JP6576523B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer.

  The image forming apparatus as described above is equipped with a fixing device that fixes an unfixed toner image formed on a recording material as a fixed image. As a fixing device, a roller type fixing device using a heating roller (fixing roller) and a pressure roller, which is excellent in thermal efficiency and durability, is widely known. A belt-type fixing device using a heating belt (fixing belt) and a pressure belt has been devised.

  Here, the heating roller and the heating belt are collectively referred to as a heating rotator (fixing rotator), and the pressure roller and the pressure belt are collectively referred to as a pressure rotator. A recording material carrying an unfixed toner image is sandwiched and conveyed at a nip formed by a heating rotator and a pressure rotator to fix the toner image by heat and pressure.

  The recording material is a sheet-like recording material (hereinafter referred to as paper or paper) that can form a toner image, and examples thereof include plain paper, coated paper, envelopes, postcards, labels, and OHP sheets. The toner is a non-magnetic or magnetic microscopic fine powder that adheres to the latent image and develops the latent image. In addition to chromatic ones, there are white and transparent ones.

  In these fixing devices, there is toner that adheres to the surface of the heating rotator without being fixed on the paper when the toner image is fixed at the nip portion. Such toner is referred to as offset toner. Some offset toners are returned to the sheet when the heating rotator rotates once and returns to the nip portion, and are discharged together with the sheet. Some remain on the surface of the heating rotor. There may also be a transfer to the pressure rotating body at the nip.

  In order to make it difficult to accumulate offset toner, a heating rotator whose surface is coated in a tube shape or a coat shape with a fluorine-based resin such as PFA or PTFE is often used.

  On the other hand, some papers contain a large amount of heavy calcium carbonate as a filler. In recent years, in order to improve the texture of paper, there is a tendency to increase the filling amount of calcium carbonate for reasons such as high whiteness, excellent opacity, and low cost. However, the paper powder mainly composed of calcium carbonate generated in such paper is strongly positively charged by friction with fluororesin compared to paper powder mainly composed of other fillers such as kaolin and talc. Has triboelectric charging characteristics.

  Therefore, if a sheet containing a large amount of calcium carbonate passes through the nip portion, the paper dust is easily electrostatically adsorbed on the surface of the heating rotating body whose surface is covered with a fluorine-based resin such as PFA or PTFE as described above. Become. Further, when paper dust adheres to the surface of the heating rotator as described above, the releasability of the surface of the heating rotator is significantly reduced. Once the releasability is lowered, the toner gradually starts to accumulate in the heated rotator portion where the releasability is lowered, and the toner is fixed and grows to the toner stain on the surface of the heated rotator. As the amount of accumulated toner stains increases, the toner stains are transferred to the paper, causing image defects.

  As means for removing such toner stains, Patent Document 1 proposes a method of using a sheet on which a solid image is printed as a cleaning sheet (cleaning sheet). The accumulated toner stains do not transfer to the white background of the paper because the adhesive force of the toner to the heating rotator is high. In order to remove the toner stains, it is necessary to use the adhesive force between the toners, and the heating rotator can be cleaned by transferring the toner stains to the solid image portion printed on the cleaning paper.

JP-A-2-160276

  However, if the size of the cleaning paper for cleaning the heating rotator is not appropriate, cleaning of the heating rotator becomes insufficient. For example, if the width of the cleaning paper (the dimension in the direction orthogonal to the paper transport direction) is small, the cleaning paper cannot contact the toner contamination portion, and the toner contamination cannot be cleaned. Alternatively, when the length of the cleaning paper (size in the paper conveyance direction) is shorter than the circumference of the heating rotator, the entire circumference of the heating rotator may not be cleaned with a single sheet of cleaning paper. In this case, the user of the image forming apparatus cannot remove the toner on the entire circumference of the heating rotator unless the cleaning mode is performed several times.

  However, the user has a wide variety of sizes, and does not know how many sheets of cleaning paper that can be selected arbitrarily can be washed to clean the toner contamination around the heating rotator. Normally, the circumferential phase of the heating rotator and the position of the leading edge of the paper when the paper is passed are not controlled. The circumference cannot be cleaned without gaps.

  The present invention is a further development of the above prior art. An object of the present invention is to provide an image forming apparatus capable of efficiently cleaning a heating rotator and a pressure rotator.

  A typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows.

An image forming unit for forming a toner image on a sheet;
A heating rotator and a pressure rotator for fixing the toner image formed on the sheet by the image forming unit at the nip,
A printing range in which a solid image having a toner amount of 0.4 mg / cm ² or more is removed from the sheet having the maximum width in the width direction intersecting with the sheet conveyance direction by the image forming unit excluding the minimum margin width. by forming the by Rukoto is fixed by the sheet solid image is formed of the unfixed is introduced into the nip portion, the cleaning mode for cleaning at least one surface of the heating rotating body and the pressure rotating body An execution unit to execute;
A control unit that controls the number of sheets used in the cleaning mode according to the length of the sheet in the conveyance direction;
A shift mechanism that changes the position of the sheet conveyed to the nip portion in the width direction,
The execution unit uses two or more sheets on which the solid image is formed in the cleaning mode, and the width direction with respect to a region through which the sheet passes the nip portion at the time of image formation output input by a user The sheet moved to each of the one side and the other side is conveyed to the nip portion.
An image forming apparatus comprising and this.

  Another typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows.

An image forming unit for forming a toner image on a sheet;
A heating rotator and a pressure rotator for fixing the toner image formed on the sheet by the image forming unit at the nip,
A printing range in which a solid image having a toner amount of 0.4 mg / cm ² or more is removed from the sheet having the maximum width in the width direction intersecting with the sheet conveyance direction by the image forming unit excluding the minimum margin width. by forming the by Rukoto is fixed by the sheet solid image is formed of the unfixed is introduced into the nip portion, the cleaning mode for cleaning at least one surface of the heating rotating body and the pressure rotating body An execution unit to execute ;
A shift mechanism that changes the position of the sheet conveyed to the nip portion in the width direction,
The execution unit moves the sheet on which the solid image is formed to an amount larger than the minimum margin width to one side and the other side in the width direction, and satisfies at least the following relational expression in one cleaning mode. Only to the nip part ,
An image forming apparatus comprising and this.

