Image forming apparatus

Abstract

To provide an image forming apparatus capable of suppressing the likelihood of a cleaning blade being turned up even when monochrome and multicolor image forming operations are performed in combination.SOLUTION: An image forming apparatus 100 includes a control part 130, and the control part 130, during execution of either a first image forming operation or a second image forming operation, refrains from performing a first reverse rotation operation and a second reverse rotation operation until a first count value counted by a first counting part Q1 reaches a predetermined first threshold, determines, in accordance with a second count value counted by a second counting part Q2 at the time when the first count value reaches the first threshold, whether to perform the first reverse rotation operation or the second reverse rotation operation, and performs the first reverse rotation operation or the second reverse rotation operation on the basis of the determination result.SELECTED DRAWING: Figure 6B

Description

[Technical Field]

[0001] The present disclosure relates to image forming apparatuses such as copiers, multifunction peripherals, printers, and facsimile machines. [Background technology]

[0002] A conventional image forming apparatus includes a rotatable first image carrier on which a first toner image is formed, a rotatable second image carrier on which a second toner image is formed, a first cleaning blade that contacts the surface of the first image carrier and removes any adhering matter adhering to the first image carrier, a second cleaning blade that contacts the surface of the second image carrier, and a rotatable intermediate transfer body, and is capable of selectively performing a monochrome image forming operation (first image forming operation) in which the first toner image is intermediately transferred to the intermediate transfer body and then transferred to a sheet, and a multicolor image forming operation (second image forming operation) in which the first toner image and the second toner image are sequentially intermediately transferred to the intermediate transfer body and then transferred to a sheet.

[0003] For example, in an image forming apparatus that forms images of each color, the intermediate transfer body is an intermediate transfer belt, the first toner image is a black toner image, the second toner image is one or more color toner images such as a cyan toner image, a magenta toner image, and a yellow toner image, the first image carrier is a black photosensitive drum, the second image carrier is one or more color photosensitive drums such as a cyan photosensitive drum, a magenta photosensitive drum, and a yellow photosensitive drum, the first cleaning blade is a black cleaning blade, and the second cleaning blade is one or more color cleaning blades such as a cyan cleaning blade, a magenta cleaning blade, and a yellow cleaning blade.

[0004] A black toner image is formed on the surface of the black photosensitive drum, and the black cleaning blade removes the black toner and other adhering matter adhering to the surface of the black photosensitive drum.

[0005] Cyan toner images, magenta toner images, and yellow toner images are formed on the surfaces of the cyan, magenta, and yellow photosensitive drums, and the cyan, magenta, and yellow cleaning blades remove the cyan toner, magenta toner, yellow toner, and other deposits that have adhered to the surfaces of the cyan, magenta, and yellow photosensitive drums, respectively.

[0006] The single-color image forming operation is a monochrome image forming operation in which a black toner image is intermediately transferred to an intermediate transfer belt and then transferred to a sheet, and the multi-color image forming operation is a color image forming operation in which a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image are sequentially intermediately transferred to an intermediate transfer belt and then transferred to a sheet. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-311771 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in such an image forming device, when forming the second toner image and / or the first toner image, the rotation of the second image carrier and / or the first image carrier (photosensitive drum) causes the following inconvenience to the second cleaning blade and / or the first cleaning blade (cleaning blade).

[0009] 10 is an explanatory diagram for explaining the inconvenience of the second cleaning blade and / or the first cleaning blade (cleaning blade 36) due to the rotation of the second image carrier and / or the first image carrier (photosensitive drum 31) when the second toner image and / or the first toner image is formed. In FIG. 10, the symbol T indicates toner (transfer residual toner).

[0010] As shown in FIG. 10 , when the second image carrier and / or the first image carrier (photosensitive drum 31) rotates in the forward rotation direction R1 to form the second toner image and / or the first toner image, the tip 36a of the second cleaning blade and / or the first cleaning blade (cleaning blade 36) moves in the forward rotation direction R1 of the photosensitive drum 31 due to frictional force (sliding frictional force) with the photosensitive drum 31. This movement of the tip 36a in the forward rotation direction R1 causes the cleaning blade 36 to bend and distort. As long as the frictional force between the photosensitive drum 31 and the cleaning blade 36 is small, the cleaning blade 36 maintains its distorted state and removes deposits attached to the photosensitive drum 31. However, if the surface of the photosensitive drum 31 becomes rough due to changes over time or the generation of discharge products by the charging device, etc., and the frictional force (sliding frictional force) with the cleaning blade 36 increases, there is a risk that the cleaning blade 36 will reverse. 12A and 12B, as the frictional force between the cleaning blade 36 and the photosensitive drum 31 increases, the amount of movement of the cleaning blade 36 in the forward rotation direction R1 increases, causing an increase in distortion, and when this distortion exceeds a limit, the cleaning blade 36 turns over (reverses) due to the rotational force of the photosensitive drum 31. When the cleaning blade 36 turns over, for example, the cleaning blade 36 loses its ability to clean the photosensitive drum 31, causing poor image quality due to insufficient cleaning on the image, and furthermore, the rotational torque of the photosensitive drum 31 becomes significantly large, which may damage the drive gear or the like.

[0011] In this regard, there is a conventional image forming device in which, each time the value of the number of images formed, which is counted each time a toner image is formed on a sheet, reaches a predetermined number, the image carrier is rotated a predetermined surface movement distance in a reverse rotation direction, which is opposite to the forward rotation direction R1, which is the rotation direction when the toner image is formed, to remove toner and other adhering matter from the cleaning blade, thereby cleaning the cleaning blade and recovering any distortion in the cleaning blade (see, for example, Patent Document 1).

[0012] In the image forming apparatus, when performing monochromatic and multicolor image formation operations, during or after the image formation operation, a first reverse rotation operation is performed in which the first image carrier is rotated a predetermined first surface movement distance (e.g., 1 mm to 2 mm) in a reverse rotation direction R2 opposite to the forward rotation direction R1 during the image formation operation, and a second reverse rotation operation is performed in which both the first image carrier and the second image carrier are rotated a predetermined second surface movement distance (e.g., 1 mm to 2 mm) in the reverse rotation direction R2. This allows the distortion (stress) of the first and second cleaning blades caused by the rotation of the first and second image carriers in the forward rotation direction R1 to be released. Furthermore, the first and second cleaning blades can be cleaned by removing toner and other adhering matter from them.

[0013] For example, in the first reverse rotation operation, the black photoconductor drum is rotated in the reverse rotation direction R2 by a first surface movement distance, and in the second reverse rotation operation, the black, cyan, magenta, and yellow photoconductor drums are rotated in the reverse rotation direction R2 by a second surface movement distance.

[0014] 11 is a graph showing the possibility of the cleaning blade turning over relative to the frequency of reverse rotation operations. Here, the frequency of reverse rotation operations refers to the number of images formed from one reverse rotation operation to the next reverse rotation operation.

[0015] As shown in Figure 11, the possibility of the cleaning blade 36 curling up depends on the usage conditions and environment, but there is an appropriate operation frequency range α within which the possibility of the cleaning blade 36 curling up is low. For example, the upper limit operation frequency Ca of the appropriate operation frequency range α can be approximately 170 A4-sized image formations, and the lower limit operation frequency Cb of the appropriate operation frequency range α can be approximately 30 A4-sized image formations. Note that in Figure 11, the symbol C indicates the optimum operation frequency at which the possibility of the cleaning blade 36 curling up is lowest. For example, the optimum operation frequency C can be approximately 100 A4-sized image formations.

[0016] Here, the possibility of the cleaning blade turning over increases in a first implementation frequency range βa in which the frequency of the reverse rotation operation exceeds the upper limit implementation frequency Ca, and in a second implementation frequency range βb in which the frequency of the reverse rotation operation falls below the lower limit implementation frequency Cb.

[0017] 12A and 12B are diagrams illustrating the ease with which the cleaning blade 36 turns over in the first cleaning frequency range βa and the second cleaning frequency range βb, respectively.

[0018] In the first frequency range βa where the frequency of the reverse rotation operation exceeds the upper limit frequency Ca, rotation in the reverse rotation direction R2 reduces the amount of residual toner present at the contact point between the cleaning blade 36 and the photosensitive drum 31. In other words, the toner T, which acts as a lubricant when present between the cleaning blade 36 and the photosensitive drum 31, is expelled. This increases the frictional force between the cleaning blade 36 and the photosensitive drum 31, making it more likely that the cleaning blade 36 will be turned over.

