JP6620508B2 - Image forming apparatus, image forming system, and paper conveyance control method - Google Patents

Description

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

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photosensitive drum (image carrier) 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, for example, when density unevenness or the like occurs in a toner image during a continuous paper printing operation, an operation of changing image forming conditions during the printing operation (hereinafter, referred to as “correction of density unevenness”) is performed. , Correction operation) may be performed. For example, in the case of the intermediate transfer system configuration, the correction operation is performed by forming a patch image on the intermediate transfer belt.

  When the correction operation is performed in the middle of the printing operation in this way, the intermediate transfer belt is separated from the transfer roller so that the patch image on the intermediate transfer belt is not transferred onto the paper located at the transfer nip between the intermediate transfer belt and the transfer roller. Interrupt the printing operation. If the conveyance of the continuous paper is stopped as the printing operation is interrupted, the part located at the fixing nip of the paper is affected by the heat of the fixing unit when the printing operation is interrupted, and the paper becomes a waste paper. Problems arise.

  For example, Patent Document 1 discloses a technique for changing the length of the conveyance path between the transfer nip and the fixing unit when the printing operation is interrupted during the printing operation. . In the technique of Patent Document 1, when the conveyance of the portion located in the transfer nip of the continuous paper is stopped, the path length is changed so as to increase, and the portion located between the transfer nip and the fixing nip of the continuous paper. Increase the length of. Then, after the conveyance of the portion located at the transfer nip of the continuous paper is stopped, the path length is changed to be gradually shortened without stopping the conveyance by the fixing unit. By doing in this way, it can suppress that the continuous paper turns into a waste paper by conveying only the part between the transfer nip and fixing nip of a continuous paper toward a fixing nip.

  Further, in Patent Document 2, even when printing is interrupted, the continuous paper is not transported by the fixing unit without being stopped. When the printing is resumed, the continuous paper transfer nip is stopped when printing is resumed. A configuration is disclosed in which printing after resumption is performed after backfeeding the portion located in the position to the position of the transfer nip.

JP 05-158309 A JP 2010-102158 A

  By the way, when the correction operation is performed in the middle of the printing operation, the intermediate transfer belt is separated from the transfer roller. Therefore, in the techniques of Patent Documents 1 and 2, the portions located in the transfer nip of the continuous paper are the transfer nip and the fixing nip. When the intermediate transfer belt and the transfer roller are pressure-bonded again, there is a possibility that the image shifts due to the positional deviation with respect to the transfer nip due to the conveyance of the portion between them.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus, an image forming system, and an image forming apparatus capable of suppressing the positional deviation of a continuous sheet relative to a transfer nip while suppressing the sheet from turning into paper due to heat from the fixing unit. It is to provide a paper conveyance control method.

An image forming apparatus according to the present invention includes:
A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous paper in a transfer nip formed between the image carrier and a transfer roller;
A fixing unit for fixing the toner image transferred to the continuous paper by the transfer unit at a fixing nip;
A separating portion for separating the transfer roller from the image carrier;
A path length changing unit that changes a path length of the continuous sheet conveyance path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
A transport unit that transports the continuous paper from the transfer nip toward the fixing nip;
In the transfer nip, a potential difference generating unit that generates a potential difference between the continuous paper and the transport unit;
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. A control unit that performs control to change the path length of the second path length from the second path length to the first path length;
With
When the image carrier and the transfer roller are separated from each other, the transport unit electrostatically positions a position corresponding to the transfer nip of the continuous sheet due to a potential difference generated between the transfer sheet and the continuous sheet. Adsorb to.

An image forming system according to the present invention includes:
An image forming system including a plurality of units including an image forming apparatus,
A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous paper in a transfer nip formed between the image carrier and a transfer roller;
A fixing unit for fixing the toner image transferred to the continuous paper by the transfer unit at a fixing nip;
A separating portion for separating the transfer roller from the image carrier;
A path length changing unit that changes a path length of the continuous sheet conveyance path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
A transport unit that transports the continuous paper from the transfer nip toward the fixing nip;
In the transfer nip, a potential difference generating unit that generates a potential difference between the continuous paper and the transport unit;
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. A control unit that performs control to change the path length of the second path length from the second path length to the first path length;
With
When the image carrier and the transfer roller are separated from each other, the transport unit electrostatically positions a position corresponding to the transfer nip of the continuous sheet due to a potential difference generated between the transfer sheet and the continuous sheet. Adsorb to.

