JP6601196B2 - Fixing apparatus, image forming apparatus, and nip width changing method - Google Patents

Description

  The present invention relates to a fixing device, an image forming apparatus, and a nip width changing method.

  Conventionally, as a fixing device used in an image forming apparatus of an electronic transfer system such as a copying machine, a printer, and a fax machine, for example, an upper pressure roller having a rubber layer on a surface layer and having a heat source therein, and an upper pressure roller And a lower pressure roller that forms a fixing nip. During printing, a transfer material (for example, a recording medium) on which an unfixed toner image is formed is sandwiched and heated by the upper and lower pressure rollers. In some cases, a toner image is fixed on a recording sheet (heat roller method).

  Further, for example, a heating roller having a heat source inside, an upper pressure roller, a fixing belt wound around these rollers, and a lower pressure roller that is pressed against the upper pressure roller via the fixing belt to form a fixing nip. There is a belt-type fixing device that includes a pressure roller, and fixes a toner image on a recording paper by heating the recording paper medium while nipping and conveying the recording paper medium by a fixing belt and a lower pressure roller during printing. .

  In any type of fixing device, when an envelope in which two sheets of paper are stacked and bonded is carried in, a difference in the recording paper peripheral speed occurs between the upper and lower pressure rollers, and consequently the conveyance speed of the two sheets of paper. There will be a difference. As a result, there has been a problem that wrinkles and image misalignment may occur in the envelope after the fixing process. To solve this problem, there is a technique for reducing the nip load when the recording paper is pressed by the pressure rollers above and below the recording paper.

  Although Patent Document 1 is not a technique for preventing wrinkles and image misalignment in an envelope, it has three support rollers and a belt wound around these rollers, and fixes a recording paper (recording medium). A technique in which three support rollers are arranged so as to increase the curvature of the belt on the side to be carried out from the nip is disclosed. According to the technique described in Patent Document 1, it is possible to improve the separation (removability) of the recording paper.

JP-A-10-228198

  However, if the nip load is reduced to prevent wrinkles and image deviation from occurring on the recording paper recording paper envelope, the fixing nip width is shortened, that is, the surface pressure against the envelope is reduced at the fixing nip, resulting in fixing performance. There has been a problem of lowering.

  An object of the present invention is to provide a fixing device, an image forming apparatus, and a nip width changing method capable of preventing the occurrence of wrinkles on a recording medium and the occurrence of image displacement without deteriorating the fixability.

The fixing device in the present invention is
A fixing surface side member disposed on the fixing surface side of the recording medium on which the toner image is formed;
A back surface side support member that forms a fixing nip that sandwiches and conveys the recording medium with the fixing surface side member;
A belt member provided on at least one of the fixing surface side member and the back surface side support member;
A nip width changing unit that changes a nip width of the fixing nip in the conveyance direction of the recording medium by changing a mode of applying tension to the belt member;
Is provided.

An image forming apparatus according to the present invention is
An image is formed by fixing the toner image formed on the recording medium by the fixing device.

Furthermore, the nip width changing method according to the present invention is:
Forming a fixing nip for nipping and conveying the recording medium between a fixing surface side member disposed on the fixing surface side of the recording medium on which the toner image is formed and a back surface side support member;
The nip width of the fixing nip in the conveyance direction of the recording medium is changed by changing the manner of tension applied to the belt member provided on at least one of the fixing surface side member and the back surface side support member.

  According to the present invention, it is possible to prevent occurrence of wrinkles on the recording medium and image misalignment without deteriorating the fixability.

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. 1 is a diagram schematically illustrating a fixing device according to an exemplary embodiment. 1 is a diagram schematically illustrating a fixing device according to an exemplary embodiment. It is a figure which shows roughly the nip width change part which concerns on this Embodiment. It is a figure which shows schematically the upper and lower pressure rollers which concern on this Embodiment. It is a figure which shows the pressure of a fixing nip. FIG. 6 is a diagram schematically illustrating a fixing device according to a comparative example. FIG. 10 is a diagram schematically illustrating a fixing device according to a first modification. FIG. 10 is a diagram schematically illustrating a fixing device according to a second modification. FIG. 10 is a diagram schematically illustrating a fixing device according to a second modification. FIG. 10 is a diagram schematically illustrating a fixing device according to a second 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 an embodiment of the present invention. FIG. 2 shows a main part of the control system of the image forming apparatus 1 according to the present embodiment.

