Image forming apparatus

Abstract

To provide an image forming apparatus that introduces an appropriate amount of toner to a cleaning member at a time, and efficiently reduces a defect in which filming occurs on a surface of an image carrier.SOLUTION: A cleaning mode is executed, during a non-transfer process, for forming a plurality of toner image patterns TP on a surface of an intermediate transfer belt 8 in a travel direction at a predetermined interval B, and outputting a reverse bias having a polarity opposite to that of a secondary transfer bias when the toner image patterns TP pass through a secondary transfer nip. A travel direction length A of the toner image pattern TP is determined by the formula of X / (2n-1) when X is the peripheral length of a secondary transfer roller 70 and N is a natural number of 2 or more, and when a determined value has a value at the third decimal place or less, the value is truncated. The predetermined interval B is determined by the formula of (X-A×n) / (n-1), and when a determined value has a value at the fourth decimal place or less, the value is truncated. B≥A is established.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine thereof. [Background technology]

[0002] Conventionally, in image forming devices such as copiers and printers, in order to reduce the problem of filming occurring on the surface of an image carrier such as an intermediate transfer belt, a technique has been known in which a toner image pattern is formed on the surface of the image carrier before printing begins, and the toner image pattern passes through a transfer nip as is without being transferred, and is input to a cleaning member such as a cleaning blade that contacts the image carrier downstream (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0003] In conventional technology, the toner image pattern (toner) is forcibly input to the cleaning member at a predetermined timing, which is expected to reduce the problem of filming on the surface of the image carrier and make it less likely for abnormal images to occur. However, if too much toner is input to the cleaning member at one time, problems such as toner slipping through the cleaning member and resulting in poor cleaning, or toner adhering to the transfer rotating body at the transfer nip position, causing the back side of the sheet to become dirty with toner during the transfer process, occur.

[0004] This invention has been made to solve the above-mentioned problems, and aims to provide an image forming apparatus in which the amount of toner input into the cleaning member at one time is appropriate, thereby efficiently reducing the problem of filming on the surface of the image carrier. [Means for solving the problem]

[0005] The image forming apparatus of the present invention includes an image carrier that travels in a predetermined traveling direction, a transfer rotating body that contacts the image carrier to form a transfer nip and performs a transfer step of transferring a toner image formed on the surface of the image carrier to a sheet that is transported to the transfer nip, a transfer bias output means that outputs a transfer bias when the transfer step is performed, and a cleaning member that contacts the image carrier downstream of the transfer nip in the traveling direction and cleans the surface of the image carrier, and during a non-transfer step when the transfer step is not performed at the transfer nip, a cleaning member that cleans the surface of the image carrier by forming a plurality of rectangular toner image patterns on the surface of the image carrier at predetermined intervals B in the traveling direction. a control mode is configured to be executable in which a reverse bias having a polarity opposite to that of the transfer bias is output by the transfer bias output means when each of the multiple toner image patterns passes through the transfer nip, and the length A of the toner image pattern in the running direction is calculated by the formula X / (2n-1) where X is the circumferential length of the transfer rotating body and n is a natural number greater than or equal to 2, and any value obtained to three decimal places or less is rounded down; and the predetermined interval B is calculated by the formula (XA×n) / (n-1), and any value obtained to four decimal places or less is rounded down, and the configuration is such that B≧A is satisfied. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an image forming apparatus in which the amount of toner input to the cleaning member at one time is appropriate, and the problem of filming on the surface of the image carrier is efficiently reduced. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged structural view showing a part of an image forming unit. [Figure 3] FIG. 2 is a schematic diagram showing an intermediate transfer belt and its vicinity. [Figure 4]2 is a schematic diagram showing the positional relationship between a toner image pattern formed on the surface of an intermediate transfer belt, a density detection sensor, a secondary transfer roller, and a cleaning blade. FIG. [Figure 5] 10 is a timing chart showing an example of control of the secondary transfer bias output when the cleaning mode is executed. [Figure 6] 10 is a diagram showing the relationship between the positions of a plurality of toner image patterns formed on the surface of the intermediate transfer belt in a cleaning mode and the circumferential length of the secondary transfer roller. FIG. [Figure 7] FIG. 10 is a diagram showing, as a comparative example, the relationship between the positions of a plurality of toner image patterns formed on the surface of the intermediate transfer belt in the cleaning mode and the circumferential length of the secondary transfer roller. [Figure 8] FIG. 10 is a diagram illustrating the overall configuration of an image forming apparatus as a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0009] First, the overall configuration and operation of an image forming apparatus 100 will be described with reference to FIGS. FIG. 1 is a structural diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing a part of the image forming unit. 1, an intermediate transfer belt 8 (intermediate transfer body) serving as an image carrier is installed in the center of the image forming apparatus main body 100. Also, imaging units 6Y, 6M, 6C, and 6K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side so as to face the intermediate transfer belt 8.

[0010] 2, the image forming unit 6Y corresponding to yellow is made up of a photosensitive drum 1Y as a photosensitive member, a charging device 4Y, a developing device 5Y, a cleaning device 2Y, a lubricant supplying device 3, a static eliminator (not shown), etc., which are arranged around the photosensitive drum 1Y. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, static eliminator process) is performed on the photosensitive drum 1Y, and a yellow image is formed on the photosensitive drum 1Y.

[0011] The other three image forming units 6M, 6C, and 6K are configured in a manner similar to that of the image forming unit 6Y corresponding to yellow, except that they use different toner colors, and form images corresponding to their respective toner colors. Below, we will omit the explanation of the other three image forming units 6M, 6C, and 6K as appropriate, and will only explain the image forming unit 6Y corresponding to yellow.

[0012] 2, the photosensitive drum 1Y as a photosensitive member is rotated counterclockwise by a motor. Then, at the position of the charging device 4Y, the surface of the photosensitive drum 1Y is uniformly charged (charging process). Note that the charging device 4Y in this embodiment is a charging roller, to which a charging bias is applied from a charging power source 110. Also, the magnitude of the charging bias can be adjusted by the control of the charging power source 110 by the control unit 90. Thereafter, the surface of the photosensitive drum 1Y reaches a position irradiated with exposure light L (laser light) emitted from the exposure device 7, and an electrostatic latent image corresponding to yellow is formed by exposure scanning at this position in the width direction (the direction perpendicular to the paper surface of FIGS. 1 and 2, which is the main scanning direction) (exposure process). Note that in this embodiment, the exposure device 7 is controlled by the control unit 90 so that the magnitude of the exposure energy (exposure amount) of the exposure light L irradiated from the exposure device 7 to the photosensitive drum 1Y can be adjusted.

