JP2011095428A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device, which can further suppress the occurrence of wrinkles, when fixing an image to a tubular article object and suitably fix an image to normal target transfer material that is not cylindrical. <P>SOLUTION: The fixing device includes a first rotor 9a; a heater 913; a second rotor 920; a third rotor 930; a rotating belt 9b; a fixing nip N9 including a main fixing nip MN and capable of forming an auxiliary fixing nip HN; a fourth rotor 940 for pressing against the internal circumferential surface of the upstream portion 965 in the rotating belt 9b; a fixing nip-pressure changing section 511 for changing to a first nip pressure or a second nip pressure; a fixing nip-length changing section 512 for changing to a first nip length or a second nip length; a fixing nip-pressure changing control section 971 for controlling the fixing nip-pressure changing section 511, according to whether or not target transfer material T is a tubular article; and a fixing nip-length changing control section 972 for controlling the fixing nip-length changing section 512, according to whether the target transfer material T is a tubular article. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus including the same.

  Conventionally, as an apparatus for forming (printing) an image on a sheet, an image forming apparatus such as a copier, a printer, a facsimile, or a complex machine of these is known. In the image forming apparatus, a charging step for charging the surface of the photosensitive drum, an exposure step for irradiating the charged photosensitive drum with laser light to form an electrostatic latent image on the surface of the photosensitive drum, and the surface of the photosensitive drum A developing process for developing the toner by attaching toner to the electrostatic latent image formed thereon, a transferring process for transferring the toner image formed from the toner attached to the surface of the photosensitive drum to the paper, and the toner transferred to the paper An image is formed on the paper by sequentially performing each of the fixing steps for fixing the image on the paper.

  Of the above steps, in the fixing step, it is necessary to melt the toner in order to fix the toner image transferred to the paper to the paper. Conventionally, as a fixing device that performs a fixing process, a fixing device including a heating roller (first rotating body), a pressure roller that forms a fixing nip together with the heating roller, and a heater disposed inside the heating roller is used. Has been. In such a fixing device, a pressure nip is pressed against the heating roller to form a fixing nip therebetween, and a predetermined nip pressure is secured in the fixing nip.

  On the other hand, in the fixing device, a heating roller (first rotator), a pressure roller (second rotator), a tension roller (third rotator), and an annular ring stretched over the pressure roller and the tension roller. A rotation belt is proposed (for example, refer to Patent Document 1). In such a fixing device, a rotating belt is sandwiched between a heating roller and a pressure roller, and a main fixing nip is formed by the heating roller and the rotating belt. Further, an auxiliary fixing nip continuous with the main fixing nip is formed by the contact between the heating roller and the rotating belt. When the sheet is conveyed to the fixing nip (main fixing nip and auxiliary fixing nip), the toner transferred to the sheet is melted and pressurized and fixed on the sheet.

  By the way, depending on the image forming apparatus, an image can be formed (printed) on a cylindrical object such as an envelope. A cylindrical object such as an envelope is formed into a cylindrical shape by folding paper and partially bonding the paper. Therefore, when the cylindrical object is passed through the fixing nip of the fixing device, distortion and wrinkles (wrinkles) associated with the cylindrical object are likely to occur. For this reason, when a cylindrical object is passed through the fixing nip, the fixing nip pressure is generally reduced as much as possible.

  Patent Document 2 describes a fixing device in which the fixing nip pressure is reduced when an image is fixed on a cylindrical object. The fixing device described in Patent Document 2 is provided with an operation lever portion in the fixing device, and when the image is fixed on the cylindrical object, the fixing member applied to the cylindrical object by manually operating the operation lever portion. The nip pressure can be reduced, and therefore generation of wrinkles generated in the cylindrical object can be suppressed.

JP 52-69337 A JP 2004-279702 A

  However, as described above, the fixing device described in Patent Document 2 is intended to suppress wrinkles generated in the cylindrical object by providing a manual operation lever portion in the fixing device, and the wrinkle generated in the cylindrical object. No further contrivances have been made regarding the suppression of the problem. Therefore, there has been a demand for a fixing device that can further suppress the generation of wrinkles when fixing an image on a cylindrical object such as an envelope. In addition, there has been a demand for a fixing device that can suitably fix an image to a normal transfer material that is not a cylindrical object.

Accordingly, the present invention provides a fixing device including a first rotating body, a second rotating body, a third rotating body, and a rotating belt stretched over the second rotating body and the third rotating body. An object of the present invention is to provide a fixing device that can further suppress the generation of wrinkles when fixing an image on a sheet and can also suitably fix an image on a normal transfer material that is not a cylindrical object. To do.
Another object of the present invention is to provide an image forming apparatus including the fixing device.

  In the present invention, a first rotating body that is rotatable about a first rotating shaft, a heater that heats the first rotating body, and a first rotating body that are disposed opposite to the first rotating body and parallel to the first rotating shaft. A second rotating body rotatable about the second rotating shaft, a third rotating body rotatable about a third rotating shaft parallel to the first rotating shaft, and having a predetermined width and rotating in the ring direction An annular rotating belt that is capable of being spanned between the second rotating body and the third rotating body, and that is sandwiched between the first rotating body and the second rotating body; Formed by a rotating belt having a second portion formed continuously with a portion and contacting the first rotating body, and a portion of the rotating belt facing the first portion and the first portion of the first rotating body. At least a main fixing nip that is formed on the rotating belt. A fixing nip formed by a portion facing the second portion of the first rotating body and capable of forming an auxiliary fixing nip positioned continuously with the main fixing nip, the second rotating body, and the second rotating body. A fourth rotating body arranged between the three rotating bodies and rotatable about a fourth rotating shaft parallel to the first rotating shaft, wherein the second rotating body and the third rotating body in the rotating belt A fourth rotating body that presses the inner peripheral surface of the upstream portion located upstream of the fixing nip in the ring direction of the rotating belt, and the second rotating body to the first rotating body A fixing nip pressure changing unit that changes the nip pressure in the fixing nip to a first nip pressure and a second nip pressure smaller than the first nip pressure by moving in a direction toward or away from the first rotating body. And the first A fixing nip length changing unit that changes a nip length of the fixing nip to a first nip length and a second nip length shorter than the first nip length by changing a position of the fourth rotating body with respect to the body. The fixing nip pressure changing unit is controlled so that the nip pressure is set to the second nip pressure when the transfer material is a cylindrical material, and when the transfer material is other than the cylindrical material, the nip pressure is controlled. A fixing nip pressure change control unit for controlling the fixing nip pressure changing unit so that the pressure becomes the first nip pressure; and, when the transfer material is a cylindrical object, the nip length is set to the second nip length. The fixing nip length changing portion is controlled so that the fixing nip length is changed to the first nip length when the material to be transferred is other than a cylindrical object. A fixing nip length change control unit for controlling the unit The present invention relates to a fixing device.

  Further, it is preferable that the fixing nip length changing unit changes the nip length by moving the fourth rotating body in a direction toward the first rotating body or in a direction away from the first rotating body.

  The present invention also provides one or more image carriers on which electrostatic latent images are formed on the surface, and a developer for developing a toner image on the electrostatic latent images formed on the one or more image carriers. The present invention relates to an image forming apparatus comprising: a transfer unit that directly or indirectly transfers a toner image formed on the image carrier to a transfer material; and the fixing device.

According to the present invention, in a fixing device including a first rotating body, a second rotating body, a third rotating body, and a rotating belt stretched over the second rotating body and the third rotating body, a cylinder such as an envelope It is possible to provide a fixing device that can further suppress the generation of wrinkles when fixing an image on a sheet and can also suitably fix an image to a normal transfer material that is not a cylindrical object.
In addition, the present invention can provide an image forming apparatus including the fixing device.

It is a front view for demonstrating arrangement | positioning of each component in the printer 1 of one Embodiment of this invention. FIG. 6 is a perspective view showing the fixing device 9 in a normal fixing mode. It is a perspective view which shows the fixing device 9 in a cylindrical article fixing mode. FIG. 3 is a cross-sectional view of the fixing device 9 in a normal fixing mode, taken along the line AA shown in FIG. 2A. It is sectional drawing cut | disconnected by the BB cutting line shown to FIG. 2B of the fixing device 9 in a cylindrical article fixing mode. 3 is an explanatory diagram conceptually showing a fixing device 9 in a normal fixing mode. FIG. It is explanatory drawing which shows notionally the fixing apparatus 9 in a cylindrical article fixing mode. 7 is a functional block diagram relating to control of a fixing mode changing mechanism 510 in the fixing device 9. FIG. 10 is a flowchart illustrating an example of control of a fixing mode change mechanism 510 by a fixing mode change control unit 970.

Hereinafter, an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.
The overall structure of a printer 1 as an image forming apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a front view for explaining the arrangement of components in a printer 1 according to an embodiment of the present invention.

As shown in FIG. 1, a printer 1 as an image forming apparatus includes an apparatus main body M and an image forming unit GK that forms a predetermined toner image on a transfer material (paper, envelope, etc.) T based on predetermined image information. And a paper supply / discharge unit KH that supplies the transfer material T to the image forming unit GK and discharges the transfer material T on which the toner image is formed.
The outer shape of the apparatus main body M is configured by a case body BD as a casing.

  As shown in FIG. 1, the image forming unit GK includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers (photosensitive members), charging units 10a, 10b, 10c, and 10d, and a laser as an exposure unit. Scanner units 4a, 4b, 4c, 4d, developing devices 16a, 16b, 16c, 16d, toner cartridges 5a, 5b, 5c, 5d, toner supply units 6a, 6b, 6c, 6d, drum cleaning unit 11a, 11b, 11c, 11d, static eliminators 12a, 12b, 12c, 12d, intermediate transfer belt 7, primary transfer rollers 37a, 37b, 37c, 37d, secondary transfer roller 8, counter roller 18, fixing And a device 9.

  As shown in FIG. 1, the paper supply / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 64, a conveyance path L for the transfer material T, a registration roller pair 80, and a plurality of rollers or roller pairs. And a paper discharge unit 50. As will be described later, the transport path L is an aggregate of a first transport path L1, a second transport path L2, a third transport path L3, a manual transport path La, and a return transport path Lb.

