100. 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 100 by executing various control programs pre-stored in the ROM 52.

[0034] 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).

[0035] In the image forming apparatus 100, at any position in the width direction D12 within the overlap region OL10 where multiple nozzles 37A and multiple nozzles 37B overlap, the nozzle 37 that ejects ink is switched between nozzle 37A and nozzle 37B.

[0036] In the image forming apparatus 100, mounting errors of the recording heads 36A and 36B may cause the nozzle spacing at the switching section where the nozzles 37 that eject ink in the overlap region OL10 switch to deviate from the design value. In this case, streaky images along the transport direction D11 may appear in the image formed on the sheet. In response to this, an image forming apparatus is known as a related technology that reduces the amount of ink ejected from one of the two nozzles 37 included in the switching section based on the separation distance in the width direction D12 between nozzles 37A and nozzle 37B included in the switching section.

[0037] However, in the image forming apparatus relating to the above-mentioned related technologies, a function is needed to excessively reduce the ink discharge amount of one of the two nozzles 37 included in the switching section in case the deviation of the spacing distance between the two nozzles 37 in the width direction D12 from the design value is excessively large. This complicates the configuration of the image forming apparatus. Furthermore, if the ink discharge amount of one of the two nozzles 37 included in the switching section is excessively reduced, the large fluctuation from the original droplet amount causes an unnatural appearance in the printed image, and the image quality formed on the sheet deteriorates.

[0038] In contrast, the image forming apparatus 100 according to an embodiment of the present invention can suppress the generation of muscle images without complicating the configuration, as will be explained below.

[0039] Specifically, the engine control unit 8 includes the acquisition processing unit 61, the first setting processing unit 62, the adjustment processing unit 63, and the second setting processing unit 64 shown in Figure 4.

[0040] In addition, the main control unit 7 may include the above-mentioned processing units instead of the engine control unit 8. Specifically, the CPU 51 of the main control unit 7 may function as the above-mentioned processing units by executing the control program stored in the ROM 52 in advance.

[0041] The acquisition processing unit 61 acquires the distance δ (see Figure 6) (an example of the first distance in the present invention) in the width direction D12 between a nozzle 71 (see Figure 6) (an example of the third nozzle in the present invention) which is included in the overlapping portion of the multiple nozzles 37A with multiple nozzles 37B, and a nozzle 72 (see Figure 6) (an example of the fourth nozzle in the present invention) which is located on the side of the nozzle 37B that is closer to the nozzle 71 (see Figure 6) (an example of the fourth nozzle in the present invention).

[0042] Nozzle 71 is the nozzle 37A located furthest downstream in a specific direction D13 among the nozzles 37A used for ink ejection in the recording head 36A. In other words, among the multiple nozzles 37A, those downstream of nozzle 71 in a specific direction D13 are not used for ink ejection.

[0043] For example, in the image forming apparatus 100, the separation distance δ measured during the manufacturing of the image forming apparatus 100 is stored in the memory unit 6.

[0044] In this case, the acquisition processing unit 61 acquires the separation distance δ from the storage unit 6.

[0045] The image forming apparatus 100 may also include an image reading unit for reading images formed on a sheet. In this case, the acquisition processing unit 61 may acquire the separation distance δ based on the image reading result of the image formed on the sheet using nozzles 71 and 72 by the image reading unit.

[0046] The first setting processing unit 62, when the separation distance δ acquired by the acquisition processing unit 61 is greater than or equal to a predetermined threshold, sets the nozzles 37B on the side of nozzle 72 in a specific direction D13 as the usable area for ink ejection. In this case, the nozzles 37B upstream of nozzle 72 in the specific direction D13 are not used for ink ejection.

[0047] Furthermore, if the separation distance δ acquired by the acquisition processing unit 61 is less than the threshold, the first setting processing unit 62 sets the area on the side of the specific direction D13 of the nozzle 72 from among the multiple nozzles 37B, starting from nozzle 73 (see Figure 6) (an example of the fifth nozzle of the present invention) adjacent to nozzle 72 in a specific direction D13.

