JP2017146459A - Image formation apparatus, image formation system and cleaning control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus, image formation system and cleaning control method which can suppress the occurrence of a stain on a rear surface of a sheet while preventing the service life of a transfer member and cleaning member from becoming short.SOLUTION: An image formation apparatus includes: an image carrier; a transfer member; an image formation unit which forms a first image band, a second image band for forcible toner discharge, a third image band on the image carrier in this order in an inter-sheet region of the image carrier; a cleaning member which scrapes a toner image transferred from the image carrier to the transfer member in a state of being in contact with the transfer member; a contact/separation unit which brings the cleaning member into contact with the transfer member, and separates the cleaning member from the transfer member; and a control unit which controls the contact/separation unit so as to bring the cleaning member into contact with the transfer member at the timing of starting scraping of the first image band and separate the cleaning member from the transfer member at the timing of finishing scraping of the third image band.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, an image forming system, and a cleaning control method.

  In general, an image forming apparatus (printer, copying machine, facsimile, etc.) using an electrophotographic process technology irradiates (exposes) a charged photosensitive drum (image carrier) with laser light based on image data. To form an electrostatic latent image. Then, by supplying toner from the developing device to the photosensitive drum on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image. Further, after the toner image is directly or indirectly transferred to the sheet, the toner image is formed on the sheet by fixing it by heating and pressing at the fixing nip.

  In such an image forming apparatus, if the average image area ratio at the time of continuous image formation (continuous printing) is small, the replacement of the toner in the developing device deteriorates, and the toner deteriorates. Therefore, for example, a configuration is known in which the discharge belt is discharged to the intermediate transfer belt at a timing between sheets on which the intermediate transfer belt (image carrier) does not carry a toner image, and the deteriorated toner is forcibly replaced.

  When the image forming apparatus includes a secondary transfer unit, for example, the discharge band may be transferred from the transfer nip portion with the intermediate transfer belt to the secondary transfer belt in the secondary transfer unit. When the toner in the discharge band adheres to the secondary transfer belt, the toner attached to the secondary transfer belt adheres to the back side of the next sheet to be transported, and the back side of the sheet is stained. Therefore, a cleaning device having a cleaning member for cleaning the secondary transfer unit can be provided.

  However, if the cleaning member is kept in contact with the secondary transfer belt during continuous printing, the secondary transfer belt and the cleaning member are damaged by the frictional force caused by the contact, and the life of the secondary transfer belt and the cleaning member is shortened. It will be early. Therefore, a configuration in which the cleaning member is brought into contact with the secondary transfer belt in accordance with the timing at which the discharge band is formed can be considered.

  For example, Patent Document 1 discloses a technology for bringing a cleaning unit into pressure contact with a transfer belt only when a density adjustment patch or a large amount of toner when a jam occurs is transferred to the transfer belt.

JP 2013-182153 A

  However, it is difficult to bring the cleaning member into contact with the secondary transfer belt precisely in accordance with the timing at which the discharge band is formed. When the timing is shifted, the toner in the discharge band remains on the secondary transfer belt, and the next This causes a problem that the back-stained paper is caused to be conveyed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus, an image forming system, and a cleaning control method capable of suppressing the occurrence of backside contamination of a sheet while suppressing the life of a transfer member and a cleaning member from being shortened. It is to be.

An image forming apparatus according to the present invention includes:
An image carrier capable of carrying a toner image;
A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet with the image carrier;
An image forming unit for forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
A cleaning member that scrapes off the toner image transferred from the image carrier to the transfer member in contact with the transfer member;
A contact / separation part for bringing the cleaning member into contact with the transfer member and separating the cleaning member from the transfer member;
The cleaning member is brought into contact with the transfer member at the timing of starting scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing scraping of the third image band. A control unit for controlling the contact / separation unit;
Is provided.