[0013] Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the developing device 5Y, where the electrostatic latent image is developed to form a yellow toner image (developing step). Thereafter, the surface of the photosensitive drum 1Y reaches a position facing an intermediate transfer belt 8 (image carrier) and a primary transfer roller 9Y (primary transfer member) as an intermediate transfer body, and at this position the toner image formed on the surface of the photosensitive drum 1Y is primarily transferred onto the surface of the intermediate transfer belt 8 (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

[0014] Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the cleaning device 2Y, and at this position, the untransferred toner remaining on the photosensitive drum 1Y is collected into the cleaning device 2Y by the cleaning blade 2a (cleaning process). Here, a lubricant supplying device 3 (photosensitive drum lubricant supplying device) consisting of a lubricant supplying roller 3a, a solid lubricant 3b, a compression spring 3c, etc. is installed inside the cleaning device 2Y. The lubricant supplying roller 3a, which rotates clockwise in Fig. 2, scrapes off the lubricant little by little from the solid lubricant 3b, and the lubricant is supplied to the surface of the photosensitive drum 1Y by the lubricant supplying roller 3a. Finally, the surface of the photosensitive drum 1Y reaches a position facing the charge eliminating device, where the residual potential on the photosensitive drum 1Y is eliminated. Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

[0015] The above-described image forming process is performed in the other image forming units 6M, 6C, and 6K in the same manner as in the yellow image forming unit 6Y. That is, exposure light L based on image information is irradiated from an exposure device 7 disposed above the image forming units onto the photosensitive drums 1M, 1C, and 1K of the image forming units 6M, 6C, and 6K. Thereafter, the toner images of each color formed on the photosensitive drums 1M, 1C, and 1K through the development process by the developing devices 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 8 in a superimposed manner. In this way, a color image is formed on the intermediate transfer belt 8.

[0016] 3, the intermediate transfer belt device is composed of an intermediate transfer belt 8 (intermediate transfer body) as an image carrier, four primary transfer members including primary transfer rollers 9Y, 9M, 9C, and 9K, a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning counter roller 20, a lubricant counter roller 21, a backup roller 22, an intermediate transfer cleaning device 10, a lubricant supply device 30 (intermediate transfer lubricant supply device), a secondary transfer counter roller 80, and a secondary transfer roller 70 as a transfer rotating body. The intermediate transfer belt 8 is stretched and supported by a plurality of roller members 16-22 and 80, and is moved endlessly in the direction of the arrow in FIG. 3 by the rotation of one roller member (drive roller 16) driven by a drive motor.

[0017] Four primary transfer rollers 9Y, 9M, 9C, and 9K (primary transfer members) sandwich an intermediate transfer belt 8 serving as an intermediate transfer body between them and photosensitive drums 1Y, 1M, 1C, and 1K, respectively, to form primary transfer nips. A transfer voltage (primary transfer bias) of a polarity opposite to that of the toner is applied from a primary transfer power source 112 to the primary transfer rollers 9Y, 9M, 9C, and 9K. Then, the intermediate transfer belt 8 travels in the direction of the arrow and passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K in sequence. In this way, the toner images of each color on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred onto the surface of the intermediate transfer belt 8 in a superimposed manner (this is the primary transfer process). In this embodiment, the control unit 90 controls the primary transfer power supply 112 so that the magnitude of the primary transfer bias can be adjusted.

[0018] In the intermediate transfer belt device, the drive roller 16 is disposed downstream of the four photosensitive drums in the running direction of the intermediate transfer belt, and is disposed so as to abut against the inner circumferential surface of the intermediate transfer belt 8 with the intermediate transfer belt 8 wrapped around it at a wrap angle of approximately 120 degrees. The drive roller 16 is driven to rotate in the clockwise direction in FIG. 3 by a drive motor Mt1 controlled by the control unit 90. This causes the intermediate transfer belt 8 to run in a predetermined running direction (clockwise in FIG. 3).

[0019] Thereafter, the intermediate transfer belt 8 onto which the toner images of each color are superimposed and primarily transferred reaches a position facing a secondary transfer roller 70 serving as a transfer rotator (secondary transfer rotator). At this position, a secondary transfer opposing roller 80 sandwiches the intermediate transfer belt 8 between itself and the secondary transfer roller 70, forming a transfer nip (secondary transfer nip). The four-color toner images formed on the intermediate transfer belt 8 are then secondarily transferred onto a sheet P such as paper transported to the position of this secondary transfer nip (secondary transfer process). At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 8.

[0020] Thereafter, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning device 10. At this position, untransferred toner, lubricant, and other deposits adhering to the surface of the intermediate transfer belt 8 are mechanically removed by the cleaning blade 10a and collected inside the intermediate transfer cleaning device 10. The cleaning blade 10a is a plate-shaped member made of an elastic material such as urethane rubber, and is in contact with the surface of the intermediate transfer belt 8 in the counter direction at a predetermined contact pressure and angle. Furthermore, the intermediate transfer belt 8 reaches the position of a lubricant supplying device 30, which serves as an intermediate transfer lubricant supplying device. At this position, a lubricant is supplied to the surface of the intermediate transfer belt 8. Thus, the series of transfer processes performed on the intermediate transfer belt 8 is completed. In addition, density detection sensors 95A to 95C are installed as detection means at a position facing the intermediate transfer belt 8, upstream of the secondary transfer nip in the running direction, and downstream of the photosensitive drums 1Y, 1M, 1C, and 1K in the running direction, and will be described in detail later.

[0021] Referring to FIG. 1, the sheet P transported to the secondary transfer nip position is transported from a paper feed device 26 disposed below the image forming apparatus main body 100 via a paper feed roller 27, a pair of registration rollers 28, etc. More specifically, a plurality of sheets P such as paper are stacked and stored in the paper feed device 26. When the paper feed roller 27 is rotated counterclockwise in FIG. 1, the topmost sheet P is fed through the first transport path K1 toward between the rollers of the pair of registration rollers 28.

