JP6922589B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Conventionally, a continuous paper printing apparatus that performs a printing process on continuous paper has been known. Some continuous paper printing devices can perform double-sided printing by performing a printing process on the back surface after a drying or fixing process is performed after the printing process on the front surface.

In such a continuous paper printing apparatus capable of double-sided printing, the paper may expand and contract due to drying or fixing treatment after the printing treatment of the front surface. When the paper expands and contracts, there may be a problem that the printed image on the back side is displaced from the printed image on the front side.

Conventionally, in view of the above problems, a technique has been proposed in which the size of the image to be printed on the back surface is corrected and then the back surface is printed (for example, Patent Document 1).

JP 2011-12137A

In double-sided printing on continuous paper, generally, the front side page image is printed on the front side of the continuous paper, and the start position indicating the start position (upper end position of the page image) of the front side page image is shown. The indicator is printed. The start position of the back page image is determined based on the start position index. As a result, the positions of the front page image and the back page image in the paper transport direction are aligned.

On the other hand, in printing on continuous paper, from the viewpoint of effectively utilizing the paper surface of the continuous paper, a plurality of page rows each consisting of a plurality of page images corresponding to a plurality of printing commands (jobs) are formed on the continuous paper. It may be printed side by side in the width direction.

Conventionally, even when a plurality of page rows are arranged side by side in the paper width direction for printing on the front side and the back side of continuous paper, the above-mentioned start position index is used for each page included in one of the page rows. Only the ones related to the image were printed.

Here, when the page length (length in the paper transport direction) of the page image included in one page column on which the start position index is printed and the page length of the page image included in the other page columns are different from each other, the relevant case is concerned. There may be a problem that the page image contained in another page column is interrupted. This will be described with reference to FIGS. 5 and 6.

FIG. 5A shows the state of the continuous paper immediately after the front surface printing in the conventional case. In the example of FIG. 5A, there are two page columns, the first page column includes table pages 1-1 and 1-2, and the second page column includes table pages 2-1 and 2. -2 and 2-3 are included. As described above, only the start position index MK related to each page image included in the first page column is printed. The start position index MK is generally printed at the start position of each page image in the paper transport direction.

As shown in FIG. 5A, the page length, which is the length of each page image included in the front surface first page column in the paper transport direction, and each page included in the front surface second page column. The page length of the image is different. As a result, the start position of the page image in the front surface first page row in the paper transport direction may be in the middle of the page image included in the front surface second page row. In the example of FIG. 5A, the start position of the table page 1-1 and the start position of the table page 2-1 are the same, but the start position of the table page 1-2 is the paper of the table page 2-2. It is in the middle position in the transport direction (center position in this example). In the example of FIG. 5A, the page length of each page image included in the front surface first page column is the same, and the page length of each page image included in the front surface second page column is the same. Is the same.

FIG. 5B shows the state of continuous paper after the front surface printing and the drying treatment. As can be seen by comparing FIG. 5 (a) and FIG. 5 (b), the continuous paper is shrunk in the paper transport direction due to the drying process.

FIG. 6 shows how the back side page image is printed on the back side of the continuous paper that has been shrunk by the drying process. In FIG. 6, the page row described as "back side first page row" indicates the state of the back side first page row when the continuous paper is viewed from the back, and the page described as "back side second page row". The columns show the state of the second page column on the back surface when the continuous paper is viewed from the back. The back side first page row is printed on the back side of the front side first page row, and the back side second page row is printed on the back side of the front side second page row. be.

When printing the back page image, the continuous paper printing device reads the start position index MK printed on the front surface by a sensor, so that the back page image can be printed from the position determined based on the start position index MK. Start printing. In the examples of FIGS. 5 and 6, since the start position index MK is printed at the start position of the front page image, the continuous paper printing device prints the back page image from the position of the start position index MK. Become.

Since the continuous paper has shrunk due to the drying process, the page length of the front page 1-1 on the continuous paper corresponds to the corresponding back page 1-1 (the page printed with "I" in FIG. 6). The longer one is longer. Therefore, the start position index MK of the front page 1-2 is detected while the back page 1-1 is being printed. Therefore, before the printing of the back page 1-1 is completed, the printing of the back page 1-2 (the page printed with "II" in FIG. 6) is started. As a result, the rear end portion of the back page 1-1 in the paper transport direction is interrupted without being printed. However, there are many cases where the rear end of the page image in the paper transport direction has a margin, and it can be easily dealt with by moving the content in the page image to the front side in the paper transport direction in advance. In many cases, the print interruption at the rear end of the page image in the paper transport direction is not a problem.

