JP2020179557A - Image forming device and image forming method - Google Patents

Abstract

To provide an image forming device and an image forming method that can improve accuracy in registering of the front and back sides in an image formed by an inkjet method.SOLUTION: The image forming device comprises: a printing processing part 84 that generates multiple copies of a plurality of printed sheets having images formed on both sides thereof respectively; a detection processing part 85 that when each of the plurality of printed sheets in the first copy is generated, detects sizes of the sheet at first timing before when a first image is formed on the front side of the printed sheet and at second timing before when a second image is formed on the back side of the printed sheet after the first image is formed, respectively; and an expansion/contraction processing part 83 that expands and contracts the second image formed on each of the plurality of printed sheets in the second copy and thereafter, on the basis of a detected result by the detection processing part 85.SELECTED DRAWING: Figure 3

Description

The present invention relates to an inkjet image forming apparatus and an image forming method.

An image forming apparatus such as a printer capable of forming an image based on image data on both sides of a sheet is known. Further, the amount of expansion and contraction of the sheet by forming an image on the front surface of the sheet is calculated, and the image data corresponding to the image formed on the back surface of the sheet transported after the sheet based on the calculated expansion and contraction amount. An electrophotographic image forming apparatus for correcting the above is known as a prior art (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-777977

By the way, in an inkjet type image forming apparatus, the amount of expansion and contraction of the sheet by forming an image on the surface of the sheet changes according to the amount of ink used for forming the image. That is, in the inkjet type image forming apparatus, when a plurality of double-sided printed sheets having different print contents are generated, the sheet is formed by forming an image on the surface of each sheet on which double-sided printing is performed. The amount of expansion and contraction is different. Therefore, in the above-mentioned prior art in which the calculated expansion / contraction amount is uniformly applied to the second and subsequent sheets, it is not possible to accurately register the front and back surfaces in the inkjet image forming apparatus.

An object of the present invention is to provide an image forming apparatus and an image forming method capable of improving the accuracy of registering the front and back sides of an image formed by an inkjet method.

The image forming apparatus according to one aspect of the present invention includes an image forming unit, a printing processing unit, a detection processing unit, and an expansion / contraction processing unit. The image forming unit forms an image based on image data on a sheet using a developing agent. The print processing unit controls the image forming unit to generate a plurality of printed sheets in which the image is formed on both sides of the image forming unit. When each of the plurality of printed sheets of the first copy is generated, the detection processing unit is the first of the two first images and the second images formed on the printed sheet, the first of which is formed in the order of formation. At each of the first timing before the one image is formed and the second timing after the first image is formed on the printed sheet and before the second image is formed after the formation order. The size of the sheet on which the first image and the second image are formed is detected. The expansion / contraction processing unit expands / contracts the second image formed on each of the plurality of printed sheets in the second and subsequent parts based on the detection result by the detection processing unit.

The image forming method according to another aspect of the present invention is executed by an image forming apparatus including an image forming portion for forming an image based on image data on a sheet using a developer, and the following printing step, detection step, and Including telescopic steps. In the printing step, the image forming unit is controlled to generate a plurality of printed sheets in which the image is formed on both sides of each. In the detection step, when each of the plurality of printed sheets in the first copy is generated, the first of the two first images and the second images formed on the printed sheets is formed first. The said at each of the first timing before the image is formed and the second timing after the first image is formed on the printed sheet and before the second image is formed after the formation order. The size of the sheet on which the first image and the second image are formed is detected. In the expansion / contraction step, the second image formed on each of the plurality of printed sheets in the second and subsequent copies is expanded / contracted based on the detection result of the detection step.

According to the present invention, it is possible to improve the accuracy of registering the front and back sides of an image formed by an inkjet method.

FIG. 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of an image forming unit of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a block diagram showing a system configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the amount of ink used for forming an image and the amount of expansion and contraction of the sheet. FIG. 5 is a flowchart showing an example of a printed sheet generation process executed by the image forming apparatus according to the embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiments are examples that embody the present invention, and do not limit the technical scope of the present invention.

[Structure of image forming apparatus 10]
First, the configuration of the image forming apparatus 10 according to the embodiment of the present invention will be described with reference to FIGS. 1 to 3. Here, FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 10. Further, FIG. 2 is a plan view showing the configuration of the image forming unit 3. In FIG. 1, the sheet transport paths R1, R2, and R3 are indicated by the alternate long and short dash lines.

