JP2011248093A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus provided with a fixing device capable of switching a nip pressure in a fixing nip depending on environmental conditions.SOLUTION: The provided fixing device 9 comprises a storage part 52; a first rotating body 9a; a second rotating body 9b; a support member 524 capable of changing the position of the second rotating body 9b with respect to the first rotating body 9a; a switching member 521 capable of switching between states, in one of which the pressing force of a first biasing member 522 capable of generating a first nip pressure is transmitted to the second rotating body 9b and in another of which the pressing force of a second biasing member 525 capable of generating a second nip pressure smaller than the first nip pressure is transmitted to the second rotating body 9b; a pressing member 523 capable of moving the switching member 521; a pressing member position change part 512 for moving the pressing member 523; a temperature detection member 70; and a fixing nip change control section 110 for controlling the pressing member position change part 512 so that the switching member 521 is positioned at a predetermined position based on the humidity detected by the humidity detection member 70.

Description

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

  2. Description of the Related Art Conventionally, as an apparatus for forming (printing) an image on a sheet as a transfer material, 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, a fixing device including a heating roller (first rotating body) and a pressure roller (second rotating body) that forms a fixing nip together with the heating roller is used as a fixing device that performs a fixing process. 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. In such a fixing device, when the paper is conveyed to the fixing nip, the toner transferred onto the paper is melted and pressurized, and is fixed to the paper.

  By the way, depending on the image forming apparatus, an image can be formed (printed) on a cylindrical object (transfer material) 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. Thus, when a cylindrical object is passed through the fixing nip, the fixing nip pressure is generally reduced as much as possible.

  Patent Document 1 describes a fixing device in which the fixing nip pressure is reduced (the fixing nip pressure is switched) when an image is fixed on a cylindrical object. The fixing device described in Patent Document 1 includes a biasing member that biases the heating roller toward the pressure roller, and a cam member that rotates so as to press the biasing member against the biasing force. Therefore, the fixing nip pressure applied to the cylindrical object can be reduced, and the generation of wrinkles generated on the cylindrical object can be suppressed.

JP 2007-79160 A

The fixing device described in Patent Document 1 is configured to switch the fixing nip pressure when fixing an image on a cylindrical object between the cylindrical object and a normal transfer material. However, in the fixing device described in Patent Document 1, no consideration has been given to switching the fixing nip pressure when fixing an image on the same type of transfer material.
Therefore, there has been a demand for a fixing device that can switch the fixing nip pressure when the state of the material to be transferred changes due to a change in the environmental condition in the same type of material to be transferred.

  Accordingly, an object of the present invention is to provide an image forming apparatus including a fixing device that can switch a nip pressure at a fixing nip according to an environmental situation.

  The present invention relates to a casing, a storage unit that is disposed inside the casing and that stores a transfer material, and a toner that forms a toner image transferred to the transfer material in a state of being provided in the image forming apparatus. A fixing device that melts and fixes the toner to the transfer material, the first rotating body being rotatable about a first rotating shaft, the first rotating body being disposed opposite to the first rotating body, Forming a fixing nip through which the transfer material is conveyed and a second rotating body rotatable about a second rotating shaft parallel to the first rotating shaft, wherein the fixing nip is formed The second rotating body biased in a direction away from the first rotating body, and supporting the second rotating body and changing the position of the second rotating body relative to the first rotating body by swinging And a nip pressure at the fixing nip of the first support. A first urging member capable of urging the second rotator in a direction toward the first rotator via the support member so as to obtain a nip pressure, and a nip pressure at the fixing nip as the first nip pressure. A second urging member capable of urging the second rotating body in a direction toward the first rotating body via the support member so as to have a smaller second nip pressure, and the first urging member or A switching member that can be switched to a state in which the urging force of any one of the second urging members is transmitted to the second rotating body, and a contact member that is in contact with the switching member, and that is urged by the first urging member. A first position where the switching member is positioned in a state where force is transmitted to the second rotating body, and a position where the switching member is positioned where the biasing force of the second biasing member is transmitted to the second rotating body. A pressing member movable to a second position to be moved, and the pressing Based on the pressing member position changing unit that moves the material to the first position and the second position, a humidity detecting member disposed in the housing or the housing unit, and the humidity detected by the humidity detecting member And a fixing device including a fixing nip pressure change control unit that controls the pressing member position changing unit so that the switching member is positioned at the first position or the second position.

  The fixing nip pressure change control unit controls the pressing member position changing unit so that the switching member is positioned at the second position when the humidity value detected by the humidity detecting member is equal to or greater than a predetermined value. It is preferable to do.

  The pressing member position changing unit is disposed in contact with the pressing member, and a first rotation position that positions the pressing member at the first position and a second position that positions the pressing member at the second position. A cam member capable of rotating to a rotation position; and a rotation drive unit for rotating the cam member to the first rotation position and the second rotation position, and the fixing nip pressure change control unit, It is preferable to control the rotation driving unit.

  Moreover, it is preferable that the said cam member does not rotate at the said 1st rotation position with the urging | biasing force applied from the said 1st urging member via the said press member.

  The switching member is disposed between the support member and the first urging member, and is engaged with the support member so that the urging force of the first urging member is applied to the second rotating body. It is movable between an engagement position, which is a transmitted position, and a non-engagement position, which is a position where the urging force of the first urging member is not transmitted to the second rotating body without being engaged with the support member. The cam member positions the switching member at the engagement position via the pressing member at the first rotation position, and disengages the switching member via the pressing member at the second rotation position. The second rotating body is biased by the first biasing member via the switching member and the support member when the switching member is in the engagement position, and the switching member is When in the disengaged position Serial are preferably biased by the second biasing member through the supporting member.

  According to another aspect of the present invention, a toner image transferred to a transfer material is configured in a state of being provided in a housing, a housing portion that is disposed inside the housing and that houses the transfer material, and the image forming apparatus. A fixing device that melts and fixes toner to be transferred onto the transfer material, and is arranged to face the first rotating body, a first rotating body that is rotatable about a first rotating shaft, and the first rotating body. A rotating body forms a fixing nip through which the material to be transferred is conveyed, and is a second rotating body rotatable around a second rotating shaft parallel to the first rotating shaft, and the fixing nip is formed. A second rotating body biased in a direction away from the first rotating body in a state where the second rotating body is supported, and a position of the second rotating body with respect to the first rotating body by supporting and swinging the second rotating body And a nip pressure at the fixing nip. A first urging member capable of urging the second rotator in a direction toward the first rotator via the support member so as to obtain a nip pressure; A second urging member capable of urging the second rotator in a direction toward the first rotator via the support member so as to have a second nip pressure smaller than a pressure; and the first urging member Or a switching member that can be switched to a state in which the urging force of either one of the second urging members is transmitted to the second rotating body, and a contact member that is in contact with the switching member. A first position where the switching member is positioned in a state where the urging force is transmitted to the second rotating body, and the switching member in a state where the urging force of the second urging member is transmitted to the second rotating body. A pressing member movable to a second position to be positioned; A pressing member position changing unit that moves the pressing member to the first position and the second position, and a moisture content detection unit that directly or indirectly detects the moisture content of the transfer material accommodated in the accommodation unit. And a fixing nip pressure change control unit that controls the pressing member position changing unit so that the switching member is positioned at the first position or the second position based on the moisture content detected by the moisture content detecting unit. And an image forming apparatus including the fixing device.

  According to the present invention, it is possible to provide an image forming apparatus including a fixing device that can switch the nip pressure in the fixing nip according to an environmental situation.

It is a front view for demonstrating arrangement | positioning of each component in the printer 1 of one Embodiment of this invention. 1 is a perspective view showing a fixing device 9 according to an embodiment of the present invention. FIG. 3 is a perspective view of the fixing device 9 at a normal fixing position as viewed from the center in the Y direction. FIG. 5 is a perspective view of the fixing device 9 at a low nip pressure fixing position when viewed from the center in the Y direction. FIG. 6 is a front view showing the fixing device 9 in a normal fixing position. FIG. 6 is a front view showing the fixing device 9 at a low nip pressure fixing position. FIG. 10 is a perspective view showing the position of a rotating member 551 of a cam position detection unit 550 when the fixing device 9 is at a normal fixing position. 6 is a perspective view showing the position of a rotating member 551 of a cam position detecting unit 550 when the fixing device 9 is at a low nip pressure fixing position. FIG. 3 is a functional block diagram relating to a fixing nip pressure change control unit 110 in the fixing device 9. FIG. 5 is a flowchart illustrating an example of control by a fixing nip pressure change control unit 110.

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 an image forming apparatus in the present embodiment 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 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 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 as a transfer unit, and a fixing device 9.

  As shown in FIG. 1, the paper supply / discharge unit KH includes a paper feed cassette 52 as a storage unit, a manual paper feed unit 64, a conveyance path L for a transfer material 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 the arrow about an axis extending in a direction orthogonal to the conveyance direction of the transfer material 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 transfer material T. A transfer bias for transferring the toner image formed on the photosensitive drum 2 to the transfer material T is applied to the transfer roller 8 by a transfer bias applying unit (not shown). The transfer roller 8 is configured to be rotatable while being in contact with the photosensitive drum 2.