[0019] In the second frequency range βb, where the frequency of the reverse rotation operation is below the lower limit frequency Cb, the compressive strain (stress) of the cleaning blade 36 increases as the photosensitive drum 31 rotates in the forward rotation direction R1. When the photosensitive drum 31 is continuously driven, the compressive strain of the cleaning blade 36 is not released, and the low frequency of the reverse rotation operation makes it easy for the strain of the cleaning blade 36 to exceed its limit of curling. This increases the likelihood of the cleaning blade curling.

[0020] In this regard, in an image forming apparatus equipped with a first counting unit that counts the number of images formed on the first image carrier each time a first toner image or a second toner image is formed to be transferred to a sheet, and a second counting unit that counts the number of images formed on the second image carrier each time a second toner image is formed to be transferred to a sheet, and performing a first reverse rotation operation when the first count value counted by the first counting unit reaches a predetermined threshold value during execution of a monochrome image forming operation, and performing a second reverse rotation operation when the second count value counted by the second counting unit reaches the threshold value during execution of a multicolor image forming operation, the following inconveniences arise.

[0021] For example, consider a case where the threshold is set to 100 sheets. Here, when a color image forming operation (multicolor image forming operation) is performed and 99 sheets of first and second toner images to be transferred to sheets are formed, the first count value and the second count value are 99 sheets. Thereafter, when a monochrome image forming operation (single-color image forming operation) is accepted and one first toner image to be transferred to a sheet is formed, the first count value becomes 100 sheets, reaching the threshold of 100 sheets. At this time, even if a first toner image to be transferred to a sheet is subsequently formed, the first reverse rotation operation is performed on the black cleaning blade (first cleaning blade) before forming the first toner image to be transferred to the next sheet. Then, if there is no first toner image to be transferred to the next sheet and the monochrome image forming operation is completed, the first count value becomes 0 sheets and the second count value remains at 99 sheets. In this state, when a color image forming operation (multicolor image forming operation) is next received and one first toner image and one second toner image to be transferred to the sheet are formed, the first count value becomes 1 sheet and the second count value becomes 100 sheets, and the second count value reaches the threshold value of 100 sheets. Therefore, the second reverse rotation operation is performed on the black cleaning blade (first cleaning blade) and the cyan, magenta, and yellow cleaning blades (second cleaning blades). In this case, after the first reverse rotation operation is performed on the black cleaning blade (first cleaning blade), the second reverse rotation operation is performed on the black cleaning blade just after one first toner image and one second toner image to be transferred to the sheet are formed, and the reverse rotation operation is performed excessively on the black cleaning blade.

[0022] Therefore, an object of the present disclosure is to provide an image forming apparatus that can reduce the possibility of the cleaning blade being turned over even when a mixture of monochromatic image forming operations and multi-color image forming operations is performed. [Means for solving the problem]

[0023] In order to solve the above-mentioned problem, an image forming apparatus according to the present disclosure is an image forming apparatus including: a rotatable first image carrier on which a first toner image is formed; a rotatable second image carrier on which a second toner image is formed; a first cleaning blade that comes into contact with the first image carrier and removes deposits adhering to the first image carrier; a second cleaning blade that comes into contact with the second image carrier and removes deposits adhering to the second image carrier; a rotatable intermediate transfer body; and a control unit that can selectively execute a first image forming operation in which the first toner image is intermediately transferred to the intermediate transfer body and then transferred to a sheet, and a second image forming operation in which the first toner image and the second toner image are intermediately transferred sequentially to the intermediate transfer body and then transferred to a sheet, wherein the control unit is configured to perform a first reverse rotation operation in which the first image carrier is rotated by a predetermined first surface movement distance in a direction opposite to that in which the first toner image is formed; a first counting unit that counts the number of images formed on the first image carrier each time the first toner image or the second toner image to be transferred to the sheet is formed, and a second counting unit that counts the number of images formed on the second image carrier each time the second toner image to be transferred to the sheet is formed, and a determination unit that, during the first image forming operation or the second image forming operation, does not perform the first reverse rotation operation or the second reverse rotation operation until a first count value counted by the first counting unit reaches a predetermined first threshold, and determines whether to perform the first reverse rotation operation or the second reverse rotation operation depending on a second count value counted by the second counting unit at the time when the first count value reaches the first threshold, and performs the first reverse rotation operation or the second reverse rotation operation based on the determination result of the determination control unit. [Effects of the Invention]

[0024] According to the present disclosure, it is possible to reduce the possibility of the cleaning blade being turned over, regardless of the number of sheets on which images are formed in a single-color image forming operation or a multi-color image forming operation. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view showing an image forming unit in the image forming apparatus according to the present embodiment. FIG. [Figure 3] 2 is a cross-sectional view showing a contact / separation mechanism portion in the image forming apparatus according to the present embodiment. FIG. [Figure 4A] 5A and 5B are schematic diagrams illustrating a state in which an intermediate transfer belt is brought into contact with and separated from a photosensitive drum by a contact / separation mechanism during a monochrome image forming operation. [Figure 4B] 5A and 5B are schematic diagrams illustrating a state in which an intermediate transfer belt is brought into contact with and separated from a photosensitive drum by a contact / separation mechanism during a multi-color image forming operation. [Figure 5] FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus according to the present embodiment. [Figure 6A] 10 is a flowchart showing the first half of an example of the processing flow of the first reverse rotation operation or the second reverse rotation operation when performing image formation in a single-color image forming operation and a multi-color image forming operation. [Figure 6B] 10 is a flowchart showing the latter half of an example of the processing flow of the first reverse rotation operation or the second reverse rotation operation when performing image formation in a monochromatic image forming operation and a multicolor image forming operation. [Figure 7A] 10 is a diagram showing an example of Case 1. [Figure 7B] 10 is a diagram showing another example of Case 1. [Figure 8A] 10 is a diagram showing an example of Case 2. [Figure 8B] 10 is a diagram showing another example of Case 2. [Figure 9A] 10 is a diagram showing an example of Case 3. [Figure 9B] 10 is a diagram showing another example of Case 3. [Figure 10] 10A and 10B are explanatory diagrams for explaining inconveniences of the first cleaning blade and / or the second cleaning blade caused by the forward rotation of the first image carrier and / or the second image carrier. [Figure 11] 10 is a graph showing the possibility of the cleaning blade being turned over relative to the frequency of reverse rotation operations. [Figure 12A] FIG. 10 is an explanatory diagram for explaining the ease of turning over of the cleaning blade in the first implementation frequency range. [Figure 12B] FIG. 10 is an explanatory diagram for explaining the ease of turning over of the cleaning blade in the second frequency range. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0027] FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to the present embodiment. In the drawing, X indicates the left-right direction, Y indicates the depth direction (front-rear direction), and Z indicates the up-down direction. FIG. 2 is a cross-sectional view showing an image forming unit 110 in the image forming apparatus 100 according to the present embodiment. FIG. 3 is a cross-sectional view showing a contact / separation mechanism 20 in the image forming apparatus 100 according to the present embodiment. FIGS. 4A and 4B are schematic diagrams showing contact / separation states of the intermediate transfer belt 41 with respect to the photosensitive drums 31K, 31C, 31M, and 31Y by the contact / separation mechanism 20 during a monochrome image forming operation MDa and a multicolor image forming operation MDb, respectively. FIG. 5 is a block diagram showing a schematic control configuration of the image forming apparatus 100 according to the present embodiment.

[0028] [Image forming equipment] As shown in Fig. 1, image forming apparatus 100 is a color (full-color) image forming apparatus that forms a multicolor or monochrome image on a sheet P such as recording paper based on image data read from an original. Examples of the sheet include sheet-like recording media such as plain paper, cardboard, photographic paper, and OHP film. Image forming apparatus 100 includes an image reading device 120 provided on image forming apparatus main body 101, and image forming unit 110 and paper feed tray 11 are provided in image forming apparatus main body 101.

[0029] The image reading device 120 generates image data by irradiating the image surface of the document with light and detecting the amount of reflected light.

