JP6459436B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  Conventionally, image forming apparatuses such as printers and copiers employing an electrophotographic system have been widely used. In an image forming apparatus, an image is formed on a sheet through a series of processes in which an image is transferred onto a sheet by an image forming unit, and then the image is fixed on the sheet by a fixing unit. In the fixing unit, the toner transferred on the surface of the paper is melted by heating with a heater. However, when the toner adhesion amount increases, the viscosity at the time of toner melting increases and the paper does not peel off from the fixing belt or the like. A separation failure may occur.

  FIG. 9 is a diagram for explaining the occurrence of fixing separation failure. As shown in FIG. 9, for example, when an image composed of a plurality of layers of toner having a predetermined width is formed at the front end of the paper P, the toner adhesion amount of the image increases. For this reason, during the fixing process, the toner passes through the fixing unit 440 from the leading edge of the paper P in this toner state, so that the toner melted by the heating process in the fixing unit 440 easily adheres to the belt of the fixing unit 440.

  In order to improve the fixing and separating function, the paper is pre-fixed before the image forming process to increase the rigidity of the paper, blow air on the leading edge of the paper, or increase the image margin area of the paper. Various methods have been developed.

  Patent Document 1 describes an image forming apparatus that increases the rigidity of a transfer material by reducing the moisture content of the transfer material by pre-fixing during image formation. Patent Document 2 describes an image forming apparatus that controls a fixing temperature or the like for an image portion on the leading end side in the conveyance direction of a recording sheet based on a basis weight value of the recording sheet. Patent Document 3 describes an image forming apparatus that reflects a determination result by a paper eye detection unit in paper separation control of a fixing device. Patent Document 4 describes an image forming apparatus that shortens the nip portion formed by an elastic pad when the sheet thickness is thin, and lengthens the nip portion when the sheet thickness is thick.

JP 2006-195347 A JP 2014-81473 A JP 2011-170281 A JP 2010-20129 A

  However, Patent Documents 1 to 4 have the following problems. That is, in Patent Document 1, there is a problem in that productivity is lowered because the time for normal image formation processing is increased by the time for pre-fixing. In Patent Document 2, since fixing conditions such as a fixing temperature are controlled, there is a problem that an optimal fixing process cannot be performed. In Patent Documents 3 and 4 and the like, since the position of an image formed on a sheet is not considered, fixing separation failure may not be surely solved even if the grain of the sheet, the nip time, and the like are controlled.

  In addition, the above-described method using the air blowing has a demerit that the fixing device is cooled by the air blown, and there is a problem that the fixing performance is lowered and the power consumption is increased. Further, the method of increasing the margin has a problem that it is not acceptable to a user who wants to form an image on the entire sheet by reducing the margin.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of improving the fixing separation performance.

In order to solve the above problems, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet based on image data, and a fixing unit that fixes an image formed by the image forming unit on the sheet. And fixing separation is advantageous when it is determined that a fixing separation failure occurs in the fixing unit based on the image data and a rotating unit that is provided upstream of the image forming unit in the transport direction and rotates the paper. A control unit that controls the image forming unit so as to form an image by rotating the image data in a predetermined direction, and the control unit has both ends on the upstream side and the downstream side in the transport direction on the front side of the sheet. And when no image is formed on at least one of both ends in the direction orthogonal to the paper transport direction, the edge on which the paper image is not formed. There is for controlling the rotating section so that the paper is rotated with the rotation of the image data so that the downstream end of the paper.

The image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet based on image data, a fixing unit that fixes an image formed by the image forming unit on the sheet, and the image forming unit. In the case of double-sided printing , which is provided on the upstream side of the transport direction, and determined to cause a fixing separation failure in the fixing unit on the front side of the paper based on the image data. A control unit that controls the image forming unit to change the order of the surfaces on which image formation is performed to form image data on the back side of the paper on the back side of the paper, and the control unit includes the back side of the paper In the case where an image is formed at both upstream and downstream ends of the conveyance direction on the back side of the sheet, and the conveyance direction of the sheet. When an image is not formed on at least one of both ends in the orthogonal direction, the paper rotates in accordance with the rotation of the image data so that the end on which the image of the paper is not formed becomes the downstream end of the paper. The rotating unit is controlled to do so.

  In the present invention, the direction in which fixing separation is advantageous refers to a direction in which image data or paper is rotated so that an image is not formed at the leading edge of the paper, for example.