An image forming system according to the present invention includes:
An image forming system including a plurality of units including an image forming apparatus,
An image carrier capable of carrying a toner image;
A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet with the image carrier;
An image forming unit for forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
A cleaning member that scrapes off the toner image transferred from the image carrier to the transfer member in contact with the transfer member;
A contact / separation part for bringing the cleaning member into contact with the transfer member and separating the cleaning member from the transfer member;
The cleaning member is brought into contact with the transfer member at the timing of starting scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing scraping of the third image band. A control unit for controlling the contact / separation unit;
Is provided.

The cleaning control method according to the present invention includes:
A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet between the image carrier capable of carrying a toner image and the image carrier; and A cleaning control method for an image forming apparatus, comprising: a cleaning member that scrapes off a toner image transferred from the image carrier to the transfer member in a contact state,
Forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
Bringing the cleaning member into contact with the transfer member, separating the cleaning member from the transfer member,
Control so that the cleaning member is brought into contact with the transfer member at the timing of starting the scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing the scraping of the third image band. To do.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the back soiling of the paper to print generate | occur | produces, suppressing the lifetime of a transfer member and a cleaning member becoming short.

1 is a diagram schematically illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 6 is an enlarged view showing the periphery of a secondary transfer cleaning unit. It is an enlarged view which shows the image belt | band | zone formed between images. It is a time chart which shows each state of paper passing, the 1st field, the 2nd field, the 3rd field, and the position of a cleaning member. 6 is a time chart showing each state of paper passing, a third region, a position of a cleaning member, and a secondary transfer bias. 6 is a flowchart illustrating an example of an operation example of cleaning control in the image forming apparatus. It is a time chart which shows each state of contact pressure of paper passing, the 1st field, the 2nd field, the 3rd field, and a cleaning member in a modification.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus 1 according to the present embodiment.

  An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421. After the four color toner images are superimposed on the intermediate transfer belt 421, the images are formed by secondary transfer onto the paper S.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  The image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data (input image data) transmitted from an external device, and forms an image on the paper S based on the image data. The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on the document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 21 and the operation unit 22. The display unit 21 displays various operation screens, image states, operation states of functions, and the like according to a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. A secondary transfer unit 90, a secondary transfer cleaning unit 200, and the like.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and explanation, common constituent elements are denoted by the same reference numerals, and in order to distinguish them, Y, M, C, or K is added to the reference numerals. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has, for example, an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). It is a negatively charged organic photoreceptor (OPC: Organic Photo-conductor) in which CTL (Charge Transport Layer) is sequentially laminated.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to negative polarity by generating corona discharge.

  The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is a two-component reversal developing device, and attaches toner of each color component to the surface of the photosensitive drum 413 to visualize the electrostatic latent image to form a toner image. The developing device 412 forms a toner image on the surface of the photosensitive drum 413 by supplying toner contained in the developer to the photosensitive drum 413.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a belt cleaning device 426, and the like. The intermediate transfer belt 421 corresponds to the “image carrier” of the invention.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. As the drive roller rotates, the intermediate transfer belt 421 travels at a constant speed in the A direction.

  The intermediate transfer belt 421 is a belt having conductivity and elasticity, and is rotationally driven by a control signal from the control unit 100.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The belt cleaning device 426 removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

  The secondary transfer unit 90 includes a secondary transfer roller 91, a downstream roller 92 positioned downstream of the secondary transfer roller 91 in the transport direction of the paper S, and an endless secondary transfer belt 93. ing. The secondary transfer belt 93 corresponds to the “transfer member” of the present invention.

  The secondary transfer roller 91 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 91 is controlled to be driven and stopped by the control unit 100.

  The secondary transfer roller 91 is pressed against the backup roller 423B across the intermediate transfer belt 421 and the secondary transfer belt 93, so that a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S is formed. It is formed. The secondary transfer nip corresponds to the “transfer nip” of the present invention.

  The secondary transfer belt 93 is stretched in a loop by a secondary transfer roller 91 and a downstream roller 92. The upper surface of the secondary transfer belt 93 is a transport surface for transporting the paper S.