[0022] The sheet P conveyed to the registration roller pair 28 (timing roller pair) is temporarily stopped at the roller nip position of the registration roller pair 28, which has stopped rotating. Then, the registration roller pair 28 is rotated in synchronization with the color image on the intermediate transfer belt 8, and the sheet P is conveyed toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0023] Thereafter, the sheet P onto which the color image has been transferred at the position of the secondary transfer nip is sent out from the secondary transfer nip and then conveyed by the conveyor belt 60 to the position of the fixing device 50. Then, at this position, the color image transferred onto the surface is fixed onto the sheet P by the heat and pressure of the fixing belt and pressure roller (fixing process). Thereafter, the sheet P passes through the second transport path K2 and is discharged to the outside of the apparatus by the pair of discharge rollers. The sheets P discharged to the outside of the apparatus by the pair of discharge rollers are sequentially stacked on a stack unit as output images. In this way, a series of image forming processes in the image forming apparatus is completed.

[0024] Next, the configuration and operation of the developing device 5Y in the image forming section will be described in more detail with reference to FIG. The developing device 5Y is composed of a developing roller 51Y facing the photosensitive drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two conveying screws 55Y disposed in a developer container, and a toner concentration sensor 56Y that detects the toner concentration in the developer. The developing roller 51Y is composed of a magnet fixed inside and a sleeve that rotates around the magnet. A two-component developer G consisting of a carrier and toner is contained in the developer container.

[0025] The developing device 5Y configured in this manner operates as follows. The sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. 2. Developer G, which is carried on the developing roller 51Y by the magnetic field formed by the magnet, moves on the developing roller 51Y as the sleeve rotates. The developer G in the developing device 5Y is adjusted so that the proportion of toner in the developer G (toner concentration) falls within a predetermined range. Specifically, when a toner concentration sensor 56Y installed in the developing device 5Y detects that the toner concentration is low, the control unit 90 controls the toner supply device 113 (see FIG. 3) to supply new toner from the toner container 58 into the developing device 5Y so that the toner concentration falls within the predetermined range. Thereafter, the toner supplied from the toner container 58 to the developer storage section circulates between the two separated developer storage sections (movement in the direction perpendicular to the plane of the paper in FIG. 2) while being mixed and stirred by the two transport screws 55Y together with the developer G. Then, the toner in the developer G is attracted to the carrier due to frictional charging with the carrier, and is carried on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

[0026] The developer G carried on the developing roller 51Y is transported in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. The developer G on the developing roller 51Y is then adjusted to an appropriate amount at this position, and then transported to a position facing the photosensitive drum 1Y (the developing area). The toner is then attracted to the latent image formed on the photosensitive drum 1Y by an electric field formed in the developing area. Thereafter, the developer G remaining on the developing roller 51Y reaches above the developer storage section as the sleeve rotates, and is separated from the developing roller 51Y at this position. In the developing device 5Y of this embodiment, a developing bias is applied to the developing roller 51Y from a developing power source 111. The developing power source 111 is controlled by the control unit 90 to adjust the magnitude of the developing bias. A developing electric field is formed in the developing gap by the developing bias and the latent image potential, and the toner on the developing roller 51Y is caused to adhere to the latent image by the developing electric field, thereby developing the image. Furthermore, the toner container 58 is installed so as to be detachable (replaceable) with respect to the developing device 5Y (image forming apparatus 100). When the new toner stored therein becomes empty, the toner container 58 is removed from the developing device 5Y (image forming apparatus 100) and replaced with a new one.

[0027] Next, the secondary transfer roller 70 (secondary transfer device) in this embodiment will be described in detail with reference to FIG. Referring to FIG. 3, a secondary transfer roller 70 as a transfer rotator sandwiches the intermediate transfer belt 8 between itself and a secondary transfer opposing roller 80, forming a secondary transfer nip. 3 by a drive motor Mt2 controlled by the control unit 90. In this embodiment, the linear velocity ratio of the secondary transfer roller 70 to the intermediate transfer belt 8 at the secondary transfer nip is adjustable to 1. Specifically, the rotation speed of at least one of the drive motor Mt1 that drives the drive roller 16 around which the intermediate transfer belt 8 is stretched, and the drive motor Mt2 that drives the secondary transfer roller 70, is adjusted and controlled by the control unit 90, thereby appropriately adjusting the linear velocity ratio at the secondary transfer nip.

[0028] In this embodiment, a secondary transfer bias is applied as a transfer bias to the secondary transfer roller 70 as a transfer rotating body from a secondary transfer power supply 115 as a transfer bias output device. This secondary transfer bias is used to secondarily transfer the toner image that has been primarily transferred onto the surface of the intermediate transfer belt 8 onto the sheet P being conveyed to the secondary transfer nip, and is a secondary transfer bias (a DC voltage or a DC current superimposed with an AC current) of a polarity different from that of the toner (positive polarity in this embodiment). As a result, the toner carried on the toner carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved toward the secondary transfer roller 70 by the secondary transfer electric field. In this embodiment, the control unit 90 controls the secondary transfer power supply 115 so that the magnitude of the secondary transfer bias output can be adjusted. In this embodiment, a secondary transfer bias of a polarity different from the toner polarity is applied to the secondary transfer roller 70, but a secondary transfer bias of the same polarity as the toner polarity may be applied to the secondary transfer opposing roller 80, or a secondary transfer bias of the above-mentioned polarity may be applied to both rollers 70, 80. In such a case, the secondary transfer bias output applied to the secondary transfer opposing roller 80 is also configured to be adjustable.

[0029] The configuration and control of image forming apparatus 100, which are characteristic of this embodiment, will be described in detail below with reference to FIGS. As previously explained using Figure 3 etc., the image forming apparatus 100 in this embodiment is provided with an intermediate transfer belt 8 as an image carrier, a secondary transfer roller 70 as a transfer rotating body, a secondary transfer power supply 115 as a transfer bias output means, a cleaning blade 10a as a cleaning member, and the like.

[0030] The intermediate transfer belt 8 functions as an image carrier that travels in a predetermined traveling direction (the direction of the arrow (clockwise) in FIG. 3), and is provided with a plurality of photosensitive drums 1Y, 1M, 1C, and 1K arranged side by side so as to face each other. The toner images (images) formed on the surfaces of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred onto the intermediate transfer belt 8. The secondary transfer roller 70 contacts the intermediate transfer belt 8 (image carrier) to form a secondary transfer nip as a transfer nip. The secondary transfer roller 70 functions as a transfer rotating body for performing a transfer step (secondary transfer step) in which a toner image formed on the surface of the intermediate transfer belt 8 (image carrier) is transferred to a sheet P conveyed to the secondary transfer nip. The secondary transfer roller 70 (transfer rotating body) contacts the secondary transfer opposing roller 80 via the intermediate transfer belt 8 to form a secondary transfer nip (transfer nip) between itself and the intermediate transfer belt 8.