The image forming apparatus 10 is a printer capable of forming an image on both sides of a sheet by an inkjet method. The present invention may be applied to an image forming apparatus such as a facsimile machine, a copier, and a multifunction device capable of forming an image by an inkjet method.

As shown in FIGS. 1 and 3, the image forming apparatus 10 includes a housing 1, a sheet conveying unit 2, an image forming unit 3, a conveying unit 4, an image reading unit 5, an operation display unit 6, a storage unit 7, and a storage unit 7. A control unit 8 is provided.

The housing 1 houses each component of the image forming apparatus 10. A paper cassette 11 is detachably provided on the housing 1. The paper cassette 11 houses a sheet to be printed. For example, the sheets housed in the paper cassette 11 are sheet materials such as paper, coated paper, postcards, envelopes, and transparencies. A paper output tray 12 is provided on the outer surface of the housing 1. The sheet on which the image is formed by the image forming unit 3 is discharged to the paper ejection tray 12.

Inside the housing 1, sheet transport paths R1, R2, and R3 for guiding the sheets transported by the sheet transport unit 2 are provided. The sheet transport path R1 is a passage for moving sheets from the paper feed cassette 11 to the paper output tray 12 via the image forming unit 3. The sheet transport path R2 is used for reversing the sheet on which the image is formed by the image forming unit 3. The sheet transport path R3 is used for re-transporting the sheet inverted using the sheet transport path R2 to the image forming unit 3.

The sheet transport unit 2 transports the sheet inside the housing 1. As shown in FIG. 1, the sheet transport unit 2 includes a pickup roller 21, a first transport roller pair 22, a second transport roller pair 23, and a third transport roller pair 24.

The pickup roller 21 takes out the sheets one by one from the paper cassette 11, and sends the sheets to the sheet transport path R1. The first transport roller pair 22 is provided in the sheet transport path R1 and transports the sheet in the transport direction D1 (see FIG. 1). The second transport roller pair 23 is provided in the sheet transport path R2, transports the sheet in the transport direction D2 (see FIG. 1), and then transports the sheet in the direction opposite to the transport direction D2, and transports the sheet in the sheet transport path R3. Send to. The third transfer roller pair 24 is provided in the sheet transfer path R3, and transfers the sheet in the transfer direction D3 (see FIG. 1).

The image forming unit 3 forms an image based on the image data on the sheet supplied from the sheet conveying unit 2 by using the ink which is a developing agent. As shown in FIG. 1, the image forming unit 3 includes line heads 31, 32, 33, 34 corresponding to each color of black, cyan, magenta, and yellow, and a head frame 35 supporting them. The head frame 35 is supported by the housing 1. The number of line heads included in the image forming unit 3 may be one, or may be a plurality of line heads excluding 4.

The line heads 31 to 34 are so-called line head type recording heads. That is, the image forming apparatus 10 is a so-called line head type image forming apparatus. As shown in FIG. 2, the line heads 31 to 34 are elongated in the width direction D4 orthogonal to the transport direction D1. Specifically, each of the line heads 31 to 34 has a length corresponding to the width of the maximum size sheet among the sheets that can be accommodated in the paper cassette 11 in the width direction D4. Each of the line heads 31 to 34 is fixed to the head frame 35 at a predetermined interval along the transport direction D1.

As shown in FIG. 2, each of the line heads 31 to 34 has a plurality of recording heads 30. The recording head 30 ejects ink toward the sheet conveyed by the transfer unit 4. Specifically, a large number of nozzles 30A (see FIG. 2) for ejecting ink having openings are provided on the surface of the recording head 30 facing the sheet conveyed by the transfer unit 4. Further, the recording head 30 has a pressurizing chamber (not shown) corresponding to each of the nozzles 30A, a piezoelectric element (not shown) provided corresponding to each of the pressurizing chambers, and a communication flow communicating with each of the pressurizing chambers. It has a road (not shown). The piezoelectric element ejects ink from the nozzle 30A in response to the application of a predetermined drive voltage. Specifically, the piezoelectric element pressurizes the ink contained in the pressurizing chamber to eject the ink from the nozzle 30A.