  According to the first aspect of the present invention, image formation is performed by rotating the image data in a direction in which fixing separation is advantageous, so that image formation can be performed without causing fixing separation failure. According to the second aspect of the present invention, when it is determined that fixing separation failure occurs on the front side of the paper, the order of the surfaces on which the image is formed on the paper is changed, and the image is formed from the back side of the paper. Image formation can be performed without causing poor separation.

1 is a diagram illustrating a configuration example of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a block configuration example of an image forming apparatus. 6 is a flowchart (part 1) illustrating an operation example of the image forming apparatus during fixing separation failure avoidance control according to the first embodiment of the present invention. 6 is a flowchart illustrating an operation example of the image forming apparatus during fixing separation failure avoidance control (part 2). FIG. 10 is an explanatory diagram in a case where image data is rotated as an avoiding means when a fixing separation failure occurs. FIG. 10 is an explanatory diagram when a sheet and image data are rotated as an avoiding means when a fixing separation failure occurs. It is a figure for demonstrating the generation | occurrence | production conditions of the fixing separation defect which concerns on the 2nd Embodiment of this invention. 6 is a diagram illustrating a configuration example of a table used when determining whether or not a fixing separation failure occurs in the image forming apparatus. FIG. It is a figure for demonstrating the problem at the time of the fixing process in the past.

  Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the dimension ratio of drawing is expanded on account of description and may differ from an actual ratio.

<First Embodiment>
[Configuration example of image forming apparatus]
FIG. 1 shows an example of the configuration of an image forming apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 100 is called a tandem type image forming apparatus, and includes an automatic document feeder 80 and an apparatus main body 102. The automatic document conveyance unit 80 is attached to the upper part of the apparatus main body 102 and sends out the paper set on the conveyance table to the image reading unit 90 of the apparatus main body 102 by a conveyance roller or the like.

  The apparatus main body 102 includes an operation display unit 70, an image reading unit 90, an image forming unit 10, an intermediate transfer belt 8, a paper feeding unit 20, a registration roller 32, a paper rotating unit 130, and a fixing unit 44. And a post-processing unit 140 and an automatic paper reversal conveyance unit 60 (hereinafter referred to as ADU).

  The operation display unit 70 is attached to the upper part of the image forming apparatus main body 102, and has a touch panel in which a display device composed of a liquid crystal panel or the like and a position input device are combined, and a plurality of operation keys including numeric keys and a determination key. doing. The operation display unit 70 displays an operation screen and receives image forming conditions such as a paper type and a paper size input by a user operation on the operation screen or operation keys. The operation display unit 70 constitutes an example of a notification unit.

  The image reading unit 90 scans and exposes a document placed on a document table or a document transported by the automatic document transport unit 80 by an optical system of a scanning exposure device, and an image of the scanned document is CCD (Charge Coupled Device). An image information signal is generated by photoelectric conversion by an image sensor. The image information signal is output to the image forming unit 10 after being subjected to analog processing, analog / digital (hereinafter referred to as A / D) conversion processing, pseudo correction, image compression processing, and the like by an image processing unit (not shown).

  The image forming unit 10 forms an image by electrophotography, and includes an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, The image forming unit 10C forms a cyan (C) color image, and the image forming unit 10K forms a black (K) color image. In this example, common function names, for example, Y, M, C, and K indicating colors to be formed are added after the reference numeral 10 for description.

  The image forming unit 10Y includes a photosensitive drum 1Y, a charger 2Y, an exposure unit (optical writing unit) 3Y, a developing unit 4Y, and a cleaning unit 6Y arranged around the photosensitive drum 1Y. The image forming unit 10M includes a photosensitive drum 1M, a charger 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 6M disposed around the photosensitive drum 1M. The image forming unit 10C includes a photosensitive drum 1C, and a charger 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 6C disposed around the photosensitive drum 1C. The image forming unit 10K includes a photosensitive drum 1K, a charger 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 6K disposed around the photosensitive drum 1K.

  Respective photosensitive drums (image carriers) 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, chargers 2Y, 2M, 2C, and 2K, exposure units 3Y, 3M, 3C, and 3K, development The devices 4Y, 4M, 4C, and 4K and the cleaning units 6Y, 6M, 6C, and 6K have the same configuration. In the following description, Y, M, C, and K are not used unless particularly distinguished.

  The charger 2 charges the surface of the photosensitive drum 1 almost uniformly. The exposure unit 3 includes, for example, an LPH (LED Print Head) having an LED array and an imaging lens, or a polygon mirror type laser exposure scanning device, and scans the photosensitive drum 1 with laser light based on an image information signal. Thus, an electrostatic latent image is formed. The developing device 4 develops the electrostatic latent image formed on the photosensitive drum 1 with toner. As a result, a toner image which is a visible image is formed on the photosensitive drum 1.