[0031] The secondary transfer power supply 115 functions as a transfer bias output means that outputs a secondary transfer bias as a transfer bias when the secondary transfer step (transfer step) is performed. The secondary transfer power supply 115 (transfer bias output means) is configured to be able to apply a secondary transfer bias or a reverse bias (a bias used in a cleaning mode, which will be described later) to at least one of the secondary transfer roller 70 and the secondary transfer opposing roller 80 (to the secondary transfer roller 70 in this embodiment). The cleaning blade 10a contacts the intermediate transfer belt 8 (image carrier) downstream of the secondary transfer nip (transfer nip) in the running direction (downstream of the running direction of the intermediate transfer belt 8) and functions as a cleaning member that cleans the surface of the intermediate transfer belt 8.

[0032] 4, 5, etc., image forming apparatus 100 in this embodiment is configured to be able to execute a "control mode" in which, during non-transfer steps when the secondary transfer step (transfer step) is not performed at the secondary transfer nip (transfer nip) (such as during warm-up, before or after the start of a printing operation, or between sheets during continuous printing), multiple rectangular toner image patterns TP (see FIG. 4) are formed on the surface of intermediate transfer belt 8 (image carrier) at predetermined intervals B in the running direction (the direction of the arrow in FIG. 4), and a reverse bias of opposite polarity to the secondary transfer bias is output by secondary transfer power supply 115 (transfer bias output means) when each of the multiple toner image patterns TP passes through the secondary transfer nip. Hereinafter, this control mode will be referred to as a "cleaning mode" as appropriate.

[0033] Specifically, the "cleaning mode (control mode)" is executed to forcibly input a certain amount of toner to the cleaning blade 10a in the width direction (the direction perpendicular to the paper surface in FIG. 3, the up-and-down direction in FIG. 4, which is the main scanning direction) to reduce the problem of filming occurring on the surface of the intermediate transfer belt 8. Here, "filming" refers to the phenomenon in which toner components and lubricant components are transferred and adhered to the surface of the intermediate transfer belt 8 (image carrier), or to the adhered matter, which can cause abnormal images and poor cleaning. This "cleaning mode (control mode)" is executed at a predetermined timing (for example, each time the number of printed sheets reaches a predetermined number) during a non-transfer process (when no image is being formed), such as before printing starts when normal printing (secondary transfer process) is not performed, or between sheets (between an image to be transferred to a preceding sheet and an image to be transferred to a succeeding sheet). Therefore, during the cleaning mode, the sheet P is not transported (passed through) (at least, the sheet P is not transported to the position of the secondary transfer nip).

[0034] In the "cleaning mode (control mode)," a plurality of band-shaped toner image patterns TP (solid images in this embodiment) are formed at intervals B within a maximum image area M on the surface of at least one of the four photosensitive drums 1Y, 1M, 1C, and 1K (in this embodiment, only the black photosensitive drum 1K) using the image formation process previously described with reference to FIGS. 1 and 2. The plurality of toner image patterns TP formed on the photosensitive drum 1K are then primarily transferred onto the intermediate transfer belt 8 within the maximum image area M (see FIG. 4). When the plurality of toner image patterns TP formed on the intermediate transfer belt 8 pass the secondary transfer nip, a reverse bias (a bias of the same negative polarity as the toner polarity in this embodiment) is applied to the secondary transfer roller 70 by the secondary transfer power supply 115 so that the toner image patterns TP are not transferred to the secondary transfer roller 70. Therefore, the multiple toner image patterns TP formed on the intermediate transfer belt 8 hardly transfer to the surface of the secondary transfer roller 70, but pass through the secondary transfer nip position directly and reach the position of the cleaning blade 10a. As a result, toner is input (adhered to and retained) across the width of the edge portion of the cleaning blade 10a (the portion that comes into contact with the intermediate transfer belt 8), and this input toner acts as an abrasive or adsorbent to remove filming on the intermediate transfer belt 8. In the present specification and the like, the "maximum image area M" is the transferable (printable) widthwise range of a sheet P of the maximum size that can be passed (conveyed).

[0035] In this way, the cleaning mode (control mode) is intended to reduce the problem of filming occurring on the surface of the intermediate transfer belt 8 (or to remove any filming that has occurred), but if too much toner is input to the cleaning blade 10a at one time, problems such as toner slipping through the cleaning blade 10a and causing poor cleaning, or toner adhering to the secondary transfer roller 70 at the secondary transfer nip position, causing the back surface of the sheet P to become soiled with toner during subsequent printing (secondary transfer process) can occur. However, if the amount of toner input to the cleaning blade 10a is too small, the effect of reducing the above-mentioned filming cannot be fully achieved.

[0036] Therefore, the inventors of the present application have made extensive efforts and conducted repeated experiments and simulations, and as a result have discovered a method of forming a toner image pattern TP as follows, which optimizes the amount of toner that is input to the cleaning blade 10a at one time and efficiently reduces the problem of filming occurring on the surface of the intermediate transfer belt 8. Referring to Figure 4 etc., first, the length A of the toner image pattern TP in the running direction is calculated by the formula (Formula 1) of X / (2n-1), where X (= diameter D × π) is the circumferential length of the secondary transfer roller 70 (transfer rotating body) and n is a natural number greater than or equal to 2. If the value obtained has three decimal places or less, the value is rounded down. That is, the length A of the toner image pattern TP in the running direction is set to be at least 1 / 3 or less of the circumferential length X of the secondary transfer roller 70, and to be a value obtained by dividing the length by an odd number of 3 or more. Here, roller members such as the secondary transfer roller 70 are typically not designed or manufactured by controlling the circumference X, but by controlling the diameter D (setting the value so that the decimal point is not too small). Therefore, the circumference X of the secondary transfer roller 70 is calculated by multiplying the diameter D by the constant π (3.141592...), which results in a small decimal point. For example, if the diameter D is set to 20 mm and the natural number n is set to 2, the value of the above-mentioned equation 1 (X / (2n-1)) becomes 20.943946..., and it is difficult to control the length A of the toner image pattern TP (which is controlled by the irradiation time (exposure time) of the exposure light L) to match this value. Therefore, in this embodiment, the length A of the toner image pattern TP is set by calculating the value X / (2n-1) (Equation 1), and if the value obtained is less than three decimal places, the value is rounded down (in the above example, this becomes 20.94).