The paper transport control method according to the present invention includes:
A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous sheet at a transfer nip formed between the image carrier and a transfer roller; and the transfer unit The image forming apparatus includes: a fixing unit that fixes the toner image transferred onto the continuous sheet by a fixing nip; and a conveyance unit that conveys the continuous sheet from the transfer nip toward the fixing nip. A control method,
Separating the transfer roller from the image carrier,
Changing the path length of the continuous paper transport path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
In the transfer nip, a potential difference is generated between the continuous paper and the transport unit,
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. To change the path length of the second path length from the second path length to the first path length,
The transport unit, when the image bearing member and the transfer roller are spaced apart, electrostatically position corresponding to the transfer nip of the continuous paper by the potential difference generated between the continuous paper in the transfer nip Adsorb to.

  According to the present invention, it is possible to prevent the paper from being displaced with respect to the transfer nip while suppressing the paper from being spoiled by the heat of the fixing unit.

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. 4 is an enlarged view of the periphery of a secondary transfer unit when the path length of a conveyance path during image formation is a first path length. FIG. 6 is an enlarged view of the periphery of a secondary transfer unit when a path length of a conveyance path during image formation is a second path length. FIG. 6 is an enlarged view of the periphery of a secondary transfer unit when the path length of a transport path during patch image formation is a second path length. FIG. 10 is an enlarged view of the periphery of the secondary transfer unit when the path length of the transport path during patch image formation is displaced from the second path length to the first path length. FIG. 10 is an enlarged view of the periphery of the secondary transfer unit when the path length of the transport path during patch image formation is the first path length. 6 is a flowchart illustrating an example of an operation example of path length change control in the image forming apparatus. It is an enlarged view of a secondary transfer unit according to 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 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 unit 42 corresponds to the “transfer portion” of the invention, and 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 has a high resistance layer having a volume resistivity of 8 to 11 [log Ω · cm] on the surface. The intermediate transfer belt 421 is rotationally driven by a control signal from the control unit 100. Note that the material, thickness, and hardness of the intermediate transfer belt 421 are not limited as long as they have conductivity and elasticity.

  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, an endless secondary transfer belt 92, a path length changing roller 93, a downstream roller 94, a tension roller 95, and the like. The secondary transfer roller 91 corresponds to the “transfer roller” of the invention, and the secondary transfer belt 92 corresponds to the “conveying unit” and the “endless belt” of the 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 92, 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 92 is formed of a semiconductive belt made of polyvinylidene fluoride, and is stretched in a loop by a secondary transfer roller 91, a path length changing roller 93, a downstream roller 94, and a tension roller 95. In the secondary transfer belt 92, the upper surface of the upper portion is a conveyance surface for the sheet S, and the conveyance surface forms a conveyance path for the sheet S between the secondary transfer nip and the fixing nip. Yes.

  The path length changing roller 93 is in contact with the opposite side of the conveyance surface of the secondary transfer belt 92, that is, the back side surface. The downstream roller 94 is positioned downstream of the secondary transfer roller 91 in the rotational direction of the secondary transfer belt 92, that is, at the downstream end of the secondary transfer belt 92.

  The tension roller 95 is in contact with the surface facing the inside of the portion located on the lower side of the secondary transfer belt 92, and applies an appropriate tension to the secondary transfer belt 92. The path length changing roller 93 and the tension roller 95 are connected by a link member 96 extending vertically, and are configured to be able to continuously change the path length of the transport path of the paper S. The operation for changing the length of the transport path 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 a voltage application unit (not shown), 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. Thus, 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. The voltage application unit corresponds to the “potential difference generation unit” of the present invention.

  Further, for example, when a negative charge is applied to the front side of the paper S by the secondary transfer bias, the positive charge is biased to the back side of the paper S. For this reason, the secondary transfer belt 92 in contact with the back surface of the paper S also induces a negative charge on the front side and a positive charge on the back side due to dielectric polarization. As a result, a potential difference is generated between the sheet S and the secondary transfer belt 92, and the sheet S and the secondary transfer belt 92 are electrically attracted to each other. The position corresponding to is electrostatically attracted.

  Further, the image forming unit 40 corrects the image forming conditions by the control unit 100 when, for example, density unevenness or the like occurs in the toner image. Specifically, the image forming unit 40 forms a patch image on the intermediate transfer belt 421, and corrects the image forming condition by detecting the density of the patch image by a density detection unit (not shown). When such a correction operation is executed, the patch image on the intermediate transfer belt 421 adheres to the secondary transfer belt 92 if the intermediate transfer belt 421 and the secondary transfer belt 92 remain in contact with each other.

