JP2016075769A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress cleaning failure caused by foreign substances such as paper powder clogging into a space between a cleaning blade and a moving body, and extend the life of the cleaning blade.SOLUTION: When the number of images formed while the length in the width direction of a transfer material P is not changed from a first length is a predetermined value or more, and images are formed while the transfer material P having the first length in the width direction is changed to a transfer material P having a second length longer than the first length in the width direction, an execution part 150 included in an image forming apparatus 100 having a cleaning blade 82 cleaning a moving body 7 executes a reverse movement operation to move the moving body 7 in a direction reverse to a predetermined direction after images are formed onto the transfer material P having the first length and before forming images onto the transfer material P having the second length.SELECTED DRAWING: Figure 6

Description

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

  Conventionally, in an image forming apparatus such as an electrophotographic system, a toner image formed on an electrophotographic photosensitive member (photosensitive member) or an electrostatic recording dielectric is directly or once transferred to an intermediate transfer member and then transferred to a transfer material such as paper. Transfer to form an image. There is also an image forming apparatus having a transfer material carrier that carries and conveys a transfer material onto which a toner image is transferred. Such an image forming apparatus is generally provided with a cleaning device that removes deposits from a moving body such as a photosensitive member, an electrostatic recording dielectric, an intermediate transfer member, and a transfer material carrier.

  Further explanation will be given by taking an intermediate transfer member as an example of the moving member. On the intermediate transfer member, deposits such as toner remaining after the transfer process of the toner image from the intermediate transfer member to the transfer material (transfer residual toner) and paper dust due to contact with the transfer material adhere. In order to remove such deposits, the image forming apparatus is provided with a cleaning device.

  As this cleaning device, there is a blade type cleaning device in which a cleaning blade is brought into contact with an intermediate transfer member to scrape off deposits such as transfer residual toner on the intermediate transfer member. In this cleaning device, foreign matter such as paper dust is sandwiched between the cleaning blade and the intermediate transfer member due to repeated use, and the cleaning performance of the cleaning blade may deteriorate, resulting in poor cleaning. This is because when a foreign substance such as paper dust is sandwiched between the cleaning blade and the intermediate transfer member, the cleaning blade partially floats from the surface of the intermediate transfer member, and adhering matters such as transfer residual toner are easily slipped through.

  On the other hand, in Patent Document 1, after the rotation of the intermediate transfer member at the end of image formation, the intermediate transfer member is rotated in the opposite direction to that at the time of image formation, and the paper is sandwiched between the cleaning blade and the intermediate transfer member. It has been proposed to remove the powder.

Japanese Patent Laid-Open No. 10-10939

  However, as described in Patent Document 1, if the intermediate transfer member is reversely rotated every time image formation is completed, there is a problem that the life of the cleaning blade tends to be shortened. That is, when the intermediate transfer member rotates in the rotation direction at the time of image formation (forward rotation), as shown in FIG. 7A, the intermediate transfer member of the cleaning blade is pulled in the moving direction of the surface of the intermediate transfer member. The abutting part is deformed. On the other hand, when the intermediate transfer member is rotated (reversely rotated) in the opposite direction to the image formation, the intermediate transfer member of the cleaning blade is pulled so as to be pulled in the opposite direction to the image formation as shown in FIG. The abutting part is deformed. If this is repeated more than necessary, the edge portion of the tip located at the contact portion of the cleaning blade with the intermediate transfer member tends to be damaged, and the life of the cleaning blade tends to be shortened.

  In the above, the conventional problem has been described by taking as an example the case where the moving body is an intermediate transfer body. However, this problem is that the moving body to be cleaned by the cleaning blade is a photosensitive body, an electrostatic recording dielectric, an intermediate transfer body, or The same applies to any transfer material carrier.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of extending the life of a cleaning blade while suppressing a cleaning failure caused by foreign matter such as paper dust being sandwiched between the cleaning blade and a moving body. That is.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention moves in a predetermined direction and carries a toner image to be transferred to a transfer material and conveys it to a contact portion with the transfer material, or carries a transfer material to which the toner image is transferred. In the image forming apparatus comprising: a moving body that conveys the moving body; and a cleaning device that is disposed in contact with the moving body and includes a cleaning blade that removes deposits from the moving body. The number of image formations performed without changing the length in the width direction orthogonal to the direction from the first length is a predetermined value or more, and the transfer of the first length in the width direction When an image is formed by changing from a material to a transfer material having a second length larger than the first length in the width direction, image formation is performed on the transfer material having the first length. Then, image formation is performed on the transfer material having the second length. In, the movable body from the predetermined direction is an image forming apparatus characterized by comprising an execution unit for executing an inverse movement operation to move in the opposite direction.