  As shown in FIGS. 1 and 2, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus using an electrophotographic process technology. That is, the image forming apparatus 1 transfers the toner images of Y (yellow), M (magenta), C (cyan), and K (black) formed on the photosensitive drum 413 to the intermediate transfer belt 421 (primary transfer). Then, after superposing four color toner images on the intermediate transfer belt 421, the toner image is transferred (secondary transfer) to the recording medium P fed from the paper feeding device 2 to form an image.

  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.

  As illustrated in FIG. 2, 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 101.

  The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads out a program corresponding to the processing content from the ROM 103 and develops it in the RAM 104, 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 112 are referred to. The storage unit 112 is configured by, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 101 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 111. Do. For example, the control unit 101 receives image data (input image data) transmitted from an external device, and forms an image on the recording medium P based on the image data (input image data). The communication unit 111 is configured by 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 a display unit 21 and an 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 101. 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 101.

  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 101. 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. Etc.

  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 Y, M, C, or K are added to the reference numerals when distinguished from each other. 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) and a charge generation layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube) having a drum diameter of 80 mm. A negatively charged organic photoreceptor (OPC: Organic Photo-conductor) in which a charge transport layer (CTL) is sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The controller 101 controls the drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413 to rotate the photosensitive drum 413 at a constant peripheral speed.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. 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 developing type 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 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 secondary transfer roller 424, a belt cleaning device 426, and the like.

  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. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  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 101. 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 secondary transfer roller 424 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 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the recording medium P.

  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, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the recording medium P passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the recording medium P. Specifically, the toner is obtained by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the recording medium P (the side in contact with the secondary transfer roller 424). The image is electrostatically transferred to the recording medium P. The recording medium P to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration in which the secondary transfer belt is stretched in a loop shape on a plurality of support rollers including the secondary transfer roller may be employed.

  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, recording media P (standard paper, special paper) identified based on basis weight, size, etc. are stored for each preset type. The The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The recording media P accommodated in the paper 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 recording medium P and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred to one surface of the recording medium P at a time, and a fixing process is performed in the fixing unit 60. The recording medium P on which the image has been formed is discharged out of the apparatus by a paper discharge unit 52 having a paper discharge roller 52a.

3 and 4 are diagrams schematically showing the fixing device according to the present embodiment.
As shown in FIGS. 3 and 4, the fixing unit 60 includes a heating roller 61, an upper pressure roller 62, a fixing belt 63 (corresponding to the “fixing surface side member” of the present invention), and a lower pressure roller 64 (the present invention). 2), a belt member 66, a nip width changing portion 70, and the like.

  The fixing unit 60 is disposed in the fixing device F as a unit. The fixing unit 60 and the control unit 101 that controls the fixing unit 60 correspond to the “fixing device” of the present invention.

  The heating roller 61 is a hollow roller member made of a metal material having high thermal conductivity such as aluminum, and a heater 61a (heat source) is provided inside the cylindrical body. The heater 61a is a halogen heater, and both ends thereof are fixed to a side plate (not shown) of the fixing device F. The heating roller 61 is heated by radiant heat from the heater 61a whose output is controlled by the power supply unit (AC power supply) of the apparatus main body.

  The upper pressure roller 62 is rotatably disposed on the fixing surface (surface on which the toner image is formed) side of the recording medium P and below the heating roller 61. The upper pressure roller 62 is a sponge roller in which an elastic layer made of a sponge material is formed on a core metal such as SUS304, and is in pressure contact with the lower pressure roller 64 via the fixing belt 63.

  The fixing belt 63 is an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer made of a resin material. The elastic layer of the fixing belt 63 is formed of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. The release layer is formed of PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin), polyimide resin, polyetherimide resin, PES (polyether sulfone resin), or the like. By providing the release layer, the releasability for the toner image is secured.

  The fixing belt 63 is wound around the upper pressure roller 62 and the heating roller 61. The fixing belt 63 is sandwiched between the upper pressure roller 62 and the lower pressure roller 64 to heat the recording paper P.