  The intermediate transfer belt 8 is stretched by a plurality of primary transfer rollers 7 or the like and is rotatably supported. Along with the rotation of the intermediate transfer belt 8, the primary transfer roller 7 and the photosensitive drum 1 rotate, and a predetermined voltage is applied between the primary transfer roller 7 and the photosensitive drum 1, whereby the photosensitive drum. 1 is transferred onto the intermediate transfer belt 8 (primary transfer).

  The paper feed unit 20 has a plurality of paper feed trays 20A and 20B in which paper P such as A3 and A4 is accommodated. The paper P transported from the paper feed trays 20A, 20B by the rollers 22, 24, 26, 28, etc. is transported to the registration rollers 32. Note that the number of paper feed trays is not limited to two. Further, a single or a plurality of large-capacity paper feeders that can accommodate a large-capacity paper P may be connected as necessary.

  The paper P conveyed to the registration roller 32 has its leading end abutted against the registration roller 32 by the loop roller 30 to form a loop and correct the bending (for example, skew) in the conveyance direction D of the paper P. . The paper P in which the bending of the paper P is corrected is conveyed to the secondary transfer roller 34 at a predetermined timing. In the secondary transfer roller 34, the Y, M, C, and K toner images transferred on the intermediate transfer belt 8 in a superimposed manner are collectively transferred onto the surface of the sheet P conveyed by the registration roller 32 (secondary transfer). Transcription). The second-transferred sheet P is conveyed to the fixing unit 44 on the downstream side in the conveyance direction D.

  The sheet rotating unit 130 is provided in a conveyance path between the sheet feeding unit 20 and the secondary transfer roller 34, and when it is determined that a fixing separation failure occurs based on image data for image formation, the sheet rotating unit 130 rotates the sheet P by a predetermined angle. And rotated to the secondary transfer roller 34. The paper rotation unit 130 can be configured by a suction unit that sucks the paper P on the transport path and a rotation mechanism that rotates the suction unit. Further, the sheet rotating unit 130 may be configured by a rotatable stage provided in the transport path. Of course, other known techniques can be employed as a mechanism for rotating the paper P. In this example, the sheet rotating unit 130 is not used when there is no fixing separation failure or when the fixing separation failure can be avoided by rotating the image data.

  The fixing unit 44 includes a pressure roller and a heating roller. The fixing unit 44 fixes the toner image on the surface of the paper P to the paper P by applying pressure and heat treatment to the paper P on which the toner image has been transferred by the secondary transfer roller 34.

  A transport path switching unit 48 for switching the transport path of the paper P to the paper discharge path side or the ADU 60 side is provided on the downstream side in the transport direction D of the fixing unit 44. The transport path switching unit 48 performs transport path switching control based on the selected print mode (single-sided print mode, double-sided print mode, or the like).

  The paper P that has been printed on one side in the single-sided printing mode or the paper P that has been printed on both sides in the double-sided printing mode is provided in the transport path downstream of the fixing unit 44 in the transport direction D. 140. The post-processing unit 140 returns the paper P and the image to the original state by rotating the paper P when the fixing separation failure avoidance control is performed. The post-processing unit 140 can be configured by a suction unit or a rotation mechanism, similarly to the sheet rotation unit 130, or can be configured by a rotatable stage provided in the conveyance path. The post-processed paper P is discharged to a paper discharge tray (not shown).

  In the double-sided printing mode, when an image is formed on the back side of the paper P, the paper P on which the image is formed on the front side is transported to the ADU 60 via the transport roller 62 and the like. In the switchback path of the ADU 60, the reverse rotation control of the ADU roller 64 causes the rear end of the paper P to be transported to the U-turn path section, and is reversed by the transport rollers 66 and 68 provided in the U-turn path section. In this state, the paper is fed again to the secondary transfer roller 34.

[Block Configuration Example of Image Forming Apparatus]
FIG. 2 is a block diagram illustrating a functional configuration example of the image forming apparatus 100. As shown in FIG. 2, the image forming apparatus 100 includes a control unit 50 that controls the operation of the entire apparatus. The control unit 50 includes a CPU (Central Processing Unit) 52, a ROM (Read Only Memory) 54, and a RAM (Random Access Memory) 56. The CPU 52 executes the software (program) read from the ROM 54 to control each unit of the image forming apparatus 100 and realize a function related to a mode for preventing occurrence of fixing separation failure and a normal image forming process.