  The secondary transfer cleaning unit 200 cleans the toner image attached to the secondary transfer belt 93. Details of the secondary transfer cleaning unit 200 will be described later.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, by applying a primary transfer bias to the primary transfer roller 422 and applying a charge having a polarity opposite to that of the toner to the back side of the intermediate transfer belt 421, that is, the side in contact with the primary transfer roller 422, the toner image Is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet S. Specifically, a secondary transfer bias is applied to the backup roller 423B by the bias applying unit 73, and a charge having the same polarity as the toner is applied to the surface side of the sheet S, that is, the side that contacts the intermediate transfer belt 421. The toner image is electrostatically transferred to the paper S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  Further, the bias applying unit 73 can apply a secondary transfer bias having positive and negative values to the secondary transfer belt 93 via the backup roller 423B. Therefore, under the control of the control unit 100, for example, when the printing operation is not performed, the bias is applied to the secondary transfer belt 93 by applying a bias having a polarity opposite to the secondary transfer bias to the secondary transfer belt 93. The toner thus returned can be returned to the intermediate transfer belt 421. The secondary transfer bias corresponds to the “transfer bias” of the present invention.

  The fixing unit 60 includes an upper fixing unit 60A having a fixing surface side member disposed on the surface of the sheet S on which the toner image is formed, and the fixing unit 60 on the surface opposite to the fixing surface that is the back surface of the sheet S. A lower fixing unit 60B having a rear side support member to be disposed is provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the paper S is formed.

  The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the paper S on which the toner image is secondarily transferred and conveyed at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the sheet S from the fixing surface side member or the back surface side support member by blowing air.

  The upper fixing unit 60A includes an endless fixing belt 61, a heating roller 62, and a fixing roller 63, which are fixing surface side members. The fixing belt 61 is stretched between a heating roller 62 and a fixing roller 63.

  The heating roller 62 includes a heating source (halogen heater) and heats the fixing belt 61. The heating roller 62 is heated by the heating source, and as a result, the fixing belt 61 is heated.

  The fixing roller 63 rotates in the clockwise direction by being controlled by the control unit 100. As the fixing roller 63 rotates, the fixing belt 61 and the heating roller 62 are driven to rotate clockwise.

  The lower fixing unit 60B includes a pressure roller 64 that is a back side support member. The pressure roller 64 forms a fixing nip that sandwiches and conveys the sheet S with the fixing belt 61. The pressure roller 64 is driven and controlled by the control unit 100 to rotate counterclockwise.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

  In the present embodiment, the control unit 100 performs discharge control for discharging an image band including deteriorated toner in the developing device 412. The image band is an area between the sheets on which the intermediate transfer belt 421 does not carry a toner image, specifically, an image that is a timing between sheets of the plurality of sheets S when continuous image formation is performed on the plurality of sheets S. In the meantime, the sheet is discharged onto the intermediate transfer belt 421.

  Further, when printing of a toner image with a low area ratio continues, toner replacement in the developing device 412 becomes worse and the toner tends to deteriorate. In such a case, the image band is discharged onto the intermediate transfer belt 421. Is desirable.

  Therefore, the control unit 100 determines whether or not to perform the discharge control based on the area ratio of the toner image when continuous image formation is performed on the plurality of sheets S. Specifically, the control unit 100 discharges the image band to the intermediate transfer belt 421 when the area ratio of the toner image is smaller than a predetermined area ratio (for example, 3%). Thereby, deterioration of the toner in the developing device 412 is suppressed. The area ratio of the toner image can be, for example, a value obtained by averaging the area ratios of the toner colors for a certain period.

  By the way, when the image band is discharged to the intermediate transfer belt 421, it is transferred to the secondary transfer belt 93 at the secondary transfer nip portion, and the toner adheres to the secondary transfer belt 93, so that the secondary transfer nip portion is conveyed. The toner adheres to the back side of the paper S to be printed, and the back side of the paper S becomes dirty.

  Therefore, in the present embodiment, the secondary transfer belt 93 is cleaned by the secondary transfer cleaning unit 200. Thereby, the back stain | pollution | contamination of the paper S can be suppressed. Details of the secondary transfer cleaning unit 200 will be described below. FIG. 3 is an enlarged view showing the periphery of the secondary transfer cleaning unit 200.