  ADVANTAGE OF THE INVENTION According to this invention, the lifetime of a cleaning blade can be extended, suppressing the cleaning defect by foreign materials, such as paper dust, being pinched | interposed between a cleaning blade and a moving body.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus. It is a schematic cross-sectional block diagram of a belt cleaning apparatus. 2 is a schematic control block diagram of a main part of the image forming apparatus. FIG. It is a graph which shows the relationship between the number of image formation, and the deformation amount of a cleaning blade. It is a graph which shows the relationship between the position of the longitudinal direction of a cleaning blade, and the deformation amount of a cleaning blade. FIG. 6 is a flowchart for explaining a reverse movement operation of a secondary transfer belt. It is a schematic diagram of the vicinity of the tip of the cleaning blade. It is a schematic diagram which shows the relationship between the size of a transfer material, and the position where paper dust is pinched.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. FIG. 1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type copier that employs an intermediate transfer method capable of forming a full-color image using an electrophotographic method, and a multifunction device having a printer function.

  The image forming apparatus 100 includes first, second, third, and third images that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units, respectively. 4 image forming units SY, SM, SC, and SK. These four image forming units SY, SM, SC, and SK are arranged in one row. In this embodiment, the configurations and operations of the image forming units SY, SM, SC, and SK are substantially the same except that the color of the toner used is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol indicating an element for any color will be omitted, and the element will be described generally.

  In each image forming unit S, a photosensitive drum 1 which is a drum-type (cylindrical) electrophotographic photosensitive member (photosensitive member) as an image carrier is disposed. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. Around the photosensitive drum 1, the following devices are arranged in order along the rotation direction. First, a charging roller 2 which is a roller-shaped charging member as a charging unit is disposed. Next, an exposure device (laser scanner) 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-shaped primary transfer member as a primary transfer means is disposed. Next, a drum cleaning device 6 as a photosensitive member cleaning unit is disposed.

  Further, the image forming apparatus 100 is formed by an endless belt as an intermediate transfer member disposed to face the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units SY, SM, SC, and SK. And an intermediate transfer belt 7. The intermediate transfer belt 7 is an example of a moving body that is a cleaning target of a cleaning blade and that carries a toner image that moves in a predetermined direction and is transferred to a transfer material and conveys the toner image to a contact portion with the transfer material. The intermediate transfer belt 7 is wound around a plurality of support rollers 71 to 76 and given a predetermined tension. The intermediate transfer belt 7 is rotated (circularly moved) in the direction of arrow R2 in the drawing when the driving roller 71, which is one of a plurality of support rollers, is rotationally driven to transmit the driving force. On the inner peripheral surface (back surface) side of the intermediate transfer belt 7, the primary transfer rollers 5Y, 5M, 5C, and 5K described above are disposed at positions facing the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is urged (pressed) toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 7 and the photosensitive drum 1 are in contact with each other. . Further, on the outer peripheral surface (front surface) side of the intermediate transfer belt 7, a roller-like secondary transfer member serving as a secondary transfer unit is provided at a position facing a counter roller 76 that is one of a plurality of support rollers. A secondary transfer roller 9 is disposed. The secondary transfer roller 9 is urged (pressed) toward the opposing roller 76 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 7 and the secondary transfer roller 9 come into contact with each other. ) N2 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a belt cleaning device 8 as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 71.

  In addition, the image forming apparatus 100 includes a feeding unit for the transfer material P, a fixing device 10 as a fixing unit for fixing the toner image on the transfer material P, and the like.

  When an image is formed by the image forming apparatus 100 of this embodiment, the outer peripheral surface (surface) of the photosensitive drum 1 that is rotationally driven is uniformly charged by the charging roller 2. At this time, a predetermined charging voltage (charging bias) is applied to the charging roller 2 from a charging power source (not shown). The charged photosensitive drum 1 is irradiated with laser light from the exposure device 3 to form an electrostatic latent image (electrostatic image) on the surface thereof. In this embodiment, an image signal is input to an image signal processing unit (not shown) of the image forming apparatus 100 from a reader unit (not shown) provided in the image forming apparatus 100 or an external device (for example, a personal computer). The image signal processing unit creates a digital image signal obtained by color-converting the image signal into yellow, cyan, magenta, and black. Then, the exposure device 3 of each image forming unit S scans and exposes the photosensitive drum 1 with laser light based on the corresponding color component signal among the signals. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by the developing device 4 using toner as a developer. At this time, a predetermined developing voltage (developing bias) is applied to a developing roller as a developer carrying member provided in the developing device 4 from a developing power source (not shown). In this embodiment, a toner image is formed by image portion exposure and reversal development. That is, the exposed portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged is charged to the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1. Adhered toner adheres. The toner image on the photosensitive drum 1 is transferred (primary transfer) on the rotating (moving) intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion N1. At this time, the primary transfer roller 5 is supplied with a predetermined DC voltage having a polarity (positive in this embodiment) opposite to the charging polarity (normal charging polarity) of the toner at the time of development from a primary transfer power source (not shown). Primary transfer voltage (primary transfer bias) is applied. For example, when a full-color image is formed, the toner images of the respective colors formed on the respective photosensitive drums 1 in the respective image forming units SY, SM, SC, and SK as described above are transferred onto the intermediate transfer belt 7 in the respective primary transfer units N1. The primary transfer is carried out so as to be superimposed on each other.