  The control unit 50 includes an operation display unit 70, an image reading unit 90, an image forming unit 10, a paper feeding unit 20, a fixing unit 44, a storage unit 110, a paper rotating unit 130, and a post-processing unit 140. And are connected to each other.

  The operation display unit 70 displays an operation screen or the like on the display device based on a display signal supplied from the control unit 50, or image forming conditions (such as paper type, paper size, weight, stiffness, etc. received on the operation screen). Information about a print job) is supplied to the control unit 350.

  The image reading unit 90 reads a document or the like placed on the document table to generate image data, and supplies the generated image data to the control unit 50. The image forming unit 10 controls the operation of the exposure unit and the developing unit based on the image information supplied from the control unit 50 to form an image on the paper P. The paper feeding unit 20 takes out the paper P designated on the basis of an instruction from the control unit 50 one by one and sends it to the secondary transfer roller 34 of the image forming unit 10. Based on the control signal supplied from the control unit 50, the fixing unit 44 turns on the heater or presses the rollers to form a nip portion.

  The storage unit 110 includes, for example, a nonvolatile semiconductor memory, an HDD (Hard disk drive), or the like. The storage unit 110 stores a table TB used when determining whether or not a fixing separation failure occurs, and image forming conditions such as image data, paper type, and paper size transmitted from a computer or the like. .

  The paper rotation unit 130 is driven based on the drive signal supplied from the control unit 50 and rotates the paper P by a predetermined angle. The post-processing unit 140 is driven based on the drive signal supplied from the control unit 50 and rotates the paper P in the reverse direction by the angle rotated by the paper rotation unit 130.

  Based on the image data to be printed, the control unit 50 determines whether or not images (patches) having a predetermined width are formed on the leading edge, the trailing edge, the left edge, and the right edge of the four sides of the paper P. When the control unit 50 determines that the image is formed on the leading edge of the paper P, the control unit 50 controls the image forming unit 10 to rotate the image data, or controls the paper rotation unit 130 to rotate the paper P. To suppress the occurrence of fixing separation failure.

  In the present embodiment, the leading end of the paper P indicates the downstream side in the transport direction D of the paper P, and the rear end of the paper P indicates the upstream side in the transport direction D of the paper P. The right end of the paper P is a direction orthogonal to the conveyance direction D of the paper P and indicates the back side of the image forming apparatus 100, and the left end of the paper P is a direction orthogonal to the conveyance direction D of the paper P. The front side of the image forming apparatus 100 is shown.

[Operation example of image forming apparatus]
3 and 4 show an example of the operation of the image forming apparatus 100 when performing fixing separation failure avoidance control according to the present invention. As illustrated in FIG. 3, when a print instruction is received in step S <b> 100, the control unit 50 acquires image data of a job transmitted from, for example, a computer connected via a network. The image data is stored in a memory such as the storage unit 110. If image data is acquired, it will progress to step S110.

  In step S110, the control unit 50 determines whether an image is formed at the front end of the front side of the paper P based on the acquired image data (whether the front end is advantageous for fixing separation). If the control unit 50 determines that an image is formed at the leading edge of the paper P, the control unit 50 proceeds to step S120. On the other hand, if the control unit 50 determines that an image is not formed at the leading edge of the paper P, the control unit 50 proceeds to step S160 without executing the fixing separation failure avoidance control because the possibility of occurrence of fixing separation failure is low.

  In step S120, when an image is formed on the front end of the paper P, the control unit 50 determines whether an image is formed on the rear end on the front side of the paper P based on the acquired image data (the rear end is advantageous for fixing separation). Determine whether or not. If the controller 50 determines that an image is formed at the trailing edge of the paper P, the process proceeds to step S140. If the controller 50 determines that an image is not formed at the trailing edge of the paper P, the control unit 50 proceeds to step S130.

  In step S <b> 130, when an image is formed at the front end of the surface of the paper P and no image is formed at the rear end, the control unit 50 has an advantage of the rear end of the paper P for fixing separation. The image data is rotated by a predetermined angle so that becomes the rear end. 5A, 5B, and 5C are explanatory diagrams when the image data is rotated 180 degrees on the paper P. FIG. As shown in FIG. 5A, when the image GF is formed at the leading edge of the paper P, there is a high possibility that a fixing separation failure will occur. Therefore, as shown in FIG. 5B, the image GF is rotated (inverted) 180 degrees to form an image, thereby moving the image GF at the front end of the paper P to the rear end of the paper P. As shown in FIG. 5C, the rotation control of the image data of the present invention is applied to the case where the image GR or the like is formed at the right end of the paper P in addition to the image GF at the leading edge of the paper P. be able to.