Hereinafter, each configuration of the image forming unit GK and the paper supply / discharge unit KH will be described in detail.
First, the image forming unit GK will be described.
In the image forming unit GK, charging by the charging units 10a, 10b, 10c, and 10d in order from the upstream side to the downstream side in order along the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, the laser scanner unit 4a, 4b, 4c, 4d exposure, development devices 16a, 16b, 16c, 16d development, intermediate transfer belt 7 and primary transfer rollers 37a, 37b, 37c, 37d primary transfer, static eliminators 12a, 12b, 12c, 12d Is eliminated, and cleaning is performed by the drum cleaning units 11a, 11b, 11c, and 11d.
In the image forming unit GK, secondary transfer by the intermediate transfer belt 7, the secondary transfer roller 8 and the opposing roller 18, and fixing by the fixing device 9 are performed.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is formed of a cylindrical member and functions as a photosensitive member or an image carrier. Each of the photosensitive drums 2 a, 2 b, 2 c, and 2 d is disposed so as to be rotatable in the direction of an arrow about an axis that extends in a direction orthogonal to the traveling direction of the intermediate transfer belt 7. An electrostatic latent image can be formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d.

  Each of the charging units 10a, 10b, 10c, and 10d is disposed to face the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the charging units 10a, 10b, 10c, and 10d uniformly charges the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d negatively (minus polarity) or positively (plus polarity).

  The laser scanner units 4a, 4b, 4c, and 4d function as exposure units, and are spaced apart from the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the laser scanner units 4a, 4b, 4c, and 4d includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  Each of the laser scanner units 4a, 4b, 4c, and 4d scans and exposes the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d based on image information input from an external device such as a PC (personal computer). The scanning exposure is performed by each of the laser scanner units 4a, 4b, 4c, and 4d, thereby removing the charges on the exposed portions of the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Thereby, electrostatic latent images are formed on the respective surfaces of the photosensitive drums 2a, 2b, 2c, and 2d.

  The developing devices 16a, 16b, 16c, and 16d are provided corresponding to the photosensitive drums 2a, 2b, 2c, and 2d, respectively, and are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the developing devices 16a, 16b, 16c, and 16d attaches the toner of each color to the electrostatic latent image formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, and converts the color toner image into the photosensitive drum. 2a, 2b, 2c and 2d are formed on the respective surfaces. Each of the developing devices 16a, 16b, 16c, and 16d corresponds to four colors of yellow, cyan, magenta, and black. Each of the developing devices 16a, 16b, 16c, and 16d includes a developing roller disposed opposite to the surface of the photosensitive drums 2a, 2b, 2c, and 2d, a stirring roller for stirring the toner, and the like.

  Each of the toner cartridges 5a, 5b, 5c, and 5d is provided corresponding to each of the developing devices 16a, 16b, 16c, and 16d, and each color toner supplied to each of the developing devices 16a, 16b, 16c, and 16d. To accommodate. Each of the toner cartridges 5a, 5b, 5c, and 5d accommodates yellow toner, cyan toner, magenta toner, and black toner.

  The toner supply units 6a, 6b, 6c, and 6d are provided corresponding to the toner cartridges 5a, 5b, 5c, and 5d and the developing devices 16a, 16b, 16c, and 16d, respectively. The toners of the respective colors accommodated in 5d are supplied to the developing devices 16a, 16b, 16c, and 16d, respectively. Each of the toner supply units 6a, 6b, 6c, and 6d and each of the developing devices 16a, 16b, 16c, and 16d are connected by a toner supply path (not shown).

  To the intermediate transfer belt 7, the toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred. The intermediate transfer belt 7 is stretched around a driven roller 35, a counter roller 18 including a driving roller, a tension roller 36, and the like. Since the tension roller 36 biases the intermediate transfer belt 7 from the inside to the outside, a predetermined tension is applied to the intermediate transfer belt 7.

  Primary transfer rollers 37a, 37b, 37c, and 37d are arranged to face each other on the side opposite to the photosensitive drums 2a, 2b, 2c, and 2d with the intermediate transfer belt 7 interposed therebetween.

  A predetermined portion of the intermediate transfer belt 7 is sandwiched between the primary transfer rollers 37a, 37b, 37c, and 37d and the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The predetermined portion thus sandwiched is pressed against the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Primary transfer nips N1a, N1b, N1c, and N1d are formed between the photosensitive drums 2a, 2b, 2c, and 2d and the primary transfer rollers 37a, 37b, 37c, and 37d, respectively. In each of the primary transfer nips N1a, N1b, N1c, and N1d, the toner images of the respective colors developed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred onto the intermediate transfer belt 7, respectively. As a result, a full-color toner image is formed on the intermediate transfer belt 7.

  To the primary transfer rollers 37a, 37b, 37c, and 37d, toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are respectively transferred to the intermediate transfer belt 7 by a primary transfer bias applying unit (not shown). A primary transfer bias for transferring the toner image is applied.

  The static eliminators 12a, 12b, 12c, and 12d are arranged to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The static eliminators 12a, 12b, 12c, and 12d respectively irradiate the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d to irradiate light, and the photosensitive drums 2a, 2b, and 2c after the primary transfer is performed. 2d, each surface is neutralized (charge is removed).

  The drum cleaning units 11a, 11b, 11c, and 11d are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. Each of the drum cleaning units 11a, 11b, 11c, and 11d removes toner and adhering matter remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and conveys the removed toner to a predetermined recovery mechanism. And collect it.

  The secondary transfer roller 8 secondarily transfers the full color toner image primarily transferred to the intermediate transfer belt 7 to the transfer material T. A secondary transfer bias for transferring the full color toner image formed on the intermediate transfer belt 7 to the transfer material T is applied to the secondary transfer roller 8 by a secondary transfer bias applying unit (not shown).

  The secondary transfer roller 8 contacts or separates from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is configured to be movable between a contact position where the secondary transfer roller 8 is in contact with the intermediate transfer belt 7 and a spaced position where the secondary transfer roller 8 is separated from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is disposed at the contact position when the full-color toner image primarily transferred onto the surface of the intermediate transfer belt 7 is secondarily transferred to the transfer material T, and in other cases. Is disposed at a separated position.

  A counter roller 18 is disposed on the opposite side of the intermediate transfer belt 7 from the secondary transfer roller 8. A predetermined portion of the intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the opposing roller 18. Then, the transfer material T is pressed against the outer surface of the intermediate transfer belt 7 (the surface on which the toner image is primarily transferred). A secondary transfer nip N <b> 2 is formed between the intermediate transfer belt 7 and the secondary transfer roller 8. In the secondary transfer nip N2, the full-color toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the transfer material T.

The fixing device 9 fuses and presses the toner of each color constituting the toner image secondarily transferred to the transfer material T to fix it on the transfer material T. The fixing device 9 includes a heating roller 9a as a first rotating body, a pressure roller 920 as a second rotating body, and a third rotating body that are heated by heaters 913 and 913 (see FIGS. 4A and 4B) described later. A first tension roller 930, a pressure roller 920, a rotary belt 9b stretched over the first tension roller 930, a second tension roller 940 as a fourth rotating body, and a guide member 960. . The heating roller 9a and the pressure roller 920 sandwich and press the transfer material T onto which the toner image has been secondarily transferred via the rotating belt 9b, and convey the material. When the transfer material T is conveyed while being sandwiched between the heating roller 9a and the rotating belt 9b, the toner transferred to the transfer material T is melted and pressed to be fixed to the transfer material T. Is done.
Details of the configuration of the fixing device 9 will be described later.

Next, the paper supply / discharge unit KH will be described.
As shown in FIG. 1, a paper feed cassette 52 that accommodates a transfer material T is disposed below the apparatus main body M. The paper feed cassette 52 is configured to be pulled out from the housing of the apparatus main body M in the horizontal direction. A placement plate 60 on which the transfer material T is placed is disposed in the paper feed cassette 52. In the paper feed cassette 52, the transfer material T is accommodated in a state of being stacked on the mounting plate 60. The material T to be transferred placed on the placement plate 60 is sent out to the transport path L by the cassette paper feed unit 51 disposed at the end of the paper feed cassette 52 on the paper feed side (the left end in FIG. 1). It is. The cassette paper feed unit 51 includes a forward feed roller 61 for taking out the transfer material T on the mounting plate 60 and a feed roller pair 81 for sending the transfer material T one by one to the transport path L. A double feed prevention mechanism is provided.

  A manual paper feed unit 64 is provided on the left side surface (left side in FIG. 1) of the apparatus main body M. The manual paper feed unit 64 is provided mainly for supplying to the apparatus main body M a transfer material (paper, envelope, etc.) T having a size and type different from that of the transfer material T set in the paper feed cassette 52. . The manual paper feed unit 64 includes a manual feed tray 65 that forms a part of the left side surface of the apparatus main body M in the closed state, and a paper feed roller 66. The lower end of the manual feed tray 65 is attached to the vicinity of the paper feed roller 66 so as to be rotatable (openable and closable). The transfer material T is placed on the open manual feed tray 65. The paper feed roller 66 feeds the transfer material T placed on the open manual feed tray 65 to the manual feed path La.

  The conveyance path L for conveying the transfer material T includes a first conveyance path L1 from the cassette paper feeding unit 51 to the secondary transfer nip N2, a second conveyance path L2 from the secondary transfer nip N2 to the fixing device 9, and A third conveyance path L3 from the fixing device 9 to the paper discharge section 50, a manual conveyance path La that joins the transfer material T supplied from the manual sheet feeding section 64 to the first conveyance path L1, and a third conveyance path L3. And a return conveyance path Lb that reverses the transfer material T that conveys the medium from the downstream side to the upstream side and returns it to the first conveyance path L1.

Moreover, the 1st junction part P1 and the 2nd junction part P2 are provided in the middle of the 1st conveyance path L1. A first branch portion Q1 is provided in the middle of the third transport path L3.
The first joining part P1 is a joining part where the manual feed path La joins the first transport path L1. The second junction P2 is a junction where the return conveyance path Lb merges with the first conveyance path L1.
The first branch portion Q1 is a branch portion where the return transport path Lb branches from the third transport path L3.