Next, pay attention to the second page column on the back side. Since the start position index MK for each page image in the second row on the front side is not printed, each page image in the second page row on the back side is also printed for each page image in the first page row on the front side. The print start position is determined based on the start position index MK. That is, since the start position of the front page 1-1 and the start position of the front page 2-1 are the same, the same position as the start point of the back page 1-1 based on the start position index MK regarding the front page 1-1. Then, printing of the back page 2-1 (the page printed with "1" in FIG. 6) is started. Since the page length of each page image of the back side 2nd page row is shorter than the page length of each page image of the back side 1st page row, when the printing of the page image of the 1st page of the back side 2nd page row is completed, the back side first In the second page row, the page image of the second page (the page printed with "2" in FIG. 6) is continuously started.

The following points are problematic. Since the start position of table page 1-2 is the middle position of table page 2-2 in the paper transport direction (center position in this example), table page 1- When the start position index MK with respect to 2 is detected, printing of the back page 2-2 is interrupted at the same position as the start position of the back page 1-2, and the center of the back page 2-2 in the paper transport direction from that position. Printing will start from the position. Since the start position of the back page 2-2 is behind the start position of the front page 2-2 due to the shrinkage of the continuous paper, the start position index MK for the front page 1-2 is detected. At the timing, the printing of the back page 2-2 has not reached the center position. As a result, as shown in FIG. 6, printing is interrupted in the middle of the back page 2-2 (a part of the back page 2-2 is not printed).

An object of the present invention is a plurality of page columns corresponding to a plurality of printing commands on the front surface and the back surface of continuous paper, the page length of a page image included in one page column, and another page sequence. This is to prevent the page image from being interrupted in the middle of the page image when a plurality of page rows having different page lengths are arranged side by side in the paper width direction of the continuous paper.

The invention according to claim 1 is a plurality of page rows corresponding to a plurality of printing commands on the front surface and the back surface of continuous paper, and the length of a page image included in one page row in the paper transport direction. An image forming apparatus for forming a plurality of page rows having different page lengths and page lengths of page images included in other page rows in the width direction of the continuous paper. A plurality of front surface page rows are printed on the front surface, and a start position index indicating the start position of each front surface page image included in the plurality of front surface page rows is printed. A front side printing unit, a detection unit that detects each start position index corresponding to each front side page image, and a back side printing unit that prints a plurality of back side page rows on the back side of the continuous paper. Therefore, printing of each back page image included in the plurality of back page rows from a position determined based on each start position index corresponding to each front page image detected by the detection unit. It is an image forming apparatus including a back side printing unit which starts the process.

The invention according to claim 2 is a raster data generation unit that generates raster data for each page image, and includes page column information indicating which page column of the plurality of page columns the page image is included in. The image forming apparatus according to claim 1, further comprising a raster data generation unit for generating raster data.

The image according to claim 2, wherein the invention according to claim 3 further includes a plurality of page buffers corresponding to the plurality of page rows and storing the raster data related to the corresponding page rows, respectively. It is a forming device.

The invention according to claim 4 is a raster data generation unit that generates raster data for each page image, and prints on the back surface of the front page image based on the print rate of the front page image. The image forming apparatus according to claim 1, further comprising a raster data generation unit that adjusts the page length of the back page image to be generated and generates raster data of the back page image.

According to the invention according to claim 1, 2 or 3, a plurality of page rows corresponding to a plurality of printing commands on the front surface and the back surface of continuous paper, and page images included in one page row. When multiple page columns with different page lengths and page lengths of page images included in other page columns are arranged side by side in the paper width direction of continuous paper, it is possible to prevent the page image from being interrupted. can.

According to the invention of claim 4, it is possible to suppress the interruption of the rear end portion of the page image on the back surface.

It is a block diagram of the image forming apparatus which concerns on this embodiment. It is a figure which shows the appearance that the registration mark corresponding to each front surface page image of each front surface page row was printed. It is a figure which shows the appearance that each backside page image of each backside page row was printed based on the registration mark corresponding to each front side page image. It is a flowchart which shows the process flow of the image forming apparatus which concerns on this embodiment. It is a figure which shows the conventional example of the registration mark printed on the front surface. It is a figure which shows the state that the middle of the back page image is interrupted.

Hereinafter, embodiments of the present invention will be described.