  On the other hand, in step S140, when an image is formed on both the front end and the rear end on the front side of the paper P, the control unit 50 sets the right side and the left end on the front side of the paper P based on the acquired image data. It is determined whether an image is not formed (right edge and left edge are advantageous for fixing separation). If the control unit 50 determines that no image is formed on at least one of the right end and the left end of the front side of the paper P, the process proceeds to step S150.

  In step S150, the control unit 50 rotates the image data so that the right end or the left end on which the image is not formed becomes the front end side of the paper P because the right end or the left end on the front side of the paper P is advantageous for fixing separation. The paper P is rotated in accordance with the rotation of the image data. 6A, 6B, and 6C are explanatory diagrams when the paper P and the image data are rotated. As shown in FIG. 6A, when the images GF, GB, and GR are formed at the leading edge, the trailing edge, and the right edge of the paper P, there is a high possibility that a fixing separation defect will occur. Therefore, as shown in FIG. 6B, the left end where no image is formed is moved to the front end side of the paper P by rotating the image data and the paper P 90 degrees clockwise to form an image. Note that the rotation control of the paper P of the present invention can also be applied when the images GF and GB are formed only at the leading edge and the trailing edge of the paper P as shown in FIG. In this case, the paper P and the image data may be rotated 90 degrees clockwise or counterclockwise, or the paper P and the image data may be rotated 270 degrees clockwise.

  When the control unit 50 determines in step S140 that images are formed on all of the front end, rear end, right end, and left end of the surface of the paper P, that is, all four sides, the fixing separation failure avoidance control according to the present invention is performed. It cannot be applied. Therefore, for example, when the image forming process is performed based on the image data of the current job, the control unit 50 displays a warning on the operation screen of the operation display unit 70 that there is a high possibility that fixing separation failure will occur. . The control unit 50 stops the job (image forming process) when the user gives an instruction to stop printing based on the warning on the operation screen. On the other hand, when there is no job stop instruction, the control unit 50 proceeds to step S160 and continues the image forming process.

  In step S160, the control unit 50 determines whether the job is duplex printing. If the control unit 50 determines that the job is double-sided printing, the process proceeds to step S200 illustrated in FIG. 4. If the job is determined to be single-sided printing only on the front side instead of double-sided printing, the process proceeds to step S170.

  If the job is single-sided printing, the control unit 50 controls the operation of the image forming unit 10 and the like to form a predetermined image on the front side of the paper P in step S170. In step S180, when the image forming process is completed, the control unit 50 controls the operation of the fixing unit 44 to fix the image formed on the front side of the paper P on the paper P.

  In step S190, when the fixing process is completed, the control unit 50 controls the operation of the post-processing unit 140 to perform the post-processing on the paper P. For example, as shown in FIGS. 5A and 5B, when the image data is rotated 180 degrees, the image is returned to the original tip position by rotating the paper P 180 degrees. To discharge it onto the output tray. Also, as shown in FIGS. 6A and 6B, when the paper P is rotated 90 degrees clockwise, the original image is obtained by rotating the paper P 90 degrees counterclockwise. Return to the position to discharge the paper onto the paper discharge tray.

  In the case of single-sided printing, if it is determined that a fixing separation failure occurs, the paper P may be fixed once, and then an image forming process may be performed. According to this, the rigidity of the paper P can be increased by the fixing process before the image formation, so that occurrence of fixing separation failure can be suppressed.

  Next, the case of duplex printing will be described. As shown in FIG. 4, in step S <b> 200, the control unit 50 determines whether a fixing separation failure occurs on the front side of the paper P. For example, as fixing separation failure, an image is formed on the leading edge of the surface of the paper P in S110, or an image is formed on all of the leading, trailing, right, and left edges of the surface of the paper P in S140. Is mentioned. When it is determined that the fixing separation failure occurs on the front side of the paper P, the control unit 50 proceeds to step S210. When the control unit 50 determines that the fixing separation failure does not occur on the front side of the paper P, the control unit 50 proceeds to step S310.

  In step S <b> 210, the control unit 50 determines whether an image is formed at the front end on the back side of the paper P based on the acquired image data. When the control unit 50 determines that an image is formed at the leading edge of the paper P, the control unit 50 proceeds to step S220. On the other hand, if the control unit 50 determines that an image is not formed at the leading edge of the paper P, the control unit 50 proceeds to step S260 because it is unlikely that a fixing separation failure will occur.