  Therefore, in the present embodiment, the intermediate transfer unit 42 has a transfer position where the intermediate transfer belt 421 and the secondary transfer belt 92 are in contact with each other and a separation position where the intermediate transfer belt 421 and the secondary transfer belt 92 are separated from each other. It is configured to be movable between. When executing the correction operation, the control unit 100 controls the position of the intermediate transfer unit 42 so as to move the intermediate transfer unit 42 from the transfer position to the separated position by controlling a separation unit (not shown).

  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.

  Next, the operation of changing the path length of the transport path by the path length changing roller 93 and the tension roller 95 will be described. FIG. 3 is an enlarged view of the periphery of the secondary transfer unit 90 when the path length of the transport path during image formation is the first path length. FIG. 4 is an enlarged view of the periphery of the secondary transfer unit 90 when the path length of the transport path during image formation is the second path length.

  As shown in FIGS. 3 and 4, the link member 96 has a rack gear that extends vertically, although not shown, on the outer surface, and the pinion gear 97 that meshes with the rack gear rotates so as to move in the vertical direction. It has become. The path length changing roller 93 and the tension roller 95 are movable between the position in FIG. 3 and the position in FIG. 4, and are configured to move in the vertical direction by the movement operation of the link member 96. The link member 96 may be configured to move in the vertical direction by being biased by a cam or the like.

  When the path length changing roller 93 moves from the position of FIG. 3 toward the position of FIG. 4, the conveyance surface of the secondary transfer belt 92 is pushed upward by the path length changing roller 93 to be convex upward. It will be displaced to.

  Specifically, when the path length changing roller 93 is at the position shown in FIG. 3, the path length of the transport path is the length in the transport direction of the sheet S from the secondary transfer roller 91 to the downstream roller 94. The length is D1 (for example, 426 mm). When the path length changing roller 93 is at the position of FIG. 4, the path length of the transport path is the first length D21 (for example, 276 mm) from the position of the secondary transfer roller 91 to the path length changing roller 93 on the secondary transfer belt 92. ) And the second length D22 (for example, 276 mm) from the position of the path length changing roller 93 to the downstream side roller 94 in the secondary transfer belt 92, becomes a second path length D2 (552 mm).

  As described above, the path length changing roller 93 sets the path length of the conveyance path of the sheet S between the transfer nip and the fixing unit 60 to the first path length D1 and the second path length longer than the first path length D1. It is configured to be able to change continuously with D2.

  Here, when the correction operation is performed in the middle of the printing operation of the paper S, which is continuous paper, the conveyance of the paper S is stopped while the paper S is placed on the secondary transfer belt 92. At this time, when the conveyance of the sheet S by the fixing unit 60 is stopped, the sheet S located in the fixing nip is affected by the heat of the fixing unit 60, and the sheet S becomes a waste paper.

  Therefore, in the present embodiment, the control unit 100 changes the path length of the transport path from the first path length D1 to the second path before the correction operation of the toner image formed on the paper S by the intermediate transfer unit 42 is executed. Change to length D2. As illustrated in FIG. 5, the control unit 100 changes the path length and then moves the secondary transfer roller 91 away from the intermediate transfer belt 421 when the correction operation is performed, By stopping the rotation, the conveyance of the sheet S in the secondary transfer nip is stopped. In this state, the control unit 100 performs control to change the path length of the transport path from the second path length D2 to the first path length D1.

  By changing the first path length D1 to the second path length D2, the length of the portion located between the secondary transfer nip of the sheet S and the fixing unit 60 can be increased. Thereafter, the intermediate transfer belt 421 is moved to the separation position, and the conveyance of the sheet S at the portion of the sheet S that contacts the secondary transfer roller 91 is stopped.

  Then, by changing the second path length D2 to the first path length D1, the portion located between the secondary transfer nip of the sheet S and the fixing unit 60 is conveyed by the fixing unit 60, and thus the sheet S Even when the conveyance by the secondary transfer roller 91 is stopped, the sheet S does not stop at the fixing nip. For this reason, it is possible to suppress the paper S from being spoiled due to the heat of the fixing unit 60.

  Further, if the conveyance speed by the fixing unit 60 is left as it is while the path length of the conveyance path between the secondary transfer nip and the fixing unit 60 is increased, the distance between the secondary transfer nip and the fixing unit 60 is maintained. The balance between the path length and the conveyance speed is lost.

