JP2011043663A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device that suppresses formation of wrinkles on paper by reducing the area of the auxiliary fixing nip or shortening its length in a predetermined direction when the paper is conveyed into the auxiliary nip. <P>SOLUTION: The fixing device includes: a first rotation body 9a; a second rotation body 920; a third rotation body 930; a rotation belt 9b stretched over the second and third rotation bodies 920 and 930; a main fixing nip MN; an auxiliary fixing nip HN; a belt position changing part 934 for changing the position of a prescribed part 950 to a first position U1 for providing a first nip length HN1 and to a second position U2 for providing a second nip length HN2 longer than the first nip length HN1; a position detecting part 971; and a belt position change control part 972 configured to instruct the belt position-changing part 934 that, when a material T to be transferred enters the auxiliary fixing nip HN, the predetermined part 950 is located at the first position U1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  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.

  On the other hand, a fixing device has been proposed that includes a heating roller, a pressure roller, and an annular rotating belt that is looped around a plurality of rotating bodies including the pressure roller (for example, Patent Document 1). reference). In such a fixing device, the rotating belt is sandwiched between the heating roller and the pressure roller located on the inner peripheral surface side of the rotating belt, 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. By transporting the paper while being sandwiched between the heating roller and the rotating belt, the toner transferred onto the paper is melted and pressurized and fixed on the paper.

JP 52-69337 A

In the fixing device described in Patent Document 1, since the rotating belt is formed in a belt shape, sagging occurs in the width direction of the rotating belt, and the rotating belt rotates in an unstable state. Therefore, there is a possibility that a plurality of irregularities are formed in the rotating belt in a wavy shape in the width direction.
Further, in the fixing device described in Patent Document 1, the auxiliary fixing nip is not formed when the rotating belt is sandwiched between the heating roller and the pressure roller like the main fixing nip. Are formed in contact with each other. Therefore, the pressure in the auxiliary fixing nip is smaller than the pressure in the main fixing nip. For this reason, in the auxiliary fixing nip, the wavy unevenness formed on the rotating belt is often moved to the main fixing nip while the uneven shape is maintained. That is, in the auxiliary fixing nip, the paper placed on the wavy uneven portion is deformed along the wavy uneven shape and is moved to the main fixing nip while the shape is maintained by the auxiliary fixing nip. As a result, wrinkles may be formed on the paper.
The fixing device described in Patent Document 1 has improved fixing properties, but has a problem that wrinkles are more often formed on the paper than in the past.

The present invention provides a fixing device that suppresses the formation of wrinkles on a sheet by reducing the area in the auxiliary fixing nip or shortening the length in a predetermined direction when the sheet is carried into the auxiliary nip. With the goal.
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; A rotating belt having a second portion formed continuously with the first portion and contacting the first rotating body, the first portion of the rotating belt, and a portion of the first rotating body facing the first portion. A main fixing nip to be formed; the second part of the rotating belt; The auxiliary fixing nip formed by the portion of the one rotating body facing the second portion and continuously located in the main fixing nip, and between the second rotating body and the third rotating body of the rotating belt. A belt position changing unit that changes a position in the thickness direction of the rotating belt at a predetermined portion located upstream of the second part in the rotating direction of the rotating belt, the rotating belt at the auxiliary fixing nip. The belt position is changed to a first position where the nip length in the rotation direction is the first nip length, and a second position where the nip length is a second nip length longer than the first nip length. And a position detection unit that detects a position in the conveyance direction of the sheet-like transfer material, and the bell based on information about the position of the transfer material detected by the position detection unit. A belt position change control unit for controlling a position change unit, wherein the belt position is set so that the predetermined portion of the rotating belt is positioned at the first position when the transfer material enters the auxiliary fixing nip. The present invention relates to a fixing device including a belt position change control unit that instructs a change unit.

  The belt position changing unit may change the position of the predetermined portion of the rotating belt by moving the third rotating body in a direction toward the first rotating body or in a direction away from the first rotating body. preferable.

  In addition, a leading end portion is disposed to face the predetermined portion of the rotating belt, and is formed on the leading end side and an introduction guide member that introduces a sheet-like transfer material into the auxiliary fixing nip. It is preferable that the belt position changing unit further presses the outer peripheral surface of the predetermined portion to change the position of the predetermined portion.

  The belt position change control unit is configured to position the predetermined portion of the rotating belt at the second position after the transferred material has entered the auxiliary fixing nip or the main fixing nip. It is preferable to instruct the changing unit.

  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 sheet-like transfer material; and the fixing device.

According to the present invention, there is provided a fixing device that suppresses formation of wrinkles on a sheet by reducing the area in the auxiliary fixing nip or shortening the length in a predetermined direction when the sheet is carried into the auxiliary nip. can do.
In addition, the present invention can provide an image forming apparatus including the fixing device.

FIG. 3 is a left side view for explaining the arrangement of each component in the printer 1 of the first embodiment. 1 is a perspective view showing a fixing device 9 according to a first embodiment. FIG. 3 is a conceptual diagram illustrating a configuration of a fixing device 9 according to the first embodiment. FIG. 6 is a flowchart showing the operation of the fixing device 9 of the first embodiment. FIG. 10 is a diagram illustrating a state of the fixing device 9 when the paper T is positioned before being detected by the position detection sensor 975. FIG. 6 is a diagram illustrating a state of the fixing device 9 at the time when a sheet T is conveyed to a position detected by a position detection sensor 975. FIG. 6 is a diagram illustrating a state of the fixing device 9 immediately before the sheet T enters the auxiliary fixing nip HN. It is the figure which looked at the rotating belt 9b of the fixing device 9 in FIG. 7A from the heating roller 9a side. FIG. 6 is a diagram illustrating a state of the fixing device 9 immediately after the sheet T enters the auxiliary fixing nip HN. FIG. 10 is a diagram illustrating a state of the fixing device 9 when the length of the auxiliary fixing nip HN is set to the second nip length HN2 after the sheet T enters the auxiliary fixing nip HN. It is the figure which looked at the rotating belt 9b of the fixing device 9 in FIG. 9A from the heating roller 9a side. FIG. 6 is a diagram illustrating a state of the fixing device 9 when a sheet T passes through an auxiliary fixing nip HN and a main fixing nip MN. It is a conceptual diagram which shows the structure in the fixing device 9 of 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
With reference to FIG. 1, the overall structure of a printer 1 as a first embodiment of an image forming apparatus of the present invention will be described. FIG. 1 is a diagram for explaining the arrangement of each component of the printer 1.

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 sheet T as a sheet-like transfer material based on predetermined image information. And a paper supply / discharge unit KH that supplies the paper T to the image forming unit GK and discharges the paper 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 a photosensitive drum 2 as an image carrier (photosensitive member), a charging unit 10, a laser scanner unit 4 as an exposure unit, a developing device 16, and a toner cartridge. 5, a toner supply unit 6, a drum cleaning unit 11, a static eliminator 12, a transfer roller 8, and a fixing device 9.

  As shown in FIG. 1, the paper feed / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 64, a transport path L for paper T, a registration roller pair 80, and a paper discharge unit 50.