[0037] When the length A of the toner image pattern TP is set in this way, the predetermined interval B (the distance in the running direction between the preceding toner image pattern TP and the succeeding toner image pattern TP) is calculated by the formula (Formula 2) of (XA×n) / (n-1), and if the value obtained is less than four decimal places, the value is rounded down. The formula is configured so that B≧A holds. That is, the predetermined interval B is set to be approximately the same as the running direction length A of the toner image pattern TP, but for the same reason as in the explanation of the running direction length A above, to avoid too many decimal points in Equation 2, the value is calculated using the equation (Equation 2) of (XA×n) / (n-1), and if a value with four decimal places or less is obtained, that value is rounded down to set the predetermined interval B. For example, as in the above example, if the diameter D is set to 20 mm and the natural number n is set to 2, the value of Equation 2 above ((XA×n) / (n-1)) becomes 20.95184..., and the value with four decimal places or less is rounded down to set 20.951 as the predetermined interval B. And although B > A, B ≈ A holds true.

[0038] As described above, in the present embodiment, in the cleaning mode, a plurality of toner image patterns TP are formed on the intermediate transfer belt 8 with a sufficiently short length A in the running direction and a slightly larger and substantially equal spacing B therebetween, so that the amount of toner input to the cleaning blade 10a at one time is optimized, and the problem of filming on the surface of the intermediate transfer belt 8 can be efficiently alleviated. 6A and 6B, in particular, when multiple toner image patterns TP are formed for the time it takes for the secondary transfer roller 70 to make one or more rotations, thereby suppressing the amount of toner input to the cleaning blade 10a at one time (which depends on the running length A and the interval B) while ensuring the total amount of toner input (which depends on the number of toner image patterns TP) and enhancing the filming prevention effect, even if the history of the toner image pattern TP from one rotation ago (which is toner stains caused by slight toner adhesion) remains on the outer peripheral surface of the secondary transfer roller 70 despite the application of a reverse bias, the history from one rotation ago is unlikely to overlap with the toner image pattern TP being formed at that time. This reduces the likelihood of further toner staining of the secondary transfer roller 70. This reduces the likelihood of the back surface of the sheet P being stained with toner during subsequent printing (secondary transfer process).

[0039] Here, FIG. 6(A) is a diagram showing the relationship between the positions of the multiple toner image patterns TP formed on the surface of the intermediate transfer belt 8 in the cleaning mode, the circumferential length X of the secondary transfer roller, and the history of the toner image pattern TP on the secondary transfer roller 70 one revolution before, when the natural number n, which is 2 or greater, is set to 2 in the above-mentioned formulas 1 and 2. FIG. 6B shows the case where the natural number n, which is equal to or greater than 2, is set to 3 in the above-mentioned formulas 1 and 2. As shown in FIGS. 6A and 6B, this embodiment reduces the problem of the toner image pattern TP overlapping the history of the previous rotation.

[0040] 7A, as a comparative example, the cleaning mode has the length A of the toner image pattern TP in the running direction set to be shorter than the circumferential length X of the secondary transfer roller 70, but the interval B between the toner image patterns TP is set to be longer than the circumferential length X of the secondary transfer roller 70. Therefore, if an attempt is made to increase the number of toner image patterns TP in order to increase the amount of toner input to the cleaning blade 10a, the time required for the cleaning mode will be longer. This results in longer downtime when printing is not possible, which makes it difficult for users to use. In addition, in the cleaning mode shown in FIG. 7(B) as a comparative example, the length A of the toner image pattern TP in the running direction is set to be shorter than the circumferential length X of the secondary transfer roller 70, and the interval B between the toner image patterns TP is also set to be shorter than the circumferential length X of the secondary transfer roller 70. However, since the length A in the running direction and the interval B are significantly different, a problem occurs in which the toner image pattern TP overlaps with the history of the previous rotation. In addition, in the cleaning mode shown in FIG. 7C as a comparative example, the length A of the toner image pattern TP in the running direction is set to be approximately equal to the interval B, which is set to be a value obtained by dividing the length A by an even number, which is set to be 1 / 3 or less of the circumference X of the secondary transfer roller 70. As a result, a problem occurs in which the toner image pattern TP overlaps with the history of the previous rotation. 7D, a comparative example, the cleaning mode is set so that the length A of the toner image pattern TP in the running direction is equal to or less than one-third of the circumference X of the secondary transfer roller 70, and is then divided by an odd number. However, because the interval B is set too large relative to the length A in the running direction, if you try to increase the number of toner image patterns TP to increase the amount of toner input to the cleaning blade 10a, the time required for the cleaning mode will be longer. This results in longer downtime when printing is not possible, which makes it difficult for users to use. In contrast to these, in the cleaning mode of this embodiment, the length A of the toner image pattern TP in the running direction is set to be equal to or slightly smaller than the predetermined interval B, and is set to be 1 / 3 or less of the circumference X of the secondary transfer roller 70, and to be a value obtained by dividing by an odd number equal to or greater than 3, so that the problems described above in Figures 7(A) to (D) are less likely to occur.

[0041] In view of this, if it is possible to control the dimensions of the peripheral length X of the secondary transfer roller 70, the length A of the toner image pattern TP in the running direction, the predetermined interval B, etc., A=B It is also possible to configure the system so that In particular, in such a case, let M be a natural number that is an odd number greater than or equal to 3, A=B=X / M This makes it less likely that the toner image pattern TP will overlap with the history of the previous rotation.

[0042] Furthermore, when the peripheral length X (diameter D) of the secondary transfer roller 70 is short, A=B=X Even if the above condition is satisfied, the amount of toner input to the cleaning blade 10a at one time can be reduced. In such a case, the relationship between the positions of the multiple toner image patterns TP, the peripheral length X of the secondary transfer roller, and the history of the toner image patterns TP on the secondary transfer roller 70 one revolution before in cleaning mode is as shown in Figure 6(C). In addition, in such a case, it can be said that the fact that the natural number 1 cannot be substituted for n in the above-mentioned formulas 1 and 2 is compensated for.

[0043] Here, in this embodiment, when performing the cleaning mode, it is also possible to configure the cleaning blade 10a so that the amount of toner input at one time does not become too small, so that B≧A≧1 (preferably B≧A≧5) holds. This allows the amount of toner that is input to the cleaning blade 10a at one time to be an appropriate amount, and effectively reduces the problem of filming on the surface of the intermediate transfer belt 8.