In the present embodiment, in the line head 31, three recording heads 30 are arranged in a staggered pattern along the width direction D4. Further, in each of the other line heads 32 to 34, similarly to the line head 31, three recording heads 30 are arranged in a staggered pattern along the width direction D4. Ink of the same color as the color corresponding to the line head is supplied to each of the line heads 31 to 34 from an ink container (not shown). Note that FIG. 2 shows a state in which the image forming unit 3 is viewed from the upper side of FIG.

As shown in FIG. 1, the transport unit 4 is arranged below the line heads 31-34. The transport unit 4 transports the sheet while facing the recording head 30. Specifically, the transport unit 4 transports the sheet by a predetermined transport amount each time the ink is ejected by the recording head 30. Further, the transport unit 4 stops transporting the sheet while the ink is being ejected by the recording head 30. As shown in FIG. 1, the transport unit 4 includes a transport belt 41 on which a sheet is placed, tension rollers 42 to 44 for tensioning the transport belt 41, and a transport frame 45 for supporting these. The gap between the transport belt 41 and the recording head 30 is adjusted so that, for example, the gap between the surface of the sheet and the recording head 30 at the time of image formation is 1 mm.

The tension roller 42 is rotationally driven by a rotational driving force supplied from a motor (not shown). As a result, the transfer belt 41 rotates in the direction in which the sheet can be conveyed in the transfer direction D1 (see FIG. 1). The transport unit 4 is also provided with a suction unit (not shown) that sucks air from a large number of through holes formed in the transport belt 41 in order to attract the sheet to the transport belt 41. Further, a pressure roller 46 for pressing the sheet against the transport belt 41 and transporting the sheet is provided at a position facing the tension roller 42.

The image reading unit 5 reads the image of the sheet at the reading position P1 (see FIG. 1) on the upstream side of the image forming unit 3 in the sheet transport path R1 in the transport direction D1.

Specifically, as shown in FIGS. 1 and 3, the image reading unit 5 includes a line sensor 51 and an AFE (analog front end) circuit 52.

The line sensor 51 is provided so as to face the sheet transported along the sheet transport path R1. The line sensor 51 can read monochrome image data for one line along the main scanning direction in the same direction as the width direction D4 from the sheet passing through the reading position P1. For example, the line sensor 51 is an image sensor such as a CIS (contact image sensor) including a light emitting unit and a light receiving unit. The light emitting unit emits one line of light along the main scanning direction toward the reading position P1. The light receiving unit is provided so as to be able to receive the light emitted from the light emitting unit and reflected by the sheet passing through the reading position P1, and outputs an analog electric signal according to the amount of light received. The line sensor 51 outputs an analog electric signal corresponding to one line of image data along the main scanning direction from the light receiving unit at predetermined intervals according to the control signal input from the control unit 8. ..

The AFE circuit 52 is an electronic circuit that converts an analog electric signal output from the light receiving portion of the line sensor 51 into a digital electric signal (image data). For example, the AFE circuit 52 converts an analog electric signal output from the light receiving unit into image data represented by 256 gradations in which the pixel density is 0 to 255. The AFE circuit 52 outputs the converted image data to the control unit 8.

The operation display unit 6 includes a display unit such as a liquid crystal display that displays various information in response to a control instruction from the control unit 8, and an operation key or touch panel that inputs various information to the control unit 8 in response to a user operation. It has an operation unit such as. The operation display unit 6 is provided on the upper surface of the housing 1.

The storage unit 7 is a non-volatile storage device. For example, the storage unit 7 is a flash memory, a non-volatile memory such as EEPROM (registered trademark), an SSD (solid state drive), and a storage device such as an HDD (hard disk drive).

The control unit 8 includes control devices such as a CPU 8A, a ROM 8B, and a RAM 8C. The CPU 8A is a processor that executes various arithmetic processes. The ROM 8B is a non-volatile storage device in which information such as a control program for causing the CPU 8A to execute various processes is stored in advance. The RAM 8C is a volatile storage device used as a temporary storage memory (work area) for various processes executed by the CPU 8A. In the control unit 8, various control programs stored in advance in the ROM 8B are executed by the CPU 8A. As a result, the image forming apparatus 10 is collectively controlled by the control unit 8. The control unit 8 may be composed of an electronic circuit such as an integrated circuit (ASIC), and is a control unit provided separately from the main control unit that collectively controls the image forming apparatus 10. You may.