  On the other hand, a cassette in which a transfer material P such as paper or a synthetic resin sheet (in this embodiment, the transfer material P is paper) is detachably disposed at the lower part of the main body of the image forming apparatus 100. 11, the paper is selectively fed one by one by the supply roller 12. Thereafter, the transfer material P is transported to the registration roller 13 disposed on the downstream side in the transport direction. The transfer material P conveyed to the registration roller 13 is conveyed to the secondary transfer portion N2 in accordance with the timing at which the toner image on the intermediate transfer belt 7 is conveyed to the secondary transfer portion N2 by the rotation of the intermediate transfer belt 7. The

  The toner image on the intermediate transfer belt 7 is transferred onto the transfer material P that is sandwiched and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 9 by the action of the secondary transfer roller 9 in the secondary transfer portion N2. (Secondary transfer). At this time, the secondary transfer roller 9 receives a secondary transfer voltage (secondary voltage), which is a DC voltage having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner from the secondary transfer power source E (FIG. 3). Next transfer bias) is applied. For example, when a full-color image is formed, the toner images formed by superimposing four color toner images on the intermediate transfer belt 7 are secondarily transferred onto the transfer material P all at once.

  The transfer material P on which the toner image is formed is conveyed to the fixing device 10 and heated and pressed at the fixing nip between the fixing roller 10a and the pressure roller 10b, so that the toner image is fixed thereon. (Fixed). Thereafter, the transfer material P is discharged onto a discharge tray 14 outside the apparatus main body of the image forming apparatus 100.

  The surface of the photosensitive drum 1 after the primary transfer process is cleaned by the drum cleaning device 6. The drum cleaning device 6 scrapes off and removes adhering matter such as primary transfer residual toner from the surface of the rotating photosensitive drum 1 by a cleaning blade disposed in contact with the photosensitive drum 1 and collects it in a recovery container.

  Further, the surface of the intermediate transfer belt 7 after the secondary transfer process is cleaned by a belt cleaning device 8. The belt cleaning device 8 uses a cleaning blade disposed in contact with the intermediate transfer belt 7 to deposit the secondary transfer residual toner or the like from the surface of the rotating intermediate transfer belt 7 (hereinafter referred to as “transfer residual toner”). Scraping off and collecting in a collection container. The belt cleaning device 12 will be further described later.

2. Belt Cleaning Device FIG. 2 is a schematic cross-sectional configuration diagram of the belt cleaning device 8 in this embodiment. FIG. 2 shows a cross section substantially orthogonal to the moving direction of the surface of the intermediate transfer belt 7.

  The belt cleaning device 8 includes a collection container (casing) 81 having an opening 81a on the intermediate transfer belt 7 side. A cleaning blade 82 is attached to the opening 81 a of the collection container 81 via a support member 83. The cleaning blade 82 is predetermined in a longitudinal direction arranged along a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7 (width direction of the intermediate transfer belt 7) and a short direction perpendicular to the longitudinal direction. It is a plate-shaped member having a predetermined thickness having a length. In this embodiment, the cleaning blade 82 is made of urethane rubber as an elastic material. One end of the cleaning blade 82 in the short direction is fixed to a support member 83 and supported by a collection container 81. The cleaning blade 82 is in contact with the intermediate transfer belt 7 in the counter direction at the outer edge 82a of the free end in the short direction. That is, the cleaning blade 82 is in contact with the intermediate transfer belt 7 such that the free end is directed upstream in the movement direction of the surface of the intermediate transfer belt 7 during image formation. A contact portion between the cleaning blade 82 and the intermediate transfer belt 7 is a cleaning nip (cleaning portion) Q.