  In step S <b> 220, when an image is formed on the front end of the paper P, the control unit 50 determines whether an image is formed on the rear end on the back side of the paper P based on the acquired image data. When it is determined that an image is formed on the rear end side of the paper P, the control unit 50 proceeds to step S240, and when it is determined that no image is formed on the rear end of the paper P, the control unit 50 proceeds to step S230.

  In step S230, when an image is formed at the front end of the back side of the paper P and no image is formed at the rear end, the control unit 50 is advantageous for fixing separation. The image data is rotated by a predetermined angle so that the image becomes the rear end. For example, as shown in FIGS. 5A and 5B, the image GF at the front end of the paper P is moved to the rear end of the paper P by performing image formation by rotating the image data by 180 degrees.

  On the other hand, in step S240, when an image is formed on both the front end and the rear end of the back side of the paper P, the control unit 50 sets the at least one of the right end and the left end on the back side of the paper P based on the acquired image data. It is determined whether or not an image is formed. If the control unit 50 determines that an image is not formed on at least one of the right end and the left end of the back side of the paper P, the process proceeds to step S250.

  In step S250, the control unit 50 rotates the image data so that the right end or the left end where no image is formed is the leading end side of the sheet P, and rotates the sheet P in accordance with the rotation of the image data. For example, as shown in FIGS. 6A and 6B, the paper P and the image data are rotated 90 degrees clockwise to move the left end where no image is formed to the front end side of the paper P. Let

  In step S260, since the back surface of the paper P is more advantageous for fixing separation than the front surface, the control unit 50 changes the order of image formation between the front surface and the back surface of the paper P and performs image formation from the back surface side of the paper P. In step S210, even when an image is not formed at the leading end of the back surface of the paper P, the back surface of the paper P is more advantageous for fixing and separation, so that the image is formed from the back surface side of the paper P. In step S <b> 270, when the image forming process is completed, the control unit 50 fixes the image formed on the back surface of the paper P onto the paper P.

  In step S280, when the fixing process on the back side of the paper P is completed, the control unit 50 re-feeds the secondary transfer roller 34 with the ADU 60 being reversed, and then on the front side of the paper P. A predetermined image is formed. In step S290, when the image forming process is completed, the control unit 50 fixes the image formed on the surface of the paper P to the paper P.

  In step S <b> 300, when the fixing process is completed, the control unit 50 controls the operation of the post-processing unit 140 and executes post-processing on the paper P. For example, as shown in FIGS. 5A and 5B, when the image data is rotated 180 degrees, the sheet P is rotated 180 degrees counterclockwise, whereby the image is restored to the original leading edge. The paper is discharged onto the paper discharge tray while being returned to the position.

  On the other hand, if it is determined in step S240 that the image is formed on all of the leading edge, the trailing edge, the right edge, and the left edge on the back side of the paper P, that is, all four sides, the fixing separation failure avoidance control according to the present invention. Can not apply. Therefore, for example, when the image forming process is performed based on the image data of the current job, the control unit 50 displays a warning on the operation screen of the operation display unit 70 that there is a high possibility that fixing separation failure will occur. . The control unit 50 stops the job (image forming process) when the user gives an instruction to stop printing based on the warning on the operation screen. On the other hand, if there is no job stop instruction, the control unit 50 proceeds to step S310 and continues the image forming process.

  In step S310, the control unit 50 is likely to cause a fixing separation failure on the back side of the paper P, and the back side of the paper P is not advantageous for fixing separation. An image is formed from In step S320, when the image forming process is completed, the control unit 50 fixes the image formed on the surface of the paper P to the paper P.

  In step S330, when the fixing process on the front side of the paper P is completed, the control unit 50 re-feeds the secondary transfer roller 34 with the front and back sides of the paper P reversed in the ADU 60, and then the back side of the paper P. To form a predetermined image. In step S <b> 340, when the image forming process is completed, the control unit 50 fixes the image formed on the back surface of the paper P to the paper P. The paper P for which the fixing process has been completed is discharged onto a paper discharge tray.

  If it is determined in step S200 that no fixing separation failure occurs on the front side of the paper P, the process proceeds to step S310, and the image forming process on the front side of the paper P is performed as usual. Image forming processing on the back side is performed.

  As described above, according to the first embodiment, when an image is formed at the front end of the paper P, the image data is rotated in a direction in which fixing separation is advantageous. (Not only the rear end of the paper P but also the right end and the left end). Similarly, when an image is formed at the leading edge and the trailing edge of the paper P, the image data and the paper P are rotated in a direction in which fixing separation is advantageous. Not only the end but also the right end and the left end). As a result, even when image formation is likely to cause fixing separation failure, image formation can be performed without causing fixing separation failure. As a result, productivity reduction can be prevented.

