JP2013037087A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow output of an output paper density adjustment chart, and a sample image correction chart without decreasing productivity in an image forming apparatus that executes double-side alternate conveyance, and extend a life of the image forming apparatus.SOLUTION: In an image forming apparatus, a control unit causes an image forming unit to form an image of a single-sided correction chart during continuous image formation of front faces in double-sided image formation by double-side alternate conveyance, or in idle time between image formation of a precedent sheet and image formation of a subsequent sheet during continuous image formation of rear faces.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus capable of forming a double-sided image has a circulation path for reversing paper, and after one image surface of a document is formed on one surface (front surface) of the paper, the paper is reversed by the circulation path. Then, the reversed paper is fed again, and the other image surface of the original is image-formed on the other surface (back surface) of the paper.

  In such an image forming apparatus, a plurality of sheets can be built (held) in the circulation path and when double-sided image formation is started, as shown in FIG. After forming all the number of front-side images, the back side of the paper returned from the circulation path and the remaining front side are imaged alternately. Continuously performs image formation on the back side of the sheet returned from the circulation path (referred to as double-sided alternate conveyance). In the case of paper feeding in the double-sided alternate conveyance, in order to secure an interval for reversing the preceding paper in the circulation path, the following paper is generally fed with an interval of one paper.

  Various techniques for improving productivity in an image forming apparatus capable of forming a double-sided image have been proposed. For example, in Patent Document 1, when single-sided image formation and double-sided image formation are mixed, the first side of double-sided image formation is conveyed as much as possible in the circulation path, and then the single side and second side of double-sided image formation are arranged. A technique for forming an image according to a specified order is described. Further, in Patent Document 2, when the next document is single-sided and the next document is double-sided at the timing when the double-sided image formation is completed, if the number of single-sided sheets is smaller than the number of double-sided sheets, A technique is described in which double-sided image formation is continued by forming an image on one side and forming a blank image on the other side.

  On the other hand, in the image forming apparatus, in order to stabilize the finished quality of the image, as described in Patent Documents 3 and 4, image formation of an output paper density adjustment chart is performed for each predetermined number of printed sheets, and this is performed as a color sensor. The output paper density is adjusted by updating the γ correction curve. In addition, when a predetermined condition is satisfied, stabilization control is performed to stably supply image quality.

JP 2011-57409 A JP 2001-282050 A JP 2011-85780 A JP 2009-288389 A

  By the way, the above-described output paper density adjustment and stabilization control may be performed during a double-sided image forming job. In that case, it is necessary to form and output (that is, output) a sample image for adjusting the output paper density and a sample image for the user to confirm the machine state after the stabilization control. Conventionally, when it is time to output these correction charts at the start of a job or during a job, as shown in FIGS. 8A and 8B, the first image of the job is formed. Output was performed collectively before or after the last page of the job was ejected. For this reason, there has been a problem that productivity is reduced by the time required for outputting these correction charts.

In addition, the developing device and the photoconductor rotate idly when a paper feed interval is set to ensure time for reversing the paper in the circulation path. However, since this idling affects the life, the life is improved. In order to achieve this, it is necessary to feed paper so as to reduce this idling. Although it is possible to adopt a configuration in which the sheet feeding interval is not set, in this case, it is necessary to increase the conveyance speed of the circulation path, and the cost increases because a more expensive motor is used. In addition, since the motor repeatedly accelerates and decelerates according to the state of the roller that is biting the paper, it is not preferable because it leads to noise.
The techniques described in Patent Documents 1 to 4 cannot solve these problems.

  It is an object of the present invention to enable output sheet density adjustment charts and correction charts such as sample images to be output without reducing productivity in an image forming apparatus that performs double-sided alternating conveyance, and to improve the life of the image forming apparatus It is to plan.

In order to solve the above-mentioned problem, the invention described in claim 1
An image forming unit that forms an image on a sheet, a circulation path for inverting the front and back of the sheet during double-sided image formation, and a control unit for controlling the image forming unit, wherein the circulation path includes a plurality of sheets When the image forming unit performs continuous double-sided image formation in the image forming unit, the control unit sets an interval of at least one sheet so as to invert the paper in the circulation path. The front surface of the number of sheets that can be held in the circulation path while being vacant is continuously imaged, and then the image formation on the back surface of the paper returned from the circulation path and the image formation on the remaining surface are alternately performed. An image forming apparatus that continuously performs image formation on the back surface of the paper returned from the circulation path after all image formation is completed,
The control unit has a single-side correction chart in the empty time between the image formation of the preceding paper and the image formation of the subsequent paper during the continuous image formation of the front surface or the continuous image formation of the back surface. Image formation is performed.