Nf = Lf / Lc (where Nf is an integer, rounded up after the decimal point)
Nf: Number of sheets passing through the nip portion in the cleaning mode Lf: Total length of the heating rotating body Lc: Length in the conveyance direction of the sheet used in the cleaning mode

According to the present invention, it is possible to efficiently clean substantially the entire area of the image paper passing region including the blank portion of the heating rotator or the pressure rotator.

Cross-sectional schematic diagram showing a schematic configuration of an example of an image forming apparatus (A) is a schematic cross-sectional view showing a schematic configuration of a main part of the fixing device, and (b) is a block diagram of a control system. Schematic showing fouling of fixing belt and width of cleaning paper Control flow diagram at the start of cleaning mode (1) Control flow chart when cleaning mode starts (Part 2) Example of selecting cleaning paper from multiple paper sources Example of required number of sheets when using different lengths of cleaning paper in Example 1 The schematic diagram of the cleaning paper space | interval when the cleaning paper in Example 1 is two sheets The schematic diagram of the cleaning paper space | interval when the cleaning paper in Example 1 is three or more sheets Supplementary formula for calculating cleaning paper interval in Example 1 shown in FIG. Example between cleaning paper sheets in Example 1 Example of cleaning paper information displayed on the display unit during cleaning in the first embodiment Example of warning display on display unit in embodiment 1 Schematic which shows the pressure roller stain | pollution | contamination in Example 2, and the width | variety of the cleaning paper The schematic diagram of the cleaning paper space | interval when the cleaning paper in Example 2 is two sheets The schematic diagram of the cleaning paper space | interval when the cleaning paper in Example 2 is three or more sheets Schematic diagram of control example 1 in the third embodiment Schematic diagram of control example 2 in the third embodiment Schematic diagram of control example 3 in the third embodiment Schematic diagram of control example 4 in the third embodiment

  Hereinafter, the present invention will be described more specifically with reference to reference examples and examples. These reference examples and examples are examples of the best mode of the present invention, but the present invention is not limited only to the various configurations described in these reference examples and examples. In other words, the various configurations described in the reference examples and embodiments can be replaced with other known configurations within the scope of the idea of the present invention.

《Reference example》
(Image forming device)
FIG. 1 is a schematic cross-sectional view illustrating a schematic configuration of an example of an image forming apparatus. The image forming apparatus A is a full color laser beam printer using an electrophotographic process. That is, an image is formed on a recording material (sheet: hereinafter referred to as paper) P based on image information (electrical image signal) input from the host device 200 to the control unit (execution unit: CPU) 100.

  The control unit 100 is a control unit that comprehensively controls the operation of the image forming apparatus A, and exchanges various electrical information signals with the host device 200 and the device operation unit (control panel) 101. It also controls electrical information signals input from various process devices and sensors, processing of command signals to various process devices, predetermined initial sequence control, and predetermined image forming sequence control.

  The host device 200 is a personal computer, a network, an image reader, a facsimile, or the like. The operation unit 101 includes a main body (main) power switch, various operation keys, a display unit {liquid crystal display) 101a ((a) in FIG. 2), and the like.

  Inside the image forming apparatus A, first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are arranged side by side from the left side to the right side in the drawing. The image forming units Pa, Pb, Pc, and Pd form toner images of different colors, in this example, cyan (C) color, magenta (M color), yellow (Y) color, and black (Bk) color. An electrophotographic image forming process mechanism.

  Each of the image forming units Pa, Pb, Pc, and Pd includes a dedicated image carrier, in this example, an electrophotographic photosensitive drum (hereinafter referred to as a drum) 3a, 3b, 3c, and 3d. Each of the drums 3a, 3b, 3c, and 3d is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed.

  Drum chargers 2a, 2b, 2c, and 2d, developing devices 1a, 1b, 1c, and 1d, primary transfer chargers 6a, 6b, 6c, and 6d, and a cleaner are disposed on the outer circumferences of the drums 3a, 3b, 3c, and 3d, respectively. 4a, 4b, 4c, 4d are provided. Laser scanners 5a, 5b, 5c, and 5d are installed above the drums 3a, 3b, 3c, and 3d, respectively.

  Each of the developing devices 1a, 1b, 1c, and 1d is filled with a predetermined amount of C toner, M toner, Y toner, and Bk toner as a developer by a supply device (not shown). In the laser scanners 5a, 5b, 5c and 5d, a light source device (not shown) and a polygon mirror are provided. The laser light emitted from the light source device is scanned by rotating the polygon mirror, and the light beam of the scanning light is deflected by the reflection mirror. Then, the light is condensed and exposed on the buses of the drums 3a, 3b, 3c, and 3d that are uniformly charged to a predetermined polarity and potential by the chargers 2a, 2b, 2c, and 2d by an fθ lens (not shown).

  As a result, latent images corresponding to the image signals are formed on the drums 3a, 3b, 3c, and 3d, and the latent images are respectively developed by the developing devices 1a, 1b, 1c, and 1d. Developed as a Y color toner image and a Bk color toner image.

  An intermediate transfer belt unit 19 is disposed below the image forming units Pa, Pb, Pc, and Pd. The intermediate transfer belt unit 19 includes first to third parallel three rollers 21, 22, and 23. The first roller 21 is on the first image forming unit Pa side, the second roller 22 is on the fourth image forming unit Pda side, and the third roller 23 is the first roller between the first and second rollers. And below the second roller. Further, it has a flexible endless intermediate transfer belt 20 suspended between the three rollers 21 to 23.

  On the inner side of the belt 20, between the first and second rollers 21, 22, roller-shaped primary transfer chargers 6a, 6b, 6c, 6d respectively correspond to drums of image forming units Pa, Pb, Pc, Pd. 3a, 3b, 3c and 3d are in contact with each other via a belt 20. In each image forming unit Pa, Pb, Pc, Pd, the contact portions between the drums 3a, 3b, 3c, 3d and the belt 20 are primary transfer nip portions 7a, 7b, 7c, 7d. Further, the secondary transfer roller 11 is in contact with the third roller 23 via the belt 20. The contact between the belt 20 and the secondary transfer roller 11 is the secondary transfer nip portion 8.

  The belt 20 is rotationally driven in the clockwise direction of the arrow at the same peripheral speed as the drums 3a, 3b, 3c, and 3d. A predetermined primary transfer bias is applied to the primary transfer chargers 6a, 6b, 6c, and 6d. With the primary transfer bias and the nip pressure, the C, M, Y, and Bk colors on the drums 3a, 3b, 3c, and 3d at the primary transfer nip portions 7a, 7b, 7c, and 7d are respectively formed on the surface of the belt 20. The toner images of the respective colors are sequentially superposed in a predetermined manner for primary transfer (intermediate transfer).