  The belt member 66 is an endless belt made of metal such as nickel, a nickel alloy, or iron. The belt member 66 has a mechanical strength that can withstand high tension. As shown in FIGS. 3 and 4, the belt member 66 is wound around a lower pressure roller 64 and a pair of support rollers 72. The pair of support rollers 72 are disposed on the upstream side and the downstream side in the recording medium conveyance direction at the fixing nip position. The belt member 66 is not limited to a metal member as long as it has mechanical strength, releasability with respect to toner, flexibility, heat resistance, and the like.

  For example, the control unit 101 outputs information on the type (for example, plain paper, envelope) of the recording medium P to the fixing unit 60. The nip width changing unit 70 changes the nip width of the fixing nip in the conveyance direction of the recording medium P by changing the manner in which tension is applied to the belt member 66 according to the type of the recording medium P. The present invention is not limited to this. For example, in response to an input operation by the user, the operation unit 22 outputs an operation signal to the control unit 101, the control unit 101 outputs a control signal to the fixing unit 60, and the nip width changing unit 70 receives the control signal. The nip width of the fixing nip may be changed.

FIG. 5 is a diagram schematically showing the nip width changing unit 70.
As illustrated in FIG. 5, the nip width changing unit 70 includes a roller moving mechanism that moves the downstream support roller 72 in the vertical direction when the upstream support roller 72 is moved in the vertical direction. The nip width changing unit 70 changes the manner in which tension is applied to the belt member 66 by changing the positions of the upstream and downstream support rollers 72 using a roller moving mechanism. Since both mechanisms have the same configuration, one roller moving mechanism will be described below, and the description will be replaced with the other description. Here, the “tensioning mode of the belt member 66” refers to a direction in which tension is applied to the belt member 66 (for example, a direction parallel to the recording medium conveyance direction and a direction perpendicular to the conveyance direction) and Includes magnitude of force.

  The roller moving mechanism includes bearing portions 74a and 74b provided at both ends of the rotating shaft of the support roller 72, nut portions 75a and 75b connected to the bearing portions 74a and 74b, and nut portions 75a and 75b in the vertical direction. Guide portions 76a and 76b for guiding, screw portions 78a and 78b having screw shafts, screwed into the nut portions 75a and 75b, and moved around the screw shaft to move the nut portions 75a and 75b in the vertical direction; And motors Ma and Mb for rotating the screw portions 78a and 78b.

  When the motors Ma and Mb rotate, the screw portions 78a and 78b are rotated, the nut portions 75a and 75b are moved up and down, and the support roller 72 is moved up and down. When the motors Ma and Mb stop rotating, the screw parts 78a and 78b are stopped from rotating, the vertical movement of the nut parts 75a and 75b is stopped, and the support roller 72 is restrained to a predetermined height position.

  As shown in FIG. 3, the pair of support rollers 72 on the upstream side and the downstream side are located in the lowered position. The belt member 66 is in a free state and does not press against the upper pressure roller 62. Here, the free state refers to a state where there is no force to apply tension to the belt member 66.

  When the belt member 66 shown in FIG. 3 is in a free state, the lower pressure roller 64 pushes the fixing belt 63 to form a curved fixing nip (see FIG. 6). In the state shown in FIG. 3, the normal recording medium P is passed (a state during normal passing).

  FIG. 7 is a diagram showing the relationship between the tension of the belt member 66 and the pressure received by the recording medium P at the fixing nip. As indicated by a dotted line in FIG. 7, in the state during normal sheet passing, the length (nip width) in the recording medium conveyance direction of the fixing nip where the pressure received by the recording medium P is a predetermined value or more is short.

  When the belt member 66 shown in FIG. 3 is in a free state, the pair of support rollers 72 on the upstream side and the downstream side are positioned at the lowered position.

  The nip width changing unit 70 rotates the motors Ma and Mb according to the type (for example, envelope) of the recording medium P. Thereby, the screw parts 78a and 78b are rotated, the nut parts 75a and 75b are moved upward, and the support roller 72 is moved upward. In response to the upward movement of the pair of support rollers 72, the belt member 66 moves between the pair of support rollers 72, between the upstream support roller 72 and the lower pressure roller 64, and downstream with the support roller 72 and the lower pressure roller 64. It is stretched between the pressure roller 64.