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, in order from the upstream side to the downstream side along the surface of the photosensitive drum 2, charging by the charging unit 10, exposure by the laser scanner unit 4, development by the developing device 16, transfer by the transfer roller 8. Then, static elimination by the static eliminator 12 and cleaning by the drum cleaning unit 11 are performed.

  The photosensitive drum 2 is made of a cylindrical member and functions as a photosensitive member or an image carrier. The photosensitive drum 2 is disposed so as to be rotatable in the direction of an arrow about an axis extending in a direction orthogonal to the conveyance direction of the paper T in the conveyance path L. An electrostatic latent image can be formed on the surface of the photosensitive drum 2.

  The charging unit 10 is disposed to face the surface of the photosensitive drum 2. The charging unit 10 uniformly charges the surface of the photosensitive drum 2 to be negative (minus polarity) or positive (plus polarity).

  The laser scanner unit 4 functions as an exposure unit, and is disposed away from the surface of the photosensitive drum 2. The laser scanner unit 4 includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  The laser scanner unit 4 scans and exposes the surface of the photosensitive drum 2 based on image information input from an external device such as a PC (personal computer). By scanning exposure with the laser scanner unit 4, the charge on the exposed portion of the surface of the photosensitive drum 2 is removed. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The developing device 16 is provided corresponding to the photosensitive drum 2 and is disposed to face the surface of the photosensitive drum 2. The developing device 16 attaches a single color (usually black) toner to the electrostatic latent image formed on the photoconductive drum 2 to form a single color toner image on the surface of the photoconductive drum 2. The developing device 16 includes a developing roller 17 disposed opposite to the surface of the photosensitive drum 2, a stirring roller 18 for stirring the toner, and the like.

  The toner cartridge 5 is provided corresponding to the developing device 16 and stores toner supplied to the developing device 16.

  The toner supply unit 6 is provided corresponding to the toner cartridge 5 and the developing device 16, and supplies the toner contained in the toner cartridge 5 to the developing device 16. The toner supply unit 6 and the developing device 16 are connected by a toner supply path (not shown).

  The transfer roller 8 transfers the toner image developed on the surface of the photosensitive drum 2 to the paper T. A transfer bias for transferring the toner image formed on the photosensitive drum 2 to the paper T is applied to the transfer roller 8 by a transfer bias applying unit (not shown).

  The transfer roller 8 is brought into contact with or separated from the photosensitive drum 2. Specifically, the transfer roller 8 is configured to be movable between a contact position where the transfer roller 8 is in contact with the photosensitive drum 2 and a spaced position where the transfer roller 8 is separated from the photosensitive drum 2. Specifically, the transfer roller 8 is disposed at the contact position when the toner image developed on the photosensitive drum 2 is transferred to the paper T, and is disposed at the separation position in other cases.

  A sheet T conveyed on the conveyance path L is sandwiched between the photosensitive drum 2 and the transfer roller 8. The sandwiched paper T is pressed against the surface of the photosensitive drum 2. A transfer nip N is formed between the photosensitive drum 2 and the transfer roller 8. In the transfer nip N, the toner image developed on the photosensitive drum 2 is transferred onto the paper T.

  The static eliminator 12 is disposed to face the surface of the photosensitive drum 2. The static eliminator 12 irradiates the surface of the photosensitive drum 2 with light, thereby neutralizing the surface of the photosensitive drum 2 after the transfer is performed (removing the electric charge).

  The drum cleaning unit 11 is disposed to face the surface of the photosensitive drum 2. The drum cleaning unit 11 removes toner and deposits remaining on the surface of the photosensitive drum 2, and transports the removed toner and the like to a predetermined recovery mechanism for recovery.

The fixing device 9 melts and presses the toner constituting the toner image transferred onto the paper T and fixes the toner on the paper 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 tension as a third rotating body, which are heated by heaters 910 and 910 (see FIG. 3) described later. A roller 930, and a rotating belt 9b spanned between the pressure roller 920 and the tension roller 930. The heating roller 9a and the pressure roller 920 sandwich and press the paper T on which the toner image is transferred via the rotating belt 9b, and convey the paper T. When the paper T is conveyed while being sandwiched between the heating roller 9a and the rotating belt 9b, the toner transferred onto the paper T is melted and pressurized and fixed on the paper T.
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, in the lower part of the apparatus main body M, a single paper feed cassette 52 that stores paper T is disposed. The paper feed cassette 52 is configured to be drawable in the horizontal direction from the front side (right side in FIG. 1) of the apparatus main body M. In the paper feed cassette 52, a placement plate 60 on which the paper T is placed is disposed. In the paper feed cassette 52, the paper T is stored in a state of being stacked on the placement plate 60. The paper T placed on the placement plate 60 is sent out to the transport path L by the cassette paper feed unit 51 arranged at the paper feed side end of the paper feed cassette 52 (the right end in FIG. 1). The cassette paper feed unit 51 includes a double feed prevention mechanism including a forward feed roller 61 for taking out the paper T on the placement plate 60 and a paper feed roller pair 63 for feeding the paper T to the transport path L one by one. Prepare.

  A manual paper feed unit 64 is provided on the front surface (right side in FIG. 1) of the apparatus main body M. The manual paper feed unit 64 is provided mainly for supplying the apparatus main body M with a paper T of a size and type different from the paper 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 front 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 paper T is placed on the open manual feed tray 65. The paper feed roller 66 feeds the paper T placed on the open manual feed tray 65 to the manual feed path La.

  A paper discharge unit 50 is provided on the upper side of the apparatus main body M. The paper discharge unit 50 discharges the paper T to the outside of the apparatus main body M by the third roller pair 53. Details of the paper discharge unit 50 will be described later.

  The conveyance path L for conveying the paper T is a first conveyance path L1 from the cassette paper feeding unit 51 to the transfer nip N, a second conveyance path L2 from the transfer nip N to the fixing device 9, and a discharge from the fixing device 9. A third conveyance path L3 to the section 50, a manual conveyance path La that joins the paper supplied from the manual sheet feeding unit 64 to the first conveyance path L1, and a third conveyance path L3 from the upstream side to the downstream side. And a return transport path Lb that reverses the paper and returns it to the first transport 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, and includes a first roller pair 54a and a second roller pair 54b. One roller of the first roller pair 54a and one roller of the second roller pair 54b are combined.

  In the middle of the first transport path L1 (specifically, between the second junction P2 and the transfer roller 8), a sensor for detecting the paper T, correction of skew (oblique paper feeding) of the paper T, and image A registration roller pair 80 is arranged to synchronize with the formation of the toner image in the forming unit GK. The sensor is disposed immediately before the registration roller pair 80 in the transport direction D1 of the paper T (upstream side in the transport direction D1). The registration roller pair 80 conveys the paper T by performing the above-described correction and timing adjustment based on detection signal information from the sensor.

  A position detection sensor 975 for detecting the paper T is disposed in the middle of the second transport path L2. The position detection sensor 975 is disposed immediately before the fixing device 9 in the transport direction D1 of the paper T (upstream side in the transport direction D1). The position detection sensor 975 will be described later.