[0030] The image forming section 110 includes an intermediate transfer device 40 (intermediate transfer unit), image forming stations 30K, 30C, 30M, and 30Y, a transfer device 50 (transfer unit), a belt cleaning device 8, an exposure device 60 (exposure unit), and a fixing device 70 (fixing unit).

[0031] The intermediate transfer device 40 includes an endless (annular) intermediate transfer belt 41, a drive roller 42, a tension roller 43 (driven roller), and tension rollers 44 (see FIG. 2). The intermediate transfer belt 41 acts as an intermediate transfer body. The intermediate transfer belt 41 is tensioned between the drive roller 42, the tension roller 43, and the tension rollers 44. The tension roller 43 is a driven roller, and the tension rollers 44 have the function of adjusting the tension of the intermediate transfer belt 41.

[0032] The image forming stations 30K, 30C, 30M, and 30Y perform electrophotographic image formation (printing) processing using toner of each hue, black, cyan, magenta, and yellow, respectively. The image forming stations 30K, 30C, 30M, and 30Y are arranged side by side in a predetermined direction (horizontal direction, in this example, left-right direction X). The image forming stations 30K, 30C, 30M, and 30Y have substantially the same configuration.

[0033] Image forming station 30K is equipped with a black photoconductor drum 31K that carries black toner. Photoconductor drum 31K acts as a first carrier. Image forming stations 30C, 30M, and 30Y are equipped with a cyan photoconductor drum 31C, a magenta photoconductor drum 31M, and a yellow photoconductor drum 31Y that carry a cyan toner image, a magenta toner image, and a yellow toner image, respectively. Photoconductor drums 31C, 31M, and 31Y act as second image carriers.

[0034] Image forming station 30K has a charging device 32K, a developing device 33K, an intermediate transfer roller 34K, and a photoreceptor cleaning device 35K around photoreceptor drum 31K. Similarly, image forming stations 30C, 30M, and 30Y have intermediate transfer rollers 34C, 34M, and 34Y, and photoreceptor cleaning devices 35C, 35M, and 35Y, respectively.

[0035] Photoconductor drum 31K receives a driving force from first driving source 210 (see FIG. 5), causing photoconductor drum 31K and intermediate transfer belt 41 to rotate in a predetermined forward rotation direction R1. Charging device 32K charges the surface of photoconductor drum 31K to a predetermined potential. Photoconductor drums 31C, 31M, and 31Y receive a driving force from second driving source 220 (see FIG. 5), causing them to rotate in the predetermined forward rotation direction R1. Charging devices 32C, 32M, and 32Y charge the surfaces of photoconductor drums 31C, 31M, and 31Y to a predetermined potential.

[0036] The exposure device 60 drives a semiconductor laser based on image data of each hue of black, cyan, magenta, and yellow, and distributes the laser light of each hue to the photosensitive drums 31K, 31C, 31M, and 31Y of the image forming stations 30K, 30C, 30M, and 30Y, respectively. Electrostatic latent images based on the image data of each hue of black, cyan, magenta, and yellow are formed on the surfaces of the photosensitive drums 31K, 31C, 31M, and 31Y.

[0037] Developing devices 33K, 33C, 33M, and 33Y supply toner of the hues of image forming stations 30K, 30C, 30M, and 30Y, namely black, cyan, magenta, and yellow, respectively, to the surfaces of photosensitive drums 31K, 31C, 31M, and 31Y, and develop (visualize) the electrostatic latent images into black toner images, cyan toner images, magenta toner images, and yellow toner images.

[0038] The black toner image, cyan toner image, magenta toner image, and yellow toner image formed on the surfaces of photosensitive drums 31K, 31C, 31M, and 31Y by developing devices 33K, 33C, 33M, and 33Y, respectively, are intermediately transferred onto intermediate transfer belt 41 by intermediate transfer rollers 34K, 34C, 34M, and 34Y, which will be described next.

[0039] The intermediate transfer rollers 34K, 34C, 34M, and 34Y are provided at positions facing the photosensitive drums 31K, 31C, 31M, and 31Y with the intermediate transfer belt 41 interposed therebetween. In this example, the photosensitive drums 31K, 31C, 31M, and 31Y are provided below the intermediate transfer belt 41.

[0040] During the single-color image forming operation MDa (see Figure 5) (monochrome mode in this example), in the image forming process of the black image forming station 30K, the intermediate transfer roller 34K is applied with an intermediate transfer bias of the opposite polarity (e.g., positive) to the charging polarity (e.g., negative) of the black toner, thereby causing the black toner image carried on the photosensitive drum 31K to be primarily transferred onto the surface of the intermediate transfer belt 41. Furthermore, during the multi-color image forming operation MDb (see Figure 5) (color mode in this example), in the image forming process of image forming stations 30K, 30C, 30C, 30M, and 30Y, intermediate transfer rollers 34K, 34C, 34M, and 34Y are applied with an intermediate transfer bias of the opposite polarity (e.g., positive) to the charging polarity (e.g., negative) of the black toner, cyan toner, magenta toner, and yellow toner, respectively, so that the black toner image, cyan toner image, magenta toner image, and yellow toner image carried on photosensitive drums 31K, 31C, 31M, and 31Y are sequentially intermediate transferred onto the surface of intermediate transfer belt 41 so that they are superimposed on one another.

[0041] The black toner, cyan toner, magenta toner, and yellow toner remaining on the surfaces of the photosensitive drums 31K, 31C, 31M, and 31Y without being intermediately transferred to the intermediate transfer belt 41 are removed by the photosensitive drum cleaning devices 35K, 35C, 35M, and 35Y.

[0042] The photoconductor cleaning devices 35K, 35C, 35M, and 35Y are equipped with cleaning blades 36K, 36C, 36M, and 36Y. The black cleaning blade 36K functions as a first cleaning blade. The cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y function as second cleaning blades. The cleaning blades 36K, 36C, 36M, and 36Y are formed of flexible members (e.g., rubber members). The cleaning blades 36K, 36C, 36M, and 36Y contact the surfaces of the photoconductor drums 31K, 31C, 31M, and 31Y to scrape off and remove toner (waste toner) remaining on the surfaces of the photoconductor drums 31K, 31C, 31M, and 31Y that has not been transferred to the intermediate transfer belt 41 by the intermediate transfer rollers 34K, 34C, 34M, and 34Y.

[0043] A sheet conveying path W1 is provided in the image forming apparatus main body 101. Near the sheet conveying path W1, a sheet supply unit 11a, a plurality of conveying rollers 12a, a registration roller 13, a transfer roller 51, a fixing roller 71 and a pressure roller 72 in a fixing device 70, and a discharge roller 14 are arranged.

[0044] The sheet supply unit 11a supplies the sheet P stored in the paper feed tray 11 to the sheet transport path W1. The sheet transport path W1 guides the sheet P to the discharge tray 15 via the transfer roller 51 of the transfer device 50 and the fixing device .

[0045] The transfer device 50 includes a transfer member (in this example, a transfer roller 51). The transfer roller 51 transfers the toner image transferred onto the intermediate transfer belt 41 onto the sheet P fed from the paper feed tray 11.

[0046] The belt cleaning device 8 removes toner (waste toner) remaining on the intermediate transfer belt 41 without being transferred to the sheet P by the transfer device 50. The fixing device 70 includes a fixing roller 71 and a pressure roller 72, and heats and fixes the toner image formed on the sheet P by the transfer device 50 to the sheet P by the fixing roller 71 and the pressure roller 72.

[0047] In the image forming apparatus 100, a sheet P supplied from a paper feed tray 11 to a sheet conveying path W1 by a sheet supply unit 11a is conveyed via conveying rollers 12a to registration rollers 13. Next, the sheet P is conveyed to a transfer roller 51 by the registration rollers 13 at a timing when the sheet P and the toner image on the intermediate transfer belt 41 are aligned, and the toner image intermediately transferred to the intermediate transfer belt 41 is transferred onto the sheet P by the transfer roller 51. Thereafter, the sheet P passes through a fixing roller 71 and a pressure roller 72 in a fixing device 70, and is discharged onto a discharge tray 15 via conveying rollers 12a and discharge rollers 14. When an image is to be formed on the back side of the sheet P as well as the front side, the sheet P is conveyed in the reverse direction from the discharge rollers 14 to a reverse sheet conveying path W2. The sheet P passes through reverse conveying rollers 12b to 12b, and is then reversed and guided again to the registration rollers 13. Then, the sheet P has a toner image formed and fixed on the back side in the same manner as on the front side, and is then discharged to the discharge tray 15.