By the way, the amount of expansion and contraction of the sheet by forming an image on the front surface of the sheet is calculated, and the image data corresponding to the image formed on the back surface of the sheet conveyed after the sheet based on the calculated amount of expansion and contraction. An electrophotographic image forming apparatus for correcting the above is known as a prior art.

On the other hand, in the inkjet type image forming apparatus, the amount of expansion and contraction of the sheet by forming an image on the surface of the sheet changes according to the amount of ink used for forming the image. That is, in the inkjet type image forming apparatus, when a plurality of double-sided printed sheets having different print contents are generated, the sheet is formed by forming an image on the surface of each sheet on which double-sided printing is performed. The amount of expansion and contraction is different. Therefore, in the above-mentioned prior art in which the calculated expansion / contraction amount is uniformly applied to the second and subsequent sheets, it is not possible to accurately register the front and back surfaces in the inkjet image forming apparatus.

On the other hand, in the image forming apparatus 10 according to the embodiment of the present invention, as described below, it is possible to improve the accuracy of registering the front and back sides of the image formed by the inkjet method.

Specifically, the ROM 8B of the image forming apparatus 10 stores in advance a printed sheet generation program for causing the CPU 8A of the control unit 8 to execute the printed sheet generation process (see the flowchart of FIG. 5) described later. The printed sheet generation program is recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and installed in the storage unit 7.

Then, as shown in FIG. 3, the control unit 8 includes a second acquisition processing unit 81, a first acquisition processing unit 82, an expansion / contraction processing unit 83, a printing processing unit 84, a detection processing unit 85, an update processing unit 86, and The recording processing unit 87 is included. Specifically, the control unit 8 uses the CPU 8A to execute the printed sheet generation program stored in the ROM 8B. As a result, the control unit 8 functions as a second acquisition processing unit 81, a first acquisition processing unit 82, an expansion / contraction processing unit 83, a printing processing unit 84, a detection processing unit 85, an update processing unit 86, and a recording processing unit 87. ..

The second acquisition processing unit 81 sets a predetermined standard for each of the first direction orthogonal to the paper grain and the second direction along the paper grain based on the size of the sheet to be printed and the grain of the sheet. Obtain the amount of expansion and contraction.

Here, the reference expansion / contraction amount indicates the expansion / contraction amount of the sheet when a predetermined specific image is formed on the sheet using a predetermined reference amount of ink. For example, the reference amount is the upper limit of the amount of ink that can be absorbed in the sheet to be printed. For example, the reference expansion / contraction amount is the ratio of the size of the sheet after forming the specific image to the size of the sheet before forming the specific image using the reference amount of ink.

For example, in the image forming apparatus 10, the combination of the size of the sheet to be printed and the grain of the sheet is associated with the reference expansion / contraction amount in each of the first direction and the second direction corresponding to the combination. The table data is stored in the storage unit 7 in advance. The table data can be created by measuring the size before and after absorbing the reference amount of ink for each sheet having a different combination of size and grain.

The second acquisition processing unit 81 uses the table data stored in the storage unit 7 in the first direction and the second direction corresponding to the combination of the size of the sheet to be printed and the grain of the sheet. The reference expansion / contraction amount for each is acquired.

The second acquisition processing unit 81 may acquire the reference expansion / contraction amount in only the first direction based on the size of the sheet to be printed and the grain of the sheet. Further, the second acquisition processing unit 81 acquires the reference expansion / contraction amount in each of the first direction and the second direction based on the type or basis weight of the sheet to be printed and the grain of the sheet. May be good. Further, the second acquisition processing unit 81 describes the first direction and the second direction, respectively, based on any one or more of the size, type, and basis weight of the sheet to be printed and the grain of the sheet. The reference expansion / contraction amount may be acquired.

The print processing unit 84 controls the sheet transport unit 2, the image forming unit 3, and the transport unit 4 to generate a printed sheet in which an image based on image data is formed on both sides.

Specifically, the print processing unit 84 controls the sheet transfer unit 2, the image forming unit 3, and the transfer unit 4 to form the image on the surface of the sheet. Next, the printing processing unit 84 controls the sheet transport unit 2 to invert the sheet by passing the sheet on which the image is formed on the surface through the sheet transport path R2 and the sheet transport path R3. Then, the print processing unit 84 controls the sheet transfer unit 2, the image forming unit 3, and the transfer unit 4 to form the image on the back surface of the sheet via the sheet transfer path R3.