The invention according to claim 2 is the invention according to claim 1,
With multiple output trays,
The control unit discharges the correction chart to a paper discharge tray different from the paper on which images are formed on both sides.

The invention according to claim 3 is the invention according to claim 1 or 2,
When the output paper density adjustment timing is reached during the double-sided image formation, the control unit causes the output paper density adjustment chart to be formed as the correction chart in the subsequent idle time.

The invention according to claim 4 is the invention according to claim 1 or 2,
When the stabilization control is performed during the double-sided image formation, the control unit causes the sample image to be formed as the correction chart in the subsequent idle time.

  According to the present invention, in an image forming apparatus that performs double-sided alternating conveyance, it is possible to output a correction chart such as an output paper density adjustment chart and a sample image without reducing productivity. In addition, it is possible to reduce the time during which the photoconductor rotates idly and improve the life of the image forming apparatus.

2 is a block diagram illustrating a functional configuration of the image forming apparatus. FIG. 1 is a diagram illustrating a schematic configuration example of an image forming apparatus. FIG. 6 is a diagram schematically illustrating a sheet conveyance path. It is a flowchart which shows the output control process A performed by the control part of FIG. 1 in 1st Embodiment. It is a figure which shows the correction chart output possible timing at the time of performing image formation based on the job of A4 size and 10 sheets on both sides by the output control processing A. It is a flowchart which shows the output control process B performed by the control part of FIG. 1 in 2nd Embodiment. It is a figure for demonstrating the conventional double-sided image formation. FIG. 10 is a diagram illustrating the output timing of a correction chart when the timing to output a correction chart has arrived during a double-sided image formation job in the prior art.

  The configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. In the embodiment of the present invention, the color image forming apparatus 1 will be described as an example. However, the present invention is not limited to this, and the present invention can be realized by, for example, a monochrome image forming apparatus. .

[First Embodiment]
(Configuration of image forming apparatus 1)
FIG. 1 shows a functional block diagram of the image forming apparatus 1. FIG. 2 shows a schematic configuration inside the image forming apparatus 1.
As shown in FIG. 1, the image forming apparatus 1 includes a control unit 10, an operation display unit 20, a storage unit 30, a communication unit 40, an image reading unit 50, an image processing unit 60, an image forming unit 70, a color sensor 80, and a rear sensor. A processing unit 90 and the like are provided, and each unit is connected via a bus 101.

  The control unit 10 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The CPU of the control unit 10 reads the system program and various processing programs stored in the storage unit 30 and develops them in the RAM, and centrally controls the operation of each part of the image forming apparatus 1 according to the developed programs.

For example, the control unit 10 reads an image from a document placed on the document tray 11a by the image reading unit 50 in cooperation with a program stored in the storage unit 30, and reads the image of the read document and an operation display unit. The job is executed based on the job information such as the image forming condition input from 20, and the image forming unit 70 is controlled to form an image on the sheet. In addition, the control unit 10 receives job information including image data transmitted from an external device or the like, image forming conditions of each image data, and the like by the communication unit 40 in cooperation with a program stored in the storage unit 30. Then, a job is executed based on the received job information, and the image forming unit 70 is controlled to form an image on a sheet.
Further, the control unit 10 executes an output control process A described later in cooperation with a program stored in the storage unit 30 and performs a front surface continuous image formation in double-sided alternating conveyance or a backside continuous image formation in advance. Control is performed to output a correction chart during the idle time of at least one sheet between the image formation of the paper and the image formation of the succeeding paper.

  The operation display unit 20 is configured by an LCD (Liquid Crystal Display) or the like, and displays various operation buttons, device statuses, operation statuses of functions, and the like on the display screen in accordance with display signal instructions input from the control unit 10. I do. The LCD display screen is covered with a pressure-sensitive (resistive film pressure) touch panel configured with transparent electrodes arranged in a grid, and the XY coordinates of the force point pressed with a finger or a touch pen are expressed as voltage values. The detected position signal is output to the control unit 10 as an operation signal. The operation display unit 20 includes various operation buttons such as a numeric button and a start button, and outputs an operation signal generated by the button operation to the control unit 10.