  For this reason, the control unit 100 increases the conveyance speed of the fixing unit 60 from the first speed (for example, 157.5 mm / sec) that is the conveyance speed by the secondary transfer roller 91 while increasing the length of the conveyance path. The speed is changed to a second speed (for example, 152.5 mm / sec) slower than the first speed. By doing so, it is possible to prevent the balance between the path length between the secondary transfer nip and the fixing unit 60 and the conveyance speed from being lost.

  On the other hand, after the path length is set to the second path length D2, if the conveyance speed of the fixing unit 60 is maintained at the second speed, the sheet S is conveyed by the secondary transfer roller 91 that is the first speed. The sheet S is likely to be loosened between the secondary transfer nip and the fixing unit 60. Therefore, the control unit 100 controls the conveyance speed of the fixing unit 60 so that the sheet S does not sag.

  More specifically, when the path length of the transport path between the secondary transfer nip and the fixing unit 60 becomes the second path length D2, the control unit 100 changes the transport speed of the fixing unit 60 from the second speed to the first speed. Change to As a result, it is possible to match the conveyance speed by the secondary transfer roller 91, so that it is possible to suppress the slackness of the paper S between the secondary transfer nip and the fixing unit 60.

  By the way, during the correction operation, the secondary transfer roller 91 is stopped, but the fixing unit 60 continues to operate. Therefore, the position P1 corresponding to the secondary transfer nip of the sheet S is shifted by the conveyance by the fixing unit 60. There is a risk that. If the position P1 of the sheet S shifts, an image shift occurs when the intermediate transfer belt 421 is moved to the transfer position and the image forming operation is restarted after the correction operation is completed.

  However, in the present embodiment, the secondary transfer belt 92 electrostatically attracts the position corresponding to the secondary transfer nip of the paper S, so that the paper S is stopped as long as the conveyance by the secondary transfer roller 91 is stopped. The position P1 corresponding to the secondary transfer nip is restricted from moving the secondary transfer belt 92 with respect to the secondary transfer nip.

  In this way, the position P1 of the sheet S is restricted from moving relative to the secondary transfer nip, so that the position corresponding to the downstream roller 94 of the sheet S when the path length of the transport path is the second path length D2. P2 gradually approaches the fixing unit 60 by the conveyance of the fixing unit 60 in the operation of shortening the path length, as shown in FIGS. 6 and 7, and the path length becomes the first path length D1. Even if the fixing nip is reached, the position P1 of the paper S can be prevented from shifting.

  Then, at the timing when the path length becomes the first path length D1, the control unit 100 controls the intermediate transfer belt 421 to move from the separation position to the transfer position and resume the conveyance of the secondary transfer roller 91. Thereby, the image forming operation can be resumed smoothly.

  Further, the control unit 100 may control the moving speed of the path length changing roller 93 so that the control for shortening the path length is completed within the time required for the correction operation (for example, 0.8 seconds). By doing so, it is possible to smoothly shift from the correction operation to the image forming operation.

  Next, an operation example of path length change control in the image forming apparatus 1 including the control unit 100 as described above will be described. FIG. 8 is a flowchart illustrating an example of an operation example of path length change control in the image forming apparatus 1. The process in FIG. 8 is executed when the control unit 100 receives an instruction to execute a correction operation.

  First, the control unit 100 operates the path length changing roller 93 so that the path length of the transport path is changed from the first path length D1 to the second path length D2 (step S101).

  Next, the control unit 100 determines whether or not the path length of the transport path has reached the second path length D2 (step S102). As a result of the determination, when the path length is not the second path length D2 (step S102, NO), the control unit 100 repeats the determination of step S102, and the path length is the second path length D2 (step S102). (S102, YES), the path length changing roller 93 is stopped (step S103).

  Next, the control unit 100 determines whether an instruction to start the correction operation has been received (step S104). As a result of the determination, when the correction operation has not been started (NO in step S104), the control unit 100 repeats the determination process in step S104. On the other hand, when the correction operation is started (YES in step S104), the control unit 100 stops the rotation operation of the secondary transfer roller 91 (step S105).

  Next, the control unit 100 moves the intermediate transfer unit 42 to the separation position (step S106). Next, the control unit 100 operates the path length changing roller 93 so that the path length of the transport path is changed from the second path length D2 to the first path length D1 (step S107). Note that the processes in steps S105 to S107 are performed simultaneously.

  Next, the control unit 100 determines whether or not the path length of the transport path has reached the first path length D1 (step S108). As a result of the determination, when the path length of the transport path is not the first path length D1 (NO in step S108), the control unit 100 repeats the determination process in step S108. On the other hand, when the path length of the transport path becomes the first path length D1 (step S108, YES), the control unit 100 stops the path length changing roller 93 (step S109).