For example, the print processing unit 84 generates a plurality of the printed sheets.

The print processing unit 84 may generate one copy of the plurality of printed sheets. Further, the print processing unit 84 may generate one or a plurality of the printed sheets.

The first acquisition processing unit 82 is based on the amount of ink used to form the first image, which is formed in the order of the two first images and the second images formed on the printed sheet. The amount of expansion and contraction of the sheet due to the formation of the first image is acquired for each of the one direction and the second direction.

For example, the first acquisition processing unit 82 uses the first amount of ink used to form the first image and the reference expansion / contraction amount corresponding to each of the first direction and the second direction. The amount of expansion and contraction of the sheet due to the formation of the first image is calculated for each of the direction and the second direction. The first acquisition processing unit 82 can calculate the amount of ink used to form the first image based on the image data corresponding to the first image.

Here, FIG. 4 shows the relationship between the amount of ink used to form the image and the amount of expansion and contraction of the sheet due to the formation of the image when the image is formed on the sheet using ink. The horizontal axis in FIG. 4 indicates the amount of ink used to form the image. The vertical axis in FIG. 4 indicates the amount of expansion and contraction of the sheet due to the formation of the image. As shown in FIG. 4, when an image is formed on a sheet using ink, the amount of expansion and contraction of the sheet due to the formation of the image is proportional to the amount of ink used for forming the image. Therefore, based on the amount of ink used to form the first image and the reference expansion / contraction amount corresponding to each of the first direction and the second direction, each of the first direction and the second direction. It is possible to calculate the amount of expansion and contraction of the sheet due to the formation of the first image.

Specifically, the first acquisition processing unit 82 can calculate the amount of expansion and contraction of the sheet due to the formation of the first image in the first direction by the following formula (1). In the formula (1), X indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the first direction. Further, in the formula (1), A represents the amount of ink used for forming the first image. Further, in the formula (1), L represents the reference expansion / contraction amount in the first direction. Further, in the formula (1), B represents the reference amount.

X = A × L ÷ B ... (1)

In addition, the first acquisition processing unit 82 can calculate the amount of expansion and contraction of the sheet due to the formation of the first image in the second direction by the following formula (2). In the formula (2), Y indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the second direction. Further, in the formula (2), A represents the amount of ink used for forming the first image. Further, in the formula (2), M represents the reference expansion / contraction amount in the second direction. Further, in the formula (2), B represents the reference amount.

Y = A × M ÷ B ・ ・ ・ (2)

For example, when the print processing unit 84 produces the first printed sheet, the first acquisition processing unit 82 determines the amount of ink used to form the first image and the second acquisition processing unit 81. The amount of expansion and contraction of the sheet due to the formation of the first image in each of the first direction and the second direction based on the reference expansion and contraction amount corresponding to each of the first direction and the second direction acquired by Is calculated.

Further, after the print processing unit 84 generates the first printed sheet, the first acquisition processing unit 82 updates the amount of ink used for forming the first image and the update processing unit 86. The amount of expansion and contraction of the sheet due to the formation of the first image is calculated for each of the first direction and the second direction based on the reference expansion and contraction amount corresponding to each of the first direction and the second direction. To do.

The first acquisition processing unit 82 may acquire the amount of expansion and contraction of the sheet due to the formation of the first image only in the first direction based on the amount of ink used for forming the first image. Further, the first acquisition processing unit 82 transmits the amount of ink used for forming the first image and the reference expansion / contraction amount corresponding to each of the first direction and the second direction to an external information processing device. Even if it is transmitted and the amount of expansion and contraction of the sheet due to the formation of the first image in each of the first direction and the second direction calculated by the external information processing device is acquired from the external information processing device. Good.

Further, the first acquisition processing unit 82 determines the amount of ink used for forming the first image and the second acquisition processing unit even after the print processing unit 84 has generated the first printed sheet. Based on the reference expansion and contraction amount corresponding to each of the first direction and the second direction acquired by 81, expansion and contraction of the sheet by forming the first image in each of the first direction and the second direction. The amount may be calculated. In this case, the control unit 8 does not have to include the detection processing unit 85 and the update processing unit 86.