  As shown in FIG. 4, the belt member 66 includes a pair of support rollers 72, between the upstream support roller 72 and the lower pressure roller 64, and between the downstream support roller 72 and the lower pressure roller 64. It becomes a stretched state. At this time, the rotation of the motors Ma and Mb is stopped and the screw portions 78a and 78b are stopped to stop the vertical movement of the nut portions 75a and 75b, and the pair of support rollers 72 on the upstream side and the downstream side are moved. Restrain to the raised position.

  In a state where the pair of support rollers 72 is constrained to the raised position, the belt member 66 is applied with a tension in a direction parallel to the conveyance direction of the recording medium, and the belt member 66 pushes up the upper pressure roller 62 via the fixing belt 63. . The upper pressure roller 62 has a soft elastic layer. As a result, a linear fixing nip (flat nip) is formed, and the length (nip width) of the fixing nip in the recording medium conveyance direction is increased (see FIGS. 4 and 7). In the state shown in FIG. 4, the recording medium P such as an envelope in which two sheets of paper are stacked and bonded is passed (state when the envelope is passed).

  As shown by a solid line in FIG. 7, the nip width in the state of passing an envelope or the like is longer than the nip width in the state of passing a normal sheet. Here, the fixing nip is not only a portion where the fixing belt 63 and the lower pressure roller 64 are pressed against each other via the belt member 66 but also a portion where the belt member 66 is pressed against the upper pressure roller 62. (Pseudo nip) is also included. The convex portion at the center of the solid line shown in FIG. 7 indicates the pressure applied to the portion where the fixing belt 63 and the lower pressure roller 64 are pressed against each other, and both side portions of the convex portion indicate the pressure of the pseudo nip. As shown in FIG. 8, when the distance between the central axes of the upper and lower pressure rollers 62 and 64 is longer than usual when passing an envelope or the like, the pressure in the fixing nip is as shown by the broken line in FIG. Go down. Further, the nip width is also narrowed.

  The nip width changing unit 70 rotates the motors Ma and Mb according to the type (for example, plain paper) of the recording medium P. Thereby, screw part 78a, 78b is rotated, nut part 75a, 75b is moved below, and support roller 72 is moved below. In response to the downward movement of the pair of support rollers 72, the belt member 66 moves between the pair of support rollers 72, between the upstream support roller 72 and the lower pressure roller 64, and between the downstream support roller 72 and the lower support roller 72. It is loosened between the pressure roller 64 and enters the free state shown in FIG. Thereby, the fixing nip has a curvature, and the plain paper can be easily separated.

  According to the fixing device according to the above-described embodiment, a tension in a direction parallel to the conveyance direction of the recording medium is applied to the belt member 66, and the belt member 66 is brought into pressure contact with the upper pressure roller 62 so that a linear fixing nip is formed. And the nip width is increased, so that it is possible to prevent wrinkling of the recording medium P and occurrence of image displacement when fixing the recording medium P such as an envelope without deteriorating the fixing property. .

  In the fixing nip, pressure is applied to the recording medium P by the upper and lower pressure rollers 62 and 64. As a result, the peak pressure remains the same as during normal paper feeding, and the fixability does not deteriorate.

  In addition, since the belt member 66 is in a free state during normal paper feeding, it can be used for a normal recording medium P. Therefore, without preparing an envelope-dedicated machine corresponding to the recording medium P such as an envelope, an envelope or the like can be used. It is possible to pass the recording medium.

  Furthermore, since the curvature of the fixing medium nip of the fixing nip between the fixing belt 63 and the belt member 66 is ensured during normal sheet passing, the separation property of the recording medium P is not impaired.

  In the above-described embodiment, the nip width changing unit 70 that adjusts the tension of the belt member 66 in two stages of normal paper passing and envelope paper passing is shown, but depending on the type of the recording medium, the belt member The tension of 66 may be adjusted to three or more stages. As a result, in the case of a recording medium with poor separation, the separation of the recording medium can be ensured by providing a slight curvature on the recording medium discharge side of the fixing nip between the fixing belt 63 and the belt member 66. .