  In addition, a squeeze sheet 84 as a contact member is attached to the opening 81 a of the recovery container 81 on the upstream side (lower part in the drawing) of the surface of the intermediate transfer belt 7 with respect to the cleaning blade 82. The squeeze sheet 84 is a sheet having a predetermined thickness having a predetermined length in a longitudinal direction arranged along a direction substantially perpendicular to the moving direction of the surface of the intermediate transfer belt 7 and a short direction perpendicular to the longitudinal direction. It is a shaped member. In this embodiment, the squeeze sheet 84 is formed of a plastic sheet having flexibility. One end of the squeeze sheet 84 in the short direction is fixed to and supported by the collection container 81. The squeeze sheet 84 is brought into contact with the intermediate transfer belt 7 at the free end in the short direction. The squeeze sheet 84 is brought into contact with the intermediate transfer belt 7 such that the front end of the squeeze sheet 84 faces the downstream side in the moving direction of the surface of the intermediate transfer belt 7 during image formation. The squeeze sheet 84 drops the toner scraped off by the cleaning blade 82 into the collection container 81 and suppresses the toner from flowing backward to the intermediate transfer belt 7 side.

  In the collection container 81, a conveyance screw 85 for conveying the collected toner in the longitudinal direction and discharging it to a collection toner box (not shown) separately provided in the image forming apparatus 100 is disposed. .

3. Control Mode FIG. 3 shows a schematic control mode of the main part of the image forming apparatus 100 of the present embodiment. In the present exemplary embodiment, a control unit 150 serving as a control unit provided in the image forming apparatus 100 comprehensively controls each unit of the image forming apparatus 100. The control unit 150 includes a CPU 151 that is a central element that performs arithmetic processing, a ROM 152 and a RAM 153 that are storage elements, and the like. The RAM 153 stores sensor detection results, calculation results, and the like, and the ROM 152 stores a control program, a previously obtained data table, and the like. Each control object in the image forming apparatus 100 is connected to the control unit 150. In relation to the present embodiment, the control unit 150 includes a secondary transfer power source E, a drive circuit 20 of a drive motor M that is a drive source of the intermediate transfer belt 7, a counter 30 that counts the number of formed images, and image formation. The operation unit 40 of the apparatus 100 is connected. The control unit 150 functions as an execution unit that controls an image forming operation and a reverse movement operation of an intermediate transfer belt 7 described later.

  Here, the image forming apparatus 100 performs a series of image forming operations (jobs) for forming and outputting an image on a single or a plurality of transfer materials P, which is started by one start instruction. In general, a job includes an image forming process (printing process), a pre-rotation process, a paper-to-paper (inter-transfer material) process when images are formed on a plurality of transfer materials P, and a post-rotation process. The image forming process is a period in which an electrostatic latent image of an image that is actually formed and output on the transfer material P, a toner image, a primary transfer or a secondary transfer of the toner image is performed. This is the period. The pre-rotation process is a period for performing a preparatory operation before the image forming process from when the start instruction is input until the actual image formation is started. The inter-sheet process is a period corresponding to the interval between the transfer material P and the transfer material P when the image forming process is continuously performed on a plurality of transfer materials P (continuous image formation). The post-rotation process is a period during which an organizing operation (preparation operation) after the image forming process is performed. The non-image forming period is a period other than the image forming time, and is a preparatory operation at the time of turning on the power of the image forming apparatus 100 or returning from the sleep state. This is included during the previous multi-rotation process.

4). Reverse Transfer Operation of Intermediate Transfer Belt As described above, the intermediate transfer belt 7 is cleaned by the belt cleaning device 8 having the cleaning blade 82.

  However, foreign matters such as paper dust (hereinafter referred to as “paper dust”) may be caught in the cleaning nip Q formed between the cleaning blade 82 and the intermediate transfer belt 7. The paper dust caught in the cleaning nip Q is difficult to remove simply by continuing the normal image forming operation, and the cleaning blade 82 is partially lifted from the intermediate transfer belt 7. In this state, if the transfer residual toner on the intermediate transfer belt 7 is conveyed to the cleaning nip Q, it may pass through the cleaning blade 82, resulting in poor cleaning. When a cleaning failure occurs, an image failure may occur due to, for example, toner stains attached to subsequent images.

  For this reason, in this embodiment, paper dust caught in the cleaning nip Q is removed by performing a reverse movement operation that moves the intermediate transfer belt 7 in a direction opposite to a predetermined direction during image formation at a predetermined timing. To do.

  However, if the intermediate transfer belt 7 is reversely moved every time image formation is completed as described above, the life of the cleaning blade 82 can be reduced even though the paper dust caught in the cleaning nip Q can be removed. May be shortened.

  Therefore, in this embodiment, the paper powder caught between the cleaning blade 82 and the intermediate transfer belt 7 is efficiently removed by performing the reverse movement operation of the intermediate transfer belt 7 at an effective timing. The wasteful movement of the intermediate transfer belt 7 is reduced, the load applied to the cleaning blade 82 is reduced, and the consumption of the cleaning blade 82 is suppressed. Thereby, the life of the cleaning blade 82 is extended while suppressing cleaning failure due to paper dust being sandwiched between the cleaning blade 82 and the intermediate transfer belt 7. This will be described in detail below.