[0048] The threshold value is set to a value greater than "0" and less than or equal to the nozzle spacing Δ (see Figure 6) between recording heads 36A and 36B. For example, the threshold value may be set to half the nozzle spacing Δ.

[0049] If the separation distance δ acquired by the acquisition processing unit 61 is greater than or equal to the threshold, the adjustment processing unit 63 reduces the amount of ink discharged from either nozzle 71 or nozzle 72 based on the separation distance δ.

[0050] Furthermore, if the separation distance δ acquired by the acquisition processing unit 61 is less than the threshold, the adjustment processing unit 63 increases the amount of ink discharged from either nozzle 71 or nozzle 73 based on the separation distance δ' (see Figure 6) between nozzle 71 and nozzle 73 in the width direction D12 (an example of the second separation distance in the present invention).

[0051] For example, if the separation distance δ acquired by the acquisition processing unit 61 is greater than or equal to the threshold, the adjustment processing unit 63 reduces the ink discharge amount of either nozzle 71 or nozzle 72, with S being the dot area determined according to the grayscale of the pixels, so that the area S' of the dot formed by the nozzle whose ink discharge amount is reduced satisfies the following condition (1).

[0052] S' = S * δ / Δ ... (1)

[0053] Furthermore, if the separation distance δ acquired by the acquisition processing unit 61 is less than the threshold, the adjustment processing unit 63 increases the ink discharge amount of either nozzle 71 or nozzle 73 so that the area S' of the dot formed by the nozzle with increased ink discharge amount satisfies the following condition (2).

[0054] S' = S*δ' / Δ ··· (2)

[0055] The second setting processing unit 64 sets the threshold based on the type of sheet.

[0056] For example, in the image forming apparatus 100, table data showing the correspondence between the sheet type and the threshold value is stored in the storage unit 6 in advance. In the table data, the correspondence between the sheet type and the threshold value is defined such that the threshold value decreases as the sheet becomes less prone to ink bleeding. This is because the lower the tendency of the sheet to bleed ink, the smaller the upper limit distance between nozzles 71 and 73, which can be corrected by increasing the discharge amount.

[0057] The second setting processing unit 64 sets the threshold using the table data.

[0058] [Discharge volume adjustment process] The adjustment method of the present invention will be described below with reference to Figure 5, along with an example of the procedure for the discharge volume adjustment process performed by the engine control unit 8. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) performed by the engine control unit 8. Note that when a printing process to form an image on a sheet is performed, the engine control unit 8 performs the discharge volume adjustment process before the execution of the printing process.

[0059] <Step S11> First, in step S11, the engine control unit 8 sets the threshold value. The process in step S11 is performed by the second setting processing unit 64 of the engine control unit 8.

[0060] Specifically, the engine control unit 8 acquires type information indicating the type of sheet used to form the image in the printing process. The engine control unit 8 also acquires a value in the table data that corresponds to the acquired type information. The engine control unit 8 then sets the acquired value as the threshold value.

[0061] <Step S12> In step S12, the engine control unit 8 acquires the separation distance δ (see Figure 6). The process in step S12 is an example of the acquisition step of the present invention and is performed by the acquisition processing unit 61 of the engine control unit 8.

[0062] Specifically, the engine control unit 8 obtains the separation distance δ from the memory unit 6.

[0063] <Step S13> In step S13, the engine control unit 8 determines whether the separation distance δ obtained in step S12 is greater than or equal to the threshold set in step S11.

[0064] If the engine control unit 8 determines that the separation distance δ is greater than or equal to the threshold (Yes in S13), it proceeds to step S14. If the separation distance δ is not greater than or equal to the threshold (No in S13), the engine control unit 8 proceeds to step S16.

[0065] <Step S14> In step S14, the engine control unit 8 sets the area from nozzle 72 (see Figure 6) to the side D13 in a specific direction among the plurality of nozzles 37B as the usage area. The process in step S14 is an example of the setting step of the present invention and is performed by the first setting processing unit 62 of the engine control unit 8.