  Between the photosensitive drum 2 and the transfer roller 8, the transfer material T conveyed through the conveyance path L is sandwiched. The transferred material T sandwiched between them 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 to the transfer material 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 transfer material T and fixes the toner on the transfer material T. The fixing device 9 includes a heating rotator (heating roller) 9a as a first rotator that is heated by a heater (not shown), and a pressure rotator (pressurization) as a second rotator that is pressed against the heating rotator 9a. Roller) 9b. The heating rotator 9a and the pressure rotator 9b sandwich and pressurize and transfer the transfer material T onto which the toner image has been transferred. When the transfer material T is conveyed while being sandwiched between the heating rotator 9a and the pressure rotator 9b, the toner transferred to the transfer material T is melted and pressurized, and the transfer material T Fixed to 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, one sheet feeding cassette 52 that accommodates the transfer material T is disposed. The paper feed cassette 52 is disposed inside the case body BD. The paper feed cassette 52 is configured to be drawable in the horizontal direction from the right side (the right side in FIG. 1) of the apparatus main body M. 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 transfer material T 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 right end in FIG. 1). It is. The cassette paper feeding 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 63 for feeding the transfer material T one by one to the transport path L. A double feed prevention mechanism is provided.

  The case body BD or the paper feed cassette 52 is provided with a humidity detection sensor 70 as a humidity detection member. In the present embodiment, the humidity detection sensor 70 is disposed in the paper feed cassette 52. The humidity detection sensor 70 detects the humidity around the transfer material T accommodated in the paper feed cassette 52. The humidity detection sensor 70 outputs detection signal information, which is detected information, to the rotation drive control unit 115 of the fixing nip pressure change control unit 110 described later.

  As the humidity detection sensor 70, for example, a resistance change type humidity sensor using a resistance type humidity element whose resistance changes according to the moisture absorption / desorption of the moisture sensitive material, or a capacitance according to the moisture absorption / desorption of the moisture sensitive material. There is a capacitance change type humidity sensor using a capacitance type humidity element that changes.

  On the right side (right side in FIG. 1) of the apparatus main body M, a manual paper feed unit 64 is provided. The manual paper feed unit 64 is provided mainly for supplying a transfer material T having a size and type different from that of the transfer material T set in the paper feed cassette 52 to the apparatus main body M. 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 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.

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

  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 transfer nip N, a second conveyance path L2 from the transfer nip N to the fixing device 9, and a fixing device 9. The third conveyance path L3 to the paper discharge section 50, the manual conveyance path La that joins the paper supplied from the manual sheet feeding section 64 to the first conveyance path L1, and the third conveyance path L3 from the downstream side to the upstream side. A transfer conveyance path Lb that reverses the transfer material T to be conveyed and returns it to the first conveyance path L1 is provided.

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 joining portion P2 and the transfer roller 8), a sensor for detecting the transfer material T and a skew (oblique paper feed) of the transfer material T. ) A registration roller pair 80 is arranged for matching the timing of correction and toner image formation in the image forming unit GK. The 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-described correction and timing adjustment based on detection signal information from the sensor.

The return conveyance path Lb is a conveyance path that is provided in order to make the opposite surface (unprinted surface) opposite to the surface that has already been printed face the photosensitive drum 2 when performing double-sided printing on the transfer material T.
According to the return conveyance path Lb, the transfer material T conveyed from the first branching section Q1 to the sheet discharge section 50 side by the first roller pair 54a is reversed, and the second roller pair 54b enters the first conveyance path L1. It can be returned 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 unprinted surface at the transfer nip N on the transfer material T that is reversed 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 right 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 transfer material T conveyed on the third conveyance path L <b> 3 to the outside of the apparatus main body M by the discharge 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, 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 paper detection sensor is disposed 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. 2 is a perspective view showing the fixing device 9 according to the embodiment of the present invention. FIG. 3A is a perspective view of the fixing device 9 at the normal fixing position as viewed from the center in the Y direction. FIG. 3B is a perspective view of the fixing device 9 at the low nip pressure fixing position as viewed from the center in the Y direction. FIG. 4A is a front view showing the fixing device 9 in the normal fixing position. FIG. 4B is a front view showing the fixing device 9 at the low nip pressure fixing position. FIG. 5A is a perspective view showing the position of the rotation member 551 of the cam position detection unit 550 when the fixing device 9 is in the normal fixing position. FIG. 5B is a perspective view showing the position of the rotation member 551 of the cam position detection unit 550 when the fixing device 9 is at the low nip pressure fixing position.

  In the description of the printer 1 of the present embodiment, the rotation axis direction of various rotating bodies (rollers and the like) in the photosensitive drum 2, the fixing device 9 and the like is “Y direction” (direction passing through FIG. That's it. The Y direction is also a direction orthogonal to the transport direction of the transfer material T. 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 “+ (plus) 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, the specific description of the fixing device 9 and the like will be described with reference to FIG. 2 as viewed from the “+ (plus) side” in the Y direction in FIG. 3A to 5B, description will be given with reference to the view from the “− (minus) side” in the Y direction in FIG.

  As shown in FIGS. 2 to 3B, the fixing device 9 according to the present embodiment has a transfer material (paper) on which a non-fixed toner image (toner) is transferred (formed) on the peripheral surface of a heated heating roller 9a. The envelope T) is conveyed in the conveying direction while being pressed by the pressure roller 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.

  The fixing device 9 includes a normal fixing position (see FIGS. 3A, 4A, and 5A) for performing a fixing operation on the transfer material T in an environment where the moisture content of the transfer material T is low, and the moisture content of the transfer material T. It is possible to switch between two fixing positions, that is, a low nip pressure fixing position (see FIGS. 3B, 4B, and 5B) in which the fixing operation is performed with a nip pressure smaller than the fixing operation at the normal fixing position in an environment where the ratio is high. Yes. The fixing position is switched by, for example, controlling the driving of a fixing nip pressure changing unit 511 (described later) by a fixing nip pressure changing control unit 110 (described later).

As shown in FIGS. 2 to 5B, the fixing device 9 includes a fixing frame 500, a heating roller 9 a, a pressure roller 9 b, a fixing nip pressure changing unit 511, and a cam position detecting unit 550.
The fixing nip pressure changing section 511 moves the pressure roller 9b relative to the heating roller 9a to change the nip pressure of the fixing nip N9 shown in FIG. The cam position detector 550 (see FIGS. 5A, 5B, and 6) detects whether a nip pressure changing cam 515, which will be described later, is positioned at the second rotation position.

Each component constituting the fixing device 9 will be described in detail.
The fixing frame 500 will be described. As shown in FIGS. 2 to 4B, the fixing frame 500 constitutes a housing of the fixing device 9, and includes a pair of side plates 501 and a connecting member 502 that connects the pair of side plates 501 in the Y direction. Prepare. The pair of side plates 501 are spaced apart on both sides in the Y direction in the second transport path L2.

To the fixing frame 500, a heating roller 9a, a pressure roller 9b, and some constituent members of the fixing nip pressure changing unit 511 are rotatably connected. The side plate 501 includes a bearing (not shown) for supporting the heating roller 9a and an engagement hole 503 for supporting the pressure roller 9b via a support member 524 (described later) (see FIGS. 4A and 4B). And have.
As shown in FIG. 2, 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. 3A to 4B, 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 the bearing (not shown) in the side plate 501 of the fixing frame 500. 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 (fixing frame 500).

  A heater (not shown) is disposed inside the heating roller 9a. The heater is disposed in a state where the axial direction thereof is parallel to the first rotation axis J1 (Y direction) of the heating roller 9a. The heater generates heat when energized, and heats the heating roller 9a from the inside. The heater is composed of, for example, a halogen heater or a ceramic heater. The heater heats the fixing nip N9 via the heating roller 9a.

  The pressure roller 9b will be described. The pressure roller 9b is configured to be rotatable around a second rotation axis J2 that is parallel to the first rotation axis J1 and extends in the Y direction. The pressure roller 9b 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.

  As shown in FIGS. 4A and 4B, 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. A gear drive mechanism 530 having a rotation drive unit 531 such as a motor is connected to the second rotation shaft J2 (see FIG. 2).

  The pressure roller 9b is configured to be rotationally driven by the rotational driving unit 531 via the second rotational axis J2. Further, the pressure roller 9 b is rotatably supported by a support member 524 (described later) in the fixing nip pressure changing unit 511 via the second shaft member 922. The pressure roller 9b is disposed on the opposite side of the heating roller 9a with the fixing nip N9 interposed therebetween. Accordingly, the pressure roller 9b is disposed to be rotatable about the second rotation axis J2 and opposed to the heating roller 9a.

  The pressure roller 9b forms a fixing nip N9 (see FIG. 1) through which the transfer material T is conveyed by the heating roller 9a. The pressure roller 9b is disposed so as to press the heating roller 9a in a state where the fixing nip N9 is formed. Therefore, the pressure roller 9b is elastically deformed along the surface shape of the heating roller 9a at a portion facing the heating roller 9a. Thus, the pressure roller 9b is urged away from the heating roller 9a by a repulsive force generated by the nip pressure of the fixing nip N9 in a state where the fixing nip N9 is formed.

  Although details will be described later, the support member 524 in the fixing nip pressure changing portion 511 swings with respect to the side plate 501 of the fixing frame 500. By the swinging of the support member 524, the pressure roller 9b approaches (see FIGS. 3A and 4A) or separates (see FIGS. 3B and 4B) from the heating roller 9a.