  In this embodiment, in the reverse movement operation of the intermediate transfer belt 7, the photosensitive drum 1 is also moved in the reverse direction to that during image formation in synchronization with the intermediate transfer belt 7 moving in the reverse direction from that during image formation. Move to. However, the present invention is not limited to this, and in the reverse movement operation of the intermediate transfer belt 7, the photosensitive drum 1 may be separated from the intermediate transfer belt 7.

  Here, in the cleaning nip Q, the paper dust is likely to be nipped as a lump in a portion corresponding to an end (edge, edge) in a direction (width direction) substantially orthogonal to the transfer direction of the transfer material P. This is because the paper dust on the cut surface (paper edge) of the transfer material P is easily detached from the transfer material P and easily adheres to the intermediate transfer belt 7. Therefore, the amount of paper dust conveyed to the cleaning nip Q has a distribution at the longitudinal position of the cleaning blade 82. In many cases, there is almost no paper dust at a position corresponding to a portion where the transfer material P does not contact the intermediate transfer belt 7. On the other hand, at the position corresponding to the portion where the edge of the transfer material P of the intermediate transfer belt 7 contacts, the amount of paper dust conveyed to the cleaning nip Q is relatively large, and the other portions of the transfer material P There are relatively few positions corresponding to the contact portions. Then, at a position where the amount of paper dust conveyed to the cleaning nip Q is large, the cleaning blade 82 is likely to float from the intermediate transfer belt 7, and residual toner passes through the cleaning blade 82 at that position, resulting in a cleaning failure. It becomes easier (FIG. 8).

  Therefore, the length of the transfer material P used for image formation in the direction substantially orthogonal to the moving direction of the surface of the intermediate transfer belt 7 (hereinafter also referred to as “length in the width direction”) is relatively small to large. When it is changed to an image, an image defect tends to occur on the changed image. On the contrary, when the length of the transfer material P used for image formation is changed from a relatively large one to a small one, or when it is not changed, paper dust is temporarily caught in the cleaning nip Q, and slip-through occurs. Even if it occurs, it is rarely an image problem.

  Further, the amount of paper dust and the degree of pinching between the cleaning nips Q vary depending on the number of image formations. Typically, as the number of image formations increases, the amount of paper dust sandwiched between the cleaning blades Q increases, and the sheets are more firmly sandwiched. Therefore, when the number of image formations performed without changing the length in the width direction of the transfer material P is equal to or greater than a predetermined value, the transfer from the transfer material P having a relatively small length in the width direction is performed. When the material P is changed, it is desired to remove the paper dust from the cleaning nip Q.

  In addition, when image formation is continuously performed without changing the length of the transfer material P in the width direction, the amount of paper dust sandwiched between the cleaning nips Q tends to increase more remarkably. FIG. 4 shows an example of the relationship between the number of images formed and the amount of deformation of the cleaning blade 82 when 1000 continuous images are formed. The amount of deformation of the cleaning blade 82 is a value obtained by measuring a measurement gauge signal corresponding to the amount of distortion of the cleaning blade 82. Here, a strain measurement gauge for detecting the distortion of the cleaning blade 82 is provided on the surface of the cleaning blade 82 on the side of the intermediate transfer belt 7 near 1.5 mm from the edge portion 82a of the free end side of the cleaning blade 82 to the fixed end side. Attached. The measurement gauges were attached at three locations, both ends and the center, in the longitudinal direction of the cleaning blade 82. Then, the value of the measurement gauge signal when the intermediate transfer belt 7 is stopped is set to 0, and a signal corresponding to the distortion amount of the cleaning blade 82 when the intermediate transfer belt 7 is rotated in the rotation direction during image formation is measured. Thus, the amount of deformation of the cleaning blade 82 was determined. A value of + indicates that the cleaning blade 82 is distorted in a state where the cleaning blade 82 is pulled in the moving direction of the surface of the intermediate transfer belt 7. Conversely, a value of − indicates that the cleaning blade 82 is lifted from the intermediate transfer belt 7 in a state where the cleaning blade 82 is extended.

  4 that the amount of deformation of the cleaning blade 82 increases as the number of images formed increases. In addition, it can be seen that the deformation amount is larger at the end portion than at the center portion in the longitudinal direction of the cleaning blade 82. This is presumably because the supply of lubricant such as toner is less at the end of the cleaning blade 82 in the longitudinal direction than at the center. That is, as the number of continuous image formations increases, the longitudinal end of the cleaning blade 82 is pulled in the moving direction of the intermediate transfer belt 7 rather than the center. As a result, the amount of deformation of the blade 82 differs at the longitudinal position of the cleaning blade 82.