[0066] <Step S15> In step S15, the engine control unit 8 reduces the amount of ink discharged from the nozzle 71 based on the separation distance δ. The process in step S15 is an example of the adjustment steps of the present invention and is performed by the adjustment processing unit 63 of the engine control unit 8.

[0067] Specifically, the engine control unit 8 adjusts the amount of ink ejected from the nozzle 71 so as to satisfy the above-described condition (1). The adjustment of the ink ejection amount from the nozzle 71 can be achieved by adjusting either the voltage and / or waveform of the drive signal input to the piezoelectric element 39 corresponding to the nozzle 71.

[0068] <Step S16> In step S16, the engine control unit 8 sets the area from nozzle 73 (see Figure 6) to the usage area in a specific direction D13 among the plurality of nozzles 37B. The process in step S16 is an example of the setting step of the present invention and is performed by the first setting processing unit 62 of the engine control unit 8.

[0069] <Step S17> In step S17, the engine control unit 8 increases the amount of ink discharged from the nozzle 71 based on the separation distance δ' (see Figure 6). The process in step S17 is an example of the adjustment step of the present invention and is performed by the adjustment processing unit 63 of the engine control unit 8.

[0070] Specifically, the engine control unit 8 adjusts the amount of ink ejected from the nozzle 71 so as to satisfy the above-described condition (2).

[0071] Thus, in the image forming apparatus 100, when the separation distance δ is greater than or equal to the threshold, the portion of the plurality of nozzles 37B from nozzle 72 toward a specific direction D13 is set as the usage area, and the amount of ink ejected from nozzle 71 is reduced based on the separation distance δ. Conversely, in the image forming apparatus 100, when the separation distance δ is less than the threshold, the portion of the plurality of nozzles 37B from nozzle 73 toward a specific direction D13 is set as the usage area, and the amount of ink ejected from nozzle 71 is increased based on the separation distance δ'. This eliminates the need to provide a function to excessively reduce the amount of ink ejected from nozzle 71 in case the separation distance δ is excessively small. Therefore, the generation of muscle images can be suppressed without complicating the configuration.

[0072] Furthermore, if the separation distance δ acquired by the acquisition processing unit 61 is greater than or equal to the threshold, the adjustment processing unit 63 may reduce the amount of ink discharged from both nozzles 71 and 72 based on the separation distance δ.

[0073] In this case, the adjustment processing unit 63 only needs to reduce the amount of ink ejected from both nozzles 71 and 72 so that the area S' of each dot formed by nozzles 71 and 72 satisfies the following condition (3).

[0074] S' = S*(1+δ / Δ) / 2 ··· (3)

[0075] Furthermore, if the separation distance δ acquired by the acquisition processing unit 61 is less than the threshold, the adjustment processing unit 63 may increase the amount of ink discharged from both nozzles 71 and 73 based on the separation distance δ'.

[0076] In this case, the adjustment processing unit 63 should increase the amount of ink ejected from both nozzles 71 and 73 so that the area S' of each dot formed by nozzles 71 and 73 satisfies the following condition (4).

[0077] S´=S*(1+δ´ / Δ) / 2 ··· (4)

[0078] [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.

[0079] <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 discharges ink from each of the first nozzles; a second discharge unit that 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, on a specific side of the width direction from the first discharge unit and discharges the ink from each of the second nozzles; an acquisition processing unit that acquires a first separation distance in the width direction between a third nozzle included in the overlapping portion of the plurality of second nozzles in the plurality of first nozzles and a fourth nozzle that is closest to the third nozzle among the second nozzles located on a specific side of the third nozzle; and if the first separation distance acquired by the acquisition processing unit is greater than or equal to a predetermined threshold, a plurality of front Image forming apparatus comprising: a first setting processing unit which sets the side of the fourth nozzle from the second nozzle in the specific direction to be used as a usage area for ejecting the ink, and if the first separation distance is less than the threshold, sets the side of the fifth nozzle adjacent to the fourth nozzle in the specific direction from the fourth nozzle from among the plurality of second nozzles to be used as the usage area; and an adjustment processing unit which, if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, reduces the amount of ink ejected from either one or both of the third nozzle and the fourth nozzle based on the first separation distance, and if the first separation distance is less than the threshold, increases the amount of ink ejected from either one or both of the third nozzle and the fifth nozzle based on the second separation distance between the third nozzle and the fifth nozzle in the width direction.