  As shown in FIG. 3, the secondary transfer cleaning unit 200 includes a housing 201 and a cleaning member 202 provided in the housing 201.

  The cleaning member 202 is a rubber blade, and extends from an appropriate position of the housing 201 in a direction opposite to the rotation direction (arrow direction) of the secondary transfer belt 93.

  The cleaning member 202 can move between a contact position (a position indicated by a two-dot chain line) that contacts the secondary transfer belt 93 and a separation position (a position indicated by a solid line) that is separated from the secondary transfer belt 93. Specifically, the housing 201 moves between the position of the two-dot chain line and the position of the solid line in accordance with the operation of a cam (not shown) under the control of the control unit 100, so that the cleaning member 202 is in the contact position. And between the separated positions. The secondary transfer cleaning unit 200 corresponds to the “contact / separation unit” of the present invention.

  When the cleaning member 202 is located at the contact position, the toner on the secondary transfer belt 93 can be cleaned.

  By the way, if the cleaning member 202 remains in the contact position during continuous printing, the frictional force at the portion where the cleaning member 202 and the secondary transfer belt 93 come into contact increases. When the frictional force of the portion increases, the driving torque of the secondary transfer belt 93 increases, the cleaning member 202 is turned over or damaged, the surface of the secondary transfer belt 93 becomes rough, and the filming of the secondary transfer belt 93 occurs. Problems occur.

  In order to solve the above problem, for example, it is desirable that the cleaning member 202 is brought into contact with and separated from the secondary transfer belt 93 at a timing between images from which the image band is discharged. However, if the timing at which the cleaning member 202 is brought into contact with and separated from the secondary transfer belt 93 is shifted, an image band remains on the secondary transfer belt 93, so that the backside of the paper still occurs.

  Therefore, as shown in FIG. 4, in the present embodiment, the control unit 100 sets the image band G in which the first region G1, the second region G2, and the third region G3 are arranged in order to the timing between images, for example, the first The sheet is formed on the intermediate transfer belt 421 at the timing between one sheet S1 and the next second sheet S2. The first region G1 corresponds to the “first image band” of the present invention, the second region G2 corresponds to the “second image band” of the present invention, and the third region corresponds to the “third image band” of the present invention. Corresponds to "obi".

  The second region G2 is a discharge zone region for forcibly discharging deteriorated toner. The first region G1 and the third region G3 are formed in a lighter color than the second region G2. Specifically, the toner used in the first region G1 and the third region G3 has a color that is inconspicuous when attached to the secondary transfer belt 93, such as yellow, white, and transparent. Color.

  The first region G1 and the third region G3 have a lower toner density than the second region G2. Specifically, the first region G1 and the third region G3 are formed of a thin film such as a 10% halftone dot pattern, for example.

  The controller 100 moves the cleaning member 202 to the secondary transfer belt 93 at the same timing as the timing at which the first region G1 is carried on the intermediate transfer belt 421 at the time of discharge control, that is, the timing at which scraping of the first region G1 is started. Contact. The control unit 100 separates the cleaning member 202 from the secondary transfer belt 93 after the scraping of the third region G3 during the discharge control, specifically, after the cleaning member 202 scrapes the third region G3. .

  As a result, in the second region G2 that is the discharge band of the deteriorated toner, the cleaning member 202 is surely in contact with the secondary transfer belt 93, so that the sheet of paper caused by the discharge band adhering to the secondary transfer belt 93 is removed. It is possible to suppress back dirt.

  Further, “the same timing as the timing at which the first region G1 is carried on the intermediate transfer belt 421” herein refers to the leading end of the first region G1 that has been discharged to the intermediate transfer belt 421 and then transferred to the secondary transfer belt 93. Is the timing when the cleaning member 202 has moved to a position corresponding to the contact position.