  Further, according to the first embodiment, in the case of double-sided printing, when fixing separation failure occurs on the front side of the paper P, the order of image formation is changed to change the back side of the paper P. Then, image formation is performed. Therefore, by fixing the back surface of the paper P for the first time, the moisture content of the paper P can be reduced and the rigidity can be increased. As a result, it is possible to prevent the occurrence of fixing separation failure during the second fixing process on the surface of the paper P. Further, even when a fixing separation failure occurs on the back side of the paper P, the image data and the paper P are rotated in a direction in which fixing separation is advantageous based on the image conditions of the four sides of the image data. Occurrence of poor separation can be reliably prevented. As a result, image forming processing can be performed without reducing productivity.

  In the above-described example, the sheet rotating unit 130 that rotates the sheet P is provided in the image forming apparatus 100 as a fixing separation failure avoiding unit. However, the present invention is also applied to the image forming apparatus 100 that does not include the sheet rotating unit 130. Can be applied. In this case, when it is determined that images are formed at the leading and trailing edges of the paper P, a message to change the orientation of the paper P placed on the paper feed trays 20A and 20B is displayed on the screen of the operation display unit 70. Display and warn the user that a fixing separation failure will occur when the current job is executed. Specifically, when it is determined that a fixing separation failure occurs when the paper P is in the portrait orientation, the user is notified to set the portrait paper P in the paper feed unit 20 in the landscape orientation. On the other hand, when it is determined that a fixing separation failure occurs when the paper P is in the landscape orientation, the user is notified to set the landscape paper P in the paper feed unit 20 in the portrait orientation. Thereby, even when the paper rotation part 130 is not provided, the orientation of the paper P can be changed. As a result, it is possible to reliably prevent the occurrence of fixing separation failure.

<Second Embodiment>
In the second embodiment, the above-described first condition is that, in addition to the image formation position, conditions such as the image margin area and the amount of paper P are included as conditions for determining whether or not fixing separation failure occurs. This is different from the first embodiment. Note that other configurations, operations, and the like of the image forming apparatus 100 are the same as those in the first embodiment, and therefore, common constituent elements are denoted by the same reference numerals and detailed description thereof is omitted.

  FIG. 7 is a diagram for explaining conditions for occurrence of fixing separation failure. As shown in FIG. 7, the control unit 50 has two layers of toners of different colors with a predetermined image width X1 in the transport direction D at the leading edge of the paper P based on image data to be printed and paper conditions. When the above image (patch) is formed and the image margin area X2 at the front end of the paper P is short, it is determined that a fixing separation defect occurs. The image margin area at the front end of the paper P is an area between the side (edge) GL at the front end of the paper P and the image G formed on the front end side of the paper P.

  The image width X1 is, for example, 30 mm or more, and the image margin area X2 at the front end of the paper P is, for example, less than 20 mm. These numerical values are determined depending on the fixing unit 44 used. Note that it may be determined that a fixing separation failure occurs even when the image has one layer instead of two or more layers. In the above example, it is determined that a fixing separation failure occurs when the two conditions of the image width X1 and the image margin area X2 are satisfied. However, if either of these two conditions is satisfied, a fixing separation failure occurs. You may judge.

  Further, when determining whether or not fixing separation failure occurs, the basis weight of the paper P can be considered in addition to the image width and the image margin area of the paper P. This is because if the amount of the paper P is small, the paper P is not stiff and the fixing separation defect occurs even when the image margin area is long. This is because if the amount of paper P is large, the paper P has rigidity, and even if the length of the image margin area is short, fixing separation failure does not occur. Therefore, the occurrence of fixing separation failure can be determined with high accuracy and accuracy by including the amount of paper P as a condition for determining whether or not fixing separation failure has occurred.

The storage unit 110 stores a table TB used when determining whether or not a fixing separation failure occurs (see FIG. 2). FIG. 8 shows an example of the configuration of the table TB. As shown in FIG. 8, in the table TB, the amount of paper P and the image margin area at the front end of the paper are stored in association with each other. Specifically, the table TB stores “50 g / m ² or less” as the amount of paper P and “less than 20 mm” as the image margin area in association with each other. Note that a paper type such as plain paper or coated paper can be added as a condition for occurrence of fixing separation failure.