[0080] <Note 2> The image forming apparatus according to Appendix 1, wherein the adjustment processing unit reduces the amount of ink discharged from either the third nozzle or the fourth nozzle based on the first separation distance if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, and increases the amount of ink discharged from either the third nozzle or the fifth nozzle based on the second separation distance if the first separation distance is less than the threshold, and the adjustment processing unit increases the amount of ink discharged from either the third nozzle or the fifth nozzle based on the second separation distance if the first separation distance is less than the threshold, with respect to the nozzle spacing between the first and second discharge units being Δ, the second separation distance being δ', and the dot area being determined according to the grayscale of the pixels being S, such that the area S' of the dot formed by the nozzle from which the amount of ink discharged is increased satisfies the following condition (1). S' = S*δ' / Δ ··· (1)

[0081] <Note 3> The image forming apparatus according to Appendix 1, wherein the adjustment processing unit reduces the amount of ink discharged from both the third nozzle and the fourth nozzle based on the first separation distance if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, increases the amount of ink discharged from both the third nozzle and the fifth nozzle based on the second separation distance if the first separation distance is less than the threshold, and the adjustment processing unit increases the amount of ink discharged from both the third nozzle and the fifth nozzle so that the area S' of each dot formed by the third nozzle and the fifth nozzle satisfies the following condition (2), where Δ is the nozzle spacing between the first and second discharge units, δ' is the second separation distance, and S is the dot area determined according to the grayscale of the pixel. S´=S*(1+δ´ / Δ) / 2 ··· (2)

[0082] <Note 4> An image forming apparatus according to any one of the appendices 1 to 3, comprising a second setting processing unit that sets the threshold based on the type of sheet.

[0083] <Note 5> An adjustment 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 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, on a specific side of the width direction from the first discharge unit, and discharges the ink from each of the second nozzles, the method comprising: an acquisition step of acquiring a first separation distance in the width direction between a third nozzle included in the overlapping portion of the plurality of first nozzles with the plurality of second nozzles and a fourth nozzle that is closest to the third nozzle among the second nozzles located on a specific side of the third nozzle; and the first separation distance acquired by the acquisition step is set to a predetermined threshold. An adjustment method comprising: a setting step in which, if the above is true, the fourth nozzle among the plurality of second nozzles is set to be used as the work area for ejecting the ink on the side facing the specific direction, and if the first separation distance is less than the threshold, the fifth nozzle adjacent to the fourth nozzle on the side facing the specific direction among the plurality of second nozzles is set to be used as the work area on the side facing the specific direction; and an adjustment step in which, if the first separation distance obtained by the acquisition step is greater than or equal to the threshold, the amount of ink ejected from either one or both of the third nozzle and the fourth nozzle is reduced based on the first separation distance, and if the first separation distance is less than the threshold, the amount of ink ejected from either one or both of the third nozzle and the fifth nozzle is increased based on the second separation distance between the third nozzle and the fifth nozzle in the width direction. [Explanation of symbols]

[0084] 1 cabinet 2 Sheet transport section 3 Image forming unit 4. Conveyor Unit 5 Operation display section 6 Memory section 7 Main Control Unit 8. Engine Control Unit 30 line heads 36 Recording head 37 nozzles 61 Acquisition Processing Unit 62 First setting processing unit 63 Adjustment Processing Unit 64 Second Configuration Processing Unit 100 Image forming apparatus