[0048] The image forming apparatus 100 further includes a control unit 130 (see FIG. 5). The control unit 130 has a processing unit 131 and a storage unit 132. The processing unit 131 is made up of a microcomputer such as a CPU. The storage unit 132 includes a non-volatile memory such as a ROM and a volatile memory such as a RAM. The control unit 130 controls the operation of various components by having the processing unit 131 load a control program stored in advance in the ROM of the storage unit 132 onto the RAM of the storage unit 132 and execute the program.

[0049] The control unit 130 controls the entire image forming apparatus 100. The control unit 130 is electrically connected to the image forming unit 110, and is capable of selectively executing a single-color image forming operation (first image forming operation) MDa (monochrome mode in this example) in which a monochrome image of a black toner image is intermediately transferred onto the intermediate transfer belt 41 and then transferred onto the sheet P, and a multi-color image forming operation (second image forming operation) MDb (color mode in this example) in which color images of a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image are intermediately transferred sequentially onto the intermediate transfer belt 41 and then transferred onto the sheet P.

[0050] [Intermediate transfer device] Next, the configuration of the intermediate transfer device 40 shown in FIG. 1 will be described below with reference to FIG.

[0051] 2, intermediate transfer belt 41 is stretched between drive roller 42 and tension roller 43, and has a linear portion along linear direction M (left-right direction X in this example) when no image is formed (see FIG. 3). Opposite the linear portion of intermediate transfer belt 41, photosensitive drums 31K, 31C, 31M, and 31Y are provided in this order from the downstream side in belt movement direction F (see FIGS. 2 and 3).

[0052] The tension rollers 44 are pressed against the inner peripheral surface of the intermediate transfer belt 41 on the same side as the intermediate transfer rollers 34K, 34C, 34M, and 34Y. This allows the intermediate transfer belt 41 to be maintained at a constant tension throughout the non-image formation period (see FIG. 3), the monochrome image formation operation MDa (see FIG. 4A), and the multicolor image formation operation MDb (see FIG. 4B).

[0053] 3, 4A, and 4B, the intermediate transfer rollers 34K, 34C, 34M, and 34Y are configured to be movable in a direction toward and away from the corresponding photosensitive drums 31K, 31C, 31M, and 31Y, respectively. The image forming apparatus 100 is provided with a contact / separation mechanism 20, which will be described in detail later, and by this, the intermediate transfer rollers 34K, 34C, 34M, and 34Y are movable between a pressing position where the intermediate transfer belt 41 is pressed against the corresponding photosensitive drums 31K, 31C, 31M, and 31Y, respectively, and a separating position where the intermediate transfer belt 41 is separated from the opposing photosensitive drums 31K, 31C, 31M, and 31Y.

[0054] As shown in FIG. 3, when no image is formed, all of the intermediate transfer rollers 34K, 34C, 34M, and 34Y are located at the separated positions, and the intermediate transfer belt 41 is separated from the photosensitive drums 31K, 31C, 31M, and 31Y.

[0055] 4A, during monochrome image formation operation MDa, the black intermediate transfer roller 34K is located at the pressing position, and the intermediate transfer belt 41 is pressed against the photosensitive drum 31K. Meanwhile, the cyan, magenta, and yellow intermediate transfer rollers 34C, 34M, and 34Y are located at the separated positions, and the intermediate transfer belt 41 is separated from the photosensitive drums 31C, 31M, and 31Y.

[0056] As shown in FIG. 4B, during multi-color image forming operation MDb, all intermediate transfer rollers 34K, 34C, 34M, and 34Y are positioned at the pressing position, and the intermediate transfer belt 41 is pressed against the photosensitive drums 31K, 31C, 31M, and 31Y.

[0057] [Contact / separation mechanism] Here, a detailed description will be given of the contact / separation mechanism 20 provided in the image forming apparatus 100. As shown in Fig. 3, the contact / separation mechanism 20 includes a first moving member 21, a second moving member 22, a contact / separation drive unit 23 (see Fig. 5), swing members 24A, 24B, 24C, 24D, and 24E for black, cyan, magenta, and yellow, and biasing members 45A, 45B, 45C, and 45D (coil springs) for black, cyan, magenta, and yellow.

[0058] The first moving member 21 and the second moving member 22 are elongated members that are provided on the intermediate transfer unit main body 40a (transfer device main body) (main body frame) so as to be movable in the linear direction M (left-right direction X) with their longitudinal directions aligned with the linear direction M. The first moving member 21 is urged by the urging member 45A toward the other side M2 ​​in the linear direction M (left X2 in the illustrated example) via the swinging member 24A. The second moving member 22 is urged by the urging members 45B, 45C, and 45D toward one side M1 in the linear direction M (right X1 in the illustrated example) via the swinging members 24B, 24C, 24D, and 24E.

[0059] The first moving member 21 and the second moving member 22 are located between the drive roller 42 and the tension roller 43 and are provided on the front side Y1 and the rear side Y2 of the image forming apparatus 100, respectively. The swinging member 24A is supported by the first moving member 21 provided on the front side Y1 and the first moving member 21 provided on the rear side Y2 so as to be swingable about a swing axis (swing shaft 26A) along the rotation axis direction (depth direction Y) of the intermediate transfer roller 34K. The swinging members 24B, 24C, 24D, and 24E are supported by the second moving member 22 provided on the front side Y1 and the second moving member 22 provided on the rear side Y2 so as to be swingable about swing axes (swing shafts 26B, 26C, 26D, and 26E) along the rotation axis direction (Y) of the intermediate transfer rollers 34C, 34M, and 34Y, respectively.

[0060] The swinging members 24A, 24B, 24C, and 24D are each bent into an L-shape. The swinging members 24B, 24C, and 24D are configured similarly to the swinging member 24A except for the mounting direction relative to the second moving member 22 in the linear direction M. The swinging members 24B, 24C, and 24D are mounted symmetrically with respect to the swinging member 24A, with the axis extending in a direction (vertical direction Z) perpendicular to both the linear direction M and the rotational axis direction (Y) of the intermediate transfer roller 34K as the axis of symmetry.

[0061] The swinging member 24A is supported by the intermediate transfer unit main body 40a on the photosensitive drum 31K side (bent portion) from the first moving member 21 so as to be swingable about a swing axis (swing shaft 26A) along the rotational axis direction (Y) of the intermediate transfer roller 34K. The swinging member 24A rotatably supports the intermediate transfer roller 34K at its tip end on the opposite side of the swing shaft 26A from the support shaft 25A, with the swing shaft 26A between them. Similarly, the swinging members 24B, 24C, and 24D are supported by the intermediate transfer unit main body 40a on the photosensitive drum 31C, 31M, and 31Y side (bent portion) from the second moving member 22 so as to be swingable about swing axes (swing shafts 26B, 26C, and 26D) along the rotational axis direction (Y) of the intermediate transfer rollers 34C, 34M, and 34Y, respectively. The pivoting members 24B, 24C, and 24D rotatably support the intermediate transfer rollers 34C, 34M, and 34Y at their tips opposite the support shafts 25B, 25C, and 25D, with the pivoting shafts 26B, 26C, and 26D interposed therebetween. The pivoting members 24A, 24B, 24C, and 24D are biased by biasing members 45A, 45B, 45C, and 45D, respectively, in directions that move the intermediate transfer rollers 34K, 34C, 34M, and 34Y away from the photosensitive drums 31K, 31C, 31M, and 31Y.

[0062] A support shaft 25A extending along the depth direction Y is fixed to the swinging member 24A. The first moving member 21 is provided with a long through-hole 27A through which the support shaft 25A is inserted so as to be movable in the vertical direction Z. Furthermore, support shafts 25B, 25C, and 25D extending along the depth direction Y are fixed to the swinging members 24B, 24C, and 24D, respectively. The second moving member 22 is provided with long through-holes 27B, 27C, and 27D through which the support shafts 25B, 25C, and 25D are inserted so as to be movable in the vertical direction Z, respectively. The swinging member 24E is supported so as to be swingable around the support shaft 25E. The swinging member 24E extends toward the tension roller 43, and its tip on the opposite side in the longitudinal direction from the support shaft 25E rotatably supports the tension roller 43. The swinging member 24E is provided with a slit 25a that penetrates in the rotational axis direction (Y) of the tension roller 43 and extends along the longitudinal direction. An insertion member 46 (insertion shaft) that is aligned with the rotational axis direction (Y) of the tension roller 43 is fixed to the intermediate transfer unit main body 40a. The insertion member 46 is positioned closer to the photosensitive drums 31K, 31C, 31M, and 31Y than the support shafts 25B, 25C, and 25D. The insertion member 46 is inserted into the slit 25a in the swinging member 24E.