  The drums 3a, 3b, 3c, and 3d after the primary transfer are cleaned (removed) of the transfer residual toner by the respective cleaners 4a, 4b, 4c, and 4d, and are subsequently prepared for the formation of the next latent image.

  The four-color superimposed toner image (synthetic color toner image) is conveyed to the secondary transfer nip portion 8 by the subsequent movement of the belt 20. A sheet P is fed from a sheet storage section (recording material storage section: sheet storage section) 10 to the secondary transfer nip section 8. In this example, there are first to third three paper feed cassettes 10a, 10b, and 10c in the upper and lower three stages as a plurality of paper storage units.

  Hereinafter, the first sheet cassette 10a is referred to as sheet feeder 1, the second sheet cassette 10a is referred to as sheet feeder 2, and the third sheet cassette 10a is referred to as sheet feeder 3. In the paper feeding units 1, 2, and 3, sheets P having different width sizes (longitudinal widths) orthogonal to the sheet conveyance direction (recording material conveyance direction) are stacked and stored.

  Sensors 26a, 26b, and 26c serving as recording material size detection mechanisms in which the size information of the paper P stored in each of the paper feeding units 1-3 corresponds to the respective paper feeding units (in FIGS. b)) to the control unit 100.

  The user can select and designate a desired size sheet to be used in a print job or a cleaning mode of the fixing device 9 described later from the display unit 101a of the operation unit 101 or the operation unit of the host device 200 to the control unit 100.

  When a print job is input, the control unit 100 drives the feeding rollers 13a, 13b, or 13c corresponding to the paper feeding unit in which the paper P of the size selected and specified as described above is stored. As a result, the sheets P are separated one by one from the sheet feeding unit on which the feeding roller is driven, and conveyed to the registration tor 12 through the feeding path 15 having the conveying roller 14. In this example, the paper P is fed and conveyed by so-called central reference conveyance with the width center of the paper P as a reference.

  The registration roller 12 corrects the skew of the paper P fed from the paper feed cassette and introduces the paper P into the secondary transfer nip portion 8 through the pre-transfer guide 16 at a predetermined control timing. The predetermined control timing is a control timing at which the leading end portion of the toner image formed on the belt 20 reaches and the leading end portion of the paper P reaches the secondary transfer nip portion 8 and reaches the predetermined position. is there.

  Reference numeral 12a denotes a registration sensor that detects and controls the arrival of the leading edge of a sheet conveyed from the paper feeding unit or the leading edge of a sheet returned and conveyed (both sides conveyed) from a duplex path 113 described later to the registration roller 12. Feedback to the unit 100.

  The control unit 100 controls the feeding timing of the paper P by driving the registration roller 12 based on the paper leading edge detection signal input from the registration sensor 12a. Further, the registration sensor 12 a detects that the rear end portion of the sheet P sent out by the registration roller 12 has passed through the registration roller 12. The control unit 100 controls the driving stop of the registration roller 12 based on the sheet trailing edge detection signal input from the registration sensor 12a.

  The registration sensor 12a also functions as a detection mechanism that detects the timing of a sheet that passes through a fixing nip N of the fixing device 9 described later. The control unit 100 also functions as a control mechanism that controls the timing of the sheet passing through the fixing nip N of the fixing device 9.

  Then, the sheet P that has been fed to the secondary transfer nip 8 by the registration roller 12 is nipped and conveyed by the secondary transfer nip 8. A secondary transfer bias is applied to the secondary transfer roller 11. By the secondary transfer bias and the nip pressure, the four-color superimposed toner images on the belt 20 side are secondarily transferred to the surface of the paper P sequentially and collectively. In this example, the toner image is formed on the paper P, leaving a certain margin from the four side edges of the paper P.

  The paper P exiting the secondary transfer nip 8 is separated from the surface of the belt 20 and introduced into a fixing device (fixing part) 9, and the toner image is fixed on the paper P as a fixed image by heat and pressure. The toner and other foreign matters remaining on the belt 20 after separation of the paper P are wiped off by contacting a cleaning web (nonwoven fabric) 30 with the surface of the belt 20.

  In the single-sided printing mode, the single-sided (first side) printed paper P that has exited the fixing device 6 enters the discharge path 17 through the upper surface side of the flapper 110 that has been switched to the substantially horizontal first posture. The paper is discharged to the discharge tray 25 by the discharge roller 18.

  In the double-sided printing mode, the single-sided (first side) printed paper P that has exited the fixing device 6 is lowered by the lower surface side of the flapper 110 that has been switched from a substantially horizontal large first posture to an obliquely upward second posture. To the reversing path 111. It is reversed (switched back) by the reversing roller 112 and guided to the double-sided path 113, and conveyed back to the feeding path 15 in a state where the front and back are reversed. Then, the toner image is re-introduced into the secondary transfer nip portion 8 (double-sided conveyance) to receive the secondary transfer of the toner image on the second side of the paper P.

  Thereafter, as in the case of single-sided printing, the paper P is discharged as a double-sided printed matter through the fixing device 9, the upper surface side of the flapper 110 switched to the first posture, the discharge path 17, and the discharge roller 18. It is discharged to the tray 25.

  In the image forming apparatus A of this example, the four image forming units Pa, Pb, Pc, Pd and the intermediate transfer belt unit 19 including the secondary transfer roller 11 are fed from the sheet storage unit 10. An image forming unit B that forms an unfixed toner image on P. Further, the reverse path 111 and the double-sided path 113 constitute a double-sided conveyance mechanism for forming an image on both sides of the paper P.

(Fixing device)
2A is a schematic cross-sectional view showing a schematic configuration of a main part of the fixing device 9 in this example, and FIG. 2B is a block diagram of a control system. The fixing device 9 serves as a heating rotator (fixing rotator) that forms a nip portion (fixing nip portion) N for nipping and conveying the paper P conveyed from the image forming portion B side to fix the toner image T by heat and pressure. The heating belt 52 and the pressure roller 51 as a pressure rotator are provided.

  A heating belt (hereinafter referred to as a fixing belt) 52 is a heat-resistant endless belt having flexibility, and is suspended between two parallel fixing rollers 50 and a tension roller 56 with a predetermined tension. Yes. The pressure roller 51 is arranged substantially parallel to the fixing roller 50 below the fixing roller 50, and the fixing roller 50 and the pressure roller 51 are pressed against each other with a predetermined pressing force with the fixing belt 52 interposed therebetween. Yes.