  FIG. 5 shows an example of the relationship between the position in the longitudinal direction of the cleaning blade and the deformation amount of the cleaning blade 82. The horizontal axis represents the position in the longitudinal direction of the cleaning blade 82 (showing from one end to the center), and the vertical axis represents the amount of deformation of the cleaning blade 82. The portion of the cleaning blade 82 located outside the image forming region (region where the toner image is formed) on the intermediate transfer belt 7 is hardly supplied with toner as a lubricant. Therefore, in this portion, the cleaning blade 82 is pulled relatively strongly in the moving direction of the intermediate transfer belt 7, and the deformation amount is relatively large. On the other hand, the toner, which is a lubricant, is supplied to the portion of the cleaning blade 82 located in the image forming area on the intermediate transfer belt 7. Therefore, in this portion, the force of the cleaning blade 82 pulling in the moving direction of the intermediate transfer belt 7 is relatively weak, and the deformation amount is relatively small.

  As described above, as the number of image formations increases, a deformation amount change region (A in FIG. 5) occurs between the end portion and the central portion having different deformation amounts in the longitudinal direction of the cleaning blade 82. As a result, in this portion, the contact pressure of the cleaning blade 82 against the intermediate transfer belt 7 is relatively weakened, and paper dust is likely to be caught between the cleaning blade 82 and the intermediate transfer belt 7. Then, when paper dust is caught in the portion, the cleaning blade 82 partially floats from the intermediate transfer belt 7, and the transfer residual toner passes through the cleaning blade 82 and causes image defects due to poor cleaning. Become. In addition, since the change region of the deformation amount of the cleaning blade 82 is relatively close to the position in contact with the widthwise end of the transfer material P in the width direction of the intermediate transfer belt 7, the cleaning nip Q is located at this position. Paper powder is easily caught.

  Therefore, in this embodiment, when the size of the transfer material P is changed, the necessity for the reverse movement operation of the intermediate transfer belt 7 is determined. The transfer material P used for image formation is a transfer in which the length in the width direction of the transfer material P is changed to a predetermined value or more and the length in the width direction is relatively small. When the material P is changed to a large transfer material P, the intermediate transfer belt 7 is reversely moved. The reverse movement operation of the intermediate transfer belt 7 is performed before the image formation after changing the length of the transfer material P in the width direction. Thereby, the paper dust caught in the cleaning nip Q is removed.

  The number of image formations performed without changing the length of the transfer material P in the width direction may be an integrated value of the number of image formations intermittently performed over a plurality of jobs. It may be the number of image formations continuously executed in one job. In the case of the number of image formations performed continuously, before the change in the length of the transfer material P in the width direction, in particular, when continuous image formation in which paper dust tends to be caught in the cleaning nip Q is performed more than a certain amount. In addition, the reverse movement operation of the intermediate transfer belt 7 is executed. Although not limited to this, the number of image formations performed without changing the length of the transfer material P in the width direction can be appropriately set within a range of 10 to 5000 sheets, for example.

  FIG. 6 is a flowchart showing an example of the flow of the image forming operation for explaining the procedure for executing the reverse movement operation of the intermediate transfer belt 7 in this embodiment.

  When an image formation start instruction is input (S301), the control unit 150 detects the size of the transfer material P used for image formation (S302). The size of the transfer material P can be detected, for example, by designation information on the size of the transfer material P input from the operation unit 40 (FIG. 3) of the image forming apparatus 100. Alternatively, the image forming apparatus 100 has a sensor that detects the size of the transfer material P, and the sensor can detect it.

  The control unit 150 determines whether the length in the width direction of the transfer material P is larger or smaller than the transfer material P used at the previous image formation (S303). If the control unit 150 determines that the length in the width direction of the transfer material P is smaller than the transfer material P used at the previous image formation or is not changed, the control unit 150 directly executes the image formation (S306). On the other hand, when the controller 150 determines that the length in the width direction of the transfer material P is larger than the transfer material P used at the previous image formation, the length in the width direction of the transfer material P is changed. It is determined whether or not the number of image formations performed is equal to or greater than a predetermined value (S304). In this embodiment, when the image forming operation is executed, the counter 30 counts and stores the number of image formed sheets for each length in the width direction of the transfer material P used for image formation. The count value for each length in the width direction of the transfer material P by the counter 30 is reset every time the length in the width direction of the transfer material P used for image formation is changed. If the controller 150 determines that the number of images formed without changing the length of the transfer material P in the width direction is less than a predetermined value, the controller 150 directly performs image formation (S306). On the other hand, when the controller 150 determines that the number of images formed without changing the length of the transfer material P in the width direction is equal to or greater than a predetermined value, the controller 150 causes the intermediate transfer belt 7 to perform a reverse movement operation. (S305). Thereafter, the control unit 150 causes image formation (S306).