Further, when only a sheet having a specific size and a specific grain is used for printing in the image forming apparatus 10, the first acquisition processing unit 82 has the first direction and the said first stored in the ROM 8B in advance. The amount of expansion and contraction of the sheet due to the formation of the first image may be calculated for each of the first direction and the second direction by using the pair of the reference expansion and contraction amounts corresponding to each of the second directions. In this case, the control unit 8 does not have to include the second acquisition processing unit 81.

The expansion / contraction processing unit 83 expands / contracts the second image after the formation order formed on the printed sheet based on the acquisition result by the first acquisition processing unit 82.

Specifically, the expansion / contraction processing unit 83 expands / contracts the second image by expanding / contracting the image data corresponding to the second image.

When the expansion / contraction processing unit 83 uses only a sheet having a grain orthogonal to the transport direction D1 in the image forming apparatus 10 for printing, the expansion / contraction processing unit 83 has a sub-scanning direction (in the sub-scanning direction by the image forming unit 3 at the time of forming the second image). The second image may be expanded and contracted in the transport direction D1 by changing the image formation interval in the transport direction D1). For example, the expansion / contraction processing unit 83 can change the image formation interval in the transport direction D1 by the image forming unit 3 by changing the transport amount of the sheet by the transport unit 4 at the time of forming the second image. .. In this case, the second acquisition processing unit 81 may acquire the reference expansion / contraction amount only in the first direction. In addition, the first acquisition processing unit 82 may acquire the amount of expansion and contraction of the sheet due to the formation of the first image only in the first direction.

When each of the plurality of printed sheets in the first copy is generated, the detection processing unit 85 has a first timing before the first image is formed on the sheet used for generating the printed sheet, and The size of the sheet is detected at each of the second timings after the first image is formed on the sheet and before the second image is formed. The "first copy" here may include proof printing and a trial copy.

Specifically, the detection processing unit 85 controls the image reading unit 5 to detect the size of the sheet at each of the first timing and the second timing.

The update processing unit 86 updates the reference expansion / contraction amount in each of the first direction and the second direction based on the amount of ink used for forming the first image and the detection result by the detection processing unit 85.

For example, the update processing unit 86 can update the reference expansion / contraction amount in the first direction by the following equation (3). In the formula (3), L'indicates the reference expansion / contraction amount after the update in the first direction. Further, in the formula (3), X'indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the first direction acquired based on the detection result by the detection processing unit 85. Further, in the formula (3), B represents the reference amount. Further, in the formula (3), A represents the amount of ink used for forming the first image. Further, in the formula (3), L represents the reference expansion / contraction amount before the update in the first direction. Further, in the formula (3), P indicates the number of printed sheets from the start of the process by the print processing unit 84.

L'= (X'x B ÷ A + L x (P-1)) ÷ P ... (3)

Further, the update processing unit 86 can update the reference expansion / contraction amount in the second direction by the following equation (4). In the formula (4), M'indicates the reference expansion / contraction amount after the update in the second direction. Further, in the formula (4), Y'indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the second direction acquired based on the detection result by the detection processing unit 85. Further, in the formula (4), B represents the reference amount. Further, in the formula (4), A represents the amount of ink used for forming the first image. Further, in the formula (4), M represents the reference expansion / contraction amount before the update in the second direction. Further, in the formula (4), P indicates the number of printed sheets from the start of the process by the print processing unit 84.

M'= (Y' × B ÷ A + M × (P-1)) ÷ P ... (4)

The update processing unit 86 may update the reference expansion / contraction amount in the first direction by the following formula (5). In the formula (5), L'indicates the reference expansion / contraction amount after the update in the first direction. Further, in the formula (5), X'indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the first direction acquired based on the detection result by the detection processing unit 85. Further, in the formula (5), B represents the reference amount. Further, in the formula (5), A represents the amount of ink used for forming the first image.

L'= X'x B ÷ A ... (5)

Further, the update processing unit 86 may update the reference expansion / contraction amount in the second direction by the following formula (6). In the formula (6), M'indicates the reference expansion / contraction amount after the update in the second direction. Further, in the formula (6), Y'indicates the amount of expansion and contraction of the sheet due to the formation of the first image in the second direction acquired based on the detection result by the detection processing unit 85. Further, in the formula (6), B represents the reference amount. Further, in the formula (6), A represents the amount of ink used for forming the first image.