  The timing at which the cleaning member 202 is moved to the contact position may be later than the timing at which the tip of the first region G1 moves to a position corresponding to the contact position of the cleaning member 202. In other words, the control unit 100 may bring the cleaning member 202 into contact with the secondary transfer belt 93 so that a part of the first region G1 of the image band G can be scraped off. When the timing at which the cleaning member 202 comes into contact with the secondary transfer belt 93 is delayed with respect to the timing at which the tip of the first region G1 reaches the position of the cleaning member 202, toner adheres to the secondary transfer belt 93. It will remain. However, since the first region G1 has a color that is not noticeable visually, and the toner image density is smaller than that of the second region G2, the toner in the region attached to the secondary transfer belt 93 is applied to the sheet. Even if it adheres, it becomes only a slight stain of a level that does not cause a problem in practice, so it does not become a stain on the back of the paper.

  In addition, after the cleaning member 202 scrapes off the third region G3, the cleaning member 202 is separated. However, since the toner of the third region G3 in the image band G is collected at the tip portion of the cleaning member 202, The toner functions as a lubricant. Therefore, the cleaning member 202 and the secondary transfer belt 93 can be prevented from being damaged by separating the cleaning member 202 from the secondary transfer belt 93 before the toner is exhausted.

  FIG. 4 shows an image band G having three regions G1, G2, and G3 between one image between the first sheet S1 and the next second sheet S2. It is not limited to this. In general, in consideration of the fact that an image band made up of discharge bands is often discharged across a plurality of images, the control unit 100 assigns each region G1, G2, G3 between different images. The intermediate transfer belt 421 may be supported. In such a case, the cleaning member 202 remains in the contact position even when the sheet is being transported between images and the next image.

  By the way, when the cleaning member 202 is sufficiently worn, the edge portion of the blade is worn, so that even if there is no toner as a lubricant, the cleaning member 202 does not sag.

  Therefore, the control unit 100 performs control so that the toner amount in the first region G1 in the image band G is changed according to the usage history of the cleaning member 202. Specifically, when the cleaning member 202 is sufficiently worn, the control unit 100 performs control so as not to discharge the first region G1 or reduce the consumed toner by shortening the belt length. .

  By doing so, it is possible to reduce the amount of toner consumed in the first region G1. The usage history of the cleaning member 202 is, for example, the number of times the cleaning member 202 is used, and the threshold may be set as appropriate according to the embodiment.

  Next, an example of the timing at which the cleaning member 202 contacts and separates from the secondary transfer belt 93 will be described. FIG. 5 is a time chart showing the respective states of the sheet passing, the first area, the second area, the third area, and the position of the cleaning member. FIG. 6 is a time chart showing each state of the sheet passing, the third region, the position of the cleaning member, and the secondary transfer bias.

  In FIG. 5, “1” in “paper passing” indicates that the paper is being conveyed, and “0” indicates that the image is between images. Further, “1” in “first region”, “second region”, and “third region” indicates that the corresponding region of the image band is formed on the intermediate transfer belt 421, and “0” indicates This shows that the corresponding area is not formed on the intermediate transfer belt 421. Further, “1” in “position of cleaning member” indicates that the cleaning member 202 is located at the contact position, and “0” indicates that the cleaning member 202 is located at the separated position. . FIG. 5 shows a case where the first region G1, the second region G2, and the third region G3 are formed between different images.

  As shown in FIG. 5, after the sheet conveyance in the case where it is determined that the image area ratio is a low area ratio (time t0), the first area G1 of the image band G between the images is the intermediate transfer belt 421. (Time t1). At the same time as the first region G1 is discharged, the cleaning member 202 is positioned at the contact position.

  Next, at time t2, the next sheet is passed while the cleaning member 202 remains in the contact position. Thereafter, the second region G2 is discharged to the intermediate transfer belt 421 between the next images (time t3 to t4). At this time, since the cleaning member 202 remains in the contact position, the second region G2 transferred to the secondary transfer belt 93 is surely removed by the cleaning member 202. For this reason, it is possible to prevent the back side of the paper from being stained by the second region G2 that could not be removed by the cleaning member 202.