Specifically, the pressure roller 9b can take two different positions with respect to the heating roller 9a. The two-stage position of the pressure roller 9b is such that the "normal fixing position" (see FIGS. 3A and 4A) where the outer peripheral surface of the pressure roller 9b most interferes with the outer peripheral surface of the heating roller 9a (see FIGS. 3A and 4A). The “low nip pressure fixing position” (FIG. 3B and FIG. 4B) has a smaller amount of interference with the pressure roller 9b than the amount of interference at the normal fixing position.
The position of the pressure roller 9b is changed by a fixing nip pressure changing unit 511.

  The heating roller 9a rotates as follows. Specifically, when the pressure roller 9b rotates, the heating roller 9a that contacts the outer peripheral surface of the pressure roller 9b is driven to rotate.

The fixing nip pressure changing unit 511 will be described.
As shown in FIGS. 3A to 4B, the fixing nip pressure changing unit 511 can support the supporting member 524 that supports the pressure roller 9b, the switching member 521 that can be engaged with the supporting member 524, and the switching member 521. The pressing member 523, the nip pressure changing cam 515 as a cam member for pressing the switching member 521 via the pressing member 523, and the switching member 521 are biased toward the support member 524 (to the plus side in the Z direction). A first urging member 522, a second urging member 525 capable of urging the pressure roller 9b toward the heating roller 9a via the support member 524, the first urging member 522, and the second urging member 525. A regulating member 528 that regulates the movement in the negative direction in the Z direction, a gear 513 coupled to the nip pressure changing cam 515, and the nip pressure changing cam 515 via the gear 513. To include a rotary drive unit 531 of the gear drive mechanism 530, the cam shaft member 514 for connecting the nip pressure changing cam 515 and the gear 513, (see FIG. 2).
Here, the nip pressure changing cam 515 and the rotation driving unit 531 are configured as a pressing member position changing unit 512.

  A pair of components in the fixing nip pressure changing unit 511 is provided in the Y direction except for the gear 513 and the gear drive mechanism 530. Only one of the pair of components in the Y direction will be described unless otherwise required. The gear 513 and the gear drive mechanism 530 are provided only on the plus side in the Y direction.

  The support member 524 will be described. As shown in FIGS. 3A to 4B, the support member 524 is an arm-shaped member and is formed of a plate material having a predetermined thickness such as a steel plate. The support member 524 includes a roller support portion 524A, an engagement fulcrum portion 524B, a first extension portion 524C, an operation arm 524D, a second extension portion 524E, a second spring locking portion 524F, and a convex shape. Part 524G.

  The roller support portion 524A has a bearing, and the second shaft member 922 of the pressure roller 9b is rotatably supported by the bearing. The engagement fulcrum portion 524B extends from the outer peripheral edge of the roller support portion 524A so as to be bent at a substantially right angle outward in the Y direction and is formed in a hook shape. The engagement fulcrum part 524B is engaged with an engagement hole 503 provided in the side plate 501. Accordingly, the support member 524 can swing with respect to the side plate 501 in the XZ plane with the engagement hole 503 as a fulcrum. When the support member 524 swings around the engagement hole 503, the pressure roller 9b approaches or separates from the heating roller 9a. That is, the support member 524 supports the pressure roller 9b so as to be movable by its swinging.

  Further, since the pressure roller 9b is urged away from the heat roller 9a in a state where the fixing nip N9 is formed, the support member 524 is heated by using the engagement hole 503 as a fulcrum via the pressure roller 9b. It is energized in the direction away from 9a.

The first extending portion 524C is a portion extending a predetermined length obliquely upward from the roller support portion 524A.
The operation arm 524D is formed to extend from the upper end portion of the first extending portion 524C to the plus side in the X direction. The operation arm 524D is inserted into a long hole 521D (described later) in the first vertical arm 521B of the switching member 521.

  The operation arm 524D can be engaged with the lower end of the long hole 521D in the first vertical arm 521B of the switching member 521. Specifically, the operation arm 524D is engaged with the lower end of the long hole 521D (see FIGS. 3A and 4A) and the lower end of the long hole 521D when the switching member 521 moves in the Z direction. It is changed to a state that does not (see FIG. 3B and FIG. 4B).

  In a state where the operation arm 524D is engaged with the lower end of the long hole 521D of the switching member 521 (see FIGS. 3A and 4A), the urging force of the first urging member 522 to be described later is passed through the switching member 521 and the support member 524. Is transmitted to the pressure roller 9b.

  Further, in a state where the operation arm 524D is not engaged with the long hole 521D of the switching member 521 (see FIGS. 3B and 4B), the operation arm 524D swings due to the urging force away from the heating roller 9a in the support member 524, which will be described later. The urging force of the second urging member 525 is transmitted to the pressure roller 9b via the support member 524.

The second extending portion 524E is formed so as to extend from the upper end portion side of the first extending portion 524C to the minus side in the Z direction.
The convex portion 524G is formed so as to extend from the end portion on the minus side in the Z direction of the second extending portion 524E to the minus side in the Z direction. The width of the convex portion 524G in the X direction is narrower than that of the second extending portion 524E. The convex portion 524G is inserted into a second urging member 525 described later.

The second spring locking portion 524F is formed along the X direction across the convex portion 524G at the end in the Z direction of the second extending portion 524E. The second spring locking portion 524F is configured to be able to lock an end portion on the plus side in the Z direction of a second biasing member 525 described later.
Specifically, the second spring locking portion 524F is in a state where the upper end of the second urging member 525 is locked by the support member 524 swinging (see FIGS. 3B and 4B), and in the second state. The biasing member 525 is changed to a state where the upper end of the biasing member 525 is not locked (see FIGS. 3A and 4A).

The switching member 521 will be described. The switching member 521 is a member that can be switched to a state in which the urging force of either the first urging member 522 or the second urging member 525 is transmitted to the pressure roller 9b. The switching member 521 is a member that can move to an engagement position (see FIGS. 3A and 4A) that engages with the support member 524 and a non-engagement position (see FIGS. 3B and 4B) that does not engage with the support member 524. is there. The switching member 521 is formed from a plate material having a predetermined thickness such as a steel plate.
As shown in FIGS. 3A to 4B, the switching member 521 includes a horizontal arm 521A extending in the X direction, a first vertical arm 521B extending from the horizontal arm 521A to the negative side in the Z direction, and a Z direction from the first vertical arm 521B. A second vertical arm 521C extending to the negative side of the first and a protruding portion 521F protruding from the horizontal arm 521A to the positive side in the Z direction.

  The switching member 521 has a shape in which the horizontal arm 521A and the first vertical arm 521B are bent in an L shape. That is, the horizontal arm 521A and the first vertical arm 521B are substantially orthogonal to each other. Further, the protruding portion 521F, the first vertical arm 521B, and the second vertical arm 521C are formed linearly along the Z direction.

  The first vertical arm 521B is formed in a rectangular plate shape having a predetermined width in the Y direction. The first vertical arm 521B has a long hole 521D and a first spring locking portion 521E. The long hole 521D is formed so as to extend in the Z direction at substantially the center of the first vertical arm 521B, and penetrates in the X direction.

  The first spring locking portions 521E are formed at both ends of the end surface of the first vertical arm 521B facing the negative side in the Z direction. The first spring locking portion 521E is formed along the Y direction across the second vertical arm 521C. The first spring locking portion 521E locks the positive end of the first urging member 522, which will be described later, in the Z direction.

  The second vertical arm 521C has a narrower width in the Y direction than the first vertical arm 521B, and is formed so as to extend from the negative end side in the Z direction of the first vertical arm 521B to the negative side in the Z direction. The

  The switching member 521 has an engagement position (see FIGS. 3A and 4A) where the end of the elongated hole 521D in the Z direction engages with the operation arm 524D of the support member 524, and a non-engagement that does not engage with the support member 524. It is configured to be movable to an engagement position (see FIGS. 3B and 4B).

  When the switching member 521 is located at the engagement position, the urging force of the first urging member 522 is transmitted to the pressure roller 9b via the switching member 521 and the support member 524 (see FIGS. 3A and 4A). . In this case, the switching member 521 is urged by the first urging member 522 toward the support member 524 (toward the positive side in the Z direction). Accordingly, the urging force of the first urging member 522 is transmitted to the pressure roller 9b via the switching member 521 and the support member 524.

  On the other hand, when the switching member 521 is positioned at the non-engagement position, the urging force of the first urging member 522 is not transmitted to the pressure roller 9b (see FIGS. 3A and 4A). That is, the position of the support member 524 when the switching member 521 is in the non-engagement position is located on the negative side in the Z direction with respect to the position of the support member 524 when the switching member 521 is in the engagement position.

  In this case, the support member 524 is swung by a biasing force in a direction away from the heating roller 9a generated by a repulsive force of the pressure roller 9b with respect to the heating roller 9a. Thereby, the second urging member 525 is locked to the second spring locking portion 524F of the support member 524. As a result, the urging force of the second urging member 525 is transmitted to the pressure roller 9b via the support member 524.

  The pressing member 523 will be described. The pressing member 523 is disposed in contact with the switching member 521. The pressing member 523 is formed from a plate material having a predetermined thickness such as a steel plate. The pressing member 523 is configured to be pressed by rotation of a nip pressure changing cam 515 (described later). The pressing member 523 is a member that presses the switching member 521 to the minus side in the Z direction by being pressed by the nip pressure changing cam 515.