The return conveyance path Lb is a conveyance path that is provided so that the opposite surface (non-printing surface) to the surface that has already been printed faces the photosensitive drum 2 when performing duplex printing on the paper T.
According to the return conveyance path Lb, the sheet T conveyed from the first branching section Q1 to the paper discharge section 50 side by the first roller pair 54a is reversed and returned to the first conveyance path L1 by the second roller pair 54b. , And can be conveyed to the upstream side of the registration roller pair 80 disposed on the upstream side of the transfer roller 8. A predetermined toner image is transferred onto the non-printing surface by the photosensitive drum 2 on the paper T that has been turned upside down by the return conveyance 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 front side of the apparatus main body M (the right side in FIG. 1, the manual paper feed unit 64 side). The paper discharge unit 50 discharges the paper T conveyed on the third conveyance path L3 to the outside of the apparatus main body M by the third roller pair 53.

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, sheets T formed with a predetermined toner image and discharged from the paper discharge unit 50 are stacked and stacked.
A paper detection sensor is disposed at a predetermined position on each conveyance path.

  Hereinafter, with reference to the drawings, a configuration related to a characteristic part in the printer 1 of the present embodiment will be described. FIG. 2 is a perspective view showing the fixing device 9 of the first embodiment. FIG. 3 is a conceptual diagram illustrating a configuration of the fixing device 9 according to the first embodiment.

  As shown in FIGS. 2 and 3, the fixing device 9 of the present embodiment includes a heating roller 9a, two heaters 910 and 910, a pressure roller 920, a tension roller 930, a pressure roller 920, and a tension roller. Rotating belt 9b spanned to 930, belt position changing unit 934, position detection sensor 975, and control unit 970 are provided.

As shown in FIGS. 2 and 3, the heating roller 9 a is configured to be rotatable about a first rotation axis I extending in a second direction D <b> 2 orthogonal to the transport direction D <b> 1 of the paper T. The heating roller 9a has a cylindrical metal member and a release layer formed on the outer peripheral surface of the metal member. For example, the heating roller 9a 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 further on the outer peripheral surface of the magnetic metal layer. It is formed by providing a release layer made of a fluororesin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) having a thickness of about 20 μm on the surface.
A cylindrical first shaft member 911 parallel to the first rotation axis I protrudes from both ends of the heating roller 9a in the first rotation axis direction. The first shaft member 911 is rotatably supported by a case of the apparatus main body M in the printer 1 and other members.

  As shown in FIGS. 2 and 3, the rotating belt 9b is disposed so as to contact the heating roller 9a. The rotating belt 9b is formed in a belt shape having a predetermined width. The rotating belt 9b is formed in a roll shape (endless belt shape) and has heat resistance. For example, the rotating belt 9b is provided with a nonmagnetic metal layer such as SUS (stainless steel) plating having a thickness of about 50 μm on the outer peripheral surface of the polyimide film, and the thickness is 100 μm on the outer peripheral surface of the nonmagnetic metal layer. And 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 stretched between a pressure roller 920 described later and a tension roller 930 described later. The outer peripheral surface of the pressure roller 920 and the outer peripheral surface of the 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.
The pressure roller 920 and the tension roller 930 will be described in detail later.

The pressure roller 920 is configured to be rotatable about a second rotation axis J extending in a second direction D2 parallel to the first rotation axis I, as shown in FIGS.
The pressure roller 920 includes, for example, a cylindrical metal pressure roller shaft member 921 and an elastic layer 922 such as silicon rubber formed on the outer peripheral surface of the pressure roller shaft member 921. The The surface of the elastic layer 922 in the pressure roller 920 is generally covered with a fluorine-based release layer.
The pressure roller shaft member 921 is formed to protrude in parallel with the second rotation axis J from both ends of the pressure roller 920 in the second rotation axis J direction. The pressure roller shaft member 921 is rotatably supported by a case of the apparatus main body M in the printer 1 and other members.

  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 942 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.

As shown in FIGS. 2 and 3, the tension roller 930 is configured to be rotatable around a third rotation axis K extending in a second direction D2 parallel to the first rotation axis I. The tension roller 930 is formed of a cylindrical metal member.
The tension roller 930 is rotatably supported by the shaft member 932. The shaft member 932 protrudes outward in the third rotation axis K direction at both ends of the tension roller 930. The shaft member 932 is formed with a smaller diameter than the tension roller 930 and is rotatably supported by the case of the apparatus main body M in the printer 1 and other members.

The outer peripheral surface of the tension roller 930 is in contact with the inner peripheral surface of the rotating belt 9b.
The tension roller 930 is disposed on the upstream side in the transport direction D1 of the paper T with respect to the first portion 942 of the rotating belt 9b. The tension roller 930 presses the rotating belt 9b stretched around the pressure roller 920 from the inner peripheral surface side toward the outer side. As a result, the tension roller 930 applies tension to the rotating belt 9b so as to extend in the rotation direction R.

The position detection sensor 975 is disposed in the middle of the second transport path L2 and detects the position of the paper T (see FIG. 1). As shown in FIG. 3, the position detection sensor 975 detects the sheet when the leading edge of the sheet T is located at a predetermined position C on the upstream side in the conveyance direction D1 of the fixing device 9 (immediately before the conveyance direction D1 of the fixing device 9). The position of the paper T conveyed to the fixing device 9 without contacting the surface of T is detected.
The position detection sensor 975 is composed of, for example, an optical sensor, and detects the passage of the conveyed paper T using reflected light generated by irradiating the surface of the paper T with light. The position detection sensor 975 outputs detection information including identification information of the position detection sensor 975 to the position detection unit 971 described later when the paper T is detected by reflected light of light emitted from the position detection sensor 975.

  A pressure roller driving unit (not shown) such as an electric motor that rotates the pressure roller 920 is connected to the pressure roller shaft member 921 of the pressure roller 920. When the pressure roller 920 is rotated by the pressure roller driving unit, the rotating belt 9b rotates in the rotation direction R. When the rotating belt 9b is rotated, the heating roller 9a that contacts the outer peripheral surface of the rotating belt 9b and the tension roller 930 that contacts the inner peripheral surface of the rotating belt 9b are driven to rotate.

As shown in FIG. 3, a main fixing nip MN and an auxiliary fixing nip HN are formed by the heating roller 9a and the rotating belt 9b.
The main fixing nip MN is formed by an outer peripheral surface corresponding to the first portion 942 sandwiched between the heating roller 9a and the pressure roller 920 in the rotating belt 9b and a surface facing the first portion 942 in the heating roller 9a. . The auxiliary fixing nip HN is formed by an outer peripheral surface corresponding to the abutting second portion 943 continuously formed on the upstream side of the first portion 942 in the rotation direction R and a surface facing the second portion 943 of the heating roller 9a. It is formed. The auxiliary fixing nip HN is formed continuously to the main fixing nip MN on the upstream side in the rotation direction R of the rotary belt 9b.