  As a result, it is possible to effectively remove the paper dust from the cleaning nip Q when necessary, while suppressing the wear of the cleaning blade 82 and the rise time of image formation, and to suppress poor cleaning due to slipping of the transfer residual toner. It becomes possible.

  Here, the amount of reverse movement in the reverse movement operation of the intermediate transfer belt 7 is typically sufficient if the movement distance of the intermediate transfer belt 7 is about 1 mm or more and about 5 mm or less (about 20 ms). If the reverse movement amount is larger than necessary, the time required for the reverse movement operation of the intermediate transfer belt 7 increases, and the productivity may decrease. Further, if the reverse movement amount is increased more than necessary, the deviation control of the intermediate transfer belt 7 is required, and the control becomes complicated. Therefore, the reverse movement amount is made as small as possible within a range where paper dust can be sufficiently removed from the cleaning nip Q. It is desirable to suppress.

  However, the reverse movement amount in the reverse movement operation of the intermediate transfer belt 7 moves until at least the portion that was in the cleaning nip Q reaches (typically passes) the contact portion between the squeeze sheet 84 and the intermediate transfer belt 7. An amount is preferred. This is because the paper dust in the cleaning nip Q is scraped off by the squeeze sheet 84.

  Further, a supply operation for supplying toner to the cleaning blade 82 may be performed after the reverse movement operation of the intermediate transfer belt 7 is performed. In other words, by performing the reverse movement operation of the intermediate transfer belt 7, the toner accumulated in the edge portion 82a of the cleaning blade 82 is exhausted, and thereafter there is no blocking layer that prevents paper dust from being caught in the cleaning nip Q. It is conceivable that the powder is easily caught. Further, when the toner accumulated on the edge portion 82a of the cleaning blade 82 is depleted, it is conceivable that the friction between the cleaning blade 82 and the intermediate transfer belt 7 increases and the cleaning performance changes. Therefore, after the reverse transfer operation of the intermediate transfer belt 7 and before the next image formation, a toner image for supplying toner to the cleaning blade 82 is formed on the intermediate transfer belt 7 and this is formed in the cleaning nip Q. Supply operation is carried out. As a result, as shown in FIG. 7C, it is possible to form a blocking layer that prevents toner from accumulating on the edge portion 82 a of the cleaning blade 82 and preventing paper dust from being caught in the cleaning nip Q. In addition, an increase in friction between the cleaning blade 82 and the intermediate transfer belt 7 can be suppressed. The toner image formed on the intermediate transfer belt 7 by this supply operation can be set as appropriate so that a desired amount of toner can be supplied to the cleaning blade 82. For example, the toner image formed in the longitudinal direction of the cleaning blade 82 has a belt-like shape. It can be a toner image.

  In this embodiment, the reverse movement amount of the reverse movement operation of the intermediate transfer belt 7 is preferably changed according to the number of images formed without changing the length of the transfer material P in the width direction. This is because, as described above, the amount of paper dust and the degree of pinching between the cleaning nips Q vary depending on the number of formed images. Typically, it is preferable to increase the reverse movement amount in the reverse movement operation of the intermediate transfer belt 7 as the number of images formed increases. In this case, the relationship between the number of formed images and the intermediate transfer belt 7 in the reverse movement operation is stored in the ROM 152 of the control unit 150. Then, the controller 150 determines the amount of movement of the intermediate transfer belt 7 in the reverse movement operation as compared with the case where the number of image formations performed without changing the length in the width direction of the transfer material P is the first value. Also, the second value larger than the first value is set larger.

  Further, the set value of the number of image formations performed without changing the length in the width direction of the transfer material P for determining execution of the reverse movement operation of the intermediate transfer belt 7 is, for example, the cleaning required by the user. It may be changed according to the defect suppression level. For example, it is possible to change the value stored in the ROM 152 of the control unit 150 or to select a desired value from a plurality of values stored in the ROM 152 by an input from the operation unit 40. The set value of the number of formed images can be changed.