The storage unit 30 is configured by a non-volatile memory or the like, and is a system program that can be executed by the image forming apparatus 1, various processing programs that can be executed by the system program, data that is used when these various processing programs are executed, and a control unit The data of the processing result calculated by 10 is stored.
For example, the storage unit 30 stores output paper density adjustment chart image data, a γ correction curve, a count value of the number of image formations, and the like.

  Here, the output paper density adjustment chart is a correction chart used to create a γ correction curve. The γ correction curve is used to correct the relative relationship between values (input values) such as the density and brightness of an input image and the density (output value) of an image actually formed on a sheet based on the input image. A function or table. The output paper density adjustment chart includes, for example, a plurality of density patches having gradation differences for each color of Y (yellow), M (magenta), and C (cyan) and K (black) over a plurality of sheets (one side). It is a formed image.

  The communication unit 40 includes a modem, a LAN adapter, a router, and the like, and controls communication with an external device such as a PC (Personal Computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network). To receive job information and the like.

  As shown in FIG. 2, the image reading unit 50 includes an automatic document feeder 11 called an ADF (Auto Document Feeder) and a reading unit 12. The automatic document feeder 11 conveys the document d placed on the document tray 11a to a contact glass as a reading location. The reading unit 12 projects light on the document d placed on the contact glass, reads the reflected light with a CCD (Charge Coupled Device), and performs photoelectric conversion to obtain an image signal of the document d, and performs image processing. To the unit 60.

  The image processing unit 60 subjects the image (analog image signal) output from the image reading unit 50 to A / D conversion processing, shading correction, image compression processing, γ correction processing based on a γ correction curve, etc. The data is output to the image forming unit 70 as data.

  The image forming unit 70 forms an image on a sheet by electrophotography based on the input image data. As shown in FIG. 2, the image forming unit 70 includes exposure units 2Y, 2M, 2C, and 2K, developing units 3Y, 3M, 3C, and 3K, photosensitive drums 4Y, 4M, 4C, and 4K, and a charging unit 5Y. 5M, 5C, and 5K, cleaning units 6Y, 6M, 6C, and 6K, primary transfer rollers 7Y, 7M, 7C, and 7K as transfer members, an intermediate transfer belt 8 as an intermediate transfer member, and a belt cleaning unit 9 And a secondary transfer roller 21, a fixing unit 22, a paper feed unit 25, and a transport unit 26 including a paper discharge roller 27. Hereinafter, the symbols Y, M, C, and K in each part represent yellow, magenta, cyan, and black, respectively.

  The exposure units 2Y, 2M, 2C, and 2K include a laser light source such as an LD, a polygon mirror, and a plurality of lenses. The exposure units 2Y, 2M, 2C, and 2K scan and expose the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K with laser beams based on the image data sent from the image processing unit 60. By this laser beam scanning exposure, latent images are formed, that is, images are written at the image forming positions of the photosensitive drums 4Y, 4M, 4C, and 4K charged by the charging units 5Y, 5M, 5C, and 5K. The image forming positions of the photoconductor drums 4Y, 4M, 4C, and 4K are positions where a latent image is formed on the photoconductor drum.

  The latent images formed on the photoconductive drums 4Y, 4M, 4C, and 4K are visualized by development by the corresponding developing units 3Y, 3M, 3C, and 3K, and are formed on the photoconductive drums 4Y, 4M, 4C, and 4K. A toner image is formed on.

  The toner images formed and carried on the photosensitive drums 4Y, 4M, 4C, and 4K are transferred onto the intermediate transfer belt 8 by primary transfer rollers 7Y, 7M, 7C, and 7K to which a constant voltage is applied from a power source (not shown). Are sequentially transferred to a predetermined position and primary transferred. Residual toner is removed from the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K after the transfer of the toner image by the cleaning units 6Y, 6M, 6C, and 6K.