[0044] 4, in this embodiment, the cleaning blade 10a (cleaning member) is configured to contact at least the entire maximum image area M of the intermediate transfer belt 8 (image carrier). As a result, no matter where a toner image (image) is formed within the maximum image area M, untransferred toner associated with the toner image is cleaned by the cleaning blade 10a. Furthermore, the toner image pattern TP formed in the cleaning mode is a belt-shaped pattern formed on the intermediate transfer belt 8 (image carrier) over at least the entire maximum image area M. This ensures that toner is input reliably to the maximum image area M of the cleaning blade 10a in the cleaning mode, making it difficult for filming to occur at least in the maximum image area M, and making it difficult for abnormal images (including abnormal images due to poor cleaning) to occur in the printed image.

[0045] 4, image forming apparatus 100 in this embodiment is provided with three density detection sensors 95A to 95C, which serve as detection means capable of detecting the amount of toner adhesion (image density) of toner image pattern TP, and which are arranged to face both end portions and the center portion of maximum image area M on intermediate transfer belt 8 (image carrier). In other words, belt-shaped toner image pattern TP is formed over at least the range from density detection sensor 95B on one end side in the width direction to density detection sensor 95C on the other end side in the width direction. Then, the image density of the toner image pattern TP is adjusted based on the detection results of the three density detection sensors 95A to 95C (detection means).

[0046] In more detail, the density detection sensors 95A to 95C are reflective photosensors that irradiate the toner image pattern TP with light emitted from a light-emitting element and determine the amount of toner adhesion (image density) of the toner image pattern TP based on the magnitude of the output value when the reflected light is received by a light-receiving element. The control unit 90 is responsible for various controls in the image forming apparatus 100, and also functions as an image creation condition adjusting unit that adjusts the image creation conditions for forming a toner image pattern TP on the surface of the intermediate transfer belt 8 during cleaning mode. The "image creation conditions" adjusted and controlled by the control unit 90 in this way are at least one of the charging bias, exposure energy, development bias, toner concentration in the developer, and primary transfer bias, all of which are factors for adjusting the image density.

[0047] Then, the image forming conditions are adjusted so that the average value of the toner adhesion amounts detected by the three density detection sensors 95A to 95C falls within a predetermined range. If it is desired to adjust the image density to a lower level, the control unit 90 controls the charging power supply 110 to adjust the charging bias to be larger, the control unit 90 controls the exposure device 7 to adjust the exposure energy to be smaller, the control unit 90 controls the development power supply 111 (a power supply that applies a development bias to the development roller 51Y that develops the latent image formed on the surface of the photosensitive drum 1Y) to adjust the development bias to be smaller, the control unit 90 controls the toner supply device 113 to adjust the toner concentration (the concentration of the two-component developer G contained inside the development device 5Y (the proportion occupied by toner)) to be smaller, or the control unit 90 controls the primary transfer power supply 112 to adjust the primary transfer bias to be smaller. Furthermore, the exposure energy at positions outside the predetermined range is adjusted so that the toner adhesion amounts detected by the three density detection sensors 95A to 95C fall within the respective predetermined ranges. By carrying out these controls, it is possible to input an appropriate amount of toner uniformly across the width of the cleaning blade 10a in the cleaning mode.

[0048] 5, in this embodiment, the secondary transfer power supply 115 (transfer bias output means) is configured to alternately output a reverse bias and a positive bias (in this embodiment, a bias of the same magnitude and polarity as the secondary transfer bias) that has a different polarity from the reverse bias when the cleaning mode (control mode) is executed. Then, in the cleaning mode, the secondary transfer power supply 115 is controlled to output a positive bias when each of the plurality of predetermined intervals B passes through the secondary transfer nip. Specifically, during cleaning mode, a reverse bias is applied to the secondary transfer roller 70 when the toner image pattern TP passes through the secondary transfer nip, and a positive bias (secondary transfer bias) is applied to the secondary transfer roller 70 at other times (including when the gap B passes through the secondary transfer nip). By performing such control, in the cleaning mode, the toner adhering to the outer peripheral surface of the secondary transfer roller 70 is less likely to adhere to the intermediate transfer belt 8 when the gap B passes through the secondary transfer nip. Therefore, the configuration is maintained such that the toner is not input to the cleaning blade 10a when the gap B reaches the position of the cleaning blade 10a. In the cleaning mode, when the secondary transfer power supply 115 is configured to output an alternating bias that periodically repeats a reverse bias and a forward bias, the length A in the running direction of the toner image pattern TP and the interval B are configured to be approximately equal, so that simply by matching the timing at which the alternating bias output starts with the timing at which the leading toner image pattern TP reaches the secondary transfer nip, the bias switching intended to achieve the above-mentioned effect can be accomplished.

[0049] <Modification> As shown in FIG. 8, the image forming apparatus 100 in the modified example is a copying machine in which a scanner unit 40 is installed at the top and an internal space is formed below the scanner unit 40 into which printed sheets P are discharged and stacked. Moreover, the image forming apparatus 100 in the modified example is configured to convey the sheet P vertically. In addition, the image forming apparatus 100 in this modification is configured so that the lower surface of the intermediate transfer belt 8 faces photosensitive drums 1Y, 1M, 1C, and 1K (imaging units 6Y, 6M, 6C, and 6K) corresponding to four colors. In the image forming apparatus 100 configured in this manner, the cleaning mode (control mode) previously described with reference to FIGS. 4 to 6 is also executed. The concentration detection sensors 95A to 95C as detection means are disposed downstream of the secondary transfer nip (secondary transfer roller 70) in the belt running direction and upstream of the cleaning blade 10a in the belt running direction. Therefore, to prevent the toner image pattern TP formed on the surface of the intermediate transfer belt 8 from adhering to the secondary transfer roller 70 at the secondary transfer nip, a bias of a polarity that causes the toner image pattern TP to be attracted to the intermediate transfer belt 8 side is applied to the secondary transfer roller 70 or the secondary transfer opposing roller 80, or the secondary transfer roller 70 is separated from the intermediate transfer belt 8. Furthermore, the control of the secondary transfer bias output when the cleaning mode is executed can be the same as that shown in Fig. 5. In particular, the length A of the toner image pattern TP in the running direction can be set to approximately the circumferential length X of the secondary transfer roller 70. In the image forming apparatus 100 configured in this manner, the amount of toner that is input to the cleaning blade 10a at one time is appropriate, and the problem of filming on the surface of the intermediate transfer belt 8 can be efficiently reduced.