Specifically, the pressing member 523 is movable to a first position (see FIGS. 3A and 4A) and a second position (see FIGS. 3B and 4B) by being pressed by the nip pressure changing cam 515. It is.
As shown in FIGS. 3A and 4A, the first position of the pressing member 523 is a position where the switching member 521 is positioned in a state in which an urging force of a first urging member 522 (described later) is transmitted to the pressure roller 9b. is there. 3B and 4B, the second position of the pressing member 523 is a position where the switching member 521 is positioned so that the urging force of the second urging member 525 is transmitted to the pressure roller 9b. .
The pressing member 523 is moved to a first position and a second position by a pressing member position changing unit 512 configured by a nip pressure changing cam 515 and a rotation driving unit 531.

  The pressing member 523 includes a pressing fulcrum 523A that is rotatably supported by the side plate 501, a pressing support plate 523B that is arranged along the side plate 501, and a positive side (inside) in the Y direction from the pressing support plate 523B. And a pressing lateral arm 523C extending.

  The pressing member 523 has a shape in which the pressing support plate 523B and the pressing lateral arm 523C are bent in an L shape. That is, the pressing support plate 523B and the pressing lateral arm 523C are orthogonal to each other.

  The pressing fulcrum portion 523A is slidably engaged with the side plate 501. Thus, the pressing member 523 can swing with respect to the side plate 501 in the XZ plane with the pressing fulcrum portion 523A as a fulcrum.

  The pressing lateral arm 523C is disposed between the switching member 521 and a nip pressure changing cam 515 (described later). The lower surface on the positive side end portion in the X direction of the pressing lateral arm 523C faces the upper surface of the lateral arm 521A of the switching member 521. When the pressing member 523 swings around the pressing fulcrum portion 523A, the lower surface of the pressing lateral arm 523C presses the upper surface of the lateral arm 521A of the switching member 521, and the switching member 521 moves to the negative side in the Z direction.

  A slide through hole 523D that extends long in the X direction and penetrates in the Z direction is formed in the pressing lateral arm 523C. The protrusion 521F of the switching member 521 is inserted through the slide through hole 523D.

  The pressing member 523 swings around the pressing fulcrum portion 523A when the upper surface of the pressing lateral arm 523C is pressed by the nip pressure changing cam 515. Then, the pressing horizontal arm 523C of the pressing member 523 has the protruding portion 521F inserted through the slide through hole 523D slidable through the slide through hole 523D, and the horizontal arm 521A of the switching member 521 is directed to the negative side in the Z direction. Move with or without pressing.

  The nip pressure changing cam 515 will be described. As shown in FIGS. 3A to 4B, the nip pressure changing cam 515 is arranged in contact with the pressing member. The nip pressure changing cam 515 is disposed on the plus side in the Z direction with respect to the pressing lateral arm 523C of the pressing member 523. The nip pressure changing cam 515 is formed in a shape such that a part of the outer periphery of the cylindrical member is recessed. The outer peripheral surface of the nip pressure changing cam 515 includes an arc-shaped portion 515A as a cam surface and a pair of curved portions 515B and 515B.

  The pair of curved portions 515B and 515B are disposed in the vicinity of a portion where a part of the outer periphery of the cylindrical member of the nip pressure changing cam 515 is recessed. The pair of curved portions 515 </ b> B and 515 </ b> B has a curved shape that protrudes toward the outside of the nip pressure changing cam 515. Each vertex of the pair of curved portions 515B and 515B is formed at a position where the distance from the cam shaft member 514 is substantially the same. The pair of curved portions 515B and 515B are formed apart from each other by a predetermined interval so that the apexes thereof can simultaneously contact the pressing lateral arm 523C of the pressing member 523.

A surface connecting the vertices of the pair of curved portions 515B and 515B is configured as a cam surface.
As shown in FIGS. 3A and 4A, the cam surfaces connecting the vertices of the pair of curved portions 515B and 515B are the upper surfaces of the pressing lateral arms 523C of the pressing member 523 at the same time as the vertices of the pair of curved portions 515B and 515B. Is positioned along the upper surface of the pressing lateral arm 523C. Thereby, a pair of curved part 515B, 515B is comprised so that it may contact | abut simultaneously with the upper surface of the pressing horizontal arm 523C in the stable state. The cam surface formed by the pair of curved portions 515B and 515B has a shorter distance from the center of the shaft of the cam shaft member 514 than the cam surface formed by the arc-shaped portion 515A.

  The arc-shaped portion 515A is formed on the opposite side of the pair of curved portions 515B and 515B in the radial direction of the nip pressure changing cam 515. Specifically, the arc-shaped portion 515A is disposed on the opposite side with respect to the shaft center of the cam shaft member 514 and on the opposite side to the pair of curved portions 515B and 515B. The arc-shaped portion 515A and the pair of curved portions 515B and 515B are disposed at positions where the positions are interchanged when the nip pressure changing cam 515 is rotated by approximately 180 °.

  As shown in FIGS. 3B and 4B, the arc-shaped portion 515A is formed in an arc shape. The arc-shaped portion 515A is configured as a cam surface, and abuts against the pressing lateral arm 523C of the pressing member 523 on the opposite side to the pair of curved portions 515B and 515B in the radial direction of the nip pressure changing cam 515. The arc-shaped portion 515A is configured to come into contact with the upper surface of the pressing lateral arm 523C in a stable state.

  The cam surface constituted by the arcuate portion 515A has a longer distance from the center of the shaft of the cam shaft member 514 than the cam surface constituted by the pair of curved portions 515B and 515B. Therefore, the cam surface constituted by the arcuate portion 515A can move the switching member 521 to the negative side in the Z direction via the pressing member 523 rather than the cam surface constituted by the pair of curved portions 515B and 515B. it can.

  The cam shaft member 514 extends in the Y direction and connects the pair of nip pressure changing cams 515. The cam shaft member 514 is rotationally driven by the rotational drive unit 531 of the gear drive mechanism 530 via the gear 513.

  The rotational drive unit 531 of the gear drive mechanism 530 is configured to rotationally drive a pair of nip pressure changing cams 515 and 515 connected to the cam shaft member 514 via the gear 513. The rotation driving unit 531 rotates and moves the nip pressure changing cam 515 between the first rotation position and the second rotation position.

  The first rotation position of the nip pressure changing cam 515 (see FIGS. 3A and 4A) is such that the pair of curved portions 515B and 515B are located on the negative side in the Z direction, and the pair of curved portions 515B and 515B are the pressing members. This is a rotational position where the switching member 521 is positioned at the first position in contact with 523.

  The nip pressure changing cam 515 is configured not to rotate and move by the urging force applied from the first urging member 522 via the pressing member 523 at the first rotation position (see FIGS. 3A and 4A). In other words, the nip pressure changing cam 515 is in contact with the pressing member 523 at the first rotational position so that the nip pressure changing cam 515 does not rotate unless a rotational force is applied by the rotational drive unit 531 from the outside.

  The second rotation position (see FIGS. 3B and 4B) of the nip pressure changing cam 515 is such that the arcuate portion 515A is positioned on the negative side in the Z direction, and the arcuate portion 515A abuts against the pressing member 523 to move the pressing member 523 to the second position. It is a rotation position located in 2 positions.

As shown in FIGS. 3A and 4A, when the nip pressure changing cam 515 is in the first rotation position, the nip pressure changing cam 515 is pressed by a biasing force applied from a first biasing member 522 described later. In the state, the switching member 521 is positioned at the engagement position via the pressing member 523.
As shown in FIGS. 3B and 4B, when the nip pressure changing cam 515 is in the second rotational position, the nip pressure changing cam 515 is pressed by the urging force applied from the first urging member 522. The switching member 521 is positioned at the non-engagement position via the pressing member 523.

The first urging member 522 will be described. As shown in FIGS. 3A to 4B, the first urging member 522 is formed of a coil spring having a predetermined length, and is disposed in a state where the second vertical arm 521C of the switching member 521 is disposed on the inner side. That is, the second vertical arm 521C of the switching member 521 is inserted inside the first biasing member 522. Further, the positive end of the first biasing member 522 in the Z direction is locked to the first spring locking portion 521E. The first urging member 522 has a length and an urging force to urge the switching member 521 by engaging the support member 524 when the nip pressure changing cam 515 is located at the first rotation position. .
The first urging member 522 is expanded and contracted while the switching member 521 moves in the Z direction and is locked to the first spring locking portion 521E.

  As shown in FIGS. 3A and 3B, when the nip pressure changing cam 515 is located at the first rotation position, the first biasing member 522 is supported in the elongated hole 521D of the switching member 521 by its elastic return force. In a state where the operation arm 524D of the member 524 is engaged, the switching member 521 is urged toward the support member 524 (toward the positive side in the Z direction). Thereby, the first urging member 522 can urge the pressure roller 9b toward the heating roller 9a via the support member 524 so that the nip pressure at the fixing nip N9 becomes the first nip pressure.

  The second urging member 525 will be described. As shown in FIGS. 3A to 4B, the second urging member 525 is made of a coil spring having a predetermined length, and is arranged in a state where the convex portion 524G of the switching member 521 is arranged inside. That is, the convex portion 524G of the switching member 521 is inserted inside the second urging member 525. Further, the positive end of the second urging member 525 in the Z direction can be locked to the second spring locking portion 524F.

  The second biasing member 525 is not locked by the second spring locking portion 524F (see FIGS. 3A and 4A) due to the swing of the support member 524, and the second biasing member 525 is elastically restored by the elastic return force of the second biasing member 525. It is expanded and contracted to a state (see FIGS. 3B and 4B) that is locked to the two spring locking portion 524F.