  A transfer material detection sensor (not shown) for detecting the transfer material T is provided in the middle of the first transport path L1 (specifically, between the second joining portion P2 and the secondary transfer roller 8). A registration roller pair 80 is arranged for adjusting the skew (oblique feeding) of the transfer material T and the formation of the toner image in the image forming unit GK. The transfer material detection sensor is disposed immediately before the registration roller pair 80 in the transport direction of the transfer material T (upstream in the transport direction). The registration roller pair 80 conveys the transfer material T by performing the above correction and timing adjustment based on the detection signal information from the transfer material detection sensor.

  An intermediate roller pair 82 is disposed between the first joining portion P1 and the second joining portion P2 in the first transport path L1. The intermediate roller pair 82 is disposed on the downstream side of the paper feed roller pair 81, sandwiches the transfer material T transported from the paper feed roller pair 81, and transports it to the registration roller pair 80.

  The return conveyance path Lb is a conveyance path that is provided so that the opposite surface (non-printing surface) to the intermediate transfer belt 7 is opposed to the surface already printed when performing double-sided printing on the transfer material T. According to the return transport path Lb, the transfer material T transported from the first branching section Q1 to the paper discharge section 50 is reversed and returned to the first transport path L1 to the upstream side of the secondary transfer roller 8. It can be conveyed upstream of the registered registration roller pair 80. A predetermined toner image is transferred onto the non-printing surface at the secondary transfer nip N2 on the transfer material T that is reversed upside down by the return conveyance path Lb.

  A rectifying member 58 is provided in the first branch portion Q1. The rectifying member 58 rectifies the conveyance direction of the transfer material T, which is carried out of the fixing device 9 and conveyed from the upstream side to the downstream side, in the direction toward the paper discharge unit 50, and discharged. The transport direction of the transfer material T transported from the unit 50 along the third transport path L3 from the downstream side toward the upstream side is rectified in a direction toward the return transport path Lb.

  A paper discharge unit 50 is formed at the end of the third transport path L3. The paper discharge unit 50 is disposed on the upper side of the apparatus main body M. The paper discharge unit 50 opens toward the right side of the apparatus main body M (the right side in FIG. 1). The paper discharge unit 50 discharges the transfer material T to the outside of the apparatus main body M. The paper discharge unit 50 includes a discharge roller pair 53. According to the discharge roller pair 53, the transfer material T transported from the upstream side to the downstream side in the third transport path L3 is discharged to the outside of the apparatus main body M, and the transfer material T is transported in the discharge unit 50. The transfer material T can be transported toward the upstream side of the third transport path L3 by reversing the direction.

On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the apparatus main body M. The paper discharge stacking unit M1 is a part formed by the upper surface of the apparatus main body M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the apparatus main body M. In the paper discharge stacking unit M1, a transfer material T on which a predetermined toner image is formed and discharged from the paper discharge unit 50 is stacked and stacked.
A sensor for detecting a transfer material is arranged at a predetermined position on each conveyance path.

Next, a configuration related to the fixing device 9 which is a characteristic part of the printer 1 of the present embodiment will be described in detail. FIG. 2A is a perspective view showing the fixing device 9 in the normal fixing mode. FIG. 2B is a perspective view showing the fixing device 9 in the cylindrical object fixing mode. 3A is a cross-sectional view of the fixing device 9 in the normal fixing mode, taken along the line AA shown in FIG. 2A.
3B is a cross-sectional view of the fixing device 9 in the cylindrical object fixing mode, taken along the line BB in FIG. 2B. FIG. 4A is an explanatory diagram conceptually showing the fixing device 9 in the normal fixing mode. FIG. 4B is an explanatory diagram conceptually showing the fixing device 9 in the cylindrical object fixing mode. FIG. 5 is a functional block diagram relating to the control of the fixing mode changing mechanism 510 in the fixing device 9.

In the description of the printer 1 of the present embodiment, the rotational axis direction of various rotating bodies (rollers, belts, etc.) in the photosensitive drums 2a to 2d, the fixing device 9 and the like is referred to as “Y direction” (direction passing through FIG. 2A etc.). The Y direction is also a direction orthogonal to the transport direction D1 of the transfer material T (see FIGS. 4A and 4B). In the Y direction, the front side in FIG. 1 is also referred to as “+ (plus) side”, and the rear side in FIG. 1 is also referred to as “− (minus) side”. The direction that is horizontal and orthogonal to the Y direction is referred to as the “X direction”. In the X direction, the right side in FIG. 1 is also referred to as “+ side”, and the left side in FIG. 1 is also referred to as “− (minus) side”. The vertical direction is referred to as the Z direction (also a direction orthogonal to the X direction and the Y direction). In the Z direction, the upper side is also referred to as “+ side” and the lower side is also referred to as “− (minus) side”.
Further, as shown in FIGS. 2A to 4B, the specific description of the fixing device 9 and the like will be made with reference to the view from the “− (minus) side” in the Y direction in FIG.

  As shown in FIGS. 4A and 4B, the fixing device 9 of the present embodiment has a transfer material (non-fixed toner image (toner TN) transferred (formed) on the peripheral surface of the heated heating roller 9a (transferred material). (Paper, envelope, etc.) T is conveyed in the conveying direction D1 while being pressed by the rotating belt 9b. Accordingly, the fixing device 9 melts the toner image while heating and pressing to fix (fix) the toner image on the surface of the transfer material T.

  Further, the fixing device 9 includes a normal fixing mode (see FIG. 3A and the like) in which a fixing operation is performed on a normal transfer material (transfer material other than a cylindrical material, for example, paper) T, and a cylindrical material such as an envelope. On the other hand, it is possible to switch between two fixing modes, a cylindrical material fixing mode (see FIG. 3B and the like) in which a fixing operation is performed. Although details will be described later, as shown in FIG. 5, the fixing mode change control unit 970 having a fixing nip pressure change control unit 971 and a fixing nip length change control unit 972 performs switching of the fixing mode. This is done by controlling the driving of a fixing mode changing mechanism 510 having a changing unit 511 and a fixing nip length changing unit 512.

  2A to 5, the fixing device 9 includes a fixing frame (not shown), a heating roller 9a, a heater 913, a pressure roller 920, a first tension roller 930, and a pressure roller 920. A rotation belt 9b stretched over the first tension roller 930, a second tension roller 940, a guide member 960, a fixing nip pressure changing unit 511 and a fixing nip length changing unit 512, and a fixing mode changing mechanism 510. A fixing mode change control unit 970 (see FIG. 5) having a fixing nip pressure change control unit 971 and a fixing nip length change control unit 972.

The fixing mode changing mechanism 510 changes the fixing mode.
In the normal fixing mode and the cylindrical object fixing mode, the fixing mode changing mechanism 510 is driven to move the pressure roller 920 in a direction toward the heating roller 9a or away from the heating roller 9a. As a result, the nip pressure of the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN) shown in FIGS. 4A and 4B is changed.
Further, the fixing mode changing mechanism 510 moves the second tension roller 940 relative to the heating roller 9a, so that the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN) shown in FIGS. 4A and 4B is moved. Change the nip length.
The fixing mode change control unit 970 controls the driving of the fixing mode change mechanism 510.

  Each component constituting the fixing device 9 will be described in detail. The fixing frame (not shown) constitutes the casing of the fixing device 9. A heating roller 9a, a pressure roller 920, a first tension roller 930, and the like are rotatably connected to the fixing frame. The fixing device 9 constitutes one assembly from these components. The fixing device 9 is mounted on the case body BD (see FIG. 1) in the printer 1 (see FIG. 1) in the assembled state.

  The heating roller 9a will be described. As shown in FIGS. 2A and 2B, the heating roller 9a is configured to be rotatable about a first rotation axis J1 extending in the Y direction. The heating roller 9a includes a heating roller main body 911 and a first shaft member 912 that is coaxial with the first rotation axis J1. The heating roller main body 911 includes a cylindrical metal member and a release layer formed on the outer peripheral surface of the metal member. For example, the heating roller body 911 is provided with a magnetic metal layer plated with nickel or the like on the outer peripheral surface of a metal tube such as aluminum or iron having a diameter of about 40 mm, and a PFA having a thickness of about 20 μm on the outer peripheral surface of the magnetic metal layer. It is formed by providing a release layer made of a fluororesin such as (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).

  The first shaft member 912 is formed so as to protrude outward from the both ends of the heating roller body 911 in the Y direction. The first shaft member 912 is rotatably supported via a bearing (not shown) in the case body BD or the like. A driving source (not shown) such as a motor is connected to the first rotating shaft J1. The heating roller 9a is configured to be rotationally driven by this drive source via the first shaft member 912. Thereby, the heating roller 9a can rotate around the first rotation axis J1 extending in the Y direction. The heating roller 9a does not move relative to the case body BD in the printer 1.

  As shown in FIGS. 4A and 4B, two heaters 913 are arranged inside the heating roller 9a. The two heaters 913 are arranged in parallel so that the axial direction thereof is parallel to the first rotation axis J1 (Y direction) of the heating roller 9a. The heater 913 generates heat when energized, and heats the heating roller 9a from the inside. The heater 913 is composed of, for example, a halogen heater or a ceramic heater. The heater 913 heats the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN) via the heating roller 9a.

  The pressure roller 920 will be described. As shown in FIGS. 2A and 2B, the pressure roller 920 is configured to be rotatable about a second rotation axis J2 extending in the Y direction parallel to the first rotation axis J1. The pressure roller 920 includes a pressure roller body 921 and a second shaft member 922 that is coaxial with the second rotation axis J2. The pressure roller main body 921 has an elastic layer having a predetermined thickness made of silicon rubber or the like on the outer periphery of a metal columnar member, and is formed in a columnar shape having a predetermined outer diameter. A fluorine-based release layer is formed on the surface of the elastic layer.