[0063] When the first moving member 21 moves to one side M1 in the linear direction M (right side X1 in the illustrated example), the intermediate transfer roller 34K moves to one side Z1 in the vertical direction Z (lower side in this example) against the biasing force of the biasing member 45A and is positioned at the pressing position. Similarly, when the second moving member 22 moves to the other side M2 ​​in the linear direction M (left side X2 in the illustrated example), the intermediate transfer rollers 34C, 34M, and 34Y move to one side Z1 in the vertical direction Z (lower side in this example) against the biasing forces of the biasing members 45B, 45C, and 45D and are positioned at the pressing position. At this time, the slit 25a of the swinging member 24E slides against the insertion member 46, and the tension roller 43 moves to one side Z1 in the vertical direction Z (lower side in this example) and is positioned at the pressing position. This allows the intermediate transfer belt 41 to be pressed against the photosensitive drums 31K, 31C, 31M, and 31Y.

[0064] On the other hand, when the first moving member 21 moves to the other side M2 ​​(left side X2 in the illustrated example) in the linear direction M, the intermediate transfer roller 34K moves to the other side Z2 (upper side in this example) in the vertical direction Z due to the biasing force of the biasing member 45A and is positioned at the separated position. Similarly, when the second moving member 22 moves to one side M1 (right side X1 in the illustrated example) in the linear direction M, the intermediate transfer rollers 34C, 34M, and 34Y move to the other side Z2 (upper side in this example) in the vertical direction Z due to the biasing forces of the biasing members 45B, 45C, and 45D and are positioned at the separated position. At this time, the slit 25a of the swinging member 24E slides against the insertion member 46, and the tension roller 43 moves to the other side Z2 (upper side in this example) in the vertical direction Z and is positioned at the separated position. This allows the intermediate transfer belt 41 to be separated from the photosensitive drums 31K, 31C, 31M, and 31Y.

[0065] The contact and separation drive unit 23 is electrically connected to the output system of the control unit 130 (see FIG. 5), and moves the first moving member 21 and the second moving member 22 independently under instructions from the control unit 130. That is, the contact and separation drive unit 23 does not move the first moving member 21 or the second moving member 22 during non-image formation, as shown in FIG. 3. On the other hand, during monochrome image formation operation MDa, the contact and separation drive unit 23 moves only the second moving member 22 of the first moving member 21 and the second moving member 22 to one side M1 in the linear direction M, as shown in FIG. 4A. During multi-color image formation operation MDb, the contact and separation drive unit 23 moves the first moving member 21 to one side M1 in the linear direction M and moves the second moving member 22 to the other side M2 ​​in the linear direction M, as shown in FIG. 4B.

[0066] In this way, the contact / separation mechanism 20 moves the intermediate transfer rollers 34K, 34C, 34M, and 34Y in the contact / separation direction.

[0067] The control unit 130 is capable of selectively executing a single-color image forming operation MDa (in this example, monochrome mode) in which a monochrome image of a black toner image is transferred to the intermediate transfer belt 41, and a multi-color image forming operation MDb (in this example, color mode) in which color images of a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image are transferred sequentially to the intermediate transfer belt 41.

[0068] The control unit 130 is also capable of performing a first reverse rotation operation MD1 and a second reverse rotation operation MD2. In the first reverse rotation operation MD1, the black photoconductor drum 31K is rotated a predetermined first surface movement distance (e.g., 1 mm to 2 mm) in a reverse rotation direction R2 (see FIG. 2), which is the opposite direction to the forward rotation direction R1, which is the rotation direction when forming a black toner image. In the second reverse rotation operation MD2, the black photoconductor drum 31K and the cyan, magenta, and yellow photoconductor drums 31C, 31M, and 31Y are rotated a predetermined second surface movement distance (e.g., 1 mm to 2 mm) in the reverse rotation direction R2, which is the opposite direction to the forward rotation direction R1.

[0069] In other words, the control unit is capable of performing a first reverse rotation operation MD1 in which the black photosensitive drum 31K is rotated a predetermined first surface movement distance in the opposite direction to when a black toner image is formed, and a second reverse rotation operation MD2 in which the black photosensitive drum 31K and the cyan, magenta and yellow photosensitive drums 31C, 31M and 31Y are rotated a predetermined second surface movement distance in the opposite direction to when a black toner image, a cyan toner image, a magenta toner image and a yellow toner image are formed.

[0070] By performing the first reverse rotation operation MD1 or the second reverse rotation operation MD2 as described above, the monochrome image forming operation MDa or the multicolor image forming operation MDb can be performed, thereby releasing distortions (shapes) accumulated in the black cleaning blade 36K (first cleaning blade), the cyan cleaning blade 36C, the magenta cleaning blade 36M, and the yellow cleaning blade 36Y (second cleaning blade). Furthermore, deposits (such as residual toner and paper dust) adhering to the black cleaning blade 36K and the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y can be removed, thereby cleaning the black cleaning blade 36K and the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y.

[0071] First Embodiment In this embodiment, as shown in FIG. 5, the control unit 130 includes a first counting unit Q1, a second counting unit Q2, a determination control unit Q3, and an operation execution control unit Q4.

[0072] The first counting unit Q1 counts the number of images formed on the black photosensitive drum 31K each time a black toner image (monochrome image) and a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image (color image) to be transferred to a sheet P are formed, and stores the counted first count value CT1 in the memory unit 132. The second counting unit Q2 counts the number of images formed on the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y each time a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image (color toner image) to be transferred to a sheet are formed, and stores the counted second count value CT2 in the memory unit 132.

[0073] During execution of a monochrome image forming operation MDa or a multi-color image forming operation MDb, the determination control unit Q3 does not perform the first reverse rotation operation MD1 or the second reverse rotation operation MD2 until the first count value CT1 counted by the first counting unit Q1 reaches a predetermined first threshold value TH1 (see FIG. 5) (e.g., 100 sheets). The determination control unit Q3 determines whether to perform the first reverse rotation operation MD1 or the second reverse rotation operation MD2 based on the second count value CT2 counted by the second counting unit Q2 at the time when the first count value CT1 reaches the first threshold value TH1 (e.g., 100 sheets). The operation execution control unit Q4 performs the first reverse rotation operation MD1 or the second reverse rotation operation MD2 based on the determination result of the determination control unit Q3. The first threshold value TH1 can be set in advance through experiments or the like and is pre-stored in the memory unit 132.

[0074] According to this embodiment, whether to perform the first reverse rotation operation MD1 or the second reverse rotation operation MD2 is determined based on the second count value CT2 at the time when the first count value CT1 reaches the first threshold value TH1 (e.g., 100 sheets). This makes it possible to prevent the first reverse rotation operation MD1 and the second reverse rotation operation MD2 from being performed at very short intervals, thereby effectively preventing the cleaning blades 36K, 36C, 36M, and 36Y from being turned over. This is particularly effective when, for example, charging the surfaces of the photosensitive drums 31K, 31C, 31M, and 31Y by the charging devices 32K, 32C, 32M, and 32Y causes discharge products such as nitrogen oxides to adhere to the surfaces of the photosensitive drums 31K, 31C, 31M, and 31Y, increasing the frictional resistance of the surfaces of the photosensitive drums 31K, 31C, 31M, and 31Y.

[0075] In this embodiment, the determination control unit Q3 determines that the first reverse rotation operation MD1 is to be performed if the second count value CT2 at the time when the first count value CT1 reaches the first threshold value TH1 (for example, 100 sheets) has not yet reached a second threshold value TH2 (for example, 50 sheets, which is about 50% of the first threshold value TH1) that is smaller than the first threshold value TH1, and that the second reverse rotation operation MD2 is to be performed if the second count value CT2 has reached the second threshold value TH2. The second threshold value TH2 can be set in advance by experiment or the like and is pre-stored in the memory unit 132.