  The second urging member 525 has a natural length and does not urge the support member 524 when the second urging member 525 is not locked to the second spring locking portion 524F. Further, the second urging member 525 urges the support member 524 to press toward the plus side in the Z direction in a state where the second urging member 525 is locked to the second spring locking portion 524F by the elastic return force.

Specifically, the second urging member 525 has a natural length that does not contact the second spring locking portion 524F when the nip pressure changing cam 515 is located at the first rotation position. . Further, the second urging member 525 causes the second spring locking portion 524F to move more when the nip pressure changing cam 515 is located at the second rotational position than when the nip pressure changing cam 515 is located at the first rotational position. It has a length to be locked at the negative position in the Z direction.
Thus, the second biasing member 525 moves the pressure roller 9b toward the heating roller 9a via the support member 524 so that the nip pressure at the fixing nip N9 is a second nip pressure smaller than the first nip pressure. Can be energized.

  The regulating member 528 will be described. The regulating member 528 is attached to the side plate 501. The regulating member 528 is formed from a plate material having a predetermined thickness such as a steel plate. The restricting member 528 includes a base plate 528A disposed along the side plate 501 and a restricting plate 528B extending from the base plate 528A to the plus side (inward) in the Y direction. The regulating member 528 has a shape in which the base plate 528A and the regulating plate 528B are bent in an L shape.

The restriction plate 528B is formed to extend in the X direction on the negative side of the first biasing member 522 and the second biasing member 525 in the Z direction.
The negative end portion in the Z direction of the first biasing member 522 and the negative end portion in the Z direction of the second biasing member 525 are in contact with the upper surface of the regulating plate 528B. Thereby, the restricting plate 528B restricts the movement of the first urging member 522 and the second urging member 525 to the minus side in the Z direction.

  The restriction plate 528B is formed with a through hole 528C penetrating in the Z direction. The through hole 528 </ b> C is inserted with the negative end side in the Z direction of the second vertical arm 521 </ b> C of the switching member 521. The second vertical arm 521C is movable in the Z direction while being inserted through the through hole 528C. Therefore, the switching member 521 is movable in the Z direction in a state where the second vertical arm 521C is inserted through the through hole 528C.

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

  In brief, the switching member 521 moves in the Z direction by being pressed by the pressing member 523 corresponding to the displacement of the cam surface of the nip pressure changing cam 515 due to the rotation of the nip pressure changing cam 515. As the switching member 521 moves in the Z direction, the support member 524 swings. Therefore, the urging force of either the first urging member 522 or the second urging member 525 can be applied to the pressure roller 9b via the support member 524.

  Thereby, the position of the pressure roller 9b supported by the support member 524 is different when the urging force of either the first urging member 522 or the second urging member 525 is applied. Therefore, the position of the pressure roller 9b with respect to the heating roller 9a can be changed. As a result, the nip pressure of the fixing nip N9 can be changed.

Next, the fixing position in the fixing device 9 of this embodiment will be described in detail.
As described above, the nip pressure changing cam 515 is rotationally driven by the rotation driving portion 531 of the fixing nip pressure changing portion 511, and the pair of curved portions 515B and 515B attach the switching member 521 to the first via the pressing member 523. A first rotation position (see FIGS. 3A and 4A) pressed against the urging force of the urging member 522, and an arcuate portion 515 </ b> A that rotates approximately 180 ° from the first rotation position via the pressing member 523. The rotational position can be changed to the second rotational position (see FIGS. 3B and 4B) pressed against the urging force of the first urging member 522.

As shown in FIGS. 3A and 4A, when the nip pressure changing cam 515 is located at the first rotation position, the normal fixing position is obtained. When the nip pressure changing cam 515 is located at the first rotational position, the nip pressure changing cam 515 is also referred to as being in the “normal posture”.
Further, as shown in FIGS. 3B and 4B, when the nip pressure changing cam 515 is located at the second rotational position, the low nip pressure fixing position is obtained. When the nip pressure changing cam 515 is located at the second rotational position, it is also said that the nip pressure changing cam 515 is in the “pressure-reducing posture”.

More specifically, as shown in FIGS. 3A and 4A, when the nip pressure changing cam 515 is located at the first rotation position (normal fixing position), the pressing member 523 has a pair of curves of the nip pressure changing cam 515. It is the state which contact | abutted to the shape parts 515B and 515B. In this state, the support member 524 is urged toward the heating roller 9 a by the first urging member 522 via the switching member 521. In this case, the switching member 521 is positioned at an engagement position where the operation arm 524D of the support member 524 engages with the negative end of the elongated hole 521D in the switching member 521 in the Z direction.
The pressure roller 9b supported by the support member 524 is positioned at a normal fixing position where the outer peripheral surface of the pressure roller 9b interferes with the outer peripheral surface of the heating roller 9a most greatly.

The nip pressure at the fixing nip N9 at the normal fixing position is also referred to as “first nip pressure”.
When the fixing device 9 is in the normal fixing position, the urging force of the first urging member 522 acts on the pressure roller 9b via the switching member 521 and the support member 524. Note that the urging force of the second urging member 525 does not act on the pressure roller 9b because the support member 524 is not in contact with the second urging member 525.

  In the normal fixing position, the pressure roller 9b interferes with the outer peripheral surface of the heating roller 9a and elastically deforms. The pressure roller 9b is urged away from the heating roller 9a by the elastic restoring force of the elastic layer of the pressure roller 9b. The first urging member 522 urges the pressure roller 9b toward the heating roller 9a so as to resist the urging force caused by the elastic return force of the elastic layer of the pressure roller 9b, whereby the nip pressure in the fixing nip N9 is obtained. Is the first nip pressure.

  On the other hand, as shown in FIG. 3B and FIG. 4B, when the nip pressure changing cam 515 is at the second rotational position (low nip pressure fixing position) rotated approximately 180 ° from the first rotational position (normal fixing position), The member 523 is pressed by the arcuate portion 515A of the nip pressure changing cam 515 and swings. The switching member 521 is pressed to the negative side in the Z direction by being pressed by the pressing member 523. Thereby, the switching member 521 is positioned at a non-engagement position where the operation arm 524D does not engage with the end portion on the minus side in the Z direction in the long hole 521D.

  The support member 524 swings in the direction away from the heating roller 9a in order to support the pressure roller 9b biased in the direction away from the heating roller 9a. Accordingly, the second spring locking portion 524F of the support member 524 is locked to the second biasing member 525. As a result, the pressure roller 9b supported by the support member 524 is positioned at the low nip pressure fixing position where the outer peripheral surface interferes with the outer peripheral surface of the heating roller 9a with a smaller amount of interference than at the normal fixing position. become. That is, in the case of the low nip pressure fixing position, the outer peripheral surface of the pressure roller 920 is further away from the outer peripheral surface of the heating roller 9a than in the normal fixing position.

The nip pressure of the fixing nip N9 at the low nip pressure fixing position is also referred to as “second nip pressure”. The second nip pressure is smaller than the first nip pressure at the normal fixing position.
When the fixing device 9 is at the low nip pressure fixing position, the urging force of the second urging member 525 acts on the pressure roller 9b via the support member 524. Note that the urging force of the first urging member 522 does not act on the pressure roller 9b because the support member 524 does not transmit the urging force from the first urging member 522.

  In the low nip pressure fixing position, the pressure roller 9b interferes with the outer peripheral surface of the heating roller 9a with a smaller amount of interference than in the normal fixing position, and is elastically deformed. The pressure roller 9b is urged away from the heating roller 9a by the elastic restoring force of the elastic layer of the pressure roller 9b. The second urging member 525 urges the pressure roller 9b toward the heating roller 9a so as to resist the urging force caused by the elastic return force of the elastic layer of the pressure roller 9b. Is the second nip pressure.

The cam position detection unit 550 will be described.
As shown in FIG. 2, the cam position detector 550 is arranged on the negative side of the fixing device 9 in the Y direction. The cam position detection unit 550 includes a rotation member 551, a sensor 555 having a light emitting unit 555A and a light receiving unit 555B, and a detection unit 560 (see FIG. 6) as a functional unit described later.

The rotating member 551 includes a plate-like member 552 that is long in a predetermined direction and a shielding plate 553. One end side of the plate-like member 552 in the length direction is connected to the cam shaft member 514 outside the side plate 501 of the fixing frame 500 (minus side in the Y direction). Thus, the rotating member 551 is connected to the nip pressure changing cam 515 via the cam shaft member 514.
A shielding plate 553 is disposed at the other end in the length direction of the plate-like member 552. The shielding plate 553 is formed to extend from the other end of the plate-like member 552 to the minus side in the Y direction.

The rotating member 551 rotates in conjunction with the rotation of the nip pressure changing cam 515 by the rotational drive of the cam shaft member 514.
Specifically, as shown in FIG. 5A, the rotating member 551 is configured such that when the nip pressure changing cam 515 is rotated to the first rotation position (see FIGS. 3A and 4A), the shielding plate 553 is moved in the Z direction. It is rotated so that it is located on the plus side of the. Further, as shown in FIG. 5B, when the nip pressure changing cam 515 is rotationally moved to the second rotational position (see FIGS. 3B and 4B), the rotating member 551 is configured such that the shielding plate 553 is on the negative side in the Z direction. It is rotated so that it is located in

  The sensor 555 detects the position of the rotating member 551. The sensor 555 is disposed outside the side plate 501 of the fixing frame 500 (minus side in the Y direction) on the minus side in the Z direction with respect to the cam shaft member 514. The sensor 555 is disposed so that the shielding plate 553 is positioned between the light emitting unit 555A and the light receiving unit 555B when the shielding plate 553 of the rotating member 551 is positioned on the minus side in the Z direction.