  In this example, the fixing belt 52 is formed by coating a Ni rubber base layer having a thickness of 60 μm with a Si rubber layer having a thickness of 300 μm as an elastic layer and a PFA tube having a thickness of about 50 μm as a release layer on the outer peripheral surface thereof. Yes. In a cylindrical free state, the outer diameter is 140 mm (overall circumference is about 440 mm).

  The fixing roller 50 has an Si rubber layer 50b having a thickness of about 12 mm on an Al hollow core metal 50a having an outer diameter of 50 mm and a thickness of 12 mm. One end side and the other end side in the rotation axis direction of the fixing roller 50 are rotatably arranged via a bearing member with respect to a frame portion on one end side and the other end side of a fixing device casing (not shown), respectively. .

  The tension roller 56 is an Al hollow roller having an outer diameter smaller than that of the fixing roller 50. The tension roller 56 is slidably moved so that one end side and the other end side thereof in the rotation axis direction can be rotated via a bearing member with respect to the frame portion on the one end side and the other end side of the fixing device casing and away from the fixing roller 50. It is arranged to be possible. Then, it is urged to move away from the fixing roller 50 by an elastic urging member (not shown). As a result, the fixing belt 52 is suspended with a predetermined tension applied between the fixing roller 50 and the tension roller 56.

  The pressure roller 51 has a silicon rubber layer 51b having a thickness of 200 μm on an Al hollow core metal 51a having an outer diameter of 40 mm and a thickness of 12 mm, and a PFA tube having a thickness of about 50 μm as a release layer on the outer peripheral surface thereof. 51c is covered. One end side and the other end side of the pressure roller 51 in the rotation axis direction are disposed so as to be rotatable with respect to a frame portion on one end side and the other end side of the fixing device housing via a bearing member, respectively.

  Then, the fixing roller 50 and the pressure roller 51 sandwich the fixing belt 52, and a predetermined resistance against the elasticity of the elastic layer 50b of the fixing roller 50, the elastic layer of the fixing belt 52, and the elastic layer 51b of the pressure roller 51 is obtained. It is pressed by pressing force. As a result, a fixing nip portion N having a predetermined width (short width) is formed between the fixing belt 52 and the pressure roller 51 in the conveyance direction a of the paper P.

  The fixing roller 50 is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving mechanism M controlled by the control unit 100. As the fixing roller 50 is driven to rotate, the fixing belt 52 rotates in a clockwise direction indicated by an arrow at a peripheral speed corresponding to the rotational peripheral speed of the fixing roller 50. The tension roller 56 rotates following the rotation of the fixing belt 52. The pressure roller 51 also rotates following the rotation of the fixing belt 52 by the frictional force with the fixing belt 52 in the nip portion N.

  Halogen heaters H50, H56, and H51 are inserted and disposed in the inner hollow portions of the cores of the fixing roller 50, the tension roller 56, and the pressure roller 51, respectively. Each of the halogen heaters H50, H56, H51 receives heat from the power supply units 102, 103, 104 controlled by the control unit 100 and generates heat. As a result, the fixing roller 50, the tension roller 56, and the pressure roller 51 are each heated from the inside.

  The fixing operation of the fixing device 9 is as follows. The control unit 100 turns on the driving mechanism M at a predetermined control timing to rotate the fixing roller 50. Following the rotation of the fixing roller 50, the fixing belt 52, the tension roller 56, and the pressure roller 51 also rotate.

  In addition, the control unit 100 supplies power to the halogen heaters H50, H56, and H51 from the power supply units 102, 103, and 104 at a predetermined control timing to heat the fixing roller 50, the tension roller 56, and the pressure roller 51. The surface temperatures of the fixing roller 50, the tension roller 56, and the pressure roller 51 are detected by the thermistors TH50, TH56, and TH51, respectively, and fed back to the controller 100.

  Based on the feedback information, the control unit 100 controls each of the fixing roller 50, the tension roller 56, and the pressure roller 51 so that the respective surface temperatures rise to a predetermined temperature and are maintained. That is, power supply from the power supply units 102, 103, and 104 to the halogen heaters H50, H56, and H51 is controlled.

  The surface temperature of the fixing roller 50 is raised to a predetermined fixing temperature, and the temperature is adjusted. The fixing belt 52 is heated by the fixing roller 50 so that the surface temperature becomes a temperature corresponding to the surface temperature of the fixing roller 50. In this example, the tension roller 56 and the pressure roller 51 are raised to a predetermined surface temperature set lower than that of the fixing roller 50, and are adjusted in temperature.

  In this state, the sheet P carrying the unfixed toner image T conveyed from the image forming unit B side is guided upward by the conveyance guide 54 and introduced into the fixing device 9 along the surface of the pressure roller 51. Then, the toner enters the fixing nip portion N and is nipped and conveyed. The sheet P is conveyed while being nipped and conveyed through the fixing nip N with the image surface carrying the toner image T in close contact with the surface of the fixing belt 52.

  In this nipping and conveying process, the unfixed toner image T is heated by the fixing belt 52 heated by the heat of the fixing roller 50 and is pressed by the nip pressure and fixed on the paper surface as a fixed image. The paper portion that has passed through the fixing nip portion N is sequentially separated from the surface of the fixing belt 52 and the pressure roller 51 by the separation guide 55 at the paper exit portion of the fixing nip portion N, and is discharged and conveyed from the fixing device 9.

  By using the fixing belt 52, the circumferential length of the fixing member 52 can be made longer than that of the fixing roller 50, and when the circumferential length of the fixing member 52 is shorter than the length dimension of the paper P in the paper transport direction a, the gloss level is easy to see. Can be reduced. When the fixing member 52 makes two or more turns with respect to the length of one sheet of paper, the gloss level difference is because the fixing member temperature is lower in the second round where the heat is taken away from the paper than in the first round of the fixing member. This is a phenomenon in which the temperature difference of the fixing member 52 becomes apparent as the gloss difference of the image.

(Fixing device cleaning mode)
FIG. 3 shows an outline of dirt on the fixing belt 52 as a fixing rotator. The following matters can be cited as causes of the contamination of the fixing belt 52. As an additive (filler) contained in the paper P introduced into the fixing nip N, for example, calcium carbonate has a triboelectric charge characteristic that is strongly charged by friction with the PFA tube as the surface layer of the fixing belt 52. Therefore, when the paper P containing a large amount of calcium carbonate passes through the fixing nip portion N, it becomes easy to be electrostatically attracted to the PFA tube on the surface of the fixing belt 52.