FIG. 1 shows a schematic configuration diagram of the image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 is a continuous paper printer, which sequentially prints on the continuous paper to be conveyed, and cuts the continuous paper after printing if necessary.

The image forming apparatus 10 according to the present embodiment can print a plurality of print jobs as a plurality of print commands at the same time. That is, the image forming apparatus 10 prints a plurality of page rows corresponding to a plurality of print jobs side by side in the paper width direction of continuous paper. Further, the image forming apparatus 10 is capable of double-sided printing on the front side and the back side of continuous paper. That is, the image forming apparatus 10 can print a plurality of page rows arranged in the paper width direction on each of the front surface and the back surface. In this specification, an example in which the image forming apparatus 10 prints two page rows (first page row and second page row) on the front surface and the back surface, respectively, will be described. The number is not limited to this.

Each page row is composed of a plurality of page images arranged in the paper transport direction. Further, in the present embodiment, the page length (hereinafter referred to as "FCB (Forms Control Buffer) length"), which is the length of each page image (front side and back surface) included in the first page column in the paper transport direction, is described. The FCB length of each page image (front side and back side) included in the second page column is the same, but each page image of the first page column and each page image of the second page column are the same. It is assumed that the FCB lengths of the page images are different from each other.

The DFE (Digital Front End) 12 executes a process for a print job input by the user. As shown in FIG. 1, the DFE 12 includes a raster data generation unit 14.

The raster data generation unit 14 generates raster data in a data format that can be processed by the front side printing unit 24 and the back side printing unit 30, which will be described later, by performing rasterization processing on the print job. In the present embodiment, the raster data generation unit 14 generates raster data for each page image. Further, the raster data generation unit 14 includes page column information indicating which page column of the plurality of page columns includes the page image corresponding to the raster data in the generated raster data. In the present embodiment, the raster data generation unit 14 has page column information indicating whether the page image corresponding to the raster data is included in the first page column or the second page column in the header unit of the raster data. Include. Specifically, each raster data generated from the first print job contains page column information indicating the first page column, and each raster data generated from the second print job indicates the second page column. Contains page column information.

The raster data generated by the raster data generation unit 14 is sent to the storage unit 16.

The storage unit 16 includes, for example, a hard disk, a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The storage unit 16 stores a program for operating each part of the image forming apparatus 10. Further, a plurality of page buffers corresponding to each page column are defined in the storage unit 16. In the present embodiment, as shown in FIG. 1, a first page buffer 18 corresponding to the first page column and a second page buffer 20 corresponding to the second page column are defined.

Each raster data is stored in either the first page buffer 18 or the second page buffer 20 based on the page string information included in the raster data. Specifically, the raster data corresponding to the first page column is stored in the first page buffer 18, and the raster data corresponding to the second page column is stored in the second page buffer 20.

The paper feeding device 22 is a device that conveys continuous paper toward each processing unit below the front surface printing unit 24. The paper feeding device 22 is configured to include, for example, a rotatable shaft, and the continuous paper is conveyed by rotating the shaft with the roll-shaped continuous paper set on the shaft.

The front side printing unit 24 is mainly on the front side of the continuous paper sent by the paper feed device 22 based on the raster data stored in the first page buffer 18 and the second page buffer 20. Print the face page image. In the present embodiment, the front surface printing unit 24 reads the raster data stored in the first page buffer 18 and prints each front surface page image included in the front surface first page column. At the same time, the raster data stored in the second page buffer 20 is read out, and each front page image included in the front page second page column is printed.

FIG. 2A shows a state in which a plurality of front surface page rows are printed by the front surface printing unit 24. As shown in FIG. 2A, the front page first page column includes the table page 1-1 and the table page 1-2, and the front surface second page column includes the table page. 2-1 and table pages 2-2 and table pages 2-3 are included. For example, "front page 1-2" means the front page image of the second page included in the front page first page column, and "front page 2-1" mainly means. It means the front page image of the first page included in the second page column.

As shown in FIG. 2A, the front page image (front pages 1-1 and 1-2) of the front page 1 row and the front page 2 row of the front page Since the FCB length is different from that of the front page images (front pages 2-1, 2-2 and 2-3), the start position of the front page image of the first page row of the front surface and the front surface The start position of the front page image of the second page column may be different. In the example of FIG. 2A, the start position of the table page 1-2 is the intermediate position of the table page 2-2.