The second shaft member 922 is formed so as to protrude outward from the both ends of the pressure roller main body 921 in the Y direction. The second shaft member 922 is rotatably supported via a bearing (not shown) in a fixing frame or the like.
The pressure roller 920 is disposed on the opposite side of the heating roller 9a across the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN). Accordingly, the pressure roller 920 is disposed so as to be rotatable about the second rotation axis J2 and opposed to the heating roller 9a. The pressure roller 920 changes the nip pressure in the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN) so as to move in a direction toward the heating roller 9a or in a direction away from the heating roller 9a. The pressure roller 920 does not substantially move relative to the case body BD in the printer 1, but has a minute amount for changing the nip pressure in the fixing nip N9 (the main fixing nip MN and the auxiliary fixing nip HN). Movement is allowed.

  Although the details will be described later, the fixing mode changing mechanism 510 includes an operation arm 524 that can press the pressure roller 920 toward the heating roller 9a. The operation arm 524 swings with respect to the fixing frame. By the swinging of the operation arm 524, the operation arm 524 presses or releases the pressure roller 920 in the direction toward the heating roller 9a or away from the heating roller 9a, and the fixing nip N9 is released. The nip pressure in the (main fixing nip MN and auxiliary fixing nip HN) is changed.

  Specifically, as shown in FIGS. 2A and 2B, the operation arm 524 is located at a position (see FIG. 2A) that contacts the outer peripheral surface of the second shaft member 922 of the pressure roller 920 or the second shaft of the pressure roller 920. It is comprised so that it may be located in the position (refer FIG. 2B) spaced apart from the outer peripheral surface of the member 922. FIG. As a result, the pressure roller 920 is in two different stages of pressing against the heating roller 9a. The two-stage pressing state of the pressure roller 920 includes a “normal fixing nip pressure state” in which the pressure roller 920 most strongly presses the outer peripheral surface of the heating roller 9a via the rotating belt 9b, and a pressure roller for the heating roller 9a. “Cylinder fixing nip pressure state” in which the pressing force of 920 is smaller than the pressing force in the normal fixing nip state.

As will be described later, the position of the rotating belt 9b is also changed corresponding to the two-stage pressing state of the pressure roller 920. The change of the position of the rotating belt 9b is performed by the fixing mode changing mechanism 510, similarly to the change of the pressing state of the pressure roller 920.
In the normal fixing mode, the pressing state in which the pressure roller 920 presses the heating roller 9a via the rotating belt 9b is a normal fixing nip pressure state. In the cylindrical object fixing mode, the pressing state in which the pressure roller 920 presses the heating roller 9a is the cylindrical object fixing nip pressure state.

  The first tension roller 930 will be described. As shown in FIGS. 2A and 2B, the first tension roller 930 is configured to be rotatable about a third rotation axis J3 extending in the Y direction and parallel to the first rotation axis J1. The first tension roller 930 includes a first tension roller main body 931 and a third shaft member 932 coaxial with the third rotation axis J3. The first tension roller body 931 is formed of a cylindrical metal material or the like and has a predetermined outer diameter.

The third shaft member 932 is formed so as to protrude from the both ends of the first tension roller body 931 outward in the Y direction. The third shaft member 932 is rotatably supported via a bearing (not shown) in a fixing frame or the like. As a result, the first tension roller 930 can rotate around the third rotation axis J3 extending in the Y direction. The first tension roller 930 does not move relative to the case body BD in the copying machine 1.
The first tension roller 930 is disposed at a position separated from the pressure roller 920 on the minus side (minus side) in the Z direction.

  The rotating belt 9b will be described. As shown in FIGS. 3A to 4B, the rotating belt 9b has a predetermined width and a predetermined length, and is composed of an annular (band-shaped) endless belt that can rotate in the ring direction. The rotating belt 9b is formed of a heat-resistant flexible material, for example, by providing a nonmagnetic metal layer such as a SUS (stainless steel) plating having a thickness of about 50 μm on the outer peripheral surface of the polyimide film. An elastic layer of silicon rubber having a thickness of 100 μm is provided on the outer peripheral surface of the layer, and further, a release layer made of a fluororesin such as PFA having a thickness of about 50 μm is provided on the outer peripheral surface of the elastic layer. .

The rotating belt 9b is wound around the pressure roller 920 and the first tension roller 930 so as to be able to go around. The outer peripheral surface of the pressure roller 920 and the outer peripheral surface of the first tension roller 930 are in contact with the inner peripheral surface of the rotating belt 9b. The rotating belt 9b is formed in a ring shape so as to be rotatable in a rotating direction (ring direction) R.
As shown in FIGS. 4A and 4B, the rotating belt 9b is disposed so as to contact the heating roller 9a. The rotating belt 9b includes a first portion 951 sandwiched between the heating roller 9a and the pressure roller 920, and a second portion 952 formed continuously from the first portion 951 and in contact with the heating roller 9a.

  The outer peripheral surface of the first tension roller 930 is in contact with the inner peripheral surface of the rotating belt 9b. The first tension roller 930 is disposed upstream of the first portion 951 of the rotating belt 9b in the transport direction D1 of the transfer material T. The first tension roller 930 presses the inner peripheral surface of the rotating belt 9b hung on the pressure roller 920 outward. As a result, the first tension roller 930 applies tension to the rotating belt 9b so as to extend in the rotation direction R.

  The second tension roller 940 will be described. As shown in FIGS. 2A to 4B, the second tension roller 940 is disposed between the pressure roller 920 and the first tension roller 930 in the Z direction. The second tension roller 940 is located between the pressure roller 920 and the first tension roller 930 in the rotating belt 9b and in the inner circumference of the upstream portion 965 positioned upstream of the fixing nip N9 in the ring direction R of the rotating belt 9b. A roller that presses the surface.

  The second tension roller 940 is configured to be rotatable about a fourth rotation axis J4 that is parallel to the first rotation axis J1 and extends in the Y direction. The second tension roller 940 includes a second tension roller main body 941 and a fourth shaft member 942 that is coaxial with the fourth rotation axis J4. The second tension roller main body 941 is formed of a cylindrical metal material or the like and has a predetermined outer diameter. The fourth shaft member 942 is formed so as to protrude from the both ends of the second tension roller body 941 outward in the Y direction. The second tension roller 940 is supported by a support hole 533 of the operation plate member 530 described later so as to be rotatable and movable by a predetermined distance in the X direction.

  Further, the second tension roller 940 is urged toward a direction toward the heating roller 9a (minus side in the X direction) by a second urging member (not shown). Therefore, like the first tension roller 930, the second tension roller 940 presses the inner peripheral surface of the rotary belt 9b hung on the pressure roller 920 and the first tension roller 930 outward. As a result, the second tension roller 940 applies tension to the rotating belt 9b so as to extend in the rotation direction R.

  Although details will be described later, the fixing mode changing mechanism 510 includes an operation plate member 530 that moves to the plus side in the X direction and the minus side in the X direction. The operation plate member 530 resists the urging force of a first urging member (not shown) that urges the guide member 960 and a second urging member (not shown) that urges the second tension roller 940. The member 960 and the second tension roller 940 are pressed in the direction toward the heating roller 9a (plus side in the X direction). Thereby, the operation plate member 530 in the fixing mode changing mechanism 510 moves the second tension roller 940 in a direction toward the heating roller 9a (X direction plus side) or away from the heating roller 9a (X direction minus side). .

  Specifically, as shown in FIGS. 2A to 3B, the second tension roller 940 is configured to be capable of taking two different contact positions by the movement of the operation plate member 530. The two-stage contact position includes the “normal fixing position” where the outer peripheral surface of the second tension roller 940 is in contact with the inner peripheral surface of the upstream portion 965 of the rotating belt 9b, and the upstream portion 965 of the rotating belt 9b. The “cylindrical material fixing position” is located inside the rotating belt 9b from the fixing position.

The two-stage contact position corresponds to the two-stage pressing state of the pressure roller 920 described above. Thereby, the fixing mode can be switched between the “normal fixing mode” and the “cylindrical material fixing mode”.
Specifically, in the normal fixing mode, the pressing state in which the pressure roller 920 presses against the heating roller 9a is the “normal nip pressure state”, and the position of the upstream portion 965 on the rotating belt 9b is the “normal fixing position”. In this case, the fixing mode is used.
Further, in the cylindrical object fixing mode, the pressing state in which the pressure roller 920 presses toward the heating roller 9a is the “cylindrical object nip pressure state”, and the position of the upstream portion 965 in the rotating belt 9b is “cylindrical. This is the fixing mode in the case of the “object fixing position”.

  The heating roller 9a, the pressure roller 920, the rotating belt 9b, the first tension roller 930, and the second tension roller 940 rotate as follows. Specifically, when the heating roller 9a rotates, the rotating belt 9b that contacts the outer peripheral surface of the heating roller 9a is driven to rotate. As the rotating belt 9b rotates, the first tension roller 930, the pressure roller 920, and the second tension roller 940 that are in contact with the inner peripheral surface of the rotating belt 9b are driven to rotate.

The first part 951 and the second part 952 in the rotating belt 9b will be further described.
As shown in FIGS. 4A and 4B, in the rotating belt 9b, the first portion 951 is a portion sandwiched between the heating roller 9a and the pressure roller 920. In the rotating belt 9b, the second portion 952 is a portion that is formed continuously with the first portion 951 and is in contact with the heating roller 9a.

Specifically, the pressure roller 920 is disposed so as to press the heating roller 9a via the rotating belt 9b. As a result, the pressure roller 920 is elastically deformed along the surface shape of the heating roller 9a via the rotating belt 9b at the portion facing the heating roller 9a. The pressure roller 920 sandwiches a part of the rotating belt 9b with the heating roller 9a. Thus, the pressure roller 920 forms a first portion 951 as a sandwiched portion of the rotating belt 9b by sandwiching a part of the rotating belt 9b between the pressure roller 920 and the heating roller 9a. To do.
The second portion 952 is a portion continuous with the first portion 951, and is in contact with the heating roller 9a, but is formed from a portion that is not sandwiched between the heating roller 9a and the pressure roller 920.