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 overlaps with a portion of the plurality of first nozzles in the width direction on a specific direction along the width direction from the first discharge unit, and the second discharge unit discharges the ink from each of the second nozzles, An acquisition processing unit that acquires a first separation distance in the width direction between a third nozzle included in the overlapping portion of a plurality of first nozzles with a plurality of second nozzles and a fourth nozzle that is the closest to the third nozzle among the second nozzles located on the side of the third nozzle in the specific direction, If the first separation distance acquired by the acquisition processing unit is greater than or equal to a predetermined threshold, the first setting processing unit sets the area from the fourth nozzle on the specific direction side of the plurality of second nozzles to the area used for ink ejection, and if the first separation distance is less than the threshold, the first setting processing unit sets the area from the fifth nozzle adjacent to the fourth nozzle on the specific direction side of the plurality of second nozzles to the area on the specific direction side of the fourth nozzle, An adjustment processing unit that, if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, reduces the amount of ink discharged from either one or both of the third nozzle and the fourth nozzle based on the first separation distance, and increases the amount of ink discharged from either one or both of the third nozzle and the fifth nozzle based on the second separation distance between the third nozzle and the fifth nozzle in the width direction, An image forming apparatus equipped with the following features.

2. The adjustment processing unit, if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, reduces the amount of ink discharged from either the third nozzle or the fourth nozzle based on the first separation distance, and if the first separation distance is less than the threshold, increases the amount of ink discharged from either the third nozzle or the fifth nozzle based on the second separation distance. When the first separation distance is less than the threshold, the adjustment processing unit increases the ink discharge amount of either the third nozzle or the fifth nozzle, such that the area S' of the dot formed by the nozzle whose ink discharge amount is increased among the third nozzle and the fifth nozzle satisfies the following condition (1), with Δ being the nozzle spacing between the first and second discharge units, δ' being the second separation distance, and S being the dot area determined according to the grayscale of the pixels. The image forming apparatus according to claim 1. S'=S*δ' / Δ... (1)

3. The adjustment processing unit, if the first separation distance acquired by the acquisition processing unit is greater than or equal to the threshold, reduces the amount of ink discharged from both the third nozzle and the fourth nozzle based on the first separation distance, and if the first separation distance is less than the threshold, increases the amount of ink discharged from both the third nozzle and the fifth nozzle based on the second separation distance. When the first separation distance is less than the threshold, the adjustment processing unit increases the amount of ink ejected from both the third nozzle and the fifth nozzle, such that the area S' of each dot formed by the third nozzle and the fifth nozzle satisfies the following conditional equation (2), with Δ being the nozzle spacing between the first and second ejection units, δ' being the second separation distance, and S being the dot area determined according to the grayscale of the pixels. The image forming apparatus according to claim 1. S'=S*(1+δ' / Δ) / 2... (2)

4. The system includes a second setting processing unit that sets the threshold based on the type of sheet. An image forming apparatus according to any one of claims 1 to 3.

5. An adjustment 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 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 on a specific direction side of the width direction from the first discharge unit and discharges the ink from each of the second nozzles; A step of obtaining a first separation distance in the width direction between a third nozzle included in the overlapping portion of a plurality of first nozzles with a plurality of second nozzles and a fourth nozzle that is the closest to the third nozzle among the second nozzles located on the side of the third nozzle in the specific direction, If the first separation distance obtained by the acquisition step is greater than or equal to a predetermined threshold, the area from the fourth nozzle on the side in the specific direction among the plurality of second nozzles is set as the usage area used for ejecting the ink; if the first separation distance is less than the threshold, the area from the fifth nozzle adjacent to the fourth nozzle on the side in the specific direction among the plurality of second nozzles is set as the usage area; If the first separation distance obtained by the acquisition step is greater than or equal to the threshold, the amount of ink discharged from either one or both of the third nozzle and the fourth nozzle is reduced based on the first separation distance, and if the first separation distance is less than the threshold, the amount of ink discharged from either one or both of the third nozzle and the fifth nozzle is increased based on the second separation distance between the third nozzle and the fifth nozzle in the width direction is an adjustment step. Adjustment methods including those mentioned.

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