The front surface printing unit 24 further prints the registration mark MK as a start position index indicating the start position of each front page image included in the plurality of front surface page rows. In the present embodiment, as shown in FIG. 2A, the registration mark MK is printed for each of the front page images (front pages 1-1 and 1-2) of the front page 1 row. Not only that, the registration mark MK is printed on each of the front page images (front pages 2-1, 2-2 and 2-3) of the front page 2 row.

In this embodiment, the registration mark MK is printed at the start position of each front page image. Specifically, for each front page image in the front page 1 row, the registration mark MK is printed on the upper left of the front page image, and each front page image in the front page 2 row is printed. The cash register mark MK is printed on the upper right of the image. As a result, each registration mark MK is printed along both ends in the width direction of the continuous paper. However, the position of the registration mark MK is not limited to the start position of each front page image, and as long as it indicates the start position of the corresponding front page image, it is more continuous than the corresponding front page image. It may be provided at another position as long as it is on the upstream side in the transport direction of. The registration mark MK corresponding to the first page row of the front surface and the registration mark MK corresponding to the second page row of the front surface may be marked differently from each other so as to be identifiable.

The dryer 26 is provided on the downstream side of the front surface printing unit 24 in the continuous paper transport path. The dryer 26 executes a process of drying the ink of the front page image printed by the front surface printing unit 24. For example, the dryer 26 dries the ink of the front page image with hot air. The drying process causes the continuous paper to expand and contract. As shown in FIG. 2B, in the present embodiment, the continuous paper is shrunk in the transport direction due to the drying process of the dryer 26.

The mark sensor 28 as a detection unit is provided on the downstream side of the dryer 26 in the continuous paper transport path. The mark sensor 28 detects the registration mark MK corresponding to each front surface page image printed by the front surface printing unit 24, and sends a notification signal for notifying that the registration mark MK has been detected. It is transmitted to the back side printing unit 30 described later. The mark sensor 28 is provided at a position where the registration mark MK printed on the front surface can be preferably read. As described above, in the present embodiment, since each registration mark MK is printed along both ends in the width direction of the continuous paper, the mark sensor 28 is used on the front surface of the continuous paper during the transport path of the continuous paper. It is provided at a position where the vicinity of both ends can be sensed. Specifically, mark sensors 28 are provided on one end side and the other end side of the front surface of the continuous paper, respectively. That is, the mark sensor 28 is a first mark sensor that detects the registration mark MK corresponding to each front page image of the front page first page row, and each main of the front surface second page row. It is configured to include a second mark sensor that detects the registration mark MK corresponding to the surface page image.

The back side printing unit 30 is provided on the downstream side of the dryer 26 in the continuous paper transport path. The back side printing unit 30 prints the back side page image on the back side of the continuous paper sent by the paper feeding device 22 based on the raster data stored in the first page buffer 18 and the second page buffer 20. In the present embodiment, the back side printing unit 30 reads the raster data stored in the first page buffer 18 and prints each back side page image included in the back side first page column, and together with this, the second page buffer 20 The raster data stored in is read out, and each back page page image included in the back surface second page column is printed.

The back side printing unit 30 starts printing each back side page image from a position determined based on the position of the registration mark MK detected by the mark sensor 28. Here, the back side printing unit 30 independently detects the registration mark MK, reads out raster data, and prints the back side page image on each back side page row.

Hereinafter, the processing of the back side printing unit 30 will be described with reference to FIG. In FIG. 3, the page row described as "back side first page row" indicates the state of the back side first page row when the continuous paper is viewed from the back, and the page described as "back side second page row". The columns show the state of the second page column on the back surface when the continuous paper is viewed from the back. The first page row on the back side is printed on the back side of the first page row on the front side, and the second page row on the back side is printed on the back side of the second page row on the front side. Is. Further, "back page 1-2" means a back page image of the second page included in the back page first page column.

In the present embodiment, when the mark sensor 28 detects the first registration mark MK corresponding to the front page first page row (that is, the registration mark MK corresponding to the front page 1-1), that is, the first When the mark sensor detects the first register mark MK, the back side printing unit 30 reads raster data corresponding to the back page 1-1 from the first page buffer 18 and back page 1 from the position of the detected register mark MK. Start printing -1. As a result, the start position of the front page 1-1 and the start position of the back page 1-1 match. Hereinafter, each time the mark sensor 28 (first mark sensor) detects the registration mark MK corresponding to the first page row on the front surface, the back surface printing unit 30 reads raster data from the first page buffer 18. Printing of the back page image is started from the position of the detected registration mark MK.