  The surface of the fixing belt 52 to which calcium carbonate has adhered is remarkably reduced in releasability, and when the paper P carrying the toner image T is passed through the fixing nip N, the toner gradually moves from the paper P to the surface of the fixing belt 52. (FIG. 3A). In FIG. 3A, α schematically represents a state in which paper dust and calcium carbonate in the margins on both sides in the width direction of the paper P that has passed through the fixing nip portion N adhere to the surface of the fixing belt 52 as toner stains. Show.

  If toner or paper powder is supplied to the toner nip α by paper P having the same longitudinal width that is passed through the fixing nip N thereafter, as shown in FIG. Gradually grow. When the stain grows to some extent, as shown in FIG. 3C, when a sheet P larger than the stain width is subsequently passed, the stain α adheres to the image portion of the sheet P and a defective image is formed.

Since the toner stain α is firmly fixed on the surface of the fixing belt 52, it is difficult to transfer to a blank portion of the paper P where there is no toner or an image area where the amount of toner is small. For this reason, when the fixing belt 52 is in the cleaning mode, a predetermined image is formed with a density of not less than a predetermined amount (for example, 0.4 mg / cm ² ) of toner having high adhesive strength in order to remove the accumulated toner contamination α. The paper P can be used as a cleaning paper (hereinafter referred to as cleaning paper).

  Therefore, in this example, in the cleaning mode of the fixing device 9, the sheet P is fed from the sheet storage unit 10 and a solid image is formed as a predetermined image by the image forming unit B. The paper is introduced into the fixing device 9 as cleaning paper. This is a mode in which at least one surface of the fixing rotator 52 and the pressure rotator 51 is cleaned based on the above principle. This cleaning mode is executed by the control unit (execution unit) 100 based on the execution command.

  The cleaning mode can be executed by the user operating the execution key 101b (FIG. 2B) on the operation unit 101. The execution key 101b is a manual input means that allows the user to arbitrarily input a cleaning mode execution command to the control unit 100. The cleaning mode can be automatically executed by the control unit 100 based on predetermined determination information. Alternatively, the control unit 100 can display on the operation unit 101 or the display unit of the host device 200 to prompt the user to execute the cleaning mode based on the predetermined determination information.

  The longitudinal width of the cleaning paper used in the cleaning mode is sufficiently wider than the stain width of the fixing belt 52, or at least the width of the fixing belt 52 is not the same as the width size (longitudinal width) of the paper that causes the stain. The toner stain α cannot be sufficiently cleaned ((d) in FIG. 3).

  Therefore, in this example, the control as shown in FIGS. 4A and 4B is performed. That is, at the start of the cleaning mode, the size of the paper used as the cleaning paper is selected and specified to the control unit 100 from the display unit 101a of the operation unit 101 or the operation unit of the host device 200. When the width size of the sheet is not the maximum width size Wmax usable in the apparatus, a notification or warning is displayed on the display unit 101b so as to use the sheet having the maximum width size Wmax.

  Further, even if the width of the cleaning paper is satisfied, if the length of the cleaning paper in the conveyance direction is shorter than the circumference of the fixing belt 52 or the pressure roller 51 to be cleaned, the toner of the fixing belt 52 or the pressure roller 51 The dirt cannot be cleaned sufficiently. Therefore, as shown in FIG. 5, when the length L2 of the paper selected and designated as the cleaning paper is not longer than the circumferential length L4 of the fixing belt 52 or the pressure roller 51 at the start of the cleaning mode, the display unit 101b. A warning or warning is displayed.

  The display unit 101b in FIG. 4B displays a warning in step S4 in FIG. 4A and step S5 in FIG. Based on this warning display, when reselecting paper, the user presses the paper reselection key 101c and returns to step S1 to reselect an appropriate size cleaning paper. If no paper of an appropriate size is stored in any of the paper supply units 1-3, the paper of an appropriate size is stored in any of the paper supply units 1-3, and the paper is selected again.

  Further, the size information of the paper stored in each of the paper feeding units 1-3 is input to the control unit 100 from the sensors 26a, 26b, and 26c of the paper feeding units. Therefore, the control unit 100 automatically selects a sheet having the maximum width among the sheets stored in the plurality of sheet feeding units 1-3 and feeds it as a cleaning sheet in the cleaning mode. It is also possible to set the control mode to execute the cleaning mode.

  More specifically, the paper having the maximum width size is used among the papers stored in the three paper supply units 1-3 as the plurality of paper storage units (recording material storage units) in FIG. For example, when the paper size as shown in FIG. 6 is set in the paper supply unit 1-3, the maximum width size among the set paper widths, FIG. 6A is 330 mm, and FIG. In b), only a sheet having a width of 297 mm can be selected as the cleaning sheet.

  The printing range of the toner image in the cleaning mode is preferably set so that the cleaning effect of the fixing belt 52 can be exhibited in a wide range of the cleaning paper as much as possible with a minimum margin.

Example 1
In recent years, the use of a large-diameter fixing belt 52 is increasing, and there are cases where the entire circumferential length Lf of the fixing belt 52 is longer than the length Lc in the conveyance direction of the paper P. Further, not only in the cleaning mode, the paper P at the time of image formation (during normal printing) is passed with a predetermined paper gap (interval) Ld. The part to be cleaned cannot be cleaned. Therefore, it is necessary to arrange (apply) the cleaning paper with no gap between the fixing belt 52 and the fixing belt 52 at least twice.

  At this time, in order to minimize the number of cleaning sheets used, it can be determined mechanically by the length Lf of the entire circumference of the fixing belt 52 (about 440 mm in this example) and the length Lc in the conveyance direction of the cleaning sheet. It is. That is, at least the cleaning paper is required by the number obtained by dividing the fixing belt circumferential length Lf by the conveyance direction length Lc of the cleaning paper P and rounding it up to a whole number (FIG. 7).

  Further, when trying to minimize the number of used cleaning papers, the interval Ld between the cleaning papers needs to be controlled within a certain range represented by the following relationship. For example, FIG. 7 is applied to the case where the entire circumference of the fixing belt can be cleaned with two cleaning papers (the length of the cleaning paper is 220 mm or more and less than 440 mm), for example, when A3 (420 mm) is used as the cleaning paper.