The intermediate transfer belt 8 is a semiconductive endless belt that is suspended and supported rotatably by a plurality of rollers, and is driven to rotate as the rollers rotate.
The intermediate transfer belt 8 is pressure-bonded to the respective photosensitive drums 4Y, 4M, 4C, and 4K by the primary transfer rollers 7Y, 7M, 7C, and 7K. A transfer current corresponding to the applied voltage flows through each of the primary transfer rollers 7Y, 7M, 7C, and 7K. As a result, the toner images developed on the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K are sequentially transferred (primary transfer) to the intermediate transfer belt 8 by the primary transfer rollers 7Y, 7M, 7C, and 7K, respectively. .
On the other hand, in the paper feeding unit 25, the type of paper instructed by the control unit 10 is fed and conveyed by the conveyance unit 26 to a transfer position by the secondary transfer roller 21. The toner image of the color image is transferred (secondary transfer) to the conveyed paper by the secondary transfer roller 21. As a result, a color image is formed on one surface (front surface) of the paper. After the transfer, the sheet is conveyed to the fixing unit 22 and the toner image transferred to the sheet is thermally fixed. Residual toner on the intermediate transfer belt 8 is removed by the belt cleaning unit 9.
In the case of single-sided image formation, the paper discharged from the fixing unit 22 is conveyed to the post-processing unit 90 and is placed on the paper discharge tray (main tray T1 or sub-tray T2) by the post-processing unit 90 (see FIG. 3). At the time of double-sided image formation, the sheet formed on the surface of the sheet and discharged from the fixing unit 22 is reversed through the circulation path and then fed again toward the transfer position.

Here, with reference to FIG. 3, paper conveyance during double-sided image formation will be described. FIG. 3 is a diagram schematically illustrating a sheet conveyance path of the conveyance unit 26.
At the time of front surface image formation, the paper P fed from the paper feed unit 25 is first transported to the position of the transport roller 26a (arrow 1). Here, if there is another sheet at the position of the registration roller 26b, the sheet P is stopped by the transport roller 26a, and if not, the sheet P is transported to the registration roller 26b without stopping (arrow 2). The paper P transported to the registration roller 26b is temporarily stopped and then transported at the transfer position when the leading edge of the image coincides with the leading edge of the image writing position of the paper. At the transfer position, the paper P is transported by the secondary transfer roller 21. An image is formed on the surface.

  The sheet P on which the image has been formed on the front surface is branched from the paper discharge path 26A by the branching unit 26c and conveyed to the reversing roller 26d. When the trailing edge of the paper P passes through the reverse roller 26d, the rotation direction of the reverse roller 26d is switched to the reverse direction, thereby reversing the transport direction of the paper P (arrow 4). At this time, the front surface of the paper P becomes the lower surface and the back surface becomes the upper surface. Then, when the branching unit 26e is switched to the refeed side, the paper P is conveyed toward the refeed pre-registration portion 26f (arrow 5). Note that the branching unit 26c is switched to the paper discharge path side with the switching of the branching unit 26e to the refeeding side.

  The paper P transported to the refeed pre-registration unit 26f is temporarily stopped at the position of the registration roller 26b, and then transported at a timing when the leading edge of the image coincides with the leading edge of the image writing position of the paper P (arrow). 6) An image is formed on the back surface of the paper P by the secondary transfer roller 21 at the transfer position. The sheet P on which images have been formed on both sides is fixed and then conveyed to the post-processing unit 90 (arrow 7) and placed on the main tray T1.

In the present embodiment, a path for reversing the paper, which is deviated from a path common to image formation on one side, is collectively referred to as a circulation path. The circulation path is configured to hold (hold) multiple sheets of paper, and when double-sided image formation is continuous, the number of front surface images that can be built into the circulation path is the first step in order to improve productivity. After the formation is repeated, image formation on the front side and the back side that has returned through the circulation path is alternately performed. When image formation on the front side is completed, image formation on the back side of the paper that has returned from the circulation path is continued. Done. That is, a plurality of double-sided images are formed by double-sided alternating conveyance. When continuously feeding for the front side, at least an interval for one sheet (here, one sheet) is provided in order to secure time for inverting the preceding sheet by the reversing roller 26d. Subsequent paper is fed. Even during continuous image formation on the back side, image formation is performed with an interval of one sheet left as it is, as in paper feeding.
In this embodiment, the upper limit of the number of sheets that can be incorporated in the circulation path is 4 for A4 and 3 for A3.

(Operation of Image Forming Apparatus 1)
Next, the operation in the image forming apparatus 1 will be described.
FIG. 4 shows a flowchart of the output control process A executed in the image forming apparatus 1. The output control process A is executed in cooperation with the program stored in the control unit 10 and the storage unit 30 at the start of a job (Job).