The second portion 943 includes the heating roller 9a and the heating roller 9a and the pressure roller 920 aligned in the vertical direction in a state where the rotating belt 9b is stretched between the pressure roller 920 and a tension roller 930 described later. It is a portion formed by being arranged on the upstream side in the rotation direction R of the rotating belt 9b rather than being arranged.
The second portion 943 is configured so that the heating roller 9a and the pressure roller 920 are arranged in the vertical direction so as to straddle the heating roller 9a between the first portion 942 and the second portion 943. It is formed by shifting the position on the upstream side in the rotation direction R of 9b.
Thereby, in addition to the main fixing nip MN, the auxiliary fixing nip HN continuous to the main fixing nip MN is formed, so that the amount (area) of the fixing nip is increased.

The two heaters 910 and 910 are respectively arranged on the downstream side (left side in FIG. 3) and the upstream side (right side in FIG. 3) in the conveyance direction D1 inside the heating roller 9a.
The two heaters 910 and 910 heat the main fixing nip MN and the auxiliary fixing nip HN via the heating roller 9a. The heaters 910 and 910 are composed of, for example, a halogen heater or a ceramic heater.

  As shown in FIG. 3, the belt position changing unit 934 includes a rotating belt driving unit 935. The rotating belt drive unit 935 is connected to the shaft member 932 of the tension roller 930. Based on a control signal from a belt position change control unit 972, which will be described later, the rotating belt drive unit 935 moves the tension roller 930 toward the heating roller 9a around the pressure roller 920 or away from the heating roller 9a (see FIG. 3 in the vertical direction). As a result, the rotating belt 9b stretched between the tension roller 930 and the pressure roller 920 follows and moves, so that the predetermined portion 950 of the rotating belt 9b moves.

Here, the “predetermined portion 950” in the rotating belt 9b will be described.
First, a virtual reference line X extending in the thickness direction of the rotating belt 9b is set at a predetermined position between the pressure roller 920 and the tension roller 930.
The rotating belt 9b rotated in the rotation direction R sequentially passes through the virtual reference line X while intersecting the virtual reference line X substantially perpendicularly. In the present embodiment, the “predetermined portion 950” in the rotating belt 9b refers to a portion located on the virtual reference line X in the rotating belt 9b.
Further, the “predetermined portion 950” in the rotating belt 9b moves on the virtual reference line X. The rotating belt 9b actually moves sequentially in the rotation direction R. However, in the present embodiment, the “predetermined portion 950” in the rotating belt 9b is the predetermined portion 950 that is sequentially positioned on the virtual reference line X and does not move in the rotation direction R of the rotating belt 9b, A description will be given assuming that the reference line X moves.
Note that the position of the virtual reference line X can be changed as appropriate.

The rotating belt driving unit 935 is a predetermined position located between the pressure roller 920 and the tension roller 930 in the rotating belt 9b and upstream of the second portion 943 of the rotating belt 9b in the rotation direction R of the rotating belt 9b. The position of the portion 950 in the thickness direction is changed.
Specifically, as shown in FIG. 3, the predetermined portion 950 of the rotating belt 9b moves in the thickness direction of the rotating belt 9b on the virtual reference line X by the movement of the rotating belt 9b.

As shown in FIG. 3, the position of the predetermined portion 950 on the rotating belt 9b is changed to the first position U1 and the second position U2 on the virtual reference line X by the rotating belt driving unit 935.
The first position U1 is a position where the predetermined portion 950 is disposed such that the nip length in the rotation direction R of the auxiliary fixing nip HN is formed with the first nip length HN1. The sheet T enters the auxiliary fixing nip HN when the predetermined portion 950 is positioned at the first position U1 (entry position).

  The second position U2 is a position where the predetermined portion 950 is positioned such that the nip length in the rotation direction R of the auxiliary fixing nip HN is formed with the second nip length HN2. The sheet T is fixed by the auxiliary fixing nip HN and the main fixing nip MN in the fixing device 9 when the predetermined portion 950 is positioned at the second position U2 (fixing position).

The second nip length HN2 is formed longer than the first nip length HN1.
Since the second nip length HN2 is longer than the first nip length HN1, the area of the fixing nip in the auxiliary fixing nip HN is larger than that in the case where the predetermined portion 950 of the rotating belt 9b is located at the first position U1 (entrance position). Is larger in the second position U2 (fixing position). The area of the fixing nip in the auxiliary fixing nip HN is changed by changing the position of the predetermined portion 950 on the rotating belt 9b to the first position U1 or the second position U2 by the rotating belt driving unit 935.

  A pressure roller driving unit (not shown) such as an electric motor that rotates the pressure roller 920 is connected to the pressure roller shaft member 921 of the pressure roller 920. When the pressure roller 920 is rotated by the pressure roller driving unit, the rotating belt 9b rotates in the rotation direction R. When the rotating belt 9b is rotated, the heating roller 9a that contacts the outer peripheral surface of the rotating belt 9b and the tension roller 930 that contacts the inner peripheral surface of the rotating belt 9b are driven to rotate.

The control unit 970 includes a position detection unit 971 and a belt position change control unit 972.
The position detection unit 971 detects that the leading edge of the paper T is at the predetermined position C based on detection information from the position detection sensor 975 (see FIG. 6). Further, the position detection unit 971 outputs detection information including the position information of the paper T to the belt position change control unit 972.

  Based on the detection information from the position detection unit 971, the belt position change control unit 972 moves the tension roller 930 to the rotating belt drive unit 935 in a direction in which the length of the auxiliary fixing nip HN becomes shorter (at a predetermined timing ( The pressure roller 920 is moved in the direction away from the heating roller 9a), or the tension roller 930 is moved in the direction in which the length of the auxiliary fixing nip HN is increased (the pressure roller 920 is moved in the direction approaching the heating roller 9a). Instruct them to do so. The belt position change control unit 972 calculates a predetermined timing for moving the tension roller 930 based on the detection information from the position detection unit 971.

  Specifically, the rotating belt drive unit 935 instructed by the belt position change control unit 972 moves the tension roller 930 toward the heating roller 9a around the pressure roller 920 (upward in FIG. 3) or the tension roller 930. Is moved in the direction away from the heating roller 9a (downward in FIG. 3) with the pressure roller 920 as the center. Then, the predetermined portion 950 in the rotating belt 9b is moved in the thickness direction of the rotating belt 9b on the virtual reference line X. As a result, the belt position change control unit 972 can position the predetermined portion 950 of the rotating belt 9b at the first position (entrance position) U1 or the second position (fixing position) U2.

  Thus, the fixing device 9 is controlled by the belt position change control unit 972, and the first position (entrance position) U1 at which the nip length in the rotation direction R of the auxiliary fixing nip HN becomes the first nip length HN1. In a state where the predetermined portion 950 is positioned, the paper T enters the auxiliary fixing nip HN. Further, after the sheet T enters the auxiliary fixing nip HN, the fixing device 9 has the second nip length HN2 in which the nip length in the rotation direction R of the auxiliary fixing nip HN is longer than the first nip length HN1. With the predetermined portion 950 positioned at the second position (fixing position) U2, an operation of fixing the toner image on the paper T is performed.