  As shown in FIG. 8A, the sheet spacing Ld between the cleaning sheets at this time must be not less than twice the difference between the fixing belt length Lf and the cleaning sheet length Lc (2 (Lf−Lc)). The entire circumference of the fixing belt cannot be covered. Further, as shown in FIG. 8B, if the sheet spacing Ld between the cleaning sheets is longer than the entire circumferential length Lf of the fixing belt 52, the entire circumferential surface of the fixing belt cannot be covered.

  Further, in FIG. 9, when two or more cleaning papers are used and the entire fixing belt is cleaned (three sheets are required when the cleaning paper length Lc is 147 to 219 mm, and four sheets are required when the cleaning paper length Lc is 110 to 146 mm). Ld is shown. According to FIG. 9A, the cleaning paper interval Ld needs to be equal to or greater than the following relationship.

Cleaning paper interval Ld = cleaning paper length Lc + 2 × (total circumferential length Lf of fixing belt 52−number of cleaning paper passes Nf × cleaning paper length Lc) ÷ (number of cleaning paper passes Nf− 1)
That is, Ld = Lc + 2 (Lf−NfLc) / (Nf−1). The calculation process is supplemented in FIG. Also, according to FIG. 9B, it can be seen that the cleaning paper interval Ld must be less than or equal to the cleaning paper length Lc.

  Therefore, the paper used in the cleaning mode is the paper having the maximum width among the set papers stored in the plurality of paper feeding units 1-3, and at least the following relational expression is satisfied in one cleaning mode. A configuration is adopted in which the paper P passes through the nip portion N of the fixing device 9 as many times as it is satisfied. With this configuration, it is possible to clean the entire length of the normally used paper.

Nf = Lf / Lc (where Nf is an integer, rounded up after the decimal point)
Nf: Number of sheets P that pass through the nip portion N in the cleaning mode Lf: Total length of the fixing belt 52 Lc: Length in the conveyance direction of the sheet P used in the cleaning mode A detection mechanism 12a for detecting timing and a control mechanism 100 for controlling the timing of the sheet passing through the nip portion N are provided. When a plurality of sheets are used in one cleaning mode, the interval between the sheets in the cleaning mode is controlled so as to satisfy the following relational expression. With this configuration, it is possible to clean the entire circumference of the fixing belt with the minimum number of sheets and time (cleaning of the entire surface with two circumferences of the fixing belt). That is, by controlling the sheet interval Ld so as to satisfy the following relational expression, it is possible to minimize the number of cleaning sheets used in any case.

Ld: interval between sheets in the cleaning mode When Nf = 2 (when Lc <Lf <= 2Lc) 2 (Lf−Lc) <Ld <Lf
When Nf = 3 or more (when 2Lc <Lf), Lc + 2 (Lf−Nf * Lc) / (Nf−1) <Ld <Lc
From the above results, as shown in FIG. 11, when three types of papers having different widths are stored in the paper feeding unit 1-3, the paper feeding unit that can be selected as cleaning paper and the paper feeding unit are used. In this case, the required number of cleaning sheets and the interval Ld between the cleaning sheets are controlled. This interval control is performed by the detection mechanism 12a that detects the timing of the paper P that passes through the nip portion N and the control mechanism 100 that controls the timing of the paper that passes through the nip portion N in the cleaning mode. Thereby, the fixing belt 52 can be efficiently cleaned with a minimum amount of cleaning paper.

  Supplementally, as shown in FIG. 11B, the sheet spacing Ld when a plurality of sheets are flowed can be used in a wide range. However, if the distance between the sheets during normal printing is included in this range, it is necessary to change it. There is no. However, in order to minimize the number of sheets of cleaning paper, if it is necessary to change the distance between the sheets during normal printing, it is better to reduce the paper interval Ld so that the first and last sheets of cleaning paper do not extend. It is desirable because time can be shortened.

  Alternatively, if there is a margin where there is no toner at the leading and trailing edges of the paper in the cleaning mode, the cleaning efficiency is not good if there is no toner, so it is better to overlap the cleaning papers as much as possible. Use it.

  Further, when there are a plurality of options as the cleaning paper as shown in FIG. 11B, which one is used may be arbitrary. However, it is conceivable that either one of the paper types being fed is expensive and not suitable for the use of cleaning paper. Therefore, when the cleaning mode is performed, the control unit 100 displays the sheet information of the sheet feeding unit 1-3 and the number of sheets used in the cleaning mode on the display unit 101a of the operation unit 101 as shown in FIG. It is more effective if the user can select whether to use part 1-3.

  Whichever paper of FIG. 12 is selected, the width of the cleaning paper is only 297 mm with respect to the fixing belt 52. For example, when the maximum size of paper that can be used in the image forming apparatus is 330 mm × 483 mm (13 inches × 19 inches), if a paper having a width of 330 mm is used after the cleaning mode is performed, the image is stained.

  Therefore, if the maximum size paper is not set in the paper feeding unit 1-3 when the cleaning mode is performed, the control unit 100 determines that the maximum size paper is not stored in the paper feeding unit 1-3. Is displayed on the display unit 101a. Alternatively, the control unit 100 may display on the display unit 101a of the operation unit 101 that there is a possibility that smearing may occur when using a paper having a size larger than the paper width used in the cleaning mode. As an example, FIG. 13 shows a display example on the display unit 101a.

  As described above, this example includes the display unit 101a and the operation unit 101 for selecting the paper P in order to execute the cleaning mode. When the cleaning mode is performed, as shown in FIG. 13, the display unit 101 a is used in the cleaning mode for the paper feeding unit storing sheets usable in the cleaning mode and each paper feeding unit. The number of sheets to be printed is displayed, and the paper feed unit to be used can be selected from the operation unit 101.

Example 2
In this embodiment, a case where dirt is accumulated on the pressure roller 51 serving as a pressure rotator will be described. Description of the same elements as those in the first and second embodiments, such as an image forming apparatus and a fixing apparatus, is omitted.

(Fixing device cleaning mode)
FIG. 14 shows an outline of pressure roller contamination in this embodiment. The cause of the contamination of the fixing belt 52 is the calcium carbonate contained in the paper, which is the same as the description in the reference example. The pressure roller contamination occurs when the toner contamination on the fixing belt 52 shifts to the pressure roller 51 between paper sheets (FIG. 14A). The dirt α of the pressure roller 51 also grows in the longitudinal direction little by little ((b) in FIG. 14). During single-sided printing, there is no toner image on the pressure roller 51 side, so the paper is less likely to get dirty. An image defect occurs ((c) in FIG. 14).