Similarly, when the mark sensor 28 detects the first registration mark MK corresponding to the second page row on the front surface (that is, the registration mark MK corresponding to the front page 2-1), that is, the second mark sensor. When the first registration mark MK is detected, the back side printing unit 30 reads raster data corresponding to the back page 2-1 from the second page buffer 20 and back page 2-1 from the position of the detected registration mark MK. Start printing. As a result, the start position of the front page 2-1 and the start position of the back page 2-1 match. Hereinafter, each time the mark sensor 28 (second mark sensor) detects the registration mark MK corresponding to the front surface second page row, the back surface printing unit 30 reads raster data from the second page buffer 20. Printing of the back page image is started from the position of the detected registration mark MK.

As described above, the back side printing unit 30 independently prints the back side first page row and the back side second page row. Specifically, referring to FIG. 3, after the printing of the back page 2-1 is completed, the second mark sensor detects the registration mark MK corresponding to the front page 2-2, so that the back page 2 is displayed. Printing of the back page 2-2 is started on the column side, but printing of the back page 1-1 is continued on the back page 1st page column side even after that. At that time, when viewed in the main scanning direction, the back page 1-1 and the back page 2-2 are printed at the same time. Then, after the printing of the back page 1-1 is completed, the first mark sensor detects the registration mark MK corresponding to the front page 1-2, so that the printing of the back page 1-2 is started. In that case, On the back side of the second page column side, printing of the back page 2-2 is continued. That is, the printing of the back page image in the back surface 1st page column is not affected by the registration mark MK printed on the front surface 2 page column, and the printing of the back page image in the back surface 2 page column is not affected. , It is not affected by the registration mark MK printed on the first page column of the front side.

As a result, as shown in FIG. 3, the problem that the back page image is interrupted, which is a conventional problem (see FIG. 6), is solved. As shown in FIG. 3, since the continuous paper is shrunk due to the drying process after printing the front page image, the rear end portion of each back page image in the paper transport direction is interrupted without being printed. .. However, as described above, the problem is that the rear end of the page image in the paper transport direction is often a margin, and the content in the page image is moved to the front side in the paper transport direction in advance. In many cases, it does not matter because it can be easily dealt with.

In addition, in order to suppress the printing interruption of the rear end portion of the back page image in the paper transport direction, the raster data generation unit 14 may generate raster data after adjusting the FCB length of each back page image. .. In the present embodiment, the continuous paper on which the front page image has been printed shrinks in the paper transport direction due to the drying process of the dryer 26, so that the raster data generation unit 14 shortens the FCB length of each back page image. By generating raster data above, it is possible to suppress print interruptions at the rear end of the back page image in the paper transport direction.

Here, the amount of shrinkage of the continuous paper corresponds to the printing rate of the front page image (the ratio of the area to which the ink is applied to the total area of the front page image). Specifically, the larger the print rate of the front page image, the larger the amount of shrinkage. Therefore, it is preferable that the raster data generation unit 14 determines the amount of shrinkage of the FCB length of the corresponding back page image based on the print rate of each front page image.

Returning to FIG. 1, the dryer 32 is provided on the downstream side of the back surface printing unit 30 in the continuous paper transport path. The dryer 32 executes a process of drying the ink of the back page image printed by the back side printing unit 30. For example, the dryer 32 dries the ink of the front page image with hot air.

The take-up device 34 is a device that winds up continuous paper that is printed by the front side printing unit 24 and the back side printing unit 30 and is conveyed. The take-up device 34 is configured to include, for example, a rotatable shaft, and winds the continuous paper by rotating the shaft with the roll-shaped continuous paper set on the shaft.

The outline of the configuration of the image forming apparatus 10 is as described above. According to the image forming apparatus 10, when printing a plurality of page rows having different FCB lengths of each page image on the front side and the back side of continuous paper, the middle of the back side page image is interrupted. Is prevented.

Hereinafter, the processing flow of the image forming apparatus 10 will be described with reference to the flowchart shown in FIG.

In step S10, the raster data generation unit 14 generates a plurality of raster data corresponding to each front page image and each back page image based on the two print jobs input by the user. Each raster data generated from the first print job contains page column information indicating the first page column, and each raster data generated from the second print job contains page column information indicating the second page column. Be done.

In step S12, the raster data generated in step S10 is stored in the first page buffer 18 or the second page buffer 20. The raster data corresponding to the first page column is stored in the first page buffer 18, and the raster data corresponding to the second page column is stored in the second page buffer 20.