When a print instruction is received from the operation display unit 70 or the like, the control unit 50 acquires image data from the job information and acquires the amount information of the paper P on which image formation is performed. When the control unit 50 determines that the amount information of the acquired sheet P is, for example, “50 g / m ² or less”, the image margin area based on the image data is, for example, “less than 20 mm”, and satisfies the condition of the table TB Then, it is determined that there is a possibility that fixing separation failure may occur. Note that the above-described determination conditions are also used when determining the occurrence of fixing separation failure in each image formed on the leading edge, rear edge, left edge, and right edge of the paper P described in FIGS. 3 and 4 of the first embodiment. Can be applied.

  As described above, according to the second embodiment, the condition for occurrence of fixing separation failure is set in accordance with the amount of paper P and the image margin area, so that the occurrence of fixing separation failure can be more accurately and accurately performed. Presence / absence can be determined. Thereby, it is possible to reliably prevent occurrence of fixing separation failure.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. For example, in the above embodiment, as a notification method, a message for changing the orientation of the paper P is displayed on the screen of the operation display unit 70. However, the present invention is not limited to this. For example, the user may be notified by voice, or a message may be displayed on the screen of a computer connected via a network.

  The present invention can also be applied when the image formed on the paper P is a photograph formed on the entire surface of the paper P. In this case, as described in the second embodiment, the side of the paper P that does not satisfy the fixing separation failure occurrence condition is selected in consideration of the number of toner layers, the image margin area, the basis weight of the paper P, and the like. The image data and the paper P are rotated so that the selected side is the leading edge of the paper P. On the other hand, when the images on all sides of the paper P satisfy the fixing separation failure occurrence condition, the side with the smallest number of gradations and toner adhesion amount is selected from the four sides, and the selected side is You may make it rotate image data and the paper P so that it may become the front end side of the paper P. FIG.

  Furthermore, in the above-described embodiment, the paper rotation unit 130 is provided as a means for rotating the paper P. However, the present invention is not limited to this. For example, when there are a paper feed tray in which the paper P is placed vertically and a paper feed tray in which the paper P is placed horizontally, a paper feed tray that is advantageous for fixing separation is selected based on the input image data. You may make it do. According to this, since it is not necessary to provide the sheet rotating unit 130, the apparatus configuration can be simplified.

10 Image forming units 20A, 20B Paper feed tray 44 Fixing unit 50 Control unit 70 Operation display unit (notification unit)
100 Image forming apparatus 130 Paper rotation unit (rotation unit)
P paper

Claims (4)

An image forming unit that forms an image on a sheet based on image data;
A fixing unit for fixing the image formed by the image forming unit to the paper;
A rotating unit that is provided upstream of the image forming unit in the conveying direction and rotates the paper;
A controller that controls the image forming unit to form an image by rotating the image data in a direction in which fixing separation is advantageous when it is determined that a fixing separation failure occurs in the fixing unit based on the image data; , equipped with a,
The control unit is a case where images are formed at both upstream and downstream ends in the transport direction on the front side of the paper, and at least one of both ends in a direction perpendicular to the transport direction of the paper. When the image is not formed, the rotating unit is controlled so that the sheet rotates in accordance with the rotation of the image data so that the end of the sheet on which the image is not formed becomes the downstream end of the sheet.
An image forming apparatus comprising and this. The image forming apparatus according to claim 1, wherein the control unit causes the notification unit to notify the user to place the sheet on a sheet feeding tray in accordance with the rotation of the image data. An image forming unit that forms an image on a sheet based on image data;
A fixing unit for fixing the image formed by the image forming unit to the paper;
A rotating unit that is provided upstream of the image forming unit in the conveying direction and rotates the paper;
In the case of duplex printing, if it is determined that a fixing separation failure occurs in the fixing unit on the front side of the paper based on the image data, the image data on the back side of the paper is changed by changing the order of the surfaces on which the image is formed. A control unit that controls the image forming unit to form on the back side of the paper ,
In the case where the control unit determines that a fixing separation defect also occurs on the back side of the sheet, and in the case where images are formed on both upstream and downstream ends of the conveyance direction on the back side of the sheet. And when no image is formed on at least one of both ends in the direction orthogonal to the paper transport direction, the image is formed such that the end on which the image of the paper is not formed is the downstream end of the paper. The rotating unit is controlled so that the sheet rotates in accordance with the rotation of data.
An image forming apparatus comprising and this. The control unit determines whether or not a fixing separation failure occurs based on at least one condition of a length of a paper margin, a paper type, a weight, and a stiffness. the image forming apparatus according to any one of 3.

Images