  Therefore, it is desirable to perform the cleaning mode on the pressure roller 51 to remove dirt. Also in this case, the longitudinal width of the cleaning paper used in the cleaning mode is sufficiently wider than the dirt width of the pressure roller 51, or at least the same width as the width size (longitudinal width) of the paper on which the dirt is generated. Otherwise, the pressure roller toner stain α cannot be sufficiently cleaned ((d) in FIG. 14).

  The appropriate width for the cleaning paper is the same as that for cleaning the fixing belt 52, and it is necessary to select the maximum width paper type installed in the paper supply unit 1-3. The number of cleaning sheets required for the cleaning mode is the number of sheets obtained by dividing the pressure roller circumference by the length of the cleaning sheet and rounding it up to a whole number.

  When the pressure roller 51 is in the cleaning mode, a predetermined image (solid image) is placed on the first side of the paper by double-sided printing, or paper once fixed with a predetermined toner image by single-sided printing is used as a cleaning paper. It is necessary to install the pressure roller 51 so that the image surface is in contact with the pressure roller 51.

  In the case of cleaning by double-sided printing, it is difficult to define the gap between sheets because the first and second sides are not regularly fed depending on the paper size. However, when the cleaning paper prepared in advance is placed in contact with the pressure roller side and one-side printing is performed, the interval between the cleaning papers may be defined in the same way as the cleaning of the fixing belt 52. At this time, by replacing the circumference of the fixing belt with the circumference of the pressure roller, the relational expression of Example 1 can be used as it is.

  FIG. 15 and FIG. 16 show a sheet interval when a cleaning sheet on which a toner image is fixed as a cleaning sheet is passed through one side so as to come into pressure contact in the cleaning mode for the pressure roller 51. In the following, the relational expression of Example 1 is described by replacing the pressure roller 51 with cleaning.

  (1) The paper used in the cleaning mode is the paper having the maximum width among the papers stored in the plurality of paper supply units 1-3, and the number of times satisfying at least the following relational expression in one cleaning mode. A sheet printed on both sides is used. With this configuration, it is possible to cope with the occurrence of contamination on the pressure roller 51.

Np = Lp / Lc (where Np is an integer, rounded up after the decimal point)
Np: Number of sheets used at least in the pressure roller cleaning mode Lp: Circumferential length of the pressure roller Lc: Length in the conveyance direction of the sheet P used in the cleaning mode (2) Timing of the sheet P passing through the nip portion N A detection mechanism for detection and a control mechanism for controlling the timing of the sheet passing through the nip portion N are provided. The paper used in the cleaning mode is set in the paper feed unit so that the solid image is fixed to the pressure roller, and the paper used in the cleaning mode is set in the paper feeding unit. It is the largest paper among the papers that are being used. The sheet passes through the nip portion N by the number satisfying at least the following relational expression in one cleaning mode.

Np = Lp / Lc (where Np is an integer, rounded up after the decimal point)
Np: Number of sheets used at least in the pressure roller cleaning mode Lp: Perimeter of the pressure roller 51 Lc: Length in the conveyance direction of the sheet P used in the cleaning mode Multiple sheets used in one cleaning mode In this case, control is performed so that the interval between sheets in the cleaning mode satisfies the following relational expression. With this configuration, it is possible to cope with the occurrence of contamination on the pressure roller 51.

When Np = 2 (when Lc <Lp <= 2Lc) 2 (Lp−Lc) <Ld <Lp
When Np = 3 or more (when 2Lc <Lp), Lc + 2 (Lp−NpLc) / (Np−1) <Ld <Lc
Example 3
In the cleaning mode of the reference example and Example 1-2, it is possible to perform control so that the cleaning paper passing through the nip portion N is moved by a predetermined amount to one side and the other side in the longitudinal width direction. As a result, dirt on the fixing belt 52 and the pressure roller 51 can be removed more satisfactorily.

(1) Control example 1
In this control example 1, as shown in FIG. 17, the cleaning paper P passes through the fixing nip portion N twice by feeding both sides of the single cleaning paper P. That is, this cleaning mode is a mode in which a sheet on which a solid image (predetermined image) is formed in the image forming unit B is fed to the nip N of the fixing device 9 at least twice by a single execution command. .

  The relative position in the longitudinal width direction of the nip portion N and the paper P at the time of feeding the first side (first time) and the second side (second time) of the paper P is relative to the paper feeding position at the time of normal image formation. In this case, the paper is shifted so that one side and the other side in the width direction are moved in a predetermined amount in the reverse direction in random order. This sheet shift control is performed, for example, by a sheet shift mechanism 105 (FIG. 2B: position control mechanism) having an appropriate configuration disposed upstream of the secondary transfer nip portion 8 in the sheet conveyance direction.

  The first sheet and the second sheet are the same sheet, and the second sheet of the first sheet that has passed through the nip N is reversed by the reverse path 111 and the duplex path 113 and returned to the image forming section B. It is a sheet that has been conveyed (double-sided conveyance).

  In the cleaning mode, the relative movement amount of the nip portion N and the paper P in the width direction by the paper shift mechanism is the minimum of the one side and the other side of the paper in the width direction that can be selected during normal image formation. It is larger than the margin width.

  As a result, the cleaning paper P can be passed outside the region through which the paper P passes during normal image formation, and the image portion on the cleaning paper P can be reliably brought into contact with the toner stain α of the fixing belt 52. Therefore, the toner stain can be removed well.

(2) Control example 2
In an image forming apparatus or the like that does not have a double-sided conveyance mechanism, the same effect can be obtained by using a control method in which two cleaning papers P are sequentially fed on one side as shown in FIG. That is, the first and second sheets in Control Example 2 are two separate sheets.

  (2) Control Example 3 In this control example 3, as shown in FIG. 19, the two cleaning papers P are conveyed on both sides and passed through the nip portion N four times in total, so that the fixing belt 52 and the pressure roller The toner stain α adhering to 51 can be cleaned well.

  In other words, in this cleaning mode, at least two sheets on which the solid image (predetermined image) is formed on the first side of the image forming unit B are conveyed on both sides by a single execution command and fed to the nip N a total of four times. This is the mode to be sent. The relative positions when feeding the first and second sheets of paper are opposite to each other in the width direction with respect to the sheet feeding position during normal image formation. The paper shift mechanism 105 is controlled so as to be moved quantitatively.