  In the above embodiment, the belt member 66 is wound around the lower pressure roller 64. However, the present invention is not limited to this. The belt member 66 may be wound around the upper pressure roller 62. In this configuration, when the support roller 72 is moved to the lowered position, a tension in a direction parallel to the recording medium conveyance direction is applied to the belt member 66, the nip width of the fixing nip is widened, and the support roller 72 is raised. When moved to the position, the belt member 66 is in a free state, and the nip width is narrowed.

  In the above-described embodiment, the belt member 66 is wound around the pair of support rollers 72 and the lower pressure roller 64. Accordingly, the belt member 66 can be rotated by the rotational force of the lower pressure roller 64, and the belt member 66 can be interlocked with the lower pressure roller 64 with a simple configuration. However, the present invention is not limited to this. Although the belt member 66 is wound around the pair of support rollers 72, the belt member 66 may not be wound around the lower pressure roller 64. Thereby, for example, the belt member 66 can be arranged in a small space.

(Modification 1)
Next, a first modification of the fixing device will be described with reference to FIG.
An envelope has a flap part which is a cover of an enclosure port. When the envelope is passed through the fixing nip, the flap portion is thicker than the other portion and a higher pressure is applied than the other portion, so that wrinkles are easily generated. In order to prevent generation of wrinkles in the flap portion, the angle of the rotation shaft of the support roller 72 may be adjusted so as to reduce the pressure applied to the flap portion of the envelope and not to reduce the pressure applied to other portions. .

  A detection unit 82 (see FIG. 2) for detecting the position of the flap unit is provided. For the detection unit 82, for example, a technique for identifying the flap unit by detecting the paper thickness (double feed detection) is used. The control unit 101 receives a detection result of the detection unit 82 and outputs a control signal to the fixing unit 60. The position of the flap portion may be input manually by the operation unit 22 (see FIG. 2). In this case, the control unit 101 outputs a control signal to the fixing unit 60 based on the position of the flap unit. The nip width changing portion 70 is configured so that the end portion on the side corresponding to the flap portion on the rotation axis of the support roller 72 is separated from the end portion on the opposite side with respect to the central axis of the upper pressure roller 62. The nut portions 75a and 75b are moved up and down by the rotation of 78b, and the angle of the rotation shaft of the support roller 72 is adjusted. This makes it easier for the flap portion to pass through the fixing nip.

Referring to FIG. 9, the angle of the rotation shaft of the support roller 72 is adjusted so that the position of the left end portion on the rotation shaft of the support roller 72 is lower than the position of the right end portion.
According to the fixing device according to Modification 1 described above, it is possible to automatically detect the flap portion and prevent generation of wrinkles or the like in the flap portion.

  In addition, although the angle of the rotating shaft of the support roller 72 was adjusted based on the detection result of the detection part 82, it is not restricted to this. For example, in response to an input operation (an operation for designating the position of the flap portion) by the user, the operation unit 22 outputs an operation signal to the control unit 101, and the control unit 101 outputs a control signal to the fixing unit 60, and the nip width The changing unit 70 may receive a control signal and adjust the angle of the rotation shaft of the support roller 72.

(Modification 2)
Next, a second modification of the fixing device will be described with reference to FIGS. 10A to 10C. 10A to 10C are diagrams illustrating a fixing device according to a second modification.
In the above embodiment, by applying tension in a direction parallel to the recording medium conveyance direction (horizontal direction) to the belt member 66 and pressing the belt member 66 against the upper pressure roller 62, the nip width is wide, and A flat fixing nip can be formed. Accordingly, when a recording medium such as an envelope in which two sheets of paper are bonded is passed through the fixing nip, the two sheets can be prevented from shifting.

  However, depending on the type of the recording medium, the two sheets may be misaligned, and wrinkles may or may occur on the upper and lower sheets. In order to prevent generation of wrinkles and the like and to make it difficult to generate wrinkles or the like, the recording medium entrance angle with respect to the fixing nip and the recording medium discharge angle with respect to the fixing nip may be adjusted. In addition, as shown to FIG. 10A, in said embodiment, both an approach angle and discharge | emission angle are horizontal directions.

  The nip width changing unit 70 adjusts the positions of the upstream and downstream support rollers 72 so as to adjust at least one of the entry angle and the discharge angle.