M'= Y'x B ÷ A ... (6)

The recording processing unit 87 records the detection result by the detection processing unit 85 corresponding to each of the plurality of printed sheets in the first copy.

For example, the recording processing unit 87 stores the detection result information indicating the detection result by the detection processing unit 85 corresponding to the printed sheet in the storage unit 7 for each of the first printed sheets.

Here, the expansion / contraction processing unit 83 expands / contracts the second image formed on each of the first printed sheets based on the acquisition result by the first acquisition processing unit 82. Further, the expansion / contraction processing unit 83 expands / contracts the second image formed on each of the second and subsequent printed sheets based on the recording result by the recording processing unit 87.

The control unit 8 does not have to include the recording processing unit 87. In this case, the expansion / contraction processing unit 83 may also expand / contract the second image formed on each of the second and subsequent printed sheets based on the acquisition result by the first acquisition processing unit 82.

[Printed sheet generation process]
Hereinafter, with reference to FIG. 5, the procedure of the image forming method according to the present invention will be described together with an example of the procedure of the printed sheet generation processing executed by the control unit 8 in the image forming apparatus 10. Here, steps S11, S12 ... Represent the number of the processing procedure (step) executed by the control unit 8. The printed sheet generation process is executed when an execution instruction for a print process for generating a plurality of the printed sheets is input.

<Step S11>
First, in step S11, the control unit 8 acquires the reference expansion / contraction amount in each of the first direction and the second direction based on the size of the sheet to be printed and the grain of the sheet. Here, the process of step S11 is executed by the second acquisition processing unit 81 of the control unit 8.

Specifically, the control unit 8 uses the table data stored in the storage unit 7 to use the first direction and the second direction corresponding to the combination of the size of the sheet to be printed and the grain of the sheet. The reference expansion / contraction amount for each of the above is acquired.

<Step S12>
In step S12, the control unit 8 acquires two image data corresponding to the first image and the second image.

<Step S13>
In step S13, the control unit 8 applies the reference expansion / contraction amount for each of the first direction and the second direction acquired in step S11, and the image data corresponding to the first image acquired in step S12. Based on this, the amount of expansion and contraction of the sheet due to the formation of the first image is acquired for each of the first direction and the second direction. Here, the process of step S13 is executed by the first acquisition processing unit 82 of the control unit 8.

Specifically, the control unit 8 calculates the amount of ink used to form the first image based on the image data corresponding to the first image. Then, the control unit 8 calculates the amount of expansion and contraction of the sheet due to the formation of the first image in each of the first direction and the second direction by the equations (1) and (2).

<Step S14>
In step S14, the control unit 8 expands and contracts the image data corresponding to the second image acquired in step S12 based on the acquisition result in step S13. Here, the process of step S14 is executed by the expansion / contraction processing unit 83 of the control unit 8.

<Step S15>
In step S15, the control unit 8 generates the printed sheet based on the two image data acquired in step S12. Here, the processing of step S15 is an example of the printing step in the present invention, and is executed by the printing processing unit 84 of the control unit 8.

<Step S16>
In step S16, the control unit 8 forms the second image before the first image is formed in step S15 and after the first image is formed in step S15. The size of the sheet at each of the second timings before the operation is detected. Here, the processing of step S16 is an example of the detection step in the present invention, and is executed by the detection processing unit 85 of the control unit 8.

<Step S17>
In step S17, the control unit 8 determines each of the first direction and the second direction based on the amount of ink used for forming the first image calculated in step S13 and the detection result in step S16. The reference expansion / contraction amount is updated. Here, the process of step S17 is executed by the update processing unit 86 of the control unit 8.

Specifically, the control unit 8 updates the reference expansion / contraction amount in each of the first direction and the second direction according to the equations (3) and (4).

<Step S18>
In step S18, the control unit 8 records the detection result in step S16. Here, the process of step S18 is executed by the recording processing unit 87 of the control unit 8.

Specifically, the control unit 8 stores the detection result information indicating the detection result in step S16 corresponding to the printed sheet generated in step S15 in the storage unit 7.

<Step S19>
In step S19, the control unit 8 determines whether or not the printing of the first copy is completed.

Here, when the control unit 8 determines that the printing of the first copy is completed (Yes side of S19), the control unit 8 shifts the process to step S20. If the printing of the first copy is not completed (No side of S19), the control unit 8 shifts the process to step S12.