Next, the operation of the printer 1 of the first embodiment will be briefly described with reference to FIGS. 1 to 3.
First, a case where single-sided printing is performed on the paper T stored in the paper feed cassette 52 will be described.
The paper 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 63, and then the registration rollers via the first junction P1 and the first transport path L1. Transported to pair 80.
In the registration roller pair 80, skew correction of the paper T and timing adjustment with the toner image are performed.

The paper T discharged from the registration roller pair 80 is introduced between the photosensitive drum 2 and the transfer roller 8 through the first conveyance path L1. A toner image is transferred onto the paper T between the photosensitive drum 2 and the transfer roller 8.
Thereafter, the paper T is discharged from between the photosensitive drum 2 and the transfer roller 8, and is supplied to the auxiliary fixing nip HN formed by the heating roller 9a and the rotating belt 9b in the fixing device 9 via the second conveyance path L2. And the main fixing nip MN. Then, the paper T is heated in the auxiliary fixing nip HN and the main fixing nip MN, the toner TN is melted, and the toner TN (toner image) is fixed on the paper T.

Next, the paper T is conveyed to the paper discharge unit 50 through the third conveyance path L3 by the first roller pair 54a, and is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1 by the third roller pair 53.
In this way, single-sided printing of the paper T stored in the paper feed cassette 52 is completed.

  When single-sided printing is performed on the paper T placed on the manual feed tray 65, the paper 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 the first joining portion. It is conveyed to the registration roller pair 80 via P1 and the first conveyance path L1. Subsequent operations are the same as the one-side printing operation of the paper T accommodated in the paper feed cassette 52 described above, and a description thereof will be 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 paper T on which single-sided printing has been performed is discharged from the paper discharge unit 50 to the paper discharge stacking unit M1, and the printing operation is completed.
On the other hand, when performing double-sided printing, the paper T on which single-sided printing has been performed is reversed from the time of single-sided printing and conveyed again to the registration roller pair 80 via the return conveyance path Lb. Then, double-sided printing is performed on the paper T.

  More specifically, the operation is the same as the above-described single-sided printing operation until the paper T on which single-sided printing has been performed is discharged from the paper discharge unit 50 by the third roller pair 53. Thus, in the case of double-sided printing, the rotation of the third roller pair 53 is stopped and rotated in the opposite direction while the paper T on which single-sided printing has been held by the third roller pair 53. Thus, when the third roller pair 53 is rotated in the reverse direction, the paper T held by the third roller pair 53 moves in the reverse direction (from the paper discharge unit 50 to the first branching unit Q1) along the third conveyance path L3. Transported in the direction of heading).

  As described above, when the paper T is transported in the reverse direction on the third transport path L3, it is introduced into the second roller pair 54b (not the first roller pair 54a). The paper T then joins the second transport path L2 via the return transport path Lb and the second joining portion P2. Here, the paper T is turned upside down from the one-side printing.

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

Next, the operation of the fixing device 9 which is a characteristic part of the printer 1 of the present embodiment will be described with reference to FIGS. 1 to 3.
In the printer 1 of the present embodiment, when the printer 1 is turned on, the charging unit 10, the laser scanner unit 4, the developing device 16, the transfer roller 8, the printer control unit (not shown), and the fixing device 9 are turned on from the power supply unit. Power is supplied to each of them, and the charging unit 10, the laser scanner unit 4, the developing device 16, the transfer roller 8 and the fixing device 9 are controlled by a control signal from the printer control unit. Then, the charging process, the exposure process, the development process, the transfer process, and the fixing process are sequentially performed.

  Specifically, in the printer 1 of the present embodiment, the paper T sent out from the registration roller pair 80 passes through the first conveyance path L1 to the transfer nip N between the photosensitive drum 2 and the transfer roller 8. Be transported. When the paper T is conveyed toward the photosensitive drum 2 as described above, first, the charging unit 10 charges the entire surface of the photosensitive drum 2 in the charging process, and the laser scanner unit 4 performs laser irradiation in the exposure process. Laser light is irradiated from a light source (not shown) toward the photosensitive drum 2 to form an electrostatic latent image on the surface of the photosensitive drum 2 irradiated with the laser light.

  Next, the developing device 16 supplies the toner charged in the developing process to the photosensitive drum 2 by the developing roller 17, thereby attaching the toner to the electrostatic latent image formed on the surface of the photosensitive drum 2, Develop the toner image. Subsequently, the transfer roller 8 transfers the toner image attached to the surface of the photoconductive drum 2 onto the paper T that passes between the photoconductive drum 2 and the transfer roller 8 in the transfer process. The paper T onto which the toner image has been transferred in the transfer process is transported toward the fixing device 9 through the second transport path L2, and the fixing process is performed.

  Here, a specific operation of the fixing device 9 in the fixing process will be described with reference to FIGS. FIG. 4 is a flowchart showing the operation of the fixing device 9 of the first embodiment. FIG. 5 is a diagram illustrating a state of the fixing device 9 when the paper T is positioned before being detected by the position detection sensor 975. FIG. 6 is a diagram illustrating a state of the fixing device 9 when the paper T is conveyed to a position detected by the position detection sensor 975. FIG. 7A is a diagram illustrating a state of the fixing device 9 immediately before the sheet T enters the auxiliary fixing nip HN. FIG. 7B is a view of the rotating belt 9b of the fixing device 9 in FIG. 7A as viewed from the heating roller 9a side. FIG. 8 is a diagram illustrating a state of the fixing device 9 immediately after the sheet T enters the auxiliary fixing nip HN. FIG. 9A is a diagram illustrating a state of the fixing device 9 when the length of the auxiliary fixing nip HN is set to the second nip length HN2 after the sheet T enters the auxiliary fixing nip HN. FIG. 9B is a view of the rotating belt 9b of the fixing device 9 in FIG. 9A viewed from the heating roller 9a side. FIG. 10 is a diagram illustrating a state of the fixing device 9 when the paper T passes through the auxiliary fixing nip HN and the main fixing nip MN.

  In step ST1, as shown in FIG. 5, preparation for fixing by the fixing device 9 is performed. First, an ON signal is output from the printer control unit (not shown) to the pressure roller driving unit (not shown), so that power supply from the power supply unit to the pressure roller driving unit is started. . As a result, the pressure roller 920 is rotationally driven, and the rotary belt 9b, the heating roller 9a, and the tension roller 930 are driven to rotate as the pressure roller 920 is rotationally driven.

Next, when an ON signal is output from the printer control unit (not shown) to the heater 910, supply of electric power from the power source unit to the heater 910 is started. Thereby, the heater 910 generates heat, and the heating of the heating roller 9a by the heater 910 is started.
When heating of the heating roller 9a by the heater 910 is started, the heating of the heating roller 9a is started. The heat transmitted to the heating roller 9a is also transmitted to the pressure roller 920 and the tension roller 930 via the rotating belt 9b and the rotating belt 9b. After the surface temperature of the heating roller 9a reaches the set temperature, the conveyed paper T is conveyed toward the auxiliary fixing nip HN and the main fixing nip MN. Here, as shown in FIG. 5, the predetermined portion 950 of the rotating belt 9b is located on the virtual reference line X at the second position U2 where the nip length of the auxiliary fixing nip HN becomes the second nip length HN2. is doing. The predetermined portion 950 in the rotating belt 9b refers to a portion located on the virtual reference line X in the rotating belt 9b.
In step ST1, after the fixing preparation by the fixing device 9 is completed, the process proceeds to step ST2.