  In this cleaning mode, the relative movement amount of the nip portion N and the paper in the width direction by the paper shift mechanism is the minimum margin width on one side and the other side of the paper in the width direction that can be selected during normal image formation. Bigger than.

  As a result, the cleaning paper P can be passed outside the region through which the paper P passes during normal image formation, and the image portion on the cleaning paper P can be reliably brought into contact with the toner stain α, and the toner stain can be removed. It can be removed well.

(4) Control example 4
This control example 3 is to form solid images (predetermined images) on both sides of the double-sided cleaning paper P in the control example 3 as shown in FIG. That is, this is a mode in which at least two cleaning papers P having a solid image formed on both sides are conveyed on both sides and passed through the nip portion N a total of four times.

  In the control example 3, a solid image is formed only on the first surface, and the solid image portion on one side is passed through the nip portion N twice, so that the surfaces of both the fixing belt 52 and the pressure roller 51 are stained. I was trying to remove it.

  If a solid image is also formed on the second surface as in this control example 4, the image surface of the cleaning paper P can be contacted and cleaned twice on the fixing belt 52 side. For this reason, it is possible to clean even the dirt that cannot be removed at one time, and the fixing belt 52 and the pressure roller 51 can be cleaned more effectively.

《Other matters》
(1) The image forming unit B that forms an unfixed toner image T on the recording material P is not limited to one using an electrophotographic process. It may be an image forming unit using an electrostatic recording process or a magnetic recording process. Alternatively, the image forming unit may form a monochrome image. The image forming unit is not limited to the transfer method, and may form a toner image by a direct method using photosensitive paper or electrostatic recording paper as a recording material.

  (2) The fixing device 9 is an apparatus configuration in which the fixing rotator 52 is a roller and the pressure rotator 51 is a belt, and an apparatus configuration in which both the fixing rotator 52 and the pressure rotator 51 are rollers or both are belts. It may be.

  A ·· Image forming device, B ·· Image forming portion, 9 ·· Fixing device (fixing portion), 52 ·· Fusing rotator (fixing belt), 51 ·· Pressure rotator (pressure roller), N ··・ Nip part (fixing nip part), 10 ..Recording material storage part, P ..Recording material, T ..Toner image, 100 ..Control part

Claims (6)

An image forming unit for forming a toner image on a sheet;
A heating rotator and a pressure rotator for fixing the toner image formed on the sheet by the image forming unit at the nip,
A printing range in which a solid image having a toner amount of 0.4 mg / cm ² or more is removed from the sheet having the maximum width in the width direction intersecting with the sheet conveyance direction by the image forming unit excluding the minimum margin width. by forming the by Rukoto is fixed by the sheet solid image is formed of the unfixed is introduced into the nip portion, the cleaning mode for cleaning at least one surface of the heating rotating body and the pressure rotating body An execution unit to execute;
A control unit that controls the number of sheets used in the cleaning mode according to the length of the sheet in the conveyance direction ;
A shift mechanism that changes the position of the sheet conveyed to the nip portion in the width direction,
The execution unit uses two or more sheets on which the solid image is formed in the cleaning mode, and the width direction with respect to a region through which the sheet passes the nip portion at the time of image formation output input by a user The sheet moved to each of the one side and the other side is conveyed to the nip portion.
An image forming apparatus comprising and this. An image forming unit for forming a toner image on a sheet;
A heating rotator and a pressure rotator for fixing the toner image formed on the sheet by the image forming unit at the nip,
A printing range in which a solid image having a toner amount of 0.4 mg / cm ² or more is removed from the sheet having the maximum width in the width direction intersecting with the sheet conveyance direction by the image forming unit excluding the minimum margin width. by forming the by Rukoto is fixed by the sheet solid image is formed of the unfixed is introduced into the nip portion, the cleaning mode for cleaning at least one surface of the heating rotating body and the pressure rotating body An execution unit to execute ;
A shift mechanism that changes the position of the sheet conveyed to the nip portion in the width direction,
The execution unit moves the sheet on which the solid image is formed to an amount larger than the minimum margin width to one side and the other side in the width direction, and satisfies at least the following relational expression in one cleaning mode. Only to the nip part ,
An image forming apparatus comprising and this.
Nf = Lf / Lc (where Nf is an integer, rounded up after the decimal point)
Nf: Number of sheets passing through the nip portion in the cleaning mode Lf: Total length of the heating rotating body Lc: Length in the conveyance direction of the sheet used in the cleaning mode A detection mechanism that detects the timing of the sheet passing through the nip portion and a control mechanism that controls the timing of the sheet passing through the nip portion, and when a plurality of sheets are used in one cleaning mode, The image forming apparatus according to claim 2, wherein an interval between sheets in the cleaning mode is controlled to satisfy the following relational expression.
When Nf = 2 (when Lc <Lf <= 2Lc) 2 (Lf−Lc) <Ld <Lf
When Nf = 3 or more (when 2Lc <Lf), Lc + 2 (Lf−Nf * Lc) / (Nf−1) <Ld <Lc
Ld: interval between recording materials in the cleaning mode 3. The sheet according to claim 2, further comprising a double-sided conveyance mechanism for forming an image on both sides of the sheet, wherein a sheet that has been printed on both sides by a number that satisfies at least the following relational expression in one cleaning mode is used. Image forming apparatus.
Np = Lp / Lc (where Np is an integer, rounded up after the decimal point)
Np: number of sheets used at least in the cleaning mode of the pressure rotator Lp: peripheral length of the pressure rotator Lc: length in the conveyance direction of the sheet used in the cleaning mode 5. The image forming apparatus according to claim 4, wherein when a plurality of sheets are used in one cleaning mode, the interval between the sheets in the cleaning mode is controlled so as to satisfy the following relational expression.
When Np = 2 (when Lc <Lp <= 2Lc) 2 (Lp−Lc) <Ld <Lp
When Np = 3 or more (when 2Lc <Lp), Lc + 2 (Lp−NpLc) / (Np−1) <Ld <Lc   A display unit and an operation unit for selecting a sheet for executing the cleaning mode; and when the cleaning mode is performed, the display unit includes a sheet storage unit storing sheets usable in the cleaning mode; The number of sheets used in the cleaning mode is displayed for each sheet storage unit, and the sheet storage unit to be used can be selected from the operation unit. Image forming apparatus.