The fixing nip N9 will be described. As shown in FIGS. 4A and 4B, the fixing nip N9 includes a main fixing nip MN and an auxiliary fixing nip HN.
The main fixing nip MN is a nip formed by the first portion 951 of the rotating belt 9b and the portion of the heating roller 9a facing the first portion 951.
The auxiliary fixing nip HN is a nip that is formed by the second portion 952 of the rotating belt 9b and the portion of the heating roller 9a facing the second portion 952, and is located continuously with the main fixing nip MN.
As described above, the nip length (area) of the fixing nip N9 is increased by forming the auxiliary fixing nip HN continuous to the main fixing nip MN in addition to the main fixing nip MN.

  The guide member 960 will be described. As shown in FIGS. 4A and 4B, the guide member 960 is a member for guiding the transfer material T conveyed on the second conveyance path L2 (see FIG. 1) to the fixing nip N9. The guide member 960 is located between the pressure roller 920 and the first tension roller 930 in the rotating belt 9b, and faces the upstream portion 965 located upstream of the fixing nip N9 in the ring direction R of the rotating belt 9b. Arranged. The guide member 960 is disposed away from the rotary belt 9b.

  The guide member 960 is formed of a substantially rectangular plate material. The guide member 960 is disposed at a position and an angle at which the transfer material T conveyed on the second conveyance path L2 can be guided to the fixing nip N9. In the present embodiment, in the Z direction, the guide member 960 is formed so as to extend from the position facing the outer peripheral surface of the upstream portion 965 of the rotating belt 9b to the minus side in the Z direction. In the Y direction, the guide member 960 is formed to extend in the Y direction by the length of the width of the rotating belt 9b corresponding to the width of the rotating belt 9b. That is, part of the guide member 960 is disposed substantially parallel to the ZY plane so as to face the outer peripheral surface of the upstream portion 965 of the rotating belt 9b.

As shown in FIGS. 3A and 3B, the end of the guide member 960 opposite to the fixing nip N9 is fixed to the support member 963. The support member 963 is disposed at a position spaced apart from the first tension roller 930 on the negative side in the Z direction.
The guide member 960 is urged by a first urging member (not shown) in the direction in which the end portion on the fixing nip N9 side is directed toward the rotating belt 9b (toward the minus side in the X direction).

The fixing mode changing mechanism 510 will be described.
The fixing mode changing mechanism 510 includes a fixing nip pressure changing unit 511 and a fixing nip length changing unit 512.
The fixing nip pressure changing unit 511 moves the pressure roller 920 toward the heating roller 9a or away from the heating roller 9a so that the nip pressure at the fixing nip N9 is greater than the first nip pressure and the first nip pressure. Is also changed to a small second nip pressure.

  Further, the fixing nip length changing unit 512 changes the position of the upstream portion 965 in the rotating belt 9b by changing the position of the second tension roller 940. As a result, the fixing nip length changing unit 512 changes the nip length of the fixing nip N9.

  Specifically, the fixing nip length changing unit 512 changes the nip length by changing the position of the upstream portion 965 by the second tension roller 940 pressing the inner peripheral surface of the upstream portion 965 in the rotating belt 9b. Let The fixing nip length changing unit 512 changes the nip length to a first nip length and a second nip length shorter than the first nip length.

The fixing nip pressure changing unit 511 will be described in detail.
2A to 3B, the fixing nip pressure changing unit 511 includes an operation arm 524 that presses the pressure roller 920, an operation arm shaft member 525 that rotatably supports the operation arm 524, and an operation arm 524. The operation fitting 521 that operates in conjunction with the swing of the movement, the mode change cam 515 that presses the operation fitting 521, and the operation fitting 521 are biased toward the mode change cam 515 (to the minus side in the Z direction). Third urging member 522, push rod 523 that supports third urging member 522, restriction arm 505 that restricts movement of push rod 523 to the plus side in the Z direction, and gear that drives mode change cam 515 A drive mechanism (not shown), and a cam shaft member 516 that couples the mode change cam 515 and the gear drive mechanism.

  Each component in the fixing mode changing mechanism 510 is provided in a pair in the Y direction except for the gear driving mechanism. Only one of the pair of components in the Y direction will be described unless otherwise required. The gear drive mechanism is provided only on the plus side in the Y direction.

  As shown in FIGS. 2A to 3B, the operation arm 524 is an arm-shaped member and is formed of a plate material having a predetermined thickness such as a steel plate. The operation arm 524 includes a roller pressing portion 524A, a fulcrum hole portion 524B, and an extending portion 524C.

  The roller pressing portion 524A is disposed on the positive side in the Z direction of the second shaft member 922 of the pressure roller 920. The lower surface (surface formed by the thickness portion) of the roller pressing portion 524A faces the outer peripheral surface of the second shaft member 922 of the pressure roller 920. The lower surface of the roller pressing portion 524A is curved so as to follow the outer peripheral surface of the second shaft member 922.

  The roller pressing portion 524A can press the outer peripheral surface of the second shaft member 922 of the pressure roller 920 from the plus side in the Z direction. The roller pressing portion 524A is separated from a position for pressing the pressure roller 920 so as to move in the direction toward the heating roller 9a (see FIG. 2A) and so as to move the pressure roller 920 in a direction away from the heating roller 9a. Position (see FIG. 2B).

  The fulcrum hole 524B is formed at the end on the plus side in the X direction of the roller pressing portion 524A. The operation arm 524 is supported by the operation arm shaft member 525 so as to be rotatable about the fulcrum hole 524B. The operation arm shaft member 525 is formed to extend in the Y direction and is supported by the case body BD of the printer 1 or the like. The operation arm shaft member 525 does not move relative to the case body BD.

  Accordingly, the operation arm 524 can swing with respect to the fixing frame in the XZ plane with the fulcrum hole 524B as a fulcrum. When the operating arm 524 swings around the fulcrum hole 524B as a fulcrum, the pressure roller 920 moves to the heating roller 9a via the rotating belt 9b so as to move in a direction toward the heating roller 9a or away from the heating roller 9a. Pressing or pressing is released.

  The extending part 524C is a part extending from the roller pressing part 524A to the minus side in the predetermined length X direction. An upper end portion (a positive end portion in the Z direction) of a vertical arm 521B of the operation fitting 521, which will be described later, is connected and fixed to an end portion on the negative side in the X direction of the extending portion 524C.

  The operation fitting 521 will be described. As shown in FIGS. 2A to 3B, the operation fitting 521 has a horizontal arm 521A extending in the X direction and a vertical arm 521B extending in the Z direction. The operation fitting 521 has a shape in which the horizontal arm 521A and the vertical arm 521B are bent in an L shape. That is, the horizontal arm 521A and the vertical arm 521B are orthogonal to each other. The operation fitting 521 is formed from a plate material having a predetermined thickness such as a steel plate.

  As shown in FIGS. 2A to 3B, the horizontal arm 521A is arranged on the upper side (plus side in the Z direction) of a mode change cam 515 described later. The lower surface of the horizontal arm 521A faces the mode change cam 515. A through hole 521C is formed in the horizontal arm 521A. A push rod 523 is disposed through the through hole 521C. The lateral arm 521A is urged by the third urging member 522 in the direction toward the mode change cam 515 (toward the negative side in the Z direction).

As described above, the operation arm 524 is connected and fixed to the upper end portion (the end portion on the plus side in the Z direction) of the vertical arm 521B. Therefore, the operation fitting 521 is fixed without moving relative to the operation arm 524. That is, the operation arm 524 and the operation fitting 521 integrally swing with respect to the fixing frame in the XZ plane with the fulcrum hole 524B as a fulcrum.
Since the operation arm 524 and the operation fitting 521 swing together, the movement of the operation arm 524 to the negative side in the Z direction is restricted at a position where the operation arm 524 contacts the outer peripheral surface of the second shaft member 922 of the pressure roller 920. The

Next, the mode change cam 515 will be described.
As shown in FIGS. 2A to 3B, the mode change cam 515 is composed of two sheets of the same shape with a predetermined thickness. The mode change cam 515 has an outer edge in which a plurality of curves and a plurality of straight lines are combined, and is formed by a member that is long in one direction.
The mode change cam 515 is disposed on the lower side (minus side in the Z direction) of the horizontal arm 521A of the operation fitting 521. The mode change cam 515 is configured by arranging two plate members facing each other so as to sandwich the push rod 523. The mode change cam 515 is eccentrically connected to the cam shaft member 516 on the end side in the Y direction of the cam shaft member 516.
The mode changing cam 515 rotates in an eccentric state by rotating about the axis center J5 of the cam shaft member 516. That is, the mode change cam 515 has a so-called eccentric cam function.

  The outer peripheral surface of the mode change cam 515 is a cam surface. The cam surface includes a first arcuate portion 515A, a first straight portion 515B, and a second arcuate portion 515C.

  The first arcuate portion 515A has an arcuate edge at a position farthest from the axial center J5 of the cam shaft member 516. The first straight portion 515B is formed on the opposite edge of the first arcuate portion 515A with the camshaft member 516 interposed therebetween, and the distance from the axial center J5 of the camshaft member 516 is greater than that of the first arcuate portion 515A. Are also formed in a straight line at close positions.

  The second arcuate portion 515C is formed continuously with the first straight portion 515B, and is formed in an arc shape at a position where the distance from the axial center J5 of the cam shaft member 516 is closer to the first straight portion 515B.

  That is, the mode change cam 515 has the cam surfaces of the first arc-shaped portion 515A, the first linear portion 515B, and the second arc-shaped portion 515C in order from the cam surface far from the axis center J5 of the cam shaft member 516 (the first arc-shaped portion 515C). 1 arc-shaped portion 515A> first straight portion 515B> second arc-shaped portion 515C).

The cam shaft member 516 extends in the Y direction and connects the pair of mode change cams 515. The cam shaft member 516 is rotationally driven around the shaft center J5 by a gear drive mechanism (not shown).
By the rotation of the cam shaft member 516, the mode change cam 515 has the first arcuate portion 515A separated from the lateral arm 521A of the operation fitting 521 and the first arcuate portion 515A in the X direction, as shown in FIGS. 2A and 3A. 2B and FIG. 3B, the first arcuate portion 515A comes into contact with the lower surface of the lateral arm 521A of the operation fitting 521 to push up the operation fitting 521, as shown in FIGS. 2B and 3B. The one arcuate portion 515A rotates between a posture (tubular object posture) facing the plus side in the Z direction.