[0050] As described above, image forming apparatus 100 in this embodiment is provided with intermediate transfer belt 8 (image carrier) that travels in a predetermined travel direction, and secondary transfer roller 70 (transfer rotator) that contacts intermediate transfer belt 8 to form a secondary transfer nip (transfer nip) and performs a secondary transfer process (transfer process) in which a toner image formed on the surface of intermediate transfer belt 8 is transferred to sheet P transported to the secondary transfer nip. Also provided are secondary transfer power supply 115 (transfer bias output means) that outputs a secondary transfer bias (transfer bias) when the transfer process is performed, and cleaning blade 10a (cleaning member) that contacts intermediate transfer belt 8 downstream of the secondary transfer nip in the travel direction and cleans the surface of intermediate transfer belt 8. In addition, during the non-transfer process when the secondary transfer process is not performed at the secondary transfer nip, a cleaning mode (control mode) can be executed in which a plurality of rectangular toner image patterns TP are formed on the surface of the intermediate transfer belt 8 at a predetermined interval B in the running direction, and when each of the plurality of toner image patterns TP passes through the secondary transfer nip, a reverse bias of the opposite polarity to the secondary transfer bias is output by the secondary transfer power source 115. The length A of the toner image pattern TP in the running direction is calculated by the formula X / (2n-1), where X is the circumferential length of the secondary transfer roller 70 and n is a natural number greater than or equal to 2. If this value reaches three decimal places or less, this value is rounded down. The predetermined interval B is calculated by the formula (XA×n) / (n-1), and if this value reaches four decimal places or less, this value is rounded down, so that B≧A is satisfied. This allows the amount of toner input to the cleaning blade 10a (cleaning member) at one time to be appropriate, and effectively reduces the problem of filming on the surface of the intermediate transfer belt 8 (image carrier).

[0051] In this embodiment, the present invention is applied to an image forming apparatus 100 that uses a secondary transfer roller 70 as a transfer rotator. However, the present invention can also be applied to an image forming apparatus that uses a secondary transfer belt as a transfer rotator. Furthermore, in this embodiment, the present invention is applied to an image forming apparatus 100 that uses an intermediate transfer belt 8 (intermediate transfer body) as an image carrier and a secondary transfer roller 70 as a transfer rotator. However, the present invention can also be applied to an apparatus that does not have an intermediate transfer body such as an intermediate transfer belt or intermediate transfer drum, but instead has a developing device that develops toner, a photosensitive drum (photosensitive body) as an image carrier on which a toner image developed by the developing device is formed, and a transfer rotator that abuts against the photosensitive drum to form a transfer nip and transfers the toner image on the photosensitive drum to a sheet transported to the transfer nip, that is, a so-called direct transfer type image forming apparatus. In the present embodiment, the present invention is applied to the image forming apparatus 100 that forms color images. However, the present invention can also be applied to an image forming apparatus that forms only monochrome images. Furthermore, in this embodiment, the present invention is applied to the image forming apparatus 100 equipped with the lubricant supplying device 30 that supplies lubricant to the surface of the intermediate transfer belt 8, but the present invention can also be applied to an image forming apparatus that does not have such a lubricant supplying device 30. In that case, filming is likely to form on the surface of the intermediate transfer belt 8, making the configuration of the present invention even more useful. Even in such cases, the same effects as those of this embodiment can be obtained.

[0052] It is to be noted that the present invention is not limited to the present embodiment, and it is clear that the present embodiment can be appropriately modified within the scope of the technical concept of the present invention in addition to the modifications suggested in the present embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. of the components can be any number, position, shape, etc. that is suitable for implementing the present invention. [Explanation of symbols]

[0053] 1Y, 1M, 1C, 1K photosensitive drum (photosensitive body), 8 Intermediate transfer belt (image carrier, intermediate transfer body), 10 intermediate transfer cleaning device, 10a cleaning blade (cleaning member), 70 Secondary transfer roller (transfer rotating body), 80 Secondary transfer opposing roller, 95A to 95C: concentration detection sensor (detection means), 100 Image forming apparatus (image forming apparatus main body), 115 secondary transfer power supply (transfer bias output means), TP toner image pattern (toner image for control mode), M maximum image area, P sheet (recording medium).