  In step ST2, as shown in FIG. 6, the position detection sensor 975 detects that the leading edge of the paper T is at a predetermined position C on the upstream side in the conveyance direction D1 of the fixing device 9 (a position immediately before the fixing device 9 in the conveyance direction D1). When the position is detected, the detection information including the identification information of the position detection sensor 975 is output to the position detection unit 971.

  In step ST3, the position detection unit 971 detects that the leading edge of the paper T is at the predetermined position C based on the detection information from the position detection sensor 975, and detects the detection information including the position information of the paper T as the belt position. The data is output to the change control unit 972.

  In step ST4, the belt position change control unit 972 sets the length of the auxiliary fixing nip HN to the rotary belt driving unit 935 at a predetermined timing based on the detection information from the position detection unit 971. It is instructed to move in a direction of shortening (a direction away from the heating roller 9a around the pressure roller 920).

  Specifically, as shown in FIG. 7A, the belt position change control unit 972 moves the predetermined portion 950 of the rotating belt 9b to the second position on the virtual reference line X before the paper T enters the auxiliary fixing nip HN. The rotating belt driving unit 935 is instructed to be positioned from the position U2 to the first position U1. As a result, as shown in FIGS. 7A and 7B, when the paper T enters the auxiliary fixing nip HN, the nip length of the auxiliary fixing nip HN is changed to the first nip length HN1. Specifically, the belt position change control unit 972 causes the rotary belt driving unit 935 to move the tension roller 930 away from the heating roller 9a around the pressure roller 920 (downward direction in FIG. 7A). Accordingly, the predetermined portion 950 of the rotating belt 9b is moved on the virtual reference line X in a direction away from the heating roller 9a in the thickness direction of the rotating belt 9b, and is positioned from the second position U2 to the first position U1.

  The belt position change control unit 972 instructs the rotary belt driving unit 935 to maintain the nip length of the auxiliary fixing nip HN at the first nip length HN1 until the paper T enters the main fixing nip MN. In step ST4, the process proceeds to step ST5 in a state where the nip length of the auxiliary fixing nip HN is maintained at the first nip length HN1.

In step ST5, as shown in FIG. 8, the auxiliary fixing nip HN of the paper T is maintained in a state where the nip length of the auxiliary fixing nip HN is maintained at the first nip length HN1 (see FIGS. 7A and 7B). To enter.
Here, the main fixing nip MN has a pressure to push the rotating belt 9b in the width direction D2. The auxiliary fixing nip HN is formed continuously with the main fixing nip MN. The pressure in the auxiliary fixing nip HN is smaller than the pressure in the main fixing nip MN. For this reason, the wavy unevenness formed in the rotating belt 9b (the wavy portion W formed in a wavy shape by arranging a plurality of unevenness in the width direction D2 of the rotating belt 9b) becomes uneven when entering the auxiliary fixing nip HN. In many cases, the shape passes through the auxiliary fixing nip HN while maintaining the shape.

On the other hand, the rotating belt 9b passing through the auxiliary fixing nip HN is affected by the force of pushing the rotating belt 9b by the main fixing nip MN in the width direction D2. In particular, the portion of the rotating belt 9b that passes through the auxiliary fixing nip HN is closer to the main fixing nip MN and is more susceptible to the force of the main fixing nip MN that pushes the rotating belt 9b in the width direction D2.
In the present embodiment, since the nip length of the auxiliary fixing nip HN is the first nip length HN1 shorter than the second nip length HN2, the rotating belt 9b entering the auxiliary fixing nip HN has the main fixing nip HN. The MN is easily stretched in the width direction D2 under the influence of the force that pushes the rotating belt 9b in the width direction D2.
As a result, the wavy portion W formed on the rotating belt 9b is stretched in the width direction D2 of the rotating belt 9b when entering the auxiliary fixing nip HN whose nip length is the first nip length HN1. As it enters, the unevenness tends to be small.

  Further, the nip length of the auxiliary fixing nip HN is the first nip length HN1 shorter than the second nip length HN2. Therefore, the unevenness of the wavy portion W entering the auxiliary fixing nip HN in the rotating belt 9b is not easily held by the auxiliary fixing nip HN, and is easily extended in the width direction D2 in the rotating belt 9b immediately before reaching the main fixing nip MN. Therefore, the formation of wrinkles on the paper T on which the toner image is transferred by the auxiliary fixing nip HN and the main fixing nip MN is suppressed.

As described above, in the present embodiment, the wavy portion W formed on the rotating belt 9b has the unevenness of the wavy portion W easily reduced when the paper T enters the auxiliary fixing nip HN, and the wavy portion W. Passes through the auxiliary fixing nip HN while being stretched in the width direction D2. That is, the rotary belt 9b on which the paper T is placed is moved to the main fixing nip MN without the wavy portion W. Therefore, it is possible to suppress the formation of wrinkles on the paper T placed on the rotating belt 9b.
After the paper T enters the auxiliary fixing nip HN in step ST5, the process proceeds to step ST6.

  In step ST6, as shown in FIG. 9A, after the conveyed paper T enters the main fixing nip MN, the belt position change control unit 972 moves the predetermined portion 950 of the rotating belt 9b to the first on the virtual reference line X. The rotating belt drive unit 935 is instructed to be positioned from the position U1 to the second position U2. As a result, as shown in FIG. 9B, the nip length of the auxiliary fixing nip HN is increased from the first nip length HN1 at the first position U1 to the second nip length HN2 at the second position U2. That is, the area of the fixing nip of the auxiliary fixing nip HN is increased.

Specifically, the belt position change control unit 972 is based on the detection information from the position detection unit 971, and at a predetermined timing after the conveyed paper T enters the main fixing nip MN, the rotary belt driving unit 935. The tension roller 930 is instructed to move in a direction in which the length of the auxiliary fixing nip HN becomes longer (a direction in which the pressure roller 920 is closer to the heating roller 9a). For example, when the paper T passes through the auxiliary fixing nip HN, the timing of moving the tension roller 930 is as long as the rotating belt 9b is extended to a state where no wrinkles are formed on the paper T. It may be a predetermined timing after T enters the auxiliary fixing nip HN.
The predetermined portion 950 of the rotating belt 9b is moved by the rotating belt driving unit 935 in a direction toward the heating roller 9a in the thickness direction of the predetermined portion 950.
Note that the predetermined timing after the sheet T enters the main fixing nip MN or the auxiliary fixing nip HN is calculated by the belt position change control unit 972 based on detection information from the position detection unit 971.