  The sensor 555 detects that the shielding plate 553 is positioned on the negative side in the Z direction by positioning the shielding plate 553 between the light emitting unit 555A and the light receiving unit 555B. The sensor 555 outputs a detection signal to the detection unit 560 described later when the shielding plate 553 is positioned between the light emitting unit 555A and the light receiving unit 555B.

Next, referring to FIG. 6, a functional block diagram in the present embodiment will be described. FIG. 6 is a functional block diagram relating to the fixing nip pressure change control unit 110 in the fixing device 9.
As shown in FIG. 6, the printer 1 includes a receiving unit 120 and a control unit 100 in addition to the components described above.

  The receiving unit 120 includes image information of an image to be printed on the transfer material T, type information regarding whether the type of the paper T is a cylindrical transfer object such as an envelope or a normal transfer transfer material, and a transfer target. Image formation information including sheet number information relating to the number of materials T is received. For example, the receiving unit 120 receives image forming information including image information and type information transmitted from an external device (such as a personal computer) connected to the printer 1 via a communication unit (such as a network). Can do. Note that the receiving unit 120 may receive image formation information including image information and type information using a keyboard, a touch panel, or the like disposed in the apparatus main body M of the printer 1.

  The control unit 100 includes a fixing nip pressure change control unit 110 and a detection unit 560 in the cam position detection unit 550. The fixing nip pressure change control unit 110 controls the change of the fixing nip pressure.

  The fixing nip pressure change control unit 110 controls the pressing member position changing unit 512 based on the humidity detected by the humidity detection sensor 70 so that the switching member 521 is positioned at the first position or the second position. In the present embodiment, the pressing member position changing unit 512 includes a nip pressure changing cam 515 and a rotation drive control unit 115. Therefore, the rotation drive control unit 115 (fixing nip pressure change control unit 110) determines that the humidity value detected by the humidity detection sensor 70 is a predetermined value (threshold value) based on the humidity detected by the humidity detection sensor 70. In the above case, the rotation driving unit 531 (the pressing member position changing unit 512) is controlled so that the nip pressure changing cam 515 is positioned at the second rotation position.

  Further, the fixing nip pressure change control unit 110 changes the pressing member position so that the switching member 521 is positioned at the second position when the humidity value detected by the humidity detection sensor 70 is equal to or greater than a predetermined value (threshold value). The unit 512 is controlled. In the present embodiment, the rotation drive control unit 115 (fixing nip pressure change control unit 110) causes the nip pressure change cam 515 to be operated when the humidity detected by the humidity detection sensor 70 is equal to or higher than a predetermined value (threshold value). The rotation driving unit 531 (the pressing member position changing unit 512) is controlled so as to be positioned at the second rotation position.

  This is because when the humidity value detected by the humidity detection sensor 70 is equal to or greater than a predetermined value (threshold value), the moisture content of the transfer material T is high and the fixing nip pressure is the first nip pressure. This is because when the fixing operation of the fixing device 9 is performed at the fixing position, the transfer material T is likely to be wrinkled. That is, there is a correlation between the humidity value detected by the humidity detection sensor 70 and the moisture content value of the transfer material T. Specifically, when the humidity detected by the humidity detection sensor 70 is high, there is a correlation that the moisture content of the transfer material T is high.

  Therefore, as the predetermined value (threshold value) of the humidity value detected by the humidity detection sensor 70, for example, a lower limit humidity value corresponding to the lower moisture content value at which wrinkles occur in the transfer material T is set. Is done. Specifically, when the material to be transferred is a normal sheet T, for example, the predetermined value of the humidity value is set to 80% relative humidity corresponding to the lower moisture content at which wrinkles occur in the material to be transferred T. .

  As described above, when the humidity value detected by the humidity detection sensor 70 is equal to or greater than the predetermined value (threshold value), the fixing nip pressure change control unit 110 positions the switching member 521 at the second position. Then, the pressing member position changing unit 512 is controlled so that the fixing device 9 performs the fixing operation with the fixing nip pressure positioned at the low nip pressure fixing position where the second nip pressure is set. Thereby, generation | occurrence | production of wrinkles in the to-be-transferred material T can be reduced.

  Further, the rotation drive control unit 115 is configured to detect that the nip pressure changing cam 515 is positioned at the second rotation position by the detection unit 560 of the cam position detection unit 550 described later in the initial state of the printer 1. The rotation driving unit 531 is controlled so that the nip pressure changing cam 515 is rotationally moved to the first rotation position.

The detection unit 560 monitors the detection signal output from the sensor 555. Thereby, the detection unit 560 detects whether the nip pressure changing cam 515 is located at the first rotation position or the second rotation position.
The detection unit 560 outputs a detection signal to the rotation drive control unit 115 when detecting that the nip pressure changing cam 515 is positioned at the second rotation position. In the present embodiment, the detection unit 560 is included in the control unit 100 of the printer 1, but may be included in the fixing device 9.

Here, the initial position of the nip pressure changing cam 515 in the fixing device 9 will be described.
In an initial state such as immediately after the printer 1 is turned on, the first rotation position of the nip pressure changing cam 515 is set as the initial position in order to position the fixing device 9 at the normal fixing position. Then, by setting the first rotational position of the nip pressure changing cam 515 as the initial position, it is possible to simplify the control for switching the fixing position of the fixing device 9 performed thereafter.

  Therefore, the nip pressure changing cam 515 according to the present invention is configured to be easily at the first rotation position as the initial position. Specifically, as described above, the nip pressure changing cam 515 is configured not to be rotationally moved by the urging force applied from the first urging member 522 via the pressing member 523 at the first rotation position. Thus, when the nip pressure changing cam 515 is positioned at the first rotation position, the nip pressure changing cam 515 maintains the first rotation position unless the rotation driving force of the rotation driving unit 531 is transmitted.

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 photosensitive drum 2 and the transfer roller 8 (transfer nip N) via the first conveyance path L1. Then, a toner image is transferred to the transfer material T between the photosensitive drum 2 and the transfer roller 8.
Thereafter, the transfer material T is discharged from between the photosensitive drum 2 and the transfer roller 8, and the fixing nip between the heating roller 9 a and the pressure roller 9 b in the fixing device 9 through the second conveyance path L 2. Introduced to 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 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 transfer roller 8, the toner image is transferred to the non-printing surface, and as a result, duplex printing is performed.

  Next, the control flow of the fixing device 9 will be described with reference to FIG. FIG. 7 is a flowchart illustrating an example of control by the fixing nip pressure change control unit 110. In the control flow of the fixing device 9, a case where an image is formed on a paper T as a transfer material will be described.

In step ST1, the power of the printer 1 is turned on by the user.
In step ST2, the cam position detector 550 detects whether the nip pressure changing cam 515 is located at the second rotational position.

  If it is detected that the nip pressure changing cam 515 is located at the second rotational position (YES), the nip pressure changing cam 515 is not located at the first rotational position as the initial position, so the process proceeds to step ST3. On the other hand, when it is not detected that the nip pressure changing cam 515 is located at the second rotational position (NO), the nip pressure changing cam 515 is located at the first rotational position as the initial position, and thus the process proceeds to step ST4.

  In step ST3, the rotation drive control unit 115 controls the rotation drive unit 531 so that the nip pressure changing cam 515 is rotationally moved from the second rotation position to the first rotation position. Specifically, the rotation driving unit 531 rotates the nip pressure changing cam 515 by 180 ° from the second rotation position. As a result, the nip pressure changing cam 515 is positioned at the first rotation position as the initial position. That is, the fixing device 9 is positioned at the normal fixing position in the initial state. After the nip pressure changing cam 515 is positioned at the first rotation position in step ST3, the process proceeds to step ST5.

  In step ST4, the nip pressure changing cam 515 is located at the first rotation position as the initial position. Therefore, the rotation drive control unit 115 controls the rotation drive unit 531 so that the nip pressure changing cam 515 is maintained at the first rotation position. The fixing device 9 is positioned at the normal fixing position in the initial state.

  In step ST <b> 5, an image forming command is transmitted from the external device (such as a personal computer) to the printer 1 by the user. As a result, the receiving unit 120 receives image forming information including type information of the transfer material T and number information of the transfer material T. The received type information of the transfer material T and the number information of the transfer material T are output from the receiving unit 120 to the rotation drive control unit 115 of the fixing nip pressure change control unit 110. In the present embodiment, the type of transfer material is paper T.

  When the reception unit 120 receives the image formation information, in step ST6, the fixing nip pressure change control unit 110 determines whether or not the humidity detected by the humidity detection sensor 70 is equal to or higher than a predetermined value. This is because when the humidity detected by the humidity detection sensor 70 is equal to or higher than a predetermined value, the moisture content of the paper T is high and the paper T is likely to wrinkle during the fixing operation by the fixing device 9.

  When the fixing nip pressure change control unit 110 determines that the humidity value detected by the humidity detection sensor 70 is equal to or higher than a predetermined value (for example, relative humidity 80%) (YES), the fixing position of the fixing device 9 is determined. In order to be positioned at the low nip pressure fixing position, the process proceeds to step ST7. When the fixing nip pressure change control unit 110 determines that the humidity detected by the humidity detection sensor 70 is less than a predetermined value (for example, relative humidity 80%) (NO), the fixing position of the fixing device 9 is normally fixed. In order to make it position, it progresses to step ST12.