In this case, in step S12 to be executed again, the control unit 8 acquires two image data corresponding to the first image and the second image to be printed next. Further, in step S13 to be executed again, the control unit 8 has the reference expansion / contraction amount for each of the first direction and the second direction updated in step S17, and the first step acquired in the latest step S12. Based on the image data corresponding to one image, the amount of expansion and contraction of the sheet due to the formation of the first image is acquired in each of the first direction and the second direction. Further, in step S17 to be executed again, the control unit 8 updates the reference expansion / contraction amount in each of the first direction and the second direction again.

<Step S20>
In step S20, the control unit 8 prints a plurality of the first printed sheets in the printed sheet generation process based on the detection results in step S16 for each of the first printed sheets recorded in step S18. Each of the plurality of image data corresponding to the two images is expanded and contracted. Here, the process of step S20 is an example of the expansion / contraction step in the present invention, and is executed by the expansion / contraction processing unit 83 of the control unit 8.

<Step S21>
In step S21, the control unit 8 generates the printed data for the second and subsequent units. Here, the control unit 8 forms the second image by using the image data expanded and contracted in step S20.

The processes of step S18, step S20, and step S21 may be omitted. That is, in the printed sheet generation process, only one or more printed sheets may be generated.

Further, the processes of steps S16 and S17 may be omitted. That is, in the printed sheet generation process, the reference expansion / contraction amount acquired in step S11 may be used without being updated.

Further, the process of step S11 may be omitted. That is, in the printed sheet generation process, the expansion / contraction amount of the sheet due to the formation of the first image may be acquired by using the predetermined reference expansion / contraction amount.

As described above, in the image forming apparatus 10, the amount of ink used for forming the first image of the first image and the second image formed on the printed sheet of the first copy is the first. The amount of expansion and contraction of the sheet due to the formation of the first image is acquired based on the above. Further, in the image forming apparatus 10, based on the detection result of the expansion / contraction amount of the sheet by forming the first image in each of the plurality of printed sheets in the first part, the printed sheets in the second and subsequent parts are formed. The second image is expanded and contracted. Therefore, it is possible to improve the accuracy of registering the front and back sides of the image formed by the inkjet method.

1 Housing 2 Sheet transport unit 3 Image forming unit 4 Transport unit 5 Image reading unit 6 Operation display unit 7 Storage unit 8 Control unit 10 Image forming device 81 Second acquisition processing unit 82 First acquisition processing unit 83 Expansion and contraction processing unit 84 Printing Processing unit 85 Detection processing unit 86 Update processing unit 87 Recording processing unit

Claims (4)

An image forming unit that forms an image based on image data on a sheet using a developer,
A print processing unit that controls the image forming unit to generate a plurality of printed sheets on which the image is formed on both sides.
When each of the plurality of printed sheets in the first copy is generated, the first image having the first formation order among the two first images and the second images formed on the printed sheets is formed. The first image and the first image at each of the first timing before and the second timing after the first image is formed on the printed sheet and before the second image is formed after the formation order. A detection processing unit that detects the size of the sheet on which the second image is formed, and
Based on the detection result by the detection processing unit, the expansion / contraction processing unit that expands / contracts the second image formed on each of the plurality of printed sheets in the second and subsequent copies, and
An image forming apparatus comprising. The expansion / contraction processing unit expands / contracts the second image by expanding / contracting the image data corresponding to the second image.
The image forming apparatus according to claim 1. The expansion / contraction processing unit expands / contracts the second image in the sheet transport direction by changing the image formation interval in the sheet transport direction by the image forming section at the time of forming the second image.
The image forming apparatus according to claim 1. An image forming method executed by an image forming apparatus including an image forming portion for forming an image based on image data on a sheet using a developing agent.
A printing step of controlling the image forming unit to generate a plurality of printed sheets in which the image is formed on both sides thereof.
When each of the plurality of printed sheets in the first copy is generated, the first image having the first formation order among the two first images and the second images formed on the printed sheets is formed. The first image and the first image at each of the first timing before and the second timing after the first image is formed on the printed sheet and before the second image is formed after the formation order. A detection step for detecting the size of the sheet on which the second image is formed, and
Based on the detection result of the detection step, the expansion / contraction step of expanding / contracting the second image formed on each of the plurality of printed sheets in the second and subsequent copies,
Image forming method including.

Images