  The third urging member 522 will be described. As shown in FIGS. 2A to 3B, the third urging member 522 is formed of a coil spring having a predetermined length, and is disposed in a state where a push rod 523 described later is disposed on the inner side. That is, the push rod 523 is inserted inside the third urging member 522. The third urging member 522 urges the lateral arm 521A of the operation fitting 521 toward the mode change cam 515 (toward the negative side in the Z direction) by its elastic return force.

  The push rod 523 will be described. As shown in FIGS. 2A to 3B, the push rod 523 is made of an axial member having a predetermined length, and extends along the Z direction. The movement of the upper surface of the upper end portion 523A of the push rod 523 to the plus side in the Z direction is restricted by a restriction arm 505 described later.

  The push rod 523 has a third urging member 522 disposed on the outside thereof, and is inserted through a through hole 521C (see FIGS. 3A and 3B) of the lateral arm 521A of the operation fitting 521. Further, the upper end portion 523A of the push rod 523 is restricted from moving to the plus side in the Z direction by the third urging member 522. Therefore, the third biasing member 522 biases the lateral arm 521A of the operation fitting 521 so as to move toward the mode change cam 515.

As shown in FIGS. 2A to 3B, the restriction arm 505 is made of an arm-like member, and is supported by a holding shaft 506 provided on a fixing frame or the like at a substantially central position in the longitudinal direction. The lower end portion of the restriction arm 505 is in contact with the upper end portion 523A of the push rod 523.
The gear drive mechanism rotationally drives a pair of mode change cams 515 connected to the cam shaft member 516.

  Although details will be described later, the fixing nip pressure changing unit 511 rotates the mode change cam 515 to move the pressure roller 920 in a direction toward the heating roller 9a or in a direction away from the heating roller 9a. The nip pressure of the fixing nip N9 is changed.

Next, the fixing nip length changing unit 512 will be described in detail. The fixing nip length changing unit 512 is partly in common with the fixing nip pressure changing unit 511. For example, the mode change cam 515, the gear drive mechanism (not shown), and the cam shaft member 516 have the same configuration as the fixing nip pressure change unit 511.
More specifically, the fixing nip length changing unit 512 includes a mode changing cam 515, a gear drive mechanism, a cam shaft member 516, and an operation plate member 530.

2A to 3B, the operation plate member 530 is disposed between the guide member 960 and the cam shaft member 516 in the X direction. The operation plate member 530 is disposed outside the end portion in the Y direction with respect to the first tension roller 930 and the second tension roller 940.
The operation plate member 530 is formed in an L-shaped flat plate as a whole.

  2A and 2B, the second tension roller 940 presses the inner peripheral surface of the upstream portion 965 of the rotating belt 9b outward by an unillustrated operation plate guide member or the like. Movement in only the direction or the direction away from the inner peripheral surface of the upstream portion 965 toward the inside is allowed. In the present embodiment, the operation plate member 530 is allowed to move only in the X direction.

The operation plate member 530 has a support hole 533 (see FIGS. 2A and 2B) for supporting the second tension roller 940 on the plus side in the Z direction.
A second tension roller 940 is rotatably connected to the support hole 533. As a result, the operation plate member 530 is biased toward the minus side in the X direction.
The second tension roller 940 supported by the support hole 533 moves a predetermined distance in the X direction when the operation plate member 530 moves in the X direction.

  A first convex portion 531 that protrudes toward the guide member 960 (plus side in the X direction) is formed at the end of the operation plate member 530 on the guide member 960 side. The first convex portion 531 contacts the guide member 960. As a result, the operation plate member 530 is biased toward the minus side in the X direction.

  A second convex portion 532 is formed at the end of the operation plate member 530 on the cam shaft member 516 side so as to protrude toward the mode change cam 515 side (minus side in the X direction). The second convex portion 532 contacts the first linear portion 515B or the second arcuate portion 515C of the mode change cam 515 by the rotation of the mode change cam 515. Thereby, the operation plate member 530 can move in the X direction against the urging force of the guide member 960 according to the position of the cam surface of the mode change cam 515. That is, the operation plate member 530 can move the second tension roller 940 and the guide member 960 in the X direction. Therefore, when the mode change cam 515 rotates, the positions of the second tension roller 940 and the guide member 960 are changed via the operation plate member 530.

  Specifically, the position of the operation plate member 530 in the X direction is changed by the position of the cam surface of the mode change cam 515 that contacts the second convex portion 532 of the operation plate member 530. Specifically, the operation plate member 530 has a first position where the first linear portion 515B formed at a position away from the axis center J5 of the cam shaft member 516 in the mode change cam 515 contacts the second convex portion 532 (FIG. 2A). 3A) and the second position where the second arcuate portion 515C formed at a position where the distance from the cam shaft member 516 is shorter than the first straight portion 515B contacts the second convex portion 532 (FIG. 2B and FIG. 3). 3B) and the two-stage position.

  As described above, the mode change cam 515 has the posture (normal posture) when the operation plate member 530 is in the first position (see FIGS. 2A and 3A) and the operation plate member 530 in the second position (FIGS. 2B and 5B). It is configured to rotate between the posture (cylindrical object posture) in the case of 3B).

  The position of the second tension roller 940 in the X direction is changed by changing the position of the operation plate member 530 in the X direction. Accordingly, the second tension roller 940 changes the position of the upstream portion 965 in the rotating belt 9b.

  In this way, the fixing nip length changing unit 512 uses the mode changing cam 515 that is one of the components thereof, and the second tension roller 940 presses the inner peripheral surface of the upstream portion 965 of the rotating belt 9b. By changing the position of the upstream portion 965, the nip length of the fixing nip N9 is changed.

  Next, the relationship between the fixing nip pressure changing unit 511 and the fixing nip length changing unit 512 in the fixing mode changing mechanism 510 will be described. The fixing mode changing mechanism 510 changes the nip pressure of the fixing nip between the pressure roller 920 and the heating roller 9a using the mode changing cam 515 which is one of the components, and at the same time, the nip length of the fixing nip N9. Change the size.

  In the fixing nip pressure changing portion 511, the position of the operation fitting 521 in the Z direction is defined, and the swing position of the operation arm 524 engaged with the operation fitting 521 is also defined. As a result, the force for pressing the pressure roller 920 against the heating roller 9a is determined.

  The operation fitting 521 moves in the Z direction corresponding to the displacement of the cam surface of the mode change cam 515 due to the rotation of the mode change cam 515. When the operation fitting 521 moves in the Z direction, the operation arm 524 swings. Thereby, the pressure roller 920 pressed by the operation arm 524 is pressed so as to move in a direction toward the heating roller 9a or in a direction away from the heating roller 9a. Thereby, the nip pressure of the fixing nip N9 is changed.

  On the other hand, in the fixing nip length changing unit 512, the operation plate member 530 moves in the X direction corresponding to the displacement of the cam surface due to the rotation of the mode change cam 515. When the operation plate member 530 moves in the X direction, the second tension roller 940 presses the upstream portion 965 of the rotating belt 9b and the direction toward the inner peripheral surface of the upstream portion 965 of the rotating belt 9b or the upstream portion. It moves in a direction away from the inner peripheral surface of 965. As a result, the nip length of the fixing nip N9 is changed.

The mode change cam 515 changes the nip length at the same time as changing the nip pressure of the fixing nip between the pressure roller 920 and the heating roller 9a.
As shown in FIGS. 2A, 3A, and 4A, the mode change cam 515 includes a fixing nip pressure changing portion 511 in which the first arcuate portion 515A is separated from the lateral arm 521A of the operation fitting 521 and the first arcuate portion 515A is X. At the same time as a posture facing the minus side of the direction (normal posture), the first linear portion 515B is brought into contact with the second convex portion 532 of the operation plate member 530 (normal posture) in the fixing nip length changing portion 512.

  As shown in FIGS. 2B, 3B, and 4B, the mode change cam 515 includes the operation fitting 521 in which the first arcuate portion 515A abuts the lower surface of the horizontal arm 521A of the operation fitting 521 in the fixing nip pressure changing portion 511. At the same time as the first arcuate portion 515A is directed to the positive side in the Z direction (tubular object posture), and at the fixing nip length changing portion 512, the second arcuate portion 515C is the second convex portion of the operation plate member 530. It becomes a posture (cylindrical body posture) that contacts 532.

  Next, the fixing mode change control unit 970 will be described. As shown in FIG. 5, the fixing mode change control unit 970 includes a fixing nip pressure change control unit 971 and a fixing nip length change control unit 972. The fixing mode change control unit 970 controls changing of the fixing mode.

  The fixing nip pressure change control unit 971 controls the fixing nip pressure changing unit 511 so that the nip pressure becomes the second nip pressure when the transfer material T is a cylindrical material. Further, the fixing nip pressure change control unit 971 controls the fixing nip pressure changing unit 511 so that the nip pressure becomes the first nip pressure when the transfer material T is other than the cylindrical material.

  The fixing nip length change control unit 972 controls the fixing nip length changing unit 512 so as to change the position where the second tension roller 940 contacts the inner peripheral surface of the upstream portion 965 of the rotating belt 9b. As a result, the fixing nip length change control unit 972 controls the fixing nip length changing unit 512 to change the nip length of the fixing nip N9.

  The fixing nip length changing control unit 972 controls the fixing nip length changing unit 512 so that the nip length is set to the second nip length when the transfer material T is a cylindrical material. Further, the fixing nip length changing control unit 972 controls the fixing nip length changing unit 512 so that the nip length is set to the first nip length when the transfer material T is other than the cylindrical material.

  The fixing mode change control unit 970 is input with fixing mode selection information from a fixing mode selection button 581 provided on the operation panel 580 (see FIG. 5) of the printer 1. The fixing mode change control unit 970 controls the fixing nip pressure changing unit 511 and the fixing nip length changing unit 512 in the fixing mode changing mechanism 510 based on the fixing mode selection information input from the fixing mode selection button 581. .