  First, it is determined whether or not it is the output paper density adjustment timing (step S1). Here, the output paper density adjustment is executed, for example, every predetermined number of image formations. The storage unit 30 is provided with a counter for counting the number of image formations in the image forming unit 70, and based on the value of this counter, it is determined whether or not the output paper density adjustment timing has come. Even when the output paper density adjustment flag is set to ON in the RAM of the control unit 10, it is determined that the output paper density adjustment timing is reached. Note that the output paper density adjustment timing is not limited to this, and may be, for example, a timing when environmental fluctuations such as temperature and humidity exceed a predetermined threshold.

  If it is determined in step S1 that the output paper density adjustment timing is not reached (step S1; NO), an image is formed on the paper based on the job by the image forming unit 70 and discharged to the main tray T1 (step S9). A counter for counting the number of formations is incremented by 1 (step S10), and the process proceeds to step S11.

  If it is determined in step S1 that the output paper density adjustment timing is reached (step S1; YES), the output paper density adjustment flag is set to ON (step S2). Next, based on the job information, it is determined whether the job is a double-sided image formation job (step S3). If it is determined that the job is not a double-sided image formation job (step S3; NO), the process proceeds to step S5.

  If it is determined in step S3 that the job is a double-sided image formation job (step S3; YES), it is determined whether or not it is the timing when there is a gap between sheets (step S4). That is, it is determined whether or not it is the timing at which a paper gap is formed during the continuous image formation on the front side at the start of the job or the paper gap is formed at the back side continuous image formation after the latter half of the job. Here, as described above, in the double-sided image formation, in order to secure time for reversing the preceding sheet, at least one sheet (in this case, one sheet) is spaced and the subsequent is followed. Paper is fed. The timing at which the gap between the sheets is opened is the timing at which the feeding of at least one sheet during the continuous image formation on the front side is vacated, or the preceding sheet generated during the continuous image formation on the back side by feeding at least one sheet. It means the idle time that occurs between the image formation of the next sheet and the image formation of the succeeding sheet (between sheets). If it is determined that it is not the time when there is a gap between sheets (step S4; NO), the image forming unit 70 forms an image on the sheet based on the job and discharges it to the main tray T1 (step S9). Then, the counter for counting the number of image formations is incremented by 1 (step S10), and the process proceeds to step S11.

  On the other hand, if it is determined in step S4 that it is time to clear the paper (step S4; YES), the image data of the output paper density adjustment chart is read from the storage unit 30, and the image forming unit 70 applies it to the paper. An output paper density adjustment chart is formed. The output paper density adjustment chart is measured by the color sensor 80 and then discharged to the sub-tray T2 by the post-processing unit 90 (step S5), and the process proceeds to step S6. The output value from the color sensor 80 is stored in the RAM.

  In step S6, it is determined whether or not the output paper density adjustment chart has been output a specified number (here, 3). If it is determined that the specified number of output paper density adjustment charts have not been output (step S6; NO), the process proceeds to step S11. When it is determined that the specified number of output paper density adjustment charts have been output (step S6; YES), output paper density adjustment processing is executed (step S7), and the output paper density adjustment flag is cleared (step S8). The process proceeds to step S11. The output paper density adjustment process is performed in parallel with this process, and a γ correction curve is created based on the value obtained by reading the output paper density adjustment chart, and the storage unit 30 uses the created γ correction curve. The γ correction curve is updated.

  In step S11, it is determined whether or not the job has ended. If it is determined that the job has not ended (step S11; NO), the process returns to step S1. When it is determined that the job is finished (step S11; YES), the output control process A is finished.

  FIG. 5 shows the elapsed time from the start of the job and the surface on which the image is formed at each time when the image is formed based on the A4-size, 10-sided job by the output control process A (the difference between the front and back surfaces and what FIG. 6 is a diagram illustrating a number of sheets), a sheet to be discharged (a number indicating how many sheets are discharged), and a correction chart output possible timing. Here, the unit of the time axis is a unit time t required to form an image on one side of one sheet (the same applies to FIGS. 7 and 8).