  The nip width changing unit 70 fixes the position of the upstream support roller 72 higher than the fixing nip and fixes the position of the downstream support roller 72 when wrinkles are generated or may occur on the lower paper. The nut portions 75a and 75b are moved up and down by rotation of the screw portions 78a and 78b so as to be lower than the nip. As a result, as shown in FIG. 10B, the entry angle is such that the recording medium is carried into the fixing nip obliquely upward. Further, the discharge angle is such that the recording medium is carried out from the fixing nip obliquely upward.

  When the wrinkle is generated or may occur on the upper paper, the nip width changing unit 70 sets the position of the upstream support roller 72 lower than the fixing nip and sets the position of the downstream support roller 72 to the fixing nip. The nut portions 75a and 75b are moved up and down by rotation of the screw portions 78a and 78b so as to be higher. As a result, as shown in FIG. 10C, the entry angle is such that the recording medium is carried into the fixing nip obliquely downward. The discharge angle is provided so that the recording medium is carried out obliquely downward. .

  According to the fixing device according to the second modification, the entrance angle and the discharge angle of the recording medium are adjusted by adjusting the positions of the upstream and downstream support rollers 72. Thereby, generation | occurrence | production of wrinkles etc. can further be prevented.

  Depending on the type of recording medium, if there is a tendency for wrinkles to occur on the upper side or the lower side of the paper, the nip width changing section 70 The height position of the support roller 72 on the downstream side may be adjusted.

  In addition, each of the above-described embodiments is merely an example of a specific example for 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 main features thereof.

60 fixing unit 62 upper pressure roller 64 lower pressure roller 66 belt member 70 nip width changing unit 72 support roller 82 detecting unit 101 control unit

Claims (8)

A fixing surface side member disposed on the fixing surface side of the recording medium on which the toner image is formed;
A back surface side support member that forms a fixing nip that sandwiches and conveys the recording medium with the fixing surface side member;
A pair of support rollers disposed on the upstream side and downstream side in the conveyance direction of the recording medium at the position of the fixing nip;
A belt member spanned between the pair of support rollers ;
By changing the position of the pair of support rollers, the manner of applying tension to the belt member is changed, and one of the fixing surface side member and the back surface side support member is pushed through the belt member, A nip width changing unit that changes the shape of the fixing nip and changes the nip width of the fixing nip in the conveyance direction of the recording medium;
A fixing device. The nip width changing unit changes the nip width of the fixing nip according to the type of the recording medium.
The fixing device according to claim 1. In the case where the recording medium is an envelope, the nip width changing unit is configured to be applied to the belt member at one end and the other end in a direction orthogonal to the conveyance direction of the recording medium according to a position of a flap portion provided in the envelope. Change the application mode of tension,
The fixing device according to claim 1. A detection unit for detecting the position of the flap unit;
The nip width changing unit changes a manner of applying tension to the belt member at one end and the other end in a direction perpendicular to the conveyance direction of the recording medium according to a detection result of the detection unit.
The fixing device according to claim 3 . When the recording medium is an envelope, the nip width changing unit changes an approach angle of the recording medium with respect to the fixing nip by changing a manner of applying a tension to the belt member.
The fixing device according to any one of claims 1 to 4. When the recording medium is an envelope, the nip width changing unit changes a discharge angle of the recording medium with respect to the fixing nip by changing a tension application mode with respect to the belt member.
The fixing device according to any one of claims 1 to 5. An image is formed by fixing the toner image formed on the recording medium by the fixing device, comprising the fixing device according to any one of claims 1 to 6 .
Image forming apparatus. Forming a fixing nip for nipping and conveying the recording medium between a fixing surface side member disposed on the fixing surface side of the recording medium on which the toner image is formed and a back surface side support member;
By changing the positions of the pair of support rollers disposed on the upstream side and the downstream side in the recording medium conveyance direction at the fixing nip position, tension is applied to the belt member spanned between the pair of support rollers. By changing one of the fixing surface side member and the back surface side supporting member through the belt member, the shape of the fixing nip is changed, and the nip width of the fixing nip in the conveyance direction of the recording medium is changed. change,
How to change the nip width.

Images