  Next, after time t4, the cleaning member 202 is still in the contact position, the next sheet is passed, and the third region G3 is intermediately transferred between the next images (time t5 to t6). It is discharged to the belt 421. Since the cleaning member 202 remains in the contact position between the images (time t5 to t6), the third region G3 transferred to the secondary transfer belt 93 is removed.

  Thereafter, after the start of passing the next sheet (time t6), the cleaning member 202 is controlled to move to the separation position at time t7 during the sheet passing. At this time, there is a possibility that toner accumulated at the tip of the cleaning member 202 is transferred to the secondary transfer belt 93 and fine streaky toner adheres to the secondary transfer belt 93. However, since the image band G to be removed last is the third region G3, even if it adheres to the secondary transfer belt 93, it is a slight stain with no practical problem, and the backside of the paper does not occur.

  Further, if the cleaning member 202 is in contact with the secondary transfer belt 93 in the absence of toner as a lubricant, the cleaning member 202 is likely to be damaged. Therefore, after the third region G3 has passed, the cleaning member 202 is near the cleaning member 202. It is desirable to set the time t7 so that the timing before the accumulated toner is exhausted is reached.

  Further, since toner is accumulated in the vicinity of the cleaning member 202, the toner at the contact / separation position of the cleaning member 202 on the secondary transfer belt 93 when the cleaning member 202 is separated from the secondary transfer belt 93 is removed. Is desirable.

  The toner at the contact / separation position can be removed by returning to the intermediate transfer belt 421 by setting the secondary transfer bias to a reverse polarity bias between images under the control of the control unit 100. is there. Therefore, as shown in FIG. 6, the time t7 is set so that the contact / separation position passes through the position of the secondary transfer nip between the next images (time t8 to t9). Is more desirable.

  After time t7, when the sheet passing is completed and the next image interval (time t8 to t9), under the control of the control unit 100, the secondary transfer bias is reversed from the normal value Vb. By setting the value to −Vb, the toner accumulated at the contact position is returned from the secondary transfer belt 93 to the intermediate transfer belt 421. As a result, most of the adhered toner on the secondary transfer belt 93 can be cleaned.

  Even if cleaning is performed by the intermediate transfer belt 421, a slight amount of toner may remain on the secondary transfer belt 93. However, since the toner is in the third region G3, it is slightly contaminated at a level that causes no practical problem. , The back of the paper does not get dirty.

  Next, an example of the cleaning control operation in the image forming apparatus 1 including the control unit 100 as described above will be described. FIG. 7 is a flowchart illustrating an example of an operation example of the cleaning control in the image forming apparatus 1. The process in FIG. 7 is executed when the control unit 100 receives an instruction to execute a print job.

  As shown in FIG. 7, the control unit 100 determines whether the area ratio of the toner image is smaller than a predetermined area ratio (step S101). As a result of the determination, when the area ratio of the toner image is equal to or larger than the predetermined area ratio (step S101, NO), the control unit 100 ends this control. On the other hand, when the area ratio of the toner image is smaller than the predetermined area ratio (step S101, YES), the control unit 100 discharges the first region G1 to the intermediate transfer belt 421 between the most recent images (step S102).

  Next, the control unit 100 moves the cleaning member 202 to the contact position (step S103). Specifically, the control unit 100 moves the cleaning member 202 to the contact position at a timing when the tip of the first region G1 transferred to the secondary transfer belt 93 moves to a position corresponding to the contact position.

  Next, the controller 100 causes the intermediate transfer belt 421 to eject the second region G2 between the next images between the images from which the first region G1 has been ejected (step S104). Next, the control unit 100 discharges the third region G3 to the intermediate transfer belt 421 between the next images between the images in which the second region G2 is formed (step S105).

  Next, the control unit 100 moves the cleaning member 202 to the separation position during the sheet passing after the third region G3 is formed (step S106). Next, the control unit 100 sets the secondary transfer bias to a reverse polarity to the normal value between the next images (step S107). Next, the control unit 100 returns the secondary transfer bias to the normal value at the timing when the next sheet is passed (step S108), and ends this control.