[0076] This makes it possible to accurately determine whether to perform the first reverse rotation operation MD1 or the second reverse rotation operation MD2 in accordance with the second count value CT2.

[0077] However, if the second threshold value TH2 is too small or too large, the first reverse rotation operation MD1 and the second reverse rotation operation MD2 cannot be performed at appropriate timing.

[0078] In this regard, in this embodiment, it is preferable that the second threshold TH2 be set to a value in the range of, for example, 30% or more and 70% or less of the first threshold TH1, and it is more preferable that it be set to a value in the range of 40% or more and 60% or less.

[0079] In this way, the first reverse rotation operation MD1 and the second reverse rotation operation MD2 can be performed at appropriate timing.

[0080] In this embodiment, the first count value CT1 is reset when the first reverse rotation operation MD1 is performed, and the second count value CT2 is reset when the second reverse rotation operation MD2 is performed.

[0081] In this way, in the monochrome image forming operation MDa, the first reverse rotation operation MD1 is performed near the first threshold value TH1 (e.g., 100 sheets) as the center value of the appropriate execution frequency range α (e.g., a range of 30 sheets to 170 sheets) shown in Figure 11, and in the multi-color image forming operation MDb, the second reverse rotation operation MD2 can be performed at any image formation number interval between the lower limit execution frequency Cb (e.g., 30 sheets) and the upper limit execution frequency Ca (e.g., 170 sheets) shown in Figure 11.

[0082] In this embodiment, the first toner image formed in the single-color image forming operation MDa is a monochrome toner image, which allows the single-color image forming operation MDa to be compatible with the monochrome mode.

[0083] Second Embodiment Next, an example of a control configuration for the first drive source 210, the second drive source 220, and the contact / separation mechanism 20 (contact / separation drive unit 23) will be described below.

[0084] 5, the first drive source 210 is electrically connected to the output system of the control unit 130, and rotates the photosensitive drum 31K and the intermediate transfer belt 41 under instructions from the control unit 130. The second drive source 220 is electrically connected to the output system of the control unit 130, and rotates the photosensitive drums 31C, 31M, and 31Y under instructions from the control unit 130. The contact / separation drive unit 23, which drives the contact / separation mechanism 20, is electrically connected to the output system of the control unit 130, and moves the first moving member 21 and the second moving member 22 independently under instructions from the control unit 130, thereby moving the positions of the intermediate transfer rollers 34K, 34C, 34M, and 34Y and causing the intermediate transfer belt 41 to contact or separate from the photosensitive drums 31K, 31C, 31M, and 31Y.

[0085] In this configuration, when the contact / separation mechanism 20 causes the intermediate transfer belt 41 to contact the photosensitive drums 31C, 31M, and 31Y together with the photosensitive drum 31K, the control unit 130 causes the photosensitive drums 31K and the photosensitive drums 31C, 31M, and 31Y to rotate together with the intermediate transfer belt 41. On the other hand, when the contact / separation mechanism 20 causes the intermediate transfer belt 41 to be separated from the photosensitive drums 31C, 31M, and 31Y, the control unit 130 causes the photosensitive drums 31K and the intermediate transfer belt 41 to rotate but does not cause the photosensitive drums 31C, 31M, and 31Y to rotate.

[0086] In this embodiment, when performing a monochrome image forming operation MDa, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 is separated from the photosensitive drums 31C, 31M, and 31Y. When performing a multi-color image forming operation MDb, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 is brought into contact with the photosensitive drums 31C, 31M, and 31Y.

[0087] In addition, when the control unit 130 performs the first reverse rotation operation MD1 only on the photosensitive drum 31K during the execution of the multi-color image forming operation MDb, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 is separated from the photosensitive drums 31C, 31M, and 31Y.

[0088] By doing so, during the first reverse rotation operation MD1, the intermediate transfer belt 41 can be separated from the photosensitive drums 31C, 31M, and 31Y, thereby avoiding unnecessary rotation of the photosensitive drums 31C, 31M, and 31Y.

[0089] Next, another example of the control configuration for the first drive source 210, the second drive source 220, and the contact / separation mechanism 20 (contact / separation drive unit 23) will be described below.

[0090] In the second embodiment, in the first reverse rotation operation MD1 and the second reverse rotation operation MD2, the intermediate transfer belt 41 rotates even though it is not necessary to rotate the intermediate transfer belt 41, and therefore an unnecessary rotation operation is performed.

[0091] Therefore, when the contact / separation mechanism 20 is causing the intermediate transfer belt 41 to contact the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y, the control unit 130 may cause the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y to rotate together with the intermediate transfer belt 41, while on the other hand, when the contact / separation mechanism 20 is causing the intermediate transfer belt 41 to be separated from the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y, the control unit 130 may prevent the intermediate transfer belt 41 from rotating.

[0092] In the present embodiment, when a monochrome image forming operation MDa is performed, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 contacts the photosensitive drum 31K and is separated from the photosensitive drums 31C, 31M, and 31Y. When a multi-color image forming operation MDb is performed, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 contacts the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y.

[0093] Furthermore, when the first reverse rotation operation MD1 or the second reverse rotation operation MD2 is performed, the control unit 130 controls the contact / separation mechanism 20 so that the intermediate transfer belt 41 is separated from the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y.

[0094] By doing this, during the first reverse rotation operation MD1 and the second reverse rotation operation MD2, the intermediate transfer belt 41 can be separated from the photosensitive drum 31K and the photosensitive drums 31C, 31M, and 31Y, thereby preventing the intermediate transfer belt 41 from rotating and thereby eliminating unnecessary rotational movement of the intermediate transfer belt 41.

[0095] <Processing example> Next, a processing example in which the first reverse rotation operation MD1 or the second reverse rotation operation MD2 is performed when performing image formation in the monochrome image forming operation MDa and the multi-color image forming operation MDb will be described below with reference to FIGS. 6A and 6B.

[0096] 6A and 6B are flowcharts showing the first and second halves of an example of the processing flow of the first reverse rotation operation MD1 or the second reverse rotation operation MD2 when performing image formation of the monochrome image forming operation MDa and the multi-color image forming operation MDb, respectively.

[0097] In the flowcharts shown in FIGS. 6A and 6B, the single-color image forming operation MDa is in the monochrome mode, and the multi-color image forming operation MDb is in the color mode.

[0098] As shown in FIG. 6A, when the control unit 130 receives a command to start printing, i.e., to form a toner image to be transferred to the sheet P, it first reads the first count value CT1 and the second count value CT2 from the storage unit 132 (S1). Next, the control unit 130 determines whether the mode is color mode (MDb) (S2). Next, if the control unit 130 determines that the mode is not color mode (MDb) [i.e., if the mode is monochrome mode (MDb)] (S2: No), it performs a monochrome image formation operation (S3), increments the first count value CT1 by "1" (S4), and proceeds to S7 shown in FIG. 6B. On the other hand, if the control unit 130 determines that the mode is color mode (MDb) (S2: Yes), it performs a multicolor image formation operation (S5), increments the first count value CT1 by "1" and the second count value CT2 by "1" (S6), and proceeds to S7 shown in FIG. 6B.

[0099] Next, as shown in FIG. 6B, the control unit 130 reads the first threshold value TH1 from the memory unit 132 and determines whether the first count value CT1 is greater than or equal to the first threshold value TH1 (S7), and if it determines that the first count value CT1 is less than the first threshold value TH1 (S7: No), it proceeds to S17.

[0100] On the other hand, if the control unit 130 reads the first threshold value TH1 from the memory unit 132 and determines that the first count value CT1 is equal to or greater than the first threshold value TH1 (S7: Yes), the control unit 130 reads the second threshold value TH2 from the memory unit 132 and determines whether the second count value CT2 is equal to or greater than the second threshold value TH2 (S8). Next, if the control unit 130 determines that the second count value CT2 is equal to or greater than the second threshold value TH2 (S8: Yes), the control unit 130 performs a second reverse rotation operation MD2 (S9), resets the first count value CT1 to "0" and resets the second count value CT2 to "0" (S10), and proceeds to S17.