  Then, the paper T is passed through the auxiliary fixing nip HN in a state where the nip length of the auxiliary fixing nip HN is positioned at the second position U2 where the second nip length HN2 is reached. That is, when the paper T enters the auxiliary fixing nip HN, the nip length of the auxiliary fixing nip HN is the first nip length HN1 (see FIG. 8), but the paper T on which the toner image is formed is used. At the time of fixing, as shown in FIG. 9A, the nip length of the auxiliary fixing nip HN becomes a second nip length HN2 longer than the first nip length HN1. Accordingly, since the area of the fixing nip of the auxiliary fixing nip HN is increased, the toner image can be satisfactorily fixed on the paper T by the auxiliary fixing nip HN and the main fixing nip MN.

Note that the sheet T has entered the main fixing nip MN with no wrinkles formed at the leading end of the sheet T when the nip length of the auxiliary fixing nip HN is the first nip length HN1. Therefore, even when the nip length of the auxiliary fixing nip HN is changed to the second nip length HN2, no wrinkles are formed on the paper T that is sequentially moved after the leading edge enters the main fixing nip MN. This suppresses the formation of wrinkles on the paper T passing through the auxiliary fixing nip HN and the main fixing nip MN.
In step ST6, the process proceeds to step ST7 in a state where the nip length of the auxiliary fixing nip HN is maintained at the second nip length HN2.

  In step ST7, as shown in FIG. 10, the paper T is passed through the auxiliary fixing nip HN and the main fixing nip MN, and the toner image formed on the paper T is fixed by the fixing device 9. With the nip length of the auxiliary fixing nip HN being the second nip length HN2, the sheet T passes through the auxiliary fixing nip HN and the main fixing nip MN formed by the heating roller 9a and the rotating belt 9b. As a result, the fixing device 9 melts the toner TN adhering to the paper 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 910 via the heating roller 9a. Then, the toner image is fixed on the paper T by applying pressure to the paper T via the rotary belt 9 b by the pressure roller 920.

According to the fixing device 9 of the first embodiment, the following effects are exhibited.
According to the present embodiment, the fixing device 9 includes the first position U1 where the nip length in the auxiliary fixing nip HN is the first nip length HN1, and the nip length longer than the first nip length HN1. A rotating belt driving unit 935 (belt position changing unit 934) that changes the second nip length HN2 to the second position U2, a position detecting unit 971 that detects the position of the paper T in the transport direction D1, and a position detecting unit A belt position change control unit 972 that controls the rotary belt drive unit 935 (belt position change unit 934) based on the information on the position of the paper T detected by 971, when the paper T enters the auxiliary fixing nip HN. , The belt that instructs the rotating belt drive unit 935 (belt position changing unit 934) to position the predetermined portion 950 of the rotating belt 7b at the first position U1. It includes a location change control unit 972, a.

  Therefore, when the paper T enters the auxiliary fixing nip HN, the nip length in the auxiliary fixing nip HN is the first nip length HN1. As a result, the corrugated portion W formed on the rotating belt 9b tends to be less uneven when the paper T enters the auxiliary fixing nip HN, and the corrugated portion W is extended in the width direction D2. While passing through the auxiliary fixing nip HN. That is, the rotary belt 9b on which the paper T is placed is moved to the main fixing nip MN without the wavy portion W. As a result, the formation of wrinkles on the paper T placed on the rotating belt 9b can be suppressed.

  In addition, according to the present embodiment, the rotating belt drive unit 935 (belt position changing unit 934) moves the tension roller 930 in the direction toward the heating roller 9a or away from the heating roller 9a, thereby causing a predetermined portion of the rotating belt 9b. 950 is configured to change the position. Therefore, the position of the rotating belt 7b can be changed with a simple configuration that only moves the tension roller 930. That is, the nip length of the auxiliary fixing nip HN can be easily changed to the first nip length HN1 and the second nip length HN2. Accordingly, it is possible to easily suppress the formation of wrinkles on the paper T on which the toner image is transferred by the auxiliary fixing nip HN and the main fixing nip MN.

  In the present embodiment, the belt position change control unit 972 positions the predetermined portion 950 of the rotating belt 9b at the second position U2 after the sheet T enters the main fixing nip MN or the auxiliary fixing nip HN. The rotating belt driving unit 935 (belt position changing unit 934) is configured to instruct. Therefore, after the paper T enters the auxiliary fixing nip HN, the nip length of the auxiliary fixing nip HN can be increased to the second nip length HN2. As a result, the toner image can be fixed on the paper T in a state where the fixing nip has a large area.

  Next, the fixing device 9A of the second embodiment will be described. The second embodiment will be described mainly with respect to differences from the first embodiment, the same reference numerals are given to the same configurations as those of the first embodiment, and detailed description thereof will be omitted. In the second embodiment, the description of the first embodiment is appropriately applied to points that are not particularly described. Also in the second embodiment, the same effects as in the first embodiment are achieved. FIG. 11 is a conceptual diagram illustrating a configuration of the fixing device 9A according to the second embodiment.

As shown in FIG. 11, the fixing device 9 </ b> A of the second embodiment is different from the fixing device 9 of the first embodiment in that the introduction guide member 960 is provided and the belt position changing unit 934 is configured by a guide driving unit 965. Different.
As shown in FIG. 11, the introduction guide member 960 includes a guide plate 961 and a pressing portion 962. The introduction guide member 960 is a member for introducing the paper T conveyed to the auxiliary fixing nip HN and the main fixing nip MN.

The guide plate 961 is formed of a substantially rectangular plate material.
The guide plate 961 is disposed at a position and an angle at which the conveyed paper T can be guided to the auxiliary fixing nip HN and the main fixing nip MN. Specifically, the guide plate 961 is arranged along the paper T when the paper T is transported so as not to hinder the transport of the paper T at least when the paper T is transported in the transport direction D1. It is arranged in a state of being substantially parallel to the paper T or being inclined from the substantially parallel state. The sheet T is conveyed so that the direction along the upper surface of the guide plate 961 is directed to the auxiliary fixing nip HN and the main fixing nip MN when the auxiliary fixing nip HN and the main fixing nip MN are positioned.

The leading end 961a of the guide plate 961 is disposed between the pressure roller 920 and the tension roller 930 in the rotating belt 9b and is opposed to the predetermined portion 950 in the rotating belt 9b.
The pressing portion 962 is linear at the distal end portion 961a of the guide plate 961 and is disposed along the width direction (second direction) D2 of the rotating belt 9b.
The pressing portion 962 is configured by a sliding member that slidably contacts the rotating belt 9b. The pressing portion 962 is disposed on the rotating belt 9 b side at the distal end portion 961 a of the guide plate 961 of the introduction guide member 960. The pressing portion 962 is formed to extend in the width direction D2 of the rotating belt 9b so as to follow the distal end portion 961a of the guide plate 961. The length of the pressing portion 962 is longer than the width of the paper T conveyed to the main fixing nip MN (length along the width direction D2). The pressing portion 962 is configured by, for example, a pad with good sliding properties. The pressing portion 962 presses and contacts the outer peripheral surface of the predetermined portion 950 of the rotating belt 9b.