  In step ST7, since the humidity value detected by the humidity detection sensor 70 is equal to or higher than a predetermined value (for example, relative humidity 80%), the rotation drive control unit 115 positions the nip pressure changing cam 515 at the second rotation position. The rotation driving unit 531 is controlled so that As a result, the fixing device 9 is positioned at the low nip pressure fixing position. The nip pressure of the fixing nip N9 at the low nip pressure fixing position is a second nip pressure smaller than the first nip pressure at the normal fixing position. By performing the image fixing operation on the paper T at the low nip pressure fixing position, the formation of wrinkles on the paper T is reduced.

  The control unit 100 in the printer 1 monitors the detection signal from the cam position detection unit 550 so that the nip pressure changing cam 515 is positioned at the second rotation position in accordance with the control command of the rotation drive control unit 115. It can also be confirmed. In this case, the control unit 100 in the printer 1 can form an image on the paper T after the nip pressure changing cam 515 is reliably positioned at the second rotation position.

  In step ST8, the paper T is supplied to the image forming unit GK. Then, a toner image is transferred between the photosensitive drum 2 and the transfer roller 8 on the paper T conveyed on the conveyance path L. The paper T discharged from between the photosensitive drum 2 and the transfer roller 8 is conveyed toward the fixing device 9.

In step ST9, an image fixing operation on the paper T is performed by the fixing device 9 positioned at the low nip pressure fixing position. Specifically, the fixing device 9 dissolves the toner TN attached to the transfer material T passing through the heating roller 9a and the pressure roller 9b by the heat applied to the toner TN from the heater through the heating roller 9a. The toner image is fixed on the paper T by applying pressure to the transfer material T by the pressure roller 9b.
As described above, when the humidity value detected by the humidity detection sensor 70 is equal to or higher than a predetermined value (for example, relative humidity 80%), the image is fixed on the paper T with the second nip pressure at the low nip pressure fixing position. By doing so, the occurrence of wrinkles on the paper T is reduced. Accordingly, the nip pressure of the fixing nip N9 in the fixing device 9 can be switched according to the humidity condition (environmental condition).

  In step ST <b> 10, the control unit 100 determines whether to continuously print on the paper T based on the number information of the paper T received by the receiving unit 120. When printing the paper T continuously (YES), the process returns to step ST6. If the paper T is not printed continuously, the process proceeds to step ST11.

  In step ST11, since the nip pressure change cam 515 is positioned at the second position, the rotation drive control unit 115 controls the rotation drive unit 531 so that the nip pressure change cam 515 is positioned at the first rotation position. As a result, the nip pressure changing cam 515 is positioned at the first rotation position which is the initial position and the stable rotation position. Control ends after step ST11.

  In step ST12 when the fixing nip pressure change control unit 110 determines that the humidity value detected by the humidity detection sensor 70 in step ST6 is less than a predetermined value (for example, relative humidity 80%) (NO), The rotation drive control unit 115 controls the rotation drive unit 531 so that the nip pressure changing cam 515 is positioned at the first rotation position as the initial position. That is, the fixing device 9 is positioned at the normal fixing position. The nip pressure of the fixing nip N9 at the normal fixing position is a first nip pressure larger than the second nip pressure at the low nip pressure fixing position.

In step ST13, the paper T is supplied to the image forming unit GK. Thereafter, as in step ST8, the paper T is conveyed.
In step ST14, an image fixing operation is performed by the fixing device 9 positioned at the normal fixing position, as in step ST9 described above.

  In step ST <b> 15, the control unit 100 determines whether to continuously print the paper T based on the number information of the paper T received by the receiving unit 120. When printing the paper T continuously (YES), the process returns to step ST6. If the paper T is not printed continuously, the control is terminated. Here, after the control is completed, the nip pressure changing cam 515 is positioned at the first rotation position which is the initial position.

According to the fixing device 9 of the present embodiment, for example, the following effects are exhibited.
The printer 1 in the present embodiment supports the paper feed cassette 52, the heating roller 9a, the pressure roller 9b, and the pressure roller 9b, and swings the position of the heating roller 9a with respect to the heating roller 9a. A support member 524 that can be changed, a first biasing member 522 that can be biased so that the nip pressure is the first nip pressure, and a nip pressure that is lower than the first nip pressure. A second biasing member 525 that can be biased, and a switching member 521 that can be switched to a state in which the biasing force of either the first biasing member 522 or the second biasing member 525 is transmitted to the pressure roller 9b, A first position that is disposed in contact with the switching member 521 and positions the switching member 521 in a state where the urging force of the first urging member 522 is transmitted to the pressure roller 9b, and the urging force of the second urging member 525 A pressing member 523 that can be moved to a second position where the switching member 521 is positioned so as to be transmitted to the pressure roller 9b, and a pressing member position changing unit 512 that moves the pressing member 523 to the first position and the second position. And a humidity detection sensor 70 disposed inside or around the paper feed cassette 52, and a pressing member so that the switching member 521 is positioned at the first position or the second position based on the humidity detected by the humidity detection sensor 70. A fixing device 9 having a fixing nip pressure change control unit 110 that controls the position changing unit 512;

  Therefore, the fixing nip pressure change control unit 110 controls the pressing member position changing unit 512 based on the humidity value detected by the humidity detecting member 70 so that the switching member 521 is located at the first position or the second position. can do. Accordingly, the fixing operation can be performed by switching the fixing nip pressure to an appropriate nip pressure based on the humidity condition having a correlation with the moisture content of the paper T. Accordingly, the fixing device 9 can be switched to an appropriate fixing nip pressure according to the humidity condition (environmental condition). As a result, wrinkles generated on the paper T due to humidity conditions can be reduced.

  In the fixing device 9 of the present embodiment, the fixing nip pressure change control unit 110 determines that the switching member 521 is located at the second position when the humidity value detected by the humidity detection sensor 70 is equal to or greater than a predetermined value. The pressing member position changing unit 512 is controlled.

  Therefore, when the humidity value correlated with the moisture content of the paper T is high, the fixing position of the fixing device 9 can be positioned at the low nip pressure fixing position. Thereby, the paper T can be fixed with the second nip pressure smaller than the first nip pressure at the normal fixing position. Therefore, when the moisture content of the paper T is high, wrinkles generated on the paper T can be reduced.

  Further, in the fixing device 9 of the present embodiment, the pressing member position changing unit 512 is disposed in contact with the pressing member 523, and includes a first rotation position where the pressing member 523 is positioned at the first position, and the pressing member 523. A nip pressure changing cam 515 that can be rotated to a second rotational position that is positioned at the second position, and a rotation drive unit 531 that rotationally moves the nip pressure changing cam 515 to the first rotational position and the second rotational position. The fixing nip pressure change control unit 110 (rotation drive control unit 115) controls the rotation drive unit 531.

  Therefore, in the fixing device 9 of this embodiment, the nip pressure change cam 515 can be positioned at the first rotation position and the second rotation position in a state where the nip pressure change cam 515 is in contact with the pressing member 523. Accordingly, the nip pressure changing cam 515 can be positioned in a stable state at the first rotation position and the second rotation position. Therefore, the urging force of either the first urging member 522 or the second urging member 525 can be stably applied to the pressure roller 9b.

Specifically, when fixing an image on the paper T having a low moisture content, the first urging member 522 heats the pressure roller 9b by positioning the nip pressure changing cam 515 at the first rotation position. The urging is performed in the direction toward the roller 9a. In this case, the first urging member 522 urges the nip pressure of the fixing nip N9 to be the first nip pressure.
When the image is fixed on the paper T having a high moisture content, the second urging member 525 causes the pressure roller 9b to the heating roller 9a by positioning the nip pressure changing cam 515 at the second rotational position. Energize in the direction you head. In this case, the second urging member 525 urges the nip pressure of the fixing nip N9 to be the second nip pressure.
Accordingly, when fixing an image on the paper T having a high moisture content, wrinkles generated on the paper T can be reduced and a fixing nip can be stably provided.

  Further, in the fixing device 9 of the present embodiment, the nip pressure changing cam 515 does not rotate by the urging force applied from the first urging member 522 via the pressing member 523 at the first rotation position. Therefore, the nip pressure changing cam 515 is held in a stable state at the first rotational position. Thereby, the initial position in the nip pressure changing cam 515 can be ensured by setting the initial position as the first rotational position.

  Further, in the fixing device 9 of the present embodiment, the switching member 521 is disposed between the support member 524 and the first biasing member 522 and engages with the support member 524 to engage with the first biasing member 522. The engagement position is a position where the urging force of the first urging member 522 is not engaged with the support member 524 and the position where the urging force of the first urging member 522 is not transmitted to the pressure roller 9b. The nip pressure change cam 515 can be switched to the engagement position via the pressing member 523 at the first rotation position and switched via the pressing member 523 at the second rotation position. The member 521 is positioned at the non-engagement position, and the pressure roller 9b is applied by the first urging member 522 via the switching member 521 and the support member 524 when the switching member 521 is in the engagement position. Is, the switching member 521 is biased by the second biasing member 525 via the support member 524 when in the disengaged position.

  Therefore, the urging force of either the first urging member 522 or the second urging member 525 can be transmitted to the pressure roller 9b with a simple configuration. Thereby, when the image is fixed on the paper T, the nip pressure in the fixing nip N9 can be more stably applied.