[0101] Furthermore, if the control unit 130 determines that the second count value CT2 is lower than the second threshold value TH2 (S8: No), it determines whether the mode is the color mode (MDb) (S11), and if it determines that the mode is not the color mode (MDb) [i.e., the mode is the monochrome mode (MDa)] (S11: No), it performs the first reverse rotation operation MD1 (S12), resets the first count value CT1 to “0” (S16), and proceeds to S17. On the other hand, if the control unit 130 determines that the mode is the color mode (MDb) (S11: Yes), the intermediate transfer belt 41 is in contact with the photosensitive drums 31C, 31M, and 31Y, and therefore, the contact / separation mechanism 20 separates the intermediate transfer belt 41 from the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y (S13). Next, the control unit 130 performs a first reverse rotation operation MD1 (S14), and causes the contact / separation mechanism 20 to contact the intermediate transfer belt 41 with the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y in preparation for image formation in the next color mode (MDb) (S15). Next, the control unit 130 sets the first count value CT1 to "0" (S16), and proceeds to S17.

[0102] Next, the control unit 130 determines whether or not there is a next image formation (S17), and if it determines that there is a next image formation (S17: Yes), it proceeds to S2 shown in FIG. 6A, and if it determines that there is no next image formation (S17: No), it ends the processing.

[0103] Next, a specific example of the processing of the flowcharts shown in FIGS. 6A and 6B will be described below with reference to FIGS. 7A to 9B.

[0104] 7A and 7B are diagrams showing an example and another example of Case 1, respectively. FIGS. 8A and 8B are diagrams showing an example and another example of Case 2, respectively. Also, FIGS. 9A and 9B are diagrams showing an example and another example of Case 3, respectively. Note that in the diagrams of FIGS. 7A to 9B, the shading of the first count value CT1 indicates the case of "Yes" in S7 shown in FIG. 6B, and the shading of the second count value CT2 indicates the case of "Yes" in S8 shown in FIG. 6B.

[0105] <Case 1> Case 1 shown in FIGS. 7A and 7B shows the implementation status of the first reverse rotation operation MD1 and the second reverse rotation operation MD2 when the first threshold value TH1 is 100 sheets and the second threshold value TH2 is 50 sheets.

[0106] -An example of Case 1- 7A, in the first print job, a monochrome image forming operation (S3) is performed on 51 sheets in monochrome image forming operation MDa (S2: No). When the monochrome image forming operation on the 51st sheet is completed, the first count value CT1 becomes "51." However, since a multi-color image forming operation (S5) is not performed in multi-color image forming operation MDb, the second count value CT2 remains "0." Therefore, when the first print job is completed, the value of the first count value CT1 is below the first threshold value TH1 (S7: No), so the first reverse rotation operation MD1 and the second reverse rotation operation MD2 are not performed, and the first count value CT1 and the second count value CT2 remain unchanged without being reset.

[0107] In the next second print job, when a multi-color image forming operation (S5) for 49 sheets is performed in color mode (MDb), the first count value CT1 will be "100" and the second count value CT2 will be "49" when the multi-color image forming operation for the 49th sheet is completed. In this case, since S8 is "No" and S11 is "Yes," the processes of S13 to S15 (first reverse rotation operation MD1) are performed, and the first count value CT1 is reset (to "0") in the process of S16, but the second count value CT2 remains at "49."

[0108] In the next third print job, when a multi-color image forming operation (S5) for 100 sheets is performed in color mode (MDb), the first count value CT1 will be "100" and the second count value CT2 will be "149" when the multi-color image forming operation for the 100th sheet is completed. In this case, since the answer is "Yes" in S8, the process of S9 (second reverse rotation operation MD2) is performed, and the first count value CT1 and the second count value CT2 are reset (to "0") in the process of S10.

[0109] In other words, the black photosensitive drum 31K performs a first reverse rotation operation MD1 every time 100 image formation operations are performed, and the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y perform a second reverse rotation operation MD2 every time 149 image formation operations are performed, and in all cases, the interval at which the reverse rotation operations are performed does not exceed the upper limit execution frequency Ca (for example, 170 sheets) at which the cleaning blades 36K, 36C, 36M, and 36Y may be turned over, allowing stable image formation.

[0110] -Another example of Case 1- 7B, the number of image forming operations performed in each print job is different. Specifically, in the first print job, a 50-sheet monochrome image forming operation (S3) is performed in monochrome image forming operation MDa (S2: No). When the 50th monochrome image forming operation is completed, the first count value CT1 becomes "50." However, since a multi-color image forming operation (S5) in multi-color image forming operation MDb is not performed, the second count value CT2 remains "0." Therefore, when the first print job is completed, the value of the first count value CT1 is below the first threshold value TH1 (S7: No). Therefore, the first reverse rotation operation MD1 and the second reverse rotation operation MD2 are not performed, and the first count value CT1 and the second count value CT2 remain unchanged without being reset.

[0111] In the second print job, when the multi-color image forming operation MDb is performed on 50 sheets (S5), the first count value CT1 is "100" and the second count value CT2 is "50" at the end of the 50th multi-color image forming operation. In this case, since the answer to S8 is "Yes," the process of S9 (the second reverse rotation operation MD2) is performed, and the first count value CT1 and the second count value CT2 are reset (to "0") at S10. In other words, the second reverse rotation operation MD2 is performed on the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y at the time when the image forming operation on 50 sheets has been performed. Because this value exceeds the lower limit execution frequency Cb (e.g., 30 sheets), there is no risk of the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over.

[0112] As described above, in other examples of Case 1, there is no risk of the black, cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over, and it is clear that stable image formation can be performed.

[0113] <Case 2> In addition, case 2 shown in Figures 8A and 8B shows the implementation status of the first reverse rotation operation MD1 and the second reverse rotation operation MD2 when the first threshold TH1 is set to 100 sheets and the second threshold TH2 is set to 70 sheets (70% of the first threshold TH1).

[0114] -An example of Case 2- An example of Case 2 shown in FIG. 8A is similar to the example of Case 1 shown in FIG. 7A in processing mode, but differs from the example of Case 1 in the value of the second threshold value TH2 and the number of image forming operations performed in each print job. Specifically, in the first print job, a 31-sheet monochrome image forming operation (S3) is performed in monochrome image forming operation MDa (S2: No). In the second print job, a 69-sheet multicolor image forming operation (S5) is performed in color mode (MDb). In the third print job, a 100-sheet multicolor image forming operation (S5) is performed. Therefore, in the example of Case 2 shown in FIG. 8A, when the second print job is completed, the first count value CT1 reaches "100" and becomes the same value as the first threshold value TH1. However, since the second count value CT2 is "69" and is below the second threshold value TH2, the first reverse rotation operation MD1 is performed. Then, the first count value CT1 is reset to "0," and the second count value CT2 is not reset and remains "69." Next, when the third print job is completed, the first count value CT1 becomes "100", reaching the first threshold value TH1, and the second count value CT2 becomes "169", exceeding the second threshold value TH2, so the second reverse rotation operation MD2 is performed.

[0115] As described above, in one example case, by setting the second threshold value TH2 to 70% of the first threshold value TH1, the second reverse rotation operation MD2 is performed when a maximum of 169 images have been formed on the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y. Therefore, it can be seen that stable image formation can be performed without the interval at which the reverse rotation operation is performed exceeding the upper limit execution frequency Ca, at which there is a risk of the cleaning blades 36C, 36M, and 36Y being turned over.

[0116] -Another example of Case 2- In another example of Case 2 shown in FIG. 8B, the number of image forming operations performed in each print job is different. Specifically, in the first print job, a monochrome image forming operation MDa performs a monochrome image forming operation on 30 sheets, and in the second print job, a multicolor image forming operation MDb performs a multicolor image forming operation on 70 sheets. When the first print job is completed, the first count value CT1 is "30," which is below the first threshold value TH1, so the first reverse rotation operation MD1 is not performed. When the second print job is completed, the first count value CT1 is "100," which reaches the first threshold value TH1. At this time, the second count value CT2 also reaches "70," which reaches the second threshold value TH2, so the second reverse rotation operation MD2 is performed.

[0117] That is, the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y perform the second reverse rotation operation MD2 when 70 images have been formed on the drums. This value exceeds the lower limit Cb (e.g., 30), so there is no risk of the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over.

[0118] As described above, in other examples of Case 2, there is no risk of the black, cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over, and it can be seen that stable image formation can be performed.