  In addition, the reverse movement amount of the reverse movement operation of the intermediate transfer belt 7 in this embodiment is preferably changed according to the size of the transfer material P used for the previous image formation. This is because the contact pressure distribution of the cleaning blade 82 differs depending on the configuration of the belt cleaning device 8, and it may be difficult to remove the paper dust depending on the position where the paper dust is sandwiched. For example, there is a configuration of the belt cleaning 82 provided with a mechanism that balances the contact pressure of the cleaning blade 82 in the longitudinal direction and reduces the difference between both end portions. In such a configuration, the contact pressure at the central portion in the longitudinal direction of the cleaning blade 82 increases, and it may be difficult to remove the paper dust at this portion. Therefore, in this case, it is preferable to increase the reverse movement amount of the transfer material P as the length in the width direction of the transfer material P used in the previous image forming apparatus is smaller. Further, in such a configuration, on the contrary, the contact pressure is low at the end portion in the longitudinal direction of the cleaning blade 82, and thus paper dust may be easily removed at this portion. Accordingly, in this case, the reverse movement amount of the transfer material P can be reduced as the size of the transfer material P used in the previous image forming apparatus is larger.

  Further, unlike the above configuration, the relationship between the central portion and the end portion of the contact pressure of the cleaning blade 82 may be reversed or the same. Therefore, it is preferable to set the reverse movement amount according to the size of the transfer material P before the change as appropriate depending on the configuration of the belt cleaning device 8.

  Further, instead of or in addition to changing the reverse movement amount of the intermediate transfer belt 7 as described above, the reverse movement speed (acceleration) of the intermediate transfer belt 7 may be changed. As described above, when the reverse movement amount of the intermediate transfer belt 7 is increased, the reverse movement speed (acceleration) of the intermediate transfer belt 7 can be increased instead of or in addition. Accordingly, it is possible to sufficiently remove the paper dust from the cleaning nip Q with a smaller amount of reverse movement of the intermediate transfer belt 7.

  As described above, according to the present embodiment, it is possible to extend the life of the cleaning blade while suppressing a cleaning failure caused by foreign matters such as paper dust being sandwiched between the cleaning blade 82 and the intermediate transfer belt 7.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, the case where the moving body to be cleaned by the cleaning blade is an intermediate transfer body has been described. However, the present invention is not limited to this. The present invention is equally applicable regardless of whether the moving member is an image bearing member such as a photosensitive member, an electrostatic recording dielectric or an intermediate transfer member, and the moving member is a transfer material bearing member. An effect is obtained. That is, when the moving body is a member with which the transfer material P comes into contact, the present invention works effectively if the cleaning device has a cleaning blade. The moving body is not limited to an endless belt wound around a plurality of support rollers, and may be a drum or a sheet stretched around a frame, for example.

  Further, the deposits removed from the surface of the moving body with the cleaning blade are mainly transfer residual toner, but there are other cases such as paper powder and powder generated by scraping the moving body and its supporting roller. Similarly, the foreign matter sandwiched between the cleaning blade and the moving body is mainly paper powder, but there are also cases such as toner agglomerates, powder generated by scraping the moving body and its supporting roller, and the like.

1 Photosensitive drum 7 Intermediate transfer belt 8 Belt cleaning device 82 Cleaning blade

Claims (6)

A moving body that moves in a predetermined direction and carries the toner image to be transferred to the transfer material and conveys it to the contact portion with the transfer material, or carries and conveys the transfer material to which the toner image is transferred;
A cleaning device provided with a cleaning blade disposed in contact with the moving body to remove deposits from the moving body;
In an image forming apparatus having
The number of image formations performed without changing the length of the transfer material in the width direction orthogonal to the moving direction of the moving body from the first length is greater than or equal to a predetermined value, In the case where an image is formed by changing the transfer material from the first length to a transfer material having a second length larger than the first length in the width direction, the first length of the transfer material is changed. Execution of executing a reverse movement operation for moving the moving body in a direction opposite to the predetermined direction after image formation on the transfer material and before image formation on the transfer material having the second length. An image forming apparatus having a section.   The said execution part changes the moving amount or moving speed of the said mobile body in the said reverse movement operation | movement according to the length of the said width direction of the transfer material before the said change. Image forming apparatus.   The execution unit determines the moving amount or moving speed of the moving body in the reverse movement operation from the first value, compared to the case where the length in the width direction of the transfer material before the change is the first value. The image forming apparatus according to claim 2, wherein the smaller value of the second value is set larger.   The execution unit is configured so that the moving amount or moving speed of the moving body in the reverse movement operation is not changed from the first length, and the number of image formations executed is a first value. The image forming apparatus according to claim 1, wherein the second value larger than the first value is set larger.   The cleaning device includes a sheet-like contact member disposed in contact with the moving body on an upstream side of a contact portion between the moving body and the cleaning blade in the predetermined direction, and the execution unit includes 5. The image formation according to claim 1, wherein in the reverse movement operation, the moving body is moved at least from a contact portion with the cleaning blade to a contact portion with the contact member. apparatus.   The execution unit executes a supply operation of supplying toner to a contact portion between the cleaning blade and the moving body after the reverse movement operation and before the next image formation. The image forming apparatus according to any one of 1 to 5.

Images