  In the second embodiment, the virtual reference line X extends in the thickness direction of the rotating belt 9b at a position where the pressing portion 962 between the pressure roller 920 and the tension roller 930 presses the outer peripheral surface of the rotating belt 9b. Is set as follows. Note that the position of the virtual reference line X can be changed as appropriate. The “predetermined portion 950” refers to a portion located on the virtual reference line X in the rotating belt 9b, as in the first embodiment.

  In addition, in this embodiment, although the press part 962 was set as the structure extended in the width direction D2 of the rotating belt 9b, it is not limited to this. For example, the pressing portion 962 is configured by a plurality of members that press both end portions and the center portion in the width direction D2 of the rotating belt 9b, and is configured to press a plurality of portions in the width direction D2 in the predetermined portion 950 of the rotating belt 9b. May be.

  The introduction guide member 960 has an end portion in the width direction D2 of the rotating belt 9b connected to a guide driving unit 965 described later in the belt position changing unit 934. The introduction guide member 960 is configured to be movable in a direction toward the rotation belt 9b and a direction away from the rotation belt 9b so that the guide plate 961 is moved in parallel. The introduction guide member 960 is movably attached to the case of the apparatus main body M in the printer 1 and other members.

The belt position changing unit 934 includes a guide driving unit 965.
The guide drive unit 965 moves the introduction guide member 960 to change the position of the predetermined portion 950 on the rotating belt 9b. When the paper T enters the auxiliary fixing nip HN, the guide driving unit 965 rotates the pressing portion 962 of the introduction guide member 960 by pressing the outer peripheral surface of the predetermined portion 950 of the rotating belt 9b along the width direction D2. The position in the thickness direction of the predetermined portion 950 in the belt 9b is changed.

Specifically, as illustrated in FIG. 11, the guide driving unit 965 presses the predetermined portion 950 of the rotating belt 9 b from a position away from the pressing portion 962 of the introduction guide member 960. Accordingly, the guide driving unit 965 changes the predetermined portion 950 of the rotating belt 9b from the second position U2 to the first position U1 on the virtual reference line X.
Further, the guide drive unit 965 separates the pressing portion 962 of the introduction guide member 960 from the position where the pressing portion 962 is pressed against the predetermined portion 950 of the rotating belt 9b. Accordingly, the guide driving unit 965 changes the predetermined portion 950 of the rotating belt 9b from the first position U1 to the second position U2 on the virtual reference line X.

  As in the first embodiment described above, the present embodiment includes the position detection unit 971 and the belt position change control unit 972, so that the predetermined portion 950 of the rotating belt 9b has a first position U1 on the virtual reference line X. Or it can move to the 2nd position U2.

According to the fixing device 9A of the second embodiment, the same effects as the fixing device 9 of the first embodiment are exhibited, and further, the following effects are achieved.
According to the present embodiment, the fixing device 9A has the leading end portion 961a opposed to the predetermined portion 950 of the rotating belt 9b, the introduction guide member 960 for introducing the paper T into the auxiliary fixing nip HN, and the predetermined portion 950. A pressing portion 962 capable of pressing the outer peripheral surface. And the guide drive part 965 is comprised so that the press part 962 may press the outer peripheral surface of the predetermined part 950, and may change the position of the predetermined part 950. FIG. Therefore, the fixing device 9A can achieve the same effect as that of the first embodiment with a simple configuration.
Moreover, since the press part 962 can be arrange | positioned using the introductory guide member 960, cost can be reduced. Furthermore, the pressing unit 962 can be arranged in a narrow space inside the copying machine 1.

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 each of the above-described embodiments, the pressure roller 920 (second rotating body) is driven to rotate and the rotating belt 9b is driven to rotate. However, the present invention is not limited to this, and the first rotating body is driven to rotate. 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 above-described embodiment, the position detection sensor 975 for detecting the paper T is arranged immediately before the fixing device 9 in the transport direction D1 of the paper T (upstream in the transport direction D1). It is not limited. As long as the position detection sensor 975 is configured to output position information related to the position of the paper T, there is no limitation on the position and sensor type.

  In the above-described embodiment, the belt position changing unit 934 includes the rotating belt driving unit 935 or the guide driving unit 965. However, the configuration is not limited thereto.

  In the above-described embodiment, the predetermined portion 950 of the rotating belt is positioned at the second position U2 before the sheet T enters the auxiliary fixing nip HN. However, the present invention is not limited to this. The predetermined portion 950 in the rotating belt 9b may be positioned at the first position U1 when the paper T enters the auxiliary fixing nip HN.

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.
The sheet-shaped transfer material is not limited to paper, and may be a film sheet, for example.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photosensitive drum (image carrier), 16 ... Developing device, 9 ... Fixing device, 9a ... Heating roller (first rotating body), 9b ... Rotation Belt, 910... Heater, 920... Pressure roller (second rotating body), 930 .. tension roller (third rotating body), 934... Belt position changing section, 942. Second part, 950... Predetermined part, 972... Belt position change control part, I... First rotation axis, J... Second rotation axis, K. HN1 ... 1st nip length, HN2 ... 2nd nip length, HN ... Auxiliary fixing nip, MN ... Main fixing nip, T ... Paper (transfer material), TN ... Toner, U1 ... 1st position, U2 ... 2nd position

Claims (5)

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;
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;
An auxiliary fixing nip formed by the second portion of the rotating belt and a portion of the first rotating body facing the second portion and positioned continuously to the main fixing nip;
Position of the rotating belt in the thickness direction at a predetermined portion located between the second rotating body and the third rotating body of the rotating belt and upstream of the second portion in the rotating direction of the rotating belt. A belt position changing unit for changing the first fixing position, wherein a first nip length is a nip length in the rotation direction of the rotating belt in the auxiliary fixing nip, and a nip length is the first nip length. A belt position changing portion that changes the second nip length to a second position that is longer than the second nip length;
A position detection unit that detects a position in the conveyance direction of the sheet-shaped transfer material;
A belt position change control unit that controls the belt position change unit based on information on the position of the transfer material detected by the position detection unit, and when the transfer material enters the auxiliary fixing nip. Includes a belt position change control unit that instructs the belt position change unit to position the predetermined portion of the rotating belt at the first position. The belt position changing unit moves the third rotating body in a direction toward the first rotating body or in a direction away from the first rotating body to change the position of the predetermined portion in the rotating belt. The image forming apparatus described. An introduction guide member having a front end portion arranged to face the predetermined portion of the rotating belt and introducing a sheet-shaped transfer material into the auxiliary fixing nip;
A pressing portion formed on the tip portion side and capable of pressing the outer peripheral surface of the predetermined portion;
The image forming apparatus according to claim 1, wherein the belt position changing unit changes the position of the predetermined portion by the pressing portion pressing an outer peripheral surface of the predetermined portion. The belt position change control unit is configured to position the predetermined portion of the rotating belt at the second position after the material to be transferred has entered the auxiliary fixing nip or the main fixing nip. The image forming apparatus according to claim 1, wherein an image forming apparatus is instructed. 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 sheet-like transfer material;
An image forming apparatus comprising: the fixing device according to claim 1.

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