  According to the image forming apparatus 1 configured as described above, since the cleaning member 202 is reliably in contact with the secondary transfer belt 93 in the second area G2 that is the discharge band area, the second area G2 is used. The toner in is reliably removed by the cleaning member 202. For this reason, it is possible to suppress the occurrence of back stain on the paper to be printed.

  Further, when the cleaning member 202 moves to the contact position, the cleaning member 202 comes into contact with the secondary transfer belt 93 covered with the toner in the first region G1, which serves as a lubricant. Can be suppressed. Further, even if the movement of the cleaning member 202 to the contact position is slightly delayed from the front end of the first region G1, and the front end of the first region G1 is not removed by the cleaning member 202, the level is not practically problematic. Therefore, the problem of the back side of the paper does not occur.

  Further, the cleaning member 202 is quickly moved to the separation position after the discharge control is completed, so that the driving force of the secondary transfer belt 93 is increased due to the increase in the frictional force between the cleaning member 202 and the secondary transfer belt 93, and the cleaning member. It is possible to suppress the occurrence of problems such as twisting and damage of 202, surface roughness of the secondary transfer belt 93, and filming in the secondary transfer belt 93. Therefore, it is possible to suppress the life of the cleaning member 202 and the secondary transfer belt 93 from being shortened.

  Further, since the above control is executed between images during continuous printing, productivity in continuous printing can be maintained.

  Further, when the cleaning member 202 is separated from the secondary transfer belt 93, the toner adhering to the contact / separation position of the secondary transfer belt 93 is changed to a reverse polarity bias between the most recent images. The intermediate transfer belt 421 can be returned. As a result, the toner adhering to the secondary transfer belt 93 can be reliably removed.

  Next, a modified example will be described. FIG. 8 is a time chart showing the states of the sheet passing, the first region, the second region, the third region, and the contact pressure of the cleaning member in the modified example.

  As shown in FIG. 8, in the modification, the cleaning member 202 is moved under the control of the control unit 100 so that the contact pressure of the cleaning member 202 against the secondary transfer belt 93 gradually increases.

  For example, the posture of the cleaning member 202 is changed so that the inclination angle of the cleaning member 202 with respect to the secondary transfer belt 93 is gradually increased. Specifically, the cleaning member 202 is first brought into contact with the secondary transfer belt 93 with the cleaning member 202 laid down (time t01).

  Here, in the example of FIG. 8, the cleaning member 202 is controlled to contact the secondary transfer belt 93 at time t01, which is before the interval (time t0 to t2) during which the first region G1 is discharged. The That is, the timing when the cleaning member 202 is brought into contact with the secondary transfer belt 93 is before the intermediate transfer belt 421 carries the first region G1.

  Since the first area G1 has a low image density, it can be sufficiently scraped even with a relatively weak contact pressure. Further, by bringing the cleaning member 202 into contact before the first region G1 is transferred to the secondary transfer belt 93, all the first regions G1 can be scraped off. Further, the cleaning member 202 is brought into contact with the secondary transfer belt 93 in a state where there is no toner as a lubricant, but since the contact pressure is sufficiently weak, the cleaning member 202 is not dripped.

  The cleaning member 202 is gradually increased in inclination angle with respect to the secondary transfer belt 93, and the contact pressure with respect to the secondary transfer belt 93 is optimal for the cleaning member 202 to clean the secondary transfer belt 93. The pressure is controlled to be N (time t3). That is, in the cleaning member 202, the contact pressure with respect to the secondary transfer belt 93 when cleaning the second region G2 is greater than the contact pressure with respect to the secondary transfer belt 93 when the cleaning member 202 is in contact with the secondary transfer belt 93. Controlled to increase.

  As described above, the contact pressure of the cleaning member 202 gradually increases, but the first region G1 that becomes toner as the lubricant is transferred to the secondary transfer belt 93, so that it does not drown.

  In the example of FIG. 8, the time when the optimum contact pressure is reached is t3. However, the optimum contact pressure may be reached before time t31 when the second region G2 is formed. In other words, the control unit 100 uses the contact pressure of the cleaning member 202 to the secondary transfer belt 93 before the second region G2 starts to be scraped, and is optimal for the cleaning member 202 to clean the secondary transfer belt 93. Contact pressure may be used.