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, since there is a correlation between the humidity value detected by the humidity detection sensor 70 and the moisture content value of the paper T, it is based on the humidity detected by the humidity detection sensor 70. Although the fixing nip pressure change control unit 110 is controlled, the present invention is not limited to this. For example, the fixing device 9 includes a moisture content detection unit (not shown) that directly or indirectly detects the moisture content of the paper T stored in the paper feed cassette 52, and has a moisture content detected by the moisture content detection unit. Based on this, the fixing nip pressure change control unit 110 may be controlled. By detecting the moisture content directly or indirectly by the moisture content detection unit, it is possible to grasp the finer moisture content of the paper T.

  For example, the moisture content detection unit that directly detects the moisture content of the paper T includes a weight measurement unit (not shown) that measures the weight of the paper T placed on the placement plate 60 of the paper feed cassette 52, and a paper A weight measurement unit including a sheet thickness detection unit (not illustrated) that detects the thickness of T, and a storage unit (not illustrated) that stores the thickness of one sheet T and the weight of one sheet T during drying. The water content is obtained by referring to the storage unit based on the weight of the paper T measured by the above and the thickness of the paper T detected by the paper thickness detection unit.

  For example, as a moisture content detection unit that indirectly detects the moisture content of the paper T, a temperature sensor (not shown) that detects the temperature around the paper T and a humidity that is not shown that detects the humidity around the paper T. A humidity sensor and a storage unit (not shown) having a storage table in which the correlation between temperature, humidity and moisture content is stored, based on the temperature detected by the temperature sensor and the humidity detected by the humidity sensor, Some devices detect moisture content by referring to a storage table.

  As described above, the fixing position of the fixing device 9 can be switched between the normal fixing position and the low nip pressure fixing position based on the moisture content detected directly or indirectly by the moisture content detecting unit. Thereby, when the water content of the paper T is high, wrinkles generated on the paper T when the fixing device 9 fixes the paper can be reduced.

  In the above-described embodiment, the pressure roller 9b is driven to rotate and the heating roller 9a is driven to rotate. However, the present invention is not limited to this, and the heating roller 9a is driven to rotate and the pressure roller 9b is driven to rotate. Also good.

  In the embodiment, the heating roller 9a is used as the first rotating body and the pressure roller 9b is used as the second rotating body. However, the present invention is not limited to this. While using the pressure roller 9b as the first rotating body, the heating roller 9a may be used as the second rotating body.

  In the above embodiment, the heating roller 9a is used as the first rotating body. However, instead of this, a heating rotating body formed of an endless belt may be used. Similarly, the pressure roller 9b is used as the second rotator, but instead, a pressure rotator formed of an endless belt may be used.

  In the embodiment, the nip pressure in the fixing nip N9 is changed by changing the position of the pressure roller 9b. However, the present invention is not limited to this. Fixing 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 pressure roller 9b (second rotating body). The nip pressure at the nip N9 may be changed.

  In the above-described embodiment, the first urging member 522 that uses the nip pressure at the fixing nip N9 as the first nip pressure and the second urging member 525 that uses the nip pressure at the fixing nip N9 as the second nip pressure are provided. However, it is not limited to this. For example, the pressure roller 9b can be biased in the direction toward the heating roller 9a via the support member 524 so that the nip pressure at the fixing nip N9 is a nip pressure different from the first nip pressure and the second nip pressure. The urging member may be further provided. Thereby, a nip pressure different from the first nip pressure and the second nip pressure can be stably applied.

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 transfer material T is not limited to paper, and may be, for example, a cylindrical object such as an envelope or a film sheet. For example, control may be performed to switch the fixing position of the fixing device 9 between a normal fixing position and a low nip pressure fixing position when the moisture content in a cylindrical object such as an envelope is low or high. In this case, the normal fixing position in the cylindrical object is positioned so that the first nip pressure in the fixing nip pressure is smaller than the normal fixing position in the paper T.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photosensitive drum (image carrier), 8 ... Transfer roller (transfer part), 9 ... Fixing device, 9a ... Heating roller (1st rotary body), 9b: Pressure roller (second rotating body), 16: Developer, 52: Paper feed cassette (housing unit), 70: Humidity detection sensor (humidity detection member), 110: Fixing nip pressure change control 115, rotational drive control unit, 511 ... fixing nip pressure changing unit, 512 ... pressing member position changing unit, 515 ... nip pressure changing cam (cam member), 521 ... switching member, 522 ... first 1 biasing member, 523... Pressing member, 524... Support member, 525... 2nd biasing member, 531. ... Rotating member, 555 ... Sensor, BD ... Case body (housing , J1 ...... first rotation axis, J2 ...... second axis of rotation, N9 ...... fixing nip, T ...... paper (transfer material)

Claims (6)

A housing,
An accommodating portion that is disposed inside the housing and accommodates a transfer material;
A fixing device that melts toner constituting a toner image transferred to a transfer material and fixes the toner on the transfer material while being provided in the image forming apparatus,
A first rotating body rotatable about a first rotation axis;
The first rotating body is disposed opposite to the first rotating body, forms a fixing nip through which the transfer material is transported by the first rotating body, and is rotatable about a second rotating shaft parallel to the first rotating shaft. A second rotating body that is biased in a direction away from the first rotating body in a state where the fixing nip is formed,
A support member that supports the second rotating body and can change the position of the second rotating body with respect to the first rotating body by swinging;
A first urging member capable of urging the second rotator in a direction toward the first rotator via the support member so that a nip pressure at the fixing nip is a first nip pressure;
A second capable of urging the second rotating body toward the first rotating body via the support member so that the nip pressure at the fixing nip is a second nip pressure smaller than the first nip pressure; A biasing member;
A switching member capable of switching to a state in which the urging force of either the first urging member or the second urging member is transmitted to the second rotating body;
A first position that is disposed in contact with the switching member and that positions the switching member in a state where the urging force of the first urging member is transmitted to the second rotating body, and the urging of the second urging member. A pressing member movable to a second position for positioning the switching member in a state in which a force is transmitted to the second rotating body;
A pressing member position changing unit that moves the pressing member to the first position and the second position;
A humidity detection member disposed in the housing or the housing;
A fixing nip pressure change control unit that controls the pressing member position changing unit so that the switching member is positioned at the first position or the second position based on the humidity detected by the humidity detecting member. An image forming apparatus. The fixing nip pressure change control unit controls the pressing member position changing unit so that the switching member is positioned at the second position when a humidity value detected by the humidity detecting member is a predetermined value or more. Item 2. The image forming apparatus according to Item 1. The pressing member position changing unit is
A cam member disposed in contact with the pressing member and capable of rotating and moving between a first rotational position where the pressing member is positioned at the first position and a second rotational position where the pressing member is positioned at the second position. When,
A rotational drive unit that rotationally moves the cam member between the first rotational position and the second rotational position;
The image forming apparatus according to claim 1, wherein the fixing nip pressure change control unit controls the rotation driving unit. 4. The image forming apparatus according to claim 3, wherein the cam member is not rotated by an urging force applied from the first urging member via the pressing member at the first rotation position. 5. The switching member is disposed between the support member and the first biasing member, and engages with the support member to transmit the biasing force of the first biasing member to the second rotating body. And an engagement position that is a position where the urging force of the first urging member is not transmitted to the second rotating body without being engaged with the support member,
The cam member positions the switching member at the engagement position via the pressing member at the first rotation position, and moves the switching member via the pressing member at the non-engagement position at the second rotation position. The second rotating body is biased by the first biasing member via the switching member and the support member when the switching member is in the engagement position, and the switching member is 5. The image forming apparatus according to claim 3, wherein the image forming apparatus is urged by the second urging member via the support member when in the non-engagement position. A housing,
An accommodating portion that is disposed inside the housing and accommodates a transfer material;
A fixing device that melts toner constituting a toner image transferred to a transfer material and fixes the toner on the transfer material while being provided in the image forming apparatus,
A first rotating body rotatable about a first rotation axis;
The first rotating body is disposed opposite to the first rotating body, forms a fixing nip through which the transfer material is transported by the first rotating body, and is rotatable about a second rotating shaft parallel to the first rotating shaft. A second rotating body that is biased in a direction away from the first rotating body in a state where the fixing nip is formed,
A support member that supports the second rotating body and can change the position of the second rotating body with respect to the first rotating body by swinging;
A first urging member capable of urging the second rotator in a direction toward the first rotator via the support member so that a nip pressure at the fixing nip is a first nip pressure;
A second capable of urging the second rotating body toward the first rotating body via the support member so that the nip pressure at the fixing nip is a second nip pressure smaller than the first nip pressure; A biasing member;
A switching member capable of switching to a state in which the urging force of either the first urging member or the second urging member is transmitted to the second rotating body;
A first position that is disposed in contact with the switching member and that positions the switching member in a state where the urging force of the first urging member is transmitted to the second rotating body, and the urging of the second urging member. A pressing member movable to a second position for positioning the switching member in a state in which a force is transmitted to the second rotating body;
A pressing member position changing unit that moves the pressing member to the first position and the second position;
A moisture content detection unit for directly or indirectly detecting the moisture content of the transfer material accommodated in the accommodation unit;
A fixing nip pressure change control unit that controls the pressing member position changing unit so that the switching member is located at the first position or the second position based on the moisture content detected by the moisture content detecting unit; An image forming apparatus.

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