  Next, the control unit 100 drives the secondary transfer roller 91, that is, starts the rotation operation of the secondary transfer roller 91 (step S110). Next, the control unit 100 moves the intermediate transfer unit 42 to the transfer position (step S111), and ends this control. Note that the processes in steps S109 to S110 are performed simultaneously.

  As described above in detail, the image forming apparatus 1 in the present embodiment forms a toner image on the intermediate transfer belt 421, and the secondary formed between the intermediate transfer belt 421 and the secondary transfer roller 91. An intermediate transfer unit 42 that transfers the toner image formed on the intermediate transfer belt 421 to a sheet at the transfer nip; a fixing unit 60 that fixes the toner image transferred to the sheet S by the intermediate transfer unit 42 at the fixing nip; A separation portion for separating the next transfer roller 91 from the intermediate transfer belt 421 and a path length of the conveyance path of the sheet S between the secondary transfer nip and the fixing nip are continuously between the first path length and the first path length. A secondary transfer bell that transports the sheet S from the secondary transfer nip to the fixing nip by the rotation of the path length changing roller 93 and the secondary transfer roller 91, 92 and the secondary transfer nip, a potential difference is generated between the sheet S and the secondary transfer belt 92, and before the density transfer operation of the toner image formed on the sheet S by the intermediate transfer unit 42 is executed, the path of the transport path After the length is changed from the first path length to the second path length, when the density correction operation is executed, the secondary transfer roller 91 is separated from the intermediate transfer belt 421 and the secondary transfer roller 91 is rotated. A control unit 100 that performs control to change the path length of the transport path from the second path length to the first path length in a state where the transport of the sheet S in the secondary transfer nip is stopped by stopping. When the intermediate transfer belt 421 and the secondary transfer roller 91 are separated from each other, the secondary transfer belt 92 is opposed to the secondary transfer nip of the paper S due to a potential difference generated between the secondary transfer belt 421 and the secondary transfer roller 91. Position adsorbed electrostatically to the.

  According to the present embodiment configured as described above, the sheet S is prevented from being misaligned with respect to the secondary transfer nip while the sheet S is prevented from being spoiled by the heat of the fixing unit 60. Can do.

  In the above embodiment, the path length of the transport path is changed by only one path length change roller 93. However, the present invention is not limited to this, and the path length of the transport path by a plurality of path length change rollers. May be changed.

FIG. 9 is an enlarged view of a secondary transfer unit 90 according to a modification.
For example, as shown in FIG. 9, the secondary transfer unit 90 includes a first roller 98A that contacts the back side of the transport surface of the secondary transfer belt 92 as a path length changing unit 98, and a downstream side with respect to the first roller 98A. A second roller 98B in contact with the back side of the conveying surface of the secondary transfer belt 92 on the roller 94 side.

  Further, a rotation shaft 98C is provided at a position apart from the secondary transfer belt 92 between the first roller 98A and the second roller 98B in the paper transport direction. The rotating shaft 98C is linked to the first roller 98A by the first link 98D, and is linked to the second roller 98E by the second link 98E.

  The control unit 100 rotates the paper D and the second link 98E of the first link 98B around the rotation shaft 98C according to the rigidity of the paper, so that the curvature on the transport surface of the secondary transfer belt 92, that is, the transport. Change the curvature of the route.

  Specifically, when the paper has high rigidity, the first roller 98A and the second roller 98B are rotated so that the first roller 98A and the second roller 98B approach each other. Further, when the rigidity of the sheet is low, the first roller 98A and the second roller 98B are rotated to the side where the first roller 98A and the second roller 98B are separated from each other. In this way, the adhesion of the sheet to the secondary transfer belt 92 can be ensured according to the rigidity of the sheet, so the adsorbability of the sheet S on the secondary transfer belt 92 according to the rigidity of the sheet S can be increased. Can be secured.

  In order to change the path length of the transport path with this configuration, for example, the path length can be changed by moving the rotating shaft 98C and the tension roller 95 in the vertical direction.

  In the above embodiment, continuous paper is exemplified as the paper, but the continuous paper may be folded paper or continuous paper roll paper.