Next, the fixing mode in the fixing device 9 of this embodiment will be described in detail.
As described above, the mode change cam 515 is rotationally driven by the fixing mode change mechanism 510 controlled by the fixing mode change control unit 970, and the first arcuate portion 515A faces the negative side in the X direction and is located beside the operation fitting 521. A normal posture (see FIGS. 2A and 2A) in which the first straight portion 515B is in contact with the operation plate member 530, and the first arcuate portion 515A is rotated by 90 degrees from the normal posture and the first arcuate portion 515A is on the plus side in the Z direction. Facing the bottom surface of the horizontal arm 521A of the operation fitting 521 to push up the operation fitting 521, and the cylindrical object posture (see FIGS. 2B and 3B) in which the second arcuate portion 515C contacts the operation plate member 530. Can be changed.

  The fixing device 9 is in the normal fixing mode when the mode change cam 515 is in the normal posture, and is in the cylindrical material fixing mode when the mode change cam 515 is in the cylindrical material posture.

  More specifically, as shown in FIGS. 2A, 3A and 4A, when the mode change cam 515 is in the normal posture (normal fixing mode), the mode change cam 515 contacts the horizontal arm 521A of the operation fitting 521. Not in a position. In this state, the operation fitting 521 is located on the most minus side in the movement range in the Z direction. In this state, the operating arm 524 swings most negatively in the Z direction within the swing range. Then, the pressure roller 920 supported by the operation arm 524 is positioned at a normal fixing position where the outer peripheral surface gives the force that most greatly presses the outer peripheral surface of the heating roller 9a.

The nip pressure at the fixing nip N9 in the normal fixing mode is also referred to as “first nip pressure”.
In the normal fixing mode, as shown in FIG. 4A, the pressure roller 920 interferes with the outer peripheral surface of the heating roller 9a and elastically deforms. Then, due to the elastic restoring force of the elastic layer of the pressure roller 920, the pressure roller 920 presses the surface of the rotating belt 9b interposed between the pressure roller 920 and the heating roller 9a against the outer peripheral surface of the heating roller 9a. The main fixing nip MN (MN1) is formed.

  Further, a portion of the rotating belt 9b between the second tension roller 940 and the pressure roller 920 is wound around the outer peripheral surface of the pressure roller 920 (on the upstream side in the conveyance direction D1 of the transfer material T). Then, it is brought into contact with the outer peripheral surface of the heating roller 9a for a predetermined length, and then introduced between the heating roller 9a and the pressure roller 920.

As a result, an auxiliary fixing nip HN (HN1) is formed on the upstream side of the main fixing nip MN in which the outer surface of the rotating belt 9b contacts the outer peripheral surface of the heating roller 9a.
In the normal fixing mode, the nip length in the transport direction D1 of the transfer material T at the main fixing nip MN is also referred to as “nip length MN1”. Further, the nip length of the auxiliary fixing nip HN is also referred to as “nip length HN1”. The nip length MN1 and the nip length HN1 are also collectively referred to as “first nip length”.

  That is, the auxiliary fixing nip HN (HN1) in which only the rotating belt 9b is brought into contact with the outer peripheral surface of the heating roller 9a without being pressed by the pressure roller 920, and the rotating belt 9b is pressed by the pressing roller 920 so that the rotating belt 9b A fixing nip N9 having a first nip length is formed, which is continuous with the main fixing nip MN (MN1) in close contact with the outer peripheral surface.

  As shown in FIG. 4A, in the normal fixing mode in which the fixing nip N9 having the first nip length is formed, the transfer material T is introduced into the main fixing nip MN following the auxiliary fixing nip HN. Thus, the transfer material T on which an unfixed toner image is formed (toner TN is transferred) is pre-pressurized in the auxiliary fixing nip HN and then pressed with a higher pressure in the main fixing nip MN. And will be heated. As a result, it is possible to suppress image disturbance in the fixing process and perform a stable fixing operation.

  On the other hand, as shown in FIGS. 2B, 3B, and 4B, in the cylindrical object fixing mode in which the mode change cam 515 is rotated from the normal attitude to the cylindrical object attitude, the operation fitting 521 has the first arc shape of the mode change cam 515. The portion 515A is pressed to the plus side in the Z direction. Therefore, the operation fitting 521 is operated to the plus side in the Z direction against the urging force of the third urging member 522, and is located most on the plus side in the Z direction in the movement range. As a result, the operation arm 524 swings, and the force that the pressure roller 920 presses toward the heating roller 9a via the rotating belt 9b becomes smaller than that in the normal mode. That is, in the cylindrical object fixing mode, the pressure roller 920 is not pressed toward the heating roller 9a than in the normal fixing mode.

When the nip pressure of the fixing nip N9 in the cylindrical article fixing mode is referred to as “second nip pressure”, the second nip pressure is smaller than the first nip pressure in the normal fixing mode.
In the cylindrical fixing mode, as shown in FIG. 4B, the nip length MN2 of the main fixing nip MN and the nip length HN2 of the auxiliary fixing nip HN are equal to the nip length MN1 of the main fixing nip MN in the normal fixing mode. Further, the nip length HN1 of the auxiliary fixing nip HN becomes shorter (MN2 <MN1, HN2 <HN1).

  A “non-interference state” in which the outer peripheral surface of the pressure roller 920 does not interfere with the outer peripheral surface of the heating roller 9 a can be realized by swinging the restriction arm 505. That is, by swinging the restricting arm 505 in the direction indicated by the arrow D3 in FIG. 2A, the third urging member 522 extends in a substantially free state and does not press the operation fitting 521.

  Accordingly, the operation arm 524 that supports the pressure roller 920 can freely swing, and the pressure roller 920 does not press the outer peripheral surface of the heating roller 9a. As a result, it is possible to easily remove the transfer material T that has caused a conveyance failure such as jamming (JAM) during the fixing process. This is the same whether the mode change cam 515 is in the normal posture or the cylindrical object posture. Although detailed description is omitted, the restricting arm 505 is configured to swing in conjunction with opening of a printer cover (not shown). As a result, when the conveyance failure of the transfer material T such as clogging occurs, the pressure roller 920 can be brought into a non-interference state by opening the printer cover.

Next, the operation of the printer 1 of the present embodiment will be briefly described with reference to FIG.
First, a case where single-sided printing is performed on the transfer material T accommodated in the paper feed cassette 52 will be described.
The transfer material T accommodated in the paper feed cassette 52 is sent out to the first transport path L1 by the forward feed roller 61 and the paper feed roller pair 81, and then passes through the first junction P1 and the first transport path L1. Then, the sheet is conveyed to the registration roller pair 80 by the intermediate roller pair 82.
In the registration roller pair 80, skew correction of the transfer material T and timing adjustment with the toner image are performed.

The transfer material T discharged from the registration roller pair 80 is introduced between the intermediate transfer belt 7 and the secondary transfer roller 8 (secondary transfer nip N2) via the first conveyance path L1. Then, a toner image is transferred onto the transfer material T between the intermediate transfer belt 7 and the secondary transfer roller 8.
Thereafter, the transfer material T is discharged from between the intermediate transfer belt 7 and the secondary transfer roller 8, and is fixed between the heating roller 9a and the rotary belt 9b in the fixing device 9 via the second conveyance path L2. It is introduced into the nip N9. Then, the toner melts in the fixing nip N9 and the toner is fixed to the transfer material T.

Next, the transfer material T is transported to the paper discharge unit 50 through the third transport path L3, and is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1 by the discharge roller pair 53.
In this way, single-sided printing of the transfer material T accommodated in the paper feed cassette 52 is completed.

  When performing single-sided printing on the transfer material T placed on the manual feed tray 65, the transfer material T placed on the manual feed tray 65 is sent out to the manual feed path La by the paper feed roller 66, and then It is conveyed to the registration roller pair 80 via the first junction P1 and the first conveyance path L1. The subsequent operation is the same as the above-described one-side printing operation of the transfer material T accommodated in the paper feed cassette 52, and the description thereof is omitted.

Next, the operation of the printer 1 when performing duplex printing will be described.
In the case of single-sided printing, as described above, the transfer material T on which single-sided printing has been performed is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1 to complete the printing operation.
On the other hand, in the case of performing double-sided printing, the transfer material T on which single-sided printing has been performed is reversely conveyed from the time of single-sided printing and conveyed again to the registration roller pair 80 via the return conveyance path Lb. Thus, double-sided printing is performed on the transfer material T.

  More specifically, the operation is the same as the above-described single-sided printing operation until the transfer material T on which single-sided printing has been performed is discharged from the paper discharge unit 50 by the discharge roller pair 53. Thus, in the case of double-sided printing, in a state where the transfer material T on which single-sided printing has been performed is held by the discharge roller pair 53, the rotation of the discharge roller pair 53 is stopped and rotated in the reverse direction. When the discharge roller pair 53 is thus rotated in the reverse direction, the transfer material T held by the discharge roller pair 53 moves in the reverse direction (from the paper discharge section 50 to the first branch section Q1). Transported in the direction of heading).

  As described above, when the transfer material T is conveyed in the reverse direction on the third conveyance path L3, the transfer material T is rectified to the return conveyance path Lb by the rectifying member 58, and then the second joining portion. It merges with the 1st conveyance path L1 via P2. Here, the material T to be transferred is reversed from the one side printing.

  Further, the transfer material T is corrected or adjusted by the registration roller pair 80, and is introduced between the photosensitive drum 2 and the secondary transfer roller 8 through the first conveyance path L1. Since the non-printing surface of the transfer material T passes through the return conveyance path Lb and faces the secondary transfer roller 8, the toner image is transferred to the non-printing surface, and as a result, double-sided printing is performed.

  Next, a control flow of the fixing mode change mechanism 510 by the fixing mode change control unit 970 will be described with reference to FIG. FIG. 6 is a flowchart illustrating an example of control of the fixing mode change mechanism 510 by the fixing mode change control unit 970.

When the printer 1 is turned on, the fixing device 9 prepares for a fixing operation. First, supply of electric power to the heater 913 is started. Thereby, the heater 913 generates heat, and the heating of the heating roller 9a by the heater 913 is started. When heating of the heating roller 9a by the heater 913 is started, the temperature increase of the heating roller 9a is started. The heat transmitted to the heating roller 9a is also transmitted to the pressure roller 920, the first tension roller 930, and the second tension roller 940 via the rotating belt 9b.
In addition, the heating roller 9a is driven to rotate, and the rotating belt 9b, the pressure roller 920, the first tension roller 930, and the second tension roller 940 are driven to rotate as the heating roller 9a rotates.