  As shown in FIG. 5, in the output control process A, an output paper density adjustment chart is output as a correction chart in the time when there is a gap between one sheet of paper during continuous front surface image formation or back surface continuous image formation. To do. Therefore, when the output paper density adjustment chart needs to be output, the productivity is higher than in the case of providing a time for separately outputting the output paper density adjustment chart before or after the start of the double-sided image forming job as in the past. Can be improved. In addition, since the output paper density adjustment chart is output using the idle time of the job, the output paper density can be reduced without lowering the productivity compared to the case where the output paper density adjustment chart is not required. An adjustment chart can be output. Further, since the time for which the developing device and the photoconductor are idling without any image formation is reduced by the output of the output paper density adjustment chart, the life of the device can be improved. Note that the number of output sheets of the output paper density adjustment chart may be any number as long as it is within the number of sheets between the empty papers at the time of front surface continuous image formation or back surface continuous image formation.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
Since the configuration of the second embodiment is the same as that described in the first embodiment, the description will be used and the operation of the second embodiment will be described below.
FIG. 6 shows a flowchart of the output control process B executed in the image forming apparatus 1. The output control process B is executed in cooperation with the control unit 10 and the program stored in the storage unit 30 at the start of the job.

First, it is determined whether or not the stabilization control execution condition is satisfied (step S21).
The stabilization control is control for stably supplying image quality against changes in environmental factors such as temperature and humidity in the image forming apparatus 1 or developer replacement. The stabilization control execution conditions are, for example, as follows.
-When idling has continued for 6 hours or more-When a predetermined number of images have been formed since the previous stabilization control execution-When the temperature and humidity in the machine have changed by more than a predetermined percentage since the previous stabilization control execution with the power turned on- When changing the developer

  If it is determined that the stabilization execution condition is not satisfied (step S21; NO), the image forming unit 70 forms an image on the sheet based on the job and ejects it from the main tray T1 (step S28). Is incremented by 1 (step S29), and the process proceeds to step S30.

If it is determined that the stabilization control condition is satisfied (step S21; YES), it is determined whether or not the job can be divided for the stabilization control (step S22). Here, it is determined that the job can be divided when there is no longer any sheet in the transport path.
If it is determined that it is not possible to divide the job for stabilization control (step S22; NO), the image forming unit 70 forms an image on the sheet based on the job and discharges it to the main tray T1 (step S28). ), The counter for counting the number of image formations is incremented by 1 (step S29), and the process proceeds to step S30.

  If it is determined that the job can be divided for the stabilization control (step S22; YES), the stabilization control is performed (step S23). In the stabilization control, for example, maximum density adjustment, photoreceptor surface potential uniformity correction, and halftone density correction are performed.

When the stabilization control is completed, the job is resumed (step S24), and it is determined whether or not the resumed job is double-sided image formation (step S25). If it is determined that the resumed job is not double-sided image formation (step S25; NO), the process proceeds to step S27.
If it is determined that the resumed job is the double-sided image formation (step S25; YES), it is determined whether or not it is the timing when the paper gap is available (step S26). If it is determined that it is not the time to make a gap between the sheets (step S26; NO), the image forming unit 70 forms an image on the sheet based on the job and discharges it to the main tray T1 (step S28). Is incremented by 1 (step S29), and the process proceeds to step S30. If it is determined that it is time to leave a gap (step S26; YES), the process proceeds to step S27.

  In step S27, the image forming section 70 discharges the sample. Here, the sample discharge means outputting a sample image for the user to confirm the machine state after the stabilization control. The sample is discharged by the post-processing unit 90 to the sub-tray T2. As a sample image, for example, the top image of a job to be resumed is formed on one side of a sheet. The user may set in advance what kind of image is output as the sample image. After sample discharge, the process proceeds to step S30.

  In step S30, it is determined whether or not the job has ended. If it is determined that the job has not ended (step S30; NO), the process returns to step S21. When it is determined that the job is finished (step S30; YES), the output control process B is finished.

  In the output control process B, when stabilization control is performed during double-sided image formation, a sample paper discharge is output as a correction chart in the time when there is a gap between sheets during front surface continuous image formation or back surface continuous image formation ( (See FIG. 5). Therefore, when output of sample discharge is required, productivity can be improved as compared with a case where a time for outputting a correction chart is separately provided before or after the start of a double-sided image forming job. . Further, since the sample paper discharge is output using the idle time of the job, the productivity is not lowered even when compared with the case where the sample paper discharge is not required. Furthermore, since the time during which the developing device and the photoconductor are idly rotated without forming any image is reduced by the output of the correction chart, the life of the device can be improved. Note that the number of sample images to be output may be any number as long as it is within the number of empty sheets during the front surface continuous image formation or the back surface continuous image formation.