  In addition, each of the above-described embodiments is merely an example of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the gist or 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, for example, external devices such as post-processing devices and network-connected control devices.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 40 Image forming part 60 Fixing part 91 Secondary transfer roller 92 Secondary transfer belt 93 Path length change roller 94 Downstream roller 95 Tension roller 100 Control part 421 Intermediate transfer belt D1 1st path length D2 2nd path length

Claims (8)

A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous paper in a transfer nip formed between the image carrier and a transfer roller;
A fixing unit for fixing the toner image transferred to the continuous paper by the transfer unit at a fixing nip;
A separating portion for separating the transfer roller from the image carrier;
A path length changing unit that changes a path length of the continuous sheet conveyance path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
A transport unit that transports the continuous paper from the transfer nip toward the fixing nip;
In the transfer nip, a potential difference generating unit that generates a potential difference between the continuous paper and the transport unit;
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. A control unit that performs control to change the path length of the second path length from the second path length to the first path length;
With
When the image carrier and the transfer roller are separated from each other, the transport unit electrostatically positions a position corresponding to the transfer nip of the continuous sheet due to a potential difference generated between the transfer sheet and the continuous sheet. Adsorb to the
Image forming apparatus. The transport unit is an endless belt,
A downstream roller located downstream of the transfer roller in the rotational direction of the endless belt;
A tension roller for maintaining the tension of the endless belt;
With
The path length changing unit includes a roller that winds the endless belt together with the transfer roller, the downstream roller, and the tension roller.
The image forming apparatus according to claim 1. The path length changing unit, in the transport direction of the continuous paper, between the downstream roller and the transfer roller into contact with the surface opposite to the transport surface facing the continuous paper of the endless belt, the continuous Changing the path length of the transport path by moving toward the paper side;
The image forming apparatus according to claim 2. The tension roller is connected to the path length changing unit,
The image forming apparatus according to claim 3. The path length changing unit changes the curvature of the conveyance path of the continuous paper between the transfer nip and the fixing nip,
The control unit controls the path length changing unit to change the curvature of the conveyance path according to the rigidity of the continuous paper .
The image forming apparatus according to claim 2. The path length changing unit includes a first roller that contacts a surface of the endless belt that is opposite to a conveyance surface that faces the continuous paper , and the opposite side at a position on the downstream roller side with respect to the first roller. A second roller in contact with the surface of the sheet , a rotation shaft positioned between the first roller and the second roller in the conveyance direction of the continuous paper inside the endless belt, the rotation shaft, and the first A first link that connects a roller, a second link that connects the rotating shaft and the second roller,
The image forming apparatus according to claim 5. An image forming system including a plurality of units including an image forming apparatus,
A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous paper in a transfer nip formed between the image carrier and a transfer roller;
A fixing unit for fixing the toner image transferred to the continuous paper by the transfer unit at a fixing nip;
A separating portion for separating the transfer roller from the image carrier;
A path length changing unit that changes a path length of the continuous sheet conveyance path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
A transport unit that transports the continuous paper from the transfer nip toward the fixing nip;
In the transfer nip, a potential difference generating unit that generates a potential difference between the continuous paper and the transport unit;
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. A control unit that performs control to change the path length of the second path length from the second path length to the first path length;
With
When the image carrier and the transfer roller are separated from each other, the transport unit electrostatically positions a position corresponding to the transfer nip of the continuous sheet due to a potential difference generated between the transfer sheet and the continuous sheet. Adsorb to the
Image forming system. A transfer unit that forms a toner image on an image carrier and transfers the toner image formed on the image carrier to a continuous sheet at a transfer nip formed between the image carrier and a transfer roller; and the transfer unit The image forming apparatus includes: a fixing unit that fixes the toner image transferred onto the continuous sheet by a fixing nip; and a conveyance unit that conveys the continuous sheet from the transfer nip toward the fixing nip. A control method,
Separating the transfer roller from the image carrier,
Changing the path length of the continuous paper transport path between the transfer nip and the fixing nip between a first path length and a second path length longer than the first path length;
In the transfer nip, a potential difference is generated between the continuous paper and the transport unit,
The density correction operation is performed after the path length of the transport path is changed from the first path length to the second path length before the density correction operation of the toner image formed on the continuous paper is performed by the transfer unit. In the state where the transfer roller is separated from the image carrier and the transfer roller is stopped by rotating the transfer roller in a state where the transfer of the continuous paper in the transfer nip is stopped. To change the path length of the second path length from the second path length to the first path length,
The transport unit, when the image bearing member and the transfer roller are spaced apart, electrostatically position corresponding to the transfer nip of the continuous paper by the potential difference generated between the continuous paper in the transfer nip Paper conveyance control method to be adsorbed on the paper.

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