[0119] <Case 3> In addition, case 3 shown in Figures 9A and 9B shows the implementation status of the first reverse rotation operation MD1 and the second reverse rotation operation MD2 when the first threshold TH1 is set to 100 sheets and the second threshold TH2 is set to 30 sheets (30% of the first threshold TH1).

[0120] -An example of Case 3- In an example of Case 3 shown in FIG. 9A, the value of the second threshold TH2 and the number of image forming operations performed in each print job differ from those in Example 1. Specifically, in the first print job, monochrome image forming operation MDa performs monochrome image forming operations on 71 sheets, in the second print job, multicolor image forming operation MDb performs multicolor image forming operations on 29 sheets, and in the third print job, multicolor image forming operation MDb performs multicolor image forming operations on 100 sheets. When the first print job is completed, the first count value CT1 is "71," which is below the first threshold TH1, so the first reverse rotation operation MD1 is not performed. When the second print job is completed, the first count value CT1 reaches the first threshold TH1 at "100," and the second count value CT2 at this time is "29," which does not exceed the second threshold TH2 of "30," so the first reverse rotation operation MD1 is performed. When the third print job is completed, the first count value CT1 reaches "100" and reaches the first threshold value TH1, and the second count value CT2 reaches "129" and exceeds the second threshold value TH2, so the second reverse rotation operation MD2 is performed. In other words, the second reverse rotation operation MD2 is performed on the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y when 129 images have been formed. Because this value is below the upper limit execution frequency Ca (e.g., 170 sheets), there is no risk of the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over.

[0121] As described above, in other examples of Case 2, there is no risk of the black, cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over, and it can be seen that stable image formation can be performed.

[0122] -Another example of Case 3- In another example of Case 3 shown in FIG. 9B, the number of image forming operations performed in each print job is different. Specifically, in the first print job, monochrome image forming operation MDa performs monochrome image forming operation on 70 sheets, and in the second print job, multicolor image forming operation MDb performs multicolor image forming operation on 30 sheets. When the first print job is completed, the first count value CT1 is "70," which is below the first threshold value TH1, so the first reverse rotation operation MD1 is not performed. When the second print job is completed, the first count value CT1 is "100," which reaches the first threshold value TH1. At this time, the second count value CT2 also reaches "30," which reaches the second threshold value TH2, so the second reverse rotation operation MD2 is performed.

[0123] That is, the cyan, magenta, and yellow photosensitive drums 31C, 31M, and 31Y perform the second reverse rotation operation MD2 when 30 image formation operations have been performed. Because this value is the same as the lower limit execution frequency Cb (e.g., 30 sheets), there is no risk of the cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over.

[0124] As described above, in other examples of Case 2, there is no risk of the black, cyan, magenta, and yellow cleaning blades 36C, 36M, and 36Y being turned over, and it can be seen that stable image formation can be performed.

[0125] In this way, by performing the processing shown in Figures 6A and 6B, in any of cases 1 to 3 in which the second threshold value TH2 is set to 30% (30 sheets in this example) to 70% (70 sheets in this example) of the first threshold value TH1 (100 sheets in this example), the first count value CT1 and the second count value CT2 will fall within the appropriate implementation frequency range α (a range of 30 sheets to 170 sheets in this example), as shown in the example in Figure 11.

[0126] The present disclosure is not limited to the above-described embodiments, but can be embodied in various other forms. Therefore, the embodiments are merely examples in all respects and should not be interpreted as being limiting. The scope of the present disclosure is defined by the claims and is not bound by the text of the specification. Furthermore, all modifications and variations within the equivalent scope of the claims are within the scope of the present disclosure. [Explanation of symbols]

[0127] 100 Image forming device 110 Image forming unit 20 Approach / separation mechanism 210 First driving source 220 Second driving source 23 Drive unit for contact and separation 31 Photosensitive drum 36 Cleaning blade 36a Tip 41 Intermediate transfer belt (an example of an intermediate transfer body) CT1 First count value CT2 Second count value C. Optimal frequency of implementation Ca upper limit execution frequency Cb Lower Limit Implementation Frequency MD1 1st reverse rotation operation MD2 Second reverse rotation operation MDa Monochrome image formation operation MDb multicolor image forming operation P-sheet Q1 1st Counting Section Q2 2nd Counting Section Q3 Judgment control section Q4 Operation execution control section R1 Forward rotation direction R2 Reverse rotation direction TH1 First threshold TH2 Second threshold X Left / right direction Y depth direction Z vertical direction α Appropriate implementation frequency range βa First implementation frequency range βb Second implementation frequency range

Claims

1. a rotatable first image carrier on which a first toner image is formed; a rotatable second image carrier on which a second toner image is formed; a first cleaning blade that contacts the first image carrier and removes material adhering to the first image carrier; a second cleaning blade that contacts the second image carrier and removes material adhering to the second image carrier; a rotatable intermediate transfer member; a control unit capable of selectively executing a first image forming operation in which the first toner image is intermediately transferred to the intermediate transfer body and then transferred to a sheet, and a second image forming operation in which the first toner image and the second toner image are intermediately transferred successively to the intermediate transfer body and then transferred to a sheet; An image forming apparatus comprising: The control unit a first reverse rotation operation for rotating the first image carrier by a predetermined first surface movement distance in a direction opposite to that for forming the first toner image, and a second reverse rotation operation for rotating both the first image carrier and the second image carrier by a predetermined second surface movement distance in the opposite direction, a first counting unit that counts the number of images formed on the first image carrier each time the first toner image or the second toner image is formed on the sheet; a second counting unit that counts the number of sheets on which the second toner image is formed each time the second toner image is transferred to the sheet as the number of sheets on which the image is formed on the second image carrier; a determination unit that, during execution of the first image forming operation or the second image forming operation, does not perform the first reverse rotation operation or the second reverse rotation operation until a first count value counted by the first count unit reaches a predetermined first threshold value, and determines whether to perform the first reverse rotation operation or the second reverse rotation operation according to a second count value counted by the second count unit at a time when the first count value reaches the first threshold value, The first reverse rotation operation or the second reverse rotation operation is performed based on the determination result of the determination control unit. An image forming apparatus characterized by:

2. 2. The image forming apparatus according to claim 1, wherein the determination control unit determines to perform the first reverse rotation operation if the second count value at the time when the first count value reaches the first threshold has not reached a second threshold that is smaller than the first threshold, and determines to perform the second reverse rotation operation if the second count value has reached the second threshold.

3. 3. The image forming apparatus according to claim 2, wherein the second threshold value is set to a value in a range of 30% to 70% of the first threshold value.

4. the first count value is reset when the first reverse rotation operation is performed; 4. The image forming apparatus according to claim 1, wherein the second count value is reset when the second reverse rotation operation is performed.

5. 4. The image forming apparatus according to claim 1, wherein the first toner image formed in the first image forming operation is a monochrome toner image.

6. a first drive source that rotates the first image carrier and the intermediate transfer member; a second drive source that rotates the second image carrier; a contact / separation mechanism that brings the intermediate transfer body into contact with or separates it from the second image carrier while keeping the intermediate transfer body in contact with the first image carrier, The control unit When the first image forming operation is performed, the contact / separation mechanism is controlled so that the intermediate transfer body is separated from the second support body; When the second image forming operation is performed, the contact / separation mechanism is controlled so that the intermediate transfer body contacts the second image carrier; 2. The image forming apparatus according to claim 1, wherein when the first reverse rotation operation is performed only on the first image carrier during the execution of the second image forming operation, the contact / separation mechanism is controlled so that the intermediate transfer body is separated from the second image carrier.

7. a first drive source that rotates the first image carrier; a second drive source that rotates the second image carrier; a contact / separation mechanism that brings the intermediate transfer body into contact with or separates it from the first image carrier and the second image carrier, The control unit When the first image forming operation is performed, the contact / separation mechanism is controlled so that the intermediate transfer body contacts the first image carrier and is separated from the second image carrier; When the second image forming operation is performed, the contact / separation mechanism is controlled so that the intermediate transfer body contacts both the first image carrier and the second image carrier; 2. The image forming apparatus according to claim 1, wherein the contact / separation mechanism is controlled so that the intermediate transfer body is separated from both the first image carrier and the second image carrier when the first reverse rotation operation or the second reverse rotation operation is performed.

Images