As described above, according to the image forming apparatus 1, the control unit 10 causes the image forming unit 70 to copy the preceding sheet during the continuous image formation on the front surface or the back surface continuous image formation in the double-sided image formation by the double-sided alternate conveyance. The image formation of the correction chart on one side is performed in the idle time for one sheet between the image formation and the image formation of the succeeding sheet.
For example, when the output paper density adjustment timing is reached during double-sided image formation, the control unit 10 performs image formation on the preceding paper and subsequent paper during the subsequent continuous image formation on the front surface or the continuous image formation on the back surface. The image formation of the output paper density adjustment chart is performed as a correction chart in the idle time during image formation. Also, for example, when stabilization control is performed during double-sided image formation, there is a gap between image formation on the preceding paper and image formation on the subsequent paper during subsequent continuous image formation on the front surface or continuous image formation on the back surface. The sample image is formed as a correction chart in time.
Therefore, the correction chart can be output without reducing the productivity. Further, it is possible to improve the life of the image forming apparatus 1 by reducing the time during which the developing device, the photosensitive member, and the like are idle without image formation.

  In addition, the correction chart is mixed into the paper on which the image is formed by the job by discharging the correction chart to a paper discharge tray having a plurality of paper discharge trays and different from the paper on which the image is formed on both sides. Can be prevented.

  Note that the description in the above embodiment shows a preferred example of the image forming apparatus according to the present invention, and the present invention is not limited to this.

  For example, in the above-described embodiment, as an example of the correction chart output between the sheets during the double-sided alternating conveyance, the case where the output paper density adjustment chart and the sample image are output has been described as an example. The type of chart for use is not particularly limited. Regardless of the type of correction chart, according to the present invention, it is possible to output a correction chart without reducing productivity in an image forming apparatus that performs double-sided alternating conveyance. In addition, the life of the apparatus can be improved.

  Further, in the above embodiment, during continuous image formation on the back side, image formation is performed with a space of one sheet as it is as in the case of paper feeding. However, during continuous image formation on the back side, It is also possible to provide a mechanism for adjusting the distance between the preceding paper and the succeeding paper to be reduced. As described above, in the configuration in which the adjustment is performed between the sheets during the image formation on the back surface, the time for which the sheet interval for one sheet at the time of continuous surface image formation is available can be output as the correction chart.

  Further, for example, in the above embodiment, the case where the present invention is applied to the image forming apparatus configured to transfer the toner image formed on the photosensitive drum to the intermediate transfer belt has been described. The present invention can be similarly applied to an image forming apparatus configured to directly transfer a toner image formed on a drum onto a transfer material such as paper.

  In the above description, an example in which a ROM, a nonvolatile memory, a hard disk, or the like is used as a computer-readable medium for the program according to the present invention is disclosed, but the present invention is not limited to this example. As another computer-readable medium, a portable recording medium such as a CD-ROM can be applied. A carrier wave is also applied as a medium for providing program data according to the present invention via a communication line.

  In addition, the detailed configuration and detailed operation of the image forming apparatus 1 can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 20 Operation display part 30 Storage part 40 Communication part 50 Image reading part 11 Automatic document feeding part 12 Reading part 60 Image processing part 70 Image forming part 80 Color sensor 90 Post-processing part 101 Bus

Claims (4)

An image forming unit that forms an image on a sheet, a circulation path for inverting the front and back of the sheet during double-sided image formation, and a control unit for controlling the image forming unit, wherein the circulation path includes a plurality of sheets When the image forming unit performs continuous double-sided image formation in the image forming unit, the control unit sets an interval of at least one sheet so as to invert the paper in the circulation path. The front surface of the number of sheets that can be held in the circulation path while being vacant is continuously imaged, and then the image formation on the back surface of the paper returned from the circulation path and the image formation on the remaining surface are alternately performed. An image forming apparatus that continuously performs image formation on the back surface of the paper returned from the circulation path after all image formation is completed,
The control unit has a single-side correction chart in the empty time between the image formation of the preceding paper and the image formation of the subsequent paper during the continuous image formation of the front surface or the continuous image formation of the back surface. An image forming apparatus for performing image formation. With multiple output trays,
The image forming apparatus according to claim 1, wherein the control unit causes the correction chart to be discharged to a paper discharge tray different from a sheet on which images are formed on both sides.   The control unit causes image formation of an output paper density adjustment chart as the correction chart in the idle time after the output paper density adjustment execution timing is reached during the double-sided image formation. Or the image forming apparatus according to 2;   3. The image formation according to claim 1, wherein when the stabilization control is performed during the double-sided image formation, the control unit causes the sample image to be formed as the correction chart in the free time thereafter. apparatus.

Images