In step S14, the front side printing unit 24 reads raster data corresponding to the front side page image from the first page buffer 18 and the second page buffer 20, and reads the raster data corresponding to the front side page image, and puts the front side first page sequence on continuous paper. And the second page row on the front side is arranged side by side in the paper width direction for printing. Here, the front side printing unit 24 prints the registration mark MK at the start position of each front side page image included in the front side first page row and the front side second page row.

In step S16, the drying process is executed by the dryer 26. As a result, the continuous paper shrinks in the paper transport direction. Hereafter, the back side printing process is started.

In step S18, the back side printing unit 30 determines whether or not the mark sensor 28 has detected the registration mark MK. If the mark sensor 28 does not detect the registration mark MK, the process returns to step S18 again. That is, the back side printing unit 30 waits until the mark sensor 28 detects the registration mark MK. When the mark sensor 28 detects the registration mark MK, the process proceeds to step S20.

In step S20, the back side printing unit 30 indicates that the registration mark MK detected by the mark sensor 28 corresponds to the first page row of the front surface or the second page row of the front surface. Determine if there is. In the present embodiment, when the first mark sensor detects the registration mark MK, it is determined that the registration mark MK corresponding to the first page column of the front surface is detected, and the second mark sensor detects the registration mark MK. If so, it is determined that the registration mark MK corresponding to the second page column of the front surface has been detected. If the registration mark MK corresponding to the first page row of the front surface is detected, the process proceeds to step S22, and if the registration mark MK corresponding to the second page row of the front surface is detected, the process proceeds to step S24.

In step S22, the back side printing unit 30 reads the raster data corresponding to the back side page image from the first page buffer 18, and the back side page image of the back side first page row from the start position indicated by the registration mark MK detected in step S18. To print.

In step S24, the back side printing unit 30 reads the raster data corresponding to the back side page image from the second page buffer 20, and the back side page image of the back side second page row from the start position indicated by the registration mark MK detected in step S18. To print.

When the back page image is printed in step S22 or S24 and the paper is conveyed, the drying process by the dryer 32 is executed in step S26.

In step S28, the back side printing unit 30 determines whether or not the back side printing process is completed. If the back side printing process is not completed, that is, if there is a back side page image that has not been printed yet, the process returns to step S18 again. Then, the processes of steps S18 to S28 are repeated until the back side printing process is completed. When it is determined in step S28 that the back side printing process is completed, the printing process of the print job is completed.

Although the embodiments according to the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

For example, in the present embodiment, the front surface printing unit 24 prints the front surface page image and then the drying process is performed by the dryer 26. However, in the case of a laser printer, the front surface printing is performed after the front surface printing. The continuous paper also expands and contracts due to the fixing process. Therefore, the present invention can be suitably applied to a laser printer having a fixing machine instead of the dryer 26.

10 Image forming device, 12 DFE, 14 Raster data generator, 16 Storage unit, 18 Page 1 buffer, 20 Page 2 buffer, 22 Paper feed device, 24 Front surface printing unit, 26, 32 Dryer, 28 Mark sensor, 30 back side printing unit, 34 winding device.

Claims (4)

On the front side and the back side of continuous paper, a page length that is a plurality of page rows corresponding to a plurality of printing commands and is a length of a page image included in one page row in the paper transport direction, and another page length. An image forming apparatus for forming a plurality of page rows having different page lengths from the page images included in the page rows in the paper width direction of the continuous paper.
A plurality of front side page rows are printed on the front side of the continuous paper, and a start indicating the start position of each front side page image included in the plurality of front side page rows is started. The front side printing section that prints the position index, and
A detection unit that detects each start position index corresponding to each front page image, and
It is a back surface printing unit that prints a plurality of back surface page rows on the back surface of the continuous paper, and is determined based on each start position index corresponding to each front surface page image detected by the detection unit. From the position, the back side printing unit that starts printing each back side page image included in the plurality of back side page rows, and
An image forming apparatus comprising. A raster data generation unit that generates raster data for each page image, and generates raster data that includes page column information indicating which page column of the plurality of page columns the page image is included in. With more parts,
The image forming apparatus according to claim 1. A plurality of page buffers corresponding to the plurality of page columns and storing the raster data related to the corresponding page columns are further provided.
The image forming apparatus according to claim 2. A raster data generator that generates raster data for each page image, and the page length of the back page image printed on the back side of the front page image based on the print rate of the front page image. Is further provided with a raster data generation unit that generates raster data of the back page image.
The image forming apparatus according to claim 1.

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