[0054] The present invention can also be embodied in a combination of Supplementary Notes 1 to 10, for example, as follows. (Appendix 1) an image carrier that travels in a predetermined travel direction; a transfer rotating body for performing a transfer step in which the transfer rotating body abuts against the image carrier to form a transfer nip and transfers a toner image formed on the surface of the image carrier to a sheet conveyed to the transfer nip; a transfer bias output unit that outputs a transfer bias when the transfer step is performed; a cleaning member that contacts the image carrier downstream of the transfer nip in the traveling direction and cleans the surface of the image carrier; Equipped with a control mode is configured to be executable in which, during a non-transfer process in which the transfer process is not performed at the transfer nip, a plurality of rectangular toner image patterns are formed on the surface of the image carrier at predetermined intervals B in the traveling direction, and a reverse bias having a polarity opposite to that of the transfer bias is output by the transfer bias output means when each of the plurality of toner image patterns passes through the transfer nip; The length A of the toner image pattern in the running direction is calculated by the formula X / (2n-1), where X is the circumferential length of the transfer rotary body and n is a natural number equal to or greater than 2, and if the calculated value has three decimal places or less, the value is rounded down; The predetermined interval B is calculated by the formula (XA×n) / (n-1), and if the value has four decimal places or less, the value is rounded down. An image forming apparatus characterized in that it is configured so that B≧A holds. (Appendix 2) an image carrier that travels in a predetermined travel direction; a transfer rotating body for performing a transfer step in which the transfer rotating body abuts against the image carrier to form a transfer nip and transfers a toner image formed on the surface of the image carrier to a sheet conveyed to the transfer nip; a transfer bias output unit that outputs a transfer bias when the transfer step is performed; a cleaning member that contacts the image carrier downstream of the transfer nip in the traveling direction and cleans the surface of the image carrier; Equipped with a control mode is configured to be executable in which, during a non-transfer process in which the transfer process is not performed at the transfer nip, a plurality of rectangular toner image patterns are formed on the surface of the image carrier at predetermined intervals B in the traveling direction, and a reverse bias having a polarity opposite to that of the transfer bias is output by the transfer bias output means when each of the plurality of toner image patterns passes through the transfer nip; an image forming apparatus configured so that A=B holds true regarding the length A of the toner image pattern in the running direction and the predetermined interval B; (Appendix 3) 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is configured so that A=B=X holds, where A is the peripheral length of the transfer rotor and B is the peripheral length of the transfer rotor. (Appendix 4) The image forming apparatus according to claim 2, characterized in that it is configured so that A=B=X / M holds when M is a natural number that is an odd number greater than or equal to 3, where X is the circumferential length of the transfer rotor and M is the odd number greater than or equal to 3. (Appendix 5) 5. The image forming apparatus according to any one of claims 1 to 4, wherein the image forming apparatus is configured so that B≧A≧1 is satisfied. (Appendix 6) 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured so that B≧A≧5 holds. (Appendix 7) the cleaning member is configured to contact at least the entire maximum image area of ​​the image carrier, 7. The image forming apparatus according to claim 1, wherein the toner image pattern is a belt-shaped pattern formed over at least the entire maximum image area on the image carrier. (Appendix 8) three detection means that are disposed so as to face each other at both ends and a center of the maximum image area on the image carrier, and that are capable of detecting the amount of toner adhesion of the toner image pattern; 8. The image forming apparatus according to claim 7, wherein the image density of the toner image pattern is adjusted based on the detection results of the three detection means. (Appendix 9) The image forming apparatus according to any one of Appendix 1 to Appendix 8, characterized in that when the control mode is executed, the transfer bias output means is configured to alternately output the reverse bias and a positive bias having a polarity different from that of the reverse bias, and outputs the positive bias when each of the plurality of predetermined intervals passes through the transfer nip. (Appendix 10) The image carrier is an intermediate transfer belt onto which a plurality of photosensitive members are arranged in parallel to face each other, and onto which toner images formed on the surfaces of the plurality of photosensitive members are primarily transferred, the transfer rotating body is a secondary transfer roller that contacts a secondary transfer opposing roller via the intermediate transfer belt and forms the transfer nip between itself and the intermediate transfer belt, The cleaning member is a cleaning blade, The image forming apparatus according to any one of appendices 1 to 9, characterized in that the transfer bias output means is configured to be able to apply the transfer bias or the reverse bias to at least one of the secondary transfer roller and the secondary transfer opposing roller. [Prior art documents] [Patent documents]

[0055] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-20970

Claims

1. an image carrier that travels in a predetermined travel direction; a transfer rotating body for performing a transfer step in which the transfer rotating body abuts against the image carrier to form a transfer nip and transfers a toner image formed on the surface of the image carrier to a sheet conveyed to the transfer nip; a transfer bias output unit that outputs a transfer bias when the transfer step is performed; a cleaning member that contacts the image carrier downstream of the transfer nip in the traveling direction and cleans the surface of the image carrier; Equipped with a control mode is configured to be executable in which, during a non-transfer process in which the transfer process is not performed at the transfer nip, a plurality of rectangular toner image patterns are formed on the surface of the image carrier at predetermined intervals B in the traveling direction, and a reverse bias having a polarity opposite to that of the transfer bias is output by the transfer bias output means when each of the plurality of toner image patterns passes through the transfer nip; The length A of the toner image pattern in the running direction is calculated by the formula X / (2n-1), where X is the circumferential length of the transfer rotary body and n is a natural number equal to or greater than 2, and if the calculated value has three decimal places or less, the value is rounded down. The predetermined interval B is calculated by the formula (X-A×n) / (n-1), and if the value has four decimal places or less, the value is rounded down. An image forming apparatus configured so that B≧A is satisfied.

2. an image carrier that travels in a predetermined travel direction; a transfer rotating body for performing a transfer step in which the transfer rotating body abuts against the image carrier to form a transfer nip and transfers a toner image formed on the surface of the image carrier to a sheet conveyed to the transfer nip; a transfer bias output unit that outputs a transfer bias when the transfer step is performed; a cleaning member that contacts the image carrier downstream of the transfer nip in the traveling direction and cleans the surface of the image carrier; Equipped with a control mode is configured to be executable in which, during a non-transfer process in which the transfer process is not performed at the transfer nip, a plurality of rectangular toner image patterns are formed on the surface of the image carrier at predetermined intervals B in the traveling direction, and a reverse bias having a polarity opposite to that of the transfer bias is output by the transfer bias output means when each of the plurality of toner image patterns passes through the transfer nip; an image forming apparatus configured so that the relationship A=B holds true, where A is the length of the toner image pattern in the running direction and B is the predetermined interval;

3. 3. The image forming apparatus according to claim 2, wherein the relationship A=B=X is satisfied, where A is the peripheral length of the transfer rotary member and B is the circumferential length of the transfer rotary member.

4. 3. The image forming apparatus according to claim 2, wherein A=B=X / M is satisfied when M is a natural number that is an odd number equal to or greater than 3, and A is a peripheral length X of the transfer rotor.

5. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured so that B≧A≧1 is satisfied.

6. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured so that B≧A≧5 is satisfied.

7. the cleaning member is configured to contact at least the entire maximum image area of ​​the image carrier, 3. The image forming apparatus according to claim 1, wherein the toner image pattern is a band-shaped pattern formed over at least the entire maximum image area on the image carrier.

8. three detecting means that are disposed so as to face each other at both ends and a center of the maximum image area on the image carrier, and that are capable of detecting the amount of toner adhesion of the toner image pattern; 8. The image forming apparatus according to claim 7, wherein the image density of the toner image pattern is adjusted based on the detection results of the three detection means.

9. 3. The image forming apparatus according to claim 1, wherein the transfer bias output means is configured to alternately output the reverse bias and a positive bias having a polarity different from that of the reverse bias when the control mode is executed, and outputs the positive bias when each of the plurality of predetermined intervals passes through the transfer nip.

10. The image carrier is an intermediate transfer belt onto which a plurality of photosensitive members are arranged in parallel to face each other, and onto which toner images formed on the surfaces of the plurality of photosensitive members are primarily transferred, the transfer rotating body is a secondary transfer roller that contacts a secondary transfer opposing roller via the intermediate transfer belt and forms the transfer nip between itself and the intermediate transfer belt, The cleaning member is a cleaning blade, 3. The image forming apparatus according to claim 1, wherein the transfer bias output unit is configured to be able to apply the transfer bias or the reverse bias to at least one of the secondary transfer roller and the secondary transfer opposing roller.

Images