  In this way, the second region G2 can be reliably removed by the cleaning member 202. Even if the first region G1 cannot be scraped off, the residual toner in the first region G1 is a light stain that is not problematic in practice, and therefore does not become a stain on the back of the paper.

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

  The present invention can be applied to an image forming system including a plurality of units including an image forming apparatus. The plurality of units include external devices such as post-processing devices and network-connected control devices, for example.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 93 Secondary transfer belt 100 Control part 202 Cleaning member

Claims (13)

An image carrier capable of carrying a toner image;
A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet with the image carrier;
An image forming unit for forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
A cleaning member that scrapes off the toner image transferred from the image carrier to the transfer member in contact with the transfer member;
A contact / separation part for bringing the cleaning member into contact with the transfer member and separating the cleaning member from the transfer member;
The cleaning member is brought into contact with the transfer member at the timing of starting scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing scraping of the third image band. A control unit for controlling the contact / separation unit;
An image forming apparatus comprising: The first image band and the third image band are formed in a lighter color than the second image band,
The image forming apparatus according to claim 1. The first image band and the third image band have a lower toner image density than the second image band.
The image forming apparatus according to claim 1. The controller is configured to bring the cleaning member into contact with the transfer member such that a contact pressure of the cleaning member with respect to the transfer member increases as time elapses;
The image forming apparatus according to claim 1. The control unit makes a contact pressure of the cleaning member to the transfer member when cleaning the second image band larger than a contact pressure of the cleaning member to the transfer member when contacting the transfer member;
The image forming apparatus according to claim 4. The timing for bringing the cleaning member into contact with the transfer member is before the first image band is formed on the image carrier.
The image forming apparatus according to claim 4 or 5. A bias applying unit that applies a transfer bias to the transfer member for transferring the toner image from the image carrier to a sheet in the transfer nip;
The control unit controls the bias applying unit so that a bias having a polarity opposite to the transfer bias is applied to the transfer member at a timing between next sheets after the cleaning member is separated from the transfer member. ,
The image forming apparatus according to claim 1. The timing at which the reverse polarity bias is applied to the transfer member is such that the position where the cleaning member is in contact with the transfer member passes through the transfer nip when the cleaning member is separated from the transfer member. Is the timing,
The image forming apparatus according to claim 7. The cleaning member is a rubber blade,
The image forming apparatus according to claim 1. Each of the first image band, the second image band, and the third image band is formed on the image carrier at a timing between different papers.
The image forming apparatus according to claim 1. The control unit changes a toner amount of the first image band according to a use history of the cleaning member;
The image forming apparatus according to claim 1. An image forming system including a plurality of units including an image forming apparatus,
An image carrier capable of carrying a toner image;
A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet with the image carrier;
An image forming unit for forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
A cleaning member that scrapes off the toner image transferred from the image carrier to the transfer member in contact with the transfer member;
A contact / separation part for bringing the cleaning member into contact with the transfer member and separating the cleaning member from the transfer member;
The cleaning member is brought into contact with the transfer member at the timing of starting scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing scraping of the third image band. A control unit for controlling the contact / separation unit;
An image forming system comprising: A transfer member that forms a transfer nip for transferring a toner image formed on the image carrier to a sheet between the image carrier capable of carrying a toner image and the image carrier; and A cleaning control method for an image forming apparatus, comprising: a cleaning member that scrapes off a toner image transferred from the image carrier to the transfer member in a contact state,
Forming a first image band, a second image band for forced toner discharge, and a third image band in this order on the image carrier in the inter-paper area of the image carrier;
Bringing the cleaning member into contact with the transfer member, separating the cleaning member from the transfer member,
Control so that the cleaning member is brought into contact with the transfer member at the timing of starting the scraping of the first image band, and the cleaning member is separated from the transfer member at the timing of finishing the scraping of the third image band. Cleaning control method to do.

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