First, image formation is started. Specifically, image formation is started by operating an image formation start button (not shown) or the like.
When image formation is started, the fixing mode change control unit 970 drives the fixing mode changing mechanism 510 (rotation of the mode changing cam 515) based on the fixing mode selection information input via the fixing mode selection button 581. I do.
For example, when the fixing mode selection button 581 is operated (ON), the fixing mode change control unit 970 recognizes the cylindrical object fixing mode and the fixing mode selection button 581 is not operated (OFF). ), It is recognized as the normal fixing mode.
In this control, the normal fixing mode is the initial mode (normal mode), and the fixing operation is performed in the normal fixing mode unless the cylindrical object fixing mode is designated.

  In step ST1, the fixing mode change control unit 970 determines whether or not the fixing mode selection button 581 has been operated. If it is determined by the fixing mode change control unit 970 that the fixing mode selection button 581 has been operated (YES), the process proceeds to step ST2. On the other hand, if the fixing mode change control unit 970 determines that the fixing mode selection button 581 is not operated (NO), the process proceeds to step ST5.

  In step ST2, the fixing mode change control unit 970 drives the gear driving mechanism in the fixing mode changing mechanism 510 to rotationally drive the mode changing cam 515 to the cylindrical object posture. As a result, the fixing device 9 enters the cylindrical object fixing mode. Specifically, the nip pressure of the fixing nip N9 is a second nip pressure that is smaller than the first nip pressure in the normal fixing mode. Further, the nip length MN2 of the main fixing nip MN and the nip length HN2 of the auxiliary fixing nip HN are shorter than the nip length MN1 of the main fixing nip MN and the nip length HN1 of the auxiliary fixing nip HN in the normal fixing mode. .

  In step ST3, the fixing device 9 performs an image fixing operation on the transfer material T. Specifically, the fixing device 9 dissolves the toner TN attached to the transfer material T passing through the auxiliary fixing nip HN and the main fixing nip MN by the heat applied to the toner TN from the heater 913 via the heating roller 9a. Let Then, the toner image is fixed on the transfer material T by applying pressure to the transfer material T via the rotary belt 9 b by the pressure roller 920.

  In step ST4, the fixing mode change control unit 970 drives the gear drive mechanism 513 in the fixing mode change mechanism 510 to rotationally drive the mode change cam 515 to the normal posture so that the fixing device 9 is set to the normal fixing mode. Exit.

  If it is determined that the fixing mode selection button 581 has not been operated (NO), an image fixing operation is performed by the fixing device 9 in step ST5.

According to the fixing device 9 of the present embodiment, for example, the following effects are exhibited.
The fixing device 9 in the present embodiment moves the pressure roller 920 in the direction toward the heating roller 9a or in the direction away from the heating roller 9a so that the nip pressure in the fixing nip N9 is based on the first nip pressure and the first nip pressure. The nip length of the fixing nip N9 is changed from the first nip length to the first nip length by changing the position of the second tension roller 940 with respect to the heating roller 9a and the fixing nip pressure changing portion 511 that changes the nip pressure to a smaller second nip pressure. The fixing nip length changing unit 512 that changes the second nip length shorter than the length, and the fixing nip pressure changing unit 511 so that the nip pressure is set to the second nip pressure when the transfer material T is a cylindrical material. The fixing nip pressure is changed by controlling the fixing nip pressure changing unit 511 so that the nip pressure is set to the first nip pressure when the transfer material T is not a cylindrical object. When the control portion 971 and the transfer material T are cylindrical, the fixing nip length changing unit 512 is controlled so that the nip length becomes the second nip length, and the transfer material T is other than the cylindrical material. In this case, a fixing nip length change control unit 972 that controls the fixing nip length changing unit 512 so as to set the nip length to the first nip length is provided.

Therefore, in the fixing device 9 according to the present embodiment, when the transfer material T is a cylindrical object, the nip pressure at the fixing nip N9 in the fixing process is higher than when the transfer material T is other than the cylindrical object. And the nip length of the fixing nip is shortened. Therefore, the generation of wrinkles can be further suppressed when fixing an image on a cylindrical object such as an envelope.
Further, when the transfer material T is other than a cylindrical material (such as paper), the nip pressure at the fixing nip N9 in the fixing process is increased and the fixing is performed as compared with the transfer material T being a cylindrical material. The nip length of the nip becomes longer. Therefore, it is possible to suitably fix the image to the transfer material T other than the cylindrical object.

As mentioned above, although preferred embodiment of this invention was described, this invention can be implemented with a various form, without being limited to embodiment mentioned above.
For example, in the above-described embodiment, the heating roller 9a (first rotating body) is driven to rotate and the rotating belt 9b is driven to rotate. However, the invention is not limited to this, and the pressure roller 920 (second rotating body). May be driven to rotate, and the rotating belt 9b may be driven to rotate.

Further, although the heating roller 9a is used as the first rotating body, a heating rotating body formed of an endless belt may be used instead.
In the cylindrical object fixing mode, the fixing nip N9 has only the main fixing nip MN and may not have the auxiliary fixing nip HN.

  In the above embodiment, the nip pressure in the fixing nip N9 is changed by moving the pressure roller 920 in the direction toward the heating roller 9a or in the direction away from the heating roller 9a. However, the present invention is not limited to this. Fixing by moving only the heating roller 9a (first rotating body) or by moving both the heating roller 9a (first rotating body) and the pressure roller 920 (second rotating body). The nip pressure at the nip N9 may be changed.

  In the above embodiment, the nip length of the fixing nip N9 is changed by changing the position of the second tension roller 940, but the present invention is not limited to this. By changing the position of only the heating roller 9a (first rotating body), or by changing the position of both the heating roller 9a (first rotating body) and the second tension roller 940 (fourth rotating body), The nip length of the fixing nip N9 may be changed.

  In the embodiment, the fixing mode changing mechanism 510 uses the mode changing cam 515 to move the pressure roller 920 (second rotating body) and move the second tension roller 940. However, it is not limited to this. The fixing mode changing mechanism 510 may independently perform an operation for moving the pressure roller 920 (second rotating body) and an operation for moving the second tension roller 940.

The type of the image forming apparatus of the present invention is not particularly limited, and may be a color copier, a printer, a facsimile, or a complex machine thereof.
Further, the material to be transferred is not limited to paper or a cylindrical material, and may be a film sheet, for example.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2a, 2b, 2c, 2d ... Photosensitive drum (image carrier), 8 ... Secondary transfer roller (transfer part), 9 ... Fixing device, 9a ... Heating Roller (first rotating body), 9b... Rotating belt, 16a, 16b, 16c, 16d... Developer, 37a, 37b, 37c, 37d... Primary transfer roller (transfer section), 511. Changing unit, 512... Fixing nip length changing unit, 913... Heater, 920... Pressure roller (second rotating body), 930... First tension roller (third rotating body), 940. Tension roller (fourth rotating body), 951... 1st part, 952... 2nd part, 965... Upstream part, 971... Fixing nip pressure change control part, 972. J1 …… first rotation axis, J2 …… second rotation axis, J3 ... third rotation axis, J4 ...... fourth rotation axis, N9 ...... fixing nip, MN ...... main fixing nip, HN ...... auxiliary fixing nip, T ...... transfer material (paper, tubular material)

Claims (3)

A first rotating body rotatable about a first rotation axis;
A heater for heating the first rotating body;
A second rotating body that is disposed opposite to the first rotating body and is rotatable about a second rotating shaft parallel to the first rotating shaft;
A third rotating body rotatable about a third rotating shaft parallel to the first rotating shaft;
An annular rotating belt having a predetermined width and capable of rotating in the ring direction. The belt is stretched between the second rotating body and the third rotating body, and is sandwiched between the first rotating body and the second rotating body. A rotating belt having a first portion that is formed and a second portion that is formed continuously with the first portion and contacts the first rotating body;
At least a main fixing nip formed by the first portion of the rotating belt and a portion of the first rotating body facing the first portion, and the second portion of the rotating belt and the first rotating body of the first rotating body. A fixing nip formed by a portion facing the second part and capable of forming an auxiliary fixing nip positioned continuously to the main fixing nip;
A fourth rotating body disposed between the second rotating body and the third rotating body and capable of rotating around a fourth rotating shaft parallel to the first rotating shaft, wherein the second rotating body has a second rotating body. A fourth rotating body that presses an inner peripheral surface of an upstream portion located between the rotating body and the third rotating body and upstream of the fixing nip in the ring direction of the rotating belt;
The nip pressure at the fixing nip is smaller than the first nip pressure and the first nip pressure by moving the second rotator in a direction toward the first rotator or away from the first rotator. A fixing nip pressure changing portion to be changed to 2 nip pressure;
A fixing nip length that changes a nip length of the fixing nip to a first nip length and a second nip length shorter than the first nip length by changing a position of the fourth rotating body with respect to the first rotating body. Change part,
When the transfer material is a cylindrical object, the fixing nip pressure changing unit is controlled so that the nip pressure is the second nip pressure. When the transfer material is other than a cylindrical object, the nip pressure is controlled. A fixing nip pressure change control unit for controlling the fixing nip pressure changing unit so as to make the first nip pressure equal to the first nip pressure;
When the transfer material is a cylindrical object, the fixing nip length changing unit is controlled so that the nip length becomes the second nip length, and when the transfer material is other than a cylindrical object, A fixing nip length change control unit that controls the fixing nip length changing unit so that the nip length becomes the first nip length. 2. The fixing nip length changing unit changes the nip length by moving the fourth rotating body in a direction toward the first rotating body or in a direction away from the first rotating body. Fixing device. One or more image carriers on which electrostatic latent images are formed; and
A developer for developing a toner image on the electrostatic latent image formed on the one or more image carriers;
A transfer unit that directly or indirectly transfers the toner image formed on the image carrier to a transfer material;
An image forming apparatus comprising: the fixing device according to claim 1.

Images